DE4422770A1 - Catalyst and process for the catalytic oxidative dehydrogenation of alkyl aromatics and paraffins - Google Patents

Abstract

A process for the catalytic-oxidising dehydrogenation of alkyl aromatics or paraffin hydrocarbons to the corresponding alkenyl aromatics or olefines by means of a redox catalyst (oxygen transmitter), in which in a first reaction stage the alkyl aromatic or paraffin hydrocarbon (educt) is dehydrogenated with a catalyst composed of a reducible metal oxide and chrominum oxide in the absence of molecular oxygen and the catalyst is reduced, and in a second stage the reduced catalyst is reoxidised with an oxidising agent.

Description

The invention relates to a method and a catalyst for the catalytic oxidative dehydrogenation of alkyl aromatics and Paraffin hydrocarbons to the corresponding alkenyl aromatics and olefins, preferably from ethylbenzene to styrene, where Water is formed and the dehydration is absent of free (i.e. continuously added to the educt stream) Oxidizing agents such as molecular oxygen or oxygen containing gases and that from at least one reduced existing metal oxide redox catalyst as the sole acid substance source the function of an oxygen storage or transfer carrier takes over.

Olefins and alkenylbenzenes, especially styrene and divinyl benzene, are important monomers for engineering plastics and are produced in large quantities. Styrene is predominant by non-oxidative dehydrogenation of ethylbenzene on one modified iron oxide catalyst prepared, with per mol Styrene produces one mole of hydrogen. It disadvantageously acts is an equilibrium reaction that occurs at high temperatures from typically 600 to 700 ° C and with a 60% conversion with a styrene selectivity of around 90% runs.

By oxidative dehydrogenation, in which the educt flow with a Oxidizing agents such as molecular oxygen or an acid substance-containing gas is applied, the balance can be overcome and achieve almost quantitative sales as Coproduct water is now formed. Are also for this Implementation of lower reaction temperatures required. After however, part of this process is that of the present oxygen-related loss of selectivity for the value product because of the high oxygen concentration in the reaction zone as a side reaction favors total oxidation.

It has therefore been suggested instead of free oxidati onsmittel (oxygen) one of a reducible metal oxide use existing catalyst as an oxygen carrier. Here the catalyst (at the same time oxygen carrier) all gradually consumed and must be regenerated in a second step which will restore the initial activity. In the regeneration phase can, for. B. also burnt coke deposits  will. The regeneration is highly exothermic, so that the free waste heat z. B. can be used for the production of steam can.

By decoupling the reduction and oxidation step the selectivity can be increased significantly.

There are two for the technical implementation of this proposal Variants, namely the spatial and temporal separation of the two substeps.

The former becomes a walking bed or a circulating vertebra layer used so that the catalyst particles from the Dehydrogenation zone, after separation of the reaction products formed, to be promoted to a separate regeneration reactor in which the reoxidation is carried out. The regenerated catalyst is returned to the dehydrogenation zone. The catalyst is exposed to high mechanical stresses and must therefore have sufficient hardness.

When running with a fixed bed, periodically between the educt feed and if necessary after a rinsing phase Regeneration gas switched.

This principle of separating the two substeps of redox reaction using a reducible and regenerable Catalyst was first used for the oxidation or ammoxidation from propene to acrolein and acrylic acid or acrylonitrile wrote (GB 885422; GB 999629; K. Aykan, J. Catal. 12 (1968) 281-190), using arsenate and molybdate catalysts were. The use of the method in oxidative dehy aliphatic alkanes to mono- and diolefins Ferrite catalysts (e.g. US 3,440,299, DE 21 18 344, DE 17 93 499) is also known, as is its use for oxidative coupling of methane to higher hydrocarbons, different classes of catalyst are used (e.g. US 4,795,849, DE 35 86 769 with Mn / Mg / Si oxides; US 4,568,789 with Ru oxide; EP 254 423 with Mn / B oxides on MgO; GB 2 156 842 with Mn₃O₄ spinels). Dehydrodimerization, too from toluene to stilbene in the absence of free oxygen reducing catalysts such as Bi / In / Ag oxides (EP 30 837) is known. Finally, the principle applies to dehydration tion, dehydrocyclization and dehydroaromatization of paraffin hydrocarbons used for gasoline refinement (US 4,396,537 with Co / P oxide catalysts).  

The process principle is known from EP 397 637 and 403 462 for the oxidative dehydrogenation of paraffin hydrocarbons and to use alkyl aromatics. After that, reducible metal oxide used, selected from the group V, Cr, Mn, Fe, Co, Pb, Bi, Mo, U and Sn, applied to supports made of clays, zeolites and oxides of Ti, Zr, Zn, Th, Mg, Ca, Ba, Si, Al. Especially V / MgO is preferred.

Although a high yield can be achieved with these catalysts may occur in the early stages of dehydration when the Hydrocarbon with the freshly regenerated and therefore special active catalyst comes into contact, to a very strong Gasification (total combustion). Except for the loss of raw materials significantly more oxygen is consumed than for the mere dehydration so that much of the oxygen is is exhausted prematurely and the cycle times become unnecessary shorten.

The invention solves the problem of an oxygen-transmitting Finding catalyst that has higher sales than the non-oxidative Dehydration enables and at the same time the disadvantageous behavior the catalysts of the oxidative dehydrogenation in the initial phase largely avoided, so that the selectivity is increased and additional procedural steps, e.g. B. a partial Pre-reduction of the oxygen carrier can be saved. On Another concern of the invention is a particularly hard Manufacture catalyst that the mechanical stress in withstands technical reactors without disintegrating.

It has now been found that reducible metal oxides such as oxides of Bi, V, Ce, Fe, In, Ag, Cu, Co, Mn, Pb, Sn, Mo, W, As, Sb, before adds bi, Ce and V oxide, and particularly preferably Bi₂O₃ or CeO₂ and chromium oxide, preferably Cr₂O₃, as a particularly cheap oxygen transferring catalysts for the absence of free Oxidative dehydration carried out using oxidants can be. Chromium oxide is preferably predominant Amount used; it can therefore - at least in part - also as a catalyst support. It was also found that the catalysts according to the invention by adding an inorganic peptizable binder in the production such as Al₂O₃, SiO₂ etc., preferably a hydroxylated Al oxide Selectivity and better mechanical hardness at the same time hold. It was also found that an addition of alkali and / or Alkaline earth, preferably Li, Na or Cs, especially K, the initial gasification suppressed particularly effectively and high selectivity and thus enables yield gains on dehydrated product.  

A preferred catalyst contains or consists of 5 to 60% by weight, preferably 10 to 45% by weight of vanadium, 10 to 95% by weight, preferably 30 to 80% by weight of chromium and 1 to 40% by weight, preferably 3 to 20 wt .-% alkali and / or alkaline earth (each determined as most resistant oxide) and contains 0 to 70 wt .-%, preferably 10 to 50% by weight of a catalytically inactive oxide, i.e. H. one inorganic binder, preferably an aluminum oxide. The above proportions also apply to the above standing called other elements instead of vanadium can be used.

An equally favorable catalyst contains or consists of 5 to 60% by weight, preferably 10 to 45% by weight of cerium (4) oxide a carrier of 10 to 95% by weight, preferably 20 to 80% by weight Chromium (3) oxide with 1 to 40% by weight, preferably 3 to 20% by weight Alkali and / or alkaline earth (determined as oxide) and contains 0 to 70 wt .-%, preferably 10 to 60 wt .-% alumina.

A particularly preferred catalyst contains or consists of 5 to 60% by weight, preferably 10 to 45% by weight bismuth (3) oxide a carrier of 10 to 95% by weight, preferably 30 to 80% by weight Chromium (3) oxide with 1 to 40% by weight, preferably 3 to 20% by weight Alkali and / or alkaline earth and contains 0 to 70% by weight, preferably 10 to 60 wt% alumina.

The above proportions relate to the finished catalyst in the most stable or the most given oxidation level. About the actual relationship Nisse is not intended to make a statement and the invention is so far not be restricted; e.g. B. can also when calcining Form phases, the higher oxidation levels of chromium ent speak like chromates or bichromates of potassium or bismuth.

The catalyst can be used in a conventional manner such as dry mixing slurrying, impregnation, precipitation, spray drying etc. will. The ingredients can e.g. B. in the form of their oxides, hydro xides, carbonates, acetates, nitrates or generally more water-soluble Salts with organic or inorganic anions are used the one that when heated (calcined) into the corresponding oxides pass over. Transition metal complexes can e.g. B. used will. The calcination takes place at temperatures in the range of 200 to 1000 ° C, preferably from 200 to 800 ° C and in particular from 400 to 700 ° C.  

The dehydrogenation reaction requires a temperature of 200 to 800 ° C, preferably 350 to 550 ° C and atmospheric or slightly reduced or increased pressure z. B. from 100 mbar to 10 bar, preferably 500 mbar to 2 bar, with an LHSV of 0.01 to 20 hours ^-1 , preferably 0.1 to 5 hours ^-1 . In addition to the hydrocarbon to be dehydrogenated, diluents such as CO₂, N₂, noble gases or steam can be present. The regeneration of the reduced catalyst requires temperatures between 300 and 900 ° C, preferably 400 and 800 ° C, with the oxidizing agent, for. B. N₂O or an oxygen-containing gas is used. Here too, diluents can be contained in the reactor inflow. Suitable regeneration gases are e.g. B. air, lean air or N₂O mixtures. The regeneration can be carried out at reduced or atmospheric or elevated pressure.

Pressures in the range from 500 mbar to 10 bar are preferred.

example 1

200 g Cr₂O₃ and 135.8 g basic bismuth carbonate (contains 81% by weight of Bi) are mixed dry and proceed as described in Comparative Example 3. On the x-ray Diffraction diagram shows bismuth (3) oxide phase Bi₂O₃ and the Chromium (3) oxide phase Cr₂O₂. The catalyst contains 38% by weight Bi₂O₃ and 62 wt .-% Cr₂O₃.

Example 2

50 g of Cr₂O₃ and 33.95 g of basic bismuth carbonate with 33.55 g Alumina Pural SB dry blended and continue as above method. The catalyst contains 29 wt .-% Bi₂O₃, 47.3 wt .-% Cr₂O₃ and 23.7 wt .-% Al₂O₃.

Example 3

100 g of Cr₂O₃ and 67.9 g of basic bismuth carbonate 67.1 g of aluminum oxide Pural SB and 41.5 g of K₂CO₃ mixed dry and proceed as above. The catalyst contains 25.6 wt .-% Bi₂O₃, 41.7 wt .-% Cr₂O₃, 11.7 wt .-% K₂O and 21.0 wt .-% Al₂O₃. The catalyst is extremely hard. The cutting hardness of 73 N is more than three times as high that of the catalyst from comparative experiment 3.  

Example 4

83.4 g of Cr₂O₃, 116.42 g of CeO₂ and 56 g of commercially available aluminum oxide (AlO (OH); Pural SB®) were mixed dry with 34.34 g K₂CO₃ and proceed as above.

The catalyst contains
41.7% Cr₂O₃
25.6% CeO₂
21.0% Al₂O₃
11.7% K₂O

Comparative experiment 1 (according to EP 397637)

100 g SiO₂ powder D11-10 from BASF are at 500 ° C for 3 h calcined. 85 g of the calcined SiO₂ are with a solution of 102.5 g of Fe (NO₃) ₃ · 9 H₂O in deionized water until a final weight of 216 g has been reached. The mixture is left at RT for 18 h stand, filter and dry at 110 ° C for 18 h. Subsequently is heated at a rate of 30 ° C / h up to 600 ° C and for Calcined at 600 ° C for 10 h. The catalyst is in powder form and contains 20 wt .-% Fe₂O₃ and 80 wt .-% SiO₂.

Comparative experiment 2 (according to EP 397637)

336.3 g of ammonium metadvanadate and 900 g are added to 8 l of water Magnesium oxide stirred in and then stirred vigorously for 1 h. It is then sprayed on the spray dryer. The received Spray powder is treated in a kneader for 2 h, using little water and extrusion aids are kneaded into the modeling clay. Then the plasticine is added using an extruder 3 mm full strands deformed. The strands are kept at 120 ° C for 16 h dried and then calcined at 600 ° C for 4 h. You get uniform yellow colored strands with low hardness. For the A 0.05 to 0.1 mm grit fraction is emitted from the reactor seven. The catalyst contains 22.5 wt .-% V₂O₅ and 77.5 wt .-% MgO.

Comparative experiment 3

100 g of MgO powder and 58.1 g of NH₄VO₃ powder are dry for 1 h mixed. The mixture is then kneaded for 2.5 h kneaded. Then the plasticine is added using an extruder 3 mm full strands deformed. The strands are kept at 120 ° C for 2 h dried. It is then calcined at 500 ° C for 2 h. For the reactor tests will be a 0.05 to 0.1 mm grit fraction sifted out. XRD only shows the lines of V₂O₅ and MgO. The kata Lysator contains 31 wt .-% V₂O₅ and 69 wt .-% MgO.  

Comparative experiment 4

276.85 g of basic bismuth carbonate are presented and continue as Proceed above (comparative experiment 3). The catalyst be is made of pure Bi₂O₃.

Comparative experiment 5

150 g of Cr₂O₃ are presented and proceed as above. The catalyst consists of pure Cr₂O₃.

Comparative experiment 6

200 g Cr₂O₃ are mixed dry with 61.6 g NH₄VO₃ and continue proceed as above. The catalyst contains 32 wt .-% V₂O₅ and 68 wt .-% Cr₂O₃.

Comparative experiment 7

200 g Cr₂O₃ with 205.8 g of basic cerium (3) carbonate (contains 35.8 wt .-% Ce) dry mixed and further according to Example 3 ver drive. The catalyst contains 31 wt .-% CeO₂ and 69 wt .-% Cr₂O₃.

Comparative experiment 8

167.9 g of Cr₂O₃ are dry with 69.3 g of Pural SB aluminum oxide mixed and proceed as above. The catalyst consists of 23.7 wt .-% Al₂O₃ and 76.3 wt .-% Cr₂O₃.

The cutting hardness of the catalysts is on the 3 mm full strand determined by cutting the strand with a sharp knife (blade width 0.6 mm) required force in N is measured.

The catalytic-oxidative dehydrogenation of ethylbenzene to styrene is carried out in a pulse reactor at a temperature of 500 ° C leads. A microfixed bed (sample weight of catalyst: 0.3 g) pulsed with pure ethylbenzene and the result which reaction products for each pulse quantitatively gaschromato graphically recorded. Between two successive ethylbenzene Pulses (approx. 1.5 min) helium flows through the reactor. A single The pulse contains 380 µg of ethylbenzene. The flow rate of the carrier gas is 21.5 ml / min. In this way the time behavior of the catalyst without dead times from the beginning track with high time resolution.  

At the beginning of the reaction, the catalyst is highly active, so that high, almost quantitative sales of ethylbenzene observed will. In the further course of the reaction, the Selectivity to styrene steadily to an end value. With away the duration of the experiment, however, becomes the catalyst in the Measures of how its oxygen content is being consumed, more and more deactivated so that sales decrease. Depending on the catalyst regenerated after 90 to 200 pulses. The styrene yield as Product from selectivity and turnover generally goes through a flat one Maximum. The yield listed in the table relates to this maximum value.

After the dehydration reaction is complete, an air flow is applied switched from 25 ml / min and the catalyst for about 1 h 500 ° C regenerated. Then the next cycle follows. Several cycles are examined in each case.

The results of the examples / experiments are as follows Reproduced table. The table contains a summary the catalysts produced, the relative mass ratios the components, the hardness of the cut and the results of the tests (Mean values from several experiments) for the dehydrogenation of ethyl benzene in a fixed bed reactor.  

By thermogravimetry combined with chemical analysis on deactivated reactor expansion samples, it was found that the catalyst of the prior art (V₂O₅ / MgO) was reduced to V₂O _3.6 by ethylbenzene (ie the oxidation levels 3 and 4 were present side by side), i.e. 1.4 formula units of oxygen are given per mole of vanadium pentoxide. In contrast, the active component Bi₂O₃ of a preferred catalyst according to the invention (Bi₂O₃ / K₂O / Cr₂O₃ / Al₂O₃) is reduced in formula to Bi₂O _0.5 , ie approximately to the metal. So 2.5 formula units of oxygen are transferred per mole of bismuth oxide.

Technically, the reaction will generally not to the full Take advantage of deactivation of the catalyst, but before regenerate, d. H. as long as the styrene yields are still economically viable are acceptable, e.g. B. about 10 to 20% below the achieved Maximum value have fallen. The regeneration time can be adjusted accordingly be shorter.

The following conclusions can be drawn from the table den: Catalysts according to the prior art (comparative experiments 2 and 3) are active and allow a high maximum styrene yield, but have the decisive disadvantage of a strong one Initial gasification (total oxidation). The Kataly according to the invention Sators, especially Bi / Cr₂O₃, V / Cr₂O₃ and Ce / Cr₂O₃, are against it advantageous catalysts. In particular, Bi / Cr₂O₃ is distinguished with a high activity and almost full of ethylbenzene constantly around (Ex. 1). However, the initial performance and hardness still room for improvement.

By adding hydroxylated aluminum oxide AlO (OH) can the hardness and abrasion resistance are increased (Ex. 2). also it was surprisingly found that the beginning performance is improved and therefore the styrene yield over the Overall cycle increases.

One can be promoted with alkali and / or alkaline earth on the other hand increase the hardness, so that now the Kataly mechanical properties fulfilled by far are; on the other hand, the disadvantageous is also advantageous Initial gasification almost completely suppressed, and without on loss of activity, d. H. with still high sales. At first selectivity and a higher overall yield per cycle again improved, so that in the non-oxidizing process achievable yield is achieved (Ex. 3).  

The styrene selectivity in the activity maximum is only a little less than the non-oxidizing process. This is because that the catalyst of the invention in the initial phase slightly increased amount of by-products benzene and toluene, which then decrease rapidly as the response time progresses. The formation of benzene and toluene is not a problem in the Comparison to CO₂ formation because toluene is a salable product is and benzene are returned to the ethylbenzene production can and is not lost.

As the comparative experiments 4 and 5 show, are pure Bi₂O₃ and pure Cr₂O₃ taken alone, inactive. Cr₂O₃ is accordingly not just a mechanical support, but only that Activation of the compounds regarded as redox catalysts Bi₂O₃, V₂O₅ and CeO₂.

On the other hand, as comparative experiment 6 shows, that too Mixture of Cr₂O₃ and Al₂O₃ catalytically inactive, so that the pre presence of a redox active ingredient is indispensable.

Claims (22)

1. Process for the catalytic oxidative dehydrogenation of alkyl aromatics or paraffin hydrocarbons to the corresponding alkenyl aromatics or olefins by means of a redox catalyst (oxygen transfer agent), characterized in that in a first reaction step the alkyl aromatic or paraffin hydrocarbon (educt) with the catalyst from a reducible catalyst Metal oxide and chromium oxide is dehydrated in the absence of molecular oxygen, the catalyst being reduced, and in a second reaction step the reduced catalyst is reoxidized with an oxidizing agent. 2. The method according to claim 1, characterized in that the first and second reaction step temporally or spatially take place alternately and the catalyst is firmly arranged is. 3. The method according to claim 2, characterized in that the Decoupling of the sub-steps in time by periodic Switching the reactor input current between educt and Oxidizing agent is effected. 4. The method according to claim 2, characterized in that the Catalyst is fixed and between the part steps a rinsing phase is inserted in which the feast a purge gas flows through the bed reactor. 5. The method according to claim 4, characterized in that as Purge gas CO₂, N₂, H₂O or noble gas is used. 6. The method according to claim 2, characterized in that the spatial decoupling of the sub-steps using a circulating fluidized bed is caused by catalyst particles cyclically between a dehydrogenation reactor and a Regeneration reactor are circulated. 7. The method according to claim 1, characterized in that ethyl benzene is dehydrated to styrene. 8. The method according to claim 1, characterized in that as Oxidizing agent an oxygen-containing gas is used.   9. The method according to claim 1, characterized in that N₂O is used as an oxidizing agent. 10. The method according to claim 1, characterized in that as A reducible metal oxide catalyst selected from the Oxides of Bi, V, Ce, Fe, In, Ag, Cu, Co, Mn, Pb, Sn, Mo, Sb, As, W or their mixtures, on a chromium oxide support is set. 11. The method according to claim 10, characterized in that as Catalyst on a reducible oxide of V, Bi or Ce a chromium oxide support is used. 12. The method according to claim 11, characterized in that the Bismuth oxide at least in the oxidized form contains a chromium oxide support. 13. The method according to claim 11, characterized in that the reducible catalyst vanadium oxide on a chromium oxide carrier contains. 14. The method according to claim 10, characterized in that the Contains catalyst cerium oxide on a chromium oxide support. 15. The method according to claim 10, characterized in that the Contains catalyst alkali and / or alkaline earth oxide. 16. The method according to claim 10, characterized in that the Catalyst an inorganic binder such as alumina contains. 17. The method according to claim 1, wherein the dehydrogenation in the temperature range between 200 and 800 ° C at a pressure of 100 mbar to 10 bar with a liquid hourly space velocity (LHSV) from 0.01 to 20 hours ^{-1 is} carried out . 18. Reducible catalyst, especially for the oxidative Dehydration containing side by side or as a compound Chromium (3) oxide and at least one reducible metal oxide, selected from the oxides of Bi, V, Ce, Fe, In, Ag, Cu, Co, Mn, Pb, Sn, Mo, W, As or their mixtures. 19. A catalyst according to claim 18, with the composition according to one of claims 12, 13 or 14.   20. A catalyst according to claim 18, consisting essentially from 5 to 60% by weight bismuth (3) oxide, 1 to 40% by weight alkali and / or alkaline earth oxide and 10 to 50% by weight of aluminum oxide a carrier of 10 to 95 wt .-% chromium (3) oxide with the measure that the sum of the weight percent is 100. 21. A catalyst according to claim 18 consisting essentially of 5 to 60% by weight cerium (4) oxide, 1 to 40% by weight alkali and / or Alkaline earth oxide and 10 to 50 wt .-% aluminum oxide on one Carriers made of up to 95% by weight chromium (3) oxide with the proviso that the sum of the weight percent is 100. 22. A catalyst according to claim 20 or 21, wherein the alkali oxide Is potassium oxide.