Biocrude upgrading with tandem catalysts via hydrothermal liquefaction of biomass feedstocks

Abstract

This study investigates biocrude production via direct hydrothermal liquefaction (HTL-D) using three biomass types: lignocellulosic agro-industrial waste (noted as BCA), microalgae (third-generation biomass, MSCT), and underutilized defatted seed from energy crops (TYH). Comprehensive characterization of the biomass samples, including elemental, proximate, structural, and calorific analyses, was performed to evaluate their suitability for HTL. The process was conducted in subcritical water conditions at 260°C and 7–10 MPa, with a residence time of 40 min. Results were compared with advanced catalytic hydrothermal liquefaction (HTL-ACT) using tandem Ni-Pt/Al2O3 and Pd-C/Al2O3 conformed catalysts, with glycerol as an in situ hydrogen donor. Lipid and protein-rich biomasses, such as microalgae and energy crop seeds, achieved higher biocrude yields (∼50 %) with elevated Higher Heating Values (HHVs) ranging from 21–32 MJ·kg−1 under HTL-D. Conversely, lignocellulosic biomass, such as sugarcane bagasse, yielded significantly to lower biocrude fraction (9–10 %) due to its high cellulose and lignin content. The introduction of tandem catalysts and glycerol in HTL-ACT slightly enhanced biocrude yields, up to 65 %, increased the H/C ratio, reduced the O/C ratio, and improved deoxygenation and calorific value compared to HTL-D, obtaining a biocrude with 40 and 42 MJ·kg−1 for the Scenedesmus tubularis microalgae and Yellow Horn defatted seed, respectively. This study highlights the potential of catalytic HTL to optimize biocrude production and improve energy properties, addressing the influence of biomass composition on process efficiency.