Green recovery of platform chemicals from hydrothermal carbonization process water

This study explores the side-recovery of platform chemicals in the hydrothermal carbonization waste-to-energy chain. Up to 90 % of target chemicals, furfural and 5-hydroxymethylfurfural, were green extracted from the process waters using the hydrophobic deep eutectic solvent decanoic acid/thymol. Wheat straw and rice husk reacted (1/4 solid/water ratio) for up to 120 min and at 180 and 230 ◦C. The dissolved chemicals built up to 5.9 g/L, accounting for 12 % of the total carbon. Extractions from the process waters and those from reference solutions behaved similarly. The solvent affinity toward furfural is 3.5 times higher than that of 5-hydroxymethylfurfural. The aqueous raffinates chromatographic outline demonstrated the recyclability for prosecuting the HTC. Focused experiments mimicked the functioning of an industrial cascade of two crosscurrent mixer settlers. Extraction yields were 90.7 and 65.8 % for furfural and 5-hydroxymethylfurfural. The counterflow arrangement, simulated by the Kremser method, gave corresponding higher yields, 96.9 and 73.4 %, respectively.