Hydrothermal conversion of black liquor to phenolics and hydrochar: Characterization, application and comparison with lignin

The hydrothermal conversion (HTC) of black liquor solid (BLS) was investigated for producing phenolics and hydrochar. For comparison, the precipitated lignin (PL) was also investigated. The HTC experiments were conducted under different temperatures, holding times and reaction solvents to examine the optimum conditions for producing bio-oil. The maximum bio-oil yield of BLS of 53.3% was achieved at 50 wt% ethyl acetate/water cosolvent under 300 °C for 30 min. For PL, it was 86.7% at 50 wt% ethanol/water cosolvent under 300 °C for 30 min. GC–MS analysis showed that phenolics were the main products in bio-oil. The phenolics obtained from PL HTC were mainly S-type, followed by G-type; while H-type phenols were the main products in bio-oil from BLS. The hydrochar was characterized by FT-IR, BET and SEM. Moreover, the adsorption performance for Cr(VI) was investigated, which indicated that hydrochar from BLS was a promising candidate for heavy metals adsorption.