Effects of temperature and solvent on hydrothermal liquefaction of the corncob for production of phenolic monomers

Abstract

The hydrothermal liquefaction (HTL) process is a promising direction for the conversion of waste biomass into valuable chemicals/fuels. Optimization of the process parameters for HTL of biomass has been the research scope in recent years. The study aims to examine the effects of process variables such as the effect of temperature, the role of solvents: water (H2O), methanol (CH3OH), and ethanol (C2H5OH) on hydrothermal liquefaction of the corncob biomass. Hydrothermal liquefaction has been carried out at temperatures of 260, 280, and 300 °C with a reaction holding time of 15 min. The maximum bio-oil yield was obtained (38.0 wt%) at 280 °C in the presence of H2O, whereas in the case of CH3OH and C2H5OH solvents, the maximum bio-oil yield was 18.67 wt.% and 16.83 wt.% at 260 °C and 300 °C, respectively. The solvent efficiency in corncob liquefaction was observed as H2O ˃ CH3OH ˃ C2H5OH for bio-oil production. The obtained bio-oils were characterized in detail using GC-MS, FT-IR, and 1H NMR. From the GC-MS analysis of bio-oil, the phenolic compounds were observed to a higher degree (60%) in the case of H2O solvent than CH3OH and C2H5OH solvent (57% and 46%). Also, FT-IR analysis showed that higher aromatic functional groups present in bio-oil obtained with water solvent while liquefaction with alcoholic solvent showed higher ester functional groups. Moreover, the analysis of bio-residues indicated that the decomposition of the corncob occurred in a different way during HTL with the presence of different solvents.