Molecular simulation study of metal organic frameworks for methane capture from low-concentration coal mine methane gas

Abstract

Methane and nitrogen are the main components in the coal mine drainage gases. However, it is the most difficult to separate methane from CH4 to N2 mixtures due to the completely nonpolar molecule for these two components. Research on the adsorption and separation properties of CH4 and N2 may have great significance for methane purification from coal mine methane. In the present work, adsorption and separation performance of 22 different metal–organic frameworks (MOFs) for CH4, N2 and their binary mixtures at room temperature have been investigated using molecular simulation method. Results show that the adsorption capacity is mainly dominated by the occupied sites and small pore spaces for pure CH4 or N2 adsorption. Compared with N2, CH4 would be preferentially adsorbed in all MOFs, which is consistent with the rules of adsorption heat, especially at low pressure ranges. Methane uptake with low gas adsorption loadings is mainly controlled by the interactions between adsorbate and frameworks caused by small pore spaces. And, there is a linear rule between methane uptakes and surface areas or pore volumes. The adsorption isotherms of CH4/N2 binary mixtures could be well predicted based on single-component isotherms using IAST method. Analyses on CH4/N2 mixture adsorption selectivity show that MOFs are the promising candidate for methane capture from CH4/N2 mixtures. Among all the selected MOFs, ZIF-7 is the most promising porous material for CH4/N2 mixture separation. The parameter of adsorbility is showing well correlations with the selectivity of CH4/N2 mixture, which can be served as a general criterion for the preliminary screening of MOFs for methane separation applications.