Valorization of humins by phosphoric acid activation for activated carbon production

Humins, the solid wastes from biomass acid hydrolysis, were value-added applied for activated carbon production through the phosphoric acid activation method with pyrolysis temperature ranging from 300 to 700 °C. Studies on structure and properties found that pyrolysis temperature is a key factor affecting pore formation of activated carbons. A good yield of 51.4 wt%, high BET surface area of 2375 m²/g, Barrett-Joyner-Halenda (BJH) pore volume of 0.88 cm³/g, and an excellent Langmuir adsorption capacity of 1125 mg/g on methylene blue (MB) were obtained under the preferred temperature of 400 °C (AC400). The adsorption of MB was well explained by the pseudo-second-order kinetic model, and the adsorption behavior complied with Langmuir isotherm model. Dichloromethane (DCM) was found a most effective extractant in AC400 regeneration by using Soxhlet apparatus. A comparable adsorption capacity of 680 mg/g MB was maintained for the fifth reusing of the AC400, illustrating the application potential of humins valorization for biomass residues recycling industry.