Investigation on the selective adsorption and separation properties of coal mine methane in ZIF-68 by molecular simulations

Abstract

Methane adsorption separation by ZIF-68 had been investigated using Grand Canonical Monte Carlo and Molecular dynamics simulations. Results show that ZIF-68 is a more desirable material for CH4 separation, even with CO2 and H2O presences. At 298 K and 1000 kPa condition, diffusion selectivity and permselectivity of ZIF-68 are 6.07 and 24.01 respectively. With temperature increasing, the adsorbed amount, selectivity of CH4/N2 and affinity constant (k1) of CH4 and N2 would be reduced correspondingly. However, presences of moisture and CO2 have more significant influence on the adsorption selectivity for CH4 than for N2, which would reduce the CH4/N2 separation effects as the moisture content increases. For CO2 impurity, it is preferentially adsorbed at low pressures and lead to rapid saturations. However, CH4 would be adsorbed more easily at higher pressure conditions, which can be attributed to the additional site IV. Methane adsorption selectivity of ZIF-68 at 298 K and 8000 kPa would be up to 16.48 and 15.37, respectively. Results indicate that ZIF-68 could be a promising candidate for methane adsorption separation efficiently and effectively. Research work may have important significance to the industrial application of ZIF-68 for methane separation from coal mine gases.