EP0931040A1

EP0931040A1 - Process and catalyst for the catalytic oxidative dehydrogenation of alkyl aromatics and paraffins

Info

Publication number: EP0931040A1
Application number: EP97942868A
Authority: EP
Inventors: Alfred Hagemeyer; Otto Watzenberger; Andreas PÜTTNER; Martin TRÖMEL
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1996-09-11
Filing date: 1997-08-21
Publication date: 1999-07-28
Also published as: JP2001500137A; WO1998011038A1; DE19636884A1

Abstract

The invention concerns a process for the heterogenocatalytic oxidative gaseous phase dehydrogenation of alkyl aromatics or aliphatics (educts) to form the corresponding alkenyl aromatics or olefins. In a first reaction step, the educt is dehydrogenated with a bismuth-containing redox catalyst (oxygen carrier) in the absence of molecular oxygen, and, in a second reaction step, the reduced catalyst is reoxidized with an oxidizing agent. The reaction steps are chronologically or spatially decoupled, and at least one reducible bismuthate (5) on a basic or neutral carrier is used as the bismuth-containing catalyst. The invention further concerns Ba-bismuthate (5) having the composition Ba9Bi3O14 as novel substance.

Description

Process and catalyst for the catalytic oxidative dehydrogenation of alkyl aromatics and paraffins

description

The invention relates to a process for the catalytic oxidative dehydrogenation of alkyl aromatics and paraffin hydrocarbons to the corresponding alkenyl aromatics and olefins, preferably dehydrogenation of ethylbenzene to styrene, water being formed and the dehydrogenation in the absence of free (ie continuously added to the educt stream) oxidizing agent such as molecular Oxygen or gases containing oxygen takes place and a bismuth oxide-containing redox catalyst acts as the sole oxygen source

Oxygen storage or transfer takes over. The catalyst is reduced during the dehydrogenation and regenerated in a second step using an oxidizing agent, preferably an oxygen-containing gas or N ₂ O. The bismuth compound to be used according to the invention can be applied to a carrier.

Olefins and alkenylbenzenes, especially styrene and divinylbenzene, are important monomers for engineering plastics and are produced in large quantities. Styrene is predominantly produced by non-oxidative dehydrogenation of ethylbenzene over a modified iron oxide catalyst, whereby one mole of hydrogen is produced per mole of styrene. Disadvantageously, it is an equilibrium reaction which is carried out at high temperatures of typically 600 to 700 ° C and with a conversion of about 60% with a styrene selectivity of about 90%.

By means of oxidative dehydrogenation, in which an oxidizing agent such as molecular oxygen or an oxygen-containing gas is applied to the educt stream, the equilibrium can be overcome and an almost quantitative conversion can be achieved since water is now formed as a co-product. Lower reaction temperatures are also required for this reaction. A disadvantage of this process, however, is the loss of selectivity for the product of value associated with the presence of oxygen, since the high oxygen concentration in the reaction zone favors total oxidation as a side reaction. It has therefore already been proposed to use a catalyst consisting of a reducible bismuth oxide instead of free oxidizing agent (oxygen) as an oxygen carrier.

The catalyst (oxygen carrier at the same time) is gradually consumed and regenerated in a second step, which restores the initial activity. In contrast to dehydration with elemental oxygen, hardly any side reactions (so-called total combustion) are observed. In the regeneration phase e.g. coke deposits are burned off. The regeneration is highly exothermic, so that the waste heat released is e.g. can be used for the production of steam.

The separation of dehydration and oxidation makes it easier

Mastery of the highly exothermic implementation. In the dehydrogenation step, the reaction proceeds through the fixed catalyst bed in the form of a reaction front. The local heat release is determined solely by the local concentration of reactive oxygen in the catalyst. The same naturally applies to the oxidation step. The dehydrogenation is only slightly endothermic, but the oxidation is strongly exothermic. Through the targeted design of the catalyst, i.e. the local storage capacity for active oxygen, i.e. Oxygen that is consumed during dehydration can be used to control the local heat release. For example, this can be achieved by appropriately diluting the catalytically active material with low or inactive metal oxides, by applying the active material to a carrier or by mixing active catalyst-oxygen storage material with inert material. The local temperature rise can thus be determined in advance and the thermal load on the catalytic converter can thus be set to an acceptable level.

There are two variants for the technical implementation of the two-stage concept, the spatial or temporal separation of the two sub-steps.

In the former, a moving bed or a circulating fluidized bed is used, so that the catalyst particles from the

Dehydrogenation zone, after separation of the reaction products formed, are conveyed to a separate regeneration reactor in which the reoxidation takes place. The regenerated catalyst is returned to the dehydrogenation zone. The catalytic converter is exposed to high mechanical loads and must therefore have sufficient hardness. In the case of the design with a fixed bed, the regeneration gas is periodically switched between the educt supply and, if necessary, after a winding phase. The technical implementation with two alternating fixed bed reactors enables the advantageous decoupling and beneficial use of the thermal energy released during reoxidation.

The principle of separating two substeps of the redox reaction using a reducible and regenerable catalyst was first described for the oxidation or ammoxidation of propene to acrolein and acrylic acid or acrylonitrile (GB 885422; GB 999629; K. Aykan, J. Catal. 12 (1968) 281-190) using arsenate and molybdate catalysts. The use of the process in the oxidative dehydrogenation of aliphatic alkanes to mono- and diolefins with ferrite catalysts (for example US 3 440 299, DE 21 18 344, DE 17 93 499 and US 3 118 007) is also known, as is the use for the oxidative coupling of methane to higher hydrocarbons, different catalyst classes being used (eg US 4,795,849, DE 3,586,769 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 Mn ₃ 0 spells). The dehydrodi erization of toluene to stilbene in the absence of free oxygen by means of reducible catalysts such as Bi / In / Ag oxides (EP 30 837) is known. Finally, the principle is also used for the dehydrogenation, dehydrocyclization and dehydroaromatization of paraffin hydrocarbons for refining petrol (US Pat. No. 4,396,537 with Co / P oxide catalysts).

It is known from EP 397 637 and 403 462 to use the process principle for the oxidative dehydrogenation of paraffin hydrocarbons and alkyl aromatics. Thereafter, reducible metal oxides are 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, AI. Catalysts that contain vanadium on magnesium oxide and those that contain bismuth on titanium dioxide are specifically emphasized.

It is obvious that the catalyst for the dehydrogenation reaction should be in the highest possible oxidation state. For example, when using vanadium you will submit V0 ₅ .

Although a high yield can be achieved with these catalysts, in the initial phase of the dehydrogenation, when the hydrocarbon comes into contact with the freshly regenerated and therefore particularly active catalyst, side effects nevertheless occur. reactions (total combustion). Apart from the loss of raw materials, considerably more oxygen is used than for mere dehydration, so that the cycle times and ultimately the life of the catalyst are unnecessarily shortened.

The invention solves the problem of finding an oxygen-transferring catalyst which enables higher conversions than the non-oxidative dehydrogenation and at the same time largely avoids side reactions of the oxidative dehydrogenation in the initial phase, so that the selectivity is increased and additional procedural steps, e.g. a partial pre-reduction of the oxygen carrier can be saved. Another object of the invention is to produce a particularly hard catalyst which can withstand the mechanical stress in industrial reactors without disintegrating. In addition, inexpensive and available carriers with a high surface area and a high pore volume should be able to be used.

Catalysts suitable according to the invention consist of one or more reducible bismuth (5) mixed oxide phases which can be applied to a basic or neutral support and can be regarded as bismuthates (5). Bismutates of Na, K, Cs, Sr, Ba, and La are particularly preferred. K-bismuthates (5) of the general formula KBi _y O _z are particularly preferred, where y can have a value between 0.5 and 2 and z a value between 1.25 and 5.5, so that Bi is at least partially in the high range Oxidation level +5 is present and therefore the catalyst has a high oxide ion potential. Also preferred active phases are Na and Ba bismuthates (5) of the general formula NaBi _s O _c and Ba (Bi _s O _t ) ₂ where s has a value between 0.25 and 3 and t has a value between 1.625 and 5.5 can accept.

K- and Na-bismuthates have already been produced (a production specification is given by Scholder, R. Stobbe, H. in Z. anorg. Allg, Chem. 247, 392 (1941)), which was modified for the present purposes Ba bismuthate according to the invention is a new substance.

A preferred production process for the bismuthates according to the invention is the wet-chemical preparation by oxidation of Bi ₂ 0 ₃ in alkaline solution with bromine, since it can be calcined at low temperature (in comparison to solid-body reactions) and thus maintain the high surface area and the pore volume of the support stay. The bi-mixed oxide active phases are preferably applied to a support, for mechanical reasons

Stability and a high surface area or dispersion. Because acidic carriers promote side reactions such as cracking and coking and thereby reducing the product selectivities of value, basic or at most neutral carriers should be used for the process according to the invention. Basic carriers suitable according to the invention are selected from the group consisting of alkali / alkaline earth / SE / Zn-titanates, alkali / alkaline earth / SE / Zn-Al spinels, alkali / alkaline earth / SE / Zn-silicates, MgO, CaO, hydrotalcites, pyroaurites or alkalized supports such as KF / AI ₂ O3, LiPθ ₄ / Al ₂ θ3 with a basic surface finish or neutral supports selected from the group Sie, Sij ₄ . MgO, Al spinel, SiC are particularly preferred. Such carriers are advantageously inexpensive, easy to manufacture, have large surfaces and good hardness.

The bismuth (5) mixed oxide support catalysts according to the invention can be prepared by known methods, such as dry mixing, precipitation, conspicuity, co-precipitation, spray drying, impregnation, drinking, spray impregnation, hicoating, washcoating, etc.

The dehydrogenation is carried out at 200 to 800 ° C, preferably 350 to 550 ° C, and preferably in the range of atmospheric pressure. For example, the pressure 100 mbar to 10 bar, preferably 500 mbar to 2 bar. The space-time yield (LHSV; liquid hourly space velocity) is 0.01 to 20 h- ¹ , preferably 0.1 to 5 h- ¹ . In addition to the hydrocarbon to be dehydrogenated, diluents such as CO ₂ , N ₂ , an inert gas or water vapor can be present in the feed stream.

The regeneration of the reduced catalyst is carried out in the range 300 to 900, preferably 400 to 800 ° C. with a free oxidizing agent, preferably air, lean air, oxygen or NO. Diluents may be present in the reactor feed. The regeneration can be carried out at subatmospheric negative pressure, atmospheric or superatmospheric pressure. Pressures in the range from 500 mbar to 10 bar are preferred.

Investigation of the catalysts

The catalytic-oxidative dehydrogenation of ethylbenzene to styrene is investigated in a so-called pulse reactor at 500 ° C. 0.3 to 0.6 g of catalyst in a microfixed bed are "pulsating", ie alternately, for 90 seconds with pure ethylbenzene (without carrier gas) and helium as a substitute and the resulting reaction products are quantitatively recorded for each pulse by gas chromatography. The flow rate of the gases is 21.5 ml / min. A single pulse contains approx. 380 μg ethylbenzene. In this way, the time behavior of the catalyst can be tracked from the beginning with a high time resolution without dead times.

At the beginning of the reaction, the catalyst is highly active, so that almost quantitative conversion of ethylbenzene is observed. In the further course of the reaction, the selectivity to styrene steadily improves to an end value. As the duration of the experiment progresses, the catalyst is deactivated more and more as its oxygen content is consumed, so that the conversion decreases. Depending on the catalyst, regeneration takes place after 90 to 200 pulses. The styrene yield as a product of selectivity and conversion generally goes through a flat maximum. The yields determined are listed in the table in part (1st-4th-7th-11th-21st-31st pulse).

After completing a series of measurements, the air flow is switched to 25 ml / min and the catalyst is regenerated for about 1 hour at the reaction temperature. Then the next cycle follows. Several cycles are examined in each case.

General instructions for the production of alkali ismutate (5):

150 ml of 40% sodium hydroxide solution are placed in a 250 ml three-necked flask with a reflux condenser, gas discharge hose, 100 ml dropping funnel and about 10 g of Bi ₂ O _{3 are} added. While stirring, 22.6 ml of bromine are added dropwise in small portions over the course of 2 hours. Brown solid, which is filtered off, washed with 40% sodium hydroxide solution and then in 500 ml of dist. Water is suspended. The suspension is stirred for 3 hours at RT, the color changing from brown to light brown to orange-brown.

It is filtered off, introduced into 100 ml of 53% sodium hydroxide solution and refluxed for 30 min. Brown precipitation. It is suctioned off, washed first with 50% sodium hydroxide solution, then with distilled water. Water and still suspended in 500 ml of distilled water. Water. The mixture is stirred at RT for 30 min, filtered off, washed with dist. Water up to pH 6 and dries over silica gel. Orange solid. Well soluble in HC1, poorly soluble in other acids. Contains about 90% of bismuth as Bi (5). Water content approx. 10% by weight. Water release from approx. 100 ° C. Melting point> 600 ° C. Release of oxygen from approx. 220 ° C.

Production of KBi0 ₃ as above with appropriate adjustment of the amounts of dark red solid. Well soluble in HC1, poorly soluble in other acids. Contains only Bi (5). Water content 1.5 mol per formula unit. Water release from 100 ° C. Melting point above 650 ° C. Release of oxygen from 250 ° C. example 1

Unsupported Ba bismutate full catalyst

(Production of Barium peroxide (Ba0 ₂ ) and Bι ₂ 0 ₃ are mixed in a molar ratio 9: 1 (76.6 and 23.4 wt .-%) and in a tube furnace with a heating and cooling rate of 3 ° C / min twice e six hours calcined at 700 ° C under oxygen. After the first implementation, the mixture is ground again to improve homogeneity.

Olive green material with a melting point above 800 ° C, which contains bismuth exclusively as Bi (5). Sensitive to C0 and water. At around 200 ° C, oxygen is reversibly released.

Example 2

Unsupported K bismutate full catalyst

In 130 ml of 50% KOH solution, 7 g Bι _? 0 ₃ added. With stirring, 13.6 ml of bromine are slowly added in small portions over the course of 2 hours. 50 ml of 40% KOH solution are then added and the mixture is boiled under reflux for 30 mm. The precipitate is filtered off, with 20% potassium hydroxide solution, then with distilled water. Washed water and in 500 ml dist. Water suspended.

The suspension is stirred for 8 hours at room temperature, filtered off, with distilled water. Washed water and dried over P ₄ O ₁₀ .

Production of a Zn-Al-O spinel support (ZnAl ₂ 0)

An aqueous solution of Zn and Al nitrate (atomic ratio

Zn: Al = 12:10) falls is precipitated with aqueous sodium carbonate solution at 70 ^C C while maintaining a constant pH of 7.0 and obtain a white precipitate of sodium with water and nitrate-free, dried at 120 ° C and 16 hours is calcined at 350 ° C. A white powder is obtained.

Example 3

To produce a catalyst which contains 15% by weight of K ₂ 0 and 25% by weight of Bi ₂ 0 ₃ on the aforementioned spinel support (60% by weight), 7.85 g of basic bicarbonate (Bi ₂ C0 ₃ ), 6.24 g K ₂ C0 ₃ and 17 g ZnAl ₂ θ4 spinel, in dist. Slurried water, mixed well and brought to dryness on the water bath with constant stirring. It is calcined at 500 ° C. for 2 hours and a yellow powder is obtained; Surface (BET) of the powder 9 m ² / g. Example 4

K-Bismutate catalyst on MgO as a carrier

For producing 7 g Bi ₂ θ be in 130 mL of 50% KOH solution added, with stirring at the boiling point within 2 hours 13.6 ml of bromine was slowly added in small portions, and then 21 g MgO was added. 50 ml of 40% KOH are added, the mixture is boiled under reflux for 30 min, suction filtered, washed with 20% KOH, then with distilled water. Water and suspended in 500 ml of dist. Water. The suspension is stirred for 8 hours at room temperature, filtered off, with distilled water. Washed water and dried over P ₄ O ₁₀ .

Example 5

K bismuthate on Zn-Al spinel

Preparation of the Zn-Al-O spinel as in Example 3; Application of the K-bismuthate as in example 4

Example 6 K-Bismutate on SiC

Catalyst preparation: 7 g of Bi ₂ O ₃ and 21 g of SiC are added to 130 ml of 50% KOH solution and the rest of the procedure is as described above.

Example 7

Na bismuthate on MgO, analogously to example 4

Comparison test

A catalyst is produced according to the specification of EP-Al-0482 276. 336.3 g of ammonium metavanadate and 900 g of magnesium oxide are stirred into 8 l of water and then stirred vigorously for 1 hour. It is then sprayed on the spray dryer. The spray powder obtained is treated in a kneader for 2 hours, with little water and extractive agents being kneaded into the kneading compound. The modeling clay is then shaped into 3 mm full strands using an extruder. The strands are dried at 120 ° C. for 16 hours and then calcined at 600 ° C. for 4 hours. A uniformly yellow-colored strand with very low hardness is obtained. A 0.05 to 0.1 mm grit fraction is sieved out for the experiments. The catalyst contains 22.5% by weight of V ₂ O and 77.7% by weight of MgO. Table: Sales results in the pulse reactor at 500 ° C

Pulse no .: 1 4 7 11 21 31

Ethylbenzene share (area%)

Comparison 0 0 0 0 0.3 1.1

Example 1 82.6 91 92.3 93 93.8 94.3

Example 2 54.3 63.2 64.8 66.9 73.1 77.2

Example 3 0 0 0 0.4 1.7 4.3

Example 4 5.1 7.6 9.2 11.7 16.4 21.2

Example 5 0 0 0 0.2 1 2.2

Example 6 2.6 5 6.6 9 15.7 17.7

Example 7 15.6 18.9 21.1 26.6 33.1 39

Styrene share (area%)

Comparison 0 0 39.3 74.1 92.5 95.9 Example 1 14 7.9 6.8 6.4 5.6 5.2

Example 2 38.2 35.3 33.9 32 26.1 22.2

Example 3 60.9 79.3 83.4 85.9 88.4 90.9

Example 4 72.4 81.6 83.7 84.2 80.5 76.8

Example 5 64.8 82.3 85.6 87.1 90.4 92.5

Example 6 80.7 86.9 86.2 84.6 79 77.1

Example 7 71 75.5 76.2 71.7 65.2 59.7

CO _x share (area%)

Pulse no .: 1 4 7 11 21 31

Comparison 100 79.2 46.2 25.3 6.9 2.4

Example 1 1.9 0.7 0.5 0.5 0.3 0.3 Example 2 6 0.5 0.3 0.2 0.1 0.1

Example 3 13.4 1.7 0.8 1.2 0.9 0.6

Example 4 9.8 1.8 1.2 0.9 0.8 0.6

Example 5 10.4 1.5 0.9 0.7 0.6 0.3

Example 6 6 1.6 1.4 1.2 0.9 0.9

Example 7 5.1 1.5 1.1 0.9 0.9 0.7 discussion of the results

The comparative catalyst is very active and allows a high maximum styrene yield. The decisive disadvantage is the strong initial gasification, which leads to enormous losses of ethylbenzene and is at the expense of the oxygen reservoir of the catalyst. In particular, the first ethylbenzene pulses are completely burned (100% gasification to worthless carbon dioxide), so that the calculated initial selectivity for styrene over the first pulses is zero. In contrast, the systems according to the invention are characterized by significantly lower gasification with likewise very high activity.

The styrene yield and conversion are clearly above those which can be achieved with the industrially introduced process (non-oxidative dehydrogenation) and at a lower reaction temperature.

The maximum selectivity of the catalyst according to the invention for styrene is comparable to the prior art, the catalyst preparation offering advantages.

Although the catalyst according to the invention produces slightly increased amounts of benzene and toluene in the initial phase, these then decrease rapidly as the reaction time progresses. The formation of benzene and toluene is unproblematic compared to

C0 formation because toluene is a salable product and benzene can be recycled to ethylbenzene production. The catalyst according to the invention is therefore also superior to the prior art in this regard, regardless of the fact that the mean styrene yield, i.e. the total yield of styrene recorded over a whole measuring cycle and related to one cycle is higher than the yield achievable with the known catalysts.

The decisive advantage of the method according to the invention is a significantly reduced one compared to the known methods

Initial gasification, i.e. the overall performance of the catalyst is made possible by better selectivity for styrene at the beginning of a cycle.

With the same manufacturing process, the catalyst according to the invention also has significantly better mechanical strength than the comparison catalyst and is particularly resistant to abrasion.

Claims

claims

1. Process for the oxidative gas phase dehydrogenation of alkyl aromatics or paraffin hydrocarbons to the corresponding alkenyl aromatics or olefins in the presence of an oxygen-transferring catalyst based on bismuth oxide, the alkyl aromatic or paraffin hydrocarbon (educt) being absent in a first reaction step dehydrated by molecular oxygen and in a second

Reaction step, the reduced catalyst is reoxidized, characterized in that a reducible bismuth (5) salt, preferably applied to a support, is used as the catalyst.

Process according to Claim 1, characterized in that a catalyst is used which contains 3 to 70% by weight of alkali metal or alkaline earth metal bismuthate (5) on a basic or neutral support.

3. The method according to .Anspruch 1, characterized in that the catalyst is fixed and the reaction steps are decoupled in time that the input stream of the reactor is periodically switched between the starting material and the regeneration gas.

4. The method according to claim 3, characterized in that a rinsing phase is inserted between the dehydrogenation step and the regeneration step in which the fixed bed reactor is flowed through by a chemically indifferent purge gas.

5. The method according to claim 1, characterized in that the substeps take place spatially separated, the catalyst being particulate and in the form of a circulating fluidized bed or a moving bed.

6. The method according to claim 1, characterized in that the reduced catalyst is regenerated with molecular oxygen or an oxygen gas.

7. The method according to claim 1, characterized in that the reduced catalyst is regenerated with N ₂ 0.

8. The method according to claim 1, characterized in that ethylbenzene is dehydrogenated to styrene.

9. The method according to claim 1, characterized in that at least one bismuthate (5) selected from the 5 calysator

Group Na, K, Cs, Sr, Ba or La bismuthate (5), applied to a basic support, selected from the group alkali, alkaline earth, rare earth, Zn titanate, alkali, alkaline earth -, rare earth, Zn-Al spinel, MgO, CaO, hydrotalcite, 0 pyroaurite, an alkalized carrier such as KF / A1 ₂ 0,

LiP0 / Al ₂ 0 or applied to a neutral support selected from the group SiC and SiN _{4 is} used.

10. Ver ears according to claim 1, characterized in that K or 5 Na bismuthate of the composition KBi0 ₃ or NaBi0 is used.

11. The method according to claim 9, characterized in that K or Na bismuthate (5) is used, as by oxidation of

20 Bi ₂ 0 _{3 is obtained} with bromine in aqueous KOH or NaOH.

12. The method according to claim 1, wherein the oxidative dehydrogenation between 200 and 800 ° C at pressures from 100 mbar to 10 bar with an LHSV of 0.01 to 20 hr ¹ , is carried out.

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13. The method according to claim 12, wherein the oxidative dehydrogenation between 350 and 550 ° C, at pressures from 500 mbar to 2 bar with an LHSV of 0.1 to 5 h ^{-1 is} carried out.

14. Catalyst, in particular for carrying out the method according to claim 1, consisting essentially of Ba bismutate (5) of the composition BagBi ₂ θι carrier-free or on a carrier.

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