WO2008135581A1

WO2008135581A1 - Iridium catalysts for converting hydrocarbons in the presence of water vapour and especially for the steam dealkylation of alkyl-substituted aromatic hydrocarbons

Info

Publication number: WO2008135581A1
Application number: PCT/EP2008/055584
Authority: WO
Inventors: Marco Bosch; Dirk Neumann; Götz-Peter SCHINDLER; Heinrich Laib; Armin Lange De Oliveira
Original assignee: Basf Se
Priority date: 2007-05-08
Filing date: 2008-05-07
Publication date: 2008-11-13

Abstract

The invention relates to a catalyst containing iridium, to the use thereof for converting hydrocarbons in the presence of water vapour, and especially the use thereof for the dealkylation of alkyl-substituted aromatic hydrocarbons comprising between 7 and 12 carbon atoms to form benzene. The invention also relates to a method for converting hydrocarbons in the presence of water vapour using the catalyst containing iridium.

Description

Iridium catalysts for the reaction of hydrocarbons in the presence of water vapor and in particular for the vapor dealkylation of alkyl-substituted aromatic hydrocarbons

description

The present invention relates to an iridium-containing catalyst, its use for the reaction of hydrocarbons in the presence of water vapor and in particular its use for the dealkylation of alkyl-substituted aromatic hydrocarbons having 7 to 12 carbon atoms to benzene and a process for the reaction of hydrocarbons in the presence of Water vapor using the iridium-containing catalyst.

The utilization of hydrocarbons in the presence of water vapor can be done by various reactions and processes. A common process is the so-called steam reforming, in which the hydrocarbons are converted in the presence of water vapor to hydrogen, carbon monoxide and carbon dioxide. Alkyl-substituted aromatic hydrocarbons can be reacted in the presence of steam in the so-called steam dealkylation to the corresponding aromatics, hydrogen, CO, CO ₂ and further reaction products.

The dehydrogenation of hydrocarbons is often carried out in the presence of water, although the water does not participate in the actual dehydrogenation reaction. However, it has an advantageous effect on the catalyst service lives, since the water vapor reduces coke deposition by converting the coke into carbon monoxide and carbon dioxide.

The reactions listed above for the reaction of hydrocarbons in the presence of water vapor usually take place in the presence of a catalyst. US 4,233,186 describes a catalyst for the steam dealkylation of mono- and poly-alkyl-substituted aromatic hydrocarbons, the 0.1 to 5 wt .-% of a metal of group 8, 9 or 10 of the Periodic Table of the Elements (PSE, IUPAC nomenclature) on a Contains spinel carrier. The carrier has the composition (M _x MV _x) Al ₂ O _4, where M denotes a metal from group 8, 9 or 10 of the Periodic Table and M 'is a metal of Group 2, 7, 11 or 12 of the PTE. With (Nio, ₂₅ Mgo, ₇₅ ) Al ₂ O ₄ as carrier, which contains 0.5% by weight of rhodium and 0.1% by weight of iridium as catalytically active metals, in the reaction of toluene with water vapor 48, 5 wt .-% of the toluene reacted with a selectivity to benzene of 93.5 Wt .-%. When using 0.1% by weight of palladium instead of the iridium, a toluene conversion of 45.5% by weight is achieved with a benzene selectivity of 95.5% by weight. The yields of benzene are thus 43 to 45 wt .-%.

No. 4,207,169 discloses a catalytic process for the steam dealkylation of alkyl-substituted aromatics on catalysts based on an alumina carrier which contains 0.1 to 1% by weight of rhodium and 0.05 to 1% by weight of titanium dioxide. On the catalyst support further metals of the Pt group, alkali metals and other metals may be applied. When rhodium was used in combination with iridium (0.3 or 0.4% by weight), 39% by weight of benzene were obtained on reaction of toluene in the presence of steam, the combination of rhodium with palladium (0.3 or 0.4% by weight) 0.4% by weight) led, depending on the content of further metal compounds, to 37% and 40% by weight, respectively, of benzene yield.

No. 3,775,504 relates to the dealkylation of alkyl-substituted aromatics in the presence of water vapor over catalysts comprising at least one group 8, 9 or 10 metal of the PSE on a support, the support comprising at least 50% by weight of α-Al ₂ O ₃ has. Furthermore, the catalyst may optionally contain alkali and alkaline earth oxides. The reaction of the alkyl-substituted aromatics proceeds not only in accordance with the steam dealkylation reaction but also with consumption of the resulting hydrogen according to the hydrodealkylation reaction in which alkyl-substituted aromatics react to the corresponding aromatics and alkanes. Both reactions are catalyzed by the same catalyst. In the example given, in the reaction of toluene in the presence of a catalyst with 0.55 wt% Pt on a support consisting mainly of Ci-Al ₂ O ₃ , a benzene yield of 32 wt .-% was obtained.

In US 3,829,519, the reaction of alkyl-substituted benzene having 7 to 9 carbon atoms in the presence of water vapor and hydrogen is described tor to a catalytic converters, whose carrier consists essentially of Al ₂ O ₃ and at least one metal of group 8, 9 or 10 of the PSE. Preferred active metal components are iridium and platinum. In addition to vapor alkylation, steam reforming also takes place during the reaction and, in the presence of aliphatics in the reaction mixture, their conversion to aromatics. In the reaction of toluene in the presence of steam and hydrogen, 80% by weight benzene yield was achieved when using 0.5% by weight Ir on .alpha.O.sub.2 O.sub.3 as the catalyst, and 0.7% by weight Pt was used as the catalyst. Al ₂ O ₃ 79 wt .-% benzene yield. Duprez (Appl. Catal. A: Gen. 1992, 82, 111-157) has compiled a comprehensive review of studies on the vapor dealkylation of toluene and other alkyl-substituted aromatics. Alumina-based catalysts, each containing a Group 8, 9 or 10 metal of the PSE, are compared by rhodium-based relative "turn over frequencies" (TOF), which provides a measure of the catalytic activity of the individual metals Rhodium is the most active metal by far and iridium is one of the least active metals, by definition the relative TOF of rhodium is 100%, but iridium is 14% or less Selectivities of the various platinum metals in the vapor dealkylation of toluene to benzene, the metals Rh, Pd, Os, Ir, and Pt have higher benzene selectivities than Ni, Co, and Ru. Pt, Pd and Ir, however, perform significantly better than Rh Pt, Thus, Pd and Ir have higher selectivities to benzene in the vapor dealkylation of toluene, but at the same time they are significantly less reactive than Rh. Rh is that in catalyzato For the vapor dealkylation of alkyl-substituted aromatics the most commonly used metal. This leads to a dependence on this metal, which can have a negative economic impact on fluctuating raw material costs.

The object of the present invention is therefore to provide an alternative catalyst for the reaction of hydrocarbons in the presence of water vapor, with which similar or better yields can be achieved as with the catalysts of the prior art. In addition, the catalyst should have long-term stability and high yields even at low molar S / C ratios (steam to carbon, molar ratio of water vapor molecules to C atoms present in the mixture), since less is present at low S / C ratios Steam to be heated and condensed in the workup of the reaction mixture again. This has the consequence that the heat exchanger surfaces can be made smaller.

The problem is solved by a catalyst which

a) 0.1 to 3.0% by weight Ir, b) 0.1 to 10.0% by weight of at least one promoter and c) 87.0 to 99.8% by weight of a support comprising zirconium oxide, optionally 0 to 20% by weight, based on the weight of the zirconium oxide, of one or more

Contains elements selected from the group Si, Y, Ce and La as stabilizer,

includes. The erfϊndungsgemäße catalyst contains as component a) 0.1 to 3 wt .-%, based on the total weight of the catalyst, iridium. In a preferred embodiment, the catalyst contains from 0.2 to 2.0% by weight, preferably from 0.4 to 1.6% by weight, based on the total weight of the catalyst, of iridium.

As component b), the catalyst according to the invention contains 0.1 to 10.0% by weight, based on the total weight, of at least one promoter, preferably 0.5 to 8.0% by weight, particularly preferably 1.5 to 5, 0th

In a preferred embodiment, the promoter is selected from the group comprising alkali metals, alkaline earth metals and lanthanides. Particularly preferred promoters are Cs, Ba, Sr, La, Ce, Pr, Nd and Eu.

The promoter (s) may be applied to the carrier in the form of their salts, as described below. However, after calcination and activation of the catalyst, they are preferably present as oxides in the catalyst.

In a particular embodiment, the catalyst contains a promoter from the above-mentioned group.

In a further particular embodiment, two promoters from the above-mentioned group are used.

The catalyst according to the invention comprises, as component c), 87.0 to 99.8% by weight, based on the total weight of the catalyst, of a support which contains zirconium oxide (ZrO 2). The zirconium oxide may optionally contain 0 to 20% by weight, based on the weight of the zirconium oxide, of one or more elements selected from the group Si, Y, Ce and La as stabilizer. The ZrO ₂ may be in monoclinic or tetragonal crystal structure or in mixed crystal structure (X. Turrillas, J. Mater. Res. 1993, 8, 163-168). The stabilizer or stabilizers serve to stabilize a specific crystal structure of the zirconium oxide (R. Franklin et al., Catal. Today 1991, 10, 405-407).

The crystal structure of the zirconia can be determined by taking an XRD spectrum. This is a common method of X-ray diffraction.

As stabilizers for the zirconium oxide, all compounds which are generally suitable Stabilize tetragonal or monoclinic structure of the zirconia. The stabilized zirconium oxide-containing support preferably contains cerium, lanthanum, yttrium and / or silicon, in particular cerium (III) oxide, lanthanum (III) oxide and / or silicon (IV) oxide. One or more stabilizers can be used.

If cerium (III) oxide is used as stabilizer, the stabilized zirconium oxide-containing carrier usually contains up to 15% by weight, preferably 1 to 10% by weight, in particular 3 to 7% by weight, based on the weight of Zirconium oxide, cerium (III) oxide. In the case of the lanthanum (III) oxide, the stabilized zirconia-containing support usually contains up to 15% by weight, preferably from 2 to 15% by weight, in particular from 5 to 15% by weight, based on the weight of zirconium oxide , Lanthanum (III) oxide

If silicon (IV) oxide is used as stabilizer, the stabilized zirconium oxide-containing support usually contains up to 10% by weight, preferably 1 to 7% by weight, in particular 2 to 5% by weight, based on the Weight of zirconium oxide, silicon (IV) oxide.

In the event that both cerium (III) oxide and lanthanum (III) oxide are used as stabilizers, the stabilized zirconium oxide-containing support generally contains up to 20% by weight, preferably 5 to 15% by weight, in particular 10 to 15 wt .-%, based on the weight of zirconium oxide, cerium (III) oxide and usually up to 20 wt .-%, preferably 1 to 15 wt .-%, in particular 2 to 10 wt. -%, based on the weight of zirconium oxide, lanthanum (III) oxide.

The support preferably contains oxides from the group of zirconium oxide having a tetragonal crystal structure, zirconium oxide having a monoclinic crystal structure and stabilized zirconium oxide having a tetragonal crystal structure. Particularly preferred is stabilized zirconia having a tetragonal crystal structure.

The amount specified for component c) from 87.0 to 99.8 wt .-% applies to the non-stabilized oxide or oxide mixture as well as for the one or more stabilizers containing oxide or oxide mixture, based on the total amount of the catalyst.

Furthermore, the carrier c) may also contain auxiliaries. These are suitable for facilitating the shaping of the carrier. Usual aids are, for example, graphite and waxes, but it is also possible to use silicon dioxide and aluminum oxide as auxiliaries. Another common tool is pore former. These adjuvants can either be added by themselves or in the form of their precursors that are convert to the appropriate excipient during calcining. Examples include silicon dioxide precursors such as tetraethyl orthosilicate (TEOS) and colloidal silica and alumina precursors such as Boehmite, for example Pural ® (Fa. Sasol). Preferably, aluminas are used as auxiliaries.

The carrier c) may contain up to 10% by weight, based on the total weight of the carrier, of auxiliaries. In a preferred embodiment, the carrier contains from 0.1 to 10% by weight, preferably from 0.5 to 2% by weight, based on the total weight of the carrier, of auxiliaries.

The preparation of the catalyst can be carried out by customary methods known to the person skilled in the art.

For example, it is possible to prepare the zirconia-containing support from corresponding compounds which convert to the corresponding oxide upon calcining. For this purpose, in particular hydroxides, carbonates and carboxylates are suitable. The corresponding oxide or precursors, which are converted to the oxide upon calcination, may be prepared by methods known per se, e.g. according to the So 1 gel method, by precipitation, dewatering of the corresponding carboxy late, dry mixing, slurrying or spray drying. In the precipitation, usually soluble metal salts are used, e.g. the corresponding halides, preferably chloride, alkoxides, nitrate, etc., preferably nitrate.

Stabilized zirconia-containing supports can i.a. can be prepared by zirconium oxide or the corresponding precursor with soluble salts of the stabilizers, such as described above. the corresponding halides, preferably chlorides, alkoxides, nitrates, etc., soaks. But it is also possible to apply the stabilizers on the zirconia-containing carrier by precipitation from corresponding soluble salts of the stabilizers. As soluble salts of the stabilizers, in turn, the corresponding halides, preferably chlorides, alkoxides, nitrates, etc., are generally suitable.

It is furthermore possible to prepare the stabilized zirconium oxide-containing support from compounds which on calcining convert into zirconium oxide or cerium (III) oxide, lanthanum (III) oxide, silicon (IV) oxide. For this purpose, in particular hydroxides, carbonates and carboxylates are suitable. These are for example precipitated together, spray-dried together etc. The zirconia and stabilized zirconia or precursors prepared by the above processes may be added with the above-mentioned auxiliary agents suitable for facilitating the shaping of the zirconia-containing carrier. Subsequently, the shaping takes place. As a rule, strands, tablets, spheres, chippings, monoliths, etc. are prepared by the usual methods.

The zirconium oxide described above and the stabilized zirconium oxides or the corresponding precursors, which are optionally mixed with auxiliaries, are calcined. This is usually done with air or a mixture of air and nitrogen, at a temperature of 300 to 800 ⁰ C, preferably at 500 to 600 ⁰ C. It may be advantageous to add water vapor to the air or the air / nitrogen mixture.

The iridium can now be applied to the zirconia-containing support. Usually, the carrier is impregnated with a solution of an iridium precursor. The impregnation can be carried out by the incipient-wetness method, in which the porous volume of the support is filled up with approximately the same volume of impregnating solution and, optionally after maturation, the support is dried; or you work with an excess of solution, the volume of this solution is greater than the porous volume of the carrier. In this case, the carrier is mixed with the impregnating solution and stirred for a sufficient time. Furthermore, it is possible to spray the carrier with a solution of the metal precursor.

But also other known to those skilled manufacturing methods, such. Precipitation, chemical vapor deposition, sol impregnation etc. are possible.

Suitable iridium precursors are the respective metal salts, i.a. Halides, especially chloride, nitrate, acetate, alkaline carbonates, formate, oxalate, citrate, tartrate, iridium-organic compounds, but also iridium complexes. The latter may contain as ligands acetylacetonate, amino alcohols, carboxylates such as oxalates, citrates, etc. or hydroxycarboxylic acid salts, etc.

Promoted catalysts are prepared by applying the promoter precursor or the promoter precursors in analogy to the methods for iridium application.

Suitable promoter precursors include halides, especially chlorides, nitrates, acetates, alkaline carbonates, formates, oxalates, citrates, tartrates, corresponding me- organometallic compounds, but also promoter complexes. The latter may contain as ligands acetylacetonate, amino alcohols, carboxylates such as oxalates, citrates, etc. or hydroxycarboxylic acid salts, etc.

If the catalyst contains a promoter, the promoter precursor can be applied together with the iridium precursors. But it is also possible to apply them one after the other. It may also be advantageous to apply the individual precursors in a certain order.

If the catalyst contains several promoters, the promoter precursors can be applied together or separately. It is also possible to apply the iridium precursor together or separately with one or more promoter precursors. In the case of a separate application, it may also be advantageous to apply the individual precursors in a certain order. Between the applications of the individual solutions, the impregnated carrier can be dried before the next solution is applied.

The zirconia-containing support on which the iridium precursor and the promoter precursor (s) has been applied is calcined. The calcination is usually carried out with air or a mixture of air and nitrogen, at a temperature of 300 to 800 ⁰ C, preferably at 400 to 600 ⁰ C. It may be advantageous to add water vapor to the air or the air / nitrogen mixture ,

The catalyst thus obtained is usually activated before its use, the reaction of hydrocarbons in the presence of water vapor. For this he is with

Hydrogen or a mixture of hydrogen and nitrogen at temperatures of

100 to 800 ⁰ C, preferably at 400 to 600 ⁰ C, treated. In this case, it may be advantageous to start with a low hydrogen content in the hydrogen / nitrogen mixture and to increase the hydrogen content continuously during the activation process. In a particular embodiment, the activation process is in

Presence of water vapor performed.

The activation of the catalyst is usually carried out in the reactor in which the reaction of the hydrocarbons is to take place. However, it is also possible to carry out the activation of the catalyst before installation in the corresponding reactor.

However, it is also possible to use the catalyst without prior activation in the reaction. tion of hydrocarbons use.

The catalyst usually has a BET surface area (determined to DIN 66131) of up to 500 m ² / g, preferably from 10 to 300 m ² / g, in particular from 20 to 200 m ² / g, particularly preferably at least 25 m ² / g on.

As a rule, the pore volume of the catalyst (determined by means of Hg porosimetry according to DIN 66133) is 0.1 to 1 ml / g, preferably 0.15 to 0.8 ml / g, in particular 0.2 to 0.6 ml / g.

The support preferably has a monomodal or bimodal pore size distribution, the proportion of pores having a diameter greater than 10 nm being at least 30% by volume.

The cutting hardness of the carrier is at least 5 N / mm. In the context of the present invention, the cutting hardness was measured on a Zwick type BZ2.5 / TS1S apparatus with a preliminary force of 0.5 N, a precursor thrust speed of 10 mm / min, and a subsequent test speed of 1.6 mm / min, certainly. The device had a fixed turntable and a freely movable punch with built-in cutting edge of 0.3 mm thickness. The movable punch with the cutting edge was connected to a load cell for power absorption and moved during the measurement against the fixed turntable on which the catalyst molding to be examined was located. The tester was controlled by a computer, which registered and evaluated the measurement results. The values obtained represent the average of the measurements for each of 10 shaped catalyst bodies. The shaped catalyst bodies had a cylindrical geometry with their average length approximately equal to two to three times the diameter, and were measured with the blade of 0.3 mm thickness loaded with increasing force until the molding was severed. The cutting edge was applied perpendicular to the longitudinal axis of the molding on the molding. The required force per mm diameter of the carrier is the cutting hardness (unit N / mm).

Depending on the application technique, heat treatment, activation, support material and other factors, the concentration of active, ie the reaction actually available, metal atoms in or on the catalyst can vary. This phenomenon is also called dispersity. According to the present invention, catalysts are used in which the dispersity of iridium is at least 20%. The dispersity is measured by volumetric measurement of CO uptake 40 ⁰ C after reduction of the metal atoms in the presence of hydrogen at 450 ⁰ C for at least 2h.

When applied to the substrate, the iridium has a radial concentration distribution on the substrate, with the major portion, i. at least 55% of the iridium, or located directly below the surface of the support material. Such catalysts are also referred to as shell catalysts. The layer in which the iridium is on the substrate usually has a thickness of 50 to 350 micrometers.

Another object of the present invention is the use of the above-described catalyst for the reaction of hydrocarbons in the presence of water vapor. These reactions include, for example, steam reforming, in which hydrocarbons are catalytically converted to hydrogen, carbon monoxide, and carbon dioxide in the presence of water vapor, and steam dealkylation, in which alkyl-substituted aromatic hydrocarbons react to aromatics, hydrogen, carbon monoxide, and carbon dioxide. In the context of the present invention, the dehydrogenation of hydrocarbons in the presence of water is counted among these reactions, although the water vapor is not involved in the actual dehydrogenation reaction, but its presence has a positive effect on the life of the catalyst. The water vapor reduces the deposition of coke and can react with the coke to form hydrogen and carbon monoxide or carbon dioxide.

The catalyst according to the invention is preferably used for reacting hydrocarbons having 1 to 12 carbon atoms in the presence of steam. Particular preference is given to reacting mixtures of hydrocarbons having 5 to 10 carbon atoms which are formed in the streamcracker as a by-product in the production of ethylene and / or propylene from naphtha. In particular, this is the so-called pyrolysis gasoline, which is obtained after hydrotreating (removal of sulfur components, dienes and olefins with the aid of hydrogen). The pyrolysis gasoline typically consists of a mixture of saturated linear and branched hydrocarbons (paraffins), saturated cyclic hydrocarbons (naphthenes) and alkyl-substituted aromatics. The ratio of saturated hydrocarbons to alkyl-substituted aromatics is typically between 5:95 and 95:75. Individual fractions, such as hydrocarbons with 5 carbon atoms (Cs cut) can be obtained by distillative separation. The separation of the paraffin and naphthenic mixtures of the alkyl-substituted aromatics succeed, for example, by an extractive distillation.

According to the invention, the use of the above-described catalyst for the steam dealkylation of alkyl-substituted aromatic hydrocarbons is preferred. Very particular preference is given to the use of the above-described catalyst for the steam dealkylation of alkyl-substituted aromatic hydrocarbons having 7 to 12 carbon atoms, in particular its use for the preparation of benzene by reacting alkyl-substituted benzenes in the presence of water vapor.

Another object of the present invention is a process for the reaction of hydrocarbons in the presence of steam on the catalyst of the invention described above, preferably the reaction of Kohlenwasserstof fen with 1 to 12 carbon atoms.

Particular preference is given to a process for the steam dealkylation of mono- and poly-alkyl-substituted aromatic hydrocarbons in which the mono- and poly-alkyl-substituted aromatic hydrocarbons in the presence of steam on the catalyst according to the invention described above to aromatic hydrocarbons, hydrogen, carbon dioxide and carbon monoxide be implemented.

Another preferred object of the present invention is a process for the preparation of benzene by reacting alkyl-substituted benzenes having 7 to 12 carbon atoms in the presence of water vapor on the catalyst according to the invention described above.

According to the invention, mono- or polysubstituted alkyl-substituted aromatic hydrocarbons can be dealkylated in the presence of the catalyst described above. Alkyl in the context of the present invention means branched and linear C ₁ -C 6 -alkyl groups. One or more alkyl-substituted aromatic hydrocarbons means that one, two or more of the H atoms attached to the aromatic nucleus can be replaced by alkyl up to the case where all the corresponding H atoms have been replaced by alkyl. In the context of the present invention, "aromatics" and "aromatic hydrocarbons" are used synonymously. In particular, according to the present invention, one or more alkyl-substituted benzenes containing 7 to 12 carbon atoms may be dealkylated. Preferably suitable mono-alkyl-substituted benzenes such as toluene, ethylbenzene or propylbenzene, polyhydric alkyl-substituted benzenes such as o-, m- and p-xylenes, mesitylene and mixtures thereof. In a preferred embodiment, toluene is used. In a further preferred embodiment, mixtures containing substantially mono- and poly-alkyl-substituted benzenes are used; For example, the resulting during steam cracking so-called TX cut.

Sources of the mono- and poly-alkyl-substituted benzenes having 7 to 12 carbon atoms to be used according to the present invention are:

Fully hydrogenated pyrolysis gasoline, which is obtained as a by-product in the production of ethylene and propylene from naphtha in the presence of steam in a steam cracker, the so-called TX cut is obtained therefrom.

Cokererase extract obtained by scrubbing gas with higher boiling hydrocarbons and / or by adsorption on activated charcoal from raw coal resulting from the coking of coal,

• reformate gas produced by catalytic reforming of paraffinic and naphthenic crude oils,

Alkyl-substituted benzenes having more than 8 carbon atoms which are by-produced in the disproportionation of toluene to benzene,

Coal oil obtained by hydrogenation of the sump phase of stony and / or lignite suspensions,

• coal extract obtained by extraction of coal and / or brown coal with solvent such as tetralin or toluene at 350-400 ⁰ C and 100-300 bar,

Aromatic fraction which is formed during the reaction of synthesis gas with methanol on zeolite catalysts or directly from synthesis gas by reaction on a bifunctional catalyst such as ZSM-5 / zinc chromite,

Aromatic fraction obtained by a dehydrocyclization of methane, ethane, propane and / or butane, this process is also called cyclic process, as well • Aromatic fractions resulting from the processing of Canadian "sand oil".

The feed stream used in the steam dealkylation generally contains at least 50% by weight, preferably at least 80% by weight, particularly preferably at least 90% by weight, of a mono- or polysubstituted alkyl-substituted aromatic hydrocarbon or a mixture thereof ,

In a further embodiment, it is also possible to use a feed stream which, in addition to the mono- or poly-alkyl-substituted aromatic hydrocarbon or mixtures thereof, up to 50 wt .-%, preferably up to 30 wt .-%, particularly preferably to to 20 wt .-% of non-aromatics having 7 to 12 carbon atoms. These non-aromatics may be paraffins and / or naphthenes.

In a further embodiment, the feed stream may contain up to 40% by weight, preferably up to 10% by weight, more preferably up to 2% by weight, of hydrocarbons having 5 and / or 6 carbon atoms.

In a further embodiment, the so-called BTX cut, which is obtained in steam cracking, can also be used as the feed stream.

In a further embodiment, the feed stream may contain sulfur containing compounds, such as e.g. Mercaptans, thiophene, benzothiophene, alkyl-substituted thiophenes and / or benzothiophenes. Typically, the sulfur content of the feed stream may be up to 100 ppm, usually 10 ppm or less, more preferably 2 ppm or less.

The dealkylation is usually carried out from 300 to 800 ^° C., preferably from 400 to 600 ^° C., in particular from 400 to 550 ^° C. The pressure is in this case in a range of 1 to 50 bar, preferably from 3 to 30 bar, in particular from 5 to 25 bar.

The LHSV ("Liquid Hourly Space Velocity") is usually 0.1 to 10 parts by volume of feed stream per part by volume of catalyst per hour (l / l * h), preferably 0.5 to 5 1/1 h, especially at 1 to 3 (l / l «h).

The molar ratio of steam / carbon (steam / carbon, S / C) is generally from 0.1 to 10, preferably from 0.2 to 5, in particular from 0.5 to 2.

In one embodiment of the inventive use of the above-described described catalyst, the feed used and the water is evaporated in an evaporator at 100 to 400 ⁰ C, this steam brought in a preheater and / or by a heat network to the desired reaction temperature, preferably at 400 to 600 ⁰ C, in particular 400 to 550 ⁰ C and then introduced into the reactor.

In the course of the reaction, under the given reaction conditions, coke and / or coke precursors can form at the active centers and in the pores of the catalyst. Coke is usually high-boiling unsaturated hydrocarbons. Coke precursors are typically low-boiling alkenes, alkynes and / or saturated high molecular weight hydrocarbons.

The deposition of the coke or coke precursor has the effect that the activity and / or selectivity of the catalyst is adversely affected. In order to guarantee an optimal driving style, there is therefore the need to regenerate the catalyst at regular intervals. The aim of the regeneration is the removal of the coke or the coke precursor, without the physical properties of the catalyst being adversely affected.

The coke precursors can be removed in the presence of an oxygen-containing gas mixture by evaporation in the presence of an inert gas at an elevated temperature (T> 250 ⁰ C) and / or hydrogenation in the presence of a wasserstoffhal- term gas mixture and / or incineration.

The coke deposits are usually removed by burning the coke in the presence of an oxygen-containing gas mixture (= oxidative regeneration).

The regeneration of the catalyst can be carried out in situ or ex situ, preferably an in situ regeneration is carried out. The inlet temperature for the oxidative regeneration is usually between 350 and 550 ^° C. The oxygen concentration of the oxygen-containing gas mixture is usually between 0.1 and 10% by volume. The pressure is typically between 0.1 and 10 bar.

In a particular embodiment, the oxidative regeneration of the catalyst is carried out in the presence of water vapor.

After the oxidative regeneration of the catalyst is usually carried out an activation in the presence of hydrogen. The reactors used are generally fixed-bed reactors, tube-bundle reactors or fluid-bed reactors.

In one embodiment, i.a. simple fixed bed reactors, fixed bed reactors with upstream combustion zone, a cascade of fixed bed reactors or tray reactors are used (Rompp Lexikon Chemistry, editor J. Falbe, M. Regitz, Thieme Verlag, 10th edition, Bd. 5, p 3739)

The reaction of the alkyl-substituted aromatics by means of steam dealkylation is an endothermic reaction. The heat required to maintain the reaction can be supplied by heating from the outside. In this case, the reaction or reaction zones can be heated, but it is also possible to switch between two reactors or reaction zone an intermediate heating and to heat the reaction mixture.

However, the reaction can also be carried out autothermally, i. the heat requirement of the conversion is covered by a second, exothermic reaction in the system itself. For example, the desired reaction temperature may be established by feeding an oxygen-containing gas into the catalyst bed and by combustion of a portion of the feed hydrocarbon and / or a portion of the dealkylation catalyst The resulting hydrogen and / or the carbon monoxide forming during the reaction and / or the coke formed in the reaction, which generates the necessary heat, whereupon the oxidation is assisted by the catalyst used as an oxygen. enriched air, such as a mixture of oxygen and nitrogen, or pure oxygen, but other oxygenated gases may be used in addition to enriched air, provided that the other components of the mixture are inert under the reaction conditions.

The supply of the oxygen-containing gas can take place at one or more points of the reactor used / the reactors used, in particular at one or more points along the catalyst bed (s). It is also possible to add the oxygen-containing gas already to the hydrocarbon feed used and the water vapor.

In this case, it may be advisable to partially or completely recover the formed arm gas which contains the hydrogen formed during the inventive reaction. lead, that at the entrance of the first catalyst bed already hydrogen is present, so that preferably this formed during the reaction and recycled hydrogen reacts with the oxygen of the oxygen-containing gas to generate heat.

In a further embodiment, it is also possible to feed a hydrogen-containing gas into the reactor.

Furthermore, the process can be designed so that the dealkylation reaction and the oxidation reaction are carried out in different regions. This is possible in particular in a tray reactor, but also in a cascade of fixed bed reactors. In the former, the reaction zones of the vapor decomposition and the reaction zones of the oxidation preferably alternate. Here it may be advantageous to feed oxygen-containing gas in each case into the corresponding zone of the oxidation. In the reactor cascade, respective combustion chambers are interposed between the reactors in which the oxygen-containing gas is reacted with a portion of the hydrocarbon feed and / or a portion of the hydrogen formed in the steam dealkylation, the latter being preferred.

The reaction of the hydrogen formed in the reaction with the oxygen of the oxygen-containing gas can be carried out in the presence or in the absence of oxidation catalysts. The oxidation catalysts used are those known to those skilled in the art, preference being given to those which are selective with respect to the oxidation of hydrogen with oxygen, in order to avoid undesired consumption of hydrocarbons used by oxidation.

In a particular embodiment, the oxidation catalysts contain, as described in US 4,435,607, a noble metal of groups 8, 9 or 10 of the Periodic Table on a porous support. In addition, metals of group 4 can be contained, and if desired, at least one metal of groups 1 or 2 of the periodic table. As the carrier, alumina carriers are preferably used.

In a particular embodiment, the reaction is carried out in the presence of an oxidation catalyst, in particular if the steam dealkylation reaction and the oxidation reaction are carried out in different regions, for example in a tray reactor or in a reactor cascade with interposed combustion chambers.

The molar ratio of oxygen / carbon (oxygen / carbon) is usually so It is established that the oxidation of the hydrogen formed in the dealkylation reaction and, if appropriate, the carbon monoxide formed in the steam dealkylation reaction and, if appropriate, the coke formed during the reaction, can produce the heat necessary to maintain the reaction temperature. Furthermore, the molar ratio of oxygen / carbon is adjusted so that practically no hydrocarbons used or formed are burned with the oxygen. In general, the molar ratio of oxygen / carbon is from 1:10 to 1: 2000, preferably from 1:50 to 1: 1000, in particular from 1: 100 to 1: 900.

In a further embodiment, it is possible to increase the feed stream, whose temperature is below the reaction temperature, to the latter by oxidizing the recycled, formed in the Dampfdeealkylierung hydrogen and / or hydrocarbons and / or formed carbon monoxide, with oxygen.

The reaction gas obtained by the process according to the invention is rich in hydrogen and dealkylated aromatic hydrocarbons, in particular benzene and / or alkyl-substituted aromatic hydrocarbons, whose number of alkyl radicals is reduced compared to the alkyl-substituted aromatic hydrocarbons used. In a particular embodiment, the reaction gas contains benzene as the aromatic hydrocarbon, especially for the case when the alkyl-substituted aromatic hydrocarbon used is mainly toluene.

It has also been found that aromatize optionally contained in the feed non-aromatics having 7 or more carbon atoms. Paraffinic compounds may possibly be partially decomposed to methane, carbon dioxide and hydrogen.

The dealkylated aromatic hydrocarbons formed and the arm gas formed, which contains the hydrogen formed in the reaction according to the invention, are separated from the reaction gas by customary processes. Furthermore, the arm gas or the hydrogen separated therefrom can be returned to the reaction apparatus. Typically, the ratio between cycle gas (in Nl) and feed (in kg) is from 10: 1 to 2000: 1, preferably from 20: 1 to 1000: 1 and especially from 50: 1 to 500: 1.

In one embodiment of the inventive method in autothermal driving, the feed used and the water are evaporated in an evaporator at 100 to 400 ⁰ C, this vapor in a preheater to the desired reaction temperature brought, which is preferably at 400 to 600 ⁰ C, in particular at 400 to 550 ⁰ C, and then introduced into the reactor. Immediately before entering the catalyst bed containing the catalyst according to the invention, the oxygen-containing gas, preferably air, is fed.

The reaction gas, which is obtained according to the erfϊndungsgemäßen method, is passed from the reactor into a heat exchanger and cooled there, preferably at 10 to 100 ⁰ C. It is expedient to integrate the heat released in this process in the process (heat combination), for example to heat the feed stream or other streams to be heated (eg evaporator of the column). The forming liquid phase containing the dealkylated aromatic hydrocarbon, preferably benzene, is fed to a phase separator and the organic phase is separated from the water phase. If desired, the organic phase containing the dealkylated aromatic hydrocarbon, preferably benzene, can be further purified, for example by distillation. If desired, the separated off-gas may be returned to the reactor.

In a particular embodiment, benzene and, if appropriate, impurities are removed via overheads and hydrocarbons having 7 or more carbon atoms are removed via the bottom in a distillation column. The separated mixture can be recycled to the steam dealkylation. Optionally, it may be advantageous to subject this mixture to further distillation, wherein high boilers are separated and only the resulting low boiler fraction are recycled to the steam dealkylation.

In order to separate off the water dissolved in the organic phase (in small amounts) and low-boiling components from the top fraction of said distillation, the benzene fraction can be passed to a further distillation column in which the dissolved water and the low boilers are passed overhead via azeotropic distillation Reinbenzol be separated via sump.

In a particular embodiment, the columns are carried out as columns with side draw or as dividing wall columns.

In a further embodiment, it is also possible to use only one column or even more columns. Columns which can be used here in addition to the classical columns, for example, columns with side draw or dividing wall columns. In other embodiments, units for reducing the sulfur content of the hydrocarbons to be converted are incorporated into the process. Here, method steps according to the prior art are used.

This embodiment of the process according to the invention makes it possible to produce benzene in high purity, the hydrogen which is formed in the steam dealkylation reaction being used, via a coupling with an oxidation reaction, the heat required, the reaction temperature uphold, win. Therefore, on the one hand, the hydrogen formed can be used immediately, and further the heat is formed directly in the reactor, so that heat losses e.g. can be avoided on external heat exchangers.

In the following, the present invention is explained in more detail by means of exemplary embodiments.

Examples

Preparation of the catalyst

The monoclinic zirconia support and the Si-stabilized tetragonal zirconia support are commercially available from NorPro under designation SZ 3164 and SZ 6152, respectively. The La, Ce-stabilized tetragonal zirconia support and Ce-stabilized zirconia support were obtained by deformation of the corresponding zirconium hydroxide precursors respectively at the company. MEL Chemicals under the name XZO 892 or XZO 857 available boehmite Fa. Sasol (Pural ^® SB). The titanium oxide support is the commercially available product P25 from Degussa. The Al, Mg spinel supports (I) and (II) were prepared by precipitating the appropriate amounts of Mg (NOs) ₂ and Al (NOs) ₃ in an aqueous solution in the presence of Na ₂ CO ₃ at pH = 5. The solid was filtered off, washed with deionized water and dried at 100 ^° C. for 72 h. Subsequently, the powder was formed in an extruder into 1.5 mm strands. The strands were dried at 120 ^° C. for 16 h and then calcined in a rotary kiln at 600 ^° C. (residence time 1 h).

The BET surface area (BET) was determined according to DIN 66131, the pore volume (PV) was measured by means of Hg porosimetry measurement according to DIN 66133. The compositions, BET and pore volumes of the carriers used are summarized in Table 1. Table 1

Designation Share [weight%] BET PV

ZrO ₂ La ₂ O ₃ Ce ₂ O ₃ Al, O ₃ SiO ₂ TiO ₂ [m ² / g] [ml / g] monoclinic ZrO 2> 99 - - - 76 0.29 tetr. La, Ce- 71 , 9 4.5 15.5 8 1 _ _ 100 0.33

ZrO ₂ tetr. -Ce-ZrO ₂ 68.9 24.2 6 9 - - 141 0.28 tetr-Si-ZrO ₂ 95.5 - 4.5 - 156 0.32

TiO ₂ - - -> 99 41 0.25

The catalysts were prepared by impregnation of the support material to the maximum water absorption (incipient wetness method). For this purpose, water-soluble salts of the components to be applied were combined together in a solution and the carrier material was impregnated with this solution. In the subsequent step, the catalysts were dried for at least 6 h at 80 ⁰ C. Optionally, the impregnation was repeated to obtain the desired concentrations of the elements on the support. After drying, the catalysts were calcined in a muffle furnace with air addition for 3 hours at 500 ⁰ C.

Carrying out the experiments

The experiments were carried out in a 48-fold tubular reactor at a pressure of 5 bar with a gas mixture of 30% by volume of nitrogen, 60.8% by volume of water and 9.2% by volume of toluene. This corresponds to a steam-to-carbon (S / C) ratio of 0.94. In each case 1 ml of catalyst in the form of chippings with a particle size of 0.5 to 1.0 mm was used. The catalysts were activated before the reaction in the reactor with a gas mixture of 3 vol .-% hydrogen in nitrogen for 3 h at 450 ⁰ C.

The experiments were carried out at an LHSV (Liquid Hourly Space Velocity) of 2 h ^"1 (settings I and II), and in some experiments (C, E, F, G and H) the LHSV was subsequently reduced to 1 h ^"1 lowered (setting III).

The LHSV is defined as the amount of liquid toluene in ml per ml of catalyst and Hour [= 1 (toluene) / (1 (cat) * h)].

In the experiments, the temperature was maintained at 450 ^° C. (I), after a running time (= time-on-stream = TOS) of 18 hours the composition of the reaction product was determined and the temperature increased to 500 ^° C. (II). The composition was redetermined after a total run time of 24 hours. Subsequently, reaction was further 12 h at 500 ⁰ C, however, at a LHSV of 1 h ^{"continued 1} (setting III), and again determines the composition of the product stream after 36 hours total run time.

The analysis of the composition is carried out by gas chromatography.

The results are shown in the following Tables 2 to 6. The conversion refers to the conversion of toluene, the selectivity is the benzene selectivity in mol%. The conversion and selectivity were calculated from the gas chromatographic data. The percentages in the parentheses behind the elements indicate the concentration of each element in weight percent based on the total weight of the catalyst. The elements listed under composition are the iridium and the elements of component b) used as promoters. The column Carrier lists the zirconium oxide or stabilized zirconium oxide used as support, which is contained in the catalyst as component c).

Table 2

Cat. Composition Carrier TemperaTOS UmSet ter M etect.

[%] [%]

A Ir (0.3%), La (5.0%) monoclonal I 18 1> 99 erfϊn- ZrO ₂ tion according to

II 24 2 96

B Ir (0.6%), La (5.0%) monoclonal I 18 18 93 erfϊn- ZrO ₂ according to

II 24 49 94

C Ir (l, 2%), La (5.0%) monoclonal I 18 39 96 erfϊn- ZrO ₂ according to

II 24 81 94

D Ir (2.4%), La (5.0%) monoclonal I 18 51 96 erfϊn- ZrO ₂ according to

II 24 94 80 monocl. ZrO? = Zirconium oxide with monoclinic crystal structure.

The values in Table 2 show that an increase in the iridium concentration leads to a higher activity of the catalyst.

Table 3

Cat. Composition Carrier EinTOS Turnover Selekt. position M [%] [%]

E Ir (l, 2%), La (5.0%) TiO ₂ I 18 O - not according to the invention

II 24 3 89

III 36 9 94

C Ir (l, 2%), La (5.0%) monoclonal I 18 39 96 erfϊn- ZrO ₂ according to

II 24 81 94

III 36 91 89

F Ir (l, 2%), La (5.0%) tetr. I 18 16 94 erfϊn- La, Ce

ZrO ₂ according to

II 24 36 97

III 36 43 95

G Ir (l, 2%), La (5.0%) tetr.-Ce- I 18 29 94 erfϊn- ZrO ₂ according to

II 24 73 95

III 36 93 91

H Ir (l, 2%), La (5.0%) tetr. Si 18 29 95 erfrn ZrO ₂ according to

II 24 76 92

III 36 94 74 monoclinic ZrO ₂ = zirconium oxide with monoclinic crystal structure; tetr.-ZrO ₂ = zirconium oxide with tetragonal crystal structure

The results summarized in Table 3 show that, in addition to zirconium oxide with a monoclinic crystal structure, it is also possible to use zirconium oxide with a tetragonal crystal structure without a noticeable decrease in catalyst performance. The best result is achieved with a cerium-stabilized zirconia. In contrast, the catalyst with titanium oxide as a carrier shows a very low activity. The tetragonal phase of the zirconia is stabilized by addition of the elements Si, Ce and / or La.

Table 4

Cat. Composition Carrier one TOS reposition [h] set lect. r% i r% i

J Ir (1, 2%) tetr. La, Ce- I 18 6 94 erfϊn- ^Zr ° ² tion ^¬ ge

II 24 24 95

^~ F Ir (l, 2%), La (5.0%) tetr.-La, Ce- ϊ Ϊ8 Ϊ6 94 ^~ erfϊn- ZrO ₂ tion ^¬ geäß

II 24 36 97 tetr.-ZrO ₂ = zirconium oxide with tetragonal crystal structure

Table 5

Cat. Composition Carrier OnTOS repaRt M ity lect.

[%] [%]

L Ir (0.6%) monocl. ZrO? 18> 99 not erfϊn- tion ^¬ ge

II 24 96

M Ir (0.6%), Sr (2.2%) monoclinic ZrO 2 18 16 93 erfϊn- tion ^¬ geäß

II 24 40 96

N Ir (0.6%), La (3.5%) monocl. ZrO? 18 20 93 erfϊn- tion ^¬ geäß

II 24 29 95 monoclinic ZrO? = Zirconium oxide with monoclinic crystal structure

From the values in Tables 4 and 5, it can be seen that by adding a promoter, the activity of the iridium catalysts can be significantly increased while the selectivity remains the same.

Table 6

Cat. Composition Carrier OnTOS repaRt M ity lect.

[%] [%]

O Ir (1, 1%), Sr (3.0%) monoclinic ZrO 2 I 18 11 92 erfϊn- tion ge ^¬ according to

II 24 13 94

P Ir (2.2%), Sr (3.0%) monoclinic ZrO 2 I 18 46 94 erfϊn- ge ^¬ tion

II 24 93 86

Q Ir (l, l%), La (5.0%) monocl.-ZrO 2 I 18 30 95 erfϊn- tion ^¬ ge

II 24 72 94

R Ir (2.2%), La (5.0%) monocl.-ZrO 2 I 18 64 93 erfϊn- tion ^¬ ge

II 24 99 74 monoclinic ZrCK = zirconium oxide with monoclinic crystal structure

The results shown in Table 6 demonstrate that the addition of 3.0 wt.% Strontium leads to lower catalyst activities compared to the addition of 5.0 wt.% Lanthanum.

Claims

claims

1. Catalyst for reacting hydrocarbons in the presence of water vapor comprising

a) 0.1 to 3.0% by weight of Ir, based on the total weight of the catalyst, b) 0.1 to 10.0% by weight of at least one promoter, based on the total weight of the catalyst, and c) 87 From 0 to 99.8% by weight of a support, based on the total weight of the catalyst, comprising zirconium oxide, optionally containing from 0 to 15% by weight, based on the weight of the zirconium oxide, of one or more elements selected from the group of Si, Contains Y, Ce and La.

2. A catalyst according to claim 1, characterized in that the promoter is selected from the group comprising alkali metals, alkaline earth metals and lanthanides.

3. A catalyst according to claim 1 or 2, characterized in that the promoter is selected from the group comprising Cs, Ba, Sr, La, Ce, Pr, Nd and Eu.

4. Catalyst according to one of claims 1 to 3, characterized in that the promoter is present as an oxide.

5. Catalyst according to one of claims 1 to 4, characterized in that the carrier is selected from the group comprising zirconium oxide with monoclinic

Crystal structure, tetragonal crystal structure zirconia, mixed crystal structure zirconia and tetragonal crystal structure stabilized zirconia with one or more elements of Si, La, Ce and Y group.

6. A catalyst according to any one of claims 1 to 5, characterized in that is used with one or more elements of the group Si, La, Ce and Y stabilized zirconia with tetragonal crystal structure as a carrier.

7. A catalyst according to any one of claims 1 to 6, characterized in that the carrier has a BET surface area of at least 25 m ² / g.

8. A catalyst according to any one of claims 1 to 7, characterized in that the carrier has a pore volume of at least 0.1 ml / g.

9. Use of a catalyst according to any one of claims 1 to 8 for the reaction of hydrocarbons in the presence of water vapor.

10. Use of a catalyst according to claim 9 for Dampfdealkylierung of alkyl-substituted aromatic hydrocarbons in the presence of water vapor.

11. Use of a catalyst according to claim 9 or 10 for the preparation of benzene by reacting alkyl-substituted benzenes in the presence of

Water vapor on a catalyst described in any one of claims 1 to 8.

12. Use of a catalyst according to one of claims 9 to 11, characterized in that the reaction is carried out autothermally.