Catalytic and Noncatalytic Upgrading of Bio-Oil to Synthetic Fuels: An Introductory Review

Abstract

Biofuels can potentially address greenhouse gas emissions and related environmental issues caused by fossil fuels. Fossil fuels such as gasoline and diesel have been the preferred fuels for the automotive sector. Although promising, crude bio-oil derived from pyrolysis and liquefaction of waste biomass does not meet the fuel standards for direct use in combustion engines and power plants. Bio-oil has a considerable amount of water as well as components containing oxygen, nitrogen, sulfur, metals, and aromatic compounds. Such components add many undesired properties to bio-oil such as high viscosity, low fluidity, low heating value, greater acidity, and thermal instability. This chapter is an introductory review of some notable catalytic and noncatalytic bio-oil upgrading technologies that make them compatible with transportation fuels. The catalytic upgrading technologies reviewed include hydrogenation, hydrocracking, esterification, and transesterification. The noncatalytic upgrading techniques reviewed are emulsification, solvent addition, supercritical fluids, and electrochemical stabilization. The strengths, weaknesses, opportunities, and threats for each of these bio-oil upgrading technologies are comprehensively discussed along with their operational mechanisms and challenges.