A silver catalyst for olefin epoxidation and its preparation method and application

Abstract

The present invention belongs to the field of catalysts, and relates to a silver catalyst for olefin epoxidation, a preparation method and application thereof. The preparation method comprises the following steps: (1) preparing a mixed solution comprising a silver compound, an organic compound containing a thiol group, an organic amine, an auxiliary agent and water; (2) allowing an alumina carrier to fully contact the mixed solution and calcine to obtain the silver catalyst. When the silver catalyst of the present invention is used to catalyze the gas-phase direct oxidation of ethylene to produce ethylene oxide, the stability is significantly improved, and the selectivity is further improved, thereby greatly improving the comprehensive performance of the catalyst.

Description

Technical Field

[0001] The present invention belongs to the field of catalysts, and more specifically, relates to a method for preparing a silver catalyst for olefin epoxidation, a silver catalyst for olefin epoxidation prepared by the method, and application of the silver catalyst for olefin epoxidation in direct oxidation of olefins to produce alkylene oxides. Background Art

[0002] Alkylene oxides are important products and intermediates in the petrochemical industry and are widely used in various industries such as light industry, chemical industry, medicine, textile and food. Among them, ethylene oxide (EO) is an important ethylene derivative product, mainly used in the production of ethylene glycol (EG), synthetic detergents, non-ionic surfactants, antifreeze agents, emulsifiers, ethylene glycol condensates and other products. It has extensive and important applications in many fields such as laundry, electronics, medicine, pesticides, textiles, automobiles, oil extraction and refining.

[0003] At present, most of the industrial facilities producing EO in the world adopt the ethylene process, that is, ethylene and oxygen are directly epoxidized to produce EO under the action of silver catalyst, and the side reaction products are mostly CO2. In existing research, silver catalyst is currently the only effective catalyst in this process and is the core of ethylene epoxidation reaction.

[0004] Silver catalysts used in industrial EO / EG devices can be mainly divided into three types: high-activity silver catalysts, high-selectivity silver catalysts and medium-selectivity silver catalysts. Among them, the high-activity silver catalyst is characterized by high activity and good stability, with a selectivity of about 80% to 82%, which is more suitable for traditional devices with high CO2 concentration at the reactor inlet (generally 5% to 10%); the high-selectivity silver catalyst is characterized by high selectivity, which can generally exceed 88%, but has a high requirement for the inlet CO2 concentration, which generally needs to be less than 1%, and is suitable for devices with relatively low space-time yield; the medium-selectivity silver catalyst is characterized by activity and selectivity between the above two catalysts, with a selectivity of about 85%, and generally requires the inlet CO2 concentration to be below 3%.

[0005] The activity, selectivity and stability of silver catalysts are the main indicators for evaluating the performance of silver catalysts. With the continuous improvement of energy consumption and environmental protection requirements in recent years, new or modified devices have increasingly begun to use high-selectivity or medium-selectivity silver catalysts, gradually replacing traditional high-activity silver catalysts. In the decades of silver catalyst development, the modification of silver catalysts has mainly focused on carriers, additives and preparation methods.

[0006] US4833261 and US4761394 disclose silver catalysts with added rhenium additives, which opened the prelude to the research of high-selectivity silver catalysts. CN105233824A discloses a silver catalyst composed of mixed additives such as Na, Cs, Ce, Re, and Zr, and during the reaction process, a regulating gas that promotes the stability of catalyst activity is introduced into the reaction system along with the reaction raw materials to improve the stability of the catalyst. CN108160075A discloses a silver catalyst with added polypeptide additives. CN106492799A discloses a preparation method using a solution of one or more organic carboxylic acids and / or inorganic acids as a competitive adsorbent to improve the catalytic performance of the silver catalyst.

[0007] In the above patent documents, some of them have adjusted and changed the additives of silver catalysts, while others have studied the preparation method and reaction process, but there is still a lot of room for improvement in the comprehensive performance of silver catalysts, especially stability. Therefore, it is of great significance to develop an olefin epoxidation catalyst with higher stability and high selectivity. Summary of the invention

[0008] In view of the problems that the current catalysts for preparing ethylene oxide by epoxidation of ethylene are generally poor in stability, the inventors of the present invention have conducted extensive and in-depth research in the field of heterogeneous metal catalysts and nanocatalysts. As a result, it is found that by utilizing the mechanism that strong SM bonds can be formed between sulfur (S) and metal (M), under the condition of strictly controlling the content, the introduced -SH can be bonded with the silver in the silver catalyst, forming a "bridging effect" between the silver nanoparticles and the carrier, anchoring and protecting the silver particles, and regulating the size of the silver particles, thereby significantly improving the dispersion state of the silver particles. When the silver catalyst obtained in this way is used to catalyze the direct gas-phase oxidation of ethylene to prepare ethylene oxide, the stability is significantly improved, and the selectivity is further improved, which greatly improves the comprehensive performance of the catalyst.

[0009] The first aspect of the present invention provides a method for preparing a silver catalyst for olefin epoxidation, the preparation method comprising the following steps:

[0010] (1) preparing a mixed solution comprising a silver compound, an organic compound containing a thiol group, an organic amine, an auxiliary agent and water;

[0011] (2) The alumina carrier is fully contacted with the mixed solution and calcined to obtain the silver catalyst.

[0012] The second aspect of the present invention provides a silver catalyst for olefin epoxidation prepared by the above preparation method.

[0013] The third aspect of the present invention provides the use of the above silver catalyst for olefin epoxidation in the direct oxidation of olefins to produce alkylene oxides.

[0014] The beneficial technical effect of the present invention is that the dispersibility of the active metal of the high-stability epoxidation catalyst prepared by the method of the present invention is significantly improved, so that the catalyst has excellent catalytic performance. Compared with the prior art, the catalyst of the present invention has higher stability and selectivity, saves reaction raw materials, reduces reaction by-products, prolongs the service life of the catalyst, and has significant application advantages.

[0015] Other features and advantages of the present invention will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0016] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0017] The present invention provides a method for preparing a silver catalyst for olefin epoxidation, the preparation method comprising the following steps:

[0018] (1) preparing a mixed solution comprising a silver compound, an organic compound containing a thiol group, an organic amine, an auxiliary agent and water;

[0019] (2) The alumina carrier is fully contacted with the mixed solution and calcined to obtain the silver catalyst.

[0020] In a preferred embodiment of the present invention, the silver-containing compound is selected from at least one of silver nitrate, silver carbonate, silver oxalate and silver oxide.

[0021] According to the present invention, the role of adding the thiol-containing organic compound is to utilize -SH to bond with the silver in the silver catalyst to form a "bridging effect" between the silver nanoparticles and the carrier. Therefore, the present invention can use various thiol-containing organic compounds. Preferably, the thiol-containing organic compound is a thiol-containing organic small molecule compound, preferably with a molecular weight of less than 150 g / mol, and specifically preferably at least one of methyl mercaptan, ethyl mercaptan, ethanedithiol, 1,3-propanedithiol and benzyl mercaptan.

[0022] In a preferred embodiment of the present invention, based on the total weight of the mixed solution, the weight content of the organic compound containing a mercapto group in the mixed solution calculated as sulfur element is 20-500 ppm, preferably 100-200 ppm.

[0023] The mercapto-containing organic compound of the present invention can be added to the mixed solution before or after the silver compound, preferably before the silver compound.

[0024] The organic amine in the present invention can be selected from a variety of organic amine compounds, as long as they can form a complex with the silver compound. In a preferred embodiment of the present invention, the organic amine is selected from at least one of ethylamine, ethylenediamine, n-propylamine, 1,3-propylenediamine, n-butylamine, 1,4-butylenediamine, ethanolamine and propanolamine.

[0025] In a preferred embodiment of the present invention, the auxiliary agent may be selected from at least one of an alkali metal auxiliary agent, an alkaline earth metal auxiliary agent, a rhenium auxiliary agent and an optional rhenium co-auxiliary agent.

[0026] In a preferred embodiment of the present invention, the alkali metal promoter may be one or more soluble compounds of lithium, sodium, potassium, rubidium and cesium, such as sulfates, nitrates and hydroxides of the above alkali metal elements. The alkaline earth metal promoter may be one or more soluble compounds of magnesium, calcium, strontium and barium, such as sulfates, nitrates and acetates of the above alkaline earth metal elements. The rhenium promoter may be one or more selected from rhenium oxides, ammonium rhenate, perrhenic acid and perrhenate. The rhenium co-promoter may be one or more selected from molybdenum compounds, tungsten compounds, chlorine compounds, manganese compounds, nickel compounds, phosphorus compounds and boron compounds.

[0027] According to the present invention, preferably, the amount of each component used is such that, based on the total weight of the catalyst, the silver content in the catalyst as an element is 5-40wt%, preferably 10-30wt%; the weight content of the auxiliary agent in the catalyst as a metal element is 35-5500ppm, preferably 70-3500ppm.

[0028] According to the present invention, preferably, the dosage of each auxiliary agent is such that the weight content of alkali metal is preferably 10-2000ppm, more preferably 20-1200ppm; the weight content of alkaline earth metal is preferably 10-1200ppm, more preferably 20-800ppm; the weight content of rhenium metal is preferably 10-1500ppm, more preferably 20-1000ppm; the weight content of rhenium co-auxiliary agent calculated as metal is preferably 5-800ppm, more preferably 10-500ppm.

[0029] According to the present invention, the remainder of the catalyst other than the contents of the above components is the weight of the carrier.

[0030] The method of sufficient contact in the present invention can be any industrial method for preparing supported catalysts, such as impregnation, spraying, coating, etc., preferably impregnation, such as reduced pressure impregnation.

[0031] In a preferred embodiment of the present invention, the silver-containing mixed solution is impregnated into the carrier under the condition of a vacuum degree less than 10 mmHg, the temperature of the mixed solution is preferably controlled at 0-30° C., and the impregnation time is preferably 10-60 minutes. The impregnation solution is then drained off.

[0032] In order to reduce and fix silver on the surface of the carrier, the carrier impregnated with the silver-containing mixed solution needs to be calcined. The calcination process is preferably carried out in a gas phase fluid, and the gas phase fluid is selected from at least one of air flow, nitrogen / oxygen mixed flow and nitrogen / hydrogen mixed flow. The calcination conditions preferably include: a temperature of 150-400°C, preferably 200-350°C; a time of 1-100 minutes, preferably 2-60 minutes.

[0033] When it is necessary to increase the silver content in the catalyst, a silver-containing mixed solution with a higher concentration can be prepared, or the catalyst obtained after activation in step (2) can be impregnated, leached, dried and activated again to achieve the purpose of increasing the loaded silver content.

[0034] In the present invention, the alumina carrier can be a conventional carrier in the field of alkylene oxide catalysts, such as a shaped porous α-alumina carrier; the carrier preferably has the following characteristics: a crushing strength of 20-200N / grain, preferably 50-100N / grain; a specific surface area of ​​0.2-5m 2 / g, preferably 0.5-2m 2 / g; water absorption rate is 30-80%, preferably 40-60%; pore volume is 0.2-1.2 ml / g, preferably 0.5-1.0 ml / g. The shape of the porous α-alumina carrier can be in a common form in the art, such as spherical, annular or cylindrical.

[0035] The catalyst of the present invention can be tested by the following performance test method:

[0036] The catalyst of the present invention is tested for activity and selectivity using a laboratory fixed bed microreactor (hereinafter referred to as "microreactor") evaluation device. The microreactor evaluation device uses a stainless steel reaction tube with an inner diameter of 4 mm, and the reaction tube is placed in a heating jacket. The catalyst filling volume is 1 ml (12-18 mesh), and an inert filler is provided at the bottom so that the catalyst bed is located in the constant temperature zone of the heating jacket.

[0037] The micro-reaction evaluation process conditions of the catalyst of the present invention are as follows:

[0038] Reaction gas composition: ethylene 30.0±2.0mol%, oxygen 7.4±0.2mol%, carbon dioxide <2.0mol%, appropriate amount of dichloroethane, the balance is nitrogen balance gas; reaction pressure 2.1MPa; space velocity 6000h -1 ; Set the target concentration of ethylene oxide in the reactor outlet tail gas to 2.5%.

[0039] The second aspect of the present invention provides a silver catalyst for olefin epoxidation prepared by the above-mentioned preparation method, wherein the silver catalyst for olefin epoxidation is a high-stability epoxidation catalyst. The high-stability epoxidation catalyst can directly catalytically oxidize olefins to produce alkylene oxides, is particularly suitable for direct catalytic oxidation of ethylene to produce ethylene oxide, and has improved stability and selectivity.

[0040] The present invention will be further described below in conjunction with embodiments, but the scope of the present invention is not limited to these embodiments.

[0041] In all the following examples and comparative examples, the carriers used were industrially produced α-alumina carriers with the following characteristics: a crushing strength of 70 N / particle, a specific surface area of ​​1.10 m 2 / g, water absorption is 52.5%, and pore volume is 0.8ml / g.

[0042] In all the following examples and comparative examples, the catalyst was tested for activity and selectivity 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 jacket. The catalyst loading volume was 1 ml (12-18 mesh), with an inert filler at the bottom so that the catalyst bed was located in the constant temperature zone of the heating jacket.

[0043] In the process conditions of the micro-reaction evaluation of the catalyst, the reaction gas composition is: ethylene 30.0±2.0mol%, oxygen 7.4±0.2mol%, carbon dioxide <2.0mol%, dichloroethane in appropriate amount, and the balance is nitrogen balance gas; reaction pressure 2.1MPa; space velocity 6000h -1 ; Set the target concentration of ethylene oxide in the reactor outlet tail gas to 2.5%.

[0044] When the above reaction conditions are stably reached, the gas composition at the reactor inlet and outlet is continuously measured. The selectivity is calculated according to the following formula after the volume shrinkage correction is performed on the measured results:

[0045]

[0046] ΔEO is the difference in ethylene oxide concentration between the outlet gas and the inlet gas. The average of more than 10 groups of test data is taken as the test result of the day.

[0047] The activity of the catalyst is determined by the reaction temperature. The lower the reaction temperature, the higher the activity. The stability of the catalyst is determined by the reaction temperature rise. Within the same evaluation time, the smaller the reaction temperature rise, the better the stability.

[0048] Example 1

[0049] 18g of ethylenediamine, 6g of ethanolamine, 0.058g of benzyl mercaptan and 44.5g of deionized water are mixed to obtain a mixed solution. After the mixture is completely dissolved, 31.5g of silver nitrate is slowly added to the mixed solution while stirring. The solution temperature is maintained at 0-15°C to completely dissolve the silver nitrate. Then 0.175g of lithium hydroxide, 0.105g of strontium sulfate, 0.055g of cesium hydroxide, 0.065g of perrhenic acid and 0.040g of ammonium molybdate are added to prepare a silver-containing impregnation solution for standby use. 10g of α-alumina carrier is placed in a container, evacuated to below 10mmHg, and then the above-mentioned silver-containing impregnation solution is added thereto so that the carrier is immersed. After maintaining for 30 minutes, the excess impregnation solution is drained off. Then roasted in an air flow at 300°C for 5 minutes to prepare the silver catalyst S1.

[0050] Example 2

[0051] 18g of ethylenediamine, 6g of ethanolamine and 44.5g of deionized water are mixed to obtain a mixed solution. After the mixture is completely dissolved, 31.5g of silver nitrate is slowly added to the mixed solution while stirring. The solution temperature is maintained at 0-15°C to completely dissolve the silver nitrate. Then 0.058g of benzyl mercaptan, 0.175g of lithium hydroxide, 0.105g of strontium sulfate, 0.055g of cesium hydroxide, 0.065g of perrhenic acid and 0.040g of ammonium molybdate are added to prepare a silver-containing impregnation solution for standby use. 10g of the α-alumina carrier is placed in a container, evacuated to below 10mmHg, and then the above-mentioned silver-containing impregnation solution is added thereto so that the carrier is immersed. After maintaining for 30 minutes, the excess impregnation solution is drained off. Then roasted in an air flow at 300°C for 5 minutes to prepare the silver catalyst S2.

[0052] Example 3

[0053] 18g of ethylenediamine, 6g of ethanolamine, 0.038g of benzyl mercaptan and 44.5g of deionized water are mixed to obtain a mixed solution. After the mixture is completely dissolved, 31.5g of silver nitrate is slowly added to the mixed solution while stirring. The solution temperature is maintained at 0-15°C to completely dissolve the silver nitrate. Then 0.175g of lithium hydroxide, 0.105g of strontium sulfate, 0.055g of cesium hydroxide, 0.065g of perrhenic acid and 0.040g of ammonium molybdate are added to prepare a silver-containing impregnation solution for standby use. 10g of the α-alumina carrier is placed in a container, evacuated to below 10mmHg, and then the above-mentioned silver-containing impregnation solution is added thereto so that the carrier is immersed. After maintaining for 30 minutes, the excess impregnation solution is drained off. Then roasted in an air flow at 300°C for 5 minutes to prepare the silver catalyst S3.

[0054] Example 4

[0055] 18g of ethylenediamine, 6g of ethanolamine, 0.023g of methyl mercaptan and 44.5g of deionized water are mixed to obtain a mixed solution. After the mixture is completely dissolved, 31.5g of silver nitrate is slowly added to the mixed solution while stirring. The solution temperature is maintained at 0-15°C to completely dissolve the silver nitrate. Then 0.175g of lithium hydroxide, 0.105g of strontium sulfate, 0.055g of cesium hydroxide, 0.065g of perrhenic acid and 0.040g of ammonium molybdate are added to prepare a silver-containing impregnation solution for standby use. 10g of the α-alumina carrier is placed in a container, evacuated to below 10mmHg, and then the above-mentioned silver-containing impregnation solution is added thereto so that the carrier is immersed. After maintaining for 30 minutes, the excess impregnation solution is drained off. Then roasted in an air flow at 300°C for 5 minutes to prepare the silver catalyst S4.

[0056] Example 5

[0057] 18g of ethylenediamine, 6g of ethanolamine, 0.029g of ethanethiol and 44.5g of deionized water are mixed to obtain a mixed solution. After the mixture is completely dissolved, 31.5g of silver nitrate is slowly added to the mixed solution while stirring. The solution temperature is maintained at 0-15°C to completely dissolve the silver nitrate. Then 0.175g of lithium hydroxide, 0.105g of strontium sulfate, 0.055g of cesium hydroxide, 0.065g of perrhenic acid and 0.040g of ammonium molybdate are added to prepare a silver-containing impregnation solution for standby use. 10g of α-alumina carrier is placed in a container, evacuated to below 10mmHg, and then the above-mentioned silver-containing impregnation solution is added thereto to immerse the carrier. After maintaining for 30 minutes, the excess impregnation solution is drained off. Then, it is roasted in an air flow at 300°C for 5 minutes to prepare the silver catalyst S5.

[0058] Example 6

[0059] 18g of ethylenediamine, 6g of ethanolamine, 0.044g of ethanedithiol and 44.5g of deionized water are mixed to obtain a mixed solution. After the mixture is completely dissolved, 31.5g of silver nitrate is slowly added to the mixed solution while stirring. The solution temperature is maintained at 0-15°C to completely dissolve the silver nitrate. Then 0.175g of lithium hydroxide, 0.105g of strontium sulfate, 0.055g of cesium hydroxide, 0.065g of perrhenic acid and 0.040g of ammonium molybdate are added to prepare a silver-containing impregnation solution for standby use. 10g of the α-alumina carrier is placed in a container, evacuated to below 10mmHg, and then the above-mentioned silver-containing impregnation solution is added thereto to immerse the carrier. After maintaining for 30 minutes, the excess impregnation solution is drained off. Then, the mixture is roasted in an air flow at 300°C for 5 minutes to prepare the silver catalyst S6.

[0060] Example 7

[0061] 18g of ethylenediamine, 6g of ethanolamine, 0.051g of 1,3-propanedithiol and 44.5g of deionized water were mixed to obtain a mixed solution. After the mixture was completely dissolved, 31.5g of silver nitrate was slowly added to the mixed solution while stirring. The solution temperature was maintained at 0-15°C to completely dissolve the silver nitrate. Then 0.175g of lithium hydroxide, 0.105g of strontium sulfate, 0.055g of cesium hydroxide, 0.065g of perrhenic acid and 0.040g of ammonium molybdate were added to prepare a silver-containing impregnation solution for use. 10g of the α-alumina carrier was placed in a container, evacuated to below 10mmHg, and then the above-mentioned silver-containing impregnation solution was added to immerse the carrier. After 30 minutes, the excess impregnation solution was drained. Then it was roasted in an air flow at 300°C for 5 minutes to prepare the silver catalyst S7.

[0062] Comparative Example 1

[0063] 18g of ethylenediamine, 6g of ethanolamine and 44.5g of deionized water are mixed to obtain a mixed solution. After the mixture is completely dissolved, 31.5g of silver nitrate is slowly added to the mixed solution while stirring. The solution temperature is maintained at 0-15°C to completely dissolve the silver nitrate. Then 0.175g of lithium hydroxide, 0.105g of strontium sulfate, 0.055g of cesium hydroxide, 0.065g of perrhenic acid and 0.040g of ammonium molybdate are added to prepare a silver-containing impregnation solution for standby use. 10g of the α-alumina carrier is placed in a container, evacuated to below 10mmHg, and then the above-mentioned silver-containing impregnation solution is added thereto so that the carrier is immersed. After maintaining for 30 minutes, the excess impregnation solution is drained off. Then roasted in an air flow at 300°C for 5 minutes to prepare the comparative silver catalyst DS1.

[0064] Test Case

[0065] Catalysts S1-S7 of Examples 1-7 and catalyst DS1 of Comparative Example 1 were heated to room temperature under the above-mentioned gas composition and space velocity of 6000 h / min. -1 The comparative evaluation was carried out for one month under the conditions of reaction pressure of 2.1 MPa. The results are shown in Table 1 below.

[0066] Table 1 Micro-reaction evaluation results of catalysts S1-S7 and comparative catalyst DS1

[0067] sample Average selectivity (%) Initial reaction temperature (%) Reaction temperature rise (℃) Catalyst S1 87.3 223.0 6.8 Catalyst S2 86.1 222.8 7.2 Catalyst S3 84.6 223.1 8.2 Catalyst S4 85.2 223.2 8.6 Catalyst S5 85.8 222.8 9.1 Catalyst S6 86.0 222.6 8.8 Catalyst S7 85.4 223.3 9.2 Comparative catalyst DS1 82.5 223.2 11.4

[0068] It can be seen from Table 1 that after introducing an appropriate amount of mercapto-containing organic compound during the preparation of the catalyst, the initial activity of the prepared silver catalyst was not greatly affected when used to catalyze the gas-phase direct oxidation of ethylene to produce ethylene oxide, but the reaction selectivity and stability were significantly improved, and the catalytic performance was further improved.

[0069] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

[0070] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

Claims

1. A method for preparing a silver catalyst for olefin epoxidation, characterized in that: The preparation method comprises the following steps: (1) preparing a mixed solution comprising a silver compound, an organic compound containing a thiol group, an organic amine, an auxiliary agent and water; wherein the organic amine is selected from at least one of ethylamine, ethylenediamine, n-propylamine, 1,3-propylenediamine, n-butylamine, 1,4-butylenediamine, ethanolamine and propanolamine; (2) fully contacting the alumina carrier with the mixed solution and calcining the mixture to obtain the silver catalyst; Based on the total weight of the mixed solution, the weight content of the thiol-containing organic compound in the mixed solution calculated as sulfur element is 100-500 ppm; The thiol-containing organic compound is selected from at least one of methyl mercaptan, ethyl mercaptan, ethanedithiol, 1,3-propanedithiol and benzyl mercaptan; The organic compound containing a thiol group is added to the mixed solution before the silver compound; The dosage of each component is such that, based on the total weight of the silver catalyst, the silver content in the silver catalyst as an element is 10-30wt%; the weight content of the auxiliary agent in the silver catalyst as a metal element is 70-3500ppm.

2. The preparation method according to claim 1, wherein The silver-containing compound is selected from at least one of silver nitrate, silver carbonate, silver oxalate and silver oxide.

3. The preparation method according to claim 1, wherein The auxiliary agent is selected from at least one of an alkali metal auxiliary agent, an alkaline earth metal auxiliary agent, a rhenium auxiliary agent and an optional rhenium co-auxiliary agent.

4. The preparation method according to claim 3, wherein in, The rhenium co-promoter is selected from at least one of molybdenum compounds, tungsten compounds, chlorine compounds, manganese compounds, nickel compounds, phosphorus compounds and boron compounds.

5. The preparation method according to claim 1, wherein Based on the total weight of the mixed solution, the weight content of the organic compound containing a mercapto group in the mixed solution calculated as sulfur element is 100-200 ppm.

6. The preparation method according to claim 3, wherein: The dosage of each auxiliary agent is such that, based on the total weight of the silver catalyst, the weight content of alkali metal in the silver catalyst is 10-2000ppm; the weight content of alkaline earth metal is 10-1200ppm; the weight content of rhenium metal is 10-1500ppm; and the weight content of rhenium co-auxiliary agent in terms of metal is 5-800ppm.

7. The preparation method according to claim 6, wherein: The dosage of each auxiliary agent is such that, based on the total weight of the silver catalyst, the weight content of alkali metal in the silver catalyst is 20-1200ppm; the weight content of alkaline earth metal is 20-800ppm; the weight content of rhenium metal is 20-1000ppm; and the weight content of rhenium co-auxiliary agent in terms of metal is 10-500ppm.

8. The preparation method according to claim 1, wherein The sufficient contacting method is selected from dipping, spraying or coating.

9. The preparation method according to claim 8, wherein: The method of sufficient contact is immersion.

10. The preparation method according to claim 1, wherein: The calcination is carried out in a gas phase fluid, the gas phase fluid is selected from at least one of air flow, nitrogen / oxygen mixed flow and nitrogen / hydrogen mixed flow; the calcination temperature is 150-400° C.; the calcination time is 1-100 minutes.

11. The preparation method according to claim 10, wherein: The calcination temperature is 200-350° C. and the calcination time is 2-60 minutes.

12. The preparation method according to any one of claims 1 to 11, wherein: The alumina carrier is a shaped porous α-alumina carrier.

13. The preparation method according to claim 12, wherein: The carrier has a crushing strength of 20-200 N / particle and a specific surface area of ​​0.2-5 m 2 / g; water absorption rate is 30-80%; pore volume is 0.2-1.2ml / g.

14. The preparation method according to claim 13, wherein: The carrier has a crushing strength of 50-100 N / particle and a specific surface area of ​​0.5-2 m 2 / g; water absorption rate is 40-60%; pore volume is 0.5-1.0ml / g.

15. A silver catalyst for olefin epoxidation prepared by the preparation method according to any one of claims 1 to 14.

16. Use of the silver catalyst for olefin epoxidation according to claim 15 in the production of alkylene oxide by direct oxidation of olefins.

17. The use according to claim 16, wherein: The invention relates to an application of the silver catalyst for olefin epoxidation in the production of ethylene oxide by direct oxidation of ethylene.

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