Conversion of waste biomass to bio-oils and upgradation by hydrothermal liquefaction, gasification, and hydrodeoxygenation

Abstract

Biofuels produced from biomass are clean, renewable, and eco-friendly alternatives to the conventional fossil fuels in the transportation sector. However, the presence of high-water content, low pH, high viscosity, and oxygenates limits the direct use of biofuel in vehicular engines. The in situ and ex situ catalytic as well as noncatalytic hydrothermal upgradation of bio-oil (converting into hydrocarbons or less oxygenated compounds) are very promising. The recent advances in thermochemical conversion processes, improved strategies in feedstock pretreatment, and optimized use of both homogeneous and heterogeneous catalysts have enhanced the fuel properties of biofuels. The available literature was reviewed extensively to perceive the pros and cons in the selection of the suitable upgrading process to produce the bio-oil based on the end use. In this chapter, the technical developments toward improving the bio-oil properties, both in quality and quantity, the influence of process parameters, reactor configurations, and their primal source were discussed in detail. By comparing the various conversion and upgrading technologies, hydrodeoxygenation is considered as the prominent alternative and the latest technology in contrast to gasification and liquefaction. However, the complexities of the hydrodeoxygenation mechanism, optimal processing conditions, and the choice of the catalysts are yet to be understood. Furthermore, the chapter points out the main barriers for the commercialization of bio-oil upgrading technologies for the future.