Gas Separation Properties of Polyimide Thin Films on Ceramic Supports for High Temperature Applications

Novel selective ceramic-supported thin polyimide films produced in a single dip coating step are proposed for membrane applications at elevated temperatures. Layers of the polyimides P84^®, Matrimid 5218^®, and 6FDA-6FpDA were successfully deposited onto porous alumina supports. In order to tackle the poor compatibility between ceramic support and polymer, and to get defect-free thin films, the effect of the viscosity of the polymer solution was studied, giving the entanglement concentration (C*) for each polymer. The C* values were 3.09 wt. % for the 6FDA-6FpDA, 3.52 wt. % for Matrimid^®, and 4.30 wt. % for P84^®. A minimum polymer solution concentration necessary for defect-free film formation was found for each polymer, with the inverse order to the intrinsic viscosities (P84^® ≥ Matrimid^® >> 6FDA-6FpDA). The effect of the temperature on the permeance of prepared membranes was studied for H₂, CH₄, N₂, O₂, and CO₂. As expected, activation energy of permeance for hydrogen was higher than for CO₂, resulting in H₂/CO₂ selectivity increase with temperature. More densely packed polymers lead to materials that are more selective at elevated temperatures.