Continuous process for manufacture of a purified lactide
First Claim
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1. A process for the continuous conversion of a crude lactic acid feed in an aqueous medium to substantially purified lactide, said process comprising the steps of:
- a) providing a source of lactic acid in an aqueous medium;
b) concentrating the lactic acid in the aqueous medium by evaporating a substantial portion of the aqueous medium to form a concentrated lactic acid solution;
c) polymerizing lactic acid in the concentrated lactic acid solution of step (b) by further evaporation of the aqueous medium to form polylactic acid molecules having an average molecular weight of between about 100 and 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; and
e) purifying the crude lactide formed in step (d) to form a substantially purified lactide by distilling the crude lactide, wherein distilling the crude lactide comprises fractionating the crude lactide into at least three component streams, an overhead low-boiling stream, a high-boiling bottoms stream and an intermediate boiling sidedraw stream.
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Abstract
A process for the continuous conversion of crude lactic acid to a substantially purified lactide or polylactide including the steps of polymerizing the lactic acid to form a prepolymer with subsequent depolymerization to form a crude lactide in the presence of a catalyst. The crude lactide is purified in an improved distillation system in which at least three fractions are formed with the substantially purified lactide removed as an intermediate boiling sidedraw stream. The substantially purified lactide may then be polymerized.
136 Citations
30 Claims
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1. A process for the continuous conversion of a crude lactic acid feed in an aqueous medium to substantially purified lactide, said process comprising the steps of:
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a) providing a source of lactic acid in an aqueous medium; b) concentrating the lactic acid in the aqueous medium by evaporating a substantial portion of the aqueous medium to form a concentrated lactic acid solution; c) polymerizing lactic acid in the concentrated lactic acid solution of step (b) by further evaporation of the aqueous medium to form polylactic acid molecules having an average molecular weight of between about 100 and 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; and e) purifying the crude lactide formed in step (d) to form a substantially purified lactide by distilling the crude lactide, wherein distilling the crude lactide comprises fractionating the crude lactide into at least three component streams, an overhead low-boiling stream, a high-boiling bottoms stream and an intermediate boiling sidedraw stream. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. 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:
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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 of step (b) by further evaporation of the hydroxylic medium to form polylactic acid molecules having an average molecular weight of between about 100 and 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; and e) purifying the crude lactide formed in step (d) to form a substantially purified lactide by distilling the crude lactide, wherein distilling the crude lactide comprises fractionating the crude lactide into at least three component streams, an overhead low-boiling stream, a high-boiling bottoms stream and an intermediate boiling sidedraw stream. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
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Specification