EAGER: Towards Development of High Performance Mixed-Matrix-Membrane for Separation Applications

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Efficient and cost-effective separation of mixtures of gases or mixtures of liquids into pure components is important for a variety of industries, including oil and gas, food, chemical, and pharmaceutical.  A membrane is a material that separates molecules via differences in their ability to traverse the pores of the membrane. While many techniques for gas and liquid separations have been developed, membranes have shown increasing promise as sophisticated new materials have been developed.  An emerging field in membrane technology involves a special type of membrane called ?Mixed-Matrix-Membranes? (or MMMs), in which nanoparticles (particles of inorganic matter that have a diameter on the order of tens of nanometers) are dispersed within a matrix of long chain molecules, also known as polymers.  Challenges in making MMMs include insuring that high concentrations of nanoparticles are well distributed throughout the polymer and that the nanoparticles adhere strongly to the polymer molecules.  This research project combines novel coating and materials processing technologies to uniformly distribute the nanoparticles in MMMs at high concentrations and to produce high performance membranes that are free of defects.  The results will yield insights into how to produce membranes for a broad range of applications and will lead to a better understanding of how to process nanoparticles.The main objective of this research project is to develop a solvothermal annealing process for producing defect-free MMMs, with an emphasis on high-throughput affordable techniques that yield both good dispersion and strong adhesion of the nanoparticles in the polymer phase. The hypothesis is that the fibrous mats produced by dispersive electrostatic forces induced during the electrospinning process may be used as a precursor to MMMs with high particle dispersion and strong nanoparticle-polymer adhesion after a coalescing process adapted from powder coating techniques. Specifically, zeolitic imidazolate framework (ZIF-8), a well-studied metal-organic framework (MOF) for gas separations is selected as the particle phase, and Matrimid, a polyimide widely used in commercial membranes, is selected as the polymer phase for the preliminary study. The key fundamental questions that are being explored are: (1) what are the important mechanisms involved in nanoparticle dispersion during electrospinning and how can they be leveraged to maximize dispersion, (2) how do fibers level into mats during solvothermal coalescence and how can this process be controlled to promote polymer transport while minimizing attraction between nanoparticles, and (3) how far can loading and thinness be pushed with this technique while retaining theoretical separation and permeation properties. Preliminary experiments indicate that it is possible to control the coalescence of the fibers by incrementally increasing a solvent to non-solvent ratio, and thus the equilibrium of fiber coalescence, but the underlying phenomena are not well understood. Successful conclusion of this research project will have a positive impact on many fields, such as hydrogen storage, carbon capture, adsorptive separation of hydrocarbons, and heterogeneous catalysis.