Process for the preparation of solutions of anionic organic compounds

Abstract

A process for the preparation of concentrated solutions or suspensions of anionic organic compounds is described, which process comprises a) acidifying an aqueous solution or dispersion of an anionic organic compound that comprises salts and/or impurities to a pH of 4.5 or less, if the pH is above that value, so that the anionic organic compound becomes insoluble in water and precipitates out in the form of the free acid, b) bringing the suspension obtained from the previous step to a salt content below 2% by weight, based on the total weight of retentate, by means of ultra-filtration with a ceramic membrane or an acid-resistant organic membrane having a pore size of from 1 to 20 nm, and c) optionally washing out of the salts with water at a pH of less than 4.5, d) optionally carrying out acid-free washing with water thereafter, and then e) concentrating so that the content of anionic organic compound is from 5 to 50 % by weight, and f) optionally bringing the anionic organic compound into solution by adding a suitable base.

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