Effect of Physical aging on gas transport in asymmetric polyimide hollow fibers prepared by triple orifice spinneret

The systematic evaluation of the gas transport properties related to dierences in the history of the samples is a useful tool to appropriately design a membrane-based gas separation system. The permeation rate of six pure gases was measured over time in asymmetric hollow-fiber (HF) samples, that were prepared according to the non-solvent-induced phase separation in dierent operation conditions, in order to identify their response to physical aging. Four types of HFs having a dierent structure were analyzed, comparing samples spun in a triple-orifice spinneret to HFs prepared using a conventional spinneret. A generalized gas permeance decline, coupled to a maintained permselectivity for the dierent gas pairs, was observed for all HFs. Instead, H2/N2 permselectivity values were enhanced upon aging. Cross-linked hollow-fiber samples showed a marked size-sieving behavior that favored the separation of small species, e.g., hydrogen, from other larger species and a good stability over time. Some HFs, post-treated using dierent alcohols, presented a permeance decay independently on the alcohol type and a greater selectivity over time.