Epoxidation catalyst

Abstract

An epoxidation catalyst comprises silver, cesium, rhenium, and tungsten deposited on a low silicon alpha alumina support comprising at least 50 wt.-% alpha alumina and silicon cS-Si in an amount of at most 8.9 mmol per kg of support, and the catalyst further comprising potassium and optionally sodium. The catalyst comprises 25 to 50 wt.-% silver, cesium cCs in an amount of at least 6.0 mmol per kg of the catalyst, rhenium CRe in an amount of at least 6.0 mmol per kg of the catalyst, tungsten CW in an amount of at least 3.0 mmol per kg of the catalyst, potassium CK in an amount of at least 3.0 mmol per kg of the catalyst, and sodium CNa in an amount of at most 4.0 mmol per kg of the catalyst. The catalyst has a value of PA in the range of from 0.62 to 0.76 (formula (I)). The catalyst allows more efficient conversion of ethylene oxide by gas phase oxidation of ethylene, exhibits high initial selectivity and activity, and maintains selectivity over time. A method for preparing the epoxidation catalyst comprises: i) impregnating a low silicon alpha alumina support with a silver impregnation solution; and ii) subjecting the impregnated refractory support to a calcination process wherein steps i) and ii) are optionally repeated and the at least one silver impregnation solution comprises rhenium, tungsten, cesium, potassium and optionally sodium. # imgabs0 #

Description

[0001] The present invention relates to a catalyst effective in the oxidative conversion of ethylene to ethylene oxide, a method for preparing the catalyst, and a method for preparing ethylene oxide by the gas-phase oxidation of ethylene in the presence of the catalyst with oxygen.

[0002] Ethylene oxide is produced in large quantities and is mainly used as an intermediate for the production of several industrial chemicals. For the industrial oxidation of ethylene to ethylene oxide, heterogeneous catalysts containing metallic silver are used. Catalyst performance can be characterized, for example, by selectivity, activity, persistence of catalyst selectivity, and / or persistence of catalyst activity. Selectivity is the mole fraction of the converted olefins that produce the desired oxidation olefin. Even a minor improvement in selectivity and the maintenance of selectivity over a longer period of time can result in significant gains in process efficiency.

[0003] Suitable epoxidation catalysts are generally obtained by depositing metallic silver on a support. Highly selective silver-based epoxidation catalysts have been developed that extend the selectivity to values closer to the stoichiometric limit. In addition to silver as the active component, such highly selective catalysts also contain promoter substances for improving the catalytic properties of the catalyst, as described, for example, in WO 2007 / 122090 A2 and WO 2010 / 123856 A1. Examples of promoter substances include alkali metal compounds and / or alkaline earth metal compounds and transition metals such as rhenium, tungsten, or molybdenum.

[0004] The supports for epoxidation catalysts are characterized by both their chemical composition and their physical properties (such as surface area and porosity). Both the chemical composition and the physical properties of the support affect the performance of the catalyst based on the support, and different formulations of the promoter substances deposited on the support are generally required to achieve optimal catalyst performance.

[0005] Aluminum oxide (Al 2 O 3 ) is ubiquitous in supports and / or catalysts used in 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 aluminum oxide has many crystalline phases, such as alpha-aluminum oxide (commonly denoted as α-aluminum oxide or α-Al 2 O 3 ), gamma-aluminum oxide (commonly denoted as γ-aluminum oxide or γ-Al 2 O 3 ) and many alumina polymorphs. Alpha-aluminum oxide is the most stable at high temperatures but has the lowest surface area.

[0006] In the method of preparing a catalyst support, alpha-alumina phase is typically mixed with temporary and permanent binders. The temporary binder is a thermally decomposable organic compound of medium to high molecular weight, which generates the pore structure of the support upon decomposition. The permanent binder is an inorganic clay-type material with a melting temperature lower than that of alumina and is responsible for imparting mechanical strength to the final support. An adequate amount of silica can also be added to obtain a final support with desired strength and composition. For example, EP 1 955 766 A1 describes an epoxidation catalyst comprising a support with a silicon content of 0.5 wt.-% to 7.0 wt.-% based on silica. Generally, the silicon incorporated into the support in this way must be taken into account in the formulation of the promoting substances deposited on the support to achieve optimal catalyst performance.

[0007] WO 2018 / 029189 A1 describes an ethylene oxide catalyst comprising silver, cesium, and rhenium applied to an alumina support. The support contains silicon, calcium, and magnesium, where the amount of silicon exceeds the total amount of calcium and magnesium.

[0008] WO 2019 / 154832 A1 describes a catalyst effective in the oxidative conversion of ethylene to ethylene oxide, which catalyst comprises an alumina support and silver applied to the support, wherein the catalyst contains a limited amount of cesium, rhenium, tungsten, and a specific molar ratio of silicon to alkaline earth metal.

[0009] WO 2021 / 260138 A1 describes a catalyst compact for ethylene oxide production, which catalyst compact comprises silver and rhenium promoters deposited on a porous alpha-alumina support, characterized in that the support has a calcination history of at least 1460 °C.

[0010] WO 2021 / 260182 A1 describes a method for producing a porous alpha-alumina catalyst support from a precursor material comprising at least 50 wt.-% of a transitional alumina with specific loose bulk density and porosity. By using transitional alumina as the starting material, permanent binders such as silicates or silica can be omitted, thereby producing a low-silica binder.

[0011] WO 2021 / 260185 A1 describes a tableted alpha-alumina catalyst support. The tableted support has high geometric precision and can be obtained from high-purity transitional alumina, which limits the content of impurities such as sodium or silicon in the support.

[0012] WO 2022 / 161924 A1 describes an epoxidation catalyst comprising silver, cesium, rhenium, tungsten deposited on an alumina support, wherein the amounts of cesium, rhenium, and the combined amount of rhenium and tungsten are specified.

[0013] To obtain a catalyst with high activity and high selectivity for the production of ethylene oxide, the combination of catalyst components and support characteristics is important. The raw materials for support production are usually natural minerals, which inevitably contain impurities such as alkali metals, especially sodium or potassium. The impurities are not lost during the manufacturing process and are ultimately found in the catalyst support and the catalyst. This has an unreliable impact on the performance of the catalyst. Therefore, the alkali metal content must be systematically considered in the catalyst preparation method.

[0014] In addition, the potential interactions between promoter substances and the interactions between impurities and between promoter substances and impurities must be considered in the catalyst preparation method. Therefore, the development of an effective catalyst for the catalyst support is by no means easy.

[0015] There is still a significant need for an epoxidation catalyst based on a support with a low silicon content, which allows for more efficient conversion of ethylene oxide by gas-phase oxidation of ethylene, especially a catalyst that exhibits high initial selectivity and activity and maintains selectivity over time.

[0016] The present invention relates to an epoxidation catalyst comprising silver, cesium, rhenium, and tungsten deposited on a low-silicon alpha-alumina support, the low-silicon alpha-alumina support comprising at least 50 wt.-% alpha-alumina and at most 8.9 mmol of silicon per kg of support c S- Si ,

[0017] The catalyst further comprises potassium and optionally sodium, wherein the catalyst comprises

[0018] - 25 wt.-% to 50 wt.-% of silver relative to the weight of the catalyst,

[0019] - at least 6.0 mmol of cesium per kg of catalyst c Cs ,

[0020] - at least 6.0 mmol of rhenium per kg of catalyst c Re ,

[0021] - at least 3.0 mmol of tungsten per kg of catalyst c W ,

[0022] - at least 3.0 mmol of potassium per kg of catalyst c K ,and

[0023] - at most 4.0 mmol of sodium per kg of catalyst c Na ;and

[0024] where P A value

[0025]

[0026] in the range from 0.62 to 0.76;

[0027] The elemental composition of the catalyst support and the catalyst was determined by elemental analysis via inductively coupled plasma optical emission spectrometry.

[0028] It has been found that an alpha-alumina support with a low silicon content requires a specific optimum amount of promoter substances, and furthermore, the optimum amounts of the promoter substances are to some extent interdependent. By selecting the amounts of rhenium c Re and tungsten c W and the amounts of cesium c Cs potassium c K and sodium c Na such that they fall within the specified ranges of P A the synergistic effect observed allows the catalyst to have particularly high selectivity.

[0029] Without wishing to be bound by theory, it is believed that rhenium and tungsten are to some extent interchangeable because these two elements can exist in the form of oxygen

[0030] tetra- or hexa-coordination (i.e., as perrhenates and tungstates); and cesium is to some extent interchangeable with potassium and sodium which are also alkali metals. The formula contains factors determining the ratio by which a part of the rhenium can be replaced by tungsten or the ratio by which a part of the cesium can be replaced by sodium and / or potassium

[0031] rates.

[0032] The P A value

[0033]

[0034] is in the range from 0.62 to 0.76, preferably from 0.62 to 0.72, more preferably from 0.64 to 0.70. If the P A value is outside these ranges, poorer results may be achieved.

[0035] Furthermore, it has been found that the ratio of the total amount of potassium c K and sodium c Na to the amount of cesium c Cs affects the stability of the catalyst selectivity over time.

[0036] Preferably, the P B value

[0037]

[0038] In the range of 0.62 to 0.94, preferably 0.63 to 0.90, more preferably 0.64 to 0.90. It has been found that P in this range B The value of allows to achieve particularly high selectivity stability. The alkali metal can be present in the catalyst as an oxide, hydroxide or as a counterion to the oxygen anion of other promoting elements. Without wishing to be bound by theory, it is believed that potassium and sodium and cesium in the presence of P B Combinations within defined ranges can control the mobility of the alkali metal and help maintain a balance of promoting species on the silver and support surfaces during catalyst operation.

[0039] The catalyst comprises 25 wt.-% to 50 wt.-% of silver relative to the weight of the catalyst. Preferably, the catalyst comprises 26 wt.-% to 40 wt.-% of silver relative to the weight of the catalyst. Most preferably, the catalyst comprises 27 to 35 % of silver relative to the weight of the catalyst. A silver content within this range allows achieving a favourable balance between the turnover rate induced by the catalyst and the cost efficiency of producing the catalyst.

[0040] The catalyst comprises cesium in an amount of at least 6.0 mmol per kg of catalyst. Cs Particularly preferably, the catalyst comprises per kg of catalyst

[0041] 6.0 to 9.0 mmol, especially 6.0 to 8.5 mmol per kg of catalyst, of cesium c Cs .

[0042] The catalyst comprises rhenium in an amount of at least 6.0 mmol per kg of catalyst. Re Preferably, the catalyst comprises 6.0 to 9.0

[0043] mmol, especially 6.0 to 8.0 mmol per kg of catalyst. Re .

[0044] The catalyst contains tungsten c in an amount of at least 3.0 mmol per kg of catalyst. W Preferably, the catalyst comprises 3.0 to 5.0

[0045] mmol, especially 3.0 to 4.0 mmol per kg of catalyst. W .

[0046] The catalyst comprises potassium c in an amount of at least 3.0 mmol per kg of catalyst. K Preferably, the catalyst comprises 3.0 to 6.0

[0047] Potassium c in an amount of 3.0 to 5.0 mmol, more preferably 3.0 to 4.5 mmol per kg of catalyst K .

[0048] The catalyst contains sodium c in an amount of at most 4.0 mmol per kg of catalyst Na . Preferably, the catalyst contains at most 3.0

[0049] mmol, especially 0.5 to 2.2 mmol per kg of catalyst of sodium c Na .

[0050] The support is a low-silica alpha-alumina support, as described in detail below. Preferably, no silicon is applied during the preparation of the catalyst. Without wishing to be bound by theory, for example, it is believed that silicon induces acidic groups on the surface of the support, which promote the undesired conversion of ethylene oxide to acetaldehyde, thereby reducing the selectivity of the ethylene oxide process.

[0051] The catalyst preferably contains silicon c in an amount of at most 6.7 mmol per kg of catalyst, preferably at most 5.4 mmol per kg of catalyst, more preferably at most 4.0 mmol per kg of catalyst Si . Due to the nature of the raw materials typically used to obtain the alpha-alumina support, the support can typically inherently contain silicon, potassium, and / or sodium. The catalyst can contain silicon c in an amount of 0.001 mmol or more, 0.01 mmol or more, 0.1 mmol or more, or 0.25 mmol or more per kg of catalyst Si .

[0052] Silicon content Si Should be understood to relate to the total amount of silicon in the catalyst (i.e., the amount of silicon added to the support via, for example, impregnation and the amount of silicon inherently contained in the support). In addition, the potassium content K Should be understood to relate to the total amount of potassium in the catalyst (i.e., the amount of potassium added to the support via, for example, impregnation and the amount of potassium inherently contained in the support). Similarly, the sodium content Na Should be understood to relate to the total amount of sodium in the catalyst (i.e., the amount of sodium added to the support via, for example, impregnation and the amount of sodium inherently contained in the support).

[0053] The elemental composition of the catalyst support, as well as that of the catalyst and the starting materials used to obtain the catalyst support, can be determined by elemental analysis via inductively coupled plasma optical emission spectrometry (ICP-OES), by flame atomic absorption spectrometry (F-AAS), or by other established methods, in particular by inductively coupled plasma optical emission spectrometry (ICP-OES). To obtain accurate results for the total weight content of impurities, a sample of the alumina support should be completely dissolved and the solution analyzed. A suitable method for completely dissolving the alumina support is described in Method 1 below.

[0054] In some embodiments, the catalyst may contain a promoting amount of an alkali metal other than cesium, potassium, and sodium (“additional alkali metal”) or a mixture of two or more of such alkali metals, such as lithium or rubidium or a combination thereof.

[0055] If lithium is used as the additional alkali metal, the amount of lithium will typically be in the range of 14.0 to 100 mmol per kg of catalyst, more typically 40.0 to 100 mmol per kg of catalyst.

[0056] If rubidium is used as the additional alkali metal, the amount of rubidium will typically be at most 10.0 mmol per kg of catalyst, more typically at most 7.0 mmol per kg of catalyst, and most typically at most 4.0 mmol per kg of catalyst, relative to the total weight of the catalyst. The catalyst may contain an amount of additional alkali metal of 0.001 mmol or more per kg of catalyst, 0.01 mmol or more per kg of catalyst, 0.1 mmol or more per kg of catalyst, or 0.25 mmol or more per kg of catalyst.

[0057] Preferably, the additional alkali metal is lithium.

[0058] The catalyst may also contain an alkaline earth metal of Group IIA or a mixture of two or more alkaline earth metals of Group IIA. Suitable alkaline earth metal promoters include, for example, beryllium, magnesium, calcium, strontium, and barium or a combination thereof. The amount of alkaline earth metal promoter used may be similar to that of the additional alkali metal promoter.

[0059] The catalyst may also contain a promoting amount of a main group element or a mixture of two or more main group elements. Suitable main group elements include any element in Groups IIIA (boron group) to VIIA (halogen group) of the periodic table. For example, the catalyst may contain a promoting amount of sulfur, phosphorus, boron, a halogen (e.g., fluorine), gallium, or a combination thereof.

[0060] In a preferred embodiment, the catalyst contains sulfur. Preferably, the catalyst contains sulfur in an amount of 10.0 mmol or less per kg of catalyst, preferably 0.1 to 5.0 mmol per kg of catalyst. S。

[0061] The catalyst 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 element having an atomic number from 57 to 103. Some examples of these elements include lanthanum (La), cerium (Ce), and samarium (Sm). The amount of the rare earth metal promoter used may be similar to the amount of the transition metal promoter used.

[0062] The catalyst comprises an alumina support on which silver, cesium, rhenium, and tungsten are deposited. The alumina support comprises a high proportion of alumina, i.e., Al 2 O 3 , and in particular alpha-alumina. Specifically, based on the total weight of the support, the alumina support contains at least 50 wt.-% of alpha-alumina, such as at least 70 wt.-%, at least 80 wt.-% or at least 90 wt.-%, preferably at least 95 wt.-%, most preferably at least 97.5 wt.-% or at least 99 wt.-%. In addition to alumina, the support may also contain other components, such as other refractory oxides, such as zirconia or titanium dioxide.

[0063] The support is a low-silica alpha-alumina support. The support contains silicon in an amount of at most 8.9 mmol per kg of the support, preferably at most 5.4 mmol per kg of the support, more preferably at most 4.0 mmol per kg of the support. S-Si . In one embodiment, the support contains silicon in an amount of 0.001 mmol or more per kg of the support, 0.01 mmol or more per kg of the support, 0.1 mmol or more per kg of the support, or 0.25 mmol or more per kg of the support. S-Si 。

[0064] The amount of potassium in the support S-K is typically in the range of at most 3.0 mmol per kg of the support, preferably at most 2.5 mmol per kg of the support, more preferably at most 2.0 mmol per kg of the support, and most preferably at most 1.3 mmol per kg of the support. In one embodiment, the support contains potassium in an amount of 0.001 mmol or more per kg of the support, 0.01 mmol or more per kg of the support, 0.1 mmol or more per kg of the support, or 0.25 mmol or more per kg of the support. S-K 。

[0065] The amount of sodium in the support S-Na is typically in the range of at most 4.0 mmol per kg of the support, preferably from 0.67 to 3.0 mmol per kg of the support, and more preferably from 1.0 to 2.0 mmol per kg of the support.

[0066] In one embodiment, the support contains

[0067] - Potassium c in an amount of at most 3.0 mmol per kg of carrier, preferably at most 2.5 mmol per kg of carrier, more preferably at most 2.0 mmol per kg of carrier, and most preferably at most 1.3 mmol per kg of carrier S-K , and

[0068] - Sodium c in an amount of at most 4.0 mmol per kg of carrier, preferably from 0.67 to 3.0 mmol per kg of carrier, more preferably from 1.0 to 2.0 mmol per kg of carrier S-Na .

[0069] In a preferred embodiment, the carrier comprises

[0070] - Silicon in an amount of at most 8.9 mmol per kg of carrier, preferably at most 5.4 mmol per kg of carrier, more preferably at most 4.0 mmol per kg of carrier S-Si ,

[0071] - Potassium c in an amount of at most 3.0 mmol per kg of carrier, preferably at most 2.5 mmol per kg of carrier, more preferably at most 2.0 mmol per kg of carrier, and most preferably at most 1.3 mmol per kg of carrier S-K , and

[0072] - Sodium c in an amount of at most 4.0 mmol per kg of carrier, preferably from 0.67 to 3.0 mmol per kg of carrier, more preferably from 1.0 to 2.0 mmol per kg of carrier S-Na .

[0073] The carrier may contain impurities other than sodium and potassium, such as iron, magnesium, calcium, and zirconium in an amount of 2 to 200 mmol / kg based on the total weight of the carrier.

[0074] It is desirable that silver be relatively uniformly dispersed on the inner and outer surfaces of the carrier. The high surface area of the carrier allows for a high dispersion of silver. However, increasing the surface area of the carrier may promote side reactions that may occur on the surface of the carrier. Alpha-alumina carriers with a BET surface area of 3.0 m 2 / g or less provide a good compromise between silver dispersion and side reactions.

[0075] The carrier preferably has a BET surface area of 0.5 to 3.0 m 2 / g, more preferably 1.0 to 2.5 m 2 / g, and most preferably 1.2 m 2 / g to 2.0 m 2 / g. The BET method is a well-known and widely used standard method in surface science for measuring the surface area of solids by physical adsorption of gas molecules. Unless otherwise stated, the BET surface is determined herein in accordance with DIN ISO 9277.

[0076] The support is a porous support and generally has a total Hg pore volume in the range of 0.4 to 1.2 mL / g, preferably 0.45 to 0.9 mL / g, more preferably 0.5 to 0.8 mL / g, as determined by mercury porosimetry. The catalyst generally has a total Hg pore volume in the range of 0.2 to 1.0 mL / g, preferably 0.3 to 0.8 mL / g, as determined by mercury porosimetry. Mercury porosimetry can be carried out using a Micrometrics AutoPore IV 9500 mercury porosimeter (140-degree contact angle, 485 dynes / cm Hg surface tension, 60,000 psia maximum discharge pressure). Unless otherwise stated, Hg porosity is determined herein according to DIN 66133. It is believed that the Hg pore volume within the above ranges allows for a favorable duration of exposure of the obtained ethylene oxide to the catalyst.

[0077] The support preferably has a water absorption rate in the range of 0.35 to 1.2 mL / g (milliliters of water / gram of support). Preferably, the water absorption rate of the support is in the range of 0.4 to 1.0 mL / g, most preferably 0.4 to 0.80 mL / g. The water absorption rate refers to the amount of cold water absorbed under a vacuum of 80 mbar absolute.

[0078] The cold water absorption under vacuum is determined by placing approximately 100 g of the support ("initial support weight") in a rotary flask, covering the support with deionized water, and rotating the rotary evaporator at approximately 30 rpm for 5 min. Subsequently, a vacuum of 80 mbar is applied for 3 min, the water and the support are transferred to a glass funnel, and the support is held in the funnel for approximately 5 min with occasional shaking to ensure that the attached water runs down the funnel. The support is weighed ("final support weight"). The water absorption rate is calculated by subtracting the initial support weight from the final support weight and then dividing the difference by the initial support weight. It is believed that the water absorption rate within the above ranges allows for a favorable duration of exposure of the obtained ethylene oxide to the catalyst.

[0079] The support preferably comprises individual shaped bodies. The size and shape of the individual shaped bodies and thus the size and shape of the catalyst are selected to allow the shaped bodies to be properly filled in the reactor tube. The shaped bodies of the catalyst suitable for the present invention are preferably used in a reactor tube having a length of 6 to 14 m and an inner diameter of 20 mm to 50 mm. Generally, the support consists of individual bodies having a maximum extension in the range of 3 to 20 mm, such as 4 to 15 mm, especially 5 to 12 mm. The maximum extension should be understood to mean the longest straight line between two points on the outer circumference of the support.

[0080] The shape of the carrier is not particularly limited and can take any technically feasible form, which depends, for example, on the extrusion method. For example, the carrier can be a solid carrier or a hollow carrier, such as a hollow cylinder. In another embodiment, the carrier can be characterized by a multi-leaf structure. A multi-leaf structure is intended to denote a cylindrical structure having a plurality of void spaces (e.g., grooves or channels) extending along the height of the cylinder on the outer circumference of the cylinder. Generally, these void spaces are arranged substantially equidistantly around the circumference of the cylinder.

[0081] Hollow cylinders are characterized by their geometric dimensions, in particular the outer diameter × length × inner diameter. The outer diameter is preferably in the range of 5 to 15 mm, preferably 7 to 10 mm. The length is preferably in the range of 5 to 15 mm, preferably 7 to 11 mm. The inner diameter is preferably in the range of 1 to 5 mm, preferably 2 to 4 mm. Specific examples are hollow cylinders with outer diameter (mm) × length (mm) × inner diameter (mm) of 5×5×2, 6×6×3, 7×7×3, 8×8×3, 8×8.5×3, 8.5×8.5×3, 9×9×3 and 9×9×3.5.

[0082] In another embodiment, the catalyst carrier can be in the shape as described in US 9,409,160 B2, where the catalyst formed body has the form of a cylinder, which has a bottom, a cylindrical surface, a cylindrical axis and at least one continuous opening extending parallel to the cylindrical axis (a channel extending from the first end face surface of the tableted catalyst carrier to the second end face surface), and the bottom of the cylinder has at least four leaves.

[0083] The catalyst carrier can also be in the shape as described in WO 2012 / 091898 A2, which has at least three leaves, a first end, a second end, a wall between the two ends and a non-uniform transition radius at the intersection of the end and the wall.

[0084] In one embodiment, the catalyst carrier has more than one channel extending from the first end face surface of the tableted catalyst carrier to the second end face surface. Such a shape is known in the art as described below.

[0085] For example, US 5,861,353 A describes a catalyst and a catalyst carrier in the form of cylindrical pellets, which are characterized in that each pellet exhibits at least three through-holes (channels extending from the first end face surface of the tableted catalyst carrier to the second end face surface), the axes of these through-holes are substantially parallel to each other and parallel to the axis of the pellet and are substantially equidistant from each other.

[0086] US 9,138,729 B2 describes a shaped catalyst having a substantially cylindrical body with a longitudinal axis, wherein the cylindrical body has at least two parallel internal holes (channels extending from a first end face surface to a second end face surface of a tableted catalyst support), the parallel internal holes being substantially parallel to the cylindrical axis of the body and passing directly through the body, and wherein the internal holes have a circular or oval cross-section.

[0087] WO 2020 / 108872 A1 describes a catalyst shaped body for the production of ethylene oxide by gas-phase oxidation of ethylene, which comprises silver deposited on a porous refractory support, the catalyst shaped body having a first end face surface, a second end face surface and a circumferential surface, a cylindrical structure having n void spaces (the void spaces extending along the height of the cylinder on the outer circumference of the cylinder to form an n-lobe structure, where n is 2, 3, 4, 5 or 6), n channels extending from the first end face surface to the second end face surface (each channel being assigned to a lobe, with adjacent channels being arranged substantially equidistantly relative to each other), n-fold rotational symmetry, a shortest distance A between two adjacent channels in the range from 1.0 to 2.0 mm, and a shortest distance B between each channel and the circumferential surface in the range from 1.1 to 2.0 mm.

[0088] In a preferred embodiment, the alpha-alumina support is a tableted alpha-alumina support. In this case, the support can be obtained by typically forming a precursor material into a shaped body by tableting in the absence of liquid and subsequently subjecting the shaped body to a heat treatment. Tableting is a pressure agglomeration method. A powdery or previously agglomerated bulk material is introduced into a pressing tool having a die between two punches, and is compacted and shaped by uniaxial compression to obtain a solid compact. This operation is divided into four parts: metering introduction, compaction (elastic deformation), plastic deformation and ejection. Tableting is carried out, for example, on a rotary press or an eccentric press.

[0089] If desired, the upper punch and / or the lower punch can include projecting pins to form internal channels. The pressing punches can also be provided with a plurality of movable pins such that the punch can be made, for example, of four pins to create a shaped body having four holes (channels). Typical design features of such tools can be seen, for example, in US 8,865,614 B2.

[0090] The tableting method allows for the accurate manufacture of catalyst supports, i.e., the manufacture of a plurality of catalyst supports with relatively small external dimensional deviations. Such supports are almost identical geometrically, allowing for better calculation of their behavior during the reaction and lower pressure losses, for example, in gas-phase catalysis.

[0091] The shape of the tableted catalyst support is not particularly limited as long as it can be obtained by a tableting machine of the type of conventional known punches and dies. The shape of the tableted catalyst support generally consists of a circumferential surface corresponding to the inner wall of the die cavity and a top end surface and a bottom end surface corresponding to the operating head of the punch. The upper punch and the lower punch may also touch each other during the tableting process. In this case, discrete circumferential and end surfaces are not formed. Thus, a tableted catalyst support having an outer shape such as a sphere or an ellipsoid can be obtained.

[0092] For tableting, it is generally preferred to use lubricants, especially those discussed above. To improve the tableting properties, pre-granulation and / or screening steps can be used. For pre-granulation, a roll press can be used, such as one from Fitzpatrick Additional information regarding tableting, especially regarding pre-granulation, screening, lubricants, and tools, can be found in WO 2010 / 000720 A2.

[0093] It has been found that highly porous transition aluminas with low bulk density, especially those with relatively high pore volume and large pore size, are useful starting materials for producing alpha-alumina catalyst supports with a beneficial pore structure. Such transition aluminas are suitable for shaping via a tableting method to obtain geometrically accurate supports with a high total pore volume. Further details regarding useful starting materials and the tableting method itself have been described, for example, in WO 2021 / 260185 A1.

[0094] Furthermore, the tableting technique allows the use of specific pore-forming materials that are particularly suitable for obtaining a favorable pore structure while allowing the catalyst support to have high purity. Thus, low concentrations of sodium and potassium in the support can be achieved. Pore-forming materials especially include substances that are not easily used or controlled in the extrusion process due to their tendency to lose their structural integrity under extrusion conditions, such as water-soluble, moisture-sensitive, or shear-degradable pore-forming materials. Suitable pore-forming materials include thermally decomposable materials such as ammonium bicarbonate, ammonium carbonate, ammonium carbamate, ammonium nitrate, urea, malonic acid, and oxalic acid, especially malonic acid and ammonium bicarbonate; and organic polymers such as microcrystalline cellulose and cellulose fiber granules, such as agglomerated spray-dried cellulose fibers (cellulose pulp granules), especially ammonium bicarbonate.

[0095] In one embodiment, the carrier is in the shape of a solid extrudate (such as a pellet or a cylinder) or a hollow extrudate (such as a hollow cylinder). In a preferred embodiment, the shaped body is formed by extrusion of a precursor material (e.g., microextrusion). In this case, the precursor material suitably contains a liquid, especially water, in order to form a malleable precursor material. The precursor material typically includes alpha-aluminum oxide, hydrated aluminum oxide, and / or transitional aluminum oxide. Further details regarding useful starting materials and the extrusion method itself have been described, for example, in WO 2021 / 260182 A1.

[0096] In a preferred embodiment, the extrusion includes loading at least one solid component into a mixing device before adding the liquid. Preferably, a muller (H-roll) or a horizontal mixer such as a mixer (from Gebrüder Maschinenbau) is used for mixing. The formation of the extrudable paste of the precursor material can be monitored and controlled based on data reflecting the power consumption of the mixing device.

[0097] The precursor material is typically extruded through a die. The cross-section of the die opening is adapted to the desired geometry of the shaped body.

[0098] The extrusion die can include a matrix and a mandrel, where the matrix substantially determines the circumferential shape of the shaped body and the mandrel substantially determines the shape, size, and position of the channel (if any). Suitable extrusion dies are described, for example, in WO 2019 / 219892 A1.

[0099] The geometry of the shape of the shaped body is defined by the geometry of the extrusion device through which the precursor material is extruded. Generally, the geometry of the shape of the extrudate is slightly different from the geometry of the extrusion device while substantially having the geometric characteristics described above. The absolute size of the shape is typically slightly smaller than the size of the extrudate due to the high temperature required to form alpha-aluminum oxide and the shrinkage during cooling of the extrudate. The degree of shrinkage depends on the temperature applied during calcination and the composition of the shaped body. Therefore, the size of the extrusion die should be routinely adjusted in a manner that takes into account the shrinkage of the extrudate during subsequent calcination.

[0100] When the shaped body comprises a plurality of channels, the axes of the channels typically extend parallel. However, the shaped bodies may be slightly bent or twisted along their z-axis (height). The shape of the cross-section of the channels may deviate slightly from the perfect geometry envisaged above. When a large number of shaped bodies are obtained, the individual channels of a small number of catalyst shaped bodies may be blocked. Typically, due to the production method, the end faces of the catalyst shaped bodies in the xy-plane are more or less uneven rather than smooth. The height of the shaped body (the length of the shaped body in the z-direction) is not usually exactly the same for all shaped bodies, but rather forms a distribution with the average height as its arithmetic mean.

[0101] The extrudate is preferably cut into the desired length while still wet. Preferably, the extrudate is cut at an angle substantially perpendicular to its circumferential surface. To reduce undesired deviations from the geometry of the extrusion equipment, the extrudate may alternatively be cut at an inclination angle of up to 30° (such as 10° or 20°) relative to the angle perpendicular to the circumferential surface of the extrudate.

[0102] Geometric shape deviations, such as those arising during the extrusion process and / or during further processing of the extrudate (such as the cutting step), may also typically be present in the alpha-alumina catalyst support. Those skilled in the art understand that due to the inaccuracies inherent to some extent in all production methods, a perfect geometric form is essentially unattainable.

[0103] In another embodiment, a micro-extrusion method (such as the method described in WO 2019 / 072597 A1) is used to form the precursor material into a shaped body.

[0104] In another embodiment, a gel casting method (such as the method described in WO 2020 / 053563 A1) is used to form the precursor material into a shaped body.

[0105] Furthermore, the present invention relates to a method for preparing an epoxidation catalyst as described above, the method comprising

[0106] i) impregnating an alumina support as described above with a silver impregnation solution; and

[0107] ii) subjecting the impregnated support to a heat treatment;

[0108] wherein steps i) and ii) are optionally repeated, and at least one silver impregnation solution contains rhenium, tungsten, cesium, potassium and optionally sodium.

[0109] It should be understood that, where applicable, all embodiments of the catalyst and the support are also applicable to the method for preparing the catalyst.

[0110] In order to obtain a catalyst compact with a high silver content, steps i) and ii) can be repeated several times. In this case, it should be understood that the intermediate product obtained after the first (or subsequent up to the penultimate) impregnation / heat treatment cycle contains a part of the total target Ag and / or promoter concentration. The intermediate product is then impregnated again with the silver impregnation solution and calcined to produce the target Ag and / or promoter concentration. The desired composition of the catalyst can also be established by applying only one impregnation.

[0111] Any silver impregnation solution known in the art and suitable for impregnating a refractory support can be used. The silver impregnation solution typically contains silver carboxylate, such as silver oxalate, or a combination of silver carboxylate and oxalic acid in the presence of an amine complexing agent such as C 1 -C 10 -alkylenediamine, especially ethylenediamine. Suitable impregnation solutions are described in EP 0 716 884 A2, EP 1 115 486 A1, EP 1613 428 A1, US 4,731,350 A, WO 2004 / 094055A2, WO 2009 / 029419 A1, WO 2015 / 095508A1, US 4,356,312 A, US 5,187,140 A, US 4,908,343A, US 5,504,053 A, WO 2014 / 105770A1 and WO 2019 / 154863. Cesium can be provided appropriately as cesium hydroxide. Rhenium and tungsten can be provided appropriately as oxygen anions (e.g., as perrhenate or tungstate in the form of a salt or acid).

[0112] At least one silver impregnation solution contains rhenium, tungsten, cesium, potassium and optionally sodium. Particularly preferably, the silver impregnation solution used at least in the final impregnation step contains rhenium, tungsten, cesium and potassium.

[0113] 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 part of the deposited silver ions are then converted to metallic silver upon further heating. Preferably, based on the total molar amount of silver in the impregnated porous alpha-alumina support, at least 70 mol-% of the silver compounds, 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-%, i.e., substantially all silver ions. The amount of silver ions converted to metallic silver can be determined, for example, via an X-ray diffraction (XRD) pattern.

[0114] The heat treatment can also be referred to as a calcination method. Any calcination method known in the art for this purpose can be used. Suitable examples of the calcination method are described in US 5,504,052 A, US 5,646,087 A, US 7,553,795 A, US 8,378,129 A, US 8,546,297 A, US2014 / 0187417A1, EP 1 893 331 A1 or WO 2012 / 140614A1. The heat treatment can be carried out in a direct-through mode or with at least partial recirculation of the calcination gas.

[0115] The heat treatment is generally carried out in a furnace. The type of furnace is not particularly limited. For example, a stationary recirculating air furnace, a rotary cylindrical furnace or a conveyor belt furnace can be used. In one embodiment, the heat treatment includes guiding a heated gas stream through the impregnated body. The duration of the heat treatment is generally in the range of 5 min to 20 h, preferably 5 min to 30 min.

[0116] The temperature of the heat treatment is generally in the range of 200 °C to 800 °C, preferably 210 °C to 650 °C, more preferably 220 °C to 500 °C, most preferably 220 °C to 350 °C. Preferably, the heating rate in the temperature range of 40 °C to 200 °C is at least 20 K / min, more preferably at least 25 K / min, such as at least 30 K / min. A high heating rate can be achieved by guiding the heated gas through the impregnated refractory carrier or the impregnated intermediate catalyst at a high gas flow rate.

[0117] A suitable flow rate of the gas can be, for example, in the range of 1 to 1,000 Nm 3 / h, 10 to 1,000 Nm 3 / h, 15 to 500 Nm 3 / h or 20 to 300 Nm 3 / h. In a continuous process, the term "kilograms of impregnated body" should be understood to mean the amount of impregnated body (in kg / h) multiplied by the time (in hours) during which the gas stream is guided through the impregnated body. It has been found that when the gas stream is guided through a relatively large amount of impregnated body, such as 15 to 150 kg of impregnated body, the flow rate can be selected at the lower end of the above range while achieving the desired effect.

[0118] There may be practical difficulties in directly determining the temperature of the heated impregnated body. Therefore, when guiding the heated gas through the impregnated body during the heat treatment, the temperature of the heated impregnated body is considered to be the gas temperature just after the gas has passed 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 calcining belt, and the temperature of the gas is measured by one or more thermocouples arranged adjacent to the side of the impregnated body opposite to the side first contacting the gas. The thermocouple is placed appropriately close to the impregnated body, for example, at a distance of 1 to 30 mm from the impregnated body, such as 1 to 3 mm or 15 to 20 mm.

[0119] Using multiple thermocouples can improve the accuracy of temperature measurement. In the case of using several thermocouples, these thermocouples can be evenly spaced over the area where the impregnated body is placed on the wire mesh or the width of the perforated calcining belt. The average value is considered to be the gas temperature just after the gas has passed through the impregnated body. To heat the impregnated body to the temperature as described above, the gas typically has a temperature of 220 °C to 800 °C, more preferably 230 °C to 550 °C, and most preferably 240 °C to 350 °C.

[0120] Preferably, the heating is carried out in a stepwise manner. In the stepwise heating, the impregnated body is placed on a moving belt that moves through a furnace having a plurality of heating zones (for example, 2 to 8 or 2 to 5 heating zones). The heat treatment is preferably carried out in an inert atmosphere, such as nitrogen, helium or a mixture thereof, especially in nitrogen.

[0121] There is further provided a method for producing ethylene oxide by gas-phase oxidation of ethylene, which method comprises reacting ethylene and oxygen in the presence of the epoxidation catalyst as described above.

[0122] The epoxidation can be carried out by all methods known to those skilled in the art. All reactors that can be used in the prior art ethylene oxide production methods can be used; for example, an externally cooled shell-and-tube reactor (see Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, Volume A-10, pages 117-135, pages 123-125, VCH-Verlagsgesellschaft, Weinheim, 1987) or a reactor having a loose catalyst bed and cooling tubes, such as the reactors described in DE 34 14 717 A1, EP 0082 609 A1 and EP 0 339 748 A2.

[0123] Epoxidation is preferably carried out in at least one tubular reactor, preferably in a shell-and-tube reactor. On a commercial scale, the epoxidation of ethylene is preferably carried out in a multitubular reactor containing thousands of tubes. The catalyst is filled into the tubes, and these tubes are placed in a shell filled with a coolant. In commercial applications, the inner tube diameter is typically in the range of 20 to 40 mm (see, for example, US 4,921,681 A) or greater than 40 mm (see, for example, WO 2006 / 102189 A1).

[0124] To prepare ethylene oxide from ethylene and oxygen, the reaction can be carried out under conventional conditions as described, for example, in DE 25 21 906 A, EP 0 014 457A2, DE 23 00 512A1, EP 0 172 565 A2, DE 24 54 972 A1, EP 0 357 293 A1, EP 0 266015 A1, EP 0 085 237 A1, EP 0 082 609A1, and EP 0 339 748 A2. An inert gas such as nitrogen or a gas that is inert under the reaction conditions (e.g., steam, methane), and also optionally a reaction moderator (e.g., a halogenated hydrocarbon such as chloroethane, vinyl chloride, or 1,2-dichloroethane) can be additionally mixed into the reaction gas containing ethylene and molecular oxygen.

[0125] The oxygen content of the reaction gas is advantageously in a range where no explosive gas mixture exists. A suitable composition of the reaction gas for preparing ethylene oxide can, for example, contain an ethylene amount in the range of 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, based on the total volume of the reaction gas. The oxygen content of the reaction gas is advantageously in the 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, based on the total volume of the reaction gas.

[0126] The reaction gas preferably contains a chlorine-containing reaction moderator, such as chloroethane, vinyl chloride, or 1,2-dichloroethane, in an amount of from 0 to 15 ppm by weight, preferably from 0.1 to 8 ppm by weight, based on the total weight of the reaction gas. The remainder of the reaction gas generally includes hydrocarbons such as methane and also inert gases such as nitrogen. Additionally, other materials such as steam, carbon dioxide, or noble gases can also be contained in the reaction gas.

[0127] The concentration of carbon dioxide in the feed (i.e., the gas mixture fed to the reactor) typically depends on the catalyst selectivity and the efficiency of the carbon dioxide removal equipment. The carbon dioxide concentration in the feed is preferably at most 3 vol.-% relative to the total volume of the feed, more preferably less than 2 vol.-%, and most preferably less than 1 vol.-%. Examples of carbon dioxide removal equipment are provided in US 6,452,027 B1.

[0128] The above components of the reaction mixture may optionally each have small amounts of impurities. Ethylene can be used, for example, in 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 particularly include ethane, propane, and / or propylene.

[0129] The reaction or oxidation of ethylene to ethylene oxide is typically carried out at an elevated catalyst temperature. The catalyst temperature is preferably in the range of 150 °C to 350 °C, more preferably 180 °C to 300 °C, particularly preferably 190 °C to 280 °C, and especially preferably 200 °C to 280 °C. Accordingly, the present invention also provides a method as described above, wherein the oxidation is carried out at a catalyst temperature in the range of 180 °C to 300 °C, preferably 200 °C to 280 °C. The catalyst temperature can be determined by a thermocouple located inside the catalyst bed. As used herein, the catalyst temperature or the temperature of the catalyst bed is considered to be the weighted average temperature of the catalyst particles.

[0130] The reaction (oxidation) according to the present invention is preferably carried out at a pressure in the range of 5 to 30 bar. Unless otherwise stated, all pressures herein are absolute pressures. The oxidation is more preferably carried out at a pressure in the range of 5 to 25 bar, such as 10 to 24 bar, and particularly 14 to 23 bar. Accordingly, the present invention also provides a method as described above, wherein the oxidation is carried out at a pressure in the range of 14 to 23 bar.

[0131] The physical characteristics of the catalyst shaped bodies, in particular the BET surface area and the pore size distribution, have a significant positive effect on the catalyst selectivity. This effect is particularly evident when the catalyst is operating at an extremely high working rate (i.e., a high level of ethylene oxide production).

[0132] The method according to the present 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 (the concentration of ethylene oxide 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 vol.-% to 4.0 vol.-%, and most preferably in the range of 2.7 vol.-% to 3.5 vol.-%.

[0133] This oxidation is preferably carried out by a continuous process. If the reaction is carried out continuously, depending on the type of reactor selected, for example depending on the size / cross-sectional area of the reactor, the shape and size of the catalyst, 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, where the indicated values are based on the volume of the catalyst.

[0134] According to another embodiment, the present invention also relates to a process for preparing ethylene oxide (EO) by gas-phase oxidation of ethylene with oxygen as disclosed above, wherein the measured EO space-time yield is greater than 180 kg EO / (m 3 cat h), preferably greater than 200 kg EO / (m 3 cat h) such as greater than 250 kg EO / (m 3 cat h), greater than 280 kg EO / (m 3 cat h) or greater than 300 kg EO / (m 3 cat h) of EO space-time yield. Preferably, the measured EO space-time yield is less 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).

[0135] The preparation of ethylene oxide from ethylene and oxygen can advantageously be carried out by a recycle process. After each pass, the newly formed ethylene oxide and the 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. The separation of ethylene oxide from the product gas stream and its subsequent treatment can be carried out by conventional methods of the prior art (see Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Volume A-10, pages 117-135, pages 123-125, VCH-Verlagsgesellschaft, Weinheim, 1987).

[0136] Figures 1A to 1C Shows the shape of the support used in the catalyst of the preparation example. Figure 1A and 1C Shows a side view, Figure 1B Shows a top view. The support has a domed top surface, and these domed top surfaces have a dome height a, a length b, an outer diameter c, a channel diameter d, and a distance e between the channel centers.

[0137] Figure 2 Shows the P A values and the ethylene oxide selectivity [%] after 11 days of operation.

[0138] Figure 3 Shows the P A values and the ethylene oxide selectivity [%] after 25 days of operation.

[0139] Figure 4 Shows the P B values and its ΔS 28-25 value, that is, the selectivity difference after 28 days and 25 days of operation.

[0140] Figure 5 Shows the ethylene oxide selectivity [%] of Catalysts 1-1 and 1-6 over time during operation.

[0141] The present invention will be described in more detail by the following examples.

[0142] Method 1: Analysis of the total content of Ca, Mg, Si, Fe, K, Na, and Ti in the alpha-alumina support

[0143] 1A. Sample preparation

[0144] Weigh two samples (0.1 to 0.2 g) into a microwave digestion vessel. Then, add 10.5 mL of an acid mixture (6.5 mL of phosphoric acid (80% to 85%), 3.5 mL of sulfuric acid (96%), and 0.5 mL of nitric acid (65%)). Place the microwave digestion vessel in a microwave digestion system, heat to 230 °C, and hold at this temperature for 45 min.

[0145] After cooling, transfer the sample to a volumetric flask and fill it with deionized water to a volume of 50 mL. Prepare a blank sample s by the same procedure.

[0146] 1B. Measurement

[0147] Analyze the resulting digestion solution by inductively coupled plasma optical emission spectrometry (ICP-OES) using an internal standard (Sc) and blank subtraction.

[0148]

[0149] The reported results were calculated from the average of two prepared replicates of each sample.

[0150] Method 2: Mercury porosimetry

[0151] Mercury porosimetry was performed using a Micrometrics AutoPore IV 9500 mercury porosimeter (140-degree contact angle, 485 dynes / cm Hg surface tension, 60,000 psia maximum ejection pressure). The mercury porosity was determined according to DIN 66133.

[0152] Method 3: Nitrogen adsorption

[0153] Nitrogen adsorption measurements were performed using a Micrometrics ASAP 2420. The nitrogen porosity was determined according to DIN 66134. The samples were degassed under vacuum at 200 °C for 16 h before measurement.

[0154] Method 4: BET surface area

[0155] The BET surface area was determined according to DIN ISO 9277.

[0156] Method 5: Water absorption

[0157] Water absorption refers to the amount of cold water absorbed under vacuum. The amount of cold water absorbed under vacuum was determined by placing approximately 100 g of the carrier (“initial carrier weight”) in a rotary flask, covering the carrier with deionized water, and rotating the rotary evaporator at approximately 30 rpm for 5 min. Subsequently, a vacuum of 80 mbar was applied for 3 min, the water and the carrier were transferred to a glass funnel, and the carrier was held in the funnel for approximately 5 min with occasional shaking to ensure that the attached water drained down the funnel.

[0158] The carrier was weighed (“final carrier weight”). The water absorption was calculated by subtracting the initial carrier weight from the final carrier weight and then dividing the difference by the initial carrier weight.

[0159] Examples

[0160] Example 1 - Preparation of carriers

[0161] The alumina raw materials (transition alumina and hydrated alumina obtained from Sasol) and paraffin-coated ammonium bicarbonate (ABC-O, BASF) as pore-forming materials specified in Table 1 were combined with HCO (hydrogenated castor oil waxy substance from BASF) and T44 (graphite from TimCal Graphite & Carbon) was mixed as a processing aid to obtain a free-flowing powder mixture. The vaseline-coated ammonium bicarbonate was prepared by mixing 99 wt.-% ammonium bicarbonate with 1 wt.-% (Unilever) in a plowshare mixer (e.g., L5, Maschinenfabrik Rottiger GmbH) at 175 rpm for 20 min. The weight ratios of all components in the formulation are shown in Table 1.

[0162] Table 1

[0163]

[0164] Each powder mixture was subjected to tableting in a rotary tablet press (Kilian E150 Plus, Romaco) equipped with a four-lobed punch having four holes with an outer diameter of approximately 16.5 mm and a hole diameter of approximately 3.8 mm. The tablets were produced at a pre-compaction pressure in the range of 0.5 to 0.9 kN, a main compaction pressure in the range of 7 to 10 kN, and a rotational speed of 8 to 11 rpm. The average height of the green tablets obtained was 12.5 mm.

[0165] The green tablets were heat-treated in a muffle furnace. The furnace temperature was ramped up to 500 °C at a heating rate of 2 °C / min, held at 500 °C for 30 min, then the temperature was ramped up to the target temperature at a heating rate of 2 °C / min and held at that target temperature for 4 h. The heat treatment was carried out under lean air with 5 vol.-% oxygen.

[0166] In Figures 1A to 1C the final shape of the four-lobed tablet carrier is shown, depicting a side view and a top view. The carrier has a rounded top face surface with a dome height a of 0.88 mm each, a length b of 9.6 mm, an outer diameter c of 13.2 mm, a channel diameter d of 3.0 mm each, and a distance e between the channel centers of 6.6 mm each.

[0167] To achieve the target BET surface area, each carrier was calcined at the specific temperatures indicated in Table 2. Table 2 shows the physical properties of carriers A to D. Table 3 shows the Ca, Mg, Si, Fe, K, Na, and Ti contents of carriers A to D.

[0168] Table 2

[0169]

[0170] *Determined by mercury porosimetry

[0171] Table 3

[0172]

[0173] Example 2 - Preparation of Catalyst Moldings

[0174] The catalyst moldings according to Table 6 below were prepared by impregnating supports A to D with a silver impregnation solution.

[0175] 2.1 Production of Silver Complex Solution

[0176] 689 kg of an aqueous ethylenediamine solution with an ethylenediamine content of 58 wt.-% was pumped into stirred reactor 1. Subsequently, the 58 wt.-% ethylenediamine solution was diluted with 140 kg of deionized water under stirring. Next, 24.5 kg of a 0.9 wt.-% KOH aqueous solution was added to form a KOH / ethylenediamine aqueous solution. Then, 300 kg of oxalic acid dihydrate (purity ≥ 99.6%) was gradually added to stirred reactor 1 (total addition time about 1 h). During the addition of oxalic acid dihydrate, the temperature was controlled in the range of 18 °C to 38 °C. After adding the last portion of oxalic acid dihydrate, the reaction mixture was stirred for the next 30 minutes at a temperature in the range of 25 °C to 30 °C to form an oxalic acid - ethylenediamine aqueous solution.

[0177] Next, 1052 kg of the resulting oxalic acid - ethylenediamine aqueous solution was transferred from stirred reactor 1 to stirred reactor 2. Then, 500 kg of silver oxide powder (Ag 2 O content ≥ 99.90%) was gradually added to stirred reactor 2 (total addition time about 1 h). During the addition of silver oxide, the temperature was controlled in the range of 18 °C to 38 °C. After adding the last portion of silver oxide, the reaction mixture was stirred for the next 60 minutes at a temperature in the range of 25 °C to 35 °C to form an aqueous silver complex solution or suspension. The solution or suspension was passed through a filtration unit to remove undissolved solids. The resulting silver complex solution had a density of 1.547 g / ml, a silver content of 29.9 wt.-%, and a potassium content of 90 ppmw.

[0178] 2.2 Preparation of Ag-Containing Intermediate

[0179] Place 145.6 g of support A into a 2 L glass flask. Attach the flask to a rotary evaporator that is set at a vacuum pressure of 80 mbar. The rotary evaporator system is set to rotate at 30 rpm. Add 108.0 g of the silver complex solution prepared according to Step 2.1 to support A under a vacuum pressure of 80 mbar over 15 min. After adding the silver complex solution, the rotary evaporator system continues to rotate under vacuum for an additional 15 min. Then place the impregnated support in the apparatus at room temperature (about 25 °C) and atmospheric pressure for 1 h and mix gently every 15 min.

[0180] Place the impregnated material on a mesh to form 1 to 2 layers (about 100 to 200 g per calcination run). Subject the mesh to a nitrogen gas flow of 23 Nm 3 / h, where the gas flow is preheated to a temperature of 305 °C. Heat the impregnated material to a temperature of 290 °C at a heating rate of about 30 K / min and then hold at 290 °C for 8 min to produce Ag-containing intermediate I-1 according to Table 4. Measure the temperature by placing three thermocouples 1 mm below the calcination mesh. Subsequently, cool the catalyst to ambient temperature by removing the intermediate catalyst body from the mesh using an industrial vacuum cleaner.

[0181] As indicated in Table 4, Ag-containing intermediates I-2 to I-5 are prepared similarly using supports A to D by adjusting the weight ratio of the support used to the Ag complex solution.

[0182] Table 4 (The Ag content is a value calculated based on the amounts of the support and Ag complex solution used and is reported as a weight percentage relative to the total weight of the catalyst)

[0183] Intermediate product Carrier Ag [wt.-%] I-1 A 18.15 I-2 A 18.75 I-3 B 18.75 I-4 C 18.75 I-5 D 17.71

[0184] 2.3. Preparation of the final catalyst

[0185] Place the amount of Ag-containing intermediate indicated in Table 5 into a 2 L glass flask. Attach the flask to a rotary evaporator that is set at a vacuum pressure of 80 mbar. The rotary evaporator system is set to rotate at 30 rpm. Mix the amount of silver complex solution prepared according to Step 2.1 listed in Table 5 with the amounts of promoter solution I, promoter solution II, and promoter solution III listed in Table 5.

[0186] Promoter solution I is obtained by dissolving lithium nitrate (FMC, 99.3%) and ammonium sulfate (Merck, 99.4%) in deionized (DI) water to achieve a target Li content of 2.85 wt.-% and a target S content of 0.182 wt.-%.

[0187] The promoter solution II is obtained by dissolving tungstic acid (HC Starck, 99.99%) in a mixture of DI water and cesium hydroxide in water (HC Starck, 50.42%), potassium hydroxide in water (BASF, 2.0%) and sodium hydroxide in water (BASF, 2.0%) to achieve the target Cs, W, K and Na contents listed in Table 5.

[0188] The promoter solution III is obtained by dissolving ammonium perrhenate (Buss & Buss Spezialmetalle GmbH, 99.9%) in 29 wt.-% aqueous ethylenediamine solution to achieve a target Re content of 10.0 wt.-%.

[0189] The impregnation solution containing the combination of the silver complex solution, promoter solutions I, II and III and the amount of DI water listed in Table 5 is stirred for 5 min. The combined impregnation solution is added to the amount of silver-containing intermediate prepared according to Step 2.2 listed in Table 4 under a vacuum pressure of 80 mbar over 15 min. After adding the combined impregnation solution, the rotary evaporator system continues to rotate under vacuum for another 15 min. Then the impregnated support is placed in the apparatus at room temperature (about 25 °C) and atmospheric pressure for 1 h and gently mixed every 15 min.

[0190] Table 5

[0191]

[0192]

[0193] The impregnated material is placed on a mesh to form 1 to 2 layers (about 100 to 250 g per calcination run). The mesh is subjected to a nitrogen gas flow of 23 Nm 3 / h (oxygen content: < 20 ppm), where the gas flow is preheated to a temperature of 305 °C. The impregnated material is heated to a temperature of 290 °C at a heating rate of about 30 K / min and then held at 290 °C for 7 min to produce the catalyst according to Table 6. The temperature is measured by placing three thermocouples 1 mm below the calcination mesh. Subsequently, the catalyst is cooled to ambient temperature by removing the catalyst body from the mesh using an industrial vacuum cleaner. All the catalysts shown in Table 6 contain lithium c in an amount of 67.7 mmol / kg Li and cesium c in an amount of 0.94 mmol / kg S .

[0194] Table 6 (Ag content is reported as weight percentage of the total catalyst, and the amounts of all other elements are reported as mmol / kg of the total catalyst)

[0195] Catalyst Carrier Ag* <![CDATA[c Re > <![CDATA[c W > <![CDATA[c Cs > <![CDATA[c Si > <![CDATA[IM K **]]> <![CDATA[c K ***]]> <![CDATA[IM Na **]]> <![CDATA[c Na ***]]> 1-1 A 28.1 7.09 3.43 7.90 2.56 2.15 2.15-2.33 0.0 1.25 <![CDATA[1-2 # > A 28.9 6.28 3.02 9.03 2.53 5.19 5.19-5.37 1.77 3.00 <![CDATA[1-3 # > A 28.9 6.28 3.70 9.03 2.53 5.24 5.24-5.42 1.77 3.00 <![CDATA[1-4 # > A 28.9 7.89 3.70 8.65 2.53 5.24 5.24-5.42 1.77 3.00 <![CDATA[1-5 # > A 28.9 7.89 3.02 9.03 2.53 3.89 3.89-4.07 0.89 2.12 1-6 B 28.9 7.09 3.43 7.15 <2.53 3.30 3.30-3.48 0.46 1.84 1-7 B 28.9 7.89 3.43 7.90 <2.53 3.30 3.30-3.48 0.46 1.84 1-8 B 28.9 6.28 3.43 6.40 <2.53 3.30 3.30-3.48 0.46 1.84 <![CDATA[1-9 # > B 28.9 6.28 3.43 7.90 <2.53 3.30 3.30-3.48 0.46 1.84 <![CDATA[1-10 # > B 28.9 7.89 3.43 6.40 <2.53 3.30 3.30-3.48 0.46 1.84 1-11 B 28.9 6.66 3.43 6.40 <2.53 5.17 5.17-5.35 0.0 1.39 1-12 B 28.9 6.66 3.43 6.40 <2.53 3.94 3.94-4.12 0.0 1.39 <![CDATA[1-13 # > B 28.9 7.89 3.43 7.90 <2.53 7.06 7.06-7.24 0.0 1.39 1-14 C 28.9 7.09 3.43 7.15 <2.53 3.30 3.30-3.48 0.0 1.39 1-15 C 28.9 7.09 3.43 7.15 <2.53 3.30 3.30-3.48 0.46 1.84 1-16 C 28.9 7.89 3.43 7.90 <2.53 3.30 3.30-3.48 0.0 1.39 1-17 C 28.9 6.28 3.43 6.40 <2.53 3.30 3.30-3.48 0.0 1.39 1-18 D 27.3 7.09 3.43 7.15 <2.59 3.17 3.17-3.35 0.0 1.42 1-19 D 27.3 7.89 3.43 7.90 <2.59 3.17 3.17-3.35 0.0 1.42 <![CDATA[1-20 # > D 27.3 6.28 3.43 6.40 <2.59 7.09 7.09-7.26 0.0 1.42 <![CDATA[1-21 # > D 27.3 6.28 3.43 7.90 <2.59 7.09 7.09-7.26 0.0 1.42 <![CDATA[1-22 # > D 27.3 7.89 3.43 6.40 <2.59 3.27 3.27-3.45 0.0 1.42

[0196] *The values of Ag and all promoters are calculated values # Comparative example

[0197] **IMP K and IMP Na should be understood to mean the amounts of potassium and sodium added during impregnation and do not include the amounts of potassium and sodium contained in the alumina support respectively before impregnation

[0198] ***c K and c Na should be understood to mean respectively the total amounts of potassium and sodium in the catalyst. The amount of potassium derived from the support is in the range of 0 to 0.183 mmol / kg relative to the total weight of the catalyst

[0199] Example 3 - Catalyst testing

[0200] The epoxidation reaction was carried out in a vertically placed test reactor constructed of stainless steel with an inner diameter of 6 mm and a length of 2.2 m. The reactor was heated at a specified temperature using hot oil contained in a heating jacket. All temperatures in Table 7 below refer to the temperature of the hot oil. The reactor was filled with 9 g of inert talc balls (0.8 to 1.1 mm), 27.0 g of crushed catalyst with a desired particle size screened to 1.12 to 1.4 mm was loaded on the inert talc balls, and another 29 g of inert talc balls (0.8 - 1.1 mm) was loaded on the crushed catalyst. The inlet gas was introduced into the top of the reactor in a "once-through" operation mode

[0201] The catalyst was loaded into the reactor at a reactor temperature of 90 °C under a nitrogen flow rate of 130 NL / h at an absolute pressure of 1.5 mbar. Then, the reactor temperature was ramped up to 210 °C at a heating rate of 50 K / h, and the catalyst was maintained under these conditions for 15 h. Subsequently, the nitrogen flow was replaced by a flow of 114 NL / h methane and 1.5 NL / h CO 2 The reactor was pressurized to 16 bar absolute pressure. Subsequently, 30.4 NL / h of ethylene and a mixture of 0.8 NL / h of 500 ppm vinyl chloride in methane were added. Then, oxygen was gradually introduced to reach a final flow rate of 6.1 NL / h. At this time, the inlet composition was adjusted to consist of 20 vol.-% ethylene, 4 vol.-% oxygen, 1 vol.-% carbon dioxide, and 2.5 parts per million by volume (ppmv) of vinyl chloride (EC), with methane as the balance and a total gas flow rate of 152.7 NL / h

[0202] The reactor temperature was ramped up to 225 °C at a heating rate of 5 K / h and thereafter to 240 °C at a heating rate of 2.5 K / h. The catalyst was held under these conditions for 135 h. Thereafter, the EC concentration was reduced to 2.2 ppmv and the temperature was reduced to 225 °C. Subsequently, the inlet gas composition was gradually changed to 35 vol.-% ethylene, 7 vol.-% oxygen, 1 vol.-% carbon dioxide, with methane serving as the balance and the total gas flow rate being 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 the selectivity. The results of the catalyst tests are summarized in Table 7.

[0203] Table 7: Results of the catalyst tests.

[0204]

[0205]

[0206] # Comparative example § Running time: Determined from the time point of oxygen introduction

[0207] *The target EO outlet of 3.05% could not be achieved **“-” = not determined

[0208] Obviously, P A -value catalysts within a specific range showed higher selectivity than the comparative catalyst after 11 days and 25 days. These findings are depicted in Figure 2 and 3 in.

[0209] In addition, it is evident that P B -value catalysts within a specific range showed higher stability of ethylene oxide selectivity than catalysts outside this range, as is clearly seen from the value of ΔS 28-25 (i.e., the difference in selectivity after 28 days of operation and after 25 days of operation). These findings are depicted in Figure 4 and 5 in.

Claims

1. An epoxidation catalyst comprising silver, cesium, rhenium and tungsten deposited on a low-silica alpha-alumina support, the low-silica alpha-alumina support comprising at least 50 wt.-% alpha-alumina and at most 8.9 mmol of silicon per kg of support c S-Si , The catalyst further contains potassium and optionally sodium, wherein the catalyst comprises - 25 wt.-% to 50 wt.-% of silver relative to the weight of the catalyst, - cesium c in an amount of at least 6.0 mmol per kg of catalyst Cs , - Rhenium c in an amount of at least 6.0 mmol per kg of catalyst Re , - tungsten c in an amount of at least 3.0 mmol per kg of catalyst W , - Potassium c in an amount of at least 3.0 mmol per kg of catalyst K , and - sodium c in an amount of at most 4.0 mmol per kg of catalyst Na ; and Among which P A value in the range of 0.62 to 0.76, preferably 0.62 to 0.72, more preferably 0.64 to 0.70; The elemental composition of the catalyst support and the catalyst is determined by elemental analysis via inductively coupled plasma optical emission spectrometry.

2. The catalyst according to claim 1, wherein, P B value in the range of 0.62 to 0.94, preferably 0.63 to 0.92, more preferably 0.64 to 0.

90.

3. The catalyst according to any one of the preceding claims, which comprises cesium in an amount of from 6.0 to 9.0 mmol per kg of catalyst, preferably from 6.0 to 8.5 mmol per kg of catalyst Cs .

4. The catalyst according to any one of the preceding claims, which comprises rhenium in an amount of 6.0 to 9.0 mmol, preferably 6.0 to 8.0 mmol, per kg of catalyst Re .

5. The catalyst according to any one of the preceding claims, which comprises tungsten in an amount of from 3.0 to 5.0 mmol, preferably from 3.0 to 4.0 mmol, per kg of catalyst c W .

6. The catalyst according to any one of the preceding claims, which comprises potassium in an amount of 3.0 to 6.0 mmol per kg of catalyst, preferably 3.0 to 5.0 mmol per kg of catalyst, more preferably 3.0 to 4.5 mmol per kg of catalyst K .

7. The catalyst according to any one of the preceding claims, which comprises sodium in an amount of at most 3.0 mmol per kg of catalyst, preferably 0.5 to 2.2 mmol per kg of catalyst Na .

8. The catalyst according to any one of the preceding claims, wherein, the alumina support contains at least 80 wt.-% alpha-alumina.

9. The catalyst according to any one of the preceding claims, wherein, the alpha-alumina support is a tableted alpha-alumina support.

10. The catalyst according to any one of the preceding claims, wherein, The alpha-alumina support has a BET surface area of 0.5 to 3.0 m 2 / g, preferably 1.0 to 2.5 m 2 / g, more preferably 1.2 m 2 / g to 2.0 m 2 / g.

11. The catalyst according to any one of the preceding claims, wherein, the catalyst has a total Hg pore volume of 0.2 to 1.0 mL / g, preferably 0.3 to 0.8 mL / g, as determined by mercury porosimetry.

12. A method for preparing an epoxidation catalyst according to any one of claims 1 to 11, the method comprising i) impregnating a low-silica alpha-alumina support with a silver impregnation solution; and ii) subjecting the impregnated refractory support to a calcination process; wherein steps i) and ii) are optionally repeated, and at least one silver impregnation solution contains rhenium, tungsten, cesium, potassium and optionally sodium.

13. The method according to claim 12, wherein, The carrier contains silicon c in an amount of at most 5.4 mmol per kg of the carrier, preferably at most 4.0 mmol per kg of the carrier S-Si .

14. The method according to claim 12 or 13, wherein, the support contains - potassium c in an amount of at most 3.0 mmol per kg of carrier, preferably at most 2.5 mmol per kg of carrier, more preferably at most 2.0 mmol per kg of carrier, and most preferably at most 1.3 mmol per kg of carrier S-K , and - Sodium c in an amount of at most 4.0 mmol per kg of carrier, preferably 0.67 to 3.0 mmol per kg of carrier, more preferably 1.0 to 2.0 mmol per kg of carrier S-Na .

15. A method for producing ethylene oxide by gas-phase oxidation of ethylene, the method comprising reacting ethylene and oxygen in the presence of an epoxidation catalyst according to any one of claims 1 to 11.

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