Abstract
The elimination of the additional defect healing post-treatment step in asymmetric hollow fiber manufacturing would result in a significant reduction in membrane production cost. However, obtaining integrally skinned polymeric asymmetric hollow fiber membranes with an ultrathin and defect-free selective layer is quite challenging. In this study, P84® asymmetric hollow fiber membranes with a highly thin (~56 nm) defect-free skin were successfully fabricated by fine tuning the dope composition and spinning parameters using volatile additive (tetrahydrofuran, THF) as key parameters. An extensive experimental and theoretical study of the influence of volatile THF addition on the solubility parameter of the N-methylpyrrolidone/THF solvent mixture was performed. Although THF itself is not a solvent for P84®, in a mixture with a good solvent for the polymer, like N-Methyl-2-pyrrolidone (NMP), it can be dissolved at high THF concentrations (NMP/THF ratio > 0.52). The as-spun fibers had a reproducible ideal CO2/N2 selectivity of 40, and a CO2 permeance of 23 GPU at 35 °C. The fiber production can be scaled-up with retention of the selectivity.
Highlights
In order to assess gas separation at large scale, membrane products need to be highly productive.For this reason, there are two features that commercial membranes generally meet
Optimization of polymer solution composition is a key to success for the formation of defect-free hollow fiber membranes
Using volatile THF in combination with non-volatile NMP allows the fabrication of defect-free ultra-thin (~56 nm) P84® asymmetric hollow fiber membranes with no need for defect healing post treatment
Summary
In order to assess gas separation at large scale, membrane products need to be highly productive. One approach was to add a highly volatile additive in the dope to facilitate the skin formation Following this approach, defect-free Matrimid® 5218 hollow fiber membranes have been developed by several authors [13,14]. Defect-free as-spun Torlon® hollow fibers were successfully produced by Peng et al [17] from a simple polymer/solvent spinning dope, resulting in ultra-thin dense layers of around 54 nm. This work is focused on developing defect-free as-spun ultrathin P84® asymmetric hollow fiber membranes that do not require a silicone rubber coating post-treatment step. For this purpose, the approach reported in literature of using a dope solution comprising volatile and non-volatile solvents was followed. The as-spun P84® asymmetric hollow fiber membranes were characterized by their performance in CO2 and N2 permeation
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