Utilization of Madhuca indica ash as a green catalyst for transesterification of Madhuca indica oil: process optimization and engine analysis

This study investigates a heterogeneous catalyst derived from calcined and NaOH-treated Madhuca indica (M. indica) shell ash for the transesterification of M. indica seed oil. Process parameters were optimized using a central composite design (CCD) within response surface methodology (RSM), resulting in a maximum biodiesel yield of 92.3% (GC-MS area-based ester content). The optimal conditions were a methanol:crude oil molar ratio of 22.5:1, a reaction temperature of 70 °C, a catalyst loading of 2.5 wt%, and a reaction time fixed at 6 h. Engine performance was evaluated on a single-cylinder diesel engine operating at 1,500 rpm, utilizing B10 and B20 biodiesel blends. Under full load conditions, B10 reduced hydrocarbon (HC), carbon monoxide (CO), and smoke emissions by 21.43%, 12.78%, and 5.97%, respectively. B20 reduced HC, CO, and smoke emissions by 27.55%, 20.3%, and 12.23%, respectively, relative to diesel. Nitrogen oxides (NOx) emissions increased by 8.37% for B10% and 17.1% for B20 relative to conventional diesel. A techno-economic analysis (TEA) was performed using an Aspen Plus economic analysis process model; results and underlying assumptions are detailed in the TEA section.