Novel Soybean Soapstock Biodiesel Synthesis Through Esterification / Transesterification Reactions Using Methanol and N-hexane Solvents

Soybean soapstock (SS) a by-product from the soybean processing food chain can serve as a viable feedstock for biodiesel production. This viability was attributed to its low costs and high conversion rates. Biodiesel from this feedstock required both esterification and transesterification reactions, using methanol and n-hexane as solvents. Determination of the component fatty acids was carried out using gas chromatography while functional groups were obtained using the FTIR (Fourier transform infrared spectroscopy) for both feedstock and biodiesel. The produced biodiesel had a higher percentage of unsaturated fatty acids when compared to its feedstock (soybean soapstock) with oleic acid (26.045%) and linolenic acid (22.344%) constituting the bulk of the unsaturated fatty acids. This conversion of saturated fatty acids into unsaturated fatty acids as confirmed in the GC analysis highlighted the effect of transesterification in biodiesel production. The effect of transesterification was further confirmed by the presence of cyclic ester compounds and carbonyl groups as observed in the FTIR analysis. Desirable fuel properties for the produced biodiesel were confirmed by comparing its physico-chemical properties with standard fuel properties. A high biodiesel yield of 96.8wt% and positive economic indices (38% ROI) obtained further validated soybean soapstock as a viable feedstock for biodiesel production.