HK1108155B - Catalyst and process for the preparation of alkylated aromatic hydrocarbons - Google Patents

Description

Catalyst and process for preparing alkylated aromatic hydrocarbons

The present invention relates to a novel zeolite having a beta-type crystal structure characterized by a specific distribution of acid site type. The novel zeolites are useful in processes for the production of alkylated aromatics by alkylation and/or transalkylation of aromatics. In particular, it is useful for the alkylation of benzene with ethylene or propylene and the transalkylation of benzene with polyisopropylbenzenes or polyethylbenzenes to yield cumene and ethylbenzene, respectively. The preparation of the novel zeolites is also an object of the present invention.

The use of zeolite beta as an alkylation or transalkylation catalyst for aromatic substrates has been known for some time. The best results have been obtained in industrial applications, for example the synthesis of cumene and ethylbenzene using zeolites with a beta-type structure as described in EP432,814, in particular using catalysts containing beta zeolite as described in EP 687,500 and EP 847,802.

Industrial processes for producing cumene and ethylbenzene over a zeolite catalyst are generally characterized by the presence of an alkylation stage in which a monoalkylated product is obtained together with a specific portion of polyalkylated by-products and impurities and by the presence of a transalkylation stage in which polyalkylated by-products are recovered to reproduce the monoalkylated product and impurities.

In these processes, the selectivity of the monoalkylated product of the alkylation stage is of critical importance (it must be as high as possible, so that the polyalkylated product content to be recovered in the subsequent transalkylation stage is low), and it is also important that the yield of impurities is low, in particular those having boiling points very close to that of the monoalkylated product, such as n-propylbenzene when cumene is produced, or xylenes when ethylbenzene is produced.

In the industrial production of cumene and ethylbenzene, the reduction of other impurities, such as oligomers, butylbenzene in the production of cumene, pentylbenzene or diphenylethane in the production of ethylbenzene, also plays an important role.

It has been found that a novel zeolitic material having a beta-type crystal structure and particular acidity characteristics, is capable of achieving higher selectivity to monoalkylated product with less formation of impurities.

Beta zeolites are described for the first time in U.S. patent 3,308,069, having a chemical composition of the general formula:

(x/n)M·(1.0-x)TEA·AlO₂·ySiO₂·wH₂O (I)

wherein y is 5 to 100, w is less than or equal to 4, M is a metal ion such as, for example, sodium, n is the valence of the metal ion M, x can be a number from 0 to 1, and TEA is a tetraethylammonium ion.

It is known that metal ions can be removed from zeolites by ion exchange, for example using ammonium nitrate. After the subsequent calcination, the zeolite is obtained in its so-called acid form.

The presence of different types of acid sites in beta zeolite, known as bronsted sites (proton sites), and acid sites known as lewis sites (aprotic sites), is described, for example, in Zeolites, 1990, 10, 304, v.l.zhoolobenko et al and j.cat., 1998, 180, 234, p.j.kunkeler et al.

Qualitative and quantitative determination of bronsted and lewis acid sites by infrared spectroscopy can be carried out, for example, as described by c.a. emeris in Journal of Catalysis, 1993, 141, 347, with the aid of probe molecules, of which pyridine is the most widely used.

It is known that the amount and nature (bronsted or lewis) of acid sites in most zeolites, especially beta zeolite, can be altered by post-synthesis operations on the zeolitic material, including ion exchange treatment, steam treatment, treatment with acid or thermal treatment.

These treatments are generally aimed at detaching the aluminium structures present in the zeolite lattice and redistributing them in positions outside the lattice, or at removing said aluminium from the zeolite to obtain, for example, a zeolite with a high Si/Al ratio.

Dealumination treatments represent in fact a major and most widely used class of zeolite post-synthesis treatments for enhancing catalytic performance.

The use of steam for post-synthesis dealumination treatment was described in Zeolites 1990, 10, 304, v.l.kholobenko et al and the results demonstrate that the catalytic activity of HZSM-5 zeolite for cracking n-hexane is considerably improved. The improvement in the performance of the HZSM-5 zeolite may result from the presence of lewis acid sites, presumably due to the extra-structural aluminum produced by the action of the dealumination treatment with steam. On the other hand, in other cases, the presence of lewis acid sites generated by post-synthesis treatments such as those described above may prove to be disadvantageous, depending on the particular chemical reaction in which the catalyst is used.

According to the description of appl.cal.a, 1999, 185, 123, Baburek j.et al, in the case of beta zeolite, the presence of, for example, lewis sites is disadvantageous in terms of the catalytic performance of the n-butane isomerization reaction.

For example, dealumination post-synthesis treatment on beta zeolite is described in US5,310,534, wherein the beta zeolite used is in non-calcined form and still contains organic compounds resulting from the synthesis, and also in EP 0690024, wherein the beta zeolite is instead in calcined form, i.e. in a form free of organic compounds from the synthesis.

For example, j.catal., 1998, 180, 234p.j.kunkeler et al, describes post-synthesis treatment of beta zeolite by calcination under controlled conditions, which should result in the formation of lewis acid sites capable of enhancing the catalytic properties of beta zeolite in the Meerwein-Ponndorf-Verley reaction for the reduction of ketones.

In US5,116,794, a beta zeolite is described, prepared by a series of conventional ion exchange, calcination and activation treatments at temperatures in the range of 625-675 ℃, resulting in an increased activity in the cracking reaction of n-butane.

The applicant has found that it is possible to synthesize, without any post-synthesis treatment, a beta zeolite characterized by a particular distribution of acid sites type on the surface, which catalyst achieves enhanced catalytic performance in a process for the preparation of alkylated aromatic compounds by alkylation and/or transalkylation of aromatic compounds.

Accordingly, a first object of the present invention relates to a beta zeolite characterized by a distribution of lewis acid sites (non-protonic acid sites) and bronsted acid sites (protonic acid sites), expressed as the molar ratio [ lewis sites ]/[ bronsted sites ], of greater than or equal to 1.5.

In the crystal lattice of the zeolite of the invention, SiO₂/Al₂O₃The molar ratio may vary within the range of 10 to 30, preferably 10 to 25.

In the acid form of zeolite obtained after calcination, Na⁺The ion content is preferably less than 200ppm relative to the weight of the zeolite.

The characterization and quantification of Broensted and Lewis acid sites is carried out in the target material of the invention by infrared spectroscopy with pyridine as probe molecule, as described by C.A. Emeis in Journal of Catalysis 1993, 141, 347.

The particular distribution characteristics of the lewis and bronsted acid sites of the material of the present invention allows the material to be optimally effective in the alkylation and transalkylation reactions of aromatic compounds. In particular, the materials used in the preparation reaction of alkylated aromatics may result in higher selectivity to monoalkylated products, reduced production of unrecoverable polyalkylated byproducts, reduced production of key byproducts, and reduced catalyst deactivation rates due to coke formation.

In the particular case of the industrial synthesis of cumene from benzene and propylene, the novel zeolite object of the present invention enables the reduction of the formation of propylene oligomers, which generally act as precursors of the heavy organic compounds forming so-called coking, which are responsible for the deactivation of the solid acid catalysts, in particular of the zeolite catalysts. In the industrial synthesis of cumene, this characteristic of the zeolitic material which is the object of the present invention is important for obtaining other particularly important results, namely a reduction in the formation of n-propylbenzene impurities. In the synthesis of cumene from benzene and propylene, increasing the reaction temperature actually contributes to the formation of n-propylbenzene, while decreasing the reaction temperature instead contributes to the formation of propylene oligomers. By using the zeolitic materials of the present invention, the reaction can be carried out at lower temperatures without compromising the duration of the catalyst, due to the reduced formation of propylene oligomers, with the advantage of a consequent reduction in the formation of n-propylbenzene.

The zeolitic materials of the present invention are prepared by a suitable process wherein the generation of the specific molar ratio of lewis and bronsted acid sites is determined.

Accordingly, a further object of the present invention relates to a process for the preparation of a beta zeolite characterized by a molar ratio of lewis-type and bronsted-type acid sites equal to or greater than 1.5.

U.S. patent 3,308,069 describes a process for the preparation of a beta zeolite, essentially comprising hydrothermal synthesis in an aqueous environment starting from a reaction mixture containing sources of silicon and aluminum and the templating agent tetraethylammonium hydroxide (TEAOH) in the following molar ratios:

[SiO₂]/[Al₂O₃]is 10-200

[TEAOH]/[SiO₂]Is 0.1-1.0

[H₂O]/[TEAOH]Is 20 to 75

[Na₂O]/[TEAOH]Is 0.0-0.1.

The reaction mixture is maintained at a temperature of 75-200 ℃ until a crystalline product of formula (I) is obtained.

It has now surprisingly been found that the acidity characteristics of the material, in particular the molar ratio of lewis and bronsted acid sites, i.e. the ratio [ lewis sites ]/[ bronsted sites ], can be predetermined by appropriate selection of the composition of the reaction mixture to be hydrothermally crystallized.

1. An acid form beta zeolite, said acid form beta zeoliteSiO in the crystal lattice of₂/Al₂O₃Is 10 to 25, and the distribution of Lewis acid sites and Bronsted acid sites, expressed as [ Lewis sites ], measured by infrared spectroscopy using pyridine as probe molecule is represented by]/[ Bronsted site]Equal to or higher than 1.5, wherein the infrared spectrum is recorded after desorption of the excess pyridine for 1 hour at 250 ℃ under vacuum.

2. The beta zeolite of item 1, wherein SiO₂/Al₂O₃Is 10 to 17.2.

3. The beta zeolite of item 1, in the form of submicron aggregates of crystals, wherein at least 90% of the crystals have a size less than

4. A catalytic composition comprising:

-the zeolite beta of item 1;

-an inorganic binder.

5. The catalytic composition of item 4, wherein the inorganic binder is selected from the group consisting of alumina, silica or magnesia, natural clays or mixtures thereof.

6. The catalytic composition of item 4, wherein the weight ratio of the binder to the zeolite is from 80: 20 to 5: 95.

7. Catalytic composition according to item 4, characterized in that the total volume of the zeolitic superporous porosity is greater than or equal to 0.80ml/g and at least 25% of the pore radii are greater than

8. A method for preparing a beta zeolite of item 1, comprising crystallizing at 190 ℃ at 150 ℃ in an aqueous environment under hydrothermal conditions for 10 to 240 hours a reaction mixture containing sodium aluminate and aluminum alkoxide or aluminum inorganic salt as aluminum sources, a silica source selected from the group consisting of colloidal silica, tetraalkyl silicate and amorphous silica, and tetraethylammonium hydroxide as a templating agent, the mixture having the following composition in terms of mole ratio:

[SiO₂]/[Al₂O₃]＝10-30

[TEAOH]/[SiO₂]＝0.10-0.35

[H₂O]/[SiO₂]＝7-20

[Na₂O]/[TEAOH]higher than 0.1

[ Na ]/[ Al ] is greater than 0.68 and less than 1.00, wherein TEAOH is tetraethylammonium hydroxide,

the mixture resulting from the crystallization is filtered, and the resulting solid product is ion-exchanged with an ammonium salt, followed by drying and calcination.

9. The process of item 8, wherein the crystallization is carried out at a temperature of 165-180 ℃ for 18-150 hours.

10. The method of item 8, wherein the aluminum alkoxide is selected from aluminum isopropoxide or aluminum tert-butoxide, the tetraalkyl silicate is selected from tetramethylsilicate, tetraethyl silicate or tetrapropyl silicate, and the inorganic salt of aluminum is selected from nitrate and sulfate.

11. The process of item 8, wherein the reaction mixture has the following composition in terms of molar ratios:

[SiO₂]/[Al₂O₃]＝10-25

[TEAOH]/[SiO₂]＝0.15-0.30

[H₂O]/[SiO₂]＝8-15

[Na₂O]/[TEAOH]greater than 0.1

[ Na ]/[ Al ] is greater than 0.68 and less than 1.00, wherein TEAOH is tetraethylammonium hydroxide.

12. The process of item 8, wherein the suspension resulting from the crystallization is acidified to pH3-6 and diluted with water in a ratio of (volume of water added)/(volume of suspension) of 1 to 10 before being subjected to filtration.

13. The process of item 8, wherein the solid product obtained by filtering the crystallized mixture is redispersed in water, subjected to an ion exchange treatment with an ammonium salt, filtered, dried at a temperature of 100 ℃ and 200 ℃ for 8 to 16 hours, and calcined at a temperature of 450 ℃ and 650 ℃ for 4 to 8 hours.

14. A process for alkylating an aromatic hydrocarbon, which comprises contacting an aromatic hydrocarbon with an olefin selected from the group consisting of ethylene and propylene in the presence of the zeolite beta of item 1.

15. The process of item 14, which is carried out at a temperature of 100 ℃ and 300 ℃ and the reaction pressure is generally from 1 to 100 bar.

16. The process of item 14, wherein the aromatic hydrocarbon is benzene.

17. The process of item 15, wherein the aromatic hydrocarbon is benzene and the olefin is propylene, and the reaction is carried out at a temperature of 100 ℃ and 200 ℃.

18. The method of item 17, carried out at a temperature of 120-180 ℃.

19. The process of item 15, wherein the aromatic hydrocarbon is benzene and the olefin is ethylene, and the reaction is carried out at a temperature of 150 ℃ and 250 ℃.

20. The method of item 19, conducted at a temperature of 170 ℃ and 230 ℃.

21. The method of item 15, conducted in at least a partial liquid phase.

22. The process of item 21, carried out at a pressure of from 10 to 50 bar.

23. The process of clause 14, wherein the molar ratio of aromatic compound to olefin introduced to the reaction is typically from 1 to 30.

24. A process for the transalkylation of aromatic hydrocarbons, the process comprising contacting an aromatic hydrocarbon with one or more polyalkylated aromatic hydrocarbons in the presence of the zeolite beta of item 1.

25. The process of item 24, wherein the aromatic hydrocarbon is benzene.

26. The process of clause 24 or 25, wherein the polyalkylated aromatic hydrocarbon is a mixture comprising predominantly dialkyl aromatic hydrocarbons.

27. The process of item 24 or 25, wherein the polyalkylated aromatic hydrocarbon is selected from diethylbenzene, optionally in admixture with triethylbenzene, and diisopropylbenzene, optionally in admixture with triisopropylbenzene.

28. The method of item 24, conducted at a temperature of 100 ℃ to 350 ℃.

29. The process of item 28, wherein the aromatic hydrocarbon is benzene and the polyalkylated aromatic hydrocarbon is polyisopropylbenzene at a temperature in the range of 150 ℃ to 250 ℃.

30. The process of item 28, wherein the aromatic hydrocarbon is benzene and the polyalkylated aromatic hydrocarbon is polyethylbenzene at a temperature in the range of 180 ℃ to 300 ℃.

31. The method of item 28, conducted under at least partial liquid phase conditions.

32. The method of item 31, conducted under liquid phase conditions.

33. The process of item 31 or 32, carried out at a pressure of from 20 to 50 bar.

34. The process of clause 24, wherein the molar ratio of aromatic hydrocarbon to total polyalkylated aromatic hydrocarbon is 1 to 40.

35. The method of clause 34, wherein the molar ratio is 3 to 30.

36. The method of item 14, comprising the steps of:

(a) contacting an aromatic hydrocarbon with an olefin selected from the group consisting of ethylene and propylene under alkylation conditions in the presence of the zeolite beta of item 1;

(b) separating the obtained product into a fraction containing aromatic hydrocarbons, a fraction containing monoalkylated aromatic hydrocarbons, a fraction containing polyalkylated aromatic hydrocarbons, a fraction mainly containing dialkylated aromatic hydrocarbons, and a fraction of heavy aromatic hydrocarbons;

(c) contacting a fraction comprising polyalkylated aromatic hydrocarbons, predominantly dialkylated aromatic hydrocarbons, with an aromatic hydrocarbon under transalkylation conditions in the presence of the zeolite beta of item 1;

(d) the product obtained in stage (c) is separated into the same fraction obtained in stage b), and the fraction containing aromatic hydrocarbons is subsequently partly recycled to stage (a) and partly to stage (c), and the fraction containing polyalkylated aromatic hydrocarbons is recycled to stage (c).

37. The process of clause 14 or 24, carried out in the presence of a catalytic composition comprising:

-the zeolite beta of item 1;

-an inorganic binder.

38. The method of clause 37, wherein the catalytic composition is characterized by a zeolite macroporosity greater than or equal to 0.80ml/g in total volume and at least 25% of the pore radius being greater than

According to the invention, zeolite beta is synthesized in an aqueous environment from a reaction mixture consisting of sodium aluminate and aluminum alkoxide, or aluminum inorganic salt instead of aluminum alkoxide as aluminum source, and a silica source selected from colloidal silica, tetraalkyl silicate and amorphous silica, and tetraethylammonium hydroxide as a templating agent.

The reaction mixture containing the above compounds is characterized by the following molar ratios:

[SiO₂]/[Al₂O₃]10-30, preferably 10-25

[TEAOH]/[SiO₂]0.10-0.35, preferably 0.15-0.30

[H₂O]/[SiO₂]7-20, preferably 8-15

[Na₂O]/[TEAOH]Higher than 0.1

For the purposes of the present invention, in addition to the abovementioned parameters, it is necessary to control the [ Na ]/[ Al ] molar ratio in the synthesis mixture to be strictly above 0.68 and below 1. As shown in the examples provided below, this parameter is particularly critical for the successful synthesis of the beta zeolite targeted by the present invention. In fact, if the molar ratio [ Na ]/[ Al ] is less than or equal to 0.68, no beta zeolite is obtained, but rather an amorphous and non-crystalline end product, if the molar ratio [ Na ]/[ Al ] is greater than or equal to 1.00, a well-crystallized beta zeolite is obtained, which is characterized in that the molar ratio of Lewis and Bronsted acid sites is always less than 1.5.

The tetraalkyl silicate may be selected from tetramethylsilicate, tetraethyl silicate or tetrapropyl silicate.

The aluminum alkoxide is preferably aluminum isopropoxide or aluminum tert-butoxide.

The aluminium salt may be aluminium nitrate or aluminium sulphate.

Crystallization of the zeolite from the reaction mixture is carried out under hydrothermal conditions at a temperature of 150 ℃ and 190 ℃, preferably 165 ℃ and 180 ℃ for 10 to 240 hours, preferably 18 to 150 hours.

The suspension or slurry thus obtained is filtered. The suspension obtained at the end of the crystallization can optionally be acidified, for example with acetic acid, hydrochloric acid, nitric acid, formic acid, propionic acid, oxalic acid, until a pH in the range 3-6 is reached, before filtration, and subsequently diluted with water in a ratio (volume of water added)/(volume of slurry) of 1-10.

The solid product obtained by filtration is redispersed in water and subjected to an ion exchange treatment with an ammonium salt, such as ammonium acetate, according to techniques known in the art, to give an ammonium/alkylammonium zeolite. At the end of the run, the solid thus obtained was filtered, dried at a temperature of 100-200 ℃ for a period of 8-16 hours, and subsequently calcined in air at a temperature of 450-650 ℃ for a period of 4-8 hours. The beta zeolite thus obtained has an L/B [ Lewis site ]/[ Bronsted site ] molar ratio of 1.5 or more.

The beta zeolite obtained according to the process of the invention also demonstrates a size generally smaller thanPreferably at least 90% of the crystals have a size less thanThis feature contributes to the beta zeolite in the present inventionCatalytic activity in the chemical reaction of interest.

Object of the invention-beta zeolite containing catalysts suitable for use in fixed bed catalyst reactors are prepared from an active phase of beta zeolite and an inorganic binder.

The inorganic binder is selected from alumina, silica or magnesia, natural clay or mixtures thereof, and the weight ratio of zeolite is 80: 20-5: 95, preferably 70: 30-10: 90. The mixture may also contain a peptizer and a plasticizer. The conditions and steps of formation are all known to those skilled in the art, and the catalyst may be made into pellets, tablets, cylinders, or any other shape suitable for the purpose. EP 847,802 describes a procedure for forming a catalyst based on beta zeolite, wherein, according to a specific procedure, it is particularly preferred to bind beta zeolite of the ammonium/alkylammonium type using an inorganic binder: the catalyst obtained is then suitable for use in a fixed-bed reactor, containing the beta zeolite according to the invention and characterized by a zeolite hypercompoporation (ex t ra-zeolite porosity), i.e. a porosity obtained by adding the mesoporosity to the macroporosity of the catalyst composition and then excluding the contribution of the microporosity of the zeolite, the total volume being at least equal to 0.80ml/g and at least 25% of the pore radius being greater than that of the zeoliteA particular aspect of the zeolitic materials targeted by the present invention lies in the surprising properties observed in terms of selectivity in the alkylation and transalkylation reactions of aromatic compounds, in particular the alkylation reaction of benzene with propylene or ethylene, and the transalkylation of benzene with polyisopropylbenzene and polyethylbenzene to give cumene and ethylbenzene, respectively: regardless of the total aluminum content, the subject beta zeolite of the invention, and the catalysts produced therefrom, demonstrate greater selectivity for monoalkylation, with reduced formation of unrecoverable polyalkylated byproducts and other hazardous byproducts, and reduced catalyst deactivation rates.

Accordingly, a further object of the present invention relates to a process for the alkylation of aromatic hydrocarbons, preferably benzene, with ethylene or propylene, carried out in the presence of a catalyst comprising a beta zeolite characterized by a molar ratio between the amount of lewis acid sites (L) and the amount of bronsted acid sites (B) equal to or greater than 1.5.

The alkylation of aromatic compounds, in particular benzene with propylene or ethylene to give cumene or ethylbenzene, respectively, is carried out according to what is known in the art, at reactor temperatures of generally 100-300 ℃ and reaction pressures of generally 1-100 bar. In the case of the alkylation of benzene with propylene to give cumene, the temperature is generally 100-200 deg.C, preferably 150-200 deg.C, more preferably 120-180 deg.C.

In the case of alkylation of benzene with ethylene to produce ethylbenzene, the reactor temperature is preferably 150 ℃ to 250 ℃, more preferably 170 ℃ to 230 ℃.

In the alkylation of benzene with propylene and ethylene, the reaction pressure is preferably chosen such that the reaction is carried out under at least partial liquid phase conditions, and is therefore preferably in the range of from 10 to 50 bar.

The molar ratio of aromatic compound and olefin introduced into the reaction is generally in the range from 1 to 30, preferably from 2 to 15.

The process may be carried out batchwise, semi-continuously or continuously as is known in the art and may be carried out in several reactors, but is preferably carried out in a continuous manner in one or more fixed bed catalyst reactors in series. The space velocity (WHSV, in kg of reaction mixture introduced/kg of catalyst/h, referred to only the weight of zeolite contained in the catalyst) is in this case generally in the range from 0.1 to 20hrs^-1Preferably 0.5 to 10hrs^-1. When the process is carried out continuously, it is also possible to use a plant comprising a reactor system in which the effluent is partly recycled, possibly after cooling, to the reactor itself.

In order to overcome the exothermic nature of the reaction and to ensure that the temperature is maintained within a selected range, the catalyst may be distributed in multiple layers or placed in several reactors in series, cooling may be effected between catalyst layers or between one reactor and another. The reactants may be introduced into the first catalytic bed or reactors in series, or one or both reactants may be split between a single bed or a single reactor.

As will be appreciated by those skilled in the art, this operating step allows the maximum reaction temperature limit to be more efficient and higher ratios of aromatic compound to alkylating agent to be obtained, with the same overall feed ratio and a distinct advantage for the monoalkylated product.

Yet another object of the present invention relates to a process for the transalkylation of aromatic hydrocarbons with one or more polyalkylated aromatic hydrocarbons carried out in the presence of a catalyst comprising a beta zeolite characterized by a molar ratio between the amount of lewis acid sites (L) and the amount of bronsted acid sites (B) equal to or greater than 1.5. The aromatic hydrocarbon is preferably benzene. The polyalkylated aromatic hydrocarbon is preferably a mixture of aromatic hydrocarbons, typically dialkyl aromatic hydrocarbons. More preferably, the polyalkylated aromatic hydrocarbon is selected from diethylbenzene, which may be a mixture with triethylbenzene, and diisopropylbenzene, which may be a mixture with triisopropylbenzene. Particular preference is given to the transalkylation of benzene with diethylbenzene and possibly triethylbenzene and the transalkylation of benzene with diisopropylbenzene and possibly triisopropylbenzene.

The reaction is carried out at a temperature of 100 ℃ and 350 ℃. In the case of the transalkylation of benzene with polyisopropylbenzene to give cumene, the temperature is preferably 150 ℃ and 250 ℃. In the case of the transalkylation of benzene with polyethylbenzene to give ethylbenzene, the temperature is preferably 180-300 ℃. The reaction pressure is preferably chosen such that the reaction is carried out under at least partially liquid phase conditions, more preferably under liquid phase conditions, and is therefore preferably in the range from 20 to 50 bar. The reaction is preferably carried out continuously in a fixed bed reactor. In this case, the space velocity (WHSV, expressed as kg of reaction mixture introduced/kg of catalyst/h, referred to only the weight of zeolite contained in the catalyst) is generally in the range from 0.5 to 10hrs^-1. The molar ratio of aromatic hydrocarbon to the sum of polyalkylated aromatic hydrocarbons introduced into the transalkylation mixture may be in the range of from 1 to 40, preferably from 3 to 30.

Yet another aspect of the present invention is an improved process for the preparation of monoalkylaromatic hydrocarbons comprising:

a) contacting an aromatic hydrocarbon with an olefin under alkylation conditions in the presence of the subject catalyst;

b) separating the obtained product into a fraction containing aromatic hydrocarbons, a fraction containing monoalkylated aromatic hydrocarbons, a fraction containing polyalkylated aromatic hydrocarbons, preferably a fraction mainly containing dialkylated aromatic hydrocarbons, and a fraction of heavy aromatic hydrocarbons;

c) contacting a fraction containing polyalkylated aromatic hydrocarbons, preferably predominantly dialkylated aromatic hydrocarbons, with an aromatic hydrocarbon under transalkylation conditions in the presence of the subject catalyst;

d) the product obtained in step c) is separated into the same fraction already obtained in step b), and the fraction containing the aromatic hydrocarbon is then partly recycled to step a) and partly recycled to step c), and the fraction containing the polyalkylated aromatic hydrocarbon is recycled to step c).

The fraction containing monoalkylaromatic hydrocarbons from step b) is the desired product, wherein the effluents of steps c) and a) are discharged.

The olefin used in the alkylation step is preferably selected from ethylene and propylene. The aromatic hydrocarbon used in the alkylation and transalkylation steps is preferably benzene. When the alkylation product is obtained by the alkylation of benzene with propylene, the first fraction of step (b) consists essentially of benzene, the second fraction is essentially cumene and the third fraction is essentially diisopropylbenzene. When the alkylation product is obtained by alkylation of benzene with ethylene, the first fraction of step (b) consists essentially of benzene, the second fraction is essentially ethylbenzene and the third fraction is essentially diethylbenzene.

Some illustrative examples are provided for a better understanding of the present invention and its embodiments, but should in no way be considered as limiting the scope of the invention itself.

Example 1

157.1g of 35% by weight tetraethylammonium hydroxide aqueous solution were added to 35.6g of deionized water. 14.0g of sodium aluminate (54% by weight Al) are subsequently added with continuous stirring at about 70 ℃₂O₃) And 12.2g of aluminum isopropoxide until a clear solution is obtained. To this solution was added 280.4g of LudoxHS 40 colloidal silica (40% Si)O₂). A homogeneous suspension was obtained, which was added to an AISI316 steel autoclave equipped with a paddle stirrer. The mixture was crystallized under hydrothermal conditions at 170 ℃ for 24 hours.

At this point, the autoclave was cooled. The crystallization slurry was treated with 130g of 3N strength aqueous acetic acid with stirring to give a slightly thick suspension to which 3 l of deionized water was added. The suspension thus obtained was filtered. The zeolite obtained is subsequently redispersed in 3 liters of deionized water in which 50g of ammonium acetate had previously been dissolved. After 3 hours the solid material was filtered off. This gave moist, plate-shaped ammonium/alkylammonium beta zeolite. The zeolite plates were dried at 150 ℃ and subsequently calcined in air at 550 ℃ for 5 hours. The final product was analyzed by X-ray powder diffraction method and was shown to consist of high purity beta zeolite. Chemical analysis of the final product showed [ SiO ]₂]/[Al₂O₃]The molar ratio was 17.2.

Qualitative and quantitative determination of bronsted and lewis acid sites by infrared spectroscopy with pyridine as probe molecule was performed as described in c.a. emeris of Journal of Catalysis, 1993, 141, 347. The method comprises the following steps:

1. beta zeolite samples were pressed into tablets suitable for IR spectrometry

2. Under high vacuum (10)^-5Torr), the sample was placed in a cell suitable for measuring IR spectra at 400 ℃ for 1 hour.

3. The sample thus treated is brought into contact with pyridine at room temperature for 15 minutes at a pressure equal to atmospheric pressure, the vapour of said pyridine being introduced into the tank by a suitable liquid supply

4. Excess pyridine was desorbed from the sample for 1 hour at 250 ℃ under vacuum

5. The IR spectrum was recorded and the 1545cm relative to the pyridinium ion formed by Bronsted acid site interaction was measured^-1Bands, and 1455cm in relation to pyridine adsorbed on Lewis acid sites^-1Integrated intensity of the band (called I).

The concentration of acid sites A (mmol/g zeolite) was obtained by the following equation

A＝I/(∈xS)

Wherein S is the "thickness" of the sheet and is in (mg/cm)²) Expressed as e is the molar extinction coefficient (cm/micromole) for 1545cm^-1And 1455cm^-1The bands used were 2.22 and 1.67 (cm/micromole), respectively (according to the description of C.A. Emeis in Journal of Catalysis, 1993, 141, 347).

IR analysis performed on the zeolite showed that the molar ratio of the amount of lewis acid sites (L) to the amount of bronsted acid sites (B) was 2.0.

The synthesis conditions and the associated results are shown in table 1.

Example 2 (control)

157.1g of 35% by weight tetraethylammonium hydroxide aqueous solution were added to 299.5g of deionized water. Subsequently, 20.8g of sodium aluminate (54% by weight Al) are added at about 70 deg.C₂O₃) The mixture was kept under stirring until a clear solution was obtained. To this solution was added 280.4g of Ludox HS 40 colloidal silica (40% SiO)₂). A homogeneous suspension was obtained, which was added to a steel AISI316 autoclave equipped with a paddle stirrer. The gum crystallized under hydrothermal conditions at 170 ℃ for 168 hours.

The autoclave was then cooled and the slurry treated as described in example 1.

The final product was analyzed by powder X-ray diffraction, and as a result, the product consisted of high-purity beta zeolite. Chemical analysis of the final product showed [ SiO ]₂]/[Al₂O₃]The molar ratio was 26.

By performing IR analysis as described in example 1, it was revealed that the molar ratio (L/B) of the amount of Lewis acid sites (L) to the amount of Bronsted acid sites (B) of the zeolite was equal to 1.2.

The synthesis conditions and the associated results are shown in table 1.

Example 3 (control)

157.1g of 35% by weight tetraethylammonium hydroxide aqueous solution were added to 36.3g of deionized water. 14.2g of sodium aluminate (54% by weight Al) are subsequently added at about 70 deg.C₂O₃) The mixture was kept under stirring until a clear solution was obtained. To this solution was added 280.4g of Ludox HS 40 colloidal silica (40% SiO)₂). A homogeneous suspension was obtained, which was added to a steel AISI316 autoclave equipped with a paddle stirrer. The gum crystallizes under hydrothermal conditions at 170 ℃ for 24 hours.

The autoclave was then cooled and the slurry treated as described in example 1.

The final product was analyzed by powder X-ray diffraction, and as a result, the product consisted of high-purity beta zeolite. Chemical analysis of the final product showed [ SiO ]₂]/[Al₂O₃]The molar ratio was 16.4.

By performing IR analysis as described in example 1, it was revealed that the molar ratio of the amount of Lewis acid sites (L) to the amount of Bronsted acid sites (B) of the zeolite was equal to 0.97. The synthesis conditions and the associated results are shown in table 1.

Example 4 (control)

157.1g of a 35% by weight aqueous tetraethylammonium hydroxide solution were added to 35.9g of deionized water. 14.2g of sodium aluminate (54% by weight Al) are subsequently added with continuous stirring at about 70 ℃₂O₃) And 14.3g of aluminum isopropoxide until a clear solution is obtained. To this solution was added 280.4g of LudoxHS 40 colloidal silica (40% SiO)₂). A homogeneous suspension was obtained, which was added to a steel AISI316 autoclave equipped with a paddle stirrer. The gum crystallized under hydrothermal conditions at 170 ℃ for 168 hours.

The autoclave was then cooled and the slurry treated as described in example 1.

Analysis by X-ray diffraction showed that the product thus obtained was amorphous.

The synthesis conditions and the associated results are shown in table 1.

In the table, the first column represents the number of the examples and the second, third, fourth and fifth columns represent the molar ratios of the different reagents in the respective examples. The sixth column represents the duration of the hydrothermal synthesis. Column seven represents the phase properties obtained on the basis of XRD analysis-crystalline or amorphous. Column eight represents the results of the chemical analysis of the silica/alumina SAR (silica/alumina ratio) and the last column represents the results obtained by pyridine titration of the acid sites (as described above), expressed as the molar ratio of lewis acid sites to bronsted acid sites.

It can be observed that a ratio of [ L ]/[ B ] of more than 1.5 as in example 1 can only be obtained by operating at a [ Na ]/[ Al ] molar ratio of more than 0.68 and less than 1.

In contrast, the ratio of [ L ]/[ B ] obtained when operating even only at the upper end of the range required for the [ Na ]/[ Al ] parameters is less than 1.5 for examples 2 and 3. When operating below the lower limit of the required range for the [ Na ]/[ Al ] parameters, amorphous material as in example 4 is obtained.

Example 5

0.4g of beta zeolite prepared as described in example 1, previously dried at 120 ℃ for 16 hours, are introduced into an electrically heated autoclave having an internal volume equal to 0.5 litre, equipped with a mechanical stirrer and with the means necessary for feeding the benzene and propylene reagents.

The autoclave was closed and evacuated by means of an externally connected pump, and then 352g of benzene were added through the evacuation port. The autoclave was pressurized with nitrogen until the pressure reached about 6bar and heating was started to a predetermined programmed temperature of 150 ℃. When the temperature inside the autoclave stabilized at the preselected value, 26g of propylene were rapidly fed through the pressure tank, and the mixture was reacted for a period of about 1 hour, calculated from the end of the propylene feed.

At the end of the reaction, the product was discharged and analyzed by gas chromatography. At the end of the reaction the following products were present in the reaction mixture: c of benzene, cumene and propylene₆And C₉Oligomers, diisopropylbenzenes, other diisopropylbenzene isomers (C)₆-phenyl ═ typically of the formula C₁₂H₁₈Aromatic product as represented), triisopropylbenzene, other triisopropylbenzene isomers (C)₉-phenyl ═ typically of the formula C₁₅H₂₄Aromatic products as indicated), polyalkylated products having a molecular weight greater than triisopropylbenzene (heavy polyalkylated products).

The propylene conversion shows higher than 97.0%, the selectivity of the converted propylene to the monoalkylated product (cumene) is equal to 91.3% and the selectivity of the converted propylene to (cumene + diisopropylbenzenes + triisopropylbenzenes) is equal to 97.5%.

(diisopropylbenzenes + triisopropylbenzenes + C₆-phenyl + C₉Phenyl + heavy polyalkylated products) with (cumene + diisopropylbenzenes + triisopropylbenzenes + C₆-phenyl + C₉Phenyl + heavy polyalkylated products) is equal to 0.052.

The ratio R is a measure of the total amount of polyalkylated byproducts alone relative to the total products and alkylated byproducts formed in the reaction.

Example 6 (control)

The catalytic experiment described in example 5 was repeated using the beta zeolite prepared in example 2.

On the basis of the gas chromatographic analysis of the reaction products, it was calculated that the propylene conversion was higher than 97.0%, that the selectivity for the conversion of propylene on the monoalkylated product (cumene) was equal to 90.9% and that the selectivity for the conversion of propylene on the (cumene + diisopropylbenzenes + triisopropylbenzenes) was equal to 96.6%. Example 1 defines a ratio R equal to 0.061.

Clearly, in contrast to the results obtained with the catalyst of the invention, a higher proportion of polyalkylated by-products is obtained with a catalyst not representing the invention.

Example 7 (control)

The catalytic experiment described in example 5 was repeated using the beta zeolite prepared in example 3.

On the basis of the gas chromatographic analysis of the reaction products, it was calculated that the propylene conversion was higher than 98.1%, the selectivity for the converted propylene with respect to the monoalkylated product (cumene) was equal to 89.8% and the selectivity for the converted propylene with respect to (cumene + diisopropylbenzenes + triisopropylbenzenes) was equal to 95.0%. The ratio R defined in example 1 is equal to 0.064.

Clearly, in contrast to the results obtained with the catalyst of the invention, a higher proportion of polyalkylated by-products is obtained with a catalyst not representing the invention.

Example 8

The zeolite beta of the ammonium/alkylammonium formula (i.e. in a form not subjected to the final calcination step) of example 1 was used to prepare a catalyst in pellet form following the procedure described in EP 847,802, example 4. Alumina in the form of p-boehmite is used as a square binder. The catalyst thus formed was calcined at 550 ℃ for 5 hours. The percentage of zeolite in the final catalyst was equal to 55% by weight and the catalyst had the following porosity characteristics: EPV (zeolite ultra pore volume) 0.85cc/g, radius >The proportion of pores of (a) was 51%.

The catalyst thus obtained was referred to as catalyst a and was subjected to successive catalytic experiments using the following experimental apparatus for alkylation of benzene and propylene.

The experimental device comprises a reaction tank, an independent feeding pump, a static mixer for reagents before feeding to a reaction, a steel reactor (a temperature adjusting system is arranged in the reactor) positioned in an electric heating furnace, a pressure adjusting system for adjusting the pressure in the reactor through a pneumatic valve, a cooler for reaction effluent and a collecting system for liquid and gas products.

The reactor, located inside the furnace, consists of a cylindrical steel tube with a mechanical sealing system and an internal diameter of about 2 cm.

Inside the reactor, along the longer axis, a temperature measuring mantle, having a diameter of 1mm and containing a thermocouple, which was freely slidable along the longer axis of the reactor, was installed. Catalyst A was previously ground and sieved to obtain a particle size of 1-1.25mm, and 5g of said catalyst was added to the reactor so that the total height of the catalyst bed was 6 cm.

An amount of inert quartz material was added above and below the catalyst bed such that the height of the material above and below the catalyst bed was 3cm each.

The electrical heating of the reactor was started while a nitrogen flow was introduced to dry the catalyst, so that the temperature of the reactor rose to the predetermined 150 ℃. Once the selected temperature was reached, the nitrogen flow was maintained for 16 hours, then it was interrupted and benzene was introduced first for 2 hours, followed by propylene, in order to maintain a total WHSV of 20h "1 and a molar ratio of [ benzene ]/[ propylene ] in the feed equal to 7. The reaction was carried out at a pressure of 38 bar.

After the reaction was continued for 21, 93, 118, 260 and 284 hours, a sample was taken from the reaction effluent, followed by gas chromatography.

On the basis of the analysis of the various samples of the reaction effluent, it was confirmed that the conversion of propylene was always higher than 99.0%. The following average properties of catalyst a were also obtained:

-selectivity to cumene of 90.2% for the conversion of propylene and 0.4% for the standard deviation;

-selectivity of converted propylene to (cumene + diisopropylbenzenes + triisopropylbenzenes) 99.7%, standard deviation 0.06%;

-concentration of n-propylbenzene with respect to cumene of 238ppm and standard deviation of 14ppm

C of propene₆-to C₉Concentration of oligomer to cumene 204ppm

During the experiment, the position corresponding to the maximum temperature determined by the exothermic heat of reaction was indicated by a thermocouple sliding along the longer axis of the reactor. In this way, the rate of rise of so-called hot spots, which represent a direct measure of the rate of catalyst deactivation, can be measured. By extrapolating the measurements up to the end of the catalyst bed, it can be concluded that the cumene production reaches said end of the catalyst bed, based on the fact that the total amount of catalyst added is 2,800kg cumene/kg catalyst A.

Example 9 (control)

The zeolite beta of example 2 of the ammonium/alkylammonium formula was used to prepare a catalyst in pellet form following the procedure described in EP 847,802, example 4. Alumina in the form of p-boehmite was used as a binder. The catalyst thus formed was calcined at 550 ℃ for 5 hours. The percentage of zeolite in the final catalyst was equal to 55% by weight and the catalyst had the following porosity characteristics: EPV (zeolite ultra pore volume) 0.82cc/g, radius >The proportion of pores in (a) was 52%.

The catalyst thus obtained is referred to as catalyst B and does not represent the present invention.

Catalyst B was used in a catalytic experiment for carrying out the continuous alkylation of benzene and propylene using an experimental set-up such as that described in example 8 and with the same deactivation procedure as the catalytic experiment.

After carrying out the reactions under the same reaction conditions for 47, 124, 165, 190 and 286 hours in succession, the reaction effluents were sampled and subsequently subjected to gas chromatography analysis.

On the basis of the analysis of the various samples of the reaction effluent, it was confirmed that the conversion of propylene was always higher than 99.0%. The following average properties of catalyst B were also obtained:

-selectivity to cumene of 87.5% for the conversion of propylene and 0.4% for the standard deviation;

-selectivity of converted propylene to (cumene + diisopropylbenzenes + triisopropylbenzenes) 99.7%, standard deviation 0.03%;

-concentration of n-propylbenzene relative to cumene 253ppm, standard deviation 8ppm

C of propene₆-to C₉The concentration of oligomer relative to cumene is 264ppm

Here again, during the experiment, the position corresponding to the highest temperature was indicated by a thermocouple sliding along the longer axis of the reactor, for measuring the rate of rise of the so-called hot spot, which represents a direct measure of the rate of deactivation of the catalyst. By extrapolating the measurements up to the end of the catalyst bed, cumene production can be judged based on the total amount of catalyst added being 2,150kg cumene/kg catalyst B.

It does not represent the selectivity of catalyst B of the invention with respect to the conversion of propylene to cumene, i.e. with respect to the monoalkylated product, which is much worse than that obtained with catalyst A of the invention. On the other hand, it is evident from the results relating to the selectivity of catalyst B for the conversion of propylene to (cumene + diisopropylbenzenes + triisopropylbenzenes), which are substantially similar to those already obtained with catalyst A. In other words, the distribution of the mono-and dialkylated products obtained when using catalyst A according to the invention is more directly directed towards the monoalkylated product than the results obtained with catalyst B not representing the invention-the selectivity towards the total production of mono-and dialkylated products is the same.

Furthermore, catalyst B deactivated at a higher rate than catalyst A, most probably due to C of propylene for catalyst B₆-C₉The formation of oligomeric products is greater.

Example 10

The same catalyst a that had been used in example 8 was subjected to a catalytic experiment under the same conditions as described in example 8, except that the reactor temperature was set to 140 ℃.

After carrying out the reactions under the same reaction conditions for 46, 119, 137, 142 and 160 hours in succession, the reaction effluents were sampled and subsequently subjected to gas chromatography analysis.

On the basis of the analysis of the various samples of the reaction effluent, it was confirmed that the conversion of propylene was always higher than 99.0%. The following average properties of catalyst a were also obtained:

-selectivity to cumene of 89.9% for propylene conversion and standard deviation of 0.8%;

-selectivity of converted propylene to (cumene + diisopropylbenzenes) 99.5%, standard deviation 0.08%;

-187 ppm concentration of n-propylbenzene relative to cumene and 7ppm standard deviation

C of propene₆-to C₉Concentration of oligomer to cumene 279ppm

Here again, during the experiment, the position corresponding to the highest temperature was indicated by a thermocouple sliding along the longer axis of the reactor, for measuring the rate of rise of the so-called hot spot, which represents a direct measure of the rate of deactivation of the catalyst. By extrapolating the measurements up to the end of the catalyst bed, cumene production can be judged based on the total amount of catalyst added being 1,730kg cumene/kg catalyst A.

The formation of n-propylbenzene and propylene oligomer impurities is therefore according to the expected trend: the former forms less with decreasing temperature; the latter, however, increases with decreasing temperature, according to the results already obtained for catalyst A, in which the reaction is carried out at higher temperatures, as described above in example 8.

Lower reaction temperatures can therefore be selected for the production of cumene of a specific and higher purity.

Example 11 (control)

The same catalyst B that had been used in example 9 was subjected to a catalytic experiment under the same conditions as described in example 10, but with the reactor temperature set to 140 ℃.

After carrying out the reactions under the same reaction conditions for 28, 94, 100, 118 and 122 hours in succession, the reaction effluents were sampled and subsequently subjected to gas chromatography analysis.

On the basis of the analysis of the various samples of the reaction effluent, it was confirmed that the conversion of propylene was always higher than 99.0%. The following average properties of catalyst B were also obtained:

-selectivity to cumene of 87.3% for propylene conversion and 0.4% standard deviation;

-selectivity to propylene over (cumene + diisopropylbenzenes) 99.2%, standard deviation 0.2%;

188ppm concentration of n-propylbenzene relative to cumene and 2ppm standard deviation

C of propene₆-to C₉Concentration of oligomer to cumene 443ppm

Here again, during the experiment, the position corresponding to the highest temperature was indicated by a thermocouple sliding along the longer axis of the reactor, for measuring the rate of rise of the so-called hot spot, which represents a direct measure of the rate of deactivation of the catalyst. By extrapolating the measurements up to the end of the catalyst bed, cumene production can be judged based on the total amount of catalyst added being 1,020kg cumene per kg catalyst B.

It is clear that the use of catalyst B at 140 ℃ effectively reduces the formation of n-propylbenzene compared to the results obtained when the reaction is carried out at 150 ℃ using catalyst B. The reduction is however associated with a significant increase in the formation of propylene oligomers and thus a significant reduction in the catalyst life, which is very different from the results obtained with catalyst A at the same temperature.

Thus, catalyst A, which represents the present invention, allows the reaction to proceed at a more favorable temperature with reduced formation of n-propylbenzene impurities, whereas catalyst B, which does not represent the present invention, does not achieve such an effect.

Claims (38)

1. An acid form of beta zeolite, SiO in the crystal lattice of said acid form of beta zeolite₂/Al₂O₃Is 10 to 25, and the distribution of Lewis acid sites and Bronsted acid sites, expressed as [ Lewis sites ], measured by infrared spectroscopy using pyridine as probe molecule is represented by]/[ Bronsted site]Equal to or higher than 1.5, wherein the infrared spectrum is recorded after desorption of the excess pyridine for 1 hour at 250 ℃ under vacuum.

2. The process of claim 1Beta zeolite of which SiO is₂/Al₂O₃Is 10 to 17.2.

3. The beta zeolite of claim 1 in the form of submicron aggregates of crystals wherein at least 90% of the crystals are less than the size of

4. A catalytic composition comprising:

-the beta zeolite of claim 1;

-an inorganic binder.

5. The catalytic composition of claim 4, wherein the inorganic binder is selected from the group consisting of alumina, silica or magnesia, natural clays or mixtures thereof.

6. The catalytic composition of claim 4, wherein the weight ratio of binder to zeolite is from 80: 20 to 5: 95.

7. Catalytic composition according to claim 4, characterized in that the total volume of the zeolite macroporosity is greater than or equal to 0.80ml/g and at least 25% of the pores have a radius greater than that of the zeolite

8. A process for the preparation of the beta zeolite of claim 1 comprising crystallizing at 150-190 ℃ in an aqueous environment under hydrothermal conditions for 10 to 240 hours a reaction mixture comprising sodium aluminate and aluminum alkoxide or aluminum inorganic salt as aluminum source, a silica source selected from the group consisting of colloidal silica, tetraalkyl silicate and amorphous silica and tetraethylammonium hydroxide as templating agent, said mixture having the following composition in molar ratios:

[SiO₂]/[Al₂O₃]＝10-30

[TEAOH]/[SiO₂]＝0.10-0.35

[H₂O]/[SiO₂]＝7-20

[Na₂O]/[TEAOH]higher than 0.1

[ Na ]/[ Al ] is greater than 0.68 and less than 1.00, wherein TEAOH is tetraethylammonium hydroxide,

the mixture resulting from the crystallization is filtered, and the resulting solid product is ion-exchanged with an ammonium salt, followed by drying and calcination.

9. The process of claim 8, wherein the crystallization is carried out at a temperature of 165-180 ℃ for 18-150 hours.

10. The method of claim 8 wherein the aluminum alkoxide is selected from aluminum isopropoxide or aluminum t-butoxide, the tetraalkyl silicate is selected from tetramethyl silicate, tetraethyl silicate or tetrapropyl silicate and the inorganic salt of aluminum is selected from nitrate and sulfate.

11. The process of claim 8 wherein the reaction mixture has the following composition in terms of mole ratios:

[SiO₂]/[Al₂O₃]＝10-25

{TEAOH]/[SiO₂]＝0.15-0.30

[H₂O]/[SiO₂]＝8-15

[Na₂O]/[TEAOH]greater than 0.1

[ Na ]/[ Al ] is greater than 0.68 and less than 1.00, wherein TEAOH is tetraethylammonium hydroxide.

12. The process of claim 8, wherein the suspension resulting from the crystallization is acidified to a pH of 3-6 and diluted with water in a ratio of (volume of water added)/(volume of suspension) of 1-10 before being subjected to filtration.

13. The process as claimed in claim 8, wherein the solid product obtained by filtering the crystalline mixture is redispersed in water, ion-exchanged with an ammonium salt, filtered, dried at a temperature of 100 ℃ and 200 ℃ for 8 to 16 hours, and calcined at a temperature of 450 ℃ and 650 ℃ for 4 to 8 hours.

14. A process for alkylating an aromatic hydrocarbon which comprises contacting the aromatic hydrocarbon with an olefin selected from the group consisting of ethylene and propylene in the presence of the zeolite beta of claim 1.

15. The process of claim 14, carried out at a temperature of 100 ℃ and 300 ℃ and the reaction pressure is generally from 1 to 100 bar.

16. The process of claim 14 wherein the aromatic hydrocarbon is benzene.

17. The process of claim 15 wherein the aromatic hydrocarbon is benzene, the olefin is propylene, and the reaction is carried out at a temperature of 100 ℃ and 200 ℃.

18. The process of claim 17, carried out at a temperature of 120-180 ℃.

19. The process of claim 15 wherein the aromatic hydrocarbon is benzene, the olefin is ethylene, and the reaction is carried out at a temperature of 150 ℃ and 250 ℃.

20. The process of claim 19, carried out at a temperature of 170-230 ℃.

21. The process of claim 15, carried out in at least a partial liquid phase.

22. The process of claim 21, carried out at a pressure of from 10 to 50 bar.

23. The process of claim 14 wherein the molar ratio of aromatic compound to olefin introduced to the reaction is generally from 1 to 30.

24. A process for the transalkylation of aromatic hydrocarbons, the process comprising contacting an aromatic hydrocarbon with one or more polyalkylated aromatic hydrocarbons in the presence of the zeolite beta of claim 1.

25. The process of claim 24 wherein the aromatic hydrocarbon is benzene.

26. The process of claim 24 or 25 wherein the polyalkylated aromatic hydrocarbon is a mixture comprising predominantly dialkyl aromatic hydrocarbons.

27. The process of claim 24 or 25 wherein the polyalkylated aromatic hydrocarbon is selected from diethylbenzene, optionally in admixture with triethylbenzene, and diisopropylbenzene, optionally in admixture with triisopropylbenzene.

28. The process of claim 24, carried out at a temperature of 100-350 ℃.

29. The process of claim 28 wherein the aromatic hydrocarbon is benzene and the polyalkylated aromatic hydrocarbon is polyisopropylbenzene at a temperature in the range of 150 ℃ and 250 ℃.

30. The process of claim 28 wherein the aromatic hydrocarbon is benzene and the polyalkylated aromatic hydrocarbon is polyethylbenzene at a temperature in the range of 180 ℃ to 300 ℃.

31. The process of claim 28 conducted under at least partial liquid phase conditions.

32. The process of claim 31, carried out under liquid phase conditions.

33. The process of claim 31 or 32, carried out at a pressure of from 20 to 50 bar.

34. The process of claim 24 wherein the molar ratio of aromatic hydrocarbon to total polyalkylated aromatic hydrocarbon is from 1 to 40.

35. The method of claim 34, wherein the molar ratio is 3 to 30.

36. The method of claim 14, comprising the steps of:

(a) contacting an aromatic hydrocarbon with an olefin selected from the group consisting of ethylene and propylene under alkylation conditions in the presence of the zeolite beta of claim 1;

(b) separating the obtained product into a fraction containing aromatic hydrocarbons, a fraction containing monoalkylated aromatic hydrocarbons, a fraction containing polyalkylated aromatic hydrocarbons, a fraction mainly containing dialkylated aromatic hydrocarbons, and a fraction of heavy aromatic hydrocarbons;

(c) contacting a fraction comprising polyalkylated aromatic hydrocarbons, predominantly dialkylated aromatic hydrocarbons, with aromatic hydrocarbons under transalkylation conditions in the presence of the zeolite beta of claim 1;

(d) the product obtained in stage (c) is separated into the same fraction obtained in stage b), and the fraction containing aromatic hydrocarbons is subsequently partly recycled to stage (a) and partly to stage (c), and the fraction containing polyalkylated aromatic hydrocarbons is recycled to stage (c).

37. The process of claim 14 or 24, carried out in the presence of a catalytic composition comprising:

-the beta zeolite of claim 1;

-an inorganic binder.

38. The process of claim 37, wherein said catalytic composition is characterized by a total volume of zeolite macroporosity greater than or equal to 0.80ml/g and at least 25% of pore radius greater than