Effect of Physical Aging on Gas Transport in Asymmetric Polyimide Hollow Fibers Prepared by Triple-Orifice Spinneret

Abstract

The systematic evaluation of the gas transport properties related to differences 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 different operation conditions, in order to identify their response to physical aging. Four types of HFs having a different 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 different 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 different alcohols, presented a permeance decay independently on the alcohol type and a greater selectivity over time.

Hollow Fiber Polyimide Membranes Prepared in a Triple Orifice Spinneret: Effect of a Reduced Water Activity in the Bore Fluid on the Gas Separation Performance

“…In order to evaluate their durability, the HFs were tested over time, after 18 months from their spinning. As commonly observed for membranes based on polyimides [ 9 , 39 ], the HFs displayed a reduced gas permeance, but the selectivity increased upon aging ( Table 7 ). However, some specific peculiarities occurred for the different samples.…”

“…Two flow-rate values were used for the dope extrusion. Some HF batches were spun at 5.0 g min −1 to make a comparison with previous works [ 7 , 9 ], while a lower flow-rate (3.6 g min −1 ) was adopted in order to increase the contact time of the nascent HF with the EF. A reduced take-up speed allows the nascent fiber to go through the air gap for a longer time period.…”

“…In previous works, we proved it was possible to tailor the morphology and performance of polymeric HFs for gas separation by using a triple orifice spinneret for the dry-jet/wet spinning and by selecting specific post-treatment protocols [ 7 , 8 , 9 ]. In particular, by working on the outer layer in order to create a porous surface, it is possible to enhance both the gas permeance and selectivity of the HF membranes intended for gas separation [ 7 ].…”

Recent Advances of Polymeric Membranes in Tackling Plasticization and Aging for Practical Industrial CO2/CH4 Applications—A Review

“…Further research is necessary to minimize the membrane aging and compaction issues during high-pressure operation, which will reduce the membrane lifetime. Polymer-aging reduction approaches that have been proposed are copolymerization and polymer modification [4], backbone redesign [80], filler incorporation, and polymer blending [71]. On top of that, incorporation of filler in a polymer matrix such as metal-organic framework (MOF) can also decrease the effects of physical aging.…”

Exploring the Potential Application of Matrimid® and ZIFs-Based Membranes for Hydrogen Recovery: A Review

“…Long-term aging studies in Matrimid ® double skin layer HFMs displayed a diminishment in the gas permeance after 30 months as a consequence of polymer chain relaxation in thin films and the densification of the polymer matrix, which causes lower free volume availability, eliciting a size-sieving effect in molecules such as H 2 /N 2 that enhances selectivity [ 103 ]. This phenomenon was observed either with or without ethylendiamine crosslinking.…”