SI9620079A - Process and catalyst for producing vinyl acetate - Google Patents

Abstract

A process and catalyst are disclosed for producing vinyl acetate in the gaseous phase from ethylene, acetic acid and oxygen or oxygen-containing gases on a catalyst that contains palladium and/or its compounds, cadmium compounds and alkaline metal compounds on a substrate. The invention is characterised in that the catalyst further contains at least one rhenium and/or zirconium compound.

Description

Catalyst and process for the preparation of vinyl acetate

It is known that ethylene in the gaseous phase can be converted by acetic acid and oxygen, or oxygen-containing gases, on palladium / cadmium / alkali metal containing catalysts to vinyl acetate. This gives a space-time gain greater than 20 g / l. h (US-A-3 939 199, US-A-4 668 819, US-A-4 902 823, EP-A-0 403 950, US-A-5 225 388, EP-A-0 565 952, EP-A-0 634 208, EP-A-0 634 209, EP-A-0 634 214).

It has now surprisingly been found that such catalysts are significantly improved by the addition of at least one rhenium and / or at least one zirconium compound, that is, they give higher space-time yields at the same or higher selectivity of vinyl acetate synthesis and are slower to deactivate.

The subject of the invention is therefore a process for the preparation of vinyl acetate in the gaseous phase from ethylene, acetic acid and oxygen or oxygen-containing gases on a catalyst containing palladium and / or its compounds, cadmium compounds, as well as alkali compounds, characterized in , that the catalyst further comprises at least one rhenium and / or at least one zirconium compound.

A further object of the invention is a catalyst containing on the carrier palladium and / or its compounds, cadmium compounds as well as alkali compounds, characterized in that the catalyst further comprises at least one rhenium and / or at least one zirconium compound.

Suitable inert carriers, such as silica, alumina, alumosilicates, silicates, titanium oxide, zirconium oxide, titanates, silicon carbide and charcoal, are suitable carriers. Carriers of this type with a specific surface area of 40 to 350 m ² / g (measured by the BET method) and with a mean pore radius of 50 to 2000 x IO ¹⁰ m (measured by mercury porosimetry), in particular silica (SiO ₂ ) are particularly suitable. and SiO ₂ A1 ₂ O ₃ mixtures. These carriers are used in the form of beads, tablets, rings, asterisks or other shaped particles whose diameter or size. whose length and thickness are generally 3 to 9 mm.

Preferably, the total pore volume of the support is 0.4-1.2 ml / g, with less than 10% of this volume forming micropores with pore diameters below 30 χ 10 * ^1θ m. Such carriers can be prepared from aerogenic SiO ₂ or an aerogenic mixture of SiO ₂ -Al ₂ O ₃ , which is in the form of glass microcircuits, which can be prepared e.g. by flame hydrolysis of silicon tetrachloride or a mixture of silicon tetrachloride-aluminum trichloride in a hydrogen / oxygen flame (US-A-3 939 199). These microspheres are commercially available under the brand name ®Aerosil or ®Cabosil.

Particularly preferred is the use of a SiO _{2 support} or a mixture of SiO ₂ -Al ₂ O ₃ with a surface area of 50,250 m ² / g and a pore volume of 0.4-1.2 ml / g, which is compressed from such microspheres using organic fillers (EP-A-0 403 950). The particles of this carrier have a size of 4 to 9 mm, forming 5 to 20% of the pore volume of the pore carrier with a radius of 200 to 3000 χ 10 ' ^1θ m and 50 to 90% of the pore volume of the pore with a radius of 70 to 100 χ 10 ¹⁰ m. It is particularly advantageous to prepare these carrier particles from microspheres by tableting or extruding with the addition of one or more C ₂ - C ₂₀ -carboxylates of Li, Mg, Al, Zn, Fe or Mn as a binder and with the addition of organic fillers (such as sugar, urea , higher fatty acids, long chain paraffins, microcrystalline cellulose) and lubricants (such as kaolin, graphite, metal soaps) (US-A-5 225 388). The particles are then annealed in gases containing O ₂ at about 500-900 ° C for about 0.25-5 hours.

Catalytically active substances can be applied to the carrier in a conventional manner, e.g. by single or multiple impregnation of the carrier with a solution of the active substances, subsequent drying and, optionally, reduction. Of course, the active substances can also be applied by e.g. single or multiple spraying, steaming or dipping, or precipitation on a carrier.

Water or unsubstituted carboxylic acids of 2 to 10 carbon atoms, such as acetic acid, propionic acid, n- and iso-butyric acids and various valeric acids, are particularly suitable as solvents for catalytically active substances. Due to its physical properties and also for economic reasons, acetic acid is preferably used as a carboxylic acid. The additional use of an inert solvent makes sense when using a carboxylic acid in which the substances are not sufficiently soluble. Thus, e.g. Palladium chloride dissolves significantly better in aqueous acetic acid than in glacial acetic acid. As additional solvents, those which are inert and which are miscible with carboxylic acid, e.g. water or ethers such as tetrahydrofuran or dioxane, as well as hydrocarbons such as benzene.

It is possible to prepare either so-called fully impregnated catalysts in which the catalytically active metal compounds penetrated to the core in the carrier particle, or so-called surface-impregnated catalysts (shell catalysts) in which the metal salts did not penetrate to the core but only more or less thick the outer portion of the carrier particles, i the so-called particle shell. In both cases, the elements to be applied can be applied individually in the form of solutions of their compounds, or in any combination. Preferably we use solutions containing at least one compound of each of the elements to be applied. Particularly preferred is the use of a single solution containing exactly one compound of each of the elements to be applied. When we refer to a solution below, we mean a solution containing at least one compound of one of the elements Pd, an alkali metal, Cd, Re, Zr, or a solution containing at least one compound of two or more of these elements.

For the preparation of fully impregnated catalysts, the following steps are preferred (US-A-4 902 823, US-A-3 393 190, US-A-4 668 819):

Impregnation of the catalyst support with the active component solution is carried out by coating the carrier material with the solution and then optionally casting or filtering the excess solution. In view of the losses of the solution, it is advantageous to use only the amount of solution corresponding to the integral pore volume of the catalyst support and to mix carefully so that the particles of the carrier material are wetted evenly. It is advantageous to carry out the impregnation process and mixing simultaneously, e.g. in a rotating drum or in a drum dryer, followed immediately by drying. Furthermore, it is generally advantageous to dimension the composition of the solution that is used to impregnate the catalyst carrier to apply the desired amount of active substance by a single impregnation. Of course, this amount can also be applied with several impregnations, preferably after each impregnation, drying is carried out.

For the preparation of surface-impregnated catalysts, it is preferable to proceed by one of the following three methods, always using a solution of at least one compound of at least one of the elements Pd, alkali metal, Cd, Re and / or Zr, with a dynamic viscosity of at least 0.003 Pa.s, preferably 0.005 to 0.009 Pa.s:

1. While vigorously stirring the carrier particles, spray one or more times with a droplet solution having an average diameter of at least 0.3 mm, or in the form of liquid jets, and dry immediately after each spray. Immediate drying means that the drying of the sprayed particles must start quickly. It is generally sufficient to start drying the particles within 30 minutes at the latest after finishing the spraying. The volume of solution for each spray is 5 to 80% of the pore volume of the carrier particles. This method is extensively described in EP-A-0 634 214, which is specifically referenced herein (incorporated by reference).

2. While stirring vigorously, the carrier particles are impregnated once or more with the solution and immediately dried after each impregnation. The instant drying means the same as in Method 1, and the volume of the solution at each impregnation is 5 to 80% of the volume of the pore particles of the support. This method is extensively described in EP-A-0 634 209, to which we also refer expressly.

3. The carrier particles are impregnated once or more with the solution and dried after each impregnation, but the volume of the solution, unlike method 2, is not limited upwards: it now amounts to more than 80% of the pore volume at each impregnation. Due to the larger volume of the solution, strong mixing is no longer necessary, although it is generally useful. Instead, the duration of each impregnation should be as well as the time until the next drying to begin, i.e. the time from the beginning of each impregnation to the onset of drying followed by such a short time that, once the last drying has been completed, the shell with 5-80% volume of pore volume of the carrier particles contains catalytically active elements. How short we must choose for this purpose can be easily determined by previous experiments. This method is extensively described in EP-A-0 634 208, which is also explicitly referred to herein.

A suitable method for determining the achieved shell thickness for prepared surface-impregnated catalysts consists of cutting a representative number of impregnated and dried carrier particles and measuring shell thicknesses under a microscope. Preferably, less than 5% of the particles have a shell thickness that deviates from the desired value by more than 15%.

Drying impregnated The catalyst carrier sputtering can be carried out on both fully impregnated catalysts and surface-impregnated catalysts, preferably under reduced pressure (0.1 to 0.8 bar). The drying temperature should generally be 50 to 80 ° C, preferably 50 to 70 ° C. Furthermore, it is generally recommended that the drying be carried out in an inert gas stream, e.g. in a stream of nitrogen or carbon dioxide. The residual solvent content after drying should preferably be less than 8% by weight, in particular less than 6% by weight.

Finished catalysts should contain the following quantities of catalytically active elements:

The palladium content is generally 0.6 to 3.5% by weight, preferably 0.8 to 3.0% by weight, in particular 1.0 to 2.5% by weight. The alkali element content is generally 0.3 to 10% by weight.

Preferably we use potassium, generally 0.5 to 4.0% by weight, preferably 1.0 to 3.0% by weight, in particular 1.5 to 2.5% by weight.

The cadmium content is generally 0.1 to 2.5% by weight, preferably 0.4 to 2.5% by weight, in particular 1.3 to 2% by weight.

The rhenium or zirconium content is generally 0.05 to 3% by weight, preferably 0.05 to 1% by weight, in particular 0.05 to 0.5% by weight.

Rhenium and zirconium may be present in the catalyst together, in which case the total content of both elements is within the indicated ranges.

The percentages given refer to the quantities of elements Pd, alkali element, Cd, Zr and / or Re already present in the catalyst with respect to the total mass of the catalyst (active elements plus anions plus carrier material).

All palladium, cadmium, alkali metal, rhenium and zirconium compounds, which are soluble and which do not contain any of the toxic components of the catalyst, such as e.g. sulfur; acetates and chlorides are preferred. However, in the case of chlorides, it must be ensured that the chloride ions are removed before using the vinyl acetate synthesis catalyst. This is accomplished by flushing the varnish carrier, e.g. with water, after the palladium, applied as chloride, is converted into insoluble form, e.g. by reduction and / or precipitation by hydroxides.

Carboxylates, preferably salts of aliphatic monocarboxylic acids with 2 to 5 carbon atoms, such as acetate, propionate or butyrate, are particularly suitable as palladium compounds. Furthermore, e.g. nitrate, nitrite, oxyhydrate, oxalate, acetylacetonate, acetoacetate. Due to its good solubility and accessibility, palladium compound palladium acetate is particularly preferred.

At least one K-, Rb- or Cs-compound, in particular at least one K-compound, is preferably used as the alkali compound. Carboxylates, in particular acetates and propionates, are particularly suitable as compounds. Also suitable are compounds which under reaction conditions convert to acetate such as hydroxide, oxide or carbonate.

Acetate is particularly suitable as a cadmium compound.

Acetone and acetylacetonate are particularly suitable as zirconium compounds.

Re ₂ O ₇ and (NH ₄ ) ReO ₄ are particularly suitable as the rhenium compound.

If a palladium compound is reduced, which is sometimes useful, a gaseous reducing agent can be used for this purpose. They are suitable e.g. hydrogen, methanol, formaldehyde, ethylene, propylene, isobutylene, butylene and other olefins. The reaction temperature is generally between 40 and 260 ° C, preferably between 70 and 200 ° C. It is generally advantageous to use a reducing agent diluted with an inert gas containing 0.01 to 50% by volume, preferably 0.5 to 20% by volume of the reducing agent. As an inert gas, for example, nitrogen, carbon dioxide or noble gas. The amount of reducing agent depends on the amount of palladium; the reducing equivalent is expected to be at least 1 to 1.5 times the oxidizing equivalent, but larger amounts of the reducing agent do no harm. The reduction is carried out after drying.

The preparation of vinyl acetate is carried out by administering acetic acid, ethylene and oxygen or oxygen-containing gases at temperatures of 100 to 220 ° C, preferably 120 to 200 ° C, and at pressures of 1 to 25 bar, preferably 1 to 20 bar, via a finished catalyst whereby unreacted components can circulate. It is reasonable to keep the oxygen concentration below 10% by volume (relative to the gas mixture without acetic acid). Dilution with inert gases such as nitrogen or carbon dioxide may also be useful. Carbon dioxide is particularly suitable for dilution in the case of a circular process, since it forms in small quantities during the reaction.

The catalysts of the invention achieve higher yield, space-time, and equal or higher selectivity over the longer catalyst life than with rhenium or zirconium-free catalysts.

The following examples are intended to illustrate the invention. The percentages of the elements Pd, Cd, Zr, Re and K are mass percentages based on the total mass of the catalyst.

SiO ₂ in the form of tablets with a diameter and height of mm was used as the catalyst support. The tablets were pressed from ®Aerosil powder using magnesium stearate as a binder, according to US-A-5 225 388. The carrier surface was 120 mg ² / g, its pore volume was 0.784 ml / g and its bulk weight was was 500 g / l. The pore volume of the 11 media was 392 ml.

I. Fully impregnated catalysts

Comparative Case 1

1 silica support was impregnated with a solution of 24.3 g of palladium acetate,

21.3 g of cadmium acetate and 23.8 g of potassium acetate in 392 ml of glacial acetic acid (solution volume = 100% pore volume of the vehicle), at 60 ° C. It was then dried in an oven at 200 mbar under nitrogen until the residual acetic acid content was 6% by weight; the drying temperature was 65 ° C. The finished catalysts contained

2.3 wt% Pd, 1.8 wt% Cd and 1.9 wt% K. It is completely, i.e. impregnated to the core.

ml of this catalyst was filled into a reaction tube with an inside diameter of 8 mm and a length of 1.5 m. Then, at 8 bar (reactor inlet) and catalyst temperature of 150 ° C, the gas we wanted to react was run through the catalyst for several days. This gas consisted of 27% ethylene, 55% nitrogen, 12% acetic acid and 6% oxygen. The results are shown in Table 1. In this table, the relative rate of decline in productivity is the quotient of the fall in productivity (= initial performance of the trial minus the final performance of the trial) and the duration of the experiment with respect to the quotient of the catalyst used in Comparative Example 1. This catalyst therefore has the quotient ( = relative rate of decline in productivity) 1.

EXAMPLE la

Proceed as in Comparative Example 1, except that the solution additionally contains 7.5 g of zirconium acetylacetonate and the amount of glacial acetic acid is 389 ml. The results are shown in Table 1.

EXAMPLE lb

The catalyst prepared as in Comparative Example 1 was impregnated with a solution of 4.2 g of Re ₂ O ₇ in 308 ml of water (solution volume = 100% catalyst pore volume) at room temperature. It is then dried as in Comparative Example 1 until a water content of 6% by weight is reached. Testing is performed as in Comparative Example 1. The results are shown in Table 1.

TABLE 1 (Fully impregnated catalysts)

Productivity * (g / lh) Selectivity (%) Relative rate of decline in productivity Comparative Case 1 813 94,3 1 Example la 870 94.5 0.7 Example lb 840 94.8 0.7

* Initial productivity (gram of vinyl acetate per liter of catalyst and hour).

II. Surface impregnated catalysts

Comparative Example 2

At 65 ° C, dissolve 25.3 g of palladium acetate, 25 g of cadmium acetate and 25.3 g of potassium acetate in 130.0 ml of anhydrous acetic acid (glacial acetic acid) (solution volume = 33% pore volume) and a high viscous solution (7 mPa.s) is filled into a vessel preheated to 65 ° C. It is also heated to 65 ° C 1 1 of the catalyst support and placed in the flask. The carrier particles are then poured over the entire impregnation solution and stirred vigorously until the particles have completely absorbed this solution. This process is completed after 3 minutes.

The catalyst is then dried as in Comparative Example 1. The finished catalyst contains

2.3 wt% Pd, 1.8 wt% Cd and 1.9 wt% K. The shell thickness is 0.8 mm.

Testing is performed as in Comparative Case 1. The results are shown in Table 2. The relative rate of productivity decline is defined as in Comparative Case 1, i.e. again relative to the catalyst used therein.

EXAMPLE 2a

Proceed as in Comparative Example 2, except that the solution additionally contains 7.0 g of zirconium acetylacetonate. The shell thickness is 0.8 mm. The results are shown in Table 2.

EXAMPLE 2b of the catalyst prepared as in Comparative Example 2 was impregnated with a solution of 3.5 g of Re ₂ O ₇ in 300 ml of water (solution volume = 100% catalyst pore volume) at room temperature. It is then dried as in Comparative Example 1 until a water content of 6% by weight is reached. Testing is performed as in comparative example 1. The results are shown in Table 2.

Table 2 (Surface impregnated catalysts)

Productivity * (g / lh) Selectivity (%) Relative rate of decline in productivity Comparative Example 2 922 95,8 1.4 Example 2a 950 96.1 0.9 Example 2b 940 96.0 1.0

'Initial productivity (gram of vinyl acetate per liter of catalyst and hour)

Claims (10)

A process for the preparation of gaseous phase vinyl acetate from ethylene, acetic acid and oxygen or oxygen-containing gases on a catalyst containing palladium and / or its compounds, cadmium and alkali compounds on the carrier, characterized in that the catalyst additionally contains at least one rhenium and / or at least a zirconium compound. Process according to claim 1, characterized in that the catalyst contains at least one potassium compound. A process according to claim 1 or 2, characterized in that the catalyst contains 0.05% to 3% by weight of rhenium and / or zirconium relative to the total weight of the catalyst. A process according to any one of claims 1 to 3, characterized in that the catalyst contains 0.05% to 1% by weight of rhenium and / or zirconium relative to the total weight of the catalyst. Process according to any one of claims 1 to 4, characterized in that the catalyst contains 0.05% to 0.5% by weight of rhenium and / or zirconium relative to the total weight of the catalyst. 6. A catalyst containing palladium and / or its compounds, cadmium as well as alkali compounds on the carrier, characterized in that the catalyst further comprises at least one rhenium and / or at least one zirconium compound, and where, when containing the catalyst palladium and / or its compounds, cadmium and at least one rhenium compound, an alkali compound potassium compound. Catalyst according to claim 6, characterized in that the catalyst contains at least one potassium compound. A catalyst according to claim 6 or 7, characterized in that the catalyst contains 0.05% to 3% by weight of rhenium and / or zirconium relative to the total weight of the catalyst. A catalyst according to any one of claims 6 to 8, characterized in that the catalyst contains 0.05% to 1% by weight of rhenium and / or zirconium relative to the total weight of the catalyst. Catalyst according to any one of claims 6 to 9, characterized in that the catalyst contains 0.05% to 0.5% by weight of rhenium and / or zirconium relative to the total weight of the catalyst.