Co-production of biooil and biochar from microwave co-pyrolysis of food-waste and plastic using recycled biochar as microwave susceptor

Abstract

Microwave (MW) co-pyrolysis of food-waste (FW) and plastic with recycled biochar as MW susceptor was investigated for co-production of biooil and biochar. Effect of biochar recirculation (3–10 wt%) was analysed on end product yield and properties and compared with conventional MW susceptor (Granular Activated Carbon, GAC). Highest biooil yield (52 wt%) along with 30 wt% of biochar yield were obtained with 7 wt% biochar recirculation. pH and density of biooil were 4.12 and 1.09 g/mL, respectively. Increase in biochar recirculation caused substantial reduction in phenols, acids, alcohols, furans and oxygenated compounds in biooil due to rapid feedstock volatilization, end-chain β-scission and/or disengaging of the long carbon chain of FW and LDPE and transference of oxygenated functional groups into the gaseous phase. Similarly, with increased biochar recirculation, biochar showed decrease in volatile matter (by 47 %) with a simultaneous increase in fixed carbon (by 10 %), carbon (by ∼ 6 %), higher heating value (by ∼ 27 %) and morphological properties. 70 % of biooil energy yield and 45 % of biochar energy yield (obtained with 7 wt% biochar recirculation) accounted for the highest net energy efficiency of 115 %, which was comparable to that of GAC (117 %).