Rational Improvement for the Catalytic Alcoholysis of Straw Biomass by Understanding the Role of Inorganic Components

Ethyl levulinate (EL) is a crucial biomass-derived compound with diverse applications in pesticides, rubber, pharmaceuticals, and fuel. The efficient conversion of straw into EL presents significant challenges, primarily due to the interference of inorganic components (IOCs). In this study, we aim to enhance the alcoholysis of straw by identifying the specific inhibitory factors and mechanisms of IOCs. A case study on rice straw as a reactant in ethanol over Al(OTf)3 revealed that K+ is a critical inhibitory factor impeding the hydrolysis of cellulose into glucose. Specifically, K+ is adsorbed on O of S–O–Al in [Al(EtOH)m](OTf)3, thus inhibiting the release of H+ and the cleavage of the glycosidic bond. Further, simulating computation reveals that K+ exhibits stronger electrophilicity than H of O–H in [Al(EtOH)m](OTf)3, thus inhibiting the cleavage of H from O–H in ethanol. Consequently, a simple, green acetic acid pretreatment strategy has been developed to enhance the alcoholysis of straw by efficiently eliminating K+, resulting in an EL yield of more than 10 times that of the pristine straw. In conclusion, this study improves the alcoholysis activity of straw and provides novel insights and potential strategies for biorefinery.