CO2 - Reinforced nanoporous carbon potential energy field during CO2/CH4 mixture adsorption. A comprehensive volumetric, in-situ IR, and thermodynamic insight

CO2/CH4 mixture adsorption is very important in different fields like, for example, a biogas purification. Using a comprehensive experimental approach based on volumetric and in-situ FTIR measurements the new results of CO2/CH4 mixture separation on a carbon film are reported. The application of this experimental approach makes it possible to elaborate the effect of enhanced CH4 adsorption at low CO2 concentrations in the adsorbed phase. The presence of this effect is proved experimentally for the first time. This effect is responsible for the deviation of Ideal Adsorption Solution model from the experimental data. To discuss separation mechanism the activity coefficients at constant spreading pressure values are calculated. At low spreading pressure, CO2 activity coefficient is strongly disturbed by the presence of CH4 molecules in the surface mixture. In contrast, the CH4 activity coefficients are remarkably influenced by adsorbed CO2 only at higher CO2 surface concentrations. The obtained activity coefficients are successfully described by a new modification of the Redlich-Kister equation. This modification takes into account the interaction between binary mixture components and an adsorbent. Finally we show that the studied carbon possesses very good CO2/CH4 mixture separation properties, comparable to those reported for other adsorbents.

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