Process for preparing l- (+) -lactic acid

Abstract

The present invention provides a commercially viable process for the preparation of highly pure and optically active L-(+)-lactic acid and S-(−)-methyl lactate, in high yield, obtained from esterification of aqueous crude lactic acid solution produced by sugar cane juice fermentation broth and methanol in continuous counter current trickle phase approach or in continuous counter current bubble column manner, using stabilizers and the methyl lactate so obtained is recovered and followed by purification of reasonably pure methyl lactate using reagent mixture such as sodium bi-carbonate, mono-ethanolamine or di-ethanolamine, urea or sodium-bicarbonate, mono-ethanolamine or di-ethanolamine, thiourea to reduce the impurity of dimethyl ester of dicarboxylic such as dimethyl oxalate or di-methyl succinate or methyl ester of mono-carboxylic acid such as methyl pyruvate present as an impurity, so as to get highly pure S-(−)-methyl lactate followed by hydrolyzing highly pure S-(−)-methyl lactate using highly pure lactic acid as a catalyst, using highly pure water as the hydrolysis media and by using pre-treated activated carbon with dilute L-(+)-lactic acid, in batch or continuous mode. This very high pure S-(−)-methyl lactate constitutes an important product having interesting possibilities of application at an industrial level, in pharmaceuticals. Highly pure L-(+)-lactic acid thus obtained is used as an acidulant, as a food additive, for pharmaceutical applications, a monomer for making poly-lactic acid, as a monomer to prepare biodegradable polymer which are useful for manufacturing bags, application films, in the field of sanitary field, and has medical applications.