Hydrothermal Liquefaction and Photocatalytic Reforming of Pinewood (<i>Pinus ponderosa</i>)-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.