Enhancement of the gas separation performance of polymeric membranes by conditioning with ionic liquids

Under the right conditions, semi-crystalline polymers and appropriate ionic liquids (ILs) can form stable gels with high ionic liquid content. The solution casting and solvent evaporation process allows the formation of homogeneous dense films with good performance as gas or vapour separation membranes. Various semi-crystalline rubbery polymers such as poly(vinylidene fluoride-co-hexa¬fluoro¬propylene) [1] and poly(ether-block-amide) [2] have been successfully used in combination with a suitable IL and a volatile organic solvent. Such films are relatively thick, up to 100 micron and higher, whereas practical applications require thin films to ensure sufficiently high gas fluxes. It is still a challenge to form thin film membranes with a maximum thickness in the order of several micrometres. The present work shows a different approach in which integrally skinned or thin film composite membranes were prepared separately and then post-treated with a compatible ionic liquid. The poly(ether-b-amide) (PEBAX® 1657) /polyacrylonitrile (PAN) composite hollow fiber membranes were prepared by a new continuous coating method based on cross flow-filtration of a PEBAX solution. This technique allows simultaneous internal coating of a large number of the porous PAN hollow fibres with a thin selective dense layer of PEBAX®, directly inside the module. The membrane performance was improved by the addition of ionic liquid. The IL has a duplicate function. Firstly, it fills any remaining pores or pinhole defects by capillarity, thus increasing the permselectivity. Secondly, upon prolonged contact of the membrane with the IL, the latter is absorbed into the polymer matrix up to its equilibrium concentration. Strong swelling of the polymer can lead to significant changes of the transport parameters, typically an increase of the permeability and a modest reduction of the selectivity. The effect of the materials choice and the membrane preparation conditions on the properties and performance of the membranes will be discussed in view of important separations such as biogas separation or CO2 sequestration from flue gas. Acknowledgements: funding was received from the Italian "Programma Operativo Nazionale Ricerca e Competitività" 2007-2013, project PON01_01840 "MicroPERLA". 1.K. Friess, J.C. Jansen, F. Bazzarelli, P. Izák, V. Jarmarová, M. Ka?írková, J. Schauer, G. Clarizia, P. Bernardo, J. Membr. Sci. 415-416 (2012) 801-809. 2.P. Bernardo, J.C. Jansen, F. Bazzarelli, F. Tasselli, A. Fuoco, K. Friess, P. Izák, V. Jarmarová, M. Ka?írková, G. Clarizia, Sep. Purif. Technol., 97 (2012), 73-82.