Silver catalyst for producing ethylene oxide through ethylene epoxidation as well as preparation method and application of silver catalyst

Abstract

The invention belongs to the technical field of silver catalysts, and discloses a preparation method of a silver catalyst for producing ethylene oxide through ethylene epoxidation, and the preparation method comprises the following steps: preparing a silver amine solution; uniformly mixing a silver amine solution, a water-soluble surfactant, an organic rhenium auxiliary agent, water, an optional alkali metal auxiliary agent and an optional co-auxiliary agent of a rhenium auxiliary agent to obtain impregnation liquid; impregnating a carrier in the impregnation liquid, leaching, drying and heating to obtain the silver catalyst, wherein the water-soluble surfactant is at least one of water-soluble fatty alcohol-polyoxyethylene ether, water-soluble alkylphenol polyoxyethylene ether and water-soluble fatty acid polyoxyethylene ester; the polymerization degree of polyoxyethylene in the water-soluble fatty alcohol-polyoxyethylene ether, the polymerization degree of polyoxyethylene in the water-soluble alkylphenol polyoxyethylene ether and the polymerization degree of polyoxyethylene in the water-soluble fatty acid polyoxyethylene ester are all greater than 5 and less than 15. The silver catalyst prepared by the method provided by the invention has high activity and selectivity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silver catalyst, more particularly, to a silver catalyst for ethylene epoxidation to produce ethylene oxide and a preparation method and application thereof. BACKGROUND

[0002] Silver catalyst is a catalyst used in the industrial production of ethylene oxide (EO) by ethylene epoxidation. Shell Company, Dow Chemical (UCC), S.D Company and China Petroleum and Chemical Corporation have done a lot of research on silver catalyst. The first patent for the production of EO by direct oxidation of ethylene was published in 1931, and it has been more than 80 years since then. After continuous experiments and improvements by researchers around the world, the selectivity of EO has been improved from 70% in the early 1970s to nearly 90% at present.

[0003] There are three types of silver catalysts used in industrial EO / EG production devices: high-activity silver catalyst, high-selectivity silver catalyst and medium-selectivity silver catalyst. The high-activity silver catalyst has high activity and good stability, with a selectivity of 80-82% and a service life of 2-5 years, which is suitable for traditional EO / EG production devices with a high CO2 concentration (usually 5%-10%) at the inlet of the reactor. The high-selectivity silver catalyst has a selectivity of more than 88%, but requires a CO2 concentration of less than 1.0% in the reaction gas, which is suitable for newly built EO / EG production devices with relatively low space-time yield. The medium-selectivity silver catalyst has a selectivity of 84-85%, and requires a CO2 concentration of less than 3% in the reaction gas, and the selectivity of the catalyst is adjusted according to the space-time yield of production.

[0004] With the increasing scarcity of petroleum resources and the increasing demand for energy saving, high-selectivity silver catalysts and medium-selectivity silver catalysts have been widely used in industrial production to replace the original high-activity silver catalysts. The activity, selectivity and stability of the catalyst are the main performance indicators for evaluating silver catalysts. The performance of silver catalysts is related to the composition and preparation method of the catalyst, in addition to the performance of the carrier and its preparation method.

[0005] From the composition of the catalyst, the active component is metallic silver, and organic solvents and additives are added to improve the selectivity of the product. The additive components of silver catalysts mainly include alkali metals, alkaline earth metals, rare earth metals and transition metals, etc. Literature reports that alkali metals can make silver particles more evenly distributed on the carrier, and can promote the generation of electrophilic oxygen and the transition state oxygen-metal ring (OMC) of ethylene epoxidation; some literature also introduces that alkali metals can make silver generate more lattice defects on the surface of the carrier, which is easy for the adsorption of subsurface oxygen and the generation of EO. USP 6762311 prefers to add alkali metal in the form of hydroxide, and USP 6815395 prefers to add alkali metal in the form of nitrate, which improves the performance of the catalyst by impregnating different alumina carriers.

[0006] Another very important promoter is rhenium, the difference between high activity catalyst and medium and high selectivity silver catalyst is that the latter two contain rhenium promoter in the catalyst composition, the selectivity of the catalyst is significantly improved. USP 4761394 first reported the use of rhenium (Re) as a promoter for silver catalyst, USP 4548921 described the role of rhenium promoter in silver catalyst, Re exists as uniformly dispersed metal particles on the carrier, and the active component silver is supported on the outer surface of rhenium, which improves the performance of silver catalyst. Some literature also believes that the rhenium promoter competes with the adsorbed oxygen on the surface of the catalyst and attracts the electrons in the silver lattice, resulting in a decrease in the electron density of the adsorbed oxygen and an increase in the selectivity of the product EO. USP 7259129 rhenium promoter can be added in the form of chloride, rhenate and perrhenate, CN 201010622856.4 and CN 201010534019.6 rhenium promoter is an inorganic compound containing rhenium, such as perrhenic acid, rhenate, or a mixture thereof. There is basically no report on organic rhenium promoter.

[0007] The co-promoter of the rhenium promoter can keep the rhenium promoter in a high valence state and ensure that the catalyst has high selectivity. USP 7538235 describes that the co-promoter of the rhenium promoter includes one or more than two compounds containing tungsten, chromium, molybdenum, and sulfur, and the preferred compound contains tungsten.

[0008] The preparation method of silver catalyst, i.e. the method of applying the active component silver and various promoters to the carrier, mainly uses impregnation method. The classical impregnation liquid preparation method is the patent US3702259 of Shell Company in 1972, which uses silver oxalate as raw material to react with organic amine to generate silver amine complex, and then adds other promoters to prepare. For the promoters added in the impregnation liquid of silver catalyst, the patent has basically covered all elements in the periodic table. Whether to use one-step or multi-step impregnation and whether to perform an activation step in the middle of multi-step impregnation mainly depends on the concentration of silver in the impregnation liquid.

[0009] In addition, the addition of different precursors of the same promoter has an important influence on the performance of the catalyst. USP 6762311 alkali metal is preferably added in the form of hydroxide, USP 6815395 alkali metal is preferably added in the form of nitrate, and the performance of the catalyst is improved by impregnating different alumina carriers, CN 00127435 alkali metal is preferably added in the form of carbonate; USP 7259129 rhenium promoter can be added in the form of chloride, rhenate and perrhenate, CN 201010622856.4 and CN 201010534019.6 rhenium promoter is an inorganic compound containing rhenium, such as perrhenic acid, rhenate, or a mixture thereof. As a co-promoter of the rhenium promoter, it can keep the rhenium promoter in a high valence state and ensure that the catalyst has high selectivity.

[0010] In summary, the rhenium promoter has a great influence on the selectivity of the catalyst, and the inventors have found that the solubility of the organic rhenium compound is low, which leads to a low rhenium content in the finished catalyst, and therefore, the organic rhenium promoter is rarely added. SUMMARY

[0011] The object of the present application is to provide a silver catalyst for ethylene epoxidation to produce ethylene oxide and a preparation method and application thereof. The inventors have conducted in-depth research on the preparation process of domestic medium and high selectivity silver catalysts containing rhenium, and on the basis of the existing carrier and catalyst preparation process, the solubility of the organic rhenium promoter is improved by adding a surfactant to the impregnation solution, thereby further improving the performance of the medium and high selectivity silver catalyst.

[0012] To achieve the above object, the first aspect of the present application provides a preparation method of a silver catalyst for ethylene epoxidation to produce ethylene oxide, which comprises:

[0013] (1) preparing a silver amine solution with an aqueous solution of an organic amine and a silver-containing compound;

[0014] (2) uniformly mixing the silver amine solution, a water-soluble surfactant, an organic rhenium promoter, water, an optional alkali metal promoter and an optional co-promoter of the rhenium promoter to obtain an impregnation solution;

[0015] (3) impregnating a carrier in the impregnation solution, then performing leaching, drying treatment and heating to obtain the silver catalyst;

[0016] The water-soluble surfactant is at least one of a water-soluble fatty alcohol polyoxyethylene ether, a water-soluble alkyl phenol polyoxyethylene ether and a water-soluble fatty acid polyoxyethylene ester.

[0017] The polymerization degree of the polyoxyethylene in the water-soluble fatty alcohol polyoxyethylene ether, the polymerization degree of the polyoxyethylene in the water-soluble alkyl phenol polyoxyethylene ether and the polymerization degree of the polyoxyethylene in the water-soluble fatty acid polyoxyethylene ester are all greater than 5 and less than 15.

[0018] The second aspect of the present application provides a silver catalyst for ethylene epoxidation to produce ethylene oxide prepared by the above preparation method.

[0019] The third aspect of the present application provides the application of the above silver catalyst in the direct oxidation of ethylene to produce ethylene oxide.

[0020] The technical solution of the present application has the following beneficial effects: the silver catalyst prepared according to the method of the present application has high activity and selectivity, and is particularly suitable for the reaction of ethylene epoxidation to produce ethylene oxide.

[0021] Other features and advantages of the present application will be described in detail in the following specific embodiment part. BRIEF DESCRIPTION OF DRAWINGS

[0022] The application will be described in greater detail by reference to the accompanying drawings.

[0023] Figure 1a An electron microscope image of a catalyst according to Comparative Example 1 of the application is shown.

[0024] Figure 1b An electron microscope image of a catalyst according to Example 1 of the application is shown. DETAILED DESCRIPTION

[0025] Preferred embodiments of the application will be described in greater detail below. While the following describes preferred embodiments of the application, it should be understood that the application can be implemented in various forms and should not be limited by the embodiments set forth herein.

[0026] A first aspect of the application provides a method for preparing a silver catalyst for ethylene epoxidation to produce ethylene oxide, the method comprising:

[0027] (1) preparing a silver amine solution with an aqueous solution of an organic amine and a silver-containing compound;

[0028] (2) mixing the silver amine solution, a water-soluble surfactant, an organic rhenium promoter, water, optionally an alkali metal promoter, and optionally a co-promoter of the rhenium promoter uniformly to obtain an impregnation solution;

[0029] (3) impregnating a carrier in the impregnation solution, then performing leaching, drying treatment, and heating to obtain the silver catalyst;

[0030] wherein the water-soluble surfactant is at least one of a water-soluble fatty alcohol polyoxyethylene ether, a water-soluble alkyl phenol polyoxyethylene ether, and a water-soluble fatty acid polyoxyethylene ester;

[0031] The polymerization degree of the polyoxyethylene in the water-soluble fatty alcohol polyoxyethylene ether, the polymerization degree of the polyoxyethylene in the water-soluble alkyl phenol polyoxyethylene ether, and the polymerization degree of the polyoxyethylene in the water-soluble fatty acid polyoxyethylene ester are all greater than 5 and less than 15.

[0032] In the application, the solubility of the organic rhenium compound in the impregnation solution is improved by adding a specific surfactant in the impregnation solution, the content of the rhenium promoter in the finished catalyst is improved, and the selectivity of the catalyst is improved. At the same time, the specific surfactant can also better reduce the interfacial surface tension between the impregnation solution and the carrier, promote the dispersion of silver on the carrier wafer, and improve the activity of the silver catalyst.

[0033] In the application, preferably, the water-soluble fatty alcohol polyoxyethylene ether is purchased from Aladdin Company, with a model number of AEO-9.

[0034] In the present application, preferably, step (1) is: under stirring, the silver-containing compound is added into the aqueous solution of the organic amine, and the silver-containing compound is completely dissolved to obtain the silver amine solution. Further preferably, under stirring, the silver-containing compound is added into the aqueous solution of the organic amine, and the temperature is kept below 40℃, and the silver-containing compound is completely dissolved to obtain the silver amine solution.

[0035] In the present application, in step (3), the leaching is leaching of the excess solution.

[0036] According to the present application, preferably, the weight concentration of silver in the impregnation solution is 10-25%.

[0037] According to the present application, preferably, the amount of the water-soluble surfactant is 1.0-20% of the weight of silver in the impregnation solution, preferably 5.0-15%.

[0038] In the present application, preferably, the mass concentration of rhenium in the impregnation solution is 100-1000ppm.

[0039] According to the present application, preferably, the organic amine is ethylenediamine.

[0040] The silver-containing compound is silver oxalate.

[0041] The organic rhenium-containing adjuvant includes: methyltrioxorhenium and / or ethyltrioxorhenium.

[0042] The co-adjuvant of rhenium includes: at least one of the oxo acid of the element of group VIB, the oxo acid of the element of group VIIB, the oxo acid salt of the element of group VIB, the oxo acid salt of the element of group VIIB, and the salt of the rare earth element; preferably at least one of tungstic acid, cesium tungstate, molybdic acid, ammonium molybdate, ammonium chromate, and cerium sulfate.

[0043] The alkali metal adjuvant is one or two of the compound of lithium, the compound of sodium, the compound of potassium, the compound of rubidium, and the compound of cesium.

[0044] According to the present application, preferably, the carrier is an α-alumina carrier, and preferably is prepared by the following steps:

[0045] I) mixing 25-500μm of trihydrate α-A12O3, pseudo-monohydrate A12O3 with particle size less than 100μm, 5-50μm of trihydrate α-A12O3, compound of alkaline earth metal and silicon-containing compound to obtain a solid mixture; wherein the amount of 25-500μm of trihydrate α-A12O3 is 30-80wt%, the amount of pseudo-monohydrate A12O3 with particle size less than 100μm is 10-45wt%, the amount of 5-50μm of trihydrate α-A12O3 is 1.0-25wt%, the amount of compound of alkaline earth metal is 0.01-3.5wt%, and the amount of silicon-containing compound is 0.01-3.0wt%, based on the total weight of the solid mixture;

[0046] II) adding combustible lubricating material and binder to the solid mixture of step I), and performing kneading, extrusion molding, drying, calcination to obtain the α-alumina carrier; wherein the amount of combustible lubricating material is 0.01-5.0wt% and the amount of binder is 10-35wt%, based on the total weight of the solid mixture; the temperature of calcination is 1350-1480℃.

[0047] In the present application, preferably, the combustible lubricating material is vaseline and the binder is dilute nitric acid.

[0048] In the present application, the porous alumina carrier prepared according to the above method has the following characteristics: specific surface area is 0.5m 2 / g-2.5m 2 / g; pore volume is 0.20ml / g-0.75ml / g; and crushing strength is 50N / particle-180N / particle, preferably 60N / particle-150N / particle.

[0049] In the present application, the carrier used is a porous α-alumina, and the mass content of α-alumina in the carrier is more than 90%.

[0050] According to the present application, preferably, the mass percentage content of silver element is 5-37wt%, preferably 8-32wt%, based on the total mass of the silver catalyst; the mass percentage content of alkali metal element is 0-2000ppm, preferably 5-2000ppm, and further preferably 10-1500ppm; the mass percentage content of rhenium element is 10-3000ppm, preferably 100-2500ppm; the mass percentage content of co-adjuvant of rhenium adjuvant is 0-300ppm, preferably 5-300ppm, and further preferably 10-250ppm; and the balance is the carrier.

[0051] According to the present application, preferably, in step (3), the impregnation is performed under the condition that the vacuum degree is less than 10mmHg, and the time of impregnation is 10-60 minutes.

[0052] The drying treatment is drying at 60-100℃ for 30-90 minutes in air atmosphere;

[0053] The heating is carried out in air flow or nitrogen-oxygen mixed gas with oxygen volume content not more than 21%, and the temperature is 180-400℃ and the time is 1-120 minutes.

[0054] According to the present application, preferably, the preparation method further comprises: (4) repeating step (3) with the obtained silver catalyst.

[0055] In the present application, when step (3) is repeated, the silver catalyst obtained in the previous step is used as the carrier for impregnation, and then is drained, dried and heated to obtain the final silver catalyst.

[0056] The second aspect of the present application provides a silver catalyst for ethylene epoxidation to produce ethylene oxide, which is prepared by the above preparation method.

[0057] The third aspect of the present application provides the use of the above silver catalyst in the direct oxidation of ethylene to produce ethylene oxide.

[0058] The present application is further illustrated by the following examples, but the scope of the present application is not limited to these examples.

[0059] In the following various examples and comparative examples:

[0060] The AEO-9 used is a water-soluble fatty alcohol polyoxyethylene ether, and the polyoxyethylene in the water-soluble fatty alcohol polyoxyethylene ether has a degree of polymerization of 9, which is purchased from Aladdin Company;

[0061] The Peregal O used is a water-soluble fatty alcohol polyoxyethylene ether, and the polyoxyethylene in the water-soluble fatty alcohol polyoxyethylene ether has a degree of polymerization of 15-20, which is purchased from Aladdin Company.

[0062] The silver catalysts prepared in the following various examples and comparative examples are tested for activity and selectivity by a laboratory reactor (hereinafter referred to as "micro reactor") evaluation device. The reactor used in the micro reactor evaluation device is a stainless steel tube with an inner diameter of 4 mm, and the reactor is placed in a heating jacket. The loading volume of the catalyst is 1 ml, and there is inert filler at the lower part to make the catalyst bed located in the constant temperature zone of the heating jacket.

[0063] The conditions for measuring the activity and selectivity are as follows: the gas composition (mol%) at the inlet of the reactor: ethylene (C2H4), 28.0% ± 1.0; oxygen (O2), 7.4% ± 0.2; carbon dioxide (CO2), < 1.0%; inhibitor dichloroethane, 0.1 ppm to 2.0 ppm; stabilizer gas (N2), the balance. The reaction pressure, 2.1 MPa; the space velocity, 6000 / h; the concentration (mol%) at the outlet of the reactor (EO), 2.50%.

[0064] After the reaction conditions are stabilized, the gas composition at the inlet and outlet of the reactor is continuously measured. The measurement results are corrected for volume shrinkage and the selectivity is calculated according to the following formula:

[0065] Selectivity

[0066] where ΔEO is the difference between the ethylene oxide concentration at the outlet and at the inlet of the reactor, and the average of more than 10 sets of test data is taken as the test result for the day.

[0067] Preparation of the carrier

[0068] Put 450 g of 25-500 μm trihydrated α-A12O3, 100 g of pseudohydrated Al2O3100 g of 5-50 μm α-A12O3, 21 g of barium nitrate and 18 g of silicon dioxide into a mixer and mix them uniformly, transfer them into a kneader, add 12 g of vaseline and 100 ml of dilute nitric acid (nitric acid: water = 1:5, by weight), knead them into a paste that can be extruded into a shape, extrude them into a five-hole columnar shape with an outer diameter of 8.0 mm, a length of 6.0 mm and an inner diameter of 1.0 mm, dry them at 80°C for more than 2 hours to reduce the free moisture content to less than 10%, put the carrier after the kneading and shaping into a bell jar kiln, raise the temperature from room temperature to 1350°C over 33 hours, calcine them at 1350°C for 8 hours, and obtain a white α-A12O3 carrier; the water absorption of the α-A12O3 carrier is 43.5%.

[0069] Preparation of the catalyst Comparative Example 1

[0070] (1) Dissolve 7.61 g of ethylenediamine in 22.97 g of deionized water, slowly add silver oxalate to the above aqueous ethylenediamine solution under stirring, keep the temperature below 40°C, and make the silver oxalate completely dissolved, the amount of silver oxalate added is such that the final prepared impregnation solution contains 21% (by weight) of silver, add 0.068 g of cesium nitrate, 0.027 g of methyltrioxorhenium, 0.002 g of ammonium chromate and deionized water to make the total mass of the solution reach 50 g, and prepare the impregnation solution for use.

[0071] (2) Take 15 g of the carrier sample prepared in the above carrier preparation example, put it into a flask, vacuumize to a vacuum degree less than 10 mmHg, after vacuumizing, introduce the impregnation solution prepared in step (1), immerse the carrier, keep for 30 min, and drain the excess solution; dry at 80°C in air atmosphere for 60 min; heat the dried carrier in air flow at 350°C for 10 min, and after cooling, prepare a primary impregnated catalyst; repeat the above primary impregnation step of step (2) to perform secondary impregnation, and prepare a finished catalyst.

[0072] Catalyst preparation comparative example 2

[0073] (1) Dissolve 7.61 g of ethylenediamine in 22.97 g of deionized water, slowly add silver oxalate to the above ethylenediamine aqueous solution under stirring, keep the temperature below 40°C, and make the silver oxalate completely dissolved, the amount of silver oxalate added is such that the finally prepared impregnation solution contains 21% (by weight) of silver, add 0.105 g of peregal O, 0.068 g of cesium nitrate, 0.027 g of methyltrioxorhenium, 0.002 g of ammonium chromate, and deionized water to make the total mass of the solution reach 50 g, and prepare an impregnation solution for use.

[0074] (2) Take 15 g of the carrier sample prepared in the above carrier preparation example, put it into a flask, vacuumize to a vacuum degree less than 10 mmHg, after vacuumizing, introduce the impregnation solution prepared in step (1), immerse the carrier, keep for 30 min, and drain the excess solution; dry at 80°C in air atmosphere for 60 min; heat the dried carrier in air flow at 350°C for 10 min, and after cooling, prepare a primary impregnated catalyst; repeat the above primary impregnation step of step (2) to perform secondary impregnation, and prepare a finished catalyst.

[0075] Catalyst preparation comparative example 3

[0076] (1) Dissolve 7.61 g of ethylenediamine in 22.97 g of deionized water, slowly add silver oxalate to the above ethylenediamine aqueous solution under stirring, keep the temperature below 40°C, and make the silver oxalate completely dissolved, the amount of silver oxalate added is such that the finally prepared impregnation solution contains 21% (by weight) of silver, add 1.05 g of AEO-9, 0.068 g of cesium nitrate, 0.003 g of ammonium chromate, and deionized water to make the total mass of the solution reach 50 g, and prepare an impregnation solution for use.

[0077] (2) Take 15 g of the carrier sample prepared in the above carrier preparation example, put it into a flask, vacuumize to a vacuum degree less than 10 mmHg, after vacuumizing, introduce the impregnation solution prepared in step (1), immerse the carrier, keep for 30 min, and drain the excess solution; dry at 80°C in air atmosphere for 60 min; heat the dried carrier in air flow at 350°C for 10 min, and after cooling, prepare a primary impregnated catalyst; repeat the above primary impregnation step of step (2) to perform secondary impregnation, and prepare a finished catalyst.

[0078] Catalyst preparation comparative example 4

[0079] Dissolve 7.61 g of ethylenediamine in 22.97 g of deionized water, slowly add silver oxalate under stirring to the above ethylenediamine aqueous solution, keep the temperature below 40°C, and make the silver oxalate completely dissolved, the amount of silver oxalate added is such that the finally prepared impregnation solution contains 21% (by weight) of silver, add 0.068 g of cesium nitrate, 0.033 g of methyltrioxorhenium, 0.002 g of ammonium chromate, and deionized water to make the total mass of the solution reach 50 g, during the preparation process, it is found that the methyltrioxorhenium is not completely dissolved, and the impregnation solution is not prepared.

[0080] Catalyst preparation example 1

[0081] (1) Dissolve 7.61 g of ethylenediamine in 22.97 g of deionized water, slowly add silver oxalate under stirring to the above ethylenediamine aqueous solution, keep the temperature below 40°C, and make the silver oxalate completely dissolved, the amount of silver oxalate added is such that the finally prepared impregnation solution contains 21% (by weight) of silver, add 0.105 g of AEO-9, 0.068 g of cesium nitrate, 0.027 g of methyltrioxorhenium, 0.002 g of ammonium chromate, and deionized water to make the total mass of the solution reach 50 g, and prepare the impregnation solution for use.

[0082] (2) Take 15 g of the carrier sample prepared in the above carrier preparation example, put it into a flask, vacuumize to a vacuum degree less than 10 mmHg, after vacuumizing, introduce the impregnation solution prepared in step (1), immerse the carrier, keep for 30 min, and drain the excess solution; dry at 80°C in air atmosphere for 60 min; heat the dried carrier in air flow at 350°C for 10 min, and after cooling, prepare a primary impregnated catalyst; repeat the above primary impregnation step of step (2) to perform secondary impregnation, and prepare a finished catalyst.

[0083] Catalyst preparation example 2

[0084] (1) Dissolve 7.61 g of ethylenediamine in 22.97 g of deionized water, slowly add silver oxalate to the ethylenediamine solution under stirring, keeping the temperature below 40°C, and make sure that the silver oxalate is completely dissolved. The amount of silver oxalate added is such that the final impregnation solution contains 21% by weight of silver. Add 0.525 g of AEO-9, 0.068 g of cesium nitrate, 0.033 g of methyltrioxorhenium, 0.002 g of ammonium chromate, and deionized water to make the total mass of the solution 50 g, and prepare the impregnation solution.

[0085] (2) Put 15 g of the carrier sample prepared in the above carrier preparation example into a flask, and vacuumize to a vacuum degree of less than 10 mmHg. After vacuumizing, introduce the impregnation solution prepared in step (1), immerse the carrier, and keep it for 30 min. Drain the excess solution, dry the carrier in an air atmosphere at 80°C for 60 min, heat the dried carrier in an air stream at 350°C for 10 min, and cool it to prepare a once-impregnated catalyst. Repeat the above once-impregnation step of step (2) to perform a twice-impregnation, and prepare a finished catalyst.

[0086] Catalyst preparation example 3

[0087] (1) Dissolve 7.61 g of ethylenediamine in 22.97 g of deionized water, slowly add silver oxalate to the ethylenediamine solution under stirring, keeping the temperature below 40°C, and make sure that the silver oxalate is completely dissolved. The amount of silver oxalate added is such that the final impregnation solution contains 21% by weight of silver. Add 0.525 g of AEO-9, 0.068 g of cesium nitrate, 0.033 g of methyltrioxorhenium, 0.002 g of ammonium chromate, and deionized water to make the total mass of the solution 50 g, and prepare the impregnation solution.

[0088] (2) Put 15 g of the carrier sample prepared in the above carrier preparation example into a flask, and vacuumize to a vacuum degree of less than 10 mmHg. After vacuumizing, introduce the impregnation solution prepared in step (1), immerse the carrier, and keep it for 30 min. Drain the excess solution, dry the carrier in an air atmosphere at 80°C for 60 min, heat the dried carrier in an air stream at 350°C for 10 min, and cool it to prepare a once-impregnated catalyst. Repeat the above once-impregnation step of step (2) to perform a twice-impregnation, and prepare a finished catalyst.

[0089] Catalyst preparation example 4

[0090] (1) 7.61 g ethylenediamine was dissolved in 22.97 g deionized water, and silver oxalate was slowly added to the ethylenediamine solution under stirring, with the temperature kept below 40°C, so that the silver oxalate was completely dissolved, and the amount of silver oxalate added was such that the prepared impregnation solution contained 21% (by weight) of silver, 1.575 g AEO-9, 0.068 g cesium nitrate, 0.047 g methyltrioxorhenium, 0.003 g ammonium chromate and deionized water were added to the solution to make the total mass of the solution reach 50 g, and the impregnation solution was prepared for use.

[0091] (2) 15 g of the carrier sample prepared in the above carrier preparation example was placed in a flask, vacuum was drawn to a vacuum degree less than 10 mmHg, and the impregnation solution prepared in step (1) was introduced after vacuuming, so that the carrier was immersed and kept for 30 min, and the excess solution was drained; the carrier was dried at 80°C in an air atmosphere for 60 min; and the dried carrier was heated in an air stream at 350°C for 10 min, and after cooling, a primary impregnated catalyst was prepared; and the above primary impregnation step of step (2) was repeated to perform secondary impregnation, and a finished catalyst was prepared.

[0092] Catalyst preparation example 5

[0093] (1) 7.61 g ethylenediamine was dissolved in 22.97 g deionized water, and silver oxalate was slowly added to the ethylenediamine solution under stirring, with the temperature kept below 40°C, so that the silver oxalate was completely dissolved, and the amount of silver oxalate added was such that the prepared impregnation solution contained 21% (by weight) of silver, 2.1 g AEO-9, 0.068 g cesium nitrate, 0.054 g methyltrioxorhenium, 0.004 g ammonium chromate and deionized water were added to the solution to make the total mass of the solution reach 50 g, and the impregnation solution was prepared for use.

[0094] (2) 15 g of the carrier sample prepared in the above carrier preparation example was placed in a flask, vacuum was drawn to a vacuum degree less than 10 mmHg, and the impregnation solution prepared in step (1) was introduced after vacuuming, so that the carrier was immersed and kept for 30 min, and the excess solution was drained; the carrier was dried at 80°C in an air atmosphere for 60 min; and the dried carrier was heated in an air stream at 350°C for 10 min, and after cooling, a primary impregnated catalyst was prepared; and the above primary impregnation step of step (2) was repeated to perform secondary impregnation, and a finished catalyst was prepared.

[0095] Test example 1

[0096] The activity and selectivity of the catalyst sample prepared above were determined under the aforementioned process conditions using a microreactor evaluation device, and the space-time yield was 295 g EO / ml Cat. / h, and the experimental results are shown in Table 1 below.

[0097] Table 1 Effect of AEO-9 addition ratio in impregnation solution on organic rhenium concentration and silver catalyst performance

[0098]

[0099] Test Example 2

[0100] The silver catalysts prepared by catalyst preparation comparative example 1 (no surfactant added in the impregnation solution) and catalyst preparation example 1 (surfactant added in the impregnation solution) were subjected to morphology characterization, and the catalysts were magnified 20000 times as shown in Figure 1a and Figure 1b .

[0101] As can be seen from Figure 1a and Figure 1b , after adding the surfactant in the impregnation solution, the silver particles of the prepared catalyst are more uniformly distributed on the carrier wafer, the bare area of the carrier is less, the catalyst activity is improved, and the reaction temperature is reduced.

[0102] The above has described various embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing a silver catalyst for the epoxidation of ethylene to ethylene oxide, characterized in that, The preparation method includes: (1) Prepare a silver amine solution using an aqueous solution of an organic amine and a silver-containing compound; (2) The silver amine solution, water-soluble surfactant, organic rhenium auxiliaries, water, optional alkali metal auxiliaries and optional rhenium auxiliaries are mixed evenly to obtain an impregnation solution; (3) The carrier is impregnated in the impregnation solution, and then filtered, dried and heated to obtain the silver catalyst; The water-soluble surfactant is at least one of water-soluble fatty alcohol polyoxyethylene ether, water-soluble alkylphenol polyoxyethylene ether, and water-soluble fatty acid polyoxyethylene ester. The degree of polymerization of polyethylene oxide in the water-soluble fatty alcohol polyoxyethylene ether, the degree of polymerization of polyethylene oxide in the water-soluble alkylphenol polyoxyethylene ether, and the degree of polymerization of polyethylene oxide in the water-soluble fatty acid polyoxyethylene ester are all greater than 5 and less than 15.

2. The preparation method according to claim 1, wherein, The silver concentration in the impregnation solution is 10-25% by weight.

3. The preparation method according to claim 1, wherein, The amount of the water-soluble surfactant is 1.0 to 20% of the weight of silver in the impregnation solution, preferably 5.0 to 15%.

4. The preparation method according to claim 1, wherein, The organic amine is ethylenediamine; The silver-containing compound is silver oxalate; The organic rhenium-containing additives include: methyl rhenium trioxide and / or ethyl rhenium trioxide; The rhenium co-catalyst includes at least one of the following: oxyacids of Group VIB elements, oxyacids of Group VIIB elements, oxyacid salts of Group VIB elements, oxyacid salts of Group VIIB elements, and salts of rare earth elements; preferably at least one of tungstic acid, cesium tungstate, molybdic acid, ammonium molybdate, ammonium chromate, and cerium sulfate. The alkali metal auxiliaries are one or two of the following: lithium compounds, sodium compounds, potassium compounds, rubidium compounds, and cesium compounds.

5. The preparation method according to claim 1, wherein, The support is an α-alumina support, preferably prepared by the following steps: I) A solid mixture is obtained by uniformly mixing 25-500 μm trihydrate α-Al₂O₃, pseudomonohydrate Al₂O₃ with a particle size of less than 100 μm, 5-50 μm α-Al₂O₃, an alkaline earth metal compound, and a silicon-containing compound; wherein, based on the total weight of the solid mixture, the amount of 25-500 μm trihydrate α-Al₂O₃ is 30-80 wt%, the amount of pseudomonohydrate Al₂O₃ with a particle size of less than 100 μm is 10-45 wt%, the amount of 5-50 μm trihydrate α-Al₂O₃ is 1.0-25 wt%, the amount of alkaline earth metal compound is 0.01-3.5 wt%, and the amount of silicon-containing compound is 0.01-3.0 wt%. II) Add a combustible lubricant and a binder to the solid mixture from step I), knead, extrude, dry, and calcine to obtain the α-alumina carrier; wherein, based on the total weight of the solid mixture, the amount of combustible lubricant added is 0.01–5.0 wt%, and the amount of binder added is 10–35 wt%; the calcination temperature is 1350–1480 °C.

6. The preparation method according to claim 1, wherein, Based on the total mass of the silver catalyst, the mass percentage of silver is 5-37 wt%, preferably 8-32 wt%; the mass percentage of alkali metal is 0-2000 ppm, preferably 5-2000 ppm, more preferably 10-1500 ppm; the mass percentage of rhenium is 10-3000 ppm, preferably 100-2500 ppm; the mass percentage of the rhenium auxiliary agent, calculated as metal element, is 0-300 ppm, preferably 5-300 ppm, more preferably 10-250 ppm; the balance is the carrier.

7. The preparation method according to claim 1, wherein, In step (3), the impregnation is carried out under a vacuum of less than 10 mmHg, and the impregnation time is 10 to 60 minutes. The drying process involves drying in air at 60–100°C for 30–90 minutes. The heating is carried out in an air stream or a nitrogen-oxygen mixture with an oxygen volume content of no more than 21%, and the heating temperature is 180–400°C for 1–120 minutes.

8. The preparation method according to claim 1, wherein, The preparation method further includes: (4) repeating step (3) on the obtained silver catalyst.

9. A silver catalyst for the epoxidation of ethylene to produce ethylene oxide prepared by the preparation method according to any one of claims 1-8.

10. The application of the silver catalyst according to claim 9 in the direct oxidation of ethylene to produce ethylene oxide.

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