Adsorption separation of CO2, CH4, and N2 on microwave activated carbon

In this study, the adsorption equilibrium isotherms of carbon dioxide, methane and nitrogen on microwave activated carbon (MAC) at three temperatures (298, 308 and 323 K) have been obtained by a static volume instrument. The adsorption equilibrium data of CO2, CH4 and N2 at various temperatures were fitted to Langmuir and Toth isotherm models. It was found that the fitting results of Toth model were fine. The capacities of pure gas CO2, CH4 and N2 were 2.13, 0.98 and 0.33 mmol g−1 at 298 K and the partial pressure of 100 kPa. The competition adsorption behavior of multi component was predicted by the extend Langmuir and Toth model. The results indicated that CO2 still dominate the adsorption system in the ternary mixtures. Additionally, the separation factors of the binary mixtures CO2/CH4, CO2/N2 and CH4/N2 were calculated from the isotherms data. The results showed that the separation factors (S) of different binary mixtures at 298 K and the total pressure of 100 kPa were as follows: CO2/N2 (14.6) > CO2/CH4 (4.37) > CH4/N2 (3.33). Finally, thermodynamic functions integral Gibbs’ free energy (ΔG), integral molar enthalpy change (ΔH) and entropy change (ΔS) were calculated to characterize adsorption behavior.

Graphical abstractCompetitive effect for adsorption of multi component (CO2, CH4 and N2) at 298 K. The adsorption isotherms of the pure gases and the prediction adsorption isotherms of multi component which were calculated by two models were depicted in the figure. It can be seen that each component gets large loss in adsorption amount due to the existence of competition adsorption for both prediction models. The loss of adsorption amount varies with pressure. The higher the pressure, the greater the loss is. In addition, CO2 still dominate the adsorption system and accounts for large share in multi component adsorption with the lower partial pressure compared with CH4, N2 are trace components.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights• The adsorption capacities of three gases on MAC follow the order: CO2 > CH4 > N2. • CO2 still dominate the adsorption system in dynamic adsorption of ternary mixture. • The separation factors of mixtures follow the order: CO2/N2 > CO2/CH4 > CH4/N2. • MAC may be a new material candidate for the purification of biogas.