Porous Al 2 O 3 /TiO 2 tubes in combination with 1-ethyl-3-methylimidazolium acetate ionic liquid for CO 2 /N 2 separation Jonathan Albo, Tomohisa Yoshioka, Toshinori Tsuru ⇑ Department of Chemical Engineering, Hiroshima University, 1-4-1 Kagayami-yama, Higashi-Hiroshima 739-8527, Japan article info Article history: Received 16 October 2013 Received in revised form 20 November 2013 Accepted 20 November 2013 Available online 4 December 2013 Keywords: CO 2 recovery Supported liquid membranes Ionic liquids Ceramic supports Membrane stability abstract The highest CO 2 solubility and commercially-available ionic liquid, 1-ethyl-3-methylimidazolium acetate ([emim][Ac]), was immobilized in porous Al 2 O 3 /TiO 2 tubes in order to study the potential of using supported ionic liquid membranes based on ceramic supports for CO 2 /N 2 separation. The supported ionic liquid membranes (SILMs) were first prepared using a conventional immobilization procedure based on ionic liquid impregnation, and then, by coating the TiO 2 mesoporous outer layer, reducing the membrane resistance to gas permeation. The permeation of these membranes to carbon dioxide and nitrogen was measured, yielding a CO 2 permeance as high as P CO 2 = 2.78 ± 0.11 Â 10 À8 mol/(m 2 s Pa), with an ideal CO 2 /N 2 selectivity of a(CO 2 / N 2 ) = 30.72 ± 0.86 for membranes prepared under the coating procedure, which outperformed the state of the art for CO 2 /N 2 separation in polymeric materials. The membrane stability tests demonstrated that the hydrophilic ceramic support was very effective for the immobilization of the liquid phase in the membrane for a period of 25 h and at applied feed pressures of 4 bar. Finally, the effect of water vapor in the gas stream and the effect of operation temperature on membrane separation performance were evaluated and compared. The high CO 2 permeance values and comparable selectivity to polymeric materials may suggest the potential application of using Al 2 O 3 /TiO 2 tubes in combination with [emim][Ac] ionic liquid for the selective removal/recovery of CO 2 from a gas stream in industrial applications. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The constraints of the current methods of dealing with CO 2 emissions—technologies and methods for gas separation in energy production processes—are being re-investigated in order to maxi- mize cost-efficiency and to mitigate the undesirable effects of glo- bal warming. Combination of membranes and ionic liquids (ILs), with negligible vapor pressure and thermal stability above 200 °C [1], are expected to play a leading role in cost-effective, energy- efficient and simple CO 2 separation technology to replace tradi- tional amine absorption units, where solvent losses associated with the direct contact between gas and liquid phases occurs [2,3]. Interest has recently increased in ILs for applications involving CO 2 separation due to the high degree of CO 2 solubility in selected ILs [4–6]. Among the broad diversity of ILs, those based on an imi- dazolium cation typically present a higher degree of CO 2 solubility, which could be even higher with the appropriate IL anion due to a weak CO 2 –IL anion Lewis acid/base complexation [6]. A literature search shows that ILs containing the acetate anion possess a strong absorption for CO 2 across a wide range of temperatures and applied pressures [7–10]. Therefore, it is possible to design tailor- made membrane systems based on task-specific ILs with an enhanced selectivity towards CO 2 . Previous studies have applied a non-dispersive (with zero solvent losses) membrane-based technology for CO 2 absorption, where gas and IL flow on opposite sides of the membrane equip- ment and a fluid/fluid interface forms inside each membrane pore [2,3,11–14]. Specifically, recent works have combined hollow membrane contactors with ILs for CO 2 absorption [15–17], because these can have an extraordinary affinity for this gas. However, it is still possible to improve the permselectivity of the gas separation process by using supported ionic liquid membranes (SILMs). In a SILM, the IL is immobilized inside the pores of a polymeric or cera- mic support. In this configuration, the CO 2 dissolves into the mem- brane at the feed/membrane interface, diffuses through the membrane, and it is desorbed at the opposite membrane surface [18–23]. Polymeric substrates were first proposed as supports, but the performance of polymer-based SILMs is limited under industrially relevant conditions because of their low flux and lack of high-tem- perature stability. As an alternative, ceramic membranes, such as alumina (Al 2 O 3 ), silica (SiO 2 ), zirconia (ZrO 2 ), or titania (TiO 2 ) have received a great deal of attention in applications of gas separation 1383-5866/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.seppur.2013.11.024 ⇑ Corresponding author. Tel.: +81 824 24 7714; fax: +81 824 22 7191. E-mail address: tsuru@hiroshima-u.ac.jp (T. Tsuru). Separation and Purification Technology 122 (2014) 440–448 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur