Coproduction of Hydrogen and Methanol from Methane by Chemical

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Kinetics, Catalysis, and Reaction Engineering

Co-production of Hydrogen and Methanol from Methane by Chemical Looping Reforming Xinhe Wang, Xuancheng Du, Wenbo Yu, Junshe Zhang, and Jinjia Wei Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.9b01695 • Publication Date (Web): 30 May 2019 Downloaded from http://pubs.acs.org on June 6, 2019

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Industrial & Engineering Chemistry Research

Co-production of Hydrogen and Methanol from Methane by Chemical Looping Reforming Xinhe Wanga, Xuancheng Dub, Wenbo Yub, Junshe Zhangb,*, Jinjia Weia,b,* aState

Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China

bSchool

of Chemical Engineering and Technology, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China

Abstract Co-production of hydrogen and methanol from methane by chemical looping reforming is a novel approach to transform natural gas. Compared with conventional reforming processes, the mole ratio of methane to water fed to a chemical looping reactor can be the stoichiometric ratio without concerns over coking. In this work, the redox scheme was experimentally and numerically investigated, where SrFeO3-δ perovskite acted as the oxygen transfer agent. To improve its redox performance, SrFeO3-δ was dispersed into three oxides: CaO, MnO, and CaO•MnO. Among them, CaO•MnO enhances the reforming performance best. Specifically, SrFeO3-δ/CaO•MnO composites exhibit 6.9% coke selectivity, 66.2% maximum instantaneous methane conversion, and 91.5% syngas (H2:CO≈2) selectivity in methane partial oxidation step and up to 90% H2O to H2 conversion in water splitting step at a redox temperature of 900 oC. Further studies suggest that

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the low coke selectivity stems from the reaction between manganese oxide and coke or its precursor, which becomes more favorable at high temperatures. To evaluate the process of solar fuel production by chemical looping technology, an economic analysis of the co-production of hydrogen and methanol process was carried out and compared with conventional methanol synthesis. Compared with thermally-driven methanol synthesis, the solar-driven co-production scheme demonstrates 14% exergy efficiency improvement, 63% CO2 emission reduction and 1.9 times more net income than the former. Our findings demonstrate that solar-driven chemical looping reforming is a very promising option for solar fuel production. Keywords: Hydrogen, Methanol, Methane, Chemical looping reforming, Coke selectivity


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Introduction With rapidly increasing demands for global energy consumption and continuous concerns about the greenhouse effect, natural gas, a clean-burning fossil fuel and chemical feedstock, has drawn more and more attention1,2, especially with the boom of shale gas. The predominant component of natural gas is methane (CH4), which can be transformed to liquid fuels and commodity chemicals either directly or indirectly3,4. Although significant progress has been made in recent years5,6, direct conversion of methane to useful chemicals remains very difficult7,8. On the other hand, the indirect transformation is widely used in industry. In this route, methane is first transformed to syngas that is subsequently converted to gasoline, diesel, methanol, or ethylene9. Currently, steam methane reforming (SMR) is a mature technology to produce hydrogen and/or syngas from methane10,11. In a conventional SMR reactor, nickel-based catalyst particles are packed inside a tube and the heat is provided by natural gas combustion outside the tube, which produces substantial CO2. Steam and methane are co-fed to the reactor with a mole ratio (H2O:CH4) of 3~5:1 to suppress coke deposition on catalyst particles. Thus, it requires a large amount of energy to generate steam12,13. In addition, the H2/CO ratio in the product stream is 3 which is not suitable for the subsequent gas-to-liquid (GTL) processes14. To produce high purity hydrogen, a separation unit is needed, incurring high costs and energy penalty. The above challenges can be addressed by chemical looping technology15,16. In a chemical looping process, one chemical reaction is split into two or more ones that take place sequentially in one reactor or simultaneously in different reactors, where matter and energy



transfer is achieved via a solid material. In this process, in-situ separation of products is realized. Chemical looping steam methane reforming (CL-SMR) provides an energy-efficient and low-cost route for co-production of hydrogen and methanol (Figure 1). Compared with conventional SMR, CL-SMR is operated in a cyclic redox mode17-22, where methane and steam are fed to the reactor alternatively (Figure 1). In this mode, methane is partially oxidized by a metal oxide to produce syngas (MeOx+δCH4=MeOx-δ+δCO+2δH2) with a H2 to CO ratio of 2 (reduction step), which is then fed to a methanol reactor. Subsequently, the reduced oxide reacts with steam to replenish the depleted oxygen (MeOx-δ+δH2O=MeOx+δH2), generating hydrogen and closing the loop (oxidation step). Because coke, if formed, can be removed by steam in the oxidation step, feeding excess steam to the reactor becomes unnecessary. However, the coke formation must be minimized because it decreases the purity of hydrogen in the oxidation step.

Figure 1. Co-production of hydrogen and syngas from methane by chemical looping reforming.


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The property of the metal oxides, also known as oxygen carriers (OCs), is critical for chemical looping reforming23. A high-performance OC should have sufficiently high reactivity toward partial oxidation (POx) and water splitting as well as excellent thermal stability under the operating conditions24-29. Among various single metal oxides, Ni, Cu, Fe, Mn, Co and Ce have been extensively investigated25-28. However, they have some disadvantages28: low reactivity of Fe, Mn and Co oxides; high agglomeration tendency of Cu; high toxicity of Ni; high cost of cerium oxide29. Being potential candidate OCs for chemical looping reforming, perovskite oxides with a general formula of ABO3 (A and B are usually alkaline earth and transition metal cations, respectively) have drawn lots of attention because of their high activity and fast oxygen mobility30. To date, several strategies have been proposed to further enhance the redox performance of perovskitetyped OCs. Neal et al. reported a core-shell structured OC in which iron oxide is encapsulated in a LaySr1-yFeO3 shell, and they found that Fe2O3@LaySr1-yFeO3 outperforms Fe2O3-LaySr1-yFeO3 composites regarding activity, stability, and syngas selectivity in methane POx. However, with the improvement of methane conversion, the coke selectivity increased31. Haribal et al. found that iron-doped BaMnO3 exhibits high efficiency of solar to chemical energy in solar-driven CLSMR32. Zhang et al. reported a perovskite composite that exhibits excellent performance toward chemical looping dry reforming of methane at relatively high temperatures (980 ℃)33. Ding et al. investigated CeO2-supported BaCoO3−δ and they found that oxygen transfer from CeO2 to BaCoO3−δ perovskite can improve syngas production in methane POx. Coke formation was observed34. Zhao et al. studied the performance of double perovskite-type oxides LaxSr2-xFeyCo2yO6

for CL-SMR, and they demonstrated that the synergistic effects of double-metals could



effectively promote the methane partial oxidation and water splitting. The cycle performance was not investigated in detail35,36. He and Li reported a hybrid solar-redox scheme for liquid fuel and hydrogen co-production from methane37, in which water to hydrogen conversion is as high as 77% but syngas yield is below 65% over LSF-promoted Fe3O4 perovskite promoted iron oxide at 930 ℃ in methane POx step. In CL-SMR literature, most studies focused on the improvement in methane conversion and syngas yield over iron-based oxygen carriers (OCs) that are the most promising candidate materials. By contrast, inhibition of coke deposition is less investigated. Coking causes both hydrogen purity and syngas selectivity to decrease. In addition, the reported water to hydrogen conversion over the iron-based OCs remains well below 100%. Low water to hydrogen conversion results in extra energy loss, making this process less energy efficient. In this work, we exploited one strategy to reduce coke selectivity. Our results clearly exhibit that dispersing OC particles into another substance that reacts with coke or its precursor significantly suppress coking and it also improves water conversion. Specifically, SrFeO3-δ/CaO•MnO composites has a coke selectivity of 6.9% in methane POx step and up to 90% H2O to H2 conversion in water splitting step at a redox temperature of 900 ℃. For a high-performance core-shell OC, the coke selectivity is 43% at 900 oC31.

For LSF-promoted Fe3O4, water to hydrogen is 77% that is much higher than that over other

simple oxides at 930 ℃37,38. In the second part of this paper, the hydrogen and methanol co-production scheme based on CL-SMR is simulated and compared with conventional SMR-based methanol synthesis. Generally, natural gas combustion provides heat to SMR reactors, which contributes a lot to anthropogenic


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CO2 emission. Because of that renewable energy such as solar, wind, and hydro is projected to become the predominant energy sources in the near future. Specifically, solar energy is being considered as the most promising one39-44. Therefore, we compare the process economics of solardriven (CL-SMR and conventional SMR) and thermally-driven (CL-SMR and conventional SMR) schemes. The simulation results demonstrate that the solar-driven co-production scheme exhibits 12% overall energy consumption reduction, 63% CO2 emission decrease and 1.9-fold net income increase compared with the thermally-driven conventional methanol synthesis. Rationale of selecting SrFeO3-δ Potential high-performance OCs were selected based on thermodynamic analysis45. The standard Gibbs free energy of formation of four iron-based oxides and their corresponding equilibrium partial pressure of oxygen (PO2) at a temperature range of 400 to 1000 ℃ is presented in Figure S1, along with the equilibrium syngas yield and H2O to H2 conversion. At a specific temperature, a redox pair (MeOx/MeOx-δ) with a high PO2 gives rises to complete oxidation of methane, but redox pairs with a low PO2 result in low CH4 conversion. In both cases, syngas yield is low. Thus, there exists an appropriate PO2 region where methane is partially oxidized with high syngas yield. As illustrated in Figure S1, the boundary of the green region is equilibrium PO2 corresponding to syngas yield of 90%. In addition, the PO2 region where water to hydrogen conversion between 95% and 99% is also presented in Figure S1. Regarding syngas yield and water conversion, SrFeO2.5 outperforms other iron-based OCs at 850-950 ℃. SrFeO2.5 is a perovskite-typed OC, and it has the highest oxygen capacity among the Ruddlesden-Popper



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perovskite family (Srn+1FenO3n+1). It was found that pure SrFeO3-δ shows relatively low redox kinetics and thermal stability but these challenges can be overcome by dispersing SrFeO3-δ into a medium33. Thus, we speculated that if a medium could react with coke or its precursor, then coking is suppressed. To prove that concept, we dispersed SrFeO3-δ into an oxide matrix. Experimental Synthesis of OCs The chemicals used in preparing OCs were: Sr(NO3)2 (99.5% purity), Fe(NO3)3·9H2O (98.5% purity), Ca(NO3)2·4H2O (99.0% purity), Mn(NO3)2 solution (49.0-51.0 wt.%), citric acid (99.5% purity) and ethylene glycol (99.0% purity). All chemicals were purchased from SINOPHARM and used as received without further purification. For synthesis of SrFeO3-δ/CaO (SF-C) composites (30 wt.% SrFeO3-δ), 0.99 g of Sr(NO3)2, 1.80 g of Fe(NO3)3·9H2O, 8.84 g of Ca(NO3)2·4H2O, and 22.50 g of C6H8O7 (CA) were dissolved into 80 mL of D.I. water (CA: cations=2.5). The solution was heated up to 40 ℃ under agitation (600 rpm), and maintained at this temperature for 30 min. Afterward, 10.90 g of ethylene glycol (EG) was added to the above solution (EG:CA=1.5). The temperature of the resulted solution was increased to 80 ℃ and maintained at this temperature until a gel formation. After that, the gel was dried at 120 ℃ for 12 hr to evaporate the residual water. Subsequently, it was treated at 400 ℃ in the air. Finally, the precursor was calcined at 1200 ℃ in the flowing air for 12 hr. The same procedure was used to prepare SrFeO3-δ/MnO (SF-M, 30 wt.% SrFeO3-δ) and SrFeO3-δ/CaO•MnO (SF-CM, 30 wt.% SrFeO3-δ) composites. The amount of precursors and other chemicals used in preparing above three OCs are listed in Table 1.


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Table 1. The amount of precursors and other chemicals used in preparing three OCs. Ca(NO3)2∙4H2O Mn(NO3)2 C6H8O7 Sample Sr(NO3)2 Fe(NO3)3∙9H2O SF-C 0.99 g 1.90 g 8.84 g N/A 22.50 g SF-M 0.99 g 1.90 g N/A 5.3 g 18.74 g SF-CM 0.99 g 1.90 g 3.90 g 2.96 g 20.40 g

(CH2OH)2 10.90 g 9.08 g 9.88 g

Materials characterization The crystalline phase of composites was examined by X-ray diffraction (XRD) that was performed on a D/Max-R diffractometer equipped with a Cu Kα radiation source (λ = 0.15406 nm). The operating voltage and current of diffractometer were 40 kV and 30 mA, respectively. The samples were scanned over a 2θ range of 10-90° with a scan rate of 1°/min under ambient conditions. To determine the bulk composition of OCs, the sample was digested with hot concentrated nitric acid. The resulted aliquot was analyzed by an inductively coupled plasma mass spectrometer (ICP-MS) (NexION 350D, PerkinElmer). The morphology of the sample was investigated by scanning electron microscope (SEM) on a TESCAN MALA3 LMH scanning electron microscope operated at the accelerating voltage of 5-15 kV. Samples for SEM were dusted onto an adhesive conductive carbon belt attached to the sample holder. Field emission scanning transmission electron microscope (JEM-F200) was used to obtain the high resolution transmission electron microscopy (TEM) images and energy dispersive X-ray (EDS) mappings. The operating voltage was 200 kV. To prepare the sample, a suspension of the sample in ethanol was drop-casted on a carbon-coated copper grid and then was dried at ambient conditions.



Redox testing The redox performance of OCs was evaluated in a quartz tubular fixed-bed reactor with an outer diameter of 8 mm (Figure S2). The reactor was externally heated by an electric furnace with K-type thermocouple monitoring the furnace temperature. Another thermocouple was placed into the OC bed to measure the reaction temperature. A gas mixing panel with three mass flow controllers (KM3100, ALICAT) was used to deliver gaseous mixtures. In a typical experiment, about 2 g of OC particles (200-450 μm) was loaded to the top of a quartz wool plug. The steam was carried by argon passing through two bubblers in series which were filled with D. I. water. The first bubbler was kept at 80 ℃ and the second at 20 ℃ to ensure that argon was saturated. The composition of output stream was monitored by a mass spectrometer (LC-D200M, Tilon). The methods to calculate methane conversion, syngas and coke selectivity, water conversion, and hydrogen purity are presented in the Supporting Information. The sample was pretreated in 20 vol.% oxygen balance with argon at 900 ℃ for 1 hr, followed by purging the reactor with argon (190 STP mL/min) for 15-30 min at the above temperature. Afterward, a gas mixture of 5 vol.% methane balance with argon (total flowrate was 200 STP mL/min) was fed into the reactor. Methane POx lasted until the hydrogen flowrate dropped to 10% of the maximum value. Subsequently, the reactor was purged with argon (190 STP mL/min) for 30 min, followed by feeding steam-argon mixture (argon flowrate was 190 STP mL/min) to the reactor. After water splitting was completed, the reactor was purged with argon (190 STP mL/min) again for 30 min and then the next redox cycle started.


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Results and discussion Redox performance of three composites Over SF-CM composites whose bulk composition was verified by ICP-MS (Table S1) at a redox temperature of 900 ℃, the reduction step can be divided into four phases based on the output flowrate of methane (Figure 2a): I) Initial phase. Methane flowrate in the output stream rises sharply to a local maximum, along with the appearance of both CO2 and CO. The formation of CO2 is attributed to deep oxidation of methane (CH4+4[O]S→CO2+2H2O) by surface oxygen ([O]S). In the output stream, CO2 flowrate maximizes before methane flowrate reaches the local maximum. The instantaneous CO2 flowrate depends on the concentrations of both methane in the input stream and surface oxygen of OCs, and they vary in opposite directions. The former continuously increases, whereas the later continuously decreases. The combustion reaction is accompanied by partial oxidation of methane (CH4+[O]L→CO+2H2) by lattice oxygen ([O]L) located at the outermost layer of OC particles. II) Transition phase. Methane flowrate in the output stream drops dramatically, whereas both CO and H2 flowrates rise quickly. At this phase, more strontium ferrite is reduced, generating metallic iron particles over which methane is activated. III) Stationary phase. Methane flowrate in the output stream changes insignificantly, and the same trend is also observed for CO and H2 flowrates. At this phase, the available amount of lattice oxygen is consumed, but more active sites are created, resulting in marginal change in the output flowrates. IV) Demise phase. Methane flowrate in the output stream rises drastically, and the



opposite trend is observed for CO and H2 flowrates. At the same time, CO2 flowrate almost drops to zero. At this phase, the availability of lattice oxygen comes to an end.

Figure 2. Evolution profiles of H2, CO, and CO2 in methane POx step (a) and water splitting step (b) of the 2nd cycle over SF-CM composites. Reaction conditions: mSF-CM=2 g; T=900 °C, Fox=200 STP mL/min (5 vol.% methane), Fre=194.5 STP mL/min (2.31 vol.% steam), P=1 atm.


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As illustrated in Figure 2a, the period of first phase is relatively short in the POx step. It is worthwhile to note that CO2 flowrate in the last three phases are much lower than CO flowrate, clearly demonstrating that methane POx is the predominant reaction. Another observation is that H2:CO mole ratio fluctuates around 2 in the POx step and it is a little bit higher than 2 in the last two phases. This implies that methane cracking (CH4→C+2H2) occurs and we surmise it mainly takes place in phase IV. After most lattice oxygen is consumed, steam is fed to the reactor. In water splitting step at 900 ℃, water reacts with both reduced composites and coke, replenishing the depleted oxygen species and producing H2 and CO (Figure 2b). Figure 2b shows that the profile of both H2 and CO flowrates looks like a step function. In the output stream, H2 flowrate is much higher than CO flowrate and CO2 is ignorable. Methane conversion over SF-CM composites is 41.3%. It should be mentioned that appropriately shortening the POx period can improve methane conversion, as evidenced by the flowrate profile of methane in the output stream (Figure 2a). For instance, it rises up to 55% at 900 ℃ when methane in the input stream was cut off at the end of phase III. There are other strategies like reducing the input flowrate of methane and/or increasing reaction temperature to improve methane conversion further. To obtain insights into the role of dispersing media, the performance of three OCs (SF-C, SFCM and SF-M composites) were evaluated at 900 ℃, and the results are presented in Figure 3. In terms of methane conversion, SF-CM composites outperform the others. Specifically, the maximum instantaneous methane conversion over SF-CM is 66.2%. By contrast, it is 47.6 and 44.2% over SF-C and SF-M, respectively. The improved methane conversion most likely comes



from partially A- and B-site substitution by Ca and Mn, respectively. The formation of coke is significantly suppressed by the presence of manganese oxide. Specifically, coke selectivity is 5.2, 6.9 and 16.6% over SF-M, SF-CM, and SF-C composites, respectively. Correspondingly, the syngas selectivity decreases, which are 95.3, 91.5 and 88.4% over the above three composites, respectively. In water splitting step, hydrogen purity over each composite shows a trend opposite to that of coke selectivity. Specifically, hydrogen purity over SF-M, SF-CM, and SF-C composites is 95.5, 94.6 and 86.4%, respectively. The dispersing medium, however, has little effect on water conversion, which is around 90% at 900 ℃. These findings suggest that manganese oxide could effectively inhibit coking.

Figure 3. Performance of three composites in the 2nd cycle. (a: coke selectivity; b: maximum instantaneous methane conversion; c: H2 purity; d: water conversion). Reaction conditions: mOC=2


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g; T=900 °C, Fox=200 STP mL/min (5 vol.% methane), Fre=194.5 STP mL/min (2.31 vol.% steam), P=1 atm. The mechanism of manganese oxide suppressing coke formation was inferred from thermal treatment of reduced composites in argon followed by re-introducing methane after phase IV. Typically, the reduced composite bed was purged with argon at 900 ℃ until CO was negligible in the output stream, and then the reactor was ramped up to 1000 ℃ at 10 ℃/min in argon. Afterward, the reactor was cooled down to 900 ℃. Finally, methane was re-introduced into the reactor. The output flowrates of both CO and H2 as a function of time are presented in Figure 4, in which A, B, C, D, and E stand for the start of feeding methane, the end of feeding methane, the onset of ramping, the endset of ramping, and the start of re-feeding methane after the temperature dropped to 900 ℃, respectively. When the reactor temperature increases from 900 to 1000 ℃, only CO is detected in the output stream which comes from the reaction between coke and lattice oxygen. We observed that the amount of CO formed over SF-CM composite is 60% more than that over SF-C composite. Therefore, it is reasonable to speculate that some coke or its precursor reacts with manganese oxide. After re-introducing methane, both cracking and partial oxidation occurs but the former is predominant. One interesting observation is the maximum instantaneous hydrogen flowrate over SF-CM composites is about 8-fold of that over SF-C composites. Coke gasification regenerates the active sites for methane activation, thus methane cracking proceeds much faster over SF-CM composites than that over SF-C composites. Based on these observations, we believe that manganese oxide reacts with coke or coke precursor.



Figure 4. Evolution profiles of H2 and CO in methane POx over SF-CM (a) and SF-C (b) composites with intermediate thermal treatment in argon.


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More information about the property of OCs was gained from XRD patterns of as-prepared, methane-reduced, and water-regenerated samples. For SF-C composites (Figure S3a), the predominant phases of as-prepared sample are SrFeO2.73 and CaO, and former is transformed to SrO, Fe and Fe3C in methane POx step. After regenerating the reduced composite with water, SrFeO2.5 becomes the active phase. In the subsequent redox cycles, the oxidation state of iron swings between +3 and 0. For SF-CM and SF-M composites (Figure 5, Figure S3b), the principal phases of as-prepared samples are (Ca0.5Sr0.5)MnO3 and SrMn3O6-x, respectively. For the reduced SF-CM and SF-M composites, the diffraction patterns of MnxCy are observed which may result from the reaction between coke and manganese oxide. After oxidation by water, SrFeO2.5 and Sr4Fe3O10 become the active phases of SF-CM and SF-M composites, respectively. Subsequently, neither SrMn3O6-x nor (Ca0.5Sr0.5)MnO3 occurs in the redox cycles. From the diffraction patterns of reduced and regenerated composites, we confirm that CaO•MnO and MnO are the dispersing medium of SF-CM and SF-M composites, respectively.



Figure 5. XRD patterns of as-prepared, CH4-reduced, H2O-regenerated SF-CM samples. The morphology of SF-CM images revealed by SEM images (Figure S4). The composite particles become large after redox cycles, indicating agglomeration occurs. Further insights into the nature of SF-CM composites were provided by TEM images and elemental mappings (Figure 6). For as-prepared sample, Sr, Fe, Ca, and Mn distribute uniformly. For the reduced sample, nanosized iron particles are observed (Figure S5). After oxidation by water, these four elements redistribute uniformly (Figure 6). These observations clearly demonstrate that the redox process is reversible. Furthermore, the cyclability of SF-CM composites, one of key properties of OCs, was investigated. Starting from the fresh sample, 10 redox cycles were carried out at 900 ℃. Both syngas productivity in methane POx step and hydrogen productivity in water splitting step change slightly over the last 9 cycles (Figure 7). Specifically, syngas productivity varies from 6.7 to 7.5


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mmol/gSF-CM from the 2nd to the 10th cycle and hydrogen productivity fluctuates around 3.1 mmol/gSF-CM.

a

b



c Figure 6. Superposition of EDS elemental maps of Sr, Fe, Ca, Mn and O (insert is dark field STEM images) and the elemental map of Fe for SF-CM sample: as-prepared (a), CH4-reduced (b), H2Oregenerated (c). Reaction conditions: mSF-CM=2 g; T=900 °C, Fox=200 STP mL/min (5 vol.% methane), Fre=194.5 STP mL/min (2.31 vol.% steam), P=1 atm.

Figure 7. Productivity of H2, CO, and CO2 of SF-CM sample in methane POx and H2 in water splitting steps. Reaction conditions: mSF-CM=2 g; T=900 °C, Fox=200 STP mL/min (5 vol.% methane), Fre=194.5 STP mL/min (2.31 vol.% steam), P=1 atm. Besides thermal stability testing, we also investigated the effect of operating conditions on the redox performance. Figure 8 exhibits the performance of three OCs at three temperatures (900, 950, and 1000 ℃). As expected, methane conversion increases with increasing reaction temperatures. For example, the maximum instantaneous methane conversion reaches 88.5% over SF-CM composites at 1000 ℃, about 1.5 times as high as that at 900 ℃ (Figure 8a). Coke selectivity over three composites, however, changes slightly as the temperature increases from 900


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to 950 ℃ (Figure 8b). With a further increase in the reduction temperature, coke selectivity over SF-C composite increases but that over SF-CM and SF-M composites decreases.



Figure 8. Maximum instantaneous methane conversion (a), coke selectivity (b) and the amount of lattice oxygen transferred at three temperatures (c) in methane POx step for three composites. Generally speaking, high temperatures favor methane cracking which gives rise to more coke. However, the reaction between coke or its precursor and manganese oxide is also accelerated at high temperatures. These two opposite factors make the manganese-containing composites more coke-resistant at high temperature. Specifically, coke selectivity over SF-CM and SF-M composites are 4.8 and 3.4% at 1000 ℃, respectively. The former is about 1/4 of that over SF-C at the same temperature. The participation of manganese oxide in methane POx step is also inferred from the amount of oxygen transferred. As illustrated in Figure 8c, the amount of oxygen involved in the reduction reaction decreases from 5.61 to 4.71 mmol/gOC for SF-C composites but it


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increases from 4.59 to 8.44 mmol/gOC for SF-M composite as the temperature increases from 900 to 1000 ℃. The latter trend is also observed for SF-CM composites. Simulation of methanol and hydrogen co-production system As mentioned before, both syngas and hydrogen streams are produced in CL-SMR process. Because gas products are not very suitable for large-scale storage and long-distance transportation, it is desired to convert them to liquid products. Additionally, the mole ratio of H2:CO in the syngas stream is close to 2, which is very suitable for subsequent GTL processes. Methanol is not only an important raw material but also a potential fuel for automobiles. Here, we numerically investigate the solar-driven methanol and hydrogen co-production scheme based on CL-SMR (hereafter referred to as MeH2 scheme), in which concentrated solar radiation is used as the source of energy (in form of heat) to drive the chemical looping reactions. Solar energy can be integrated into the chemical looping system either directly or directly46,47. In the first case, solar radiation is focused on the reactor that also serves as the solar receiver (directly irradiated reactor). By contrast, in the indirectly irradiation configuration, a heat transfer fluid is used to conduct solar heat from the receiver to the reactor (indirectly heated reactor). Regardless of the reactor type, higher temperatures required for SMR effectively limit the choice of solar concentrator to solar dishes and towers. Moreover, the intermittent nature of solar energy arising from fluctuations in weather conditions can addressed by introducing a thermal chemical storage system41. As illustrated in Figure S6, MeH2 scheme consists of four modules: chemical looping reforming (CLR), water gas shift (WGS), heat recovery with steam generation (HRSG), and methanol synthesis (MS). The first module includes two reactors of which the heat source is



concentrated solar power or natural gas combustion, and syngas is produced in the reducer and pure hydrogen is generated in the oxidizer. The WGS module is used to adjust the mole ratio of COx:H2 in the input stream fed to the MS reactor. The HRSG module is implemented to recover the waste heat of the stream from WSG module to generate electricity. The MS module has reaction (MeOH reactor) and separation subsystems, where syngas is converted into crude methanol in a fixed-bed reactor48,49, and then it is cooled and purified to obtain high-quality methanol. The process was simulated by ASPEN Plus® and the details of each stream of MeH2 scheme are listed in Table S2. The reducer and oxidizer are modeled as Gibbs reactors (900 ℃ and 1 atm). The WGS reactor is also modeled as a Gibbs reactor (400 ℃ and 20 atm). In the HRSG module, the stream is cooled down to ca. 100 ℃ and then compressed to 105 atm, followed by condensing water out before entering the MS module. The methanol reactor is operated at 265 ℃ and 105 atm in a recycling mode, with overall 95% conversion of COx to MeOH50. The product capacity, economy, CO2 emission, and energy efficiency of methanol and hydrogen co-production scheme were compared with those of conventional SMR-based methanol synthesis (hereafter referred to as MeOH scheme). Similar to MeH2 scheme, MeOH scheme consists of SMR, RWGS, HRSG, and MS modules (Figure S7). Because the theoretical H2:CO ratio of SMR reaction is 3, CO2 is fed to the reactant stream in MeOH scheme (Figure S7, Table S3). The RWGS module is used to adjust the mole ratio of COx:H2 of the input stream fed to the MS module. The HRSG and MS modules were the same as in MeH2 scheme. The details of each stream are listed in Table S3.


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Table 2 lists the feed and product flowrates with CO2 emission of two schemes. For the comparison purpose, the input flowrate of methane and the reaction conditions of MeH2 and MeOH scheme were set to the same. To suppress coking, the feeding rate of water in the latter is 3.1 times as high as that in the former. The products of MeH2 scheme are methanol and hydrogen. The MeOH scheme produces methanol only. For MeOH scheme, additional CO2 is fed to the SMR reactor. Thus, methanol production rate in MeOH scheme is higher than that in MeH2 scheme. We calculated CO2 emission of thermally-driven and solar-driven MeH2 and MeOH schemes, and the results are listed in Table 2. The results clearly demonstrate the CO2 emission of MeH2 scheme is less than that of MeOH scheme for the same heat source (solar or natural gas combustion). When both MeH2 and MeOH schemes are driven by solar energy, for each tonne of methanol produced, the former shows 45% less CO2 emission than the latter. On the other hand, when the heat is provided by natural gas combustion, MeH2 scheme still shows nearly 13% CO2 emission less than MeOH scheme. Table 2. Feed and product flowrates with CO2 emission of MeH2 and MeOH schemes. MeH2 MeOH Solar-driven Thermally-driven Solar-driven Thermally-driven Methane input (kg/hr) 1,440 1,440 H2O input (kg/hr) 1,569 4,860 CO2 input (kg/hr) N/A 1408 Methanol yield (kg/hr) 2,628 3,414 Hydrogen yield (kg/hr) 173 N/A CO2 emission (tonne/tonne methanol) 0.631 1.488 1.152 1.709 Economic analysis An economic analysis without considering the total CAPEX was conducted for both MeH2 and MeOH schemes, and the results are listed in Table 3. The price of hydrogen, methanol, and



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natural gas was set to 3,560 USD/tonne, 484 USD/tonne and 300 USD/tonne, respectively51. The price of electricity is set to 0.093 USD/kWh (Table S4). The net income of solar-driven MeH2 scheme is 1,356 USD/hr, roughly 1.9 times as high as that of thermally-driven MeOH one. Even if natural gas combustion provides heat in both schemes, the net income of thermally-driven MeH2 scheme process is still 53% higher than that of thermally-driven MeOH one. If solar energy is used in both schemes, the net income of MeH2 scheme is around 18% higher than that of MeOH one.

Table 3. Economic data of MeH2 and MeOH schemes. MeH2 Solar-driven Thermally-driven Electricity need (kWh/hr) 1,076 Electricity cost (USD/hr) 100 Total natural gas cost (USD/hr) 680 Fuel natural gas cost (USD/hr) 248 Methanol earnings (USD/hr) 1,272 Hydrogen earnings (USD/hr) 616 Net income (USD/hr) 1,356 1,108

MeOH Solar-driven Thermally-driven 818 76 854 422 1,652 N/A 1,144 722

The influence of the price of methane, methanol, hydrogen and electricity on the net income was also analyzed. The price range of reactants, products and electricity was obtained from the pricing platform51. As shown in Figure S8, the net income of solar-driven MeH2 scheme is higher than that of solar-driven MeOH one. Moreover, the price of products significantly affects the net income. On the other hand, the net income is weakly dependent on electricity price. This is because electricity consumption is not significant. Energy and exergy analysis


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The energy demand for each reactor and the total energy consumption are listed in Table S5. Because SMR reaction is highly endothermic, the energy demand for this reaction accounts for the most energy consumption, which is provided by solar energy or natural gas combustion. The Grand Composite Curves of MeH2 and MeOH schemes, where cold water fed to the HRSG unit is considered as the cold stream, are presented in Figure S9. For the former, the amount of steam at 150 ℃ generated from waste heat is 3.75 GJ/h. For the latter, no useful steam can be generated because the pitch point temperature is as low as 115 oC. The exergy efficiency of MeH2 and MeOH schemes was also calculated by Equations S23. The exergy input or output consists of chemical and physical exergy of all streams, work exergy (pumps and compressors), and heat exergy. The exergy distribution is illustrated in Figure 9. The exergy efficiency of MeH2 scheme is 84.3%, which is 14% higher than that of MeOH scheme (Figure 9). The total exergy inputs of MeH2 and MeOH scheme are identical, but the exergy loss of MeH2 scheme is less than that of MeOH one (5.07 and 8.44 MW for MeH2 and MeOH schemes, respectively). The circulation of OC in chemical looping process reduces the exergy loss in MeH2 scheme. This reduction, along with the exergy output of hydrogen, makes the exergy efficiency of MeH2 scheme higher than that of MeOH one.



a

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b

Figure 9. The input and output exergy distribution of MeH2 (a) and MeOH (b) schemes. Conclusions In this work, a strategy of both suppressing coke deposition in methane partial oxidation step and improving water to hydrogen conversion in water splitting step of chemical looping steam methane reforming was explored. Ferrite-contained composites were prepared by the sol-gel method, and the redox performance of oxygen carriers was evaluated in a fixed-bed tubular reactor at 900-1000 ℃ and atmospheric pressure. In addition, a scheme of solar-driven co-production of hydrogen and methanol was numerically investigated and compared with methanol schemes. Among three oxygen carriers that contain 30 wt.% of strontium ferrite, SrFeO3-δ/CaO•MnO (SF-CM) composites outperform the others. In methane POx step, the instantaneous methane conversion reaches 66.2% at 900 ℃ and nearly 90% at 1000 ℃. At 900 ℃, coke selectivity is 6.9% and syngas selectivity is 91.5% in the reduction step and water to hydrogen conversion is 90% in the oxidation step. Besides high redox activity, SF-CM composites also exhibit remarkable cyclability at 900 ℃. The redox performance changes marginally in 10 cycles.


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The mechanism of suppressing coke formation by manganese oxide is attributed to the reaction between manganese oxide and coke or its precursor which is inferred from thermal treatment. This reaction is favored over methane cracking at high temperatures, resulting in a decrease in coke selectivity as reduction temperature increases from 900 to 1000 ℃. To achieve high syngas yield and pure hydrogen, it is desired to operate the redox reactions at high temperatures. However, given the energy consumption, thermal stability, type of solar reactor and reactor materials, the operating temperature should be optimized. The techno-economic analysis suggests that chemical looping technology increases exergy efficiency. When using the same heat source, MeH2 scheme exhibits superiority to MeOH one. The CO2 emission of solar-driven MeH2 is 0.631 tonne/tonne methanol, 63% less than that of thermally-driven MeOH one. With regard to the process economics and overall energy consumption, the former scheme is superior to the latter. Supporting Information Equations S1-S23, Figures S1-S9, Tables S1-S5 (PDF) The Supporting Information is available free of charge on the ACS Publications website. Corresponding Author *E-mail address: [email protected] (Junshe Zhang), [email protected] (Jinjia Wei) ORCID Junshe Zhang: 0000-0002-0668-5456. Jinjia Wei: 0000-0001-7355-415X.



Acknowledgements The present work is supported by the Key Research Project of Shaanxi Province (No.2017ZDXM-GY-017), Shaanxi Key Science and Technology Innovation Team (No.2019TD039), Yulin Science and Technology Project (No.2017KJJH-03) and New Faculty Start-up Funding of Xi’an Jiaotong University (No. 7121181226). The authors would like to thank Dr. Minbo Yang from Xi’an Jiaotong University for valuable suggestions on simulation. References (1) Guo X.; Fang G.; Li G.; Ma H.; Fan H.; Yu L.; Ma C.; Wu X.; Deng D.; Wei M.; Tan D.; Si R.; Zhang S.; Li J.; Sun L.; Tang Z.; Pan X.; Bao X. Direct, nonoxidative conversion of methane to ethylene, aromatics and hydrogen. Science 2014, 344, 616-619. (2) Gao, J.; Zheng Y.; Jehng J. M.; Tang, Y.; Wachs, I.E.; Podkolzin, S.G. Identification of Molybdenum Oxide Nanostructures on Zeolites for Natural Gas Conversion. Science. 2015, 348, 686–690. (3) Horn, R.; Schlögl, R. Methane Activation by Heterogeneous Catalysis. Catal. Lett. 2014, 145, 23–39. (4) Mesters, C. A selection of recent advances in C1 chemistry. Annu. Rev. Chem. Biomol. Eng. 2016, 7, 223-238. (5) Morejudo, S. H.; Zanón, R.; Escolástico, S.; Yuste-Tirados, I.; Malerød-Fjeld, H.; Vestre, P. K.; Coors, W. G.; Martínez, A.; Norby, T.; Serra, J. M.; Kjølseth, C. Direct Conversion of


Page 30 of 37

Page 31 of 37 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


Methane to Aromatics in a Catalytic Co-Ionic Membrane Reactor. Science. 2016, 353, 563– 566. (6) Sushkevich, V. L.; Palagin, D.; Ranocchiari, M.; van Bokhoven, J. A. Selective Anaerobic Oxidation of Methane Enables Direct Synthesis of methanol. Science. 2017, 527, 523–527. (7) Taifan, W.; Baltrusaitis, J. CH4 Conversion to Value Added Products: Potential, Limitations and Extensions of a Single Step Heterogeneous Catalysis. Appl. Catal. B 2016, 198, 525–547. (8) Schwach P.; Pan X.; Bao X. Direct conversion of methane to value-added chemicals over heterogeneous catalysts: challenges and prospects. Chem. Rev. 2017,117, 8497-8520. (9) De Vos, Y.; Jacobs, M.; Van Der Voort, P.; Van Driessche, I.; Snijkers, F.; Verberckmoes, A. Optimization of Spray Dried Attrition-Resistant Iron Based Oxygen Carriers for Chemical Looping Reforming. Chem. Eng. J. 2017, 309, 824–839. (10) Simpson, A. P.; Lutz, A. E. Exergy Analysis of Hydrogen Production via Steam Methane Reforming. Int. J. Hydrogen Energy 2007, 32, 4811–4820. (11) Salkuyeh, Y. K.; Saville, B. A.; MacLean, H. L. Techno-Economic Analysis and Life Cycle Assessment of Hydrogen Production from Natural Gas Using Current and Emerging Technologies. Int. J. Hydrogen Energy 2017, 42, 18894–18909. (12) Khodakov, A. Y.; Chu, W.; Fongarland, P. Advances in the Development of Novel Cobalt Fischer-Tropsch Catalysts for Synthesis of Long-Chain Hydrocarbons and Clean Fuels. Chem. Rev. 2007, 107, 1692–1744.



(13) Dagle, R. A.; Lizarazo-Adarme, J. A.; Leatmbier Dagle, V.; Gray, M. J.; White, J. F.; King, D. L.; Palo, D. R. Syngas Conversion to Gasoline-Range Hydrocarbons over Pd/ZnO/Al2O3 and ZSM-5 Composite Catalyst System. Fuel Process. Technol. 2014, 123, 65–74. (14) Warren, K. J.; Reim, J.; Randhir, K.; Greek, B.; Carrillo, R.; Hahn, D. W.; Scheffe, J. R. Theoretical and Experimental Investigation of Solar Methane Reforming through the Nonstoichiometric Ceria Redox Cycle. Energy Technol. 2017, 5, 2138–2149. (15) Zeng, L.; Cheng, Z.; Fan, J. A.; Fan, L.-S.; Gong, J. Metal Oxide Redox Chemistry for Chemical Looping Processes. Nat. Rev. Chem. 2018, 2, 349–364. (16) Fan L. Chemical Looping Partial Oxidation: Gasification, Reforming, and Chemical Syntheses; Cambridge Univ. Press: Cambridge, 2017. (17) S G Adiya, Z. I.; Dupont, V.; Mahmud, T. Steam Reforming of Shale Gas in a Packed Bed Reactor with and without Chemical Looping Using Nickel Based Oxygen Carrier. Int. J. Hydrogen Energy 2018, 43, 6904–6917. (18) Chueh, W. C.; Falter Christoph, F.; Abbott, M.; Scipio, D.; Furler, P.; Haile, S. M.; Steinfeld, A. High-Flux Solar-Driven Thermochemical Dissociation of CO2 and H2O Using Nonstoichiometric Ceria. Science. 2011, 330, 1797-1801. (19) Mattisson, T.; Keller, M.; Linderholm, C.; Moldenhauer, P.; Rydén, M.; Leion, H.; Lyngfelt, A. Chemical-Looping Technologies Using Circulating Fluidized Bed Systems: Status of Development. Fuel Process. Technol. 2018, 172, 1–12.


Page 32 of 37

Page 33 of 37 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


(20) Agrafiotis, C.; Roeb, M.; Sattler, C. A Review on Solar Thermal Syngas Production via Redox Pair-Based Water/Carbon Dioxide Splitting Thermochemical Cycles. Renew. Sustain. Energy Rev. 2015, 42, 254–285. (21) Gao, X.; Vidal, A.; Bayon, A.; Bader, R.; Hinkley, J.; Lipiński, W.; Tricoli, A. Efficient Ceria Nanostructures for Enhanced Solar Fuel Production: Via High-Temperature Thermochemical Redox Cycles. J. Mater. Chem. A 2016, 4, 9614–9624. (22) Muhich, C. L.; Ehrhart, B. D.; Al-Shankiti, I.; Ward, B. J.; Musgrave, C. B.; Weimer, A. W. A Review and Perspective of Efficient Hydrogen Generation via Solar Thermal Water Splitting. Wiley Interdiscip. Rev. Energy Environ. 2016, 5, 261–287. (23) Scheffe, J. R.; Steinfeld, A. Oxygen Exchange Materials for Solar Thermochemical Splitting of H2O and CO2: A Review. Mater. Today 2014, 17, 341–348. (24) Luo, M.; Yi, Y.; Wang, S.; Wang, Z.; Du, M.; Pan, J.; Wang, Q. Review of Hydrogen Production Using Chemical-Looping Technology. Renew. Sustain. Energy Rev. 2018, 81, 3186–3214. (25) Cho, P.; Mattisson, T.; Lyngfelt, A. Comparison of Iron-, Nickel-, Copper- and ManganeseBased Oxygen Carriers for Chemical-Looping Combustion. Fuel 2004, 83, 1215–1225. (26) Fan, Y.; Siriwardane, R. Novel New Oxygen Carriers for Chemical Looping Combustion of Solid Fuels. Energy Fuels 2014, 28, 2248–2257. (27) Johansson, M.; Mattisson, T.; Lyngfelt, A. Investigation of Mn3O4 with Stabilized ZrO2 for Chemical-Looping Combustion. Chem. Eng. Res. Des. 2006, 84, 807–818.



(28) Tang, M.; Xu, L.; Fan, M. Progress in Oxygen Carrier Development of Methane-Based Chemical-Looping Reforming: A Review. Appl. Energy 2015, 151, 143–156. (29) Zhu, X.; Wang, H.; Wei, Y.; Li, K.; Cheng, X. Hydrogen and Syngas Production from TwoStep Steam Reforming of Methane Using CeO2 as Oxygen Carrier. J. Nat. Gas Chem. 2011, 20, 281–286. (30) Lim, H. S.; Lee, M.; Kang, D.; Lee, J. W. Role of Transition Metal in Perovskites for Enhancing Selectivity of Methane to Syngas. Int. J. Hydrogen Energy 2018, 43, 20580–20590. (31) Neal, L. M.; Shafiefarhood, A.; Li, F. Dynamic Methane Partial Oxidation Using a [email protected]δ Core-Shell Redox Catalyst in the Absence of Gaseous Oxygen. ACS Catal. 2014, 4, 3560-3569. (32) Haribal, V. P.; He, F.; Mishra, A.; Li, F. Iron-Doped BaMnO3 for Hybrid Water Splitting and Syngas Generation. ChemSusChem 2017, 10, 3402–3408. (33) Zhang, J.; Haribal, V.; Li, F. Perovskite Nanocomposites as Effective CO2-Splitting Agents in a Cyclic Redox Scheme. Sci. Adv. 2017, 3 (8), 2–10. (34) Ding, H.; Xu, Y.; Luo, C.; Wang, Q.; Shen, C.; Xu, J.; Zhang, L. A Novel Composite Perovskite-Based Material for Chemical-Looping Steam Methane Reforming to Hydrogen and Syngas. Energy Convers. Manag. 2018, 171, 12–19. (35) Zhao, K.; Zheng, A.; Li, H.; He, F.; Huang, Z.; Wei, G.; Shen, Y.; Zhao, Z. Exploration of the Mechanism of Chemical Looping Steam Methane Reforming Using Double Perovskite-Type Oxides La1.6Sr0.4FeCoO6. Appl. Catal. B 2017, 219, 672–682.


Page 34 of 37

Page 35 of 37 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


(36) Zhao, K.; Chen, J.; Li, H.; Zheng, A.; He, F. Effects of Co-Substitution on the Reactivity of Double Perovskite Oxides LaSrFe2-xCoxO6 for the Chemical-Looping Steam Methane Reforming. J. Energy Inst. 2018, 1–10. (37) He, F.; Li, F. Perovskite Promoted Iron Oxide for Hybrid Water-Splitting and Syngas Generation with Exceptional Conversion. Energy Environ. Sci. 2015, 8, 535–539. (38) Solunke, R. D.; Veser, G. Hydrogen Production via Chemical Looping Steam Reforming in a Periodically Operated Fixed-Bed Reactor. Ind. Eng. Chem. Res. 2010, 49, 11037–11044. (39) Chuayboon, S.; Abanades, S.; Rodat, S. Syngas Production via Solar-Driven Chemical Looping Methane Reforming from Redox Cycling of Ceria Porous Foam in a Volumetric Solar Reactor. Chem. Eng. J. 2019, 356, 756–770. (40) Prieto, C.; Cooper, P.; Fernández, A. I.; Cabeza, L. F. Review of Technology: Thermochemical Energy Storage for Concentrated Solar Power Plants. Renew. Sustain. Energy Rev. 2016, 60, 909–929. (41) Carrillo, A. J.; González-Aguilar, J.; Romero, M.; Coronado, J. M. Solar Energy on Demand: A Review on High Temperature Thermochemical Heat Storage Systems and Materials. Chem. Rev. 2019, 119, 4777–4816. (42) Yadav, D.; Banerjee, R. A Review of Solar Thermochemical Processes. Renew. Sustain. Energy Rev. 2016, 54, 497–532. (43) Aydin, D.; Casey, S. P.; Riffat, S. The Latest Advancements on Thermochemical Heat Storage Systems. Renew. Sustain. Energy Rev. 2015, 41, 356–367.



(44) Pelay, U.; Luo, L.; Fan, Y.; Stitou, D.; Rood, M. Thermal Energy Storage Systems for Concentrated Solar Power Plants. Renew. Sustain. Energy Rev. 2017, 79, 82–100. (45) Fossdal, A.; Einarsrud, M. A.; Grande, T. Phase Equilibria in the Pseudo-Binary System SrOFe2O3. J. Solid State Chem. 2004, 177, 2933–2942. (46) Agrafiotis, C.; Von Storch, H.; Roeb, M.; Sattler, C. Solar Thermal Reforming of Methane Feedstocks for Hydrogen and Syngas Production—A Review. Renew. Sustain. Energy Rev. 2014, 29, 656–682. (47) Simakov, D. S. A.; Wright, M. M.; Ahmed, S.; Mokheimer, E. M. A.; Román-Leshkov, Y. Solar Thermal Catalytic Reforming of Natural Gas: A Review on Chemistry, Catalysis and System Design. Catal. Sci. Technol. 2015, 5 (4), 1991–2016. (48) Jones J. H. The CativaTM process for the manufacture of acetic acid. Platinum Metals Rev. 2000, 44, 94–105. (49) Waugh K. C. Methanol synthesis. Catal. Lett. 2012, 142, 1153–1166. (50) Merte, L. R.; Peng, G.; Bechstein, R.; Rieboldt, F.; Farberow, C. A.; Grabow, L. C.; Kudernatsch, W.; Wendt, S.; Lægsgaard, E.; Mavrikakis, M.; Besenbacher F. Water-Mediated Proton Hopping on an Iron Oxide Surface. Science. 2012, 336, 889–893. (51) Sublime China Information Co., Ltd. China commodity pricing platform. 2019; www.sci99.com (accessed May 2019).


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For Table of Contents Only


Coproduction of Hydrogen and Methanol from Methane by Chemical

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