A Study on the Degradation and Recovery Mechanisms of Perovskite

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Article

A Study on the Degradation and Recovery Mechanisms of Perovskite Ba Co Fe Nb O Membrane under CO-Containing Atmosphere 1.0

0.7

0.2

0.1

3-#

2

Jianfang Zhou, Xia Tang, Chengzhang Wu, He Wang, Yuwen Zhang, Weizhong Ding, Yonggang Jin, and Chenghua Sun J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b05920 • Publication Date (Web): 09 Oct 2015 Downloaded from http://pubs.acs.org on October 10, 2015

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The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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The Journal of Physical Chemistry

A Study on the Degradation and Recovery Mechanisms of Perovskite Ba1.0Co0.7Fe0.2Nb0.1O3-δ Membrane Under CO2-containing Atmosphere

Jianfang Zhou,† Xia Tang,† Chengzhang Wu,*,† He Wang,† Yuwen Zhang,† Weizhong Ding,† Yonggang Jin,‡ and Chenghua Sun§

†

State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai

200072, China ‡

CSIRO Energy Flagship, PO Box 883, Kenmore, QLD 4069, Australia

§

School of Chemistry, Monash University, Clayton, VIC 3800, Australia

ACS Paragon Plus Environment


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ABSTRACT: In this study, the degradation and recovery mechanisms of perovskite Ba1.0Co0.7Fe0.2Nb0.1O3−δ (BCFN) membrane under a CO2–containing atmosphere were investigated. The oxygen permeability of BCFN membrane is degraded quickly with pure CO2 gas in the sweep side and then would be partially recovered if the sweep gas changes to 5 % CO2. It is found that the existence of oxygen can stabilize the cubic perovskite structure of BCFN. Isotopic exchange test confirms the fast exchange of oxygen between the lattice oxygen of BCFN bulk and the oxygen in the formed carbonate. Pores or cracks are generated during the dynamical exchange of oxygen and serve as the permeable channels of oxygen, resulting in the partial recovery of oxygen permeability under 5 % CO2 concentration. INTRODUCTION Oxy-fuel combustion, with concentrated CO2 gas streams produced from the combustion of fossil fuel using CO2-diluted O2, enables efficient carbon storage and capture (CCS) in Integrated Gasification Combined Cycle (IGCC) plants.1,2 To provide pure oxygen for the combustion, oxygen transport membranes reactor (OTMR) has been developed, which is more efficient than the traditional technology based on cryogenic processes or pressure swing adsorption (PSA). Among various materials, mixed ionic-electronic conductors (MIEC), which are mostly oxygen-deficient perovskite oxides with ABO3-δ structure, are particularly attractive due to their high oxygen

permeation

flux,3,4

such

as

Ba0.5Sr0.5Co0.8Fe0.2O3−δ

(BSCF),5-7

La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF)8,9 and Ba1.0Co0.7Fe0.2Nb0.1O3−δ (BCFN)10-12. Currently, one of the major challenges is the CO2 corrosion of OTM materials when the transported O2 is swept using the plant flue gas, which always contains concentrated carbon dioxide and steam. MIEC with ABO3-δ structure contains rare-earth or alkaline-earth metals at its A-site, such as Ba, Sr or La, Pr, etc. It is well known that alkaline-earth metals would be easily reacted with CO2 to form carbonate, which may cover the surface of MIEC membrane and thus suppress the oxygen permeation.13-18 For instance, for the above mentioned LSCF,9 BSCF15 or BCFN18 membranes, a sudden drop of oxygen permeation flux has been observed when pure CO2 is introduced as the sweep gas. Interestingly, the oxygen flux could


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be totally recovered when inert gas is switched back for sweeping at high temperature. Tong et al. firstly investigated such recovery behaviour in the BaCo0.4Fe0.4Zr0.2O3−δ membrane, which is pre-poisoned by highly concentrated CO2 for 15 h and found that oxygen flux could reach or even exceed the original value before poisoning.13 Similar result was obtained subsequently by Arnold et al15 , who studied the recovery performance of BSCF at 875 °C, and a permeation flux of 1.9 ml·cm-2·min-1 or even higher was achieved in each cycle by He sweeping. In addition, similar recovery behaviour has been widely observed in BCFN membrane,16 dual phase membranes17 and K2NiF4 type membranes19, and generally it is believed that the decomposition of formed carbonates during the CO2 calcining is responsible for this. It is speculated that the porous and rough layer formed during the decomposition of carbonates is no longer blocking the oxygen permeation, or even is in favour of the permeation of oxygen. In recent years, our group has paid much attentions on oxygen separation11,20 and also on partial oxidation of CH4 in coke oven gas to syngas by using Ba1.0Co0.7Fe0.2Nb0.1O3-δ disk membrane reactor21,22 or one-end tubular membrane reactor.12 The microstructure evolution and oxidation states of transit metals of BCFN materials calcined under CO2 atmosphere were systematically studied.23 Moreover, although thermodynamics decomposition pressure of the formed carbonate of BaCO3 at experimental temperature is close to 100 ppm, we found that the oxygen flux recovery can happen readily when the sweep gas is changed from high concentration of CO2 to 1.0 % CO2.24 Obviously, the flux recovery in the low concentration of CO2 could not be simply attributed to the thermal decomposition of carbonate. This study aims to achieve an advanced understanding of the effect of CO2 concentration and oxygen partial pressure on the oxygen permeation of BCFN membrane. As presented below, the decomposition of carbide layer and fast oxygen exchange between the BCFN main body and the carbide coat have been fully investigated. It is found that the pores and cracks in the carbide layer play the key role for the observed recovery when CO2 with low partial pressure is employed as the seeping gas.



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EXPERIMENTAL SECTION Sample preparation Ba1.0Co0.7Fe0.2Nb0.1O3−δ powder was synthesized by a conventional solid state reaction process from the reagents of BaCO3, Co3O4, Fe2O3 and Nb2O5 (all reagents purchased from Sinopharm, with a purity > 99 %). Firstly, stoichiometric reagents were weighted and fully mixed through a ball-milling (ZrO2 balls) for 24 h. Then the powder was uniaxially pressed under a pressure of 75 MPa, and the pressed pellet was calcined in air at 950 °C for 10 h to form the oxide with cubic perovskite structure. The synthesized oxides were then ball milled again for 24 h to get BCFN powder. The calcined powder was uniaxially pressed at 100 MPa, and the green disk membranes (20 mm in diameter) were sintered at 1110 °C for 10 h in air, with the actual densities of the sintered membranes exceeding 95 % of the theoretical densities in all cases. Microstructure characterization The phase structure of oxides was characterized with an X-ray diffractometer (XRD, Rigaku DLMAX-2200) using Cu Kα radiation. Membrane microstructure was observed by field emission scanning electron microscope (FE-SEM, JSM-6700F). O2/CO2 temperature programmed desorption Temperature programmed desorption (TPD) was measured on the flowing reaction system using a mass spectrometer (Hiden, HPR20) for the detection of the desorbed compounds. The BCFN powder (100 mg) was pre-treated for 1 h at different temperatures under CO2 (10 %)/ Ar (90 %) or CO2 (10 %)/O2 (9 %)/ Ar (81 %) gas stream, followed by cooling down to room temperature in the same atmosphere. The BCFN samples after sintering under different atmosphere at various temperatures were hereinafter referred as abbreviations shown in Table 1. Finally, the post-treated samples were heated up to 950 °C at a heating rate of 10 °C/min using He stream as the carrier gas for TPD measurements. Oxygen permeation properties


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Oxygen permeation of the disk-shaped membranes was measured using a high-temperature permeation apparatus with the gas analysis conducted by gas chromatography (GC, Varian CP-3800).11 After being polished to the thickness of 1.0 mm, the membrane was sealed onto a quartz glass tube by a silver ring. The effective area exposed to gas was 1.30 cm2. In order to create an oxygen partial pressure gradient across the membrane, ambient air (110 ml/min) was fed to the feed side and helium (80 ml/min, 99.995%) was applied at the sweep side. The gas flow rates were controlled by the mass flow controller. Permeation measurements were performed from 900 °C to 800 °C at a cooling rate of 1 °C/min and no leakage was detected during the measurements. For BCFN membranes, it usually takes about 2 h to reach a steady state, but in some cases the oxygen flux would deteriorate with time (see below text). Therefore, all data for comparison were collected within 2 h. TABLE 1 Abbreviations for the BCFN powder after sintering under different atmosphere at various temperatures (Ar as balance gas). Abbreviation

Temp. (°C)

Atmosphere

BCFN-CO2-600

600

10 % CO2

BCFN-CO2-700

700

10 % CO2

BCFN-CO2-800

800

10 % CO2

BCFN-CO2-900

900

10 % CO2

BCFN-CO2/O2-600

600

10% CO2/9% O2

BCFN-CO2/O2-700

700

10% CO2/9% O2

BCFN-CO2/O2-800

800

10% CO2/9% O2

BCFN-CO2/O2-900

900

10% CO2/9% O2

Isotopic exchange In-situ C18O2 Isotopic exchange was performed on the TPD-MS setup. Firstly, BCFN powder (150 mg) was annealed at 850 °C for 2 h in He to remove possible contaminations, then annealed at the same temperature for 4 h under a mixture gas



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of C18O2/He in a volume ratio of 1:1 and cooled down to the room temperature in the same atmosphere. After the isotope gas in tube line was totally exchanged with the flowing He, TPD-MS measurement was conducted based on the same procedure as above mentioned to monitor the desorption of O2 and CO2. RESULTS AND DISCUSSION Oxygen permeability Figure 1 shows the dependence of oxygen permeation flux on the concentration of CO2 on the sweep side. Here, a thickness of 1.0 mm of BCFN membrane is used for the oxygen permeation measurement at 850 °C by using air as the feed gas and He and/or CO2 as the sweep gas, with a flow rate of 110 ml/min on the feed side and 80 ml/min in the sweep side, respectively. As shown in Figure 1, if pure He is applied as the sweep gas, a stable oxygen permeation flux through the BCFN membrane is obtained, with a constant flux of 1.78 ml·cm-2·min-1. When a small amount of CO2 (5 %) is introduced into the sweeping helium gas, the oxygen permeation flux slowly decreases from 1.78 ml·cm-2·min-1 to 0.22 ml·cm-2·min-1 within 10 h, and then remains stable. However, if the sweep gas directly changes from pure He to pure CO2, the oxygen permeation flux would drop down to zero quickly, indicating that the oxygen permeation process is totally inhibited. If the sweep gas is switched back from pure CO2 to pure He, the oxygen permeation flux would recover back to 1.6 ml·cm-2·min-1 within 600 min. In addition, it is worth noting that, when the sweep gas changes to low CO2 concentration of 5 % after former oxygen permeation for 600 min with pure CO2 sweeping, the oxygen permeation flux will be partly recovered, gradually increasing to 0.15 ml·cm-2·min-1 after a long time of 2000 min, and then the oxygen permeation flux will no longer increase with the increase of permeation time.


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2.1

-2

-1

JO2(ml⋅cm ⋅min )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


pure He

1.8 1.5 1.2

from pure CO2 to He

0.9 from He to 5%CO2

0.6 0.3 pure CO2

0.0

-0.3

from pure CO2 to 5%CO2

0

500

1000

1500

2000

2500

Time (min) Figure 1. Time dependence of oxygen permeation fluxes on the concentration of CO2 in the sweep side. Conditions: flow rate of air as feed gas is 110 ml/min; flow rate of He or CO2-containing gas as sweep gas is 80 ml/min. Microstructural investigations Oxygen permeation results show that oxygen flux is partially recovered for the BCFN membrane after the sweep gas changes from pure CO2 to 5 % CO2. Moreover, the results also show that the final oxygen fluxes in the two cases of 5 % CO2 in the sweep side have no much difference, regardless of how the partial pressure of CO2 reaches: lowering down from pure CO2 or raising up from pure He. To clarify the possible mechanism, the microstructure of spent BCFN membrane was identified by XRD and SEM. Figure 2 presents the XRD patterns of the as-prepared BCFN membrane and the BCFN membranes after oxygen permeation measurement with different sweeping conditions. For the membrane after oxygen permeation swept by 5.0 % CO2 for 60 h, as shown in Figure 2b, the main phase still is the cubic perovskite oxide. Besides of the perovskite oxide, the reflection peaks of BaCoO2.93 with orthorhombic structure are also appeared. In addition, the diffraction peaks of BaCO3 and Ba(CO3)0.9(SO4)0.123 with very weak intensities can also be observed. Nomura et al.25 reported that cubic perovskite phase was formed for oxides of Ba0.95Ca0.05Co1-xFexO3-δ when x > 0.4, whereas, the orthorhombic structure of BaCoO2.93 could be the dominant phase while x < 0.4 for the oxides. In the case of BCFN, low concentration of CO2 seems to destabilize the cubic structure of BCFN and



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results in the new phase formation of BaCoO2.93. Figure 2c shows the diffraction peaks of BCFN membrane swept by pure CO2 for 10 h, which are clearly different from those diffraction peaks collected from the membrane by using 5.0 % CO2 as sweep gas. The strongest diffraction peak at 2θ = 27.7° is assigned to the (002) reflection of witherite BaCO3, indicating that there is a preferred orientation at the refection. Another strong peak at 2θ = 57.3° could be indexed to the (004) plane, which is just the half interplanar spacing of (002) plane. Similar result was also reported by Yi et al., the XRD patterns for the pellets of BCFN442 and BCFN622 membranes annealed in CO2 at 900 °C showed that the formed BaCO3 was most likely preferentially oriented on the pellets surface.18 In this study, the peaks intensities of cubic BCFN are really weak after 10 h with pure CO2 in the sweep side. Followed the oxygen permeation test using pure CO2 for 10 h, the sweep gas was then shifted to 5.0 % CO2 or pure He for 60 h measurement. Afterwards, the permeate side of spent membranes was identified by XRD again and the patterns are shown in Figure 2d and Figure 2e, respectively. For the membrane which the sweep gas changes to low concentration of 5.0 % CO2, the intensities of preferentially orientated planes (002) and (004) decrease slightly but other diffraction peaks such as (111) and (021) plane of witherite appear. For the membrane which the sweep gas was shifted from pure CO2 to pure He for 60 h, as shown in Figure 2e, the diffraction peaks for witherite BaCO3 cannot be observed anymore, indicating that the formed witherite is decomposed. Moreover, after the decomposition of carbonate, the reflection peaks can be indexed to three phases: the major phase of original cubic perovskite, and the other two minor phases of orthorhombic Co-rich phase of BaCoO2.93 and hexagonal Fe-rich phase of BaFeO2.9. In addition, from the reflection peaks of cubic perovskite samples subjected by pure CO2 sweeping and the one treated with 5.0 % CO2 sweeping followed by oxygen permeation with pure CO2, it is clear that the peaks intensities are similar and really weak. To clarify whether the detected small peaks of cubic perovskite come from the surface or from the bulk due to the depth of X-ray detection, further investigations on the surface morphology and elemental distribution should be performed.


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a b c d e

Intensity (a.u.)

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Perovskite BaCoO2.93 BaFeO2.90 BaCO3 Ba(CO3)0.9(SO4)0.1

20

25

30

35

40 45 o 2θ ( )

50

55

60

Figure 2. XRD patterns of (a) as-prepared BCFN membrane, (b-e) permeate side of BCFN membrane after the oxygen permeation measurement with (b) 5.0 % CO2 for 60 h, (c) pure CO2 for 10 h, (d) 5.0 % CO2 for 60 h followed (c), (e) pure He for 60 h followed (c). BaCoO2.93: JCPDS 26-0144; BaFeO2.9: JCPDS 25-0068; BaCO3: JCPDS 71-2394; Ba(CO3)0.9(SO4)0.1: JCPDS 41-0631; CoO: JCPDS 43-1004 The microstructure evolution and elemental distribution of BCFN membranes after the oxygen permeation measurement using CO2 as sweep gas were then studied by SEM and EDX analyses. SEM images of the surface on the sweep side and fracture surface of membranes are shown in Figure 3. Grain boundaries cannot be observed anymore for all BCFN membranes after the oxygen permeation operation due to the CO2 corrosion (Figure 3a~3d). From the fracture surface view, the membrane with 5 % CO2 for 60 h only shows a very thin decomposed layer (Figure 3e). After using pure CO2 as the sweep gas for 10 h at 850 °C (Figure 3f), however, the decomposed layer with 20 ~30 μm thick has been found, no matter the following sweeping is by pure He or low partial pressure of CO2 (Figure 3g~3h). From the EDX results given in Table 2, we could obtain the elemental distribution of Ba, Co, Fe in the decomposed layer (only the three metallic elements were examined due to higher detection precision). In comparison of the atomic ratio of Ba/Co/Fe for above four treated membranes, it is almost same in the bulk zone of membranes and only a few differences in the middle position of decomposed layer. However, on the surface of membrane, for the membrane with pure CO2 for 10 h, Co and Fe elements can



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hardly be seen, indicating that a whole carbonate layer covered the membrane surface. This result implies that the detected diffraction peaks of cubic perovskite by XRD is from the bulk of BCFN due to the detection depth of X-ray is much deeper than the formed carbonate thickness. In addition, after recovering with pure He for 60 h, the atomic ratio of Ba/Co/Fe seems to be similar to that of the membrane with only treated by 5 % CO2 for 60 h, just the Co content is a little bit higher compared with that of bulk position. If the membrane was continuously swept by 5.0 % CO2 for 60 h followed pure CO2 for 10 h, the atomic ratio of Ba/Co/Fe is 1.00:0.14:0.02. In spite of the content of Co and Fe is very small, they can be redetected by electron probe anyway. In comparison of the images shown in Figure 3b and Figure 3c we can find that totally covered BaCO3 layer (Figure 3b) has broken (Figure 3c) when the sweep gas was switched to 5 % CO2 for 60 h from pure CO2. Therefore, the detected Co should be from below surface layer in the decomposed zone. The difference between XRD and EDX results may be attributed to the distinction of interaction depth of X-ray and electron beam, e.g., XRD patterns give signals not only from the surface but also the bulk. TABLE 2 Atomic ratio of Ba, Co, Fe obtained by EDXS at the membrane surface (area scan analysis) and fracture surface (point analysis) of spent membranes. s: membrane surface; m: middle position of decomposed layer; b: bulk of membrane. Normalized atomic ratio of Ba:Co:Fe in BCFN membrane is 1.0:0.7:0.2. with 5% CO2 for 60 h

with pure CO2 for 10 h

recovering with 5 % CO2 for 60 h

recovering with helium for 60 h

s

m

b

s

m

b

s

m

b

s

m

b

Ba

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

Co

0.87

0.79

0.75

0.01

0.77

0.75

0.14

0.80

0.77

0.90

0.78

0.75

Fe

0.20

0.23

0.22

0.00

0.22

0.22

0.02

0.12

0.22

0.21

0.20

0.22


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Figure 3. SEM images of permeate side of BCFN membranes after the oxygen permeation measurement with 5.0 % CO2 for 60 h (a, e), pure CO2 for 10 h (b, f), 5.0 % CO2 for 60 h followed pure CO2 for 10 h (c, g), pure He for 60 h followed pure CO2 for 10 h (d, h). Surface view shown on left and cross section view shown on right. It is worthy of note that, CO2 corrosion behaviour of BCFN membrane in the “static” mode (just annealed under CO2 atmosphere without oxygen permeation) is different from that of the membrane in the “permeation” mode (oxygen permeation test using CO2 as sweep gas). Figure 4 shows the XRD patterns of BCFN membrane



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pre-treated in the “static” mode for 20 h and in the “permeation” mode for 60 h under 5.0 % CO2 at 850 °C, respectively. It is clear to see that, in the static mode, except for the cubic phase, there are strong diffraction peaks for the phases of witherite BaCO3, sulfate stabilized BaCO3 and CoO. However, in the permeation mode, even after long time test of 60 h, the diffraction peaks intensities for the witherite BaCO3 and sulfate stabilized BaCO3 are very weak, the main phase is still the perovskite BCFN. These results imply that the permeated oxygen from feed side can stabilize the cubic structure and suppress the formation of carbonate. Given the formation of BaCO3 needs the participation of lattice oxygen, i.e., Ba2+ + O2- + CO2 = BaCO3, the existence of sulfate ion (around 900 ppm sulfur from the raw reagent of Fe2O3 existed as sulfate23) in BCFN membrane may exhibit the same effect as lattice oxygen, i.e., CO2 could “pump” sulfate ion and oxygen ion out to the surface to form sulfate stabilized BaCO3, Ba2+ + 0.9O2- + 0.1(SO4)2- + 0.9CO2 = Ba(CO3)0.9(SO4)0.1, which also explains that why the phase of BaSO4 is hardly observed for the spent membrane just using He as sweep gas.12 As reported by Arnold et al. and Xue et al., carbonate species can form on the surface of perovskite membrane when the sweep gases contain a certain content of CO2.15,17 When the sweep gas shifts back to pure He at high temperature, the formed carbonate will be decomposed. Accordingly, the degradation and recovery of the oxygen permeation flux are related to the formation and decomposition of carbonate, respectively.15,17 Interestingly, it does make sense for the case that the sweep gas changes from CO2 to inert gas like He. However, in the case of the sweep gas from pure CO2 to a certain pressure of CO2, the insulating carbonate layer may not decompose at the experimental temperature under the partial pressure of CO2. According to thermodynamics calculations, the partial pressure of CO2 for the decomposition of barium carbonate at 850 °C is less than 100 ppm. If the partial pressure of CO2 rises to 5 %, the decomposition temperature of BaCO3 would reach to 1232 °C, which is 382 °C higher than the oxygen permeation temperature. It is to say, BaCO3 definitely cannot decompose to BaO and CO2 at 850 °C under the pressure of 5 % CO2. Thus, why will there be a small amount of oxygen flux recovered with 5 % CO2 sweeping?


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a Intensity (a.u.)

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b Perovskite BaCoO2.93 BaCO3 Ba(CO3)0.9(SO4)0.1 CoO

15 18 21 24 27 30 33 36 39 42 45 48 o 2θ ( )

Figure 4. XRD patterns of the permeate side of BCFN membranes after (a) oxygen permeation measurement at 850 °C for 60 h using 5.0 % CO2 as sweep gas and (b) annealing at 850 °C under 5.0 % CO2 for 20 h. BaCoO2.93: JCPDS 26-0144; BaCO3: JCPDS 71-2394; Ba(CO3)0.9(SO4)0.1: JCPDS 41-0631; CoO: JCPDS 43-1004

Dependence of O2 partial pressure It is well acknowledged that oxygen permeation rate may be controlled by oxygen diffusion in the membrane bulk or the interfacial oxygen exchange or both. When the thickness of membrane is thicker than its critical thickness Lc (c = ⁄ , Do and k are oxygen anion diffusion coefficient and surface-exchange coefficient, respectively), the flux should be governed by bulk oxygen diffusion, and Wagner theory can be applied to this case: 26

= − ln

(1)

Where R is molar gas constant; T is temperature; F is Faraday constant; L is membrane thickness; ! and " are the oxygen partial pressure in sweep side and feed side, respectively; σ% and σ& are the electronic and ionic conductivity, respectively.



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Normally, the oxygen permeation of BCFN membrane with a thickness of 1.0 mm is controlled by the bulk oxygen diffusion and its conductivity is predominated by electronic conduction, i.e. σ% ≫ σ& .27 In this case the Wagner equation could be approximately simplified if an average value of σ& is taken. Thus, the oxygen permeation flux is directly proportional to σ& and ln( " / ! ). According to the simplified equation, the oxygen partial pressure ratio at the two sides of membrane could be the most significant factor in determining the oxygen permeation flux. At the temperature of oxygen permeation test, the oxygen partial pressure of different concentration of CO2 would be different. Hence, a Zirconia Oxygen Analyzer (MX-923, Muxin Analytical Instrument Co. Ltd.) was used to determine the oxygen partial pressure of pure CO2 and 5 % CO2 after flowing through a furnace with a temperature of 850 °C. As shown in Table 3, the average oxygen partial pressure is 16 ppm for 5 % CO2 stream and 43.2 ppm for pure CO2 (average of ten times measurements). The results indicate that the oxygen partial pressure in the sweep side decreases by 1.7 times while the sweep gas changes from pure CO2 to 5 % CO2. TABLE 3 Oxygen partial pressure for 5 % and pure CO2 at 850 °C. Average

CO2 concen.

Oxygen partial pressure (ppm)

5%

15.8 17.1 16.5 15.4 15.7 16.4 15.9 15.6 15.3 16.5

16.0

100%

47.0 45.6 40.3 39.1 39.7 43.5 44.5 46.5 42.3 43.6

43.2

(ppm)

To figure out the effect of the change of oxygen partial pressure ratio at two sides of membrane( " / ! ) due to the sweep gas shifts from pure CO2 to 5 % CO2, we may fix pure CO2 as the sweep gas and just increase the oxygen partial pressure in the feed side, same oxygen partial pressure ratio can also be obtained. Figure 5 shows the effect of O2 partial pressure in the feed gas and/or CO2 concentration in the sweep gas on the oxygen permeation properties through BCFN membrane. There are six stages totally. In the first two stages, the oxygen permeation flux drops down to zero with changing sweep gas from He to pure CO2. In the next three stages,


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the oxygen concentration in the feed side is enhanced from 21 % (air) to 40 %, 60 % and 100 %, but fix the CO2 concentration in the sweep side as pure CO2. Interestingly, although oxygen partial pressure in the feed side increases almost by 4 times, the oxygen permeation flux still keeps zero. At the last stage, when air and 5 % CO2 are introduced into the feed side and the sweep side, respectively, the oxygen permeation flux can be found again. In comparison of the oxygen partial pressure ratio ( " / ! ) at the last two stages, obviously, " / ! at the fifth stage is larger than that at the sixth stage. If the partial recovery of oxygen flux in the last stage is really governed by oxygen partial pressure ratio, a small amount of oxygen flux could also be monitored while the pure O2 is introduced into feed side in the fifth stage. 2.1

-2

-1

JO2(mlcm min )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


a

1.8

b

c

d

e

f

O2 con. at feed side

1.5

CO2 con. at sweep side

1.2 21% 0%

0.9

40% 60% 100% 100% 100% 100%

21% 100%

21% 5%

0.6 0.3 0.0 0

100

200

300

400

500

600

Time (min) Figure 5. Effect of O2 concentration in the feed gas and/or CO2 concentration in the sweep gas on the oxygen permeation properties of BCFN membrane. Conditions: total flow rate of feed gas is 110 ml/min; total flow rate of sweep gas is 80 ml/min. Numerators and denominators show the oxygen concentration and carbon dioxide concentration at two sides of membrane, respectively.

O2 and CO2 TPD In order to investigate the influence of sintering temperature and O2/CO2 partial pressure on the CO2 corrosion of BCFN materials, BCFN powder was firstly sintered in



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

pure CO2 (10 %) or mixed CO2 (10 %) and O2 (9 %) with Ar as the balance gas at various temperature of 600 °C, 700 °C, 800 °C and 900 °C, respectively. Then the calcined samples were examined by TPD-MS and X-ray diffraction measurement. Figure 6 shows the O2 and CO2 TPD profiles for all samples. It is well known that perovskite oxides will release lattice oxygen upon heating up. For as-prepared BCFN, O2 desorption occurs at about 400 °C and centred at 513 °C, which is related to the reduction of Co 4+ and/or Fe 4+ to Co 3+ and/or Fe 3+ (denoted as α-O2), and another desorption peak at around 828 °C is corresponding to the reduction of Co 3+ to Co 2+ (denoted as β-O2). For the samples calcined under 10 % CO2 atmosphere, with increasing the sintering temperature, the onset desorption temperature shifts to higher temperature, which are about 580 °C for BCFN-CO2-600, 664 °C for BCFN-CO2-700, 810 °C for BCFN-CO2-800, and about 915 °C for BCFN-CO2-900, respectively. Meanwhile, α-O2 desorption peak area, which represented the reduction degree of transition metal from oxidation state of +4 to +3, decreases when the sample calcined under CO2 atmosphere at 600 °C and 700 °C. Furthermore, at the elevated sintering temperature of 800 °C and 900 °C, α-O2 desorption peak disappears. It is worth noting that β-O2 desorption peak for BCFN pre-treated under 10 % CO2 at 600 °C and 700 °C seems to be the same as that of as-prepared BCFN (Figure 6a). In addition, CO2-TPD profiles as shown in Figure 6b display that CO2 desorption amount increases with increasing the sintering temperature, and the onset desorption temperatures of CO2 are around 660 °C ~ 700 °C. In comparison with the O2/CO2 desorption behaviour of samples annealed under pure CO2 atmosphere, the samples annealed under the O2/CO2 mixture exhibit different characteristics. O2-TPD profiles shown in Figure 6c show that O2 onset desorption temperatures of BCFN-CO2/O2-600 and BCFN-CO2/O2-700 are similar to those of BCFN-CO2-600 and BCFN-CO2-700, respectively. However, with the further increase of sintering temperature, the desorption temperature of O2 shifts to lower temperature, e.g., the sample of BCFN-CO2/O2-900 starts to desorb O2 at only 500 °C, which is about 415 °C lower than that of the sample of BCFN-CO2-900. Additionally, from the CO2-TPD profiles as shown in Figure 6b and 6d, it can be seen that the onset temperature of CO2 is almost same. Nevertheless, the CO2 desorption peak area


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Page 17 of 36

becomes smaller for the sample with O2/CO2 co-adsorbed. Moreover, when the sintering temperature increases to 900 °C, CO2 desorption peak area is even smaller than that of the sample treated at 600 °C.

o

(b)

600 C o 700 C o 800 C o 900 C

(a)

as prepared

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(c)

300

450

600

750

900

(d)

300

450

600

750

900

o

Temperature ( C)

Figure 6. O2 -TPD profiles (a, c) and CO2 -TPD profiles (b, d) of BCFN and BCFN powder after sintering at various temperatures of 600 °C, 700 °C, 800 °C and 900 °C under 10 % CO2 (top), 10 % CO2 /9 % O2 (bottom) atmosphere.

XRD measurement was also performed for all the calcined samples prepared for TPD and the patterns are shown in Figure 7. Except for the main phase of perovskite, witherite BaCO3 is also formed after CO2 treatment at various temperatures. It is clear to see that, on the one hand, with the increase of the sintering temperature under CO2 atmosphere, the amount of witherite BaCO3 is increased; on the other hand, O2 introduction is in favour of suppressing the witherite formation, which is remarkably reduced when the temperature rises to 900 °C.



:Witherite BaCO3

o

600 C

:CoO

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

o

700 C

o

800 C

●

:Perovskite

o

900 C

As prepared

20

Page 18 of 36

30

40

50

60

70

o

2θ ( ) Figure 7. XRD patterns of as-prepared BCFN and BCFN powder after sintering at various temperatures of 600 °C, 700 °C, 800 °C and 900 °C under 10 % CO2 (red color) or 10 % CO2 / 9 % O2 (blue color).

The increase of α-O2 onset desorption temperature implies the transition metal cations with a higher valence state are partially reduced when BCFN annealed under CO2-containing atmosphere, which is in good agreement with the result of that Co K-edge shifts to low energy under same treatment conditions.23 Above TPD and XRD results also illustrate that, BCFN particles may be completely covered and surrounded by carbonate layer at the temperature above 700 °C. Thus, prior to the decomposition, the carbonate layer would restrain lattice oxygen desorption, i.e., the desorption temperature of lattice oxygen is higher than that of CO2 desorption. However, the additional introduction of O2 during the sintering, will lead to O2 and CO2 competitive adsorption on the BCFN surface. In other words, O2 can stabilize the perovskite structure of BCFN, especially at high temperature like 900 °C.


Page 19 of 36

Isotopic exchange

16

C O2 16

Ion Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


18

C O O 18 C O2 16

18

O O 18 O2

200 300 400 500 600 700 800 900 o Temperature ( C) Figure 8. TPD-MS profiles of BCFN annealed in C18O2 at 850 °C for 4 h upon a heating rate of 10 °C/min. To gain the further insight into the recovery mechanism of oxygen permeation flux for the BCFN membrane with low concentration of CO2 sweeping, isotopic exchange technique was used for monitoring oxygen migration. Figure 8 shows the TPD-MS profiles of BCFN powder which was pre-annealed at 850 °C for 4 h under C18O2 isotopic gas. From carbon dioxide desorption profile, we can find that the intensity of desorption peaks decreases remarkably by the order of C16O2, C16O18O and C18O2. Moreover, oxygen signals shows that the desorption peak of 16O18O is much higher than that of

18

O2. It is undoubted that

18

O-labeled carbonate should be formed on

the surface of BCFN powder following the reaction of Ba2+ +

16 2-

O + C18O2 =

BaC16O18O2 when the BCFN powder is annealed in C18O2 isotopic gas atmosphere. If there is no oxygen exchange between carbonate and bulk cubic oxide, with the temperature increasing, only 16O2 from BCFN and C16O18O or C18O2 from carbonate of BaC16O18O2 could be detected by mass spectrometry. However, the MS profiles show that the strongest signal of carbon dioxide is C16O2, which is much higher than that of C16O18O or C18O2. In addition, both

16 18

O O and

18

O2 signals can also be observed,

suggesting that the fast oxygen ions exchange happens between carbonate and



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BCFN bulk. Interestingly, similar discovery was also reported by Tsuji et al.,28 who found that the bidentate carbonate migrates over the surface of basic metal oxides and the three oxygen atoms composing carbonate are entirely scrambled before desorption as CO2. Discussion Tejuca et al.29,30 reported that monodentate and bidentate carbonates are formed upon CO2 adsorption on perovskite oxides. In the case of oxygen permeation using CO2-containing gas as sweep gas, CO2 would be firstly adsorbed on the surface of membrane and then carbonate species would be formed. Therefore, the degradation of oxygen permeation flux by using CO2 as sweep gas for the MIEC perovskite membrane, particularly for the membrane with alkaline earth metals partly or fully occupied in A-site, could be attributed to the inhibition of the formed carbonate species. Several studies on the CO2 corrosion of BSCF or BCFN have been presented that the oxygen permeability vanished with pure CO2 sweeping, and then totally recovered with He sweeping.15-17,31 In addition, Tan et al.9 investigated the oxygen permeation behaviour of LSCF hollow fibre membranes with CO2 as sweep gas and they also found an immediate and sharp decrease in O2 flux. Similarly, after the CO2 sweep gas was switched to He, the oxygen permeation flux of LSCF membrane was recovered. Moreover, for the reason of the immediate poisoning effect of CO2, Tan et al. emphasized that the sharp drop of oxygen permeation flux should be resulted from the chemisorbed CO2 on the surface of membrane.9 We know, CO2 adsorption must be the negative effect in the oxygen permeation process due to the decrease of oxygen vacancy concentrations, which plays a vital role in the surface reactions for oxygen permeation. A direct evidence is, even for the CO2-stable materials, the oxygen flux decrease with the switch of the sweep gas from pure He to CO2.32,33 However, for the membrane materials with alkaline earth metals fully occupied in A-site, e.g. SCF or BCFN, TG results indicated that the kind of materials will be reacted with CO2 at high temperature quickly.34,35 Additionally, different to the membranes containing rare-earth metals, the oxygen permeation flux of these membranes will be decreased to zero soon with pure CO2 sweeping. Above results indicated that the poisoning effect of CO2 in oxygen permeation process for this kind


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of membrane is dominated by formed carbonates, which would be monodentate or bidentate carbonates caused by CO2 chemisorption in the initial stage, then would be the stable alkaline earth metal carbonate (BaCO3 or SrCO3). Besides of CO2 poisoning, the recovery mechanism in He is easily to understand because the formed carbonate will be decomposed in the inert gas at the experimental temperature. However, the recovery mechanism of oxygen permeation flux under low concentration of CO2 has never been reported before. According to the thermodynamics calculation, the whole covered barium carbonate starts to decompose at 1232 °C under 5 % CO2, i.e., distinguished from the carbonate decomposition behaviour occurred in the case of He sweeping, BaCO3 should not decompose at 850 °C in 5 % CO2 atmosphere, which is also proved by XRD result. However, the fact is that, oxygen permeation flux is partially recovered for BCFN membrane while the sweep gas changes from pure CO2 to 5 % CO2. Our results suggested that the oxygen permeability should not only be dominated by CO2 partial pressure in the sweep side, but also affected by the permeated oxygen from feed side. TPD profiles displayed that there is a competitive adsorption of O2/CO2 on BCFN powder, indicating that O2 existence restrains the degree of carbonate formation and stabilizes the cubic perovskite structure. Moreover, different phase components after BCFN membrane treated in the static mode and in the permeation mode also indicated that permeated oxygen could stabilize cubic structure. Additionally, isotopic exchange experiments gave the further evidence of oxygen exchange among the lattice oxygen of BCFN and the oxygen in carbonate, implying that the formed carbonate layer will be strongly influenced by adjacent BCFN oxides. Although carbonate can’t decompose under 5 % CO2 atmosphere at 850 °C, the fast exchange of oxygen ions between BCFN and carbonate might result in a dynamical equilibrium of carbonate decomposition and formation process. Under high CO2 partial pressure like pure CO2, a full coat of barium carbonate layer would always be existed, thus the oxygen permeability is completely shutoff. Nevertheless, if low partial pressure of CO2 (5 %) is applied, the dynamical exchange process of oxygen would provide a possibility for the generation of cracks or pores in the full coat layer of BaCO3. Once the holes or cracks are generated, they might be maintained under low partial



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

pressure of CO2 due to the permeated oxygen participation. SEM image of the sample after oxygen permeation with 5 % CO2 for 60 h followed pure CO2 sweeping gave the direct evidence for the speculation. Thus, a small amount of oxygen flux recovered due to the emerging cracks or holes in the permeate side. CONCLUSIONS The degradation and recovery mechanism of perovskite BCFN membrane under CO2 – containing atmosphere has been investigated in this study. We firstly confirmed the quick dropping down of the oxygen permeability of BCFN membrane when pure CO2 is employed as the sweep gas, which is essentially due to the full coating of barium carbonate layers. When the sweep gas is changed from pure CO2 to low partial pressure of CO2, the oxygen flux can be partially recovered. We further clarified that the oxygen permeability under low partial pressure of CO2 is dominated by not only the CO2 concentration, but also the permeated oxygen from feed side. The role contributed by CO2 is to restrain the carbonate decomposition, and fast oxygen exchange between BCFN bulk and its carbonate coat can generate cracks or pores in the carbonate layer. Once the pores or cracks are generated, they can be maintained due to the effect of permeated oxygen, which could stabilize the cubic perovskite structure. Therefore, pores and cracks generated under the low-CO2 sweeping has been identified as the effective channels for the oxygen permeation, which is the reason for the recovering behaviour observed at the low CO2 pressure.

AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]. Tel/Fax: +86 21 56338244 (C. Wu) Notes The authors declare no competing ﬁnancial interest.

ACKNOWLEDGEMENTS


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We gratefully acknowledge the financial supports from the National Natural Science Foundation of China (No. 51274139 and 51174133), Science and Technology Commission of Shanghai Municipality (11ZR1412900), the Innovation Program of Shanghai Municipal Education Commission (13YZ019) and Doctoral Fund of Ministry of Education of China (20123108120020). REFERENCES (1) Colombo, K. E.; Kharton, V. V.; Bolland, O. Simulation of an Oxygen Membrane-Based Gas Turbine Power Plant: Dynamic Regimes with Operational and Material Constraints. Energy Fuels 2010, 24, 590-608. (2) Smart, S.; Lin, C. X. C.; Ding, L.; Thambimuthu, K.; da Costa, J. C. D. Ceramic Membranes for Gas Processing in Coal Gasification. Energy Environ. Sci. 2010, 3, 268-278. (3) Sunarso, J.; Baumann, S.; Serra, J. M.; Meulenberg, W. A.; Liu, S.; Lin, Y. S.; Diniz da Costa, J. C. Mixed Ionic–electronic Conducting (MIEC) Ceramic-based Membranes for Oxygen Separation. J. Membr. Sci. 2008, 320, 13-41. (4) Zhang, K.; Sunarso, J.; Shao, Z. P.; Zhou, W.; Sun, C. H.; Wang, S. B.; Liu, S. M. Research Progress and Materials Selection Guidelines on Mixed Conducting Perovskite-type Ceramic Membranes for Oxygen Production. Rsc Advances 2011,

1, 1661-1676. (5) Shao, Z. P.; Yang, W. S.; Cong, Y.; Dong, H.; Tong, J. H.; Xiong, G. X. Investigation of the Permeation Behavior and Stability of a Ba0.5Sr0.5Co0.8Fe0.2O3-δ Oxygen Membrane. J. Membr. Sci. 2000, 172, 177-188. (6) Wang, H. H.; Cong, Y.; Yang, W. S. Oxygen Permeation Study in a Tubular Ba0.5Sr0.5Co0.8Fe0.2O3-δ Oxygen Permeable Membrane. J. Membr. Sci. 2002, 210, 259-271. (7) Arnold, M.; Gesing, T. M.; Martynczuk, J.; Feldhoff, A. Correlation of the Formation and the Decomposition Process of the BSCF Perovskite at Intermediate Temperatures. Chem. Mater. 2008, 20, 5851-5858. (8) Serra, J. M.; Garcia-Fayos, J.; Baumann, S.; Schulze-Kuppers, F.; Meulenberg, W. A. Oxygen Permeation through Tape-cast Asymmetric All-La0.6Sr0.4Co0.2Fe0.8O3-δ Membranes. J. Membr. Sci. 2013, 447, 297-305.



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(9) Tan, X. Y.; Liu, N.; Meng, B.; Sunarso, J.; Zhang, K.; Liu, S. M. Oxygen Permeation Behavior of La0.6Sr0.4Co0.8Fe0.2O3 Hollow Fibre Membranes with Highly Concentrated CO2 Exposure. J. Membr. Sci. 2012, 389, 216-222. (10) Harada, M.; Domen, K.; Hara, M.; Tatsumi, T. Oxygen-permeable Membranes of Ba1.0Co0.7Fe0.2Nb0.1O3-δ for Preparation of Synthesis Gas from Methane by Partial Oxidation. Chem. Lett. 2006, 35, 968-969. (11) Geng, Z.; Ding, W. Z.; Wang, H. H.; Wu, C. Z.; Shen, P. J.; Meng, X. Y.; Gai, Y. Q.; Ji, F. T. Influence of Barium Dissolution on Microstructure and Oxygen Permeation Performance of Ba1.0Co0.7Fe0.2Nb0.1O3-δ Membrane in Aqueous Medium. J.

Membr. Sci. 2012, 403, 140-145. (12) Zhang, Y. W.; Su, K.; Zeng, F. L.; Ding, W. Z.; Lu, X. G. A Novel Tubular Oxygen-permeable Membrane Reactor for Partial Oxidation of CH4 in Coke Oven Gas to Syngas. Int. J. Hydrogen Energy 2013, 38, 8783-8789. (13) Tong, J. H.; Yang, W. S.; Zhu, B. C.; Cai, R. Investigation of Ideal Zirconium-doped Perovskite-type Ceramic Membrane Materials for Oxygen Separation. J. Membr.

Sci. 2002, 203, 175-189. (14) Yi, J. X.; Feng, S. J.; Zuo, Y. B.; Liu, W.; Chen, C. S. Oxygen Permeability and Stability of Sr0.95Co0.8Fe0.2O3-δ in a CO2- and H2O- containing Atmosphere. Chem.

Mater. 2005, 17, 5856-5861. (15) Arnold, M.; Wang, H. H.; Feldhoff, A. Influence of CO2 on the Oxygen Permeation Performance and the Microstructure of Perovskite-type (Ba0.5Sr0.5)(Co0.8Fe0.2)O3-δ Membranes. J. Membr. Sci. 2007, 293, 44-52. (16) Yi, J. X.; Weirich, T. E.; Schroeder, M. CO2 Corrosion and Recovery of Perovskite-type BaCo1-x-yFexNbyO3-δ Membranes. J. Membr. Sci. 2013, 437, 49-56. (17) Xue, J.; Liao, Q.; Wei, Y. Y.; Li, Z.; Wang, H. H. A CO2-tolerance Oxygen Permeable 60Ce0.9Gd0.1O2-δ-40Ba0.5Sr0.5Co0.8Fe0.2O3-δ Dual Phase Membrane. J. Membr. Sci. 2013, 443, 124-130. (18) Yi, J. X.; Schroeder, M.; Weirich, T.; Mayer, J. Behavior of Ba(Co, Fe, Nb)O3-δ Perovskite in CO2-Containing Atmospheres: Degradation Mechanism and Materials Design. Chem. Mater. 2010, 22, 6246-6253. (19) Wei, Y. Y.; Ravkina, O.; Klande, T.; Wang, H. H.; Feldhoff, A. Effect of CO2 and SO2 on Oxygen Oermeation and Microstructure of (Pr0.9La0.1)2(Ni0.74Cu0.21Ga0.05)O4+δ


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Membranes. J. Membr. Sci. 2013, 429, 147-154. (20) Meng, X.; Ding, W.; Jin, R.; Wang, H.; Gai, Y.; Ji, F.; Ge, Y.; Xie, D. Two-step Fabrication of Ba1.0Co0.7Fe0.2Nb0.1O3-δ Asymmetric Oxygen Permeable Membrane by Dip Coating. J. Membr. Sci. 2014, 450, 291-298. (21) Zhang, Y. W.; Li, Q.; Shen, P. J.; Liu, Y.; Yang, Z. B.; Ding, W. Z.; Lu, X. G. Hydrogen Amplification of Coke Oven Gas by Reforming of Methane in a Ceramic Membrane Reactor. Int. J. Hydrogen Energy 2008, 33, 3311-3319. (22) Shen, P. J.; Ding, W. Z.; Zhou, Y. D.; Huang, S. Q. Reaction Mechanism on Reduction Surface of Mixed Conductor Membrane for H2 Production by Coal-gas.

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Membrane

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CO2-containing

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on the Oxygen Permeation Performance of Perovskite-type BaCoxFeyZrzO3-δ Hollow Fiber Membranes. J. Membr. Sci. 2010, 364, 132-137. (32) Zhu, X. F.; Liu, H. Y.; Cong, Y.; Yang, W. S. Novel Dual-phase Membranes for CO2 Capture via an Oxyfuel Route. Chem. Commun. 2012, 48, 251-253. (33) Wei, Y. Y.; Tang, J.; Zhou, L. Y.; Xue, J.; Li, Z.; Wang, H. H. Oxygen Separation through U-shaped Hollow Fiber Membrane using Pure CO2 as Sweep Gas. AIChE

J. 2012, 58, 2856-2864. (34) Chen, W.; Chen, C. S.; Bouwmeester, H. J. M.; Nijmeijer, A.; Winnubst, L. Oxygen-selective Membranes Integrated with Oxy-fuel Combustion. J. Membr.

Sci. 2014, 463, 166-172. (35) Zhang, X. X.; Wu, C. Z.; Zhou, J. F.; Yang, G. H.; Liu, Y. H.; Zhang, Y. W.; Ding, W. Z. Oxygen

Permeation

Property

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Structural

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La-doped

BaCo0.88Nb0.12O3-δ Membranes in CO2 Atmosphere. Chem. J. Chinese Univ. 2015,

36, 1246-1253.


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BRIEFS Degradation and recovery mechanism of perovskite-type oxygen permeable membrane swept by CO2 is clarified.



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Table of Contents (TOC) Image


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2.1

pure He

1.8

-2

-1

JO2(mlcm min )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47


1.5 1.2

from pure CO2 to He

0.9 from He to 5%CO2

0.6 0.3 pure CO2

0.0

-0.3

from pure CO2 to 5%CO2

0

500

1000

1500

Time (min) ACS Paragon Plus Environment

2000

2500


a b c d e

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

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Perovskite BaCoO2.93 BaFeO2.90 BaCO3 Ba(CO3)0.9(SO4)0.1

20

25

30

35

40 45 o 2 ( )


50

55

60

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(aa)

(e))

(bb)

(f))

(cc)

(g))

(d)

(h)



a Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Page 32 of 36

b Perovskite BaCoO2.93 BaCO3 Ba(CO3)0.9(SO4)0.1 CoO

15 18 21 24 27 30 33 36 39 42 45 48 o 2 ( ) ACS Paragon Plus Environment

Page 33 of 36

-1

JO2(ml·cm ·min )

2.1

-2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47


a

1.8

b

c

d

e

f

O2 con. at feed side

1.5

CO2 con. at sweep side

1.2 21% 0%

0.9

40% 60% 100% 100% 100% 100%

21% 100%

21% 5%

0.6 0.3 0.0 0

100

200

300

400

Time (min)


500

600


o

(b)

600 C o 700 C o 800 C o 900 C

(a)

as prepared

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Page 34 of 36

(c)

300

450

600

750

900

(d)

300


450 o

Temperature ( C)

600

750

900

Page 35 of 36

:Witherite BaCO3

o

600 C

:CoO

o

700 C

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


 

o



800 C

 





:Perovskite



o

900 C







As prepared







20

30

40

50 o

2 ( )




60

70


16

C O2 16

18

C O O 18 C O2

Ion Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Page 36 of 36

16

18

O O 18 O2

200

300

400 500 600 700 o Temperature ( C) ACS Paragon Plus Environment

800

900

A Study on the Degradation and Recovery Mechanisms of Perovskite

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