(285e) The Preparation and Characterization of Hydrotalcite Membranes

CO₂ emissions are thought to be responsible for global warming. In order to overcome this problem, in recent years, CO₂-selective inorganic membranes have been prepared and studied. Hydrotalcite (HT) compounds are a class of materials, which consist of layers containing octahedrally-coordinated bivalent and trivalent cations, as well as compensating interlayer anions and water ⁽¹⁾. Hydrotalcites are, potentially, good candidate materials for preparing CO₂-selective membranes, due to their high CO₂ adsorption capacity at elevated temperatures, thermal stability, and their ability to reconstruct and regenerate their structure ^(1,2) . The purpose of this study was to prepare effective CO₂-selective HT membrane, and to understand the transport of gases through them. Several methods have been used for the synthesis of the HT membranes, and the permeation characteristics of single gases and mixtures of gases have been studied. The HT membranes have also been characterized using analytical methods such as SEM, XRD, and BET. Most of the preparation techniques tested have resulted in mesoporous membranes. Microporous membranes have also been prepared, however, using the electrophoretic deposition (EPD) and vacuum suction methods. During EPD, positively charged HT colloidal particles migrate to the membrane support surface to form uniform, thin membrane films. EPD membranes show selectivity towards CO₂, with permeances in the range of 10^-7(mol/m²sec Pa). Microporous membranes were also prepared by coating HT colloidal particles on macroporous α-alumina supports by the vacuum-suction method. The He/CO₂ separation factor for these membranes was significantly higher than the corresponding Knudsen value, however, these membranes are not CO₂-permselective.

References

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2. E. Gardner, K. M. Huntoon, and T. J. Pinnavaia, ?Direct synthesis of alkoxide-intercalated derivatives of hydrotalcite-like layered double hydroxides: Precursors for the formation of colloidal layered double hydroxide suspensions and transparent thin films?, Adv. Mater., 13, 1263, 2001.