High-defect sulfonated carbon derived from beet molasses for effectively biodiesel production by esterification of methanol and oleic acid

A highly defective sulfonated carbon catalyst has been successfully synthesized from beet molasses via carbonization and sulfonation. This catalyst exhibited a high acid density of 2.47 mmol/g. Prepared under optimized conditions (carbonization at 550 °C for 4 h and sulfonation at 110 °C for 8 h), the catalyst exhibited a defective carbon structure with an ID/IG ratio of 1.36 and a high specific surface area of 221.7 m 2 /g. Moreover, the optimized catalyst was used for the esterification of oleic acid with methanol to produce biodiesel. The esterification process was further optimized through single factor and RSM box-behnken design (BBD), and the oleic acid esterification rate reached a maximum of 91.57 % under optimal conditions. Furthermore, the catalyst retained 87.2 % activity after 10 cycles, demonstrating excellent stability. Fuel properties of the produced biodiesel met ASTM D6751 and GB/T 25199-2017 standards. This work presents a sustainable strategy for valorizing industrial molasses waste into an efficient solid acid catalyst, contributing to green biodiesel synthesis and biomass resource utilization.