Computer simulations for the adsorption and separation of CO2/CH4/H2/N2 gases by UMCM-1 and UMCM-2 metal organic frameworks

Abstract

The adsorption of pure N2/H2/CH4/CO2 along with the adsorption and separation of mixtures thereof in two metal organic frameworks (MOFs) of UMCM-1 and UMCM-2 have been extensively studied using a hybrid method of computer simulation and adsorption theory. It is found that the excess adsorption isotherms from grand canonical Monte Carlo (GCMC) simulations basically agree with the available experimental data of pure gases, except for H2 adsorption in UMCM-1 at 298 K. Moreover, the GCMC results show that both MOF materials exhibit an excellent storage capacity for pure CH4 and CO2 at room temperature. The excess uptakes of CH4 by UMCM-1 and UMCM-2 for at 5000 kPa are 12.53 and 15.06 mmol g−1, while those of CO2 at 4500 kPa are 30.13 and 36.04 mmol g−1, respectively, which approaches and even exceeds the 30.82 mmol g−1 of MOF-177. In addition, dual-site Langmuir–Freundlich (DSLF)-based ideal adsorption solution theory (IAST) is also used to correlate the simulated adsorption isotherms of pure gases and further predict the separation of equimolar mixtures. IAST shows a good agreement with the GCMC results in most cases studied here. The selectivities of both MOF materials in CH4/H2 and CH4/N2 are insensitive to the pressure. The selectivities of both MOF materials for CH4/H2 are almost the same having a value of 4, while they are 2 for CH4/N2. By contrast, the selectivities for CO2/H2, CO2/N2 and CO2/CH4 apparently rely on the pressure, showing 16.4 and 26.9, 5.4 and 7.8, and 2.9 and 4.7 at 4000 kPa for UMCM-1 and UMCM-2, respectively. Compared with other MOFs materials, their separation ability is not prominent, but they are suitable for gas storage.