Melt crystallization purification of lactides
AssigneeE.I. du Pont de Nemours and Company
InventorsWilliam George O'Brien, Gilbert Jacob Sloan
Life of this patent
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Abstract
Melt crystallization purification of lactide; and separation and purification of lactides existing in more than one isomeric form.
Claims22
A solvent-free method for the purification of a non-eutectic lactide mixture derived from the depolymerizaton of lactic acid oligomers comprising by weight a major amount of one lactide isomer and a minor amount of at least one other lactide isomer and acidic and other impurities comprising the steps:
- (1) melting the lactide mixture;
- (2) cooling the molten lactide mixture to the freeze point or slightly below the freeze point of the lactide mixture to effect partial crystallization of the mixture and formation of a solid phase having a higher content than the molten mixture of the major isomer and a lower content of the minor isomer(s) and acidic and other impurities;
- (3) separating the solid phase from the liquid phase;
- (4) forming an additional molten mixture by melting the separated solid phase;
- and
- (5) repeating steps (2)-(4) with the additional molten mixture until a predetermined degree of putity is obtained in the separated solid phase.
A solvent-free method for the purification of a lactide mixture derived from the depolymerization of lactic acid oligomers comprising by weight a major amount of one lactide isomer and a minor amount of at least one other lactide isomer and acidic and other impurities comprising the steps:
- (1) melting the lactide mixture;
- (2) cooling the molten lactide mixture to the freeze point or slightly below the freeze point of the lactide mixture to effect partial crystallization of the mixture and formation of a solid phase having a higher contenty than the molten mixture of the major isomer and a lower content of the minor isomer(s) and acidic and other impurities;
- (3) separating the solid phase from the liquid phase;
- (4) forming a further liquid phase by gradually warming the separated solid phase to a temperature below its melting point;
- (5) separating the solid phase form the further liquid phase;
- and
- (6) repeating steps (2)-(4) until a predetermined degree of purity is obtained in the separated solid phase.
A solvent-free method for the recover of DL lactide from a non-eutectic lactide mixture derived from the depolymerization of lactic acid oligomers comprising between 20 and 80% by weight each of D and L lactide and a minor amount of acidic and other impurities comprising the steps:
- (1) melting the lactide mixture;
- (2) cooling the molten lactide mixture to the freeze point or slightly below the freeze point of the lactide mixture to effect partial crystallization of the mixture and formation of a solid phase comprising DL lactide and a lowe content of acidity and other impurities;
- (3) separating the solid phase from the liquid phase;
- (4) forming an additional molten mixture by melting the separated solid phase;
- and
- (5) repeating steps (2)-(4) with the addtional molten mixture until a predetermined degree of purity is obtained in the separated solid phase.
A process for the melt recrystallization of lactide, comprising
- (a) heating lactide to a temperature suffiecent to form a melt;
- (b) cooling the melt in at least one recrystallizer to cause a lactide composition having a relatively higher content of a major isomer to crystallize on a surface of the recrystallizer while maintaining a lactide composition having a relatively lower content of the major isomer and a relatively higher content of impurities in a liquid phase;
- and
- (c) separating the crystallized lactide composition from the liquid lactide composition.
Dependencies are inferred from the claim text.