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    • 专利摘要:
    continuous or batch process 9 for the preparation of a superabsorbent polymer. The present invention relates to a continuous or batch process for preparing a superabsorbent polymer comprising: a) submitting an aqueous nonomeric mixture containing: - at least one unsaturated ethylene monomer; - at least one monomer containing at least two unsaturated <244> ethylenic groups; - iron ions in an amount between 0.1 and 3 wppm, based on the total weight of the aqueous monomer mixture; and at least one amount chelating agent capable of providing a chelating agent: iron ion molar ratio of 0.8 to 4.0 reactor radical polymerization to obtain a superabsorbent polymer; and b) recovery of the superabsorbent polymer, where, if the process is continuous and carried out in a stirred reactor, the upper limit of the chelating molar: iron ion ratio is - 4.0 for a total reactor mixture flow in the reactor of at most 1.3 kg / h per liter reactor, - 3.5 for a total reactor reaction mixture flow greater than 1.3 kg / h per liter reactor and less than or equal to 2.5 kg / h per liter and - 1,5 for a total reactor reaction mixture flow greater than 2,5 kg / h per liter of the reactor.
    公开号:BR112012024517B1
    申请号:R112012024517
    申请日:2011-03-01
    公开日:2019-11-19
    发明作者:Fricker Daniel；Plöchinger Harald；Gartner Herbert；Kohler Hans-Peter；Harren Jörg；Hager Marc；Auernig Sabine
    申请人:Evonik Degussa Gmbh；Evonik Stockhausen Gmbh；
    IPC主号:
    专利说明:

    CONTINUOUS PROCESS FOR THE PREPARATION OF A SUPERabsorbent POLYMER [0001] The present invention relates to a process for the preparation of a superabsorbent polymer.
    BACKGROUND OF THE INVENTION [0002] The preparation of hydro-absorber polymers is summarized, for example, in "Modern Superabsorbent Polymer Technology", F. L. Buchholz and A.T. Graham, Wiley-VCH, 1998, or Ullmann's Encyclopedia of Industrial Chemistry, 6- ed. vol. 35 p. 73-103. The preferred preparation process is solution, or gel, polymerization. When using this technology, a mixture of monomers is usually prepared, which are neutralized and then transferred to the
    polymerization reactor; it is is realized continuously or discontinuous, forming one gel polymeric what, in case in polymerization under agitation, is comminuted. The gel polymeric is,
    then dried, crushed and sieved. Optionally, a surface treatment is also applied.
    [0003] Continuous polymerization methods are described, for example, in WO-A-01/38402, WO-A-03/004237, WO-A-03/022896 and WO-A-01/16197.
    [0004] On a laboratory scale, high-purity raw materials can be used, but for production, the use of this type of material has limitations. For economic reasons, raw materials such as acrylic acid and technical grade caustic soda are used preferentially. It is also possible to give preference to the use of normal tap water or partially demineralized water, which can be supplied
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    2/52 specifically for this from spring water or other available sources, instead of using more expensive fully deionized or distilled water.
    [0005] In scale production, therefore, it would be interesting to recycle the washing water resulting from cleaning the ventilation circuit of the regular production plants to the monomer solution before polymerization, as well as the part of the superabsorbent polymers that is below the specification. in terms of (fine) particle size. Technical grade raw material, filtered water and fines, however, can contribute to the level of impurity present in the monomer mixture and, in the end, will possibly disturb the polymerization reaction and perhaps result in an inferior product.
    [0006] Among the various impurities that may be present, heavy metal ions - especially iron ions - have a significant disturbing role. It is known that iron is a very active co-initiator in redox systems, which has a significant impact on product quality. US patent 4,659,793 discloses a method for preparing aqueous solutions of dicarboxylic acid copolymers with α, β-ethylenic unsaturated monomers, such as (meth) acrylic acids, in which there are 1 to 250 ppm of metal ions, especially iron, in the mixture reacional. The purpose of the presence of these iron ions is to reduce the residual content of unreacted dicarboxylic acids.
    [0007] In controlled polymerization reactions for the manufacture of superabsorbent polymers (SAP) of high
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    3/52 performance, iron ions are undesirable because they can interfere with the initiator system by reducing molecular weight, promoting unwanted graftization, etc. Iron ions are particularly undesirable because their concentration cannot be reliably controlled under the usual conditions of production. Well-designed initiator systems are employed, preferably containing, for example, the redox pair sodium persulfate and / or hydrogen peroxide and ascorbic acid or another high performance initiator system in concentrations that, on the one hand, result in high conversion of the monomer into the polymer and, on the other hand, it allows the formation of cross-linked product with high molecular weight, with homogeneous structure and small fraction of low molecular weight polymers (extractable). Any additional co-trader will not
    controllable, such as ions in iron, could disturb the planned system judiciously causing effects unwanted. [0008] The presence From ions in iron causes greater
    initiation and polymerization speeds, as it increases the concentration of radicals. As a result, the temperature of the reaction mass will rise more rapidly, thereby further increasing the formation of radicals. These undesirable conditions of rapid polymerization result in polymers with lower average molecular weights, lower molecular weight distribution and also, a higher fraction of low molecular weight polymers, which will not be connected to the network (extractable). In general, a lower, less homogeneous network is formed during such polymerization conditions that, therefore,
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    4/52 are not ideal for the production of high-performance superabsorbent polymers.
    [0009] Another undesired effect of spontaneous initiation and the very high rate of polymerization, promoted by the presence of iron ions, is that in the place where the coiniciator, for example, ascorbic acid or its salts - comes into contact with the monomeric solution, the initiation and polymerization is so fast that it gets stuck in the formed gel. The reaction and gel formation are so fast that a homogeneous distribution of the co-offcorer in the solution is not possible. This non-homogeneous distribution therefore leads to non-homogeneous polymerization.
    [0010] Another serious problem with these unwanted conditions caused by the presence of iron ions in the monomeric solution is the risk that premature polymerization may occur in stages of the process that happen higher in the reactor, in particular, after deoxygenation, causing blockages in the system of transport of the preparation. This situation can lead to constant stoppages of the production plant, considerably reducing the commercial efficiency of the process.
    [0011] WO 03/022896 describes a process of continuous polymerization, where the maximum reactor temperature is controlled, preferably below 85 ° C, with the initiation zone preferably remaining between 40 and 85 ° C. In cases of very high initiation and polymerization speeds, the energy absorption by the reaction may be so high that the temperature cannot be maintained within the preferred range. As a result, very high temperatures will, as already mentioned,
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    5/52 lead to a very high speed of radical formation and, therefore, to even faster initiation and polymerization speeds. It is believed that iron ions are primarily responsible for this uncontrollable speed of radical formation and the fact that the polymerization kinetics cannot be controlled sufficiently.
    [0012] WO 93/05080 suggests the use of chelating agents, such as pentasodium salts of diethylene triamino-pentacetic acids, to remove traces of metals from the reaction mixture. These agents are used in amounts between 100 and 2,000 ppm, in relation to α, β-unsaturated monomers. The smallest amount of chelator used in the examples in WO 93/05080 is 171 ppm relative to the monomeric mixture. Similarly, WO 03/022896 uses chelating amounts of around 280 ppm in its examples, relative to the total monomeric mixture.
    [0013] Another group of prior art references, EP-A 257 951, US 6,313,231, EP-A-1 108 745, US 6, 335, 398 and US 2007/01411338, addresses the problem of the effect of combined iron ions to ascorbic acid originating from body fluids, such as urine or blood, in superabsorbent polymers, capable of resulting in their degradation into superabsorbent structures like a diaper. To counteract the effect of iron ions on the degradation of the superabsorbent polymer already formed, these references suggest adding a chelator to the polymer.
    [0014] However, these references deal only with the effect of iron on the superabsorbent polymer already formed in a superabsorbent structure. They do not discuss the effect of ions
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    6/52 iron on the polymerization process and polymer properties.
    [0015] In general, the state of the art highlights the deleterious effect of iron ions in the preparation of superabsorbent polymers or in the polymer already ready when in contact with body fluids. In any case, the only suggestion obtained from the existing literature is that iron ions could be completely removed by considerably high amounts of chelating agents to avoid their negative effects.
    [0016] When investigating what was presented in the state of the art on the use of the chelating agent in the amounts generally described, to avoid the negative effects of iron ions, an undesired delay of several minutes was observed on the start of polymerization and a reduction , also undesired, of its speed, which resulted in properties below the ideal for the obtained superabsorbent polymer. Thus, it is an objective of the present invention to avoid the disadvantages existing in the state of the art, by means of what was discovered in this invention and to present a process for the production of a superabsorbent polymer with better properties.
    SUMMARY OF THE INVENTION [0017] The objective above was obtained by means of a process, continuous or in batch, for the preparation of a superabsorbent polymer comprising:
    a) submission of a monomeric mixture containing:
    - at least one α, β-unsaturated monomer;
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    7/52
    - at least one monomer containing at least two α, β-unsaturated ethylenic groups;
    iron ions in an amount between 0.1 and 3 wppm, relative to the total weight of the aqueous monomer mixture; and at least one chelating agent in quantity capable of providing a molar ratio of chelating agent: iron ion between 0.8 and 4.0 to radical polymerization in the reactor, to obtain a superabsorbent polymer; and
    b) recovery of the superabsorbent polymer, where, if the process is continuous and carried out in a reactor with agitation, the upper limit of the chelating molar ratio: iron ion is
    4.0 for a total reaction mixture flow in the reactor of a maximum of 1.3 kg / h per liter of the reactor volume,
    3.5 for a flow of the total reaction mixture in the reactor of more than 1.3 kg / h per liter of the reactor up to 2.5 kg / h per liter of the reactor, and
    1.5 for a flow of the total reaction mixture in the reactor greater than 2.5 kg / h per liter of the reactor.
    [0018] When carrying out the process according to the present invention, the polymeric gel formed in the reactor is non-adherent and has excellent flow behavior, the total polymerization speed is within the preferred range for batch and, particularly, for continuous production, and a final product as desired can be obtained.
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    8/52 [0019] The present inventors have discovered, unexpectedly, that the negative impact of iron, on the one hand, and that of the chelating agent on the other, can be reduced or even eliminated if their concentrations are well balanced. Thus, contrary to what is described in the prior art, it is important that the iron ions are present in the reaction mixture of the radical polymerization and, in addition, that it is present in a narrow range of molar ratio chelating agent: iron ions, as defined above.
    [0020] Furthermore, the present inventors have found that, if the process is continuous and carried out in a reactor with agitation, the molar ratio of chelating agent: iron ions to be adjusted to solve the problem described above will depend on the flow in the reactor and the adjustment should be made according to the conditions defined above.
    [0021] It is interesting that when doing the reaction, either in batch or in a continuous conveyor reactor, the molar ratio of chelating agent: iron ions is within the broader range defined above.
    [0022] In accordance with an embodiment of the present invention, the chelating agent is generally present in an amount sufficient to provide a molar ratio of chelating agent: iron ions between 0.9 and 3.5 or between 1.0 and 3 , 5 or between 1.0 and 2.5 or between 1.0 and 2.0 or between 1.0 and 1.5.
    Obviously, when executing the process continuously in a stirred reactor, the upper limit, depending on the flow, is maintained.
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    9/52 [0023] If the process of the present invention is carried out continuously, in a reactor under agitation, the upper limit of the molar ratio of chelating agent: iron ions is 3.5, preferably 3.0, for a flow of the total reaction mixture throughout the reactor of a maximum of 1.3 kg / h per liter of the reactor; 2.5, preferably 2.0, for a flow of the total reaction mixture throughout the reactor from more than 1.3 kg / h per liter of the reactor to 2.5 kg / h per liter of the reactor; and 1.3, preferably 1.2, for a flow of the total reaction mixture through the reactor of more than 2.5 kg / h per liter of the reactor.
    [0024] In addition, it is preferable to keep the amount of iron ions in the aqueous monomer mixture between 0.2 and 2.5 wppm or between 0.2 and 1.5 wppm or, still, between 0.2 and 1.0 wppm , relative to the total weight of the aqueous monomer mixture.
    [0025] The properties of the final superabsorbent polymer obtained by the process of the present invention that have been improved are mainly the ability of the gel to flow (measured by the flow rate of the gel, as will be described below), the ratio between CRC (Retention Capacity) Centrifuge) and extractables, and / or the color of the product.
    [0026] Therefore, adapting the concentration of iron ions and chelating agent to the limits of the present invention constitutes an important and effective tool to control the polymerization kinetics. With this measure, premature polymerization in the upper part of the polymerization reactor can be avoided and sufficient time can be allowed to guarantee the homogeneous mixing of the co-merchant with the monomeric solution after its
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    10/52 addition, without causing a very long delay in starting polymerization and without reducing its speed.
    DETAILED DESCRIPTION OF THE PRESENT INVENTION [0027] Possible sources of iron in a commercial production process of superabsorbent polymers have already been discussed above. Residual iron content in the starting materials - such as unsaturated caustic monomers, and fine polymers and recycled washing waters for monomeric mixtures. The washing water can be obtained by subjecting at least one gas flow released at any point in the process to washing with a basic solution, in a washer, before releasing it. This stream may contain carbon dioxide, which results in a washing solution containing carbonate and / or hydrogen carbonate. When recycling the wash solution, other important products contained in the released flow, such as polymers or monomer fines, can be returned to the reaction mixture. In addition, since washing water is generally basic and contains carbonate or hydrogen carbonate, it can be used to neutralize the monomeric mixture and, due to the formation of carbon dioxide in this reaction, support the removal of oxygen from the monomeric mixture before it enters the reactor.
    [0028] Preferably, the oxygen concentration in the monomeric mixture is reduced to a level of less than 0.5 wppm, or less than 0.3 wppm, or even less than 0.1 wppm, based on the total weight of the monomeric mixture.
    [0029] Depending on the raw material used to prepare the monomeric mixture according to the process of the present invention, the iron content may be different. Therefore,
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    According to the present invention, the iron content of the monomeric mixture to be used in the process is measured and, if necessary, adjusted to fall within the generally preferred range specified above, preferably by the addition of aqueous iron salts, such as sulfate iron (III) hydrated in the appropriate amount.
    [0030] According to one embodiment of the present invention, the chelating agent is selected from organic polyacids, phosphoric polyacids and their salts. Preferably, the chelating agent is selected from nitrilotriacetic, ethylenediaminetetraacetic, cyclohexanediaminetetraacetic, diethylenetriaminopentacetic, ethylene glycol-bis (aminoethylether) -N, N, N'-triacetic, N- (2-hydroxyethyl) ethyl, N '-triacetic, triethylenetetraminohexacetic, tartaric, citric, iminodisuccinic, glyconic and their salts.
    [0031] The preferred chelating agent of all is the pentasodium salt of diethylenetriaminepentacetic acid, available from the Dow Chemical Company, in the form of an aqueous solution, under the trade name of Versenex 80®.
    [0032] According to one embodiment of the present invention, the monomeric mixture contains at least one ethylenic unsaturated acid and at least one monomer containing at least two ethylenic unsaturated groups that act as a covalent crosslinker. Suitable α, β-unsaturated ethylenic acids include, for example, acrylic, methacrylic, crotonic, isocrotonic, itaconic and 2-acrylamido-2-methyl-1propanesulfonic acids. They can be used in the acid form,
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    12/52 but it is preferable to use the unsaturated α, β-ethylenic acids in their at least partially neutralized form, such as alkali metal and ammonium salts.
    [0033] Preferred unsaturated acids include acrylic and methacrylic in their respective salt forms, such as alkali metal or ammonium salts. Optionally, small amounts of other water-soluble unsaturated monomers, such as the alkaline esters of the acid monomers including, for example, methyl methacrylate, methylacrylate, acrylamide or methacrylamide or polyethylene glycol methyl ether acrylates can be present in the monomeric mixture. The monomers are used in aqueous solution, preferably in amounts between 10% by weight and up to 80% by weight, based on the total weight of the aqueous monomer solution. Preferably, the amount of monomer ranges from 15% by weight to 60% by weight, based on the total weight of the aqueous monomer solution. In addition, certain graft polymers such as, for example, polyvinyl alcohol, starch and water-soluble or water-expandable cellulose ethers can be used to prepare the products. These graft polymers, when used, are in quantities of up to 10% by weight, based on the monomer α, β-ethylenic unsaturated.
    [0034] The water-absorbing polymer is preferably slightly covalently cross-linked to keep it insoluble and non-expandable in water. The desired crosslinking structure can be obtained by including in the monomeric mixture a crosslinking agent that has at least two polymerizable double bonds in the molecular unit. The crosslinking agent is used in an amount sufficient to
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    13/52 effectively covalently cross-linked the water-soluble polymer. The preferred amount of this agent is determined by the degree of absorption desired, as well as the desired tension to retain the absorbed fluid, that is, the absorption against the desired pressure (AAP), respectively, the absorption under load (AUL). The crosslinking agent is advantageously used in quantities between 0.0005 and 5 parts by weight per 100 parts by weight of the monomer □, ethylenic D-unsaturated used. Preferably, this amount varies between 0.1 and 1 part by weight per 100 parts by weight of the monomer □, □ ethylenic unsaturated used. Generally, if an amount greater than about 5 parts by weight of crosslinking agent per 100 parts of the monomer is used, the polymers will have a very high crosslink density and will have reduced absorption capacity with increased AUL. If the cross-linking agent is used in amounts less than 0.0005 parts by weight per 100 parts of the monomer, the polymer will normally have a very low cross-linking density and, when in contact with the fluid to be absorbed, it will it will become sticky and will have a lower initial absorption capacity.
    [0035] Although the covalent crosslinking agent should preferably be soluble in the aqueous solution of the monomer □, □ ethylenic unsaturated, it can also simply be dispersed in this solution. Examples of suitable dispersing agents include carboxymethylcellulose, methylcellulose, hydroxypropylcellulose and polyvinyl alcohol suspending aids. These dispersing agents are provided, with advantages, in a concentration between 0.0005 and 0.1%
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    14/52 by weight, based on the total weight of α, β-unsaturated ethylene monomer.
    [0036] Suitable covalent cross-linking agents include compounds that have in the molecule two to four groups selected from CH2 = CHCO-, CH2 = C (CH3) CO- and CH2 = CH-CH2-. Examples of covalent crosslinking include ethylene glycol diallylamine, trialylamine, diacrylates and dimethacrylates, diethylene glycol, triethylene glycol, propylene glycol, 1,4butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, trimethyl acetate and trimethyl acrylates and pyrethylpropylene and trimethyl acrylates and pyrethyl acrylates and trimethyl acrylates and pyrethyl acrylates and trimethyl acetate and trimethyl acetate and pyrethyl acetate and trimethyl acetate. pentaerythritol, tetracrylate and pentaerythritol tetramethacrylate, allyl methacrylate, tetra allyloxyethane, acrylates of highly ethoxylated derivatives of trimethylolpropane or pentaerythritol containing from 3 to 30 units of ethylene oxide - such as trimethylethylacetate and acrylate-acrylate-acrylate-acrylate and acrylate; Other suitable cross-linking agents are monoalylether-polyether monoacrylates, such as polyethylene glycol monoalyletheracrylate (PEG MAE / A). Mixtures of covalent crosslinking agents can be used.
    [0037] Polymerization can be done using acidic monomers that are not neutralized or that have been partially or partially neutralized before polymerization. Neutralization is conveniently achieved by mixing the aqueous solution of the monomer with a sufficient amount of base to neutralize between 10 and 95% of the acid groups present in the acid monomers. Preferably, the amount of base should be sufficient to neutralize between 40 and 85%, and more
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    15/52 preferably between 55 and 80% of the acid groups present in the acid monomers.
    [0038] Compounds suitable for neutralizing the acid groups of the monomers include those bases which will sufficiently neutralize the acid groups without having a detrimental effect on the polymerization process. Examples of such compounds include alkali metal hydroxides, alkali metal carbonates and hydrogen carbonates.
    [0039] A polymerization initiator by addition of conventional vinyl can be used in the polymerization of water-soluble monomers and cross-linking agent. A radical polymerization initiator that is sufficiently soluble in the monomeric solution is preferable to initiate polymerization. For example, water-soluble persulfates such as potassium persulfate, ammonium persulfate, sodium persulfate and other alkali metal persulfates, hydrogen peroxide and water-soluble azocompounds, such as 2,2'-azobis- (2amidinopropane) hydrochloride can be used. Systems called redox initiators, such as hydrogen peroxide and sodium persulfate - which can be used as an oxidizing component - can be combined with reducing substances such as sulfites, amines
    or acid ascorbic. THE amount of initiator used can vary from 0.01 to 1% in weight, preferably in 0.01 to 0.5% in weight, with base at the total weight of the monomer α , β-ethylene unsaturated. [0040] Beyond of this , it's possible and even preferable,
    recycle fines from the superabsorbent polymers for the preparation process. As fine, those particles are considered
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    16/52 that are too small for the desired application, as defined in the product specification. This unwanted fraction of the product is therefore removed from the granulated polymer. The fraction of fines can be determined by sieving, using the EDANA standard test by the method WSP 220.2 (5). The fines can also be generated by applying a fluidized bed to heat the particulate superabsorbent polymers. The particles can be refined by the flow of hot air, so as to have a diameter of up to about 300pm. Polymer particles with a particle size less than 300 μη, or less than 200 μm are defined as fine according to the present invention.
    [0041] The fines can be recycled at any stage of the process, according to the present invention, but as will be discussed in detail below, it is particularly preferable to recycle them for the monomeric mixture. In addition, other suitable additives can be added to the monomer mixture at an appropriate point during the process, as will be discussed below. Other additives can be selected, for example, from alkali metal chlorate, polyethylene glycol, water-insoluble organic or inorganic powders, such as water-insoluble metal oxides - for example, silica or zinc oxide - surfactants, dispersion aids, agents to control odor, such as silver salts, or other processing aids.
    [0042] Without wishing to be limited, the present invention will, in the following, discuss in more detail the use of acrylic acid as the preferred unsaturated ethylenic acid for the preparation of superabsorbent polymers. An area technician, however, will
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    17/52 realize that the same process can be conducted using different monomers or mixtures of monomers.
    [0043] The polymerization according to the present invention can be carried out in batch or in continuous mode. Dispersed phase polymerization is also possible.
    Batch OPERATION [0044] A batch polymerization is generally carried out in a stirred container. Mixer-type reactors, capable of intimately mixing the reaction mass and granulating the polymeric gel formed during polymerization are particularly preferred. Preferred reactors of this type are, for example, those described in US 4,625,001, or reactors such as those available from List AG (CH) (Type DTB, CRP, ORP, CKR etc.). For standard operations, the aqueous monomer solution is prepared and charged into the reactor. This solution can have a total concentration of monomers preferably between 38 and 45% by weight and temperature between 10 and 35 ° C, preferably between 10 and 30 ° C. Acrylic acid is neutralized in the range between 40 and 85%, more preferably between 68 and 75%. The oxygen that is dissolved in the monomeric solution is preferably removed so as to be in a concentration below 0.3 ppm. This can be achieved by purging the solution with nitrogen for an appropriate time or by adding a carbonate solution - for example, washing water as discussed above - or by a combination of the two. Oxygen can also be chemically reduced by adding a reducing agent. Then, the initiators are added. First
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    18/52 the thermally decomposing initiators and / or oxidizers (azo-, peroxides or persulfates initiators) and, finally, the co-initiators (the reducing components of the redox system), such as ascorbic acid, are added. The co-initiator normally begins to polymerize after some time, and the temperature of the reaction mass begins to rise by the exothermic reaction.
    [0045] Figure 1 shows a typical temperature graph, obtained for batch polymerization in a 250 mL glass reactor without stirring, without temperature control during polymerization. It represents a quasiadiabatic polymerization of a monomeric solution with monomer concentration equal to 42% and degree of neutralization of 70%. The graph is divided into three segments: the first represents the time until the start of the reaction (delay) after mixing the coiniciator, that is, the interval between the addition of the coiniciator and the beginning of the exothermic reaction indicated by the increase in temperature, approximately 1 ° C. Segment 2 represents the increase in temperature, basically linear, until the conversion of about 35 to 75%; segment 3 represents the part where the polymerization speed increases and the conversion is completed. The increased speed of the reaction in segment 3 may be caused by the Norrish Trommsdorff effect. The polymerization speeds, V1 and V2, are taken from the temperature increase in segments 2 and 3. They are described as the average temperature increase of the reaction mass, in ° C per minute.
    [0046] Adiabatic polymerization experiments, such as those carried out in reactors without agitation described above, allow an adequate investigation of the polymerization kinetics, since the
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    19/52 increase in temperature of the reaction mass is a sufficiently accurate indication of the conversion of the monomer. Through several series of experiments, the inventors studied the impact of iron concentration and Versenex 80® on the interval until initiation and on the polymerization speed.
    [0047] Surprisingly, we found that the specific information obtained from the analysis of the adiabatic increase in temperature, which is recorded during batch polymerization of a given monomeric solution (exotherm), makes it possible to make important predictions about the polymerization behavior of the batch polymeric solution. and in continuous mode, as well as the processability of the obtained gel and the properties of the final polymer. This tool can be used to evaluate and describe the ideal requirements and conditions to which the monomer solution must be subjected in continuous polymerization. Monomeric solutions according to the present invention combined with an optimized initiator system preferably provide an initiation delay between 10 seconds and 2 minutes, preferably between 20 and 100 seconds, a polymerization V1 between 3 and 7 ° C / minute and a V2 between 50 and 90 ° C / minute. Preferably, V2 should be at least equal to V1, or greater.
    CONTINUOUS OPERATION [0048] A continuous process according to the present invention is preferably carried out in a reactor that has at least three zones, where the first is the initiation zone, the second is the gel phase zone and the third is the zone
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    20/52 granulation, and where the monomeric mixture enters the reactor through the initiation zone.
    [0049] The continuous operation can be done, preferably, applying the mixing technology or the conveyor technology. As discussed above, according to the present invention the molar ratio between chelating agent and iron ion in the aqueous monomer mixture must be adjusted according to the maximum reaction mass output if a stirred reactor is used. The term “stirred reactor” should be understood as referring to reactors that contain means to stir the reaction mass in addition to the agitation caused by the flow (for example, the turbulent flow of the reaction mass), in contrast to, for example, reactors conveyor belts. Thus, in the following, the continuous reaction will be discussed in more detail in relation to two types of reactors, those with agitation and continuous conveyor reactors.
    CONTINUOUS POLYMERIZATION IN SWITCHING REACTOR [0050] Preferred stirring reactors are continuous mixers and continuous extruders.
    [0051] Continuous polymerization in a stirred reactor will be described below with reference to the mixing technology. A detailed description of these reactors can be found in WO 03/022896. In continuous polymerization it is important that initiation occurs regularly and reliably on a continuous basis and that the polymerization speeds are in the desired ranges. The sufficiently deoxygenated monomeric solution as described above, with a temperature between 10 and 30 ° C, is fed continuously in zone 1, the initiation zone of
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    21/52 reactor. In this zone there is an intense and constant mixture of the hot gel formed and the cooled, fed solution. Depending on the formulation and conditions of the monomeric solution, substantial conversion takes place in this zone, which causes the reaction mass to heat up right there. The desired temperature range in this zone is 60 to 110 ° C (preferably 69 to 105 ° C).
    [0052] If the temperature in zone 1 falls below 60 ° C, the initiation of the reaction can become very slow, so that the incoming cold monomer will cool the reaction mass and, consequently, the total polymerization speed will will make it too low for the desired residence time for the reaction mass in the reactor. Incomplete mass converted may leave the reactor causing problems for the following operations. The temperature in zone 1 could, however, be increased by heating (heating jacket or steam injection), but this is not desired for economic reasons.
    [0053] If the temperature in the initiation zone rises above 110 ° C, the initiation speed and the total polymerization speed will become very high; thus, the obtained hydrogel will become sticky and difficult to dry (which can be evaluated by the flow index of a drop of gel), and the properties of the product, especially the ratio between the centrifugal holding capacity and the absorption against pressure , will be harmed.
    [0054] The conversion in the initiation zone is expected to be in the range of 35 to 75%. As a result, there is already a substantial amount of hydrogel present in this zone, where monomer
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    22/52 new is continuously entering and mixing by the column mixing tools. WO 03/022896 also shows that a high degree of mixing is achieved in the first zone; this is described with reference to Figure 1 of that document, as a “continuous mixing segment” containing two phases. The essential conditions in this zone are given to allow continuous transfer to the polymer and graftization takes place, leading to additional cross-linking and branching. Increasing the initiation delay will allow a more intense continuous mixing and greater absorption of the monomer, thus increasing the unwanted graft effect.
    [0055] The temperature, particularly in the first zone, is controlled by the appropriate formulation and preparation of the monomeric solution. It is preferable to control the temperature of the feed solution so that it is in the desired range and to remove oxygen at a concentration of less than 0.3 ppm based on the total weight of the monomeric solution. The monomer concentration and also the degree of neutralization is preferably controlled within the preferred ranges as defined above and the initiators should be added in the desired concentrations.
    [0056] Extra influence on the polymerization speed comes from the fines, which must be recycled to the monomeric solution. The fines swell in the monomeric solution, increase their viscosity and thus activate the Norrish Trommsdorff effect at an earlier stage of polymerization. Fines in the monomer solution accelerate polymerization. It may be desirable to recycle all the fines that accumulate during the production of the superabsorbent polymers. The recycling ratio can be
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    23/52 between 1 and 25%, based on the total weight of monomers and its effect must be considered when adjusting the concentrations of the applied initiators.
    CONTINUOUS POLYMERIZATION IN CONVEYOR REACTOR [0057] A detailed description of continuous polymerization in conveyor reactors is given in DE-A-35 44 770. The polymerization differs significantly from that which occurs in mixers and extruders, in a few aspects. The monomeric solution is introduced by the part of the mobile mat “similar to a drinking fountain”, at the point where it forms a kind of “lake” of monomeric solution. At some distance from the feeding point, that is, after some delay, polymerization begins and the gel is visibly formed as the reaction mass is transported by the moving mat. Turbulence in the “lake” of the belt's feeding zone only happens due to the flow of feed; no other stirring is produced. As a result, there is no substantial mixture between the polymeric gel and the monomer solution as it passes from liquid to a continuous polymeric gel tape, which is continuously released during the transition from the curved, water-like mat to its flat shape. Another difference in relation to the mixing technology is that the initiation occurs at a lower temperature, that is, at the feed temperature of the monomer. The reaction mass on the mat is not mixed, stirred or cut and thus is granulated only after the gel leaves the mat and the reaction is complete. The gel tape on the conveyor has a small surface compared to the granulated gel in a mixing reactor and there are very limited possibilities for controlling the temperature from the outside.
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    Thus, controlling the kinetics of the polymerization reaction in a conveyor reactor is even more important.
    SUPERABSORVENT POLYMERIC GEL WORKUP [0058] Regardless of which reactor is used, the gel is discharged from the last zone of the reactor, which is at the opposite end to the feed or initiation zone. Using a mixer-type reactor, the gel is removed by the cleaning column, over an adjustable barrier, through an opening in the cover next to the cleaning column.
    [0059] It is preferable for mild production conditions, that there is a buffer confinement of the polymeric gel between the reactor and the next unit downstream of the process. In addition to maintaining a desirable amount of buffer, the container also serves as a holding tank, to allow additional conversion of the polymeric gel reaching a conversion above 99%, preferably above 99.5%. It also provides one more place where additives can be added to the polymers and mixed. The design of this container is not critical, as long as it provides tools for proper agitation and to maintain the desired temperature in the gel. Preferably, the container should be insulated to maintain the gel at the desired temperature, allow substantial flow and be designed in such a way that the polymeric gel can be loaded and unloaded continuously and reliably. The container can be a vase placed horizontally or vertically, a single or multiple screw conveyor or a moving mat. It can be used for multiple production processes in line, in initial or final stages. In case of
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    25/52 several gel dryers are fed with gel from a buffer tank, an adequate number of joints are installed to properly divide the gel flow.
    [0060] The resulting polymer is typically dried and pre-separated by size by means well known to those skilled in the art. Suitable drying media include fluid bed dryers, rotary dryers, compressed air ovens, air circulation dryers and belt dryers. In some cases, drying will be done in two or more stages, that is, drying in multiple stages. After drying is complete, the polymer is still broken to form particles, preferably with a weighted average diameter of less than 2 mm and, more preferably, less than 1 mm. Preferably, the final polymeric product has a weighted average particle size of at least 300 μη.
    [0061] After drying and separating by size the superabsorbent polymer is generally classified, for example, by sieving, to remove particles of very small size, which are not acceptable for the intended commercial use of the superabsorbent polymers.
    [0062] These fines can be recycled to any point in the process of the present invention, but it is a particular advantage of the process of the present invention when these fines can be recycled to the monomeric mixture, as explained above.
    [0063] In addition, it is desirable that the dry particles can be heat treated or have their surface treated in order to improve the properties of the product, as already
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    26/52 is known in this field. For example, dry particles can be heat treated according to the procedures described in WO 93/05080 and / or US 5,629,377. This heat treatment is preferably carried out at a temperature of at least 170 ° C, especially at least 180 ° C, and even more especially at least 190 ° C. Preferably, this heat treatment is carried out at temperatures below 250 ° C, more especially below 240 ° C. The method used for heat treatment is not critical. For example, circulating air ovens, fluidized bed heaters, paddle dryers and heated screw conveyors can be used successfully. If desired, the heated polymer can be re-moistened to facilitate handling. One way to improve the absorption properties of the polymeric particles can be to cross-link their surface. Procedures for this are well known in the art and described, for example, in US 4,734,478 and US 4,466,983. These procedures can increase the modulus and / or the absorption capacity under load of the polymeric particles. Surface modifications can also be achieved by incorporating additives, such as aluminum or silica salts.
    [0064] Reactors with agitation can be operated under sub-atmospheric pressure; the temperature control promotes water evaporation, generating condensates during the process. The total volume of condensates generated by the polymerization reaction depends on the conditions of the process. These determine the final energy balance and, therefore, the influence that evaporation has on the temperature control system. The total amount of energy in the system is a
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    27/52 balance between energy flows, which add or remove energy from the system. Energy addition streams are polymerization and feed streams (depending on their temperature), the heat transfer from the coating to the
    reactor, dissipation gives energy in mixture and, optionally, injection in steam. The streams in removal in energy are the energy of discharged gel, in wake up with your ability
    temperature and gel discharge temperature; the heat transfer from the reactor to the cladding and column, as well as the energy consumed by evaporation. Under the preferred conditions discussed above, the amount of water to be evaporated is between 8 and 18%, based on the water present in the reaction mass. This can be removed from the reactor and treated separately or it can be condensed and returned to the gel in the reactor or directed to any of the following process steps until the gel is dry. Alternatively, it can be recycled to any of the previous process steps, preferably to the first reactor zone, along with the reducing component of the redox initiator or to the preparation unit for the monomeric solution.
    [0065] For economic reasons it would be preferable, on the one hand,
    remove the fraction evaporated in gel water a end to maximize the content of solids in it and, so avoid The need in evaporation of condensed. It was observed, at the however, what recycle at least part of condensed to the gel reduces your
    stiffness and thus improves its fluidity.
    [0066] On the other hand, it would be desirable to recycle the condensate to the monomer solution or to the unit where it is prepared, if it was not necessary to improve the fluidity of the gel.
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    Before the present invention, however, it was considered that due to possible impurities in the condensate, its recycling to an earlier stage of the process could have a negative influence on its stability and on the quality of the product. Against expectations, the inventors observed that the recycling of condensates, as described above, to replace the corresponding fraction of water in the method did not have any undesired impact if the molar fraction of chelating agent and iron ions were adjusted according to the present invention.
    EXPERIMENTAL PART
    Equipment
    250 mL glass reactor [0067] This reactor consists of a vertical glass container with an internal diameter of 6.3 cm and a lid with four openings with grounding holes. One of the openings in the cover can lead the oxygen measuring electrode or be closed; the second opening is equipped with a one-way gas valve, which serves to release the gas; the third opening carries a lined duct (Pasteur pipette made of glass, 23 mm long; supplier specification: D 79861 Wertheim) for nitrogen purging and for feeding with other additives. The coated duct is connected to the nitrogen supply by a silicone tube. Additives are injected, using a syringe and a hollow needle, through the silicone tube into the pipette. In the fourth opening, a thermocouple (PTF 100) is inserted so that its tip measures the temperature in the center of the reaction mass.
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    Laboratory mixing reactor [0068] The laboratory mixing reactor is a simple screw mixing reactor type DTB 1.5 obtained from List AG Switzerland. It is equipped with a jacket for heating and cooling, a vacuum system, a nitrogen supply system, a duct inserted at the top for the entry of additives (for example, initiators), having a valve outside the top and a control. All metallic surfaces that are in contact with the monomeric solution are protected, as needed against caustic and citric acids.
    List DTB 1.5 reactor modified [0069] The same reactor (List DTB 1.5) with a total volume of 3.1 liters was also used for continuous operation, except for the following modifications:
    [0070] The glass of the batch reactor display, which closes the horizontal cover on the side opposite the drive system, was replaced by a metal plate covered by fluorinated plastic (ChemResist) having a circular opening of 55 mm in the upper area with a discharge tube to which a receptacle for the gel has been attached. This plate allows the continuous discharge of the polymeric gel and works as a dam, allowing a theoretical degree of filling of the reactor of about 60%.
    [0071] For continuous feeding of the monomeric solution, a transfer line was installed, which forms a storage tank, to transport the solution into the reactor, from the top, through the duct. This transfer line essentially consists of a plastic hose that passes
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    30/52 near the reactor, equipped with T-junctions suitable for continuous addition of the initiators and, optionally, other additives - for example, washing water - to the continuous flow of monomer. Adequate feeding of monomeric solution and additives was achieved by means of appropriate peristaltic pumps. Integrated into the feeder system, above the T junctions, there is also a 0.5 liter bubble column equipped with a coated tube, which has a glass frit at the bottom for purging the monomeric solution with nitrogen flow, for adequate deoxygenation .
    Gel dryer
    The laboratory scale gel dryer [0072] On a laboratory scale, the gel drying experiments are carried out in a batch-operated CTL fluid bed dryer (marketed by Allgaier-Werke KG, Ulmerstr. 75, D-7336 Uhingen ). The dryer is equipped with a conical fluidization chamber with a 20 cm diameter Conidur perforated plate at the bottom, a fan, an air heater, a clean air filter and an exhaust air filter with automatic dust cleaning and a control box. The air flow is made from the bottom up and does not circulate. The fluidization chamber has a basket whose bottom is a wire mesh. The gel to be dried is placed in the
    so the to form a layer in gel with thickness in about 5 cm and dry fur jet air hot that is forced through layer. O dryer is able to simulate O
    industrial scale conveyor dryer.
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    Methods
    Analytical methods
    CRC (centrifugal holding capacity)
    EDANA, PATTERN: WSP 241.2 (05) [0073] Gravimetric determination of the fluid retention capacity in saline after centrifugation
    AAP (AUP) Pressure Absorption (Pressure Absorption)
    EDANA, PATTERN: WSP 242.2 (05) [0074] Gravimetric determination of pressure absorption
    Extractables
    EDANA, PATTERN: WSP 270.2 (05) [0075] Determination by potentiometric titration of the content of extractable polymers
    Res. AA (residual acrylic acid)
    EDANA, PATTERN: WSP 210.2 (04) [0076] Determination of the amount of residual monomers in superabsorbent materials - polyacrylate superabsorbent powders
    Oxygen in the monomeric solution [0077] An electrochemical method is used to determine the oxygen dissolved in the monomeric solution.
    Materials and Equipment
    - Oxi 2000 Type Oximeter Microprocessor
    - A membrane-covered electrochemical sensor containing a gold cathode and a silver anode (WTW Trioxmatic 203)
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    - WTW PE / OXI OxiCal calibration cell
    - Glass flask with 4 mouths, of 250 mL, equipped with magnetic stir bar, a firm connector for the sensor bar, a connector for the flow of nitrogen that passes through the balloon, a connector for the flow of ventilation gas and a connector for charging monomeric solution.
    - A magnetic stirrer
    - A rubber pear
    - PE hoses of suitable diameters and lengths
    Procedure [0078] The sensor calibration is done with air saturated with water vapor, using the calibration cell WTW PE / OXI OxiCal. It is performed exactly as described in the user manual provided by WTW. To measure the oxygen concentration in the monomeric solution, the program (PROG # 6) suitable for the monomeric solution was selected, which was developed in cooperation with the equipment supplier.
    [0079] Determination of the oxygen concentration in the monomeric solution:
    [0080] Before any measurement, the Oximeter Microprocessor is turned on and left in standby mode for at least 30 minutes, for proper polarization, as recommended by WTW.
    [0081] The monomeric solution to be measured is placed in a 250 mL glass reactor, equipped with a suitable opening containing a sensor covered by a membrane and a magnetic bar, placed on a magnetic stirrer.
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    33/52 [0082] The calibrated sensor is attached to the glass reactor or the glass flask, respectively, forming an angle of about 45 ° in relation to the surface of the monomeric solution and the agitator connected at a speed that guarantees the arrival of the flow suitable for the sensor, but which prevents gas from the dead space of the balloon from forming bubbles in the solution. After pressing the PROG button, the oxygen concentration is measured and shown in ppm (mg / L). The value is taken after it has stabilized, which can take a few seconds.
    [0083] In the presence of carbon dioxide, the buffering capacity of the electrolyte solution is sufficient for exposure for a short time; during long exposures, however, carbon dioxide changes the pH value towards the acidic range and leads to higher values. For this reason, the sensor was fully regenerated after each measurement, according to the procedure provided by WTW: the electrolyte solution of the sensor was changed, the cathode and anode were cleaned and the membrane was replaced with a new one.
    Iron in monomeric solution [0084] The viscolor® ECO iron test kit marketed by Machery-Nagel (art. 931 026) was used to determine the concentration of iron in the monomeric solution. The test is suitable for measuring iron concentrations between 0.04 and 1 mg / L (ppm) in monomer solutions. In case the monomeric solution contains more than 1 ppm, it was diluted, appropriately, with deionized water. Care was taken to make all measurements before adding any chelating agent to the solution, as this could distort the results.
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    34/52 [0085] Hydrated iron (III) sulphate (Riedel-de-Haen, n.
    31 235) was used to adjust the iron concentration in monomer solutions.
    Gel Flow Index (GFI) [0086] This method is used to assess the flow behavior of the superabsorbent gel as it is discharged from the reactor or extruded. The characteristic flow is determined as the Gel Fluidity Index (GFI). It quantifies the flow of the gel granules through a set of suitable sieves, which are mounted like a sieve tower.
    Materials and Equipment
    - 20 cm diameter sieves and 25 mm, 20 mm, 16 mm, 10 mm and 8 mm meshes
    - A plastic tray (30 cm long, 25 cm wide and 5 cm high) to load the sieve tower
    - A 2 liter plastic bag
    - A thermally insulated box to keep the sample during transportation and storage for short periods, keeping it at the desired temperature
    - 500 mL plastic beaker
    - Balance
    Procedure [0087] The screens are assembled to form the tower and placed on the plastic tray (see Figure 2).
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    35/52 [0088] A gel sample, taken from the source sample to be analyzed, is placed in the plastic bag, which is immediately placed in the thermally insulated box to be kept at the appropriate temperature until the measurement. A 200 g portion is taken from the sample in the plastic bag, carefully weighed in the plastic beaker and spread on the upper sieve of the sieve tower. Care must be taken not to touch or press the gel, nor to allow any vibration in the sieves, so as not to influence the natural, gravimetric behavior of the gel flow.
    [0089] THE sample is left Flow during 2 minutes by sieves and, then the portions that stayed in them are certain by weighing. Calculations[0090] The portion weights of gel in each one of several
    Sieves on the tray are introduced in the formula below to provide the weighted mass in the sieve (Wi weighted):
    Weighted Wi = Wi * «i / Wtot * 100 [0091] where Wi represents the weight of the gel in the sieve,« i represents a weighting factor related to the sieve where the factor is 0 for the 25 mm sieve, 0, 2 for the 20 mm one, 0.4 for the 16 mm one, 0.6 for the 10 mm one, 0.8 for the 8 mm one and 1.0 for the gel weight in the tray - and wtot represents the weight total gel.
    [0092] The Gel Fluidity Index is finally obtained by adding the weighted portions.
    GFI = Σ weighted Wi
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    36/52 [0093] For precision purposes, the procedure is repeated and the reported GFI represents the average of two measurements.
    EXAMPLES
    Laboratory scale
    Preparation of the monomeric solution for laboratory scale experiments [0094] For the preparation of the monomeric solution, 34.64 parts of 99.9% active acrylic and 25.85 parts of 50% active NaOH (degree of neutralization = 70%) were carefully mixed and cooled so that the temperature of the mixture was kept permanently below 35 ° C. To this mixture were added 30.69 parts of water and 0.09 parts of HE-TMPTA (2700 ppm based on AA), 0.35 parts of PEG 600 (6000 ppm based on AA). The concentration of iron in the mixture is measured and, optionally, supplemented if desired. Then, portions of Versenex 80 ® 5% active (sodium salt of triaminopentacetic acid) are added until the desired concentration.
    Polymerization in a 250 mL glass reactor [0095] A 229.05 gram portion of the monomeric solution is placed in the 250 mL glass reactor, which is placed in a water bath and the solution temperature adjusted to 23 ± 1 ° Ç. The nitrogen flow through the coated duct, to deoxygenate the mixture, is adjusted to 200 L / h for 5 minutes and then reduced to 50 L / h for another 3 minutes. Immediately after reduction, 17.3 grams of a 10% aqueous sodium carbonate solution is injected through the pipette, causing the final neutralization level to reach 70% and the
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    37/52 monomeric concentration (AA and Na-AA) at 42%. A vigorous reaction begins immediately after adding the carbonate solution (Na2CO3), releasing CO2 in the form of very small gas bubbles. At the end of the 3 minutes, the pipette is removed from the solution to release nitrogen into the dead space of the reactor and allow the CO2 bubbles to separate from the solution. The oxygen concentration in the monomeric solution was reduced to 0.1 ppm. Then, the pipette was again immersed in the solution, the nitrogen flow adjusted to 200 L / h, to produce intense mixing. Then, 0.58 g of a 3% active H2O2 solution (200 ppm based on AA) and 1.3 g of 10% active Na2S2O8 (1500ppm based on AA) were injected through the flexible hose into the nitrogen flow. Thirty seconds later, the addition of 1.78 g of a 0.9% active sodium ascorbate solution (185 ppm based on AA) finally initiates the polymerization, which heats the reaction mass to the maximum temperature. Immediately after initiation, the pipette is pulled into the dead space and the nitrogen flow is reduced to 50 L / h, to ensure the inert atmosphere inside the reactor. The temperature of the reaction mass is recorded using a PT100 thermocouple. After reaching the maximum temperature, the reactor was immersed in a water bath preheated to 70 ° C and kept in it for one hour. Afterwards, the reactor cover was removed and the gel block removed. In order to obtain enough gel for drying and further processing, two reactors were operated with identical monomeric solutions, under the same conditions, and the gels combined.
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    Cutting and drying, grinding and sieving the gel in the laboratory [0096] The gel blocks obtained from polymerization in the 250 mL glass reactors were cut into pieces and then, still at a temperature above 60 ° C, extruded with a grinder homemade meat, equipped with a blade with 8 mm holes. A 400 g portion of the extruded gel was then placed in the basket made of the 2 mm wire mesh. The basket with the extruded gel was placed in the laboratory dryer and the gel dried under a jet of hot air of 5 m / s with a temperature of 180 ° C for 20 minutes. The dry polymer obtained was crushed in a roller mill and sieved in a Retsch tower equipped with mesh screens between 850 and 150 microns, obtaining the particle size fraction for analysis.
    Examples 1-14 [0097] The monomeric solution was prepared, polymerized and the obtained polymeric gel processed according to the methods described above. The concentration of iron in the monomeric solution was determined and supplemented according to Table 1 below. Then, portions of a 5% active solution of Versenex 80 ® (sodium salt of diethylenetriaminopentacetic acid) were added to the solution as shown in Table 1. There was no dispersion of fines for recycling in the solution.
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    Table 1: Examples 1-14, polymerization tests in the 250 mL glass reactor (* = comparative examples)
    Example# Fe3 +(ppm) DTPA * 5Na / Fe 3+ molar ratio CRC(g / g) Extr.(%) ReasonCRC / Extr. Hunter color Delay(s) Timeup to maximum(s) V1(° C / min) V2(° C / min) L B 1* 0.5 0.000 37.8 17.6 2.1 86.6 5.6 30 110 87.9 85, 8 2 0.5 1,636 40.2 17.6 2.3 88.52 4.4 50 130 63.3 97.2 3 * 1 0.000 36.9 21.4 1.7 87.5 5.7 20 90 72.6 102.0 4 1 0.818 38.5 18.2 2.1 88.8 5.8 20 100 100.8 72.3 5 1 2,045 39.2 16.4 2.4 89.5 4.3 40 220 9.3 59.7 6 * 2 0.000 38.2 20.7 1, 8 88.3 5.6 20 120 67.5 75, 0 7 * 2 0.409 38.0 20.0 1.9 87.6 6.2 20 120 68.4 81, 6 8 2 1,022 38.2 18.6 2.1 88.0 6.4 20 120 69.0 58.5 9 2 2,045 40, 1 18.2 2.2 88.5 5, 3 30 190 12, 6 57.3
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    10 * 3 0.000 35.8 20.0 1, 8 88.7 4.9 20 140 66.0 33, 6 11 * 3 0.273 38.7 23.5 1, 6 87.6 6.1 10 130 64.5 84.0 12 * 3 0.682 38.4 20.7 1.9 86.9 6.8 20 130 77.4 59, 4 13 3 1,363 39, 3 18.2 2.2 88.2 6.8 30 120 32.4 92.7 14 3 2,045 38.8 16.8 2.3 88.9 5, 9 50 280 6, 0 49, 8
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    41/52 [0098] As is clear from Table 1, the examples according to the present invention have satisfactory properties, especially a better ratio between CRC and extractables, as well as improved color values.
    List 1.5 batch polymerization reactor [0099] The batch polymerization reactions of examples 15-22 were carried out in a simple DTB 1.5 type screw mixing reactor obtained from List AG Switzerland.
    [0100] A portion of 1194.8 g of the monomeric solution, prepared as described above, was loaded into the reactor from the top and closed, then by fixing the lid located on it. The reactor agitator was turned on and the temperature of both the reactor and the monomer solution was adjusted to around 30 ° C. For deoxygenation of the solution, the temperature inside the reactor was reduced to less than 100 mbar for two minutes, after which the vacuum was broken by nitrogen. This procedure was repeated twice. Then, 87.19 g of a 10% active sodium carbonate solution were injected through the duct at the top of the reactor and the foamed monomer solution. Again, a vacuum <100 mbar was made and the stirrer was turned off for about two minutes, to allow the CO2 bubbles to separate from the solution. After the agitator was turned on again, the initiators were aspirated through the duct: 2.91 g of a 3% active hydrogen peroxide solution and 6.54 g of 10% active sodium persulfate solution. After washing the duct with 20 ml of deionized water and mixing the monomeric solution for two minutes, 11.52 g of a sodium ascorbate solution
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    0.7% active were added through the duct. The pressure in the reactor was brought to normal value by the pressure of nitrogen to guarantee the inert atmosphere inside the reactor. After a delay as indicated in Table 2, the temperature of the reaction mass rose and the temperature of the jacket was adjusted to follow, essentially the temperature of the reaction mass. When it reached 50 ° C, the jacket temperature was adjusted to 70 ° C to finally keep the polymeric gel in the reactor for 30 minutes at this temperature. Then, the end cap of the reactor was removed to allow the discharge of the gel granules. The obtained polymer was processed as described above. Examples 15-24 were conducted according to this procedure and the results are summarized in Table 2.
    Table 2: Examples 15-24, polymerization tests in the reactor of
    List 1.5 DTB (* = comparative examples)
    Example# Fe3 +(ppm) DTPA * 5Na / Fe 3+ molar ratio CRC(g / g) Extr.(%) LightningCRC / Extr. Delay(s) V1(° C / min) 15 * 0.5 0.000 36, 7 16.3 2.3 120 7.2 16 0.5 1,636 37.2 14.7 2.5 160 7, 1 17 0.5 2,454 39, 1 16.5 2.4 80 6, 4 18 * 0.5 8.179 36, 8 13.7 2.7 410 2.5 19 * 0.5 18.403 31.0 12.4 2.5 500 2.1 20 * 2 0.000 41.9 19.4 2.2 30 11.2 21 2 1,022 43.5 17.3 2.5 70 12.2 22 2 2,044 43, 1 14.7 2.9 140 5, 5
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    23 * 3 0.000 40, 6 23.2 1.8 30 7.2 24 3 1,363 41, 8 17, 6 2.4 50 10.2
    [0101] As is apparent from Table 2, the examples according to the invention provide products with better properties, especially CRC and the CRC: extractable ratio compared to comparative examples.
    Continuous polymerization in the modified List DTB 1.5 reactor
    Examples 25-1 to 25-2 [0102] The monomeric solution was prepared as described above and the iron content adjusted to 0.5 ppm (based on the solution). It contained a chelating agent as indicated in Table 3 below and its temperature was adjusted and maintained at 22 ° C. The starter solutions were prepared and deoxygenated in separate containers, from which they were properly passed through the T bonds to the monomer flow.
    [0103] The dead space atmosphere of the modified reactor was kept inert by means of a continuous nitrogen flow of 200 L / h, and the reactor jacket temperature was maintained at 90 ° C. The monomeric solution at a temperature of 22 ° C was continuously introduced into the reactor, at a rate of 4.0 kg / h (1.29 kg / L of total volume of the reactor), which was deoxygenated in the bubble column with nitrogen flow of 20 L / h, an active aqueous solution of hydrogen peroxide (400 ppm based on AA), a 10% active aqueous solution of sodium persulfate (1800 ppm based on AA), 20% washing water (based on AA) containing 10% sodium carbonate and 2% NaOH, and a solution
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    44/52 aqueous 0.7% active sodium erythorbate (200 ppm based on AA). The carbonate in the washing water completed the perfect deoxygenation and the sodium ascorbate finally caused the polymerization reaction to start.
    [0104] In steady state conditions, the feed monomer is mixed, at least partially, with the polymeric gel present in the reactor (on average, about 1.7 kg) and the polymeric gel was continuously discharged through the opening and through the tube discharge from the reactor end into the gel receptacle. The discharged gel was kept under nitrogen for another 60 minutes and then processed as described above. Comparative Example 25-2 could be completed; however, the gel became more sticky and the reactor obstruction became visible, especially at the point where the top cover attaches to the housing. Gel lumps that accumulated in this area threatened to block the lid and had to be removed manually. This effect is recognizable as an increase in column torque.
    Examples 26-1 to 26-3 [0105] The following examples were performed as example 25, except that the discharge was maintained at 7.75 kg / h and the Versenex 80 ® concentrations adjusted according to the Table 3, where the results are also summarized. Example 26-1 failed because the monomer solution became too reactive and the gel became too sticky. Example 263 also failed because the very high concentration of Versenex 80 ® delayed the polymerization reaction in such a way that there was not enough conversion of the monomer inside the reactor and
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    45/52 the reaction mass became sticky. As a result, there was an obstruction of the column and the housing, and the reactor was overloaded; thus, the experiment had to be stopped without the steady state conditions being reached.
    Examples 27-1 to 27-3 [0106] The following examples were performed as example 25, except that the discharge was maintained at 9 kg / h and the Versenex 80® concentrations adjusted according to Table 3, where the results are also summarized. Example 27-1 did not work because the monomer solution became too reactive. Example 27-3 also failed because the very high concentration of Versenex 80 ® delayed the polymerization reaction in such a way that there was not enough conversion of the monomer inside the reactor and the reaction mass became sticky. As a result, there was an obstruction of the column and the housing, and the reactor was overloaded; thus, the experiment had to be stopped without the steady state conditions being reached. This effect is recognizable by the torque value from the acquisition unit.
    Examples 28-1 and 28-2 [0107] The following examples were performed as examples 27, except that the concentration of iron ions in the monomeric solution was adjusted to 1 ppm and the concentrations of Versenex 80 ® adjusted accordingly with the Table
    3, where the results are also summarized. Example 28-2 failed because the very high concentration of Versenex 80 ® delayed the polymerization reaction in such a way that there was not enough conversion of the monomer inside the reactor. In
    Petition 870190099875, of 10/04/2019, p. 53/74
    As a consequence, the reaction mass became sticky, there was an obstruction of the column and the housing, and the reactor was overloaded; thus, the experiment had to be stopped without the steady state conditions being reached.
    Table 3: Examples 26-29 (Continuous polymerization in the reactor of
    List 1.5 DTB
    Petition 870190099875, of 10/04/2019, p. 54/74
    47/52
    modified (* = comparative examples) Example# Fe3 +(ppm) DTPA * 5Na / Fe 3+ molar ratio CRC(g / g) Extr.(%) Res.Mon.(ppm) Hunter color GFI(%) L B 25 Yield 4kg / h (1.29kg / h and per liter of volumereactor total) 25-1 0.5 3, 806 37.2 20.7 478 90.6 6.7 23.5 25-2 * 0.5 8, 172 34.7 14.7 2212 88.9 5.1 16.7 26 Yield 7.5 kg / h (2total volume , 42 kg / h and per literl of the reactor) in 26-1 * 0.5 - 35.7 24.3 480 87 7.7 6.4 26-2 0.5 1,226 38.9 21.2 676 91.3 6.9 23.5 26-3 * 0.5 4,086 33.9 16.5 670 90.6 6.6 31.7 27 Yield 9 kg / h (2.9 kg / h and per liter of volumereactor total) 27-1 * 0.5 - 36.6 19.7 596 89.6 7.1 11.4 27-2 0.5 1, 0 38.4 20.3 430 90.4 7.4 13.4 27-3 * 0.5 1. 634 33.5 16.1 880 89.8 6.5 25, 5 28 Yield 9 kg / h (2.9 kg / h and per liter of volumereactor total) 28-1 1.0 1, 0 38.9 22.9 401 89.9 6.4 20.5 28-2 * 1, 0 1. 634 27, 6 10.2 1491 89.1 7.3 41.4
    Petition 870190099875, of 10/04/2019, p. 55/74
    48/52
    Continuous polymerization in the List ORP 4000 reactor
    Examples 29: Industrial tests on P24
    Example 29-1 [0108] The monomeric solution was produced continuously, feeding the unit of preparation of it with the solution of 3140 kg / h of the acrylic acid monomer (active content 99.7%), 4645, 7 kg / h of 24% active sodium hydroxide solution to neutralize acrylic acid to a 67% level, 1108 kg / h of deionized water and 5% active DTPA * 5Na solution (Versenex 80 ®) to obtain a monomeric solution with a concentration of iron ions of 0.3 ppm (based on the total solution) and molar fraction of DTPA * 5Na / Fe 3+ of 0.99. This monomeric solution at a temperature of 22 ° C and total solids concentration equal to 39.5% was transferred continuously to the two screw reactors (List ORP 4000) with a feed speed of 9800 kg / h. To this mixture was added, via transfer line, by injection, 5.98 kg / h of HE-TMPTA (SR9035, active content declared by Cray Valley France, 1910 ppm based on AA), 28.7 kg / h of a 60% active solution of PEG 600 (6000 ppm based on AA) and 335 kg / h of a 14% active solution of sodium sulfate (1.5% based on AA). The feed stream also injected 407 kg / h of fine SAP via a disperser (13% based on AA), 41.7 kg / h of 3% active hydrogen peroxide solution (ppm based on AA), 56, 34 kg / h of 10% active sodium persulfate solution (1800 ppm based on AA) and 470 kg / h of washing water containing 10% sodium carbonate and 2.9% NaOH, along with a flow of about of 13.5 kg / h of nitrogen. It has also been introduced continuously into the
    Petition 870190099875, of 10/04/2019, p. 56/74
    49/52 feed the reactor with a 0.7% aqueous solution of sodium erythorbate at 98.4 kg / h (220 ppm based on AA). In addition, 70 kg / h of steam at 133 ° C (2 bar) were injected through the valve at the bottom of the reactor. Including all components, the reactor was operated with a reaction mass discharge of 10407 kg / h (2.42 kg / h and per liter of the total volume of the reactor) with a total solids content equal to 41%.
    [0109] The jacket and column of zone 1 of the reactor were steam heated to 140 ° C (2.9 bar) to maintain the temperature of zone 1 between 95 and 102 ° C, recorded by the thermocouple mounted in the space between the jacket and the housing so that the tip of the thermocouple is in contact with the reaction mass. Zone 3 of the reactor was cooled by water. The columns in zones 2 and 3, as well as the jacket in zone 3, were cooled by water at 18 ° C.
    [0110] The polymerization took place in the reactor at an absolute pressure of about 940 mbar and, under these conditions, the temperature in zone 1 was recorded as 101 ° C (most likely influenced by the heated jacket), with zone 2 at 90.2 ° C and zone 3 at 92.4 ° C. The evaporated water was condensed in the condenser above the reactor and refluxed over the gel in zone 3 of the reactor. The freely flowing granulated gel was continuously discharged from the reactor into the holding tank, where it remained for about an hour at 89.5 ° C and then passed to the extruder at a temperature of 88.5 ° C to be crushed by a blade with 13 mm wide slits arranged radially and then dried in a conveyor dryer under an air jet at 145 ° C for 20 minutes. After drying, the polymer was ground in a roller mill and sieved to obtain a
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    50/52 particular polymer with particle size between 150 and 850 mm. Data obtained on product quality are shown in Table 4.
    Example 29-2 [0111] Example 29-1 was repeated, except that the concentration of Versenex 80 ® was adjusted to provide a molar ratio of DTPA * 5Na (Fe 3+ ) of 1.86 and the injection of steam for the reaction mass was automatically increased to about 110 kg / h. The temperature of zone 1 could be maintained, essentially, in the desired temperature range.
    Example 29-3 [0112] Example 29-1 was repeated, except that the concentration of Versenex 80 ® was adjusted to provide a molar ratio of DTPA * 5Na (Fe 3+ ) of 3.71 and the injection of steam, as well as jacket and spine heating were used to their full potential. However, the temperature in zone 1 fell below the critical temperature followed by a progressive displacement of the polymerization reaction to the discharge end and, finally, without reaching steady state conditions, the experiment had to be stopped to avoid problems in the following processes.
    Table 4: Examples 29 (Continuous polymerization in the reactor of
    List ORP 4000 (* = comparative examples)
    Example# Fe3 +(ppm) DTPA * 5Na / Fe 3+ molar ratio CRC(g / g) Extr.(%) Res.Mon.(ppm). Hunter color L B 29-1 0.3 0.99 39, 1 19, 4 485 93, 1 6, 1
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    51/52
    29-2 0.3 1.86 39, 7 18.9 492 94.1 5, 6 29-3 * 0.3 3.71 Failed due to insufficient reactivity of the monomer solution
    Continuous polymerization on the moving mat [0113] Monomeric solution containing 33.2% acrylic acid produced on an industrial scale, neutralized with caustic soda at a 70% neutralization degree and with a temperature of 20 ° C was placed in a storage vessel and deoxygenated by passing nitrogen. To this solution, 2700 ppm based on AA of HE-TMPTA and 6000 ppm based on AA of PEG were added; the iron concentration in the solution was adjusted to 0.5 ppm based on the solution. From this container, it was continuously loaded by the transfer line, at a flow rate of 350 kg / h, to the moving belt of the reactor, which moves at a speed of 0.33 m / min, resulting in a residence time of the mass reaction time on the mat equal to 45 minutes. To this transfer line, at the appropriate speeds to achieve the desired concentrations (based on AA), hydrogen peroxide (200 ppm), sodium persulfate (1500 ppm) and 10% active sodium carbonate solution (20% ). An in-line mixer ensured sufficient homogenization of the components. The sodium ascorbate solution, 150 ppm based on AA, was sprayed onto the monomer as it entered the mat. The CO2 resulting from the carbonate separated from the solution causing a foam to form that substantially covered the “monomer lake”, which extends for about 20 cm along the moving mat. The reaction mass
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    52/52 was polymerized and its temperature rose to about 110 ° C as it moved away from the feed point. The gel tape was continuously discharged at the end of the conveyor, but in pieces, extruded by a 13 mm blade and continuously spread over the dryer conveyor by
    a distribution mat. The gel was dry in dryer in running machine under a blast of hot air at 160 ° C per 40 minutes O polymer dry was crushed and sieved. [0114] This method and its technology were applied we
    four experiments according to Table 5, where the results are also summarized.
    Table 5: Examples 30-33 Polymerization tests on a moving mat
    Example# GFI(%) DTPA * 5Na / Fe 3+ molar ratio CRC(g / g) Extr.(%) Moisture(%)). Hunter color L B 31 30.2 - 35, 4 13.3 5.8 93.3 4.2 32 56, 5 0.818 35, 8 9.5 6.1 94.6 4.3 334.090 Polymerization failed due to insufficient initiation
    Petition 870190099875, of 10/04/2019, p. 60/74
    权利要求:
    Claims (9)
    [1]
    1. Continuous process for preparing a superabsorbent polymer, characterized by comprising:
    a) submission of an aqueous monomeric mixture containing
    - at least one α, β-unsaturated monomer;
    - at least one monomer containing at least two α, unsaturated β-ethylenic groups;
    - iron ions in an amount between 0.1 and 3 wppm, relative to the total weight of the aqueous monomer mixture; and
    - at least one chelating agent in quantity capable of providing a molar ratio of chelating agent to iron ion between 0.8 and 3.5 to the radical polymerization in a reactor, to obtain a superabsorbent polymer; and
    b) recovery of the superabsorbent polymer, in which the α, β-unsaturated monomer is an α, unsaturated β-ethylene acid, preferably comprising at least partially neutralized acrylic acid, in which the radical polymerization is initiated by a redox initiator whose oxidizing component is added to the monomeric mixture before it enters the reactor and the reducing component of which is added to the monomeric mixture immediately before the entry of the monomeric mixture into the reactor or added directly to the reactor, at a position close to the point of entry of the monomeric mixture,
    Petition 870190099875, of 10/04/2019, p. 61/74
    [2]
    2/4 where the process is carried out in a stirred reactor, the upper limit of the molar ratio of the chelating agent to iron ion is
    - 3.5, preferably 3.0, for one flow in mixture reactional total in the reactor, maximum, 1.3 kg / h per liter of reactor,- 2.5, preferably 2.0, for one flow in mixture reactional reactor total greater than 1.3 kg / h per liter of reactor and maximum 2.5 kg / h per liter of reactor, and- 1.3, preferably 1.2, for one flow in mixture reactional reactor total greater than 2.5 kg / h per liter of
    reactor, in which the said process is carried out in a reactor that has at least three zones, where the first zone is a zone of initiation, the second zone is a zone of the gel phase and the third zone is a zone of granulation, and the monomeric mixture is fed into the initiation zone.
    2. Process according to claim 1, characterized in that the chelating agent is present in an amount capable of providing a molar ratio of chelating agent: iron ion from 0.9 to 3.5 or from 1.0 to 3, 0 or 1.0 to 2.5 or 1.0 to 2.0 or 1.0 to 1.5.
    [3]
    Process according to any one of claims 1 to 2, characterized in that the chelating agent is selected from organic polyacids, phosphoric polyacids and their salts.
    [4]
    4. Process according to any one of claims 1 to 3, characterized by the fact that the chelating agent is selected from nitrilotriacetic acids,
    Petition 870190099875, of 10/04/2019, p. 62/74
    3/4 ethylenediaminetetraacetic, cyclohexanediaminetetraacetic, diethylenetriaminopentacetic, ethylenegicol-bis- (aminoethylether) N, N, N'-triacetic, N- (2-hydroxyethyl) -ethylenediamino-N, N, N'triacetic, triethylenetetramine , iminodissuccinic, glyconic and its salts.
    [5]
    Process according to any one of claims 1 to 4, characterized by the fact that iron ions are present in the aqueous monomeric mixture in an amount between 0.2 and 2.5 wppm or between 0.2 and 1.5 wppm or between 0.2 and 1.0 wppm, based on the total weight of the aqueous monomer mixture.
    [6]
    Process according to any one of claims 1 to
    5, characterized by the fact that the oxygen concentration in the monomeric mixture is reduced to a level of less than 0.5 wppm, or less than 0.3 wppm, or less than 0.1 wppm, based on the total weight of the mixture monomeric.
    [7]
    Process according to any one of claims 1 to 6, characterized in that it further comprises:
    c) drying the superabsorbent polymer;
    d) grinding and classification of the dry superabsorbent polymer with removal of fines that have a particle size less than 300 pm; and
    e) optionally, recycling the fines into the monomeric mixture before it enters the reactor or the reactor.
    [8]
    Process according to any one of claims 1 to 7, characterized by the fact that the recovered superabsorbent polymer has the surface modified by post-cross-linking, heat treatment and / or by additives.
    Petition 870190099875, of 10/04/2019, p. 63/74
    4/4
    [9]
    Process according to any one of claims 1 to 8, characterized by the fact that at least one jet of gas containing carbon dioxide is released at any point in the process and that this jet is subjected to washing with basic aqueous solution in washer, before being released, thus forming a washing solution containing carbonate and / or hydrogen carbonate and comprising iron ions, and that said washing solution is either recycled to the monomeric mixture before it enters the reactor or recycled to the reactor itself .
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    法律状态:
    2017-08-22| B25A| Requested transfer of rights approved|Owner name: EVONIK DEGUSSA GMBH (DE) |
    2018-04-10| B06F| Objections, documents and/or translations needed after an examination request according art. 34 industrial property law|
    2019-07-23| B06U| Preliminary requirement: requests with searches performed by other patent offices: suspension of the patent application procedure|
    2019-10-22| B09A| Decision: intention to grant|
    2019-11-19| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 01/03/2011, OBSERVADAS AS CONDICOES LEGAIS. (CO) 20 (VINTE) ANOS CONTADOS A PARTIR DE 01/03/2011, OBSERVADAS AS CONDICOES LEGAIS |
    2020-07-07| B25D| Requested change of name of applicant approved|Owner name: EVONIK OPERATIONS GMBH (DE) |
    优先权:
    申请号 | 申请日 | 专利标题
    EP10003452A|EP2371869A1|2010-03-30|2010-03-30|A process for the production of a superabsorbent polymer|
    US31928710P| true| 2010-03-31|2010-03-31|
    PCT/EP2011/052965|WO2011120746A1|2010-03-30|2011-03-01|A process for the production of a superabsorbent polymer|
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