法国专利FR3018207A1 METHOD FOR MANUFACTURING AEROGELS BY DIELECTRIC HEATING

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专利摘要:
The present invention relates to a method of manufacturing aerogels comprising the following successive steps: a) formation or casting of a sol in a reactor, optionally in the presence of a reinforcing material and / or an additive, b) gelling complete the soil in a lyogel; c) optionally hydrophobizing the lyogel resulting in a hydrophobic lyogel; d) drying the optionally hydrophobed lyogel to obtain an airgel; said method being characterized in that the complete gelation step b) comprises a dielectric heating, in particular by microwave or high frequency irradiation, inducing a rise in temperature to reach a complete gelation reference temperature Tb in a range of 100 ° C. at 200.degree. C., preferably from 100.degree. C. to 150.degree. C., the temperature Tb being maintained in this range for a time sufficient to reach the complete gelation of the lyogel, and more particularly the end of the syneresis of the lyogel.
公开号:FR3018207A1
申请号:FR1451910
申请日:2014-03-07
公开日:2015-09-11
发明作者:Pierre-Antoine Bonnardel；Sophie Chausson
申请人:ENERSENS；
IPC主号:

专利说明:

[0001] The present invention relates to the field of airgel type insulating materials, and more particularly to their manufacturing process. Saving energy, and more particularly thermal insulation, are today at the heart of the problems of industry and building. Thermal insulation is traditionally obtained by the use of glass wool, rock, expanded polystyrene or extruded polystyrene, often combined in industrial insulation systems on the one hand, and for the building on the other hand. The thermal insulation performance of materials is measured by their thermal conductivity. The lower the value of the thermal conductivity, the less the material conducts the heat and the better the thermal insulation. It is within this framework that the insulators based on aerogels and xerogels have been developed. Both aerogels and xerogels are very interesting not only for their quality as thermal and acoustic insulators, but also for their low density. They can be obtained in granular or monolithic form. They can also be in the form of composite materials reinforced by materials such as foams or fibrous materials. Aerogels and xerogels can be described as a special type of gel. A gel has a porous three-dimensional continuous structure. According to the nature of the fluid present in the pores of the gel, aerogels and xerogels (air), hydrogels (water), organogels (organic solvent), in particular alkogels (alcohol), are distinguished. The set of terms hydrogels, alcogels and organogels are gathered under the more general denomination of lyogels. Aerogels and xerogels are generally obtained by drying a lyogel.
[0002] Traditionally, the term airgel generally refers to a gel dried under supercritical conditions, that is to say that the majority solvent is in the state of supercritical fluid under these drying conditions, while the term xerogel is refers to a dried gel under subcritical conditions, i.e. the majority solvent is not in the state of supercritical fluid under these conditions. However, in the following, will be included under the term "airgel" both aerogels and xerogels, for simplification purposes. Traditionally, the preparation of a gel involves a sol-gel transition step, i.e., the passage of soil - suspension of solid particles in a solvent - to a gelatinous material having a three-dimensional structure in appearance network. solid, the gel. Aerogels are thus generally obtained using manufacturing processes comprising the following steps: 1) formation of a sol, in particular by hydrolysis and condensation of precursors in a solvent; 2) gelation, followed by 3) aging, these two steps leading to the formation of a lyogel; 4) optionally hydrophobization, leading to a hydrophobic lyogel; 5) drying (subcritical or supercritical), leading to the airgel. The aging step 3) results in physicochemical changes which take place after gelation. When the gel ages, the crosslinking phenomenon leads to the shrinkage of the material with expulsion of the solvent: it is called "syneresis". Aging makes it possible to improve the mechanical properties of the gel under the effect of the syneresis mechanisms (separation of the liquid and the gel). This step generally lasts several hours. In particular, in the case of a silica alkogel whose solvent is ethanol, the period of aging under reflux of ethanol at atmospheric pressure is about 3 hours. This time is necessary for the airgel obtained at the end of the process to provide the desired mechanical and thermal performance. Such a preparation method is for example illustrated in the application FR 2 873 677 (manufacture of granules) or WO 2013/053951 (manufacture of granules or self-supporting panel). Thus, a traditional manufacturing process makes it possible to obtain a lyogel (optionally hydrophobed) in a minimum of 8 hours, during which time it is necessary to add that of drying. If the duration of obtaining the lyogel is lower, the duration of the aging step in particular will be insufficient to obtain an airgel having satisfactory mechanical and thermal performance. There is therefore a need to reduce the overall production time of aerogels. Several solutions have been proposed in the prior art.
[0003] For example, US patent application US 2004/0087670 discloses a method for producing rapid aerogels. The aerogels are produced by means of rapid solvent exchange inside the gels by injecting CO2 under supercritical conditions, rather than liquid, into an extractor that has been preheated and pre-pressurized. High frequency pressure waves are applied to improve solvent exchange. The method can significantly reduce the time to form aerogels. In addition, US patent application US 2012/0112388 discloses a method and apparatus for the preparation of a hydrophobic airgel. The method consists in directly inserting a mesh-structured basket into a reactor, injecting the wet gel into the basket, installing an ultrasonic generator in a lower part of the reactor in order to emit ultrasonic waves inside the reactor, and supplying nitrogen from the bottom part of the reactor interior in order to promote a reaction and thus transform the wet gel into a hydrophobic airgel in a short time. The reaction time (aging) described in Examples 1 and 2 (page 3 paragraph 50 and page 4 paragraph 53) is however 6 hours. Furthermore, US Pat. Nos. 5,811,031 and 5,705,535 relate to a process for preparing aerogels by subcritical drying of inorganic and organic hydrogels and lyogels prepared from silicon compounds. Drying is dielectric drying such as microwave drying or high frequency drying. The production of the "wet" airgel is, it, carried out according to a conventional sol-gel process, the stages of gel formation and aging being conducted at 85 ° C for 7 days. Finally, the Chinese utility model CN 201793378 describes a process for the preparation of airgel involving a microwave irradiation, thus comprising the following steps: 1) preparation of the silicon dioxide sol; 2) preparation of the wet gel; and 3) aging of the stock solution and drying at normal pressure. The preparation of the silicon dioxide sol comprises mixing an organosilane, the organic solvent, water and an acid catalyst. The mixture is then irradiated with microwaves in order to carry out the polymerization reaction. The use of microwave irradiation is thus limited to the stage of formation of the soil, the use of these microbes only to obtain in large number microscopic bubbles leading to a porous and resistant gel. Thus, the prior art does not provide a solution for reducing the time devoted to the aging step of the lyogel, which is nevertheless a determining step in the overall duration of the aerogels production cycle. Surprisingly, the Applicant has discovered that dielectric heating, preferably by microwave or high frequency irradiation, can significantly reduce the time required for the aging step of the gel, while maintaining satisfactory mechanical and insulating properties for the production of aerogels, both in the form of granules and composite materials, for example of the monolithic type. An object of the present invention therefore relates to a method of manufacturing aerogels comprising the following successive steps: a) formation or casting of a sol in a reactor, optionally in the presence of a reinforcing material and / or an additive, b ) complete gelation of the soil into a lyogel; c) optionally hydrophobizing the lyogel resulting in a hydrophobic lyogel; d) drying the optionally hydrophobed lyogel to obtain an airgel; said method being characterized in that the complete gelation step b) comprises a dielectric heating inducing a rise in temperature to reach a complete gelation reference temperature Tb in a range from 100 ° C to 200 ° C, preferably from 100 ° C. to 150 ° C., the temperature Tb being maintained in this range for a time t1 sufficient to reach the end the complete gelation of the lyogel, and more particularly the syeresis of the lyogel. DEFINITIONS By "dielectric heating" is meant in the sense of the present invention a heating by the application of electromagnetic waves. The present invention relates to two frequency ranges: high frequency (HF) radiations whose usual frequencies are between 1 and 400 MHz, corresponding to wavelengths ranging from 300 to 0.75 m; and microwave radiation (MO) whose frequencies vary between 400 and 18,000 MHz, corresponding to wavelengths ranging from 75 cm to 1.6 cm. In the present invention, we will therefore speak of heating by microwave or high frequency irradiation, according to the selected frequency range.
[0004] Heating by HF and MO are based on the same principle. The electromagnetic energy is dissipated in the mass of the product, according to the distribution of the electric field and the dielectric moments of the reagents (solvent, sol and / or lyogel) in the reactor. This type of energy transfer is very effective because it is known to produce very intense electric field distributions, generating high power density densities (for example up to 5 kW / L of product). For the purposes of the present invention, the term "target temperature" of a process step means the target temperature of this step in the reaction medium, that is to say in the lyophil in steps b) and c) of the process according to the invention, or in the soil in step a). Thus, if the initial temperature of the reaction medium is different from the target temperature, there may be a period of time during which the temperature of the system is modified (for example by heating) so as to reach the set temperature. The set temperature may be either constant or modulated during said process step.
[0005] By "sol" is meant in the sense of the present invention a mixture of precursors, a solvent and optionally a gelling catalyst, leading, after the gelation and aging reaction, the lyogel. The set of terms hydrogels, alkogels and organogels are brought together, in the present invention, under the more general denomination of lyogels. For the purposes of the present invention, the term "airgel" will include both aerogels and xerogels for the purpose of simplification. The reaction that causes gelation does not stop at the freezing point; it continues. Indeed, the hydrolysis and condensation reactions continue during aging, which increases the connectivity of the gel structure. The whole process of evolution of the gel over time is called "aging". Aging of the gel results in physicochemical changes that take place after gelation, which can be distinguished as follows: polymerization (step of reinforcing the network through the formation of new bonds, or crosslinking, in particular by condensation, by example due to Brownian motion and network flexibility); - ripening (process of dissolution and reprecipitation), which is mainly observed in the case of an inorganic lyogel; and phase transformation or syneresis, due to shrinkage of the material with expulsion of the solvent. Thus, by "syneresis" is meant in the sense of the present invention the withdrawal of the lyogel resulting from the crosslinking or condensation reactions which cause the expulsion of the solvent (interstitial liquid) out of the lyogel. The syneresis thus generates a densification of the solid network of the gel. Thus, the pore size distribution, the specific surface as well as the permeability of the gel are modified. Moreover, the mechanical and thermal properties of the gel are improved. For the purposes of the present invention, the "complete gelation" step comprises both the gelling step in the strict sense, that is to say the sol-gel transition leading to the gel, and the aging step. . Indeed, given the very short reaction times of the process according to the present invention, it is difficult to distinguish the two steps. For the purposes of the present invention, the term "absolute pressure" means the pressure measured with respect to the vacuum (absolute pressure zero).
[0006] For the purposes of the present invention, the term "composite airgel" means an airgel comprising at least two immiscible compounds intimately bound together. The composite airgel then has properties, particularly physical properties (for example thermal conductivity, rigidity, etc.) that each of the materials taken separately does not necessarily possess.
[0007] The composite aerogels according to the present invention comprise a "reinforcing material", which is either fibrous or a foam. Within the meaning of the present invention, a "fibrous reinforcing material" comprises fibers or a nonwoven fibrous web, or a mixture thereof. Those skilled in the art will be able to choose from among the various types of fibers those which are most suitable for the manufacture of thermal insulators, for example glass fibers, mineral fibers, polyester fibers, aramid fibers, nylon fibers and vegetable fibers, or a mixture thereof. For the choice of these fibers, those skilled in the art will be able to refer to US Pat. No. 6,887,563. For the purposes of the present invention, the term "nonwoven fibrous web" means a three-dimensional web consisting of a structured but non-woven fiber entanglement. Indeed, when the fibers are woven, the thermal conductivity of the fibrous web increases and the performance of composite aerogels obtained are lower. For the purposes of the present invention, the term "foam" means a substance, in particular a polymer, trapping gas bubbles therein. Foams are distinguished by "closed cell foams", i.e. the gas pockets are fully coated with solid material, as opposed to "open cell foams", in which the gas pockets communicate with each other. . For example, mention will be made of open-cell melamine foams such as foams comprising a polymer of which one of the monomers is melamine, and in particular melamine-formaldehyde foams, resulting from a polymerization reaction between melamine and formaldehyde. For example, the foams marketed under the name BASOTECT® are open cell melamine foams. One can also mention open cell polyurethane foams, which are used in particular for sound insulation.
[0008] By "monolithic" is meant in the sense of the present invention that the airgel, in particular composite, is solid and is in the form of a block in one piece, in particular in the form of a panel. A monolithic airgel can be both rigid and flexible. By "rigid" is meant that the material can not be deformed significantly without observing the formation of cracks, or even the rupture of the monolithic material. In particular, this means that the monolithic material can not be rolled. By "flexible" is meant on the contrary that the material can be deformed, and in particular wound. The term "self-supporting" may also be used to qualify the monolithic material, which will be understood to mean that the stability of the product is not due to an external support. A self-supporting monolithic material can be both flexible and rigid. In contrast, an airgel that is not monolithic will be obtained in the form of granules. In the present invention, the thermal conductivity of the airgel is measured according to the method of the hot plate kept from the standard NF EN 12667 at 20 ° C and at atmospheric pressure as of July 2001. DESCRIPTION OF THE FIGURE FIG. 1: representation of the evolution of the temperature, the absolute pressure and the power density applied by microwave irradiation as a function of time under the reaction conditions of Example 2. The abscissa axis represents the time in minutes, the y-axis (left) represents the temperature in ° C, and the other y-axis (right) represents both the absolute pressure (in bar) and the incident power density (in kW / L).
[0009] The squares represent the pressure and the diamonds the temperature. The power density is represented as a histogram. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing aerogels comprising the following successive steps: a) formation or casting of a sol in a reactor, optionally in the presence of a reinforcing material and / or an additive (b) complete gelation of the soil into a lyogel; c) optionally hydrophobizing the lyogel resulting in a hydrophobic lyogel; d) drying the optionally hydrophobed lyogel to obtain an airgel; said method being characterized in that the complete gelation step b) comprises a dielectric heating, in particular by microwave or high frequency irradiation, inducing a rise in temperature to reach a complete gelation reference temperature Tb in a range of 100 ° C. at 200.degree. C., preferably from 100.degree. C. to 150.degree. C., the temperature Tb being maintained in this range for a time sufficient to reach the complete gelation of the lyogel, and more particularly the end of the syneresis of the lyogel.
[0010] The method according to the invention thus makes it possible to very significantly reduce the time devoted to the aging step, to the point where it becomes difficult to distinguish this step from the gelling step itself. In addition, the process according to the present invention is reproducible and reliable, the products obtained are of constant quality, and similar to those obtained according to a traditional manufacturing process involving longer reaction times. Advantageously, no binder is used or added to any stage of the process according to the invention. Step a) The sol comprises precursors and a solvent. This solvent can be organic or aqueous. In a preferred embodiment, the solvent is an alcohol, preferably ethanol. In another embodiment, the solvent is water. The soil used in step a) is organic, inorganic or hybrid.
[0011] When the soil is organic, it advantageously comprises precursors of resorcinol formaldehyde, phenol formaldehyde, melamine formaldehyde, cresol formaldehyde, phenol furfural alcohol, polyacrylamides, polyacrylonitriles, polycyanurates, polyfurfural alcohol, polyimides, polystyrenes, polyurethanes, polyvinyl alcohol, dialdehyde, epoxy, agar agar, and agarose.
[0012] Advantageously, the soil of step a) is an inorganic sol. Preferably, the inorganic sol is selected from sols of silica, titanium oxide, manganese oxide, calcium oxide, calcium carbonate, zirconium oxide, and mixtures thereof, more preferably from the group of sols of silica, titanium oxide, manganese oxide, calcium oxide, calcium carbonate and mixtures thereof, more preferably it is a silica sol. For example, a silica sol may comprise a polyalkoxydisiloxane (especially a polyethoxydisiloxane) as a precursor and ethanol as a solvent, in admixture with aqueous hydrochloric acid. In a particular embodiment, step a) comprises the formation of soil in the reactor. In a second embodiment, the sol is formed beforehand outside the reactor in which step b) is carried out, and step a) comprises or consists of pouring the sol into the reactor, optionally in the presence of Advantageously, the additive is intended to improve the material cost structure, and more specifically the mechanical, cohesion or thermal conductivity properties of the aerogels according to the invention. Preferably, this additive comprises an opacifier. Thus, advantageously, the material according to the invention further comprises an opacifier. The use of an opacifier makes it possible to reduce the value of the thermal conductivity by decreasing its radiative component. Typically, the opacifier is selected from SiC, TiO2, carbon black, graphite, ZrO2, ZnO, SnO2, MnO, NiO, TiC, WC, ZrSiO4, Fe2O3, Fe3O4, FeTiO3 or mixtures thereof. In particular, the opacifier is selected from the group consisting of SiC and TiO2 and mixtures thereof.
[0013] In a particular embodiment of the invention, a fibrous reinforcement material is placed in the reactor where the soil is poured during step a). The fibrous reinforcing material makes it possible to structure the airgel to improve its strength and hold properties while retaining its thermal insulation properties.
[0014] Preferably, the fibrous reinforcing material comprises a fibrous nonwoven web, advantageously chosen from organic webs, inorganic webs, natural fiber webs, mixed webs and mixed rolled webs. In this embodiment, the airgel obtained according to the method of the invention is a monolithic composite airgel. According to a first embodiment, the web is organic and selected from polyethylene terephthalate (PET) organic webs. According to a second embodiment, the sheet is inorganic and chosen from inorganic sheets of glass wool or sheets of rockwool. In another embodiment, a foam-type reinforcing material is placed in the reactor where the soil is poured during step a). In this case also, the airgel obtained according to the process of the invention is a monolithic composite airgel. Preferably, it is an open cell foam, typically an open cell melamine or polyurethane foam. For example, the foams marketed under the name BASOTECT® are open cell melamine foams.
[0015] Step b) The dielectric heating of step b) can be applied either by microwave irradiation or by high frequency irradiation. Advantageously, the frequency of the electromagnetic field applied is advantageously between 3 MHz and 3000 MHz, more advantageously between 3 and 2500 MHz.
[0016] In the case of microwave irradiation, the frequency range of the electromagnetic field applied is advantageously between 400 and 2500 MHz. In the case of high-frequency irradiation, the frequency range of the electromagnetic field applied is advantageously between 10 and 400 MHz.
[0017] Preferably, the full gelling target temperature range is from 100 ° C to 180 ° C, more preferably from 100 ° C to 150 ° C, most preferably from 110 ° C to 130 ° C. For example, the complete gelling control temperature of step b) is in the range of 120 ° C to 130 ° C.
[0018] In a particular embodiment, the complete gelling reference temperature is constant during step b). In another embodiment, the complete gelling set point temperature is modulated during step b). Preferably, the complete gelling reference temperature is higher than the boiling point of the solvent. Advantageously, the absolute pressure in the reactor in step b) is greater than atmospheric pressure. Preferably, step b) is therefore carried out under pressure. For example, the absolute pressure in the reaction medium in step b) is between 1 and 20 bar, more preferably it is between 1 and 15 bar, more preferably between 1.5 and 12 bar. The time t1 sufficient to reach the completion of the syneresis of the lyogel is determined according to criteria well known to those skilled in the art. For example, this time can be measured by quantifying the solvent expelled from the gel during this step: the syneresis is complete when no more expulsion of solvent is observed. In practice, the process is continued (i.e., step d) is optionally preceded by step c)) until the final airgel is obtained, and the thermal properties of the obtained airgel are measured. If these are satisfactory, that is to say that the thermal conductivity X of the final airgel is in particular less than 25 mW / mK, preferably less than 21 mW / mK, and in the case of composite aerogels monolithic between 10 and 15 mW / mK, the duration t1 is sufficient. If they are not (eg thermal conductivity X, final airgel greater than 25 mW / mK, preferably greater than 21 mW / mK, and in the case of monolithic composite aerogels greater than 15 mW / mK), the duration ti is insufficient.
[0019] In addition, it is also possible to measure the apparent density of the airgel obtained. If this is satisfactory (for example, the bulk density is less than or equal to 150 kg / mi, especially between 40 and 150 kg / mi, in the case of aerogels obtained in the form of monolithic aerogels, the airgel has preferably, an apparent density of between 70 and 150 kg, in the case of aerogels obtained in the form of granules, the airgel preferably has an apparent density of between 40 and 90 kg. It is sufficient. If they are not (for example, a bulk density greater than or equal to 150 kg in the case of a monolithic airgel or greater than or equal to 90 kg in the case of a granular airgel), the duration ti is insufficient. It is also possible to measure the mechanical properties of the airgel obtained. If these are satisfactory (for example the Young's modulus of the airgel is between 0.6 and 2 MPa), the duration t1 is sufficient. If they are not (for example Young's modulus less than 0.6 MPa), the duration ti is insufficient.
[0020] Preferably, the duration t1 is at least 6 minutes. It is found experimentally that this duration t 1 is advantageously less than or equal to 1 hour, still more advantageously less than or equal to 30 minutes, even more advantageously less than or equal to 15 minutes, even more advantageously less than or equal to 10 minutes.
[0021] The heating time to reach the temperature Tb depends on the amount of soil in the reactor and the power supplied by the generator. Thus, this heating time is directly related to the power density applied to the material (soil or lyogel). Preferably, this time is as short as possible, and if possible less than the time sufficient to obtain the complete gelling of the sol in lyogel in step b). For example, this heating time may be about 1 or 2 minutes. In one embodiment, the temperature Tb is maintained in the above temperature range by thermal insulation of the reactor or by radiant or conductive heating. In a second embodiment, the Tb is maintained in the above temperature range by dielectric heating, preferably high frequency or microwave.
[0022] In this second embodiment, advantageously, the total duration tgl of the dielectric heating in step b) is at least 7 minutes. The total heating time starts at the start of the warm-up period and ends at the end of the hold time of the full set-point temperature. In other words, it includes the duration of rise in temperature and the duration ti. It is found experimentally that this time tgl is advantageously less than or equal to 1 hour, still more advantageously less than or equal to 30 minutes, even more advantageously less than or equal to 15 minutes, even more advantageously less than or equal to 12 minutes.
[0023] Step c) Preferably, when the drying of step d) is carried out under subcritical conditions, step c) of hydrophobization is not optional. Advantageously, when the airgel is organic, step c) is not implemented.
[0024] Step c) is carried out at a hydrophobization reference temperature Tc in a range from 60 ° C to 200 ° C, the temperature Tc being maintained in this range for a sufficient time t2 to obtain the hydrophobization lyogel. The time t2 sufficient to obtain the hydrophobization of the lyogel in step c) is determined according to criteria well known to those skilled in the art. For example, this time can be measured by determining the carbon element level by elemental analysis. Depending on the nature of the hydrophobing agent, it is possible to deduce the structure of the hydrophobic groups grafted onto the lyogel. By making a difference between the carbon element content of the hydrophobed lyogel with the lyogel obtained directly at the end of step b) (non-hydrophobed), it is possible to deduce the concentration of grafted groups. For example, in the case of a silica alkogel undergoing hydrophobic treatment with hexamethyldisiloxane, the maximum grafting concentration of Si- (CH3) 3 is 60% relative to the number of Si-OH silanols. In practice, the process is continued (i.e. proceeds to step d)) until the final airgel is obtained, and the thermal properties of the obtained airgel are measured. If these are satisfactory (for example, the thermal conductivity of the airgel is less than 25 mW / mK, preferentially less than 21 mW / mK, or in the case of a monolithic composite airgel of between 10 and 15 mW / mK), the duration t2 is sufficient. If they are not (for example thermal conductivity greater than 25 mW / mK, preferably greater than 21 mW / mK, or in the case of a monolithic composite airgel greater than 15 mW / mK), the duration t2 is insufficient. . In addition, it is also possible to measure the apparent density of the airgel obtained. If this is satisfactory (for example, the bulk density is less than or equal to 150 kg / mi, especially between 40 and 150 kg / mi, in the case of aerogels obtained in the form of monolithic aerogels, the airgel has preferably, an apparent density of between 70 and 150 kg, in the case of aerogels obtained in the form of granules, the airgel preferably has an apparent density of between 40 and 90 kg. t2 is sufficient. If they are not (for example, a bulk density greater than or equal to 150 kg in the case of a monolithic airgel or greater than or equal to 90 kg in the case of a granular airgel), the duration t2 is insufficient. It is also possible to measure the mechanical properties of the airgel obtained. If these are satisfactory (for example the Young's modulus of the airgel is between 0.6 and 2 MPa), the duration t2 is sufficient. If they are not (for example Young's modulus less than 0.6 MPa), the duration t2 is insufficient.
[0025] In a particular embodiment, the temperature T is identical to the temperature of Tb. Preferably, the temperature T is greater than the boiling point of the solvent. Advantageously, the absolute pressure in the reactor in step c) is greater than atmospheric pressure. Preferably, step c) is therefore carried out under pressure. For example, the absolute pressure in the reaction medium in step c) is between 1 and 20 bar, more preferably between 1 and 15 bar, most preferably between 1.5 and 12 bar. . Advantageously, the hydrophobizing reagents (in particular the hydrophobing agent) are introduced at a pressure of between atmospheric pressure and a pressure representing 150% of the pressure inside the reactor in which step c is carried out. ). Preferably, the hydrophobizing reagents are introduced at a pressure of between 120% and 150% of the pressure inside the reactor in which step c) is carried out. In an advantageous embodiment, steps b) and c) are carried out in the same reactor. In another advantageous embodiment, steps a), b) and c) are carried out in the same reactor. Advantageously, the hydrophobizing reagents (in particular the hydrophobing agent) are introduced at a temperature of between 20 ° C. and their boiling point. For example, when the hydrophobing agent is HDMSO, the hydrophobizing reagents (especially the hydrophobing agent) are introduced at a temperature between 20 ° C and 150 ° C. In a particular embodiment, the hydrophobizing reagents are introduced at room temperature. In a particular case, step c) of hydrophobization may involve a heating or cooling phase to achieve a hydrophobization set point temperature in a range from 60 ° C to 200 ° C.
[0026] However, in general, during the introduction of the hydrophobizing reagents, especially when they are introduced at room temperature, there is a slight drop in the temperature of the lyogel. In this case, it is preferable to carry out a heating to reach the temperature of Tc. Thus, in this embodiment, the hydrophobization step c) involves heating to reach a hydrophobizing reference temperature T, in a range from 60 ° C. to 200 ° C., the temperature T being maintained in this range for a sufficient time t2 to obtain the hydrophobization of the lyogel. The heating time to reach the temperature T, depends on the amount of lyogel in the reactor, its initial temperature (ie the temperature Tb), the temperature and the amount of hydrophobization reagents introduced, and the density of power applied to the reaction mixture comprising the lyogel and the hydrophobization reagents. Preferably, this time is as short as possible, and if possible less than the time sufficient to obtain the hydrophobization of the soil in step c). For example, this heating time can be about 1 minute.
[0027] In the case where the temperature Tb is equal to the temperature Tc, the duration of the heating is such that it is sufficient to compensate for the cooling due to the introduction of the hydrophobization reagents. For example, this heating time can be about 1 minute. In a first embodiment, the heating of step c) is carried out by radiant or conductive heating. In this case, the preferred temperature range is between 70 ° C and 150 ° C, more preferably between 70 ° C and 120 ° C, most preferably between 70 ° C and 110 ° C. Preferably, in this first embodiment, the duration t2 is at least 1 hour. It is found experimentally that this duration t2 is advantageously less than or equal to 6 hours, advantageously less than or equal to 4 hours, even more advantageously less than or equal to 2 hours. The duration t2 is chosen in particular as a function of the temperature at which step c) is carried out. In a second embodiment, the heating of step c) is carried out by dielectric heating. The dielectric heating of step c) can be applied either by microwave irradiation or by high frequency irradiation. Advantageously, the frequency range of the electromagnetic field applied is between 3 MHz and 3000 MHz, even more advantageously between 3 MHz and 2500 MHz. In the case of microwave irradiation, the frequency range of the electromagnetic field applied is advantageously between 400 and 2500 MHz. In the case of high-frequency irradiation, the frequency range of the electromagnetic field applied is advantageously between 10 and 400 MHz. Preferably, in this second embodiment, the duration t2 is at least 6 minutes. It is found experimentally that this duration t2 is advantageously less than or equal to 1 hour, advantageously less than or equal to 30 minutes, even more advantageously less than or equal to 15 minutes, even more advantageously less than or equal to 10 minutes. In this second embodiment, the hydrophobization set point temperature of step c) is advantageously maintained in the above temperature range by dielectric heating, preferably high frequency or microwave. Advantageously, the total duration tg2 of the dielectric heating in step c) is then at least 7 minutes. The total duration tg2 includes the duration tg2 and possibly the rise time. It is found experimentally that this duration is advantageously less than or equal to 1 hour, advantageously less than or equal to 30 minutes, even more advantageously less than or equal to 15 minutes, even more advantageously less than or equal to 12 minutes.
[0028] In the case where the lyogel is an alcogel, step b) is advantageously followed by a step c) of hydrophobization treatment of the alcogel, at the end of which is obtained a hydrophobed alkogel. Step c) comprises, for example, bringing the alkogel obtained in step b) into contact with a hydrophobic agent in an acid medium having a pH of between 1 and 3. Advantageously, the hydrophobing agent used is chosen from the group consisting of organosiloxanes, organochlorosilanes and organoalkoxysilanes, more advantageously, the hydrophobing agent used is selected from the group consisting of hexamethyldisiloxane (HMDSO), trimethylchlorosilane, trimethylethoxysilane and hexamethyldisilazane, even more advantageously hexamethyldisiloxane (HMDSO). In addition, in this embodiment, the sol is preferably a silica sol, preferably obtained by controlled hydrolysis of tetraethoxysilane in ethanol. Advantageously, the alkogel is acidified in step c) by adding a mineral or organic acid. More advantageously, the mineral acid is hydrochloric acid and the organic acid is trifluoroacetic acid. Even more advantageously, the acid is trifluoroacetic acid or hydrochloric acid and the hydrophobicizing agent 1 'hexamethyldisiloxane (HMD SO). In the case where the hydrophobic agent is hexamethyldisilazane, it is advantageously added alone or with a solvent such as ethanol. Advantageously, in this embodiment, step c) is conducted at a temperature between 50 ° C and 150 ° C. Even more advantageously, step c) is carried out at a temperature greater than or equal to the boiling temperature of the alcohol (solvent of the alcogel). In the case where the solvent is ethanol, step c) is carried out at a temperature advantageously between 100 ° C. and 150 ° C., preferably between 110 ° C. and 130 ° C. In the case where the lyogel is a hydrogel, a step b1) of exchanging the solvent (water) with an organic solvent such as acetone, hexane or heptane leading to the formation of a lyogel is advantageously performed between steps b) and c). The conditions for carrying out step c) of hydrophobization treatment of the lyogel are similar to those described above in the case where the lyogel is an alcogel (in particular temperature, reagents, etc.) to the solvent.
[0029] In these two embodiments, the hydrophobic treatment in step c) of the process is intended in particular to reduce the water recovery of the composite material. Drying: step d) The drying in step d) is preferably carried out in such a way that the airgel obtained has a residual amount of solvent by weight of less than or equal to 3% (by weight), preferably 1% (by weight ), according to the standard EN / ISO 3251. The protocol used consists of taking 1 g of airgel according to the invention, weighing it, then drying it for 3 hours in an oven at 105 ° C., then weighing the airgel as well as dried. The ratio of the difference between these two weights on the weight of the airgel obtained after drying makes it possible to determine the residual amount of solvent in% by weight. In a particular embodiment, the drying step d) is carried out under supercritical conditions. In another particular embodiment, the drying step d) is carried out under subcritical conditions, for example by radiant, conductive, convective or dielectric drying. When step d) is a convective type drying, it is preferably carried out at a temperature of between 120 ° C. and 180 ° C., preferably between 140 ° C. and 160 ° C., and even more preferably equal to 150 ° C. ° C. Convective drying may be conducted in natural mode, but is preferably conducted in forced mode.
[0030] When step d) is a dielectric drying step, it is advantageously microwaves or high frequencies. Preferably, the power density provided during step d) of microwave drying between 0.3 kW and 3 kW per kg of lyophil optionally hydrophobed starting, preferably between 0.5 kW and 2 kW per kg of starting lyogel , more preferably equal to 1 kW per kg of starting lyogel. Said power density is adjusted during drying so that the temperature of the material is between 40 ° C and 400 ° C, more preferably between 40 ° C and 200 ° C, even more preferably between 50 ° C and 150 ° C . In a preferred embodiment of the invention, when step d) is a dielectric drying step, it is carried out in the same reactor as the reactor for implementing steps b) and c), after having adapted a system for distilling the solvent which is evaporated during drying. In a particular embodiment, step d) is preceded by a step d1) of predrying under subcritical conditions at a temperature below 80 ° C. Advantageously, the temperature of the pre-drying step dl) is between 40 ° C and 80 ° C, more preferably between 60 ° C and 80 ° C, more preferably is equal to 80 ° C. Preferably, the pre-drying d1) is continued until obtaining a condensed lyogel having lost between 10 and 80% of solvent by weight, advantageously between 20% and 60% of solvent by weight, even more advantageously between 40% and 50% of solvent by weight relative to the weight of the starting lyogel. The mass of solvent lost during step d) or dl) is measured differently according to the scale of the process. On the scale of the laboratory, this quantity is measured by the difference between the weight of the lyogel and that of the airgel obtained after step b) or c) (when this is carried out) after drying under the conditions of the step d) or dl). On an industrial scale, the solvent evaporated during the drying step d) or d1) is condensed in another reactor and then weighed. In a preferred embodiment of the invention, step d1) is carried out by circulating a hot gas stream in the reactor. The gas stream is typically a flow of inert gas such as nitrogen, air, or a rare gas. Advantageously, the hot gas stream flows vertically, even more advantageously from top to bottom.
[0031] In another embodiment, the pre-drying in step d1) is carried out under reduced pressure. Such an embodiment is advantageous because it allows, at equal temperature, to obtain shorter pre-drying times. Dielectric heating Preferably, the electromagnetic field applied for the dielectric heating (preferably by microwave or high frequency irradiation) during step b), c) or d), is homogeneous in the lyogel. Advantageously, the frequency of the electromagnetic field applied in step b), and possibly in step c) and / or d), will be chosen in a range from 3 MHz to 3 000 MHz. The geometry of the reactor is advantageously chosen by those skilled in the art so that the electromagnetic field density applied for the dielectric heating (preferably by microwave or high frequency irradiation) during step b), c) or ), is homogeneous in soil or lyogel. This geometry is especially adapted according to criteria well known to those skilled in the art as a function of the depth of penetration (dp) of the electromagnetic field, which is a function of the frequency of the electromagnetic field applied, as recalls the following formula: dp = c / (2 i (2) * nf i {E'd i (1+ (c ", - / E ', -) 2) -11I) in which: - dp represents the depth of penetration (in meters) where the microwave power reaches 1/3 (one-third) of the power applied on the surface - c represents the speed of light (in m / s-1) - f represents the frequency of the electro-magnetic field -magnetic applied (Hz) - C'r represents relative permitivity (dimensionless) - C "r represents the dielectric loss (dimensionless). The values of C'r and C "r are known to those skilled in the art, in particular C 'r is 34 for ethanol, 78 is for water, and E" r is in the range 0.1 to 5. the reagents according to the invention, in particular silica sols and optionally hydrophobic alkogels. The power density provided by the generator is adapted according to the volume of reagents (sol, solvent, lyogel, hydrophobization reagents) and their intrinsic characteristics, such as in particular their dielectric constant. To overcome possible inhomogeneities of the electromagnetic field, a sweep with a wave stirrer or moving the reaction cavity in the field can be implemented. Aerogels obtained by the process The aerogels obtained by the process according to the invention are in the form of granules or monolithic aerogels. Advantageously, the aerogels thus obtained advantageously possess a thermal conductivity X, less than or equal to 25 mW / mK, even more advantageously less than or equal to 21 mW / mK, measured according to the method of the hot plate kept from the standard NF EN 12667 at 20 ° C and at atmospheric pressure. In the case of aerogels obtained in the form of granules, the airgel preferably has a thermal conductivity X less than or equal to 21 mW / mK, advantageously between 10 and 21 mW / mK, measured according to the hot plate method. kept from standard NF EN 12667 at 20 ° C and at atmospheric pressure. In the case of aerogels obtained in the form of monolithic aerogels, the airgel preferably has a thermal conductivity X less than or equal to 20 mW / mK, advantageously between 10 and 15 mW / mK, measured according to the method of the hot plate kept from the standard NF EN 12667 at 20 ° C and at atmospheric pressure. In addition, the aerogels obtained by the process according to the present invention advantageously have a bulk density of less than or equal to 150 kg. e, for example the bulk density is between 40 and 150 kg. mid. In the case of aerogels obtained in the form of monolithic aerogels, the airgel preferably has an apparent density of between 70 and 150 kg. mi, for example between 100 and 150 kg. mid. In the case of aerogels obtained in the form of granules, the airgel preferably has an apparent density of between 40 and 90 kg. mid. Advantageously, the airgel according to the invention does not comprise a binder. Examples of inorganic binder include cements, plasters, gypsum, lime, and as an example of organic binder thermoplastics such as polyolefin waxes, styrene polymers, polyamides. The term binder also includes adhesives, such as epoxy resins, cyanoacrylates for example.
[0032] The aerogels obtained according to the process of the present invention are inorganic, organic or hybrid. In one embodiment, the airgel is an inorganic airgel, in particular chosen from the group of aerogels of silica, titanium oxide, manganese oxide, calcium oxide, calcium carbonate and oxide. zirconium, polyurethane / cellulose or mixtures thereof, preferably in the group of aerogels of silica, titanium oxide, manganese oxide, calcium oxide, calcium carbonate or mixtures thereof, more preferably it it is a silica airgel, advantageously hydrophobed.
[0033] In another embodiment, the airgel is an organic airgel, in particular chosen from the group of aerogels of resorcinol formaldehyde, phenol formaldehyde, melamine formaldehyde, cresol formaldehyde, phenol furfural alcohol, polyacrylamides, polyacrylonitriles, polyacrylates, polycyanurates, polyfurfural alcohols, polyimides, polystyrenes, polyurethanes, polyvinyl alcohol, dialdehyde, epoxy, agar agar, and agarose (for a conventional synthesis, see, for example, CS Ashley, CJ Brinker and DM Smith, Journal of Non-Crystalline Solids, Volume 285, 2001). Hybrid aerogels advantageously comprise a mixture of organic and inorganic aerogels, preferably such as those mentioned above.
[0034] The aerogels obtained according to the process of the invention preferably have a water recovery rate according to standard NF EN ISO 12571 at room temperature and at 70% relative humidity less than or equal to 5%, even more preferably less than or equal to 3%. %, and preferably a water recovery rate at room temperature and at 95% relative humidity less than or equal to 10%, more preferably less than or equal to 5%. Advantageously, the airgel according to the invention is hydrophobic, permeable to steam and has a temperature of up to 250.degree. The materials according to the invention have good properties of fire resistance, they are preferably classified at least B1 according to the German standard DIN 4102-1, M1 in France according to standard NF P-92507, or VO in the United States according to the UL94 standard. The combustion energy or higher heating value of the composite material according to the invention measured according to the NF EN ISO 1716 standard is advantageously lower than most performance insulating materials, such as polyurethane. They also have good sound insulation properties, especially comparable to those of rockwool.
[0035] The composite aerogels (i.e. comprising a reinforcing material) obtained according to the present invention combine the mechanical properties of the fibers and the insulating properties of the aerogels. In a first particular embodiment, the composite airgel comprises a fibrous reinforcement material comprising a fibrous nonwoven web, advantageously chosen from organic webs, inorganic webs, natural fiber webs, mixed webs and mixed rolled webs. . Advantageously, the organic layer is chosen from organic sheets of polyethylene terephthalate (PET). Advantageously, the inorganic web is selected from inorganic sheets of glass wool or sheets of rock wool.
[0036] Advantageously, the sheet of natural fibers is chosen from the plies of natural fibers made of sheep's wool or flax fiber. Advantageously, the fibrous nonwoven web has a thickness of between 30 and 70 mm and an open porosity of between 96% and 99.8%. The monolithic aerogels thus obtained advantageously have a thickness of between 30 mm and 70 mm, more advantageously between 30 mm and 60 mm, and even more advantageously between 40 mm and 45 mm. Advantageously, in this first embodiment, the monolithic airgel comprises between 50% and 90% by weight of airgel with respect to the weight of the panel, preferably between 60% and 80% by weight of airgel relative to the weight of the airgel. sign. In a second embodiment, the composite airgel comprises a foam as a reinforcing material. Such a foam makes it possible to improve certain mechanical properties of the airgel, while maintaining a thermal conductivity of less than 20 mW / mK measured according to the method of the hot plate kept from the standard NF EN 12667 at 20 ° C. and at atmospheric pressure. . For example, the maximum elastic phase stress of composite materials is much greater than that of the corresponding unreinforced airgel. Typical values are 3.5 MPa (for the composite material) and 1.10-4 MPa (for the corresponding unreinforced airgel). In this second embodiment, the monolithic airgel according to the invention comprises between 85% and 98% by weight of airgel relative to the weight of the composite material, preferably between 90% and 95% or between 90 and 98% by weight. airgel weight relative to the weight of the composite material. In this embodiment, the monolithic airgel according to the invention advantageously has a thickness of between 2 and 50 mm, preferably between 5 and 30 mm, for example between 10 and 20 mm. It is observed that the thickness of the monolithic composite material is correlated with the thickness of the foam used. Thus, the foam advantageously has a thickness of between 2 and 50 mm, preferably between 5 and 30 mm, for example between 10 and 20 mm.
[0037] Uses The aerogels obtained by the process according to the present invention can be used as thermal insulation, in particular for applications in the construction of buildings or in the insulation of industrial systems or processes. Thus, the aerogels obtained by the method according to the present invention are advantageously used for the manufacture of building materials, including walls and partitions, but also floors or ceilings or for the insulation of industrial pipes. The aerogels obtained by the process according to the present invention can also be used as acoustic insulators. The monolithic aerogels obtained by the process according to the present invention may in particular be used to form multilayer panels, more particularly in the form of multilayer laminated or sandwich panels, comprising at least one layer consisting essentially of a monolithic composite material according to the invention. possibly in combination with layers of different nature. In said multilayer panels, each layer is made of a monolithic material or a panel bonded to one or more other layers. By way of example, one or more plasterboards (possibly of type BA13) may be glued to one or each side of a monolithic composite material according to the invention to form a doubling complex. Mixed multilayer panels comprising a combination of one or more composite materials according to the invention and a composite material as described for example in the international application WO 2013/053951 are also contemplated. The multilayer panels thus obtained also find applications as thermal insulation, particularly for applications in the construction of buildings or in the insulation of industrial systems or processes. The monolithic aerogels obtained by the process according to the present invention can in particular be used as mechanical shock absorbers.
[0038] The following examples are intended to further illustrate the present invention, but are in no way limiting. EXAMPLES Example 1 Preparation of a silica sol A silica sol having the following composition: 36.2% of polyethoxydisiloxane in 20% solution in ethanol is obtained by partial hydrolysis of tetraethoxysilane (TEOS) in the presence of hydrochloric acid, 54.3% ethanol, 8.9% deionized water, 0.6% ammonia. EXAMPLE 2 Preparation of an Airgel According to the Invention with Microwave Heating During step c) 2 L of silica sol of Example 1 was poured before gelling in a closed chamber (step a). The reactor is then heated by the application of a microwave field until a temperature of about 120 ° C (full gel set point temperature) is reached in the bulk of the reagents (step b). The pressure inside the reactor is then 5 bars absolute. The complete gelling set point temperature is 120 ° C. The duration of step b) (tgl) is 7.5 minutes. Then, hydrochloric acid (until a pH = 1) and hexamethyldisiloxane (hydrophobic agent) are introduced at ambient temperature and pressure into the reactor so as to completely cover the alcogel (step c). There is a slight drop in temperature. The reaction medium is heated by the application of a microwave field to reach again a temperature of about 120 ° C (hydrophobization target temperature). The duration of step c) is 7.5 minutes (tg2). Then, the microwaves are stopped, and the reaction medium is separated from the hydrophobic silica alkogel by percolation. FIG. 1 represents the evolution of the temperature, the absolute pressure and the power density applied by microwave irradiation as a function of time in the mass of the reagents. The overall reaction time (steps a), b) and c)) is therefore about 15 minutes.
[0039] The alcogel is then dried in a ventilated oven at 160 ° C. for 2 hours (step d). The airgel obtained in the form of granules has a bulk density of 85 kg / m3 and a thermal conductivity of 24 mW / mK, measured according to the hot plate method of the standard NF EN 12667 at 20 ° C and atmospheric pressure. .
[0040] EXAMPLE 3 Preparation of a monolithic airgel according to the invention, with heating by microwave irradiation during step c) The silica sol of Example 1 was poured before gelation on a sheet of melamine foam of dimension 50x20x10 mm3 in a closed chamber (step a). The reactor is then heated by the application of a microwave field until a temperature of about 120 ° C (full gel set point temperature) is reached in the bulk of the reagents (step b). The pressure inside the reactor is then 5 bars absolute. The complete gelling set point temperature is 120 ° C. The duration of step b) is 1 hour (tgl).
[0041] Then, hydrochloric acid (up to pH = 1) and hexamethyldisiloxane (hydrophobing agent) are introduced at ambient temperature and pressure into the reactor so as to completely cover the composite alkogel (step c). There is a slight drop in temperature. The reaction medium is heated by the application of a microwave field to reach again a temperature of about 120 ° C (hydrophobization target temperature). The duration of step c) is 1 hour (tg2). Then, the microwaves are stopped, and the reaction medium is separated from the hydrophobic silica alkogel by percolation. The overall reaction time (steps a), b) and c)) is therefore about 2 hours.
[0042] The alcogel is then dried in a ventilated oven at 160 ° C. for 2 hours (step d). The airgel obtained in the form of a monolithic composite airgel has an apparent density of 120 kg / m3 and a thermal conductivity of 13.5 mW / mK, measured according to the hot plate method of NF EN 12667 at 20 ° C. and atmospheric pressure.
[0043] Example 4: Other Examples According to the Invention The protocol used for these tests is as follows. 50 g of silica sol of Example 1 was poured before gelling in a closed chamber (step a). The reactor is then heated by applying a microwave field to a temperature of about 120 ° C in the reagent pool (step b). The pressure inside the reactor is then 5 bars absolute. The complete gelling set point temperature is indicated in the table. The duration of step b) is tgl minutes. Then, hydrochloric acid (up to pH = 1) and hexamethyldisiloxane (hydrophobing agent) are introduced into the reactor so as to completely cover the alcogel. A slight drop in temperature is observed (step c). The reaction medium is heated by applying a microwave field to reach again a set temperature indicated in the table below. The duration of step c) is tg2 minutes.
[0044] In this case, the hydrophobization set point temperature is identical to the complete gelling set point temperature. Then, the microwaves are stopped, and the reaction medium is separated from the hydrophobic silica alkogel by percolation.
[0045] The alcogel is then dried in a ventilated oven at 160 ° C. for 2 hours (step d). The airgel obtained in the form of granules has a bulk density (in kg / m3) presented in the table below. It can be seen in this example that, when the temperature is below 100 ° C., and for short periods (tgl = 6 minutes), the apparent density of the airgel obtained is greater than 150 kg.ml. In this case, the airgel performance obtained will be insufficient, also in terms of thermal insulation and mechanical performance. Comparative Example 5: 2 L of silica sol of Example 1 was poured before gelling in a closed chamber (step a). The reactor is then heated by the application of a microwave field until a temperature of about 120 ° C (full gel set point temperature) is reached in the bulk of the reagents (step b). The pressure inside the reactor is then 5 bars absolute. The complete gelling set point temperature is about 120 ° C. The duration of step b) is 6 minutes (tgl). Then, hydrochloric acid (up to pH = 1) and hexamethyldisiloxane (hydrophobing agent) are introduced into the reactor so as to completely cover 85 180 6 6 100 85 8 8 120 60 8 8 120 50 18 18 120 50 33 33 45 31 31 150 Set temperature (Tb and Tc) (° C) time tgl (min) time tg2 (min) Bulk density (kg / m3) the alcogel. A slight drop in temperature is observed (step c). The reaction medium is heated by the application of a microwave field to reach again a temperature of about 120 ° C (hydrophobization target temperature). The duration of step c) is 9 minutes (tg2). Then, the microwaves are stopped, and the reaction medium is separated from the hydrophobic silica alkogel by percolation. The overall reaction time (steps a), b) and c)) is therefore about 15 minutes, as in Example 1, but with a duration tgl of 6 minutes instead of 7.5 minutes. The alcogel is then dried in a ventilated oven at 160 ° C. for 2 hours (step d). The airgel obtained in the form of granules has a bulk density of 140 kg / m 3 and a thermal conductivity of 32 mW / m 2, measured according to the hot plate method of NF EN 12667 at 20 ° C. and atmospheric pressure. . In this case, the duration tgl, and therefore tl, was insufficient for the airgel to have a thermal conductivity of less than or equal to 25 mW / m.K.
[0046] EXAMPLE 6 Preparation of an Airgel According to the Invention with Convective Heating in Stage c) 2 L of silica sol of Example 1 was poured before gelling in a closed chamber (stage a). The reactor is then heated by the application of a microwave field until a temperature of about 120 ° C (full gel set point temperature) is reached in the bulk of the reagents (step b). The pressure inside the reactor is then 5 bars absolute. The complete gelation set temperature is about 120 ° C, and the duration of step b) is 7.5 minutes (tgl). Then, hydrochloric acid (up to pH = 1) and hexamethyldisiloxane (hydrophobing agent) are introduced into the reactor so as to completely cover the alcogel. There is a slight drop in temperature. The reaction medium is heated by convective heating at 70 ° C. in an oven for 12 hours (step c). The reaction medium is then separated from the hydrophobic silica alkogel by percolation. The alcogel is then dried in a ventilated oven at 160 ° C. for 2 hours (step d). The airgel obtained in the form of granules has a bulk density of 63 kg / m3 and a thermal conductivity of 19.5 mW / mK, measured according to the hot plate method of the standard NF EN 12667 at 20 ° C and atmospheric pressure. .

权利要求:
Claims (16)
[0001]
REVENDICATIONS1. A method of manufacturing aerogels comprising the following successive steps: a) formation or casting of a sol in a reactor, optionally in the presence of a reinforcing material and / or an additive, b) complete gelling of the sol in a lyogel; c) optionally hydrophobizing the lyogel resulting in a hydrophobic lyogel; d) drying the optionally hydrophobed lyogel to obtain an airgel; said method being characterized in that the complete gelation step b) comprises a dielectric heating inducing a rise in temperature to reach a complete gelation reference temperature Tb in a range from 100 ° C to 200 ° C, preferably 100 ° C to 150 ° C, the temperature Tb being maintained in this range for a time ti sufficient to reach the end of the complete gelation, and more particularly the end of the syneresis of the lyogel.
[0002]
2. Method according to claim 1, characterized in that the duration ti is at least 6 minutes.
[0003]
3. Method according to any one of claims 1 and 2, characterized in that the temperature of Tb is between 110 ° C and 130 ° C.
[0004]
4. Method according to any one of claims 1 to 3, characterized in that the temperature Tb is maintained in the target range by dielectric heating, preferably high frequency or microwave.
[0005]
5. Method according to claim 4, characterized in that the total duration tgl of the dielectric heating in step b) is at least 7 minutes. 30
[0006]
6. Method according to any one of claims 1 to 5, characterized in that the step c) of hydrophobization involves heating to achieve a hydrophobization target temperature Te in a range from 60 ° C to 200 ° C, preferably from 70 ° C to 150 ° C, the temperature T being maintained in this range for a time t2 sufficient for the hydrophobization of the lyogel.
[0007]
7. Method according to claim 6, characterized in that the heating of step c) is carried out by dielectric heating, preferably by high-frequency irradiation or microwaves.
[0008]
8. Method according to claim 7, characterized in that the duration t2 is at least 6 minutes.
[0009]
9. Method according to any one of claims 6 to 8, characterized in that the temperature Tc is identical to the temperature Tb-
[0010]
10. Method according to any one of claims 1 to 9, characterized in that the electromagnetic field applied for dielectric heating in step b) and / or c) and / or d) is homogeneous in the lyogel .
[0011]
11. Method according to any one of claims 1 to 10, characterized in that the soil is an inorganic silica sol.
[0012]
12. Method according to any one of claims 1 to 11, characterized in that the lyogel is an alcogel.
[0013]
13. Process according to any one of Claims 1 to 12, characterized in that the hydrophobization reagents are introduced at a pressure comprised between atmospheric pressure and a pressure representing 150% of the pressure inside the reactor in which is carried out step c), and at a temperature between 20 ° C and their boiling point.
[0014]
14. A method according to any one of claims 1 to 13, characterized in that the drying step d) is carried out under subcritical conditions, for example by thermal or dielectric drying.
[0015]
15. Method according to any one of claims 1 to 14, characterized in that the airgel obtained by the process has a thermal conductivity. less than or equal to 25 mW / m.K, advantageously less than or equal to 21 mW / m.K, measured according to the method of the hot plate kept from the standard NF EN 12667 at 20 ° C and at atmospheric pressure.
[0016]
16. Process according to any one of claims 1 to 15, characterized in that the airgel obtained by the process has a bulk density of less than or equal to 150 kg. m-3.

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申请号 | 申请日 | 专利标题

FR1451910A|FR3018207B1|2014-03-07|2014-03-07|METHOD FOR MANUFACTURING AEROGELS BY DIELECTRIC HEATING|FR1451910A| FR3018207B1|2014-03-07|2014-03-07|METHOD FOR MANUFACTURING AEROGELS BY DIELECTRIC HEATING|

PT157082462T| PT3113875T|2014-03-07|2015-03-09|Process for producing aerogels by dielectric heating|

KR1020167027805A| KR102325491B1|2014-03-07|2015-03-09|Process for producing aerogels by dielectric heating|

US15/123,963| US10058836B2|2014-03-07|2015-03-09|Process for producing aerogels by dielectric heating|

CN201580022654.7A| CN106457193B|2014-03-07|2015-03-09|The method for manufacturing aeroge by dielectric heating|

PCT/EP2015/054859| WO2015132418A1|2014-03-07|2015-03-09|Process for producing aerogels by dielectric heating|

JP2016572918A| JP6505752B2|2014-03-07|2015-03-09|Method for producing aerogels by dielectric heating|

EP15708246.2A| EP3113875B1|2014-03-07|2015-03-09|Process of preparing aerogel by electromagnetic heating|

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