A review of recent research and developments in fast pyrolysis and bio-oil upgrading

The depletion of fossil fuels and the negative impacts of their extraction and combustion on the environment have encouraged scientists and industrial stakeholders to explore the development of alternative, renewable energy resources such as bio-oil, which can be produced from biomass by fast pyrolysis. The main disadvantages of crude bio-oils derived from fast pyrolysis are their poor quality caused by the presence of water and oxygen compounds, high viscosity, instability during storage, and their low heating value and high acidity (corrosiveness). To overcome these shortcomings and improve the properties of bio-oils, several techniques have been proposed. The present review provides an in-depth survey of recent studies in the field of fast pyrolysis of biomass and bio-oil upgrading. Different methods and various processes, including novel techniques such as those making use of plasma reactor and microwave-assisted approach, the use of algae as biomass, and pyrolysis under supercritical conditions, are reviewed to explore and critically assess the proposed improvements. We also examine recent advances in the field of bio-oil upgrading, focusing on chemical and catalytic processes such as the combination of fast pyrolysis, bio-oil upgrading utilizing zeolite and nonzeolite catalysts, and computational simulation methods. Finally, we assess recent progress in the improvement of the properties of the ultimate product and review the pros and cons of pyrolysis and upgrading techniques for bio-oils. We conclude with a section examining future challenges, perspectives, as well as the commercial feasibility/viability of fast pyrolysis and bio-oil upgrading.