A.E. Feiring, N. Shangguan, R.D. Lousenberg, S. Majumdar, H. Murnen, S. Nemser, W. Charlton
Compact Membrane Systems, Inc.,
Keywords: custom amorphous fluoropolymers, olefin/paraffin separation, chemical/thermal stability, high olefin selectivity & flux
Summary:The amorphous perfluoropolymer, Teflon™ AF, developed and commercialized by the DuPont Company, contains two monomers, perfluoro-2,2-dimethyl-1,3-dioxole (PDD) and tetrafluoroethylene (TFE). In common with most perfluoropolymers, the PDD/TFE copolymer has an extraordinary combination of properties such as high chemical and thermal stability and very low surface energy. The PDD component offers additional unique properties: amorphous nature, solubility in highly fluorinated solvents and very high free volume. These properties support uses of this copolymer as very thin, highly permeable membranes for separation of small molecules, technology which has been commercialized by Compact Membrane Systems (CMS). CMS recognized that the range of applications for the PDD-containing polymers could be greatly extended by adding other fluorinated monomers. CMS has prepared dozens of custom amorphous fluoropolymers (CAF) using a variety of comonomers with PDD on laboratory scale, several of which are showing promise for membrane separations and other applications. The furthest along in commercial development is a fluoropolymer containing PDD, and a perfluorinated vinyl ether with sulfonyl fluoride side chains. The sulfonyl fluoride groups are readily hydrolyzed to sulfonic acids leading to a polymer which is soluble in common organic solvents. The silver sulfonate form of this copolymer as a thin film in a composite membrane is showing great promise as a facilitated transport membrane for the separation of olefins from paraffins. A composite membrane containing a porous support and the silver sulfonate CAF shows commercially attractive permeability and selectivity for the energy-efficient separation of propylene from propane, a major commercial energy intensive process. Furthermore, this technology shows a lifetime and resistance to poisons which far exceed previous facilitated transport membranes. CMS will discuss both platform capabilities of CAF and the performance of olefin-paraffin separation membranes. Applications for olefin-paraffin separation membranes include enhancing new and existing refinery operations, petrochemical operations and new processes for generating ethylene (e.g., oxidative dehydrogenation of ethane, oxidative coupling of methane, and microbiological production of ethylene).