Dual phase membranes for CO2 separation in power generation

Dual-phase membranes consisting of selected molten carbonates and solid oxides have been fabricated and characterised by electrochemical methods and flux studies. The total conductivity of the molten carbonate phase embedded in an inert ceramic matrix was measured and electromotive force measurements were carried out under well-defined atmospheres in order to obtain the transport numbers of the various charged species present in the molten carbonate phase. In dry conditions the conductivity was ionic by native alkali metal cations and carbonate ions. However, there was a minor contribution from oxide ions, and in the presence of water vapour also hydroxide ions, confirming a central hypothesis of the project. A new theoretical approach was developed for correcting the transport numbers of foreign ions that takes into account the significant electrode polarisation of the native ions. Flux studies of dual-phase membranes were performed under various operating conditions. The presence of steam on the feed and permeate sides of the membrane led to an enhanced CO2 flux compared to the operation under dry conditions. The addition of selected oxides to the molten carbonate also led to an increased ambipolar CO2 transport. All in all, the results of the project are that the fluxes of CO2 through these membranes are not related to counter-ion transport in the solid matrix, but in the melt itself, having important consequences for further improvement and operation of the membranes. Long-term tests at 550°C showed that the CO2 flux is stable for more than two months. The membranes are hence promising for application in both post- and pre-combustion CO2 capture, while modelling showed that they are competitive over alternative CCS technologies mainly for pre-combustion. The main results of the project are recently published and form part of the basis for follow-up applications as coordinator to RCN and EC H2020 FET-OPEN.

The main objective of DUALCO2 is to determine transport mechanisms of dual phase membranes both at the microscopic scale by identifying chemical reactions and species involved in the molecular separation and ionic transport, and at the reactor scale, by o perating the membranes in selected operating conditions enabling to screen effect of pressure, steam, pO2, pH2 and pCO2 on flux and stability. This is a first time ever pioneering work requiring specific competences and tools brought in by the selected p artners. The project plan is defined to tackle step-wise these ambitious objectives by developing necessary knowledge on materials bulk property down to the microscopic scale, on interface interaction between functional ceramic and molten salts, and surfa ce, interface interaction with environment (multi-component gas streams, steam, pressure effect). Dedicated tools and procedures for probing and testing the produced membranes will be developed, thereby creating an advanced laboratory for these membranes. In order to tackle these ambitious objectives, four partners including two research centres from USA and France will combined their expertise and know-how in DUALCO2. They are chosen based on their world leading expertise in ion conducting materials (U iO, coordinator of the project), molten carbonate media (LECIME), gas separation membranes and process development (Argonne and SINTEF). This complementary partnership brings the required competences and tools necessary to complete this first time ever pi oneering work. An important aspect of the DUALCO2 project is thus the bridge created between the fields of advanced ceramic and molten salts science. It is thus expected that the gathering of Norwegian and worldwide experts in these fields will create de cisive impact on the science underpinning the development of dual phase membrane technologies. The project educates on PhD candidate having the possibility to increase his/her competences with world leading experts.