Dual-layer asymmetric hollow-fiber membranes for gas separation

Abstract

We have studied the fabrication of dual-layer asymmetric hollow fiber composite membranes for gas separation. The dual-layer composite membranes were prepared by simultaneously extruding a bore fluid and two polymer solutions from a specially designed triple-orifice spinneret. This technique offers a platform to construct a novel composite membrane consisted of a high-performance polymer with excellent permselectivity and a common polymer with outstanding mechanical properties. Starting from the spinneret design, the research work includes preparation of single-layer asymmetric hollow fibers, optimization of dual-layer asymmetric hollow fiber spinning, study of macrovoid formation, investigation of delamination phenomenon, as well as fabrication of lab-scale hollow fiber modules. Extensive work was introduced to explore the membrane formation induced by phase inversion. The concept of critical membrane-structure transition thickness was raised to describe the transition from a sponge-like to a macrovoid structure. The morphologies of the interfaces of dual-layer hollow fibers were revealed. The uneven shrinkage effect was applied to explain the delamination between inner and outer layers. Defect-free, delamination-free, dual-layer hollow fiber asymmetric membranes were successfully demonstrated for gas separation. The membrane plasticization caused by CO2 was also studied and its effects were significantly suppressed by surface modification using a novel chemical cross-linking approach. Lab-scale hollow fiber modules with controllable packing density were constructed and the detail procedure was developed.