RU2470697C2 - Method of cleaning abgases of methyl chloride - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to silicone synthesis. Methyl chloride is absorbed from abgases of direct synthesis of methyl chlorosilanes by liquid absorbent composed of rude mix of methyl chlorosilanes produced after methyl chloride distillation from direct synthesis products condensed earlier that flow out from reactor, at counterflow heat exchanger column at not over 20°C. After absorption, abgases contain less than 0.05 wt % of methyl chloride. Absorption column is additionally cooled by coolant with temperature equal to or lower than -20°C. Absorption column height makes, at least, four and not over eight theoretical trays, preferably, five-six trays. Adsorption pressure corresponds to that of methyl chlorosilanes synthesis with no extra compression of reaction mix.

EFFECT: wasteless and efficient process.

1 cl, 18 ex

Description

The invention relates to chemical technology of organosilicon synthesis, in particular to a method for the isolation of methyl chloride from the exhaust gases of the synthesis of methylchlorosilanes (MCS).

In the catalytic synthesis of MCS from metallic silicon and methyl chloride (XM), in addition to methylchlorosilanes, a large number of reaction by-products (gases) are formed, the main of which are hydrogen and methane. The conversion of methyl chloride during the synthesis of MHS is usually from 40% to 60%. A gas-vapor mixture consisting of MCS, XM and gas, leaving the synthesis reactor at elevated pressure (from 0.1 to 0.3 MPa gage), is subjected to sequential condensation with water (plus 20 ÷ 25 ° C) and refrigerants (minus 15 ° C and minus 30 ° C). In this case, almost all methylchlorosilanes and most of the ChM can be condensed. However, the content of methyl chloride in gases after condensation is from 85% wt. (at 0.1 MPa gage) up to 70% wt. (at 0.3 MPa gage). Such significant losses of methyl chloride with exhaust gases are not economically advantageous and are not acceptable due to environmental pollution.

A known general method for removing a volatile organic compound from a gas stream polluted by it (patent RU 2090247, IPC B01D 53/14, 1997), namely, that the polluted gas stream is in contact with a stream of less volatile liquid absorbent, followed by separation of the absorbed volatile organic compound from the absorbent by fractional distillation. Organic solvents, vegetable or mineral oil are used as absorbent.

The disadvantage of this method is the additional distillation treatment of the absorbent. In addition, methyl chloride released from the absorbent must be disposed of.

To clean gas emissions from methyl chloride, a method for the absorption of methyl chloride by an absorbent in countercurrent of contacting phases at a temperature of minus 20 ° C to minus 25 ° C is proposed, while kerosene boiling off at a temperature of 180-300 ° C is used as an absorbent (patent RU 2355465 IPC B01D 53/70, 2009). This method allows you to extract up to 89% methyl chloride from gas emissions and reduce its concentration in exhaust gases to a level of less than 3% wt. Methyl chloride is isolated as an individual product after desorption at a temperature of 20 ÷ 30 ° C.

The disadvantages of this method include a high degree of contamination of the resulting methyl chloride with kerosene. In the process of obtaining methylchlorosilanes and their subsequent distillation separation, it is organic impurities that are the most difficult to separate components that reduce the quality of commercial methylchlorosilanes.

Closest to the proposed invention and adopted as a prototype is a method for the separation of ethyl chloride from the exhaust gases of the chlorination process of ethyl alcohol, which consists in the sorption of ethyl chloride from gases using ethyl alcohol cooled to minus 35 ÷ 25 ° C, followed by rectification of the absorbate with isolation of a light fraction of ethyl chloride and bottoms, the purified absorbent is returned to the absorption of ethyl chloride or sent to the main technological process (patent RU 2063951, IPC С0 7C 17/23, 1996).

The disadvantage of this method is the need to clean the absorbent (ethyl alcohol) before returning it to the main process. In addition, during the cleaning of the absorbent, impurities are emitted in the form of bottoms, which are difficult to recycle production waste.

The objective of this invention is to create a simple safe method for the purification of gases from methyl chloride for the synthesis of methylchlorosilanes, reducing energy costs by reducing the number of associated cleaning processes used technological mixtures and reducing the amount of industrial waste.

The problem is achieved by the fact that the proposed method of purification of gases from methyl chloride by absorption, which consists in the use of a crude mixture of methylchlorosilanes as the absorbent obtained after the stage of separation of methyl chloride from the condensate of the reaction mixture of methylchlorosilanes, while the absorbent with absorbed methyl chloride is mixed with condensate the reaction mixture of methylchlorosilanes and sent to the stage of separation of methyl chloride and condensate of the reaction mixture of methylchlorosilanes, and the absorption is carried out in a bogie countercurrent mass transfer apparatus at a pressure provided by the stages of synthesis and condensation of the reaction mixture of methylchlorosilanes and at a temperature not exceeding minus 20 ° С, and the absorption column is additionally cooled by a refrigerant whose temperature is equal to or lower than minus 20 ° С.

Absorption of gases from methyl chloride is carried out by absorption in a column countercurrent mass transfer apparatus equipped with a nozzle or plate contact device with the number of theoretical plates of at least 4 and no more than 8, optimally 5 ÷ 6 theoretical plates. The crude mixture of methylchlorosilanes obtained after condensation of the products of the direct synthesis of methylchlorosilanes and separation of unreacted methyl chloride from it is fed to the column countercurrent mass transfer apparatus after cooling the methylchlorosilanes with a refrigerant at a temperature of minus 20 ° C or lower, while the amount of the crude mixture of methylchlorosilanes fed for irrigation is determined by the absorption pressure of methyl chloride. In countercurrent mode, the cooled absorbent contacts the gases of the synthesis of methylchlorosilanes and absorbs methyl chloride from them. The crude mixture of methylchlorosilanes, with the absorbed methyl chloride, is returned to the methyl chloride distillation stage for co-processing with the main condensate stream of the methylchlorosilanes reaction mixture released after the condensation system of the methylchlorosilanes synthesis reaction products. The whole process of absorption of methyl chloride from exhaust gases is carried out at the pressure provided by the stages of synthesis and condensation of the synthesis products without additional compression, in the range from 0.15 MPa (abs.) To 0.5 MPa (abs). The amount of raw methylchlorosilanes used to capture methyl chloride from exhaust gases is determined by the pressure at which absorption is carried out, and can vary from 6 kg to 12 kg of raw methylchlorosilanes per 1 kg of methyl chloride contained in the exhaust gases of the synthesis of methyl chlorosilanes at a methyl chloride absorption pressure of more 0.4 MPa. At a methyl chloride absorption pressure from 0.2 MPa to 0.4 MPa, inclusive, the amount of crude methichlorosilanes used to trap methyl chloride from exhaust gases can vary from 8 kg to 22 kg per 1 kg of methyl chloride. At a methyl chloride absorption pressure of 0.2 MPa or less, the amount of crude methylchlorosilane can vary from 18 kg to 30 kg per 1 kg of methyl chloride.

The method of purification of gases from methyl chloride is economical and waste-free, as it eliminates the stages of additional compression of gases and an additional system for the regeneration of absorbent material. In addition, contamination of methyl chloride and absorbent with foreign impurities is eliminated, which ensures complete recycling of methyl chloride and methyl chlorosilanes in the process without compromising the quality of commercial methyl chlorosilanes.

The absorption column can be cooled, providing an isothermal absorption mode. It is also possible to cool the absorbate, which is heated during the absorption process, for which remote heat exchange circuits are used. Due to cooling of the absorbate, the technical effect is achieved with less raw methylchlorosilanes used to capture methyl chloride from exhaust gases, while maintaining the absorption pressure.

When isothermal absorption is ensured by continuous cooling of the column, the amount of crude methylchlorosilanes used to capture methyl chloride from exhaust gases is determined by the pressure at which absorption is carried out, and can vary from 4 to 8 kg of crude methylchlorosilanes per 1 kg of methyl chloride contained in the exhaust gases of methylchlorosilanes at methyl chloride absorption pressure of more than 0.4 MPa. When the methyl chloride absorption pressure is from 0.2 to 04 MPa, inclusive, the amount of crude methylchlorosilanes can vary from 6 to 17 kg per 1 kg of methyl chloride. At a methyl chloride absorption pressure of 0.2 MPa or less, the amount of crude methylchlorosilane can vary from 14 to 20 kg per 1 kg of methyl chloride.

EXAMPLE 1

Absorption gases of the synthesis of methylchlorosilanes at a pressure of 0.15 MPa (abs.) And a temperature of less than minus 20 ° C exit the stage of condensation of methylchlorosilanes and enter the lower part of the column mass transfer apparatus. Abgases are composed of hydrogen, methane and methyl chloride. The concentration of methyl chloride in gases is 44 mol%. (85% wt.). Irrigation in the form of raw methylchlorosilanes with a temperature of less than minus 20 ° C in the amount of 30 kg of irrigation per 1 kg of methyl chloride is fed to the upper part of the apparatus. In countercurrent mode, the synthesis gases from the gas are contacted with the raw methylchlorosilanes, as a result of which methyl chloride from the gases is effectively captured. The residual concentration of methyl chloride in gases after the stage of absorption is 0.02% wt.

EXAMPLES 2-9.

Purification of gases is carried out as in example 1. The amount of raw methylchlorosilanes supplied for irrigation is determined by the pressure at which methyl chloride is absorbed.

Example number Synthesis pressure, MPa (abs.) The amount of raw MHS supplied for irrigation, kg / kg HM The content of XM in gases after absorption,% wt. one 0.15 thirty 0.02 2 0.2 thirty 0.014 3 0.2 22 0.016 four 0.3 22 0.01 5 0.3 12 0.02 6 0.4 12 0.01 7 0.4 8 0.02 8 0.5 8 0.01 9 0.5 6.2 0.02

EXAMPLE 10

Absorption gases of methyl chloride synthesis at a pressure of 0.15 MPa (abs.) And a temperature of less than minus 20 ° C exit the condensation stage of methylchlorosilanes and enter the lower part of the column mass transfer apparatus. Abgases are composed of hydrogen, methane and methyl chloride. The concentration of methyl chloride in gases is 44 mol%. (85% wt.). Irrigation in the form of raw methylchlorosilanes with a temperature of less than minus 20 ° C in the amount of 20 kg of irrigation per 1 kg of methyl chloride is fed to the upper part of the apparatus. The apparatus, in which the contact of gases and raw methylchlorosilanes is carried out, is continuously cooled by a refrigerant with a temperature of less than minus 20 ° С. In countercurrent mode, the synthesis gases from the gas are contacted with the raw methylchlorosilanes, as a result of which methyl chloride from the gases is effectively captured. The residual concentration of methyl chloride in gases after the stage of absorption is 0.03% wt.

EXAMPLES 10-18.

Purification of gases is carried out as in example 10. The amount of raw methylchlorosilanes supplied for irrigation is determined by the pressure at which methyl chloride is absorbed.

Example number Synthesis pressure, MPa (abs.) The amount of raw MHS supplied for irrigation, kg / kg HM The content of XM in gases after absorption,% wt. 10 0.15 twenty 0,03 eleven 0.2 twenty 0.016 12 0.2 17 0.02 13 0.3 17 0.01 fourteen 0.3 8 0,03 fifteen 0.4 8 0.01 16 0.4 5 0.05 17 0.5 5 0.02 eighteen 0.5 3 0.04

Claims (1)

The method of purification of gas from methyl chloride by absorption, which consists in the use of a crude mixture of methyl chlorosilanes as the absorbent obtained after the stage of separation of methyl chloride from the condensate of the reaction mixture of methyl chlorosilanes, while the absorbent with absorbed methyl chloride is mixed with the condensate of the reaction mixture of methyl chlorosilanes and sent to the stage separation of methyl chloride and condensate of the reaction mixture of methylchlorosilanes, and the absorption is carried out in a column countercurrent mass transfer apparatus with yes the phenomenon provided by the stages of synthesis and condensation of the reaction mixture of methylchlorosilanes, and a temperature of not higher than minus 20 ° C, and the absorption column is additionally cooled by a refrigerant whose temperature is equal to or below minus 20 ° C.