Dual Phase Membrane for High Temperature CO2 Separation

[摘要] This project aimed at synthesis of a new inorganic dual-phase carbonate membrane for high temperature CO{sub 2} separation. Metal-carbonate dual-phase membranes were prepared by the direct infiltration method and the synthesis conditions were optimized. Permeation tests for CO{sub 2} and N{sub 2} from 450-750 C showed very low permeances of those two gases through the dual-phase membrane, which was expected due to the lack of ionization of those two particular gases. Permeance of the CO{sub 2} and O{sub 2} mixture was much higher, indicating that the gases do form an ionic species, CO{sub 3}{sup 2-}, enhancing transport through the membrane. However, at temperatures in excess of 650 C, the permeance of CO{sub 3}{sup 2-} decreased rapidly, while predictions showed that permeance should have continued to increase with temperature. XRD data obtained from used membrane indicated that lithium iron oxides formed on the support surface. This lithium iron oxide layer has a very low conductivity, which drastically reduces the flow of electrons to the CO{sub 2}/O{sub 2} gas mixture; thus limiting the formation of the ionic species required for transport through the membrane. These results indicated that the use of stainless steel supports in a high temperature oxidative environment can lead to decreased performance of the membranes. This revelation created the need for an oxidation resistant support, which could be gained by the use of a ceramic-type membrane. Work was extended to synthesize a new inorganic dual-phase carbonate membrane for high temperature CO{sub 2} separation. Helium permeance of the support before and after infiltration of molten carbonate are on the order of 10{sup -6} and 10{sup -10} moles/m{sup 2} {center_dot} Pa {center_dot} s respectively, indicating that the molten carbonate is able to sufficiently infiltrate the membrane. It was found that La{sub 0.6}Sr{sub 0.4}Co{sub 0.8}Fe{sub 0.2}O{sub 3-{delta}} (LSCF) was a suitable candidate for the support material. This support material proved to separate CO{sub 2} when combined with O{sub 2} at a flux of 0.194 ml/min {center_dot} cm{sup 2} at 850 C. It was also observed that, because LSCF is a mixed conductor (conductor of both electrons and oxygen ions), the support was able to provide its own oxygen to facilitate separation of CO{sub 2}. Without feeding O{sub 2}, the LSCF dual phase membrane produced a maximum CO{sub 2} flux of 0.246 ml/min {center_dot} cm{sup 2} at 900 C.

[发布日期] 2007-06-30

[学科分类] 材料科学（综合）

[关键词] CARBONATES;ELECTRONS;FEEDING;GASES;HELIUM;IONIZATION;IRON OXIDES;LITHIUM;MEMBRANES;MIXTURES;OXIDATION;OXYGEN;PERFORMANCE;STAINLESS STEELS;SYNTHESIS;TRANSPORT;X-RAY DIFFRACTION