Direct production of biodiesel from rapeseed by reactive extraction/in situ transesterification

Biodiesel is a fuel derived from renewable resources such as edible and inedible oil-bearing seed, algae, and waste cooking oil. The conventional biodiesel process involves oil extraction, refining and transesterification. Alternatively, transesterification can actually be performed directly from the oil-bearing materials without prior extraction. This route which is often termed “reactive extraction” or “in situ transesterification” has the advantages of simplifying the biodiesel production process as well as potentially reducing production cost. In this study, the reactive extraction of rapeseed with methanol has been characterised. The effects of process parameters on the yield, conversion and reaction rate differ substantially from conventional transesterification due to the dependence on both extraction and reaction. The rate of ester formation is mainly affected by the catalyst concentration, temperature and particle size while the equilibrium yield largely depends on the solvent to oil molar ratio. A high yield of ester (>85%) can only be achieved at high solvent to oil molar ratios (>475:1). Parametric studies and light microscope images of reactively extracted seed suggested that reactive extraction occurs by transesterification of the oil inside the seed, followed by diffusion of the products into the bulk solvent. ► Reactive extraction of rapeseed to biodiesel was characterised. ► Ester formation rate depends on amount of catalyst, temperature and particle size. ► Equilibrium yield of ester is mainly affected by solvent to oil ratio. ► Reaction is postulated to occur inside the cells prior to products solubilization.