GB801127A - Method of reducing the halogen content of halohydrocarbons - Google Patents

Abstract

The halogen content of chloro- and bromo-hydrocarbons is reduced by bringing the vapours thereof into intimate contact with a fluidized bed of a cuprous halide supported on porous activated alumina at 350 DEG to 550 DEG C. until replacement of halogen atoms by hydrogen atoms occurs. This replacement may be preceded by a dehydrohalogenation. Preferably, for regeneration of catalyst contaminated with carbon, part thereof is withdrawn from the reaction zone, stripped of absorbed hydrocarbons and halohydrocarbons, contacted with air or steam at a temperature at which carbon is oxidized and returned to the reaction zone. The hydrogen may come from an outside source or be generated in the reaction zone, e.g. by the watergas reaction or by thermal cracking of some of the feed material. The amount of cuprous halide in the catalyst is preferably from 2 to 25 per cent of the weight of the alumina and the catalyst may be formed by impregnating alumina with cupric chloride solution (or other compounds convertible to cuprous chloride, such as cupric oxide), and then reducing the mass, either during the early stages of the process of the invention or by exposing it at reaction temperature to an hydrocarbon gas such as methane. In forms of apparatus suitable for effecting the process, which are described with the aid of drawings, the catalyst bed may either be wholly contained in a single reaction zone, the activity of the catalyst being restored by decreasing or stopping the halohydrocarbon feed temporarily while admitting steam or air, or the reaction zone may be connected to a reactor stripper into which part of the catalyst body falls and is stripped of reagent vapours by a stream of inert gas, the stripped catalyst passing from the stripper to an air or steam lift and being transferred to a regenerator maintained at a temperature near that of the reactor and thence via a regenerator stripper back to the reactor. In the second of these processes catalyst make up may take place at any desired point and a second fluid lift may be provided to transfer the catalyst from the regenerator to a catalyst hopper from which it falls into the regenerator stripper, the stripping gas returning to the regenerator before passing out of the system. In examples: (1) 1:1:2-trichloroethane vapour and steam are passed at 450 DEG C. through a fluidized bed of a catalyst prepared by impregnating activated alumina with 15 per cent by weight of cupric chloride and reducing to cuprous chloride with ethylene at 480 DEG C., giving a product containing major proportions of vinyl chloride and vinylidene chloride (convertible to vinyl chloride by recirculation) and a minor proportion of cis- and trans-dichloroethylene; (2) hexachlorobutadiene-1:3 and hydrogen with the catalyst of (1) at 500 DEG C. give chiefly pentachlorobutadienes; (3) hexachlorobenzene and excess hydrogen with a catalyst consisting initially of 20 per cent cupric chloride (reduced to cuprous chloride) on activated alumina at 550 DEG C. give benzene, monochlorobenzene, dichlorobenzenes, trichlorobenzenes and tetra- and penta-chlorobenzenes; (4) 1:2:3:4:5:6 - hexachlorocyclohexane and steam with the catalyst of (3) at 510 DEG C. give benzene, monochlorobenzene and dichlorobenzenes; (5) mixed trichlorobenzenes and excess hydrogen with the catalyst of (1) fluidized with methane at 500 DEG C. give benzene, monochlorobenzene and dichlorobenzenes; (6) a catalyst is prepared by mixing activated alumina with cupric chloride solution containing 20 per cent CuCl2 of the weight of alumina and reducing the mass with ethane at 450 DEG C., then mixed hydrogen and hexachlorobenzene vapours fluidize the catalyst bed at 470 DEG to 500 DEG C. giving benzene, monochlorobenzene, o-, m- and p-dichlorobenzenes and trichlorobenzenes. Reference is also made to the reaction of steam and monochlorobenzene at 500 DEG C., resulting in partial decomposition to carbon monoxide, hydrochloric acid and hydrogen, which last reduces more monochlorobenzene to benzene; to the progressive conversion of carbon tetrachloride to chloroform, methylene chloride, methyl chloride and methane; to the progressive conversion of benzotrichloride to benzal chloride, benzyl chloride and toluene; and to the conversion of pentachlorobutadienes to tetrachlorobutadienes, perchloroethylene to trichloroethylene, chloronaphthalenes to lower chloronaphthalenes and naphthalene and to the dehalohydrogenation of the corresponding bromo compounds.