Biodiesel Production from Waste Frying Oil (WFO) Using a Biomass Ash-Based Catalyst

Biodiesel, an eco-friendly alternative to conventional fossil fuels, offers reduced emissions like carbon dioxide, sulfur oxides, and soot. This study explores biodiesel production from a blend of waste oils using a novel biomass-based catalyst derived from the bottom ash of a biomass boiler. Catalyst synthesis involved wet impregnation, a unique approach using previously unreported bottom ash. Characterization via SEM-EDS, BET, FTIR, and XRD revealed its composition and structure. Optimization of biodiesel production involved assessing alcohol molar ratio, catalyst concentration, and reaction time, achieving a maximum FAME concentration of 95% under specific conditions. Blending residual palm oil with waste frying oil enhanced biodiesel properties, demonstrating a maximum FAME concentration at specific catalyst concentration (8%), molar ratio (1:10), and reaction time (2 h). Catalyst reusability, up to three cycles without significant yield variation, showcased its sustainability. The catalyst, primarily composed of calcium, a characteristic biomass bottom ash component, exhibited mesoporous features. Impregnation with eggshells not only altered composition but also ensured a uniform particle size distribution. FTIR and XRD analyses indicated calcium in hydroxide and crystallized forms. Effective catalyst separation methods included decanting or water washing, with optimal biodiesel purity achieved through 3% phosphoric acid washing at 60 °C. Various recovery methods were assessed, highlighting hexane washing as the most efficient, enabling up to three catalyst reuse cycles without substantial efficiency loss.