The bio-oil obtained from thermochemical conversions of biomass (wood and agriculture waste, animal waste, solid waste etc.) can be an alternative to conventional liquid fossil fuels used in transportation or industrial sectors. However, bio-oil in its raw form is not of good quality as a fuel compared to conventional fossil derived fuels. In particular, bio-oil in its raw form has a low heating value, high oxygen and water contents, high viscosity and corrosive behavior. So, bio-oil needs to be upgraded for its direct use as a fuel. Meanwhile, the different kinds of valuable products can be derived from bio-oil: biofuels, biochemicals, and biopolymers when bio-oil is upgraded. The conversion of bio-oil into useful products has been the focus of numerous studies. Thus, it is crucial to study the research progress of this area to get the data needed to evaluate the viability of various processes for using bio-oil as feedstock in a comparative manner. Hence, this review article focuses on these value-added products and is twofold. The first fold explains the pyrolysis and hydrothermal liquefaction of biomass and compares the bio-oil properties obtained from both methods. Further, the second fold explains the key insights and respective state-of-the-art of generation techniques of value-added products from bio-oil in detail. In addition, value-added products from catalytic pyrolysis and their respective applications are also briefly discussed. Finally, the challenges and prospects of these techniques are presented. Based on this study, most of these technologies are still in the research and development (R&D) phase and cannot be scaled up due to technological limitations and cost intensive.
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