Chemo-Physical Characterization of Castor Oil Biodiesel and B20 Blends from Gboko, Benue State: Implications for Regional Feedstock Suitability

Abstract

The increasing demand for alternative renewable fuels has intensified research into non-edible oil feedstocks for sustainable biodiesel production. This study investigates the conversion of castor seed oil sourced from Gboko, Benue State, Nigeria, into biodiesel using a two-step acid–base catalyzed transesterification process optimized for high–free-fatty-acid oils. Initial characterization of the crude castor oil revealed an acid value of 4.5 mgKOH/g, necessitating esterification before alkaline transesterification. Eight reaction rounds were conducted, incorporating systematic catalyst dosing, temperature control (65–70 °C), and sequential washing and drying to achieve optimal FFA reduction. The process yielded 60% methyl esters, demonstrating a competitive conversion efficiency compared to reports from other regions. Fuel property analysis of the biodiesel (B100), B20 blend, and petroleum diesel was conducted following standard ASTM methods. Results indicate that castor biodiesel exhibits higher flash point, viscosity, density, and carbon residue relative to petroleum diesel, while displaying significantly lower sulphur content and superior cetane numbers. Cold-flow characteristics (pour and cloud points) fall within acceptable limits for biodiesel standards, and all samples satisfied ASTM D6751 and EN 14214 acid value specifications. Overall, the study confirms that castor oil from Gboko is a viable feedstock for biodiesel production, offering favourable combustion quality, enhanced safety characteristics, and potential environmental benefits. The B20 blend, in particular, demonstrates properties closest to conventional diesel, making it suitable for practical engine applications.