Coupling biomass hydrothermal carbonization and green solvent extraction

This paper merges two leading-edge practices of sustainable waste valorization chains – biomass hydrothermal carbonization (HTC) and green solvent extraction – into an integrated process scheme. The innovation is to intersperse two hydrothermal carbonization steps with solvent extraction to recover valuable products from the reaction process water before completing the carbonization. The study uses rice husk as the waste biomass, hydrophobic deep eutectic decanoic acid/thymol (DES) as the green solvent, and furfural and 5-hydroxymethylfurfural as the target chemicals. HTC went batch-wise (230 °C, 1/4 solid/liquid ratio, total reaction time 2 h). DES extraction recovered up to 91 % of the chemicals from the process water. Although only 2 % of the original biomass converts to platform chemicals, the process illustrates a new methodology that is tailorable for other optimized productions. A flowsheet scheme helps quantify mass balances. The many degrees of freedom in the operational parameters allow for the intensification of the industrial-scale process. The new method paves the way for further developments, applying the combined process to other biomasses, solvents, and target chemicals.