GB763018A - Production of ketene - Google Patents

Abstract

Ketene is prepared by the vapour phase catalytic pyrolysis of acetic acid at a temperature between 625 DEG and 750 DEG C. and under a pressure between atmospheric pressure and about 20 p.s.i.g., using a reaction vessel in which the surfaces contacting the ketene are constructed of a steel containing between 3 and 4 per cent of molybdenum and between 17 and 20 per cent chromium and 8 to 12 per cent nickel as major alloying metals, the contact time of the vapours in the pyrolysis zone being between 5.0 and 0.1 secs. Specified steels are U.S. Types 316 and 317 stainless steels. Preferably, there is introduced into the products issuing from the reaction vessel a substance such as ammonia, pyridine, aniline or suitable aliphatic amine, which will neutralize the catalyst and retard recombination of the ketene with water or acetic acid. Thereafter, the gases may be cooled and the still gaseous ketene separated from the condensed products, e.g. by means of a cyclone separator. Advantageously, some acetic anhydride is added to the acetic acid feed-stock to reduce acetic anhydride formation in the pyrolysis; thus, the liquid condensate separated from the ketene, comprising acetic anhydride, water and unchanged acetic acid may be azeotropically distilled with e.g. benzene or hexane to remove the water and the residue recycled with fresh acid to the pyrolysis zone. Pyrolysis catalysts which may be used include volatilizable phosphates and phosphoric acid esters such as triethyl phosphate, tricresyl phosphate, ammonium and di-ammonium phosphates, dimethyl ammonium phosphate and pyridinium phosphate; the abovementioned addition of a neutralizing agent may be dispensed with when the catalyst is a volatile base salt of phosphoric acid. Examples are given.