Please cite this article in press as: A.L. Khan, et al., SPEEK/Matrimid blend membranes for CO 2 separation. J. Membr. Sci. (2011), doi:10.1016/j.memsci.2011.06.030 ARTICLE IN PRESS G Model MEMSCI-10800; No. of Pages 8 Journal of Membrane Science xxx (2011) xxx–xxx Contents lists available at ScienceDirect Journal of Membrane Science jo u rn al hom epa ge: www.elsevier.com/locate/memsci SPEEK/Matrimid blend membranes for CO 2 separation Asim Laeeq Khan a , Xianfeng Li b,∗ , Ivo F.J. Vankelecom a,∗ a Centre for Surface Chemistry and Catalysis, Faculty of Bioengineering Sciences, Katholieke Universiteit Leuven, Kasteelpark Arenberg 23, PO Box 2461, 3001 Leuven, Belgium b Lab of PEMFC Key Materials and Technologies, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China a r t i c l e i n f o Article history: Received 21 March 2011 Received in revised form 19 June 2011 Accepted 20 June 2011 Available online xxx Keywords: Polymer blending Poly(ether ether ketone) Gas separation Plasticization a b s t r a c t The miscibility and gas separation performance of Matrimid and sulfonated aromatic poly(ether ether ketone) (S-PEEK) blend membranes prepared by solution casting method were studied. A S-PEEK poly- mer with fixed degree of sulfonation was used for membrane synthesis. Both Matrimid and S-PEEK were physically miscible over the whole composition range, as confirmed by visual observation and DSC stud- ies. The effect of variation in composition on gas permeability and selectivity of blend membranes was investigated. The gas permeability and selectivity values fall in between those of the individual polymers, varying systematically with variation of S-PEEK content in the blend. The effect of feed pressure on CO 2 permeation was linked to CO 2 plasticization of the membranes. The Matrimid component of the blend membrane was cross-linked with p-xylenediamine to improve the anti-plasticization properties of the blend. In order to further study the stability and potential industrial application of these membranes, they were tested at different conditions of feed pressure, temperature and CO 2 feed concentration. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The use of fossil fuels for energy generation leads to CO 2 emis- sions into the atmosphere, which eventually contributes to global warming [1]. Furthermore, CO 2 in natural gas must be removed because its presence reduces the energy content of the fuel [2]. To date, several methods have been proposed for the separation CO 2 from gas mixtures [3]. One promising method to lower the cost of CO 2 separation is development of CO 2 separation membranes [4]. The use of polymer membranes has contributed to the commercial success of this technique due to its low capital and energy cost, less space requirement and lower ecological footprint [5]. One of the goals in the development of polymeric membranes is to achieve high selectivity and permeability. Extensive research is being focused on tailoring polymeric membranes to achieve supe- rior separation properties because individual polymers do not fulfill the required properties [5]. Another challenge associated with the commercialization of polymeric membranes for gas separation is their limitation to perform under harsh conditions. Previous stud- ies have shown that most polymeric membranes show a drastic decrease in selectivity on increasing feed pressure due to CO 2 plas- ticization [6,7]. The performance also degrades on exposure to high concentrations of CO 2 due to excessive swelling [7]. Chemical modi- fication of the polymeric material [8], blending with other polymers ∗ Corresponding author. Tel.: +32 16 32 15 94. E-mail addresses: lixianfeng@dicp.ac.cn (X. Li), ivo.vankelecom@biw.kuleuven.be (I.F.J. Vankelecom). [9], and incorporation of molecular sieving material in the poly- mer matrix [10], are among few approaches used to counter these challenges. In a recent study, our research group investigated the gas sep- aration properties of S-PEEK prepared by direct polymerization of sulfonated monomers [11]. The membranes showed good separa- tion performance, and the sulfonation of the polymer suppressed the plasticization making it an interesting candidate for gas separa- tion membranes. The combination of excellent anti-plasticization properties of S-PEEK with a compatible polymer having still supe- rior gas separation properties could result in a polymer blend with desired characteristics. Considering this opportunity, blends of S- PEEK with Matrimid were made. Matrimid was chosen because it is a commonly available commercial polymer studied for gas separation, possesses good mechanical properties and is thermally stable [8,12–14]. The effect of chemical cross-linking and different operating conditions on the performance of blend membranes was studied and compared with the individual polymers. 2. Experimental 2.1. Materials The polyimide (Matrimid 9725) was kindly provided by Hunts- man (Switzerland). The synthesis of S-PEEK with different degrees of sulfonation was described previously [15,16]. As shown in Figs. 1 and 2, the synthesis procedure involved two steps: monomer preparation and polymer synthesis. S-PEEK with fixed degree of sul- fonation, i.e. 50% was used in this study. Both polymers were dried 0376-7388/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2011.06.030