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Novel tubular composite carbon-zeolite membranes
Materials Letters 58 (2004) 2223 – 2226 www.elsevier.com/locate/matlet
Novel tubular composite carbon-zeolite membranes Xiongfu Zhang a,*, Wenqing Zhu b, Haiou Liu a, Tonghua Wang a a
Institute of Adsorption and Inorganic Membrane, School of Chemical Engineering, Dalian University of Technology, Dalian 116012, PR China b School of Environment and Chemical Engineering, Xian University of Engineering Science and Technology, Xian 710048, PR China Received 6 October 2003; accepted 23 January 2004 Available online 7 March 2004
Abstract Zeolite NaA membranes on porous carbon tubes as supports were prepared using a simple process. Nanoseeds for the regrowth of zeolites were introduced to the porous carbon supports by using a simple seeding technique in a seed ethanol solution. Continuous and highly intergrown zeolite NaA-carbon composite membranes on the seeded porous supports were obtained by hydrothermal treatment and characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). D 2004 Elsevier B.V. All rights reserved. Keywords: Zeolite; Zeolite-carbon membrane; Preparation; Characterization
1. Introduction Zeolites are crystalline microporous materials with welldefined and uniform structure and hydrophilic property. Zeolite membranes supported on various substrates including metals, ceramics and polymers have been extensively studied as a means of membrane separation and catalysis [1 – 9]. Among these substrates, ceramics and polymers are widely used. However, polymers have low chemical and thermal stabilities. Ceramics are slightly eroded by synthesis solutions during the growth of zeolite membranes. Besides, ceramics are very expensive, either as supports or as membranes. Taking into account factors such cost and resistance to chemical attack, carbon is a particularly attractive support material for the preparation of zeolite membranes. Porous carbon materials are promising candidates as supports because they are not only stable under non-oxidising conditions, but also very inexpensive [10]. Pure porous carbon materials as membranes possess relatively wide pore sizes and hydrophobic properties. They are not suitable to remove hydrophilic components from mixtures and separate some gas mixtures, such as iso-butane/n-butane and gasvapour mixtures, for instance, air/hydrocarbons and hydrogen/hydrocarbon [11]. * Corresponding author. Tel.: +86-411-8993605; fax: +86-4113633080. E-mail addresses: [email protected], [email protected] (X. Zhang). 0167-577X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2004.01.027
Composite carbon-zeolite membranes formed by the zeolite growth on porous carbon supports can possess the bifunctional properties of both carbon and zeolite, which can overcome the above drawbacks of pure carbon materials and have potential applications in catalysis and separation. Several papers on the preparation of pure carbon membranes have been reported [12 –14]. However, there are the few studies on the synthesis of zeolite membranes on activated carbon and hollow fibers as supports [15 –19]. In this report, we outline a simple method for the growth of zeolite NaA membrane on porous carbon tubes. The method includes two steps in which a thin layer of zeolite seeds was coated onto the inner surface of the tubes using a seeding technique in a seed ethanol solution and then regrown into continuous films by hydrothermal treatment.
2. Experimental Colloidal NaA seeds were prepared from the procedure described in a separate paper [20]. For this study, the seeds were redispersed in ethanol (99.8%). The concentration of colloidal seeds was adjusted to give 1 wt.% zeolite in ethanol. Porous carbon tubes prepared by Dalian University of Technology have 9 mm OD, 5 mm ID and a nominal pore size of 0.5 Am. Prior to use, the tubes were cut into smaller pieces with the length of 15 mm, rinsed with DDI water and then dried at 120 jC for 10 h. Before the inner surface of the tubes
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Fig. 1. SEM images of the porous carbon tube support: (a) surface, (b) cross section.
was coated with a layer of colloidal NaA zeolite seeds by slipcasting in 1 wt.% seed ethanol solution for 30 s, the external surface of the tubes was wrapped with Teflon ribbon. The seeded supports were dried at room temperature overnight and calcined in air at 250 jC for 6 h. After calcination, the external surface of the tubes was wrapped with Teflon ribbon to prevent zeolite deposition on the outer surface of the tubes. Then, the seeded tubes were immersed vertically in the clear synthesis solution with a molar composition of 1Al2O3/ 5SiO2/48Na2O/4500H2O at 100 jC for 12 h. The synthesis solution was prepared by mixing together the desired amounts of sodium aluminate, sodium hydroxide, tetraethyl orthosilicate and water and stirring for 12 h at room temperature. The volume of the synthesis solution was kept constant at 60 ml for 6.2 cm2 of support area. After the synthesis, the samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD).
3. Results and discussion Fig. 1 is the SEM images of the porous carbon supports used in our experiment. It reveals from the SEM images that the porous carbon tubes have extremely rough surfaces and a wide range of pore sizes. Especially, they have many
bumps and larger holes. And their surface is not smooth in comparison with ceramics materials. Therefore, it is hard to form continuous uniform zeolite membrane directly grown on the support. In fact, our experiment has proven that there are very few zeolite crystals growing on the surface of the unseeded carbon support by in situ synthesis. This is attributed to the reason that the surface of carbon materials has very few functional groups such as –OH, –COOH, – CO –, etc. [16]. From the SEM images of the carbon seeded using slipcasting technique in 1 wt.% seed ethanol solution for 30 s (Fig. 2a). It is evident that a continuous and smooth seed layer on the rough carbon surface is formed. The seed layer thickness is around 5 Am and also this thickness can be adjusted by controlling slip-casting time. The intrusion of some seeds into the large voids can increase the adhesion between the seed layer and the carbon surface. The surface property and roughness of the carbon are greatly improved by seeding in seed ethanol solution. Otherwise, it is found from our experiment that few seeds are deposited on the surface of the carbon by seeding in 2 wt.% seed water solution. The reason for this is due to the bad wettability of the carbon surface in the seed water solution. After regrowth by hydrothermal synthesis from clear solution, a continuous, dense NaA zeolite membrane with
Fig. 2. SEM images of the porous carbon tube support seeded using slip-casting in seed ethanol solution: (a) surface, (b) cross section.
X. Zhang et al. / Materials Letters 58 (2004) 2223–2226
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Fig. 3. SEM images of the NaA membrane regrown on the seeded carbon support: (a) surface, (b) cross section.
Fig. 4. XRD patterns of (a) the carbon support, (b) the carbon support seeded in seed ephanol solution, (c) the regrown NaA membrane on the seeded carbon support, (d) the standard NaA zeolite powder.
around 4 Am thickness is formed by crystals growing outward from the surface of the seed layer (Fig. 3). The zeolite crystals of the surface are very uniform and intergrown very well. The thickness of the zeolite layer can be easily controlled by modifying the synthesis conditions. The XRD spectra of the samples from Fig. 4 show that there exist no zeolite peaks on the carbon support (Fig. 4a); however, both the seeded carbon support (Fig. 4b) and the regrown seeded carbon support (Fig. 4c) exhibit strong zeolite peaks. The XRD patterns of Fig. 4b and c are consistent with the standard zeolite NaA structure (Fig. 4d), but with different relative peak intensities. This confirms that the existence of a seed layer on the support after seeding and a NaA membrane layer on the seeded support after regrowth which results in the stronger peaks.
and can be suitable for synthesizing various types of composite-zeolite membranes by modifying seed types, synthesis solution and conditions. The composite-zeolite membranes have potential applications in catalysis and separation.
Acknowledgements We are grateful for the financial support by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, the Dalian University of Technology (1000-893305).
References 4. Conclusion In summary, the present paper reports on the preparation of a composite carbon-zeolite NaA membrane using a simple process. This method is simpler and convenient
[1] W.J.W. Bakker, F. Kapteijn, J. Poppe, J.A. Moulijn, J. Membr. Sci. 117 (1 – 2) (1996) 57. [2] J. Sterte, S. Mintova, G. Zhang, B.J. Schoeman, Zeolites 18 (5 – 6) (1997) 387. [3] K. Aoki, K. Kusakabe, S. Morooka, Ind. Eng. Chem. Res. 39 (2000) 2245.
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[4] L.T.Y. Au, W.Y. Mui, P.S. Lau, C. Tellez, K.L. Yeung, Microporous Mesoporous Mater. 47 (2001) 203. [5] Y.S. Yan, M.E. Davis, G.R. Gavalas, Ind. Eng. Chem. Res. 34 (1995) 1652. [6] X. Zhang, J. Wang, H. Liu, C. Liu, K. Yeung, Sep. Purif. Technol. 32 (2003) 151. [7] Z. Lai, G. Bonilla, I. Diaz, J. Nery, K. Sujaoti, M. Amat, E. Kokkoli, O. Terasaki, R. Thompson, M. Tsapatsis, D. Vlachos, Science 300 (2003) 456. [8] M.D. Jia, K.W. Peinemann, R.D. Behling, J. Membr. Sci. 73 (1992) 119. [9] J.C. Jansen, J.H. Koegler, H. van Bekkum, H.P.A. Calis, C.M. van den Bleek, F. Kapteijn, J.A. Moulijn, E.R. Geus, N. van der Puil, Microporous Mesoporous Mater. 21 (1998) 213. [10] R. Ryoo, S.H. Joo, M. Kruk, M. Jaroniec, Adv. Mater. 13 (9) (2001) 677. [11] A.B. Fuertes, J. Membr. Sci. 177 (2000) 9.
[12] V.M. Linkov, R.D. Sanderson, E.P. Jacobs, J. Membr. Sci. 95 (1994) 93. [13] M. Ogawa, Y. Nakano, J. Membr. Sci. 162 (1999) 189. [14] V.C. Geiszler, W.J. Koros, Ind. Eng. Chem. Res. 35 (1996) 2999. [15] R. vander Vaart, H. Bosch, K. Keizer, T. Reith, Microporous Mater. 9 (1997) 203. [16] J. Garcia-Martinez, D. Cazorla-Amoros, A. Linares-Solano, Y.S. Lin, Microporous Mesoporous Mater. 42 (2001) 255. [17] S.P.J. Smith, V.M. Linkov, R.D. Sanderson, L.F. Petrik, C.T.O. Connor, K. Keiser, Microporous Mater. 4 (1995) 385. [18] V. Valtchev, B.J. Schoeman, J. Hedlund, S. Mintova, J. Sterte, Zeolites 17 (1996) 408. [19] A. Berenguer-Murcia, J. Garcia-Martiez, D. Cazorla-Amoros, A. Linares-Solano, A.B. Fuertes, Microporous Mesoporous Mater. 59 (2003) 147. [20] X. Zhang, K.L. Yeung. Microporous Mesoporous Mater., in review.
Novel tubular composite carbon-zeolite membranes Xiongfu Zhang a,*, Wenqing Zhu b, Haiou Liu a, Tonghua Wang a a
Institute of Adsorption and Inorganic Membrane, School of Chemical Engineering, Dalian University of Technology, Dalian 116012, PR China b School of Environment and Chemical Engineering, Xian University of Engineering Science and Technology, Xian 710048, PR China Received 6 October 2003; accepted 23 January 2004 Available online 7 March 2004
Abstract Zeolite NaA membranes on porous carbon tubes as supports were prepared using a simple process. Nanoseeds for the regrowth of zeolites were introduced to the porous carbon supports by using a simple seeding technique in a seed ethanol solution. Continuous and highly intergrown zeolite NaA-carbon composite membranes on the seeded porous supports were obtained by hydrothermal treatment and characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). D 2004 Elsevier B.V. All rights reserved. Keywords: Zeolite; Zeolite-carbon membrane; Preparation; Characterization
1. Introduction Zeolites are crystalline microporous materials with welldefined and uniform structure and hydrophilic property. Zeolite membranes supported on various substrates including metals, ceramics and polymers have been extensively studied as a means of membrane separation and catalysis [1 – 9]. Among these substrates, ceramics and polymers are widely used. However, polymers have low chemical and thermal stabilities. Ceramics are slightly eroded by synthesis solutions during the growth of zeolite membranes. Besides, ceramics are very expensive, either as supports or as membranes. Taking into account factors such cost and resistance to chemical attack, carbon is a particularly attractive support material for the preparation of zeolite membranes. Porous carbon materials are promising candidates as supports because they are not only stable under non-oxidising conditions, but also very inexpensive [10]. Pure porous carbon materials as membranes possess relatively wide pore sizes and hydrophobic properties. They are not suitable to remove hydrophilic components from mixtures and separate some gas mixtures, such as iso-butane/n-butane and gasvapour mixtures, for instance, air/hydrocarbons and hydrogen/hydrocarbon [11]. * Corresponding author. Tel.: +86-411-8993605; fax: +86-4113633080. E-mail addresses: [email protected], [email protected] (X. Zhang). 0167-577X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2004.01.027
Composite carbon-zeolite membranes formed by the zeolite growth on porous carbon supports can possess the bifunctional properties of both carbon and zeolite, which can overcome the above drawbacks of pure carbon materials and have potential applications in catalysis and separation. Several papers on the preparation of pure carbon membranes have been reported [12 –14]. However, there are the few studies on the synthesis of zeolite membranes on activated carbon and hollow fibers as supports [15 –19]. In this report, we outline a simple method for the growth of zeolite NaA membrane on porous carbon tubes. The method includes two steps in which a thin layer of zeolite seeds was coated onto the inner surface of the tubes using a seeding technique in a seed ethanol solution and then regrown into continuous films by hydrothermal treatment.
2. Experimental Colloidal NaA seeds were prepared from the procedure described in a separate paper [20]. For this study, the seeds were redispersed in ethanol (99.8%). The concentration of colloidal seeds was adjusted to give 1 wt.% zeolite in ethanol. Porous carbon tubes prepared by Dalian University of Technology have 9 mm OD, 5 mm ID and a nominal pore size of 0.5 Am. Prior to use, the tubes were cut into smaller pieces with the length of 15 mm, rinsed with DDI water and then dried at 120 jC for 10 h. Before the inner surface of the tubes
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X. Zhang et al. / Materials Letters 58 (2004) 2223–2226
Fig. 1. SEM images of the porous carbon tube support: (a) surface, (b) cross section.
was coated with a layer of colloidal NaA zeolite seeds by slipcasting in 1 wt.% seed ethanol solution for 30 s, the external surface of the tubes was wrapped with Teflon ribbon. The seeded supports were dried at room temperature overnight and calcined in air at 250 jC for 6 h. After calcination, the external surface of the tubes was wrapped with Teflon ribbon to prevent zeolite deposition on the outer surface of the tubes. Then, the seeded tubes were immersed vertically in the clear synthesis solution with a molar composition of 1Al2O3/ 5SiO2/48Na2O/4500H2O at 100 jC for 12 h. The synthesis solution was prepared by mixing together the desired amounts of sodium aluminate, sodium hydroxide, tetraethyl orthosilicate and water and stirring for 12 h at room temperature. The volume of the synthesis solution was kept constant at 60 ml for 6.2 cm2 of support area. After the synthesis, the samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD).
3. Results and discussion Fig. 1 is the SEM images of the porous carbon supports used in our experiment. It reveals from the SEM images that the porous carbon tubes have extremely rough surfaces and a wide range of pore sizes. Especially, they have many
bumps and larger holes. And their surface is not smooth in comparison with ceramics materials. Therefore, it is hard to form continuous uniform zeolite membrane directly grown on the support. In fact, our experiment has proven that there are very few zeolite crystals growing on the surface of the unseeded carbon support by in situ synthesis. This is attributed to the reason that the surface of carbon materials has very few functional groups such as –OH, –COOH, – CO –, etc. [16]. From the SEM images of the carbon seeded using slipcasting technique in 1 wt.% seed ethanol solution for 30 s (Fig. 2a). It is evident that a continuous and smooth seed layer on the rough carbon surface is formed. The seed layer thickness is around 5 Am and also this thickness can be adjusted by controlling slip-casting time. The intrusion of some seeds into the large voids can increase the adhesion between the seed layer and the carbon surface. The surface property and roughness of the carbon are greatly improved by seeding in seed ethanol solution. Otherwise, it is found from our experiment that few seeds are deposited on the surface of the carbon by seeding in 2 wt.% seed water solution. The reason for this is due to the bad wettability of the carbon surface in the seed water solution. After regrowth by hydrothermal synthesis from clear solution, a continuous, dense NaA zeolite membrane with
Fig. 2. SEM images of the porous carbon tube support seeded using slip-casting in seed ethanol solution: (a) surface, (b) cross section.
X. Zhang et al. / Materials Letters 58 (2004) 2223–2226
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Fig. 3. SEM images of the NaA membrane regrown on the seeded carbon support: (a) surface, (b) cross section.
Fig. 4. XRD patterns of (a) the carbon support, (b) the carbon support seeded in seed ephanol solution, (c) the regrown NaA membrane on the seeded carbon support, (d) the standard NaA zeolite powder.
around 4 Am thickness is formed by crystals growing outward from the surface of the seed layer (Fig. 3). The zeolite crystals of the surface are very uniform and intergrown very well. The thickness of the zeolite layer can be easily controlled by modifying the synthesis conditions. The XRD spectra of the samples from Fig. 4 show that there exist no zeolite peaks on the carbon support (Fig. 4a); however, both the seeded carbon support (Fig. 4b) and the regrown seeded carbon support (Fig. 4c) exhibit strong zeolite peaks. The XRD patterns of Fig. 4b and c are consistent with the standard zeolite NaA structure (Fig. 4d), but with different relative peak intensities. This confirms that the existence of a seed layer on the support after seeding and a NaA membrane layer on the seeded support after regrowth which results in the stronger peaks.
and can be suitable for synthesizing various types of composite-zeolite membranes by modifying seed types, synthesis solution and conditions. The composite-zeolite membranes have potential applications in catalysis and separation.
Acknowledgements We are grateful for the financial support by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, the Dalian University of Technology (1000-893305).
References 4. Conclusion In summary, the present paper reports on the preparation of a composite carbon-zeolite NaA membrane using a simple process. This method is simpler and convenient
[1] W.J.W. Bakker, F. Kapteijn, J. Poppe, J.A. Moulijn, J. Membr. Sci. 117 (1 – 2) (1996) 57. [2] J. Sterte, S. Mintova, G. Zhang, B.J. Schoeman, Zeolites 18 (5 – 6) (1997) 387. [3] K. Aoki, K. Kusakabe, S. Morooka, Ind. Eng. Chem. Res. 39 (2000) 2245.
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X. Zhang et al. / Materials Letters 58 (2004) 2223–2226
[4] L.T.Y. Au, W.Y. Mui, P.S. Lau, C. Tellez, K.L. Yeung, Microporous Mesoporous Mater. 47 (2001) 203. [5] Y.S. Yan, M.E. Davis, G.R. Gavalas, Ind. Eng. Chem. Res. 34 (1995) 1652. [6] X. Zhang, J. Wang, H. Liu, C. Liu, K. Yeung, Sep. Purif. Technol. 32 (2003) 151. [7] Z. Lai, G. Bonilla, I. Diaz, J. Nery, K. Sujaoti, M. Amat, E. Kokkoli, O. Terasaki, R. Thompson, M. Tsapatsis, D. Vlachos, Science 300 (2003) 456. [8] M.D. Jia, K.W. Peinemann, R.D. Behling, J. Membr. Sci. 73 (1992) 119. [9] J.C. Jansen, J.H. Koegler, H. van Bekkum, H.P.A. Calis, C.M. van den Bleek, F. Kapteijn, J.A. Moulijn, E.R. Geus, N. van der Puil, Microporous Mesoporous Mater. 21 (1998) 213. [10] R. Ryoo, S.H. Joo, M. Kruk, M. Jaroniec, Adv. Mater. 13 (9) (2001) 677. [11] A.B. Fuertes, J. Membr. Sci. 177 (2000) 9.
[12] V.M. Linkov, R.D. Sanderson, E.P. Jacobs, J. Membr. Sci. 95 (1994) 93. [13] M. Ogawa, Y. Nakano, J. Membr. Sci. 162 (1999) 189. [14] V.C. Geiszler, W.J. Koros, Ind. Eng. Chem. Res. 35 (1996) 2999. [15] R. vander Vaart, H. Bosch, K. Keizer, T. Reith, Microporous Mater. 9 (1997) 203. [16] J. Garcia-Martinez, D. Cazorla-Amoros, A. Linares-Solano, Y.S. Lin, Microporous Mesoporous Mater. 42 (2001) 255. [17] S.P.J. Smith, V.M. Linkov, R.D. Sanderson, L.F. Petrik, C.T.O. Connor, K. Keiser, Microporous Mater. 4 (1995) 385. [18] V. Valtchev, B.J. Schoeman, J. Hedlund, S. Mintova, J. Sterte, Zeolites 17 (1996) 408. [19] A. Berenguer-Murcia, J. Garcia-Martiez, D. Cazorla-Amoros, A. Linares-Solano, A.B. Fuertes, Microporous Mesoporous Mater. 59 (2003) 147. [20] X. Zhang, K.L. Yeung. Microporous Mesoporous Mater., in review.