Fluorite-perovskite-carbonate composite hollow fiber membrane for CO2 permeation

The working principle of the ceramic-carbonate dual phase (CCDP) membranes based on pure fluorite or perovskite ceramics to separate CO₂ is intensively investigated for their potential in carbon capture, utilization and storage (CCUS). However, CCDP membranes composed of fluorite-perovskite composite materials are rarely studied. The present work employed a composite of Ce_0.85Nd_0.15O_2-δ (NDC) fluorite (75 wt%) and Sm_0.6Sr_0.4Al_0.3Fe_0.7O_3-δ (SSAF) perovskite (25 wt%) as the ceramic phases to synthesize the novel hollow fiber porous support for CCDP membrane formation. The incorporation of SSAF perovskite functions not only as the partial ion-conducting phase but also as the sintering aid to improve the ceramic densification during the high temperature treatment. The mechanical strength of the resultant NDC-SSAF-carbonate membrane has been greatly improved by 100% but sacrifice CO₂ permeation flux by 5% (in case of gas mixture without O₂) compared to the fragile NDC-carbonate hollow fiber membrane. The SSAF addition enhanced the electronic conductivity of the membrane, thereby offering the membrane extra function for oxygen transport. Our further comparative studies indicate that the presence of O₂ in the feed stream actually can promote the CO₂ permeation. In general, the incorporation of perovskite and fluorite in the conducting ceramic phase greatly enhances the mechanical strength of the resultant hollow fiber CCDP membranes and is also favorable for the permeation flux of CO₂ in the carpooled manner from the feed to the sweep side when O₂ is present in the gas mixture. In regards to the selectivity of CO₂ to other gases, the presence of O₂ in the feed stream has very minimal effect due to the unique ion transport mechanism.