Stability studies of supported liquid membranes based on ionic liquids using SEM/EDX techniques
Advancing the chemical engineering fundamentals
Membranes and Membrane Science (T2-8P)
Keywords: supported liquid membranes, stability, SEM/EDX techniques, ionic liquids
Stability studies of supported liquid membranes based on ionic liquids using SEM/EDX techniques
A.P. de los Ríos a*, F.J. Hernández-Fernández a, F. Tomás-Alonso a, J.M. Palacios-Latasa b, D. Gómez a, M. Rubio a and G. Víllora a
a Department of Chemical Engineering , Faculty of Chemistry, University of Murcia,
P.O. Box 4021, Campus de Espinardo, E-30100, Murcia, Spain.
b Institute of Catalysis and Petrochemistry (CSIC) Madrid, Spain
E-mail: aprios@um.es
Among membrane-based separation processes, the use of supported liquid membranes (SLMs) has received growing attention during recent years [1]. SLMs are porous supports whose pores are filled with a liquid; among their numerous advantages is the fact that the amount of solvent needed in the SLM process is minimal and that the processes of extraction and stripping are combined into one single stage. Nevertheless, their industrial application is still limited, mainly due to concerns about SLM stability and long-term performance [2]. Supported liquid membranes with conventional liquids eventually deteriorate due to liquid vaporization, dissolution into a contacting phase, and displacement from the porous structure under low-pressure gradient (<10 kPa). A recently revealed clean alternative to the classical organic solvents are ionic liquids [3]. They are organic salts that are liquid close to room temperature and they normally consist of an organic cation and a polyatomic inorganic anion [9].
This work evaluates the effect of the ionic liquid nature on the stability of the resulting supported liquid membranes using SEM and EDX analysis. [bmim+][PF6-], [bmim+][BF4-] and [bmim+][NTf2-] were supported into the pores of Nylon –polyamide- membrane, using an ultrafiltration cell pressurized with nitrogen to assure the whole filling of pores. In the first step, the resulting supported liquid membranes were analyzed by SEM and EDX. The EDX spectra referenced to the F Ka peaks found that Nylon membranes impregnated with [bmim+][PF6-], [bmim+][BF4-] and [bmim+][NTf2-] showed the expected concentration of ILs in the bulk of membranes, in complete agreement with the morphological appearance of samples evidenced by SEM micrographs. In the cases of [bmim+][PF6-] and [bmim+][BF4-], a thin layer of ionic liquid were present on the membrane surface as was evidenced by SEM micrographs.
In the second step, stability experiments were performed keeping the membranes with supported ILs immersed for a week in a diffusion cell with hexane/hexane in both –feed and receiving- compartments. The EDX analyses showed that in all cases the ionic liquid was not displaced from the membrane pores. Furthermore, SEM micrographs of Nylon membranes impregnated with [bmim+][BF4-] and [bmim+][NTf2-] showed the same morphological appearance than before the immersion in hexane. However, SEM micrographs of Nylon membrane impregnated with [bmim+][PF6-] evidenced that part of the ionic liquid layer present on the membrane surface before the immersion in hexane was rinsed during contact with the hexane solution, which could be due to a little solubilization of the ionic liquid in hexane.
Acknowledgements:
This work was partially supported by the CICYT CTQ2005-09238/PPQ grant.
References:
[1] G. Muthuramam and K. Palanivelu, Dyes Pigments, 70 (2006) 99-104.
[2] M. Teramoto, Sakaida, S.S. Fu, N. Ohnishi, H. Matsuyama, T. Fukui and K. Arai, Sep. Purif. Technol., 21 (2000) 137-142.
[3] M.J. Earle and K.R. Seddon, Pure Appl. Chem., 72 (2000) 1391 –1398.
Presented Tuesday 18, 13:30 to 15:00, in session Membranes and Membrane Science (T2-8P).
