Fundamental understanding on the preparation conditions of high-performance polyimide-based hollow fiber membranes for organic solvent nanofiltration (OSN)

Integrally skinned asymmetric (ISA) polyimide-based hollow fiber (HF) membranes were prepared via phase inversion followed by chemical crosslinking for organic solvent nanofiltration (OSN). The effect of preparation conditions including air gap length, bore composition, and dope flow rate (expressed as shear rate in the spinneret) on structure, separation performance and solvent stability of the HF-OSN membranes were extensively investigated. Among these conditions, the air gap length has a profound effect on the compactness of the skin layer. The separation performance of the OSN membrane can be effectively tuned by changing the air gap length. The composition of the bore fluid influenced the membrane structure from the synergetic effect of both thermodynamic and kinetic aspects. The variation in elongation ratio due to the swelling of the HF-OSN membrane in different organic solvents is a crucial factor that should be considered during the design of hollow fiber modules for real OSN applications. The shear rate of the spinning solution in the spinneret remarkably impacted the swelling properties and solvent stability of the HF- OSN membrane. Under the optimized shear rate, the prepared HF-OSN membranes had a relatively low swelling tendency in both NMP and DMF and maintained a 99.5% rejection for RDB after 7 days' immersion in DMF. The above investigation might provide both fundamental understanding for the preparation mechanism of high-performance HF-OSN membranes and insightful guidance for the scaling-up of them.