Reducing fossil fuel demand by using biofuels as an alternative hydrothermal liquefaction is a promising process for transforming biomass into drop-in fuels†

Abstract

A currently accepted strategy for reducing greenhouse gas (GHG) emissions from fossil fuels is to replace them with biofuels. While total replacement is not considered a feasible option, other technologies such as hybridization, electrification and more efficient engines can help significantly reduce the total amount of fuel needed globally. Several processes are currently available for producing biofuels, of which ethanol and biodiesel are the best known. Other fuel alternatives are emerging, some of which are attracting attention due to their high treatment capacity and the production of aromatic compounds needed to ensure fuel compatibility with conventional fossil fuels. The thermal processing of biomass has proven to be an interesting ally in the rapid transformation of materials to obtain several valuable by-products that can be properly processed to obtain drop-in fuels. Among the different thermal technologies for biomass conversion is hydrothermal liquefaction (HTL). The process has a long history of research experience and is one of the most promising technologies for substituting conventional fuels. However, due to the inherent operational difficulties of the process, many aspects still require further research before it can be considered a feasible solution. The HTL process is carried out in the presence of water under moderate temperature and high pressure, resulting in the breaking of organic molecules and repolymerization to form a gas, oil and solid fraction, the yield of which is highly dependent on the characteristics of the raw material and the process conditions. Some of the challenges and difficulties found during the thermal processing of biomass are discussed, together with the issues that need to be addressed urgently if the rate of substitution of conventional fuels by biofuels is to be accelerated.