Hexafluoroethane purifying method

Abstract

The invention discloses a hexafluoroethane purifying method which includes the following steps that crude hexafluoroethane is sequentially introduced into a water washing tower and an alkaline washing tower, acid gas in the hexafluoroethane is washed way, the washed gas enters a reactor which is filled with a metal catalyst, reaction temperature is controlled between 300 DEG C and 8000 DEG C, the flow rate of the hexafluoroethane is 15-30kg / h, then the gas sequentially adsorbs CO2, H2O and HF through an adsorption tower, impurities such as H2, O2, N2, CH4, CF4, SF6 and C3F8 are removed through rectification in a rectifying tower, and hexafluoroethane gas with the purity of 99.999% can be obtained. The metal catalyst is supported, a carrier is one of active aluminum oxide, a zeolite molecular sieve and active carbon, and a body is one or more of TiO2, ZnO, WO3, SnO2, Fe2O3 or SrTiO3. By means of the method, the content of hydrochlorofluorocarbons in the hexafluoroethane can be removed to be under 1ppmv.

Description

technical field [0001] The invention relates to a method for purifying hexafluoroethane. Background technique [0002] High-purity (above 99.999%) hexafluoroethane is mainly used as a plasma etchant in the semiconductor equipment manufacturing process. In the production process of hexafluoroethane, some by-products, such as carbon tetrafluoride (CF 4 ), octafluoropropane (C 3 f 8 ), trifluoromethane (CHF 3 ), difluorodichloromethane (CF 2 Cl 2 ), trifluorochloromethane (CF 3 Cl) or trichlorofluoromethane (CFCl 3 ) such as fluorocarbons or chlorofluorocarbons. Most of the impurities can be removed through purification processes such as conventional adsorption and rectification, but some impurities are relatively stable in nature and can form azeotropic mixtures with hexafluoroethane, which are difficult to remove by ordinary purification methods. [0003] In terms of purifying hexafluoroethane, the patent document CN1165509A introduces a method of azeotropic distilla...

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Problems solved by technology

However, the catalyst used in this method needs to control the mixing ratio, and the reaction device is relatively complicated, which is not conducive to industrialization

[0007] Karmakar S, Greene H L (Catalyst.J Catal, 1995, 151 (2): 394 ~ 406) mentioned that when the reaction temperature is 300 ° C, CCl 2 f 2 in TiO 2 The decomposition conversion rate on the catalyst is higher than 90%, continuous reaction for 4 days, CCl 2 f 2 The conversion rate is not lower than 85%, but the catalytic ability of the catalyst decreases rapidly

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