Dy/ZrO2 synergy modulates sulfonic acid sites of flour-derived carbon for biodiesel preparation.

A rare earth/ZrO2 modified solid acid catalyst was prepared using flour as the carbon source and applied to produce biodiesel from waste cooking oil. Results show that ZrO2 doping modulates graphitization to stabilize [C-SO3H] formation, but causes over-graphitization and low-valence sulfur accumulation, reducing -SO3H anchoring sites. Intriguingly, Dy doping concurrently suppresses excessive graphitization and blocks low-valence sulfur formation, such that the Dy/ZrO2 synergy markedly elevates the acid content of carbon material to 5.25 mmol/g compared to that of the unmodified catalyst (3.75 mmol/g). Under optimal conditions (catalyst amount of 6 wt%, MOMR of 24, at 104 °C for 4h), the reaction conversion achieved 99.95 % and maintained > 95 % after six cycles. RSM, ANN and SVR models agreed well with the experimental results, and can be used for process optimization and prediction. Notably, kinetic studies reveal an activation energy(Ea) of 142.688 kJ·mol-1 and a pre-exponential factor(A) of 6.17213 × 1019h-1. The E-factor and PMI could decrease from 2.8734 to 0.7058 and from 3.8734 to 1.7058, respectively, and no heavy-metal or sulfur impurities, confirming economic and environmental feasibility. This work may provide a strategy for preparing of metal modified carbon-based solid acid and a reference for biodiesel process modeling.