DE4025930A1 - High selectivity self-regenerating dehydrogenation catalyst - comprises iron cpd., potassium cpd., tungsten cpd., chromium-, aluminium- or rare earth-cpd., etc. - Google Patents

Abstract

A novel catalyst, esp. for use in the dehydrogenation of satd. hydrocarbons to give olefins, comprises (a) 40-90 wt.% calculated as Fe2O3, of an Fe cpd.; (b) 5-40 wt.% calculated as K2O, of a K cpd.; (c) 1-15 wt.%, calculated as WO3, of a W cpd.; (d) 0.1-15 wt.%, calculated as Me2O3, of a Cr, Al or rare-earth cpd.; (e) 0.1-15 wt.%, calculated as MeO, of a Zn, Cd or alkaline earth metal cpd.; and (f) other components obtd. when Fe and K are predominantly or wholly introduced in the form of the water-insol. K ferrite K2Fe22O34. USE/ADVANTAGE - The catalyst is in ready-to-use form esp. for the prepn. of styrene from Et benzene, giving high activity and high selectivity simultaneously, and being self-regenerating under the reaction conditions, such properties being attained by introducing the Fe and K predominantly or solely as the ferrite K2Fe22O34.

Description

The invention relates to a catalyst for the dehydrogenation of saturated Hydrocarbons to olefinically unsaturated hydrocarbons, especially for the production of styrene from ethylbenzene, which in sintered, ready-to-use condition essentially consists of

• a) 40 to 95% by weight of an iron compound, calculated as Fe₂O₃,
• b) 5 to 40% by weight of a potassium compound, calculated as K₂O,
• c) 1 to 15% by weight of a tungsten compound, calculated as WO₃,
• d) 0.1 to 15 wt .-% of at least one compound of chromium, aluminum or a rare earth, calculated as Me₂O₃,
• e) 0.1 to 15 wt .-% of at least one compound of Zn, Cd or one Alkaline earth metal, calculated as MeO,

and possibly other additives.

The prior art results, for example, from the following Publications:

(1) Kunststoff-Handbuch, Volume V, Polystyrol, Carl-Hanser-Verlag, pp. 39-47 (1969)
(2) US 41 44 197
(3) DE 25 44 185
(4) DE 31 32 014
(5) US 33 61 683
(6) US 30 84 125
(7) DE 28 15 812
(8) US 32 23 743
(9) DE 24 06 280
(10) US 29 90 432
(11) DE 38 21 431
(12) DE 35 06 022
(13) EP 00 72 439
(14) DE 28 15 874

Olefins, especially butadiene and vinylbenzenes such as styrene, are important Starting materials for the production of plastics, synthetic resins and rubbers.

In general, these olefins are produced on an industrial scale Transfer of partially saturated hydrocarbons, e.g. B. ethylbenzene or Butene, along with steam over a fixed bed catalyst at a Dehydrated temperature between 450 and 700 ° C. The process can be isothermal or be carried out adiabatically (cf. 1).

Potassium iron oxide compounds are used as catalysts, which for increasing selectivity and structural stabilization of metal compounds be added.

As with any large-scale process, large quantities of substances are converted, so that even a small percentage improvement in the yield of is of great economic interest. The yield is on the one hand from the Selectivity, on the other hand determined by the activity of the catalyst. A high activity leads to a high turnover; the yield is that Product of selectivity and sales. A cheap catalyst is therefore which is both high selectivity and high activity owns. In general, these properties are opposed to each other, d. H. a selective catalyst is usually not very active and vice versa - the Adding selectivity-enhancing promoters often leads to one Reduction in activity.

The loss of activity can in some cases be added by adding another Promotors are balanced again. According to the information in (5) and (6) the selectivity of iron oxide-chromium oxide-potassium oxide catalysts the addition of vanadium pentoxide can be improved. According to (7) he can loss of activity caused by simultaneous addition of a or several oxides of Al, Cd, Cu, Mg, Mn, Ni, W, Zn or one Rare earth metal oxide can be balanced again. In (2) Vanadium oxide, tungsten oxide, cerium oxide and cobalt oxide catalysts described.

(13) describes catalysts with Cr or Al, Mo or W, V and lithium described.  

For the life of a catalyst, the addition of structure-stabilizing Components crucial. These structural stabilizers are often promoters at the same time. They affect selectivity and Activity of the catalysts. In (8) the combination chromium oxide / cerium oxide and in (9) molybdenum oxide / cerium oxide as a structural stabilizer and promoter suggested.

To increase physical strength and improve Selectivity and activity is based on (10) hydraulic cement used.

Now it is known that when operating on the catalysts for their use adverse structural changes occur in the fixed bed; as a so-called stable Phase becomes (water-insoluble) potassium iron ferrite (K₂Fe₂₂O₃₄) observed. It was suggested in (11) potassium ferrite of the composition K₂Fe₂₂O₃₄ as a catalyst for the catalytic dehydrogenation of Use ethylbenzene. However, potassium ferrite is not a catalyst sufficiently selective or active.

Based on this state of the art, the task was one special catalyst for the dehydrogenation of alkylated aromatics, especially from ethylbenzene to styrene, with higher activity and To propose selectivity of the reaction conditions itself regenerates.

The solution to this problem consists in a catalyst of the above Type in which iron and potassium are wholly or predominantly produced in Form of water-insoluble potassium ferrite K₂Fe₂₂O₃₄ can be used. The catalyst preferably contains iron exclusively in the K₂Fe₂₂O₃₄ amount used and additional potassium carbonate.

The structure of the catalyst according to the invention is shown in the following Components a) to e) and its preparation are described.

The ready-to-use catalyst contains components a) to e) or preferably consists of these. Other ingredients, e.g. B. Residual impurities from the production usually do not make than 3%. Deformation aids such as graphite, Cellulose, starch, bentonite, Portland cement etc. can be used, whereby Burn off organic additives when the catalyst is calcined can and thus the composition of the catalyst i. a. Not significantly affect. Obtain the information on the composition always refer to the calcined "oxidic form" before first use.  

Especially for those proportions in which Fe and K are not according to the formula K₂Fe₂₂O₃₄, the following applies.

Component a)

As an iron compound, in addition to K₂Fe₂₂O₃₄ various iron oxides or iron oxide hydrates can be used. Fine crystalline yellow (alpha-FeOOH), red (alpha-Fe₂O₃) or black (Fe₃O₄) Pigments.

Component b)

Potassium can in addition to K₂Fe₂₂O₃₄ as oxide, hydroxide, carbonate, Hydrogen carbonate or potassium salt, which when heated in the oxide passes, are used. In general, potassium carbonate is preferred.

Component c)

Tungsten is preferably in the form of tungsten oxide or one Tungsten compound used, which passes into the oxide when heated.

Component d)

Chromium, aluminum and the rare earths are preferred in the form of their Oxides or carbonates used. However, nitrates or Hydroxides are used. The rare earths become scandium, Yttrium and lanthanum, also preferred cerium, praseodymium and europium.

Component e)

Zinc, cadmium and the alkaline earth metals are preferably in the form of their Oxides and carbonates used. Calcium carbonate is particularly preferred.

With the catalysts of the invention, the activity in Increase compared to the catalysts described in DE 35 06 022. The selectivity remains unchanged. The increase in activity with unchanged selectivity in the case of a full or partial Use of Fe and K in the form of K₂Fe₂₂O₃₄ is all the more astonishing than in the teaching of DE 38 21 431 expressly to a higher selectivity as well as a lower tendency for styrene catalysts to shrink due to the Use of K₂Fe₂₂O₃₄ for catalyst production is lifted off, and it is generally known that an increase in selectivity with a Decrease in catalyst activity is associated. In fact, they are in the Catalysts described in DE 35 06 022 are comparatively little active.  

The catalyst according to the invention can be prepared in various ways Way. The finely powdered ingredients can be in water suspended or spray dried or, what is easier, just dry be mixed.

The dry mixture is then, optionally after adding a suitable deformation aids, either to mechanically stable Shaped tablets or with the addition of water to a pasty Pasted mass and extruded into strands. The extrudates are dried and can at temperatures of over 300 to about 900 ° C. be calcined.

Example of the preparation of a catalyst according to the invention

The following raw ingredients, namely

950 g K₂Fe₂₂O₃₄
286 g K₂CO₃
62 g WO₃
111 g Ce₂ (CO₃) ₃
280 g CaCO₃

are finely ground, carefully pre-mixed and after adding 270 ml Kneaded water for three hours. The pasty mass becomes strands with a Extruded 6 mm diameter, dried at 80 ° C for one hour, annealed at 400 ° C for two hours and calcined at 900 ° C for one hour.

The further catalysts of the invention listed in Table 1 2 to 4 were also produced according to this regulation.

The required K₂Fe₂₂O₃₄ was according to the rule of Example 6 of DE 38 21 431 obtained by a mixture of 1000 g of alpha-FeOOH and 215 g K₂CO₃ sintered at 950 ° C for one hour after thorough mixing, after which Cooling was washed with water and then dried again.

The comparative catalysts (5 to 8 of the table) were like the Catalysts according to the invention produced with the proviso that instead of of K₂Fe₂₂O₃₄ equivalent amounts of alpha-FeOOH and anhydrous K₂CO₃ in addition to the other specified ingredients including potassium carbonate was used.  

Dehydrogenation of ethylbenzene to styrene on an experimental scale

The catalysts 1 to 8 were granulated to 0.5 to 1 mm crushed. 20 ml of these contact masses are put into one Reactor filled with 6 mm inside diameter. 10 ml per hour Water and 10 ml of ethylbenzene in a tube reactor heated by a salt bath dosed. The temperature is adjusted so that the organic fraction of the reactor discharge consists of 50% styrene. To 5 days is an analysis of the organic phase and the exhaust gas carried out and the selectivity of the catalyst is calculated. The results of the catalytic tests with the catalysts 1 to 8 are in Table 2 compiled.  

Table 1

Composition of the catalysts

Table 2

Test results

Claims (2)

Catalyst consisting essentially of

• a) 40 to 90 wt .-% of an iron compound, calculated as Fe₂O₃,
• b) 5 to 40% by weight of a potassium compound, calculated as K₂O,
• c) 1 to 15% by weight of a tungsten compound, calculated as WO₃,
• d) 0.1 to 15% by weight of at least one compound of chromium, aluminum or a rare earth, calculated as Me₂O₃,
• e) 0.1 to 15% by weight of at least one compound of zinc, cadmium or an alkaline earth metal, calculated as MeO,

and possibly other components, as it is obtained when one Iron and potassium predominantly or exclusively in the form of the water-insoluble Potassium ferrite K₂Fe₂₂O₃₄ used.