Extraction and purification of lactic acid from fermentation broth by esterification and hydrolysis method

Abstract

Lactic acid (LA) is easily produced in bacterial fermentations, but a substantial processing and cost are involved in extraction and purification of LA in the fermentation broth. Conversion of LA or ammonium lactate (NH 4LA) into esters and subsequent hydrolysis of the purified ester into LA is a widely accepted way to extract and purify because using this method can obtain high pure LA. In this study, using two reactors with a rectifying column carried out recovery of LA from the fermentation broth. NH 4LA obtained by fermentation was used directly to produce butyl lactate by reacting with butanol for 6 h, and the esterification yield of NH 4LA was 87.7%. In this procedure, a cation exchange resin which was modified by SnCl 2 replaced sulphuric acid as a catalyst, and neutral NH 4LA replaced former LA as a starting material, which not only eliminated corrosion of a reactor, but also avoid generating calcium salts as a by-product. Then butyl lactate was rectified, and the purified butyl lactate was sequentially hydrolyzed into LA in presence of the cation exchange resin in the H + form as a catalyst for 4 h, and the hydrolysis yield was 89.7% and the purity of recovered LA was 90%. In the present recovery process, the liberated butanol in hydrolysis procedure and unreacted butanol in esterification procedure can be recycled to the above esterification, and the recovery ratio of butanol was 85.6%.