Characterization and Evaluation of Hydrothermal Liquefaction Char from Alkali Lignin in Subcritical Temperatures

Abstract

An evaluation of hydrothermal liquefaction (HTL) char is investigated in this work. Morphological studies, N2 adsorption behavior, FTIR analysis, thermal behavior, and elemental composition are studied. The HTL char yield showed an increase with higher operating temperatures. It increased from 11.02% to 33% when the temperature increased from 573 K to 623 K. At lower temperatures, the residence time showed an impact on the yield, while close to the critical point, residence time became less impactful. Elemental analysis showed that both higher operating temperatures and longer residence times increased the nitrogen content of the chars from 0.32% to 0.51%. FTIR analysis suggested the char became more aromatic with the higher temperatures. The aliphatic groups present diminished drastically with the increasing temperature. Residence time did not show a significant impact as much as the temperature when considering the functional group elimination. An increase in operating temperatures and residence times produced thermally stable chars. HTL char produced at the lowest operating temperature and showed both the highest surface area and pore volume. When temperature and residence time increase, more polyaromatic char is produced due to carbonization.

Hydrothermal Treatment of Biomass Feedstocks for Sustainable Production of Chemicals, Fuels, and Materials: Progress and Perspectives

“…The hydrochar produced under HTL conditions was mainly secondary hydrochar formed from repolymerization and carbonization of hydrolysis intermediates of lignin via radical reactions . Jayathilake et al found that the yield of hydrochar increased from 11% at 300 °C to 33% at 350 °C of HTL . The increasing residence time from 10 to 30 min slightly increased the yield of hydrochar at 300 and 330 °C of HTL.…”

“…The increasing residence time from 10 to 30 min slightly increased the yield of hydrochar at 300 and 330 °C of HTL. However, there was no effect of residence time under subcritical conditions . The formation mechanism of hydrochar during HTL conditions included solid-to-solid (undissolved lignin) and dissolution-formation (hydrolyzed lignin) pathways, which is similar to that of HTC of lignin .…”

“…The formation mechanism of hydrochar during HTL conditions included solid-to-solid (undissolved lignin) and dissolution-formation (hydrolyzed lignin) pathways, which is similar to that of HTC of lignin . However, the dissolution-formation route was dominant via repolymerization and carbonization to produce phenolic hydrochar and polyaromatic hydrochar …”

A review of mechanism and adsorption capacities of biochar-based engineered composites for removing aquatic pollutants from contaminated water

“…Higher pyrolysis temperature resulted in an elevation of carbonized fractions, surface area, volatile matter, and pH and a decrease in surface functional groups and CEC (Tomczyk et al, 2020). Additionally, ester groups, aliphatic alkyls, and exposure to aromatic lignin core under high temperatures may increase the surface area (Jayathilake et al, 2021). Ambaye et al (2021) reported that at low temperatures/slow pyrolysis, lignin content is not converted into hydrophobic PAHs and BC develops more hydrophilic characteristics.…”

Molten Salt Carbonization and Activation of Biomass to Functional Biocarbon

“…[ 24 ] HTC accommodates a broad range of feedstocks including wet feedstock sources like sugar cane bagasse, [ 25 ] and lignin. [ 26 ] The advantage of this process is using wet biomass compared to pyrolysis which uses dried stock saving the cost of energy required for drying. The pressurized condition for the process is a major challenge leading to complicated process equipment making it expensive compared to conventional pyrolysis.…”