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• The HTC of BLS was conducted under different conditions and solvents. • The maximum bio-oil yield from HTC of BLS achieved at 53.4%. • The phenols in BLS bio-oil were mainly H-type. • BLS char showed excellent Cr(VI) adsorption performance. 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. [ABSTRACT FROM AUTHOR]

In this work, industrial black liquor (BL) was directly used to prepare activated carbons with high surface area and large pore volume through K 2 CO 3 activation. The effect of activation temperature on the properties and the Cr(VI) removal performance of activated carbons were investigated. For comparison, the purified lignin (PL) was also investigated. The specific surface area and the total pore volume of BL derived carbon prepared at 800 °C (CBLS 800) were 1335.58 m2/g and 1.79 cm3/g, while those of PL derived carbon prepared at 900 °C (CPL 900) were 1715.16 m2/g and 1.12 cm3/g. The Cr(VI) removal process conforms to the pseudo-second-order kinetic model, indicating that the adsorption process is mainly controlled by chemical interaction. The fitting of isotherm was more consistent with Langmuir model. The maximum adsorption amount of Cr(VI) on CBLS 800 and CPL 900 was 669.70 and 645.73 mg/g at 45 °C and pH 2.0, respectively. The negative Δ G ° and positive Δ H ° confirmed that the adsorption of Cr(VI) onto CBLS 800 and CPL 900 was an endothermic and spontaneous process. The removal mechanism of Cr(VI) mainly includes three aspects: intra particle diffusion, electrostatic attraction and adsorption-coupled reduction. This work not only provides a theoretical basis for transforming BL into functionalized biochar materials, but also makes the efficient removal of Cr(VI) from wastewater possible. [Display omitted] • K 2 CO 3 activation was used to prepare black liquor-derived porous carbon (CBLS). • The specific surface area of CBLS 800 is 1335.58 m2/g. • The maximum adsorption amount of Cr(VI) on CBLS 800 is 669.70 mg/g. • The removal mechanism of Cr (VI) is mainly adsorption-coupled reduction. • The inherent alkali plays a role of self-chemical activation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pyrolysis characteristics and product distribution of BLS were studied. • The activation energy of BLS was higher than that of lignin. • The aromatic hydrocarbon content of BLS through down tube reactor pyrolysis was 90.15%. • The inorganic salt in BLS promoted the removal of phenolic hydroxyl groups. • The mechanism of bond breaking during PL pyrolysis was proposed. In this study, the pyrolysis behaviors, kinetics and product distribution of black liquor solid (BLS) and precipitated lignin (PL) were studied by TGA, Py-GC/MS and a homemade down tube reactor. Compared with PL, the pyrolysis process of BLS was more complex and the residue was lower based on TG/DTG analysis. The average activation energy of BLS (440 ~ 456 KJ/mol) calculated by three model-free methods were higher than that of PL (293 ~ 339 KJ/mol). Py-GC/MS analysis showed that the total content of aromatic monomers in BLS bio-oil products was 26.02 ~ 26.50% (750 ~ 850 °C), while it was 57.86 ~ 66.58% in PL bio-oil products. Moreover, BLS obtained a maximum aromatic hydrocarbon content of 90.15% (950 °C) through down tube reactor pyrolysis, while it was 81.38% for PL. The alkali catalysis of the inorganic salt in BLS promoted the removal of phenolic hydroxyl groups. [ABSTRACT FROM AUTHOR]