Dual valorisation of oil-bearing agricultural waste (rice bran) into biodiesel and syngas via integrated transesterification and pyrolysis

This study aimed to develop a thermochemical valorisation platform that enables the simultaneous production of biodiesel and syngas from inedible oil-bearing biomass. Rice bran, an agricultural waste, was selected as the model compound because of its substantial oil content (15.73 wt%). Non-catalytic transesterification for biodiesel production from impurity-rich rice bran oil, which exhibited superior tolerance against impurities and faster transesterification kinetics than the acid-catalysed (trans)esterification method, was investigated in this study. The yield of the non-catalytic biodiesel produced from rice bran oil was 97.3 wt% in 1 min, whereas the acid-catalysed biodiesel yielded 80.7 wt% over 24 h. For syngas production from defatted rice bran, CO2-assisted catalytic pyrolysis was used, and introducing CO2 to the catalytic pyrolysis process enhanced production of syngas, particularly CO. Compared to the catalytic pyrolysis of defatted rice bran under an inert atmosphere, CO production increased by 2.7 times, which was attributed to the homogeneous reaction between CO2 and the volatile matter stemming from defatted rice bran. Consequently, CO2-driven homogeneous reaction increased the energy potential of the resulting syngas from 3.5 to 4.1 MJ kgsample−1 compared to the conventional catalytic pyrolysis process.