Phase behavior and permeability of Alkyl-Methyl-Imidazolium Tricyanomethanide ionic liquids supported in nanoporous membranes Ourania Tzialla b , Anastasios Labropoulos a,⇑ , Athanasia Panou a , Meropi Sanopoulou a , Evaggelos Kouvelos a , Chrysoula Athanasekou a , Konstantinos Beltsios b , Vlassis Likodimos a , Polycarpos Falaras a , George Romanos a a Institute of Advanced Materials, Physicochemical Processes, Nanotechnology and Microsystems – Division of Physical Chemistry, NCSR ‘‘Demokritos’’, Aghia Paraskevi Attikis, 15341 Athens, Greece b Materials Science and Engineering Dept., University of Ioannina, 45110 Ioannina, Greece article info Article history: Received 15 April 2014 Received in revised form 23 July 2014 Accepted 24 July 2014 Available online 1 August 2014 Keywords: Ceramic membranes Ionic liquids Nanopores Gas transport CO 2 separation abstract This work presents an investigation of the CO 2 and N 2 single and mixed gas phase permeability through supported ionic liquid membranes (SILMs) developed on ceramic nanoporous substrates with different pore size (1, 5 and 10 nm). ILs from the 1-alkyl-3-methylimidazolium tricyanomethanide family ([RMIM][TCM], with alkyl group, R: ethyl, butyl or octyl) were used as nanopore modifiers. These ILs exhi- bit high chemical and thermal stability, low viscosity and enhanced CO 2 absorption capacity compared to other imidazolium based ILs. Thermal analysis of the developed SILMs unveiled a drastic liquid-to-solid transition upon confinement of the ILs into the pore channels with a size of 1 nm. The IL crystals formed inside these extremely small cavities possessed considerable thermal stability and underwent thermally induced phase transitions that differed significantly from those occurring in the unconfined bulk IL phase or in the IL phase when entrapped into the larger pore channels. The different physical state of the IL under confinement into the pores of different size resulted to significant variation of the flux properties between the developed SILM membranes. The effect of temperature on the CO 2 permeability dependend strongly on the crystal thermal stability and microstructure dictated by the confinement into the nanopores. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Interest in ionic liquids continues to grow, primarily because of their unique and tunable properties. The possibility of tuning their properties by selecting a specific combination of cations and anions among a great variety of possible ion pairs has led to an exponentially growing list of potential applications, such as gas separation and capture via selective absorption. The solubility and diffusion of several gases, has already been studied in a high number of Room Temperature Ionic Liquids (RTILs) [1–19] and the results showed very promising CO 2 absorption capacity and CO 2 /N 2 selectivity performance, which might be suitable for energy and environmental applications such as carbon capture and sepa- ration (CCS). However one of the major drawbacks of RTILs, when used as net liquid solvents, is their relatively high viscosity (com- pared to common liquid absorbers and solvents) which leads to very slow CO 2 diffusion and makes their industrial scale applica- tion unfeasible. As a more convenient solution, immobilisation of very thin layers of ILs on the top surface or into the pores of suffi- ciently permeable membranes has already evidenced the possibil- ity to overcome the problem of slow diffusivity and improve the efficiency of CO 2 removal from flue gas. Up to date RTILs have been immobilized in macroporous, polymeric supports [20–31] and scarcely on inorganic nanoporous ones [32,33]. Previous testing of polymer based, Supported Ionic Liquid Membranes (SILMs) showed promising results with permeabilities/selectivities that were consistently above the upper bound of a Robeson plot for CO 2 /N 2 separation [20,34,35]. With respect to polymeric membranes, the use of ceramic substrates allows for operation at higher temperature and trans- membrane pressure. As a result, higher flux can be achieved with- out compromising the good separation performance. Moreover, issues related to the long-term stability of the support and the effects of acidic gases or the IL itself are not of concern. On the other hand, immobilisation into nanopores, instead of macropores can significantly contribute to the stability of the SILM membrane and the avoidance of phenomena such as the dissolution into the feed phase and the displacement of the IL from the pore structure. http://dx.doi.org/10.1016/j.seppur.2014.07.042 1383-5866/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +30 210 6503972; fax: +30 210 6511766. E-mail address: anst_lab@chem.demokritos.gr (A. Labropoulos). Separation and Purification Technology 135 (2014) 22–34 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur