Separation of volatile organic compounds from air by PEBAX®/room temperature ionic liquid gel membranes

Gas and vapour separations In recent years membrane-based separation processes have become an established technology in the field of bulk gas separations and separations of volatile organic compounds from air [1]. Despite this fact, solvent recovery membrane processes require more resistant materials with sufficiently longstanding properties which conventional polymeric materials do not always possess. Incorporation of ionic liquids (ILs) into the various polymer matrices represents the new way to improve membrane properties. Recent studies show the gas separation performance improvements in terms of permeability and also of selectivity in the case of separation of the CO2/H2 gas pair [2]. In this work elastomeric copolymer poly(ether-block-amide) commercially available as PEBAX® was combined with the ionic liquid trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate in order to prepare stable selfstanding membranes. By simple solution casting method from the solution in the butanol/isopropylalcohol mixture, thin polymeric films containing up to 40% of the ionic liquid were obtained. Single gas and vapour permeation tests were carried out on these novel materials by fixed-volume pressure increase instrument in the time-lag mode. Transport properties - permeability, solubility and diffusion coefficients of various species - were evaluated by fitting of the experimental data by the following equation, describing the typical shape of the permeate pressure in the permeation transient. The effect of the ionic liquid in the polymer on the transport of the permanent gases CO2, CH4, O2, N2, H2, He, propane and butane, and different vapours (pentane, hexane, cyclohexane, toluene, ethanol) was studied. For the gases the diffusion coefficients of all tested species follow the same declining trend with increasing ionic liquid content. Transport mechanism shifts slightly from diffusion-controlled to be solubility controlled as confirmed by the overall increase in solubility coefficients. Figure 1.Permeability of various vapours as a function of their activity in a PEBAX membrane containing 40% of the ionic liquid trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate. For all vapors the permeability increases with increasing activity, both in neat PEBAX and in the PEBAX/IL blend. The alkanes show the same trend, whereas the trend is slightly different for the cyclic and aromatic species. The permeability of the alkanes increases with increasing molar mass. The fundamental difference between the permeation of permanent gases and organic vapours makes these membranes suitable for separation of volatile organic compounds from air (Fig. 1). For this purpose the mixed-gas permeation set-up will be used for further study on these materials based on ionic liquid modified polymers. Acknowledgements The work leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° NMP3-SL-2009-228631, project DoubleNanoMem, from the 2010-2012 CNR-AVCR bilateral agreement, and from the Czech Science Foundation (Grant No. P106/10/1194). This publication was created in connection with the project "Unipetrol research and education center" ev. No CZ.1.05/2.1.00/03.0071. References [1]P. Bernardo, E. Drioli, G. Golemme, Membrane Gas Separation: A. Review/State of the Art, Ind. Eng. Chem. Res. 48 (2009) 4638-4663. [2]J.C. Jansen, G. Clarizia, K. Friess, J. Schauer, P. Izák, High ionic liquid content polymeric gel membranes: preparation and performance, Macromolecules 44 (2011) 39-45. [3]P. Bernardo, J.C. Jansen, F. Bazzarelli, F. Tasselli, A. Fuoco, K. Friess, P. Izák, V. Jarmarová, M. Ka?írková, G. Clarizia, Gas transport properties of PEBAX®/Room Temperature Ionic Liquid gel membranes, Sep. Purif. Technol., in press. DOI: 10.1016/j.seppur.2012.02.041.