CO2 capture for environmental remediation with hollow fibre membrane: Impact of air gap and bore fluid ratio onto the morphology and performance

Abstract

Hollow fibre membrane (HFM) is favourable for carbon dioxide (CO2) due to its high packing density and high volume to area ratio. In this study, the effect of air gap and bore fluid ratio is explored to study its influence on the morphology and separation performance. With high dope extrusion rate (DER), the shear‐induced polymer orientation can be preserved with low air gap which come with the cost of deformed lumen. As such, the coagulant activity of the bore fluid can be reduced by introducing solvent, which in turn reduces rate of phase inversion to prevent sudden contraction of polymer at low air gap, thus allowing proper formation of lumen. With the presence of solvent, the flowability of the dope solution increased due to reduced viscosity as the bore fluid with high solvent content make contact the external coagulant. HFM spun with low air gap with the presence of solvent in the bore fluid shows increased stretched ratio due to the influence of gravitational pull upon being extruded from the spinneret. This in turn improved the polymer chain orientation due to the stretch across the spinning line. Subsequently, HFM spun with 80 wt.% of N‐methyl‐2‐pyrollidone (NMP) in the bore fluid using narrow gap spinneret with 5‐cm air gap shows the highest ideal CO2/N2 and CO2/CH4 selectivity at 23.4 and 28 respectively, even though it also exhibit the lowest CO2 permeance at only 3.1 GPU which was ascribed to the formation of dense skin layer. Meanwhile, when HFM was spun with a bigger annulus gap, the ideal CO2/N2 and CO2/CH4 selectivity slightly dropped, however the CO2 permeance exhibit increment.