Ethylene oxide high-selectivity catalyst adjusting process

Abstract

A conditioning process employing a high selectivity catalyst (HSC) during the initial stage (i.e., start-up) of the epoxidation process is provided. The HSC conditioning process of the present disclosure ensures that the heat released from a catalyst bed containing the HSC during a start-up operation is less than 2000 kJ / Kgcat.hr. HSC-containing catalyst beds that have been conditioned by the processes of the present disclosure exhibit improved performance (i.e., EO selectivity) and reduced hot spots.

Description

Technical Field

[0001] The present disclosure relates to the epoxidation of olefins, particularly ethylene, to olefin oxides, particularly ethylene oxide (EO), using a high selectivity catalyst (HSC). More specifically, the present disclosure relates to a conditioning process that can be used with an HSC during the initial stages (i.e., startup) of an epoxidation process. Background Art

[0002] The catalytic epoxidation of olefins to produce olefin oxides in the presence of silver-based catalysts is well known in the art. The selectivity of olefin oxides provided by conventional silver-based catalysts is very low. To a large extent, selectivity determines the economic attractiveness of the epoxidation process. For example, a one percent increase in the selectivity of the epoxidation process can significantly reduce the annual operating costs of a large olefin oxide plant.

[0003] As known to those skilled in the art, olefin oxides produced by epoxidation using silver-based catalysts can react with water, alcohols or amines to form 1,2-diols, 1,2-diol ethers, alkanolamines or other derivatives. For example, ethylene oxide can react with water to form ethylene glycol, which can be used as a component of antifreeze compounds, a solvent or a base material in the production of polyethylene terephthalate. Any improvement in the selectivity of the epoxidation process can also reduce the annual operating cost of the entire process for the production of these products.

[0004] High selectivity silver-based epoxidation catalysts have been developed that extend selectivity to over 90 mole %. Such high selectivity catalysts include a porous refractory support such as alpha alumina having a catalytic amount of silver on its surface and at least one promoter that improves catalyst performance in the epoxidation process.

[0005] For the production of ethylene oxide by the selective oxidation of gas phase ethylene, the use of alkali metals and transition metals as promoters for silver catalysts is well known; see, for example, U.S. Pat. Nos. 4,010,155, 4,012,425, 4,123,385, 4,066,575, 4,039,561, and 4,350,616. Highly selective catalysts containing, in addition to silver, selectivity enhancing promoters such as compounds in the form of rhenium, molybdenum, tungsten, nitrates or nitrites are discussed in U.S. Pat. Nos. 4,761,394 and 4,766,105. The catalyst may contain additional elements such as alkali metals as described in U.S. Pat. Nos. 3,962,136 and 4,010,115.

[0006] Over the past two decades, rhenium has been described as being effective in improving the selectivity of alkali metal-promoted silver-based catalysts supported on refractory porous supports; see, for example, U.S. Pat. Nos. 4,761,394 and 4,833,261. Further improvements in silver-based catalysts promoted with alkali metals and rhenium have been achieved by using sulfur, Mo, W, Cr, as disclosed in U.S. Pat. Nos. 4,766,105, 4,820,675, and 4,808,738.

[0007] When using a highly selective silver-based epoxidation catalyst as described above, a reaction modifier such as an organic halide may be added to the feed to further improve the selectivity of the process. The use of reaction modifiers is disclosed in, for example, EP0352850A1, US Pat. Nos. 4,761,394 and 4,766,105.

[0008] Despite all the progress made in developing HSCs, these catalysts, like their conventional counterparts, still require conditioning during the initial operation phase of the epoxidation process. To ensure optimal reactivity and high selectivity of the catalyst, the HSC needs to be conditioned. The conditioning process typically occurs during the start-up of the epoxidation reaction, i.e., before sufficient amounts of oxidized olefin product are obtained.

[0009] Start-up processes and thus conditioning of epoxidation catalysts are also described in the prior art. For example, U.S. Pat. No. 5,155,242 relates to the start-up of an epoxidation process wherein a non-HSC catalyst undergoes a pre-soak period in the presence of an organic halide at a temperature below the reactor operating temperature. U.S. Pat. No. 4,874,879 relates to the start-up of an epoxidation process wherein an HSC undergoes a pre-soak period in the presence of an organic halide at a temperature below the reactor operating temperature.

[0010] In addition to these disclosures, U.S. Patent No. 7,102,022 discloses another start-up process using HSC. According to this disclosure, the process comprises the steps of: keeping a catalyst bed comprising a silver-based high selectivity epoxidation catalyst or a catalyst precursor comprising silver in cationic form with a feed comprising oxygen at a temperature above 260° C. for a period of up to 150 hours, and subsequently reducing the temperature of the catalyst bed to a value of up to 260° C. Another such start-up process is disclosed in U.S. Patent Application Publication No. 2004 / 0049061A1, wherein a supported high selectivity epoxidation catalyst comprising silver in an amount of up to 0.17 g per square meter of support surface area is used. According to this publication, the process comprises contacting the catalyst or a catalyst precursor comprising silver in cationic form with a feed comprising oxygen at a catalyst temperature above 250° C. for a duration of up to 150 hours, and subsequently reducing the catalyst temperature to a value of up to 250° C.

[0011] Although various HSC conditioning processes are described in the prior art, there remains a need to provide improved conditioning processes that can be used with HSCs. Summary of the invention

[0012] The present disclosure provides a conditioning process for using a high selectivity catalyst (HSC) during the initial stages (i.e., startup) of an epoxidation process. The term "high selectivity catalyst or HSC" refers to a silver-based catalyst having a selectivity of greater than 85 mol%, typically greater than 87 mol%, and more typically greater than 90 mol% during normal ethylene oxide (EO) production. Such silver-based catalysts typically contain at least a promoting amount of rhenium and one or more other promoters as will be described herein. It is noteworthy that the HSC conditioning process of the present disclosure ensures that the heat released from the catalyst bed containing the HSC during startup operation is less than 2000 kJ / Kgcat.hr, preferably less than 1750 kJ / Kgcat.hr, and more preferably less than 1500 kJ / Kgcat.hr. The catalyst bed containing the HSC that has been conditioned by the process of the present disclosure exhibits improved performance (i.e., EO selectivity) during ethylene oxide production. Additionally, catalyst beds containing HSCs conditioned using the conditioning process of the present disclosure have reduced hot spots compared to catalyst beds containing HSCs conditioned using processes in which heat release rates are not controlled as described in the present disclosure.

[0013] In one aspect of the present disclosure, a HSC conditioning process for use during the initial startup of an epoxidation process is provided. In one embodiment, the HSC conditioning process of the present disclosure includes initiating an epoxidation reaction by reacting a feed gas composition comprising ethylene and oxygen in the presence of a catalyst bed comprising a highly selective silver-based ethylene oxide catalyst at a first temperature of about 180°C to about 210°C. After confirming that EO is produced from the initial feed, a moderator is added to the feed gas composition at a concentration of about 0.05 ppm to about 2 ppm. After confirming chloride breakthrough, the first temperature is increased to a second temperature of about 240°C to about 270°C over a period of about 6 hours to about 60 hours, and thereafter the second temperature is maintained for about 50 hours to about 150 hours. According to the present disclosure, during the process of increasing the first temperature to the second temperature and maintaining the second temperature, the heat release rate of the catalyst bed is controlled to be less than 2000 kJ / Kgcat.hr.

[0014] In the present disclosure, the heat release rate of the catalyst bed can be controlled by measuring oxygen consumption and EO selectivity during the startup process. In some embodiments, the heat release rate of the catalyst bed can be controlled by maintaining the oxygen conversion rate at less than about 70 mol%, more preferably less than 60 mol%, and even more preferably about 50 mol%.

[0015] In some embodiments, maintaining the oxygen conversion rate comprises controlling the ramp rate from the first temperature to the second temperature between 3° C. / hour and 5° C. / hour while increasing carbon dioxide in the feed gas composition stream.

[0016] In some embodiments, the heat release rate of the catalyst bed can be controlled by maintaining the selectivity of the high selectivity silver-based ethylene oxide catalyst at greater than or equal to 75 mol%, preferably greater than or equal to 80 mol%, and even more preferably greater than or equal to 85 mol%.

[0017] In a preferred embodiment, the heat release rate of the catalyst bed can be controlled by maintaining the oxygen conversion at about 50 mol % and by maintaining the selectivity of the high selectivity silver-based ethylene oxide catalyst bed at greater than or equal to 80 mol %. It should be noted that the oxygen conversion referred to in this disclosure refers to the oxygen consumption directly related to the heat release rate, rather than the oxygen conversion percentage.

[0018] In addition to the specific startup processes mentioned above, the present disclosure contemplates that embodiments in which the above-described controlled heat release rate of the HSC catalyst bed to a value of less than 2000 kJ / Kgcat.hr can be used for any startup process that includes initiating an epoxidation reaction using a feed gas composition of ethylene and oxygen, adding a modifier to the feed gas composition, and increasing ethylene oxide production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1A is a scanning microscope (SEM) image of a new HSC before performing the conditioning process of the present disclosure.

[0020] Figure 1B is after performing the conditioning process of the present disclosure, Figure 1A Scanning microscope (SEM) image of new HSCs shown in .

[0021] Figure 2A is a graph of selectivity (mol %) of HSC A versus reactor time (hours) using an uncontrolled startup process (not part of the present disclosure) and a controlled startup process (part of the present disclosure).

[0022] Figure 2B is a graph of temperature (° C.) versus reactor time (hours) for HSC A using an uncontrolled startup process (not part of the present disclosure) and a controlled startup process (part of the present disclosure).

[0023] Figure 2Cis a graph of heat release rate (kJ / Kgcat / hr) versus run time (hrs) for HSCA using an uncontrolled startup process (not disclosed herein) and a controlled startup process (disclosed herein); note that the heat release rate expressed in units of kJ / Kgcat / hr in the accompanying figure is equivalent to the heat release rate expressed in units of kJ / Kgcat.hr throughout the disclosure.

[0024] Figure 3A is a graph of selectivity (mol %) of HSC B versus reactor time (hours) using an uncontrolled startup process (not part of the present disclosure) and a controlled startup process (part of the present disclosure).

[0025] Figure 3B is a graph of temperature (° C.) versus reactor time (hours) for HSC B using an uncontrolled startup process (not part of the present disclosure) and a controlled startup process (part of the present disclosure).

[0026] Figure 3C is a graph of heat release rate (kJ / Kgcat / hr) versus run time (hrs) for HSCA using an uncontrolled startup process (not disclosed herein) and a controlled startup process (disclosed herein); note that the heat release rate expressed in units of kJ / Kgcat / hr in the accompanying figure is equivalent to the heat release rate expressed in units of kJ / Kgcat.hr throughout the disclosure. DETAILED DESCRIPTION

[0027] The present disclosure will now be described in more detail by reference to the following discussion. In the following discussion, many specific details are set forth, such as specific structures, parts, materials, sizes, processing steps and technologies, so as to provide an understanding of the various embodiments of the present disclosure. However, it will be appreciated by those of ordinary skill in the art that the various embodiments of the present disclosure can also be put into practice without these specific details. As used throughout the present disclosure, the term "about" generally represents a difference of no more than ±10%, ±5%, ±2%, ±1% or ±0.5% with a numeral. When a range is expressed as from a number to another number (e.g., 20 to 40) in the present disclosure, the present disclosure encompasses any numerical value (i.e., 22, 24, 26, 28.5, 31, 33.5, 35, 37.7, 39 or 40) within the range or any amount (e.g., 28.5-35) limited by any two values ​​within the range.

[0028] The terms used herein are only used for the purpose of describing specific embodiments and are not intended to limit the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to also include plural forms unless the context clearly indicates otherwise. It should also be understood that the terms "comprising" and / or "including" when used in the present disclosure specify the presence of stated features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0029] As described above, the present disclosure provides an HSC adjustment process used during the startup of the epoxidation process. The HSC adjustment process of the present disclosure ensures that the heat release rate from the catalyst bed containing HSC during the startup operation is less than 2000kJ / Kgcat.hr. In the present disclosure, the heat release rate of the catalyst bed is calculated by the oxygen conversion rate, the catalyst selectivity and the gas hourly space velocity of the reaction. Before discussing this HSC adjustment process in detail, a description of the HSC that can be used is provided. The HSC used in the present disclosure is any silver-based supported catalyst, and the selectivity achieved in the normal ethylene oxide production process is greater than 85 mol%, preferably greater than 87 mol%, and more preferably greater than 90 mol%. The HSC includes a carrier (i.e., a catalyst carrier). The carrier can be selected from a large number of solid refractory carriers that can be porous. The carrier can include materials such as alpha-alumina, charcoal, pumice, magnesium oxide, zirconium oxide, titanium dioxide, diatomaceous earth, bleaching earth, silicon carbide, silicon dioxide, silicon carbide, clay, artificial zeolite, natural zeolite, silicon dioxide and / or titanium dioxide, ceramics and combinations thereof. A preferred support is composed of α-alumina having a high purity; that is, at least 95% by weight purity, or more preferably at least 98% by weight α-alumina. The remaining ingredients may include inorganic oxides other than α-alumina, such as silica, alkali metal oxides (e.g., sodium oxide), and trace amounts of other metal-containing or metal-free additives or impurities.

[0030] The support is preferably porous and has a BET surface area of ​​up to 20 m2 / g, preferably 0.1 to 10 m2 / g, more preferably 0.5 to 5 m2 / g. As used herein, the BET surface area is considered to be measured by the method described by Brunauer, Emmet and Teller in J. Am. Chem. Soc. 60 (1938) 309-316. The support may have a unimodal pore size distribution or a multimodal pore size distribution. Regardless of the characteristics of the support used, it is usually made into the shape of particles, chunks, sheets, pellets, rings, balls, cartwheels, cross-spaced hollow cylinders, etc., and a size suitable for a fixed bed epoxidation reactor. Ideally, the support particles may have an equivalent diameter in the range of about 3 mm to about 12 mm, preferably in the range of about 5 mm to about 10 mm, which is generally compatible with the inner diameter of the tubular reactor in which the catalyst is placed. The equivalent diameter is the diameter of a sphere having the same external surface (i.e., ignoring the surface in the pores of the particles) to volume ratio as the support particles used.

[0031] In order to produce a catalyst for the oxidation of ethylene to ethylene oxide, a catalytically effective amount of silver is then provided on the surface of a carrier having the above-mentioned characteristics. The catalyst is prepared by impregnating the carrier with a silver compound, complex or salt dissolved in a suitable solvent sufficient to cause the silver precursor compound to be deposited on the carrier. Preferably, an aqueous silver solution is used. After impregnation, excess solution is removed from the impregnated carrier, and the impregnated carrier is heated to evaporate the solvent and deposit the silver or silver compound on the carrier, as known in the art. The preferred HSC prepared according to the present disclosure contains up to 45% by weight of silver (expressed as metal) accounting for the total weight of the catalyst including the carrier. Silver is deposited on the surface and throughout the pores of the porous refractory carrier. The silver content expressed as metal is preferably from about 1% to about 40% based on the total weight of the catalyst, and more preferably the silver content is from about 8% to about 35%. The amount of silver deposited on the carrier or present on the carrier is the amount of silver in a catalytically effective amount, that is, the amount that economically catalyzes the reaction of ethylene and oxygen to produce ethylene oxide. As used herein, the term "catalytically effective amount of silver" refers to an amount of silver that provides a measurable conversion of ethylene and oxygen to ethylene oxide. Useful silver-containing compounds as silver precursors non-exclusively include silver oxalate, silver nitrate, silver oxide, silver carbonate, silver carboxylates, silver citrate, silver phthalate, silver lactate, silver propionate, silver butyrate, and higher fatty acid salts, and combinations thereof.

[0032] Also deposited on the support prior to, simultaneously with, or after the silver deposition is a promoting amount of a rhenium component, which may be a rhenium-containing compound or a rhenium-containing complex. The rhenium promoter may be present in an amount of from about 0.001 wt % to about 1 wt %, preferably from about 0.005 wt % to about 0.5 wt %, and more preferably from about 0.01 wt % to about 0.1 wt %, based on the weight of the total catalyst including the support (expressed as rhenium metal).

[0033] Also deposited on the support before, simultaneously with, or after the silver and rhenium deposition is a promoting amount of an alkali metal or a combination of two or more alkali metals, and optionally a promoting amount of a Group IIA alkaline earth metal component or a combination of two or more Group IIA alkaline earth metal components, and / or a transition metal component or a combination of two or more transition metal components, all of which may be in the form of metal ions, metal compounds, metal complexes, and / or metal salts dissolved in an appropriate solvent. The support may be impregnated with the various promoters simultaneously or in separate steps. The specific combination of silver, support, alkali metal promoter, rhenium component, and optional additional promoter disclosed herein will provide an improvement in one or more catalytic properties over the same combination of silver and support and no promoter or only one promoter.

[0034] As used herein, the term "promoting amount" of a certain component of a catalyst refers to the amount of the component that effectively improves the catalytic performance of the catalyst when compared to a catalyst that does not contain the component. Of course, the exact concentration used depends, in particular, on the desired silver content, the nature of the carrier, the viscosity of the liquid, and the solubility of the specific compound used to deliver the promoter to the impregnation solution. Examples of catalytic properties include, in particular, operability (anti-runaway), selectivity, activity, conversion, stability, and yield. It will be appreciated by those skilled in the art that one or more individual catalytic properties may be enhanced by a "promoting amount," while other catalytic properties may or may not be enhanced or may even be weakened. It will also be appreciated that different catalytic properties may be enhanced under different operating conditions. For example, a catalyst having enhanced selectivity under one set of operating conditions may be operated under another set of different conditions, where the improvement is in activity rather than selectivity. In an epoxidation process, it may be necessary to intentionally change the operating conditions to take advantage of certain catalytic properties, even at the expense of other catalytic properties. Preferred operating conditions depend, in particular, on raw material costs, energy costs, by-product removal costs, and the like.

[0035] Suitable alkali metal promoters may be selected from lithium, sodium, potassium, rubidium, cesium or combinations thereof, with cesium being preferred in some embodiments and cesium in combination with other alkali metals such as lithium being particularly preferred in other embodiments. The amount of alkali metal deposited or present on the support is a promoting amount. Preferably, the total catalyst weight measured as metal ranges from about 10 ppm to about 3000 ppm, more preferably from about 15 ppm to about 2000 ppm, even more preferably from about 20 ppm to about 1500 ppm, and particularly preferably from about 50 ppm to about 1000 ppm.

[0036] Suitable alkaline earth metal promoters include elements from the periodic table IIA group, which can be beryllium, magnesium, calcium, strontium and barium or a combination thereof. Suitable transition metal promoters can include elements from the periodic table IVA, VA, VIA, VIIA and VIIIA groups and combinations thereof. Most preferably, the transition metal includes an element selected from the periodic table IVA, VA or VIA groups. Preferred transition metals that may be present include molybdenum, tungsten, chromium, titanium, hafnium, zirconium, vanadium, tantalum, niobium or a combination thereof.

[0037] The amount of the alkaline earth metal promoter and / or transition metal promoter deposited on the carrier is the promotion amount. Transition metal promoters can be present in the total catalyst (expressed as metal) with an amount of about 0.1 micromole per gram to about 10 micromole per gram, preferably about 0.2 micromole per gram to about 5 micromole per gram, more preferably about 0.5 micromole per gram to about 4 micromole per gram. Catalysts may also include one or more sulfur compounds, one or more phosphorus compounds, one or more boron compounds, one or more halogen-containing compounds or combinations thereof that promote the amount. In one embodiment, catalysts include about 5 to about 200ppm, preferably about 10 to about 100ppm of sulfur.

[0038] As is known in the art, the silver solution used to impregnate the support may also include an optional solvent or complexing / solubilizing agent. A variety of solvents or complexing / solubilizing agents may be used to dissolve the silver to the desired concentration in the impregnation medium. Useful complexing / solubilizing agents include amines, ammonia, oxalic acid, lactic acid, and combinations thereof. Amines include alkylenediamines having 1 to 5 carbon atoms. In a preferred embodiment, the solution comprises an aqueous solution of silver oxalate and ethylenediamine. The complexing / solubilizing agent may be present in the impregnation solution in an amount of about 0.1 to about 5.0 moles per mole of silver, preferably about 0.2 to about 4.0 moles, and more preferably about 0.3 to about 3.0 moles per mole of silver.

[0039] When a solvent is used, it can be an organic solvent or water and can be polar or substantially or completely non-polar. In general, the solvent should have sufficient solubility to dissolve the solution components. At the same time, the solvent is preferably selected to avoid undue influence on the solvation promoter or interaction with the solvation promoter. Examples of organic solvents include, but are not limited to, alcohols, especially alkanols; glycols, especially alkyl glycols; ketones; aldehydes; amines; tetrahydrofuran; nitrobenzene; nitrotoluene; glycol dimethyl ether, especially glycol dimethyl ether, diglycol dimethyl ether and tetraglycol dimethyl ether and the like. Organic solvents having 1 to about 8 carbon atoms per molecule are preferred. Combinations of several organic solvents or combinations of one or more organic solvents and water can be used, as long as such mixed solvents can play the role required by this article.

[0040] The concentration of silver in the impregnation solution is generally in the range of about 0.1% by weight to the maximum solubility provided by the particular solvent / solubilizer combination used. Solutions containing 0.5% to about 45% by weight silver are generally well suited for use, with concentrations of 5% to 35% by weight silver being preferred.

[0041] Impregnation of the selected support is accomplished using any conventional method; for example, excess solution impregnation, incipient wetness impregnation, spraying, and the like. Typically, the support material is placed in contact with the silver-containing solution until a sufficient amount of the solution is absorbed by the support. Preferably, the amount of silver-containing solution used to impregnate the porous support does not exceed the amount necessary to fill the pores of the support. A single impregnation or a series of impregnations with or without intermediate drying may be used, depending in part on the concentration of the silver component in the solution. Impregnation procedures are described in U.S. Patent Nos. 4,761,394, 4,766,105, 4,908,343, 5,057,481, 5,187,140, ​​5,102,848, 5,011,807, 5,099,041, and 5,407,888. Existing known procedures for pre-deposition, co-deposition, and post-deposition of various promoters may be used.

[0042] After impregnation of the support with the silver-containing compound, i.e., the silver precursor, the rhenium component, the alkali metal component, and optionally other promoters, the impregnated support is calcined for a sufficient time to convert the silver-containing compound to active silver species and remove volatile components from the impregnated support to produce a catalyst precursor. Calcination can be accomplished by heating the impregnated support, preferably gradually, to a temperature in the range of about 200°C to about 600°C, preferably about 200°C to about 500°C, and more preferably about 200°C to about 450°C, at a pressure in the range of 0.5 to 35 bar. In general, the higher the temperature, the shorter the heating time required. A wide range of heating periods has been proposed in the art; for example, U.S. Pat. No. 3,563,914 suggests a heating time of less than 300 seconds, while U.S. Pat. No. 3,702,259 discloses heating at a temperature of 100°C to 375°C for 2 to 8 hours, typically for a duration of about 0.5 to about 8 hours. However, the only important thing is that the heating time is related to the temperature so that substantially all of the contained silver is converted to active silver species. Continuous or stepwise heating can be used for this purpose.

[0043] During calcination, the impregnated support may be exposed to a gaseous environment comprising an inert gas or a combination of an inert gas and about 10 ppm to 21% by volume of an oxygen-containing oxidizing component. For the purposes of this disclosure, an inert gas is defined as a gas that does not substantially react with the catalyst or catalyst precursor under the conditions selected for calcination. Non-limiting examples include nitrogen, argon, krypton, helium, and combinations thereof, with the preferred inert gas being nitrogen. Non-limiting examples of oxygen-containing oxidizing components include molecular oxygen (O2), NO, NO2, N2O, N2O3, N2O4, or N2O5, or substances capable of forming NO, NO2, N2O, N2O3, N2O4, or N2O5 under calcination conditions, or combinations thereof, and optionally SO3, SO2, trimethyl phosphite, or a combination thereof. Among them, molecular oxygen is a useful embodiment, and a combination of O2 with NO or NO2 is another useful embodiment. In a useful embodiment, the gaseous environment comprises about 10 ppm to about 1% by volume of an oxygen-containing oxidizing component. In another useful embodiment, the gaseous environment comprises from about 50 ppm to about 500 ppm of the oxygen-containing oxidizing component.

[0044] After calcining the HSC, the HSC is loaded into the reactor tube of the epoxidation reactor using conventional loading methods well known to those skilled in the art to provide a catalyst bed containing the HSC. The catalyst bed can have a packing density suitable for the size of the reactor tube used. After the HSC is loaded into the reactor tube, an inert gas (e.g., nitrogen) can be blown through the catalyst bed to remove any unwanted contaminants from the surface of the packed catalyst bed containing the HSC.

[0045] Thereafter, the catalyst bed containing the HSC is first heated to a first temperature of about 180°C to about 210°C, which is sufficient to initiate the epoxidation reaction, while the recycle loop to the ethylene oxide reactor is pressurized with a feed gas composition containing ethylene, oxygen, and a suitable ballast gas, such as methane or nitrogen. Oxygen and ethylene are initially present in low concentrations, such as about 1% to about 4% ethylene and about 0.3% to 0.5% oxygen. After the start of ethylene oxide production is confirmed, a modifier is typically added to the feed gas composition at a concentration of about 0.05 ppm to about 10 ppm, preferably about 0.5 ppm to about 5 ppm; all concentrations listed in this paragraph are by volume. The concentration of the moderator is typically maintained until chlorides are observed in the outlet stream. In some embodiments, chlorides can be observed in the outlet stream within a period of about 2 hours to about 10 hours after the start of the addition of the moderator. At this point, the concentration of the moderator is typically reduced to a value less than the initial concentration of the moderator added to the feed gas composition, which can be referred to as chloride breakthrough. In one embodiment, the demulcent is about 30% to about 50% less than its initial value.

[0046] After chlorine penetration is observed, the temperature (i.e., catalyst bed temperature) is gradually increased from the first temperature to a second temperature of about 240°C to about 270°C, preferably about 260°C, over a period of about 6 hours to about 60 hours. As the catalyst bed temperature increases, the levels of ethylene and oxygen in the feed also increase to increase the production level of ethylene oxide to, as measured by ΔEO in the reactor effluent, greater than about 0.6%, preferably greater than about 1.5%. Therefore, during this stage of the startup process, the feed gas composition will contain about 4% to about 20% ethylene and about 3% to about 5% oxygen. In some embodiments, the chloride level is maintained at the same level as in the previous step. In other embodiments, if the activity is too high, the chloride level is adjusted to promote the temperature increase.

[0047] After reaching the second temperature, the temperature is maintained or held for a period of about 50 hours to about 150 hours during which the ethylene and oxygen concentrations in the feed gas are further increased until the ethylene oxide production level is comparable to full production levels, during which the ΔEO is greater than about 1.5%, preferably greater than about 2.5%, and more preferably in the range of 1.5% to 4.0%. At this point, the ethylene and oxygen levels will be close to or at final operating conditions, and the ethylene oxide production level will be comparable to full production levels upon completion of this step, and the epoxidation process will then continue to operate under these conditions.

[0048] During the process of increasing from the first temperature to the second temperature and maintaining the second temperature (i.e., the adjustment stage), the heat release rate of the catalyst bed containing the high selectivity silver-based ethylene oxide catalyst is controlled to be less than 2000 kJ / Kgcat.hr, preferably less than 1750 kJ / Kgcat.hr, and more preferably less than 1500 kJ / Kgcat.hr. It has been determined that the HSC adjusted by controlling the heat release rate exhibits improved EO performance. In the present disclosure, oxygen consumption and EO selectivity determine the heat release rate. During the adjustment stage, the temperature of the catalyst bed should not exceed 270°C. Typically, and during the adjustment stage, the temperature of the catalyst bed is typically from about 240°C to below 270°C. Moreover, during the adjustment stage, the oxygen in the outlet stream should not be zero, and zero oxygen in the outlet stream generally indicates that the reaction is out of control.

[0049] The heat released by the catalyst bed can be calculated from the total oxygen consumption and the EO selectivity. The heat distribution in the catalyst bed should be controlled to be as smooth as possible in order to minimize temperature variations (less than 10°C) over the entire length of the catalyst bed during the conditioning process.

[0050] In one embodiment of the present disclosure, the heat release rate of the catalyst bed is controlled by maintaining the oxygen conversion at less than about 70 mol%, preferably less than 60 mol%, and more preferably 50 mol%. Once the oxygen conversion is controlled to a value less than about 70 mol%, the reaction conditions for achieving the oxygen conversion should remain substantially constant during the adjustment period. However, if the oxygen conversion exceeds 70 mol% during the adjustment phase, adjustments can be made. According to the present application and in order to reduce the heat release rate in the first stage of the EO reactor, the oxygen conversion should not exceed 70 mol%. The oxygen conversion percentage is related to heat release. However, the most important factor is the total oxygen consumption, not the oxygen conversion percentage. When the oxygen concentration in the feed is very low (i.e., 1%), the oxygen conversion may be very high (i.e., up to 80%). If the oxygen concentration in the feed is high (i.e., 5%), the percentage change needs to be controlled. In some embodiments of the present invention, the oxygen conversion (ΔO2) can be measured by the following formula ΔO2=(O 2-入口 -O 2-出口 / O 2-入口 ) x 100%, where O 2-入口 is the amount of oxygen in the inlet feed gas stream (in mole %) and O 2-出口 The amount of oxygen in is the amount of oxygen in the outlet gas stream (in mol %). In other embodiments, shrinkage and water are also considered when calculating ΔO2.

[0051] In an embodiment, maintaining the oxygen conversion rate includes increasing the heating rate from the first temperature to the second temperature while increasing the carbon dioxide in the feed gas composition. The increase in the concentration of carbon dioxide in the feed gas composition may occur during the step of increasing from the first temperature to the second temperature, or during the step of maintaining the second temperature, or during these two steps. Typically, the increase in the carbon dioxide concentration of the feed gas composition occurs before and during the step of increasing the temperature. The carbon dioxide concentration then decreases as the selectivity develops to maintain a stable heat release. In an embodiment, the heating rate may be increased to a rate of about 1°C / hour to about 10°C / hour, preferably a rate of about 2°C / hour to about 8°C / hour, and more preferably, about 3°C / hour to about 5°C / hour. The carbon dioxide in the feed gas composition may be increased to a value of about 1 mol % to about 25 mol %, more preferably a value of about 2 mol % to about 15 mol %.

[0052] In an embodiment, the heat release rate of the catalyst bed is controlled by maintaining the selectivity of the HSC at greater than or equal to 70 mol%, preferably greater than or equal to 80 mol%, and even more preferably greater than or equal to 85 mol%. In embodiments of the present disclosure, the selectivity of the HSC is preferably maintained at a value greater than or equal to 75 mol%. In some embodiments, maintaining the selectivity may include adjusting the concentration of the modifier during the maintenance phase. Adjusting the concentration of the modifier may include increasing and / or decreasing the concentration of the modifier according to the observed selectivity. The heat release rate is calculated by oxygen consumption and EO selectivity. In order to control the heat release rate, the EO production can be reduced (which is undesirable) or the EO selectivity can be increased. In order to improve the EO selectivity, the feed concentration (C2H4 and O2, which is not always ideal or possible) or the chloride concentration can be adjusted. Adjusting the chloride concentration gives more flexibility. Increasing or decreasing the chloride concentration will depend on the activity of the catalyst.

[0053] In some embodiments, the heat release rate of the catalyst bed is controlled by maintaining the oxygen conversion at about 50 mole % and by maintaining the selectivity of the high selectivity silver-based ethylene oxide catalyst at greater than or equal to 78 mole %.

[0054] After the conditioning process of the present application, the epoxidation process can be carried out by continuously contacting an oxygen-containing gas with an olefin (preferably ethylene) in the presence of the HSC as described above. After maintaining the second temperature, the high selectivity silver-based catalyst has substantially round silver particles with a diameter of about 75 nm to about 500 nm, more typically about 100 nm to about 300 nm. "Substantially round" means that the average roundness of the silver particles is at least 0.80.

[0055] First reference Figure 1A , shows fresh HSCs prior to performing the conditioning process of the present disclosure. Figure 1A The fresh HSCs shown in FIG. 5 have irregularly shaped silver particles with a particle size of less than 75 nm. Figure 1B Shows Figure 1A FIG. 5 is a diagram of fresh HSCs shown in FIG. 5 after performing the conditioning process of the present invention. Figure 1B The conditioned HSCs shown in have substantially round silver particles, and these round silver particles of the conditioned HSCs have a diameter (ie, particle diameter) of about 100 nm to about 300 nm.

[0056] A catalyst bed containing HSC that has been conditioned by the process of the present disclosure described above exhibits improved performance (i.e., EO selectivity) and reduced hot spots compared to an equivalent catalyst bed containing HSC that is conditioned without controlling the heat released by the catalyst bed. In one embodiment of the present application, the conditioning process can provide an improvement of 1.1 to 1.3 times in EO yield compared to an equivalent catalyst bed containing HSC that is conditioned without controlling the heat released by the catalyst bed. In one embodiment of the present application, the conditioning process can provide an improvement of 0.5%-1.5% in EO selectivity compared to an equivalent catalyst bed containing HSC that is conditioned without controlling the heat released by the catalyst bed. In one embodiment of the present application, the conditioning process can provide a reduction in catalyst hot spots compared to an equivalent catalyst bed containing HSC that is conditioned without controlling the heat released by the catalyst bed.

[0057] In addition to the specific startup process mentioned above, the present disclosure contemplates some embodiments that can be used with the following startup process, wherein the above-mentioned controlled heat release rate of the HSC catalyst bed is to a value of less than 2000 kJ / Kgcat.hr, and the startup process includes using a feed gas composition of ethylene and oxygen, adding a modifier to the feed gas composition, and increasing the ethylene oxide production to initiate the epoxidation reaction.

[0058] Oxygen can be supplied to the reaction in substantially pure molecular form or in the form of a composition such as air. Molecular oxygen used as a reactant can be obtained from conventional sources. The reactant feed composition may contain about 0.5% to about 45% ethylene and about 3% to about 15% oxygen, and the balance (mainly methane) comprises relatively inert materials, including substances such as carbon dioxide, water, inert gases, other hydrocarbons and one or more reaction modifiers (such as organic halides, inorganic halides, nitrogen oxides, phosphorus compounds, sulfur compounds and mixtures thereof). Non-limiting examples of inert gases include nitrogen, argon, helium and mixtures thereof. Non-limiting examples of other hydrocarbons include methane, ethane, propane and mixtures thereof. Carbon dioxide and water are byproducts of epoxidation processes. Both can have an adverse effect on catalyst performance, so the concentrations of these components are generally kept at a minimum level. Non-limiting examples of reaction modifiers include organic halides, such as C1 to C halogenated hydrocarbons. Preferably, the reaction modifier is methyl chloride, ethyl chloride, ethylene dichloride, ethylene dibromide, vinyl chloride or a mixture thereof. The most preferred reaction modifiers are ethyl chloride and ethylene dichloride. Typically, such reaction modifiers are used in an amount of about 0.5 to 15 ppmv, preferably 1 to 8 ppmv, based on the total volume of the feed gas.

[0059] The common method of ethylene epoxidation process comprises phase oxidation of ethylene with molecular oxygen in the presence of HSC in a fixed bed tubular reactor. Conventional commercial fixed bed ethylene oxide reactors are usually in the form of a plurality of parallel elongated tubes (in a suitable shell), the outer diameter of the tubes being about 0.7 to 2.7 inches, the inner diameter being 0.5 to 2.5 inches, and being 15-45 feet long, filled with catalyst and some packing material at the top and bottom of the tubes. Typical operating conditions of ethylene epoxidation process include temperatures of about 180°C to about 330°C, preferably about 200°C to about 325°C, and more preferably about 225°C to about 270°C. The operating pressure can vary between about atmospheric pressure and about 30 atmospheres, depending on the desired mass velocity and productivity. Higher pressures can be used within the scope of the present invention. The residence time in commercial scale reactors is usually about 0.3-3 seconds.

[0060] Ethylene oxide is separated and recovered from the reaction products using conventional methods. For the present disclosure, the ethylene epoxidation process may include a gas recycle in which substantially all of the reactor effluent is reintroduced into the reactor inlet after substantially or partially removing the ethylene oxide product and byproducts. In the recycle mode, the carbon dioxide concentration in the reactor gas inlet may be, for example, about 0.1% to 10% by volume.

[0061] The conditioning process of the present application is particularly suitable for the oxidation of ethylene to ethylene oxide with molecular oxygen. The conditions for carrying out this oxidation reaction in the presence of a catalyst broadly include those described in the prior art. This applies to suitable temperatures, pressures, residence times, diluent materials, conditioning agents, and cyclic operation, or the application of continuous conversion in different reactors to increase the yield of ethylene oxide. For illustrative purposes only, the following are the conditions often used in current commercial ethylene oxide reactor units: gas hourly space velocity 1500-10,000h -1 , reactor inlet pressure 150-400 psig, coolant temperature 180-315°C, oxygen conversion 10%-60%, EO productivity (operating rate) 50-500 kg EO / m 3 The feed compound at the reactor inlet may typically comprise 1%-40% ethylene, 3%-12% O2, 0.3%-40% CO2, 0-3% ethane, 0.3-20 ppmv total concentration of an organic chloride moderator and the balance of the feed consisting of argon, methane, nitrogen or a mixture thereof.

[0062] For the purpose of illustrating the present disclosure, examples have been given below. The scope of the present disclosure is not limited to the examples set forth herein.

[0063] Implementation 1

[0064] In this example, a comparison is made between a controlled startup process according to the present disclosure and an uncontrolled startup process not according to the present disclosure, both using the same HSC, HSC A. In both cases, the amount of HSC A loaded into the tubular reactor is the same and adjusted to achieve the same target conditions (GHSV = 4475 hr -1 , WR = 220kg EO / m 3 Catalyst. hours, feed composition (C2H4 / O2 / CO2=30 / 8 / 1 molar ratio) and pressure = 300psig).

[0065] Uncontrolled conditioning consisted of raising the temperature to 245°C coolant temperature (about 255°C bed temperature) for a set period of time (100 hours total). Throughout the conditioning period, the carbon dioxide concentration was maintained between 1-2 mol%, while the C2H4 and O2 concentrations were gradually increased over 100 hours. The heat release rate exceeded 2700 kJ / Kgcat.hr.

[0066] Controlled conditioning involves simultaneously increasing temperature and CO2 until 250-252°C coolant temperature (about 260-265°C bed temperature) and obtaining 15 mol% ethylene. Ethylene and O2 are simultaneously increased to target concentrations until EO production reaches 2 mol%. After EO selectivity exceeds 80 mol% selectivity, the carbon dioxide concentration is reduced. Once a 1 mol% CO2 concentration is reached and the selectivity stops increasing, conditioning is terminated. The heat release rate is always kept below 2000 kJ / Kgcat.hr.

[0067] Implementation 2

[0068] In this example, a comparison is made between a controlled startup process according to the present disclosure and an uncontrolled startup process not of the present disclosure, both using the same HSC, HSC B. Note that HSC B is different from HSC A used in Example 1 above.

[0069] In both cases, the same amount of HSC B was loaded into the tubular reactor and the same target conditions (GHSV = 4475 hr) were achieved after adjustment. -1 , WR = 220kg EO / m 3 cat.hr, feed composition (C2H4 / O2 / CO2=30 / 8 / 1 molar ratio) and pressure=300psig).

[0070] Uncontrolled conditioning consisted of raising the temperature to 260°C coolant temperature (about 270-275°C bed temperature) for a set period of time (100 hours at this temperature). The carbon dioxide concentration was maintained between 1-2 mol% throughout the conditioning period, while the CH and O concentrations were gradually increased over a 100 hour period to reach 9 mol% and 5 mol%, respectively. The heat release rate reached 3000 kJ / Kgcat.hr.

[0071] The controlled regulation consisted of the same scheme, but the CO2 concentration was initially increased to 9 mol% while the temperature was increased. The heat release by increasing CO2 never exceeded 2300 kJ / Kgcat.hr. After the EO selectivity exceeded 75 mol% selectivity, the carbon dioxide concentration was reduced to 1 mol%.

[0072] Although the present disclosure has been specifically shown and described with respect to its preferred embodiments, it will be appreciated by those skilled in the art that the foregoing and other changes in form and detail may be made without departing from the spirit and scope of the present disclosure. Therefore, it is intended that the present application be not limited to the exact forms and details described and illustrated, but fall within the scope of the appended claims.

Claims

1. A process to be used during the initial start-up of an epoxidation process, the process comprising: Initiating an epoxidation reaction by reacting a feed gas composition comprising ethylene and oxygen at a first temperature of about 180° C. to about 210° C. in the presence of a catalyst bed comprising a high selectivity silver-based ethylene oxide catalyst; After confirming the production of ethylene oxide, adding about 0.05 ppm to 2 ppm of a modifier to the feed gas composition; After adding the conditioning agent, increasing the first temperature to a second temperature of about 240° C. to about 270° C. over a period of about 6 hours to about 60 hours; and The second temperature is maintained for a period of about 50 hours to about 150 hours, wherein during the process of increasing the first temperature to the second temperature and maintaining the second temperature, the heat release rate of the catalyst bed is controlled to be less than 2000 kJ / Kgcat.hr.

2. The process of claim 1 wherein the heat release rate of the catalyst bed is controlled by maintaining an oxygen conversion of less than about 70 mole percent.

3. The process of claim 2, wherein the oxygen conversion is about 50 mol%.

4. The process of claim 2, wherein said maintaining said oxygen conversion comprises controlling a rate of temperature increase from said first temperature to said second temperature while increasing carbon dioxide in said feed gas composition.

5. The process of claim 4, wherein the temperature ramp rate is controlled between 3°C / hour and 5°C / hour, and the carbon dioxide in the feed gas composition is increased to a value of about 1 mol% to about 15 mol%.

6. The process of claim 1 wherein the heat release rate of the catalyst bed is controlled by maintaining the selectivity of the high selectivity silver-based ethylene oxide catalyst to greater than or equal to 70 mole percent.

7. The process of claim 6, wherein the selectivity is greater than or equal to 78 mol %.

8. The process of claim 1 wherein the heat release rate of the catalyst bed is controlled by maintaining an oxygen conversion of about 50 mole percent and by maintaining a selectivity of the high selectivity silver-based ethylene oxide catalyst at greater than or equal to 78 mole percent.

9. The process according to claim 1, wherein: After said maintaining the second temperature, the high selectivity silver-based catalyst has substantially round silver particles having a diameter of about 100 nm to about 300 nm.

10. The process of claim 1 wherein the high selectivity silver-based catalyst comprises up to 45% silver by weight.

11. A process according to claim 10 wherein the silver is supported on a support comprising alpha alumina, the support having a surface area of ​​at most 20 m 2 / gram.

12. The process of claim 10 wherein the high selectivity silver-based catalyst further comprises a promoting amount of rhenium.

13. The process of claim 12 wherein the promoting amount of rhenium is from about 0.01 wt% to about 1 wt%.

14. The process of claim 12, wherein the high selectivity silver-based catalyst further comprises a promoting amount of at least one alkali metal.

15. The process of claim 14, wherein the at least one alkali metal is a combination of lithium and cesium.

16. The process of claim 14, wherein the high selectivity silver-based catalyst further comprises a promoting amount of at least one transition metal selected from the group consisting of Mo, W, Cr, Ti, Hf, Zr, V, Ta and Nb.

17. The process of claim 1 wherein the high selectivity silver-based catalyst comprises an alpha aluminum support, up to 45 weight percent silver, and promoting amounts of rhenium, lithium, cesium, tungsten, and sulfur.

18. A start-up process for conditioning a highly selective silver-based catalyst, the start-up process comprising initiating an epoxidation reaction using a feed gas composition of ethylene and oxygen, adding a conditioning agent to the feed gas composition, and increasing ethylene oxide production, characterized in that: The heat release rate of the catalyst bed containing the high selectivity silver-based ethylene oxide catalyst is controlled to a value less than 2000 kJ / Kgcat.hr.

19. The start-up process of claim 18, wherein the heat release rate of the catalyst bed is controlled by maintaining an oxygen conversion of less than about 70 mole percent.

20. The start-up process of claim 19, wherein the oxygen conversion is about 50 mol%.

21. The start-up process of claim 18, wherein said maintaining said oxygen conversion rate comprises controlling a rate of temperature increase from a first temperature to a second temperature while increasing carbon dioxide in said feed gas composition.

22. The start-up process of claim 18, wherein the heat release rate of the catalyst bed is controlled by maintaining the selectivity of the high selectivity silver-based ethylene oxide catalyst greater than or equal to 75 mole percent.

23. The start-up process of claim 22, wherein the selectivity is greater than or equal to 80 mol%.

24. The start-up process of claim 18, wherein the heat release rate of the catalyst bed is controlled by maintaining the oxygen conversion at about 50 mole percent and by maintaining the selectivity of the high selectivity silver-based ethylene oxide catalyst at greater than or equal to 80 mole percent.

25. The start-up process of claim 18, wherein the high selectivity silver-based catalyst after performing the start-up process has substantially round silver particles having a diameter of about 100 nm to about 300 nm.

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