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

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 a traditional two-step process involving harsh conditions of high temperature and high vacuum with limited yield. A recently developed one-step approach based on heterogeneous catalysts (e.g., Beta zeolites) 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 LA conversion reaching 98% and an LT yield of 91%, substantially outperforming previously reported zeolite-based catalysts. 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, demonstrates that such superior catalytic performance of EMM-17 is derived from its unique external surface acid sites, which effectively promote the conversion of L _n A (n ≥ 3) oligomers into LT and smaller substrates within high-concentration LA systems.