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Novel SrCe0.75Zr0.20Tm0.05O3−δ membrane for hydrogen separation
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Chinese Chemical Letters 21 (2010) 369–372 www.elsevier.com/locate/cclet
Novel SrCe0.75Zr0.20Tm0.05O3d membrane for hydrogen separation Wen Hui Yuan a,*, Ling Ling Mao a, Li Li b a
b
School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China College of Environmental Science and Engineering, South China University of Technology, Guangzhou 510640, China Received 25 May 2009
Abstract Dense ceramic membranes with protonic and electronic conductivity have attracted considerable interest in recent years. In this paper, the powders of SrCe0.75Zr0.20Tm0.05O3d were synthesized via the liquid citrate method, and the membranes of SrCe0.75Zr0.20Tm0.05O3d were prepared by pressing followed by sintering. X-ray diffraction (XRD) was used to characterize the phase structure of both the powder and sintered membrane. The microstructure of the sintered membranes was studied by scanning electron microscopy (SEM). Hydrogen permeation through the SrCe0.75Zr0.20Tm0.05O3d membranes was carried out using gas permeation setup at 900 8C. Hydrogen permeation flux of SrCe0.75Zr0.20Tm0.05O3d membrane reaches up to 0.042 mL/ min cm2 at H2 partial pressure of 0.4 atm. The hydrogen permeation fluxes obtained in this paper are similar to that of SrCe0.95Tm0.05O3d, and Zr doping can increase mechanical strength of SrCe0.75Zr0.20Tm0.05O3d membranes and the resistance to reducing circumstance. # 2009 Wen Hui Yuan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Hydrogen permeation; Ceramic membrane; Perovskite; Mixed conductor
Dense ceramic membranes with protonic and electronic conductivity have been attracting significant attention over the past few decades, due to their potential application in hydrogen-based energy, petrochemical processes, fuel cells, separation membrane, and other technologies [1]. In the early 1980s, Iwahara et al. [2] firstly reported proton conduction in SrCeO3 based perovskite-type materials. Later doped BaCeO3, SrZrO3, CaZrO3 as well as SrTiO3 were also found to exhibit both protonic and electronic conductivity [3]. In most cases, trivalent dopants in SrCeO3 or BaCeO3 play an essential role in the proton or electron transport due to pure SrCeO3 and BaCeO3 exhibiting only low electronic conductivity. For instance, electrical properties of Eu, Ho, Mg, Sc, Sm, Tm, Y, Yb or Tb doped SrCeO3 were studied [4]. Song et al. [5] investigated the hydrogen permeability of SrCe1xMxO3d (x = 0.05, M = Eu, Sm) (SCM). It was found that the hydrogen permeation flux is about 0.0035 mL/min cm2 at 850 8C under dry condition. Hydrogen permeation flux of 1.6 mm thick SrCe0.95Tm0.05O3d membrane is about 0.039 mL/min cm2, under upstream H2 partial pressure of 0.1 atm [6]. In general, SrCeO3 protonic conductors have high conductivities but rather poor chemical and thermal stability, which decomposes to SrCO3 and CeO2. In contrast, SrZrO3 protonic conductors are stable but have rather low conductivity. The combination of Ce and Zr may have both high protonic conductivity and
* Corresponding author. E-mail address: [email protected] (W.H. Yuan). 1001-8417/$ – see front matter # 2009 Wen Hui Yuan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2009.11.002
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good chemical stability. From this point of view, Matzke and Cappadonia [7] reported conductivity and chemical stability of Zr-substituted, Yb-doped strontium cerates. When a portion of B-site Ce(IV) is replaced by Tm(III) and Zr(IV), oxygen vacancies VO and electronic holes (h) are created in order to maintain the charge neutrality. Tm2 O3 ! 2TmCe0 þ 3OX (1) O þ VO The electronic hopping mechanism of semiconductor [8] for pure SrCeO3 between Ce and Tm ions can be represented by: Ce4þ þ h , Ce3þ
Tm2þ þ h , Tm3þ Zr is stable without charge transfer, so Zr doping perovskite can increase mechanical strength of SrCe0.75Zr0.20Tm0.05O3d membrane and the resistance to reducing circumstance than other M (M represents rare earth elements) doped SrCeO3. In this paper, novel SrCe0.75Zr0.20Tm0.05O3d was synthesized by the liquid citrate method. A total of 0.1 mol appropriate metal nitrates of cerium nitrate, strontium nitrate, zirconium nitrate, thulium nitrate, in stoichiometry was dissolved in 250 mL distilled water. After adding 0.15 mol citric acid, the solution was heated to 100 8C and stirred for 4 h for polymerization reactions to take place, and a sticky gel was obtained. After drying, the precursor was precalcined at 450 8C for 10 h. The resulting powders were ground and calcined at 1000 8C for 10 h to obtain a pure perovskite phase. The calcined powders were pressed into disks under a hydraulic pressure of 10 MPa. The final SrCe0.75Zr0.20Tm0.05O3d membranes were sintered at 1525 8C for 20 h with a heating and cooling rate of 2 8C/min. The hydrogen permeation experiments were carried out on the self-made high temperature permeation cell. All tests were conducted with silver seals, and the membranes were sealed within the temperature range of 948–953 8C below the melting temperature of silver about 962 8C. During the hydrogen permeation experiment, H2/He mixture were introduced to the feed side, while Ar was used as the sweep gas on the permeate side. The downstream chamber effluent was analyzed with the HP, 5890 GC, equipped with a Carboxen 1000 column. The hydrogen permeation flux was calculated as following [9]: pffiffiffi 2F H2 C He F 2 (2) J H2 ðmL=min cm Þ ¼ CH2 S F He Where CH2 , CHe are the hydrogen and helium concentrations calculated from GC calibration. F H2 and F He are the flow rates of H2 and He in the feed side respectively. F is the total flow rate of the effluent gases in the permeate side which could be measured by a soap film meter. S is the membrane area. The leakage was evaluated by measuring the amount of He in the permeate stream. In our experiments, the leakage is lower than 2%, which was subtracted when the hydrogen permeation flux was calculated. X-ray diffraction (XRD) patterns of SrCe0.75Zr0.20Tm0.05O3d powder calcined at 1000 8C for 10 h and of the membrane sintered at 1525 8C for 20 h show that both the powder and the membrane exhibit single-phase of pervoskite-type SrCeO3 orthorhombic system, and indicate a uniform distribution of Zr and Tm in the lattice of SrCe0.75Zr0.20Tm0.05O3d, as shown in Fig. 1. Fig. 2 shows scanning electron microscope (SEM) views of SrCe0.75Zr0.20Tm0.05O3d membranes sintered at 1520 8C for 20 h. A dense membrane with clear crystal could be prepared, Fig. 2A and B shows the SEM micrograph of the fractured cross-section, no hole was observed in the bulk phase of the membrane which indicating that the membrane was compact. The hydrogen permeation fluxes through the SrCe0.75Zr0.20Tm0.05O3d membrane with a thickness of 1.20 mm as a function of H2 Partial Pressure (atm) were measured using Ar as sweep gas at 900 8C, as shown in Fig. 3. It can be seen that the hydrogen permeation fluxes increase with the upstream H2 partial pressure, due to increasing H2 partial pressure increases the net driving force for H2 permeation and the concentration of protons and electrons on the feed side. At H2 partial pressure of 0.4 atm, the hydrogen permeation flux reaches up to 0.042 mL/min cm2, which is similar to that of SrCe0.95Tm0.05O3d with the same condition. Zr doping perovskite can obviously increase mechanical strength of SrCe0.75Zr0.20Tm0.05O3d membranes and the resistance to reducing circumstance. The SrCe0.75Zr0.20Tm0.05O3d membrane shows appreciable hydrogen permeability. A hydrogen permeation flux of 0.042 mL/min cm2 can be obtained at 900 8C, at H2 partial pressure of 0.4 atm. Although the hydrogen
W.H. Yuan et al. / Chinese Chemical Letters 21 (2010) 369–372
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Fig. 1. XRD patterns of SrCe0.75Zr0.20Tm0.05O3d powder and sintered membrane.
Fig. 2. SEM pictures of the sintered membrane: (A) surface view; (B) cross-section of the broken membrane.
Fig. 3. Effect of upstream partial pressure of H2 on the H2 permeation flux of SrCe0.75Zr0.20Tm0.05O3d membrane. Membrane thickness: 1.2 mm, feed side: H2 + He = 100 mL/min, sweep side: Ar 30 mL/min.
fluxes through 1.2 mm thick membranes are not high enough for practical separations, hydrogen permeation flux can be improved by more effective permeator design and decreasing the membrane thickness to the micrometer range or improving the surface exchange kinetics by coating the membrane surface with a porous layer [10].
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W.H. Yuan et al. / Chinese Chemical Letters 21 (2010) 369–372
Acknowledgment This work was supported by Joint Funds of NSFC-Guangdong (No. U0834004), NSFC (No. 20976057) and Guangdong Provincial Natural Science Funding (No. 06025657). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
H. Iwahara, Solid State Ionics 125 (1–4) (1999) 271. F.S. Anthony, V.M. Michael, Nonporous Inorganic Membranes, WILEY-VCH Verlag GmbH & Co. KGaA, 2006,, p. 49. C. Zuo, S.E. Dorris, U. Balachandran, et al. Chem. Mater. 18 (2006) 4648. X. Wei, Y.S. Lin, Solid State Ionics 178 (2008) 1804. S.J. Song, E.D. Wachsman, J. Rhodes, et al. Solid State Ionics 167 (2004) 99. X. Qi, Y.S. Lin, Solid State Ionics 130 (2000) 149. T. Matzke, M. Cappadonia, Solid State Ionics 86–88 (1996) 659. R.J. Phillips, N. Bonanos, F.W. Poulsen, et al. Solid State Ionics 125 (1–4) (1999) 389. M.Y. Cai, Z. Li, H.H. Wang, et al. Chin. Chem. Lett. 19 (2008) 1256. S. Cheng, V.K. Gupta, Y.S. Lin, Solid State Ionics 176 (2005) 2653.
Chinese Chemical Letters 21 (2010) 369–372 www.elsevier.com/locate/cclet
Novel SrCe0.75Zr0.20Tm0.05O3d membrane for hydrogen separation Wen Hui Yuan a,*, Ling Ling Mao a, Li Li b a
b
School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China College of Environmental Science and Engineering, South China University of Technology, Guangzhou 510640, China Received 25 May 2009
Abstract Dense ceramic membranes with protonic and electronic conductivity have attracted considerable interest in recent years. In this paper, the powders of SrCe0.75Zr0.20Tm0.05O3d were synthesized via the liquid citrate method, and the membranes of SrCe0.75Zr0.20Tm0.05O3d were prepared by pressing followed by sintering. X-ray diffraction (XRD) was used to characterize the phase structure of both the powder and sintered membrane. The microstructure of the sintered membranes was studied by scanning electron microscopy (SEM). Hydrogen permeation through the SrCe0.75Zr0.20Tm0.05O3d membranes was carried out using gas permeation setup at 900 8C. Hydrogen permeation flux of SrCe0.75Zr0.20Tm0.05O3d membrane reaches up to 0.042 mL/ min cm2 at H2 partial pressure of 0.4 atm. The hydrogen permeation fluxes obtained in this paper are similar to that of SrCe0.95Tm0.05O3d, and Zr doping can increase mechanical strength of SrCe0.75Zr0.20Tm0.05O3d membranes and the resistance to reducing circumstance. # 2009 Wen Hui Yuan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Hydrogen permeation; Ceramic membrane; Perovskite; Mixed conductor
Dense ceramic membranes with protonic and electronic conductivity have been attracting significant attention over the past few decades, due to their potential application in hydrogen-based energy, petrochemical processes, fuel cells, separation membrane, and other technologies [1]. In the early 1980s, Iwahara et al. [2] firstly reported proton conduction in SrCeO3 based perovskite-type materials. Later doped BaCeO3, SrZrO3, CaZrO3 as well as SrTiO3 were also found to exhibit both protonic and electronic conductivity [3]. In most cases, trivalent dopants in SrCeO3 or BaCeO3 play an essential role in the proton or electron transport due to pure SrCeO3 and BaCeO3 exhibiting only low electronic conductivity. For instance, electrical properties of Eu, Ho, Mg, Sc, Sm, Tm, Y, Yb or Tb doped SrCeO3 were studied [4]. Song et al. [5] investigated the hydrogen permeability of SrCe1xMxO3d (x = 0.05, M = Eu, Sm) (SCM). It was found that the hydrogen permeation flux is about 0.0035 mL/min cm2 at 850 8C under dry condition. Hydrogen permeation flux of 1.6 mm thick SrCe0.95Tm0.05O3d membrane is about 0.039 mL/min cm2, under upstream H2 partial pressure of 0.1 atm [6]. In general, SrCeO3 protonic conductors have high conductivities but rather poor chemical and thermal stability, which decomposes to SrCO3 and CeO2. In contrast, SrZrO3 protonic conductors are stable but have rather low conductivity. The combination of Ce and Zr may have both high protonic conductivity and
* Corresponding author. E-mail address: [email protected] (W.H. Yuan). 1001-8417/$ – see front matter # 2009 Wen Hui Yuan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2009.11.002
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W.H. Yuan et al. / Chinese Chemical Letters 21 (2010) 369–372
good chemical stability. From this point of view, Matzke and Cappadonia [7] reported conductivity and chemical stability of Zr-substituted, Yb-doped strontium cerates. When a portion of B-site Ce(IV) is replaced by Tm(III) and Zr(IV), oxygen vacancies VO and electronic holes (h) are created in order to maintain the charge neutrality. Tm2 O3 ! 2TmCe0 þ 3OX (1) O þ VO The electronic hopping mechanism of semiconductor [8] for pure SrCeO3 between Ce and Tm ions can be represented by: Ce4þ þ h , Ce3þ
Tm2þ þ h , Tm3þ Zr is stable without charge transfer, so Zr doping perovskite can increase mechanical strength of SrCe0.75Zr0.20Tm0.05O3d membrane and the resistance to reducing circumstance than other M (M represents rare earth elements) doped SrCeO3. In this paper, novel SrCe0.75Zr0.20Tm0.05O3d was synthesized by the liquid citrate method. A total of 0.1 mol appropriate metal nitrates of cerium nitrate, strontium nitrate, zirconium nitrate, thulium nitrate, in stoichiometry was dissolved in 250 mL distilled water. After adding 0.15 mol citric acid, the solution was heated to 100 8C and stirred for 4 h for polymerization reactions to take place, and a sticky gel was obtained. After drying, the precursor was precalcined at 450 8C for 10 h. The resulting powders were ground and calcined at 1000 8C for 10 h to obtain a pure perovskite phase. The calcined powders were pressed into disks under a hydraulic pressure of 10 MPa. The final SrCe0.75Zr0.20Tm0.05O3d membranes were sintered at 1525 8C for 20 h with a heating and cooling rate of 2 8C/min. The hydrogen permeation experiments were carried out on the self-made high temperature permeation cell. All tests were conducted with silver seals, and the membranes were sealed within the temperature range of 948–953 8C below the melting temperature of silver about 962 8C. During the hydrogen permeation experiment, H2/He mixture were introduced to the feed side, while Ar was used as the sweep gas on the permeate side. The downstream chamber effluent was analyzed with the HP, 5890 GC, equipped with a Carboxen 1000 column. The hydrogen permeation flux was calculated as following [9]: pffiffiffi 2F H2 C He F 2 (2) J H2 ðmL=min cm Þ ¼ CH2 S F He Where CH2 , CHe are the hydrogen and helium concentrations calculated from GC calibration. F H2 and F He are the flow rates of H2 and He in the feed side respectively. F is the total flow rate of the effluent gases in the permeate side which could be measured by a soap film meter. S is the membrane area. The leakage was evaluated by measuring the amount of He in the permeate stream. In our experiments, the leakage is lower than 2%, which was subtracted when the hydrogen permeation flux was calculated. X-ray diffraction (XRD) patterns of SrCe0.75Zr0.20Tm0.05O3d powder calcined at 1000 8C for 10 h and of the membrane sintered at 1525 8C for 20 h show that both the powder and the membrane exhibit single-phase of pervoskite-type SrCeO3 orthorhombic system, and indicate a uniform distribution of Zr and Tm in the lattice of SrCe0.75Zr0.20Tm0.05O3d, as shown in Fig. 1. Fig. 2 shows scanning electron microscope (SEM) views of SrCe0.75Zr0.20Tm0.05O3d membranes sintered at 1520 8C for 20 h. A dense membrane with clear crystal could be prepared, Fig. 2A and B shows the SEM micrograph of the fractured cross-section, no hole was observed in the bulk phase of the membrane which indicating that the membrane was compact. The hydrogen permeation fluxes through the SrCe0.75Zr0.20Tm0.05O3d membrane with a thickness of 1.20 mm as a function of H2 Partial Pressure (atm) were measured using Ar as sweep gas at 900 8C, as shown in Fig. 3. It can be seen that the hydrogen permeation fluxes increase with the upstream H2 partial pressure, due to increasing H2 partial pressure increases the net driving force for H2 permeation and the concentration of protons and electrons on the feed side. At H2 partial pressure of 0.4 atm, the hydrogen permeation flux reaches up to 0.042 mL/min cm2, which is similar to that of SrCe0.95Tm0.05O3d with the same condition. Zr doping perovskite can obviously increase mechanical strength of SrCe0.75Zr0.20Tm0.05O3d membranes and the resistance to reducing circumstance. The SrCe0.75Zr0.20Tm0.05O3d membrane shows appreciable hydrogen permeability. A hydrogen permeation flux of 0.042 mL/min cm2 can be obtained at 900 8C, at H2 partial pressure of 0.4 atm. Although the hydrogen
W.H. Yuan et al. / Chinese Chemical Letters 21 (2010) 369–372
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Fig. 1. XRD patterns of SrCe0.75Zr0.20Tm0.05O3d powder and sintered membrane.
Fig. 2. SEM pictures of the sintered membrane: (A) surface view; (B) cross-section of the broken membrane.
Fig. 3. Effect of upstream partial pressure of H2 on the H2 permeation flux of SrCe0.75Zr0.20Tm0.05O3d membrane. Membrane thickness: 1.2 mm, feed side: H2 + He = 100 mL/min, sweep side: Ar 30 mL/min.
fluxes through 1.2 mm thick membranes are not high enough for practical separations, hydrogen permeation flux can be improved by more effective permeator design and decreasing the membrane thickness to the micrometer range or improving the surface exchange kinetics by coating the membrane surface with a porous layer [10].
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W.H. Yuan et al. / Chinese Chemical Letters 21 (2010) 369–372
Acknowledgment This work was supported by Joint Funds of NSFC-Guangdong (No. U0834004), NSFC (No. 20976057) and Guangdong Provincial Natural Science Funding (No. 06025657). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
H. Iwahara, Solid State Ionics 125 (1–4) (1999) 271. F.S. Anthony, V.M. Michael, Nonporous Inorganic Membranes, WILEY-VCH Verlag GmbH & Co. KGaA, 2006,, p. 49. C. Zuo, S.E. Dorris, U. Balachandran, et al. Chem. Mater. 18 (2006) 4648. X. Wei, Y.S. Lin, Solid State Ionics 178 (2008) 1804. S.J. Song, E.D. Wachsman, J. Rhodes, et al. Solid State Ionics 167 (2004) 99. X. Qi, Y.S. Lin, Solid State Ionics 130 (2000) 149. T. Matzke, M. Cappadonia, Solid State Ionics 86–88 (1996) 659. R.J. Phillips, N. Bonanos, F.W. Poulsen, et al. Solid State Ionics 125 (1–4) (1999) 389. M.Y. Cai, Z. Li, H.H. Wang, et al. Chin. Chem. Lett. 19 (2008) 1256. S. Cheng, V.K. Gupta, Y.S. Lin, Solid State Ionics 176 (2005) 2653.