: We have found that the chemistries of inner and external coagulants, gelation bath temperature, and air gap distance have profound effects on 6FDA-polyimde hollow-fiber morphology and performance. This 6FDA-polyimide is made of 50 mol % 2,2-bis(3,4-dicarboxyphenyl) hexafluoro propane dianhydride (6FDA) and 50 mol % 2,2-bis(3-aminophenyl) hexafluoro propane (4,4 6F-diamine) (6FDAM). An increase in air gap distance tends to induce three-dimensional open-cell pore formation. Raising bath temperature has a similar effect. Multilayer finger-void structure can be completely eliminated if one properly chooses a bore-fluid flow rate and a gelation bath temperature. Experimental data demonstrate that the location of the dense layer can be shifted from the inner skin to the outer skin based on the chemistry (solubility parameter) of coagulants. The location of finger voids is also dependent on the chemistry of coagulants, and the dense layer location may shift from the inner surface to the external surface or appear in both surfaces dependent on the differences in solubility and coagulation rate. A defect-free 6FDA/6FDAM polyimide fiber with a selectivity of 4.73 and a permeance of 38.1 GPU is produced.

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SYNOPSISBy 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 (GFDA) /PAN composite hollow fiber, and the other was a 6FDA-3,5-diaminobenzonitrile/GFDA-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 GFDA-durene on PAN was carried out by prewetting PAN fibers with Fluorinert@ before solution coating. The topcoating of a thin layer (200-300 A ) of PVP or GFDA-3,5-diaminobenzonitrile on PAN/GFDA-durene fibers was conducted using a conventional solution coating method. The selectivity of 0.7% 4-PVP/2% GF-durene/PAN composite fibers for 0 2 / N 2 was 5.6 with an 0, permeance of 32.2 X cc ( S T P ) /cm2 s cmHg, whereas the selectivity of 0.5% GFDA-3,5-diaminobenzonitrile/2% 6F-durene/PAN fibers was 5.1 with an 0, permeance greater than 37.2 X cc( STP)/ cm2 s cmHg. Both fiber selectivities can be further improved by increasing the thicknesses of the selective layer.

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