acrylic acid manufacturing process

专利摘要:
HOUSING AND TUBE OXIDATION REACTOR WITH IMPROVED INCRUSTAL RESISTANCE. The present disclosure relates to a single-frame open inter-step reactor ("SSOI"). The SSOI comprises a first reaction step, an inter-step heat exchanger, an open inter-step region, and a second reaction step. The SSOI can be configured for upward or downward flow operation. In addition, the open inter-step region of the SSOI may comprise a supplementary oxidant feed. When the open inter-step region comprises a supplementary oxidant feed, the SSOI may additionally comprise a supplementary oxidant mixture assembly. Processes for producing acrylic acid through propylene oxidation are also disclosed.
公开号:BR112015006503B1
申请号:R112015006503-1
申请日:2013-08-20
公开日:2021-03-02
发明作者:Michael S. Decourcy；John L. Steinbach；Nicolas Dupont；Roger L. Roundy
申请人:Arkema Inc；
IPC主号:

专利说明:

Invention Area
[0001] The present invention relates to housing and tube oxidation reactors and processes for the manufacture of acrylic acid by means of propylene oxidation. Discussion of Related Technique
[0002] The production of acrylic acid by catalytic oxidation in a fixed bed of propylene is widely practiced and involves oxidation of propylene to the intermediate acrolein and then further oxidation of acrolein to acrylic acid. Numerous solid particulate type catalysts have been developed to facilitate this two-stage oxidation process and methods for preparing these catalysts are well documented in the literature.
[0003] In general, commercial-scale manufacturing facilities use two catalysts with different composition, a catalyst from the first stage and a catalyst from the second stage, in the production of acrylic acid. First stage catalysts (referred to here as “R1 catalysts”) are mixed metal oxide (“MMO”) catalysts generally comprising molybdenum, bismuth, and optionally iron, and are used to promote the conversion of propylene to acrolein. Second stage catalysts (referred to here as "R2 catalysts") are also mixed metal oxide (MMO) catalysts, but these generally comprise molybdenum and vanadium, and are used to promote the conversion of acrolein to acrylic acid.
[0004] Current commercial-scale processes for the production of acrylic acid often use reactors modeled on the basis of shell and tube heat exchangers. Typically, such commercial reactors comprise from about 12,000 to about 22,000 tubes in a single reaction vessel and can have acrylic acid production capacities of up to 100 kT / year (220,000,000 pounds / year) operating with an onstream factor of 93%. Large-scale commercial reactors, although less common, can comprise 25,000 to about 50,000 tubes in a single reaction vessel, with production capacities of up to 225 kT / year (500,000,000 pounds / year). In such shell and tube reactors, a fixed catalyst bed can be assembled by loading particulate type MMO catalysts into the tubes in the reactor. Process gases can flow through the tubes, in direct contact with the catalyst particles, while refrigerant can be passed through the vessel housing to remove the reaction heat. Typical refrigerants include molten nitrate salts and organic heat transfer fluids, such as Dowtherm ™. The product gas resulting from the reactor can be collected and purified in additional downstream equipment, such as one or more of extinguishing vessels, absorption columns, dehydration columns, extractors, azeotropic distillation towers, and crystallizers, to obtain product of acrylic acid suitable for sale, or for use in the production of acrylate esters, superabsorbent polymers, or the like.
[0005] There are two basic designs of shell-type oxidation reactors and tubes commonly used in the prior art: tandem reactors and single reactor shell reactors (“SRS”).
[0006] Tandem reactors generally comprise two housing-type reaction vessels and separate tubes connected in series by an intermediate duct. The two reaction vessels are operated in series, such that the conversion of propylene to acrolein can be carried out in the first reaction vessel (using an R1 catalyst) and the conversion of acrolein to acrylic acid can be carried out in the second reaction vessel ( using an R2 catalyst). Each housing of the reaction vessel can be supplied with its own refrigerant circulation such that the operating temperatures of the first reaction vessel and the second reaction vessel can be controlled independently of each other. Representative examples of tandem reactors are provided in U.S. Patent No. 4,147,885; U.S. Patent No. 4,873,368; and U.S. Patent No. 6,639,106. In some embodiments, an additional heat exchanger can be added between the first reaction vessel and the second reaction vessel to cool the intermediate process gas stream before entering the second reaction vessel. In other embodiments, the tandem reactor design may incorporate “supplementary oxidant feed” capability, in which additional oxygen (or air) is provided to the second reaction vessel via a connection in the intermediate conduit; such a feature may allow the tandem reactor to be operated at a higher production rate and / or decrease the oxygen concentration in the reactor supply, thereby reducing the potential for fires in the supply system (see for example U.S. Patent No. 7,038,079). Despite many years of development and optimization, however, the auto-oxidation of acrolein, organic fouling of the intermediate duct, and the high cost of capital associated with having two reaction vessels (vs. one) remain major disadvantages of tandem reactors. .
[0007] SRS reactors typically comprise a single shell-and-tube reaction vessel with tubes that are approximately twice as long as the tubes within a Tandem reaction vessel. The upstream end of each tube can be loaded with R1 catalyst and the downstream end of each tube can be loaded with R2 catalyst, forming two sequential reaction zones within each tube. An amount of inert material - such as Raschig rings - can be placed approximately at the midpoint of each tube, forming a so-called layer of inert substance, which separates the two catalytic reaction zones from one another. In addition, a sheet of the intermediate tube can be placed inside the SRS reactor housing, roughly coincident with the layer of inert substance, to divide the housing into upper and lower cooling zones. Each cooling zone can be supplied with its own refrigerant circulation such that the operating temperatures of the first reaction zone and the second reaction zone can be controlled independently of each other. Representative examples of SRS reactors are provided in U.S. Patent No. 6,069,271 and U.S. Patent No. 6,384,274. Although acrolein auto-oxidation can be largely eliminated in the SRS reactor, the accumulation of molybdenum and carbonaceous materials within both the inter-step zone and the second reaction zone remains a significant problem; these accumulations not only restrict the flow through the reaction tubes, thereby limiting productivity, but also reduce the yield, due to masking of the catalytic surface in the reaction zone R2. In addition, the long tubes used in the design of the SRS reactor make it very difficult to remove accumulated solids from the midpoint of the tubes, requiring the use of aggressive techniques, such as high pressure water blasting and the use of drilling devices, such as the device disclosed in U.S. Patent Application Publication No. US 2009/0112367. Another disadvantage of the SRS reactor design is that it cannot be easily modified to accommodate supplemental oxidant feed. Brief Summary of the Invention
[0008] One aspect of the invention provides an open, single-shell inter-step reactor (“SSOI”) comprising a shell and tube type reactor design that takes into account some of the disadvantages of prior art tandem reactors and SRS reactors while economically producing commercial quantities of acrylic acid. The SSOI reactor of the invention can provide at least one or more of the following advantages compared to known housing and tube reactors: lower capital costs by using a single reaction vessel, enhanced accessibility during cleaning and replacement of catalysts, accumulation of carbonaceous solids and decreased molybdenum oxides within the reactor, decreased pressure drop throughout the reactor, decreased downtime required for decoking, decreased loss of catalytic activity due to solids deposition, decreased acrolein auto-oxidation, formation of by-products of decreased acetic acid, decreased partial catalyst repackaging by matching the life span of the catalysts, and the ability to provide supplemental oxidant between reaction steps.
[0009] One aspect of the invention relates to an open interconnect reactor of single casing with upward flow comprising: a) a first reaction stage of carcass and tubes comprising a plurality of reaction tubes, in which the reaction tubes of the first reaction step comprises a first catalyst; b) an inter-stage heat exchanger; c) an open inter-step region; and d) a second carcass and tube reaction step comprising a plurality of reaction tubes, wherein the reaction tubes of the second reaction step comprise a second catalyst; wherein said inter-step heat exchanger is positioned between said first reaction step and said open inter-step region, and wherein said reactor is configured for upward flow.
[0010] Another aspect of the invention relates to a single-stage open-step inter-step reactor, comprising, in order of process flow: a) a first stage of reaction of carcass and tubes comprising a plurality of reaction tubes containing a first catalyst; b) an integrated inter-step heat exchanger comprising a plurality of coaxially continuous tubes with the plurality of reaction tubes from the first reaction step; c) an open inter-step region comprising a supplementary oxidant mixture assembly; and d) a second carcass and tube reaction step comprising a plurality of reaction tubes containing a second catalyst.
[0011] Yet another aspect of the invention relates to a single-cased open inter-step reactor comprising: a) a first casing and tube reaction stage comprising a plurality of reaction tubes; b) an inter-stage heat exchanger; c) an open inter-step region; and d) a first carcass and tube reaction step comprising a plurality of reaction tubes; wherein the reaction tubes of the second reaction step have a diameter greater than the diameter of the reaction tubes of said first reaction step.
[0012] Other additional aspects of the invention relate to methods of making acrylic acid using the reactors disclosed here.
[0013] Additional aspects of the invention relate to an open single-stage inter-step reactor for the production of acrylic acid from propylene, in order of process flow: a) a first stage of the reaction of the carcass and tubes comprising a plurality of tubes reaction, wherein the reaction tubes of the first reaction step comprise a first catalyst for oxidizing propylene to produce acrolein; b) an inter-stage heat exchanger; c) an open inter-step region; and d) a second carcass and tube reaction step comprising a plurality of reaction tubes, wherein the reaction tubes of the second reaction step comprise a second catalyst for oxidizing acro to produce acrolein to produce acrylic acid; and where the reaction tubes of the second reaction step have a diameter greater than 22.3 mm (0.878 inches).
[0014] Still further aspects of the invention relate to an acrylic acid manufacturing process comprising: a) providing a mixed feed gas comprising propylene to a first reaction step located at a lower end of a single-shell open inter-step reactor , wherein the first reaction step comprises a mixed metal oxide catalyst; b) oxidizing the propylene in the first reaction step to produce a process gas comprising acrolein; c) cooling of the process gas in an inter-stage heat exchanger; d) passage of the cooled process gas upwards through an open inter-step region; e) passage of the process gas upwards to a second reaction step, wherein the second reaction step comprises a mixed metal oxide catalyst; and f) oxidizing acrolein in the second reaction step to produce a product gas comprising acrylic acid. Brief Description of Drawings
[0015] Figure 1a is a side view representing the characteristics of the tube side (process) for a first embodiment of an SSOI reactor.
[0016] Figure 1b is a side view representing the characteristics of the housing (refrigerant) side for a first embodiment of an SSOI reactor.
[0017] Figure 1c is a top view representing the layout of the tube sheet for a first embodiment of an SSOI reactor.
[0018] Figure 1d is a side view of a conical catalyst retention spring.
[0019] Figure 1e is a top view of a catalyst retaining clip.
[0020] Figure 2 is a side view representing the characteristics of the tube side (process) for a second embodiment of an SSOI reactor.
[0021] Figure 3a is a side view representing the characteristics of the tube side (process) for a third embodiment of an SSOI reactor.
[0022] Figure 3b is a side view representing the characteristics of the housing (refrigerant) side for a third embodiment of an SSOI reactor.
[0023] Figure 4 is a side view representing the characteristics of the tube (process) side for an embodiment of an SSOI reactor comprising mixing means for adding supplemental oxidant.
[0024] Figure 5 is a side view representing the characteristics of the tube (process) side for another embodiment of an SSOI reactor comprising mixing means for adding supplemental oxidant.
[0025] Figure 6 is a cross-sectional side view of a Venturi mixer for adding supplemental oxidant.
[0026] Figure 7 is a graph showing the ratio of% yield in Acetic Acid vs. pressure in the second reaction step.
[0027] Figure 8 is an embodiment of an integrated process for the manufacture of acrylic acid, comprising the SSOI reactor of the present invention and a solvent-free acrylic acid collection and purification system. Detailed Description
[0028] It is to be understood that both the previous general description and the following detailed description are only exemplary and explanatory and are not restrictive of the present teachings. All patents and patent applications mentioned in this application are expressly incorporated by reference in their entirety for any purpose. When definitions of terms in embedded references appear to differ from the definitions provided in the present teachings, the definition provided in the present teachings should prevail. It will be appreciated that there is an implicit “fence” before temperatures, dimensions, flow rates, concentrations, times, etc. discussed in the present teachings, such that slight and insubstantial deviations are within the scope of the present teachings.
[0029] Unless otherwise defined, the scientific and technical terms used in connection with the present teachings described here shall have the meanings that are commonly understood by those of ordinary skill in the art. Additionally, unless otherwise required, singular terms must include pluralities and plural terms include the singular. Generally, the nomenclatures used in connection with, and techniques for, housing and tube reactor design, acrylic acid production, and oxidation reactions, are those well known and commonly used in the art. As used in accordance with the embodiments provided herein, the following terms, unless otherwise indicated, should be understood to have the following meanings:
[0030] As used here, the phrase "inter-stage heat exchanger" or "ISHX" refers to a heat exchanger located between steps of a single reactor. For example, ISHX can be positioned between a first reaction step and a second reaction step.
[0031] The phrase "integrated inter-step heat exchanger", or "integrated ISHX", refers to a heat exchanger having tubes that are coaxially continuous with the reaction tubes of a reaction step.
[0032] The phrase "open inter-steps" or "OIS" refers to the region not comprising any reaction tubes and located between steps of a single reactor or between a step and an inter-step heat exchanger of a single reactor. For example, the OIS can be positioned between an inter-step heat exchanger and a second reaction step.
[0033] As used here, the phrase “material with high surface area”, and its variations, refers to a surface area to volume ratio of at least 78.7 m2 / m3 (24 feet2 / feet3).
[0034] As used here, the term "inert material" means a material that is substantially ineffective in catalyzing a reaction from feed materials or reaction products. For example, in a reactor producing acrylic acid through the oxidation of propylene, an inert material is one that is substantially ineffective in catalyzing the propylene oxidation or the catalysis of the acrolein oxidation.
[0035] The term “stable material”, as used here, refers to materials that do not deform, melt, vaporize, decompose, or combust when exposed to process temperatures, process operating pressures, or chemical components within of the process.
[0036] As used here, the term "interface" refers to the boundary between two adjacent reactor sections. The term “connection” refers to the circumferential contact point between adjacent reactor sections at an interface and can be temporary or permanent. The term "tube sheet" refers to a planar surface positioned at an interface, said surface extending substantially along the entire cross section of the reactor and comprising a plurality of holes through which the ends of the reaction tubes pass. The ends of the reaction tubes are attached to the tube sheet by known means such as welding or laminating, and the tube sheet is additionally attached on its outer circumference to the vessel housing, thereby preventing the refrigerant from passing through the housing side. one section to another. The term "interstage chicane" refers to a planar surface positioned at an interface, said surface extending substantially along the entire cross section of the reactor and comprising a plurality of holes through which the ends of the reaction tubes pass. Unlike a tube sheet, however, the reaction tubes are not attached to the baffle, and fluid communication of the refrigerant on the housing side between adjacent sections is permitted. Finally, the term “segment baffle” refers to a planar surface NOT positioned at an interface, the said surface extending only over a portion of the entire cross section of the reactor and comprising a plurality of holes through which the ends of the reaction tubes pass. As with an inter-stage baffle, the reaction tubes are not attached to a segment baffle, and fluid communication of the refrigerant on the side of the housing between opposite surfaces of the baffle is permitted.
[0037] The terms "diameter" and "cross-sectional area", when referring to a tube, are used to define the size of the tube rather than the shape of the tube. The examples provided here use tubes having a circular cross section, but tubes having other shapes can be used. For tubes having other shapes, one of ordinary skill in the art would understand that the diameters disclosed here can be converted into the appropriate dimension for alternative shapes by determining the cross-sectional area while taking into account any variations (eg, heat transfer) , mass transfer, etc.) resulting in the alternative way. The terms "diameter" and "cross-sectional area" are used to refer to the diameter or cross-sectional area of the tube opening, i.e., the diameter or area of the internal cross-section.
[0038] As used here, the terms "upward flow" and "downward flow" relate to the direction of flow through the reactor with respect to the gravitational force. Upward flow describes an upward vertical process flow that proceeds against the gravitational force. Downward flow describes a downward process flow that proceeds in the direction of the gravitational force.
[0039] The term "residence time" refers to the amount of time the gas spends in one or more specified sections. For example, residence time can refer to the amount of time spent at ISHX. Similarly, residence time can refer to the amount of time spent in multiple sections, such as, for example, the combined amount of time spent in ISHX and the OIS region. Unless otherwise specified, the residence time of the process gas flow within the reactor is determined at reference conditions of 240 ° C and pressure of 30 psia (2 atm).
[0040] In at least one embodiment, the SSOI reactor comprises, in order of flow process: a) an input reactor head; b) a first stage of reaction of carcass and tubes; c) an integrated inter-stage heat exchanger; d) an open inter-step region; e) a second stage of reaction of carcass and tubes; and f) an output reactor head.
[0041] The first reaction step ("R1") can comprise a plurality of reaction tubes, each of which can be filled with a catalyst, e.g., an R1 catalyst. When used for the oxidation of propylene to form acrylic acid, the R1 catalyst can be an MMO catalyst chosen from molybdenum, bismuth, and iron oxides.
[0042] The first reaction step may comprise a refrigerant on the side of the housing. One with ordinary skill in the art would appreciate that the refrigerant and circulation of the refrigerant can be selected and designed to meet the heat transfer needs of the specific application.
[0043] The second reaction step ("R2") can comprise a plurality of reaction tubes. The reaction tubes of R2 can be filled with a catalyst (a catalyst of R2) to catalyze the second reaction step. In the exemplary reaction, where acrolein is oxidized to R2 to form acrylic acid, the R2 catalyst can comprise an MMO chosen from molybdenum and vanadium oxides. The housing side of the second reaction step may comprise a refrigerant. The refrigerant of the second reaction step can be controlled independently of the refrigerant of the first reaction step. Alternatively, the refrigerant from the second reaction step can be controlled with the refrigerant from the first reaction step.
[0044] In at least one embodiment, ISHX can comprise a refrigerant on the side of the housing. The ISHX refrigerant can be controlled separately or in conjunction with the refrigerant from the first reaction step. In at least one embodiment, the ISHX refrigerant is controlled independently of the refrigerant in the first reaction step. According to at least one embodiment, the ISHX refrigerant maintains the temperature of the process gas leaving the ISHX between 240 ° C and 280 ° C.
[0045] In at least one embodiment of the present disclosure, the reaction tubes of R1 and R2 may have a different diameter or cross-sectional area. For example, the reaction tubes of R2 may be larger than the reaction tubes of R1. Alternatively, the reaction tubes of R1 and R2 can have the same diameter or cross-sectional area. In at least one embodiment, the reaction tubes of R2 may have a cross-sectional area at least 25% larger than the cross-sectional area of the reaction tubes of R1. In an additional embodiment, the reaction tubes of R2 may have a cross-sectional area at least 50% larger than the cross-sectional area of the reaction tubes of R1.
[0046] In at least one embodiment, the reaction tubes of R1 can have a diameter of 22.3 mm (0.878 inches) or less. In other embodiments, the R1 reaction tubes may have a diameter greater than 22.3 mm (0.878 inches), such as, for example, 25.4 mm (1 inch) or more.
[0047] In at least one embodiment, the internal diameter of the tubes of the second reaction step inside the SSOI reactor can be greater than 22.3 mm. In at least one embodiment, the reaction tubes of R1 and R2 have a diameter greater than 22.3 mm (0.878 inches). In an additional embodiment, the internal diameter of the tubes of the second reaction step inside the SSOI reactor ranges from 23.6 mm to 50 mm. In at least one embodiment, the internal diameter of the tubes of the second reaction step inside the SSOI reactor is at least 25.4 mm (1 inch). According to an embodiment of the present disclosure, the tubes of the second reaction stage are no more than 4,500 mm (177 inches) in length.
[0048] The negative impact on heat removal from tubes with a larger diameter can be compensated with appropriate adjustments in one or more of the other design variables, such as, for example, the number of baffles on the side of the housing, the geometry and placement of the baffles, the arrangement of the tube sheet and spacing between tubes (also known as the tube pitch), the rate of circulation of the cooling salt, and the temperature of the supply of the cooling salt. For example, in one embodiment, low rates of salt circulation through the reactor housing are employed, thereby minimizing power requirements for salt circulation pumps; such a design philosophy can generally result in an increase in the temperature of the salt through the reactor housing (temperature of the salt at the outlet in relation to the temperature of the salt at the inlet) by as much as 14 to 17 ° C (25 to 30 ° F) . In an alternative embodiment, high rates of salt circulation are used and the increase in the temperature of the salt through the reactor housing is restricted to the range of only 1 to 3 ° C (2 - 5 ° F).
[0049] Such design adjustments may be made by one of ordinary skill in the technique of designing heat exchangers, using design software commercially available from HTRI or the like; alternatively, cooling system design systems can be outsourced to established reactor manufacturing companies such as, for example, MAN Turbo AG (formerly Deggendorfer Werft and Eisenbau GmbH), which will use their well-established design rules and methodologies.
[0050] Similarly, the number of reaction tubes in R1 and R2 can be the same or different. In at least one embodiment, the number of reaction tubes in R1 may be greater than the number of reaction tubes in R2. In at least one additional embodiment, the number of reaction tubes of R1 may be greater than the number of reaction tubes of R2, and the reaction tubes of R2 may have a diameter or cross-sectional area greater than the reaction tubes of R1.
[0051] The SSOI reactors disclosed here can be configured for operation with upward or downward flow. In at least one embodiment, the SSOI reactors are configured for upward flow operation. In an upstream SSOI reactor, the head of the input reactor is located at the bottom and the head of the output reactor is located at the top of the SSOI reactor.
[0052] In at least one embodiment, the OIS region comprises a supply of supplemental oxidant. When the supply of supplemental oxidant is present, the OIS region may additionally comprise a supplementary oxidant mixture assembly.
[0053] In embodiments in which acrylic acid is produced from the oxidation of propylene, the combined residence time within both ISHX and OIS (known as the “inter-step residence time”) is 3 seconds or less. In at least one embodiment, the residence time within the ISHX is less than 1.5 seconds.
[0054] In at least one embodiment, the process gases from the SSOI reactor in operation can be monitored for the concentration of unreacted propylene and unreacted acrolein concentration using at least one online analyzer, such as, for example, an or more than a gas chromatograph, a near infrared analyzer (“NIR”), a tunable diode laser analyzer (“TDL”), or a Raman spectrograph, and the temperatures of the salt supply to the first reaction step and the second reaction step can be adjusted to control the conversions of propylene and acrolein. In one embodiment, the temperature of the first stage cooling salt supply (TsalR1) can be adjusted to maintain conversion of propylene to 94% or greater, 95% or greater, or 96.5% or greater.
[0055] In another embodiment, the temperature of the supply of the cooling salt of the first stage (TsalR1) can be adjusted to maintain the concentration of unreacted propylene in the product gas of the SSOI reactor at between 0.05 and 0, 35% per mol, such as, for example, between 0.13 - 0.26% per mol. In one embodiment, the temperature of the second stage cooling salt supply (TsalR2) can be adjusted to maintain 98% or greater acrolein conversion, such as 99% or greater, or 99.5% or bigger.
[0056] In another embodiment, the temperature of the cooling salt supply of the second stage (TsalR2) can be adjusted to maintain the unreacted acrolein concentration in the product gas of the SSOI reactor at no more than 500 ppm, such as, for example, no more than 300 ppm.
[0057] In at least one embodiment, temperature measurement devices, such as thermocouples or Thermal Resistance Devices (RTDs), can be provided within the reaction system to monitor process operating conditions and to optionally serve as sensors within instrumented safety systems (SIS) for the reaction system. Type E, Type J, and Type K single and multipoint thermocouples are all available for use with the SSOI reactor of the present invention and are commercially available from multiple suppliers, including STI manufacturing Inc. of Willis, Texas USA; Watlow Electric Manufacturing Company of St. Louis, Missouri USA; Sandelius Instruments, Inc of Houston, Texas USA, and Gayesco International Inc. of Pasadena, Texas USA.
[0058] One or more thermocouples can optionally be placed inside one or more of the inlet head, outlet head, inlet tubing, outlet tubing, and open inter-step region. In one embodiment, a plurality of thermocouples can be placed inside the head of the input reactor for use with a SIS stop system. According to at least one embodiment, at least 4 thermocouples can be installed within the open inter-step region and these thermocouples can be uniformly distributed throughout the inter-step region. Additionally, thermocouples can optionally be attached directly to the tube sheets inside the reactor.
[0059] A plurality of multipoint process thermocouples can be used inside the reactor tubes to monitor catalyst temperature on the process side at varying distances along the tube axis. In at least one embodiment, a plurality of multipoint salt thermocouples can be placed within the reactor tubes to monitor the temperature of the salt on the side of the shell along the length of the reactor. It should be noted, however, that a multipoint process thermocouple and a multipoint salt thermocouple cannot coexist in the same reactor tube.
[0060] In one embodiment, an assembly of multipoint process thermocouples, comprising 14 thermocouple junctions placed at variable intervals along their length, and housed within a 3.2 mm outer diameter liner, is used within a reaction tube of the first reaction with an internal diameter of 22.3 mm. In another embodiment, an assembly of multipoint process thermocouples, comprising at least 10 thermocouple junctions placed at equal intervals along their length, and housed within a 6 mm outer diameter liner, is used within a tube. reaction of the first reaction of internal diameter 25.4 mm. In either embodiment, the assembly of process thermocouples can be oriented along the center line of the reactor tube and the catalyst and inert parts can be located within the remaining annular space of the tube.
[0061] In at least one embodiment, at least 4 reactor tubes may be equipped with such multipoint process thermocouple assemblies, such as, for example, at least 6 tubes, or at least 10 tubes. Similarly, in one embodiment, an assembly of multipoint salt thermocouples, comprising 4 thermocouple junctions placed at equal intervals along their length, and housed within a 3.2 mm outer diameter liner, is used within a tube of the first reaction step with an internal diameter of 22.3 mm.
[0062] In an alternative embodiment, an assembly of multipoint salt thermocouples, comprising at least 3 thermocouple junctions placed at equal intervals along their length, and housed within a 6 mm outer diameter liner, can be used inside a tube of the first reaction step with an internal diameter of 25.4 mm. At least 4 reactor tubes can be equipped with such multipoint salt thermocouple assemblies, such as, for example, at least 6 tubes, or at least 10 tubes. In one embodiment, the assembly of salt thermocouples can be oriented along the center line of the reactor tube, inert spheres are placed within the remaining annular space of the tube, and a sealable plug or plug is placed at least at the end pipe riser to prevent axial process gas flow through the pipe. In an alternative embodiment, the assembly of salt thermocouples can be oriented along the central line of the reactor tube and inert particles of small diameter (eg, no more than 4 mm in diameter), such as, for example, sand, alumina powder, or silicon carbide gravel, can be placed within the remaining annular space of the tube to provide high resistance to axial process gas flow; such an embodiment may additionally optionally include a sealable plug or plug at least at the upstream end of the tube.
[0063] In one embodiment, an assembly of multipoint process thermocouples, comprising at least 8 thermocouple junctions placed at variable intervals along their length, and housed within a 3.2 mm outer diameter liner, can be used inside a tube of the second reaction step with an inner diameter of 22.3 mm. In another embodiment, an assembly of multipoint process thermocouples, comprising at least 10 thermocouple junctions placed at equal intervals along their length, and housed within a 6 mm outer diameter liner, can be used inside a tube of the second reaction step with an internal diameter of 25.4 mm. The assembly of process thermocouples can be oriented along the center line of the reactor tube and inert ones can be placed within the remaining annular space of the tube. In at least one embodiment, at least 4 reactor tubes are equipped with such multipoint process thermocouple assemblies, such as, for example, at least 6 tubes, or at least 10 tubes. Similarly, in one embodiment, an assembly of multipoint salt thermocouples, comprising at least 2 junctions of thermocouples placed at equal intervals along their length, and housed within a 3.2 mm outer diameter liner, can be used inside a tube of the second reaction stage with an internal diameter of 22.3 mm.
[0064] In an alternative embodiment, an assembly of multipoint salt thermocouples, comprising at least 3 thermocouple junctions placed at equal intervals along their length, and housed within a 6 mm outer diameter liner, can be used inside a tube of the first reaction step with an internal diameter of 25.4 mm. In at least one embodiment, at least 4 reactor tubes can be equipped with such multipoint salt thermocouple assemblies, such as, for example, at least 6 tubes, or at least 10 tubes. In one embodiment, the assembly of salt thermocouples can be oriented along the center line of the reactor tube, inert spheres are placed within the remaining annular space of the tube, and a sealable plug or plug is placed at least at the end pipe riser to prevent axial process gas flow through the pipe. In an alternative embodiment, the assembly of salt thermocouples can be oriented along the central line of the reactor tube and inert particles of small diameter (eg, no more than 4 mm in diameter), such as, for example, sand, alumina powder, or silicon carbide gravel, are placed within the remaining annular space of the tube to provide high resistance to axial process gas flow; such an embodiment may additionally optionally include a sealable plug or plug at least at the upstream end of the tube.
[0065] Figures 1a, 1b, and 1c in combination represent an embodiment of a single-frame open inter-step reactor design (“SSOI”). The reactor in this embodiment has a housing diameter of about 5,600 mm (18.4 feet) and an overall length of more than 15,240 mm (50 feet). At typical feed rates and spatial speed of total feed gas of 1770 hr -1 (determined at 0 ° C and 1 atm), the reactor in this embodiment has a nominal annual production capacity of about 100 kT of acrylic acid .
[0066] Feed gases (comprising, for example, propylene, steam, oxygen, and nitrogen) enter the reactor from the top (see Figure 1a), flow vertically down through the reactor, and exit the reactor at the bottom. This arrangement is therefore a downward flow process configuration.
[0067] The main sections of the reactor include the inlet head 100, the first reaction step 110 (“R1”), the inter-step heat exchanger 130 (“ISHX”), the open inter-step region 150, the second reaction step 160 (“R2”), and the output head 180. Unless otherwise specified, all reactor components may be constructed of carbon steel, such as for example ASME SA-516 grade 70 carbon steel.
[0068] The interface between adjacent sections, identified in the figures as 105, 125, 145, 155, and 175, can comprise permanent connections (eg, welded) or can optionally comprise separable connections, such as connections with secure flanges with a plurality of fasteners, such as for example screws or clamps. In the embodiment of Figure 1a, interfaces 105 and 175 are separable connections, allowing the input head 100 and output head 180 to be easily removed for replacement of the catalysts, while interfaces 125, 145 and 155 are welded connections.
[0069] In this embodiment, the inlet head of reactor 100 is constructed of 316 stainless steel for added corrosion resistance. Both the inlet head 100 and the outlet head 180 of the reactor also incorporate optional temperature control components (not shown), such as, for example, electrical tracing, steam heating liners, and circulating salt heat transfer coils , for use in maintaining internal surface temperatures above the dew point temperature of the process gas stream. External insulation can also be employed on the reactor heads as well as elsewhere on the reactor housing and associated piping systems.
[0070] The reactor inlet head 100 and outlet head 180 may be additionally equipped with one or more optional emergency pressure relief devices (not shown), such as, for example, pressure relief valves (PSVs) or rupture discs. In some embodiments, such emergency pressure relief devices may instead be installed in the inlet and / or outlet pipes connected to the reactor.
[0071] With reference again to Figure 1a, the first reaction step 110 has a length of 4,600 mm (15 feet) and contains a plurality of seamless carbon steel tubes, generally represented in the figure as 115a, 115b, 115c. The inlet end of each tube in the first reaction step can be attached, for example by welding or rolling, to the sheet of the inlet tube of R1 (not shown per se, but located in the same position in the figure as the detachable connection 105) . Each tube within the first reaction step 100 extends through the inter-step baffle 126 (see Figure 1b) and passes completely through the inter-step heat exchanger 130, which has a length of 2,100 mm (6.9 feet). This means that tube segment 135a is the bottom end of tube 115a, tube segment 135b is the bottom end of tube 115b, tube segment 135c is the bottom end of tube 115c, and so on. As a result, the actual length of these coaxially continuous tubes is 6,700 mm (22 feet), equivalent to the distance between the separable connection 105 and the welded connection 145. The outlet end of each pipe segment 135a, 135b, 135c, can be attached, for example by welding or rolling, to the ISHX tube sheet (not shown per se, but located in the same position in the figure as the welded connection 105). This design feature, in which the tubes of the first reaction step are continuous with the tubes of the inter-step heat exchanger, and in which both the first reaction step and the inter-step heat exchanger share a common vessel housing, is referred to here as an integrated inter-step heat exchanger. It should be noted that the interstage baffle 126 differs from a real tube sheet in that there are no tube-to-baffle attachments (eg, welds); instead, the perforations through the inter-chicane 126 have an internal diameter slightly larger than the outer diameter of the tubes (115 a, b, c), such that a small annular gap (not shown) between 0.25 and 2.5 mm wide around each tube. Due to this annular interval, a small volume of ISHX cooling salt (which is preferably supplied at a slightly higher pressure than the cooling salt of R1) can pass continuously through the inter-chicane baffle and mix with the salt circulation cooling capacity of R1. Given the benefit of the present disclosure, means for recycling an appropriate volume of salt from the R1 circulation system back to the ISHX circulation system is easily specified by one of ordinary skill in the process engineering technique and does not need to be described in further detail here.
[0072] In this embodiment, the R1 inlet tube sheet is 5,517 mm (18.1 feet) in diameter and comprises 22,000 tubes. Figure 1c represents the arrangement of the leaf of the inlet tube of R1 as seen from above. This view shows that there is a circular region (indicated by the dashed circle) in the center of the tube sheet in which there are no tubes; this empty circular region has a diameter of about 1,144 mm (3.75 feet). The tubes have an internal diameter of 22.3 mm (0.878 ”) and an external diameter of 26.9 mm (1.060”). The tubes are arranged in a 60 degree triangular pattern, with a 34 mm (1.34 ”) tube leaf pitch, resulting in a 7 mm (0.275”) spacing between the tubes. From these dimensions, the spacing ratio of tubes (t) in relation to the outer diameter of the tube (da) can be calculated, as defined in US patent 7,226,567: t = (26,9 + 7) and da = (26, 9), therefore t / da = 1.26
[0073] Many R1 catalysts are commercially available and suitable for use in the SSOI reaction device of the present invention. Examples include but are not limited to the first stage (R1) catalysts ACF, ACF-2, ACF-4, ACF-7, and ACF-8, all commercially available from Japan's Nippon Shokubai, and YX-38, YX- 111 and YX-129, all commercially available from Japan's Nippon Kayaku. Some of these R1 catalysts are available in more than one size. For example, the ACF-7 catalyst is available as cylinders of large and small dimensions, designated here as ACF-7L (large) and ACF-7S (small), and can be used individually or in combination. Portions of the R1 tubes may also contain inert materials, such as for example 6.4 mm (0.25 inch) Denstone 57 beads (available from Norton Chemical Process Products Corp, Akron OH, USA), to create pre- heating or cooling at specified locations within each tube. The selection and installation of appropriate R1 catalysts and insertions in the tubes of the first reaction step are within the capacity of one of ordinary skill in the art.
[0074] Turbulence induction inserts with a high void fraction can be placed inside the tube segments (135 a, b, c) of the inter-stage heat exchanger to intensify heat transfer without the buildup of fouling. The high fraction of voids means more than 85% void fraction and preferably more than 90% void fraction. In this specific embodiment, a helical metal strip, here referred to as a “twistee” insert, is placed inside each tube. Each twistee insert is manufactured from a single rectangular strip of carbon steel 1.57 mm (0.062 inches) thick, measuring 19.1 mm (0.750 inches) wide by 2,057 mm (81 inches) long. The strip can be mechanically twisted along its long axis to obtain a uniform helical geometry comprising 360 degree rotation per foot (305 mm) in length and a final length of 2,032 mm (80 inches). A metal ring with an external diameter of 17.5 mm (11/16 inches) can then be formed from wire with a diameter of 1.6 mm (1/16 inches) and attached to the upstream end of the twistee, oriented perpendicularly to the long axis of the twistee insert, in order to facilitate the placement of the insert which induces turbulence within the tube.
[0075] In some embodiments, a piece of 8x8 wire mesh, comprising 0.035 inch (0.9 mm) wire, may also be affixed to the metal ring at the end of the twistee insert to form a planar flow barrier. , thereby allowing the end upstream of the twistee insert to function as a catalyst holding device. The resulting twistee inserts can have a void fraction of about 92% and an effective outer diameter that is about 85% of the inner diameter of the reactor tubes in this embodiment, allowing them to be easily installed and removed manually. Given the benefit of the present disclosure, it will be evident that the twistee inserts can also be manufactured for use in tubes of a different internal diameter. In at least one embodiment, the width of the initial metal strip (and the outer diameter of the attached upstream ring) varies between about 80 and 99.5% of the inner diameter of the tube.
[0076] In other embodiments, modified twistee inserts may be used instead of affixing 8x8 wire mesh to the twistees. Such modified twistee inserts may comprise a conical catalyst retaining spring (see Figure 1d) welded to the upstream end of one of the previously described twistee inserts. When used on an ISHX tube with an inner diameter of 22.3 mm (0.878 inches), the tapered spring may have, for example, an outer diameter at the top, dTS, of 6.1 mm (0.241 inches) and an outer diameter at the bottom, dBS, 19.1 mm (0.75 inches) - equal to the effective diameter of the twistee insert. The conical catalyst retention spring can be manufactured, for example, from eleven uniformly spaced coils of stainless steel wire with a diameter of 1.47 mm (0.058 inches) to form a conical spring with an overall height (hs) of 25.4 mm (1 inch) and coil spacing narrow enough to allow the upstream end of the modified twistee insert to act as a catalyst holding device.
[0077] In at least one embodiment, twistee inserts can be installed in combination with a removable retaining device, such as, for example, a catalyst clamp of the type illustrated in Fig 1e, which is commercially available from MAN Turbo AG ( formerly Deggendorfer Werft and Eisenbau GmbH) from Oberhausen, Germany, in order to retain it inside the reactor tube ends under process flow conditions.
[0078] Although the present embodiment uses twistee inserts within the inter-step heat exchanger, several alternative turbulence induction inserts have been disclosed in the literature and many of these are commercially available for use in heat exchanger tubes. Given the benefit of the present disclosure, it is within the ability of one of ordinary skill to select turbulence-inducing inserts with a high fraction of voids suitable for use in the SSOI reactor design of the present invention; it should be understood that, in at least one embodiment, the term “turbulence induction inserts with a high void fraction” is not intended to encompass inert particulate type materials, such as for example Denstone 57 inert spheres, which have a fraction of voids in typical volume of less than 50%. Examples of commercially available void induction turbulence inserts include but are not limited to wire turbulence generators, disclosed in U.S. Patent No. 4,201,736 and commercially available from Ormiston Wire Ltd of Isleworth, England; Kenics Static Mixer elements, commercially available from Chemineer, Inc. of Dayton, Ohio USA; and Twisted Tapes, commercially available from Koch Heat Transfer Company, LP from Houston, Texas USA.
[0079] In at least one embodiment, the open inter-step region 150 has, for example, a diameter of 5,517 mm (18.1 feet) and a length of 2,100 mm (6.9 feet). According to at least one embodiment of the SSOI reactor design of the present invention, the open inter-step region is at least partially filled with one or more stable, high surface area inert materials 151, in an amount sufficient to provide at least 930 m2 (10,000 square feet) of total surface area for scale removal, such as, for example, 2,790 m2 (30,000 square feet), or 3,720 m2 (40,000 square feet).
[0080] In at least one embodiment, inert materials can comprise at least one type of material selected from the group consisting of ceramic, mineral, metal and polymer.
[0081] In at least one embodiment relating to processes in which propylene is oxidized to acrylic acid, stable materials of materials tolerant to temperatures up to about 365 ° C, pressures up to about 3 atm, and compounds chemicals such as for example propylene, acrylic acid, carbon monoxide, acetic acid, and acrolein. Examples of inert materials, stable for use in the SSOI reactor of the present invention include but are not limited to carbon steel, 316 stainless steel, monel, alumina, silica, silicon carbide, and porcelain.
[0082] Examples of inert materials with a high, stable surface area include but are not limited to 6 mm x 6 mm aluminum Raschig rings, 5 mm diameter silicon carbide spheres, 20-pore open cell ceramic foam -per-inch (ppi), 16 mm (5/8 inch) diameter stainless steel Pall rings, or 13 mm MacroTrap ™ Media 1.5 (available from Norton Chemical Process Products Corp, Akron OH, USA). Obviously, given the teachings of the present disclosure, it is within the ability of one of ordinary skill in the process engineering technique to select other inert materials with a high surface area, stable, not specifically named here, for use with the inventive SSOI reactor.
[0083] The open inter-step carcass 150 may comprise two lower covers with a diameter of 832 mm (32.75 inches) (not shown in Figure 1a), on opposite sides of the reactor (separated by 180 degrees), placed such that the center line of the lower cover is located at a distance of about 500 mm (19.7 inches) from the leaf of the R2 155 inlet tube. In addition, the open inter-step housing 150 may comprise two upper covers with a diameter of 667 mm (26.26 inches) (not shown in Figure 1a), on opposite sides of the reactor (separated by 180 degrees), placed such that the center line of the cover is located at a distance of about 420 mm (16.5 inches) from the ISHX 145 tube sheet. These covers can provide personnel access to the interior of the open inter-step region 150 for catalyst replacements and other maintenance work. The upper lids can also be beneficially employed for transferring particulate materials - such as loose filler spheres, cylinders, tablets, pellets, and granules - in the open inter-step region. In this embodiment, EnviroStone 66 ceramic spheres with a diameter of 38 mm (1.5 inches) in volume (available from Crystaphase Technologies, Inc of Houston Texas USA) are placed in supply distributors, connected via temporary conduits to the lids higher, and then transferred to the inter-step region opened by “pouring” under the influence of gravity.
[0084] When the transfer is complete, the spheres, which self-assemble after pouring into a bed with a fraction of voids of about 40% and a surface area in relation to the apparent volume of 94.5 m2 per cubic meter (28, 8 square feet per cubic meter), occupy about 93% of the volume within the open inter-step region, leaving an empty space of about 150 mm (6 inches) between the top of the EnviroStone 66 layer and the bottom surface of the foil. ISHX tube. The resulting bed of ceramic spheres has an average depth of 1,957 mm (6.4 feet) and occupies an apparent volume of 46.7 m3 (1,650 feet3), thus providing more than 4,400 m2 (47,300 feet2) of surface area for removal of scale.
[0085] In the previous embodiment, the second reaction step 160 has a length of 4,500 mm (14.76 feet) and contains a plurality of seamless carbon steel tubes, generally represented in the figure as 165a, 165b, 165c . The inlet end of each tube in the second reaction step can be attached, for example by welding or rolling, to the R2 inlet tube sheet (not shown per se, but located in the same position in the figure as the welded connection 155) . The outlet end of each section of tube 165a, 165b, 165c can be attached, for example by welding or rolling, to the sheet of the outlet tube of R2 (not shown per se, but located in the same position in the figure as the connection separable 175).
[0086] The R2 inlet tube sheet of this embodiment is 5,517 mm (18.1 feet) in diameter and comprises 22,000 tubes. The layout of the R2 inlet tube sheet is the same as the R1 inlet tube sheet (see Figure 1c), including the empty circular region in the center of the tube sheet in which there are no tubes; this empty circular region also has a diameter of 1,144 mm (3.75 feet). The tubes within the second reaction step have an internal diameter of 22.3 mm (0.878 inches) and an external diameter 26.9 mm (1.060 inches). The tubes are arranged in a 60 degree triangular pattern, with a 34 mm (1.34 ft) tube foil pitch, resulting in a 7 mm (0.275 ft) tube spacing.
[0087] Many R2 catalysts are commercially available and suitable for use in the SSOI reaction device of the present invention. Suitable second stage (R2) catalysts include but are not limited to ACS, ACS-2, ACS-6, ACS-7, and ACS-8, commercially available from Japan's Nippon Shokubai and T-202, commercially available from Nippon Kayaku from Japan. Some of these catalysts are also available in more than one size, for example the ACS-7 catalyst is available as spheres with large and small diameters, designated here as ACS-7L (large) and ACFS-7S (small) , and can be used individually or in combination. Portions of R2 tubes may also contain inert materials, such as 5 mm (3/16 inch) diameter silica-supported spheres (designated as “SA-5218” and available from Norton Chemical Process Products Corp, Akron OH, USA), to create preheating or cooling zones at specified locations within each tube. The selection and installation of appropriate R2 catalysts and insertions in the tubes of the second reaction step are within the capacity of one of ordinary skill in the art.
[0088] In this embodiment, the twistee inserts within the inter-step heat exchanger as well as the catalyst of the second reaction step (R2) are retained in the reactor tubes using catalyst support grid panels comprising wire mesh. The use of catalyst support grid panels comprising wire mesh can provide significant savings in manpower and time during installation and removal of the catalyst compared to the use of traditional catalyst clamps or other means of retaining the tubes. In this specific embodiment, the catalyst support grid panels comprising 2.7 mm wire mesh segments formed from 0.6 mm diameter wire. The wire mesh segments are welded to a support plate with a thickness of 15 mm (0.6 inches), comprising a plurality of holes with a diameter of 22.3 in a pattern that corresponds to the specific geometry of the outlet tube sheet of R2; this results in a set of generally rectangular catalyst support grid panels, with a nominal rectangular dimension of about 918 mm x 471 mm (36 inches x 18.5 inches); the panels to be adjusted along the circumference of the reactor tube sheet obviously have to deviate from a true rectangular shape due to the presence of one or more arcs, and therefore outline an area somewhat smaller than the full size rectangular panels .
[0089] In this embodiment, a total of 60 catalyst support grid panels are employed to retain the R2 catalyst within the tubes of the second reaction step. Prior to the introduction of catalyst into the reactor tubes, each catalyst support grid panel can be placed with the wire mesh in direct contact with the bottom surface of the R2 outlet tube sheet and the panel can be secured with screws which pass through solid regions of the panel and are anchored directly to the tube sheet. In at least one embodiment, the screws may be permanently attached to the R2 outlet tube sheet and have sufficient exposed perpendicular length to extend completely through the catalyst support grid panel; the catalyst support grid panel can then be secured in place using removable metal fasteners comprising two teeth, such as braces. The end of each screw comprises a hole running perpendicular to the axis of the screw, through which the key teeth pass; the two teeth are then bent out after installation to secure the key to the screw. Twistee inserts are also retained within the inter-step heat exchanger tubes using similar catalyst support grid panels secured to the bottom surface of the ISHX tube sheet with screws and keys.
[0090] Although described here in relation to the 22,000-tube SSOI reactor in this embodiment, the use of catalyst support grid panels comprising wire mesh will provide even greater benefits for large-scale commercial SSOI reactors, such as for example reactors SSOI comprising 25,000 tubes, 30,000 tubes, 45,000 tubes, or more. In the present invention it is therefore most preferred that the catalyst is retained within the SSOI reactor tubes comprising 25,000 tubes or more with catalyst support grid panels comprising wire mesh. It will also be apparent from the present disclosure that the catalyst support grid panels comprising wire mesh disclosed herein can be beneficially incorporated into other reactor designs, such as for example tandem reactors and SRS reactors. The present invention therefore further includes catalyst retention within the tubes of tandem reactors or SRS reactors with catalyst support grid panels comprising wire mesh.
[0091] With reference now to Figure 1b, this embodiment of the inventive SSOI reactor comprises three independently controlled refrigerant circulation systems, which provide the ability to individually adjust the temperature of each chilled section (110, 130, 160 ) as necessary. HITEC® heat transfer salt, available from Coastal Chemical Co. of Houston, Texas USA, is used as the refrigerant for all three circulation systems in this embodiment. The systems are referred to here as the R1 salt circulation system, supporting the first reaction step 110; the ISHX salt circulation system, supporting the inter-step heat exchanger 130; and the R2 salt circulation system, supporting the second reaction stage 160.
[0092] Consistent with at least one embodiment of the present invention, such a refrigerant system configuration can allow the temperature of the process side of the inter-stage heat exchanger to be controlled independently of the process temperature of the first reaction step, allowing that the process gas leaving the ISHX is maintained at a temperature of at least 240 ° C and no more than 280 ° C. Although not an essential feature of the inventive design, this embodiment also provides the ability to control the temperature of the process side of the second reaction step regardless of the process temperature of the inter-step heat exchanger; such additional ability to control the operation of the oxidation process is used in at least one embodiment of the present invention.
[0093] Each of the three refrigerant circulation systems in this embodiment can comprise one or more salt circulation pumps, waste heat boilers, and associated transfer tubing (not shown), through which exothermic heat from the oxidation reaction can be recovered to produce a by-product stream. Optional equipment, such as salt storage tanks, gas salt heaters, integral thermal expansion vessels (also known as salt "stranglers"), and salt transfer pumps can also be included in the salt circulation system. In addition, each of these circulation systems may comprise instrumentation (not shown), such as thermocouples, and automated controls, such as flow control valves, to maintain the temperature and circulation rate of the salt supplied to the reactor at target values. desired.
[0094] For the support section of the R1 110 salt circulation system, the cooling salt can enter through the supply lines of R1 121 near the bottom of the section and can be evenly distributed around the circumference of the reactor through a inlet channel (not shown), comprising internal flow distribution means such as one or more baffles, flow vanes, weirs, sieves, and perforated plate dispensers, and commonly referred to as a "lower salt dispenser". Once inside the reactor housing, salt can flow upwards, repeatedly passing through the reactor housing in the radial direction flowing around a series of evenly spaced plates on the housing side known in the heat exchange technique as “segment baffles. double ”122. This radial flow pattern can ensure good salt-to-tube contact in order to achieve high heat removal efficiency from the tubes. After reaching the top of the R1 section, the hot salt can be collected via another circumferential outlet channel (not shown), which can additionally comprise flow distribution means, commonly referred to as an “upper salt distributor” and can be transferred through the return lines of R1 123 to waste heat boilers (not shown).
[0095] For the support section of the ISHX salt circulation system (“bottom salt dispenser”, not shown), the cooling salt can enter through the ISHX 141 supply lines near the bottom of the section and can be evenly distributed around the circumference of the reactor through an inlet channel ("bottom salt dispenser", not shown), comprising internal flow distribution means such as one or more baffles, flow vanes, weirs, sieves, and dispensers with perforated plate. Once inside the reactor housing, salt can flow upward, repeatedly passing through the reactor housing in the radial direction flowing around a series of evenly spaced double segment baffles 142. After reaching the top of the ISHX section, the salt hot water can be collected via another circumferential outlet channel (“upper salt dispenser” - not shown), which can additionally comprise flow distribution means, and is transferred via the ISHX 143 return lines to waste heat boilers 143 (not shown).
[0096] Similarly, for the support section of the R2 salt circulation system, the cooling salt can enter through the R2 171 supply lines near the bottom of the section and can be evenly distributed around the circumference of the reactor through a "lower salt dispenser" (not shown), comprising internal flow distribution means such as one or more baffles, flow vanes, dams, sieves, and perforated plate dispensers. Once inside the reactor housing, salt can flow upwards, repeatedly passing through the reactor housing in the radial direction flowing around a series of evenly spaced double segment baffles 172. Upon reaching the top of the R2 section, the salt The hot can be collected via another circumferential “upper salt dispenser” (not shown), which can additionally comprise flow distribution means, and is transferred via the R2 173 return lines to waste heat boilers (not shown) .
[0097] The configuration of refrigerant flows moving in a direction generally opposite to the process flow (in this case, salt flowing upwards through the housing while the process gas flows downwards through the tubes) is commonly referred to as a countercurrent refrigerant circulation. It should be noted that an alternative configuration in which the refrigerant generally flows downward through the housing and the process gas flows upward through the tubes would also be considered a countercurrent refrigerant circulation. In addition, although the present embodiment comprises three refrigerant circulation systems of the same configuration, it must be recognized that in some cases it may be beneficial to configure some refrigerant circulations as countercurrents while other circulations within the same reactor can be configured as co-currents; such heterogeneous configurations are known as “hybrid” refrigerant circulations.
[0098] An "upstream" configuration of the inventive SSOI reactor process is illustrated in Figure 2. Process gases (comprising propylene, steam, oxygen, and nitrogen) enter the reactor from the bottom, flow vertically upward through of the reactor, and leave the reactor at the top.
[0099] The main sections of the reactor include the inlet head 200, the first reaction step 210 (also referred to here as “R1”), the inter-step heat exchanger 230 (also referred to here as “ISHX”), the inter-step region open 250, the second reaction step 260 (also referred to here as “R2”), and the output head 280. Interfaces 225, 245, and 255 are all permanent connections (eg, welded), while interfaces 205 and 275 are separable connections, allowing reactor heads 200 and 280 to be removed for maintenance.
[00100] The first reaction step 210 contains a plurality of tubes, generally represented in the figure as 215a, 215b, 215c. The inlet end of each of these tubes is attached, for example by welding or rolling, to the sheet of the inlet tube of R1 (not shown per se, but located in the same position in the figure as the detachable connection 205). The inter-step heat exchanger 230 also contains a plurality of tubes, generally represented in the figure as 235a, 235b, 235c, and equivalent in number, diameter, and placement to the tubes of the first reaction step. The outlet end of each ISHX tube segment 235a, 235b, 235c, can be attached, for example by welding or rolling, to the ISHX tube sheet (not shown per se, but located in the same position in the figure as the connection welded 245).
[00101] The inter-step heat exchanger tubes are said to be coaxially continuous with the tubes of R1 of the first reaction step, meaning that tube segment 235a is the upper end of tube 215a, tube segment 235b is the end top of tube 215b, tube segment 235c is the top end of tube 215c, and so on. As previously noted, the direct connection of the inter-step heat exchanger to the first reaction step is referred to here as an integrated inter-step heat exchanger.
[00102] The circulation of refrigerant on the side of the housing R1 can be separated from the refrigerant on the side of the ISHX housing by an inter-stage baffle (not shown per se, but located in the same position in the figure as connection 225); each of the coaxially continuous tubes extending from the R1 inlet tube sheet to the ISHX outlet tube sheet can pass through this inter-stage baffle. It should be noted that the interstage baffle differs from a real tube sheet in that there are no tube-with-baffle welds; instead, the perforations through the interstage chicane have an internal diameter slightly larger than the outer diameter of the tubes (215 a, b, c), such that a small annular gap (not shown) between 0.25 and 2 is formed , 5 mm wide around each tube. The refrigerant circulation on the side of the frame of R1 (not shown) can be arranged in a co-current or counter-current configuration; similarly, the refrigerant circulation on the ISHX housing side can be arranged in a co-current or countercurrent configuration as well, and does not need to correspond to the refrigerant circulation configuration on the R1 housing side.
[00103] In at least one embodiment, the open inter-step region 250 does not contain any tubes. According to the SSOI reactor design of at least one embodiment of the present invention, an open inter-step region may be at least partially filled with one or more inert materials with a high surface area, stable 251, in an amount sufficient to provide at least least 930 m2 (10,000 square feet) of total surface area for scale removal, preferably at least 2,790 m2 (30,000 square feet), and most preferably 3,720 m2 (40,000 square feet).
[00104] The second reaction step 260 may contain a plurality of tubes, generally represented in the figures as 265a, 265b, 265c. The inlet end of each tube in the second reaction step can be attached, for example by welding or rolling, to the R2 inlet tube sheet (not shown per se, but located in the same position in the figure as the welded connection 255) . The outlet end of each section of tube 265a, 265b, 265c, can be attached, for example by welding or laminating, to the sheet of the outlet tube of R2 (not shown per se, but located in the same position in the figure as the interface 275). A new feature of the embodiment illustrated in Figure 2 is that one or more of the number, diameter, and placement of the tubes in the second reaction step (the R2 tubes) are different than the tubes in the first reaction step (the tubes of R1).
[00105] One embodiment of the reactor in Figure 2 has a nominal annual production capacity of 120 kT of acrylic acid. The refrigerant used in this embodiment is DowthermTM heat transfer fluid, available from Dow Chemical Co. of Midland, Michigan USA. In this embodiment there are 22,669 tubes in the first reaction step (R1) and 14,523 tubes in the second reaction step (R2). The tubes of R1 have an internal diameter of 25.4 mm (1 inch) and a length of 4,700 mm (15.4 feet) (from the sheet of the tube of R1 to the interstage baffle) and the tubes of R2 have an internal diameter of 31.8 mm (1.25 inches) and a length of 4,500 mm (14.75 feet). The previously described twistee inserts are installed in each pipe segment of the ISHX. The open inter-step region of this embodiment has a total volume of 40 m3 (1,413 ft3) and is completely filled with 16 mm (5/8 inch) stainless steel Pall rings as the inert material. Such Pall rings have a void fraction of 93% and a specific surface area of 316 m2 / m3, thus providing a total surface area within the open inter-step region of more than 41,480 m2 (446,500 square feet). The Inter-Step Residence Time for this embodiment is 3 seconds.
[00106] One embodiment of the reactor in Figure 2 also has a nominal annual production capacity of 120 kT of acrylic acid. In this embodiment, however, there are 29,410 tubes from the first reaction stage (R1) and 22,672 tubes from the second reaction stage (R2). The tubes of R1 are 22.3 mm (0.878 inches) in internal diameter and 4,600 mm (15.1 feet) long (from the sheet of the tube of R1 to the interstage baffle) and the tubes of R2 are 25.4 mm (1 inch) in internal diameter and 4,200 mm (13.8 feet) in length. Instead of placing the previously described twistee inserts inside the ISHX tubes, the ISHX tubes in this embodiment are instead constructed using “Twisted Tubes”, which are a special helical tube design that induces turbulent flow without the use of insertions that induce turbulence; Twisted Tubes are commercially available from Koch Heat Transfer Company, LP in Houston, Texas USA. The open inter-step region has a total length of 2,438 mm (8 feet) and is filled with 2-inch diameter EnviroStone 66 spheres, providing a total surface area of more than 4,450 m2 (48,000 square feet) and an Inter-Step Residence Time about 2.1 seconds. The refrigerant used in this embodiment is HITEC® salt transfer salt.
[00107] Figures 3a and 3b in combination represent another embodiment of the inventive single-frame open inter-step reactor (SSOI) design comprising more than 16,000 tubes. The reactor in this embodiment has a casing diameter of about 4,800 mm (15.75 feet) and an overall length of more than 18,290 mm (60 feet). At typical feed rates and a propylene feed rate of 2,935 Nm3 / hr (110 MSCFH), the reactor in this embodiment has a nominal annual production capacity of about 63 kT of acrylic acid.
[00108] Feed gases (which may comprise, for example, propylene, steam, oxygen, and nitrogen) enter the reactor from the top (see Figure 3a), flow vertically down through the reactor, and exit the reactor at bottom, ie, operation with downward flow.
[00109] The main sections of the reactor include the inlet head 300, the first reaction step 310 (also referred to here as “R1”), the inter-step heat exchanger 330 (also referred to here as “ISHX”), the inter-step region open 350, the second reaction step 360 (also referred to here as “R2”), and the output head 380. Unless otherwise specified, all components of the reactor in this embodiment are constructed of steel of carbon. The interfaces between adjacent sections, identified in the figures as 305, 325, 345, 355 and 375, can all be permanent connections (eg, welded).
[00110] The inlet head of reactor 300 is about 4,040 mm (13.25 feet) in height and is not removable. It comprises a plurality of 610 mm (24 inch) covers (not shown) on the sides and top of the head for maintenance access. The inlet head additionally comprises a 508 mm (20 inch) process gas inlet.
[00111] According to this embodiment, the first reaction step 310 has a length of 4,600 mm (15.1 feet) and contains a plurality of seamless carbon steel tubes, generally represented in the figure as 315a, 315b , 315c. The inlet end of each tube in the first reaction step is attached, for example by welding or rolling, to the sheet of the inlet tube of R1 (not shown per se, but located in the same position in the figure as connection 305). Each tube within the first reaction step 310 extends through the inter-step baffle 326 (reference to Figure 3b) and passes completely through the inter-step heat exchanger 330, which has a length of 1,956 mm (6.4 feet). This means that tube section 335a is the bottom end of tube 315a, tube section 335b is the bottom end of tube 315b, tube section 335c is the bottom end of tube 315c, and so on. As a result, the actual length of these coaxially continuous tubes is about 6,556 mm (21.5 feet), equivalent to the distance between interfacial connection 305 and interfacial connection 345. The outlet end of each pipe segment 335a, 335b, 335c, is attached, for example by welding or rolling, to the ISHX tube sheet (not shown per se, but located in the same position in the figure as the welded connection 345). As previously described, this design feature is referred to here as an integrated inter-step heat exchanger. It should be noted that, in this embodiment, the inter-step baffle 326 differs from a real tube sheet in that there are no tube-with-baffle welds; instead, the perforations through the interstitch chicane 326 have an internal diameter slightly larger than the outer diameter of the tubes (315 a, b, c), such that a small annular gap (not shown) between 0.25 and 2.5 mm long around each tube. Due to this annular interval, a small volume of ISHX cooling salt (which is preferably supplied at a slightly higher pressure than the R1 cooling salt) can pass continuously through the interstage baffle and mix with the salt circulation cooling capacity of R1. Given the benefit of the present disclosure, means for recycling an appropriate volume of salt from the R1 circulation system back to the ISHX circulation system is easily specified by one of ordinary skill in the process engineering technique and does not need to be described in further detail here.
[00112] As generally indicated in Figure 3a, the region of the first reaction stage of the reactor can comprise an empty cylindrical volume located in the center of the tube sheet, and aligned with the longitudinal axis of the reactor, in which there are no tubes; this empty cylindrical volume has an average diameter of more than 610 mm (2 feet) and extends through the ISHX as well. The annular volume remaining in the first reaction step and in the ISHX comprises more than 16,000 coaxially continuous tubes. Each of these continuous tubes has an internal diameter of 22.3 mm (0.878 inches) and an external diameter 27.3 mm (1.074 inches). The tubes are arranged in a 60 degree triangular pattern, with a tube sheet pitch of 33.73 mm (1.358 inches), resulting in a distance between the tubes of about 6.5 mm (0.254 inches).
[00113] To retain catalyst within these continuous tubes, a plurality of the catalyst support grid panels comprising wire mesh previously described can be directly attached to the ISHX 345 outlet tube sheet. Each of the continuous tubes can then be loaded as follows, starting with the upstream (inlet) end of the tube: • 282 mm (11 inch) spheres with silica-aluminum support SA-5218 with 3/16 inch (4.75 mm) diameter (available from Norton Chemical Process Products Corp, Akron OH, USA) • 905 mm (36 inches) of ACF7-L catalyst (large cylinder) • 3.413 mm (134 inches) of ACF7-S catalyst (small cylinder) • 51 mm (2 inches) ) of 5/16 inch diameter silicon carbide rings (available from Norton Chemical Process Products Corp, Akron OH, USA) • a 1,905 mm (75 inch) length Twistee turbulence induction insert equipped with mesh optional 8x8 wire at the end to be mounted you
[00114] This loading program results in a load of 1.253 kg of total ACF7 catalyst (large + small size cylinders) in each tube of the first reaction step.
[00115] In this embodiment, it is found that the residence time of the process gas through the Inter-Step Heat Exchanger is 0.96 seconds.
[00116] The open inter-step region 350 of this embodiment has a total length of 2,134 mm (7 feet). Its housing comprises two lower covers with a diameter of 610 mm (24 inches) (not shown in Figure 3a), on opposite sides of the reactor (separated by 180 degrees), placed such that the center line of the covers is located at a distance of about 356 mm (14 inches) from the R1 355 inlet tube sheet. In addition, the open inter-step region housing 350 comprises two 610 mm (24 inch) diameter top caps (not shown), on opposite sides of the reactor (separated by 180 degrees), placed such that the center line of the covers is located at a distance of about 356 mm (14 inches) from the ISHX 345 tube sheet. These covers can provide personnel access to the interior of the open inter-step region 350 for catalyst replacements and other maintenance work. The upper lids can also be beneficially employed for transferring particulate materials - such as loose filler spheres, cylinders, tablets, pellets, and granules - in the open inter-step region such as by pouring.
[00117] As indicated generally in Figure 3a, the open inter-step region comprises an internal salt transfer tubing with a diameter of 610 mm (2 feet) 353, aligned with the longitudinal axis of the reactor. The internal salt transfer tubing 353 extends along the length of the open inter-step region, from the ISHX 345 tube sheet to the R2 355 inlet tube sheet, and additionally comprises an integral expansion joint (not shown) to accommodate thermal growth. In this embodiment, about 75% of the remaining annular volume of the open inter-step region is filled with inert Denstone 2000 spheres with a diameter of 38 mm (1.5 inches) in volume (available from Norton Chemical Process Products Corp, Akron OH, USA), generally indicated as 351 in Figure 3a.
[00118] In at least one embodiment, the inert spheres, which self-assemble after pouring into a bed with a fraction of voids of about 40% and a surface area in relation to the apparent volume of 94.5 m2 / m3 ( 28.8 ft2 / ft3), form a bed with an average depth of about 1,600 mm (5.25 feet), and leave an empty space of about 533 mm (1.75 feet) between the top of the Denstone layer 2000 and the bottom surface of the ISHX tube sheet. Therefore, the bed of ceramic spheres occupies an apparent volume of 28.5 m3 (1,006 ft3), and provides more than 2,690 m2 (28,695 square feet) of surface area for removing scale.
[00119] It is found that the residence time of the process gas through the inter-step region is 1.79 seconds. The sum of residence times through ISHX and the Open Inter-step Region results in a combined inter-step residence time of 2.75 seconds.
[00120] In this embodiment, the second reaction step 360 has a length of 2.925 mm (9.76 feet) and contains a plurality of seamless carbon steel tubes, generally represented in the figure as 365a, 365b, 365c. The inlet end of each tube in the second reaction step is attached, for example by welding or rolling, to the sheet of the R2 inlet tube (not shown per se, but located in the same position in the figure as the welded connection 355). The outlet end of each section of the pipe 365a, 365b, 365c, is attached, for example by welding or rolling, to the sheet of the outlet pipe of R2 (not shown per se, but located in the same position in the figure as the welded connection 375).
[00121] As indicated generally in Figure 3a, the region of the second reaction stage of the reactor can comprise an empty cylindrical volume located in the center of the tube sheet, and aligned with the longitudinal axis of the reactor, in which there are no tubes; this empty cylindrical volume has an average diameter of more than 610 mm (2 feet). The remaining annular volume of the second reaction step comprises more than 16,000 tubes, arranged in the same way as the first reaction step, and each of these tubes has an inner diameter of 22.3 mm (0.878 inches) and an outer diameter 27 , 3 mm (1.074 inches). As with the first reaction step, these tubes are arranged in a 60 degree triangular pattern, with a tube sheet pitch of 33.73 mm (1.328 inches).
[00122] To retain catalyst within the tubes of the second reaction step, a plurality of catalyst support grid panels comprising wire mesh previously described can be directly attached to the R2 375 outlet tube sheet. Each of the tubes from the second reaction step it can then be loaded as follows, starting with the upstream end (inlet) of the tube: • 102 mm (4 inches) of balls with 3/16 inch diameter silica-aluminum support SA-5218 ( 4.75 mm) (available from Norton Chemical Process Products Corp, Akron OH, USA) • 800 mm (31.5 inches) of ACS7-L catalyst (large cylinder) • 2,023 mm (79.6 inches) of ACF7-S catalyst ( small cylinder)
[00123] This loading program results in a load of 1.338 kg of total ACS7 catalyst (large + small size cylinders) in each tube of the second reaction step, and a global Catalyst Mass Ratio of 1.05 for the reactor.
[00124] The output head of reactor 380 is about 3,430 mm (11.25 feet) in height and is not removable. It comprises two 610 mm (24 inch) covers (not shown) at the bottom of the head for maintenance access. The outlet head additionally comprises a 610 mm (24 inch) process gas outlet nozzle.
[00125] With reference now to Figure 3b, this embodiment of the inventive SSOI reactor comprises two refrigerant circulation systems independently controlled: the R1 salt circulation system, supporting the first reaction stage 310, and the system ISHX / R2 salt circulation system, supporting the inter-step heat exchanger 330 and the second 360 reaction stage combined. HITEC® heat transfer salt, available from Coastal Chemical Co. of Houston, Texas USA, is used as the refrigerant for both circulation systems in this embodiment.
[00126] Consistent with the teachings of the present disclosure, such a refrigerant system configuration allows the temperature of the process side of the inter-stage heat exchanger to be controlled independently of the process temperature of the first reaction step, allowing the process gas to leave ISHX is kept, for example, at a temperature of at least 240 ° C and not more than 280 ° C. It should be noted, however, that, in this embodiment, the process side temperature of the second reaction step is not controlled independently of the inter-step heat exchanger process temperature.
[00127] Each of these refrigerant circulation systems can comprise one or more salt circulation pumps, waste heat boilers, and associated transfer tubing (not shown), through which the exothermic heat from the oxidation reaction can be recovered to produce a chain of by-products. Optional equipment, such as salt storage tanks, gas salt heaters, integral thermal expansion vessels (also known as salt "stranglers"), and salt transfer pumps can also be included in the salt circulation system. In addition, each of these circulation systems may comprise instrumentation (not shown), such as thermocouples, and automated controls, such as flow control valves, to maintain the temperature and circulation rate of the salt supplied to the reactor at target values. desired.
[00128] For the support section of the R1 310 salt circulation system, the cooling salt enters through the R1 323 supply lines near the top of the section and is evenly distributed around the circumference of the reactor through a channel inlet (not shown), comprising internal flow distribution means such as one or more baffles, flow straws, weirs, sieves, and perforated plate dispensers, and commonly referred to as an “upper salt dispenser”. Once inside the reactor housing, salt can flow downwards, repeatedly passing through the reactor housing in the radial direction, flowing around a series of eleven plates on the side of the housing, placed at approximately 380 mm (1.25 mm) intervals. feet), and known in the heat exchange technique as “double segment baffles” 122 (usually shown as 322). This radial flow pattern ensures good salt-to-tube contact in order to achieve high heat removal efficiency from the tubes. After reaching the bottom of the R1 section, the hot salt can be collected via another circumferential outlet channel (not shown), which can additionally comprise means of distributing the flow, commonly referred to as a “lower salt distributor” and can be transferred through the return lines of R1 321 to waste heat boilers (not shown).
[00129] For the support section of the ISHX / R2 330 and 360 salt circulation system, the cooling salt enters through the ISHX 343 supply lines near the top of section 330 and is evenly distributed around the circumference of the reactor through an inlet channel, comprising internal flow distribution means such as one or more baffles, flow vanes, weirs, sieves, and perforated plate dispensers (“upper salt dispenser”, not shown). Once inside the reactor housing, salt flows downward, repeatedly passing through the reactor housing in the radial direction flowing around a series of four double-segment baffles 342, placed at intervals of approximately 366 mm (1.20 feet) ). After reaching the bottom of the ISHX section, the salt can be transferred through the open inter-step region 350 by flowing down through the internal salt transfer tubing 353 and into the R2 360 section. Once inside the R2 360 section housing , the salt can continue to pass through the reactor housing in the radial direction flowing downward around another series of six Double Segment Chicanes (372), placed at intervals of approximately 390 mm (1.30 feet). After reaching the bottom of the R2 section, the hot salt can be collected through another circumferential outlet channel (not shown), which can additionally comprise means of distribution of the flow (“bottom salt dispenser” - not shown) and transferred through return lines from R2 371 to waste heat boilers (not shown).
[00130] This configuration of salt flows moving in a direction generally equivalent to the process flow (in this case, the salt flowing down through the housing while the process gas flows down through the tubes) is commonly referred to as circulation of refrigerant in competitor. It should be noted that an alternative configuration in which the salt generally flows upwards through the housing and the process gas flows upwards through the tubes would also be considered a co-current refrigerant circulation.
[00131] Figure 4 represents another embodiment of the inventive single-stage Open Intercapas (SSOI) reactor design comprising 22,000 tubes, each with an internal diameter of 22.3 mm (0.878 inches). The reactor in this embodiment has a casing diameter of about 5,600 mm (18.4 feet) and an overall length of no more than 15,240 mm (50 feet). This reactor embodiment further comprises means for adding supplemental oxidant to the inter-step region of the reactor. The flexibility of operation provided by the addition of supplemental oxidant allows some of the oxygen normally fed to the first reaction step to be returned to a point downstream of R1, resulting in a molar ratio of propylene: increased air in the reactor supply, and a reduction favorable in the flammability of the feed gas of the reactor. As will be described in more detail below, the addition of supplemental oxidant may also allow the reactor to operate effectively at higher propylene design feed rates than similarly sized SSOI reactors, thereby providing acrylic acid production capacity. increased. For example, at typical feed rates, the reactor in this embodiment has a nominal annual production capacity of about 110 kT of acrylic acid compared to the reactor embodiment in Figure 1a, which also comprises 22,000 tubes in diameter internal diameter of 22.3 mm, but has a nominal annual production capacity of only about 100 kT of acrylic acid.
[00132] With reference to Figure 4, the feed gases (eg, propylene, steam, oxygen, and nitrogen) enter the reactor from the bottom, flow vertically upwards through the reactor, and exit the reactor on the top. This arrangement is therefore known as an “upward flow” process configuration.
[00133] The main sections of the reactor include the inlet head 400, the first reaction step 410 (also referred to here as “R1”), the inter-step heat exchanger 430 (also referred to here as “ISHX”), the inter-step region open 450, the second reaction step 460 (also referred to here as “R2”), and the output head 480.
[00134] The interfacial connections between adjacent sections, identified in the figures as 405, 425, 445, 455, and 475, can comprise permanent connections (eg, welded) or can optionally comprise separable connections, such as secure flange connections with a plurality of fasteners, such as for example screws or clamps. In the embodiment of Figure 4, interfaces 405 and 475 are separable connections, allowing the input head 400 and output head 480 to be easily removed to replace the catalysts; in addition, interfaces 445 and 455 can also be separable connections, thereby providing improved maintenance access to components within the open inter-step region 450. Interface 425 can be a welded connection.
[00135] The first reaction step 410 has a length of 4,600 mm (15 feet) and contains a plurality of tubes, generally represented in the figure as 415a, 415b, 415c. The inlet end of each of these tubes is attached, for example by welding or laminating, to the sheet of the inlet tube of R1 (not shown per se, but located in the same position in the figure as the detachable connection 405). The R1 inlet tube sheet is 5,517 mm (18.1 feet) in diameter and comprises 22,000 tubes. The tubes have an internal diameter of 22.3 mm (0.878 inches) and an external diameter of 26.9 mm (1.060 inches). The tubes are arranged in a 60 degree triangular pattern, with a 34 mm (1.34 inch) tube leaf pitch, resulting in a 7 mm (0.275 inch) tube spacing.
[00136] The inter-step heat exchanger 430 may also contain a plurality of tubes, generally represented in the figure as 435a, 435b, 435c, and equivalent in number, diameter, and placement in the tubes of the first reaction step. The outlet end of each pipe segment of the ISHX 435a, 435b, 435c, can be attached, for example by welding or rolling, to the ISHX pipe sheet (not shown per se, but located in the same position in the figure as the connection 445).
[00137] The inter-step heat exchanger tubes can be coaxially continuous with the tubes of R1 of the first reaction step, meaning that the tube segment 435a is the downstream end of tube 415a, the tube segment 435b is the end to downstream of tube 415b, tube segment 435c is the downstream end of tube 415c, and so on. As previously noted, such a direct connection from the inter-step heat exchanger to the housing and tubes of the first reaction step is referred to here as an integrated inter-step heat exchanger.
[00138] Turbulence induction inserts, with high void fraction are placed inside the tube segments (435 a, b, c) of the inter-step heat exchanger to intensify heat transfer without the accumulation of fouling. In this specific embodiment, a twistee insert is placed within each pipe segment of the ISHX.
[00139] The circulation of refrigerant on the side of the R1 housing is separated from the refrigerant on the ISHX housing side by an inter-stage baffle (not shown per se, but located in the same position in the figure as connection 425); each of the coaxially continuous tubes extending from the sheet of the R1 inlet tube to the ISHX outlet tube sheet can pass through this interstage baffle. As previously described, the interstage baffle differs from a real tube sheet in that there are no tube-with-baffle welds; instead, the perforations through the interstage baffle have an internal diameter slightly larger than the outer diameter of the tubes (415 a, b, c), such that a small annular gap (not shown) between 0.25 and 2 is formed , 5 mm wide around each tube. The refrigerant circulation on the side of the frame of R1 can be arranged in a co-current or counter-current configuration; similarly, the refrigerant circulation on the ISHX housing side can be arranged in a co-current or countercurrent configuration as well, and does not need to correspond to the refrigerant circulation configuration on the R1 housing side.
[00140] The open inter-step region 450 does not contain any tubes and has a total length of 3,137 mm (10.3 feet). According to the SSOI reactor design of the present invention, the open inter-step region is at least partially filled with one or more inert materials with a high surface area, stable 451, in an amount sufficient to provide at least 930 m2 (10,000 square feet) of total surface area for removing scale, such as, for example, 2,790 m2 (30,000 square feet), or 3,720 m2 (40,000 square feet). In this embodiment, the inert material with a high, stable surface area is ceramic foam tiles with 20 ppi ("pores-per-inch"), generally rectangular in shape and available in thicknesses between about 12 mm and 305 mm (between 0.5 and 12 inches). Suitable ceramic foam tiles are commercially available from several suppliers, including: Ultramet from Pacoima, California USA; ERG Aerospace Corporation of Oakland, California USA; Selee Corporation of Hendersonville, North Carolina USA; Sud-Chemie Hi-Tech Ceramics from Alfred, New York USA.
[00141] Ceramic foam tiles with 20 ppi specific to this embodiment have a thickness of 51 mm (2 inches), a relative density of 8%, a fraction of voids of 92%, and an effective surface area of about 1,260 m2 / m3 (384 ft2 / ft3). These ceramic foam tiles can be placed directly on the ISHX 445 outlet tube sheet and adjusted together to uniformly cover the entire surface of the tube sheet. Multiple layers of tiles are stacked to achieve a continuous bed of ceramic foam with a planar top surface and a uniform thickness of 152.4 mm (6 inches). Such a bed of ceramic foam provides a total surface area of more than 4,550 m2 (49,000 square feet) for removing scale.
[00142] Within the inter-step 450 region and immediately downstream of the ceramic foam bed is a supplementary oxidant mixture assembly. In this embodiment, the specific mixer assembly is referred to herein as a "Venturi mixer", but other supplementary oxidant mixer assemblies can also be used without departing from the spirit of the present invention.
[00143] Supplemental oxidant supply line 446 provides supplemental oxidant, comprising, for example, oxygen and optionally one or more inert, such as, for example, nitrogen, water, or carbon dioxide, as a gas stream to the gas mixer Venturi. Supplementary oxidizer heat exchanger 447 can be used to adjust the temperature of the supplemental oxidizer before reaching the Venturi mixer. Optional flow control means, such as a flow control valve (not shown), may also be present in the supplementary oxidizer supply line 446.
[00144] The Venturi mixer of this embodiment comprises three sections, interconnected to form a flow-through mixing assembly, continuous: an inlet shrink section 452, an intermediate throat section 453, and an expansion section of outlet 454. The overall length of the Venturi mixer is 2,985 mm (9.79 feet).
[00145] In this embodiment, the inlet contraction section 452 is a truncated cone with an inlet diameter of 5,517 mm (18.1 feet), an outlet diameter of 1,219 mm (4 feet), a length 378 mm (1.24 ft) and an included 160 degree angle. Optionally, the contraction section 452 comprises a plurality of separable segments, or “staves”, each with a selected geometry to allow easy passage of the staves through an access distributor (not shown) on the open inter-step carcass wall 450 The use of such separable segments can improve access for maintenance within the open inter-step region and can reduce the need to use separable connections on interfaces 445 and 455.
[00146] The intermediate throat section 453 is a cylinder with an internal diameter of 1,219 mm (4 feet) and an overall length of 457 mm (18 inches); this throat section comprises one or more combination elements (not shown) selected from the list including nozzles, injectors, gas-gas mixing elements, distributors, vacuum cleaners, coanda effect mixing elements, sprinklers, static mixing elements, eductors, and spears.
[00147] The outlet expansion section 454 is a truncated, inverted cone with an inlet diameter of 1,219 mm (4 feet), an outlet diameter of 5,517 mm (18.1 feet), an overall length of 2,149 mm ( 7.05 feet), and an included 90 degree angle. Optionally, the expansion section 454 comprises a plurality of separable segments, or staves, each with a selected geometry to allow easy passage of the staves through an access distributor (not shown) on the casing wall of the open inter-step region 450. O use of such separable segments can improve access for maintenance within the open inter-step region and can reduce the need to use separable connections on interfaces 445 and 455.
[00148] The second reaction step 460 has a length of 4,500 mm (14.76 feet) and contains a plurality of tubes, generally represented in the figure as 465a, 465b, 465c. The inlet end of each tube in the second reaction step is attached, for example by welding or rolling, to the R2 inlet tube sheet (not shown per se, but located in the same position in the figure as the 455 interfacial connection). The outlet end of each section of tube 465a, 465b, 465c, can be attached, for example by welding or laminating, to the R2 outlet tube sheet (not shown per se, but located in the same position in the figure as the connection separable 475). The R2 inlet tube sheet is 5,517 mm (18.1 feet) in diameter and comprises 22,000 tubes. The leaf arrangement of the R1 inlet tube is the same as the leaf of the R1 inlet tube. The tubes within the second reaction step have an internal diameter of 22.3 mm (0.878 inches) and an external diameter 26.9 mm (1.060 inches). The tubes are arranged in a 60 degree triangular pattern, with a 34 mm (1.34 inch) tube leaf pitch, resulting in a 7 mm (0.275 inch) tube spacing. Therefore, in the embodiment illustrated in Figure 4, the number, diameter, and placement of the tubes in the second reaction step (the tubes of R2) are the same as those of the tubes in the first reaction step (the tubes of R1 ).
[00149] In this embodiment, the catalyst of the first reaction step (R1) and the catalyst of the second reaction step (R2) are both retained in their respective reactor tubes using catalyst support grid panels comprising mesh of wire. Each of the R1 tubes is loaded with 1.295 kg of ACF7 catalyst and each of the R2 tubes is loaded with 1.962 kg of ACS7 catalyst, resulting in a catalyst mass ratio of 1.52.
[00150] Although not shown in Figure 4, this embodiment of the inventive SSOI reactor can comprise three independently controlled refrigerant circulation systems, which provide the ability to individually adjust the temperature of each chilled section (410, 430, 460) as necessary. HITEC® heat transfer salt, available from Coastal Chemical Co. of Houston, Texas USA, is used as the refrigerant for all three circulation systems in this embodiment. The systems are referred to here as the R1 salt circulation system, supporting the first reaction step 410; the ISHX salt circulation system, supporting the 430 inter-step heat exchanger; and the R2 salt circulation system, supporting the second reaction stage 460.
[00151] Consistent with the design of the present invention, such a refrigerant system configuration allows the temperature of the process side of the inter-stage heat exchanger to be controlled independently of the process temperature of the first reaction step, ensuring that the process gas leaving ISHX can be maintained, for example, at a temperature of at least 240 ° C and not more than 280 ° C. Although not an essential feature of the inventive design, this specific embodiment also provides the ability to control the temperature of the process side of the second reaction step regardless of the process temperature of the inter-step heat exchanger. Other characteristics of the salt circulation systems on the carcass side, including system equipment and baffles on the carcass side, are consistent with the previously described embodiment of Figure 1b. It should be noted that the refrigerant flows of the present embodiment, generally moving in a direction that is equivalent to the process flow - that is, salt flowing upward through the housing while the process gas also flows upward through the tubes - are commonly referred to as a co-current refrigerant circulation. It is possible to configure the refrigerant flow of this embodiment to generally flow downwards in a countercurrent refrigerant circulation, or even a "hybrid" refrigerant circulation. In at least one embodiment of the present disclosure, the use of co-current refrigerant circulation is used.
[00152] In the operation of this exemplary embodiment, the feed gas mixture enters the first reaction step 410 to produce an output gas stream of R1 comprising acrolein. The outgoing gas stream of R1 is rapidly cooled in the integral inter-step heat exchanger 430 to a temperature of between 240 ° C and 280 ° C and then passed through the uncooled bed of inert ceramic foam with a high surface area 451. The gas outlet of cooled and filtered R1 then enters the contraction section 452 of the Venturi mixer. The supplementary oxidant supply line 446 continuously provides a supplementary oxidant stream, comprising air and water vapor, to the heat exchanger 447 where the supplemental oxidant stream is brought to a temperature of about 260 ° C before being transferred for the throat section 453. In the throat section 453, combining elements (not shown) quickly mix the supplemental oxidant stream with the R1 outlet gas to form an oxygen enriched feed stream of R2 at a temperature of between 240 ° C and 280 ° C. The oxygen-enriched R2 feed stream then passes through the expansion section 454 of the Venturi mixer and is distributed to the tubes in the second reaction step for further conversion to acrylic acid.
[00153] The supply gases for this embodiment are described in Table 7A (see "Case 2" on the right side of the table), together with those for the embodiment of Figure 1a (see "Case 1" on the side left of the table). Note that chemical grade propylene is used as the primary hydrocarbon feed in both of these embodiments (hereinafter “C3”), which comprises 90% of propylene molecules. Table 7A illustrates how the operation of the inventive SSOI reactor with the supplementary oxidant addition feed of this embodiment can increase the propylene rate, and therefore the reactor productivity, by at least 10%.


[00154] Figure 5 represents a further embodiment of the inventive single-shell Open Inter-step reactor (SSOI) design comprising means for adding supplemental oxidant to the inter-step region of the reactor.
[00155] Feed gases (eg, propylene, steam, oxygen, and nitrogen) enter the reactor from the top, flow vertically down through the reactor, and exit the reactor at the bottom. This arrangement is a “downward flow” process configuration.
[00156] The main sections of the reactor include the domed inlet head 500, the first reaction step 510 (also referred to here as “R1”), the inter-step heat exchanger 530 (also referred to here as “ISHX”), the region open inter-steps 550, the second reaction step 560 (also referred to here as “R2”), and the conical exit head 580.
[00157] The interfacial connections between adjacent sections, identified in the figures as 505, 525, 545, 555, and 575, can comprise permanent connections (eg, welded) or can optionally comprise separable connections, such as secure flange connections with a plurality of fasteners, such as for example screws or clamps. In the embodiment of Figure 5, interfaces 505 and 575 are separable connections, allowing the inlet head 500 and the conical outlet head 580 to be easily removed to replace the catalysts; additionally, in at least one embodiment, at least one of interfaces 545 and 555 is also separable connections, thereby providing improved maintenance access to components within the open inter-step region 550. Interface 525 can be a welded connection.
[00158] The first reaction step 510 contains a plurality of tubes with an internal diameter of 22.3 mm (0.878 inches), generally represented in the figure as 515a, 515b, 515c. The inlet end of each of these tubes is attached, for example by welding or laminating, to the sheet of the inlet tube of R1 (not shown per se, but located in the same position in the figure as the separable connection 505). The inter-step heat exchanger 530 can also contain a plurality of tubes with an internal diameter of 22.3 mm (0.878 inches), generally represented in the figure as 535a, 535b, 535c, and equivalent in number, diameter, and placement in the tubes of the first reaction step. The outlet end of each pipe segment of the ISHX 535a, 535b, 535c, can be attached, for example by welding or rolling, to the ISHX pipe sheet (not shown per se, but located in the same position in the figure as the connection interfacial 545).
[00159] The inter-step heat exchanger tubes are coaxially continuous with the tubes of R1 of the first reaction step, meaning that the tube segment 535a is the lower end of tube 515a, the tube segment 535b is the lower end of the tube 515b, tube segment 535c is the bottom end of tube 515c, and so on. As previously noted, such a direct connection from the inter-step heat exchanger to the housing and tubes of the first reaction step is referred to here as an integrated inter-step heat exchanger.
[00160] Turbulence induction inserts, with high void fraction are placed inside the tube segments (535 a, b, c) of the inter-step heat exchanger to intensify heat transfer without the accumulation of fouling.
[00161] The circulation of refrigerant on the side of the housing of R1 is separated from the refrigerant on the side of the ISHX housing by an inter-stage baffle (not shown per se, but located in the same position in the figure as connection 525); each of the coaxially continuous tubes extending from the R1 inlet tube sheet to the ISHX outlet tube sheet can pass through this inter-stage baffle. As previously described, the interstage baffle differs from a real tube sheet in that there are no tube-with-baffle welds; instead, the perforations through the interstage baffle have an internal diameter slightly larger than the outer diameter of the tubes (515 a, b, c), such that a small annular gap (not shown) between 0.25 and 2 is formed , 5 mm wide around each tube. The refrigerant circulation on the side of the frame of R1 can be arranged in a co-current or counter-current configuration; similarly, the refrigerant circulation on the ISHX housing side can be arranged in a co-current or countercurrent configuration as well, and does not need to correspond to the refrigerant circulation configuration on the R1 housing side.
[00162] In this specific embodiment, the open inter-step region 550 does not contain any tubes and has a total length of about 6,170 mm (20.25 feet). According to the SSOI reactor design of the present invention, the open inter-step region can be at least partially filled with one or more inert materials with a high surface area, stable 551 and 556, in an amount sufficient to provide at least 930 m2 (10,000 square feet) of total surface area for scale removal, preferably at least 2,790 m2 (30,000 square feet), and most preferably 3,720 m2 (40,000 square feet). In this embodiment, the inert material with a high, stable surface area 556 is ceramic foam tiles with 20 ppi (“pores-per-inch”), generally rectangular in shape and having a relative density of 8%, a fraction of 92% voids, and an effective surface area of about 1,260 m2 / m3 (384 ft2 / ft3). The ceramic foam tiles are placed in direct contact with the ISHX outlet tube sheet (545) and arranged in such a way as to achieve a continuous bed of ceramic foam with a planar top surface and a uniform thickness of 76 mm (3 inches). It is preferred that this ceramic foam bed is held in place using catalyst support grid panels comprising wire mesh, although other means of protection can optionally be used. As configured in this embodiment, such a ceramic foam bed provides a total surface area of more than 2,229 m2 (24,650 square feet) for removing scale.
[00163] Within the inter-step 550 region and immediately downstream of the ceramic foam bed is a supplementary oxidant mixture assembly; in this embodiment, the specific mixer assembly is a "Venturi mixer", but other supplementary oxidant mixer assemblies can also be used without departing from the spirit of the present invention.
[00164] Supplemental oxidant supply line 546 provides supplemental oxidant comprising oxygen and optionally one or more inert, such as for example nitrogen, water, or carbon dioxide, as a gas stream for the Venturi mixer. Supplementary oxidizer heat exchanger 547 can be used to adjust the temperature of the supplemental oxidizer before reaching the Venturi mixer. Optional flow control means, such as a flow control valve (not shown), may also be present in the supplementary oxidant supply line 546.
[00165] The Venturi mixer in this embodiment comprises three sections, interconnected to form a continuous flow mixing assembly: an inlet shrink section 552, an intermediate throat section 553, and an outlet expansion section 554 The overall length of the Venturi mixer is 6,096 mm (20 feet).
[00166] Inlet twitch section 552 is a truncated, inverted cone with an inlet diameter of 5,486 mm (18 feet), an outlet diameter of 305 mm (12 inches), an overall length of 1,494 mm (4, 9 feet) and an included 120 degree angle. In this embodiment, inert material with an additional high, stable surface area 551 is placed within the inlet shrink section 552; specifically, the shrinkage section 552 is completely filled with inert ceramic balls EnviroStone 66 with a diameter of 25.4 mm (1 inch), which provide an additional 1,769 m2 (19,000 square feet) of surface area for removing scale. When combined with the 20 ppi ceramic foam layer adjacent to the ISHX tube sheet, this results in a total surface area within the 550 open inter-step region of more than 4,060 m2 (43,700 square feet). A horizontal wire mesh screen (not shown) is also placed at the intersection of the shrink section 552 and throat section 553 to support the inert spheres and prevent them from entering the throat section 553.
[00167] The intermediate throat section 553 is a cylinder with an internal diameter of 305 mm (12 inches) and an overall length of 1,219 mm (4 feet); this throat section comprises one or more combination elements 548 selected from the list including nozzles, injectors, gas-gas mixing elements, dispensers, vacuum cleaners, coanda effect mixing elements, sprinklers, static mixing elements, eductors, and lances. Without being combination elements, it is preferable that the throat section 553 is free of obstructions such that the mixing efficiency is maximized, eg, in at least one embodiment, the throat section does not comprise inert material with a high area superficial, stable.
[00168] In this specific embodiment, the combining element 548 comprises a gas-gas mixing element. An example of a suitable gas-gas mixing element is disclosed in EP1726355 (B1). Other examples of suitable gas-gas mixture elements include commercially available elements, such as OXYNATORTM Oxygen Injectors (available from Air Liquide Paris, France) and OXYMIXTM (available from Linde Gas Division of Linde AG, Hollriegelskreuth, Germany).
[00169] When a gas-gas mixing element is used as the combining element, the element may be placed near the upstream end of the throat section 553, such that there are diameters of at least 3 unobstructed length pipes downstream of the element. Accordingly, in this embodiment, the combining element 548 is placed at a distance of no more than 305 mm (12 inches) from the upstream end of the throat section 553.
[00170] Output expansion section 554 is a truncated cone with an inlet diameter of 305 mm (12 inches), an outlet diameter of 5,486 mm (18 feet), an overall length of 3,377 mm (11.1 feet) ), and an included angle of 75 degrees. Expansion section 554 is empty, i.e., it does not comprise inert material with a high, stable surface area.
[00171] Optionally, at least a portion of the open interstage carcass wall 550 comprises removable carcass segments, as indicated by the dotted lines in Figure 5. In one embodiment, the removable carcass segments extend from the interface 545 to 555, providing sufficient access to remove one or more complete sections (552, 553, or 554) of the Venturi mixer from the open inter-step region 550. In another embodiment, the casing wall of the open inter-step region 550 may be completely removed from the reactor, providing sufficient clearance to remove all three sections of the Venturi mixer simultaneously. The use of such removable housing segments can reduce the need for access covers on the housing wall of the inter-step 550 region.
[00172] The second reaction step 560 contains a plurality of tubes with an internal diameter of 31.75 mm (1.25 inches), generally represented in the figure as 565a, 565b, 565c. The inlet end of each tube in the second reaction step is attached, for example by welding or rolling, to the R2 inlet tube sheet (not shown per se, but located in the same position in the figure as the 555 interfacial connection). The outlet end of each section of tube 565a, 565b, 565c, is attached, for example by welding or rolling, to the sheet of the outlet tube of R2 (not shown per se, but located in the same position in the figure as the separable connection 575). In this embodiment, the number and diameter of the tubes in the second reaction step (the tubes of R2) differ from those of the tubes in the first reaction step (the tubes of R1).
[00173] Although not shown in Figure 5, this embodiment of the inventive SSOI reactor additionally comprises three independently controlled refrigerant circulation systems, which provide the ability to individually adjust the temperature of each chilled section (510, 530, 560) as necessary. The systems are referred to here as the R1 salt circulation system, supporting the first reaction step 510; the ISHX salt circulation system, supporting the 530 inter-step heat exchanger; and the R2 salt circulation system, supporting the second reaction step 560. In at least one embodiment, Syltherm ™ heat transfer fluid (available from Dow Chemical Co. of Midland, Michigan USA) is used as the refrigerant medium for all three circulation systems.
[00174] Consistent with the design of the present invention, such a refrigerant system configuration allows the temperature of the process side of the inter-stage heat exchanger to be controlled independently of the process temperature of the first reaction step, ensuring that the process gas leaving ISHX can be maintained at a temperature of at least 240 ° C and not more than 280 ° C. Although not an essential feature of the inventive design, this specific embodiment also provides the ability to control the temperature on the process side of the second reaction step regardless of the process temperature of the inter-step heat exchanger; such additional ability to control the operation of the oxidation process is used in at least one embodiment of the present invention. Other characteristics of the salt circulation systems on the carcass side, including system equipment and baffles on the carcass side, are consistent with the previously described embodiment of Figure 1b. It should be noted that the refrigerant flows of the present embodiment, generally moving in a direction that is opposite to the process flow - that is, refrigerant medium flowing upward through the housing while the process gas also flows downward through the tubes - are commonly referred to as countercurrent refrigerant circulation. It is also feasible to configure the refrigerant flow of this embodiment to generally flow downward in a co-current refrigerant circulation, or even a "hybrid" refrigerant circulation, in which some refrigerant flows are co-current while others are counter-current. Additionally, it is envisaged that in some embodiments it may be advantageous to use more than one refrigerant medium for a single reactor, such as, for example, Syltherm ™ fluid transfer fluid in the R1 refrigerant circulation system and the circulation system of ISHX refrigerant, and HITEC® salt in the refrigerant circulation system of R2.
[00175] When operated under the supplementary oxidant addition conditions summarized in Case 2 of Table 7A, the reactor in this embodiment has a nominal acrylic acid capacity of 110 kT per year. It has also been determined that the inter-step residence time for this embodiment, the total sum of the residence time through the inter-step heat exchanger, the ceramic foam layer, and each section of the Venturi mixer, is 2.56 seconds. Example 7 (below) illustrates how the inter-step residence time is calculated for SSOI reactors operated with the addition of supplemental oxidant.
[00176] Figure 6 provides a detailed view of an embodiment of a supplementary oxidant mixture assembly, useful in SSOI reactors operated with the addition of supplemental oxidant. In this embodiment, the supplementary oxidant mixture assembly is a Venturi mixer comprising a new injector ring, and said Venturi mixer is shown in an upward process flow orientation, in which the process gases enter from from the bottom through the inlet shrink section 650, pass through the middle throat section 630, and exit through the outlet expansion outlet 640. Such an orientation can be useful in upstream process reactors, such as for example reactor embodiment of Figure 4. Although described here in an upward flow orientation of the process it should be noted that the Venturi mixer device of Figure 6 could also be beneficially employed in a downward flow orientation.
[00177] In this embodiment, the Venturi mixer rests on a 150 mm (6 inch) thick layer of 660 stainless steel open cell foam. The inlet shrink section 650 has a conical shape, with a D1 base dimension of 5517 mm (18.1 feet), an H1 height of 379 mm (1.24 feet), and an included A1 angle of 160 degrees. Section 650 additionally comprises mounting flange 651, which is approximately 76 mm (3 inches) thick. In at least one embodiment, the interior volume of the inlet contraction section comprises a particulate internal material having an apparent void fraction of less than 50%. In one embodiment, for example, 50% of the interior volume of the inlet shrink section 650 is occupied with inert Denstone 57 spheres with a diameter of 25.4 mm (1 inch) (represented in the figure as 655) to reduce the time of residence in this section of the Venturi mixer.
[00178] The intermediate throat section 630 is cylindrical, with an internal diameter D0 of 1,219 mm (4 feet). Section 630 has an overall H0 height of 457 mm (1.5 feet), which results from a 305 mm (12 inch) thick wall section in combination with a pair of 76 mm (3 inch) mounting flanges 641 and 651; mounting flanges 641 and 651 provide a separable connection to section 630 and are held in place with removable fasteners (not shown), such as screws. The interior of the throat section 630 comprises an integral annular channel 631 which is fluidly connected to a plurality of injection ports 635 and is referred to herein as an "injection ring"; injection ports 635 are the combining elements of the injection ring and serve to distribute the supplementary oxidant stream evenly across the throat section of the Venturi mixer device.
[00179] In the embodiment of Figure 6, the injector ring employs a total of 216 injection ports, each 9.5 mm (3/8 inches) in diameter. As shown in the figure, these injection ports are configured in three parallel lines, placed in a regular triangular / staggered pattern along the inner surface of the injection ring. Each line contains 72 injection ports, evenly spaced around the inner circumference of the injection ring, with a distance of about 44 mm (1.7 inches) between each port on the line. At least one Supplemental Oxidant supply line 633 is connected to throat section 630, providing a path for supplementary oxidant feed gas to enter annular channel 631. In this embodiment, supplemental oxidant supply line 633 has 203 mm (8 inches) in diameter and comprises means for temperature control, such as an optional upstream temperature control heat exchanger (not shown), and also means for flow control, such as a flow control valve upstream (not shown). In at least one embodiment, the diameter of the supply line 633 is large in relation to the size of the injection ports 635 to intensify the distribution of the feed gas around the entire circumference of the injection ring; for example, the ratio of the diameter of the supply line 633 to the diameter of the injection port 635 can be at least 10, such as at least 15 or at least 20. In this specific embodiment, the diameter of the supply line is 203 mm and the diameter of the injection port is 9.5 mm, making the ratio of the diameter of the supply line 633 to the diameter of the injection port 635 21. This large ratio also ensures a sufficient pressure drop to withstand reflux of exhaust gases. potentially flammable process from the injector ring to the supplementary oxidant supply line 633. Optional filtration of the supplementary oxidant gas stream can also be employed to minimize potential blockage of small diameter injection ports with unwanted material, such as rust particles, or trapped liquid droplets.
[00180] The output expansion segment 640 can be tapered, with a D2 base dimension of 5517 mm (18.1 feet), an H2 height of 2149 mm (7 feet), and an included A2 angle of 90 degrees . The segment 640 additionally comprises the mounting flange 641, which is approximately 76 mm (3 inches) thick. In at least one embodiment, the interior volume of the output expansion segment 640 is empty.
[00181] When the supplementary oxidant mixture assembly of this embodiment, which includes the Denstone beads mentioned above in the shrink segment 650, is installed in an SSOI reactor of the type previously illustrated in Figure 4, and is additionally operated under the conditions of Table 7A, Case 2 (eg, a propylene rate of 9,702 kg / hr and a total supplemental oxidant flow of 6,437 Nm3 / hr), the resulting SSOI reactor will operate with an inter-step residence time of about 2 , 5 seconds and will have more than 4,850 m2 (52,300 square feet) of inert surface area within the inter-step region.
[00182] The combination of the SSOI reactor of the present invention with an acrylic acid collection and purification system can result in an improved process for the manufacture of commercially pure acrylic acid. For example, a countercurrent absorption tower provided with an absorbent liquid stream, such as for example water or diphenyl, can be used to collect acrylic acid from the reactor product gas, thereby forming a crude product solution comprising acrylic acid. and absorbent. The acrylic acid can then be recovered from the crude product solution using separation steps such as solvent extraction and azeotropic distillation. Examples of such absorption-based acrylic acid collection and purification systems are provided in U.S. Pat. 5,426,221; 6,639,106; and 6,998,505.
[00183] Figure 8 shows an embodiment of the present invention relating to an integrated process for the manufacture of acrylic acid, comprising an SSOI reactor with upward flow (830) and a solvent-free acrylic acid collection and purification system. The solvent-free acrylic acid collection and purification system comprises a dehydration column and a finishing column.
[00184] The large scale commercial SSOI reactor of this specific embodiment has an advertised acrylic acid capacity of 160 kT / year and the solvent-free acrylic acid collection and purification system, referred to here as the “SFT” system, is sized to provide equivalent (matched) acrylic acid processing capacity. An example of an SFT system is disclosed in U.S. Patent No. 8,242,308, which is incorporated herein by reference. The use of an SFT system in combination with the SSOI reactor of the present invention can provide at least one of the following benefits over the combination of the SSOI reactor with traditional acid absorption based acrylic acid collection and purification processes: (1) The system SFT does not comprise any absorption tower, and therefore does not require the addition of absorbents, such as for example liquid streams comprising diphenyl or water (2) The SFT system is capable of dehydrating crude acrylic acid without using extraction solvents, such as such as ethyl acrylate, or distillation solvents that form azeotropic mixtures with water, such as for example methyl and isobutyl ketone (MIBK), ethyl acetate, toluene, or isopropyl acetate.
[00185] Such improvements can vastly simplify the production of acrylic acid and reduce the amount of process equipment required, thereby resulting in significant savings in operating costs and capital over prior art processes.
[00186] With regard to Figure 8, the 830 reactor is built with removable inlet and outlet reactor heads. At design conditions propylene is provided to the reactor at a flow rate of more than 14,100 kilograms per hour (31,000 pounds per hour). Propylene, Air, Recycle Gas (stream 814), and optionally steam, are combined together using in-line static mixing elements to form a mixed feed gas with a propylene concentration of at least 7.5% per mol, a molar ratio of oxygen to propylene of between 1.6 and 2.0, and a molar ratio of water vapor to propylene of about 1.2 or less. In one embodiment, the mixed feed gas has a propylene concentration of at least 8% per mol, and the molar ratio of oxygen to propylene is about 1.8, and the molar ratio of water vapor to propylene ratio is about 0.75 or less
[00187] The mixed feed gas enters the bottom of the reactor through the common feed line 831 at a temperature higher than the dew point temperature of the mixture. In one embodiment, the mixed feed gas enters the reactor at a temperature of less than about 200 ° C, for example about 195 ° C or even about 145 ° C. One or more heat exchangers and propylene vaporizers (not shown) can optionally be used to control the temperature of the individual feed gases, thereby controlling the temperature of the mixed feed gas entering the reactor. Optionally, the temperature of the recycle gas stream 814 can be controlled by exchanging heat with the Product gas stream 801; the heat exchanger device 832 may be configured for this purpose (not shown). The first reaction step, which is at the bottom of the reactor, comprises more than 33,000 seamless carbon steel tubes with an inner diameter of 25.4 mm, arranged in a 60 degree triangular pattern, and has a length of 3,750 mm (12.3 feet). Each tube within the first reaction step is coaxially continuous with the inter-step heat exchanger tubes, located immediately downstream of the first reaction step and referred to here as an integrated inter-step heat exchanger. Therefore, the inter-step heat exchanger (ISHX) also comprises more than 33,000 seamless carbon steel tubes with an internal diameter of 25.4 mm. The ISHX has a length of 2,100 mm (6.9 feet). The total length of the continuous tubes passing through both the first reaction step and the inter-step heat exchanger is therefore 5,850 mm (19.2 feet). To retain catalyst within these continuous tubes, a plurality of the previously described catalyst support grid panels comprising wire mesh is directly attached to the tube sheet of the first stage. Each of the continuous tubes is then loaded as follows, starting with the upstream (inlet) end of the tube: • 250 mm (10 inches) of inert ceramic balls EnviroStone 66 with a diameter of M inches (6 mm) • 730 mm ( 29 inches) of ACF7-L catalyst (large cylinder) • 2770 mm (109 inches) of ACF7-S catalyst (small cylinder) • a 2100 mm (83 inch) length twistee turbulence induction insert
[00188] This loading program results in a load of 1.042 kg of total ACF7 catalyst (large + small size cylinders) in each tube of the first reaction step. The residence time of the process gas through the inter-stage heat exchanger is about 0.94 seconds.
[00189] The process gases leave the heat exchanger inter-steps at a temperature of no more than about 280 ° C (536 ° F) and then pass through the open inter-step region. Additional supplemental oxidizer 835, such as air or other oxygen-containing gases, can be passed through the optional heat exchanger 836 and then added to the open inter-step region; in such cases, optional mixing devices, such as for example a Venturi mixer of the type previously described here and further illustrated in Figure 6, can be used to safely homogenize the process gas and supplemental oxidant mixture. In this specific embodiment, however, no additional oxidant is added to the open inter-step region.
[00190] The open inter-step region has a length of 2,100 mm (6.9 feet) and is loaded with inert EnviroStone 66 spheres with a diameter of 38 mm (1.5 inches) enough to occupy about 90% of the volume within the inter-step region open, thus providing a bed of ceramic spheres with an average depth of more than 1,895 mm (6.2 feet) and more than 4,180 m2 (more than 45,000 square feet) of surface area for removing scale. Additionally, the inter-step residence time (ISHX residence times and open inter-step region combined), as measured at the reference conditions of 240 ° C and 30 psia (2 atm), is about 2.2 seconds, ie, residence of less than 3 seconds.
[00191] The process gases then pass to the second reaction stage, located in the upper portion of the reactor. The second reaction step has a length of 3,405 mm (11.2 feet). The second reaction step has a tube count, tube inner diameter, and tube arrangement equal to that of the first reaction step, thus also comprising more than 33,000 seamless carbon steel tubes with an inner diameter of 25.4 mm, arranged in a 60 degree triangular pattern. To retain catalyst within these continuous tubes, a plurality of the previously described catalyst support grid panels comprising wire mesh is directly attached to the tube sheet of the second stage. Each of these tubes is loaded as follows, starting with the upstream (inlet) end of the tube: • a modified twistee insert of overall length 305 mm (12 inches), comprising a tapered retaining spring with a length of 25.4 mm (1 inch) attached to the upstream end of a 280 mm (11 inch) length twistee turbulence induction insert • 640 mm (25 inch) ACS7-L catalyst (large cylinder) • 2260 mm (89 inch) ACS7-S catalyst (small cylinder) • 200 mm (7.9 inches) of inert ceramic EnviroStone 66 balls with a diameter of M inches (6 mm)
[00192] This loading program results in a load of 1.417 kg of total ACS7 catalyst (large + small size cylinders) in each tube of the second reaction step, and provides a global Catalyst Mass Ratio of 1.36 for the reactor .
[00193] All three primary regions of the reactor (first reaction stage, inter-step heat exchanger, and second reaction stage) can be cooled by their refrigerant circulation systems on the side of the housing, independently. One or more of DowthermTM, SylthermTM, or HITEC® salt can be used as the cooling medium; in this specific embodiment, molten HITEC® salt is used. Although not specifically shown in the figure, each of these refrigerant circulation systems comprises other components, such as pumps, refrigerant flow control valves, and steam boilers, and operates in a co-current circulation configuration, meaning that , for each region of the reactor, a stream of cold salt enters the lower portion of the region and a stream of hot salt leaves the upper portion of the region.
[00194] The product gas comprising acrylic acid 801 leaves the top of the reactor and is cooled in the indirect heat exchanger 832 to a temperature of about 225 ° C (437 ° F). The indirect heat exchanger 832 can comprise one or more heat transfer devices, including but not limited to shell and tube heat exchangers, jacketed tubes, plate heat exchangers (PHEs), heat exchangers with twisted tubes, and spiral heat exchangers. In this embodiment, the heat exchanger 832 is a shell and tube heat exchanger. In an alternative embodiment, the indirect heat exchanger 832 is omitted and the SSOI reactor comprises an integral outlet cooler (not shown), located between the outlet tube (top) leaf of the second reaction step and the head of the output reactor. Such an integral outlet cooler has a design similar to the inter-step heat exchanger, having tubes that are coaxially continuous with the tubes of the second reaction step, an independent refrigerant circulation, and turbulence induction inserts with a high fraction of voids within each pipe.
[00195] The cooled product gas then enters the lower portion of the dehydration column 810, where it is directly contacted by a spray of circulating liquid. A stream of liquid dehydration waste 816 is removed from the bottom of the column 810 and a portion of the stream (820) is transferred to the cooler 812, which may comprise one or more cooler or forced circulation coolers. The heated stream is then supplied (via transfer line 811) to the spray device within the lower portion of the dewatering column 810; such a dehydration column configuration is known here as an "integrated extinction" step. In an alternative embodiment, this step of extinguishing liquid contact is carried out in one or more vessels (not shown) immediately upstream of the dehydration column 810; such an alternative embodiment is referred to as a “phased extinction” step.
[00196] In the embodiment of Figure 8, after contact with the liquid spray inside the dehydration column, the extinguished process gas then passes upwards through a series of separation step components, such as, for example, a or more of sieve trays, dual flow trays, blister bell trays, coarse fill packaging, valve trays, and structured packaging, to separate acrylic acid from impurities in light fractions. A stream of intermediate process gas, comprising water vapor and non-condensable gases, such as, for example, nitrogen, carbon dioxide, propane, and unreacted propylene, leaves the top of column 810 and passes through condenser 813, generating the condensate 807 which is returned to column 810, and a higher vapor stream from dehydration column 802 comprising water vapor and non-condensable gases. In one embodiment, the upper vapor stream of the dewatering column 802 comprises less than 25% per mole of water vapor. In one embodiment, stream 802 comprises about 80% nitrogen and no more than 5% CO2 and CO combined. The upper vapor stream of the dehydration column 802 is divided into two portions, a stream of recycle gas 814 and a purge stream 815. The stream of recycle gas 814 has a mass flow rate of between 5 and 50% of the mass flow rate. of the upper steam stream 802, such as, for example, between 10 and 40% of the upper steam stream 802, or between 15 and 35% of the upper steam stream 802. The recycle gas stream 814 is returned to the SSOI reactor 830. Optionally, the recycle gas stream 814 can be processed in one or more conditioning steps, such as for example filtration, coalescence, preheating, and compression (not shown) before being returned to the 830 reactor. used compressors it is preferable that at least one of the aforementioned compressors be of the type selected from the list including insufflators (also known in the art as radial compressors or centrifugal compressors), oil-free screw compressors, and comprise ejectors with liquid jet. In one embodiment, the recycle gas stream 814 is first combined with process air and then processed in a centrifugal compressor before returning to the SSOI 830 reactor. In at least one embodiment, the interior surfaces of the process lines through which the recycle gas stream 814 flows are maintained at a temperature of not less than about 90 ° C, above the water dew point, to prevent condensation of water vapor there. Purge stream 815 can be vented or, in at least one embodiment, can be further processed, for example, in one or more of a catalytic combustion unit (CCU), a thermal oxidizer, and a heat recovery system of waste (not shown).
[00197] Chain 803, the portion of the liquid dewatering bottom stream 816 not transferred to the refiner 812, is provided to the finishing column 817. The finishing column 817 operates at subatmospheric pressure and comprises a series of step components separation, such as, for example, one or more of sieve trays, dual flow trays, blister bell trays, coarse fill packaging, valve trays, and structured packaging, to separate acrylic acid from heavy fraction impurities and produce the side acrylic acid product stream 805. The side acrylic acid stream 508 comprises at least 99.5% acrylic acid by weight, less than 0.15% water, and less than 0.075% acetic acid ; therefore, the stream meets the purity specifications for “Technical Grade Acrylic Acid” and can be used without further purification for this purpose. Optionally, the 805 side acrylic acid product stream can be further processed in a melt crystallization process (not shown) to obtain acrylic acid of even higher purity.
[00198] Generally, the recirculation of waste 809, comprising heavy fractions, such as, for example, acrylic acid dimer, is circulated through the refiller 818, which can comprise one or more refillers of the thermosiphon or forced circulation type, and returned to the lower portion the finishing column. At least a portion of the waste recycle 809 is transferred to an ester process (via the ester grade product stream 806), such as for example a butyl acrylate production process, comprising a dimer cracker. In one embodiment, the flow rate of the ester grade product stream 806 to the lateral acrylic acid product stream 805 is no more than 1.5. In another embodiment, the flow rate of the ester grade product stream 806 to the lateral acrylic acid product stream 805 is no more than 1.0. Optionally, a portion of the 809 waste recirculation is recycled to the top of the finish column to reduce polymerization inhibitor consumption. The upper current from the finishing column 808 is passed through the total capacitor 819; none of the resulting liquid condensate is returned to column 817; instead, the entire condensate stream from the finishing column 508 is combined with the stream 820 and returned to the spray device within the lower portion of the dewatering column 810.
[00199] It is recognized that a substantial number of known additional features and details, such as the use of tracking, insulation, cleaning equipment, instrumentation, in-line filters, multipoint thermocouples, safety equipment, energy recovery equipment, spraying and distribution of inhibitor, and specific building materials, as well as the addition of polymerization inhibitors, oxygen-containing gas, antifouling, and corrosion inhibitors at specific points within the process, can be additionally incorporated into this process design without out of the scope of the present inventive embodiment.
[00200] In at least one embodiment, means for reducing the operating pressure can be employed within the second reaction step. Such media can be used individually, but they can also be used in combination with one or more features of the design, such as the aforementioned use of tubes with internal diameters greater than 22.3 mm. In one embodiment, a conical outlet reactor head (as shown in Figure 5 by component 580) can be used, instead of a domed or elliptical head, to reduce the turbulent flow pressure loss at the reactor outlet.
[00201] In another embodiment (see Figure 8) 801 large diameter outlet tubing can be used to transfer product gas from the reactor (also known as “reaction gas”) between the reactor outlet and the collection equipment and downstream purification, such as, for example, dehydration column 810, in order to minimize the pressure inside the SSOI 830 reactor. to achieve a ratio of exit diameters, KO, of 0.08 or more. The outlet diameter ratio, KO, is defined here as the ratio of the diameter of the outlet pipe (DP) to the diameter of the outlet reactor head (DR) - that is, KO = DP / DR. As an example, for the embodiment of the reactor in Figure 1, which has an outlet reactor head diameter of 5,517 mm (18.1 feet), an outlet pipe with a diameter of 305 mm (12 inches) would not be considered “large diameter outlet piping”, because KO = 0.055. Therefore, for an embodiment in which the diameter of the outlet reactor head is 5,517 mm (18.1 feet), the outlet tubing from the reactor outlet to the dehydration column would be at least 457 mm (18 inches) in diameter (K = 0.083), such as, for example, at least 610 mm (24 inches) in diameter (K = 0.111), at least 762 mm (30 inches) in diameter (K = 0.138), or at least 914 mm (36 inches) in diameter (K = 0.166). Similar calculations can obviously be performed by one of ordinary skill, given the benefit of this disclosure, to determine appropriate dimensions for another "large diameter outlet tubing" given a known reactor outlet head diameter.
[00202] In some embodiments, an optional heat exchanger, hereinafter referred to as an “R2 outlet cooler”, is placed downstream of the reactor outlet to adjust the temperature of the product gas prior to its transfer to heating equipment. collects downstream, such as an aqueous absorber or a dehydration column. Carcass and tube designs are well represented in the prior art for use in service of R2 outlet coolers (see for example U.S. Patent No. 7,038,079) and, if used, could be designed to minimize pressure drop on the gas side of process. In addition, because encrustation of such R2-type outlet coolers and optional tubes are common, in at least one embodiment, the process gas side of the R2 outlet cooler can be constructed of scale-resistant materials, such as such as monel or other copper-containing metals (see, for example, U.S. Patent No. 7,906,679, hereby incorporated by reference). Geometric design features, such as slanted process lines and vertically oriented heat exchanger tubes, can also be beneficial in resisting scale build-up. The use of liquid phase or vapor phase inhibitors and antifouling can also be beneficial. Finally, the incorporation of low point drains and continuous monitoring of the exchanger surfaces on the process gas side for fouling, combined with expeditious removal of any accumulations identified during said monitoring, can help to minimize increases in pressure drop over along the exchanger and help prevent the operating pressure of the second associated upstream reaction step from rising.
[00203] An alternative to the aforementioned R2 housing and tube outlet cooler mentioned above is a liquid contact heat exchanger with low pressure drop, also known as a "spray cooler", which is described in the U.S. Patent No. 8,242,308 (see, eg, Figure 2) and incorporated herein by reference. In some embodiments, both a shell and tube outlet R2 cooler and a spray cooler may be employed; if both types of heat exchangers are used in combination with the SSOI reactor of the present invention, in at least one embodiment, the liquid contact heat exchanger can be placed downstream of the R2 outlet cooler of the housing and tube type. EXAMPLES Example 1 - Decoking Tests
[00204] It has been reported in the literature that special methods can be employed to "decouple" and / or "regenerate" MMO catalysts, thereby improving their conversion and selectivity. The method generally involves using brief treatment periods of 12 hours or more in which the reactor is taken out of production and the MMO catalysts are exposed to air, or a combination of steam and air, in situ. According to the literature, such treatments can be expected to intensify the oxidation states of the MMO catalysts, remove carbonaceous deposits (by oxidizing them), and reduce the pressure drop on the process side along the reactor, thereby intensifying performance (see, for example, Column 7, lines 33 - 67, U.S. Patent No. 7,897,813). Example 1 was performed to determine whether the use of these treatment methods could provide benefits when applied to the SSOI reactor of the present invention.
[00205] To carry out this test, the previously described SSOI reactor represented in Figures 1a, 1b & 1c was loaded with new commercial catalysts. In this particular example, ACF-7 and ACS-7 catalysts were selected for use in the inventive SSOI reactor.
[00206] Each tube of the first reaction step 110 was loaded with ACF-7 catalyst. Starting from the tube inlet at the R1 inlet tube sheet, the tubes from the first reaction step (115 a, b, c) were loaded as follows: about 267 mm inert spheres, 905 mm ACF- catalyst 7L, and 3445 mm ACF-7S catalyst. This resulted in a total mass (ACF-7L + ACF-7S) of 1.295 kg / catalyst tube from the first stage.
[00207] The pipe segment with a length of 2,057 mm remaining (135 a, b, c), which passes through the integral inter-step heat exchanger 130, was occupied by a short transition layer (depth 25-50 mm) of inert 5/16 ”(8 mm) silicon carbide rings (available from Norton Chemical Process Products Corp, Akron OH, USA), resting on top of a modified twistee insert. As previously described, such a modified twistee insert comprised a 25.4 mm (1 inch) tapered catalyst retaining spring (see Figure 1d) welded to the upstream end of one of the 2,032 mm (80 inch length twistee inserts) ) the previously described. The conical spring had an outer diameter at the top, dTS, of 6.1 mm (0.241 ”) and an outer diameter at the bottom, dBS, of 19.1 mm (0.75”) - equal to the effective diameter of the twistee insert. The conical catalyst retention spring was manufactured from eleven uniformly spaced coils of stainless steel wire with a diameter of 1.47 mm (0.058 inches) to form a conical spring with an overall height (hs) of 25.4 mm ( 1 inch) and coil spacing narrow enough to prevent silicon carbide rings from going through it. Therefore, by attaching the conical catalyst retaining spring to the end of the twistee insert, a transition layer between 25.4 mm and 51 mm in height was held in place just upstream of the twistee insert. This transition layer in turn supported the ACF-7S catalyst upstream, keeping it within the section of the first reaction step and preventing it from occupying the lower ends of the tubes (135 a, b, c) inside the inter-step heat exchanger . The twistee inserts within the inter-step heat exchanger were themselves retained in the ISHX tubes using the catalyst support grid panels comprising previously described wire mesh.
[00208] The open inter-step region 150 was loaded with EnviroStone66 ceramic spheres with a diameter of 1.5 inches sufficient to fill approximately 93% of the available inter-step volume. These spheres were loaded by pouring into the reactor and allowed to self-assemble in a bed with a fraction of voids of around 40%. As previously stated, this resulted in approximately 4,400 m2 (47,500 square feet) of surface area for removing scale.
[00209] Each tube of the second reaction stage 160 was loaded with ACS-7 catalyst. Starting from the tube inlet at the R2 inlet tube sheet, the tubes from the second reaction step (165 a, b, c) were loaded as follows: 200 mm inert spheres, 800 mm ACS-7L catalyst , and 3500 mm of ACS-7S catalyst. This resulted in a total mass (ACS-7L + ACS-7S) of 2.122 kg / catalyst tube from the second stage and a Catalyst Mass Ratio R2: R1 of 1.64. The catalyst of the second reaction step (R2) is retained in the reactor using the catalyst support grid panels comprising wire mesh previously described.
[00210] The SSOI reactor in this example was then operated over a long period with a target propylene feed concentration of between 6.5% and 7.1% by volume, an average feed concentration of 13.6% per oxygen volume, an average feed concentration of 27.7% per volume of water, and the balance being inert gases including nitrogen.
[00211] After 4,776 hours of operation have passed, the reactor was taken out to perform the first test of the "decoking" or "regenerative" treatment method. The treatment consisted of supplying only air to the reactor at a flow rate of 13,170 m3 / hr (465 MSCFH) and a temperature of 224 ° C (435 ° F). The temperature of the R1 salt supply (TsalR1) was gradually increased over a period of about 9 hours to a maximum of 347 ° C (657 ° F) and maintained at this temperature for 21 hours. During this period, the temperature of the R2 salt supply (TsalR2) was maintained at 285 ° C (545 ° F) to protect the R2 catalyst from overheating. During the 30-hour total regeneration period, the temperatures of the catalysts and exhaust process gases were monitored. Surprisingly, no exotherm was detected, nor any indication of CO or CO2 formation (denoting oxidation of carbonaceous solids). In fact, during the 21-hour maximum heating period, the difference between the temperature of the catalyst in the first stage (TcatR1) and the temperature of the salt supply in the first stage (TsalR1) was essentially zero (TsalRl - TcatRl <0.33 ). When treatment was complete, the reactor was returned to normal operation. After 24 hours of steady state operation, no improvement in conversion or selectivity was evident. Likewise, no change in the pressure drop along the reactor was detected. It was concluded that there was no removal of carbon deposits, nor any significant regeneration of the MMO catalysts in this treatment method.
[00212] After about another 3,400 hours of operation (8.184 hours of operation elapsed), the reactor was again pulled out to perform a second test treatment. The treatment again consisted of supplying only air to the reactor at a flow rate of 1.70 m3 / hr (465 MSCFH) and 224 ° C (435 ° F). The temperature of the salt supply of R1 (TsalRl) was maintained between 350 ° C (662 ° F) and 365 ° C (690 ° F) and the temperature of the salt supply of R2 (TsalR2) was maintained at 300 ° C ( 572 ° F) to protect the R2 catalyst from overheating. During the 21-hour treatment period, there was no evidence of CO or CO2 generation, nor any indication of exothermic reactions. The reactor was returned to normal operation. After 24 hours, no improvement in conversion or selectivity was evident. Likewise, no change in the pressure drop along the reactor was detected. It was concluded that there was no removal of carbon deposits, nor any significant regeneration of the MMO catalysts in this treatment method.
[00213] The air-only treatment was repeated four times more to determine whether benefits could be taken after the catalyst had experienced significant Tempo OnStream. The results obtained were no different than those of the first two trials. All treatment tests are summarized in Table 1A. TABLE 1A

[00214] Additional pressure measurement data for the reactor are summarized in Table 1B. This table compares pressure values within the reactor for the period before any regeneration treatments are carried out with pressure values within the period reactor after completion of all regeneration treatments. The table includes data for two essentially equivalent flow conditions during each period. TABLE 1B

[00215] It is evident from these experimental tests that, for the SSOI reactor of the present invention, there are no improvements in the performance of "decoking" or "regenerative" treatments. This result is surprising given that such treatments appear to provide benefits with other reactor designs, such as tandem reactors and SRS. Without wishing to be limited to theory, the hypothesis arises that the reason why no indication of removing carbonaceous deposits was seen is that the inventive SSOI reactor design effectively prevented the formation of these carbonaceous deposits. This conclusion is further supported by the pressure profile of the essentially unchanged reactor (Table 1B) over an operating period of more than 28,000 hours; if significant deposits were accumulating, it would be expected that the pressure drop across the SSOI reactor would have increased significantly over such a long period of operation. Finally, when the reactor was removed from the line to replace the catalysts, the interior of the reactor was inspected and no significant carbonaceous deposits were found within the inter-step heat exchanger or in the open inter-step region. Accordingly, the SSOI reactor design of the present invention clearly performed better than prior art reactor designs, such as, for example, U.S. Patent No. 7,897,813. Example 2 - ISHX + OIS residence time
[00216] The reactor embodiment previously described in Figure 1 has 22,000 tubes and an announced capacity of 100 kTA acrylic acid. It was desired to determine the inter-step residence time, as well as the residence time of the process gas flow along the inter-step heat exchanger tubes (the ISHX residence time) at operating rates of the design.
[00217] The reactor was designed for operation at a propylene feed rate of 19,400 pph (8,799 kg / hr), an O2 volume ratio: propylene of 1.8, and a vapor volume ratio: propylene of 3 , 6. As measured at the reference conditions of 240 ° C and 30 psia (2 atm), the total gas flow through the inter-step region was about 2,284,360 ft3 / hr (64,694 m3 / hr). TABLE 2A - Residence Time within Inter-Stage Heat Exchanger Tubes (ISHX)

[00218] This 0.93 second result was within the requirement of the target SSOI reactor design that the process gas residence time along the inter-step heat exchanger was not more than 1.5 seconds.

[00219] The sum of residence times across ISHX and the open inter-step region resulted in a combined time of 2.17 seconds, which was defined here as the integrated residence time. This result was consistent with the target SSOI reactor design requirement that the Inter-Step Residence Time should not be more than 3 seconds. Example 3 - Acetic Acid Yield
[00220] A pilot plant scale reaction system was used to study the response of oxidation reactors to changes in process variables. The first reaction stage comprised two vertical tubes with an internal diameter of 22.1 mm (0.87 inches) inside a cooling jacket of the circulating salt of the first common stage. The tubes in the first reaction step were loaded to a length of 4,191 mm (13.75 feet) with a cylindrical R1 ACF catalyst, commercially available from Nippon Shokubai Kagaku Kogyo Co., Ltd in Japan. The second reaction step comprised three tubes vertical internal diameter of 22.1 mm (0.87 inches) inside a jacket for cooling the circulating salt of the second common stage. The tubes in the second reaction stage were loaded to a length of 2,743 mm (9 feet) with spherical R2 ACS catalyst, commercially available from Nippon Shokubai Kagaku Kogyo Co., Ltd in Japan. The two reaction stages were connected by piping well-isolated inter-steps, sized to maintain the residence time between the two reaction steps for no more than 3 seconds. The process gas flow was configured to enter the top of the first reaction step, flow down through the vertical tubes, and exit at the bottom of the first reaction step; the inter-step “S” shaped tubing then directed the flow of process gas to the top of the second reaction step, where it flowed down through the vertical tubes, and came out at the bottom of the second reaction step. The salt circulations for both the first and second reaction steps were set up for countercurrent flow, with the salt entering the bottom of the jacket, fluid upwards, and exiting at the top of the jacket. Supply temperatures for both R1 and R2 salt circulations could be independently controlled.
[00221] The pilot plant scale reaction system had been used in previous experimentation, such that, at the time of this study, the catalysts of R1 and R2 had previously been operated for about 2,450 hours.
[00222] In these studies, propylene was supplied to the first stage at a rate of 0.32 kg / hr per tube (0.71 pounds / hr per tube). The gas fed to the reaction system had a nominal propylene concentration of 6% by volume and was operated with an oxygen / propylene volume ratio of 2.07 +/- 0.02 and a water / propylene volume ratio of 5.15 +/- 0.10. The product gas stream leaving the second reaction stage was analyzed for propylene and acrolein content to determine conversions. During the study, the temperature of the R1 salt supply (TsalR1) was adjusted to maintain conversion of propylene to 95.5% or 96.5%, depending on the experimental plan; the temperature of the R2 salt supply (TsalR2) was similarly adjusted to maintain 99.5% Acrolein conversion. The operating pressure inside the reactor was controlled by adjusting a valve at the outlet of the second reaction step.
[00223] As can be seen from Figure 7, it was discovered in these experiments that the yield of the acetic acid by-product is highly dependent on the operating pressure within the second reaction step (R2 value of 0.9676, showing a strong correlation) . Because the purpose of the propylene oxidation reaction system was to produce acrylic acid, it was preferred to minimize the yield of the acetic acid by-product by operating the second low pressure reaction step. EXAMPLE 4 - Tube Size Selection
[00224] (A) Section 11 of the Perry's Chemical Engineers' Handbook (6th ed., 1984) teaches that standard heat exchanger tubes range from 6.35 mm (0.25 inches) to 38 mm (1.50 inches) ) in internal diameter and that the wall thickness of the heat exchanger tubes is measured in Birmingham wire measurement units (BWG). Descriptions using this terminology are well known in the art of designing heat exchangers, but may not be familiar to those outside the area. For example, the description “1 inch x 16 BWG heat exchanger tube” means a tube with the following dimensions: outer diameter of 25.4 mm (1 inch), wall thickness of 1.65 mm (0.065 inches) ), and an internal diameter of 22.1 mm (0.87 inches). Similarly, the description a “1.06 inch x 18 BWG heat exchanger tube” means a tube with an outer diameter of 26.9 mm (1.06 inches), wall thickness of 1.24 mm (0.049 inches) , and internal diameter of 24.4 mm (0.962 inches). In addition, the description “1.5 inch x 13 BWG heat exchanger tube” means a tube with an outside diameter of 38.1 mm (1.5 inches), wall thickness of 2.4 mm (0.095 inches), and an internal diameter of 33.3 mm (1.31 inches). Given these examples, it will be evident that the inaccurate descriptions used in some prior art documents, such as for example the phrase “a one-inch pipe”, can lead to unnecessary confusion; to avoid such issues, the actual internal pipe diameters will therefore be specified in the examples here.
[00225] (B) As a practical matter, the use of heat exchanger tubes larger than about 51 mm (2 inches) in outer diameter is very unusual, as this is typically the largest size of stored seamless tubes routinely by tube manufacturers (sizes larger than about 51 mm are typically considered custom orders with premium prices and longer distribution).
[00226] (C) In addition, the commercially available catalyst pellets that are to be loaded into the reactor tubes are typically a minimum of 5 to 6 mm in diameter. Therefore, the range of internal diameters that can be specified for reactor tubes is effectively limited to the range of 7 mm to no more than about 50 mm.
[00227] (D) It is widely known in the propylene oxidation technique that higher operating temperatures give lower selectivity for acrylic acid and concurrently increased generation of by-products, such as for example CO / CO2 and acetic acid. It is therefore an objective of the oxidation reactor design to minimize operating temperatures by effectively balancing the rate of heat removal through the surface area of the tube wall (Qr) against the rate of heat generation from the volume of MMO catalyst within of the tube (Qg).
[00228] Those with ordinary skill in the heat transfer technique will recognize that Qr is dependent on the surface area of the tube, A, through the relationship: Qr = UA (ΔT) and that the surface area of the tube can be calculated from the ratio geometric: A = 2π (r) l where r is the radius of the tube and l is the length of the tube.
[00229] Similarly, Qg is dependent on the volume of MMO catalyst inside the tube, V, which can be calculated from the geometric relationship: V = π (r) 2l where r is again the radius of the tube and l is the length of the pipe.
[00230] One of ordinary skill will additionally recognize that as the radius of the tube, r, increases, the volume of MMO catalyst inside the tube (and therefore the heat generation rate, Qg) increases much more rapidly than the surface area of the tube (and consequently the rate of heat removal, Qr). This relationship [(r) 2> (r)] clearly leads to the conclusion that small diameter reaction tubes, in which the surface heat transfer area of the tube wall (A) is large in relation to the volume of catalyst inside tube (V), will be more effective in minimizing operating temperatures than large diameter reaction tubes.
[00231] (E) Additionally, Peters and Timmerhaus (Plant Design and Economics for Chemical Engineers, 3rd ed., 1980) teach that “Heat exchangers with small diameter tubes are less expensive per square foot of heat transfer surface than those with large diameter tubes, because a given surface area can be adjusted to a smaller housing diameter ... ”
[00232] Therefore, the general consensus of those with ordinary expertise in the propylene oxidation reactor design technique was the preferential use of small diameter tubes.
[00233] The present inventors surprisingly discovered that adherence to the common teachings of the technique was in fact counterproductive. Within the range of tube sizes up to about 50 mm, the present inventors have surprisingly discovered that it is rather preferable to use larger, rather than smaller, inner diameter tubes within the second reaction stage of the inventive SSOI reactor. Without wishing to be limited by theory, it is believed that the use of larger diameter tubes in the second reaction step makes it possible to decrease the pressure drop along the tube containing catalyst, resulting in a substantial reduction in the formation of the acetic acid by-product (see Figure 7 ), without changing the total space velocity across the MMO catalyst.
[00234] To illustrate this effect, the pressure drop across tubes of different diameters was determined using the following methodology. It is obviously possible to collect these data by direct mediation, but such an approach is both time consuming and expensive, and is unnecessary given the calculation method disclosed here.
[00235] The reactor of Example 1, comprising tubes from the second reaction step (R2) with an internal diameter of 22.3 mm and a length of 4500 mm, was used to gather the initial process data for this example. The reactor was operated at a propylene feed rate of 4,745 Nm3 / hour (177.1 MSCFH at 60 ° F / 1 atm) with an average feed composition of: 6.5% by volume of propylene, 13% by volume oxygen, 31% by volume of water, and the balance being inert gases including nitrogen. By direct measurement it was found that the reactor pressures inside the reactor were:

[00236] Based on the studies of M. Leva, et al. (Bulletin 504, Bureau of Mines, 1951), relationships for pressure drop through spherical catalyst particles within reactor tubes were developed and refined through additional laboratory studies. For tubes of different geometry, filled with spherical MMO catalyst particles, and operating under the same process conditions (flow, temperature, inlet pressure, and composition), it was determined that the simplified ratio of the pressure drop was: dP = (k) (L / e3) (1-e) 1.1 where dP is the pressure drop across a single pipe, k is a constant linked to process conditions, L is the length of the pipe and e is the fraction of actual voids between catalyst particles inside the tube
[00237] Because the void fraction (e) is dependent on the ratio of particle diameter to pipe diameter, it must be determined by measurement for each combination of particle diameter and pipe size; a significant collection of this data is available from A. Dixon’s Correlations for Wall and Particle Shape Effects on Fixed Bed Bulk Voidage (Canadian Journal of Chemical Engineering, Vol. 66, October 1988, pp 705-708) and was used for this example.
[00238] The total volume of the 22,000 reactor tubes with internal diameter dimensions of 22.3 mm and length of 4500 mm was 38.65 m3. For each alternative pipe diameter considered in this example, this total volume was kept constant and the resulting pipe length (L) was calculated, as shown in Table 4. The void fractions and pressure drop for each pipe size were then determined. Finally, these values were combined with the experimental data from Example 3 to obtain the results summarized in Table 4 below: TABLE 4


[00239] It was clear from this example that tubes larger than the inner diameter of 22.3 mm of base provide lower amounts of acetic acid by-product, while those tubes smaller than the inner diameter of 22.3 mm of base provide higher amounts of acetic acid by-product. In addition, it is evident from the experimental data that a beneficial reduction in the production of the acetic acid by-product can be achieved even with relatively minimal changes in the internal diameter of the tubes. Additionally, because the inventive SSOI reactor design resisted the accumulation of carbonaceous scale, the pressure drop across the reactor, and therefore the operating pressure of the second reaction step, has not changed significantly over time; as a result, the benefit of reducing the diameter pressure of the tubes in the second reaction step was detected over the entire life of the catalyst load - and not just in the first few months of operation. EXAMPLE 5 - Tube Counting
[00240] Another approach to minimizing pressure within the second reaction step is to reduce the overall length of the tubes while simultaneously increasing the total number of tubes (also known as "tube count") within the reactor. This design optimization can be used without changing the internal diameter of the tubes or the total volume of each reaction step. Although the reactor housing diameter, and therefore manufacturing cost, increases with increasing pipe count it can sometimes be advantageous to incur this additional capital cost in order to achieve reduced pressure drop and the associated reduction in acetic acid yield . Such economic assessments are within the capacity of one with ordinary expertise in the process design technique, given the benefit of the present disclosure.
[00241] Table 5A illustrates how the length of each tube occupied by catalyst and the tube count can be varied in the design of an SSOI reactor, while maintaining a fixed tube inner diameter of 22.3 mm and a step volume fixed reaction inside the reactor.

[00242] Table 5B illustrates how the length of each tube occupied by catalyst and the tube count can be varied in the design of an SSOI reactor, while maintaining a fixed tube inner diameter of 25.4 mm and a step volume fixed reaction inside the reactor.

[00243] Table 5C illustrates how the length of each tube occupied by catalyst and the tube count can be varied in the design of an SSOI reactor with a fixed reaction step volume; this table also demonstrates that an equivalent change in catalyst length produces the same percentage increase in tube count, regardless of the tube's internal diameter.
Example 6 - Mass Ratio of Catalysts
[00244] The following example is exceptional in the technique due to both the long duration of the individual experiments and the large number of commercial scale tests carried out. In this example, a series of catalyst evaluations were carried out using commercially scale SSOI propylene oxidation reactors, comprising between 15,000 and 25,000 tubes each. In each reactor there was an equal number of tubes in both the first reaction step (R1) and the second reaction step (R2) and all tubes had an internal diameter of 22.3 mm (0.878 inches).
[00245] For each experimental assay, all reaction tubes within a given reactor were filled with an equal mass of catalyst and any empty space at the ends of the tubes was filled with 6.4 mm (0, 25 ”) sufficient to achieve a uniform pressure drop across each tube.
[00246] Consistent with at least one embodiment of the present disclosure, the inter-step cooling section of each reactor was equipped with turbulence intensification inserts with a high void fraction (void fraction of at least 90%), the inter-step region open was loaded with EnviroStone 66 ceramic spheres with a high surface area and 1.5 ”diameter, and the combined process gas residence time within the inter-step refrigerator and the open inter-step region (here referred to as the“ inter-step residence time ” ) was restricted to no more than 3.0 seconds.
[00247] During the tests, propylene was supplied to each tube inside the test reactor at an average flow rate of between 0.16 to 0.21 Nm3 / hour (6 and 8 SCFH at 60 F / 1 atm) per tube. The feed gas composition for each reactor was controlled at an average of 7 +/- 0.5% propylene, a vapor volume ratio: propylene of about 3.6 +/- 2, and a volume ratio oxygen: propylene of about 1.8 +/- 1.
[00248] All reactors were cooled with HITEC salt circulation currents. AT the start of the operation, the cooling salt for the first reaction step was initially supplied at a temperature, TsalR1, of about 315 ° C (600 ° F) and the cooling salt for the second reaction step was initially supplied at a temperature, TsalR2, of about 265 ° C (510 ° F).
[00249] The composition of the gas stream exiting the second reaction step of each reactor, here referred to as the “reactor product gas stream”, was monitored using online gas chromatography analyzers. Specific measurements included the concentration of unreacted propylene and the concentration of unreacted acrolein remaining in the product gas.
[00250] Throughout the experimental operation period, TsalR1 (temperature of the salt supply of the first stage) was adjusted to maintain the concentration of unreacted propylene in the product gas at between 0.13 - 0.26% per mol , and TsalR2 (salt supply temperature from the first stage) was adjusted to maintain the unreacted acrolein concentration in the product gas at about 300 ppm. In addition, the temperature of the cooling salt supplied to the inter-step heat exchanger (TsalISHX) has been adjusted to maintain the temperature of the process gas entering the open inter-step region between about 240 ° C and 280 ° C.
[00251] Over long periods of operation, the aging of the catalysts made it necessary to gradually increase the TR1salt and TR2salt in order to maintain the reactor's acrylic acid yield. Eventually, however, the operating temperatures of the catalysts reached a maximum and further increases in TsalR1 or TsalR2 became ineffective in improving acrylic acid yield. At this point, the catalyst had reached the end of its service life and needed to be replaced. Generally, these final TsalR1 and TsalR2 values were about 355 ° C (670 ° F) and about 295 ° C (560 ° F), respectively.

[00252] As shown in Table 6, runs 1, 2, 4, and 6 all required partial R2 catalyst repackages; that is, the service life of the R2 catalyst charge was roughly half that of the R1 catalyst charge, making it necessary to replace the R2 catalyst well before the required replacement of the R1 catalyst. In test 8, the service life of the R2 catalyst charge exceeded that of the R1 charge. However, in tests 3, 5, and 7, the useful life of the R1 and R2 catalyst loads was effectively matched, eliminating the need for partial repackaging. These experiments showed that, for the SSOI reactor design of at least one embodiment of the present invention, it was possible to operate with corresponding first stage and second stage catalyst lives when the catalyst mass ratio (kg of first stage catalyst) / kg catalyst of the second step) was between about 1.25 and about 1.60. At mass ratios of catalysts of less than about 0.95, the service life of the R2 catalyst was substantially shorter than that of the R1 catalyst. At mass ratios of catalysts of more than about 1.60, such as in the case of test 8, the service life of the R2 catalyst was longer than that of the R1 catalyst. Furthermore, the data suggested that at mass ratios of catalysts substantially higher than about 1.65, for example at a ratio of 1.80, or even 2.0, the life span of the catalyst could be expected of R2 was significantly longer than that of the R1 catalyst, thus requiring early replacement of the R1 catalyst. It was especially surprising to find that this discovery applied to many different types of commercial catalysts, including catalysts from more than one supplier. The operation of the reactor with matched catalyst lives provided significant economic benefit by eliminating repackaging without incurring additional costs for installing excessive amounts of catalyst. It has been found that the amount of catalysts loaded into the SSOI reactor tubes of certain embodiments can be controlled to achieve a mass ratio of catalysts (kg of catalyst from the first stage / kg catalyst from the second stage) of not less than about 0.95 and no more than about 1.65 such as, for example, between about 1.25 and about 1.60 Example 7 - Addition of Supplemental Oxidizer / Residence Time
[00253] The reactor embodiment previously described in Figure 4 had 22,000 tubes and was operated with the addition of supplemental oxidant to achieve an announced acrylic acid capacity of 110 kT per year. If you wanted to determine the inter-stage residence time, as well as the residence time of the process gas flow through the inter-stage heat exchanger tubes (the ISHX residence time) at design operating rates.
[00254] As previously indicated in Table 7A (Case 2), the reactor embodiment of Figure 4 was designed for operation at a propylene feed rate of 21,344 pph (9,702 kg / hr), a propylene volume ratio: air of 0.122, and a vapor volume to air ratio of 0.367. As measured at the reference conditions of 240 ° C and 30 psia (2 atm), the total gas flow entering the inter-step region was about 2,187,662 ft3 / hr (61,956 m3 / hr).

[00255] This result of 0.969 seconds was completely consistent with the target embodiment of a process gas residence time through the Inter-Step Heat Exchanger no more than 1.5 seconds.



[00256] In the middle throat section of the mixer, the total volumetric flow increased due to the addition of the supplementary oxidant feed. As measured at 240 ° C and 30 psia (2 atm) reference conditions, the total gas flow passing through the intermediate throat section and the outlet expansion section increased to about 2,408,820 ft3 / hr (68,220 m3 / hr).

[00257] According to the definition of the previous examples, the residence time for this embodiment was the total sum of the residence time through the inter-step heat exchanger, the ceramic foam, and each section of the Venturi mixer. Therefore, combining the results of Tables 7B to 7E, it was determined that the inter-step residence time was 2.56 seconds. This result was consistent with the target inter-step residence time of no more than 3 seconds.

权利要求:
Claims (28)
[0001]
1. Acrylic acid production process, characterized by the fact that it comprises the following steps, in order of process flow: a) providing a mixed feed gas comprising propylene to a first reaction stage of a single-frame open inter-step reactor and tubes comprising a plurality of reaction tubes, the first reaction step comprising a mixed metal oxide catalyst for oxidizing propylene to acrolein; b) oxidizing the propylene in the first reaction step to produce a process gas comprising acrolein; c) cooling of the process gas in an inter-step heat exchanger disposed between the first reaction step and a second reaction step; d) passage of the cooled process gas through an open inter-step region; e) passing the process gas to a second reaction stage of carcass and tubes comprising a plurality of reaction tubes, wherein the second reaction stage comprises a mixed metal oxide catalyst for oxidation of acrolein to acrylic acid; and f) oxidizing acrolein in the second reaction step to produce a product gas comprising acrylic acid.
[0002]
Process according to claim 1, characterized in that the mixed feed gas comprises at least 7.5% per mole of propylene.
[0003]
Process according to claim 1, characterized in that the mixed feed gas additionally comprises oxygen at a molar ratio of oxygen to propylene of between 1.6 and 2.0.
[0004]
Process according to claim 1, characterized in that the mixed feed gas additionally comprises water vapor at a molar ratio of water vapor to propylene of about 1.2 or less.
[0005]
Process according to claim 1, characterized in that the mixed feed gas is provided to the first reaction step at a temperature higher than the dew point temperature of the mixed feed gas.
[0006]
Process according to claim 1, characterized in that the cooling of the process gas comprises cooling the process gas to a temperature not greater than 280 ° C.
[0007]
Process according to claim 6, characterized in that the cooling of the gas comprises cooling of the process gas to a temperature ranging from 240 ° C to 280 ° C.
[0008]
Process according to claim 1, characterized in that it additionally comprises providing supplementary oxidant to the process gas in the open inter-step region.
[0009]
Process according to claim 8, characterized in that it additionally comprises a mixture of process gas and supplementary oxidant in the open inter-step region.
[0010]
Process according to claim 9, characterized in that the mixture of the process gas and supplementary oxidant in the open inter-step region comprises mixing in a mixing device.
[0011]
Process according to claim 1, characterized in that the process gas is present in the inter-stage heat exchanger for a residence time of no more than 1.5 seconds.
[0012]
Process according to claim 1, characterized in that the process gas is present in the inter-stage heat exchanger and in the open inter-stage for a residence time of no more than 3 seconds.
[0013]
Process according to claim 1, characterized in that the passage of the cooled process gas through an open inter-step comprises removal of scale from the process gas by passing the process gas through an inert material having a total surface area of at least 930 m2.
[0014]
Process according to claim 13, characterized in that the inert material has a total surface area of at least 2790 m2.
[0015]
Process according to claim 1, characterized in that the mixed metal oxide catalyst in the first reaction step comprises at least one compound selected from the group consisting of molybdenum, bismuth, and iron oxides.
[0016]
16. Process according to claim 1, characterized in that the mixed metal oxide catalyst in the second reaction stage comprises at least one compound selected from the group consisting of molybdenum and vanadium oxides.
[0017]
17. Process according to claim 1, characterized by the fact that it additionally comprises circulation of a refrigerant through the first reaction step, the inter-step heat exchanger, and the second reaction step.
[0018]
18. Process according to claim 17, characterized in that the refrigerant is circulated independently in at least one of the first reaction step, the inter-step heat exchanger, and the second reaction step.
[0019]
19. Process according to claim 17, characterized by the fact that the refrigerant is circulated in a co-current configuration.
[0020]
20. Process according to claim 1, characterized in that the inter-step heat exchanger comprises inserts and the cooling of the process gas does not condense the process gas on the surface of the inserts.
[0021]
21. Process according to claim 1, characterized in that the mass of catalyst in the second reaction step is about 0.95 to about 1.65 times the mass of catalyst in the first reaction step.
[0022]
22. Process according to claim 21, characterized in that the mass of catalyst in the second reaction step is about 1.25 to about 1.6 times the mass of catalyst in the first reaction step.
[0023]
23. Process according to claim 1, characterized in that it further comprises: i) cooling the product gas to form a cooled product gas; ii) transfer of the cooled product gas to a solvent-free acrylic acid collection and purification system comprising a dehydration column and a finishing column; iii) removal of a higher vapor stream comprising non-condensable gases and water vapor from the dehydration column; iv) removing a side acrylic acid stream comprising at least 98% by weight of acrylic acid from the finish column; and (v) removing a waste recycling stream comprising heavy fractions of the finish column.
[0024]
24. Process according to claim 23, characterized in that it further comprises processing the side acrylic acid stream in a melt crystallization process.
[0025]
25. Process according to claim 23, characterized in that it further comprises transferring at least a portion of the waste recirculation stream comprising heavy fractions to an ester process comprising a dimer cracker.
[0026]
26. The method of claim 23, further comprising: vi) dividing the upper vapor stream comprising non-condensable gases and water vapor into a recycle gas stream and a purge stream; vii) return of the recycle gas stream to the open, single-cased inter-step reactor; and viii) processing of the purge stream in one or more of a catalytic combustion unit, a thermal oxidizer, and a waste heat recovery system.
[0027]
27. Process according to claim 26, characterized in that the mass flow rate of the recycle gas stream is between 5% and 50% of the mass flow rate of the upper vapor stream comprising non-condensable gases and water vapor.
[0028]
28. Process according to claim 1, characterized by the fact that the reaction tubes of the second reaction step have a diameter greater than 22.3 mm.

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法律状态:
2019-09-17| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|

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2020-12-29| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

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2021-03-02| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 20/08/2013, OBSERVADAS AS CONDICOES LEGAIS. |

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