Gas Transport Properties of Polybenzimidazole Blends

Polybenzimidazoles (PBIs) have recently been studied for use as gas separation membranes for aggressive, high temperature applications such as hydrogen separations due to their high chemical and thermal stability. Commercial PBI (Celazole^®) has been shown to have exceptional H₂/CO₂ selectivities, but suffers from low permeabilities. Several strategies exist for improving the permeabilities of PBI including changing functional groups and blending with other polymers, but these often suffer from the intrinsic trade-off between permeability and selectivity.

We have recently discovered that blending PBI with certain polyimides followed by post-treatment yields materials that exceed the 2008 Robeson upper bound for H₂/CO₂ separation. These materials are mechanically-robust, phase separated blends that contain PBI in the continuous phase, so the selectivity can be maintained while the permeability is enhanced by the polyimide. In some cases, a substantive improvement in permeability is observed while H₂/CO₂ selectivities are maintained or in some cases even increased.