Fabrication of Single-Layer and Dual-Layer ExtemŽ Hollow Fiber Membranes for Gas Separation

The fast industrialization and global depletion of energy resources have inspired polymer and membrane scientists to develop new materials with designed functional groups and performance for gas separation. GE launched a new product of polyetherimide (PEI), ExtemŽ UH, in Europe in 2007. Since this amorphous thermoplastic ExtemŽ UH has stable characteristics and good processabiliy at high temperatures, it may have potential for gas separation operated in harsh environments. The aims of this work are to fabricate ExtemŽ hollow fibers with an ultra-thin dense-selective layer for gas separation and to use this brand new amorphous thermoplastic PEI as a model material to reveal the fundamentals of hollow fiber membrane fabrication. The molecular engineering of membrane morphology and the evolution of the resultant dense-selective layer thickness and O2/N2 selectivity from single-layer to dual-layer spinning have been disclosed with an integrated understanding of dope formulation, solution rheology, elongational rate, phase inversion path and co-extrusion method. Without heat-treatment, single-layer ExtemŽ hollow fibers are all defective due to the substructure resistance even if the silicon rubber coating is applied. Neither changes in spinning conditions nor increase in polymer concentration could improve the O2/N2 selectivity of single-layer ExtemŽ hollow fibers. Only by taking the advantages of the characteristics of rapid phase inversion, lower shear and elongational viscosities, and co-extrusion technology, dual-layer ExtemŽ hollow fibers with an O2/N2 selectivity of 6.15 and an ultrathin dense-layer thickness of about 876Ĺ have been successful fabricated for the first time since ExtemŽ was commercialized in 2007. Mainly due to the formation of an ultra-thin dense layer and a porous substructure, the gas permeance of our ExtemŽ hollow fibers is higher than that of UltemŽ PEI hollow fibers reported in the literature.