MXPA97003629A - Compressed based on silicon dioxide produced pirogenicame - Google Patents

Abstract

The silicon dioxide-based tablets produced pyrogenic with the following physical and chemical characteristics: Outside diameter 0.8 - 20 mm Surface BET 30 - 400 m2 / g Volume of pores 0.5 - 1.3 ml / g Resistance to break 10 to 250 N Composition > 99.8% by weight of SiO2 Abrasion < 5% by weight Gravimetric density 350 - 750 g / l are produced by homogenizing the pyrogenically produced silicon dioxide with methylcellulose, microcera and / or polyethylene glycol with the addition of water, drying it at a temperature of 80-150 ° C, crushing it to powder , eventually compress the powder to transform it into tablets that are subjected to calcination for a period of time 0.5 to 8 hours at a temperature of 400 to 1200øC. These tablets can be applied as catalysts or catalyst vehicles in the production of vinyl acetate monomer and in the hydration of ethylene

Description

COMPRESSES BASED ON PIROGENICALLY PRODUCED SILICON DIOXIDE The invention relates to tablets based on pyrogenicly produced silicon dioxide, with a process for their manufacture and with their use as catalyst vehicles or as catalysts. The pyrogenicly produced silicon dioxides are characterized by the fact that "they are composed of extremely fine particles and by correspondingly possessing a large specific surface, by a high degree of purity, by the spherical shape of the particles and by the absence of pores. Due to these characteristics, the interest in pyrogenicly produced oxides as catalyst vehicles is constantly increasing (D. Koth, H. Ferch, Chem. Ing. Techn. 52, 628 (1980)). Since "the pyrogenicly produced oxides are composed of particularly fine particles, the shaping or deformation into catalytic converters or catalytic converters presents some difficulties. DE-A 31 32 674 discloses a process for the production of pyrogenic-produced oxide tablets, in which siliceous salt is used as binder or binder.

REF: 24770 From DE-A 34 06 185 a process for the production of tablets is known, in which glass frit powder is used as a binder or binder and glycerin as a lubricant. From DE-B 21 00 778 it is known to use granules based on silicon dioxides produced pyrogenically as catalyst carriers in the manufacture of vinyl acetate monomer. From DE-A 39 12 504 a process for the production of tablets is known, in which aluminum stearate, magnesium stearate and / or graphite are used as lubricant, and urea as well as methylcellulose as pore formers. These known tablets are available for sale through the company Cia. "Degussa", under the name "Aerosil No. 350 - Tablets". They have approximately 0.4% by weight Mg. From EP-B 0 519 435 it is known to compress Si02 by means of binders to form vehicles, to anneal the obtained vehicles, and to wash the annealed particles of the vehicle by acid, until no more cations are released from the binder. The known processes suffer from the disadvantage that, for certain catalytic reactions, such as for example the production of vinyl acetate from ethylene, acetic acid and oxygen, or the hydration of ethylene to transform it into ethanol, the tablets obtained with they do not possess the desired optimum characteristics, such as, for example, a high degree of purity, a high degree of activity, a high degree of selectivity, a high rate of yield (or production) and a high degree of stability. The object of the invention are tablets based on pyrogenicly produced silicon dioxide, which have the following distinguishing physico-chemical characteristics: Outside diameter 0.8 - 20 mm BET surface 30 - 400 m2 / g Pore volume 0.5 - 1.3 ml / g Resistance to breakage 10 to 250 N Composition > 99.8% by weight of Si02 Other components < 0.2% by weight Abrasion < 5% by weight Gravimetric density 350 - 750 g / 1 Another additional object of the invention is a process for the production of pyrogenic-based silicon dioxide-based tablets, which have the following distinguishing physico-chemical characteristics: Outside diameter 0.8 - 20 mm Surface BET 30 - 400 m2 / g Volume of pores 0.5 - 1.3 ml / g Resistance to breakage 10 to 250 N Composition > 99.8% by weight of Si02 Other components < 0.2% by weight Abrasion < 5% by weight Gravimetric density 350 - 750 g / 1 which is characterized by the fact that the pyrogenically produced silicon dioxide is homogenized with methylcellulose, microcera and / or polyethylene glycol with the addition of water, dried at a temperature of 80 - 150 ° C, possibly crushed to powder, the powder is compressed to transform it into tablets, which are subjected to calcination for a period of time from 0.5 to 8 hours at a temperature of 400 to 1200 ° C. In order to carry out the process according to the invention, all the mixers or mills that allow to obtain a good homogenization are suitable, such as, for example, blade mixers, turbulent bed mixers, or air stream mixers. Mixers that allow additional compression or compaction of the ingredients, such as for example plow grinders, vertical grinders or ball mills, are particularly suitable. After homogenising, a considerable drying can be carried out at 80-150 ° C, so that after a possible grinding, a sprayable powder is obtained. The manufacture of the tablets can be carried out in stamping presses, eccentric presses, isostatic presses, extrusion presses or rotary presses, as well as in compactors. In a special embodiment of the invention, the mixture can have the following composition before compacting or compressing: 50-90% by weight of silicon dioxide, preferably 65-85% by weight 0.1-20% by weight of methylcellulose, preferably from 5 - 15% by weight 0.1 - 15% by microcrack, preferably from 5-10% by weight 0.1 - 15% by weight of polyethylene glycol, preferably by 5-10% by weight. The tablets may have various shapes, such as cylindrical, spherical or annular, with an external diameter of 0.8 to 20 mm. The tablets are subjected to calcination at a temperature of 400-1200 ° C for a period of time from 30 minutes to 8 hours. By varying the amounts of starting materials or fillers, and the compression pressure, the breaking strength, the total surface area and the pore volume can be adjusted to some degree.

The tablets according to the invention can be used, either directly as catalysts, or as catalyst vehicles. In the latter case, after their manufacture the tablets can be brought into contact with a catalytically active substance, and can eventually be activated by suitable subsequent processing. The pyrogenically produced silicon dioxide tablets are especially suitable for use as vehicles for the catalyst in the production of vinyl acetate monomer from ethylene, acetic acid and oxygen, as well as catalyst vehicles in the hydration process of olefins. The tablets according to the invention have the following advantages: Unlike the tablets according to DE-A 39 12 504, the tablets according to the invention, with the exception of silicon dioxide, do not have other components or ingredients inorganic Known tablets suffer from the disadvantage that they contain about 0.4% by weight of Mg, which is leached during the process to hydrate the olefins. In contrast, the tablets according to the invention have improved hydrothermal stability in this type of hydration process. Additionally they present a high degree of purity and a high volume of pores. Another object of the invention is a catalyst vehicle for the production of vinyl acetate monomer (VAM), which contains palladium, gold and alkali compounds as catalytically active components on the silicon dioxide carrier according to the invention, as well as a procedure for its manufacture, and its use. Catalyst vehicles containing gold, palladium and alkaline compounds are used for the production of vinyl acetate. For this purpose, ethene, acetic acid and molecular oxygen or gas phase air are reacted in the presence of the catalyst vehicle, optionally with the addition of inert gases, at temperatures between 100 and 250 ° C and under normal or increased pressure. A production process of this kind is known from DE 16 68 088, US 4,048,096 and EP 0 519 435 Bl. These patent documents also reveal a process for the manufacture of catalyst vehicles containing gold, palladium and alkaline compounds. Depending on the way to proceed, catalysts with a homogeneous distribution of the noble metals are obtained through the transverse action of the vehicle, and with a more or less pronounced profile of the envelope. These catalysts are usually obtained by impregnating the vehicle with a basic solution (alkaline) and a solution containing gold and palladium salts, for which the stages of impregnation are carried out simultaneously or successively, with or without drying intermediate. The vehicle is then washed to remove any portions or portions of chloride that may possibly be present. Before or after washing, the insoluble noble metal compounds precipitated on the vehicle are reduced. The previous catalyst stage obtained in this way is dried and, in order to activate the catalyst, it is impregnated with alkali acetates or alkali compounds, which are completely or partially converted into alkali acetates under the reaction conditions prevailing in the production of the monomer of vinyl acetate. The reduction of the catalyst can be carried out in the aqueous phase or in the gas phase. For reduction in aqueous phase, for example, formaldehyde or hydrazine are suitable. The reduction in gas phase can be carried out with hydrogen or mixed gas (95% by volume of N2 + 5% by volume of H2) or ethene. According to EP 0 634 209, the reduction with hydrogen is carried out at temperatures between 40 and 260 ° C, preferably between 70 and 200 ° C. However, it is common for the catalyst to be directly reduced with ethene in the production reactor until after activation with alkaline acetate. In the production process the catalyst is slowly subjected to the loading of the reactants at the beginning. During this start-up phase the catalyst activity increases and, in general, it is only after days or weeks that it reaches its final level. The task of the present invention is to specify a catalyst vehicle for the production of vinyl acetate monomer, which, with an equal or improved selectivity, exhibits a higher activity than the known catalysts. The object of the invention is a catalyst vehicle containing palladium, gold and alkaline acetate as catalytic components active on the silicon dioxide carrier according to the invention. As the carrier material for the catalyst, the pyrogenically produced silicon dioxide-based tablet according to the invention is suitable. The important thing is that the vehicles of the catalysts retain their strength or mechanical consistency under the reaction conditions of the catalytic process, in particular under the influence of acetic acid. The tablets according to the invention can take the form of extruded tablets, tablets, rings or other forms common to solid-bed catalysts. The tablets according to the invention are impregnated with a solution containing palladium and gold. Simultaneously with the solution containing noble metals, or successively in any order of sequence, the tablets according to the invention are impregnated with a basic solution (alkaline), which may contain one or more basic compounds. The basic compound or basic compounds serve to transform palladium and gold into their hydroxides. The compounds within the basic solution (alkaline) may consist of alkali hydroxides, alkali bicarbonates, alkali carbonates, alkali silicates or a mixture of these substances. Preference is given to potassium hydroxide and sodium hydroxide. For the preparation of the solution containing noble metals, palladium salts, for example, palladium chloride, sodium palladium chloride or potassium palladium chloride, or palladium nitrate can be used as palladium salts. As gold salts, gold (III) chloride and gold (III) tetrachloric acid are suitable. Preferably potassium palladium chloride or sodium palladium chloride and gold tetrachloric acid can be used. The impregnation with the basic (alkaline) solution of the tablets according to the invention exerts an influence on the precipitation of the noble metals in the tablet. The basic solution can be brought into contact with the tablet according to the invention, either simultaneously with the noble metal solution, or in any sequence with that solution. In the event that the tablet according to the invention is subjected to successive impregnation with the two solutions, an intermediate drying can be carried out after the first impregnation phase. Preferably, the tablet according to the invention is impregnated first with the basic solution (alkaline). The subsequent impregnation with the solution containing palladium and gold leads to the precipitation of palladium and gold so as to form a surface envelope on the tablet according to the invention. The reverse sequence of the impregnations generally leads to a more or less homogeneous distribution of the noble metals through the cross section of the tablet according to the invention. However, if the process is carried out properly, also in the case of a reverse impregnation sequence, catalysts with a defined envelope can be obtained (see, for example, US 4,048,096). Catalysts with a homogeneous or almost homogeneous distribution of noble metals generally have lower activity and selectivity. Catalysts having a shell thickness of less than 1 mm, preferably of less than 0.5 mm, are particularly suitable. The thickness of the envelope is a function of the amount of basic compound (alkaline) that is applied to the material of the vehicle with respect to the desired amount of noble metals. The higher this ratio, the smaller the thickness of the envelope that is formed. The ratio of amounts of basic compound to noble metal compounds that is required for a desired envelope thickness depends on the composition of the vehicle material as well as the basic (alkaline) compound and selected noble metal compounds. The proportion of quantities conveniently required is established by a few preliminary tests. The resulting envelope thickness can be determined simply by simply cutting the catalyst particles. The minimum required amount of basic compound results from the amount of hydroxide ions calculated stoichiometrically, which is required to transform palladium and gold into hydroxides. As an approximate or normative value it is valid that for a thickness of the envelope of 0.5 mm, the basic compound should be used in a stoichiometric excess of 1 to 10 times. The tablets according to the invention are coated with the basic compounds and noble metal salts according to the pore volume impregnation process. In case of working with the intermediate drying, the volumes of the two solutions are selected in such a way that they correspond respectively to about 90 to 100% of the absorption capacity of the tablets according to the invention. If the intermediate drying is omitted, then the sum of the individual volumes of the two impregnation solutions must correspond to the preceding condition, being that the individual volumes can keep a ratio of 1: 9 up to 9: 1. Preferably a volume ratio of 3: 7 to 7: 3 is used, especially of 1: 1. In both cases it can be used Water preference as solvent. However, suitable organic or aqueous-organic solvents can also be used. The reaction of the noble metal salt solution with the basic solution to obtain insoluble noble metal compounds occurs slowly and, depending on the method of preparation, will generally only be completed after 1 to 24 hours. After this, the noble metal compounds insoluble in water are treated with reducing agents. A wet reduction (in aqueous phase) can be carried out, for example with aqueous hydrazine hydrate, or a reduction in gas phase with hydrogen, ethene, mixed gas or also with methanol vapors. The reduction can be carried out at normal temperature or at elevated temperature, and under normal pressure or under elevated pressure; possibly also with the addition of inert gases. Before or after the reduction of the noble metal compounds, the chloride optionally present in the vehicle is removed by thorough washing. After washing, the catalyst should contain less than 500, and still better less than 200 ppm of chloride. The preliminary phase of the catalyst obtained after the reduction is dried and impregnated to finish with alkaline acetates or alkaline compounds, which are completely or partially converted into alkali acetates under the reaction conditions in the production of vinyl acetate monomer . It is preferably impregnated with potassium acetate. Also in this case again preferably proceeds according to the pore volume impregnation process, ie, the required amount of potassium acetate is dissolved in a solvent, preferably water, whose volume corresponds approximately to the absorption capacity of the vehicle material that is presented for the selected solvent. This volume is approximately equal to the total pore volume of the vehicle material. The finished catalyst is then dried to a residual moisture content of less than 2%. The drying can be carried out in the air, optionally also under nitrogen as an inert gas. For the synthesis of the vinyl acetate monomer it is convenient to coat the catalyst with 0.2 to 4, preferably 0.3 to 3 wt.% Palladium, 0.1 to 2, preferably 0.15 to 1.5 wt.% Gold, and 1 to 10. , preferably 3.5 to 10% by weight of potassium acetate, respectively in relation to the weight of the vehicle used. In the case of catalyst vehicles having a gravimetric density of 500 g / 1, these concentration indications correspond to concentrations referred to volume of 1.0 to 20 g / 1 of palladium, 0.5 to 10 g / 1 of gold, and 5 to 50 g / 1 of potassium acetate. For the preparation of the impregnation solutions the corresponding amounts of palladium and gold compounds are dissolved in a volume of water corresponding approximately to 90 to 100% of the water absorption capacity of the presented vehicle material. The same procedure is followed in the case of the basic solution. The invention also relates to the hydration of olefins for the preparation of their corresponding alcohols, in the presence of phosphoric acid or of another active component, for example a heteroaryl polyacid, as a catalyst vehicle on the tablet according to the invention. A method of this kind is described, for example, in EP 0 578 441 A2. According to this procedure, water and ethylene are transformed into ethanol at temperatures between 225 and 280 ° C at pressures between 20 and 240 bar. For this, a molar ratio of water / ethylene in the range of 0.15 to 0.5 is used. The catalyst load, measured in grams of the water / ethylene mixture per minute and millimeter of catalyst, can be selected within the range 0.01 to 0.1 g / (min x ml). Diethyl ether is formed as a by-product of this reaction. The manufacture of isopropanol by the hydration of propylene is carried out under similar conditions, but at a somewhat lower temperature in the range between 180 and 225 ° C. As a by-product of this reaction, n-propanol is produced. As a catalyst vehicle for the active component phosphoric acid, synthetic pellets of synthetic silicon dioxide with high breaking strength, high porosity and low metal impurities can be used according to EP 0 578 441 A2. The pores of the vehicle serve to absorb the active component. The average radius of the pores before use in the hydration process is in the range of 1 to 50 nm. The catalysts are subject to aging during the operation, which is manifested by a decrease in activity and / or selectivity. Frequently the deactivation has its origin in a reduction of the specific surface of the vehicle caused by high temperatures. The specific surface of the vehicle is intimately related to the structure of its pores. In addition to this, the materials or solid substances of great surface present in most cases a completely amorphous or predominantly amorphous structure, which has the tendency to pass a thermodynamically stable state under crystallite growth and reduction of the specific surface.

It has been found that catalytic converter vehicles containing silicon dioxide are subject to aging of this nature. The conditions of hydration accelerate aging. It is also known that impurities, in particular in the form of alkali metals, promote the aging of vehicles containing silicon dioxide under hydrothermal conditions (see, for example, RK Iler in "The Chemistry of Silica" ), page 544, editorial John Wiley &Sons (1079)). Also the catalyst vehicles described in EP 0 393 356 based on pyrogenicly produced silicon dioxide are subjected to aging under hydrothermal conditions, where smaller pores grow together to form a larger one with the consequent loss of specific surface area. The volume of pores for this at first hardly changes. The task of the present invention therefore consists in specifying catalyst vehicles containing silicon dioxide, which when used under hydrothermal conditions have an improved stability to aging. This task is solved by the use of catalysts which have an active component on the tablet according to the invention.

The use according to the invention is especially advantageous for the hydration of olefins.

However, the stabilization of the vehicle is also advantageous in the case of other catalytic reactions under hydrothermal conditions. In the case of the hydration of olefins, phosphoric acid is introduced as an active component in the catalyst vehicle. For this, the vehicle is immersed in an aqueous solution of phosphoric acid and impregnated with it. In this, phosphoric acid solutions with 15 to 85% by weight of phosphoric acid are used in relation to the total weight of the solution. A principal field of application for the hydration of olefins is the hydration of ethylene for the production of ethanol and diethyl ether, as well as the hydration of propylene for the production of isopropanol. For this, the reactive conditions known by the state of the art are used. Next, the modification of the pore structure of vehicles containing silicon dioxide-containing catalysts under hydrothermal conditions is investigated. A known vehicle is compared with a vehicle according to the invention. They show: Figure 1: The pore structure of a catalyst vehicle containing Mg after a hydrothermal aging test. Figure 2: The pore structure of a catalyst vehicle according to the invention, after a hydrothermal aging test. The pore distribution curves shown in Figures 1 and 2 are determined using the known Hg porosimetry. They indicate the differential intrusion of mercury according to the diameter of the pores. For the differential intrusion, arbitrary units are selected, and the curves are extended in each case through the available region of the diagram. As silicon dioxide produced pyrogenically, silicon dioxides with the following physico-chemical characteristics can be used: Degussa gAktiengesellschaf 960005 FH / KL 60311 Frankfurt Íó 1) ACCORDING TO DIN 53194. 2) S £ G.JN DIN 55921. 3) S? GUH D | N 53200 4) ACCORDING TO DIN 53580 P REFERRED TO SUSPENSION DRY FOR 2 HOURS AT IOS0C 6) REFERRED TO THE RELATED SUBSTANCE DURING 2 HOURS AT 1000 C 8) ATTENTION OF HCL IS PART OF THE LOSS BY RECOCIDO For the production of AEROSIL, a volatile silicic compound is introduced in an atomized form into an oxyhydrogen gas flame or hydrogen and air detonator. In most cases, silicon tetrachloride is used. This substance hydrolyzes under the influence of the water resulting from the reaction of oxyhydrogen or detonating gas, to be transformed into silicon dioxide and hydrochloric acid. After leaving the flame, the silicon dioxide enters a so-called coagulation zone, in which the primary particles and the primary aggregates of AEROSIL are agglomerated. The product, which at this stage is in the form of a kind of aerosol, is separated in cylindrical parts from the gaseous impurities, and then subjected to treatment with moist hot air. By means of this procedure it is possible to reduce the hydrochloric acid residue to below 0.025%. Since the AEROSIL is obtained at the end of this process with a gravimetric density of only about 15 g / 1, it is then passed to a vacuum concentration, whereby tamping densities of approximately 50 g / 1 and more are obtained. . The particle sizes of the products obtained in this way can be varied by resorting to the reaction conditions, such as the temperature of the flame, the parts or portions of hydrogen or oxygen, the amount of silicon tetrachloride, the residence time in the flame or the length of the coagulation section. The BET surface is determined according to DIN 66 131 with nitrogen. The volume of the pores is determined by calculation from the sum of the volumes of the micro-, meso and macropores. The breaking strength is determined by means of a break resistance tester type TBH 28 from the company Erweka. The determination of the micro- and mesopores is carried out by capturing an N2 isotherm and its interpretation or analysis according to BET, by Boer and Barret, Joyner, Halenda. The determination of the macropores is carried out by means of the pressure intrusion method of Hg. Abrasion is determined by the TAR type abrasion and friability tester from the company Erweka. Examples 1 - 5 71.5% by weight of Aerosil 200 13% by weight of methylcellulose 7% by weight of microwell 8.5% by weight of polyethylene glycol are compacted by adding water, dried for 16 hours at 110 ° C, crushed to form a powder sprayable and made into tablets with an eccentric press. The crude tablets are calcined for 6 hours at 750 ° C. The tablets obtained have the following physico-chemical characteristics: EXAMPLE 1 2 3 4 5 Cylinder shape cylinder cylinder cylinder cylinder cylinder External diameter x Height x Diám.Int. (mm) 3 x 3 4 x 4 5 x 5 5 x 5 9 x 5 x 3 BET surface area (m2 / g) 170 164 168 163 165 Pore volume (ml / g) 0.75 0.84 0.84 0.97 0.79 Resistance to breakage (N) 49 42 60 31 22 Abrasion (% by weight) 0.9 1.6 1.3 3.8 3.8 Bulk weight (g / D 535 485 470 430 400 Content of Si02 (% by weight) 99.9 99.9 99.9 99.9 99.9 EXAMPLE 6 75% by weight of Aerosil 200 11.5% by weight of methylcellulose 6% by weight of microcera 7.5% by weight of polyethylene glycol are compacted by adding water, dried for 16 hours at 110 ° C, crushed to form a sprayable powder and they are compressed with an eccentric press. The crude tablets are calcined for 6 hours at 750 ° C. The tablets obtained have the following physico-chemical characteristics: Shape of the cylinder tablet Diameter ext. x Height x Diam.int. (mm) 5 x 5 BET surface area (m2 / g) 168 Pore volume (ml / g) 0.71 Breaking strength (N) 61 Abrasion (% by weight) 2.3 Bulk weight (g / 1) 510 Si02 content (% by weight) 99.9 Examples 7 and 8 71.5% by weight of Aerosil 300 / Aerosil 130 (Example 7) (Example 8) 13% by weight of methylcellulose 7% by weight of microwell 8.5% by weight of polyethylene glycol are compacted by adding water , they are dried for 16 hours at 110 ° C, crushed to form a sprayable powder and compressed with an eccentric press. The crude tablets are calcined for 6 hours at 750 ° C. The tablets obtained have the following physico-chemical characteristics: EXAMPLE 7 8 Ext. x Height x Diam.int. (mm) 5 x 5 5 x 5 BET surface (m / g) 210 117 Pore volume (ml / g) 0.85 0.89 Breaking strength (N) 55 39 Abrasion (weight%) 2.0 2.4 Bulk weight (g / 1) 465 450 Si02 content (% by weight) 99.9 99.9 Comparative example 1 A tablet not according to the invention (catalyst vehicle 350, Co. Degussa, with 0.4% by weight Mg (elemental), BET surface 180m2 / g, gravimetric density 490 g / 1, total pore volume 0.8 cm3 / g, tablets with 6 mm diameter and 5.5 mm height) is charged with phosphoric acid (60% by weight) and exposed for 41 hours in a facility of high pressure at a steam pressure of 15 bar and 350 ° C. The pore distribution of the aged catalyst is determined by Hg porosimetry. The measured pore distribution is graphically represented in Figure 1. The hydrothermally aged vehicles have a maximum distribution of pores in the pore diameters between 20 and 30 μm. The portion or portion of pores with a diameter smaller than 10 μm is almost equal to zero. Example 9 A vehicle according to the invention according to Example 3 (Mg content < 50 micrograms / g) is charged with phosphoric acid (60% by weight) and exposed for 40 hours in a high pressure installation at a pressure of water vapor of 15 bar and 350 ° C. The pore distribution of the aged catalyst was determined again with Hg prosimetry. The pore distribution is represented graphically in Figure 2. The maximum in the pore distribution is 30 μm. In comparison with the catalyst used in Comparative Example 1, the catalyst (vehicle or catalyst) according to the invention also presents after aging a greater proportional part of smaller pores, with a diameter below 10 μm. Comparative Example 2 A pyrogenic silica catalyst vehicle (BET surface 180m / g, gravimetric density 490 g / 1, total pore volume 0.8 cm3 / g, tablets with a diameter of 6mm and 5.5 mm height, with 0.4% by weight Mg (elemental)), proceeding according to Example 1 of EP 0 519 435, was contacted for 14 hours with 10% hydrochloric acid at room temperature, and then washed under a stream of water to liberate it from the chloride , and then it's dry. Next, a palladium-gold-potassium acetate catalyst was produced on the previously treated catalyst vehicle. The concentration of the impregnation solutions was selected in such a way, that the finished catalyst contained a concentration of 0.55% by weight of palladium, 0.25% by weight of gold, and 5.0% by weight of potassium acetate. In a first phase the vehicle was first impregnated with a basic solution of sodium hydroxide in water. The volume of the aqueous NaOH solution corresponded to 50 percent of the water absorption capacity of the dry vehicle. After impregnation with sodium hydroxide, the vehicle was directly impregnated, without intermediate drying, with a noble metal aqueous solution consisting of sodium palladium chloride and gold tetrachloro acid, whose volume (of the solution) also corresponded to 50% by weight. One hundred percent of the water absorption capacity of the dry material of the vehicle.

After a waiting time of 1.5 hours for the hydrolysis effect of the noble metal compounds, the particles of the vehicle were washed to liberate them from the chloride. The catalyst was dried and reduced to 450 ° C in the gas phase with mixed gas. After this the catalyst was impregnated with an aqueous solution of potassium acetate, and dried again. The drying was carried out in the gas phase with nitrogen. The sodium hydroxide concentration of the basic solution was calculated in such a way that an envelope containing noble metals of < 1.0 mm Example 10 On the catalyst vehicle according to the invention according to Example 3 (Mg content <50 micrograms / g) a palladium-gold-potassium acetate catalyst was prepared as described in Comparative Example 2, but with a diameter of 6 mm and a height of 5.5 mm. But unlike Comparative Example 2, the previous treatment with 10% hydrochloric acid was omitted. Example 11 A palladium-gold-potassium acetate catalyst according to Example 10 was prepared on the catalyst vehicle according to the invention according to Example 5, but with the measurements of 8 x 5 x 3 mm and edges in the form of facets. Application Example 1 The activity and selectivity of the catalysts of Comparative Example 2 and Examples 10 and 11 were measured during a test that lasted for up to 24 hours. The catalysts were tested in a hydrodynamic tubular reactor (reactor length 710 mm, inside diameter 23.7 mm) under normal pressure and a flow rate of 550 h "1 with the following gas composition: 75 5 per volume of ethene, 16.6% by volume of acetic acid, 8.3% by volume of oxygen The catalysts were examined in the temperature range of 120 to 165 ° C, measured in the catalyst bed The products of the reaction were analyzed at the reactor exit by chromatography of gases in line As a measure of catalyst activity, the volumetric time yield of the catalyst was determined in grams of vinyl acetate monomer per hour and kilogram of catalyst (g MAV / (hx kgCat.). of carbon, which is formed mainly by the combustion of ethene, and was used for the evaluation of the selectivity of the catalyst. of the catalysts of Comparative Example 2 and Examples 10 and 11. The catalyst activity and the catalyst selectivity of the catalyst according to Comparative Example 2 were each taken as 100 percent. Table 1: Catalyst Activity Selectivity T «emperati [g MAV / C02 in gas (hx kgCat:] burned in [° C] [% of surface] in [%] of in [%] of Comp. Ex. 2 Ex. comp. 2 Comp. ex. 2 100 100 159.6 Example 10 121.1 72.0 155.6 122.7 96.8 161.1 Example 11 106.8 58.5 142.1 124.9 103.9 154.1 The results demonstrate that the catalysts according to the invention, at comparable or even improved selectivity, have a clearly higher activity than the comparative catalyst.

Claims (11)

1. CLAIMS 1. Pyrogenic-based silicon dioxide based tablets, which are characterized by the following physico-chemical characteristics: Outer diameter 0.8 - 20 mm BET surface 30 - 400 m2 / g Pore volume 0.5 - 1.3 ml / g Resistance to Break 10 to 250 N Composition > 99.8% by weight of Si02 Other components < 0.2% by weight Abrasion < 5% by weight Gravimetric density 350 - 750 g / 1 2. Process for the production of silicon dioxide-based tablets produced pyrogenic with the following physico-chemical characteristics: External diameter 0.8 - 20 mm BET surface 30 - 400 m2 / g Pore volume 0.5 - 1.3 ml / g Resistance to break 10 to 250 N Composition > 99.8% by weight of Si02 Other components < 0.2% by weight Abrasion < 5% by weight Gravimetric density 350 - 750 g / 1 which is characterized by the fact that the pyrogenically produced silicon dioxide is homogenized with methylcellulose, microcera and / or polyethylene glycol with the addition of water, dried at a temperature of 80 - 150 ° C, if necessary crushed to powder, the powder is compressed into tablets that are calcined for a period of 0.5 to 8 hours at a temperature of 400 to 1200 ° C. 3. The use of the tablets according to claim 1 as catalysts or catalyst vehicles. 4. Catalyst vehicle for the production of vinyl acetate monomer containing on a vehicle the active components palladium, gold and potassium acetate, characterized in that the vehicle is a tablet according to claim 1. Process for the production of the catalyst vehicle according to claim 4 for the production of vinyl acetate monomer, by impregnating the vehicle with a basic solution (alkaline) and a solution containing gold and palladium salts, where the impregnation phases are carried out simultaneously or successively, with or without intermediate drying, washing the vehicle to remove any parts or portions of chloride that eventually can be present, and the reduction of the insoluble compounds precipitated on the vehicle, before or after washing, the drying of the previous stage of the catalyst obtained in this way, and the impregnation with alkaline acetates or alkaline compounds, which are completely transformed or partially in alkali acetates during the production of vinyl acetate monomer, characterized in that the vehicle is a tablet according to claim 1. 6. The use of catalysts containing an active component deposited on a tablet according to claim 1, characterized in that it is applied for catalytic reactions under c hydrothermal conditions. 7. The use according to claim 6, characterized in that it is applied to the hydration of olefins. 8. The use according to claim 7, characterized in that phosphoric acid is used as the active component. 9. The use according to claim 7, characterized in that a polyhetero acid is applied as an active component. The use according to claim 8 or 9, characterized in that it is applied for the hydration of ethylene to manufacture ethanol and diethyl ether. 11. The use according to claim 8 or 9, characterized in that it is applied for the hydration of propylene to manufacture isopropanol.