Screening of Copper Open Metal Site MOFs for Olefin/Paraffin Separations Using DFT-Derived Force Fields

Efficient processes for adsorptive separation of light olefin/paraffin mixtures are likely to have many advantages over traditional separation techniques for these commodity chemicals. Although some metal organic frameworks (MOFs) have been studied experimentally for this process, a large-scale computational screening study has not been reported due to the inherent difficulty in describing the critical role of interactions of olefins with open metal sites (OMS). In this paper, we introduce new density functional theory (DFT) derived force fields (FFs) that accurately describe adsorption of C₂ and C₃ olefins and paraffins in CuBTC. Using detailed DFT calculations for MOF-505 and PCN-16, we show that the energetics predicted by our FFs are transferable to other related MOFs that contain Cu OMS. Next, we evaluate the performance of 94 distinct Cu–OMS MOFs for the industrially important propylene/propane separation and identify 18 MOFs predicted to have attractive properties as adsorbents. Finally, we show that the ideal adsorbed solution theory is inaccurate for inhomogeneous olefin/MOF systems and present extensive binary propane/propylene adsorption isotherms for the top-performing MOFs identified in our calculations.