Valorization of restaurant waste oil and cow-bone doped siliceous termite hills towards biodiesel production: Kinetics and thermodynamics

The type of feedstock and catalyst selected are major factors in determining the process efficiency, product cost and fuel yield obtained from a biodiesel production process. The use of termite hill as a highly reusable inert support, doped with cow bones in the synthesis of biodiesel from restaurant waste oil (RWO) could be a cost-effective alternative to other conventional catalyst types or processes. Therefore, two catalysts (raw cow-bone supported on silica; R–SC_1.5 and calcined cow bone supported on silica; C-SC_1.5) were developed and used in biodiesel production. The maximum conversion of RWO was 95.12% using C-SC_1.5 at reaction time 2.5 h, methanol to oil ratio 9:1, temperature 65 °C and catalyst loading of 2 %w/w. The prepared catalysts were characterized using SEM, EDX, FTIR, XRD and BET analysis. The kinetics of the RWO with R–SC_1.5 and C-SC_1.5 was further studied. The activation energy (E_a) and frequency factor (A) were found to be 41.4 kJ/mol, 53.41 kJ/mol and 2.24 × 10⁴ min^?1, 2.29 × 10⁶ min^?1 respectively. The transesterification reaction adhered to first order law, while physicochemical properties of the biodiesel obtained were within the American Standard for Testing and Materials (ASTM) limits, since the product has low FFA content, low viscosity, high thermal stability with high energy content and improved combustion characteristics. Reusability of C-SC_1.5 was also examined, which revealed effectiveness up to 5 reuses without significant reduction in biodiesel yield.