Valorization of Slaughterhouse Waste Fats Using Hybrid Catalysis: Process Optimization, Fuel Characterization, and Engine Performance

Abstract

Abstract The increasing demand for sustainable energy, coupled with the environmental challenges associated with fossil fuels, has intensified interest in renewable fuel alternatives. This study investigates the conversion of slaughterhouse waste fats, specifically goat and cow fats, into biodiesel using a hybrid catalytic process that integrates acid-catalyzed esterification and base-catalyzed transesterification. The study employs Response Surface Methodology (RSM) for process optimization, addressing the high free fatty acid (FFA) content of animal fats while enhancing overall conversion efficiency. Waste lipids were rendered and pretreated, after which key process parameters were optimized by varying the methanol-to-oil molar ratio (6:1–12:1), catalyst loading (0.5–1.5 wt%), reaction temperature (55–65 °C), and reaction time (60–150 minutes). Under optimal conditions (9:1 molar ratio, 1 wt% catalyst, 65 °C, and 120 minutes), a biodiesel yield of 90.6–91.2% was achieved. The resulting biodiesel exhibited favorable fuel properties, including density (0.835 g/cm³), kinematic viscosity (4.6 mm²/s), cetane number (63.17), and calorific value (40.21 MJ/kg), all of which meet ASTM D6751 specifications. Engine performance evaluation showed a slightly higher brake-specific fuel consumption compared to conventional diesel, while emissions of carbon monoxide and particulate matter were reduced, indicating improved combustion characteristics. The integration of homogeneous and heterogeneous catalysis enhances process efficiency and supports catalyst sustainability. The study concludes that the valorization of slaughterhouse waste into biodiesel is both feasible and effective, providing a sustainable pathway for waste management, energy diversification, and reduced environmental impact.