Comparative pilot-scale synthesis of methyl and ethyl ester from waste cooking oil using hydrodynamic cavitation: techno-economic insights
摘要
Despite extensive research on biodiesel synthesis, very few pilot-scale studies have evaluated hydrodynamic cavitation (HC) reactors-especially venturi-based systems which remain limited, and performance comparisons between methanol and ethanol in terms of energy consumption, reaction time, and scalability have not been adequately explored. To address the research gap, this study presents a pilot-scale (100 L/batch) techno-economic assessment of biodiesel production from waste cooking oil (WCO) using HC, incorporating ethanol for the first time in a venturi cavitation system. Process was carried out using a methanol-to-oil molar ratio of 6.1:1 (ethanol-to-oil ratio of 7.9:1), 0.9 wt% KOH, 3 bar inlet pressure, 60 °C, and 1 h reaction time. The cavitation numbers of 0.18 (methanol) and 0.36 (ethanol) with high biodiesel yields of 90.75 ± 0.05% (methanol) and 87.47 ± 0.05% (ethanol) were achieved, corresponding to yield efficiencies of 0.90 ± 0.01 × 10− 3 and 0.83 ± 0.01 × 10− 3 kg/kJ, respectively. Fuel properties were confirmed through FTIR, GC-FID, and 1H NMR, and complied with ASTM D6751 and EN 14,214 standards. Notably, ethyl esters exhibited improved cold-flow performance due to their lower saturation content, making it advantageous for low-temperature applications despite their slightly reduced yield compared to methyl esters. Techno-economic assessment revealed strong profitability at ≥ 300 L/day production scale, with ROI and IRR exceeding 89% and EROI of 9.56 for methanol, and ROI, IRR > 67%, and EROI of 6.46 for ethanol, resulting in a payback period below 1.1 years. Overall, the results demonstrate venturi-based HC as a highly scalable, energy-efficient, and commercially viable technology for converting WCO into high-quality biodiesel, with ethanol offering enhanced cold-flow behaviour.