Thermal optimization of polybenzimidazole meniscus membranes for the separation of hydrogen, methane, and carbon dioxide

Membranes of the glassy polymer polybenzimidazole (PBI) were formed and tested at temperatures above 300degreesC. The membrane formation method provides a rapid screening technique for the evaluation of polymeric systems at elevated temperatures. The rigidity in the structure that limits appreciable gas transport at room temperature appears to be responsible for the retention of permselectivities in the material at temperatures above 100degreesC. The notion that PBI is a poor room temperature gas separation polymer is supported by its extremely low flux for hydrogen and carbon dioxide at room temperature. The rigid structure of PBI appears to be more suited to the type of diffusivity-based selectivity at temperatures above 150degreesC. This result opens a new tool for studying gas separation by polymeric membranes. By selecting the optimal temperature for a membrane suited for a specific objective, it will be possible to develop tools for separating high temperature gas streams at their processing temperature. This advantage could offer cost savings that may provide a new incentive for polymeric membranes. (C) 2003 Elsevier Science B.V. All rights reserved.