Defect-free PIM-1 hollow fiber membranes

Abstract

A modified dual-bath method of spinning was employed to fabricate defect-free, integrally skinned, asymmetric PIM-1 hollow fiber membranes utilizing an immiscible liquid protective layer. Spinning techniques capable of addressing specific challenges presented by PIM-1 solutions are discussed. In particular, dual-bath spinning via a triple orifice spinneret circumvents the primary issue associated with spinning PIM-1, namely the lack of suitable nonvolatile solvents. The water-immiscible sheath layer coextruded with the PIM-1 polymer solution reduces evaporation of the volatile solvent (tetrahydrofuran) relative to fibers directly exposed to air, thus producing an asymmetric hollow fiber membrane structure. The work here describes the process of developing spin dopes, fabricating hollow fibers, and testing the resulting membrane modules. Ideal selectivity between various gas pairs was used to assess the quality of the membranes. Pure component permeances, selectivities, and activation energies of permeation were measured for helium, hydrogen, oxygen, nitrogen, argon, carbon dioxide, methane, ethane, and ethylene at 25, 35, and 45°C. The observed selectivities are in good agreement with previously reported PIM-1 flat sheet membrane analogs, and in fact slightly higher. Defect-free fibers with skin thicknesses from 3 to 6µm were observed with a relatively high CO2 permeance of 360 GPUs and CO2/CH4 selectivity of 23.