A process for the preparation of hydroxybenzoic acid.

摘要

In the Kolbe-Schmitt process for the preparation of hydroxybenzoic acid by the reaction of potassium phenolate with carbon dioxide gas followed by precipitation of the hydroxybenzoic acid in the mixture acidified with hydrochloric acid, the potassium value in the acidified mother liquor is conventionally recovered by electrolysis after removing the organic impurities by chlorination with chlorine. The disadvantages in the use of chlorine can be dissolved by replacing the chlorine treatment with (a) dehydration of the acidified mother liquor followed by calcination of the dehydrated product, (b) salting-out by blowing hydrogen chloride gas into the acidified mother liquor, or (c) reverse osmosis treatment prior to the electrolysis to convert potassium chloride into potassium hydroxide, for example, by using an ion exchange membrane.