- Email: [email protected]
Hydrothermal synthesis of NaA zeolite membrane together with microwave heating and conventional heating
Available online at www.sciencedirect.com
Materials Letters 61 (2007) 5129 – 5132 www.elsevier.com/locate/matlet
Hydrothermal synthesis of NaA zeolite membrane together with microwave heating and conventional heating Aisheng Huang a,⁎, Weishen Yang b a
b
Department of Chemistry, Tongji University, Shanghai 200092, China State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China Received 25 January 2007; accepted 2 April 2007 Available online 19 April 2007
Abstract Uniform and dense NaA zeolite membrane was prepared by hydrothermal synthesis method together with microwave heating and conventional heating. The properties of the as-synthesized zeolite membrane were investigated by XRD, SEM and pervaporation evaluation for dehydration of 95 wt.% isopropanol/water mixture at 343 K, respectively. After microwave heating, the α-Al2O3 support surface was covered with homogeneous zeolite nuclei, which facilitated to form uniform, pure and dense NaA zeolite membrane in the following conventional heating process. High quality NaA zeolite membrane, i.e., with a separation factor (water/isopropanol) of 10,000 and a flux of 1.44 Kg/(m2 h), could be hydrothermal synthesized together with microwave heating and conventional heating. © 2007 Elsevier B.V. All rights reserved. Keywords: Composite materials; Crystal growth; Thin film
1. Introduction In the last two decades, many efforts have been made aiming to synthesis and application of the zeolite membranes for their excellent properties. Several synthesis strategies and methods have been developed, such as in-situ hydrothermal synthesis [1–4], secondary growth [5–7], vapor phase transport [8], dry gel conversion [9] and microwave synthesis [10]. The in-situ hydrothermal synthesis is the best-studied method, in which the porous support is immersed into the synthesis solution, and then the membrane is formed by direct crystallization. However, in this method the quality of the as-synthesized membrane significantly depends on the characteristics of the support surface [11]. It is usually difficult to prepare high quality zeolite membrane by insitu hydrothermal synthesis directly. The secondary growth method, which firstly proposed by Lovallo et al. [5], exhibits many advantages, such as better control over membrane microstructure (thickness, orientation) and higher reproducibility [7,12]. Recently, a new synthesis method named microwave synthesis has been developed for synthesis of zeolite membranes. ⁎ Corresponding author. Tel.: +86 021 65988570; fax: +86 021 65982287. E-mail address: [email protected] (A. Huang). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.04.017
Compared with the conventional hydrothermal synthesis, microwave synthesis exhibits many advantages, including a very short synthesis time, uniform and small crystal sizes and broad synthesis composition. Up to date, LTA [10,13], Sodalite [14], FAU [15], MFI [16], SAPO-5 [17] and AlPO4-5 [18] zeolite membranes have been synthesized by microwave synthesis method. However, It is not easy to prepare high performance zeolite membranes only by use of microwave synthesis. Recently, It was also proved that in-situ aging is necessary for microwave synthesis of LTA zeolite membrane without seeding [13]. In this paper, we report a novel synthesis stratagem for hydrothermal synthesis of NaA zeolite membrane together with microwave heating and conventional heating. The effect of microwave heating procedure on the membrane formation and pervaporation properties of the NaA zeolite membrane is investigated. 2. Experimental 2.1. Synthesis of NaA zeolite membrane Schematic diagram for the synthesis of NaA zeolite membrane together with microwave heating and conventional heating is illustrated schematically in Fig. 1. Porous α-Al2O3
5130
A. Huang, W. Yang / Materials Letters 61 (2007) 5129–5132
tube (home-made: 11 mm in outer diameter, 7 mm in inner diameter, 70 mm in length, 0.5 ∼ 1.0 μm pore radius, about 40% porosity) was used as supports. The outer surface of the support was polished with 700 grit sand papers and was cleaned several times with deionized water in a Branson SB2200 ultrasonic cleaner. Before hydrothermal synthesis, the cleaned support was calcined in air at 673 K for 3 h. The solution for synthesizing NaA zeolite membrane was prepared according to the procedure reported previously [12]. The aluminate solution was prepared by dissolving sodium hydroxide in deionized water, then adding aluminum foil to the solution at room temperature. The silicate solution was prepared by mixing silica sol and deionized water at 333 K with vigorous stirring. After 10 min of stirring, the preheated aluminate solution was added with stirring to produce a clear and homogenous solution. The molar ratio of this mixture solution was 50Na2O:Al2O3:5SiO2:1000H2O. The α-Al2O3 support was sealed with two Teflon caps at both the ends and placed vertically in a Teflon autoclave. The synthesis solution was poured into the autoclave and the autoclave was sealed. Before conventional heating, the autoclave was put in a microwave oven (Haier, HR-8801M) with a working frequency of 2450 MHz. The synthesis solution was quickly heated to 363 K and then held at invariable temperature for 25 min. After microwave synthesis, the autoclave was put in an air oven immediately and the crystallization was carried out. After crystallizing 4 h at 363 K, the solution was decanted off and the membrane was thoroughly washed with deionized water, and then dried in air at 423 K for 3 h. 2.2. Characterization of NaA zeolite membrane The structure of the as-synthesized zeolite membrane was confirmed by X-ray diffraction (XRD) patterns. XRD was carried out on a Rigaku D max/rB power diffractometer using CuKα radiation operating at 40 Kv and 50 mA. The morphology and thickness of the as-synthesized zeolite membrane were examined by scanning electron microscopy (SEM). The SEM
Fig. 2. XRD pattern of the NaA zeolite membrane:(a) XRD pattern of the NaA zeolite membrane:(a) prepared with microwave heating; (b) prepared together with microwave heating and conventional heating; (c) prepared with conventional heating. (n) NaA zeolite, (x) hydroxy-sodalite zeolite, (•) α-Al2O3.
photographs were obtained on a JEM-1200E scanning electron microscopy. The pervaporation properties were evaluated for dehydration of 95 wt.% isopropanol/water mixtures at 343 K. The apparatus used for the pervaporation experiments is illustrated schematically in elsewhere [19]. The isopropanol/water mixtures were fed to the out side of the zeolite membrane in the membrane model. The inside of the membrane was evacuated with a vacuum pump. Two cold traps with liquid N2 cooling were used to collect the permeate. The compositions of the feed and the permeate were analyzed by gas chromatogram (HP5890). The total flux (J), the component flux (Ji) and the separation factor (α) are defined as respectively: J¼
xi;p xj;f W Ji ¼ Jxi;p ai1j ¼ d DtA xi;f xi;n
Where W is total weight of the permeate (Kg), Δt is collecting time (h), A is separation area of the membrane, xi,p is the weight fraction of species i in the permeate and xi,f is the weight fraction of species i in the feed. 3. Results and discussion
Fig. 1. Schematic diagram for synthesis of NaA zeolite membrane together with microwave heating and conventional heating method.
Fig. 2a and b shows the XRD pattern of the as-synthesized zeolite membrane prepared with 25 min microwave heating and with the following 4 h conventional heating, respectively. As shown in Fig. 2a, the peaks of NaA zeolite appeared besides those of α-Al2O3 support, indicated purity NaA zeolite layer was formed on support surface after microwave heating. As shown in Fig. 2b, It can be seen that the intensity of the peaks of the NaA zeolite increased after the following 4 h conventional heating, contributing to a further growth of the NaA zeolite layer. In addition, no peaks other than those of NaA zeolite and α-Al2O3 support were detected in the as-synthesized membrane, indicating high pure NaA zeolite membrane could be prepared together with microwave heating and conventional heating. One explanation is large numbers of zeolite particles are rapidly produced with microwave heating, thus supplying more nucleus centers on the support surface, which are benefit to restrain from forming impure crystalline phase.
A. Huang, W. Yang / Materials Letters 61 (2007) 5129–5132
Fig. 3a and b show the SEM images of the as-synthesized NaA zeolite membrane after microwave heating. As shown in Fig. 3a and b, after microwave synthesis, the support was covered with uniform and small zeolite particles, with crystals size of about 2 ∼ 3 μm, but there were no continuous zeolite membrane formed judged by the image of the cross-section. Fig. 3c and d show the SEM images of the assynthesized NaA zeolite membrane prepared with the following 4 h conventional heating. As shown in Fig. 3c and d, after the following hydrothermal synthesis, the support surface was completely covered with uniform and compact NaA zeolite crystals. The zeolite crystals were found to be highly inter-grown and no observable inter-crystalline gaps presented. The surface of the as-synthesized membrane was very smooth with a thickness of about 10 μm as revealed from the crosssection.
5131
Fig. 2c show the XRD pattern of the as-synthesized zeolite membrane directly prepared with 4 h conventional heating. It can be seen that, some crystal phase other than those of NaA zeolite and αAl2O3 support were detected, which indicated that NaA zeolite crystals transformed to other types crystals. Fig. 3e and f show the SEM images of the NaA zeolite membrane directly prepared with 4 h conventional heating. As shown in Fig. 3e and f, the crystals sizes were not uniform, and some of these larger zeolite crystals seem almost detached from the zeolite layer. The growth of zeolite crystals on the support surface seems to be less ordered in the direct hydrothermal synthesis, and the surface of the as-synthesized membrane was very rough and loose. Moreover, it can be seen that cabbage-like spherical crystals as well as octahedral crystals was formed among the cubic NaA zeolite crystals, indicating that NaA zeolite crystals transformed to other types crystals.
Fig. 3. SEM images of the NaA zeolite membrane: (a) (b) prepared with microwave heating; (c) (d) prepared together with microwave heating and conventional heating; (e) (f) prepared with conventional heating.
5132
A. Huang, W. Yang / Materials Letters 61 (2007) 5129–5132
Table 1 Pervaporation properties of the as-synthesized zeolite membrane Codes Synthesis method
Properties of the membranes Membrane αwater/isopropanol Flux thickness (μm) (kg/m2 h)
1 2 3 4[12] 5[19]
MH for 25 min at 363 K MH for 25 min + CH for 4 h at 363 K CH for 4 h at 363 K Secondary growth 24 h 333 K EPD for 6 h at 363 K
/ 10
28.5 10,000
3.16 1.44
11 12
171 10,000
1.59 1.38
3281
1.24
7
MH: microwave heating; CH: conventional heating.
the abundant zeolite nuclei facilitated to form uniform, pure and dense NaA zeolite membrane in the following conventional heating process. The as-synthesized NaA zeolite membrane exhibited good pervaporation properties, i.e., with the separation factor (water/isopropanol) of 10,000 and the flux of 1.44 Kg/(m2 h). Acknowledgements This work was supported by the National Science Foundation of China (20607015) and Program for Young Excellent Talents in Tongji University (2006KJ057). References
This observation was in good agreement with the XRD patterns of the NaA zeolite membrane. Table 1 shows pervaporation properties of the as-synthesized membrane. As shown in Table 1, after 25 min microwave heating at 363 K, the as-synthesized NaA zeolite membrane exhibit poor pervaporation properties, i.e., the separation factor (water/isopropanol) was only 28.5 although the flux was high to 3.16 Kg/(m2 h). When the following 4 h conventional heating was carried out, the pervaporation properties of the as-synthesized membrane improved. The separation factor (water/ isopropanol) increases to 10,000, and the flux was 1.44 Kg/(m2 h). When the as-synthesized zeolite membrane was directly prepared by hydrothermal synthesis method, there was no dense membrane formed on the support surface and NaA zeolite crystals transformed to other crystals. These resulted in poor pervaporation properties of the assynthesized membrane compared with that prepared together with microwave heating and conventional heating. The separation factor (water/isopropanol) and flux was 171 and 1.59 Kg/(m2 h), respectively.
4. Conclusion Uniform and dense NaA zeolite membranes were prepared on the α-Al2O3 support together with microwave heating and conventional heating. The α-Al2O3 support surface was covered with homogeneous zeolite nuclei after microwave heating, and
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
Y. Yan, M.E. Davis, G.R. Gavalas, Ind. Eng. Chem. Res. 34 (1995) 165. J. Sterte, S. Mintova, G. Zhang, B.J. Schoeman, Zeolites 18 (1997) 387. T. Sano, H. Yanagishita, Y. Kiyozumi, et al., J. Membr. Sci. 95 (1994) 221. M. Kondo, M. Komori, H. Kita, K.I. Okamota, J. Membr. Sci. 133 (1997) 133. M.C. Lovallo, M. Tsapatsis, AICHE J. 42 (1996) 3020. R. Lai, G.R. Gavalas, Ind. Eng. Chem. Res. 37 (1998) 4275. L.C. Boudreau, J.A. Kuck, M. Tsapatsis, J. Membr. Sci. 152 (1999) 41. J. Dong, T. Dow, X. Zhao, L. Gao, J. Chem. Commun. (1992) 1056. Y.H. Ma, Y.J. Zhou, R. Poladi, E. Engwall, Sep. Purif. Technol. 25 (2001) 235. X.C. Xu, W.S. Yang, J. Liu, L.W. Lin, Adv. Mater. 12 (3) (2000) 195. V. Valtchev, S. Mintova, Zeolites 15 (1995) 171. A.S. Huang, Y.S. Lin, W.S. Yang, J. Membr. Sci. 245 (2004) 41. Y. Li, H. Chen, J. Liu, W. Yang, J. Membr. Sci. 277 (2006) 230. A. Julbe, J. Motuzas, F. Cazevielle, G. Volle, Sep. Purfi. Technol. 32 (2003) 139. K. Weh, M. Noack, I. Sieber, J. Caro, Microporous Mesoporous Mater. 54 (2002) 27. J. Motuzas, A. Julbe, R.D. Noble, et al., Microporous Mesoporous Mater. 92 (2006) 259. T. Tsai, H. Shih, S. Liao, K. Chao, Microporous Mesoporous Mater. 22 (1998) 333. S. Mintova, S. Mo, T. Bein, Chem. Mater. 10 (1998) 4030. A.S. Huang, W.S. Yang, Microporous Mesoporous Mater. 102 (2007) 58.
Materials Letters 61 (2007) 5129 – 5132 www.elsevier.com/locate/matlet
Hydrothermal synthesis of NaA zeolite membrane together with microwave heating and conventional heating Aisheng Huang a,⁎, Weishen Yang b a
b
Department of Chemistry, Tongji University, Shanghai 200092, China State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China Received 25 January 2007; accepted 2 April 2007 Available online 19 April 2007
Abstract Uniform and dense NaA zeolite membrane was prepared by hydrothermal synthesis method together with microwave heating and conventional heating. The properties of the as-synthesized zeolite membrane were investigated by XRD, SEM and pervaporation evaluation for dehydration of 95 wt.% isopropanol/water mixture at 343 K, respectively. After microwave heating, the α-Al2O3 support surface was covered with homogeneous zeolite nuclei, which facilitated to form uniform, pure and dense NaA zeolite membrane in the following conventional heating process. High quality NaA zeolite membrane, i.e., with a separation factor (water/isopropanol) of 10,000 and a flux of 1.44 Kg/(m2 h), could be hydrothermal synthesized together with microwave heating and conventional heating. © 2007 Elsevier B.V. All rights reserved. Keywords: Composite materials; Crystal growth; Thin film
1. Introduction In the last two decades, many efforts have been made aiming to synthesis and application of the zeolite membranes for their excellent properties. Several synthesis strategies and methods have been developed, such as in-situ hydrothermal synthesis [1–4], secondary growth [5–7], vapor phase transport [8], dry gel conversion [9] and microwave synthesis [10]. The in-situ hydrothermal synthesis is the best-studied method, in which the porous support is immersed into the synthesis solution, and then the membrane is formed by direct crystallization. However, in this method the quality of the as-synthesized membrane significantly depends on the characteristics of the support surface [11]. It is usually difficult to prepare high quality zeolite membrane by insitu hydrothermal synthesis directly. The secondary growth method, which firstly proposed by Lovallo et al. [5], exhibits many advantages, such as better control over membrane microstructure (thickness, orientation) and higher reproducibility [7,12]. Recently, a new synthesis method named microwave synthesis has been developed for synthesis of zeolite membranes. ⁎ Corresponding author. Tel.: +86 021 65988570; fax: +86 021 65982287. E-mail address: [email protected] (A. Huang). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.04.017
Compared with the conventional hydrothermal synthesis, microwave synthesis exhibits many advantages, including a very short synthesis time, uniform and small crystal sizes and broad synthesis composition. Up to date, LTA [10,13], Sodalite [14], FAU [15], MFI [16], SAPO-5 [17] and AlPO4-5 [18] zeolite membranes have been synthesized by microwave synthesis method. However, It is not easy to prepare high performance zeolite membranes only by use of microwave synthesis. Recently, It was also proved that in-situ aging is necessary for microwave synthesis of LTA zeolite membrane without seeding [13]. In this paper, we report a novel synthesis stratagem for hydrothermal synthesis of NaA zeolite membrane together with microwave heating and conventional heating. The effect of microwave heating procedure on the membrane formation and pervaporation properties of the NaA zeolite membrane is investigated. 2. Experimental 2.1. Synthesis of NaA zeolite membrane Schematic diagram for the synthesis of NaA zeolite membrane together with microwave heating and conventional heating is illustrated schematically in Fig. 1. Porous α-Al2O3
5130
A. Huang, W. Yang / Materials Letters 61 (2007) 5129–5132
tube (home-made: 11 mm in outer diameter, 7 mm in inner diameter, 70 mm in length, 0.5 ∼ 1.0 μm pore radius, about 40% porosity) was used as supports. The outer surface of the support was polished with 700 grit sand papers and was cleaned several times with deionized water in a Branson SB2200 ultrasonic cleaner. Before hydrothermal synthesis, the cleaned support was calcined in air at 673 K for 3 h. The solution for synthesizing NaA zeolite membrane was prepared according to the procedure reported previously [12]. The aluminate solution was prepared by dissolving sodium hydroxide in deionized water, then adding aluminum foil to the solution at room temperature. The silicate solution was prepared by mixing silica sol and deionized water at 333 K with vigorous stirring. After 10 min of stirring, the preheated aluminate solution was added with stirring to produce a clear and homogenous solution. The molar ratio of this mixture solution was 50Na2O:Al2O3:5SiO2:1000H2O. The α-Al2O3 support was sealed with two Teflon caps at both the ends and placed vertically in a Teflon autoclave. The synthesis solution was poured into the autoclave and the autoclave was sealed. Before conventional heating, the autoclave was put in a microwave oven (Haier, HR-8801M) with a working frequency of 2450 MHz. The synthesis solution was quickly heated to 363 K and then held at invariable temperature for 25 min. After microwave synthesis, the autoclave was put in an air oven immediately and the crystallization was carried out. After crystallizing 4 h at 363 K, the solution was decanted off and the membrane was thoroughly washed with deionized water, and then dried in air at 423 K for 3 h. 2.2. Characterization of NaA zeolite membrane The structure of the as-synthesized zeolite membrane was confirmed by X-ray diffraction (XRD) patterns. XRD was carried out on a Rigaku D max/rB power diffractometer using CuKα radiation operating at 40 Kv and 50 mA. The morphology and thickness of the as-synthesized zeolite membrane were examined by scanning electron microscopy (SEM). The SEM
Fig. 2. XRD pattern of the NaA zeolite membrane:(a) XRD pattern of the NaA zeolite membrane:(a) prepared with microwave heating; (b) prepared together with microwave heating and conventional heating; (c) prepared with conventional heating. (n) NaA zeolite, (x) hydroxy-sodalite zeolite, (•) α-Al2O3.
photographs were obtained on a JEM-1200E scanning electron microscopy. The pervaporation properties were evaluated for dehydration of 95 wt.% isopropanol/water mixtures at 343 K. The apparatus used for the pervaporation experiments is illustrated schematically in elsewhere [19]. The isopropanol/water mixtures were fed to the out side of the zeolite membrane in the membrane model. The inside of the membrane was evacuated with a vacuum pump. Two cold traps with liquid N2 cooling were used to collect the permeate. The compositions of the feed and the permeate were analyzed by gas chromatogram (HP5890). The total flux (J), the component flux (Ji) and the separation factor (α) are defined as respectively: J¼
xi;p xj;f W Ji ¼ Jxi;p ai1j ¼ d DtA xi;f xi;n
Where W is total weight of the permeate (Kg), Δt is collecting time (h), A is separation area of the membrane, xi,p is the weight fraction of species i in the permeate and xi,f is the weight fraction of species i in the feed. 3. Results and discussion
Fig. 1. Schematic diagram for synthesis of NaA zeolite membrane together with microwave heating and conventional heating method.
Fig. 2a and b shows the XRD pattern of the as-synthesized zeolite membrane prepared with 25 min microwave heating and with the following 4 h conventional heating, respectively. As shown in Fig. 2a, the peaks of NaA zeolite appeared besides those of α-Al2O3 support, indicated purity NaA zeolite layer was formed on support surface after microwave heating. As shown in Fig. 2b, It can be seen that the intensity of the peaks of the NaA zeolite increased after the following 4 h conventional heating, contributing to a further growth of the NaA zeolite layer. In addition, no peaks other than those of NaA zeolite and α-Al2O3 support were detected in the as-synthesized membrane, indicating high pure NaA zeolite membrane could be prepared together with microwave heating and conventional heating. One explanation is large numbers of zeolite particles are rapidly produced with microwave heating, thus supplying more nucleus centers on the support surface, which are benefit to restrain from forming impure crystalline phase.
A. Huang, W. Yang / Materials Letters 61 (2007) 5129–5132
Fig. 3a and b show the SEM images of the as-synthesized NaA zeolite membrane after microwave heating. As shown in Fig. 3a and b, after microwave synthesis, the support was covered with uniform and small zeolite particles, with crystals size of about 2 ∼ 3 μm, but there were no continuous zeolite membrane formed judged by the image of the cross-section. Fig. 3c and d show the SEM images of the assynthesized NaA zeolite membrane prepared with the following 4 h conventional heating. As shown in Fig. 3c and d, after the following hydrothermal synthesis, the support surface was completely covered with uniform and compact NaA zeolite crystals. The zeolite crystals were found to be highly inter-grown and no observable inter-crystalline gaps presented. The surface of the as-synthesized membrane was very smooth with a thickness of about 10 μm as revealed from the crosssection.
5131
Fig. 2c show the XRD pattern of the as-synthesized zeolite membrane directly prepared with 4 h conventional heating. It can be seen that, some crystal phase other than those of NaA zeolite and αAl2O3 support were detected, which indicated that NaA zeolite crystals transformed to other types crystals. Fig. 3e and f show the SEM images of the NaA zeolite membrane directly prepared with 4 h conventional heating. As shown in Fig. 3e and f, the crystals sizes were not uniform, and some of these larger zeolite crystals seem almost detached from the zeolite layer. The growth of zeolite crystals on the support surface seems to be less ordered in the direct hydrothermal synthesis, and the surface of the as-synthesized membrane was very rough and loose. Moreover, it can be seen that cabbage-like spherical crystals as well as octahedral crystals was formed among the cubic NaA zeolite crystals, indicating that NaA zeolite crystals transformed to other types crystals.
Fig. 3. SEM images of the NaA zeolite membrane: (a) (b) prepared with microwave heating; (c) (d) prepared together with microwave heating and conventional heating; (e) (f) prepared with conventional heating.
5132
A. Huang, W. Yang / Materials Letters 61 (2007) 5129–5132
Table 1 Pervaporation properties of the as-synthesized zeolite membrane Codes Synthesis method
Properties of the membranes Membrane αwater/isopropanol Flux thickness (μm) (kg/m2 h)
1 2 3 4[12] 5[19]
MH for 25 min at 363 K MH for 25 min + CH for 4 h at 363 K CH for 4 h at 363 K Secondary growth 24 h 333 K EPD for 6 h at 363 K
/ 10
28.5 10,000
3.16 1.44
11 12
171 10,000
1.59 1.38
3281
1.24
7
MH: microwave heating; CH: conventional heating.
the abundant zeolite nuclei facilitated to form uniform, pure and dense NaA zeolite membrane in the following conventional heating process. The as-synthesized NaA zeolite membrane exhibited good pervaporation properties, i.e., with the separation factor (water/isopropanol) of 10,000 and the flux of 1.44 Kg/(m2 h). Acknowledgements This work was supported by the National Science Foundation of China (20607015) and Program for Young Excellent Talents in Tongji University (2006KJ057). References
This observation was in good agreement with the XRD patterns of the NaA zeolite membrane. Table 1 shows pervaporation properties of the as-synthesized membrane. As shown in Table 1, after 25 min microwave heating at 363 K, the as-synthesized NaA zeolite membrane exhibit poor pervaporation properties, i.e., the separation factor (water/isopropanol) was only 28.5 although the flux was high to 3.16 Kg/(m2 h). When the following 4 h conventional heating was carried out, the pervaporation properties of the as-synthesized membrane improved. The separation factor (water/ isopropanol) increases to 10,000, and the flux was 1.44 Kg/(m2 h). When the as-synthesized zeolite membrane was directly prepared by hydrothermal synthesis method, there was no dense membrane formed on the support surface and NaA zeolite crystals transformed to other crystals. These resulted in poor pervaporation properties of the assynthesized membrane compared with that prepared together with microwave heating and conventional heating. The separation factor (water/isopropanol) and flux was 171 and 1.59 Kg/(m2 h), respectively.
4. Conclusion Uniform and dense NaA zeolite membranes were prepared on the α-Al2O3 support together with microwave heating and conventional heating. The α-Al2O3 support surface was covered with homogeneous zeolite nuclei after microwave heating, and
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
Y. Yan, M.E. Davis, G.R. Gavalas, Ind. Eng. Chem. Res. 34 (1995) 165. J. Sterte, S. Mintova, G. Zhang, B.J. Schoeman, Zeolites 18 (1997) 387. T. Sano, H. Yanagishita, Y. Kiyozumi, et al., J. Membr. Sci. 95 (1994) 221. M. Kondo, M. Komori, H. Kita, K.I. Okamota, J. Membr. Sci. 133 (1997) 133. M.C. Lovallo, M. Tsapatsis, AICHE J. 42 (1996) 3020. R. Lai, G.R. Gavalas, Ind. Eng. Chem. Res. 37 (1998) 4275. L.C. Boudreau, J.A. Kuck, M. Tsapatsis, J. Membr. Sci. 152 (1999) 41. J. Dong, T. Dow, X. Zhao, L. Gao, J. Chem. Commun. (1992) 1056. Y.H. Ma, Y.J. Zhou, R. Poladi, E. Engwall, Sep. Purif. Technol. 25 (2001) 235. X.C. Xu, W.S. Yang, J. Liu, L.W. Lin, Adv. Mater. 12 (3) (2000) 195. V. Valtchev, S. Mintova, Zeolites 15 (1995) 171. A.S. Huang, Y.S. Lin, W.S. Yang, J. Membr. Sci. 245 (2004) 41. Y. Li, H. Chen, J. Liu, W. Yang, J. Membr. Sci. 277 (2006) 230. A. Julbe, J. Motuzas, F. Cazevielle, G. Volle, Sep. Purfi. Technol. 32 (2003) 139. K. Weh, M. Noack, I. Sieber, J. Caro, Microporous Mesoporous Mater. 54 (2002) 27. J. Motuzas, A. Julbe, R.D. Noble, et al., Microporous Mesoporous Mater. 92 (2006) 259. T. Tsai, H. Shih, S. Liao, K. Chao, Microporous Mesoporous Mater. 22 (1998) 333. S. Mintova, S. Mo, T. Bein, Chem. Mater. 10 (1998) 4030. A.S. Huang, W.S. Yang, Microporous Mesoporous Mater. 102 (2007) 58.