High flux polyethersulfone-polyimide blend hollow fiber membranes for gas separation

In this work, the preparation of gas separation hollow fibers based on polyethersulfone Sumikaexcel (PES) and polyimide Matrimid 5218 (PI) blends, for three different compositions (i.e. PES/PI: 80/20, 50/50 and 20/80 wt.%), is reported. The dry/wet spinning process has been applied to prepare asymmetric hollow fibers by using blends of two different polymers with a common solvent. Dope viscosity measurements were performed to locate the blend concentrations where significant chain entanglement occurs. Cloud point measurements were carried out to estimate the tolerance of both pure components and blends in water. Scanning electron microscopy (SEM) was used to investigate the morphological characteristics and the structure of asymmetric hollow fibers. The permeation rates of CO2 and N2 were measured by the variable pressure method. In all cases, hollow fibers exhibit a typical asymmetric structure with a dense skin layer and a finely porous substructure. Macrovoids in the membrane substructure were observed only for the fibers spun at high PES concentration (80 wt.%). After coating with a silicone rubber solution, the developed hollow fibers exhibit a CO2 permeance varying from 31 to 60 gas permeation units (GPU) and a CO2/N2 selectivity varying from 40 to 35, at room temperature. The thickness of the skin layer, which corresponds to these permeation rates, varies from 0.1 to 0.15 μm. The effect of air-gap distance on hollow fibers structure and permeation performance is examined. The aforementioned permeation properties, establish PES/PI hollow fibers as excellent candidates membranes for the separation of gaseous mixtures in industrial level.