The polymeric upper bound for N₂/NF₃ separation and beyond; ZIF-8 containing mixed matrix membranes

Global production for NF₃ is continuously increasing, especially due to its heavy consumption in the semiconductor industry. Even though the amount of its emission is relatively small compared to other greenhouse gases, particularly CO₂, the relatively long atmospheric lifetime of NF₃ makes its emission cumulative, possibly contributing to the global climate change. Membrane-based separation techniques are very promising for the energy-efficient NF₃ recovery. It is, therefore, critically important to evaluate the N₂/NF₃ separation performance by using commercial polymeric membranes. Here, for the first time, the empirical N₂/NF₃ upper bound relationship is established by using a wide variety of commercial polymeric membranes including both glassy and rubbery polymers based on their single gas (i.e. N₂ and NF₃) permeation characterization. Among those tested, 6FDA-DAM:DABA (3:2), Teflon^® AF 2400 and PTMSP exhibited relatively high N₂/NF₃ separation performance. The theoretical N₂/NF₃ upper bound curve was also defined and found comparable with our empirical upper bound limit. In an effort to improve the N₂/NF₃ separation performance, mixed matrix membranes were prepared by incorporating zeolitic imidazolate framework molecular sieves into Matrimid^® 5218. The effects of solvents, particle sizes, and ligands on the transport properties in mixed matrix membranes were investigated.