Hydrothermal Liquefaction (HTL) of Lignin: The Adsorption Separation of Catechol Guaiacol and Phenol

The complex nature of the hydrothermal liquefaction (HTL) of lignin product downstream requires an effective separation strategy. In this study, the use of adsorption separation was undertaken using deep eutectic solvent (DES) modified Amberlite XAD-4 adsorbents to achieve this goal. The XAD-4 was modified with a choline chloride: ethylene glycol DES and characterized using scanning electron microscopy (SEM), Fourier transform nfrared spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET). In addition, the HTL product was characterized using Gas Chromatography with Flame Ionization Detection (GC-FID). The performance of unmodified and DES modified adsorbents were initially tested on the model compounds of guaiacol, phenol and catechol before being extended to the HTL product in a batch adsorption system. Adsorbent mass was varied and the data fitted to the Freundlich model. The experiments showed an increase in adsorption capacity and selectivity for all species in solution when the DES modified adsorbents were used at all mass loadings. GC-FID analytics showed that DES modified XAD-4 (300 mg) as having the highest selectivity for guaiacol, with an equilibrium concentration of 121.45 mg/L representing an 85.25 % uptake, while catechol was the least favorably adsorbed. These results suggest the potential of DES modified adsorbents in the selective separation of HTL of lignin products.