Sustainable production of biodiesel enabled by acid-base bifunctional ZnF2 via one-pot transformation of Koelreuteria integrifoliola oil: Process optimization, kinetics study and cost analysis

Against the backdrop of energy crisis and quest for carbon neutrality, efficient utilization of heterogeneous catalysts to facilitate one-pot conversion of low-quality nonedible oils into biodiesel, shows enormous promise for the reduction of carbon footprints and environmental pollution. In this study, an effective heterogeneous catalyst, acid-base bifunctional mesoporous ZnF2 (MP-ZnF2) was successfully fabricated for biodiesel synthesis from Koelreuteria integrifoliola oil (KIO, acid values of 8.26 mg KOH/g) via facile one-pot process. Meanwhile, systematic characterization showed the large specific surface area (62.9 m2/g), abundant mesoporous (12.15 nm), outstanding thermal stability, and plentiful stable acid-base sites (1.22 and 0.56 mmol/g) of MP-ZnF2. Consequently, MP-ZnF2 achieved a high biodiesel yield of 97.15% under moderate conditions (103 °C, 6.2 h, 10.2 wt% catalyst dosages, 29:1 MeOH/KIO molar ratio) optimized by response surface methodology (RSM). More importantly, through the kinetic investigation, a low activation energy of 49.24 kJ/mol explained the reason for its high activity, and the possible reaction mechanism of (trans)esterification was also proposed. In addition, MP-ZnF2 demonstrated satisfactory reusability (6th cycle, >90%), water resistance (8 wt% water content, 89.25%), and versatility (all yields >90%). According to cost analysis, the price of biodiesel in this work was about 0.64 $/kg. Notably, the as-prepared biodiesel conformed to ASTM D6751 and EN 14214 standards, indicating great application prospects. It was demonstrated that one-pot transformation of KIO into biodiesel using acid-base bifunctional MP-ZnF2 contributes to the sustainable development of clean energy.