Alpha-alumina carrier, method for preparing the same, silver catalyst and application thereof

Abstract

This invention belongs to the field of silver catalysts, and relates to an α-alumina support, its preparation method, and silver catalysts and their applications. The preparation method of the α-alumina support includes the following steps: at least one of α-Al₂O₃ and α-Al₂O₃ trihydrate is mixed uniformly with pseudo-Al₂O₃ to obtain a solid mixture; this mixture is then wet-milled with deionized water in a ball mill to obtain a slurry; the resulting slurry is spray-granulated to obtain solid microsphere powder; the solid microsphere powder is mixed uniformly with a binder, flow aid, lubricant, and pore-forming agent to obtain pressed granules; the pressed granules are dry-pressed to obtain a molded body, which is then calcined to obtain the α-alumina support. The support obtained by this invention has a more controllable shape, and when used for the oxidation of ethylene to ethylene oxide, its selectivity and stability are significantly improved while maintaining activity.

Description

Technical Field

[0001] This invention belongs to the field of silver catalysts, specifically relating to a method for preparing an α-alumina support, and the α-alumina support obtained by the method. This invention also provides a silver catalyst for ethylene epoxidation, and the application of the α-alumina support or the silver catalyst for ethylene epoxidation in the production of ethylene oxide. 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 closely related to the performance of the support used and the preparation method. Currently, α-alumina is generally used as the support for silver catalysts. The main indicators for evaluating the performance of α-alumina supports include: compressive strength, specific surface area, pore volume, and water absorption rate. Suitable compressive strength ensures the catalyst can withstand reaction pressure for extended periods; a suitable specific surface area provides space for the deposition of active components and catalyst promoters; a suitable pore volume provides adequate space for ethylene oxidation, allowing for timely dissipation of reaction heat; and a suitable water absorption rate controls the loading of active components and catalyst promoters on the support.

[0004] Existing molding technologies include compression molding, extrusion molding, rotational molding, pressure molding, and spray drying molding. Among these, extrusion molding is commonly used to prepare alumina carriers. The general steps involve mixing alumina raw materials and additives evenly, adding a binder and water, kneading, extruding, and then drying and calcining to form the carrier. The quality of extruded products is affected by the properties of the raw materials, the kneading method, and the extrusion method. Specifically, when using extrusion molding to form carriers, in addition to requiring specific types and proportions of raw materials to achieve suitable carrier properties, the ease and effectiveness of molding also depend on the raw materials. This limits the applicability of extrusion molding to some extent. Furthermore, in extrusion molding, the binder added during kneading is acid, which releases gases such as nitrogen oxides during carrier calcination, causing environmental pollution. Summary of the Invention

[0005] In view of the above-mentioned situation in the prior art, the inventors of the present invention have conducted extensive and in-depth research in the field of silver catalyst and its support preparation. The results show that when the support is prepared by the method of "wet milling of raw materials - spray granulation - dry pressing," a wider range of raw material types and ratios can be accommodated, resulting in a more regular support shape and a more controllable pore size distribution. 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 activity. Based on this, the purpose of the present invention is to provide an α-alumina support and its preparation method, a silver catalyst for ethylene epoxidation, and an ethylene oxidation method. The silver catalyst prepared from the α-alumina support of the present invention, after being loaded with silver and preferably various active components, exhibits good selectivity and stability in the process of ethylene oxidation to ethylene oxide.

[0006] The first aspect of the present invention provides a method for preparing an α-alumina support, comprising the following steps:

[0007] (1) Mix at least one of α-Al2O3 and α-Al2O3 trihydrate with Al2O3 pseudo-monohydrate to obtain a solid mixture. Add the solid mixture and deionized water to a ball mill for wet milling to obtain a slurry.

[0008] (2) Spray granulation of the slurry obtained in step (1) to obtain solid microsphere powder, and mix the solid microsphere powder with binder, flow aid, lubricant and pore-forming agent evenly to obtain pressed granules;

[0009] (3) The pressed granules obtained in step (2) are dry-pressed to obtain a molded body;

[0010] (4) The molded body obtained in step (3) is calcined to obtain the α-alumina carrier.

[0011] A second aspect of the present invention provides an α-alumina support prepared by the aforementioned preparation method.

[0012] A third aspect of the present invention provides a silver catalyst for ethylene epoxidation, the silver catalyst comprising a support and an active component silver supported on the support, wherein the support is the α-alumina support.

[0013] A fourth aspect of the present invention provides a method for ethylene oxidation, the method comprising: subjecting ethylene to an ethylene epoxidation reaction under the action of the above-described α-alumina support and / or the above-described silver catalyst to obtain ethylene oxide.

[0014] This invention prepares the support using a "wet grinding of raw materials - spray granulation - dry pressing" method, which is suitable for a wider range of raw material types and ratios, resulting in a more regular support shape and a more controllable pore size distribution. Compared with existing technologies, this invention avoids the use of acid as a binder. When the silver catalyst prepared on the resulting α-alumina support is used for the oxidation of ethylene to ethylene oxide, it has the advantages of higher selectivity and stability while maintaining activity.

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

[0016] 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.

[0017] A method for preparing an α-alumina support includes the following steps:

[0018] (1) Mix at least one of α-Al2O3 and α-Al2O3 trihydrate with Al2O3 pseudo-monohydrate to obtain a solid mixture. Add the solid mixture and deionized water to a ball mill for wet milling to obtain a slurry.

[0019] (2) Spray granulation of the slurry obtained in step (1) to obtain solid microsphere powder, and mix the solid microsphere powder with binder, flow aid, lubricant and pore-forming agent evenly to obtain pressed granules;

[0020] (3) The pressed granules obtained in step (2) are dry-pressed to obtain a molded body;

[0021] (4) The molded body obtained in step (3) is calcined to obtain the α-alumina carrier.

[0022] In this invention, solid mixtures are wet-milled and spray-granulated to produce solid microsphere powder, which can reduce the particle size while improving its flowability, thus facilitating subsequent dry pressing. The inventors of this invention have discovered that preparing carriers using the "raw material wet milling-spray granulation-dry pressing" method is suitable for a wider range of raw material types and ratios, resulting in more regular carrier shapes and more controllable pore size distribution.

[0023] According to the present invention, preferably, in step (3), the dry pressing is carried out in a precision mold, the pressure of the dry pressing is 40-200MPa, and the time is 25-60s; the precision mold is preferably gear-shaped, cylindrical or porous cylindrical.

[0024] In this invention, the precision mold in step (3) can be of any shape, preferably gear-shaped, cylindrical or porous cylindrical.

[0025] Although the invention objective can be achieved simply by using "wet grinding of raw materials - spray granulation - dry pressing", from the perspective of further improving the selectivity and stability of the silver catalyst made of the alumina support in the ethylene oxidation to produce ethylene oxide, the dry pressing pressure is 40-200 MPa and the pressing time is 25-60 s.

[0026] According to the present invention, preferably, in step (1), based on the weight of the solid mixture, the amount of α-Al2O3 and α-Al2O3 trihydrate is 80-95 wt%, and the amount of Al2O3 pseudo-monohydrate is 5-20 wt%; preferably, the amount of α-Al2O3 and α-Al2O3 trihydrate is 80-90 wt%, and the amount of Al2O3 pseudo-monohydrate is 10-20 wt%; the slurry is a slurry with a solid mixture content of 20-50 wt% and a particle size of 0.3-2 μm.

[0027] In this invention, the trihydrate α-Al2O3 is converted into stable α-Al2O3 during high-temperature calcination; the pseudomonohydrate Al2O3 can play a lubricating role during dry pressing and is also converted into stable α-Al2O3 during high-temperature calcination, becoming part of the α-Al2O3 carrier.

[0028] According to the present invention, preferably, in step (2), the particle size of the solid microsphere powder is <100μm; based on the weight of the pressed granules, the amount of the solid microsphere powder is 65-98wt%, preferably 75-90wt%.

[0029] According to the present invention, preferably, in step (2), the binder is at least one of polyvinyl alcohol, polyacrylate and methylcellulose; the amount of binder is 0.5-10 wt%, preferably 2-8 wt%, based on the weight of the pressed granules.

[0030] In this invention, the addition of the binder serves to form a very thin film on the surface of the raw material particles, which has a binding effect on the particles and gives the pressed molded body a certain strength.

[0031] According to the present invention, preferably, in step (2), the flow aid is micronized silica gel and / or talc; based on the weight of the pressed granules, the amount of the flow aid is 0.01-2wt%, preferably 0.1-0.5wt%.

[0032] According to the present invention, preferably, in step (2), the lubricant is at least one of magnesium stearate, calcium stearate, stearic acid and paraffin; the amount of the lubricant is 0.1-5 wt%, preferably 0.5-5 wt%, based on the weight of the pressed granules.

[0033] In this invention, the addition of the flow aid increases the fluidity of the particles, and the lubricant reduces the friction between the particles, working together with the flow aid to increase the fluidity of the particles.

[0034] According to the present invention, preferably, in step (2), the pore-forming agent is at least one of polymethyl methacrylate, petroleum coke, activated carbon and graphite; the amount of the pore-forming agent is 1-20 wt%, preferably 3-15 wt%, based on the weight of the pressed granules.

[0035] In this invention, the pore-forming agent is added to adjust the pore structure of the carrier and form a certain pore size distribution.

[0036] According to the present invention, preferably, in step (4), the roasting temperature is 1200-1500°C and the time is 1-20h, preferably 2-15h.

[0037] A second aspect of the present invention provides an α-alumina support prepared by the aforementioned preparation method.

[0038] According to the present invention, preferably, the α-alumina carrier has the following characteristics: α-Al₂O₃ content is 90 wt% or more; crushing strength is 70–180 N / particle, preferably 80–150 N / particle; specific surface area is 1.0–2.0 m². 2 / g, preferably 1.2~1.8m 2 / g; water absorption rate of 30-55%, preferably 40-55%; pore volume of 0.30-0.55mL / g, preferably 0.40-0.55mL / g; bulk density of 0.75-1.05g / mL, preferably 0.80-1.00g / mL.

[0039] In this invention, the lateral crushing strength of the carrier is determined 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 boiling method. The specific surface area is determined by nitrogen physical adsorption BET method. The pore structure is determined by mercury intrusion porosimetry method. The bulk density is determined by crushing the carrier to 12-18 mesh and weighing it.

[0040] A third aspect of the present invention provides a silver catalyst for ethylene epoxidation, the silver catalyst comprising a support and an active component silver supported on the support, wherein the support is the α-alumina support.

[0041] According to the present invention, preferably, the silver catalyst further includes:

[0042] Alkali metals and / or alkaline earth metals or compounds based on alkali metals and / or alkaline earth metals;

[0043] Rhenium metal and / or rhenium-based compounds; and

[0044] 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.

[0045] According to the present invention, in the above-mentioned silver catalyst, based on the total weight of the silver 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 0-1000 ppm.

[0046] The silver catalyst of the present invention can be prepared in a conventional manner by impregnating the above-mentioned α-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.

[0047] The organic amine can be any organic amine compound suitable for preparing silver catalysts for ethylene oxide production, as long as the organic amine compound can form a silver amine complex with the silver compound. For example, it can be selected from one or more of pyridine, butylamine, ethylenediamine, 1,3-propanediamine and ethanolamine, preferably a mixture of ethylenediamine and ethanolamine.

[0048] The alkali metal auxiliaries may be compounds of lithium, sodium, potassium, rubidium or cesium or any combination of two 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.

[0049] 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.

[0050] The rhenium-containing additive may be an oxide of rhenium, perrhenic acid, perrhenate, or a mixture thereof, preferably perrhenic acid and / or perrhenate, such as perrhenic acid, cesium perrhenate, and ammonium perrhenate.

[0051] The rhenium-containing 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 promoter 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 promoter and its co-promoter can further improve the activity, selectivity, and stability of the resulting silver catalyst.

[0052] 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. The above-mentioned auxiliary agent is then added to prepare an impregnation solution. The above-mentioned α-alumina support is then impregnated with 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% by weight (e.g., containing 8% by weight of oxygen) at a temperature range of 180-700°C, preferably 200-500°C, for 0.5-120 minutes, preferably 1-60 minutes, to produce the finished silver catalyst.

[0053] A fourth aspect of the present invention provides a method for ethylene oxidation, the method comprising: subjecting ethylene to an ethylene epoxidation reaction under the action of the above-described α-alumina support and / or the above-described silver catalyst to obtain ethylene oxide.

[0054] In this invention, the ethylene oxidation reaction apparatus can be any apparatus capable of performing an epoxidation reaction.

[0055] 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.

[0056] In the following embodiments and comparative examples:

[0057] 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.

[0058] The assay conditions for activity and selectivity used are shown in Table 1:

[0059] Table 1

[0060]

[0061] 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:

[0062]

[0063] 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.

[0064] Lateral 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.

[0065] Water absorption rate: determined by boiling method.

[0066] Specific surface area: determined by the nitrogen physical adsorption BET method.

[0067] Pore ​​structure: determined using mercury porosimetry.

[0068] Bulk density: determined by weighing the carrier after crushing it to 12-18 mesh.

[0069] Examples 1-8 illustrate the preparation of the alumina support provided by the present invention.

[0070] Example 1

[0071] 80g of pseudo-al2O3 monohydrate and 520g of α-al2O3 were mixed evenly and then wet-milled with an appropriate amount of deionized water in a ball mill to obtain a slurry with a solid mixture content of 37% by weight and a particle size distribution of 0.3-2μm. The slurry was spray-granulated to obtain solid microspheres <100μm in size. 30g of polyvinyl alcohol, 2g of micronized silica gel, 18g of magnesium stearate, and 50g of polymethyl methacrylate were added and mixed evenly to obtain pressed granules. The pressed granules were dry-pressed using a seven-hole cylindrical mold at a pressure of 100MPa for 40s to obtain a molded body with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. This body was then calcined at 1400℃ to obtain an α-alumina carrier. The carrier molding process and measured carrier properties are shown in Table 2 below.

[0072] Example 2

[0073] 80g of pseudo-monohydrate Al₂O₃ and 520g of α-Al₂O₃ were mixed evenly and then wet-milled with an appropriate amount of deionized water in a ball mill to obtain a slurry with a solid mixture content of 37% by weight and a particle size distribution of 0.3-2μm. The slurry was spray-granulated to obtain solid microspheres <100μm in size. 30g of polyvinyl alcohol, 2g of micronized silica gel, 18g of magnesium stearate, and 100g of polymethyl methacrylate were added and mixed evenly to obtain pressed granules. The pressed granules were dry-pressed using a seven-hole cylindrical mold at a pressure of 100MPa for 40s to obtain a molded body with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. This body was then calcined at 1400℃ to obtain an α-alumina carrier. The carrier molding process and measured carrier properties are shown in Table 2 below.

[0074] Example 3

[0075] 80g of pseudo-monohydrate Al₂O₃ and 520g of α-Al₂O₃ were mixed evenly and then wet-milled with an appropriate amount of deionized water in a ball mill to obtain a slurry with a solid mixture content of 37% by weight and a particle size distribution of 0.3-2μm. The slurry was spray-granulated to obtain solid microspheres <100μm in size. 30g of polyvinyl alcohol, 2g of micronized silica gel, 18g of magnesium stearate, and 100g of polymethyl methacrylate were added and mixed evenly to obtain pressed granules. The pressed granules were dry-pressed using a seven-hole cylindrical mold at a pressure of 200MPa for 40s to obtain a molded body with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. This body was then calcined at 1400℃ to obtain an α-alumina carrier. The carrier molding process and measured carrier properties are shown in Table 2 below.

[0076] Example 4

[0077] 80g of pseudo-monohydrate Al₂O₃ and 520g of α-Al₂O₃ were mixed evenly and then wet-milled with an appropriate amount of deionized water in a ball mill to obtain a slurry with a solid mixture content of 37% by weight and a particle size distribution of 0.3-2μm. The slurry was spray-granulated to obtain solid microspheres <100μm in size. 30g of polyvinyl alcohol, 2g of micronized silica gel, 18g of magnesium stearate, and 50g of polymethyl methacrylate were added and mixed evenly to obtain pressed granules. The pressed granules were dry-pressed using a seven-hole cylindrical mold at a pressure of 40MPa for 40s to obtain a molded body with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. This body was then calcined at 1400℃ to obtain an α-alumina carrier. The carrier molding process and measured carrier properties are shown in Table 2 below.

[0078] Example 5

[0079] 30g of pseudo-monohydrate Al₂O₃ and 570g of α-Al₂O₃ were mixed evenly and then wet-milled with an appropriate amount of deionized water in a ball mill to obtain a slurry with a solid mixture content of 37% by weight and a particle size distribution of 0.3-2μm. The slurry was spray-granulated to obtain solid microspheres <100μm in size. 30g of polyvinyl alcohol, 2g of micronized silica gel, 18g of magnesium stearate, and 50g of polymethyl methacrylate were added and mixed evenly to obtain pressed granules. The pressed granules were dry-pressed using a seven-hole cylindrical mold at a pressure of 100MPa for 40s to obtain a molded body with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. This body was then calcined at 1400℃ to obtain an α-alumina carrier. The carrier molding process and measured carrier properties are shown in Table 2 below.

[0080] Example 6

[0081] 120g of pseudo-monohydrate Al₂O₃ and 480g of α-Al₂O₃ were mixed evenly and then wet-milled with an appropriate amount of deionized water in a ball mill to obtain a slurry with a solid mixture content of 37% by weight and a particle size distribution of 0.3-2μm. The slurry was spray-granulated to obtain solid microspheres <100μm in size. 30g of polyvinyl alcohol, 2g of micronized silica gel, 18g of magnesium stearate, and 50g of polymethyl methacrylate were added and mixed evenly to obtain pressed granules. The pressed granules were dry-pressed using a seven-hole cylindrical mold at a pressure of 100MPa for 40s to obtain a molded body with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. This body was then calcined at 1400℃ to obtain an α-alumina carrier. The carrier molding process and measured carrier properties are shown in Table 2 below.

[0082] Example 7

[0083] 80g of pseudo-monohydrate Al₂O₃ and 520g of trihydrate α-Al₂O₃ were mixed evenly and then wet-milled with an appropriate amount of deionized water in a ball mill to obtain a slurry with a solid mixture content of 37% by weight and a particle size distribution of 0.3-2μm. The slurry was spray-granulated to obtain solid microspheres <100μm in size. 30g of polyvinyl alcohol, 2g of micronized silica gel, 18g of magnesium stearate, and 50g of polymethyl methacrylate were added and mixed evenly to obtain pressed granules. The pressed granules were dry-pressed using a seven-hole cylindrical mold at a pressure of 100MPa for 40s to obtain a molded body with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. This body was then calcined at 1400℃ to obtain an α-alumina carrier. The carrier molding process and measured carrier properties are shown in Table 2 below.

[0084] Example 8

[0085] 80g of pseudo-monohydrate Al₂O₃ and 520g of α-Al₂O₃ were mixed evenly and then wet-milled with an appropriate amount of deionized water in a ball mill to obtain a slurry with a solid mixture content of 37% by weight and a particle size distribution of 0.3-2μm. The slurry was spray-granulated to obtain solid microspheres <100μm in size. 30g of polyvinyl alcohol, 2g of micronized silica gel, 18g of magnesium stearate, and 50g of polymethyl methacrylate were added and mixed evenly to obtain pressed granules. The pressed granules were dry-pressed using a seven-hole cylindrical mold at a pressure of 250MPa for 40s to obtain a molded body with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. This body was then calcined at 1400℃ to obtain an α-alumina carrier. The carrier molding process and measured carrier properties are shown in Table 2 below.

[0086] Examples 9-17 illustrate the preparation of the silver catalyst provided by the present invention.

[0087] Example 9

[0088] 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.

[0089] 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.

[0090] 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.

[0091] Example 10

[0092] Same as Example 9, 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.

[0093] Example 11

[0094] Same as Example 9, except that the support sample prepared in Example 1 was replaced with the support sample prepared in Example 3. The resulting silver catalyst was C-3.

[0095] Example 12

[0096] Same as Example 9, 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.

[0097] Example 13

[0098] Same as Example 9, 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.

[0099] Example 14

[0100] Same as Example 9, except that the support sample prepared in Example 1 was replaced with the support sample prepared in Example 6. The resulting silver catalyst was C-6.

[0101] Example 15

[0102] Same as Example 9, except that the support sample prepared in Example 7 was used instead of the support sample prepared in Example 1. The resulting silver catalyst was C-7.

[0103] Example 16

[0104] Same as Example 9, except that the support sample prepared in Example 8 was used instead of the support sample prepared in Example 1. The resulting silver catalyst was C-8.

[0105] Comparative Example 1

[0106] This comparative example is used to illustrate the preparation of the reference alumina support.

[0107] 80g of 1-120μm pseudo-monohydrate Al₂O₃, 520g of 20-200μm trihydrate α-Al₂O₃, 20g of magnesium fluoride, and 50g of polymethyl methacrylate were mixed evenly in a mixer, then transferred to a kneader. 30g of petrolatum and 200mL 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 a seven-hole cylindrical shape with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. The extruded paste was dried at 100℃ for at least 2 hours to reduce the free water content to below 10% by weight. The kneaded carrier was then calcined at 1400℃ to obtain a white α-Al₂O₃ carrier. The carrier molding conditions and measured carrier properties are shown in Table 2 below.

[0108] Comparative Example 2

[0109] This comparative example is used to illustrate the preparation of the reference alumina support.

[0110] 80g of 1-120μm pseudo-monohydrate Al₂O₃, 520g of 0.3-2μm α-Al₂O₃, 20g of magnesium fluoride, and 50g of polymethyl methacrylate were mixed evenly in a mixer, then transferred to a kneader. 30g of petrolatum and 200mL 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 a seven-hole cylindrical shape with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. The extruded paste was dried at 100℃ for at least 2 hours to reduce the free water content to below 10% by weight. The kneaded carrier was then calcined at 1400℃ to obtain a white α-Al₂O₃ carrier. The carrier molding conditions and measured carrier properties are shown in Table 2 below.

[0111] Comparative Example 3

[0112] This comparative example is used to illustrate the preparation of the reference alumina support.

[0113] 80g of 1-120μm pseudo-monohydrate Al₂O₃, 520g of 0.3-2μm α-Al₂O₃, 30g of polyvinyl alcohol, 2g of micronized silica gel, 18g of magnesium stearate, and 50g of polymethyl methacrylate were mixed evenly in a mixer, transferred to a kneader, and 200mL of deionized water were added. The mixture was kneaded to form a paste that could be extruded. The paste was extruded into a seven-hole columnar shape with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. The extruded material was dried at 100℃ for at least 2 hours to reduce the free water content to below 10% by weight. The kneaded carrier was then calcined at 1400℃ to obtain a white α-Al₂O₃ carrier. The carrier molding conditions and measured carrier properties are shown in Table 2 below.

[0114] Comparative Example 4

[0115] This comparative example is used to illustrate the preparation of the reference silver catalyst.

[0116] Same as Example 9, 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.

[0117] Comparative Example 5

[0118] This comparative example is used to illustrate the preparation of the reference silver catalyst.

[0119] Same as Example 9, 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.

[0120] Table 2

[0121]

[0122]

[0123] 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.

[0124] Table 3

[0125]

[0126]

[0127] As shown in Tables 2 and 3, when preparing the support according to the method of the present invention, a more regular support shape can be obtained with a wider range of raw material types and ratios. Simultaneously, while maintaining specific surface area and compressive strength, the support exhibits high pore volume and bulk density, a large average pore size, and a narrow pore size distribution. The catalyst prepared from the support of the present 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. Furthermore, the present invention avoids the use of acid as a binder, making the preparation process more environmentally friendly.

[0128] 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.

[0129] 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. A method for preparing an α-alumina support, characterized in that, Includes the following steps: (1) Mix at least one of α-Al2O3 and α-Al2O3 trihydrate with Al2O3 pseudo-monohydrate to obtain a solid mixture. Add the solid mixture and deionized water to a ball mill for wet milling to obtain a slurry. Based on the weight of the solid mixture, the amount of α-Al₂O₃ and α-Al₂O₃ trihydrate is 80-95 wt%, and the amount of Al₂O₃ pseudomonohydrate is 5-20 wt%. (2) Spray granulation is performed on the slurry obtained in step (1) to obtain solid microsphere powder. The solid microsphere powder is mixed evenly with binder, flow aid, lubricant and pore-forming agent to obtain pressed granules. The binder is at least one of polyvinyl alcohol, polyacrylate and methylcellulose. (3) The pressed granules obtained in step (2) are dry-pressed to obtain a molded body; the dry pressing is carried out in a precision mold, the pressure of the dry pressing is 40-200MPa, and the time is 25-60s; (4) The molded body obtained in step (3) is calcined to obtain the α-alumina carrier.

2. The method for preparing the α-alumina support according to claim 1, wherein, The precision mold is gear-shaped, cylindrical, or porous cylindrical.

3. The method for preparing the α-alumina support according to claim 1, wherein, In step (1), the slurry is a slurry with a solid mixture content of 20-50 wt% and a particle size of 0.3-2 µm.

4. The method for preparing the α-alumina support according to claim 3, wherein, The amount of α-Al2O3 and α-Al2O3 trihydrate used is 80-90 wt%, and the amount of Al2O3 pseudomonohydrate used is 10-20 wt%.

5. The method for preparing the α-alumina support according to claim 1, wherein, In step (2), the particle size of the solid microsphere powder is <100µm; based on the weight of the pressed granules, the amount of the solid microsphere powder is 65-98 wt%.

6. The method for preparing the α-alumina support according to claim 5, wherein, Based on the weight of the pressed granules, the amount of the solid microsphere powder is 75-90 wt%.

7. The method for preparing the α-alumina support according to claim 1, wherein, In step (2), the amount of binder used is 0.5-10 wt%, based on the weight of the pressed granules.

8. The method for preparing the α-alumina support according to claim 7, wherein, The amount of binder is 2-8 wt% based on the weight of the pressed granules.

9. The method for preparing the α-alumina support according to claim 1, wherein, In step (2), the flow aid is micronized silica gel and / or talc; the amount of the flow aid is 0.01-2 wt% based on the weight of the pressed granules.

10. The method for preparing the α-alumina support according to claim 9, wherein, Based on the weight of the pressed granules, the amount of the flow aid is 0.1-0.5 wt%.

11. The method for preparing the α-alumina support according to claim 1, wherein, In step (2), the lubricant is at least one of magnesium stearate, calcium stearate, stearic acid and paraffin; the amount of lubricant used is 0.1-5 wt% based on the weight of the pressed granules.

12. The method for preparing the α-alumina support according to claim 11, wherein, Based on the weight of the pressed granules, the amount of lubricant used is 0.5-5 wt%.

13. The method for preparing the α-alumina support according to claim 1, wherein, In step (2), the pore-forming agent is at least one of polymethyl methacrylate, petroleum coke, activated carbon and graphite; the amount of the pore-forming agent is 1-20 wt% based on the weight of the pressed granules.

14. The method for preparing the α-alumina support according to claim 13, wherein, Based on the weight of the pressed granules, the amount of the pore-forming agent is 3-15 wt%.

15. The method for preparing the α-alumina support according to claim 1, wherein, In step (4), the roasting temperature is 1200~1500℃ and the time is 1~20h.

16. The method for preparing the α-alumina support according to claim 15, wherein, The time is 2 to 15 hours.

17. The α-alumina support prepared by the preparation method according to any one of claims 1-16.

18. The α-alumina support according to claim 17, wherein, The α-alumina carrier has the following characteristics: α-Al₂O₃ content is above 90 wt%; crushing strength is 70–180 N / particle; specific surface area is 1.0–2.0 m². 2 / g; water absorption rate is 30-55%; pore volume is 0.30-0.55mL / g; bulk density is 0.75-1.05g / mL.

19. The α-alumina support according to claim 18, wherein, Crushing strength is 80–150 N / particle; specific surface area is 1.2–1.8 m². 2 / g; water absorption rate 40-55%; pore volume 0.40-0.55mL / g; bulk density 0.80-1.00 g / mL.

20. A silver catalyst for ethylene epoxidation, said silver catalyst comprising a support and an active component silver supported on the support, characterized in that, The carrier is the α-alumina carrier according to any one of claims 17-19.

21. The silver catalyst for ethylene epoxidation according to claim 20, wherein, The silver catalyst also includes: Alkali metals and / or alkaline earth metals or compounds based on alkali metals and / or alkaline earth metals; Rhenium metal and / or rhenium-based compounds; and 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.

22. A method for ethylene oxidation, characterized in that, The method comprises: subjecting ethylene to an ethylene epoxidation reaction in the presence of an α-alumina support as described in any one of claims 17-19 or a silver catalyst for ethylene epoxidation as described in claims 20 or 21, to obtain ethylene oxide.

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