RS49604B - THE CATALYST AND ITS USE IN THE PRODUCTION OF VINYLACETATE - Google Patents

Abstract

A catalyst used for the production of vinyl acetate, comprising (1) a catalyst support selected from porous silica, aluminum oxide, silica / aluminum oxide, titanium dioxide, zirconium oxide and carbon, ( 2) palladium, (3) heteropoly acid, (4) at least one acetic acid catalyst promoter selected from a compound containing selenium, titanium, tellurium and / or vanadium, (5) at least one vinyl acetate promoter selected from the group consisting of cadmium acetate, gold , copper and nickel. The application contains 1 more independent and 7 dependent claims.

Description

The present invention relates to a process for the production of vinyl acetate and to a new catalyst used in that process.

Vinyl acetate is usually obtained commercially by bringing acetic acid and ethylene into contact with molecular oxygen, in the presence of a catalyst active for the production of vinyl acetate.

A catalyst suitable for the production of vinyl acetate may be a Group VIII metal, preferably palladium, the promoter is an alkali metal acetate, for example sodium or potassium acetate, and optionally a co-promoter, for example cadmium acetate or gold. The publication US 5185308 describes in detail the process of producing vinyl acetate by catalytic oxidation of ethylene in the presence of acetic acid. The catalyst used is a supported palladium catalyst, with promoter gold and potassium acetate.

Acetic acid, which is used as a feedstock in the production of vinyl acetate, can be obtained in several processes, which are used in industry, for example, by carbonylation in the liquid phase of methanol and/or its reactive derivative, in the presence of a catalyst, a noble metal of Group VIII, an alkyl iodide promoter and a final concentration of water. The acetic acid produced is then used as a reactant to produce vinyl acetate. Therefore, this procedure is actually in two stages.

US 3373189 relates to a process for the production of vinyl acetate from ethylene and oxygen, using a palladium catalyst. US 4188490 describes a process for the production of acetic acid and vinyl acetate using a zinc oxide supported palladium catalyst. US 3637818 describes a process for the production of acetaldehyde. acetic acid and vinyl acetate by ethylene oxidation in the presence of a noble metal and manganese or cobalt oxides. The above-mentioned procedures are carried out in the liquid phase.

We have now found that vinyl acetate can be obtained directly from a mixture of reactants consisting of ethylene, optionally water and an oxygen-containing gas. without the need to produce acetic acid first. in a special stage of the overall procedure. Using a modified palladium catalyst, vinyl acetate can be produced directly in a one-step process.

Accordingly, the present invention provides a process for the production of vinyl acetate consisting of reacting ethylene with a gas containing oxygen, and optionally water, in the presence of a catalyst consisting of: (1) a catalyst support, (2) palladium, (3) an acid, (4) at least one acetic acid catalyst promoter, and (5) at least one vinyl acetate catalyst promoter and/or co-promoter.

Another embodiment of the present invention provides a catalyst for use in the production of vinyl acetate comprising: (1) a catalyst support, (2) palladium, (3) an acid, (4) at least one acetic acid catalyst promoter, and (5) at least one vinyl acetate catalyst promoter and/or co-promoter.

The present invention provides a new and economical route for the production of vinyl acetate. The process is not only highly selective in relation to the production of vinyl acetate, but does not require the independent and separate production of acetic acid, which is then used as a co-reactant in the process. In contrast, using a modified palladium catalyst leads to in situ oxidation of the reactants from which acetic acid is obtained, which is then oxidized with ethylene to vinylacetate. The bifunctional nature of the catalyst leads to a direct process.

The disclosed invention provides a process for the production of vtnll acetate from ethylene, a gas containing oxygen and optionally water. Ethylene can be essentially pure or mixed with one or more of the following: nitrogen, methane, ethane, carbon dioxide, hydrogen, and low levels of CJC* alkenes or alkanes.

The oxygen-containing gas can be air or a gas richer or poorer in molecular oxygen than air. Conveniently, the gas can be oxygen diluted with a suitable diluent, for example nitrogen H1 carbon dioxide. Preferably, the oxygen-containing gas is oxygen.

Optionally, water can be co-introduced into the reaction chamber. Where water is present in the reaction chamber, it may be in an amount of up to 50 volume percent, preferably in the range of 10 to 30 volume percent.

A small amount of acetic acid can also be introduced into the reaction chamber. Conveniently, the acetic acid can be introduced via the recycle stream. Where it is desirable to introduce acetic acid, it may be in an amount of up to 50 volume percent, preferably in the range of 5 to 20 volume percent.

The catalyst according to the presented invention contains palladium. The concentration of palladium can be greater than 0.5% by weight, preferably greater than 1% by weight in relation to the total weight of the catalyst. The concentration of palladium can be as high as 10% by weight when used in a stationary column or a fluidization column.

The catalyst according to the presented invention is a supported catalyst. Suitable catalyst supports may contain porous silica, alumina, silica/alumina, titanium dioxide, zirconium dioxide, or carbon. Preferably, the carrier is silicon dioxide. Suitably, the carrier may have a pore size of 0.2 to 3.5 ml per gram of carrier, a surface area of 5 to 800 m<2>per gram of carrier, and a density of 0.3 to 1.5 g/ml. For catalysts used in a fixed column process, the support typically has dimensions of 3 to 9 mm and may be spherical, tablet, extrudate, shaped pill, or any suitable shape. For catalysts used in a fluidization column, the carrier may typically have a particle size distribution such that at least 60% of the catalyst particles have a particle diameter below 200 µm, preferably at least 50% below 105 µm, and no more than 40% of the catalyst particles have a diameter of less than 40 µm.

The catalyst composition includes at least one acetic acid catalyst promoter. Suitable promoters are compounds containing selenium, titanium, tellurium and/or vanadium. It is preferable that the acetic acid catalyst promoter is an oxide, acetate or acetylacetonate of at least one of the mentioned metals. It is desirable that the content of the acetic acid catalyst promoter in the finished catalyst is up to 10% by mass.

In addition to the palladium compound and the acetic acid promoter, this catalyst contains at least one vinyl acetate catalyst promoter and/or co-promoter, preferably both promoter and co-promoter. Suitable promoters are gold, copper and/or nickel and cadmium acetate. The preferred promoter is gold. Suitable sources of gold are gold chloride, tetrachloroauric acid HAuCl4>NaAuCl4, KAuCl4, dimethyl gold acetate, barium acetoaurate and gold acetate. The preferred gold compound is HAuCl4. In the finished catalyst, this metal can be present in a content of 0.1 to 10% by mass. Suitable co-promoters include alkali and alkaline earth metal salts, preferably acetate salts, such as potassium and sodium acetate. The preferred co-promoter content in the finished catalyst is in the range of 0.1 to 9.5 wt%, calculated as acetate. The preferred catalyst component (5) is gold and either sodium or potassium acetate.

The catalyst also contains acid. It is preferably a strong acid. Suitable acids are heteropolyacids, which can be aluminum-tungstic acid, phosphorous-tungstic acid, phosphorous-molybdic acid, silicon-molybdic acid, tungsten-molybdic acid, boron-vanadium-allicium acid, boron-tungstic acid, boron-molybdic acid, tungsten-molybdenum-bomic acid, molybdenum-aluminic acid, tungsten-aluminum acid, molybdenum-tungsten-aluminum acid. acid, molybdenum-germanium acid, tungsten-germanium acid, molybdenum-tungsten-germanium acid, molybdenum-titanium acid, tungsten-titanium acid, molybdenum-tungsten-titanium acid, cerium(IIl)-molybdenic acid, cerium(III)-tungstenic acid, cerium(III) molybdenum-tungsten acid, molybdenum-cobalt acid, tungsten-cobalt acid, molybdenum-tungsten-cobalt acid, phosphoric niobium acid, silicon-niobium acid and silicon-tantalic acid. Among these, silicon-tungstic acid, phosphorous-tungstic acid, phosphorous-molybdic acid, allicium-molybdic acid, tungsten-molybdenum-phosphoric acid, tungsten-molybdenum-silicic acid, tungsten-vanadium-phosphoric acid, boron-tungstic acid, boron-molybdenic acid and boron-molybdenum-tungstic acid are particularly preferred. It is desirable that the acid content in the finished catalyst be up to 50% by mass.

It is suitable that the composition of the finished catalyst can be adjusted in order to maximize vinyl acetate production with maximum selectivity

The catalyst of the present invention can conveniently be prepared by the process described in detail in GB-A-1559540. In the first stage of the preparation process, the carrier is impregnated with a solution containing the desired palladium and metal promoter, for example, gold, in the form of soluble salts. Examples of such salts are growth derivatives of halides. Preferably, the impregnating solution is an aqueous solution, and the volume of the solution used corresponds to between 50 and 100% of the pore volume of the support, preferably 95 to 99% of the pore volume for catalysts immobilized in the column, or 50 to 99% of the pore volume for catalysts in a fluidization column.

After impregnation, the wet support is optionally treated with an aqueous solution of an alkali metal salt, selected from alkali metal silicates, carbonates or hydroxides, to develop a smooth metal structure, as is known to those skilled in the art. The amount of alkali metal salt used is such that after 12 to 24 hours of contact of this solution with the impregnated carrier, the pH of the solution is suitably in the range of 6.5 to 9.5, preferably 7.5 to 8, when measured at 25°C. Preferred metal salts are sodium silicate, sodium carbonate and sodium hydroxide.

During the treatment described above, palladium hydroxides and promoters, for example gold, are believed to be precipitated and incorporated into the support. Alternatively, the impregnated support can be dried at ambient pressure or lower, and at a temperature from ambient temperature to 150°C, preferably between 60 and 120°C, before the metals are reduced. In order to convert such materials to the metallic state, the impregnated support is treated with a reducing agent, such as ethylene, hydrazine, formaldehyde or hydrogen. If hydrogen is used, it is usually necessary to heat the catalyst from 100 to 300°C in order to achieve complete reduction.

After the completion of the above-described stages, the reduced catalyst is washed with water and dried. The dry support is then impregnated with the desired amount of a vinyl acetate catalyst co-promoter, for example, an aqueous solution of alkali metal acetate, and an acetic acid catalyst promoter, for example, an aqueous solution of a selenium-containing compound, and then dried. The dry carrier is further treated with an appropriate amount of heteropoly acid dissolved in water, and the finished product is dried.

The catalyst preparation procedure can be varied in order to optimize the performance of the catalyst and maximize the yield and selectivity of vinyl acetate.

The production of vinyl acetate using the catalyst of the present invention is typically performed by bringing ethylene, water and oxygen-containing gas, such as oxygen or air, into contact with the catalyst at a temperature of 100 to 400°C, preferably 140 to 210°C and an overpressure of 1 to 20 bar, preferably 6 to 15 bar.

The procedure can be conducted in a reactor - a column in which the catalyst is immobile or in a fluidization column, and it is preferable to conduct it in the gaseous phase.

The present invention will now be illustrated by reference to the following Examples.

Example 1 is an example according to the present invention. Comparative examples A, B and C are not in accordance with the present invention, because the process used a catalyst that is not in accordance with the present invention, in Example A it does not contain a promoter or co-promoter of the vinyl acetate catalyst, in Example B it does not contain an acid or acetic acid catalyst promoter, and in Example C, the acetic acid catalyst component and the vinyl acetate catalyst component are in separate columns.

Example 1.

(a) Preparation of the catalyst

In an aqueous solution containing 1.7 g of sodium tetrachloropalladate(II) and 1.5 g of sodium tetrachloroaurate(III) hydrate, dissolved in 34 g of water, 68.4 g of a porous silicon dioxide carrier (KA 160 ex Sud Chemie), with a particle diameter of 5 mm to 7 mm, is added, so that it absorbs the entire solution. The mixture is left to stand for 18 hours, and then 20 g of 99% hydrazine hydrate is added to this solution to reduce Pd and Au. The resulting mixture is left to stand for 4 hours, until the reduction is completed. The carrier is separated from the solution, washed with deionized water, until there is no reaction to chlorides in the washed solution using the AgN03 solution. The resulting support is dried for 24 hours at 60°C. 10 g of dry carrier is added to an aqueous solution containing 0.0071 g of potassium selenate(VI) and 0.51 g of potassium acetate dissolved in 5 g of water. The carrier absorbs the entire solution, so it is dried for 24 hours at 60°C. After that, an aqueous solution containing 3.3 g of alicium-tungstic acid hydrate dissolved in 5 g of water is added to the carrier, which absorbs it in its entirety. The resulting carrier containing Pd, Au, selenium salt and alicium-tungstic acid is dried for 24 hours at 60°C.

Vinyl acetate production

In the reactor, distribute 5 g of the obtained catalyst per 60 mL of glass beads (diameter 1 mm). A mixture of ethylene, oxygen, water vapor and inert gas is introduced into the reactor, in a volume ratio of 40:6:31:23, at a temperature of 160°C and an overpressure of 8 bar, with a flow rate of 15.8 NL/h, in order for the reaction to proceed. The effluent is analyzed on-line by gas chromatography. A volume-time yield of vinyl acetate of 84.5 g/(h-L) and a selectivity of 76%, calculated on the carbon balance, was obtained. COzbila selectivity was 22%.

Comparative example A

Refuting the catalyst

Sodium tetrachloropalladate(II) (9.5 g) is dissolved in water (90 g). A porous silica support (KA 160 ex Sudchemie, particle diameter 5 mm to 7 mm) (180 g) is impregnated with this aqueous solution until the entire solution is absorbed. The carrier thus obtained is added to an aqueous solution (170 g) containing sodium metasilicate (17.7 g). The mixture is left to stand for 18 hours, then 20 g of 99% hydrazine hydrate is added to this solution, in order to reduce the palladium. The resulting mixture is left to stand for 4 hours until the reduction is complete. The support is separated from the solution and washed with deionized water, until the chloride ion reaction is negative in the washed solution, using AgN03 solution. The carrier obtained in this way is dried for 48 hours at 60°C. Potassium selenate(VI) (0.164 g) is dissolved in water (10 g), and it is completely absorbed in 20 g of dry carrier. Then the support is dried again for 24 hours at 60°C. After that, an aqueous solution containing silicon-tungstic acid hydrate (6.3 g) dissolved in water (10 g) is added, and the carrier absorbs it in its entirety. The resulting support containing palladium, selenium salt and alicium-tungstenic acid is dried for 24 hours at 60°C.

In the reactor, 5 g of the obtained catalyst is evenly distributed per 60 mL of glass beads (size 1 mm), then a mixture of ethylene, oxygen, water vapor and inert gas is introduced in a volume ratio of 40:6:31:23, at a temperature of 150°C and an overpressure of 8 bar, with a flow rate of 15.5 Nb/h in order for the reaction to proceed. The effluent is analyzed on-line by gas chromatography.

The following data were obtained as a result: space-time yield of acetic acid 235 g'(hL), space-time yield of vinyl acetate 2.1 g/(h-L), space-time yield of acetaldehyde 3.5 o/(h'L) and space-time yield of carbon dioxide 21.2 g/(hL). The overall selectivity for acetic acid was 87% and the overall selectivity for vinyl acetate was 0.54%.

Comparative example B

(a) Preparation of the catalyst

The vinyl acetate catalyst was prepared according to US 5185308, with nominal contents of 0.9 Pd, 0.4 Au and 7 wt% KOAc, at KA 160.

In the reactor, 2.5 g of the resulting catalyst is evenly distributed to 60 mL of glass beads (size 1 mm), then ethylene, acid, water vapor and inert gas are introduced, in a volume ratio of 47:7:19:27, at a temperature of 150°C, an overpressure of 8 bar and a flow rate of 21.1 NL/h, in order for the reaction to proceed. The effluent is analyzed on-line by gas chromatography.

As a result, the following data were obtained: space-time yield of carbon dioxide 119.6 g</>(h-L), and acetic acid, vinyl acetate or other side products were not detected.

Comparative example C

(a) Preparation of the catalyst

Catalysts were prepared as in Reference Examples A and B.

( b) Rebuttal of vinyl acetate

The reactor is packed with Catalyst 1 (5 g) and 2 (2.5 g) on glass beads (60 mL, size 1 mm). Catalyst 1 is distributed evenly over the glass beads (32 mL) and placed in the upper part of the reactor, and catalyst 2 over the glass beads (16 mL) in the lower part of the reactor. There are 2 mL of glass beads between the sections with Catalyst 1 and Catalyst 2, and 5 mL each at both ends of the reactor, upper and lower. A mixture of ethylene, oxygen, water vapor and inert gas, in a volume ratio of 50:8:21:21, is introduced into the reactor at a temperature of 150°C. an overpressure of 8 bar and a flow rate of 15.8 NL/h, in order for the reaction to proceed. The effluent is analyzed on-line by gas chromatography.

The following results were obtained: time-time yield of vinyl acetate 115 g/(hL) and selectivity 77%, calculated on carbon balance, selectivity for C0211% and selectivity for acetic acid 5%. Minor side products were ethyl acetate and ethanol.

It can be observed that the selectivities of the reaction, achieved when using the two-step procedure, are comparable to the same in the current procedure.

Claims (9)

1. A catalyst used for the production of vinyl acetate, characterized in that it contains (1) a catalyst support selected from porous silica, alumina, silica/alumina, titanium dioxide, zirconium oxide and carbon, (2) palladium, (3) heteropoly acid, (4) at least one acetic acid catalyst promoter selected from compounds containing selenium, titanium, tellurium and/or vanadium, (5) at least one vinyl lactate promoter selected from the group consisting of cadmium acetate, gold, copper and nickel. 2. Catalyst according to claim 1, characterized in that the heteropoly acid content is up to 50 wt.%. 3. Catalyst according to claim 1, characterized in that the promoter of the acetic acid catalyst is oxide, acetate or acetylacetonate. 4. Catalyst according to any one of the preceding claims, characterized in that the vinyl acetate catalyst promoter is gold. 5. Catalyst according to any of the preceding claims, further comprising at least one vinyl acetate co-promoter 6. Catalyst according to claim 5, characterized in that the co-promoter of the vinyl acetate catalyst is selected from salts of alkali metals or alkaline earth metals. 7. Catalyst according to patent claim 6, characterized in that the co-promoter of the catalyst is vinyl acetate, sodium acetate or potassium acetate. 8. A process for the production of vinyl acetate, characterized in that it consists in the reaction of ethylene with a gas containing oxygen and optionally water, in the presence of a catalyst according to any of claims 1 to 7 9. The method according to claim 8, characterized in that it is carried out at a temperature of 100 to 400° and an overpressure of 1 to 20 bar.