ZIF-8/styrene-IL polymerization hollow fiber membrane for improved CO2/N2 separation

Abstract

Compared to supported ionic liquid membranes, poly(ionic liquid) membranes are synthesized by the polymerization of ionic liquid monomers to develop polymeric backbone to improve its membrane stability for gas separation process. However, the resulting dense membrane structure induced the lower gas permeance of the poly(ionic liquid) membranes. To overcome this limitation, in this study, ZIF-8, possessing the property of molecular sieves, was added to poly(styrene-ionic liquid) hollow fiber membranes (p(SIL) HFMs), providing a transport pathway. SIL monomers with different lengths of alkyl chain were polymerized and integrated with ZIF-8 fillers to synthesize ZIF-8/poly(ionic liquid) mixed matrix hollow fiber membranes (ZIF-8/p(SIL) MMHFMs). When the chain length of SIL monomers was increased, the CO2 permeance of p(SIL) HFMs increased from 3.6 to 4.6 GPU, while CO2/N2 selectivity decreased from 29 to 23. Additionally, the CO2 permeance of ZIF-8/p(SIL) MMHFMs was enhanced by 33% compared to that of p(SIL) HFMs. However, chain rigidification phenomenon was observed which cause the ZIF-8/p(SIL) MMHFMs showed the decreasing CO2 permeance when the ZIF-8 content was increased. The best separation performance of ZIF-8/p(SIL) MMHFMs was obtained with 0.5 wt% ZIF-8 addition, which exhibited a CO2 permeance and CO2/N2 selectivity of 6 GPU and 30. Therefore, adding ZIF-8 into p(SIL) HFMs to form the ZIF-8/p(SIL) MMHFMs is beneficial to enhance the CO2 permeance of membranes because of the characteristic of the pore size of 3.4 Å and transport pathway provided by ZIF-8 fillers.