Adsorption Equilibrium and Diffusion of CH(4), CO(2), and N(2) in Coal-Based Activated Carbon

[Image: see text] Coal-based activated carbon is an ideal adsorbent for concentrating CH(4) from coalbed methane and recovering CO(2) from industrial waste gas. In order to upgrade the environmentally protective preparation technology of coal-based activated carbons and clarify the adsorption equilibrium and diffusion rules of CH(4), CO(2), and N(2) in these materials, we prepared granular activated carbon (GAC) via air oxidation, carbonization, and physical activation using anthracite as the raw material. Also, we measured the adsorption isotherms and adsorption kinetic data of GAC by the gravimetric method and characterized its surface chemical properties. According to the results, GAC had abundant micropore structures with a pore size mainly in the range of 5.0–10.0 Å, and its surface was covered with plentiful oxygen-containing functional groups. The specific pore structure and surface chemical properties could effectively improve the separation and purification effects of GAC on CH(4) and CO(2). In the temperature range of 278–318 K, the equilibrium separation of CH(4)/N(2) by GAC with a coefficient between 3 and 4 could be achieved. Also, the CO(2)/CH(4) separation coefficient decreased with the increase in temperature but remained around 3. The bivariate Langmuir equation could describe the adsorption behaviors of GAC on CH(4)/N(2), CO(2)/N(2), and CH(4)/CO(2). With the increase in the concentrations of CH(4) and CO(2) in the gas phase, the difference between the adsorption capacity of CH(4) or CO(2) and that of N(2) became greater. The change of the gas ratio did not affect the characteristics of preferential adsorption of CH(4) and CO(2). At different temperatures (278, 298, and 318 K), the diffusion coefficients of CH(4), N(2), and CO(2) at various pressure points showed predominately a small variation without an obvious trend. These results demonstrated that the separation of CH(4)/N(2), CO(2)/N(2), and CH(4)/CO(2) by the activated carbon could only rely on the equilibrium separation effect rather than the kinetic effect.