Fe-Assisted Hydrothermal Liquefaction of Lignocellulosic Biomass for Producing High-Grade Bio-Oil

Abstract

Although bio-oils produced by pyrolysis and hydrothermal synthesis demonstrate potential toward building a sustainable society, large amounts of char generated as a byproduct and their thermal instability owing to high oxygen content hinder their applications. Hence, a novel approach for the production of high-grade bio-oil was proposed herein. In this approach, zerovalent Fe was used as an agent for generating hydrogen in situ in the hydrothermal liquefaction of oil palm empty fruit bunch (EFB), a lignocellulosic biomass source, affording bio-oil containing water-soluble (WS) and water-insoluble (WI) fractions in high yields. Hydrogen generated by the reaction between Fe and H2O efficiently converted unstable intermediates obtained from the degradation of EFB into stable compounds, resulting in reduced char formation. Hydroxyketones were detected as components characteristic of the WS fraction in the H2O/EFB/Fe system, which were stable under hydrothermal condition. WS fractions were treated with the HZSM-5 zeolite, affording light olefins (C2-C4), as well as benzene, toluene, and xylene. This conversion was more efficient with the WS fraction obtained in the presence of Fe. The liquefaction of EFB and the conversion of WS fractions into olefins via catalytic cracking were also achieved using recycled Fe.