Upgrading of the aqueous product stream from hydrothermal liquefaction: Simultaneous removal of minerals and phenolic components using waste-derived hydrochar

We investigated the co-adsorption of AAEM and phenolic components onto hydrochar prepared from the organic fraction of MSW. HCl washing of the char removed more AAEM (up to 1 g L-1) than phenols from the hydrochar and improved the oxygen content from 21.31% to 24.9%. A relationship between the number and type of functional groups of phenolic components determined the order of adsorption: guaiacol > phenol > vanillyl alcohol > resorcinol. For AAEM the order of adsorption was Ca2+ (103 mg g-1) > K+ (95.7 mg g-1) > Na+ (8.7 mg g-1) > Mg2+ (3.4 mg g- 1). Removal efficiency increased with an increase in initial adsorbate concentration with values of 94, 94, 91 and 91% (base on original mass present) obtained for Ca2+, K+, Mg2+, and Na+, respectively. Hydrochar could remove 100% of guaiacol, phenol and resorcinol present and 61% of vanillyl alcohol in the presence of AAEMs. The Dubinin-Radushkevich isotherm best fitted the multilayer adsorption of phenolic components with a calculated qmax of 68.7 mg g-1 and 50.3 mg g-1 for vanillyl alcohol and resorcinol respectively. Henry's law best described the adsorption of AAEMs. A mass transfer analysis showed that film diffusion controls the adsorption process at low adsorbate concentrations (Bi < 100). At higher initial sorbate concentration, the rate of transport was controlled by intra-particle diffusion. AAEM components were exchanged for phenolic components to form stronger hydrogen bonds, resulting in initial preferential adsorption of phenolics with AAEM only adsorbing at higher initial concentrations.