J. S. Ali, H.L Rutto, T. Seodigeng, S.L Kiambi, C. Maende
Basic oxygen furnace (BOF) slag, once considered a waste product in the steel industry, has evolved into a valuable resource with diverse applications. Its versatility in construction, agriculture, and environmental remediation showcases the potential of byproducts to contribute to sustainable practices. As industries continue to prioritize resource efficiency and waste reduction, the utilization of BOF slag exemplifies the circular economy concept, turning waste into valuable raw materials for various sectors. BOF slag is a byproduct of the steel-making process that occurs in the Basic Oxygen Furnace. This type of slag is generated when impurities in iron ore react with the oxygen and carbon in the molten iron to form a waste material rich in various oxides and with a complex mineralogical composition. The main constituents include calcium oxide (CaO), silicon dioxide (SiO2), iron oxide (Fe2O3), and magnesium oxide (MgO). If properly extracted or recycled, these materials could contribute to economic growth and reduce the demand for virgin raw materials, like catalysts, in chemical material production.
Furthermore, energy security is critical for development since reliable and economical energy sources are required for economic growth and higher living standards. Bio-diesel derived from waste cooking oil provides an alternative energy source that minimizes reliance on fossil fuels, frequently imported at exorbitant prices. They help cut greenhouse gas emissions, which aids worldwide efforts to battle climate change. When waste cooking oil is dumped improperly, it can contaminate waterways and destroy ecosystems. Transforming this trash into bio-diesel will help prevent environmental deterioration and encourage resource sustainability.
From this perspective, this research worked towards utilizing air-cooled BOF slag as the heterogeneous catalyst in the conversion of waste cooking oil to bio-diesel through the transesterification reaction. The BOF was size reduced to > 75 μm, calcined at 850 °C for 5 h, and characterized using BET, SEM, XRD, XRF, and FTIR techniques. The Box Behnek experimental design (BBD) optimized the transesterification process. The catalyst amount (20–30 wt%), reaction time (9–12 h), and methanol–oil ratio (15–25:1 mol/mol) were varied, while reaction temperature and mixing rate were held constant at 60 °C and 750 rpm, respectively. The impact of the variables on the bio-diesel yield and the catalyst’s re-usability was studied, and the physio-chemical properties of the bio-diesel were established using the ASTM D6751 standards.
The BBD generated a quadratic model that correlated with the experimental data with an R2 of 0.9823. The maximum yield obtained after model validation was 91.67% at a methanol-oil ratio of 21:1, a reaction time of 10 h, and a catalyst of 20 wt.%. The catalyst amount and the methanol-to-oil ratio greatly impacted the bio-diesel yield. The WCO fatty acid percentage was reduced from 1.461 to 0.189%, and the bio-diesel quality met the ASTM standards for kinematic viscosity, density, and cloud point. The catalyst was able to sustain activity for a maximum of two cycles. This study shows that the BOF can be an effective catalyst for converting waste cooking oil to bio-diesel.