Method for producing silica aerogel and silica aerogel blanket

Abstract

The present invention relates to a method for producing silica aerogel using prehydrolyzed polysilicate, in which polysilicate is used as a reactant during synthesis of the prehydrolyzed polysilicate, and the polysilicate is hydrated in the presence of an alcohol-based compound produced by hydration of a compound represented by Chemical Formula 1 without the addition of a separate alcohol-based solvent.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0074292 filed on June 8, 2021, and all contents disclosed in the documents of said Korean patent application are incorporated by reference into this specification.

[0002] The present invention relates to a method for producing a silica aerogel and a silica aerogel blanket by producing a prehydrolyzed polysilicate by a method that does not require a separate reaction solvent during the reaction, and using the prehydrolyzed polysilicate as a precursor. [Background technology]

[0003] Aerogel is a super-porous, high-specific surface area (≧500m2) material with a porosity of 90-99.9% and a pore size in the range of 1-100 nm. 2 Aerogel is a material with excellent properties such as being ultralight, extremely insulating, and extremely low dielectric constant. Needless to say, research into the development of aerogel materials is being conducted, but research into its applications as an environmentally friendly high-temperature insulating material, extremely low dielectric thin film for highly integrated devices, catalysts and catalyst supports, electrodes for supercapacitors, and electrode materials for seawater desalination is also being actively conducted.

[0004] The greatest advantage of aerogel is that it has super-insulation properties, exhibiting a thermal conductivity of less than 0.300 W / m·K, which is lower than conventional organic insulation materials such as Styrofoam®, and that it can solve the fatal weaknesses of organic insulation materials, namely, vulnerability to fire and generation of harmful gases during fire.

[0005] Generally, aerogel is produced by producing a wet gel from silica precursors such as water glass and alkoxysilanes (TEOS, TMOS, MTMS, etc.), and then removing the liquid components inside the wet gel without destroying the microstructure. Representative silica aerogel forms are divided into three types: powder, granules, and monoliths, and are generally produced in powder form.

[0006] In particular, among the silica precursors, tetraethyl orthosilicate (TEOS) is a material that is widely used in industrial fields such as coating agents, insulating agents, and the manufacture of porous ceramics, and various products such as pure TEOS, condensed TEOS, and pre-hydrolyzed TEOS (HTEOS) are available on the market.

[0007] Among them, HTEOS is an ethyl polysilicate oligomer material with a wide molecular weight distribution. When synthesizing TEOS monomer into oligomer form, physical properties such as gelation time can be adjusted, so it can be easily applied according to the user's reaction conditions. In addition, it has the advantage of creating reproducible physical properties of the final result.

[0008] The HTEOS is generally synthesized by performing partial hydration and condensation reactions on an alkoxysilane monomer compound such as TEOS under acidic conditions. Here, the condensation reaction is performed by refluxing under acidic conditions, and the condensation rate is very slow, so the condensation reaction needs to be performed for a long period of time to achieve the desired level of condensation, which results in high energy costs, reduced process efficiency, and high raw material costs for alkoxysilane monomer compounds such as TEOS used as reactants, resulting in increased manufacturing costs. Meanwhile, a condensation catalyst can be used to increase the condensation rate, but in this case, it is difficult to control the molecular weight of the reaction product, catalyst purchase costs are incurred, and a catalyst separation process needs to be added to the synthesis step, making the process more complicated and increasing manufacturing costs.

[0009] Therefore, a method for synthesizing prehydrolyzed polysilicate has been proposed, which uses polysilicate as a reactant instead of an alkoxysilane monomer compound such as TEOS, and thus can omit a condensation reaction compared to the conventional manufacturing method using TEOS, simplifying the process and significantly reducing manufacturing costs.

[0010] In the method using polysilicate as the reactant, a method is used in which polysilicate is reacted with an acidic aqueous solution using ethanol as a solvent. The use of an amphipathic solvent such as ethanol is necessarily required because layer separation occurs when an acidic aqueous solution is added to polysilicate. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent Publication No. 2014-501320 (Published on January 20, 2014) [Patent Document 2] Korean Patent Publication No. 2020-0062506 (2020.06.04) Summary of the Invention [Problem to be solved by the invention]

[0012] The problem to be solved by the present invention is to provide a method for producing a silica aerogel by using a polysilicate as a reactant for synthesizing a prehydrolyzed polysilicate in a manner that does not require a separate reaction solvent during the reaction.

[0013] Another object of the present invention is to provide a method for producing a prehydrolyzed polysilicate without requiring a separate reaction solvent during the reaction, and to provide a method for producing a silica aerogel blanket using the prehydrolyzed polysilicate. [Means for solving the problem]

[0014] In order to solve the above problems, the present invention provides a method for producing silica aerogel. (1) The present invention provides a method for producing a silica aerogel, the method including the steps of: charging a polysilicate and a compound represented by the following chemical formula 1 into a reactor (step 1); further charging an acidic aqueous solution into the reactor to produce a reaction mixture (step 2); stirring the reaction mixture to carry out a hydration reaction to produce a prehydrolyzed polysilicate (step 3); adding a catalyst solution to the prehydrolyzed polysilicate and mixing to prepare a silica sol (step 4); and gelling the silica sol to form a silica wet gel (step 5).

[0015] [ka]

[0016] R1 is alkyl having 1 to 20 carbon atoms, cycloalkyl having 3 to 20 carbon atoms, or vinyl having 1 to 20 carbon atoms, and each R2 is independently alkyl having 1 to 20 carbon atoms.

[0017] (2) The present invention provides the method for producing a silica aerogel according to (1) above, further comprising, after step 5, a step (step 6) of aging the silica wet gel.

[0018] (3) The present invention provides a method for producing a silica aerogel according to (1) or (2) above, further comprising a step (step 7) of drying the silica wet gel.

[0019] (4) The present invention provides the method for producing silica aerogel according to (3), wherein the drying step is performed by supercritical drying, and the method further includes a step of reusing the waste liquid after the supercritical drying in the production of the catalyst solution in step 4 without a separate purification process.

[0020] (5) The present invention provides the method for producing a silica aerogel according to any one of the above (1) to (4), wherein the catalyst solution contains water, an alcohol compound, a basic catalyst, and an organosilane compound.

[0021] (6) The present invention provides a method for producing a silica aerogel in any one of the above (1) to (5), wherein the compound represented by the chemical formula 1 is hydrated to form an alcohol compound represented by the following chemical formula 2 and a silanol compound represented by the following chemical formula 3:

[0022] [ka]

[0023] R1 is alkyl having 1 to 20 carbon atoms, cycloalkyl having 3 to 20 carbon atoms, or vinyl having 1 to 20 carbon atoms, and R2 is alkyl having 1 to 20 carbon atoms.

[0024] (7) The present invention provides a method for producing a silica aerogel according to any one of the above (1) to (6), wherein the hydration of the polysilicate in step 3 is carried out in the presence of an alcohol compound represented by chemical formula 2 formed by hydrating a compound represented by chemical formula 1.

[0025] [ka]

[0026] R2 is an alkyl group having 1 to 20 carbon atoms.

[0027] (8) The present invention provides a method for producing a silica aerogel according to any one of the above (1) to (7), wherein the polysilicate and the compound represented by Chemical Formula 1 have a molar ratio of 5:1 to 15:1.

[0028] (9) The present invention provides the method for producing a silica aerogel according to any one of the above items (1) to (8), wherein the acidic aqueous solution contains 0.005 to 0.20 parts by weight of an acid catalyst relative to 100 parts by weight of the polysilicate.

[0029] (10) The present invention provides a method for producing a silica aerogel according to any one of the above (1) to (9), in which the method for producing a prehydrolyzed polysilicate does not require any other alcohol-based solvent to be added to a reactor other than the polysilicate and the compound represented by Chemical Formula 1.

[0030] (11) The present invention provides a method for producing a silica aerogel according to any one of the above (1) to (10), wherein the polysilicate includes one or more selected from the group consisting of methyl polysilicate, ethyl polysilicate, propyl polysilicate, isopropyl polysilicate, butyl polysilicate, secondary butyl polysilicate, tertiary butyl polysilicate, hexyl polysilicate, cyclohexyl polysilicate, and dodecyl polysilicate.

[0031] (12) The present invention provides a method for producing a silica aerogel according to any one of the above (1) to (11), wherein the compound represented by Chemical Formula 1 includes one or more compounds selected from the group consisting of alkyltriethoxysilanes and alkyltrimethoxysilanes.

[0032] (13) The present invention provides the method for producing a silica aerogel according to any one of the above (1) to (12), wherein the compound represented by Chemical Formula 1 is methyltriethoxysilane.

[0033] (14) The present invention provides the method for producing a silica aerogel according to any one of (1) to (13), wherein the compound represented by chemical formula 1 is alkyltriethoxysilane, the alkyltriethoxysilane is hydrated to form alkylsilanol and ethanol, and the hydration of the polysilicate in step 3 is performed in the presence of the ethanol formed by hydration of the alkyltriethoxysilane.

[0034] In order to solve the above-mentioned other problems, the present invention provides a method for producing a silica aerogel blanket.

[0035] (15) The present invention provides a method for producing a silica aerogel blanket, the method including the steps of: charging a polysilicate and a compound represented by the following chemical formula 1 into a reactor (Step 1); further charging an acidic aqueous solution into the reactor to produce a reaction mixture (Step 2); stirring the reaction mixture to carry out a hydration reaction to produce a prehydrolyzed polysilicate (Step 3); adding a catalyst solution to the prehydrolyzed polysilicate and mixing to prepare a silica sol (Step 4); and impregnating a blanket substrate with the silica sol, followed by gelation to form a silica wet gel blanket (Step 5).

[0036] [ka]

[0037] R1 is alkyl having 1 to 20 carbon atoms, cycloalkyl having 3 to 20 carbon atoms, or vinyl having 1 to 20 carbon atoms, and each R2 is independently alkyl having 1 to 20 carbon atoms. Effect of the Invention

[0038] The method for producing silica aerogel and the method for producing silica aerogel blanket according to the present invention use polysilicate as a reactant for synthesizing prehydrolyzed polysilicate, and therefore, unlike a method using an alkoxysilane monomer compound as a reactant, it is possible to omit a condensation reaction and significantly shorten the synthesis time. Furthermore, since no separate reaction solvent is required during the hydration reaction of polysilicate, even when the supercritical drying waste liquid generated during the production of silica aerogel and silica aerogel blanket is reused, it can be reused without a purification process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] The present invention will be described in more detail below to aid in understanding the present invention. In this regard, the terms and words used in the specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical ideas of the present invention, in accordance with the principle that the inventors can appropriately define the concepts of terms in order to best describe their inventions.

[0040] A method for preparing silica aerogel according to an embodiment of the present invention includes the steps of: adding polysilicate and a compound represented by the following formula 1 to a reactor (step 1); further adding an acidic aqueous solution to the reactor to prepare a reaction mixture (step 2); stirring the reaction mixture to carry out a hydration reaction to prepare a prehydrolyzed polysilicate (step 3); adding a catalyst solution to the prehydrolyzed polysilicate and mixing to prepare a silica sol (step 4); and gelling the silica sol to form a silica wet gel (step 5).

[0041] [ka]

[0042] R1 is alkyl having 1 to 20 carbon atoms, cycloalkyl having 3 to 20 carbon atoms, or vinyl having 1 to 20 carbon atoms, and each R2 is independently alkyl having 1 to 20 carbon atoms.

[0043] In general, when a monomer compound such as prehydrolyzed TEOS is used as a silica precursor for manufacturing silica aerogel or silica aerogel blanket, it is difficult to control the molecular weight or gelation reaction time of the final product, and the stability is reduced, so a prehydrolyzed polysilicate oligomer with a molecular weight of about 1000 is manufactured and used. This is because, unlike a monomer such as TEOS, when an oligomer-type substance is used, stability can be ensured even when the degree of hydration is increased to control the gelation reaction time. However, in the conventional process for synthesizing the prehydrolyzed polysilicate, an alkoxysilane monomer compound such as a TEOS monomer is used as a reactant, so a condensation reaction must be performed after partial hydration. Here, the condensation reaction is performed by reflux reaction under acidic conditions, and the condensation rate is very slow, so the condensation reaction must be performed for a long period of time to achieve the desired level of condensation, which results in high energy costs and reduced process efficiency, and the raw material cost of the alkoxysilane monomer compound such as TEOS used as a reactant is high, which increases the manufacturing cost. On the other hand, a condensation catalyst can be used to increase the condensation rate, but in this case, it is difficult to control the molecular weight of the reaction product, the catalyst purchase cost is incurred, and a catalyst separation step needs to be added to the synthesis step, which makes the process more complicated and increases the production cost.

[0044] However, in the method for producing silica aerogel of the present invention, in the process for producing prehydrolyzed polysilicate, an alkoxysilane monomer compound such as TEOS is not used as a reactant, and only a step of partial hydration is included by using polysilicate, and a condensation reaction is omitted, thereby improving the efficiency of the synthesis process, and the raw material cost is relatively low, so that an economic effect can be obtained in terms of production cost. Furthermore, a prehydrolyzed polysilicate with excellent storage stability can be synthesized using a method in which the gelation reaction time and weight average molecular weight can be easily controlled by adjusting the content and pH of the acid catalyst. In addition, since the method for producing silica aerogel of the present invention does not require a separate reaction solvent during the hydration reaction of the prehydrolyzed polysilicate, it can be usefully used when the reaction needs to be carried out under conditions where the use of a solvent is not desired or when a high concentration prehydrolyzed polysilicate is to be obtained. Since a separate alcohol solvent is not required in the process for producing the hydrated polysilicate, which is a silica precursor, the supercritical waste liquid generated in the supercritical drying step in the process for producing silica aerogel or silica aerogel blanket can be reused in the process for producing a catalyst solution without a separate purification process, and can be easily reused in the process for producing a silica sol.

[0045] Hereinafter, each step of the method for producing silica aerogel according to an embodiment of the present invention will be described in detail.

[0046] Step 1) Step 1) of the present invention is a step of feeding reactants, ie, polysilicate and the compound represented by Chemical Formula 1, into a reactor.

[0047] [ka]

[0048] R1 is alkyl having 1 to 20 carbon atoms, cycloalkyl having 3 to 20 carbon atoms, or vinyl having 1 to 20 carbon atoms, and each R2 is independently alkyl having 1 to 20 carbon atoms.

[0049] In one example of the present invention, specifically, R1 can be alkyl having 1 to 12 carbon atoms, cycloalkyl having 3 to 12 carbon atoms, or vinyl having 1 to 12 carbon atoms, more specifically, alkyl having 1 to 6 carbon atoms, or alkyl having 1 to 4 carbon atoms, and specifically, R2 can each independently be alkyl having 1 to 12 carbon atoms, more specifically, alkyl having 1 to 6 carbon atoms, or alkyl having 1 to 5 carbon atoms.

[0050] In one example of the present invention, the R1 can be alkyl having 1 to 4 carbon atoms, and the R2 can be ethyl.

[0051] By using polysilicate as a reactant, the present invention can omit the condensation reaction in the prehydrolyzed polysilicate synthesis process, and can show a better silica production yield per unit content than when an alkoxysilane-based monomer compound is used as a reactant.

[0052] The polysilicate according to an embodiment of the present invention may have a silica (SiO2) production yield of 30% by weight or more, specifically, 30 to 45% by weight. Here, the silica (SiO2) production yield is a value that indicates the content of silica that can be produced from 100% by weight of polysilicate as a ratio, and a material with a higher silica production yield indicates that a larger amount of silica can be produced with the same content. If the silica production yield is high, a relatively small amount of raw material can be used to obtain a silica precursor having a desired level of silica content, which has the effect of reducing raw material costs.

[0053] The polysilicate usable in the present invention is not limited as long as it is a polysilicate that can form a prehydrolyzed polysilicate that can be used as a silica precursor of silica aerogel or aerogel blanket by partial hydration reaction, and specifically, an alkyl polysilicate can be used, and more specifically, it can include one or more selected from the group consisting of methyl polysilicate, ethyl polysilicate, propyl polysilicate, isopropyl polysilicate, butyl polysilicate, secondary butyl polysilicate, tertiary butyl polysilicate, hexyl polysilicate, cyclohexyl polysilicate, and dodecyl polysilicate.

[0054] According to an embodiment of the present invention, the polysilicate may have an average degree of polymerization of 3 to 30, specifically 5 to 15, more specifically 5 to 12, and specifically, the polysilicate may be an oligomer having the above-mentioned degree of polymerization. When the polysilicate satisfies the above-mentioned average degree of polymerization, storage stability and fluidity are ensured, and ease of use is excellent. Here, the average degree of polymerization was measured using GPC (Gel Permeation Chromatography, Waters 2489 UV-vis Detector).

[0055] The compound represented by Chemical Formula 1 can be hydrated by the water of the acidic aqueous solution introduced into the reactor in step 2) to form an alcohol compound represented by Chemical Formula 2 and a silanol compound represented by Chemical Formula 3 below, and the alcohol compound represented by Chemical Formula 2 acts as an amphipathic solvent used for hydrating the polysilicate in the following step 3.

[0056] [ka]

[0057] R1 is an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or a vinyl group having 1 to 6 carbon atoms, and R2 is an alkyl group having 1 to 6 carbon atoms. Specific examples of R1 and R2 are as defined in Chemical Formula 1.

[0058] According to one embodiment of the present invention, in step 1), the amount of the compound represented by Chemical Formula 1 can be varied, and the amount of the compound represented by Chemical Formula 1 can be determined according to the amount of alcohol solvent required for the reaction and the content of silica (SiO2) contained in the final prehydrolyzed polysilicate.

[0059] The polysilicate and the compound represented by Chemical Formula 1 may have a Si molar ratio of 5:1 to 15:1, and may be used at a molar ratio of 6:1 to 15:1, taking into consideration the concentration of the hydrated polysilicate obtained as the final product and the content of silica (SiO2) contained in the prehydrolyzed polysilicate finally produced. In addition, the polysilicate and the compound represented by Chemical Formula 1 may specifically have a Si molar ratio of 7:1 to 14:1, 8:1 to 13:1, and more specifically, may have a Si molar ratio of 8:1 to 12:1. The Si molar ratio refers to the ratio of the number of moles of Si contained in the polysilicate to the number of moles of Si contained in the compound represented by Chemical Formula 1. When the Si content of the compound represented by Formula 1 relative to the Si content of the polysilicate is too low, the amount of alcohol formed by hydration of the compound represented by Formula 1 is small, and the amount of alcohol may be insufficient for the polysilicate to be properly hydrated, and when the Si content of the compound represented by Formula 1 relative to the Si content of the polysilicate is too high, the amount of alcohol formed by hydration of the compound represented by Formula 1 is too high, and the concentration of the hydrated polysilicate obtained as the final product may be low. In addition, when the polysilicate and the compound represented by Formula 1 satisfy the above-mentioned Si molar ratio range, the degree of hydration of the prehydrolyzed polysilicate to be synthesized may have an appropriate range.

[0060] The alcohol compound of Chemical Formula 1 produced above is not limited to a specific type as long as it is an alcohol known to be usable in producing a prehydrolyzed polysilicate, and specifically, it may be an alcohol having 1 to 20 carbon atoms, more specifically, an alcohol having 1 to 12 carbon atoms, an alcohol having 1 to 6 carbon atoms, or an alcohol having 1 to 5 carbon atoms.

[0061] Step 2) Step 2) according to one embodiment of the present invention is a step of preparing a reaction mixture for partial hydration by further adding an acidic aqueous solution to a reactor containing the reactants and stirring the mixture to prepare a reaction mixture.

[0062] In addition, the reaction mixture produced in step 2) may contain 2 parts by weight to 42 parts by weight, specifically, 3 parts by weight to 30 parts by weight, and more specifically, 3 parts by weight to 20 parts by weight of water per 100 parts by weight of polysilicate.

[0063] Here, the acidic aqueous solution is a mixture containing an acid catalyst and water. The water contained in the acidic aqueous solution first hydrates the compound represented by Chemical Formula 1 added in step 1 to form an alcohol compound represented by Chemical Formula 2 and a silanol compound represented by Chemical Formula 3 as described above, and the formed alcohol compound represented by Chemical Formula 2 serves as an amphipathic solvent to further hydrate the polysilicate.

[0064] The amount of water and acid catalyst contained in the acidic aqueous solution and the pH of the acidic aqueous solution can be adjusted to control the degree of hydration of the polysilicate, and the gelation time and pH of the final prehydrolyzed polysilicate can be adjusted by controlling the degree of hydration of the polysilicate.

[0065] The acidic aqueous solution may contain 0.005 to 0.20 parts by weight of an acid catalyst relative to 100 parts by weight of the polysilicate reactant, specifically, 0.008 to 0.10 parts by weight, more specifically, 0.010 to 0.090 parts by weight.

[0066] In the present invention, the content of the acid catalyst contained in the acidic aqueous solution is the same as the content of the acid catalyst in the entire reaction mixture. By satisfying the above-mentioned acid catalyst content, the hydration rate during the hydration reaction described below can be improved, and the efficiency of the hydration reaction can be further improved. As a result, the gelling reactivity of the synthesized prehydrolyzed polysilicate can be improved, and the polycondensation reaction of the prehydrolyzed polysilicate itself can be suppressed, thereby ensuring excellent storage stability and preventing the problem of corrosiveness caused by an excessive amount of acid catalyst.

[0067] The acid catalyst according to one embodiment of the present invention is not particularly limited, but may be, for example, one or more selected from the group consisting of hydrochloric acid, nitric acid, acetic acid, sulfuric acid, and hydrofluoric acid, and is preferably hydrochloric acid.

[0068] In addition, the acidic aqueous solution according to one embodiment of the present invention may be an acidic aqueous solution having a pH of 0.5 to 2.5, and in terms of synthesizing a prehydrolyzed polysilicate having an optimal hydration degree and gelation reactivity, the pH of the acidic aqueous solution may be 1.0 to 2.5. When the pH range is satisfied, a prehydrolyzed polysilicate having an optimal pH and gelation time can be produced.

[0069] In addition, the reaction mixture prepared in step 2) may contain 2 to 42 parts by weight, specifically 3 to 30 parts by weight, and more specifically 3 to 20 parts by weight of water, relative to 100 parts by weight of the polysilicate. If the water is contained in an amount less than 3 parts by weight, the water is contained in an excessively small amount compared to the amount of the polysilicate, and the desired degree of hydration cannot be achieved during the hydration reaction. When a prehydrolyzed polysilicate with a low degree of hydration is used as a silica precursor in the process of preparing an aerogel, the ratio of hydroxyl groups (-OH) that induce gelation may be low, and the gelation reaction may not proceed smoothly. In addition, if the water is too much, the degree of hydration of the final prehydrolyzed polysilicate becomes excessively high, and most of the alkoxy functional groups of the silica precursor are replaced with hydroxyl groups, which may cause a gelation reaction during storage and preservation, and the viscosity may easily increase, resulting in a decrease in storage stability and processability.

[0070] In step 2), the degree of hydration can be controlled by adjusting the contents of water and acid catalyst in the reaction mixture and the pH of the acidic aqueous solution, and thus, an undesired gelation reaction can be prevented during storage and keeping, thereby ensuring excellent storage stability. The gelation time of the prehydrolyzed polysilicate can also be adjusted according to the above variables, and when a gelation reaction is induced, a desired gelation time can be achieved.

[0071] Step 3) Step 3) according to one embodiment of the present invention is to stir the prepared reaction mixture to carry out the hydration reaction, forming a prehydrolyzed polysilicate in a partially hydrated state.

[0072] Specifically, in step 3) of the present invention, the hydration reaction can be carried out by stirring the reaction mixture. As described above, the hydration of the polysilicate in step 3) is carried out in the presence of the alcohol compound represented by Chemical Formula 2 formed by hydrating the compound represented by Chemical Formula 1. Therefore, in step 3) according to one example of the present invention, hydration with the compound represented by Chemical Formula 1 is first carried out in the presence of the acid catalyst of the acid aqueous solution.

[0073] [ka]

[0074] When only the acidic aqueous solution is added to the polysilicate, phase separation occurs between the polysilicate and the acidic aqueous solution, and there is no reactivity between them. In order to cause a reaction between the polysilicate and the acidic aqueous solution, the presence of an amphipathic solvent such as an alcohol is essential. The amphipathic solvent such as an alcohol remains in the final product, so that the final product, the prehydrolyzed polysilicate, is obtained in a form diluted in the amphipathic solvent.

[0075] In step 3) according to an embodiment of the present invention, the reaction mixture is stirred to first hydrate the compound represented by Chemical Formula 1, thereby forming an alcohol compound represented by Chemical Formula 2, and the alcohol compound represented by Chemical Formula 2 acts as an amphipathic solvent between the polysilicate and the acid aqueous solution to hydrate the polysilicate. In addition, for example, as shown in the following reaction formula 2, the hydration of the polysilicate can be more easily carried out by the alcohol generated by the hydration of the polysilicate. Therefore, the present invention does not require the introduction of another amphipathic solvent, for example, an alcohol-based solvent, for the hydration of the polysilicate, other than the compound represented by Chemical Formula 1. Therefore, the present invention does not require a separate alcohol-based solvent for the hydration of the polysilicate, and thus a high-concentration prehydrolyzed polysilicate can be obtained as a final product.

[0076] [ka]

[0077] In one example of the present invention, the compound represented by Chemical Formula 1 may include, for example, one or more selected from the group consisting of alkyltriethoxysilane and alkyltrimethoxysilane, specifically, alkyltriethoxysilane, and more specifically, the compound represented by Chemical Formula 1 may be methyltriethoxysilane.

[0078] In one embodiment of the present invention, when the compound represented by Chemical Formula 1 is alkyltriethoxysilane, the alkyltriethoxysilane is hydrated by the aqueous acid solution added in step 2 to form alkylsilanol and ethanol, and the hydration of the polysilicate in step 3 can be performed in the presence of the ethanol formed by hydration of the alkyltriethoxysilane.

[0079] In the step 3) according to one embodiment of the present invention, partial hydration can be performed by stirring for 30 minutes to 2 hours at room temperature, specifically, at 15 to 25° C. In the present invention, a prehydrolyzed polysilicate can be synthesized only by carrying out the hydration reaction in step 3) by using polysilicate as a reactant, and since it is not necessary to carry out a condensation reaction that is always involved in synthesizing a prehydrolyzed polysilicate using an alkoxysilane monomer compound as a reactant, the synthesis process is simple and the energy cost is relatively low.

[0080] The prehydrolyzed polysilicate thus prepared can exhibit excellent viscosity characteristics, storage stability and processability. In addition, the prehydrolyzed polysilicate can be specifically a prehydrolyzed alkyl polysilicate, and more preferably, can be a prehydrolyzed ethyl polysilicate (HTEOS), which has the highest usability as a silica precursor when preparing a silica aerogel or a silica aerogel blanket.

[0081] In the present invention, the prehydrolyzed polysilicate may refer to a polysilicate that has been partially hydrated, specifically, a polysilicate in which some of the alkoxy functional groups of the polysilicate have been replaced with hydroxyl groups.

[0082] Step 4) Step 4 according to one embodiment of the present invention is to add a catalyst solution to the prehydrolyzed polysilicate and mix to prepare a silica sol.

[0083] The catalyst solution may include water, an alcohol compound, a basic catalyst, and an organosilane compound.

[0084] In one embodiment of the present invention, the alcohol compound is not limited to a specific type as long as it is an alcohol known to be usable in the production of an aerogel, and specifically, it may be an alcohol having 1 to 20 carbon atoms, more specifically, an alcohol having 1 to 12 carbon atoms, an alcohol having 1 to 6 carbon atoms, or an alcohol having 1 to 5 carbon atoms.

[0085] In one embodiment of the present invention, the basic catalyst serves to increase the pH of the silica sol to promote gelation.

[0086] The basic catalyst usable in the silica sol according to one embodiment of the present invention can be an inorganic base such as sodium hydroxide or potassium hydroxide; or an organic base such as ammonium hydroxide. Specifically, sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2), ammonia (NH3), ammonium hydroxide (NH4OH), tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH), methylamine, ethylamine, isopropylamine, monoisopropylamine, diethylamine, diisopropylamine, dibutylamine, trimethylamine, triethylamine, triisopropyl ... The amine may be one or more selected from the group consisting of butylamine, choline, monoethanolamine, diethanolamine, 2-aminoethanol, 2-(ethylamino)ethanol, 2-(methylamino)ethanol, N-methyldiethanolamine, dimethylaminoethanol, diethylaminoethanol, nitrilotriethanol, 2-(2-aminoethoxy)ethanol, 1-amino-2-propanol, triethanolamine, monopropanolamine, dibutanolamine and pyridine, and preferably sodium hydroxide, ammonia, ammonium hydroxide or a mixture thereof.

[0087] The basic catalyst may be included in an amount that allows the pH of the silica sol to be 4 to 8. When the base is added within the above range, the silica sol can have an optimal gelation rate. In addition, since the base may precipitate when added in a solid phase, it is preferable to add the base in a solution phase diluted with the above-mentioned alcohol (polar organic solvent). Here, the dilution ratio of the base catalyst and the alcohol may be 1:4 to 1:100 on a volume basis.

[0088] The organosilane compound may be included as a surface modifier for hydrophobizing the aerogel and the aerogel blanket. Although the dried silica aerogel maintains a low thermal conductivity immediately after drying, the hydrophilic silanol group (Si-OH) present on the silica surface absorbs water in the air, which causes the thermal conductivity to gradually increase. Therefore, in order to maintain a low thermal conductivity, it is necessary to modify the surface of the silica aerogel to be hydrophobic. Therefore, in the method for producing a silica aerogel according to one embodiment of the present invention, the surface of the silica aerogel can be hydrophobized by the organosilane compound.

[0089] The organic silane compound may be one selected from the group consisting of trimethylchlorosilane (TMCS), hexamethyldisilazane (HMDS), methyltrimethoxysilane, trimethylethoxysilane, ethyltriethoxysilane, and phenyltriethoxysilane, and may be specifically trimethylethoxysilane.

[0090] The amount of the organosilane compound can be 20 to 60 parts by weight, specifically 30 to 55 parts by weight, and more specifically 40 to 50 parts by weight, relative to 100 parts by weight of the prehydrolyzed polysilicate. If the organosilane compound is too small compared to the prehydrolyzed polysilicate, the reaction time may be excessively long and the surface modification efficiency may be poor, and if the organosilane compound is too large compared to the prehydrolyzed polysilicate, there is a problem of increased costs.

[0091] Step 5) Step 5 according to one embodiment of the present invention is gelling the silica sol to form a silica wet gel.

[0092] The gelation carried out in step 5) of the present invention may be the formation of a network structure from a silica precursor material, and the network structure refers to a planar network structure in which certain polygons having one or more types of atomic arrangements are connected, or a structure in which vertices, corners, faces, etc. of certain polyhedra are shared to form a three-dimensional framework structure.

[0093] The gelation according to one embodiment of the present invention may be carried out under conditions of pH 3-10, preferably pH 4-8 in terms of ensuring an optimal gelation rate.

[0094] The present invention also provides a method for producing a silica aerogel blanket, the method including the steps of: (1) introducing polysilicate and a compound represented by the following formula 1 into a reactor; (2) introducing an acidic aqueous solution into the reactor to produce a reaction mixture; (3) stirring the reaction mixture to carry out a hydration reaction to produce a prehydrolyzed polysilicate; (4) adding a catalyst solution to the prehydrolyzed polysilicate and mixing to prepare a silica sol; and (5) impregnating a blanket substrate with the silica sol, followed by gelation to form a silica wet gel blanket.

[0095] [ka]

[0096] R1 is alkyl having 1 to 20 carbon atoms, cycloalkyl having 3 to 20 carbon atoms, or vinyl having 1 to 20 carbon atoms, and each R2 is independently alkyl having 1 to 20 carbon atoms.

[0097] The blanket substrate according to the embodiment of the present invention may be a porous substrate in order to improve the thermal insulation of the silica aerogel blanket. When a porous blanket substrate is used, the silica sol can easily penetrate into the substrate and aerogel can be uniformly formed inside the blanket substrate, so that the manufactured silica aerogel blanket can have excellent thermal insulation.

[0098] The blanket substrate usable in accordance with one embodiment of the present invention may be a film, sheet, net, fiber, foam, nonwoven fabric, or a laminate of two or more layers thereof. In addition, the surface of the blanket substrate may be roughened or patterned depending on the application. More specifically, the blanket substrate may be a fiber that includes spaces or voids in the blanket substrate that allow easy insertion of silica aerogel, thereby further improving the insulation performance. In addition, the blanket substrate preferably has low thermal conductivity.

[0099] Specifically, the blanket substrate may be polyamide, polybenzimidazole, polyaramid, acrylic resin, phenolic resin, polyester, polyetheretherketone (PEEK), polyolefin (e.g., polyethylene, polypropylene, or copolymers thereof), cellulose, carbon, cotton, wool, hemp, nonwoven fabric, glass fiber, ceramic wool, or the like. More specifically, in the present invention, the blanket substrate may be glass felt.

[0100] In addition, in the steps of the present invention, the silica sol is impregnated into the blanket substrate, for example, in a reaction vessel capable of accommodating the blanket substrate, and the silica sol can be poured into the reaction vessel in which the blanket substrate is accommodated, or the blanket substrate can be placed in a reaction vessel containing the silica sol to wet the substrate. Here, in order to improve the bonding between the blanket substrate and the silica sol, the blanket substrate can be lightly pressed to be sufficiently impregnated. In addition, the blanket substrate can be subsequently pressed to a predetermined thickness with a certain pressure to remove the remaining silica sol, thereby shortening the subsequent drying time.

[0101] In the manufacturing process of the silica aerogel blanket, the steps 1 to 4 are the same as the steps 1 to 4 of the silica aerogel described above, and the step of gelling the silica sol can be performed under the same conditions and in the same manner as the gelling of the silica aerogel in step 5 described above.

[0102] In addition, the method for producing silica aerogel and / or silica aerogel blanket according to an embodiment of the present invention may further include, after step 5, a step of aging the silica wet gel (step 6), a step of drying the silica wet gel (step 7), or both of steps 6 and 7.

[0103] The aging step is a process for leaving the silica wet gel or silica wet gel blanket at an appropriate temperature to complete chemical changes. An aging step can be further performed, which can make the formed network structure stronger and enhance the mechanical stability of the silica aerogel or silica aerogel blanket of the present invention.

[0104] In the aging step of the present invention, a solution of a basic catalyst such as sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide (NH4OH), triethylamine, pyridine, etc., diluted in an organic solvent at a concentration of 1 to 10% is added to maximize Si-O-Si bonding in the aerogel, strengthening the silica gel network structure and making it easier to maintain the pore structure in the subsequent rapid drying process. Here, the organic solvent can be the above-mentioned alcohol (polar organic solvent), and specifically can include ethanol.

[0105] In addition, the aging step must be performed within an appropriate temperature range to optimally strengthen the pore structure, and the aging step of the present invention can be performed by leaving the material for 1 to 10 hours at a temperature of 30 to 70° C. If the aging temperature is less than 30° C., the aging time becomes too long, which increases the overall process time and may result in a decrease in productivity, whereas if the aging temperature is more than 70° C., the temperature deviates from the boiling point of ethanol, which may result in a large loss of solvent due to evaporation, and an increase in raw material costs.

[0106] The step of drying the silica wet gel in step 7 can be performed by removing the solvent while maintaining the pore structure of the aged silica gel, and the drying step can be performed by a supercritical drying process or a normal pressure drying process.

[0107] The supercritical drying process can be performed using supercritical carbon dioxide. Carbon dioxide (CO2) is in a gaseous state at room temperature and pressure, but when it exceeds a certain temperature and pressure limit called a supercritical point, it enters a critical state where it is indistinguishable between gas and liquid without undergoing an evaporation process. Carbon dioxide in this critical state is called supercritical carbon dioxide.

[0108] Supercritical carbon dioxide has molecular density close to that of a liquid, but low viscosity and similar properties to that of a gas. It has fast diffusion and high thermal conductivity, which increases drying efficiency and shortens the drying process time.

[0109] Specifically, the supercritical drying process is a solvent replacement process in which the aged silica gel is placed in a supercritical drying reactor, and then liquid CO2 is filled in to replace the alcohol solvent inside the silica aerogel with CO2. Thereafter, the temperature is raised to 40-50°C at a predetermined heating rate, specifically at a rate of 0.1°C / min to 1°C / min, and then a pressure equal to or higher than the pressure at which carbon dioxide becomes supercritical, specifically at a pressure of 100 bar to 150 bar, is maintained, and the carbon dioxide supercritical state is maintained for a predetermined time, specifically, 20 minutes to 1 hour. Generally, carbon dioxide becomes supercritical at a temperature of 31°C and a pressure of 73.8 bar. After maintaining the predetermined temperature and pressure at which carbon dioxide becomes supercritical for 2 hours to 12 hours, more specifically 2 hours to 6 hours, the pressure is gradually removed to complete the supercritical drying process and produce an aerogel blanket.

[0110] In the case of the normal pressure drying step, the step can be carried out by a conventional method such as natural drying at a temperature of 70 to 200° C. and normal pressure (1±0.3 atm).

[0111] As a result of the drying process, a porous silica aerogel having nano-sized pores and / or a blanket containing the porous silica aerogel can be produced. The silica aerogel has excellent physical properties, particularly low tap density and high porosity, along with a high degree of hydrophobicity, and the silica aerogel-containing blanket containing the same has excellent mechanical flexibility along with low thermal conductivity.

[0112] In addition, before or after the drying process, a pressing process for adjusting the thickness and making the internal structure and surface shape of the blanket uniform, a molding process for providing an appropriate shape or morphology depending on the application, or a lamination process for laminating another functional layer may be further performed.

[0113] Meanwhile, the method according to an embodiment of the present invention may further include a washing step before the drying step. The washing step is for removing impurities (sodium ions, unreacted materials, by-products, etc.) generated during the reaction and residual ammonia that may react with CO2 to generate ammonium carbonate during supercritical drying, thereby obtaining a high-purity hydrophobic silica aerogel, and may be performed by a dilution process or an exchange process using a non-polar organic solvent.

[0114] In addition, the method for producing a silica aerogel or a silica aerogel blanket according to an embodiment of the present invention may further include a step of reusing a supercritical waste liquid generated after the supercritical drying.

[0115] When the drying step is performed by supercritical drying, the supercritical waste liquid after the supercritical drying may contain water, alcohol compounds, and organosilane compounds contained in the catalyst solution. A part of the organosilane compound contained in the catalyst solution added in step 4 is used to hydrophobize the silica aerogel, and the remaining amount remains in the aging solution and the supercritical waste liquid. The supercritical waste liquid containing the organosilane compound has been reused as a solvent for producing a silica precursor and a solvent for producing a silica sol. However, when the supercritical waste liquid is used as a solvent for producing a silica precursor, the physical properties of the silica aerogel produced by the organosilane compound are deteriorated and the gelation time is changed, so a purification process is required to reuse the supercritical waste liquid.

[0116] However, since the method for producing silica aerogel and the method for producing silica aerogel blanket of the present invention do not require an amphipathic solvent such as alcohol in the process for producing the prehydrolyzed polysilicate, a separate purification process is not required for the supercritical waste liquid to be used in the process for producing the prehydrolyzed polysilicate, and the supercritical waste liquid can be reused in the process for producing the catalyst solution and used to prepare the silica sol.

[0117] In addition, the organosilane compound contained in the supercritical waste liquid is also an expensive compound and needs to be reused, so a separate supercritical waste liquid purification process may be required to reuse it. However, the method for producing silica aerogel and the method for producing silica aerogel blanket of the present invention can reuse the organosilane compound represented by Chemical Formula 3 as a hydrophobizing agent in the process for producing a catalyst solution, and does not require a separate purification process to remove it. Therefore, the organosilane compound can be reused as it is without loss due to the purification process.

[0118] When the supercritical waste liquid is reused, a process of confirming the amount of the organosilane compound contained in the catalyst solution may be further performed, and the amount of the organosilane compound may be used in an amount that satisfies an appropriate ratio of the organosilane compound to the prehydrolyzed polysilicate.

[0119] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to exemplary embodiments thereof, so that those skilled in the art can easily practice the present invention. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0120] [Example 1] 13.841g of ethyl polysilicate (TEOS40, ethyl polysilicate with SiO2 content of 40%) and 1.220g of methyltriethoxysilane (MTES) were added to the reactor (Si molar ratio of polysilicate to MTES 9:1). Next, 1.525g of HCl aqueous solution with pH 1.8 was added to the reactor to prepare a reaction mixture. The mixture was stirred at room temperature (20±5°C) for 1 hour. At the beginning of the reaction, the reaction mixture was opaque, but became transparent due to the generation of ethanol by the hydration of MTES, and then the partial hydration of ethyl polysilicate took place. The final product, prehydrolyzed ethyl polysilicate (HTEOS) oligomer in ethanol, was collected.

[0121] A catalyst solution of 93.992 g of ethanol, 8.998 g of water (H2O), 7.772 g of trimethylethoxysilane, and 0.388 g of NaOH was added to 16.589 g of the produced prehydrolyzed ethyl polysilicate (HTEOS) oligomer, and gelled to produce a silica wet gel.

[0122] The prepared silica wet gel was aged in an aging solution of 114.243 g of ethanol and 10.205 g of water at 60° C. for 18 hours.

[0123] The silica wet gel was placed in a 7.2 L supercritical extractor and CO2 was injected. The temperature in the extractor was then raised to 60°C for 1 hour, and supercritical drying was performed at 50°C and 100 bar. Here, the supercritical waste liquid was collected through the bottom of the separator.

[0124] [Example 2] 106.876 g of the waste liquid recovered in Example 1 was added to 16.589 g of prehydrolyzed ethyl polysilicate (HTEOS) oligomer prepared in the same manner as in Example 1, and the trimethylethoxysilane content of the recovered waste liquid was measured using gas chromatography (GC). Then, 3.886 g of trimethylethoxysilane was added thereto, and 0.388 g of NaOH was added thereto, followed by gelation to prepare a silica wet gel.

[0125] The prepared silica wet gel was aged in an aging solution of 114.243 g of ethanol and 10.205 g of water at 60° C. for 18 hours.

[0126] The silica wet gel was placed in a 7.2 L supercritical extractor and CO2 was injected. The temperature in the extractor was then raised to 60°C for 1 hour, and supercritical drying was performed at 50°C and 100 bar. Here, the supercritical waste liquid was collected through the bottom of the separator.

[0127] [Example 3] 106.876 g of the waste liquid recovered in Example 2 was added to 16.589 g of the prehydrolyzed ethyl polysilicate (HTEOS) oligomer prepared in the same manner as in Example 1, and the trimethylethoxysilane content of the recovered waste liquid was measured. Then, 3.886 g of trimethylethoxysilane was added thereto, and 0.388 g of NaOH was added thereto, followed by gelation to prepare a silica wet gel.

[0128] The prepared silica wet gel was aged in an aging solution of 114.243 g of ethanol and 10.205 g of water at 60° C. for 18 hours.

[0129] The silica wet gel was placed in a 7.2 L supercritical extractor and CO2 was injected. The temperature in the extractor was then raised to 60°C for 1 hour, and supercritical drying was performed at 50°C and 100 bar. Here, the supercritical waste liquid was collected through the bottom of the separator.

[0130] [Example 4] 13.182g of ethyl polysilicate (TEOS40, ethyl polysilicate with SiO2 content of 40%) and 1.743g of methyltriethoxysilane (MTES) were added to the reactor (Si molar ratio of polysilicate to MTES 6:1). Next, 1.543g of HCl aqueous solution with pH 1.8 was added to the reactor to prepare a reaction mixture. The mixture was stirred at room temperature (20±5°C) for 1 hour. At the beginning of the reaction, the reaction mixture was opaque, but became transparent due to the generation of ethanol by the hydration of MTES, and then the partial hydration of ethyl polysilicate took place. The final product, prehydrolyzed ethyl polysilicate (HTEOS) oligomer in ethanol, was collected.

[0131] 16.469 g of the produced prehydrolyzed ethyl polysilicate (HTEOS) oligomer was added with 93.931 g of ethanol, 8.998 g of water (H2O), 7.772 g of trimethylethoxysilane, and 0.388 g of NaOH as a catalyst solution, and gelled to produce a silica wet gel.

[0132] Next, the same aging process and supercritical drying as in Example 1 were performed to prepare an aerogel.

[0133] [Example 5] 13.671g of ethyl polysilicate (TEOS40, ethyl polysilicate with SiO2 content of 40%) and 1.356g of methyltriethoxysilane (MTES) were added to the reactor (Si molar ratio of polysilicate to MTES: 8:1). Next, 1.531g of HCl aqueous solution with pH 1.8 was added to the reactor to prepare a reaction mixture. The mixture was stirred at room temperature (20±5°C) for 1 hour. At the beginning of the reaction, the reaction mixture was opaque, but became transparent due to the generation of ethanol by the hydration of MTES, and then the partial hydration of ethyl polysilicate took place. The final product, prehydrolyzed ethyl polysilicate (HTEOS) oligomer in ethanol, was collected.

[0134] A catalyst solution of 93.977 g of ethanol, 8.998 g of water (H2O), 7.772 g of trimethylethoxysilane, and 0.388 g of NaOH was added to 16.558 g of the produced prehydrolyzed ethyl polysilicate (HTEOS) oligomer, and gelled to produce a silica wet gel.

[0135] Next, the same aging process and supercritical drying as in Example 1 were performed to prepare an aerogel.

[0136] [Example 6] 13.981g of ethyl polysilicate (TEOS40, ethyl polysilicate with SiO2 content of 40%) and 1.109g of methyltriethoxysilane (MTES) were added to the reactor (Si molar ratio of polysilicate to MTES: 10:1). Next, 1.524g of HCl aqueous solution with pH 1.8 was added to the reactor to prepare a reaction mixture. The mixture was stirred at room temperature (20±5°C) for 1 hour. At the beginning of the reaction, the reaction mixture was opaque, but became transparent due to the generation of ethanol by the hydration of MTES, and then the partial hydration of ethyl polysilicate took place. The final product, prehydrolyzed ethyl polysilicate (HTEOS) oligomer in ethanol, was collected.

[0137] 94.007 g of ethanol, 8.998 g of water (H2O), 7.772 g of trimethylethoxysilane, and 0.388 g of NaOH were added as a catalyst solution to 16.614 g of the produced prehydrolyzed ethyl polysilicate (HTEOS) oligomer, and gelled to produce a silica wet gel.

[0138] Next, the same aging process and supercritical drying as in Example 1 were performed to prepare an aerogel.

[0139] [Example 7] 14.196g of ethyl polysilicate (TEOS40, ethyl polysilicate with SiO2 content of 40%) and 0.939g of methyltriethoxysilane (MTES) were added to the reactor (Si molar ratio of polysilicate to MTES: 12:1). Next, 1.519g of HCl aqueous solution with pH 1.8 was added to the reactor to prepare a reaction mixture. The mixture was stirred at room temperature (20±5°C) for 1 hour. At the beginning of the reaction, the reaction mixture was opaque, but became transparent due to the generation of ethanol by the hydration of MTES, and then the partial hydration of ethyl polysilicate took place. The final product, prehydrolyzed ethyl polysilicate (HTEOS) oligomer in ethanol, was collected.

[0140] 94.027 g of ethanol, 8.997 g of water (H2O), 7.772 g of trimethylethoxysilane, and 0.388 g of NaOH were added as a catalyst solution to 16.654 g of the produced prehydrolyzed ethyl polysilicate (HTEOS) oligomer, and gelled to produce a silica wet gel.

[0141] Next, the same aging process and supercritical drying as in Example 1 were performed to prepare an aerogel.

[0142] [Example 8] 12.816g of ethyl polysilicate (TEOS40, ethyl polysilicate with SiO2 content of 40%) and 2.034g of methyltriethoxysilane (MTES) were added to the reactor (Si molar ratio of polysilicate to MTES: 5:1). Next, 1.552g of HCl aqueous solution with pH 1.8 was added to the reactor to prepare a reaction mixture. The mixture was stirred at room temperature (20±5°C) for 1 hour. At the beginning of the reaction, the reaction mixture was opaque, but became transparent due to the generation of ethanol by the hydration of MTES, and then the partial hydration of ethyl polysilicate took place. The final product, prehydrolyzed ethyl polysilicate (HTEOS) oligomer in ethanol, was collected.

[0143] 16.402 g of the produced prehydrolyzed ethyl polysilicate (HTEOS) oligomer was added with 93.897 g of ethanol, 8.998 g of water (H2O), 7.772 g of trimethylethoxysilane, and 0.388 g of NaOH as a catalyst solution, and gelled to produce a silica wet gel.

[0144] Next, the same aging process and supercritical drying as in Example 1 were performed to prepare an aerogel.

[0145] [Example 9] 13.841g of ethyl polysilicate (TEOS40, ethyl polysilicate with SiO2 content of 40%) and 2.129g of propyltriethoxysilane (PTES) were added to the reactor (Si molar ratio of polysilicate to PTES 9:1). Next, 1.527g of HCl aqueous solution with pH 1.8 was added to the reactor to prepare a reaction mixture. The mixture was stirred at room temperature (20±5°C) for 1 hour. At the beginning of the reaction, the reaction mixture was opaque, but became transparent due to the generation of ethanol by the hydration of MTES, and then the partial hydration of ethyl polysilicate took place. The final product, prehydrolyzed ethyl polysilicate (HTEOS) oligomer in ethanol, was collected.

[0146] A catalyst solution of 93.046 g of ethanol, 8.998 g of water (H2O), 7.772 g of trimethylethoxysilane, and 0.388 g of NaOH was added to 17.498 g of the produced prehydrolyzed ethyl polysilicate (HTEOS) oligomer, and gelled to produce a silica wet gel.

[0147] Next, the same aging process and supercritical drying as in Example 1 were performed to prepare an aerogel.

[0148] [Comparative Example 1] 15.497 g of ethyl polysilicate (TEOS40) and 13.858 g of ethanol were added to the reactor. Then, 1.491 g of an aqueous HCl solution with a pH of 1.8 was added to the reactor to prepare a reaction mixture. The amount of ethanol was determined to be the minimum amount that would allow the ethyl polysilicate and the aqueous HCl solution to be mixed transparently. The mixture was stirred at room temperature (20±5°C) for 1 hour, and the final product, prehydrolyzed ethyl polysilicate (HTEOS) oligomer in ethanol, was collected.

[0149] A catalyst solution of 89.029 g of ethanol, 7.949 g of water (H2O), 7.772 g of trimethylethoxysilane, and 0.388 g of NaOH was added to 30.846 g of the produced prehydrolyzed ethyl polysilicate (HTEOS) oligomer, and gelled to produce a silica wet gel.

[0150] The prepared silica wet gel was aged in an aging solution of 114.243 g of ethanol and 10.205 g of water at 60° C. for 18 hours.

[0151] The silica wet gel was placed in a 7.2 L supercritical extractor and CO2 was injected. The temperature in the extractor was then raised to 60°C for 1 hour, and supercritical drying was performed at 50°C and 100 bar. The supercritical waste liquid was then collected through the bottom of the separator.

[0152] [Comparative Example 2] The supercritical wastewater recovered in Comparative Example 1 was fractionally distilled, and then 13.858 g of ethanol was added instead of the prehydrolyzed ethyl polysilicate (HTEOS) oligomer preparation in Comparative Example 1, to prepare a prehydrolyzed ethyl polysilicate (HTEOS) oligomer in ethanol.

[0153] 100.864 g of the waste liquid recovered in Comparative Example 1 was added to 30.846 g of the prehydrolyzed ethyl polysilicate (HTEOS) oligomer prepared above, and the trimethylethoxysilane content of the recovered waste liquid was measured. Then, 3.886 g of trimethylethoxysilane was added thereto, and 0.388 g of NaOH was added thereto, followed by gelation to prepare a silica wet gel.

[0154] The prepared silica wet gel was aged in an aging solution of 114.243 g of ethanol and 10.205 g of water at 60° C. for 18 hours.

[0155] The silica wet gel was placed in a 7.2 L supercritical extractor and CO2 was injected. The temperature in the extractor was then raised to 60°C for 1 hour, and supercritical drying was performed at 50°C and 100 bar. Here, the supercritical waste liquid was collected through the bottom of the separator.

[0156] [Comparative Example 3] The supercritical wastewater recovered in Comparative Example 2 was fractionally distilled, and then 13.858 g of ethanol was added instead of the prehydrolyzed ethyl polysilicate (HTEOS) oligomer preparation in Comparative Example 1, to prepare a prehydrolyzed ethyl polysilicate (HTEOS) oligomer in ethanol.

[0157] 100.864 g of the waste liquid recovered in Comparative Example 2 was added to 30.846 g of the prehydrolyzed ethyl polysilicate (HTEOS) oligomer prepared above, and the trimethylethoxysilane content of the recovered waste liquid was measured. Then, 3.886 g of trimethylethoxysilane was added thereto, and 0.388 g of NaOH was added thereto, followed by gelation to prepare a silica wet gel.

[0158] The prepared silica wet gel was aged in an aging solution of 114.243 g of ethanol and 10.205 g of water at 60° C. for 18 hours.

[0159] The silica wet gel was placed in a 7.2 L supercritical extractor and CO2 was injected. The temperature in the extractor was then raised to 60°C for 1 hour, and supercritical drying was performed at 50°C and 100 bar. Here, the supercritical waste liquid was collected through the bottom of the separator.

[0160] [Experimental example: Measurement of the physical properties of aerogel] 1) Measurement of thermal conductivity The thermal conductivity of the silica aerogels prepared in the examples and comparative examples was measured at room temperature (about 23° C.) using a NETZSCH HFM 436 device, and the results are shown in Table 1.

[0161] 2) Measurement of absorption rate A 100mm x 100mm test piece (10mm thick) was floated on distilled water at 21±2°C, and a mesh screen was placed on top of the test piece, which was then submerged 127mm below the water surface. After 15 minutes, the screen was removed, and when the test piece floated up, it was clamped and hung vertically for 60±5 seconds. The weights before and after impregnation were then measured, the weight increase rate was confirmed, and the absorption rate was calculated.

[0162] [Table 1]

[0163] From Examples 1 to 9, it was confirmed that ethanol can be effectively produced by the hydration reaction of methyltriethoxysilane (MTES) or triethoxy(propyl)silane, which is a compound represented by Chemical Formula 1, without the need for adding a separate ethanol solvent, and thus the hydration reaction of ethyl polysilicate can be carried out. Aerogel can be produced using the produced prehydrolyzed ethyl polysilicate (HTEOS) oligomer.

[0164] Examples 2 and 3 are examples in which the supercritical waste liquid recovered in Examples 1 and 2 was used in the silica gel manufacturing process without a separate purification process. The results of Examples 2 and 3 confirmed that the supercritical waste liquid generated in Examples 1 and 2 according to the present invention does not cause a deterioration in the properties of the produced silica aerogel even when used in the silica gel manufacturing process without a separate purification process, and that the supercritical waste liquid can be effectively reused without a separate purification process for the supercritical waste liquid.

[0165] The silica aerogels of Examples 1 to 3, 5 to 7, and 9 exhibited the same levels of thermal conductivity and absorptivity as the silica aerogels of Comparative Examples 1 to 3, and the silica aerogels of Examples 4 and 8 exhibited the same levels of absorptivity as the silica aerogels of Comparative Examples 1 to 3.

[0166] As a result, it was confirmed that in Examples 1 to 9, prehydrolyzed polysilicate can be effectively produced without adding additional ethanol during the hydration reaction of ethyl polysilicate, and that silica aerogel can be produced using this.

[0167] The above description of the present invention is for illustrative purposes only, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical concept or essential features of the present invention. Therefore, the above-described embodiments should be understood to be illustrative in all respects and not limiting.

Claims

1. Step 1: adding polysilicate and a compound represented by the following formula 1 to a reactor; Step 2: further adding an acidic aqueous solution to the reactor to prepare a reaction mixture; (Step 3) stirring the reaction mixture to carry out a hydration reaction to produce a prehydrolyzed polysilicate; Step 4: adding a catalyst solution to the prehydrolyzed polysilicate and mixing to prepare a silica sol; and (5) gelling the silica sol to form a silica wet gel. 【Chemistry 1】 In the formula, R １ is an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, or a vinyl group; R ２ are each independently alkyl having 1 to 20 carbon atoms.

2. The method for producing silica aerogel according to claim 1, further comprising the step of aging the silica wet gel (step 6) after step 5.

3. The method for producing silica aerogel according to claim 1 or 2, further comprising a step (step 7) of drying the silica wet gel.

4. The drying step is carried out by supercritical drying; 4. The method for producing silica aerogel according to claim 3, further comprising the step of reusing the waste liquid after the supercritical drying in the production of the catalyst solution in step 4 without a separate purification process.

5. 2. The method for producing silica aerogel according to claim 1, wherein the catalytic solution comprises water, an alcohol compound, a basic catalyst, and an organosilane compound.

6. The method for producing silica aerogel according to claim 1, wherein the compound represented by Chemical Formula 1 is hydrated to form an alcohol compound represented by Chemical Formula 2 and a silanol compound represented by Chemical Formula 3 below. 【Chemistry 2】 In the formula, R １ is an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, or a vinyl group; R ２ is alkyl having 1 to 20 carbon atoms.

7. 2. The method for producing silica aerogel according to claim 1, wherein the hydration of the polysilicate in step 3 is carried out in the presence of an alcohol compound represented by Chemical Formula 2 formed by hydrating a compound represented by Chemical Formula 1. 【Chemistry 3】 In the formula, R ２ is alkyl having 1 to 20 carbon atoms.

8. The method for producing silica aerogel according to claim 1, wherein the polysilicate and the compound represented by Chemical Formula 1 have a molar ratio of 5:1 to 15:

1.

9. 2. The method for producing silica aerogel according to claim 1, wherein the acidic aqueous solution contains 0.005 to 0.20 parts by weight of an acid catalyst relative to 100 parts by weight of the polysilicate.

10. 2. The method for producing silica aerogel according to claim 1, wherein the prehydrolyzed polysilicate is produced by adding no other alcohol-based solvent to a reactor other than the polysilicate and the compound represented by Chemical Formula 1.

11. 2. The method for producing silica aerogel according to claim 1, wherein the polysilicate comprises at least one selected from the group consisting of methyl polysilicate, ethyl polysilicate, propyl polysilicate, isopropyl polysilicate, butyl polysilicate, secondary butyl polysilicate, tertiary butyl polysilicate, hexyl polysilicate, cyclohexyl polysilicate, and dodecyl polysilicate.

12. 2. The method for producing silica aerogel according to claim 1, wherein the compound represented by Chemical Formula 1 includes at least one selected from the group consisting of alkyltriethoxysilane and alkyltrimethoxysilane.

13. The method for producing silica aerogel according to claim 1 , wherein the compound represented by Chemical Formula 1 is methyltriethoxysilane.

14. The compound represented by Chemical Formula 1 is an alkyltriethoxysilane, which is hydrated to form an alkylsilanol and ethanol; 2. The method for producing silica aerogel according to claim 1, wherein the hydration of the polysilicate in step 3 is carried out in the presence of the ethanol formed by hydrating the alkyltriethoxysilane.

15. Step 1: adding polysilicate and a compound represented by the following formula 1 to a reactor; Step 2: further adding an acidic aqueous solution to the reactor to prepare a reaction mixture; (Step 3) stirring the reaction mixture to carry out a hydration reaction to produce a prehydrolyzed polysilicate; Step 4: adding a catalyst solution to the prehydrolyzed polysilicate and mixing to prepare a silica sol; and (5) impregnating a blanket substrate with the silica sol and then gelling the same to form a silica wet gel blanket. 【Chemistry 4】 In the formula, R １ is an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, or a vinyl group; R ２ are each independently alkyl having 1 to 20 carbon atoms.

Images