KR100458786B1 - Heterogeneous bimetal palladium-gold catalyst for the production of vinyl acetate - Google Patents

Abstract

The present invention relates to heterogeneous bimetallic palladium-gold catalysts for the production of vinyl acetate from ethylene, acetic acid and oxygen. The catalyst of the present invention is prepared by forming a first shell dispersion film of colloidal palladium on the surface of a catalyst support, and adding a second shell dispersion film of colloidal gold metal on the surface of the catalyst support. The organometallic gold compound is used to apply the gold dispersion onto the surface of the catalyst support. Organometallic gold compounds do not require a fixation process. Preferred palladium-gold catalysts of the invention have high gold metal retention and exhibit durability and long selectivity in the production of vinyl acetate.

Description

Heterogeneous bimetallic palladium-gold catalyst for the production of vinyl acetate

The present invention relates to a process for providing a supported palladium-gold catalyst composition having improved activity and selectivity when producing vinyl acetate from ethylene, acetic acid and oxygen.

Well known commercial processes for the production of vinyl acetate are by gas phase reaction of ethylene, acetic acid and oxygen in the presence of a supported catalyst containing palladium.

A preferred type of vinyl acetate catalyst is one containing palladium metal and gold metal distributed on the surface of a supporting substrate such as silica or alumina.

Prior art documents describing supported palladium-gold catalysts for the production of vinyl acetate are described in US Pat. No. 3,761,513, which is incorporated herein by reference. 3,775,342, 3,822,308, 3,939,199, 4,048,096, 4,087,622, 4,133,962, 4,902,823, 5,194,417 and 5,314,858.

The activity and selection properties of the supported palladium-gold catalyst are influenced by the physicochemical form of palladium and gold metal content on the catalyst substrate.

US Pat. No. 4,048,096 describes a catalyst consisting of a palladium-gold alloy distributed as a shell coating on the outer surface of a catalyst support such as porous silica. The space-time-yield activity is enhanced when the vapor phase reaction of ethylene, oxygen and carboxylic acid to produce vinyl acetate by shell distribution of the palladium-gold alloy.

The selectivity of the palladium-gold catalyst during vinyl acetate synthesis, such as, for example, carbon dioxide selectivity and oxygen conversion rate during ethylene, oxygen and acetic acid vapor phase reactions, may also depend on palladium metal and gold on the outer and / or inner surface of the porous catalyst support substrate. It is influenced by the degree and uniformity of the metal distribution.

It is therefore an object of the present invention to provide a supported palladium-gold catalyst composition with improved activity and selectivity when producing vinyl acetate from ethylene, acetic acid and oxygen.

Another object of the present invention is to provide a supported vinyl acetate catalyst having a separately applied shell coating of dispersed colloidal palladium metal and gold metal.

Another object of the present invention is to provide a supported palladium-gold vinylacetate catalyst having a high gold retention, which shows durability and long-term selectivity when preparing vinylacetate from ethylene, acetic acid and oxygen.

It is another object of the present invention to provide a process for preparing a supported vinyl acetate catalyst having a separately applied shell coating of colloidal palladium metal and gold metal dispersed on a support surface.

Still other objects and advantages of the present invention will become apparent from the following detailed description and examples.

At least one object of the present invention is a process for preparing a catalyst for producing vinyl acetate from ethylene, acetic acid and oxygen, which comprises (1) impregnating a porous catalyst support medium with a solution of a palladium compound, the palladium compound on the surface of the catalyst support Reducing to a first shell dispersion film of colloidal palladium metal to prepare a precursor catalyst; And (2) impregnating the precursor catalyst with an organic solvent solution of an organometallic gold compound, and reducing this gold compound to a second shell dispersion film of colloidal gold metal on the surface of the catalyst support to produce a bimetallic palladium-gold catalyst. Achieved by a process comprising the steps, which provides improved carbon dioxide selectivity and oxygen conversion when making vinyl acetate from ethylene, acetic acid and oxygen.

The catalyst support medium is selected from porous substrates such as silica, alumina, silica / alumina, titania and zirconia in the form of spheres, tablets, Raschig rings and the like.

Typical catalyst support media are described by porous silica spheres having a radius of 1 to 8 mm, a pore volume of 0.1 to 2 cc / g and an internal surface area of 10 to 350 m 2 / g. Commercial catalyst support media are widely commercially available and are, for example, porous 5 mm silica spheres sold under the trade name KA-160 by Sud-Chemie.

In one method for preparing the improved vinyl acetate catalyst of the present invention, the catalyst support is once impregnated with an aqueous solution of a water soluble palladium compound. Suitable palladium compounds include palladium (II) chloride, palladium (II) nitrate, palladium (II) sulfate, sodium tetrachloropalladium (II) and the like.

The volume of the aqueous impregnation solution is preferably about 95 to 100% of the absorption capacity of the catalyst support.

The impregnated catalyst support is treated with an aqueous solution of a basic alkali metal salt such as sodium silicate, sodium carbonate or sodium hydroxide. A sufficient amount of basic alkali metal salt is used to immobilize the palladium compound on the catalyst support, i.e., to precipitate the palladium hydroxide and introduce it onto the catalyst support surface.

In another method of preparing the catalyst, the catalyst support is once impregnated with an organic solvent solution of one or more organometallic palladium compounds. Suitable organometallic compounds include palladium acetylacetonate, palladium acetate, bis (η ³ -allyl) palladium (II), η ³ -allyl (η ⁵ -cyclopentadienyl) palladium (II), η ³ -allyl (1, 5-cyclooctadiene) palladium (II) tetrafluoroborate and the like.

Organic solvents that can be used for the organometallic palladium solution include pentane, hexane, cyclohexane, heptane, octane, isooctane, naphtha, naphthene, benzene, chlorobenzene, nitrobenzene, dichloromethane and the like.

There may be significant advantages by using organic solutions of organometallic palladium compounds instead of aqueous solutions of water soluble palladium compounds. After impregnation of the catalyst support with a solution of the organometallic palladium compound, no fixed treatment is necessary with the basic alkali metal salt. The omission of precious metal fixation procedures prevents the loss of metals that typically occur during fixation and cleaning steps. High precious metal loadings in the catalyst are essential for optimum activity and selectivity in the -vinyl acetate process.

After impregnating the catalyst support with the palladium compound, the catalyst support is treated with a reducing agent to convert the palladium compound into a shell coating of colloidal palladium metal particles on the catalyst support surface. Examples of reducing agents are hydrazine, formaldehyde, ethylene, hydrogen and the like.

A precursor catalyst having a content of palladium metal previously reduced is impregnated with an organic solvent solution of one or more organometallic gold compounds. Suitable organometallic gold compounds include trimethylsiloxydimethyl gold, trimethylsilylmethyltriphenylphosphine gold, dimethyl gold acetate, gold triacetate and the like.

Any suitable organic solvent can be used for the organometallic gold impregnation solution, such as those listed above for the organometallic palladium solution.

After the impregnation step, the organometallic gold compound is reduced to a second shell coating of colloidal gold metal particles dispersed on the catalyst support surface. When introducing the colloidal gold metal into the vinyl acetate catalyst, it is particularly important that the pre-reduction fixation procedure is omitted. Gold is more difficult to immobilize with basic alkali metal salts, and the immobilization procedure results in a low and inconsistent gold retention during catalyst preparation. The high and constant retention of gold in the catalyst composition is possible by the process of the present invention for the production of vinyl acetate catalysts.

In the process of the present invention for the production of vinyl acetate catalysts, palladium and gold starting materials are used in amounts that provide about 1 to 10 g of palladium metal and about 1 to 10 g of gold metal per liter of finished catalyst.

The catalyst of the present invention may have a palladium metal content of about 0.2 to 2.5 weight percent, and a gold metal content of about 0.2 to 2.5 weight percent. The weight ratio of palladium: gold may be about 0.5 to 10: 1.

Optionally, the process of the present invention for preparing the catalyst may comprise an additional process for increasing the selectivity of the catalyst during vinyl acetate production. The palladium-gold catalyst obtained by the process described above is treated with an aqueous solution of alkali metal acetate, for example potassium acetate, and then dried. Alkali metal acetate content may range from about 2 to 10 weight percent based on the weight of the finished catalyst.

An important advantage of the present invention is achieved by a heterogeneous bimetallic palladium-gold catalyst for producing vinyl acetate from ethylene, acetic acid and oxygen, wherein the catalyst composition is a first shell dispersion coating of colloidal palladium metal on the catalyst support surface. And a porous catalyst support medium containing a second shell dispersion film of colloidal gold metal on the surface of the catalyst support.

In general, the catalyst of the present invention is used during the vinyl acetate process by contacting ethylene, acetic acid and oxygen or air with the catalyst at a temperature of about 100 to 200 ° C. and a pressure of about 1 to 10 atmospheres. The reaction is usually carried out in excess of ethylene.

Preferred catalysts of the process of the invention are characterized by high palladium metal and gold metal retention and exhibit durability and improved long time selectivity when producing vinyl acetate from ethylene, acetic acid and oxygen.

The catalyst of the present invention can provide an efficient production of vinyl acetate while producing less carbon dioxide than conventional Bayer vinyl acetate catalysts of the type described in British Patent No. 1,246,015, which is incorporated herein by reference.

The following examples further illustrate the invention. While components and specific components are generally shown, various modifications may be made within the scope of the present invention in light of the above description.

In the examples the palladium-gold catalyst is prepared in different combinations and ratios of palladium and gold starting materials and compared with Bayer-type palladium-gold catalysts for the production of vinyl acetate from ethylene, acetic acid and oxygen.

Palladium-gold catalyst was prepared from Na ₂ PdCl ₄ / Au (OAc) ₃ (OAc = acetate) on silica, as described by catalysts A through E in the examples.

Palladium-gold catalyst was prepared from Na ₂ PdCl ₄ / Ph ₃ PAuCH ₂ SiMe ₃ on silica, as described by catalysts F and G in the examples.

Palladium-gold catalyst was prepared from Na ₂ PdCl ₄ / Me ₂ AuOSiMe ₃ on silica, as described by catalysts H and 1 in the examples.

In the following examples, the vinyl acetate stirred tank reactor (VAST) unit is a Berty reactor, or a continuous continuous stirred tank that is run at a constant oxygen conversion (about 45%). The catalyst (62 cc) is loaded into a basket in the reactor, the measured amounts of acetic acid, ethylene and oxygen are added to the nitrogen diluent and the reactor is brought to a predetermined temperature by a heating mantle, which temperature is measured above and below the catalyst. . The reaction ends after approximately 18 hours at a temperature maintaining 45% oxygen conversion. The product is measured by gas phase chromatography. CO ₂ selectivity tends to be slightly higher for the same catalyst when tested in the VAST unit compared to VAMU because the product vinyl acetate is regenerated in contact with the catalyst in the reaction sequence.

In an embodiment, the vinyl acetate micro unit (VAMU) reactor operates in a plug flow type at constant temperature. The VAMU reactor is 3ft long with 3mm coaxial tropical couple wells. 16 mm inner diameter stainless steel tube. The reactor is equipped with a heating jacket through which the water and steam circulate. A 30 cc sample of catalyst is diluted with up to 150 cc of support and loaded into the reactor. The catalyst / support mixture is finished with 30 cc of support. After one pass of oxygen, ethylene and acetic acid in a nitrogen diluent at constant temperature or constant oxygen conversion, the product is analyzed by gas phase chromatography.

Example 1

This example describes a method for preparing gold (III) triacetate according to US Pat. No. 4,933,204.

Gold hydroxide [Au (OH) ₃ ] was prepared by heating HAuCl ₄ for 3 h at pH 8 in aqueous Na ₂ CO ₃ . The resulting red solution was filtered and the Au (OH) ₃ precipitate was washed with water and air dried. Au (OH) ₃ was dissolved while heating in glacial acetic acid to form a solution of gold triacetate.

Example 2

This example describes the preparation of pre-reduced palladium from a Na ₂ PdCl ₄ composition on silica, using a palladium-gold type catalyst as an intermediate in the synthesis of the present invention.

250 cc of 5 mm silica sphere (KA-160, Shed Chemie) was impregnated with 82.5 ml of aqueous Na ₂ PdCl ₄ (7 g Pd / L support) to initial humidity. The impregnated support was treated with aqueous NaOH 283 cc (50% by weight NaOH / H ₂ O: 120% of the amount required to convert the metal salt in hydroxide form). The supported catalyst was spun for 2.5 hours at Rotovap at about 5 rpm.

After fixation, the treated carrier was washed continuously with distilled water to remove chloride ions until the tested wash eluent was negative for silver nitrate. The flow rate of water was about 200 cc / min for each wash. The carrier from each set was dried under continuous nitrogen flow at a temperature of about 150 ° C. The dried support was reduced to 5% ethylene in nitrogen at 150 ° C. for 5 hours.

Example 3

This example illustrates the properties of the catalyst of the present invention when preparing vinyl acetate from ethylene, acetic acid and oxygen in the VAST and VAMU systems as compared to the Pd-Au catalyst preparation method of the present invention, Bayer Pd-Au catalyst.

Catalyst A

0.88 g of Au (OH) _{3 in} 35 ml of acetic acid in the reaction flask was heated at 60 ° C. for 2 hours to prepare a clear reddish brown solution of Au (OAc) ₃ . 35 ml of this solution was added to 100 ml of pre-reduced Pd (Example 2) on silica in a reaction flask at 60 ° C. and impregnation was carried out for about 30 minutes. The solvent medium was removed under vacuum at 60 ° C. The treated silica support was reduced with 5% ethylene in nitrogen at 120 ° C. for 5 hours. The resulting catalyst was impregnated with 33 g of KOAc in 33 ml of water and then dried in a fluid phase dryer at 100 ° C. for 1 hour to prepare Pd-Au Catalyst A.

Catalyst B

A Pd-Au catalyst B was prepared according to the preparation of Catalyst A, except that 0.69 g of Au (OH) _{3 in} 38 ml of acetic acid was used.

Catalyst C

A Pd-Au catalyst C was prepared according to the preparation of Catalyst A, except that 0.5 g of Au (OH) _{3 in} 35 ml of acetic acid was used.

Catalyst D

A Pd-Au catalyst D was prepared according to the preparation of Catalyst A, except that 0.25 g of Au (OH) _{3 in} 35 ml of acetic acid was used.

Catalyst E

A Pd-Au catalyst E was prepared according to the preparation of Catalyst A, except that 0.88 g of Au (OH) _{3 in} 17 ml of acetic acid and 45 ml of pre-reduced Pd (Example 2) on silica were used.

Catalysts A to D were tested in VAST systems compared to Bayer Pd-Au catalysts for the production of vinyl acetate from ethylene, acetic acid and oxygen.

Comparison data is summarized in Table I. Activity increased with increasing palladium to gold ratios in catalysts A to D. Catalysts A through D tend to produce less CO ₂ than Bayer catalysts. Catalyst A has improved CO ₂ selectivity (8.7 vs 9.5), higher activity (2.23 vs 1.37), and lower EtOAc (0.054 vs 0.06) than Bayer's commercial catalyst.

Catalysts A through E were tested on VAMU systems as compared to Bayer Pa-Au catalyst for the production of vinyl acetate.

To evaluate the catalytic activity, the midpoint shell temperature of the unit was recorded at a fixed oxygen conversion (about 45%). Lower temperatures mean higher catalytic activity at constant oxygen consumption.

Comparative data is summarized in Table II below. Catalysts D and E showed higher CO ₂ selectivity and lower catalyst activity compared to catalysts A through C. Catalysts A to C have improved CO ₂ selectivity and higher catalytic activity than Bayer's Pd-Au catalyst.

SEM-EDX X-ray results indicated that Catalysts A through E had palladium metal dispersed as shell coating on the outer surface of the silica support. Gold metal was mainly dispersed on the outer surface of the silica support as a second shell coating, and gold metal was dispersed on the inner pore surface of the silica support at a lower rate.

Example 4

This example illustrates the properties of the catalyst of the invention in the preparation of the Pd-Au catalyst of the invention, in the production of vinyl acetate from ethylene, acetic acid and oxygen in the VAST and VAMU systems compared to Bayer's Pd-Au catalyst. .

Catalyst F and Catalyst G

Ph ₃ PAuCH ₂ SiMe ₃ (1 g) 34 mL CH ₂ Cl ₂ solution was added to 90 mL of pre-reduced palladium on silica (Example 2) in a reaction flask and the impregnation was carried out for about 30 minutes. Solvent medium was removed under vacuum. The treated silica support was reduced with 5% ethylene in nitrogen at 120 ° C. for 5 hours. The resulting catalyst was washed with toluene and dried at 120 ° C. for about 16 hours under vacuum. The catalyst was impregnated with 3.8 g of KOAc in 30 ml of water and then dried in a fluid phase dryer at 100 ° C. for 1 hour to give Pd = Au catalyst F. Catalyst G was prepared in the same manner.

Catalyst H

16 ml of a hexane solution of Me ₂ AuOSiMe ₃ (0.38 g) was added to 45 ml of pre-reduced Pd (Example 2) on silica in a reaction flask and the impregnation was carried out for about 30 minutes. Solvent medium was removed under vacuum. The treated silica support was reduced with 5% ethylene in nitrogen at 120 ° C. for 5 hours. The resulting catalyst was impregnated with 1.8 g of KOAc in 15 ml of water and then dried in a fluid phase dryer at 100 ° C. for 1 hour to prepare Pd-Au catalyst H.

Catalyst I

Pd-Au catalyst I was prepared following the procedure of catalyst H, except that 32 mL of a hexane solution of Me ₂ AuOSiMe ₃ (0.85 g) and 90 mL of pre-reduced Pd (Example 2) on silica were used. Prepared.

Catalysts F through I were tested on VAMU systems as compared to Bayer Pd-Au catalyst for vinyl acetate preparation.

Comparative data is summarized in Table III. Catalysts F through I showed improved CO ₂ selectivity over Bayer catalysts. Catalyst I had a much lower shell temperature (high catalytic activity) than Bayer catalyst. Catalysts H and I had high gold metal retentions of 86% and 98%, respectively. Catalysts F and G had a gold retention of 52% and 57%, respectively. Catalysts F and I were tested on a VAST system as compared to Bayer Pd / Au catalyst for the production of vinyl acetate.

Comparative data is summarized in Table IV below. Catalysts F and I had improved CO ₂ selectivity and higher catalytic activity than Bayer catalysts.

SEM-EDX X-ray results show that Catalyst I has a Pd-Au shell dispersion coating of metal on the silica outer surface. Catalyst F had a palladium metal dispersed as a shell coating on the silica outer surface. Gold metal was mainly dispersed on the outer surface of the silica support as a second shell coating, and a smaller proportion of gold metal was dispersed on the inner pore surface of the silica support.

Catalyst G was tested in a VAMU system continuously over seven days for the production of vinyl acetate. The extended test period was to monitor the catalyst durability, and long time selectivity of the catalyst of the present invention. Data was recorded every 24 hours.

The data is summarized in Table V below. The data showed that catalyst G of the present invention has long term catalyst durability and selectivity.

Claims (19)

A process for preparing a catalyst for producing vinyl acetate from ethylene, acetic acid and oxygen, (1) impregnating the porous catalyst support medium with a solution of the palladium compound and reducing the palladium compound to a first shell dispersion film of colloidal palladium metal on the catalyst support surface to produce a precursor catalyst; And (2) impregnating the precursor catalyst with a solution of an organometallic gold compound and reducing this gold compound to a second shell dispersion film of colloidal gold metal on the surface of the catalyst support to provide improved carbon dioxide selectivity and oxygen conversion. A method of making a catalyst comprising the step of preparing a bimetallic palladium-gold catalyst. The method of claim 1, The catalyst support medium is impregnated in step (1) with an aqueous solution of a palladium compound and the palladium compound is immobilized on the support medium with an aqueous alkaline solution prior to reduction. The method of claim 1, A process for preparing a catalyst, wherein in step (1) the catalyst support medium is impregnated with an organic solvent solution of organometallic palladium compound. The method of claim 1, The process for preparing a catalyst, wherein the organometallic gold compound in step (2) is gold triacetate. The method of claim 1, The process for preparing a catalyst, wherein the organometallic gold compound in step (2) is dimethyl gold acetate. The method of claim 1, The process for preparing a catalyst, wherein the organometallic gold compound in step (2) is trimethylsiloxydimethyl gold. The method of claim 1, The process for preparing a catalyst, wherein the organometallic gold compound in step (2) is trimethylsilylmethyltriphenylphosphine gold. The method of claim 1, Wherein the catalyst product has a palladium metal content of about 0.2 to 2.5 weight percent, and a gold metal content of about 0.2 to 2.5 weight percent, based on the weight of the catalyst. The method of claim 1, A process for preparing a catalyst, wherein the catalyst support medium is based on silica. The method of claim 1, A process for preparing a catalyst, wherein the catalyst support medium is based on alumina. The method of claim 1, The catalyst product has a palladium: gold weight ratio of about 0.5 to 10: 1. The method of claim 1, In a further step, the catalyst product is impregnated with an aqueous solution of an alkali metal alkanoate activator and dried to provide a catalyst product with increased selectivity for vinyl acetate production. The method of claim 12, The activator additive is an alkali metal acetate. Catalyst composition for producing vinyl acetate from ethylene, acetic acid and oxygen, prepared according to the method of claim 1. A heterogeneous bimetallic palladium-gold catalyst composition for producing vinyl acetate from ethylene, acetic acid and oxygen, comprising a first shell dispersion film of colloidal palladium metal on the catalyst support surface, and a colloidal gold metal film on the catalyst support surface. A catalyst composition prepared according to the method of claim 1, containing the second shell dispersion film. The method of claim 15, A catalyst composition having a palladium metal content of about 0.2 to 2.5 weight percent and a gold metal content of about 0.2 to 2.5 weight percent based on the weight of the catalyst. The method of claim 15, A catalyst composition having a palladium: gold weight ratio of about 0.5 to 10: 1. The method of claim 15, A catalyst composition wherein the catalyst support medium is based on silica. The method of claim 15, A catalyst composition wherein the catalyst support medium is based on alumina.