Neem (Azadirachta Indica) Seed Oil as a Sustainable Diesel Substitute: A Comparative Assessment of Homogeneous Base-Catalyzed Ethanolysis and Direct Fuel Blending

Growing concern over dwindling fossil reserves and the environmental toll of petroleum use has renewed interest in renewable liquid fuels. This study explored neem (Azadirachta indica) seed oil, an abundant non-edible feedstock from Northwestern Nigeria, as a diesel alternative. Soxhlet-extracted crude oil, characterized by GC-FID, showed a fatty acid profile dominated by oleic (43.2%), linoleic (20.21%), stearic (19.32%), and palmitic (17.02%) acids. Two valorization routes were compared: NaOH-catalyzed ethanolysis and direct blending with petrodiesel. Transesterification gave 96% FAEE yield (90 min, 75 °C, 1.0 wt% NaOH, 6:1 ethanol-to-oil ratio), but the biodiesel showed unusually high viscosity (35.80 mm²/s) linked to saponification from the oil's elevated free fatty acid content. In contrast, a 1:5 crude oil–petrodiesel blend met key fuel standards (viscosity 7.24 mm²/s, cetane number 43.42, pour point 0 °C) without chemical conversion. Kinetic and thermodynamic analysis suggests direct blending is a more practical, low-cost route for decentralized biofuel production.