Gas adsorption separation of CO2/CH4 system using zeolite 5A

• CO2 and CH4 binary adsorption equilibrium data on zeolite 5A were measured.
• Adsorption selectivity was measured over a wide range of pressure and composition.
• Experimental data were validated by predicted results of some thermodynamic models.
• The x–y phase diagram of the system was studied experimentally and theoretically.
• The binary selectivity data indicate that zeolite 5A is very selective to CO2.

Pure gas adsorption isotherms of carbon dioxide at (273, 283, 303, 323, 343) K and binary adsorption isotherms of carbon dioxide and methane at (303, 323) K and pressures up to 10 bar on Zeochem Co. Zeolite 5A were measured using a volumetric method. Equilibrium gas phase compositions have been determined using a gas chromatograph (GC). The experimental binary equilibrium data were compared with equilibrium data calculated by ideal adsorbed solution theory (IAST), and vacancy solution model (VSM). A model analysis of the experimental data has been performed with real adsorbed solution theory (RAST) owing to not satisfactory prediction of multi-component behavior with IAST and VSM. For this purpose, activity coefficients, accounting for the non-ideality of the adsorbed mixture, were calculated from the experimental data. The results of the pure experimental data showed that, the heat of adsorption for methane is approximately independent of loading (about 20 kJ/mol), and for carbon dioxide decreases by increasing loading when q < 0.5 mol/kg. Subsequently, by increasing loading, the heat of adsorption increases up to q = 2 mol/kg. The selectivity of both simulated landfill and biogas mixtures have been also measured experimentally. These data indicated that zeolite 5A can be successfully applied in CO2/CH4 separation for landfill gas and biogas upgrading.

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