Investigating an indigenously designed multi-cavitation shockwave power reactor for single-step biodiesel production with enriched fuel properties using high-free fatty acid containing blended Karanja and castor oils and novel bifunctional magnetic catalyst: Process optimization, kinetic, and energy analysis

This study investigates the application of a novel designed multi-cavitation shockwave power reactor and synthesized bifunctional magnetic catalyst (Sr0.5.Zn0.5/Fe3O4) for single-step biodiesel production from high-free fatty acid containing raw Karanja oil and raw castor oil blends with a 2.5 kg batch. A bifunctional catalyst was synthesized using co-precipitation and characterized via ICP-MS, BET, VSM, SEM and XPS. Single-step biodiesel production was optimized using response surface methodology (RSM) based on a Box–Behnken design. Optimal conditions observed were: 5:1 (w/w) methanol/oil ratio, 4.21 wt% bifunctional catalyst, and 6.28 min with a maximum biodiesel yield of 99.21 ± 0.80 % under fixed condition 70RKO:30RCO blend ratio, 2252 rpm, and 50 °C temperature. The reaction followed a pseudo-first-order kinetic model with activation energy (29.01 ± 1.68 kJ/mol) ∼11 times lower than mechanical stirring. SPR exhibited 6-times higher energy efficiency and 16 times lower specific energy consumption than the conventional technique. The catalyst maintained strong performance for up to 6 cycles, with a yield of 85.21 % in the 6th-cycle reducing post-processing time and cost. The blended biodiesel showed improved calorific value by 9 %, viscosity and cold-flow properties. Overall, the SPR approach offers a highly energy-efficient, cost-effective and scalable method for biodiesel production suitable for commercial application.