A catalyst for olefin epoxidation, its preparation method and application

Abstract

This invention belongs to the field of catalyst technology and discloses a catalyst for olefin epoxidation, its preparation method, and its application. The preparation method includes: (1) preparing a mixture containing a silver compound precursor, an organic amine, water, and optional auxiliary agents to obtain a silver-containing mixture; (2) fully contacting the silver-containing mixture with an alumina support, and leaching off excess mixture from the surface of the support to obtain a support carrying the silver-containing mixture; (3) irradiating the support carrying the silver-containing mixture with microwaves to obtain the catalyst. The olefin epoxidation catalyst prepared by the method of this invention avoids local overheating during the preparation process, improves the dispersion of active centers, and thus has excellent catalytic performance.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and more specifically, to a method for preparing a catalyst for olefin epoxidation, the catalyst obtained by this method, and its application. Background Technology

[0002] Epoxyalkanes are an important class of products and intermediates in the petrochemical industry, and are widely used in various sectors such as light industry, chemicals, pharmaceuticals, textiles, and food. Ethylene oxide (EO), in particular, is an important ethylene derivative, primarily used in the production of ethylene glycol (EG), synthetic detergents, nonionic surfactants, antifreeze, emulsifiers, and ethylene glycol derivatives. It has wide and significant applications in numerous fields, including laundry and dyeing, electronics, pharmaceuticals, pesticides, textiles, automobiles, and oil extraction and refining.

[0003] Currently, the vast majority of industrial plants worldwide producing EO (ethylene oxide) use the ethylene process, where ethylene reacts directly with oxygen via epoxidation in the presence of a silver catalyst to produce EO. The main byproduct is CO2. In existing research, silver catalysts are currently the only effective catalyst in this process and are central to the ethylene epoxidation reaction.

[0004] Silver catalysts used in industrial EO / EG units can be mainly classified into three types: highly active silver catalysts, highly selective silver catalysts, and moderately selective silver catalysts. Highly active silver catalysts are characterized by high activity and good stability, with a selectivity of approximately 80%–82%, making them suitable for traditional units with relatively high inlet CO2 concentrations (generally 5%–10%). Highly selective silver catalysts are characterized by high selectivity, typically exceeding 88%, but require a relatively high inlet CO2 concentration, generally below 1%, making them suitable for units with relatively low space-time yields. Moderately selective silver catalysts have activity and selectivity between the two types mentioned above, with a selectivity reaching approximately 85%, and generally require an inlet CO2 concentration below 3%.

[0005] The activity, selectivity, and stability of silver catalysts are the main indicators for evaluating their performance. With increasingly stringent energy and environmental protection requirements in recent years, newly built or upgraded equipment is increasingly using highly selective or moderately selective silver catalysts, gradually replacing traditional highly active silver catalysts. Over the decades of silver catalyst development, modification has primarily focused on the modification of supports and additives, with relatively little research on preparation and activation processes.

[0006] US4833261 and US4761394 disclose silver catalysts with added rhenium, opening the prelude to the research of highly selective silver catalysts. CN105233824A discloses a silver catalyst composed of a mixture of Na, Cs, Ce, Re, Zr and other additives, and introduces a regulating gas to promote the stability of catalyst activity into the reaction system along with the reactants during the reaction process, thereby improving the stability of the catalyst. CN112206798A discloses a silver catalyst based on a composite support composed of α-silicon carbide and α-alumina.

[0007] Most of the aforementioned patent literature focuses on the modification of supports and additives. While selectivity has improved to some extent, the basic preparation process remains unchanged, still employing traditional preparation and activation techniques. For traditional thermal activation processes, the instantaneous heat conduction easily leads to uneven heating of the catalyst, thus affecting catalytic performance and significantly impacting the overall performance of silver catalysts, especially their stability. Furthermore, the process consumes a significant amount of energy. Therefore, developing a more efficient method for preparing silver catalysts with better overall performance is of great importance. Summary of the Invention

[0008] The purpose of this invention is to address the problem that the current preparation process of catalysts for the epoxidation of ethylene to ethylene oxide suffers from severe heating, which limits the improvement of the overall performance of the catalyst. The inventors of this invention have conducted extensive and in-depth research in the field of nanocatalysts and their preparation processes. The results show that the use of microwave irradiation can make the catalyst more uniformly activated and avoid local overheating compared with traditional processes, thus making the prepared catalyst have better overall performance. The silver catalyst obtained in this way exhibits better overall catalyst performance when used for the direct oxidation of olefins to produce ethylene oxide.

[0009] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a catalyst for olefin epoxidation, the method comprising:

[0010] (1) Prepare a mixture containing a silver compound precursor, an organic amine, water and optional auxiliaries to obtain a silver-containing mixture;

[0011] (2) The silver-containing mixture is brought into full contact with the alumina carrier, and the excess mixture on the surface of the carrier is drained off to obtain a carrier containing the silver-containing mixture;

[0012] (3) The carrier containing the silver mixture is subjected to microwave irradiation to obtain the catalyst.

[0013] A second aspect of the present invention provides a catalyst for olefin epoxidation prepared by the above-described preparation method.

[0014] A third aspect of the invention provides the application of the above-described catalyst in the direct oxidation of olefins to produce alkylene oxides, preferably in the direct oxidation of ethylene to produce ethylene oxide.

[0015] The beneficial technical effects of this invention are as follows:

[0016] The olefin epoxidation catalyst prepared by the method of the present invention avoids local overheating during the preparation process, improves the dispersion of active centers, and thus exhibits excellent catalytic performance. Compared with the prior art, it further improves the overall performance of the catalyst, reduces reaction by-products, and extends the catalyst's lifespan.

[0017] The preparation method of this invention improves the catalyst preparation efficiency and reduces the energy consumption in catalyst production. It has significant application advantages.

[0018] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0019] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0020] A first aspect of the present invention provides a method for preparing a catalyst for olefin epoxidation, the method comprising:

[0021] (1) Prepare a mixture containing a silver compound precursor, an organic amine, water and optional auxiliaries to obtain a silver-containing mixture;

[0022] (2) The silver-containing mixture is brought into full contact with the alumina carrier, and the excess mixture on the surface of the carrier is drained off to obtain a carrier containing the silver-containing mixture;

[0023] (3) The carrier containing the silver mixture is subjected to microwave irradiation to obtain the catalyst.

[0024] To reduce and fix the silver onto the carrier surface, the carrier containing the silver-containing mixture needs to be activated. In this invention, activation is performed by microwave irradiation. Preferably, the microwave irradiation is carried out in a furnace or tunnel equipped with a microwave emission source.

[0025] The power of the microwave irradiation is 1-15 kW, preferably 1-12 kW; the temperature of the irradiated material is controlled at 120-500℃, preferably 150-400℃; the duration of the microwave irradiation is 0.5-50 min, preferably 0.5-30 min, and more preferably 0.5-3 min.

[0026] According to the present invention, preferably, the microwave irradiation is carried out in a gaseous atmosphere, which is preferably selected from at least one of an air flow, a nitrogen / oxygen mixed flow, a helium / oxygen mixed flow, and a nitrogen / hydrogen mixed flow.

[0027] In this invention, the microwave irradiation is carried out in a flowing gaseous atmosphere or in a non-flowing gaseous atmosphere, preferably in a flowing gaseous atmosphere.

[0028] When the microwave irradiation is carried out in a flowing gaseous atmosphere, the flow rate of the gaseous atmosphere is 20-500 ml / min, preferably 20-300 ml / min, and more preferably 100-200 ml / min.

[0029] According to the present invention, preferably, the silver compound precursor is selected from at least one of silver nitrate, silver carbonate, silver oxalate and silver oxide;

[0030] The organic amine described in this invention can be selected from a variety of organic amine compounds, as long as they can form a complex with silver compounds. According to this invention, preferably, the organic amine is selected from at least one of ethylamine, ethylenediamine, n-propylamine, 1,3-propanediamine, n-butylamine, 1,4-butanediamine, ethanolamine, and propanolamine.

[0031] The additive is selected from at least one of alkali metal additives, alkaline earth metal additives, rhenium additives, and optionally rhenium co-additives.

[0032] In a preferred embodiment of the present invention, the alkali metal auxiliaries may be one or more soluble compounds of lithium, sodium, potassium, rubidium, and cesium, such as at least one of sulfates, nitrates, and hydroxides of the aforementioned alkali metal elements. The alkaline earth metal auxiliaries may be one or more soluble compounds of magnesium, calcium, strontium, and barium, such as at least one of sulfates, nitrates, and acetates of the aforementioned alkaline earth metal elements. The rhenium auxiliaries may be one or more selected from rhenium oxides, ammonium rheniumate, perrhenic acid, and perrhenate. The rhenium co-auxiliaries may be one or more selected from molybdenum compounds, tungsten compounds, chloride compounds, manganese compounds, nickel compounds, phosphorus compounds, and boron compounds.

[0033] According to the present invention, preferably, the amount of each raw material is such that, based on the total weight of the catalyst, the silver content in the catalyst, calculated by element, is 5-40 wt%, preferably 10-30 wt%; the weight content of the auxiliary agent in the catalyst, calculated by metal element, is 0-5500 ppm, preferably 90-3800 ppm; and the balance is an alumina support.

[0034] Among the additives, calculated by metal element, the weight content of alkali metals is preferably 10-2000 ppm, more preferably 50-1500 ppm; the weight content of alkaline earth metals is preferably 5-1200 ppm, more preferably 10-800 ppm; the weight content of rhenium metal is preferably 10-1500 ppm, more preferably 20-1000 ppm; and the weight content of rhenium co-additives, calculated by metal element, is preferably 0-800 ppm, more preferably 10-500 ppm.

[0035] According to the present invention, preferably, the sufficient contact is any industrial preparation method for supported catalysts, such as impregnation, spraying or coating, preferably impregnation, and more preferably vacuum impregnation.

[0036] In a preferred embodiment of the present invention, a silver-containing mixture is impregnated onto a carrier under a vacuum of less than 10 mmHg. The temperature of the mixture is preferably controlled at 0-30°C, and the impregnation time is preferably 10-60 minutes. The impregnation solution is then drained off.

[0037] According to the present invention, preferably, the preparation method further includes: (4) repeating steps (2) and (3) on the obtained catalyst.

[0038] When it is necessary to increase the silver content in the catalyst, a higher concentration of silver-containing mixture can be prepared; or the above method can be followed to perform at least one step (4), that is, to impregnate and activate the catalyst obtained after activation in step (3) again to achieve the purpose of increasing the loaded silver content.

[0039] In this invention, the alumina support can be a conventional support in the field of epoxide alkane catalysts. According to this invention, preferably, the alumina support is a shaped porous α-alumina support. The alumina support preferably has the following characteristics: a crushing strength of 20-200 N / particle, preferably 50-100 N / particle; and a specific surface area of ​​0.2-5 m². 2 / g, preferably 0.5-2m 2 / g; water absorption rate of 30-80%, preferably 40-60%; pore volume of 0.2-1.2ml / g, preferably 0.5-1.0ml / g.

[0040] In this invention, the porous α-alumina support can be in any shape commonly found in the art, such as spherical, annular, or cylindrical.

[0041] A second aspect of the present invention provides a catalyst for olefin epoxidation prepared by the above-described preparation method.

[0042] The olefin epoxidation catalyst of the present invention can directly catalytically oxidize olefins to epoxides, and is particularly suitable for the direct catalytic oxidation of ethylene to ethylene oxide, and has further improved catalytic performance.

[0043] As described above, the catalyst comprises a porous α-alumina support and the following components deposited thereon, based on the total weight of the catalyst:

[0044] i) 5-40 wt%, preferably 10-30 wt% of silver active component based on elemental silver;

[0045] ii) 10-2000 ppm, preferably 50-1500 ppm, of alkali metal additives calculated as alkali metal elements;

[0046] iii) 5-1200 ppm, preferably 10-800 ppm, of alkaline earth metal additives calculated as alkaline earth metal elements;

[0047] iv) 10-1500 ppm, preferably 20-1000 ppm, of rhenium additives based on rhenium atoms;

[0048] v) An optional rhenium co-auxiliary, if present, has a weight content of 5-800 ppm, preferably 10-500 ppm, based on the metal element.

[0049] The remaining space serves as a carrier.

[0050] The catalyst of this invention can be tested using the following performance testing methods:

[0051] The catalyst of this invention was evaluated using a laboratory fixed-bed microreactor (hereinafter referred to as "microreactor") to test its activity and selectivity. The microreactor evaluation device uses a stainless steel reaction tube with an inner diameter of 4 mm, which is placed within a heating jacket. The catalyst loading volume is 1 ml (12-18 mesh), with inert packing material at the bottom, ensuring the catalyst bed is located in the constant-temperature zone of the heating jacket.

[0052] The microreactor evaluation process conditions for the catalyst of this invention are as follows:

[0053] The composition of the reactant gases was as follows: ethylene 30.0 ± 2.0 mol%, oxygen 7.4 ± 0.2 mol%, carbon dioxide < 2.0 mol%, dichloroethane in appropriate amount, and the balance being nitrogen as a balance gas; the reaction pressure was 2.1 MPa; the space velocity was 6000 h⁻¹. -1 The target concentration of ethylene oxide in the reactor outlet tail gas is set at 2.5%.

[0054] A third aspect of the invention provides the application of the above-described catalyst in the direct oxidation of olefins to produce alkylene oxides, preferably in the direct oxidation of ethylene to produce ethylene oxide.

[0055] The present invention is further illustrated by the following examples:

[0056] In all the following examples and comparative examples, the carriers used were industrially produced molded porous α-alumina carriers with the following characteristics: crushing strength of 80 N / particle and specific surface area of ​​1.20 m². 2 / g, water absorption rate is 54%, and pore volume is 0.8ml / g.

[0057] The microwave irradiation furnace used in all the following embodiments is a furnace equipped with a microwave emission source.

[0058] In all the following examples and comparative examples, the activity and selectivity of the catalysts were tested using a laboratory fixed-bed microreactor (hereinafter referred to as "microreactor") evaluation device. The microreactor evaluation device used a stainless steel reaction tube with an inner diameter of 4 mm, which was placed in a heating mantle. The catalyst was packed in 1 ml (12-18 mesh) with inert packing material at the bottom, so that the catalyst bed was located in the isothermal zone of the heating mantle.

[0059] In the microreactor evaluation process conditions for the catalyst, the composition of the reaction gas was as follows: ethylene 30.0±2.0 mol%, oxygen 7.4±0.2 mol%, carbon dioxide <2.0 mol%, dichloroethane in appropriate amount, and the balance being nitrogen balance gas; the reaction pressure was 2.1 MPa; and the space velocity was 6000 h⁻¹. -1 The target concentration of ethylene oxide in the reactor outlet tail gas is set at 2.5%.

[0060] Once the above reaction conditions are stabilized, the composition of the inlet and outlet gases of the reactor is continuously measured. After volume shrinkage correction, the selectivity is calculated using the following formula:

[0061]

[0062] ΔEO represents the difference in ethylene oxide concentration between the outlet gas and the inlet gas, and the average of more than 10 sets of test data is taken as the test result for that day.

[0063] Catalyst activity is determined by reaction temperature; the lower the reaction temperature, the higher the activity. Catalyst stability is determined by reaction temperature rise; within the same evaluation period, the smaller the temperature rise, the better the stability.

[0064] Example 1

[0065] A mixture of 22g ethylenediamine, 8g ethanolamine, and 31.6g deionized water was prepared. After complete dissolution, 37.8g silver nitrate was slowly added to the mixture while stirring, maintaining the solution temperature at 0-15℃ to ensure complete dissolution of the silver nitrate. Then, 0.345g lithium hydroxide, 0.105g strontium sulfate, 0.065g cesium hydroxide, 0.065g perrhenic acid, and 0.040g ammonium molybdate were added to prepare a silver-containing impregnation solution. 10g of α-alumina support was placed in a container, and a vacuum was drawn to below 10mmHg. The aforementioned silver-containing impregnation solution was then added to immerse the support. After 30 minutes, excess impregnation solution was drained off, ensuring no residual liquid drips from the surface. The impregnated material was then activated in a microwave irradiation furnace with flowing air. The microwave power was set to 5kW, the material temperature was controlled at 340℃, and the material was irradiated with an air flow rate of 120ml / min for 0.5 minutes to obtain the silver catalyst S1.

[0066] Example 2

[0067] The catalyst was prepared according to the method of Example 1, except that the steps of "then activating the impregnated material in a microwave irradiation furnace with flowing air" and "microwave irradiating for 0.5 minutes in an air flow with a gas flow rate of 120 ml / min" in Example 1 were changed to "then activating the impregnated material in a microwave irradiation furnace with non-flowing air" and "microwave irradiating for 0.5 minutes in a non-flowing air atmosphere". Other conditions were the same as in Example 1, and catalyst S2 was prepared.

[0068] Example 3

[0069] The catalyst was prepared according to the method of Example 1, except that "microwave irradiation for 0.5 minutes" in Example 1 was changed to "microwave irradiation for 1 minute", and other conditions were the same as in Example 1, and catalyst S3 was prepared.

[0070] Example 4

[0071] A mixture of 22g ethylenediamine, 8g ethanolamine, and 31.6g deionized water was prepared. After complete dissolution, 37.8g silver nitrate was slowly added to the mixture while stirring, maintaining the solution temperature at 0-15℃ to ensure complete dissolution of the silver nitrate. Then, 0.345g lithium hydroxide, 0.105g strontium sulfate, 0.065g cesium hydroxide, 0.065g perrhenic acid, and 0.040g ammonium molybdate were added to prepare a silver-containing impregnation solution. 10g of α-alumina support was placed in a container, and a vacuum was drawn to below 10mmHg. The aforementioned silver-containing impregnation solution was then added to immerse the support. After 30 minutes, excess impregnation solution was drained off, ensuring no residual liquid drips from the surface. The impregnated material was then activated in a microwave irradiation furnace with flowing air. The microwave power was set to 3kW, the material temperature was controlled at 330℃, and the material was irradiated with an air flow rate of 120ml / min for 0.5 minutes to obtain silver catalyst S4.

[0072] Example 5

[0073] The catalyst was prepared according to the method of Example 3, except that "microwave irradiation for 0.5 minutes" in Example 3 was changed to "microwave irradiation for 1 minute", and other conditions were the same as in Example 3, and catalyst S5 was prepared.

[0074] Example 6

[0075] The catalyst was prepared according to the method of Example 3, except that "microwave irradiation for 0.5 minutes" in Example 3 was changed to "microwave irradiation for 2 minutes", and other conditions were the same as in Example 3, and catalyst S6 was prepared.

[0076] Example 7

[0077] A mixture of 20g ethylenediamine, 6g ethanolamine, and 42g deionized water was prepared. After complete dissolution, 31.5g silver nitrate was slowly added to the mixture while stirring, maintaining the solution temperature at 0-15℃ to ensure complete dissolution of the silver nitrate. Then, 0.288g lithium hydroxide, 0.088g strontium sulfate, 0.054g cesium hydroxide, 0.054g perrhenic acid, and 0.033g ammonium molybdate were added to prepare a silver-containing impregnation solution. 10g of α-alumina support was placed in a container, and a vacuum was drawn to below 10mmHg. The aforementioned silver-containing impregnation solution was then added to immerse the support. After 30 minutes, excess impregnation solution was drained off, ensuring no residual liquid drips from the surface. The impregnated material was then activated in a microwave irradiation furnace with flowing air. The microwave power was set to 3kW, the material temperature was controlled at 330℃, and the material was irradiated with an air flow rate of 120ml / min for 0.5 minutes to prepare the silver catalyst S7.

[0078] Example 8

[0079] The catalyst was prepared according to the method of Example 6, except that "microwave irradiation for 0.5 minutes" in Example 6 was changed to "microwave irradiation for 1 minute", and other conditions were the same as in Example 6, and catalyst S8 was prepared.

[0080] Comparative Example 1

[0081] A mixture of 22g ethylenediamine, 8g ethanolamine, and 31.6g deionized water was prepared. After complete dissolution, 37.8g silver nitrate was slowly added to the mixture while stirring, maintaining the solution temperature at 0-15℃ to ensure complete dissolution of the silver nitrate. Then, 0.345g lithium hydroxide, 0.105g strontium sulfate, 0.065g cesium hydroxide, 0.065g perrhenic acid, and 0.040g ammonium molybdate were added to prepare a silver-containing impregnation solution. 10g of α-alumina support was placed in a container, and a vacuum was drawn to below 10mmHg. The aforementioned silver-containing impregnation solution was then added to immerse the support. After 30 minutes, excess impregnation solution was drained off, ensuring no residual liquid dripped from the surface. The solution was then calcined in an air stream at 330℃ for 1 minute to prepare the silver catalyst DS1.

[0082] Comparative Example 2

[0083] The catalyst was prepared according to the method of Comparative Example 1, except that "calcination for 1 minute" in Comparative Example 1 was changed to "calcination for 5 minutes", and other conditions were the same as those in Comparative Example 1. Catalyst DS2 was prepared.

[0084] Comparative Example 3

[0085] A mixture of 20g ethylenediamine, 6g ethanolamine, and 42g deionized water was prepared. After complete dissolution, 31.5g silver nitrate was slowly added to the mixture while stirring, maintaining the solution temperature at 0-15℃ to ensure complete dissolution of the silver nitrate. Then, 0.288g lithium hydroxide, 0.088g strontium sulfate, 0.054g cesium hydroxide, 0.054g perrhenic acid, and 0.033g ammonium molybdate were added to prepare a silver-containing impregnation solution. 10g of α-alumina support was placed in a container, and a vacuum was drawn to below 10mmHg. The aforementioned silver-containing impregnation solution was then added to immerse the support. After 30 minutes, excess impregnation solution was drained off, ensuring no residual liquid dripped from the surface. The solution was then calcined in an air stream at 330℃ for 5 minutes to prepare the silver catalyst DS3.

[0086] Test case

[0087] The catalysts S1-S8 of Examples 1-8 and the catalysts DS1-DS3 of Comparative Examples 1-3 were subjected to the gas composition and space velocity of 6000 h⁻¹ as described above. -1 The results of the comparative evaluation under a reaction pressure of 2.1 MPa for two months are shown in Table 1 below.

[0088] Table 1. Microreactor evaluation results for catalysts S1-S7 and comparative catalysts DS1-DS3

[0089]

[0090]

[0091] As can be seen from the above examples, comparative examples, and Table 1, the silver catalyst prepared by microwave irradiation exhibits improved performance across all indicators compared to silver catalysts prepared by conventional methods when used for the direct gas-phase oxidation of ethylene to ethylene oxide. In particular, the reaction temperature rise is significantly reduced. That is, the silver catalyst prepared according to the method of the present invention possesses better overall performance, including better stability. Furthermore, the preparation time required by the method of the present invention is significantly shortened, improving production efficiency. Simultaneously, the energy efficiency of microwave irradiation is far higher than that of conventional activation, thereby reducing production energy consumption.

[0092] 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.

Claims

1. A method for preparing a catalyst for olefin epoxidation, characterized in that, The preparation method includes: (1) Prepare a mixture containing a silver compound precursor, an organic amine, water and optional auxiliaries to obtain a silver-containing mixture; (2) The silver-containing mixture is brought into full contact with the alumina carrier, and the excess mixture on the surface of the carrier is drained off to obtain a carrier containing the silver-containing mixture; (3) The carrier containing the silver mixture was subjected to microwave irradiation to obtain a catalyst; The power of the microwave irradiation is 1-12 kW; the temperature of the irradiated material is controlled at 150-400℃; and the duration of the microwave irradiation is 0.5-3 min.

2. The preparation method according to claim 1, wherein, The microwave irradiation is carried out in a furnace or tunnel equipped with a microwave emission source.

3. The preparation method according to claim 1, wherein, The microwave irradiation is carried out in a gaseous atmosphere.

4. The preparation method according to claim 3, wherein, The gaseous atmosphere is selected from at least one of an air flow, a nitrogen / oxygen mixed flow, a helium / oxygen mixed flow, and a nitrogen / hydrogen mixed flow.

5. The preparation method according to claim 1, wherein, The silver compound precursor is selected from at least one of silver nitrate, silver carbonate, silver oxalate, and silver oxide; The organic amine is selected from at least one of ethylamine, ethylenediamine, n-propylamine, 1,3-propanediamine, n-butylamine, 1,4-butanediamine, ethanolamine, and propanolamine; The additive is selected from at least one of alkali metal additives, alkaline earth metal additives, rhenium additives, and optionally rhenium co-additives.

6. The preparation method according to claim 1, wherein, The amount of each raw material used is such that, based on the total weight of the catalyst, the silver content in the catalyst, calculated as an element, is 5-40 wt%; the weight content of the auxiliary agent in the catalyst, calculated as a metal element, is 0-5500 ppm; and the balance is an alumina support.

7. The preparation method according to claim 6, wherein, The amount of each raw material used is such that, based on the total weight of the catalyst, the silver content in the catalyst, calculated as an element, is 10-30 wt%; the weight content of the auxiliary agent in the catalyst, calculated as a metal element, is 90-3800 ppm; and the balance is an alumina support.

8. The preparation method according to claim 6, wherein, The additives, calculated by metal element, contain 10-2000 ppm by weight of alkali metals; 5-1200 ppm by weight of alkaline earth metals; 10-1500 ppm by weight of rhenium metals; and 0-800 ppm by weight of rhenium co-additives, calculated by metal element.

9. The preparation method according to claim 8, wherein, The additives, calculated by metal element, contain 50-1500 ppm by weight of alkali metals; 10-800 ppm by weight of alkaline earth metals; 20-1000 ppm by weight of rhenium metals; and rhenium co-additives, calculated by metal element, contain 10-500 ppm by weight.

10. The preparation method according to claim 1, wherein, The full contact refers to immersion, spraying, or coating.

11. The preparation method according to claim 10, wherein, The term "full contact" refers to immersion.

12. The preparation method according to claim 11, wherein, The full contact refers to depressurized impregnation.

13. The preparation method according to claim 1, wherein, The preparation method further includes: (4) Repeat steps (2) and (3) with the obtained catalyst.

14. The preparation method according to claim 1, wherein, The alumina carrier is a shaped porous α-alumina carrier.

15. The preparation method according to claim 1, wherein, The alumina carrier has a crushing strength of 20-200 N / particle and a specific surface area of ​​0.2-5 m². 2 / g; water absorption rate is 30-80%; pore volume is 0.2-1.2ml / g.

16. The preparation method according to claim 15, wherein, The alumina carrier has a crushing strength of 50-100 N / particle and a specific surface area of ​​0.5-2 m². 2 / g; water absorption rate 40-60%; pore volume 0.5-1.0ml / g.

17. A catalyst for olefin epoxidation prepared by any one of claims 1-16.

18. The application of the catalyst of claim 17 in the direct oxidation of olefins to produce epoxides.

19. The application of the catalyst according to claim 17 in the direct oxidation of ethylene to produce ethylene oxide.

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