Patent GB-531927-A (GB)
Title: Improvements in or relating to process for the substitution chlorination of saturated aliphatic hydrocarbons, apparatus therefor and the product resulting therefrom
IPC: C07C17/10
Filed: 1939-08-08
Abstract: 531,927. Chlorinated hydrocarbons. STEVENS, A. H. (Dow Chemical Co.). Aug. 8, 1939, No. 22846. [Class 2 (iii)] Substitution chlorination of saturated aliphatic hydrocarbons is effected by subjecting a mixture of chlorine and one or more hydrocarbons in the gas phase to light to promote the reaction while confining the mixture between closely adjacent surfaces, the distance between said surfaces not exceeding that required by the equation Pd<SP>2</SP> =375 where P is the absolute pressure in pounds per square inch and d is the distance between said surfaces measured in millimetres.Thus methane is chlorinated photo - chemically using light of wave length 3000-4400Š and intensity four times greater than that of noon sunlight at approximately atmospheric pressure in a glass vessel, the walls of which are not over 5 millimetres apart, or at a pressure of about 2¢ atmospheres in a vessel with the surfaces 3 millimetres apart. Methane is chlorinated thermally by passing the chlorine-methane mixture at 30‹C. at approximately atmospheric pressure into a reactor whose walls are about <SP>1</SP>/ 32 of an inch apart and are maintained at 360‹C. The walls of the reactors can be made of glass, graphite or carborundum and in the case of photo-chemical chlorination should usually be kept cold, i.e. at a temperature insufficient in itself to produce appreciable thermal chlorination. In the production of carbon tetrachloride it is advantageous to use a combined vapour and liquid phase process, e.g. by reacting the chlorine-methane mixture initially in the vapour phase and then injecting this into a body of irradiated carbon tetrachloride or other suitable inert materials. Using the apparatus described in Fig. 1, chlorine and methane in stoichiometric proportions for the production of carbon tetrachloride is passed via line 8 into the space between the glass shells 11 and 12 usually kept 3 or 5 millimeters apart, where partial chlorination occurs under the influence of light from the source 15. The mixture is released into the liquid carbon tetrachloride in the vessel 9 at a point of relatively intense radiation and vapour phase chlorination proceeds in each bubble of unreacted material. Partly chlorinated methane such as methyl chloride and some methane itself, dissolve in the irradiated carbon tetrachloride and react with dissolved chlorine to form more carbon tetrachloride, while unreacted gases may be allowed to remain in the vapour space 17 for some time, where further chlorination takes place. The carbon tetrachloride in vessel 9 is maintained warm, usually at about 50‹-60‹C., so that the products are vaporized and, except for the hydrogen chloride, returned to 9 via condenser 19, while the liquified products can be drawn off and refined. In a modification, Fig. 2, the chlorine-methane mixture is partially chlorinated between the glass walls 32 and 33 of the reactor under the influence of light from the source 31 and then released via inlet pipe 41 to rise past light sources 46 and 47 when the materials are effectively chlorinated; reaction is also allowed to take place in space 54. Instead of first chlorinating the materials in the vessel provided by walls 32 and 33, premixed chlorine and methane may be introduced directly into pipe 41 via valve 53. The invention is applicable to the chlorination of other saturated hydrocarbons, e.g. those having less than 7 carbon atoms such as ethane, propane, butane, pentane and hexane, either as separate components or as mixtures such as casinghead gasoline. Partially chlorinated methane such as chloroform and dichloromethane can be obtained by increasing the ratio of methane in the reaction mixture.