Focus on hydrochars produced from hydrothermal liquefaction of beech wood, soda lignin and black liquor

Previous studies on the hydrothermal liquefaction (HTL) of biomass have primarily focused on bio-oil production, overlooking the significant hydrochar by-product. In this work, the HTL of beech wood, soda lignin, and black liquor was performed at temperatures of 300 °C and 350 °C for 20 min. The effect of temperature and biomass type on hydrochar yields and properties was thoroughly investigated. The mass yields of the hydrochars varied between 25.92 wt% and 32.70 wt%. An increase in temperature from 300 °C to 350 °C led to a decrease in hydrochar mass yields. The carbon yield was found to be highest (51 wt%) at 300 °C using beech wood. The highest heating value, 30.97 MJ/kg, was obtained with hydrochar derived from soda lignin at 300 °C. Solid-state carbon NMR demonstrated that the hydrochars derived from black liquor contain condensed aromatic structures. Both the type of biomass and temperature significantly influenced the characteristics of the resulting hydrochar. This research demonstrates that hydrochar holds promise as a solid biofuel due to its advantageous energy content and carbon yield, highlighting its potential for sustainable energy applications.