Recycling waste plastics as hollow fiber substrates to improve the anti-wettability of supported ionic liquid membranes for CO2 separation

Abstract

In this study, hydrophobic waste poly(styrene-co-butadiene)-derived polymeric hollow fiber fabricated via a dry-jet wet spinning method were used as substrates to support ionic liquid (IL) membranes via the dip-coating method. The surface properties of the substrates, such as pore size and its distribution, roughness, and wettability, were adjusted by changing the air gap distance during the spinning process. The roughness of the outer surface of the substrates decreased from 5.57 nm to 3.81 nm as the air gap increased from 0 cm to 20 cm. As a smoother surface was obtained, the wetting stability of the substrate was enhanced, thereby promoting thin supported ionic liquid membranes (SILMs) formation. The SILMs obtained were used to separate CO2 gas from N2, and the separation performance of single and binary gases and long-term stability of SILMs were evaluated. Results indicated that the use of sponge-like hollow fibers as a substrate yields a CO2 permeability of over 745.74 barrer and CO2/N2 selectivity of 17.8. Furthermore, when the transmembrane pressure was enhanced to 2.25 bar, the SILMs exhibited good membrane stability, an enhanced CO2 permeability of 1018.54 barrer, and a CO2/N2 selectivity of 20.17. This study revealed that the wetting behavior of IL is affected by the pore structure and surface roughness of the hollow fibers. Therefore, the surface property of substrates is a key point in improving the completeness and stability of SILMs in the gas separation process.