Valorisation of lactic acid stream in the production process of polylactic acid

The method according to claim 11, wherein the distillation is carried out at a pressure of from 0.1 to 20 mbar and a temperature of from 100 to 200° C.

A method of valorization of a flux containing undesired D-lactic acid and/or one or more undesired D-lactic acid esters in the production process of L-polylactic acid, wherein the D-lactic acid and the one or more D-lactic acid ester(s) obtained by recycling during the various stage of the production of L-PLA are forming a recycle stream subjected to a treatment in order to selectively separate a fraction rich in L-lactic acid and/or L-lactic acid ester(s) from a fraction containing most of the D-lactic acid and/or D-lactic acid ester(s), said treatment comprising the following steps:

• (i) concentration in one or more evaporator(s) to obtain a concentrated lactic acid solution having a total acid content of at least 90% by weight and a content of monomeric lactic acid of at least 80% by weight based on the lactic acid concentrate;
• (ii) crystallization of the concentrated lactic acid in one or more stage(s) to obtain a lactic acid with a higher chiral purity;
• wherein some or all of said recycle stream is used as a base for the synthesis of molecules selected from the group consisting of acrylic acid, acrylic ester, acetaldehyde, 2,3-pentanedione, pyruvic acid, and 1,2 propanediol.