Towards the development of materials for chemically stable carbonate-ceramic membranes to be used for CO2 separation in water-gas-shift reactors

Abstract

Synthesis gas with a CO/H2 ratio suitable for production of energy carriers, e.g. hydrogen, methanol, and gasoline, can be produced by gasification of solid fuels with subsequent water-gas-shift (WGS) reaction. The separation of CO2 using conventional absorption processes leads to high efficiency losses. In contrast, a membrane reactor containing a catalyst provides the opportunity for significantly reduced efficiency losses.The present work aims at developing a chemically stable membrane for separation of carbon dioxide in gasification atmosphere. The desired membrane consists of two phases, a porous ceramic oxygen ion conductor filled with molten carbonate. Both phases need to be stable under the relevant process conditions, i.e. syngas at up to 800 °C, and compatible with each other and the water gas shift catalyst. The potential oxygen ion conductor materials, e.g. cerium gadolinium oxide (Ce0.8Gd0.2O2-δ) and cerium samarium oxide (Ce0.8Sm0.2O2-δ), which are known from literature to be compatible with alkali carbonate melts, were exposed to different gasification-relevant gas atmospheres at 600–900 °C and subsequently investigated regarding chemical reactions. Furthermore thermodynamic properties of alkali and alkaline earth carbonate systems were studied to identify a mixture with suitable melting behavior and high chemical stability as well as low volatility under relevant syngas conditions.