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|1. (WO2018176884) METHOD FOR PRODUCING OPTICALLY PURE L-/D-LACTIDE WITH ALL-GREEN CLOSED CYCLE PROCESS|
|Title:||METHOD FOR PRODUCING OPTICALLY PURE L-/D-LACTIDE WITH ALL-GREEN CLOSED CYCLE PROCESS|
Disclosed is a method for producing optically pure L-/D-lactide with an all-green closed cycle process, with an aqueous L-/D-lactic acid solution and polylactic acid, which is produced as a by-product, being used as raw materials, wherein first, a dehydration oligomerization reaction is carried out to obtain an L-/D-lactic acid oligomer, then, L-/D-lactide is synthesised under the catalysis of a ternary composite catalytic system, wherein the synthesised product achieves optical purity without further purification being required; and the polylactic acid, which is produced as a by-product, is directly mixed with the aqueous L-/D-lactic acid solution to carry out a further dehydration oligomerization reaction, thereby achieving recycling. Advantages: the L-/D-lactic acid monomer has a high utilization rate (95-97%); the ternary composite catalyst has a high catalytic activity, is reusable, and has a high stereospecificity and selectivity; the use of a rectification purification process involving a great number of column plates and a plurality of columns is avoided; and the reaction temperature of the lactide synthesis procedure is lower than that of conventional processes, thereby reducing the energy consumption of production.