Polybenzimidazoles (PBIs) are a class of polymer materials that have the potential to improve and expand the applications of commercial gas separation membranes. While many commercial membranes can only perform gas separations up to 100 °C, PBIs are both chemically and thermally stable at temperatures up to 400 °C. A potential application of PBI membranes is the high temperature hydrogen-hydrocarbon separations proposed by the NSF Engineering Research Center for Innovative and Strategic Transformation of Alkane Resources (CISTAR). Two novel aspects of this work are the previously unstudied ethane and ethylene gas separation properties at elevated temperatures and the temperature dependence of gas transport in sub-micron films over an expansive temperature range. Hydrocarbon gas separation properties of Celazole® PBI membranes were characterized at temperatures up to 190 °C. Gas permeabilities, gas selectivities, activation energies of permeation, and physical aging rates differed significantly between thin sub-micron and bulk 20-micron Celazole® films. In particular, the activation energies of permeation were 1.5 to 4 times higher in an aged 450-nm thin film than in a 27-micron bulk film, suggesting a denser membrane structure and greater size-sieving ability. The first known evidence of physical aging in PBIs showed an 80 percent decrease in methane permeability over a 1000-hour period at 190 °C for a 450-nm Celazole® film. This study elucidates the effects of elevated operating temperature on thin films by encompassing a broader and higher temperature range than previous studies of flat, sub-micron polymer membranes.

High-temperature gas separation properties of sub-micron polybenzimidazole membranes

2019 Spring National Meeting

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