(626h) Hollow Fiber Spinning of Defect-Free Asymmetric Poly(arylene ether) Membranes for Gas Separations

Polymer hollow fibers represent an important membrane form factor for use in energy-efficient gas separations. These membranes offer unique advantages over traditional flat sheet membranes, including higher surface-area-to-volume ratios, thinner selective layers, and improved mechanical stability due to their asymmetric structure. Asymmetric hollow fibers were spun, resulting in either an internal or external skin layer, using an emerging class of microporous polymers known as poly(arylene ethers) (PAEs). The PAEs used in the spinning process owe their enhancements in penetrant size sieving, solution processability, and plasticization resistance to free volume-promoting spirobifluorene (SBF) and tert-butyl triptycene (TBTrip) units in their backbone. Dope solution composition and ternary phase diagrams for the polymer, SBF-TBTrip-I, were investigated, along with details on fiber morphology. However, microporous polymers often face challenges with spinnability, requiring relatively large quantities of tetrahydrofuran to facilitate the formation of the external skin layer. Therefore, an alternate spinning procedure was developed that removed the need for volatile solvents, resulting in a defect-free internal skin layer for low-pressure applications. Regardless of the spinning method used, the SBF-TBTrip-I fibers exhibited desirable gas transport properties, with the selectivities of many gas pairs such as O₂/N₂ and CO₂/CH₄ being comparable to both dense films and thin films. By creating thin selective layers, the permeances for all tested gases were significantly higher than those of corresponding thick films. This work represents an initial effort to adapt this class of polymers into the hollow fiber membrane geometry suitable for industrial applications, while also offering valuable insights into the unique challenges involved in spinning microporous polymers.