WO2001036091A1

WO2001036091A1 - Vinyl acetate catalyst comprising metallic palladium and gold and prepared utilizing sonication

Info

Publication number: WO2001036091A1
Application number: PCT/US2000/028723
Authority: WO
Inventors: Tao Wang; Jerry A. Broussard; H. Robert Gerberich
Original assignee: Celanese International Corporation
Priority date: 1999-11-17
Filing date: 2000-10-17
Publication date: 2001-05-25
Also published as: CN1391496A; KR20020048435A; CA2389448A1; EP1237650A1; JP2003513788A; MXPA02004920A; CZ20021630A3; BR0015179A

Abstract

A catalyst effective for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid, comprising a porous support on the porous surfaces of which is deposited catalytically effective amounts of metallic palladium and gold, and optionally, one or more additional catalytically active metals such as copper, prepared by steps comprising impregnating the support with one or more aqueous solutions, of water-soluble compounds of the metals, fixing the metals on the support as water-insoluble compounds in one or more fixing steps by reaction with an appropriate alkaline compound, at least one of said fixing steps being carried out in a solution of the alkaline compound in which the impregnated support is immersed, while sonicating, i.e., applying ultrasound waves to, such solution, and reducing the water-insoluble compounds of the catalytically active metals to their free metallic form.

Description

VINYL ACETATE CATALYST COMPRISING METALLIC PALLADIUM AND GOLD AND PREPARED UTILIZING SONICATION

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to new and improved catalysts comprising metallic palladium and gold, which are useful for the production of vinyl acetate by reaction of ethylene oxygen and acetic acid.

Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98

It is known to produce vinyl acetate by reaction of ethylene, oxygen and acetic acid using a catalyst comprising palladium and gold, supported on a carrier. While the process utilizing such a catalyst is capable of producing vinyl acetate at relatively high levels of productivity, any expedient which could possibly result in even greater productivity or a reduction in byproducts would be very desirable.

The following references may be considered material to the invention claimed herein. U.S. Patents Nos. 3,775,342 issued November 27, 1973, and 3,822,308 issued July 2,

1974, both to Kronig et al., each discloses a method of making vinyl acetate catalysts comprising treating a support simultaneously or successively with a solution A containing dissolved salts of noble metals such as palladium and gold and a solution B containing compounds able to react on the support with the noble metal salts to form water-insoluble compounds, treating such water- insoluble compounds with a reducing agent to convert the water-insoluble noble metal compounds to the free metals, washing the catalyst to remove water-soluble compounds, and applying an alkali metal compound, e.g., an alkali metal carboxylate before or after treatment with the reducing agent. Solution A can optionally also contain salts of other metals such as magnesium, calcium, barium and copper.

U.S. Patent No. 5,322,710, issued July 26, 1994, to Nicolau et al., discloses a method of preparing a catalyst useful for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid, comprising impregnating a porous support with water soluble salts of palladium and gold, fixing the palladium and gold as insoluble compounds on the support by immersing and tumbling the impregnated support in a reactive solution for at least ! _ hour to precipitate such compounds, and subsequently reducing the compounds to free metallic form.

U.S. Patent No. 5,347,046, issued September 13, 1994 to White et al., discloses catalysts for the production of vinyl acetate by reaction of ethylene, oxygen, and acetic acid, comprising a palladium group metal 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.

Suslick, K.8., "Organometallic Sonochemistry," Advances in Organometallic Chemistry 25, 73-119 (1986) is a general article on the application of ultrasound waves to organometallic reactions.

Suslick, K.S.; Fang, M.; Hyeon, T.; and Cichowlas, A.A., "Nanostructured Fe-Co Catalysts Generated by Ultrasound," Materials Research Society Symposia Proceedings. 351. 443-448 (1994), discuss the preparation and activity of Fe-Co catalysts generated with ultrasound waves. Okitsu, K.; Bandow, H.; and Maeda, Y.; "Sonochemical Preparation of Ultrafine

Palladium Particles," Chemistry of Materials 8, 315-317 (1996) discuss the sonochemical reduction of Pd (II) to produce ultrafine Pd particles and state that colloidal dispersion of these particles "exhibit interesting catalytic activity."

BRIEF SUMMARY OF THE INVENTION

In accordance with this invention, a catalyst effective for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid, comprising a porous support on the porous surfaces of which is deposited catalytically effective amounts of metallic palladium and gold, and optionally, one or more additional catalytically active metals such as copper, is prepared by steps comprising impregnating the support with one or more aqueous solutions of water-soluble compounds of the metals, fixing the metals on the support as water-insoluble compounds in one or more fixing steps by reaction with an appropriate alkaline compound, at least one of such fixing steps being carried out in a solution of the alkaline compound in which the impregnated support is immersed, while sonicating, i.e., applying ultrasound waves to, such solution, and reducing the water-insoluble compounds of the catalytically active metals to their free metallic form. Catalysts may be prepared by the method of this invention utilizing sonication in the fixing step, which are capable of implementing the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid with relatively low selectivities to C0₂ and/or heavy ends such that the use of such catalysts may result in greater vinyl acetate productivity than when any of various catalysts known in the art is employed.

DETAILED DESCRIPTION OF THE INVENTION

In preparing the catalysts under this invention, the catalyst support material is composed of particles having any of various regular or irregular shapes, such as spheres, tablets, cylinders, rings, stars, or other shapes, and may have dimensions such as diameter, length, or width of about 1 to about 10 mm., preferably about 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, e.g., 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 the range, for example, of about 10 to about 350, preferably about 100 to about 200 m²/g, an average pore size in the range, for example, of about 50 to about 2000 angstroms, and a pore volume in the range, for example, of about 0.1 to 2, preferably about 0.4 to about 1.2 ml/g.

In the preparation of the catalysts of this invention, the support material may be treated to deposit catalytic amounts of palladium, gold, and any additional catalytically active metal, if any, on the porous surfaces of the support particles. Any of various methods for accomplishing this purpose may be used, all of which involve simultaneous or separate impregnations of the support with one or more aqueous solutions of water-soluble compounds of the catalytically active metals. Palladium(II)chloride, sodium palladium(II)chloride, potassium palladium(II)chloride, palladium(II)nitrate or palladium(II)sulfate are examples of suitable water-soluble palladium compounds; an alkali metal, e.g., sodium or potassium salt of auric(III)chloride or tetrachloroauric(III)acid can be used as the water-soluble gold compound; and, if, for example, copper is utilized as an additional catalytically active metal, cupric nitrate trihydrate or hexahydrate, cupric chloride (anliydrous 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(III)acid, sodium palladium(II)chloride and cupric nitrate trihydrate or cupric chloride are preferred salts for impregnation of gold, palladium and copper respectively because of their good water solubility.

In preparing the catalyst, the impregnations of the support material with solutions of water-soluble salts of the catalytically active metals may be effected by any method known to those skilled in the art. Preferably, however, such impregnations are accomplished by the

"incipient wetness" method wherein an amount of water-soluble salt solution used for the impregnation is from about 95 to about 100 percent of the absorptive capacity of the support material. The concentration of the solution or solutions is such that the amounts of catalytically active metals in the solution or solutions absorbed on the support is equal to a desired predetermined amount. If more than one such impregnation is carried out, then each impregnation may contain water-soluble compound equivalent to all or only a portion of the amount of one or any combination of the catalytically active metals desired in the final catalyst, as long as the amounts of such metals in the total of the impregnating solutions absorbed are equal to the final desired amounts. The impregnations are such as to provide, for example, about 1 to about 10 grams of elemental palladium; for example, about 0.5 to about 10 grams of elemental gold; and, for example, if copper is utilized as an additional catalytically active metal, 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 impregnation of the support with an aqueous solution of at least one water- soluble salt of a catalytically active metal, the metal is "fixed," i.e., precipitated, as a water- insoluble compound such as the hydroxide, by reaction with an appropriate alkaline compound, e.g., an alkali metal hydroxide, silicate, borate, carbonate or bicarbonate, in aqueous solution. Sodium and potassium hydroxides are preferred alkaline fixing compounds. The alkaline compound should be in an amount of, for example, about 1 to about 2, preferably about 1.1. to about 1.8 times the amount necessary to completely precipitate the cations of the catalytically active metals present in the water-soluble salts. At least one of such fixing steps is accomplished with the aid of sonication, i.e., the application of ultrasound waves to a solution of the alkaline fixing compound in which is immersed the support material impregnated with at least one water- soluble salt of a catalytically active metal. In catalyst preparations including more than one fixing step, one or all of the fixing steps may be carried out utilizing sonication. However, if less than all of the fixing steps employ sonication, then the fixing steps other than those employing sonication may be done by the incipient wetness method wherein the impregnated support is dried, e.g., at a temperature of about 150°C for one hour, contacted with an amount of solution of the alkaline material equal to about 95-100% of the pore volume of the support, and allowed to stand for a period of about ^lA hour to about 16 hours; or the roto-immersion method wherein the impregnated support without drying is immersed in a solution of the alkaline material and is rotated and/or tumbled during at least the initial period of precipitation such that a thin band of the precipitated water-soluble compound is formed at or near the surface of the support particles. In carrying out the fixing of metals by roto-immersion, the rotation and tumbling may be carried out, for example, at about 1 to about 10 rpm for a period of, for example, at least about 0.5 hour, preferably about 0.5 to about 4 hours. The contemplated roto-immersion method is disclosed in previously cited U.S.

Patent No. 5,332,710, the entire disclosure of which is incorporated herein by reference.

The fixed, i.e. precipitated compounds of palladium, gold, other catalytically active metals, if any, such as copper, may be reduced, for example, in the vapor phase with ethylene, e.g., about 5% in nitrogen at about 150°C for about 5 hours after first washing the catalyst containing the fixed metal compounds, until it is free of anions such as halide, and drying, e.g., at about 150°C for about 1 hour, or such reduction may be accomplished before washing and drying in the liquid phase at room temperature with sonication with an aqueous solution of hydrazine hydrate wherein the excess of hydrazine over that required to reduce all the metal compounds present on the support is in the range, for example, of about 8: 1 to about 15:1, followed by washing drying. Other reducing agents and means for reducing the fixed metal compounds present on the support may be employed as conventional in the art. The reduction of the fixed palladium, gold and other metal compounds, if any, mainly results in the formation of the free metal, although a minor amount of metal oxide may also be present. In preparations using more than one impregnation and fixing steps, the reduction may be carried out after each fixing step or after the total of the metallic elements have been fixed on the support. In addition to being utilized in one or more fixing steps as described previously, sonication may also be utilized in one or more reduction steps, e.g., by applying the sonication to water containing immersed therein the catalyst support containing the fixed (water-insoluble) metal compounds and through which is bubbled 5% ethylene in nitrogen, or the sonication may be applied to an aqueous solution of hydrazine hydrate containing immersed therein the catalyst support containing the fixed metal compounds. A simple example of carrying out the foregoing catalyst preparation includes a single impregnation of the support with water soluble salts such that the impregnated support contains the palladium and gold desired in the final catalyst, a single fixing step by immersing the impregnated support in a solution of the alkaline compound while applying sonication to the solution, and a single reducing step whereby the fixed palladium and gold are reduced to their free metallic form.

As another example of foregoing general procedure, a "separate fix" method may be used to fix the catalytically active metallic elements on the support and reduce the water-insoluble metal compounds to the desirable free metallic form. In this method, using the specific procedures described previously, the support is first impregnated with an aqueous solution of a water-soluble compound of palladium and of any additional catalytically active metal, if any, other than gold, e.g. copper, by incipient wetness, and the palladium, and additional metal, if present, are then fixed by treatment with an alkaline fixing solution utilizing sonication. The catalyst is then dried and separately impregnated with a solution of a soluble gold compound having the amount of elemental gold desired in the catalyst, and the gold is fixed by treatment with an alkaline fixing solution by sonication. If a hydrocarbon such as ethylene, or hydrogen is to be used in the vapor phase as reducing agent, the catalyst containing the fixed metal compounds is washed until it is free of dissolved anions, dried , and reduced with ethylene or other hydrocarbon, or hydrogen, as previously described. If hydrazine is to be used in the liquid phase as reducing agent, the catalyst containing the fixed metal compounds is treated with an aqueous solution of excess hydrazine hydrate with sonication before washing and drying to reduce the metal compounds to the free metals, and the catalyst is then washed and dried as described. Sonication may be utilized in the reduction step as described previously.

After the catalyst containing palladium, gold and any additional catalytically active metal, if any, e.g., copper, in a free metallic form, deposited on a support material, is prepared by any of the foregoing methods, it is advantageously further impregnated with a solution of an alkali metal acetate, preferably potassium or sodium acetate, and most preferably potassium acetate. The catalyst is then dried such that the finished catalyst contains, for example, about 10 to about 70, preferably about 20 to about 60 grams of alkali metal per liter of finished catalyst. When vinyl acetate is prepared using a catalyst according to the present invention, a stream of gas, which contains ethylene, oxygen or air, acetic acid, and desirably an alkali metal acetate, is passed over the catalyst. The composition of the gas stream can be varied within wide limits, taking into account explosive limits. For example, the molar ratio of ethylene to oxygen can be about 80:20 to about 98:2, the molar ratio of acetic acid to ethylene can be about 2:1 to about 1 :10, preferably about 1 : 1 to about 1 :5, and the content of gaseous alkali metal acetate can be about 1-100 ppm, relative to the acetic acid employed. The alkali metal acetate may be conveniently added to the feed stream as a spray of an aqueous solution of such acetate. The gas stream also can contain other inert gases, such as nitrogen, carbon dioxide and/or saturated hydrocarbons. Reaction temperatures which can be used are elevated temperatures, preferably those in the range of about 150-220°C. The pressure employed can be a somewhat reduced pressure, normal pressure or elevated pressure, preferably a pressure of up to about 20 atmospheres gauge.

The following non-limiting examples further illustrate the invention. In each example, the sonication was carried out in a 250-ml round bottom sonication flask (Misonix) with three 24/40 side necks using an XL2020 Sonicator Programmable Ultrasonic Processor (Misonix) fitted with a flat-tipped tapped disrupter horn (titanium alloy, 3/4" diameter). The ultrasound waves emitted by the sonicator had a frequency of about 20 kHz. Sonication was carried out for about 1 hour to about 20 hours. The sonication may be effected by any of the various types of sonicators known in the art, several of which are commercially available. The support material for the catalyst consisted of Sud Chemie KA-160 silica spheres having a nominal diameter of 5 mm., a surface area of about 160 to 175 m²/g, and a pore volume of about 0.68 ml/g.

EXAMPLES Example 1

100 cc of the 5 mm silica support material for the catalyst was measured into a 500-ml round bottom flask. In a 100-ml graduated cylinder, aqueous Na₂PdCl₄ (7 g Pd/1 support), aqueous NaAuCl₄ (4 g Au/1 support), and deionized water were added to produce a total solution volume equal to the total volume the support could absorb. The Pd/Au-containing solution was poured into the silica support to impregnate the support to incipient wetness, and the support was shaken for approximately 5 minutes to ensure complete absorption of the solution. The treated support was then poured into a 250-ml sonication flask containing 1 14 cc of aqueous NaOH (from 50% w/w NaOH/H₂O, 120% of the amount of NaOH needed to convert the metal salts to their hydroxides). The flask was immediately placed on the sonicator to sonicate for 1 hour at level 2. The solution was drained from the treated support, and the treated support was poured in a 500-ml graduated cylinder with dip tube to wash with a continuous flow of deionized water for 5 hours. The effluent was tested with AgNO₃ to detect the presence of chlorides via formation of insoluble AgCl. The effluent was drained from the treated support, and the treated support was transferred to a 500-ml round bottom flask. The flask was placed in an oven, and the treated support was dried overnight at 150° C under constant N₂ purge. The metal hydroxides were reduced with 5% C₂H₄ in N₂ at a flow rate of 0.5 SCFH at 150°C for 5 hours. KOAc (40 g/1 support) and deionized water were added to a 100-ml graduated cylinder to produce a solution volume equal to the amount of solution the support would absorb. The treated support was impregnated by incipient wetness with the aqueous KOAc and let stand for 15 minutes. The catalyst was transferred to a fluid-bed dryer to dry for 1 hour at 100°C.

Example 2

The procedure of Example 1 was followed through sonication at level 2 for 1 hour. 3.0 ml of hydrazine hydrate, N₂H₄»H₂O was added to the NaOH solution (large excess of the amount necessary to reduce the metal hydroxides to the metals), and the sonication was continued at level 2 for 1 hour. After sonication, the washing, drying, reduction, and impregnation with KOAc were carried out following the procedure of Example 1.

Example 3 100 cc of the 5 mm silica catalyst support material was measured into a 500-ml bottom flask. In a 100-ml graduated cylinder, aqueous Na₂PdCl₄ (7 g Pd/1 support), aqueous NaAuCL, (4 g Au/1 support), CuCl₂ (0.9264 g/1 support), and deionized water were added to produce a total solution volume equal to the total volume the support could absorb. The Pd/Au/Cu- containing solution was poured into the silica support to impregnate the support by incipient wetness, and the support was shaken for approximately 5 minutes to ensure complete absorption of the solution. The treated support was then poured into a 250-ml sonication flask containing 114 cc of aqueous NaOH (from 50% w/w NaOH/H₂O, 120% of the amount needed to convert the metal salts to their hydroxides). The flask was immediately placed on the sonicator for 1 hour at level 2. After sonication, the washing, drying, reduction, and impregnation with KOA_c were carried out following the procedure of Example 1. Example 4

100 cc of the 5 mm silica catalyst support material was measured into a 500-ml round bottom flask. In a 100-ml graduated cylinder, aqueous Na₂PdCl₄ (7 g Pd/1 support), CuCl₂ (0.9264 g Cu/1 support), and deionized water were added to produce a total solution volume equal to the total volume the support could absorb. The Pd/Cu-containing solution was poured into the silica support to impregnate the support by incipient wetness, and the support was shaken for approximately 5 minutes to ensure complete absorption of the solution. The treated support was then poured into a 250-ml sonication flask containing 114 cc of aqueous NaOH (from 50%) w/w NaOH/H₂O, 120% of the amount needed to convert the metal salts to their hydroxides). The flask was immediately placed on the sonicator to sonicate for 1 hour at level 2.

After sonication, the solution was drained from the treated support, and the support was dried on a fluid-bed dryer at 100° C for 1 hour. In a 100-ml graduated cylinder, aqueous NaAuCl₄ (4 g Au/1 support), NaOH (as 50% w/w NaOH/H₂O, 180% of the amount needed to convert the Au salt to its hydroxide), and deionized water were added to produce a total solution volume equal to the amount of solution the support could absorb. The solution was allowed to stand for up to one hour before being added to the treated support to avoid precipitation of the Au hydroxide. The treated support was impregnated by incipient wetness with the Au/NaOH-containing solution, and it was shaken for approximately 5 minutes to ensure complete absorption of the solution. The treated support was allowed to stand for 16 hours, then it was poured in a 500-ml graduated cylinder with a dip tube. The washing, drying, reduction, and impregnation with

KOAc were carried out following the procedure of Example 1.

Example 5

The procedure of Example 1 was followed up through washing of the catalyst for 5 hours in a 500-ml graduated cylinder with a dip tube. After washing, the effluent was drained from the treated support, and the support was transferred to a sonication flask, and approximately 114 cc of deionized H₂0 was added with 4.71 ml of N₂H₄H₂O (1200% of the amount necessary to reduce the metal hydroxides to the metals). The solution was sonicated for 1 hour at level 2. The flask was removed from the sonicator, and the excess solution was drained from the treated support. After 30 minutes, the treated support was rinsed with deionized H₂O several times to remove excess hydrazine. The treated support was poured into a 500-ml graduated cylinder with a dip tube and washed continuously with deionized H₂O for 35 minutes. The treated support was transferred to a round bottom flask and dried overnight under constant N₂ purge. The reduction and impregnation with KOAc were carried out following the procedure of Example 1.

5 Example 6

The procedure of Example 1 was followed except that the sonication was carried out for 3.5 hours at level 2.

Example 7 o The procedure of Example 1 was followed up through washing the catalyst for 5 hours in a 500-ml graduated cylinder with a dip tube. After washing, the effluent was drained from the treated support, and the support was placed in a round bottom flask to dry overnight at 150°C. The treated support was transferred to a sonication flask, and approximately 114 cc of deionized H₂O was added with 4.71 ml of N₂H₄ H₂O (approximately 1200% of the amount necessary to 5 reduce the metal hydroxides to the metals). The solution was sonicated at level 2 for 3 hours.

The flask was removed from the sonicator, and the excess solution was drained from the treated support. The treated support was rinsed with deionized H₂O several times to remove excess N₂H₄. The treated support was poured into a 500-ml graduated cylinder with a dip tube and washed continuously with deionized H₂O for 3 hours and 15 minutes. The treated support was 0 transferred to a fluid bed dryer and dried for 1 hour at 100°C. The reduction and impregnation with KOAc were carried out following the procedure of Example 1.

Example 8

The procedure of Example 1 was followed, except that the sonication was carried out for 5 16 hours at level 2.

Example 9

The procedure of Example 1 was followed, except that the sonication was carried out for 1 hour at level 2, and the support was impregnated to 95% by incipient wetness. 0 Example 10

The procedure of Example 1 was followed, except that the sonication was carried out for 1 hour at level 4 and the support was impregnated to 95% by incipient wetness.

Example 11

100 cc of the 5 mm silica catalyst support material was measured into a 500-ml round bottom flask. In a 100-ml graduated cylinder, aqueous Na₂PdCl₄ (7 g Pd/1 support) and deionized water were added to produce a total solution volume equal to the total volume the support could absorb. The Pd-containing solution was poured into the silica support to impregnate the support by incipient wetness, and the support was shaken for approximately

5 minutes to ensure complete absorption of the solution. The treated support was then poured into a 250-ml sonication flask containing 114 cc of aqueous NaOH (from 50% w/w NaOH/H₂O, 120% of the amount needed to convert the metal salts to their hydroxides). The flask was immediately placed on the sonicator to sonicate for 1 hour at level 4. The solution was drained from the treated support, and the treated support was poured in a 500-ml graduated cylinder with a dip tube to wash with a continuous flow of deionized water for 1 hour. The catalyst was left overnight, and the washing was continued for 3 hours and 45 minutes. The effluent was tested with AgNO₃ to detect the presence of chlorides via formation of insoluble AgCl. The effluent was drained from the treated support, and the treated support was transferred to a fluid bed dryer to dry at 100°C for 1 hour. In a 100-ml graduated cylinder, aqueous NaAuCl₄ (7 g Au/1 support) and deionized water were added to produce a total solution volume equal to the total volume the support could absorb. The Au-containing solution was poured into the Pd-containing silica support to impregnate the support by incipient wetness, and the support was shaken for approximately 5 minutes to ensure complete absorption of the solution. The treated support was then poured into a 250-ml sonication flask containing 114 cc of aqueous NaOH (from 50% w/w

NaOH/H₂O, 180% of the amount needed to convert the metal salts to their hydroxides). The flask was drained from the treated support, and the treated support was poured in a 500-ml graduated cylinder with a dip tube to wash with continuous flow of deionized water for 5 hours. The effluent was tested with AgNO₃ to detect the presence of chlorides via formation of insoluble AgCl. The effluent was drained from the treated support, and the treated support was transferred to a 500-ml round bottom flask. The flask was placed in an oven, and the treated support was dried overnight at 150°C under constant N₂ purge. The reduction and impregnation with KOAc were carried out following the procedure of Example 1.

Example 12 The procedure of Example 4 was followed, except that the sonication was carried out for

1 hour at level 4.

Example 13

The procedure of Example 4 was followed , except that the amount of Cu from CuCl₂ was 2.084 g/1 support, and the sonication was carried out for 1 hour at level 4.

Example 14

The procedure of Example 1 was followed, except that the sonication was carried out for 1 hour at level 3 and the catalyst was dried (after washing) on a fluid-bed dryer at 100°C for 1 hour instead of in an oven at 150°C under constant N₂ purge.

Example 15

The procedure of Example 1 was followed, except that the amount of Pd from Na₂PdCl₄ was 9.844 g/1 and the amount of the Au from NaAuCl₄ was 5.625 g/1; the sonication was carried out for 1 hour at level 2; and the catalyst was dried (after washing) on a fluid-bed dryer at 100 °C for 1 hour instead of in an oven at 150°C under constant N₂ purge.

Example 16

The procedure of Example 11 was followed, except that the amount of Au from NaAuCL, was 4 g/1 and the sonications were carried out for 1 hour at level 2.

The catalysts of the examples were tested for their selectivity to various byproducts in the production of vinyl acetate by reaction of ethylene, oxygen and acetic. This was accomplished using the Vinyl Acetate Micro Unit (VAMU) which is a plug flow reactor run at a temperature sufficient to effect an oxygen conversion of 45%. The VAMU reactor is a 3 ft-long. 16 mm i.d. stainless steel tube with a 3 mm concentric thermocouple well. The reactor is equipped with a heating jacket or "shell" through which hot water and steam are circulated. A 30 cc sample of catalyst is diluted with support up to 150 cc and loaded to the reactor. The catalyst/support mixture is topped with 30 cc of support. After a single pass-through of the oxygen, ethylene and acetic acid in a Nitrogen dilutent, at either constant temperature or constant oxygen conversion, the products were analyzed by gas-phase chromatography.

Table I shows for each example details of the method of making the catalyst and its make-up, in terms of the nominal amounts, i.e. total of the catalytically active metals Pd, Au, and optionally Cu, impregnated onto the support (Metal Content of Catalyst, Nominal Amount), the percentage of the amount of each metal initially impregnated onto the support and retained in the final catalyst (Metal Content of Catalyst, % Retention), the intensity level of sonication applied to each fixing of the metals on the catalyst (Sonication, Level), the period of time of such fixing (Sonication, t., hr.), and the reducing agent (Red. Agent) used for the reduction, and details of the process of synthesizing VA from the components of the gaseous feed in terms of the selectivity to CO₂ and heavy ends (HE), the temperature of the shell or jacket (Shell Temp., oQ to achieve close to 45% oxygen conversion, and the specific measured percent oxygen conversion (O₂ Conv, %).

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The results shown in Table I establish that the supported Pd and Au containing catalysts prepared by a method utilizing sonication in the fixing step are effective in the production of VA by reaction of ethylene, oxygen and acetic acid. In particular, the results of Examples 1,3, 4, 9, 10, 12, 13, and 14 show that the catalyst made by the method of this invention is capable of catalyzing the reaction with a C0₂ selectivity below that resulting from the use of prior art catalysts, for example, Bayer VA catalysts of the type described in GB 1,246,015 and US 5,700,753; incorporated by reference herein. VAMU unit performance data for Bayer catalyst was found to be:

%C0₂ selectivity : 6.54

%HE selectivity : 0.652

%Oxygen Conversion : 45.3

Claims

CLAIMSWe claim:

1. A method for the preparation of a catalyst effective for the production of vinyl acetate by reaction of ethylene, oxygen and acetic acid, comprising the steps of impregnating a porous support with one or more aqueous solutions, of water-soluble compounds of catalytically active metals including palladium and gold, fixing said metals on the support as water-insoluble compounds in one or more fixing steps by reaction with an appropriate alkaline compound, at least one of said fixing steps being carried out in a solution of said alkaline compound in which the impregnated support is immersed while applying sonication to said solution, and reducing said water-insoluble compounds to their free metallic form.

2. The method of claim 1 wherein copper is included as a catalytically active metal with said palladium and gold.

3. The method of claim 1 wherein said porous support is initially impregnated with a single solution of water-soluble palladium and gold salts containing all the palladium and gold desired in the final catalyst, the palladium and gold are fixed as water-insoluble compounds on the support in a single fixing step by immersing said impregnated support in a said solution of said alkaline compound while applying sonication to the latter solution, and said water-insoluble palladium and gold compound are reduced in a single reducing step to their free metallic form.

4. The method of claim 1 wherein said porous support is initially impregnated with an aqueous solution of a water-soluble palladium salt, said palladium is fixed on the support by immersing said impregnated support in a solution of an alkaline compound capable of reacting with said palladium salt to form a water-insoluble palladium compound, with said sonication being applied to the latter solution, the support containing the fixed palladium is separately impregnated with a water-soluble gold salt, the gold is fixed by reaction with an alkaline fixing compound and the palladium and gold are reduced to their free metallic form.

5. The method of claim 4 wherein said fixing of gold is accomplished utilizing sonication.

6. The method of claim 4 wherein said aqueous solution of a water-soluble palladium salt also contains dissolved therein a water-soluble copper salt, resulting in the presence of metallic copper in the final catalyst.

7. The method of claim 1 wherein an alkali metal acetate is deposited on the catalyst after the deposition of palladium on the support of said palladium and gold in free metallic form.

8. The method of claim 7 wherein said alkali metal acetate is potassium acetate.