Hydrothermal Liquefaction and Photocatalytic Reforming of Pinewood (Pinus ponderosa)-Derived Acid Hydrolysis Residue for Hydrogen and Bio-oil Production

Abstract

Pretreatment of lignocellulosic biomass (LCB) is a prerequisite for downstream bioconversion of its cellulosic components to second-generation biofuels. Acid hydrolysis pretreatment separates most of the hemicellulose and cellulose from lignin. However, the lignin-rich acid hydrolysis residue (AHR) may contain 20–50 wt % feedstock biomass. To improve the economics of LCB-based biorefinery, the AHR needs to be valorized. In this study, we have performed hydrothermal liquefaction (HTL) of AHR derived from the dilute acid treatment of pinewood for H₂ and bio-oil generation. A slurry of AHR at a biomass-to-water ratio of 1:30 was hydrothermally liquefied in the presence of a homogeneous Ni(NO₃)₂ catalyst at 250, 275, and 300 °C. About 16 wt % bio-oil and 51 mL of H₂ were generated at 300 °C and 60 min into the reaction. Based on elemental analysis, the higher heating value of bio-oil was found to be 29.8 MJ/kg. The aqueous coproduct generated during the HTL reaction was treated with activated carbon and subjected to the photocatalytic reforming (PR) process in the presence of a Pt/TiO₂ catalyst that produced an additional 90 mL of H₂ at NTP conditions. Preliminary calculations were performed to understand the energy recovery in terms of the products generated based on the total energy consumed for both HTL and PR processes.