A method for preparing a supported silver catalyst for the production of ethylene oxide from ethylene, the silver catalyst and the use thereof

Abstract

The application belongs to the field of silver catalysts, and relates to a preparation method of a supported silver catalyst for ethylene oxidation to produce ethylene oxide, a silver catalyst and application. The method comprises the following steps: (1) immersing an alumina carrier in a fatty amine solution, removing the solvent through drying to obtain a treated and modified alumina carrier; the fatty amine solution is a solution obtained by dissolving an alkyl primary amine and / or an alkenyl primary amine in an organic solvent; (2) preparing a silver ammine solution containing a silver compound, an organic amine, water, an alkali metal additive, an alkaline earth metal additive, an optional rhenium additive and a co-additive thereof, and immersing the treated and modified alumina carrier obtained in step (1) in the silver ammine solution; (3) performing solid-liquid separation on the solution obtained in step (2) to obtain a solid, and drying and activating the solid to obtain the silver catalyst. The silver catalyst reduces the total loading amount of final silver, reduces the use cost of the silver catalyst and improves the comprehensive performance of the silver catalyst.

Description

Technical Field

[0001] The present invention belongs to the field of silver catalysts, and specifically relates to a method for preparing a supported silver catalyst for producing ethylene oxide by ethylene oxidation, a silver catalyst prepared by the method, and application of the silver catalyst in the reaction of producing ethylene oxide by ethylene oxidation. Background Art

[0002] Ethylene oxide is the second most in-demand organic chemical product among ethylene industrial derivatives. It is primarily used to produce polyester fibers, resins, ethylene glycol, detergents, and disinfectants. The primary production method for ethylene oxide is direct oxygen oxidation. This process involves the epoxidation of ethylene and oxygen under certain reaction conditions with a silver catalyst, producing ethylene oxide with the side effect of carbon dioxide.

[0003] Improvements in silver catalysts used in ethylene oxide production typically focus on support, trace additives, and preparation methods, generally aiming to enhance the catalytic performance of silver catalysts in ethylene epoxidation and reduce costs. Silver catalyst users generally prefer catalysts with low silver content, low price, and excellent activity, selectivity, and stability. In practical applications, the silver content of a silver catalyst represents the percentage of silver in the final supported precious metal. Catalyst performance is primarily assessed by three key performance indicators: activity, selectivity, and stability. Activity refers to the amount of reactant converted per unit volume (or mass) of catalyst per unit time under specific reaction conditions. For ethylene epoxidation, catalyst activity is often measured by the applicable space-time yield (STY) or the reaction temperature required to achieve a given STY. The higher the STY or the lower the reaction temperature required to achieve a given STY, the higher the activity of the silver catalyst. Selectivity refers to the degree to which a catalyst promotes different reactions in a reaction system capable of multiple reactions. In this case, it refers to the ratio of the number of moles of ethylene converted to the main product, ethylene oxide, to the total number of moles of ethylene reacted. Stability refers to the ability of a catalyst to maintain its activity, selectivity, toxicity resistance, thermal stability, and other properties and structure during the catalytic reaction. The better the catalyst's stability, the longer its lifespan. Furthermore, the silver catalyst's tolerance to different operating conditions (such as varying carbon dioxide and oxygen concentrations) is crucial. This can mitigate the adverse effects of fluctuations in various reaction factors in actual applications on the catalyst's performance, enabling the silver catalyst to maintain high activity and selectivity over the long term and improving its stability.

[0004] Introducing other substances to play different roles in the catalyst preparation process to optimize the catalyst is a common improvement method in this field. CN106492799A uses a solution of one or more organic carboxylic acids and / or inorganic acids as a competitive adsorbent to prepare a silver catalyst to improve catalytic performance. EP3325455B1 impregnates the solid components of deposited silver and main additives with two other salt solutions to obtain an epoxidation reaction catalyst. Some methods not only improve the performance of the catalyst, but also maintain the performance while reducing the silver content, thereby improving the catalytic efficiency of the precious metal and reducing costs. CN111556786A introduces a surfactant into the silver-containing impregnation solution to improve solution leaching and reduce the silver content without reducing the catalytic performance.

[0005] Although the above patent documents adopt different methods to prepare silver catalysts for producing ethylene oxide, or adopt different process methods to bring different degrees of improvement in various aspects, there is still room for improvement in the preparation of silver catalysts for ethylene oxide in terms of improving the catalytic efficiency of silver. Summary of the Invention

[0006] Against the backdrop of the aforementioned prior art, the inventors of the present invention conducted extensive and multifaceted experimental research in the preparation of silver catalysts and other nanomaterials. They found, consistent with industry consensus, that the catalytic nanosilver particles in silver catalysts below 50 nm are unsuitable for industrial production to fully realize their performance. Furthermore, as with most porous catalysts, the good permeability of the silver catalyst's interior has a positive impact on the reaction. Excessively small pores prolong the residence time of the reactant gases, potentially favoring the complete oxidation of side reactions. To address the problems inherent in the prior art, the present invention provides a method for preparing an ethylene oxide silver catalyst. By pretreating a support with a high molecular weight amine containing hydrophobic groups, the present invention reduces the possibility of the silver-and-water impregnation solution being lost in the support's micropores to form silver particles of a size unfavorable for the reaction, thereby reducing the final total silver loading of the silver catalyst, lowering the cost of the silver catalyst, and improving the overall performance of the silver catalyst.

[0007] In order to achieve the object of the present invention, the first aspect of the present invention provides a method for preparing a supported silver catalyst for producing ethylene oxide from ethylene, comprising the following steps:

[0008] (1) immersing the alumina support in a fatty amine solution, and drying and removing the solvent to obtain a treated and modified alumina support; the fatty amine solution is a solution obtained by dissolving an alkyl primary amine and / or an alkenyl primary amine in an organic solvent;

[0009] (2) preparing a silver ammonia solution containing a silver compound, an organic amine, water, an alkali metal additive, an alkaline earth metal additive, an optional rhenium additive and a co-additive thereof, and impregnating the treated and modified alumina support obtained in step (1) into the silver ammonia solution;

[0010] (3) subjecting the solution obtained in step (2) to solid-liquid separation to obtain a solid, which is then dried and activated to obtain the silver catalyst.

[0011] The second aspect of the present invention provides a silver catalyst prepared by the preparation method.

[0012] The third aspect of the present invention provides an application of the silver catalyst in the production of ethylene oxide by oxidation of ethylene.

[0013] The silver particles in the silver catalyst obtained by the present invention are not easily adhered, the distribution of silver in micropores and other pores with poor permeability is reduced, the total silver loading of the silver catalyst is reduced, the use cost of the silver catalyst is reduced, and the comprehensive performance of the silver catalyst is improved.

[0014] Other features and advantages of the present invention will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0015] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0016] In order to achieve the object of the present invention, the first aspect of the present invention provides a method for preparing a supported silver catalyst for producing ethylene oxide from ethylene, comprising the following steps:

[0017] (1) immersing the alumina support in a fatty amine solution, and drying and removing the solvent to obtain a treated and modified alumina support; the fatty amine solution is a solution obtained by dissolving an alkyl primary amine and / or an alkenyl primary amine in an organic solvent;

[0018] (2) preparing a silver ammonia solution containing a silver compound, an organic amine, water, an alkali metal additive, an alkaline earth metal additive, an optional rhenium additive and a co-additive thereof, and impregnating the treated and modified alumina support obtained in step (1) into the silver ammonia solution;

[0019] (3) subjecting the solution obtained in step (2) to solid-liquid separation to obtain a solid, which is then dried and activated to obtain the silver catalyst.

[0020] In the present invention, the solid-liquid separation in step (3) can be a common solid-liquid separation method such as centrifugation and leaching, and the impregnation liquid adsorbed in the carrier is retained.

[0021] In step (1) of the present invention, the fatty amine selected is an alkyl primary amine and / or an alkenyl primary amine, which has an amino group that can react with silver or aluminum oxide and a hydrophobic group of a long-chain alkyl or long-chain alkenyl group. Preferably, the fatty amine is C8-C 22Alkyl primary amine and / or C8~C 22 Alkenyl primary amine, preferably C 12 ~C 20 Alkyl primary amine and / or C8~C 18 Alkenyl primary amine. Specifically, the fatty amine is selected from at least one of octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, heptadecanylamine, octadecylamine, nonadecanylamine, octenylamine, nonenylamine, decenylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, heptadecanylamine, and oleylamine.

[0022] According to the present invention, the organic solvent is selected from a solvent that can dissolve aliphatic amine and has a boiling point lower than that of the aliphatic amine. Selecting a solvent with a lower boiling point is more energy-efficient in the subsequent drying process. Specifically, the organic solvent is at least one of chloroform, methanol, ethanol, ether and toluene. Based on the total weight of the aliphatic amine solution, the content of the organic solvent can be 0.0001 to 99.9999 wt%, preferably 10 to 95 wt%, and more preferably 30 to 90 wt%.

[0023] According to the present invention, preferably, the alumina carrier is a porous α-alumina carrier with a crushing strength of 30 to 500 N / particle and a specific surface area of ​​0.6 to 2.6 m 2 / g, and the pore volume is 0.3~1.0ml / g.

[0024] According to the present invention, preferably, in step (1), the impregnation time is 1 to 300 minutes, and the drying temperature is between the boiling point of the solvent and the boiling point of the fatty amine; preferably, the impregnation is carried out under repeated decompression and pressurization of the air above the impregnation liquid.

[0025] In the present invention, the process can be accelerated by repeatedly reducing and increasing the pressure of the air above the impregnation liquid, so that the inner and outer surfaces of the carrier are fully wetted and no fine bubbles are precipitated on the surface. The drying temperature is selected between the boiling points of the solvent and the fatty amine, and the drying is considered complete when the weight remains substantially unchanged. The purpose is to remove the solvent and allow the micropores of the carrier to adsorb the selected fatty amine.

[0026] According to the present invention, preferably, in step (2), the silver-containing compound is at least one of silver acetate, silver nitrate and silver oxalate; and the amount of the silver-containing compound added is such that the content of silver in the silver catalyst in terms of atoms is 10 to 40 wt % based on the total weight of the silver catalyst.

[0027] In the present invention, the silver catalyst can be prepared by impregnation according to methods known to those skilled in the art of silver catalyst preparation or conventionally disclosed methods. The temperature of the impregnation solution is maintained below 30° C. to prevent the silver-containing compound from being decomposed and precipitated prematurely due to heat.

[0028] According to the present invention, preferably, in step (2), the organic amine is selected from at least one of ethylamine, ethylenediamine, n-propylamine, 1,3-propylenediamine, n-butylamine, 1,4-butylenediamine, ethanolamine and propanolamine; and the content of the organic amine is 10 to 90 wt% based on the total weight of the silver ammonia solution.

[0029] In the present invention, the organic amine mainly plays the role of solvent and complexing agent, and plays the role of promoting the dissolution of solute.

[0030] According to the present invention, preferably, in step (2), the alkali metal promoter is selected from at least one of soluble salts of lithium, sodium, potassium, rubidium and cesium; the alkaline earth metal promoter is selected from at least one of soluble salts of magnesium, calcium, strontium and barium; the rhenium promoter is selected from at least one of potassium perrhenate, perrhenic acid and ammonium rhenate; the rhenium co-promoter is selected from at least one of salts or acids containing chromium, sulfur, cobalt, molybdenum and nickel; based on the total weight of the silver catalyst, the amount of the alkali metal promoter is 100%. The amount of addition is such that the content of the alkali metal in the silver catalyst is 50 to 2000 ppm, the amount of addition of the alkaline earth metal additive is such that the content of the alkaline earth metal in the silver catalyst is 0.1 to 2000 ppm, the amount of addition of the rhenium additive is such that the content of the rhenium metal in the silver catalyst in terms of atoms is 0 to 2000 ppm, and the amount of addition of the rhenium co-additive is such that the content of the rhenium co-additive in the silver catalyst in terms of atoms is 0 to 2000 ppm.

[0031] According to the present invention, preferably, in step (2), the immersion time is 1 to 300 minutes. Preferably, the immersion is performed under repeated decompression and pressurization of the air above the immersion liquid.

[0032] The impregnation time described in the present invention is 1 to 300 minutes. This process can be accelerated by repeatedly reducing and increasing the pressure of the air above the impregnation solution, so that the inner and outer surfaces of the carrier are fully wetted and no fine bubbles are precipitated on the surface. Because the impregnation solution contains a large amount of water, the fatty amine has a very low solubility in it, which can act as a hydrophobic agent in the micropores of the carrier, preventing the silver-containing impregnation solution from being absorbed into the micropores.

[0033] According to the present invention, preferably, in step (3), the drying is carried out in air and / or an inert gas atmosphere, the drying temperature is 50 to 120° C., and the drying time is 0.5 to 1 h;

[0034] The activation is carried out in flowing air or inert gas atmosphere, the activation temperature is 120-480° C., and the activation time is 0.1-60 min.

[0035] According to the present invention, preferably, the method further includes the following steps: (4) repeating steps (2) and (3).

[0036] In the present application, when it is necessary to increase the silver content in the catalyst, an impregnation solution with a higher silver concentration can be prepared, or the catalyst obtained after activation in step (3) can be impregnated again in step (2) and (3), solid-liquid separated, dried, and activated, so as to greatly increase the silver content.

[0037] The second aspect of the present application provides a silver catalyst prepared by the preparation method.

[0038] The third aspect of the present application provides the use of the silver catalyst in the reaction of ethylene oxidation to produce ethylene oxide.

[0039] In the present application, in the presence of the silver catalyst, a mixed gas of ethylene and oxygen and the like is reacted in a fixed-bed micro-tube reactor.

[0040] The present application will be further described in conjunction with examples, but the scope of the present application is not limited to these examples.

[0041] Method for measuring the performance of the silver catalyst:

[0042] The various silver catalysts prepared in the present application are evaluated for initial catalytic reaction performance and stability using a micro-tube reactor (hereinafter referred to as "micro reactor"). The tube reactor used in the micro reactor evaluation device is a stainless steel reaction tube with an inner diameter of 4 mm, and the reaction tube is placed in a copper or aluminum heating jacket. After being crushed, the silver catalyst particles are sieved to obtain catalyst particles with a size of 12-18 mesh, and 0.7 g of the catalyst particles are loaded into the reactor and compacted. Inert fillers are placed in the lower part of the reactor to make the catalyst bed located in the constant temperature zone of the heating jacket.

[0043] The standard evaluation conditions for catalytic activity and selectivity used in the present application are as follows (the actual reaction conditions are described in the examples) :

[0044] The gas composition at the reaction inlet (mol%) is as follows: ethylene, 30.0±2.0; oxygen, 6.0-8.0; carbon dioxide, <3.0; nitrogen, the balance; dichloroethane, 0.1-2.0 ppm. The reaction pressure is 2.1 MPa; the space velocity is 6000 h -1 ; the reaction temperature is manually controlled; the target concentration of ethylene oxide in the reactor outlet tail gas is set to 2.5%.

[0045] The reactor is gradually heated from room temperature, and after the reaction is stabilized at the operating conditions, the gas composition at the reactor inlet and outlet is continuously measured. After the measurement results are corrected for volume shrinkage, the selectivity (S) is calculated according to the following formula:

[0046]

[0047] Where ΔEO is the concentration difference of ethylene oxide between the reactor outlet gas and the reactor inlet gas, and ΔCO2 is the concentration difference of carbon dioxide between the reactor outlet gas and the reactor inlet gas.

[0048] Example 1

[0049] A solution of 90g of ethanol and 10g of oleylamine was prepared and used to fully impregnate 20g of a porous alumina support selected for industrial silver catalyst production. The support sample, which appeared as a white, seven-hole cylinder with a crush strength of 150N / pellet, a specific surface area of ​​1.5m2 / g, and a pore volume of 0.7ml / g, was then immersed in the oleylamine solution. The support sample was then placed in a vacuum container and the pressure was reduced to below 10mmHg. After full immersion for half an hour, the support was dried in an oven at 80°C for 1 hour to obtain the oleylamine-modified alumina support.

[0050] Mix 40 g of 1,3-propylenediamine, 40 g of n-propylamine, and 90 g of deionized water, and cool them to 20°C in a water bath. Slowly add 100 g of silver nitrate. After the silver nitrate is completely dissolved, add 0.09 g of lithium nitrate, 0.09 g of calcium nitrate, 0.1 g of potassium perrhenate, and 0.02 g of nickel sulfate. Mix well and use this as an impregnation solution.

[0051] Immerse the carrier sample with the prepared impregnation liquid, place it in a vacuum container, evacuate the container to reduce the pressure to below 10 mmHg, fully soak for half an hour, separate the solid and liquid, dry it in an oven at 80°C for 1 hour, take it out, and activate it in air at 300°C to obtain the silver catalyst.

[0052] Example 2

[0053] The catalyst was prepared in the same manner as in Example 1, except that the solution of 90 g of ethanol and 10 g of oleylamine in step (1) was replaced by a solution of 40 g of ether and 60 g of dodecylamine.

[0054] Example 3

[0055] The catalyst was prepared in the same manner as in Example 1, except that the solution of 90 g of ethanol and 10 g of oleylamine in step (1) was replaced by a solution of 40 g of ether and 60 g of octylamine.

[0056] Comparative Example 1

[0057] The catalyst was prepared in the same manner as in Example 1, except that step (1) was not performed.

[0058] Comparative Example 2

[0059] The preparation of the catalyst was the same as in Example 1, except that in step (1), the solution of 90 g of ethanol and 10 g of oleylamine was replaced by 100 g of ethanol.

[0060] Comparative Example 3

[0061] The catalyst was prepared as in Example 1, except that step (1) was omitted and 10 g of oleylamine was added in step (2). Oleylamine exhibited significant stratification in the mixed solution and was poorly dispersed in the solution under high-speed stirring. Color differences in the prepared catalyst were visible to the naked eye due to uneven silver distribution.

[0062] Comparative Example 4

[0063] The catalyst was prepared in the same manner as in Example 1, except that step (1) was not performed and in step (2), 90 g of deionized water was replaced by a mixture of 10 g of oleylamine, 10 g of ethanol and 70 g of deionized water.

[0064] The reaction characteristics of the catalyst samples were measured under the aforementioned process conditions using a microreactor evaluation apparatus. Each sample was evaluated for one month after the process conditions stabilized, and the silver content was determined by chemical titration. The test results are listed in Table 1.

[0065] Table 1

[0066]

[0067] As can be seen from Table 1, the silver catalyst examples prepared by modifying the carrier with hydrophobic fatty amines have significantly improved activity compared with the comparative examples, and the silver content is significantly reduced while achieving similar selectivity, indicating that the utilization rate of the active component silver and the reaction efficiency are higher.

[0068] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

[0069] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

Claims

1. A method for preparing a supported silver catalyst for producing ethylene oxide from ethylene, characterized in that: The steps include: (1) Immersing the alumina support in a fatty amine solution, drying and removing the solvent to obtain a treated and modified alumina support; the fatty amine solution is C8~C 22 Alkyl primary amine and / or C8~C 22 A solution obtained by dissolving a primary alkenyl amine in an organic solvent; (2) preparing a silver ammonia solution containing a silver compound, an organic amine, water, an alkali metal additive, an alkaline earth metal additive, an optional rhenium additive and a co-additive thereof, and impregnating the treated and modified alumina support obtained in step (1) into the silver ammonia solution; (3) subjecting the solution obtained in step (2) to solid-liquid separation to obtain a solid, which is then dried and activated to obtain the silver catalyst.

2. The preparation method according to claim 1, wherein In step (1), the fatty amine is C 12 ~C 20 Alkyl primary amine and / or C8~C 18 primary alkenyl amines; The organic solvent is a fatty amine-soluble solvent having a boiling point lower than that of the fatty amine; Based on the total weight of the fatty amine solution, the content of the organic solvent is 0.0001 to 99.9999 wt %.

3. The preparation method according to claim 1, wherein The organic solvent is at least one of chloroform, methanol, ethanol, ether and toluene.

4. The preparation method according to claim 1, wherein Based on the total weight of the fatty amine solution, the content of the organic solvent is 10 to 95 wt %.

5. The preparation method according to claim 4, wherein Based on the total weight of the fatty amine solution, the content of the organic solvent is 30 to 90 wt%.

6. The preparation method according to any one of claims 1 to 5, wherein In step (1), the alumina carrier is a porous α-alumina carrier with a crushing strength of 30 to 500 N / particle and a specific surface area of ​​0.6 to 2.6 m 2 / g, and the pore volume is 0.3~1.0ml / g.

7. The preparation method according to any one of claims 1 to 5, wherein In step (1), the immersion time is 1 to 300 minutes, and the drying temperature is between the boiling point of the solvent and the boiling point of the fatty amine.

8. The preparation method according to claim 7, wherein The impregnation is carried out under the condition of repeated decompression and pressurization of the air above the impregnation liquid.

9. The preparation method according to any one of claims 1 to 5, wherein In step (2), the silver-containing compound is at least one of silver acetate, silver nitrate and silver oxalate; and the amount of the silver-containing compound added is such that the content of silver in the silver catalyst, calculated as an atom, is 10 to 40 wt % based on the total weight of the silver catalyst.

10. The preparation method according to any one of claims 1 to 5, wherein In step (2), the organic amine is selected from at least one of ethylamine, ethylenediamine, n-propylamine, 1,3-propylenediamine, n-butylamine, 1,4-butylenediamine, ethanolamine and propanolamine; and the content of the organic amine is 10 to 90 wt % based on the total weight of the silver ammonia solution.

11. The preparation method according to any one of claims 1 to 5, wherein In step (2), the alkali metal promoter is selected from at least one of soluble salts of lithium, sodium, potassium, rubidium and cesium; the alkaline earth metal promoter is selected from at least one of soluble salts of magnesium, calcium, strontium and barium; the rhenium promoter is selected from at least one of potassium perrhenate, perrhenic acid and ammonium rhenate; the rhenium co-promoter is selected from at least one of salts or acids containing chromium, sulfur, cobalt, molybdenum and nickel; Based on the total weight of the silver catalyst, the amount of the alkali metal additive added is such that the content of the alkali metal in the silver catalyst is 50 to 2000 ppm, the amount of the alkaline earth metal additive added is such that the content of the alkaline earth metal in the silver catalyst is 0.1 to 2000 ppm, the amount of the rhenium additive added is such that the content of the rhenium metal in the silver catalyst, calculated on an atomic basis, is 0 to 2000 ppm, and the amount of the rhenium co-promoter added is such that the content of the rhenium co-promoter in the silver catalyst, calculated on an atomic basis, is 0 to 2000 ppm.

12. The preparation method according to any one of claims 1 to 5, wherein In step (2), the immersion time is 1 to 300 minutes.

13. The preparation method according to claim 12, wherein The impregnation is carried out under the condition of repeated decompression and pressurization of the air above the impregnation liquid.

14. The preparation method according to any one of claims 1 to 5, wherein In step (3), the drying is carried out in air and / or an inert gas atmosphere, the drying temperature is 50 to 120° C., and the drying time is 0.5 to 1 h; The activation is carried out in flowing air or inert gas atmosphere, the activation temperature is 120-480° C., and the activation time is 0.1-60 min.

15. The preparation method according to claim 1, wherein The following steps are also included: (4) Repeat steps (2) and (3).

16. A silver catalyst prepared by the preparation method according to any one of claims 1 to 15.

17. Use of the silver catalyst according to claim 16 in the production of ethylene oxide by oxidation of ethylene.

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