Alpha-alumina support, process for its preparation and silver catalyst and its use in the preparation of ethylene oxide by ethylene epoxidation

Abstract

The application belongs to the field of silver catalysts, and relates to an alpha-alumina carrier, a preparation method thereof, and a silver catalyst and application thereof in the preparation of ethylene oxide by ethylene epoxidation. The alpha-alumina carrier comprises single-crystal flaky alumina, and the content of the single-crystal flaky alumina is 0.1-50 wt% based on the total weight of the alpha-alumina carrier. The preparation method comprises the following steps: preparing a mixture comprising micron-sized alumina, pseudo-monohydrate alumina, a mineralizer, and single-crystal flaky alumina, and mixing the mixture with an acid solution; kneading and extruding the obtained material, and then drying and calcining the material to obtain the alpha-alumina carrier. The silver catalyst prepared from the alpha-alumina carrier can significantly improve the selectivity and stability of the reaction, can obviously reduce the emission of carbon dioxide byproducts, can improve the utilization rate of ethylene raw materials, and has a wide industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of silver catalysts, specifically relating to an α-alumina support, a method for preparing the α-alumina support, the α-alumina support obtained by the method, a silver catalyst prepared from the α-alumina support, and the application of the silver catalyst in the epoxidation of ethylene to prepare ethylene oxide. Background Technology

[0002] In the oxidation of ethylene to ethylene oxide under the action of a silver catalyst, side reactions occur to produce carbon dioxide and water. Activity, selectivity, and stability are the main performance indicators of silver catalysts. Activity refers to the reaction temperature required to reach a certain reaction load in the ethylene oxide production process; the lower the reaction temperature, the higher the catalyst activity. Selectivity is the ratio of the number of moles of ethylene converted to ethylene oxide to the total number of moles of ethylene reacted. Stability is represented by the rate of decrease in activity and selectivity; the smaller the rate of decrease, the better the catalyst stability. Using highly active, highly selective, and stable silver catalysts in the ethylene oxidation process to produce ethylene oxide can significantly improve economic efficiency. Therefore, the manufacture of highly active, highly selective, and stable silver catalysts is a major research direction for silver catalysts. The performance of silver catalysts is not only significantly related to the composition and preparation method of the catalyst, but also to the performance and preparation of the support used for the catalyst.

[0003] The existing methods for preparing silver catalysts include two processes: preparing a porous support (such as alumina) and loading the active component and additives onto the support.

[0004] Improving the performance of silver catalysts by adding other components to alumina supports is an important research direction, including the addition of alkaline earth metal oxides or other salt compounds. EP0150238 (US4428863) uses a small amount of barium aluminate or barium silicate binder in the manufacture of high-purity, low-surface-area alumina supports, claiming to improve the support's crush resistance and wear resistance, with a specific surface area of ​​less than 0.3 μm. 2 The catalyst prepared with a concentration of / g exhibits relatively low activity and selectivity. US5384302 claims that pretreating α-Al₂O₃ to reduce the content of Na, K, Ca, and Al ions in the support can improve the support's crush resistance and wear resistance. US5739075 describes a silver catalyst prepared by pre-depositing a rare earth metal and another metal salt (alkaline earth metal or group VIII transition metal) onto the surface of an alumina support, followed by calcination. Evaluation results show that the selectivity of this catalyst decreases at a lower rate than that of the untreated catalyst sample.

[0005] Fluorides, as mineralizing agents, have wide applications in the preparation of alumina supports. CN1034678A describes the preparation of an alumina support by mixing trihydrate and pseudo-monohydrate alumina with appropriate particle size and proportions, along with carbon-containing materials, flux, fluorides, binders, and water, kneading the mixture, and then drying and calcining it. The specific surface area of ​​this support is 0.2–2 μm. 2 / g, with pores having a radius greater than 30μm accounting for less than 25% of the total pore volume; this support, after being impregnated with silver compounds and a co-catalyst and then dried and activated, is used for the oxidation of ethylene to ethylene oxide, with a selectivity as high as 83-84%. CN101007287A mixes trihydrate α-alumina, pseudo-monohydrate α-alumina, a certain amount of combustible carbonaceous material, flux, fluoride, and optionally a heavy alkaline earth metal compound of a certain particle size, adds a binder and water after uniform mixing, kneads evenly, extrudes and molds, and then calcines to produce an α-alumina support; the specific surface area of ​​the support is 0.2-2.0 μm. 2 The carrier has a pore volume of 0.35–0.85 ml / g, a water absorption rate ≥30%, and a crushing strength of 30–120 N / particle. This carrier is impregnated with solutions of silver amine complexes, alkali metal compounds, and alkaline earth metal compounds, and after drying and activation, a silver catalyst is prepared for the epoxidation of ethylene to produce ethylene oxide. CN1634652A, in the carrier preparation process, does not use a pore-forming agent, but directly mixes trihydrate α-alumina with pseudo-monohydrate alumina, flux, and fluoride in a certain proportion. After uniform mixing, a binder and water are added, kneaded evenly, extruded, and then dried and calcined to produce an α-alumina carrier. The carrier produced by this invention has a specific surface area of ​​0.2–2.0 μm. 2 The silver catalyst, with a pore volume of 0.35–0.85 ml / g, a water absorption rate ≥30%, and a crushing strength of 20–90 N / particle, is prepared by impregnating this carrier with solutions of silver amine complexes, alkali metal compounds, and alkaline earth metal compounds, followed by drying and activation. This catalyst is then used for the epoxidation of ethylene to produce ethylene oxide.

[0006] Although the aforementioned patent documents employ methods such as adding alkaline earth metal compounds to alumina raw materials or pre-depositing auxiliary rare earth metals on the surface of alumina supports to improve the alumina support, resulting in varying degrees of improvement in the activity or selectivity of the catalyst, the requirements for the performance of alumina supports in this field are constantly increasing with the large-scale industrial application of medium- and high-selectivity silver catalysts. Summary of the Invention

[0007] In view of the above-mentioned state of the prior art, the inventors of the present invention have conducted in-depth experimental research in the field of silver catalysts and their alumina supports. The results show that by adding an appropriate amount of monocrystalline alumina to the support raw material to prepare the alumina support, the selectivity and stability of the silver catalyst prepared using the support are significantly improved.

[0008] To achieve the objectives of the present invention, a first aspect of the present invention provides an α-alumina carrier comprising monocrystalline alumina, wherein the content of monocrystalline alumina is 0.1 to 50 wt%, preferably 1 to 40 wt%, and more preferably 5 to 35 wt%, based on the total weight of the α-alumina carrier.

[0009] A second aspect of the present invention provides a method for preparing an α-alumina support, comprising the following steps:

[0010] (1) Prepare a mixture comprising micron-sized alumina, pseudo-monohydrate alumina, a mineralizer and monocrystalline alumina, and mix the mixture with an acid solution; based on the total weight of the mixture, the content of micron-sized alumina is 4.5-90 wt%, the content of pseudo-monohydrate alumina is 5-95 wt%, the content of mineralizer is 0.01-3 wt%, and the content of monocrystalline alumina is 0.1-50 wt%.

[0011] (2) After kneading and extruding the material obtained in step (1), the α-alumina carrier is obtained by drying and calcining.

[0012] A third aspect of the present invention provides an α-alumina support prepared by the method described above.

[0013] A fourth aspect of the present invention provides a silver catalyst for the oxidation of ethylene to produce ethylene oxide, said silver catalyst being prepared by impregnating the α-alumina support in a solution containing a silver compound.

[0014] A fifth aspect of the present invention provides the application of the silver catalyst described herein in the epoxidation of ethylene to prepare ethylene oxide.

[0015] The silver catalyst prepared on an α-alumina support provided by this invention can be used for the epoxidation of ethylene to prepare ethylene oxide. It can significantly improve the selectivity and stability of the reaction, significantly reduce the emission of carbon dioxide byproducts, and improve the utilization rate of ethylene feedstock, and has broad prospects for industrial application.

[0016] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0017] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0018] To achieve the objectives of the present invention, a first aspect of the present invention provides an α-alumina carrier comprising monocrystalline alumina, wherein the content of monocrystalline alumina is 0.1 to 50 wt%, preferably 1 to 40 wt%, and more preferably 5 to 35 wt%, based on the total weight of the α-alumina carrier.

[0019] According to the present invention, preferably, the α-alumina support has the following characteristics: a specific surface area of ​​0.3 to 3.0 m². 2 / g, water absorption rate not less than 25%, mechanical strength not less than 30N.

[0020] In this invention, the specific surface area of ​​the carrier is determined by the BET method, the water absorption rate is determined by the boiling method, and the mechanical strength is determined by the radial crushing method.

[0021] A second aspect of the present invention provides a method for preparing an α-alumina support, comprising the following steps:

[0022] (1) Prepare a mixture comprising micron-sized alumina, pseudo-monohydrate alumina, a mineralizer and monocrystalline alumina, and mix the mixture with an acid solution; based on the total weight of the mixture, the content of micron-sized alumina is 4.5-90 wt%, the content of pseudo-monohydrate alumina is 5-95 wt%, the content of mineralizer is 0.01-3 wt%, and the content of monocrystalline alumina is 0.1-50 wt%.

[0023] (2) After kneading and extruding the material obtained in step (1), the α-alumina carrier is obtained by drying and calcining.

[0024] In this invention, the addition of the minerals can accelerate the crystal transformation of alumina.

[0025] According to the present invention, preferably, in step (1), the particle size of the micron-sized alumina is 1 to 500 μm.

[0026] According to the present invention, preferably, in step (1), based on the total weight of the mixture, the amount of micron-sized alumina added is 23-80 wt%, the amount of pseudo-monohydrate alumina added is 18-75 wt%, the amount of mineralizer added is 0.1-2.5 wt%, and the amount of monocrystalline alumina added is 1-40 wt%, preferably 5-35 wt%.

[0027] According to the present invention, preferably, in step (1), the acid solution is an aqueous solution of nitric acid, wherein the volume ratio of nitric acid to water in the aqueous solution of nitric acid is 1:1.25 to 10, preferably 1:2 to 8; and the amount of acid solution added is 5 to 50 wt% based on the total weight of the mixture.

[0028] According to the present invention, preferably, all or part of the pseudo-monohydrate alumina and acid solution are replaced by aluminum sol.

[0029] In this invention, the acid solution can react with pseudo-monohydrate alumina to form an aluminum sol, which can then be used as a binder. In a specific embodiment of this invention, when the pseudo-monohydrate alumina and the acid solution can be completely replaced by aluminum sol, the aluminum sol content in the mixture comprising micron-sized alumina, aluminum sol, mineralizing agent, and single-crystal alumina is 18–75 wt%.

[0030] According to the present invention, preferably, the micron-sized alumina is selected from at least one of trihydrate α-alumina, trihydrate β-alumina and γ-alumina; the mineralizing agent is selected from at least one of boric acid, boron oxide, hydrogen fluoride, aluminum fluoride, ammonium fluoride, calcium fluoride, magnesium fluoride and cryolite.

[0031] According to the present invention, preferably, in step (2), the roasting temperature is 800-1800℃, more preferably 1100-1500℃.

[0032] In this invention, the alumina is almost entirely converted into α-Al2O3 by calcination, for example, more than 90% is converted into α-Al2O3, to obtain the α-Al2O3 support.

[0033] A third aspect of the present invention provides an α-alumina support prepared by the method described above.

[0034] A fourth aspect of the present invention provides a silver catalyst for the oxidation of ethylene to produce ethylene oxide, said silver catalyst being prepared by impregnating the α-alumina support in a solution containing a silver compound.

[0035] In this invention, the solution containing the silver compound may also contain other additives, such as alkali metal additives or rhenium additives. The silver catalyst can be prepared using conventional methods.

[0036] A fifth aspect of the present invention provides the application of the silver catalyst described herein in the epoxidation of ethylene to prepare ethylene oxide.

[0037] The present invention will be further described below with reference to the embodiments, but the scope of the present invention is not limited to these embodiments.

[0038] Determination of catalyst performance:

[0039] The activity and selectivity of various silver catalysts of the present invention were tested using a laboratory microreactor evaluation apparatus. The reactor used in the microreactor evaluation apparatus was a stainless steel reaction tube with an inner diameter of 4 mm, placed within a heating mantle. The catalyst loading volume was 1 ml, with inert packing material at the bottom, ensuring the catalyst bed was located in the isothermal zone of the heating mantle.

[0040] The selective measurement conditions used in this invention are shown in Table 1:

[0041] Table 1. Reaction conditions for catalysts

[0042]

[0043] Once the reactor has stabilized and met the above reaction conditions, the composition of the gas at the reactor inlet and outlet is continuously measured. After volume shrinkage correction, the selectivity is calculated using the following formula:

[0044]

[0045] Where ΔEO is the difference in ethylene oxide concentration between the reactor outlet gas and the inlet gas, and ΔCO2 is the difference in carbon dioxide concentration between the reactor outlet gas and the inlet gas, the average of more than 10 sets of test data is taken as the test result for that day.

[0046] Comparative Example 1

[0047] 498g of α-Al₂O₃ trihydrate (particle size 50-150μm), 102g of pseudo-monohydrate Al₂O₃, and 2.5g of boric acid were mixed evenly in a mixer, and then poured into a kneader. 120ml of a dilute nitric acid aqueous solution (nitric acid:water = 1:6, volume ratio) was added to the kneader, and the mixture was kneaded into an extrudable paste. Finally, the paste was loaded into an extruder and extruded into cylindrical shapes with a diameter of 8.0mm and a length of 6.0mm. These cylindrical shapes were dried at 80-120℃ for at least 2 hours to reduce the free water content to below 10% by weight. The dried cylindrical shapes were then placed in a high-temperature kiln and heated from room temperature to 1390℃ over 36 hours, then held at that temperature for 2 hours to obtain a white solid product. XRD analysis of this solid indicated that it was α-Al₂O₃, and its relevant physical properties are shown in Table 2.

[0048] Example 1

[0049] 448g of trihydrate α-alumina (particle size 50-150μm), 102g of pseudo-monohydrate Al2O3, 2.5g of boric acid, and 50g of monocrystalline alumina were mixed evenly in a mixer. 120ml of dilute nitric acid solution (nitric acid:water = 1:6, volume ratio) was poured into a kneader and kneaded to form an extrudable paste. The paste was then extruded into cylindrical shapes with an outer diameter of 8.0mm and a length of 6.0mm. These cylindrical shapes were dried at 80-120℃ for at least 2 hours to reduce the free moisture content to below 10wt%. The dried cylindrical shapes were then placed in a high-temperature kiln and heated from room temperature to 1390℃ over 36 hours, followed by a 2-hour constant temperature period to obtain the α-Al2O3 support. Its relevant physical properties are shown in Table 2.

[0050] Example 2

[0051] 398g of α-alumina trihydrate (particle size 50-150μm), 102g of pseudo-monohydrate Al2O3, 2.5g of boric acid, and 100g of monocrystalline alumina were mixed evenly in a mixer. 120ml of dilute nitric acid solution (nitric acid:water = 1:6, volume ratio) was poured into a kneader and kneaded into an extrudable paste. The paste was then extruded into cylindrical shapes with an outer diameter of 8.0mm and a length of 6.0mm. These cylindrical shapes were dried at 80-120℃ for at least 2 hours to reduce the free moisture content to below 10wt%. The dried cylindrical shapes were then placed in a high-temperature kiln and heated from room temperature to 1390℃ over 36 hours, followed by a 2-hour hold at that temperature to obtain the α-Al2O3 support. Its relevant physical properties are shown in Table 2.

[0052] Example 3

[0053] 298g of α-alumina trihydrate (particle size 50-150μm), 102g of pseudo-monohydrate Al2O3, 2.5g of boric acid, and 200g of monocrystalline alumina were mixed evenly in a mixer. 120ml of dilute nitric acid solution (nitric acid:water = 1:6, volume ratio) was poured into a kneader and kneaded to form an extrudable paste. The paste was then extruded into cylindrical shapes with an outer diameter of 8.0mm and a length of 6.0mm. These cylindrical shapes were dried at 80-120℃ for at least 2 hours to reduce the free moisture content to below 10wt%. The dried cylindrical shapes were then placed in a high-temperature kiln and heated from room temperature to 1390℃ over 36 hours, followed by a 2-hour constant temperature period to obtain the α-Al2O3 support. Its relevant physical properties are shown in Table 2.

[0054] Example 4

[0055] 398g of β-alumina trihydrate (particle size 50-150μm), 102g of pseudo-monohydrate Al2O3, 2.5g of boric acid, and 100g of monocrystalline alumina were mixed evenly in a mixer. 120ml of dilute nitric acid solution (nitric acid:water = 1:6, volume ratio) was poured into a kneader and kneaded to form an extrudable paste. The paste was then extruded into cylindrical shapes with an outer diameter of 8.0mm and a length of 6.0mm. These cylindrical shapes were dried at 80-120℃ for at least 2 hours to reduce the free moisture content to below 10wt%. The dried cylindrical shapes were then placed in a high-temperature kiln and heated from room temperature to 1390℃ over 36 hours, followed by a constant temperature of 2 hours to obtain the α-Al2O3 support. Its relevant physical properties are shown in Table 2.

[0056] Example 5

[0057] 398g of γ-alumina (particle size 50-150μm), 102g of pseudo-monohydrate Al2O3, 2.5g of boric acid, and 100g of monocrystalline alumina were mixed evenly in a mixer. 120ml of dilute nitric acid solution (nitric acid:water = 1:6, volume ratio) was poured into a kneader and kneaded to form an extrudable paste. The paste was then extruded into cylindrical shapes with an outer diameter of 8.0mm and a length of 6.0mm. These cylindrical shapes were dried at 80-120℃ for at least 2 hours to reduce the free moisture content to below 10wt%. The dried cylindrical shapes were then placed in a high-temperature kiln and heated from room temperature to 1390℃ over 36 hours, followed by a 2-hour constant temperature period to obtain the α-Al2O3 support. Its relevant physical properties are shown in Table 2.

[0058] Example 6

[0059] 398g of trihydrate α-alumina (particle size 50-150μm), 102g of pseudo-monohydrate Al2O3, 2.5g of calcium fluoride, and 100g of monocrystalline alumina were mixed evenly in a mixer. 120ml of dilute nitric acid solution (nitric acid:water = 1:6, volume ratio) was poured into a kneader and kneaded into an extrudable paste. The paste was then extruded into cylindrical shapes with an outer diameter of 8.0mm and a length of 6.0mm. These cylindrical shapes were dried at 80-120℃ for at least 2 hours to reduce the free moisture content to below 10wt%. The dried cylindrical shapes were then placed in a high-temperature kiln and heated from room temperature to 1390℃ over 36 hours, followed by a 2-hour constant temperature period to obtain the α-Al2O3 support. Its relevant physical properties are shown in Table 2.

[0060] Example 7

[0061] 398g of trihydrate α-alumina (particle size 50-150μm), 102g of pseudo-monohydrate Al2O3, 2.5g of boron oxide, and 100g of monocrystalline alumina were mixed evenly in a mixer. 120ml of dilute nitric acid solution (nitric acid:water = 1:6, volume ratio) was poured into a kneader and kneaded into an extrudable paste. The paste was then extruded into cylindrical shapes with an outer diameter of 8.0mm and a length of 6.0mm. These cylindrical shapes were dried at 80-120℃ for at least 2 hours to reduce the free moisture content to below 10wt%. The dried cylindrical shapes were then placed in a high-temperature kiln and heated from room temperature to 1390℃ over 36 hours, followed by a 2-hour hold at that temperature to obtain the α-Al2O3 support. Its relevant physical properties are shown in Table 2.

[0062] Example 8

[0063] 398g of trihydrate α-alumina (particle size 250-300μm), 102g of pseudo-monohydrate Al2O3, 2.5g of boric acid, and 100g of monocrystalline alumina were mixed evenly in a mixer. 120ml of dilute nitric acid solution (nitric acid:water = 1:6, volume ratio) was poured into a kneader and kneaded into an extrudable paste. The paste was then extruded into cylindrical shapes with an outer diameter of 8.0mm and a length of 6.0mm. These cylindrical shapes were dried at 80-120℃ for at least 2 hours to reduce the free moisture content to below 10wt%. The dried cylindrical shapes were then placed in a high-temperature kiln and heated from room temperature to 1390℃ over 36 hours, followed by a 2-hour hold at that temperature to obtain the α-Al2O3 support. Its relevant physical properties are shown in Table 2.

[0064] Example 9

[0065] 398g of α-alumina trihydrate (particle size 5-10μm), 102g of pseudo-monohydrate Al2O3, 2.5g of boric acid, and 100g of monocrystalline alumina were mixed evenly in a mixer. 120ml of dilute nitric acid solution (nitric acid:water = 1:6, volume ratio) was poured into a kneader and kneaded to form an extrudable paste. The paste was then extruded into cylindrical shapes with an outer diameter of 8.0mm and a length of 6.0mm. These cylindrical shapes were dried at 80-120℃ for at least 2 hours to reduce the free moisture content to below 10wt%. The dried cylindrical shapes were then placed in a high-temperature kiln and heated from room temperature to 1390℃ over 36 hours, followed by a constant temperature of 2 hours to obtain the α-Al2O3 support. Its relevant physical properties are shown in Table 2.

[0066] Table 2 Physical property data of the carrier

[0067] Comparative Example 1 57 42.8 0.91 Example 1 68 41.7 1.05 Example 2 64 40.2 1.12 Example 3 72 38.5 1.13 Example 4 77 40.1 1.21 Example 5 66 38.2 1.09 Example 6 81 41.0 1.01 Example 7 61 40.4 1.14 Example 8 59 40.6 1.07 Example 9 67 40.0 1.15

[0068] Catalyst preparation

[0069] Add 32.1g of ethylenediamine, 10.8g of ethanolamine, and 179.8g of deionized water to a stirred glass beaker to obtain a mixture. Slowly add 72.2g of silver oxalate to the mixture while maintaining the temperature below 40℃ and stirring continuously until the silver oxalate is completely dissolved. Then add 2.25mL of cesium nitrate aqueous solution (concentration of 0.03995g / mL, based on the atomic weight of cesium) and 2.78mL of ammonium perrhenate aqueous solution (concentration of 0.0162g / mL, based on the atomic weight of rhenium) in sequence, mix well to prepare 300g of impregnation solution for later use.

[0070] Take 15g of the supports prepared in Examples 1-9 and Comparative Example 1, respectively, and place them in a vacuum-capable glass container. Add the silver amine impregnation solution described above, ensuring the supports are completely submerged. Evacuate to a vacuum of 10 mmHg or higher and maintain this for approximately 15 minutes. Then, filter to remove excess solution. Finally, place the impregnated support sample in a 350°C air stream and heat for approximately 2 minutes to prepare the silver catalysts for Examples 1-9 and Comparative Example 1.

[0071] The performance of the corresponding silver catalysts obtained from the supports in Examples 1-9 and Comparative Example 1 was determined using a microreactor evaluation device under the aforementioned process conditions. The data results on the 20th day after the start of the reaction are shown in Table 3.

[0072] Table 3. Results of catalyst performance testing

[0073] Comparative Example 1 237.8 86.69 Example 1 232.1 88.11 Example 2 230.6 88.34 Example 3 230.4 88.23 Example 4 228.5 87.52 Example 5 229.8 88.01 Example 6 231.7 88.45 Example 7 229.2 88.07 Example 8 230.9 88.56 Example 9 230.0 88.13

[0074] As can be seen from Table 3, compared with the silver catalyst prepared by the support without the addition of monocrystalline alumina in Comparative Example 1, the silver catalyst prepared by the alumina support with the addition of monocrystalline alumina under the same conditions according to the present invention has higher selectivity and stability.

[0075] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

[0076] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. An α-alumina support for the epoxidation of ethylene to prepare ethylene oxide, characterized in that, The α-alumina carrier comprises monocrystalline alumina, and the content of monocrystalline alumina is 0.1~50 wt% based on the total weight of the α-alumina carrier. The preparation method of the α-alumina support includes the following steps: (1) Prepare a mixture comprising micron-sized alumina, pseudo-monohydrate alumina, a mineralizer, and monocrystalline alumina, and mix the mixture with an acid solution; based on the total weight of the mixture, the content of the micron-sized alumina is 4.5~90wt%, the content of the pseudo-monohydrate alumina is 5~95wt%, the content of the mineralizer is 0.01~3wt%, and the content of the monocrystalline alumina is 0.1~50wt%; (2) After kneading and extruding the material obtained in step (1), the α-alumina carrier is obtained by drying and calcining.

2. The α-alumina support according to claim 1, wherein, The content of the single-crystal alumina is 1~40wt%.

3. The α-alumina support according to claim 2, wherein, The content of the single-crystal alumina is 5~35wt%.

4. The α-alumina support according to claim 1, wherein, The α-alumina support has the following characteristics: a specific surface area of ​​0.3~3.0 m². 2 / g, water absorption rate not less than 25%, mechanical strength not less than 30N.

5. A method for preparing an α-alumina support for the epoxidation of ethylene to ethylene oxide, characterized in that, Includes the following steps: (1) Prepare a mixture comprising micron-sized alumina, pseudo-monohydrate alumina, a mineralizer, and monocrystalline alumina, and mix the mixture with an acid solution; based on the total weight of the mixture, the content of the micron-sized alumina is 4.5~90wt%, the content of the pseudo-monohydrate alumina is 5~95wt%, the content of the mineralizer is 0.01~3wt%, and the content of the monocrystalline alumina is 0.1~50wt%; (2) After kneading and extruding the material obtained in step (1), the α-alumina carrier is obtained by drying and calcining.

6. The method for preparing the α-alumina support according to claim 5, wherein, In step (1), the particle size of the micron-sized alumina is 1~500μm.

7. The method for preparing the α-alumina support according to claim 5, wherein, In step (1), based on the total weight of the mixture, the amount of micron-sized alumina added is 23~80wt%, the amount of pseudo-monohydrate alumina added is 18~75wt%, the amount of mineralizer added is 0.1~2.5wt%, and the amount of single-crystal alumina added is 1~40wt%.

8. The method for preparing the α-alumina support according to claim 7, wherein, The amount of single-crystal alumina added is 5~35 wt%.

9. The method for preparing the α-alumina support according to claim 5, wherein, In step (1), the acid solution is an aqueous solution of nitric acid, and the volume ratio of nitric acid to water in the aqueous solution of nitric acid is 1:1.25~10; the amount of acid solution added is 5~50wt% based on the total weight of the mixture.

10. The method for preparing the α-alumina support according to claim 9, wherein, The volume ratio of nitric acid to water in the nitric acid aqueous solution is 1:2~8.

11. The method for preparing the α-alumina support according to claim 9, wherein, The pseudo-alumina monohydrate and acid solution are all or partly replaced by aluminum sol.

12. The method for preparing the α-alumina support according to claim 5, wherein, In step (1), the micron-sized alumina is selected from at least one of trihydrate α-alumina, trihydrate β-alumina and γ-alumina; the mineralizing agent is selected from at least one of boric acid, boron oxide, hydrogen fluoride, aluminum fluoride, ammonium fluoride, calcium fluoride, magnesium fluoride and cryolite.

13. The method for preparing the α-alumina support according to claim 5, wherein, In step (2), the roasting temperature is 800~1800℃.

14. The method for preparing the α-alumina support according to claim 13, wherein, The roasting temperature is 1100~1500℃.

15. An α-alumina support prepared by the method for preparing an α-alumina support according to any one of claims 5-14.

16. A silver catalyst for the oxidation of ethylene to produce ethylene oxide, characterized in that, The silver catalyst is prepared by impregnating the α-alumina support as described in any one of claims 1-4 and 15 in a solution containing a silver compound.

17. The application of the silver catalyst according to claim 16 in the epoxidation of ethylene to prepare ethylene oxide.

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