Catalyst based on IZM-2 zeolite with a low alkali metal content and its use for the isomerization of aromatic C8 fractions

Abstract

The present invention relates to a catalyst comprising at least one IZM-2 zeolite, at least one matrix, and at least one metal from group VIII of the periodic table, wherein the total weight content of alkali and / or alkaline earth elements in the catalyst is less than 200 ppm by weight, preferably less than 150 ppm by weight, preferably less than 100 ppm by weight, preferably less than 90 ppm by weight, preferably less than 85 ppm by weight, more preferably less than 80 ppm by weight, more preferably less than 75 ppm by weight, and even more preferably less than 70 ppm by weight, relative to the total weight of the catalyst. The present invention also relates to a process for isomerizing a fraction containing at least one aromatic compound having 8 carbon atoms per molecule, comprising contacting the aromatic fraction with at least the catalyst according to the present invention in a catalytic reactor. The present invention also relates to a catalyst comprising a zeolite designated IZM-2 and a specific alkali or alkaline earth metal content. The present invention also relates to a process for isomerizing an aromatic C8 fraction using the isomerization catalyst.

Description

[Technical Field]

[0001] The main sources of aromatic compounds containing eight carbon atoms are obtained from reforming processes (reformate) and steam cracking processes (pyrolysis gasoline). The distribution of aromatic compounds containing eight carbon atoms in these fractions varies; generally, 10% to 30% is ethylbenzene, and the remainder is formed from three xylene isomers: para-xylene, meta-xylene, and ortho-xylene. Typically, the distribution of xylenes within this remainder is 50% meta-xylene, 25% ortho-xylene, and 25% para-xylene. Among this remaining xylene, para-xylene is the highly sought-after isomer. In particular, via dimethyl terephthalate and terephthalic acid, this isomer enables the production of polyester fibers used in polyethylene terephthalate (PET) clothing, resins, and films. Therefore, it is desirable to maximize the production of para-xylene at the expense of other aromatic compounds containing eight carbon atoms. This is accomplished by implementing a catalytic isomerization process. After extraction of para-xylene, the remaining fraction, rich in meta-xylene, ortho-xylene, and ethylbenzene, is sent to a catalytic isomerization unit, which recovers a mixture of aromatic compounds containing eight carbon atoms. In this mixture, the proportion of xylenes is near thermodynamic equilibrium, and the amount of ethylbenzene is reduced by the conversion of ethylbenzene. This mixture is again sent to the para-xylene extraction unit, and the remaining fraction is sent to an isomerization unit. In this way, an "aromatic C8 loop" is formed, which maximizes the production of para-xylene (E. Guillon, P. Leflaive, Techniques de l'Ingenieur, J5920, V3). The isomerization unit may be used to isomerize xylenes to para-xylene and convert ethylbenzene to benzene via an ethylbenzene dealkylation reaction. In this case, the fraction is said to have undergone "dealkylation-type" isomerization. The remaining fraction may be sent to a catalytic isomerization unit to isomerize xylenes to para-xylene and convert ethylbenzene to xylenes via an ethylbenzene dealkylation reaction.This fraction is said here to have undergone an "isomerization type" isomerization. These industrial processes generally employ heterogeneous catalysts, which are used in fixed beds and operate in the gas phase under hydrogen pressure. These two types of process differ by the operating conditions and by the formulation of the catalysts used (their nature and / or their content of hydrogenation-dehydrogenation and / or acid functional groups). The present invention belongs to the field of "isomerization type" isomerization. [Background technology]

[0002] In "isomerization-type" isomerization, the catalyst is bifunctional, containing both acid functionality (generally provided by at least one zeolite) and hydrogenation-dehydrogenation functionality provided by a noble metal (typically platinum). Specifically, the isomerization of ethylbenzene to xylenes has been demonstrated to involve a bifunctional mechanism. Ethylbenzene is first hydrogenated to ethylcyclohexene at the metal sites, and then these cycloolefin intermediates are isomerized to dimethylcyclohexene at the Brønsted acid sites. Finally, dimethylcyclohexene is dehydrogenated to xylene at the metal sites. The use of a strong hydrogenation-dehydrogenation functionality, such as platinum, also induces the hydrogenation of the corresponding aromatic ring to form naphthenic rings.

[0003] In addition to the desired isomerization reaction, it is desirable to limit side reactions such as: · Dealkylation of ethylbenzene to benzene and ethylene; · Disproportionation of ethylbenzene to diethylbenzene and benzene, or disproportionation of xylene to toluene and aromatic compounds containing 9 carbon atoms; Transalkylation between ethylbenzene and xylenes and between xylenes; Naphthenic ring opening and cracking.

[0004] All these reactions result in the production of less valuable molecules, which are not recycled into the "aromatic C8 loop" and are considered a net loss to the process. Therefore, all molecules other than cyclic molecules containing 8 carbon atoms are considered a net loss.

[0005] The isomerization and side reactions are primarily catalyzed by acid functional groups. The properties of the zeolite acting as the acid functional group (number and strength of Brønsted acid sites, topology of the microporous network, etc.) therefore have a direct impact on the properties of the bifunctional catalyst, especially its selectivity.

[0006] The catalysis of the isomerization of aromatic C8 fractions to xylenes has therefore been the subject of numerous patents relating to various zeolites. Among the zeolites used for the isomerization of aromatic C8 fractions is ZSM-5, used alone or in mixtures with other zeolites, such as mordenite. These catalysts are described in particular in US Pat. Nos. 5,629,291 and 5,629,291. Other catalysts based primarily on mordenite are described, for example, in US Pat. No. 5,629,291. Similarly proposed catalysts include catalysts based on zeolites of the EUO structural type (US Pat. No. 5,629,291) or zeolites of the MTW structural type (US Pat. Nos. 5,629,291; ...

[0007] These examples demonstrate the ongoing research being conducted to develop more effective catalysts for the isomerization of aromatic C8 fractions, particularly while minimizing the production of net losses through the use of appropriate zeolites. It has been reported that for catalysts containing a given zeolite, the presence of alkali metals and / or alkaline earth metals in the catalyst can improve the selectivity of the catalyst toward isomerization, but generally at the expense of a loss in the activity of the catalyst. Studies by Moreau et al. (Non-Patent Documents 1 and 2) concerned the study of catalysts containing mordenite zeolite partially exchanged with sodium. It was shown that the exchange with sodium improves the selectivity toward isomerization during the conversion of m-xylene and during the conversion of ethylbenzene. In both cases, this selectivity gain is accompanied by a loss in the activity of the catalyst due to partial neutralization of the acid sites by sodium. Studies by L.D. Fernandes et al. (Non-Patent Document 3) concerned, inter alia, the study of catalysts containing mordenite zeolite that was not exchanged or exchanged with calcium. The presence of calcium can improve the selectivity of the catalyst during the conversion of ethylbenzene. Loss of activity in the presence of calcium has also been reported.

[0008] Patent Document 9 claims a catalyst for the isomerization of aromatic C8 compounds, containing a metal from Group VIII, a binder, and a zeolite containing 2% to 3% alkali metal. The examples include catalysts using mordenite zeolite with various sodium contents. The examples show that the presence of 2% to 3% by weight of sodium in the MOR zeolite makes it possible to reduce the loss of C8 aromatic compounds.

[0009] Patent Document 10 describes a catalyst for isomerizing C8 aromatic compounds, which contains an MTW-type zeolite, a binder, a noble metal, and at least one alkali metal element, which may be lithium, sodium, potassium, rubidium, cesium, francium, or a combination of these elements, wherein the total amount of alkali metals in the catalyst is at least about 100 ppm by weight relative to the mass of the catalyst. Preferably, the catalyst does not contain any alkali metals other than those already contained in the zeolite and / or binder. Preferably, the total content of alkali metals in the catalyst is at least about 200 ppm by weight, preferably at least 300 ppm by weight, and preferably less than about 2500 ppm by weight, preferably less than 2000 ppm by weight, preferably less than 1000 ppm by weight. Preferably, washing with an ammonium nitrate solution is not performed so that the alkali metals present can remain on the catalyst. However, if the catalyst, particularly the zeolite and / or binder, has an excessively high alkali metal content, washing with ammonium nitrate or ammonium hydroxide solution may be performed to restore the catalyst to the desired alkali metal content. The examples include catalysts using MTW zeolites and binders, as well as varying amounts of sodium and potassium. In particular, the examples show that catalysts with total alkali metal contents greater than about 200 ppm have a loss of cyclic molecules containing eight carbon atoms (C8RL) of 2.0 mol% to 2.4 mol%, whereas catalysts with different alumina binders containing lower alkali metal contents than the catalyst of the present invention have a higher loss of cyclic molecules containing eight carbon atoms (C8RL) of 2.6 mol% to 3.4 mol%.

[0010] In its research, the applicant has recently developed a new zeolite, IZM-2 zeolite (Patent Document 11, incorporated herein by reference), and its use in catalysis for the isomerization of fractions containing at least one aromatic compound containing 8 carbon atoms (Patent Documents 12 and 13).

[0011] During its research directed to developing a catalyst for the isomerization of aromatic C8 fractions, comprising said IZM-2 zeolite, the applicant discovered the surprising effect of the presence of alkali metals and / or alkaline earth metals on the performance qualities of the catalyst. Surprisingly, the applicant demonstrated that catalysts containing reduced total contents of alkali metals and / or alkaline earth metals relative to prior art catalysts have increased activity without reducing their selectivity towards isomerization relative to prior art catalysts.

[0012] Therefore, one object of the present invention is to provide a novel catalyst for the isomerization of aromatic C8 fractions, which is based on IZM-2 zeolite and contains limited amounts of alkali metals and / or alkaline earth metals so as to limit the production of net losses.

[0013] Another subject of the present invention relates to a process for the isomerization of a fraction containing at least one aromatic compound containing 8 carbon atoms per molecule, comprising placing said aromatic compound fraction in contact with at least said catalyst according to the invention present in a catalytic reactor. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] U.S. Patent No. 4,467,129 [Patent Document 2] U.S. Patent No. 4,482,773 [Patent Document 3] French Patent No. 2477903 [Patent Document 4] European Patent Application Publication No. 0923987 (JP Patent Publication No. 11-244704) [Patent Document 5] International Publication No. 2005 / 065380 [Patent Document 6] International Publication No. 2010 / 000652 [Patent Document 7] US Patent Application Publication No. 2014 / 0296601 [Patent Document 8] U.S. Patent No. 7,091,190 [Patent Document 9] European Patent No. 0458378 [Patent Document 10] US Patent Application Publication No. 2009 / 0093662 [Patent Document 11] French Patent Application Publication No. 2918050 [Patent Document 12] French Patent Application Publication No. 2934793 [Patent Document 13] French Patent Application Publication No. 3054454 [Non-patent literature]

[0015] [Non-Patent Document 1] Moreau et al., Microporous and Mesoporous Materials, 2002, Vol. 51, pp. 211-221 [Non-patent document 2] Moreau et al., "Applied Catalysis, A: General", 2002, Volume 230, pp. 253-262 [Non-patent document 3] LD Fernandes et al., Journal of Catalysis, 1998, Volume 177, pp.363-337 Summary of the Invention [Means for solving the problem]

[0016] (Summary of the Invention) In particular, the present invention relates to a catalyst comprising at least one IZM-2 zeolite, at least one matrix and at least one metal from group VIII of the periodic table of the elements, characterized in that the total weight proportion of alkali metals and / or alkaline earth metals in said catalyst is less than 200 ppm by weight, relative to the total mass of said catalyst, preferably less than 150 ppm by weight, preferably less than 100 ppm by weight, preferably less than 90 ppm by weight, preferably less than 85 ppm by weight, more preferably less than 80 ppm by weight, highly preferably less than 75 ppm by weight, even more preferably less than 70 ppm by weight, and more than 20 ppm by weight, preferably more than 30 ppm by weight.

[0017] In the remainder of this specification, the weight contents given are considered relative to the dry mass of the solid, which corresponds to the mass of the solid after calcination at 1000° C. in air in a muffle furnace for 2 hours.

[0018] For the purposes of the present invention, the various embodiments presented may be used alone or in combination with one another, without any restrictions on combinations, provided this is technically feasible.

[0019] For purposes of the present invention, various ranges of parameters for a given process, such as pressure ranges and temperature ranges, may be used alone or in combination. For example, for purposes of the present invention, a preferred range of pressure values ​​may be combined with a more preferred range of temperature values.

[0020] The catalyst according to the invention is advantageously used in a process for the isomerization of an aromatics fraction comprising at least one aromatic compound containing 8 carbon atoms per molecule under the following operating conditions: ·Temperature: 300℃~500℃, Hydrogen partial pressure: 0.3 to 1.5 MPa Total pressure: 0.45~1.9Mpa, and Feed space velocity: Expressed as the weight (kilograms) of the feed introduced per weight (kilograms) of catalyst per hour, and is 0.25 to 30 h-1 .

[0021] It has surprisingly been found that a catalyst according to the invention comprising at least one IZM-2 zeolite, a matrix, at least one metal from group VIII of the periodic table of the elements and an alkali metal and / or alkaline earth metal element content in said catalyst of less than 200 ppm by weight and more than 20 ppm by weight, has improved catalytic performance qualities in terms of activity, without loss of selectivity, during a process for isomerization of an aromatic feedstock comprising at least one aromatic fraction comprising at least one aromatic compound containing 8 carbon atoms per molecule.

[0022] Such catalysts are substantially more active than catalysts containing IZM-2 zeolite with an alkali metal and / or alkaline earth metal content of more than 200 ppm. Therefore, reducing the alkali metal content to a content below 200 ppm makes it possible to improve the activity of such catalysts without losing selectivity. This can be exploited by those skilled in the art in two ways: to increase the activity of the catalyst for the same content of IZM-2, or to maintain the activity of the catalyst by reducing the content of IZM-2 zeolite in the catalyst.

[0023] The total weight content of alkali and / or alkaline earth metal elements in the catalyst is determined by atomic absorption spectroscopy on a Varian Spectr'AA 240FS Flame Atomic Absorption Spectrometer (FAAS) after dissolving the solids by wet mineralization of the solids. The term "mineralization of the solids" refers to dissolution of the solids, typically in concentrated aqueous solutions of perchloric, hydrofluoric and hydrochloric acid. This may be done at high temperature on a hotplate or by microwave. DETAILED DESCRIPTION OF THE INVENTION

[0024] (Description of the embodiment) The present invention relates to a catalyst comprising, preferably consisting of, at least one IZM-2 zeolite, preferably an IZM-2 zeolite containing silicon atoms and optionally aluminum atoms, at least one matrix, and at least one metal from group VIII of the periodic table of the elements, characterized in that the total weight content of alkali metal and / or alkaline earth metal elements in said catalyst is less than 200 ppm by weight and more than 20 ppm by weight relative to the total mass of the catalyst.

[0025] Preferably, the catalyst has a total weight content of alkali metal and / or alkaline earth metal elements of less than 150 ppm by weight, preferably less than 100 ppm by weight, preferably less than 90 ppm by weight, preferably less than 85 ppm by weight, preferably less than 80 ppm by weight, more preferably less than 75 ppm by weight, even more preferably less than 70 ppm by weight, and more than 20 ppm by weight, preferably more than 30 ppm by weight, relative to the total mass of the catalyst.

[0026] Preferably, the catalyst does not contain any added alkali metal and / or alkaline earth metal elements other than those associated with the zeolite and / or matrix used in the catalyst.

[0027] The catalyst according to the invention more particularly comprises, and preferably consists of: IZM-2 zeolite: from 1% to 90% by weight, preferably from 3% to 80% by weight, even more preferably from 4% to 60% by weight, relative to the total mass of the catalyst according to the invention, at least one metal from group VIII of the periodic table of the elements, preferably platinum: from 0.01% to 4% by weight, preferably from 0.05% to 2% by weight, relative to the total mass of the catalyst; optionally at least one additional metal selected from the group formed by metals from groups IIIA, IVA and VIIB: from 0.01% to 2% by weight, preferably from 0.05% to 1% by weight, relative to the total mass of the catalyst, optional sulfur: the content is preferably such that the ratio of the number of moles of sulfur to the number of moles of metal(s) of group VIII is between 0.3 and 3, alkali metal and / or alkaline earth metal elements: the total weight content is less than 200 ppm by weight, preferably less than 150 ppm by weight, preferably less than 100 ppm by weight, preferably less than 90 ppm by weight, preferably less than 85 ppm by weight, preferably less than 80 ppm by weight, highly preferably less than 75 ppm by weight, even more preferably less than 70 ppm by weight, and more than 20 ppm by weight, preferably more than 30 ppm by weight, relative to the total mass of the catalyst, At least one matrix, preferably alumina, which provides the remainder up to 100% in the catalyst.

[0028] (IZM-2 zeolite) According to the invention, the catalyst comprises IZM-2 zeolite, whose X-ray diffraction pattern comprises at least the lines recorded in Table 1. IZM-2 zeolite has a crystalline structure.

[0029] Advantageously, the diffractogram is α1 The lattice constant distances d, characteristic of the sample, are obtained by radiation crystallographic analysis using a diffractometer using conventional powder techniques with radiation (λ = 1.5406 Å). Based on the positions of the diffraction peaks expressed by the angle 2θ, hkl is calculated using the Bragg relation. hkl Measurement error Δ(d hkl ) is calculated by the Bragg relation as a function of the absolute error Δ(2θ) assigned to the measurement of 2θ. An absolute error Δ(2θ) equal to ±0.02° is generally accepted. hkl The relative intensity I assigned to each value of rel are measured according to the height of the corresponding diffraction peak. The X-ray diffraction diagram of the IZM-2 zeolite contained in the catalyst according to the invention is given in Table 1. hkl It includes at least a line at the value of d. hklThe value column gives the average interplanar spacing in angstroms (Å). Each of these values ​​has a measurement error Δ(d hkl ) ±0.6Å to ±0.01Å must be assigned.

[0030] Table 1 shows the d measured by X-ray diffraction pattern of the calcined IZM-2 crystalline solid. hkl The mean and relative intensities are shown.

[0031] [Table 1]

[0032] Relative Intensity I rel is given as a relative intensity scale in which a value of 100 is assigned to the most intense line in the X-ray diffractogram: vw<15; 15≦w<30; 30≦mw<50; 50≦m<65; 65≦S<85; VS≧85.

[0033] Said solid IZM-2 advantageously has the following general formula: XO2:aY2O3:bM 2 / n 0, wherein X represents at least one tetravalent element, Y represents at least one trivalent element, and M represents at least one alkali metal and / or alkaline earth metal element of valence n. In the above said formula, a represents the number of moles of YO, a is between 0 and 0.5, highly preferentially between 0.05 and 0.05, and even more preferably between 0.0016 and 0.02, and b is the number of moles of M. 2 / n It represents the number of moles of O, and is 0 to 1, preferably 0 to 0.5, and even more preferably 0.005 to 0.5.

[0034] Preferably, X is selected from silicon, germanium, titanium, and a mixture of at least two of these tetravalent elements; highly preferentially, X is silicon; Y is preferentially selected from aluminum, boron, iron, indium, and gallium; highly preferentially, Y is aluminum. M is preferentially selected from lithium, sodium, potassium, calcium, magnesium, and a mixture of at least two of these metals, highly preferentially M is sodium. Preferably, X represents silicon, and the crystalline solid IZM-2 is a completely siliceous solid when element Y is absent from the composition of the solid IZM-2. It is also advantageous to use a mixture of several elements X as the element X, in particular a mixture of silicon with another element X selected from germanium and titanium, preferably germanium. Therefore, when silicon is present in a mixture with another element X, the crystalline solid IZM-2 is a crystalline metallosilicate having, in its calcined form, an X-ray diffraction pattern identical to that set forth in Table 1. Even more preferably, in the presence of element Y, X is silicon and Y is aluminum; said crystalline solid IZM-2 is a crystalline aluminosilicate having an X-ray diffraction pattern identical to that set out in Table 1 when in its calcined form.

[0035] More generally, the solid IZM-2 used in the support of the catalyst implemented in the process according to the invention advantageously has the following general formula: XO2:aY2O3:bM 2 / n O:cR:dH2O, where R represents an organic species containing two quaternary nitrogen atoms, X represents at least one tetravalent element, Y represents at least one trivalent element, M is an alkali metal and / or alkaline earth metal of valence n; a, b, c, and d are, respectively, YO, M 2 / n represents the number of moles of O, R, and HO, a is 0 to 0.5, b is 0 to 1, c is 0 to 2, and d is 0 to 2. This formula and the values ​​taken by a, b, c, and d are such that the solid IZM-2 is preferentially in its calcined form.

[0036] More precisely, said solid IZM-2, in its raw synthetic form, advantageously has the following general formula: XO2:aY2O3:bM 2 / n O:cR:dHO(I), where R represents an organic species containing two quaternary nitrogen atoms, X represents at least one tetravalent element, Y represents at least one trivalent element, M is an alkali metal and / or alkaline earth metal of valence n; a, b, c, and d are YO, M, and OH, respectively. 2 / n represents the number of moles of O, R, and H2O, a is 0 to 0.5, b is 0 to 1, c is 0.005 to 2, preferably 0.01 to 0.5, and d is 0.005 to 2, preferably 0.01 to 1.

[0037] In the above formula (I), which defines the chemical composition of the crystalline solid IZM-2 in its raw synthetic form, the value of a is between 0 and 0.5, highly preferentially between 0 and 0.05, and even more preferably between 0.0016 and 0.02. Preferably, b is between 0 and 1, highly preferably between 0 and 0.5, and even more preferably between 0.005 and 0.5. The value of c is between 0.005 and 2, advantageously between 0.01 and 0.5. The value of d is between 0.005 and 2, preferably between 0.01 and 1.

[0038] In its crude synthesis form, i.e. obtained directly from the synthesis and before any calcination steps known to those skilled in the art, said solid IZM-2 advantageously comprises at least an organic species R containing two quaternary nitrogen atoms, as described below, or its decomposition product or its precursor. According to a preferred embodiment of the present invention, in the above formula (I), the element R is 1,6-bis(methylpiperidinium)hexane, the structural formula of which is given below. Said organic species R, acting as a structuring agent, may be removed via conventional routes known in the prior art, such as thermal and / or chemical treatments.

[0039] A method for preparing IZM-2 zeolite is taught in patent FR2 918 050 B, which is incorporated herein by reference. Advantageously, when X is silicon and Y is aluminum, an aqueous mixture comprising at least one source of at least one oxide SiO 2 , optionally at least one source of at least one oxide Al 2 O 3 , optionally at least one source of at least one alkali metal and / or alkaline earth metal of valence n, and preferably at least one organic species R comprising two quaternary nitrogen atoms is reacted, the mixture preferentially having the following molar composition: SiO2 / Al2O3: at least 2, preferably at least 20, more preferably 60-600; H2O / SiO2: 1 to 100, preferably 10 to 70, R / SiO2: 0.02 to 2, preferably 0.05 to 0.5, M 2 / n O / SiO2: 0 to 1, preferably 0.005 to 0.5, wherein M is one or more alkali metals and / or alkaline earth metals chosen from lithium, sodium, potassium, calcium and magnesium, and mixtures of at least two of these metals; preferably, M is sodium. Advantageously, the element R is 1,6-bis(methylpiperidinium)hexane.

[0040] The Si / Al molar ratio of the IZM-2 zeolite may be adjusted to the desired value by post-treatment of the IZM-2 zeolite obtained after synthesis. Such methods are known to those skilled in the art and allow dealumination or desilication of the zeolite. Preferably, the adjustment of the Si / Al molar ratio of the IZM-2 zeolite contained in the composition of the catalyst according to the invention is carried out by appropriate selection of the conditions for the synthesis of said zeolite.

[0041] Among IZM-2 zeolites, it is usually preferred to use IZM-2 zeolites having an overall silicon / aluminum (Si / Al) atomic ratio of greater than about 3, more preferably IZM-2 zeolites having an Si / Al ratio of 5 to 200, and even more preferably 10 to 150.

[0042] Therefore, according to a preferred embodiment of the method for preparing the crystalline solid IZM-2, an aqueous mixture containing silicon oxide, optionally alumina, 1,6-bis(methylpiperidinium)hexane dibromide and sodium hydroxide is reacted. According to another preferred embodiment of the method according to the invention, an aqueous mixture containing silicon oxide, optionally alumina and 1,6-bis(methylpiperidinium)hexane dihydroxide is reacted.

[0043] The method for preparing said crystalline solid IZM-2 advantageously consists in preparing an aqueous reaction mixture, called a gel, containing at least one source of at least one oxide XO2, optionally at least one source of at least one oxide YO3, at least one organic species R, optionally at least one source of at least one alkali metal and / or alkaline earth metal of valence n, the amounts of said reagents being advantageously such that in this gel, a compound of general formula (I) XO2:aYO3:bM 2 / n The gel is adjusted to give a composition that allows its crystallization as crystalline solid IZM-2 in its crude synthesis form of O:cR:dH2O (where a, b, c, and d satisfy the above-defined criteria when c and d are greater than 0). The gel is then subjected to hydrothermal treatment until said crystalline solid IZM-2 is formed. The gel is advantageously placed under hydrothermal conditions at autogenous reaction pressure, optionally with the addition of a gas such as nitrogen, at temperatures between 120°C and 200°C, preferably between 140°C and 180°C, and even more preferably between 160°C and 175°C, until crystallization of solid IZM-2 in its crude synthesis form occurs. The time required to obtain crystallization generally ranges from one hour to several months, depending on the composition of the reagents in the gel, the stirring, and the reaction temperature. Preferably, the crystallization time ranges from 2 hours to 21 days. The reaction is generally carried out with or without stirring, preferably with stirring.

[0044] It may be advantageous to add seed crystals to the reaction mixture to shorten the time required for crystal formation and / or the total crystallization time. It may also be advantageous to use seed crystals to promote the formation of the crystalline solid IZM-2 at the expense of impurities. Such seeds advantageously contain crystalline solids, in particular solid IZM-2 crystals. Crystal seeds are generally added in a proportion of 0.01% to 10% of the mass of the oxide XO2 used in the reaction mixture.

[0045] At the end of the hydrothermal treatment step leading to the crystallization of the solid IZM-2, the solid phase is advantageously filtered off, washed, dried and then calcined. The calcination step is advantageously carried out via one or more heating steps at temperatures between 100 and 1000°C, preferably between 400 and 650°C, for a period of several hours to several days, preferably between 3 and 48 hours. Preferably, the calcination is carried out in two successive heating steps.

[0046] At the end of the calcination step, the solid IZM-2 obtained advantageously has an X-ray diffraction pattern including at least the lines recorded in Table 1. It is free of water and of the organic species R present in solid IZM-2 in its crude synthesis form. After the calcination step, the IZM-2 zeolite may typically contain 2000 to 8000 ppm of alkali metal and / or alkaline earth metal elements, preferably sodium.

[0047] After calcination, the solid IZM-2 contained in the composition of the support for the catalyst according to the invention is advantageously washed by at least one treatment with a solution of at least one ammonium salt to reduce the alkali metal and / or alkaline earth metal, preferably sodium, content in the zeolite, thereby obtaining the ammonium form of solid IZM-2. The M / Y atomic ratio is generally advantageously less than 0.1, preferably less than 0.05, and even more preferably less than 0.01. This washing step can be carried out at any stage in the preparation of the support for the catalyst or the catalyst, i.e., after the step of preparing solid IZM-2, after the step of forming solid IZM-2, or after the step of introducing the hydrogenation / dehydrogenation metals. Preferably, the washing step is carried out after the step of forming solid IZM-2. The washing step is preferably carried out by immersing the solid in an aqueous solution of at least one ammonium salt with stirring. The ammonium salt may be selected from ammonium nitrate (NH4NO3), ammonium chloride (NH4Cl), ammonium hydroxide (NH4OH), ammonium bicarbonate (NH4HCO3), ammonium acetate (NH4H3C2O2), or ammonium sulfate (NH4)2SO4. The duration of immersion of the solid in the solution may typically range from 15 minutes to several hours. The concentration of the ammonium salt(s) in the solution is typically 0.1 mol / L to 10 mol / L. Washing is preferably carried out at a temperature between room temperature and 100°C. The ratio between the volume (mL) of the involved solution and the mass (g) of the involved zeolite is preferably 1 to 100. It may prove necessary to repeat the washing process several times to reduce the alkali metal and / or alkaline earth metal, preferably sodium, content to the desired level. At the end of the last wash, the solid is filtered off, washed with deionized water, and then dried. The IZM-2 zeolite is finally calcined to obtain it in its proton form. The calcination conditions are typically the same as those used to calcinate the solids at the conclusion of the hydrothermal treatment step.

[0048] After washing, the zeolite may typically contain less than 200 ppm, and preferably more than 20 ppm or even more than 30 ppm of alkali metal and / or alkaline earth metal elements, preferably sodium.

[0049] (Matrix) According to the invention, the catalyst comprises at least one matrix, said matrix may advantageously be amorphous or crystalline.

[0050] Preferably, the matrix is ​​advantageously selected from the group formed by alumina, silica, silica-alumina, clay, titanium oxide, boron oxide and zirconia, used alone or in mixture, or an aluminate may be selected. Preferably, alumina is used as the matrix. Preferably, the matrix contains alumina in all forms known to those skilled in the art, such as alpha, gamma, eta and delta alumina. The aluminas differ in their specific surface area and their pore volume. The alkali metal and / or alkaline earth metal content of the matrix can vary and depends on the method for obtaining the matrix, as is well known for alumina, for example (Handbook of Porous Solids, 2008, Wiley-VCH chapter 4.7.2).

[0051] The support for the catalyst used in the present invention comprises, and preferably consists of, the matrix and the IZM-2 zeolite.

[0052] The alkali metal and / or alkaline earth metal content of the matrix can be adjusted advantageously by any method known to those skilled in the art to obtain the catalyst according to the invention. The matrix or matrix precursor can therefore be washed by placing it in contact with an aqueous solution whose pH is below the zero charge point of the matrix, as shown for alumina matrices in Catalysis Supports and Supported Catalysts, Butterworth Publishers (1987). By way of example, boehmite can be washed by placing the solid in contact with an aqueous ammonium nitrate solution. The duration of immersion of the solid in the solution can typically range from 15 minutes to several hours. The concentration of the ammonium salt(s) in the solution is typically between 0.1 mol / L and 10 mol / L. Washing is preferably carried out at a temperature between room temperature and 100°C. The ratio between the volume (mL) of the involved solution and the mass (g) of the involved boehmite is preferably between 1 and 100. It may prove necessary to repeat the washing step several times to reduce the alkali metal and / or alkaline earth metal content to the desired level. At the end of the last wash, the solid is filtered off, washed with deionized water, then dried and calcined.

[0053] If it contains alkali metal and / or alkaline earth metal elements, the matrix may typically contain less than 200 ppm, and preferably more than 20 ppm or even more than 30 ppm, of alkali metal and / or alkaline earth metal elements, preferably sodium.

[0054] (metallic phase) According to the present invention, the catalyst comprises at least one Group VIII metal, preferably selected from iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum, preferably selected from the noble metals of Group VIII, very preferably selected from palladium and platinum, and even more preferably selected from platinum.

[0055] Preferably, the catalyst comprises a content of group VIII metals between 0.01% and 5% by weight, preferably between 0.1% and 4% by weight, relative to the total mass of the catalyst.

[0056] When the catalyst comprises at least one noble metal from group VIII, the noble metal content of the catalyst is advantageously between 0.01% and 5% by weight, preferably between 0.1% and 4% by weight, highly preferably between 0.1% and 2% by weight, relative to the total mass of the catalyst.

[0057] The catalyst of the invention may advantageously contain at least one metal selected from the group IIIA, IVA and VIIB metals, selected from gallium, indium, tin and rhenium, in which case the content of metal selected from the group IIIA, IVA and VIIB metals is preferably between 0.01% and 2% by weight, preferably between 0.05% and 1% by weight, relative to the total weight of said catalyst.

[0058] The dispersion of the Group VIII metal(s), as determined by chemisorption, e.g., H2 / O2 titration or carbon monoxide chemisorption, is 10% to 100%, preferably 20% to 100%, and more preferably 30% to 100%. The macroscopic distribution coefficient of the Group VIII metal(s), obtained from its (their) profile determined with a Castaing microprobe and defined as the ratio of the concentration of the Group VIII metal(s) in the core of a granule relative to the edge of this same granule, is 0.7 to 1.3, preferably 0.8 to 1.2. This ratio, in the region of 1, is evidence of the homogeneity of the distribution of the Group VIII metal(s) in the catalyst.

[0059] (Catalyst Preparation) The catalyst according to the invention may advantageously be prepared according to any of the methods known to those skilled in the art.

[0060] (molding) Advantageously, the various components of the catalyst support can be shaped by blending to form a paste followed by extrusion of the paste obtained, or else by mixing powders followed by pelletizing, or else by any other known method for agglomerating powders containing alumina. The support thus obtained can be of various shapes and sizes. Preferably, shaping is carried out by blending and extrusion.

[0061] During blending and subsequent extrusion to form a support, the IZM-2 zeolite may be introduced into the dissolution or suspension of an alumina compound or alumina precursor, such as boehmite. The IZM-2 zeolite may be in the form of, for example, but not limited to, a powder, a crushed powder, a suspension, or a suspension that has undergone a deagglomeration treatment. Thus, for example, the zeolite may be advantageously placed in an acidified or non-acidified suspension at a concentration adjusted to the final IZM-2 content targeted in the catalyst according to the invention. This suspension, commonly referred to as a slip, is then mixed with an alumina compound or alumina precursor.

[0062] Furthermore, additives may be advantageously used to facilitate shaping and / or improve the final mechanical properties of the carrier, as is well known to those skilled in the art. Examples of additives that may be mentioned in particular include cellulose, carboxymethyl cellulose, carboxyethyl cellulose, tall oil, xanthan gum, surfactants, flocculating agents such as polyacrylamide, carbon black, starch, stearic acid, polyacrylic alcohol, polyvinyl alcohol, biopolymers, glucose, polyethylene glycol, etc.

[0063] Water may be advantageously added or removed to adjust the viscosity of the paste to be extruded. This step may advantageously be carried out at any stage of the blending process.

[0064] To adjust the solids content of the paste to be extruded so that it is extrudable, a predominantly solid compound, preferably an oxide or a hydrate, may be added. Preferably, a hydrate is used, more preferably an aluminum hydrate. The loss on ignition of this hydrate is advantageously greater than 15%.

[0065] The extrusion of the paste obtained from the blending step can be advantageously carried out using any conventional commercially available tool. The paste obtained from the blending is advantageously extruded through a die, for example using a piston or single-screw or twin-screw extruder. The extrusion can advantageously be carried out via any method known to those skilled in the art.

[0066] The catalyst supports according to the invention are generally in the form of cylindrical or polylobal extrudates, for example, bilobal, trilobal, or multilobal extrudates in a straight or twisted form, but may also be produced and used in the form of crushed powders, lozenges, rings, beads, and / or wheels. Preferably, the catalyst supports according to the invention are in the form of spheres or extrudates. Advantageously, the supports are in the form of extrudates having a diameter of 0.5 to 5 mm, more particularly 0.7 to 2.5 mm. The form may be cylindrical (which may or may not be hollow) and / or twisted and / or multilobal (for example, 2-, 3-, 4-, or 5-lobed) and / or annular. Advantageously, multilobal forms are preferably used.

[0067] (Dry) The support thus obtained may then be subjected to a drying step, said drying step being advantageously carried out via any technique known to those skilled in the art.

[0068] Preferably, drying is carried out under a stream of air. Said drying may be carried out under a stream of any oxidizing, reducing or inert gas. Preferably, drying is carried out at a temperature advantageously between 50 and 180°C, preferably between 60 and 150°C, and highly preferably between 80 and 130°C.

[0069] (Firing) The optionally dried support then preferably undergoes a calcination step.

[0070] The calcination step is advantageously carried out in the presence of molecular oxygen, for example by flushing with air, advantageously at a temperature above 200°C and up to 1100°C. The calcination step may advantageously be carried out in a traverse bed, in a licked bed or in a static atmosphere. For example, the oven used may be a rotary oven or a vertical oven with radial transverse layers. Preferably, the calcination step is carried out at 200°C for more than 1 hour and at 1100°C for less than 1 hour. Calcination may advantageously be carried out in the presence of water vapor and / or acidic or basic vapors. For example, calcination may be carried out under a partial pressure of ammonia.

[0071] (Post-firing treatment) A post-calcination treatment may optionally be carried out to improve the properties, particularly the textural properties, of the support.

[0072] The catalyst support according to the invention may therefore be subjected to hydrothermal treatment in a confined atmosphere. The term "hydrothermal treatment in a confined atmosphere" means treatment in an autoclave in the presence of water at a temperature above room temperature, preferably above 25°C, preferably above 30°C.

[0073] During this hydrothermal treatment, the support may advantageously be impregnated before its treatment in an autoclave (autoclaving is carried out either in the vapour or liquid phase, this vapour or liquid phase of the autoclave being acidic or not, as the case may be). This impregnation before autoclaving may advantageously be acidic or not. This impregnation may advantageously be carried out dry or by immersing the support in an acidic aqueous solution before autoclaving. The term "dry impregnation" means that the support is placed in contact with a volume of solution not greater than the total pore volume of the support. Preferably, the impregnation is carried out dry. The autoclave is preferably a rotating basket autoclave, such as that defined in patent application EP 0 387 109 A. The temperature during autoclaving may be between 100 and 250°C for a period of between 30 minutes and 3 hours.

[0074] The preformed mixture of matrix and IZM-2 zeolite constitutes the support for the catalyst. The alkali metal and / or alkaline earth metal content of the support may be adjusted via any method known to those skilled in the art to obtain the catalyst according to the invention.

[0075] Preferably, a washing treatment may be carried out to reduce the alkali metal and / or alkaline earth metal content of the support. The operating conditions for washing are typically the same as those described for washing zeolites. After washing, the support is then calcined again, preferably under the same conditions as those described for washing zeolites.

[0076] (Deposition of metal phase) For the deposition of metals from group VIII of the periodic table, any deposition technique known to those skilled in the art and any precursor of such metals may be suitable. Deposition techniques by dry impregnation or excess impregnation of a solution containing a precursor of the metal, in the presence or absence of a competing agent, may be used. The introduction of the metal may be carried out at any stage of the preparation of the catalyst: onto the IZM-2 zeolite and / or onto the matrix, in particular before, during, or after the shaping step, onto the support for the catalyst. Preferably, the deposition of the metal is carried out after the shaping step.

[0077] By controlling certain parameters used during deposition, in particular the nature of the precursors of the group VIII metal(s) used, it is possible to direct the deposition of said metal(s) mainly onto the matrix or onto the zeolite.

[0078] Therefore, to introduce the Group VIII metal(s), preferentially platinum and / or palladium, primarily onto the matrix, anion exchange may be carried out with hexachloroplatinic acid and / or hexachloropalladic acid in the presence of a competing agent, such as hydrochloric acid, and deposition is generally followed by calcination, for example at a temperature of 350-550° C. for a period of 1-4 hours. With such precursors, the Group VIII metal(s) are deposited primarily onto the matrix, with the metal(s) exhibiting good dispersion and good macroscopic distribution throughout the catalyst granules.

[0079] It is also possible to envisage depositing the group VIII metal(s), preferentially platinum and / or palladium, by cation exchange, in such a way that said metal(s) are mainly present on the zeolite. Thus, in the case of platinum, the precursors may be chosen, for example, from: ammoniacal compounds such as platinum(II) tetramine salts of the formula Pt(NH3)4X2; platinum(IV) hexamine salts of the formula Pt(NH3)6X4; platinum(IV) halopentamine salts of the formula (PtX(NH3)5)X3; platinum N-tetrahalodiamine salts of the formula PtX4(NH3)2; and Halogenated compounds of the formula H(Pt(acac)2X); X is a halogen selected from the group formed by chlorine, fluorine, bromine and iodine, X is preferably chlorine and "acac" represents an acetylacetonate group (empirical formula C5H7O2) derived from acetylacetone. With such precursors, the Group VIII metal(s) are deposited primarily on the zeolite, with said metal(s) showing good dispersion and good macroscopic distribution throughout the catalyst granules.

[0080] The impregnation solution may advantageously comprise at least one ammonium salt chosen from ammonium nitrate NH4NO3, ammonium chloride NH4Cl, ammonium hydroxide NH4OH, ammonium bicarbonate NH4HCO3 and ammonium acetate NH4H3C2O2, alone or in mixture, the molar ratio between the ammonium salt and the precursor noble metal being between 0.1 and 400.

[0081] When the catalyst of the present invention also contains at least one metal selected from metals from groups IIIA, IVA and VIIB, any technique for the deposition of such metals and any precursor of such metals known to those skilled in the art may be suitable for use.

[0082] The Group VIII metal(s) and the Group IIIA, IVA and VIIB metal(s) may be added separately or simultaneously in at least one unitary step. If at least one metal from Groups IIIA, IVA and VIIB is added separately, it is preferably added after the Group VIII metal.

[0083] The additional metal selected from metals from groups IIIA, IVA, and VIIB may be introduced by compounds such as chlorides, bromides, and nitrates of metals from groups IIIA, IVA, and VIIB. For example, in the case of indium, nitrates or chlorides are advantageously used, and in the case of rhenium, perrhenic acid is advantageously used. The additional metal selected from metals from groups IIIA, IVA, and VIIB may be introduced in the form of at least one organic compound selected from the group consisting of complexes of the metal, in particular polyketone complexes of metals with hydrocarbyl metals such as alkyl, cycloalkyl, aryl, alkylaryl, and arylalkyl metals. In this form, the introduction of the metal is advantageously carried out using a solution of an organometallic compound of the metal in an organic solvent. Organohalogen compounds of the metal may also be used. Particular mention may be made of organic compounds of the metal, such as tetrabutyltin in the case of tin and triphenylindium in the case of indium.

[0084] If an additional metal selected from Groups IIIA, IVA, and VIIB is introduced before the metal from Group VIII, the compound of the metal from Group IIIA, IVA, and / or VIIB used is generally selected from the group consisting of metal halides, nitrates, acetates, tartrates, carbonates, and oxalates. The introduction is advantageously carried out in aqueous solution. However, it can also be carried out using an organometallic compound of the metal, for example, a solution of tetrabutyltin. In this case, calcination in air is carried out before the introduction of at least one Group VIII metal.

[0085] Furthermore, intermediate treatments, such as calcination and / or reduction, may be applied between successive depositions of various metals.

[0086] After calcination, a washing treatment may be carried out to adjust the alkali metal and alkaline earth metal content of the catalyst. The operating conditions for washing are typically the same as those described for washing zeolites. After washing, the catalyst is calcined again.

[0087] Before its use in the isomerization process, the catalyst according to the invention is preferably reduced. This reduction step is advantageously carried out by treatment under hydrogen at a temperature of 150°C to 650°C and a total pressure of 0.1 to 25 MPa. For example, the reduction may consist of a 2-hour stage at 150°C, followed by a temperature increase to 450°C at a rate of 1°C / min, and a 2-hour stage at 450°C; throughout this reduction step, the hydrogen flow rate is 1000 normal m3 of hydrogen per tonne of catalyst. 3 and the total pressure is kept constant at 0.2 MPa. Any ex-situ reduction method may be advantageously envisaged. The ex-situ pre-reduction of the final catalyst under a flow of hydrogen may be carried out, for example, at a temperature between 450°C and 600°C for a period of 0.5 to 4 hours.

[0088] The catalyst advantageously also contains sulfur. When the catalyst of the present invention contains sulfur, the sulfur may be introduced at any step in the preparation of the catalyst: before or after the molding and / or drying and / or calcination steps, before or after the introduction of the aforementioned metal(s), or by in-situ and / or ex-situ sulfurization before the catalytic reaction. In the case of in-situ sulfurization, reduction is carried out before sulfurization if the catalyst has not been reduced before. In the case of ex-situ sulfurization, reduction is also carried out, followed by sulfurization. The sulfurization is preferably carried out in the presence of hydrogen using any sulfurizing agent known to those skilled in the art, such as dimethyl sulfide or hydrogen sulfide.

[0089] The catalysts according to the invention come in a variety of shapes and sizes. They are generally used in the form of cylindrical extrudates and / or multilobal extrudates of linear and / or twisted morphology, for example, bilobal, trilobal, or multilobal extrudates, although they may also be produced and used in the form of crushed powders, rhomboids, rings, beads, and / or wheels. Preferably, the catalysts used in the process according to the invention are in the form of spheres or extrudates. Advantageously, the catalysts are in the form of extrudates having a diameter of 0.5 to 5 mm, more particularly 0.7 to 2.5 mm. The morphology may be cylindrical (which may or may not be hollow) and / or twisted and / or multilobal (for example, 2-, 3-, 4-, or 5-lobed) cylindrical and / or annular. Multilobal morphologies are advantageously preferred. The metal deposit does not change the morphology of the support.

[0090] (isomerization method) The subject of the present invention is also a process for the isomerization of a fraction containing at least one aromatic compound containing 8 carbon atoms per molecule, comprising placing said aromatic compound fraction in contact with at least said catalyst according to the invention present in a catalytic reactor.

[0091] Said aromatics fraction containing at least one aromatic compound containing 8 carbon atoms per molecule comprises in particular, as aromatic compound containing 8 carbon atoms per molecule, either a mixture of xylenes only, or ethylbenzene only, or a mixture of xylene(s) and ethylbenzene.

[0092] The isomerization process is generally carried out according to the following operating conditions: Temperature: 300°C to 500°C, preferably 320°C to 450°C, even more preferably 340°C to 430°C; Hydrogen partial pressure: 0.3 to 1.5 MPa, preferably 0.4 to 1.2 MPa, more preferably 0.7 to 1.2 MPa; Total pressure: 0.45 to 1.9 MPa, preferably 0.6 to 1.5 MPa; and Feed space velocity: expressed in kilograms of feed introduced per kilogram of catalyst weight per hour, 0.25 to 30 h -1 , preferably 1 to 10 hours -1 , more preferably 2 to 6 hours -1 .

[0093] The following examples illustrate the present invention but do not limit the scope of the invention.

[0094] (Example) Example 1: Synthesis of IZM-2 zeolite IZM-2 zeolite was synthesized according to the teachings of Patent FR 2 918 050 B. A colloidal silica suspension known under the trade name Ludox HS-40, sold by Aldrich, was incorporated into a solution composed of sodium hydroxide (Prolabo), 1,6-bis(methylpiperidinium)hexane dibromide structurant, aluminum hydroxide (Aldrich), and deionized water. The molar composition of the mixture was as follows: 1 SiO2; 0.0042 Al2O3; 0.1666 Na2O; 0.1666 1,6-bis(methylpiperidinium)hexane; 33.3333 H2O. The mixture was vigorously stirred for 30 minutes. After homogenization, the mixture was then transferred to a Parr autoclave. The autoclave was heated at 170°C with spindle stirring (30 rpm) for 5 days. The product obtained is filtered, washed with deionized water to reach a neutral pH, and then dried in an oven at 100°C overnight. The solid is then introduced into a muffle furnace and calcined to remove the structuring agent. The calcination cycle includes a temperature increase to 200°C, a 2-hour stage at this temperature, a temperature increase to 550°C, followed by an 8-hour stage at this temperature, and finally a return to room temperature. The temperature increase is carried out at a gradient of 2°C / min. The sodium content of the solid thus obtained, as measured by atomic absorption, is 3695 ppm.

[0095] To reduce the sodium content, the solid thus obtained is then refluxed in an aqueous ammonium nitrate solution (10 mL of solution per gram of solid weight, ammonium nitrate concentration 3 M) for 2 hours. This refluxing step is repeated four times with fresh ammonium nitrate solution, and the solid is then filtered off, washed with deionized water and dried overnight in an oven at 100°C. Finally, the zeolite is treated with an acid (protonated H + The calcination step is carried out in a traverse bed under dry air (2 normal liters per hour per gram of solid) at 550°C for 10 hours (heating rate 2°C / min) to obtain the IZM-2 zeolite solid in the form IZM-2. The solid thus obtained is analyzed by X-ray diffraction and identified as being composed of IZM-2 zeolite. The sodium content of the solid thus obtained, determined by atomic absorption, is 142 ppm.

[0096] Example 2: Preparation of a first IZM-2 / alumina support The IZM-2 zeolite prepared in Example 1 is blended with a first batch of boehmite supplied by Axens, containing 268 ppm by weight of sodium, and extruded to obtain an IZM-2 / alumina support. The blended paste is extruded through a four-lobed die with a diameter of 1.5 mm. After drying overnight in an oven at 110°C, the extrudates are calcined in a cross-bed oven at 550°C for 2 hours (heating rate 5°C / min) under dry air (2 normal liters per hour and per gram of solids). The support is not washed. After calcination, the weight content of IZM-2 zeolite in the support is 14% by weight. The sodium content in the support is 250 ppm, as determined by atomic absorption spectroscopy.

[0097] Example 3 (Not in Accordance with the Invention): Preparation of Isomerization Catalyst A Catalyst A is a catalyst comprising IZM-2 zeolite, platinum, and an alumina matrix. This catalyst is prepared by dry impregnation of the IZM-2 / alumina support prepared in Example 2 with an aqueous solution containing platinum tetramine nitrate Pt(NH3)4(NO3)2. 20 g of support is typically used and dry impregnated in a rotating barrel. After impregnation, the solid is left to age in laboratory air for at least 5 hours, then dried in an oven at 110°C overnight, and finally, a calcination step is carried out in a tubular oven under a flow of dry air (1 normal liter per hour and per gram of solid weight) under the following conditions: · Temperature ramp from room temperature to 150°C at 5°C / min; · 1 hour stage at 150°C; · Temperature ramp from 150°C to 450°C at 5°C / min; · 1 hour stage at 450°C; - Cool to room temperature.

[0098] The Pt content, measured by XRF on the calcined catalyst, is 0.3 wt. % and its coefficient of distribution, measured by Castaing microprobe, is 0.96. The catalyst obtained is not subjected to a washing step with ammonium nitrate solution. The sodium content in the catalyst, measured by atomic absorption, is 245 ppm.

[0099] The textural properties of catalyst A were characterized by nitrogen porosimetry at 196 °C on a Micromeritics ASAP 2010 machine. Prior to nitrogen adsorption, the solid is degassed under vacuum at 90 °C for 1 hour and then at 350 °C for 4 hours. The total pore volume corresponds to the volume of nitrogen adsorbed at a relative pressure of 0.97. The specific surface area of ​​the solid was calculated by the BET method, and the pore median diameter, calculated according to the BJH adsorption model, corresponds to the diameter at which half the volume of nitrogen is adsorbed. Catalyst A has a specific surface area of ​​294 m 2 / g, the total pore volume is 0.74 mL / g, and the median diameter is 12 nm.

[0100] Example 4: Preparation of a second IZM-2 / alumina support The IZM-2 zeolite prepared in Example 1 is blended with a second batch of boehmite supplied by Axens and extruded to obtain an IZM-2 / alumina support. This second batch of boehmite differs from the first batch by its lower sodium content; the second batch of boehmite contains 63 ppm by weight of sodium. The blended paste is extruded through a four-lobed die with a diameter of 1.5 mm. After drying overnight in an oven at 110°C, the extrudates are calcined in a transverse bed at 550°C for 2 hours (heating rate 5°C / min) under dry air (2 normal liters per hour and per gram of solids). The second support does not undergo a washing step. After calcination, the weight content of IZM-2 zeolite in the support is 14% by weight. The sodium content in the support is 74 ppm, as determined by atomic absorption spectroscopy.

[0101] Example 5 (In Accordance with the Invention): Preparation of Isomerization Catalyst B Catalyst B is a catalyst comprising IZM-2 zeolite, platinum and an alumina matrix. This catalyst is prepared by dry impregnation of the IZM-2 / alumina support prepared in Example 3 with an aqueous solution containing platinum tetramine nitrate Pt(NH3)4(NO3)2. 20 g of support is typically used and dry impregnated in a rotating barrel. After impregnation, the solid is left to age in laboratory air for at least 5 hours, then dried in an oven at 110°C overnight, and finally, a calcination step is carried out in a tubular oven under a flow of dry air (1 normal liter per hour and per gram of solid weight) under the following conditions: · Temperature ramp from room temperature to 150°C at 5°C / min; · 1 hour stage at 150°C; · Temperature ramp from 150°C to 450°C at 5°C / min; · 1 hour stage at 450°C; - Cool to room temperature.

[0102] The Pt content is 0.3 wt. % on the calcined catalyst, measured by XRF, and its distribution coefficient is 1.03, measured by Castaing microprobe. The catalyst obtained is not subjected to a washing step with ammonium nitrate solution. The sodium content in the catalyst is 69 ppm, measured by atomic absorption.

[0103] The textural properties of catalyst B were characterized by nitrogen porosimetry at 196 °C on a Micromeritics ASAP 2010 machine. Prior to nitrogen adsorption, the solid is degassed under vacuum at 90 °C for 1 hour and then at 350 °C for 4 hours. The total pore volume corresponds to the volume of nitrogen adsorbed at a relative pressure of 0.97. The specific surface area of ​​the solid was calculated by the BET method, and the pore median diameter, calculated according to the BJH adsorption model, corresponds to the diameter at which half the volume of nitrogen is adsorbed. Catalyst B has a specific surface area of ​​298 m 2 / g, the total pore volume is 0.76 mL / g, and the median diameter is 13 nm.

[0104] Example 6: Preparation of a third IZM-2 / alumina support The IZM-2 zeolite prepared in Example 1 is blended with a third batch of boehmite supplied by Axens, containing 130 ppm sodium by weight, and extruded to obtain an IZM-2 / alumina support. The blended paste is extruded through a four-lobe die with a diameter of 1.5 mm. After drying overnight in an oven at 110°C, the extrudates are calcined under the following conditions: - Temperature increase from room temperature to 150°C at 5°C / min in dry air (1 normal liter per hour and per gram of solids), A 1 hour stage at 150°C in dry air (1 normal liter per hour and per gram of solids). - Temperature increase from 150 ° C to 550 ° C at 5 ° C / min; in dry air (1 normal liter per hour and per gram of solids) up to 480 ° C, then starting from 480 ° C in an air-water mixture (30 volumes of water), a 2-hour stage at 550°C in an air-water mixture (1 normal liter per hour and per gram of solids), - Drop to 480°C in a mixture of air and water (1 normal liter per hour and per gram of solids), - Decrease from 480°C to room temperature in dry air (1 normal liter per hour and per gram of solid).

[0105] The support is not washed. The weight content of IZM-2 zeolite in the support after calcination is 13% by weight. The sodium content in the support is 132 ppm as measured by atomic absorption.

[0106] Example 7 (In Accordance with the Invention): Preparation of Isomerization Catalyst C Catalyst C is a catalyst comprising IZM-2 zeolite, platinum, and an alumina matrix. This catalyst is prepared by dry impregnation of the IZM-2 / alumina support prepared in Example 6 with an aqueous solution containing platinum tetramine nitrate Pt(NH3)4(NO3)2. 20 g of support is typically used and dry impregnated in a rotating barrel. After impregnation, the solid is left to age in laboratory air for at least 5 hours, then dried in an oven at 110°C overnight, and finally, a calcination step is carried out in a tubular oven under a flow of dry air (1 normal liter per hour and per gram of solid weight) under the following conditions: - Temperature ramp from room temperature to 150°C at 5°C / min. 1 hour stage at 150°C, - Temperature ramp from 150°C to 450°C at 5°C / min, 1 hour stage at 450°C, - Cooling down to room temperature.

[0107] The Pt content is 0.26 wt. % on the calcined catalyst, as determined by XRF, and its distribution coefficient is 1.1, as determined by Castaing microprobe. The catalyst obtained is not subjected to a washing step with ammonium nitrate solution. The sodium content in the catalyst is 130 ppm, as determined by atomic absorption spectroscopy.

[0108] The textural properties of catalyst C were characterized by nitrogen porosimetry at 196 °C on a Micromeritics ASAP 2010 machine. Prior to nitrogen adsorption, the solid was degassed under vacuum at 90 °C for 1 hour and then at 350 °C for 4 hours. The total pore volume corresponds to the volume of nitrogen adsorbed at a relative pressure of 0.97. The specific surface area of ​​the solid was calculated by the BET method, and the pore median diameter, calculated according to the BJH adsorption model, corresponds to the diameter at which half the volume of nitrogen is adsorbed. Catalyst C has a specific surface area of ​​268 m 2 / g, the total pore volume is 0.73 mL / g, and the median diameter is 14.5 nm.

[0109] Example 8: Preparation of a fourth IZM-2 / alumina support The IZM-2 zeolite prepared in Example 1 is blended with a fourth batch of boehmite supplied by Axens, containing 297 ppm sodium by weight, and extruded to obtain an IZM-2 / alumina support. The blended paste is extruded through a four-lobe die with a diameter of 1.5 mm. After drying overnight in an oven at 110°C, the extrudates are calcined under the following conditions: - Temperature increase from room temperature to 150°C at 5°C / min in dry air (1 normal liter per hour and per gram of solids), a 1 hour stage at 150°C in dry air (1 normal liter per hour and per gram of solids), Ramp from 150°C to 550°C at 5°C / min; up to 480°C in dry air (1 normal liter per hour and per gram of solids), then starting from 480°C in a mixture of air and water (30% water by volume); a 2-hour stage at 550°C in an air-water mixture (1 normal liter per hour and per gram of solids), - in a mixture of air and water (1 normal liter per hour and per gram of solids) down to 480°C, - Decrease from 480°C to room temperature in dry air (1 normal liter per hour and per gram of solid).

[0110] The support is not washed. The weight content of IZM-2 zeolite in the support after calcination is 13% by weight. The sodium content in the support is 276 ppm, as measured by atomic absorption.

[0111] Example 9 (Not in Accordance with the Invention): Preparation of Isomerization Catalyst D Catalyst D is a catalyst comprising IZM-2 zeolite, platinum, and an alumina matrix. This catalyst is prepared by dry impregnation of the IZM-2 / alumina support prepared in Example 8 with an aqueous solution containing platinum tetramine nitrate Pt(NH3)4(NO3)2. 20 g of support is typically used and dry impregnated in a rotating barrel. After impregnation, the solid is left to age in laboratory air for at least 5 hours, then dried in an oven at 110°C overnight, and finally, a calcination step is carried out in a tubular oven under a flow of dry air (1 normal liter per hour and per gram of solid weight) under the following conditions: - Temperature ramp from room temperature to 150°C at 5°C / min, 1 hour stage at 150°C, - Temperature ramp from 150°C to 450°C at 5°C / min, 1 hour stage at 450°C, - Cool down to room temperature.

[0112] The Pt content is 0.26 wt. % on the calcined catalyst as determined by XRF, and its coefficient of distribution is 1.0 as determined by Castaing microprobe. The catalyst obtained is not subjected to a washing step with ammonium nitrate solution. The sodium content in the catalyst is 278 ppm as determined by atomic absorption.

[0113] The textural properties of catalyst D were characterized by nitrogen porosimetry at 196°C on a Micromeritics ASAP 2010 machine. Prior to nitrogen adsorption, the solid is degassed under vacuum at 90°C for 1 hour and then at 350°C for 4 hours. The total pore volume corresponds to the volume of nitrogen adsorbed at a relative pressure of 0.97. The specific surface area of ​​the solid was calculated by the BET method, and the pore median diameter, calculated according to the BJH adsorption model, corresponds to the diameter at which half the volume of nitrogen is adsorbed. Catalyst D has a specific surface area of ​​276 m 2 / g, the total pore volume is 0.69 mL / g, and the median diameter is 13 nm.

[0114] Example 10: Preparation of a fourth IZM-2 / alumina support The IZM-2 zeolite prepared in Example 1 is blended with a fourth batch of boehmite supplied by Axens, containing 84 ppm sodium by weight, and extruded to obtain an IZM-2 / alumina support. The blended paste is extruded through a four-lobed die with a diameter of 1.5 mm in an oven. After drying overnight at 110°C, the extrudates are calcined under the following conditions: - Temperature increase from room temperature to 150°C at 5°C / min in dry air (1 normal liter per hour and per gram of solids), a 1 hour stage at 150°C in dry air (1 normal liter per hour and per gram of solids), Ramp from 150°C to 550°C at 5°C / min; up to 480°C in dry air (1 normal liter per hour and per gram of solids), then starting from 480°C in a mixture of air and water (30% water by volume); a 2-hour stage at 550°C in an air-water mixture (1 normal liter per hour and per gram of solids), - in a mixture of air and water (1 normal liter per hour and per gram of solids) down to 480°C, - Decrease from 480°C to room temperature in dry air (1 normal liter per hour and per gram of solid).

[0115] The support is not washed. The weight content of IZM-2 zeolite in the support after calcination is 13% by weight. The sodium content in the support is 91 ppm as measured by atomic absorption.

[0116] Example 11 (In Accordance with the Invention): Preparation of Isomerization Catalyst E Catalyst E is a catalyst comprising IZM-2 zeolite, platinum, and an alumina matrix. This catalyst is prepared by dry impregnation of the IZM-2 / alumina support prepared in Example 10 with an aqueous solution containing platinum tetramine nitrate Pt(NH3)4(NO3)2. 20 g of support is typically used and dry impregnated in a rotating barrel. After impregnation, the solid is left to age in laboratory air for at least 5 hours, then dried overnight in an oven at 110°C, and finally, a calcination step is carried out in a tubular oven under a flow of dry air (1 normal liter per hour and per gram of solid weight) under the following conditions: - Temperature ramp from room temperature to 150°C at 5°C / min, 1 hour stage at 150°C, - Temperature ramp from 150°C to 450°C at 5°C / min, 1 hour stage at 450°C, - Cool down to room temperature.

[0117] The Pt content, determined by XRF on the calcined catalyst, is 0.27 wt. % and its coefficient of distribution, determined by Castaing microprobe, is 0.96. The catalyst obtained is not subjected to a washing step with ammonium nitrate solution. The sodium content in the catalyst, determined by atomic absorption, is 89 ppm.

[0118] The textural properties of catalyst E were characterized by nitrogen porosimetry at 196 °C on a Micromeritics ASAP 2010 machine. Prior to nitrogen adsorption, the solid is degassed under vacuum at 90 °C for 1 hour and then at 350 °C for 4 hours. The total pore volume corresponds to the volume of nitrogen adsorbed at a relative pressure of 0.97. The specific surface area of ​​the solid was calculated by the BET method, and the pore median diameter, calculated according to the BJH adsorption model, corresponds to the diameter at which half the volume of nitrogen is adsorbed. Catalyst D has a specific surface area of ​​272 m 2 / g, the total pore volume is 0.67 mL / g, and the median diameter is 12 nm.

[0119] Example 12: Evaluation of the catalytic properties of catalysts A, B, C, D and E in the isomerization of an aromatic C8 fraction The catalyst was tested in the isomerization of an aromatic C8 fraction consisting of ethylbenzene (19 wt%), ortho-xylene (16 wt%), meta-xylene (58 wt%) and ethylcyclohexane (7 wt%). The tests were carried out in a microunit, which uses a fixed-bed reactor, operates in downflow and without recycle. Analysis of the hydrocarbon effluent is carried out online by gas chromatography. Before loading into the unit, the catalyst is first dried in an oven at 110°C for at least overnight. Once loaded into the unit, the catalyst undergoes a first drying step under nitrogen under the following conditions: Nitrogen flow rate: 5 normal liters per hour and per gram of catalyst weight, ·Total pressure: 1.3MPa, -Temperature rise rate from room temperature to 150℃: 10℃ / min Step at 150°C for 30 minutes.

[0120] After drying, the nitrogen is replaced by hydrogen and a step of reduction under a stream of high purity hydrogen is carried out under the following conditions: Hydrogen flow rate: 4 normal liters per hour and per gram of catalyst weight, ·Total pressure: 1.3MPa, Temperature increase rate from 150℃ to 480℃: 5℃ / min · Stage at 480°C for 2 hours.

[0121] The temperature is then reduced to 425° C. and the catalyst is then stabilized under a flow of hydrogen and hydrocarbon (a mixture of 20% by weight of ethylbenzene and 80% by weight of ortho-xylene) for 24 hours under the following operating conditions: Feed space velocity: 5 g of hydrocarbon per hour and per gram of catalyst weight; · Molar ratio of hydrogen to hydrocarbon: 4, ·Total pressure: 1.3MPa.

[0122] After the stabilization step, the temperature is reduced to 385°C and the catalyst is placed in contact with the above aromatic C8 fraction under the following conditions: Feed space velocity: 3.5 g of aromatic C8 fraction per hour and per gram of catalyst weight, · Molar ratio of hydrogen to hydrocarbon: 4, Total pressure: 0.86MPa.

[0123] The catalyst is maintained under these operating conditions for 7 hours, and then the catalyst performance quality is evaluated according to various operating conditions summarized in Table 2 below. Varying the feed space velocity makes it possible to vary the level of conversion to ethylbenzene and xylene isomerization, and therefore the production of para-xylene. For each operating condition, two chromatographic analyses are performed to measure the catalyst performance quality.

[0124] [Table 2]

[0125] Feedstock space velocity 12h -1 The yield of para-xylene (PX) in the hydrocarbon effluent obtained in makes it possible to evaluate the activity of the catalyst towards the production of para-xylene. PX = wt% para-xylene in hydrocarbon effluent where PX is the yield of para-xylene (wt%).

[0126] On the other hand, the change in the yield of net losses (NL) as a function of the yield of para-xylene allows the selectivity of the catalyst to be evaluated in part: all hydrocarbon molecules except cyclic molecules containing eight carbon atoms are considered net losses. NL=100-PX-EB-OX-MX-N8 where: NL: Net loss yield in hydrocarbon effluent (wt%); PX: wt% of para-xylene in the hydrocarbon effluent; EB: wt% of ethylbenzene in hydrocarbon effluent; OX: wt% of ortho-xylene in the hydrocarbon effluent; MX: weight percent meta-xylene in the hydrocarbon effluent; N8: Wt% of naphthenes containing 8 carbon atoms in the hydrocarbon effluent.

[0127] Table 3 therefore shows the results for a space velocity of 20 h -1 The para-xylene yields of catalysts A, B, C, D, and E at 18% para-xylene yield are reported, as well as the estimated net losses for the catalysts. The net losses (NL) at 18% para-xylene yield are estimated by linear interpolation or extrapolation of experimental data for the variation in yield of net losses as a function of para-xylene yield. It is observed that the five catalysts exhibit the same net losses, and therefore the same selectivity, for an 18% para-xylene yield. On the other hand, they differ in their activity: catalysts B, C, and E according to the invention, which have reduced sodium contents, have higher activities than catalysts A and D, which do not according to the invention.

[0128] [Table 3]

Claims

1. A catalyst for the isomerization of a fraction containing at least one aromatic compound containing 8 carbon atoms per molecule, comprising at least one IZM-2 zeolite, at least one matrix, and at least one metal from group VIII of the periodic table of the elements, wherein the total weight content of alkali metal and / or alkaline earth metal elements in said catalyst is less than 200 ppm by weight and more than 20 ppm by weight relative to the total mass of said catalyst.

2. 10. The catalyst of claim 1, comprising at least one Group VIII metal selected from iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum.

3. 3. The catalyst of claim 2, comprising at least one Group VIII metal selected from palladium and platinum, preferably platinum.

4. Catalyst according to any one of claims 1 to 3, comprising a content of group VIII metals ranging from 0.01% to 5% by weight relative to the total mass of the catalyst.

5. Catalyst according to any one of claims 1 to 4, wherein said matrix is ​​selected from the group formed by alumina, silica, silica-alumina, clay, titanium oxide, boron oxide and zirconia, used alone or in a mixture.

6. Catalyst according to any one of claims 1 to 5, having a total weight content of alkali metal and / or alkaline earth metal elements of less than 150 ppm by weight relative to the total mass of the catalyst.

7. 7. The catalyst according to claim 6, having a total weight content of alkali metal and / or alkaline earth metal elements of less than 100 ppm by weight relative to the total mass of the catalyst.

8. 8. The catalyst according to claim 7, having a total weight content of alkali metal and / or alkaline earth metal elements of less than 90 ppm by weight relative to the total mass of the catalyst.

9. 9. The catalyst according to claim 8, having a total weight content of alkali metals and / or alkaline earth metals of less than 80 ppm by weight relative to the total mass of the catalyst.

10. 10. The catalyst according to claim 9, having a total weight content of alkali metal and / or alkaline earth metal elements of less than 70 ppm by weight relative to the total mass of the catalyst.

11. Catalyst according to any one of claims 1 to 10, wherein the alkali metal and / or alkaline earth metal element is selected from lithium, sodium, potassium, beryllium, magnesium, barium and calcium, preferably sodium.

12. 12. A process for the isomerization of a fraction containing at least one aromatic compound containing 8 carbon atoms per molecule, comprising isomerizing said aromatic compound fraction with at least said catalyst according to any one of claims 1 to 11 under the following operating conditions: ・Temperature: 300℃~500℃, Hydrogen partial pressure: 0.3 to 1.5 MPa, Total pressure: 0.45 to 1.9 MPa, and Feed space velocity: expressed in kilograms of feed introduced per kilogram of catalyst weight per hour, from 0.25 to 30 h －１ placing the substrate in contact with the substrate.

13. 13. The isomerization process of claim 12, wherein the aromatics fraction containing at least one aromatic compound containing 8 carbon atoms per molecule comprises, as the aromatic compound containing 8 carbon atoms per molecule, either a mixture of xylenes only, or ethylbenzene only, or a mixture of xylene(s) and ethylbenzene.

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