A method for preparing an alpha-alumina support, a silver-supported catalyst, and a method for preparing the same

Abstract

The application discloses a preparation method of an alpha-alumina carrier, which comprises the following steps: a) dry mixing alpha-Al2O3 seed crystals in a "platelet" shape with hydrated alumina, an inorganic compound containing B and an additive to obtain a dry powder mixture, wherein the additive is an inorganic compound containing one or more of Ca, Sr, Ba, Si, Zn, Zr and Y; b) adding a binder and an extrusion aid to the dry powder mixture to continue wet mixing, and then performing shaping, drying and calcination to obtain the alpha-alumina carrier. The alpha-alumina carrier with both "non-platelet" and "platelet" micro-morphologies can be prepared by the method.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalysts, and particularly relates to a preparation method of an alpha-alumina carrier, a silver-loaded catalyst and a preparation method thereof. BACKGROUND

[0002] Ethylene oxide is an important derivative of ethylene downstream next to polyethylene, and is mainly used for the production of chemical raw materials such as ethylene glycol and polyether monomer, and is an important chemical product today. Ethylene oxide is produced by using ethylene oxygen selective oxidation process, and the technical core is an ethylene epoxidation silver catalyst. The catalyst takes alpha-Al2O3 as a carrier, and is loaded with Ag main component and auxiliary elements such as Cs and Re. The physical properties and surface chemical properties of the carrier significantly affect the reaction performance of the catalyst, so adjusting the carrier performance is an important means to improve the reaction performance of the catalyst.

[0003] The micro-morphology of the alpha-Al2O3 carrier has a significant influence on the physical properties of the carrier and the performance of the catalyst. The carrier with the so-called "non-flaky" micro-morphology has a slow migration and agglomeration speed of silver atoms during the reaction process, which is reflected in the high reaction stability and long service life of the catalyst. However, the carrier with this micro-morphology has low mechanical strength and narrow pore size, which is not conducive to the improvement of selectivity. The carrier with the so-called "flaky" micro-morphology has high mechanical strength and wide pore size, which is conducive to the improvement of selectivity, but the loaded silver component migrates and agglomerates quickly, and the catalyst has low stability.

[0004] For the carrier with "flaky" micro-morphology, the existing technology mostly uses the method of adding metal oxides to try to create protrusions on the "flaky" particles to slow down the agglomeration of silver, but the effect is still limited. For the carrier with "non-flaky" micro-morphology, the existing technology mostly uses the method of adding fluxing components to solve the problem of low mechanical strength, and uses the method of adding pore-forming agents to increase the pore size to improve the selectivity, but the two methods sometimes offset each other, and the overall improvement effect is not satisfactory.

[0005] Patent CN103372466A adopts the method of mixing different proportions of trihydrate alpha-alumina, pseudo-monohydrate alumina, mineralizer, alkaline earth metal compound additives and combustible lubricating materials, etc. uniformly, and then kneading, extruding, forming and high-temperature calcining to prepare the carrier. The mineralizer can reduce the crystallization temperature of alumina, and the alumina crystal sheet is distributed in a cross shape, and the carrier has high strength. Although this method can obtain an alpha-Al2O3 catalyst carrier with the characteristics of flaky particle matrix, it cannot realize a catalyst carrier with both micro-morphology characteristics of alpha-Al2O3 particles.

[0006] Patent CN200680008891.9 introduces fluorine in the preparation of the support. The support can comprise, and preferably comprises, a particulate matrix having a morphology characterized as lamellar or platelet-like. As such, the particles having a dimension greater than 0.1 microns in at least one direction have at least one substantially flat major surface. Such particles can have two or more flat major surfaces. This method is capable of producing a catalyst support of a-Al2O3 having a lamellar or platelet-like particulate matrix characteristic, but is not capable of producing a catalyst support of a-Al2O3 particles having both microtopographical characteristics.

[0007] Patent CN201180011967.4 discloses a method for producing a support of a-Al2O3 having a non-platelet morphology. "Non-platelet morphology" refers to the morphology of the support as imaged by a scanning electron microscope at 2000 magnification, and refers to the substantial absence of structures having substantially flat surfaces in the image. "Substantial absence of such structures means that at most 25% of such structures have substantially flat surfaces. "Substantially flat" means that the radius of curvature of the surface is at least 2 times the length of the largest dimension of the surface. Structures having substantially flat surfaces typically have an aspect ratio of at most 4: 1, the aspect ratio of a structure being the ratio of the largest dimension to the smallest dimension of the structure. The term "structure" refers to a structural entity in the support that can be assigned to represent a single particle of the support material that is fused or agglomerated together to form the support. This method is capable of producing a catalyst support of a-Al2O3 having a non-platelet particulate matrix characteristic, but is not capable of producing a catalyst support of a-Al2O3 particles having both microtopographical characteristics.

[0008] Patent CN200580032036.7 discloses that mineralizing alumina supports with fluorides can result in a particulate matrix having a morphology that can be characterized as lamellar or platelet-like. The matrix has particles having a dimension greater than 1 micron in at least one direction that have at least one substantially flat major surface. This method is capable of producing a catalyst support of a-Al2O3 having a lamellar or platelet-like particulate matrix characteristic, but is not capable of producing a catalyst support of a-Al2O3 particles having both microtopographical characteristics.

[0009] Patent CN109835929A discloses a method for preparing flaky alpha-alumina powder by calcining in a sagger, comprising the following steps: A, stirring and mixing aluminum hydroxide, fluoride and water in a certain proportion, and injecting into a reaction kettle, hydrothermal reaction at a temperature of 160-320 DEG C for 2-7 hours, and after the reaction kettle is discharged, filtering, drying and crushing to prepare flaky alumina seeds; B, using one or more of aluminum oxide or alumina hydrate as raw material, the seeds prepared in step A as template agent, boric acid, fluoride, silicofluoride and alkali metal oxide as mineralizer, mixing and stirring uniformly in a certain proportion, and loading into a sagger, calcining at a temperature of 1300-1700 DEG C for 5-10 hours, and after cooling, the calcined product is taken out from the sagger; C, after the calcined product obtained in step B is ground and sieved, flaky alpha-alumina powder is prepared. The method can only obtain flaky carrier.

[0010] The document "Effect of nano-TiO2 and nano-SiO2 addition on the morphological control of alpha-Al2O3 platelets via solid-state reaction" discloses a method for preparing plate-like alpha-Al2O3 powder by introducing high-activity metal Al using Na2O-CaO-SiO2 glass as medium, and adjusting the size of micro-alpha-Al2O3 by changing the heating temperature. Although the method can prepare alpha-Al2O3 with different sizes, it cannot realize the catalyst carrier with two micro-morphology characteristics.

[0011] The document "NH4F content and calcination process on the phase transition of alumina and the influence of alpha-Al2O3 micro-morphology" discloses a method for realizing the adjustment of alpha-Al2O3 micro-morphology by introducing different mass fractions of NH4F into Al(OH)3 powder. Although the method can prepare flaky alpha-Al2O3 with different thickness-to-diameter ratios, it cannot realize the catalyst carrier with two micro-morphology characteristics. SUMMARY

[0012] The purpose of the present application is to provide a preparation method of alpha-alumina carrier, which has both "flaky" and "non-flaky" micro-morphologies, to solve the defects of the single-morphology carrier obtained by the prior art method.

[0013] The purpose of the present application is also to provide a silver-loaded catalyst.

[0014] The purpose of the present application is also to provide a preparation method of silver-loaded catalyst.

[0015] To achieve the above object, the present application provides a preparation method of α-alumina carrier, comprising the following steps:

[0016] a) dry mixing "plate-like" α-Al2O3 seed crystal with hydrated alumina, B-containing inorganic compound and auxiliary agent to obtain dry powder mixture, wherein the auxiliary agent is one or more inorganic compounds containing Ca, Sr, Ba, Si, Zn, Zr and Y;

[0017] b) adding binder and extrusion aid to the dry powder mixture for further wet mixing, then shaping, drying and calcining to obtain the α-alumina carrier.

[0018] In the preparation method of the α-alumina carrier, one or more inorganic salts or oxides of Ca, Sr, Ba, Si, Zn, Zr and Y are further added as auxiliary agent components in step a).

[0019] The "plate-like" α-Al2O3 seed crystal refers to α-Al2O3 particles with "plate-like" microscopic morphology characteristics, and the size is in the range of 10-900 nm. The "plate-like" refers to the microscopic morphology observed by scanning electron microscope, and the area of the substantially flat single surface is more than 50% of the outer surface area of the particle. The "substantially flat" means that the curvature radius of the surface is at least 2 times the length of the maximum dimension of the surface.

[0020] The "plate-like" α-Al2O3 seed crystal can be prepared by ordinary technical knowledge in the art, for example, by the following method:

[0021] a) mixing hydrated alumina and F-containing inorganic salt;

[0022] b) adding binder for further mixing;

[0023] c) calcining the mixed material;

[0024] d) primary crushing the calcined material, and then ball milling to obtain the seed crystal.

[0025] In step a), the hydrated alumina is one or more combinations of monohydrate alumina, pseudoboehmite and trihydrate alumina; and the F-containing inorganic salt is one or more combinations of ammonium fluoride, aluminum fluoride and hydrofluoric acid. The mass ratio of hydrated alumina to F-containing inorganic salt is 100:1-100:10.

[0026] The binder mentioned in step b) is a substance that can react with hydrated alumina to form aluminum sol, which can give the raw materials a certain degree of adhesion. Specifically, it can be an aqueous solution of one or more of hydrochloric acid, sulfuric acid, nitric acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, and citric acid, with a mass concentration of 10% to 90%.

[0027] In step c), the calcination equipment can be one of a muffle furnace, a tunnel kiln, or a bell kiln. The atmosphere in contact with the carrier during calcination can be air, an inert atmosphere, or an inert atmosphere with a certain proportion of oxygen added. The inert atmosphere can be nitrogen, argon, or helium. The heating rate during calcination is 2–20 °C / min, preferably 3–18 °C / min, reaching 1200–1400 °C, holding for 5–8 hours, and then naturally cooling to room temperature.

[0028] In step d), the initial crushing can be carried out using various mechanical processing methods, as long as more than 90% of it can pass through a 10-mesh sieve. The ball-to-material ratio for ball milling is 50:1, the ball milling speed is 500 r / min, and the ball milling time is 3 to 10 hours. Dry milling or wet milling can be used, but wet milling is preferred. The dispersant can be deionized water, glacial acetic acid, or ethanol.

[0029] The method for preparing the α-alumina support of this invention uses hydrated alumina, which is a precursor compound that can be dehydrated by heat treatment to form various crystalline phases of alumina. Specifically, it can be one or more of monohydrated alumina, boehmite, and trihydrated alumina; preferably, it is a mixture of boehmite and trihydrated alumina. Compared with alumina, hydrated alumina has better formability, and its physicochemical properties can be controlled by heat treatment, doping, and other means.

[0030] The method for preparing the α-alumina support described in this invention uses one or more of the boron-containing inorganic compounds selected from boric acid, boron carbide, boron nitride, and borax. The role of the boron-containing inorganic salt is to lower the crystallization temperature of alumina, accelerate the transformation of the support into α-phase alumina, and simultaneously, boron can guide the growth of α-alumina into particles with a "non-flaky" microstructure.

[0031] The method for preparing the α-alumina carrier according to the present invention uses a binder that can react with hydrated alumina to form an aluminum sol, thereby achieving a certain degree of adhesion between the raw materials. Specifically, it can be an aqueous solution of one or more of the following: hydrochloric acid, sulfuric acid, nitric acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, and citric acid, with a mass concentration of 20-50%.

[0032] The method for preparing the α-alumina carrier according to the present invention uses an extrusion aid that is one or more of white oil, paraffin wax, petrolatum, stearic acid, and guar gum powder. Its function is to reduce the friction and adhesion of materials in the molding equipment, thus helping the carrier to form better.

[0033] The preparation method of the alpha-alumina carrier, the forming process can adopt extrusion and slicing or direct tablet forming. The particle shape after forming can be a Lacey ring, a short cylindrical shape with no hole or multiple holes. Preferably, the Lacey ring particle, the outer diameter of the Lacey ring is 5-10 mm, the particle length is 5-10 mm, and the middle hole diameter is 1.5-4.5 mm; the drying treatment is to remove most of the free water in the carrier precursor after forming, so as to prevent the subsequent roasting process from causing adverse effects on the strength of the carrier particles and the inside of the furnace. The drying method can be selected from, but not limited to, track drying, hot air blowing, and oven drying. Regardless of which method, the drying temperature is 100-200℃, preferably 110-150℃. The drying time is 2-12h; the roasting equipment can be one of a muffle furnace, a tunnel kiln or a bell jar kiln. The hydrated alumina will be converted into alpha-alumina through dehydration and phase change at high temperature. The atmosphere contacted by the carrier during roasting can be air, inert atmosphere or inert atmosphere with a certain proportion of oxygen. The inert atmosphere can be nitrogen, argon or helium. The heating rate of roasting is 2-20℃ / min, preferably 3-18℃ / min, the temperature is raised to 1200-1400, the holding time is 5-8h, and the temperature is naturally cooled to room temperature.

[0034] The preparation method of the alpha-alumina carrier, the mass ratio of the hydrated alumina, the alpha-Al2O3 seed crystal, the additive, and the inorganic compound containing B in step a) is 100:1-3:1-3:1-5.

[0035] The preparation method of the alpha-alumina carrier, the mass ratio of the dry powder mixture, the binder, and the extrusion aid in step b) is 100:20-25:3-5.

[0036] To achieve the above-mentioned purpose, the application also provides a silver-loaded catalyst, and the carrier of the catalyst is the above-mentioned alpha-alumina carrier.

[0037] To achieve the above-mentioned purpose, the application also provides a preparation method of the above-mentioned silver-loaded catalyst, which comprises the following steps:

[0038] a) reacting the aqueous solution of the silver salt compound with the aqueous solution containing oxalate to obtain a silver oxalate precipitate;

[0039] b) dissolving the washed silver oxalate in an aqueous organic amine solution, and adding a substance containing an additive element to prepare an impregnation solution, wherein the additive element is one or more of Li, K, Cs, Re, Ca, Sr, Ba, Mo, W, Ni and Mn;

[0040] c) impregnating the above-mentioned alpha-alumina carrier in the impregnation solution;

[0041] d) the catalyst is obtained after the impregnated carrier is activated.

[0042] The preparation method of the silver-loaded catalyst according to the present application, the silver salt compound is one or more of silver acetate, silver nitrate, silver carbonate and silver lactate, preferably silver nitrate; the oxalate-containing aqueous solution is oxalic acid or aqueous ammonium oxalate, preferably oxalic acid.

[0043] The preparation method of the silver-loaded catalyst according to the present application, the organic amine is one or more of ethylenediamine, ethanolamine and 1,3-propanediamine.

[0044] The preparation method of the silver-loaded catalyst according to the present application, the content of a single auxiliary element is 10-1000 ppm of the mass of the catalyst.

[0045] The preparation method of the silver-loaded catalyst according to the present application, the impregnation solution and the impregnated alpha-alumina carrier are prepared at 20-40℃.

[0046] The preparation method of the silver-loaded catalyst according to the present application, the alpha-alumina carrier is impregnated with equal volume or excess under normal pressure or vacuum conditions, preferably, the alpha-alumina carrier is impregnated with excess under vacuum conditions.

[0047] The preparation method of the silver-loaded catalyst according to the present application, the activation treatment is heating at 150-500℃ for 2-30 minutes under air atmosphere. The activation mode can be selected from mesh belt furnace, hot air blowing or oven, and the heating mode can be natural gas heating, electric heating, steam heating or infrared heating.

[0048] The present application has the following beneficial effects:

[0049] The application provides an alpha alumina carrier and a silver catalyst prepared from the alpha alumina carrier. B can accelerate the conversion of alumina into alpha phase, and the converted alumina can form alpha alumina with a non-flaky morphology. By adding alpha-Al2O3 seeds with a flaky micro-morphology and a B-containing additive into hydrated alumina, the seeds induce a part of the hydrated alumina around the seeds to grow into flaky alpha alumina, and other hydrated alumina forms alpha alumina with a non-flaky morphology under the action of the B-containing additive. In addition, no F-containing substance is added in the preparation process of the carrier, so that the alumina is not easy to form flaky particles during the conversion into alpha phase due to the induction of F, and alpha alumina with both non-flaky and flaky micro-morphologies cannot be obtained. By the method, the alpha alumina carrier with both non-flaky and flaky micro-morphologies can be prepared. In addition, other elements in the additive, such as Ca, Si and Zr, mainly form low-melting solid solution composite oxides by combining with Al and O, so as to help the carrier to improve the strength. Another part of the elements, such as Ba, Zn and Y, can form some oxide particle substructures on the surface of the alumina micro-particles formed after sintering, so as to realize the surface modification of the alumina, improve the energy barrier of the migration and agglomeration of the loaded metal particles, and prolong the service life of the catalyst.

[0050] The silver catalyst prepared from the alpha alumina carrier with both non-flaky and flaky micro-morphologies has the performance advantages of the catalysts prepared from the carriers with the two micro-morphologies, that is, the catalyst has high mechanical strength and high selectivity, and the migration and agglomeration speed of the loaded silver component is slow, and the catalyst has a longer service life. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 It is a scanning electron microscope photo of the seed D;

[0052] Figure 2 It is a scanning electron microscope photo of the seed E;

[0053] Figure 3 It is a scanning electron microscope photo of the carrier A prepared in Example 1. DETAILED DESCRIPTION

[0054] The application will be described in detail through the following examples. It is necessary to point out here that the following examples are only used for further illustrating the application, and cannot be understood as the limitation of the protection scope of the application. Those skilled in the art can make some non-essential improvements and adjustments to the application according to the above content of the application.

[0055] Evaluation and analysis method:

[0056] [Carrier characterization method]

[0057] A. Specific surface area:

[0058] The surface area described in the present application specifically refers to the B.E.T surface area, which can be measured by any feasible method and reliable instrument, but here it is preferred to use the ASAP 2020 instrument of American Micromeritics Company and the method in the standard GB / T 19587-2004 to determine.

[0059] B. Pore structure:

[0060] Since most of the pores in the carrier are macropores, only mercury injection can obtain reliable results. The pore structure characterization here includes pore size distribution, pore volume and porosity. The equipment used in the examples is the American Micromeritics mercury injection instrument AutoPore 9500, and the test method refers to GB / T 21650.1-2008.

[0061] C. Micro-morphology:

[0062] The carrier micro-morphology analysis uses a Japanese Hitachi S-4800 scanning electron microscope with a magnification of 10,000 times.

[0063] D. Carrier strength:

[0064] In industry, the actual compression or impact of the catalyst particles in the reactor is mainly lateral compression, and vertical compression is very little. By using a suitable range of intelligent particle strength tester (such as the ASTMD-4179 particle strength tester produced by Vinci Company), the length of the prepared sample is measured one by one, and the pressure is applied to the point in the radial direction of the catalyst one by one until the particle is broken. The force applied by the machine at the moment of just breaking is recorded as N c , unit: Newton (N), the length of the catalyst particle is recorded as D p , unit: centimeter (cm), then the carrier strength = N c / D p , unit: Newton per centimeter (N / cm).

[0065] [Catalyst evaluation experimental method]

[0066] E. Reaction device:

[0067] The reaction device mainly consists of five parts: gas mixing reservoir, mass flow meter, pressure sensor, reactor and back pressure valve. The reaction raw materials are prepared in the gas mixing reservoir according to the reaction conditions, then measured and controlled by the mass flow meter, and then introduced into the reactor for reaction. The reactor is composed of a stainless steel pipe, an internal thermocouple sleeve and an electric heater, the reaction pressure is adjusted and controlled by the back pressure valve and the pressure sensor, 5 grams of broken catalyst particles are put into the reactor, and the bottom is supported by quartz wool.

[0068] F. Reaction conditions:​​

[0069] Airspeed = 4800h -1 Reaction pressure = 1.60 MPa;

[0070] Reactant raw materials: ethylene = 28 mol%, oxygen = 7.5 mol%, CO2 = 0.5 mol%, N2 as balance gas, containing about 0.5 to 2 ppm of 1,2-dichloroethane.

[0071] G. Analytical Methods:

[0072] The reaction gas after the pressure relief valve is connected to an online magnetic fan mass spectrometer via an online pipeline for analysis.

[0073] H. Performance evaluation methods:

[0074] Catalyst activity: Introduce the well-mixed reaction raw materials and gradually increase the reaction temperature until the ethylene oxide content at the reactor outlet stabilizes at 2.5 mol% ± 0.1 mol%. Record the initial reaction temperature at that time. The lower the temperature, the higher the catalyst activity.

[0075]

[0076] Catalyst stability:

[0077] Since it is difficult to determine the entire life cycle of a catalyst during the experimental stage (this process often takes 2-3 years or even longer), we often use the catalyst stability index to judge the catalyst's lifespan by measuring the increase in reaction temperature per unit time while maintaining a certain content of ethylene oxide in the reactor outlet atmosphere. The greater the increase in reaction temperature per unit time, the worse the catalyst stability and the shorter its lifespan.

[0078] The method is as follows: when the initial ethylene oxide content at the reactor outlet reaches 2.5 mol%, the reaction temperature T1 is recorded. When the catalyst runs continuously for 500 hours, the reaction temperature T2 is recorded. ΔT = T2 - T1. The larger the value, the worse the catalyst stability.

[0079] 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 examples.

[0080] The boehmite, alumina monohydrate, and alumina trihydrate used in the embodiments of this invention are all from Shandong Aluminum Industry.

[0081] All other chemicals are from Sinopharm Corporation and are of chemical purity or other equivalent purity available.

[0082] Preparation of "plate-like" α-Al2O3 seed crystals:

[0083] a) mixing 100 grams of hydrated alumina and X grams of F-containing inorganic salt;

[0084] b) adding Y grams of binder with mass concentration P and continuing to mix;

[0085] c) calcining the mixed material;

[0086] d) primary crushing the calcined material, and then ball milling to obtain the seed crystal.

[0087] The specific implementation is shown in Table 1.

[0088] The obtained seed crystal is characterized by scanning electron microscopy, and the seed crystals A, B, C and D all have the "flaky" α-Al2O3 morphology characteristics. The scanning electron microscope photograph of the seed crystal D is selected as a representative example, as shown in Figure 1 The seed crystals E and F do not have the "flaky" α-Al2O3 morphology characteristics, and the scanning electron microscope photograph of the seed crystal F is selected as a representative comparative example, as shown in Figure 2

[0089]

[0090] Example 1

[0091] The 28 grams of seed crystal A are dry mixed with 250 grams of pseudoboehmite, 750 grams of alumina trihydrate, 19 grams of barium oxide, 11 grams of zinc oxide, and 28 grams of boric acid, and then wet mixed with 220 grams of 30% acetic acid aqueous solution and 35 grams of sesbania powder to form a Laxi ring-shaped particle with an outer diameter of 5 mm, a particle length of 5 mm, and a mesopore diameter of 1.5 mm. The particle is dried at 120°C for 2 hours, and finally calcined at a temperature increasing rate of 3°C / min to 1300°C for 6 hours to prepare the carrier A. Figure 3 The scanning electron microscope image of the carrier A, in which both "flaky" and "non-flaky" micro-morphologies can be seen.

[0092] Example 2

[0093] The 20 grams of seed crystal B are dry mixed with 400 grams of pseudoboehmite, 600 grams of alumina trihydrate, 15 grams of calcium oxide, 10 grams of silicon oxide, and 45 grams of borax, and then wet mixed with 250 grams of 35% sulfuric acid aqueous solution and 50 grams of white oil to form a Laxi ring-shaped particle with an outer diameter of 6 mm, a particle length of 6 mm, and a mesopore diameter of 2.0 mm. The particle is dried at 110°C for 4 hours, and finally calcined at a temperature increasing rate of 8°C / min to 1400°C for 5 hours to prepare the carrier B.

[0094] Example 3

[0095] ​Example 1

[0096] Example 4

[0097] Example 5

[0098] Comparative Example 1

[0099] Comparative Example 2

[0100] Comparative Example 3

[0101] Comparative Example 4

[0102] Comparative Example 5

[0103] Comparative Example 6

[0104] Comparative Example 7

[0105] Comparative Example 8

[0106] Comparative Example 9

[0107] Comparative Example 10

[0108] Comparative Example 11

[0109] Comparative Example 12

[0110] The characterization data of the above carrier are shown in Table 2.

[0111] Table 2

[0112]

[0113] Examples 5-8 and Comparative Examples 5-10

[0114] Take 500 g of the carrier, dissolve at least one of silver nitrate, silver carbonate and silver lactate in deionized water, and react with an aqueous solution containing oxalate to obtain silver oxalate precipitate. The aqueous solution containing oxalate is an aqueous solution of oxalic acid or ammonium oxalate. The silver oxalate precipitate is filtered out, then repeatedly washed with deionized water and suction filtered until the filtrate is neutral. The washed silver oxalate is dissolved in an aqueous solution of an organic amine such as ethylenediamine, ethanolamine or a mixture thereof, then a mixture containing one or more of Li, K, Cs, Re, Mn, Sr, Ni, Co, Mo, W, Cu element promoters is added to prepare an impregnation solution, wherein the content of a single promoter element is 10-1000 ppm of the mass of the catalyst. The temperature of the impregnation solution is maintained at 30°C, and then the carrier is impregnated under vacuum. The impregnated carrier is dried at 110°C for 10 min, and then treated in an air stream at 300°C for 6 min to obtain the catalyst.

[0115] The prepared catalysts are tested by the aforementioned evaluation device and process conditions.

[0116] The specific preparation conditions and test results are shown in Table 3.

[0117] Table 3

[0118]

[0119]

[0120] Comparing Example 5 with Comparative Examples 5 and 9, Example 6 with Comparative Examples 6 and 10, Example 7 with Comparative Example 7, and Example 8 with Comparative Example 8, it can be found that although the silver content and promoter formulation of the catalysts in each comparison group are completely the same, the selectivity and stability of the carrier prepared by the technical scheme of the present application have been significantly improved.

[0121] Of course, the present application can have other various embodiments, and those skilled in the art can make various corresponding changes and modifications according to the present application without departing from the spirit and essence of the present application, but these corresponding changes and modifications should all belong to the protection scope of the claims of the present application.

Claims

1. A method for preparing an α-alumina support, characterized in that, Includes the following steps: a) Dry-mixing "flaky" α-Al2O3 seed crystals with hydrated alumina, a boron-containing inorganic compound, and additives to obtain a dry powder mixture, wherein the additives are one or more inorganic compounds containing Ca, Sr, Ba, Si, Zn, Zr, and Y; the mass ratio of hydrated alumina, α-Al2O3 seed crystals, additives, and boron-containing inorganic compounds is 100:1~3:1~3:1~5; b) Add binder and extrusion aid to the dry powder mixture and continue wet mixing, then shape, dry and calcine to obtain α-alumina carrier.

2. The method for preparing the α-alumina support according to claim 1, characterized in that, The "flaky" α-Al2O3 seed crystals are obtained by mixing hydrated alumina and an F-containing inorganic salt, then adding a binder and continuing to mix, followed by calcination, crushing, and ball milling of the resulting mixture.

3. The method for preparing the α-alumina support according to claim 1 or 2, characterized in that, The hydrated alumina is one or more of monohydrated alumina, boehmite, and trihydrated alumina; the binder is an aqueous solution of one or more of hydrochloric acid, sulfuric acid, nitric acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, and citric acid with a mass concentration of 20-50%.

4. The method for preparing the α-alumina support according to claim 1 or 2, characterized in that, The hydrated alumina is a mixture of boehmite and alumina trihydrate.

5. The method for preparing the α-alumina support according to claim 1, characterized in that, The inorganic compound containing B in step a) is one or more of boric acid, boron carbide, boron nitride, and borax.

6. The method for preparing the α-alumina support according to claim 1, characterized in that, In step b), the extrusion aid is one or more of the following: white oil, paraffin wax, petrolatum, stearic acid, and guar gum powder.

7. The method for preparing the α-alumina support according to claim 1, characterized in that, In step b), the mass ratio of the dry powder mixture, binder, and extrusion aid is 100:20~25:3~5.

8. A silver-supported catalyst, characterized in that, The catalyst support is an α-alumina support prepared by any one of claims 1 to 6.

9. The method for preparing the silver-supported catalyst according to claim 8, characterized in that, Includes the following steps: a) Reaction of an aqueous solution of a silver salt compound with an aqueous solution containing oxalate ions yields silver oxalate precipitate; b) Dissolve the washed silver oxalate in an aqueous organic amine solution and add a substance containing an auxiliary element to prepare an impregnation solution, wherein the auxiliary element is one or more of Li, K, Cs, Re, Ca, Sr, Ba, Mo, W, Ni and Mn; c) Immerse the α-alumina support prepared by the preparation method according to any one of claims 1 to 6 in the impregnation solution; d) The catalyst is obtained after the impregnated support is activated.

10. The method for preparing the silver-supported catalyst according to claim 9, characterized in that, The organic amine is one or more of ethylenediamine, ethanolamine, and 1,3-propanediamine.

11. The method for preparing the silver-supported catalyst according to claim 9, characterized in that, The content of a single auxiliary element, calculated by mass, is 10 to 1000 ppm of the catalyst mass.

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