Fabrication of dual-layer polyethersulfone (PES) hollow fiber membranes with an ultrathin dense-selective layer for gas separation

By using co-extrusion and dry-jet wet-spinning phase-inversion techniques with the aid of heat-treatment at 75°C, we have fabricated dual-layer polyethersulfone (PES) hollow fiber membranes with an ultrathin dense-selective layer of 407 Å. To our best knowledge, this is the thinnest thickness that has ever been reported for dual-layer hollow fiber membranes. The dual-layer hollow fibers have an O ₂ permeance of 10.8 GPU and O ₂/N ₂ selectivity of 6.0 at 25°C. The effects of post heat-treatment on the membrane morphology and gas separation performance were also studied. It was found that heat-treatment at 75°C improves the gas permeance and ideal selectivity, while heat-treatment at 150°C results in a significant reduction in both permeance and selectivity due to the enhanced substructure resistance. SEM pictures confirmed that a higher heat-treatment temperature can significantly reduce pore sizes and the amount of pores in the substructure immediately underneath the dense-selective layer.