Gas sorption and transport in thermally rearranged polybenzoxazole membranes derived from polyhydroxylamides

Abstract

The sub-nano-sized microcavities in microporous thermally rearranged (TR) polymers can be tuned by varying the conditions of thermal rearrangement. Relatively small cavities were formed by thermal rearrangement of poly(o-hydroxylamide) (PHA) precursors compared to the cavities formed by that of polyimide precursors. TR polymers derived from PHAs, so-called TR-beta-polymers, are known to exhibit a well-tuned cavity structure that can be used for H-2/CO2 separation. According to a solution-diffusion model, both the permeability and selectivity for H-2/CO2 separation were improved at elevated temperatures due to a significant increase in H-2 diffusion and a decrease in CO2 sorption. In this study, gas solubility and permeability of five representative small gas molecules (H-2, N-2, O-2, CH4, and CO2) through TR-beta-polymer membranes were characterized between 20 degrees C and 65 degrees C for gas solubility measurement and between 35 degrees C and 300 degrees C for gas permeability measurement. These measurements allowed for the calculation of thermodynamic factors such as the activation energy and heat of sorption. (C) 2014 Elsevier B.V. All rights reserved.