Α-aluminum oxide carrier and preparation method therefor, and silver catalyst and use thereof in preparation of ethylene oxide by ethylene epoxidation

Abstract

The present invention relates to the field of silver catalysts, and relates to an α-aluminum oxide carrier and a preparation method therefor, and a silver catalyst and a use thereof in preparation of ethylene oxide by ethylene epoxidation. The specific surface area of the α-aluminum oxide carrier is 0.3-4.0 m2 / g, the water absorption rate is not lower than 25%, the mechanical strength is not lower than 40 N / particle, and the proportion of the volume of pores having a pore size of greater than or equal to 20 μm to the total pore volume is greater than 4%.

Description

Alpha-alumina support, its preparation method and silver catalyst and its use in the production of ethylene oxide by ethylene epoxidation TECHNICAL FIELD

[0001] The present invention belongs to the field of silver catalysts, and in particular, relates to an alpha-alumina support, a preparation method of the alpha-alumina support, an alpha-alumina support obtained by the method, a silver catalyst prepared from the alpha-alumina support, and the use of the silver catalyst in the production of ethylene oxide by ethylene epoxidation. BACKGROUND

[0002] Under the action of silver catalyst, ethylene oxidation mainly generates ethylene oxide, and side reactions of generating carbon dioxide and water also occur, wherein activity, selectivity and stability are the main performance indicators of silver catalyst. Activity refers to the reaction temperature required to reach a certain reaction load in the production process of ethylene oxide; the lower the reaction temperature, the higher the activity of the catalyst. Selectivity refers to the ratio of the number of moles of ethylene converted into ethylene oxide and the total reaction moles of ethylene in the reaction. The use of silver catalysts with high activity and high selectivity in the production of ethylene oxide can greatly improve the economic benefits, so the manufacture of silver catalysts with high activity and high selectivity is the main direction of silver catalyst research. The performance of silver catalysts is not only related to the composition and preparation method of the catalyst, but also related to the performance of the carrier used by the catalyst and its preparation.

[0003] The preparation method of silver catalyst in the prior art includes two processes of preparation of porous carrier (such as alumina) and loading of active components and adjuvants onto the carrier, for example, US4428863, US5384302, US5739075, CN1034678A, CN101007287A, CN1634652A, etc.

[0004] Although the above patent documents respectively use the methods of adding alkaline earth metal compounds in alumina raw materials or pre-depositing a small amount of rare earth metals on the surface of alumina carrier to improve the alumina carrier, which brings different degrees of improvement to the activity or selectivity of the catalyst, but with the large-scale industrial application of silver catalysts with medium-high selectivity, the requirements for the performance of alumina carrier in the field are also increasing. SUMMARY

[0005] In view of the above prior art situation, the inventors of the present application have conducted in-depth experimental research in the field of silver catalysts and their alumina carriers, and as a result, it has been found that by adding an appropriate amount of modified alumina hollow spheres to the carrier raw material to prepare an alumina carrier, the ash impurities brought by the addition of carbon-containing pore-forming agents can be avoided, and at the same time, the modified metal is doped in the hollow spheres, so that the modified metal can be concentratedly distributed near the large pores brought by the hollow spheres, on the one hand, the utilization efficiency of the modified metal is improved, on the other hand, the performance of the catalyst prepared from the carrier is also improved, so that finally the silver catalyst prepared from the carrier is obviously improved in both activity and selectivity.

[0006] In order to achieve the object of the present application, the first aspect of the present application provides an α-alumina carrier having the following characteristics: a specific surface area of 0.3-4.0 m 2 / g, a water absorption rate of not less than 25%, a mechanical strength of not less than 40 N / particle, and a proportion of pores with a pore size of ≥20 μm to the total pore volume of more than 4%; the α-alumina carrier contains a modified metal, and the content of the modified metal in terms of modified metal atoms is 0.1-3 wt‰ based on the total weight of the α-alumina carrier; the modified metal atoms are unevenly distributed in the α-alumina carrier; preferably, the modified metal atoms exist in the form of hollow sphere(s) in the α-alumina carrier, wherein the hollow sphere has a sphere wall and an internal cavity defined by the sphere wall,

[0007] <1> in the sphere wall, the ratio of (the number of modified metal atoms) to (the sum of the number of modified metal atoms and the number of aluminum atoms) based on the maximum cross section and a depth of 0-5 nm is not more than 0.04, for example 0.015-0.03; and / or

[0008] <2> the equivalent diameter of the internal cavity is not more than 300 μm, for example 20-300 μm; and / or

[0009] <3> the equivalent wall thickness of the sphere wall is not more than 75 μm, for example 10-75 μm.

[0010] The second aspect of the present application provides a preparation method of an α-alumina carrier, comprising the following steps:

[0011] (1) modifying alumina hollow spheres by at least one modified metal-containing compound by an impregnation method, so that the content of the modified metal in terms of modified metal atoms of the modified alumina hollow spheres is 0.1-2.5 wt% (not including the end value 2.5 wt%) based on the total weight of the modified alumina hollow spheres, preferably 0.2-2.0 wt%;

[0012] (2) mixing the alumina, the pseudo-boehmite, and the modified alumina hollow spheres obtained in step (1) with an acid to obtain a mixture; wherein the content of the alumina is 4.5-90 wt%, the content of the pseudo-boehmite is 5-95 wt%, and the content of the modified alumina hollow spheres is 0.1-50 wt%, based on the total weight of the alumina, the pseudo-boehmite, and the modified alumina hollow spheres;

[0013] (3) molding the mixture obtained in step (2) (for example by kneading or extrusion), drying, and calcining to obtain the α-alumina carrier.

[0014] Specifically, an example of a method for preparing an α-alumina carrier includes the following steps:

[0015] (1) obtaining a zirconium compound aqueous solution, placing alumina hollow spheres in the zirconium compound aqueous solution, and performing ultrasonic oscillation immersion, then performing leaching and first calcination to obtain modified alumina hollow spheres; the concentration of the zirconium compound aqueous solution is such that the content of the zirconium compound in the obtained modified alumina hollow spheres is 0.1-2.5 wt% (not including the endpoint value 2.5 wt%) in terms of zirconium atoms, based on the total weight of the modified alumina hollow spheres, and is preferably 0.2-2.0 wt%;

[0016] (2) preparing a mixture containing microscale alumina, pseudo-boehmite, and the modified alumina hollow spheres obtained in step (1), and mixing the mixture with an acid; the content of the microscale alumina is 4.5-90 wt%, the content of the pseudo-boehmite is 5-95 wt%, and the content of the modified alumina hollow spheres is 0.1-50 wt%, based on the total weight of the mixture.

[0017] (3) kneading or extruding the material obtained in step (2), and then drying and second calcining to obtain the α-alumina carrier.

[0018] A third aspect of the present application provides an α-alumina carrier prepared by the method for preparing an α-alumina carrier.

[0019] A fourth aspect of the present application provides a silver catalyst for the production of ethylene oxide by the oxidation of ethylene, wherein the silver catalyst is prepared by impregnating the α-alumina carrier described above in a solution containing a silver compound.

[0020] A fifth aspect of the present application provides the use of the silver catalyst described above in the production of ethylene oxide by the epoxidation of ethylene.

[0021] The silver catalyst prepared by the alpha-alumina carrier provided by the application is used for preparing ethylene oxide by ethylene epoxidation, can significantly improve the selectivity of the reaction, can obviously reduce the emission of carbon dioxide by-products, can improve the utilization rate of ethylene raw materials, and has a wide industrial application prospect.

[0022] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0023] The exemplary embodiments of the present application will be described in more detail by combining with the accompanying drawings.

[0024] Figure 1 shows a schematic structural diagram of the alpha-alumina carrier comprising modified alumina hollow spheres of the present application. DETAILED DESCRIPTION

[0025] The specific embodiments of the present application are described in detail below. 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.

[0026] The present application provides an alpha-alumina carrier, characterized in that the alpha-alumina carrier has the following characteristics:

[0027] The specific surface area is 0.3-4.0m 2 / g, for example, 1.2-2.92m 2 / g,

[0028] The water absorption rate is not less than 25%, for example, 39.5-45.2%,

[0029] The mechanical strength is not less than 40N / particle, for example, 45-100N / particle or 47-75N / particle; and

[0030] The proportion of the pores with a pore size of ≥20μm to the total pore volume is greater than 4%, preferably 5-15%, for example, 6.9-11.7%;

[0031] Preferably, the alpha-alumina carrier contains a modified metal, and the content of the modified metal, calculated as the modified metal atoms, is 0.1-3wt‰, for example, 0.3-1wt‰ or 0.3-0.5wt‰, based on the total weight of the alpha-alumina carrier; and / or

[0032] Preferably, the modified metal atoms are unevenly distributed in the alpha-alumina carrier, and / or

[0033] Preferably, the alpha-alumina carrier has the following properties:

[0034] The modified metal atoms are present in the alpha-alumina carrier in the form of hollow spheres, wherein the hollow spheres have a sphere wall and an internal cavity defined by the sphere wall,

[0035] <1> In the sphere wall, the ratio of (number of atoms of modified metal) to (sum of number of atoms of modified atom and number of atoms of aluminum) based on the largest cross section, 0-5 nm in depth, is not more than 0.04, for example 0.015-0.03, further for example 0.017-0.028; and / or

[0036] <2> The internal cavity has an equivalent diameter of not more than 300 μm, for example 20-300 μm, further for example 33-200 μm, yet further for example 33-67 μm; and / or

[0037] <3> The sphere wall has an equivalent wall thickness of not more than 75 μm, for example 10-75 μm, further for example 16-50 μm, yet further for example 16-34 μm.

[0038] The form of the modified metal atoms in the alpha-alumina carrier can be observed by electron microscopy.

[0039] For example, the object to be measured can be placed on a horizontal surface, and when the object can be stably placed and the projected area of the object on the horizontal surface is the largest, this state is taken as the reference. The largest cross section parallel to the horizontal surface and having the largest area is obtained as the observation surface by mechanical processing such as grinding. When there are multiple reference states, the height (the distance between the plane that does not contact the object to be measured and is parallel to the horizontal surface and has the shortest distance, denoted as Hi) is measured for each reference state (denoted as i, i = 1, 2, 3,...). In any one reference state, if there are multiple largest cross sections, the largest cross section closest to the center plane (which is the horizontal plane at a distance of Hi / 2 from the horizontal surface) is selected as the largest cross section in this reference state, and if there are two such largest cross sections above and below the center plane, respectively, the largest cross section closest to the horizontal surface is selected as the largest cross section in this reference state. The distance between the largest cross section and the center plane in each reference state is measured, and the shortest distance is selected as the largest cross section of the object to be measured. The number of largest cross sections of the object to be measured can be one or more. When the number of largest cross sections of the object to be measured is more than one, one of the largest cross sections is randomly selected. For example, for a cube, the number of reference states is 6, and the number of largest cross sections in each reference state is also 6.

[0040] The observation and measurement can be carried out by scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX / EDS), high resolution transmission electron microscope (HR-TEM), X-ray photoelectron spectroscopy (XPS) test (for example, a British VG Sigma Probe X-ray photoelectron spectrometer can be used, test conditions: monochromator Al target 400um [100W], pass energy 50eV, dwell time 50ms, narrow scan step 0.1eV, full scan step 1eV, binding energy test), etc.

[0041] After the ball wall of the α-alumina carrier hollow sphere is determined, the ratio of the above <1>, the equivalent diameter of the above <2>, and the equivalent wall thickness of the above <3> can be measured and calculated.

[0042] The ball wall of the α-alumina carrier hollow sphere can be determined by the following process: first, determine the maximum section and measure the maximum section by electron microscopy, wherein the part with a depth of 0-5nm from the surface of the maximum section is analyzed; cover the maximum section of the α-alumina carrier to be analyzed with the least number of 1μm×1μm squares (the number is denoted as n), and the center of gravity of the maximum section is at the vertex of one of the n squares (for example, the center of gravity can be calculated by computer programming); in each square, if the proportion of the number of modified metal atoms to the total number of atoms is not less than 9 / 1000, the square is called a ball wall square, otherwise it is called a non-ball wall square; the ball wall of the hollow sphere is composed of the ball wall squares.

[0043] The ball walls of two or more hollow spheres can not intersect with each other or can partially intersect (tangentially). According to the trend of the curvature of the figure, the inner contour and the outer contour of the ball wall can be determined, the inner contour defines the internal cavity of the hollow sphere, and the outer contour defines the extension of the hollow sphere. If a certain circle defines an area equal to the area defined by the inner contour, it is called an internal equivalent circle, and if a certain circle defines an area equal to the area defined by the outer contour, it is called an external equivalent circle. The diameter of the internal equivalent circle is the equivalent diameter of the internal cavity; and half of the difference between the diameter of the external equivalent circle and the diameter of the internal equivalent circle is the equivalent wall thickness of the ball wall.

[0044] The α-alumina carrier according to any one of the preceding technical solutions, wherein the α-alumina carrier is prepared from a raw material for preparing an α-alumina carrier comprising modified alumina hollow spheres,

[0045] The modified alumina hollow spheres comprise alumina hollow spheres and a modified metal (such as zirconium) supported thereon (the "supported thereon" means that the modified metal exists in the wall of the hollow spheres or on the inner and outer surfaces of the hollow spheres), and the content of the modified metal in terms of modified metal atoms in the modified alumina hollow spheres is 0.1-2.5wt% (not including the end value 2.5wt%), preferably 0.2-2.0wt%, for example 0.55-1.1wt%, based on the total weight of the modified alumina hollow spheres;

[0046] The content of the modified alumina hollow spheres is 0.1-50.0wt%, for example 0.2-40.0wt%, preferably 0.5-25.0wt%, based on the total weight of the α-alumina carrier.

[0047] The α-alumina carrier according to any one of the preceding technical solutions, wherein the alumina hollow spheres are α-alumina hollow spheres and / or γ-alumina hollow spheres, preferably α-alumina hollow spheres.

[0048] The α-alumina carrier according to any one of the preceding technical solutions, wherein the particle size of the alumina hollow spheres is 1-500μm, preferably 5-300μm, more preferably 100-300μm.

[0049] The α-alumina carrier according to any one of the preceding technical solutions, wherein the wall thickness size of the alumina hollow spheres is less than or equal to 1 / 3 of the particle size, preferably less than or equal to 1 / 4, more preferably less than or equal to 1 / 6.

[0050] The α-alumina carrier according to any one of the preceding technical solutions, wherein the modified metal is zirconium.

[0051] The α-alumina carrier according to any one of the preceding technical solutions, wherein the modified metal is derived from a zirconium compound selected from zirconium nitrate, zirconium oxynitrate, zirconium sulfate, zirconium oxysulfate, zirconium fluoride, zirconium silicate, zirconium hydroxide and zirconium oxide, preferably at least one of zirconium nitrate, zirconium oxynitrate, zirconium sulfate and zirconium oxysulfate.

[0052] The present application also provides a preparation method of the α-alumina carrier according to any one of the preceding technical solutions, characterized by comprising the following steps:

[0053] (1) modifying the alumina hollow spheres by at least one modified metal-containing compound by an impregnation method, so that the content of the modified metal in terms of modified metal atoms in the modified alumina hollow spheres is 0.1-2.5wt% (not including the end value 2.5wt%), preferably 0.2-2.0wt%, for example 0.55-1.1wt%, based on the total weight of the modified alumina hollow spheres;

[0054] (2) mixing the alumina (preferably micron grade), pseudo boehmite and the modified alumina hollow spheres obtained in step (1) with an acid to obtain a mixture; wherein the content of the alumina (preferably micron grade) is 4.5-90wt%, the content of the pseudo boehmite is 5-95wt% and the content of the modified alumina hollow spheres is 0.1-50wt%, based on the total weight of the alumina (preferably micron grade), pseudo boehmite and the modified alumina hollow spheres;

[0055] (3) shaping the mixture obtained in step (2) (for example by kneading, extruding), drying and calcining to obtain the α-alumina carrier.

[0056] The preparation method of the α-alumina carrier according to any one of the preceding technical solutions has the characteristics that it comprises the following steps:

[0057] (1) obtaining an aqueous solution containing a modified metal compound, putting alumina hollow spheres into the aqueous solution, ultrasonically oscillating and immersing, then draining and first calcining to obtain modified alumina hollow spheres; the concentration of the aqueous solution is such that the content of the modified metal, calculated as the total weight of the modified alumina hollow spheres, is 0.1-2.5wt% (not including the end value 2.5wt%), preferably 0.2-2.0wt%, for example 0.55-1.1wt%, of the modified metal atoms in the obtained modified alumina hollow spheres;

[0058] (2) preparing a mixture containing alumina (preferably micron grade), pseudo boehmite and the modified alumina hollow spheres obtained in step (1), and mixing the mixture with an acid; the content of the alumina (preferably micron grade) is 4.5-90wt%, the content of the pseudo boehmite is 5-95wt% and the content of the modified alumina hollow spheres is 0.1-50wt%, based on the total weight of the mixture;

[0059] (3) kneading, extruding and shaping the material obtained in step (2), and then drying and second calcining to obtain the α-alumina carrier.

[0060] The preparation method of the α-alumina carrier according to any one of the preceding technical solutions has the characteristics that the modified metal is zirconium.

[0061] The preparation method of the α-alumina carrier according to any one of the preceding technical solutions has the characteristics that it comprises the following steps:

[0062] (1) obtaining a zirconium compound aqueous solution, putting the alumina hollow spheres into the zirconium compound aqueous solution, and then performing ultrasonic oscillation and immersion, followed by leaching and first calcination to obtain modified alumina hollow spheres; the concentration of the zirconium compound aqueous solution is such that the content of the zirconium compound in the obtained modified alumina hollow spheres is 0.1-4.0wt%, preferably 0.2-2.0wt%, based on the total weight of the modified alumina hollow spheres;

[0063] (2) preparing a mixture containing alumina (preferably micron-sized), pseudo-boehmite, and the modified alumina hollow spheres obtained in step (1), and mixing the mixture with an acid; the content of the alumina (preferably micron-sized) is 4.5-90wt%, the content of the pseudo-boehmite is 5-95wt%, and the content of the modified alumina hollow spheres is 0.1-50wt%, based on the total weight of the mixture;

[0064] (3) after kneading and extruding the material obtained in step (2), drying and second calcination are performed to obtain the α-alumina carrier.

[0065] According to any one of the preceding technical solutions, in step (1), the zirconium compound is selected from zirconium nitrate, zirconyl nitrate, zirconium sulfate, zirconyl sulfate, zirconium fluoride, zirconium silicate, zirconium hydroxide, and zirconium oxide, preferably at least one of zirconium nitrate, zirconyl nitrate, zirconium sulfate, and zirconyl sulfate;

[0066] The alumina hollow spheres are selected from α-alumina hollow spheres and / or γ-alumina hollow spheres; preferably, the particle size of the alumina hollow spheres is 1-500μm, preferably 5-300μm, more preferably 100-300μm, and the wall thickness is less than or equal to 1 / 3 of the particle size, preferably less than or equal to 1 / 4, more preferably less than or equal to 1 / 6;

[0067] Preferably, in step (1), the alumina hollow spheres to be modified are subjected to acid treatment, and the acid is preferably at least one of phosphoric acid, sulfuric acid, hydrochloric acid, and nitric acid.

[0068] According to any one of the preceding technical solutions, in step (1),

[0069] The conditions for the ultrasonic oscillation and immersion include a vacuum degree of 10mmHg or higher.

[0070] The calcination temperature is 200-1200℃, for example 600-1200℃, such as 800℃.

[0071] The preparation method of the alpha-alumina carrier according to any one of the preceding technical solutions, wherein in step (2), the added amount of the alumina (preferably micron grade) is 23-80 wt% based on the total weight of the mixture, the added amount of the pseudo monohydrate alumina is 18-75 wt%, and the content of the modified alumina hollow sphere is 0.2-40.0 wt%, preferably 0.5-25.0 wt%.

[0072] The preparation method of the alpha-alumina carrier according to any one of the preceding technical solutions, wherein in step (2), the alumina (preferably micron grade) is selected from at least one of trihydrate alpha-alumina, trihydrate beta-alumina and gamma-alumina, and the particle size of the alumina (preferably micron grade) is 1-500 μm.

[0073] The preparation method of the alpha-alumina carrier according to any one of the preceding technical solutions, wherein in step (2), the acid is nitric acid aqueous solution, the volume ratio of nitric acid to water in the nitric acid aqueous solution is 1:1.25-10, preferably 1:2-8, and the added amount of the acid is 5-50 wt% based on the total weight of the mixture.

[0074] The preparation method of the alpha-alumina carrier according to any one of the preceding technical solutions, wherein the pseudo monohydrate alumina and the acid are all or partially replaced by an aluminum sol.

[0075] The preparation method of the alpha-alumina carrier according to any one of the preceding technical solutions, wherein in step (3), the temperature of the calcination is 800-1800 °C, preferably 1100-1500 °C.

[0076] The present application also provides an alpha-alumina carrier, characterized in that the alpha-alumina carrier comprises modified alumina hollow spheres, the modified alumina hollow spheres comprising alumina hollow spheres and zirconium compounds loaded thereon, and the alpha-alumina carrier is prepared by the preparation method of the alpha-alumina carrier according to any one of the preceding technical solutions.

[0077] The present application also provides a silver catalyst for the production of ethylene oxide by ethylene oxidation, characterized in that the silver catalyst comprises the following components:

[0078] (1) silver element, wherein the content of the silver element in the silver catalyst is 1-40 wt% based on the total weight of the silver catalyst, for example 5-25 wt% based on the total weight of the silver catalyst;

[0079] (2) optionally, alkali metal element, wherein the content of the alkali metal element in the silver catalyst is 0 or 5-2000 ppm such as 5-1500 ppm based on the total weight of the silver catalyst;

[0080] (3) optionally, an alkaline earth metal element, wherein the content of the alkaline earth metal element in the silver catalyst is 0 or 5-10000 ppm, such as 5-8000 ppm, based on the total weight of the silver catalyst, in terms of atoms;

[0081] (4) optionally, a rhenium element, wherein the content of the rhenium element in the silver catalyst is 0 or 10-2000 ppm, such as 100-1000 ppm, based on the total weight of the silver catalyst, in terms of atoms;

[0082] (5) the balance of the α-alumina support according to any one of the preceding technical solutions;

[0083] Preferably, the modified metal atoms are distributed non-uniformly in the silver catalyst,

[0084] Preferably, the silver catalyst has the following properties:

[0085] The modified metal atoms are present in the silver catalyst in the form of a (plurality of) hollow spheres, wherein the hollow sphere has a sphere wall and an internal cavity defined by the sphere wall,

[0086] <1> in the sphere wall, the ratio of (the number of atoms of the modified metal) to (the sum of the number of atoms of the modified metal and the number of atoms of aluminum) based on the largest cross section and a depth of 0-5 nm is not more than 0.04, such as 0.015-0.03, further such as 0.017-0.028; and / or

[0087] <2> the internal cavity has an equivalent diameter of not more than 300 μm, such as 20-300 μm, further such as 33-200 μm, yet further such as 33-67 μm; and / or

[0088] <3> the sphere wall has an equivalent wall thickness of not more than 75 μm, such as 10-75 μm, further such as 16-50 μm, yet further such as 16-34 μm;

[0089] Preferably, the modified metal is zirconium.

[0090] The present application also provides a method for preparing the silver catalyst for the oxidation of ethylene to produce ethylene oxide according to any one of the preceding technical solutions, characterized in that the method comprises:

[0091] (1) impregnating the α-alumina support according to any one of technical solutions 1-6 with an impregnation solution containing a sufficient amount of a silver compound, an organic amine, optionally an alkali metal adjuvant, optionally an alkaline earth metal adjuvant, and optionally a rhenium adjuvant;

[0092] (2) leaching the impregnation solution; and

[0093] (3) activating the support obtained in step 2) in an oxygen-containing gas to form the silver catalyst;

[0094] Preferably, the silver compound is silver oxide, silver nitrate and / or silver oxalate, and the amount of the silver compound used should be such that the content of silver in the silver catalyst is 1-40 wt%, such as 5-25 wt%, based on the total weight of the silver catalyst;

[0095] Preferably, the alkali metal promoter is one or more compounds selected from lithium, sodium, potassium, rubidium and cesium, and the amount of the alkali metal promoter added to the impregnation solution should be such that the content of the alkali metal in the silver catalyst is 5-2000 ppm, such as 5-1500 ppm, based on the total weight of the silver catalyst; for example, the alkali metal promoter is cesium nitrate, lithium nitrate and / or potassium hydroxide;

[0096] Preferably, the alkaline earth metal promoter is one or more compounds selected from magnesium, calcium, strontium and barium, and the amount of the alkaline earth metal promoter added to the impregnation solution should be such that the total content of the alkaline earth metal in the silver catalyst is 5-10000 ppm, such as 5-8000 ppm, based on the total weight of the silver catalyst, for example, the alkaline earth metal promoter is one or more compounds selected from oxides, oxalates, sulfates, acetates and nitrates of magnesium, calcium, strontium and barium;

[0097] Preferably, the rhenium promoter is one or more compounds selected from oxides of rhenium, perrhenic acid, cesium perrhenate and ammonium perrhenate, and the amount of the rhenium promoter added to the impregnation solution should be such that the total content of rhenium metal in the silver catalyst is 10-2000 ppm, such as 100-1000 ppm, based on the total weight of the silver catalyst; for example, the rhenium promoter is ammonium perrhenate;

[0098] Preferably, the activation process in step 3) is carried out in air or a nitrogen-oxygen mixture with an oxygen content of not more than 21% by volume, for example, the temperature of the activation process in step 3) is controlled to be 180-700°C, such as 200-500°C, and the time of the activation process is 1-120 minutes, such as 2-60 minutes.

[0099] The present application also provides a use of the silver catalyst according to any one of the preceding technical solutions in the preparation of ethylene oxide by ethylene epoxidation.

[0100] Further, the present application also provides an α-alumina carrier, which comprises modified alumina hollow spheres, wherein the modified alumina hollow spheres comprise alumina hollow spheres and a zirconium compound loaded thereon, and the content of the zirconium compound is 0.1-2.5wt% (not including the end value 2.5wt%), preferably 0.2-2.0wt%, for example 0.55-1.1wt%, based on the total weight of the α-alumina carrier.

[0101] wherein the content of the modified alumina hollow spheres is 0.1-50.0wt%, based on the total weight of the α-alumina carrier.

[0102] According to the present application, the content of the modified metal (such as the content of zirconium) of the modified alumina hollow spheres can be measured by X-ray fluorescence spectroscopy XRF and chemical analysis method; and the morphology of the modified alumina hollow spheres of the α-alumina carrier can be measured by scanning electron microscopy SEM and mercury porosimeter.

[0103] According to the present application, preferably, the zirconium compound is selected from zirconium nitrate, zirconyl nitrate, zirconium sulfate, zirconyl sulfate, zirconium fluoride, zirconium silicate, zirconium hydroxide, zirconium oxide, preferably at least one of zirconium nitrate, zirconyl nitrate, zirconium sulfate and zirconyl sulfate.

[0104] According to the present application, preferably, the content of the modified alumina hollow spheres is 0.2-40.0wt%, preferably 0.5-25.0wt%, based on the total weight of the α-alumina carrier.

[0105] According to the present application, preferably, the alumina hollow spheres in the modified alumina hollow spheres are α-alumina hollow spheres and / or γ-alumina hollow spheres, preferably α-alumina hollow spheres. The crystal phase characteristics of the alumina hollow spheres in the modified alumina hollow spheres depend on the calcination temperature used in the preparation process thereof.

[0106] According to the present application, the particle size of the alumina hollow spheres in the modified alumina hollow spheres is 1-500μm, preferably 5-300μm, more preferably 100-300μm, and the wall thickness size is less than or equal to 1 / 3 of the particle size, preferably less than or equal to 1 / 4, more preferably less than or equal to 1 / 6. The particle size and wall thickness of the alumina hollow spheres in the modified alumina hollow spheres can be obtained by microscopic observation.

[0107] In the present application, the alumina hollow spheres as raw materials can be directly commercially purchased, or can be synthesized by using a template method, a spray drying method or a solvothermal method, and the size and the wall thickness size and other parameters can be adjusted according to different application conditions. Taking the spray drying method as an example, first, an alumina slurry is prepared, and the slurry is sprayed to generate droplets, and the droplets are dried by heating to form hollow spheres. The size and the wall thickness of the hollow spheres mainly depend on the process parameters of the spray drying method, such as the slurry concentration, the raw material ratio, the droplet size, the feeding speed, the evaporation rate and the calcination temperature.

[0108] According to the present application, preferably, the α-alumina carrier has one or more of the following characteristics: the specific surface area is 0.3-4.0 m 2 / g, preferably 2.7-2.92 m 2 / g, the water absorption is not less than 25%, for example, 41.8-45.2%, the mechanical strength is not less than 40 N / particle, for example, 47-73 N / particle, the proportion of the pores with a pore size ≥20 μm in the total pore volume is greater than 4%, preferably 5-15%, for example, 6.9-11.7%.

[0109] In the present application, the specific surface area of the carrier is determined by the BET method, the water absorption rate is determined by the boiling method, the mechanical strength is determined by the radial crushing method, the pore distribution is determined by the mercury intrusion method, and the chemical element content is determined by XRF or chemical analysis method. Specifically, the specific surface area (m2 / g) is determined according to the method in GB / T 6609.35-2023 "Alumina - Methods of chemical analysis and physical properties determination - Part 35: Determination of specific surface area"; the water absorption rate (%) is determined according to the method in GB / T 3810.3-2016 "Ceramic tiles - Test methods - Part 3: Determination of water absorption, apparent porosity, apparent relative density and bulk density"; the mechanical strength (also referred to as "strength", N / particle) is determined according to ASTM D 6175-03 (Standard Test Method for Radial Crush Strength of Extruded Catalyst and Catalyst Carrier Particles) (wherein the force application speed is 20 N / s, and the sample size L is the length of the carrier); the pore size (≥20 μm) ratio (%) is obtained from the pore size distribution determined according to RIPP 150-90 "Determination of Pore Size Distribution of Catalysts by Mercury Intrusion Method" (Yang Cuiding et al. "Petroleum Chemical Industry Analysis Methods" (RIPP Test Methods)); the content of modified metal, such as Zr content (wt‰), can be determined according to the method (XRF method) described in HJ1211-2021 "Solid waste - Determination of inorganic elements - Wavelength dispersive X-ray fluorescence spectrometry" or according to the method described in RIPP 43-90 "Determination of Mixed Rare Earths in Catalytic Cracking Catalysts" (Yang Cuiding et al. "Petroleum Chemical Industry Analysis Methods" (RIPP Test Methods)).

[0110] The present application also provides a preparation method of the α-alumina carrier, comprising the following steps:

[0111] (1) modifying the alumina hollow spheres with at least one zirconium compound by the impregnation method, so that the content of the zirconium compound in the modified alumina hollow spheres is 0.1-2.5 wt% (not including the end value 2.5 wt%), preferably 0.2-2.0 wt%, based on the total weight of the modified alumina hollow spheres, in terms of zirconium atoms;

[0112] (2) mixing the micron-sized alumina, pseudo-monohydrate alumina, and the modified alumina hollow spheres obtained in step (1) with an acid to obtain a mixture; wherein the content of the micron-sized alumina is 4.5-90 wt%, the content of the pseudo-monohydrate alumina is 5-95 wt%, and the content of the modified alumina hollow spheres is 0.1-50 wt%, based on the total weight of the micron-sized alumina, pseudo-monohydrate alumina, and modified alumina hollow spheres obtained in step (1);

[0113] (3) molding the mixture obtained in step (2) (e.g. by kneading, extrusion), drying and calcining to obtain the α-alumina carrier;

[0114] Specifically, the method comprises the following steps:

[0115] (1) obtaining a zirconium compound aqueous solution, and immersing the alumina hollow spheres in the zirconium compound aqueous solution under ultrasonic oscillation to obtain modified alumina hollow spheres after leaching and first calcination; the concentration of the zirconium compound aqueous solution is such that the content of the zirconium compound in the modified alumina hollow spheres obtained is 0.1-2.5wt% (not including the end value 2.5wt%) and preferably 0.2-2.0wt% in terms of zirconium atoms based on the total weight of the modified alumina hollow spheres;

[0116] (2) preparing a mixture comprising micron-sized alumina, pseudo-boehmite and the modified alumina hollow spheres obtained in step (1), and mixing the mixture with an acid; the content of the micron-sized alumina is 4.5-90wt%, the content of the pseudo-boehmite is 5-95wt% and the content of the modified alumina hollow spheres is 0.1-50wt% based on the total weight of the mixture;

[0117] (3) kneading, extruding and molding the material obtained in step (2), and drying and second calcining to obtain the α-alumina carrier.

[0118] In the present application, by adding the modified alumina hollow spheres in the preparation process, the modified alumina hollow spheres loaded with the zirconium compound exist inside the α-alumina carrier, the pore size is increased, the internal diffusion and permeability are obviously improved, and the ash impurities brought by the carbon-containing pore-forming agent are avoided, the silver particles loaded on the surface of the hollow spheres can effectively combine with the zirconium compound, and the distribution state of the electron cloud in the epoxidation process is improved, thereby when used for preparing ethylene oxide by ethylene epoxidation, the selectivity of the reaction can be significantly improved, and the emission of carbon dioxide byproducts is greatly reduced.

[0119] According to the present application, preferably in step (1), the zirconium compound is selected from zirconium nitrate, zirconyl nitrate, zirconium sulfate, zirconyl sulfate, zirconium fluoride, zirconium silicate, zirconium hydroxide and zirconium oxide, and is preferably at least one of zirconium nitrate, zirconyl nitrate, zirconium sulfate and zirconyl sulfate.

[0120] Preferably, the alumina hollow spheres are selected from α-alumina hollow spheres and / or γ-alumina hollow spheres; preferably, the particle size of the alumina hollow spheres is 1-500μm, preferably 5-300μm, and more preferably 100-300μm, and the wall thickness size is less than or equal to 1 / 3 of the particle size, preferably less than or equal to 1 / 4, and more preferably less than or equal to 1 / 6.

[0121] Preferably, the ultrasonic oscillation impregnation conditions include a vacuum degree of 10 mmHg or more.

[0122] Preferably, the temperature of the calcination in step (1) is 200-1200℃, for example, 600-1200℃, such as 800℃.

[0123] According to the present application, preferably, in step (2), the amount of the micro-sized alumina added is 23-80wt%, the amount of the pseudo-boehmite added is 18-75wt%, and the content of the modified alumina hollow sphere is 0.2-40.0wt%, preferably 0.5-25.0wt%, based on the total weight of the mixture (i.e. the micro-sized alumina, the pseudo-boehmite, and the modified alumina hollow sphere).

[0124] According to the present application, preferably, in step (2), the micro-sized alumina is selected from at least one of trihydrate α-alumina, trihydrate β-alumina, and γ-alumina, and the particle size of the micro-sized alumina is 1-500μm.

[0125] According to the present application, preferably, in step (2), the acid is nitric acid aqueous solution, the volume ratio of nitric acid to water in the nitric acid aqueous solution is 1:1.25-10, preferably 1:2-8, and the amount of the acid added is 5-50wt% based on the total weight of the mixture.

[0126] According to the present application, preferably, the pseudo-boehmite and the acid are replaced in whole or in part by an aluminum sol.

[0127] According to the present application, preferably, in step (3), the temperature of the calcination is 800-1800℃, preferably 1100-1500℃.

[0128] The present application also provides an α-alumina carrier prepared by the method for preparing the α-alumina carrier.

[0129] The present application also provides a silver catalyst for the production of ethylene oxide by the epoxidation of ethylene, which is prepared by impregnating the α-alumina carrier in a solution containing a silver compound.

[0130] The present application also provides the use of the silver catalyst in the preparation of ethylene oxide by the epoxidation of ethylene.

[0131] The present application will be further described in conjunction with the following examples, but the scope of the present application is not limited to these examples.

[0132] Determination of catalyst performance:

[0133] The various silver catalysts of the present application were evaluated for activity and selectivity using a laboratory microreactor evaluation apparatus. The reactor used in the microreactor evaluation apparatus was a stainless steel reactor tube with an internal diameter of 4 mm, which was placed in a heating jacket. The catalyst was packed in a volume of 1 ml, with inert packing in the lower part to position the catalyst bed in the constant temperature zone of the heating jacket.

[0134] The selective determination conditions used in the present application are shown in Table 1.

[0135] Table 1 Reaction determination conditions for catalysts

[0136] After the reaction conditions described above were stabilized and reached, the gas composition at the inlet and outlet of the reactor was continuously determined. The determination results were corrected for volume shrinkage and the selectivity S was calculated according to the following formula:

[0137] where ΔEO is the difference in ethylene oxide concentration between the outlet gas and the inlet gas of the reactor, ΔCO2 is the difference in carbon dioxide concentration between the outlet gas and the inlet gas of the reactor, and the average of more than 10 sets of test data was taken as the test result for that day.

[0138] The present application will be further described with reference to the following examples, but the scope of the present application is not limited to these examples.

[0139] Comparative Example 1

[0140] 498 g of α-A12O3 trihydrate and 102 g of pseudo-monohydrate A12O3 were mixed uniformly in a mixer, and then poured into a kneader. 120 ml of dilute nitric acid aqueous solution (nitric acid: water = 1:6, by volume) was poured into the kneader, and kneaded into a paste that could be extruded into a shape. Finally, the paste was loaded into an extruder, and extruded into a columnar shape with a diameter of 8.0 mm and a length of 6.0 mm. The columnar shape was dried at 80-120°C for more than 2 hours to reduce the free moisture content to 10 wt% or less. The dried columnar shape was placed in a high-temperature kiln, and raised from room temperature to 1390°C over 36 hours, and then held at this temperature for 2 hours to obtain a white solid product. XRD analysis of the solid showed that it was α-A12O3, and the relevant physical property data are shown in Table 2.

[0141] Comparative Example 2

[0142] A mixture of 448 g of α-A1203 trihydrate, 102 g of pseudo-boehmite A1203, and 50 g of graphite pore former was mixed in a mixer and then put into a kneader. 120 ml of dilute nitric acid aqueous solution (nitric acid: water = 1:6 by volume) was put into the kneader, and kneaded into a paste which could be extruded into a shape. The paste was put into an extruder, and extruded into a columnar shape having a diameter of 8.0 mm and a length of 6.0 mm. The columnar shape was dried at 80-120°C for 2 hours or more to reduce the free moisture content to 10 wt% or less. The dried columnar shape was put into a high-temperature furnace, and raised from room temperature to 1390°C over 36 hours, and then kept at 1390°C for 2 hours to obtain a white solid product. XRD analysis of the solid product showed that it was α-A1203. The physical properties of the α-A1203 support are shown in Table 2.

[0143] Comparative Example 3

[0144] The difference from Example 1 was that the α-alumina hollow spheres used were not treated. The other conditions were the same. An α-A1203 support was obtained. The physical properties of the α-A1203 support are shown in Table 2.

[0145] Comparative Example 4

[0146] A mixture of 473 g of α-alumina trihydrate (particle size 1-500 μm), 102 g of pseudo-boehmite A1203, and 25 g of α-alumina hollow spheres (particle size 100 μm, wall thickness less than or equal to 1 / 6 of the particle size) was mixed in a mixer. 120 ml of dilute nitric acid solution (nitric acid: water = 1:6 by volume) and 206 ml of zirconium nitrate aqueous solution (1.0 wt% of Zr element) were put into a kneader, and kneaded into a paste which could be extruded into a shape. The paste was put into an extruder, and extruded into a columnar shape having an outer diameter of 8.0 mm and a length of 6.0 mm. The columnar shape was dried at 80-120°C for 2 hours or more to reduce the free moisture content to 10 wt% or less. The dried columnar shape was put into a high-temperature furnace, and raised from room temperature to 1390°C over 36 hours, and then kept at 1390°C for 2 hours to obtain an α-A1203 support. The Zr element content of the α-A1203 support was about 0.55 wt% of the total weight of the support. The physical properties of the α-A1203 support are shown in Table 2.

[0147] Comparative Example 5

[0148] Mix 498 g of α-alumina trihydrate (1-500 μm in size), 102 g of pseudo-boehmite Al203, and 30 g of the modified alumina hollow sphere in a mixer to obtain a uniform mixture. Pour 120 ml of a dilute nitric acid solution (nitric acid: water = 1:6 by volume) and 206 ml of a zirconium nitrate aqueous solution (1.0 wt% in mass concentration of Zr element) into a kneader to knead the mixture into a paste that can be extruded into a shape. The paste is put into an extruder to be extruded into a columnar shape having an outer diameter of 8.0 mm and a length of 6.0 mm. The columnar shape is dried at 80-120°C for more than 2 hours to reduce the free water content to less than 10 wt%. The dried columnar shape is put into a high-temperature furnace, and the temperature is raised from room temperature to 1390°C over 36 hours, and then kept constant for 2 hours to obtain an α-Al203 support. The Zr element accounts for about 0.57 wt% of the total weight of the support. The relevant physical property data are shown in Table 2.

[0149] Example 1

[0150] Prepare 300 ml of a zirconium nitrate aqueous solution (1.0 wt% in mass concentration of Zr element) in a glass bottle, and continuously ultrasonically agitate the solution. Pour 30 g of α-alumina hollow spheres (100 μm in size, and a wall thickness of less than or equal to 1 / 6 of the size) into the glass bottle to completely immerse the hollow spheres. Vacuumize the glass bottle to 10 mmHg or more, and ultrasonically agitate the solution for about 15 minutes. Then, drain the excess solution, and finally heat the immersed hollow sphere sample at 800°C for about 30 minutes to obtain modified alumina hollow spheres. The Zr element loaded on the hollow spheres accounts for about 0.55 wt% of the total weight of the hollow spheres.

[0151] Mix 473 g of α-alumina trihydrate (1-500 μm in size), 102 g of pseudo-boehmite Al203, and 25 g of the modified alumina hollow spheres in a mixer to obtain a uniform mixture. Pour 120 ml of a dilute nitric acid solution (nitric acid: water = 1:6 by volume) into a kneader to knead the mixture into a paste that can be extruded into a shape. The paste is put into an extruder to be extruded into a columnar shape having an outer diameter of 8.0 mm and a length of 6.0 mm. The columnar shape is dried at 80-120°C for more than 2 hours to reduce the free water content to less than 10 wt%. The dried columnar shape is put into a high-temperature furnace, and the temperature is raised from room temperature to 1390°C over 36 hours, and then kept constant for 2 hours to obtain an α-Al203 support. The relevant physical property data are shown in Table 2.

[0152] Example 2

[0153] A 300-ml zirconium sulfate aqueous solution (1.0 wt% in terms of Zr element) was prepared in a glass bottle and subjected to ultrasonic oscillation. Then, 55 g of α-alumina hollow spheres (100 μm in particle size and less than or equal to 1 / 6 of the particle size in wall thickness) were poured into the glass bottle so as to be completely immersed. After the vacuum was drawn to more than 10 mmHg and the ultrasonic oscillation was continued for about 15 minutes, the excess solution was removed by decantation. Finally, the immersed hollow sphere sample was kept at 800°C for about 30 minutes to obtain modified alumina hollow spheres. The Zr element supported on the hollow spheres accounted for about 0.55 wt% of the total weight of the hollow spheres.

[0154] A 300-ml zirconium sulfate aqueous solution (1.0 wt% in terms of Zr element) was prepared in a glass bottle and subjected to ultrasonic oscillation. Then, 55 g of α-alumina hollow spheres (100 μm in particle size and less than or equal to 1 / 6 of the particle size in wall thickness) were poured into the glass bottle so as to be completely immersed. After the vacuum was drawn to more than 10 mmHg and the ultrasonic oscillation was continued for about 15 minutes, the excess solution was removed by decantation. Finally, the immersed hollow sphere sample was kept at 800°C for about 30 minutes to obtain modified alumina hollow spheres. The Zr element supported on the hollow spheres accounted for about 0.55 wt% of the total weight of the hollow spheres.

[0155] Example 3

[0156] A 300-ml zirconium sulfate aqueous solution (1.0 wt% in terms of Zr element) was prepared in a glass bottle and subjected to ultrasonic oscillation. Then, 55 g of α-alumina hollow spheres (100 μm in particle size and less than or equal to 1 / 6 of the particle size in wall thickness) were poured into the glass bottle so as to be completely immersed. After the vacuum was drawn to more than 10 mmHg and the ultrasonic oscillation was continued for about 15 minutes, the excess solution was removed by decantation. Finally, the immersed hollow sphere sample was kept at 800°C for about 30 minutes to obtain modified alumina hollow spheres. The Zr element supported on the hollow spheres accounted for about 0.55 wt% of the total weight of the hollow spheres.

[0157] 473g of α-alumina trihydrate (particle size 1-500μm), 102g of pseudo-boehmite Al203, and 25g of the modified alumina hollow spheres described above were mixed uniformly in a mixer; 120ml of dilute nitric acid solution (nitric acid: water = 1:6 by volume) was poured into a kneader to knead into a paste that could be extruded into a shape. The paste was put into an extruder to be extruded into a columnar shape with an outer diameter of 8.0mm and a length of 6.0mm, and dried at 80-120°C for more than 2 hours to reduce the free water content to less than 10wt%. The dried columnar shape was put into a high-temperature furnace, and raised from room temperature to 1390°C over 36 hours, and then kept at 1390°C for 2 hours to obtain an α-Al203 carrier. The relevant physical property data of the carrier are shown in Table 2.

[0158] Example 4

[0159] A 300ml aqueous solution of zirconium sulfate (1.0wt% in terms of Zr element) was prepared in a glass bottle, and 30g of α-alumina hollow spheres (particle size 100μm, wall thickness less than or equal to 1 / 6 of the particle size) were poured into the glass bottle to be completely immersed. The solution was vacuumed to 10mmHg or more, and the immersion was continued for about 15 minutes with ultrasonic oscillation. The excess solution was removed by decanting, and the immersed hollow sphere sample was kept at 800°C for about 30 minutes to obtain modified alumina hollow spheres. The Zr element loaded on the hollow spheres was about 0.55wt% of the total weight of the hollow spheres.

[0160] 473g of β-alumina trihydrate (particle size 1-500μm), 102g of pseudo-boehmite Al203, and 25g of the modified alumina hollow spheres described above were mixed uniformly in a mixer; 120ml of dilute nitric acid solution (nitric acid: water = 1:6 by volume) was poured into a kneader to knead into a paste that could be extruded into a shape. The paste was put into an extruder to be extruded into a columnar shape with an outer diameter of 8.0mm and a length of 6.0mm, and dried at 80-120°C for more than 2 hours to reduce the free water content to less than 10wt%. The dried columnar shape was put into a high-temperature furnace, and raised from room temperature to 1390°C over 36 hours, and then kept at 1390°C for 2 hours to obtain an α-Al203 carrier. The relevant physical property data of the carrier are shown in Table 2.

[0161] Example 5

[0162] A 300-ml aqueous solution of zirconyl sulfate (1.0 wt% of Zr element) was prepared in a glass bottle and subjected to ultrasonic oscillation. Then, 30 g of γ-alumina hollow spheres (100 μm in diameter and less than or equal to 1 / 6 of the diameter in wall thickness) were poured into the glass bottle so as to be completely immersed. The solution was vacuumed to more than 10 mmHg and subjected to ultrasonic oscillation for about 15 minutes. The excess solution was removed by decantation. The impregnated hollow spheres were finally kept at 800°C for about 30 minutes to obtain modified alumina hollow spheres. The Zr element supported on the hollow spheres accounted for about 0.55 wt% of the total weight of the hollow spheres.

[0163] 473 g of β-alumina trihydrate (1-500 μm in diameter), 102 g of pseudo-monohydrate Al203, and 25 g of the modified alumina hollow spheres were mixed in a mixer. A 120-ml dilute nitric acid solution (nitric acid: water = 1:6 by volume) was poured into a kneader to knead the mixture into a paste-like material that could be extruded. The paste-like material was put into an extruder to be extruded into columnar materials having an outer diameter of 8.0 mm and a length of 6.0 mm. The columnar materials were dried at 80-120°C for more than 2 hours to reduce the free moisture content to less than 10 wt%. The dried columnar materials were put into a high-temperature furnace and raised from room temperature to 1390°C over 36 hours and then kept at the temperature for 2 hours to obtain α-Al203 supports. The physical properties of the α-Al203 supports are shown in Table 2.

[0164] Example 6

[0165] A 300-ml aqueous solution of zirconyl sulfate (1.0 wt% of Zr element) was prepared in a glass bottle and subjected to ultrasonic oscillation. Then, 30 g of γ-alumina hollow spheres (100 μm in diameter and less than or equal to 1 / 6 of the diameter in wall thickness) were poured into the glass bottle so as to be completely immersed. The solution was vacuumed to more than 10 mmHg and subjected to ultrasonic oscillation for about 15 minutes. The excess solution was removed by decantation. The impregnated hollow spheres were finally kept at 800°C for about 30 minutes to obtain modified alumina hollow spheres. The Zr element supported on the hollow spheres accounted for about 0.55 wt% of the total weight of the hollow spheres.

[0166] 473g of γ-alumina (1-500μm in size), 102g of pseudo boehmite AI2O3, and 25g of the modified alumina hollow spheres described above were mixed uniformly in a mixer; 120ml of dilute nitric acid solution (nitric acid: water = 1:6 in volume ratio) was poured into a kneader to knead into a paste that could be extruded into a shape. The paste was put into an extruder to be extruded into a columnar shape with an outer diameter of 8.0mm and a length of 6.0mm, and dried at 80-120°C for more than 2 hours to reduce the free water content to less than 10wt%. The dried columnar shape was put into a high-temperature kiln, and raised from room temperature to 1390°C over 36 hours, and then kept at the temperature for 2 hours to obtain an α-AI2O3 carrier. The relevant physical property data of the carrier are shown in Table 2.

[0167] Example 7

[0168] A 300ml aqueous zirconium nitrate solution (1.0wt% in mass concentration of Zr element) was prepared in a glass bottle, and 30g of γ-alumina hollow spheres (100μm in size, and the wall thickness less than or equal to 1 / 6 of the size) were poured into the glass bottle to be completely immersed. The solution was vacuumed to more than 10mmHg, and ultrasonically vibrated for about 15 minutes, and then the excess solution was removed by decantation. Finally, the immersed hollow sphere sample was kept at 800°C for about 30 minutes to obtain modified alumina hollow spheres, and the Zr element loaded on the hollow spheres accounted for about 0.55wt% of the total weight of the hollow spheres.

[0169] 473g of γ-alumina (1-500μm in size), 102g of pseudo boehmite AI2O3, and 25g of the modified alumina hollow spheres described above were mixed uniformly in a mixer; 120ml of dilute nitric acid solution (nitric acid: water = 1:6 in volume ratio) was poured into a kneader to knead into a paste that could be extruded into a shape. The paste was put into an extruder to be extruded into a columnar shape with an outer diameter of 8.0mm and a length of 6.0mm, and dried at 80-120°C for more than 2 hours to reduce the free water content to less than 10wt%. The dried columnar shape was put into a high-temperature kiln, and raised from room temperature to 1390°C over 36 hours, and then kept at the temperature for 2 hours to obtain an α-AI2O3 carrier. The relevant physical property data of the carrier are shown in Table 2.

[0170] Example 8

[0171] The difference from Example 1 was only that the particle size of the α-alumina hollow spheres used was 300μm, and the other conditions were the same. An α-AI2O3 carrier was obtained, and the relevant physical property data of the carrier are shown in Table 2.

[0172] Example 9

[0173] The difference from Example 1 is that the thickness of the wall of the α-alumina hollow sphere used is 1 / 4-1 / 3 of the particle size, and the other conditions are the same. An α-A1203 support is obtained, and the relevant physical property data are shown in Table 2.

[0174] Example 10

[0175] First, 300 ml of a 9 wt% aqueous nitric acid solution is prepared, and 30 g of α-alumina hollow spheres (particle size 100 μm, wall thickness less than or equal to 1 / 6 of the particle size) are poured into the nitric acid solution, and ultrasonic agitation is continued for about 120 minutes. After the excess solution is removed by decanting, the hollow spheres are soaked in 300 ml of deionized water, and then dried at 110°C for about 4 hours.

[0176] In a glass bottle, 300 ml of a zirconium nitrate aqueous solution (1.0 wt% in terms of the mass concentration of Zr element) is prepared, and the above-mentioned 30 g of the pretreated α-alumina hollow spheres (particle size 100 μm, wall thickness less than or equal to 1 / 6 of the particle size) are poured into the glass bottle so as to be completely immersed. The glass bottle is evacuated to 10 mmHg or more, and ultrasonic agitation is continued for about 15 minutes. After the excess solution is removed by decanting, the impregnated hollow sphere sample is finally heat-treated at 800°C for about 30 minutes to obtain modified alumina hollow spheres, and the Zr element supported on the hollow spheres is about 0.55 wt% of the total weight of the hollow spheres.

[0177] 473 g of α-alumina trihydrate (particle size 1-500 μm), 102 g of pseudo-monohydrate A1203, and 25 g of the above-mentioned modified alumina hollow spheres are put into a mixer and mixed uniformly. 120 ml of a dilute nitric acid solution (nitric acid: water = 1:6 by volume) is poured into a kneader, and kneaded into a paste that can be extruded into a shape. The paste is put into an extruder, and extruded into a columnar shape having an outer diameter of 8.0 mm and a length of 6.0 mm. The columnar shape is dried at 80-120°C for 2 hours or more so that the free water content is reduced to 10 wt% or less. The dried columnar shape is put into a high-temperature furnace, and raised from room temperature to 1390°C over 36 hours, and then heat-treated at this temperature for 2 hours to obtain an α-A1203 support, and the relevant physical property data are shown in Table 2.

[0178] Example 11

[0179] This example is performed in the same manner as described in Example 4, except that the dried columnar shape is put into a high-temperature furnace, and raised from room temperature to 1520°C over 36 hours, and then heat-treated at this temperature for 2 hours to obtain an α-A1203 support, and the relevant physical property data are shown in Table 2.

[0180] Reference Example 1

[0181] The difference from Example 1 is that the particle size of the α-alumina hollow spheres used is 600 μm, and the other conditions are the same. The α-A1203 support obtained has the physical property data shown in Table 2.

[0182] Reference Example 2

[0183] The difference from Example 1 is that the mass concentration of Zr element in the aqueous zirconium nitrate solution is 4.5 wt%, and the other conditions are the same. The modified alumina hollow spheres obtained have Zr element loaded on the hollow spheres, which accounts for about 2.5 wt% of the total weight of the hollow spheres. The α-A1203 support obtained has the physical property data shown in Table 2.

[0184] Table 2 Physical property data of the supports

[0185] Catalyst preparation

[0186] In a glass beaker with stirring, 32.1 g of ethylenediamine, 10.8 g of ethanolamine and 179.8 g of deionized water were added to obtain a mixture; 72.2 g of silver oxalate was slowly added to the mixture while the temperature was kept below 40°C and stirring was continued until the silver oxalate was completely dissolved; then 2.25 mL of aqueous cesium nitrate solution (concentration 0.03995 g / mL, based on the atomic weight of cesium), 2.78 mL of aqueous high-rhenium ammonium solution (concentration 0.0162 g / mL, based on the atomic weight of rhenium) were added in sequence, and the mixture was mixed uniformly to obtain 300 g of impregnation solution for use.

[0187] 15 g of the support prepared in each of Examples 1-11 and Reference Examples 1-2 and Comparative Examples 1-5 above was taken and placed in a glass container capable of being evacuated, and the above silver amine impregnation solution was added to completely immerse the support. The container was evacuated to above 10 mmHg and kept for about 15 minutes, and then the excess solution was removed by decanting. Finally, the impregnated support sample was heated in a stream of air at 350°C for about 2 minutes to obtain the silver catalysts of Examples 1-11, Reference Examples 1-2 and Comparative Examples 1-5.

[0188] The performances of the corresponding silver catalysts obtained from the supports in Examples 1-11, Reference Examples 1-2 and Comparative Examples 1-5 were measured under the aforementioned process conditions using a micro-reactor evaluation device, and the data results on the 20th day after the start of the reaction are shown in Table 3.

[0189] Table 3 Performance measurement results of the catalysts

[0190] As can be seen from Table 3, the silver catalysts prepared from the alumina carriers to which the alumina hollow spheres were added according to the present application all have higher selectivity than the silver catalyst of Comparative Example 1 prepared from the carrier to which no alumina hollow spheres were added, under the same conditions. However, the particle size of the hollow spheres should not exceed 500 μm, otherwise the mechanical strength of the carrier will be low and the reaction temperature of the catalyst prepared therefrom will be high. The catalyst prepared from the carrier to which the carbon-containing pore-forming agent was added in Comparative Example 2 also has a decreased performance due to the ash impurities introduced by the carbon-containing material. The silver catalysts prepared from the alumina carriers to which the modified alumina hollow spheres were added all have higher selectivity than the silver catalyst of Comparative Example 3 prepared from the carrier to which the untreated alumina hollow spheres were added, under the same conditions. The α-alumina carriers used in the above Examples 1 to 11 have the following properties: the modified metal atoms exist in the form of hollow spheres (plural) in the α-alumina carrier, wherein the hollow spheres have a sphere wall and an internal cavity defined by the sphere wall, <1> in the sphere wall, the ratio of (the number of atoms of the modified metal) to (the sum of the number of atoms of the modified metal and the number of atoms of aluminum), based on the largest cross section and a depth of 0 to 5 nm, is between 0.017 and 0.028; and / or <2> the equivalent diameter of the internal cavity is between 33 and 200 μm; and / or <3> the equivalent wall thickness of the sphere wall is between 16 and 50 μm. The above features can be obtained by theoretical calculation using the parameters in the preparation process, or by measurement using the measurement method as described herein. By using the modified hollow spheres, the modified metal can be concentratedly distributed near the macropores brought by the hollow spheres, and these regions constitute the modified metal atom concentration regions. On the one hand, the utilization efficiency of the modified metal is improved, and on the other hand, the performance of the catalyst prepared from the carrier is also improved, so that the silver catalyst prepared using the carrier is obviously improved in both activity and selectivity.

[0191] The above description of the various embodiments of the present application has been presented for the purpose of illustration and description and is not intended to be exhaustive or to limit the application to the precise forms disclosed. Many modifications and variations will be apparent to practitioners skilled in the art.

[0192] The endpoints of the ranges and any values described herein are not limited to the precise values stated. The ranges and values should be construed to be roughly about the ranges or values stated. For numerical ranges, the end points of the ranges are included in the ranges, the end points of the ranges are not included in the ranges, and individual points within the ranges are included in the ranges.

Claims

1. An α-alumina support, characterized in that, The α-alumina support has the following characteristics: Specific surface area is 0.3-4.0 m². 2 / g, Water absorption rate not less than 25%, Mechanical strength not less than 40N / particle; and The proportion of pores with a diameter ≥ 20 μm to the total pore volume is greater than 4%; Preferably, the α-alumina support contains modified metal, and the content of modified metal, calculated as atoms, is 0.1-3 wt‰ based on the total weight of the α-alumina support. Preferably, the α-alumina support has the following properties: The modified metal atoms exist in the form of hollow spheres (complex number) in the α-alumina support, wherein the hollow spheres have spherical walls and internal cavities defined by the spherical walls. <1> Within the sphere wall, the ratio of (the number of atoms of the modified metal) to (the sum of the number of modified atoms and the number of aluminum atoms), based on the maximum cross-section and a depth of 0-5 nm, is no greater than 0.04, for example, 0.015-0.03; and / or <2> The equivalent diameter of the internal cavity is no greater than 300 μm, for example, 20-300 μm; and / or <3> The equivalent wall thickness of the sphere is no greater than 75 μm, for example, 10-75 μm.

2. The α-alumina support according to claim 1, wherein the α-alumina support is prepared from raw materials comprising modified hollow alumina spheres. The modified alumina hollow spheres include alumina hollow spheres and modified metals loaded on them. Based on the total weight of the modified alumina hollow spheres, the content of modified metals, calculated as modified metal elements, is 0.1-2.5 wt% (excluding the endpoint value of 2.5 wt%). in, Based on the total weight of the α-alumina carrier, the content of the modified alumina hollow spheres is 0.1-50.0 wt%.

3. The α-alumina support according to claim 2, wherein, The hollow alumina spheres are α-alumina hollow spheres and / or γ-alumina hollow spheres.

4. The α-alumina support according to any one of claims 2-3, wherein, The alumina hollow spheres have a particle size of 1-500 μm, preferably 5-300 μm, and more preferably 100-300 μm.

5. The α-alumina support according to any one of claims 2-4, wherein, The wall thickness of the alumina hollow spheres is less than or equal to 1 / 3 of the particle size, preferably less than or equal to 1 / 4, and more preferably less than or equal to 1 / 6.

6. The α-alumina support according to any one of claims 1-5, wherein the modified metal is zirconium.

7. The α-alumina support according to any one of claims 1-6, wherein, The modified metal is derived from zirconium compounds selected from zirconium nitrate, zirconium oxynitrate, zirconium sulfate, zirconium oxysulfate, zirconium fluoride, zirconium silicate, zirconium hydroxide, and zirconium oxide.

8. A method for preparing an α-alumina support according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Alumina hollow spheres are modified by impregnation with at least one compound containing a modified metal, such that the content of modified metal in the modified alumina hollow spheres, based on the total weight of the modified alumina hollow spheres, is 0.1-2.5 wt% (excluding the endpoint value of 2.5 wt%). (2) A mixture is obtained by mixing alumina, pseudo-monohydrate alumina and the modified alumina hollow spheres obtained in step (1) with acid; wherein, based on the total weight of alumina, pseudo-monohydrate alumina and the modified alumina hollow spheres obtained in step (1), the content of alumina is 4.5-90 wt%, the content of pseudo-monohydrate alumina is 5-95 wt%, and the content of modified alumina hollow spheres is 0.1-50 wt%. (3) The mixture obtained in step (2) is shaped, dried and calcined to obtain the α-alumina carrier.

9. The method for preparing the α-alumina support according to claim 8, characterized in that, The hollow alumina spheres are selected from α-alumina hollow spheres and / or γ-alumina hollow spheres; preferably, the particle size of the hollow alumina spheres is 1-500 μm, more preferably 5-300 μm, more preferably 100-300 μm, and the wall thickness of the hollow alumina spheres is less than or equal to 1 / 3 of the particle size, more preferably less than or equal to 1 / 4, and more preferably less than or equal to 1 / 6; Preferably, the alumina hollow sphere to be modified in step (1) is an acid-treated alumina hollow sphere.

10. The method for preparing the α-alumina support according to any one of claims 8-9, wherein, In step (2), the alumina is selected from at least one of trihydrate α-alumina, trihydrate β-alumina and γ-alumina, and the particle size of the alumina is 1-500 μm, preferably 5-300 μm, and more preferably 100-300 μm.

11. The method for preparing the α-alumina support according to any one of claims 8-10, characterized in that, The modified metal is zirconium.

12. The method for preparing the α-alumina support according to any one of claims 8-11, wherein, In step (1), the compound containing the modified metal is selected from zirconium nitrate, zirconium oxynitrate, zirconium sulfate, zirconium oxysulfate, zirconium fluoride, zirconium silicate, zirconium hydroxide and zirconium oxide.

13. A silver catalyst for the oxidation of ethylene to produce ethylene oxide, characterized in that, The silver catalyst comprises the following components: (1) Silver element, wherein the silver element is present in the silver catalyst in an atomic quantity of 1-40 wt%, based on the total weight of the silver catalyst; (2) An alkali metal element, wherein the alkali metal element is present in the silver catalyst at a content of 0 or 5-2000 ppm on an atomic basis, based on the total weight of the silver catalyst. (3) Alkaline earth metal elements, wherein the content of the alkaline earth metal elements in the silver catalyst is 0 or 5-10000 ppm on an atomic basis, based on the total weight of the silver catalyst. (4) Rhenium, wherein the amount of rhenium in the silver catalyst is 0 or 10-2000 ppm on an atomic basis, based on the total weight of the silver catalyst; (5) The remaining amount is the α-alumina carrier according to any one of claims 1-7. Preferably, the silver catalyst has the following properties: The modified metal atoms exist in the silver catalyst in the form of hollow spheres (plural), wherein the hollow spheres have spherical walls and internal cavities defined by the spherical walls. <1> Within the sphere wall, the ratio of (the number of atoms of the modified metal) to (the sum of the number of modified atoms and the number of aluminum atoms), based on the maximum cross-section and a depth of 0-5 nm, is no greater than 0.04, for example, 0.015-0.03; and / or <2> The equivalent diameter of the internal cavity is no greater than 300 μm, for example, 20-300 μm; and / or <3> The equivalent wall thickness of the sphere is no more than 75 μm, for example, 10-75 μm; Preferably, the modified metal is zirconium.

14. A method for preparing the silver catalyst for the ethylene oxidation to ethylene oxide of claim 13, characterized in that, The method includes: (1) Impregnate the α-alumina carrier according to any one of claims 1-7 with an impregnation solution containing sufficient amounts of silver compound, organic amine, optional alkali metal auxiliaries, optional alkaline earth metal auxiliaries and optional rhenium auxiliaries. (2) Leaching impregnation solution; and (3) The support obtained in step 2) is activated in oxygen-containing gas to prepare the silver catalyst.

15. The application of the silver catalyst according to claim 13 in the epoxidation of ethylene to prepare ethylene oxide.

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