Propylene/propane separation with copolyimides containing benzo-15-crown-5-ether to incorporate silver ions

A 6FDA (4,4‘-hexafluoro isopropylidene diphthalic anhydride) based copolyimide has been synthesized containing the diamines DABA (3,5-diamino benzoic acid) and a 15-crown-5-diamine to separate propylene/ propane mixtures. With the carboxylic acid group of DABA crosslinking the polymer chains is possible leading to a suppression of plasticization of the polymer. Thereby the loss of separation performance at higher pressures of membranes made from such a polymer can be avoided. The crown ether group allows to incorporate silver ions by complexation in the membrane polymer. As a consequence facilitated transport of olefins is possible. Pure gas permeation and sorption experiments at 35°C and feed pressures up to 8 bar have been carried out with propylene and propane using non-crosslinked and EG-crosslinked copolyimide membranes, the latter ones with and without silver ions.

The following conclusions can be drawn from this work: • • • • Crosslinking of the polymer chains with EG increases permeability of propylene as well as of propane while selectivity decreases. Incorporating silver ions into the EGcrosslinked membrane leads to a de-crease of permeability correlated with an increase of selectivity. The sorption of propylene and propane of the EG-crosslinked membrane is lower than that of the non-crosslinked one. The sorption of propylene and propane increases by incorporating silver ions in the EG-crosslinked membrane.