Adsorption equilibrium and kinetics of CO2, CH4, N2O and N2 on two adsorbents (metal-organic frameworks MOF-5 and MOF-177) and one traditional adsorbent (zeolite 5A), were determined. Adsorption equilibrium and kinetics data for CO2, CH4, N2O and N2 on all three adsorbents were measured volumetrically at 298K and gas pressures up to 800Torr. Adsorption equilibrium capacities of CO2 and CH4 on all three adsorbents were determined gravimetrically at 298K and elevated pressures (14bar for CO2 and 100bar for CH4). The Henry's law and Langmuir adsorption equilibrium models were applied to correlate the adsorption isotherms, and a classical micropore diffusion model was used to analyze the adsorption kinetic data. The adsorption equilibrium selectivity was calculated from the ratio of Henry's constants, and the adsorbent selection parameter for pressure swing adsorption processes were determined by combining the equilibrium selectivity and working capacity ratio. Based on the selectivity and adsorbent selection parameter results, zeolite 5A was a better adsorbent for removing CO2 and N2O from air and separation of CO2 from CH4, whereas MOF-177 was the adsorbent of choice for removing CH 4 from air. However, both MOF adsorbents have larger adsorption capacities for CO2 and CH4 than zeolite 5A at elevated pressures, suggesting MOF-5 and MOF-177 were better adsorbents for CO2 and CH4 storage. The CH4 adsorption capacity of 22wt% on MOF-177 at 298K and 100bar was probably the largest adsorption uptake of CH4 on any dry adsorbents. The average diffusivity of CO2, CH4 and N2O in MOF-5 and MOF-177 was of the order of 10-9m2/s, as compared to 10-11m2/s for CO2, CH4 and N2O in zeolite 5A. The effects of gas pressure on diffusivity for different adsorbate-adsorbent systems were also investigated.

Adsorption of CO2, CH4, N2O, and N 2 on MOF-5, MOF-177, and Zeolite 5A. D.Saha, Z.Bao, F.Jia, S.Deng: Environmental Science and Technology, 2010, 44[5], 1820-6