Highly selective asymmetric polybenzimidazole-4,4′-(hexafluoroisopropylidene) bis(benzoic acid) hollow fiber membranes for hydrogen separation

Abstract

We herein report the fabrication of a hydrogen-selective membrane, which primarily comprises asymmetric polybenzimidazole (PBI). The membrane is based on a 4,4′-(hexafluoroisopropylidene)bis(benzoic acid) (PBI–HFA) hollow fiber, which has beenis produced by dry-jet wet spinning.; Ssubsequently, the morphological and mechanical properties of the fabricated hollow fiber membrane arewere elucidated. This membrane allowed H2 to pass through it as a single gas under 1 bar at a rate of 664 cc min−1; similarly, N2, CO2, and CO under 1 bar passed through the membrane at rates of and 15.3, 263.4, and 18.6 cc min−1, respectively. The permselectivities of the membrane (43.4 (H2/N2) and 35.7 (H2/CO)) were higher than the previously reported values. Furthermore, the PBI–HFA hollow fiber membrane exhibited a permeability of >90% in the permeation tests performed for mixed gases. For preparation of the hollow fiber membranes, a PBI–HFA solution was prepared using NMP as the solvent and LiCl as an additive to increase the density of the polymer chain. The polymer solution prepared using an optimal quantity of LiCl (10 wt% to polymer weight) afforded a 15 wt% polymer solution, which wasis twice as concentrated as the solution without LiCl. In addition, the polymer solution prepared using 10 wt% LiCl formed a more stable hollow fiber structure than those prepared using other LiCl concentrations. Moreover, it was found that microvoids were formed in the polymer sublayers upon the addition of NMP to the bore fluid during membrane synthesis.