Blended catalyst mix for epoxidation

Abstract

A blended catalyst mix comprising two populations of epoxidation catalyst particles, wherein a first population catalyst is comprised in an amount m1 and comprises silver deposited on a first support at a silver loading cAg-1 of at most 19 wt.-%, and a second population catalyst is comprised in an amount m2 and comprises silver deposited on a second support at a silver loading cAg-2 of at least 25 wt.-%. The sum of m1 and m2, relative to the total weight of the blended catalyst mix, is at least 80 wt.-%. Further provided is an epoxidation reactor comprising a bed of the blended catalyst mix, a process for preparing the blended catalyst mix, and a process for producing ethylene oxide. The blended catalyst mix shows increased selectivity at equivalent selectivity stability and activity stability compared to the second population catalyst on its own, while also exhibiting improved activity stability compared to the first population catalyst on its own.

Description

[0001] BLENDED CATALYST MIX FOR EPOXIDATION

[0002] The present invention relates to a blended catalyst mix, a process for preparing the catalyst mix, a reactor comprising a bed of the blended catalyst mix, and a process for producing ethylene oxide.

[0003] Ethylene oxide is produced in large volumes and is primarily used as an intermediate in the production of several industrial chemicals. For the industrial oxidation of ethylene to ethylene oxide, heterogeneous catalysts comprising metallic silver are used. Catalyst performance may be characterized, e.g., by selectivity, activity and longevity of catalyst activity. Selectivity is the molar fraction of the converted olefin yielding the desired olefin oxide. Even small improvements in, e.g., selectivity and the maintenance of selectivity over longer time yield huge dividends in terms of process efficiency.

[0004] Suitable epoxidation catalysts are generally obtained by depositing metallic silver on a support. Highly selective silver-based epoxidation catalysts ("high selectivity catalysts”) have been developed, which extend the start-of-run (SOR) carbon-based selectivity to a value beyond 85.7%. Such high selectivity catalysts comprise, in addition to silver as the active component, promoting species for improving the catalytic properties of the catalyst, as described in, e.g., US 4,766,105, WO 2004 / 089539, WO 2008 / 141027, WO 2012 / 140613 and WO 2012 / 140614.

[0005] High selectivity catalysts typically comprise silver in relatively low amounts well below 20 wt.-% and may be prepared by single impregnation of carriers with low BET surface areas of less than 1.5 m2 / g. Such high selectivity catalysts are typically provided for customers operating ethylene oxide plants at work rates below 220 kg of ethylene oxide per m3of catalyst per hour, such as below 200 kg or below 180 kg of ethylene oxide per m3of catalyst per hour. While exhibiting excellent SOR-selectivity, this catalyst family demonstrates low SOR-activity. Such catalysts are prompt to fast deactivation and quick selectivity declines, in particular when being subjected to high work rates conditions, thus requiring a frequent catalyst exchange.

[0006] Moreover, silver-based epoxidation catalysts have been developed which typically show a lower initial selectivity than high selectivity catalysts, but which exhibit improved selectivity stability, higher initial activity and thus longer life-times ("high performance catalysts”). The schematic difference in long-term performances of high selectivity and high performance catalysts is illustrated, e.g., in Figure 1 of a White Paper of Shell Global Solutions by van Milligen et al., entitled "Enhancements in Ethylene Oxide I Ethylene Glycol Manufacturing Technology” (2016).

[0007] High performance catalysts generally comprise more than 25 wt.-% of silver and may be obtained by double impregnation of carriers which typically exhibit BET surface areas above 1.5 m2 / g. The high silver loading permits the application of less stringent conditions in the manufacturing ethylene oxide, in particular lower temperature, for the achievement of a given work rate, along with the achievement of an improved selectivity and catalyst life, in particular in terms of activity stability and selectivity stability.

[0008] High performance catalysts are typically provided for customers operating ethylene oxide plants at work rates above 240 kg of ethylene oxide per m3of catalyst per hour, such as work rates above 260 kg or above 280 kg of ethylene oxide per m3of catalyst per hour. In contrast, operation of such catalysts at low work rate conditions such as those used for high selectivity catalysts can be challenging, as low work rates with high initial catalyst activity require very low operation temperatures, resulting in decreased performance over a significant initial period which may extend to several months. In order to increase the operating temperature so as to achieve a more stable plant operation, it has been proposed to use the catalyst under sub-optimal feed compositions, as proposed, e.g., in WO 2012 / 149098. In comparison to high selectivity catalysts, the production process of high performance EO catalysts is more complex and more expensive. Examples of high performance catalysts are described, e.g., in WO 2019 / 154832, WO 2022 / 161924, WO 2024 / 079247.

[0009] There is a demand for cost-efficient ethylene oxide catalysts which can be operated at increased work rates in comparison to high selectivity catalysts. Desirably, the catalysts are operated at lower initial temperatures than high selectivity catalysts but at higher initial temperatures than high performance catalysts, and provide higher initial selectivity than high performance catalysts.

[0010] US 8,580,982 describes a process for preparing ethylene oxide by reaction of ethylene with oxygen in the presence of at least one silver-comprising catalyst, wherein the reaction takes place in a reactor which has a catalyst packed bed having at least two zones (I) and (ii) and the silver content of the catalyst in zone (I) is lower than the silver content of the catalyst in zone (II).

[0011] WO 2018 / 017453 describes a method for producing ethylene oxide by contacting one or more feed components with an ethylene oxide catalyst bed comprising an upstream ethylene oxide catalyst having a first cesium concentration and a downstream ethylene oxide catalyst having a second cesium concentration.

[0012] The present invention provides a blended catalyst mix comprising two populations of epoxidation catalyst particles, wherein a first population catalyst comprises silver deposited on a first support at a silver loading CAg-i of at most 19 wt.-%, and a second population catalyst comprises silver deposited on a second support at a silver loading CA9-2 of at least 25 wt.-%.

[0013] In particular, the present invention provides a blended catalyst mix comprising two populations of epoxidation catalyst particles, wherein a first population catalyst is comprised in an amount mi and comprises silver deposited on a first support at a silver loading CA9-I of at most 19 wt.-%, and a second population catalyst is comprised in an amount m2 and comprises silver deposited on a second support at a silver loading CA9-2 of at least 25 wt.-%, and the sum of mi and m2, relative to the total weight of the blended catalyst mix, is at least 80 wt.-%.

[0014] It was found that the blended catalyst mix shows increased selectivity at equivalent selectivity stability and activity stability compared to the second population catalyst on its own. Moreover, the blended catalyst mix was found to exhibit improved activity stability compared to the first population catalyst. Moreover surprisingly, it was found that the blended catalyst mix performance does not suffer from the fact that two significantly different populations of silver-based catalyst are subjected to the same reaction conditions, rather than being individually optimized.

[0015] The blended catalyst mix comprises two populations of epoxidation catalysts. The two populations are physically blended rather than placed in layers in the reactor. As used herein, the term "physically blended” and variations thereof refer to a process or composition wherein discrete particles of the first population catalyst are mixed with discrete particles of the second population catalyst. The first population catalyst comprises silver deposited on a first support at a silver loading CA9-I of at most 19 wt.-%, based on the weight of the catalyst. In one embodiment, the first population catalyst comprises silver deposited on the first support at a silver loading CA9-I of at most 18 wt.-%, preferably at most 17 wt.-%, more preferably at most 16 wt.-%, based on the weight of the catalyst. The first population catalyst preferably comprises silver deposited on the first support at a silver loading CA9-I of at least 8 wt.-%, based on the weight of the catalyst. In one embodiment, the first population catalyst comprises silver deposited on the first support at a silver loading CA9-I of at least 10 wt.-%, preferably at least 12 wt.-%, based on the weight of the catalyst.

[0016] The second population catalyst comprises silver deposited on a second support at a silver loading CA9-2 of at least 25 wt.-%, based on the weight of the catalyst. In one embodiment, the second population catalyst comprises silver deposited on the second support at a silver loading CA9-2 of at least 26 wt.-%, preferably at least 27 wt.-%, more preferably at least 28 wt.-%, based on the weight of the catalyst. The second population catalyst preferably comprises silver deposited on the second support at a silver loading CA9-2 of at most 50 wt.-%, based on the weight of the catalyst. In one embodiment, the second population catalyst comprises silver deposited on the first second at a silver loading CA9-2 of at most 45 wt.-%, preferably at most 40 wt.-%, more preferably at most 36 wt.-%, based on the weight of the catalyst.

[0017] In one embodiment, the averaged silver loading calculated according to formula (1) is 20 to 24 wt.-%:

[0018] Amounts mi and m2 are by weight. In formula (1), amounts mi and m2 are expressed in the same unit of mass, e.g., both mi and m2 are expressed in kilogram or both mi and m2 are expressed in gram. In one embodiment, the averaged silver loading calculated according to formula (1) is 20.5 to 23.5 wt.-%, in particular 21 .0 to 23.0 wt.-%.

[0019] The sum of mi and m2, relative to the total weight of the blended catalyst mix, is preferably at least 85 wt.-%, more preferably at least 90 wt.-%, such as at least 95 wt.-%. In one embodiment, the blended catalyst mix consists of the first population catalyst and second population catalyst. In this embodiment, the sum of mi and m2, relative to the total weight of the blended catalyst mix, is 100 wt.-%.

[0020] The ratio of mi to m2 may vary depending on the desired averaged silver loading. In one embodiment, the ratio of r to m2 is in the range of 1 :10 to 10: 1, preferably 7:1 to 1 :7, more preferably 5: 1 to 1 :5 and most preferably 3: 1 to 1 :3.

[0021] The first support and / or the second support may be characterized by specific chemical compositions, physical properties and geometric configuration or shape.

[0022] In one embodiment, the first support and / or the second support is an alumina support. In a preferred embodiment, the first support and the second support are each an alumina support. The alumina support typically comprises a high proportion of alumina, i.e. AI2O3, and in particular alphaalumina, for example at least 50 wt.-%, 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.-%, based on the total weight of the support. Besides alumina, the support may comprise other components, for example binders such as silicates, or other refractory oxides such as zirconia or titania.

[0023] In one embodiment, the first support and the second support are each an alumina support comprising at least 80 wt.-% alpha-alumina, or at least 90 wt.-%, preferably at least 95 wt.-%, most preferably at least 97.5 wt.-% or at least 99 wt.-%, based on the total weight of the support.

[0024] The support may comprise trace amounts of further elements, such as sodium, potassium, iron, silica, magnesium, calcium, zirconium in an amount of 20 to 200 mmol / kg, based on the total weight of the support.

[0025] The supports are typically porous supports and preferably have a water absorption in the range of 0.30 to 1 .00 mL / g (mL of water / gram of support). Preferably, the first support and the second support have different water absorptions. The water absorption of the first support for the first population catalyst is preferably in the range of 0.30 to 0.60 mL / g, more preferably 0.35 to 0.55 mL / g, most preferably 0.40 to 0.50 mL / g. The water absorption of the second support is preferably in the range of 0.40 to 1 .00 mL / g, more preferably 0.45 to 0.90 mL / g, most preferably 0.50 to 0.80 mL / g. Water absorption refers to vacuum cold water uptake measured at a vacuum of 80 mbar absolute.

[0026] Vacuum cold water uptake is determined by placing about 100 g of support ("initial support weight”) in a rotating flask, covering the support with deionized water, and rotating the rotary evaporator for 5 min at about 30 rpm. Subsequently, a vacuum of 80 mbar is applied for 3 min, the water and the support are transferred into a glass funnel, and the support is kept in the funnel for about 5 min with occasional shaking in order to ensure that adhering water runs down the funnel. The support is weighed ("final support weight”). The water absorption is calculated by subtracting the initial support weight from the final support weight and then dividing this difference by the initial support weight.

[0027] The supports generally have a total Hg pore volume in the range of 0.30 to 1.00 mL / g, as determined by mercury porosimetry. Preferably, the first support and the second support have different total Hg pore volumes. The total Hg pore volume of the first support is preferably in the range of 0.30 to 0.60 mL / g, more preferably 0.35 to 0.55 mL / g, most preferably 0.40 to 0.50 mL / g. The total Hg pore volume of the second support is preferably in the range of 0.40 to 1.00 mL / g, most preferably 0.45 to 0.90 mL / g, in particular in the range of 0.50 to 0.80 mL / g.

[0028] Mercury porosimetry may be performed using a Micrometrics AutoPore IV 9500 mercury porosimeter (140 degrees contact angle, 485 dynes / cm Hg surface tension, 60000 psia max head pressure). The Hg porosity is determined according to DIN 66133 herein, unless stated otherwise. It is believed that a Hg pore volume in this range allows for a favorable duration of exposure of the obtained ethylene oxide to the catalyst.

[0029] In one embodiment, the BET surface area of the first support is less than 1.5 m2 / g, preferably less than 1 .4 m2 / g, more preferably less than 1 .3 m2 / g. For example, the BET surface area of the first support may be in the range of 0.4 to 1.3 m2 / g, preferably 0.5 to 1.2 m2 / g, more preferably 0.6 to 1.1 m2 / g. In one embodiment, the BET surface area of the second support is at least 1.5 m2 / g, preferably at least 1.6 m2 / g, more preferably at least 1.7 m2 / g. For example, the BET surface area of the second support may be in the range of 1.5 to 10 m2 / g, preferably 1.6 to 5.0 m2 / g, or 1.7 to 3.0 m2 / g.

[0030] The BET method is a standard, well-known method and widely used method in surface science for the measurements of surface areas of solids by physical adsorption of gas molecules. The BET surface is determined according to DIN ISO 9277 herein, unless stated otherwise.

[0031] In one embodiment, the first support and the second support comprise individual shaped bodies, wherein the individual shaped bodies of the first support and the second support have the same shape or different shapes.

[0032] The size and shape of the individual shaped bodies and thus of the catalyst is selected to allow a suitable packing of the shaped bodies in a reactor tube. In general, the support is comprised of individual bodies having a maximum extension in the range of 3 to 20 mm, such as 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 outer circumference of the support.

[0033] The shape of the first and second supports is not especially limited, and may be in any technically feasible form, depending, e.g., on the shaping process. For example, the first and / or second support may be a solid extrudate or a hollow extrudate, such as a hollow cylinder, for example a ring. In another embodiment, the first and / or second support may be characterized by a cylinder shape with multiple passageways extending from a first face side surface to a second face side surface, such as a 5-hole cylinder or a 7-hole cylinder, a wagon wheel shape, such as a pentaring, or a multilobe shape.

[0034] In a cylinder shape with multiple passageways extending from a first face side surface to a second face side surface, the passageways are typically arranged essentially equidistantly to each other. In one embodiment, multiple passageways are arranged essentially equidistantly around a central passageway. In one embodiment, the passageways have an essentially circular cross-section.

[0035] A wagon wheel shape, which is a hollow cylinder having multiple vanes which extend from the center of the axis of rotation to the cylindrical wall. For instance, a wagon wheel shape in the form of a pentaring is a hollow cylinder having five vanes which extend from the center of the axis of rotation to the cylindrical wall.

[0036] A multilobe shape is meant to denote a cylinder structure which has a plurality of void spaces, e.g., grooves or furrows, running in the cylinder periphery along the cylinder height. Generally, the void spaces are arranged essentially equidistantly around the circumference of the cylinder. A multilobe shape may comprise passageways extending from a first face side surface to a second face side surface. The passageways are typically arranged essentially equidistantly to each other. In one embodiment, multiple outer passageways, each of which is preferably assigned to one lobe, are arranged equidistantly around a central passageway.

[0037] Preferably, the first and / or second support is in the shape of a solid extrudate, such as pellets or cylinders, or a hollow extrudate, such as a hollow cylinder, for example a ring. Alternatively, the support may be shaped by tableting. In one embodiment, the first support is in the shape of a hollow cylinder such as a ring. In one embodiment, the second support has a cylinder shape with multiple passageways, a wagon wheel shape, or a multilobe shape. In one embodiment, the first support is in the shape of a hollow cylinder such as a ring, and the second support has cylinder shape with multiple passageways, a wagon wheel shape, or a multilobe shape.

[0038] Silver is deposited on the support by contacting it with a silver solution formed by dissolving a silver salt, or silver compound, or silver complex in a suitable solvent.

[0039] Any silver impregnation solution suitable for impregnating a refractory support known in the art can be used. Silver impregnation solutions typically contain a silver carboxylate, such as silver oxalate, or a combination of a silver carboxylate and oxalic acid, in the presence of an aminic complexing agent like a Ci-Cio-alkylenediamine, in particular ethylenediamine. Suitable impregnation solutions are described in EP 0 716 884, EP 1 115 486, EP 1 613 428, US 4,731 ,350, WO 2004 / 094055 , WO 2009 / 029419, WO 2015 / 095508, US 4,356,312, US 5, 187,140, US 4,908,343, US 5,504,053, WO 2014 / 105770 and WO 2019 / 154863.

[0040] During subsequent heat treatment, liquid components of the silver impregnation solution evaporate, causing a silver compound comprising silver ions to precipitate from the solution and be deposited onto the porous support. At least part of the deposited silver ions is subsequently converted to metallic silver upon further heating.

[0041] The first population catalyst and / or the second population catalyst may comprise promoters. The one or more promoters can be deposited on the carrier either prior to, coincidentally with, or subsequent to the deposition of the silver, but, preferably, the one or more promoters are deposited on the carrier coincidentally or simultaneously with the silver. When the catalyst comprises silver, rhenium and a co-promoter for rhenium, it may be advantageous to deposit the co-promoter prior to or simultaneous with the deposition of silver, and to deposit rhenium after at least a portion of the silver has been deposited.

[0042] For the preparation of the first population catalyst, the contacting or impregnation is preferably done in a single impregnation step, whereby the silver is deposited onto the carrier so as to provide a silver loading CAg-i of at most 19 wt.-%.

[0043] For the preparation of the second population catalyst, a substantially higher silver loading CA9-2 of at least 25 wt.-% is deposited onto the carrier, and the silver is preferably deposited in more than one impregnation step, for example in two, three or four impregnation steps.

[0044] Hence, in an embodiment the present invention provides a process for preparing a blended catalyst mix as defined above, comprising obtaining a first population catalyst by steps I) and II):

[0045] I) impregnating a first support with a first silver impregnation solution in a single impregnation step; and

[0046] II) subjecting the impregnated first support to a calcination process; obtaining a second population catalyst by steps ill) to vi): ill) impregnating a second support with a second silver impregnation solution; iv) subjecting the impregnated second support to a calcination process to obtain an intermediate catalyst; v) impregnating the intermediate catalyst with a third silver impregnation solution; vi) subjecting the impregnated intermediate catalyst to a calcination process; wherein steps ill) and iv) are optionally repeated; and vii) physically blending the first epoxidation catalyst and the second epoxidation catalyst.

[0047] It is understood that the intermediate product obtained after step iv) comprises a part of the total amount of target Ag and I or promoter concentrations. The intermediate product is then impregnated with the third silver impregnation solution and calcined to yield the target Ag and I or promoter concentrations.

[0048] It is understood that each of the first, second and third silver impregnation solutions may have the same composition or differ from one or both of the other silver impregnation solutions. In one embodiment, the second silver impregnation solution and the third silver impregnation solution have the same composition. Preferably, the second silver impregnation solution and the third silver impregnation solution differ in composition.

[0049] Suitable promoters include rare earth metals, magnesium, rhenium and alkali metals (lithium, sodium, potassium, rubidium and cesium), or compounds thereof, and, optionally, one or more co-promoters, such as, for example, sulfur, molybdenum, tungsten and chromium, or compounds thereof. Among the promoter components that can be incorporated, rhenium and the alkali metals, in particular, the combination of light and higher alkali metals, such as a combination of lithium with potassium, rubidium and cesium, are preferred. Most preferred among the higher alkali metals is cesium, which may be most preferably used in a mixture together with for example potassium and / or lithium. The co-promoters for use in combination with rhenium can include one or more of sulfur, molybdenum, tungsten, and chromium.

[0050] Promoting amounts of alkali metal or mixtures of alkali metal can be deposited on a carrier using a suitable solution. Alkali metals are generally used as compounds of the alkali metals dissolved in a suitable solvent for impregnation purposes. The carrier may be impregnated with a solution of the alkali metal compound(s) before, during or after impregnation of the silver in a suitable form has taken place. An alkali metal promoter may even be deposited on the carrier after the silver component has been reduced to metallic silver.

[0051] The promoting amount of alkali metal utilized will depend on several variables, such as, for example, the surface area and pore structure and surface chemical properties of the carrier used, the silver content of the catalyst and the particular ions and their amounts used in conjunction with the alkali metal cation.

[0052] The amount of alkali metal promoter present in the catalyst is generally in the range of from 100 to 3,000 ppm by weight of the metal relative to the weight of total catalyst. This amount includes alkali metals inherently comprised in the support, e.g., as trace amounts of sodium or potassium.

[0053] The carrier can also be impregnated with rhenium ions, salt(s), compound(s), and / or complex(es). This may be done at the same time that the alkali metal promoter is added, or before or later; or at the same time that the silver is added, or before or later. Rhenium, alkali metal, and silver may be in the same impregnation solution.

[0054] The preferred amount of rhenium, calculated as the metal, present on the support ranges from 100 to 3,000 ppm by weight relative to the weight of total catalyst. The references to the amount of rhenium present on the catalyst are expressed as the metal, irrespective of the form in which the rhenium is actually present. Preferably, the first population catalyst and the second population catalyst have different rhenium concentrations. Preferably, the first population catalyst has a rhenium concentration in the range of 50 to 550 ppm, more preferably 100 to 450 ppm, most preferably 200 to 400 ppm relative to the weight of first population catalyst. Preferably, the second population catalyst has a rhenium concentration in the range of 600 to 3,000 ppm, more preferably 700 to 2,000 ppm, most preferably 800 to 1 ,500 ppm relative to the weight of second population catalyst.

[0055] Examples of suitable rhenium compounds used in making the inventive catalyst include the rhenium salts such as rhenium halides, the rhenium oxyhalides, the rhenates, the perrhenates, the oxides and the acids of rhenium. A preferred compound for use in the impregnation solution is the perrhenate, preferably ammonium perrhenate. However, the alkali metal perrhenates, alkaline earth metal perrhenates, silver perrhenates, other perrhenates and rhenium heptoxide can also be suitably utilized.

[0056] Cesium may suitably be provided as cesium hydroxide. Rhenium and tungsten may suitably be provided as an oxyanion, for example, as a perrhenate or tungstate in salt or acid form.

[0057] At least one silver impregnation solution comprises rhenium, tungsten and cesium. It is especially preferred that at least the silver impregnation solution employed in the final impregnation step comprises rhenium, tungsten and cesium.

[0058] The heat treatment may also be referred to as a calcination process. Any calcination processes known in the art for this purpose can be used. Suitable examples of calcination processes 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, US 2014 / 0187417 A1, EP 1 893 331 A1 or WO 2012 / 140614 A1. Heat treatment can be carried out in a pass-through mode or with at least partial recycling of the calcination gas.

[0059] Heat treatment is usually carried out in a furnace. The type of furnace is not especially limited. For example, stationary circulating air furnaces, revolving cylindrical furnaces or conveyor furnaces may be used. In one embodiment, heat treatment constitutes directing a heated gas stream over the impregnated bodies. The duration of the heat treatment is generally in the range of 5 min to 20 h, preferably 5 min to 30 min.

[0060] The temperature of the heat treatment is generally in the range of 200 to 800 °C, preferably 210 to 650 °C, more preferably 220 to 500 °C, most preferably 220 to 350 °C. Preferably, the heating rate in the temperature range of 40 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 may be achieved by directing a heated gas over the impregnated refractory support or the impregnated intermediate catalyst at a high gas flow. A suitable flow rate for the gas may be in the range of, e.g., 1 to 1,000 Nm3 / h, 10 to 1 ,000 Nm3 / h, 15 to 500 Nm3 / h or 20 to 300 Nm3 / h per kg of impregnated bodies. In a continuous process, the term "kg of impregnated bodies” is understood to mean the amount of impregnated bodies (in kg / h) multiplied by the time (in hours) that the gas stream is directed over the impregnated bodies. It has been found that when the gas stream is directed over higher amounts of impregnated bodies, e.g., 15 to 150 kg of impregnated bodies, the flow rate may be chosen in the lower part of the above-described ranges, while achieving the desired effect.

[0061] Preferably, heating takes place in a step-wise manner. In step-wise heating, the impregnated bodies are placed on a moving belt that moves through a furnace with multiple heating zones, e.g., 2 to 8 or 2 to 5 heating zones. Heat treatment is preferably performed in an inert atmosphere, such as nitrogen, helium, or mixtures thereof, in particular in nitrogen.

[0062] In an aspect, the invention provides an epoxidation reactor comprising a bed of the blended catalyst mix.

[0063] Further provided is a process for producing ethylene oxide by gas-phase oxidation of ethylene, comprising reacting ethylene and oxygen in the presence of an epoxidation catalyst as described above.

[0064] The epoxidation can be carried out by all processes known to those skilled in the art. It is possible to use all reactors which can be used in the ethylene oxide production processes of the prior art; for example externally cooled shell-and-tube reactors (cf. Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, vol. A-10, pp. 117-135, 123-125, VCH-Verlagsgesellschaft, Weinheim 1987) or reactors having a loose catalyst bed and cooling tubes, for example the reactors described in DE 34 14 717 A1 , EP 0 082 609 A1 and EP 0 339 748 A2.

[0065] The epoxidation is preferably carried out in at least one tube reactor, preferably in a shell-and-tube reactor. On a commercial scale, ethylene epoxidation is preferably carried out in a multi-tube reactor that contains several thousand tubes. The catalyst is filled into the tubes, which are placed in a shell that is filled with a coolant. In commercial applications, the internal tube diameter is typically in the range of 20 to 40 mm (see, e.g., US 4,921 ,681 A) or more than 40 mm (see, e.g., WO 2006 / 102189 A1).

[0066] To prepare ethylene oxide from ethylene and oxygen, it is possible to carry out the reaction under conventional reaction conditions as described, e.g., in DE 25 21 906 A, EP 0 014 457 A2, DE 23 00 512 A1 , EP 0 172 565 A2, DE 24 54 972 A1 , EP 0 357 293 A1 , EP 0 266 015 A1 , EP 0 085 237 A1 , EP 0 082 609 A1 and EP 0 339 748 A2. Inert gases such as nitrogen or gases which are inert under the reaction conditions, e.g. steam, methane, and also optionally reaction moderators, for example halogenated hydrocarbons such as ethyl chloride, vinyl chloride or 1 ,2-dichloroethane (ethylene dichloride) can additionally be mixed into the reaction gas comprising ethylene and molecular oxygen.

[0067] The oxygen content of the reaction gas is advantageously in a range in which no explosive gas mixtures are present. A suitable composition of the reaction gas for preparing ethylene oxide can, for example, comprise an amount of ethylene in the range from 10 to 80% by volume, preferably from 20 to 60% by volume, more preferably from 25 to 50% by volume and particularly preferably in the range 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.

[0068] The reaction gas preferably comprises a chlorine-comprising reaction moderator such as ethyl chloride, vinyl chloride or 1,2-dichloroethane (ethylene dichloride) in an amount of from 0 to 15 ppm by volume, preferably in an amount of from 0.1 to 8 ppm by volume, based on the total volume of the reaction gas. The remainder of the reaction gas generally comprises hydrocarbons such as methane and also inert gases such as nitrogen. In addition, other materials such as steam, carbon dioxide or noble gases can also be comprised in the reaction gas.

[0069] The optimal concentration of reaction moderator depends on plant conditions and on the type of catalyst used. It has been considered necessary to individually optimize the moderator concentration for different types of catalysts depending on the specific composition. Selectivity may vary considerably with relatively small changes in moderator concentration. With the blended catalyst mix of the invention, the two populations of epoxidation catalyst particles are necessarily operated at the same moderator concentration. Preferably, the moderator concentration should be optimized for the blended catalyst mix of the invention, which that typically falls within the range of individually optimized moderator concentrations for the different types of catalysts used in the blend.

[0070] 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. Carbon dioxide concentration in the feed is preferably at most 3 vol.-%, more preferably less than 2 vol.-%, most preferably less than 1 vol .-%, relative to the total volume of the feed. An example of carbon dioxide removal equipment is provided in US 6,452,027 B1 .

[0071] The above-described constituents of the reaction mixture may optionally each have small amounts of impurities. Ethylene can, for example, be used in any degree of purity suitable for the gas-phase oxidation according to the invention. Suitable degrees of purity 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%. The impurities typically comprise, in particular, ethane, propane and / or propene.

[0072] The reaction or oxidation of ethylene to ethylene oxide is usually carried out at elevated catalyst temperatures. Preference is given to 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. The present invention therefore also provides a process as described above in which the oxidation is carried out at a catalyst temperature in the range 180 to 300 °C, preferably 200 to 280 °C. Catalyst temperature can be determined by thermocouples located inside the catalyst bed. As used herein, the catalyst temperature or the temperature of the catalyst bed is deemed to be the weight average temperature of the catalyst particles.

[0073] The reaction according to the invention (oxidation) is preferably carried out at pressures in the range of 5 to 30 bar. All pressures herein are absolute pressures, unless noted otherwise. The oxidation is more preferably carried out at a pressure in the range of 5 to 25 bar, such as 10 bar to 24 bar and in particular 14 bar to 23 bar. The present invention therefore also provides a process as described above in which the oxidation is carried out at a pressure in the range of 14 bar to 23 bar.

[0074] The physical characteristics of the shaped catalyst body, especially the BET surface area and the pore size distribution, may have a significant impact on the catalyst selectivity. This effect is especially pronounced when the catalyst is operated at very high work rates, i.e., high levels of olefin oxide production.

[0075] The process according to the invention is preferably carried out under conditions conducive to obtain a reaction mixture containing at least 1.6 vol.-% of ethylene oxide. In other words, the ethylene oxide outlet gas phase volume fraction (ethylene oxide gas phase volume fraction at the reactor outlet) is preferably at least 1.6 vol.-%. The ethylene oxide outlet volume fraction is more preferably in the range of 1.8 to 3.4 vol.-%, most preferably in the range of 2.0 to 3.0 vol.-%.

[0076] The oxidation is preferably carried out in a continuous process. If the reaction is carried out continuously, the GHSV (gas hourly space velocity) is, depending on the type of reactor chosen, for example on the size / cross-sectional area of the reactor, the shape and size of the catalyst, preferably in the range from 800 to 10,000 / h, preferably in the range from 2,000 to 8,000 / h, more preferably in the range from 2,500 to 6,000 / h, most preferably in the range from 4,500 to 5,500 / h, where the values indicated are based on the volume of the catalyst.

[0077] According to a further embodiment, the present invention is also directed to a process for preparing ethylene oxide (EO) by gas-phase oxidation of ethylene by means of oxygen as disclosed above, wherein the EO- space-time-yield measured is greater than 180 kgEo / (m3cath), preferably to an EO-space-time-yield of greater than 200 kgEo / (m3cath), such as greater than 220 kgEo / (m3cath), greater than 240 kgEo / (m3cath). Preferably the EO-space-time-yield measured is less than 350 kgEo / (m3cath), more preferably the EO-space-time-yield is less than 310 kgEo / (m3cath), most preferably the EO-space-time-yield is less than 290 kgEo / (m3cath).

[0078] The preparation of ethylene oxide from ethylene and oxygen can advantageously be carried out in 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 moderators and reintroduced into the reactor. The separation of the ethylene oxide from the product gas stream and its work-up can be carried out by customary methods of the prior art (cf. Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, vol. A-10, pp. 117-135, 123- 125, VCH-Verlagsgesellschaft, Weinheim 1987).

[0079] The invention is described in more detail by the subsequent examples. Examples

[0080] Method 1 : Analysis of the Total Amount of Ca-, Mg-, Si-, Fe-, K-, and Na-Contents in Alpha-Alumina Supports

[0081] 1A. Sample Preparation

[0082] Two aliquots of a sample (0.1 to 0.2 g) were weighed into microwave digestion vessels. Then, 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%) were added to each aliquot. The microwave digestion vessels were placed in a microwave digestion system, heated up to 230 °C and held at this temperature for 45 min.

[0083] After cooling down, the two obtained samples were each transferred into a volumetric flask and filled up to a volume of 50 mL with de-ionized water to obtain digested solutions ("replicates”). Blank samples were prepared by the same procedure.

[0084] 1 B. Measurement

[0085] The obtained digested solutions were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) using internal standard (Sc) and blank subtraction.

[0086] Instrument: Thermo ICAP Pro XP Duo

[0087] Wavelength: K 766.490 nm

[0088] Dilution: Direct measurement (no dilution)

[0089] Calibration: External

[0090] Integration time: 10 s / replicate

[0091] Replicates: 3

[0092] Plasma power: 1.20 kW

[0093] Pump speed: 10 rpm

[0094] Nebulizer: Conical 1 mL

[0095] Nebulizer gas: Ar, 0.70 L / min

[0096] The reported results were calculated from the mean of the two prepared replicates for each sample.

[0097] Method 2: Mercury Porosimetry

[0098] Mercury porosimetry was performed using a Micrometrics AutoPore IV 9500 mercury porosimeter (140 degrees contact angle, 485 dynes / cm Hg surface tension, 60,000 psia max head pressure). Mercury porosity was determined in accordance with DIN 66133. Method 3: BET Surface Area

[0099] The BET surface area was determined in accordance with DIN ISO 9277.

[0100] Method 4: Water Absorption

[0101] Water absorption refers to vacuum cold water uptake. Vacuum cold water uptake is determined by placing about 100 g of support ("initial support weight”) in a rotating flask, covering the support with deionized water, and rotating the rotary evaporator for 5 min at about 30 rpm. Subsequently, a vacuum of 80 mbar is applied for 3 min, the water and the support are transferred into a glass funnel, and the support is kept in the funnel for about 5 min with occasional shaking in order to ensure that adhering water runs down the funnel.

[0102] The support is weighed ("final support weight”). The water absorption is calculated by subtracting the initial support weight from the final support weight and then dividing this difference by the initial support weight.

[0103] Method 5: Packed Tube Density Dcat

[0104] The packed tube density Dcat was determined by filling an amount of x g of support bodies into a cylindrical glass tube with an inner diameter of 39.5 mm up to a marker marking an inner tube volume of y mL. The glass tube was placed on a weighing scale and the weight increase from the filled-in support was determined as x. The density in g / mL was calculated as (x / y) x 1000.

[0105] Supports

[0106] Support A was an alumina support (> 99 wt.-% alpha-alumina) with a BET surface area of 0.8 m2 / g and a total pore volume of 0.40 mL / g. Support A was in the shape of a ring having the dimensions 8.9 mm x 8.7 mm x 3.0 mm (outer diameter x height x wall thickness).

[0107] Support B was an alumina support (> 99 wt.-% alpha-alumina) with a BET surface area of 2.0 m2 / g and a total pore volume of 0.52 mL / g. Support B was in the shape of a pentaring (a wagon wheel shape, which is a hollow cylinder having five vanes which extend from the center of the axis of rotation to the cylindrical wall) having the dimensions 9.7 mm x 9.8 mm x 1.4 mm (outer diameter x height x wall thickness).

[0108] Both supports A and B had impurities of Na, K, Si, Fe, Ca, Mg in the range of 10 to 1000 ppmw each, relative to the weight of the respective support. Supports with these properties are state of the art supports well- known in the field and may be obtained from Exacer Catalyst Support, Saint-Gobain NorPro, Ceramtec and Noritake. Catalysts

[0109] Catalyst 1 was prepared in accordance with Example 3.3 of US 11 ,400,437 B2 by impregnating Support A with an impregnation solution containing Ag and Li, S, W, Re, Cs, K promoters and subsequent calcination to yield Catalyst 1 having the properties shown in Tables 1 and 2.

[0110] Catalyst 2 was prepared in accordance with Example 3 of EP 3 749 450 B1 by first impregnating Support B with an impregnation solution containing Ag and K, followed by calcination, and subsequently impregnating the obtained intermediate with a solution containing Ag and Li, S, W, Re, Cs, K promoters, followed by calcination, to yield Catalyst 2 having the properties shown in Tables 1 and 2.

[0111] Table 1 : Catalyst compositions (Ag contents are reported in percent by weight of total catalyst, promoter values are reported in mmol / kg of total catalyst).

[0112] Table 2: Physical Properties of Catalysts

[0113] Catalyst Testing

[0114] An epoxidation reaction was conducted in a vertically-placed test reactor constructed from stainless steel with an inner 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 in Table 3 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), onto which an amount of crushed catalyst screened to a desired particle size of 1.12 to 1.4 mm were packed, and thereon an additional 29 g of inert steatite balls (0.8 - 1.1 mm) were packed. The amount of crushed catalyst was calculated by the following equation mass [g] = Vcat-bed [mL] x Dcat[g / mL] wherein Vcat-bed was 31.1 mL and Dcat = (DcatixF-Volcati + Dcat2xF-Volcat2) 1 100, and wherein Dcati and Dcat2 are the packed tube densities of catalysts 1 and 2, respectively, as measured in a tube having a diameter of 39.5 mL; and F-Volcati and F-Volcat2 are volume fractions of Catalysts 1 and 2, respectively, in accordance with Table 3.

[0115] Catalyst 3 was obtained by gently mixing particles of Catalysts 1 and 2 in the mass proportions according to Table 3, prior to charging the obtained blended catalyst mix into the reactor.

[0116] An inlet gas was introduced to the top of the reactor in a "once-through” operation mode.

[0117] The catalysts were charged into the reactor at a reactor temperature of 90 °C under nitrogen flow of 130 NL / h at a pressure of 1 .5 bar absolute. Then, the reactor temperature was ramped up to 210 °C at a heating rate of 50 K / h and the catalysts were maintained under these conditions for 15 h. Subsequently, the nitrogen flow was substituted by a flow of 114 NL / h methane and 1 .5 NL / h CO2. The reactor was pressurized to 16 bar absolute. Subsequently, 30.4 NL / h ethylene and 0.8 NL / h of a mixture of 500 ppm ethyl chloride in methane were added. Then, oxygen was introduced stepwise to reach a final flow of 6.1 NL / h. At this point, the inlet composition consisted of 20 vol.-% ethylene, 4 vol.-% oxygen, 1 vol.-% carbon dioxide, and ethyl chloride (EC) moderation of 2.5 parts per million by volume (ppmv), with methane used as a balance at the total gas flow rate of 152.7 NL / h.

[0118] The reactor temperature was ramped up to 225 °C at a heating rate of 5 K / h, and afterwards to 240 °C at a heating rate of 2.5 K / h. The catalysts were maintained under these conditions for 135 hours. Afterwards, EC concentration was decreased to 2.2 ppmv, and the temperature was decreased to 225 °C. Subsequently, the inlet gas composition was gradually changed to 35 vol.-% ethylene, 7 vol.-% oxygen, 1 vol.-% carbon dioxide with methane used as a balance and a total gas flow rate of 147.8 NL / h. The temperature was adjusted to achieve an ethylene oxide (EC) concentration in the outlet gas of 3.05%. The EC concentration was adjusted to optimize the selectivity. The results of the catalyst tests are summarized in T able 3, wherein "Sei. at Cum(EO)" indicates the selectivity at a given cumulative ethylene oxide production and "Temp, at Cum(EO)" indicates the temperature at a given cumulative ethylene oxide production.

[0119] Table 3: Summary of Catalyst Tests

[0120] * comparative example

[0121] It is evident that Catalyst 3, which is a blended catalyst mix according to the invention, exhibits an ethylene oxide selectivity between that of Catalyst 1, a "pure" high selectivity catalyst, and Catalyst 2, a "pure" high performance catalyst, at initial state of operation, i.e. , at Cum(EO) of 200 t / m3(cat)). As the time on-stream progresses, Catalyst 3 reaches the ethylene oxide selectivity of Catalyst 1, and continues to display higher selectivity than Catalyst 2. Additionally, Catalyst 3 consistently exhibits significantly lower temperature than Catalyst 1, i.e., higher activity.

[0122] Furthermore, Catalyst 3 exhibits a much lower temperature deactivation rate compared to Catalyst 1, and a comparable temperature deactivation rate to Catalyst 2, as is evident from the ATemp. at Cum(EO) values. This demonstrates the high stability of the blended catalyst mix catalyst according to invention.

Claims

Claims1 . A blended catalyst mix comprising two populations of epoxidation catalyst particles, wherein a first population catalyst is comprised in an amount mi and comprises silver deposited on a first support at a silver loading CA9-I of at most 19 wt.-%, and a second population catalyst is comprised in an amount m2 and comprises silver deposited on a second support at a silver loading CA9-2 of at least 25 wt.-%, and the sum of mi and m2, relative to the total weight of the blended catalyst mix, is at least 80 wt.-%.

2. The blended catalyst mix according to claim 1, wherein the averaged silver loading calculated according to formula (1) is 20 to 24 wt.-%:

3. The blended catalyst mix according to claim 1 or 2, wherein the first support and / or the second support is an alumina support.

4. The blended catalyst mix according to claim 3, wherein the first support and the second support are each an alumina support comprising at least 80 wt.-% alpha-alumina.

5. The blended catalyst mix according to any one of the preceding claims, wherein the BET surface area of the first support is less than 1 .5 m2 / g.

6. The blended catalyst mix according to any one of the preceding claims, wherein the BET surface area of the second support is greater than 1 .5 m2 / g.

7. The blended catalyst mix according to any one of the preceding claims, wherein the Hg pore volume of the first support is in the range of 0.30 to 0.60 mL / g, and the Hg pore volume of the second support is in the range of 0.40 to 1 .00 mL / g, as determined by mercury porosimetry.

8. The blended catalyst mix according to any one of the preceding claims, wherein the first support and the second support comprise individual shaped bodies, wherein the individual shaped bodies of the first support and the second support have the same shape or different shapes.

9. The blended catalyst mix according to claim 8, wherein the first support is in the shape of a hollow cylinder such as a ring.

10. The blended catalyst mix according to claim 8, wherein the second support has a cylinder shape with multiple passageways, a wagon wheel shape, or a multilobe shape.11 . The blended catalyst mix according to any one of the preceding claims, wherein a first population catalyst comprises 50 to 550 ppmw of rhenium, based on the total weight of the catalyst, and the second population catalyst comprises 600 to 3000 ppmw of rhenium, based on the total weight of the catalyst.

12. An epoxidation reactor comprising a bed of the blended catalyst mix according to any one of the preceding claims.

13. A process for preparing a blended catalyst mix as defined in any one of claims 1 to 11, comprising obtaining a first population catalyst by steps i) and ii): i) impregnating a first support with a first silver impregnation solution in a single impregnation step; and ii) subjecting the impregnated first support to a calcination process; obtaining a second population catalyst by steps iii) to vi): iii) impregnating a second support with a second silver impregnation solution; iv) subjecting the impregnated second support to a calcination process to obtain an intermediate catalyst; v) impregnating the intermediate catalyst with a third silver impregnation solution; vi) subjecting the impregnated intermediate catalyst to a calcination process; wherein steps iii) and iv) are optionally repeated; and vii) physically blending the first population catalyst and the second population catalyst.

14. A process for producing ethylene oxide by gas-phase oxidation of ethylene, comprising reacting ethylene and oxygen in the presence of a blended catalyst mix according to any one of claims 1

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