Terminalia arjuna bark – A highly efficient renewable heterogeneous base catalyst for biodiesel production

In agreement with the necessity for green synthesis, the present study elevates the feasibility of exploiting Terminalia arjuna bark calcined ash (TABCA) - a highly functional renewable heterogeneous alkaline catalyst for the cost-effective synthesis of fuel-grade fatty acid methyl esters (FAME) by soybean oil (SO) transesterification under microwave irradiation. The mesoporous nature, significant surface area, and an extreme degree of basicity owing to the presence of CaO, MgO, K2O, SiO2, Na2O, and P2O5 effectively facilitate the SO conversion. Under the optimal conditions of 24:1 M ratio of methanol: SO, 8 wt % catalyst concentration, 80 °C temperature and time period of 60 min, microwave irradiation exhibits highest biodiesel yield (99.2 ± 0.6%) and improved selectivity (100%). Likewise, FAME content in the biodiesel was found to be 99.01% from 1H NMR. The produced SO biodiesel meets the ASTM D6751 and EN 14214 standard requirements, making it compatible in existing engines. In addition, the mesoporous TABCA catalyst showed high stability for five consecutive transesterification reactions which yielded 80 ± 0.8% biodiesel without additional treatments.