Thermochemical Production of Bio-Oil

Abstract

Bio-oil produced from biomass pyrolysis and hydrothermal liquefaction are considered the most sustainable alternatives for depleting fossil fuels. However, the poor bio-oil properties, such as high viscosity, presence of solid particles, low calorific value, and high instability, restrict its use as a drop-in fuel. The bio-oil properties can be significantly improved using different methods, such as catalytic upgrading, biomass pre-treatment, and downstream bio-oil upgrading. This article focuses on the widely used methods for downstream bio-oil upgrading, such as hydrotreatment, solvent addition, emulsification, microfiltration, and electrocatalytic hydrogenation. The bio-oil upgrading using non-polar solvents or preparing emulsions using surfactants has shown a significant increase in the calorific values and a considerable decrease in the viscosity of the bio-oil. On the other hand, filtration of the bio-oil using membranes can remove the char particles and alkali and alkali earth metals from the bio-oil, consequently leading to higher stability of the bio-oil. Electrocatalytic hydrogenation of the bio-oil has shown promising results in increasing the content of hydrocarbons and pH by removing the carbonyl group-containing compounds from the bio-oil. The bio-oil can also be upgraded to other clean fuels, such as H2, using a steam reforming approach, which has been critically reviewed. Basic principles of the processes and effects of different parameters on bio-oil upgrading are thoroughly discussed. In addition, techno-economic analysis, policy analysis, challenges, and future recommendations related to downstream processes are provided in the article. Overall, this chapter provides critical information about downstream bio-oil upgrading and the production of other high-value-added fuels. Abbreviations AEM Anion Exchange Membrane; Al aluminum; C carbon; Ca calcium; CO2 carbon dioxide; CEM Cation Exchange Membrane; cP Centipoise; cSt Centistokes; DMF N, N-dimethylformamide; DMSO dimethyl sulfoxide; ER energy recovery; ECR energy conversion rate; CHR carbon and hydrogen recovery; Fe iron; GDP Gross Domestic Product; GHG greenhouse gas; Gt gigaton; h hydrogen; h hour; HCl Hydrochloric Acid; HER Hydrogen Evolution Reaction; HTL Hydrothermal Liquefaction; HHV Higher Heating Values; HLB Hydrophilic-Lipophilic Balance; HVF Hot Vapor Filtration; L liter; kg kilogram; kJ kilo joule; m meter; M molar; Mg magnesium; MJ mega Joule; mg milligram; Mg magnesium; MPa Mega Pascal; MFC Microbial Fuel Cell; N nitrogen; Na sodium; Ni nickel; NOx nitrogen oxides; NaCl sodium chloride; NaOH sodium hydroxide; O oxygen; O/W Oil in Water; P phosphorus; PEG polyethylene glycol; PEG-DPHS Polyethylene Glycol-Dipolyhydroxy Stearate; ppm parts per million; s second; Si silicon; SOx sulfur oxides; SR steam reforming; S/C steam/carbon; T temperature; W watt; W/O Water in Oil; µm micro meter; °C degree Celsius