Defect-free asymmetric hollow fiber membranes from Torlon®, a polyamide–imide polymer, for high-pressure CO2 separations

Torlon®, a polyamide–imide polymer, was used for high-pressure CO2 separations, as it can form inter- and intra-chain hydrogen bonding that may provide stability against plasticization. Asymmetric hollow fiber membranes with a defect-free selective skin were successfully formed from Torlon® using a dry–wet spinning process. Dope and spinning parameters were optimized to obtain these fibers, which had CO2/CH4 selectivity of 44 and O2/N2 selectivity of 7.7. These selectivities are about 85% of the intrinsic (dense film) value of 52 for CO2/CH4 and 90% of the intrinsic value of 8.3 for O2/N2, respectively. Based on analyses presented, the reduced selectivities are attributed to substructure resistance rather than actual skin layer defects. Macrovoids, which compromise the strength of the fiber, were reduced by increasing the polymer concentration. The resulting fiber could withstand up to 2000 psi of N2, and a CO2 permeation study indicates that this fiber can perform selective separations under supercritical conditions of 1100 psi of CO2 at 35 °C.