Oxygen Transport Membrane for Thermochemical Conversion of

Subscriber access provided by - Access paid by the | University Library, UC Santa Cruz

Article

Oxygen Transport Membrane for Thermochemical Conversion of Water and Carbon Dioxide into Synthesis Gas Wenyuan Liang, Zhengwen Cao, Guanghu He, Jürgen Caro, and Heqing Jiang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b01305 • Publication Date (Web): 30 Aug 2017 Downloaded from http://pubs.acs.org on September 3, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Sustainable Chemistry & Engineering 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.

Page 1 of 25

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

ACS Sustainable Chemistry & Engineering

Oxygen Transport Membrane for Thermochemical Conversion of Water and Carbon Dioxide into Synthesis Gas Wenyuan Liang,†§∇ Zhengwen Cao,‡♯∇ Guanghu He,† Jürgen Caro,‡* and Heqing Jiang†*

† Qingdao Key Laboratory of Functional Membrane Material and Membrane Technology, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Songling Road No.189, Laoshan District, 266101 Qingdao, China.

‡ Institute of Physical Chemistry and Electrochemistry, Leibniz University of Hannover, Callinstrasse 3A, 30167 Hannover, Germany.

§University of Chinese Academy of Sciences, 100049 Beijing, China

Corresponding Author *E-mail: [email protected]; [email protected] KEYWORDS: Oxygen transport membrane, Synthesis gas, H2O splitting, CO2 decomposition.

1 ACS Paragon Plus Environment


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

Page 2 of 25

ABSTRACT

Conversion of CO2 and H2O into synthesis gas via the solar thermochemical process usually carries out at a high temperature of above 1500 °C and requires long-term durability of metal oxide

catalysts

during

frequent

heating-cooling

cycles.

Herein,

dual-phase

Ce0.9Pr0.1O2-δ-Pr0.6Sr0.4FeO3-δ oxygen transport membrane made of mixed metal oxides was employed for the one-step thermochemical conversion of CO2 and H2O to synthesis gas with a H2/CO ratio of 2:1. Benefiting from the in situ removal of the generated oxygen through the highly oxygen-ion permeable membrane, the effective splitting of CO2 and H2O was achieved at the relatively low temperature of < 1000 °C. A synthesis gas production rate of 1.3 ml min-1cm-2 was obtained at 930 °C for a H2O/CO2 feed ratio of 5:1 with a H2O conversion of above 1.7% and a CO2 conversion of above 4.2%. Compared with the discontinuous two-step thermochemical decomposition, the combination of solar energy, catalytic thermolysis, and oxygen transport membrane reactor as proposed in this work, offers a new perspective and an alternative route to convert H2O and CO2 into synthesis gas.

ACS Paragon Plus Environment

2

Page 3 of 25

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


INTRODUCTION In the past few decades, transforming H2O and CO2 into high-energy chemicals by artificial photosynthesis with the aid of solar power, is getting more and more attractive, because of its important role in mitigation of energy shortage and global warming.1-2 Synthesis gas, a mixture of CO and H2, is a precursor to liquid hydrocarbon fuels. Synthesis gas can be obtained from splitting of CO2 and H2O using photocatalytic processes3-7, high-temperature steam/CO2 co-electrolysis8-11, or solar thermochemical loop processes.12-13 In the photo-catalytic process, oxidic materials can decompose H2O and/or CO2 into H2 and/or CO. However, photo-catalysis is impeded by its inherently limited energy conversion efficiency associated with band-gap excitation.14 By contrast, thermo-chemical processes operating at elevated temperature can use the solar spectrum for thermal energy and possess fast chemical reaction kinetics. Previous research has demonstrated that the direct thermolysis of H2O and CO2 requires ultra-high temperatures (>2500 K). To avoid the recombination and the formation of an explosive mixture, the generated gas products have to be separated at such high temperatures.15 To tackle the two issues of (i) ultra-high temperature, and (ii) gas separation at these temperatures, multi-step thermo-chemical cycles - especially two-step thermochemical loop cycles using metal oxide redox reactions - have been put forward and widely studied in the past several decades.16-17 In these cases, oxygen is extracted from H2O or CO2, and stored during the oxidation step in the oxygen-deficient metal oxides such as ceria18-19 and perovskites,20 and it was further released during the next step at high temperature, leading to the acquisition of H2/CO and oxygen, respectively. However, two-step thermo-chemical cycles still are subjected to a relatively high


3


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

Page 4 of 25

temperature (usually above 1500 ◦C) in the first endothermic step for reducing the metal oxides, and put forward a high request for long-term durability of solar reactors and metal oxides during frequent heating-cooling cycles. To lower the operating temperature, one possible solution is to remove the oxygen generated from the equilibrium-limited decomposition of H2O and CO2 using a dense oxygen transport membrane (OTM) with mixed oxygen ion and electron conductivity.21-25 The thermal splitting of either H2O or CO2 as individual feed in oxygen transport reactor has been repeatedly reported.26-35 The concept of thermal water splitting using oxygen transport membranes was proposed about 40 years ago,26-27 and first pioneering experimental studies were published in ref.28-29 Decisive progress in the hydrogen production by thermal water splitting using ceramic mixed conducting membranes has been obtained by Balachandran et al.30-31 Recently, we also demonstrated the effective hydrogen production by coupling water splitting with selective oxidation of methane or ethane in perovskite membrane reactor.32-33In addition, CO2 decomposition combined with the partial oxidation of methane has been demonstrated in oxygen transport membrane reactor by Jin et al.34-35 Different to the previous studies on the individual H2O or CO2 decomposition, herein, we experimentally demonstrated the simultaneous thermal decomposition of H2O and CO2 for producing synthesis gas in an oxygen transport membrane reactor. By simultaneously splitting H2O and CO2 in a single process, a unit of adjusting the ratio of H2/CO can be saved leading to the reduction of energy loss and equipment investment in synthesis gas production. As illustrated in Scheme 1, by in situ removing of the generated oxygen from thermal H2O and CO2 splitting through an oxygen transport membrane, the thermodynamic equilibrium limit of the two decomposition reactions can be overcome through the continuous oxygen removal. The oxygen


4

Page 5 of 25

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


generated from the co-splitting of H2O and CO2 in the membrane reactor will be continuously removed as long as an oxygen partial pressure gradient exists between the permeate side and the H2O/CO2 feed side. This very low oxygen partial pressure on the permeate side can be reached by (i) vacuum pumps, (ii) an inert sweep gas, or (iii) by an oxygen-consuming reaction such as selective methane oxidation, as in our case. Since H2O and CO2 splitting are strongly endothermic, and this heat demand cannot be compensated by the slightly exothermic partial oxidation of methane (Table S1 in Supporting Information), the necessary energy for H2O and CO2 splitting can come from the sun, for instance, by using a normal solar oven as shown in Figure S2. Due to this mechanism, a higher syngas production rate can be expected in the oxygen transport membrane reactor at a lower temperature (< 1000 ◦C), compared to the previously discussed thermo-chemical loop processes. EXPERIMENTAL SECTION Synthesis of powders and membranes The Ce0.9Pr0.1O2−δ-Pr0.6Sr0.4FeO3−δ (CPO-PSFO) powders were prepared via a simple glycine-nitrate combustion process (GNP), as described in detail elsewhere.36 The CPO-PSFO powders were calcined in a high-temperature furnace at 950 °C for 10 h. The CPO-PSFO disks obtained under 5 MPa in a steel module were sintered under ambient pressure at 1400 ◦C for 5 h in air to become gas-tight membrane disks. To get thin CPO-PSFO membranes with a thickness of 0.6 mm, these membrane disks were polished by carborundum paper. Characterization of membrane materials XRD study was carried out at room temperature to determine the phase composition of the CPO-PSFO powders, fresh membranes and spent membranes. Bruker-AXS D8 Advance diffractometer was employed using a step-scan mode with intervals of 0.02 in 2θ range of 20-80◦.


5


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

Page 6 of 25

A SEM (JEOL JSM-6700F) was applied to characterize the surface morphology of the fresh and spent CPO-PSFO membranes. The performance measurements of oxygen permeability The permeation tests were performed in a self-made device as described in our previous work.52,53 The CPO-PSFO dual-phase membrane was fixed to an alundum tube, and sealed with ceramic glue (Huitian rubber industry, China). Herein, high-temperature tube furnace was used as a substitution of solar furnace (see Figure S1). A Ni/Al2O3 catalyst with a particle size of 0.3-0.5 mm was packed on the top of CPO-PSFO membrane surface. The feed side was fed with a mixture of H2O, CO2 and N2, and N2 was used as a diluent gas and an indication of leaking. Ne co-fed with He and CH4 on the sweep side was served as an internal standard. The leakage was less than 3%. The effective membrane area is around 0.7 cm2. The gas flow rates were controlled by mass-flow controllers (MFC, Bronkhorst, Germany) and calibrated by a bubble flow meter. The H2O was controlled by a liquid MFC and sent to the reactor after being heated and evaporated at 180 ◦C. The concentration of the gases at the exit of the reactor was analysed by an on-line gas chromatograph (Agilent 7890A). Calculation formulas No oxygen was detected by GC, thus the oxygen generated from H2O and CO2 splitting was assumed to be removed and the total gas flow rate did not change on feed side. The production rate of hydrogen vH2 and CO vCO, the conversion of H2O X(H2O) and that of CO2 X(CO2) are calculated according to the equations as follows: (1)


6

Page 7 of 25

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


(2)

(3)

(4)

where, CH2, CCO, A, FH2O, FCO2, Fout are concentrations of H2 and CO on the feed side, membrane area, flow rates of H2O and CO2, and the total flow rate at the outlet of the feed side, respectively. On the permeate/sweep side, methane conversion X(CH4) and CO selectivity S(CO) are calculated based on the following equations:

(5)

(6)

where, FCH4,out, FCH4,in, FCO,out are CH4 flow rates at outlet and inlet, CO flow rate at outlet, respectively. RESULTS AND DISCUSSION A dual-phase membrane Ce0.9Pr0.1O2−δ-Pr0.6Sr0.4FeO3-δ (CPO-PSFO) was employed in this work because it gives stable oxygen permeability under carbon dioxide atmosphere as found in our previous study.36 Figure 1 presents the back-scattered electron micrograph (BSEM) and


7


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

Page 8 of 25

EDXS images of the CPO-PSFO membrane after being sintered at 1400 oC for 5 h. It is observed that the CPO and PSFO phases are well-distributed with clear grain boundaries. This suggests that the CPO and PSFO phases have a good chemical compatibility after a high-temperature sintering. Here, fluorite CPO phase and perovskite PSFO phase are mainly responsible for oxygen ionic and electronic transport, respectively. The H2/CO ratio in a synthesis gas is an important parameter for the following downstream process. In this work, this ratio was adjusted by changing the H2O/CO2 ratio of the feed gases, as shown in Figure 2. Under standard conditions, Gibbs’ free energy change (∆G) of CO2 splitting is larger than that of water dissociation. However, the values of ∆G for these two reactions become close with increasing temperature.37 The ∆G of CO2 splitting is becoming lower than that of H2O when the temperature is above 830 °C, indicating the equilibrium constant of CO2 splitting is larger than that of H2O splitting at higher temperatures. Thus, to obtain the gas mixture with H2/CO ratio of 2 by splitting H2O and CO2, the H2O/CO2 feed ratio should be above 2. As shown in Figure 2, with increasing H2O/CO2 ratio in the feed from 1 to 28, the H2/CO ratio could be tuned from 1 to 10. The H2 production rate at 930 °C increased from 0.64 to 1.1 ml min-1cm-2 with a H2O conversion decreased from 3.1% to 2.5%, the CO production rate decreased from 0.62 to 0.14 ml min-1cm-2 with a CO2 conversion increased from 2.9% to 7.5%, respectively. A desired H2/CO ≈ 2 for methanol or Fischer–Tropsch synthesis was achieved at H2O/CO2 ratio of 5 in the feed with H2 and CO production rates of 0.88 and 0.42 ml min-1cm-2, respectively. It is noteworthy that synthesis gas was obtained continuously from CO2 and H2O splitting at 930 ◦C in an oxygen transport membrane reactor, and the operating temperature is obviously lower than that in the common thermochemical loop cycles using metal oxide redox reactions.


8

Page 9 of 25

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


To increase the synthesis gas production rate, the fast removal of oxygen generated in the H2O and CO2 decomposition is necessary. The driving force of oxygen transport is the gradient cross the membrane, which can be established - as said above - by ultra-high vacuum, using a sweep gas, or by using a reactive gas on the permeat side. In this work, methane was sent to the sweep side to consume the permeated oxygen according to CH4+ ½ O2 → CO + 2 H2. Figure S4 presents the H2, CO production rate and the H2/CO ratio on the H2O/CO2 feed side of the membrane as a function of the methane flow on the permeate side. It was observed that with increasing methane flow from 1.5 to 10 ml min-1, the H2 production rate increased from 0.88 to 1.14 ml min-1cm-2, and the CO production rate increased from 0.42 to 0.54 ml min-1cm-2, respectively. Obviously, by increasing methane flow on the permeation side, a larger gradient across the membrane as driving force was established, more CO and H2 was generated from CO2 and H2O splitting, and the H2/CO ratios in the synthesis gas were maintained approximately 2 in the investigated CH4 flux range. Figure 3 shows the temperature dependence of the H2 and CO production rate as well as the H2/CO ratio on the H2O/CO2 feed side of the CPO-PSFO membrane reactor. When raising the temperature from 870 ◦C to 950 ◦C, both the H2 and CO production rate increased, which is based on the following reasons: 1) the equilibrium constants and kinetic reaction rates of the endothermic H2O & CO2 decomposition reaction were increased leading to higher conversions; 2) the oxygen permeation rate of the CPO-PSFO membrane was also enhanced with the increase of temperature; 3) the gradient of the oxygen partial pressure was further increased by a faster consumption of oxygen in the POM reaction. In the whole temperature range, the rate of H2 production was always higher than that of CO, however, the H2/CO ratio decreased from 3.7 to 2 when rising the temperature from 870 ◦C to 950 ◦C. The activation energy of CO2 decomposition


9


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

Page 10 of 25

is higher than that of H2O decomposition based on previous studies.28, 38 Increasing temperature is, therefore, more favorable for promoting the decomposition of CO2 than that of H2O according to Arrhenius equation.39 In addition, as mentioned above, the Gibbs’ free energy change of CO2 splitting is decreasing much faster than that of water splitting with increasing temperature, which means that the CO2 dissociation becomes thermodynamically more favorable in comparison with water splitting at higher temperatures.37 In this work, methane was used not only as a sweep gas to consume the permeated oxygen by the POM reaction, but also to produce additional synthesis gas with a H2/CO ratio of 2. Figure S5 presents the influence of temperature on the CH4 conversion, CO selectivity and yield on the permeate/sweep side. It is shown that both CH4 conversion and CO yield increased with rising temperature. At 930 ◦C, a CH4 conversion of 62% and a CO selectivity of 99% were achieved, and synthesis gas at a rate of 3.9 ml min-1cm-2 was obtained. Accordingly, the O2-consumption rate on the permeate side is 0.66 ml min-1cm-2 based on the membrane area of 0.7 cm2, indicating the good oxygen balance (the O2-supply rate from CO2and H2O splitting under these conditions is 0.65 ml min-1cm-2, as mentioned above). Figure 4 presents the stability of H2 and CO production rate as well as H2/CO ratio during 100 hours time on stream on the H2O/CO2 feed side. As we can see from Figure 4, both the production rates of H2 and CO gradually decreased in the first 20 hours. H2 production rate decreased from 0.9 to 0.6 ml min-1cm-2 with a H2O conversion decreasing from 2.5% to 1.7%, and CO production rate decreased from 0.5 to 0.3 ml min-1cm-2 with a CO2 conversion decreasing from 7% to 4.2%. Afterward, the performance of the CPO-PSFO membrane reactor was almost constant with increasing time on stream.


10

Page 11 of 25

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


It has been reported that both ceria-based materials and perovskites were often used as electrocatalysts in the decomposition of H2O and CO2.40-41 Both the CPO and PSFO phases probably show similar catalytic behavior in our membrane reactor since an oxygen transport membrane can be regarded as a short-circuit solid oxide fuel cell. For the non-stoichiometric oxygen transport materials Ce0.9Pr0.1O2-δ (CPO) or Pr0.6Sr0.4FeO3-δ (PSFO), to maintain their electrical neutrality the amounts of oxygen vacancies (indicated by the value of δ) and the valences of Ce (+4/+3) or Fe (+4/+3/+2) will vary with the change of temperature and oxygen partial pressure. During the activation stage, the mixture of H2O/CO2 is reduced by the oxygen vacancies on the surface of the CPO-PSFO membrane at the H2O/CO2 side, following the gas-solid reactions: Ce0.9Pr0.1O2-δ + f (H2O/CO2) → Ce0.9Pr0.1O2-δ+f + f (H2/CO)

(7)

Pr0.6Sr0.4FeO3-δ +f (H2O/CO2) → Pr0.6Sr0.4FeO3-δ+f + f (H2/CO)

(8)

On the other side of the CPO-PSFO membrane, methane will be oxidized following the gas-solid reactions: Ce0.9Pr0.1O2-δ + p CH4 → Ce0.9Pr0.1O2-δ-p + p (2H2 + CO)

(9)

Pr0.6Sr0.4FeO3-δ +p CH4 → Pr0.6Sr0.4FeO3-δ-p + p (2H2 + CO)

(10)

After the fast accomplishment of the activation process, the concentration gradient of oxygen vacancies

across

the

membrane

is

established:

Ce0.9Pr0.1O2-δ+f/Ce0.9Pr0.1O2-δ-p

and

Pr0.6Sr0.4FeO3-δ+f/Pr0.6Sr0.4FeO3-δ-p, and oxygen ion (O2-) derived from the splitting of H2O/CO2 on the feed side will transport along the oxygen vacancies to the other side, where it will react with methane. The continuous oxygen transportation can be maintained if the oxygen


11


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

Page 12 of 25

concentration on the permeate side is much lower than that on the H2O/CO2 feed side. During the continuous oxygen transport process, the membrane surface of CPO-PSFO membrane on the H2O/CO2 feed side actually played the role of thermolysis catalyst and the oxygen vacancies of that served as the catalytically active sites.42,43 However, metal oxides might decompose if the oxygen partial pressure is too low. Here, the CPO-PSFO dual-phase membrane is used in coupling the decomposition of H2O&CO2 with the POM reaction on the two opposite sides, and both sides of the membrane are exposed to a reducing atmosphere. The change of the membrane is demonstrated by comparing the XRD patterns of the spent membrane with those of the fresh membrane, as shown in Figure 5. It is found that the CPO phase with fluorite structure remains unchanged with time on stream. The perovskite structure of PSFO phase, however, was gradually degraded into other oxidic compounds (SrFeO3, Pr2O3, FeOx, Fe) due to the deep reduction of iron in the perovskite lattice and some carbonates, hydrocarbonates and hydroxides also might be produced due to the reaction of degraded components with CO2/H2O. Both catalytic activity and oxygen permeability became reduced due to a gradual structural failure in a surface-near layer of the perovskite phase. Although the membrane was gradually eroded on both sides, it is noted that the dual-phase CPO-PSFO membrane was still gas-tight after 100 h operation, indicating that its stability under reducing atmosphere is higher than that of cobalt-based perovskite membranes.44 Conclusions In conclusion, for the first time the effective generation of synthesis gas with H2/CO ratio of 2 by the simultaneous decomposition of water and carbon dioxide at the relatively low temperature of < 1000 °C was experimentally demonstrated in an oxygen transport membrane reactor. Benefiting from the in situ fast removal of the generated oxygen by the membrane, the effective


12

Page 13 of 25

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


splitting of CO2 and H2O was achieved at lower temperatures, compared to the usual thermochemical decomposition. A synthesis gas flow rate of 1.3 ml min-1cm-2 on the feed side was obtained at 930 ◦C at a H2O/CO2 feed ratio of 5. To have a stable and sufficient driving force for oxygen permeation through the membrane, the oxygen partial pressure on sweep side was effectively reduced using reactive methane as sweep gas. Simultaneously, synthesis gas at a rate of 3.9 ml min-1cm-2 was obtained on the methane side. In consideration of the disadvantages of conventional two-step thermochemical route on the requirement of ultra-high temperature and discontinuous oxygen transport, the combination of solar energy, catalytic thermolysis, and oxygen transport membrane reactor proposed in this work offer a new perspective and an alternative route to convert water and CO2 into synthesis gas. A high solar-to-fuel efficiency can be expected when bringing such ceramic oxygen permeable membranes into the world of solar reactors in future. In fact, recent thermodynamic studies on hydrogen production by H2O splitting in solar thermochemical oxygen permeation membrane reactors show that net efficiency up to 63% can be reached at 850-900°C, using methane partial oxidation as the source for a high driving force for oxygen removal.45 It should be pointed out that developing ultra-stable oxygen transport membrane materials under such reaction conditions is still a challenging topic as outlined in literature.46 ASSOCIATED CONTENT Supporting Information. Image of solar oven, experimental data on the permeate/sweep side and thermodynamic analysis. The following files are available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author


13


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

Page 14 of 25

*E-mail: [email protected]; [email protected] Present Addresses ♯Max Planck Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ∇These authors contributed equally to this work. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT We kindly thank financial support from National Natural Science Foundation of China (No. 21501186, 21471156), the project of Science and Technology Development Program in Shandong Province (2014GSF117031), Strategic Priority Research Program of the Chinese Academy of Sciences (XDB17020100), and the Recruitment Program of Global Youth Experts of China. REFERENCES 1. Lewis, N. S., Research opportunities to advance solar energy utilization. Science 2016,351 (6271). DOI: 10.1126/science.aad1920 2. Armaroli, N.; Balzani, V., The future of energy supply: challenges and opportunities. Angew. Chem. Int. Ed. 2007,46 (1-2), 52-66. DOI: 10.1002/anie.200602373 3. Wang, Y.; Wang, F.; Chen, Y.; Zhang, D.; Li, B.; Kang, S.; Li, X.; Cui, L., Enhanced photocatalytic performance of ordered mesoporous Fe-doped CeO2 catalysts for the reduction of


14

Page 15 of 25

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


CO2 with H2O under simulated solar irradiation. Appl. Catal. B-Environ 2014,147, 602-609. DOI: 10.1016/j.apcatb.2013.09.036 4. Zou, Z.; Ye, J.; Sayama, K.; Arakawa, H., Direct splitting of water under visible light irradiation with an oxide semiconductor photocatalyst. Nature 2001,414 (6864), 625-627. DOI:10.1038/414625a 5. Wang, S.; Yao, W.; Lin, J.; Ding, Z.; Wang, X., Cobalt imidazolate metal–organic frameworks photosplit CO2 under mild reaction conditions. Angew. Chem. Int. Ed. 2014,53 (4), 1034-1038. DOI: 10.1002/anie.201309426 6. Lehn, J.-M.; Ziessel, R., Photochemical generation of carbon monoxide and hydrogen by reduction of carbon dioxide and water under visible light irradiation. PNAS 1982,79 (2), 701-704. 7. Weng, X.; Zeng, Q.; Zhang, Y.; Dong, F.; Wu, Z., Facile approach for the syntheses of ultrafine TiO2nanocrystallites with defects and C heterojunction for photocatalytic water splitting. ACS Sustain. Chem. Eng. 2016,4 (8), 4314-4320. DOI: 10.1021/acssuschemeng.6b00828 8. Naik, S. N.; Goud, V. V.; Rout, P. K.; Dalai, A. K., Production of first and second generation biofuels: A comprehensive review. Renew. Sust. Energ. Rev. 2010,14 (2), 578-597. DOI: 10.1016/j.rser.2009.10.003 9. Stoots, C.; O'Brien, J.; Hartvigsen, J., Results of recent high temperature coelectrolysis studies at the Idaho National Laboratory. Int. J. Hydrogen Energ. 2009,34 (9), 4208-4215. DOI: j.ijhydene.2008.08.029 10. Jiang, N.; You, B.; Sheng, M.; Sun, Y., Electrodeposited cobalt-phosphorous-derived films as competent bifunctional catalysts for overall water splitting. Angewandte Chemie 2015,127 (21), 6349-6352. DOI: 10.1002/ange.201501616 11. Torella, J. P.; Gagliardi, C. J.; Chen, J. S.; Bediako, D. K.; Colón, B.; Way, J. C.; Silver, P. A.; Nocera, D. G., Efficient solar-to-fuels production from a hybrid microbial–water-splitting catalyst system. PNAS 2015,112 (8), 2337-2342. DOI: 10.1073/pnas.1424872112 12. Muhich, C. L.; Evanko, B. W.; Weston, K. C.; Lichty, P.; Liang, X.; Martinek, J.; Musgrave, C. B.; Weimer, A. W., Efficient generation of H2 by splitting water with an isothermal redox cycle. Science 2013,341 (6145), 540-542. DOI: 10.1126/science.1239454 13. Steinfeld, A., Solar thermochemical production of hydrogen––a review. Sol. Energy 2005,78 (5), 603-615. DOI: 10.1016/j.solener.2003.12.012 14. Park, J. H.; Kim, S.; Bard, A. J., Novel carbon-doped TiO2nanotube arrays with high aspect ratios for efficient solar water splitting. Nano Lett. 2006,6 (1), 24-28. DOI: 10.1021/nl051807y 15. Kogan, A.; Spiegler, E.; Wolfshtein, M., Direct solar thermal splitting of water and on-site separation of the products. III.: Improvement of reactor efficiency by steam entrainment. Int. J. Hydrogen Energ. 2000,25 (8), 739-745. DOI: 10.1016/S0360-3199(99)00102-0 16. Kodama, T.; Gokon, N., Thermochemical cycles for high-temperature solar hydrogen production. Chemical Rev. 2007,107 (10), 4048-4077. DOI: 10.1021/cr050188a 17. Roeb, M.; Neises, M.; Säck, J.-P.; Rietbrock, P.; Monnerie, N.; Dersch, J.; Schmitz, M.; Sattler, C., Operational strategy of a two-step thermochemical process for solar hydrogen production. Int. J. Hydrogen Energ. 2009,34 (10), 4537-4545. DOI: 10.1016/j.ijhydene.2008.08.049 18. Chueh, W. C.; Falter, C.; Abbott, M.; Scipio, D.; Furler, P.; Haile, S. M.; Steinfeld, A., High-flux solar-driven thermochemical dissociation of CO2and H2O using nonstoichiometric ceria. Science 2010,330 (6012), 1797-1801. DOI: 10.1126/science.1197834


15


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

Page 16 of 25

19. Bulfin, B.; Call, F.; Lange, M.; Lübben, O.; Sattler, C.; Pitz-Paal, R.; Shvets, I. V., Thermodynamics of CeO2thermochemical fuel production. Energy Fuels 2015,29 (2), 1001-1009. DOI: 10.1021/ef5019912 20. Scheffe, J. R.; Weibel, D.; Steinfeld, A., Lanthanum–strontium–manganese perovskites as redox materials for solar thermochemical splitting of H2O and CO2. Energy Fuels 2013,27 (8), 4250-4257. DOI: 10.1021/ef301923h 21. Thursfield, A.; Murugan, A.; Franca, R.; Metcalfe, I. S., Chemical looping and oxygen permeable ceramic membranes for hydrogen production - a review. Energ. Environ. Sci. 2012,5 (6), 7421-7459. DOI: 10.1039/C2EE03470K 22. 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 (1–2), 13-41. DOI: 10.1016/j.memsci.2008.03.074 23. Chen, C.; Feng, S.; Ran, S.; Zhu, D.; Liu, W.; Bouwmeester, H. J. M., Conversion of methane to syngas by a membrane-based oxidation–reforming process. Angew. Chem. Int. Ed. 2003,42 (42), 5196-5198. DOI: 10.1002/anie.200351085 24. Liu, Y.; Tan, X.; Li, K., Mixed conducting ceramics for catalytic membrane processing. Catal. Rev. 2006,48 (2), 145-198. DOI: 10.1080/01614940600631348 25. Cheng, H.; Zhang, N.; Xiong, X.; Lu, X.; Zhao, H.; Li, S.; Zhou, Z., Synthesis, oxygen permeation, and CO2-tolerance properties of Ce0.8Gd0.2O2−δ–Ba0.95La0.05Fe1–xNbxO3−δdual-phase membranes. ACS Sustain. Chem. Eng. 2015,3 (9), 1982-1992. DOI: 10.1021/acssuschemeng.5b00693 26. Browall, K. W.; Doremus, R. H., Synthesis and evaluation of doped Y2O3-Stabilized ZrO2 for the production of hydrogen. J. Am. Ceram. Soc. 1977,60 (5-6), 262-267. DOI: 10.1111/j.1151-2916.1977.tb14121.x 27. Calès, B.; Baumard, J. F., Mixed conduction and defect structure of ZrO2-CeO2 -Y2O3 solid solutions. Journal of The Electrochemical Society 1984,131 (10), 2407-2413. DOI: 10.1149/1.2115267 28. Lede, J.; Lapicque, F.; Villermaux, J.; Cales, B.; Ounalli, A.; Baumard, J. F.; Anthony, A. M., Production of hydrogen by direct thermal decomposition of water: Preliminary investigations. Int. J. Hydrogen Energ. 1982,7 (12), 939-950. DOI: 10.1016/0360-3199(82)90162-8 29. Naito, H.; Arashi, H., Hydrogen production from direct water splitting at high temperatures using a ZrO2-TiO2-Y2O3 membrane. Solid State Ionics 1995,79, 366-370. DOI: 10.1016/0167-2738(95)00089-O 30. Balachandran, U.; Lee, T. H.; Wang, S.; Dorris, S. E., Use of mixed conducting membranes to produce hydrogen by water dissociation. Int. J. Hydrogen Energ. 2004,29 (3), 291-296. DOI: 10.1016/S0360-3199(03)00134-4 31. Balachandran, U.; Lee, T. H.; Dorris, S. E., Hydrogen production by water dissociation using mixed conducting dense ceramic membranes. Int. J. Hydrogen Energ. 2007,32 (4), 451-456. DOI: 10.1016/j.ijhydene.2006.05.010 32. Jiang, H.; Wang, H.; Werth, S.; Schiestel, T.; Caro, J., Simultaneous production of hydrogen and synthesis gas by combining water splitting with partial oxidation of methane in a hollow-fiber membrane reactor. Angew. Chem. Int. Ed. 2008,47 (48), 9341-9344. DOI: 10.1002/anie.200803899


16

Page 17 of 25

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


33. Jiang, H.; Cao, Z.; Schirrmeister, S.; Schiestel, T.; Caro, J., A coupling strategy to produce hydrogen and ethylene in a membrane reactor. Angew. Chem. Int. Ed. 2010,49 (33), 5656-5660. DOI: 10.1002/anie.201000664 34. Jin, W.; Zhang, C.; Zhang, P.; Fan, Y.; Xu, N., Thermal decomposition of carbon dioxide coupled with POM in a membrane reactor. AIChE J. 2006,52 (7), 2545-2550. DOI: 10.1002/aic.10850 35. Zhang, K.; Zhang, G.; Liu, Z.; Zhu, J.; Zhu, N.; Jin, W., Enhanced stability of membrane reactor for thermal decomposition of CO2 via porous-dense-porous triple-layer composite membrane. J. Membr. Sci. 2014,471, 9-15. DOI: 10.1016/j.memsci.2014.06.060 36. Luo, H.; Jiang, H.; Klande, T.; Cao, Z.; Liang, F.; Wang, H.; Caro, J., Novel cobalt-free, noble metal-free oxygen-permeable 40Pr0.6Sr0.4FeO3-δ–60Ce0.9Pr0.1O2−δ dual-phase membrane. Chem. Mater. 2012,24 (11), 2148-2154. DOI: 10.1021/cm300710p 37. Graves, C.; Ebbesen, S. D.; Mogensen, M.; Lackner, K. S., Sustainable hydrocarbon fuels by recycling CO2 and H2O with renewable or nuclear energy. Renew. Sust. Energ. Rev. 2011,15 (1), 1-23. DOI: 10.1016/j.rser.2010.07.014 38. Ibragimova, L. B.; Smekhov, G. D.; Shatalov, O. P.; Eremin, A. V.; Shumova, V. V., Dissociation of CO2 molecules in a wide temperature range. High Temp. 2000,38 (1), 33-36. DOI: 10.1007/BF02755563 39. Chueh, W. C.; Haile, S. M., Ceria as a thermochemical reaction medium for selectively generating syngas or methane from H2O and CO2. ChemSusChem 2009,2 (8), 735-739. DOI: 10.1002/cssc.200900138 40. Demont, A.; Abanades, S.; Beche, E., Investigation of perovskite structures as oxygen-exchange redox materials for hydrogen production from thermochemical two-step water-splitting cycles. J. Phys. Chem. C 2014,118 (24), 12682-12692. DOI: 10.1021/jp5034849 41. Zhang, C.; Yu, Y.; Grass, M. E.; Dejoie, C.; Ding, W.; Gaskell, K.; Jabeen, N.; Hong, Y. P.; Shavorskiy, A.; Bluhm, H.; Li, W.-X.; Jackson, G. S.; Hussain, Z.; Liu, Z.; Eichhorn, B. W., Mechanistic studies of water electrolysis and hydrogen electro-oxidation on high temperature ceria-based solid oxide electrochemical cells. J. Am. Chem. Soc. 2013,135 (31), 11572-11579. DOI: 10.1021/ja402604u 42. Feng, Z; Gabaly, F.; Ye, X., Shen, Z.; Chueh, W., Fast vacancy-mediated oxygen ion incorporation across the ceria–gas electrochemical interface. Nat. Comm. 2014,5, 4374. DOI: 10.1038/ncomms5374 43. Chen, D.; Chen, C.; Baiyee, Z.; Shao, Z.; Ciucci, F., Nonstoichiometric oxides as low-cost and highly-efficient oxygen reduction/evolution catalysts for low-temperature electrochemical devices. Chem. Rev. 2015,115 (18), 9869-9921. DOI: 10.1021/acs.chemrev.5b00073 44. Yi, J.; Feng, S.; Zuo, Y.; Liu, W.; Chen, C., Oxygen permeability and stability of Sr0.95Co0.8Fe0.2O3-δ in a CO2- and H2O-containing atmosphere. Chem. Mater. 2005,17 (23), 5856-5861. DOI: 10.1021/cm051636y 45. Vahabi, H.; Sonnier, R.; Ferry, L., Effects of ageing on the fire behaviour of flame-retarded polymers: a review. Polym. Int. 2015,64 (3), 313-328. DOI: 10.1002/pi.4841 46. Roeb, M.; Neises, M.; Monnerie, N.; Call, F.; Simon, H.; Sattler, C.; Schmücker, M.; Pitz-Paal, R., Materials-related aspects of thermochemical water and carbon dioxide splitting: A Review. Materials 2012,5 (11), 2015. DOI:10.3390/ma5112015


17


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

Page 18 of 25

Scheme 1. Synthesis gas production by simultaneous splitting of H2O and CO2 as oxygen generating reactions on one side of the oxygen transport membrane; and partial oxidation of methane as oxygen consuming reaction on the other side of the ceramic membrane. Figure 1. Back-scattered electron micrographs (BSEM) and EDXS images of the CPO-PSFO membrane.For the BSEM in a), the light grains present CPO grains, the dark grains present PSF grains. For the EDXS mapping in b), superimpositions of the Pr-Lα, Pr-Lβ, Sr-Lα, and Fe-Kα and Fe-Kβ (green) and Pr-Lα, Pr-Lβ and Ce-Lα, Ce-Lβ (yellow) signals have been used. Figure 2. Thermal co-splitting of H2O and CO2 at 930 °C. Left ordinate: production rate of hydrogen (vH2) and carbon monoxide (vCO) per membrane area and time; right ordinate: H2/CO ratio as a function of H2O/CO2 ratio in the feed. Feed side: FH2O + FCO2 = 30 ml min-1 and FN2 = 3 ml min-1, sweep side: FNe= 0.5 ml min-1, FCH4 = 1.5 ml min-1 and FHe=28 ml min-1. Figure 3. Thermal co-splitting of H2O and CO2 as a function of temperature. Left ordinate: production rate of hydrogen (vH2) and carbon monoxide (vCO); right ordinate: H2/CO ratio. Feed side: FH2O = 25 ml min-1, FCO2 = 5 ml min-1 and FN2 = 3 ml min-1, sweep side: FNe= 0.5 ml min-1, FCH4 = 1.5 ml min-1 and FHe= 28 ml min-1. Figure 4. Thermal co-splitting of H2O and CO2 at 930 °C as a function of time. Left ordinate: production rate of hydrogen (vH2) and carbon monoxide (vCO); right ordinate: H2/CO ratio. Feed side: FH2O = 25 ml min-1, FCO2 = 5 ml min-1 and FN2 = 3 ml min-1, sweep side: FNe = 0.5 ml min-1, FCH4 = 1.5 ml min-1 and FHe = 28 ml min-1. Figure 5. XRD patterns of the fresh powder, fresh membrane and spent membrane.


18

Page 19 of 25

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


Scheme 1. Synthesis gas production by simultaneous splitting of H2O and CO2 as oxygen generating reactions on one side of the oxygen transport membrane; and partial oxidation of methane as oxygen consuming reaction on the other side of the ceramic membrane.


19


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

Page 20 of 25

Figure 1. Back-scattered electron micrographs (BSEM) and EDXS images of the CPO-PSFO membrane. For the BSEM in a), the light grains present CPO grains, the dark grains present PSFO grains. For the EDXS mapping in b), superimpositions of the Pr-Lα, Pr-Lβ, Sr-Lα, and Fe-Kα and Fe-Kβ (green) and Pr-Lα, Pr-Lβ and Ce-Lα, Ce-Lβ (yellow) signals have been used.


20

Page 21 of 25

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


Figure 2. Thermal co-splitting of H2O and CO2 at 930 °C. Left ordinate: production rate of hydrogen (vH2) and carbon monoxide (vCO) per membrane area and time; right ordinate: H2/CO ratio as a function of H2O/CO2 ratio in the feed. Feed side: FH2O + FCO2 = 30 ml min-1 and FN2 = 3 ml min-1, sweep side: FNe = 0.5 ml min-1, FCH4 = 1.5 ml min-1 and FHe = 28 ml min-1.


21


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

Page 22 of 25

Figure 3. Thermal co-splitting of H2O and CO2 as a function of temperature. Left ordinate: production rate of hydrogen (vH2) and carbon monoxide (vCO); right ordinate: H2/CO ratio. Feed side: FH2O = 25 ml min-1, FCO2 = 5 ml min-1 and FN2 = 3 ml min-1, sweep side: FNe= 0.5 ml min-1, FCH4 = 1.5 ml min-1 and FHe = 28 ml min-1.


22

Page 23 of 25

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


Figure 4. Thermal co-splitting of H2O and CO2 at 930 °C as a function of time. Left ordinate: production rate of hydrogen (vH2) and carbon monoxide (vCO); right ordinate: H2/CO ratio. Feed side: FH2O = 25 ml min-1, FCO2 = 5 ml min-1 and FN2 = 3 ml min-1, sweep side: FNe= 0.5 ml min-1, FCH4 =1.5 ml min-1 and FHe=28 ml min-1.


23


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

Page 24 of 25

Figure 5. XRD patterns of the fresh powder and spent membrane.


24

Page 25 of 25

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


For Table of Contents Use Only

SYNOPSIS Effective production of synthesis gas by the simultaneous decomposition of water and carbon dioxide at the relatively low temperature of < 1000 °C was successfully demonstrated in an oxygen transport membrane reactor.


25

Oxygen Transport Membrane for Thermochemical Conversion of

Recommend Documents