MXPA98007507A - Catalytic alloy coloidal of paladio and oropara the production of vin acetate - Google Patents

Abstract

The present invention relates to: providing a microemulsion process for the preparation of a palladium-gold reinforced catalyst for the production of vinyl acetate from ethylene, acetic acid and oxygen, the preferred catalyst composition having a content of colloidal palladium and gold evenly distributed over a " -aluminium; a catalyst according to the invention exhibits a sustained level of selectivity for the production of vinyl acetate over a prolonged period of the process

Description

PALO IO AND GOLD COLOID ALLOY CATALYST FOR THE PRODUCTION OF VINYL ACETATE FIELD OF THE INVENTION The present invention relates generally to the preparation of catalysts and especially to the preparation of a reinforced catalyst for use in the production of vinyl acetate (AV).

BACKGROUND OF THE INVENTION A well-known commercial process for the production of vinyl acetate is by the gas phase reaction of ethylene, acetic acid and oxygen in the presence of a palladium-containing reinforced catalyst. A preferred type of vinyl acetate catalyst is one that has a content of palladium metal and gold metal distributed on the surface of a reinforcing substrate such as silica or alumina. Numerous methods are known in the art for the production of a reinforced catalyst for use in the production of AV. A general sequence employed in the art for preparing a catalyst used for the production of AV involves impregnating a reinforcement (eg, alumina or silica) with metal solution, fixing the metals on the reinforcement and reduce the metal. It has been discovered that when this general technique is used for palladium and gold, it frequently produces a catalyst in which palladium and gold are partially or totally segregated. Prior art references disclosing palladium and gold reinforced catalysts for the production of vinyl acetate include U.S. Patent Nos. 3,761,5135 3,775,342; 3,822,308; 3,939,199; 4,048,096; 4.087, G22; 4,133,962; 4,902,832; 5,194,417; 5,314,858! references cited therein; incorporated by reference. The activity and selectivity of a palladium and gold reinforced catalyst is affected by the ischemic form of the content of the palladium and gold metals on the reinforcing surface. It is difficult to achieve a uniform microstructure of metal particles by any of the sequences currently known in the art. The performance of a vinyl acetate manufacturing process is affected by the uniformity of the palladium and gold catalyst structure. In view of the previous points, the technique is always looking for new procedures to develop a reinforced catalyst with improved microstructure, metal distribution and selectivity for the production of vini acetate.

BRIEF PES? RIPCIQN OF. lf \ INENCIÓ It is an object of this invention to provide a palladium and gold reinforced catalyst composition with improved selectivity in the production of vinyl acetate from ethylene, acetic acid and oxygen. It is another object of this invention to provide a reinforced vinyl acetate catalyst having a uniform microstructure of the palladium and gold metals on a reinforcing substrate. It is a further object of this invention to provide a process for producing a vinyl acetate catalyst that provides a uniform distribution of a palladium and gold colloidal alloy on a reinforcing surface. Other objects and advantages of the present invention will be apparent from the description and the accompanying examples. The present invention relates generally to the preparation of a reinforced catalyst for use in the production of ethyl acetate. Specifically refers to a process for the preparation of a reinforced catalyst and the catalyst prepared by said process, for the production of vinyl acetate from ethylene, acetic acid and oxygen, which process consists in: 1) forming an aqueous solution of water soluble palladium and gold compounds; 2) dispersing an aqueous solution in a hydrophobic solvent with an effective amount of surfactant to form a microemulsion mixture; 3) treating the microemulsion mixture with a reactor agent; and 4) impregnating a reinforcement with the mixture of step (3) to form a reinforced metal catalyst. Optionally, the reinforced catalyst of step (4) can be washed and dried. The inventive preparation differs from the technique, in part, in its preparation sequence. Unlike the technique, here, the metals are reduced before the substrate is impregnated. It has been found that this sequence difference results in a reinforced catalyst having improved efficiency for the production of AV.

PESCRT-PCIpN PETALLAP? PE l, A INV IC One or more objects of the present invention is achieved by a process for the preparation of a catalyst for the production of vinyl acetate from ethylene, acetic acid and oxygen, which process consists in: 1) forming an aqueous solution of palladium and gold soluble in water; 2) dispersing an aqueous solution in a hydrophobic solvent with an effective amount of surfactant to form a microemulsion mixture; 3) treating the microemulsion mixture with a reactor agent; and 4) impregnating a reinforcement with the mixture of step (3) to form a reinforced metal catalyst. Optionally, the reinforced catalyst from step (4) can be washed and dried. The term "hydrophobic" as used herein refers to an organic hydrocarbon solvent having a solubility in water of less than about 1 gram per 100 grams of water at 100 ° C. The term "microemulsion" as used herein refers to a type of water-in-oil mixture in which the dispersed aqueous phase preferably has an average droplet size of less than about 5 microns. The term "alloy" as used herein refers to a molecule mixture of at least two different metals. The discussion herein refers to palladium and gold metals, and the term "alloy" implies molecular mixtures that are substantially free of palladium and gold segregated. The terms "reinforcement", "reinforcement means" and "substrate" are used interchangeably herein. The inventive method will be described in relation to each step. The description illustrates a preferred embodiment of the present invention. It is directed in general to the discussion of palladium and gold on the reinforcement of alumina or silica. It should be understood by those skilled in the art that this method is suitable for use with a variety of metal alloys and reinforcing substrates. It is not intended that the description herein be limited to palladium and gold alloy on alumina or silica substrates. Other reinforcing substrates may be employed and will be discussed in more detail below. Unless indicated otherwise, the order of addition of the reagents within each "q" is not crucial to the invention.

Step < i > In the inventive process, the first step involves forming an aqueous solution of water soluble palladium and gold compounds. Generally, the sequence employed for step (1) involves dissolving the metal salts in water. It is preferred to use water that is deionized or distilled to avoid additional salt impurities. The metal salts, sodium chloride or (Na-, 0dCl. *) And chlorohydraulic acid (HAuCl., - Ha0), were placed in a round bottom flask with a stir bar and added water to it. Agitation is carried out at room temperature under atmospheric conditions. Agitation may be carried out in the inert atmosphere if desired. Water is added in as little amount as possible. The amount of water is reduced to a minimum to facilitate the formation of a dispersion of water in oil, in which The water droplets are in icro-ized form, ie the droplets have an average size of approximately or less than 5 microns in diameter. It is preferred to add a sufficient amount of water to the metal salts to form a saturated salt solution. An interval consists of approximately 1: 1 (1 gram of water: 1 gram of metal salt) until the saturation of the metal salt in the water. Preferably, the interval is approximately 1: 3.

P199 1%) Step (2) refers to dispersing the aqueous solution of step (1) in a hydrophobic solvent with an effective amount of surfactant to form a microemulsion mixture. In the inventive process, between about 0.5 and 5 milliliters of water per 30 milliliters of microemulsion mixture is employed in step (2) of the process. The micronized dispersion of water-in-oil solution of the palladium and gold compounds effectively provide a colloidal dispersion of the palladium and gold alloy in step (3), step for the reduction of metal in the process of the invention. Suitable hydrophobic organic solvents for use in step (2) include, but are not limited to, pentane, hexane, cyclohexane, heptane, octane, iso-octane, naphthalene, naphthene, benzene, chlorobenzene, dichloromethane, and the like . Pentane is a preferred solvent. The preferred amount of hydrophobic solvent is dependent on the pore volume of the reinforcement. Preferably, a sufficient or effective amount of solvent is used to saturate the pore volume of the reinforcement. It is convenient to avoid excess solvent. Routine experimentation to analyze the absorbency of the reinforcement in relation to the solvent will determine the amount of solvent that should be used. The surfactant ingredient can be selected from a wide variety of nonionic, anionic and cationic products that are commercially available. They are illustrative of the suitable surfactants of cetyltrimethylammonium bromide; lauri lsul ato de sodio; Sodium benzene sodium onate; ammonium lignosulfate; condensation products of ethylene oxide with fatty alcohols, amines or alkyl enols; f - partial fatty acids and anhydrides of success!; and to me lares. A nonionic surfactant is preferred for the purposes of the process of the present invention. Preferred surfactants include pentaethylene glycol coldedecyl ether, trioctyl oxide and Genepol * (product commercially available from Hoechst Celanese Corporation), with Genepol * being the most preferred surfactant. The surfactant ingredient may be employed in an amount of between about 2 and 20 grams per 30 milliliters of the microemulsion mixture. It was observed that too small a quantity of surfactant does not allow the formation of a microemulsion. Although no upper limit was detected for a quantity of surfactant to be employed, an excess of surfactant is uneconomical. It is convenient to use a sufficient or effective amount of surfactant to form a microemulsion. The amount of surfactant will vary based on the amount employed in step (1) and the type of surfactant that is used. Generally, by routine experimentation in the laboratory, a satisfactory minimum amount of the surfactant to be employed can be determined. The order of addition for step II generally involves adding solvent to the surfactant, followed by mixing (blending can be effected by any conventional means). Generally, the mixture of solvent and surfactant was mixed until a homogeneous and pourable solution was obtained. This pourable mixture was then added to the metal salt solution of step (1) and the mixing was conducted until a microemulsion was formed. Using salts of the metals palladium and gold and pentane as solvent, a color change was observed in step (2). The color will vary depending on the metal and solvent used.

Pasp < 3E Step (3) defines a particularly inventive aspect of the method according to the present invention. In step (3) the microemulsion mixture is treated with an excess amount of reducing agent, such as hydrazine, gas ethylene or ormaldehyde, to reduce palladium and gold to the metallic state and form a colloidal alloy phase suspended from the palladium and gold metals in the microemulsion mixture. According to the inventive method, the reaction step is conducted before the metal mixture is impregnated on the reinforcement. If the reaction step is conducted after the microemulsion mixture is impregnated onto the reinforcement, it has been found that the resulting catalyst has the palladium and gold metals segregated and that it is less selective for the production of vinyl acetate from ethylene. , acetic acid and oxygen. It is highly beneficial and recommended to complete the reduction reaction as much as possible. Generally, when hydrazine or a reducing agent that causes gas evolution is used, the reaction can be monitored on the basis of gas evolution, in which case it is best to continue the reaction until no gas is released from the reaction. In the preferred embodiment, hydrazine is added to the microemulsion mixture in a range of about 1 to 2 ml per 3 grams of the metal salts employed. The resulting reaction was exothermic. The mixture was allowed to cool before proceeding to step (4). ago H > Step (4) involves impregnating an inorganic reinforcement with the reduced metal mixture of step (3) to form a reinforced metal catalyst. The impregnation can be conducted following conventional procedures. The reinforcing substrate for the vinyl acetate catalyst can be selected from organic or inorganic reinforcing substrates. Due to their stability for AV production, inorganic reinforcements are preferred. Suitable inorganic reinforcements include, but are not limited to, silica, alumina, a mixture of silica and alumina, zirconium dioxide, titanium dioxide, calcium dioxide and the like, as well as other types of solid carriers which are widely used. in the manufacture of vinyl acetate catalysts. Silica and alumina are the preferred solid carriers used for the production of AV, with o-alumina being the most preferred. The vinyl acetate catalyst reinforcing means can be in the form of spheres, tablets, Raschig rings and the like. Generally for the present invention, the reinforcing medium was used as received without preparative treatment. The reinforcement was added to the cooled mixture of step (3) under atmospheric conditions and mixed. The mixing took place manually, however any conventional suitable means is acceptable.

The reinforced catalyst is impregnated with an activating ingredient, such as an alkali metal alacanoate (eg, potassium acetate, potassium borate), to provide a catalyst product with enhanced selectivity for the production of vinyl acetate from ethylene, acetic acid and oxygen.

Pftfc * Qpcjo? Al < 5 > Although not a necessary step, the impregnated catalyst reinforcement formed during step (4) was repeatedly washed with cosolvent for water and solvent and surfactant, such as alcohol (ethanol) followed by a water wash. This wash eliminated any residual hydrophobic solvent, surfactant and salts of the reinforced catalyst. If desired, the washing step can be omitted, since the catalyst residues will be removed by combustion in the reactor during the use of the reinforced catalyst. The reinforced catalyst was then dried in a convection oven or a typical fluid bed dryer. Drying by conventional means is acceptable. The drying temperatures used ranged from approximately 150 ° C to approximately 300 ° C and in the nitrogen atmosphere. If this step is used, the impregnation of KOAc follows.

PISCISIQN E LPS EXAMPLES, As demonstrated in the Examples, alumina is a preferred type of reinforcing medium. Although a reinforced catalyst was prepared using the present technique with silica, it was observed that greater metal retention was obtained to the substrate when alumina was employed. In Examples of Catalysts 1-3, the palladium and gold reinforced catalysts have a silica substrate. It was observed that these reinforced catalysts did not possess a uniform and homogeneous physical appearance as the reinforced catalyst on an alumina substrate. It was further noted that the catalysts of Examples 1-3, with a silica substrate, had insufficient metal loading on the surface to conduct the performance test. This is in contrast to Example 9, in that it exhibited a high retention and colloidal alloy of palladium and gold on the alumina surfaces of the substrate and exhibited excellent selectivity for the production of vinyl acetate from ethylene »acetic acid and oxygen.

GQttPqs? CjPN G? TAUZADPRA REFPRZ? PA In addition to providing a method for preparing a reinforced catalyst, this invention provides a catalyst composition for the preparation of vinyl acetate from ethylene, acetic acid and oxygen, containing gold and gold colloidal alloy on a reinforcing medium, preferably on a medium of alumina. "Colloidal" herein refers to a composition of uniform particles on the reinforcement with respect to the palladium and gold; "uniform" as a composite to the reinforced Pd / Au catalyst produced by the reinforcement processes according to the prior art. The colloidal alloy of palladium and gold on the alumina reinforcement typically has an average particle size between about 1 and 20 nanometers. A vinyl acetate catalyst according to the invention on alumina can have a palladium metal content of between about 0.1 and 2.5% by weight, and a gold metal content of between about 0.05 and 0.06H by weight based on the weight of the catalyst . The weight ratio of palladium and gold of the catalyst can vary approximately 1-10: 1. A catalyst composition of the present invention has a particular advantage when used in the manufacture of vinyl acetate monomer from ethylene, acetic acid and oxygen. A typical procedure for vinyl acetate involves reaction of ethylene, acetic acid and oxygen or air in the gas phase at about 100-250 ° C and under normal or high pressure in the presence of a palladium-containing reinforced catalyst. Various modalities for the preparation of vinyl acetate are described in the references cited in the Background section. The following examples are even more illustrative of the present invention. The components and the ingredients specific ones are presented as typical and various modifications can be derived in view of the foregoing disclosure within the scope of the invention.

H ^ PS GENERAL PRQCEPINIENTQ FOR L? PRQPU? CiQN PE AV When employing a stirred tank reactor for vinyl acetate (TAAV) in the examples, the following general procedure is employed. The TAAV is a Serty reactor or a continuous reactor with stirred tank of the recirculating type that is driven with constant oxygen conversion (approximately to 4554). The reinforced catalyst is loaded into a reactor jacket, a measured amount of acetic acid, ethylene and oxygen is added in a nitrogen diluent and adjusted to the reactor at a temperature by means of a heat jacket. A reactor temperature is measured above and below the catalyst. The reaction is terminated after about IB hours at a temperature at which an oxygen conversion to the 45JI is maintained. The products are measured for gas phase chromatography. The C0W selectivities tend to be little higher for the same catalyst when tested in the unit with TAAV compared to the MUAV. since the vinyl acetate product is recirculated in contact with the catalyst during the reaction sequence. ÍS The reaction in the icrounidad with acetate of vinyl (MUAV) in the examples is a system of reaction of the type of flow by valve operated at constant temperature. The MUAV reactor is a stainless steel tube 91.4 cm long and 16 mm internal diameter, with a concentric 3 mm thermocouple receptacle. The reactor is equipped with a heating jacket through which hot water and steam circulate. Generally, a sample of 30 cm 3 of catalyst is diluted up to 150 cm 3 of reinforcement and introduced into the reactor. The mixture of catalyst and reinforcement is completed with 30 cm 3 of reinforcement. After a single oxygen conduction »ethylene and acetic acid in a constant temperature nitrogen monitor, the products are analyzed by gas phase chromatography.

E EMPLO O EF RZP giP, This example illustrates the preparation of a type of Pd-Au metal catalyst on the silica reinforcement by a microemulsion method. Na ^ P Cl ^ (2.26 g, 7.8 mmol) was dissolved and HAuCl ^ -SHaO (827 mg, 2.1 mmol) in 1.6 ml of deionized water under nitrogen in a reaction flask. A solution of Genapol * 26-L-60 (12.5 g Hoechst Celanese) in pentane (35 ml) was prepared. The two solutions were mixed to form a microemulsion of the aqueous phase in the solvent phase organic Hydrazine-reducing agent monohydrate (2 ml) was added under nitrogen and the solution turned black and gas evolution was evident. The reduced solution was applied to Aerosil 200 with MgO binder (Degussa). The formed reinforced catalyst was stirred for 10 minutes and purged under nitrogen to remove the pentane solvent. The reinforced catalyst was washed with ethanol and then washed with demineralised water for 16 hours. The reinforced catalyst was dried in a fluidized bed dryer for 1 hour at 100 ° C and then dried at 150 ° C for 20 hours under nitrogen. The reinforced catalyst with potassium acetate activator (6 g in 50 ml of water) was impregnated., and dried in a fluidized bed dryer at 100 ° C for 1 hour.

E EM LO? . { EXAMPLE PE FU ZO PE SjQ,) This example illustrates the preparation of a catalyst type of the Pd-Au metals on silica reinforcement by a microemulsion method. The reinforced catalyst of this example was prepared according to Example 1, using the following reagents and amounts.

Na-ePdCl-, 2.26 g, 7.8 mmoles HAuCl "-3Ha0 827 mg, 2.1 mmoles hydrazine monohydrate 2 ml Aerosil 300 with binder kaolin binder (Degusa) 64.1 g potassium acetate 6.0 g (EXAMPLE OF REINFORCEMENT OF SiO,) This example illustrates the preparation of a type of Pd-Au metal catalyst on silica reinforcement by a microemulsion method. The reinforced catalyst of this example was prepared according to Example 1, using the following reagents and amounts.

Naa dCl ^ 2.26 g, 7.8 mmoles HAuCl -, - 3Ha0 827 mg, 2.1 mmolee hydrazine monohydrate 2 ml Aerosil 300 with Ala03 binder (Degusa) 56.6 g potassium acetate 5.0 g EXAMPLE 4 This example illustrates the preparation of a type of Pd-Au alloy catalyst on the reinforcement of alumina according to the invention by a microemulsion method.

NaßPdCl ^ 2.26 g, 7.8 mmoles HAuCl ^ -3Ha0 827 mg, 2.1 mmoles hydrazine monohydrate 2 ml Raschig rings of alumina 88.0 g potassium diet 4.0 gn X-ray absorption spectroscopy indicated a distribution of a colloidal alloy of Pd-Au which has a mean particle size in the range of 1-20 nanometers. The selectivity of the catalyst tr of Example 4 was tested in a stirred constant process (TAAV) for the preparation of vinyl acetate from ethylene, acetic acid and oxygen. The comparative data and Tables I-II are summarized. 0 EXAMPLE 5 (EXAMPLE OF REINFORCEMENT OF SiO,) This example illustrates the preparation of a catalyst type of the Pd-Au metals on silica reinforcement by a microemulsion method. The reinforced catalyst of this example was prepared according to Example 1, using the following reagents and amounts.

NaaPdCl. * 2.26 g, 7.8 mmoles HAuCl ^ -3Ha0 827 mg, 2.1 mmoles hydrazine hydrated 2 ml Süd Cmemie T-435B-E-1 59.3 g potassium acetate 5.0 g The selectivity of this catalyst was tested in an icrounit (MUAV) for the preparation of vinyl acetate. The comparative data are summarized in Table II and III.

(EXAMPLE OF REINFORCEMENT OF YES0-) This example illustrates the preparation of a catalyst type of the Pd-Au metals on silica reinforcement by a microemulsion method. The reinforced catalyst of this example was prepared according to Example 1 using the following reagents and amounts.

Na ^ PtíCl ^ 2.26 g, 7.8 mmoles HAuCl ^ -SHaO 827 mg, 2.1 mmoles hydrazi to monohydrate 2 ml Süd Cmemie T-4358-E-1 59.3 g potassium acetate 5.0 g The selectivity of this catalyst in a microunit for the preparation of vinyl acetate was tested. The comparative data are summarized in Table I and III.

EXAMPLE 7 This example illustrates the preparation of a type of alloy catalyst of the Pd-Au metals on the alumina reinforcement according to the invention by a microemulsion method.

Na2PdCl ^ 2.35 g, 8 mmoles HAuCl ^ -SHaO 788 g, 2 mmoles hydrazine monohydrate 1.5 ml tablets -AlaQ3 (Aesar) 155.0 g potassium acetate 5.0 g EXAMPLE B This example illustrates the preparation of a catalyst type of the Pd-Au metals on silica reinforcement by a microemulsion method. The reinforced catalyst of this example was prepared according to Example 1, using the following reagents and amounts. He repeated himself procedure to form a double coating of Pd-Au alloy on the alumina reinforcement.

NajjPdCl ^ 2.65 g, 9 mmol is hydrazine monohydrate 1.5 ml tablets of -A1aOa (Aesar) 155.0 g potassium acetate 5.0 g (second coating) The selectivity of this catalyst in a microunit for the preparation of vinyl acetate was tested. The comparative data are summarized in Table I and IV.

EXAMPLE 9 This example illustrates the preparation of a catalyst type of the Pd-Au metals on silica reinforcement by a microemulsion method. The reinforced catalyst of this example was prepared according to Example 1 using the following reagents and amounts. The procedure was repeated to form a double coating of Pd-Au alloy on the alumina reinforcement.

NaaPdCl ^ 2.35 g, 8 mmoles 788 g, 2 mmol hydrazine monohydrate 1.5 ml -AlaOa tablets (Aesar) 155.0 g potassium acetate 5.0 g The selectivity of this catalyst in a microunit for the preparation of vinyl acetate was tested. The comparative data are summarized in Table I and V.

This example illustrates the preparation of a catalyst type of Pd-Au metals on silica reinforcement by a microemulsion method, in which the palladium metal gold metal is applied in separate coatings. The reinforced catalyst of this example was prepared according to Example 1, using the following reagents and amounts.

First coating NaaPdCl ^ 2.94 g, 10 mmoles hydrazine monohydrate 1.5 ml -AlaOa tablets (Aesar) 155 g Second coating HAuCl ^ -SHaO 985 mg, 2.5 mmoles hydrazine monohydrate 1.0 ml potassium acetate 5.0 g The selectivity of this catalyst in a microunit for the preparation of vinyl acetate was tested. The comparative data are summarized in Table I and V.

These examples illustrate the preparation of the type of alloy catalysts of the Pd-Au metals on the alumina reinforcement by a microemulsion method.

NaaPdCl ^ 4.41 g, 15 mmoles HAuCl ^ -3Ha0 1.97g, 5 mmoles hydrazine monohydrate 3.0 ml -AlaOa tablets (Aesar) 310.0 g potassium acetate 5.0 g The initial reprossed catalyst was prepared by a procedure similar to the microemulsion method of Example 1 and the catalyst product was then divided into two 155 g portions. A portion was applied at 150 ° C for 16 hours under nitrogen and impregnated with potassium acetate (5 g in water) and dried at 100 ° C for one hour (Example 11).

The second portion was calcined at 300 ° C for 5 hours in air, impregnated with potassium acetate (5 g in water) and dried at 100 ° C for one hour (Example 12). The selectivity of these catalysts of a microunit for the preparation of vinyl acetate was tested. The comparative data are summarized in Tables I and V.

These examples illustrate the preparation of the type of Pd-Au metal catalysts on the lumina reinforcement by an incipient damp method. Raschig rings of AlaOa were impregnated with 32 ml of an aqueous solution containing NaaPdC1 - ^ (3.47 g) and NaAuCl-4 (3.47 g). NaOH (1.1 g in 120 ml of H 2 O) was added and the mixture was allowed to stand for 20 hours. The resulting catalyst precursor was washed with demineralized water and dried. The catalyst was then impregnated again with the same type of Pd-Au solution. The catalyst was dried at 100 ° C for 1 hour, then it was impregnated with aqueous NaOH (1.1 g in 32 ml of Ha0). After standing for 15 hours, the catalyst was washed with demineralized water for 25 hours, dried at 100 ° C for 1 hour and then at 150 ° C for 24 hours under nitrogen. The potassium acetate catalyst (5 g in 32 mil of Ha0) was impregnated and dried at 100 ° C for one hour (Example 13).

The reinforced catalyst of Example 14 was prepared following the incipient moisture method described above, with Pd-Au in a ratio of 6: 1 on a-alu-ina tablets. The selectivity of the catalyst of Example 13 was tested in a stirred tank process for the preparation of vinyl acetate. The data is summarized in Table II. The selectivity of the catalyst of Example 14 was tested in a microunit procedure for the preparation of vinyl acetate. The comparative data are summarized in Table V.

Comments regarding the Tables It is reported that the selectivity data are differentiated either in MUAV or TAAV unit. The catalysts reinforced by fluorescence aßpectoscopy with X-rays (EFX) were analyzed unless otherwise indicated. Temp.

Shell is the temperature of the hot water around the provalola flow reactor. Double = means that catalytic rebounds were placed on the reinforcement or substrate.

Abbreviations in the tables RTE = space and time performance PIA = nductively coupled plasma spectroscopy CONV A Oa = adjusted oxygen conversion PE = heavy ends EtOAc = ethyl acetate HOAc = acetic acid MET = transmission electron microscopy TTL = total BEA = bases found after CUAPRP l DATA OF CATALYSTS PREPARED THROUGH THE PROCEDURE PE MICRQEMULSIQN DESCRIPTION ANALYSIS Example 1 »SiO-, 0.23% Pd, 0.10% Au Mottled catalyst Binder 75 ppm Cl, 4.9% insufficient Aerosil 200 / MgO KOAc metal loading for BET analysis SA = 186 m * / g Pore Volume 0.82 cc / g Pd : Au of 4: 1 Example 2, Si0-? 0.30% Pd, 0.13% Au Catalyst Speckle Binder < 50ppm Cl »5.4% insufficient load of Aerosi 1 300 / kaolin in KOAc metal for analysis BET SA = 245 ma / g Pore Volume 0.81 cc / g Pd: Au of 4: 1 TABLE I (CONTINUED) Example 3, SiO-v 0.30% Pd, 0.13% Au Mottled catalyst Agluti ante < 50ppm Cl, 5.3% insufficient load of Aerosil Al .-. 03 KOAc metal for BET analysis SA = 238 ma / g Pore Volume 1.02 cc / g PIC: AU of 4: 1 Example 4 0.58% Pd, 0.35% Ay (uco) Operation in TAAV Raschig rings 46.9 g catalyst BET SA = 0.7 ma / g Temp. 173 C Pore Volume 0.45 cc / g Selectivity of C0-. 3: 1 Example 5, SiO -. * 0.86% Pd, 0.52% Au Operation in MVAV Raschig Rings 16.2 g Catalyst of T-4358-E-1 < 50 ppm Cl, 5.1% K0Ac BET SA = 235 mag Reaction analysis Temp. 179 C Pore Volume 0.63% Pd, 0.34% AU 0.91 cc / g 9.1% KOAC Select CO quality, Pd: Au of 3: 1 10.7% CPAPRQ I (CONTINUED) Example 6, SiO ", 0.53% Pd, 0.25% Au Operation in MVAV Raschig rings 16.3 g catalyst of T-4358-E-1 < 50 ppm Cl, 7.1% K0AC BET SA = 235 ma / g Reaction analysis Temp. 179 C Pore Volume 0.43% Pd, 0.20% Au 0.91 cc / g 8.4% KOAc Selectivity of C0; Pd: Au of 4: 1 8.5% Example 7 0.37% Pd, 0.17% Au (ICP) Operation of VAM Tablets of 35.5 g catalyst a-Ala03 BET SA = 4 ma / g Temp 155 c; 160 C Pore Volume Selectivity of C0.?. "* 5 cc / g 18.7% 21.1% 7.1% .7.7% Example 8 0.80% Pd, 0.21% Au (ICP) VAM operation Tablets of 35.5 g catalyst a-Ala0a BET SA = 4 ma / g Temp 145 c; 150 C Pore Volume Selectivity of CO. 0. 25 cc / g conv. 02 30.3%, 36.7% Coa double coating 7.1%, 7.7% Pd: Au of 7: 1 CUAPRQ I < CONTINUATION) Example 9 0.502% Pd, 0.24% Operation of VAM Tablets of 0.54% K (ICP) 35.1 g catalyst -A1aOa BET SA = 4 ma / g Temp 151 C; Pore Volume Selectivity of CO .., 0.25 cc / g conv. 02 35.6% Coating double CO »7.7%» Pd: Au of 4: 1 Example 10 0.47 %% Pd, 0.25% Au Operation of VAM Tablets of 0.65% K (ICP) 35.9 g catalyst or? -Al aOa "* = 4 ma / g Temp 155 C; Pore Volume Selectivity of CO, 0.25 cc / g conv. 02 21.31% Coated with pd, coated after CO to 8.39% Au CAfAPRQ l < CQNTINUA? IPN > Example 11 0.30% Pd, 0.18% Au Operation of VAM Tablets of 0.65% K (ICP) 35.5 g catalyst a-AlaOa BET SA = 4 ma / g Temp 155 C; Pore Volume Selectivity of CO, 0. 25 cc / g conv. 02 24% Coated with pd »coated after COa 7.1% Example 12 0.2B %% Pd. 0.17% Au Operation of VAM Tablets of 0.88% K (ICP) 35.5 g catalyst tx-AlaOa BET SA = 4 m3 / g Temp 155 c; Pore Volume Selectivity of CO, 0. 25 cc / g conv. 02 23% Pd: Au 3: 1 calcined at 300 ° C C0_ 9.0% TABLE II? COMPARATIVE CUAPRQ PE DUCKS) PROCEDURE IN AGITATED TANK FOR VINYL ACETATE. WITH Pd-AU ON AN A-ALUMINA REINFORCEMENT Example Number 4 8 13 Identification of the AlaOa to 3.i: i AlaOa to 7: 1 2.2: 1 AlaOj catalyst of the tasting- 18.00 20.000 19,500 lizatíor Sel. to C0_. (a, b) 11,984 12,285 11,152 Sel. to EP 0.504 0.569 0.614 Sel. a ETOAC 0.068 0.144 0.063 RET g AV / L / Hr (a, C) 6 67755..775544 544.238 695, 656 CONV aj. Or ... (d) 45,755 45,224 46,575 Reactor Top Deg. 172,800 156,300 164,270 C (e) Reactor Bot Deg. 175,500 160,800 167,230 C (e) Pressure Kg / cma 111,958 11,951 11,940 Supply of 1,017 1,020 1,016 Ow mol / hr 1,017 1,020 1,016 Amount of 5,007 5,007 5,000 -, H- ,, moles / hr Supply of 1,976 1,908 1,937 CU? PRQ II (CONTINUED) HOAC, moles / hr Supply of A. SAZ A. SAZ 4.940 w, moles / hr Supply of 5,007 5,007 5,000 % Oa considered 96,802 94,645 96,643 (f)% C .., H-4 considered 99,083 98,057 99,152 (g)% HOAC considered 101,118 99,994 106,462 (h)% Mass considered 99,711 98,897 101,156 (i)% weight Pd (PIA) 0.58% 0.80% 1.1%% weight Au 0.35% 0.21% 0.89% Particle size 8.3 nm (K) 10.7 nm Notes (a) Normalized to 45% conversion of 0.?,. (b) Adjusted selectivity of COa = (moles of the CO product to less moles of COa supply) 100/2 (adjusted conversion of CaH-) where adjusted conversion of aH- = moles of C-.H- * considered less moles of the product of CßH. (c) RET, g AV / 1 hr = (AV produced, g / hr x 1000) / volume of catalyst m.

TABLE II (CONTINUED) (d) Conv. aj. of Oa = (moles of 0a supplied, BED minus moles of Oa product) lOO / moles of Oa supplied, where BED = mass considered. (e) The temperature of the reactor, degrees C »is the average of the circulation range temperature above and below the catalyst, (f) 0a considered = (total moles of 0a recovered, BED / total moles of supply of 0-. ) 100. (g) CaH- «. considered = (total moles of CaH-, recovered, BED / total moles of supply of C ^ H ^ 100. (h) HOAc considered = (total cumulative HOAc, BED / total HOAc supply moles) 100 (i) ) Mass considered = (total grams of product recovered / total grams of supply) 100. (K) Measurement of MET performed after the operation in an AAV unit.

CUAPRP III Microunit procedure for vinyl acetate. with Pd-Au sftbre reinforcement dg s lj? s Example Number 5 6 Catalyst identification Metals Pd / Au Metals Pd / Au to 3: 1 over to 4: 1 over T-4358-E-1 T-4358-E-1 Size 5 mm 5 mm Temp. Cat. 178.800 179.500 Shell temp. 173.900 177.650 Pressure 100,000 100,000 Speed of Oa / N_a 89 .840 897.290 (cm3 / min) Speed of C., H ^ 1014.070 1014.580? En3 / m) Speed of C ^ H ^ 0.800 0.800 (mL / min) RET (g / L / hr 352.024 262.756 Mass considered (%) 100.001 99.826 Conv. of 0 ^ (%) 31.502 18.76 Conv. of CJ-, (%) 13.395 10.630 Conv. of AcOH (%) 7.129 5.367 O ,, considered (%) 101.141 103.298 C-.H., Considered (%) 98.466 98.709 AcOH considered (%) 101.370 100.390 TABLE III (CONTINUED) Sel. of VA (%) 88,751 90,911 Sel. of C0 ,,? (%) 10.745 8.555 Sel. of EtOAc (%) 0.126 0.130 Sel. of EtOAc < %) 0.126 0.130 Sel. of TTL HE (%) 0.379 0.403 The selectivity values are normalized and based on the label.

TABLE IV PROCEDURE IN HICROUNITY FOR VINYL ACETATE WITH Pd-Au REINFORCEMENT OF «-ALUMIN Exemplary Number 7 7 8 8 9 Identification of the cataPd / Au alloyed to 4: 1 Pd / Au alloyed to 4: 1 Pd / Au alloyed to 7: 1 Pd / Au alloyed to 7: 1 Pd / Au alloyed to 4: 1 liner on AI2O3 on AI2O3 on AI2O3 on AI2O3 on AI2O3 No. of coatings Double Double Double Taiaño 3 II 3 II 3 ii 311 3 ii Teip. Med. Cat. 157,130 162,130 147,730 152,930 154,520 Teip. Shell 155,450 160,500 145,650 149,950 151,050 Pressure 100,000 100,000 100,000 100,000 100,000 -) Speed of O2 / N2 902,000 894,210 904,530 905,070 928,700 °° Speed of C2H4 (c? 3 / ain) 1015.090 1006.320 1023.700 1024.310 1056.420 Speed of HOA (iL / iin) 251.442 309.747 417.847 492.272 435.261 RET (g / L / hr) 251.442 309.747 417.847 492.742 435.261 Hasa considered () 99.658 100.308 100.696 100.855 98.248 Conv. of O2 (\) 18,174 21,118 30,353 36,754 35,648 CQBEBO IV (CONTI DBS ION) Conv of C2H, (\) 8.973 8.979 13.667 14.892 20.508 Conv. of AcOH (.) 6,364 7,564 7,685 9,858 9,820 0 considered (.) 101,807 104,459 102,739 103,375 98,985 C2H * considered (I) 97,489 97,252 98,648 97,646 96,631 AcOH considered. { %) 101,522 103,767 103,485 105,289 97,886 Sel. of VA 91,952 91,416 92,185 91,617 91,361 Sel. of CO2 0.149 0.132 0.198 0.186 0.175 Sel. of EtOAc 0.149 0.132 0.198 0.186 0.175 Sel. Total EP 0.817 0.714 0.518 0.462 0.751 \ Weight Pd 0.37 0.37 0.80 0.80 0.50 g * Au Weight 0.17 0.17 0.21 0.21 0.24 TABLE V PROCEDURE IN HICROUNIDÉ FOR HIV-ACETATE WITH Pd-Au REINFORCEMENT OF «-ALUMINATION Hose of Ejeplelo 10 11 12 13 14 14 Identification of the cataRevestment of 3: 1 Pd / Au 3: 1 Pd / Au 3: 1 Pd / Au 3: 1 Pd / au to 4: 1 Pd lizer, after reverse- over AI2O3 on AI2O3 on AI2O3 on AI2O3 on Double Double Double AI2O3 3 ii 3 ii 311 311 Taiaño 3 II 3 ?? 3 II 3 II 3 ?? Teip. Med. Cat. 157,500 157,920 156,620 167,800 159,370 Teip. Shell 155,750 155,350 153,610 163,800 156,050 é Pressure 100,000 100,000 100,000 100,000 928,700 Speed O2 / N2 (15/85) 918,860 913,090 903,530 907,510 915,180 (c? 3 /? In) Speed of C2H * 1045.230 1038.670 1021.430 1030.460 1038.180 HOAc speed (iL / iin) 0.790 0.800 0.850 0.800 0.800 RET (g / L / hr) 236.543 321.512 279.441 375.372 443.986 Mass considered (t) 98.350 99.232 99.539 99.378 99.253 TABLE V (C-ONTENOACION) Conv. of O2 (%) 21,311 23,811 23,402 34,379 35,950 Conv. of C2H-, (.) 11,611 13,351 9,962 14,937 19,988 Conv. of AcOH 6,785 7,520 6,942 8,417 8,383 O2 considered. { %) 97,799 101,512 100,641 99,206 101,523 C2H4 considered (X) 96,788 97,295 97,397 97,447 98,371 AcOH considered [%) 98,517 100,213 101,125 100,856 98,664 Sel. of VA 90,600 91,967 90,183 88,868 90,570 Sel. of C02 8,395 7,169 9,046 10,458 8,778 Sel. of EtOAc 0.212 0.192 0.144 0.128 0.224 Sel. Total EP 0.793 0.672 0.627 0.546 0.429 \ Weight Pd 0.47 0.30 0.28 0.28 0.36 \ Au Weight 0.25 0.18 0.17 0.17 0.11

Claims (4)

1. NOVELTY OF THE INVENTION REIVI DICACIONES 1. - A process for the preparation of a catalyst for the production of vinyl acetate from ethylene »acetic acid and oxygen, which process consists of: 1) forming an aqueous solution of water soluble palladium and gold compounds; 2) dispersing the aqueous solution in a hydrophobic solvent with an effective amount of surfactant to form a microemulsion mixture; 3) treating the mixture in microemulsion with a reducing agent; and 4) impregnating a reinforcement with the mixture of step 3) to form a reinforced metal catalyst; and optionally »washing and drying the reinforced catalyst from step 4).
2. 2. The process according to claim 1 »further characterized in that the hydrophobic solvent is a hydrocarbon medium.
3. 3. The process according to claim 1 »further characterized in that the amount of surfactant ingredient is between about 2 and 20 grams per 30 milliliters of the microemulsion mixture.
4. 4. The process according to claim 1 »further characterized in that the surfactant is a nonionic surfactant. 5.- The procedure in accordance with the claim 1 »further characterized in that the reducing agent is hydrazine. 6. The method according to claim 1 »further characterized in that the reinforcement is an inorganic reinforcement. 7. The process according to claim S »further characterized in that the reinforcement is selected from the group consisting of silica» alumina »mixture of silica and aluminum» zirconium dioxide »titanium dioxide and calcium dioxide. B. The process according to claim 7. further characterized in that the reinforcement is alumina. 9. The method according to claim S »further characterized in that the reinforcement is in the form of spherical structures. 10. The method according to claim 6 »further characterized in that the reinforcing means is in the form of tablets. 11. The method according to claim 6 »further characterized in that the reinforcement means is in the form of Raschig rings. 12. The process according to claim 7 »further characterized in that the alumina of the catalyst reinforcement is α-alumina. 13.- The procedure in accordance with the claim 1. further characterized in that the reinforced metal catalyst of step 4) has a palladium metal content of between approximately 0.05 and 2.5% by weight and a gold metal content of between 0.05 and 0.6% by weight. based on the weight of the catalyst. 14. The process according to claim 1 »further characterized in that the reinforced metal catalyst of step 4) has a palladium: gold weight ratio of approximately 1-10: 1. 15. The process according to claim 1 »further comprising the step of impregnating the reinforced metal catalyst of step (4) with an aqueous solution of an alkali metal alkanoate activator and then drying the resulting catalyst. 1S.- The method according to claim 15 »further characterized in that the activating additive is alkali metal acetate. 17. A catalyst composition for the preparation of vinyl acetate from ethylene »acetic acid and oxygen» consisting of a colloidal alloy of palladium and gold on a reinforcing medium »prepared said composition according to any of claims 1 -1S. 18. The catalyst composition according to claim 17, further characterized in that the colloidal alloy of palladium and gold on the reinforcement has an average particle size of between about 1 and 20 nanometers. 19. - The catalyst composition according to claim 17 which has a palladium metal content of between about 0.1 and 2.5% and a gold metal content of between about 0.05 and 0.6% by weight, based on the weight of the catalyst. 20. The catalyst composition according to claim 17, which has a palpate weight ratio: gold of approximately 1-10: 1. 21. The catalyst composition according to claim 17 which has a palladium content of between about 0.1 and 2% by weight, based on the weight of the catalyst. 22. The catalyst composition according to claim 17 »further characterized in that the reinforcing means is alumina in the form of spherical structures. 23. The catalyst composition according to claim 17 »further characterized in that the reinforcing means is alumina in the form of tablets. 24. The catalyst composition according to claim 17 »further characterized in that the reinforcement means is alumina in the form of Raschig rings. 25. The catalyst composition according to claim 17, further characterized in that the reinforcing means is α-alumina. ESUMEN PE THE INVENTION This invention provides a microemulsion process for the preparation of a palladium and gold reinforced catalyst for the production of vinyl acetate from ethylene »acetic acid and oxygen; the preferred catalyst composition has a palladium and gold colloidal alloy content evenly distributed over an α-alumina backing; A catalyst according to the invention exhibits a sustained level of selectivity for the production of vinyl acetate over a prolonged period of the process. < 3C / b1m *? Ma * xal * ram * mmr P9B-T10F