GB998804A - Production of carbon tetrachloride - Google Patents

Abstract

Carbon tetrachloride is made by passing phosgene over a volatile chloride of molybdenum or tungsten supported on active carbon, or a mixture of such chlorides supported on active carbon, at 300 DEG to 600 DEG C., the carbon having been treated to remove substantially all oxygen prior to use in the disproportionation of the phosgene. Preferably the chloride is added to the phosgene being fed over the catalyst, the partial pressure of the chloride vapour being sufficient to load the carbon at a rate comparable with the slow desorption of metal chloride from it. Metal chloride is removed from the product gases and recycled. Preferred are catalysts made from charcoal, e.g. coconut charcoal. Preferably the carbon catalyst is treated in situ. Desirably the carbon is purged with argon to remove water before treatment for the removal of oxygen. Oxygen may be removed by saturating the carbon with hydrogen at above 200 DEG C., preferably 300 DEG to 500 DEG C., and then treated with chlorine at similar temperatures. The hydrogen treatment may be omitted and after about 4 hours treatment with chlorine a volatile metal chloride e.g. aluminium chloride, is added to the feed gases. The chlorine in the above treatments may be substituted by phosgene. In a modification in which the volatile chloride is recycled, the carbon may be deoxygenated by passing tungsten hexachloride in argon, and tungsten oxychlorides, condensed from the product gases, on recycling through the reactor with phosgene, are converted back to hexachloride. Pressures of 25 to 50 atmospheres may be used. Reaction temperatures of 350 DEG to 450 DEG C. are appropriate. The feed may be diluted with chlorine, to avoid the production of catalyst poisons, but preferably contains at least 70% of phosgene. The phosgene may be formed in situ from carbon monoxide and chlorine. The residence time, when working under pressure, is conveniently 30 seconds to 5 minutes. Examples are provided of the use of molybdenum pentachloride and tungsten hexachloride. Specification 847,552 is referred to.ALSO:Catalysts consisting of a volatile chloride of molybdenum and/or tungsten supported on active carbon are, before use in the production of carbon tetrachloride from phosgene at 300-600 DEG C., treated substantially to remove all of the oxygen from the carbon. Preferably the volatile chlorides are added with the phosgene feed so that a high concentration of catalyst on the carrier is maintained. Preferred active carbons are charcoals, e.g. coconut charcoal. Before removal of oxygen the carbon is preferably purged with argon to remove water. Oxygen may be removed by saturation with hydrogen at above 200 DEG C., preferably 300-500 DEG C., followed by chlorine-treatment at similar temperatures. The treatment with hydrogen may be omitted and phosgene used instead of chlorine. When hydrogen treatment is omitted the chlorine treatment is followed by the addition of a volatile metal chloride, e.g. aluminium chloride, and molybdenum or tungsten chlorides. Where provision is made for recycling metal chloride vapour separated from product gases deoxygenation may be effected by passing a stream of tungsten hexachloride vapour in argon through the catalyst. Preferably the carbon is treated in situ. Examples illustrate the preparation of catalysts from charcoal and molybdenum pentachloride or tungsten hexachloride by methods outlined above.