Catalytic hydrothermal liquefaction of biomass into bio-oils and other value-added products – A review

Abstract

Hydrothermal liquefaction (HTL) is an effective method for the conversion of biomass into biofuel involving moderate temperature and high pressure. However, the yield and quality of bio-oil are not sufficient for commercialization under normal HTL conditions. In this regard, the review emphasizes the need to select the appropriate catalyst for achieving high bio-oil yields with improved quality. Besides, the factors influencing the catalytic HTL, including the types of catalyst used in HTL, the mechanism of catalytic-HTL reaction, the effect of the catalyst on other HTL products including biochar, aqueous phase extracts, and gas, are discussed in detail. This review also summarizes by mentioning the barriers to be overcome in catalytic HTL by focusing on promising approaches.