MXPA99011181A - Vinyl acetate process utilizing a palladium-gold-copper catalyst - Google Patents

Abstract

A process is disclosed for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid as reactants comprising contacting said reactants and a non-halogen containing copper compound with a catalyst comprising a porous support on the porous surfaces of which is deposited catalytically effective amounts of metallic palladium, gold and copper. During the process to prepare vinyl acetate, a stream of alkali metal acetate is preferably passed over the catalyst. The process results in higher vinyl acetate selectivity and productivity due to lower CO2 selectivity during the life of the catalyst.

Description

PROCEDURE TO PRODUCE VINYL ACETATE USING A PALADIO-GOLD-COPPER CATALYST BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to a new and improved process for the production of vinyl acetate ("VA") by reacting ethylene, oxygen and acetic acid. Particularly, this invention relates to the use of a copper compound that does not contain halogen during the production of GOES.

FORMATION OF THE BACKGROUND INCLUDING THE DESCRIPTION OF THE RELATED TECHNIQUE The technique for producing vinyl acetate by reacting ethylene, oxygen and acetic acid using a catalyst consisting of palladium, gold and copper supported in a vehicle is already known. Although the process using such a catalyst can produce vinyl acetate at relatively high levels of productivity, any resulting resource in higher productivity over the life of the catalyst would be desirable.

The following references can be considered as materials for the invention claimed herein. The patent of E.U.A. No. 5,332,710, issued July 26, 1994 to Nicolau et al, discloses a method for preparing a catalyst useful in the production of vinyl acetate by reacting ethylene, oxygen and acetic acid, which comprises the impregnation of a porous support with salts water-soluble palladium and gold, fixing the palladium and gold as insoluble compounds in the support by immersion and stirring the impregnated support in a reaction solution to precipitate such compounds, and subsequently reducing the compounds to free metal form. The patent of E.U.A. No. 5,347,046, issued September 13, 1994 to White et al, discloses catalysts for the production of vinyl acetate by reacting ethylene, oxygen and acetic acid, which comprises a metal of the palladium group and / or a compound thereof, gold and / or a compound thereof and copper, nickel, cobalt, iron, manganese, lead or silver, or a compound thereof, preferably deposited on a support material.

BRIEF DESCRIPTION OF THE INVENTION In accordance with this invention, there is provided a process for the production of vinyl acetate by reacting ethylene, oxygen and acetic acid with a low selectivity of carbon dioxide using a catalyst comprising a porous support on the porous surfaces in which it is deposited. catalytically effective amounts of metallic palladium, gold and copper, where a copper compound containing no halogen is included in the feed of reagents to the process. By this method, the amount of copper loss is replaced by volatilization of the catalyst during long-term use, resulting in a smaller increase in carbon dioxide selectivity, and therefore a lower loss in productivity of the catalyst. vinyl acetate due to such use, that when a copper compound is not included in the feed.

DETAILED DESCRIPTION OF THE INVENTION It is related to the invention that the discovery is claimed herein, not having been previously noted, that during the production of vinyl acetate using a catalyst supported on palladium-gold-copper, the copper content of the catalyst has to be substantially reduced. during the life of the catalyst, that is, before it is necessary to replace or regenerate the catalyst, which may reach or exceed two years. Such copper loss is apparently due to the fact that under the reaction conditions, the copper that is on or near the surface of the catalyst particles, reacts with one or more of the reactive materials to form a compound with a tendency to sublimate. However, in the process of the invention a significant amount or all the copper deposited initially on the surfaces of the catalyst support, which ordinarily would be lost during the life of the catalyst, it is replaced by copper in the feed. This causes a smaller increase in the amount of copper in the catalyst due to sublimation than when no copper compound is included in the feed. In this regard, it is noted that while the carbon dioxide selectivity of a vinyl acetate process using any catalyst supported by palladium-copper tends to rise during the life of the catalyst, i.e. from the moment it is charged the catalyst fresh to the reactor until the moment the reactor is turned off for the purpose of replacing or regenerating the catalyst, such carbon dioxide selectivity is generally lower at any point in the life of the catalyst when the catalyst contains a certain amount of copper in addition of palladium and gold that when copper is not present or a smaller amount of it. In this way, the loss of a lower amount of copper during the life of a catalyst under this invention results in a generally higher productivity of vinyl acetate than when a platinum-gold-copper catalyst is employed where it is not included during Feeding no compound with copper. The catalyst support material is composed of particles having one or several regular or irregular shapes, such as spheres, tablets, cylinders, rings, stars, or other shapes, and may have dimensions such as diameter length or width from about 1 to about 10 mm, preferably 3 to 9 mm. Spheres having a diameter of about 4 to about 8 mm are preferred. The support material may be composed of any suitable porous substance, for example, silica, alumina, silica-alumina, titania, zirconia, silicates, aluminosilicates, titanates, spinel, silicon carbide, or carbon and the like. The support material may have a surface area within a scale, for example, from about 10 to about 350 m2 / g, preferably about 100 to about 200 m2 / g, an average pore size on a scale, for example, from about 50 to about 2000 angstroms, and a pore volume on the scale of, for example, about 0.1 to 2, preferably about 0.4 to about 1.2 ml / g. In the preparation of the catalyst used in the process of the present invention, the support material is treated to deposit catalytic amounts of palladium, gold and copper on the porous surfaces of the support particles. Any method can be used to achieve this objective, all involve simultaneous impregnations of the support or separately with one or more aqueous solutions of the water-soluble copper, palladium and / or gold compounds. Palladium chloride (ll), palladium (II) chloride and sodium, palladium (II) and potassium chloride, palladium (II) nitrate or palladium (II) sulfate are examples of suitable water-soluble palladium compounds, although an alkali metal, for example, sodium or potassium salt of auric chloride (III) or tetrachloroauric acid (III) can be used as the water-soluble gold compound, and cupric nitrate trihydrate or hexahydrate, cupric chloride (anhydrous or dihydrate), cupric acetate Monohydrate, cupric sulfate (anhydrous or pentahydrate), cupric bromide or cupric formate (anhydrous or tetrahydrate) can be used as the water-soluble copper compound. An alkali metal salt of tetrachloroauric acid (III), sodium palladium chloride (II) and cupric nitrate trihydrate or cupric chloride are the preferred salts for impregnation due to their good water-soluble character. As mentioned above, any method known to those skilled in the art can be used for the impregnation of palladium, gold or copper in the support. Preferably, the impregnation is carried out by the method "incipient wetting" where an amount of water-soluble metal compound solution used for the impregnation is from about 95 to about 100% of the absorption capacity of the support material. The concentration of the solution or solutions is such that the elemental amount of palladium, gold and copper in the solution or solutions absorbed in the support is equal to the desired predetermined amount. If more than one impregnation is carried out, then each impregnation can contain the hydrosoluble compound equivalent to all or only a portion of the amount of one or any combination of the three catalytically desired active metals in the final catalyst, while the amounts of such metals in the total of absorbed impregnation solutions are equivalent to the desired final amounts. In particular, it may be desirable to impregnate the support with more than one solution of a water-soluble gold compound, as described in greater detail hereinafter. Impregnation is such as to provide, for example, from about 1 to about 10 grams of elemental palladium; for example, about 0.5 to about 10 grams of elemental gold and, for example, about 0.3 to about 5.0 grams, preferably about 0.5 to about 3.0 grams, of elemental copper per liter of finished catalyst, with the amount of gold being from about 10 to about 125 weight percent based on the weight of palladium. After each support impregnation with an aqueous solution of water-soluble salt of a catalytically active metal, the metal is "fixed", ie precipitated, as a water-soluble compound such as the hydroxide, by reaction with a suitable alkaline component, for example , an alkali metal hydroxide, silicate, borate, carbonate or bicarbonate in aqueous solution. Sodium and potassium hydroxides are the preferred alkaline binding compounds. The alkali metal in the alkaline compound should be in an amount of, for example, about 1 to about 2, preferably about 1.1 to about 1.6 moles per mole of anion present in the water-soluble salt. The fixing of the metal can be done by the incipient wetting method, where the impregnated support is dried, for example, at a temperature of 150 ° C for 1 hour, in contact with a solution of alkaline material equal to about 95-100% of the pore volume of the support, and allowed to stand for a period of about 1/2 hour to about 16 hours; or the roto-immersion method, wherein the impregnated undried support is immersed in a solution of alkaline material and rotated and / or stirred during at least the initial precipitation period such that a thin band of the precipitated non-water soluble compound is formed at or near the surface of the support particles. The rotation and stirring can be developed, for example, from about 1 to about 10 rpm for a period of from about 0.5 to about 4 hours. The contemplated roto-immersion method is described in the US patent. No. 5,332,710, the full disclosure of which is incorporated herein by reference. The precipitated compounds, ie precipitated palladium, gold and copper can be reduced, for example, in the vapor phase with ethylene, for example 5% in nitrogen at 150 ° C for about 5 hours after the first washing of the catalyst containing the compounds fixed metal, unless it has no anions such as halide, and drying, for example at 150 ° C for about 1 hour, or such reduction can be carried out before washing and drying in the liquid phase at room temperature with an aqueous solution hydrazine hydrated where the excess of hydrazine higher than that required to reduce all metal compounds present in the support is on the scale of, for example, about 8: 1 to about 15: 1, followed by washing and drying. Other reducing agents and means for reducing the fixed metal compounds present in the support can be employed as are known in the art. The reduction of the metal compound mainly fixed results in the formation of free metal,. although a smaller amount of metal oxide may also be present. In preparations using more than one impregnation or fixation step, the reduction may be developed after each fixing step or after the total of the metal elements are fixed to the support. As an example of the above general procedure, a "separate fixation" method can be used to fix the catalytically active metal elements in the support and reduce the water insoluble metal compounds to the desirable free metal form. In this method, using the specific procedures described above, the support is first impregnated with an aqueous solution of water-soluble palladium and copper compounds by incipient wetting, and the palladium and copper are subsequently fixed by treatment with an alkaline fixation solution by means of techniques conventional as incipient wetting or roto-immersion, preferably roto-immersion. The catalyst is subsequently dried and impregnated separately with a solution of a soluble gold compound having the desired amount of elemental gold in the catalyst, and the gold is fixed by treatment with an alkaline fixing solution by incipient wetting or roto-immersion, preferably incipient humidification. In case the gold is fixed by the incipient wetting method, such fixation can be combined with the impregnation step using a single aqueous solution of a soluble gold compound and an alkaline fixing compound in an amount greater than what is needed. to convert all the gold in the solution to a fixed insoluble gold compound, for example, auric hydroxide. In the case where hydrocarbon is used as ethylene, or hydrogen in the vapor phase as a reducing agent, the catalyst containing the fixed metal compound is washed until it does not contain anions, dry and reduce with ethylene or other hydrocarbon as indicated. described earlier. In the case of using hydrazine in the liquid phase as a reducing agent, the catalyst containing the bound metal compounds is treated with an excess hydrated hydrazine solution before washing and drying to reduce the metal compounds to free metals, and the catalyst is subsequently washed and dried as described. Another alternative method for preparing the catalyst is a "modified roto-immersion" method wherein only a part of the gold is impregnated with palladium and copper in a first impregnation, the metals are fixed by reaction with an alkaline binding compound by roto-immersion, the compounds fixed metals are reduced to free metals, for example, with ethylene or hydrated hydrazine, with washing and drying carried out before the reduction of ethylene or after reduction of hydrazine. The catalyst is subsequently impregnated with the remaining gold in the form of a solution of a soluble gold compound, and the catalyst is again reduced, for example with ethylene or hydrazine, after or before washing and drying, as described above.

A useful variant of a catalyst that can be used in the process of the present invention comprises a porous support on the porous surfaces where the metallic copper is deposited in an area surrounded by deposits of catalytically effective amounts of palladium and metallic gold, none of the which is substantially mixed with said copper. This catalyst can be prepared using various impregnation, fixation and reduction techniques, as described above. The use of the catalyst in which the copper zone is surrounded by palladium and gold and, therefore, copper is less exposed to environmental reaction conditions, contributes to a reduction in copper loss and thus to the reduction of copper. the productivity of vinyl acetate, during the view of the catalyst. After the catalyst containing palladium, gold and copper in a metal-free form deposited on a support material is prepared by any of the above methods, it is further usefully impregnated with an alkali metal acetate solution, preferably potassium acetate or sodium, and most preferably potassium acetate. The catalyst is subsequently dried in such a way that the finished catalyst contains, for example, from about 10 to about 70 grams, preferably about 20 to about 60 grams of alkali metal acetate per liter of finished catalyst. When vinyl acetate is prepared by the process of the present invention, a gas stream, which contains ethylene, oxygen or air, acetic acid, a copper compound that does not contain halogen and desirably an alkali metal acetate, is passed over the catalyst. The copper compound that does not contain halogen is preferably somehow water-soluble or soluble in acetic acid, for example, at least about 0.3 g / l at 20 ° C, and can be, for example, cupric acetate dihydrate, which is preferred , cupric nitrate trihydrate or hexahydrate, cupric sulfate (anhydrous or pentahydrate), or cupric formate (anhydrous or pentahydrate) and the like. The composition of the gas stream can be varied within wide limits, taking into account explosion limits. For example, the molar ratio of ethylene to oxygen can be from about 80:20 to about 98: 2, the molar ratio of acetic acid to ethylene can be, for example, from about 100: 1 to about 1: 100. , the content of the copper compound can be such as to provide, for example, about 10 ppb (parts per billion) to about 50 ppm (parts per million), preferably about 20 ppb to about 10 ppm elemental copper in relation to the acetic acid in the feed stream and the alkali metal acetate content, if used, it may be, for example, approximately 2-200 ppm, relative to the acetic acid employed. The copper and alkali metal acetate compound can be usefully added to the feed stream by injecting in the stream a spray of an aqueous or acetic acid solution of both compounds or separate solutions of each compound, with the amounts of solution and concentration levels of compounds sufficient to provide the desired levels of added alkali metal and copper acetate to cover all or part of such loss of components during the process. In addition to the above active components of the feed stream, such a stream may also contain inert gases, such as nitrogen, carbon dioxide and / or saturated hydrocarbons. The reaction temperatures that can be used are elevated temperatures, preferably those on a scale of approximately 150-220 ° C. The pressure employed can be a pressure of some reduced way, normal pressure or high pressure, preferably a pressure of up to about 20 atmospheres gauge. The presence of copper in the catalyst generally produces greater selectivity and productivity of initial vinyl acetate in the VA process, due to a lower selectivity of CO2 than a catalyst limited to equivalent amounts of palladium and gold as catalytically active metals. However, due to the loss of copper due to its volatilization during the VA reaction, the decrease in selectivity and productivity of vinyl acetate due to an increase in the selectivity of CO2 over the life of the catalyst tends to be greater than if the copper loss rate was significantly reduced. When the procedure described herein is followed with the exception that 0.5 ppm of cupric acetate dihydrate based on the weight of the acetic acid is added to the feed stream, the initial productivity of vinyl acetate is comparable to that obtained when copper compound is not included in the feed stream, since the initial catalyst composition is the same. However, after the start of the procedure, the copper loss is lower when the feed stream contains cupric acetate, since the deposition of cupric acetate from the feed stream in the catalyst particles tends to cover the loss of copper due to the volatilization. It should be understood that although the present invention describes the addition of a copper metal feed stream in combination with a Pd / Au / Cu catalyst, other feed streams will function with the corresponding metal catalyst combination. For example, a copper acetate feed stream will fill the copper loss due to copper volatilization, likewise a current of potassium acetate or cadmium will fill the loss of potassium or cadmium, respectively, in a Pd / catalyst. Au / K or Pd / Au / Cd.

Claims (19)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for the production of vinyl acetate by the reaction of ethylene, oxygen and acetic acid as reactive materials comprising that said reactive materials and a copper compound not containing halogen make contact with a catalyst comprising a porous support on the porous surfaces in which catalytically effective amounts of palladium, gold and metallic copper are deposited.

2. The process according to claim 1, further characterized in that said copper compound is a soluble salt and is sprayed as an aqueous solute in the feed stream comprising said reactive materials.

3. The process according to claim 1, further characterized in that said copper compound is cupric acetate dihydrate.

4. The process according to claim 1, further characterized in that said copper compound is added in an amount to provide from about 10 ppb to about 50 ppm elemental copper based on the weight of the acetic acid.

5. - The method according to claim 4, further characterized in that said copper compound provides from about 20 ppb to about 10 ppm elemental copper.

6. The process according to claim 1, further characterized in that said porous support is silica.

7 .- The method according to claim 1, further characterized in that said catalyst contains from about 0.3 to about 5.0 grams of copper per liter of catalyst.

8. The process according to claim 7, further characterized in that said amount of copper is from about 0.5 to about 0.3 grams per liter of catalyst.

9. The process according to claim 7, further characterized in that said catalyst contains from about 1 to about 10 g of palladium, and from about 0.5 to 10 grams of gold per liter of catalyst, with a quantity of gold from about 10 to about 125 weight percent on a weight basis of palladium.

10. The process according to claim 1, further characterized in that said catalyst also contains a deposit of an alkali metal acetate. 1.

The process according to claim 10, further characterized in that said alkali metal acetate is potassium acetate, which is present in the catalyst in an amount of about 10 to about 70 grams / liter of catalyst

12. The process according to claim 1, further characterized in that said catalyst is prepared by impregnating a porous support with an aqueous solution of water-soluble palladium and copper salts, fixing said palladium and copper as water-insoluble compounds by reaction with a suitable alkaline compound , subsequently impregnating the catalyst with a solution of water-soluble gold salt, the amounts of elemental palladium, copper and gold in the impregnation solutions being equivalent to the predetermined amounts of palladium, copper and metallic gold desired in the catalyst, fixing in the catalyst the gold in the solution present in the last impregnation by reaction of the water-soluble salt dissolved in such solution with a suitable alkaline compound to precipitate a gold compound insoluble to water, and reducing the water-insoluble compounds of palladium to metal-free form, copper and gold present in the catalyst.

13. The process according to claim 12, further characterized in that after the reduction of the total palladium, copper and gold in the catalyst, the catalyst is impregnated with an alkali metal acetate solution.

14. The process according to claim 12, further characterized in that the preparation of said catalyst, said water-soluble copper salt is cupric nitrate dihydrate or cupric chloride dihydratesaid water-soluble palladium salt is palladium (II) chloride, palladium (II) chloride and sodium, palladium (II) chloride and potassium, palladium (II) nitrate or palladium (II) sulfate, said gold salt Water-soluble is an alkali metal salt of aureric chloride (III) or tetrachloroauric acid (III), and said alkaline compound for fixing the palladium, copper and gold mentioned is sodium hydroxide.

15. The process according to claim 10, further characterized in that said alkali metal acetate is potassium acetate.

16. The process according to claim 1, further characterized in that said catalyst is prepared by impregnating the support with a solution of a quantity of water-soluble palladium and copper salts containing all the desired palladium and elemental copper in the finished catalyst and a amount of water-soluble gold salt containing only part of the desired elemental gold in the finished catalyst, fixing palladium, copper and gold in the latter solution as water-soluble compounds by rotation and / or stirring of the impregnated support while immersed in a solution of a suitable alkaline compound, reducing the palladium, copper and gold fixed to their free metallic state, impregnating the catalyst with a solution of a quantity of water-soluble gold salt in such a way that the total amount of elemental gold in the catalyst is equal to that is desired in the finished catalyst, said latter solution also contains a quantity of the compue Sufficient alkaline enough to fix the added gold as an insoluble compound in water, reducing the added gold fixed to its free metallic state.

17. The process according to claim 16, further characterized in that after reduction of the total palladium, copper and gold in the catalyst, the catalyst is impregnated with an alkali metal acetate solution.

18. The process according to claim 16, further characterized in that in the preparation of said catalyst, said water-soluble copper salt is cupric nitrate trihydrate or cupric chloride dihydrate, said water-soluble palladium salt is palladium (II) chloride, chloride of palladium (II) and sodium, palladium (II) and potassium chloride, palladium (II) nitrate or palladium (II) sulfate, said water-soluble gold salt is an alkali metal salt of auretic chloride (III) or acid tetrachloroauric (III), and said alkaline compound for fixing said palladium, copper and gold is sodium hydroxide.

19. The process according to claim 17, further characterized in that said alkali metal acetate is potassium acetate.