Bruna SILVA SOARES1, Moisés PINTO2, Isabel MARRUCHO1
1Centro de Química Estrutural and Departamento de Engenharia Química, Instituto Superior Técnico, Lisboa, Portugal
2CERENA, Departamento de Engenharia Química, Instituto Superior Técnico, Lisboa, Portugal
Gas separation is a significant and common industrial procedure used to remove impurities and undesirable substances from mixed gas streams, such as extracting carbon dioxide from other gases for carbon capture or separating hydrogen for use as a carbon-free transportation fuel. It is well known that using membranes to separate gas compounds is both economically more advantageous and significantly more effective than methods like distillation or absorption.
The extensive knowledge of single gas permeability and ideal permselectivity of supported IL membranes (SILMs) are critical to leverage the use of IL-based membranes for industrial gas separation. Despite their incomplete perspective, these data provide valuable insights on the identification of the best ILs chemical structures for a given gas separation. For instance, and using the IL designer solvents properties, the best CO2/N2 separation performances among pure SILMs were attained by the [C2mim][TFSAM] and [C2mim][FSI] SILMs, that are on top of or beyond the Robeson 2008 upper bound, with CO2 permeabilities of 753 and 843 Barrer and CO2/N2 permselectivities of 43.9 and 46.1, respectively . However, the CO2 separation properties of industrially relevant mixtures are often greatly changed by the presence of different gases in the mixture which result in limiting events, such as competitive sorption, penetrant-induced plasticization, or concentration polarization . On the other hand, numerous ecotoxicity studies have demonstrated that some ILs are toxic to a variety of species, from bacteria to higher organisms. Although toxicity has been mainly linked to the cation and the length of its side chain, recent studies show that anions, especially fluorine containing anions, also contribute to their toxicity . It is, thus, important to develop new fluorinated anions and test their CO2 separation performance, in particular in the presence of other gases.
In this work, the mixed gas permeation properties of SILMs using pure ILs bearing the [C2mim]+ cation and various unconventional anions still bearing fluorinated moieties, such as [TFSAM], [FSI], [C4F9SO3], [FAP], [BETI], and [TFSI], are presented. Industrially relevant CO2 containing gas pairs , such as CO2/N2, CO2/H2, and CO2/CH4 in several compositions, are discussed and compared with those of single gas permeation properties.
 A. S. L. Gouveia, L. C. Tome, E. I. Lozinskaya, A. S. Shaplov, Y. S. Vygodskii, and I. M. Marrucho, “Exploring the effect of fluorinated anions on the CO2/N-2 separation of supported ionic liquid membranes,” PHYSICAL CHEMISTRY CHEMICAL PHYSICS, vol. 19, no. 42, pp. 28876–28884, Nov. 2017, doi: 10.1039/c7cp06297d.
 P. Bakonyi, N. Nemestóthy, and K. Bélafi-Bakó, “Biohydrogen purification by membranes: An overview on the operational conditions affecting the performance of non-porous, polymeric and ionic liquid based gas separation membranes,” Int J Hydrogen Energy, vol. 38, no. 23, pp. 9673–9687, 2013, doi: https://doi.org/10.1016/j.ijhydene.2013.05.158.
 J. Flieger and M. Flieger, “Ionic liquids toxicity—benefits and threats,” International Journal of Molecular Sciences, vol. 21, no. 17. MDPI AG, pp. 1–41, Sep. 01, 2020. doi: 10.3390/ijms21176267.
Bruna F. Soares gratefully acknowledges the financial support of FCT/MCTES (Portugal) for PhD fellowship 2021.05450.BD. This work was financed by CQE project (UIDB/00100/2020).