Characterising Transport Routes in Dual-phase Molten-salt Membranes for Carbon Dioxide Separation

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Supported molten-salt membranes (MSMs) are a type of dual-phase gas separation membrane, consisting of a solid inorganic support (typically a ceramic e.g., alumina) which has been impregnated with a molten salt such as an alkali metal carbonate. The molten salt (MS) is retained within the pore space of the support via capillary forces. Over the past few decades work has demonstrated these membranes' notably high selectivities and permeabilities, which are orders of magnitude beyond those of common polymeric membranes, attributed to the facilitated-transport mechanism in MSMs for gas transfer. In this process, the gas undergoes chemical reactions with ions at the feed side of the membrane, forming new ionic species e.g., carbonate ions, that diffuse through the membrane to the permeate side. There, the gas is released from the membrane, and the ions are regenerated through the reverse of the feed side reaction. The development of this class of membrane leads into many potential advantages in terms of a smaller footprint compared to current CCS technologies and as such, these membranes present an appealing option for the separation of carbon dioxide from mixed gas streams.Detailed investigations into modifying support functionality reveal impacts on transport mechanisms and CO2 flux. While extensive research has addressed the influence of support modification, limited exploration exists on the MS's specific interactions with the support material and their effects on CO2 permeation. The nature of the inorganic support dictates the mechanism of CO2 transport. Various types of membrane support, such as inert ones like alumina, electron-conducting supports like silver, and oxide ion conducting materials such as perovskite, all result in different transport mechanisms. While transportation methods tend to be mutually exclusive, efforts have been directed toward combining multiple approaches, leading to higher recorded fluxes. This has promoted the development of mixed ionic electronic conducting supports, facilitating both oxide ion and electron conduction.This research will probe the transport mechanism through a range of spectroscopic, permeation, and diffraction techniques to investigate the solid support, MS, and the interface between the two. Key inquiries will focus on elucidating the speciation of the MS, understanding the role of ion transport in either or both phases, and identifying novel interfacial species. The project aims to reveal further insights into the mechanisms governing CO2 separation in dual-phase molten-salt membranes.