Biomass-derived mesoporous carbons: a sustainable bifunctional catalyst for biodiesel production

[EN] Biodiesel remains a promising alternative to conventional diesel owing to its renewable nature, biodegradability, and reduced environmental impact. However, its production still relies on refined edible oils, which raises economic and ethical concerns, as well as increases production costs. As such, non-edible and waste oils have been explored as more sustainable feedstocks; however, their high free fatty acid content necessitates catalysts capable of simultaneously catalysing esterification and transesterification reactions. In this work, a mesoporous carbon derived from tannin, a renewable carbon precursor, was synthesized using a solvent-free methodology and used as a bifunctional catalyst to convert an acidified canola oil with 20% free fatty acids into biodiesel. The material was doped in situ with Zn and Ni to introduce acidic and basic catalytic sites. The structure and properties of the catalyst were investigated by TEM, BET, PXRD, XPS, and NH3/CO2-TPD analyses. The catalyst showed a well-defined mesoporous structure, with a surface area of 411 m(2) g(-1) and an average pore size of 7.7 nm. Moreover, characterization confirmed the successful incorporation of the metals, conferring a bifunctional nature to the material. Reaction parameters were optimized, and a conversion of 98.2% was achieved at an oil-to-methanol ratio of 1 : 18, a catalyst loading of 5 wt%, a reaction time of 3 h, and a reaction temperature of 150 degrees C. The catalyst maintained 92.5% conversion after five cycles and showed good acid resistance, ranging from 4 to 100% FFA. Our findings demonstrate that these metal-doped tannin-derived catalysts offer high efficiency and durability even at high free fatty acid conditions, making them viable for the sustainable conversion of low-grade feedstocks into biodiesel.