GB653879A - Improvements in or relating to the production of fluoro- and fluorochloro carbons - Google Patents

Abstract

Fluorocarbons and/or fluorochlorocarbons are made by reacting on carbon jointly with fluorine and chlorine at above 350 DEG C. Amongst the products of reaction there are specified tetrafluorochloroethane and tetrafluorodichloroethane together with compounds such as hydrogen fluoride, carbon dioxide and silicon tetrafluoride. The reactive gases may be derived from a mixture of these gases or a compound thereof, e.g. chlorine mono- or tri-fluoride, or from mixtures of such compounds with themselves or with chlorine or fluorine. The carbon may be in the form of graphite or wood charcoal. Reactor temperatures of 500-550 DEG C. are given and the gases may be preheated. Ratios of fluorine to chlorine may be widely varied, e.g. 1 : 3 to 3 : 1 ratios are quoted, and where large proportions of chlorine are used only small amounts of tetrafluoromethane are obtained. The reactor should be made of material such as recrystalline alumina or a metal such as nickel which is resistant to reactants and products. The gases may be passed through a bed of carbon or a fluidized technique may be used. In examples: (1) fluorine and chlorine in mol. ratio of 0.9 : 1 are passed through Acheson graphite at 500 DEG C. in a stream of nitrogen products being collected in a catch-pot at 5-10 DEG C. and then in traps immersed in liquid air, the pot providing a brown resinous material, possibly a polynuclear aromatic fluorocarbon, and the traps yielding on fractionation after scrubbing with caustic soda solution the above specified compounds, mainly trifluorochloromethane and tetrafluorodichloroethane, and some heptafluorochloropropane; (2) fluorine and chlorine in a mol. ratio of 1.8 : 1 are passed through wood charcoal at 500 DEG C. in a stream of nitrogen and products isolated as in (1) save that HF is removed before the traps by NaF treatment, trifluorochloromethane and tetrafluoromethane are the chief products, and in (3) chlorine trifluoride diluted in a ratio of 1 : 3 with nitrogen is passed through artificial graphite at 500 DEG C. and products are isolated as before excess chlorine trifluoride and its derivatives being removed by scrubbing with sodium hydroxide and sulphite, the main products being trifluorochloromethane and carbon tetrafluoride.