Influence of membrane skin morphology on CO2/N2 separation at sub-ambient temperatures

Matrimid® hollow fiber membranes with silicone rubber (PDMS) calked fused nodular selective layers display much higher CO2/N2 selectivity as well as higher CO2 permeance than those with isotropic dense selective layers at 253.15 K. Two kinds of asymmetric hollow fiber membranes were successfully spun: fibers with fused nodular skins and fibers with truly dense skins. The skin morphologies were confirmed with SEM images. CO2/N2 mixed gas permeation characterization was carried out within the temperature range of 253.15 K to 308.15 K. Permeation results showed that, at 253.15 K, the nodular-skinned fibers displayed CO2/N2 selectivity of 90.5, and CO2 permeance of 63.3GPU after standard PDMS calking; while the dense-skinned fibers displayed CO2/N2 selectivity of 52.5, and CO2 permeance of 16.6GPU. The PDMS calking had negligible effect on the dense-skinned fibers, but it was necessary for the fused nodular-skinned fibers. A hypothesis regarding the introduction of Langmuir sorption sites and a local orientation of polymer chain segments is proposed to explain the better performance of the calked nodular-skinned fibers. This work provides a promising method for improved hollow fiber membranes for the removal of CO2 from flue gas. •Formation of asymmetric hollow fiber membranes with fused nodular selective layers.•Nodular skin has high permeance and high selectivity at sub-ambient temperatures.•Propose a hypothesis of added Langmuir sorption sites.•Propose a hypothesis of local orientation of polymer chain segments.