Direct Catalytic Liquefaction Technology of Biomass: Status and Review

Abstract

Direct catalytic liquefaction of biomass is one approach to produce liquid fuels and chemicals from biomass. In contrast to pyrolysis, in which thermal treatment only leads to depolymerization of the macromolecules of biomass (carbohydrates and lignin), further reactions are introduced in direct liquefaction by addition of pressurized reducing gas (hydrogen or carbon monoxide) and a catalyst to the reactor. High biomass conversion rates of up to 95% are obtained because char formation is suppressed as recondensation and recombination of thermal cracking products are reduced. Generally, the oils are more stable than pyrolysis oils due to the lower content of unsaturated compounds and lower oxygen content, which is in the range of 8–12%. As direct catalytic liquefaction of biomass is a high-technology method depending on many parameters, development has not been as rapid as in pyrolysis. However, yields and qualities of liquid products are promising and it is possible that some of the experience gained with existing coal liquefaction technologies can be adopted to the new feedstock biomass.