A process for the epoxidation of ethylene to ethylene oxide

Abstract

The application belongs to the field of catalysts and relates to a method for preparing ethylene oxide by ethylene epoxidation. The method comprises the following steps: mixing a silver catalyst, ethylene, oxygen, a stabilizing gas and a chloride in a reactor to perform an ethylene epoxidation reaction; after the operation of the reactor, the concentration of the chloride is controlled to be stabilized at 2-5 ppm; when the concentration of ethylene oxide at the outlet of the reactor reaches 0.5-3.0 mol%, the concentration of the chloride is reduced to 0.1-2 ppm; the silver catalyst comprises an alpha-alumina carrier and an active component silver supported on the alpha-alumina carrier; the alpha-alumina carrier contains manganese elements, and the content of the manganese elements is 0.001-2.0 wt.% based on the weight of the alpha-alumina carrier.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of catalysts, and in particular, relates to a method for preparing ethylene oxide by ethylene epoxidation. BACKGROUND

[0002] So far, silver catalyst is still the only effective catalyst for the production of ethylene oxide by ethylene epoxidation in industry. Under the action of silver catalyst, ethylene oxidation mainly generates ethylene oxide, and side reactions such as generation of carbon dioxide and water also occur. Activity, selectivity and stability are the main performance indicators of silver catalyst. Among them, the activity generally refers to the reaction temperature required when the ethylene oxide production process reaches a certain reaction load, the lower the reaction temperature, the higher the activity of the catalyst; the selectivity refers to the ratio of the number of moles of ethylene converted into ethylene oxide to the total number of moles of ethylene in the reaction; and the stability is expressed as the decline rate of activity and selectivity, the smaller the decline rate, the better the stability of the catalyst. In the process of producing ethylene oxide by ethylene oxidation, the performance of silver catalyst has a great influence on economic benefits, and improving the activity, selectivity and stability of silver catalyst is an important direction of silver catalyst research.

[0003] In order to improve the effect and efficiency of silver catalyst for preparing ethylene oxide, adding additives is one of the important means to improve the performance of silver catalyst, and the addition of additives can significantly affect the performance of the catalyst. At present, the addition of additives has developed from single additive to combined or synergistic additive containing multiple components, and the composition of the additive and its content in the catalyst have become an important part of the research of silver catalyst. US4761394A greatly improves the selectivity of the reaction by introducing rhenium and a synergistic additive of rhenium into the silver catalyst, and a high selectivity silver catalyst with a selectivity of more than 88% is developed. US4766105A introduces a silver catalyst for preparing ethylene oxide, which contains alkali metal, rhenium as an additive, and sulfur, molybdenum, tungsten, chromium and their mixtures as co-additives. WO1997036680A1 reports that adding a co-promoter selected from sulfur, molybdenum, tungsten, chromium, phosphorus, boron and their mixtures as a co-promoter of rhenium in a rhenium-containing ethylene oxide catalyst improves the performance of the catalyst. CN101678332A more specifically proposes that adding a first co-promoter selected from sulfur, phosphorus, boron and their mixtures and a second co-promoter selected from tungsten, molybdenum, chromium and their mixtures in a rhenium-containing silver catalyst helps to improve the selectivity of producing ethylene oxide. The above patent documents mainly use the addition of other elements in the formula of silver catalyst to improve the performance of silver catalyst. With the large-scale industrial application of medium-high selectivity silver catalyst, the requirements for the performance of silver catalyst are also increasing, and appropriate methods are needed to dope and modify the additives to improve the performance of the catalyst without causing negative effects.

[0004] The performance of silver catalysts is not only related to the composition and preparation method of the catalyst, but also to the performance of the carrier used by the catalyst and its preparation. For the alumina carrier used by silver catalysts, researchers usually change its chemical composition and physical properties such as specific surface area, pore size, pore distribution and porosity by adding trace components to the carrier to improve its performance, including pretreatment by adding metal oxides or other compounds. In WO1997040933A1, oxides of zirconium, titanium, silicon and alkaline earth metals (calcium, magnesium, strontium) are added to the carrier. In CN1467022A, to improve the activity of the catalyst, the carrier obtained after high-temperature calcination is treated with water and alkali, including two treatment methods using an alkali solution or gas, the amount of alkali substance is 0.01-500% based on the weight of the carrier, the treatment temperature is 30-800°C, and the treatment time is 1-30 hours. After the water and alkali treatment, the carrier is dried until the effluent is neutral, and a silver catalyst carrier is obtained. The alkali washing adjusts the micropore structure of the surface and interior of the carrier, so that more high-energy sites are generated on the surface of the carrier, thereby making the silver and promoter supported on these high-energy sites exhibit higher reaction activity than usual, and the performance of the silver catalyst prepared from the silver catalyst carrier is significantly improved. In US5929259A, the calcined carrier is immersed in a liquid phase containing titanium dioxide, and then calcined to uniformly disperse the generated titanium dioxide in the carrier, and then silver and an alkali metal are loaded to prepare a catalyst, which improves the initial activity and selectivity of the silver catalyst. In CN1400048A, an α-alumina carrier is treated with a cerium or zirconium-containing sol, and then silver and a promoter are loaded to prepare a silver catalyst, which solves the problems of easy aggregation of silver particles in the catalyst with the extension of reaction time, resulting in insufficient stability of the silver catalyst or insufficient activity of the catalyst, and the activity, selectivity and stability of the catalyst are improved to different degrees.

[0005] Although the above patent documents use methods such as adding different promoters to the alumina raw material or the calcined carrier to improve the alumina carrier, which brings different degrees of improvement to the activity, selectivity and stability of the catalyst, how to more economically exert the promoting effect of the corresponding promoters and further improve the performance of the silver catalyst is still the goal of researchers. SUMMARY

[0006] According to the deficiencies of the prior art, the inventors of the present application have conducted extensive and in-depth experimental research in the field of silver catalysts and their alumina carriers, application processes, etc., and found that by adding manganese compounds to the carrier raw material to prepare an alumina carrier, and then preparing a silver catalyst from the carrier, and adjusting the concentration of chlorides in the reactor, the selectivity of the silver catalyst can be significantly improved in a short time.

[0007] The present application provides a method for preparing ethylene oxide by ethylene epoxidation, comprising the following steps: mixing silver catalyst, ethylene, oxygen, stabilizing gas and chloride in a reactor to carry out ethylene epoxidation reaction, after the reactor is operated, the concentration of chloride is controlled to be stabilized at 2-5 ppm, and when the concentration of ethylene oxide at the outlet of the reactor reaches 0.5-3.0 mol%, the concentration of chloride is reduced to 0.1-2 ppm, preferably to 0.2-1.5 ppm, more preferably to 0.8-1.5 ppm; specifically, it can be reduced to 0.9 ppm, 1.0 ppm, 1.1 ppm, 1.2 ppm, 1.3 ppm, 1.4 ppm, or other concentrations within the above range.

[0008] The silver catalyst comprises an α-alumina carrier and an active component silver supported thereon; the α-alumina carrier contains manganese element, and the content of the manganese element is 0.001-2.0 wt.% based on the weight of the α-alumina carrier, preferably 0.005-1.5 wt.%, more preferably 0.01-0.5 wt.%, specifically, the content of the manganese element can be 0.005 wt.%, 0.006 wt.%, 0.007 wt.%, 0.008 wt.%, 0.009 wt.%, 0.01 wt.%, 0.02 wt.%, 0.03 wt.%, 0.04 wt.%, 0.05 wt.%, 0.06 wt.%, 0.07 wt.%, 0.08 wt.%, 0.09 wt.%, 0.1 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1.0 wt.%, 1.1 wt.%, 1.2 wt.%, 1.3 wt.%, 1.4 wt.%, 1.5 wt.%.

[0009] The present application significantly improves the selectivity of the catalyst in a short time by selecting the manganese-containing alumina carrier and adjusting the concentration of chloride in the reactor. Since the present application only involves the adjustment of the above steps, other process conditions and materials involved in the method of the present application can be the conventional selection in the art.

[0010] Specifically, the stabilizing gas includes but is not limited to nitrogen, argon, helium, methane, or mixtures thereof. The chloride refers to a chlorine-containing component as an inhibitor, and the chlorine-containing component can be at least one of C1-C8 chlorinated hydrocarbons, including but not limited to methyl chloride, dichloromethane, chloroethane, dichloroethane, chloroethylene, dichloroethylene, or mixtures thereof.

[0011] The α-alumina support used in the method according to the present application can be any α-alumina support containing manganese in the above-mentioned amount, and the other components contained in the α-alumina support can be conventional components in the field, and the method for preparing the α-alumina support can be a conventional method in the field.

[0012] According to a specific embodiment of the present application, the α-alumina support is prepared by a method comprising the following steps:

[0013] Step I, preparing a mixture comprising the following components:

[0014] Component a: aluminum trihydrate;

[0015] Component b: pseudo-boehmite;

[0016] Component c: fluoride mineralizer;

[0017] Component d: manganese compound;

[0018] Component e: other auxiliary agent, in an amount of 0.001 to 3.0 wt.%, based on the total weight of components a to e;

[0019] Component f: binder;

[0020] Component g: optional deionized water;

[0021] Step II, drying and calcining the mixture obtained in Step I after kneading and extruding the mixture to obtain the α-alumina support.

[0022] According to an embodiment of the present application, the amount of component a is 4.5 to 90 wt.%, the amount of component b is 5 to 95 wt.%, and the amount of component c is 0.01 to 15 wt.%, based on the total weight of components a to e.

[0023] According to a preferred embodiment of the present application, the amount of component a is 23 to 85 wt.%, the amount of component b is 16 to 75 wt.%, the amount of component c is 0.1 to 12 wt.%, the amount of component e is 0.005 to 2.0 wt.%, and the amount of component f is 5 to 50 wt.%, based on the total weight of components a to e.

[0024] According to a more preferred embodiment of the present application, the amount of component a is 50 to 60 wt.%, the amount of component b is 35 to 45 wt.%, the amount of component c is 0.8 to 10 wt.%, the amount of component e is 0.1 to 1.5 wt.%, and the amount of component f is 10 to 40 wt.%, based on the total weight of components a to e.

[0025] The content of component d is determined based on the content of manganese element in the aforementioned catalyst. For example, the content of component d is 0.001-10.0 wt.%, preferably 0.005-4.0 wt.%, and further preferably 0.01-3.0 wt.%, based on the total weight of components a-e.

[0026] The specific selection of the precursor compound of the manganese element in the catalyst carrier, i.e. the manganese compound, is not particularly limited in the present application. Preferably, the manganese compound is selected from one or more of ammonium manganese sulfate, manganese citrate, manganese acetate, manganese oxalate, manganese nitrate, manganese sulfate and potassium permanganate.

[0027] According to the method of the present application, the alumina trihydrate and the pseudo-boehmite are raw materials commonly used in the art, and the parameters such as mesh size are conventional parameters. For example, the mesh size of the alumina trihydrate can be 50-500 mesh, which will not be described herein again. The alumina trihydrate can be alumina trihydrate α and / or alumina trihydrate β. According to a specific embodiment of the present application, the alumina trihydrate is selected from at least one of alumina trihydrate α and alumina trihydrate β.

[0028] In the preparation of the α-alumina carrier of the present application, the fluoride mineralizer is added to accelerate the crystal transformation of alumina, change the surface morphology of the carrier and reduce the formation of small pores with a pore size of less than 0.1 μm. In the embodiment of the present application, the fluoride mineralizer is selected from one or more of hydrogen fluoride, aluminum fluoride, ammonium fluoride, magnesium fluoride, sodium fluorosilicate and cryolite.

[0029] In the preparation of the α-alumina carrier of the present application, the other additives, i.e. component e, include one or more of a silicon-containing compound and an alkaline earth metal compound, which aims to improve the performance of the carrier. Among them, the silicon-containing compound is preferably silicon dioxide and / or silicate, and the content thereof can be 0.01-1.0 wt.%, based on the total weight of components a-e. The alkaline earth metal compound is preferably one or more of oxides, nitrates, acetates, oxalates and sulfates of strontium, magnesium, calcium and barium, and the content thereof can be 0.01-1.0 wt.%, based on the total weight of components a-e.

[0030] In the present application, the binder can be added in the form of a binder aqueous solution, and the binder is preferably one or more of nitric acid, formic acid, acetic acid, propionic acid and hydrochloric acid. According to a preferred embodiment, the weight ratio of the binder to water in the binder aqueous solution is 1:(1.25-10), preferably 1:(2-5). According to an embodiment, the binder is an aluminum sol, which is provided in the form of pseudo-boehmite and acid, and the weight ratio of the two can adopt a conventional ratio, for example, the weight ratio is 1:(0.5-1.5).

[0031] In step I of the present application, deionized water can be optionally added according to the situation. Here, the deionized water refers to the water added additionally, excluding the water contained in other components. The amount of water added can be determined according to the need, and is generally 5-30 wt.%. Generally, when the binder is provided in the form of pseudo one water aluminum oxide and an aqueous acid solution, no additional water can be added to the system.

[0032] According to the present application, the kneading can be carried out by a method known to those skilled in the art, preferably in a kneader, for 10-100 min, to form a paste that can be extrusion molded. According to the present application, the molding can be carried out by a method known to those skilled in the art, preferably in a molding machine. After extrusion molding, drying is carried out at 80-120°C to reduce the free moisture content to below 10 wt.%, and the solid shape after molding is not limited, and is preferably a single-hole or seven-hole columnar shape.

[0033] In step II of the present application, the calcination is one-step calcination. With the carrier raw material composition of the present application, the silver catalyst prepared can achieve high selectivity and / or catalyst activity stability through one-step calcination, avoiding a complex process flow, saving time and cost. The calcination temperature can be 700-1700°C, preferably 900-1500°C. The alumina is substantially converted into α-alumina through calcination, for example, more than 90% of the alumina is converted into α-alumina, thereby obtaining an α-alumina carrier.

[0034] The α-alumina carrier of the present application contains α-alumina in an amount of not less than 90 wt.%, preferably not less than 95 wt.%, and more preferably not less than 97 wt.%.

[0035] The silver catalyst of the present application can achieve the desired effect as long as it has the above-mentioned carrier characteristics. The other components contained in the silver catalyst can be various components conventional in the art, including but not limited to: a silver-containing compound, an alkali metal promoter, an alkaline earth metal promoter, an optional rhenium promoter and / or a synergistic promoter thereof. The method for preparing the silver catalyst is not particularly limited in the present application. For example, the above-mentioned alumina carrier is impregnated with a solution containing a silver-containing compound, an organic amine, an alkali metal promoter, an alkaline earth metal promoter and an optional rhenium promoter to prepare.

[0036] According to one specific embodiment of the present application, the silver catalyst is prepared by a method comprising the following steps:

[0037] Step S1, dissolving a silver-containing compound, an alkali metal promoter, an alkaline earth metal promoter, an optional rhenium promoter and / or a synergistic promoter thereof in an amine-containing solution and / or ammonia water to prepare a silver-ammonia solution;

[0038] Step S2, the α-alumina carrier is soaked in the silver-ammonia solution obtained in step I, and after being drained and dried, is calcined to obtain the silver catalyst.

[0039] According to a more specific embodiment of the present application, the silver catalyst is prepared by a method comprising the following steps: firstly, reacting an aqueous silver nitrate solution with an aqueous ammonium oxalate solution or an aqueous oxalic acid solution to precipitate silver oxalate, filtering and washing with deionized water until no nitrate ions are present, then dissolving the silver oxalate in an amine-containing solution (for example, an aqueous solution of an organic amine such as butylamine, ethylenediamine, 1,3-propanediamine, ethanolamine, or a mixture thereof) or aqueous ammonia, adding an additive to prepare a silver-ammonia impregnation solution. The obtained impregnation solution is then used to impregnate the above-mentioned alumina carrier, which is drained and calcined in a stream of air or a nitrogen-oxygen mixture having an oxygen content of not more than 21% to perform thermal decomposition. Alternatively, silver oxide can be used instead of silver nitrate, and the silver oxalate can be directly complexed with the organic amine without being precipitated and filtered, and then the carrier is impregnated.

[0040] The present application does not have specific limitations on the selection of the above-mentioned components in the silver catalyst.

[0041] Preferably, the silver-containing compound is an organic compound and / or an inorganic compound containing silver, further preferably an organic acid salt and / or an inorganic acid salt of silver, and particularly preferably silver nitrate and / or silver oxalate; the silver compound is added in an amount such that the content of silver in the silver catalyst is 2-39 wt.%, preferably 10-35 wt.%, based on the total weight of the silver catalyst.

[0042] Preferably, the alkali metal additive is a compound containing at least one of lithium, sodium, potassium, rubidium, and cesium, and the alkali metal additive is added in an amount such that the content of the alkali metal in the silver catalyst is 10-3000 ppm, preferably 20-2000 ppm, based on the total weight of the silver catalyst.

[0043] Preferably, the alkaline earth metal additive is a compound containing at least one of beryllium, magnesium, calcium, strontium, and barium, and the alkaline earth metal additive is added in an amount such that the content of the alkaline earth metal in the silver catalyst is 1-1000 ppm, preferably 10-800 ppm, based on the total weight of the silver catalyst.

[0044] Preferably, the rhenium additive is selected from one or more of oxides of rhenium, perrhenic acid, cesium perrhenate, methyltrioxorhenium, and ammonium perrhenate, and the rhenium additive is added in an amount such that the content of rhenium metal in the silver catalyst is 0-2000 ppm, preferably 100-1000 ppm, based on the total weight of the silver catalyst.

[0045] The present application also does not have specific limitations on the conditions of each step in the preparation of the catalyst.

[0046] According to the present application, preferably, the calcination is carried out in air or in a nitrogen-oxygen mixture having an oxygen content of not more than 21%. The temperature of the calcination is controlled between 180 and 700°C, preferably between 200 and 500°C, and the time of the calcination is between 1 and 120 minutes, preferably between 2 and 30 minutes.

[0047] In addition to the above-mentioned additives, other additives such as co-additives of rhenium (chromium, molybdenum, tungsten, etc.) can be added to further improve the activity, selectivity and stability of the obtained silver catalyst.

[0048] In the process of preparing the catalyst according to the present application, the above-mentioned additives can be applied to the carrier before, simultaneously with or after the impregnation of silver, or can be impregnated to the carrier after the reduction of the silver compound.

[0049] According to the present application, the selectivity of the silver catalyst can be significantly improved in a short time by adding a manganese compound to the alumina carrier and preparing the silver catalyst from the carrier, in combination with the adjustment of the chloride concentration in the reactor.

[0050] Other features and advantages of the present application will be described in detail in the following specific embodiments. DETAILED DESCRIPTION

[0051] The following describes the specific embodiments of the present application in detail. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0052] Measurement of catalyst performance:

[0053] The initial performance and stability of various silver catalysts according to the present application are tested 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 pipe 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.

[0054] The measurement conditions of activity and selectivity used in the present application are as follows:

[0055] Composition of reaction gas (mol%)

[0056]

[0057] After the stability reaches the above-mentioned reaction conditions, the composition of the inlet and outlet gas of the reactor is continuously measured. After the measurement results are corrected by volume shrinkage, the selectivity is calculated according to the following formula:

[0058]

[0059] where ΔEO is the difference in ethylene oxide concentration between the outlet gas and the inlet gas, and ΔCO2 is the difference in carbon dioxide concentration between the outlet gas and the inlet gas of the reactor, the average of 10 or more test data is taken as the test result of the day.

[0060] The present application is further illustrated in connection with the following examples, but the scope of the present application is not limited to these examples.

[0061] Carrier Preparation Comparative Example 1

[0062] 3000 g of 50-500 mesh trihydrate α-Al2O3, 2100 g of pseudo-monohydrate Al2O3 of more than 200 mesh, 300 g of aluminum fluoride, and 30 g of sodium silicate were mixed in a mixer, and then transferred to a kneader, 1800 mL of dilute nitric acid (nitric acid: water = 1:4.5 by weight) was added, and kneaded into a paste that could be extruded into a shape. The extruded shape was a seven-hole columnar shape having an outer diameter of 8.0 mm, a length of 6.0 mm, and an inner diameter of 1.0 mm, and dried at 100°C for 20 h or more to reduce the free moisture content to 10% or less. The support after kneading and shaping was placed in a bell jar kiln, and raised from room temperature to 1300°C over 32 h, and then baked at 1300°C for 4 h to obtain a white α-Al2O3 support sample, which was designated as DB-C1.

[0063] Carrier Preparation Comparative Example 2

[0064] 3020 g of 50-500 mesh trihydrate β-Al2O3, 2150 g of pseudo-monohydrate Al2O3 of more than 200 mesh, 300 g of aluminum fluoride, 30 g of sodium silicate, and 40 g of barium nitrate were mixed in a mixer, and then transferred to a kneader, 1860 mL of dilute nitric acid (nitric acid: water = 1:5 by weight) was added, and kneaded into a paste that could be extruded into a shape. The extruded shape was a seven-hole columnar shape having an outer diameter of 8.0 mm, a length of 6.0 mm, and an inner diameter of 1.0 mm, and dried at 90°C for 20 h or more to reduce the free moisture content to 10% or less. The support after kneading and shaping was placed in a bell jar kiln, and raised from room temperature to 1300°C over 32 h, and then baked at 1200°C for 4 h to obtain a white α-Al2O3 support sample, which was designated as DB-C2.

[0065] Carrier Preparation Example 1

[0066] The 3000 g of 50-500 mesh trihydrate α-Al203, 2100 g of more than 200 mesh pseudo monohydrate Al203, 300 g of ammonium fluoride, 30 g of sodium silicate, 40 g of barium nitrate, and 2.75 g of manganese acetate were mixed in a mixer and transferred to a kneader, 1800 mL of dilute nitric acid (nitric acid: water = 1:4.5 by weight) was added, and kneaded into an extrusion-moldable paste. The extrusion-molding was performed into a seven-hole columnar shape having an outer diameter of 8.0 mm, a length of 6.0 mm, and an inner diameter of 1.0 mm, and dried at 100°C for 20 h or more to reduce the free moisture content to 10% or less. The carrier after kneading and molding was put into a bell jar kiln, and the temperature was increased from room temperature to 1300°C over 32 h, and the temperature was kept constant at 1300°C for 4 h to obtain a fine powder of α-Al203 carrier sample, which is denoted as C1. The content of α-alumina was more than 98 wt.% and the content of manganese was 0.05 wt.% based on the weight of the carrier.

[0067] Carrier Preparation Example 2

[0068] The 3020 g of 50-500 mesh trihydrate β-Al203, 2150 g of more than 200 mesh pseudo monohydrate Al203, 300 g of sodium fluorosilicate, 30 g of sodium silicate, and 11 g of manganese citrate were mixed in a mixer and transferred to a kneader, 1860 mL of dilute nitric acid (nitric acid: water = 1:5 by weight) was added, and kneaded into an extrusion-moldable paste. The extrusion-molding was performed into a seven-hole columnar shape having an outer diameter of 8.0 mm, a length of 6.0 mm, and an inner diameter of 1.0 mm, and dried at 90°C for 20 h or more to reduce the free moisture content to 10% or less. The carrier after kneading and molding was put into a bell jar kiln, and the temperature was increased from room temperature to 1300°C over 32 h, and the temperature was kept constant at 1200°C for 4 h to obtain a fine powder of α-Al203 carrier sample, which is denoted as C2. The content of α-alumina was more than 98 wt.% and the content of manganese was 0.2 wt.% based on the weight of the carrier.

[0069] Carrier Preparation Example 3

[0070] 3120 g of 50-500 mesh trihydrate α-Al203, 2190 g of more than 200 mesh pseudo monohydrate Al203, 500 g of aluminum fluoride, 35 g of sodium silicate, 45 g of barium nitrate, and 22 g of manganese acetate were put into a mixer and mixed uniformly, transferred into a kneader, 1900 mL of dilute nitric acid (nitric acid: water = 1:4, weight ratio) was added, and kneaded into an extrusion-moldable paste. The extrusion-molding was performed into a seven-hole columnar shape having an outer diameter of 8.0 mm, a length of 6.0 mm, and an inner diameter of 1.0 mm, and dried at 100°C for 20 h or more to reduce the free moisture content to 10% or less. The support after the kneading and molding was put into a bell jar kiln, raised to 1300°C from room temperature over 32 h, and fired at 1300°C for 4 h to obtain a light pink α-Al203 support sample, which was designated as C3. The content of α-alumina was more than 98 wt.% and the content of manganese was 0.4 wt.% based on the weight of the support.

[0071] Carrier Preparation Example 4

[0072] 3120 g of 50-500 mesh trihydrate β-Al203, 2190 g of more than 200 mesh pseudo monohydrate Al203, 500 g of sodium fluorosilicate, 35 g of sodium silicate, 45 g of barium nitrate, and 22 g of manganese oxalate were put into a mixer and mixed uniformly, transferred into a kneader, 1900 mL of dilute nitric acid (nitric acid: water = 1:4, weight ratio) was added, and kneaded into an extrusion-moldable paste. The extrusion-molding was performed into a seven-hole columnar shape having an outer diameter of 8.0 mm, a length of 6.0 mm, and an inner diameter of 1.0 mm, and dried at 100°C for 20 h or more to reduce the free moisture content to 10% or less. The support after the kneading and molding was put into a bell jar kiln, raised to 1300°C from room temperature over 32 h, and fired at 1300°C for 4 h to obtain a light pink α-Al203 support sample, which was designated as C4. The content of α-alumina was more than 98 wt.% and the content of manganese was 0.4 wt.% based on the weight of the support.

[0073] Carrier Preparation Example 5

[0074] Put 3120 g of 50-500 mesh trihydrated α-Al2O3, 2190 g of pseudo monohydrated Al2O3 greater than 200 mesh, 500 g of aluminum fluoride, 35 g of sodium silicate, and 60 g of manganese nitrate into a mixer and mix them uniformly, transfer them into a kneader, add 1900 mL of dilute nitric acid (nitric acid: water = 1:4, weight ratio), and knead them into a paste that can be extruded into a shape. Extrude the paste into a seven-hole columnar shape having an outer diameter of 8.0 mm, a length of 6.0 mm, and an inner diameter of 1.0 mm, and dry it at 100°C for 20 hours or more to reduce the free moisture content to 10% or less. Put the support after kneading into a bell jar kiln, raise the temperature from room temperature to 1300°C over 32 hours, and heat it at 1300°C for 4 hours to obtain a pink α-Al2O3 support sample, which is designated as C5. In the support, the content of α-alumina is more than 98 wt.% and the content of manganese is 1.0 wt.% based on the weight of the support.

[0075] Catalyst Preparation Comparative Examples 1-2 and Catalyst Preparation Examples 1-5

[0076] To investigate the catalytic performance of the supports in the support preparation comparative examples and the support preparation examples, silver catalysts were prepared using the same method. The specific preparation method of the silver catalyst was as follows: 140 g of silver nitrate was dissolved in 150 mL of deionized water, 64 g of ammonium oxalate was dissolved in 520 mL of deionized water, and the two solutions were mixed under vigorous stirring to form white silver oxalate precipitate, which was aged for 30 minutes or more and then filtered and washed with deionized water until no nitrate ions were present. The filter cake contained about 60% silver and about 15% water. 60.0 g of ethylenediamine and 22.0 g of ethanolamine were dissolved in 75.0 g of deionized water, and the silver oxalate filter cake prepared by the above method was added. The silver oxalate was completely dissolved by continuous stirring, and then 0.88 g of cesium nitrate, 0.17 g of potassium nitrate, 0.86 g of ammonium perrhenate, and deionized water were added in sequence to make the total mass of the solution reach 400 g, and an impregnation solution was prepared.

[0077] 20 g of the support samples of the support preparation comparative examples DB-C1, DB-C2, and the support preparation examples C1-C5 were taken into a container capable of being evacuated, vacuumed to 10 mmHg or more, and the above impregnation solution was introduced and kept for 30 minutes, and then the excess solution was drained. The impregnated support was heated in an air stream at 350°C for 3 minutes and then cooled to obtain silver catalysts DBCat-1, DBCat-2 (corresponding to the support preparation comparative examples) and Cat-1-Cat-5 (corresponding to the support preparation examples). The content of manganese in Cat-1-Cat-5 was 0.04%, 0.16%, 0.30%, 0.30%, and 0.78%, respectively, based on the total weight of the catalyst.

[0078] Catalyst Preparation Comparative Example 3

[0079] The carrier prepared in Comparative Example 1 was used to further prepare a silver catalyst.

[0080] The silver catalyst was prepared as follows: 140 g of silver nitrate was dissolved in 150 mL of deionized water, and 64 g of ammonium oxalate was dissolved in 520 mL of deionized water to obtain a silver nitrate solution and an ammonium oxalate solution. The two solutions were mixed under vigorous stirring to form a white silver oxalate precipitate, which was aged for more than 30 minutes, filtered, and washed with deionized water until no nitrate ions were present. The filter cake contained about 60% silver and about 15% water. 60.0 g of ethylenediamine and 22.0 g of ethanolamine were dissolved in 75.0 g of deionized water, and the silver oxalate filter cake prepared above was added. The silver oxalate was completely dissolved by continuous stirring, and then 9.82 g of manganese acetate, 0.88 g of cesium nitrate, 0.17 g of potassium nitrate, 0.86 g of ammonium perrhenate, and deionized water were added in sequence to make the total mass of the solution reach 400 g, to prepare an impregnation solution.

[0081] A 20 g sample of the carrier of Comparative Example 1 was placed in a container that could be evacuated, and vacuumed to more than 10 mmHg. The impregnation solution described above was introduced, and maintained for 30 minutes. The excess solution was drained. The impregnated carrier was heated in an air stream at 350°C for 3 minutes, and then cooled to obtain a silver catalyst DB-Cat3. The content of manganese in DB-Cat3 was 0.78% based on the total weight of the catalyst.

[0082] Example 1

[0083] The process conditions of the reactor were as follows: the concentration of dichloroethane was stabilized at 4.0 ppm after the reactor was operated, and then the concentration of dichloroethane was reduced to 1.1 ppm when the concentration of ethylene oxide at the outlet of the reactor reached 2.0 mol%. The performance of each catalyst sample was determined under the aforementioned process conditions using a microreactor evaluation device, and the results are shown in Table 1.

[0084] Table 1: Performance determination results of the catalysts

[0085]

[0086]

[0087] As shown in Table 1, adjusting the concentration of dichloroethane can improve the selectivity of the catalyst. Furthermore, compared with the carrier without manganese compounds, the silver catalyst prepared using the carrier with manganese compounds has a significantly higher speed of improving selectivity after adjusting the concentration of chlorides.

[0088] Example 2

[0089] The reactor process conditions were such that the concentration of dichloroethane was stabilized at 3.0 ppm after the reactor was operated, and the concentration of dichloroethane was reduced to 0.8 ppm after the concentration of ethylene oxide at the reactor outlet reached 1.5 mol%. The performance of Cat-1 was measured under the same process conditions as in Example 1 using a microreactor evaluation apparatus, and the results of the evaluation are shown in Table 2.

[0090] Example 3

[0091] The reactor process conditions were such that the concentration of dichloroethane was stabilized at 2.5 ppm after the reactor was operated, and the concentration of dichloroethane was reduced to 0.2 ppm after the concentration of ethylene oxide at the reactor outlet reached 2.5 mol%. The performance of Cat-1 was measured under the same process conditions as in Example 1 using a microreactor evaluation apparatus, and the results of the evaluation are shown in Table 2.

[0092] Example 4

[0093] The reactor process conditions were such that the concentration of dichloroethane was stabilized at 3.0 ppm after the reactor was operated, and the concentration of dichloroethane was reduced to 1.5 ppm after the concentration of ethylene oxide at the reactor outlet reached 2.5 mol%. The performance of Cat-1 was measured under the same process conditions as in Example 1 using a microreactor evaluation apparatus, and the results of the evaluation are shown in Table 2.

[0094] Table 2 Results of performance measurement of catalysts

[0095]

[0096] Example 5

[0097] The reactor process conditions were such that the concentration of dichloroethane was stabilized at 3.5 ppm after the reactor was operated, and the concentration of dichloroethane was reduced to 2.0 ppm after the concentration of ethylene oxide at the reactor outlet reached 1.5 mol%. The performance of each catalyst was measured under the same process conditions as in Example 1 using a microreactor evaluation apparatus, and the results of the evaluation are shown in Table 3.

[0098] Table 3 Results of performance measurement of catalysts

[0099]

[0100]

[0101] The above has described various embodiments of the present application, and the above description is exemplary and is 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.

[0102] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as exactly that endpoint point. Any of the endpoints of the ranges or values should be considered to be approximately that range or value, encompassing anything approximating that range or value. For ranges of values, the endpoints of the ranges are combined with the individual points to form one or more new ranges, which are considered to be within the scope of the ranges disclosed herein.

Claims

1. A method for preparing ethylene oxide by ethylene epoxidation, comprising the steps of: mixing a silver catalyst, ethylene, oxygen, a stabilizing gas and a chloride in a reactor, performing ethylene epoxidation, after the reactor is operated, controlling the concentration of the chloride to be stabilized at 2-5 ppm, and reducing the concentration of the chloride to 0.1-2 ppm when the concentration of ethylene oxide at the outlet of the reactor reaches 0.5-3.0 mol%. The silver catalyst comprises an α-alumina carrier and an active component silver supported thereon; the α-alumina carrier contains manganese element, and the content of the manganese element is 0.01-0.5 wt.% based on the weight of the α-alumina carrier.

2. The method of claim 1, wherein, The concentration of the chloride is reduced to 0.2-1.5 ppm.

3. The method of claim 2, wherein, The concentration of the chloride is reduced to 0.8-1.5 ppm.

4. The method of claim 1, wherein, The α-alumina carrier is prepared by a method comprising the following steps: Step I, preparing a mixture comprising the following components: Component a: aluminum oxide trihydrate; Component b: pseudo-aluminum oxide monohydrate; Component c: a fluoride mineralizer; Component d: a manganese compound; Component e: other additives, the content of which is 0.001-3.0 wt.% based on the total weight of components a-e; Component f: a binder; Component g: optional deionized water; Step II, drying and calcining the mixture obtained in step I after kneading and extruding the mixture uniformly to obtain the α-alumina carrier.

5. The method of claim 4, wherein, The content of component a is 4.5-90 wt.% based on the total weight of components a-e, the content of component b is 5-95 wt.% based on the total weight of components a-e, and the content of component c is 0.01-15 wt.% based on the total weight of components a-e.

6. The method of claim 5, wherein, The content of component a is 50-60 wt.% based on the total weight of components a-e, the content of component b is 35-45 wt.% based on the total weight of components a-e, the content of component c is 0.8-10 wt.% based on the total weight of components a-e, the content of component e is 0.1-1.5 wt.% based on the total weight of components a-e, and the amount of component f is 10-40 wt.% based on the total weight of components a-e.

7. The method of claim 4, wherein, The manganese compound is selected from one or more of ammonium manganese sulfate, manganese citrate, manganese acetate, manganese oxalate, manganese nitrate, manganese sulfate and potassium permanganate.

8. The method of claim 4, wherein, The aluminum oxide trihydrate is α-aluminum oxide trihydrate and / or β-aluminum oxide trihydrate; and the fluoride mineralizer is selected from one or more of hydrogen fluoride, aluminum fluoride, ammonium fluoride, magnesium fluoride, sodium fluorosilicate and cryolite.

9. The method of claim 4, wherein, The other additives comprise one or more of a silicon-containing compound and an alkaline earth metal compound.

10. The method of claim 9, wherein, The silicon-containing compound is silicon dioxide and / or a silicate.

11. The method of claim 9, wherein, The alkaline earth metal compound is one or more of oxides, nitrates, acetates, oxalates and sulfates of strontium, magnesium, calcium and barium.

12. The method of claim 11, wherein, The binder is added in the form of a binder aqueous solution, and the binder is one or more of nitric acid, formic acid, acetic acid, propionic acid and hydrochloric acid.

13. The method of claim 12, wherein, In the binder aqueous solution, the weight ratio of the binder to water is 1:(1.25-10).

14. The method of claim 13, wherein, In the binder aqueous solution, the weight ratio of the binder to water is 1:(2-5).

15. The method of claim 4, wherein, The calcination is one-step calcination, and the calcination temperature is 700-1700 ℃.

16. The method of claim 15, wherein, The calcination temperature is 900-1500 ℃.

17. The method of any one of claims 1-16, wherein, The silver catalyst is prepared by a method comprising the following steps: Step S1, dissolving a silver-containing compound, an alkali metal promoter, an alkaline earth metal promoter, an optional rhenium promoter and / or a synergistic promoter thereof in an amine-containing solution and / or aqueous ammonia to prepare a silver-ammonia solution; Step S2, soaking the α-alumina carrier in the silver-ammonia solution obtained in step I, draining and drying, and then calcining to obtain the silver catalyst.

18. The method of claim 17, wherein, The silver-containing compound is an organic compound and / or an inorganic compound containing silver; the silver compound is added in an amount such that the content of silver in the silver catalyst is 2-39 wt.%, based on the total weight of the silver catalyst.

19. The method of claim 18, wherein, The silver-containing compound is an organic acid salt and / or an inorganic acid salt of silver.

20. The method of claim 19, wherein, The silver-containing compound is silver nitrate and / or silver oxalate.

21. The method of claim 18, wherein, The silver compound is added in an amount such that the content of silver in the silver catalyst is 10-35 wt.%, based on the total weight of the silver catalyst.

22. The method of claim 17, wherein, The alkali metal promoter is a compound containing at least one of lithium, sodium, potassium, rubidium and cesium; the alkali metal promoter is added in an amount such that the content of the alkali metal in the silver catalyst is 10-3000 ppm, based on the total weight of the silver catalyst.

23. The method of claim 22, wherein, The alkali metal promoter is added in an amount such that the content of the alkali metal in the silver catalyst is 20-2000 ppm, based on the total weight of the silver catalyst.

24. The method of claim 17, wherein, The alkaline earth metal promoter is a compound containing at least one of beryllium, magnesium, calcium, strontium and barium; the alkaline earth metal promoter is added in an amount such that the content of the alkaline earth metal in the silver catalyst is 1-1000 ppm, based on the total weight of the silver catalyst.

25. The method of claim 24, wherein, The alkaline earth metal promoter is added in an amount such that the content of the alkaline earth metal in the silver catalyst is 10-800 ppm, based on the total weight of the silver catalyst.

26. The method of claim 25, wherein, The rhenium promoter is selected from one or more of oxides of rhenium, perrhenic acid, cesium perrhenate, methyltrioxorhenium and ammonium perrhenate; the rhenium promoter is added in an amount such that the content of rhenium metal in the silver catalyst is 0-2000 ppm, based on the total weight of the silver catalyst.

27. The method of claim 26, wherein, The rhenium promoter is added in an amount such that the content of rhenium metal in the silver catalyst is 100-1000 ppm, based on the total weight of the silver catalyst.

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