Production of renewable diesel through the hydroprocessing of lignocellulosic biomass-derived bio-oil: A review

Abstract

Due to the scarcity of fossil fuels and to population increases, there is an urgent need for renewable energy sources that can replace petroleum-derived fuels. Lignocellulosic biomass, a renewable resource, can be converted to bio-oil by fast pyrolysis and further upgraded to renewable diesel through hydroprocessing. The upgrading of oil by fast pyrolysis is the main focus of this paper. Bio-oil has a higher energy density and heating value than biomass, but it cannot be used in place of petro-diesel as it is highly unstable, polar, and immiscible with hydrocarbons. Thus upgrading is necessary as it removes oxygen-containing compounds from bio-oil. Hydroprocessing was chosen for this review paper as the method of upgrading bio-oil because there are hydrotreating units in place in refineries. To upgrade bio-oil, hydrodeoxygenation (HDO) in the presence of both a catalyst and hydrogen can replace hydrodesulfurization (the removal of sulfur compounds from crude oil). A sulfided NiMo/CoMo catalyst supported on gamma alumina is used as a benchmark catalyst for a hydrodesulfurization reaction in refineries and is considered the reference catalyst for HDO in the production of renewable diesel. The properties of renewable diesel made through hydroprocessing are similar to those of petro-diesel. Catalyst deactivation and techno-economic assessments of the whole pathway are areas that need more attention before renewable diesel can be commercialized. This review paper concentrates on the reaction mechanism in bio-oil upgrading, process parameters, and the limitations of hydroprocessing technology. This paper will be helpful for further modeling of techno-economic analysis in renewable diesel production from lignocellulosic biomass.