Effect of the Ceramic Phase On the CO2 Permeation Properties of the Ceramic-Carbonate Dual-Phase Membrane At High Temperature

The use of membranes to separate CO₂ from a pre-combustion gas mixture is an attractive option due to its continuous nature that can handle large flow rates. A significant amount of research in this area has centered on the use of polymeric and microporous inorganic membranes. These membranes, however, are not selective for CO₂at high temperature. To improve upon the limitations of these membranes, the use of a dual-phase membrane consisting of a ceramic phase and a molten carbonate phase at high temperature has been studied. To this point, there has been no comparative study on the effects of the ceramic phase of the dual-phase membrane, which is the objective of this work.

The dual-phase membrane is composed of an ionic conducting ceramic support infiltrated with a eutectic molten carbonate mixture. In this study, the carbonate phase of each dual-phase membrane was composed of Li₂CO₃, Na₂CO₃, and K₂CO₃ in a 0.425, 0.325, and 0.25 molar ratio, respectively. Three ceramic materials were chosen to serve as the ceramic support: La_0.6Sr_0.4Co_0.8Fe_0.2O_3-σ (LSCF), La_0.85Ce_0.1Ga_0.3Fe_0.65Al_0.05O_3-σ (LCGFA), and Ce_0.8Sm_0.2O_1.9 (SDC). These materials were selected due to their ionic conducting properties as well as their reported stability in CO₂ environments. Porous ceramic supports are made by sintering pressed powder of each ceramic material at a temperature below its densification temperature resulting in a support with an open porosity ranging between 40-50%. Dense dual-phase membranes are prepared by direct infiltration of the ceramic supports in molten carbonate at 600^oC. Room temperature helium permeation of membranes before and after carbonate infiltration decreases by four orders of magnitude from 10^-6 to 10^-10 mol^.m^-2.s^-1.Pa^-1, respectively.

For each dual-phase membrane, CO₂ permeation results show exponential dependence to increasing system temperature as well as a logorithmic dependence to increasing CO₂ partial pressure gradients across the membrane. LSCF-carbonate membranes show promising initial CO₂ permeance on the order of 10^-8 mol^.m^-2.s^-1.Pa^-1, but poor permeation stability in low O₂ environments due to decomposition of the ceramic phase. LCGFA-carbonate membranes exhibit a stable, yet poor permeation performance on the order of 10^-9 mol^.m^-2.s^-1.Pa^-1 due to the low ionic conductivity of the ceramic support. SDC-carbonate membranes exhibit a high CO₂ permeance on the order of 10^-7 mol^.m^-2.s^-1.Pa^-1 that is stable for at least 30 days at 900^oC due to the stability of the ceramic phase in low O₂ and high CO₂ partial pressure environments. This work provides a valuable comparative study resulting in a promising ceramic-carbonate membrane that can be studied further for high temperature CO₂ separation.