Green and environment-friendly recycling method of trichlorosilane tail gas

Abstract

The invention discloses a green and environment-friendly recycling method of trichlorosilane tail gas, which comprises the following steps: (1) transmitting the tail gas generated in the process of synthesizing trichlorosilane to an absorption tower, adopting two-stage absorption by an absorption tower, cooling hydrogen exhausted from the tower top of the absorption tower to obtain a liquid phase component, reflowing the liquid phase component to the top of the absorption tower, conducting heat exchange for coarse chlorosilane and hydrogen chloride exhausted from the tower bottom of the absorption tower, and transmitting chlorosilane condensate to a rectifying tower for rectification with the coarse chlorosilane and the hydrogen chloride after heat exchange; (2) completely reflowing overhead fraction in the rectifying tower after passing through the condensed liquid phase, and simultaneously entering into a cryogenic device in a gaseous phase mode for condensation, extracting hydrogen chloride in a liquid phase mode, and returning the gaseous phase mixture extracted from the cryogenic device to the absorption tower as feeds; and (3) enabling one part of tower bottom discharged material to enter into coarse chlorosilane rectification system and the other part thereof after cooling to return the absorption tower as a main absorption liquid in step (1). The invention adopts a recycling system which comprises a single tower for two-stage absorption and rectification so as to obtain hydrogen, hydrogen chloride and chlorosilane with high purity and completely eliminate tail gas emission.

Description

technical field [0001] The invention relates to an environmentally friendly recycling method for tail gas, in particular to a green and environmentally friendly recycling method for trichlorosilane tail gas. Background technique [0002] Trichlorosilane is an important chemical raw material, which can be used to produce silane coupling agent and prepare polysilicon. With the continuous increase of polysilicon production, the demand for trichlorosilane continues to expand. [0003] Trichlorosilane is synthesized by hydrogen chloride and silicon powder in a fluidized bed reactor under the reaction conditions of 0.12-0.20MPa (absolute pressure) and 250-350°C. The equation of reaction is: Si+3HCl==HSiCl 3 +H 2 , the main side reaction is Si+4HCl==SiCl 4 +2H 2 , In addition, a small amount of dichlorodihydrosilane is generated. In order to make the silicon powder react completely, there is a 5%-10% excess of hydrogen chloride in the reactor, so the trichlorosilane synthesis ...

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Problems solved by technology

However, in this process, on the one hand, the water washing of the tail gas will produce waste hydrochloric acid. On the other hand, after the condensate enters the rectification system, the hydrogen chloride and hydrogen in it will become non-condensable gases during the rectification process, and part of the trichlorohydrogen will be taken away. Silicon, discharged into the atmosphere or water wash system, becomes a source of pollution

[0009] In response to the above problems, Chinese Patent Application No. 200710018581.1 proposed a membrane separation method for tail gas treatment, which effectively solved the problem of direct discharge of tail gas to pollute the environment, but the recovered hydrogen chloride contained 27.77% trichlorosilane, and the recovered hydrogen contained trichlorohydrogen The content of silicon is very high, and the recovered chlorosilane also contains 4.77% hydrogen chloride, which will take away trichlorosilane and discharge it as non-condensable gas during the rectification process. Therefore, the membrane separation method only solves the problem of partial tail gas recovery

[0010] Chinese Patent Application No. 200810044477.4 proposes a process of absorbing tail gas with silicon tetrachloride, and further absorbing hydrogen chloride with dilute hydrochloric acid, but the chlorosilane discharged from the primary absorption tower will contain hydrogen chloride and hydrogen, which will affect the subsequent rectification process, and the introduction of dilute hydrochloric acid will increase the difficulty of equipment selection

[0011] Chinese Patent Application No. 200810163037.0 proposes to use the delightened chlorosilane as the absorption liquid, discharge hydrogen chloride at the top of the absorption tower 4, and discharge and recover hydrogen in the tower 4 with silicon tetrachloride as the absorbent, and proposes many claim, but its process has the following fatal flaws: its absorption and regeneration towers 5 and 6 have no outlets and inlets for absorbents, and the discharged gas will contain absorbent silicon tetrachloride, and the absorption and desorption system will make the initial addition The absorption fluid is quickly consumed

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