Collaborative Research: Reverse-Selective Membrane Materials for the Purification of Hydrogen and Other Light Gases

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AbstractProposal Title: Reverse-selective Membrane Materials for the Purification of Hydrogen and Other Light GasesProposal Number: CTS-0515425Principal Investigator: Benny FreemanInstitution: University of Texas at AustinThe objective of this collaborative proposal is the formulation and optimization of a new generation of gas separation membrane materials designed for the selective permeation of larger, polar or quadrupolar species over smaller, non-polar species. The membrane materials in this work are rubbery, crosslinked copolymer networks specifically formulated to achieve high solubility selectivity for larger, polar or quadrupolar gas molecules over smaller, non-polar molecules while simultaneously minimizing size sieving. The networks are prepared via copolymerization of polyethylene glycol (PEG)-rich acrylate and diacrylate monomers. Preliminary permeation studies on non-optimized membranes have demonstrated that preferential transport of carbon dioxide over hydrogen can be accomplished with PEG-based networks, with the highest combination of carbon dioxide permeability and selectivity yet reported for non-facilitated transport membranes. These pilot studies also indicate that the gas separation performance is sensitive to the details of the network structure, with variations in crosslink density and backbone pendant groups leading to significant changes in both permeability and overall selectivity. To fully realize the potential of this new class of membranes, a systematic experimental study is proposed based on the preparation and characterization of networks with controlled variations in structure and crosslink density. The membranes will be strategically designed to optimize their performance both in terms of separation properties and overall mechanical integrity. Keys to understanding the relationship between network structure and gas separation properties are the polymer chain dynamics and local free volume, as related to the diffusivity selectivity of the membranes. The project will lead to enhanced fundamental understanding as to the correlation of chain dynamics and morphology with gas separation performance for rubbery networks, and the emergence of molecular-based design paradigms for this industrially-relevant class of membrane materials. In addition to the fundamental materials and membrane science goals associated with the proposal, broader impacts include the potential application of these new membranes as replacements for industrial gas separation processes based on cumbersome, energy-intensive methods such as absorption. This work will lead to important educational benefits through graduate student training. Further, the planned industrial liaison with Air Liquide and interaction with CSIRO (Australia) will provide direct input regarding industrial goals and priorities for gas separation membranes, and expanded resources for the characterization of these materials. This work could lead to a new class of membranes for industrially important gas separations.