In situ zinc-induced pore engineering: High-performance and inexpensive ZnC1000@SO3H catalyst derived from zinc citrate for biodiesel production

Carbon-based solid acid catalysts have widespread applications in biodiesel production from feedstocks with high free fatty acid. However, developing high-performance and cost-effective catalysts through the selection of appropriate carbon sources and optimized preparation methods remains a key focus of research. Herein, we report a mesoporous carbon-based catalyst, ZnC1000@SO 3 H, synthesized from zinc citrate via in-situ Zn self-activation and diazotization. Zinc citrate serves as a low-cost precursor generates ZnO templates during carbonization, facilitating highly porous structures without additional activators. The catalyst was characterized using BET, EA, XRD, TGA, SEM, FTIR, and XPS, while the products were analyzed with GC and GC-MS. ZnC1000@SO 3 H exhibits a high surface area of 720 m 2 /g, a pore volume of 1.48 cm 3 /g, and a -SO 3 H density of 2.43 mmol/g. These features endow ZnC1000@SO 3 H with outstanding catalytic performance for esterification of oleic acid as a modal reaction, achieving a biodiesel yield of 97.3% under Response Surface Method optimized conditions (Temperature: 80 °C, Methanol/oleic acid molar ratio: 9.24:1, Catalyst dosage: 4.12 wt%, Time: 1.67 h). Kinetic and thermodynamic analyses reveal that the activation energy (Ea) for the esterification catalyzed by ZnC1000@SO 3 H is 36.65 kJ/mol, with an enthalpy change (ΔH) of 33.85 kJ/mol and an entropy change (ΔS) of −147.04 J/(K·mol). ZnC1000@SO 3 H also exhibited excellent substrate applicability for soybean oil and soybean oil (30 wt% oleic acid), achieving biodiesel yields of 63% and 70%, respectively. The catalyst demonstrates remarkable reusability, retaining 80% yield after eight cycles. The cost of catalyst ($3.29/kg) indicates significant potential for commercial application.