MXPA98009420A - Pressed parts based on silicon dioxide prepared by via pirog - Google Patents

Abstract

Prepared pressed pieces based on fumed silicon dioxide are prepared, with a pore volume of 0.5% at 1.8ml / g, for which proceeds to homogenize silicon dioxide obtained by pyro, using methylhydroxyethyl cellulose, wax and polyethylene glycol, under the addition of water, is subjected to a kneading and shaping process, is extruded, the extruded material is eventually cut to the desired length by a cutting device, it is dried at a temperature of 70 to 150 §C, and it is tempered for a time interval of 30 minutes to 10 hours at a temperature of 400 to 1200 ° C. Said pressed pieces can be applied as catalysts or as catalyst carriers in the manufacture of vinyl acetate monomer, in the hydration of ethylene and in the hydration of propylene.

Description

PRESSED PARTS BASED ON SILICON DIOXIDE PREPARED BY VIA PIROGENA Field of the invention The present invention relates to pressed parts based on fumed silicon dioxide, to a process for its manufacture, and to its use as a catalyst carrier or catalyst. . The silicon dioxides prepared by the pyrogenic route are distinguished by having a very fine granulometry and therefore have a specific and high surface area, have a very high purity, consist of spherical particles and lack pores. Thanks to these properties, the oxides prepared by the pyrogenic route are of increasing interest to be used as carriers or carriers of catalysts (D. Koth, H. Ferch, Chem. Ing., Techn., 52, 628 (1980)). Since the oxides prepared by the pyrogenic route have a particularly fine granulometry, their configuration as catalyst supports, or as catalysts, presents some difficulties.

REF .: 28749 DE-A 31 32 674 discloses a process for the manufacture of pressed parts from fumed oxides, in which process silica sol is used as a binding agent. DE-A 34 06 185 discloses a process for the manufacture of pressed parts, in which process glass frit in powder form is used as a binding agent, and glycerin as a gliding agent. DE-A 21 00 778 discloses the application of granules based on silicon dioxides prepared by the pyrogenic route, as catalyst support, in the manufacture of vinyl acetate monomer. DE-A 39 12 504 discloses a process for the manufacture of pressed parts, in which process aluminum stearate, magnesium stearate and / or graphite, as a gliding agent, and urea and also methyl cellulose are used, as pore formers Pressed pieces prepared with magnesium stearate, known, are sold by the firm Degussa under the designation of Aerosil Tablets No. 350.

They have a content of approximately 0.4% by weight of Mg. DE-B 0 519 435 discloses how to compress Si02 by binding agents, obtaining carriers or supports; the supports obtained are then brought to their incandescence, and the support particles, or carriers, incandescent are washed by acid until more cations of the binding agent are no longer released. The known processes have the disadvantage that for certain catalytic reactions such as for example the preparation of vinyl acetate from ethylene, acetic acid and oxygen, the hydration of ethylene to obtain ethanol, or the hydration of propylene to obtain isopropanol, the parts The obtained pressings do not exhibit the desired optimum properties such as, for example, high purity, high activity, high selectivity, high yield, and high stability. In the. Previous Patent Application, but not published, DE 196 19 961.1-41 described pressed pieces based on fumed silicon dioxide prepared with the following physico-chemical characteristics; Outer diameter 0.8-20 mm BET surface 30-400m2 / g Pore volume 0.5-l, 3ml / g Resistance to breakage from 10 to 250 N Composition > 99.8% by weight of Si02 Other Components > 0.2% by weight Abrasion > 5% by weight apparent specific weight (in bulk) 350-750g / l Description of the invention The object of the present invention consists of pressed pieces based on fumed silicon dioxide, characterized in that they have a pore volume of 0.5 to 8 ml / g, preferably of 1.31 to 8 ml / g.

The pressed parts of the present invention may have an outer diameter of 0.8 to 20 mm, a BET surface of 30 to 400 m2 / g, as well as a breaking strength of 7 to 250 N. It is preferable that the content of Si02 present in the pressed pieces of the present invention is greater than 99, 0% by weight. The incidence of the other components present may be less than 0.2% by weight. Therefore, the pressed parts of the present invention can be considered as free of binding agents. The abrasion may be less than 5% by weight. The specific graded weight (compacted) can be from 300 to 750 g / l. Another object of the present invention is a process for the manufacture of pressed pieces based on fumed silicon dioxide, with a pore volume of 0.5 to 8 ml / g, a process characterized in that it is homogenized silicon dioxide obtained by pyrogenic route, with methyl hydroxy ethyl cellulose, wax and polyethylene glycol, under the addition of water, is subjected to a kneading and shaping process, is extruded, the extruded material is eventually cut to the desired length by a cutting device, it is dried at a temperature of 70 to 150 ° C, and it is tempered for a time interval of 30 minutes to 10 hours at a temperature of 400 to 1200 ° C. In order to carry out the process according to the invention, all mixers, mixers or mills which allow a good homogenization and compaction of the mixed material, such as, for example, paddle, fluidized bed, rotary or stream mixers, are suitable. air. Especially suitable are the mixers by means of which further compaction of the mixed material is possible, such as, for example, plow grinders, vertical grinders, or ball mills. However, mixing and kneading can also be done directly in an extruder. The preparation of the extruded material can be done in extruders of one or two screws, extrusion presses, as well as in compactors. It is preferable that the pressed parts of the present invention can be manufactured by extruders. In a special embodiment of the invention, the mixture can have before its pressing the following composition: from 50 to 90% by weight, of silicon dioxide, preferably from 65 to 85% by weight; from 0.1 to 20% by weight, of methylhydroxy ethyl cellulose, preferably from 5 to 15% by weight; from 0.1 to 15% by weight, of wax, preferably from 5 to 12% by weight of 0.1 to 15% by weight, of polyethylene glycol, preferably from 5 to 10% by weight.

The pressed parts can have various shapes, for example cylindrical, spherical or annular, with an outer diameter of 0.8 to 20 mm. The pressed pieces are tempered at a temperature of 400 ° C to 1200 ° C for 30 minutes to 10 hours. By varying the amounts of the materials to be applied and the pressing pressure, it is possible to regulate in a given environment the resistance against breakage, the total surface area and the volume of pores. The pressed pieces can be applied either directly as catalysts or as catalyst supports. In the latter case, after their manufacture the pressed pieces can be put in contact with a catalytically active substance and eventually activated by suitable subsequent treatment. Pressed pieces of silicon dioxide prepared by the pyrogenic route can be used especially as carriers or catalyst supports for the preparation of vinyl acetate monomer from ethylene, acetic acid and oxygen, as well as carriers or carriers of catalysts in the processes of hydration of olefins, for example for the manufacture of ethanol and isopropanol. The pressed parts of the present invention have the following advantages: Compared with the pressed pieces according to DE-A 39 12 504, the pressed parts of the present invention do not have, apart from silicon dioxide, any other inorganic component . The known pressed pieces have the disadvantage of containing approximately 0.4% by weight of Mg which is separated by leaching during the process for the hydration of the olefins. In contrast, in hydration processes of this type, the pressed parts of the present invention have improved hydrothermal stability. In addition, they have a high purity and a high volume of pores.

Another advantage is that hydration is achieved a greater space-time performance. In the hydration of olefins, the pore volume of the catalyst support plays a very important role. With some surprise it has been proven that the greater volume of the pores allows the incorporation of a greater quantity of active phase. The consequence of this is that space-time performance increases. Another object of the present invention is a supported catalyst for the production of vinyl acetate monomer (VAM, Vinyllacetatmonomer), which carries on a carrier or support (pressed part) as catalytically active components; palladium and / or compounds thereof, alkali compounds, as well as additionally gold and / or compounds thereof (Pd / alkali / Au system) or cadmium and / or compounds thereof (Pd / alkali / Cd system) or barium and / or compounds thereof (Pd / alkali / Ba system), or palladium, alkaline compounds and mixtures of gold and / or cadmium and / or barium, characterized in that the support or carrier is a pressed part of the present invention. As potassium compounds, potassium compounds are preferred, such as, for example, potassium acetate. The catalytically active components may be available in the following systems: Pd / Au / alkali Compounds Pd / Cd / alkali Compounds Pd / Ba / Alkali The supported catalysts of the present invention are used for the production of vinyl acetate monomer. For this purpose, ethene, acetic acid and molecular oxygen, or air, in the gas phase, optionally under the addition of inert gases, are reacted at temperatures of between 100 and 250 ° C under a usual or high pressure, in the presence of the supported catalyst of the present invention. A production process of this type has been disclosed in DE 16 68 088, US 4,048,096, EP-A 0 519 4535, EP-A 0 634 208, EP-A 0 723 810, EP-A 0 634 209, EP- A 0 632 314 and EP-A 0 654 301. In said patent documents there is also disclosed a process for the manufacture of supported catalysts. Depending on the embodiment, supported catalysts are obtained with a homogeneous distribution of the noble metal through the cross section of the support or carrier and with a profile of shells (coating) more or less accentuated. Another object of the present invention is a process for the manufacture of the supported catalyst for the production of vinyl acetate monomer by impregnation, coating application, steam application, immersion or precipitation of the compounds of the metals Pd, Au , Cd, Ba, possibly reduction of the reducible metallic compounds applied on the support, washing for the removal of the chloride components eventually present, impregnation with alkaline acetates or alkaline compounds, which under the conditions of the reaction prevailing in the production of the monomer Vinyl acetate is completely or partially converted into alkaline acetates, in a suitable sequence, a process characterized in that the support is a pressed part according to the invention. Another object of the present invention is a process for the manufacture of the supported catalyst for the production of vinyl acetate monomer by impregnation of the support with a basic solution and with a solution containing gold and palladium salts, having the impregnation place simultaneously or consecutively, with or without intermediate drying, washing of the support in order to remove the chloride components possibly present, and reduction of the insoluble compounds precipitated on the support, before or after washing, drying of the catalyst precursor , and impregnation with alkaline acetates or alkaline compounds, which under the reaction conditions prevailing in the production of the vinyl acetate monomer are totally or partially converted into alkali acetates, this process characterized in that the support is a pressed part according to the invention. The supported catalysts of the present invention can be applied in the manufacture of unsaturated esters from olefins, acids and oxygen, in the gas phase. The catalysts of the present invention, of the Pd / alkali / Au catalyst system, are usually obtained by impregnation of the support with a basic solution and a solution containing gold and palladium salts, the steps of the impregnation taking place simultaneously or consecutively , with or without intermediate drying. Next, the support is washed in order to remove any chloride components present. Before or after the washing, the insoluble, noble metal compounds, separated from the support by precipitation, are reduced. The catalyst precursor, thus obtained, is dried, and for the activation of the catalyst it is impregnated with alkaline acetates or alkali compounds which, under the reaction conditions prevailing in the production of the vinyl acetate monomer, are totally or partially converted into acetates of vinyl. Therefore, in the case of the Pd / Au catalysts, the noble metals are present in the form of shells or casings on the support. In the case of the Pd / alkali / Ba catalysts, the metal salts are applied by impregnation, spraying, application in the vapor state, immersion or precipitation (EP 0 519 436). The same methods are known for the Pd / alkali / Cd catalysts (US-PS 4,902,823, US-PS 3,393,199, US-PS 4,668,819). Depending on the catalyst system, it is possible to undertake a reduction of the supported catalyst. The reduction of the catalyst can be carried out in the aqueous phase or in the gas phase. For reduction in the aqueous phase, formaldehyde or hydrazine are suitable, for example. The reduction in the gas phase can be undertaken with hydrogen or with synthetic gas (95% by volume of -N2 + 5% by volume of H2), ethene or ethene reduced with nitrogen. According to EP 0 634 209, the reduction takes place «.n hydrogen at temperatures between 40 and 260 ° C, preferably between 70 to 200 ° C. According to EP-A 0 723 810, the reduction takes place with synthetic gas (95% volume of N2 and 5% volume of H2) at temperatures between 300 and 550 ° C, preferably between 350 and 500 ° C. However, it is frequent that the catalyst is reduced only after its activation with alkaline acetate, directly in the production reactor, with ethene. In the production process, one begins by exposing the catalyst slowly to the reactants. During this initial phase the activity of the catalyst rises and usually it reaches its final level only after days or weeks. The object of the present invention is to indicate a supported catalyst for the production of vinyl acetate monomer, which together with an equal or improved selectivity, has an activity that is higher than that of the known catalysts. The object of the present invention is a supported catalyst, on the support according to the invention consisting of silicon dioxide, contains as catalytically active components; palladium and / or its compounds and alkali compounds, as well as additionally gold and / or compounds thereof (Pd / alkali / Au system) or cadmium and / or compounds (Pd / alkali / Cd system) or barium and / or its compounds (Pd / alkali / Ba system) or palladium, alkaline compounds and mixtures of gold and / or cadmium and / or barium, as well as a process for their manufacture. As the support material for the catalyst, a pressed part of the present invention based on fumed silicon dioxide obtained is suitable. It is important that the catalyst supports retain their mechanical strength under the reactive conditions of the catalytic process, especially under the influence of acetic acid. The pressed parts of the present invention may be in the form of extruded pressed pieces, tablets, rings or in other customary forms for solid bed catalysts. The manufacturing of supported catalysts of the Pd / alkali / Au system on the pressed part of the invention is described in more detail below. The pressed pieces of the invention are impregnated with a solution containing palladium and gold. At the same time as the solution containing the noble metals, or in an arbitrary consecutive sequence, the pressed pieces are impregnated with a basic solution which may contain one or more basic compounds. The basic composition (s) are used for the conversion of palladium and gold, in their respective hydroxides. The compounds present in the basic solution may consist of alkali hydroxides, alkali bicarbonates, alkali carbonates, alkali silicates, or mixtures of said substances. Preference is given to using potassium hydroxide and / or sodium hydroxide. For the preparation of the solution containing the noble metals, they can be used as palladium salts, for example palladium chloride, sodium chloride or potassium chloride and palladium or palladium nitrate. As gold salts, gold chloride (III) and tetrachloro gold (III) acids are suitable. Preference is given to using potassium chloride and palladium, sodium chloride and palladium and / or tetrachloroauric acid. The impregnation of the pressed parts of the present invention with the basic solution influences the separation of the noble metals in the pressed part. The basic solution can be put in contact with the pressed part of the invention, either simultaneously with the solution of the noble metals or in an arbitrary sequence with said solution. In the case of consecutive impregnation of the pressed part of the invention with both solutions, it is possible to carry out an intermediate drying after the first impregnation step. It is preferable that the pressed part is first impregnated with the basic compound. The subsequent impregnation with the solution containing gold and palladium leads to precipitation of the palladium and gold in the form of a surface shell on the pressed part of the invention. In general, the inverted sequence of the impregnation leads to a more or less homogeneous distribution of the noble metals on the cross section of the pressed part of the invention. However, if an adequate control of the process is applied, it is possible to obtain, also in the case of an inverted impregnation sequence, catalysts with a defined shell (see, for example, US 4,068,096). In general, catalysts with a homogeneous, or almost homogeneous, distribution of noble metals have a lower activity and selectivity. Catalysts whose shell has a thickness of less than 1 mm, preferably less than 0.5 mm, are particularly suitable. The thickness of the shell is influenced by the amount of the basic composition applied on the support material, related to the desired amount of the noble metals. The greater this ratio, the smaller the thickness of the shell that is formed. The ratio between the amounts needed for a given thickness of the shell, of the basic compound and the noble metal compounds, depends on the suitability of the support material, as well as on the basic composition and composition of the noble metals, chosen. It is convenient that the necessary relationship between the quantities is determined by a few preliminary tests. In this case, the thickness of the shell can be determined in a simple manner by making a cut through the catalyst particle. The minimum necessary amount of the basic composition is the theoretical stoichiometric amount of hydroxydiones that are necessary to convert palladium and gold into their hydroxides. As a directive, it is considered that to obtain a shell with a thickness of 0.5 mm, the basic composition should be applied with a stoichiometric excess of 1 to 10. The pressed pieces are coated according to the procedure of impregnation of the pore volume, with the basic compounds and with the salts of the noble metals. If working with an intermediate drying, the volumes of both solutions are selected in such a way that in each case they correspond to approximately 90 to 100% of the capacity of incorporation of the pressed pieces of the invention. If the intermediate drying is dispensed with, in this case the sum of the individual volumes of both impregnation solutions must comply with the aforementioned condition, in which case the individual volumes may be in a ratio of 1.; 9 to 9; 1 to each other. A volumetric ratio of 3 is preferably applied; 7 to 7; 3, especially 1; 1. In both cases it can be used, and this is preferable, to use water as a solvent. However, organic and aqueous-organic solvents may also be suitable. The reaction of the solution of the noble metals with the basic solution, to obtain the insoluble compositions of noble metals, proceeds slowly, and usually ends only after 1 to 24 hours, depending on the method of preparation. Next, the compositions of the noble metals, insoluble in water, are treated with reducing agents. A wet reduction can be undertaken, for example with a hydrazine hydrate, aqueous, or a reduction in gas phase, for example with hydrogen, ethene, synthetic gas or also methanol vapors. The reduction can be carried out at normal temperature or at elevated temperature, and under normal or high pressure, possibly also under the addition of inert gases. Before and / or after the reduction of the noble metal compositions, the chlorides eventually present on the support are removed by intensive washing. After washing, the catalyst should contain less than 500 ppm of chlorides, preferably less than 200 ppm. The catalyst precursor, obtained after the reduction, is dried and then impregnated with alkaline acetates or with alkaline compositions which under the reactive conditions prevailing in the production of the vinyl acetate monomer are completely or partially converted into alkali acetates. It is preferable to impregnate with potassium acetate. In this case, preference is given to impregnation of the pore volume. That is to say; the necessary amount of potassium acetate is dissolved in a solvent, preferably water, whose volume corresponds approximately to the capacity of incorporation of the present support material. Said volume is approximately equal to the total volume of the pores of the support material. The catalyst is then dried until a residual humidity of less than 2% is reached: The drying can be carried out in the air, optionally also under nitrogen as an inert gas. The manufacture of the supported catalysts, of the Pd / alkali / Cd and Pd / alkali / Ba systems, on the pressed pieces, takes place following the aforementioned patent documents. For the synthesis of the vinyl acetate monomer it is convenient to coat the catalyst with from 0.2 to 4, preferably from 0.3 to 3% by weight, of palladium, from 0.1 to 2, preferably from 0.15 to 1.5. % by weight, of gold, and from 1 to 10, preferably from 1.5 to 9% by weight, of potassium acetate; in each case, referred to the weight of the support used. These indications apply to the Pd / alkali / Au- system. In the case of catalyst supports with an apparent specific weight of 500 g / l, these indications of the concentrations correspond to concentrations expressed in volume, from 1.0 to 20 g / l, of palladium from 0.5 to 10 g / l, of gold and from 5 to 50g / l, of potassium acetate. For the preparation of the impregnation solutions, the corresponding amounts of the palladium and gold compositions are dissolved in a volume of water corresponding to approximately 90 to 100% of the capacity of the support material present to incorporate water. The procedure is analogous to the preparation of the basic solution. The cadmium content in the Pd / alkali / Cd catalysts is generally from 0.1 to 2.5% by weight, preferably from 0.4 to 2.0% by weight. The barium content in the Pd / alkali / Ba catalysts is generally from 0.1 to 2.0% by weight, preferably from 0.2 to 1.8% by weight. The palladium content of the catalysts Pd / alkali / Cd and Pd / alkali / Ba can be from 0.2 to 4% palladium by weight, preferably from 0.3 to 3% by weight. Potassium content in Pd / alkali / Cd or Pd / alkali / Ba catalysts, is generally from 1 to 10% by weight, preferably from 1.5 to 9% by weight. The invention also relates to catalytic reactions under hydro-thermal conditions such as, for example, the hydration of olefins to obtain the corresponding alcohols, in the presence of phosphoric acid or of another active component, for example a hetero-poly-acid, serving the pressed part of the invention, as a catalyst holder. A method of this type is described, for example, in EP 0 578 441 A2. According to said process, water and ethylene are reacted at temperatures between 225 and 280 ° C and under pressures between 20 and 240 bar, obtaining ethanol. For this purpose, a water / ethylene ratio in the range of 0.15 to 0.5 is used. The catalyst charge, measured in grams of the water / ethylene mixture per minute and milliliter of catalyst, can be chosen in the range of 0.01 to 0.1 g / (min x ml). By way of sub / product, diethyl ether is formed in said reaction.

The process parameters for the preparation of the ethanol may also be located outside the aforementioned ranges. An example of this can be found in DE / OS 20 15 5365 (Example 1); in this case, the temperature was about 300 ° C, and the ratio between water and ethylene was 0.74 Mol / mol, the total pressure being 70 bar. In this case it is important that the temperature and the pressure of the water vapor are regulated one according to the other.

The preparation of isopropanol by hydration the propylene takes place under similar conditions. However, in this case the temperature is in the range between 180 and 225 ° C. As a secondary product, n-propanol is obtained in this reaction.

According to EP 0 578 441 A21, synthetic silicon dioxide pellets with high breaking strength, high porosity and reduced metal impurities can be used as the catalyst carrier for the active component phosphoric acid. The pores of the support serve to incorporate the active component. The average radius of the pores before application in the hydration process is in the range between 1 and 50 nm.

In the case of the hydration of the olefins, phosphoric acid is introduced into the catalyst carrier as an active component. To this end, the support is immersed in an aqueous solution of phosphoric acid and impregnated with it. To this end, phosphoric acid solutions containing from 15 to 85% by weight of phosphoric acid, based on the total weight of the solution, are used. It is also possible to coat with a hetero poly acid as an active component.

One of the main applications of the hydration of olefins is the hydration of ethylene to obtain ethanol and diethyl ether, as well as the hydration of propylene to obtain isopropanol. In this case, the reactive conditions known in the state of the art are used.

By way of pyrogenic silicon dioxide preparer, silicon dioxides with the following physico-chemical characteristics can be used: 1) according to DIN 53 194 5) Referred to 2 hours for the substance dried to 105 SC) ße DIN DIN 9 921 6) Referred to 2 hours for the substance taken to 3) ße DINGO 53200 incandescence to 1000 SC) ße DINGO 53 580 7) The content of HCl 'is a component of the loss by incandescence To prepare the Aerosil, a volatile silicon composition is sprayed into a hydrogen and air fulminating gas flame. In most cases, silicon tetrachloride is used. Said substance is hydrolysed under the influence of water that is originated by the reaction of the fulminating gas, obtaining 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 agglomerate. The product which at this stage of the process is present in the form of a kind of aerosol, is separated in cyclones from the accompanying gasiform substances, and is then subjected to further treatment with moist hot air. Thanks to this process, the content of residual hydrochloric acid can be brought to less than 0.25%. Since at the end of this process the AEROSIL is presented with a specific bulk weight of only approximately 15g / l, the vacuum is continued with a compaction, by means of which specific tamping weights of approximately 50g / l and more can be achieved. The particle size of the products obtained in this way can be varied by adjusting the reactive conditions such as, for example, the flame temperature, the incidence 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 in accordance with DIN 66 131, with nitrogen. The volume of the pores is determined by calculation, as the sum of the volume of the micropores, mesopores and macropores. The resistance against breakage is determined by the tester of the resistance against breakage, of the company Erweka, Typ TBH 28. The determination of the micro- and mesoporos takes place by means of the tracing of an isotherm of N2 and of the evaluation of this according to the BET, from Boer und Barret, Joyner, Halenda. The determination of the macropores is carried out by means of the pressing or injection with Hg process.

Abrasion is determined by the abrasion and friability tester, from Erweka, Typ TAR.

Examples Example 1 69% by weight Aerosil 200 12.5% by weight Methylhydroxyethylcellulose 10.2% by weight Wax 8.3% by weight Polyethylene glycol is compacted in a kneader together with the addition of water. The kneaded dough is transformed into a single-screw extruder, obtaining pressed pieces in the form of a filament which, by means of a cutting device, are cut to the desired length of 3 to 5 mm. The pressed pieces are dried at 90 ° C in a continuous desiccator. The blanks are calcined for 6 hours at a temperature of 750 ° C. The pressed pieces obtained have the following physical and chemical characteristics: Dimensions of the pressed pieces; diameter 3.75 mm .. length 4 + 1 mm BET surface 160 m2 / g Pore volume 1.41 ml / g Resistance against break 25N Abrasion 2.1% by weight Specific weight tamping 348g / l Si02 content 99.85% Examples 2 and 3 71.4% by weight Aerosil 200 12.9% by weight Methylhydroxyethylcellulose 7.1% by weight Wax 8.6% by weight Polyethylene glycol are processed under the addition of water in a twin screw extruder, obtaining pressed pieces in filament shape that by means of a trimmer device are cut to the desired length of 3 to 5mm, or 2 to 4mm. The pressed pieces are dried at 110 ° C in a desiccator cabinet. The blanks are calcined for 6 hours at a temperature of 750 ° C. The pressed pieces obtained have the following physicochemical characteristics: Example 2 Example 3 Dimensions of the pressed pieces; diameter 3.7 mm; 2, 65mm length 4 + lmm 3 + lmm BET surface 160m2 / g 163m2 / g Poros Volume l, 46ml / gl, 54ml / g Resistance against Breakage 20 N 7 N Abrasion 0.8% by weight 1,15% in weight Padding 327 g / l 310g / l Si02 content 99.9% 99.9% Example 4 Hydration of Ethylene by Application of a Known Catalyst Holder. The catalyst holder 350, corresponding to the current state of the art, of the company Degussa AG, has a pore volume of 0.8 ml / g. This catalyst holder is impregnated in a 60% by weight H3P04 solution, and then dried, 50 ml of this catalyst are incorporated in a solid bed reactor and reheated to 240 ° C under a stream of nitrogen gas. Then the N2 is replaced by a gasiform mixture of ethylene and water. The water flow rate is 0.20 g / min. And the relation between water and ethylene is 0.27 Mol / Mol. The analysis of the evacuated gases is carried out by means of gas chromatography. To assess the catalytic activity, the surface relationship between ethanol and ethylene is evaluated. In the case of an average catalyst temperature of 240 ° C, a ratio of 0.078 is achieved for the catalyst based on catalyst carrier 350.

Example 5 Hydration of Ethylene by Application of a Catalyst Holder according to the Invention. A catalyst holder, of Si02, of the invention, with a pore volume of 1.36 ml / g, is charged with a solution of H3P04 as the catalyst carrier of Example 4, and subjected to testing. The flow of water is 0.22 g / min, the ratio between water and ethylene is 0.30 Mol / Mol. In the case of this catalyst applied on the portacatalyst according to the invention, the ratio between the surfaces in gas chromatography is 0.103, that is, it is 32% higher than for the catalyst on the known catalyst carrier.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following:

Claims (14)

R E I V I N D I C A C I O N S

1. Pressed pieces based on fumed silicon dioxide, characterized in that they have a pore volume of 0.5 to 1.8 ml / g.

2. Process for the manufacture of pressed pieces based on fumed silicon dioxide, with a pore volume of 0.5 to 8 ml / g, according to claim 1, characterized in that silicon dioxide is homogenized obtained by pyrogenic route, with methyl hydroxy ethyl cellulose, wax and polyethylene glycol, under the addition of water, is subjected to a kneading and shaping process, is extruded, the extruded material is eventually cut to the desired length by a cutting device, it is dried at a temperature of 70 to 150 ° C, and it is tempered for a time interval of up to 10 hours at a temperature of 400 to 1200 ° C.

3. Use of the pressed pieces according to claim 1, as a catalyst or catalyst carrier.

4. Supported catalyst for the production of vinyl acetate monomer (VAM), which catalyst applied on a support (pressed part) contains as catalytically active components; palladium and / or its compounds and alkali compounds, as well as gold and / or its compounds (Pd / alkali / Au system) or cadmium and / or its compounds (Pd / alkali / Cd system) or barium and / or compounds (Systems Pd / alkali / Ba), or palladium, alkaline compounds and mixtures of gold and / or cadmium and / or gold, characterized in that the support is a pressed part according to claim 1.

5. Process for manufacturing the supported catalyst, according to claim 4, for the production of vinyl acetate monomer, by impregnation, application by coating, application in the vapor state, immersion or precipitation of the compounds of the metals Pd, Au, Cd, Ba, possibly reduction of the reducible metallic compounds applied on the support, washed for the removal of any chloride components present, impregnation with alkaline acetates or alkaline compounds, which under the conditions of the reaction prevailing in the The production of the vinyl acetate monomer is completely or partially converted into alkali acetates, in a suitable sequence, characterized in that the support is a pressed part according to claim 1.

6. Process for the manufacture of the supported catalyst, in accordance with claim 4, for the production of vinyl acetate monomer, by impregnation of the support with a basic solution and with a solution containing gold and palladium salts, having the impregnation take place simultaneously or consecutively, with or without a intermediate drying, washing of the support in order to remove any chloride components present, and reduction of the insoluble compounds precipitated on the support, before or after washing, drying of the catalyst precursor thus obtained, and impregnation with alkaline acetates or alkaline compounds, that under the reaction conditions prevailing in the production of the monomer acetat or of vinyl are totally or partially converted into alkali acetates, characterized in that the support is a pressed piece according to claim 1.

7. Catalyst supported according to claim 4 to 6, characterized in that the alkaline acetate or the alkaline compound is potassium acetate.

8. Use of the catalyst according to claim 4 to 6 for the manufacture of unsaturated esters from olefins, organic acids and oxygen in the gas phase.

9. Use of catalysts containing an active component that has been applied to a pressed part according to claim 1, for catalytic reactions under hydrothermal conditions.

10. Use in accordance with the claim 9, for the hydration of olefins.

11. Use according to claim 10, characterized in that phosphoric acid is used as an active component.

12. Use in accordance with the claim 10, characterized in that a heteropoly acid is applied as an active component.

13. Use in accordance with the claim 11 or 12 for the hydration of ethylene for the manufacture of ethanol and diethyl ether.

14. Use according to claim 11 or 12, for the hydration of propylene for the manufacture of isopropanol.