Propene/propane separation with copolyimide membranes containing silver ions

The aim of this project was to produce crosslinked, plasticization resistant facilitated transport membranes which can be used for the separation of olefin/paraffin mixtures. Different crosslinkable 4,4′-hexafluoro-isopropylidene diphthalic anhydride (6FDA) based copolyimides were synthesized using 3,5-diamino benzoic acid as one of the monomers providing a crosslinkable group and 15-crown-5-ether diamine suitable for creating facilitated transport sites. Crown ethers are well known for strong complexation of light metal ions but also complex formation with silver ions is possible. Thereby the ions are bonded into the cavity of the crown ether. The main advantage of this type of facilitated transport polymers is that no carrier medium is necessary which means “dry” membranes can be applied. Separation characteristics for the 15-crown-5-ether copolyimides were determined by pure gas sorption and mixed gas permeation experiments using propene and propane up to feed pressures of 8 × 105 Pa (8 bar) at a membrane temperature of 35 °C. Besides this a short overview on facilitated transport membranes is given discussing the several existing mechanisms as well as membrane materials investigated in the last years.