Preparation of binder-less shaped activated carbon from enzymatic hydrolysis lignin using H₃PO₄ activation

The depletion of fossil fuels caused by increased population and industrialization drives biorefineries to produce biofuel from lignocellulosic biomass, resulting in massive production of lignin with a large potential to be converted to value-added products. In this study, Binder-less shaped activated carbon (AC) has been prepared from the enzymatic hydrolysis residue (EHR) of a corncob furfural production process using H₃PO₄ activation. To restrain swelling of lignin during the activation and achieve its self-sintering upon molding, a strategy of lignin condensation with furfural has been developed. Firstly, the EHR was demineralized with NaOH to get the enzymatic hydrolysis lignin (EHL). The EHL was then dehydrated with H₃PO₄. The dehydrated EHL named as DEHL was mixed with furfural for the condensation with H₃PO₄ as catalyst. The condensed product, i.e., CEHL, was finally molded into tablets followed by activation with H₃PO₄. The processes were analyzed with the aid of proximate analysis, ultimate analysis, FTIR, TGA, DSC, SEM, and CNMR. The effects of reaction conditions including that of demineralization, dehydration, condensation, molding and activation of the molded tablets on the texture and adsorption performance of the AC were investigated. Under the optimized condition, an AC with the specific surface area (S_BET) of 1382 m²/g, iodine adsorption value 990.0 mg/g and methylene blue adsorption value 329.3 mg/g was obtained in an activation yield of 61.0 wt %.