A ternary iron-based oxygen carrier, a preparation method and application thereof

Abstract

The application discloses a ternary iron-based oxygen carrier and a preparation method and application thereof. The ternary iron-based oxygen carrier takes inert carrier ZrO2 and perovskite LaFeO3 as a composite carrier, and includes 60% of Fe2O3, 10-30% of ZrO2 and 30-10% of LaFeO3 in percentage by mass. Fe2O3, ZrO2 and LaFeO3 are uniformly distributed in the ternary iron-based oxygen carrier. Water-soluble salts of Fe, Zr and La are dissolved in deionized water to obtain a mixed solution, and an ammonia water solution is added dropwise after heating to precipitate metal ions. The ternary iron-based oxygen carrier particles are obtained through aging, filtration, drying, decomposition, calcination and grinding and screening. The preparation method is simple, and a preparation period is short. The ternary iron-based oxygen carrier has the characteristics of high deep reduction activity, strong anti-coking and anti-sintering capacities and the like under the synergistic action of ZrO2 / LaFeO3, and is superior to a binary iron-based oxygen carrier in H2 yield, H2 purity and cycle stability in chemical chain hydrogen production.

Description

TECHNICAL FIELD

[0001] The application relates to a ternary iron-based oxygen carrier for chemical looping hydrogen production and a preparation method and application thereof, in particular to a Fe2O3 / ZrO2 / LaFeO3 ternary iron-based oxygen carrier for chemical looping hydrogen production and a preparation method and application thereof, and belongs to the field of chemical looping hydrogen production. BACKGROUND

[0002] Hydrogen energy is a high-efficiency energy storage carrier with large energy density, high heat value and low carbon emission, and can be widely applied to fuel cells, power generation and other fields. Chemical looping hydrogen production technology is a new hydrogen production technology, and has the advantages of preparing high-purity hydrogen and realizing intrinsic separation and capture of CO2. The chemical looping hydrogen production system is composed of three reactors in series, i.e. a fuel reactor, a steam reactor and an air reactor. Metal oxides are reduced by fuel in the fuel reactor to generate low-valence metal oxides, and the fuel is completely converted into CO2 and H2O; the low-valence metal oxides are partially oxidized in the steam reactor to produce H2; finally, the partially oxidized metal oxides are completely oxidized and regenerated in the air reactor. The gas product at the outlet of the steam reactor can be condensed to obtain high-purity H2.

[0003] Developing high-performance oxygen carriers is a major challenge for the large-scale application of chemical looping hydrogen production technology. Domestic and foreign scholars have explored Fe2O3, WO3 and CeO2 metal oxide oxygen carriers, and found that Fe2O3 has the advantages of low cost, strong oxygen carrying capacity and environmental friendliness, and has good industrial application prospect. Since single iron oxide will quickly lose redox activity due to sintering, iron oxide is usually loaded on a high-temperature-resistant carrier to enhance its cycle stability. Common carriers include Al2O3, MgAl2O4, TiO2, SiO2, YSZ and ZrO2, and research shows that ZrO2-loaded iron oxide has high porosity and sintering resistance. However, since the reaction activity of Fe3O4→Fe / FeO is much lower than that of Fe2O3→Fe3O4, the former is the limiting step in the chemical looping hydrogen production process, and it is necessary to further improve the deep reduction reaction activity of iron oxide. In addition, the relatively serious carbon deposition in Fe2O3 / ZrO2 reduces the H2 purity in CLHG, and the enrichment of Fe ions on the surface of the particles after redox cycling reduces its sintering resistance, resulting in a decrease in reaction activity and cycle stability. Therefore, further improving the deep reduction activity, cycle stability and anti-carbon deposition capacity of the iron-based oxygen carrier is one of the key problems in the development of chemical looping hydrogen production technology.

[0004] Improving the oxygen lattice conductivity of the oxygen carrier can promote its redox reaction activity, in addition, high oxygen ion conductivity can also enhance the anti-coking ability and inhibit the migration of Fe ions from the inside to the outside of the particles, thereby improving the H2 purity and cycle stability. LaFeO3 is a classic ABO3 type perovskite, which has high oxygen storage and release capacity, reaction activity and structural stability, can enhance the deep redox reaction activity and cycle stability during the cycle process. SUMMARY

[0005] The first object of the present application is to provide a ternary iron-based oxygen carrier to solve the problems of low deep reduction activity, poor cycle stability and weak anti-coking ability of iron-based oxygen carriers in the chemical chain hydrogen production process, the second object of the present application is to provide a preparation method of the ternary iron-based oxygen carrier, and the third object of the present application is to provide the application of the ternary iron-based oxygen carrier in the chemical chain hydrogen production reaction, which utilizes the anti-sintering ability of the inert carrier ZrO2 and the high oxygen ion conduction ability of the LaFeO3 perovskite to improve the redox reaction activity, cycle stability, anti-sintering and anti-coking ability of the iron-based oxygen carrier in the chemical chain hydrogen production, so as to overcome the inherent defects of the iron-based oxygen carrier.

[0006] Technical scheme: The ternary iron-based oxygen carrier comprises an inert carrier ZrO2 and a perovskite LaFeO3, and contains 60% Fe2O3, 10-30% ZrO2 and 30-10% LaFeO3 by mass percentage, wherein Fe2O3, ZrO2 and LaFeO3 are uniformly distributed in the ternary iron-based oxygen carrier.

[0007] Further, the ternary iron-based oxygen carrier contains 60% Fe2O3, 10% ZrO2 and 30% LaFeO3 by mass percentage.

[0008] The preparation method of the ternary iron-based oxygen carrier comprises the following steps:

[0009] (1) Dissolve water-soluble iron salt, water-soluble zirconium salt and water-soluble lanthanum salt in deionized water respectively, stir, prepare a mixed solution, heat the mixed solution, and add ammonia solution to adjust the pH value to make the metal ions completely precipitate, to obtain a metal ion precipitate;

[0010] (2) Age the metal ion precipitate at room temperature, filter, and obtain a cake-shaped precipitate;

[0011] (3) Dry, decompose and calcine the cake-shaped precipitate to obtain an oxygen carrier;

[0012] (4) Grind and sieve the calcined oxygen carrier to obtain ternary iron-based oxygen carrier particles.

[0013] Further, in step (1), the water-soluble iron salt is ferric nitrate, ferric sulfate or ferric acetate, the water-soluble zirconium salt is zirconium nitrate, zirconium sulfate or zirconium acetate, and the water-soluble lanthanum salt is lanthanum nitrate, lanthanum sulfate or lanthanum acetate.

[0014] Further, in step (1), the heating temperature is 40-70℃.

[0015] Further, in step (1), the concentration of the ammonia solution is 25%-28%.

[0016] Further, in step (1), the solution is adjusted to a pH of 9.0 or higher to completely precipitate the three metal ions.

[0017] Further, in step (2), the aging time is 2-24h.

[0018] Further, in step (3), the drying temperature is 100℃ or higher, and the drying time is 12h or more.

[0019] Further, in step (3), the decomposition temperature is 350-400℃, and the decomposition time is 1h or more.

[0020] Further, in step (3), the calcination temperature is 900℃ or higher, and the calcination time is 2h or more.

[0021] Further, in step (4), the particle size of the ternary iron-based oxygen carrier particles is 150-350μm.

[0022] The application also includes the use of the ternary iron-based oxygen carrier in a chemical looping hydrogen production reaction.

[0023] Further, the temperature of the chemical looping hydrogen production reaction is 800-950℃.

[0024] In the chemical chain hydrogen production reaction, in the oxygen carrier reduction stage, the ternary iron-based oxygen carrier reacts with the carbon-containing gas fuel, the carbon-containing gas fuel is completely oxidized, and the ternary iron-based oxygen carrier is deeply reduced; in the steam oxidation stage, the reduced ternary iron-based oxygen carrier reacts with water vapor to generate high-purity H2, and the ternary iron-based oxygen carrier is partially oxidized; in the air oxidation stage, the partially oxidized ternary iron-based oxygen carrier reacts with air to realize the cyclic regeneration of the ternary iron-based oxygen carrier. During the redox cycle of the oxygen carrier, part of LaFeO3 reacts with ZrO2 to generate high-melting-point pyrochlore La2Zr2O7. Although it will cause the decrease of the content of LaFeO3 in the iron-based oxygen carrier, La2Zr2O7 has the characteristics of high melting point (2280℃), sintering resistance and phase stability, which is beneficial to improve the sintering resistance and cyclic stability of the ternary iron-based oxygen carrier. The high oxygen vacancy concentration of the perovskite LaFeO3 can improve the oxygen ion conductivity, and enhance the redox reaction activity and cyclic stability of the ternary iron-based oxygen carrier.

[0025] Advantages: Compared with the prior art, the present application has the following significant advantages:

[0026] (1) The preparation method of the ternary iron-based oxygen carrier is simple, and no other impurity phase appears in the synthesis process, and the synthesis period is short.

[0027] (2) The ternary iron-based oxygen carrier can withstand high temperature of 800-950℃, has the characteristics of high reaction activity, good cyclic stability, strong anti-carbon deposition and anti-sintering ability.

[0028] (3) During the redox cycle of the oxygen carrier, part of LaFeO3 reacts with ZrO2 to generate high-melting-point pyrochlore La2Zr2O7, which is beneficial to improve the sintering resistance and cyclic stability of the ternary iron-based oxygen carrier.

[0029] (4) The ternary iron-based oxygen carrier for chemical chain hydrogen production reaction has high hydrogen production efficiency, and the hydrogen purity is as high as 99.5% or more, which is 44.8% and 21.7% higher than that of the ZrO2-loaded binary iron-based oxygen carrier and the LaFeO3-loaded binary iron-based oxygen carrier, respectively. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the SEM diagram of the ternary iron-based oxygen carrier obtained in Example 3 and the binary iron-based oxygen carrier obtained in Comparative Examples 1-2;

[0031] Figure 2 is the cross-sectional diagram of the ternary iron-based oxygen carrier particles obtained in Example 3 and the cross-sectional line scanning EDS diagram.

[0032] Figure 3are XRD patterns of the ternary iron-based oxygen carriers obtained in Examples 1-3 and the binary iron-based oxygen carrier obtained in Comparative Example 1-2;

[0033] Figure 4 are H2-TPR results of the ternary iron-based oxygen carriers obtained in Examples 1-3 and the binary iron-based oxygen carrier obtained in Comparative Example 1-2;

[0034] Figure 5 are plots of H2 yield and H2 purity of the ternary iron-based oxygen carriers obtained in Examples 1-3 and the binary iron-based oxygen carrier obtained in Comparative Example 1-2 at 850℃ during steam oxidation stage versus cycle number;

[0035] Figure 6 are XRD patterns of the ternary iron-based oxygen carrier obtained in Example 3 at the end of the CO reduction stage (reduced state), at the end of the air oxidation stage (oxidized state) and in fresh state, respectively, after the 12th cycle.

[0036] Figure 7 are plots of the effect of CO concentration (4.8%, 9.0%, 13.0%, 16.7%) on the H2 purity and the yield of carbon-containing gases (CO and CO2) of the ternary iron-based oxygen carrier obtained in Example 3 during steam oxidation stage when using CO as carbon-containing fuel;

[0037] Figure 8 are plots of the effect of different reduction times (30 min, 20 min) on the H2 purity of the ternary iron-based oxygen carrier obtained in Example 3 during steam oxidation stage;

[0038] Figure 9 are plots of the results of the long-term (50 cycles) cycle stability test of the ternary iron-based oxygen carrier obtained in Example 3. DETAILED DESCRIPTION

[0039] The technical solutions of the present application will be further described below with reference to the accompanying drawings.

[0040] Example 1

[0041] A ternary iron-based oxygen carrier 20 g co-supported with 10 wt% LaFeO3and 30 wt% ZrO2, denoted as 1LF, was prepared:

[0042] Take 64.03 g Fe(NO3)3·9H2O, 3.41 g La(NO3)4·5H2O, 20.91 g Zr(NO3)4·5H2O, and dissolve them in a proper amount of deionized water to obtain a salt solution. Heat the salt solution to 70°C with a magnetic stirrer and stir for 20 min to make it uniformly dispersed. Then gradually add an ammonia solution with a mass fraction of 25%-28% to the salt solution to increase the PH value of the salt solution to 9.5 to obtain a metal ion precipitate. Age the metal ion precipitate at room temperature for 6 h, and then filter to obtain a cake-shaped precipitate. Dry the metal ion at 105°C for 24 h. Place the dried cake-shaped precipitate in a muffle furnace at 350°C for 2 h, and then calcine it at 900°C for 2 h to improve the mechanical strength of the oxygen carrier. Finally, grind and sieve the cake-shaped precipitate to obtain ternary iron-based oxygen carrier particles with a particle size of 150-350 μm.

[0043] Example 2

[0044] Prepare 20 g of a ternary iron-based oxygen carrier co-loaded with 20 wt% LaFeO3 and 20 wt% ZrO2, denoted as 2LF. The specific operation process is the same as that in Example 1, except that 67.35 g Fe(NO3)3·9H2O, 6.81 g La(NO3)3·5H2O, and 13.94 g Zr(NO3)4·5H2O are taken to obtain ternary iron-based oxygen carrier particles with a particle size of 150-350 μm.

[0045] Example 3

[0046] Prepare 20 g of a ternary iron-based oxygen carrier co-loaded with 30 wt% LaFeO3 and 10 wt% ZrO2, denoted as 3LF. The specific operation process is the same as that in Example 1, except that 70.66 g Fe(NO3)3·9H2O, 10.22 g La(NO3)4·5H2O, and 6.97 g Zr(NO3)4·5H2O are taken to obtain ternary iron-based oxygen carrier particles with a particle size of 150-350 μm.

[0047] Comparative Example 1

[0048] Prepare 20 g of a binary iron-based oxygen carrier loaded with 40 wt% LaFeO3, denoted as 4LF. The specific operation process is the same as that in Example 1, except that 73.98 g Fe(NO3)3·9H2O and 13.62 g La(NO3)4·5H2O are taken, and Zr(NO3)4·5H2O is not used, to obtain binary iron-based oxygen carrier particles with a particle size of 150-350 μm.

[0049] Comparative Example 2

[0050] Preparation of 40wt% ZrO2supported binary iron-based oxygen carrier 20g, marked as 0LF. The specific operation process is the same as that of Example 1, except that 60.72g Fe(NO3)3·9H2O, 27.87g Zr(NO3)4·5H2O, and no La(NO3)4·5H2O are used, to obtain binary iron-based oxygen carrier particles with a particle size of 150-350μm.

[0051] The iron-based oxygen carriers obtained in Example 3 and Comparative Examples 1 and 2 were subjected to scanning electron microscope analysis, and the results are shown in Figure 1 Figure 1 SEM images of the ternary iron-based oxygen carrier obtained in Example 3 and the binary iron-based oxygen carriers obtained in Comparative Examples 1-2; wherein (a) is the SEM image of 0LF in fresh state in Comparative Example 2, (b) is the SEM image of 0LF after 12 cycles in Comparative Example 2, (c) is the SEM image of 3LF in fresh state in Example 3, (d) is the SEM image of 3LF after 12 cycles in Example 3, (e) is the SEM image of 4LF in fresh state in Comparative Example 1, and (f) is the SEM image of 4LF after 12 cycles in Comparative Example 1. As can be seen from Figure 1 , the surfaces of the three fresh oxygen carriers all exhibit good porous structure, and 3LF has the lowest sintering degree after multiple cycles, showing the best pore characteristics. In addition, the cross-sectional image of the 3LF oxygen carrier particles and the element distribution analysis results of the cross-sectional line scanning are shown in Figure 2 Figure 2 Cross-sectional image of the ternary iron-based oxygen carrier particles obtained in Example 3 and EDS image of cross-sectional line scanning; wherein (a) is the cross-sectional image of the ternary iron-based oxygen carrier particles, and (b) is the EDS image of cross-sectional line scanning of the ternary iron-based oxygen carrier particles. As can be seen from Figure 2 (b), the O, Zr, La and Fe elements are uniformly distributed, indicating that Fe2O3, LaFeO3 and ZrO2 are uniformly distributed in the particles.

[0052] The fresh iron-based oxygen carriers obtained in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 were subjected to X-ray diffraction test, and the results are shown in Figure 3 Figure 3 XRD images of the ternary iron-based oxygen carriers obtained in Examples 1-3 and the binary iron-based oxygen carriers obtained in Comparative Examples 1-2, wherein Figure 3 As can be seen from, the characteristic diffraction peaks of perovskite LaFeO3(PDF 74-2203) can be observed at 2θ=22.6°, 32.2°, 39.7°, 46.1°, 57.4°, 67.3° and 76.6° for 4LF, 3LF and 2LF, and the peak intensity gradually increases with the increase of the mass ratio of LaFeO3. For 1LF, the characteristic diffraction peaks of LaFeO3 can also be observed at 2θ=22.6°. From Figure 3 ​​It can be seen that the diffraction peaks of Fe2O3 (PDF 73-2234), LaFeO3 (PDF 74-2203) and ZrO2 (PDF 79-1763) exist in 3LF, 2LF and 1LF, which indicates that the metal oxide-inert carrier-perovskite structure Fe2O3 / ZrO2 / LaFeO3 ternary iron-based oxygen carrier is successfully synthesized. That is, only Fe2O3, LaFeO3 and ZrO2 three phases exist in the fresh ternary iron-based oxygen carrier. ZrO2 exists in the form of tetragonal phase in the ternary oxygen carrier, while it exists in the form of tetragonal phase and monoclinic phase in the binary oxygen carrier.

[0053] Example 4 Evaluation of oxygen carrier H2-TPR

[0054] The H2 temperature programmed reduction (H2-TPR) evaluation of the ternary iron-based oxygen carriers obtained in Example 1, Example 2 and Example 3 was carried out with 0LF and 4LF as control groups. The test was carried out on the chemical adsorption analyzer (AutoChem 2920) produced by American Micromeritics Company. The amount of oxygen carrier was 100 mg. The reactor temperature was increased from 50°C to 1000°C at a heating rate of 10°C / min in a H2 / Ar atmosphere with a flow rate of 15 mL / min and a H2 volume fraction of 10%. The reaction time was about 100 min, and the reaction pressure was atmospheric pressure. The change in H2 consumption signal intensity during the reaction is shown in Figure 4 .

[0055] Figure 4 is the H2-TPR result graph of the ternary iron-based oxygen carriers obtained in Example 1-3 and the binary iron-based oxygen carriers obtained in Comparative Example 1-2. According to the TPR experimental results, since the oxygen carrying capacity of LaFeO3 is much lower than that of Fe2O3, the three similar reduction peaks in the H2-TPR graph of 4LF, 3LF, 2LF and 1LF all correspond to the reduction of Fe2O3, i.e. Fe2O3→Fe3O4→FeO→Fe. With the increase of the LaFeO3 loading, the starting temperature of the α reduction peak shows a downward trend, from 332°C of 0LF to 300°C of 2LF, while 2LF, 3LF and 4LF remain almost constant. The β and γ reduction peaks of 4LF, 3LF, 2LF and 1LF are basically the same, which are located at 365°C and 480°C, respectively. Therefore, in view of the weak oxygen carrying capacity of LaFeO3, it can be concluded that LaFeO3 can significantly promote the reduction activity of Fe2O3 in the ternary iron-based oxygen carrier.

[0056] Example 5 Hydrogen yield and purity test in multiple cycles of steam oxidation stage of different oxygen carriers

[0057] The ternary iron-based oxygen carriers obtained from Example 1, Example 2, Example 3 and the binary iron-based oxygen carriers obtained from Comparative Example 1 and Comparative Example 2 were subjected to chemical looping hydrogen cycle reaction activity and stability tests in a fixed bed reactor. The oxygen carrier was used in an amount of 1.0 g, the particle size was 150-350 μm, and the temperature during the entire cycle was constant at 850℃; the fuel gas composition in the oxygen carrier reduction stage was CO and N2, the total flow rate was 220 mL / min (of which the CO flow rate was 20 mL / min and the N2 flow rate was 200 mL / min), the reduction time was 30 min, after which the CO was turned off and the N2 (flow rate 300 mL / min) was purged for about 15 min; then the mixed gas of water vapor and N2 was introduced, the total flow rate was 200.19 mL / min (of which the water vapor flow rate was 0.19 mL / min and the N2 flow rate was 200 mL / min), the water vapor oxidation time was 5 min, after which the water vapor was turned off and the N2 (flow rate 300 mL / min) was purged for about 5 min; the gas composition in the air oxidation stage was O2 and N2, the total flow rate was 230 mL / min (of which the O2 flow rate was 30 mL / min and the N2 flow rate was 200 mL / min), the oxidation time was 5 min to achieve regeneration of the oxygen carrier; the reaction activity and stability of the oxygen carrier were tested by cycling 12 times according to the above reaction steps. The reactor outlet gas was subjected to online detection by a flue gas analyzer after removal of water vapor by a molecular sieve. The H2 yield and H2 purity results are shown in Figure 5

[0058] Figure 5 Figure 1 is a diagram showing the change in H2 yield and H2 purity with cycle number for ternary iron-based oxygen carriers obtained from Examples 1-3 and binary iron-based oxygen carriers obtained from Comparative Examples 1-2 in the steam oxidation stage at 850℃; wherein (a) is a diagram showing the change in H2 yield with cycle number, and (b) is a diagram showing the change in H2 purity with cycle number. In Figure 5 (a), the average H2 yield of 4LF, 3LF, 2LF, 1LF and 0LF in 12 cycles was 6.9 mmol·g -1 -1, 8.4 mmol·g -1 -1, 8.0 mmol·g -1 -1, 8.1 mmol·g -1 -1 and 5.8 mmol·g -1 ​, the average H2 yield order is: 3LF > 2LF > 1LF > 4LF > 0LF. The ternary iron-based oxygen carriers (especially Fe2O3 / ZrO2 / LaFeO3) exhibit higher H2 yield than the binary iron-based oxygen carriers (i.e. 0LF and 4LF). Among them, the average H2 yield of 3LF, which has the highest H2 yield, is 1.45 times that of 0LF and 1.22 times that of 4LF. After 7 cycles, the H2 yield of the ternary iron-based oxygen carriers 3LF, 2LF and 1LF tends to be stable, while the H2 yield of the binary iron-based oxygen carriers 4LF and 0LF shows a continuous downward trend, indicating that the synergistic effect of ZrO2 and LaFeO3 can improve the reactivity and stability. Figure 5 In (b), the H2 purity of the 5 groups of oxygen carriers can all reach above 99.5%, and relatively, the Fe2O3 / ZrO2 / LaFeO3 ternary iron-based oxygen carrier can maintain higher and more stable H2 purity. The average H2 purity of 4LF, 3LF, 2LF, 1LF and 0LF in 12 cycles is 99.58%, 99.83%, 99.80%, 99.72% and 99.57% respectively, and the H2 purity order is: 3LF > 2LF > 1LF > 4LF > 0LF.

[0059] The ternary iron-based oxygen carriers obtained in Example 3 were subjected to X-ray diffraction tests at the end of the CO reduction stage (reduced state) and at the end of the air oxidation stage (oxidized state) of the 12th cycle respectively, and the test results were compared and analyzed with the X-ray diffraction test results of the fresh oxygen carrier, and the results are shown in Figure 6 Figure 6 is the XRD pattern of the ternary iron-based oxygen carrier obtained in Example 3 at the end of the CO reduction stage (reduced state), at the end of the air oxidation stage (oxidized state) and in the fresh state respectively. As can be seen from Figure 6 , the cycled oxygen carrier has high melting point pyrochlore La2Zr2O7 compared with the fresh state, which is beneficial to improve the anti-sintering ability and cycle stability of the ternary iron-based oxygen carrier.

[0060] The ternary iron-based oxygen carriers obtained in Example 3 and the binary iron-based oxygen carriers obtained in Comparative Example 1-2 were subjected to EDS particle surface scanning tests before and after 12 cycles respectively, and the results are shown in Figure 1 . And the analysis of the molar fraction of Fe atoms is shown in Table 1.

[0061] Table 1 Change of molar fraction of Fe atoms on the surface of the ternary iron-based oxygen carriers obtained in Example 3 and the binary iron-based oxygen carriers obtained in Comparative Example 1-2 before and after 12 cycles

[0062]

[0063] ​As can be seen from Table 1, relative to the pre-cycling state (i.e. fresh state), the molar fraction of Fe atoms on the surface of 0LF, 3LF and 4LF oxygen carrier particles increased by 21.4%, 9.2% and 12.1% respectively after cycling. The ternary iron-based oxygen carrier showed stronger inhibition of Fe atom migration than the binary iron-based oxygen carrier, thereby improving the sintering resistance and cycling stability of the iron-based oxygen carrier.

[0064] Example 6 Effect of different CO concentrations on carbon-containing gas yield and H2 purity in steam oxidation stage

[0065] Using the 3LF ternary iron-based oxygen carrier in Example 3, the effect of different CO concentrations (4.8%, 9.0%, 13.0% and 16.7%) on the amount of carbon-containing gas generated and H2 purity in the steam oxidation stage was tested on a fixed bed reactor; in the oxygen carrier reduction stage, the total flow rates of CO and N2 were 210 mL / min (of which the CO flow rate was 10 mL / min and the N2 flow rate was 200 mL / min), 220 mL / min (of which the CO flow rate was 20 mL / min and the N2 flow rate was 200 mL / min), 230 mL / min (of which the CO flow rate was 30 mL / min and the N2 flow rate was 200 mL / min) and 240 mL / min (of which the CO flow rate was 40 mL / min and the N2 flow rate was 200 mL / min) at CO concentrations of 4.8%, 9.0%, 13.0% and 16.7% respectively, and the other specific operating procedures in a single cycle were the same as in Example 5; the cycle was repeated 6 times according to the above reaction steps, and the results are shown in Figure 7 .

[0066] Figure 7 The effect of different CO concentrations as carbon-containing fuel gas on carbon-containing gas (CO and CO2) yield and H2 purity in the steam oxidation stage is shown in the graph. Among them, (a) is the graph of carbon-containing gas yield changing with cycle number, (b) is the graph of H2 purity changing with cycle number. According to Figure 7 (a), the amount of carbon-containing gas at CO concentrations of 4.8%, 9.0% and 13.0% fluctuated at relatively low values with cycle number; while the carbon deposition at a CO concentration of 16.7% showed a trend of continuous increase during the cycle, which was due to the fact that at a higher CO concentration, the 3LF oxygen carrier was rapidly and deeply reduced in the CO reduction stage and produced more Fe on the surface of the oxygen carrier particles, thereby catalyzing the Boudouard reaction to produce more carbon-containing gas. Figure 7(b) shows the H2 purity during the steam oxidation stage in the six cycles. Relatively high H2 purity was observed at CO concentrations of 9% and 13%. At a CO concentration of 16.7%, the yield of carbon-containing gases was high, leading to a continuous decrease in H2 purity throughout the redox cycle. A low H2 yield at a CO concentration of 4.8% also resulted in low H2 purity. Therefore, selecting CO concentrations of 9% and 13.0% yields higher H2 purity.

[0067] Example 7: Effect of different reduction times on H2 purity

[0068] Using the ternary iron-based oxygen carriers obtained in Examples 1, 2, and 3, and the binary iron-based oxygen carriers obtained in Comparative Examples 1 and 2, the effect of different reduction times on H2 purity was tested in a fixed-bed reactor. The specific operation procedure for a single cycle was the same as in Example 5, and the cycle was repeated 6 times. In the oxygen carrier reduction stage, the first group's reduction time was 30 min, and the results are as follows: Figure 8 As shown in (a); the second group had a reduction time of 20 min, and the results are as follows: Figure 8 As shown in (b).

[0069] Figure 8 This is a graph showing the effect of different reduction times (30 min, 20 min) on the H2 purity during the steam oxidation stage of the ternary iron-based oxygen carrier obtained in Example 3. (a) shows the change in H2 purity with the number of cycles after 30 min of reduction, and (b) shows the change in H2 purity with the number of cycles after 20 min of reduction. Figure 8 It is evident that by appropriately extending the reduction time, the increase in H2 yield is greater than the increase in coke deposit, which further improves the purity of H2 generated during the steam oxidation stage.

[0070] Example 8: Long-term cyclic stability test of ternary iron-based oxygen carrier

[0071] Using the ternary iron-based oxygen carrier obtained in Example 3, the long-cycle reactivity and stability of chemical looping hydrogen production were tested in a fixed-bed reactor. The reactivity and stability of the ternary iron-based oxygen carrier were tested by cycling 50 times according to the reaction steps described in Example 5. The reactor outlet gas was monitored online using a gas analyzer. The results are as follows: Figure 9 As shown.

[0072] Figure 9 This is a graph showing the long-term (50 cycles) cyclic stability test results of the ternary iron-based oxygen carrier obtained in Example 3. Figure 9 It is evident that the H2 yield of the Fe2O3 / ZrO2 / LaFeO3 ternary iron-based oxygen carrier decreases only slightly with the progress of cycling, and the H2 purity remains essentially unchanged, demonstrating its superiority as an oxygen carrier for chemical looping hydrogen production.

[0073] Finally, it should be understood that the embodiments described herein should be considered in a descriptive sense only and not as a limitation on the scope of the present application. Descriptions of examples of implementations using terms such as "comprising", "having", "containing" or "including" to describe combinations of elements should be considered synonymous with alternative terms such as "consisting essentially of" or "consisting of".

Claims

1. A ternary iron-based oxygen carrier for chemical looping hydrogen production, characterized in that, The ternary iron-based oxygen carrier uses inert ZrO2 and perovskite LaFeO3 as composite carriers, and includes 60% Fe2O3, 10~30% ZrO2 and 30~10% LaFeO3 by mass percentage. Fe2O3, ZrO2 and LaFeO3 are uniformly distributed in the ternary iron-based oxygen carrier. The preparation method of the ternary iron-based oxygen carrier includes the following steps: (1) Dissolve water-soluble iron salt, water-soluble zirconium salt and water-soluble lanthanum salt in deionized water, stir to prepare a mixed solution, heat the mixed solution, add ammonia solution dropwise to adjust the pH value so that the three metal ions in the solution are completely precipitated to obtain metal ion precipitate; (2) The metal ion precipitate was aged at room temperature and filtered to obtain a cake-like precipitate; (3) The cake-shaped precipitate is dried, decomposed, and calcined to obtain an oxygen carrier; (4) Grind and sieve the calcined oxygen carrier to obtain ternary iron-based oxygen carrier particles.

2. The ternary iron-based ferrite for chemical loop hydrogen production according to claim 1, characterized in that, The ternary iron-based oxygen carrier comprises 60% Fe2O3, 10% ZrO2, and 30% LaFeO3 by mass percentage.

3. The method for preparing the ternary iron-based oxygen carrier for chemical looping hydrogen production reaction as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Dissolve water-soluble iron salt, water-soluble zirconium salt and water-soluble lanthanum salt in deionized water, stir to prepare a mixed solution, heat the mixed solution, add ammonia solution dropwise to adjust the pH value so that the three metal ions in the solution are completely precipitated to obtain metal ion precipitate; (2) The metal ion precipitate was aged at room temperature and filtered to obtain a cake-like precipitate; (3) The cake-shaped precipitate is dried, decomposed, and calcined to obtain an oxygen carrier; (4) Grind and sieve the calcined oxygen carrier to obtain ternary iron-based oxygen carrier particles.

4. The preparation method according to claim 3, characterized in that, In step (1), the water-soluble iron salt is ferric nitrate, ferric sulfate or ferric acetate, the water-soluble zirconium salt is zirconium nitrate, zirconium sulfate or zirconium acetate, and the water-soluble lanthanum salt is lanthanum nitrate, lanthanum sulfate or lanthanum acetate.

5. The preparation method according to claim 3, characterized in that, In step (1), the heating temperature is 40~70℃, the concentration of the ammonia solution is 25%~28%, and the pH is adjusted to above 9.0 to completely precipitate the three metal ions in the solution.

6. The preparation method according to claim 3, characterized in that, In step (2), the aging time is 2 to 24 hours.

7. The preparation method according to claim 3, characterized in that, In step (3), the drying temperature is above 100 ℃ and the drying time is above 12 h; the decomposition temperature is 350 ~ 400 ℃ and the decomposition time is above 1 h; the calcination temperature is above 900 ℃ and the calcination time is above 2 h.

8. The preparation method according to claim 3, characterized in that, In step (4), the particle size of the ternary iron-based oxygen carrier particles is 150~350 μm.

9. The application of the ternary iron-based oxygen carrier for chemical looping hydrogen production as described in claim 1 or 2 in chemical looping hydrogen production.

10. The application according to claim 9, characterized in that, The temperature of the chemical chain hydrogen production reaction is 800 ~ 950℃.

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