JPH05178864A - Production of trialkoxysilane - Google Patents

Abstract

PURPOSE:To provide a method for efficiently producing a trialkoxysilane. CONSTITUTION:A method for producing a trialkoxysilane is characterized by reacting metal silicon with a 1-4C alkyl alcohol in the presence of a catalyst in a gaseous phase under vacuum. The trialkoxysilane can obtained in a high selectivity and in a high silicon conversion, and the reaction is stable for a long time. The trialkoxysilane can readily be separated and obtained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an efficient method for producing trialkoxysilane.

[0002]

BACKGROUND OF THE INVENTION Alkoxysilanes are useful as various silane coupling agents and raw materials for insulating thin films. Trialkoxysilanes have SiH bonds in their molecules.
Moreover, since it is chemically more stable than monoalkoxysilane and dialkoxysilane, there is a demand for a highly costly and efficient manufacturing method.

Conventionally, as a method for producing trialkoxysilane, a method using chlorosilanes and lower alkyl alcohols as raw materials has been known. However, chlorosilanes are expensive and, in addition to the desired alkoxysilane, hydrochloric acid. As a by-product, it is difficult to purify the product, and the reaction apparatus is corroded.

On the other hand, a method of directly reacting silicon metal with an alkyl alcohol is also known. This method is carried out in a gas phase or a liquid phase in the presence of a copper catalyst. Since the production of higher-order tetraalkoxysilane has priority over that of trialkoxysilane and the selectivity of trialkoxysilane becomes low, the industrial development in recent years has been carried out exclusively in the liquid phase.

However, the liquid phase system has a lower reaction rate per reactor volume than the gas phase system, and the cost is high because a reaction solvent having a high boiling point is used, and the reaction residue contains a product having a high boiling point. As a result, there are problems that the reaction product becomes sludge-like and it is difficult to process the reaction residue, and that the reaction solvent is mixed in the product, so that the purification of the reaction product is complicated.

Therefore, a method for efficiently producing trialkoxysilane by a vapor phase method is desired, but the conventional vapor phase method has the following problems in addition to the above-mentioned problems. When metal silicon and an alkyl alcohol are reacted in the presence of a copper catalyst, tetraalkoxysilanes such as tetraethoxysilane and high-boiling products such as dimers and trimers of silicon are produced. In the case of the above, since powders become wet due to these high boiling point products, there are problems such as uneven gas flow in the fixed bed system and fluidization hindered in the fluidized bed system, which causes a problem for a long time. It was difficult for the reaction to proceed smoothly. In order to solve this problem, for example, a method has been proposed in which a large amount of inert gas is caused to flow into the reactor volume to smoothly proceed the reaction. In addition to increasing the cost, the partial pressure of the lower alkyl alcohol as a raw material was lowered, and the reaction rate was slow, so it was difficult to say that this method was industrially appropriate.

[0007]

DISCLOSURE OF THE INVENTION The present invention is a method for producing trialkoxysilane by reacting metallic silicon and an alkyl alcohol in a gas phase system in the presence of a catalyst. The present invention has been completed as a result of earnest research to provide a manufacturing method that is stable for a long time and that facilitates the separation and acquisition of trialkoxysilane.

[0008]

DISCLOSURE OF THE INVENTION According to the present invention, metallic silicon and an alkyl alcohol having 1 to 4 carbon atoms (hereinafter referred to as lower alkyl alcohol) are reacted in the gas phase in the presence of a catalyst to give trialkoxysilane. In the production, a trialkoxysilane production method is characterized in that the reaction is carried out under reduced pressure.

The metallic silicon used as one of the raw materials in the method of the present invention preferably has a purity of 80% by weight or more, and the shape is preferably granular, and the particle size is not particularly limited. Generally, the average particle size is preferably 2 mm or less, more preferably 25 to 500 μm, and particularly preferably 50 to 300 μm.

The lower alkyl alcohol, which is another raw material, may be linear or branched, and specifically, methanol, ethanol, n-propanol, iso-propanol, n-butanol, There are sec-butanol, iso-butanol, and tert-butanol, and among these, as will be apparent from comparison between Example 2 and Comparative Example 2 below, the selectivity of trialkoxysilane by the reduced pressure method of the present invention is shown. The effect of improving the silicon conversion rate is particularly remarkable in the method for producing triethoxysilane using ethanol as a raw material.

The lower alkyl alcohol preferably has a purity of 95 wt% or more, and it is preferable that the water content is set to 2000 ppm or less, more preferably 500 ppm or less by dipping a dehydrating agent.

The supply rate of the lower alkyl alcohol to the reaction system is preferably 10 to 1,000 mmol / hr of the lower alkyl alcohol, and more preferably 50 to 500 mmol / hr, to 1 mol of metal silicon. When it exceeds 1,000 mmol / hr, unreacted lower alkyl alcohol increases, which is not economical, and when it is too small, the yield of trialkoxysilane may decrease.

The trialkoxysilane obtained according to the present invention has an alkoxy group corresponding to the alkyl alcohol used as a raw material, and specifically, trimethoxysilane, triethoxysilane, tri-n-propoxysilane, and tri-n-propoxysilane. There are isopropoxysilane, tri-n-butoxysilane, tri-sec-butoxysilane, triisobutoxysilane and tri-tert-butoxysilane.

As the catalyst in the present invention, any of a copper catalyst, a zinc catalyst and a nickel catalyst can be used, and it is not particularly limited, but a copper catalyst is particularly preferable. Specific examples thereof include copper salts such as cuprous chloride, cupric chloride, copper bromide, copper iodide, copper fluoride, copper carbonate, copper sulfate, copper acetate, copper oxalate, and copper thiocyanate, or copper hydroxide. Examples thereof include copper-containing inorganic compounds such as copper cyanide, copper sulfide, and copper oxide, organic copper compounds such as methyl copper and ethyl copper, or metallic copper. The catalyst may be mixed in powder form with metal silicon or supported on metal silicon and then supplied to the reaction system. If necessary, activation treatment such as heat treatment may be performed.

The catalyst is supplied to the reaction system at a rate of 1% metallic silicon.
The amount is preferably 0.5 to 20% by weight, more preferably 1 to 10% by weight, based on g. If it is too large, the cost will be high, and if it is less than 0.5 wt%, the conversion rate of silicon may be lowered.

The present invention is carried out in a gas phase system. That is, a gaseous lower alkyl alcohol is brought into contact with metallic silicon and a catalyst to cause a reaction. The reaction system may be either a batch system in which the entire amount of metallic silicon and the catalyst are initially charged, or a continuous system in which the metallic silicon and the catalyst are continuously charged during the reaction. Fluidized bed system in which the reaction is carried out by fluidizing with gas, moving bed system in which the reaction is carried out while moving metallic silicon and catalyst by vibration or physical force, or fixed bed system in which the reaction is carried out by fixing metallic silicon and catalyst. Either of these may be adopted. In any of these methods, the lower alcohol is generally supplied as a gas to the reaction system, and the supply is generally carried out continuously, but it can also be carried out intermittently.

The reaction temperature of the present invention is preferably 100 ° C to 450 ° C, particularly preferably 100 ° C to 300 ° C.
If the temperature is less than 100 ° C, the reaction rate will decrease,
If the temperature exceeds ℃, the lower alkyl alcohol may be decomposed by contact with metallic silicon and the catalyst, leading to deactivation of the catalyst.

The reaction of the present invention is carried out under reduced pressure. A suitable pressure is a pressure at which tetraalkoxysilane or other high-boiling products can vaporize at the reaction temperature, specifically, 7
10 mmHg-60 mmHg, more preferably 660-460 mm
Hg. If it exceeds 710 mmHg, the distillation of the high boiling point product to the outside of the reaction system may not be carried out smoothly, and the selectivity of trialkoxysilane may decrease. If it is less than 60 mmHg, the lower alkyl alcohol will be diluted and the reaction amount will decrease. As a result, the yield of trialkoxysilane may decrease.

The material of the reactor may be a quartz tube, a glass tube, a metal tube or the like, and is not particularly limited, but the structure of the reactor is a lower alkyl alcohol inlet, a heating and cooling device. , With product outlet,
An airtight structure is suitable.

The reaction product solution according to the reaction system of the present invention contains a high concentration of trialkoxysilane, and further contains tetraalkoxysilane and other side reaction products.
The target product trialkoxysilane can be easily separated and obtained from this reaction product solution by distillation or another ordinary method, and in the present invention in which the amount of the side reaction product is suppressed, This is easier than the conventional gas phase reaction method that is performed at atmospheric pressure or higher.

[0021]

In the present invention, by reducing the pressure of the reaction system, the high boiling point product is smoothly distilled out of the system, and the metallic silicon and the catalyst in the reactor are kept in a dry state throughout the reaction, and the reaction proceeds uniformly. .. Since the lower alkyl alcohol in the reaction system becomes leaner than in the reaction under atmospheric pressure, the amount of contact between the gaseous alcohol and the surface of solid metallic silicon decreases, resulting in a decrease in the reaction amount. However, such a decrease does not occur over a long period of time, the conversion rate of silicon is high, and the target trialkoxysilane can be obtained in a high yield.

The reason for this is not clear, but it is believed to be due to the following action. When the gas phase reaction is carried out at a pressure higher than atmospheric pressure as in the prior art, according to the findings obtained by the present inventors, in addition to the above-mentioned problems, tetraalkoxysilane and dimer formed by the side reaction And high boiling point products such as trimer silane compounds adhere to the surface of metallic silicon and do not separate,
The side reaction proceeds further and the high boiling point product becomes high molecular weight, and the metallic silicon becomes covered with the high boiling point product, so that the reaction rate gradually decreases and finally the reaction is deactivated. And the conversion rate of silicon was lowered. Further, the high-boiling product dissolves the trialkoxysilane which is the target product, and when the high-boiling product remains in the reaction system, the produced trialkoxysilane dissolves in the high-boiling product on the surface of the metal silicon, and further alkoxy The chemical reaction proceeded, resulting in a decrease in the selectivity of trialkoxysilane.

On the other hand, in the present invention, as described above,
The high boiling point product generated by the side reaction is rapidly removed before it becomes a high molecular weight because of the reduced pressure condition, and the reaction is carried out while the surface of the metallic silicon is always kept fresh. Therefore, the reaction amount does not decrease, the conversion rate of silicon is high, the selectivity of the trialkoxysilane which is the target is improved, and it is possible to stably manufacture for a long time.

[0024]

EXAMPLES Next, the present invention will be described with reference to Examples and Comparative Examples. Example 1 Metallic silicon having a chemical purity of 98 wt% and an average particle size of about 100 μm
300 g (10.68 mol) and 15 g of cuprous chloride were placed in a porcelain pot mill and pulverized and mixed for 8 hours, and the mixture was packed in a quartz tube having an inner diameter of 30 mm and a length of 600 mm. The inlet of this quartz tube is equipped with an inlet tube for blowing in the lower alkyl alcohol vaporized through the vaporizer, and the outlet is set with a cooler and a receiver to receive the produced liquid. Is connected to an aspirator via a pressure reduction degree adjusting valve, so that the inside of the reaction system can be adjusted to any degree of pressure reduction. While activating nitrogen gas at a flow rate of 30 ml / min in the reactor, the reactor was heated at 350 ° C. for 5 hours to activate the catalyst. Then, the nitrogen gas was stopped, the temperature of the reactor was maintained at 180 ° C., the pressure of the reactor was maintained at 660 mmHg by an aspirator, and 50 g / hr (1.5 g) of methanol vaporized from the inlet pipe of the reactor inlet was maintained.
It was introduced at a ratio of 6 mol / hr) and reacted. After 1 to 2 minutes from the start of the reaction, the product liquid started to distill out from the cooler. The time-dependent change in the composition of the product liquid distilled out was analyzed by gas chromatography, and the composition was 100% by weight of alcohol.
Was the end of the reaction. After 19 hours from the start of the reaction, the reaction was completed, and a reaction product liquid containing the target substance, trimethoxysilane, was obtained. Table 1 shows the analysis results of the composition of all the obtained product liquids, the selectivity of trialkoxysilane based on the analysis results, and the silicon conversion ratio. In addition,
The selectivity of trialkoxysilane and the conversion rate of silicon were calculated by the following formulas.

[0025]

[Table 1]

Comparative Example 1 The reaction was carried out in the same manner as in Example 1 except that the reaction was carried out in a normal pressure system in which the exhaust gas was opened to the atmosphere through an air washing bottle. 16 hours after the start of the reaction, the reaction was completed. Table 1 shows the analysis results of the composition of all the obtained product liquids, and the selectivity of trimethoxysilane based on the analysis results and the conversion rate of silicon.

Example 2 Instead of methanol, vaporized ethanol was added at 50 g / hr.
The reaction was carried out in the same manner as in Example 1 except that it was introduced at a ratio of (1.09 mol). After 31 hours from the start of the reaction, the reaction was completed, and a reaction product liquid containing the target product, triethoxysilane, was obtained. Table 1 shows the analysis results of the composition of all the obtained product liquids, the triethoxysilane selectivity based on the results, and the silicon conversion ratio.

Comparative Example 2 The reaction was carried out in the same manner as in Example 2 except that the reaction was carried out in a normal pressure system in which the exhaust gas was opened to the atmosphere through an air washing bottle. 16 hours after the start of the reaction, the reaction was completed. Table 1 shows the analysis results of the composition of all the obtained product liquids, and the selectivity of triethoxysilane based on the analysis results and the conversion rate of silicon.

[0029]

INDUSTRIAL APPLICABILITY The present invention is a method for producing trialkoxysilane by reacting metallic silicon and an alkyl alcohol having 1 to 4 carbon atoms in a gas phase system in the presence of a catalyst, wherein the reaction is carried out under reduced pressure. Thus, the production method has a high selectivity of trialkoxysilane, a high conversion rate of silicon, a stable reaction for a long period of time, and can easily separate and obtain trialkoxysilane.

Claims (1)

[Claims] 1. When a trialkoxysilane is produced by reacting metallic silicon with an alkyl alcohol having 1 to 4 carbon atoms in a gas phase in the presence of a catalyst, the reaction is performed under reduced pressure. Method for producing trialkoxysilane.