Bio-Oil Production from Prosopis juliflora via Microwave Pyrolysis

Microwave pyrolysis is an efficient technique to valorize the abundantly available Prosopis juliflora (PJF) biomass into fuel intermediates. In this study, the effects of microwave power, susceptor, PJF particle size, PJF to susceptor mass ratio, and initial mass of PJF on bio-oil, gas, and char yields, composition of bio-oil, and energy recovery in bio-oil and char were evaluated. Five different susceptors, namely, graphite, char, aluminum, silicon carbide, and fly ash, an industry waste, were utilized. A high bio-oil yield of 40 wt % with a heating value of 26 MJ kg–1 was achieved with fly ash at a microwave power of 560 W, PJF particle size of 2–4 mm, and PJF (50 g)/fly ash composition of 100:1 (wt/wt). The bio-oil contained a mixture of phenolic compounds, aromatic hydrocarbons, cyclopentanones, carboxylic acids, ketones, and furan derivatives. Nearly 51% deoxygenation of PJF was achieved with an atomic O/C ratio of 0.24 in bio-oil. This work demonstrates that the yield and quality of bio-oil are dependent on key parameters such as microwave power, biomass particle size/composition, and type of susceptor.