CN1309725C - Method for preparing dimethyldichlorosilane by using organosilicon high boiler - Google Patents

Abstract

A method for preparing dimethyldichlorosilane comprises the following steps: the high boiling point residue in the synthesis of methyl chlorosilane monomer is used as material, chloromethane (or hydrogen chloride) gas is passed through a gas preheater filled with catalyst and fed into a reactor with catalyst, and simultaneously high boiling point substance is introduced, and the condensate at the top of the tower is separated conventionally to obtain dimethyl dichlorosilane product. The method can improve the utilization rate of high-boiling-point substances to the maximum extent, and the dimethyl dichlorosilane (M)₂) The selectivity can reach more than 50 percent, the process is simple and convenient (the operation pressure is normal pressure), the condition is mild, the technical index is prominent (the conversion per pass is more than 90 percent), the requirement on a reactor is not harsh, the continuous production is easy, and the safety is also very high.

Description

Method for preparing dimethyldichlorosilane by using organosilicon high boiler

Technical field

The invention relates to a method for preparing dimethyldichlorosilane from a high-boiling residue of organic silicon through a gas-liquid phase cracking reaction and improving its selectivity.

Background technique

Silicone high boiling point residue (high boiling point) refers to the high boiling point polysilane with silicon-silicon bond and silicon-carbon-silicon bond in the boiling range of 80-215 °C produced during the synthesis of methyl chlorosilane monomer mixture. With the continuous expansion of the production scale of methyl chlorosilane monomer, the utilization of high boilers accounting for 5% of the monomer composition is becoming more and more important. At present, domestic high boiling substances are mainly used for the production of silicone waterproofing agents and defoaming agents. The market capacity is limited, and only about one-fifth of high boiling substances can be used every year. Environmental protection and safety issues, and a large amount of effective resources are wasted. The utilization of high boiling substances has become a serious obstacle restricting the development of China's organic silicon industry. Therefore, it is imminent to develop an effective industrial method for utilizing high boiling substances. .

Organic high boilers can be converted into monosilane by thermal cracking and catalytic cracking, and the main cracking products are methylhydrogendichlorosilane (MeHSiCl ₂ ), methyltrichlorosilane (MeSiCl ₃ ), dimethyldichlorosilane (Me ₂ SiCl ₂ ) and unreacted high boilers. From the 1950s to the 1970s, the thermal cracking method was mainly used. US Patent 2.598.435 and US Patent 2.681.355 introduced the thermal cracking reaction method of high boilers. The cracking temperature is 200-900 ° C, and the reactor is a heating tube type. Reactor, which can be empty or filled with quartz packing or some active material. Due to the high reaction temperature, the material in the reactor is seriously carbonized, and the selectivity of dimethyldichlorosilane (M ₂ for short) is low, generally 10-20%. After the 1970s, catalytic cracking gradually replaced thermal cracking and was in the leading position.

US Pat 4.059.608 and US Pat 4.079.071 introduced the use of active metals such as nickel and copper as catalysts, the cracking reaction of high boilers and hydrogen, and the reaction temperature dropped below 250-350 ° C. Even under such conditions, high The boiling conversion rate is still not very good, generally 60-70%, and there are great difficulties in industrial scale-up.

US 5 430 168 and US 5 321 147 introduce the use of aluminum trichloride as a catalyst. The process is as follows: first, the high boiler is mixed with organochlorosilane (low-boiling point monosilane), and the mixture is present in the presence of aluminum trichloride catalyst. Under the condition of hydrogen or hydrogen chloride, the reaction of bond breaking, rearrangement, hydrogenation, etc. is carried out, and the type of the final product obtained is controlled by controlling the type of organochlorosilane added. The reactor is a nickel, cadmium and copper alloy autoclave, the reaction temperature is 300-500 DEG C, the pressure is 4-7Mpa, the reaction time is 1-5h, and the consumption of aluminum trichloride is 0.1-30% (wt%). Aluminum trichloride can be recycled, but the reaction temperature is high. In addition, a composite catalyst of aluminum trichloride and palladium was also reported to improve the conversion rate of high boilers and the selectivity of dimethyldichlorosilane (M ₂ ). The effect is good, but the catalyst is expensive and difficult to prepare , the reaction conditions are harsh, and the high boiler must be separated from the solid residue, otherwise it will easily lead to catalyst poisoning.

JP 54-9228, JP 54-119 417 introduced the use of palladium phosphorus complexes, such as methyl phenyl phosphorus palladium as a catalyst, toluene or xylene as a solvent, high boiling matter (separation of solid impurities) and hydrogen chloride at 170 ° C The reaction time is 6-7 hours, and dimethyldichlorosilane can account for 40-50% of the obtained product.

US 5 627 297 reports that a metal phosphate is preferably combined with an alkaline impregnated substance, the catalyst form is powder or block, φ20mm×150mm quartz fixed bed reactor, high boiling material and hydrogen chloride are in the fixed bed The reaction can crack high boilers. For alkyl-rich high boilers, the _M2 selectivity is above 80%, but for chlorine-rich disilanes, the _M2 selectivity is not ideal.

U.S.5.288.892 introduces an improved method for separating methylchlorosilane monomers from high boilers synthesized from methylchlorosilanes. In this method, the cleavable methylchlorodisilane should have at least two chlorine atoms and one silicon Atoms are connected and cracked in the presence of hydrogen chloride; the process includes: separating methylchlorodisilane synthesis by-products with a boiling point of at least 70°C under normal conditions from methylchlorodisilane with a boiling point greater than 160°C; Cleavage of methylchlorodisilane under conditions higher than the presence of by-products of cleavable methylchlorodisilane; removed from the reaction mixture. The catalyst in this method is a triamine.

JP 52-83419 introduces N,N-dimethylaniline as catalyst, and the composition of high boilers is Me ₃ Si ₂ Cl ₃ , Me ₂ Si ₂ Cl ₄ . 110°C, the temperature of the tower body is 75°C, and the reaction is carried out under normal pressure.

The characteristics of various catalytic systems in the prior art are compared in Table 1:

Table 1 Comparison of technical indicators of different catalytic systems in the prior art catalyst Reactant Dimethicone selectivity technical features Organic amine aluminum trichloride hydrogen chloride hydrogen chloride 15-30% 10-27% M ₂ selectivity is low, and cleavable methyl chlorodisilane should have at least two chlorine atoms connected to a silicon atom (boiling point greater than 160 ° C) M ₂ selectivity is low, and the reactor cost is high (nickel, cadmium, copper alloy reactor ) operating pressure is high, between Palladium phosphorus complex metal phosphate hydrogen chloride hydrogen chloride 40～50%～80% The processing capacity of batch reaction is limited, the reaction time is long, the catalyst is expensive, and it is difficult to regenerate, so it is difficult to industrialize.

To sum up, the method for synthesizing monosilane by organosilicon high boiler cracking reaction can use different types of catalysts according to the different requirements for the target product. The main advantage of using organic amines as catalysts is that the conversion rate of high boilers is good, and the selection of _M2 The stability is basically between 15% and 30%. Industrial scale-up is easy, the reaction is easy to control, and the conditions are loose. However, the methods provided in the literature still have the following disadvantages:

1) Most of the high boilers are composed of some high boilers with a distillation range of 150-160°C. The methylchlorodisilane that can be cracked should have at least two chlorine atoms connected to a silicon atom, but it cannot crack Si-O -Si, Si-CH2-Si bonds (these bonds have high bond energy and are not easy to crack), and this part of high-boilers accounts for about 35% of all industrially obtained high-boilers.

2) Low selection (≤30%) for _M2 in the cleavage product.

3) In order to improve the _M2 selectivity, it is necessary to react under pressurized conditions, which requires relatively harsh equipment.

Contents of Invention

The purpose of the present invention is to overcome the deficiencies of the prior art, and to provide a kind of dimethyl dichlorosilane with high selectivity to prepare dimethyl dichlorosilane by gas-liquid phase cracking reaction using the whole component of organosilicon high boiler as raw material Methods.

The method for preparing dimethyldichlorosilane provided by the present invention is as follows: using the high-boiling point residue in the synthesis of methylchlorosilane monomer as a raw material, the methyl chloride (or hydrogen chloride) gas is preheated by the gas filled with the catalyst The reactor carries the catalyst into the reactor, and at the same time feeds high boilers, and the top product is routinely separated to obtain the dimethyl dichlorosilane product.

The raw material of the present invention is the whole component of the high boiling point residue in the synthesis of methylchlorosilane monomer, and its composition is shown in the following table:

Table 2. Composition table of high boilers Component molecular formula 1234567891011 Me ₃ Si-SiMe ₂ ClMe ₂ ClSi-O-SiMe ₂ ClMe ₂ ClSi-O-SiMeCl ₂ Me ₂ ClSi-SiMe ₂ ClMe ₂ ClSi-SiMeCl ₂ MeCl ₂ Si-SiMeCl ₂ Me ₂ ClSi-CH ₂ -SiMe ₂ ClMe ₂ ClSi-CH ₂ -SiCl ₃ Me _{3 Si} -SiCl ₂ -SiMe ₂ ClMe ₃ Si-CH ₂ -SiCl ₂ -CH ₂ -SiMeCl 2Others

The reactor in this method is a tower reactor type cracking reactor, which is divided into a stripping section and a rectifying section. Ring, the condensing medium of the top condenser is brine (-10~0°C), a high boiler feed distributor is set between the two sections of the tower, and a gas inlet is set at the lower part of the reaction tower.

The reaction pressure in the method is normal pressure, and the temperature of the reactor is 120-150°C, preferably 130-140°C. The temperature in the rectifying section can be controlled at greater than 140-150°C, and the temperature in the stripping section is between 60-100°C, preferably 70-90°C.

The molar ratio of high boiling point residue to methyl chloride or hydrogen chloride is 1:1.05-1.1. The catalyst is 1.0-1.5% (wt) of the high boiling point residue. The catalyst used is tri-n-butylamine, which can be industrial tri-n-butylamine with a purity greater than 98%.

Accompanying drawing 1 is process flow diagram of the present invention, wherein:

1-High boiling material storage tank 2-Gas dryer

3-Gas preheater 4-Cracking kettle

5-Pyrolysis reaction tower 6-Pyrolysis stripping tower

7-condenser 8-product storage tank

9- Unreacted substance storage tank

The method provided by the present invention uses the full components of the high-boiling point composition in the synthesis of methylchlorosilane monomers as raw materials, which overcomes the problem that the crackable methylchlorodisilane should have at least two chlorine atoms and one silicon atom in the prior art. Linked, but can not crack the disadvantages of components containing Si-O-Si, Si-CH ₂ -Si bonds, can maximize the utilization of high-boiling substances synthesized from methyl chlorosilane monomers, and have significant economic and social benefits . The method can continuously crack high boilers in a tower reactor cracking reactor, and the selectivity of dimethyldichlorosilane (M ₂ ) in the cracking product is generally 35-50%, which overcomes the use of organic amine catalysts in the prior art At that time, its _M2 selectivity is generally only a shortcoming of 15 to 30%, and the _M2 selectivity of the present invention can reach more than 50%. To sum up, the inventive technology can successfully solve the problem of a large excess of high boilers in the current domestic organosilicon monomer production equipment, so that as many high boilers as possible can be converted into monosilane. This reaction is relatively easy to control, the process is simple (the operating pressure is normal pressure), the conditions are mild, and the technical indicators are outstanding (the _M2 selectivity in monosilane is 35-50%, and the single-pass conversion rate is greater than 90%), and the requirements for the reactor are not harsh. , easy continuous production, and high safety.

Detailed ways

Example 1:

High boilers (see table for composition) are added to the tower still type cracking reactor at a speed of 40g/h, the hydrogen chloride feed rate is 75ml/min, and the tri-n-butylamine consumption in the gas preheater is the total amount of high boiler monomers 1%, the reaction temperature is 125-130°C, the temperature in the rectification section is 140±2°C, the temperature in the stripping section is 85°C, and it operates under normal pressure. The top product is 43-47g/h, the reaction is carried out for 50h, and the conversion rate is 91.62%. The composition of the lysate is shown in Table 3.

Table 3 Product Gas Chromatography Analysis MeHSiCl ₂ MeSiCl ₃ Me ₂ SiCl ₂ 1～10h11～20h21～30h31～40h41～50h1～50h 38.1844.5943.9739.0026.5939.79 16.0520.2621.2016.8526.8521.03 42.7132.6629.8741.3043.4536.93

Example 2:

The reaction process is the same as in Example 1, the amount of tri-n-butylamine is 1.5% of the total amount of high boiler monomers, the overhead product is 45-48g/h, the reaction is carried out for 50h, and the conversion rate is 92.9%. The composition of the cleavage product is shown in Table 4.

Table 4 Product Gas Chromatography Analysis Reaction time MeHSiCl ₂ MeSiCl ₃ Me ₂ SiCl ₂ 1～10h11～20h21～30h31～40h41～50h1～50h 38.6632.5631.1919.2415.6629.44 7.847.5427.3431.1140.6120.32 48.7856.4338.4345.7140.3246.41

Example 3:

The reaction process is the same as in Example 2, using tri-n-butylamine as a catalyst, the overhead product is 28-32g/h, the reaction is carried out for 50h, and the conversion rate is 70.47%. The composition of the cleavage product is shown in Table 5.

Table 5 Product Gas Chromatography Analysis Reaction time _MeCl3 MeSiCl ₃ Me ₂ SiCl ₂ high boiler 1~10h 5.39 25.31 56.42 11.18 11~20h 6.20 34.69 49.93 8.39 21~30h 6.02 31.26 54.38 10.28 31~40h 5.48 28.79 47.61 9.97 41~50h 6.51 29.98 53.19 11.06 1~50h 5.78 30.06 52.68 10.01

Claims (5)

1. method for preparing dimethyldichlorosilane(DMCS): the full component of high boiling residue with the methyl chlorosilane monomer in synthetic is a raw material, methyl chloride gas is passed through the gas preheater of catalyst filling, carry catalyzer secretly and entering reactor, and feeding high boiling material simultaneously, overhead condensate obtains the dimethyldichlorosilane(DMCS) product through the routine separation.

2. method according to claim 1 is characterized in that reaction pressure is a normal pressure, and temperature of reactor is 120-150 ℃.

3. method according to claim 1, it is characterized in that wherein high boiling residue and the mol ratio of methyl chloride be 1: 1.05～1.1.

4. method according to claim 1 is characterized in that catalyzer wherein is 1.0% weight～1.5% weight of the high boiling residue of methyl chlorosilane monomer in synthetic.

5. method according to claim 1 is characterized in that catalyzer wherein is a tri-n-butylamine.

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