Multicomponent‐liquid‐membrane permeation of organic acids

Abstract

AbstractThe parameters of lactic acid separation from fermentation broths by Emulsion‐Liquid Membranes (ELMs) have been optimized. Using these parameters, lactic acid can be separated up to 90%, concentrated up to 3 times and cleared of most of its by‐products. Only about 1% of glucose and amino acids is permeated together with the lactic acid. With these parameters, not only lactic acid but also other monocarboxylic acids can be separated, the better and faster the lower the pKa‐value of the acid the fewer polar side groups it carries. When separating dicarboxylic acids, the mass transfer is hindered by the second carboxylic group. The smaller the distance between the two carboxylic groups, the slower is the separation of the acid. When several organic acids are separated from the same fermentation broth, their mutual influence is not very strong, at least when the concentrations of the acids are about 100 mmol/l. However, sulphuric acid which is added to the fermentation broth throughout permeation to maintain the broth at a constant pH, does exert a strong influence. In order to reduce the competition between the organic and sulphuric acids during permeation to a minimum, as little as possible sulphuric acid is used. However, a certain quantity of sulphuric acid is necessary to maintain the pH of the fermentation broth during permeation at 4.5, otherwise organic acid separation would become too slow.