JPH10158270A - Separation of trimethoxysilane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously and accurately separate trimethoxysilane from a mixture containing methanol and the trimethoxysilane. SOLUTION: This distillation is carried out at a weight ratio of cyclohexane to methanol fed to a distillation column per unit time within the range of 2.0 <=cyclohexane/methanol <= 4.0 in the method for continuously separating trimethoxysilane from a mixture containing the methanol and the trimethoxysilane according to the azeotropic distillation using the cyclohexane as an azeotropic agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for continuously separating methanol and trimethoxysilane from a mixture containing methanol and trimethoxysilane, and finally isolating industrially useful trimethoxysilane. About.

[0002]

2. Description of the Related Art Trimethoxysilane is widely used as a raw material for a silane coupling agent, a raw material for producing monosilane gas serving as a semiconductor substrate, or a raw material for an insulating film (silica film) for a semiconductor itself. With its remarkable growth, its usefulness has attracted attention. Therefore, development of a method for industrially and inexpensively producing trimethoxysilane is strongly desired.

As a method for producing trimethoxysilane, generally, a method of reacting trichlorosilane with methanol (reaction formula [1]) and a method of reacting silicon metal with methanol (reaction formula [2]) are known. However, trichlorosilane is difficult to handle, and hydrochloric acid is generated in the former, so that the latter is more industrially advantageous from the viewpoint of equipment advantages and production costs.

HSiCl ₃ + 3CH ₃ OH → HSi (OCH ₃ ) ₃ + 3HCl ... [1] Si (s) + 3CH ₃ OH → HSi (OCH ₃ ) ₃ + 3 / 2H ₂ ... [2] More specifically, a method in which metal silicon powder and methanol are reacted at 200 to 300 ° C. under normal pressure or pressure under the presence of copper or its compound catalyst. Several methods have been disclosed for enhancement.

For example, a method of reacting silicon and methanol in a specific solvent (for example, Japanese Patent Publication No. 63-3869 and Japanese Patent Application Laid-Open No. 57-99593), a method of reacting using a specific catalyst ( For example, JP-A-62-2869
92, JP-A-5-170773). However, regardless of which method is used, the product is a mixture of trimethoxysilane, unreacted methanol, and by-product tetramethoxysilane. Therefore, an operation for separating trimethoxysilane from these mixtures is required.

[0006] Distillation is a common operation, but methanol and trimethoxysilane form a minimum azeotrope, and cannot be separated accurately by ordinary distillation operations. For this reason, several separation methods have been devised.

For example, Japanese Patent Publication No. 4-55556 discloses a method of extracting and distilling a compound having a dipole moment of 1.61 Debye or less as an extraction solvent. According to this method, methanol and trimethoxysilane can be separated.However, in order to isolate trimethoxysilane, a separation operation between an extraction solvent and trimethoxysilane is required. However, since one distillation column is required, the equipment becomes large and energy is disadvantageous.

Further, Japanese Patent Publication No. 7-17657 discloses that in the reaction of silicon metal with methanol, a mixture having an increased azeotropic composition of methanol and trimethoxysilane in which the production ratio of trimethoxysilane is increased is distilled. A method for obtaining trimethoxysilane from is disclosed. According to this method,
An azeotropic composition of methanol and trimethoxysilane is obtained from the top of the column and circulated to the reaction system.At this time, the reaction between methanol and trimethoxysilane produces tetramethoxysilane, so that trimethoxysilane is practically used. Is lost.

On the other hand, Japanese Patent Publication No. 61-39955 discloses benzene, cyclohexane, n-hexane and n-hexane.
A method for performing azeotropic distillation using heptane as an azeotropic agent is disclosed. This is a method in which a substance that forms the lowest azeotrope with methanol at a temperature lower than the azeotropic point of methanol and trimethoxysilane is added as a third component and distilled. However, there is no mention of a method for industrially separating methanol and trimethoxysilane continuously,
Also, the separation accuracy between methanol and trimethoxysilane was not sufficient.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for continuously and accurately separating trimethoxysilane from a mixture containing methanol and trimethoxysilane.

[0011]

Means for Solving the Problems The present inventors have studied the purpose presented above, that is, a method for continuously and accurately separating trimethoxysilane from a mixture containing methanol and trimethoxysilane. Industrially, the distillation operation described in JP-B-61-39955 is most advantageous. As the azeotropic agent, cyclohexane is used from the viewpoints of azeotropic temperature with methanol, azeotropic composition, raw material unit price and the like. Was concluded that the azeotropic agent was cyclohexane, and the study was conducted in further detail.

As a result, a series of distillation experiments and vapor-liquid equilibrium data collection by the present inventors have provided new knowledge that trimethoxysilane forms the lowest azeotrope not only with methanol but also with cyclohexane. The present inventors have found that it is necessary to limit the ratio of cyclohexane to methanol to a specific range in order to carry out a desired distillation separation with high accuracy, and have completed the present invention.

That is, the present invention relates to a method for continuously separating methanol and trimethoxysilane from a mixture containing methanol and trimethoxysilane by azeotropic distillation using cyclohexane as an azeotropic agent. The present invention relates to a method for separating trimethoxysilane, wherein distillation is performed in a weight ratio of supplied cyclohexane and methanol in a range of 2.0 ≦ cyclohexane / methanol ≦ 4.0.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The mixture containing methanol and trimethoxysilane as the raw materials in the present invention is a mixture obtained by reacting silicon metal powder and methanol as described above. Usually, it is composed of trimethoxysilane, unreacted methanol, by-product tetramethoxysilane, and in some cases a small amount of by-products or high-boiling substances, and the composition is not particularly limited.

However, when the ratio of methanol to trimethoxysilane is much larger than the azeotropic composition, that is, when the amount of methanol is much larger, ordinary distillation is performed before performing the operation of the present invention. It is more efficient to separate excess methanol.

Although the purity of cyclohexane used as an azeotropic agent is not particularly limited, it may affect the distillation itself depending on the type of impurities contained. Even if there is no influence, the diameter of the distillation column is unnecessarily required or the energy is disadvantageous. Therefore, it is preferable to use a distillation column having a purity of 90% or more, which is higher than a normal industrial grade.

There are no particular restrictions on the type of distillation column.
Both packed towers can be suitably used. Examples of the fluid supplied to the distillation column per unit time include a distillation raw material, an azeotropic agent, an extractant, a reflux liquid, and a fluid supplied through a reboiler (hereinafter abbreviated as a reboiler fluid). The weight ratio of cyclohexane and methanol supplied per unit time to the distillation column according to the present invention refers to the ratio of cyclohexane and methanol contained in the fluid supplied to the distillation column as the distillation raw material, azeotropic agent and reflux liquid per hour. It refers to the ratio of the total weight, and the variation every few seconds or minutes does not matter. For the purposes of the present invention, the reboiled fluid contains almost no cyclohexane and methanol, and in fact the scope should be specified in the present invention because it is limited to the distillation feed and the reflux liquid.

There are no particular restrictions on the location where each fluid is supplied. Even if a mixture of a mixture containing methanol and trimethoxysilane (hereinafter abbreviated as “raw material”) and cyclohexane is supplied in the same stage, they may be supplied in separate stages. Even if supplied, there is no problem in performing the present invention.

However, since methanol and cyclohexane form two liquid phases at room temperature, for industrially continuous separation, for example, the Chemical Engineering Handbook, 4th edition, "azeotropic distillation"
Or the method described in JP-A-7-53568 is preferable. Specifically, as shown in FIG. 1, the top vapor of the distillation column (a) is completely condensed by a condenser (a) and then separated into two liquid phases by a liquid separator (c). Reflux. In this method, cyclohexane which is lost in a methanol phase liquid or the like is newly supplied from a considerable amount.

Next, the essence of the present invention will be described. In order to carry out the present invention and to accurately separate methanol and trimethoxysilane using cyclohexane as an azeotropic agent, the weight ratio of cyclohexane and methanol supplied to the distillation column per unit time is 2.0 ≦ cyclohexane / methanol. ≤
Distillation must be carried out in the range of 4.0.

Methanol and cyclohexane form the lowest azeotropic composition at a molar ratio of about 3: 2 and a weight ratio of about 36.4: 63.6. Therefore, in order to separate methanol from a mixture containing methanol and trimethoxysilane using cyclohexane as an azeotropic agent, the weight ratio of cyclohexane to methanol is 63.6 / 36, that is, cyclohexane having a composition of about 41.75. It is considered that the desired separation can be achieved by supplying.

However, when the present inventors conducted distillation experimentally, it was not possible to carry out separation with high accuracy when the weight ratio of cyclohexane to methanol was in the range of around 1.75, and the conditions were set to a higher weight ratio. However, there is a region that can be separated with high precision, and it is 2.0 ≦ cyclohexane / methanol ≦ 4.0, preferably 2.0 ≦ cyclohexane / methanol ≦ 3.5, more preferably 2.0 ≦
Cyclohexane / methanol ≦ 3.0.

If distillation is carried out in a region where the weight ratio of cyclohexane to methanol is less than 2.0, trimethoxysilane is distilled off at the top of the column even in a distillation column having about 40 theoretical plates, and at the top of the column, Methanol is also mixed on the side, and accurate separation cannot be performed. Further, even if distillation is performed in a region where the weight ratio of cyclohexane to methanol exceeds 4.0, trimethoxysilane is still distilled out in a considerable amount at the top of the column, and cyclohexane is mixed at the bottom of the column. Good separation cannot be performed.
Further, in this case, cyclohexane is used more than necessary, which is disadvantageous in energy.

Although the cause of the existence of this most suitable region cannot be clarified, the present inventors have measured the vapor-liquid equilibrium data between each of the two components, and found that the ratio of cyclohexane and trimethoxysilane was 86:14. (Weight ratio), a new finding that a minimum azeotropic composition is formed at 79 ° C was obtained. Therefore, distillation of the three components of methanol-cyclohexane-trimethoxysilane is a system in which a minimum azeotropic composition is formed between each of the two components, and the azeotropic composition between the three components has not been actually confirmed. It is also conceivable to form the composition. That is, since the azeotropic composition is distillation of a system in which the azeotropic composition is intricately entangled, the objective cannot be achieved by simply supplying cyclohexane having an azeotropic composition with methanol, and accurate separation can be performed under higher weight ratio conditions. We speculate that there is an area where we can do it.

By satisfying all the above conditions, methanol and trimethoxysilane can be continuously and accurately separated from a mixture containing methanol and trimethoxysilane. In addition, even when the raw material contains tetramethoxysilane, a mixture of trimethoxysilane and tetramethoxysilane is obtained from the bottom of the column, so that when isolating trimethoxysilane, it can be achieved by performing the distillation operation again. it can.

[0026]

The present invention will be described below in detail with reference to examples. In addition,% and part represent weight% and part by weight unless otherwise specified. Example 1 After 100 parts of commercially available silicon powder (manufactured by Wako Pure Chemical) and 10 parts of metal copper powder (manufactured by Wako Pure Chemical) were mixed in a V-type blender,
Heat treatment was performed at 1,000 ° C. for 1 hour in a hydrogen atmosphere to obtain a methoxysilane production raw material. This raw material is packed in a reactor as a fixed bed, and is gaseous methanol (at a gas obtained by gasifying special grade methanol manufactured by Wako Pure Chemical Industries) under the conditions of normal pressure and 200 to 220 ° C.
Was contacted and reacted to obtain a mixed solution having a composition of 32% of methanol, 38% of trimethoxysilane, and 30% of tetramethoxysilane. A liquid composition was prepared by adding a special grade methanol reagent manufactured by Wako Pure Chemical and a tetramethoxysilane reagent manufactured by Tokyo Chemical Industry to this mixed solution, and a distillation raw material of methanol 25%, trimethoxysilane 25%, and tetramethoxysilane 50%, that is, A mixture containing methanol and trimethoxysilane according to the invention was obtained. The distillation column is made of SUS304 and has a column inner diameter of about 80
A Dickson packing having a diameter of 6 mm and a length of 5 m was used. When the theoretical plate number of this column was measured in a methanol-water system with a known vapor-liquid equilibrium, it was found to be in the range of 39 to 42 plates (the distillation column used for simplicity is a column having 40 theoretical plates). It is described as there is).

Cyclohexane /
Cyclohexane (Wako Pure Chemical first grade) was mixed so that methanol = 2.5 (weight ratio), and this prepared solution was continuously supplied to the 21st stage counted from the top of the column, as shown in FIG. Distillation was performed in a simple manner. About three hours after the start of the operation, the temperature distribution in the tower stabilizes and reaches a steady state. After that, the heat load of the reboiler is changed by several points, that is, the amount of distillate is changed by several points. Prepare the conditions that can be separated accurately,
The top liquid and the bottom liquid were sampled, and the composition was analyzed by gas chromatography. As a result, the composition at the top of the column was methanol 28.0%, cyclohexane 70.3%, and trimethoxysilane 1.7%. From the bottom of the column, both methanol and cyclohexane were less than 1,000 ppm.

Examples 2 to 4 In the same manner as in Example 1, a distillation material of 25% methanol, 25% trimethoxysilane and 50% tetramethoxysilane was prepared. Using the same distillation column as in Example 1, the distillation raw material is continuously supplied to the 21st stage and cyclohexane is continuously supplied to the first stage while maintaining the feed rate at the 21st stage, as shown in FIG. When a steady state was reached under the possible conditions, the top liquid and the bottom liquid were analyzed. The same operation was performed by changing the weight ratio of cyclohexane / methanol by several points, and the state of separation was examined. Table 1 shows the weight ratio of cyclohexane / methanol, the composition of the top liquid, and the composition of the bottom liquid.

Comparative Example 1 A distillation operation was carried out in the same manner as in Example 1 except that cyclohexane / methanol was changed to 1.8 (weight ratio). When a steady state was reached, the composition of the top liquid and the bottom liquid was analyzed. Was performed, the results shown in Table 2 were obtained.

Comparative Examples 2 and 3 Distillation was performed in the same manner as in Example 2 except that the weight ratio of cyclohexane / methanol was set outside the range of the present invention, and the results shown in Table 2 were obtained.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

As described in detail above, according to the present invention, trimethoxysilane, which is difficult to separate, can be accurately separated from a mixed solution containing methanol and trimethoxysilane with little loss. Is big.

[0034]

[Brief description of the drawings]

FIG.

FIG. 2 and

FIG. 3 is a process diagram of a distillation column used in the present invention.

[Explanation of symbols]

 A Distillation tower b Condenser c Liquid phase separator (decanter) d Reboiler e Distillate tank raw material Cyclohexane overhead vapor Cyclohexane phase liquid Methanol phase bottoms Reflux liquid Distillate

Claims (1)

[Claims] 1. A method for continuously separating methanol and trimethoxysilane from a mixture containing methanol and trimethoxysilane by azeotropic distillation using cyclohexane as an azeotropic agent, wherein cyclohexane is supplied to a distillation column per unit time. A method for separating trimethoxysilane, wherein the distillation is performed at a weight ratio of 2.0 ≦ cyclohexane / methanol ≦ 4.0.