Oxygen release type perovskite oxygen carrier and preparation method and application thereof

Abstract

The invention relates to the technical field of carbon capture, and discloses an oxygen release type perovskite oxygen carrier and a preparation method and application thereof. The method comprises the following steps: (1) in the presence of a solvent, contacting and mixing calcium nitrate, manganous nitrate, magnesium nitrate, cobalt nitrate, a complexing agent and ethylene glycol to obtain a mixture I; (2) heating the mixture I, and drying to obtain a mixture II; and (3) calcining the mixture II to obtain the oxygen release type perovskite oxygen carrier. The method provided by the invention is simple and feasible to operate, and the prepared oxygen release type perovskite oxygen carrier is high in oxygen release amount and has excellent high-temperature oxygen decoupling performance and high-temperature cycling stability.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon capture, and in particular to an oxygen-releasing perovskite oxygen carrier and a preparation method and application thereof. Background Art

[0002] As a new generation of carbon capture technology, chemical looping combustion achieves the coupling of combustion process and CO2 separation through a unique oxygen carrier medium, which can reduce carbon capture energy consumption by about 70% compared with traditional post-combustion capture technology. Its technical core lies in the oxidation-reduction cycle ability of the oxygen carrier, which directly determines the CO2 capture efficiency and system operation economy. The key bottleneck restricting the large-scale application of this technology is the high-temperature deactivation problem of the oxygen carrier. Conventional metal oxides generally have defects such as low lattice oxygen migration rate, sintering of surface active sites, and irreversible degradation of phase structure during the cycle process, resulting in incomplete conversion of reducing gases (CO / H2 / CH4) in the fuel reactor, significantly increasing the subsequent CO2 purification energy consumption.

[0003] At present, oxygen-releasing oxygen carriers with high-temperature oxygen decoupling characteristics, such as Cu-based, Mn-based, and Co-based oxides, all have certain defects that limit their application. Perovskite ABO3-type composite metal oxides have good oxygen ion and electron conductivity at the same time, and their surface reactivity and bulk oxygen diffusion performance can be flexibly controlled by replacing ions at the A and B positions in the structure. They are the most studied type of composite metal oxide oxygen carriers. According to the type of A-position main element, the perovskite oxygen carriers that have been studied and can be applied to the chemical looping combustion process mainly include three types: Ca-based, La-based, and Sr-based (such as CaMnO 3-δ , LaMnO 3-δ , SrFeO 3-δ ), but the oxygen release is generally less than 1wt%, and it is impossible to change the reaction path of the reducing gas in the fuel reactor through the rapid and large-scale oxygen release of the oxygen carrier. At the same time, the existing oxygen-releasing perovskite oxygen carriers have problems such as high-temperature sintering agglomeration and phase separation, and cannot maintain high reactivity and structural stability during long-term cycles. There is still a certain gap between them and the standards of high-performance oxygen decoupling oxygen carriers that can be applied to chemical chain combustion processes. 3-δ As an example, at high temperature, CaMnO 3-δ It will decompose into Ruddlesden-Popper phase Ca2MnO4 and spinel phase CaMn2O4, because CaMn2O4 cannot be reoxidized to CaMnO 3-δ , resulting in CaMnO 3-δ The reduction is delayed and the oxidation is not complete, so it cannot be recycled for a long time. In recent years, many studies have been conducted to improve the CaMnO 3-δ Comprehensive properties, such as CaMnO 3-δDoping an appropriate amount of Co element can significantly improve the oxygen release rate at high temperatures. However, when the Co element exceeds its solubility limit in CaMnO 3-δ a second phase of Ca3CoMnO6 will be generated. Tests show that CaMn 0.95 Co 0.05 O 3-δ After 20 cycles, its reactivity decays by about 25%. This phase separation phenomenon may be the reason for the poor high-temperature cyclic stability of the Co-doped CaMnO 3-δ oxygen carriers.

[0004] Based on this, there is an urgent need in this field to develop a controllable preparation technology for new perovskite oxygen carriers, achieving precise doping of multiple elements at the molecular scale while constructing an anti-sintering nanoporous structure. In particular, a breakthrough in the preparation method to meet the special requirements of oxygen carriers in the carbon capture process (high oxygen decoupling ability, fast bulk oxygen diffusion, excellent cyclic stability) will promote the industrial application process of chemical looping combustion technology in the field of carbon capture. Summary of the Invention

[0005] The object of the present invention is to solve the problems existing in the prior art, such as the low high-temperature oxygen decoupling characteristics of perovskite-type oxygen carriers CaMnO 3-δ and the easy occurrence of high-temperature sintering agglomeration, phase separation and other problems.

[0006] To achieve the above object, the first aspect of the present invention provides a method for preparing an oxygen-releasing perovskite oxygen carrier, which includes the following steps: (1) In the presence of a solvent, calcium nitrate, manganese nitrate, magnesium nitrate, cobalt nitrate, a complexing agent and ethylene glycol are contacted and mixed to obtain a mixture I; (2) The mixture I is heat-treated and then dried to obtain a mixture II; (3) The mixture II is calcined to obtain an oxygen-releasing perovskite oxygen carrier.

[0007] The second aspect of the present invention provides an oxygen-releasing perovskite oxygen carrier prepared by the method described in the first aspect.

[0008] The third aspect of the present invention provides the application of the oxygen-releasing perovskite oxygen carrier described in the second aspect in carbon capture technology.

[0009] Compared with the prior art, the method provided by the present invention has at least the following beneficial effects: The preparation method of the oxygen-releasing perovskite oxygen carrier provided by the present invention is simple and feasible. Through the molecular-level mixing and complexation control of the precursor solution, the atomic-level uniform doping of Mg / Co elements in the CaMnO3 lattice is realized. Combining with the gradient calcination process to form a through-mesoporous structure, the material maintains a high oxygen release amount, and has excellent high-temperature oxygen decoupling performance and high-temperature cycle stability. Compared with the case of only Co doping, it shows excellent cycle stability in the 20-cycle long-term cycle test, and there is no obvious sintering agglomeration and phase separation before and after the reaction. It provides an effective way to improve the fuel conversion efficiency in the chemical-looping combustion fuel reactor, and is more suitable for the field of carbon capture technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Mass change in the oxygen decoupling performance test at 900 °C of the oxygen-releasing perovskite oxygen carrier prepared in the preferred embodiment and the comparative example of the present invention; Figure 2 Oxygen release rate at 900 °C of the oxygen-releasing perovskite oxygen carrier prepared in the preferred embodiment and the comparative example of the present invention; Figure 3 Mass change in the long-term oxygen release-oxidation cycle test at 800 °C of the oxygen-releasing perovskite oxygen carrier prepared in the comparative example of the present invention; Figure 4 Oxygen release rate at different cycles in the long-term oxygen release-oxidation cycle test at 800 °C of the oxygen-releasing perovskite oxygen carrier prepared in the comparative example of the present invention; Figure 5 Mass change in the long-term oxygen release-oxidation cycle test at 800 °C of the oxygen-releasing perovskite oxygen carrier prepared in the preferred embodiment of the present invention; Figure 6 Oxygen release rate at different cycles in the long-term oxygen release-oxidation cycle test at 800 °C of the oxygen-releasing perovskite oxygen carrier prepared in the preferred embodiment of the present invention; Figure 7 Scanning electron microscope images of the oxygen-releasing perovskite oxygen carrier prepared in the comparative example of the present invention before and after the long-term oxygen release-oxidation cycle test at 800 °C; Figure 8 Scanning electron microscope images of the oxygen-releasing perovskite oxygen carrier prepared in the preferred embodiment of the present invention before and after the long-term oxygen release-oxidation cycle test at 800 °C; Figure 9 X-ray diffraction patterns of the oxygen-releasing perovskite oxygen carrier prepared in the comparative example of the present invention before and after the long-term oxygen release-oxidation cycle test at 800 °C; Figure 10 X-ray diffraction patterns of the oxygen-releasing perovskite oxygen carrier prepared in the preferred embodiment of the present invention before and after the long-term oxygen release-oxidation cycle test at 800 °C. Detailed implementation manners

[0011] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0012] As described above, the first aspect of the present invention provides a method for preparing an oxygen-releasing perovskite oxygen carrier, and the method includes the following steps: (1) In the presence of a solvent, calcium nitrate, manganese nitrate, magnesium nitrate, cobalt nitrate, a complexing agent, and ethylene glycol are brought into contact and mixed to obtain a mixture I; (2) The mixture I is heat-treated and then dried to obtain a mixture II; (3) The mixture II is calcined to obtain an oxygen-releasing perovskite oxygen carrier.

[0013] Preferably, in step (1), the molar ratio of the amounts of calcium nitrate, manganese nitrate, magnesium nitrate, and cobalt nitrate used is 1:0.8:0.15:0.05.

[0014] Preferably, in step (1), the molar ratio of the amounts of ethylene glycol and the complexing agent used is 1:1.

[0015] According to a preferred implementation manner, in step (1), the molar ratio of the total amount of metal cations in calcium nitrate, manganese nitrate, magnesium nitrate, and cobalt nitrate to the amount of the complexing agent used is 1:1 - 1.1.

[0016] Preferably, in step (1), the solvent is deionized water.

[0017] Preferably, in step (1), the complexing agent is anhydrous citric acid.

[0018] More preferably, the step of bringing into contact and mixing includes: first dissolving calcium nitrate, manganese nitrate, magnesium nitrate, and cobalt nitrate in deionized water, then adding anhydrous citric acid and mixing evenly, and then adding the ethylene glycol and mixing evenly.

[0019] Preferably, in step (2), the heat treatment is carried out under stirring conditions and at least satisfies: the temperature is 70 - 80 °C and the time is 4 - 6 h.

[0020] It should be noted that in the present invention, in step (2), there is no specific requirement for the stirring speed of the heat treatment, and conventional technical parameters in the art can be adopted. Exemplarily, when using a magnetic stirrer for stirring, it is only necessary to ensure that the magnetic bar fully drives the solution and does not collide with the beaker wall.

[0021] According to a preferred embodiment, in step (2), the drying conditions at least satisfy: the temperature is 110 - 120 °C, and the time is 24 - 40 h.

[0022] Preferably, in step (3), the calcination is carried out using a muffle furnace or a tube furnace and in an air atmosphere.

[0023] Preferably, the method of the present invention further includes: in step (3), first pre-burn the mixture II at 300 - 350 °C for 30 - 60 min, and then raise the temperature to 900 - 950 °C at a rate of 3 - 4 °C / min and carry out high-temperature calcination for 7 - 8 h. In this preferred case, it is more conducive to forming a stable crystal structure.

[0024] Preferably, the method of the present invention further includes: in step (3), first grind the mixture II to an average volume diameter of 100 - 200 μm and then carry out the pre-burning.

[0025] As described above, the second aspect of the present invention provides an oxygen-releasing perovskite oxygen carrier prepared by the method described in the first aspect.

[0026] Preferably, the general formula of the oxygen-releasing perovskite oxygen carrier is CaMn 0.8 Mg 0.15 Co 0.05 O 3-δ .

[0027] As described above, the third aspect of the present invention provides the application of the oxygen-releasing perovskite oxygen carrier described in the second aspect in carbon capture technology.

[0028] The present invention is described in detail below through examples. Without special instructions, the raw materials used are all ordinary commercially available products.

[0029] Complexing agent: anhydrous citric acid; Calcium nitrate: Ca(NO3)2·4H2O; Manganese nitrate: Mn(NO3)2·4H2O; Magnesium nitrate: Mg(NO3)2·6H2O; Cobalt nitrate: Co(NO3)2·6H2O. Example 1: This example is used to illustrate that the method for preparing the oxygen-releasing perovskite oxygen carrier provided by the present invention is carried out according to the following steps: (1) Dissolve calcium nitrate, manganese nitrate, magnesium nitrate, and cobalt nitrate in deionized water at a molar ratio of 1:0.8:0.15:0.05. Subsequently, add anhydrous citric acid and mix evenly, then add the ethylene glycol and mix evenly to obtain Mixture I; Among them, the molar ratio of the total amount of metal cations in the calcium nitrate, manganese nitrate, magnesium nitrate, and cobalt nitrate to the amount of the complexing agent is 1:1, and the molar ratio of ethylene glycol to the complexing agent is 1:1; (2) Heat-treat Mixture I in a magnetic stirrer at 80 °C for 5 h, ensuring that the magnetic stirrer fully drives the solution without colliding with the beaker wall during stirring. Then, dry it in a muffle furnace at 120 °C for 40 h to obtain Mixture II; (3) First, grind Mixture II to an average volume diameter of 200 μm, then pre-burn it in an air atmosphere at 300 °C for 30 min, and then raise the temperature to 900 °C at a rate of 3 - 4 °C / min and perform high-temperature calcination for 8 h. After the furnace temperature naturally cools down, an oxygen-releasing perovskite oxygen carrier is obtained, and its general formula is CaMn 0.8 Mg 0.15 Co 0.05 O 3-δ , named P1.

[0030] Comparative Example 1 This comparative example was carried out using a method similar to that of Example 1. The difference is that in step (1), magnesium nitrate was not used for the contact mixing, specifically including: (1) Dissolve calcium nitrate, manganese nitrate, and cobalt nitrate in deionized water at a molar ratio of 1:0.95:0.05. Subsequently, add anhydrous citric acid and mix evenly, then add the ethylene glycol and mix evenly to obtain Mixture I; Among them, the molar ratio of the total amount of metal cations in the calcium nitrate, manganese nitrate, and cobalt nitrate to the amount of the complexing agent is 1:1, and the molar ratio of ethylene glycol to the complexing agent is 1:1; Finally, an oxygen-releasing perovskite oxygen carrier is obtained, and its general formula is CaMn 0.95 Co 0.05 O 3-δ , named DP1.

[0031] Test Example 1 Detect the high-temperature oxygen decoupling performance test of the oxygen-releasing perovskite oxygen carriers (hereinafter referred to as samples) prepared in the above partial examples: This test was carried out on a thermogravimetric analyzer. 10 mg of the above-mentioned sample was taken and placed in an alumina crucible respectively. Subsequently, the crucible was placed on the balance of the thermogravimetric analyzer for the high-temperature oxygen decoupling performance test. The test temperature was 900 °C. The temperature was increased in an air atmosphere at a heating rate of 20 °C / min. After the temperature was stabilized, the alternate switching test of inert gas and oxidizing gas was carried out at this temperature, and the total gas flow rate was kept constant at 120 mL / min. The atmosphere during the oxygen release stage of the oxygen carrier was N2, lasting for 30 min; the atmosphere during the oxidation stage was air, lasting for 30 min, and the total test duration was about 240 min.

[0032] Figure 1 The mass change curve of the sample during the oxygen decoupling performance test at 900 °C is shown. Figure 2 The oxygen release rate of the sample during the oxygen decoupling performance test is shown. Figure 1 The results show that under the same operating conditions, the oxygen decoupling mass change of P1 (CaMn 0.8 Mg 0.15 Co 0.05 O 3-δ ) and DP1 (CaMn 0.95 Co 0.05 O 3-δ ) is quite equivalent. Except for the relatively unstable first oxygen release-oxidation cycle, the oxygen release amount is within the range of 1.5-1.7 wt%. However, it can be seen from Figure 2 that for the oxygen carrier CaMn 0.8 Mg 0.15 Co 0.05 O 3-δ doped with Mg, compared with undoped CaMn 0.95 Co 0.05 O 3-δ , the oxygen release rate is significantly accelerated, which indicates that CaMn 0.8 Mg 0.15 Co 0.05 O 3-δ can release more gaseous oxygen in a short time to participate in the conversion of reducing gases in the actual fuel reactor, which is more conducive to reducing the oxygen demand fraction.

[0033] Test Example 2 The long-cycle oxygen release-oxidation cycle stability performance test was carried out on the oxygen-releasing perovskite oxygen carrier (hereinafter referred to as the sample) prepared in some of the above examples by using a thermogravimetric analyzer: 10 mg of the sample was weighed respectively. The test temperature was 800 °C. It was heated to 800 °C at a heating rate of 20 °C / min in an air atmosphere. After the temperature was stabilized, the long-cycle performance test was carried out. The atmosphere during the oxygen release stage was N2, and the atmosphere during the oxidation stage was air. Each stage lasted for 30 min respectively. The number of test cycles was 20, and the total test duration was about 1330 min.

[0034] During the 800 °C long - term cyclic stability test, for CaMn 0.95 Co 0.05 O 3-δ the mass change curve and the oxygen release rate for different cycles are shown in Figure 3 and Figure 4 respectively. For CaMn 0.8 Mg 0.15 Co 0.05 O 3-δ the mass change curve and the oxygen release rate for different cycles are shown in Figure 5 and Figure 6 .

[0035] Figure 3 and Figure 4 The results show that CaMn 0.95 Co 0.05 O 3-δ cannot maintain stable reaction performance during 20 oxygen release - oxidation cycles. The oxygen release amount gradually decreases from 1.2 wt% in cycle 1 to 1.0 wt% in cycle 20, and the oxygen release rate also decreases significantly with the increase in the number of cycles. This indicates that CaMn 0.95 Co 0.05 O 3-δ has poor high - temperature stability and cannot be applied to an actual chemical - looping combustion reactor.

[0036] However Figure 5 and Figure 6 The results show that after doping with an appropriate amount of Mg, CaMn 0.8 Mg 0.15 Co 0.05 O 3-δ exhibits good high - temperature stability during 20 oxygen release - oxidation cycles. The oxygen - carrying capacity of the oxygen carrier does not decrease with the increase in the number of cycles. The oxygen release amount gradually increases from 1.24 wt% in cycle 1 to 1.28 wt% in cycle 20, and the oxygen release rate stabilizes and rapidly releases oxygen after the oxygen carrier is activated in the first 3 cycles. This indicates that CaMn 0.8 Mg 0.15 Co 0.05 O 3-δ exhibits excellent long - term cyclic stability and oxygen decoupling performance under high - temperature conditions and has the potential to be applied to an actual chemical - looping combustion reactor.

[0037] The surface morphologies of the samples before and after 20 oxygen release - oxidation cycles were observed using a scanning electron microscope, as shown in Figure 7 (CaMn 0.95 Co 0.05 O 3-δ ) and Figure 8 (CaMn 0.8 Mg 0.15 Co0.05 O 3-δ ), CaMn 0.95 Co 0.05 O 3-δ After cycling, the grain size slightly increases and slight sintering occurs, while for CaMn 0.8 Mg 0.15 Co 0.05 O 3-δ The particle sizes before and after cycling are basically the same, indicating that the poor high-temperature stability of CaMn 0.95 Co 0.05 O 3-δ may be related to its sintering and agglomeration.

[0038] Meanwhile, X-ray diffraction technology was used to analyze the phases contained in the samples before and after 20 oxygen release-oxidation cycles, Figure 9 and Figure 10 respectively show the XRD patterns of DP1 (CaMn 0.95 Co 0.05 O 3-δ ) and P1 (CaMn 0.8 Mg 0.15 Co 0.05 O 3-δ ). The figure shows that obvious phase separation occurs in CaMn 0.95 Co 0.05 O 3-δ after 20 oxygen release-oxidation cycles, and the spinel phase CaMn2O4 is formed. The formation of this phase is not conducive to the re-oxidation of CaMn 0.95 Co 0.05 O 3-δ , thus significantly deteriorating its high-temperature stability; while for CaMn 0.8 Mg 0.15 Co 0.05 O 3-δ the phase is stable as CaMnO 3-δ after 20 oxygen release-oxidation cycles, and the unreacted and incompletely fused oxide phase Co 0.4 Mn 0.6 before the reaction no longer exists after cycling, indicating that the addition of Mg has the effect of stabilizing the structure of the Ca-Mn-Co-based perovskite oxygen carrier.

[0039] From the above results, it can be seen that the method provided by the present invention is simple and feasible to operate, and the prepared oxygen-release type perovskite oxygen carrier has a high oxygen release amount, excellent high-temperature oxygen decoupling performance and high-temperature cycle stability, can improve the fuel conversion efficiency in the chemical-looping combustion fuel reactor, and is more suitable for the carbon capture technology field than the traditional oxygen-release type perovskite oxygen carrier of the Ca-Mn-Co system.

[0040] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing an oxygen-releasing perovskite oxygen carrier, characterized in that: The method comprises the following steps: (1) contacting and mixing calcium nitrate, manganese nitrate, magnesium nitrate, cobalt nitrate, a complexing agent and ethylene glycol in the presence of a solvent to obtain a mixture I; (2) heating the mixture I and drying it to obtain a mixture II; (3) calcining the mixture II to obtain an oxygen-releasing perovskite oxygen carrier.

2. The method according to claim 1, characterized in that In step (1), the molar ratio of the calcium nitrate, the manganese nitrate, the magnesium nitrate and the cobalt nitrate is 1:0.8:0.15:0.

05.

3. The method according to claim 1 or 2, characterized in that: In step (1), the molar ratio of the total molar amount of metal cations in the calcium nitrate, the manganese nitrate, the magnesium nitrate and the cobalt nitrate to the molar amount of the complexing agent is 1:1-1.

1.

4. The method according to claim 1 or 2, characterized in that: In step (1), the complexing agent is anhydrous citric acid.

5. The method according to claim 1 or 2, characterized in that: In step (2), the heating treatment is carried out under stirring conditions and at least meets the following conditions: the temperature is 70-80° C. and the time is 4-6 hours.

6. The method according to claim 1 or 2, characterized in that: The method also includes: in step (3), pre-burning the mixture II at 300-350°C for 30-60 minutes, then heating it to 900-950°C at a rate of 3-4°C / min and calcining it at high temperature for 7-8 hours.

7. The method according to claim 6, characterized in that The method further comprises: in step (2), first grinding the mixture II to an average volume diameter of 100-200 μm and then performing the pre-combustion.

8. An oxygen-releasing perovskite oxygen carrier prepared by the method described in any one of claims 1 to 7.

9. Use of the oxygen-releasing perovskite oxygen carrier according to claim 8 in carbon capture technology.

Images