GB567575A - Improvements in and relating to the production of hydroxy carboxylic acids - Google Patents

Abstract

A process for the production of mixtures consisting of hydroxyacetic acid and a high proportion of polyhydroxyacetic acid comprises evaporating within a period of two minutes and, preferably, in less than 0.6 min., substantially the whole of the water from an aqueous solution of hydroxyacetic acid, the said aqueous solution containing less than 40 per cent by weight of water. The aqueous acid solution may be obtained by the hydrolysis of a water-miscible alkyl ester of hydroxyacetic acid, for example, the methyl, ethyl, propyl, or butyl esters, in the absence of added hydrolysis catalyst other than hydroxyacetic acid and removing the alcohol produced thereby before the rapid evaporation step. Evaporation of the water from the aqueous acid solution takes place preferably at temperatures between 78-110 DEG C. and in the presence of a stream of dry inert gas such as carbon dioxide or nitrogen. The evaporation process may be carried out by "flash" evaporation and a suitable process is described which is identical as regards apparatus and conditions, with the process described in Specification 567,237. The molten dehydrated acid thus obtained may be cooled rapidly; when the polyacid content is less than 10 per cent it should be cooled in less than 45 seconds, preferably in less than 30 seconds, yielding micro-flake crystals. If desired, the molten or the solid product may be further dehydrated by heating and the application of reduced pressure to remove combined water and so give a product which may contain up to 131 per cent hydroxyacetic acid.