VERFAHREN ZUR REINIGUNG VON CARBONSAEUREN

1434062 Purification of carboxylic acids HOECHST AG 29 Nov 1973 [29 Nov 1972] 55349/73 Heading C2C Formic acid is removed from a crude carboxylic acid containing formic acid by treating the crude acid with a carboxylic acid anhydride, or with a compound capable of forming a carboxylic anhydride with a carboxylic acid, or a mixture of two or more such reagents, in the presence of an acidic catalyst comprising a mineral acid, a sulphonic acid, an acid salt, a heterogeneous acidic catalyst or a mixture of these. The crude acid, e.g. acetic or propionic, may be the product of an oxidation; the anhydride or anhydride-forming compound (e.g. ketene or carboxylic acid halide) is preferably one which, in the reaction with formic acid, yields the carboxylic acid already present as the crude acid. Heterogeneous oxidic catalysts, e.g. acidic ion exchangers, activated, bentonites, zeolites and acid-treated montmorillonites and bleaching earths, are preferred; such solid catalysts may be used in fixed or fluid beds for continuous processing of the crude acid. In the process, the formic acid is-decomposed to yield carbon monoxide.