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.