Patent ID: 7820859
Filing Date: 2010-10-26
Classification: C07C,Y02P

Abstract:
1. A process for preparation of highly pure L-(+)-Lactic acid, the said process comprising the steps of: (a) esterifying crude dilute lactic acid solution in water using mineral acid by preheating the above said crude dilute lactic acid at a temperature of about 105° C. and allowing it to react with superheated methanol vapors maintained at about 150° C., wherein the molar ratio of methanol to lactic acid is 2.8:1 to 4:1, in the presence of stabilizer, in continuous counter current trickle phase mode to obtain the methyl lactate, removing continuously unreacted methanol and water rich layer separately as distillate and crude methyl lactate in a continuous manner as overflow from reactor bottoms followed by recovery of methyl lactate using evaporator with lactic acid to methyl lactate conversion of about 98.5% with no other by-product formation, (b) reacting the above pure methyl lactate having purity 93-95% wt. with a mixture of sodium bicarbonate and a reagent selected from the group consisting of urea or thiourea, monoethanlomine or di-ethanolamine or a mixture thereof, under reflux, for a period of 1 hr. to convert volatile impurities into non-volatile components, followed by distillation with or without vacuum to obtained desired highly pure S-(−)-methyl lactate having purity of 99.8% by wt, moisture of 0.03% and optical purity of (−) 8.43°, (c) hydrolyzing the above S-(−)methyl lactate obtained in step (b) with distilled, metal contamination free or de-mineralized or de-ionized water, in the presence of pure L(+)-lactic acid as catalyst with a molar ratio of S-(−)-methyl lactate to catalyst in the range of 10.8:1 to 3.4:1, at a temperature in the range of 85-105° C., for a period of 2-6 hrs. and allowing hydrolysation of S-(−)-methyl lactate to L-(+)lactic acid with the removal of methanol obtained during hydrolysis reaction continuously under reflux, at controlled temperature and pressure to obtain the pure L-(+)-lactic acid followed by treating with pretreated activated carbon, wherein pre-treatment is carried out by washing activated carbon with a solution of pure lactic acid, to obtain the highly pure L-(+)-lactic acid solution in water and concentrating it in an evaporator to attain purity in the range of 99-99.8% and optical purity of 99-99.9% on water free basis and continuously collecting the methanol in a reservoir for being used/recycled in step (a).