Upgrading of bio-oil from thermochemical conversion of various biomass – Mechanism, challenges and opportunities

Abstract Bio-oil is being investigated as a plausible alternate to petro-crude due to its almost akin composition profile with crude oil. However, the extracted bio-oil from various biomasses revealed an intricate composition with majorly acids, phenols and aldehydes, which confers thermal instability and corrosiveness and bio-oil possesses nitrogen and oxygen heteroatoms. Therefore, handful of research attempts were undertaken to enhance the quality and composition of bio-oil to penetrate the bio-oil into petroleum refinery. With this in view, this article provides a broad and informative discussion on the mechanism of conventional and contemporary upgrading techniques for bio-oil quality improvement. The underlying principle and previous research works on the upgrading methods viz., emulsification, steam reforming, catalytic cracking, zeolite cracking, alcoholysis/esterification, supercritical fluids, hydrogenation, hydrotreating/hydrodeoxygenation, and molecular distillation on enhancing the bio-oil quality was elaborated.