Reducing meso -lactide formation from racemic lactic acid using shape-selective H-Beta zeolite

The utilization of racemic lactic acid ( rac -LA) produced via chemocatalytic conversion for polylactic acid (PLA) synthesis remains limited due to the formation of undesired mesomeric lactide ( meso -LD), a by-product that arises during the conversion process. This study proposes the use of shape-selective H-Beta zeolite to reduce the formation of meso -LD in lactide (LD) by leveraging its selectivity towards different lactic dimers (L 2 A) in a one-step catalytic conversion of rac -LA to LD. Experimental results from various LA solutions with different L 2 A content indicate that the L 2 A content is critical for maximizing the selectivity of racemic lactide ( d / l -LD), thus confirming the shape-selective nature of H-Beta zeolite towards L 2 A. Additionally, it is found that increasing the reaction temperature and employing structurally reconstructed H-Beta zeolite with more regularized channels as a catalyst can further decrease meso -LD formation, and a LD yield of 60% with a d / l -LD/ meso -LD ratio of 2.26 can be achieved under optimal catalyst and reaction conditions. Despite the coexistence of d / l -LD and meso -LD in the final product, this study marks a significant step towards controlling the stereoisomer distribution of LD synthesized from rac -LA derived from chemical conversion.