阅读说明：本技术 疏水改性α-氧化铝载体及其制备方法和银催化剂及应用 (Hydrophobic modified α -alumina carrier and preparation method thereof, silver catalyst and application ) 是由 廉括 韩红苓 魏会娟 李金兵 代武军 汤之强 王辉 于 2018-09-03 设计创作，主要内容包括：本发明涉及烯烃环氧化反应领域,提供了一种疏水改性α-氧化铝载体及其制备方法和银催化剂及应用,该疏水改性α-氧化铝载体包括成型α-氧化铝载体和其表面上连接的疏水基团；所述疏水改性α-氧化铝载体的压碎强度为55-220N,比表面积为1.00-2.5m<Sup>2</Sup>/g,孔容为0.40-0.80mL/g,吸水率不低于35％。与现有技术制得的载体相比,本发明的疏水改性α-氧化铝载体可改善催化剂活性组分在载体上的分散性。由该疏水改性α-氧化铝载体制成的银催化剂在乙烯氧化生产环氧乙烷的过程中显示出良好的活性和较高的选择性。(The invention relates to the field of olefin epoxidation, and provides a hydrophobically modified α -alumina carrier, a preparation method thereof, a silver catalyst and application thereof, wherein the hydrophobically modified α -alumina carrier comprises a molded α -alumina carrier and hydrophobic groups connected on the surface of the alumina carrier, the crushing strength of the hydrophobically modified α -alumina carrier is 55-220N, and the specific surface of the hydrophobically modified α -alumina carrier isThe product is 1.00-2.5m 2 Compared with the carrier prepared by the prior art, the hydrophobically modified α -alumina carrier can improve the dispersibility of the active component of the catalyst on the carrier, and the silver catalyst prepared from the hydrophobically modified α -alumina carrier shows good activity and higher selectivity in the process of producing ethylene oxide by oxidizing ethylene.)

1. The hydrophobically modified α -alumina carrier is characterized in that the hydrophobically modified α -alumina carrier comprises a molded α -alumina carrier and hydrophobic groups connected on the surface of the alumina carrier, wherein the crushing strength of the hydrophobically modified α -alumina carrier is 55-220N, and the specific surface area of the hydrophobically modified α -alumina carrier is 1.00-2.5m²The pore volume is 0.40-0.80mL/g, and the water absorption is not less than 35%.

2. The hydrophobically modified α -alumina support of claim 1, wherein the hydrophobic groups are obtained by subjecting the shaped α -alumina support to a surface hydrophobizing treatment with a hydrophobizing agent, preferably wherein the surface hydrophobizing treatment comprises immersing the shaped α -alumina support in a solution of a hydrophobizing agent.

3. The hydrophobically modified α -alumina support of claim 1, wherein the hydrophobic agent is a siloxane and/or a long chain alkyl surfactant.

4. A preparation method of a hydrophobically modified α -alumina carrier is characterized by comprising the steps of soaking a formed α -alumina carrier into a hydrophobic reagent solution, and carrying out reaction, drying and roasting to obtain the hydrophobically modified α -alumina carrier.

5. The production method according to claim 4, wherein the hydrophobic agent is a siloxane and/or a long-chain alkyl surfactant.

6. The production method according to claim 5, wherein the siloxane is a fluorosilicone and/or a hydrocarbon siloxane;

the fluorosilicone is preferably selected from at least one of poly (heptadecafluorodecyl) methylsiloxane, poly (nonafluorohexyl) siloxane, polymethyl (trifluoropropyl) siloxane, and polydimethylsiloxane;

the hydrocarbyl siloxane is represented by formula IStructure (I) wherein R¹And R²Each independently selected from C₁-C₁₂Hydrocarbyl, preferably, R¹Is C₁-C₁₂Alkyl or C₂-C₄Alkenyl radical, R²Is C₁-C₄An alkyl group; m and n are non-negative integers, m + n is 4, preferably, m is less than or equal to 2, and n is more than or equal to 2; the hydrocarbyl siloxane is further preferably selected from at least one of isobutyl triethoxysilane, tetramethoxysilane, dodecyl trimethoxysilane, and allyl triethoxysilane;

SiR¹ _m(OR²)_nformula I

The long-chain alkyl surfactant is selected from sodium hexadecyl sulfate and/or ammonium hexadecyl trimethyl bromide.

7. The production method according to claim 4, wherein the concentration of the hydrophobic reagent solution is 0.005 to 0.1 mol/L; preferably, the concentration of the hydrophobic reagent solution is 0.03-0.07 mol/L.

8. The preparation method according to claim 4, wherein the molar ratio of the formed α -alumina carrier to the hydrophobic agent is 1: 0.05-0.8, preferably 1: 0.2-0.5.

9. The process according to claim 4, wherein the process further comprises the step of pretreating the shaped α -alumina support with a dilute acid, preferably hydrochloric acid, sulfuric acid or nitric acid.

10. The preparation process of claim 9, wherein the pre-treatment includes soaking the formed α -alumina carrier in dilute acid solution at 10-30 deg.c for 2-5 hr.

11. The preparation method of any one of claims 4 to 10, wherein the shaped α -alumina carrier is prepared by mixing alumina raw materials, preferably α -alumina trihydrate and pseudo-monohydrate alumina, binder and water, optionally with the addition of auxiliaries, to obtain a α -alumina carrier precursor mixture, and then kneading, shaping, drying and calcining the α -alumina carrier precursor mixture.

12. A hydrophobically modified α -alumina support prepared by the process of any one of claims 4 to 11.

13. A silver catalyst, comprising:

component a, a hydrophobically modified α -alumina support as claimed in any of claims 1 to 3 and 12;

component b, silver;

component c, an alkali metal and/or an alkaline earth metal;

component d, rhenium and optionally a co-promoter.

14. Use of the hydrophobically modified α -alumina support of any one of claims 1 to 3 and 12, or the silver catalyst of claim 13, in an ethylene epoxidation reaction.

Technical Field

The invention relates to the field of olefin epoxidation, and particularly provides a hydrophobically modified α -alumina carrier, a preparation method of the hydrophobically modified α -alumina carrier, a hydrophobically modified α -alumina carrier prepared by the method, a silver catalyst, and application of the hydrophobically modified α -alumina carrier or the silver catalyst in ethylene oxidation production of ethylene oxide.

Background

Under the action of the silver catalyst, ethylene is oxidized to mainly generate ethylene oxide, and byproducts of carbon dioxide, water and the like are generated at the same time, wherein the activity, the selectivity and the stability are main performance indexes of the silver catalyst. The activity refers to the reaction temperature required when the ethylene oxide production process reaches a certain reaction load, and the lower the reaction temperature is, the higher the activity of the catalyst is; selectivity refers to the ratio of moles of ethylene converted to ethylene oxide in the reaction to the total reacted moles of ethylene; stability is expressed as the rate of decline of activity and selectivity, the smaller the rate of decline, the better the stability of the catalyst. The silver catalyst with high activity, high selectivity and good stability is used in the process of producing ethylene oxide by oxidizing ethylene, so that the economic benefit can be greatly improved, and the preparation of the silver catalyst with high activity, high selectivity and good stability is the main direction of research on the silver catalyst. The performance of the silver catalyst is not only related to the composition of the catalyst and the preparation method, but also related to the performance of the carrier used in the catalyst and the preparation method.

The preparation method comprises the steps of preparing an alumina carrier, wherein the main raw material for preparing the alumina carrier is aluminum hydroxide, and the aluminum oxide is a dehydration product of aluminum oxide, so the physical properties of the aluminum oxide and the aluminum hydroxide are closely related, the physical properties of the aluminum hydroxide are influenced by the preparation conditions of the aluminum hydroxide, and the preparation conditions mainly comprise raw materials, neutralization pH and temperature, aging pH, temperature and the like.

For example, in the patents of US 5063195 and CN1034678A, α -alumina trihydrate and α -alumina pseudomonohydrate with proper granularity and proportion, a carbon-containing material, a fluxing agent, a fluoride, a binder and water are mixed, kneaded, molded and dried and roasted to prepare a α -alumina carrier, wherein the specific surface of the carrier is 0.2-2 m²And/g, the pores with the pore radius larger than 30 mu m account for 25-10% of the total pore volume. The carrier is used for preparing ethylene oxide by ethylene oxidation after being impregnated with silver compounds and promoters, dried and activated, and the selectivity is up to 83-84%.

CN101007287A mixes α -alumina trihydrate with a certain particle size, α -alumina pseudomonohydrate, a certain amount of combustible carbonaceous material, a fluxing agent and an optional heavy alkaline earth metal compound, adds a binder and water after uniformly mixing, uniformly kneads, extrudes and dries and bakes to prepare the α -alumina carrier, wherein the specific surface of the carrier is 0.2-2.0 m²The pore volume is 0.35-0.85 ml/g, the water absorption rate is more than or equal to 30 percent, and the crushing strength is high30-120N/grain. The carrier is soaked with the solution of silver-amine complex, alkali metal compound and alkaline earth metal compound, and after drying and activation, the silver catalyst is prepared for preparing epoxy ethane by ethylene epoxidation.

CN1634652A in the preparation of the carrier, a pore-forming agent is not used, α -alumina trihydrate is directly mixed with pseudo-monohydrate alumina, a fluxing agent and fluoride according to a certain proportion, a binder and water are added after the mixture is uniformly mixed, the mixture is uniformly kneaded, extruded and molded, and dried and roasted to prepare the α -alumina carrier, wherein the specific surface of the carrier prepared by the method is 0.2-2.0 m²The pore volume is 0.35-0.85 ml/g, the water absorption rate is more than or equal to 30%, and the crushing strength is 20-90N/grain. The carrier is soaked with the solution of silver-amine complex, alkali metal compound and alkaline earth metal compound, and after drying and activation, the silver catalyst is prepared for preparing ethylene oxide by ethylene epoxidation.

The silver catalyst carrier should not only have high strength, but also provide a suitable specific surface and pore structure. The formed carrier is treated to modify the surface of the carrier, improve the dispersion condition of the catalytic active component silver, change the acidity and alkalinity of the surface of the carrier, and modulate the electronic condition of the surface of the metallic silver and the absorption and desorption conditions of reaction species, thereby improving the catalytic performance of the silver catalyst. There have been some studies reported in this regard.

Japanese patent JP2002136868 reports a method for preparing an alumina carrier: firstly, forming a carrier raw material, roasting at the temperature of 500-2000 ℃ to form a carrier precursor with the main component of alumina, treating the obtained precursor by adopting a hydrofluoric acid solution with the concentration of 0.1-15%, and roasting at the temperature of 1000-2000 ℃ for a plurality of hours to form a carrier finished product, wherein the silver catalyst prepared from the obtained carrier has excellent performance.

German patent DE2933950 reports a process for purifying silver catalyst supports, which is believed to use pure α -alumina as the support material, and without this purity of alumina, commercially available ordinary α -alumina can be purified by boiling with about equal amounts of 1 wt% NaOH solution for 30min, followed by washing with deionized water until the pH of the wet α -alumina is below 8.

The above patent documents refer to methods for treating alumina carriers which are directly treating on the surface of formed α -alumina carriers, and these methods have limited activity improvement effect on silver catalysts and insignificant improvement effect on selectivity.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a hydrophobic modified α -alumina carrier which enables a silver catalyst to meet high activity and simultaneously has higher selectivity and a preparation method thereof, the silver catalyst comprising the hydrophobic modified α -alumina carrier and the application of the hydrophobic modified α -alumina carrier or the silver catalyst in the production of ethylene oxide by ethylene oxidation.

The inventors of the present invention have made extensive studies on α -alumina carrier, and have found that the hydrophobic property of a silver catalyst can be improved by performing hydrophobic treatment on the surface of α -alumina carrier, and a silver catalyst with better selectivity can be prepared based on the carrier.

According to a first aspect of the invention, the invention provides a hydrophobically modified α -alumina carrier, wherein the hydrophobically modified α -alumina carrier comprises a shaped α -alumina carrier and hydrophobic groups connected on the surface of the shaped α -alumina carrier, and the hydrophobically modified α -alumina carrier has a crushing strength of 55-220N and a specific surface area of 1.00-2.5m²The pore volume is 0.40-0.80mL/g, and the water absorption is not less than 35%.

According to a second aspect of the invention, the invention provides a preparation method of a hydrophobically modified α -alumina carrier, which comprises the steps of dipping a formed α -alumina carrier into a hydrophobic reagent solution, and carrying out reaction, drying and roasting to obtain the hydrophobically modified α -alumina carrier.

According to a third aspect of the present invention there is provided a hydrophobically modified α -alumina support prepared by the above method.

According to a fourth aspect of the present invention, there is provided a silver catalyst comprising:

component a, the hydrophobically modified α -alumina carrier;

component b, silver;

component c, an alkali metal and/or an alkaline earth metal;

component d, rhenium and optionally a co-adjuvant therefor;

optional component e: an organic amine.

According to a fifth aspect of the present invention there is provided the use of a hydrophobically modified α -alumina support as described above or a silver catalyst as described above in the oxidation of ethylene to produce ethylene oxide.

The hydrophobic treatment is carried out on the surface of α -alumina carrier, so that the hydrophobic property of the catalyst is improved, compared with the carrier prepared by the prior art, the hydrophobic modified α -alumina carrier has better hydrophobic property, so that the dispersity of the active component of the catalyst on the carrier can be improved, and the silver catalyst prepared from the hydrophobic modified α -alumina carrier shows good activity and higher selectivity in the process of producing ethylene oxide by oxidizing ethylene.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Detailed Description

The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

According to a first aspect of the invention, the invention provides a hydrophobically modified α -alumina carrier, wherein the hydrophobically modified α -alumina carrier comprises a shaped α -alumina carrier and hydrophobic groups attached to the surface of the shaped α -alumina carrier, and the hydrophobic modification α -alumina carrier is pressedThe crushing strength is 55-220N, and the specific surface area is 1.00-2.5m²The pore volume is 0.40-0.80mL/g, and the water absorption is not less than 35%.

Preferably, the crushing strength of the hydrophobically modified α -alumina carrier is 70-170N, and the specific surface area is 1.10-2.1m²The pore volume is 0.50-0.65mL/g, and the water absorption is not less than 40%.

The hydrophobic modified α -alumina is particularly suitable for being used as a carrier of a silver catalyst for ethylene epoxidation reaction, and the hydrophobic groups attached to the surface of the formed α -alumina can reduce the fluidity of silver particles, improve the sintering resistance of the silver catalyst, improve the selectivity of the catalyst and prolong the service life of the catalyst.

In the present invention, the hydrophobic group includes various groups capable of playing a hydrophobic role, such as OH formed on the surface of alumina^-Radical, H⁺The hydrophobic group is preferably obtained by performing surface hydrophobic treatment on the formed α -alumina carrier by using a hydrophobic reagent, and further preferably, the step of performing the surface hydrophobic treatment comprises the step of soaking the formed α -alumina carrier in a hydrophobic reagent solution.

In the present invention, preferably, the hydrophobic agent is a siloxane and/or a long chain alkyl surfactant. Further preferably, the siloxane is a fluorosilicone and/or a hydrocarbyl siloxane; the fluorosilicone is preferably selected from at least one of poly (heptadecafluorodecyl) methylsiloxane, poly (nonafluorohexyl) siloxane, polymethyl (trifluoropropyl) siloxane, and polydimethylsiloxane.

Preferably, the hydrocarbyl siloxane has the structure shown in formula I, wherein R is¹And R²Each independently selected from C₁-C₁₂Hydrocarbyl radical, further preferably R¹Is C₁-C₁₂Alkyl or C₂-C₄Alkenyl radical, R²Is C₁-C₄An alkyl group; m and n are non-negative integers, m + n is 4, preferably, m is less than or equal to 2, and n is more than or equal to 2;

SiR¹ _m(OR²)_nformula I

In the present invention, theC₁-C₁₂Alkyl groups include, but are not limited to: methyl, ethyl, propyl, n-butyl, isobutyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl.

Said C is₂-C₄Alkenyl groups include, but are not limited to: vinyl, propenyl, allyl.

Said C is₁-C₄Alkyl groups include, but are not limited to: methyl, ethyl, propyl, n-butyl, isobutyl.

Particularly preferably, the hydrocarbyl siloxane is selected from at least one of isobutyl triethoxysilane, tetramethoxysilane, dodecyl trimethoxysilane, and allyl triethoxysilane.

The long chain alkyl surfactant may be any long chain alkyl surfactant conventional in the art, and is preferably selected from sodium cetyl sulfate and/or cetyltrimethylammonium bromide.

According to a second aspect of the invention, the invention provides a preparation method of a hydrophobically modified α -alumina carrier, which comprises the steps of dipping a formed α -alumina carrier into a hydrophobic reagent solution, and carrying out reaction, drying and roasting to obtain the hydrophobically modified α -alumina carrier.

In the present invention, the shaped α -alumina carrier can be prepared according to conventional methods in the art, according to a preferred embodiment, the shaped α -alumina carrier is prepared by mixing alumina raw materials, a binder and an appropriate amount of water, optionally with an addition of an auxiliary agent, to obtain a precursor mixture of a α -alumina carrier, and then kneading, shaping, drying and calcining the precursor mixture.

According to a preferred embodiment, the alumina raw materials are α -alumina trihydrate and pseudo-alumina monohydrate, generally, the amount of the α -alumina trihydrate is 50-90 wt% and the pseudo-alumina monohydrate is 10-50 wt% based on the total weight of the alumina raw materials.

In addition, the particle size of the alumina feedstock is conventionally selected, for example, the α -trihydrate alumina can be 50-500 mesh and the pseudo-monohydrate alumina can be greater than 200 mesh.

The binder can generate alumina sol with alumina raw materials, and the components are bound together to form paste which can be extruded and formed. For example, the binder may be mixed with pseudo-hydrated alumina as an alumina sol, and thus, the pseudo-hydrated alumina, the binder, and water may be provided directly in the form of an alumina sol. The binder may be selected from acids, such as at least one of nitric acid, formic acid, acetic acid, propionic acid and hydrochloric acid, preferably nitric acid.

The binder and water may be added separately or in the form of an aqueous binder solution, which may be added in an amount of 15 to 60 wt%, preferably 15 to 45 wt%, more preferably 15 to 35 wt%, and still more preferably 15 to 25 wt%, based on the total weight of the precursor mixture. In the aqueous binder solution, the weight ratio of the binder to water may be 1: 1.25-10, and preferably the weight ratio of the binder to water is 1: 4-5. In the case of separate addition, the addition amounts of the binder and water also satisfy the above ranges.

The addition of the auxiliary agent can improve the pore structure and the mechanical strength of the α -alumina carrier, and the auxiliary agent is preferably one or more of silicon simple substance, silicon-containing compound and alkaline earth metal compound, and the silicon-containing compound is SiO for example₂. The assistant may be used in an amount of 0 to 5 parts by weight with respect to 100 parts by weight of the alumina raw material.

In order to mix the components of the α -alumina carrier precursor mixture uniformly, the α -alumina carrier precursor mixture is kneaded in a kneader for 5-90min, and after the α -alumina carrier precursor mixture is sufficiently kneaded, the carrier is formed into a certain shape (molding) which can be performed in a molding machine, wherein the molded α -alumina carrier can be in a shape conventional in the art, and the shape includes but is not limited to a ring shape, a spherical shape, a columnar shape or a porous columnar shape, specifically, honeycomb cylindrical particles with an outer diameter of 7-9mm and a honeycomb pore diameter of 1-3mm, honeycomb cylindrical particles with five or three pores, single-pore annular particles with an outer diameter of 7-9mm and an inner diameter of 3-6mm, and the like.

Drying the formed product after the precursor mixture is formed, wherein the drying can be carried out at 80-130 ℃, the water content in the formed product is controlled to be below 10 percent, and the drying time is determined according to the water content; typically the drying time may be from 1 to 24 hours.

In order to obtain the formed α -alumina carrier with proper characteristics, the dried formed object is roasted, the roasting comprises the processes of temperature programming and constant-temperature roasting, the temperature of the constant-temperature roasting can be 1000-1600 ℃, the preferred temperature of the constant-temperature roasting is 1100-1500 ℃, and the time of the constant-temperature roasting can be 2-24 h.

According to a specific embodiment, the formed α -alumina carrier is prepared by the following method:

step A, mixing α -alumina trihydrate, pseudo-monohydrate alumina trihydrate and optional auxiliaries to prepare a solid mixture;

step B, adding a binder aqueous solution into the solid mixture to obtain an α -alumina carrier precursor mixture;

and step C, kneading, molding, drying and roasting the α -alumina carrier precursor mixture to obtain the molded α -alumina carrier.

According to a particular embodiment of the invention, the hydrophobic reagent solution is a mixture comprising a hydrophobic reagent, an organic solvent and/or water. For example, when fluorosilicone is used, it is preferable to use a fluorosilicone chloroform solution; when a hydrocarbyl siloxane or long chain alkyl surfactant is employed, it is preferred to use an aqueous solution thereof.

The hydrophobic reagents used in the methods of the invention are as described above and will not be described in detail herein.

In the present invention, the concentration of the hydrophobic reagent solution can be adjusted in a wide range, and preferably, the concentration of the hydrophobic reagent solution is 0.005-0.1 mol/L; further preferably, the concentration of the hydrophobic reagent solution is 0.03-0.07 mol/L.

In the present invention, the molar ratio of the formed α -alumina carrier to the hydrophobic agent is preferably 1: 0.05-0.8, and preferably 1: 0.2-0.5.

In the preparation method of the invention, the method preferably further comprises the step of pretreating the formed α -alumina carrier with dilute acid, wherein the pretreatment comprises the step of soaking the formed α -alumina carrier in dilute acid solution to remove impurities in the carrier and simultaneously generate Al on the surface of the carrier³⁺(ii) a The dilute acid is preferably hydrochloric acid, sulfuric acid or nitric acid.

After the soaking is finished, the method also comprises the steps of cleaning and drying the soaked reaction product. For example, the reaction product is washed in an absolute ethanol solution with an ultrasonic washer, washed with deionized water twice, and dried.

The specific conditions for soaking are not particularly limited in the present invention, and preferably, the soaking conditions include: the soaking temperature is 10-30 deg.C, and the soaking time is 2-5 h.

According to a preferred embodiment of the present invention, the method for preparing hydrophobically modified α -alumina comprises the steps of:

1) preparing dilute acid solution with the mass fraction of 5-20%, soaking the formed α -alumina carrier to remove impurities in the carrier and simultaneously generate Al on the surface of the carrier³⁺；

2) Preparing fluorosilicone chloroform impregnation liquid with the concentration of 0.005-0.1mol/L, and impregnating for 2-5h at 20 ℃.

3) And (3) placing the product obtained in the step 2) in an absolute ethyl alcohol solution, cleaning for 30min by using an ultrasonic cleaning instrument, cleaning twice by using secondary deionized water, and drying.

According to another preferred embodiment of the present invention, when the hydrophobic agent is selected from the group consisting of a hydrocarbyl siloxane or a long chain alkyl surfactant, the method for preparing the hydrophobically modified α -alumina comprises the steps of:

1) preparing dilute acid solution with the mass fraction of 5-20%, soaking the formed α -alumina carrier to remove impurities in the carrier and simultaneously generate Al on the surface of the carrier³⁺；

2) Preparing a water impregnation solution of a hydrocarbon siloxane/long-chain alkyl surfactant with the concentration of 0.005-0.1mol/L, and impregnating for 2-5h at the temperature of 20 ℃.

3) And (3) placing the product obtained in the step 2) in an absolute ethyl alcohol solution, cleaning for 30min by using an ultrasonic cleaning instrument, cleaning twice by using secondary deionized water, and drying.

According to the third aspect of the invention, the hydrophobically modified α -alumina carrier prepared by the method is provided, and the prepared hydrophobically modified α -alumina carrier has the structure and physical parameters of the hydrophobically modified α -alumina carrier of the first aspect of the invention, which are not described in detail herein.

According to a fourth aspect of the present invention, there is provided a silver catalyst comprising:

component a, the above-mentioned hydrophobically modified α -alumina carrier;

component b, silver;

component c, an alkali metal and/or an alkaline earth metal;

component d, rhenium and optionally co-adjuvants thereof;

optional component e: an organic amine.

In the silver catalyst, components c and d are both promoters of the silver catalyst. Components b to d refer to the corresponding elements present in the silver catalyst.

The alkali metal is at least one selected from lithium, sodium, potassium, rubidium and cesium; the alkaline earth metal is selected from at least one of calcium, magnesium, strontium and barium.

In the present invention, the silver catalyst may be prepared in a conventional manner, for example by applying (coating or impregnating) a silver-containing compound, an organic amine, an alkali metal promoter, an alkaline earth metal promoter, a rhenium-containing promoter and optionally a co-promoter thereof to the hydrophobically modified α -alumina support.

The silver-containing compound may be any silver-containing compound suitable for preparing a silver catalyst for ethylene oxide production, such as one or more of silver oxalate, silver oxide and silver nitrate.

The organic amine may be any organic amine compound suitable for preparing a silver catalyst for ethylene oxide production as long as the organic amine compound is capable of forming a silver amine complex with a silver compound, for example, one or more selected from the group consisting of pyridine, butylamine, ethylenediamine, 1, 3-propylenediamine, ethanolamine and triethylamine. Preferably, the organic amine is ethylenediamine and/or ethanolamine.

The alkali metal auxiliary agent is selected from compounds corresponding to alkali metals (lithium, sodium, potassium, rubidium or cesium); for example, one or more selected from the group consisting of nitrates, sulfates and hydroxides of the alkali metals.

Preferably, the alkali metal assistant is one or more of lithium sulfate, cesium sulfate and cesium nitrate.

In the present invention, the content of the alkali metal element in the finally prepared silver catalyst is usually 0 to 2000ppm, preferably 5 to 1500ppm, based on the total weight of the silver catalyst.

The alkaline earth metal auxiliary agent is selected from compounds corresponding to alkaline earth metals (magnesium, calcium, strontium or barium); for example, one or more selected from the group consisting of oxides, oxalates, sulfates, acetates, and nitrates of the alkaline earth metals. The alkaline earth metal promoter is preferably selected from barium and/or strontium compounds, more preferably from barium acetate and/or strontium acetate.

In the present invention, the content of the alkaline earth metal element in the finally prepared silver catalyst is usually 0 to 2000ppm based on the total weight of the silver catalyst.

In the present invention, the rhenium promoter and optionally the rhenium co-promoter added during the preparation of the silver catalyst, in addition to the alkali metal and alkaline earth metal promoters mentioned above, can further improve the activity, selectivity and stability of the silver catalyst.

The rhenium-containing auxiliary agent can be selected from one or more of elementary rhenium, rhenium oxide, perrhenic acid and perrhenate, is preferably selected from perrhenic acid and perrhenate, and is more preferably selected from at least one of perrhenic acid, cesium perrhenate and ammonium perrhenate.

In the present invention, the rhenium element content in the finally obtained silver catalyst is usually 5 to 1500ppm, preferably 10 to 1200ppm, based on the total weight of the silver catalyst.

The rhenium co-promoter can be any transition metal simple substance in the periodic table of elements, boron or a compound corresponding to the transition metal simple substance, and the rhenium co-promoter can be one or more of a chromium simple substance, a molybdenum simple substance, a tungsten simple substance, a boron simple substance, a chromium metal compound, a molybdenum metal compound, a tungsten metal compound and a boron compound.

In the present invention, the rhenium co-promoter content of the finally prepared silver catalyst is generally 0 to 1200ppm, based on the total weight of the silver catalyst.

In addition, the above auxiliaries may be applied to the alumina support before, simultaneously with, or after impregnation with silver, or may be impregnated on the support after the silver compound is reduced.

According to one embodiment, the silver catalyst is prepared by:

1) impregnating the hydrophobically modified α -alumina support with a solution containing sufficient amounts of a silver compound, an organic amine, an alkali metal promoter, a rhenium-containing promoter, and optionally a co-promoter;

2) filtering off the impregnation solution and drying the impregnated carrier; and

3) activating the impregnated carrier in an oxygen-containing mixed gas to produce the silver catalyst.

In the step 1), the silver compound (e.g., silver oxalate) may be dissolved in an aqueous solution of an organic amine (e.g., ethylenediamine and/or ethanolamine) to generate a silver-amine complex, and then the silver-amine complex and the alkali metal and other additives are mixed to prepare the immersion liquid;

in the step 3), the activation aims to carry out thermal decomposition on the product to prepare the finished product of the silver catalyst. Wherein the activation can be carried out in air flow or nitrogen-oxygen mixed gas with oxygen content not more than 21 v% (such as oxygen content of 8.0 v%), the temperature of the activation is generally 180-700 ℃, preferably 200-500 ℃, and the time of the activation can be 20 seconds to 120 minutes, preferably 1-60 minutes.

According to a more specific embodiment, the silver catalyst is prepared by the following method:

firstly, reacting a silver nitrate aqueous solution with an ammonium oxalate or oxalic acid aqueous solution to precipitate a silver oxalate precipitate, filtering, washing with deionized water until no nitrate ions exist, then dissolving the silver oxalate into an organic amine aqueous solution, and adding the other additives (an alkali metal additive and/or an alkaline earth metal additive, a rhenium metal additive and an optional rhenium co-additive) to prepare a dipping mixed solution;

then, the above-mentioned hydrophobically modified α -alumina carrier is impregnated with the impregnation mixed solution, drained, and activated in the air stream or nitrogen-oxygen mixed gas to perform thermal decomposition.

In this embodiment, silver oxide may be used instead of silver nitrate, or silver oxalate may be directly complexed with an organic amine without leaching, followed by impregnation of the support.

In the present invention, the amount of the silver compound used in the impregnation process is such that the content of silver element in the finally prepared silver catalyst is 1 to 35 wt%, preferably 4 to 25 wt%, based on the total weight of the silver catalyst.

According to the fifth aspect of the invention, the invention provides the application of the modified α -alumina carrier or the silver catalyst in the production of ethylene oxide by ethylene oxidation.

The term "optional" or "optionally" as used herein means either with or without, and with or without the addition of.

The term "water" as used herein refers to one or more of deionized water, distilled water and ultrapure water, unless otherwise specified or indicated.

The term "rhenium co-promoter" as used in the present invention is also referred to as "rhenium co-promoter" or rhenium co-promoter.

The molecular formula of the term "alumina" described in the present invention is Al₂O₃。

In order that the present invention may be more readily understood, the present invention will now be described in further detail with reference to the following examples, which are intended to be illustrative only and not to limit the scope of the invention.

The detection method of the physical properties of the hydrophobically modified α -alumina carrier comprises the following steps:

the specific surface area of the support is determined according to the international test standard ISO-9277 using the nitrogen physisorption BET method. For example, the specific surface area of the carrier can be measured using a nitrogen physisorption apparatus of model NOVA2000e, conta, usa.

The term "water absorption" as used in the present invention refers to the volume of saturated adsorbed water per unit mass of the carrier, in mL/g. The determination method comprises the following steps: first, a certain amount of carrier (assuming its mass m) is weighed₁) Boiling in boiling water for 1 hr, taking out the carrier, standing on wet gauze with moderate water content to remove excessive water on the surface of the carrier, and weighing the mass of the carrier after water adsorption (assuming that the mass is m)₂) The water absorption of the carrier was calculated by the following formula.

Where ρ is_{Water (W)}Is the density of water at the measurement temperature under atmospheric pressure.

The evaluation method of the performance of the silver catalyst in the invention is as follows:

various silver catalysts involved in the present invention were tested for their initial activity and selectivity using a laboratory microreactor (hereinafter referred to as "microreaction") evaluation device. The reactor used in the microreaction evaluation apparatus was a stainless steel tube having an inner diameter of 4mm, and the reaction tube was placed in a heating mantle. The filling volume of the catalyst is 1mL, and the lower part of the catalyst is provided with an inert filler, so that a catalyst bed layer is positioned in a constant temperature area of a heating sleeve.

The measurement conditions for the activity and selectivity of the catalyst used in the present invention are shown in table 1:

TABLE 1 determination of catalyst Activity and selectivity

When the reaction conditions are stably achieved, the gas composition at the inlet and outlet of the reactor is continuously measured. The measurement results were corrected for volume shrinkage and the selectivity S was calculated as follows:

where Δ EO is the difference in ethylene oxide concentration between the reactor outlet gas and the inlet gas, Δ CO₂Is a reactorThe carbon dioxide concentration difference between the outlet gas and the inlet gas is taken as the average of more than 10 groups of test data to be used as the test result of the day.

Preparation example 1

This preparation example is used to illustrate a shaped α -alumina carrier and a method for preparing the same.

Mixing 50-500 mesh α -trihydrate A1₂O₃400g of pseudo-monohydrate A1 larger than 200 meshes₂O₃100g of the mixture is put into a mixer to be uniformly mixed, the mixture is transferred into a kneader, 90mL of dilute nitric acid (nitric acid: water: 1: 5, weight ratio) is added, the mixture is kneaded into paste which can be extruded and formed, the paste is extruded and formed into a five-hole column with the outer diameter of 8.0mm, the length of 6.0mm and the inner diameter of 1.0mm, the five-hole column is dried for more than 2 hours at the temperature of 80-120 ℃ to reduce the free water content to below 10 percent, then the green body is put into an electric furnace, the room temperature is increased to 1150 ℃ after about 18 hours, the temperature is kept for 8 hours, and white formed α -A1 is obtained₂O₃The support sample, designated support D1, has the relevant physical property data shown in table 2.