Modulation of the gas and vapour transport in polymeric membranes by ionic liquids

Introduction A well-known limitation of polymeric membranes is the trade-off between their permeability and their selectivity, defined by the so called Robeson upper bound [?1]. Polymers form the most abundant class of materials used for commercial membranes and with membrane operations becoming increasingly important for industrial gas and vapour separations in the last several decades [?2], there is a strong need to improve the materials' performance. The major challenge is to overcome the upper bound limit. Among the various approaches used for optimization of the membrane performance, the incorporation of room temperature ionic liquids (RTILs) into the polymer matrix has demonstrated promising perspectives [?3]. Results and discussion We have found that membranes of 1-ethyl-3-methyl¬imidazolium bis(trifluoro¬methyl-sulfonyl)¬imide ([EMIM][TFSI]) in poly(vinylidene fluoride-co-hexafluoropropylene) (poly(VDF-co-HFP)) have a particularly interesting CO2/H2 selectivity [?4]. In the present study we will discuss different polymeric membranes with tailored gas and vapour transport properties, obtained by incorporation of variable amounts of RTILs. The materials choice is discussed on the basis of mutual compatibility, ability to form self-standing membranes, for instance in the form of stable gels. Detailed analysis of the transport properties will be carried out by gas and vapour permeation measurements in the time lag mode. Correlations between the transport properties of the polymer/IL blend membranes and important structural properties like the elastic modulus, give deep insight into the transport phenomena and demonstrate for instance the transition from diffusion controlled to solubility controlled permeation (Fig. 1). Figure 1. Correlation between permeability and Young's modulus for a polymer gel membrane with 80% of [EMIM][TFSI] in poly(VDF-co-HFP) [?5]. Beside the single gas permeation measurements to study the fundamental transport parameters, the membrane properties and separation performance will be further studied by mixed gas and gas/vapour permeation measurements to evaluate the separation performance. In addition to self-supported dense membranes, also the possibility to produce supported thin film composite membranes will be evaluated. Acknowledgements Funding was received from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. NMP3-SL-2009-228631, project DoubleNanoMem, from the Czech Science Foundation (Grant No. P106/10/1194) and from the CNR - Czech Academy of Science bilateral agreement 2010-2012. References [1]L. M. Robeson, The upper bound revisited, J. Membr. Sci. 320 (2008) 390-400. [2]P. Bernardo, E. Drioli, G. Golemme, Membrane gas separation. A review / State of the art, Ind. Eng. Chem. Res. 48 (2009) 4638-4663. [3]P. Scovazzo, Determination of the upper limits, benchmarks and critical properties for gas separations using stabilized room temperature ionic liquid membranes (SILMs) for the purpose of guiding future research, J. Membr. Sci. 343 (2009) 199-211. [4]J.C. Jansen, K. Friess, G. Clarizia, J. Schauer, P. Izák, High ionic liquid content polymeric gel membranes: preparation and performance. Macromolecules 44 (2011) 39-45. [5]K. Friess, J.C. Jansen, F. Bazzarelli, P. Izák, V. Jarmarová, M. Ka?írková, J. Schauer, G. Clarizia, P. Bernardo, High ionic liquid content polymeric gel membranes: correlation of membrane structure with gas and vapour transport properties, J. Membr. Sci., submitted.