Formation of defect-free polyimide hollow fiber membranes for gas separations

Ultra-thin and defect-free polyimide hollow fiber membranes were formed using a dry-jet, wet quench process with spin dopes both with and without volatile solvents. Fibers were spun from the commercially available polyimide, Matrimid® 5218, and were precipitated in an aqueous quench bath. Spin dopes comprised volatile and non-volatile solvents, polymer, and non-solvent. The influences of dope composition, spinning parameters, and dehydration procedures on the membrane morphology and performance were investigated. Without post-treatment (i.e., defect repair), the fibers exhibited skin thicknesses on the order of 1000 Å and O2/N2 selectivities ranging from 90 to 100% of those determined for dense, solution-cast films. The 250 μm OD/125 μm ID fibers were spun at take-up rates comparable to those used in commercial processes (i.e., 50 m/min) and had macrovoid-free morphologies.