EA044603B1 - CATALYST CONTAINING COKE AND METHOD FOR PRODUCING DIENES - Google Patents

Description

The invention relates to a catalyst containing coke.

More particularly, the invention relates to a catalyst containing coke, characterized in that said coke, when analyzed by diffuse reflectance infrared spectroscopy (DRIFTS), has at least two peaks at a wavelength between 1450 cm ^-1 and 1700 cm ^-1 .

The above-mentioned coke-containing catalyst may be preferably used in a process for producing a diene, preferably a conjugated diene, more preferably 1,3-butadiene, comprising dehydration of at least one alkenol having a carbon number greater than or equal to 4.

Accordingly, the invention also relates to a process for producing a diene, preferably a conjugated diene, more preferably 1,3-butadiene, comprising dehydrating at least one alkenol having a carbon number greater than or equal to 4, in the presence of said coke-containing catalyst.

Preferably, said alkenol having a carbon number greater than or equal to 4 can be obtained directly from biosynthetic processes or through catalytic dehydration processes of at least one diol.

When said alkenol is butenol, said diol is preferably butanediol, more preferably 1,3-butanediol, even more preferably bio-1,3butanediol, that is, 1,3-butanediol obtained from biosynthetic processes.

When said diol is 1,3-butanediol or bio-1,3-butanediol, the diene obtained by the method according to the present invention is, respectively, 1,3-butadiene or bio-1,3-butadiene.

1,3-butadiene is a fundamental product for the petrochemical industry: it is a substrate for the production of chloroprene, adiponitrile and hexamethylenediamine, among other products.

In fact, 1,3-butadiene can be used in many industries, including plastics, synthetic rubber, resin, latex, terpolymer (such as acrylonitrile butadiene styrene ABS), paints and synthetic fibers.

The product of copolymerization of 1,3-butadiene with styrene is included in mixtures for the production of tires.

Currently, more than 95% of the 1,3-butadiene produced on an annual basis is obtained as a by-product obtained from steam cracking processes to produce ethylene and other olefins, from which it is separated by extractive distillation, where it is formed in small quantities ( <5%). 1,3-Butadiene can also be produced from fossil sources through other processes such as, for example, the catalytic/oxidative dehydrogenation of butane and/or butenes. All of these processes are particularly energy-intensive and release large quantities of carbon dioxide (CO2).

Due to the need to reduce the environmental impact of chemical production, as well as the need to use raw materials obtained from renewable sources (for example, biomass), various processes are used to obtain bio-1,3-butadiene. Examples of these processes are: dehydration of diols obtained as a result of biomass fermentation; direct fermentation of biomass to bio-1,3-butadiene; conversion of ethanol in one or two steps to bio1,3-butadiene; dehydration followed by dehydrogenation of biobutanol obtained by fermentation or gasification of biomass.

For example, the dehydration of diols obtained from biomass fermentation can be carried out by two successive dehydration stages according to the following scheme:

proceeding as described, for example, by Sato S. et al., in the article Future Prospect of the Production of 1,3Butadiene from Butanediols, Chemistry Letters (2016), Vol. 45, pp. 1036-1047.

The production of olefins and/or dienes (eg 1,3-butadiene) by dehydration of unsaturated alcohols can be carried out in the presence of acid catalysts. The type of acidity, i.e. Brønsted acid or Lewis acid, as well as the strength of the acidic sites, may vary. Typically used catalyst systems are based on metal oxides, such as, for example, silicon (Si), aluminum (Al), zirconium (Zr), zinc (Zn), magnesium (Mg), in amorphous form or based on zeolites . The production of olefins and/or dienes (eg 1,3-butadiene) by dehydration of unsaturated alcohols can also be carried out in the presence of cerium-based catalysts, in particular in two-stage processes.

In the current state of the art, much effort has been made to find catalysts suitable for the dehydration of unsaturated alcohols to produce olefins and/or dienes.

For example, British patent GB 1275171 describes a process for preparing a lithium phosphate catalyst for use in the dehydration of an epoxide or diol to produce a diene. The use of this catalyst in the dehydration of epoxides or diols to produce dienes is said to produce by-products, mainly carbonyl products, which can be converted to olefins. In addition, it is reported that said catalyst has the advantage that it can be calcined at 600° C. without losing its activity, so as to be able to regenerate it after use.

US Pat. No. 2,420,477 describes a process for the production of butadiene comprising reacting vinyl ethyl ether with ethylene at a temperature ranging from 125° C. to 250° C. in the presence of a catalyst containing a metal core selected from the group consisting of beryllium, magnesium, zinc, cadmium, aluminum or alloys thereof, said core being coated with a metal oxide such as, for example, vanadium, niobium, tantalum, chromium, molybdenum, tungsten and uranium. The above process is said to be carried out at temperatures lower than those typically used to produce butadiene and is essentially capable of preventing the production of by-products.

International patent application WO 2013/017496 describes the use of a phosphorus-modified zeolite containing catalyst for the dehydration of alcohols to produce low molecular weight olefins, said catalyst being produced by a specific process which is said to be easily reproducible to produce the catalyst at good levels productivity.

US Pat. No. 4,260,845 describes the dehydration of a saturated alcohol to an olefin in the presence of a zinc aluminate dehydration catalyst having a ZnO/Al ₂ O ₃ molar ratio of about 1, which catalyst is heated in air for a sufficient time and at a sufficient temperature to activate it. . The above catalyst is reported to have good performance levels in terms of selectivity.

Despite the efforts made in the art, the discovery of dehydration catalysts having good performance levels and higher durability, and/or processes that can increase the durability of said catalysts and/or reduce the formation of by-products, which, as mentioned above, can cause catalyst poisoning is still a target and therefore of great interest.

It is known that in the dehydration reactions of unsaturated alcohols in the presence of acid catalysts, as well as the main product obtained, that is, olefin and/or dienes, secondary reactions also occur that lead to the formation of carbonyl compounds, such as, for example, aldehydes, ketones, carboxylic acids . Said carbonyl compounds may be formed due to a dehydrogenating component present in certain dehydration catalysts, such as, for example, alumina and aluminosilicates, which component may be more or less pronounced. Other secondary reactions that may occur are olefin oligomerization and cracking phenomena. These secondary reactions produce compounds that act as coke precursors and consequently lead to deactivation of the dehydration catalyst due to the formation of coke and/or tar, which relatively quickly coats the active surface of the catalysts used for dehydration, rendering it completely inactive.

The mechanisms of catalyst deactivation are widely known in the literature. Detailed descriptions of these mechanisms can be found, for example, in: Petersen Z. and Bell A. T., Catalyst Deactivation (1987), Marcel Dekker, INC, New York; Forzatti P. et al., Catalyst deactivation, Catalysis Today (1999), Vol. 52, pp. 165-181; Bartholomew S. N., Mechanisms of catalyst deactivation, Applied Catalysis A: General (2001), Vol. 212, pp. 17-60.

Makshina E. V. et al., in Review of old chemistry and new catalytic advances in the on-purpose synthesis of butadiene, Chemical Society Reviews (2014), Vol. 43, pp. 7917-7953, describe the state of the art regarding the production of 1,3-butadiene from renewable sources and catalyst systems used for this purpose. The bibliography they refer to is very extensive (246 entries are actually mentioned), but the catalysts used never mention catalysts containing coke, in which said coke is active in the catalysis.

There is also extensive patent literature related to the production of 1,3-butadiene by dehydration of unsaturated alcohols and/or production of unsaturated alcohols, which can be used in the production of 1,3-butadiene, and/or catalytic systems used, but also in

- 2 044603 in this case, catalysts containing coke are never mentioned, in which said coke is active in catalysis. For example, the following US patents may be mentioned: US 2310809, US

2426678, US 4400562, US 5406007, US 6278031, US 9434659; as well as European patent applications EP

3262023, EP 3230236, EP 3142785 and International Patent Application WO 2018/073282, all on behalf of one of the applicants.

Coke active in catalyzing the conversion of methanol and dimethyl ether (DME) to olefin (MTO E DTO) is described in Chen D. et al., The Role of Coke Deposition in the Conversion of Methanol to Olefins over SAPO-34. coke precipitation in the conversion of methanol to olefins over SAPO-34), Catalyst Deactivation (1997), Bartholomew S.H. and G.A. Fuentes Eds., Elsevier ScienceB.V., pp. 159-166. However, the said article makes no suggestion as to the possibility that said coke may also be an active catalyst in the dehydration reaction of alkenols to form 1,3-butadiene.

Applicants therefore set out to solve the problem of finding a coke-containing catalyst which could be advantageously used in a process for the production of dienes, in particular conjugated dienes, especially 1,3-butadiene and even more particularly bio-1,3-butadiene, by catalytic dehydration of at least at least one alkenol having a number of carbon atoms greater than or equal to 4, in particular at least one alkenol obtained from biosynthetic processes, commonly known as bioalkenol.

Applicants have now discovered a catalyst containing coke, wherein said coke, when analyzed by diffuse reflectance infrared spectroscopy (Diffuse Reflectance Fourier Transform Infrared Spectroscopy - DRIFTS), has at least two peaks in a certain wavelength range, which can be advantageously used in the production process dienes. In particular, said coke-containing catalyst can be advantageously used in a process for the production of dienes, in particular conjugated dienes, more particularly 1,3-butadiene and even more particularly bio-1,3-butadiene, by catalytic dehydration of at least one alkenol having a number of carbon atoms greater than or equal to 4, in particular at least one alkenol obtained from biosynthetic processes, commonly known as bio-alkenol. In addition, said coke-containing catalyst is capable of producing 1,3-butadiene with high yield and selectivity.

Accordingly, the subject matter of this invention is a catalyst containing coke, characterized in that said coke, when analyzed by diffuse reflectance infrared spectroscopy (DRIFTS), has at least two peaks at a wavelength between 1450 cm ^-1 and 1700 cm ^-1 .

Diffuse reflectance infrared spectroscopy (DRIFTS) analysis was performed as described in the following examples.

For the purposes of this description and subsequent claims, definitions of numerical intervals always include extreme values unless otherwise indicated.

For the purposes of this description and the following claims, the term including also includes the terms which essentially consists of or which consists of.

According to a preferred embodiment of the invention, said coke-containing catalyst may contain at least one compound selected, for example, from: aluminum oxide (y-Al ₂ O ₃ ), aluminum silicate, aluminosilicates (SiO ₂ -Al ₂ O ₃ ) , aluminum oxides, zeolites, metal oxides (for example, lanthanum oxide, zirconium oxide, tungsten oxide, thallium oxide, magnesium oxide, zinc oxide, silver oxide); preferably selected from aluminosilicates (SiO2-Al2O3).

According to another preferred embodiment of the invention, said coke containing catalyst may comprise:

(a) from 2% by weight to 30% by weight, preferably from 6% by weight to 20% by weight coke, based on the total weight of said catalyst;

(b) from 70% by weight to 98% by weight, preferably from 80% by weight to 94% by weight, based on the total weight of said catalyst, of at least one compound selected, for example, from: alumina (y -Al ₂ O ₃ ), aluminum silicate, aluminosilicates (SiO ₂ -Al ₂ O ₃ ), aluminum oxides, zeolites, metal oxides (for example, lanthanum oxide, zirconium oxide, tungsten oxide, thallium oxide, magnesium oxide, zinc oxide, oxide silver); preferably selected from aluminosilicates (SiO2-Al2O3);

where the sum (a)+(b) is equal to 100.

For the purposes of this invention, said coke containing catalyst may contain binders such as, for example, alumina, silica and/or optionally be supported on inert supports such as, for example, pumice, graphite, silica.

For the purposes of this description and subsequent claims, the term zeolites should be considered in its broadest meaning, that is, it also includes well-known materials, such as, for example, zeolite-like; zeotype; zeolites modified with phosphorus or metals, such as, for example, sodium, potassium, boron, or a lanthanide metal; etc.

The catalyst of the invention containing coke can be obtained by the catalytic dehydration reaction of at least one alkenol, preferably 3-buten-2-ol (3-Bu2-OH) and 2-buten-1-ol (2-Bu-1 -OH), to produce dienes, preferably to produce 1,3-butadiene. In fact, the coke contained in said catalyst is a by-product that is formed during said dehydration reaction.

Therefore, another subject of the present invention is a process for producing a diene, preferably a conjugated diene, more preferably 1,3-butadiene, comprising dehydrating at least one alkenol having a carbon number greater than or equal to 4, in the presence of at least one coke-containing catalyst , characterized in that said coke, when analyzed by diffuse reflectance infrared spectroscopy (Diffuse Reflectance Infrared Spectroscopy with Fourier Transform - DRIFT), has at least two peaks at a wavelength located between 1450 cm ^-1 and 1700 cm ^-1 .

According to a preferred embodiment of the invention, said alkenol, linear or branched, has the general formula C _n H _2n O, where n is an integer greater than or equal to 4 and less than or equal to 8, preferably greater than or equal to 4 and less than or equal to 6, even more preferably equal to 4.

Specific examples of alkenols that are particularly useful for the purposes of this invention are: 2-buten-1-ol, 3-buten-1-ol, 3-buten-2-ol, 2-methyl-3-buten-2-ol, 4-penten-1-ol, 4-penten-2-ol, 4-penten-3-ol, 3-penten-1-ol, 3-penten-2-ol, 2-penten-1-ol, 5- hexen-1-ol, 5-hexen-2-ol, 5-hexen-3-ol, 5hexen-4-ol, 4-hexen-1-ol, 4-hexen-2-ol, 4-hexen-3- ol, 3-hexen-2-ol, 2-hexen-1-ol, 2-methyl-3-penten2-ol, 2-methyl-4-penten-2-ol, 3-methyl-4-penten-2- ol, 6-hepten-1-ol, 6-hepten-2-ol, 6-hepten-3-ol, 6-hepten-4-ol, 6-hepten-5-ol, 5-hepten-1-ol, 5- hepten-2-ol, 5-hepten-3-ol, 5-hepten-4-ol, 4-hepten-1-ol, 4-hepten-2-ol, 4-hepten-3-ol, 3-hepten-1- ol, 3-hepten-2-ol, 2-hepten-1-ol, 7-octen-1-ol, 7-octen-2-ol, 7-octen-3-ol, 7-octen-4-ol, 7- octen-5-ol, 7-octen-6-ol, 6-octen-1-ol, 6-octen-2-ol, 6-octen-3-ol, 6-octen-4ol, 6-octen-5- ol, 5-octen-1-ol, 5-octen-2-ol, 5-octen-3-ol, 5-octen-4-ol, 4-octen-1-ol, 4-octen-2-ol, 4-octen-3-ol, 3-octen-1-ol, 3-octen-2-ol, 2-octen-1-ol.

According to another preferred embodiment of the invention, said alkenol has a carbon number of 4 and is therefore butenol.

According to another preferred embodiment of the invention, said butenol may be selected from 2-buten-1-ol (crotyl alcohol) (2-Bu-1-OH), 3-buten-2-ol (methyl vinyl carbinol) (3 -Bu-2-OH), 3-buten-1-ol (allylcarbinol) (3-Bu-I-OH) or mixtures thereof, and even more preferably 2-buten-1-ol (2-Bu-1- OH), 3-buten-2-ol (3-Bu-2-OH) or mixtures thereof.

It should be noted that when an alkenol can exist in various enantiomeric or stereoisomeric forms, it is understood that the process of the invention can be carried out with any of these types, either in purified form or in mixtures.

For example, in the above method, the E isomer (trans) of 2-buten1-ol (2-Bu-1-OH), the Z isomer (cis) of 2-buten-1-ol (2-Bu-1-OH) or a mixture of these two isomers. Similarly, (R) enantiomer of 3-buten-2-ol (3-Bu-2-OH), (S) enantiomer of 3-buten-2-ol (3-Bu-2-OH) can be used in the above method or a racemic mixture of these two enantiomers.

According to a preferred embodiment of the invention, said alkenol having a carbon number greater than or equal to 4 can be obtained directly from biosynthetic processes or through catalytic dehydration processes of at least one diol.

According to a preferred embodiment of the invention, when said alkenol has a carbon number of 4 and is therefore a butenol, said butenol can be obtained by catalytic dehydration of butanediol, preferably 1,3-butanediol, in the presence of a cerium oxide catalyst, wherein said cerium oxide catalyst is obtained by precipitation, in the presence of at least one base, of at least one cerium-containing compound. More detailed information relating to this process can be found, for example, in international patent application WO 2015/173780, filed in the name of one of the applicants and included herein for reference purposes.

According to a preferred embodiment of the invention, said diol, preferably butanediol, more preferably 1,3-butanediol, may be derived from the fermentation of sugars, preferably from the fermentation of sugars derived from biomass.

For the purposes of this description and the following claims, the term biomass refers to any organic material of plant origin, which includes: products obtained from agriculture, such as, for example, plants and plant parts of guayule, thistle, corn, soybean, cotton, flax, rapeseed, sugar cane, palm, including trimmings, residues and waste obtained from these products or as a result of their processing; products obtained from agricultural crops of plant species specially cultivated for energy use,

- 4 044603 such as, for example, miscanthus, millet, common reed, including trimmings, residues and waste obtained from these products or their processing; products resulting from forest management or forestry, including trimmings, residues and waste obtained from such products or their processing; waste of agri-food products intended for human nutrition or livestock production; residues from the paper industry; waste from separate collection of municipal solid waste, such as, for example, fruit and vegetable trimmings, paper.

According to a particularly preferred embodiment of the invention, said diol, preferably butanediol, more preferably 1,3-butanediol is produced by fermentation of sugars obtained from guayule and/or thistle biomass, including trimmings, residues and wastes obtained from guayule and/or thistle or from their processing. Even more preferably, said diol, preferably butanediol, more preferably 1,3-butanediol, is produced by fermentation of sugars derived from guayule biomass, including trimmings, residues and waste derived from guayule or its processing.

In order to obtain the above-mentioned sugars, said biomass can be subjected to physical processing (for example, extrusion, steam explosion, etc.) and/or chemical hydrolysis and/or enzymatic hydrolysis, obtaining mixtures of carbohydrates, aromatic compounds and other products that are obtained from cellulose, hemicellulose and lignin present in biomass. In particular, the resulting carbohydrates are mixtures of glucides with 5 and 6 carbon atoms, which include, for example, sucrose, glucose, xylose, arabinose, galactose, mannose, fructose, which are used in fermentation. Processes associated with the production of sugars from biomass, in particular sugars from lignocellulosic biomass, are described in the prior art, such as, for example, in international patent application WO 2015/087254 in the name of one of the applicants, and are included herein for reference purposes.

Other biotechnological processes for the production of bio-1,3-butanediol, starting from renewable sources, are described, for example, in US patent US 9017983, as well as in US patent applications US 2012/0329113 and US 2013/0109064.

When a diol, preferably butanediol, more preferably 1,3-butanediol, is produced by biosynthetic processes, for example by fermentation of sugars as described above, said diol is usually obtained as an aqueous mixture. Before proceeding with the catalytic dehydration of the diol, which leads to the production of the corresponding alkenol, it is possible to subject the above-mentioned aqueous mixture containing said diol obtained by biosynthetic processes to well-known separation processes, such as, for example, complete or partial distillation of water and the diol contained in the specified mixture. In fact, said aqueous mixture after filtration and deionization can preferably be used as such in a catalytic dehydration process, resulting in the corresponding alkenol without the need to subject it to expensive water removal processes or in any way limiting such removal.

In turn, alkenol can be obtained in the form of an aqueous mixture.

This aqueous mixture can be distilled to recover the alkenol, pure or as an azeotrope with water, or used as such.

For example, catalytic dehydration of 1,3-butanediol results in a mixture of butenols [2-buten-1-ol (2-Bu-1-OH), 3-buten-2-ol (3-Bu-2-OH), 3-butene -1-ol (3-Bu-I-OH)], which can be separated by distillation as minimal azeotropes with water. Azeotropic mixtures of butenols can be used as such, mixed with each other or mixed with added butenols, in a mixture or alone, or with the addition of water, so that they can be used in the catalytic dehydration process according to the invention for the production of 1,3-butadiene .

According to an embodiment of the invention, in the above-mentioned method for producing a diene, said alkenol having a number of carbon atoms greater than or equal to 4 can be mixed with a diluent, which can be selected, for example, from an inert gas such as, for example, nitrogen (N2), argon (Ar), preferably N2; or it may be mixed with a compound having a boiling point of 25°C to 150°C under normal conditions, and preferably a boiling point of 50°C to 125°C under normal conditions, and a melting point less than or equal to 20°C under normal conditions, which can be selected, for example, from water, tetrahydrofuran, cyclohexane, benzene or mixtures thereof. Nitrogen (N ₂ ) and water are preferred, and water is particularly preferred.

It is important to note that said water may be residual water obtained from the biosynthetic process used to produce said at least one alkenol.

According to a preferred embodiment of the invention, said process for producing a diene can be carried out, in the case where the diluent is selected from inert gases, at a molar ratio between the diluent and the alkenol (or alkenols) of more than 0.3, preferably from 0.5 to 2.

According to a preferred embodiment of the invention, said process for producing a diene can be carried out if the diluent is selected from compounds having a boiling point of between 25° C. and 150° C. under normal conditions, preferably between

- 5 044603

50°C to 125°C under normal conditions, and a melting point less than or equal to 20°C under normal conditions, with a molar ratio between diluent and alkenol (or alkenols) ranging from 0.01 to 100, preferably ranging from 0.1 to 50, more preferably ranging from 1 to 10.

According to a preferred embodiment of the invention, said process for producing the diene can be carried out at a temperature ranging from 250°C to 500°C, preferably ranging from 280°C to 450°C.

According to a preferred embodiment of the invention, said process for producing the diene can be carried out at a pressure ranging from 5 kPa to 5000 kPa, preferably ranging from 30 kPa to 350 kPa, more preferably ranging from 80 kPa to 250 kPa.

The process for producing the diene according to the invention can be carried out in the gas phase or in a mixed liquid/gas phase.

According to an embodiment of the invention, the above-mentioned process for producing a diene is carried out in the gas phase.

This process for producing a diene can be carried out in any type of reactor, preferably a fixed bed reactor, a moving bed reactor or a fluidized bed reactor.

According to an embodiment of the present invention, this process for producing a diene can be carried out in a fixed bed reactor.

In the case where a fixed bed reactor is used, the catalyst containing coke can be separated into different layers.

The reactor arrangement may include recycling a portion of the reaction effluents or catalyst material in a recycle reactor configuration.

In accordance with an alternative embodiment of the invention, when the process for producing the diene is carried out in a mixed liquid/gas phase, a continuous stirred tank reactor (CSTR) containing a coke-containing catalyst in the form of a dispersion can be used.

It is important to note that when the process for producing the diene of the invention uses at least one alkenol which is obtained from the catalytic dehydration of at least one diol, but the latter is also obtained, then dehydration of said at least one diol to obtain at least at least one alkenol and subsequent dehydration of said at least one alkenol to obtain a diene can be carried out:

in the same reactor or in different reactors, and preferably in different reactors;

continuously or periodically, and preferably continuously.

The process for producing the diene according to the invention can also be carried out continuously in a reactor configuration which includes at least two reactors connected in parallel, preferably two fixed bed reactors connected in parallel, wherein when one reactor is operating, in the other reactor there is a catalyst containing coke, can be regenerated.

When the diene production process is carried out continuously, the WHSV (mass hourly space velocity), that is, the ratio between the amount by weight of the reactant fed into the reactor and the amount by weight of the catalyst containing coke in the reactor itself, can range from 0.5 h ^{- 1} to 10 h ^-1 , preferably can be from 1 h ^-1 to 5 h ^-1 .

The contact time (τ), calculated as the ratio between the volume of coke-containing catalyst charged into the dehydration reactor and the flow rate under the reaction conditions, is preferably 0.01 s to 10 s, more preferably 0.05 s to 8 s , even more preferably is from 0.1 s to 4 s.

As mentioned above, the coke containing catalyst, the subject of this invention, can be obtained by the catalytic dehydration reaction of at least one alkenol, preferably 3-buten-2-ol (3-Bi-2-OH) and 2-buten- 1-ol (2-Bu-1-OH).

Thus, another subject of the present invention is a method for producing a catalyst containing coke, characterized in that said coke, when analyzed by diffuse reflectance infrared spectroscopy (DRIFTS), has at least two peaks at a wavelength , located between 1450 cm ^-1 and 1700 cm ^-1 , this method involves the dehydration of a mixture of alkenols containing 3-buten-2ol (3-Bi-2-OH) and 2-buten-1-ol (2-Bu- 1-OH), in the presence of at least one compound selected from: aluminum oxide (γ-Α1 ₂ Ο ₃ ), aluminum silicate, aluminosilicates (SiO ₂ -Al ₂ O ₃ ), aluminum oxides, zeolites, metal oxides (for example , lanthanum oxide, zirconium oxide, tungsten oxide, thallium oxide, magnesium oxide, zinc oxide, silver oxide), preferably selected from aluminosilicates (SiO ₂ -Al ₂ O ₃ ), this method being carried out at a temperature ranging from 250° C. to 500°C, preferably ranging from 280°C to 450°C for a time of from 2 to 10 hours, preferably from 2.5 to 9 hours.

It should be noted that the performance conditions of the above method for producing a coke-containing catalyst not specifically mentioned, such as WHSV (mass hourly space velocity), contact time (τ), types of reactors, etc., are as follows: the same as those described above in the case of a method for producing a diene, which is another subject of the present invention.

It should be noted that for the purpose of demonstrating the presence of the above peaks, in the following example three catalysts containing coke obtained by dehydration of individual butenols, i.e. 2-buten-1-ol (2-Bu-1-OH), 3-buten-2-ol (3-Bu-2-OH), 3-buten-1-ol (3-Bu-I-OH), was analyzed by diffuse reflectance infrared spectroscopy (DRIFTS).

In order to practice the present invention and illustrate it more clearly, some non-limiting examples are given below.

Example 1.

(i) Preparation of crude butenol mixture.

For this purpose, a mixture of 1,3-butanediol (1,3-BDO) was prepared, having a mass content equal to 83% 1,3-butanediol (1,3-BDO) and 17% water (mixture 1), respectively, which was then used for the dehydration reaction.

The reactor in which said dehydration reaction was carried out contained a tubular element made of AISI 304 stainless steel with a height (h) of 260 mm and an internal diameter (Φ) of 10 mm, in front of which an evaporator was located and connected to it, both equipped with electric heating. In contrast, the outlet of the reactor was connected to a first condenser connected to the receiving flask and operating at 15°C, in order to ensure that the products obtained from the first dehydration reaction were released as a liquid at room temperature (25°C) at the specified receiving flask. Said receiving flask was in turn connected to a sampling system comprising a steel cylinder with a volume (V) of 300 ml and equipped with shut-off valves at both ends. The vapors/gases resulting from the first dehydration reaction and possibly not condensed in the above-described system can further flow through the aforementioned steel cylinder connected in turn to a volumetric meter, which therefore measures their quantity.

The resulting products, both liquid and vapor/gas, were characterized by gas chromatography using:

for liquid products - a Thermo Trace gas chromatograph equipped with a FID (flame ionization) detector and an AQUA WAX column (Grace, length 30 m x internal diameter 0.53 mm x film thickness 1.0 µm);

for products in gaseous form - gas chromatograph 490 micro GC Varian/Agilent with four channels equipped with the following columns: Pora Plot Q 10 m long, MolSieve 5 A 4 m long, A12O3 10 m long with backwash function, CPSil-19 CB long 7.5 m.

The catalyst used in the said dehydration reaction was a cerium oxide (CeO ₂ ) based material in granules of 0.5 mm to 1 mm size, and was charged into the above reactor in an amount of 10 g (3.5 ml). The specified catalyst was prepared in accordance with the laboratory procedure described below.

To this end, 500 g of a commercial aqueous solution of approximately 30% ammonium hydroxide ( _NH4OH ), (28%-30% Aldrich NH3 reagent) was added to the first 3-liter beaker, equipped with a Teflon semicircular stirrer blade, with 500 g of water , and the pH electrode [Metrohm pH glass electrode (6.0248.030) connected to a Metrohm 780 pH meter] was inserted. In a second 2-liter beaker equipped with a magnetic anchor stirrer, a solution of 100 g of cerium nitrate hexahydrate (99% Aldrich) in 1000 g of water was prepared; Cerium nitrate hexahydrate was then dissolved by vigorous stirring at room temperature (25°C). The resulting solution was introduced into a dropping funnel and added dropwise over 2 hours to the ammonium hydroxide solution described above, contained in a 3-liter beaker, with constant vigorous stirring. The pH value of the resulting suspension was 10.2. The solid in suspension was filtered, washed with 2 L of water, and then dried in an oven at 120°C for 2 hours. The synthesis was repeated until 2000 g of solid was obtained.

1270 g of the solid thus obtained, screened at 0.125 mm, was placed in an extruder to which 175.9 g of a 25% ammonium hydroxide (NH ₄ OH) solution (obtained by diluting a solution containing 28%-30% of the reagent) was also added Aldrich based NH3) using a Watson Marlow peristaltic pump set at 5 rpm. Following this addition, 158 g of demineralized water was also added to ensure the correct consistency for extrusion. The granules exiting the extruder were air dried and then a 100 g portion was calcined at 800°C with a rise of 1°C/min to 800°C followed by a temperature isotherm for 6 hours. The calcined solid was granulated and sieved , and a fraction of granules ranging in size from 0.5 mm to 1 mm was used as a catalyst.

The said dehydration reaction was then carried out by feeding mixture 1, first into the above evaporator, preheated to a temperature of 250°C, and thereafter into the above tubular reactor, preheated so that its internal temperature during the dehydration reaction was equal to 400°C. Both the evaporator and the reactor were maintained at atmospheric pressure (0.1 MPa, 1 bar).

The flow rate of mixture 1 into the evaporator was 100 g/h, while the flow rate into the reactor, expressed as WHSV, was 10 h' ¹ .

The test was carried out for sufficient time to collect a suitable amount of crude product.

(i) Purification of crude butenols.

The mixture of crude butenols obtained as described above was subjected to a first purification by distillation to remove unreacted 1,3-butane diol a (1,3-BDO). It should be noted that the butenols present in this mixture form azeotropic mixtures with water, for which it is impossible to separate them from water by simple distillation in order to obtain them in pure form.

Distillation was carried out at atmospheric pressure by adding 3,5-di-tert-4-butylhydroxytoluene (BHT) to the mixture contained in the still, so that its concentration in the mixture was approximately 200 ppm. This distillation was carried out using an Oldershaw column having 40 trays (2 sections with 20 trays), by loading the said mixture into the still in one feed and taking various samples of the head fraction based on the recorded temperatures, gradually concentrating the heavier components in the still. Distillation conditions (reflux coefficient, heating power of the distillation cube, amount of distillate taken) varied depending on the boiling point of the molecules being separated and the recorded temperatures of the head fraction.

Distillation conditions are given in table. 1.

Table 1

Conditions for distillation of alkenols at atmospheric pressure ΔΤ distillation, cube ΔΤ goals, fr. cd ⁽¹⁾ (°C) (°C) Loading - - - Faction 1 101.3 - 103.0 56.0 - 84.5 100 Faction 2 103.1 - 104.3 85.0-86.8 100-30 Faction 3 104.9- 133.6 86.4-87.1 thirty Faction 4 114.6-152.3 87.1 -94.4 30-40 Fraction 5 154.3 - 167.9 93.6-119.4 40-60 Fraction 6 169.2-208.6 120.1 - 121.2 60-70 Fraction 7 208.6-210.8 121.2-130.1 70 Alembic - - -

(1): reflux ratio. In particular:

fraction 1 (up to approximately 84°C) corresponds to the lightest part to be removed;

fraction 2 and fraction 3 correspond to an azeotrope at T = 86.5 ° C - 87 ° C between the alkenol with the lowest boiling point, that is, 3-buten-2-ol (methyl vinyl carbinol) (3-Vi-2-OH) and water (moreover, the specified azeotrope has the composition: 73% by weight of 3-buten-2-ol (3-Vn-2-OH) and 27% by weight of water);

in fraction 4, 2-buten-1-ol (crotyl alcohol in cis- and trans forms) (2-Bu-l-OH) and a small part of 3-buten-1-ol (allylcarbinol) (3-Bi-1) also begin to distill -OH) together with 35% by weight water;

in fraction 5, water comes out and, therefore, the temperature rises to approximately 120°C;

fraction 6 and fraction 7 correspond to 2-buten-1-ol (crotyl alcohol) (2-Bu-l-OH) at a content of 95% - 97%.

The butenol-containing fractions were combined into one fraction representing the mixture used to prepare the coke-containing catalyst of the present invention. The composition is described in table. 2.

table 2

Water 37.0% Light connections ⁽¹⁾ 0.1% 2-Bu-l-OH+3-Bu-2-OH 60.3% 3-Bu-l-OH 0.2% Medium boiling compounds ⁽²⁾ 2.2% Heavy connections ⁽³⁾ 0.2%

(1): the lightest butenol compounds with a low boiling point, that is, 3-buten-2-ol (3-Bu2-OH) (Bp = 97°C);

(2): the lightest butenol compounds with a high boiling point, that is, 2-buten-1-ol (2Bu-1-OH) ( _bp = 121.5 ° C); heavier than low boiling alkenol, i.e. 3-buten-2ol (3-Bu-2-OH) ( _bp =97°C), excluding 1,3-butadiene (1,3-BD) [includes 3-buten-1-ol (3-Bu-I-OH) with an average boiling point (Tki _p = 113.5)];

(3): heavier butenol compounds with a high boiling point, i.e. 2-buten-1-ol (2Bu-1-OH) (Bp=121.5°C).

Example 2.

Preparation of catalyst containing coke and production of 1,3-butadiene (1,3-BD).

The first test was carried out by feeding a mixture of butenols, obtained as described in example 1 and presented in table 2, into a tubular fixed bed reactor - PFR (Plug Flow Reactor, plug flow reactor), made of AISI 316L stainless steel, with a length of 400 mm, and with a diameter equal to 9.65 mm, loaded with 0.6 g of aluminosilicate containing 3.8% Al and obtained as described below.

7.55 g of aluminum tri-sec-butoxide (Aldrich) as alumina precursor (Al ₂ O ₃ ) was introduced into the first 500 ml round bottom flask, and 50.02 g of orthosilicic acid (Aldrich, <20 mesh) as silicon dioxide precursor (SiO ₂ ) were introduced into a second 500 ml round bottom flask with 250.02 g of demineralized water. The resulting orthosilicic acid suspension was slowly added (10 min) to the first round bottom flask containing aluminum tri-sec-butoxide and the resulting mixture was kept at 90° C. for about 1 hour with vigorous stirring (500 rpm). After cooling to room temperature (25°C), the resulting suspension was filtered and the resulting solid was washed with 5 L of demineralized water, dried at 120°C for one night and then calcined at 500°C for 5 hours to obtain a colorless powder ( 47.95 g) (defined as active phase).

A portion of the above active phase, 40.42 g, was mixed with 24.43 g of Versal™ V-250 pseudoboehmite (UOP), as an aluminum oxide (Al ₂ O ₃ ) precursor in the binder, and 302 ml of a 4% acetic acid solution in 800 ml glass. The resulting mixture was kept under stirring at 60°C for 2 hours. The beaker was then transferred to a heating plate and, with vigorous stirring, the mixture was heated overnight to 150°C until dry. The resulting solid was then calcined at 550° C. for 5 hours to obtain 60.45 g of a colorless product, which was mechanically granulated, and a fraction of granules ranging in size from 0.1 mm to 1.0 mm was used as a dehydration catalyst in the said tubular reactor

The catalyst prepared as described above (0.6 g) was introduced into the reactor using quartz wool as a support for the granules so that they were located in the isothermal region of the reactor. The reactor was installed in a downflow configuration.

The catalyst was pretreated in situ at 300°C in a stream of nitrogen ( _N2 ).

The above mixture of butenols was fed from the top of the reactor, at atmospheric pressure (0.1 MPa), by evaporation to allow the reactants to reach the reaction temperature before coming into contact with the catalyst, using an infusion pump and a 5 ml Hamiltonian pump. , connected to a heated steel line, and then fed into the reactor, in a stream of nitrogen (N2): the total volumetric flow rate was equal to 28 ml/min, of which 2% by volume was the specified mixture of butenols. The said reactor was heated to a temperature of 300°C using an electric furnace, and the temperature was controlled using a built-in thermocouple connected to the temperature controller of the electric furnace and a second axial thermocouple placed inside the said tubular reactor, which indicates the actual temperature of the catalytic bed and was selected as reference temperature.

The tubular reactor temperature was maintained at 300°C as described above, and the contact time (τ) was 0.67 s.

After the reactor, the resulting products were selected online in a gas chromatograph (GC) for analysis. On-line analysis of gases was carried out using an Agilent HP6890 (GC) gas chromatograph equipped with two capillary columns: an HP-5 column (cross-linked 5% phenylmethylsiloxane) 50 m long, 0.2 mm in diameter, 0.33 μm film connected to a flame ionization detector

- 9 044603 (FID), and an HP-Plot-Q column (cross-linked polystyrene-divinylbenzene) 30 m long, 0.32 mm in diameter, 20 µm film, connected to a thermal conductivity detector (TCD). The carrier used in both columns was helium at a flow rate of 0.8 mL/min (HP-5 column) and 3.5 mL/min (HP-Plot-Q column).

The results are shown in Fig. 1 [the y-axis shows the conversion and yield as a percentage (%); The x-axis shows the reaction time in hours (h)].

The catalytic efficiency levels shown in FIG. 1, are expressed by calculating the conversion of alkenols (C _alk .), selectivity for 1,3-butadiene (S _1,3-bg ) and the yield of 1,3-butadiene Shch _1,3-bd ) in accordance with the formulas presented below:

C = ^alc.

$1,3-BD ( ^moli ^Jex~ ( ^t0 ^alk)out ( ^m0li aJe _X _ ^t °H1,3-BD ( ^t01 'alk^x-( ^t °I _alk ) _bb1X „ _ Salk. ^x ^1, 3-DB ^/Z-DB = where:

- moli al _to = moles of alkenols [meaning 3-buten-2-ol (3-Bu-2-OH) and 2-buten-1-ol (2-Bu-1-OH)];

- (moli _alk .) _in = moles of alkenols at the inlet;

- (moli _alk .) _you x = moles of alkenols at the outlet;

- moli _1;3-B d=moles of 1,3-butadiene produced (1,3-BD).

From the data presented in Fig. 1, we can conclude that the yield of 1,3-butadiene (Y 1,3BD) starts from an initial value of about 47%, settling after 4 hours at about 70%. After 4 hours, the yield of 1,3-butadiene (Y 1,3BD) continues to increase slowly until it stabilizes at an average value of 80% after 10 hours. In FIG. 1 also shows the trend of carbon loss (C loss), which is an indicator of the coke that is gradually formed on the catalyst. In fig. 1:

- X 2-Bu-1-OH refers to the conversion of 2-buten-1-ol (2-Bu-1-OH);

- X 3-Bu-2-OH refers to the conversion of 3-buten-2-ol (3-Bu-2-OH);

- X 3-Bu-1-OH refers to the conversion of 3-buten-1-ol (3-Bu-1-OH).

In order to better illuminate the role of coke in increasing the yield, the above example 1 was repeated 3 times, stopping the reaction after 3 hours, 8 hours and 20 hours. The catalysts discharged from the reactor at the indicated times were subjected to thermogravimetric analysis (TGA) in air to calculate the amount of adsorbed coke . This analysis was carried out using an SDT Q 600 instrument (TA Instruments), loading 15 mg of catalyst, in an air flow (100 ml/min) and with a temperature rise (10°C/min to 900°C and a subsequent isotherm at 900°C at for 5 min) in such a way as to quantify the organic residues present. The results are shown in Fig. 2 [the y-axis shows mass loss as a percentage (%); The x-axis shows the temperature in degrees Celsius (°C)]. From fig. 2, considering the mass loss associated with the presence of coke (temperatures above 380°C), we can conclude that in the first 3 hours, rapid formation of coke occurs (mass loss by 5%): this time interval corresponds to the fastest increase in yield up to to pre-adjusted values (as shown in Fig. 1). The other two TGA curves show that at values greater than 3 h, coke continues to form, but more slowly: this condition corresponds to the calculation at maximum yield values (as shown in Fig. 1), which occurs slowly until 10 h until complete stabilization.

Example 3.

In order to test which type of catalyst contained the coke active in the catalysis, Example 2 was repeated, but instead of using a mixture of butenols, the individual isomers fed separately, i.e. 3-buten-2-ol (3-Bu-2-OH), were used. 2-buten-1-ol (2-Bu-1-OH) and 3-buten-1-ol (3-Bu-I-OH). The conditions used were the same as in Example 2. From these experiments it can be concluded that both 3-buten-2-ol (3-Bu-2-OH) [Fig. 3, in which the ordinate indicates the conversion and yield in percent (%) and the abscissa indicates the time in hours (h)], and 2-buten-1-ol (2-Bu-1-OH) [Fig. 4, in which the y-axis indicates conversion and yield in percent (%) and the x-axis indicates time in hours (h)], have a yield profile similar to that of the butenol mixture used in Example 2, as shown in FIG. 1 (rapid increase in output between 0 and 3 hours, and then further increase until settling at maximum values after 10 hours).

The behavior of 3-buten-1-ol (3-Bu-1-OH) is completely different [Fig. 5, in which the conversion and yield in percent (%) are indicated on the ordinate axis and the time in hours (h) is indicated on the abscissa axis], and from it propylene is mainly obtained (with a yield of 40%-50%) and a large amount of coke ( loss C). In fig. 3:

- X 3-Bu-2-OH refers to the conversion of 3-buten-2-ol (3-Bu-2-OH);

- C loss refers to the trend of carbon loss. In fig. 4:

-

Claims (10)

- X 2-Bu-1-OH refers to the conversion of 2-buten-1-ol (2-Bu-1-OH); - C loss refers to the trend of carbon loss. In fig. 5: - X 3-Bu-I-OH refers to the conversion of 3-buten-1-ol (3-Bu-I-OH). Catalysts containing coke formed by the three isomers were analyzed by diffuse reflectance infrared spectroscopy (DRIFTS) as follows. For this purpose, three samples of fresh catalyst (i.e. 0.6 g of aluminosilicate containing 3.8% di-Al) were prepared, operating as described in Example 2. Each sample was diluted with potassium bromide (KBr) in a ratio of 1:10 , treated at 450°C in helium (He) for 20 min and then cooled to 50°C; then a single pulse of the reagent was injected onto the sample, that is, the isomer 3-buten-2-ol (3-Bu-2-OH) (first sample), 2-buten-1-ol (2-Bu-1-OH) (second sample) and 3-buten-1-ol (3Bu-1-OH) (third sample) and then, after that, the temperature was increased and the spectrum was recorded at 300°C. The above analysis was performed using a Bruker Vertex 70 FT-IR spectrophotometer equipped with a Pike DiffusIR cell and an MCT detector; spectra were recorded and processed using data processing obtained with OPUS software. The analysis parameters were as follows: - scanning interval: 4000 cm ^-1 - 450 cm ^-1 ; - number of scans per sample: 32; - background: the spectrum is recorded by placing the initial catalyst (without coke) in the body of the attachment; - spectral resolution: 4 cm ^-1 ; - mirror adjustment: 3.5 mm (DRIFTS mirrors were aligned in such a way that the device detector could detect maximum absorption). The results obtained are shown in Fig. 6, on which the ordinate shows absorption in units of specific absorption (optical density); The wave number in cm ^-1 is indicated on the abscissa axis. From the spectrum shown in FIG. 6, we can conclude that it is effective in the case of two isomers, which mainly form 1,3-butadiene (1,3-BD), i.e. 3-buten-2-ol (3-Bu-2-OH) (first sample - indicated in Fig. 6 as 3But2ol) and 2-buten-1-ol (2-Bu-1-OH) (second sample - indicated in Fig. 6 as 2Butlol), the coke of the resulting coke-containing catalyst has two characteristic bands at 1465 cm ^-1 and 1573 cm ^-1 , while the isomer 3-buten-1-ol (3-Bu-I-OH ) (the third sample - indicated in Fig. 6 as 3Butlol) (which leads to the formation of propylene and coke, as indicated in Fig. 5) has a band at 1650 cm ^-1 , confirming the different nature of the two types of coke. The indicated bands refer to tensile deformation of C=C and C-H aromatic type (coke bands), as reported in the literature by Ibarra A. et al., in the article Dual coke deactivation pathways during the catalytic cracking of raw bio-oil and vacuum gasoil in FCC conditions (Ways for double deactivation of coke during catalytic cracking of crude bio-oil and vacuum gas oil under FCC conditions), Applied Catalysis B: Environmental (2016), Vol. 182, pp. 336-346. Example 4. For comparative purposes, Example 2 was repeated with only 3-buten-1-ol (3-Bu-1-OH) fed for 4 hours. After 4 hours, 3-buten-1-ol (3-Bu-1-OH) was replaced with the same butenol mixture used in Example 2 (i.e., the butenol mixture prepared as described in Example 1 and presented in Table 2) . The results are shown in Fig. 7, where the y-axis shows the conversion and yield in percent (%), and the x-axis shows the time in hours (h). From fig. 7 we can conclude that the coke formed by 3-buten-1ol (3-Bu-1-OH) has no effect on increasing the catalyst yield: in fact, only after replacing 3-buten-1-ol (3-Bu -1-OH) with the same mixture of butenols as in example 2, an increase in the yield of 1,3-butadiene (Y 1,3BD) can be observed. In fig. 7: - X 2-Bu-1-OH refers to the conversion of 2-buten-1-ol (2-Bu-1-OH); - X 3-Bu-2-OH refers to the conversion of 3-buten-2-ol (3-Bu-2-OH); - X 3-Bu-1-OH refers to the conversion of 3-buten-1-ol (3-Bu-1-OH); - C loss refers to the trend of carbon loss. CLAIM 1. A catalyst containing coke, characterized in that said coke, when analyzed by diffuse reflectance infrared spectroscopy, has at least two peaks at a wavelength located between 1450 cm ^-1 and 1700 cm ^-1 , and the specified catalyst is obtained by a process including dehydration of a mixture of alkenols containing 3-buten-2-ol and 2-buten-1-ol, in the presence of at least one compound selected from: aluminum oxide, aluminum silicate, aluminosilicates, aluminum oxides, zeolites, metal oxides, and the specified the method is carried out at a temperature ranging from 280°C to 450°C, for a time ranging from 2 to 10 hours. 2. The coke-containing catalyst according to claim 1, wherein said catalyst contains at least - 11 044603 one compound selected from: aluminum oxide (γ-Α12Ο ₃ ), aluminum silicate, aluminosilicates (SiO ₂ Al2O ₃ ), aluminum oxides, zeolites, metal oxides. 3. A coke-containing catalyst according to claim 1 or 2, where said catalyst contains: (a) from 2% by weight to 30% by weight of coke, based on the total weight of said catalyst; (b) from 70% by weight to 98% by weight, preferably from 80% by weight to 94% by weight, based on the total weight of said catalyst, of at least one compound selected from: alumina, aluminum silicate, aluminosilicates, aluminum oxides, zeolites, metal oxides; where the sum (a)+(b) is equal to 100. 4. A method for producing a diene, comprising dehydrating at least one alkenol having a number of carbon atoms equal to or greater than 4, in the presence of at least one coke-containing catalyst according to claim 1. 5. A method for producing a diene according to claim 4, wherein said linear or branched alkenol has the general formula C _n H _2n O, where n is an integer greater than or equal to 4 and less than or equal to 8. 6. A method for producing a diene according to claim 4 or 5, wherein said alkenol has a carbon number of 4 and is therefore a butenol selected from 2-buten-1-ol, 3-buten-2-ol, 3-buten-1-ol or mixtures thereof. 7. The method for producing a diene according to claim 4, in which said alkenol having a number of carbon atoms equal to or greater than 4 is mixed with a diluent selected from: an inert gas selected from nitrogen, argon; or it is mixed with a compound having a boiling point of from 25°C to 150°C under normal conditions, and a melting point less than or equal to 20°C under normal conditions, selected from water, tetrahydrofuran, cyclohexane, benzene or mixtures thereof. 8. A method for producing a diene according to claim 7, in which: in case the diluent is selected from inert gases, this method is carried out with a molar ratio of diluent to alkenol or alkenols ranging from 0.5 to 2; in case the diluent is selected from compounds having a boiling point of from 25°C to 150°C under normal conditions, and a melting point less than or equal to 20°C under normal conditions, the said method is carried out with a molar ratio of the diluent to the alkenol or alkenols , ranging from 0.01 to 100. 9. A method for producing a diene according to any one of claims 4-8, where the specified method is carried out: at a temperature ranging from 280°C to 450°C; and/or at a pressure ranging from 5 kPa to 5000 kPa; and/or in the gas phase or mixed liquid/gas phase; and if it is carried out in a mixed liquid/gas phase using a continuous stirring reactor containing a catalyst containing coke in a dispersion; and/or continuously or periodically, and preferably continuously; and/or if it is carried out continuously, then the space velocity WHSV, that is, the ratio by weight of the reactant supplied to the reactor to the weight of the catalyst in the reactor, is from 0.5 h ^-1 to 10 h ^-1 , preferably from 1 h ^-1 to 5 h ^-1 ; and/or contact time (τ), calculated as the ratio of the volume of coke-containing catalyst charged into the dehydration reactor to the flow rate at the reaction conditions, preferably from 0.01 s to 10 s, more preferably from 0.05 s to 8 s, even more preferably from 0.1 s to 4 s. 10. A method for producing a diene according to any one of claims 4-8, where the specified method is carried out: at a temperature ranging from 280°C to 450°C; and/or at a pressure ranging from 5 kPa to 5000 kPa; and/or in a fixed bed reactor, a moving bed reactor or a fluidized bed reactor; and continuously or periodically, and preferably continuously; and if it is carried out continuously, then the space velocity WHSV, that is, the ratio of the amount by weight of the reagent supplied to the reactor to the amount of the mass of the catalyst in the reactor, ranges from 0.5 h ^-1 to 10 h ^-1 ; and/or contact time (τ), calculated as the ratio of the volume of catalyst containing coke loaded into the dehydration reactor to the flow rate under reaction conditions, ranges from 0.01 s to 10 s. -