WO1997017312A1

WO1997017312A1 - Catalyst and method for the production of styrene and ethylbenzene by the heterogenous-phase catalytic oxidative dehydrogenation of vinylcyclohexenes

Info

Publication number: WO1997017312A1
Application number: PCT/EP1996/004711
Authority: WO
Inventors: Otto Watzenberger; Alfred Hagemeyer
Original assignee: Basf Aktiengesellschaft
Priority date: 1995-11-07
Filing date: 1996-10-30
Publication date: 1997-05-15
Also published as: EP0861222A1; DE19541383A1

Abstract

Proposed is a method for the oxidative dehydrogenation of 4-vinylcyclohexene, in the absence of molecular oxygen, over a redox catalyst used as the oxygen source, the catalyst consisting of a reducible metal oxide selected from the oxides of Bi, Ce, Co, Cr, Cu, Fe, In, Mn, Mo, Nb, Ni, Sb, Sn, Pb and V and being regenerated, when it is exhausted, with an oxygen-containing gas or pure oxygen. The catalyst is either rigidly mounted in a preferably tubular reactor or is used in a circulating fluidized bed or in a travelling bed in the form of mobile granules which travel in a circuit between a dehydrogenation chamber and a separate regeneration chamber.

Description

Catalyst and process for the preparation of styrene and ethylbenzene by heterogeneously catalyzed, oxidative dehydrogenation of vinylcyclohexene

description

The invention relates to a process for the preparation of styrene and / or ethylbenzene from 4-vinylcyclohexene (VCH).

Styrene (SM) is an important monomer for engineering plastics and is used in large quantities. It is produced practically exclusively by non-oxidative dehydrogenation of ethylbenzene (EB). The cost-effectiveness of producing styrene is therefore dependent on the availability of ethylbenzene and thus on the raw material source used to obtain ethylbenzene.

In the so-called steam cracker process for producing ethylene, a butadiene-containing crude C ₄ stream is obtained as a by-product, from which butadiene can be obtained, which can be converted into 4-vinylcyclohexene in very high yield by dimerization. VCH is therefore available as a cheap intermediate for the production of styrene.

The object of the invention is to provide a route which is competitive with the usual synthetic route for styrene and which starts from the availability of vinylcyclohexene.

It is known per se to dehydrate 4-vinylcyclohexene to ethylbenzene (on platinum catalysts; cf. US Pat. No. 3,903,185 (1)). A process using an alkali metal catalyst is described in DE-A-25 11 674 (2). According to (1), the selectivity should be 90% with complete conversion. Hydrogen is added to avoid catalyst coking. As byproducts, 0.2-1% of xylene isolates are formed in each case, which, because of the very similar boiling points of ethylbenzene or styrene and xylenes, must be separated off before the ethylbenzene is dehydrated to styrene on iron catalysts as usual can. For the production of styrene in this way, at least three steps would be necessary to get from VCH to styrene. This is disadvantageous in terms of investment requirements and energy costs.

The dehydrogenation of VCH to a mixture of styrene and ethylbenzene is also known (SU-A-330 346; WO 94/01385). According to SU-A-1 616 885, VCH can be added to the non-oxidative dehydration of ethylbenzene to styrene.

Other methods of this type are e.g. in U.S. Patent Nos. 4,665,252, 4,367,358, 4,375,571, 4,029,715, 4,163,761, 4,237,070, 4,429,175 and 4,359,594. A disadvantage of these processes is the excess EB formed or the low selectivity for styrene, so that a second dehydrogenation stage and possibly an upstream distillative purification is necessary.

Basically, oxidative dehydration, i.e. Implementation of VCH with a suitable oxidizing agent, such as molecular oxygen, overcome the thermodynamically based equilibrium limitation of the nonoxidative dehydrogenation and achieve almost quantitative conversion. In this way, the SM / EB ratio in the product range can be increased. This implementation can also take place at a lower temperature because there is no need to consider the establishment of an equilibrium. However, the occurrence of side reactions, in particular total oxidation to carbon oxides, is disadvantageous.

The possibility of oxidative dehydrogenation of VCH with molecular oxygen is e.g. with Dixit and Murchison "Crude Butadiene to Styrene Process", AICHE 1994; Spring National

Meeting, Atlanta, 1994 described that a selectivity of 85.1% (styrene) or 8.2% (ethylbenzene) is achieved at 82.2% conversion, and in an SRI report (PEP review 77-1-4). An overview of the state of the art can also be found in these publications.

The oxidative dehydrogenation of VCH with molecular oxygen is highly exothermic; The technical feasibility depends, among other things, on how the heat can be dissipated via the reactor walls. For example, a corresponding salt bath reactor must be equipped with a very large number of relatively thin tubes, which leads to correspondingly high investment costs. In addition, a slow deactivation of the catalyst, presumably due to the formation of coke, is observed. The use of a fluidized bed reactor has therefore been proposed. Fluidized bed reactors are disadvantageous due to the inevitable backmixing if a high turnover is to be achieved. Another disadvantage of oxidative dehydrogenation with molecular oxygen is the formation of partially oxidized compounds such as benzoic acid and benzaldehyde, which can cause corrosion problems. ^"

The object of the invention is to overcome the disadvantages described above and is therefore based on a process for the non-stationary oxidative dehydrogenation of a hydrocarbon in the presence of a redox catalyst, the dehydrogenation reaction being carried out in the absence of molecular oxygen and instead the redox catalyst consisting of at least one reducible metal oxide acts as the sole oxygen source, which thus takes over the function of an oxygen store and is regenerated in each case after exhaustion.

According to the invention, it is proposed to dehydrogenate 4-vinylcyclohexene to styrene and / or ethylbenzene according to the above process, VCH in a first step with a catalyst acting as an oxygen carrier essentially consisting of at least one reducible metal oxide in the absence of free molecule ¬ larem oxygen and the catalyst is reduced and in a second step, after separation of the products formed, the reduced catalyst is reoxidized (regenerated) with an oxidizing agent.

Metal oxides selected from the group of the oxides of Bi, Ce, Co, Cr, Cu, Fe, In, Mn, Mo, Nb, Ni, Sb, Sn, Pb and V are preferably used as regenerable catalysts. The metal oxides can be applied carrier-free or on a carrier which is optionally selected from the group of clays, PILC, zeolites, aluminum phosphates, silicon carbide and nitride, boron nitride and carbon and the metal oxides from the group of the oxides of Al, Ba , Ca, Mg, Th, Ti, Si, Zn or Zr.

The principle of separating two sub-steps into a working and a regeneration phase using a reducible and regenerable catalyst that is involved in the implementation (regenerative principle) is known per se and was used, for example, for the oxidation or ammoxidation of propene to acrolein and Acrylic acid or acrylonitrile is described (GB-A-885 422; GB-A-999 629; K. Aykan, J. Catal. 12 (1968) 281-190. It has also been proposed to use the principle of the process for the oxidative dehydrogenation of aliphatics and alkyl aromatics using catalysts based on V / MgO (EP-A-397 637, EP-A-403 462) However, the feasibility of such a process depends to a large extent on the availability of a suitable catalyst. The invention provides such a catalyst. When using the regenerative principle according to the invention, the oxidized catalyst releases lattice oxygen during the reaction and is regenerated in a second step with an oxidizing agent, preferably oxygen or N ₂ O.

By decoupling the reduction and oxidation step, the selectivity is increased and the controllability is improved: Thereby, when the catalyst is arranged in a fixed bed, it progresses

- The implementation and regeneration in the form of a front continues, so it is easy to monitor.

The absence of free oxygen during the conversion of the valuable substance (the work phase) largely avoids total combustion, since the lattice oxygen of the catalyst serves as a targeted oxygen source and the conversion of VCH to styrene is slightly endothermic. Any coke deposits are removed during reoxidation (regeneration phase).

The strongly exothermic regeneration can be used for the production of steam, the local heat release being determined by the local concentration of available oxygen.

Apart from the dilution of the regeneration gas, such as the use of air, the local heat release can also be controlled by measures on the catalyst itself. 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 support or by mixing active catalyst storage material with inert material. The local temperature rise can thus be determined in advance and the thermal load on the catalytic converter can be limited to a permissible level.

In the technical implementation of the method according to the invention, the work phase can also be spatially separated from the regeneration phase in addition to time.

The time separation can, as already indicated, be realized with a fixed bed in alternating operation, with periodic between the educt supply and - possibly after a purging phase with inert gas

- The regeneration gas is switched. The technical implementation with two or more alternately operated fixed bed reactors enables the decoupling and beneficial use of the heat energy released.

In the case of spatial separation (circulating fluidized bed or moving bed), a technology can be used as is known from refinery technology, e.g. using a so-called riser reactor, the catalyst being moved in a circle between a dehydrogenation space, separation of the reaction products formed and a regeneration space. However, the catalyst is exposed to high mechanical stress and must be sufficiently hard and resistant to abrasion.

The invention provides a particularly suitable catalyst system which, with complete conversion, enables a higher selectivity to styrene and ethylbenzene than the oxidative dehydration and at the same time largely avoids the disadvantage of the strong gasification observed in the initial phase of the dehydration, so that the value-product selectivity is increased and complex additional procedural steps (eg partial pre-reduction with expensive reducing agents) can be completely dispensed with.

Catalysts suitable for the process according to the invention can be unsupported or supported on redox catalysts, the active ingredient of which consists of at least one oxide selected from the group of oxides of the elements Bi, Ce, Co, Cr, Cu, Fe, In, Mn, Mo, Nb, Ni, Sb, Sn, Pb and V. The carrier can be selected from the group of clays, PILC, zeolites, aluminum phosphates, silicon carbide and nitride, boron nitride and carbon as well as metal oxides from the group of oxides of Al, Ba, Ca, Mg, Th, Ti, Si, Zn or Zr.

Bi- and V-containing redox catalysts are preferred. Mixtures and reaction products of the elements mentioned can also be used. The catalysts can also additives, in particular (earth) alkali metals and / or rare earths i.a. contained in the form of their oxides.

Reducible bismuth oxide such as Bi ₂ θ ₃ on a basic support, preferably basic titanium dioxide, is preferably used as a catalyst for the process according to the invention. It was also found that by doping this catalyst with K, Cs, Ba and / or La the selectivity can be increased without loss of activity and the gasification (total oxidation) can be significantly reduced. A preferred catalyst contains 3 to 30, preferably 5 to 20% by weight of K ₂ 0.0 to 30, preferably 0 to 20% by weight of Cs ₂ 0.0 to 30, preferably 0 to 20% by weight of BaO, 0 to 40, preferably 5 to 30% by weight La ₂ θ ₃ , 5 to 50, preferably 10 to 30% by weight Bi ₂ 0 ₃ , balance Ti0 ₂ . It goes without saying that several promoters can be present at the same time, for example K / La / Ti0 _{2 in} addition to the element - preferably bismuth - which carries the oxygen balance.

The catalysts can be prepared in a customary manner, such as dry mixing, slurrying, impregnation, co or separate precipitation of the raw materials, spray drying, etc. A large number of compounds can be used as raw materials, e.g. the oxides, hydroxides, carbonates, acetates, nitrates or generally water-soluble salts of the respective metal atoms with inorganic or organic anions. Transition metal complexes can also be used. The calcination then takes place at temperatures at which the raw materials are converted into the active phase, usually oxides. Typical calcining temperatures are in the range from 300 to 1000, preferably 400 to 800 ° C.

If lanthanum is also used, experience has shown that La oxide carbonate, La (OH) ₃ , La ₂ (00 ₃ ) ₃ or organic La compounds, preferably acetate, formate or oxalate, should be used instead of La ₂ 0 ₃ , since A finely divided and surface-rich active La phase then forms in the catalyst during the calcination. A preferred calcining temperature for La (Ac) ₃ is 550 to 700 ° C. The material conversion (dehydration; working phase) is carried out at 100 to 800, preferably 350 to 550 ° C, and at pressures from 100 mbar to 10 bar, preferably 500 mbar to 2 bar, with a liquid hourly space velocity (LHSV) from 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 , noble gases or steam can be present.

The regeneration of the catalyst is carried out in the range 300-900 ° C., preferably 400-800 ° C. with preferably N ₂ 0 or an oxygen-containing gas including pure oxygen. Diluents can also be present. The regeneration can be operated at subatmospheric, atmospheric or overpressure. Pressures in the range from 500 mbar to 10 bar are preferred.

Examples

A catalyst was obtained as follows: Lanthanum acetate, bismuth carbonate and potassium carbonate were used in the intended

Appropriate composition dry mixed with Ti0 ₂ and compressed in a kneader. During the kneading phase is distilled with Water and an extrusion aid. The mass is dried at 120 ° C for 16h and then calcined at 600 ° C. A beige-yellow powder is obtained, which is comminuted (split) to a grain diameter of less than 1 mm. A portion of the chippings is mixed with a tabletting aid and compressed to ring tablets of 5 x 5 x 2 mm. The side pressure of the tablets before the calcination is 16.4 N. It is calcined for 2 hours at 500 ° C. in order to burn out the tabletting aids. Light gray tablets are obtained.

The side pressure after the calcination is 12 N. The BET surface area is 14.8 m ² / g. The finished catalyst finally contains - arithmetically - 13% by weight K ₂ 0, 13% by weight La ₂ θ ₃ , 25% by weight Bi ₂ 0 ₃ and 49% by weight Ti0 ₂ .

VCH was diluted with nitrogen at a space velocity of 0.41 ml per ml of catalyst bed and passed over the catalyst fixedly arranged in a tube (50% by volume of the rings and grit of 1-2 mm size described above) . The initial weight was 470 g of catalyst and the residence time was 3.7 s.

The gas leaving the reactor was condensed and the condensed liquid phase was analyzed by gas chromatography 7, 9, 10 and 16 minutes after the start of the experiment. The result is shown in Table 1 for two experiments. Between the two tests, the catalyst was reoxidized with air for 10 min. The rinsing phase before and after the oxidation with air was 6 minutes.

Table 1

Time turnover selectivity T% 1

[min] VCH [% enzol toluene EB styrene

Trial 1:

7 99.1 2.3 0.8 75.0 17.9

9 99.5 2.8 1.1 40.0 53.7

10 99.2 2.5 0.9 57.7 35.7

16 99.6 2.7 1.6 44.2 49.2

Trial 2:

7 99.6 2.5 1.8 49.3 43.8

9 99.7 2.9 1.4 37.8 55.6

10 99.5 2.6 1.0 54.0 39.3

16 99.4 2.3 0.9 73.9 19.3 A temperature drop of 20 K was observed in the reaction front during the working phase (dehydration of VCH). A corresponding temperature rise of up to ^" 120 K occurred in the oxidation step.

Claims

claims

1. Process for the non-stationary oxidative dehydrogenation, whereby the dehydrogenation reaction is carried out in the absence of molecular oxygen and instead the redox catalyst consisting of at least one reducible metal oxide acts as the essentially sole oxygen source and is regenerated after exhaustion, characterized in that in a first reaction step

4-vinylcyclohexene with a catalyst acting as an oxygen transfer agent is converted essentially from at least one reducible metal oxide in the absence of free molecular oxygen to styrene and / or ethylbenzene, the catalyst being reduced and the reduced catalyst in a second reaction step, after separation of the products formed, is reoxidized with an oxidizing agent.

2. The method according to claim 1, characterized in that the

Partial steps are decoupled in time by the catalyst being fixedly arranged in a reactor which is preferably designed as a tube and which is periodically alternately charged with the starting material and the regeneration gas.

3. The method according to claim 2, characterized in that the

Flushing gas flows through the catalyst between the dehydrogenation step and the regeneration step.

4. The method according to claim 1, characterized in that the

Partial steps are spatially decoupled by the catalyst being in a circulating fluidized bed or a moving bed in the form of movable particles which are circulated between a dehydrogenation space and a separate regeneration space.

5. The method according to claim 1, characterized in that the reduced catalyst is regenerated with an oxygen-containing gas or pure oxygen.

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

7. The method according to claim 1, characterized in that the dehydrogenation between 200 and 800 ° C, at pressures from 100 mbar to 10 bar with a space velocity (LHSV) of 0.01 to 20 h " ^{1 is} carried out.

5

8. The method according to claim 7, characterized in that the dehydrogenation between 350 to 550 ° C, at pressures from 500 mbar to 2 bar, with a space velocity (LHSV) of 0.1 to 5 h ^{_1 is} carried out.

10

9. The method according to claim 1, characterized in that a carrier-free or on a carrier selected from the group of clays, PILC, zeolites, aluminum phosphates, silicon carbide and nitride, boron nitride and carbon and the metal oxides,

15 selected from the group of oxides of Al, Ba, Ca, Mg, Th,

Ti, Si, Zn or Zr applied redox catalyst made from at least one oxide, selected from the group of oxides of the elements Bi, Ce, Co, Cr, Cu, Fe, In, Mn, Mo, Nb, Ni, Sb, which assume several oxidation levels , Sn, Pb and V is used.

20th

10. The method according to claim 9, characterized in that the redox catalyst further comprises at least one component from the group of alkali metals, alkaline earth metals and / or rare earth metals, optionally in the form of an oxide or one

25 contains compound with another catalyst component.

11. The method according to claim 1, characterized in that the redox catalyst contains at least one reducible vanadium oxide on a magnesium oxide support.

30

12. The method according to claim 1, characterized in that the redox catalyst contains at least one reducible bismuth oxide on a titanium dioxide support.

35 13. The method according to claim 1, characterized in that the

Redox catalyst contains at least one reducible bismuth oxide on a titanium dioxide support and at least one further component, selected from the alkali, alkaline earth and / or rare earth metals.

40

14. The method according to claim 13, characterized in that the redox catalyst contains K, Cs, Ba and / or La.

45

15. The method according to claim 1, characterized in that the catalyst - arithmetically - 3 to 30 wt .-% K ₂ CT, 0 to 20 wt .-% Cs ₂ 0, 0 to 30 wt .-% BaO, 0 to 25 Wt .-% La ₂ 0 ₃ , 5 to 50 wt .-% Bi ₂ Ü ₃ and the rest contains Ti0 ₂ .