JPH10152492A - Separation of trimethoxysilane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for separating trimethoxysilane, enabling to continuously and precisely separate the trimethoxysilane. SOLUTION: This method for separating trimethoxysilane comprises continuously separating the trimethoxysilane from a mixture of the trimethoxysilane with methanol by an azeotropic distillation method using n-hexane as an azeotropic agent. Therein, the weight ratio of the n-hexane to the methanol charged into a distillation tower per unit time is controlled within a range: 3.0 <= n-hexane/methanol <= 5.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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, there are generally known a method of reacting trichlorosilane with methanol (reaction formula [1]) and a method of reacting silicon metal with methanol (reaction formula [2]). However, trichlorosilane is difficult to handle, and the former produces hydrochloric acid.
Industrially, the latter is more advantageous.

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 It is an object of the present invention to separate trimethoxysilane continuously and accurately by specifying the weight ratio of n-hexane and methanol to a mixture containing methanol and trimethoxysilane. It is to provide a method.

[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 as described in JP-B-61-39955 is most advantageous, and n-hexane is used as the azeotropic agent in view of the azeotropic temperature with methanol, the azeotropic composition, the unit price of the raw material and the like. Is reached, and the azeotropic agent is changed to n-
The study was conducted in more detail by specifying hexane.

As a result, a series of distillation experiments and vapor-liquid equilibrium data collection by the present inventors have obtained new knowledge that trimethoxysilane forms the lowest azeotrope not only with methanol but also with n-hexane. At the same time, they have found that it is necessary to limit the ratio of n-hexane to methanol to a specific range in order to perform the desired distillation separation with high accuracy, and have completed the present invention.

That is, the present invention relates to a method of continuously separating azeotropically n-hexane from a mixture containing methanol and trimethoxysilane by azeotropic distillation, wherein n-hexane supplied to a distillation column per unit time is used. The present invention relates to a method for separating trimethoxysilane, wherein the distillation is performed in a weight ratio of 3.0 ≦ n-hexane / methanol ≦ 5.0.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The mixture containing methanol and trimethoxysilane as raw materials in the present invention is a mixture obtained by reacting metal silicon 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 n-hexane used as an azeotropic agent is not particularly limited, it may affect the distillation itself depending on the type of impurities contained. Since the diameter of the distillation column is unnecessarily required even if there is no influence on the energy, and the energy is disadvantageous, the purity of the distillation column is higher than that of a normal industrial grade.
It is preferable to use one having 0% or more.

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 n-hexane and methanol supplied to the distillation column per unit time according to the present invention is defined as the distillation material, azeotropic agent, and n-contained in the fluid supplied to the distillation column as a reflux per hour. It refers to the ratio of the total weight of hexane and methanol, and the variation every few seconds or minutes does not matter.
For the purposes of the present invention, the reboiled fluid contains almost no n-hexane and methanol, and in fact the scope should be specified in the present invention because it is limited to distillation feed and reflux.

There are no particular restrictions on the supply points of the respective fluids. Even if a mixture of methanol and trimethoxysilane (hereinafter abbreviated as raw material) and n-hexane are supplied in the same stage, they may be supplied separately. There is no problem in carrying out the present invention even if it is supplied to the stage.

However, since methanol and n-hexane form two liquid phases at room temperature, in order to carry out industrially continuous separation, for example, the section of “Azeotropic Distillation” in Chemical Engineering Handbook, 4th edition, or The method described in JP-A-7-53568 is preferred. Specifically, as described in FIG.
After the top vapor of the distillation column (a) is totally contracted by the condenser (a), it is separated into two liquid phases by the liquid separator (c), and the n-hexane phase liquid is refluxed to the distillation column (a). In this method, n-hexane that is lost in a methanol phase solution 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 n-hexane as an azeotropic agent, the weight ratio of n-hexane and methanol supplied per unit time to the distillation column must be 3.0. ≦ n-hexane / methanol ≦ 5.0
The distillation must be carried out within the range.

Methanol and n-hexane form the lowest azeotropic composition at a molar ratio of about 1: 1 and a weight ratio of about 27:73. Therefore, in order to separate methanol from a mixture containing methanol and trimethoxysilane using n-hexane as an azeotrope, the weight ratio of n-hexane to methanol is 73/27, that is, a composition having a weight ratio of about 2.7. It is considered that if n-hexane is supplied at, the desired separation is possible.

However, when the present inventors conducted distillation experimentally, it was not possible to carry out separation with high accuracy when the weight ratio of n-hexane and methanol was in the range of about 2.7, and the condition where the weight ratio was higher was higher. Where there is a region that can be separated with high precision, and 3.0 ≦ n-hexane /
Methanol ≦ 5.0, preferably 3.0 ≦ n-hexane / methanol ≦ 4.5, more preferably 3.0 ≦ n-hexane / methanol ≦ 4.0.

The weight ratio of n-hexane to methanol is 3.
When distillation is performed in a region of less than 0, even in a distillation column having about 30 theoretical plates, trimethoxysilane is distilled at a non-negligible amount at the column top, and methanol is mixed into the column bottom, thereby achieving accurate separation. Can't do it. Also, the weight ratio of n-hexane to methanol is 5. Even if distillation is performed in a region exceeding 0, trimethoxysilane is still distilled out in a considerable amount at the top of the column, and n-hexane is mixed at the bottom of the column, so that accurate separation cannot be performed. Further, in this case, the use of n-hexane more than necessary is disadvantageous in terms of 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 for each of the two components and found that n-hexane and trimethoxysilane were 80%. : 20 (weight ratio) at 67 ° C. to form a lowest azeotropic composition. Therefore, distillation of the three components of methanol-n-hexane-trimethoxysilane is a system in which a minimum azeotropic composition is formed between each of the two components. It is fully conceivable to form an azeotropic composition.
That is, since the azeotropic composition is distillation of a system in which the azeotropic composition is intricately entangled, simply supplying n-hexane having an azeotropic composition with methanol cannot achieve the object, and the conditions are accurate to a higher weight ratio. It is assumed that there is an area where separation can be performed.

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 express 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. To this mixture, a special grade methanol reagent manufactured by Wako Pure Chemical and a tetramethoxysilane reagent manufactured by Tokyo Chemical Industry are added to prepare a liquid composition, and a distillation raw material of methanol 25%, trimethoxysilane 25%, and tetramethoxysilane 50%, that is, A mixture containing methanol and trimethoxysilane according to the present invention was obtained.

The distillation column was made of SUS304 and had a column inner diameter of about 80.
What was filled with 5 mm of Raschig rings of 6 mm in diameter was used. The theoretical plate number of this column was measured in a methanol-water system with a known vapor-liquid equilibrium, and was found to be in the range of 30 to 34 plates (the distillation column used for simplicity is a column having 30 theoretical plates). It is described as there is). N-Hexane / Methanol = 3.4 (weight ratio) was mixed with n-hexane (first grade, manufactured by Wako Pure Chemical Industries, Ltd.) to the previously prepared distillation raw material, and this preparation was counted from the top of the column for 16 stages. The mixture was continuously supplied to the eyes and separated by distillation in the manner shown in FIG. About two hours after the start of the operation, the temperature distribution in the column 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. The conditions were set so that separation could be performed accurately, the top liquid and the bottom liquid were sampled, and their compositions were analyzed by gas chromatography. As a result, the top composition was methanol 22.2. 9% by weight, n-hexane 76.5%, trimethoxysilane 0.
At 6%, less than 1,000 ppm of both methanol and n-hexane were detected from the bottom of the column.

Examples 2 to 5 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, in the manner shown in FIG. 3, the distillation raw material was continuously supplied to the 16th stage and n-hexane was continuously supplied to the first stage while the supply speed was kept constant. When a steady state was established under conditions that allowed good separation, the top liquid and the bottom liquid were analyzed. The same operation was carried out while changing the weight ratio of n-hexane / methanol by several points, and the state of separation was examined. Table 1 shows the weight ratio of n-hexane / 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 n-hexane / methanol was changed to 2.8 (weight ratio). When the composition was analyzed, the results shown in Table 2 were obtained.

Comparative Examples 2 and 3 Distillation was carried out in the same manner as in Example 2 except that the weight ratio of n-hexane / methanol was set outside the range of the present invention. Was.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

According to the present invention, by specifying the weight ratio of n-hexane / methanol to a mixed solution containing methanol and trimethoxysilane, trimethoxysilane, which has been difficult to separate, is reduced in loss and accuracy. Since the separation can be performed well, the effect is great.

[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 material inlet n-hexane overhead vapor n-hexane phase liquid Methanol phase liquid Bottom liquid Reflux liquid Top liquid

Claims (1)

[Claims] 1. A method for continuously separating n-hexane from a mixture containing methanol and trimethoxysilane by azeotropic distillation using n-hexane as an azeotropic agent, wherein n-hexane and methanol supplied to a distillation column per unit time are used. A method for separating trimethoxysilane, wherein the distillation is performed at a weight ratio of 3.0 ≦ n-hexane / methanol ≦ 5.0.