Exothermicity study of wet oxidation of hydrothermal liquefaction aqueous phase using high-pressure differential scanning calorimetry

Abstract

Hydrothermal liquefaction (HTL) represents a promising technology to convert biomass into energy-rich biocrude, but the resulting aqueous byproduct requires further treatment. Wet oxidation (WO) is a potential method for aqueous phase (AP) treatment, degrading water-soluble organics (WSO) in an oxidative, exothermic process. This study investigates the heat release from WO of different types of HTL-AP using high-pressure differential scanning calorimetry (HP-DSC). Seven HTL-APs derived from typical feedstocks were analyzed, revealing a dependence on feedstock composition, specifically the N/C ratio. Lignocellulosic feedstocks led to lower heat release in the range of –(256–327) kJ/mol_{O2 consumed}, while nitrogen-rich APs reached up to −500 kJ/mol_{O2 consumed}. Compositional analyses using total organic carbon, total nitrogen and Fourier transform ion cyclotron resonance spectrometry showed that higher N/C and H/C ratios in WSO correspond to more reduced and unsaturated species with higher exothermic potential. The study reveals, for the first time, how the composition of the HTL aqueous phase governs WO heat release, providing a quantitative foundation for designing next-generation autothermal integration of HTL and WO systems to enhance energy efficiency and process scalability.