Developments of composite adsorbents by incorporation of MOFs for separation of methane: by GCMC simulations and experiments

Efficiently recovering the natural gas from the gas mixture is crucial to its application. Grand Canonical Monte Carlo (GCMC) molecular simulations were performed to screen MOFs from 100 samples covering four typical kinds of MOFs based on the selective performance of methane and carbon dioxide mixtures at 298 K and 0–0.1 MPa. Incorporation was introduced to ameliorate the performances of the selected MOFs, and the effect of mixing carbon molecular sieve (CMS), activated carbon and graphene oxide (GO) on the structure, the adsorption selectivity as well as the adsorbent performance score (APS) for carbon dioxide was also evaluated. Researches were conducted on the samples by performing the structural characterization, microscopic morphology observation and the measurements of the adsorption isotherms of methane and carbon dioxide. It shows that, at 298 K under pressure 0.1 MPa, the adsorption selectivity coefficient for the gas mixture contained the equal molar volume fraction of methane and carbon dioxide on Ni-MOF-74 is about 60 and the APS is larger than 500; within the range of incorporated amount 1–15 wt%, only the sample prepared by 5 wt% GO respectively obtained 15.4% and 47.9% increment in the adsorption selectivity coefficient and the adsorption capacity of CO₂. Results also reveal that, during three adsorption and desorption cycles, the fluctuation amplitude of the adsorption capacity, adsorption selectivity coefficient, APS on the sample can all be kept within 0.03%, and the largest adsorption selectivity coefficient is about 25.65 with 4.1% increment in APS within the molar volume fraction range of methane 50–90%. It suggests that the composite of Ni-MOF-74 incorporated by 5 wt% GO is suitable for separating the natural gas from the mixture of methane and carbon dioxide.