DE3228879A1 - Dehydrogenation catalyst - Google Patents

Abstract

The dehydrogenation catalyst consisting of 50 to 95% by weight of an iron compound and 5 to 50% by weight of at least one promoter and/or at least one stabiliser is prepared by using maghaemite, gamma -Fe2O3 of a specific surface area of 1 to 50 m<2>/g measured by BET, is as the iron compound and is mixed or kneaded with the further component or components and then moulded. The catalyst is used for the dehydrogenation of ethylbenzene to styrene.

Description

tDehydrogenation catalyst

The invention relates to a dehydrogenation catalyst containing a) 50 to 95% by weight, based on a + b, of at least one iron compound, calculated as Fe 2 O 3, and b) 5 to 50% by weight, based on a + b, of at least one promoter and / or at least one stabilizer, calculated as the most stable oxide.

Olefins, in particular butadienes and vinylbenzenes, are important starting materials for the production of plastics, synthetic resins and rubbers.

In general, they are carried out in the technically practiced procedures Passing over partially saturated hydrocarbons e.g. ethylbenzene or butene together with steam over a fixed bed catalyst at temperatures between 450 and 7000C dehydrated. The process can be carried out isothermally or adiabatically (see 1).

With regard to the state of the art, we mention: (1) Kunststoff-Handbuch, Volume V, Polystyrene, Carl Hanser - Verlag, pp. 39 to 47 (1969), (2) US Pat. No. 4,144,197, (3) DE-OS 25 44 185 and (4) German patent application P 31 32 014.7 'As Catalysts are iron oxides, promoted with oxide-forming alkali salts and others Selectivity-increasing and structure-stabilizing metal compounds are used. For the production of the catalyst can iron oxides produced by thermal decomposition obtained from iron nitrate, iron oxalate or iron sulfate are also used are like iron oxide pigments produced technically on a large scale, e.g. iron red (Hematite-alpha - Fe203) and iron yellow (goethite-alpha-FeOOH).

The ground iron oxide - 50 to 95% by weight of the contact mass - will with the promoters in powder form or dissolved in water with further addition mixed with water and kneaded into a plastic mass, extruded into strands, dried and at temperatures between 500 and 100,000 (usually in the range between 850 and 9500 ° C.) calcined for 0.5 to 3 hours [cf. (2), (3) and (4)]. Included A contact surface between 3 and 4 m2 / g is aimed for.

According to X-ray diffraction recordings, the iron oxide is in the catalysts produced in this way as hematite (alpha-Fe203) interspersed with potassium ferrates and other promoter salts before.

At the beginning of the reaction, the catalyst is initiated by the Ethylbenzene reduced. It forms in a water vapor / hydrogen atmosphere thermodynamically stable magnetite, Fe304.

So far it was assumed that the reduction was inevitable Occurring conversion of the oxygen skeleton in the iron oxide from a hexagonal one (alpha-Fe 203) in a cubic close packing of spheres (Fe304) is a necessary prerequisite for the activation of the catalyst is there this process one Significant increase in defects and disorder in the iron oxide lattice result should have (see E. Lichtner and A. Weiss, Z. anorg. general.

Chem. 359: 214-219 (1968)). Hence the use of maghemite (tFe203) as an iron oxide component is only possible if you go through oxidizing Calcining at temperatures above 700 ° C carried out the conversion to hematite.

Surprisingly we have now found that one of Maghämit at the production of an active dehydrogenation catalyst can start without the detour to have to go to an intermediate oxidation.

The invention therefore relates to a dehydrogenation catalyst containing a) 50 to 95% by weight, preferably from 6o to 91% by weight, based on a + b, at least an iron compound, calculated as Fe 2 O 3, and b) 5 to 50% by weight, preferably from 10 to 40 wt. S, based on a + b, at least one promoter and / or at least a stabilizer, calculated as the most stable oxide, optionally containing c) usual additives.

characterized in that for the preparation of the catalyst as Component a) Maghem with a specific 2 surface area of 1 to 50 m / g, preferably from 2 to 40 m2 / g, measured according to BET, and this with the other component (s) mixes or kneads and then shapes.

The advantage of the invention consists on the one hand in the substantial simplification the preparation of the catalyst It is sufficient even simple, dry mixing of the Components and subsequent tabletting. The aforementioned production steps kneading and calcining can be omitted. A saving in energy costs is obvious. The influences of the promoters and / or stabilizers added remain in effect unchanged; a loss of quality can therefore be ruled out. With regard to the type of promoters, stabilizers and additives and their definition reference is made to (1), (2) and in particular to (4).

A maghemite is said to be used for the production of the catalyst according to the invention can be used, the BET surface area of which is 1 to 50 m2 / g. One is preferable Surface area from 4 to 40 m2 / g and in particular between 10 and 25 m2 / g. (The BET surface area is measured according to Brunauer, Emett, Teller, J. Amer. Chem. Soc. 60 (1938), page 309.) The simplest production method is dry Mix the powdered maghemite with the also finely ground promoters and subsequent tabletting after adding a tabletting aid (e.g. graphite) to mechanically stable moldings. The promoters can be in oxidic form or used as oxide-forming metal salts, in particular as carbonates and hydroxides will.

In addition to purely dry mixtures, it is also possible to use kneading compounds made from the β-iron oxide pigment and the promoters are prepared with the addition of water, the, to strands extruded, dried at temperatures up to 2000C if necessary under vacuum will. Aqueous suspensions of the contact mixture can be tabletted after spray-drying will Solid cylinders from 3 to are suitable as tablet shapes 5 10 mm diameter. Due to kinetic and operational conditions are However, ring tablets with comparable external diameters are preferable. Same thing applies to extrudates, where preference should also be given to hollow strands.

Examples for the preparation of inventive catalysts: A: t-Fe203, After the addition of promoters, maghemite is made into a paste with water and then either dried after shaping (extrusion) or tabletted after drying.

B: t-Fe203, maghemite / is promoted with finely ground metal salts dry mixed, 2% graphite added and tableted.

Table 1 shows a number of catalysts according to the invention Production method (A or B) and composition, as well as their selectivity indicated. In Table 2 are the conditions for the preparation of the catalysts 1 to 5 listed.

Test specification for the catalysts according to the invention for example Dehydrogenation of ethylbenzene: Catalysts 1 to 5, prepared by method A in the form of tablets and the catalysts 6 to 12, prepared by method B were crushed to a grain size of 0.5 to 1 mm. From these contact masses 20 ml each were filled into a reactor with an internal diameter of 6 mm. Per 10 ml of water and 10 ml of ethylbenzene were metered into the reactor for an hour. The temperature of the salt bath used to heat the reactor was adjusted in each case so that the organic phase of the reactor discharge 50% Contains styrene. To A total analysis of the organic phase and the exhaust gas was carried out for 6 days and the selectivity of the catalyst is calculated.

Table 1 Catalyst Test Results No. Her Catalyst Composition [g] React- (a) styrene- (b) st- (wt.% based on a + b assuming the oxides action- selection Fe2O3, K2O, Cr2O, V2O5, WO3) tempe- rature method temperature [° C] [%] 1 A 100 (85.6) G-20 (c) 18.6 (10.8) K2CO3 1.1 (0.9) V2O5 3.1 (2.7) WO3 595 95.33 2 A 100 (84.3) G-20 17.1 (12.1) KOH 1.1 (094) V2O5 3.1 (2.7) WO3 598 94.91 3 A 100 (85.6) G-20 22.6 (10.8) K (HCO2) 1.1 (0.9) V2O5 3.1 (2.7) WO3 597 95.84 4 A 100 (84.3) G-16 18.6 (10.7) K2CO3 1.8 (1.5) CrO3 1.1 (0.9 V2O5 3.1 (2.6) 596 96.05 5 A 100 (84.3) G-16 18.6 (10.7) K2CO3 1.8 (1.5) CrO3 1.1 (0.9) V2O5 3.1 (2.6) WO3 600 95.34 6 B 100 (88.8) G-20 18.6 (11.2) K2CO3 592 94.51 7 B 100 (88.8) G-16 18.6 (11.2) K2CO3 567 88.94 8 B 100 (85.6) G-20 22.6 (10.8) K (HCO2) 1.1 (0.9) V2O5 3.1 (2.7) WO3 607 95.21 9 B 100 (85.6) G-16 18.6 (10.8) K2CO3 1.1 (0.9) V2O5 3.1 (2.7) WO3 595 96.77 10 B 100 (85.6) G-16 15.96 (10.8) K2CO3 1.1 (0.9) V2O5 3.1 (2.7) WO3 595 96.50 11 B 100 (84.3) G-16 18.6 (10.7) K2CO3 1.8 (1.5) CrO3 1.1 (0.9) V2O5 3.1 (2.6) WO3 594 95.34 a) reaction temperature with 50% styrene in the organic part of the furnace oil; b) styrene selectivity, based on the ethylbenzene used; c) G-X: G = γ-Fe2O3; X = surface area of γ-Fe2O3 (given in m² / g); d) used as a powder.

Table 2 9 catalyst water drying sator addition time Tgmp. Remarks [ml] [h] [° C l 120 16 100 2 112 16 100 3 90 16 100 4 50 24 100 5 45 24 100 The components were kneaded for 3 h, extruded into 1 mm strands, dried, ground and after Addition of 2% graphite tablets.

Claims (2)

Claims 1. Dehydrogenation catalyst containing a) 50 to 95% by weight, based on a + b, of at least one iron compound, calculated as Fe203, and b) 5 to 50% by weight, based on a + b, of at least one promoter and / or at least a stabilizer, calculated as the most stable oxide, optionally containing c) Usual additives, characterized in that one for the preparation of the catalyst Measured as component a) Maghem with a specific surface area of 1 to 50 m2 / g according to BET, and this is mixed or kneaded with the other component (s) and then shapes. 2. Use of the catalyst according to claim 1 for the dehydrogenation of Ethylbenzene to styrene.