Zeolite adsorbent for separating hydrocarbon isomers

Abstract

NOT VISIBLE DUE TO STATUS OF PATENT

Description

Zeolite adsorbent for the separation of hydrocarbon isomers TECHNICAL FIELD

[0001] The field of the invention is that of the production in liquid phase or gas phase of xylene isomers, and in particular of very pure para-xylene from a feedstock of aromatic hydrocarbons containing isomers with 8 carbon atoms.

[0002] The aim of the invention is to improve the productivity of existing processes by varying the nature of the adsorbent. The invention therefore relates to adsorbents based on agglomerated crystals of faujasite zeolite, comprising barium or barium and potassium and having a specific mesoporous distribution. These adsorbents have improved selectivity properties for obtaining specific xylene isomers and in particular high-purity para-xylene. PRIOR TECHNIQUE

[0003] The xylenes market, and in particular high-purity para-xylene, is considered to be a rapidly expanding market, its outlets being mainly the production of terephthalic acid (PTA) obtained by oxidation of paraxylene, the origin of polyester fibres used in particular for clothing and polyethylene terephthalate resins and films (PET).

[0004] High-purity paraxylene is produced by upgrading xylenes using a so-called "C8-aromatics loop" process, including separation steps (removal of heavy compounds in the "xylene column", extraction of paraxylene) and isomerization of xylenes. The extraction of high-purity paraxylene by selective adsorption is well known in the prior art. The technological background describing the production of paraxylene is illustrated in patent FR2681066, and is mainly based on the separation of paraxylene from a feedstock of aromatic hydrocarbons with essentially 8 carbon atoms. within an adsorber by contact with a bed of zeolite adsorbent in the presence of a suitable desorption solvent (desorbent).

[0005] The process of separating xylenes, for example in a simulated moving bed (SMB), has undergone numerous technological improvements, particularly in the fluid distribution trays, and also substantial developments in the chemical characteristics of the adsorbent solids.

[0006] Patents US3558732 and US4255607 show that zeolite adsorbents comprising potassium or barium-based aluminosilicates, or potassium and barium-based aluminosilicates, are effective for the separation of para-xylene present in C8 aromatic cuts (cuts comprising aromatic hydrocarbons with 8 carbon atoms).

[0007] The general lesson on the chemical characteristics of these adsorbent solids is that it is necessary to use a zeolite with a faujasite structure (zeolite X or Y) exchanged with barium (at least 90%, expressed in exchange rate) or exchanged very predominantly with barium and to a lesser extent with potassium (for example from 2 to 33%).

[0008] In particular, to increase the productivity of the separation process, the prior art teaches that one way is to improve the selectivity of the adsorbent for para-xylene.

[0009] To improve the adsorption selectivity of zeolites with the faujasite structure for C8 aromatic isomers, many studies have mentioned the influence of the Si / Al ratio of the zeolite, the nature of the exchange cations, as well as their water content.

[0010] Patent US8735643 discloses an agglomerated adsorbent based on LSX zeolite exchanged with barium and possibly potassium. Patents US10913695 and US10745329 also disclose agglomerated adsorbents based on X zeolite exchanged with barium and potassium, which exhibit improved productivities depending on the cation content present in the adsorbent.

[0011] Furthermore, in patent US10940458, zeolite adsorbents in the form of agglomerates have optimized properties for the separation of gaseous or liquid mixtures of isomers with in particular maximum properties of selectivity towards para-xylene and mass transfer, while with improved resistance and high adsorption capacity per volume of adsorbent. This patent teaches that it is not desirable to significantly increase macroporosity and / or mesoporosity, therefore grain porosity, because this porosity does not contribute to the adsorption capacity. Optimization of diffusion properties and optimal adsorption capacities were obtained by specifically selecting both the porosity and the tortuosity factor: conditions on the mesoporous volume noted Vmeso, a controlled tortuosity factor and a high adsorption capacity (grain porosity between 25-35% and Vmi / Vmeso+Vmacro+Vmi > 0.4).

[0012] Research is therefore being carried out on adsorbents, in order to improve their selectivity, their diffusion properties and their adsorption capacity for xylenes.

[0013] It was found by the inventors that mesoporosity, so-called "small mesoporosity", ranging from 2 to 15 nm, and in particular the pore size distribution in this specific range, had a direct impact on the selectivity for the desired isomer.

[0014] Generally, adsorbents used in xylene separation all exhibit macroporosity and mesoporosity. Small mesoporosity is generally neglected. Indeed, it is difficult to measure. It can be measured by comparing mesoporosity measured by nitrogen adsorption and mesoporosity measured by mercury intrusion porosimetry. Usually, one or the other measurement is performed, rarely both.

[0015] However, it was found that by selecting specific ratios of these mesopores in the range of 2 to 15 nm, the adsorbents exhibited a more selective behavior towards the desired xylene isomer present in the feedstock of aromatic hydrocarbons containing 8-carbon isomers to be separated.

[0016] The invention relates to agglomerated zeolite adsorbents based on faujasite (FAU) type zeolite crystals, zeolite adsorbents comprising barium or barium and potassium and exhibiting selective behavior with respect to para-xylene present in the feedstock of aromatic hydrocarbons containing isomers with 8 carbon atoms to be separated.

[0017] The particularity of this adsorbent is that it presents a mesoporous distribution which satisfies the following two inequalities: 0.050 more preferably 0 < - - < 0.045 Vma ig+ Vme^2 2) 2.5 preferably 0 < 1 / 2 ~ 3,6 < 2.0 more preferably 0 < 1 / 2 ~ 3,6 < 1.8. SUMMARY OF THE INVENTION

[0018] Thus, and according to a first aspect, the invention relates to an agglomerated zeolite adsorbent based on faujasite (FAU) type zeolite crystals, zeolite adsorbents comprising barium or barium and potassium, said adsorbent having a pore distribution meeting the following two inequalities: 1) 0.060 and 2) 2.5 in which VmaHg denotes the macropore volume of the adsorbent measured by mercury intrusion porosimetry, VmeN2 denotes the mesoporous volume of the adsorbent measured by nitrogen adsorption, V2-3.6 corresponds to the mesoporous volume for pore sizes ranging from 2 nm to 3.6 nm, V3.6-15 corresponds to the mesoporous volume for pore sizes ranging from 3.6 nm to 15 nm, V2-3.6 is equal to: V2-3.6 = VmeN2 - VmeHg in which VmeHg denotes the mesoporous volume of the adsorbent measured by mercury intrusion porosimetry, V3.6-15 is determined by the difference between the volume of mercury introduced at 15 nm and the one introduced at 3.6 nm, the volumes being expressed in cm 3 . g' 1 .

[0019] In embodiments, the adsorbent according to the invention comprises one or more of the following additional features: - the porous distribution responds to the following inequality: preferably 0.045 and - the porous distribution responds to the following inequality: 0 < 2.0, preferably 0 < 1.8 -the agglomerated zeolite adsorbent has a Si / AI ratio greater than or equal to 1.0 and less than or equal to 3 (such that 1.0 < Si / AI < 3.0), in particular greater than or equal to 1.0 and less than or equal to 1.5 (1.0 < Si / AI < 1.5), preferably strictly greater than 1.0 and strictly less than 1.5, and advantageously the Si / AI ratio is between 1.1 and 1.4, limits included - the adsorbent comprises crystals of size (or average diameter) less than or equal to 1.50 pm measured by observation under a scanning electron microscope, and preferably between 0.05 pm and 1.50 pm, preferably between 0.10 pm and 1.00 pm, preferably between 0.10 pm and 0.80 pm and even more preferably between 0.30 pm and 0.80 pm, -the adsorbent is in the form of beads having a number average diameter of between 0.1 mm and 2 mm, preferably between 0.3 mm and 2 mm, and in particular between 0.3 mm and 0.8 mm, determined by analysis of the particle size distribution of an agglomerate sample by imaging according to standard ISO 13322-2:2006, then calculated by applying standard ISO 9276-2:2001.

[0020] The invention also relates to a process for preparing a zeolitic adsorbent as defined above, comprising at least the following steps: a) mixing crystals of at least one faujasite zeolite, with an agglomeration binder containing at least 80%, by weight, of zeolithizable clay, and optionally a source of silica, shaping the mixture obtained, and firing at a temperature of between 500°C and 700°C, for a period of between a few minutes and a few hours, typically between 2 minutes and 12 hours, b1) a first step of immersion in an alkaline basic solution, with a concentration of between 0.2 M and 2 M, inclusive, at a temperature of between room temperature and 50°C, with a contact time of between a few minutes and a few hours, preferably between 5 minutes and 3 hours, b2) at the end of this contacting step, a temperature increase is imposed ranging from room temperature to a temperature of between 90°C and 105°C for a duration of one second to less than one hour, c) exchange of the cations of the agglomerates by contacting with a solution of barium ions, or barium ions and potassium ions, d) washing and drying the zeolite agglomerates thus obtained, and e) activation by heating of the zeolite adsorbent in the form of agglomerates obtained in step d), at a temperature of between 100°C and 400°C.

[0021] The invention also relates to a use of an adsorbent as defined above or capable of being prepared according to the process defined above, in the processes of: • separation of C8 aromatic isomer cuts and in particular xylenes, • separation of substituted toluene isomers such as nitrotoluene, diethyltoluene, toluenediamine, and others, • separation of cresols, • separation of polyhydric alcohols, for example sugars.

[0022] The invention also relates to a process for separating para-xylene from fractions of aromatic hydrocarbon isomers containing 8 carbon atoms, in the liquid phase, by adsorption of para-xylene, comprising a step of bringing the feedstock into contact with a bed of agglomerated zeolitic adsorbent as defined above or capable of being prepared according to the process defined above, in the presence of a desorbent.

[0023] The invention finally relates to a process for separating para-xylene from cuts of aromatic hydrocarbon isomers containing 8 carbon atoms, in the gas phase, by adsorption of para-xylene comprising a step of bringing the feedstock into contact with a bed of agglomerated zeolitic adsorbent as defined above or capable of being prepared according to the process defined above, in the presence of a desorbent. DESCRIPTION OF THE EMBODIMENTS

[0024] The zeolite adsorbent of the invention comprises both macropores, mesopores and micropores. By "macropores" is meant pores whose opening is greater than 50 nm, preferably between 50 nm and 400 nm. By "mesopores" is meant pores whose opening is between 2 nm and 50 nm, limits not included. By "micropores" is meant pores whose opening is less than 2 nm.

[0025] As indicated previously, the adsorbent according to the present invention is in the form of an agglomerated zeolite adsorbent based on faujasite (FAU) type zeolite crystals, a zeolite adsorbent comprising barium or barium and potassium, said adsorbent having a pore distribution corresponding to the following two inequalities: 0.060 2) 0 < < 2.5 V 3.6-1S in which VmaHg denotes the macropore volume of the adsorbent measured by mercury intrusion porosimetry, VmeN2 denotes the mesoporous volume of the adsorbent measured by nitrogen adsorption, V2-3.6 corresponds to the mesoporous volume for pore sizes ranging from 2 nm to 3.6 nm, V3.6-15 corresponds to the mesoporous volume for pore sizes ranging from 3.6 nm to 15 nm, X / 2-3.6 is equal to: X / 2-3.6 = VmeN2 - VmeHg in which VmeHg denotes the mesoporous volume of the adsorbent measured by mercury intrusion porosimetry, V3.6-15 is determined by the difference between the volume of mercury introduced at 15 nm and that introduced at 3.6 nm, the volumes being expressed in cm 3 . g -1 . The volumes are determined by characterization techniques defined below.

[0026] The agglomerated zeolite adsorbent comprises a faujasite type zeolite. Preferably, it has a Si / Al ratio greater than or equal to 1.0 and less than or equal to to 3 (such that 1.0 < Si / AI < 3.0), in particular greater than or equal to 1.0 and less than or equal to 1.5 (1.0 < Si / AI < 1.5), preferably strictly greater than 1.0 and strictly less than 1.5, and advantageously the Si / AI ratio is between 1.1 and 1.4, limits included.

[0027] The agglomerated zeolite adsorbent may comprise zeolite LSX (Low Silica X), MSX (Medium Silica X), X, faujasite Y and mixtures thereof. Preferably, the adsorbent comprises faujasite LSX, MSX or X and mixtures thereof, and more preferably MSX or X and mixtures thereof.

[0028] According to yet another preferred embodiment, the mass fraction of FAU zeolite is greater than or equal to 80% relative to the total weight of adsorbent of the present invention, the remainder to 100% preferably consisting of non-zeolitic phase.

[0029] The zeolite adsorbent agglomerates according to the present invention may contain a non-zeolitic phase (NZP), i.e. a non-crystalline phase which is essentially inert with respect to adsorption. The degree of crystallinity (mass fraction of zeolite) of the adsorbent according to the invention can be measured by X-ray diffraction analysis, known to those skilled in the art by the acronym DRX.

[0030] Preferably, the zeolite adsorbent agglomerates according to the present invention comprise a PNZ content of less than 20% by weight relative to the total weight of the agglomerate, preferably less than 10% by weight, more particularly less than 5% by weight, more particularly still less than 3% by weight, and very preferably less than 1% by weight.

[0031] The zeolite adsorbent of the invention is preferably in the form of an agglomerate, that is to say it is made up of crystals of at least one FAU zeolite as defined above, agglomerated using a binder, for example a clay which is preferably at least partly zeolithizable, said crystals having a size (or average diameter) less than or equal to 1.50 pm and preferably between 0.05 pm and 1.50 pm, preferably between 0.10 pm and 1.00 pm, preferably between 0.10 pm and 0.80 pm and even more preferably between 0.30 pm and 0.80 pm.

[0032] According to a preferred embodiment, the barium oxide (BaO) content in the agglomerated zeolite adsorbent according to the invention is greater than 10%, more preferably greater than 15%, very preferably greater than 20%, even more preferably greater than 23%, or even greater than 33% by weight relative to the total mass of the adsorbent. According to another preferred embodiment, said barium content is between 23% and 42%, and typically between 30% and 42%, advantageously between 33% and 42%, limits included, by weight relative to the total weight of the adsorbent.

[0033] According to another preferred embodiment, the potassium oxide (K2O) content in the agglomerated zeolite adsorbent according to the invention is less than 25%, preferably between 0 and 20%, even more preferably between 0 and 15%, limits included, by weight relative to the total mass of the adsorbent.

[0034] According to another embodiment of the invention, the total content of alkali or alkali-earth ion oxides other than barium oxide BaO and potassium oxide K2O is between 0 and 5%, limits included, relative to the total mass of the adsorbent.

[0035] Advantageously, the agglomerated zeolite adsorbent is in the form of beads, preferably having a number average diameter of between 0.1 mm and 2 mm, preferably between 0.3 mm and 2 mm, and in particular between 0.3 mm and 0.8 mm.

[0036] In one embodiment, the loss on ignition of the agglomerated zeolite adsorbent according to the invention, measured at 900°C according to standard NF EN 196 2, is less than or equal to 7.7%, preferably between 0 and 7.7%, preferably between 3.0% and 7.7%, more preferably between 3.5% and 6.5% and advantageously between 4.5% and 6%, limits included.

[0037] The invention also relates to the process for preparing the zeolite adsorbent.

[0038] The process for preparing the agglomerated zeolite adsorbent as described above comprises at least the following steps: a) mixing crystals of at least one faujasite zeolite, with an agglomeration binder containing at least 80%, preferably at least 90%, of preferably still at least 95% by weight of zeolithizable clay, and optionally a source of silica, shaping the mixture obtained, and firing at a temperature of between 500°C and 700°C, for a duration of between a few minutes and a few hours, typically between 2 minutes and 12 hours, preferably between 2 and 6 hours; b1) a first step of immersion in an alkaline basic solution, with a concentration of between 0.2 M and 2 M, preferably between 0.2 M and 1 M, inclusive, at a temperature of between room temperature and 50°C, with a contact time of between a few minutes and a few hours, preferably between 5 minutes and 3 hours; preferably the contact time is carried out at room temperature, for a duration of between 30 minutes and 2 hours (inclusive);b2) at the end of this contacting step, a rapid temperature increase is imposed to go from room temperature to a temperature between 90°C and 105°C for a period of one second to less than one hour; b3) optionally maintaining the temperature at a temperature above 90°C for 30 minutes to one hour; c) exchange of the cations of the agglomerates (from steps b2) or b3) by contacting with a solution of barium ions, or barium ions and potassium ions, d) washing and drying the zeolite agglomerates thus obtained, and e) activation by heating to a temperature generally between 100°C and 400°C, preferably between 200°C and 300°C of the zeolite adsorbent in the form of agglomerates obtained in step d).;

[0039] The size of the FAU zeolite crystals used in step a) and of the FAU zeolite crystals in the agglomerates according to the invention is measured by observation under a scanning electron microscope (SEM). As indicated above, preferably, the size (or average diameter of the crystals) can vary greatly and is generally less than or equal to 1.50 μm, preferably between 0.05 μm and 1.50 μm, preferably between 0.10 μm and 1.00 μm, preferably between 0.10 μm and 0.80 μm and more preferably between 0.30 μm and 0.80 μm.

[0040] This SEM observation makes it possible to confirm the presence of a non-zeolitic phase including, for example, residual binder (not converted during the zeolitization step) or any other amorphous phase in the agglomerates.

[0041] The proportions of agglomeration binder (see definition below) and zeolite used can be from 5 parts to 20 parts by weight of binder to 95 parts to 80 parts by weight of zeolite.

[0042] The agglomerates resulting from step a) generally have an average diameter, in number, of between 0.1 mm and 2 mm, preferably between 0.3 mm and 2 mm, and in particular between 0.3 mm and 0.8 mm in diameter.

[0043] At the end of step a), the finest agglomerates can be removed by cycloning and / or screening and / or the overly coarse agglomerates by screening or crushing, in the case of extrudates, for example.

[0044] The agglomeration binder used in step a) comprises, and preferably consists of, a clay or a mixture of clays. These clays are preferably chosen from kaolins, kaolinites, nacrites, dickites, halloysites, attapulgites, sepiolites, montmorillonites, bentonites, illites and metakaolins, as well as mixtures of two or more of them in any proportions.

[0045] In the zeolitization step, the agglomeration binder used in step a) contains at least 80%, preferably at least 90%, more preferably at least 95%, more particularly at least 96%, by weight, of at least one zeolitizable clay and may also contain other mineral binders such as bentonite, attapulgite, and others. By zeolitizable clay, we mean a clay or a mixture of clays which are capable of being converted into zeolitic material, most often by the action of an alkaline basic solution. The zeolitizable clay generally belongs to the family of kaolins (such as for example kaolinites, nacrites, dickites, halloysites) and / or metakaolins.

[0046] Among the additives possibly used in step a), there may be found a source of silica of any type known to those skilled in the art, specialists in the synthesis of zeolites, for example colloidal silica, diatoms, perlite, calcination ash (“fly ash” in English), sand, or any other form of solid silica.

[0047] In step a), in addition to the FAU zeolite crystals and the binder, other additives may also be added, for example additives intended to facilitate agglomeration or to improve hardening, as well as other additives known to those skilled in the art.

[0048] In particular, the agglomeration binder containing at least 80% of one or more zeolitizable clays, calcination makes it possible to transform the zeolitizable clay, typically kaolin, into meta-kaolin which can then be converted into zeolite during the zeolitization step (step b)). The principle is explained in "Zeolite Molecular Sieves" by DW Breck, John Wiley and Sons, New York, (1973), p. 314-315.

[0049] Step a) of mixing and shaping can be carried out using any technique known to those skilled in the art, alone or in combination, such as extrusion, compaction, agglomeration on a granulating plate, granulating drum, atomization and others.

[0050] The zeolitization step comprises the following steps: b1) a first step of immersion in an alkaline basic solution, with a concentration of between 0.2 M and 2 M, inclusive, with a contact time of between room temperature and 50°C, preferably of between 5 minutes and 3 hours; preferably the contact time is carried out at room temperature, for a duration of between 30 minutes and 2 hours (inclusive), b2) at the end of this contacting step, a temperature increase is imposed ranging from room temperature to a temperature of between 90°C and 105°C, ranging from one second to less than one hour, b3) possible maintenance at a temperature above 90°C for 30 minutes to one hour.

[0051] Step b2) of increasing the temperature can be carried out by supplying external energy such as microwaves, ultrasound, electromagnetic induction, infrared, heating or a combination thereof. Preferably, the external energy is supplied by microwaves, ultrasound, electromagnetic induction, infrared or a combination thereof.

[0052] Preferably, step b2) is very rapid, it is a flash zeolitization. Preferably, step b2) lasts from one second to less than 30 minutes, more particularly from 2 seconds to less than 20 minutes, very preferably from 5 seconds to 15 minutes.

[0053] According to a preferred embodiment, step b2) is carried out by an external energy supply of the microwave, ultrasound, electromagnetic induction, infrared type or a combination of these techniques, for a duration ranging from one second to less than 30 minutes, more particularly from 2 seconds to less than 20 minutes, very preferably from 5 seconds to 15 minutes.

[0054] After step b2) and / or step b3), washing can be carried out, preferably with water.

[0055] The cation exchange steps of step c) are carried out according to conventional methods known to those skilled in the art, and most often by bringing the agglomerates resulting from step b) into contact with a barium and / or potassium salt, such as barium chloride (BaCL) and / or potassium chloride (KCI), in aqueous solution at a temperature between room temperature and 100°C, and preferably between 80°C and 100°C in order to quickly obtain high barium contents, expressed as barium oxide, i.e. preferably greater than 10%, preferably greater than 15%, very preferably greater than 20%, even more preferably greater than 23%, or even greater than 33% by weight relative to the total mass of the adsorbent.

[0056] Advantageously, the barium content, expressed as barium oxide, is between 23% and 42%, and typically between 30% and 40%, limits included, by weight relative to the total weight of the adsorbent.

[0057] It is preferred to operate with a large excess of barium ions relative to the cations of the zeolite that one wishes to exchange, typically an excess of the order of 10 to 12, advantageously by proceeding by successive exchanges.

[0058] Preferably, the potassium oxide (K2O) content in the agglomerated zeolite adsorbent according to the invention is between 0 and 20%, even more preferably between 0 and 15%, limits included, by weight relative to the total mass of the adsorbent.

[0059] The possible potassium exchange can be carried out before and / or after the barium exchange. In one embodiment, it is possible to agglomerate in step a) FAU zeolite crystals already containing barium or potassium or barium and potassium ions (pre-exchange of the cations present in the starting FAU type zeolite, typically sodium cations, with barium or potassium or barium and potassium ions before step a) and to avoid (or not) step c).

[0060] After the cation exchange step(s), washing is generally carried out, preferably with water, then the resulting agglomerate is dried.

[0061] The activation following drying is carried out in a conventional manner, according to methods known to those skilled in the art, for example at a temperature generally between 100°C and 400°C, preferably between 200°C and 300°C for a duration determined according to the desired water content and loss on ignition. This duration may be between 1 hour and 6 hours.

[0062] The method may comprise one or more additional shaping steps carried out after any of steps a), b1), b2), c), d), e).

[0063] The zeolite adsorbent in the form of agglomerates according to the invention is particularly suitable for processes for separating compounds in the liquid phase, and in particular for processes in which said material is subjected to significant mechanical stresses, for example co-current or counter-current liquid phase separation processes, and more particularly liquid phase separation processes in a simulated moving bed. The zeolite adsorbent in the form of agglomerates according to the invention is particularly suitable for processes for separating xylenes in the liquid phase.

[0064] The agglomerated zeolite adsorbent as defined above or the agglomerated zeolite adsorbent prepared according to the process as defined above can also be used for: • separation of aromatic isomer cuts in Cs and in particular xylenes, • separation of substituted toluene isomers such as nitrotoluene, diethyltoluene, toluenediamine, and others, • separation of cresols, • separation of polyhydric alcohols, for example sugars.

[0065] Thus, and according to yet another aspect, the present invention relates to the use of at least one zeolitic adsorbent in the form of agglomerates as just defined, as an adsorbent material in liquid or gas phase separation processes, co-current or counter-current, and more particularly in liquid phase separation processes in a simulated moving bed, typically in processes for separating aromatic cuts comprising mixtures of aromatic isomers with 8 carbon atoms and more particularly in liquid phase processes for separating xylenes in a simulated moving bed, alone or in coupling with a crystallization unit, and very particularly in processes for recovering high-purity para-xylene from cuts of aromatic isomers with 8 carbon atoms.

[0066] Finally, the invention also relates to the process for separating aromatic cuts comprising mixtures of isomers with 8 carbon atoms in the liquid or gas phase. The invention relates more particularly to the liquid phase process for separating xylenes in a simulated moving bed, alone or in coupling with a crystallization unit, and more particularly to the process for recovering high-purity para-xylene from cuts of aromatic isomers with 8 carbon atoms, as for example described in application WO2009081024, and in which at least one zeolitic adsorbent is used in the form of agglomerates as described above. The process is carried out in the presence of a desorbent, preferably chosen from toluene and para-diethylbenzene.

[0067] The invention also relates to the gas phase process for separating xylenes in a simulated moving bed, by adsorption of a xylene isomer, preferably para-xylene, using an adsorbent as described above in the presence of a desorbent, preferably chosen from toluene and para-diethylbenzene. Preferably, the process is carried out in a simulated moving bed, very preferably in a simulated countercurrent manner.

[0068] The invention particularly relates to a process for producing high purity and high productivity para-xylene from an aromatic hydrocarbon feedstock containing 8-carbon isomers comprising the following steps: 1) a step of bringing into contact, under suitable adsorption conditions, the charge with an adsorbent bed according to the invention, so as to preferentially adsorb paraxylene, 2) a step of bringing the adsorbent bed into contact, under desorption conditions, with a desorbent, which is preferably either toluene or para-diethylbenzene, 3) a step of withdrawing from the adsorbent bed a flow containing the desorbent and the least selectively adsorbed feed products, 4) a step of withdrawing from the adsorbent bed a flow containing the desorbent and the paraxylene, 5) a step of separating the flow from step 3) into a first flow containing the desorbent and a second flow containing the least selectively adsorbed load products, and 6) a step of separating the flow from step 4) into a first flow containing the desorbent and a second flow containing paraxylene at a purity level greater than or equal to 75% and preferably greater than or equal to 99.7%.

[0069] The process may also optionally include the following steps: 7) a crystallization step in a crystallizer consisting of the crystallization of the paraxylene from step 6), making it possible to obtain, on the one hand, paraxylene crystals soaked in their mother liquor, and on the other hand, a mother liquor which can be partly, or even entirely, recycled in a mixture with the fresh feed at the inlet of the simulated moving bed adsorption unit, and 8) a step of washing the crystals from step 7) at the end of which para-xylene is recovered with a purity of at least 99.7%, and preferably at least 99.8%.

[0070] The desired product can thus be separated by preparative adsorption liquid chromatography (in "batch"), advantageously in a simulated moving bed, i.e. with simulated countercurrent or simulated cocurrent, and more particularly with simulated countercurrent.

[0071] Simulated countercurrent moving bed chromatographic separation is well known in the art. Typically, a simulated moving bed separation unit comprises at least one adsorption column containing a plurality of beds of an adsorbent, interconnected in a closed loop. The simulated moving bed separation unit has at least three zones chromatographic, and possibly four or five, each of these zones being constituted by at least one bed or a portion of column and included between two successive feed or withdrawal points.

[0072] Typically, at least one fractionation feed and one desorbent (sometimes called eluent) are fed and at least one raffinate and one extract are withdrawn. The feed and withdrawal points are changed over time, typically shifted towards the bottom of a bed and synchronously.

[0073] By definition, each of the operating zones is designated by a number • Zone 1 = desorption zone of the desired product (contained in the extract) between the injection of the desorbent and the sampling of the extract; • Zone 2 = desorption zone of the raffinate compounds, between the extraction of the extract and the injection of the charge to be fractionated; • Zone 3 = adsorption zone of the desired product, between the injection of the feed and the withdrawal of the raffinate, and; • Zone 4 located between the raffinate withdrawal and the desorbent injection.

[0074] The operating conditions of a simulated counter-current type industrial adsorption unit are generally as follows: -number of beds 6 to 30 -number of zones at least 4 -temperature 100 to 250°C, preferably 150 to 190°C -pressure between the bubble pressure of xylenes at the process temperature and 3 MPa - ratio of desorbent flow rates to charge 0.7 to 2.5 (for example 0.9 to 1.8 for a stand-alone adsorption unit and 0.7 to 1.4 for an adsorption unit combined with a crystallization unit) - recycling rate of 2.5 to 12, preferably 3.5 to 6. The recycling rate is defined as the ratio between the average flow rate flowing in the different beds of the adsorber and the charge injection rate in this adsorber

[0075] Reference may be made to the teaching of patents US2985589, US5284992 and US5629467.

[0076] The operating conditions of a simulated co-current industrial adsorption unit are generally the same as those operating in simulated counter-current mode, with the exception of the recycling rate, which is generally between 0.8 and 7. Reference may be made to patents US4402832 and US4498991.

[0077] The desorption solvent can be a desorbent whose boiling point is lower than that of the feed, such as toluene, but also a desorbent whose boiling point is higher than that of the feed, such as para-diethylbenzene (PDEB). CHARACTERIZATION TECHNIQUES

[0078] Si / Al atomic ratio and oxide contents:

[0079] An elemental chemical analysis of the final product can be carried out using various analytical techniques known to those skilled in the art. These techniques include the X-ray fluorescence chemical analysis technique as described in standard NF EN ISO 12677: 2011 on a wavelength dispersive spectrometer (WDXRF), for example Tiger S8 from Bruker.

[0080] X-ray fluorescence is a non-destructive spectral technique that exploits the photoluminescence of atoms in the X-ray range to establish the elemental composition of a sample. The excitation of atoms, generally by an X-ray beam or by bombardment with electrons, generates specific radiation after returning to the ground state of the atom. The X-ray fluorescence spectrum has the advantage of depending very little on the chemical combination of the element, which offers a precise determination, both quantitative and qualitative. A measurement uncertainty of less than 0.4% by weight is typically obtained after calibration for each oxide.

[0081] These elementary chemical analyses make it possible to both verify the Si / AI atomic ratio of the zeolite used in the agglomerate and the Si / AI atomic ratio of the final product obtained at the end of the steps described previously, and to verify the quality of the ionic exchange by measuring the oxide contents.

[0082] In the description of the present invention, the measurement uncertainty of the Si / Al atomic ratio measured after is ± 0.2 in relative%.

[0083] The quality of the ion exchange is related to the number of moles of sodium oxide, Na2O, remaining in the zeolite agglomerate after exchange. More precisely, the exchange rate by barium ions is estimated by evaluating the ratio between the number of moles of barium oxide, BaO, and the number of moles of the whole (BaO + Na2O). Similarly, the exchange rate by barium and / or potassium ions is estimated by evaluating the ratio between the number of moles of the whole barium oxide + potassium oxide (BaO + K2O) and the number of moles of the whole (BaO + K2O + Na2O). It should be noted that the contents of different oxides are given as a percentage by weight relative to the total weight of the anhydrous zeolite adsorbent.

[0084] Size / Granulometry of zeolite crystals:

[0085] The estimation of the number-average diameter of the zeolite crystals used in step a) and of the zeolite crystals contained in the agglomerates is carried out by observation under a scanning electron microscope (SEM).

[0086] In order to estimate the size (or average diameter) of the zeolite particles (i.e. crystals) on the samples, a set of images is taken at a magnification of at least 5000. The diameter of at least 200 particles is then measured using dedicated software, for example the Smile View software from the LoGraMi publisher. The accuracy is around 3%. The measurement of the histogram formed from the said diameter measurements simultaneously allows the determination of the standard deviation o of its distribution.

[0087] This scanning electron microscope (SEM) observation of zeolite crystals also makes it possible to distinguish the crystalline structures of zeolites (LSX, MSX, X).

[0088] Granulometry of zeolite adsorbents:

[0089] The determination of the number-average diameter of the zeolite adsorbents obtained at the end of step a) of agglomeration and shaping is carried out by analyzing the particle size distribution of an agglomerate sample by imaging according to ISO 13322-2:2006, using a conveyor belt allowing the sample to pass in front of the camera lens.

[0090] The number average diameter is then calculated from the particle size distribution by applying ISO 9276-2:2001. In this document, the term "number average diameter" or "size" is used for zeolite agglomerates. The accuracy is of the order of 0.01 mm for the agglomerate size range of the invention.

[0091] Loss on ignition of zeolite adsorbents:

[0092] The loss on ignition is determined in an oxidizing atmosphere, by calcining the sample in air at a temperature of 900°C ± 25°C, following the procedure described in standard NF EN 196-2 (April 2006). The standard deviation of measurement is less than 0.1%.

[0093] Porous volumes

[0094] The volume is defined as follows: Vma is the macroporous volume grouping the volumes of pores greater than 50 nm, Vme corresponds to the mesoporous volume, i.e. the pore volumes ranging from 2 nm to 50 nm and Vmi is the micropore volume representing the volume of pores smaller than 2 nm.

[0095] Volume calculation methodology

[0096] In the present invention, we will mainly focus on the constitution of the Vme. It is known to those skilled in the art that the Vme can be determined by two distinct analyses: -mercury porosimetry, covering pore sizes ranging from 3.6 nm to 50 nm, noted VmeHg -nitrogen adsorption, covering a pore size range from 2 nm to 50 nm. The volume obtained by t-plot analysis is denoted VmeN2.

[0097] Here, we will use these two techniques known to those skilled in the art to observe an area ranging from 2 nm to 15 nm, said area is called small mesoporosity and its volume is called V2-15. The V2-15 is separated into two volumes according to the equation: ^2-15 = ^2-3.6 + ^3.6-15 In which X / 2-3.6 corresponds to the volume for pore sizes ranging from 2 nm to 3.6 nm and V3.6-15 corresponds to the volume for pore sizes ranging from 3.6 nm to 15 nm. The volume 3.6-15 nm is defined by the difference in the volume of mercury introduced at a pressure of 400 MPa (pressure corresponding to pores of 3.6 nm) and that introduced at a pressure of 100 MPa (pressure corresponding to pores of 15 nm) measured by mercury porosimetry.

[0098] To determine their value, we carried out the following calculations from the two mesoporosity measurements previously indicated: -X / 2-3.6 is obtained by subtracting the mesoporous volume from the mercury porosimetry measurement from that from the nitrogen adsorption measurement: 72-3.6 = Vme N2 - Vme Hg .

[0099] Characterization of mesoporous volumes by nitrogen adsorption:

[0100] Mesoporous volumes for pore sizes from 2 nm to 50 nm VmeN2 are determined from the measurement of the adsorption isotherm of gases, such as nitrogen, at its liquefaction temperature.

[0101] Prior to adsorption, the sample is degassed between 300°C and 450°C for a period of between 9 hours and 16 hours, under vacuum (P < 6.7.10 4 Pa). The measurement of the nitrogen adsorption isotherm at 77K is then carried out on a Micromeritics ASAP 2020 M type device, taking at least 35 measurement points at relative pressures with a P / P0 ratio between 0.002 and 1.

[0102] The mesoporous volumes VmeN2 are determined from the isotherm obtained, by the t-plot method applying the ISO 15901-3:2007 standard and calculating the statistical thickness t by the Harkins-Jura equation.

[0103] They are obtained by linear regression on the points of the t-plot between 0.35 nm and 0.60 nm, respectively from the ordinate at the origin and the slope of the linear regression.

[0104] They are expressed in cm 3 of liquid adsorbent per gram of anhydrous adsorbent.

[0105] The characterization of microporous volumes is carried out by nitrogen adsorption using the same method as that of mesoporous volumes described above.

[0106] Characterization of macroporous Vma and mesoporous Vme volumes, by mercury intrusion porosimetry.

[0107] A Micromeritics Autopore® 9500 mercury porosimeter is used to analyze the distribution of pore volume contained in macropores and mesopores.

[0108] The experimental method, described in the operating manual of the device referring to the ASTM D4284-83 standard, consists of placing a sample of adsorbent (zeolite adsorbent in the form of agglomerates to be measured) (of known loss on ignition) previously weighed, in a cell of the porosimeter, then, after a preliminary degassing (evacuation pressure of 30 pm of mercury for at least 10 minutes), to fill the cell with mercury at a given pressure (0.0036 MPa), and then to apply an increasing pressure in stages up to 400 MPa in order to gradually penetrate the mercury into the porous network of the sample, taking at least 15 pressure stages up to 0.2 MPa, and then applying increments of 0.1 MPa up to 1 MPa, then 0.5 MPa up to 10 MPa, then 2 MPa up to 30 MPa, then 5 MPa up to 180 MPa, and finally 10 MPa up to 400 MPa.

[0109] The relationship between the applied pressure and the characteristic dimension of the pore entrance threshold (corresponding to an apparent pore diameter) is established using the Laplace-Young equation and assuming a cylindrical pore opening, a contact angle between mercury and the pore wall of 140° and a mercury surface tension of 485 dynes cm' 1 . The volume increments AVi of mercury introduced at each pressure step Pi are recorded, which then allows the cumulative volume of mercury introduced to be plotted against the applied pressure V(Pi), or against the apparent pore diameter V(li). The volume V3.6-15 is determined using the plot of the cumulative volume of mercury introduced against the applied pressure V(Pi), or against the apparent pore diameter V(li) by recording the value for the 3.6 nm volume and the value for the 15 nm volume. The value at which the mercury fills all intergranular voids, and beyond this it is considered that mercury penetrates into the pores of the adsorbent.

[0110] The macroporous volume Vma of the adsorbent is defined as the cumulative volume of mercury introduced at a pressure between 0.2 MPa and 30 MPa, corresponding to the volume contained in pores with an apparent diameter greater than 50 nm.

[0111] The mesoporous volume Vme of the adsorbent is defined as the cumulative volume of mercury introduced at a pressure between 30 MPa and 400 MPa.

[0112] In this document, the macroporous and mesoporous volumes Vma and Vme of zeolite adsorbents are expressed in cm 3 . g' 1 , are thus measured by mercury intrusion porosimetry and reported to the mass of the sample in anhydrous equivalent, i.e. the mass of said adsorbent corrected for the loss on ignition.

[0113] Technique for characterizing zeolites present by DRX

[0114] The zeolites present in the adsorbent and their lattice parameter are characterized by X-ray diffraction analysis, known to those skilled in the art by the acronym DRX. This analysis is carried out on a Bruker device on a sample of zeolite adsorbent previously ground and sieved (fraction less than 50 pm). The sample is saturated with water so as to be stable for the duration of the analysis. To do this, the sample is dried at 110°C in an oven, then placed, in a thin layer, in a closed chamber at a relative humidity of 55% at room temperature, for a minimum of 48 hours. The analysis is carried out by adding an internal standard (5% silicon certified in lattice parameter), over an angular range (in °20) between 5° 20 and 72° 20, with an angular step (in °) of 0.02°.The data are processed with the TOPAS refinement software, to obtain a measurement of the lattice parameter of the zeolites present in the adsorbent with precision (to + / - 0.005 Å).

[0115] As a corollary, in the present invention, the term "non-zeolitic phase" (or "PNZ") designates any phase present in the adsorbent material, other than the zeolite(s) defined above, called "zeolitic phase" or "PZ". The quantity of non-zeolitic phase is expressed by the complement to 100% of the zeolitic phase of the adsorbent, in other words: %PNZ = 100 - %PZ where %PNZ represents the percentage by weight of PNZ and %PZ the percentage by weight of zeolite phase, relative to the total weight of the adsorbent, %PZ representing the crystallinity rate (mass fraction of zeolite) of the adsorbent measured by X-ray diffraction (XRD) analysis.

[0116] Characterization of liquid phase adsorption by drilling:

[0117] The technique used to characterize the adsorption of molecules in the liquid phase on a porous solid is the so-called breakthrough technique, described by Ruthven in "Principles of Adsorption and Adsorption Processes" (John Wiley & Sons, (1984), Chapters 8 and 9) which defines the breakthrough curve technique as the study of the response to the injection of a step of adsorbable constituents.

[0118] Analysis of the mean exit time (first moment) of the breakthrough curves provides information on the adsorbed quantities and also allows the evaluation of selectivities, i.e. the separation factor, between two adsorbable constituents. The injection of a non-adsorbable constituent used as a tracer is recommended for the estimation of non-selective volumes.

[0119] The analysis of the dispersion (second moment) of the drilling curves allows to evaluate the equivalent height of theoretical plates, based on the representation of a column by a finite number of hypothetical ideally stirred reactors (theoretical stages), which is a direct measure of the axial dispersion and the resistance to mass transfer of the system.

[0120] Definition of selectivity

[0121] The selectivity aA / B of the adsorbent for a component A over a compound B is defined as the ratio of the concentrations of the compounds in the adsorbed phase divided by the ratio of the concentrations of the compounds in the non-adsorbed phase at equilibrium according to the following formula: aA / B = Aads / Bads x Bliq / Aliq in which Aads and Bads are the concentrations of compound A and compound B in the adsorbed phase respectively and Aliq and Bliq are the concentrations of compound A and compound B in the fluid phase.

[0122] The present invention is now described with the aid of the following examples, which are intended to illustrate certain embodiments of the invention, without however limiting the scope of said invention, as claimed in the appended claims. EXAMPLES

[0123] Example 1 Comparison

[0124] This example reproduces a zeolite according to 1 comparison according to application US2023 / 0219059

[0125] A homogeneous mixture is prepared and 800 g of zeolite crystals with a size (average diameter) of 0.6 pm are agglomerated with 145 g of kaolin (expressed as calcined equivalent) and 55 g of colloidal silica sold under the trade name Klebosol™ 30N50 (containing 30% by weight of SiO2 and 0.5% by weight of Na2O) with the quantity of water that allows the extrusion of the mixture. The extrudates are dried, then calcined at 550°C (firing of the clay) under a stream of nitrogen for 2 hours, and finally crushed so as to recover agglomerates with a number average diameter of 0.5 mm.

[0126] The agglomerates obtained as described above (20 g) are placed in a glass reactor equipped with a double jacket regulated at a temperature of 95°C ± 1°C, then 250 mL of an aqueous sodium hydroxide solution with a concentration of 1.25 M are added, and the reaction medium is left stirring for a period of 4 hours.

[0127] The agglomerates are then washed in 3 successive water washing operations followed by emptying the reactor. The effectiveness of the washing is ensured by measuring the final pH of the wash water, which is between 10.0 and 10.5.

[0128] The agglomerates are exchanged by contact with a 0.5 M barium chloride solution at 95°C in 4 stages. At each stage, the ratio of volume of solution to mass of solid is 20 mL.g' 1 and the exchange is continued for 4 hours each time. Between each exchange, the solid is washed several times to remove excess salt. The agglomerates are then dried at 80°C for 2 hours and finally activated at 250°C for 2 hours under a stream of nitrogen.

[0129] The percentage of barium oxides in this adsorbent is 35.1%.

[0130] The comparative adsorbent has the following characteristics shown in Table 1:

[0131] Table 1 Thus, the following characteristics can be calculated: X / 2-3.6 = VmeN2 -VmeHg = 0.023 cm 3 / g V3.6-15 = 0.009 cm 3 / g Mesoporous volumes are measured using the techniques described above.

[0132] Example 2 according to the invention

[0133] The agglomerates of Example 1 are placed at room temperature in a glass reactor and then 450 mL of an aqueous solution of sodium hydroxide with a concentration of 0.8M are added. The mixture is kept in contact at room temperature for 1 hour. After this maturation time, the reactor is placed in a microwave cavity (power 1800 kW) and then heated to achieve a rise to a temperature of 95°C for 4 minutes.

[0134] The reactor is then placed in an oscillating thermostatic bath and maintained at a temperature of 95°C for 1 hour. The agglomerates are then washed in 3 successive water washing operations followed by emptying the reactor. The effectiveness of the washing is ensured by measuring the final pH of the wash water, which is between 10.0 and 10.5.

[0135] The agglomerates are exchanged by contact with a 0.5 M barium chloride solution at 95°C in 4 stages. At each stage, the ratio of volume of solution to mass of solid is 20 mL.g' 1 and the exchange is continued for 4 hours each time. Between each exchange, the solid is washed several times to remove excess salt. The agglomerates are then dried at 80°C for 2 hours and finally activated at 250°C for 2 hours under a stream of nitrogen.

[0136] The percentage of barium oxides in this adsorbent is 35.6%.

[0137] The adsorbent according to the invention has the following characteristics shown in Table 2:

[0138] Table 2 Thus, the characteristics can be calculated: X / 2-3.6 = VmeN2 - VmeHg = 0.012 cm 3 / g V3.6-15 = 0.009 cm 3 / g Mesoporous volumes are measured using the techniques described above.

[0139] The mesoporous profiles of each of the adsorbents in Examples 1 and 2 can then be calculated. The results are presented in Table 3 below:

[0140] Table 3

[0141] Example 3: Piercing test (frontal chromatography)

[0142] The Loss on Ignition (LOI) for each sample is adjusted to a value of 6.0%.

[0143] A breakthrough test (frontal chromatography) is then carried out on these adsorbents to evaluate their effectiveness. The quantity of adsorbent used for this test is approximately 82 g.

[0144] The procedure for obtaining the drilling curves is as follows: - Filling the column with the sieve and placing it in the test bench. - Filling with the solvent at room temperature. -Progressive rise to the adsorption temperature under solvent flow (5 cm 3 / min). -Solvent injection at 10 cm 3 / min when the adsorption temperature is reached. -Solvent / charge permutation to inject the charge (10 cm 3 / min). -The injection of the charge is then maintained for a sufficient time to reach thermodynamic equilibrium. -Collection and analysis of drilling effluent.

[0145] The pressure is sufficient for the charge to remain in the liquid phase, i.e. 1 MPa. The adsorption temperature is 175°C.

[0146] The composition of the charge is as follows: Paraxylene: 45% by weight Metaxylene: 45% by weight Iso-octane: 10% by weight (this is used as a tracer for non-selective volume estimation and is not involved in the separation).

[0147] An improvement in PX / MX selectivity between the agglomerate according to example 1 and the agglomerate according to example 2 of 5% was observed, which represents a significant gain in productivity on an industrial scale.

[0148] These results show that the adsorbent according to the invention having the claimed mesoporous distribution leads to a clear improvement in selectivity for meta-xylene.

Claims

Claims 1. Agglomerated zeolite adsorbent based on faujasite (FAU) type zeolite crystals, zeolite adsorbent comprising barium or barium and potassium, said adsorbent having a pore distribution meeting the following two inequalities: 1) 0.060 2) 2.5 in which VmaHg denotes the macropore volume of the adsorbent measured by mercury intrusion porosimetry, VmeN2 denotes the mesoporous volume of the adsorbent measured by nitrogen adsorption, V2-3.6 corresponds to the mesoporous volume for pore sizes ranging from 2 nm to 3.6 nm, V3.6-15 corresponds to the mesoporous volume for pore sizes ranging from 3.6 nm to 15 nm, X / 2-3.6 is equal to X / 2-3.6 = VmeN2 - VmeHg in which VmeHg denotes the mesoporous volume of the adsorbent measured by mercury intrusion porosimetry, V3.6-15 is determined by the difference between the volume of mercury introduced at 15 nm and that introduced at 3.6 nm, the volumes being expressed in cm 3 .g' 1 .

2. Zeolite adsorbent according to claim 1, in which the pore distribution satisfies the following inequality: preferably 0.045 3. Zeolite adsorbent according to claim 1 or 2, wherein the pore distribution satisfies the following inequality: 2.0 preferably 0 < K2 ~ 3 ' 6 < 1.8 4. Zeolite adsorbent according to any one of claims 1 to 3, wherein the agglomerated zeolite adsorbent has a Si / AI ratio greater than or equal to 1.0 and less than or equal to 3 (such that 1.0 < Si / AI < 3.0), in particular greater than or equal to 1.0 and less than or equal to 1.5 (1.0 < Si / AI < 1.5), preferably strictly greater than 1.0 and strictly less than 1.5, and advantageously the Si / AI ratio is between 1.1 and 1.

4.

5. Zeolite adsorbent according to any one of claims 1 to 4, in which the adsorbent comprises crystals of a size less than or equal to 1.50 pm measured by observation under a scanning electron microscope, and preferably between 0.05 pm and 1.50 pm, preferably between 0.10 pm and 1.00 pm, preferably between 0.10 pm and 0.80 pm and even more preferably between 0.30 pm and 0.80 pm.

6. Zeolite adsorbent according to one of claims 1 to 5, in which it is in the form of a ball having a number average diameter of between 0.1 mm and 2 mm, preferably 0.3 mm and 2 mm, and in particular between 0.3 mm and 0.8 mm, determined by analysis of the particle size distribution of an agglomerate sample by imaging according to standard ISO 13322-2:2006, then calculated by applying standard ISO 9276-2:2001.

7. Process for preparing a zeolitic adsorbent according to one of claims 1 to 6 comprising at least the following steps: a) mixing crystals of at least one faujasite zeolite, with an agglomeration binder containing at least 80%, by weight of zeolithizable clay, and optionally a source of silica, shaping the mixture obtained, and firing at a temperature between 500°C and 700°C, for a period between 2 minutes and 12 hours, b1) a first step of immersion in an alkaline basic solution, of concentration between 0.2 M and 2 M, limits inclusive, at a temperature between room temperature and 50°C, with contact time included a few minutes and a few hours, preferably between 5 minutes and 3 hours, b2) at the end of this contacting step, a temperature increase is imposed ranging from room temperature to a temperature between 90°C and 105°C for a duration of one second to less than one hour, c) exchange of the cations of the agglomerates by contacting with a solution of barium ions, or barium ions and potassium ions, d) washing and drying the zeolite agglomerates thus obtained, and e) activation by heating of the zeolite adsorbent in the form of agglomerates obtained in step d), at a temperature between 100°C and 400°C.

8. Method according to claim 7, characterized in that it comprises, after step b2), a step b3) of maintaining the adsorbent in the solution at a temperature above 90°C for 30 minutes to 1 hour.

9. Use of an adsorbent according to any one of claims 1 to 6, or according to claim 7 or 8, in the processes of: • separation of C8 aromatic isomer cuts and in particular xylenes, • separation of substituted toluene isomers such as nitrotoluene, diethyltoluene, toluenediamine, and others, • separation of cresols, • separation of polyhydric alcohols.

10. Use according to claim 9, for the separation of para-xylene from cuts of aromatic isomers with 8 carbon atoms.

11. Process for separating para-xylene from isomer cuts of aromatic hydrocarbons containing 8 carbon atoms, in liquid phase, by adsorption of para-xylene, comprising a step of bringing the feedstock into contact with a bed of agglomerated zeolitic adsorbent as defined according to one of claims 1 to 6 or capable of being prepared according to one of claims 7 and 8, in the presence of a desorbent.

12. Process for the separation of para-xylene from fractions of aromatic hydrocarbon isomers containing 8 carbon atoms, in the gas phase, by adsorption of the para-xylene comprising a step of bringing the feedstock into contact with a bed of agglomerated zeolitic adsorbent as defined according to one of claims 1 to 6 or capable of being prepared according to one of claims 7 and 8, in the presence of a desorbent.

13. Method according to claim 11 or 12, characterized in that the bed is of the simulated mobile bed type.