Novel molten phase route for composite CO2 separation membranes

Abstract

Alkali metal nitrates were successfully used as starting chemicals in the production of composite CO2 separation membranes. The easy conversion of nitrates into carbonates after high temperature annealing in CO2 is confirmed using techniques like FTIR (Fourier transform infrared) or selective NO3− electrodes. This conversion shows a step like increase at temperatures in the order of 600 °C, consistent with target utilization temperatures for these membranes. A second but equally relevant consequence of this novel route is the formation of significant concentrations of oxide ions in the molten phase, able to boost the membrane performance, where the ceramic phase modest oxide ion conductivity is rate determining. At 650 °C, a CO2 separation flux enhancement in the order of 60% was reached using nitrates as starting chemicals. A deep analysis of the oxide ion content in molten phases using a variety of analytical techniques, confirmed the specific features of the nitrates as starting chemicals but also showed that even when carbonates are used as precursors, the role of oxide ions in the molten phase can increase significantly the membrane performance.