Alpha-alumina support and method for its preparation with silver catalyst

Abstract

The application discloses an alpha-alumina carrier and a preparation method of the alpha-alumina carrier and a silver catalyst. The preparation method of the alpha-alumina carrier comprises the following steps: (1) preparing "non-flaky" alpha-Al2O3 seeds; (2) mixing the seeds obtained in the step (1), hydrated alumina, an additive and an F-containing inorganic salt according to the mass ratio of (1.5-3):100:(0.1-0.3):(1-3); (3) adding a binder with a mass concentration of 25%-45% and an extrusion aid, continuously mixing and forming into particles according to the mass ratio of the mixture in the step (2):the binder:the extrusion aid=100:(25-45):(8-12), and drying and calcining to obtain the alpha-alumina carrier. The alpha-alumina carrier prepared by the application has the advantages of "non-flaky" and "flaky" micro-morphologies, the silver catalyst prepared by the alpha-alumina carrier has the performance advantages of the catalysts prepared by the two kinds of micro-morphology carriers, and the silver catalyst has good stability.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to an α-alumina support and its preparation method with a silver catalyst. Background Technology

[0002] Ethylene oxide is a crucial downstream derivative of ethylene, second only to polyethylene. It is primarily used in the production of chemical raw materials such as ethylene glycol and polyether monomers, making it a vital chemical product today. Ethylene oxide is produced using the selective oxidation of ethylene with oxygen, with its core technology being an ethylene epoxide silver catalyst. This catalyst uses α-Al₂O₃ as a support, loaded with Ag as the main component and auxiliary elements such as Cs and Re. The physical properties and surface chemistry of the support significantly influence the catalyst's reactivity; therefore, modulating the support properties is an important means of improving the catalyst's reactivity.

[0003] The microstructure of α-Al₂O₃ supports significantly affects their physical properties and catalyst performance. Supports with a "non-plate-like" microstructure exhibit slower silver atom migration and aggregation during the reaction, resulting in higher catalyst stability and longer lifespan. However, these supports have lower mechanical strength and narrower pore sizes, which are detrimental to improving selectivity. Conversely, supports with a "plate-like" microstructure have higher mechanical strength and wider pore sizes, which are beneficial for improving selectivity. However, the silver components migrate and aggregate more rapidly, leading to lower catalyst stability.

[0004] For supports with a non-flaky microstructure, existing technologies often employ the addition of fluxing agents to address their low mechanical strength, while simultaneously adding pore-forming agents to increase pore size and improve selectivity. However, these two methods sometimes cancel each other out, resulting in a less than satisfactory overall improvement. For supports with a flaky microstructure, existing technologies often use the addition of metal oxides to attempt to create protrusions on the flaky particles to slow down silver agglomeration, but the effect remains limited.

[0005] CN103372466A describes a method for preparing a catalyst support by uniformly mixing trihydrate α-alumina, pseudo-monohydrate alumina, mineralizers, alkaline earth metal compound additives, and combustible lubricants in different proportions, followed by kneading, extrusion molding, and high-temperature calcination. The mineralizer lowers the alumina crystallization temperature, resulting in alumina wafers with a flaky, interwoven distribution, and the support exhibiting high strength. While this method can produce an α-Al₂O₃ catalyst support with flaky granular matrix characteristics, it cannot simultaneously achieve a catalyst support with two different microscopic morphologies of α-Al₂O₃ particles, which is significantly different from the approach described in this invention. CN200680008891.9 describes introducing fluorine into the support preparation process. The support may contain, and preferably contains, granular matrices with a layered or sheet-like morphology. Similarly, particles with a size greater than 0.1 micrometers in at least one direction have at least one substantially flat main surface; such particles may have two or more flat main surfaces. While this method can produce α-Al₂O₃ catalyst supports with layered or plate-like granular matrix characteristics, it cannot simultaneously produce catalyst supports with α-Al₂O₃ particles exhibiting both microscopic morphologies, which is significantly different from the approach of this invention. CN201180011967.4 discloses a method for preparing α-Al₂O₃ supports with a non-platelet morphology. "Non-platelet morphology" refers to the morphology of the support when imaged by a scanning electron microscope at 2000 magnification, and specifically refers to the absence of structures with substantially flat surfaces in the image. "Substantially nonexistent of such a structure 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 twice the length of the surface's largest dimension. Structures with substantially flat surfaces typically have a maximum aspect ratio of 4:1, where the aspect ratio is the ratio of the structure's largest dimension to its smallest dimension. The term "structure" refers to the structural entity within the support, which can be specified as a single particle of the support material that is molten or bonded together to form the support. While this method can achieve α-Al₂O₃ catalyst supports with non-sheet-like granular matrix characteristics, it cannot simultaneously achieve... The catalyst support for α-Al₂O₃ particles exhibiting two different microscopic morphologies differs significantly from the approach of this invention. CN200580032036.7 discloses that fluoride-mineralized alumina supports can yield granular matrices with morphologies characterized as layered or plate-like. This matrix has particles larger than 1 micrometer in size in at least one direction possessing at least one substantially flat main surface. While this method can produce α-Al₂O₃ catalyst supports with layered or plate-like granular matrix characteristics, it cannot achieve catalyst supports with α-Al₂O₃ particles exhibiting both microscopic morphologies simultaneously, which is significantly different from the approach of this invention.The paper "Effect of nano-TiO2 and nano-SiO2 addition on the morphological control of α-Al2O3 platelets via solid-state reaction" discloses a method for adjusting the microstructure of α-alumina by regulating the addition of fluorides and the ratio of nano-silica and nano-titanium oxide. While this method can prepare α-Al2O3 with either plate-like or non-plate-like microstructures, it cannot achieve catalyst supports with α-Al2O3 particles possessing both microstructure characteristics simultaneously, which is significantly different from the approach described in this invention. Summary of the Invention

[0006] In view of the defects of the above-mentioned technology, the purpose of the present invention is to provide a method for preparing an α-alumina support that has both "non-sheet" and "sheet" micromorphologies, and the silver catalyst supported thereon can simultaneously have the performance advantages of catalysts prepared by supports with both micromorphologies.

[0007] To achieve the above objectives, this invention proposes a method for preparing an α-alumina support, comprising the following steps:

[0008] (1) Preparation of “non-plate” α-Al2O3 seed crystals:

[0009] a. Mix hydrated alumina and boron-containing compounds at a mass ratio of 100:(2~8);

[0010] b. Add 10% to 90% of the binder by mass and continue mixing. Then, calcine the mixture at a heating rate of 3 to 15°C / min, raise the temperature to 1250 to 1400°C, hold for 5 to 8 hours, and allow it to cool naturally to room temperature.

[0011] c. Perform initial crushing and ball milling for 3-10 hours to obtain "non-flaky" α-Al2O3 seed crystals. Dry milling or wet milling is used, with wet milling being preferred. A dispersant can be used for ball milling, and the dispersant is deionized water or ethanol.

[0012] (2) Mix the seed crystals obtained in step (1) in the following mass ratio: hydrated alumina: additive: F-containing inorganic salt = (1.5~3): 100: (0.1~0.3): (1~3);

[0013] (3) Add binder and extrusion aid with a mass concentration of 25%~45%, and mix according to the mass ratio of mixture in step (2): binder: extrusion aid = 100: (25~45): (8~12) to form granules. After drying and calcination, α-alumina carrier is obtained.

[0014] The initial crushing in the preparation of "non-flaky" α-Al2O3 seed crystals can be carried out by various mechanical processing methods, as long as more than 90% of them can pass through a 10-mesh sieve.

[0015] The “non-flaky” α-Al2O3 seed crystals are α-Al2O3 particles with a size in the range of 10~900nm.

[0016] Here, "non-flaky" refers to a microscopic morphology where the surface area of ​​a single side does not exceed 25% of the outer surface of the particle, and the radius of curvature of the single side surface is at least twice the length of the maximum dimension of the surface.

[0017] The hydrated alumina is selected from at least one of alumina monohydrate, boehmite, and alumina trihydrate, preferably a combination of boehmite and alumina trihydrate; the boron-containing compound is selected from at least one of boric acid, boron carbide, boron nitride, and borax; the additive is selected from at least one of inorganic salts or oxides of Ca, Sr, Ba, Si, Zn, Zr, Y, and F; the binder is an aqueous solution of at least one of hydrochloric acid, sulfuric acid, nitric acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, and citric acid; the extrusion aid is selected from at least one of white oil, paraffin wax, petrolatum, stearic acid, and guar gum; and the F inorganic salt is selected from at least one of ammonium fluoride and aluminum fluoride.

[0018] Compared to alumina, hydrated alumina exhibits better formability, and its physicochemical properties can be controlled through heat treatment and doping. The additives serve two purposes: firstly, by combining with Al and O to form low-melting-point solid solution composite oxides, they help improve the strength of the support; secondly, they can form substructures of oxide particles on the surface of the final sintered alumina microparticles, thereby modifying the alumina surface, increasing the energy barrier for the aggregation and movement of the supported metal, and extending the catalyst lifetime. The F-containing inorganic salt lowers the alumina transformation temperature, accelerating the transformation of the support to α-phase alumina. Simultaneously, F can guide the growth of α-alumina into particles with a "non-flaky" microstructure. The binder reacts with hydrated alumina to form an alumina sol, providing a certain degree of adhesion between the raw materials. The extrusion aid reduces friction and adhesion of the materials in the molding equipment, helping the support to form better.

[0019] Preferably, in step (3), the forming process can be extruded into strips and then sliced ​​or directly pressed into tablets; the shaped particles after forming are Raschig rings, short cylindrical particles with no or many holes in the middle, preferably with an outer diameter of 5~10mm, a particle length of 5~10mm, and a central hole diameter of 1.5~4.5mm; the drying temperature is 100~200℃, preferably 110~150℃, and the drying time is 2~12h; the heating rate of the calcination 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.

[0020] The calcination equipment used is a muffle furnace, tunnel kiln, or bell kiln. Drying is performed to remove most of the free water from the shaped carrier precursor, preventing the excessive evaporation of moisture during subsequent calcination from adversely affecting the strength of the carrier particles and the interior of the furnace. Hydrated alumina undergoes dehydration and phase transformation at high temperatures, converting to α-alumina. 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.

[0021] The present invention also proposes an α-alumina carrier, characterized in that the α-alumina carrier simultaneously possesses both "non-sheet" and sheet-like micromorphologies.

[0022] This invention first prepares α-Al₂O₃ seed crystals with a "non-plate-like" microstructure. These seed crystals, along with an F-containing additive, are added to hydrated alumina. During high-temperature calcination, the seed crystals induce the growth of "non-plate-like" α-alumina in a portion of the surrounding hydrated alumina, while the remaining hydrated alumina, under the influence of the F-containing additive, forms a "plate-like" α-alumina support. This results in an α-alumina support possessing both "non-plate-like" and "plate-like" microstructures. The "non-plate-like" support exhibits slower silver atom migration and aggregation during the reaction, resulting in higher catalyst stability and longer service life. However, it also has lower mechanical strength and narrower pore size, which is detrimental to improving selectivity. Conversely, the "plate-like" support has higher mechanical strength and wider pore size, which is beneficial for improving selectivity. However, the silver atom migrates and aggregates more rapidly, leading to lower catalyst stability. The support protected by this invention combines both of these advantages.

[0023] This invention also proposes a method for preparing a supported silver catalyst, comprising the following steps:

[0024] (1) Silver oxalate precipitate is obtained by reacting an aqueous solution of a silver salt compound with an aqueous solution containing oxalate.

[0025] (2) Dissolve the washed silver oxalate in an organic amine solution and add one or more of the following additives containing Li, K, Cs, Re, Ca, Sr, Ba, Mo, W and Cu to prepare an impregnation solution. The amount of additive element added is 0.11~0.15% of the Ag element content in the impregnation solution by mass. The temperature of the impregnation solution is maintained at 20~40℃.

[0026] (3) Immerse the α-alumina carrier in the impregnation solution described in step (2) under normal pressure or vacuum conditions in equal volume or excess.

[0027] (4) The impregnated carrier is activated in an air atmosphere heated to 150-500℃ for 2-30 minutes to obtain the catalyst.

[0028] Wherein, the silver salt compound is at least one of silver acetate, silver nitrate, silver carbonate, and silver lactate, preferably silver nitrate; the aqueous solution containing oxalate is an aqueous solution of oxalic acid or ammonium oxalate, preferably oxalic acid; the aqueous solution of organic amine is an aqueous solution of ethylenediamine, ethanolamine, 1,3-propanediamine, or a mixture thereof.

[0029] Preferably, in step (3), the impregnation conditions are to impregnate the α-alumina support under vacuum conditions.

[0030] In addition, the activation method in step (4) can be a mesh belt furnace, hot air purging or oven, and the heating method can be natural gas heating, electric heating, steam heating or infrared heating.

[0031] The beneficial effects of this invention are:

[0032] This invention first prepares α-Al2O3 seed crystals with a "non-plate" microstructure. The seed crystals and an F-containing additive are added to hydrated alumina. After high-temperature calcination, an α-alumina support with both "non-plate" and "plate" microstructures is formed. The silver catalyst prepared with this support exhibits significantly improved stability and a longer catalyst lifetime after 500 hours of continuous operation. Attached Figure Description

[0033] Figure 1 These are typical scanning electron microscope images of the carrier of this invention. Detailed Implementation

[0034] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. These embodiments are implemented based on the technical solution of the present invention and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0035] Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and compounds are commercially available.

[0036] A. Specific surface area:

[0037] The surface area described in this invention specifically refers to the BET surface area, which can be measured by any feasible method and reliable instrument. Preferred methods are the ASAP 2020 instrument from Mack Company and the method in standard GB / T19587-2004.

[0038] B. Hole structure:

[0039] Since most of the pores in the carrier are macropores, only mercury porosimetry can yield reliable results. The pore structure characterization here includes pore size distribution, pore volume, and porosity. The equipment used in the examples is an AutoPore 9500 mercury porosimeter from the USA, and the test method follows GB / T 21650.1-2008.

[0040] C. Microstructure: The microstructure of the carrier was analyzed using a Hitachi S-4800 scanning electron microscope from Japan, with a magnification of 10,000 times.

[0041] Catalyst evaluation experimental methods:

[0042] D. Reaction apparatus:

[0043] The reaction apparatus mainly consists of five parts: a gas mixing and storage tank, a mass flow meter, a pressure sensor, a reactor, and a back pressure valve. The reaction raw materials are prepared in the gas mixing and storage tank according to the reaction conditions, and then metered and controlled by the mass flow meter before being introduced into the reactor for reaction. The reactor consists of a φ12mm stainless steel tube, an internal φ2mm thermocouple sheath, and an electric heater. The reaction pressure is regulated and controlled by the back pressure valve and the pressure sensor. Five grams of crushed catalyst particles are placed into the reactor, and the bottom is supported by quartz wool.

[0044] E. Reaction conditions:

[0045] Airspeed = 4800 h -1 ; Reaction pressure = 1.60 MPa; Reaction feedstock: ethylene = 28 mol%, oxygen = 7.5 mol%, CO2 = 0.5 mol%, N2 is the equilibrium gas, which contains about 0.5 to 2 ppm of 1,2-dichloroethane.

[0046] F. Analytical method: The reaction gas after the pressure relief valve is connected to an online magnetic fan mass spectrometer through an online pipeline for analysis.

[0047] G. Performance evaluation methods:

[0048] 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.

[0049]

[0050] Catalyst stability: When the initial ethylene oxide content at the reactor outlet reaches 2.5 mol%, record the reaction temperature T1. When the catalyst runs continuously for 500 hours, record the reaction temperature T2. ΔT = T2 - T1. The larger the value, the worse the catalyst stability.

[0051] Figure 1 These are typical scanning electron microscope images of the carrier in this invention, in which α-alumina can be seen to exhibit both "sheet-like" and "non-sheet-like" microscopic morphological characteristics.

[0052] (1) Non-plate-like α-Al2O3 seed crystals

[0053] a. Mix hydrated alumina and boron-containing compounds at a mass ratio of 100:(2~8);

[0054] b. Add 10%~90% of binder by mass and continue mixing, then calcine. The heating rate during calcineation is 3~15℃ / min, and the temperature is raised to 1250~1400℃. The temperature is held for 5~8 hours and then allowed to cool naturally to room temperature.

[0055] c. Perform initial crushing and ball milling to obtain "non-flaky" α-Al2O3 seed crystals. The ball milling ball-to-material ratio is 50:1, the rotation speed is 500 r / min, and the time is 3~10 h. Dry milling or wet milling is used, with wet milling being preferred. The ball milling can use a dispersant, which is deionized water or ethanol. Specific implementation details are shown in Table 1.

[0056] (1) Carrier

[0057] Carrier A: 28 g of seed crystal A was first dry-mixed with 250 g of boehmite, 750 g of alumina trihydrate, 1.9 g of barium oxide, 1.1 g of zinc oxide, and 30 g of ammonium fluoride. 1000 g of this mixture was then wet-mixed with 350 g of 30% acetic acid aqueous solution and 80 g of guar gum powder to form Raschig ring-shaped particles with an outer diameter of 5 mm, a particle length of 5 mm, and a mesopore diameter of 1.5 mm. The particles were then dried at 120 °C for 2 hours, and finally calcined at 1300 °C for 6 hours at a heating rate of 3 °C / min to obtain carrier A.

[0058] Carrier B: 20 ​​g of seed crystal B was first dry-mixed with 400 g of boehmite, 600 g of alumina trihydrate, 1.5 g of calcium oxide, 1.0 g of silicon oxide, and 50 g of ammonium fluoride. 1000 g of this mixture was then wet-mixed with 450 g of 35% sulfuric acid aqueous solution and 100 g of white oil to form Raschig ring-shaped particles with an outer diameter of 6 mm, a particle length of 6 mm, and a mesopore diameter of 2.0 mm. The particles were then dried at 110 °C for 4 hours, and finally calcined at 1400 °C for 5 hours at a heating rate of 8 °C / min to obtain carrier B.

[0059] Carrier C: 30 g of seed crystal C was first dry-mixed with 350 g of boehmite, 650 g of alumina trihydrate, 0.5 g of iridium dioxide, 0.8 g of strontium nitrate, and 10 g of aluminum fluoride. 1000 g of this mixture was then wet-mixed with 250 g of 45% hydrochloric acid aqueous solution and 120 g of paraffin wax to form Raschig ring-shaped particles with an outer diameter of 7 mm, a particle length of 7 mm, and a mesopore diameter of 2.5 mm. The particles were then dried at 150 °C for 3 hours, and finally calcined at 1200 °C for 8 hours at a heating rate of 6 °C / min to obtain carrier C.

[0060] Carrier D: 15 g of seed crystal D was first dry-mixed with 300 g of boehmite, 700 g of alumina trihydrate, 1.6 g of barium sulfate, 0.5 g of zirconium oxide, and 15 g of ammonium fluoride. 1000 g of this mixture was then wet-mixed with 300 g of 25% nitric acid aqueous solution and 90 g of petrolatum to form Raschig ring-shaped particles with an outer diameter of 8 mm, a particle length of 8 mm, and a mesopore diameter of 3 mm. The particles were then dried at 110 °C for 5 hours, and finally calcined at 1280 °C for 7 hours at a heating rate of 4 °C / min to obtain carrier D.

[0061] Comparative support E: The preparation method is basically the same as that of support A, except that the seed crystal used is comparative seed crystal E.

[0062] Comparative support F: The preparation method is basically the same as that of support D, except that the seed crystal used is comparative seed crystal F.

[0063] Comparison with support G: The preparation method is basically the same as that of support A, except that no seed crystals are added.

[0064] The characterization data of the above carriers are detailed in Table 2.

[0065] (2) Catalyst

[0066] Take 500g of the support, dissolve at least one silver salt selected from silver nitrate, silver carbonate, and silver lactate in deionized water, and react it 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. Filter the silver oxalate precipitate, and then wash it repeatedly with deionized water until the filtrate is neutral. Dissolve the washed silver oxalate in an aqueous solution of an organic amine such as ethylenediamine, ethanolamine, 1,3-propanediamine, or a mixture thereof, and then add one or more of the following additives: Li, K, Cs, Re, Mn, Sr, Ni, Co, Mo, W, and Cu, to prepare an impregnation solution. The total amount of additive elements added is 0.11%~0.15% by mass of the Ag element content in the impregnation solution. Maintain the temperature of the impregnation solution at 30℃, and then impregnate the support under vacuum. Dry the impregnated support at 110℃ for 10 min, and then treat it in an air stream at 300℃ for 6 min to obtain the catalyst.

[0067] The prepared catalysts were compared and tested using the aforementioned evaluation apparatus and process conditions.

[0068] The specific preparation conditions and test results are shown in Table 3.

[0069] As can be seen from Tables 3 and 4, the value of ΔT (°C) is smaller in the examples compared to the comparative examples, indicating that the stability of the supported silver catalyst prepared by the present invention is significantly improved after 500 hours of continuous operation.

[0070] In summary, the α-alumina support prepared by this invention has the advantages of both "non-sheet" and "sheet" microstructures. The silver catalyst prepared with it can simultaneously possess the performance advantages of catalysts prepared with supports of both microstructures and has good stability.

[0071] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the present invention.

[0072] Table 1

[0073] serial number Hydrated alumina Compounds containing B adhesive Adhesive mass concentration (%) Heating rate (°C / min) Maximum roasting temperature (°C) Duration (h) ball milling method Ball milling time (h) dispersant Seed Crystal A 100g of pseudoboehmite Boric acid 2(g) 60g of nitric acid aqueous solution 50 3 1250 5 Dry grinding 3 none Seed crystal B 100g of aluminum oxide monohydrate Boron carbide 4(g) 45g of acetic acid aqueous solution 90 8 1300 6 wet milling 6 Deionized water Seed C 100g of aluminum oxide trihydrate Boron nitride 6(g) 30g of sulfuric acid aqueous solution 10 15 1350 7 Dry grinding 8 none Seed Crystal D 45% boehmite + 55% alumina trihydrate 100g Boric acid 8g 15g of nitric acid aqueous solution 45 5 1400 8 wet milling 10 ethanol Comparison of seed crystal E 100g of pseudoboehmite none none 50 3 1250 5 Dry grinding 3 none Comparison of seed crystal F 45% boehmite + 55% alumina trihydrate 100g none none 45 5 1400 8 wet milling 10 ethanol

[0074] Table 2

[0075] serial number Specific surface area (m² / g) Pore ​​volume (ml / g) Average pore size (nm) Can scanning electron microscopy simultaneously observe "sheet-like / non-sheet-like" structures? Carrier A 1.187 0.445 781.19 yes Carrier B 1.232 0.491 829.43 yes Carrier C 1.351 0.462 965.66 yes Carrier D 1.558 0.434 1061.95 yes Comparison vector E 0.956 0.518 882.32 no Comparison carrier F 1.285 0.489 963.88 no Comparison carrier G 2.183 0.382 708.74 no

[0076] Table 3

[0077] serial number carrier Silver loading Silver salt Oxalate compounds Organic amines Additive dosage (ppm) Conversion rate (%) Selectivity (%) Stability ΔT (°C) Example 1 Carrier A 15% silver nitrate oxalic acid ethylenediamine Li=100Cs=400Ba=100Re=390Mo=110 10.3 87.2 6.1 Example 2 Carrier B 20% Silver carbonate ammonium oxalate ethylenediamine Cs=350K=150Ca=700Re=420Mn=50 9.5 88.5 7.8 Example 3 Carrier C 25% Silver lactate ammonium oxalate ethanolamine Cs=300K=200Ca=100Sr =400W=430Ni=40 9.0 90.1 7.5 Example 4 Carrier D 18% silver nitrate oxalic acid ethanolamine, ethylenediamine K=20Li=10Cs=70Sr=600Ba=300Re=390Mn=110 8.2 90.6 5.9

[0078] Table 4

[0079] serial number carrier Silver loading Silver salt Oxalate compounds Organic amines Additive dosage (ppm) Conversion rate (%) Selectivity (%) Stability ΔT (°C) Comparative Example 1 Comparison vector E 15% silver nitrate oxalic acid ethylenediamine Li=100Cs=400Ba=100Re=390Mo=110 11.1 86.9 10.2 Comparative Example 2 Comparison carrier F 20% Silver carbonate ammonium oxalate ethylenediamine Cs=350K=150Ca=700Re=420Mn=50 9.2 88.2 9.8 Comparative Example 3 Comparison carrier G 25% Silver lactate ammonium oxalate ethanolamine Cs=300K=200Ca=100Sr =400W=430Ni=40 12.0 85.6 8.5

Claims

1. A method for preparing an α-alumina support, comprising the following steps: (1) Preparation of "non-plate" α-Al2O3 seed crystals: a. Mix hydrated alumina and boron-containing compounds at a mass ratio of 100:(2~8); b. Add 10% to 90% of the binder by mass and continue mixing. Then, calcine the mixture at a heating rate of 3 to 15°C / min, raise the temperature to 1250 to 1400°C, hold for 5 to 8 hours, and allow it to cool naturally to room temperature. c. Perform initial crushing and ball milling for 3-10 hours to obtain "non-flaky" α-Al2O3 seed crystals, using either dry or wet milling methods. (2) Mix the seed crystals obtained in step (1) in the following mass ratio: hydrated alumina: additive: F-containing inorganic salt = (1.5~3): 100: (0.1~0.3): (1~3); (3) Add binder and extrusion aid with a mass concentration of 25%~45%, and mix according to the mass ratio of mixture in step (2): binder: extrusion aid = 100: (25~45): (8~12) to form granules. After drying and calcination, α-alumina carrier is obtained. In step (3), the heating rate of the roasting is 2 to 20 °C / min, the temperature is raised to 1200 to 1400 °C, the holding time is 5 to 8 hours, and then it is naturally cooled to room temperature; The α-alumina support has both "non-sheet" and sheet-like micromorphologies.

2. The preparation method according to claim 1, characterized in that, In step (1) c, ball milling is performed using a wet milling method. The ball milling uses a dispersant, which is deionized water or ethanol.

3. The preparation method according to claim 1, characterized in that, The "non-flaky" α-Al2O3 seed crystals are α-Al2O3 particles with a size in the range of 10~900nm.

4. The preparation method according to claim 1, characterized in that, The hydrated alumina is selected from at least one of monohydrated alumina, boehmite, and trihydrated alumina; the boron-containing compound is selected from at least one of boric acid, boron carbide, boron nitride, and borax; the additive is selected from at least one of inorganic salts or oxides of Ca, Sr, Ba, Si, Zn, Zr, and Y; the binder is an aqueous solution of at least one of hydrochloric acid, sulfuric acid, nitric acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, and citric acid; the extrusion aid is selected from at least one of white oil, paraffin wax, petrolatum, stearic acid, and guar gum; and the fluorine-containing inorganic salt is selected from at least one of ammonium fluoride and aluminum fluoride.

5. The preparation method according to claim 1, characterized in that, The hydrated alumina is a combination of boehmite and alumina trihydrate.

6. The preparation method according to claim 1, characterized in that, In step (3), the forming process can be extruded into strips and then sliced ​​or directly pressed into tablets; the granules after forming are short cylindrical shapes with Raschig rings, no holes in the middle or many holes; The drying temperature is 100-200℃, and the drying time is 2-12 hours. The heating rate during roasting is 3–18 °C / min.

7. The preparation method according to claim 6, characterized in that, The formed particles are Raschig ring particles with an outer diameter of 5-10 mm, a particle length of 5-10 mm, and a central hole diameter of 1.5-4.5 mm. The drying temperature is 110–150°C.

8. A method for preparing a supported silver catalyst, characterized in that, Includes the following steps: (1) Silver oxalate precipitate is obtained by reacting an aqueous solution of a silver salt compound with an aqueous solution containing oxalate. (2) Dissolve the washed silver oxalate in an organic amine solution and add one or more of the following additives containing Li, K, Cs, Re, Ca, Sr, Ba, Mo, W and Cu to prepare an impregnation solution. The amount of additive element added is 0.11% to 0.15% of the Ag element content in the impregnation solution by mass. The temperature of the impregnation solution is maintained at 20 to 40°C. (3) Immerse the α-alumina carrier prepared by any one of claims 1 to 7 in the impregnation solution described in step (2) under normal pressure or vacuum conditions in equal volume or excess. (4) The impregnated carrier is activated in an air atmosphere heated to 150-500℃ for 2-30 minutes to obtain the catalyst.

9. The preparation method according to claim 8, characterized in that, The silver salt compound is at least one of silver acetate, silver nitrate, silver carbonate, and silver lactate; the aqueous solution containing oxalate is an aqueous solution of oxalic acid or ammonium oxalate; the organic amine solution is an aqueous solution of ethylenediamine, ethanolamine, 1,3-propanediamine, or a mixture thereof.

10. The preparation method according to claim 8, characterized in that, The silver salt compound is silver nitrate; the aqueous solution containing oxalate is oxalic acid.

11. The preparation method according to claim 8, characterized in that, In step (3), the impregnation condition is to impregnate the α-alumina carrier excessively under vacuum conditions.

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