Double-protective strategy enabling high-efficiency production of levulinic acid from high-loading cellulose

Abstract

Valorization of renewable cellulose into initial platform chemicals (IPCs) generally suffers from low process efficiency owing to difficult depolymerization of recalcitrant cellulose and troublesome repolymerization of high-reactive intermediates to undesired humins. Herein, we report a double-protective strategy for cellulose depolymerization and orientated conversion to levulinic acid (LA), one of the important IPCs, by in-situ adding protective formaldehyde (HCHO). This approach initiates from the (hemi)acetalation of hydroxyl groups in cellulose with HCHO, causing controllable depolymerization to (hemi)acetalized glucose with increased rate kinetically and a new mechanism of its catalytic conversion to LA via (hemi)acetal-driven direct C1–C2 cleavage. As such, the cellulose-to-LA conversion is protectively proceeded with the repolymerization of reactive intermediates prevented remarkably, leading to an excellent LA yield of 87.3 mol% from high-loading microcrystalline cellulose (15.0 wt% in aqueous phase) in a biphasic solvent containing 2-methyltetrahydrofuran and water. The process efficiency, expressed as space-time yield, is improved by 3.6 fold when compared with a non-protective approach. This work highlights an advance in maximizing the utilization of biomass-derived carbons for high-efficiency production of important IPCs directly from cellulose for future biorefinery.