Synthesis of Lactide from <scp>L</scp> -Lactic Acid over the Phosphoric Acid Etched Zeolite Catalyst

Polylactic acid (PLA) is a promising biodegradable polymer. However, its large-scale production is hindered by the efficient synthesis of lactide (LT), a key intermediate. In this study, we develop a simple and effective strategy to enhance the catalytic performance of H-Beta zeolite in the one-step conversion of L-lactic acid (L-LA) to LT through phosphoric acid (H3PO4) etching. A series of acid-modified Beta zeolite catalysts were prepared by systematically varying the concentration of H3PO4 and the treatment duration. Among them, the modified H-Beta zeolite (2-Beta-P) exhibited the highest catalytic activity, obtaining an LA yield of 75%. This yield is significantly higher than that of the pristine H-Beta catalyst. Comprehensive characterization results reveal that the H3PO4 treatment can selectively remove the framework aluminum, optimize the ratio of Brønsted to Lewis acid sites, while preserving the intrinsic microporous structure, thereby facilitating molecular diffusion. Kinetic studies further demonstrated that 2-Beta-P reduced the apparent activation energy from 65.8 to 44.8, indicating that surface chemical processes primarily govern the reaction. These findings highlight phosphoric acid etching as a simple yet powerful modification strategy that can significantly enhance both the activity and selectivity of H-Beta zeolites, offering valuable insights for the sustainable and efficient production of lactide.