WO2012140617A1

WO2012140617A1 - Catalyst for the production of ethylene oxide

Info

Publication number: WO2012140617A1
Application number: PCT/IB2012/051837
Authority: WO
Inventors: Tobias Rosendahl; Torsten Mäurer; Cornelia Katharina Dobner; Jürgen ZÜHLKE
Original assignee: Basf Se; Basf (China) Company Limited
Priority date: 2011-04-14
Filing date: 2012-04-13
Publication date: 2012-10-18
Also published as: JP2014514960A; EP2696973A4; EP2696973A1; CN103608105A

Abstract

Catalyst for the production of ethylene oxide, at least comprising silver applied to a carrier, said carrier having a BET constant ranging from 0 to 800 as per DIN ISO 9277.

Description

Catalyst for the production of ethylene oxide

The present invention relates to a catalyst for the preparation of ethylene oxide, at least comprising silver, supported on a support, wherein the support has a BET constant C in the range of 0 to 800 and wherein the constant is determined according to DIN ISO 9277. Furthermore, the present invention relates to this cata- carrier in itself. Moreover, the present invention relates to a process for the preparation of the catalyst and the catalyst, which can be prepared by this process and the use of the catalyst for the oxidation of ethene to ethylene oxide. Moreover, the present invention relates to a process for the production of ethylene oxide from ethylene, comprising an oxidation of ethylene in the presence of said catalyst.

Ethylene oxide is an important basic chemical and is often produced industrially by direct oxidation of ethylene with oxygen in the presence of silver-containing catalysts. Frequently, supported catalysts are used to which the catalytically active metallic silver has been applied by a suitable method. As a carrier material can in principle different porous materials such. As activated carbon, titanium, zirconium or silica or ceramic compositions or mixtures of these materials can be used. As a rule, alpha-alumina is used as the carrier. Exemplary of the direct oxidation of ethene are DE-A-2300512, DE-A 2521906, EP-A-0014457, DE-A-2454972, EP-A-0172565, EP-A-0357293, EP-A-0266015, EP -A-001 1356, EP-A-0085237, DE 2560684 or DE-A-2753359.

In addition to silver as an active component, these catalysts often contain promoters to improve the catalytic properties. By way of example, alkali metal and / or alkaline earth metal compounds may be mentioned as promoters. Some writings teach the use of transition metals such as tungsten or molybdenum. A particularly preferred promoter for influencing the activity and selectivity of catalysts is rhenium. Catalysts containing rhenium and / or other transition metal promoters in combination with alkali and / or alkaline earth metal compounds are preferably used industrially because of their high selectivity. By selectivity is meant the molar percentage of ethylene that reacts to ethylene oxide. The activity is characterized by the ethylene oxide concentration in the reactor outlet under otherwise constant conditions, such as temperature, pressure, gas quantity, amount of catalyst, etc. The higher the ethylene oxide concentration in the reactor output stream, the higher the activity of the catalyst. The lower the temperature required to reach a given alkylene oxide concentration, the higher the activity. To achieve a high selectivity, it is usual to use the combination of the active metal with the promoters and the composition of the carrier coordinated to obtain catalysts with the best possible properties.

Starting from this prior art, it was an object of the present invention to provide novel catalysts for the epoxidation of ethylene which have advantageous activities and / or selectivities.

Another object of the present invention was to provide suitable supports for the preparation of catalysts which have particularly advantageous property profiles for the epoxidation of ethylene.

According to the invention, this object is achieved by a catalyst for the production of ethylene oxide, comprising silver, applied to a support, the support having a BET constant C in the range from 0 to 800, determined in accordance with DIN ISO 9277. Surprisingly, it has been found that the use of supports having a BET constant C in a certain range leads to particularly advantageous properties of the resulting catalyst. In particular, the catalysts show advantageous selectivities in the production of ethylene oxide.

Accordingly, the invention relates to a catalyst for the production of ethylene oxide, comprising silver, applied to a support, wherein the support has a BET constant C in the range of 0 to 800, determined in accordance with DIN ISO 9277.

Furthermore, the invention relates to the carrier per se, ie a catalyst support for a catalyst for the production of ethylene oxide, wherein the support has a BET constant C in the range of 0 to 800, determined according to DIN ISO 9277.

Furthermore, the invention relates to a process for the preparation of a catalyst for the production of ethylene oxide, and to the catalyst preparable by this process, the process comprising the steps

(i) providing a support having a BET constant C in the range of 0 to 800, determined in accordance with DIN ISO 9277, and

(ii) applying silver to the support according to (i).

Furthermore, the invention relates to the use of the catalyst or catalyst according to the invention, which can be prepared by the process according to the invention for the epoxidation of ethylene.

As far as the preparation of the catalyst is concerned, generally all processes are suitable in which silver is suitably applied to the carrier. Here, preferably at least one mixture containing silver, for example, by impregnation or Spray or mixing method on the support, as described in more detail below, applied.

As for the carrier, it is characterized by a BET constant C in the range of 0 to 800, preferably in the range of 0 to 700, more preferably in the range of 0 to 600, further preferably in the range of 25 to 500 and more preferably ranging from 50 to 450. The BET constant C (also the C value) is determined according to DIN ISO 9277 (May 2003).

The C-value determination is based on the method of Brunnauer, Emmet and Teller for determining the total specific surface area of porous solids by measuring the physisorbed amount of gas (BET) as in Journal of the American Chemical Society, Vol. 60, pp. 301-319 (1938). For the physisorption of gases, Brunnauer, Emmet, and Teller have derived a simple relationship between gas pressure and absorbed gas amount, referred to as the BET isotherm, from both a gas kinetic and a statistical model. The relationship results from the formula

where V is the molar volume of Adsorbtivs, ie, the adsorbed gaseous, liquid or solute. V _M is the volume of gas required to form a monolayer, p _r = p / p ₀ , ie the relative pressure, p is the equilibrium pressure, p _{0 is} the saturation vapor pressure of the gas at the measurement temperature. C is the BET constant to which the relationship applies:

where E-ι is the adsorption energy when forming the first layer, E _{L is} the adsorption energy of the second and higher layers, A is the kinetic factor, and R is the gas constant. T stands for the respective temperature in Kelvin.

The C value contains information about the interaction energy of the adsorbate with the carrier and gives information about the polarity of the carrier surface. Small C values are characteristic of non-polar areas, whereas large C values are indicative of highly polar or microporous areas. The C value depends, for example, on the composition of the support, the acidity of the surface and the porosity and the shape of the pores. For example, the calcination conditions used in the preparation of the carrier or the addition of polar compounds (silicon additives) or nonpolar compounds (eg waxes) to the carrier material have an influence on the C value. Suitable supports according to the invention can be prepared by processes known from the prior art. Examples include US 2009/0198076 A1, WO 2006/133187, WO 03/072244, US 2005/0096219 A1, or EP 0 496 386 B2.

Examples of suitable inert support materials are alumina, silica, silicon carbide, titania, zirconia, and mixtures thereof, with alumina being preferred. According to a preferred embodiment, the present invention accordingly relates to a catalyst as described above or a support as described above, wherein the support is an alumina support. Furthermore, the present invention also relates to a catalyst as described above, preparable by the method described above, wherein the carrier is an alumina carrier.

The term alumina, as used herein, includes all conceivable structures such as alpha, gamma or tetha alumina. According to a preferred embodiment, the carrier is an alpha alumina carrier. Accordingly, the present invention also relates to a process as described above and to a catalyst or carrier preparable by the process, wherein the support is an alpha-alumina. Furthermore, the present invention also relates to a catalyst as described above, wherein the carrier is an alpha-alumina carrier.

According to a further preferred embodiment, the alpha-alumina has a purity of at least 75%, preferably a purity of at least 80%, more preferably a purity of at least 85%, more preferably a purity of at least 90%, more preferably a purity of at least 98 %, more preferably a purity of at least 98.5%, and most preferably a purity of at least 99%.

The term alpha-alumina therefore also includes alpha-aluminas containing further constituents, for example elements selected from the group consisting of zirconium, alkali metals, alkaline earth metals, silicon, zinc, gallium, hafnium, boron, fluorine, copper, nickel, manganese, iron , Cerium, titanium, chromium and mixtures of two or more of these elements.

In general, a suitable catalyst support for the present invention can be prepared by mixing the alumina with water or other suitable liquid with a burnout material or a pore former and at least one binder. Suitable pore formers are, for example, cellulose and cellulose derivatives, such as, for example, methylcellulose, ethylcellulose, carboxymethylcellulose. loose, or polyolefins, such as polyethylenes and polypropylenes, or natural burnout materials, such as walnut shell meal. The pore formers are selected to be completely burned out of the alumina to the final alpha alumina support at the selected kiln temperatures of the calcination. Suitable binders or extrusion and extrusion aids are described, for example, in EP 0 496 386 B2. Examples are alumina gels with nitric acid or acetic acid, cellulose, for example methyl, ethyl cellulose, or carboxyethyl cellulose, or methyl or ethyl stearate, polyolefin oxides, waxes and the like.

The paste formed by mixing can be made into the desired shape by extrusion. Extrusion aids may be used to assist in the extrusion process.

Usually, the molded article obtained as described above is optionally dried following the molding and calcined to obtain the alumina support according to (i). The calcination is usually carried out at temperatures in the range of 1200 ° C to 1600 ° C. It is common to wash the alumina carrier after calcining to remove soluble ingredients.

The alpha-alumina may contain the constituents in any suitable form, for example as an element and / or in the form of one or more compounds. If the alpha-alumina contains one or more constituents in the form of a compound, it contains this, for example, as oxide or mixed oxide. Thus, the present invention also describes an alpha alumina containing at least one further constituent selected from the group consisting of silica, sodium oxide, potassium oxide, calcium oxide and magnesium oxide, nickel oxide, gallium oxide, hafnium oxide, copper oxide, iron oxide and mixed oxides thereof.

As regards the amount of the further constituents, the total content of the further constituents is preferably in a range of less than 25% by weight, more preferably less than 20% by weight, more preferably less than 15% by weight, more preferably less than 10% by weight, more preferably less than 5% by weight, more preferably less than 2% by weight, more preferably less than 1.5% by weight and particularly preferably less than 1% by weight, based on the total weight of the carrier.

For example, when the carrier contains silicon, it preferably contains it in an amount in the range of 50 to 10,000 ppm, more preferably in an amount of 50 to 5,000 ppm, further preferably in an amount of 50 to 800 ppm based on the total weight of the carrier and calculated as an element. For example, if the carrier contains alkali metals, it preferably contains them in a total amount in the range of 10 to 2500 ppm, more preferably in an amount of 10 to 1000 ppm, further preferably in an amount of 50 to 850 ppm based on the total weight of the carrier and calculated as an element. According to one embodiment, the carrier contains at least one alkali metal selected from the group consisting of sodium and potassium. For example, when the carrier contains sodium, it preferably contains it in an amount in the range of 10 to 1500 ppm, more preferably in an amount of 10 to 800 ppm, further preferably in an amount of 10 to 500 ppm based on the total weight of the carrier and calculated as an element. For example, if the carrier contains potassium, it preferably contains it in an amount in the range of 10 to 1000 ppm, more preferably in an amount of 10 to 500 ppm, further preferably in an amount of 10 to 300 ppm based on the total weight of the carrier and calculated as an element. For example, according to one embodiment of the invention, the carrier contains sodium in an amount of 10 to 1500 ppm and potassium in an amount of 10 to 1000 ppm.

Accordingly, the present invention also describes a process for preparing a catalyst and a catalyst as described above, preparable by this process, wherein the carrier sodium in an amount of 10 to 1500 ppm, potassium in an amount of 10 to 1000 ppm and cesium in a Amount of 0 to 1000 ppm, more preferably wherein the carrier sodium in an amount of 10 to 500 ppm, potassium in an amount of 10 to 300 ppm and cesium in an amount of 0 to 100 ppm, based on the total weight of the carrier and calculated as Element comprising. Furthermore, the invention describes a catalyst preparable by this method and the carrier itself. Likewise, the present invention also relates to a catalyst as described above and a carrier as described above, wherein the carrier sodium in an amount of 10 to 1500 ppm, potassium in an amount of 10 to 1000 ppm and cesium in an amount of 0 to 100 ppm, more preferably sodium in an amount of 10 to 500 ppm, potassium in an amount of 10 to 300 ppm and cesium in an amount of 0 to 100 ppm, each based on the total weight of the carrier and calculated as element comprises.

If the carrier contains, for example, alkaline earth metals, it preferably contains these in a total amount in the range of at most 2500 ppm, for example in the range from 10 to 2500 ppm, more preferably in an amount of from 10 to 1200 ppm, more preferably in an amount of from 10 to 700 ppm, based on the total weight of the carrier and calculated as element. In one embodiment, the carrier comprises at least one alkaline earth metal selected from the group consisting of calcium and magnesium. For example, when the carrier contains calcium, it preferably contains it in an amount in the range of 10 to 1500 ppm, more preferably in an amount of 10 to 1000 ppm, further preferably in an amount of 10 to 500 ppm, based on the Total weight of the carrier and calculated as an element. For example, when the carrier contains magnesium, it preferably contains it in an amount in the range of 10 to 800 ppm, more preferably in an amount of 10 to 500 ppm, further preferably in an amount of 10 to 250 ppm based on the total weight of the carrier and calculated as an element.

Accordingly, the present invention also describes a process for producing a catalyst and a catalyst prepared by this process as described above, wherein the carrier contains magnesium in an amount of 10 to 800 ppm, and calcium in an amount of 10 to 1500 ppm, respectively on the total weight of the carrier and calculated as an element that includes. Likewise, the present invention also relates to a catalyst as described above and a carrier as described above, wherein the carrier magnesium in an amount of 10 to 800 ppm, and calcium in an amount of 10 to 1500 ppm, each based on the total weight of Carrier and calculated as an element, includes. More preferably, the carrier comprises, for example, sodium in an amount of 10 to 1500 ppm, potassium in an amount of 10 to 1000 ppm, magnesium in an amount of 10 to 800 ppm, and calcium in an amount of 10 to 1500 ppm, based on the total weight of the carrier and calculated as an element.

For example, when the carrier contains silicon, it preferably contains it in an amount in the range of 50 to 10,000 ppm, more preferably in an amount of 50 to 5,000 ppm, further preferably in an amount of 50 to 600 ppm based on the total weight of the carrier and calculated as an element.

A support preferred according to the present invention is, for example, an alpha-alumina in a purity of at least 90%, which calculates 50 to 10,000 ppm of silicon, 10 to 1500 ppm of sodium and 10 to 2500 ppm of total alkaline earth metals, respectively Element and based on the total weight of the carrier. The support preferably comprises calcium and / or magnesium as the alkaline earth metal. Particularly preferred is an alpha-alumina in a purity of at least 98 wt .-%, which 50 to 5000 ppm silicon, 10 to 800 ppm of sodium and 10 to 700 ppm of alkaline earth metals in total, each calculated as an element and based on the total weight of the carrier , includes.

The carriers used according to the invention preferably have a BET surface area, determined in accordance with DIN ISO 9277, of 0.1 to 5 m ² / g, more preferably in the range of 0.1 to 2 m ² / g, more preferably in the range of 0 , 5 to 1, 5 m ² / g, more preferably in the range of 0.6 to 1, 3 m ² / g, and particularly preferably in the range of 0.6 to 1, 0 m ² / g, determined according to DIN ISO 9277th Furthermore, the supports according to the invention preferably have pores with diameters in the range from 0.1 to 100 μm, it being possible for the pore distribution to be monomodal or polymodal, for example bimodal, trimodal or tetramodal. Preferably, the carriers have a bimodal pore distribution. The supports furthermore preferably have a bimodal pore distribution with peak maxima in the range from 0.1 to 10 μm and 15 to 100 μm, preferably in the range from 0.1 to 5 μm and 17 to 80 μm, more preferably in the range from 0.1 to 3 μηη and 20 to 50 μηη, more preferably in the range of 0.1 to 1, 5 μηη and 20 to 40 μηη on. The pore diameters are determined by Hg porosimetry (DIN 66133). The term "bimodal pore distribution with peak maxima in the range from 0.1 to 10 μηη and 15 to 100 μηη", as used above, means that one of the two peak maxima in the range of 0.1 to 10 μηη and the other peak maximum in the range of 15 to 100 μηη.

Accordingly, the present invention also describes a process as described above for preparing a catalyst and a catalyst preparable by this process, wherein the support has a bimodal pore distribution, preferably a bimodal pore distribution at least containing pores having a pore diameter in the range of 0.1 to 15 μηη and pores with a pore diameter in the range of 15 to 100 μηη, determined by Hg porosimetry. Likewise, the present invention also relates to a catalyst as described above and a carrier as described above, wherein the carrier has a bimodal pore distribution, preferably a bimodal pore distribution, at least containing pores having a pore diameter in the range of 0.1 to 10 μηη and pores with a pore diameter in the range of 15 to 100 μηη, determined by Hg porosimetry (DIN 66133).

The geometrical shape of the carrier is generally of secondary importance, but the carriers should expediently be in the form of particles which allow unimpeded diffusion of the reaction gases over as large a portion of the outer surface occupied by the catalytically active silver-doped and optionally further promoters and inner surface of the carrier. In addition, the smallest possible pressure loss over the entire reactor length must be ensured by the selected geometric shape of the carrier. According to a preferred embodiment, the carrier is used as a shaped body, for example as a strand, hollow strand, star strand, sphere, ring or hollow ring. The carrier is preferably a shaped body with the geometry of a hollow body. Particularly preferred are cylinders with the following geometries (outer diameter x length x inner diameter, in each case in mm): 5x5x2, 6x6x3, 7x7x3, 8x8x3, 8x8.5x3, 8x8.5x3.5, 8.5x8x3.5, 8.5x8x3, 9x9x3, 9.5x9x3, 9.5x9x3.5. Each length specification includes tolerances in the range of ± 0.5 mm. According to the invention it is also possible that the catalyst is used in the form of a catalyst split, which is obtained from one or more of said moldings.

The water absorption of the carriers is, for example, in the range from 0.35 ml / g to 0.65 ml / g, preferably in the range from 0.42 ml / g to 0.52 ml / g, determined by a vacuum cold water absorption.

The catalyst according to the invention contains silver as the active metal. In this case, the catalyst may contain silver in an amount of, for example, 5 to 35 wt .-%, in particular from 10 to 30 wt .-%, preferably in an amount of 10 to 25 wt .-%, based on the total weight of the catalyst and calculated as an element.

Accordingly, the present invention also describes a process as described above and a catalyst preparable by the process, and a catalyst as described above, comprising silver in an amount of 5 to 35 wt .-%, based on the total weight of the catalyst.

According to a preferred embodiment, in addition to silver, the catalyst furthermore comprises at least one promoter, for example six, five, four, three or two promoters or a promoter. In the context of the invention, promoter is understood as meaning a constituent of the catalyst which, compared with a catalyst which does not contain the constituent, results in an improvement in one or more catalytic properties, eg. B. selectivity, activity, conversion and / or yield or space, time yield is achieved. Preferred compounds which are chemically stable under the reaction conditions and do not catalyze undesirable reactions.

As far as the at least one promoter is concerned, all promoters known in the art are conceivable. Preferably, the at least one promoter is selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, barium, manganese, rhenium, cadmium, tungsten, molybdenum, chromium, sulfur and mixtures of two or more of that. Most preferably, the catalyst contains at least one promoter selected from the group consisting of rhenium, cesium, lithium, tungsten, chromium, manganese, sulfur and mixtures of two or more thereof. The catalyst particularly preferably contains at least rhenium as promoter and at least one further promoter selected from the group consisting of cesium, lithium, tungsten, chromium, manganese, sulfur and mixtures of two or more thereof. Accordingly, the present invention also describes a process as described above and a catalyst preparable by the process, and a catalyst as described above, comprising at least rhenium as a promoter, preferably comprising silver in an amount of 5 to 35 wt .-%, based on the total weight of the catalyst, and at least rhenium as a promoter.

When the catalyst contains rhenium as described above, it preferably contains rhenium in an amount of 50 to 600 ppm, more preferably in an amount of 100 to 450 ppm, still more preferably in an amount of 150 to 400 ppm by total weight of the catalyst and calculated as element.

According to a particularly preferred embodiment, the catalyst additionally comprises at least one further promoter selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, barium, manganese, rhenium, cadmium, tungsten, chromium, Molybdenum, sulfur and mixtures of two or more thereof. Particularly preferably, the catalyst additionally comprises at least one promoter selected from the group consisting of cesium, lithium, tungsten, chromium, manganese, sulfur and mixtures of two or more thereof and mixtures of two or more thereof. According to a particularly preferred embodiment, the catalyst additionally contains at least cesium, lithium, tungsten, and sulfur, in particular the catalyst contains rhenium and additionally cesium, lithium, tungsten and sulfur, as promoters.

If the catalyst contains at least one further promoter, it preferably contains a total amount of these promoters in an amount of 10 to 2000 ppm, preferably in an amount of 10 to 1500 ppm, more preferably in an amount of 50 to 1300 ppm and more preferably each in an amount of 80 to 1300 ppm, based on the total weight of the catalyst and calculated as the sum of the elements.

For example, if the catalyst contains tungsten, it preferably contains it in an amount of 10 to 500 ppm, preferably in an amount of 50 to 300 ppm.

If the catalyst contains, for example, cesium, it preferably contains this in an amount of from 20 to 850 ppm, in particular in an amount of from 100 to 600 ppm, based on the total weight of the catalyst and calculated as an element.

For example, when the catalyst contains lithium, it preferably contains it in an amount of 10 to 450 ppm, more preferably in an amount of 50 to 300 ppm, based on the total weight of the catalyst and calculated as an element. For example, if the catalyst contains sulfur, it preferably contains it in an amount of 5 to 300 ppm, more preferably in an amount of 5 to 150 ppm, based on the total weight of the catalyst and calculated as an element.

According to a particularly preferred embodiment, the catalyst contains rhenium in an amount of 150 to 450 ppm, tungsten in an amount of 50 to 300 ppm, cesium in an amount of 100 to 600 ppm, lithium in an amount of 50 to 300 ppm and sulfur in one Amount of 5 to 150 ppm.

As regards the application of silver, it may be applied to the support by any of the prior art impregnation and deposition processes for preparing silver catalysts for the production of ethylene oxide, which processes may comprise one or more impregnation and calcination steps. By way of example, mention may be made of the production processes for silver catalysts, as described in DE-A 2300512, DE-A 2521906, EP-A 0 014 457, EP-A 0 085 237, EP-A 0 0384 312, DE-A 2454972, DE-A 3321895, EP-A 0 229 465, DE-A 3150205, EP-A 0 172 565 and EP-A 0 357 293 are disclosed.

If the catalyst contains at least one promoter in addition to silver, it is preferred to apply at least one mixture comprising silver or at least one promoter, for example by impregnation or spraying or mixing processes, to the support. The order of application of the at least one promoter and silver is generally arbitrary, i. Embodiments are contemplated in which silver and the at least one promoter are applied simultaneously to the support. Also included are embodiments in which silver and the at least one promoter are applied to the support in various steps, the order of the steps being generally arbitrary. Furthermore, embodiments are encompassed in which a part of the at least one promoter, which is applied to the carrier only after application of the silver, and the remaining part is applied simultaneously with silver. Preferably, silver and the at least one promoter are applied simultaneously to the support.

The silver is preferably applied to the support according to the invention in the form of a silver compound, which may be a salt or a silver complex. The silver compound is preferably dissolved, in particular dissolved in water. In order to obtain the silver compound in soluble form, the silver compound such as silver (I) oxide or silver (I) oxalate may further suitably contain a complexing agent such as ethanolamine, EDTA, 1, 3 or 1, 2-propanediamine, ethylenediamine and or alkali metal oxalate can be added, which can act simultaneously as a reducing agent. More preferably, silver is applied in the form of a silver amine compound, more preferably in the form of a silver ethylenediamine compound. Accordingly, the present invention also relates to a process as described above, wherein in step (ii) a mixture comprising silver as a silver amine compound, preferably as Silberethylendiaminverbindung, is applied to the carrier described above. The present invention likewise relates to a catalyst which can be prepared by this process.

After application of the silver, at least one post-treatment step, for example a drying step, e.g. connect one, two or more drying steps. The drying is usually carried out at temperatures in the range of 10 to 200 ° C. Preferably, the post-treatment step is a vacuum treatment. Accordingly, according to a preferred embodiment, the carrier is evacuated after application. Preferably, the evacuation is carried out at a pressure in the range of at most 500 mbar, more preferably at a pressure of at most 250 mbar and more preferably at a pressure of 30 mbar, and preferably at a temperature in the range of 2 ° C to 50 ° C, more preferably at a temperature in the range of 5 ° C to 30 ° C, and more preferably at room temperature. The vacuum treatment is carried out, for example, for a time of at least 1 min, preferably of at least 5 min, more preferably for a time in the range of 5 min to 120 min, in particular in the range of 10 min to 45 min, particularly preferably in the range of 10 min up to 20 min. After application of the silver and optionally the at least one drying step, preferably at least one calcination step follows.

Accordingly, the present invention also describes a process for preparing a catalyst as described above, and the catalyst obtainable by this process, additionally comprising a step (iii)

(iii) calcining the optionally post-treated support obtained according to (ii).

The calcination is carried out at temperatures, for example, in a range of 150 to 750 ° C, generally in the range of 200 to 500 ° C, preferably in the range of 220 to 500 ° C and more preferably in the range of 250 to 350 ° C, wherein the Calcination duration is generally at least 5 minutes or more, for example in the range of 5 minutes to 24 hours or in the range of 10 minutes to 12 hours. More preferably, the calcination time is in the range of 5 minutes to 3 hours. The calcination can be carried out at a constant temperature, further embodiments are included, in which the temperature is changed continuously or discontinuously during the Calcinierungsdauer. The calcination may be carried out under any suitable gas atmosphere, with air, nitrogen and / or lean air being preferred. Furthermore, the calcination is preferably carried out in a muffle furnace, in a rotary kiln, carried out in a convection oven and / or a belt calciner.

If the catalyst contains at least one promoter, this at least one promoter is preferably applied to the carrier in the form of compounds, for example in the form of complexes or in the form of salts, for example in the form of halides, for example in the form of compounds of fluorides, bromides or chlorides, or in the form of carboxylates, nitrates, sulfates or sulfides, phosphates, cyanides, hydroxides, carbonates or as salts of heteropolyacids, in the form of salts, for example in the form of salts of the heteropolyacids of rhenium and / or tungsten.

If the catalyst contains, for example, rhenium, this is preferably applied as a compound, for example as halide, oxyhalide, oxide or as acid. Furthermore, rhenium can be used, for example, as rhenate or perrhenate in the production process according to the invention. If rhenium is used as a promoter, it is preferably used as a compound selected from the group consisting of ammonium perrhenate, rhenium (III) chloride, rhenium (V) chloride, rhenium (V) fluoride, rhenium (VI) oxide and Rhenium (VII) oxide used. In the context of the invention, particular preference is given to applying rhenium as ammonium perrhenate to the carrier.

If the catalyst contains tungsten as a promoter, as described above, the tungsten is preferably applied to the support as a tungsten compound. Here, in principle, any suitable tungsten compound is usable. For example, tungsten is applied in the form of tungstate or tungstic acid.

If the catalyst contains lithium as a promoter, as described above, the lithium is preferably applied to the carrier as a lithium compound. Here, in principle, any suitable lithium compound is usable. Preferably, lithium is applied in the form of lithium nitrate.

If the catalyst contains cesium as a promoter, as described above, the cesium is preferably applied to the support as a cesium compound. Here, in principle, any suitable cesium compound is usable. Preferably, cesium is applied in the form of cesium hydroxide.

If the catalyst contains sulfur as a promoter as described above, the sulfur is preferably applied to the support as a sulfur compound. Here, in principle, any suitable sulfur compound is usable. Preferably, sulfur is applied in the form of ammonium sulfate. The at least one promoter, more preferably the at least one promoter compound, is preferably dissolved in a suitable solution, preferably in water, before application. The support is then preferably impregnated with the resulting solution comprising one or more of the promoters. If more promoters are added, they can be applied to the support either together or separately in a single impregnation step or in several impregnation steps. As regards the solution comprising one or more of the promoters, it may be prepared in any suitable manner. For example, the promoters can each be separately dissolved in each case in a solution and the resulting solutions, each containing a promoter, are then used for impregnation. It is also possible that two or more of the promoters are dissolved together in a solution, and the resulting solution is then used for impregnation. In addition, it is possible that the resulting solutions containing at least one promoter are combined prior to impregnation and the resulting solution containing all promoters, is applied to the support.

For example, if at least cesium, tungsten, lithium, sulfur and rhenium are used as promoters, according to a particularly preferred embodiment, at least one solution containing cesium and tungsten, another solution containing lithium and sulfur, and another solution containing rhenium, prepared. The solutions are either applied to the support in separate impregnation steps, or combined to form a solution before application and only then used for impregnation. Preferably, the solutions are applied together, more preferably together with the mixture containing silver as a silver amine compound, preferably as Silberethylendiaminverbindung, applied to the support.

The application can in principle be carried out by any suitable method, for example by soaking the carrier. Particularly preferably, the application is carried out by vacuum impregnation at room temperature. In the vacuum impregnation, the support is preferably first at a pressure in the range of at most 500 mbar, more preferably at a pressure of at most 250 mbar and more preferably at a pressure of 30 mbar, and preferably at a temperature in the range of 2 ° C to 50 ° C, more preferably at a temperature in the range of 5 ° C to 30 ° C, and most preferably treated at room temperature. The vacuum treatment is carried out, for example, for a time of at least 1 min, preferably of at least 5 min, more preferably for a time in the range of 5 min to 120 min, in particular in the range of 10 min to 45 min, particularly preferably in the range of 15 min up to 30 min. Subsequent to the vacuum treatment, the at least one solution, for example the mixture containing silver, or at least one solution is contained. at least one promoter, preferably the mixture containing silver and the at least one promoter, applied to the carrier. Preferably, the solution is dropped or sprayed on, preferably sprayed on. The application is preferably carried out by means of a nozzle. After application, the support is preferably further evacuated. Preferably, the evacuation is carried out at a pressure in the range of at most 500 mbar, more preferably at a pressure of at most 250 mbar and more preferably at a pressure of 30 mbar, and preferably at a temperature in the range of 2 ° C to 50 ° C, more preferably at a temperature in the range of 5 ° C to 30 ° C, and more preferably at room temperature. The vacuum treatment is carried out, for example, for a time of at least 1 min, preferably of at least 5 min, more preferably for a time in the range of 5 min to 120 min, in particular in the range of 10 min to 45 min, particularly preferably in the range of 10 min up to 20 min.

As regards the time of application of the promoter, this can be carried out following the calcining described in step (iii) above. Alternatively, it is possible to apply the at least one promoter together with the silver compound on the support.

Accordingly, within the scope of the invention, embodiments are encompassed in which the at least one promoter, that is to say, for example, five different promoters, four different promoters, three different promoters, two different promoters or a promoter, are applied to the support and the support treated in this way is subsequently as above is calcined to obtain a catalyst according to the invention.

Accordingly, the present invention also describes a process for preparing a catalyst, and the catalyst obtainable by this process, comprising the steps of (i) providing a support having a BET constant C in the range from 0 to 800, determined in accordance with DIN ISO 9277, (ii) applying silver and at least one promoter on the support by applying a solution containing silver and the at least one promoter, and (iii) calcining the optionally dried support according to (ii).

The promoters are preferably applied together with silver in step (ii).

The catalysts of the invention or the catalysts obtainable by a process according to the invention are particularly suitable as catalysts for the production of ethylene oxide from ethylene, comprising an oxidation of ethylene. High selectivities and good activities are achieved. The present invention therefore also relates in a further aspect to a process for the production of ethylene oxide from ethylene comprising an oxidation of ethylene in the presence of a catalyst for the production of ethylene oxide comprising silver supported on a support, the support having a BET constant C in the range of 0 to 800, determined according to DIN ISO 9277, or in the presence of a catalyst obtainable by a process for the preparation of a catalyst for the production of ethylene oxide as described above.

According to a further embodiment, the present invention therefore also relates to the process for the production of ethylene oxide from ethylene, comprising an oxidation of ethylene as described above, wherein the catalyst additionally contains rhenium.

Moreover, the present invention also relates to the use of a catalyst for the production of ethylene oxide, at least comprising silver, supported on a support, wherein the support has a BET constant C in the range of 0 to 800, determined according to DIN ISO 9277.

According to the invention, the epoxidation can take place according to all methods known to the person skilled in the art. Any of the reactors which can be used in the ethylene oxide preparation processes of the prior art can be used here, for example externally cooled tube bundle reactors (compare Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, Vol. A-10, pages 1 17-135, 123-125 , VCH-Verlagsgesellschaft, Weinheim 1987,) or reactors with loose catalyst bed and cooling tubes, for example, the reactors described in DE-A 3414717, EP 0082609 and EP-A 0339748. Preferably, the epoxidation takes place in at least one tubular reactor, preferably in a tube bundle reactor. The catalyst according to the invention can be used either alone or in admixture with other catalysts in a combined or structured catalyst bed.

For the production of ethylene oxide from ethylene and oxygen, under conventional reaction conditions, as described, for example, in DE 25 21 906 A1, EP 0 014 457 A2, DE 2 300 512 A1, EP 0 172 565 A2, DE 24 54 972 A1, EP 0 357 293 A1, EP 0 266 015 A1, EP 0 085 237 A1, EP 0 082 609 A1 and EP 0 339 748 A2. In addition, inert gases such as nitrogen or gases behaving inertly under the reaction conditions such as water vapor, methane and optionally reaction moderators, for example halides, hydrocarbons such as ethyl chloride, vinyl chloride or 1, 2-dichloroethane can be admixed with the reaction gas containing ethylene and molecular oxygen. Conveniently, the oxygen content of the reaction gas is in a range in which no explosive gas mixtures are present. A suitable composition of the reaction gas for the production of ethylene oxide may, for. Legs Amount of ethylene in the range of 10 to 80 vol .-%, preferably from 20 to 60 vol .-%, more preferably from 25 to 50 vol .-%, and particularly preferably in the range of 30 to 40 vol .-%, based on the total volume of the reaction gas. The oxygen content of the reaction gas is expediently in a range of at most 10 vol .-%, preferably of at most 9 vol .-%, more preferably of at most 8 vol .-%, and most preferably of at most 7 vol .-%, based on the total volume of the reaction gas.

Preferably, the reaction gas contains a chlorine-containing reaction moderator such as ethyl chloride, vinyl chloride or dichloroethane in an amount of 0 to 15 ppm, preferably in an amount of 0, 1 to 8 ppm. The remainder of the reaction gas usually consists of hydrocarbons, such as methane, or of inert gases such as nitrogen. In addition, other substances such as water vapor, carbon dioxide or noble gases may be contained in the reaction gas.

The components of the reaction mixture described above may optionally each have small amounts of impurities. For example, ethylene may be used at any purity level suitable for the gas phase oxidation of the present invention. Suitable levels of purity include, but are not limited to, polymer grade ethylene, which typically has a purity of at least 99%, and chemical grade ethylene which has low purity, typically less than 95%. The impurities typically consist mainly of ethane, propane and / or propene.

The epoxidation is usually carried out at elevated temperature. Preferred are temperatures in the range of 150 to 350 ° C, more preferably in the range of 180 to 300 ° C, more preferably in the range of 190 to 280 ° C, and particularly preferably in the range of 200 to 280 ° C. Accordingly, the present invention also relates to a process as described above, wherein the oxidation takes place at a temperature in the range of 180 to 300 ° C, preferably in the range of 200 to 280 ° C. The invention likewise relates to the catalyst which can be prepared by this process.

Preference is given to working at pressures in the range of 5 bar to 30 bar. More preferably, the oxidation is carried out at a pressure in the range of 5 bar to 25 bar, preferably at a pressure in the range of 10 bar to 20 bar and in particular in the range of 14 bar to 20 bar. Accordingly, the present invention also relates to a process as described above, wherein the oxidation takes place at a pressure in the range of 14 bar to 20 bar. The invention likewise relates to the catalyst which can be prepared by this process. Preferably, the oxidation is carried out in a continuous process. When the reaction is carried out continuously, a GHSV (gas hourly space velocity) is used depending on the type of reactor selected, for example, the size / average area of the reactor, the shape and size of the catalyst, which are preferably in the range of 800 to 10,000 / h, preferably in the range of 2,000 to 6,000 / h, more preferably in the range of 2,500 to 5,000 / h, the data relating to the volume of the catalyst.

Advantageously, the production of ethylene oxide from ethylene and oxygen can be carried out in a cyclic process. The reaction mixture is circulated through the reactor, where after each pass the newly formed ethylene oxide and the by-products formed in the reaction are removed from the product gas stream, which is fed back into the reactor after addition of the required amounts of ethylene, oxygen and Reaktionsmoderatoren becomes. The separation of the ethylene oxide from the product gas stream and its work-up can be carried out according to the customary processes of the prior art (compare Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A-10, pages 1 17-135, 123-125 VCH Verlagsgesellschaft, Weinheim 1987).

Moreover, the present invention accordingly also relates to the use of a catalyst for the production of ethylene oxide, at least comprising silver, applied to a support, wherein the support has a BET constant C in the range of 0 to 800, determined according to DIN ISO 9277, or as described above, the use of a catalyst obtainable by a process for producing a catalyst for the production of ethylene oxide as described above, as a catalyst for the production of ethylene oxide.

In the following, the present invention will be explained in more detail by way of examples.

Examples

1 . catalysts

Catalysts were prepared starting from 5 different carriers, the carriers differing in their C values, determined in accordance with DIN ISO 9277:

The composition of the carrier is shown in Table 1.

Table 1: Carrier used

[mm x mm x 5.7 x 5.59 x 7.55 x 7.47 x 5.46 x mm] 2.06 2.35 2.79 3.21 2.47

C-value 426 985 -249 -92 1 18

Ca [ppm] 400 800 600 600 600

Mg [ppm] 100 200 100 100 100

Na [ppm] 500 400 300 300 300

K [ppm] 300 100 100 100 100

Si [ppm] 500 800 700 700 600

BET [m * / g] 0.82 0.78 0.89 0.83 0.75

the carriers marked with ^* are comparative examples

1 .1 Preparation of the silver complex solution

It was submitted to 1, 5 L of deionized water (demineralised water = demineralized water) and added with stirring 550 g of silver nitrate and completely dissolved therein. The solution was heated to 40.degree. 402.62 g of potassium hydroxide solution (47.8%) were mixed with 1.2 L of deionized water. Subsequently, 216.31 g of oxalic acid were added and completely dissolved and the solution was heated to 40 ° C. The potassium oxalate solution was then added within about 45 min (volume flow = about 33 ml / min) to the silver nitrate solution (40 ° C) using a metering pump. After complete addition, the resulting solution was allowed to stir for 1 h at 40 ° C. The precipitated silver oxalate was filtered off and washed the filter cake obtained with 1 L portions of water (about 10 L) until it was potassium or nitrate-free (determined by conductivity measurement of the washing solution, potassium or nitrate-free in the present case means a conductivity <40 μ5 / ηη "ΐ) The water was removed as completely as possible from the filter cake and the residual moisture of the filter cake was determined to give 620 g of silver oxalate with a water content of 20.80%.

306 g of ethylenediamine were cooled with an ice bath to about 10 ° C and 245 g of water in small portions. After completion of the addition of water, 484.7 g of the obtained (still moist) Silberoxalates within about 30 minutes in small portions. The mixture was stirred overnight at RT and the residue was then removed by centrifugation. From the remaining clear solution, the Ag content was determined by refractometry and the density using a 10 mL graduated cylinder.

The resulting solution received 29.14% by weight of silver, calculated as element, and had a density of 1.532 g / mL.

1 .2 Preparation of the solution containing silver and promoters 97.1004 g of the silver complex solution were submitted. To this end, 1047 g of an aqueous solution of lithium and sulfur (2.85% lithium from lithium nitrate and 0.21 wt. Wt.% Of sulfur from ammonium sulfate), 791 g of an aqueous solution of tungsten and cesium were _1, 1 (2 wt. % Tungsten from tungstic acid and 3.5% by weight cesium from cesium hydroxide 50% in H ₂ O) _, and 1.6492 g of an aqueous solution of rhenium (3.1% by weight ammonium perrhenate) are added and the solution is stirred for 5 minutes.

1 .3 application of the solution on the support

140.61 g of the support 1 (see Table 1) were placed in a rotary evaporator and evacuated. The vacuum was 20 mbar. The carrier was pre-evacuated for about 10 min.

The solution obtained according to procedure 1.2 was dropped onto the support within 15 minutes, and then the impregnated support was allowed to rotate for a further 15 minutes in vacuo. Thereafter, the support was left for 1 h at room temperature and atmospheric pressure in the apparatus and mixed gently every 15 min.

1 .4 calcination of the impregnated carrier

The impregnated support was treated for 12 minutes at 283 ° C. under 8.3 m ^{3 of} air per hour in a circulating air oven (HORO, type 129 ALV-SP, make no .: 53270).

1 .5 Preparation of catalyst split

The resulting catalyst rings were coarsely crushed in a porcelain dish with the mortar. Subsequently, the comminuted material was brought to the desired particle size fraction (500-900 μm) by means of a screening machine, round sieve and balls. Very hard rings were completely crushed with the mortar and then sieved.

2. Epoxidation

The epoxidation was carried out in a test reactor consisting of a vertical stainless steel reaction tube having an inner diameter of 6 mm and a length of 2200 mm. The jacketed reaction tube was heated with hot oil of temperature T flowing through the jacket. With a very good approximation, the temperature of the oil corresponds to the temperature in the reaction tube and thus the reaction temperature.

For the epoxidation, the catalyst was used in the form of catalyst split. The reaction tube was from bottom to top at a height of 212 mm with inert Steatite balls (1, 0-1, 6 mm), above at a height of 1 100 mm with 38.2 g of catalyst chippings, particle size 0.5-0.9 mm, and above at a height of 707 mm with inert steatite balls (1 , 0 - 1, 6 mm) filled. The inlet gas entered the reactor from above and at the bottom, after passing through the catalyst bed again.

The input gas consisted of 35 vol.% Ethylene, 7 vol.% Oxygen, 1 vol.% C0 ₂ (EC (ethylene chloride) moderation). At the beginning, 2.5 ppm EC was used for start-up. Depending on the catalyst and performance, the EC concentration was increased every 24 h to a maximum of 4 ppm. The remainder of the input gas was methane. The experiments were carried out at a pressure of 15 bar and a gas load (GHSV) of 4750 / h and a space-time yield of 250 kg EO / (m ³ (Kat) xh).

The reaction temperature was controlled according to the specified ethylene oxide exhaust gas concentration of 2.7%. To optimize the catalyst with regard to selectivity and conversion, between 2.2 and 4.0 ppm of ethylene chloride were added as a moderator to the input gas.

The gas leaving the reactor was analyzed by online MS. The selectivity was determined from the analysis results.

The results are summarized in Table 2 below.

Table 2: Carrier samples tested with different C values

The catalysts marked with ^* are comparative examples.

Claims

claims

1 . Catalyst for the production of ethylene oxide, at least comprising silver applied to a support, wherein the support has a BET constant C in the range of 0 to 800, determined according to DIN ISO 9277.

2. Catalyst according to claim 1, wherein the carrier is an alumina carrier, preferably an alpha-alumina carrier.

3. A catalyst according to claim 2, wherein the alumina has a purity of at least 85%.

4. Catalyst according to one of claims 1 to 3, wherein the carrier has a bimodal pore distribution, preferably a bimodal pore distribution at least containing pores having pore diameters in the range of 0.1 to 10 μηη and pores with pore diameters in the range of 12 to 100 μηη determined by Hg porosimetry according to DIN 66133.

5. A catalyst according to any one of claims 1 to 4, wherein the catalyst contains silver in an amount of 5 to 35 wt .-%.

6. Catalyst according to one of claims 1 to 5, wherein the catalyst contains rhenium, preferably in an amount of 50 to 600 ppm, based on the total weight of the catalyst and calculated as element.

7. Catalyst according to one of claims 1 to 6, wherein the catalyst additionally contains at least one further promoter, preferably a promoter selected from the group consisting of tungsten, lithium, sulfur, cesium, chromium, manganese, molybdenum, potassium and mixtures of two or more of that.

8. Catalyst support for a catalyst for the production of ethylene oxide, wherein the support has a BET constant C in the range of 0 to 800, determined according to DIN ISO 9277.

A support according to claim 8, wherein the support is an alumina support, preferably an alpha alumina support.

The support of claim 9, wherein the alumina has a purity of at least 85%.

1 1. Carrier according to one of claims 8 to 10, wherein the carrier has a bimodal pore distribution, preferably a bimodal pore distribution at least containing pores having pore diameters in the range of 0.1 to 10 μηη and pores with pore diameters in the range of 12 to 100 μηη, determined by Hg - Porosimetry according to DIN 66133.

12. A process for the preparation of a catalyst for the production of ethylene oxide, comprising at least the steps

(i) providing a support having a BET constant C in the range of 0 to 800, determined in accordance with DIN ISO 9277;

(ii) applying silver to the support according to (i).

13. Catalyst, preparable or prepared by a process according to claim 12.

14. A process for the production of ethylene oxide from ethylene, comprising an oxidation of ethylene in the presence of a catalyst according to any one of claims 1 to 7 or 13.

15. Use of a catalyst according to any one of claims 1 to 7 or 13 for the production of ethylene oxide from ethylene.