PNNL

Abstract

Hydrothermal liquefaction (HTL) is a promising technology for converting wet biomass into biocrude oil, but the management of its carbon rich aqueous phase (HTL-AP) coproduct remains a key barrier to commercialization. Wet air oxidation (WAO) offers a robust route for treating HTL-AP; yet, the properties and conversion of macromolecules, along with the chemical kinetics of this complex system, remain unexplored. Here, we describe the chemical kinetics unconstrained from oxygen diffusion limits of the HTL-AP during WAO in a well-mixed reactor and use FT-ICR-MS (Fourier transform ion cyclotron resonance mass spectrometry) to elucidate the molecular composition throughout the WAO reaction. This study presents and validates a lumped parameter kinetic model for the WAO of HTL-AP, accurately capturing the complex matrix of compounds’ temperature dependent degradation behavior. We highlight how operating conditions can be tuned to favor either acetic acid formation or complete mineralization, offering guidance for WAO process optimization and achieving >95% COD reduction. FT-ICR-MS further showed that compounds not detected via HPLC analysis encompass a complex matrix of O- and N-containing macromolecules that are rapidly transformed into more oxygenated intermediates during the initial stage of WAO. Overall, this work delivers the lumped parameter kinetic framework for WAO of HTLAP, including insights into the fate of macromolecules, providing a basis for the design and optimization of HTLAP valorization strategies.