Adsorption of CO₂ by surface modified coal-based activated carbons: kinetic and thermodynamic analysis

The effects of different surface modifiers on the CO₂ adsorption capacity of coal-based activated carbons were studied, and the diffusion behavior, adsorption kinetics and thermodynamic parameters of CO₂ in activated carbons were analyzed. The results show that compared with ethylene glycol, 1,2-propylenediamine and zinc chloride, potassium hydroxide and sodium hydroxide can greatly improve CO₂ adsorption capacity. The adsorption rate is faster, and the adsorption capacity is larger, with the maximum CO₂ adsorption capacity being 33.54 mL/g. Fick's law can well describe the diffusion behavior of CO₂ in activated carbon. The addition of a surface modifier can increase the diffusion coefficient. The diffusion of CO₂ in activated carbon falls into the category of crystal diffusion. The adsorption kinetics of CO₂ before and after surface modification follow the Bangham equation. During the adsorption process, δ H < 0, δ G < 0, δ S < 0. Surface modification can reduce adsorption heat and promote adsorption, and the adsorption process is dominated by physisorption.