JPH02160792A - Preparation of tetraalkoxysilane - Google Patents

Abstract

PURPOSE:To continuously provide the subject silane useful for semiconductors, etc., in an increased production rate in a enhanced productivity by controlling the content of the produced higher tetraalkoxysilane in an ester exchange reaction system. CONSTITUTION:In an ester exchange reaction system using (A) tetramethoxysilane or alkoxysilanes containing the tetraalkoxysilane as a main component, (C) steam, the condensate thereof or one part of the reaction solution is taken out from the reaction system to separate one part or all of the produced higher tetraalkoxysilane from the component C and return the separated component C to the reaction system, thereby providing the objective silane whose alkoxy groups have >=2 carbon atoms. The methanol by-produced in the reaction is preferably reacted with silicon metal to prepare the component A.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing higher-order tetraalkoxysilane in which the alkoxy group has two or more carbon atoms.

A conventional method for producing higher tetraalkoxysilane 5i (OR) in which the alkoxy group has two or more carbon atoms (wherein R is an alkyl group having two or more carbon atoms (the same applies hereinafter)) The following three methods are known.

■ A method for producing 5L(OR)4 by reacting 5iCffi4 with an alkyl alcohol.

■ A method for producing 5i (OR) by reacting metallic silicon with an alkyl alcohol in the presence of an alkali catalyst (
For example, Japanese Patent Application Laid-open No. 149290/1983).

■ Tetramethoxysilane S in the presence of an alkali catalyst
RO to i(OMeL (Me: CH,, same below)
A method for producing 5L (OR) by transesterification reaction with H (for example, Chew, Ber, 80 1
63-4 ('47)).

However, since the higher-order tetraalkoxysilane produced by the method (2) contains zero impurities, it is not suitable for use in electronic materials that require high purity such as semiconductors.

In addition, method (2) can be produced under normal pressure conditions when the alcohol is methanol, but when producing higher tetraalkoxysilane using an alcohol with 2 or more carbon atoms, the reaction cannot be performed under normal pressure. Since the reaction rate is too slow to be practical, a pressurized reaction is required. However, compared to normal pressure reaction, pressurized reaction not only requires more investment in equipment and equipment, but also makes it difficult to make the equipment continuous and large-scale, which are essential for commercial production. Moreover, there is a problem that it is difficult to maintain the initial reaction rate thereafter.

On the other hand, the method (2) of producing higher-order tetraalkoxysilane from tetramethoxysilane by transesterification can produce higher-order tetraalkoxysilane that does not contain CU as an impurity, does not require pressurization, and can easily produce high-purity tetraalkoxysilane. This is a method by which alkoxysilane can be obtained,
When higher-order tetraalkoxysilane is produced and accumulated in the reaction system, the rate of reaction per reactor is delayed, continuous production is not possible, and productivity is poor.

That is, method (■) is carried out by the transesterification reaction shown below, Si(OMe), + 4ROH→5i(OR), +
This is due to a sequential equilibrium reaction as shown by the following equation: 4Me○H.

Si(OMe), + ROH';i Si(OMe
), (OR) +MeOH8i(OMe), OR+ R
OM';! Si(OMe), (OR), + Me
OH8i(OMe)2(OR), + ROH'd
Si(OMe)(OR), +MeOH8i(OMa
)(OR), + ROM';i 5i(OR)
, + MeOH Therefore, the product (right side) in the reaction system
As the concentration increases and approaches equilibrium, the reaction progresses more slowly. In this case, among the reaction products, methanol has a lower boiling point than alkyl alcohol (ROM), so it can be easily removed by distillation out of the reaction system.
a) 30 R-S l(OMa)2(OR)z, S
Because l(OMa)(OR)x is consumed as the transesterification reaction progresses.

It does not accumulate in the reaction system. On the other hand, the final product 5i (OR) has the highest boiling point in the reaction system and cannot be removed by distillation out of the reaction system, but gradually accumulates in the reaction system.

Therefore, the reaction rate slows down, and the Si(OR)4 in the system
As the concentration increases, the transesterification reaction becomes extremely slow as shown in Figure 4, and the immediate intermediate product Si
(OMa)(OR)3 no longer disappears.

Here, the transesterification reaction of tetramethoxysilane is carried out, for example, in an apparatus as shown in FIG. To explain this specifically, Si(OMe)4 and Na,
ROH is continuously introduced into reactor A containing a catalyst such as NaOR or para-toluenesulfonic acid, and the above equilibrium reaction is allowed to proceed at the boiling point. In this case, in order to advance the equilibrium reaction toward the production side, the vapor containing by-product M e OH is transferred to the separation column B.
where the ROH1 intermediate product S L (OMe)
4-x(OR)X and higher tetraalkoxysilane Si
(OR)4 is separated from M e OH and these are returned to the reaction system, and M e OH is discharged from the system, but as mentioned above, higher tetraalkoxysilane accumulates in the reaction solution. As the concentration of ROH increases, the reaction rate decreases extremely, so it is necessary to gradually reduce the rate of introduction of ROH. If the introduction rate of ROH is high, more ROM will be added than is consumed in the reaction, which will increase the concentration of ROH in the reaction solution and lower the reaction temperature (boiling point).
Since the reaction rate decreases, the reaction rate also decreases further. Therefore, in the above method, the introduction rate of ROH must be extremely reduced, resulting in extremely low productivity.

The present invention was made in view of the above circumstances, and an object of the present invention is to improve the production rate of higher-order tetraalkoxysilane by transesterification reaction, increase productivity, and provide a method that can continuously produce higher-order tetraalkoxysilane. With the goal.

In order to achieve the above object, the inventors of the present invention have conducted intensive studies and found that a higher order In a method for producing tetraalkoxysilane, vapor generated from the reaction system, its condensate, or a part of the reaction liquid is taken out of the reaction system, and the target substance, higher tetraalkoxysilane, is separated by means such as fractional distillation. After that, the concentration of higher tetraalkoxysilane in the reaction solution is controlled by returning it to the reaction system.
It has been found that the transesterification reaction, which is an equilibrium reaction, proceeds to the production side, improving the production rate of higher tetraalkoxysilane, and making it possible to continuously produce higher tetraalkoxysilane.

The present inventor further discovered that it is effective to use methanol produced by the transesterification reaction to react with silicon metal, and to use this reaction product as a raw material for the transesterification reaction described above. .

According to the present invention, the production speed of the entire system was extremely slow due to the speed of the transesterification reaction, and it was difficult to achieve continuous production. Two-step reaction method Si + 4MeOH→Si(OMe)4+ 2H.

Si + 4ROH ← 5i (OR), + 2H.

SL + 4ROH → Si(OR) 4+ 2H Direct reaction method of metallic silicon and higher alcohol, which required pressurization and had many industrial problems. .

On the other hand, it enables continuous production as a total system under the industrially advantageous conditions of normal pressure and with high productivity.

Therefore, the present invention produces a higher tetraalkoxysilane having an alkoxy group having two or more carbon atoms by transesterification using tetramethoxysilane or an alkoxysilane containing tetramethoxysilane as a main component and an alcohol having two or more carbon atoms. After removing a part of the vapor or its condensate or reaction liquid generated from one reaction system in the method from the reaction system, and separating part or all of the higher tetraalkoxysilane from the vapor, its condensate, or the reaction liquid. , by returning this vapor or its condensate or reaction liquid to the reaction system again,
A method for producing tetraalkoxysilane, characterized by controlling the concentration of higher tetraalkoxysilane in a reaction solution,
and a method for producing a higher tetraalkoxysilane in which the alkoxy group has two or more carbon atoms by transesterification using tetramethoxysilane or an alkoxysilane containing it as a main component and an alcohol having two or more carbon atoms,
After taking out the vapor generated from the reaction system, its condensate, or a part of the reaction liquid, and separating part or all of the higher tetraalkoxysilane from the vapor, its condensate, or the reaction liquid, the vapor is removed again. By returning the vapor or its condensate or reaction solution to the reaction system, the concentration of higher tetraalkoxysilane in the reaction solution can be controlled, and the methanol produced in the transesterification reaction can be reacted with metallic silicon to produce the tetramethoxysilane. Alternatively, it provides a method for producing tetraalkoxysilane, which is characterized by producing an alkoxysilane containing the tetraalkoxysilane as a main component.

The present invention will be explained in more detail below.

The method for producing higher tetraalkoxysilane of the present invention uses tetramethoxysilane or an alkoxysilane containing tetramethoxysilane as a main component and an alcohol having 2 or more carbon atoms as raw materials.

Here, the method for producing tetramethoxysilane or an alkoxysilane containing tetramethoxysilane as a main component is not particularly limited, and any known method may be adopted, but methanol or a mixture of it and an aliphatic lower alcohol having 2 or more carbon atoms may be used. A method of reacting the methanol with silicon under normal pressure in the presence of an alkali catalyst is preferably adopted, and as methanol, it is effective to use a by-product in the transesterification reaction according to the present invention. In addition,
As the alkali catalyst, any known one can be used, and the reaction conditions can be any conventional method.

On the other hand, the alcohol having 2 or more carbon atoms to be exchange-reacted with tetramethoxysilane or an alkoxysilane containing tetramethoxysilane as a main component is selected depending on the desired higher tetraalkoxysilane, such as ethanol or propatool, but usually has 2 carbon atoms. ~4 aliphatic alcohols are used.

In addition, for the above transesterification reaction, known alkali catalysts include alkali metal alkoxides such as sodium methylate and potassium methylate, alkali metals such as sodium and potassium, and acid catalysts such as trifluoroacetic acid and p-toluenesulfonic acid. can be added in a catalytic amount.

In the present invention, the transesterification reaction conditions can be carried out according to conventional methods, but it is preferable to carry out the transesterification reaction at normal pressure and boiling point.

Therefore, in the transesterification reaction, the present invention extracts the vapor generated from the reaction system, its condensate, or a part of the reaction liquid out of the reaction system, and extracts a part of the higher tetraalkoxysilane, which is the target substance, from the reaction system. Alternatively, after separating the entire reactor and removing methanol, this vapor, its condensate, or the reaction solution is returned to the reaction system, thereby controlling the higher tetraalkoxysilane concentration in the reaction solution. Here, the extraction of steam or its condensate or reaction liquid may be performed continuously or intermittently, but
The concentration of higher tetraalkoxysilane in the reaction solution is 10~
It is preferable to control the reaction rate to 50%, thereby making it possible to continuously and efficiently produce higher tetraalkoxysilane at a high reaction rate. In contrast,
When the concentration of higher tetraalkoxysilane exceeds 50%, the reaction rate decreases, while when it is lower than 10%, the reaction rate increases, but high Since the amount of components other than tetraalkoxysilane increases, this may be disadvantageous in terms of energy cost.

Next, the first method, which shows one embodiment of the present invention regarding the above method, will be described.
This will be explained in detail with reference to FIG.

In FIG. 1, A is a reactor, B is a first separation column, and C is a second separation column. First, reactor A is charged with Na.

A catalyst such as NaOR or paratoluenesulfonic acid is charged, and tetramethoxysilane or an alkoxysilane containing tetramethoxysilane as the main component is introduced from the raw material silane supply pipe 1.
Alcohol ROH having 2 or more carbon atoms is introduced from the raw alcohol supply pipe 2 to carry out a transesterification reaction. The vapor is then sent to the first separation column B, where methanol is separated.

Methanol is discharged to the outside of the thread through the discharge pipe 3, and the liquid from which methanol has been removed is returned to the reactor A through the return pipe 4.
Alternatively, it may be introduced into the second separation column C through the introduction pipe 5 as appropriate. In addition, in some cases, steam or a part of its condensate or reaction liquid may be directly introduced from the reactor A through the pipe 6 to the second separation column C.
send to In this second separation column C, higher tetraalkoxysilane is separated and extracted from an extraction pipe 7 provided at the bottom of the column. On the other hand, the high-order tetraalkoxysilane is separated, and the treated product containing low boiling point components S L (OMe) n-x (OR) Return to reactor A again. As a result, the higher tetraalfukidisilane Si(O
The concentration of R)4 is controlled to allow the reaction to proceed efficiently, and depending on the progress of the reaction, the reduced raw material silane and raw material alcohol are introduced from the above-mentioned tube 1.2.

In this case, if the liquid supplied to separation column C is the reaction liquid, the catalyst will accompany the target substance, higher tetraalkoxysilane, and a purification step will be required later. It is preferred to introduce a portion of the condensate of the boiling point vapor.

FIG. 2 shows another embodiment of the present invention, in which the apparatus shown in FIG. 1 is combined with an apparatus for producing raw material silane. By closing the process, higher tetraalkoxysilane is continuously produced from Si and M e OH.

That is, in FIG. 2, D is a reactor for producing raw material silane, and the methanol discharge pipe 3 is connected to this reactor, and the Si introduced from the Si supply pipe 9 and the discharged Tetramethoxysilane is produced by reaction with methanol sent from pipe 3. The reaction product thus obtained is then transferred to the introduction pipe 10.
unreacted methanol is separated from the top of the column and returned to the reactor via return pipe 11, while tetramethoxysilane is introduced into the third separation column E. The raw material silane is introduced into the transesterification reactor A from the raw material silane supply pipe 1 connected to the bottom, and the subsequent steps are the same as those in the embodiment shown in FIG. 1, so their explanation will be omitted.

Therefore, according to the method shown in Fig. 2, higher tetraalkoxysilane can be produced continuously and efficiently from metallic silicon and ROM, which was difficult to perform in a continuous system due to the slow transesterification rate. This makes it possible to manufacture.

The method of the present invention advances the transesterification reaction toward the production side by controlling the amount of higher tetraalkoxysilane present in the transesterification reaction system, which is an equilibrium reaction, to produce higher tetraalkoxysilane. In addition to improving the speed, higher tetraalkoxysilane can be produced continuously and efficiently, and the productivity of the conventional method for producing higher tetraalkoxysilane by transesterification, which has low productivity, can be increased. be. Furthermore, when the process of obtaining tetramethoxysilane from metal silicon and methanol is combined with the above process, especially when using methanol as a by-product in the above transesterification reaction, higher tetraalkoxysilane can be obtained from metal silicon. get 2
The stepwise reaction method can be made into a continuous system and can be manufactured continuously with high productivity.

EXAMPLES Hereinafter, the present invention will be specifically explained by showing examples and comparative examples, but the present invention is not limited to the following examples.

〔Example〕

According to the apparatus shown in FIG. 1, 100 g of tetramethoxysilane, 145 g of ethanol, and 0.76 g of sodium were charged into reactor A (glass flask).

The mixture was refluxed for 6 hours while stirring. At this time, the production rate of tetraethoxysilane was 31.9% based on the total alkoxysilane in one reaction solution.

Next, the methanol by-produced in the first separation column B is continuously distilled off, and 25 g of ethanol is added to the reactor A.
The reaction solution was sent to the third separation column C, and tetraethoxysilane was separated from the bottom of the column, and the remaining S x (OMe)4-1 (o E t) x and ethanol were reacted. The mixture was returned to vessel A, and tetraethoxysilane was continuously produced for 12 hours.

The total yield of tetraethoxysilane was 116.2g, the average yield per hour was 9.7g/)Ir, and the amount of ethanol consumed was 235g (theoretical amount was 121g), so tetraethoxysilane could be obtained efficiently. .

[Comparative example]

According to the apparatus shown in FIG. 3, 100 g of tetramethoxysilane, 145 g of ethanol, and 0.76 g of sodium were charged into reactor A (glass flask) and refluxed with stirring. As the transesterification reaction progresses, the proportion of by-product methanol in the reaction product increases and the steam temperature changes, but after 5 hours, the steam temperature became constant, so methanol was separated in separation column B. All methanol in the reactor was distilled off.

Next, 50 g of ethanol was added, and reflux was similarly continued until the vapor temperature became constant, and after 8 hours, all by-product methanol was similarly distilled out from the reactor.

The above operations of adding ethanol and distilling by-product methanol were repeated four more times, and the transesterification reaction was carried out over a total of 50 hours.

As a result, the yield of tetraethoxysilane was 110.3g.
The average yield per hour was 2.2 g/Hr, and the amount of ethanol consumed was 395 g, which was very inefficient compared to the example.

The relationship between the reaction rate and the tetraethoxysilane concentration obtained in the comparative example is shown in FIG. 4. From FIG. 4, when the concentration of the reaction product, tetraethoxysilane, exceeds 50%, E:SiOMe + EtOH→:'5iOEt+
It can be seen that the reaction rate of MeOH becomes very slow. For example, when the tetraethoxysilane concentration is about 30%.

While the reaction rate is 0.25 mol Eta/Hr,
When the tetraethoxysilane concentration exceeds about 80%, one reactor degree is about 0.02 mol EtO/)Ir, which is about 1/1o
It can be seen that the value decreases to .

[Brief explanation of the drawing]

Figures 1 and 2 are process diagrams for explaining one embodiment of the production method of the present invention, Figure 3 is a process diagram for explaining the conventional production method, and Figure 4 is a process diagram for explaining an embodiment of the production method of the present invention. It is a graph showing transesterification reaction rate versus production rate. A...Transesterification reactor, B...First separation column, C...Second separation column, D...
Alkoxysilane production reactor. E...Third separation tower. Applicant Shin-Etsu Chemical Co., Ltd. Agent Patent Attorney Takashi Kojima eOH Fig. 2 5i (Qg) 1 11111eOH Fig. 4 Time to Friend

Claims (1)

[Claims] 1. A higher tetraalkoxysilane having an alkoxy group having two or more carbon atoms is produced by transesterification using tetramethoxysilane or an alkoxysilane containing tetramethoxysilane as a main component and an alcohol having two or more carbon atoms. In the method of manufacturing,
After taking out the vapor generated from the reaction system, its condensate, or a part of the reaction liquid, and separating part or all of the higher tetraalkoxysilane from the vapor, its condensate, or the reaction liquid, the vapor is removed again. A method for producing tetraalkoxysilane, which comprises controlling the concentration of higher tetraalkoxysilane in a reaction solution by returning vapor, its condensate, or the reaction solution to the reaction system. 2. A method for producing a higher tetraalkoxysilane in which the alkoxy group has two or more carbon atoms by transesterification using tetramethoxysilane or an alkoxysilane containing tetramethoxysilane as a main component and an alcohol having two or more carbon atoms,
After taking out the vapor generated from the reaction system, its condensate, or a part of the reaction liquid, and separating part or all of the higher tetraalkoxysilane from the vapor, its condensate, or the reaction liquid, the vapor is removed again. By returning the vapor or its condensate or reaction solution to the reaction system, the concentration of higher tetraalkoxysilane in the reaction solution can be controlled, and the methanol produced in the transesterification reaction can be reacted with metallic silicon to produce the tetramethoxysilane. Or a method for producing tetraalkoxysilane, which comprises producing an alkoxysilane containing this as a main component.