In the past decades, the dual-layer hollow fiber membrane technology has become an emerging research area for gas separation due to its high applicability and superior saving on expensively functional materials compared to those single-layer ones. By one step co-extrusion, it may fabricate a composite hollow fiber membrane consisting of an ultra-thin dense selective skin as the function layer and a porous substrate as the supporting layer. As a result, the dual-layer hollow fiber configuration may potentially possess the most practical way that maximizes the function of a highly expensive material or brittle material for gas separation.

In this work, copoly (4,4'-diphenyleneoxide/1,5-naphthalene-2,2'-bis(3,4-dicarboxyl phenyl) hexa fluoro propane diimide) (6FDA-ODA-NDA) / polysulfone (PSF) dual-layer hollow fiber membranes with enhanced gas separation performance with minimum substructure resistance have been fabricated. Prior investigation in the interface morphology of the as-spun dual-layer fibers and its relation with gas separation performance indicate that the inner layer provides a substantial resistance to the permeating gases at various spinning conditions, thus causing the gas separation performance to be predominantly determined by the substructure layer rather than the dense outer skin layer.

To overcome the substructure problem, three novel strategies have been proposed in this work: (1) the addition of Al2O3 nanoparticles in the inner layer dope solution; (2) the introduction of early convective premixing with the aid of an indented dual-layer spinneret; and (3) the combination of methods (1) and (2).

The advantages, disadvantage and limitations of each approach have been determined, and will be discussed and revealed at the conference. In summary, dual-layer hollow fibers spun with separation performance above 90% of the intrinsic selectivity value of 6FDA-ODA-NDA dense film have been achieved when combining the first and second approaches.