Micromorphology control of the lignin-based activated carbon and the study on the pyrolysis and adsorption kinetics

Abstract The waste corncob-based lignin (AL) treated by alkali was applied as feedstock to prepared activated carbon (AC) for the methylene blue (MB) adsorption. To explore the pyrolysis mechanism of ALs, the pyrolysis kinetics were discussed by the methods of Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) equations at different heating rates, which are widely applied in the determination of dynamic parameters with reduction of the errors of multi-step dynamics. In the process of preparing lignin-based activated carbon (LC), the relationship between pyrolysis condition and structure of LCs was systematically investigated. The maximum specific surface area of LCs reached 1215.83 m2/g with high the mesoporous proportion (77.3%) at optimal activation conditions including activation temperature (550 °C), activation duration (120 min) and phosphoric acid concentration (50%). For the adsorption of methylene blue (MB) solution, the fitted kinetic model was in accordance with the pseudo-second-order kinetic model. The adsorption capacity of MB could achieve as high as 493.28 mg/g (± 5 mg/g), and the highest removal rate of MB could reach 99.0% (± 0.2%) during the secondary adsorption process. This work offers a prospective proposal to provide theoretical reference for producing LC based on pyrolysis of alkaline lignin, and utilize the LC as potential adsorbent in the dyeing wastewater treatment.