Patent ID: 6326458
Filing Date: 2001-12-04
Classification: C07D,C08G

Abstract:
A process for the continuous conversion of a crude lactic acid feed in a hydroxylic medium to polylactide, said process comprising the steps of:a) providing a source of lactic acid in a hydroxylic medium;b) concentrating the lactic acid in the hydroxylic medium by evaporating a substantial portion of the hydroxylic medium to form a concentrated lactic acid solution;c) polymerizing lactic acid in the concentrated lactic acid solution by further evaporation of the hydroxylic medium to form polylactic acid molecules having a number average molecular weight of less than about 5000;d) forming a crude lactide in the presence of catalyst means for catalyzing the depolymerization of the polylactic acid molecules to form lactide molecules; wherein said step of forming a crude lactide includes loading said polylactic acid molecules into a lactide reactor and vaporizing lactide molecules inside said reactor in such a manner that the reactor mean residence time is no greater than about 20 minutes, said lactide reactor containing a pressure less than ambient;e) purifying the crude lactide to form a substantially purified lactide by distilling the crude lactide; andf) reacting the substantially purified lactide to form polylactide.