Effect of spinning conditions on the structure and the gas permeation properties of high flux polyethersulfone-polyimide blend hollow fibers

In this work, the effects of major spinning parameters, such as: polymer concentration, air gap distance, bore fluid composition, and take-up velocity on the structure and the permeation properties of polyethersulfone-polyimide gas separation hollow fibers are discussed in detail. It is shown that a spinning dope starts to exhibit significant chain entanglement at a critical polymer concentration. Fibers spun from this critical concentration exhibit theoretically the thinnest skin layer and minimum surface porosity. The longer the nascent hollow fiber membrane is exposed to a humid air-gap, the higher the water content in the top layer before demixing occurs. This results in higher surface porosity and gas permeance. Better mixing between the polymer solution and the bore liquid is achieved by adjusting the composition of the bore fluid (NMP/H2O). Finally, by increasing the velocity of the take-up drum, the permeance of both CO2 and N-2 decrease while their permselectivity remains constant. Suitable selection of the spinning conditions results in gas separation hollow fibers with thin skin layers (0.1 mum), macrovoid-free substructure, high permeation rates (CO2: 40-60 GPU) and selectivity coefficients (a CO2/N-2: 40). These results compete directly with the performance of commercial gas separation membranes.