Hydrothermal liquefaction (HTL) processing of unhydrolyzed solids (UHS) for hydrochar and its use for asymmetric supercapacitors with mixed (Mn,Ti)-Perovskite oxides

In this study, the unhydrolyzed solid (UHS) derived from corn stover was hydrothermally processed to generate heavy bio-oil (HBO) and hydrochar. In particular, hydrothermal liquefaction (HTL) was carried out in a 300 mL high temperature and high pressure reactor with the slurry of UHS in de-ionized (DI) water, and the effect of reaction temperature, initial nitrogen pressure, reaction time, and UHS to solvent ratio on hydrochar generation was investigated. HTL processed slurries were filtered to recover the solid residue, which was extracted with acetone to recover heavy bio-oil (HBO). The solid residue was ther-mally treated further at 400 degrees C to produce hydrochar, which was thoroughly characterized by BET, SEM/ EDX, FTIR and Raman spectroscopy. Results indicated that as temperature of HTL process increased from 250 to 300 degrees C, hydrochar yield decreased. Increase in HTL temperature also resulted in decrease in BET specific surface area (SSA) and pore volume; however, increase in pore diameter. HTL parameters such as initial N2 pressure, reaction time, and UHS:water ratio was found to influence the yield, BET SSA, pore volume and pore diameter. SEM images showed porous structure whereas surface functional groups with O-H, >C=C< and C-H stretching vibrations were observed with FTIR spectroscopy. Fully characterized hydrochar obtained under different HTL processing conditions was used with sol-gel synthesized (Mn,Ti)-oxide electrode and aqueous KOH electrolyte to fabricate asymmetric supercapacitors (ASC), which were tested with cyclic voltammetry to determine specific capacitance. A maximum specific capacitance was observed for the hydrochar electrode materials obtained at the HTL processing condi-tions of 275 degrees C temperature, 1 h reaction time, and UHS:water ratios of 1:30 and 1:10 with initial ni-trogen pressure of 100 psig and 150 psig, respectively. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

In this study, heavy bio-oil (HBO) and hydrochar were generated from unhydrolyzed solid (UHS) derived from corn stover through hydrothermal liquefaction (HTL). The effects of different parameters on hydrochar yield and properties were investigated. The maximum specific capacitance was observed for the hydrochar electrode materials obtained at the HTL processing conditions of 275 degrees C temperature, 1 h reaction time, and specific UHS:water ratios.