Catalyst Containing Coke and Method for Producing Dienes

Abstract

The present invention relates to a catalyst comprising coke, characterized in that the coke has at least two peaks at wavelengths between 1450 cm-1 and 1700 cm-1 when analyzed by diffuse reflectance infrared spectroscopy (“diffuse reflectance infrared Fourier transform spectroscopy” - DRIFTS). The aforementioned catalyst comprising coke can be advantageously used in a process for producing dienes, preferably conjugated dienes, more preferably 1,3-butadiene, said process comprising dehydrating at least one enol having at least 4 carbon atoms. Preferably, the enol having at least 4 carbon atoms can be obtained directly from a biosynthetic process or by a catalytic dehydration process of at least one diol. When the enol is butenol, the diol is preferably butanediol, more preferably 1,3-butanediol, even more preferably bio-1,3-butanediol, i.e., 1,3-butanediol derived from a biosynthetic process. When the diol is 1,3-butanediol or bio-1,3-butanediol, the dienes obtained according to the process of the present invention are 1,3-butadiene or bio-1,3-butadiene, respectively.

Description

[0001] The present invention relates to a catalyst comprising coke.

[0002] More specifically, the present invention relates to a catalyst comprising coke, characterized in that the coke has at least two peaks at wavelengths between 1450 cm -1 and 1700 cm -1 .

[0003] The aforementioned catalyst comprising coke can be advantageously used in a process for producing dienes, preferably conjugated dienes, more preferably 1,3-butadiene, the process comprising dehydrating at least one enol having a carbon atom number greater than or equal to 4.

[0004] Accordingly, the present invention also relates to a process for producing dienes, preferably conjugated dienes, more preferably 1,3-butadiene, comprising dehydrating at least one enol having a carbon atom number greater than or equal to 4 in the presence of the catalyst comprising coke.

[0005] Preferably, the enol having a carbon atom number greater than or equal to 4 can be obtained directly by a biosynthetic process or by a catalytic dehydration process of at least one diol.

[0006] When the enol is butenol, the diol is preferably butanediol, more preferably 1,3-butanediol, and even more preferably bio-1,3-butanediol, i.e., 1,3-butanediol derived from a biosynthetic process.

[0007] When the diol is 1,3-butanediol or bio-1,3-butanediol, the dienes obtained according to the method of the present invention are 1,3-butadiene or bio-1,3-butadiene, respectively.

[0008] 1,3-Butadiene is a basic product of the petrochemical industry: it represents a substrate for preparing products such as chloroprene, adiponitrile, and hexamethylenediamine.

[0009] In fact, 1,3-butadiene can be used in many industrial fields, including plastics, synthetic rubbers, resins, latexes, terpolymers (such as ABS), paints, and synthetic fibers. The copolymer product of 1,3-butadiene and styrene is included in blend compositions for producing tires.

[0010] Currently, more than 95% of the 1,3-butadiene produced annually is obtained as a by-product in the "steam cracking" process for the production of ethylene and other olefins, separated from it by extractive distillation, in which a small amount (<5%) is formed. 1,3-Butadiene can also be obtained from fossil sources by other methods, such as by catalytic dehydrogenation / oxidative dehydrogenation of butane and / or butene. All these methods are particularly energy-consuming and imply the emission of large amounts of carbon dioxide (CO2).

[0011] Due to the need to reduce the environmental impact of chemical production and the need to use raw materials from renewable sources (such as biomass), different methods are used to obtain bio-1,3-butadiene. Examples of such methods are: dehydration of diols obtained from biomass fermentation; direct fermentation of biomass to bio-1,3-butadiene; conversion of ethanol to bio-1,3-butadiene in one or two stages; dehydration and then dehydrogenation of bio-butanol obtained from biomass fermentation or gasification.

[0012] For example, the dehydration of diols obtained from biomass fermentation can be carried out in two consecutive dehydration stages according to the following scheme:

[0013]

[0014] 1,3-butanediol (1,3butandiolo) = 1,3-butanediol (1,3butanediol)

[0015] 1,3-butadiene (1,3butadiene) = 1,3-butadiene (1,3butadiene)

[0016] Unsaturated alcohols (Alcoli insaturi) = Unsaturated alcohols

[0017] For example, as described by Sato S. et al. in the article "Future Prospect of the Production of 1,3-Butadiene from Butanediols" ("Chemistry Letters" (2016), Vol. 45, pp. 1036 - 1047).

[0018] The production of olefins and / or dienes (such as 1,3-butadiene) by the dehydration of unsaturated alcohols can be carried out in the presence of an acid catalyst. The type of acidity (i.e., Brønsted acid or Lewis acid) and the strength of the acid sites can vary. Catalytic systems commonly used are based on metal oxides, such as silica (Si), aluminum (Al), zirconium (Zr), zinc (Zn), magnesium (Mg) in amorphous form, or on zeolites. The production of olefins and / or dienes (such as 1,3-butadiene) by the dehydration of unsaturated alcohols can also be carried out in the presence of a cerium-based catalyst, particularly in a two-stage process.

[0019] Many efforts have been made in the prior art to identify catalysts suitable for the dehydration of unsaturated alcohols to provide olefins and / or dienes.

[0020] For example, British Patent GB 1,275,171 describes a method for preparing a lithium phosphate-based catalyst for the dehydration of epoxides or diols to provide dienes. The use of said catalyst in the dehydration of epoxides or diols to provide dienes is said to be capable of obtaining by-products, mainly carbonyl products that can be reconverted to olefins. In addition, said catalyst has the advantage of being able to be calcined at 600 °C without losing its activity and thus being able to be regenerated after use.

[0021] U.S. Patent US 2,420,477 describes a method for preparing butadiene, which includes reacting vinyl ethyl ether with ethylene in the presence of a catalyst at a temperature of 125 °C to 250 °C, said catalyst comprising a "core" of a metal selected from the group consisting of beryllium, magnesium, zinc, cadmium, aluminum or their alloys, and the "core" being coated with oxides of metals (such as vanadium, niobium, tantalum, chromium, molybdenum, tungsten and uranium). It is said that the above method is carried out at a temperature lower than that usually used for the preparation of butadiene and is substantially capable of preventing the generation of by-products.

[0022] International Patent Application WO 2013 / 017496 describes the use of a catalyst comprising a phosphorus-modified zeolite for the dehydration of alcohols to produce low-molecular-weight olefins, said catalyst being obtained by a specific method, and it is said that the method is easy to reproduce to provide a catalyst with a good performance level.

[0023] U.S. Patent US 4,260,845 describes the dehydration of saturated alcohols to olefins in the presence of a zinc aluminate-based dehydration catalyst with a ZnO / Al2O3 molar ratio of about 1, said catalyst having been heated in air for a sufficient length of time and activated at a sufficient temperature. It is said that the above catalyst has a good performance level in terms of selectivity.

[0024] Despite the efforts made in the prior art, it remains an object, and thus of great interest, to identify dehydration catalysts with a good level of performance and higher durability, and / or methods that can increase the durability of said catalysts and / or reduce the formation of by-products that can cause catalyst poisoning as described above.

[0025] It is known that in the dehydration reaction of unsaturated alcohols, side reactions leading to the formation of carbonyl compounds such as aldehydes, ketones, carboxylic acids also occur in the presence of an acid catalyst and of the main products obtained, namely olefins and / or dienes. Said carbonyl compounds can be formed due to dehydrogenating components present in some dehydration catalysts such as alumina and silica-alumina, where said components can be more or less marked. Other side reactions that can occur are the oligomerization and the "cracking" phenomenon of olefins. Said side reactions provide compounds that act as precursors of coke and thus lead to the deactivation of the dehydration catalyst due to the formation of coke and / or tar, where the coke and / or tar relatively rapidly cover the active surface of the catalyst used for dehydration, rendering it completely inactive.

[0026] The deactivation mechanism of catalysts is well known in the literature. A detailed description of said mechanism can be found, for example, in the following documents: 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 C.H., "Mechanisms of catalyst deactivation", "Applied Catalysis A: General", (2001), Vol. 212, pp. 17 - 60.

[0027] Makshina E.V. et al. presented in the review "Review of old chemistry and new catalytic advances in the on-purpose synthesis of butadiene" ("Chemical Society Reviews" (2014), Vol. 43, pp. 7917 - 7953) the state of the art regarding the production of 1,3-butadiene from renewable resources and the catalytic systems used for this purpose. The references they cited are very extensive (in fact, 246 articles are mentioned), but among the catalysts used, catalysts containing catalytically active coke have never been mentioned.

[0028] A large number of patent documents also relate to the production of 1,3-butadiene by dehydration of unsaturated alcohols, and / or the production of unsaturated alcohols and / or catalytic systems used which can be used for the production of 1,3-butadiene. In this case, however, a catalyst containing catalytically active coke has never been mentioned either. For example, the following US patents in the name of one of the applicants can be mentioned: US 2,310,809, US 2,426,678, US 4,400,562, US 5,406,007, US 6,278,031, US 9,434,659; and European patent applications EP 3,262,023, EP 3,230,236, EP 3,142,785 and international patent application WO 2018 / 073282.

[0029] Catalytically active coke in the reaction of methanol and dimethyl ether (DME) to olefins (MTO and DTO) is described in the article by Chen D et al., "The Role of Coke Deposition in the Conversion of Methanol to Olefins over SAPO-34" ("Catalyst Deactivation" (1997), Bartholomew C.H. and G.A. Fuentes Eds., Elsevier Science B.V., pages 159-166). However, in the said article, no suggestion is given as to the possibility that the said coke could also be active as a catalyst in the dehydration reaction of enols to produce 1,3-butadiene.

[0030] Therefore, the applicant set out to solve the problem of finding a catalyst containing coke which could be advantageously used in the process for producing dienes, especially conjugated dienes, more especially 1,3-butadiene and even more especially bio-1,3-butadiene, by catalytic dehydration of at least one enol having at least 4 carbon atoms, especially at least one enol derived from a biosynthetic method (commonly called bio-enol).

[0031] The applicant has now discovered a catalyst containing coke, wherein the coke has at least two peaks in a specific wavelength range when analyzed by diffuse reflectance infrared spectroscopy ("diffuse reflectance infrared Fourier transform spectroscopy" - DRIFTS), which can be advantageously used in a process for producing dienes. In particular, the catalyst containing coke can be advantageously used in a process for producing dienes, especially conjugated dienes, more particularly 1,3-butadiene, and even more particularly bio-1,3-butadiene, by catalytic dehydration of at least one enol having a carbon atom number greater than or equal to 4, especially at least one enol derived from a biosynthetic process (commonly referred to as bio-enol). In addition, the catalyst containing coke can provide 1,3-butadiene in high yield and selectivity.

[0032] Accordingly, an object of the present invention is a catalyst containing coke, characterized in that the coke has at least two peaks at wavelengths between 1450 cm -1 and 1700 cm -1 when analyzed by diffuse reflectance infrared spectroscopy ("diffuse reflectance infrared Fourier transform spectroscopy" - DRIFTS).

[0033] Diffuse reflectance infrared spectroscopy ("diffuse reflectance infrared Fourier transform spectroscopy" - DRIFTS) analysis is carried out as described in the following examples.

[0034] For the purposes of this specification and the following claims, unless otherwise indicated, the definition of a numerical range always includes the end values.

[0035] For the purposes of this specification and the following claims, the term "comprising" also includes the terms "consisting essentially of" or "consisting of".

[0036] According to a preferred embodiment of the present invention, the catalyst containing coke may comprise at least one compound selected from, for example, the following: alumina (γ-Al2O3), aluminosilicate, silica-alumina (SiO2-Al2O3), alumina, zeolite, metal oxides (such as lanthanum oxide, zirconium oxide, tungsten oxide, thallium oxide, magnesium oxide, zinc oxide, silver oxide); preferably selected from silica-alumina (SiO2-Al2O3).

[0037] According to a further preferred embodiment of the present invention, the catalyst containing coke may comprise:

[0038] (a) 2% to 30% by weight, preferably 6% to 20% by weight of coke, based on the total weight of the catalyst;

[0039] (b) 70% to 98% by weight, preferably 80% to 94% by weight, relative to the total weight of the catalyst, of at least one compound selected from, for example, the following: alumina (γ-Al2O3), aluminosilicate, silica-alumina (SiO2-Al2O3), alumina, zeolite, metal oxides (such as lanthanum oxide, zirconium oxide, tungsten oxide, thallium oxide, magnesium oxide, zinc oxide, silver oxide); preferably selected from silica-alumina (SiO2-Al2O3).

[0040] The sum of (a) + (b) is equal to 100.

[0041] For the purposes of the present invention, the catalyst containing coke may contain binders such as alumina, silica, and / or optionally be supported on an inert carrier such as pumice, graphite, silica.

[0042] For the purposes of this specification and the following claims, the term "zeolite" shall be considered in its broadest sense, i.e., also including materials commonly known as, for example, "zeolite-like"; "zeotype"; zeolites modified with phosphorus or metals such as sodium, potassium, boron, or lanthanide metals; and so on.

[0043] The catalyst containing coke according to the present invention can be obtained from the catalytic dehydration reaction of at least one enol, preferably 3-buten-2-ol (3-Bu-2-OH) and 2-buten-1-ol (2-Bu-1-OH), to provide a diene, preferably 1,3-butadiene. In fact, the coke contained in the catalyst is a by-product formed during the dehydration reaction.

[0044] Therefore, another object of the present invention is a method for producing a diene, preferably a conjugated diene, more preferably 1,3-butadiene, comprising dehydrating at least one enol having a carbon atom number greater than or equal to 4 in the presence of at least one catalyst containing coke, characterized in that the coke has at least two peaks at wavelengths between 1450 cm -1 and 1700 cm -1 upon analysis by diffuse reflectance infrared spectroscopy ("diffuse reflectance infrared Fourier transform spectroscopy" - DRIFT).

[0045] According to a preferred embodiment of the present invention, the straight-chain or branched enol 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, and even more preferably equal to 4.

[0046] Specific examples of enols that are particularly useful for the purposes of the present 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, 5-hexen-4-ol, 4-hexen-1-ol, 4-hexen-2-ol, 4-hexen-3-ol, 3-hexen-1-ol, 3-hexen-2-ol, 2-hexen-1-ol, 2-methyl-3-penten-2-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-4-ol, 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.

[0047] According to a further preferred embodiment of the present invention, the enol has 4 carbon atoms and is thus butenol.

[0048] According to a further preferred embodiment of the present invention, the 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 (allyl alcohol) (3-Bu-1-OH) or mixtures thereof, even more preferably from 2-buten-1-ol (2-Bu-1-OH), 3-buten-2-ol (3-Bu-2-OH) or mixtures thereof.

[0049] It should be noted that when the enol can exist in different enantiomeric or stereoisomeric forms, this means that the process according to the present invention can be carried out with any of these forms in purified form and in mixtures.

[0050] For example, in the above method, the E isomer (trans) of 2-buten-1-ol (2-Bu-1-OH), the Z isomer (cis) of 2-buten-1-ol (2-Bu-1-OH), or a mixture of the two isomers can be used without distinction. Similarly, in the above method, the enantiomer (R) of 3-buten-2-ol (3-Bu-2-OH), the enantiomer (S) of 3-buten-2-ol (3-Bu-2-OH), or a racemic mixture of the two enantiomers can be used.

[0051] According to a preferred embodiment of the invention, the enol having a carbon atom number of 4 or more can be obtained directly from a biosynthetic process or by a catalytic dehydration process of at least one diol.

[0052] According to a preferred embodiment of the present invention, when the carbon atom number of the enol is 4 and thus it is butenol, the butenol can be obtained by catalytic dehydration of butanediol, preferably 1,3-butanediol, in the presence of a cerium-based catalyst, wherein the cerium-based catalyst is obtained by precipitating at least one cerium-containing compound in the presence of at least one base. Further details related to the method can be found, for example, in International Patent Application WO 2015 / 173780 in the name of one of the applicants, which is incorporated herein by reference for the purpose of citation.

[0053] According to a preferred embodiment of the present invention, the diol, preferably butanediol, more preferably 1,3-butanediol can be derived from the fermentation of sugars, preferably from the fermentation of sugars from biomass.

[0054] For the purposes of this specification and the following claims, the term "biomass" means any organic material of plant origin, including: products derived from agriculture, such as the following plants and parts of plants: guayule, thistle, corn, soybean, cotton, flax, rapeseed, sugarcane, palm, including waste, residues, and waste products derived from said products or their processing; products of crops of plant species specifically grown for energy purposes, such as miscanthus, millet, common sugarcane, including waste, residues, and waste products derived from said products or their processing; products derived from forestry or forestry, including waste, residues, and waste products derived from said products or their processing; waste of agricultural food products intended for human food or livestock; residues from the paper industry; separately collected waste from municipal solid waste, such as waste of fruits and vegetables, paper.

[0055] According to a particularly preferred embodiment of the present invention, the diol, preferably butanediol, more preferably 1,3 - butanediol, is derived from the fermentation of sugars from Parthenium argentatum and / or thistle biomass, including waste, residues, and discarded materials from Parthenium argentatum and / or thistle or from their processing. Even more preferably, the diol, preferably butanediol, more preferably 1,3 - butanediol, is derived from the fermentation of sugars from Parthenium argentatum biomass (including waste, residues, and discarded materials from Parthenium argentatum or from its processing).

[0056] To produce the above - mentioned sugars, the biomass can be subjected to physical treatment (such as extrusion, "steam explosion", etc.) and / or chemical hydrolysis and / or enzymatic hydrolysis to obtain a mixture of carbohydrates, aromatic compounds, and other products derived from cellulose, hemicellulose, and lignin present in the biomass. In particular, the obtained carbohydrates are a mixture of sugars having 5 and 6 carbon atoms, which include, for example, sucrose, glucose, xylose, arabinose, galactose, mannose, fructose, and they will be used for fermentation. Methods related to the production of sugars from biomass, especially from lignocellulosic biomass, are described in the prior art, for example, in the international patent application WO 2015 / 087254 in the name of one of the applicants, which is incorporated herein for reference purposes.

[0057] For example, another biotechnological method for obtaining bio - 1,3 - butanediol starting from renewable sources is described in US Patent US 9,017,983 and US Patent Applications US 2012 / 0329113 and US 2013 / 0109064.

[0058] When the diol, preferably butanediol, more preferably 1,3 - butanediol, is derived from a biosynthetic process, such as from the fermentation of sugars as described above, the diol is generally obtained in the form of an aqueous mixture. Before performing the catalytic dehydration of the diol leading to the corresponding enol, the aforementioned aqueous mixture containing the diol obtained from the biosynthetic process can be subjected to ordinary separation processes, such as the distillation of all or part of the water and the diol contained in the mixture. In fact, after filtration and deionization, the aqueous mixture can be advantageously used as it is in the catalytic dehydration process leading to the corresponding enol, without the need for an expensive water - removal process or limiting such removal.

[0059] Furthermore, the enol can be obtained in the form of an aqueous mixture.

[0060] The aqueous mixture can be distilled to recover the enol in pure form or as an azeotrope with water, or used as it is.

[0061] For example, the catalytic dehydration of 1,3-butanediol results in the obtainment of a mixture of butenols [2-buten-1-ol (2-Bu-1-OH), 3-buten-2-ol (3-Bu-2-OH), 3-buten-1-ol (3-Bu-1-OH)], which can be separated by distillation in the form of a minimum azeotrope with water. The azeotropic mixture of butenols can be used as it is, mixed together, or mixed with added butenol, mixed or used alone, or mixed with added water, so as to be used in the catalytic dehydration process for producing 1,3-butadiene according to the present invention.

[0062] According to one embodiment of the present invention, in the aforementioned method for producing a diene, the enol having a carbon atom number greater than or equal to 4 can be mixed with a diluent, which can be selected from, for example, inert gases such as nitrogen (N2), argon (Ar), preferably N2; or it can be mixed with a compound having a boiling temperature between 25°C and 150°C under standard conditions, preferably between 50°C and 125°C under standard conditions, and a melting temperature less than or equal to 20°C under standard conditions, and the compound can be selected from, for example, water, tetrahydrofuran, cyclohexane, benzene or a mixture thereof. Preferably nitrogen (N2) and water, particularly preferably water.

[0063] It is important to note that the water can be residual water derived from the biosynthetic process for producing the at least one enol.

[0064] According to a preferred embodiment of the present invention, the method for producing a diene can be carried out when the diluent is selected from inert gases, and the molar ratio between the diluent and the enol (or enols) is greater than 0.3, preferably 0.5 to 2.

[0065] According to a preferred embodiment of the present invention, the method for producing a diene can be carried out when the diluent is selected from a compound having a boiling temperature between 25°C and 150°C under standard conditions, preferably between 50°C and 125°C under standard conditions, and a melting temperature less than or equal to 20°C under standard conditions, and the molar ratio between the diluent and the enol (or enols) is between 0.01 and 100, preferably between 0.1 and 50, more preferably between 1 and 10.

[0066] According to a preferred embodiment of the present invention, the method for producing a diene can be carried out at a temperature of 250 to 500°C, preferably 280 to 450°C.

[0067] According to a preferred embodiment of the present invention, the method for producing a diene can be carried out at a pressure of 5 kPa to 5000 kPa, preferably 30 kPa to 350 kPa, more preferably 80 kPa to 250 kPa.

[0068] The process for producing dienes according to the present invention can be carried out in the gas phase or in a mixed liquid / gas phase.

[0069] According to one embodiment of the present invention, the aforementioned process for producing dienes is carried out in the gas phase.

[0070] The process for producing dienes can be carried out in any type of reactor, preferably a fixed bed reactor, a moving bed reactor or a fluidized bed reactor.

[0071] According to one embodiment of the present invention, the process for producing dienes can be carried out in a fixed bed reactor.

[0072] In the case of using a fixed bed reactor, the catalyst containing coke can be distributed over a plurality of beds.

[0073] In a "recycle" reactor configuration, the reactor setup can include the recycle of part of the reaction effluent or the catalytic material.

[0074] According to an alternative embodiment of the present invention, when the process for producing dienes is carried out in a mixed liquid / gas phase, a continuous flow stirred tank reactor (CSTR) can be used, which contains a catalyst containing coke in a dispersion.

[0075] It is important to note that when at least one enol resulting from the catalytic dehydration of at least one diol is used in the process for producing the diene substance of the present invention, regardless of how the at least one diol is obtained, the dehydration of the at least one diol can be carried out as follows to provide at least one enol and subsequent dehydration of the at least one enol to provide the diene:

[0076] - In the same reactor or in different reactors, preferably in different reactors;

[0077] - Continuously or batchwise, preferably continuously.

[0078] The process for producing dienes according to the present invention can also be carried out continuously in a reactor configuration envisaging at least two reactors in parallel, preferably two fixed bed reactors in parallel, wherein when the reactors are operating, the catalyst containing coke can be regenerated in another reactor.

[0079] When the process for producing dienes is carried out continuously, the weight hourly space velocity WHSV ("weight hourly space velocity"), i.e. the ratio of the weight of the reactants fed to the reactor to the weight of the catalyst containing coke in the reactor itself, can be between 0.5 h -1 and 10 h -1 preferably between 1 h -1 and 5 h -1 between.

[0080] The contact time (τ) is calculated as the ratio of the volume of the catalyst containing coke loaded into the dehydration reactor under the reaction conditions to the volumetric feed flow rate, preferably between 0.01 second and 10 seconds, more preferably between 0.05 second and 8 seconds, and even more preferably between 0.1 second and 4 seconds.

[0081] As described above, the catalyst containing a coke substance of the present invention can be obtained by the catalytic dehydration reaction of at least one enol, preferably 3-buten-2-ol (3-Bu-2-OH) and 2-buten-1-ol (2-Bu-1-OH).

[0082] Accordingly, a further object of the present invention is a method for producing a catalyst containing coke, characterized in that the coke has at least two peaks at wavelengths between 1450 cm -1 and 1700 cm -1 when analyzed by diffuse reflectance infrared spectroscopy ("diffuse reflectance infrared Fourier transform spectroscopy" - DRIFTS). The method includes dehydrating an enol mixture containing 3-buten-2-ol (3-Bu-2-OH) and 2-buten-1-ol (2-Bu-1-OH) in the presence of at least one compound selected from alumina (-Al2O3), aluminosilicate, silica-alumina (SiO2-Al2O3), alumina, zeolite, metal oxides (such as lanthanum oxide, zirconium oxide, tungsten oxide, thallium oxide, magnesium oxide, zinc oxide, silver oxide), preferably selected from silica-alumina (SiO2-Al2O3). The method is carried out at a temperature of 250 °C to 500 °C, preferably 280 °C to 450 °C for 2 hours to 10 hours, preferably 2.5 hours to 9 hours.

[0083] It should be noted that the operating conditions (not specifically stated, such as the space velocity WHSV ("weight hourly space velocity"), contact time (τ), reactor type, etc.) of the above method for producing a catalyst containing coke are the same as those of the above method for producing dienes (another object of the present invention).

[0084] It should be noted that in order to prove the existence of the above peaks, in the following examples, diffuse reflectance infrared spectroscopy ("diffuse reflectance infrared Fourier transform spectroscopy" - DRIFTS) analysis was carried out on three catalysts containing coke obtained by the 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-1-OH)).

[0085] To put the present invention into practice and illustrate it more clearly, the following are some non-limiting examples.

[0086] Example 1

[0087] (i) Preparation of crude butenol mixture

[0088] For this purpose, a mixture of 1,3 - butanediol (1,3 - BDO) is prepared, which has weight concentrations of 1,3 - butanediol (1,3 - BDO) equal to 83% and water equal to 17% respectively (mixture 1), and then it is used for the dehydration reaction.

[0089] The reactor in which the dehydration reaction is carried out consists of a tubular element of AISI 304 stainless steel with a height (h) equal to 260 mm and an inner diameter (Ф) equal to 10 mm. The element is before the evaporator and connected to the evaporator, and both are equipped with electric heating. The outlet of the reactor is instead connected to a first condenser, which is connected to a receiving flask and operates at 15 °C, with the aim of being able to recover in the receiving flask the product obtained from the first dehydration reaction in liquid form at room temperature (25 °C). The receiving flask is in turn connected to a sampling system, which includes a steel cylinder with a volume (V) equal to 300 ml and equipped with shut - off valves at both ends. The vapors / gases resulting from the first dehydration reaction and optionally not condensed in the systems described above can further flow through the above - mentioned steel cylinder, which is in turn connected to a volumetric flowmeter for measuring their quantity.

[0090] The products obtained in liquid form and in vapor / gas form are characterized by gas chromatography, using:

[0091] - For the product in liquid form, a Thermo Trace gas chromatograph equipped with an FID detector and an AQUAWAX column (Grace, 30 m long x 0.53 mm inner diameter x 1.0 μm film thickness);

[0092] - For the product in gas form, a 490 Micro GC Varian / Agilent gas chromatograph with four channels, which is equipped with the following columns: Pora Plot Q, 10 m long, MolSieve 4 m long, Al2O3, 10 m long with "re - flush" function, CPSil - 19 CB, 7.5 m long.

[0093] The catalyst used for the dehydration reaction is a cerium oxide (CeO2) - based material with a particle size of 0.5 mm to 1 mm, and it is loaded into the above - mentioned reactor in an amount equal to 10 g (3.5 ml). The catalyst is prepared according to the laboratory procedure described below.

[0094] To this end, 500 g of a commercially available aqueous solution of approximately 30% ammonium hydroxide (NH4OH) (28%-30% NH3 basis ACS reagent Aldrich) and 500 g of water were added to a first 3-liter beaker equipped with a semi-circular stirring blade made of Teflon, and an electrode was introduced for measuring pH [Metrohm glass electrode for measuring pH (6.0248.030), connected to a Metrohm 780 pH meter]. In a second 2-liter beaker equipped with a magnetic anchor stirrer, a solution of 100 g of cerium(III) nitrate hexahydrate (99% Aldrich) in 1000 g of water was prepared: then cerium(III) nitrate hexahydrate was dissolved by vigorous stirring at room temperature (25 °C). The resulting solution was added to a dropping funnel and fed dropwise over 2 hours into the ammonium hydroxide solution contained in the above-mentioned 3-liter beaker with continuous vigorous stirring. The pH of the resulting suspension was equal to 10.2. The solid in the suspension was filtered, washed with 2 liters 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.

[0095] 1270 g of the solid thus obtained was sieved at 0.125 mm, and it was added to an extruder. Also, 175.9 g of a 25% ammonium hydroxide (NH4OH) solution (obtained by diluting a 28%-30% NH3 basis ACS reagent Aldrich) was added to the extruder using a Watson Marlow peristaltic pump set at 5 rpm. After said addition, 158 g of softened water was also added to provide the correct consistency for extrusion. The "pellets" obtained at the outlet of the extruder were dried in air. Subsequently, 100 g of a portion was calcined at 800 °C with a temperature ramp of 1 °C / min to 800 °C and then isothermally at that temperature for 6 hours. The calcined solid was granulated and sieved, and the particle fraction with a size of 0.5 mm to 1 mm was used as the catalyst.

[0096] Then, the dehydration reaction was carried out by first supplying mixture 1 to the above-mentioned evaporator preheated to 250 °C and from here to the above-mentioned tubular reactor preheated to have an internal temperature equal to 400 °C during the dehydration reaction. Both the evaporator and the reactor were maintained at atmospheric pressure (1 bar).

[0097] The flow rate of mixture 1 supplied to the evaporator was equal to 100 g / h, while the flow rate supplied to the reactor, expressed as WHSV, was equal to 10 h -1 。

[0098] The test was carried out for a time sufficient to collect a suitable amount of the crude product.

[0099] (ii) Purification of crude butenol

[0100] To remove unreacted 1,3 - butanediol (1,3 - BDO), the crude butenol mixture obtained as described above was first purified by distillation. It should be noted that the butenol present in the mixture forms an azeotrope with water, and for this azeotrope, it is impossible to separate them from water by simple distillation to obtain their pure substances.

[0101] The distillation was carried out at atmospheric pressure, and 3,5 - di - tert - butyl - 4 - hydroxytoluene (BHT) was added to the mixture contained in the boiler to make its concentration in the mixture equal to about 200 ppm. The distillation was carried out using a 40 - plate Oldershaw column (2 sections of 20 trays each), the mixture was loaded into the boiler in a single batch, and various overhead samples were collected according to the recorded temperature, gradually concentrating the heavier components in the boiler. The distillation conditions (reflux ratio, boiler heating power, amount of distillate withdrawn) varied with the boiling temperature of the substances to be separated and the recorded overhead temperature.

[0102] The distillation conditions are shown in Table 1.

[0103] Table 1

[0104]

[0105]

[0106] (1) : Reflux ratio.

[0107] In particular:

[0108] - Fraction 1 (up to about 84 °C) corresponds to the lightest part to be removed;

[0109] - Fractions 2 and 3 correspond to the azeotrope between the enol with the lowest boiling point (i.e., 3 - buten - 2 - ol) (methyl vinyl carbinol) (3 - Bu - 2 - OH) and water at T = 86.5 °C - 87 °C (the composition of this azeotrope is: 73 wt% 3 - buten - 2 - ol (3 - Bu - 2 - OH) and 27 wt% water);

[0110] - In fraction 4, 2 - buten - 1 - ol (cis - and trans - crotyl alcohol) (2 - Bu - 1 - OH) and a small part of 3 - buten - 1 - ol (allyl alcohol) (3 - Bu - 1 - OH) as well as 35 wt% water also start to distill;

[0111] - In fraction 5, the water is depleted, so the temperature rises to about 120 °C;

[0112] - Fractions 6 and 7 correspond to 95% - 97% of 2 - buten - 1 - ol (crotyl alcohol) (2 - Bu - 1 - OH).

[0113] The fractions containing butenol are combined into a single fraction, which represents the mixture for producing the catalyst containing coke according to the present invention. The composition is described in Table 2.

[0114] Table 2

[0115] Water 37.0％ <![CDATA[Light fraction (1) > 0.1％ 2-Bu-1-OH + 3-Bu-2-OH 60.3％ 3-Bu-1-OH 0.2％ <![CDATA[Medium boiling point (2) > 2.2％ <![CDATA[Heavy fraction (3) > 0.2％

[0116] (1) : The lightest compound of low-boiling butenol, i.e., 3-buten-2-ol (3-Bu-2-OH) (T 沸 = 97 °C);

[0117] (2) : The lightest compound of high-boiling butenol, i.e., 2-buten-1-ol (2-Bu-1-OH) (T 沸 = 121.5 °C); heavier than low-boiling enol, i.e., 3-buten-2-ol (3-Bu-2-OH) (T 沸 = 97 °C), excluding 1,3-butadiene (1,3-BDE) [including medium-boiling 3-buten-1-ol (3-Bu-1-OH) (T 沸 = 113.5)];

[0118] (3) : The heavier compound of high-boiling butenol, i.e., 2-buten-1-ol (2-Bu-1-OH) (T 沸 = 121.5 °C).

[0119] Example 2

[0120] Formation of catalyst containing coke and production of 1,3-butadiene (1,3-BDE)

[0121] The first test is carried out by supplying the butenol mixture obtained as described in Example 1 and reported in Table 2 in a fixed-bed tubular reactor - PFR ("plug flow reactor"), which is made of AISI316L stainless steel, with a length equal to 400 mm and a diameter equal to 9.65 mm, loaded with 0.6 g of silica-alumina containing 3.8% of Al and obtained as described below.

[0122] 7.55 g of aluminum tri-sec-butoxide (Aldrich) was added as an alumina precursor (Al2O3) to the first 500 ml round-bottom flask, and 50.02 g of orthosilicic acid (Aldrich, <20 mesh) as a silica precursor (SiO2) and 250.02 g of softened water were added to the second 500 ml round-bottom flask. The obtained orthosilicic acid suspension was slowly added (10 min) to the first round-bottom flask containing aluminum tri-sec-butoxide, and the obtained mixture was kept at 90 °C for about 1 hour under vigorous stirring (500 rpm). After cooling to room temperature (25 °C), the obtained suspension was filtered and the obtained solid was washed with 5 liters of softened water, dried overnight at 120 °C, and then calcined at 500 °C for 5 hours to obtain a colorless powder (47.95 g) (defined as the "active phase").

[0123] In an 800 ml beaker, a portion (40.42 g) of the above-mentioned "active phase" was mixed with 24.43 g of pseudoboehmite Versal, an alumina precursor (Al2O3), as a binder TM V-250 (UOP) and 302 ml of a 4% acetic acid solution. The obtained mixture was kept at 60 °C for 2 hours with stirring. Then the beaker was transferred to a hot plate and the mixture was heated to 150 °C overnight until dry under vigorous stirring. Then the obtained solid was calcined at 550 °C for 5 hours to obtain 60.45 g of a colorless product, which was mechanically granulated and the particle fraction with a size of 0.1 mm to 1.0 mm was used as the dehydration catalyst in the said tubular reactor.

[0124] The catalyst (0.6 g) prepared as described above was added to the reactor using quartz wool as a carrier for the particles such that they were arranged in the isothermal region of the reactor. The reactor was set up in a downflow configuration.

[0125] The catalyst was pretreated in situ at 300 °C under a nitrogen (N2) flow.

[0126] The supply of the aforementioned butenol mixture was carried out by vaporization from the top of the reactor at atmospheric pressure (0.1 MPa) so that after the reactants reached the reaction temperature, they were brought into contact with the catalyst by using an infusion pump connected to a heated steel wire and a 5 ml Hamilton pump, and were then sent to the reactor under a nitrogen (N2) flow: the total volume flow rate was equal to 28 mL / min, which was 2 vol% of the butenol mixture. The reactor was heated to a temperature of 300 °C using an electric furnace, and the temperature was controlled by an integrated thermocouple connected to the temperature controller of the electric furnace and a second axial thermocouple placed inside the tubular reactor, and the second axial thermocouple indicated the actual temperature of the catalytic bed and was selected as the reference temperature.

[0127] The temperature of the tubular reactor is maintained at 300 °C as described above and the contact time (τ) is equal to 0.67 seconds.

[0128] Downstream of the reactor, the product obtained is sampled online in a gas chromatograph (GC) for analysis. The online analysis of the gas is carried out by an Agilent HP6890 gas chromatograph (GC) equipped with two capillary columns: an HP-5 column (crosslinked 5% phenylmethylsiloxane) with a length of 50 m, a diameter of 0.2 mm, and a film of 0.33 μm, which is connected to a flame ionization detector (FID); an HP-Plot-Q column (bonded polystyrene divinylbenzene) with a length of 30 m, a diameter of 0.32 mm, and a film of 20 μm, which is connected to a thermal conductivity detector (TCD). The carrier gas used in both columns is helium, with a flow rate equal to 0.8 mL / min (HP-5 column) and 3.5 mL / min (HP-Plot-Q column).

[0129] The results are as Figure 1 shown [the conversion and yield expressed as a percentage (%) are reported on the ordinate; the reaction time in hours (h) is reported on the abscissa].

[0130] Figure 1 The shown catalytic performance level is expressed by calculating the conversion of enol (C ALCH. ), the selectivity to 1,3-butadiene (S 1,3-BDE ), and the yield of 1,3-butadiene (R 1,3-BDE ) according to the following formula:

[0131]

[0132]

[0133]

[0134] where:

[0135] - moli ALCH = the number of moles of enol [referring to 3-buten-2-ol (3-Bu-2-OH) and 2-buten-1-ol (2-Bu-1-OH)];

[0136] -(moli ALCH. ) in = the number of moles of enol at the inlet;

[0137] -(moli ALCH. ) out = the number of moles of enol at the outlet;

[0138] - moli 1,3-BDE= Moles of 1,3 - butadiene (1,3 - BDE) produced.

[0139] From Figure 1 The data reported in it can be inferred that the yield of 1,3 - butadiene (Y1,3BDE) starts from an initial value of about 47% and stabilizes at about 70% after 4 hours. After 4 hours, the yield of 1,3 - butadiene (Y1,3BDE) continues to increase slowly until it stabilizes at an average value of 80% after 10 hours. Figure 1 The trend of carbon loss (C loss) is also shown, and carbon loss represents an indicator of the coke gradually formed on the catalyst. In Figure 1 :

[0140] - X2 - Bu - 1 - OH refers to the conversion rate of 2 - butene - 1 - ol (2 - Bu - 1 - OH);

[0141] - X3 - Bu - 2 - OH refers to the conversion rate of 3 - butene - 2 - ol (3 - Bu - 2 - OH);

[0142] - X3 - Bu - 1 - OH refers to the conversion rate of 3 - butene - 1 - ol (3 - Bu - 1 - OH).

[0143] To better highlight the role of coke in the increased yield, Example 1 above was repeated 3 times, and the reaction was interrupted after 3 hours, 8 hours, and 20 hours. The catalyst unloaded from the reactor at the said time was subjected to thermogravimetric analysis (TGA) in air to calculate the amount of coke adsorbed. Using an SDT Q 600 instrument (TA Instruments), 15 mg of the catalyst was loaded, and the said analysis was carried out in an air stream (100 mL / min) at a temperature gradient (10 °C / min until 900 °C, followed by isothermal at 900 °C for 5 minutes) in order to quantify the organic residues present. The results are as Figure 2 shown [the weight loss expressed as a percentage (%) is reported on the ordinate; the temperature in degrees Celsius (°C) is reported on the abscissa]. From Figure 2 it, considering the weight loss associated with the presence of coke (temperature above 380 °C), it can be inferred that coke is rapidly formed within the first 3 h (5% weight loss): corresponding to this time interval, the yield increases fastest until the pre - stable value (as Figure 1 shown). The other two TGA curves show that at values greater than 3 h, coke continues to form but at a slower rate: corresponding to this situation, it stabilizes at the maximum yield value (as Figure 1 shown), which occurs slowly until 10 hours and then stabilizes completely.

[0144] Example 3

[0145] To verify which type of catalyst contains catalytically active coke, Example 2 was repeated, but instead of using the butenol mixture, the individual isomers provided separately were used, namely 3-buten-2-ol (3-Bu-2-OH), 2-buten-1-ol (2-Bu-1-OH), and 3-buten-1-ol (3-Bu-1-OH). The conditions used were the same as in Example 2. From these tests, it can be inferred that 3-buten-2-ol (3-Bu-2-OH) Figure 3 The conversion and yield expressed as a percentage (%) are reported on the ordinate; the time in hours (h) is reported on the abscissa] Figure 4 and 2-buten-1-ol (2-Bu-1-OH) Figure 1 both have a yield curve similar to that of the butenol mixture used in Example 2, as

[0146] shown (the yield increases rapidly between 0 and 3 hours and then further increases until it stabilizes at a maximum after 10 hours. Figure 5 The conversion and yield expressed as a percentage (%) are reported on the ordinate; the time in hours (h) is reported on the abscissa]) The behavior of 3-buten-1-ol (3-Bu-1-OH) is completely different

[0147] In Figure 3 :

[0148] - X 3-Bu-2-OH refers to the conversion of 3-buten-2-ol (3-Bu-2-OH);

[0149] - C loss refers to the trend of "carbon loss".

[0150] In Figure 4 :

[0151] - X 2-Bu-1-OH refers to the conversion of 2-buten-1-ol (2-Bu-1-OH);

[0152] - C loss refers to the trend of "carbon loss".

[0153] In Figure 5 :

[0154] - X 3-Bu-1-OH refers to the conversion of 3-buten-1-ol (3-Bu-1-OH).

[0155] Diffuse reflectance infrared spectroscopy ("Diffuse Reflectance Infrared Fourier Transform Spectroscopy" - DRIFTS) was performed on the coke-containing catalysts formed from the three isomers as follows.

[0156] For this purpose, three fresh catalyst samples (i.e., 0.6 g of silica-alumina containing 3.8% di Al) were prepared and operated as described in Example 2. Each sample was diluted in potassium bromide (KBr) at a ratio of 1:10, treated in helium (He) at 450 °C for 20 minutes, and then cooled to 50 °C: Then, a "single pulse" of the reactants was carried out, i.e., 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 (3-Bu-1-OH) (third sample) on the sample, and then the temperature was subsequently increased and the spectrum was recorded at 300 °C. The above analysis was carried out using an FT-IR Bruker Vertex 70 spectrophotometer equipped with a Pike DiffusIR cell and an MCT detector: The spectrum was recorded and processed using the processing of the data obtained through OPUS software. The analysis parameters are as follows:

[0157] - Scanning interval: 4000 cm -1 - 450 cm -1 ;

[0158] - Number of scans per sample: 32;

[0159] - Background: Spectrum recorded by placing the starting catalyst (without coke) in the accessory housing;

[0160] - Spectral resolution: 4 cm -1 ;

[0161] - Mirror calibration: 3.5 mm (mirror alignment of the DRIFTS accessory so that the instrument detector can detect the maximum absorbance).

[0162] The results obtained are as shown in Figure 6 , where the ordinate reports the absorbance in absorbance units; the abscissa reports the wave number in cm -1 as the unit. It can be inferred from the spectra reported in Figure 6 that in the case of the two isomers mainly forming 1,3-butadiene (1,3-BDE), namely 3-buten-2-ol (3-Bu-2-OH) (first sample - represented as 3But2ol in Figure 6 ) and 2-buten-1-ol (2-Bu-1-OH) (second sample - represented as 2But1ol in Figure 6 ), the coke of the obtained catalyst containing coke has two characteristic bands at 1465 cm -1 and 1577 cm -1 , while the isomer 3-buten-1-ol (3-Bu-1-OH) (third sample - inFigure 6 is represented as 3But1ol)(resulting in the formation of propylene and coke, as Figure 5 shown) has a characteristic band at 1650 cm -1 which confirms the different nature of the two types of coke. The band is attributed to stretching C═C and C-H of the aromatic type ("coke band"), as reported by Ibarra A. et al. in the literature "Dual coke deactivation pathways during the catalytic cracking of raw bio-oil and vacuum gasoil in FCC conditions", "Applied Catalysis B: Environmental" (2016), Volume 182, pages 336 - 346.

[0163] Example 4

[0164] For comparison purposes, Example 2 was repeated, supplying only 3 - buten - 1 - ol (3 - Bu - 1 - OH) for 4 hours.

[0165] After 4 hours, 3 - buten - 1 - ol (3 - Bu - 1 - OH) was replaced by the same butenol mixture used in Example 2 (i.e., the butenol mixture obtained as described in Example 1 and reported in Table 2). The results are as Figure 7 shown, where the conversion and yield expressed as a percentage (%) are reported on the ordinate; the time in hours (h) is reported on the abscissa. It can be inferred from Figure 7 that the coke formed from 3 - buten - 1 - ol (3 - Bu - 1 - OH) has no effect on the increase in the catalyst yield: in fact, an increase in the yield of 1,3 - butadiene (Y1,3BDE) was only observed after replacing 3 - buten - 1 - ol (3 - Bu - 1 - OH) with the same mixture of butenols used in Example 2 in the feed.

[0166] In Figure 7 :

[0167] - X2 - Bu - 1 - OH refers to the conversion of 2 - buten - 1 - ol (2 - Bu - 1 - OH);

[0168] - X3 - Bu - 2 - OH refers to the conversion of 3 - buten - 2 - ol (3 - Bu - 2 - OH);

[0169] - X3 - Bu - 1 - OH refers to the conversion of 3 - buten - 1 - ol (3 - Bu - 1 - OH);

[0170] - C loss refers to the trend of "carbon loss".

Claims

1. A catalyst, comprising: (a) 2% to 30% by weight of coke, based on the total weight of the catalyst; (b) 70% to 98% by weight of silica-alumina, based on the total weight of the catalyst; (a) + (b) sums to 100; It is characterized in that The coke was analyzed by diffuse reflectance infrared Fourier transform spectroscopy at 1450 cm -1 and 1700cm -1 There are at least two peaks at wavelengths between: The catalyst is obtained by a method comprising: dehydrating a mixture of enols comprising 3-buten-2-ol and 2-buten-1-ol in the presence of silica-alumina, the method being carried out at a temperature of 280 °C to 450 °C for 2 hours to 10 hours.

2. The catalyst according to claim 1, wherein the catalyst comprises: (a) 6% to 20% by weight of coke, based on the total weight of the catalyst; (b) 80% to 94% by weight of silica-alumina, based on the total weight of the catalyst; (a) + (b) sums to 100.

3. A method for producing a diene, comprising dehydrating at least one enol having 4 or more carbon atoms in the presence of the catalyst according to claim 1.

4. The method for producing a diene according to claim 3, wherein the diene is 1,3-butadiene.

5. The process for producing a diene according to claim 3 or 4, wherein the enol 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. The process for producing a diene according to claim 3 or 4, wherein the enol 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 6.

7. A process for producing a diene according to claim 3 or 4, wherein the enol has the general formula C n H 2n O, where n is equal to 4.

8. The method for producing a diene according to claim 3 or 4, wherein the enol is selected from 2-buten-1-ol, 3-buten-2-ol, 3-buten-1-ol or a mixture thereof.

9. The method for producing a diene according to claim 3 or 4, wherein the enol having 4 or more carbon atoms is directly obtained from a biocatalytic process or obtained by a catalytic dehydration process of at least one diol.

10. The method for producing a diene according to claim 3 or 4, wherein when the enol has 4 carbon atoms and is thus butenol, the butenol is obtained by catalytic dehydration of butanediol in the presence of a cerium oxide catalyst, wherein the cerium oxide catalyst is obtained by precipitating at least one cerium-containing compound in the presence of at least one base.

11. The method for producing a diene according to claim 9, wherein the diol is derived from the fermentation of sugars.

12. The method for producing a diene according to claim 11, wherein the diol is derived from the fermentation of sugars from biomass.

13. The method for producing a diene according to claim 3 or 4, wherein the enol having 4 or more carbon atoms is mixed with a diluent selected from: nitrogen, argon; or with a compound having a boiling temperature between 25 °C and 150 °C under standard conditions and a melting temperature less than or equal to 20 °C under standard conditions, the compound being selected from water, tetrahydrofuran, cyclohexane, benzene or a mixture thereof.

14. The method for producing a diene according to claim 13, wherein: - when the diluent is selected from nitrogen, argon, the method is carried out at a molar ratio of diluent to one or more enols of 0.5 to 2; - when the diluent is selected from compounds having a boiling temperature between 25 °C and 150 °C under standard conditions, the method is carried out at a molar ratio of diluent to one or more enols of 0.01 to 100.

15. The process for producing diene according to claim 3 or 4, wherein the process is carried out under the following conditions: - at a temperature of from 280 to 450 °C; and / or - at a pressure of from 5 kPa to 5000 kPa; and / or - in the gas phase or in a mixed liquid / gas phase; and / or - in a fixed bed reactor, a moving bed reactor or a fluidized bed reactor; and - if carried out in a mixed liquid / gas phase, a continuous flow stirred tank reactor is used, which reactor contains a catalyst comprising coke in a dispersion; and / or - continuously or batchwise; and - If carried out continuously, the weight hourly space velocity (WHSV), which is the ratio of the weight of the reactants fed to the reactor to the weight of the catalyst in the reactor, is between 0.5 h -1 and 10 h -1 ; and / or the contact time, calculated as the ratio of the volume of the catalyst containing coke loaded into the reactor under the reaction conditions to the volumetric feed flow rate, is between 0.01 second and 10 seconds.

16. The process for producing diene according to claim 3 or 4, wherein the process is carried out under the following conditions: - at a temperature of from 280 to 450 °C; and / or - at a pressure of from 30 kPa to 350 kPa; and / or - in a fixed bed reactor, a moving bed reactor or a fluidized bed reactor; and - continuously or batchwise; and - If carried out continuously, the weight hourly space velocity (WHSV), which is the ratio of the weight of the reactants fed to the reactor to the weight of the catalyst in the reactor, is between 1 h -1 and 5 h -1 ; and / or the contact time, calculated as the ratio of the volume of the catalyst containing coke loaded into the reactor under the reaction conditions to the volumetric feed flow rate, is between 0.05 seconds and 8 seconds.

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