Diffusion and Adsorption of CH4/CO2 Mixtures in Zn(tbip) Metal Organic Framework
Abstract
Molecular dynamics (MD) simulations were performed to investigate the self-diffusivities and the adsorption behavior of CH4 and CO2 for their equimolar mixtures in Zn(tbip), which is a metal organic framework (MOF) that has one-dimensional 4.5 -sized channels. The MD simulations yield the CH4 self-diffusivities ( ) are larger than the CO2 self-diffusivities ( ) at low concentrations, but at high concentrations. Furthermore, analysis of center of mass distribution and radial distribution function (RDF) of guest molecules shows that CH4 is preferentially adsorbed at the surface of Zn(tbip) over CO2, and the adsorption for CH4 more increases as the total concentration increases. The diffusion selectivities ( ), defined by , were calculated giving the values are in the rage of 0.6-1.5. And the calculated is different from the Knudsen selectivity, , where and are molar mass of CH4 and CO2 respectively, and the difference increased when CH4 has the higher adsorption strength over CO2. In addition, the at low concentrations and at high concentrations show that Zn(tbip) can be used for separating CH4/CO2 mixture.
Key words : molecular dynamics, metal organic framework, self-diffusion, adsorption, gas mixture
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