Abstract
Polyimide-based hollow fibers were spun using a triple orifice spinneret in order to apply them in gas separation. The membrane structure was tailored producing a porous external layer and a thin internal skin layer, that controlled the gas transport. The measurement of gas permeation rates and the morphological analysis were combined to obtain information on the performance of the membranes. The aim was to tune the inner top layer and investigate the role of the bore fluid on the gas permeation properties of the membranes. The bore fluid composition was explored by using water mixtures containing the solvent used for preparing the dope solution or a salt in order to reduce the water activity in the inner coagulant, but also a low amount of a crosslinker for improving the gas selectivity. The change of the dope flow-rate was also analyzed. At moderate dope flow-rates, the use of a saline water solution as bore fluid is more effective in enhancing the membrane gas selectivity with respect to a bore fluid containing certain amounts of solvent. This option represents a green approach for the preparation of the membrane. The behavior of the prepared hollow fibers over time (physical aging) in gas permeation was discussed.
Highlights
We proved it was possible to tailor the morphology and performance of polymeric Hollow fibers (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]
The change from one polymer to another is not trivial, we analyzed the role of the bore fluid composition in a triple orifice spinneret setup on the performance of polyimide-based HFs
This study successfully combined a triple orifice spinneret with a bore fluid at a reduced water activity for preparing gas selective hollow fibers based on a polyimide
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. In a triple orifice spinneret, a bore liquid (inner), a polymer solution (intermediate), and an additional fluid (external) are extruded at the same time This setup allows either the co-extrusion of two different polymeric dopes (dual-layer membranes) [4] or the engineering of the outermost layer of the HFs by using an external fluid based on a solvent for the polymer [5,6,7]. The change from one polymer to another is not trivial, we analyzed the role of the bore fluid composition in a triple orifice spinneret setup on the performance of polyimide-based HFs. In particular, we used aqueous solutions containing certain amounts of the same solvent used for the dope preparation or a salt. The selected concentration of NaCl was of 20 wt.%, as typically encountered in concentrated brine solutions available from desalination operations [15]
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