| Polymeric membranes offer a low energy means of gas separation. The use of polymeric membranes for separation of chemically aggressive media, or at elevated temperatures, has been limited by membrane availability. While a number of polymers are both resistant to chemical attack and thermally stable to over 300{dollar}spcirc{dollar}C, none has been shown to be capable of the selective transport of gases at high rates due to the lack of agreeable support structures. This study analyzes the fabrication of a microporous support for a composite membrane to achieve this demanding combination of properties.; In order to maximize gas transport rates, the membrane's separating layer thickness must be minimized; and consequently, this layer must be supported. In this study a stainless steel support structure is utilized. This support structure offers several advantages over either ceramic or polymeric supports because the stainless steel supports: (1) are mechanically, chemically, and thermally stable; (2) are flexible and can readily be formed into spiral-wound modules; (3) can be welded to the module housing eliminating the need for thermally unstable epoxies; and (4) exhibit an exact thermal expansion coefficient match between the membrane and the module housing. Commercially available porous metals have either pore sizes which are too large for direct application of the polyimide layer or a low porosity, which leads to high resistance to gas flux. By modifying the pore size of the metal support, application of a defect free polymer layer is feasible. Modification of both a metal/silicone rubber and virgin silicone rubber by a partial pyrolysis and oxidative process is exploited to obtain desirable pore sizes and transport properties. The post-treatment substructure is characterized, and its potential as a support structure is evaluated. Membranes produced by this project will be pivotal to the industrial application of membrane reactors. |
