WO2007051851A1

WO2007051851A1 - Method for producing aromatics, in particular benzol, by the aromatisation of non-aromatics using water vapour and the subsequent dealkylation of alkyl-substituted aromatic hydrocarbons using hydrogen

Info

Publication number: WO2007051851A1
Application number: PCT/EP2006/068117
Authority: WO
Inventors: Dirk Neumann; Michael Koch; Götz-Peter SCHINDLER; Regina Benfer; Gerd Kaibel; Hans-Günter Wagner; Peter PÄSSLER
Original assignee: Basf Se
Priority date: 2005-11-06
Filing date: 2006-11-06
Publication date: 2007-05-10
Also published as: DE102005053231A1

Abstract

The invention relates to a method for the dealkylation of alkyl-substituted aromatic hydrocarbons. According to said method, in step (I), non-aromatic hydrocarbons comprising 6 or more carbon atoms are aromatised in the presence of water vapour and a catalyst and in step (II) at least part of the product stream obtained in step (I), said stream containing alkyl-substituted aromatic hydrocarbons, is converted with the aid of hydrogen, optionally in the presence of a catalyst, dealkylating the alkyl-substituted aromatic hydrocarbons.

Description

Process for the preparation of aromatics, in particular benzene, by aromatization of non-aromatics with water vapor and subsequent dealkylation of alkyl-substituted aromatic hydrocarbons with hydrogen

The present invention relates to a process for the dealkylation of alkyl-substituted aromatic hydrocarbons, wherein in

Step (I) aromatizing non-aromatic hydrocarbons having 6 or more carbon atoms in the presence of water vapor and a catalyst; and in

Step (II) at least a portion of the product stream I obtained in step (I) (reaction product step-l) containing alkyl-substituted aromatic hydrocarbons, with the aid of hydrogen, optionally in the presence of a catalyst, is reacted by dealkylating the alkyl-substituted aromatic hydrocarbons.

Aromatic hydrocarbons are widely used in both the petrochemical and chemical industries. Large amounts of aromatic hydrocarbons are needed, for example, as additives for gasoline - to increase the octane number. In the chemical industry, benzene is a key starting material for a variety of organic compounds.

The production of aromatic hydrocarbons takes place mainly by naphtha reforming and by steam cracking. Aromatic hydrocarbons obtained by the former method are usually obtained as mixtures and can be added as such to gasoline. In steam cracking, the aim is to obtain short-chain olefins and aromatic hydrocarbons are obtained as by-products, which are separated by complex separation operations and into the individual components, such as. Benzene, toluene, etc. can be separated. The two processes mentioned have the disadvantage that the aromatic hydrocarbons are coupled with other products.

In order to meet the demand for benzene, processes have been developed which allow dealkylation of alkyl-substituted aromatic hydrocarbons, in particular toluene. Thus, for example, benzene can be produced independently and additional amounts of benzene can be provided or produced adapted to market needs. So far, the so-called hydrodealkylation has been technically realized. The hydrodealkylation is a dealkylation of alkylaromatics in the presence of hydrogen, as described, for example, in Ullman's Encyclopedia of Industrial Chemistry 6th Edition, 2000, electronic release, Chapter 5.3.1 and Industrial Organic Chemistry (K. Weissermel, H. J. Arpe), 5th Edition, 1998, Chapter 12.3.1. A distinction is made between a catalytic and a thermal hydrodealkylation. Examples of catalytic processes are the Hydeal process (UOP and Ashland OiI Co.), the Detol and / or Pyrotol process (Air Products and Chemicals, Houdry Division) and the Bextol process (Shell). Typically, these processes are carried out at temperatures between 550 and 650 ° C and pressures between 5 and 55 bar with chromium oxide / alumina catalysts, the benzene purity is usually> 99.9%. Examples of thermal processes are the MHC process (Mitsubishi Petrochemical Co.), the HDA process (Arco and Hydrocarbon Research) and the THD process (GuIf OiI).

In some cases coupled processes of naphtha reforming and hydrodealing are described. For example, S.A. Tobacco et al. in US 4,341,622 to reform heavy naphtha and hydrodealkylate the resulting heavy raffinate in the presence of an acidic catalyst. This principle is taken up in US 5,865,986 and US 2003/0038058, wherein the reforming naphtha takes place in each case on a plurality of catalyst beds and wherein for the hydrodealkylation a Co, Ni, Pt, or Pd-containing catalyst (US 5,865,986) or preferably a ZSM-5-containing catalyst (US 2003/0038058) is used.

No. 4,158,025 describes a process in which, in a first step, naphtha is reacted in the presence of hydrogen to form aromatic hydrocarbons, then in a second stage a dealkylation is carried out and in a third stage the products obtained are separated.

Since an excess of hydrogen has to be used in particular in naphtha reforming as well as in hydrodealkylation, high demands are placed on hydrogen recycling, i. in particular to the separation of the hydrogen from the resulting product gas mixture. The method used for this is called coldbox technology.

Despite these advances, there remains a need to provide alternative methods of preparing dealkylated aromatic compounds, particularly benzene.

It has now been found that aromatization of non-aromatic hydrocarbons having 6 or more carbon atoms in the presence of water vapor and a catalyst (step I) can be combined with a Hydrodealklierung the thus obtained aromatic hydrocarbons (step II), and so benzene or dealkylated aromatic hydrocarbons can be prepared in high yields with high purity.

The present invention thus relates to a process for the dealkylation of alkyl-substituted aromatic hydrocarbons, wherein in

Step (II) at least a portion of the product stream I obtained in step (I), which contains alkyl-substituted aromatic hydrocarbons, is reacted with the aid of hydrogen, optionally in the presence of a catalyst, by dealkylating the alkyl-substituted aromatic hydrocarbons.

According to the process of the invention, non-aromatic hydrocarbons can be aromatized in step (I). The non-aromatic hydrocarbons usually have at least 6 carbon atoms, in particular 6 to 20 carbon atoms. The non-aromatic hydrocarbons are paraffins, naphthenes, or mixtures thereof. Furthermore, the non-aromatic hydrocarbons may also include olefins on a case-by-case basis. The proportion is usually <1 wt.%.

The feed stream usually used in step (I) generally contains aromatic and non-aromatic hydrocarbons having 6 to 20, preferably 7 to 20, in particular 7 to 12 carbon atoms. Usually, the proportion of non-aromatic compounds (paraffins, naphthenes and optionally olefins) is at least 1 wt .-%, preferably at least 5 wt .-% and in particular at least 10 wt .-%. In a further embodiment, the proportion of non-aromatics is from 5 to 80% by weight, preferably from 10 to 50% by weight and in particular from 10 to 30% by weight. In a further embodiment, it is also possible that the feed contains only non-aromatic hydrocarbons.

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

The BTX cut is a mixture of aromatic and non-aromatic hydrocarbons composed of between 6 and 9 hydrocarbons. Typical examples of the aromatic hydrocarbons are benzene, toluene and xylene (= BTX), typical examples of the non-aromatic hydrocarbons are n-hexane, n-heptane, n-octane, cyclohexane, methylcyclopentane and methylcyclohexyl.

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 feed stream of step (I) may contain sulfur containing compounds, 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.

In a particular embodiment, the so-called TX cut of a steam cracker is used.

The aromatization according to step (I) is usually carried out between 300 and 800.degree. C., preferably between 400 and 700.degree. C., in particular between 500 and 600.degree. 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") of step (I) is usually from 0.1 to 10 parts by volume of feed stream per part by volume of catalyst per hour (l / l "h), preferably from 0.5 to 5 l / l »h, especially at 1 to 3 (l / l» h).

The molar ratio of steam / carbon (steam / carbon) of the feed stream used in step (I) is usually from 0.01 to 20, preferably from 0.1 to 15, in particular from 0.2 to 10th

As catalysts for the aromatization in the presence of water vapor (catalyst step-I) conventional catalysts known to those skilled in the art can be used. For the aromatization of non-aromatic hydrocarbons in the presence of water vapor, numerous catalysts have been proposed which contain a porous support and generally at least one metal deposited on this support. Often, alumina is used as the carrier here.

Thus, US 4,304,658 describes rhodium supported on alumina. In addition to rhodium, copper may also be supported on the alumina support, as described in US Pat. No. 4,320,240 or chromium and potassium as disclosed in US 4,304,658 or rhenium, copper and optionally potassium as taught in RU 2,193,920.

Furthermore, it is known that with the catalysts disclosed in DE 196 16 736, which contain at least one element selected from the elements of group VIII of the Periodic Table and / or rhenium and / or tin on a titania or zirconia support, from paraffinic / naphthenic hydrocarbon streams aromatic hydrocarbons can be produced.

It is likewise possible to use catalysts which contain, on the one hand, mixed carriers containing aluminum oxide and tin oxide, titanium oxide and / or zirconium oxide and, on the other hand, a metal selected from the group chromium, molybdenum and tungsten (US Pat. No. 3,197,523). Likewise catalysts are used which contain a metal of the platinum group on a support.

However, it is also possible to use aluminum spinels as supports for the corresponding catalysts. Thus, EP 454 022 teaches a carrier which also contains calcium aluminate in addition to zinc aluminate, which leads to an increase in activity and selectivity of the catalyst.

In a preferred embodiment, catalysts which contain a zirconium oxide-containing support, as well as platinum and tin, are suitable.

In particular, there are used catalysts (catalyst step-I-Pt / Sn) containing a-1) a zirconia-containing support; b-l) platinum, in particular 0.01 to 5 wt .-%, based on the total weight of

catalyst; c-l) tin, in particular 0.01 to 20 wt .-%, based on the total weight of

catalyst; wherein the weight ratio of tin to platinum is at least 1.

The catalyst step I PtySn used contains, as component a-1), a zirconium oxide-containing support.

This can consist essentially of zirconium oxide. (Commercial zirconia contains impurities that are in the range of less than 1% by weight based on the total weight of the merchandise.)

It is also possible to use a stabilized zirconia-containing carrier. Suitable stabilizers are all compounds which are tetragonal or monoclinic Stabilize structure of zirconia. In particular, the stabilizers are used which cause and / or stabilize the tetragonal structure of the zirconia. Preferably, the stabilized zirconia-containing carrier contains cerium, lanthanum and / or silicon, preferably cerium and / or lanthanum. In a further embodiment, the stabilized zirconium oxide-containing support contains in particular cerium (III) oxide, lanthanum (III) oxide and / or silicon (IV) oxide, preferably cerium (III) oxide and / or lanthanum (III) oxide. One or more stabilizers can be used. When cerium (III) oxide is used as a stabilizer, the stabilized zirconia-containing carrier usually contains up to 40% by weight, preferably 10 to 30% by weight, especially 15 to 30% 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 20% 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. And in the event that both cerium (III) oxide and lanthanum (III) oxide are used as stabilizers, the stabilized zirconia-containing carrier usually contains up to 40% by weight, preferably 5 to 30% by weight. %, in particular 10 to 25 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.

Furthermore, the zirconia-containing carrier may also contain adjuvants. These are suitable for facilitating the shaping of the zirconia-containing support. Typical auxiliaries are, for example, graphite, waxes, silicon dioxide and aluminum oxide. These adjuvants can either be added by themselves or in the form of their precursors, which convert to the corresponding excipient during calcining. Examples of these are silica precursors, e.g. Tetraalkyl orthosilicates and colloidal silica, as well as alumina precursors, e.g. Boehmite, such as Pural® (Sasol). Preferably, auxiliaries used are graphite, waxes and aluminum oxides, in particular aluminum oxides.

The zirconia-containing carrier can contain up to 40% by weight, based on the total weight of the zirconia-containing carrier, of auxiliaries. In a preferred embodiment, the zirconium oxide-containing support comprises from 5 to 40% by weight, preferably from 10 to 35% by weight, based on the total weight of the zirconium oxide support, of auxiliaries. The catalyst step I-Pt / Sn contains as component bl) 0.01 to 5 wt .-%, based on the total weight of the catalyst step-I-Pt / Sn, platinum. In a preferred embodiment, the catalyst step-I-Pt / Sn contains 0.1 to 2 wt .-%, preferably 0.3 to 1 wt .-%, based on the total weight of the catalyst step-I, Platinum.

Furthermore, the catalyst step-I-Pt / Sn as component c-1) contains from 0.01 to 20% by weight, based on the total weight of the catalyst step-I-Pt / Sn, of tin. In a preferred embodiment, the catalyst step-I-Pt / Sn contains 0.5 to 10% by weight, preferably 1 to 5% by weight, based on the total weight of the catalyst-step-I-Pt / Sn, tin ,

The weight ratio of tin to platinum is generally at least 1, preferably at least 2, in particular at least 3.

In a further embodiment, the catalyst step I-Pt / Sn as component d-1) contains at least one further promoter.

Further promoters are metals selected from the group of scandium, yttrium, lanthanum, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, rhodium, iron, ruthenium, cobalt, iridium, nickel, palladium, Copper, silver, gold, zinc, indium, germanium, lead, arsenic, antimony, bismuth, cerium, praseodymium, neodymium and europium, or mixtures thereof. Preferably, vanadium, chromium, rhenium, iron, nickel, copper or mixtures thereof are used as promoters. In particular, vanadium, chromium, copper or mixtures thereof are used.

In a particular embodiment, at least one further promoter, for example two further promoters, from the above-mentioned group is used.

In a further particular embodiment, the catalyst step I-Pt / Sn contains 0.01 to 20 wt .-%, preferably 0.1 to 15 wt .-%, in particular 0.5 to 10 wt .-%, based on the total weight of the catalyst step-I-Pt / Sn, another promoter.

In a further embodiment, the catalyst step I-Pt / Sn as component el) contains at least one metal whose metal compound is alkaline, preferably at least one metal oxide which reacts alkaline, in particular at least one oxide of an alkali metal, alkaline earth metal or lanthanum. The alkali metal is preferably potassium or cesium and alkaline earth metal preferably barium into consideration. Preferably, oxides of potassium or lanthanum are used.

In a further particular embodiment, a metal compound, wherein the metal in question is selected from the group of alkali metals, alkaline earth metals and lanthanum, and which reacts alkaline, preferably a metal oxide, as mentioned above, is used.

In a further particular embodiment, two metal compounds, wherein the metals in question are selected from the group of alkali metals, alkaline earth metals and lanthanum, and which react alkaline, preferably two metal oxides as listed above, are used.

In a further particular embodiment, the catalyst step I-Pt / Sn contains 0.01 to 20 wt .-%, preferably 0.1 to 15 wt .-%, in particular 0.5 to 10 wt .-%, based on the total weight of the catalyst step-I, at least one metal whose metal compound used is alkaline, preferably this metal compound contains an alkali metal, alkaline earth metal or lanthanum.

The catalyst step I-Pt / Sn usually has a BET surface area (determined according 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.

As a rule, the pore volume of the catalyst step I-Pt / Sn (determined by means of Hg porosimetry according to DIN 66133) is 0.1 to 1 ml / g, preferably 0.15 to 0.6 ml / g, in particular at 0.2 to 0.4 ml / g.

Usually, the zirconia phases of the catalyst step-I-Pt / Sn are tetragonal and / or monoclinic (determined by X-ray diffraction (XRD)).

In a particular embodiment, the catalyst step-I-Pt / Sn a-1) contains a zirconia-containing support;

bl) from 0.01 to 5% by weight, based on the total weight of the catalyst, of Step-I-Pt / Sn, platinum; c1) 0.01 to 20% by weight, based on the total weight of the catalyst, of step-I-Pt / Sn, tin; dl) at least one further promoter; wherein the weight ratio of tin to platinum is at least 1. In a further particular embodiment, the catalyst step-I-Pt / Sn al) comprises a zirconia-containing support; bl) from 0.01 to 5% by weight, based on the total weight of the catalyst step I

Pt / Sn, platinum; c-l) from 0.01 to 20% by weight, based on the total weight of the catalyst step I

Pt / Sn, tin; e-1) at least one metal whose metal compound is alkaline; wherein the weight ratio of tin to platinum is at least 1.

In a further particular embodiment, the catalyst step-I-Pt / Sn a-1) comprises a zirconia-containing support; b-1) from 0.01 to 5% by weight, based on the total weight of the catalyst, of step-I-Pt / Sn, platinum; c-1) from 0.01 to 20% by weight, based on the total weight of the catalyst, of step-I-Pt / Sn, tin; d-l) at least one further promoter; e-1) at least one metal whose metal compound is alkaline; wherein the weight ratio of tin to platinum is at least 1.

In a further particular embodiment, the catalyst step-I-Pt / Sn a-1) comprises a zirconia-containing support consisting essentially of zirconia; b-l) from 0.01 to 5% by weight, based on the total weight of the catalyst step I

In a further particular embodiment, the catalyst step-I-Pt / Sn a-1) comprises a zirconia-containing support which a1) contains at least one stabilizer; b-l) from 0.01 to 5% by weight, based on the total weight of the catalyst step I

Pt / Sn, tin; e-1) at least one metal whose metal compound is alkaline; the

Weight ratio of tin to platinum is at least 1.

In a further particular embodiment, the catalyst step-I-Pt / Sn al) comprises a zirconia-containing support which a1-l) at least one stabilizer; a2-l) an adjuvant; contains; bl) from 0.01 to 5% by weight, based on the total weight of the catalyst step I

The preparation of the catalyst step-I-Pt / Sn can suc conditions by conventional methods.

For example, it is possible to prepare the zirconia-containing support from corresponding compounds which convert to zirconia upon calcining. For this purpose, in particular hydroxides, carbonates and carboxylates are suitable. The zirconium oxide or the corresponding precursor, which is converted into zirconium oxide during calcining, can be prepared by methods known per se, such as e.g. by the sol-gel method, by precipitation, dehydration of the corresponding carboxylates, dry mixing, slurrying or spray-drying. The precipitation usually employs soluble zirconium salts, e.g. the corresponding halides, preferably chloride, alkoxides, nitrate, etc., preferably nitrate.

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

Furthermore, it is possible to prepare the stabilized zirconium oxide-containing support from compounds which convert to zirconium oxide or cerium (III) oxide, lanthanum (III) oxide, silicon (IV) oxide on calcination. For this purpose, in particular hydroxides, carbonates and carboxylates are suitable. These are for example precipitated together, spray-dried together etc.

The zirconia described above, the stabilized zirconia described above or the corresponding precursors can be mixed with auxiliaries which are suitable for facilitating the shaping of the zirconia support. Subsequently, the shaping takes place. As a rule, strands, tablets, spheres, chippings, monoliths, etc. are prepared by processes known to those skilled in the art.

The zirconium oxide described above, the above-described stabilized zirconium oxide 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 ° C, preferably at 500 to 600 ° C. It may be advantageous to add water vapor to the air or to the air / nitrogen mixture.

The platinum or tin can now be applied to the zirconia-containing supports. Usually, the carrier is impregnated with a solution of suitable platinum precursors or suitable tin precursors. The impregnation can be carried out by the incipient-wetness method, wherein the pore volume of the support is filled up with approximately the same volume of impregnating solution and, optionally after ripening, the support is dried; or you work with an excess of solution, the volume of this solution is greater than the pore volume of the carrier. In this case, the carrier is mixed with in the impregnating solution and stirred for a sufficient time. Furthermore, it is possible to spray the carrier with a solution of the platinum precursor or of the tin precursor. In general, the order of the impregnations does not matter. But it may also be advantageous to apply the individual precursors in a certain order. It is also possible to impregnate with a solution containing both the platinum and the tin precursor. But also other manufacturing methods known to the person skilled in the art, such as e.g. Precipitation, Chemical Vapor Deposition, Soltränkung etc. are possible.

Suitable platinum precursors are platinum salts, i.a. Halides, in particular chloride, nitrate, acetate, alkaline carbonates, formate, oxalate, citrate, tartrate, but also platinum complexes. The latter may contain, as neutral ligands, Lewis bases, such as amines or phosphanes, and as anionic ligands, halides, such as chloride, bromide or nitrate, etc.

Suitable tin precursors are tin salts, in particular tin (II) salts, i.a. Halides, especially chloride, sulfate, acetate, formate, oxalate, citrate, tartrate, but also alkali and / or Erdalkalistannate such. Sodium stannate.

Catalyst Step-I containing one or more further promoters are prepared by applying the promoter precursor or promoter precursors in analogy to the platinum or tin plating processes. Suitable promoter precursors include halides, in particular chlorides, nitrates, acetates, alkaline carbonates, formates, oxalates, citrates, tartrates, corresponding 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 further promoter, the corresponding promotor precursor can be applied together with the platinum and / or tin precursor. But it is also possible to apply them one after the other. It can also be advantageous to apply the individual precursors in a certain order.

If the catalyst contains several further promoters, then the promoter precursors can be applied together or separately. It is also possible to apply the platinum and / or tin 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.

If catalyst step I are used which contain at least one metal whose metal compound is alkaline, the alkaline metal precursor or the alkaline metal precursors are applied analogously to the processes for platinum or tin plating.

As alkaline metal precursors are usually used compounds which convert to the corresponding oxides during calcining. Suitable for this are hydroxides, carbonates, carboxylates, e.g. Formates, acetates, oxalates, nitrates, hydroxycarbonates etc.

Also in the catalyst step I-Pt / Sn, which contain one or more alkaline metal precursors, the respective precursors can be applied together or separately. In the case of a separate application, it may also be advantageous to apply the individual precursors in a certain order.

The zirconia-containing support on which the platinum precursor, the tin precursor and optionally the promoter precursor (s), and optionally the alkaline metal precursor (s) are 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 ° C, preferably at 400 to 600 ° C. It may be advantageous to add water vapor to the air or to the air / nitrogen mixture. The catalyst step I-Pt / Sn thus obtained is usually activated before it is used in the aromatization of non-aromatics. For this purpose, it is treated with hydrogen or a mixture of hydrogen and nitrogen at temperatures of 100 to 800 ° C, preferably at 400 to 600 ° C. 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.

The activation of the catalyst step-I-Pt / Sn is usually carried out in the reactor in which the aromatization of non-aromatics is to take place. However, it is also possible to carry out the activation of the catalyst step-I before installation in the corresponding reactor. (This also applies to the known catalytic converter step

I) -

However, it is also possible to use the catalyst step I-Pt / Sn without prior activation in the aromatization of non-aromatics. (This also applies to the known catalysts step I.)

In the course of the reaction, under the given reaction conditions, coke and / or coke precursors may form at the active sites and in the pores of the catalyst Step-I. 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 causes the activity and / or selectivity of the catalyst step-I 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 coke precursor without adversely affecting the physical properties of the catalyst step-l.

The coke precursors can be removed by evaporation in the presence of an intergas at elevated temperature (T> 250 ° C.) and / or hydrogenation in the presence of a hydrogen-containing gas mixture and / or combustion in the presence of an oxygen-containing gas mixture.

The removal of the coke deposits is usually carried out by combustion of the coke in the presence of an oxygen-containing gas mixture (= oxidative regeneration). The regeneration of the catalyst step-I can take place in-situ or ex-situ, preference is given to in situ regeneration. 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 step-I is carried out in the presence of water vapor.

After the oxidative regeneration of the catalyst step-I is usually carried out an activation in the presence of hydrogen.

In one embodiment of the step (I) according to the invention, the feed used and the water are in an evaporator according to the selected reaction pressure, which is usually between 1 and 50 bar, preferably between 3 and 30 bar, in particular between 5 and 25 bar 100 to 400 ° C evaporated; brought this steam in a preheater to the desired reaction temperature, which is preferably 400 to 700 ° C, in particular at 500 to 600 ° C, and then introduced into the reactor. The heating may e.g. done in a fired oven. It may also be useful to use at least partially for the heating or evaporation of the feed and the water obtained in the condensation of the product gas obtained in step II, heat.

The reactors used are generally fixed-bed reactors, tube-bundle reactors or fluid-bed reactors. In adiabatic driving usually a fixed bed reactor is used in isothermal driving usually a tube bundle reactor.

It is also possible to operate the reactor autothermally with the supply of air, oxygen or an oxygen-containing gas. To counteract the endotherm and associated temperature drop in the reactor, the hydrogen formed in the reaction (and / or the hydrocarbons and / or the carbon monoxide formed in the reaction and / or the coke formed in the reaction) is oxygenized with heat generation oxidized. For this purpose, a corresponding oxygen-containing gas is fed into the reactor.

It is also possible to operate the process according to the invention autothermally. In an autothermal procedure, the endotherm of the aromatization reaction and the associated temperature drop in the reactor is counteracted by the introduction of heat. The introduction of the heat can take place both inside and outside the reactor.

If the heat is supplied outside the reactor, this is preferably done via a heat exchanger.

In a particular embodiment, the heat is generated within the reactor by reacting the hydrogen formed during the aromatization and / or the remaining hydrocarbons and / or the methane formed during the aromatization and / or the coke formed during the aromatization with oxygen. For this purpose, air, oxygen and / or an oxygen-containing gas are fed into the reactor.

Step (I) of the process according to the invention can be carried out in a single reactor. However, it is also possible to carry out the reaction in a plurality of reactors connected in series (reactor cascade), with intermediate heating (s) optionally being inserted between the individual reactors.

The autothermal procedure by supplying air, oxygen or an oxygen-containing gas or a reactor cascade with intermediate heaters is particularly useful if the feed stream contains a larger amount of non-aromatic hydrocarbons, especially if their content is> 30 wt .-%.

The product stream obtained in step (I) ("reaction product step I") is rich in hydrogen and aromatic hydrocarbons, in particular containing, in addition to benzene, alkyl-substituted aromatic hydrocarbons which usually have 7 to 20 carbon atoms. As a rule, monoalkyl-substituted aromatic hydrocarbons are, for example, toluene, ethylbenzene or propylbenzene; with multiply alkyl-substituted aromatic hydrocarbons to xylene, mesitylene, etc. But also alkylated aromatic hydrocarbons with condensed cores, such as alkyl-substituted naphthalenes can be included. Furthermore, the reaction product step-I may contain unreacted non-aromatics and aromatics as well as cracking products.

The reaction product step-I is now - without further separation - directly subjected to step (II), wherein in the reaction product step-I contained alkyl-substituted aromatic hydrocarbons, optionally in the presence of a catalyst, by means of reaction in the reaction step-I obtained hydrogen, be dealkylated.

In a further embodiment, a condensation of the reaction product step-I is carried out and the water, for example by phase separation, separated. In the- sen case, the hydrogen-rich gas can be partially or completely separated, or preferably used in step Il. Possibly. it is necessary to meter in hydrogen-containing gas, such as pure hydrogen, in step (II), so that for the Hydrodealklierung the necessary amount of hydrogen is present.

Optionally, it may be necessary to interpose a densification step between step (I) and step (II) if the hydrodealkyation is carried out at higher pressures than the aromatization.

In one embodiment, the reaction product step-I is completely subjected to step (II).

In another embodiment, the reaction product step-I is subjected to step (II) without compression or relaxation.

In another embodiment, the two stages are operated at equal pressures.

If the process is operated with intermediate condensation, the organic phase which forms during the condensation can be brought to the desired pressure for the hydrodealkyation with the aid of a pump and the gas phase can be brought to the desired pressure with a compressor.

The feed stream used in the hydrodealkylation in step (II) as a rule contains at least 50% by weight, preferably at least 80% by weight, particularly preferably at least 90% by weight, of an alkyl-substituted aromatic hydrocarbon or a mixture of these.

The hydrodealkyation in step (II) is usually carried out between 400 and 900 ° C., preferably between 500 and 900 ° C. The pressure is in this case in a range of 5 to 100 bar, preferably from 10 to 80 bar, in particular from 20 to 70 bar.

The dehydroalkylation can be carried out with or without addition of catalyst. If no catalyst is used, the reaction is carried out in a correspondingly higher temperature range.

In one embodiment, step (II) of the process according to the invention is carried out in the presence of a catalyst (catalyst step II). For this purpose, known in the art Hydrodealkylierungskatalysatoren be used. As a rule, these are catalysts which contain a porous support and optionally at least one metal deposited on this support.

In particular, Cr ₂ O ₃ have, MO ₂ O _3, or CoO ₂ on supports such as Al ₂ O _3, as suited proven (K. Weissermel, HJHarpe, Industrial Organic Chemistry, 4th edition, p 358). Also suitable are zeolite-containing supports (US Pat. No. 4,341,622), in particular they may contain Co, Ni, Pt and / or Pd (US Pat. No. 5,865,986). Also suitable are catalysts containing a metal of the platinum group, Sn, Ti, Zr Cr, Mo, W (US 3,204,007, US 3,197,523).

It is also possible to operate the reactor autothermally with the supply of air, oxygen or an oxygen-containing gas. To counteract the endotherm and associated temperature drop in the reactor, the hydrogen formed in the reaction (and / or the hydrocarbons and / or the carbon monoxide formed in the reaction and / or the coke formed in the reaction) is oxidized with oxygen with the generation of heat. For this purpose, a corresponding oxygen-containing gas is fed into the reactor.

It is also possible to operate the process according to the invention autothermally. In an autothermal procedure, the endotherm of the dealkylation reaction and the temperature drop associated therewith in the reactor is counteracted by the introduction of heat.

The introduction of the heat can take place both inside and outside the reactor.

In a particular embodiment, the heat is generated within the reactor by reacting the hydrogen formed in the dealkylation and / or the remaining hydrocarbons and / or the carbon monoxide formed during the dealkylation and / or the coke formed in the dealkylation with oxygen. For this purpose, air, oxygen and / or an oxygen-containing gas are fed into the reactor.

In the course of the reaction, under the given reaction conditions, coke and / or coke precursors may form at the active sites and in the pores of the catalyst step-II. 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 the coke precursor causes the activity and / or selectivity of the catalyst step-II 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 coke precursor, without adversely affecting the physical properties of the catalyst step II.

The removal of the coke deposits is usually carried out by combustion of 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, preference is given to in situ regeneration. 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 step II is carried out in the presence of water vapor.

After the oxidative regeneration of the catalyst step II, activation usually takes place in the presence of hydrogen.

The product of step II ("reaction product step H") obtained according to the process of the invention is rich in methane, optionally lower alkanes, e.g. Ethane, and dealkylated aromatic hydrocarbons, especially benzene. Furthermore, it optionally contains excess hydrogen.

From the reaction product step II, the dealkylated aromatic hydrocarbons formed are separated by conventional methods. For this purpose, the reaction product step II is relaxed and cooled. It is expedient to integrate the released heat in the process (heat combination), for example, the Feed stream to the reaction step I or other heated streams (eg evaporator of the column) to heat. Upon cooling, a gas phase rich in methane and optionally hydrogen, and a liquid phase is formed.

The gas phase may e.g. be worked up in a coldbox and so the hydrogen are separated. It is also possible that the hydrogen is e.g. is separated by pressure swing adsorption (PSA). The hydrogen is recycled back into the process, preferably in step (II). However, it is also possible for the gas phase per se to be returned to the process, preferably step (II).

The liquid phase formed during the cooling, which contains the dealkylated aromatic hydrocarbon, preferably benzene, and excess water (if used without intermediate condensation) of the process, 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, may be further purified, for example by distillation. The products obtained in the distillation may optionally be recycled to steps (I) and / or (II).

In a particular embodiment, benzene and optionally impurities are removed overhead and C7 + hydrocarbons via the bottom in a distillation column. The C7 + mixture is recycled either in step (I) (if non-aromatic hydrocarbons are still present) or step (II) (if no or only a small amount of non-aromatic hydrocarbons are present).

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 designed as columns with side draw or as a dividing wall column.

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 further embodiments, prior to step (I) and / or step (II), units for reducing the olefin and sulfur content are incorporated into the process. Here, method steps according to the prior art are used.

The process according to the invention makes it possible to produce benzene in high purity without the need for complicated extractive distillations. In addition, by coupling steps (I) and (II), the hydrogen to be externally supplied to the system is reduced compared to a normal hydrodealing, since the hydrogen produced in step (I) is used immediately in step (II) can be.

Claims

1Patentansprüche

1. A process for the dealkylation of alkyl-substituted aromatic hydrocarbons, wherein in step (I) non-aromatic hydrocarbons having at least 6 carbon atoms are aromatized in the presence of water vapor and a catalyst; and in

Step (II) at least part of the product stream I (reaction product step I) obtained in step (I), which contains alkyl-substituted aromatic hydrocarbons, with

Help of hydrogen, if necessary in the presence of a catalyst is reacted by dealkylating the alkyl-substituted aromatic hydrocarbons.

2. The method of claim 1, wherein the reaction product step-I is used completely in step (II).

3. The method of claim 1 or 2, wherein from the reaction product step-I, the water contained is partially or completely separated.

4. The method according to any one of claims 1 to 3, wherein from the reaction product step-I, the hydrogen contained is partially or completely separated.

A process according to claim 1 or 2, wherein the reaction product step-I is subjected to step (II) without compression or relaxation.

6. The method of claim 1 or 2, wherein the reaction product step-I is subjected after compression to step (II).

7. The method according to any one of claims 1 to 6, wherein the step (I) is operated with the addition of an oxygen-containing gas.

8. The method according to any one of claims 1 to 7, wherein the step (II) is operated with the addition of an oxygen-containing gas.

9. The method according to any one of claims 1 to 8, wherein step (II) is carried out in the presence of a catalyst.

A process according to any one of claims 1 to 9, wherein the catalyst used in step (I) comprises a zirconia-containing carrier.

1 1. The method according to any one of claims 1 to 10, wherein the catalyst used in step (I) contains platinum.

12. The method according to any one of claims 1 to 1 1, wherein the catalyst used in step (I) contains tin.

13. The method according to any one of claims 1 to 12, wherein the catalyst used in step (II) comprises an alumina-containing carrier.

14. The method according to any one of claims 1 to 13, wherein the catalyst used in step (II) contains at least one metal selected from the group VIB, the group VIIIB, Ti, Zr or Sn.

A process according to any one of claims 1 to 14, wherein the feed stream used in step (I) contains at least 1% by volume of non-aromatic hydrocarbon having at least 6 carbon atoms or mixtures thereof.

A process according to claim 15, wherein the feed stream used in step (I) contains at least 10% by volume of non-aromatic hydrocarbon having at least 6 carbon atoms or mixtures thereof.