Fabrication of composite hollow fibers for air separation

By using microporous polyacrylonitrile (PAN) hollow fibers as the substrate, we developed two types of composite fibers for air‐separation. One was a poly(4‐vinyl pyridine) (4‐PVP)/(hexafluoro propane dianhydride)–durene (6FDA)/PAN composite hollow fiber, and the other was a 6FDA–3,5‐diaminobenzonitrile/6FDA–durene/PAN composite hollow fiber. The asymmetric PAN fiber was prepared using dry‐jet wet‐spinning technology, and the deposition of a thin gutter layer of 6FDA–durene on PAN was carried out by prewetting PAN fibers with Fluorinert® before solution coating. The topcoating of a thin layer (200–300 Å) of PVP or 6FDA–3,5‐diaminobenzonitrile on PAN/6FDA–durene fibers was conducted using a conventional solution coating method. The selectivity of 0.7% 4‐PVP/2% 6F–durene/PAN composite fibers for O2/N2 was 5.6 with an O2 permeance of 32.2 × 10−6 cc(STP)/cm2 s cmHg, whereas the selectivity of 0.5% 6FDA–3,5‐diaminobenzonitrile/2% 6F–durene/PAN fibers was 5.1 with an O2 permeance greater than 37.2 × 10−6 cc(STP)/cm2 s cmHg. Both fiber selectivities can be further improved by increasing the thicknesses of the selective layer.