Binary Equilibrium Adsorption Data and Comparison of Zeolites with Activated Carbon for Selective Adsorption of CO2 from CH4

A commercial-type activated carbon (AC) and three zeolitic materials, namely, zeolite socony mobil-5 (ZSM-5), Silicalite-1 and SAPO-34, were comparatively studied for single and binary equilibrium adsorptions of CO2 and CH4. The adsorption isotherm data were obtained experimentally by volumetric method at room temperature (30 degrees C) in the pressure range of 0-10 bar. The isotherms were used to determine the selectivity of the absorbents for CO2/CH4. The single isotherm data showed AC had the highest adsorption capacity for both CO2 and CH4; however, the CO2/CH4 ideal selectivity of AC was less than that of the zeolitic materials. These results suggest that AC is a suitable material for adsorption of both CO2 and CH4 from flue gas, whereas it would not be suitable for selective separation of CO2 from CH4. The zeolitic materials, namely, ZSM-5, Silicalite-1 and SAPO-34, had good adsorption capacity for CO2 against CH4. The molecular sieving property of SAPO-34 showed higher CO2 selectivity than that of ZSM-5 and Silicalite-1. Further investigations were conducted on SAPO-34 for binary mixtures of CO2-CH4 with different compositions at various total pressures. The results showed that strong adsorption of CO2 caused significant decrease in CH4 adsorption, and therefore, the real selectivity of CO2/CH4 was improved more than the ideal selectivity. Real selectivity of CO2/CH4 at 2.5 bar pressure for an equimolar mixture was 20% more than the ideal selectivity and by increasing total pressure up to 4.5 bar its value improved up to 70% more than the ideal selectivity.