Preparation and characterization of ITQ-29/polysulfone mixed-matrix membranes for gas separation: Effect of zeolite composition and crystal size Clara Casado-Coterillo a,n , Jaime Soto a , Marı ´a T. Jimare ´ a , Susana Valencia b , Avelino Corma b , Carlos Te ´ llez a , Joaquı ´n Coronas a a Departmento de Ingenierı ´a Quı ´mica y Tecnologı ´as del Medio Ambiente and Instituto de Nanociencia de Arago ´n (INA), Universidad de Zaragoza, c/Mariano Esquillor s/n, 50018, Zaragoza, Spain b Instituto de Tecnologı ´a Quı ´mica, Universidad Polite´cnica de Valencia, Consejo Superior de Investigaciones Cientı ´ficas, Av. de los Naranjos s/n, 46022, Valencia, Spain article info Article history: Received 11 October 2011 Received in revised form 14 January 2012 Accepted 17 January 2012 Available online 25 January 2012 Keywords: ITQ-29 LTA-type zeolite Crystallization Mixed matrix membranes Gas separation H 2 purification abstract This work concerns the preparation and characterization of ITQ-29 zeolite crystals with high Si/Ge ratio (100–N) and different particle size for obtaining mixed matrix membranes. The Si/Ge molar ratio and seeding content of the synthesis gel appeared to have an effect on the final crystal size, and particles of 2.5 mm were obtained for pure silica composition with good crystallinity. These were introduced, at 4, 8 and 12 wt% loadings, into a commercial polysulfone matrix to prepare mixed matrix membranes that showed promising results in the separation of H 2 /CH 4 mixtures (highest H 2 permeability 21.9 Barrer and a separation factor of 118 for the 4 wt% ITQ-29/polysulfone membrane). The thermal treatment of the membranes and the type of solvent were also optimized to provide good interaction between the zeolite and the polymer, limiting aggregation of the particles in the matrix, and removing all residual solvent that hinders gas permeation performance. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction Zeolite A (LTA-type structure) is a small pore zeolite contain- ing large cavities that generate a high void volume, widely used in industry as a shape-selective adsorbent, drying agent or cation exchanger in washing powders. Nevertheless, its performance as adsorbent is limited to water-free systems because of its extreme hydrophilicity, due to its low framework Si/Al ratio (Zhao et al., 2006). ITQ-29 was first presented in 2004 (Corma et al., 2004) as a zeolite with the same topological structure as zeolite A but a much higher Si/Al ratio (up to infinity, i.e. pure silica), using a bulky organic template obtained from the self-assembly of two identical organic cationic moieties through p–p type interactions. Since then, a few studies have been devoted to the fundamental understanding of the structure (Corma and Davis, 2004; Dorset et al., 2007) and the diffusion implications for adsorption kinetics and separations (Hedin et al., 2007, 2008; Palomino et al., 2009). Pure-silica ITQ-29 is a hydrophobic small-pore zeolite, which gives ITQ-29 the possibility of sieving and processing small organic molecules with high precision, even in the presence of water or other polar molecules (Corma et al., 2004). Pure silica zeolites have been prepared in the form of thin films on silicon wafers, and the study of the dielectric properties of these films confirmed the dependence of the performance properties of these materials not only on porosity but also on their structure (Hunt et al., 2010), as indicated by ring size, microporous volume and lattice symmetry (Sastre and Corma, 2006). Another research group reported the synthesis of ITQ-29 using different structure directing agents, and a variation of the morphology and size of the crystals down to 0.5 mm was observed by varying the gel composition and synthesis time (Huang and Caro, 2009; Huang et al., 2010). However, the Si/Ge ratio of the particles obtained in this way was as low as 2, making this zeolite unstable upon calcination, as it is well known that silicogermanates have limited framework stability in the presence of water or even when exposed to ambient moisture (Moliner et al., 2008; Gao et al., 2009). Zeolite membranes with pores of molecular size can perform very well in many interesting applications, such as hydrogen separations from small gases (David et al., 2011). Al-free ITQ-29 has also been prepared as pure inorganic membranes by hydro- thermal synthesis and tested on the permeation of N 2 , CH 4 and propane (Tiscornia et al., 2008). In this case, the membrane was partially activated by ozonation at 200 1C, but not all the template was removed and the permeability and selectivity were not very high. Recently, ITQ-29 membranes have been prepared using Kryptofix 222 as SDA and activated by in situ O 2 flow at 300 1C before the permeation experiments (Huang and Caro, 2010). In Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/ces Chemical Engineering Science 0009-2509/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2012.01.024 n Corresponding author. Tel.: þ34 976 762471; fax: þ34 976 76 1879. E-mail address: casadoc@unican.es (C. Casado-Coterillo). Chemical Engineering Science 73 (2012) 116–122