KR100785521B1 - Method for preparing surface-modified aerogel and surface-modified aerogel therefrom - Google Patents

Abstract

An aerogel and a method for manufacturing the same are provided to have an excellent adiabatic property and an eternal hydrophobic property under a normal pressure, by removing residual moisture within a wet silica gel using n-butanol effectively. A silica gel is formed in an acidic medium of pH 3-5, which is prepared by adding sodium silicate into HCl at a temperature of 30-90°C. The formed silica gel is washed and filtered by distilled water. A surface of the silica gel is silylated. The silylated surface-containing silica gel is solvent-replaced into n-butanol to remove moisture and reaction residues within the silica gel simultaneously. The resultant silica gel is dried.

Description

Method for preparing surface-modified aerogels and surface-modified aerogels prepared therefrom {Method for Preparing Surface-Modified Aerogel And Surface-Modified Aerogel Therefrom}

1 is a view showing an example of a method for producing an airgel hydrophobically modified by the present invention.

The present invention relates to a method for preparing a surface modified airgel and to a surface modified airgel prepared therefrom. More particularly, it relates to a hydrophobic surface modified airgel production method and a surface modified airgel prepared therefrom.

Recently, as industrial technology is advanced, interest in aerogels is increasing day by day. Aerogels have a porosity of 90% or more, a specific surface area of several hundred to 1500 m ² / g, and are extremely low-density materials with nanoporous structure. Therefore, the nanoporous aerogel can be applied in the fields of ultra low dielectric, catalyst, electrode material, soundproofing material, and the like. In particular, the silica aerogel has a low thermal conductivity, which is a very efficient super insulation material that can be used in refrigerators, automobiles, aircrafts, and the like.

Such aerogels can be prepared by various methods, for example WO 95/06617 discloses water at pH 7.5-11 to remove ionic components from silica hydrogels formed after reacting water glass with sulfuric acid at pH 7.5-11. Or washed with a dilute aqueous solution of inorganic base (sodium hydroxide or ammonia), followed by removal of water with C _1-5 alcohol, and drying under supercritical conditions at 55-90 bar at 240-280 ° C. to prepare a hydrophobic silica airgel, silyl It goes through a supercritical drying process without a ignition step.

WO96 / 22942 provides a silicate riogel and then, if necessary, solvent substitution with other organic solvents (methanol, ethanol, propanol, acetone, tetrahydrofuran, etc.) and then reacted with a silylating agent that does not contain at least one chlorine. Since a method of producing an airgel by supercritical drying is disclosed, solvent substitution is performed before silylation and undergoes a supercritical drying process.

WO98 / 23367 is also subjected to a silylation and drying process after washing a lyogel formed by reacting water glass with an acid with an organic solvent (alcohol (methanol, ethanol), acetone, ketone, etc.) so that the water content is 5% by weight or less. While a method of preparing an airgel is disclosed, a solvent substitution process takes place prior to silylation.

WO97 / 17288 also discloses a silicate sol having a pH of 4.0 or less from an aqueous glass of water solution using an organic and / or inorganic acid, and then separating the salt formed from the cation of acid and water glass at 0-30 ° C. from the silicate sol, and then After polycondensation of the SiO ₂ gel by adding a base to it, it was washed with an organic solvent (aliphatic alcohol, ether, ester, ketone, aliphatic or aromatic hydrocarbon) until the water content was 5% by weight or less, followed by aerogel through silylation and drying. It has been disclosed that a process for preparing the silane is also carried out in the solvent substitution process before silylation.

WO97 / 13721 describes the substitution of water in hydrogel particles with C _1-6 aliphatic alcohols, and the like, followed by organic reaction from hydrogels with C _1-3 alcohols, diethyl ether, acetone, n-pentane, n-hexane and the like. The process of drying the gel particles after removal of the solvent from the solvent wet gel at a temperature above the atmospheric boiling point of the solvent to below the decomposition temperature and below the supercritical pressure of the solvent is described. As a technology, the process is complicated by a two-step solvent replacement process in which water is substituted with a polar solvent (butanol, etc.), and then the polar solvent is replaced with a nonpolar solvent (pentane, etc.) for atmospheric pressure drying. In addition, WO98 / 23366 discloses that hydrogels are produced at pH 3 or higher, and then subjected to an intermediate treatment step, followed by surface modification by mixing hydrophobic agents and hydrogels, and optionally protic or aprotic solvents (aliphatic alcohols, ethers). , Esters, ketones, aliphatic or aromatic hydrocarbons, etc.) or silylating agents, followed by drying, to prepare aerogels. The exchange of water with other solvents is a waste of time and energy, and therefore can be carried out without solvent exchange. It is disclosed to be a method for producing an airgel.

There is also a technique for removing moisture in silica using butanol, propanol and mixtures thereof for preparing nano-sized silica (Korean Patent Application 2004-72145), which is reacted by adding HCl to water glass. Precisely to precipitate the silica, and then mixed with, butanol and the like, filtered and distilled to remove moisture in the silica and dried at a high temperature of 285 ℃ to produce a nano-sized silica particles, as shown in the formula 1 In the solvent replacement and subsequent drying steps, the hydroxyl group on the surface of silica reacts with butanol and is converted into butoxy group, thereby giving hydrophobicity to the surface. However, the hydrophilic group is capable of reverse reaction by reacting with moisture in the air. It is difficult to give permanent hydrophobicity to silica because it is converted into. Therefore, the silica prepared by the above invention is limited to use in applications requiring permanent hydrophobic silica particles.

[Formula 1]

Accordingly, an object of the present invention is to provide a method for producing a surface-modified airgel to solve the problems of the prior art and to impart economical permanent hydrophobicity at atmospheric pressure.

Another object of the present invention is to provide a method for producing an efficient process in which water in a hydrophobically surface modified airgel is quickly removed.

Another object of the present invention is to provide an airgel having permanent hydrophobicity prepared by the method of the present invention.

According to one aspect of the invention,

a) adding water glass (sodium silicate) to HCl at 30-90 ° C. until pH 3-5 to form silica gel under acidic conditions of pH 3-5;

b) washing and filtering the formed silica gel with distilled water;

c) silylating the surface of the silica gel of step b);

d) solvent-substituting the silylated silica gel with n-butanol to simultaneously remove water and reaction residue in the silica gel; And

e) drying the silica gel;

Provided is a method of preparing an airgel in which the surface comprising hydrophobically modified.

According to another aspect of the present invention,

An airgel having a hydrophobically modified surface obtained by the method of the present invention is provided.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention relates to a novel process for producing hydrogels that are hydrophobically surface modified to hydrophobize the surface of the silica gel and to quickly remove moisture in the silica gel. The process of the present invention is characterized by hydrolyzing, preferably permanently hydrophobizing, the silica gel surface by silylating the surface of the silica gel using a silylating agent. In addition, the method of the present invention is characterized in that water in the silica gel is solvent-substituted with butanol by using butanol solubility in water and solubility in butanol to effectively remove water in the silica gel in a short time.

A method of preparing a hydrophobically surface-modified airgel of the present invention is shown in FIG. 1.

According to the method of the present invention, as shown in FIG. 1, water silica (sodium silicate) is added to HCl at 30-90 ° C. until the pH is 3-5 to form silica gel. If the pH of the reaction medium is lower than 3 or higher than 5, it is not preferable from the viewpoint of efficiency and economic efficiency of silica gel production because the reaction is fast or difficult to control the formation of silica gel effectively. The said reaction is performed at 30-90 degreeC, Preferably it is 40-70 degreeC. The temperature below 30 ° C is not preferable in that the reaction time is long, and if it exceeds 90 ° C, it is not preferable in that it is difficult to control the structure of the silica gel.

The silica in the gel is then washed with distilled water and filtered to remove NaCl and other impurities in the silica gel. The washing process also affects the porosity of the silica gel obtained after drying. If impurities such as ionic groups mixed in the silica gel remain during drying, the gel may be damaged during drying, resulting in aerogel formation. It will damage the porosity of. In addition, in the case of ionic impurities, it also serves to reduce the hydrophobicity of the dried airgel.

On the other hand, if necessary, the gel of the silica may be formed as a gel and then aged before the washing and filtering step so that the microstructure of the particles of the silica gel may be grown. Aging can be performed by adjusting temperature and time as needed until a silica of desired microstructure is obtained. As an example, it may be aged at about room temperature (20-25 ° C.) to 80 ° C. for about 2-24 hours.

After the washing and filtration step, the surface of the silica gel is silylated to modify the surface of the silica hydrophobicly, wherein a silane compound may be used as the silylating agent, and the formula is R _{1 4-n} -SiX _n where n is 1-3 and R ₁ is C ₁ -C ₁₀ , preferably C ₁ -C ₅ alkyl or aromatic, heteroaromatic alkyl or hydrogen, X is F, Cl, A halogen element selected from Br, I, preferably Cl or C ₁ -C ₁₀ , preferably C ₁ -C ₅ alkoxy group, or aromatic alkoxy group, heteroaromatic alkoxy group. Siloxanes can also be used, the formula of which is R ₃ Si-O-SiR ₃ , wherein the R ₃ groups are the same or different and are C ₁ -C ₁₀ , preferably C ₁ -C ₅ alkyl or aromaticalkyl, hetero Aromatic alkyl or hydrogen).

Specific examples of such silylating agents include, but are not limited to, hexamethyldisilane, ethyltriethoxysilane, trimethoxysilane, triethylethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, At least one selected from the group consisting of methoxytrimethylsilane, trimethylchlorosilane and triethylchlorosilane can be used.

The silylation step is accomplished by refluxing the silica gel for 2 to 24 hours in a diluted silylating agent formed by mixing 1-30% by weight silylating agent with 70-99% by weight alcohol. Reflux is done near the boiling point of the diluted silylating agent. If the reflux time is less than 2 hours, the silylation reaction time may be insufficient depending on the type of the silylating agent, and if it is more than 24 hours, unwanted side reactions may occur. At least one selected from the group consisting of methanol, ethanol, propanol and butanol may be used as the alcohol.

By the silylation treatment as described above, the surface of the silica gel is silylated as shown in the following Chemical Formula 2 to be hydrophobic, preferably permanently hydrophobically modified.

[Formula 2]

The surface-modified silica gel as described above is immersed in n-butanol and then refluxed to solvent-substitute the water in the silica gel to remove the water in the silica gel. The reflux temperature at the time of solvent replacement is performed near the break point of the alcohol used. The reflux time is heated until the vaporized alcohol vapor is condensed by connecting the cooling tube until water no longer mixes with the alcohol. Although not limited to this, it can be refluxed for 2-24 hours as an example. If the residual moisture present in the silica wet gel is not sufficiently removed before the drying step described below, the thermal conductivity increases significantly since high capillary force caused by water acts on the gel structure and damages the porous gel structure during drying. . In addition, as in the prior art, if solvent substitution is not carried out before silylation and n-butanol is carried out after silylation, the effect of removing water in silica gel and chemicals and by-products in the silylation reaction is also removed. Therefore, solvent substitution is performed after silylation. In addition, n-butanol is used as the solvent used in the solvent substitution in the present invention, which effectively removes the water in the wet gel pores under the conditions of the solvent used for solvent substitution, and 2) the low capillary tube possible under atmospheric pressure drying. This is because it satisfies all that needs to be evaporated while applying pressure to the gel structure. That is, in order to satisfy the condition of 1), it should be a possible polar solvent, and in order to satisfy the condition of 2), it should be a solvent having a small surface tension, that is, a nonpolar solvent. In order to satisfy these two conflicting conditions, the polarity must not be large, such as methanol, ethanol, THF, acetone, and non-polar, such as heptane, pentane. That is, in the case of polarity, as in the former, a very large capillary pressure can be given to the gel structure at the gas-liquid interface produced during drying. There is a problem that it is difficult to remove the water effectively. Therefore, the present inventors have found that in the case of n-butanol, the OH group is polar, but the number of alkyl groups is 4, which is somewhat nonpolar, so that the two conditions can be satisfied most effectively.

Finally, the solvent-substituted to dry the surface-modified silica gel from which the water is removed, the drying can be carried out at 100-250 ℃ atmospheric pressure. Temperatures below 100 ° C. are undesirable because the drying rate is too slow, and temperatures above 250 ° C. are undesirable because hydrophobized silylated groups may be lost due to pyrolysis. The suitable time for drying is influenced by the structure of the resulting airgel, the particle size, the kind of solvent used and the residual content in the gel structure. Therefore, the optimum drying time can be determined by measuring the time that the dried particles are not detected by using a thermogravimetric analyzer (TGA).

As in the present invention, the structure of the hydrogel surface-modified aerogel obtained during drying is permanently maintained by undergoing a solvent replacement process after a silylation, and a drying speed is also increased.

Hereinafter, the present invention will be described in more detail with reference to the following examples. The following examples are illustrative of the invention and do not thereby limit the invention.

Example 1

To 1 L of 1N hydrochloric acid solution at 60 ° C, water glass solution (a solution of 35% sodium silicate solution diluted three times with water) is added with a little stirring until pH 4. At this time, the temperature of the reactor is 60 ℃, the reaction was stirred for 2 hours under acidic conditions of pH 4 to prepare a wet silica gel. The wet gel thus prepared is sufficiently washed after being washed several times with a sufficient amount of distilled water to remove Na ions present in the gel. Subsequently, 400 g of the silica wet gel was immersed in 500 ml of a diluted silane solution mixed with 90 wt% methanol (MeOH) and 10 wt% hexamethyl-di-silane (HMDS), and then refluxed at 120 to 150 ° C. for 4 hours. reflux). Thereafter, 400 g of the surface-modified silica gel was immersed in 500 ml of n-butanol and refluxed again at 120 to 150 ° C. for 4 hours to remove water in the gel through solvent replacement. The wet gel from which water was removed by solvent treatment was dried at 120 ° C. for 2 hours. The hydrophobic surface-modified airgel thus prepared had a thermal conductivity of 9 mW / m · K.

Comparative Example 1-1

A surface-modified airgel was prepared in the same manner as in Example 1 except that the solvent replacement step using n-butanol was omitted. The hydrophobic surface-modified silica powder thus prepared had a thermal conductivity of 32 mW / m · K.

Comparative Example 1-2

An airgel was prepared in the same manner as in Example 1 except that the surface modification step using the silane compound was omitted. The powder thus prepared had a thermal conductivity of 25 mW / m · K.

Comparative Example 1-3

The surface-modified airgel was prepared in the same manner as in Example 1 except that the airgel manufacturing procedure was changed to that of silylation after solvent replacement with n-butanol. The powder thus prepared had a thermal conductivity of 26 mW / m · K.

Comparative Example 1-4

A surface-modified airgel was prepared in the same manner as in Example 1, except that solvent replacement was performed using propanol instead of n-butanol. The hydrophobic surface-modified silica powder thus prepared had a thermal conductivity of 25 mW / m · K.

Example 2

A surface-modified airgel was prepared in the same manner as in Example 1 except that ethyltriethoxysilane (ETES) was used as a silane compound for silica surface modification. The thermal conductivity of the obtained porous airgel was 11 mW / m * K.

Comparative Example 2

A surface-modified porous silica was prepared in the same manner as in Example 2 except that the solvent replacement step using n-butanol was omitted. The thermal conductivity of the obtained porous silica powder was 41 mW / m * K.

Example 3

A surface-modified airgel was prepared in the same manner as in Example 1 except that trimethoxysilane (TMS) was used as the silane compound for silica surface modification. The thermal conductivity of the obtained porous airgel was 10 mW / m * K.

Comparative Example 3

A surface-modified porous silica was prepared in the same manner as in Example 3 except that the solvent replacement step using n-butanol was omitted. The thermal conductivity of the obtained porous silica powder was 144 mW / m * K.

Example 4

A surface-modified airgel was prepared in the same manner as in Example 1 except that ethyltrimethoxysilane (ETMS) was used as a silane compound for silica surface modification. The thermal conductivity of the obtained porous airgel was 11 mW / m * K.

Comparative Example 4

A surface-modified porous silica was prepared in the same manner as in Example 4 except that the solvent replacement step using n-butanol was omitted. The thermal conductivity of the obtained porous silica powder was 39 mW / m · K.

Example 5

A surface-modified airgel was prepared in the same manner as in Example 1 except that methoxytrimethylsilane (MTMS) was used as the silane compound for silica surface modification. The thermal conductivity of the obtained porous airgel was 18 mW / m * K.

Comparative Example 5

A surface-modified porous silica was prepared in the same manner as in Example 5 except that the solvent replacement step using n-butanol was omitted. The thermal conductivity of the obtained porous silica powder was 83 mW / m * K.

According to the present invention, a porous airgel which is hydrophobically modified, preferably permanently hydrophobically, is obtained by silylation of the surface of the airgel, and the airgel prepared by the method according to the present invention reacts with moisture in the air as the surface is hydrophobic Since it is not so, it can be usefully used as an additive such as rubber, plastic, paper. In addition, the conventional multi-stage solvent replacement step before silylation and the reaction residue removal step after silylation can be compressed into one step after the silylation reaction. The particle shape of the airgel is maintained, moisture in the silica can be removed more quickly, the loss of the solvent used at this time can be reduced, and drying is performed under normal pressure conditions, so that the airgel can be produced more efficiently and economically. Can be.

Claims (11)

a) adding water glass (sodium silicate) to HCl at 30-90 ° C. until pH 3-5 to form silica gel under acidic conditions of pH 3-5; b) washing and filtering the formed silica gel with distilled water; c) the silica gel of step b) is mixed with 1-30% by weight of the silylating agent and 70-99% by weight of alcohol, and refluxed in the diluted silylating agent for 2-24 hours to silylate the surface of the silica gel. step; d) solvent-substituting the silylated silica gel with n-butanol to simultaneously remove water and reaction residue in the silica gel; And e) drying the silica gel; Surface modified airgel manufacturing method comprising a. The method of claim 1 further comprising the step of ageing after the formation of the silica gel of a). The method of claim 2 wherein the aging step is carried out at 20-80 ° C. for 2-24 hours. The method of claim 1, wherein the silylation has the formula R _{1 4-n-} SiX _n or R ₃ Si-O-SiR ₃ , where n is 1-3, R ₁ is C ₁ -C ₁₀ alkyl, aromatic, heteroaromatic alkyl or hydrogen, X is F, Cl, A halogen element selected from Br, I, a C ₁ -C ₁₀ alkoxy group, an aromatic alkoxy group or a heteroaromatic alkoxy group, wherein the R ₃ groups are the same or different and are C ₁ -C ₁₀ alkyl or aromatic alkyl, heteroaromatic alkyl or Silylating agent) is used. The method of claim 4, wherein the silylating agent is hexamethyldisilane, trimethoxysilane, ethyltriethoxysilane, triethylethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, methoxytrimethylsilane, trimethyl At least one selected from the group consisting of chlorosilanes and triethylchlorosilanes. delete The method of claim 1, wherein the alcohol is composed of methanol, ethanol, propanol and butanol At least one selected from the group. The method of claim 1, wherein the solvent replacement is performed by refluxing for 2-24 hours. The method of claim 1 wherein the drying step is performed at 100-250 ° C. The method of claim 1, wherein the n-butanol used for solvent replacement is sent to a distillation process and reused for solvent replacement of silica gel. delete

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