Fluorinated polyimide nanocomposites for CO2/CH4 separation

The purpose of this project was to synthesize fluorinated polyimide (PI) nanocomposite membranes in order to study the gas permeation rates and selectivity of carbon dioxide and methane. PIs were synthesized from 2,2-bis(3,4-anhydrodicarboxyphenyl)hexafluoropropane (617 dianhydride, 6FDA) and 4,4'-diaminodiphenyl ether (oxydianiline, ODA) into which were incorporated nanoparticulate additives as follows: in situ TiO2, both plain and treated with dodecyl sulfate surfactant, and organo-clay (Cloisite(R)-10 angstrom) at loads of 1, 3, and 5 wt% to the polyamic acid. Polyamic acid films were solvent cast, cured at 200 degrees C then post-cured at 300 degrees C and measured for permeation data and for thermal properties. Glass transition temperatures ranged from 124 to 140 degrees C for the cured Pis and from 142 to 147 degrees C for the post-cured materials, the nano-inclusions having little discernable effect on this property. Thermogravimetric analysis (TGA) data show that the inclusion of Cloisite(R) or TiO2 caused a small decrease of thermal stability from 555 degrees C to about 532 to 541 degrees C. The inclusion of clay causes a decreased permeation rate while the addition of TiO2 improves the rate and selectivity. Treating the nanofillers with surfactant decreases selectivity and marginally increases rate of permeation of CO2 Post-curing caused a darkening of the composites, but not the neat PI. This heat treatment also resulted in a significantly decreased permeation rate, but a significantly increased selectivity. The resulting material shows superior gas separation properties to the commercially available PI, Matrimid(R) produced by Ciba-Geigy. Copyright (C) 2008 John Wiley & Sons, Ltd.