RU2203900C2 - Method for production of methylchlorosilanes - Google Patents

Abstract

FIELD: industrial organic synthesis. SUBSTANCE: methylchlorosilanes are prepared by reaction of methyl chloride with contact mass comprising (i) mixture of silicon, copper, and aluminum powders and (ii) activator consisting of zinc and/or its compounds and antimony, tin, phosphorus, or their compounds at 250-350 C and pressure 0.1-0.5 MPa. According to invention, methyl chloride first reacts with contact mass containing mixture of silicon, copper, and aluminum powders and activator until 2 to 10% of silicon is consumed, after which methyl chloride interacts with contact mass containing mixture of silicon and copper powders and activator. EFFECT: prolonged smooth process time, reduced formation of high-boiling compounds, increased silicon consumption degree and process productivity. 1 tbl, 14 ex

Description

 The invention relates to the production of organochlorosilanes, in particular to a method for producing methylchlorosilanes (MHS), which are the main raw material for the industrial production of organosilicon polymers.

The interaction of methyl chloride (XM) with silicon in the presence of a copper catalyst and activators proceeds at elevated temperatures of 250-350 ^o C. As a result of the reaction, XM is partially converted into a mixture of methylchlorosilanes (MHS), consisting of the target products: dimethyldichlorosilane (DMDCS), methyltrichlorosilane (MTHS) ), trimethylchlorosilane (TMHS), methyldichlorosilane (MDHS). Along with this, by-products are formed in appreciable quantities - silicon tetrachloride (CHC), dimethylchlorosilane (DMHS), tetramethylsilane (TMS) and waste products, for example high-boiling compounds (polysiloxanes, polysilanes, etc.). The reaction mixture is subjected to rectification with the release of target products and broad fractions containing by-products and waste. The target compounds are used in the production of organosilicon polymer products.

 A known method of producing alkylchlorosilanes by the interaction of alkyl chloride with a contact mass containing silicon, copper and activators - arsenic or phosphorus, or antimony or tin, or mixtures thereof, as well as zinc or zinc chloride - in order to increase the yield of target products (ed. Certificate. 178817 , MKI C 07 f, 1966).

 The disadvantage of this method is the low productivity of the process (37-72 g MHS with 1 kg of contact mass per 1 hour) and, accordingly, the conversion of silicon contact mass.

The closest in technical essence to the proposed method and adopted by us for the prototype is a method for producing a mixture of methylchlorosilanes (ed. Certificate. 1162200, MKI C 07 F 7/16, 1996). The method consists in the interaction of methyl chloride with siliceous contact mass, which is a mixture of powders of silicon, copper, antimony, zinc or its chloride and aluminum at a temperature of 260-330 ^o With a pressure of 0.1-0.5 MPa. The maximum declared productivity of 321 g of MHS from a kilogram of contact mass per hour at a temperature of 260 ^o C and a pressure at the top of the reactor of 0.5 MPa. The synthesis time of 7 hours. Calculated according to the data given in the examples of the description of the invention, the production of silicon is only 48-52%.

The disadvantage of this method is the relatively low productivity of the process and the production of silicon contact mass. This is most clearly manifested in continuous or prolonged process management, which indicates a low process stability. Indeed, with an increase in the duration of the experiment to 40 hours or more while loading new portions of the contact mass, the silicon conversion increased slightly (to 72.2%), and the total productivity of the process dropped to 150 g / kg • h. At the same time, the selectivity of the process for DMDCS decreases to 75.6% while increasing the yield of highly chlorinated products and pyrolysis products (trichlorosilane, CHC, abgases, etc.)
The objective of the present invention is to increase the productivity of the process as a result of maintaining stable performance over a long period of operation of the reactor.

The problem is solved by the proposed method for producing methylchlorosilanes, which consists in the interaction of methyl chloride with a contact mass, which is a mixture of powders of silicon, copper, aluminum and activators (zinc or its compounds and antimony, tin, phosphorus or their compounds) at temperatures up to 350 ^o C and pressure up to 0.5 MPa, in which, according to the invention, methyl chloride is contacted with a contact mass comprising a mixture of silicon, copper, aluminum and activator powders until a silicon production of 2-10% is reached, after four The first interaction of methyl chloride is carried out with a contact mass, including a mixture of powders of silicon, copper and activators.

 In this case, aluminum is contained only in the initial loading of the contact mass and is absent in the contact mass supplied to the partial load. The optimal aluminum content in the initial contact mass is 0.01-0.5%.

 In experiments conducted under the conditions of the prototype, it was found that aluminum is the likely cause of low stability and a decrease in process performance and silicon conversion. Indeed, the introduction of aluminum into the composition of the contact mass (in addition to aluminum, which is usually present in technical silicon) activates it, but at the same time leads to an increase in the rate of pyrolytic processes, as a result of which the content of high-boiling products in the raw material of MCS sharply increases, the yield of target products decreases, and loss of silicon and worsens the dynamics of the process.

 We have found that there is a time-optimal effect of aluminum on the contact mass, during which, apparently, a more optimal catalytic system is formed on the silicon surface, and this, along with a reduction in the induction period, leads to an increase in the stability of the process and the preservation of high selectivity by DMDCS throughout the process, reducing the yield of high-boiling products and increasing the conversion of silicon.

 This technique allows you to reduce, as is the case in the prototype method, the induction reaction period by 2–3 times, and most importantly, to conduct the process for a long time at stable high rates, significantly reduce the content of high-boiling products, and, as a result, increase the productivity of the process. The choice of the moment of starting the loading of fresh contact mass was determined by us depending on the production of silicon in the reactor, which affects the course and results of the reaction. Silicon production can be determined by the amount of silicon transferred to the reaction products, or by reducing the height of the reaction zone relative to the initial charge.

 The process according to this invention can be carried out in reactors with a fluidized bed, and with mechanical stirring or a fixed bed of contact mass.

 The contact mass before the start of the process can be further treated at elevated temperature with hydrogen chloride or chlorosilanes or a mixture of them with methyl chloride.

 Data illustrating the invention are presented in the examples and table.

Example 1
The synthesis of methylchlorosilanes is as follows. At room temperature, 243.35 g (97.3%) of silicon powder was mixed; 5.0 g (2%) of copper powder; 0.005 g (0.002%) of antimony powder; 0.005 g (0.002%) of tin powder; 0.5 g (0.2%) of an alloy of copper with phosphorus containing 14% phosphorus; 0.5 g (0.2%) of zinc powder and 0.63 g (0.25%) of aluminum powder. The resulting mixture of powders at room temperature is placed in a reactor, which is a glass tube with a diameter of 30 mm and a height of 500 mm, equipped with an electric heater over the entire height and in the lower part a porous plate for introducing methyl chloride. In the upper part of the reactor there is a device for loading fresh contact mass and a filter for cleaning solid particles coming out of the reactor mixture.

The contact mass is purged with nitrogen for 30 minutes and heated with an electric heater to 300 ^o C. In the lower part of the reactor serves methyl chloride at a speed of 150 g / h At the same time, the upper level of the contact mass in the reactor, which is located at a distance of 38 cm from the porous plate, is noted.

 The resulting reaction products are condensed in a trap, cooled with a mixture of dry ice-acetone. After 20 minutes from the start of methyl chloride supply, the contact mass drops to 37 cm. The weight of the reaction products captured is 49.5 g. According to gas-liquid chromatography, they contain 24 g of MHS of the following composition: 73.4% DMDCS, 22.8% MTHS, 3.0% TMHS, 0.2% ChHC, 2.5% MDHS, 0.1% DMHS, 0.5% TMS. The reaction products contain 5.04 g of silicon, which is 2% of the silicon powder initially loaded into the reactor. A contact mass consisting of 97.55% silicon, 2% copper, 0.004% antimony, 0.004% tin is added to the reactor to the previous level; 0.2% alloy of copper with phosphorus and 0.2% zinc.

 After that, the weight of the obtained products is determined hourly and analyzed by GLC. Based on these data, the amount of silicon transferred to the reaction products and, accordingly, the amount of necessary loading to replenish the loss of contact mass, consisting of 97.55% silicon, 2% copper, 0.004% antimony, 0.004% tin, are determined; 0.2% alloy of copper with phosphorus and 0.2% zinc.

 The main process indicators are calculated at 7 (as in the prototype) and 40 hours from the start of the process.

 Examples 1-4 are made on the composition of the contact mass presented in Example 1.

 Example 5: 243.35 g (97.3%) of silicon powder are mixed; 5.0 g (2%) of copper powder; 0.01 g (0.004%) of antimony trichloride powder; 0.005 g (0.002%) of tin powder; 0.5 g (0.2%) of an alloy of copper with phosphorus containing 14% phosphorus); 0.5 g (0.2%) of zinc powder and 0.63 g (0.25%) of aluminum powder.

 Example 6: 242.85 g (97.2%) of silicon powder are mixed; 5.0 g (2%) of copper powder; 0.005 g (0.002%) of antimony powder; 0.005 g (0.002%) of tin powder; 0.5 g (0.2%) of an alloy of copper with phosphorus containing 14% phosphorus; 1.0 g (0.4%) of anhydrous zinc chloride and 0.63 g (0.25%) of aluminum powder.

 Example 7: 243.55 g (97.4%) of silicon powder are mixed; 5.0 g (2%) of copper powder; 0.005 g (0.002%) of antimony powder; 0.01 g (0.004%) of tin dichloride; 0.3 g (0.12%) of phosphorus trichloride; 0.5 g (0.2%) of zinc powder and 0.63 g (0.25%) of aluminum powder.

 Example 8 is made by the prototype method.

 The experimental results are presented in the table.

As can be seen from the presented examples, the proposed method in comparison with the prototype has a higher performance due to
- increase the time of a stable process from 7 to 40 hours or more,
- reduce the formation of high-boiling compounds in the reaction products from 4.3-6.6 to 1.3-2.0%,
- increase the degree of production of silicon contact mass up to 92% and above.

 The optimum degree of silicon production for loading the contact mass is 2-10%. Below this value, the achieved effect is markedly reduced. The same is observed in the case of a deeper production of silicon contact mass.

Claims (1)

A method of producing methylchlorosilanes by the interaction of methyl chloride with a contact mass, which is a mixture of powders of silicon, copper, aluminum and an activator consisting of zinc or its compounds and antimony, tin, phosphorus or their compounds, at a temperature of up to 350 ^o C and pressure up to 0.5 MPa, which consists in the fact that the interaction of methyl chloride with the contact mass is carried out in the reactor until silicon production of 2-10 wt. %, after which a contact mass is added to the reactor, including a mixture of silicon, copper and activator powders, and its interaction with methyl chloride is carried out.

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