The gas separation performance of two block copolymer ion gel systems were examined for CO 2/N 2 and CO 2/CH 4 gas pairs. The ion gels were formed by self-assembly of 10-15wt% poly(styrene-b-ethylene oxide-b-styrene) (SOS) and poly(styrene-b-methyl methacrylate-b-styrene) (SMS) triblock copolymers in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIM][TFSA]), via association of the insoluble S blocks. Due to the high ionic liquid (IL) concentration, these gels exhibit rapid gas transport properties as well as high selectivity. The selectivity for both gas pairs was influenced by the type of polymer midblock: the SOS gel shows higher selectivity than both pure IL and SMS gels. Gas solubility tests on [EMI][TFSA]/PEO solutions indicate that poly(ethylene oxide) can suppress the solubility of N 2 and CH 4, and thereby increase the selectivity for CO 2. This important result qualitatively agrees with the gel gas separation performance, and confirms the importance of the midblock chemistry. Additionally, since the selectivity mainly stems from the differential gas solubility rather than gas diffusivity, the real selectivities obtained from mixed gas experiments are almost the same as the ideal selectivities. Ion gels show favorable separation performance in comparison with the corresponding "upper bound" on the Robeson plots for CO 2/N 2 and CO 2/CH 4, highlighting the potential of these gels in future CO 2-selective membrane separation.
Bibliographical noteFunding Information:
The authors acknowledge funding from the Abu Dhabi Minnesota Institute for Research Excellence (ADMIRE), a partnership between the Petroleum Institute of Abu Dhabi and the Department of Chemical Engineering and Materials Science of the University of Minnesota. This work was supported partially by the MRSEC Program of the National Science Foundation under Award Number DMR-0819885 . We gratefully acknowledge Prof. Richard Noble (U. Colorado) and Prof. Jason Bara (U. Alabama) for helpful suggestions. We also thank Sipei Zhang and Dr. Ilan Zeroni for providing the SMS, SOS triblock copolymers and PMMA homopolymer used in this study, and Dr. Brad Jones, Dr. Zhifeng Bai, Dr. Michelle Mok, Yu Lei and Dr. Hau-Nan Lee for assistance and helpful discussions.
Copyright 2012 Elsevier B.V., All rights reserved.
- Block copolymer ion gels
- CO separation
- Ionic liquids