Formylation-mediated pretreatment: Enabling high-yield production of methyl levulinate from cellulose at high substrate loading

Levulinic acid and its esters are promising biomass-derived chemicals. However, high-yield synthesis of them from cellulose is still very challenging. This paper presents a novel formylation-mediated pretreatment strategy for efficiently converting cellulose to methyl levulinate (ML). This strategy is not only straightforward but also notably enhances ML selectivity, especially at high substrate loadings. Mechanism studies show that the cellulose formylation has multiple functions: (1) it reduces the cellulose crystallinity, increases the solubility in the reaction media and thus accelerates the subsequent reactions; (2) the released formic acid from formylated cellulose helps catalyze the cleavage of glucosidic bonds; and (3) more stable intermediates due to the existence of formyl group can suppress the formation of humins. Under optimized reaction conditions, a maximum ML yield of 92.9 % was achieved at a formylated cellulose (CF) loading of 2.5 wt%. Notably, even when the CF loading was increased to 10 wt%, an ML yield of 84.8 % could still be obtained. A rough economic assessment that only took the raw material and energy consumption into account demonstrates that the formylation-mediated process has a lower total input cost and can achieve a 110.4 % profit margin as compared the benchmark due to the higher substrate loading employed and more MF produced from the formyl groups. This research provides a new approach for the large-scale production of levulinates from cellulose.