Continuous process for the manufacture of lactide and lactide polymers

A process for the continuous conversion of a crude lactic acid feed in a hydroxylic medium to a substantially purified lactide, 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 lactide 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;
• and
• e) purifying the crude lactide to form a substantially purified lactide by distilling the crude lactide.

A process for the continuous conversion of an ester of lactic acid to polylactide, said process comprising the steps of:

• a) providing a source of the ester of lactic acid;
• b) forming a condensation reaction by-product and polylactic acid in the presence of a catalyst for catalyzing the condensation of molecules of the ester of lactic acid to form polylactic acid, wherein the molecules of polylactic acid have a number average molecular weight of less than about 5,000;
• c) forming a crude lactide from the polylactic acid molecules in the presence of a catalyst for catalyzing the depolymerization of polylactic acid to form the crude lactide;
• wherein the crude lactide is formed in a lactide reactor containing a pressure less than ambient in such a manner that the lactide reactor mean residence time is not greater than about 20 minutes;
• d) purifying the crude lactide to form a substantially purified lactide by distilling the crude lactide;
• and
• e) reacting the substantially purified lactide to form a polylactide.

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 lactide reactor, said lactide reactor containing a pressure less than ambient, and said lactide reactor comprising a falling film evaporator or an agitated thin-film evaporator;
• e) purifying the crude lactide to form a substantially purified lactide by distilling the crude lactide;
• and
• f) reacting the substantially purified lactide of step (e) to form polylactide.

A process for preparation of polylactide;

• said process including the steps of:
• a) vaporizing crude lactide from a film of polylactic acid mixture having a number average molecular weight of less than about 5000, in a film generating evaporator, under a pressure less than ambient, to form a crude lactide mixture;
• b) distilling the crude lactide mixture to form at least one purified lactide stream;
• and
• c) reacting the at least one purified lactide stream to form polylactide.