Alkali-impregnated blast furnace slag heterogeneous catalyst for biodiesel production

Blast furnace slag (BFS), a waste product from the blast furnace during iron extraction, has severe environmental impacts but is also rich in compounds that, if adequately extracted or recycled, could contribute to economic growth and reduce the demand for virgin raw materials. This research, therefore, seeks to investigate the effectiveness of the BFS composition before and after impregnation with potassium hydroxide (KOH) at different concentrations (10, 30, 60, and 90 %) in catalyzing the transesterification of waste cooking oil (WCO) to biodiesel. The transesterification process was optimized using a central composite design (CCD) for response surface modeling (RSM). The catalyst amount (3–11 wt%), reaction time (2–6 h), and methanol: oil ratio (10–30:1 mol/mol) were varied while keeping the reaction temperature (60 °C) and stirring speed (750 rpm) constant. The CCD generated a quadratic model that correlated with the experimental data with an R2 of 0.9545. The maximum yield obtained after model validation was 93.15 % at a methanol: oil ratio of 15:1, a reaction time of 3 h, and a catalyst amount of 5 wt% using the 30 % KOH/BFS catalyst. The biodiesel produced met the ASTM D6751 standards for fatty acid content, kinematic viscosity, density, and cloud point. The catalyst was able to sustain activity for a maximum of three cycles.