Method for producing porous alpha-alumina catalyst supports

Abstract

A method for producing a porous alpha-alumina catalyst support, comprising: i) preparing a precursor material comprising at least 50 wt.-% transition alumina, based on inorganic solids, having a loose bulk density of at most 600 g / L, a pore volume of at least 0.6 mL / g, and a median pore diameter of at least 15 nm, and at most 30 wt.-% alumina hydrate; ii) forming the precursor material into a shaped body; and iii) calcining the shaped body to obtain a porous alpha-alumina catalyst support. The catalyst support has a high total pore volume, thus allowing it to be impregnated with a large amount of silver, while retaining its surface area sufficiently large to optimally distribute catalytically active species, in particular metal species. The present invention further relates to a shaped catalyst body for the production of ethylene oxide by the gas-phase oxidation of ethylene, comprising at least 15 wt.-% silver, based on the total weight of the catalyst, deposited on a porous alpha-alumina catalyst support obtained by the method described above. The present invention also relates to a method for preparing the above-described shaped catalyst body, comprising the steps of a) impregnating a porous alpha-alumina catalyst support obtained by the above-described method with a silver impregnation solution, preferably under reduced pressure, and optionally drying the impregnated porous alumina support; and b) subjecting the impregnated porous alpha-alumina support to a heat treatment, wherein steps a) and b) are optionally repeated.The present invention further relates to a method for producing ethylene oxide by the gas phase oxidation of ethylene, comprising the step of reacting ethylene and oxygen in the presence of the above-described shaped catalyst body.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a porous alpha-alumina catalyst support, a catalyst for the production of ethylene oxide by the vapor phase oxidation of ethylene comprising silver deposited on a porous alumina catalyst support, a method for preparing the catalyst, and a method for producing ethylene oxide by the vapor phase oxidation of ethylene. [Background technology]

[0002] Alumina (Al2O3) is ubiquitous in supports and / or catalysts for many heterogeneous catalytic processes. Some of these catalytic processes occur under conditions of high temperature, high pressure, and / or high water vapor pressure. It is well known that alumina has several crystalline phases, such as alpha-alumina (often referred to as α-alumina or α-Al2O3), gamma-alumina (often referred to as γ-alumina or γ-Al2O3), as well as several alumina polymorphs. Alpha-alumina is the most stable at high temperatures but has the smallest surface area.

[0003] Gamma-alumina has an extremely high surface area. This is generally believed to be due to the alumina molecules' crystalline structure not being very densely packed. Gamma-alumina is part of a family known as activated alumina or transition alumina, so named because it is one of a series of aluminas that can undergo transitions into different polymorphs. Unfortunately, when gamma-alumina is heated to high temperatures, the atomic structure collapses, resulting in a substantial decrease in surface area. The densest crystalline form of alumina is alpha-alumina.

[0004] Ethylene oxide is produced in large volumes and is used primarily as an intermediate in the production of several industrial chemicals. In the industrial oxidation of ethylene to ethylene oxide, heterogeneous catalysts comprising silver deposited on a porous support are typically used. To carry out heterogeneously catalyzed gas-phase oxidation, a mixture of oxygen-containing gas, e.g., air or pure oxygen, and ethylene is typically passed through multiple tubes arranged in a reactor in which a packing of shaped catalyst bodies is present.

[0005] Catalyst performance is typically characterized by selectivity, activity, catalyst selectivity and activity lifetime, and mechanical stability. Selectivity is the mole fraction of olefin converted to the desired olefin oxide. Even modest improvements in selectivity and selectivity maintenance over time can pay enormous dividends in terms of process efficiency.

[0006] For the internal surface of a porous supported catalyst to be efficiently utilized, the feedstream gas must diffuse through the pores to reach the internal surface, and the reaction products must diffuse away from the surface and out of the catalyst body. In processes for producing ethylene oxide by the vapor-phase oxidation of ethylene, the diffusion of ethylene oxide molecules out of the catalyst body can involve catalyst-induced undesired sequential reactions, such as isomerization to acetaldehyde followed by complete combustion to carbon dioxide, thereby reducing the overall selectivity of the process. The average pore residence time of the molecules, and therefore the extent to which undesired sequential reactions occur, is affected by the pore structure of the catalyst.

[0007] Therefore, the performance of a catalyst is influenced by its pore structure, which is essentially determined by the pore structure of the catalyst support. The term "pore structure" is understood to refer to the arrangement of void space within the support matrix, including the size, size distribution, shape, and interconnectivity of the pores. This can be characterized by various methods, such as mercury porosimetry, nitrogen sorption, or computed tomography. H. Giesche, "Mercury Porosimetry: A General (Practical) Overview," Part. Part. Syst. Charact. 23 (2006), pp. 9-19, provides useful insights into mercury porosimetry.

[0008] EP 2 617 489 A1 describes a catalyst support in which at least 80% of the pore volume is contained in pores having a diameter in the range of 0.1 to 10 μm, and in which at least 80% of the pore volume in pores having a diameter in the range of 0.1 to 10 μm is contained in pores having a diameter in the range of 0.3 to 10 μm.

[0009] WO03 / 072244A1 and WO03 / 072246A1 each describe a catalyst support in which at least 70% of the pore volume is contained in pores having a diameter of 0.2 to 10 μm, and the pores having a diameter between 0.2 and 10 μm represent a volume of at least 0.27 mL / g of the support.

[0010] EP 1927398 A1 describes a catalyst support having a pore size distribution with at least two maxima in the range of 0.01 to 100 μm, with at least one of these maxima being in the range of 0.01-1.0 μm.

[0011] EP 3639923 A1 describes a shaped catalyst body having a multimodal pore size distribution with a maximum in the range of 0.1 to 3.0 μm and a maximum in the range of 8.0 to 100 μm, wherein at least 40% of the total pore volume of the shaped catalyst body comes from pores having diameters in the range of 0.1 to 3.0 μm.

[0012] WO2008 / 054564A1 describes a method for producing shaped porous bodies containing alpha-alumina platelets. US2006 / 0281631A1 describes the preparation of supports containing non-platelet alumina. US6,165,437A describes the preparation of alpha-alumina powders with specific morphologies by calcining transition alumina powders in a chlorine-containing atmosphere. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] EP2617489A1 [Patent Document 2] WO03 / 072244A1 [Patent Document 3] WO03 / 072246A1 [Patent Document 4] EP1927398A1 [Patent Document 5] EP3639923A1 [Patent Document 6] WO2008 / 054564A1 [Patent Document 7] US2006 / 0281631A1 [Patent Document 8] US6,165,437A [Non-patent literature]

[0014] [Non-Patent Document 1] H. Giesche, “Mercury Porosimetry: A General (Practical) Overview, Part. Part. Syst. Charact. 23 (2006), pp. 9-19. Summary of the Invention [Problem to be solved by the invention]

[0015] There remains a significant need to improve the performance of supported catalysts by optimizing alumina-based support structures, and for methods of producing optimized porous alpha-alumina catalyst supports. The support structure should have a high total pore volume, thus allowing for high silver impregnation, while retaining its surface area large enough to optimally distribute catalytically active species, particularly metal species. A pore structure that results in the fastest possible internal support mass transfer is also desirable to minimize the average pore residence time of reactant and product molecules and limit the extent to which the primary reaction product, e.g., ethylene oxide, undergoes undesirable secondary reactions during diffusion through the pores of the supported catalyst. [Means for solving the problem]

[0016] Pore ​​structure is determined by factors including the size, size distribution, and shape of the granules that make up the matrix of the support. It has now been discovered that highly porous transition aluminas having low bulk densities, particularly transition aluminas having relatively high pore volumes and large pore diameters, are useful starting materials for producing alpha-alumina catalyst supports with beneficial pore structures. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention provides a method for producing a porous alpha-alumina catalyst support, comprising: i) For inorganic solids - at least 50 wt.-% transition alumina having a loose bulk density of at most 600 g / L, a pore volume of at least 0.6 mL / g and a median pore diameter of at least 15 nm; - preparing a precursor material containing at most 30 wt.-% alumina hydrate; ii) forming the precursor material into a compact; and iii) calcining the compact to obtain a porous alpha-alumina support.

[0018] In the resulting porous alpha-alumina catalyst support, the majority of the total pore volume is contained in pores having diameters in the range of 0.1 to 1 μm, as shown in the examples discussed below. The pores that make up the majority of the pore volume of the support are therefore surprisingly an order of magnitude larger than the median pore size of the transition alumina.

[0019] Without wishing to be bound by theory, it is believed that after application of catalytic species, for example, via impregnation, pores with diameters in the range of 0.1 to 1 μm provide a particularly favorable environment for catalytic conversion. The pores are small enough to provide a large surface area, while large enough to allow rapid diffusion of starting materials and resulting products, thus enabling high activity and selectivity of catalysts based on such catalyst supports. It is believed that pores with large diameters do not contribute significantly to the overall surface area, and therefore provide less effective reaction space. It is believed that pores with diameters smaller than 0.1 μm hinder the diffusion of resulting products, thereby prolonging their exposure to catalytic species and inducing continuous reactions, thereby reducing selectivity.

[0020] Furthermore, the process of the present invention allows for improved control over the properties of the resulting alpha-alumina support, such as BET surface area and pore volume, compared to situations where alpha-alumina supports are obtained via calcination of precursor materials containing alpha-alumina. In particular, extraneous components, such as silicon compounds, which are generally understood to stabilize BET surface area and / or pore volume, are not essential to the process of the present invention. This allows for the production of alpha-alumina supports with desirable BET surface areas and pore volumes, but with very low or no impurity content. Furthermore, the alpha-alumina supports of the present invention have been found to exhibit sufficiently high mechanical stability.

[0021] The precursor material comprises at least 50 wt.-% transition alumina relative to the inorganic solids content, preferably at least 60 wt.-%, more preferably at least 70 wt.-%, for example at least 80 wt.-% or at least 90 wt.-%, especially 95 to 100 wt.-% transition alumina relative to the inorganic solids content.

[0022] The term "transition alumina" is understood to mean an alumina comprising a metastable alumina phase, such as a gamma-, delta-, eta-, theta-, kappa- or chi-alumina phase. Preferably, the transition alumina comprises at least 80 wt.-%, preferably at least 90 wt.-%, most preferably at least 95 wt.-%, for example 95 to 100 wt.-%, of a phase selected from gamma-alumina, delta-alumina and / or theta-alumina, in particular a phase selected from gamma-alumina and / or delta-alumina, relative to the total weight of the transition alumina.

[0023] Transition aluminas are typically in the form of powders. Transition aluminas are commercially available and are obtained via thermal dehydration of hydrated aluminum compounds, particularly aluminum hydroxide and aluminum oxy-hydroxide. Suitable hydrated aluminum compounds include naturally occurring and synthetic compounds, for example, aluminum trihydroxide (Al(OH)), such as gibbsite, bayerite, and nordstrandite, or aluminum oxy-monohydroxide (AlOOH), such as boehmite, pseudoboehmite, and diaspore.

[0024] Gradual dehydration of hydrated aluminum compounds affects lattice rearrangement. For example, boehmite can be converted to gamma-alumina at about 450° C., gamma-alumina can be converted to delta-alumina at about 750° C., and delta-alumina can be converted to theta-alumina at about 1,000° C. When heated above 1,000° C., transition aluminas are converted to alpha-alumina.

[0025] The morphological properties of the resulting transitional aluminas are believed to be primarily determined by the morphological properties of the hydrated aluminum compounds from which they are derived. Thus, Busca, "The Surface of Transitional Aluminas: A Critical Review," Catalysis Today, 226 (2014), pp. 2-13, notes that aluminas derived from variegated pseudoboehmite are more likely to be oxidized than those derived from variegated pseudoboehmite, as pseudoboehmite has a similar surface area (160-200 m). 2 / g), but have various pore volumes and pore size distributions.

[0026] In a preferred embodiment, the transition alumina comprises non-platelet crystals. The term "non-platelet" refers to any morphology other than platelet morphology, such as elongated morphology, e.g., rod-like or needle-like, or a morphology having approximately the same dimensions in all three spatial directions. In a preferred embodiment, the transition alumina comprises shaped non-platelet crystals, such as rod-like crystals as described in WO 2010 / 068332 A1, or block-shaped crystals as described in Busca, "The Surface of Transitional Aluminas: A Critical Review," Catalysis Today, 226 (2014), pp. 2-13; see Figures 2c, 2d, and 2e compared with Figures 2a, 2b, and 2f. Preferably, the transition alumina has an average crystal size of at least 5 nm, preferably at least 7 nm, and most preferably at least 10 nm, as determined from the XRD pattern via the Scherrer equation.

[0027] Various synthesis methods for obtaining crystalline boehmite alumina with high pore volume, large surface area and high thermal stability are known, for example, from WO 00 / 09445 A2, WO 01 / 02297 A2, WO 2005 / 014482 A2 and WO 2016 / 022709 A1. For example, WO 2016 / 022709 A1 describes a crystalline boehmite alumina with an average pore diameter of 115 to 166 Å and a pore density of 250 to 350 kg / m, which is prepared by precipitating a basic aluminum salt with an acidic alumina salt under controlled pH and temperature. 3Bulk density of 0.8 to 1.1 m 3 Boehmite aluminas having a pore volume of 10 ...

[0028] Before the heat treatment, the hydrated aluminum compound may be washed, for example with demineralized water, to reduce impurities and obtain high-purity transition alumina. For example, crystalline boehmite obtained from gibbsite by a hydrothermal method according to Chen et al., J. Solid State Chem., 265 (2018), pp. 237-243, is preferably washed before the heat treatment.

[0029] High-purity transition alumina is preferred to limit the content of impurities, such as sodium or silicon, in the catalyst support. High-purity transition alumina can be obtained, for example, via the so-called Ziegler process, sometimes referred to as the ALFOL process, variations of which are described by Busca, "The Surface of Transitional Aluminas: A Critical Review," Catalysis Today, 226 (2014), pp. 2-13. Other processes based on precipitation of aluminates, such as sodium aluminate, tend to produce transition aluminas with relatively high impurities, such as sodium.

[0030] The transition alumina used in the present invention preferably has a total content of alkali metals, such as sodium and potassium, of at most 1,500 ppm, more preferably at most 600 ppm, and most preferably between 10 ppm and 200 ppm, relative to the total weight of the transition alumina. Various washing methods are known which allow the alkali metal content of the resulting transition alumina and / or catalyst support to be reduced. Washing may involve washing with bases, acids, water or other liquids.

[0031] US 2,411,807 A describes that the sodium oxide content in alumina precipitates can be reduced by washing with a solution containing hydrofluoric acid and another acid. WO 03 / 086624 A1 describes pretreatment of the support with an aqueous lithium salt solution to remove sodium ions from the support surface. US 3,859,426 A describes the purification of refractory oxides, such as alumina and zirconia, by repeated rinsing with hot deionized water. WO 2019 / 039930 describes a method for purifying alumina in which metal impurities are removed by extraction with alcohol.

[0032] Besides alkali metals, the levels of other naturally occurring impurities are preferably controlled as well.

[0033] The transition alumina used in the present invention preferably has a total content of alkaline earth metals, such as calcium and magnesium, of at most 2,000 ppm, more preferably at most 600 ppm, and most preferably at most 400 ppm, based on the total weight of the transition alumina.

[0034] The transition alumina used in the present invention preferably has a silicon content of at most 10,000 ppm, preferably at most 2,000 ppm, most preferably at most 700 ppm, relative to the total weight of the transition alumina.

[0035] The transition alumina used in the present invention preferably has an iron content of at most 1,000 ppm, more preferably at most 600 ppm, and most preferably at most 300 ppm, relative to the total weight of the transition alumina.

[0036] The transition alumina used in the present invention preferably has a content of metals other than those mentioned above, such as titanium, zinc, zirconium and lanthanum, of at most 1,000 ppm, more preferably at most 400 ppm, and most preferably at most 100 ppm, relative to the total weight of the transition alumina.

[0037] The transition alumina has a loose bulk density of at most 600 g / L. The term "loose bulk density" is understood to mean a "loosely packed" or "poured" density. "Loose bulk density" is therefore different from "tapped density", where a defined mechanical tapping sequence is applied and higher densities are typically obtained. Loose bulk density can be determined by pouring the transition alumina into a graduated cylinder, preferably through a funnel, taking care not to move or vibrate the graduated cylinder. The volume and weight of the alumina are determined. Loose bulk density is determined by dividing the weight in grams by the volume in liters.

[0038] A low loose bulk density can indicate high porosity and a large surface area. Preferably, the transition alumina has a loose bulk density in the range of 50 to 600 g / L, more preferably in the range of 100 to 550 g / L, most preferably in the range of 150 to 500 g / L, especially 200 to 500 g / L or 200 to 450 g / L.

[0039] The transition alumina has a pore volume of at least 0.6 mL / g. Preferably, the transition alumina has a pore volume of 0.6 to 2.0 mL / g or 0.65 to 2.0 mL / g, more preferably 0.7 to 1.8 mL / g, and most preferably 0.8 to 1.6 mL / g.

[0040] The transition alumina has a median pore diameter of at least 15 nm. The term "median pore diameter" is used herein to refer to the median pore diameter by surface area, i.e., the median pore diameter (area) is the pore diameter at the 50th percentile of the cumulative surface area graph. Preferably, the transition alumina has a median pore diameter of 15 to 500 nm, more preferably 20 to 450 nm, most preferably 20 to 300 nm, e.g., 20 to 200 nm.

[0041] Mercury porosimetry and nitrogen sorption are widely used to characterize the pore structure in porous materials, as these methods allow the determination of porosity and pore size distribution in one step. The two techniques are based on different physical interactions and optimally cover a specific range of pore sizes.

[0042] In many cases, nitrogen sorption constitutes a sufficiently accurate method of determination, especially for small pores. Thus, the pore volume and median pore diameter of transition aluminas can be determined by nitrogen sorption. Nevertheless, large pores may be underrepresented by nitrogen sorption.

[0043] Nitrogen sorption measurements may be performed using a Micrometrics ASAP 2420. Nitrogen porosity is determined herein according to DIN 66134 unless otherwise specified. Barrett-Joyner-Halenda (BJH) pore size and volume analysis is performed to obtain the total pore volume ("BJH desorption cumulative pore volume") and median pore diameter ("BJH desorption average pore diameter").

[0044] Mercury porosimetry can be performed using a Micrometrics AutoPore V 9600 mercury porosimeter (140 degree contact angle, 485 dynes / cm Hg surface tension, 61,000 psia maximum head pressure). Total pore volume and median pore diameter data for transition aluminas are obtained over the pore size range of 3 nm to 1 μm.

[0045] For sufficient accuracy, the reported pore volume and median pore diameter of the transition alumina are from nitrogen sorption if the median pore diameter from mercury porosimetry is less than 50 nm, or the reported pore volume and median pore diameter of the transition alumina are from mercury porosimetry if the median pore diameter from mercury porosimetry is 50 nm or greater.

[0046] To avoid falsifying the results, nitrogen sorption measurements and mercury porosimetry should be performed on samples that have been treated to remove physically adsorbed species, such as water, from the sample. Suitable methods are described below.

[0047] Transition aluminas are typically from 20 to 500 m 2 / g。 The BET method is a standard, well-known and widely used method in surface science to measure the surface area of ​​a solid by physical adsorption of gas molecules. BET surface is determined herein according to DIN ISO 9277 using nitrogen physical adsorption performed at 77 K unless otherwise specified. The terms "BET surface area" and "surface area" are used interchangeably herein unless otherwise noted.

[0048] The BET surface area of ​​the transition alumina can vary over a relatively large range and can be adjusted by varying the conditions of thermal dehydration of the hydrated aluminum compound from which the transition alumina is obtained. Preferably, the transition alumina has a BET surface area of ​​20 to 200 m 2 / g, more preferably in the range of 50 to 200m 2 / g or 50 to 150m 2 / g BET surface area.

[0049] Suitable transition aluminas are commercially available. In some instances, such commercially available transition aluminas are classified as "medium-porosity aluminas" or, more specifically, "high-porosity aluminas." Suitable transition aluminas include the Puralox® TH and Puralox®™ series of products, both from Sasol, and the Versal VGL series of products from UOP.

[0050] Transition alumina can be used in its commercial ("unmilled") form. Commercial forms of alumina include agglomerates (secondary particles) or granules (primary particles) of individual particles. For example, transition alumina having an average (secondary) particle size (e.g., D 50Commercial alumina particles having an average particle size (D) may contain submicron-sized primary particles. 50 ) is the particle diameter of the alumina secondary particles (D 50 ) is understood to mean

[0051] Unmilled transition alumina powders typically have a D of 10 to 100 μm, preferably 20 to 50 μm. 50 The transition alumina powder has a particle size of 0.5 to 8 μm, preferably 1 to 5 μm. 50 The particle size of the transition alumina can be measured by a laser diffraction particle size analyzer, such as a Malvern Mastersizer 2000, using water as the dispersion medium. The method includes a step of dispersing the particles by ultrasonic treatment, thus reducing the secondary particles to primary particles. This ultrasonic treatment is referred to as D 50 Continue until no further change in value is observed, for example after 3 minutes of sonication.

[0052] In a preferred embodiment, the transition alumina comprises at least 50 wt.-%, preferably 60 to 90 wt.-%, relative to the total weight of the transition alumina, of transition alumina having an average particle size of 10 to 100 μm, preferably 20 to 50 μm. Optionally, the transition alumina may comprise, for example, at most 50 wt.-%, preferably 10 to 40 wt.-%, relative to the total weight of the transition alumina, of transition alumina having an average particle size of 0.5 to 8 μm, preferably 1 to 5 μm.

[0053] The precursor material comprises at most 30 wt.-% alumina hydrate relative to the inorganic solids content, preferably 1 to 30 wt.-%, more preferably 1 to 25 wt.-%, most preferably 1 to 20 wt.-%, for example 3 to 18 wt.-% alumina hydrate relative to the inorganic solids content.

[0054] The term "alumina hydrate" is understood to refer to the hydrated aluminum compounds described above, in particular aluminum hydroxide and aluminum oxy-hydroxide. A discussion of the nomenclature of alumina can be found in K. Wefers and C. Misra, "Oxides and Hydroxides of Aluminum," Alcoa Laboratories, 1987. Suitable hydrated aluminum compounds include naturally occurring and synthetic compounds, for example, aluminum trihydroxide (Al(OH)), such as gibbsite, bayerite, and nordstrandite, or aluminum oxy-monohydroxide (AlOOH), such as boehmite, pseudoboehmite, and diaspore.

[0055] Preferably, the alumina hydrate comprises boehmite and / or pseudoboehmite. In preferred embodiments, the combined amount of boehmite and pseudoboehmite constitutes at least 80 wt.-%, more preferably at least 90 wt.-%, and most preferably at least 95 wt.-%, e.g., 95 to 100 wt.-%, of the alumina hydrate. In especially preferred embodiments, the amount of boehmite constitutes at least 80 wt.-%, more preferably at least 90 wt.-%, and most preferably at least 95 wt.-%, e.g., 95 to 100 wt.-%, of the alumina hydrate.

[0056] Suitable alumina hydrates are commercially available and include the Pural® series of products from Sasol, preferably the Pural® TH and Pural®™ series of products, and the Versal® series of products from UOP.

[0057] Without wishing to be bound by theory, it is believed that the presence of alumina hydrate increases the mechanical stability of the support. In particular, it is believed that nano-sized, highly disperse alumina hydrate suitable for colloidal applications, such as boehmite from the Disperal® or Dispal® series from Sasol, exhibits high bonding strength and can particularly efficiently improve the mechanical stability of the support. In general, the use of such nano-sized, highly disperse alumina hydrate that improves mechanical stability can make it possible to obtain a relatively smaller BET surface area at a given calcination condition.

[0058] Alumina hydrate may be partially or completely replaced by suitable alternative aluminum compounds while essentially maintaining the mechanical stability of the support, including aluminum alkoxides such as aluminum ethoxide and aluminum isopropoxide, aluminum nitrate, aluminum acetate, and aluminum acetylacetonate.

[0059] The precursor material optionally includes a liquid. The presence, type, and amount of liquid can be selected according to the desired handling properties of the precursor material. For example, the presence of a liquid may be desirable to obtain a malleable precursor material.

[0060] The liquid is typically selected from water, especially deionized water, and / or aqueous solutions containing soluble and / or dispersible compounds selected from salts such as ammonium acetate and ammonium carbonate; acids such as formic acid, nitric acid, acetic acid, and citric acid; bases such as ammonia, triethylamine, and methylamine; surfactants such as triethanolamine, poloxamers, fatty acid esters, and alkyl polyglucosides; submicron-sized particles including metal oxides such as silica, titania, and zirconia; clays; and / or polymer particles such as polystyrene and polyacrylates. The liquid is preferably water, most preferably deionized water. Typical amounts of liquid range from 10 to 60 wt.-% based on the inorganic solids content of the precursor material.

[0061] The precursor material may contain additional components, which may be processing aids or which are intentionally introduced to tailor the physical properties of the final catalyst support. These components include pore-forming materials, lubricants, organic and / or inorganic binders.

[0062] The precursor material may contain organic materials, such as pore-forming materials, lubricants and organic binders, in a combined amount of 1.0 to 60 wt.-%, preferably 3 to 50 wt.-%, based on the total weight of the precursor material.

[0063] The precursor material may contain lubricants and organic binders in an amount of 1.0 to 10 wt.-%, preferably 3 to 8 wt.-%, based on the total weight of the precursor material.

[0064] Pore-forming materials can be used to provide additional and / or wider pores in the support. The additional pore volume of wider pores can also advantageously allow for more efficient impregnation of the support during catalyst production. Preferably, the pore-forming material is essentially completely removed during heat treatment of the shaped body. The pore-forming function can be achieved by different mechanisms, such as combustion (i.e., calcination) in the presence of oxygen, decomposition, sublimation, or volatilization.

[0065] Suitable pore-forming materials are: - thermally decomposable materials, such as oxalic acid, malonic acid, ammonium carbonate or ammonium bicarbonate, - Combustible materials, such as heat-combustible biological materials, such as acacia, sawdust and cereal flours, in particular ground nut shell flours, such as pecan, cashew, walnut or hazelnut flour, and / or - organic polymers, e.g. - polysaccharides, such as starches, gums, cellulose and cellulose derivatives, including substituted celluloses such as methylcellulose, ethylcellulose and carboxyethylcellulose, and cellulose ethers; - polyolefins such as polyethylene and polypropylene, - Aromatic hydrocarbon polymers such as polystyrene polycarbonates, such as poly(propylene carbonate), - lignin, - carbonaceous materials, e.g. - graphite, powdered carbonaceous compounds, such as coke or activated carbon powder, and - Contains milled and unmilled carbon fibre.

[0066] Thermally decomposable materials, such as oxalic acid, malonic acid, ammonium bicarbonate, or ammonium carbonate, decompose upon heat treatment, breaking down into smaller, volatile molecules that may or may not be flammable. For example, malonic acid decomposes upon heat treatment to yield primarily acetic acid and carbon dioxide. Such thermally decomposable materials offer certain advantages in industrial processes, as they are generally obtained from industrial sources with a purity that does not introduce extraneous material into the support.

[0067] To avoid the formation of a potentially explosive atmosphere, when a pyrolyzable material is used, the calcination of the shaped body is preferably carried out in an atmosphere with a reduced oxygen content, for example, at most 10 vol.-% or at most 5 vol.-% oxygen. If pyrolysis occurs at a relatively low temperature, the process can be safely controlled well below the ignition temperature of the potentially flammable molecules formed during the decomposition of the pyrolyzable material. This allows for safe operation of the heat treatment even at a relatively high oxygen concentration in the atmosphere of the heat treatment apparatus. In this case, an air atmosphere can be used.

[0068] Suitable lubricants are: - graphite, - petroleum jelly, mineral oil or grease, fatty acids, such as stearic acid or palmitic acid; salts of fatty acids, such as stearates, such as potassium stearate, magnesium stearate and aluminium stearate, or palmitates, such as potassium palmitate, magnesium palmitate and aluminium palmitate; fatty acid derivatives, such as esters of fatty acids, in particular esters of saturated fatty acids, such as stearates, such as methyl and ethyl stearate, and / or - Malleable organic solids, including waxes such as paraffin wax and cetyl palmitate.

[0069] Preferably, the lubricant does not introduce inorganic contaminants into the catalyst support. Of the lubricants mentioned above, graphite, stearic acid, aluminum stearate and combinations thereof are preferred.

[0070] Organic binders, sometimes referred to as "temporary binders," may be used to improve the malleability of the precursor material and to maintain the integrity of the "green" or unfired phase in which the mixture is formed into a compact. Preferably, the organic binder is essentially completely removed during heat treatment of the compact.

[0071] Suitable organic binders are: polyvinyl lactam polymers, such as polyvinylpyrrolidone or vinylpyrrolidone copolymers, such as vinylpyrrolidone-vinyl acetate copolymers; alcohols, in particular polyols, such as glycols or glycerol, and / or - Polyalkylene glycols, including polyethylene glycol.

[0072] Advantageously, the pore formers and processing aids, such as organic binders and lubricants, exhibit a small amount of ash. The term "ash" is understood to refer to the non-combustible components remaining after combustion of the organic material in air at high temperatures, i.e., after heat treatment of the shaped body. The ash content is preferably less than 0.1 wt.-% based on the total weight of the organic material.

[0073] Furthermore, pore formers and processing aids, such as organic binders and lubricants, preferably do not form large amounts of additional volatile flammable components, such as carbon monoxide, ammonia, or flammable organic compounds, when the molded body is heat treated, i.e., pyrolyzed or combusted. Excessive volatile organic components can lead to an explosive atmosphere. Appropriate safety concepts are preferably applied to the combustion or decomposition process step.

[0074] Inorganic binders are permanent binders that contribute to sufficient bonding of the alumina particles and improve the mechanical stability of the formed alpha-alumina body. Inorganic binders include those that yield only aluminum oxide upon calcination. For the purposes of this application, these inorganic binders are referred to as intrinsic inorganic binders. Such intrinsic inorganic binders include alumina hydrates, as discussed above.

[0075] Extrinsic inorganic binders, on the other hand, do not yield only aluminum oxide upon calcination. Suitable extrinsic inorganic binders are understood to be any of the inorganic species conventionally used in the art, including clays such as kaolinite, or metal hydroxides, carbonates, nitrates, acetates, or oxides such as zirconia, titania, or alkali metal oxides, such as silicon-containing species, e.g., silica or silicates. Since extrinsic inorganic binders introduce foreign matter that may be detrimental to catalytic performance, they are preferably included in controlled amounts. Preferably, the precursor material contains 0.0 to 5.0 wt.-%, preferably 0.05 to 1.0 wt.-%, of the extrinsic inorganic binder, based on the inorganic solids content of the precursor material. In a preferred embodiment, the precursor material does not contain an extrinsic inorganic binder.

[0076] The precursor material is typically obtained by dry mixing the components thereof, followed by the optional addition of a liquid, and may be formed into a shaped body via extrusion, tableting, granulation, casting, molding or microextrusion, in particular via extrusion or tableting.

[0077] The size and shape of the shaped bodies, and thus of the catalyst, are selected to allow for suitable packing of the catalyst obtained from the shaped bodies in the reactor tube. Catalysts obtained from shaped bodies suitable for the catalyst of the present invention are preferably used in reactor tubes having a length of 6 to 14 m and an internal diameter of 20 to 50 mm. Generally, the support consists of individual parts having a maximum extension in the range of 3 to 20 mm, for example 4 to 15 mm, in particular 5 to 12 mm. The maximum extension is understood to mean the longest straight line between two points on the circumference of the support.

[0078] The shape of the shaped body is not particularly limited and may be any technically feasible form, for example, depending on the forming process. For example, the support may be a solid extrudate or a hollow extrudate, such as a hollow cylinder. In another embodiment, the support may be characterized by a multi-lobed structure. A multi-lobed structure is meant to represent a cylindrical structure having multiple void spaces, for example, recesses or grooves running around the cylinder along the cylinder height. Generally, the void spaces are arranged essentially equidistantly around the cylinder circumference.

[0079] Preferably, the support is in the form of a solid extrudate, such as a pellet or cylinder, or a hollow extrudate, such as a hollow cylinder. In a preferred embodiment, the shaped body is formed by extrusion, such as microextrusion. In this case, the precursor material preferably comprises a liquid, in particular water, to form a malleable precursor material.

[0080] In a preferred embodiment, extrusion involves the introduction of at least one solid component into a mixing device before the liquid is added. Preferably, a mixer-mill (H-roller) or a horizontal mixer, such as a Ploughshare® mixer (from Gebruder Lodige Maschinenbau), is used for mixing. The morphology of the extrudable paste of the precursor material can be monitored and controlled based on data reflecting the power consumption of the mixing device.

[0081] The precursor material is typically extruded through a die, the cross section of the die opening being adapted according to the desired geometry of the compact.

[0082] The extrusion die may comprise a matrix and a mandrel, the matrix essentially determining the circumferential shape of the shaped body, and the mandrel essentially determining the shape, size, and location of the passages, if any. Suitable extrusion dies are described, for example, in WO 2019 / 219892 A1.

[0083] The geometry of the compact shape is determined by the geometry of the extrusion device through which the precursor material is extruded. Typically, the geometry of the extrudate shape will differ slightly from the geometry of the extrusion device, but will essentially have the geometric properties described above. The actual dimensions of the shape will generally be slightly smaller than the size of the extrudate due to the high temperatures required to form alpha alumina and shrinkage as the extrudate cools. The degree of shrinkage depends on the temperature applied during calcination and the composition of the compact. Therefore, the size of the extrusion die should be routinely adjusted to account for shrinkage of the extrudate during subsequent calcination.

[0084] When a shaped body contains multiple passages, the axes of the passages typically run parallel. However, the shaped body may be slightly curved or twisted along the z-axis (height). The cross-sectional shape of the passages may differ slightly from the assumed perfect geometric shape described above. When a large number of shaped bodies are obtained, a single passage may be closed in a few shaped catalyst bodies. Usually, the surface of the shaped catalyst body in the xy plane is not smooth but more or less uneven due to the production process. The height of the shaped body (the length of the shaped body in the z-direction) is usually not exactly the same for all shaped bodies, but rather constitutes a distribution relative to the average height as its arithmetic mean.

[0085] The extrudate is preferably cut to the desired length while still wet. Preferably, the extrudate is cut at an angle essentially perpendicular to the circumferential surface. To prevent undesired deviations from the geometry of the extrusion device, the extrudate may alternatively be cut at an inclined angle of up to 30°, for example 10° or 20°, relative to the angle perpendicular to the circumferential surface of the extrudate.

[0086] Geometric anomalies incurred during the extrusion process and / or further processing of the extrudates, e.g., cutting steps, may generally be present in the porous alpha-alumina catalyst support of the present invention obtained by the method of the present invention, but do not substantially degrade the beneficial effects of the pore structure. Those skilled in the art will appreciate that due to imprecision inherent to some degree in all production processes, perfect geometric configurations are generally not attainable.

[0087] In another embodiment, the precursor material is formed into a shaped body using a microextrusion process, such as that described in WO2019 / 072597A1.

[0088] In another embodiment, the precursor material is formed into a shaped body using a gel casting method, such as that described in WO2020 / 053563A1.

[0089] In another embodiment, the precursor material is formed into a compact via tableting. In this case, the precursor material typically does not contain a liquid. Tableting is a press agglomeration process. A powder or pre-agglomerated bulk material is introduced into a press tool having a die between two punches, compacted by uniaxial compression, and shaped to obtain a solidified compact. This operation is divided into four parts: metered introduction, compaction (elastic deformation), plastic deformation, and ejection. Tableting is carried out, for example, in a rotary press or an eccentric press.

[0090] If desired, the upper punch and / or the lower punch may include a protruding pin that forms an internal passage. It is also possible to provide a pressure punch with multiple movable pins, so that the punch may have, for example, four pins that create a compact with four holes (passages). Typical design features of such tools can be found, for example, in US 8,865,614 B2.

[0091] The pressing force during tableting affects the compaction of the bulk material. In practice, it has been found useful to set the lateral compressive strength of the porous alpha-alumina catalyst support in a targeted manner by selecting an appropriate pressing force and checking this by random sampling. For the purposes of this invention, lateral compressive strength is the force that will fracture a porous alpha-alumina catalyst support positioned between two planar parallel plates, with the two planar parallel end faces of the catalyst support perpendicular to the planar parallel plates.

[0092] In tableting, it is often preferable to use lubricants, especially those discussed above. To improve tableting, a pre-granulation and / or sieving step can be used. In pre-granulation, a roll compactor, such as the Chilsonator® from Fitzpatrick, can be used. Further information on tableting, especially on pre-granulation, sieving, lubricants and tools, can be found in WO2010 / 000720A2.

[0093] Prior to calcination, the shaped body may be dried, particularly if the precursor material comprises a liquid. Preferably, drying is carried out at a temperature in the range of from 20 to 400° C., particularly from 30 to 300° C., for example from 70 to 150° C. Drying is typically carried out for a period of up to 100 hours, preferably from 0.5 to 30 hours, more preferably from 1 to 16 hours.

[0094] Drying can be carried out under any atmosphere, for example, under an oxygen-containing atmosphere such as air, under nitrogen or helium, or a mixture thereof, preferably under air. Drying is usually carried out in an oven. The type of oven is not particularly limited. For example, a fixed circulating air oven, a rotary cylindrical oven, or a conveyor oven can be used. Heat can be applied directly and / or indirectly.

[0095] Preferably, flue gas (vent gas) from a combustion process having a suitable temperature is used for the drying step. The flue gas can be used in diluted or undiluted form for direct heating and removal of evaporated water and other components liberated from the compacts. The flue gas is typically passed through an oven as described above. In another preferred embodiment, exhaust gas from the calcination process step is used for direct heating.

[0096] Drying and calcination can be performed sequentially in separate equipment and can be performed in a batch or continuous process. Intermittent cooling can be applied. In another embodiment, drying and calcination are performed in the same equipment. In a batch process, a time-resolved temperature ramp (program) can be applied. In a continuous process, for example, a spatially resolved temperature ramp (program) can be applied, where the compact is continuously moved through zones of different temperatures.

[0097] Preferably, heat integration measures known in the art are applied to improve energy efficiency. For example, relatively hot exhaust gas from one process step or stage can be used to heat the feed stream gas, equipment, or formed bodies in another process step or stage by direct (mixing) or indirect (heat exchanger) means. Heat integration can also be applied to cool the relatively hot exhaust gas stream before further processing or discharge.

[0098] The formed body is calcined to obtain a porous alpha-alumina catalyst support, where the calcination temperature and duration are sufficient to convert at least a portion of the transition alumina to alpha-alumina, which means that at least a portion of the metastable alumina phase of the transition alumina is converted to alpha-alumina.

[0099] The resulting porous alpha-alumina catalyst support typically contains a high proportion of alpha-alumina by weight of the total support, for example at least 80 wt.-%, preferably at least 90 wt.-%, more preferably at least 95 wt.-%, and most preferably at least 97.5 wt.-%. The amount of alpha-alumina can be determined, for example, via X-ray diffraction analysis.

[0100] Typically, the calcining step is carried out at a temperature of at least 1300° C., such as at least 1400° C., more preferably at least 1450° C. Preferably, the calcining step is carried out at a pressure in the range of 0.5 to 35 bar, especially in the range of 0.9 to 1.1 bar absolute, for example atmospheric pressure (approximately 1013 mbar). Typical total heating times are in the range of 0.5 to 100 hours, preferably 2 to 20 hours.

[0101] Calcination is usually carried out in a furnace. The type of furnace is not particularly limited. For example, a furnace, such as a fixed air circulation furnace, a rotary cylindrical furnace or a conveyor furnace, or a kiln, such as a rotary kiln or a tunnel kiln, in particular a roller hearth kiln, can be used.

[0102] Calcination can be carried out under any atmosphere, for example, under an oxygen-containing atmosphere such as air, under nitrogen or helium, or under a mixture thereof. Preferably, especially when the former contains pyrolyzable or combustible materials, calcination is carried out at least partially or completely under an oxidizing atmosphere, for example, under an oxygen-containing atmosphere such as air.

[0103] As described above, pore formers and processing aids, such as organic binders and lubricants, preferably do not form large amounts of additional volatile flammable components, such as carbon monoxide or flammable organic compounds, during calcination of the shaped body. An explosive atmosphere can be further avoided by limiting the oxygen concentration in the atmosphere during calcination to, for example, an oxygen concentration below the limiting oxygen concentration (LOC) for the additional flammable components. LOC, also known as minimum oxygen concentration (MOC), is the limiting concentration of oxygen below which combustion is impossible.

[0104] Preferably, a lean air or gaseous recycle stream with limited oxygen content may be used together with the oxygen make-up stream, which also offsets the gaseous purge stream. In an alternative approach, an explosive atmosphere can be avoided by limiting the rate of formation of additional combustible components. The rate of formation of additional combustible components can be limited by heating to the calcination temperature via a gradual temperature ramp or by heating in a stepwise manner. When heating in a stepwise manner, the temperature is suitably held at about the combustion temperature for several hours, and then heated to a temperature of 1000°C. In a continuous calcination process, the feed flow rate of the shaped bodies to the calcination device, e.g., a furnace, can also be controlled to limit the rate of formation of additional combustible components.

[0105] Depending on the nature of the pore-forming material, lubricant, organic binder and gas components, waste gas treatment can be applied to purify any off-gas obtained during calcination. Preferably, acid or alkaline scrubbers, flaring or catalytic combustion, denitration treatment or a combination thereof can be used for waste gas treatment.

[0106] Preferably, heating is carried out in a stepwise manner, in which the compact is placed in a high-purity and inert refractory sagger and moved through a furnace having multiple heating zones, e.g., 2 to 8 or 2 to 5 heating zones. The inert refractory sagger may be made of alpha-alumina or corundum, especially alpha-alumina.

[0107] The porous alpha-alumina catalyst support obtained by the process of the present invention typically has a surface area of ​​0.5 to 5.0 m 2 / g。 Preferably, the porous alpha-alumina catalyst support has a BET surface area in the range of 0.5 to 4.5 m 2 / g, more preferably in the range of 1.0 to 4.5m 2 / g, most preferably 1.0 to 4.0 m 2 / g BET surface area.

[0108] Porous alpha-alumina catalyst supports typically have a total pore volume of at least 0.2 mL / g, as determined by mercury porosimetry. Porous alpha-alumina catalyst supports obtained by the process of the present invention typically have a pore volume, as determined by mercury porosimetry, where at least 40% of the total pore volume is contained in pores having diameters in the range of 0.1 to 1 μm. Preferably, the porous alpha-alumina catalyst support has a pore volume where at least 50%, more preferably at least 55%, and most preferably at least 60%, e.g., at least 65%, or at least 70% of the total pore volume are contained in pores having diameters in the range of 0.1 to 1 μm. Typically, porous alpha-alumina catalyst supports obtained by the process of the present invention have a pore volume where at least 40 to 99%, more preferably 45 to 99%, and most preferably 50 to 97% of the total pore volume are contained in pores having diameters in the range of 0.1 to 1 μm.

[0109] Porous alpha-alumina catalyst supports typically have a ratio r of the pore volume contained in pores having diameters in the range of 1 to greater than 10 μm to the pore volume contained in pores having diameters in the range of 0.1 to 1 μm of at most 0.50. pv Preferably, the ratio r pv is in the range of 0.0 to 0.45, more preferably 0.0 to 0.40, or 0.0 to 0.35.

[0110] The porous alpha-alumina support generally comprises at least 80 wt.-%, preferably at least 90 wt.-%, more preferably at least 95 wt.-%, and most preferably at least 97.5 wt.-% alpha-alumina based on the total weight of the support.

[0111] In one embodiment, the porous alpha-alumina catalyst support comprises at least 80 wt.-% alpha-alumina, and the support - 0.5 to 5.0 m 2 / g, a total pore volume of at least 0.2 mL / g, as determined by mercury porosimetry, and - has a pore volume, determined by mercury porosimetry, of which at least 40% of the total pore volume is contained in pores having a diameter in the range of 0.1 to 1 μm; The ratio r of the pore volume contained in pores having a diameter in the range of 1 to more than 10 μm to the pore volume contained in pores having a diameter in the range of 0.1 to 1 μm pv is at most 0.50.

[0112] In a preferred embodiment, the porous alpha-alumina support is in the form of a discrete body, such as the shapes described above. Preferably, the porous alpha-alumina catalyst support is in the form of a discrete body having a circumferential surface, a first side, a second side, and at least one internal passageway extending from the first side to the second side.

[0113] Preferably, the geometric surface SA of the catalyst support geo of the geometric volume V of the catalyst support geo quotient (SA geo / V geo ) is at least 1.1 mm -1 and at most 10 mm -1 Preferably, SA geo V geo The quotient for -1 to 5.0 mm -1 range, more preferably 1.2 mm -1to 2.0 mm -1 The geometric surface area SA geo and the geometric volume V geo is derived from the external macroscopic dimensions of the porous alpha-alumina catalyst support, taking into account the cross-sectional area, height, and, if applicable, number of internal passages. In other words, the geometric volume V of the catalyst support geo is the volume of a solid structure with the same external dimensions minus the volume occupied by the passages. Similarly, the geometric surface area SA geo is comprised of a circumferential surface, first and second obverse surfaces, and, if applicable, a surface defining a passageway. The first and second obverse surfaces each have a surface area bounded by the circumferential line of the obverse surface minus the cross-sectional area of ​​the passageway. The surface defining a passageway is the surface area lining the passageway.

[0114] Preferred range of SA geo V geo The quotient for allows better contact of the reactant gases with the resulting catalyst surface, which favors the conversion of reactants and the limitation of internal diffusion phenomena, resulting in an increase in reaction selectivity.

[0115] The porous alpha-alumina support preferably does not have washcoat particles or washcoat layers on its surface, thereby maintaining the full porosity of the uncoated support.

[0116] The porous alpha-alumina catalyst support may contain impurities such as sodium, potassium, magnesium, calcium, silicon, iron, titanium, and / or zirconium. Such impurities may be introduced by components of the precursor material, particularly inorganic binders or mechanical stability enhancers. In one embodiment, the porous alpha-alumina catalyst support comprises, based on the total weight of the support, - Sodium and potassium in the total amount up to 1,500 ppmw; - Calcium up to 2,000 ppmw, - Magnesium up to 1,000 ppmw, - silicon up to 10,000 ppmw, - Titanium up to 1,000 ppmw, - up to 1,000 ppmw of iron, and / or - Contains up to 10,000 ppmw of zirconium.

[0117] A low sodium content is preferred to prevent separation of the supported metal and to prevent changes in the supported components.

[0118] The present invention further relates to a shaped catalyst body for the selective vapor phase oxidation (epoxidation) of ethylene to produce ethylene oxide, i.e., an epoxidation catalyst comprising at least 15 wt.-% silver, based on the total weight of the shaped catalyst body, deposited on the porous alpha-alumina catalyst support described above.

[0119] The shaped catalyst bodies typically contain 15 to 70 wt.-% silver, preferably 20 to 60 wt.-% silver, and more preferably 25 to 50 wt.-% or 30 to 50 wt.-% silver, based on the total weight of the shaped catalyst body. This range of silver content allows for a favorable balance between the turnover induced by each shaped catalyst body and the cost-effectiveness of preparing the shaped catalyst bodies.

[0120] In addition to silver, the shaped catalyst body may contain one or more promoter species. A promoter species refers to a component that results in an improvement in one or more of the catalytic properties of the catalyst when compared to a catalyst that does not contain that component. The promoter species may be any chemical species known in the art that acts to improve the catalytic properties of a silver catalyst. Examples of catalytic properties include viability (resistance to runaway), selectivity, activity, turnover, and catalyst lifetime.

[0121] The shaped catalyst body may contain an increased amount of a transition metal or a mixture of two or more transition metals. Suitable transition metals may include, for example, elements from Group IIIB (scandium group), Group IVB (titanium group), Group VB (vanadium group), Group VIB (chromium group), Group VIIB (manganese group), Group VIIIB (iron, cobalt, nickel group), Group IB (copper group), and Group IIB (zinc group) of the Periodic Table of Elements, and combinations thereof. More typically, the transition metal is an early transition metal, i.e., from Group IIIB, IVB, VB, or VIB, such as hafnium, yttrium, molybdenum, tungsten, rhenium, chromium, titanium, zirconium, vanadium, tantalum, niobium, or combinations thereof. In one embodiment, the transition metal promoters are present in a total amount of from 150 ppm to 5,000 ppm, typically from 225 ppm to 4,000 ppm, and most typically from 300 ppm to 3,000 ppm, expressed as metal based on the total weight of the shaped catalyst body.

[0122] Of the transition metal promoters listed, rhenium (Re) is a particularly effective promoter for highly selective ethylene epoxidation catalysts. The rhenium component in the shaped catalyst body can be in any suitable form, but more typically is one or more rhenium-containing compounds (e.g., rhenium oxide) or complexes.

[0123] In some embodiments, the shaped catalyst body may contain a promoting amount of an alkali metal or a mixture of two or more alkali metals. Suitable alkali metal promoters include, for example, lithium, sodium, potassium, rubidium, cesium, or combinations thereof. The amount of alkali metal, e.g., potassium, expressed as alkali metal based on the total weight of the shaped catalyst body, typically ranges from 50 ppm to 5,000 ppm, more typically from 300 ppm to 2,500 ppm, and most typically from 500 ppm to 1,500 ppm. The amount of alkali metal is determined by the amount of alkali metal contributed by the porous alpha-alumina catalyst support and the amount of alkali metal contributed by the impregnation solution, as described below.

[0124] Particularly preferred are combinations of heavy alkali metals such as cesium (Cs) or rubidium (Rb) with light alkali metals such as lithium (Li), sodium (Na) and potassium (K).

[0125] The shaped catalyst body may also contain a Group IIA alkaline earth metal or a mixture of two or more Group IIA alkaline earth metals. Suitable alkaline earth metal promoters include, for example, beryllium, magnesium, calcium, strontium, and barium, or combinations thereof. The amount of alkaline earth metal promoter may be used in amounts similar to those used for alkali or transition metal promoters.

[0126] The shaped catalyst body may also include a promoting amount of a main group element or a mixture of two or more main group elements. Suitable main group elements include any of the elements in Groups IIIA (boron group) through VIIA (halogen group) of the Periodic Table of the Elements. For example, the shaped catalyst body may include a promoting amount of sulfur, phosphorus, boron, a halogen (e.g., fluorine), gallium, or a combination thereof.

[0127] The shaped catalyst body may also contain a promoting amount of a rare earth metal or a mixture of two or more rare earth metals. Rare earth metals include any of the elements having an atomic number between 57 and 103. Some examples of these elements include lanthanum (La), cerium (Ce), and samarium (Sm). The amount of rare earth metal promoter can be similar to that used for the transition metal promoter.

[0128] The present invention relates to a method for preparing the shaped catalyst body described above, comprising the steps of: a) impregnating the porous alpha-alumina catalyst support described above with a silver impregnation solution, preferably under reduced pressure, and optionally drying the impregnated porous alumina support; b) subjecting the impregnated porous alpha-alumina support to a heat treatment; The method further relates to a method wherein steps a) and b) are optionally repeated.

[0129] It is understood that all embodiments of the shaped catalyst bodies also apply to the methods of preparing the shaped catalyst bodies, where applicable.

[0130] To obtain a shaped catalyst body with a high silver content, steps i) and ii) may be repeated several times. In this case, it is understood that the intermediate product obtained after the first (or subsequent but not the last) impregnation / calcination cycle contains a portion of the total amount of target Ag and / or promoter concentrate. The intermediate product is then re-impregnated with the silver impregnation solution and calcined to obtain the target Ag and / or promoter concentrate.

[0131] Any silver impregnation solution known in the art that is suitable for impregnating a refractory support may be used. The silver impregnation solution typically comprises a silver carboxylate, such as silver oxalate, or a combination of a silver carboxylate and a silver oxalate, in a range of from C1 to C6. 10 - alkylenediamine, in particular ethylenediamine, in the presence of an amine-based complexing agent. Suitable impregnation solutions are described in EP 0 716 884 A2, EP 1 115 486 A1, EP 1 613 428 A1, US 4,731 350 A, WO 2004 / 094055 A2, WO 2009 / 029419 A1, WO 2015 / 095508 A1, US 4,356 312 A, US 5,187 140 A, US 4,908 343 A, US 5,504 053 A and WO 2014 / 105770 A1. For a discussion of suitable silver impregnation solutions, see also Kunz, C. et al., On the Nature of Crystals Precipitating from Aqueous Silver Ethylenediamine Oxalate Complex Solutions., Z. Anorg. Allg. Chem., 2021, p. 647, DOI: 10.1002 / zaac.202100079.

[0132] During the heat treatment, the liquid components of the silver impregnation solution evaporate, causing silver compounds containing silver ions to precipitate from the solution and deposit on the porous support. At least a portion of the deposited silver ions are subsequently converted to metallic silver by further heating. Preferably, at least 70 mol-%, preferably at least 90 mol-%, more preferably at least 95 mol-%, and most preferably at least 99.5 mol-%, or at least 99.9 mol-%, of the silver compounds, i.e., essentially all of the silver ions, are present in the impregnated porous alpha-alumina support, based on the total molar amount of silver. The amount of silver ions converted to metallic silver can be determined, for example, via X-ray diffraction (XRD) patterns.

[0133] The heat treatment may also be referred to as a calcination process. Any calcination process known in the art for this purpose may be used. Suitable examples of calcination processes are described in US Pat. No. 5,504,052A, US Pat. No. 5,646,087A, US Pat. No. 7,553,795A, US Pat. No. 8,378,129A, US Pat. No. 8,546,297A, US 2014 / 0187417A1, EP 1893331A1, or WO 2012 / 140614A1. The heat treatment may be carried out in a pass-through mode or with at least partial recycle of the calcination gas.

[0134] The heat treatment is usually carried out in an oven. The type of oven is not particularly limited. For example, a static air circulation oven, a rotary cylindrical oven, or a conveyor oven may be used. In one embodiment, the heat treatment comprises directing a heated gas stream onto the impregnated body. The duration of the heat treatment generally ranges from 5 minutes to 20 hours, preferably from 5 minutes to 30 minutes.

[0135] The temperature of the heat treatment is generally in the range of from 200 to 800° C., preferably from 210 to 650° C., more preferably from 220 to 500° C., most preferably from 220 to 350° C. Preferably, the heating rate in the temperature range from 40 to 200° C. is at least 20 K / min, more preferably at least 25 K / min, for example at least 30 K / min. High heating rates can be achieved by directing a high velocity gas stream of heated gas over the impregnated refractory support or the impregnated intermediate catalyst.

[0136] A suitable flow rate of the gas is, for example, from 1 to 1,000 Nm3 per kg of impregnated body. 3 / hr range, 10 to 1,000 Nm 3 / h, 15 to 500Nm 3 / hr or 20 to 300 Nm 3 / hour. In a continuous process, the term "1 kg of impregnated body" is understood to mean the amount of impregnated body (in kg / hour) multiplied by the time (in hours) that the gas stream is directed over the impregnated body. It has been found that when the gas stream is directed over a larger amount of impregnated body, for example 15 to 150 kg of impregnated body, the flow rate may be selected in the small portion of the range described above, while still achieving the desired effect.

[0137] Determining the temperature of a heated impregnated body can be a straightforward practical challenge. Thus, when a heated gas is directed onto the impregnated body during heat treatment, the temperature of the heated impregnated body is considered to be the temperature of the gas immediately after it passes through the impregnated body. In a practical embodiment, the impregnated body is placed on a suitable surface, such as a wire mesh or a perforated calcination belt, and the temperature of the gas is measured by one or more thermocouples located adjacent to the opposite side of the impregnated body, the first of which is in contact with the gas. The thermocouples are suitably placed near the impregnated body, for example, at a distance of 1 to 30 mm, e.g., 1 to 3 mm or 15 to 20 mm, from the impregnated body.

[0138] The use of multiple thermocouples can improve the accuracy of the temperature measurement. When several thermocouples are used, they can be evenly spaced across the area of ​​the width of the wire mesh or perforated calcination belt on which the impregnated body is placed. The average value is taken as the temperature of the gas immediately after it passes through the impregnated body. To heat the impregnated body to the temperatures described above, the gas typically has a temperature of 220 to 800°C, more preferably 230 to 550°C, and most preferably 240 to 350°C.

[0139] Preferably, heating is carried out in a stepwise manner, in which the impregnated body is placed on a moving belt that moves through an oven having multiple heating zones, for example 2 to 8 or 2 to 5 heating zones. The heat treatment is preferably carried out under an inert atmosphere, such as nitrogen, helium, or a mixture thereof, especially nitrogen.

[0140] The present invention further relates to a process for producing ethylene oxide by the selective vapor phase oxidation (epoxidation) of ethylene, comprising reacting ethylene and oxygen in the presence of the shaped catalyst body described above.

[0141] It is understood that all embodiments of the shaped catalyst body also apply to the process for producing ethylene oxide in the presence of the shaped catalyst body, where applicable.

[0142] The epoxidation can be carried out by any process known to those skilled in the art. It is possible to use any reactor that can be used in prior art ethylene oxide production processes, such as an externally cooled shell-and-tube reactor (see Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, Vol. A-10, pp. 117-135, 123-125, VCH-Verlagsgesellschaft, Weinheim 1987), or a reactor with a gapped catalyst bed and cooling tubes, such as the reactors described in DE 3414717 A1, EP 0082609 A1 and EP 0339748 A2.

[0143] Epoxidation is preferably carried out in at least one tube reactor, preferably a shell-and-tube reactor. On a commercial scale, ethylene epoxidation is preferably carried out in a multi-tube reactor containing several thousand tubes. The catalyst is filled into the tubes, which are placed in a shell filled with a coolant. In commercial applications, the diameter of the inner tubes is typically in the range of 20 to 40 mm (see, e.g., US Pat. No. 4,921,681 A), or greater than 40 mm (see, e.g., WO 2006 / 102189 A1).

[0144] To prepare ethylene oxide from ethylene and oxygen, the reaction can be carried out under conventional reaction conditions, for example, as described in DE 2521906A, EP 0014457A2, DE 2300512A1, EP 0172565A2, DE 2454972A1, EP 0357293A1, EP 0266015A1, EP 0085237A1, EP 0082609A1, and EP 0339748A2. An inert gas, such as nitrogen, or a gas that is inert under the reaction conditions, such as steam or methane, and optionally a reaction moderator, such as a halogenated hydrocarbon, for example ethyl chloride, vinyl chloride, or 1,2-dichloroethane, can be further mixed into the reaction gas containing ethylene and molecular oxygen.

[0145] The oxygen content of the reaction gas is advantageously in a range in which no explosive gas mixtures are present. Suitable compositions of reaction gases for preparing ethylene oxide may, for example, contain ethylene in an amount ranging from 10 to 80% by volume, preferably from 20 to 60% by volume, more preferably from 25 to 50% by volume, and particularly preferably from 25 to 40% by volume, relative to the total volume of reaction gas. The oxygen content of the reaction gas is advantageously in a range of not more than 10% by volume, preferably not more than 9% by volume, more preferably not more than 8% by volume, and very particularly preferably not more than 7.5% by volume, relative to the total volume of reaction gas.

[0146] The reaction gas preferably contains a chlorine-containing reaction moderator, such as ethyl chloride, vinyl chloride, or 1,2-dichloroethane, in an amount of 0 to 15 ppm by weight, preferably 0.1 to 8 ppm by weight, based on the total weight of the reaction gas. The remainder of the reaction gas generally contains hydrocarbons, such as methane, and inert gases, such as nitrogen. Additionally, other materials, such as steam, carbon dioxide, or noble gases, may also be contained in the reaction gas.

[0147] The concentration of carbon dioxide in the feed stream (i.e., the gas mixture fed to the reactor) is typically determined by the catalyst selectivity and the efficiency of the carbon dioxide removal equipment. The carbon dioxide concentration in the feed stream is preferably at most 3 vol.-%, more preferably less than 2 vol.-%, and most preferably less than 1 vol.-%, based on the total volume of the feed stream. An example of a carbon dioxide removal equipment is shown in US 6,452,027 B1.

[0148] The components of the reaction mixture described above may each optionally contain small amounts of impurities. Ethylene, for example, may be used at any purity suitable for gas-phase oxidation according to the present invention. Suitable purities include, but are not limited to, "polymer-grade" ethylene, which typically has a purity of at least 99%, and "chemical-grade" ethylene, which typically has a purity of less than 95%. Impurities typically include, among others, ethane, propane, and / or propene.

[0149] The reaction or oxidation of ethylene to ethylene oxide is usually carried out at elevated catalyst temperatures. Catalyst temperatures in the range of 150 to 350°C, more preferably 180 to 300°C, particularly preferably 190 to 280°C, and especially preferably 200 to 280°C are preferred. The present invention therefore also provides the process described above, wherein the oxidation is carried out at a catalyst temperature in the range of 180 to 300°C, preferably 200 to 280°C. The catalyst temperature can be determined by a thermocouple located inside the catalyst bed. As used herein, the catalyst temperature or catalyst bed temperature is considered to be the weight-average temperature of the catalyst particles.

[0150] The reaction (oxidation) according to the present invention is preferably carried out at a pressure in the range of 5 to 30 bar. All pressures in this specification are absolute pressures unless otherwise noted. The oxidation is more preferably carried out at a pressure in the range of 5 to 25 bar, for example 10 to 24 bar, in particular 14 to 23 bar. The present invention therefore also provides the above-described process, wherein the oxidation is carried out at a pressure in the range of 14 to 23 bar.

[0151] It was found that the physical properties of the shaped catalyst bodies, particularly the BET surface area and pore size distribution, had a significant positive effect on catalyst selectivity, and this effect was particularly noticeable when the catalyst was operated at very high working rates, i.e., when high levels of olefin oxide were produced.

[0152] The process according to the invention is preferably carried out under conditions conducive to obtaining a reaction mixture containing at least 2.3 vol.-% ethylene oxide. In other words, the ethylene oxide outlet concentration (ethylene oxide concentration at the reactor outlet) is preferably at least 2.3 vol.-%. The ethylene oxide outlet concentration is more preferably in the range of 2.5 to 4.0 vol.-% and most preferably in the range of 2.7 to 3.5 vol.-%.

[0153] The oxidation is preferably carried out in a continuous process. When the reaction is carried out continuously, the GHSV (gas hourly space velocity) is preferably in the range of 800 to 10,000 / h, preferably in the range of 2,000 to 8,000 / h, more preferably in the range of 2,500 to 6,000 / h, and most preferably in the range of 4,500 to 5,500 / h, depending on the type of reactor selected, such as the size / cross-sectional area of ​​the reactor, the shape and size of the catalyst, the indicated values ​​being based on the volume of the catalyst.

[0154] According to a further embodiment, the present invention is also directed to a method for preparing ethylene oxide (EO) by gas phase oxidation of ethylene with oxygen as disclosed above, wherein the measured EO space-time yield is 180 kg / m². EO / (m3 cat h) and over 200 kg EO / (m 3 cat h) Over, e.g., 250 kg EO / (m 3 cat h) Ultra, 280kg EO / (m 3 cat h) Over or 300 kg EO / (m 3 cat h) is preferred. Preferably, the measured EO space-time yield is greater than 500 kg EO / (m 3 cat h), more preferably the EO-space time yield is less than 350 kg EO / (m 3 cat h).

[0155] The preparation of ethylene oxide from ethylene and oxygen can be advantageously carried out in a recycle process. After each pass, newly formed ethylene oxide and by-products formed in the reaction are removed from the product gas stream. The remaining gas stream is supplemented with the required amounts of ethylene, oxygen and reaction moderator and reintroduced into the reactor. Separation of the ethylene oxide from the product gas stream and subsequent treatment can be carried out by conventional methods of the prior art (see Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A-10, pp. 117-135, 123-125, VCH-Verlagsgesellschaft, Weinheim 1987).

[0156] The invention will now be described in more detail by the accompanying drawings and the examples that follow. [Brief explanation of the drawings]

[0157] [Figure 1]FIG. 1 shows the log differential indentation [mL / g] and cumulative indentation [mL / g] versus pore size diameter [mL / g] of the porous alpha-alumina catalyst support A of the present invention obtained by the method according to the present invention. [Figure 2] FIG. 1 shows the log differential indentation [mL / g] and cumulative indentation [mL / g] versus pore size diameter [mL / g] of the porous alpha-alumina catalyst support B of the invention obtained by the method according to the invention. [Figure 3] FIG. 1 shows the log differential intrusion [mL / g] and cumulative intrusion [mL / g] versus pore size diameter [mL / g] for comparative porous alpha-alumina catalyst support C. [Figure 4] FIG. 1 shows the log differential indentation [mL / g] and cumulative indentation [mL / g] versus pore size diameter [mL / g] of the porous alpha-alumina catalyst support D of the invention obtained by the method according to the invention. [Figure 5] FIG. 1 shows the log differential indentation [mL / g] and cumulative indentation [mL / g] versus pore size diameter [mL / g] of the porous alpha-alumina catalyst support E of the invention obtained by the method according to the invention. [Figure 6] FIG. 1 shows the log differential intrusion [mL / g] and cumulative intrusion [mL / g] versus pore size diameter [mL / g] for comparative porous alpha-alumina catalyst support F. [Figure 7] FIG. 1 shows an image of porous alpha-alumina catalyst support D of the present invention obtained by scanning electron microscopy. [Figure 8] FIG. 1 shows an image of comparative porous alpha-alumina catalyst support F obtained by scanning electron microscopy. [Figure 9] FIG. 1 shows the geometries of porous alpha-alumina catalyst supports S and T. [Example]

[0158] Method 1: Nitrogen Sorption Nitrogen sorption measurements were carried out using a Micrometrics ASAP 2420. Nitrogen porosity was determined according to DIN 66134. Samples were degassed under vacuum at 200° C. for 16 hours before measurements.

[0159] Method 2: Mercury porosimetry Mercury porosimetry was performed using a Micrometrics AutoPore V 9600 mercury porosimeter (140 degree contact angle, 485 dynes / cm Hg surface tension, 61,000 psia maximum head pressure). Mercury porosity was determined according to DIN 66133.

[0160] The samples were dried at 110° C. for 2 hours and degassed under vacuum before analysis to remove any physisorbed species, such as water, from the sample surface.

[0161] Method 3: Loose bulk density The loose bulk density was determined by pouring the transition alumina or alumina hydrate into a graduated cylinder through a funnel, taking care not to move or vibrate the graduated cylinder. The volume and weight of the transition alumina or alumina hydrate were determined. The loose bulk density was determined by dividing the volume in milliliters by the weight in grams.

[0162] Method 4: BET surface area The BET surface area was determined according to DIN ISO 9277 using nitrogen physisorption performed at 77 K. The surface area was obtained from a five-point BET plot. The samples were degassed under vacuum at 200° C. for 16 h before the measurement. In the case of the shaped alpha-alumina supports, samples of more than 4 g were applied due to the relatively small BET surface area.

[0163] Method 5: Scanning electron microscopy Scanning electron microscopy was performed using a Hitachi SU3500 VP SEM (12 nm Pt coating).

[0164] Method 6: Analysis of the Ca-, Mg-, Si-, Fe-, K- and Na-contents in alpha-alumina supports 6A. Sample Preparation for Measuring Ca, Mg, Si, and Fe Approximately 100 to 200 mg (with an error margin of ±0.1 mg) of support sample was weighed into a platinum crucible. 1.0 g of lithium metaborate (LiBO) was added. The mixture was melted in an automated melter with a temperature ramp up to 1150°C.

[0165] After cooling, the melt was dissolved in deionized water by careful heating. Subsequently, 10 mL of semi-concentrated hydrochloric acid (concentrated HCl diluted with deionized water, 1:1 volume ratio, equivalent to approximately 6 M) was added. Finally, the solution was filled up to a volume of 100 mL with deionized water.

[0166] 6B. Measurement of Ca, Mg, Si and Fe The amounts of Ca, Mg, Si and Fe were determined from the solution described in section 5A by inductively coupled plasma-optical emission spectroscopy (ICP-OES) using an ICP-OES Varian Vista Pro. parameter: Wavelength [nm]: Ca 317.933 Mg 285.213 Si 251.611 Fe 238.204 Integration time: 10s Nebulizer: Conikal 3ml Nebulizer pressure: 270kPa Pump speed: 30 rpm Calibration: External (matrix-matched standards)

[0167] 6C. Sample preparation for measuring K and Na Approximately 100 to 200 mg (with an error margin of ±0.1 mg) of support sample was weighed into a platinum dish. 10 mL of a mixture of concentrated aqueous H2SO4 (95 to 98%) and deionized water (volume ratio 1:4) and 10 mL of aqueous hydrofluoric acid (40%) were added. The platinum dish was placed in a sand bath and boiled down to dryness. After the platinum dish cooled, the residue was dissolved in deionized water by careful heating. Subsequently, 5 mL of semi-concentrated hydrochloric acid (concentrated HCl diluted with deionized water, volume ratio 1:1, equivalent to approximately 6 M) was added. Finally, the solution was filled up to a volume of 50 mL with deionized water.

[0168] 6D. Measurement of K and Na The amounts of K and Na were determined from the solutions described in section 5C by flame atomic absorption spectroscopy (F-AAS) using an F-AAS Shimadzu AA-7000. parameter: Wavelength [nm]: K 766.5 Na 589.0 Gas: Air / Acetylene Slit width: 0.7nm (K) / 0.2nm (Na) Nebulizer pressure: 270kPa Calibration: External (matrix-matched standards)

[0169] Preparation of porous alpha-alumina catalyst support The properties of the alumina raw materials used to obtain the porous alpha-alumina catalyst support are shown in Table 1. Transition aluminas and alumina hydrates were obtained from Sasol (Puralox® and Pural®) and UOP (Versal®). Alpha-alumina was prepared by heating Puralox TH 200 / 70 at 1200°C for 4 hours.

[0170] [Table 1]

[0171] [Example 1] Preparation of supports A, B, C, and G The alumina raw materials specified in Table 1 were mixed to obtain a powder mixture. Kollidon® VA64 (vinylpyrrolidone-vinyl acetate copolymer from BASF) was added to the powder mixture. Water was then added to obtain a malleable precursor material. The amounts of all components are shown in Table 2.

[0172] The malleable precursor materials were mixed homogeneously through a mixer-mill and then extruded using a ram extruder to form a compact. The compact was in the form of a hollow cylinder with an outer diameter of about 10 mm and an inner diameter of about 5 mm. The extrudate was dried at 110°C for approximately 16 hours and then heat-treated in a muffle furnace at 600°C for 2 hours at a ramp rate of 5°C / min, followed by 1,500°C for 2 hours at a ramp rate of 2°C / min. The heat treatment was carried out in an air atmosphere.

[0173] [Example 2] Preparation of supports D, E, F, H, I, J and K The alumina raw materials specified in Table 1 were mixed to obtain a powder mixture. Colloidal silica (Ludox® AS 40, Grace & Co.) and petroleum jelly (Vaseline®, Unilever) were added to the powder mixture. Water was then added to obtain a malleable precursor material. The amounts of all components are shown in Table 2.

[0174] The malleable precursor materials were mixed homogeneously through a mixer-mill and then extruded using a ram extruder to form compacts. The compacts were in the form of hollow cylinders with an outer diameter of approximately 10 mm and an inner diameter of approximately 5 mm. The extrudates were dried at 110°C for approximately 16 hours and then heat-treated in a muffle furnace at 600°C for 2 hours at a ramp rate of 5°C / min, followed by 1,425°C for 4 hours at a ramp rate of 2°C / min. The heat treatments were carried out in an air atmosphere.

[0175] [Example 3] Preparation of supports L, M, N, O, P, Q and R The alumina raw materials specified in Table 1 were mixed to obtain a powder mixture. Dispersible boehmite (Disperal® HP 14 / 7, Sasol) and petroleum jelly (Vaseline®, Unilever), pre-dispersed in water, were added to the powder mixture. Water was then added to obtain a malleable precursor material. The amounts of all components are shown in Table 2.

[0176] The malleable precursor materials were mixed homogeneously through a mixer-mill and then extruded using a ram extruder to form compacts. The compacts were in the form of hollow cylinders with an outer diameter of approximately 10 mm and an inner diameter of approximately 5 mm. The extrudates were dried at 110°C for approximately 16 hours and then heat-treated in a muffle furnace at 600°C for 2 hours at a ramp rate of 5°C / min, followed by 1,425°C for 4 hours at a ramp rate of 2°C / min. The heat treatments were carried out in an air atmosphere.

[0177] [Table 2] TIFF0007805320000003.tif141150

[0178] Table 3 shows the physical properties of all supports prepared as shown in Table 2. Figures 1 through 16 show the log differential and cumulative indentations versus pore size diameter for all supports prepared as shown in Table 2.

[0179] [Table 3] TIFF0007805320000005.tif67154

[0180] It is clear that the supports of the invention advantageously exhibit a higher proportion of pores with diameters in the range of 0.1 to 1 μm compared to the comparative supports C, F and Q. The supports of the invention have a lower r than the comparative supports C, F and Q. pv The surface area of ​​the supports of the invention is significantly greater than that of the comparative supports C, F and Q.

[0181] Compared to comparative supports G and R derived from alpha-alumina, the supports of the present invention exhibit significantly higher total pore volumes and BET surface areas.

[0182] At the same time, the inventive support exhibits a more open pore structure compared to the comparative support, as is evident from a comparison of Figure 7 (inventive support D) and Figure 8 (comparative support F).

[0183] [Example 4] Preparation of supports S and T for catalytic performance testing The transition alumina and alumina hydrate specified in Table 1 were mixed to obtain a powder mixture. Processing aids (Vaseline®, Unilever and glycerin, Sigma-Aldrich) and water were added to the powder mixture. Vivapur® MCC Spheres 200 (microcrystalline cellulose, JRS Pharma) was added to the mixture. Additional water was then added to obtain a malleable precursor material. The total amounts of all ingredients are shown in Table 4.

[0184] [Table 4]

[0185] The malleable precursor materials were mixed homogeneously through a mixer-mill and then extruded using a ram extruder to form compacts. The compacts were in the form of trilobes with four channels, as depicted in Figure 9. The extrudates were dried overnight (approximately 16 hours) at 110°C and then heat-treated in a muffle furnace at 600°C for 2 hours at a ramp rate of 5°C / min, followed by high temperatures (1475°C for Support S and 1430°C for Support T) for 4 hours at a ramp rate of 2°C / min. Heat treatment was carried out in an air atmosphere.

[0186] The dimensions of the dried supports were determined using calipers. The diameter of the circumscribed circle of a cross section perpendicular to the support height was 11.6 cm. The term "circumscribed circle" refers to the smallest circle that completely contains the trilobal cross section within it. The diameter of the inscribed circle of a cross section perpendicular to the support height was 5.3 cm. The term "inscribed circle" refers to the largest circle that could be drawn inside the trilobal cross section. The central passage had a diameter of 1.92 cm. The three outer passages had diameters of 1.46 cm.

[0187] The resulting supports S and T had an alpha-alumina content of more than 98 wt.-% and Na-, K-, Mg-, and Ca-contents of less than 100 ppm. The Fe-content in both supports was 200 ppm. The Si-content in support S was 100 ppm. The Si-content in support T was 200 ppm.

[0188] Table 5 shows the physical properties of the inventive support S and the comparative support T.

[0189] [Table 5]

[0190] [Example 5] Catalyst preparation Shaped catalyst bodies were prepared by impregnating supports S and T with silver impregnation solutions. The catalyst compositions are shown in Table 6 below. The silver content is given in percent of the total weight of the catalyst. The dopant values ​​are given in parts per million of the total weight of the catalyst.

[0191] [Table 6]

[0192] 5.1 Preparation of silver complex solution A silver complex solution was prepared according to Production Example 1 of WO2019 / 154863A1. The silver complex solution had a density of 1.529 g / mL, a silver content of 29.3 wt.-% and a potassium content of 90 ppm.

[0193] 5.2. Preparation of intermediate catalyst 100.0 g of Support S (Intermediate 1.1) or 100.4 g of Support T (Intermediate 1.2) were placed in a 2 L glass flask. The flask was attached to a rotary evaporator, which was set under a vacuum pressure of 80 mbar. The rotary evaporator system was set to rotate at 30 rpm. 76.55 g (Intermediate 1.1) or 76.86 g (Intermediate 1.2) of the silver complex solution prepared according to step 2.1 was added to Support S (Intermediate 1.1) or Support T (Intermediate 1.2) under a vacuum pressure of 80 mbar over 15 minutes. After the addition of the silver complex solution, the rotary evaporator system was allowed to rotate under vacuum for another 15 minutes. The impregnated support was then left in the apparatus at room temperature (approximately 25 °C) and atmospheric pressure for 1 hour, gently mixing every 15 minutes.

[0194] The impregnated material was placed on the net forming one to two layers. 3 An air flow of 1000 kJ / h was applied, and the gas flow was preheated to a temperature of 305°C. The impregnated material was heated to a temperature of 290°C at a heating rate of about 30 K / min and then maintained at 290°C for 8 minutes to obtain an Ag-containing intermediate product according to Table 7. The temperature was measured by placing three thermocouples 1 mm below the net. The intermediate catalyst body was then removed from the net using an industrial vacuum cleaner, allowing the catalyst to cool to ambient temperature.

[0195] [Table 7]

[0196] 5.3. Catalyst Preparation 120.5 g of Ag-containing intermediate product 1.1 or 122.2 g of Ag-containing intermediate product 1.2 prepared according to step 2.2 were placed in a 2 L glass flask. The flasks were attached to a rotary evaporator and set under a vacuum pressure of 80 mbar. The rotary evaporator system was set to rotate at 30 rpm. For catalyst 1, 53.80 g of the silver complex solution prepared according to step 2.1 was mixed with 2.16 g of promoter solution I, 2.80 g of promoter solution II, and 4.69 g of promoter solution III. For catalyst 2, 54.56 g of the silver complex solution prepared according to step 2.1 was mixed with 2.19 g of promoter solution I, 2.84 g of promoter solution II, and 4.76 g of promoter solution III.

[0197] Promoter solution I was obtained by dissolving lithium nitrate (Merck, 99.995%) and ammonium sulfate (Merck, 99.4%) in DI water to achieve a Li content of 2.85 wt.-% and an S content of 0.22 wt.-%. Promoter solution II was obtained by dissolving tungstic acid (HC Starck, 99.99%) and cesium hydroxide (HC Starck, 50.42%) in DI water to achieve a target Cs content of 5.0 wt.-% and a W content of 3.0 wt.-%. Promoter solution III was obtained by dissolving ammonium perrhenate (Buss & Buss Spezialmetalle GmbH, 99.9%) in DI water to achieve a Re content of 3.7 wt.-%.

[0198] The combined impregnation solution containing the silver complex solution and promoter solutions I, II, and III was stirred for 5 minutes. The combined impregnation solution was added to each of the silver-containing intermediate products 1.1 or 1.2 under a vacuum pressure of 80 mbar over 15 minutes. After the addition of the combined impregnation solution, the rotary evaporator system continued to rotate under vacuum for an additional 15 minutes. The impregnated support was then left in the apparatus for 1 hour at room temperature (approximately 25°C) and atmospheric pressure, with gentle mixing every 15 minutes.

[0199] The impregnated material was placed on the net forming one to two layers. 3 A nitrogen flow of 1000 kJ / h (oxygen content: <20 ppm) was added, the gas flow having been preheated to a temperature of 305°C. The impregnated material was heated to a temperature of 290°C at a heating rate of about 30 K / min and then maintained at 290°C for 7 minutes to obtain the catalyst according to Table 4. The temperature was measured by placing three thermocouples 1 mm below the net. The catalyst was then cooled to ambient temperature by removing the catalyst body from the net using an industrial vacuum cleaner.

[0200] [Example 6] Catalyst Test The epoxidation reaction was carried out in a vertically positioned test reactor constructed of stainless steel, with an internal diameter of 6 mm and a length of 2.2 m. The reactor was heated using hot oil contained in a heating mantle at a specified temperature. All temperatures below refer to the temperature of the hot oil. The reactor was filled with 9 g of inert steatite balls (0.8 to 1.1 mm), topped with 26.4 g of crushed catalyst screened to the desired particle size of 1.0 to 1.6 mm, and then packed with an additional 29 g of inert steatite balls (0.8 to 1.1 mm). The inlet gas was introduced into the top of the reactor in a "once-through" operating mode.

[0201] The catalyst was loaded into the reactor at a reactor temperature of 90°C under a nitrogen flow of 130 NL / h at a pressure of 1.5 bar absolute. The reactor temperature was then ramped to 210°C at a heating rate of 50 K / h, and the catalyst was maintained at this condition for 15 hours. The nitrogen flow was then replaced with a methane flow of 114 NL / h and a CO flow of 1.5 NL / h. The reactor was pressurized to 16 bar absolute. A mixture of 30.4 NL / h ethylene and 500 ppm ethylene chloride in 0.8 NL / h methane was then added. Oxygen was then gradually introduced to reach a final flow rate of 6.1 NL / h. At this time, the inlet composition consisted of 20 vol.-% ethylene, 4 vol.-% oxygen, 1 vol.-% carbon dioxide, and 2.5 parts per million by volume (ppmv) of ethylene chloride (EC), with the balance being methane, at a total gas flow rate of 152.8 NL / h. The reactor temperature was ramped to 225°C at a heating rate of 5 K / h and then to 240°C at a heating rate of 2.5 K / h. The catalyst was maintained in this condition for 135 hours. The EC concentration was then reduced to 2.2 ppmv, and the temperature was reduced to 225°C. The inlet gas composition was then gradually changed to 35 vol.-% ethylene, 7 vol.-% oxygen, 1 vol.-% carbon dioxide, with methane used as the balance, and an overall gas flow rate of 147.9 NL / h. The temperature was adjusted to achieve an ethylene oxide (EO) concentration of 3.05% in the outlet gas. The EC concentration was adjusted to optimize selectivity. The results of the catalyst tests are summarized in Table 8.

[0202] [Table 8]

[0203] It is clear that catalyst 1 obtained from support S of the invention shows a much higher selectivity than catalyst 2 obtained from comparative support T. The present invention includes the following embodiments. (Embodiment 1) 1. A method for producing a porous alpha-alumina catalyst support, comprising: i) For inorganic solids - at least 50 wt.-% transition alumina having a loose bulk density of at most 600 g / L, a pore volume of at least 0.6 mL / g and a median pore diameter of at least 15 nm; - preparing a precursor material containing at most 30 wt.-% alumina hydrate; ii) forming the precursor material into a compact; and iii) calcining the formed body to obtain a porous alpha-alumina catalyst support. (Embodiment 2) 2. The method of claim 1, wherein the transition alumina has a loose bulk density in the range of 50 to 600 g / L and a pore volume of 0.6 to 2.0 mL / g. (Embodiment 3) 3. The method of claim 1 or 2, wherein the precursor material comprises 1 to 30 wt.-% alumina hydrate. (Embodiment 4) 4. The method of any one of the preceding claims, wherein the transition alumina comprises a phase selected from gamma-alumina, delta-alumina and theta-alumina, in particular a phase selected from gamma-alumina and delta-alumina. (Embodiment 5) 5. The method of any one of the preceding embodiments, wherein the transition alumina comprises at least 50 wt.-% of transition alumina with an average particle size of 10 to 100 μm, preferably 20 to 50 μm, relative to the total weight of the transition alumina. (Embodiment 6) 6. The method of any one of the preceding claims, wherein the alumina hydrate comprises boehmite and / or pseudoboehmite. (Embodiment 7) 7. The method of any one of embodiments 1 to 6, wherein the precursor material further comprises a liquid, in particular water. (Embodiment 8) 8. The method of any one of the preceding embodiments, wherein the precursor material further comprises a pore-forming material, a lubricant, an organic binder, and / or an inorganic binder. (Embodiment 9) 9. The method according to any one of the preceding embodiments, wherein the precursor material is formed into a shaped body via extrusion, tableting, granulation, casting, molding or microextrusion, in particular via extrusion or tableting. (Embodiment 10) 10. The method of any one of the preceding embodiments, wherein the calcining step is carried out at a temperature of at least 1300°C, preferably at least 1400°C, more preferably at least 1450°C. (Embodiment 11) 11. A shaped catalyst body for producing ethylene oxide by gas phase oxidation of ethylene, comprising at least 15 wt.-% silver, based on the total weight of the catalyst, deposited on a porous alpha-alumina catalyst support obtained by the method of any one of embodiments 1 to 10. (Embodiment 12) 12. The shaped catalyst body according to embodiment 11, comprising 15 to 70 wt.-% silver, preferably 20 to 60 wt.-% silver, more preferably 25 to 50 wt.-% or 30 to 50 wt.-% silver, based on the total weight of the shaped catalyst body. (Embodiment 13) 13. A method for preparing a shaped catalyst body according to embodiment 11 or 12, comprising the steps of: a) impregnating the porous alpha-alumina catalyst support obtained by the method according to any one of embodiments 1 to 10 with a silver impregnation solution, preferably under reduced pressure, and optionally drying the impregnated porous alumina support; b) subjecting the impregnated porous alpha-alumina support to a heat treatment, wherein steps a) and b) are optionally repeated. (Embodiment 14) 13. A method for producing ethylene oxide by the gas phase oxidation of ethylene, comprising reacting ethylene and oxygen in the presence of the shaped catalytic body of embodiment 11 or 12.

Claims

1. 1. A method for producing a porous alpha-alumina catalyst support, comprising: i) For inorganic solids - at least 50 wt.-% transition alumina having a loose bulk density of at most 600 g / L, a pore volume of at least 0.6 mL / g and a median pore diameter of at least 15 nm; - preparing a precursor material containing at most 30 wt.-% alumina hydrate; ii) forming the precursor material into a compact; iii) calcining the formed body to obtain a porous alpha-alumina catalyst support; The loose bulk density of the transition alumina is determined by pouring the transition alumina into a graduated cylinder while keeping the graduated cylinder stationary or vibration-free, determining the volume and weight of the transition alumina, and dividing the weight in grams by the volume in liters; The pore volume and median pore diameter of the transition alumina are determined from nitrogen sorption when the median pore diameter from mercury porosimetry is less than 50 nm, and are determined from mercury porosimetry when the median pore diameter from mercury porosimetry is 50 nm or greater, wherein nitrogen sorption is determined according to DIN 66134 and mercury porosimetry is determined according to DIN 66133. method.

2. 10. The method of claim 1, wherein the transition alumina has a loose bulk density in the range of 50 to 600 g / L and a pore volume of 0.6 to 2.0 mL / g.

3. 3. The method of claim 1, wherein the precursor material comprises 1 to 30 wt.-% alumina hydrate.

4. 4. The method of claim 1, wherein the transition alumina comprises a phase selected from gamma-alumina, delta-alumina and theta-alumina.

5. The method of claim 4, wherein the transition alumina comprises a phase selected from gamma-alumina and delta-alumina.

6. 6. The method according to claim 1, wherein the transition alumina comprises at least 50 wt.-% of transition alumina with an average particle size of 10 to 100 μm, relative to the total weight of the transition alumina.

7. The method of claim 6, wherein the transition alumina comprises at least 50 wt.-% of transition alumina having an average particle size of 20 to 50 μm, based on the total weight of the transition alumina.

8. 8. The method of claim 1, wherein the alumina hydrate comprises boehmite and / or pseudoboehmite.

9. The method of claim 1 , wherein the precursor material further comprises a liquid.

10. The method of claim 9, wherein the precursor material further comprises water.

11. 11. The method of claim 1, wherein the precursor material further comprises a pore-forming material, a lubricant, an organic binder and / or an inorganic binder.

12. 12. The method of any one of claims 1 to 11, wherein the precursor material is formed into a shaped body via extrusion, tableting, granulation, casting, molding or microextrusion.

13. The method of claim 12, wherein the precursor material is formed into a compact via extrusion or tableting.

14. 14. The method of any one of claims 1 to 13, wherein the calcining step is carried out at a temperature of at least 1300°C.

15. The method of claim 14, wherein the calcining step is carried out at a temperature of at least 1400°C.

16. The method of claim 14 or 15, wherein the calcining step is carried out at a temperature of at least 1450°C.

17. A method for preparing a shaped catalyst body for the production of ethylene oxide by the vapor phase oxidation of ethylene, comprising at least 15 wt.-% silver, based on the total weight of the catalyst, deposited on a porous alpha-alumina catalyst support, the method comprising: Obtaining a porous alpha-alumina catalyst support by the method of any one of claims 1 to 16, and a) impregnating the porous alpha-alumina catalyst support with a silver impregnation solution and optionally drying the impregnated porous alumina support; b) subjecting the impregnated porous alpha-alumina support to a heat treatment; A method wherein steps a) and b) are optionally repeated.

18. The method of claim 17, wherein step a) comprises impregnating the porous alpha-alumina catalyst support with a silver impregnation solution under reduced pressure.

19. The method of claim 17 or 18, wherein the shaped catalyst body comprises 15 to 70 wt.-% silver based on the total weight of the shaped catalyst body.

20. The method of claim 19, wherein the shaped catalyst body comprises 20 to 60 wt.-% silver based on the total weight of the shaped catalyst body.

21. A method according to claim 19 or 20, wherein the shaped catalyst body comprises 25 to 50 wt.-% or 30 to 50 wt.-% silver based on the total weight of the shaped catalyst body.

22. 22. A process for producing ethylene oxide by the vapor phase oxidation of ethylene, comprising reacting ethylene and oxygen in the presence of a shaped catalyst body obtained by the process of any one of claims 17 to 21.

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