Design of Pore-engineered Membranes via in situ Atomic Layer Deposition Process for Improved Separations

Oklahoma State University, Stillwater OK

Investigators

Abstract

Membranes are a cost-effective and efficient technology for chemical separations that benefits the various industries that require separation, purification, and filtration processes. Membranes are materials that filter molecules based on size, charge, and other characteristics. Membranes with large pores allow liquids and gases to pass through easily (i.e., membrane permeability). However, membranes with large pores or structural defects often allow a range of molecules to pass through instead of selectively removing the desired molecules (i.e., membrane selectivity). The inherent trade-off between membrane permeability and selectivity must be considered when designing new membrane materials for commercial applications. The ability to precisely control pore size and defects is crucial for fabricating membrane materials with the optimal combination of permeability and selectivity for a given separation. Unfortunately, achieving the desired level of control is technically challenging and has limited the commercial potential of membrane technologies. This research project aims to develop membranes for difficult gas separations, specifically for olefin/paraffin separations. Due to their similar chemical properties, current techniques for separating these chemicals are energy-intensive and expensive. This project will develop pore-engineered membranes using a novel approach that allows dynamic changes to the membrane structure during gas separation testing. This will ensure precise control of structural defects and pore sizes, leading to high selectivity at any desired permeance. This approach could lead to new applications for functional materials in other gas, liquid, particle, and biomolecular separations while providing valuable insights to improve chemical separations of commercial importance. The project also offers educational opportunities for students from underserved groups in STEM fields through the Oklahoma-Louis Stokes Alliance for Minority Participation (OK-LSAMP) program. This initiative provides students with practical experience and skill development, including co-authoring research papers, presenting their work at in-state and national conferences, and publishing their findings in peer-reviewed journals. This research aims to uncover principles for designing and creating microporous membranes using Atomic Layer Deposition (ALD) for advanced separations. Zeolitic imidazolate framework (ZIF) membranes have significant potential for difficult gas separations, such as olefin/paraffin separation. However, controlling defects, pore sizes, and gas diffusion rates is crucial for realizing this potential. A new approach, in situ ALD modification, is proposed to minimize defects and control pore size in ZIF membranes to improve separation performance. This innovative method allows real-time monitoring of the membrane's transport properties and gas separation performance while being modified by in situ ALD. The research project aims to understand the relationship between the ALD process, membrane structure, and performance by combining in situ ALD processing with high-resolution characterization techniques. The key hypothesis is that ALD formation of metal oxides on membranes eliminates molecular scale membrane defects, precisely tunes pore sizes, and rationally introduces facilitating interactions between the metals and diffusing gases, maximizing gas selectivity and permeance. The research objectives are to (a) determine the effect of catalytic ALD on curing membrane defects, (b) elucidate the effect of ALD formation of metal oxide on gas selectivity by continuously controlling and monitoring pore size, and (c) exploit a metal ALD by controlling molecular interactions between metals and gases using the electronegativity of transition metals and determine the effects of such interactions on permeance. The project will yield a new understanding of the relationship between membrane structure and atomic-level processing using ALD. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.