Innovative Asymmetric Mixed Matrix Hollow Fiber Membranes for Gas Mixture Separation
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abstract
The goal of the proposed work is to develop innovative scalable approaches to prepare asymmetric metal-organic framework (MOF)-based mixed matrix hollow fiber membranes and their first-ever modules as well as to finely control their molecular sieving properties for the separations of mixture gases under consideration. The practical separation applications of energy-efficient membranes are hindered mainly due to the limitations of 1) current membrane materials (i.e., polymers) and 2) current processing technologies of new membrane materials. Metal-organic frameworks (MOFs), in particular zeolitic-imidazolate frameworks (ZIFs), offer unique opportunities for gas separations (e.g., ZIF-8 membranes for C3 separation). Polycrystalline MOF membranes are, however, prohibitively expensive. Over the last two decades, mixed matrix membranes (MMMs), composite polymer membranes with more selective fillers such as MOFs (ZIFs), have been extensively studied as an evolutionary solution. Despite their impressive success, current paradigms to produce MMMs are hardly scalable mainly due to their fundamental limitations including their inability to be spun into asymmetric hollow fibers with submicron thick selective composite skin layers. Here the PIs propose to develop transformative scalable approaches not only to prepare asymmetric mixed matrix hollow fiber membranes with unprecedentedly thin MOF(ZIF)-containing selective composite skin layers and their modules but also to precisely tailor their molecular sieving properties. The key hypothesis is that asymmetric mixed matrix hollow fiber membranes with ultra-thin selective composite skin layers can be prepared by decoupling mixed matrix formation from asymmetric hollow-fiber spinning process based on an innovative polymer-modification-enabled in situ MOF formation (coined â PMMOFâ ) technique that the PI at TAMU-CS (Jeong) has been developing, which decouples MMM formation from hollow fiber spinning process. Furthermore, sizes of apertures available in crystalline MOF (ZIF) fillers are not continuous. That is to say, fillers of desired sieve sizes are not always available for specific gas mixtures under consideration. Through both experiments (Jeong) and computations (Economou and his collaborators), the PIs have showed that the effective sieve sizes of ZIFs can be tuned by introducing various metal centers and/or linkers into the crystal structure. The innovative strategies proposed here will be demonstrated for several challenging separations such as C2H4/C2H6, C3H6/C3H8, N2/CH4, and CO2/CH4 mixtures.
