Alpha-alumina support, method for preparing the same, and silver catalyst and method for producing ethylene oxide by ethylene epoxidation

Abstract

This invention belongs to the field of industrial catalysts, and relates to an α-alumina support and its preparation method, as well as a method for producing ethylene oxide via silver catalyst and ethylene epoxidation. The α-alumina support has the following characteristics: α-Al₂O₃ content is above 90% by weight; crushing strength is 80–200 N / particle; specific surface area is 1.0–3.0 m² / particle. 2 / g; water absorption rate 30-70%; pore volume 0.30-0.75mL / g; the pore distribution curve has a bimodal structure, including macropore peaks and micropore peaks, with pores of 1.5-2.5μm accounting for more than 95% of the total pore volume of the micropore peaks; and plate-like crystals with a crystal size of 3-5μm accounting for more than 90% of the total plate-like crystals. Compared with the prior art, the silver catalyst prepared on the α-alumina support provided by this invention, when used for the oxidation of ethylene to ethylene oxide, has the advantages of higher selectivity and stability while ensuring activity.

Description

Technical Field

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

[0002] Under the action of a silver catalyst, ethylene oxidation mainly 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.

[0003] The performance of silver catalysts is not only closely related to the composition and preparation method of the catalyst, but also to the performance of the support and the preparation method used for the catalyst. Currently, α-alumina is generally used as the support for silver catalysts. The pores of alumina supports can be divided into three types: (1) intergranular pores of primary particles in alumina raw materials, which are mainly dehydration pores of alumina raw material grains, and are basically gaps between parallel plates with a size of 1-2 nm; (2) intergranular pores of secondary particles in alumina raw materials, which change with the crystal phase during calcination and are pores larger than tens of nanometers; (3) defect pores and macropores generated during the forming of pore-forming agents and supports.

[0004] Existing technologies primarily adjust the carrier pore structure by modifying the type, particle size, and dosage of the pore-forming agent, while paying less attention to the influence of the calcination atmosphere on the pore structure. Commonly used pore-forming agents, such as starch, petroleum coke, carbon powder, guar gum powder, coconut shell charcoal, and sawdust, are often affected by their place of origin, resulting in unstable quality and a wide particle size distribution, which is not conducive to achieving uniform and controllable carrier pore structure. When using organic polymer pore-forming agents with uniform and controllable particle size, the uniformity of pore formation can be improved to a certain extent, but the impact on the deposition pores between secondary alumina particles is limited. Summary of the Invention

[0005] In view of the aforementioned state of the prior art, the inventors of this invention have conducted extensive and in-depth research in the field of silver catalyst and its support preparation. The results show that the calcination atmosphere of the support affects the growth of crystal particles during the alumina phase transformation process, thereby affecting the pore structure of the support. When the oxygen content in the calcination atmosphere is higher than that in air, the difference in the growth rate of crystal particles is smaller, and the pore size distribution of the interparticle packing pores is narrower. When the silver catalyst prepared from this support is used for the oxidation of ethylene to ethylene oxide, its selectivity and stability are significantly improved while maintaining its activity. Based on this, the purpose of this invention is to provide a method for preparing an α-alumina support, a silver catalyst for ethylene epoxidation prepared by this method, and a method for ethylene oxidation. The α-alumina support of this invention, after being loaded with silver and preferably various active components to prepare a silver catalyst, exhibits good selectivity and stability in the process of ethylene oxidation to ethylene oxide.

[0006] To achieve the objectives of this invention, a first aspect of the invention provides an α-alumina support having the following characteristics: an α-Al₂O₃ content of 90% by weight or more; a crushing strength of 80–200 N / particle, preferably 100–180 N / particle; and a specific surface area of ​​1.0–3.0 m². 2 / g, preferably 1.5~2.5m 2 / g; water absorption rate of 30-70%, preferably 45-70%; pore volume of 0.30-0.75mL / g, preferably 0.45-0.70mL / g; pore distribution curve has a bimodal structure, including macropore peak and micropore peak, in which pores with a diameter of 1.5-2.5μm account for more than 95% of the total pore volume of micropore peak; and plate-like crystals with a crystal size of 3-5μm account for more than 90% of the total plate-like crystals.

[0007] A second aspect of the present invention provides a method for preparing an α-alumina support, comprising the following steps:

[0008] (1) Prepare a solid mixture having the following components: α-Al2O3 trihydrate, Al2O3 pseudo-monohydrate, organic polymer pore-forming agent, combustible lubricant, fluoride mineralizer and alkaline earth metal compound;

[0009] (2) The solid mixture, binder and water obtained in step (1) are mixed, kneaded and extruded to obtain a molded body;

[0010] (3) The molded body obtained in step (2) is dried and calcined in an atmosphere of oxygen and air mixture to obtain the carrier;

[0011] Among them, based on the total flow rate of the mixture of oxygen and air, the flow rate of oxygen is 5-85%, preferably 20-60%.

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

[0013] A fourth aspect of the present invention provides a silver catalyst for ethylene epoxidation, comprising:

[0014] a) the α-alumina support described above;

[0015] b) The active component silver deposited on the α-alumina support;

[0016] c) Alkali metals and / or alkaline earth metals, or compounds based on alkali metals and / or alkaline earth metals;

[0017] d) Rhenium metal and / or rhenium-based compounds; and

[0018] e) Optionally, the rhenium co-catalyst is selected from at least one metal selected from chromium, molybdenum, tungsten and manganese, and / or selected from compounds based on at least one metal selected from chromium, molybdenum, tungsten and manganese.

[0019] A fifth aspect of the present invention provides a method for producing ethylene oxide by epoxidation of ethylene, the method comprising: epoxidation of ethylene in the presence of the silver catalyst to obtain ethylene oxide.

[0020] This invention utilizes the influence of the calcination atmosphere on the growth of crystal particles during the alumina phase transformation process, thereby affecting the pore structure of the support. When the oxygen content in the calcination atmosphere is higher than that in air, the difference in the growth rate of crystal particles is smaller, and the pore size distribution of the inter-particle packing pores is narrower. Compared with existing technologies, the silver catalyst prepared on the α-alumina support provided by this invention, when used for the oxidation of ethylene to ethylene oxide, exhibits higher selectivity and stability while maintaining activity. Studying the influence of the calcination atmosphere on the pore structure and further improving the controllability of the pore distribution is of great significance for the research of silver catalysts and α-alumina supports.

[0021] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0022] 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.

[0023] To achieve the objectives of this invention, a first aspect of the invention provides an α-alumina support having the following characteristics: an α-Al₂O₃ content of 90% by weight or more; a crushing strength of 80–200 N / particle, preferably 100–180 N / particle; and a specific surface area of ​​1.0–3.0 m². 2 / g, preferably 1.5~2.5m2 / g; water absorption rate of 30-70%, preferably 45-70%; pore volume of 0.30-0.75mL / g, preferably 0.45-0.70mL / g; pore distribution curve has a bimodal structure, including macropore peak and micropore peak, in which pores with a diameter of 1.5-2.5μm account for more than 95% of the total pore volume of micropore peak; and plate-like crystals with a crystal size of 3-5μm account for more than 90% of the total plate-like crystals.

[0024] According to the present invention, preferably, the peak value of the large pore peak is 5.0 to 25.0 μm, and the peak value of the small pore peak is 1.6 to 2.3 μm.

[0025] A second aspect of the present invention provides a method for preparing an α-alumina support, comprising the following steps:

[0026] (1) Prepare a solid mixture having the following components: α-Al2O3 trihydrate, Al2O3 pseudo-monohydrate, organic polymer pore-forming agent, combustible lubricant, fluoride mineralizer and alkaline earth metal compound;

[0027] (2) The solid mixture, binder and water obtained in step (1) are mixed, kneaded and extruded to obtain a molded body;

[0028] (3) The molded body obtained in step (2) is dried and calcined in an atmosphere of mixed oxygen and air to obtain the carrier;

[0029] Among them, based on the total flow rate of the oxygen and air mixture, the oxygen flow rate is 5-85%, preferably 20-60%.

[0030] In this invention, the calcination atmosphere of the carrier affects the growth of crystal particles during the alumina phase transformation process, thereby influencing the carrier's pore structure. When the oxygen content in the calcination atmosphere is higher than that in air, the difference in the growth rate of crystal particles is smaller, and the pore size distribution of the interparticle-packed pores is narrower. The carrier calcined in the aforementioned specific atmosphere exhibits a smaller difference in the growth rate of crystal particles and a narrower pore size distribution among the interparticle-packed pores. It is worth noting that when the oxygen content in the calcination atmosphere is too high, substances such as organic polymer pore-forming agents and combustible lubricants decompose too quickly during the calcination process, which is detrimental to the formation of a narrower pore size distribution.

[0031] In this invention, the solid mixture is kneaded with a binder to obtain a paste, which is then extruded to form a molded body. The molded body can be dried to a water content of less than 10%, and the carrier shape can be ring-shaped, spherical, cylindrical, or porous cylindrical. The drying temperature is 80–120°C, and the drying time is controlled between 1 and 24 hours depending on the moisture content.

[0032] According to the present invention, preferably, in step (3), the roasting is carried out in an atmosphere furnace in which oxygen and air can be independently introduced, and the total flow rate of the oxygen and air mixture is 50 to 400 L / min per cubic meter of effective furnace volume, preferably 100 to 300 L / min per cubic meter of effective furnace volume.

[0033] According to the present invention, preferably, in step (3), the calcination temperature is 1200-1400℃.

[0034] In this invention, the highest calcination temperature is 1200-1400℃, and calcination causes all alumina to be converted into α-Al2O3.

[0035] According to the present invention, preferably, in step (1), the particle size of the trihydrate α-Al2O3 is 25-300 μm, and the particle size of the pseudomonohydrate Al2O3 is less than 100 μm; based on the total weight of the solid mixture, the amount of the trihydrate α-Al2O3 added is 10-85 wt%, preferably 20-82 wt%; the amount of the pseudomonohydrate Al2O3 added is 10-55 wt%, preferably 15-45 wt%.

[0036] In this invention, the pseudo-al2O3 reacts with acid during the kneading process to transform into a sol, which acts as a binder. During the high-temperature calcination process, it is also transformed into stable α-al2O3, becoming part of the α-al2O3 carrier.

[0037] According to the present invention, preferably, in step (1), the organic polymer pore-forming agent is selected from at least one of polymethyl methacrylate, polystyrene, polycarbonate, polyamide and polyvinyl alcohol; the diameter or equivalent diameter of the organic polymer pore-forming agent is 0.5 to 80 μm, preferably 5 to 50 μm; and the amount of the organic polymer pore-forming agent added is 0.1 to 25 wt%, preferably 1.0 to 10 wt%, based on the total weight of the solid mixture.

[0038] In this invention, the organic polymer pore-forming agent has a uniform and controllable particle size and can be completely decomposed during the carrier calcination process without introducing new impurities.

[0039] According to the present invention, preferably, in step (1), the combustible lubricant is petrolatum and / or white oil; based on the total weight of the solid mixture, the amount of the combustible lubricant added is 0.01 to 8.0 wt%, preferably 0.1 to 5.0 wt%.

[0040] In this invention, the addition of combustible lubricating material is to make the kneaded material easier to shape and granulate. At the same time, an oxidation reaction occurs during the roasting process of the material, generating gas that escapes. When making the carrier, no impurities are introduced or as few as possible are introduced, so as not to affect the performance of the catalyst.

[0041] According to the present invention, preferably, in step (1), the fluoride mineralizer is at least one of hydrogen fluoride, aluminum fluoride, ammonium fluoride, magnesium fluoride and cryolite; based on the total weight of the solid mixture, the amount of the fluoride mineralizer added is 0.05 to 8.0 wt%, preferably 0.5 to 5.0 wt%.

[0042] In this invention, the addition of fluoride mineralizers accelerates the crystal transformation of alumina, enabling gas-phase mass transfer crystal growth.

[0043] According to the present invention, preferably, in step (1), the alkaline earth metal compound is at least one of oxides, nitrates, acetates, oxalates and sulfates of strontium and / or barium; the amount of alkaline earth metal compound added is 0.01 to 5.0 wt%, preferably 0.05 to 2.0 wt%, based on the total weight of the solid mixture.

[0044] In this invention, the alkaline earth metal compound is an oxide, nitrate, acetate, oxalate, or sulfate of strontium and / or barium, which serves to improve the performance of the carrier.

[0045] According to the present invention, preferably, in step (2), the binder is an acid, which is provided in the form of an aqueous solution of the acid, 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:(1.25-10); the amount of the binder is 25-60 wt% of the total amount of the solid mixture; preferably, the binder and pseudo-monohydrate Al2O3 are wholly or partially replaced by aluminum sol.

[0046] In this invention, a binder and pseudo-monohydrate Al2O3 in the mixture are added to generate an aluminum sol, which binds the components together to form a paste that can be extruded.

[0047] A third aspect of the present invention provides an α-alumina support prepared by the aforementioned preparation method.

[0048] 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 boiling method. The specific surface area is determined by the nitrogen physical adsorption BET method. The pore volume and pore distribution are determined by the mercury porosimetry method.

[0049] A fourth aspect of the present invention provides a silver catalyst for ethylene epoxidation, comprising:

[0050] a) the α-alumina support described above;

[0051] b) The active component silver deposited on the α-alumina support;

[0052] c) Alkali metals and / or alkaline earth metals, or compounds based on alkali metals and / or alkaline earth metals;

[0053] d) Rhenium metal and / or rhenium-based compounds; and

[0054] e) Optionally, the rhenium co-catalyst is selected from at least one metal selected from chromium, molybdenum, tungsten and manganese, and / or selected from compounds based on at least one metal selected from chromium, molybdenum, tungsten and manganese.

[0055] According to one embodiment of the present invention, in the above-mentioned silver catalyst, based on the total weight of the catalyst, the mass content of silver is 5-37%, preferably 8-32%; the mass content of alkali metal is 5-3000 ppm, preferably 10-2000 ppm; the mass content of alkaline earth metal is 50-20000 ppm, preferably 100-15000 ppm; the mass content of rhenium metal is 10-2000 ppm, preferably 100-1500 ppm; and the content of co-auxiliaries, calculated based on the metals in the co-auxiliaries, is 0-1500 ppm, preferably 5-1000 ppm.

[0056] The silver catalyst of the present invention can be prepared in a conventional manner, for example, by impregnating the above-mentioned alumina support with a solution containing a silver compound, an organic amine, an alkali metal promoter, an alkaline earth metal promoter, a rhenium-containing promoter, and optionally a co-promoter. The organic amine compound can be any organic amine compound suitable for preparing a silver catalyst for ethylene oxide production, as long as it can form a silver amine complex with the silver compound, such as pyridine, butylamine, ethylenediamine, 1,3-propanediamine, ethanolamine, or mixtures thereof, preferably a mixture of ethylenediamine and ethanolamine.

[0057] The alkali metal auxiliaries may be compounds of lithium, sodium, potassium, rubidium or cesium or compounds of any one thereof, such as their nitrates, sulfates or hydroxides, or any combination of two or more of the aforementioned compounds, preferably cesium sulfate and / or cesium nitrate.

[0058] The alkaline earth metal additive may be a compound of magnesium, calcium, strontium, or barium, such as their oxides, oxalates, sulfates, acetates, or nitrates, or any combination of two or more of the aforementioned compounds, preferably a barium or strontium compound, more preferably barium acetate and / or strontium acetate. The alkaline earth metal additive may be applied to the carrier before, simultaneously with, or after impregnation with silver, or it may be applied to the carrier after the silver compound has been reduced.

[0059] The rhenium additive may be an oxide of rhenium, perrhenic acid, perrhenate, or a mixture thereof, preferably perrhenic acid and perrhenate, such as perrhenic acid, cesium perrhenate, and ammonium perrhenate.

[0060] The rhenium additive and its co-promoter can be a compound of any transition metal in the periodic table, or a mixture of several transition metal compounds, preferably one or more metals selected from chromium, molybdenum, tungsten, and manganese, and / or compounds based on one or more of chromium, molybdenum, tungsten, and manganese, such as chromic acid, chromium nitrate, tungstic acid, cesium tungstate, molybdic acid, ammonium molybdate, manganic acid, and potassium permanganate. The rhenium additive and its co-promoter can be applied to the support before, simultaneously with, or after impregnation of silver, or after the silver compound has been reduced. The addition of the rhenium additive and its co-promoter can further improve the activity, selectivity, and stability of the resulting silver catalyst. "Optionally, the co-promoter of the rhenium additive" indicates that it can be a co-promoter containing rhenium additive or a co-promoter without rhenium additive.

[0061] According to a specific embodiment of the present invention, the preparation method of the silver catalyst includes the following steps:

[0062] 1) Impregnate the above porous α-alumina support with a solution containing sufficient amounts of silver compound, organic amine, alkali metal auxiliaries, alkaline earth metal auxiliaries, rhenium-containing auxiliaries and their co-auxiliaries;

[0063] 2) Filter out the impregnation solution and dry the impregnated carrier; and

[0064] 3) The support obtained in step 2) is activated in an oxygen-containing mixed gas to prepare the silver catalyst.

[0065] In the preparation of the silver catalyst of the present invention, silver oxalate is first generated by mixing silver nitrate with ammonium oxalate solution, silver oxalate is dissolved in organic amine to form silver amine solution, and the above-mentioned auxiliary agent is added to prepare impregnation solution; then the above-mentioned α-alumina support is soaked in the prepared impregnation solution, drained, and thermally decomposed in an air stream or a nitrogen-oxygen mixture with an oxygen content of not more than 21% (e.g., containing 8.0% oxygen) for 0.5 to 120 minutes, preferably 1 to 60 minutes, within a temperature range of 180 to 700°C, preferably 200 to 500°C, to produce the finished silver catalyst.

[0066] A fifth aspect of the present invention provides a method for producing ethylene oxide by epoxidation of ethylene, the method comprising: epoxidation of ethylene in the presence of the silver catalyst to obtain ethylene oxide.

[0067] 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.

[0068] In the following embodiments and comparative examples:

[0069] Various silver catalysts were evaluated using a laboratory reactor (hereinafter referred to as "microreactor") to test their initial performance and stability. The microreactor evaluation apparatus used a stainless steel tube with an inner diameter of 4 mm, which was placed in a heating mantle. The catalyst was packed in 1 mL volume, with inert packing material at the bottom, so that the catalyst bed was located in the isothermal zone of the heating mantle.

[0070] The assay conditions for activity and selectivity used are shown in Table 1:

[0071] Table 1

[0072]

[0073] 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 S is calculated using the following formula:

[0074]

[0075] Wherein, ΔEO is the difference in ethylene oxide concentration between the reactor outlet gas and the inlet gas, and ΔCO2 is the difference in carbon dioxide concentration between the reactor outlet gas and the inlet gas. The average of more than 10 sets of test data is taken as the test result for that day.

[0076] Crushing strength of alumina carrier: The radial crushing strength of alumina carrier samples was measured using a DLⅡ type intelligent particle strength tester, and the average value was taken.

[0077] Water absorption rate: determined by boiling method.

[0078] Specific surface area: determined by the nitrogen physical adsorption BET method.

[0079] Pore ​​volume and pore distribution: determined by mercury porosimetry.

[0080] Examples 1-5 illustrate the preparation of the alumina support provided by the present invention.

[0081] Example 1

[0082] 300g of α-Al₂O₃ trihydrate (25-300μm), 240g of Al₂O₃ pseudomonohydrate (less than 100μm), 30g of polymethyl methacrylate (PMMA) with a diameter of 30μm, 12g of aluminum fluoride, and 4g of barium nitrate were mixed evenly in a mixer. The mixture was then transferred to a kneader, where 14g of petrolatum and 200ml of dilute nitric acid (nitric acid:water = 1:5, by weight) were added. 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. The extruded materials were dried at 80-120℃ for at least 2 hours to reduce the free water content to below 10%. The kneaded carrier was placed in an atmosphere furnace capable of simultaneously introducing oxygen and air. The oxygen flow rate was 80 L / min and the air flow rate was 120 L / min per cubic meter of effective furnace volume. The temperature was raised from room temperature to 1300 °C over 27 hours, and then calcined at 1300 °C for 5 hours to obtain a white α-Al₂O₃ carrier. The measured physical properties of the carrier are shown in Table 2 below.

[0083] Example 2

[0084] 300g of α-Al₂O₃ trihydrate (25-300μm), 240g of Al₂O₃ pseudomonohydrate (less than 100μm), 30g of polymethyl methacrylate (PMMA) with a diameter of 30μm, 12g of aluminum fluoride, and 4g of barium nitrate were mixed evenly in a mixer. The mixture was then transferred to a kneader, where 14g of petrolatum and 200ml of dilute nitric acid (nitric acid:water = 1:5, by weight) were added. 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. The extruded materials were dried at 80-120℃ for at least 2 hours to reduce the free water content to below 10%. The kneaded carrier was placed in an atmosphere furnace capable of simultaneously introducing oxygen and air. The oxygen flow rate was 40 L / min and the air flow rate was 160 L / min per cubic meter of effective furnace volume. The temperature was raised from room temperature to 1300 °C over 27 hours, and then calcined at 1300 °C for 5 hours to obtain a white α-Al₂O₃ carrier. The measured physical properties of the carrier are shown in Table 2 below.

[0085] Example 3

[0086] 300g of α-Al₂O₃ trihydrate (25-300μm), 240g of Al₂O₃ pseudomonohydrate (less than 100μm), 30g of polymethyl methacrylate (PMMA) with a diameter of 30μm, 12g of aluminum fluoride, and 4g of barium nitrate were mixed evenly in a mixer. The mixture was then transferred to a kneader, where 14g of petrolatum and 200ml of dilute nitric acid (nitric acid:water = 1:5, by weight) were added. 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. The extruded materials were dried at 80-120℃ for at least 2 hours to reduce the free water content to below 10%. The kneaded carrier was placed in an atmosphere furnace capable of simultaneously introducing oxygen and air. The oxygen flow rate was 120 L / min and the air flow rate was 80 L / min per cubic meter of effective furnace volume. The temperature was raised from room temperature to 1300 °C over 27 hours, and then calcined at 1300 °C for 5 hours to obtain a white α-Al₂O₃ carrier. The measured physical properties of the carrier are shown in Table 2 below.

[0087] Example 4

[0088] 300g of α-Al₂O₃ trihydrate (25-300μm), 240g of Al₂O₃ pseudomonohydrate (less than 100μm), 30g of polymethyl methacrylate (PMMA) with a diameter of 30μm, 12g of aluminum fluoride, and 4g of barium nitrate were mixed evenly in a mixer. The mixture was then transferred to a kneader, where 14g of petrolatum and 200ml of dilute nitric acid (nitric acid:water = 1:5, by weight) were added. 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. The extruded materials were dried at 80-120℃ for at least 2 hours to reduce the free water content to below 10%. The kneaded carrier was placed in an atmosphere furnace capable of simultaneously introducing oxygen and air. The oxygen flow rate was 40 L / min and the air flow rate was 60 L / min per cubic meter of effective furnace volume. The temperature was raised from room temperature to 1300 °C over 27 hours, and then calcined at 1300 °C for 5 hours to obtain a white α-Al₂O₃ carrier. The measured physical properties of the carrier are shown in Table 2 below.

[0089] Example 5

[0090] 300g of α-Al₂O₃ trihydrate (25-300μm), 240g of Al₂O₃ pseudomonohydrate (less than 100μm), 30g of polymethyl methacrylate (PMMA) with a diameter of 30μm, 12g of aluminum fluoride, and 4g of barium nitrate were mixed evenly in a mixer. The mixture was then transferred to a kneader, where 14g of petrolatum and 200ml of dilute nitric acid (nitric acid:water = 1:5, by weight) were added. 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. The extruded materials were dried at 80-120℃ for at least 2 hours to reduce the free water content to below 10%. The kneaded carrier was placed in an atmosphere furnace capable of simultaneously introducing oxygen and air. The oxygen flow rate was 120 L / min and the air flow rate was 180 L / min per cubic meter of effective furnace volume. The temperature was raised from room temperature to 1300 °C over 27 hours, and then calcined at 1300 °C for 5 hours to obtain a white α-Al₂O₃ carrier. The measured physical properties of the carrier are shown in Table 2 below.

[0091] Examples 6-10 illustrate the preparation of the silver catalyst provided by the present invention.

[0092] Example 6

[0093] 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 thorough dissolution, silver nitrate solution and ammonium oxalate solution are obtained. The two solutions are mixed under vigorous stirring to form 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 by weight and approximately 15% water by weight.

[0094] Dissolve 70.0g of ethylenediamine 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 2.58g of cesium nitrate, 6.22g 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.

[0095] Take 20g of the support sample prepared in Example 1, place it in a vacuum-capable container, evacuate to a vacuum level of 10mmHg or higher, introduce the above impregnation solution, maintain for 30min, and filter out excess solution. Heat the impregnated support in an air stream at 450℃ for 3min, then cool to obtain silver catalyst C-1.

[0096] Example 7

[0097] Same as Example 6, except that the support sample prepared in Example 2 was used instead of the support sample prepared in Example 1. The resulting silver catalyst was C-2.

[0098] Example 8

[0099] Same as Example 6, except that the support sample prepared in Example 3 was used instead of the support sample prepared in Example 1. The resulting silver catalyst was C-3.

[0100] Example 9

[0101] Same as Example 6, except that the support sample prepared in Example 4 was used instead of the support sample prepared in Example 1. The resulting silver catalyst was C-4.

[0102] Example 10

[0103] Same as Example 6, except that the support sample prepared in Example 5 was used instead of the support sample prepared in Example 1. The resulting silver catalyst was C-5.

[0104] Comparative Example 1

[0105] This comparative example is used to illustrate the preparation of the reference alumina support.

[0106] 300g of α-Al₂O₃ trihydrate (25-300μm), 240g of Al₂O₃ pseudomonohydrate (less than 100μm), 30g of polymethyl methacrylate (PMMA) with a diameter of 30μm, 12g of aluminum fluoride, and 4g of barium nitrate were mixed evenly in a mixer. The mixture was then transferred to a kneader, where 14g of petrolatum and 200ml of dilute nitric acid (nitric acid:water = 1:5, by weight) were added. 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. The extruded materials were dried at 80-120℃ for at least 2 hours to reduce the free water content to below 10%. The kneaded support was placed in a nitrogen-filled furnace. The nitrogen flow rate was 200 L / min per cubic meter of effective furnace volume. The temperature was raised from room temperature to 1300 °C over 27 hours, and then calcined at 1300 °C for 5 hours to obtain a white α-Al₂O₃ support. The measured physical properties of the support are shown in Table 2 below.

[0107] Comparative Example 2

[0108] This comparative example is used to illustrate the preparation of the reference alumina support.

[0109] 300g of α-Al₂O₃ trihydrate (25-300μm), 240g of Al₂O₃ pseudomonohydrate (less than 100μm), 30g of polymethyl methacrylate (PMMA) with a diameter of 30μm, 12g of aluminum fluoride, and 4g of barium nitrate were mixed evenly in a mixer. The mixture was then transferred to a kneader, where 14g of petrolatum and 200ml of dilute nitric acid (nitric acid:water = 1:5, by weight) were added. 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. The extruded materials were dried at 80-120℃ for at least 2 hours to reduce the free water content to below 10%. The kneaded carrier was placed in an atmosphere furnace capable of simultaneously introducing air and nitrogen. The air flow rate was 100 L / min and the nitrogen flow rate was 100 L / min per cubic meter of effective furnace volume. The temperature was raised from room temperature to 1300 °C over 27 hours, and then calcined at 1300 °C for 5 hours to obtain a white α-Al₂O₃ carrier. The measured physical properties of the carrier are shown in Table 2 below.

[0110] Comparative Example 3

[0111] This comparative example is used to illustrate the preparation of the reference alumina support.

[0112] 300g of α-Al₂O₃ trihydrate (25-300μm), 240g of Al₂O₃ pseudomonohydrate (less than 100μm), 30g of polymethyl methacrylate (PMMA) with a diameter of 30μm, 12g of aluminum fluoride, and 4g of barium nitrate were mixed evenly in a mixer. The mixture was then transferred to a kneader, where 14g of petrolatum and 200ml of dilute nitric acid (nitric acid:water = 1:5, by weight) were added. 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. The extruded materials were dried at 80-120℃ for at least 2 hours to reduce the free water content to below 10%. The kneaded carrier was placed in an air-breathing furnace with an air flow rate of 200 L / min per cubic meter of effective furnace volume. The temperature was raised from room temperature to 1300°C over 27 hours, and then calcined at 1300°C for 5 hours to obtain a white α-Al₂O₃ carrier. The measured physical properties of the carrier are shown in Table 2 below.

[0113] Comparative Example 4

[0114] This comparative example is used to illustrate the preparation of the reference alumina support.

[0115] 300g of α-Al₂O₃ trihydrate (25-300μm), 240g of Al₂O₃ pseudomonohydrate (less than 100μm), 30g of polymethyl methacrylate (PMMA) with a diameter of 30μm, 12g of aluminum fluoride, and 4g of barium nitrate were mixed evenly in a mixer. The mixture was then transferred to a kneader, where 14g of petrolatum and 200ml of dilute nitric acid (nitric acid:water = 1:5, by weight) were added. 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. The extruded materials were dried at 80-120℃ for at least 2 hours to reduce the free water content to below 10%. The kneaded carrier was placed in an oxygen-filled furnace with an oxygen flow rate of 200 L / min per cubic meter of effective furnace volume. The temperature was raised from room temperature to 1300 °C over 27 hours, and then calcined at 1300 °C for 5 hours to obtain a white α-Al₂O₃ carrier. The measured physical properties of the carrier are shown in Table 2 below.

[0116] Comparative Example 5

[0117] This comparative example is used to illustrate the preparation of the reference silver catalyst.

[0118] Same as Example 6, except that the support sample prepared in Example 1 was replaced with the support sample prepared in Comparative Example 1. The silver catalyst obtained was DC-1.

[0119] Comparative Example 6

[0120] This comparative example is used to illustrate the preparation of the reference silver catalyst.

[0121] Same as Example 6, except that the support sample prepared in Example 1 was replaced with the support sample prepared in Comparative Example 2. The silver catalyst obtained was DC-2.

[0122] Comparative Example 7

[0123] This comparative example is used to illustrate the preparation of the reference silver catalyst.

[0124] Same as Example 6, except that the support sample prepared in Example 1 was replaced with the support sample prepared in Comparative Example 3. The silver catalyst prepared was DC-3.

[0125] Comparative Example 8

[0126] This comparative example is used to illustrate the preparation of the reference silver catalyst.

[0127] Same as Example 6, except that the support sample prepared in Example 1 was replaced with the support sample prepared in Comparative Example 4. The silver catalyst prepared was DC-4.

[0128] Table 2

[0129]

[0130] Test case

[0131] The activity and selectivity of the catalyst samples were determined using a microreactor evaluation device under the aforementioned process conditions. The microreactor evaluation results are listed in Table 3.

[0132] Table 3

[0133]

[0134]

[0135] Data from Tables 2 and 3 show that the pore distribution curve of the support provided by the method of this invention exhibits a bimodal structure, including macropore peaks and micropore peaks. The micropore peaks have a narrower pore size distribution, with pores of 1.5–2.5 μm accounting for over 95% of the total pore volume, and plate-like crystals of 3–5 μm accounting for over 90% of the total plate-like crystals. The catalyst prepared from the support of this invention, while maintaining activity, shows significantly improved selectivity and a significantly reduced temperature rise over 50 days (i.e., improved stability), demonstrating broad application prospects.

[0136] 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.

[0137] 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, characterized in that, The α-alumina carrier has the following characteristics: α-Al₂O₃ content is above 90% by weight; crushing strength is 80~200 N / particle; specific surface area is 1.0~3.0 m². 2 / g; water absorption rate is 30~70%; pore volume is 0.30~0.75mL / g; the pore distribution curve has a bimodal structure, including macropore peak and micropore peak, in which pores with a diameter of 1.5~2.5µm account for more than 95% of the total pore volume of the micropore peak; plate-like crystals with a crystal size of 3~5µm account for more than 90% of the total plate-like crystals.

2. The α-alumina support according to claim 1, wherein, The α-alumina carrier has a crushing strength of 100~180 N / particle and a specific surface area of ​​1.5~2.5 m². 2 / g, water absorption rate of 45~70%, pore volume of 0.45~0.70mL / g.

3. The α-alumina support according to claim 1, wherein, The peak value of the large pore peak is 5.0~25.0µm, and the peak value of the small pore peak is 1.6~2.3µm.

4. A method for preparing an α-alumina support, characterized in that, Includes the following steps: (1) Prepare a solid mixture having the following components: α-Al2O3 trihydrate, Al2O3 pseudo-monohydrate, organic polymer pore-forming agent, combustible lubricant, fluoride mineralizer and alkaline earth metal compound; (2) The solid mixture obtained in step (1), the binder and water are mixed, kneaded and extruded to obtain a molded body; the binder is an acid; (3) The molded body obtained in step (2) is dried and calcined in an atmosphere of oxygen and air mixture to obtain the carrier; Based on the total flow rate of the oxygen and air mixture, the oxygen flow rate is 5-85%.

5. The preparation method according to claim 4, wherein, Based on the total flow rate of the oxygen and air mixture, the oxygen flow rate is 20-60%.

6. The preparation method according to claim 4, wherein, In step (3), the roasting is carried out in an atmosphere furnace in which oxygen and air can be introduced independently, and the total flow rate of the oxygen and air mixture is 50~400L / min relative to the effective furnace volume per cubic meter.

7. The preparation method according to claim 6, wherein, For each cubic meter of effective furnace volume, the total flow rate of the oxygen and air mixture is 100~300 L / min.

8. The preparation method according to any one of claims 4-7, wherein, In step (3), the roasting temperature is 1200-1400℃.

9. The preparation method according to any one of claims 4-7, wherein, In step (1), the particle size of the trihydrate α-Al2O3 is 25~300μm, the particle size of the pseudomonohydrate Al2O3 is less than 100μm, and the amount of trihydrate α-Al2O3 added is 10~85wt% based on the total weight of the solid mixture; the amount of pseudomonohydrate Al2O3 added is 10~55wt%.

10. The preparation method according to claim 9, wherein, Based on the total weight of the solid mixture, the amount of the trihydrate α-Al2O3 added is 20~82wt%, and the amount of the pseudomonohydrate Al2O3 added is 15~45wt%.

11. The preparation method according to any one of claims 4-7, wherein, In step (1), the organic polymer pore-forming agent is selected from at least one of polymethyl methacrylate, polystyrene, polycarbonate, polyamide and polyvinyl alcohol; the diameter or equivalent diameter of the organic polymer pore-forming agent is 0.5~80μm; and the amount of the organic polymer pore-forming agent added is 0.1~25wt% based on the total weight of the solid mixture.

12. The preparation method according to claim 11, wherein, The diameter or equivalent diameter of the organic polymer pore-forming agent is 5~50μm.

13. The preparation method according to claim 11, wherein, Based on the total weight of the solid mixture, the amount of the organic polymer pore-forming agent added is 1.0~10wt%.

14. The preparation method according to any one of claims 4-7, wherein, In step (1), the combustible lubricant is petrolatum and / or white oil; based on the total weight of the solid mixture, the amount of combustible lubricant added is 0.01~8.0wt%.

15. The preparation method according to claim 14, wherein, Based on the total weight of the solid mixture, the amount of the combustible lubricant added is 0.1~5.0 wt%.

16. The preparation method according to any one of claims 4-7, wherein, In step (1), the fluoride mineralizer is at least one of hydrogen fluoride, aluminum fluoride, ammonium fluoride, magnesium fluoride and cryolite; the amount of the fluoride mineralizer added is 0.05~8.0wt% based on the total weight of the solid mixture.

17. The preparation method according to claim 16, wherein, The amount of fluoride mineralizer added is 0.5 to 5.0 wt%, based on the total weight of the solid mixture.

18. The preparation method according to any one of claims 4-7, wherein, In step (1), the alkaline earth metal compound is at least one of oxides, nitrates, acetates, oxalates and sulfates of strontium and / or barium; the amount of alkaline earth metal compound added is 0.01 to 5.0 wt% based on the total weight of the solid mixture.

19. The preparation method according to claim 18, wherein, Based on the total weight of the solid mixture, the amount of alkaline earth metal compound added is 0.05~2.0 wt%.

20. The preparation method according to any one of claims 4-7, wherein, In step (2), the acid is provided in the form of an aqueous solution of the acid; the amount of the binder is 25 to 60 wt% of the total amount of the solid mixture.

21. The preparation method according to claim 20, wherein, The acid is an aqueous solution of nitric acid, wherein the weight ratio of nitric acid to water in the aqueous solution of nitric acid is 1:(1.25~10).

22. The preparation method according to claim 4, wherein, The binder and pseudo-al2O3 monohydrate are wholly or partially replaced by aluminum sol.

23. An α-alumina support prepared by any one of claims 4-22.

24. A silver catalyst for ethylene epoxidation, characterized in that, include: a) The α-alumina support as described in claim 1 or 23; b) The active component silver deposited on the α-alumina support; c) Alkali metals and / or alkaline earth metals, or compounds based on alkali metals and / or alkaline earth metals; d) Rhenium metal and / or rhenium-based compounds; as well as e) Optionally, the rhenium co-catalyst is selected from at least one metal selected from chromium, molybdenum, tungsten and manganese, and / or selected from compounds based on at least one metal selected from chromium, molybdenum, tungsten and manganese.

25. A method for producing ethylene oxide by epoxidation of ethylene, characterized in that, The method includes: ethylene undergoing an ethylene epoxidation reaction in the presence of the silver catalyst described in claim 24 to obtain ethylene oxide.

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