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Abstract: The silver ionic modification approach and dual-layer hollow fiber spinning technology synergistically lead to the significantly enhanced O2/N2 and CO2/CH4 selectivity of 9.5 and 118, respectively, with an ultrathin dense-selective layer of 1092Å in the pure gas measurement. Even with the presence of competition in sorption sites between two penetrants, the dual-layer hollow fiber membrane developed in this work still reveals the superior CO2/CH4 selectivity of 87.9 in the mixed gas measurement. To our best knowledge, this is the first time for the polyethersulfone (PES) material to achieve so high CO2/CH4 selectivity through the ionic modification. The electrostatic crosslinking, steric hindrance and affinity to some specific gases (e.g. O2 and CO2) induced by the incorporation of ionic groups into the PES matrix may be three dominant factors for the advanced gas separation performance in this work. [Copyright &y& Elsevier]

Abstract: This article describes the research study on exploitation of polymer blending technology and dual-layer hollow fiber spinning process for the fabrication of a novel class of high performance gas separation membranes. The specific functional material employed for this purpose is a polymer blend constructed of the interpenetrated networks of PBI and Matrimid. It is within the scope of this study to unravel the effect of various key parameters on the microstructural evolution, transport properties and separation performance of the developed hollow fiber membranes. The resultant membranes possess desirable morphological and microstructural characteristics, particularly at the outer functional layer, and are free from any delamination at the interface. Analysis of the membranes suggests that both increase in the air-gap distance and application of elongational drawing have promoting effects on the membranes’ permeance. Results also indicate that membranes with H2/CO2 selectivities as high as 11.11 () can be obtained through spinning at sufficiently large air-gap distance. On the other hand, inducing the elongational drawing to the nascent fibers offers membranes with CO2/CH4 selectivities as high as 41.81 (). Therefore, either of these approaches can be employed for desirable tuning of the membrane''s properties to suit the specific application. The variation in outer dope flow rate is identified as another effective technique amenable for tailoring the properties of the hollow fiber membranes. Other findings also show the effectiveness of chemical modification for further enhancing the H2/CO2 separation performance of the membranes. Membranes developed in this research study exhibit a very good resistance toward CO2-induced plasticization and have viable potentials for various gas separation applications including hydrogen purification and natural gas separation. [Copyright &y& Elsevier]

Abstract: Hollow fiber membranes are the most applicable form of membranes in laboratory and industrial scale with their large surface to volume ratios. Hollow fiber membranes usually are fabricated by dry–wet solution spinning, where a polymer solution is co-extruded through an annular region with a bore fluid and the nascent hollow fiber passes through an air gap and then enters a liquid coagulation bath. The spinneret dimension, dope and bore fluid flow rates, air gap length, bore fluid and dope compositions and their physical properties, coagulant composition and condition, shear stress within a spinneret, the ratio of dope to bore fluid volumetric flow rate, and the take-up-to-initial velocity ratio (draw ratio) are the primary factors that determine the final hollow fiber morphology and separation properties. All of the aforementioned parameters are not independent and some of them are functions of others. The objective of this paper is to elucidate the interdependence between some of the above parameters. For this purpose, dope and bore fluid axial velocity in the air gap was assumed as a function of the axial distance from the spinneret outlet, z, and radial velocity as a function of the radial distance from the center of the hollow fiber, r, and z. Dimensionless equations of motion and continuity were then simplified and solved simultaneously based on preceding assumptions. It was found from the analysis that the dimensionless axial velocity of dope was a function of the Reynolds number, Capillary number and Stokes number indicating that the axial velocity acceleration in the air gap is determined by viscous, capillary, and gravity force gradients. It was also concluded that the optimum value of the ratio of bore liquid flow rate to dope flow rate is equal to 0.8 of the ratio of the cross-sectional area of the bore fluid to that of the dope at the spinneret outlet. [Copyright &y& Elsevier]