GB407367A - Improvements in or relating to the manufacture of aliphatic anhydrides - Google Patents

Abstract

The production of aliphatic anhydrides by thermal treatment of the corresponding acids is effected in presence of a catalyst for the reaction such as a phosphoric acid, phosphate, tungstate, silicate or borate, and a compound which is a reduction product of the same catalyst or of a catalyst of the same type. The catalysts are not reducible to metals under the conditions of the reaction. Thus phosphates may be used with phosphites or hypophosphites of the same or other metals. Carriers or filling materials may be employed such as pumice or silica gel, or the catalysts and their reduction products may be employed as sole or part constituents of molten baths which may comprise other materials that may or may not have catalytic action. The acid vapour may be mixed with a reducing gas such as hydrogen, carbon monoxide, or water gas and both may be preheated. The reducing gas may be passed through the heated liquid acid as in Specification 304,156, [Class 2 (iii)]. The anhydride may be separated from the reaction products as described in Specifications 256,663, 279,916, 298,667, 303,772, 310,863, [all in Class 2 (iii)], and 354,199. In examples, acetic acid is vaporized with or without the introduction of hydrogen or carbon monoxide, preheated to 500 DEG C. and led through a copper tube containing calcium phosphate and phosphite at 700 DEG C. Specifications 289, 72, 336,960, [both in Class 2 (iii)], and 407,335 also are referred to.