Amino and ionic liquid modified ZIF-71 embedded mixed matrix membrane for the enhancing the separation of refrigerant R454A

Due to their high global warming potential (GWP), hydrofluorocarbons (HFCs) are included in various regulations as substances to be phased down. Gas separation membrane technology is expected to provide a better choice for refrigerant separation. In this study, a series of metal-organic frameworks (MOFs)/ polydimethylsiloxane (PDMS) mixed matrix membranes (MMMs) were prepared for the separation of the refrigerant blend R454A (GWP = 145), which consists of a near-zeotropic difluoromethane (R32, GWP = 675) and 2,3,3,3-tetrafluoropropene (R1234yf, GWP = 4). ZIF-71-NH₂ was prepared for the first time by solvent-assisted ligand exchange (SALE), and then ZIF-71-NH₂@ Ionic Liquid (IL) was prepared by embedding [C₂mim][BF₄] into the pores of ZIF-71-NH₂ by capillary action method. The results showed that a hydrogen bonding network was established between the amino group and PDMS, which improved the interfacial compatibility, and reduced the pore size of ZIF-71, which contributed to an excellent gas separation performance of ZIF-71-NH₂/PDMS MMMs. Restricting [C₂mim][BF₄] to the ZIF-71-NH₂ pore can further reduce its pore size, and enhance R32/R1234yf separation performance due to the high selective solubility for R32 and R1234yf. The selectivity of 10 wt% ZIF-71-NH₂/PDMS MMM is 25.6 % over that of 10 wt% ZIF-71/PDMS MMM. The selectivity of ZIF-71-NH₂@IL/PDMS MMM is 38.3 % higher than that of ZIF-71-NH₂/PDMS MMM. The ZIF-71-NH₂/PDMS and ZIF-71-NH₂@IL/PDMS MMMs exhibited the most excellent R32/R1234yf separation performance compared with the data currently published in the literature. Moreover, both designed MMMs demonstrated excellent resistance to ageing.