(674h) Novel Branched HKUST-1 Morphology for Improved Mixed Matrix Membrane Formation and Gas Separation Performance

Daniel Harrigan,¹ Benjamin J. Sundell,¹ Ke Zhang,¹ Steven C. Hayden,¹ Won Seok Chi,² Zachary P. Smith²*

1. Aramco Services Company: Aramco Research Center, Boston, MA, USA
2. MIT, Department of Chemical Engineering, Cambridge, MA, USA

Metal Organic Frameworks (MOFs) generate interest in gas separations due to their highly tunable pore structures and large surface area to volume ratios. Processing challenges and poor mechanical properties of MOF materials often limit free-standing film formation. Mixed matrix membranes (MMMs) attempt to address these challenges by incorporating MOF particles into mechanically robust polymer films, which enhance separation performance over the pure polymer material. However, different processing challenges often arise in MMM formation because of poor interfacial interactions between the micron-sized MOF particles and the polymer matrix. To prevent agglomeration and phase separation, we successfully engineered unique branched HKUST-1 MOF particles at one tenth the scale of traditional bulk HKUST-1 particles. The branching structure, as confirmed by SEM, and the relatively small size, as confirmed by DLS, greatly enhanced dispersion inside a 6FDA-DAM polymer matrix. The resulting MMM demonstrated enhanced gas transport properties compared to both the bulk MMMs and the base polymer membranes. The incorporation of both branched or bulk HKUST-1 particles increased gas permeability of the neat polyimide, but poor polymer-MOF interfacial properties of the bulk HKUST-1 MMM led to a significant loss in CO₂/N₂ and CO₂/CH₄ selectivity. Meanwhile, the branched HKUST-1 MMM retained high selectivities in both pure and mixed gas feeds. Interestingly, the branched HKUST-1 MMM contained a partially percolated network of MOF particles at 30% loading which was not observed using the bulk HKUST-1 particles. Notably, the branched MMMs also benefitted from improved CO₂ plasticization resistance in high pressure feeds, an attractive result for industrial application in acid gas removal from natural gas.