Fabrication of 6FDA-Durene polyimide asymmetric hollow fibers for gas separation

We have developed defect-free asymmetric hexafluoro propane diandydride (6F DA) durene polyimide (6FDA-durene) hollow fibers with a selectivity of 4.2 for O-2/N-2 and a permeance of 33.1 X 10(-6) cm(3) (STP)/cm(2)-s-cmHg for O -2. These fibers were spun from a high viscosity in situ imidization dope c onsisting of 14.7% 6FDA-durene in a NMP solvent and the inherent viscositie s (IV) of this 6FDA-durene polymer was 0.84 dL/g. Low IV dopes cannot produ ce defect-free hollow fibers, indicating a 6FDA-durene spinning dope with a viscosity in the region of chain entanglement seems to be essential to yie ld hollow fibers, with minimum defects. The effects of spinning parameters such as shear rates within a spinneret and bore fluids as well as air gap o n gas separation performance were investigated. Experimental data demonstra te that hollow fibers spun with NMP/H2O as the bore liquid have higher perm eances and selectivities than those spun with glycerol as the bore liquid b ecause the former has a relatively looser inner skin structure than the lat ter. In addition, the selectivity of hollow fibers spun with NMP/H2O as the bore liquid changes moderately with shear rate, while the selectivity of h ollow fibers spun with glycerol are less sensitive to the change of shear r ate. These distinct behaviors are mainly attributed to the different morpho logies generated by different bore fluids. (C) 2001 John Wiley & Sons, Inc.