MXPA98006623A - Process of propylene oxide using silver catalysts supported by alcalinoterr metals compounds - Google Patents

Abstract

The propylene is oxidized to propylene oxide in the vapor phase using an oxygen-containing gas and a supported silver catalyst comprising silver and a support comprised in whole or in part substantial of an alkaline earth metal-containing compound selected from alkaline earth metal titanates, tribasic calcium phosphate, calcium molybdate and calcium fluoride. Such supports provide significantly high selectivity to the desired epoxide that would be expected from the operation of related materials. The selectivity of propylene oxide can be further improved through the introduction of nitrogen oxide species such as NO, aliphatic halides such as ethyl chloride, and carbon dioxide in the oxygen-containing gas.

Description

PROCESS OF PROPYLENE OXIDE USING CATALYSTS OF SILVER SUPPORTED BY METALS COMPOUNDS ALCALINOTERREOS FIELD OF THE INVENTION This invention relates to a process for the direct oxidation of propylene to propylene oxide in the vapor phase using molecular oxygen. In particular, the invention relates to the use of catalysts comprised of silver supported on certain alkaline earth metal containing compounds to selectively form the epoxide.

BACKGROUND OF THE INVENTION The direct oxidation of ethylene to ethylene oxide by molecular oxygen is well known and is, in effect, the method commonly used for the commercial production of ethylene oxide. The typical catalyst for this purpose contains metallic or ionic silver, optionally modified with several promoters and activators. Many such catalysts contain a porous carrier or inert carrier such as alpha alumina on which silver and promoters are deposited.

REF .: 27802 A review of the direct oxidation of ethylene in the presence of supported silver catalysts is provided by Sachtler et al. in Catalyst Reviews; Science and Engineer, 23 (1 &2), 127-149 (1981) However, it is also well known that the catalysts and reaction conditions that are most suitable for the production of ethylene oxide do not provide comparable results in The direct oxidation of larger olefins such as propylene, the discovery of processes capable of providing propylene oxide by direct oxidation in the vapor phase in higher yields, which "are currently achievable, therefore, will be more desirable." Continuously new support materials have been tested, however, many of those that were used in the first development of catalysts that carry or carry silver are, with some modifications, still used.The materials that have found the widest use are typically inorganic and In general, they are of a mineral nature, and alumina, in its various forms, particularly alpha-alumina, has been preferred as a natural material. Carrier for catalysts containing silver in the preparation of epoxides. Numerous variations of surface area, pore dimensions, pore volume and particle sizes have been suggested when the ideal physical property or combination of properties is provided to improve the efficiency, activity or life of the catalyst. In the search for the ideal support material, we have started with the substances commonly used. For example, some use has been made of alkaline metals and alkaline earth metal carbonates, as well as the isolated support material and in combination with other materials as the carrier for processes such as direct oxidation of alkenes to epoxides. For example, Canadian Patent No. 1,282,772 teaches the use of alkaline earth metal carbonates as supports for silver catalysts in olefin epoxidation systems. The development of alternative supports that provide equivalent or improved performance in epoxidation processes when compared to known materials, could be highly advantageous, such alternative supports can be of lower costs or provide other practical benefits such as greater strength or structural integrity. However, selecting materials that will be suitable for such purposes is not honest. For example, as will be demonstrated below, not all alkaline earth metal containing compounds function in an equivalent manner as supports for epoxidation catalysts with silver. Structurally analogous substances often exhibit radically different functions in an epoxidation process. Therefore, predicting in advance which substances will provide the highest degree of selectivity to the epoxide that is required in a commercial process is almost impossible. Patent application US-A-2593100 discloses a catalyst comprising silver supported in spinel for the epoxidation of ethylene. Oxides are suggested as promoters, hydroxides, carbonates and peroxides of alkali or alkaline earth metals. EP-A-0 318 815 discloses a catalyst for the epoxidation of higher olefins such as propylene which is prepared by contacting in an aqueous solution a salt containing dissolved silver, at least one salt dissolved from a multivalent cation promoter and a salt that contains dissolved silicon. European Patent No. 393,785 teaches a catalyst for the manufacture of alkylene oxide containing a silver metal impregnated in a solid inert refractory support, at least one promoter to improve the efficiency of the catalyst and a manganese component. The efficiency promoter may be a compound comprising at least one alkali metal or oxyanion of an element other than manganese or oxygen selected from group 3b through 7b and 3a through 7a of the Periodic Table; Titanates and phosphates are listed as being oxyanions suitable for such purposes. A maximum of 2% by weight of the anion in the catalyst was taught. A cationic promoter such as an alkaline earth metal may also be present up to a concentration of 1 weight percent of the finished catalyst. Thus, this publication does not contemplate the use of alkaline earth metal titanates or phosphates as the inert refractory solid support.

BRIEF DESCRIPTION OF THE INVENTION According to the present invention, there is provided a supported silver catalyst useful for the epoxidation of propylene comprising silver and a support characterized in that the support comprises an alkaline earth metal-containing compound selected from tribasic calcium phosphate, magnesium aluminate, Calcium molybdate, calcium fluoride, alkaline earth metal titanates, and mixtures thereof and the supported catalyst further comprises a potassium salt comprising potassium cation and an anion selected from nitrate, nitrite, anions capable of forming nitrate under the conditions of epoxidation and mixtures thereof. The invention also provides a process for propylene epoxidation wherein a feed stream comprising oxygen and propylene is contacted in the vapor phase at a temperature of 180 ° C to 350 ° C with a supported silver catalyst as defined. previously.

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a process for the vapor phase oxidation of propylene to propylene oxide, that is, an epoxidation process carried out in the presence of molecular oxygen and a particular class of supported silver catalysts.

The support material used in the present invention is selected from one of several carrier materials that contain the alkaline earth metal compound. The alkaline earth metal compound is an inorganic compound containing one or more alkaline earth metals, particularly calcium, strontium, magnesium or barium with calcium, strontium and barium are more preferred. Depending on the selected alkaline earth metal, the alkaline earth metal compound may additionally contain, titanate, phosphate, aluminate, molybdate, fluoride, or some combination thereof. Specifically, the aralinothermic metal compound is selected from the group consisting of alkaline earth metal titanates (e.g., calcium titanate, strontium titanate), tribasic calcium phosphate, magnesium aluminate, calcium molybdate, calcium fluoride and mixtures of the same. The tribasic calcium phosphate is an inorganic substance that corresponds to the approximate empirical formula Caio (OH) 2 (P0) 6, which contains 34-40% Ca, and which has the CAS Registry number, CAS 12167-74- 7 As will be demonstrated subsequently in the examples, tribasic calcium phosphate has been unexpectedly found to be as superior as a support material than the referred substances such as tricalcium phosphate (CAS 7758-87-4) and hydroxyapatite (CAS 1306). -06-5).

Calcium molybdate is the calcium salt of molybdic acid and has the chemical composition CaMo0. Calcium fluoride has the chemical composition CaF2 and is found naturally as fluorite (pure form) or fluorspar (mineral), but can also be prepared synthetically by the reaction of a soluble calcium salt and sodium fluoride. Magnesium aluminate is a magnesium and aluminum oxide corresponding approximately to the empirical formula MgSO • A1203. The alkaline earth metal titanates comprise the class of inorganic substances which contain an alkaline earth metal such as barium, strontium, calcium or magnesium and a species of titanate. Thus, suitable alkaline earth metal titanates may correspond to the empirical formula MTi03, M2Ti04, and MTi2O5 wherein M preferably = Ba, Sr, Ca, or Mg. Any of the conventional methods for preparing such substances can be used. The barium titanafo, for example, can be prepared by heating a mixture of correct proportions of barium carbonate and titanium dioxide at 1300 ° C until the reaction is complete. The strontium titanate can be obtained in the pure form by calcining the double precipitate of titanium oxalate and strontium from the titanium tetrachloride solution. The calcium titanate may correspond to the compound CaTio3 (12049-50-2), which occurs naturally as the mineral perovs ita, but which can also be synthesized by heating equimolar amounts of the oxide to 1350 ° C. The term "calcium titanate" as used herein also encompasses substances having the formula 3CaO »2Ti02 (CAS 12013-80-8) and 3CaO • TiO (CAS 12013-70-6) Magnesium titanates include the metatitanate MgTi03, orthotitanate Mg2Ti04, and dititanate MgTi205 Such support materials are capable of providing exceptionally high propylene oxide selectivities and have been found to be surprisingly superior to other support materials in this regard. the present invention can exist in various forms In one embodiment, the carrier is one in which the alkaline earth metal compound is the predominant (i.e., at least 50% by weight) or, preferably, substantially the exclusive component of the invention. support (ie, the support consists essentially of one or more alkaline earth metal compounds). In other embodiments of the invention, the inorganic support material is used in conjunction with a solid substrate, i.e., a sub-support or substructure composed of a more conventional support material, such as alumina (preferably, alpha-alumina). This latter type of support can employ the alkaline earth metal composite material coated into relatively small, individual, substructure or sub-support particles or over a larger unit such as a three-dimensional structure or framework having a honeycomb or honeycomb structure. However, the support material of the alkaline earth metal compound will comprise at least 25 weight percent (in some embodiments, at least 35 weight percent) of the final catalyst. The concentrations of alkaline earth metal compounds in the catalysts of the present invention are thus considerably greater than the amounts of compounds typically used by previous workers or technicians, as promoters in supported silver catalysts. A granular form of the alkaline earth metal support material is preferred in the present invention, particularly when used as the exclusive or predominant component of the support. The alkaline earth metal materials suitable for use in the present invention can be obtained commercially as powders that can be converted to the preferred granular form by conventional methods. As described in greater detail below, the granular support can then be impregnated, or coated, with a solution containing a silver compound and subsequently reduced to elemental silver. Alternatively, as described below, the powdered granular support material may be combined with a suitable piata-containing solution such as that conventionally used to impregnate solid supports to form an aqueous suspension or paste. This material can then be expanded on a suitable surface and dried and calcined at an appropriate temperature, such as about 500 ° C. This results in a support of the alkaline earth metal compound with silver that is supported in its elemental state. The catalyst can then be impregnated with solutions of promoters, modifiers, co-catalysts or other additives of the types well known in the art of catalyzed oxidation of supported silver (subsequently collectively referred to as "promoters"), if desired and subsequently it dries. As an alternative, the promoters can be dissolved in the same impregnation solution containing piata used to form the paste or aqueous coating suspension with the material of the alkaline earth metal compound. The support material, before or after the incorporation of the silver and optional promoter (s), can be formed into shaped compositions suitable for use in the manufacture of propylene oxide. The compositions can be formed by any suitable technique. For example, it is possible to form the compositions by compressing the support materials in a mold having a desired configuration. The size of the particles can be selected to be appropriate for the formation of the composition and are frequently in the range of about 0.001 to about 5 millimeters in larger dimension. When coated catalysts are used, that is, those catalysts in which the material of the alkaline earth metal composite is coated on a substructure, an aqueous suspension of the material, in either powder or granular form, can be mixed with the particles of the support material of the substructure and then dry. When with the exclusive or predominant alkaline earth metal support materials described above, the coated catalyst can also be prepared using a solution of a silver compound and any promoter or the like which may be desired or separate solutions of the silver compound and promoter (s) to form the aqueous suspension, followed by adequate drying and calcination . The surface area of the support material of the alkaline earth metal compound is generally at least 0.6 m 2 / g, preferably at least 1.5 m 2 / g. However, support materials of alkaline earth metal compounds having relatively high surface areas are also effective for the purposes of this invention. For example, tribasic calcium phosphate support materials having surface areas of bO to 100 m2 / g have been found to work very effectively in the present invention. This discovery was unexpected in view of the fact that support materials such as alpha alumina which are conventionally used for silver vapor phase oxidation catalysts, preferably have many lower surface areas. The area of the surface is measured by the conventional B.T.T. method using nitrogen or krypton described by Brunauer, Emmett and Teller in J. Am. Chem. Soc. 60, 309-16 (1938). The support materials used in the present invention can generally be described as porous or microporous and typically have pore volumes in water of about 0.05 to 0.80 cc / g. The supported silver catalysts are typically used as individual particles of irregular shape and size. This is true both for the predominant or exclusive alkaline earth metal composite supports, as well as the supports coated with alkaline earth metal compound. However, in some examples the supports, particularly the coated supports, can have a particular shape and size and this is especially true from the substrates used with the alkaline earth metal compound. Typically, the sub-supports are formed into aggregates or "pills" of a size and configuration that are used in tubular reactors. These pills can be formed by convensional extrusion and burning techniques. The pills generally range in size from about 2 mm to about 15 mm, preferably from about 3 mm to about 12 mm. The size is chosen to be consistent with the type of reactor used. For example, in fixed bed reactor applications, sizes ranging from approximately 3 mm to approximately 10 mm have been found to be more suitable in commonly used tubular reactors. The forms of the carrier aggregates useful for the purposes of the present invention may vary widely and may have any of the forms conventionally used in the heterogeneous catalyst art. The alkaline earth metal compounds and supports coated with alkaline earth metal compounds can be prepared as indicated above or obtained commercially. The supported catalyst of the present invention can be prepared by any known method of introducing silver and / or a promoter in the soluble form, to a support. A preferred method of introducing piata to the support of the alkaline earth metal compound is by an impregnation process in which a solution of a soluble salt or silver compound (which can be a salt or silver complex) in a sufficient amount to deposit the desired weight of silver in the carrier, it is dissolved in a suitable solvent or "complexing / solubilizing" agent. The solution can be used to impregnate the carrier or carrier by immersing the carrier in the silver-containing impregnation solution and forming a slurry or aqueous suspension. The aqueous suspension is then dried and calcined by placing the mixture in a stove or oven of about 100 ° C at about 120 ° C for 0.5 to 6 hours and then heating the mixture to a temperature of about 250 ° C at about 600 ° C. C for another 1 to 6 hours. This procedure performs the drying of the alkaline earth metal / silver compound mixture, removes the volatile components and reduces the silver present in its elemental form. Selectively for the desired propylene oxide product can be further optimized by the incorporation of one or more promoters, additives, co-catalysts, modifying agents or the like in the supported silver catalyst. According to the invention, the catalyst contains not only a support of the alkaline earth metal compound and silver but also a potassium salt as defined above which improves the efficiency of the catalyst. The potassium salt can be introduced to the catalyst as an impregnation solution in a separate impregnation step. Again, this can be given by any known manner of impregnating a porous material. Conveniently, this can be done by placing the catalyst material in a container or container, evacuating the container or container and subsequently introducing the salt solution. Alternatively, the support can be sprayed or splashed with the impregnation solution. To the solution in excess then it can be allowed to drain it or the solvent can be removed by evaporation under reduced pressure at a suitable temperature. The catalyst can then be dried at a moderate temperature (eg, at 120 ° C) in an oven for half an hour to five hours. Such a procedure is known as a "sequential" or "sequential" preparation method. The catalyst supported with the alkaline earth metal compound can also be prepared by a "simultaneous" or "coincidental" preparation method. With this method, the potassium salt is included in the solution containing the silver compound used to impregnate the support. Catalysts coated with the alkaline earth metal compound are prepared by coating a suitable substructure or sub-support material, preferably alumina, and more preferably alpha alumina, with an aqueous suspension containing the alkali earth metal compound. This may contain only the alkaline earth metal compound, in this case the coated support is further treated as indicated above to produce a silver or a catalyst coated with the alkaline earth metal promoter compound and silver. Alternatively, an aqueous suspension of alkaline earth metal / silver compound compound or an aqueous suspension of alkaline earth metal compound / silver compound / promoter can be produced in a sequential or coincidental process. Thus, in a sequential process, the particles or pills of a suitable sub-support material, such as alpha-alumina, are coated with an aqueous suspension of an alkaline earth metal composite material and a soluble salt or silver complex dissolved in an agent complex / solubilizer former The particles or pills are subsequently drained and calcined in an oven or oven at a temperature of about 250 ° C to about 600 ° C for about three minutes to about four hours, the duration of heating is generally inversely proportional to the temperature used. The catalyst is then impregnated in the manner described above with a promoter solution, and then dried. The carriers coated with aikaline earth metal compounds can also be formed by a coincidental process in which the aqueous suspension of alkaline earth metal compound / silver compound / promoter is used to coat particles or pills of an adequate sub-support. After draining, the catalyst is dried at a temperature and for a duration indicated above for those catalysts prepared by the sequential process. The particular silver salt or compound used to form the silver-containing impregnation solution in a solvent or a complexing / solubilizing agent is not particularly critical and any silver salt or compound generally known in the art, which is both soluble in and does not react with the solvent or complexing / solubilizing agent to form an undesirable product, may be employed. Thus, the silver can be introduced to the solvent or complexing / solubilizing agent as an oxide or a salt, such as nitrate, carbonate, or carboxylate, for example, an acetate, propionate, butyrate, oxalate, malonate, malate, maleate, lactate, citrate, phthalate, fatty acid ester, and the like or combinations thereof.

A ter number of solvents or complexing agents / solubilizers can be conveniently used to form the silver-containing impregnation solution. In addition by adequately dissolving the silver or converting it to a soluble form, a suitable solvent or complexing / solubilizing forming agent should be capable of being easily removed in subsequent steps, either by a washing, volatization or oxidation procedure, or the like. The complexing / solubilizing agent, preferably, should also allow the solution to provide silver in the finished catalyst to the extent of preferably about 25 to about 60 percent silver, based on the total weight of the catalyst. It is also generally preferred that the solvents or complexing agents / solubilizers are easily miscible with water since aqueous solutions can be conveniently employed. Alcohols, including glycols, such as ethylene glycol, amines (including alkanolamines and aiquiidiamines) and carboxylic acids, such as lactic acid, are included among the materials found suitable as solvents or complexing agents / solubilizers for the preparation of the solutions containing silver. oxyaic acid, as well as also aqueous mixtures of such materials. Typically, a silver-containing solution is prepared by dissolving silver in a suitable solvent or complexing / solubilizing agent such as, for example, a mixture of water, ethylenediamine, oxalic acid, silver oxide, and monoethanolamine. The solution is then mixed with support particles and drained. Subsequently the particles are dried conveniently. As indicated above, after impregnation, support particles impregnated with silver are treated to convert the silver salt or complex to silver metal and hence the effect of deposition of silver on the surface of the support. As used herein, the term "surface", when applied to the support, includes not only the external surfaces of the support but also the internal surfaces, i.e., the surfaces that define the pores or the internal portion of the support particles. This can be done by treating the particles impregnated with a reducing agent, such as hydrogen or hydrazine and / or calcining, at an elevated temperature to decompose the silver compound and reduce the silver to its free metallic state. Certain solubilizing agents such as alkanolamines, alkyldiarnines, and the like can also function as reducing agents. Although at least a catalytically effective amount of silver should be present in the finished catalyst (meaning an amount that provides a measurement conversion of propylene to propylene oxide), the silver concentration is preferably from about 2 percent to 70 percent, by weight, based on the total weight of the catalyst. More preferably, the concentration of the silver varies from about 25 to 60 weight percent. As indicated above, the presence of certain specific potassium salts in the supported silver catalyst significantly improves the efficiency of the catalyst as a propylation epoxidation catalyst. The anion is a nitrogen oxyanion (ie, an anion or negative ion which contains both nitrogen and oxygen atoms) such as nitrate and nitrite or a precursor thereof (i.e., an anion capable of displacement or other chemical reaction and form a nitrogen oxyanion under epoxidation or catalyst preparation conditions). Potassium nitrate (KN03) is the preferred potassium salt. Potassium halide salts such as potassium fluoride can also be employed, when the halide has been found to function as a precursor for nitrate (ie, it is converted to nitrate under the epoxidation conditions). The potassium salt that improves efficiency can be introduced into the catalyst in any known manner. A) Yes, the impregnation and deposition of silver and a potassium salt can be carried out coincidentally or sequentially, as described above. To effect the coincidental impregnation, the potassium salt must be soluble in the same solvent or complex forming / solubilizing liquid used with the silver impregnation solution. With the preferred sequential procedure in which the silver is first added, any solvent capable of dissolving the salt that does not react with the silver or the leaching from the support is suitable. Aqueous solutions are generally preferred, but organic liquids, such as alcohols, can also be employed. Suitable methods for effecting the introduction of the potassium salt to the solid support are well known in the art.

The potassium salt is added in an amount sufficient to provide an improvement in one or more of the catalytic properties (eg selectivity, activity, conversion, stability, yield) of the supported silver catalyst when compared to a catalyst that does not contain the potassium salt (here referred to as "promotion amount or promoter"). The precise amount will vary depending on such variables as the nitrogen oxide species and the concentration of these used in the epoxidation process, the concentration of other components in the feed stream, the amount of silver contained in the catalyst, the area of the surface of the support, the conditions of the process, for example, space velocity and temperature, and the morphology of the support. Generally, however, a suitable concentration range of the added potassium sai, calculated as cation, is from about 0.15 to about 5 percent, preferably from about 0.5 to about 3 percent, by weight, based on the total weight of the catalyst. More preferably, the salt is added in an amount of about 1.5 to about 2.5 percent by weight of K.

The propylene and a gas containing oxygen (ie a gas comprising molecular oxygen) are conducted or introduced together into a reactor in the presence of the catalyst previously described under conditions effective to complete at least the partial epoxidation of the propylene. Typical epoxidation conditions include temperatures within the reaction zone of the reactor in the order of about 180 to 350 ° C (more preferably, 200 to 300 ° C) and pressures of about 1 to about 30.4 x 105 Pa (from approximately 1 to approximately 30 atmospheres). The internal pressures can be as low as 96.5 to 517 kPa gauge (14 to 75 lb / in2 gauge). In order to favor the high selectivity of the epoxide, it is desirable that the feed stream contains carbon dioxide and / or an organic halide (described in more detail below). A gaseous nitrogen oxide species (described in more detail below) can also be optionally supplied to the reaction zone within the reactor by introducing the species into the feed stream containing propylene (fresh or unused and / or recirculated). ) and molecular oxygen.

Examples of nitrogen oxide species suitable for optional introduction into the feedstream include at least one of NO, N02, N20, 2O3 or any gaseous substance capable of forming one of the aforementioned gases, particularly NO and N02, under epoxidation conditions, and mixtures of one of the above, particularly NO, with one or more of CO, PH3, S03 and S02. It is NOT the most preferred nitrogen oxide species. However, the inclusion of such nitrogen oxide species in the feed stream is not necessary. The amount of gaseous nitrogen oxide species present (if any) is not critical. The optimum amount is determined, in part, by the particular potassium salt used and the concentration of the same, and by other factors noted above which are in the optimum amount of potassium sai. Typically, an adequate concentration of the nitrogen oxide species for propylene epoxidation is from about 0.1 to about 2,000 ppm, by volume, when N2 is used as a reactor. When NOT used in the epoxidation of propylene, the preferred concentration is from about 5 to about 2,000 ppm, more preferably from about 20 to 500 ppm, by volume, with a N2 reactor. However, as previously explained, the concentration of nitrogen oxide species can be essentially zero. The "oxygen" used in the reaction can be defined as including pure molecular oxygen, atomic oxygen, any transient radical species derived from molecular or atomic oxygen capable of existing under epoxidation conditions, mixtures of other gaseous substances with at least one of the foregoing, and substances capable of forming one of the foregoing under epoxidation conditions. Oxygen is typically introduced into the reactor either as air, commercially pure oxygen or another substance which under epoxidation conditions exists in a gaseous state and forms molecular oxygen. The gaseous components that are supplied to the reaction zone, or that region of the reactor where the reactants and catalysts are carried or conducted under epoxidation conditions, are generally combined before being introduced to the reactor. If desired, however, such components may alternatively be introduced separately or in various combinations. The feed stream having the previously described particular composition can therefore be formed prior to, or at the same time that the individual components thereof enter the reaction zone. The use of the term "feed stream" here, therefore, does not mean limiting the present process to the mode in which all the gaseous components are combined prior to the introduction of the components in the reaction zone. The reactors in which the process and catalyst of the present invention are employed, can be of any type known to the art. A brief description of several of the reactor parameters that may be used in the present invention are presented below. In addition to propylene and oxygen (and optionally, a kind of nitrogen oxide), the feed stream also desirably contains an organic halide that improves performance such as an aliphatic halide. The organic halide is preferably a volatile compound, i.e., a substance which exists predominantly in the gaseous form under the conditions of pressure and temperature present in the reaction zone. The normal boiling point of the organic halide is more preferably less than about 100 ° C at atmospheric pressure. Compounds containing 1 to 10 carbon atoms are preferred. Most preferably, the halide is a species of chloride. The term "aliphatic halide" includes both saturated and unsaturated halides, such as ethylene dichloride, ethyl chloride, vinyl chloride, methyl chloride, and methylene chloride. Preferably, the ethyl chloride is used as the organic halide. Mixtures of different organic halides can be used. The amount of organic halide employed will vary depending on a variety of factors, including the concentration of propylene that is oxidized, the promoter (s) of the particular catalyst and the nitrogen oxide species and the concentrations thereof, as well as the 'Other factors noted above that influence the optimum amount of potassium salt and nitrogen oxide species. However, a suitable range of concentration for the organic halide in the oxidation of propylene is typically from about 0.1 to about 2,000 ppm, most preferably from about 25 to 500 ppm by volume, of the feed stream. In addition, a hydrocarbon, particularly a saturated hydrocarbon, such as methane, propane, or ethane, may be included in the feed stream. The feed stream may also contain a reactor or diluent, such as nitrogen, or another inert gas, particularly when the air is used as the oxygen-containing gas. Variant amounts of water vapor may also be present. It is also desirable to include the carbon dioxide as a component of the feed stream in the epoxidation process of this invention. The presence of carbon dioxide, within certain limits, has been found to provide surprising improvements in the selectivity of propylene oxide. Desirable improvements in selectivity are generally observed using 1 to 60% by volume C02 in the feed stream, with 5 to 25% by volume of C02 which is preferred. The components of the feed or supply stream are present more adequately in the amounts shown in the following table.

Volume in% (or ppm) Component for Propylene Oxidation propylene Approximately 2 to approximately 50% Oxygen Approximately 2 to approximately 10% Organic halide 0 to approximately 2,000 ppm, most preferably from approximately 20 to 500 ppm Oxide species from 0 to about 2,000 ppm nitrogen Hydrocarbon other than about 5% of propylene Carbon dioxide ° to 60%, most preferably from 5 to 25% Nitrogen U Other gas Remnant. reactor Although the present invention can be used with any size and type of vapor phase epoxidation reactor, including both fixed bed and fluidized bed reactors known in the art, it is contemplated that the present invention will find wider application in multi-jet reactors. tubular, fixed bed standard, such as those now in use as reactors of ethylene oxide. This generally includes wall cooling reactors as well as adiabatic reactors or non-wall coolers. Tube lengths typically can range from approximately 1.5 to approximately 18.3 m (approximately 5 to approximately 60 feet) but will frequently be in the range of approximately 4.6 to approximately 13.7 m (approximately 15 to approximately 45 feet) ). The tubes may have internal diameters of approximately 12.7 mm to approximately 63.5 mm (approximately 0.5 to approximately 2.5 inches) and are expected to be typically approximately 20.3 to approximately 38.1 mm (approximately 0.8 to approximately 1.5 inches in form). ). A plurality of tubes packed with catalyst arranged in parallel within a shell or suitable cylindrical body can be employed. The GHSV generally varies from approximately 500 to approximately 10,000 hr-1. Typically the values of GHSV vary from approximately 800 to approximately 3,000 hours-1 at pressures from approximately 1 to approximately 30.4 x 105 Pa (approximately 1 to approximately 30 atmospheres), commonly from approximately 1.1 to approximately 5.1 x 105Pa (approximately 1.1 to approximately 5 atmospheres). The contact periods should be sufficient to convert 0.5 to 70%, preferably 5 to 30%, of the propylene.

EXAMPLES Example 1 A supported silver catalyst according to the invention comprising 39% by weight of Ag and 1.9% by weight of K on a tribasic calcium phosphate support (Aldrich; CAS 12167-74-7; surface area = 65 m2 / g) is prepared according to the following procedure: At 0.121 (4 oz.) The jug is loaded with ceramic stones (5), ethylene diamine (10.30 g), distilled water (10.20 g), oxalic acid dihydrate (7.50 g), silver oxide (I) (-13.0 g), monoethanolamine (3.63 g), potassium nitrate (1.59 g) in distilled water (5.17 g), and tribasic calcium phosphate (17.0 g). The jug or tinaja is sealed and placed on a ball mill for 4 hours. The resulting mixture was dried at 110 ° C for 1 hour and then calcined at 300 ° C for hours. Subsequently, the material was granulated and sieved at 14/30 mesh. The supported silver catalyst was tested for propylene oxidation activity using a tubular reactor under the following operating conditions: 2cc catalyst, 10% by volume of propylene, 5% by volume of oxygen, 50 ppm of ethyl chloride, 200 ppm of NO, GHSV = 1200 hr-1, flow rate of 40 cc / min, 207 kPa gauge (30 pounds / in2 gauge), 250 ° C. The conversion of propylene of 5% with selectivity to propylene oxide of 27% was obtained. Increasing the concentration of ethyl chloride to 200 ppm improves the selectivity of propyiene to 34% (b% conversion of propyiene).

Example 2 A supported silver catalyst according to the invention, comprising 41% by weight of Ag and 2% by weight of K (added as KF) on a tribasic calcium phosphate support (Aldrich; CAS 12167-74-7; surface area = 65 m2 / g) was tested., for the oxidation activity of propylene using a tubular reactor using the same operating conditions as described in Example 1 (50 ppm ethyl chloride). The propylene selectivity of 36% to 6% conversion of propylene was observed. The following Comparative Examples 1-4 demonstrated the superiority of tribasic calcium phosphate as a catalyst support over other substances which also contain calcium and phosphate components.

Comparative Example 1 A supported silver catalyst comprising 40% by weight of Ag and 2% by weight of K (added as KN03) on a monobasic calcium phosphate support (CAS 7758-23-8) was prepared and tested for activity using the operating conditions described in Example 1 (50 ppm of ethyl chloride; 267 kPa gauge (40 pounds / in2 gauge)). Only 1% of the propylene conversion was made; no propylene oxide was detected.

Comparative Example 2 A supported silver catalyst comprising 39% by weight of Ag and 1.9% by weight of K (added as KN03) on a dibasic calcium phosphate support (CAS 7757-93-9) was prepared and tested for propylene oxidation activity using the same conditions as in Example 1. As in Comparative Example 1, no propylene oxide was detected and the propylene conversion was low (1%).

Comparative Example 3 A supported silver catalyst comprising 43% by weight of Ag and 2% by weight of K (added as KNO3) on a hydroxyapatite support (CAS 1306-06-5, surface area = 33 m2 / g ) was prepared and tested for the propylene oxidation activity under the operating conditions of Comparative Example 1. The results obtained (1% conversion of propylene, 0% seperation of propylene oxide) provide further confirmation of the superiority of the tribasic phosphate as a catalyst support.

Comparative Example 4 A supported silver catalyst comprising 43% by weight of Ag and 2.1% by weight of K (added as KNO3) on a tricalcium phosphate support (CAS 7758-87-4, surface area = 47 m2 / g) was prepared and evaluated for activity as a propylene oxidation catalyst using the conditions described in Example 1. (50 ppm EtCl). Surprisingly, notwithstanding compositional or compositional similarities between tribasic caustic phosphate and tricalcium phosphate, the latter compound when used as a support gives undetectable propylene oxide and only 1% propylene conversion.

Example 3 A supported silver catalyst according to the invention comprising 39% by weight of Ag and 2.1% by weight of K (added as KN03) on a calcium fluoride support was prepared and tested for the oxidation activity of propylene using the same condition described in Example 1 (50 ppm ethyl chloride). The propylene conversion was 4%; the selectivity for propyiene oxide was 3%. When the 02 level was increased to 8% by volume, the propylene conversion was 7% and the selectivity of the propylene oxide improved to 40%.

Example 4 A supported silver catalyst according to the invention comprising 50% by weight of Ag and 2% by weight of K (added as KN03) on a magnesium aluminate support was prepared and tested by the oxidation activity of propylene using the same conditions described in Example 1 (50 ppm ethyl chloride, 50% - C02 volume). The propylene conversion was 6%; the selectivity of the propylene oxide was 42%.

Example 5 A supported silver catalyst according to the invention comprising 50% by weight of Ag and 1.3% by weight of K (added as KN03) on a strontium titanate support was prepared and tested for the activity in propylene oxidation using the same conditions described in Example 1 (50 ppm ethyl chloride). The propylene conversion was 10%; the selectivity of the propylene oxide was 38%.

Example 6 A silver catalyst supported in accordance with the invention, comprising 54% by weight of Ag and 1.9% by weight of K (added as KN03) on a support of calcium molybdate, was prepared and tested for the activity in oxidation of propylene using the operating conditions identical to those of Example 1 (50 ppm ethyl chloride). Propiyeno conversion was 2%; the selectivity of propylene oxide was 26%.

Example 7 A silver catalyst supported in accordance with the invention, comprising 43% by weight of Ag and 1.6% by weight of K (added as KNO3) on a calcium titanate support, was prepared and tested for oxidation activity of propylene using the same conditions described in Example 1 except for the use of 200 ppm of ethyl chloride. The selectivity of propylene oxide from 36% to 4% conversion of propylene was observed.

Example 8 A supported silver catalyst according to the invention, comprising 42% by weight of Ag and 1.1% by weight of K (added as KNO3) on a barium titanate support, was prepared and tested for oxidation activity of propylene using the same conditions described in Example 1 except for the use of 200 ppm of ethyl chloride. The selectivity of propylene oxide from 26% to 3% conversion of propylene was observed.

Example 9 A silver catalyst supported in accordance with the invention, comprising 50% by weight of Ag and 1.5% by weight of K (added as KN03) on a magnesium titanate support, was prepared and tested for oxidation activity of propylene using the same conditions described in Example 1 except for the use of 200 ppm of ethyl chloride. The selectivity of propylene oxide from 3% to 4% propylene conversion was observed.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following is claimed as property

Claims (12)

1. A supported catalyst catalyst for the epoxidation of propylene comprising silver and a support, characterized in that the support comprises a compound containing alkaline earth metal selected from tribasic calcium phosphate, magnesium aluminate, calcium molybdate, calcium fluoride, titanates of alkaline earth metals, and mixtures thereof and the supported catalyst further comprises a potassium cation comprising potassium sai and an anion selected from nitrate, nitrite, anions capable of forming the nitrate under the epoxidation conditions and mixtures thereof.

2. A catalyst supported in accordance with claim 1, characterized in that the support containing the alkaline earth metal is a metal aminotinium titanate and the metal aralinium titanate is selected from the calcium titanate, strontium titanate, and mixtures thereof.

3. A supported catalyst according to claim 1 or claim 2, characterized in that it is obtainable by impregnation of the support with a mixture comprising water, a silver compound, the potassium salt, and a complexing / solubilizing agent selected from of amines, carboxylic acids, and mixtures thereof, followed by calcination.

4. A catalyst supported according to any of claims 1 to 3, characterized in that the support additionally comprises an inert refractory solid support in addition to the compound containing the alkaline earth metal.

5. A supported catalyst according to claim 4, characterized in that the inert refractory solid support forms up to 50 weight percent of the support.

6. A supported catalyst according to claim 4 or claim 5, characterized in that the inert refractory solid support is alpha alumina.

7. A supported catalyst according to any of claims 1 to 3, characterized in that the support consists essentially of the compound containing the alkaline earth metal.

8. A process for the epoxidation of propylene in which a feed stream or supply comprising oxygen and propylene is contacted in the vapor phase at a temperature of 180 ° C to 350 ° C with a silver catalyst supported in accordance with any of Claims 1 to 7.

9. A process according to claim 8, characterized in that the feed stream additionally comprises an aliphatic halide.

10. A process according to claim 8 or claim 9, characterized in that the feed stream further comprises a nitrogen oxide species selected from the group consisting of NO, N02, N203, N20, and mixtures thereof.

11. A process according to any of claims 8 to 10, characterized in that the feed stream additionally comprises carbon dioxide.

12. A process according to any of claims 8 to 11, characterized in that the propylene is contacted in the vapor phase at a temperature of 200 ° C to 300 ° C with oxygen, an aliphatic halide, carbon dioxide, and a species of nitrogen oxide selected from the gsupo consisting of NO, N02, N203, N20, and mixtures thereof.