(351e) Ionic Liquid-Polymer Gel Electrolytes for Electrochemical Olefin Separations in Gas-Diffusion Electrodes

The separation of olefin/paraffin mixtures is one of the most energy intensive processes in the chemical industry, accounting for more than 0.3% of total global energy consumption. Currently, light olefins (e.g., ethylene and propylene) are purified via energy-intensive cryogenic distillations. Alternative non-thermal separation methods that rely on the difference in size (i.e., size-sieving membrane separations) are not effective due to the small size difference between small olefins and paraffins. Instead, significant energy savings could be realized by targeting differences in chemical reactivity between alkenes and alkanes. Separation of alkenes can be achieved electrochemically by reversible, selective absorption by a transition metal complex which is promoted at one oxidation state and reversed at another. Such separations have demonstrated high selectivity but low throughput with the potential for significant improvement with rigorous electrochemical engineering. Given the rapid separation mechanism (electrochemical reduction/oxidation), mass transport of gasses and ionic conductivity are the key limiting parameters. In this study, we develop gas-diffusion electrodes (GDEs) for high-throughput electrochemically modulated olefin/paraffin separation. Use of hybrid ionic liquid-polymer gel (ion gel) thin films containing transition metal complexes in the GDE will promote large gas contact area, short gas diffusion pathways, and high ionic conductivity in the electrode. In this work, I will discuss early results in the synthesis of Nickel dimercaptomaleonitrile complexes (i.e., [Ni(S₂C₂(CN)₂)₂]) as reversible olefin complexing agents, and their electrochemical characterization in the presence of olefins. Furthermore, I will discuss ongoing and future work on the fabrication, transport properties, and redox modulated olefin binding properties of ion gels composed of poly(vinylidene fluoride-co-hexafluoropropylene) films swollen with imidazolium-based ionic liquids and [Ni(S₂C₂(CN)₂)₂] complexes, to be implemented in membrane-electrode-assembly swing absorbers for electrochemical separation of olefin/paraffin mixtures.