Ni3fe embedded in a niFeAlO4 spinel oxygen carrier, and preparation and application thereof

Abstract

The application discloses a Ni3Fe embedded NiFeAlO4 spinel oxygen carrier and a preparation and application thereof. The application takes a hydrotalcite-like compound as a precursor, and after calcination, a reducing atmosphere is introduced to partially reduce the oxygen carrier derived from the hydrotalcite-like compound, so that the oxygen carrier is the Ni3Fe embedded NiFeAlO4 spinel oxygen carrier, the catalytic capacity of the oxygen carrier for converting gaseous fuel such as alkane, liquid fuel such as alcohol and bio-oil, solid fuel such as biomass and organic waste solid into synthesis gas and the capacity of the oxygen carrier for converting water vapor into pure hydrogen are improved, the oxygen carrier has good anti-coking effect, can convert fuel into synthesis gas with a H2 / CO ratio of 2 under certain reaction conditions, and can efficiently convert water vapor into high-purity hydrogen, and is beneficial to the Fischer-Tropsch synthesis and hydrogen production in industry.

Description

Technical Field

[0001] This invention belongs to the field of oxygen carrier technology, specifically relating to a Ni3Fe-embedded NiFeAlO4 spinel oxygen carrier for chemical chain steam reforming, its preparation method and application. Background Technology

[0002] Hydrogen is not only an important raw material for the synthesis of ammonia, methanol, and other chemical products in the chemical industry, but also a high-energy-density, renewable, and carbon-free energy source. Therefore, the production and utilization of hydrogen is one of the most promising decarbonization strategies. However, the key to hydrogen energy development is finding an economical and efficient method for hydrogen production.

[0003] Steam methane reforming (SMR) is one of the most economical and efficient methods for large-scale hydrogen production. However, the syngas produced by traditional steam methane reforming has an H2 / CO ratio of 3, which is unfavorable for Fischer-Tropsch synthesis, and further utilization of hydrogen requires additional purification processes, which undoubtedly increases energy consumption and cost. Chemical looping reforming for hydrogen production breaks down irreversible steam reforming into two sustainable cyclic steps that produce syngas and pure hydrogen respectively, providing a new solution to these challenges. The oxygen carrier is a key factor in chemical looping reforming for hydrogen production, affecting the sustainability of the cycle and the selectivity of the products.

[0004] Considering environmental and cost factors, iron-based oxygen carriers are the most suitable oxygen carriers for large-scale chemical loop reforming hydrogen production. However, they suffer from low reactivity and poor syngas selectivity. They usually need to be modified with other active metals and special structures to improve their reactivity. However, the metal distribution of traditional oxygen carriers is uneven. Areas with less metal distribution have lower conversion efficiency, while areas with more metal distribution will experience metal accumulation effects, resulting in severe carbon deposition, which further reduces reactivity. At present, achieving low cost, high syngas selectivity, high fuel conversion efficiency, and resistance to carbon deposition remains a huge challenge for iron-based oxygen carriers.

[0005] Layered double hydroxides (LDHs) are layered composite hydroxides in which metal cations are uniformly dispersed at the molecular level. They can be assembled at the molecular level by controlling the types and amounts of metal ions and anions. After thermal conversion, layered double oxides (LDOs) exhibit high dispersibility and specific morphology at the molecular level. However, LDH-derived oxygen carriers often experience excessively rapid lattice oxygen release in the early stages of the reaction, leading to fuel over-oxidation, and excessively slow lattice oxygen release in the later stages, resulting in carbon deposition. This severely limits their application in large-scale chemical loop reforming for hydrogen production. Summary of the Invention

[0006] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a method for preparing a Ni3Fe-embedded NiFeAlO4 spinel oxygen carrier.

[0007] Another object of the present invention is to provide a Ni3Fe embedded NiFeAlO4 spinel oxygen carrier prepared by the above preparation method.

[0008] Another object of the present invention is to provide the application of the above-mentioned Ni3Fe embedded NiFeAlO4 spinel oxygen carrier.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A method for preparing a Ni3Fe-embedded NiFeAlO4 spinel oxygen carrier includes the following steps:

[0011] (1) A mixed aqueous solution of nickel nitrate, aluminum nitrate and ferric nitrate was added to a mixed alkaline solution of sodium carbonate and sodium hydroxide under stirring to coprecipitate, age, filter, wash and dry to obtain a hydrotalcite-like precursor.

[0012] (2) The hydrotalcite-like precursor was calcined to obtain a layered double oxide, and then partially reduced in a reducing atmosphere at 500-900℃ to obtain Ni3Fe embedded NiFeAlO4 spinel oxygen carrier.

[0013] The molar ratio of reducing gas to lattice oxygen in layered double oxide is 1:0.36 to 0.61.

[0014] Preferably, the nickel nitrate in step (1) is nickel nitrate hexahydrate; the aluminum nitrate is aluminum nitrate hexahydrate; and the ferric nitrate is ferric nitrate hexahydrate.

[0015] Preferably, the molar ratio of nickel nitrate, aluminum nitrate and ferric nitrate in step (1) is 2 to 3:1:1.

[0016] Preferably, in the mixed aqueous solution of nickel nitrate, aluminum nitrate and ferric nitrate in step (1), the total concentration of cations is 0.1 to 1.5 mol / L.

[0017] Preferably, in the mixed alkaline solution of sodium carbonate and sodium hydroxide in step (1), the molar ratio of sodium hydroxide to sodium carbonate is 0.3 to 3:1; more preferably, it is 2:1.

[0018] Preferably, in the mixed alkaline solution of sodium carbonate and sodium hydroxide in step (1), the total concentration of cations is 0.1 to 1.5 mol / L.

[0019] Preferably, the molar ratio of cations in the mixed aqueous solution of nickel nitrate, aluminum nitrate and ferric nitrate in step (1) to cations in the mixed alkaline solution of sodium carbonate and sodium hydroxide is 0.3 to 3:1; more preferably, it is 0.5:1.

[0020] Preferably, the stirring speed in step (1) is 500-800 r / min.

[0021] Preferably, the aging time in step (1) is 12 to 24 hours.

[0022] Preferably, the washing in step (1) refers to washing with water, and the number of washing cycles is 1 to 6.

[0023] Preferably, the drying temperature in step (1) is 70-120°C and the drying time is 15-24 hours.

[0024] Preferably, the calcination temperature in step (2) is 500-900°C and the time is 2-6 hours; more preferably, the calcination is performed at 500°C for 2 hours and then at 900°C for 4 hours.

[0025] Preferably, the calcination in step (2) is carried out in an air atmosphere.

[0026] Preferably, the heating rate of the calcination in step (2) is 2 to 15 °C / min; more preferably, it is 10 °C / min.

[0027] Preferably, after the hydrotalcite precursor described in step (2) is calcined, it needs to be ground and sieved; more preferably, the sieving refers to passing through an 80-mesh sieve.

[0028] Preferably, the reducing atmosphere in step (2) is an atmosphere containing H2; more preferably, the reducing atmosphere is H2 with a concentration of 10%.

[0029] Preferably, the flow rate of the reducing atmosphere in step (2) is 25-100 ml / min.

[0030] Preferably, the reduction time in step (2) is 15 to 25 minutes.

[0031] The above preparation method yields a Ni3Fe-intercalated NiFeAlO4 spinel oxygen carrier.

[0032] The above-mentioned Ni3Fe-intercalated NiFeAlO4 spinel oxygen carrier is used in the chemical chain steam generation of syngas and pure hydrogen.

[0033] Preferably, the application specifically involves: adding the above-mentioned Ni3Fe embedded NiFeAlO4 spinel oxygen carrier into a fuel reactor; first, introducing an inert gas to purge the air from the fuel reactor; then heating the fuel reactor to the reaction temperature; once the temperature of the fuel reactor stabilizes, introducing gaseous fuel, liquid fuel, or solid fuel to produce syngas (a mixture of H2 and CO); after the reaction is complete, introducing an inert gas to purge the syngas from the reactor; and after the steam reactor stabilizes, introducing steam and an inert gas for steam reforming to produce hydrogen.

[0034] More preferably, the gaseous fuel is an alkane fuel diluted with an inert gas to a volume percentage of 5-25%; the liquid fuel is an alcohol or bio-oil fuel; and the solid fuel is biomass or organic waste fuel.

[0035] More preferably, the gaseous fuel is methane diluted with an inert gas to a volume percentage of 5-25%.

[0036] More preferably, the flow rate of the inert gas is 90-100 ml / min, and the introduction time (inert gas scavenging) is 5-10 min.

[0037] More preferably, the flow rate of the gaseous fuel is 50-150 ml / min, and the introduction time is 20-180 min.

[0038] More preferably, the molar ratio of the gaseous fuel, liquid fuel, or solid fuel to the Ni3Fe embedded NiFeAlO4 spinel oxygen carrier is 1.2 to 0.8:1.

[0039] More preferably, the molar ratio of water vapor to lattice oxygen in the Ni3Fe embedded NiFeAlO4 spinel oxygen carrier is 0.83 to 8.3:1.

[0040] More preferably, the flow rate of the inert gas in the steam reforming stage is 50-100 ml / min.

[0041] More preferably, the reaction temperature is 500–900°C.

[0042] This invention introduces gaseous fuels such as alkanes, liquid fuels such as alcohols and bio-oils, and solid fuels such as biomass and organic waste into a fuel reactor separately, and introduces water vapor into a steam reactor. Under the action of Ni3Fe embedded in NiFeAlO4 spinel oxygen carrier, which has abundant catalytic cracking active sites and high oxygen transport rate, syngas and hydrogen are produced through oxidation and reduction reactions.

[0043] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0044] (1) This invention prepares a hydrotalcite-like precursor with uniformly dispersed active metals at the molecular level by co-precipitation method, and obtains an oxide and spinel complex with a special structure by calcination treatment. After partial reduction by reducing gas, a Ni3Fe embedded NiFeAlO4 spinel oxygen carrier is obtained. The oxygen carrier prepared by this method has the characteristics of abundant surface active catalytic sites. At the same time, the oxygen carrier has good oxygen transport capacity, syngas selectivity and anti-carbon deposition ability.

[0045] (2) In this invention, the oxygen carrier material derived from hydrotalcite is pretreated by partial reduction with reducing gas. The Ni3Fe released has a strong catalytic activity for the cracking of fuels such as biomass and methane. At the same time, spinel has a strong interaction with Ni3Fe. The suitable oxygen release capacity of spinel ensures that carbon intermediates are eliminated in time after the catalytic cracking of fuels such as biomass and methane, while inhibiting the formation of carbon deposits.

[0046] (3) The present invention uses hydrotalcite-like precursor as oxygen carrier. By adjusting the metal ratio and alkali ratio in the precursor, the oxygen carrier can be assembled at the molecular level, thereby obtaining an oxygen carrier with highly dispersed metal at the molecular level, which can prevent the enrichment and accumulation of active metals in the oxygen carrier under certain conditions.

[0047] (4) By adjusting the reduction time and temperature of the reducing atmosphere, this invention can control the degree of reduction and morphology of the oxygen carrier, thereby controlling the active metal sites and oxygen migration rate of the oxygen carrier, improving the methane conversion rate and syngas selectivity, and adjusting the ratio of syngas under certain conditions, which is beneficial for preparing syngas according to actual needs.

[0048] (5) The oxygen carrier prepared by the present invention has high cycle stability and can maintain high H2 and CO selectivity under high conversion rate, while having good anti-carbon deposition performance.

[0049] (6) The oxygen carrier preparation conditions in this invention are simple and easy to control, and the cost is low. It can achieve high stability and high reactivity, which is conducive to large-scale application in chemical chain steam reforming. Compared with the existing oxygen carrier preparation methods, it uses hydrotalcite-like precursor and adds a reducing atmosphere to partially reduce the oxygen carrier in situ, so that the surface of the oxygen carrier has rich active catalytic sites and better metal dispersion. Attached Figure Description

[0050] Figure 1 The image shows the X-ray diffraction pattern of the hydrotalcite-like precursor obtained in Example 1.

[0051] Figure 2The X-ray diffraction patterns are those of the Ni3Fe embedded NiFeAlO4 spinel oxygen carrier obtained in Example 1 with a reduction time of 20 min and the NiO / NiFeAlO4 oxygen carrier obtained in Comparative Example 1 with a reduction time of 0 min.

[0052] Figure 3 The image shows the effect of the Ni3Fe-embedded NiFeAlO4 spinel oxygen carrier obtained in Example 1 on the reforming of methane.

[0053] Figure 4 The image shows the effect of the Ni3Fe-embedded NiFeAlO4 spinel oxygen carrier obtained in Example 2 on the reforming of methane.

[0054] Figure 5 The image shows the effect of the Ni3Fe-embedded NiFeAlO4 spinel oxygen carrier obtained in Example 3 on the reforming of methane.

[0055] Figure 6 The image shows the effect of the Ni3Fe-embedded NiFeAlO4 spinel oxygen carrier obtained in Example 4 on the reforming of methane.

[0056] Figure 7 The image shows the effect of the Ni3Fe-intercalated NiFeAlO4 spinel oxygen carrier obtained in Comparative Example 1 on the reforming of methane.

[0057] Figure 8 The image shows the effect of the Ni3Fe-embedded NiFeAlO4 spinel oxygen carrier obtained in Comparative Example 2 on the reforming of methane.

[0058] Figure 9 The image shows the effect of the completely reduced oxygen carrier obtained in Comparative Example 3 on the reforming of methane.

[0059] Figure 10 The image shows the effect of the oxygen carrier obtained in Comparative Example 4 on the reforming of methane.

[0060] Figure 11 The image shows the effect of the oxygen carrier obtained in Comparative Example 5 on the reforming of methane. Detailed Implementation

[0061] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0062] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0063] Example 1

[0064] (1) Preparation of layered composite oxide: 0.05 mol nickel nitrate hexahydrate, 0.025 mol ferric nitrate nonahydrate, and 0.025 mol aluminum nitrate were dissolved in 100 ml of deionized water to prepare a metal solution with a metal ion concentration of 1 mol / L; 0.132 mol sodium hydroxide and 0.066 mol anhydrous sodium carbonate were dissolved in 200 ml of water to obtain a mixed alkaline solution with a concentration of 1 mol / L. The metal solution was rapidly poured into the mixed alkaline solution at a rotation speed of 500 r / min to obtain a precipitate. After aging at room temperature for 24 h, the precipitate was filtered and washed with deionized water until neutral, and then dried in an oven at 70 °C for 24 h to obtain a hydrotalcite-like precursor. The hydrotalcite-like precursor was placed in a muffle furnace and calcined in air atmosphere at a staged heating rate of 500 °C for 2 h and 900 °C for 4 h (heating rate 10 °C / min). After cooling, it was ground through an 80-mesh sieve to obtain a layered composite oxide.

[0065] (2) Preparation of partially reduced oxygen carrier: 1.45g of oxygen carrier was placed in a tubular atmosphere furnace and reduced for 20min at a flow rate of 100ml / L H2 (concentration of 10%) and a temperature of 900℃ to obtain partially reduced oxygen carrier.

[0066] (3) Evaluation of oxygen carrier reaction characteristics: The reaction for the chemical chaining of methane to syngas was carried out in a small fixed bed. 1.45g of oxygen carrier was placed in the center of a quartz tube, and quartz wool was plugged at both ends to fix the oxygen carrier. Nitrogen gas was introduced for 10 minutes to purge the air. After the atmosphere furnace was heated to 900℃, the quartz tube was placed in the atmosphere furnace and the temperature was allowed to stabilize. Then, the gas was switched to 100ml / min of methane (10% CH4 / 90% N2). The reaction time for this stage was 27 minutes. The syngas obtained from the reaction was collected in a gas bag and its composition was analyzed by gas chromatography. The analysis showed that the methane conversion rate was as high as 96.54%, the hydrogen selectivity was as high as 83.72%, and the carbon monoxide selectivity was as high as 76.98%. The steam reforming stage was followed by the methane stage, after which nitrogen gas was introduced for 10 min at a flow rate of 90 ml / min. Then, H₂O was injected into the quartz tube at a flow rate of 0.1 ml / min for 27 min under a nitrogen flow rate of 90 ml / min. The resulting gas was collected in a gas bag and its composition was analyzed. The hydrogen yield was found to be 26.41 mol·h⁻¹. -1 ·kg -1 The purity is 87.00%.

[0067] Example 2

[0068] The Ni3Fe-embedded NiFeAlO4 spinel oxygen carrier was prepared according to the method of Example 1. The difference is that in step (2), 1.45g of oxygen carrier was placed in a tube atmosphere furnace and reduced for 15min at a flow rate of 100ml / L H2 (concentration of 10%) and a temperature of 900℃ to obtain a partially reduced oxygen carrier.

[0069] (3) Evaluation of oxygen carrier reaction characteristics: The reaction for the chemical chaining of methane to syngas was carried out in a small fixed bed. 1.45g of oxygen carrier was placed in the center of a quartz tube, and quartz wool was plugged at both ends to fix the oxygen carrier. Nitrogen gas was introduced for 10 minutes to purge the air. After the atmosphere furnace was heated to 900℃, the quartz tube was placed in the atmosphere furnace and the temperature was allowed to stabilize. Then, the gas was switched to 100ml / min of methane (10% CH4 / 90% N2). The reaction time for this stage was 27 minutes. The syngas obtained from the reaction was collected in a gas bag and its composition was analyzed by gas chromatography. The analysis showed that the methane conversion rate was as high as 95.35%, the hydrogen selectivity was as high as 82.88%, and the carbon monoxide selectivity was as high as 76.38%. The steam reforming stage was followed by the methane stage, after which nitrogen gas was introduced for 10 min at a flow rate of 90 ml / min. Then, H₂O was injected into the quartz tube at a flow rate of 0.1 ml / min for 27 min under a nitrogen flow rate of 90 ml / min. The resulting gas was collected in a gas bag and its composition was analyzed. The analysis showed that the hydrogen yield was 23.04 mol·h⁻¹. -1 ·kg -1 .

[0070] Example 3

[0071] The Ni3Fe-embedded NiFeAlO4 spinel oxygen carrier was prepared according to the method of Example 1. The difference is that in step (2), 1.45g of oxygen carrier was placed in a tube atmosphere furnace and reduced for 25min at a flow rate of 100ml / L H2 (concentration of 10%) and a temperature of 900℃ to obtain a partially reduced oxygen carrier.

[0072] (3) Evaluation of oxygen carrier reaction characteristics: The reaction for the chemical chaining of methane to syngas was carried out in a small fixed bed. 1.45 g of oxygen carrier was placed in the center of a quartz tube, and quartz wool was plugged at both ends to fix the oxygen carrier. Nitrogen gas was introduced for 10 min to purge the air. After the atmosphere furnace was heated to 900℃, the quartz tube was placed in the atmosphere furnace and the temperature was allowed to stabilize. Then, the gas was switched to 100 ml / min of methane (10% CH4 / 90% N2). The reaction time for this stage was 27 min. The syngas obtained from the reaction was collected in a gas bag and its composition was analyzed by gas chromatography. The analysis showed that the methane conversion rate was 95.38%, the hydrogen selectivity was 87.07%, and the carbon monoxide selectivity was 78.92%. The steam reforming stage was followed by the methane stage, after which nitrogen gas was introduced for 10 min at a flow rate of 90 ml / min. Then, H₂O was injected into the quartz tube at a flow rate of 0.1 ml / min for 27 min under a nitrogen flow rate of 90 ml / min. The resulting gas was collected in a gas bag and its composition was analyzed. The hydrogen yield was found to be 28.58 mol·h⁻¹. -1 ·kg -1 The purity is 81.82%.

[0073] Example 4

[0074] The oxygen carrier was prepared according to the method in Example 1, with the difference being the preparation of the layered composite oxide in step (1): 0.06 mol nickel nitrate hexahydrate, 0.02 mol ferric nitrate nonahydrate, and 0.02 mol aluminum nitrate were dissolved in 100 ml of deionized water to prepare a metal solution with a metal ion concentration of 1 mol / L; 0.132 mol sodium hydroxide and 0.066 mol anhydrous sodium carbonate were dissolved in 200 ml of water to obtain a mixed alkaline solution with a concentration of 1 mol / L. The metal solution was rapidly poured into the mixed alkaline solution at 500 r / min to obtain a precipitate. After aging at room temperature for 24 h, the precipitate was filtered, washed with deionized water until neutral, and then dried in an oven at 70 °C for 24 h to obtain the precursor. The precursor was placed in a muffle furnace and calcined in air at stages of 500℃ for 2 hours and 900℃ for 4 hours (heating rate 10℃ / min). After cooling, it was ground through an 80-mesh sieve to obtain a layered composite oxide.

[0075] (3) Evaluation of oxygen carrier reaction characteristics: The reaction for the chemical chaining of methane to syngas was carried out in a small fixed bed. 1.45 g of oxygen carrier was placed in the center of a quartz tube, and quartz wool was plugged at both ends to fix the oxygen carrier. Nitrogen gas was introduced for 10 min to purge the air. After the atmosphere furnace was heated to 900℃, the quartz tube was placed in the atmosphere furnace and the temperature was allowed to stabilize. Then, the gas was switched to 100 ml / min of methane (10% CH4 / 90% N2). The reaction time for this stage was 27 min. The syngas obtained from the reaction was collected in a gas bag and its composition was analyzed by gas chromatography. The analysis showed that the methane conversion rate was 96.07%, the hydrogen selectivity was 95.97%, and the carbon monoxide selectivity was 75.49%. The steam reforming stage was followed by the methane stage, after which nitrogen gas was introduced for 10 min at a flow rate of 90 ml / min. Then, H₂O was injected into the quartz tube at a flow rate of 0.1 ml / min for 27 min under a nitrogen flow rate of 90 ml / min. The resulting gas was collected in a gas bag and its composition was analyzed. The hydrogen yield was found to be 23.12 mol·h⁻¹. -1 ·kg -1 The purity is 90.56%.

[0076] Comparative Example 1

[0077] The method of Example 1 was used to prepare Ni3Fe embedded NiFeAlO4 spinel oxygen carrier. The difference is that in step (2), 1.45g of oxygen carrier was placed in a tube atmosphere furnace and reduced for 0min at a flow rate of 100ml / L H2 (concentration of 10%) and a temperature of 900℃. That is, no reduction treatment was performed, and the unreduced oxygen carrier was obtained.

[0078] (3) Evaluation of oxygen carrier reaction characteristics: The reaction for the chemical chaining of methane to syngas was carried out in a small fixed bed. 1.45 g of oxygen carrier was placed in the center of a quartz tube, and quartz wool was plugged at both ends to fix the oxygen carrier. Nitrogen gas was introduced for 10 min to purge the air. After the atmosphere furnace was heated to 900℃, the quartz tube was placed in the atmosphere furnace and the temperature was allowed to stabilize. Then, the gas was switched to 100 ml / min of methane (10% CH4 / 90% N2). The reaction time for this stage was 27 min. The syngas obtained from the reaction was collected in a gas bag and its composition was analyzed by gas chromatography. The analysis showed that the methane conversion rate was 95.89%, the hydrogen selectivity was 62.94%, and the carbon monoxide selectivity was 63.65%. The steam reforming stage was followed by the methane stage, after which nitrogen gas was introduced for 10 min at a flow rate of 90 ml / min. Then, H₂O was injected into the quartz tube at a flow rate of 0.1 ml / min for 27 min under a nitrogen flow rate of 90 ml / min. The resulting gas was collected in a gas bag and its composition was analyzed. The hydrogen yield was found to be 8.88 mol·h⁻¹. -1 ·kg -1 The purity is 74.51%.

[0079] Comparative Example 2

[0080] The Ni3Fe-embedded NiFeAlO4 spinel oxygen carrier was prepared according to the method of Example 1. The difference is that in step (2), 1.45g of oxygen carrier was placed in a tube atmosphere furnace and reduced for 5min at a flow rate of 100ml / L H2 (concentration of 10%) and a temperature of 900℃ to obtain a partially reduced oxygen carrier.

[0081] (3) Evaluation of oxygen carrier reaction characteristics: The reaction for the chemical chaining of methane to syngas was carried out in a small fixed bed. 1.45 g of oxygen carrier was placed in the center of a quartz tube, and quartz wool was plugged at both ends to fix the oxygen carrier. Nitrogen gas was introduced for 10 min to purge the air. After the atmosphere furnace was heated to 900℃, the quartz tube was placed in the atmosphere furnace and the temperature was allowed to stabilize. Then, the gas was switched to 100 ml / min of methane (10% CH4 / 90% N2). The reaction time for this stage was 27 min. The syngas obtained from the reaction was collected in a gas bag and its composition was analyzed by gas chromatography. The analysis showed that the methane conversion rate was 93.46%, the hydrogen selectivity was 71.28%, and the carbon monoxide selectivity was 66.71%. The steam reforming stage was followed by the methane stage, after which nitrogen gas was introduced for 10 min at a flow rate of 90 ml / min. Then, H₂O was injected into the quartz tube at a flow rate of 0.1 ml / min for 27 min under a nitrogen flow rate of 90 ml / min. The resulting gas was collected in a gas bag and its composition was analyzed. The hydrogen yield was found to be 21.89 mol·h⁻¹. -1 ·kg -1 The purity is 85.80%.

[0082] Comparative Example 3

[0083] The method of Example 1 was used to prepare a completely reduced oxygen carrier. The difference was that in step (2), 1.45g of oxygen carrier was placed in a tubular atmosphere furnace and reduced for 120min at a flow rate of 100ml / L H2 (concentration of 10%) and a temperature of 900℃ to obtain a completely reduced oxygen carrier.

[0084] (3) Evaluation of oxygen carrier reaction characteristics: The reaction for the chemical chaining of methane to syngas was carried out in a small fixed bed. 1.45 g of oxygen carrier was placed in the center of a quartz tube, and quartz wool was plugged at both ends to fix the oxygen carrier. Nitrogen gas was introduced for 10 min to purge the air. After the atmosphere furnace was heated to 900℃, the quartz tube was placed in the atmosphere furnace and the temperature was allowed to stabilize. Then, the gas was switched to 100 ml / min of methane (10% CH4 / 90% N2). The reaction time for this stage was 27 min. The syngas obtained from the reaction was collected in a gas bag and its composition was analyzed by gas chromatography. The analysis showed that the methane conversion rate was 85.56%, the hydrogen selectivity was 92.48%, and the carbon monoxide selectivity was 0%. The steam reforming stage was followed by the methane stage, after which nitrogen gas was introduced for 10 min at a flow rate of 90 ml / min. Then, H₂O was injected into the quartz tube at a flow rate of 0.1 ml / min for 27 min under a nitrogen flow rate of 90 ml / min. The resulting gas was collected in a gas bag and its composition was analyzed. The hydrogen yield was found to be 29.03 mol·h⁻¹. -1 ·kg -1 The purity is only 58.57%.

[0085] Comparative Example 4

[0086] The oxygen carrier was prepared according to the method in Example 1, the difference being the preparation of the layered composite oxide in step (1): 0.025 mol nickel nitrate hexahydrate, 0.05 mol ferric nitrate nonahydrate, and 0.025 mol aluminum nitrate were dissolved in 100 ml of deionized water to prepare a metal solution with a metal ion concentration of 1 mol / L; 0.132 mol sodium hydroxide and 0.066 mol anhydrous sodium carbonate were dissolved in 200 ml of water to obtain a mixed alkaline solution with a concentration of 1 mol / L. The metal solution was rapidly poured into the mixed alkaline solution at 500 r / min to obtain a precipitate. After aging at room temperature for 24 h, the precipitate was filtered and washed with deionized water until neutral, and then dried in an oven at 70 °C for 24 h to obtain the precursor (a non-hydrotalcite precursor). The precursor was placed in a muffle furnace and calcined in air at stages of 500℃ for 2 hours and 900℃ for 4 hours (heating rate 10℃ / min). After cooling, it was ground through an 80-mesh sieve to obtain a layered composite oxide.

[0087] (3) Evaluation of oxygen carrier reaction characteristics: The reaction for the chemical chaining of methane to syngas was carried out in a small fixed bed. 1.45 g of oxygen carrier was placed in the center of a quartz tube, and quartz wool was plugged at both ends to fix the oxygen carrier. Nitrogen gas was introduced for 10 min to purge the air. After the atmosphere furnace was heated to 900℃, the quartz tube was placed in the atmosphere furnace and the temperature was allowed to stabilize. Then, the gas was switched to 100 ml / min of methane (10% CH4 / 90% N2). The reaction time for this stage was 27 min. The syngas obtained from the reaction was collected in a gas bag and its composition was analyzed by gas chromatography. The analysis showed that the methane conversion rate was 39.97%, the hydrogen selectivity was 20.68%, and the carbon monoxide selectivity was 0%. The steam reforming stage was followed by the methane stage, after which nitrogen gas was introduced for 10 min at a flow rate of 90 ml / min. Then, H₂O was injected into the quartz tube at a flow rate of 0.1 ml / min for 27 min under a nitrogen flow rate of 90 ml / min. The resulting gas was collected in a gas bag and its composition was analyzed. The hydrogen yield was found to be 7.40 mol·h⁻¹. -1 ·kg -1 Its purity is only 55.63%.

[0088] Comparative Example 5

[0089] The oxygen carrier was prepared according to the method in Example 1, with the difference being the preparation of the layered composite oxide in step (1): 0.066 mol nickel nitrate hexahydrate, 0.016 mol ferric nitrate nonahydrate, and 0.016 mol aluminum nitrate were dissolved in 100 ml of deionized water to prepare a metal solution with a metal ion concentration of 1 mol / L; 0.132 mol sodium hydroxide and 0.066 mol anhydrous sodium carbonate were dissolved in 200 ml of water to obtain a mixed alkaline solution with a concentration of 1 mol / L. The metal solution was rapidly poured into the mixed alkaline solution at a speed of 500 r / min to obtain a precipitate. After aging at room temperature for 24 h, the precipitate was filtered and washed with deionized water until neutral, and then dried in an oven at 70 °C for 24 h to obtain the precursor (a non-hydrotalcite precursor). The precursor was placed in a muffle furnace and calcined in air at stages of 500℃ for 2 hours and 900℃ for 4 hours (heating rate 10℃ / min). After cooling, it was ground through an 80-mesh sieve to obtain a layered composite oxide.

[0090] (3) Evaluation of oxygen carrier reaction characteristics: The reaction for the chemical chaining of methane to syngas was carried out in a small fixed bed. 1.45g of oxygen carrier was placed in the center of a quartz tube, and quartz wool was plugged at both ends to fix the oxygen carrier. Nitrogen gas was introduced for 10 minutes to purge the air. After the atmosphere furnace was heated to 900℃, the quartz tube was placed in the atmosphere furnace and the temperature was allowed to stabilize. Then, the gas was switched to 100ml / min of methane (10% CH4 / 90% N2). The reaction time for this stage was 27 minutes. The syngas obtained from the reaction was collected in a gas bag and its composition was analyzed by gas chromatography. The analysis showed that the methane conversion rate was 94.68%, the hydrogen selectivity was 91.15%, and the carbon monoxide selectivity was only 50.61%. The steam reforming stage was followed by the methane stage, after which nitrogen gas was introduced for 10 min at a flow rate of 90 ml / min. Then, H₂O was injected into the quartz tube at a flow rate of 0.1 ml / min for 27 min under a nitrogen flow rate of 90 ml / min. The resulting gas was collected in a gas bag and its composition was analyzed. The hydrogen yield was found to be 26.98 mol·h⁻¹. -1 ·kg -1 The purity is only 64.56%.

[0091] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a Ni3Fe-embedded NiFeAlO4 spinel oxygen carrier, characterized in that, Includes the following steps: (1) A mixed aqueous solution of nickel nitrate, aluminum nitrate and ferric nitrate was added to a mixed alkaline solution of sodium carbonate and sodium hydroxide under stirring to coprecipitate, age, filter, wash and dry to obtain a hydrotalcite-like precursor. (2) The hydrotalcite-like precursor was calcined to obtain a layered double oxide, and then partially reduced in a reducing atmosphere at 500-900℃ to obtain Ni3Fe embedded NiFeAlO4 spinel oxygen carrier; The molar ratio of reducing gas to lattice oxygen in layered double oxide is 1:0.36 to 0.

61. The reducing atmosphere in step (2) is an atmosphere containing H2; the flow rate of the reducing atmosphere is 25-100 ml / min; and the reduction time is 15-25 min.

2. The method for preparing a Ni3Fe embedded NiFeAlO4 spinel oxygen carrier according to claim 1, characterized in that, The molar ratio of nickel nitrate, aluminum nitrate, and ferric nitrate in step (1) is 2-3:1:1; The molar ratio of cations in the mixed aqueous solution of nickel nitrate, aluminum nitrate and ferric nitrate in step (1) to cations in the mixed alkaline solution of sodium carbonate and sodium hydroxide is 0.3 to 3:

1.

3. The method for preparing a Ni3Fe-embedded NiFeAlO4 spinel oxygen carrier according to claim 1, characterized in that, In step (1), the total concentration of cations in the mixed aqueous solution of nickel nitrate, aluminum nitrate, and ferric nitrate is 0.1–1.5 mol / L. In step (1), the molar ratio of sodium hydroxide to sodium carbonate in the mixed alkaline solution is 0.3 to 3:

1. In step (1), the total concentration of cations in the mixed alkaline solution of sodium carbonate and sodium hydroxide is 0.1 to 1.5 mol / L.

4. The method for preparing a Ni3Fe-embedded NiFeAlO4 spinel oxygen carrier according to claim 1, characterized in that, The calcination temperature in step (2) is 500-900℃ and the time is 2-6h; the calcination is carried out in an air atmosphere; the heating rate of the calcination in step (2) is 2-15℃ / min.

5. The method for preparing a Ni3Fe embedded NiFeAlO4 spinel oxygen carrier according to claim 1, characterized in that, The stirring speed in step (1) is 500-800 r / min; the aging time is 12-24 h; after the hydrotalcite precursor in step (2) is calcined, it also needs to be ground and sieved.

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