GB298667A - Improvements in or relating to the manufacture of aliphatic anhydrides - Google Patents

Abstract

298,667. British Celanese, Ltd., Dreyfus, H., and Haney, C. I. July 14, 1927. Grant of Patent opposed. Acetic and other aliphatic acid anhydrides are produced by heating the vapours of the acids, which may be dilute, and the anhydrides are condensed and separated from the water by passing the vapours under the surface of a cooled " extraction liquid " such as benzene, chloroform, or mixtures of ether or chloroform with one or more light hydrocarbons, such as petroleum ether, gasoline, or benzene or its homologues. The anhydrides dissolve in the extraction liquid " while the water condenses to form a separate layer. The extracting liquid or the water or both mav be continuously withdrawn. The invention is described with reference to acetic anhydride. Acetic acid is converted into anhvdride in a tube 1 which may be of copper, fireclay, or the material sold under the Registered Trade Mark Vitreosil, heated to 400-1200‹ C., and the vapours pass to a vessel 3 in which vapour of the extraction liquid is added by a pipe 4. The mixed vapours pass by a pipe 5 into the extraction liquid 6 in a vessel 7 having a cooling-jacket 9 and a stirrer 10. The pipe 5 dips below the surface of .the extraction liquid; if the extraction liquid is heavier than water, the pipe should be only a little below the surface, while if the liquid is lighter than water the pipe should dip deeply into the liquid so as to allow the water layer to be out of the way of the incoming vapours. The extraction liquid may be continuously withdrawn by an overflow 12, 13, the anhydride being finally separated by distillation. The water may be continuously withdrawn by a pipe 11, 11<a> to a vessel 15, and meets a stream of extraction liquid coming from a tank 16 by way of a pipe 17 and rose 18. The extraction liquid passes upwards through the pipe 11<a>, 11 into the vessel 7.