Hydrothermal liquefaction of pinewood (Pinus ponderosa) for H2, biocrude and bio-oil generation

Abstract

This study reports hydrothermal liquefaction (HTL) of pinewood at 200–275°C for H2, biocrude and bio-oil production in presence of a nitrate salt catalyst: Ni(NO3)2, Ca(NO3)2, Co(NO3)2 and Fe(NO3)3. Among these catalysts, Ni(NO3)2 showed higher selectivity towards H2 and biocrude generation. To generate H2 and biocrude, a slurry of pinewood was prepared with different biomass to solvent (B:S) ratios of 1:10, 1:30, and 1:75 and loaded in the SS316 PARR reactor and heated to different temperatures. While the reaction was in progress, gas samples were withdrawn and analyzed using GC equipped with Chrompack capillary column and thermal conductivity detector. The analysis of product gas revealed the presence of H2, CO2, CO and CH4. The liquid samples collected during the reaction were centrifuged to separate residue and analyzed using TOC analyzer, HPLC and GC–MS. Among different homogeneous catalysts used, Ni(NO3)2 yielded 12.26mol% H2 at 275°C and a maximum biocrude of 55wt% at 250°C using 200psi N2 partial pressure. The biocrude was found to contain sugars, C1-C3 carboxylic acids such as lactic, propionic, acetic and formic, HMF/furfural and other oxygenated compounds, which were thoroughly analyzed by GC–MS. Among different C1-C3 acids, lactic acid was observed in the major amount of 83.92wt% using B:S of 1:75 at 250°C. The biocrude obtained was further processed to recover light bio-oil (LBO), heavy bio-oil (HBO) and residue which were found to have higher heating value (HHV) as compared with original pinewood.