(541a) High Zeolite Loading Mixed Matrix Membranes

Traditional gas separation membranes are polymer-based and are constrained by a fundamental ?upper-bound? selectivity-permeability trade-off. Inorganic materials, such as zeolites, can exhibit desirable transport properties beyond the ?upper-bound?. Unfortunately, pure zeolite membranes are expensive, have poor mechanical properties, and cannot be made, defect-free, in useful amounts. Mixed matrix membranes (MMMs) combine the ease of processing polymers into large area, defect-free membranes with the superior transport properties of zeolites by blending the phases. Researchers have proven that MMMs can be successfully made with properties exceeding the ?upper-bound? performance for loadings of up to 40 wt.% zeolite particles in a polymer matrix. Further increasing zeolite loadings will further increase the capabilities of MMMs as alternatives to polymer gas separation membranes.

Transport properties approaching those of zeolites are predicted as zeolite loadings in MMMs increase. However, observed transport properties fall short of these predictions. In fact, creating defect-free MMMs is challenging and becomes increasingly difficult as zeolite loading increases. Stress accumulation due to decreased polymer chain mobility, polymer-zeolite incompatibility, and the increased likelihood of forming defects with increasing filler content are the primary causes believed to be responsible for such defects.

Maximizing zeolite loading while maintaining polymeric processability to make defect-free MMMs with near-model predicted transport properties is the focus of this work. We pursue this goal using zeolite 4A and polyvinyl acetate (PVAc) as model materials and will then move to ?upper-bound? polymers. Void-free, dense MMMs, with ≥ 50 vol.% zeolite 4A in PVAc, are made without exotic zeolite surface treatments or overly complex processing steps. Formation of void-free high loading MMMs is extremely sensitive to the total solids loading in the membrane casting solution. Strategies for forming void-free MMMs at this unprecedented zeolite loading are presented. Selected transport data as well as ways to avoid other undesired defects, like clogged zeolite pores, are also discussed.