MOF-based MMMs breaking the upper bounds of polymers for a large variety of gas separations

Abstract

Mixed matrix membranes (MMMs) are a strong alternative to the conventional polymeric membranes which suffer from a trade-off between selectivity and gas permeability. Considering the existence of a large number of metal-organic frameworks (MOFs) and polymers, computational screening of MOF/polymer MMMs is strongly desired to explore their upper limits in various gas separation processes before experimental efforts. In this work, we computed permeability of CO2, CH4, N-2, O-2, H-2, and He gases in 5599 metal organic frameworks (MOFs) using atomically-detailed simulations and then assessed performances of >180,000 different MOF/polymer MMMs for 11 different gas separations He/H-2, He/N-2, He/CH4, N-2/CH4, H-2/N-2, H-2/CH4 O-2/N-2, CO2/N-2, CO2/CH4, H-2/CO2, He/CO2 . Our results revealed that many MOF/polymer MMMs exceed the upper bounds due to their high gas permeability and/or selectivity. The impact of MOFs on the separation performances of polymers was examined to provide guidelines for the best MOF-polymer pairing for a variety of gas separations. Data showed that using MOFs as fillers significantly improves the permeability of CO2, CH4, N-2, O-2, H-2, and He gases in 41 different types of polymers without changing their selectivities. Many MOFs offer a great opportunity for MMM applications by improving both the permeability and selectivity of polymers such as of Teflon AF-2400 for N-2/CH4, PTMSP-co(95/5) for H-2/CH4, PTMSDPA for O-2/N-2 and PTMSP for CO2/CH4 separations. The best MOF fillers leading to MMMs with exceptional selectivities were found to have narrow pores and low porosities. These results will contribute to directing the experimental efforts to the best MOF/polymer MMM materials for numerous industrially important gas separation applications.