JP2002069077A - Method for producing trialkoxysilane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vapor-phase method for producing a trialkoxysilane in high reaction result at a low cost. SOLUTION: A trialkoxysilane is produced by removing oxide formed on the surface of silicon, bringing the silicon in contact with a copper compound, heat-treating the system and performing a vapor-phase reaction of the silicon with an alcohol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing trialkoxysilane, and more particularly to a method for producing trialkoxysilane which is effective in reducing the production equipment cost and operating cost.

[0002]

2. Description of the Related Art High-purity silicon for semiconductors and solar cells is produced by reducing silicon metal, which is a raw material ore, in an arc furnace and then converting it to a chlorine compound (trichlorosilane).
The chlorine compound is purified and then reduced or thermally decomposed again to produce.

However, since this method uses a large amount of chlorine at a high temperature, the cost of the generator and the product is increased due to measures against corrosion of materials and equipment, environmental measures such as chlorine recovery equipment and processing equipment, and the like. It was inevitable, and the technical challenges were great.

Therefore, a method of producing high-purity silicon by a method not using halogen such as chlorine has been studied, and a method by the following process has been studied.

[0005] That is, as a process for producing high-purity silicon, (1) synthesis of trialkoxysilane by reaction of silicon with an alcohol such as methanol or ethanol. (2) Production of monosilane by disproportionation reaction of trialkoxysilane. In this method, monosilane is produced using a two-stage process, and high-purity silicon is produced using this monosilane as a raw material.

[0006]

One of the prerequisites for a method of producing high-purity silicon using this two-stage process to be economically efficient is to produce trialkoxysilane at low cost. For this purpose, achieving a high production rate and high selectivity of trialkoxysilane is an issue.

[0007] Trialkoxysilane is formed by the reaction of silicon such as methanol or ethanol with silicon.
It is known to be synthesized.

Conventionally, however, the liquid phase method has been mainly used. In this method, although the conversion is relatively high, the reaction rate is lower than that in the gas phase method. The production cost was high because a complicated process was required to separate the catalyst.

[0009] On the other hand, the gas phase method has an advantage that the reaction rate is potentially higher than the liquid phase method, but it is considered that the selectivity is lower than the liquid phase method, and it has been considered that industrialization is difficult.

Accordingly, an object of the present invention is to provide a method for producing trialkoxysilane using a gas phase method which is inexpensive and has high reaction results.

[0011]

In the method for producing trialkoxysilane according to the present invention, the step of removing the oxide formed on the surface of silicon and the step of bringing silicon and a copper compound into contact with each other and performing a heat treatment are performed. In addition, silicon and alcohol are allowed to undergo a gas phase reaction to produce trialkoxysilane.

With this configuration, the trialkoxysilane can be produced with high reaction results by using a gas phase reaction.

In the present invention, trialkoxysilane can be produced using a metal reactor.
A large-sized reactor can be manufactured at low cost, which is very useful for industrialization.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the structure of a trialkoxysilane production method according to the present invention.

In the present invention, after etching the silicon surface (etching step 10), heat treatment (heat treatment step 20) is performed by bringing silicon into contact with a catalyst, and silicon and an alcohol (methanol or ethanol) are caused to react in a gas phase. Trialkoxysilane (trimethoxysilane or triethoxysilane) is generated (trialkoxysilane generation step 30).

At this time, when methanol is used, the reaction formula is as follows: The reaction formula using ethanol is Becomes

First, an oxide film formed inevitably near silicon as a raw material is etched using hydrogen fluoride or the like to expose the surface of silicon.

Here, in the etching, an aqueous solution of nitric acid, sulfuric acid, hydrochloric acid, ammonia, hydrogen fluoride or the like or a mixture thereof can be used as a wet method, and hydrogen chloride or hydrogen fluoride can be used as a dry method. Alternatively, a mixed gas of these can be used, and preferably, steam from a hydrogen fluoride aqueous solution or hydrogen fluoride gas is used.

When a wet etching process is performed to remove the oxide on the silicon surface, moisture remaining on the silicon surface is removed and dried.

Specifically, water can be removed under heating under reduced pressure, and the water concentration on the silicon surface is 1000 ppm.
The following is preferable, and particularly preferably 500 pp
m or less.

The silicon used in the present embodiment is not limited to high-purity silicon, and the use of metallic silicon is industrially useful.

Next, silicon is brought into contact with copper chloride as a catalyst, heat-treated in a non-oxidizing atmosphere such as nitrogen, argon, helium, hydrogen or the like, and subjected to alloying treatment.

The temperature range of the heat treatment is 180 ° C.
To 280 ° C, and the processing time is within 5 hours.

Then, by subjecting silicon and alcohol to a gas phase reaction, copper in copper silylene, which is a silicon alloy nucleus, is replaced with a functional group in the alcohol to produce trialkoxysilane.

In this case, trialkoxysilane is produced by reacting silicon and alcohol after heat treatment, but alloying treatment can be performed by heat treatment simultaneously with reaction between alcohol and silicon. This method is more industrially useful than a method in which heat treatment is performed as a pretreatment.

Further, by forming silicon particles by pulverizing silicon in a non-oxidizing atmosphere, it is possible to prevent an oxide film from being formed on the surface of the silicon particles and to prevent the surface of the silicon particles from being changed. If it is kept clean without being covered by the substance, the steps of etching and cleaning can be omitted.

The temperature range in the gas phase reaction is 18
The temperature is from 0 ° C. to 285 ° C., and the flow rate of the alcohol vapor is 1 to 70 L / h, preferably 2 to 160 L / h per gram of silicon at normal temperature and normal pressure.

Under the conditions of the present invention, the generated trialkoxysilane is a gas, so that the silicon in the silicon-copper alloy (coppersilylene) is transformed into trialkoxysilane by a reaction and detached from the surface of the solid silicon. However, copper silylene is newly formed on the surface of silicon, and trialkoxysilane is generated by a similar reaction mechanism.

The trialkoxysilane is separated and purified from other products and unreacted raw materials by using a known method such as distillation.

In the present embodiment, the particle size of the copper chloride catalyst is desirably about the same as or smaller than the silicon particles of the raw material.

This is because the alloying treatment forms at least 95, preferably at least 125, copper silylenes, which are alloy nuclei, on the surface of silicon particles per square millimeter. This is because a large contact area is desirable.

Here, a copper compound forming a copper silylene species such as copper hydroxide can be used as a catalyst instead of copper chloride.

In the alloying operation, any of a fixed bed in which the silicon particles and the catalyst particles are in a stationary state, and a moving bed or a fluidized bed in a moving state can be used.

The reaction utilization of the catalyst is improved by using a structure comprising a plurality of fluidized beds capable of continuous operation and supplying the silicon extracted from the upstream fluidized bed and the catalyst to the downstream fluidized bed. And the production cost of trialkoxysilane can be reduced.

Although the particle-particle contact method has been described as a method of forming the alloy nucleus, the silicon alloy nucleus may be formed on the surface of the silicon particle by using a gas-solid reaction using a vapor generated from the catalyst component. .

Further, by dissolving the catalyst in a liquid, immersing silicon in the solution, and drying the solution,
A catalyst component may be deposited on the surface of silicon to form a silicon alloy core.

After the trialkoxysilane is generated, the supply of silicon to the silicon alloy nucleus for forming new copper silylene is performed by solid-phase diffusion. Is preferably shortened, and the size of the alloy core is 5 μm or less, preferably 1 μm or less.
Submicron.

Since it is necessary to balance the rate of silicon consumption by the trialkoxysilane synthesis reaction with the rate of silicon supply by diffusion, an excessive reaction rate must be avoided. Strict control is required so as not to exceed the stated temperature range.

This is because any one of the following problems occurs when the reaction temperature exceeds this temperature range. (1) Since the growth rate of alloy nuclei increases with an increase in the temperature of the alloying treatment, the balance between the consumption rate of silicon due to the formation of trialkoxysilane and the supply rate of silicon due to solid-phase diffusion is lost, and this is suitable for the reaction. An alloy core having a size exceeding the size is formed. (2) As the reaction temperature increases, the consumption rate of silicon due to the generation of trialkoxysilane increases, and significantly exceeds the supply rate of silicon to the alloy nucleus, thereby maintaining the size of the alloy nucleus at an appropriate size. Difficult to do,
The selectivity of trialkoxysilane decreases.

The problem (1) is apt to occur in the pretreatment step, and the problem (2) is liable to occur in the reaction step.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples.

[0042]

EXAMPLE 1 In this example, silicon (manufactured by Yamaishi Metal, purity 98%) was sieved to 45 to 68 μm, washed with ion-exchanged water, and 5 g of the silicon was treated with hydrofluoric acid (manufactured by Hirota Chemical Industry Co., Ltd.). After stirring for 1 hour in 50 ml of special grade, the solution in the Teflon (registered trademark) beaker was filtered, washed with ion-exchanged water, and then reduced in pressure (640 mH).
g) It was dried to a residual moisture of 500 ppm or less using drying (hereinafter, referred to as “HF treatment”).

Then, 0.18 g of a mixture obtained by mixing HF-treated silicon and cuprous chloride (manufactured by Wako Pure Chemical Industries, Ltd.) for 10 minutes was added to a fixed-bed reactor (Pyrex (registered trademark)).
After filling into glass (8 mm inner diameter), the reactor was
Helium gas at a flow rate of 8.0 NL / h for 1 hour.
Heat treatment was performed by flowing the mixture for a time.

Here, the catalyst concentration of the catalyst formed by mixing silicon and cuprous chloride is expressed by the following equation. According to the above equation, adjustment is performed so that the catalyst concentration becomes 1 to 15 wt%.

After the heat treatment, while maintaining the reactor temperature at 240 ° C., methanol was supplied at a flow rate of 54 mmol / h to synthesize trimethoxysilane.

Here, the partial pressure of methanol is previously 60 kP
The flow rate of the helium gas was adjusted so as to be a.

The gas discharged from the outlet of the reactor was introduced into a gas chromatograph (filler SE-30, column length 2 m, column temperature 150 ° C.), and the product was removed every 2.5 minutes. Analysis was carried out.

As a result, formation of a methoxysilane compound was observed without an induction period (initial maximum formation rate: 18 mmol / h). Thereafter, three hours after the start of the reaction, no formation of methoxysilane was observed.

At this time, the silicon conversion was 85%, the selectivity for trimethoxysilane was 99.8%, and the only methoxysilane product other than trimethoxysilane was tetramethoxysilane.

[0050]

Comparative Example 1 Except for not performing HF treatment on metallic silicon,
The reaction was carried out under the same treatment and reaction conditions as in Example 1, and the reaction product was analyzed.

After an induction period of about 30 minutes, formation of methoxysilane was observed, but the formation rate was up to about 1 mmol /
h, which was much smaller than that of Example 1.

Up to 9 hours after the start of the reaction, the conversion of silicon was 29%, and the selectivity for trimethoxysilane was 100%.

[0053]

Example 2 In Example 2, the heat treatment temperature was set to 260 ° C.
Except that the temperature was changed to 80 ° C. and 300 ° C., the reaction was carried out under the same treatment and reaction conditions as in Example 1, and the reaction product was analyzed. The silicon conversion and the trimethoxysilane selectivity are summarized in Table 1. Table 1

[0054]

Example 3 In Example 3, the reaction was carried out under the same treatment and reaction conditions as in Example 1 except that the reaction was started without performing the heat treatment.

About 4 hours after the start of the reaction, the peak of the methoxysilane compound was no longer detected. At that time, the silicon conversion was 73% and the trimethoxysilane selectivity was 100%.

[0056]

Example 4 A mixture obtained by mixing HF treated silicon and cuprous chloride (manufactured by Wako Pure Chemical, special grade) for 10 minutes 0.3.
After filling 8 g (catalyst concentration 5 wt%) into a fixed bed reactor (made of Pyrex glass, inner diameter 12 mm), 2 reactors were filled.
Heating was performed at 40 ° C., and helium gas was passed at a flow rate of 6.5 NL / h in a down flow for 1 hour to perform heat treatment.

After the heat treatment, while maintaining the reactor temperature at 240 ° C., methanol was supplied at a flow rate of 50 mmol / h to synthesize trimethoxysilane.

Here, the partial pressure of methanol was previously set at 18 kP.
The flow rate of the helium gas was adjusted so as to be a.

At this time, the silicon conversion was 88%, and the selectivity for trimethoxysilane was 88%.

[0060]

Example 5 In Example 5, the material of the reactor was SUS30.
Except that the reaction was 4, the reaction was carried out under the same treatment and reaction conditions as in Example 1.

About 6 hours after the start of the reaction, the peak of the methoxysilane compound became smaller, and the reaction was terminated.

At this time, the silicon conversion was 70%, and the selectivity for trimethoxysilane was 95%.

When comparing the case where the reactor uses SUS material and the case where quartz is used, the reaction performance slightly decreases when the SUS material is used. No significant effect.

[0064]

Example 6 In Example 6, a reaction was carried out under the same processing and reaction conditions as in Example 4, except that the supply direction of the helium gas during the heat treatment was set to an upflow.

At this time, the silicon conversion was 60%, and the selectivity for trimethoxysilane was 45%.

[0066]

[Embodiment 7] In Embodiment 7, the supply rate of methanol was set to 1
00 mmol / h (partial pressure 35 kPa), 200 mmol
/ H (partial pressure 70 kPa), except that the reaction was carried out under the same treatment and reaction conditions as in Example 4, and the silicon conversion and trimethoxysilane selectivity were summarized in Table 2. Table 2

[0067]

[Embodiment 8] In Embodiment 8, the catalyst and silicon were previously set to 1
The fixed bed subjected to the pretreatment and the fluidized bed not subjected to such a pretreatment are reacted under the same treatment and reaction conditions as in Example 1 by heating and contacting with each other for a period of time to obtain a silicon conversion rate and trimethoxysilane. The selectivities are summarized in Table 3. Table 3

Although the selectivity was slightly decreased in the fluidized bed compared to the fixed bed, the conversion was significantly increased,
It can be seen that a pretreatment operation of heating and contacting the silicon and the catalyst is not necessarily required in the fluidized bed.

[0069]

Embodiment 9 In Embodiment 9, the weight of silicon was 4.5 g.
Alternatively, a fluidized bed was prepared under the same treatment and reaction conditions as in Example 1 except that the ratio of the flow rate (mol / h) of methanol to 1 g of silicon was 1 or 2, and the partial pressure of methanol was 30 kPa or 60 kPa. The reaction was carried out using the same, and the silicon conversion and trimethoxysilane selectivity are summarized in Table 4. Table 4

It is understood that a good value can be obtained between 1.0 and 2.0 when the flow rate of methanol and the amount of silicon per hour are represented by a molar ratio.

[0071]

Example 10 In Example 10, the flow rate of methanol was set to 1
The reaction was carried out using a fluidized bed under the same treatment and reaction conditions as in Example 1 except that 70 mmol / h and the catalyst concentration were 0.1 to 10 wt%, and the silicon conversion and trimethoxysilane selectivity were determined as shown in Table 5. Summarized in Table 5

[0072]

Example 11 In Example 11, a fixed bed using a Pyrex reactor and a fluidized bed using a SUS reactor were used to adjust the silicon weight to 4.5 or 9.0 g and the methanol flow rate. The reaction was carried out under the same treatment and reaction conditions as in Example 1 except that the amount was 160 or 330 mmol / h. Table 6 summarizes the silicon conversion and trimethoxysilane selectivity. Table 6

As described above, almost the same reaction results as in the case where the fixed layer made of Pyrex was used as the reaction vessel were obtained by SUS.
This can also be achieved using a fluidized bed made of

[0074]

Example 12 In Example 12, the diameter of the reaction vessel was 12
mm or 24 mm, the weight of silicon was 9.0 g, and the flow rate of methanol was 160 or 330 mmol / h. Table 7 summarizes the silane selectivities. Table 7

This result is considered to suggest a bright prospect for scale-up of the reactor.

[0076]

Example 13 In Example 13, a fluidized bed was used under the same treatment and reaction conditions as in Example 1 except that the silicon particle diameter was 45 to 105 μm or 45 μm or more and the methanol flow rate was 160 mmol / h. The reaction was performed, and the silicon conversion and trimethoxysilane selectivity are summarized in Table 8. Table 8

[0077]

Embodiment 14 In Embodiment 14, the methanol flow rate was set to 16
Example 1 was repeated except that the flow rate of helium gas was adjusted so that 0 mmol / h and the partial pressure of methanol became 44 kPa, 4.5 g of silicon were charged at the start of the reaction, and then 2 g were charged 4 times every 2 hours. The reaction was carried out using a fluidized bed under the same treatment and reaction conditions.

At this time, the silicon conversion was 78%, and the selectivity for trimethoxysilane was 95%.

The results show that the performance of the fluidized-phase reactor when the continuous operation is performed can be maintained at a high level.

[0080]

Example 15 In Example 15, the results of analysis and quantification of impurities in trimethoxysilane obtained under the conditions of Example 1 by ICP emission analysis are shown in Table 9. Table 9

This result indicates that, among the impurities contained in the raw material silicon, the amount taken up by the reaction product in the reaction process is extremely small, and it can be expected that the purification step of the reaction product will be simplified.

[0082]

According to the present invention, trialkoxysilane can be produced without passing through a halide, so that it is excellent in environmental measures and safety measures, and the production cost can be kept low.

Further, since impurities contained in silicon as a raw material are scarcely contained in the produced trialkoxysilane, highly pure trialkoxysilane can be produced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a method for producing trialkoxysilane in the present invention.

[Explanation of symbols]

 10 Etching Step 20 Heat Treatment Step 30 Trialkoxysilane Generation Step

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoshiyuki Watanabe 2205 Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki FJ-term in JGC Corporation Technical Research Institute 4H049 VN01 VP01 VQ21 VR11 VR43 VS99 VT04 VT24 VU24

Claims (4)

[Claims] 1. A method for producing trialkoxysilane by producing a trialkoxysilane by subjecting silicon and alcohol to a gas phase reaction, comprising: removing an oxide formed on the surface of silicon; Forming a catalyst alloy nucleus by heat contact. 2. The method for producing trialkoxysilane according to claim 1, wherein a metal reactor is used. 3. The process for producing trialkoxysilane according to claim 1, wherein a fluidized bed is used as the reactor, and the operation of continuously supplying and extracting silicon is performed. 4. The method for producing trialkoxysilane according to claim 1, wherein the raw material alcohol is supplied in an appropriate amount according to the amount of silicon in the reactor.