An alumina support and silver catalyst, its preparation method and application

Abstract

This invention relates to the field of catalysts, specifically to an alumina support and a silver catalyst, their preparation method, and applications. The alumina support has a sheet-like three-dimensional configuration, with each alumina sheet possessing both hexagonal and quadrilateral facets. The ratio S of the average size of the hexagonal facets to the average size of the quadrilateral facets is 5–20. The size of each hexagonal facet is the length of its longest diagonal, and the size of each quadrilateral facet is the length of its shortest side. The catalyst prepared using the support provided by this invention significantly improves the selectivity of the ethylene epoxidation reaction and has broad application prospects. Furthermore, the ratio S of the average size of the hexagonal facets to the average size of the quadrilateral facets in the alumina sheet is substantially proportional to the selectivity of the silver catalyst in the ethylene epoxidation reaction, which has a positive effect on the study of the silver catalyst support and the ethylene epoxidation reaction.

Description

Technical Field

[0001] This invention relates to the field of catalysts, specifically to an alumina support and its preparation method, as well as a silver catalyst made therefrom, its preparation method, and its application. More specifically, this invention relates to an alumina support for a silver catalyst used in the oxidation of ethylene to produce ethylene oxide, its preparation method, the silver catalyst obtained from this support, its preparation method, and its application in the oxidation of ethylene to produce ethylene oxide. Background Technology

[0002] Ethylene oxide is a derivative of ethylene. It is not only an important organic chemical raw material, ranking second only to polyethylene and polyvinyl chloride among ethylene derivatives, and mainly used to produce ethylene glycol, but also a very important fine chemical raw material. It can be used to derive a variety of fine chemical products such as nonionic surfactants, ethanolamine, and ethylene glycol ethers, and then to produce four to five thousand products such as detergents, antifreeze, emulsifiers, plasticizers, and lubricants.

[0003] To date, silver catalysts remain the only effective catalysts for the industrial epoxidation of ethylene to produce ethylene oxide. Under the action of a silver catalyst, the oxidation of ethylene primarily produces ethylene oxide, while side reactions produce carbon dioxide and water. Activity, selectivity, and stability are the main performance indicators of silver catalysts. Activity generally 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 refers to 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. Currently, silver catalysts can be mainly divided into three types: high-activity, high-selectivity, and medium-selectivity silver catalysts. Due to the increasing scarcity of petroleum resources and the requirements for energy conservation, high-selectivity and medium-selectivity silver catalysts have been widely used in industrial production in recent years, replacing the original high-activity silver catalysts.

[0004] The performance of silver catalysts is significantly influenced not only by their composition and preparation method but also by the performance of the support used and the preparation method itself. Currently, α-alumina is generally used as the support for silver catalysts. In existing technologies, key parameters for evaluating the performance of α-alumina supports include specific surface area, compressive strength, and water absorption rate.

[0005] This invention regulates the microstructure of the α-alumina support by further pulverizing the kneaded material and controlling the amount of mineralizer added and calcination conditions, thereby affecting the distribution of the active components in the silver catalyst. When this silver catalyst is used for the oxidation of ethylene to ethylene oxide, the selectivity and stability are significantly improved. However, adjusting process conditions to further enhance the performance of silver catalysts remains a continuous pursuit in this field. Summary of the Invention

[0006] The purpose of this invention is to provide an alumina support that, when loaded with silver and various active components to form a silver catalyst, exhibits high selectivity in the ethylene oxidation process to produce ethylene oxide.

[0007] The first aspect of the present invention provides an α-alumina support for a silver catalyst used in the oxidation of ethylene to produce ethylene oxide, wherein the α-alumina support has a sheet-like three-dimensional configuration, and each α-alumina sheet has both hexagonal and quadrilateral surfaces.

[0008] The ratio of the average size of the hexagonal surface to the average size of the quadrilateral surface is 5 to 20, preferably 6 to 16;

[0009] The size of the hexagonal face is the length of the longest diagonal of the hexagon, and the size of the quadrilateral face is the length of the shortest side of the quadrilateral.

[0010] A second aspect of the present invention provides a method for preparing an α-alumina support, the method comprising the following steps:

[0011] S1. Mix α-Al2O3 trihydrate, Al2O3 pseudomonohydrate, optional combustible lubricant, mineralizer, and alkaline earth metal compound to obtain a solid mixture;

[0012] S2. The solid mixture is mixed and kneaded with the binder to obtain a kneaded compound;

[0013] S3. The kneaded compound is pulverized to obtain a pulverized product;

[0014] S4. Extrude the pulverized material into a molded shape to obtain a molded body;

[0015] S5. The molded body is dried and then calcined to obtain an α-alumina carrier.

[0016] A third aspect of the present invention provides an α-alumina support prepared by the above-described method for preparing an α-alumina support.

[0017] A fourth aspect of the present invention provides a silver catalyst for the oxidation of ethylene to produce ethylene oxide, the silver catalyst comprising:

[0018] a) The aforementioned α-alumina support;

[0019] b) Silver deposited on the α-alumina support;

[0020] c) Alkali metals and / or alkali metal-based compounds;

[0021] d) Alkaline earth metals and / or compounds based on alkaline earth metals;

[0022] e) Rhenium metal and / or rhenium-based compounds;

[0023] f) Optional rhenium synergists.

[0024] A fifth aspect of the present invention provides a method for preparing the above-mentioned silver catalyst, the method comprising the following steps:

[0025] 1) Add silver compounds, organic amines, alkali metal additives, alkaline earth metal additives, rhenium-containing additives and optional rhenium synergists to deionized water to prepare an impregnation solution;

[0026] 2) Impregnate the α-alumina carrier with an impregnation solution;

[0027] 3) Filter out excess impregnation solution and dry the impregnated α-alumina support;

[0028] 4) The impregnated α-alumina support is thermally decomposed in an oxygen-containing mixed gas to prepare the silver catalyst.

[0029] A sixth aspect of the present invention provides a method for ethylene oxidation, the method comprising: performing an ethylene epoxidation reaction under the action of the above-described silver catalyst to prepare ethylene oxide.

[0030] The beneficial technical effects of this invention are as follows: the catalyst prepared by the α-alumina support according to this invention exhibits high selectivity in the ethylene epoxidation reaction and has broad application prospects. Furthermore, the average size of the hexagonal facets in the α-alumina monolayer of the support of this invention is... and the average size of the quadrilateral surface The ratio (S) is basically directly proportional to the selectivity of silver catalyst in the epoxidation of ethylene. It plays a positive role in the study of silver catalyst support and ethylene epoxidation reaction, and provides guidance for the design and preparation of industrial high-selectivity silver catalyst support and catalyst, which has important practical significance. Detailed Implementation

[0031] 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.

[0032] This invention provides an α-alumina support for a silver catalyst used in the oxidation of ethylene to produce ethylene oxide. The α-alumina support has a sheet-like three-dimensional structure, and each α-alumina sheet has both hexagonal and quadrilateral surfaces.

[0033] Average size of hexagonal surface The average size of the quadrilateral face of the sum The ratio S is 5 to 20, preferably 6 to 16;

[0034] The dimension of a hexagonal face is the length of the longest diagonal of the hexagon, and the dimension of a quadrilateral face is the length of the shortest side of the quadrilateral.

[0035] According to a preferred embodiment of the present invention, the average size of the hexagonal surface and the average size of the quadrilateral surface It was measured using the following method:

[0036] 1) Take microscopic images of α-alumina single pieces using a scanning electron microscope;

[0037] 2) Statistical analysis of individual image sizes in microscopic morphology photographs, based on the formula... Calculate the average size of the hexagonal surface and the average size of the quadrilateral surface

[0038] Among them, M i The value of n is the size of the hexagonal or quadrilateral surface, and n is the total number of α-alumina sheets. In actual testing, the value of n can be 100-1000.

[0039] As can be seen from the embodiments, when the average size of the hexagonal facets in an α-alumina monolayer... and the average size of the quadrilateral surface When the ratio S is 5 to 20, preferably 6 to 16, the silver catalyst prepared therefrom exhibits high selectivity in the ethylene epoxidation reaction.

[0040] According to the present invention, preferably, the α-alumina support has the following characteristics:

[0041] The α-alumina content is not less than 90%.

[0042] The crushing strength is 30-280 N / particle, preferably 80-180 N / particle.

[0043] Specific surface area is 0.3–6 m² 2 / g, preferably 0.6-3m 2 / g.

[0044] The water absorption rate is 30-75%, preferably 50-70%.

[0045] The α-alumina support of the present invention is prepared by a method comprising the following steps:

[0046] S1. Mix α-Al2O3 trihydrate, Al2O3 pseudomonohydrate, optional combustible lubricant, mineralizer, and alkaline earth metal compound to obtain a solid mixture;

[0047] S2. Mix and knead the solid mixture with the binder to obtain a kneaded mixture;

[0048] S3. Crush the kneaded mixture to obtain a powder;

[0049] S4. Extrude the pulverized material into a molded shape to obtain the molded body;

[0050] S5. The molded body is dried and then calcined to obtain an α-alumina carrier.

[0051] According to the present invention, the amount of α-Al2O3 trihydrate added can be 10 to 85 wt% of the total weight of the solid mixture, preferably 28 to 82 wt%.

[0052] The amount of pseudo-monohydrate Al2O3 added can be 10-55 wt% of the total weight of the solid mixture, preferably 15-50 wt%.

[0053] The amount of combustible lubricant added can be 0 to 20 wt% of the total weight of the solid mixture, preferably 0.1 to 15.0 wt%. Preferably, the combustible lubricant is selected from at least one of petroleum coke, carbon powder, graphite and petroleum jelly.

[0054] The amount of mineralizer added can be 1 to 12.0 wt% of the total weight of the solid mixture, preferably 4 to 10 wt%, more preferably 5.1 to 7.5 wt%. The function of adding the mineralizer is to accelerate the crystal transformation of alumina, thereby controlling the hexagonal and quadrilateral facet sizes in α-alumina monolayers and reducing pores smaller than 0.5 μm. The mineralizer is selected from at least one of hydrogen fluoride, ammonium fluoride, ammonium chloride, boric acid, barium fluoride, calcium fluoride, aluminum fluoride, cryolite, magnesium fluoride, and lithium fluoride.

[0055] The amount of alkaline earth metal compound added can be 0.01 to 5.0 wt% of the total weight of the solid mixture, preferably 0.05 to 2.0 wt%. The alkaline earth metal compound can be selected from at least one of oxides of strontium and / or barium, nitrates, acetates, oxalates, and sulfates.

[0056] According to a preferred embodiment of the present invention, the amount of adhesive used is 25 to 60 wt% of the total weight of the solid mixture.

[0057] The binder can be an acid, more preferably an aqueous solution of nitric acid, wherein the weight ratio of nitric acid to water in the aqueous solution of nitric acid is 1:1.25 to 10.

[0058] According to the present invention, the power of the pulverizer can be 1500-2000W, and the rotation speed is 35000-40000r / min.

[0059] The number of crushing cycles can be 1-20, preferably 2-16.

[0060] Each grinding session can last from 2 seconds to 5 minutes, preferably from 5 seconds to 60 seconds.

[0061] The particle size of the pulverized material can be 50-350 mesh, preferably 70-300 mesh.

[0062] According to the present invention, preferably, the molded body is dried to a moisture content of no more than 10 wt%.

[0063] The shape of the molded body can be selected from any one of the following: ring, sphere, cylinder, or porous cylinder.

[0064] According to one specific embodiment of the present invention, the drying temperature is 20-120°C, and the drying time is 20-48 hours.

[0065] According to the present invention, calcination can completely convert alumina into α-Al₂O₃. Specifically, calcination includes programmed heating and optional isothermal calcination.

[0066] The temperature rise rate of the programmed temperature riser can be 2-10℃ / min.

[0067] The temperature for constant temperature calcination can be 900-1600℃, preferably 950-1500℃.

[0068] The constant temperature calcination time can be 0-20 hours, preferably 0.1-15 hours.

[0069] In this invention, the crushing strength of the carrier is determined by using a DLⅡ type intelligent particle strength tester. The radial crushing strength of the carrier sample is measured and the average value is taken. The water absorption rate is determined by the density method. The specific surface area is determined by the nitrogen physical adsorption BET method. The apparent morphology is determined by SEM (scanning electron microscopy).

[0070] The present invention also provides an α-alumina support prepared by the above-described method for preparing an α-alumina support.

[0071] This invention also provides a silver catalyst for the oxidation of ethylene to produce ethylene oxide, the silver catalyst comprising:

[0072] a) The above-mentioned α-alumina support;

[0073] b) Silver deposited on an α-alumina support;

[0074] c) Alkali metals and / or alkali metal-based compounds;

[0075] d) Alkaline earth metals and / or compounds based on alkaline earth metals;

[0076] e) Rhenium metal and / or rhenium-based compounds;

[0077] f) Optional rhenium synergists.

[0078] According to the present invention, the mass content of silver can be 1 to 50 wt%, preferably 5 to 40 wt%, based on the total weight of the silver catalyst.

[0079] The mass content of alkali metals can be 5 to 3000 ppm, preferably 10 to 2000 ppm.

[0080] The mass content of alkaline earth metals can be 50 to 20,000 ppm, preferably 100 to 15,000 ppm.

[0081] The mass content of rhenium metal can be 10 to 2000 ppm, preferably 100 to 1500 ppm.

[0082] The rhenium content in the synergist, calculated as metal in the synergist, can be 0 to 1500 ppm, preferably 5 to 1000 ppm.

[0083] According to a preferred embodiment of the present invention, the alkali metal compound is selected from at least one of alkali metal nitrates, sulfates and hydroxides, preferably cesium sulfate and / or cesium nitrate.

[0084] The alkaline earth metal compound may be selected from at least one of the oxides, oxalates, sulfates, acetates and nitrates of alkaline earth metal elements, preferably barium acetate and / or strontium acetate.

[0085] The rhenium compound is selected from at least one of rhenium oxides, perrhenic acid and perrhenate, preferably perrhenic acid and perrhenate.

[0086] The synergist for rhenium may be selected from at least one metal selected from chromium, molybdenum, tungsten and manganese, and / or from compounds based on at least one element selected from chromium, molybdenum, tungsten and manganese, preferably at least one selected from chromic acid, chromium nitrate, tungstic acid, cesium tungstate, molybdic acid, ammonium molybdate, manganic acid and potassium permanganate.

[0087] The silver catalyst of the present invention is prepared by a method comprising the following steps:

[0088] 1) Add silver compounds, organic amines, alkali metal additives, alkaline earth metal additives, rhenium-containing additives and optional rhenium synergists to deionized water to prepare an impregnation solution;

[0089] 2) Impregnate the α-alumina carrier with an impregnation solution;

[0090] 3) Filter out excess impregnation solution and dry the impregnated α-alumina support;

[0091] 4) The impregnated α-alumina support is thermally decomposed in an oxygen-containing mixed gas to produce a silver catalyst.

[0092] Alkaline earth metal additives can be applied to the carrier before, during, or after silver impregnation, or they can be applied to the carrier after the silver compound has been reduced.

[0093] According to the present invention, the silver compound may be selected from at least one of silver oxalate, silver oxide and silver nitrate, preferably silver nitrate.

[0094] The organic amine may be selected from at least one of pyridine, butylamine, ethylenediamine, 1,3-propanediamine and ethanolamine, preferably a mixture of ethylenediamine and ethanolamine.

[0095] The alkali metal auxiliaries may be selected from at least one of alkali metals and alkali metal-based compounds. The alkali metal-based compounds are selected from at least one of nitrates, sulfates and hydroxides of alkali metal elements, preferably cesium sulfate and / or cesium nitrate.

[0096] The alkaline earth metal auxiliaries may be selected from at least one alkaline earth metal and alkaline earth metal-based compounds. The alkaline earth metal-based compounds are selected from at least one of oxides, oxalates, sulfates, acetates and nitrates of alkaline earth metal elements, preferably barium acetate and / or strontium acetate.

[0097] The rhenium-containing additive may be selected from at least one of rhenium metal and rhenium-based compounds, wherein the rhenium-based compounds are selected from at least one of rhenium oxides, perrhenic acid and perrhenate, preferably perrhenic acid and perrhenate.

[0098] The synergist for rhenium may be selected from at least one metal selected from chromium, molybdenum, tungsten and manganese, and / or from compounds based on at least one element selected from chromium, molybdenum, tungsten and manganese, preferably at least one selected from chromic acid, chromium nitrate, tungstic acid, cesium tungstate, molybdic acid, ammonium molybdate, manganic acid and potassium permanganate.

[0099] The synergist for rhenium can be a compound of any transition metal in the periodic table, or a mixture of several transition metal compounds.

[0100] Rhenium additives and rhenium synergists can be applied to the support before, during, or after silver impregnation, or they can be applied to the support after the silver compound has been reduced. The addition of rhenium additives and rhenium synergists can further improve the activity, selectivity, and stability of the resulting silver catalyst.

[0101] According to the present invention, the amount of deionized water added can be 20 to 60 wt% of the total weight of the impregnation solution, preferably 30 to 50 wt%.

[0102] The amount of silver compound added can be 15 to 55 wt% of the total weight of the impregnation solution, preferably 25 to 40 wt%.

[0103] The amount of organic amine added can be 10 to 35 wt% of the total weight of the impregnation solution, preferably 15 to 30 wt%.

[0104] The amount of alkali metal additive added can be 0.1 to 3.0 wt% of the total weight of the impregnation solution, preferably 0.2 to 2.0 wt%.

[0105] The amount of alkaline earth metal additive added can be 0.05 to 2.0 wt% of the total weight of the impregnation solution, preferably 0.1 to 2.0 wt%.

[0106] The amount of rhenium-containing additive added can be 0.01 to 3.0 wt% of the total weight of the impregnation solution, preferably 0.05 to 1.0 wt%.

[0107] The amount of rhenium synergist added can be 0 to 2.0 wt% of the total weight of the impregnation solution, preferably 0.1 to 1.0 wt%.

[0108] According to one specific embodiment of the present invention, the weight ratio of the impregnation solution to the α-alumina carrier is 10-30:1.

[0109] In the method of the present invention, the oxygen-containing mixed gas is preferably air.

[0110] According to the present invention, the temperature of thermal decomposition can be 180 to 700°C, preferably 200 to 500°C.

[0111] The thermal decomposition time can be 0.5 to 120 minutes, preferably 1 to 60 minutes.

[0112] The present invention also provides a method for ethylene oxidation, the method comprising: ethylene undergoing an ethylene epoxidation reaction under the action of the above-mentioned silver catalyst to prepare ethylene oxide.

[0113] The reaction apparatus can be any apparatus capable of performing an epoxidation reaction.

[0114] In this invention, the term "optional" means either containing or not containing, or adding or not adding.

[0115] In this invention, the term "water" refers to one or more of deionized water, distilled water, and ultrapure water, unless otherwise specified or described.

[0116] In this invention, the term "rhenium co-compensator" is also referred to as "rhenium co-compensator" or "rhenium synergist".

[0117] 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.

[0118] The initial performance and stability of various silver catalysts of the present invention were tested using a laboratory reactor (hereinafter referred to as "microreactor") evaluation device. The reactor used in the microreactor evaluation device is a stainless steel tube with an inner diameter of 4 mm, and the reactor is placed in a heating jacket. The catalyst loading volume is 0.8 mL, with inert packing material at the bottom, so that the catalyst bed is located in the isothermal zone of the heating jacket.

[0119] The determination conditions for activity and selectivity used in this invention are shown in Table 1:

[0120] Table 1. Determination conditions for catalyst activity and selectivity

[0121]

[0122] 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:

[0123]

[0124] Where ΔEO is the difference in ethylene oxide concentration between the outlet gas and the inlet gas, and ΔCO2 is the difference in carbon dioxide concentration between the outlet gas and the inlet gas of the reactor. The average of more than 10 sets of test data is taken as the test result for that day.

[0125] Carrier preparation Comparative Example 1

[0126] 3000g of α-Al₂O₃ trihydrate, 2100g of α-Al₂O₃ pseudo-monohydrate, 300g of petroleum coke, and 40g of barium nitrate were mixed evenly in a mixer, then transferred to a kneader. 120g of petroleum jelly and a certain amount of water were added, and the mixture was kneaded to form a paste that could be extruded. The paste was extruded into seven-hole cylindrical shapes with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. These were then dried at 80–100℃ for at least 20 hours to reduce the free moisture content to below 10%. The kneaded carrier was then placed in a bell-shaped kiln and calcined at 1320℃ for 5 hours to obtain a white α-Al₂O₃ carrier.

[0127] Carrier preparation Comparative Example 2

[0128] 3000g of α-Al₂O₃ trihydrate, 2100g of α-Al₂O₃ pseudo-monohydrate, 300g of carbon powder, 2g of ammonium fluoride, and 40g of barium nitrate were mixed evenly in a mixer, then transferred to a kneader. 120g of petroleum jelly and a certain amount of water were added, and the mixture was kneaded to form a paste that could be extruded. The paste was extruded into seven-hole cylindrical shapes with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. These were then dried at 80–100℃ for at least 20 hours to reduce the free moisture content to below 10%. The kneaded carrier was then placed in a bell-shaped kiln and calcined at 1120℃ for 5 hours to obtain a white α-Al₂O₃ carrier.

[0129] Carrier preparation Comparative Example 3

[0130] 3000g of α-Al₂O₃ trihydrate, 2100g of α-Al₂O₃ pseudo-monohydrate, 300g of carbon powder, 300g of ammonium fluoride, and 40g of barium nitrate were mixed evenly in a mixer, then transferred to a kneader. 120g of petrolatum and 1800mL of dilute nitric acid (nitric acid:water = 1:5, by weight) were added, and the mixture was kneaded to form an extrudable paste. The paste was extruded into seven-hole cylindrical shapes with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. These were then dried at 80–100℃ for at least 20 hours to reduce the free moisture content to below 10%. The kneaded carrier was then placed in a bell-shaped kiln and calcined at 1100℃ for 4 hours after being heated from room temperature to 1100℃ over 32 hours to obtain a white α-Al₂O₃ carrier.

[0131] Carrier Preparation Example 1

[0132] 3000g of α-Al₂O₃ trihydrate, 2100g of Al₂O₃ pseudo-monohydrate, 300g of carbon powder, 300g of ammonium fluoride, and 40g of barium nitrate were mixed evenly in a mixer, then transferred to a kneader. 120g of petrolatum and 1800mL of dilute nitric acid (nitric acid:water = 1:5, by weight) were added, and the mixture was kneaded to form an extrudable paste. The paste was then pulverized five times using a 1800W pulverizer at 37000r / min, with each pulverization lasting 10s, to obtain a pulverized material with a particle size of 150 mesh. The pulverized material was extruded into seven-hole cylindrical shapes with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. These were then dried at 80–100℃ for at least 20 hours to reduce the free moisture content to below 10%. The kneaded carrier was placed in a bell-shaped kiln and heated from room temperature to 1100°C for 32 hours. It was then calcined at 1100°C for 4 hours to obtain a white α-Al2O3 carrier.

[0133] Carrier Preparation Example 2

[0134] 3000g of α-Al₂O₃ trihydrate, 2100g of Al₂O₃ pseudo-monohydrate, 300g of petroleum coke, 300g of ammonium fluoride, and 40g of barium nitrate were mixed evenly in a mixer, then transferred to a kneader. 120g of petroleum jelly and 1800mL of dilute nitric acid (nitric acid:water = 1:5, by weight) were added, and the mixture was kneaded to form an extrudable paste. Next, the paste was pulverized three times using a 1800W pulverizer at 37000r / min, with each pulverization lasting 5 seconds, to obtain a pulverized material with a particle size of 100 mesh. The pulverized material was extruded into seven-hole cylindrical shapes with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. These were then dried at 80–100℃ for at least 24 hours to reduce the free moisture content to below 10%. The kneaded carrier was placed in a bell-shaped kiln and heated from room temperature to 1200°C for 33 hours. It was then calcined at 1200°C for 3 hours to obtain a white α-Al2O3 carrier.

[0135] Carrier Preparation Example 3

[0136] 3000g of α-Al₂O₃ trihydrate, 2100g of Al₂O₃ pseudo-monohydrate, 300g of carbon powder, 300g of ammonium fluoride, and 40g of barium nitrate were mixed evenly in a mixer, then transferred to a kneader. 120g of petrolatum and 1800mL of dilute nitric acid (nitric acid:water = 1:5, by weight) were added, and the mixture was kneaded to form an extrudable paste. Next, the paste was pulverized once using a 1800W pulverizer at 37000r / min for 10 seconds each time, yielding a pulverized material with a particle size of 120 mesh. The pulverized material was extruded into seven-hole cylindrical shapes with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. These were then dried at 80–100℃ for at least 28 hours to reduce the free moisture content to below 10%. The kneaded carrier was placed in a bell-shaped kiln and heated from room temperature to 1000°C for 31 hours. It was then calcined at 1000°C for 4 hours to obtain a white α-Al2O3 carrier.

[0137] Carrier Preparation Example 4

[0138] 3000g of α-Al₂O₃ trihydrate, 2400g of Al₂O₃ pseudo-monohydrate, 300g of carbon powder, 300g of ammonium fluoride, and 40g of barium nitrate were mixed evenly in a mixer, then transferred to a kneader. 120g of petroleum jelly and 2000mL of dilute nitric acid (nitric acid:water = 1:5, by weight) were added, and the mixture was kneaded to form an extrudable paste. Next, the paste was pulverized seven times using a 1800W pulverizer at 37000r / min, with each pulverization lasting 10s, to obtain a pulverized material with a particle size of 200 mesh. The pulverized material was extruded into seven-hole cylindrical shapes with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. These were then dried at 80–100℃ for at least 24 hours to reduce the free moisture content to below 10%. The above-mentioned kneaded carrier was placed in a bell-shaped kiln and heated from room temperature to 1200℃ for 33 hours. It was then calcined at 1200℃ for 0.5 hours to obtain a white α-Al2O3 carrier.

[0139] Carrier Preparation Example 5

[0140] 3000g of α-Al₂O₃ trihydrate, 2400g of Al₂O₃ pseudo-monohydrate, 280g of petroleum coke, 450g of ammonium fluoride, and 40g of barium nitrate were mixed evenly in a mixer, then transferred to a kneader. 140g of petroleum jelly and 2000mL of dilute nitric acid (nitric acid:water = 1:5, by weight) were added, and the mixture was kneaded to form an extrudable paste. Next, the paste was pulverized five times using a 1800W pulverizer at 37000r / min, with each pulverization lasting 10s, to obtain a pulverized material with a particle size of 100 mesh. The pulverized material was extruded into seven-hole cylindrical shapes with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. These were then dried at 100–120℃ for at least 24 hours to reduce the free moisture content to below 10%. The kneaded carrier was placed in a bell-shaped kiln and heated from room temperature to 1200°C for 33 hours. It was then calcined at 1200°C for 3 hours to obtain a white α-Al2O3 carrier.

[0141] Carrier Preparation Example 6

[0142] 3000g of α-Al₂O₃ trihydrate, 2400g of Al₂O₃ pseudo-monohydrate, 280g of petroleum coke, 540g of ammonium fluoride, and 40g of barium nitrate were mixed evenly in a mixer, then transferred to a kneader. 140g of petroleum jelly and 2000mL of dilute nitric acid (nitric acid:water = 1:5, by weight) were added, and the mixture was kneaded to form an extrudable paste. Next, the paste was pulverized five times using a 1800W pulverizer at 37000r / min, with each pulverization lasting 10s, to obtain a pulverized material with a particle size of 150 mesh. The pulverized material was extruded into seven-hole cylindrical shapes with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. These were then dried at 100–120℃ for at least 24 hours to reduce the free moisture content to below 10%. The kneaded carrier was placed in a bell-shaped kiln and heated from room temperature to 1200°C for 33 hours. It was then calcined at 1200°C for 3 hours to obtain a white α-Al2O3 carrier.

[0143] Carrier Preparation Example 7

[0144] 3000g of α-Al₂O₃ trihydrate, 2100g of Al₂O₃ pseudo-monohydrate, 300g of carbon powder, 300g of ammonium fluoride, and 40g of barium nitrate were mixed evenly in a mixer, then transferred to a kneader. 120g of petroleum jelly and 1800mL of dilute nitric acid (nitric acid:water = 1:5, by weight) were added, and the mixture was kneaded to form an extrudable paste. The paste was then pulverized once using a 1800W pulverizer at 37000r / min for 5 seconds each time, yielding a pulverized material with a particle size of 70 mesh. The pulverized material was extruded into seven-hole cylindrical shapes with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. These were then dried at 80–100℃ for at least 20 hours to reduce the free moisture content to below 10%. The kneaded carrier was placed in a bell-shaped kiln and heated from room temperature to 1100°C for 32 hours. It was then calcined at 1100°C for 4 hours to obtain a white α-Al2O3 carrier.

[0145] Carrier Preparation Example 8

[0146] 3000g of α-Al₂O₃ trihydrate, 2100g of Al₂O₃ pseudo-monohydrate, 300g of carbon powder, 300g of ammonium fluoride, and 40g of barium nitrate were mixed evenly in a mixer, then transferred to a kneader. 120g of petrolatum and 1800mL of dilute nitric acid (nitric acid:water = 1:5, by weight) were added, and the mixture was kneaded to form an extrudable paste. The paste was then pulverized 10 times using a 1800W pulverizer at 37000r / min, with each pulverization lasting 20s, to obtain a pulverized material with a particle size of 280 mesh. The pulverized material was extruded into seven-hole cylindrical shapes with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. These were then dried at 80–100℃ for at least 20 hours to reduce the free moisture content to below 10%. The kneaded carrier was placed in a bell-shaped kiln and heated from room temperature to 1100°C for 32 hours. It was then calcined at 1100°C for 4 hours to obtain a white α-Al2O3 carrier.

[0147] Carrier Preparation Example 9

[0148] 3000g of α-Al₂O₃ trihydrate, 2100g of Al₂O₃ pseudo-monohydrate, 300g of carbon powder, 300g of ammonium fluoride, and 40g of barium nitrate were mixed evenly in a mixer, then transferred to a kneader. 120g of petroleum jelly and 1800mL of dilute nitric acid (nitric acid:water = 1:5, by weight) were added, and the mixture was kneaded to form an extrudable paste. The paste was then pulverized 8 times using a 1800W pulverizer at 37000r / min, with each pulverization lasting 5 seconds, to obtain a pulverized material with a particle size of 170 mesh. The pulverized material was extruded into seven-hole cylindrical shapes with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. These were then dried at 80–100℃ for at least 20 hours to reduce the free moisture content to below 10%. The kneaded carrier was placed in a bell-shaped kiln and heated from room temperature to 1100°C for 32 hours. It was then calcined at 1100°C for 4 hours to obtain a white α-Al2O3 carrier.

[0149] Carrier Preparation Example 10

[0150] 3000g of α-Al₂O₃ trihydrate, 2100g of Al₂O₃ pseudo-monohydrate, 300g of carbon powder, 300g of ammonium fluoride, and 40g of barium nitrate were mixed evenly in a mixer, then transferred to a kneader. 120g of petroleum jelly and 1800mL of dilute nitric acid (nitric acid:water = 1:5, by weight) were added, and the mixture was kneaded to form an extrudable paste. The paste was then pulverized 16 times using a 1800W pulverizer at 37000r / min, with each pulverization lasting 10s, to obtain a pulverized material with a particle size of 300 mesh. The pulverized material was extruded into seven-hole cylindrical shapes with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. These were then dried at 80–100℃ for at least 20 hours to reduce the free moisture content to below 10%. The kneaded carrier was placed in a bell-shaped kiln and heated from room temperature to 1100°C for 32 hours. It was then calcined at 1100°C for 4 hours to obtain a white α-Al2O3 carrier.

[0151] Catalyst preparation

[0152] Weigh 140g of silver nitrate and dissolve it in 150mL of deionized water. Weigh 64g of ammonium oxalate and dissolve it in 520mL of deionized water. After complete dissolution, two solutions are obtained: a silver nitrate solution and an ammonium oxalate solution. The two solutions are mixed under vigorous stirring, resulting in a white silver oxalate precipitate. The precipitate is aged for at least 30 minutes, filtered, and washed with deionized water until no nitrate ions are present. The filter cake contains approximately 60% silver and 15% water.

[0153] Dissolve 60.0g of ethylenediamine and 22.0g of ethanolamine in 75.0g of deionized water, add the silver oxalate filter cake prepared by the above method, and stir continuously until the silver oxalate is completely dissolved. Then add 0.88g of cesium nitrate, 0.62g of barium acetate, 0.86g of ammonium perrhenate and deionized water in sequence to make the total mass of the solution reach 400g, and prepare the impregnation solution for later use.

[0154] Take 20g of the carrier sample and place it in a vacuum-capable container. Evacuate the container to a vacuum level of 10mmHg or higher, then introduce the above impregnation solution and maintain for 30 minutes. Filter out the excess solution. Heat the impregnated carrier in an air stream at 450℃ for 3 minutes, then cool to obtain the silver catalyst.

[0155] Test Example 1

[0156] The microstructure testing methods for the supports prepared in Comparative Examples 1-3 and Examples 1-10 are as follows:

[0157] (1) Use SEM (scanning electron microscope) to take microscopic morphology photos of the carriers prepared in Comparative Examples 1-2 and Examples 1-5;

[0158] (2) The individual dimensions of the above microscopic morphology photographs were statistically analyzed, and the results were obtained according to the formula. Calculate the average size of the hexagonal surface and the average size of the quadrilateral surface Among them, M i The size of the hexagonal or quadrilateral surface is given, and n is the total number of α-alumina sheets. In this test case, n is 200.

[0159] (3) Calculate the average size of the hexagonal surface. and the average size of the quadrilateral surface The ratio S and the microstructure data of the carrier are shown in Table 2.

[0160] Table 2 Microscopic morphology data of the carrier

[0161] carrier Is alumina in flake form? S-value of a single α-alumina sheet Comparative Example 1 no - Comparative Example 2 yes 2.3 Comparative Example 3 yes 5.0 Example 1 yes 12.5 Example 2 yes 11.6 Example 3 yes 12.0 Example 4 yes 15.4 Example 5 yes 15.6 Example 6 yes 18.9 Example 7 yes 6.7 Example 8 yes 15.8 Example 9 yes 12.9 Example 10 yes 16.2

[0162] Test Example 2

[0163] The physical property data of the carriers prepared in Comparative Examples 1-3 and Examples 1-10 were tested as follows: the crushing strength of the carrier was measured using a DLⅡ type intelligent particle strength tester. The radial crushing strength of the carrier sample was measured and the average value was taken. The water absorption rate was measured by the density method. The specific surface area was measured by the nitrogen physical adsorption BET method. The physical property data of the carrier are shown in Table 3.

[0164] Table 3. Physical property data of the carrier

[0165]

[0166]

[0167] Test Example 3

[0168] The selectivity of the catalyst samples was determined using a microreactor evaluation device under the aforementioned process conditions, and the performance of the catalysts is shown in Table 4.

[0169] Table 4 Catalyst Performance

[0170]

[0171]

[0172] As shown in Table 2-4, the catalyst prepared using the support provided by the method of this invention significantly improves the selectivity of the ethylene epoxidation reaction and has broad application prospects. Furthermore, the average size of the hexagonal facets in the α-alumina monolayer support... and the average size of the quadrilateral surface The ratio S is basically directly proportional to the selectivity of silver catalyst in ethylene epoxidation, which has a positive effect on the study of silver catalyst support and ethylene epoxidation reaction.

[0173] 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.

[0174] 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 a silver catalyst used in the oxidation of ethylene to produce ethylene oxide, characterized in that, The α-alumina carrier has a sheet-like three-dimensional structure, and each α-alumina sheet has both hexagonal and quadrilateral surfaces; The average size of the hexagonal surface ( ) and the average size of the quadrilateral surface ( The ratio (S) of ) is 5~20; The size of the hexagonal face is the length of the longest diagonal of the hexagon, and the size of the quadrilateral face is the length of the shortest side of the quadrilateral; The preparation method of the α-alumina support includes the following steps: S1. A solid mixture is obtained by mixing α-Al2O3 trihydrate, Al2O3 pseudomonohydrate, an optional combustible lubricant, a mineralizer, and a compound of alkaline earth metals. S2. The solid mixture is mixed and kneaded with the binder to obtain a kneaded compound; S3. The kneaded mixture is pulverized to obtain pulverized material; S4. Extrude the pulverized material into a molded shape to obtain a molded body; S5. The molded body is dried and then calcined to obtain an α-alumina carrier; The pulverization is carried out using a pulverizer with a power of 1500-2000W, a rotation speed of 35000-40000r / min, and a pulverization frequency of 1-20 times. Each grinding session lasts from 2 seconds to 5 minutes; The particle size of the pulverized material is 50-350 mesh; The amount of the mineralizer added is 1 to 12.0 wt% of the total weight of the solid mixture.

2. The α-alumina support according to claim 1, characterized in that, The average size of the hexagonal surface ( ) and the average size of the quadrilateral surface ( The ratio (S) of ) is 6~16.

3. The α-alumina support according to claim 1, characterized in that, The average size of the hexagonal surface ( ) and the average size of the quadrilateral surface ( It was measured using the following method: 1) Take microscopic morphology photographs of α-alumina single pieces using a scanning electron microscope; 2) The individual dimensions of the microscopic morphology photographs are statistically analyzed according to the formula. Calculate the average size of the hexagonal surface ( ) and the average size of the quadrilateral surface ( ); Among them, M i denoted as the size of the hexagonal or quadrilateral surface, and n is the total number of α-alumina sheets.

4. The α-alumina support according to any one of claims 1-3, characterized in that, The α-alumina carrier has a crushing strength of 30~280 N / particle and a specific surface area of ​​0.3~6 m². 2 / g; water absorption rate is 30~75%.

5. The α-alumina support according to claim 4, characterized in that, The α-alumina carrier has a crushing strength of 80~180 N / particle and a specific surface area of ​​0.6~3 m². 2 / g; water absorption rate is 50~70%.

6. A method for preparing an α-alumina support according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: S1. A solid mixture is obtained by mixing α-Al2O3 trihydrate, Al2O3 pseudomonohydrate, an optional combustible lubricant, a mineralizer, and a compound of alkaline earth metals. S2. The solid mixture is mixed and kneaded with the binder to obtain a kneaded compound; S3. The kneaded mixture is pulverized to obtain pulverized material; S4. Extrude the pulverized material into a molded shape to obtain a molded body; S5. The molded body is dried and then calcined to obtain an α-alumina carrier; The pulverization is carried out using a pulverizer with a power of 1500-2000W, a rotation speed of 35000-40000r / min, and a pulverization frequency of 1-20 times. Each grinding session lasts from 2 seconds to 5 minutes; The particle size of the pulverized material is 50-350 mesh; The amount of the mineralizer added is 1 to 12.0 wt% of the total weight of the solid mixture.

7. The preparation method according to claim 6, characterized in that, The amount of the trihydrate α-Al₂O₃ added is 10-85 wt% of the total weight of the solid mixture; The amount of the pseudo-monohydrate Al₂O₃ added is 10-55 wt% of the total weight of the solid mixture; The amount of the combustible lubricant added is 0-20 wt% of the total weight of the solid mixture; The amount of the alkaline earth metal compound added is 0.01 to 5.0 wt% of the total weight of the solid mixture.

8. The preparation method according to claim 6, characterized in that, The amount of the trihydrate α-Al₂O₃ added is 28-82 wt% of the total weight of the solid mixture; The amount of the pseudo-monohydrate Al2O3 added is 15-50 wt% of the total weight of the solid mixture; The amount of the combustible lubricant added is 0.1~15.0 wt% of the total weight of the solid mixture; The amount of the mineralizer added is 4-10 wt% of the total weight of the solid mixture; The amount of the alkaline earth metal compound added is 0.05 to 2.0 wt% of the total weight of the solid mixture.

9. The preparation method according to claim 6, characterized in that, The amount of the mineralizer added is 5.1-7.5 wt% of the total weight of the solid mixture.

10. The preparation method according to claim 6, characterized in that, The combustible lubricant is selected from at least one of petroleum coke, carbon powder, graphite and petroleum jelly; The mineralizing agent is selected from at least one of hydrogen fluoride, ammonium fluoride, ammonium chloride, boric acid, barium fluoride, calcium fluoride, aluminum fluoride, cryolite, magnesium fluoride, and lithium fluoride. The alkaline earth metal compound is selected from at least one of oxides, nitrates, acetates, oxalates, and sulfates of strontium and / or barium.

11. The preparation method according to claim 6, characterized in that, The amount of the adhesive used is 25-60 wt% of the total weight of the solid mixture; The adhesive is an acid.

12. The preparation method according to claim 11, characterized in that, The adhesive is an aqueous solution of nitric acid, wherein the weight ratio of nitric acid to water in the aqueous solution is 1:1.25~10.

13. The preparation method according to claim 6, characterized in that, The number of pulverization cycles is 2-16; the pulverization time for each cycle is 5-60 seconds. The particle size of the pulverized material is 70-300 mesh.

14. The preparation method according to claim 6, characterized in that, The molded body is dried to a moisture content of no more than 10 wt%, and the shape of the molded body is selected from any one of ring, sphere, column, and porous column. The drying temperature is 20-120℃; The drying time is 20-48 hours; The roasting includes programmed heating and optional isothermal roasting; The temperature rise rate of the programmed temperature rise is 2-10 °C / min; The constant temperature calcination temperature is 900-1600 ℃; The constant temperature calcination time is 0-20 h.

15. The preparation method according to claim 14, characterized in that, The constant temperature calcination temperature is 950-1500℃; The constant temperature calcination time is 0.1-15 h.

16. An α-alumina support prepared by any one of claims 6-15.

17. A silver catalyst for the oxidation of ethylene to produce ethylene oxide, characterized in that, The silver catalyst comprises: a) The α-alumina support according to any one of claims 1 to 5, 16; b) Silver deposited on the α-alumina support; c) Alkali metals and / or alkali metal-based compounds; d) Alkaline earth metals and / or compounds based on alkaline earth metals; e) Rhenium metal and / or rhenium-based compounds; f) Optional rhenium synergists.

18. The silver catalyst according to claim 17, characterized in that, Based on the total weight of the silver catalyst, the silver content is 1~50 wt%; The mass content of alkali metals is 5~3000 ppm; The mass content of alkaline earth metals is 50~20000 ppm; The mass content of rhenium metal is 10~2000 ppm; The content of rhenium as a synergist is 0~1500 ppm, calculated as metal in the synergist.

19. The silver catalyst according to claim 17, characterized in that, Based on the total weight of the silver catalyst, the silver content is 5-40 wt%; The alkali metal content is 10~2000 ppm; The mass content of alkaline earth metals is 100~15000 ppm; The mass content of rhenium metal is 100~1500 ppm; The content of rhenium as a synergist is 5 to 1000 ppm, calculated as metal in the synergist.

20. The silver catalyst according to any one of claims 17-19, characterized in that, The alkali metal compound is selected from at least one of the nitrates, sulfates and hydroxides of the alkali metal element; The alkaline earth metal compound is selected from at least one of the oxides, oxalates, sulfates, acetates, and nitrates of alkaline earth metal elements. The rhenium-based compound is selected from at least one of rhenium oxides, perrhenic acid, and perrhenate. The rhenium synergist is selected from at least one metal selected from chromium, molybdenum, tungsten and manganese, and / or selected from compounds based on at least one element selected from chromium, molybdenum, tungsten and manganese.

21. The silver catalyst according to claim 20, characterized in that, The alkali metal compound is cesium sulfate and / or cesium nitrate; The alkaline earth metal compound is barium acetate and / or strontium acetate. The rhenium-based compounds are perrhenic acid and perrhenate; Compounds based on at least one of chromium, molybdenum, tungsten and manganese are at least one of chromic acid, chromium nitrate, tungstic acid, cesium tungstate, molybdic acid, ammonium molybdate, manganic acid and potassium permanganate.

22. A method for preparing a silver catalyst according to any one of claims 17-21, characterized in that, The method includes the following steps: 1) Add silver compounds, organic amines, alkali metal additives, alkaline earth metal additives, rhenium-containing additives and optional rhenium synergists to deionized water to prepare an impregnation solution; 2) Impregnate the α-alumina carrier with an impregnation solution; 3) Filter out excess impregnation solution and dry the impregnated α-alumina support; 4) The impregnated α-alumina support is thermally decomposed in an oxygen-containing mixed gas to prepare the silver catalyst.

23. The method for preparing the silver catalyst according to claim 22, characterized in that, The silver compound is selected from at least one of silver oxalate, silver oxide, and silver nitrate; The organic amine is selected from at least one of pyridine, butylamine, ethylenediamine, 1,3-propanediamine and ethanolamine; The alkali metal auxiliaries are selected from at least one of alkali metals and alkali metal-based compounds, wherein the alkali metal-based compounds are selected from at least one of nitrates, sulfates and hydroxides of alkali metal elements. The alkaline earth metal auxiliary is selected from at least one of alkaline earth metals and alkaline earth metal-based compounds, wherein the alkaline earth metal-based compounds are selected from at least one of oxides, oxalates, sulfates, acetates and nitrates of alkaline earth metal elements. The rhenium-containing additive is selected from at least one of rhenium metal and rhenium-based compounds, and the rhenium-based compounds are selected from at least one of rhenium oxides, perrhenic acid and perrhenate. The synergist for rhenium is selected from at least one metal selected from chromium, molybdenum, tungsten and manganese, and / or from compounds based on at least one element selected from chromium, molybdenum, tungsten and manganese.

24. The method for preparing the silver catalyst according to claim 22, characterized in that, The silver compound is silver nitrate; The organic amine is a mixture of ethylenediamine and ethanolamine; The alkali metal-based compound is cesium sulfate and / or cesium nitrate; The alkaline earth metal-based compound is barium acetate and / or strontium acetate; The rhenium-based compound is perrhenic acid and / or perrhenate; Compounds based on at least one of chromium, molybdenum, tungsten and manganese are at least one of chromic acid, chromium nitrate, tungstic acid, cesium tungstate, molybdic acid, ammonium molybdate, manganic acid and potassium permanganate.

25. The method for preparing the silver catalyst according to claim 22, characterized in that, The amount of deionized water added is 20-60 wt% of the total weight of the impregnation solution. The amount of the silver compound added is 15-55 wt% of the total weight of the impregnation solution; The amount of organic amine added is 10-35 wt% of the total weight of the impregnation solution; The amount of the alkali metal additive added is 0.1~3.0 wt% of the total weight of the impregnation solution; The amount of the alkaline earth metal additive added is 0.05~2.0 wt% of the total weight of the impregnation solution; The amount of the rhenium-containing additive added is 0.01~3.0 wt% of the total weight of the impregnation solution; The amount of rhenium synergist added is 0~2.0 wt% of the total weight of the impregnation solution; The weight ratio of the impregnation solution to the α-alumina carrier is 10-30:1; The temperature of the thermal decomposition is 180~700 ℃; The thermal decomposition time is 0.5 to 120 minutes.

26. The method for preparing the silver catalyst according to claim 22, characterized in that, The amount of deionized water added is 30-50 wt% of the total weight of the impregnation solution; The amount of the silver compound added is 25-40 wt% of the total weight of the impregnation solution; The amount of organic amine added is 15-30 wt% of the total weight of the impregnation solution; The amount of the alkali metal additive added is 0.2~2.0 wt% of the total weight of the impregnation solution; The amount of the alkaline earth metal additive added is 0.1~2.0 wt% of the total weight of the impregnation solution; The amount of the rhenium-containing additive added is 0.05~1.0 wt% of the total weight of the impregnation solution; The amount of rhenium synergist added is 0.1~1.0 wt% of the total weight of the impregnation solution; The oxygen-containing mixed gas is air; The temperature of the thermal decomposition is 200~500 ℃; The thermal decomposition time is 1 to 60 minutes.

27. A method for ethylene oxidation, characterized in that, The method includes: carrying out an ethylene epoxidation reaction in the presence of a silver catalyst as described in any one of claims 17-21 to prepare ethylene oxide.

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