Castor plant for biodiesel, biogas, and ethanol production with a biorefinery processing perspective

Whole parts of castor plant, as a non-edible energy crop, were used for multiple biofuels production. Extracted castor oil was used for biodiesel production by transesterification, whereas the castor plant residues, i.e., stem, seed cake, and leaves, were employed for ethanol and biogas production. Effects of operating conditions, including methanol to oil ratio, temperature, and reaction time on biodiesel production yield were investigated. The optimum biodiesel yield was 88.2%, obtained at 0.4:1 methanol to oil mass ratio at 40°C for 90min. This yield corresponded to 155g biodiesel per kg castor plant. In addition, pretreatment using 8% w/v NaOH at 0 and 100°C for 30 and 60min was applied to improve ethanol and biogas yields. The best results for both enzymatic hydrolysis and ethanol production by simultaneous saccharification and fermentation (SSF) were obtained after alkali pretreatment at 100°C for 60min for all plant residues. The highest ethanol production yield achieved from pretreated castor stem was as high as 82.2%, corresponding to 63g ethanol per kg castor plant. In the case of biogas production, alkali pretreatment enhanced the methane production yield from castor stem; however, it could not improve the production yield of castor seed cake and leaves. Furthermore, untreated castor seed cake had the highest methane production yield of 252.1ml/g VS, equal to 68.2L per kg of castor plant.