EMM-17 as an efficient catalyst for the one-step conversion of high-concentration lactic acid into lactide

Abstract

As the key precursor for biodegradable polylactic acid (PLA), lactide (LT) is vital for sustainable polymer development, but its preparation in industry still relies on the traditional two-step process involving harsh conditions of high temperature and high vacuum with limited yield. The recently developed one-step approach based on heterogeneous catalysts (e.g., Beta zeolite) shows promising potential as a viable route, but its feasibility crucially depends on the development of highly efficient catalysts. In this work, the aluminosilicate zeolite EMM-17 featuring 11-ring channels was introduced as a novel catalyst for the conversion of 105 wt.% lactic acid (LA) for the first time, achieving record-breaking performance, with an LA conversion reaching 98% and an LT yield of 91%, substantially outperforming previously reported zeolite-based catalysts. By selective silylation of acid sites on the external surface of EMM-17, together with composition analysis of the product and density functional theory (DFT) calculations, it demonstrates that such superior catalytic performance of EMM-17 is derived from its unique external surface acid sites, which effectively promote the conversion of LnA (n≥3) oligomers into LT and smaller substrates within high-concentration LA systems.