Superparamagnetic nanospheres with efficient bifunctional acidic sites enable sustainable production of biodiesel from budget non-edible oils

The concepts of carbon neutrality and carbon peak have garnered significant attention, amongst which effective utilization of heterogeneous catalysts to prepare biodiesel from budget non-edible oils, has become one of the solutions for environmental protection and emission reduction. In this study, bifunctional acid superparamagnetic nanospheres were successfully synthesized by combining acid poly ionic liquids (PILS) with strong magnetic carrier Fe3O4-SiO2 (FS). Herein, FS-B-L-PILS (2) was determined to be equipped with mesoporous (5.7 nm), uniform acidic sites, strong superparamagnetic magnetization (19.7 emu/g), favorable hydrophobicity (81.9°), and preeminent stability and repeatability. Importantly, Euphorbia lathyris L. oil of a high acid value (AV), which was as high as 25.60 mg KOH/g, was directly transformed into biodiesel with biomass-derived co-solvent of tetrahydrofuran (THF) using one pot manner. The practical biodiesel yield of 98.1 % was attained by FS-B-L-PILS (2), where it was discovered that Brønsted (B) and Lewis (L) acid sites had important synergistic effects. Intriguingly, simple magnetic force was able to facilely and speedily separate FS-B-L-PILS (2), and a sustained satisfactory reactivity in terms of fifth recycle with 91.2 % biodiesel yield was determined. Further, kinetic studies showed that main transesterification followed a quasi-first-order kinetic model. The activation energy was calculated to be 64.6 kJ/mol. Synchronously, thermodynamics also supported the fact that transesterification was endothermic and non-spontaneous response. Density functional theory (DFT) calculations provided valuable support for the catalytic reaction mechanism, demonstrating the catalyst's advantageous role in facilitating biodiesel production. It was worth noting that Euphorbia lathyris L. biodiesel's primary fuel characteristics met EN 14212 and ASTM D6751 criteria, demonstrating great possibilities for future industrial applications. This study will open the way for biodiesel production by facile one pot manner using budget biodiesel feedstocks, and may further inform the rational design of functionalized heterogeneous acid catalysts.