Kinetic and thermodynamic study on the esterification of oleic acid over SO3H-functionalized eucalyptus tree bark biochar catalyst

Abstract

Herein, esterification of oleic acid (OA) over tosylic acid functionalized eucalyptus bark biochar (TsOH-MBC) to synthesize fatty acid methyl ester (FAME) was investigated. The TsOH-MBC catalyst was prepared via pyrolysis-activation-sulfonation process at various impregnation ratios and was characterized by SEM, FTIR, EDX, XRD, BET, TGA and acid site density techniques. The catalytic performance of the sulfonated biochar catalyst was described in terms of acidity and FAME yield. 6 g of sulfonic acid loaded on 10 g of MBC (6TsOH-MBC) appeared to be most appropriate combination to achieve a highly active catalyst for the esterification of OA with 96.28% conversion to FAME at 80 °C for 5 h with catalyst loading of 4.0 wt% and 8:1 methanol/OA molar ratio. The catalytic reaction kinetic data were very well described by the second-order model, with a rate coefficient of 0.223 mL mol−1 h−1 at 80 °C and activation energy of 81.77 kJ mol−1. The thermodynamic parameters such as Delta H, Delta S and Delta G were determined to be 78.94 kJ mol−1, 135.3 J mol−1 K−1 and 33.03 kJ mol−1, respectively. This research provided an environmentally friendly procedure for FAME production that could be replicated on a commercial scale.