Evaluation of a new supercritical CO 2 -assisted deposition method for preparing gas selective polymer/zeolite composite membranes Martin Drobek a , Julius Motuzas a , Ve ´ ronique Durand a,b , Maxime Duchateau a,b , Christophe Charmette a , Audrey Hertz b , Ce ´ dric Loubat c , Anne Julbe a,n a Institut Europe ´en des Membranes (UMR 5635 CNRS), Universite´ Montpellier 2, CC47, Place Eug  ene Bataillon, 34095 Montpellier Cedex 5, France b CEA, DEN, Marcoule, F-30207 Bagnols-sur-Ceze, France c Specific Polymers, Avenue de l’Europe, Cap Alpha, Clapiers 34830, France article info Article history: Received 14 May 2012 Received in revised form 24 October 2012 Accepted 23 November 2012 Available online 5 December 2012 Keywords: Composite membranes MFI zeolite membrane Deposition method Fluorinated oligomers Supercritical CO 2 Gas separation abstract This work evaluates a new eco-friendly strategy for preparing ultrathin gas selective membranes on top of a microporous support. The method involves the dissolution of small amounts of fluorinated oligomers with alkoxysilane functional groups in supercritical CO 2 (scCO 2 ) and their transport to the substrate followed by the subsequent deposition/filtration under high pressure using a MFI zeolite membrane support (silicalite-1 (S-1), channel size 0.55 nm. During the deposition process, the oligomers are compressed on the zeolite surface and potentially forced in the intercrystalline defects of the zeolite membrane, if any. The performance of this new type of polymer/zeolite composite membranes has been evaluated for both single gas permeation and gas mixture separations. Attractive results were obtained applying oligomers with short molecular chains ( 1.2–2 nm;  300–600 g mol 1 ), easily forming an interpenetrated compact network during the deposition process at DP ¼6 MPa and 50 1C. High permselectivities were obtained at 25 1C(a n He=N2 ¼85–135 and a n CO2=N2 ¼50–80 with the He and CO 2 permeance in the range 1–2.7n10 8 mol m 2 s 1 Pa 1 ) together with attractive separation factors (F He=N2 ¼49 and F CO2=N2 ¼18). & 2012 Elsevier B.V. All rights reserved. 1. Introduction In the past decades, a huge development has been made in the design, microstructure and formulation of polymer membranes with good efficiency, i.e. coupling both high selectivity and high fluxes [1–4]. Asymmetric polymer membranes that are suitable for gas separation should comprise a very thin skin layer (0.1– 0.5 mm) on a highly porous thick substructure (100–200 mm), thus forming so-called ultrathin-skinned or even hyperthin-skinned [5] asymmetric membranes. Ultra-thin layers are also requested when inorganic membranes are considered for gas or vapor separation applications [1,6,7]. Methods for preparing ultrathin layers with a variety of material formulations are therefore of great interest for enlarging the range of membrane applications. In such large scale of possible approaches, environment-friendly methods are receiving a specific attention. Solvent-free methods or those using green solvents such as supercritical CO 2 (scCO 2 ) are particularly attractive for materials synthesis [8]. In addition, the development of deposition methods limiting wastes of polluting and costly chemicals is also of a high interest. Supercritical CO 2 has been considered in this work, as a green solvent for the preparation of thin hybrid polymer membranes with virtually 100% yield and zero waste. The principal idea bears on using the scCO 2 solubilising and transporting properties for the deposition of the required amount of a specific oligomer to the surface of a porous support. Such support has to be able both to retain (at least partially) the oligomers on its surface and to leave the scCO 2 diffusing through it, thus operating the deposition by a filtration/compression effect. Zeolite membranes as microporous supports are typically well adapted for testing such a concept with nanometer sized oligo- mers. From that point of view, this applied deposition strategy can be ranked in the list of post-synthetic modification methods for defect repair in zeolite membranes. Zeolite membranes exhibit well calibrated channel size and provide high thermal, chemical and mechanical stability enabling their application in harsh environments [9–11]. Their separation efficiency for small gases is often based on differential adsorption effects (e.g. separation of strongly adsorbed CO 2 from poorly adsorbed species like CH 4 ,N 2 , He or H 2 ). This is due to the poor molecular sieving properties of common zeolite membranes for these small molecules and also to the contribution of non- selective intercrystalline pathways during the separation process. Various post-synthetic methods have been developed for improv- ing gas separation performance of zeolite membranes by plugging Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/memsci Journal of Membrane Science 0376-7388/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.memsci.2012.11.058 n Corresponding author. Tel.: þ33 4 67 14 91 42; fax: þ33 4 67 14 91 19. E-mail address: anne.julbe@univ-montp2.fr (A. Julbe). Journal of Membrane Science 429 (2013) 428–435