2 separation from the hot flue gas is a key technology to reduce green house gas. However, there are no efficient methods of separating carbon dioxide available at high temperature so far. This research is aimed at synthesis of a new inorganic dual-phase carbonate membrane for high temperature (>400 °C) CO2 separation.
It is well known that molten carbonate has high CO32- ion conducting properties from the research on the molten carbonate fuel cell (MCFC). From the extension of MCFC, the concept of dual-phase membrane was introduced in this research. This membrane consists of a porous solid phase and a molten carbonate phase. The solid phase serves as an electronic conductor and molten carbonate phase serves as an ionic transport channel. Metal-carbonate dual-phase membranes were prepared by the direct infiltration method with Li/Na/K (42.5/31.5/25 mol.%) carbonate mixture and porous stainless steel support. The surface of the membrane was characterized by SEM/EDS and XRD. Gas tightness was checked with helium permeation at room temperature. Permeance for different gases was measured at different temperature (450~750 °C).
SEM with EDS results show that the pores in the support were successfully filled with molten carbonate. The membrane is gas-tight with helium permeance about six orders of magnitude lower than that for the metal support. Gas permeance of CO2, N2, and CO2 with O2 were measured at various temperatures (450~750 °C). Permeance of carbon dioxide with oxygen tends to increase with temperature while others show only a slight change. Permeance of CO2, N2, and CO2 with O2 was in the range of 3~5 x 10-9, 1~3 x 10-9, and 7~25 x 10-9 mol/s.m2.Pa, respectively at 450~650 °C. At 650 °C, permeance of carbon dioxide with oxygen reached maximum, which was 16 times higher than that of nitrogen. Temperature dependence of the CO2 with O2 flux was described by modified Wagner equation and Arrhenius relationship. At high temperature the permeance of CO2 with O2 decrease dramatically with time due to the oxidation of metal and molten carbonate. XRD analysis showed that iron oxides and lithium-iron oxides were formed after CO2 with O2 permeation experiment.
The ultimate goal of this study is to prepare a stable metal-carbonate dual phase membrane and to have a better understanding of this type of the membrane in the application of CO2 separation at high temperature. Experimental results were used to study the characteristic of the membrane and its permeation properties.