RU2162835C2 - Method of preparing tetrafluoroethylene - Google Patents

Abstract

FIELD: chemical industry. SUBSTANCE: process comprises pyrolysis of difluoroechloromethane with additives of octafluorocyclobutane and 1,1,2,2-tetrafrluorochloroethane as azeotropic mixture in the presence of steam, hardening of pyrolysis products, separation of hydrogen chlorine by-product to prepare hydrochloric acid, neutralization, compression and condensation of pyrolysis products and separation of desired product, unreacted difluorochloromethane and by multistep rectification thereof. Process is carried out by adding diethylamine either into still of rectification column intended for isolation of difluorochloromethane or into still of rectification column intended for isolation of azeotropic mixture. Contamination with toxic unsaturated compounds is thus reduced due to conversion of said compounds into low-volatile compounds. EFFECT: more efficient preparation method. 3 cl, 3 ex, 1 tbl

Description

 The invention relates to the field of organic chemistry and can be used to produce tetrafluoroethylene - raw materials for the production of various fluorine-containing polymers and copolymers, as well as many organofluorine compounds.

 Tetrafluoroethylene is industrially produced by pyrolysis of difluorochloromethane. The technological process consists of the following main stages: pyrolysis, quenching, neutralization, compression and condensation of the pyrolyzate, isolation of commercial products (see Industrial organofluorine products. Handbook. St. Petersburg, Chemistry, 1996, p. 314). The pyrolysis of difluorochloromethane is accompanied by the formation of by-products that complicate the process of producing tetrafluoroethylene and reduce the utilization of raw materials.

 One of the known methods for producing tetrafluoroethylene (see RF patent N 2061672, IPC 6 C 07 C 21/185, 17/00, publ. 06/10/96) solves most of the problems of tetrafluoroethylene production, improves environmental parameters, and improves the efficiency of tetrafluoroethylene production due to utilization a number of by-products of pyrolysis. This method of producing tetrafluoroethylene is closest to the proposed combination of essential features. It includes pyrolysis of difluorochloromethane, quenching of pyrolysis products, separation of hydrogen by-product to produce hydrochloric acid, neutralization, drying, compression and condensation of pyrolysis products to isolate the desired product, while pyrolysis of difluorochloromethane is carried out in the presence of water vapor and an addition of octafluorocyclobutane and 1,1,2 , 2-tetrafluorochloroethane in the form of an azeotropic mixture in an amount of 2-15 wt.% In relation to difluorochloromethane, which is isolated by distillation from the bottom fraction obtained in the multi-stage process rectification of pyrolysis products after isolation of the target product and unreacted difluorochloromethane from them.

 As a result of sequential multi-stage distillation of the pyrolysis products in bottoms, especially in the bottoms fraction, from the evolution of an azeotropic mixture of octafluorocyclobutane and 1,1,2,2-tetrafluorochloroethane, toxic unsaturated compounds such as pentafluorochloropropylene and perfluoroisobutylene accumulate.

 The technical problem solved by the invention is to increase the safety of the process, reducing the possibility of toxic toxic unsaturated compounds due to their transfer to non-volatile compounds.

 The stated technical problem is solved in that in a method for producing tetrafluoroethylene, including the pyrolysis of difluorochloromethane with the addition of octafluorocyclobutane and 1,1,2,2-tetrafluorochloroethane in the form of an azeotropic mixture in the presence of water vapor, quenching of the pyrolysis products, separation of hydrogen by-product to produce hydrochloric acid, neutralization, compression and condensation of pyrolysis products with the isolation of the target product, unreacted difluorochloromethane and an azeotropic mixture of octafluorocyclobutane and 1,1,2,2-tetrafluorochlo ethane multistage distillation, diethylamine introduced into the distillation products.

 Diethylamine can be used as a mixture with an aqueous solution of sodium hydroxide.

 Diethylamine is introduced either at the stage of separation of the azeotropic mixture of octafluorocyclobutane and 1,1,2,2-tetrafluorochloroethane, or in the bottom fraction after isolation of the specified azeotropic mixture.

The bottoms fraction after separation of an azeotropic mixture of octafluorocyclobutane and 1,1,2,2-tetrafluorochloroethane can be rectified to isolate telomeric products of the general formula H (CF ₂ ) _n Cl, where n> 2.

Example 1. Tetrafluoroethylene is obtained in an industrial plant by pyrolysis of difluorochloromethane with the addition of an azeotropic mixture of octafluorocyclobutane and 1,1,2,2-tetrafluorochloroethane in the presence of water vapor. After quenching, the pyrolysis products are freed from hydrogen chloride to give hydrochloric acid, neutralized, and neutral pyrolysis products are compressed. By condensation rectification, tetrafluoroethylene and unreacted difluorochloromethane are sequentially isolated. The bottoms fraction after isolation of difluorochloromethane containing octafluorocyclobutane, 1,1,2,2-tetrafluorochloroethane and its homologues with the general formula H (CF ₂ ) _n Cl are analyzed for impurity content of unsaturated compounds by IR spectrometry. The sample contains an absorption region of 1790 - 1800 cm ^-1 , characteristic of fluorochlorinated unsaturated compounds, in particular, pentafluorochloropropylene, hexafluoropropylene, perfluorizobutylene. The total content of unsaturated compounds is 2.7 mol.%. This bottoms fraction, taken in an amount of 560 g, is mixed with 86 g of diethylamine in a cube of a glass laboratory distillation column with an efficiency of about 40 theoretical plates. The column was introduced into rectification mode, and 383 g of an azeotropic mixture of octafluorocyclobutane and 1,1,2,2-tetrafluorochloroethane free from unsaturated compounds were isolated into the light fraction (detection limit of unsaturated compounds was 0.05 mol%). The bottom fraction after isolation of the azeotropic mixture also does not contain unsaturated compounds (i.e., less than 0.05 mol%) and can be used to isolate hydrofluorocarbons of the general formula H (CF ₂ ) _n Cl, where n> 2, the use of which is allowed Montreal Protocol for the Protection of the Ozone Layer up to 2020

Example 2. Obtaining tetrafluoroethylene is carried out similarly to that described in example 1. The bottom fraction after separation of difluorochloromethane containing octafluorocyclobutane, 1,1,2,2-tetrafluorochloroethane and its homologues, as well as 3.5 mol.% Unsaturated compounds, taken in the amount of 740 g mixed with a composition composed of 70 g of diethylamine and 730 g of a 5% aqueous solution of sodium hydroxide, and an azeotropic mixture of octafluorocyclobutane and 1,1,2,2-tetrafluorochloroethane is isolated from the resulting mixture in the form of a light fraction in an amount of 500 g free from not redelnyh compounds (i.e. less than 0.05 mol.%). Continuing the distillation of the bottom residue, 103 g of 1,1,2,2,3,3-hexafluorochloropropane and 44 g of 1,1,2,2,3,3,4,4-octafluorochlorobutane, hydrofluorocarbons of general formula H (CF ₂₎ are additionally isolated ) _n Cl, where n = 3 and 4, which can be used as blowing agents, solvents.

Example 3. The production of tetrafluoroethylene is carried out similarly to that described in example 1. The bottom fraction after isolation of difluorochloromethane is rectified on an industrial column with the isolation of an azeotropic mixture of octafluorocyclobutane and 1,1,2,2-tetrafluorochloroethane as a light fraction. The bottom residue after isolation of the indicated azeotropic mixture is analyzed for the content of unsaturated compounds by IR spectrometry. A sample of bottoms in an amount of 430 g with a content of unsaturated compounds of 5.8 mol% was mixed with a composition composed of 55 g of diethylamine and 600 g of a 5% aqueous solution of sodium hydroxide and introduced into the rectification mode on a glass laboratory column. As a result of rectification, hydrofluorochlorocarbons of the general formula H (CF ₂ ) _n Cl are obtained, in particular (see table).

 Hydrofluorochlorocarbons isolated by rectification practically do not contain unsaturated compounds (less than 0.05 mol.%).

Thus, thanks to the proposed method increases the safety of the process. In addition, the additional isolation from the still bottoms of telomeric products of the general formula H (CF ₂ ) _n Cl, where n> 2, increases the utilization of raw materials, therefore, improves the economic performance of the method.

Claims (3)

 1. A method of producing tetrafluoroethylene, including the pyrolysis of difluorochloromethane with the addition of octafluorocyclobutane and 1,1,2,2-tetrafluorochloroethane in the form of an azeotropic mixture in the presence of water vapor, quenching of the pyrolysis products, separation of hydrogen by-product to produce hydrochloric acid, neutralization, compression and condensation of products pyrolysis with the release of the target product, unreacted difluorochloromethane and an azeotropic mixture of octafluorocyclobutane and 1,1,2,2-tetrafluorochloroethane with multi-stage distillation, characterized in that I mean that the process is conducted with the addition of diethylamine either to a cube of a distillation column designed to isolate difluorochloromethane, or to a cube of a distillation column designed to isolate an azeotropic mixture.  2. The method according to p. 1, characterized in that diethylamine is used as a mixture with an aqueous solution of sodium hydroxide. 3. The method according to claim 1 or 2, characterized in that the bottom fraction after isolation of an azeotropic mixture of octafluorocyclobutane and 1,1,2,2-tetrafluorochloroethane is rectified to isolate telomeric products of the general formula H (CF ₂ ) _n Cl, where n> 2 .

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