WO1997041192A1

WO1997041192A1 - Catalyst and its use for dehydrogenating paraffinic/naphtenic hydrocarbons

Info

Publication number: WO1997041192A1
Application number: PCT/EP1997/002040
Authority: WO
Inventors: Daniel Heineke; Alfred Hagemeyer; Joachim Wulff-Döring; Christopher William Rieker; Werner Schnurr
Original assignee: Basf Aktiengesellschaft
Priority date: 1996-04-26
Filing date: 1997-04-23
Publication date: 1997-11-06
Also published as: DE19616738A1; EP0907696A1

Abstract

This invention concerns a catalyst, particularly for producing aromatic compounds with 6 to 8 atoms from non-aromatic hydrocarbons with straight-chained, branched and/or cyclic alkyl or alkylene chains, respectively, with 6 to 8 carbon atoms containing essentially at least one oxide of a transition metal of the IVB group of the periodic system and, optionally, one alkaline metal or alkaline earth metal compound and/or a compound of the third main or secondary group of the periodic system and/or a rare earth metal zinc compound or a mixture thereof, with the condition that the compounds change into the corresponding oxides upon calcination.

Description

Catalyst and its use for the dehydrogenation of paraffinic ^■ rule / naphthenic hydrocarbons

description

The invention relates to a catalyst and its use for the dehydrogenation of paraffinic / naphthenic hydrocarbons which have straight-chain, branched or cyclic alkyl or alkylene radicals having 6 to 8 carbon atoms. The invention relates in particular to the production of aromatic compounds having 6 to 8 carbon atoms.

The most important source of technically important Cε to Ca aromatics such as benzene, xylenes or ethylbenzene is large-scale reforming. In the reforming, straight-chain paraffin hydrocarbons are converted into branched paraffin hydrocarbons and aliphatic-aromatic and aromatic hydrocarbons. This process is used on the one hand to increase the knock resistance of petrol fuels, i.e. the reaction mixtures obtained remain essentially unchanged; on the other hand, the aromatic compounds formed are e.g. separated by distillation and found as intermediates and synthesis building blocks e.g. for the production of synthetic rubbers and synthetic fibers. The ethylbenzene formed from components of the Cs fraction is used, for example, to obtain styrene, the starting material for polystyrene.

Catalytic reforming finds a variety of

Reactions instead of like isomerization, aromatization (dehydration) and cyclization. The process, which takes place at temperatures from 450 to 550 ° C and pressures from 15 to 70 bar, is usually controlled by supported platinum catalysts.

Catalysts which contain other metals besides platinum, such as Pt-Re / Al ₂ θ ₃ .Si0 ₂ or Pt / Sn / Al ₂ 0 ₃ .Si0 ₂ (so-called bimetallic catalysts) are also known; for example, a catalyst based on Pt / Sn / Al ₂ 0 ₃ in J. Mol. Catal. .88. (1994) 359-376. The carrier materials are mostly aluminosilicates or zeolites. Pt catalysts on L-zeolites (cf. Energy Progress 1, (1987), 215-222) achieve a high aromatic selectivity, which is attributed to the shape selectivity of the support, but with a low space-time yield. In contrast, multi-stage catalysts such as Pt / Co / Nd (US Pat. No. 4,136,130) or Pt / Co / Re / Ge (US Pat. No. 4,136,017) on non-zeolitic chlorinated Al ₂ O ₃ supports develop higher activity, but tend to do so to Formation of crack products and thus less aromatic selectivity, especially with regard to the formation of Cβ aromatics (ethyl- 'benzene;styrene; xylenes).

Above all, the aforementioned catalysts have the disadvantage of being precious metal catalysts, i.e. they are expensive, especially if they have to contain other, also rare, components such as rhenium or palladium. It is also disadvantageous that catalysts containing noble metals do not achieve a long service life because the active constituent, which is in elemental form, tends to agglomerate at a process temperature of 450 to 550 ° C. and possibly subsequently to sintering, that is to say to the loss of an effective surface, and is therefore rapid loses activity. Finally, it is disadvantageous that platinum catalysts promote coking and therefore from time to time - usually in a reductive atmosphere, i.e. using hydrogen - must be regenerated to remove the deposited carbon. In order to prevent coking, large amounts of hydrogen are also added to the hydrocarbons to be reacted, which counteract the formation of the target product in the case of dehydrogenation reactions such as the formation of ethylbenzene or even styrene and promote the hydrolytic cleavage to give low-molecular fragments.

Precious metal-free catalysts are in the DD patent

149 210. These are conventional dehydrogenation catalysts based on K ₂ 0 / Cr ₂ θ ₃ / Al ₂ 0 ₃ / Si0 ₂ , but which contain chromium, which is now unpopular due to its toxicity. In addition, the carrier used is again a zeolite, which experience has shown allows only a low space-time yield.

The object of the invention is to create a catalyst which does not have the disadvantages mentioned and can convert C ₆ to Cs hydrocarbon streams to aromatics in high yield.

This object was achieved by using a noble metal-free catalyst based on an oxide of a metal from group IV B of the periodic table, in particular Zr0 ₂ and Ti0 ₂ . The oxide according to the invention also acts as a catalyst and as a carrier, so that ideally no other carrier auxiliary has to be used.

A particularly favorable result is achieved if the metal oxide from group IV B together with one or more compounds from the third main or subgroup of the periodic Stems or combined with basic additives such as alkali or alkaline earth metal compounds, rare earth or zinc "compounds which are converted into the corresponding oxides by calcining at a higher temperature. Several of the compound classes mentioned can be used simultaneously.

The catalysts according to the invention are considerably cheaper than the known noble metal catalysts and their selectivity, i.e. the preference for the conversion of aliphatic to aromatic hydrocarbons is very good. In particular, however, they are very insensitive to coking and, if necessary, can be regenerated either reductively, for example with hydrogen, or oxidatively, for example with air. Regeneration with air in particular is cheaper than conventional regeneration, e.g. with hydrogen. It also proves to be an advantage that the processes can be operated using the catalysts according to the invention without adding hydrogen to the reaction mixture. Other advantages are high mechanical strength, long service life and easy shaping.

To prepare the catalysts according to the invention, amphoteric oxides of the IV-B metals in question or mixtures thereof or suitable precursors which can be converted into the oxides by calcining can be used. Known elements such as the sol-gel process, precipitation of the salts, dewatering of the corresponding acids, dry mixing, slurrying and spray drying can be used to carry out the individual steps of the production process. In the case of the basic compound, the doping can be carried out during production, for example by co-precipitation or subsequently, for example by impregnating the catalyst oxide with a dissolved alkali metal or alkaline earth metal compound or a compound of the 3rd subgroup or a rare earth metal compound and, if appropriate, re-calcining happen.

The catalyst can be in the form of shaped articles such as grit, tablets or spheres or as an extrudate with a suitable cross section, e.g. in the form of wagon wheels, stars, monoliths or rings.

The content of additives (alkali metal, alkaline earth metal, metal of the third main or subgroup, rare earth metal, zinc) can be up to 20% by weight, preferably between 1 and 15% by weight, particularly preferably between 1 and 10% by weight. -% lie. As an alkali and alkaline earth metal supplier, use is generally made of compounds which can be converted into the corresponding oxides by calcining. For example, hydroxides, carbonates, oxalates, Acetates, nitrates or mixed hydroxycarbonates of the alkali and alkaline earth metals.

If the group IV-B support is additionally or exclusively doped with a metal from the third main or subgroup, then one should also start from compounds which can be converted into the corresponding oxides by calcining. If lanthanum is used, then for example lanthanum oxide carbonate, La (OH) ₃ , La ₃ (C0 ₃ ) ₂ , La (N0 ₃ ) ₃ or lanthanum compounds containing organic anions, such as La acetate, La formate or Suitable for la-oxalate.

The catalysts of the invention have a high BET surface area. Depending on the production, a BET surface area of up to 500 m ² / g, usually up to 300 m ² / g, is observed. Are suitable

Catalysts with a surface of 10-100 m ² / g. The pore volume is generally between 0.1 and 1 ml / g, mostly between 0.1 to 0.6 ml / g, pore volumes of 0.15 to 0.5 ml / g are particularly preferred. The average pore diameter, which can be determined by mercury penetration analysis, is between 0.008 and 0.06 μm, mostly between 0.01 and 0.04 μm.

The intended use requires reaction temperatures of 300 to 800 ° C, preferably 400 to 600 ° C at pressures from 100 mbar to 100 bar, preferably 1 bar to 40 bar with an LHSV (Liquid Hourly Space Velocity) of 0.01 to 100 h 1, preferably 0.1 to 20 h " ^1. In addition to the Cβ-Cβ hydrocarbon mixture to be dehydrogenated, diluents such as C0 ₂ , N ₂ , noble gases or steam may be present separates, hydrogen can be added, the molar ratio of hydrogen to hydrocarbons being 0.1 to 100, but usually less than 20.

In addition to the continuous addition of a gas which prevents coking during the reaction, there is the possibility of regenerating the catalyst from time to time by passing hydrogen or oxygen, for example air. As already mentioned, a particular advantage of the catalyst according to the invention is that the regeneration of the catalyst can be carried out in one step, both reductively and oxidatively. Regardless of the process chosen, the regeneration takes place in the range from 300 to 900, preferably 400 to 800 ° C. and can take place at reduced, atmospheric or elevated pressure. Pressures in the range of 500 mbar to 100 bar are suitable. Examples

'' Catalyst production:

Strands with a diameter of 3 mm were produced from commercial Zr0 ₂ (commercial product XZ 16075 from Norton; largely monoclinic), which had a BET surface area of 46 m ² / g, a pore volume of 0.23 ml / g (Hg porosimetry ) and had a proportion of pores with more than 20 nm of about 15%.

The absorption capacity of these strands for water was determined and in each case 70 g were soaked in water with the required amount of correspondingly concentrated solutions of La (NO ₃ ) ₃ , so that the catalyst finally contained approx. 1 or 3 or 5% lanthanum . To produce a catalyst with about 3% lanthanum, for example, 6.75 g of La (N0 ₃ ) ₃ in 19.1 ml of water were used. The soaked strands were left to stand at room temperature for 2 hours, dried at 120 ° for 16 hours and calcined at 600 ° C. for 4 hours. A macroporous Zr0 ₂ (BET surface area approx. 10 m ² / g) and a commercially available Ti0 ₂ (Finnti S140, Kemira) were also used.

Pulse reactor

The reactions were carried out in a microfixed bed pulse reactor through which helium as the carrier gas flowed at 450 (example 2) or 500 ° C. (remaining examples). For this purpose, about 0.6 g of catalyst was weighed into a fixed micro-bed and the carrier gas was pulsed with pure n-octane at atmospheric pressure and a flow rate of approx. 21.5 ml / min. A single pulse contains approx. 100 μg n-octane. The reaction products were quantified for each pulse on-line by gas spectrometry (GC-MS) evaluated by mass spectrometry. The results (see Table 1) relate to the point in time when the maximum turnover was reached.

Table 1: Summary of the results

* Commercially available comparative catalyst a) conversion, based on n-octane (GC areas) b) sum of m- and p-xylene c) sum of all aromatics recorded d) sum of all Cβ-aromatics

At the same reaction temperature, the noble metal-free catalyst according to the invention achieves a significantly better overall selectivity (proportion of aromatics formed) than the commercially available comparative catalyst. Particularly noteworthy is the high proportion of C ₈ aromatics, which indicates that side reactions which lead to crack products are suppressed.

Claims

claims

1. Catalyst, especially for the production of aromatic

Compounds with 6 to 8 carbon atoms from non-aromatic hydrocarbons with straight-chain, branched and / or cyclic alkyl or alkylene chains with 6 to 8 carbon atoms, containing essentially at least one oxide of a transition metal from group IVB of the Periodic table.

2. Catalyst according to claim 1 or its precursor, containing an alkali or alkaline earth metal compound and / or a compound of the third main or subgroup of the periodic table and / or a rare earth or zinc compound or mixtures thereof, with the proviso that the compounds at Calcinate into the corresponding oxides.

3. Catalyst according to claim 1, essentially free of metals from subgroup 8 of the periodic table.

4. Catalyst according to claim 1, containing zirconium or titanium or their oxides.

5. Catalyst according to claim 2, containing lithium, sodium, potassium or cesium or their oxides.

6. A catalyst according to claim 2, containing a lanthanum, yttrium, gallium, indium or thallium compound as the compound of the third main or subgroup.

Catalyst according to claim 2, comprising a compound of the samarium and / or the lanthanum.

8. A catalyst according to claim 1, characterized in that the BET surface area of the catalyst is 10 to 100 m ² / g.

9. Use of the catalyst according to claim 1 for the production of aromatics from hydrocarbon streams with straight-chain, branched or cyclic alkyl or alkylene chains having 6 to 8 carbon atoms.

10. Use of the catalyst according to claim 1 for the production of a mixture of ethylbenzene and isomers of xylene from non-aromatic hydrocarbons with straight-chain, branched and / or cyclic alkyl or alkylene chains with 6 to 8 carbon atoms.