Method for catalytic dehydrogenation of cyclic alkanes in an adiabatic reactor configuration

Abstract

The present invention relates to a method for dehydrogenating a feedstock comprising methylcyclohexane in order to produce a dehydrogenation effluent comprising hydrogen and toluene, by bringing said feedstock into contact with a dehydrogenation catalyst implemented in a reaction section comprising at least one adiabatic reactor, the catalyst comprising an active phase comprising at least platinum and potassium in an amount of between 0.03% and 1% by weight of elemental potassium relative to the total weight of the catalyst, and a support comprising alumina.

Description

[0001] CATALYTIC DEHYDROGENATION PROCESS OF CYCLIC ALKANES IN AN ADIABATIC REACTOR CONFIGURATION

[0002] Scope of the invention

[0003] The present invention relates to a process for the catalytic dehydrogenation of cyclic alkanes, in particular those with a 6-carbon ring, for example mono- or multi-substituted. The present invention also relates to a process for the production of hydrogen and unsaturated / aromatic ring hydrocarbons, in particular those with a 6-carbon ring, for example mono- or multi-substituted, which comprises at least one reaction step for the catalytic dehydrogenation of cyclic alkanes, in particular those with a 6-carbon ring, for example mono- or multi-substituted.

[0004] An example of application involves the dehydrogenation of methylcyclohexane to produce hydrogen and toluene, and in the remainder of this text this example will be chosen to illustrate the invention, for the sake of brevity, without the invention being considered as limited to this one.

[0005] State of the art

[0006] The dehydrogenation of methylcyclohexane (also referred to here as MCH) into hydrogen and toluene is a well-known reaction. Indeed, the feedstocks for the catalytic reforming of naphthas contain this molecule. For several years, this methylcyclohexane molecule has been considered a potential hydrogen transport carrier, known by the acronym LOHC for "Liquid Organic Hydrogen Carrier." It is produced by the hydrogenation of toluene, and the three dihydrogen molecules that reacted with toluene to form methylcyclohexane can be released by the reverse reaction, that is, the dehydrogenation of methylcyclohexane. This produces toluene and hydrogen.

[0007] The dehydrogenation reaction of methylcyclohexane has been extensively studied and is well understood. See, in particular, the review article "A Review of Catalysts for Methylcyclohexane Dehydrogenation," Topics in Catalysis, volume 64, pages 509-520 (2021). It is a highly endothermic reaction; the enthalpy change (AH) of the reaction is approximately 215 kJ / mol. More generally, several industrial process technologies exist for dehydrogenating petroleum fractions containing methylcyclohexane, but at varying concentrations, generally less than 20% by weight relative to the total weight of the fraction being treated. For example, catalytic reforming is a refining process used to valorize heavy gasoline obtained by distillation.The hydrocarbons in the heavy gasoline feedstock (paraffins and cyclic alkanes), generally containing approximately 5 to 12 carbon atoms per molecule, are transformed during this process into aromatic hydrocarbons or, failing that, into branched paraffins. The hydrogen produced during the reforming process is most often used in other units of the refinery or aromatic complex. The main reactions involved in catalytic reforming are the dehydrogenation of cyclic alkanes, the dehydrocyclization of paraffins, and the isomerization of paraffins and cyclic alkanes. This process is generally characterized by the presence of several reactors in series, often three or four, and by the presence of furnaces between each reactor to raise the temperature of the effluent leaving a given reactor to the required inlet temperature of the next reactor.This is referred to as an adiabatic reactor because the reforming reaction is carried out without any heat transfer between the reactors and their external environment. In such a process, the furnaces compensate for the temperature drop resulting from the highly endothermic nature of the dehydrogenation reactions. In industrial processes for converting naphtha fractions into gasoline, the temperature drop per reactor can reach 80°C.

[0008] However, in the case of dehydrogenating a feedstock containing primarily methylcyclohexane, and in a process with only one reactor, the temperature drop would be nearly 900°C. Thus, even with several reactors connected in series, temperature drops of over 100°C to 150°C per reactor would need to be compensated. Furthermore, the nature of the catalyst impacts the type of catalytic reactions. In the case of the catalytic reforming process, the catalysts used are bifunctional, meaning they consist of two functional groups: a metallic group and an acidic group, each playing a well-defined role in the catalyst's activity. The metallic group primarily ensures the dehydrogenation of cyclic alkanes and paraffins, and the hydrogenation of coke precursors. The acidic group ensures the isomerization of cyclic alkanes and paraffins, and the cyclization of paraffins.The acid function is provided by the support itself, most often pure halogenated alumina. The metallic function is ensured by a noble metal from the platinum group and at least one additional metal, primarily tin for the continuous process (moving bed), and rhenium in the semi-regenerative process (fixed bed). Thus, the use of a conventional catalytic reforming catalyst is not optimal for dehydrogenating a feedstock consisting mainly of methylcyclohexane, because depending on the impurity content of the feedstock containing methylcyclohexane, so-called "parasitic" reactions can occur, potentially leading to the formation of coke that deactivates the catalyst, and therefore resulting in a decrease in toluene conversion and / or selectivity, and ultimately a reduction in hydrogen production.

[0009] Conventional catalytic reforming technology is therefore not suitable for carrying out the dehydrogenation reaction of methylcyclohexane under good conditions.

[0010] Continuing its research in the field of LOHC, the Applicant has developed a new process dedicated to the dehydrogenation of a feed consisting mainly of cyclic alkanes with a 6-carbon ring, in particular methylcyclohexane, in an adiabatic system in the presence of a specific catalyst comprising potassium at a content within a specific range of values.

[0011] Objects of the invention

[0012] A first object according to the invention relates to a process for dehydrogenating a feed comprising a cyclic alkane with a 6-carbon ring in order to produce a dehydrogenation effluent comprising hydrogen and an aromatic compound, at a temperature between 320°C and 700°C, a pressure between 0.1 and 4 MPa, and a mass flow rate of feed treated per unit mass of catalyst per hour between 0.1 and 10 h' 1 , by bringing said charge into contact with a dehydrogenation catalyst implemented in a reaction section comprising at least one adiabatic reactor, said catalyst comprising an active phase comprising at least platinum, potassium at a content of between 0.03% and 1% by weight of element potassium relative to the total weight of the catalyst, and a support comprising alumina.

[0013] In an adiabatic system where a feedstock containing cyclic alkanes is dehydrogenated, the catalyst characteristics are crucial for balancing target product conversion and temperature control. The primary dehydrogenation reaction of cyclic alkanes is endothermic, leading to a temperature drop in an adiabatic reactor. Conversely, secondary reactions, such as hydrocracking and hydrogenolysis of paraffins and naphthenes, or hydrodealkylation of alkyl aromatics, are exothermic and release heat. Therefore, a highly selective catalyst will exclusively promote the dehydrogenation of cyclic alkanes, but this will result in a significant temperature drop (and thus a decrease in conversion) in an adiabatic system due to the strongly endothermic nature of this reaction.

[0014] On the other hand, the presence of secondary reactions, although beneficial from a thermal point of view given their exothermicity, must be controllable in order to guarantee good stability of the catalyst by avoiding premature deactivation, which would degrade the performance of the hydrogenation process in the long term.

[0015] The process according to the invention overcomes the above drawbacks by controlling the amount of potassium added to the catalyst. The presence of potassium partially neutralizes the acidic sites on the catalyst, thus limiting side reactions without eliminating them entirely. Adding potassium within a specific range allows for a compromise between selectivity, conversion, and catalyst stability, thereby improving the system's lifespan. Indeed, in hydrogen transport using LOHC technology, several hydrogenation / dehydrogenation cycles are performed without removing all the impurities present in the feedstock that may have formed, particularly during side reactions. This avoids the need for costly separation of secondary compounds, which would render the hydrogen transport technology unprofitable.The process according to the invention makes it possible to find a compromise between the stability of the catalyst during the cycles, the activity and the selectivity of the catalytic dehydrogenation reaction.

[0016] According to one or more embodiments of the invention, the charge comprises at least 80% by weight of a cyclic alkane with a 6-carbon ring.

[0017] According to one or more embodiments of the invention, the filler comprises at least 80% by weight of methylcyclohexane

[0018] According to one or more embodiments of the invention, the charge also comprises 7-carbon hydrocarbon compounds without a 6-carbon ring, in particular iso-alkanes and / or alkyl-cyclopentanes, and / or n-heptane, preferably in a content of at most 20% or 15% by weight, in particular at most 10% by weight, and preferably at most 5% of the charge.

[0019] According to one or more embodiments of the invention, the filler also comprises 8-carbon hydrocarbon compounds without a 6-carbon ring, in particular 2,2,4-trimethylpentane and / or dimethylhexanes, preferably in a content of at most 20% or 15% by weight, in particular at most 10% by weight, and preferably at most 5% of the filler.

[0020] According to one or more embodiments of the invention, the platinum content is between 0.02 and 2% by weight of platinum element relative to the total weight of the catalyst.

[0021] According to one or more embodiments of the invention, said catalyst comprises an element M1 selected from tin, germanium, lead, gallium, indium and thallium.

[0022] According to one or more embodiments of the invention, the content of element M1 is between 0.01 and 10% weight by weight of element M1 relative to the total weight of the catalyst.

[0023] According to one or more embodiments of the invention, said catalyst comprises a halogen element selected from fluorine, chlorine, bromine and iodine.

[0024] According to one or more embodiments of the invention, the halogen content is between 0.75 and 5.5% by weight of halogen element relative to the total weight of the catalyst.

[0025] According to one or more embodiments of the invention, said catalyst comprises phosphorus, at a content of between 0.1 and 1% weight of phosphorus element relative to the total weight of the catalyst.

[0026] According to one or more embodiments of the invention, said alumina support comprises a specific surface area of ​​between 170 m 2 / g and 250 m 2 / g. According to one or more embodiments of the invention, said alumina support comprises a total porous volume measured by mercury porosimetry of between 0.1 cm3 / g and 1.5 cm 3 / g.

[0027] According to one or more embodiments of the invention, said reaction section comprises four adiabatic reactors in series.

[0028] According to one or more embodiments of the invention, all or part of the charge is obtained by a hydrogenation process of aromatic compounds, including toluene.

[0029] According to one or more embodiments of the invention, hydrogen is separated from the rest of the dehydrogenation effluent.

[0030] Detailed description of the invention

[0031] 1. Definitions

[0032] The present invention includes a cyclic alkane with a 6-carbon ring, the alkyl cyclohexanes, which can be substituted on one or more of the 6 carbons of the ring, by a methyl group or by a longer carbon chain, linear or branched.

[0033] In what follows, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief DR Lide, 81 ème edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IIIPAC classification.

[0034] Specific surface area refers to the specific surface area BET (SBET in m²) 2 / g) determined by nitrogen adsorption in accordance with ASTM D 3663-78 established from the BRUNAUER-EMMETT-TELLER method described in the periodical "The Journal of American Society", 1938, 60, 309.

[0035] The total pore volume of the catalyst or support used for catalyst preparation is the volume measured by intrusion with a mercury porosimeter according to ASTM D4284 at a maximum pressure of 4000 bars (400 MPa), using a surface tension of 484 dyne / cm and a contact angle of 140°, for example with an Autopore III model device from Microméritics®.

[0036] The wetting angle was set at 140° following the recommendations of the book "Techniques de l'ingénieur, traité analyse et caractérisation", pages 1050-1055, written by Jean Charpin and Bernard Rasneur. To obtain greater accuracy, the total pore volume value corresponds to the total pore volume value measured by mercury porosimeter intrusion on the sample at 4000 bar (400 MPa) minus the total pore volume value measured by mercury porosimeter intrusion on the same sample at a pressure of 2 bar (0.2 MPa).

[0037] The packed filling density (PHD) is measured as described in the book "Applied Heating" by G. Martino, J. Miquel, R. Montarnal, A. Sugier, and H. Van Landeghem, Technip, Paris, 1987, chapter 6.2.4, pages 167-168. A graduated cylinder of acceptable dimensions is filled by successive additions, and between each addition, the catalyst is compacted by shaking the cylinder until a constant volume is reached. This measurement is generally performed over 1000 cm³. 3 of catalyst or support material packed into a cylinder with a height-to-diameter ratio close to 5:1. The apparent density of the packed product is calculated by dividing the introduced mass by the volume occupied after packing. The measurement uncertainty is generally on the order of ± 0.01 g / mL. This measurement can preferably be performed on automated devices such as Autotap®, marketed by Quantachrome®.

[0038] The levels of metals, halogens, phosphorus, and potassium are measured by X-ray fluorescence.

[0039] In this description, the term "include" is synonymous with (means the same as) "include" and "contain," and is inclusive or open-ended and does not exclude other elements not listed. It is understood that the term "include" includes the exclusive and closed term "consist." Furthermore, in this description, a feed or effluent comprising essentially, substantially, or solely a compound A corresponds to a feed or effluent comprising at least 80% by weight, preferably at least 85% by weight, preferably 90% by weight, most preferably 95% by weight, or even 100% by weight of compound A relative to the total weight of the feed or effluent. For the purposes of this invention, different parameter ranges / operating conditions for a given step, such as pressure ranges and temperature ranges, may be used alone or in combination.For example, in the sense of the present invention, a preferred range of pressure values ​​can be combined with a more preferred range of temperature values.

[0040] 2. Charge

[0041] According to a preferred embodiment of the present invention, the hydrocarbon feed treated in the dehydrogenation process is a feed comprising a cyclic alkane with a 6-carbon ring, in particular methylcyclohexane. Preferably, said feed comprises at least 80% by weight of a cyclic alkane with a 6-carbon ring, in particular methylcyclohexane, preferably at least 85% by weight of a cyclic alkane with a 6-carbon ring, in particular methylcyclohexane, and preferably at least 90% by weight or at least 95% by weight of a cyclic alkane with a 6-carbon ring, in particular methylcyclohexane.

[0042] The feed for the dehydrogenation process may also optionally include other hydrocarbon compounds not comprising a 6-carbon ring, preferably at a content of less than 20% by weight, preferably less than 15% by weight, preferably less than 10% by weight or 5% by weight relative to the total weight of the feed.

[0043] Frequently, the dehydrogenation process feed may include other 7-carbon compounds without a 6-carbon ring, such as isoalkanes (3-ethylpentane and dimethylpentanes) and alkylcyclopentanes (ethylcyclopentane and dimethylcyclopentanes), and / or n-heptane, as its boiling point is very close to that of methylcyclohexane. The 7-carbon hydrocarbon compounds without a 6-carbon ring are present in the feed preferably at a concentration of at most 20% by weight, at most 15% by weight, preferably at most 10% by weight, and particularly preferably at most 5% by weight relative to the total weight of the feed.

[0044] In addition to possible 7-carbon compounds without a 6-carbon ring, the dehydrogenation process feed may also optionally include 8-carbon compounds without a 6-carbon ring, such as 2,2,4-trimethylpentane and / or dimethylhexanes, whose boiling points are also very close to that of methylcyclohexane, preferably at a content of at most 20% by weight, at most 15% by weight, preferably at most 10% by weight, and particularly preferably at most 5% by weight relative to the total weight of the feed.

[0045] The feed treated in the process according to the invention is preferably obtained by a process of hydrogenation of aromatic compounds, such as toluene or xylenes, and more particularly the aromatic compound such as toluene which has been produced in the dehydrogenation unit implementing the present invention.

[0046] 3. Dehydrogenation stage

[0047] According to the invention, the present invention relates to a process for dehydrogenating a feed comprising at least one cyclic alkane with a 6-carbon ring, in particular methylcyclohexane, so as to produce a dehydrogenation effluent comprising an aromatic compound, in particular toluene, hydrogen, and optionally unconverted methylcyclohexane. This dehydrogenation step employs a reaction section comprising at least one adiabatic reactor in which the dehydrogenation reaction takes place. Preferably, the reaction section comprises two adiabatic reactors in series, and even more preferably, four adiabatic reactors in series.According to the invention, the dehydrogenation process is carried out at a temperature between 320°C and 700°C, preferably between 350°C and 600°C, a pressure between 0.1 and 4 MPa, preferably between 0.1 and 3 MPa, and a mass flow rate of treated feed per unit mass of catalyst per hour between 0.1 and 10 h. -1 preferably between 0.5 and 6 hours -1 .

[0048] In addition to the hydrocarbon feed, the process can also be supplied with hydrogen to limit catalyst deactivation. In this case, the molar ratio of hydrogen to hydrocarbons in the feed (H2 / HC ratio) at the inlet of the reactor(s) can generally be between 0 and 10 mol / mol, preferably between 0 and 8 mol / mol, preferably between 0 and 5 mol / mol, and most preferably between 0 and 3 mol / mol. The hydrogen stream is mixed with the hydrocarbon feed before entering the reactor(s) and is therefore at the same temperature and pressure conditions as the hydrocarbon feed. The dehydrogenation step of the process according to the invention may optionally incorporate a feed heating section upstream of the reaction section. The feed can be heated in this heating section by any method known to those skilled in the art.Preferably, a heating section is placed upstream of each adiabatic reactor contained in the reaction section in order to send the reaction fluid to the desired inlet temperature.

[0049] In one embodiment according to the invention, the catalytic reactor(s) operate in a fixed bed (semi-regenerative mode). In this embodiment, the dehydrogenation process is preferably carried out at a temperature between 320°C and 700°C, preferably between 350°C and 550°C, the pressure between 0.1 MPa and 4 MPa, the mass flow rate of flux to be treated per unit mass of catalyst per hour is between 1 h' 1 and 10 a.m. 1 . In this embodiment, the catalyst support is preferably in the form of extrudates (cylinder, trilobe or quadrilobe) with a diameter between 1 mm and 3 mm, preferably between 1.5 mm and 2 mm.

[0050] In another embodiment of the invention, the catalytic reactor(s) operate in a moving bed configuration (continuous regenerative mode or Continuous Catalyst Regeneration (CCR) according to Anglo-Saxon terminology). In this embodiment, the dehydrogenation process is preferably carried out at a temperature between 320°C and 600°C, preferably between 350°C and 500°C, the pressure is between 0.1 and 0.5 MPa, preferably between 0.1 and 2 MPa, and the mass flow rate of flux to be treated per unit mass of catalyst per hour is between 1 and 2 MPa. -1 and 10 a.m. -1 In this embodiment, the catalyst support is preferably in the form of beads with sizes between 1 mm and 4 mm, preferably between 1 mm and 3 mm.

[0051] During the dehydrogenation step, the transformation of the feedstock may be accompanied by the deactivation of the dehydrogenation catalyst, for example, by coking, adsorption of inhibitory compounds, and / or sintering. The dehydrogenation catalyst can therefore advantageously undergo periodic regeneration or replacement. Thus, in a particular embodiment of the invention, the process includes a regeneration-replacement step. The objective of regeneration is to burn off the organic deposits contained on the surface and within the dehydrogenation catalyst. Replacement allows the spent catalyst, that is, the one that has been used in at least one dehydrogenation step, to be replaced with "fresh" dehydrogenation catalyst, that is, one that has not yet been used.

[0052] Advantageously, the process according to the invention can include the separation of hydrogen from the rest of the dehydrogenation effluent: the dehydrogenation effluent obtained at the end of the reaction section of the dehydrogenation step, which includes at least one aromatic of the toluene type, hydrogen, and optionally the starting unconverted cyclic alkane of the methylcyclohexane type, can be sent to a separation section to separate the hydrogen generated during the dehydrogenation reaction from the rest of the effluent.

[0053] 4. Catalyst

[0054] The catalyst used in the process according to the invention comprises, preferably, at least one platinum-based active phase and a support comprising alumina, said catalyst further comprising potassium at a content of between 0.03% and 1% by weight of element potassium relative to the total weight of the catalyst.

[0055] In one embodiment, the catalyst comprises between 0.03% and 1% by weight of potassium relative to the total weight of the catalyst, preferably between 0.03% and 0.8% by weight, preferably between 0.03% and 0.6% by weight, more preferably between 0.03% and 0.5% by weight, even more preferably between 0.03% and 0.4% by weight, and even more preferably between 0.03% and 0.3% by weight.

[0056] In another embodiment, the catalyst comprises between 0.03% and 1% by weight of potassium relative to the total weight of the catalyst, preferably between 0.05% and 0.8% by weight, preferably between 0.07% and 0.6% by weight, more preferably between 0.09% and 0.5% by weight, even more preferably between 0.1% and 0.4% by weight, and even more preferably between 0.15% and 0.3% by weight.

[0057] Beyond 1% by weight of potassium in the catalyst, the dehydrogenation reaction of methylcyclohexane is too selective towards the formation of aromatic compounds, particularly toluene when the feed consists mainly of methylcyclohexane, which causes a significant drop in temperature within the adiabatic reactor (the dehydrogenation reaction of methylcyclohexane to toluene being endothermic) and consequently reduces the conversion of methylcyclohexane to toluene.

[0058] Below 0.03% by weight of potassium, the catalyst still contains too many acidic sites, which are the location of so-called secondary reactions, such as isomerization, cyclization, and hydrocracking, promoting coke formation on the catalyst. Thus, depending on the nature of the feedstock, and in particular its degree of impurities, especially during the hydrogenation / dehydrogenation cycles, the catalyst used in the process according to the invention rapidly loses activity, leading to its premature replacement and / or regeneration.

[0059] Advantageously, the platinum content, expressed as an element, is between 0.02 and 2% by weight relative to the total weight of the catalyst, preferably between 0.05 and 1.5% by weight, even more preferably between 0.1 and 0.8% by weight, and even more preferably between 0.15 and 0.5% by weight.

[0060] Platinum can be present in the final catalyst as an oxide, sulfide, halide, oxyhalide, in chemical combination with one or more of the other components of the catalyst, or as an elemental metal.

[0061] Preferably, the active phase of the catalyst may also include at least one M1 element selected from tin, germanium, lead, gallium, indium and thallium.

[0062] Advantageously, the content of element M1, selected from tin, germanium, lead, gallium, indium and thallium, expressed as an element, in the catalyst according to the invention is between 0.01 and 10% by weight relative to the total weight of the catalyst, more preferably between 0.05 and 5% by weight and very preferably between 0.1 and 1% by weight, and even more preferably between 0.15 and 0.5% by weight.

[0063] Preferably, the M1 element is tin (Sn).

[0064] Element M1 can exist in the catalyst as an oxide, sulfide, halide, oxyhalide, in chemical combination with one or more of the other components of the catalyst, or as an elemental metal.

[0065] The catalyst may further comprise a halogen element (here referred to as X). The halogen content is advantageously between 0.75 and 5.5% by weight of halogen element relative to the total weight of the catalyst, more preferably between 0.85 and 4% by weight, very preferably between 0.9 and 3% by weight, and even more preferably between 1 and 1.5% by weight.

[0066] Preferably, the halogen element is selected from the group consisting of fluorine, chlorine, bromine, and iodine. Preferably, the halogen element is chlorine (Cl).

[0067] In one embodiment according to the invention, the catalyst may further comprise phosphorus. The phosphorus may be present in the final catalyst as an oxide or mixed oxide compound, phosphate, polyphosphate, sulfide, halide, oxyhalide, hydride, in chemical combination with one or more of the other components of the catalyst.

[0068] In this embodiment, the phosphorus content, expressed as an element, in the catalyst is between 0.1 and 1% by weight relative to the total weight of the catalyst, preferably between 0.2 and 0.8% by weight.

[0069] The specific surface area of ​​the catalyst is advantageously between 170 m 2 / g and 250 m 2 / g, preferably between 180 m 2 / g and 220 m 2 / g, preferably between 185 m 2 / g and 220 m 2 / g, more preferentially between 185 m 2 / g and 210 m 2 / g, and even more preferentially between 185 m 2 / g and 195 m 2 / g.

[0070] The catalyst advantageously has a total pore volume measured by mercury porosimetry of between 0.1 cm 3 / g and 1.5 cm 3 / g, preferably between 0.4 cm 3 / g and 0.8 cm 3 / g, and preferably between 0.4 cm 3 / g and 0.7 cm 3 / g.

[0071] Advantageously, the catalyst has a packed filling density (PTD) value between 0.50 and 0.70 g / mL, preferably between 0.60 and 0.65 g / mL.

[0072] 5. Support

[0073] The catalyst support comprises alumina, preferably is made of alumina. The alumina(s) may be of type r|, y or 5. Preferably, they are of type y or 5. Even more preferably, they are of type y.

[0074] The specific surface area of ​​the support is advantageously between 170 m 2 / g and 250 m 2 / g, preferably between 180 m 2 / g and 220 m 2 / g, preferably between 185 m 2 / g and 220 m 2 / g, more preferentially between 185 m 2 / g and 210 m 2 / g, and even more preferentially between 185 m 2 / g and 195 m 2 / g. The support advantageously has a total pore volume measured by mercury porosimetry of between 0.1 cm 3 / g and 1.5 cm 3 / g, preferably between 0.4 cm 3 / g and 0.8 cm 3 / g, and preferably between 0.4 cm 3 / g and 0.7 cm 3 / g.

[0075] Advantageously, the support has a packed filling density (DRT) value between 0.4 and 0.9 g / mL, preferably between 0.5 and 0.85 g / mL.

[0076] The support is advantageously in the form of beads, extrudates, pellets, or powder. When the support is in bead form, its diameter is generally between 0.5 mm and 5 mm, preferably between 1 mm and 2 mm. When the support is in extrudate form, the diameter of the extrudates is between 0.5 mm and 5 mm, preferably with a length-to-diameter ratio of 1:1 to 5:1.

[0077] The substrate can be obtained by any technique known to those skilled in the art. The shaping can be carried out, for example, by extrusion, by pelletizing, by the oil-drop coagulation method, by rotary plate granulation, or by any other method well known to those skilled in the art.

[0078] 6. Process for preparing the catalyst

[0079] The catalyst used in the process according to the invention can be prepared using any technique known to a person skilled in the art.

[0080] Platinum

[0081] Advantageously, platinum is supplied to the support in any suitable manner, such as coprecipitation, ion exchange, or impregnation. Preferably, it is introduced by impregnation of the support, for example, by excess or dry impregnation (the volume of solution containing the element to be introduced corresponding to the porosity of the support), and preferably by excess impregnation. For this purpose, the support is impregnated with an impregnation solution, aqueous or organic, or consisting of a mixture of water and at least one organic solvent, comprising at least one platinum precursor.

[0082] In general, hydrogen chloride or another similar acid may also be added to the impregnation solution to further facilitate the incorporation or fixation of platinum to the substrate surface and promote a uniform distribution of platinum in the substrate.

[0083] Preferably, platinum precursors belong to the following group, but this list is not exhaustive: hexachloroplatinic acid, bromoplatinic acid, ammonium chloroplatinate, platinum chlorides such as PtCh or PtCl, platinum dichlorocarbonyl dichloride, platinum tetraamine chloride, or dihydroxyplatin diammine. Organic platinum complexes, such as platinum(II) diacetylacetonate, may also be used. These precursors can be used alone or in mixtures. Preferably, the precursor used is hexachloroplatinic acid.

[0084] Element M1

[0085] The element M1 chosen from tin, germanium, lead, gallium, indium and thallium can be supplied in any suitable way, such as coprecipitation, ion exchange or impregnation, and this at any stage of the catalyst preparation process.

[0086] According to one variant, element M1 can be introduced into the support, for example, during support synthesis or during support shaping. While not exhaustive, techniques involving addition before or during the dissolution of the support's oxide precursors during support synthesis, with or without curing, are suitable. The introduction can therefore be simultaneous with or subsequent to the mixing of the support precursors. Element M1 can be introduced during support synthesis using a sol-gel technique or added to an alumina sol. Element M1 can also be introduced during support processing using prior art shaping techniques such as extrusion or oil-drop forming.

[0087] According to a second variant, element M1 can be introduced onto the substrate, for example, by impregnating the previously prepared substrate. Impregnation of the substrate with a solution, aqueous or organic, or consisting of a mixture of water and at least one organic solvent, comprising one or more precursors of elements M1, can be carried out by excess solution or dry impregnation. Impregnation of the substrate with a solution containing one or more precursors of element M1 can be carried out before, after, or simultaneously with the impregnation of the Group VIII metal. Impregnation can be carried out in the presence of species that influence the interaction between the precursor of element M1 and the substrate.These species can be, for example, and without limitation, mineral acids (HCl, HNO3) or organic acids (carboxylic or polycarboxylic acid types), and organic compounds of the complexing type, as described for example in US patents 6,872,300 and 6,291,394. Preferably, the impregnation is carried out according to any technique known to those skilled in the art allowing a homogeneous distribution of the element M1 within the support.

[0088] According to a third variant, the M1 element can also be introduced partly during the synthesis or shaping of the support and partly by deposition on the shaped support.

[0089] Preferably, the M1 component is introduced into the support, i.e., during the synthesis of the support or during the shaping of the support. In the case of an alumina-based support in the form of beads prepared by the draining technique, the precursor of the M1 component is introduced into the suspension to be drained.

[0090] The precursors of element M1 can be mineral or organometallic, possibly water-soluble organometallic. The precursor of element M1 can be selected from the group consisting of halogenated compounds, hydroxides, carbonates, carboxylates, sulfates, tartrates, and nitrates. These forms of element M1 can be introduced into the catalyst preparation medium as is or generated in situ (for example, by the introduction of tin and carboxylic acid). When the element M1 is tin, tin-based organometallic precursors can be chosen, for example, from the following list: SnF t, where R represents an alkyl group, for example the butyl group, MeaSnCl, MeaSnCh, EtaSnCl, EtSnCla, iPrSnCh and the hydroxides MeaSnOH, Me2Sn(OH)2, EtaSnOH, Et2Sn(OH)2, the oxides (BuaSnO, acetate BuaSnOC(O)Me. Preferably, halogenated tin species, particularly chlorinated ones, are used.Even more preferably, the precursor of element M1 is SnCh or SnCk.

[0091] Potassium

[0092] Potassium can be supplied in any suitable manner, such as coprecipitation, ion exchange, or impregnation, at any stage of the catalyst preparation process. In particular, it can be introduced according to the three variants described for element M1. Preferably, it is introduced by impregnation, either dry or in excess; most preferably, it is introduced in excess; and most preferably, it is introduced after the platinum has been introduced as described above.

[0093] Preferably, the precursors can be chosen from KOH, KCl, KNO3, K2CO3, or K2PtCl, taken alone or in mixture.

[0094] Element X: The element X chosen from among the halogens can be supplied in any suitable manner, such as coprecipitation, ion exchange, or impregnation, at any stage of the catalyst preparation process. In particular, it can be introduced according to the three variants described for element M1.

[0095] In a preferred embodiment, element X is chlorine. Chlorine is introduced by impregnation, and particularly preferably, it is introduced by impregnation simultaneously with platinum or prior to platinum impregnation. As a possible counter-anion of compounds containing element M1, platinum, and potassium, chlorine can also be introduced simultaneously with these elements, for example, by using precursors such as hLPtCl, SnCh, or KCl, or by treating the support with hydrochloric acid in one of the preparation steps. Chlorine can also be supplied in the preparation process by an additional oxychlorination step.

[0096] Phosphorus can be supplied in any suitable manner, such as coprecipitation, ion exchange, or impregnation, at any stage of the catalyst preparation process. In particular, it can be introduced according to the three variants described for element M1.

[0097] According to one variant, phosphorus is introduced into the support, i.e. during its shaping, for example simultaneously with element M1.

[0098] According to another variant, phosphorus is introduced by impregnation, and particularly preferably it is introduced by impregnation at the same time as the group VIII metal. In this case, the impregnation solution contains the precursor of the group VIII metal and the precursor of phosphorus.

[0099] Phosphorus precursors can be acids or salts, and can be chosen from the following compounds: H3PO4, H3PO3, H3PO2, NH4H2PO4, or (NhL^HPCU.

[0100] Order of introduction of precursors

[0101] As described above, the catalyst preparation process involves several implementation methods, distinguished primarily by the order in which platinum, element M1, potassium, element X, and optionally phosphorus are introduced onto and / or into the prepared support—that is, during support synthesis or during support preparation. The catalyst preparation process includes the simultaneous or successive introduction, in any order, of platinum, element M1, potassium, and optionally phosphorus and / or element X onto and / or into the prepared support.

[0102] When element M1 and / or potassium and / or optionally phosphorus and / or element X are introduced into the support, i.e., during support synthesis or support shaping, the preparation process generally includes a drying step and a calcination step before platinum deposition. Drying is generally carried out at a temperature of 250°C or lower, preferably between 50°C and 250°C, and more preferably between 70°C and 200°C, under air or an inert atmosphere. Calcination is preferably carried out at a temperature between 350°C and 750°C, and more preferably between 400°C and 600°C, and even more preferably between 400°C and 550°C. The temperature ramp-up may be continuous or include intermediate temperature plateaus, these plateaus being reached at fixed or variable rates of temperature ramp-up.These temperature increases can therefore be identical or differ in their rate (in degrees per minute or per hour). The gas atmosphere used during calcination contains oxygen. Air can therefore also be used during this calcination stage. The calcination gas may also contain water.

[0103] When one or more elements among platinum, element M1, potassium, element X and / or optionally phosphorus, are introduced onto the shaped support, preferably by dry or excess impregnation, the introduction of said elements may be simultaneous by a single impregnation solution or take place separately by several impregnation solutions containing one or more of the components and this in any order.

[0104] Any impregnation solution described in the present invention may comprise any polar solvent known to those skilled in the art. The polar solvent used is advantageously chosen from the group consisting of methanol, ethanol, water, phenol, and cyclohexanol, alone or in mixtures. The polar solvent may also advantageously be chosen from the group consisting of propylene carbonate, DMSO (dimethyl sulfoxide), N-methylpyrrolidone (NMP), or sulfolane, alone or in mixtures. Preferably, a polar protic solvent is used. A list of common polar solvents and their dielectric constants can be found in the book "Solvents and Solvent Effects in Organic Chemistry," C. Reichardt, Wiley-VCH, 3rd edition, 2003, pages 472-474. Most preferably, the solvent used is water or ethanol, and particularly preferably, the solvent is water.After each impregnation step, the resulting catalyst precursor is preferably dried to remove all or part of the solvent introduced during impregnation, preferably at a temperature below 250°C, more preferably between 50°C and 250°C, and most preferably between 70°C and 200°C. Drying is advantageously carried out for a period of between 1 and 24 hours, preferably between 1 and 20 hours. Drying is performed under air or under an inert atmosphere (e.g., nitrogen). After the drying step, the catalyst is preferably calcined, generally under air. The calcination temperature is generally between 350°C and 650°C, and preferably between 400°C and 650°C, and even more preferably between 450°C and 550°C. The temperature ramp may optionally include temperature plateaus. The calcination time is generally between 0.5 hours and 16 hours, preferably between 1 hour and 5 hours.The gas atmosphere used during calcination contains oxygen. Therefore, air can also be used in this calcination stage. The calcination gas may also contain water.

[0105] In a particular embodiment, the catalyst according to the invention is prepared by a preparation process comprising the following successive steps: a) a support comprising the element M1 selected from tin, germanium, lead, gallium, indium and thallium is prepared to obtain a first catalyst precursor; b) the first catalyst precursor obtained in step a) is dried under a flow of a neutral gas or under a flow of a gas containing oxygen at a temperature less than or equal to 250°C, then calcined at a temperature between 350°C and 750°C to obtain a first dried and calcined catalyst precursor; c) the first dried and calcined catalyst precursor obtained in step b) is impregnated with an impregnation solution comprising at least one platinum precursor, and optionally at least one precursor of an element X, and optionally phosphorus to obtain a second catalyst precursor;d) the second catalyst precursor obtained in step c) is dried under a flow of neutral gas or under a flow of oxygen-containing gas at a temperature of 250°C or less, and then calcined at a temperature between 350°C and 650°C to obtain a second dried and calcined catalyst precursor; e) the second dried and calcined catalyst precursor obtained in step d) is impregnated with an impregnation solution comprising a potassium precursor, and optionally at least one precursor of element X, to obtain a third catalyst precursor; f) the third catalyst precursor obtained in step e) is dried under a flow of neutral gas or under a flow of oxygen-containing gas at a temperature of 250°C or less, and then calcined at a temperature between 350°C and 650°C;(g) Optionally, an oxychlorination step is carried out at a temperature between 350°C and 550°C and under a pressure between 0.1 MPa and 1.5 MPa, then calcined at a temperature between 350°C and 650°C; it being understood that element X is supplied at least once in step (c) and / or step (e), or possibly in step (g).

[0106] In one embodiment according to the invention, when element X is chlorine, said chlorine element is supplied at least once either at step c) and / or at step e), and / or at step g).

[0107] Preferably, potassium is introduced on a catalyst precursor containing platinum, which has been previously dried and calcined. Introducing potassium after platinum prevents platinum from being leached out during platinum impregnation.

[0108] In step a), a substrate comprising element M1, preferably tin, is prepared. Element M1, preferably tin, can be introduced at any time during substrate preparation, and preferably during shaping, or by impregnation onto an already formed substrate. Preferably, element M1 is introduced during substrate shaping.

[0109] Similarly, phosphorus can be introduced at any stage of substrate preparation, and preferably during shaping, or by impregnation onto an already formed substrate. According to one variant, phosphorus is introduced into the substrate, i.e., during substrate shaping, preferably with element M1, preferably tin. According to another variant, phosphorus is introduced by impregnation, and particularly preferably it is introduced by impregnation simultaneously with platinum.

[0110] The introduction of platinum can advantageously be carried out by one or more excess impregnations of solution onto the support, or by one or more dry impregnations, and preferably by a single excess impregnation of said support (preferably containing element M1, preferably tin, and possibly phosphorus), using solution(s), preferably aqueous, containing the platinum precursor and preferably the phosphorus precursor (when the support does not contain phosphorus or only partially contains it). In step e), the second dried and calcined catalyst precursor obtained in step d) is impregnated with an impregnation solution comprising at least one potassium precursor.The introduction of potassium can advantageously be carried out by one or more excess impregnations of solution on the support, or by one or more dry impregnations, and preferably by a single dry or excess impregnation of said precursor, using solution(s), preferably aqueous, containing at least one potassium precursor.

[0111] In the optional step g), chlorine is supplied by means of an oxychlorination treatment. Such a treatment can, for example, be carried out at a temperature between 350°C and 550°C and under a pressure between 0.1 MPa and 1.5 MPa, for a duration preferably between 30 minutes and 10 hours, and under an air flow containing the desired quantity of chlorine and possibly containing water.

[0112] According to another embodiment, the catalyst according to the invention can be prepared by preparing a support comprising tin by introducing the tin precursor during the shaping of the support, followed by one or more excess impregnations of solution on the support, or by one or more dry impregnations, using solution(s), preferably aqueous, containing a platinum precursor, a phosphorus precursor and a potassium precursor, alone or in mixture, then drying and calcining under the conditions described above.

[0113] When the various precursors used in the preparation of the catalyst according to the invention do not contain halogens or contain halogens in insufficient quantities, it may be necessary to add a halogenated compound during preparation. Any compound known to those skilled in the art can be used and incorporated into any of the steps in the preparation of the catalyst according to the invention. In particular, it is possible to use organic compounds such as methyl or ethyl halides, for example dichloromethane, dichloroethane, dichloropropane, chloroform, methylchloroform, or carbon tetrachloride.

[0114] The halogen can also be added by impregnation with an aqueous solution of the corresponding acid, for example, hydrochloric acid, at any point during the preparation. A typical protocol involves impregnating the solid to introduce the desired amount of halogen. The catalyst is then kept in contact with the aqueous solution for a sufficient time to deposit this amount of halogen. Additional reduction step (optional)

[0115] In one embodiment of the invention, prior to using the catalyst in the catalytic reactor and implementing a dehydrogenation process, a reduction treatment step is carried out in the presence of a reducing gas to obtain a catalyst comprising platinum and said element M1 at least partially in metallic form. This step is advantageously carried out in-situ, that is, after loading the catalyst into a dehydrogenation reactor. Performing the reduction treatment of the catalyst in-situ eliminates the need for an additional step of passivating the catalyst with an oxygenated compound or with CO2, which is necessarily required when the catalyst is prepared by performing an ex-situ reduction treatment, that is, outside the reactor used for dehydrogenation.Indeed, when the reduction treatment is carried out ex-situ, it is necessary to carry out a passivation step in order to preserve the metallic phase of the catalyst in the presence of air (during the transport and loading operations of the catalyst in the hydrogenation reactor), and then to carry out a new step of reducing the catalyst.

[0116] The reducing gas is preferably hydrogen. Hydrogen can be used pure or in a mixture (for example, a hydrogen / nitrogen, hydrogen / argon, or hydrogen / methane mixture). When hydrogen is used in a mixture, any proportion is possible.

[0117] Preferably, the reduction treatment is carried out at a temperature between 100°C and 600°C, and more preferably between 200°C and 580°C, under a stream of pure or diluted hydrogen, up to the maximum reduction temperature, followed by holding at that temperature for, for example, 30 minutes to 6 hours. The temperature rise to the desired reduction temperature is generally slow, for example, set between 0.1 and 10°C / min, preferably between 0.3 and 7°C / min.

[0118] The hydrogen flow rate, expressed in L / hour / gram of catalyst precursor, is between 0.01 and 100 L / hour / gram of catalyst, preferably between 0.05 and 10 L / hour / gram of catalyst precursor, even more preferably between 0.1 and 5 L / hour / gram of catalyst precursor.

[0119] Passivation step (optional)

[0120] The preparation process may advantageously include a passivation step using a sulfur compound, which improves the selectivity of the catalysts and prevents thermal runaway during the start-up of new catalysts (known as "run-away" in English). The passivation step is carried out using methods known to those skilled in the art.

[0121] The passivation step with a sulfur compound is generally carried out at a temperature between 20 and 350°C, preferably between 40 and 200°C, typically for 10 to 240 minutes. The sulfur compound is chosen, for example, from the following: thiophene, thiophane, alkyl monosulfides such as dimethyl sulfide, diethyl sulfide, dipropyl sulfide, and propylmethyl sulfide, or an organic disulfide with the formula HO-R1-S-S-R2-OH, such as dithio-diethanol with the formula HO-C2H4-SS-C2H4-OH (often called DEODS). The sulfur content is generally between 0.1 and 2% by weight of the compound relative to the total weight of the catalyst.

[0122] Examples

[0123] The following examples illustrate the invention without limiting its scope.

[0124] Example 1 (not in accordance with the invention) illustrates a process for the dehydrogenation of methylcyclohexane according to an implementation with an adiabatic reactor technology with a conventional catalytic reforming catalyst (Catalyst A), i.e. not including potassium.

[0125] Examples 2 and 3 (according to the invention) illustrate a process for the dehydrogenation of methylcyclohexane according to an implementation with an adiabatic reactor technology with respectively a catalyst B and a catalyst C comprising a potassium content of 0.06% by weight and 0.25% by weight relative to the total weight of the catalyst.

[0126] Example 4 (not in accordance with the invention) illustrates a process for the dehydrogenation of methylcyclohexane according to an implementation with an adiabatic reactor technology with a catalyst D comprising a potassium content of 1.53% by weight relative to the total weight of the catalyst.

[0127] For each example, the feedstock to be treated comprises at least 99.9% by weight of methylcyclohexane. The dehydrogenation reaction is carried out using four adiabatic reactors R1, R2, R3, and R4 in series. A preheating furnace is placed at the inlet of each reactor to raise the temperature of the reaction fluid to the desired inlet temperature. Each adiabatic reactor includes a fixed bed of catalyst.

[0128] The syntheses of catalysts A, B, C and D are described below.

[0129] Catalyst A

[0130] Catalyst A is prepared on a gamma alumina support, aiming for a deposition of 0.25 wt% platinum, 0.4 wt% phosphorus, and 1.1 wt% chlorine on the final catalyst. The gamma alumina support is in the form of beads with a diameter of 1.7 mm. The properties of this support are as follows: Specific Surface Area (SBET) = 200 m² 2 .g' 1 Total pore volume (TPV) = 0.65 cm3 . g _1 , packed filling density (DRT) = 0.62 g. cm' 1 tin content 0.28% by weight.

[0131] To 100 grams of alumina support containing tin, add 400 cm 3 of an aqueous solution of hexachloroplatinic acid, phosphoric acid and hydrochloric acid. It is left in contact for 4 hours and then wrung out. It is dried at 120°C for 15 hours and then calcined at 500°C under an air flow of 100 liters per hour for 3 hours, with a temperature rise rate of 7°C per minute.

[0132] Chlorine content exceeding 1.1% by weight after calcination is adjusted to 1.1% by weight by a partial dechlorination heat treatment at 520°C under dry air and with an additive of 8000 ppm vol of water for 2.5 hours.

[0133] The catalyst A obtained after dechlorination contains 0.23% by weight of platinum, 0.28% by weight of tin, 0.39% by weight of phosphorus and 1.13% by weight of chlorine.

[0134] Catalyst B: Pt-PK / AhOa-Sn-Cl

[0135] Catalyst B is prepared from catalyst A aiming for a deposition of 0.06 wt% potassium.

[0136] To 100 g of this calcined solid, add 440 cm 3 of a potassium carbonate solution by excess impregnation. It is dried at 120°C for 15 hours then calcined at 500°C under an air flow of 100 litres per hour for 3 hours, with a temperature rise rate of 7°C per minute.

[0137] The chlorine content is adjusted to 1.1 wt% by a partial chlorination heat treatment at 520°C under dry air with the addition of 4000 ppm vol of hydrochloric acid for 2 hours. The catalyst B obtained after calcination contains 0.23 wt% of elemental platinum, 0.28 wt% of elemental tin, 0.39 wt% of phosphorus, 1.13 wt% of chlorine and 0.06 wt% of potassium.

[0138] Catalyst C: Pt-PK / A Oa-Sn-Cl

[0139] Catalyst C is prepared from catalyst A by aiming for a deposition of 0.25% weight of potassium.

[0140] To 100 g of this calcined solid, add 440 cm 3 of a potassium carbonate solution by excess impregnation. It is dried at 120°C for 15 hours then calcined at 500°C under an air flow of 100 litres per hour for 3 hours, with a temperature rise rate of 7°C per minute.

[0141] The chlorine content is adjusted to 1.1% by weight by a partial chlorination heat treatment at 520°C under dry air and with the addition of 4000 ppm vol of hydrochloric acid for 2 hours.

[0142] The catalyst B obtained after calcination contains 0.23% by weight of element platinum, 0.28% by weight of element tin, 0.39% by weight of phosphorus, 1.13% by weight of chlorine and 0.25% by weight of potassium.

[0143] Catalyst D: Pt-PK / AhCh-Sn-Cl

[0144] A catalyst D is prepared on the same support as catalyst A, aiming for a deposition of 0.25% by weight of platinum, 0.4% by weight of phosphorus, 1.5% by weight of chlorine and 1.5% by weight of potassium.

[0145] To 100g of alumina support containing tin, add 400 cm 3 of an aqueous solution of hexachloroplatinic acid, phosphoric acid and hydrochloric acid. It is left in contact for 4 hours and then wrung out. It is dried at 120°C for 15 hours and then calcined at 500°C under an air flow of 100 liters per hour for 3 hours, with a temperature rise rate of 7°C per minute.

[0146] To 100 g of this calcined solid, add 75 cm 3of a potassium carbonate solution at a concentration of 22.3 g / L by dry impregnation. It is allowed to mature, dried at 120°C for 15 hours then calcined at 500°C under an air flow of 100 litres per hour for 3 hours, with a temperature rise rate of 7°C per minute.

[0147] The catalyst D obtained after calcination contains 0.27 wt% platinum, 0.28 wt% tin, 0.38 wt% phosphorus, 1.48 wt% chlorine, and 1.53 wt% potassium. Table 1 below summarizes all the process parameters and operating conditions, which remain constant during operation. The same operating conditions are chosen for all catalysts. Table 1

[0148] Table 2 below summarizes the performance obtained with catalysts A, C and D.

[0149] Table 2 The presence of potassium increases toluene selectivity. Catalyst A has the lowest selectivity, while catalyst D has the highest. However, beyond 1 wt% potassium in the catalyst, the increased selectivity leads to a decrease in conversion because the dehydrogenation of methylcyclohexane is highly endothermic. Hydrogen production increases as the potassium content increases, up to a maximum, and then decreases when the potassium content exceeds a threshold value. Table 3 below summarizes the performance obtained with catalysts A and B in terms of the evolution of hydrogen production during the cycles. One cycle consists of the dehydrogenation of methylcyclohexane followed by the hydrogenation of toluene. It can be observed that the presence of potassium maintains performance even after 10 cycles.

[0150] Table 3

Claims

DEMANDS 1. A process for dehydrogenating a feed comprising a cyclic alkane with a 6-carbon ring to produce a dehydrogenation effluent comprising hydrogen and an aromatic compound, at a temperature between 320°C and 700°C, a pressure between 0.1 and 4 MPa, and a mass flow rate of feed treated per unit mass of catalyst per hour between 0.1 and 10 h⁻¹ 1 , by bringing said charge into contact with a dehydrogenation catalyst implemented in a reaction section comprising at least one adiabatic reactor, said catalyst comprising an active phase comprising at least platinum, potassium at a content of between 0.03% and 1% by weight of element potassium relative to the total weight of the catalyst, and a support comprising alumina.

2. A method according to claim 1, wherein the charge comprises at least 80% by weight of a cyclic alkane with a 6-carbon ring.

3. A method according to claim 1 or 2, wherein said charge comprises at least 80% by weight of methylcyclohexane 4. A process according to any one of the preceding claims, wherein the feed also comprises 7-carbon hydrocarbon compounds without a 6-carbon ring, in particular iso-alkanes and / or alkyl-cyclopentanes, and / or n-heptane, preferably in a content of at most 20% or 15% by weight, in particular at most 10% by weight, and preferably at most 5% of the feed.

5. A process according to any one of the preceding claims, wherein the feed also comprises 8-carbon hydrocarbon compounds without a 6-carbon ring, in particular 2,2,4-trimethylpentane and / or dimethylhexanes, preferably in a content of at most 20% or 15% by weight, in particular at most 10% by weight, and preferably at most 5% of the feed.

6. A method according to any one of the preceding claims, wherein the platinum content is between 0.02 and 2% by weight of element platinum relative to the total weight of the catalyst.

7. A method according to any one of the preceding claims, wherein said catalyst comprises an element M1 selected from tin, germanium, lead, gallium, indium and thallium.

8. A method according to the preceding claim, wherein the content of element M1 is between 0.01 and 10% weight by weight of element M1 relative to the total weight of the catalyst.

9. A method according to any one of the preceding claims, wherein said catalyst comprises a halogen element selected from fluorine, chlorine, bromine and iodine.

10. A process according to the preceding claim, wherein the halogen content is between 0.75 and 5.5% by weight of halogen element relative to the total weight of the catalyst.

11. A process according to any one of the preceding claims, wherein said catalyst comprises phosphorus, at a content of between 0.1 and 1% weight of element phosphorus relative to the total weight of the catalyst.

12. A method according to any one of the preceding claims, wherein said alumina support comprises a specific surface area of ​​between 170 m² 2 / g and 250 m 2 / g.

13. A method according to any one of the preceding claims, wherein said alumina support comprises a total porous volume measured by mercury porosimetry of between 0.1 cm 3 / g and 1.5 cm 3 / g.

14. A method according to any one of the preceding claims, wherein said reaction section comprises four adiabatic reactors in series.

15. A process according to any one of the preceding claims, characterized in that all or part of the feedstock is obtained by a process of hydrogenating aromatic compounds, in particular including toluene.

16. A process according to any one of the preceding claims, characterized in that hydrogen is separated from the rest of the dehydrogenation effluent.

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