WO2006018133A1 - Catalyst containing iron oxide(s) alkali metal compound(s) and cerium oxide(s) - Google Patents

Abstract

The invention relates to a catalyst containing iron oxide(s), alkali metal compound(s) and cerium oxide(s). When producing the catalyst, cerium carbonate hydrate(s) with a BET surface area of less than 0.30 m<sup

Description

Catalyst containing iron oxide (s), alkali metal compound (s) and cerium oxide (s)

description

The invention relates to a catalyst containing iron oxide (s), alkali metal compound (s) and cerium oxide (s), wherein in the preparation of the catalyst as Cer component (s) Cercarbonat hydrate (s) having a BET surface area of less than 0.30 m ² / g are used. The invention further relates to a catalyst bed which consists of at least 25% by weight of catalysts which contain iron oxide (s), alkali metal compound (s) and cerium oxide (s), in the preparation of the catalysts as cerium component (n) Cercarbonate hydrate (s) having a BET surface area of less than 0.30 m ² / g are used. Moreover, the invention relates to a process for the dehydrogenation of alkylaromatic compounds.

EP-A 177 832 describes dehydrogenation catalysts comprising iron oxide, potassium oxide, molybdenum oxide, magnesium oxide, calcium oxide and cerium oxide, which is prepared using commercially available ceria as starting material.

EP-A 894 528 discloses dehydrogenation catalysts which also contain iron oxide, potassium oxide, molybdenum oxide, magnesium oxide, calcium oxide and cerium oxide using aqueous cerium nitrate solution as the feedstock. However, the use of cerium nitrate as starting material has the disadvantage that nitrogen oxides are liberated during the calcination of the catalyst.

DE-A 101 54 718 describes catalysts comprising iron oxide, potassium oxide, molybdenum oxide, magnesium oxide, calcium oxide and cerium oxide, which is prepared using cerium carbonate hydrate.

In a review article by Trovarelli et al. The importance of the cerium doping of styrene catalysts is emphasized in "The utilization of ceria in industrial catalysis." Cerium oxides are generally used in an amount of 5 to 60% by weight as carbonates, oxides, nitrates or hydroxides. it is described that by cerium Polari¬ tion of the Fe-O bond and obstruction of reaction of Fe ³⁺ to Fe ₃ O ₄ ty the Aktivi¬ and increased stability of the K-Fe phases. probably also play a role in the cerium However, most of the published explanations about the contribution of the cerium doping are based on hypotheses and the influence of the cerium compounds-both in the preparation of the catalyst and in the dehydrogenation-is largely unexplained.

Thus, despite the versatile catalyst compositions described in the prior art, there is still room for improvement and research, in particular in With regard to the influence of the dopants on the conversion and the selectivity in the dehydrogenation of alkylaromatic compounds.

The object of the invention was therefore to show a catalyst for the dehydrogenation of alkylaromatic compounds, which has improved alkylaromatic conversion with improved or constant alkenyl aromatic selectivity. Furthermore, the object was to reduce the benzene selectivity for the same or improved activity.

Lower benzene selectivity generally leads to a reduced amount of dehydrogenation gas because of the parallel reduced formation of, in particular, ethylene and carbon dioxide. This is particularly important in styrene plants with limited vacuum compressor performance of importance.

The object has been achieved with the aid of a catalyst comprising iron oxide (s), alkali compound (s) and cerium oxide (e), in which case the preparation of the catalyst as cerium component (s) comprises cercarbonate hydrate (e) having a BET surface area be used of less than 0.30 m ² / g.

The BET surface area of the starting material cercarbonate hydrate is preferably less than 0.25 m ² / g, in particular, the BET surface area of the cercarbonate hydrates is from 0.01 to 0.20 m ² / g. A suitable method for measuring the BET surface area is described below.

The sulfur content of the cercarbonate hydrate used according to the invention is advantageously less than 100 ppm by weight, in particular less than 20 ppm by weight.

FIG. 3 shows, by way of example, scanning electron microscopy (SEM) images of rhodia cercarbonate hydrates used according to the invention. Fig. 1 (Wilhelm Priem GmbH & Co. KG) and Fig. 2 (Treibacher Auermet) show prior art bicarbonate hydrates.

The surfaces of the cercarbonate hydrates used according to the invention have, in comparison with the cercarbonate hydrates used in the prior art, larger crystals and in particular a significantly reduced proportion of smaller crystals grown on.

The properties of a crystallized solid, such as crystal size and hence BET surface area, can be substantially adjusted by crystallization conditions by various methods known to those skilled in the art. Cercarbonate hydrate is a pasty solid with varying water content. Advantageously, the cercarbonate hydrate to be used according to the invention has a composition of approximately (Ce) ₂ (CO ₃ ) ₃ .8H ₂ O and an XRD structure analogous to lanthanite (Gmelin Handbook Rare Earth A7 p.191). The use of more highly dehydrated cerium carbonates, in particular commercially available so-called dry cerium carbonates, is less preferred and generally leads to catalysts with reduced performance properties.

Cercarbonate hydrate can be obtained from numerous suppliers, for example from Treibacher Auermet Produktions GmbH in Austria, Wilhelm Priem GmbH & Co. KG in Germany or Rhodia in France. The BET surface area of the cercarbonate hydrates varies widely and is 0.38 m ² / g (Wilhelm Priem GmbH & Co. KG), 0.35 m ² / g (Treibacher Auermet) and 0.18 m ² / g. g (Rhodia).

Advantageously, catalysts are used whose preparation as cerium component at least 25 wt .-% ceric carbonate hydrate with a BET surface area of less than 0.30 m ² / g are used. The remaining up to 75 wt .-% may be Cercar¬ carbonate hydrates with a higher BET surface area or other cerium compounds such as cerium nitrates, oxides or hydroxides. Preference is given to catalysts whose preparation as cerium component at least 30 wt .-%, in particular min¬ least 50 wt .-%, more preferably exclusively Cercarbonat hydrate having a BET surface area of less than 0.30 m ² / g used become.

The invention further relates to catalyst beds which consist of at least 25% by weight of catalyst according to the invention. Advantageously, the catalyst beds consist of at least 30% by weight, preferably at least 50% by weight, of catalysts according to the invention. The catalysts of the invention may be evenly distributed over the catalyst bed or concentrated at one or more locations. Preferably, the catalysts according to the invention are used uniformly distributed over the entire dehydrogenation catalyst bed, in particular without the use of a further dehydrogenation catalyst from the prior art.

The catalyst according to the invention is particularly suitable for the dehydrogenation of hydrocarbons which have at least one saturated functional group, for example alkenes to the corresponding 1,3-alkadienes, preferably alkylaromatic compounds to the corresponding alkenylaromatic compounds. Suitable alkylaromatic compounds are all aromatic and heteroaromatic alkyl compounds, preference is given to those in which the alkyl radical is unbranched or branched and contains two to six C atoms. Suitable aromatic radicals are mono-, di- or trinuclear, preferably mono- or binuclear, particularly preferably einker¬ nige aromatics. Examples are isopropylbenzene (cumene), ethylbenzene, 1, 1-diphenyl benzene and 1,2-diphenylethane (bibenzyl), preferably isopropylbenzene (cumene), ethylbenzene and 1,1-diphenylbenzene, more preferably ethylbenzene. Suitable heteroaromatic radicals are mono-, di- or trinuclear, preferably mononuclear or dinuclear, particularly preferably mononuclear, five-membered heteroaromatic compounds having one to three nitrogen atoms and / or one oxygen atom or one sulfur atom, one, two or three ¬ Ripe, preferably mono- or binuclear, particularly preferably mononuclear, six-membered heteroaromatic having one to three nitrogen atoms as heteroatoms, in particular pyridines, such as 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine and 5-ethyl-2-methylpyridine, be ¬ preferably 2-ethylpyridine and 5-ethyl-2-methylpyridine.

For example, the dehydrogenation of ethylbenzene to styrene, of cumene to α-methyl-styrene, of butene to butadiene and of isopentene to isopentadiene (isoprene) may be mentioned.

In addition to iron oxide (s), alkali metal compound (s), preferably potassium compound (s) such as, for example, potassium oxide, the catalysts according to the invention typically contain a number of promoters, depending on their field of use. Suitable promoters for a dehydrogenation catalyst are, in addition to cerium compounds, advantageously compounds of calcium, magnesium, molybdenum, tungsten, chromium and titanium. The weight ratio of potassium (calculated as K ₂ O) to iron oxide (calculated as Fe ₂ O ₃ ) is generally from 0.01: 1 to 2: 1, preferably from 0.1: 1 to 1: 1. In addition, the catalysts preferably contain further promoters (calculated as oxides) in a weight ratio to the iron oxide of from 0.01: 1 to 1: 1, preferably from 0.02: 1 to 0.5: 1.

The catalyst according to the invention has in particular the following composition:

Iron, corresponding to 40-90% by weight of Fe ₂ O ₃ , potassium, corresponding to 1-40% by weight as K ₂ O,

Cerium, corresponding to 1 to 25% by weight of Ce ₂ O ₄ , in particular 5 to 15% by weight of Ce ₂ O ₄ ,

Magnesium, corresponding to 0-10% by weight of MgO,

Calcium, corresponding to 0-10% by weight CaO,

Tungsten, corresponding to 0-10% by weight of WO ₃ , molybdenum, corresponding to 0-10% by weight of MoO ₃ ,

Vanadium, corresponding to 0 - 10 wt .-% V ₂ O ₅ wherein said components add up to 100 wt .-%.

To prepare the catalysts according to the invention, the starting materials used can be compounds of the promoters present in the finished catalyst, or compounds which convert during the preparation process into compounds present in the finished catalyst. The starting materials can also Additives may be added to improve processability, mechanical strength or pore structure. Examples of such substances are potato starch, celluloses, stearic acid, graphite and / or Portland cement. The starting materials can be mixed directly in a mixer, kneader or preferably a Mix-Muller. Furthermore, the starting materials can also be slurried in a spray mixture and processed in a spray dryer to form a spray powder. The starting materials are preferably processed in a Mix-Muller or kneader with the addition of water to form an extrudable mass. The extrudable mass is then extruded, dried and calcined. Preferred strand forms comprise extrudates of 2 to 10 mm in diameter, in particular 2.5 to 6 mm. The cross-section of the extrudates may be round or in other forms. Particularly preferred are extrudates with rotationally symmetrical cross section, in particular with a diameter of 2 to 4 mm, preferably of 3 mm, as well as extrudates with a star-shaped or those with a gear-toothed ("toothed-wheel") cross section, in particular with a diameter of 3 to 7, preferably 3.5 mm, 4.5 mm or 6 mm. As an alternative to extrusion, the shaping of the catalysts can also be carried out by tableting. The extruded or optionally tabletted shaped catalyst bodies are then usually dried and subjected to calcining. The drying is preferably carried out on a belt dryer at temperatures between 100 and 200 ⁰ C. The calcination is preferably in a rotary kiln at temperatures between 500 and 1000 ⁰ C, preferably between 700 and 1000 ° C, in particular zwi¬ rule 800 and 950 ⁰ C, and particularly preferably 850 to 900 ⁰ C durchge leads. Particularly in the calcination in the particularly preferred temperature range, carbonate-containing feedstocks convert to oxides. Potassium and iron oxides typically form mixed potassium ferrite crystal structures in the most preferred temperature range.

The invention is explained in detail below using the example of the process for the dehydrogenation of ethylbenzene to styrene.

The dehydrogenation of hydrocarbons can be carried out by all methods known to the person skilled in the art. The dehydrogenation of alkylaromatics to alkenylaromatics is preferably carried out in adiabatic or isothermal processes, in particular in adiabatic processes. The reaction is generally distributed to several reactors in series, preferably radial flow reactors. Preferably, two to four reactors are connected in series. In each reactor is a Fest¬ bed with dehydrogenation catalysts.

In the dehydrogenation of ethylbenzene to styrene, as is generally practiced today in multi-stage processes in so-called adiabatic processes, ethylbenzene is typically heated to temperatures together with steam, advantageously in an amount of less than 30% by weight, based on ethylbenzene around 500 ⁰ C by means of a heat exchanger heated and mixed directly before entering the first reactor with superheated steam from a steam superheater, so that the desired inlet temperature in the first reactor is usually between 600 and 650 ° C. The mass ratio of water vapor (total steam) to ethylbenzene when entering the bed of the dehydrogenation catalyst in the first reactor is advantageously 0.7: 1 to 2.5: 1. It is preferred to use a steam / ethylbenzene ratio of 0.75: 1 to 1.8: 1, in particular 0.8: 1 to 1.5: 1. The process is preferably operated at reduced pressure, typical reactor pressures are in the range of 300 to 1000 mbar. The space velocity (LHSV = liquid hourly space velocity) based on the active volume of the beds (ie the volume of the beds less any dead or hardly flown dead zones) with dehydrogenation catalyst is usually 0.2 to 0.7 1 / h, preferably 0.3 to 0.6 l / h and in particular 0.32 to 0.58 l / h. The preferably hollow-cylindrical catalyst beds (radial flow reactors) are flowed through from the inside to the outside.

Before entering the next reactor, the reaction mixture is advantageously brought back to temperatures of usually 600 and 650 ⁰ C via a heat exchanger by means of superheated steam. Preferably, the pressure at the outlet of the last reactor should not be more than 700 mbar, more preferably not more than 600 mbar and in particular not more than 500 mbar.

Alternatively, instead of the heat exchanger at the inlet of the second and optionally following reactors, a bed of an oxidation catalyst with oxygen supply for combustion of a subset of the hydrogen formed in the previous reactor can be set up, as for example in the German An¬ message with the application file number 102004015800.2 is described. In such a case with partial hydrogen combustion, preference is given to an arrangement of three or more dehydrogenation reactors arranged in series, the oxidation process advantageously being in the second reactor in the direction of flow and, if appropriate, the following dehydrogenation reactors. The volume ratio of the Schüttun¬ conditions of oxidation catalyst and dehydrogenation catalyst per reactor is generally 0.1: 1 to 1: 1. In the case of an integrated oxidation catalyst, this is preferably arranged upstream of the dehydrogenation catalysts in the flow direction. Radial-flow reactors are preferably used in an integrated oxidation process in which the beds (catalyst beds) of oxidation and dehydrogenation catalysts are arranged concentrically with one another and optionally separated from one another by cylindrical sieves (screens). The oxidation catalyst is then used as the inner of the two concentrically arranged approximately hollow-cylindrical Schüt¬ lines.

The unsaturated compounds obtainable in the process according to the invention, for example alkenylaromatics or 1,3-alkadienes, can advantageously be plastics polymerized or used as building blocks for organic-chemical syntheses wer¬ the.

1 shows scanning electron microscopy (SEM) images of cercarbonate hydrates from Wilhelm Priem GmbH & Co KG.

2 shows scanning electron microscopy (SEM) images of cercarbonate hydrates from Treibacher Auermet Produktions GmbH.

FIG. 3 shows scanning electron microscopy (SEM) images of the rhodia cercarbonate hydrates from their Chinese production site (Lyang Rhodia). The company Rhodia has recently moved the production of the Cercarbonate Hydrate from a production site in France to a production site in China. Individual batches from the production of the French site that we examined did not show the properties of the invention in the past.

Example:

Table 1: Cercarbonate hydrates from different manufacturers

* see described BET surface design

Determination of the BET surface area:

In order to determine the BET surface area of samples that would change like cercarbonate hydrates during drying, no drying is necessary.

The measurement of the dead volume was therefore carried out with evacuated sample cooled in liquid nitrogen.

For this purpose, the weighed samples were built into the sample containers of the device. These were then evacuated at room temperature to a pressure <2 torr and refilled with helium to a pressure> 300 torr. This was repeated five times. After the fifth evacuation, the sample containers were immersed in Deward vessels filled with liquid nitrogen so that the samples were completely submerged. It was waited five minutes. After closing the valves, the measurements were started.

Device: ASAP 2400 from Micromeritics

Cell: ball about 30 mm in diameter

Weighing: The ball of the sample container was completely filled with the Cercarbonate hydrate in order to minimize any influence on the measurement result in view of the small BET surface areas, if possible by means of dead volume effects.

Comparative Example (corresponding to Example 8 of DE-A 101 54 718):

A slurry of 420 g of potassium carbonate (potash), 516 g of cercarbonate hydrate (40 wt .-% cerium content: mixture of cercarbonate hydrates with a BET of 0.38 m ² / g of the company Wilhelm Priem GmbH & Co KG and with a BET of 0.35 m ² / g from Treibacher Auermet Produktions GmbH in a ratio of 1: 1), 74 g of ammonium heptamolybdate, 70 g of calcium hydroxide (hydrated lime), 55 g of magnesite and 1880 g of iron oxide (type HP, the Thyssen Krupp), which had been pre-calcined at 900 ⁰ C in a rotary kiln Fa., mash in 4.5 liters of water Sprüh¬ produced was processed to a spray powder with the addition of starch in a kneader with sufficient water (about 500 ml ) that an extrudable mass is and extruded into strands of 3 mm diameter. Subsequently, the strands were dried at 120 ⁰ C, broken to a length of about 0.8 mm and finally calcined for 1 h at 875 ⁰ C in a rotary tube.

Example 1 (according to the invention):

A catalyst was prepared analogously to the comparative example using the cerium carbonate hydrate of FIG. 3 (Rhodia company).

Elemental analysis of the catalyst from Example 1:

Potassium, corresponding to 9.3 wt .-% as K ₂ O,

Cerium, corresponding to 10.7% by weight of Ce ₂ O ₄ ,

Magnesium, corresponding to 2.1% by weight of MgO,

Calcium, corresponding to 2.2% by weight of CaO,

Molybdenum, corresponding to 2.4% by weight MoO ₃ ,

Iron, corresponding to Fe ₂ O ₃ , difference to 100% by weight (calculated)

Dehydrogenation of ethylbenzene to styrene:

In a two-stage adiabatic test system, in each case 867 ml of the catalyst from Example 1 and the comparative example were tested under the conditions given in Table 2.

Table 2: Experimental conditions and results of the dehydrogenation of ethylbenzene to styrene

Claims

claims 1. Catalyst containing iron oxide (s), alkali metal compound (s) and cerium oxide (s), wherein in the preparation of the catalyst as the cerium component (s) Cercarbonat- hydrate (s) having a BET surface area of less than 0.30 m ² / g are used. 2. Catalyst according to claim 1, wherein as the cerium component (s) Cercarbonat- hydrate (s) are used with a BET surface area of less than 0.25 m ² / g. 3. Catalyst according to claim 1, wherein as cerium component (s) Cercarbonat- Hydrate (s) are used with a BET surface area of 0.01 to 0.20 m ² / g. 4. Catalyst according to claims 1 to 3, wherein the content of sulfur in the cerium carbonate hydrate is less than 20 ppm by weight. 5. Catalyst according to claims 1 to 4, in whose preparation as cerium component at least 25 wt .-% Cercarbonate hydrates are used with a BET surface area of less than 0.30 m ² / g. 6. Catalyst bed in which at least 25 wt .-% catalysts according to An¬ claims 1 to 5 are present. 7. A process for the dehydrogenation of hydrocarbons using catalysts according to claims 1 to 5. 8. A process for the dehydrogenation of alkenes to 1, 3-alkadienes using catalysts according to claims 1 to 5. 9. A process for the dehydrogenation of ethylbenzene to styrene using catalysts according to claims 1 to 5. 3 Fig. Figure 1 1/3

Figure 2 2/3

FIG. 3 3/3