Patent Description:
Aerogels are highly porous materials that are composed of nanoparticles, and have attracted attention for use as high-efficiency insulating materials, soundproof materials, and the like because they have high porosity, a high specific surface area, and low thermal conductivity. Because such aerogels have very low mechanical strength due to their porous structure, aerogel composites, in which an aerogel is impregnated into fibrous blankets formed of existing insulating fibers (such as organic or inorganic fibers) so that the aerogel is bound to the fibrous blankets, have been developed. As one example, a silica aerogel-containing blanket using a silica aerogel is manufactured through a silica sol preparation step, a gelation step, an aging step, a surface modification step, and a drying step.

A silazane-based compound used as a surface modifying agent in a step of surface modifying a silica aerogel and a silica aerogel-containing blanket is decomposed into an alkoxysilane compound or a silanol compound to generate a large amount of NH<NUM>. NH<NUM> is dissolved in a solvent present in a hydrogel, and reacted with carbon dioxide, which is used as an extraction solvent during subsequent supercritical drying, to form ammonium carbonate salts. Then, as the temperature decreases, the ammonium carbonate salts precipitate to form a solid-phase powder, which causes problems such as scale formation, pipe or valve clogging, or the like in subsequent processes.

Therefore, it has been preferred to use an alkoxysilane compound, which does not generate ammonia, instead of a silazane-based compound, as the surface modifying agent in the step of surface modifying a silica aerogel or a silica aerogel-containing blanket. Accordingly, there is a need for a novel method of manufacturing an alkoxysilane compound capable of more effectively removing ammonia generated as a by-product when an alkoxysilane compound is manufactured using the silazane-based compound.

<CIT> discloses a method for manufacturing a silica aerogel-containing blanket, comprising the steps of: preparing a reaction solution by reacting a silazane-based surface modifier and an alcohol-based compound; preparing a silica gel-substrate composite by adding a silica precursor, water and a polar organic solvent to the reaction solution so as to prepare a silica sol and then dipping a substrate for a blanket into the same so as to gellify the same; and drying the silica gel-substrate composite.

<NPL> discloses catalysts and a method for the silylation of alcohols with hexamethyldisilazane.

Therefore, it is an object of the present invention to provide a novel method of manufacturing an alkoxysilane compound capable of more effectively removing ammonia generated as a by-product during a process of manufacturing an alkoxysilane compound using a silazane-based compound.

To achieve the above object, according to one aspect of the present invention, there is provided a method of manufacturing an alkoxysilane compound, which includes: (<NUM>) adding an alcohol to a silazane-based compound represented by the following Formula <NUM> and allowing the alcohol to react with the silazane-based compound to prepare a first mixture including an alkoxysilane compound and ammonia; (<NUM>) adding an acid with pKa <NUM> to <NUM> to the first mixture and allowing the acid to react with the first mixture to prepare a second mixture including the alkoxysilane compound and an ammonium salt; (<NUM>) adding an aqueous solvent to the second mixture to dissolve the ammonium salt; and (<NUM>) separating and removing the aqueous layer, in which the ammonium salt is dissolved, to obtain the alkoxysilane compound:
<CHM>.

In the method of manufacturing an alkoxysilane compound according to the present invention, ammonia formed as a by-product can be converted into an ammonium salt and effectively removed during a process of manufacturing an alkoxysilane compound using a silazane-based compound.

Hereinafter, the present invention will be described in further detail in order to aid in understanding the present invention.

A method of manufacturing an alkoxysilane compound according to the present invention includes: (<NUM>) adding an alcohol to a silazane-based compound represented by the following Formula <NUM> and allowing the alcohol to react with the silazane-based compound to prepare a first mixture including an alkoxysilane compound and ammonia; (<NUM>) adding an acid with pKa <NUM> to <NUM> to the first mixture and allowing the acid to react with the first mixture to prepare a second mixture including the alkoxysilane compound and an ammonium salt; (<NUM>) adding an aqueous solvent to the second mixture to dissolve the ammonium salt; and (<NUM>) separating and removing the aqueous layer, in which the ammonium salt is dissolved, to obtain the alkoxysilane compound:
<CHM>.

In Step (<NUM>), an alcohol is added and reacted with a silazane-based compound represented by the following Formula <NUM> to synthesize an alkoxysilane compound. In this case, a first mixture including an alkoxysilane compound and ammonia is prepared while ammonia is generated as a by-product:
<CHM>
wherein R<NUM> is an alkyl group having <NUM> to <NUM> carbon atoms, R<NUM> is a hydrogen atom or an alkyl group having <NUM> to <NUM> carbon atoms, and n is an integer ranging from <NUM> to <NUM>.

Also, R<NUM> may be an alkyl group having <NUM> to <NUM> carbon atoms, and R<NUM> may be a hydrogen atom or an alkyl group having <NUM> to <NUM> carbon atoms.

In addition, R<NUM> may be an alkyl group having <NUM> to <NUM> carbon atoms, R<NUM> may be a hydrogen atom or an alkyl group having <NUM> to <NUM> carbon atoms.

According to one embodiment of the present invention, the silazane-based compound may include one or more selected from the group consisting of a dialkyldisilazane, a tetraalkyldisilazane, and a hexaalkyldisilazane.

Also, specific examples of the silazane-based compound may include <NUM>,<NUM>-diethyldisilazane, <NUM>,<NUM>,<NUM>,<NUM>-tetramethyldisilazane, <NUM>,<NUM>,<NUM>,<NUM>-tetraethyldisilazane, <NUM>,<NUM>,<NUM>,<NUM>,<NUM>,<NUM>-hexamethyldisilazane (HMDS), <NUM>,<NUM>,<NUM>,<NUM>,<NUM>,<NUM>-hexaethyldisilazane, <NUM>,<NUM>,<NUM>,<NUM>-tetraethyldisilazane, <NUM>,<NUM>-diisopropyldisilazane, or the like, which may be used alone or as a mixture thereof.

Meanwhile, examples of the alcohol may include monohydric alcohols such as methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, heptanol, and octanol, which may be used alone or as a mixture thereof. Specifically, the alcohol may include one or more selected from the group consisting of methanol, ethanol, propanol, isopropanol, butanol, pentanol, and hexanol. More specifically, the alcohol may include one or more selected from the group consisting of methanol, ethanol, propanol, isopropanol, and butanol.

The alkoxysilane compound synthesized by adding an alcohol to the silazane-based compound represented by Formula <NUM> and allowing the alcohol to react with the silazane-based compound may include one or more selected from the group consisting of a monoalkoxysilane compound, a dialkoxysilane compound, and a trialkoxysilane compound. When the alcohol is a compound represented by the following Formula <NUM>, the alkoxysilane compound is specifically a compound represented by the following Formula <NUM>:.

[Formula <NUM>]     (R<NUM>)n(R<NUM>)<NUM>-nSi-O-R<NUM>.

wherein R<NUM> and R<NUM> are each independently an alkyl group having <NUM> to <NUM> carbon atoms, R<NUM> is a hydrogen atom or an alkyl group having <NUM> to <NUM> carbon atoms, and n is an integer ranging from <NUM> to <NUM>.

Also, R<NUM> and R<NUM> may be each independently an alkyl group having <NUM> to <NUM> carbon atoms, and R<NUM> may be a hydrogen atom or an alkyl group having <NUM> to <NUM> carbon atoms.

In addition, R<NUM> and R<NUM> may be each independently an alkyl group having <NUM> to <NUM> carbon atoms, R<NUM> may be each independently a hydrogen atom or an alkyl group having <NUM> to <NUM> carbon atoms.

The reaction of the alcohol with the silazane-based compound may be represented by the following Scheme <NUM>. In this case, one equivalent of the silazane-based compound is reacted with <NUM> equivalents of the alcohol to generate <NUM> equivalents of the alkoxysilane compound, and one equivalent of ammonia is generated as a by-product. The first mixture thus prepared may include an alkoxysilane compound and ammonia:
<CHM>
wherein R<NUM> to R<NUM> and n are as defined in Formulas <NUM>, <NUM> and <NUM>.

In Step (<NUM>), an acid with pKa <NUM> to <NUM> is added and reacted with the prepared first mixture so that ammonia is converted into an ammonium salt through a reaction of ammonia with the acid with pKa <NUM> to <NUM>. Then, the ammonia converted into the ammonium salt may be removed through subsequent processes.

It is apparent that ammonia included in the first mixture is reacted with the acid so that the ammonia is converted into an ammonium salt through an acid-base neutralization reaction. However, it should be considered that the acid added to the first mixture may cause a side reaction with the alkoxysilane compound that is a target compound included in the first mixture. The alkoxysilane compound may be decomposed into an alkylsilanol and an alkyldisiloxane in an acidic aqueous solution, and such a side reaction causes a decrease in yield of the alkoxysilane compound to be manufactured according to the present invention. When the ammonia included in the first mixture is reacted with the acid to generate an ammonium salt and the ammonium salt is dissolved so that the first mixture becomes weakly acidic, the alkoxysilane compound included in the first mixture is decomposed into an alkylsilanol and an alkyldisiloxane.

Therefore, in Step (<NUM>), the acid with pKa <NUM> to <NUM> may be added and reacted with the first mixture. In this way, the second mixture including the alkoxysilane compound and an ammonium salt is prepared through an acid-base reaction of ammonia with the acid.

Specifically, the acid with pKa <NUM> to <NUM> may include one or more selected from the group consisting of acetic acid, phosphoric acid, fluoroacetic acid, chloroacetic acid, citric acid, and formic acid.

According to one embodiment of the present invention, the acid may also be an acid with pKa <NUM> to <NUM>, and more specifically an acid with pKa <NUM> to <NUM>. According to one embodiment of the present invention, acetic acid may be used as acid. In this case, the acetic acid has a pKa of <NUM>. When the ammonium salt generated after the acid is reacted with ammonia with pKb <NUM> is dissolved again, the pH value of the resulting solution may become close to pH <NUM>, thereby inhibiting the side reaction in which the alkoxysilane compound is decomposed into an alkylsilane and an alkyldisiloxane.

When the acid with pKa <NUM> to <NUM> is added and reacted with the first mixture to prepare the second mixture including the alkoxysilane compound and an ammonium salt, the pH of the second mixture may be in a range of pH <NUM> to <NUM>, specifically in a range of pH <NUM> to <NUM>, and more specifically pH <NUM>. When the pH of the second mixture satisfies the above pH range, a side reaction in which the alkoxysilane compound is decomposed into an alkylsilane and an alkyldisiloxane may be inhibited.

The acid with pKa <NUM> to <NUM> may be added to the first mixture at an equivalence ratio of <NUM>:<NUM> to <NUM>:<NUM>, specifically an equivalence ratio of <NUM>:<NUM> to <NUM>:<NUM>, and more specifically an equivalence ratio of <NUM>:<NUM> with respect to the ammonia in the first mixture. When the acid is added to the first mixture at the above equivalence ratio with respect to the ammonia in the first mixture, ammonia may be effectively removed, and a side reaction in which the alkoxysilane compound is decomposed into an alkylsilane and an alkyldisiloxane may also be inhibited. When the acid is added at an amount much lower than ammonia in the first mixture, ammonia may be not completely converted into the ammonium salt, which results in poor ammonia removal efficiency, or the generated ammonium salt may be dissolved again to generate ammonia. On the other hand, when the acid is added at an amount much larger than ammonia in the first mixture, the pH of the second mixture may be lowered, and a side reaction in which the alkoxysilane compound is decomposed into an alkylsilane and an alkyldisiloxane may be induced.

According to one embodiment of the present invention, when the acid with pKa <NUM> to <NUM> is acetic acid, the acetic acid may be added at the same equivalent(s) as ammonia in the first mixture. Because the acetic acid has a pKa of <NUM>, which is identical to the pKb of the ammonia, when the acetic acid is added to the first mixture at the same equivalent(s) as ammonia in the first mixture, the pH of the prepared second mixture including the alkoxysilane compound and the ammonium salt becomes close to pH <NUM>, which makes it possible to prevent the problems regarding the conversion of the alkoxysilane compound.

In order to add the acid with pKa <NUM> to <NUM> to the first mixture at the above equivalence ratio with respect to ammonia in the first mixture, the method of manufacturing an alkoxysilane compound according to one embodiment of the present invention may further include: measuring a concentration of ammonia included in the first mixture before adding the acid to the first mixture. For example, after the alcohol is added and reacted with the silazane-based compound represented by Formula <NUM> as shown in Step (<NUM>), a concentration of ammonia included in the first mixture may be measured. Thereafter, the acid may be added at an appropriate equivalence ratio based on the concentration of ammonia.

In Step (<NUM>), an aqueous solvent is added to the second mixture to dissolve the ammonium salt converted from ammonia in Step (<NUM>). The second mixture includes an alkoxysilane compound and an ammonium salt. In this case, because the alkoxysilane compound is not dissolved in the aqueous solvent and only the ammonium salt is dissolved in the aqueous solvent, the ammonium salt may be separated into an aqueous layer.

The aqueous solvent is used to dissolve the ammonium salt converted from ammonia in Step (<NUM>). Therefore, the aqueous solvent may be used to dissolve the ammonium salt without dissolving the alkoxysilane compound. For example, the aqueous solvent may be water. In this case, the water may be process water, specifically distilled water or ion-exchanged water.

In Step (<NUM>), an aqueous layer in which the ammonium salt is dissolved is separated and removed from an organic layer of the alkoxysilane compound to obtain a desired alkoxysilane compound.

As such, the alkoxysilane compound used for hydrophobic surface modification of a silica aerogel may be manufactured from the silazane-based compound using the method of manufacturing an alkoxysilane compound according to the present invention.

Specifically, according to one embodiment of the present invention, the silazane-based compound represented by Formula <NUM> may be hexamethyldisilazane, the alcohol may be ethanol, and the acid with pKa <NUM> to <NUM> may be acetic acid.

When ethanol is added and reacted with the hexamethyldisilazane, a first mixture including trimethylethoxysilane and ammonia is prepared.

When ammonia included in the first mixture is reacted with acetic acid, ammonia is converted into an ammonium salt, and the acetic acid added according to the equivalent(s) of ammonia does not affect the trimethylethoxysilane. In this way, the method of manufacturing an alkoxysilane compound according to one embodiment of the present invention may have an effect of converting ammonia, which is a by-product generated by the decomposition of the hexamethyldisilazane without any side reactions of the trimethylethoxysilane, into an ammonium salt in order to remove ammonia.

Meanwhile, according to one embodiment of the present invention, the reaction of the alcohol with the silazane-based compound of Step (<NUM>) may be performed under the condition of an acid catalyst. The acid catalyst may be used to promote a reaction of the alcohol with the silazane-based compound. In this case, the acid catalyst may include one or more selected from the group consisting of nitric acid, hydrochloric acid, acetic acid, sulfuric acid, and hydrofluoric acid.

Hereinafter, exemplary embodiments of the present invention will be described in detail so that a person having ordinary skill in the art to which the present invention belongs can easily put the invention into practice.

A solution obtained by mixing hexamethyldisilazane (HMDS), ethanol, and HCl at a mole ratio of <NUM>:<NUM>:<NUM> was stirred at room temperature for <NUM> hours to synthesize trimethylethoxysilane (TMES), and a concentration of ammonia in the synthesized trimethylethoxysilane (TMES) was measured. Thereafter, acetic acid was added at the same equivalent(s) as the measured concentration of ammonia to generate a salt precipitate. The pH of the mixture in which the salt precipitate was generated was pH <NUM>.

Distilled water was added to the generated trimethylethoxysilane at a volume ratio of <NUM>:<NUM>, and stirred to dissolve the salt precipitate. Then, an aqueous layer was discarded to obtain trimethylethoxysilane (TMES) from which ammonia was removed.

Trimethylethoxysilane from which ammonia was removed was obtained in the same manner as in Example <NUM>, except that hexamethyldisilazane and ethanol were mixed at a mole ratio of <NUM>:<NUM>, and then reacted for <NUM> hours under a reflux condition at <NUM>.

Trimethylethoxysilane from which ammonia was removed was obtained in the same manner as in Example <NUM>, except that phosphoric acid was used instead of acetic acid, and used in an amount twice the measured equivalent of ammonia. When phosphoric acid was used instead of acetic acid, as an equivalent of phosphoric acid corresponding to the measured equivalent of ammonia was added, the generated ammonium salt [(NH<NUM>)<NUM>PO<NUM>] was dissolved back in the solution to generate ammonia, thereby causing an increase in pH. Therefore, phosphoric acid was used in an amount twice the equivalent of ammonia. As result, the pH of the resulting mixture in which the salt precipitate was generated was pH <NUM>.

Trimethylethoxysilane from which ammonia was removed was obtained in the same manner as in Example <NUM>, except that citric acid was used instead of acetic acid. The pH of the mixture in which the salt precipitate was generated was pH <NUM>.

Trimethylethoxysilane from which ammonia was removed was obtained in the same manner as in Example <NUM>, except that acetic acid was used in an excessive amount (<NUM> equivalents) compared to the equivalent of ammonia. As result, the pH of the resulting mixture in which the salt precipitate was generated was pH <NUM>.

Hexamethyldisilazane and ethanol were mixed at a mole ratio of <NUM>:<NUM>, and then reacted for <NUM> hours under a reflux condition at <NUM> to synthesize trimethylethoxysilane, and the synthesized trimethylethoxysilane was distilled to obtain trimethylethoxysilane.

Hexamethyldisilazane and ethanol were mixed at a mole ratio of <NUM>:<NUM>, and then reacted for <NUM> hours under a reflux condition at <NUM> to synthesize trimethylethoxysilane, and the synthesized trimethylethoxysilane was further refluxed at <NUM> for <NUM> hours to obtain trimethylethoxysilane.

Hexamethyldisilazane and ethanol were mixed at a mole ratio of <NUM>:<NUM>, and then reacted for <NUM> hours under a reflux condition at <NUM> to synthesize trimethylethoxysilane, and the synthesized trimethylethoxysilane was further refluxed at <NUM> for <NUM> hours, and then distilled to obtain trimethylethoxysilane.

Trimethylethoxysilane from which ammonia was removed was obtained in the same manner as in Example <NUM>, except that hydrochloric acid was used instead of acetic acid.

A content of ammonia in the trimethylethoxysilane and a content of ammonia remaining in the finally obtained trimethylethoxysilane were titrimetrically analyzed using sulfuric acid, and measured using <NUM> Titrino plus commercially available from Metrohm AG.

The yield of trimethylethoxysilane was calculated according to the following Mathematical Expression <NUM>.

As shown in Table <NUM>, it can be seen that the final remaining ammonia was not observed in the case of Examples <NUM> to <NUM>, but ammonia finally remained in the case of Comparative Examples <NUM> to <NUM>, thereby confirming more effective removal of ammonia from the trimethylethoxysilane manufactured by the manufacturing method described in Examples <NUM> to <NUM>.

Also, it can be seen that ammonia was discharged in the form of a gas and removed by distillation after the trimethylethoxysilane was synthesized through a reflux reaction of hexamethyldisilazane and ethanol in the case of Comparative Example <NUM>, and that ammonia was discharged in the form of a gas by further refluxing the synthesized trimethylethoxysilane in the case of Comparative Example <NUM>, but the final remaining ammonia was included in the trimethylethoxysilane. In the case of Comparative Example <NUM>, the synthesized trimethylethoxysilane was further refluxed and then re-distilled to further reduce a content of the final remaining ammonia, but ammonia finally remained in the trimethylethoxysilane, and loss of trimethylethoxysilane by the refluxing and distillation occurred.

In terms of the manufacturing time, a total of <NUM> hours was spent to manufacture the trimethylethoxysilane in the case of Examples <NUM> to <NUM>, which was shorter than those of Comparative Examples <NUM> and <NUM> in which a total of <NUM> hours and a total of <NUM> hours were spent to manufacture the trimethylethoxysilane, respectively. In the case of Comparative Example <NUM>, because only the synthesis and distillation of the trimethylethoxysilane were performed, the manufacturing time was only <NUM> hours in total, which was shorter than those of Examples <NUM> to <NUM>. However, Comparative Example <NUM> had inferior effects to Examples <NUM> to <NUM> in that the yield of trimethylethoxysilane by distillation was low and a large amount of ammonia finally remained in the trimethylethoxysilane.

In the case of Comparative Example <NUM>, compared to Examples <NUM> to <NUM>, the final remaining ammonia was also not observed, but the yield of trimethylethoxysilane was lower. Based on the fact that the trimethylethoxysilane of Comparative Example <NUM> had a low yield, it was found that the mixture was extremely acidic because hydrochloric acid was used as the acid, and the alkoxysilane compound as the product thus synthesized was decomposed into alkylsilanol and alkyldisiloxane through a side reaction with the acid.

Meanwhile, it was confirmed from the comparison between Examples that the Examples <NUM> and <NUM> had a higher yield than Examples <NUM> to <NUM>. As a result, it was confirmed that a side reaction by which the alkoxysilane compound was decomposed into alkylsilanol and alkyldisiloxane was suppressed to the maximum extent because acetic acid was used in the case of Examples <NUM> and <NUM> so that the mixture was reacted in a pH range close to pH <NUM>. However, it was confirmed that an additional amount of phosphoric acid was used relative to the equivalent of residual ammonia in order to remove ammonia generated by dissolving the generated ammonium phosphate salt in the case of Example <NUM>, and some side reactions occurred when the mixture had a relatively low pH value of <NUM> because citric acid was used in the case of Example <NUM>. Also, it was confirmed that the yield of trimethylethoxysilane was relatively reduced when the alkoxysilane compound as the product was decomposed into alkylsilanol and alkyldisiloxane through a side reaction with the acid because the mixture had a relatively low pH value of <NUM> because an excessive amount of acetic acid was used relative to the equivalent of ammonia in the case of Example <NUM>.

Claim 1:
A method of manufacturing an alkoxysilane compound, comprising:
(<NUM>) adding an alcohol to a silazane-based compound represented by the following Formula <NUM> and allowing the alcohol to react with the silazane-based compound to prepare a first mixture comprising an alkoxysilane compound and ammonia;
(<NUM>) adding an acid with pKa <NUM> to <NUM> to the first mixture and allowing the acid to react with the first mixture to prepare a second mixture comprising the alkoxysilane compound and an ammonium salt;
(<NUM>) adding an aqueous solvent to the second mixture to dissolve the ammonium salt; and
(<NUM>) separating and removing the aqueous layer, in which the ammonium salt is dissolved, to obtain the alkoxysilane compound:
<CHM>
wherein the alcohol is a compound represented by the following Formula <NUM>, and the alkoxysilane compound is a compound represented by the following Formula <NUM>:

        [Formula <NUM>]     R<NUM>OH

        [Formula <NUM>]     (R<NUM>)n(R<NUM>)<NUM>-nSi-O-R<NUM>

wherein R<NUM> and R<NUM> are each independently an alkyl group having <NUM> to <NUM> carbon atoms, R<NUM> is a hydrogen atom or an alkyl group having <NUM> to <NUM> carbon atoms, and n is an integer ranging from <NUM> to <NUM>.