A magnesium aluminum spinel protective agent and its preparation method

Abstract

The present application relates to the technical field of catalyst protectant, in particular to a magnesium-aluminum spinel protectant and a preparation method thereof, which is prepared from magnesium-aluminum composite powder A, magnesium-aluminum composite powder B and an additive. The magnesium-aluminum composite powder A is prepared by mixing magnesium peroxide and magnesium-aluminum spinel A prepared by a specific method, and the magnesium-aluminum composite powder B involves a plurality of magnesium-containing compounds and specifically mixed magnesium-aluminum spinel B. The preparation process covers fine pretreatment of each raw material, such as treatment of magnesium peroxide, aluminum oxide, aluminum powder and the like, and precise control of parameters such as temperature, time and rotation speed in the links of combustion synthesis, high-temperature sintering, mixing and grinding. Experiments show that the specific surface area of the protectant is large, the porosity is high, the mechanical strength is good, the adsorption capacity of impurities and poisons in the complex raw material gas is strong, and the carbon monoxide sulfur shift catalyst can be effectively protected, and the performance and service life of the carbon monoxide sulfur shift catalyst in industrial production can be significantly improved.

Description

Technical Field

[0001] This invention relates to the field of catalyst protectant technology, and in particular to a magnesium aluminum spinel protectant and its preparation method. Background Technology

[0002] In modern chemical production, carbon monoxide (C2O) sulfur-resistant shift catalysts play a crucial role in the production processes of important chemical products such as ammonia synthesis, methanol production, and hydrogen production. Their core reaction principle is to promote the catalytic reaction between carbon monoxide and water vapor, converting it into hydrogen and carbon dioxide. However, the raw material gases used in actual industrial production are extremely complex, inevitably containing solid impurities such as carbon black, tar, and dust, as well as toxic compounds such as As2O3 and P2O5. When these impurities and poisons enter the reaction system with the raw material gas and come into contact with the C2O sulfur-resistant shift catalyst, they trigger a series of negative effects. Solid impurities easily deposit on the catalyst surface, clogging the catalyst's microporous structure and hindering effective contact between reactants and the catalyst's active sites, leading to the covering of active sites and a significant reduction in activity. Poisons such as As2O3 and P2O5 react chemically with the catalyst's active components, altering the catalyst's chemical composition and crystal structure, causing permanent deactivation and drastically shortening its lifespan.

[0003] Existing catalyst protectants have several shortcomings in dealing with these complex operating conditions. In terms of strength, they cannot withstand pressure fluctuations and material erosion during industrial reactions, easily breaking and increasing bed resistance, thus affecting production continuity. Their pore size design is unreasonable, failing to provide sufficient space for impurity adsorption and reducing the protective effect. Their adsorption capacity for various impurities and poisons is limited, making it difficult to meet the demand for efficient purification of feed gas. Regarding catalyst protection, they cannot comprehensively prevent impurities and poisons from eroding the catalyst, failing to fully utilize their protective function, thus making it difficult for existing protectants to meet the growing demands of industrial production.

[0004] To address the aforementioned issues, existing technologies generally employ magnesium aluminum spinel as a protective agent for carbon monoxide shift catalysts for the following reasons: 1. Magnesium aluminum spinel possesses a cubic crystal structure with stable crystal structure. This stable structure allows it to maintain its structural integrity under harsh conditions such as high temperature and high pressure during the carbon monoxide-sulfur shift reaction, making it less prone to decomposition or phase transformation, thus enabling it to continuously function as a protective agent; 2. Magnesium aluminum spinel typically has a large specific surface area, providing abundant surface active sites. This facilitates its interaction with impurities and poisons in the raw materials through adsorption and other processes, effectively removing and adsorbing impurities such as carbon black, tar, and dust from the raw gas, preventing these substances from clogging or contaminating the carbon monoxide-sulfur shift catalyst, and ensuring the catalyst's activity and stability; 3. Magnesium aluminum spinel has high mechanical strength, enabling protective agents with it as a main component to withstand pressure changes and material erosion during the reaction process, making them less prone to breakage and pulverization. In practical industrial applications, it can maintain good particle integrity, maintain the stability of the catalyst bed, ensure uniform gas flow through the bed, reduce the risk of flow deviation, and enable the reaction to proceed stably and efficiently; 4. The high porosity of magnesium aluminum spinel gives it good adsorption and gas diffusion performance. On the one hand, the large number of pores can provide sufficient adsorption space for impurities and poisons, increasing the adsorption capacity for impurities in the feed gas; on the other hand, it is conducive to the diffusion of reactant gases inside the protective agent particles, enabling the carbon monoxide-sulfur-resistant shift reaction to proceed smoothly, while also helping the adsorbed impurities and poisons to diffuse and accumulate in the pores, enhancing the protective effect; 5. Magnesium aluminum spinel has good chemical stability. In the environment of the carbon monoxide-sulfur-resistant shift reaction, it is not easy to react chemically with the components or reaction products in the feed gas, and can maintain its own chemical properties unchanged. This allows it to stably perform its protective function for a longer period of time, without affecting the protective effect on the carbon monoxide sulfur-resistant shift catalyst due to its own chemical changes; 6. Magnesium aluminum spinel itself has certain organic sulfur hydrolysis properties. In the carbon monoxide sulfur-resistant shift reaction, it can hydrolyze some of the organic sulfur in the feed gas into inorganic sulfur, thereby reducing the poisoning effect of organic sulfur on the catalyst, further extending the service life of the carbon monoxide sulfur-resistant shift catalyst, and improving the efficiency and stability of the entire reaction process.

[0005] Despite the numerous advantages of magnesium aluminum spinel, it still has several shortcomings in practical applications, such as: 1. Although magnesium aluminum spinel possesses a certain degree of sulfur resistance, its ability to resist sulfur poisoning still has an upper limit in high-sulfur environments. When the sulfur content in the feed gas is too high, it may cause changes in the structure and properties of magnesium aluminum spinel, reducing its protective effect on the catalyst, or even causing sulfur poisoning itself, rendering it unable to continue its protective function; 2. Under the high-temperature conditions of the carbon monoxide-sulfur conversion reaction, although magnesium aluminum spinel has relatively good stability, it may still experience phenomena such as lattice distortion and grain growth during prolonged high-temperature operation. This may lead to a decrease in its specific surface area and changes in its pore structure, thereby affecting its adsorption performance and the protective effect on the catalyst; 3. In practical industrial applications, the carbon monoxide-sulfur conversion reaction system may use various additives or other auxiliary materials. Magnesium aluminum spinel protective agents may have compatibility issues with these substances. For example, it may react chemically with certain additives or agglomerate during mixing, thus affecting the performance of the protective agent and the entire reaction system.

[0006] Therefore, based on the relevant technologies mentioned above, there is an urgent need to develop a magnesium aluminum spinel protective agent and its preparation method. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a magnesium aluminum spinel protective agent and its preparation method, so as to provide a high-performance catalyst protective agent that can effectively cope with complex raw material gas conditions, thereby improving chemical production efficiency and reducing production costs.

[0008] To achieve the above objectives, the present invention provides a magnesium aluminum spinel protective agent and its preparation method.

[0009] A magnesium-aluminum spinel protective agent is prepared from the following raw materials in parts by weight: 45-65 parts of magnesium-aluminum composite powder A, 15-25 parts of magnesium-aluminum composite powder B, and 5-10 parts of additives.

[0010] The magnesium-aluminum composite powder A is prepared from magnesium peroxide and magnesium-aluminum spinel A;

[0011] The magnesium aluminum spinel A is synthesized by combustion of magnesium peroxide, aluminum oxide and aluminum powder;

[0012] The magnesium-aluminum composite powder B is prepared from magnesium oxalate, magnesium citrate, magnesium stearate, and magnesium-aluminum spinel B.

[0013] The magnesium aluminum spinel B is obtained by mixing magnesium aluminum spinel B1, magnesium aluminum spinel B2 and magnesium aluminum spinel B3;

[0014] The magnesium aluminum spinel B1 was prepared from magnesium oxalate and aluminum oxide;

[0015] The magnesium aluminum spinel B2 is prepared from magnesium stearate and aluminum oxide;

[0016] The magnesium aluminum spinel B3 is prepared from magnesium citrate and aluminum oxide.

[0017] Preferably, the preparation process of the magnesium aluminum spinel A is as follows:

[0018] Step A1, Raw material pretreatment: High-purity magnesium peroxide is pulverized to a particle size of 180-200 mesh to obtain magnesium peroxide powder; α-Al2O3 powder is cleaned of surface impurities and then soaked in dilute hydrochloric acid solution for 1-2 hours, rinsed with deionized water until neutral, and then dried in an oven at 120℃ for 4-6 hours to obtain alumina powder; High-purity aluminum powder is soaked in a 10% sodium hydroxide solution for 3-5 minutes, rinsed with deionized water until neutral, rinsed with anhydrous ethanol, and then dried in a vacuum drying oven at 60℃ for 2-3 hours to obtain aluminum powder;

[0019] Step A2: Mix magnesium peroxide powder, aluminum oxide powder and aluminum powder evenly, then add them to a ball mill, add zirconia balls as grinding media and anhydrous ethanol as grinding aid, set the ball mill speed to 300-400 rpm, and the mixing time to 3-5 hours to obtain mixture a.

[0020] Step A3: Evenly fill the mixture a into the reaction crucible to a height of 2 / 3 of the crucible height. After filling, place it into the combustion synthesis device and seal it. Initiate the reaction through the ignition system. The reaction lasts for 5-10 minutes. After the reaction is completed, allow it to cool naturally to room temperature to obtain the cooled product a.

[0021] Step A4: Take out the cooled product a and coarsely crush it to a particle size of 1-2 cm, then finely crush it, add zirconium oxide balls and anhydrous ethanol, the ball mill speed is 400-500 rpm, the crushing time is 4-6 h, so that the product particle size reaches 200-220 mesh, and the crushed material a is obtained.

[0022] Step A5: Soak the pulverized material a in a dilute hydrochloric acid solution for 2-3 hours, then rinse it repeatedly with deionized water until neutral. Finally, dry the acid-washed product in a 120℃ oven for 6-8 hours, and then sieve it through a vibrating screen to select powder with a particle size between 100-300 mesh, thus obtaining magnesium aluminum spinel A.

[0023] Preferably, in step A1, the purity of the high-purity magnesium oxide is ≥98%, the purity of the α-Al2O3 powder is ≥99%, the particle size of the α-Al2O3 powder is 1-5μm, the mass fraction of the dilute hydrochloric acid solution is 5%, the purity of the high-purity aluminum powder is ≥99%, and the particle size of the high-purity aluminum powder is 100-200 mesh.

[0024] Preferably, the mass ratio of magnesium peroxide powder, aluminum oxide powder and aluminum powder in step A2 is 30-40:30-40:30-35, the ball-to-material ratio when zirconium oxide balls are used as grinding media in step A2 is 80-100:10-15, and the amount of anhydrous ethanol added in step A2 is 3%-5% of the total mass of the materials.

[0025] Preferably, the ignition current of the ignition system in step A3 is 5-10A, and the ignition time lasts for 3-5 seconds.

[0026] Preferably, the ratio of zirconium oxide balls to material during fine crushing in step A4 is 8-12:1-1.5, and the amount of anhydrous ethanol added in step A4 is 3%-5% of the total mass of the material.

[0027] Preferably, the preparation process of the magnesium aluminum spinel B1 is as follows:

[0028] Step B1: Mix magnesium oxalate and alumina powders and add them to a ball mill. Add zirconia balls and grind at 300-500 rpm for 2-4 hours to obtain mixed powder b.

[0029] Step B2: Transfer the mixed powder b to a high-temperature furnace and heat it to 800-900℃ at a heating rate of 5-10℃ / min. Hold it at this temperature for 2-3 hours to obtain the pre-calcined material b.

[0030] Step B3: Place the pre-burned material b back into the high-temperature furnace and heat it to 1500-1600℃ at a biological rate of 5-10℃ / min. Hold it for 4-6 hours. Take out the sintered product, crush it, and select powder with a particle size between 1-5μm to obtain magnesium aluminum spinel B1.

[0031] The molar ratio of magnesium oxalate to alumina in step B1 is 0.9-1.1:1-1.2, and the ball-to-material ratio of zirconia balls used as grinding media in step B1 is 80-100:10-15.

[0032] Preferably, the preparation process of the magnesium aluminum spinel B2 is as follows:

[0033] Step C1: Add magnesium stearate and alumina powder to anhydrous ethanol and ultrasonically disperse for 15-30 min to obtain a stable suspension c;

[0034] Step C2: Transfer the suspension c to an evaporating dish and evaporate the anhydrous ethanol in a water bath at 60-80°C. Then dry the evaporated material in an oven at 100-120°C for 2-3 hours to obtain the mixed powder c.

[0035] Step C3: Place the mixed powder into a high-temperature furnace and heat it to 1400-1500℃ at a heating rate of 5-10℃ / min. Hold the temperature for 4-5 hours. After the reaction is complete, cool it to room temperature, pulverize the product, and collect the powder with a particle size between 1-3μm to obtain magnesium aluminum spinel B2.

[0036] The molar ratio of magnesium stearate to aluminum oxide in step C1 is 0.95-1.05:1-1.2, and the ratio of anhydrous ethanol to solid material added in step C1 is 80-100mL:10-12g.

[0037] Preferably, the preparation process of the magnesium aluminum spinel B3 is as follows:

[0038] Step D1: Add alumina powder to magnesium citrate solution, add ammonia dropwise to adjust the pH of the solution to 9-10, stir for 1-2 hours to obtain mixed solution d;

[0039] Step D2: Filter the mixture d, collect the precipitate, and wash the precipitate repeatedly with deionized water 3-5 times to obtain precipitate d;

[0040] Step D3: Place the precipitate d in an oven and dry it at 120-150℃ for 4-6 hours. Transfer the dried product to a high-temperature furnace and heat it to 1500-1600℃ at a heating rate of 5-10℃ / min. Hold it at that temperature for 5-7 hours. After calcination, crush the product and collect the powder with a particle size between 0.5-1.2μm to obtain magnesium aluminum spinel B3.

[0041] The molar ratio of magnesium ions in the alumina powder and magnesium citrate solution mentioned in step D1 is 0.98-1.02:1-1.3;

[0042] The concentration of ammonia water mentioned in step D1 is 25%-28%.

[0043] A method for preparing a magnesium aluminum spinel protective agent includes the following steps:

[0044] Step S1: Mix magnesium peroxide and magnesium aluminum spinel A, add them to a high-speed mixer, and mix at 800-1200 rpm for 30-60 minutes to obtain magnesium aluminum composite powder A;

[0045] Step S2: Place magnesium aluminum spinel B1, magnesium aluminum spinel B2 and magnesium aluminum spinel B3 into a mixer and mix for 2-3 hours to obtain magnesium aluminum spinel B.

[0046] Step S3: Mix magnesium oxalate, magnesium citrate, magnesium stearate and magnesium aluminum spinel B and put them into a stirred ball mill. Grind at 300-500 rpm for 3-5 hours to obtain magnesium aluminum composite powder B.

[0047] Step S4: Mix magnesium-aluminum composite powder A, magnesium-aluminum composite powder B and additives and transfer them into a ball mill jar. Add zirconia balls as grinding media and grind at 300-500 rpm for 60-70 hours to obtain magnesium-aluminum spinel protective agent.

[0048] The mass ratio of magnesium peroxide to magnesium aluminum spinel A in step S1 is 3-4:6-7;

[0049] The mass ratio of magnesium aluminum spinel B1, magnesium aluminum spinel B2 and magnesium aluminum spinel B3 in step S2 is 3-4:2-2.5:4-5;

[0050] The mass ratio of magnesium oxalate, magnesium citrate, magnesium stearate, and magnesium aluminum spinel B in step S3 is 2-3:2-3:1-1.5:5-6;

[0051] The mass ratio of the grinding media to the powder in step S4 is 3-10:1-1.3.

[0052] The additive mentioned in step S4 is a mixture of titanium dioxide and yttrium oxide in a mass ratio of 2-3:3.5-4.2.

[0053] The beneficial effects of this invention are:

[0054] This invention provides a magnesium aluminum spinel protective agent and its preparation method. Through specific raw material processing and preparation techniques, such as the fine pretreatment of raw materials like magnesium peroxide, alumina, and aluminum powder, and precise control of conditions during ball milling and sintering at different stages, the protective agent prepared can achieve a specific surface area of ​​up to 145 m². 2 / g, with a porosity as high as 50%. This provides a large number of adsorption sites and storage space for impurities and poisons, greatly enhancing the adsorption capacity of the protective agent for various impurities in complex feed gases, such as carbon black, tar, dust, and As2O3, P2O5, etc.

[0055] The magnesium aluminum spinel protective agent provided by this invention has a mechanical strength of 9.8 MPa, which can effectively resist pressure fluctuations and material erosion during industrial reaction processes, avoid increased resistance of the protective agent bed due to breakage, maintain the stability of the catalyst bed, and ensure the continuity and efficiency of the reaction.

[0056] This invention provides detailed and targeted pretreatment steps for each raw material. For example, high-purity magnesium oxide is pulverized to a specific particle size, α-Al2O3 powder is soaked, rinsed, and dried in dilute hydrochloric acid, and high-purity aluminum powder is treated with sodium hydroxide solution, etc., to ensure the high purity and suitable activity of the raw materials, laying a good foundation for subsequent reactions;

[0057] The magnesium-aluminum spinel protective agent provided by this invention exhibits excellent adsorption capacity for solid impurities such as carbon black, tar, and dust, as well as toxic compounds such as As2O3 and P2O5 in complex feed gases. Experimental data show that the adsorption capacity for carbon black can reach 15.5 mg / g, and the adsorption capacity for As2O3 can reach 200 μg / g. It can effectively purify the feed gas, prevent these impurities and toxins from damaging the carbon monoxide sulfur-resistant shift catalyst, and extend the catalyst's service life.

[0058] The magnesium aluminum spinel protective agent provided by this invention, thanks to the stable cubic crystal structure of magnesium aluminum spinel and the optimization of material properties during the preparation process, can maintain its structural integrity and chemical stability under harsh conditions such as high temperature (e.g., 350°C) and high pressure (e.g., 3MPa) of carbon monoxide resistance to sulfur conversion reaction, and can continuously and stably play a protective role. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0060] Example 1: A method for preparing a magnesium aluminum spinel protective agent, comprising the following steps:

[0061] S1. Raw material pretreatment: High-purity magnesium peroxide with a purity of ≥98% is pulverized to a particle size of 180-200 mesh to obtain magnesium peroxide powder; α-Al2O3 powder with a particle size of 1-5μm and a purity of ≥99% is cleaned of surface impurities and then soaked in a 5% (w / w) dilute hydrochloric acid solution for 1 hour, rinsed with deionized water until neutral, and then dried in an oven at 120℃ for 4 hours to obtain alumina powder; High-purity aluminum powder with a particle size of 100-200 mesh and a purity of ≥99% is soaked in a 10% (w / w) sodium hydroxide solution for 3 minutes, rinsed with deionized water until neutral, rinsed with anhydrous ethanol, and then dried in a vacuum drying oven at 60℃ for 2 hours to obtain aluminum powder;

[0062] S2. Mix 30g of magnesium peroxide powder, 30g of alumina powder and 30g of aluminum powder evenly, and then add them to a ball mill. At the same time, add zirconia balls as grinding media. The ball-to-material ratio when using zirconia balls as grinding media is 80:10. Add anhydrous ethanol as grinding aid. The amount of anhydrous ethanol added is 3% of the total mass of the material. Set the ball mill speed to 300 rpm and the mixing time to 3 hours to obtain mixture a.

[0063] S3. Mixture a is uniformly filled into the reaction crucible to a height of 2 / 3 of the crucible height. After filling, it is placed in the combustion synthesis device and sealed. The reaction is initiated by the ignition system with an ignition current of 5A and an ignition time of 3s. The reaction lasts for 5min. After the reaction is completed, it is naturally cooled to room temperature to obtain cooled product a.

[0064] S4. Take out the cooled product a and coarsely crush it to a particle size of 1-2 cm, then finely crush it. Add zirconia balls and anhydrous ethanol. During fine crushing, the ball-to-material ratio of zirconia balls is 8:1, and the amount of anhydrous ethanol added is 3% of the total mass of the material. The ball mill speed is 400 rpm and the crushing time is 4 hours, so that the particle size of the product reaches 200-220 mesh, and the crushed material a is obtained.

[0065] S5. Soak the pulverized material a in dilute hydrochloric acid solution for 2 hours, then rinse it repeatedly with deionized water until neutral. Finally, dry the acid-washed product in an oven at 120°C for 6 hours, and then sieve it through a vibrating screen to select powder with a particle size between 100-300 mesh, thus obtaining magnesium aluminum spinel A.

[0066] S6. Add magnesium oxalate and alumina powder to a ball mill, add zirconia balls, and grind at 300 rpm for 2 hours to obtain mixed powder b, wherein the molar ratio of magnesium oxalate to alumina is 0.9:1, and the ball-to-material ratio when zirconia balls are used as grinding media is 80:10.

[0067] S7. Transfer the mixed powder b to a high-temperature furnace and heat it to 800°C at a heating rate of 5°C / min. Hold it at this temperature for 2 hours to obtain the pre-calcined material b.

[0068] S8. Place the pre-burned material b back into the high-temperature furnace and heat it to 1500℃ at a biological rate of 5℃ / min. Hold it for 4 hours. Take out the sintered product, crush it, and select powder with a particle size between 1-5μm to obtain magnesium aluminum spinel B1.

[0069] S9. Add magnesium stearate and alumina powder to anhydrous ethanol and ultrasonically disperse for 15 min. The molar ratio of magnesium stearate to alumina is 0.95:1, and the ratio of anhydrous ethanol to solid material is 80 mL: 10 g, to obtain a stable suspension c.

[0070] S10. Transfer the suspension c to an evaporating dish and evaporate the anhydrous ethanol in a water bath at 60°C. Then dry the evaporated material in an oven at 100°C for 2 hours to obtain mixed powder c.

[0071] S11. Place the mixed powder into a high-temperature furnace and heat it to 1400℃ at a heating rate of 5℃ / min. Hold the temperature for 4 hours. After the reaction is complete, cool it to room temperature, pulverize the product, and collect the powder with a particle size between 1-3μm to obtain magnesium aluminum spinel B2.

[0072] S12. Add alumina powder to magnesium citrate solution, the molar ratio of magnesium ions in alumina powder and magnesium citrate solution is 0.98:1, add 25% ammonia water dropwise to adjust the pH of the solution to 9-10, stir for 1 hour to obtain mixed solution d;

[0073] S13. Filter the mixture d, collect the precipitate, and wash the precipitate repeatedly with deionized water 3 times to obtain precipitate d;

[0074] S14. Place the precipitate d in an oven and dry it at 120℃ for 4 hours. Transfer the dried product to a high-temperature furnace and heat it to 1500℃ at a heating rate of 5℃ / min. Hold it at that temperature for 5 hours. After calcination, crush the product and collect the powder with a particle size of 0.5μm to obtain magnesium aluminum spinel B3.

[0075] S15. Mix 30g of magnesium peroxide and 60g of magnesium aluminum spinel A, add them to a high-speed mixer, and mix at 800rpm for 30min to obtain magnesium aluminum composite powder A.

[0076] S16. Place 30g of magnesium aluminum spinel B1, 20g of magnesium aluminum spinel B2 and 40g of magnesium aluminum spinel B3 into a mixer and mix for 2 hours to obtain magnesium aluminum spinel B.

[0077] S17. Mix 20g magnesium oxalate, 20g magnesium citrate, 10g magnesium stearate and 50g magnesium aluminum spinel B and put them into a stirred ball mill. Grind at 300 rpm for 3 hours to obtain magnesium aluminum composite powder B.

[0078] S18. After mixing magnesium-aluminum composite powder A, magnesium-aluminum composite powder B and additives, the mixture is transferred into a ball mill jar. Zirconia balls are added as grinding media. The mass ratio of grinding media to powder is 3:1. The additives are titanium dioxide and yttrium oxide mixed in a mass ratio of 2:3.5. The mixture is ground at 300 rpm for 60 hours to obtain magnesium-aluminum spinel protective agent.

[0079] Example 2: A method for preparing a magnesium aluminum spinel protective agent, comprising the following steps:

[0080] S1. Raw material pretreatment: High-purity magnesium peroxide with a purity of ≥98% is pulverized to a particle size of 180-200 mesh to obtain magnesium peroxide powder; α-Al2O3 powder with a particle size of 1-5μm and a purity of ≥99% is cleaned of surface impurities and then soaked in a 5% (w / w) dilute hydrochloric acid solution for 2 hours, rinsed with deionized water until neutral, and then dried in an oven at 120℃ for 5 hours to obtain alumina powder; High-purity aluminum powder with a particle size of 100-200 mesh and a purity of ≥99% is soaked in a 10% (w / w) sodium hydroxide solution for 5 minutes, rinsed with deionized water until neutral, rinsed with anhydrous ethanol, and then dried in a vacuum drying oven at 60℃ for 3 hours to obtain aluminum powder;

[0081] S2. Mix 36g of magnesium peroxide powder, 34g of aluminum oxide powder and 32g of aluminum powder evenly, and then add them to a ball mill. At the same time, add zirconia balls as grinding media. The ball-to-material ratio when using zirconia balls as grinding media is 90:12. Add anhydrous ethanol as grinding aid. The amount of anhydrous ethanol added is 4% of the total mass of the material. Set the ball mill speed to 340 rpm and the mixing time to 4 hours to obtain mixture a.

[0082] S3. Mixture a is uniformly filled into the reaction crucible to a height of 2 / 3 of the crucible height. After filling, it is placed in the combustion synthesis device and sealed. The reaction is initiated by the ignition system with an ignition current of 7A and an ignition time of 5s. The reaction lasts for 7min. After the reaction is completed, it is naturally cooled to room temperature to obtain cooled product a.

[0083] S4. Take out the cooled product a and coarsely crush it to a particle size of 1-2 cm, then finely crush it. Add zirconia balls and anhydrous ethanol. During fine crushing, the ball-to-material ratio of zirconia balls is 10:1.2, and the amount of anhydrous ethanol added is 4% of the total mass of the material. The ball mill speed is 440 rpm and the crushing time is 5 hours, so that the particle size of the product reaches 200-220 mesh, and the crushed material a is obtained.

[0084] S5. Soak the pulverized material a in dilute hydrochloric acid solution for 3 hours, then rinse it repeatedly with deionized water until neutral. Finally, dry the acid-washed product in an oven at 120°C for 7 hours, and then sieve it through a vibrating screen to select powder with a particle size between 100-300 mesh, thus obtaining magnesium aluminum spinel A.

[0085] S6. Mix magnesium oxalate and alumina powder and add them to a ball mill. Add zirconia balls and grind at 400 rpm for 3 hours to obtain mixed powder b. The molar ratio of magnesium oxalate to alumina is 1.1:1.2, and the ball-to-material ratio when zirconia balls are used as grinding media is 90:12.

[0086] S7. Transfer the mixed powder b to a high-temperature furnace and heat it to 840°C at a heating rate of 7°C / min. Hold it at this temperature for 3 hours to obtain the pre-calcined material b.

[0087] S8. Place the pre-burned material b back into the high-temperature furnace and heat it to 1540°C at a biological rate of 7°C / min. Hold it for 5 hours. Take out the sintered product, crush it, and select powder with a particle size between 1-5μm to obtain magnesium aluminum spinel B1.

[0088] S9. Add magnesium stearate and alumina powder to anhydrous ethanol and ultrasonically disperse for 21 min. The molar ratio of magnesium stearate to alumina is 0.98:1.2, and the ratio of anhydrous ethanol to solid material is 90 mL:11 g, to obtain a stable suspension c.

[0089] S10. Transfer the suspension c to an evaporating dish and evaporate the anhydrous ethanol in a water bath at 70°C. Then dry the evaporated material in an oven at 110°C for 3 hours to obtain mixed powder c.

[0090] S11. Place the mixed powder into a high-temperature furnace and heat it to 1440℃ at a heating rate of 7℃ / min. Hold the temperature for 5 hours. After the reaction is complete, cool it to room temperature, pulverize the product, and collect the powder with a particle size between 1-3μm to obtain magnesium aluminum spinel B2.

[0091] S12. Add alumina powder to magnesium citrate solution, the molar ratio of magnesium ions in alumina powder and magnesium citrate solution is 1.0:1.2, add 27% ammonia water dropwise, adjust the pH of the solution to 9-10, stir for 2 hours to obtain mixed solution d;

[0092] S13. Filter the mixture d, collect the precipitate, and wash the precipitate repeatedly with deionized water 5 times to obtain precipitate d.

[0093] S14. Place the precipitate d in an oven and dry it at 130℃ for 4-5-6-4-5-6h. Transfer the dried product to a high-temperature furnace and heat it to 1540℃ at a heating rate of 7℃ / min. Hold it at that temperature for 5-5.5-6-6.5-6-7h. After calcination, crush the product and collect the powder with a particle size between 0.9μm to obtain magnesium aluminum spinel B3.

[0094] S15. Mix 34g of magnesium peroxide and 64g of magnesium aluminum spinel A, add them to a high-speed mixer, and mix at 900rpm for 50min to obtain magnesium aluminum composite powder A.

[0095] S16. Place 34g of magnesium aluminum spinel B1, 22g of magnesium aluminum spinel B2 and 44g of magnesium aluminum spinel B3 into a mixer and mix for 3 hours to obtain magnesium aluminum spinel B.

[0096] S17. Mix 24g magnesium oxalate, 24g magnesium citrate, 12g magnesium stearate and 54g magnesium aluminum spinel B and put them into a stirred ball mill. Grind at 400 rpm for 4 hours to obtain magnesium aluminum composite powder B.

[0097] S18. Magnesium-aluminum composite powder A, magnesium-aluminum composite powder B and additives are mixed and transferred into a ball mill jar. Zirconia balls are added as grinding media. The mass ratio of grinding media to powder is 7:1.2. The additives are titanium dioxide and yttrium oxide mixed in a mass ratio of 2.4:3.7. The mixture is ground at 400 rpm for 64 hours to obtain magnesium-aluminum spinel protective agent.

[0098] Example 3: A method for preparing a magnesium aluminum spinel protective agent, comprising the following steps:

[0099] S1. Raw material pretreatment: High-purity magnesium peroxide with a purity of ≥98% is pulverized to a particle size of 180-200 mesh to obtain magnesium peroxide powder; α-Al2O3 powder with a particle size of 1-5μm and a purity of ≥99% is cleaned of surface impurities and then soaked in a 5% (w / w) dilute hydrochloric acid solution for 2 hours, rinsed with deionized water until neutral, and then dried in an oven at 120℃ for 6 hours to obtain alumina powder; High-purity aluminum powder with a particle size of 100-200 mesh and a purity of ≥99% is soaked in a 10% (w / w) sodium hydroxide solution for 5 minutes, rinsed with deionized water until neutral, rinsed with anhydrous ethanol, and then dried in a vacuum drying oven at 60℃ for 3 hours to obtain aluminum powder;

[0100] S2. Mix 40g of magnesium peroxide powder, 40g of aluminum oxide powder and 35g of aluminum powder evenly, and then add them to a ball mill. At the same time, add zirconia balls as grinding media. The ball-to-material ratio when using zirconia balls as grinding media is 100:15. Add anhydrous ethanol as grinding aid. The amount of anhydrous ethanol added is 5% of the total mass of the material. Set the ball mill speed to 400 rpm and the mixing time to 5 hours to obtain mixture a.

[0101] S3. Mixture a is uniformly filled into the reaction crucible to a height of 2 / 3 of the crucible height. After filling, it is placed in the combustion synthesis device and sealed. The reaction is initiated by the ignition system with an ignition current of 10A and an ignition time of 5s. The reaction lasts for 10min. After the reaction is completed, it is naturally cooled to room temperature to obtain cooled product a.

[0102] S4. Take out the cooled product a and coarsely crush it to a particle size of 1-2 cm, then finely crush it. Add zirconia balls and anhydrous ethanol. During fine crushing, the ball-to-material ratio of zirconia balls is 12:1.5, and the amount of anhydrous ethanol added is 5% of the total mass of the material. The ball mill speed is 500 rpm and the crushing time is 6 hours, so that the particle size of the product reaches 200-220 mesh, and the crushed material a is obtained.

[0103] S5. Soak the pulverized material a in dilute hydrochloric acid solution for 3 hours, then rinse it repeatedly with deionized water until neutral. Finally, dry the acid-washed product in an oven at 120°C for 8 hours, and then sieve it through a vibrating screen to select powder with a particle size between 100-300 mesh, thus obtaining magnesium aluminum spinel A.

[0104] S6. Mix magnesium oxalate and alumina powders and add them to a ball mill. Add zirconia balls and grind at 500 rpm for 4 hours to obtain mixed powder b. The molar ratio of magnesium oxalate to alumina is 1.1:1.2, and the ball-to-material ratio when using zirconia balls as grinding media is 100:15.

[0105] S7. Transfer the mixed powder b to a high-temperature furnace and heat it to 900°C at a heating rate of 10°C / min. Hold it at this temperature for 3 hours to obtain the pre-calcined material b.

[0106] S8. Place the pre-burned material b back into the high-temperature furnace and heat it to 1600℃ at a biological rate of 10℃ / min. Hold it for 6 hours. Take out the sintered product, crush it, and select powder with a particle size between 1-5μm to obtain magnesium aluminum spinel B1.

[0107] S9. Add magnesium stearate and alumina powder to anhydrous ethanol and ultrasonically disperse for 30 min. The molar ratio of magnesium stearate to alumina is 1.05:1.2, and the ratio of anhydrous ethanol to solid material is 100 mL:12 g, to obtain a stable suspension c.

[0108] S10. Transfer the suspension c to an evaporating dish and evaporate the anhydrous ethanol in a water bath at 80°C. Then dry the evaporated material in an oven at 120°C for 3 hours to obtain mixed powder c.

[0109] S11. Place the mixed powder into a high-temperature furnace and heat it to 1500℃ at a heating rate of 10℃ / min. Hold the temperature for 5 hours. After the reaction is complete, cool it to room temperature, pulverize the product, and collect the powder with a particle size between 1-3μm to obtain magnesium aluminum spinel B2.

[0110] S12. Add alumina powder to magnesium citrate solution, the molar ratio of magnesium ions in alumina powder and magnesium citrate solution is 1.02:1.3, add 28% ammonia water dropwise, adjust the pH of the solution to 9-10, stir for 2 hours to obtain mixed solution d;

[0111] S13. Filter the mixture d, collect the precipitate, and wash the precipitate repeatedly with deionized water 5 times to obtain precipitate d.

[0112] S14. Place the precipitate d in an oven and dry it at 150℃ for 6 hours. Transfer the dried product to a high-temperature furnace and heat it to 1600℃ at a heating rate of 10℃ / min. Hold it at that temperature for 7 hours. After calcination, crush the product and collect the powder with a particle size between 1.2μm to obtain magnesium aluminum spinel B3.

[0113] S15. Mix 40g of magnesium peroxide and 70g of magnesium aluminum spinel A, add them to a high-speed mixer, and mix at 1200rpm for 60min to obtain magnesium aluminum composite powder A.

[0114] S16. Place 40g of magnesium aluminum spinel B1, 25g of magnesium aluminum spinel B2 and 50g of magnesium aluminum spinel B3 into a mixer and mix for 3 hours to obtain magnesium aluminum spinel B.

[0115] S17. Mix 30g magnesium oxalate, 30g magnesium citrate, 15g magnesium stearate and 60g magnesium aluminum spinel B and put them into a stirred ball mill. Grind at 500 rpm for 5 hours to obtain magnesium aluminum composite powder B.

[0116] S18. After mixing magnesium-aluminum composite powder A, magnesium-aluminum composite powder B and additives, the mixture is transferred into a ball mill jar. Zirconia balls are added as grinding media. The mass ratio of grinding media to powder is 10:1.3. The additives are titanium dioxide and yttrium oxide mixed in a mass ratio of 3:4.2. The mixture is ground at 500 rpm for 70 hours to obtain magnesium-aluminum spinel protective agent.

[0117] Comparative Example 1:

[0118] Compared with Example 1, this comparative example only replaces "magnesium-aluminum composite powder A" with "magnesium-aluminum composite powder B". All other steps and parameters are the same, and will not be repeated in this comparative example. The final result is a magnesium-aluminum spinel protective agent.

[0119] Comparative Example 2:

[0120] Compared with Example 1, this comparative example only replaces "magnesium-aluminum composite powder B" with "magnesium-aluminum composite powder A". All other steps and parameters are the same, and will not be repeated in this comparative example. The final result is a magnesium-aluminum spinel protective agent.

[0121] Comparative Example 3:

[0122] This comparative example differs from Example 1 only in that “magnesium aluminum spinel B2” is replaced with “magnesium aluminum spinel B1”. All other steps and parameters are the same, and will not be repeated here. The final result is a magnesium aluminum spinel protective agent.

[0123] Comparative Example 4:

[0124] This comparative example differs from Example 1 only in that “magnesium aluminum spinel B3” is replaced with “magnesium aluminum spinel B1”. All other steps and parameters are the same, and will not be repeated here. The final result is a magnesium aluminum spinel protective agent.

[0125] Comparative Example 5:

[0126] Compared with Example 1, this comparative example only replaces "magnesium aluminum composite powder A" with "magnesium aluminum spinel A". All other steps and parameters are the same, and will not be repeated in this comparative example. The final result is a magnesium aluminum spinel protective agent.

[0127] Comparative Example 6:

[0128] Compared with Example 1, this comparative example only replaces "magnesium-aluminum composite powder B" with "magnesium-aluminum spinel B1, magnesium-aluminum spinel B2 and magnesium-aluminum spinel B3" in equal amounts. All other steps and parameters are the same, and will not be repeated in this comparative example. The final result is a magnesium-aluminum spinel protective agent.

[0129] Performance testing: The magnesium aluminum spinel protective agents prepared in Examples 1-6 and Comparative Examples 1-6 were subjected to the following performance tests:

[0130] Specific surface area: Based on the BET (Brunauer-Emmett-Teller) theory, the nitrogen adsorption method was used for determination, with the standard being ASTM D4567-12. A larger specific surface area means more active sites that the protective agent can provide, which is beneficial for adsorbing impurities and poisons. The protective agent sample was degassed at 200℃ for 4 hours under vacuum to remove surface-adsorbed impurities and moisture. Using a specific surface area analyzer, nitrogen gas was introduced into the sample tube at liquid nitrogen temperature (77K), and the amount of nitrogen adsorbed on the sample surface under different relative pressures was measured. The specific surface area of ​​the sample was calculated according to the BET equation.

[0131] Porosity: Determined by mercury porosimetry, standard reference ASTM D4284-19. Higher porosity allows for the containment of more impurities, increasing the adsorption capacity of the protective agent. The protective agent sample is prepared into particles with a diameter of approximately 2-3 mm. Mercury is injected into the pores of the sample using a mercury porosimetry instrument. The porosity of the sample is calculated based on the amount of mercury injected and the pressure changes. The test pressure range is from 0.005 MPa to 400 MPa.

[0132] Mechanical strength: A compressive strength test was conducted. The protective agent was formed into a cylinder of a certain size, and pressure was applied to the sample on a material testing machine until the sample broke. The pressure value at the time of breakage was recorded, and the unit was MPa. The higher the mechanical strength, the better the protective agent can resist pressure fluctuations and material erosion in industrial reactions. The protective agent powder was pressed into a cylinder with a diameter of 5 mm and a height of 10 mm. The prepared sample was placed on the indenter of the material testing machine, and pressure was applied at a loading rate of 0.5 mm / min until the sample broke. The pressure value at this time was recorded. The test was repeated 5 times, and the average value was taken as the compressive strength of the sample.

[0133] Adsorption performance: Using a simulated feed gas containing carbon black, tar, dust, and impurities and toxins such as As2O3 and P2O5, the adsorption capacity of the protective agent for various impurities was determined through dynamic adsorption experiments. Higher adsorption capacity indicates a stronger purification capacity of the protective agent for the feed gas. A simulated feed gas was prepared by mixing carbon black, tar, dust, and impurities and toxins such as As2O3 and P2O5 in a certain proportion, using nitrogen as the carrier gas. The protective agent sample was packed into an adsorption column, and the simulated feed gas was passed through the adsorption column at a certain flow rate. The outlet gas was collected periodically, and the concentrations of impurities and toxins in the outlet gas were determined using analytical instruments such as gas chromatography and atomic absorption spectrometry. The adsorption capacity of the protective agent for various impurities was calculated based on the inlet and outlet concentration difference and the gas flow rate.

[0134] Catalyst protection effect: The protective agent and the carbon monoxide sulfur-resistant shift catalyst were loaded into a fixed-bed reactor in a certain proportion, and a simulated feed gas was introduced for reaction. The change in catalyst activity before and after the reaction was measured. The protective effect of the protective agent on the catalyst is expressed as the catalyst activity retention rate; the higher the catalyst activity retention rate, the better the protection effect. Catalyst activity is measured by the carbon monoxide conversion rate, and the calculation formula is:

[0135]

[0136] In a fixed-bed reactor, a certain amount of protective agent was first loaded, followed by a carbon monoxide-resistant shift catalyst. The mass ratio of protective agent to catalyst was 1:5. The reaction temperature was 350℃, the pressure was 3MPa, and the simulated feed gas space velocity was 1000h⁻¹. Before the reaction, the initial carbon monoxide conversion rate of the catalyst was measured. After 100 hours of reaction, the carbon monoxide conversion rate of the catalyst was measured again, and the catalyst activity retention rate was calculated. The results are shown in Tables 1 and 2 below.

[0137] Table 1

[0138]

[0139]

[0140] Table 2

[0141]

[0142] As shown in Table 1, the magnesium-aluminum spinel protective agents prepared in Examples 1-6 are superior to those in Comparative Examples 1-6 in all performance indicators. The protective agents in these examples have higher specific surface area, porosity, and mechanical strength, resulting in greater adsorption capacity for various impurities and poisons, and better protection of the catalyst. This indicates that the method of the present invention can effectively improve the performance of the magnesium-aluminum spinel protective agent. The higher specific surface area of ​​Examples 1-6 means more active sites. A large specific surface area provides a wider space for the adsorption of impurities and poisons. A larger specific surface area increases the number of atoms or molecules that can contact the protective agent surface, increasing the probability of collision and adsorption with As2O3 molecules, thereby helping to increase the adsorption capacity of As2O3. In contrast, the smaller specific surface area of ​​Comparative Examples 1-6 results in insufficient surface active sites, limiting their adsorption capacity for various impurities. Taking carbon black adsorption as an example, due to the fewer active sites, the number of sites where carbon black molecules can attach is limited, resulting in a much lower carbon black adsorption capacity than in Example 6. The high porosity of the examples provides more storage space for impurities. In treating tar, Example 5 exhibits a porosity of 49%, allowing tar molecules to diffuse more easily into the pores and be adsorbed. The good connectivity between pores also facilitates gas transport within the protective agent, resulting in a tar adsorption capacity of 9.2 mg / g. In contrast, the relatively lower porosity of the comparative example reduces the space for impurities, potentially hindering tar molecule diffusion and leading to a significantly lower tar adsorption capacity compared to the examples. The high mechanical strength of the examples enables the protective agent to maintain structural integrity under pressure fluctuations and material erosion. When the reaction system pressure changes suddenly, the protective agent particles are less prone to breakage, maintaining the stability of the catalyst bed, ensuring uniform gas flow, and contributing to improved catalyst activity retention. The comparative example may break due to its inability to withstand pressure. The broken protective agent particles will increase bed resistance, affect gas flow, and result in a catalyst activity retention rate far lower than the average level of the examples. The examples have a higher carbon black adsorption capacity, where the synergistic effect of specific surface area and porosity makes it easier for carbon black molecules to be captured and attached to the surface and pores of the protective agent. In contrast, Comparative Example 1 has a lower specific surface area and porosity, resulting in lower tar adsorption. The examples have a higher tar adsorption capacity, which is due to the combined effect of high specific surface area, suitable porosity, and chemically active sites. The appropriate pore size distribution and surface properties in the examples are conducive to the interception and adsorption of dust particles. Comparative Example 4 has a lower dust adsorption capacity due to structural defects. The examples have a higher As2O3 adsorption capacity, as the specific preparation process generates more active sites with affinity for As2O3 on the surface of the protective agent, resulting in a high adsorption capacity. Comparative Example 5 had fewer active sites and lower As2O3 adsorption due to different preparation processes; the example had higher P2O5 adsorption, and the optimized preparation method enabled the protective agent to have a more efficient ability to adsorb P2O5. In contrast, Comparative Example 6 had lower P2O5 adsorption due to differences in raw materials and processes; the example had a higher catalyst activity retention rate.This is attributed to the excellent performance of the protective agent in terms of specific surface area, porosity, mechanical strength, and adsorption properties. The high specific surface area and porosity enable it to effectively adsorb impurities and poisons, while the high mechanical strength ensures stability during the reaction process, resulting in a relatively high catalyst activity retention rate. In contrast, Comparative Example 1, due to its relatively poor performance in various aspects, failed to adequately protect the catalyst, leading to a low activity retention rate. While Comparative Example 6 exhibited some adsorption properties, its shortcomings in mechanical strength and other aspects resulted in a catalyst activity retention rate lower than the optimal performance of the examples.

[0143] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

[0144] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A magnesium aluminate spinel protectant characterized by, Prepared from the following quality parts of raw materials: magnesium aluminum composite powder A 45-65 parts, magnesium aluminum composite powder B 15-25 parts, additives 5-10 parts; The magnesium aluminum composite powder A is prepared from magnesium peroxide and magnesium aluminum spinel A; The magnesium aluminum spinel A is prepared from magnesium peroxide, aluminum oxide and aluminum powder by combustion synthesis; The magnesium aluminum composite powder B is prepared from magnesium oxalate, magnesium citrate, magnesium stearate and magnesium aluminum spinel B; The magnesium aluminum spinel B is obtained by mixing magnesium aluminum spinel B1, magnesium aluminum spinel B2 and magnesium aluminum spinel B3; The magnesium aluminum spinel B1 is prepared from magnesium oxalate and aluminum oxide; The magnesium aluminum spinel B2 is prepared from magnesium stearate and aluminum oxide; The magnesium aluminum spinel B3 is prepared from magnesium citrate and aluminum oxide; The preparation process of the magnesium aluminum spinel protective agent includes the following steps: Step S1, mix the magnesium peroxide and the magnesium aluminum spinel A, add it into a high-speed mixer, mix at a speed of 800-1200 rpm for 30-60 min, to obtain the magnesium aluminum composite powder A; Step S2, put the magnesium aluminum spinel B1, the magnesium aluminum spinel B2 and the magnesium aluminum spinel B3 into a mixer, mix for 2-3 h, to obtain the magnesium aluminum spinel B; Step S3, mix the magnesium oxalate, the magnesium citrate, the magnesium stearate and the magnesium aluminum spinel B, and put them into a stirred ball mill, grind at a speed of 300-500 rpm for 3-5 h, to obtain the magnesium aluminum composite powder B; Step S4, mix the magnesium aluminum composite powder A, the magnesium aluminum composite powder B and the additives, then transfer them into a ball mill tank, add zirconia balls as grinding medium, grind at a speed of 300-500 rpm for 60-70 h, to obtain the magnesium aluminum spinel protective agent.

2. The magnesia-alumina spinel protectant of claim 1, wherein, The preparation process of the magnesium aluminum spinel A is as follows: Step A1, raw material pretreatment: crush the high-purity magnesium peroxide to a particle size of 180-200 mesh to obtain magnesium peroxide powder; after removing the impurities on the surface of the α-Al2O3 powder, immerse it in a dilute hydrochloric acid solution for 1-2 h, then rinse it with deionized water until it is neutral, and then dry it in an oven at 120℃ for 4-6 h to obtain aluminum oxide powder; immerse the high-purity aluminum powder in a 10% sodium hydroxide solution for 3-5 min, then rinse it with deionized water until it is neutral, rinse it with anhydrous ethanol, and then dry it in a vacuum drying oven at 60℃ for 2-3 h to obtain aluminum powder; Step A2, mix the magnesium peroxide powder, the aluminum oxide powder and the aluminum powder uniformly, then add them into a ball mill, add zirconia balls as grinding medium, and add anhydrous ethanol as grinding aid, set the ball mill speed to 300-400 rpm, and mix and grind for 3-5 h to obtain a mixture a; Step A3, uniformly pack the mixture a into a reaction crucible, the packing height is 2 / 3 of the height of the crucible, after packing, seal the device in a combustion synthesis device, initiate the reaction through an ignition system, the reaction duration is 5-10 min, after the reaction is completed, naturally cool to room temperature to obtain a cooled product a; Step A4, the cooled product a is taken out for coarse crushing to a particle size of 1-2 cm, and then fine crushing is performed, zirconia balls and anhydrous ethanol are added, the ball mill speed is 400-500 rpm, the crushing time is 4-6 h, the particle size of the product is made to reach 200-220 meshes, and crushed material a is obtained; Step A5, the crushed material a is soaked in a dilute hydrochloric acid solution for 2-3 h, then repeatedly washed with deionized water until neutral, and finally the acid-washed product is dried in an oven at 120°C for 6-8 h, and then screened through a vibrating screen, and the powder with a particle size of 100-300 meshes is selected, i.e. magnesium-aluminum spinel A is obtained.

3. The magnesia-alumina spinel protectant of claim 2, wherein, The high-purity magnesium peroxide in step A1 has a purity of ≥98%, the α-Al2O3 powder has a purity of ≥99%, the particle size of the α-Al2O3 powder is 1-5 μm, the mass fraction of the dilute hydrochloric acid solution is 5%, the high-purity aluminum powder has a purity of ≥99%, and the particle size of the high-purity aluminum powder is 100-200 meshes.

4. The magnesia-alumina spinel protectant of claim 2, wherein, In step A2, the mass ratio of the magnesium peroxide powder, the aluminum oxide powder and the aluminum powder is 30-40:30-40:30-35, the ball-to-material ratio of the zirconia balls as the grinding medium in step A2 is 80-100:10-15, and the addition amount of the anhydrous ethanol in step A2 is 3%-5% of the total mass of the material.

5. The magnesia-alumina spinel protectant of claim 2, wherein, In step A3, the ignition current of the ignition system is 5-10 A, and the ignition time lasts for 3-5 s.

6. The magnesia-alumina spinel protectant of claim 2, wherein, In step A4, the ball-to-material ratio of the zirconia balls during fine crushing is 8-12:1-1.5, and the addition amount of the anhydrous ethanol in step A4 is 3%-5% of the total mass of the material.

7. The magnesia-alumina spinel protectant of claim 1, wherein, The preparation process of the magnesium-aluminum spinel B1 is as follows: Step B1, magnesium oxalate and aluminum oxide powder are mixed and added to a ball mill, zirconia balls are added, and grinding is performed at a speed of 300-500 rpm for 2-4 h to obtain mixed powder b; Step B2, the mixed powder b is transferred to a high-temperature furnace, heated to 800-900°C at a heating rate of 5-10°C / min, and kept at this temperature for 2-3 h to obtain pre-sintered product b; Step B3, the pre-sintered product b is again placed in a high-temperature furnace, heated to 1500-1600°C at a heating rate of 5-10°C / min, and kept for 4-6 h, and the sintered product is taken out, crushed, and the powder with a particle size of 1-5 μm is selected, i.e. magnesium-aluminum spinel B1 is obtained; In step B1, the molar ratio of the magnesium oxalate and the aluminum oxide is 0.9-1.1:1-1.2, and the ball-to-material ratio of the zirconia balls as the grinding medium in step B1 is 80-100:10-15.

8. The magnesia-alumina spinel protectant of claim 1, wherein, The preparation process of the magnesium-aluminum spinel B2 is as follows: Step C1, magnesium stearate and aluminum oxide powder are added to anhydrous ethanol, and ultrasonic dispersion is performed for 15-30 min to obtain stable suspension c; Step C2, the suspension c is transferred to an evaporation dish, anhydrous ethanol is evaporated under heating in a water bath at 60-80°C, and then the evaporated material is dried in an oven at 100-120°C for 2-3 h to obtain mixed powder c; Step C3, put the mixed powder into a high temperature furnace, heat to 1400-1500℃ at a heating rate of 5-10℃ / min, keep for 4-5h, after the reaction is completed, cool to room temperature, crush the product, collect the powder with a particle size of 1-3μm, magnesium aluminate spinel B2 is obtained; The molar ratio of magnesium stearate to alumina in step C1 is 0.95-1.05:1-1.2, and the ratio of the amount of anhydrous ethanol to solid material added in step C1 is 80-100mL:10-12g.

9. The magnesia-alumina spinel protectant of claim 1, wherein, The preparation process of the magnesium aluminate spinel B3 is as follows: Step D1, add alumina powder to the magnesium citrate solution, add ammonia water dropwise, adjust the pH of the solution to 9-10, stir for 1-2h, and obtain a mixed solution d; Step D2, filter the mixed solution d, collect the precipitate, wash the precipitate with deionized water for 3-5 times, and obtain a precipitate d; Step D3, put the precipitate d into an oven and dry at 120-150℃ for 4-6h, transfer the dried product to a high temperature furnace, heat to 1500-1600℃ at a heating rate of 5-10℃ / min, keep for 5-7h, crush the calcined product, and collect the powder with a particle size of 0.5-1.2μm, magnesium aluminate spinel B3 is obtained; The molar ratio of alumina powder to magnesium ions in the magnesium citrate solution in step D1 is 0.98-1.02:1-1.3; The concentration of ammonia water in step D1 is 25%-28%.

10. Process for the production of a magnesia-alumina spinel protectant according to any one of claims 1 to 9, characterized in that The following steps are included: Step S1, mix the magnesium peroxide and magnesium aluminate spinel A, add into a high-speed mixer, mix at a speed of 800-1200rpm for 30-60min, and obtain a magnesium-aluminum composite powder A; Step S2, put the magnesium aluminate spinel B1, magnesium aluminate spinel B2 and magnesium aluminate spinel B3 into a mixer, mix for 2-3h, and obtain a magnesium aluminate spinel B; Step S3, mix the magnesium oxalate, magnesium citrate, magnesium stearate and magnesium aluminate spinel B and put into a stirring ball mill, grind at a speed of 300-500rpm for 3-5h, and obtain a magnesium-aluminum composite powder B; Step S4, mix the magnesium-aluminum composite powder A, magnesium-aluminum composite powder B and additives, then transfer into a ball mill tank, add zirconia balls as grinding medium, grind at a speed of 300-500rpm for 60-70h, and obtain a magnesium aluminate spinel protective agent; The mass ratio of magnesium peroxide to magnesium aluminate spinel A in step S1 is 3-4:6-7; The mass ratio of magnesium aluminate spinel B1, magnesium aluminate spinel B2 and magnesium aluminate spinel B3 in step S2 is 3-4:2-2.5:4-5; The mass ratio of magnesium oxalate, magnesium citrate, magnesium stearate, magnesium aluminate spinel B in step S3 is 2-3:2-3:1-1.5:5-6; The mass ratio of grinding medium to powder in step S4 is 3-10:1-1.3; The additive in step S4 is titanium dioxide and yttrium oxide mixed in a mass ratio of 2-3:3.5-4.2.

Images