Zeolite adsorbent for the separation of hydrocarbon isomers

Abstract

Zeolitic adsorbent for the separation of hydrocarbon isomers. The present invention relates to an agglomerated zeolitic adsorbent based on faujasite-type zeolite crystals (FAU), a zeolitic adsorbent comprising barium or barium and potassium, said adsorbent having a pore distribution satisfying the following inequalities: 1) [Math 30] 2) [Math 31] in which VmaHg denotes the macroporous 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 [Math 32] V2-3.6 = VmeN2 - VmeHg where 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 cm³.g⁻¹, and its preparation process. The invention also relates to the use of the zeolitic adsorbent agglomerate for the separation of hydrocarbon mixtures, as well as the process for separating hydrocarbon mixtures using said zeolitic adsorbent agglomerate.

Description

Title of the invention: Zeolitic adsorbent for the separation of hydrocarbon isomers. Technical field

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

[0002] The invention aims to improve the productivity of existing processes by modifying the nature of the adsorbent. The invention therefore relates to adsorbents based on agglomerated faujasite zeolite crystals, comprising barium or barium and potassium, and exhibiting a specific mesoporous distribution. These adsorbents exhibit improved selectivity properties for obtaining specific xylene isomers, and in particular high-purity para-xylene. Previous technique

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

[0004] High-purity paraxylene is produced by xylenes valorization using a process known as the "C8-aromatic loop," which includes separation steps (removal of heavy compounds in the "xylene column," extraction of paraxylene) and xylenes isomerization. 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 based primarily on the separation of paraxylene from a feed of aromatic hydrocarbons consisting mainly of 8 carbon atoms within an adsorber by contact with a zeolite adsorbent bed in the presence of a suitable desorption solvent (desorbant).

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

[0006] US patents 3558732 and 4255607 show that zeolitic adsorbents comprising potassium- or barium-based, or potassium- and barium-based, aluminosilicates are effective for separating para-xylene present in aro-sections C8 matics (cuts including aromatic hydrocarbons with 8 carbon atoms).

[0007] The general teaching on the chemical characteristics of these adsorbent solids is that it is necessary to use a zeolite of faujasite structure (zeolite X or Y) exchanged with barium (at least 90%, expressed as an exchange rate) or exchanged very predominantly with barium and in a minority 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 having 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] US patent 8735643 discloses an agglomerated adsorbent based on barium-exchanged LSX zeolite, and optionally potassium-exchanged zeolite. US patents 10913695 and 10745329 disclose agglomerated adsorbents based on barium- and potassium-exchanged X zeolite, which exhibit improved productivities depending on the cation content of the adsorbent.

[0011] Furthermore, in US patent 10940458, zeolite adsorbents in agglomerate form exhibit optimized properties for separating gaseous or liquid mixtures of isomers, with, in particular, maximum selectivity for para-xylene and mass transfer properties, while also displaying improved strength and high adsorption capacity per volume of adsorbent. This patent teaches that it is not desirable to significantly increase macroporosity and / or mesoporosity, and therefore grain porosity, because this porosity does not contribute to adsorption capacity. The optimization of diffusion properties and optimal adsorption capacities was obtained by specifically selecting both porosity and 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] The inventors found that mesoporosity, referred to as "small mesoporosity", ranging from 2 to 15 nm, and in particular the distribution of pore size in this specific range, had a direct impact on the selectivity for the isomer sought.

[0014] Generally, adsorbents used in xylene separation all exhibit macroporosity and mesoporosity. The small mesoporosity is usually neglected because it is difficult to measure. It can be

[0015]

[0016]

[0017] measured by comparing the mesoporosity measured by nitrogen adsorption and the mesoporosity measured by mercury intrusion porosimetry. Usually, one or the other measurement is performed, rarely both. 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 aromatic hydrocarbon feed containing 8-carbon isomers to be separated. The invention relates to agglomerated zeolitic adsorbents based on faujasite type zeolite crystals (FAU), zeolitic adsorbents comprising barium or barium and potassium and exhibiting selective behavior towards para-xylene present in the aromatic hydrocarbon feed containing 8-carbon isomers to be separated. The distinctive feature of this adsorbent is that it exhibits a mesoporous distribution that satisfies the following two inequalities: 1) [Math 1] Q < 2-3.6 VmaHÿ+ Vme / f, < 0.060 preferably [Math 2] q < VmaHg+ Vme^ < 0.050 more preferentially [Math 3] q 2) [Math 4] 0 K T; preferably [Math 5] q < U more preferentially [Math 6] q ---:--- < H 045 VmaHa+Vme^ ~ 2.0 V; v: Summary of the invention

[0018] Thus, and according to a first aspect, the invention relates to an agglomerated zeolite adsorbent based on faujasite type zeolite crystals (FAU), zeolite adsorbents comprising barium or barium and potassium, said adsorbent having a porous distribution satisfying the following two inequalities: 1) [Math7] 0 < --- < Q 060et VmaHÿ+ Vmex, ' 2) [Math 8] q < <25 ^3.6-15 in which VmaHg denotes the macroporous 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>615 corresponds to the mesoporous volume for pore sizes ranging from 3.6 nm to 15 nm, V2-3.6 is equal to [Math 9]: V2_3>6 = VmeN2 - VmeHg in which VmeHg denotes the mesoporous volume of the adsorbent measured by mercury intrusion porosimetry, V3.6-i5 is determined by the difference between the volume of mercury introduced at 15 nm and that introduced at 3.6 nm, volumes are expressed in cm3.g

[0019] In embodiments, the adsorbent according to the invention comprises one or several of the following additional features: - The porous distribution satisfies the following inequality: [Math 10] g < .......--- < 0 050 preferably [Math 11] g < < g ()45 and Vmang+ Vme^ ~ ' - The porous distribution satisfies the following inequality: [Math 12] q 2444 g preferably [Math 13] g 43,ms — —' -The agglomerated zeolite adsorbent has a Si / Al ratio greater than or equal to 1.0 and less than or equal to 3 (such that 1.0 < Si / Al < 3.0), in particular greater than or equal to 1.0 and less than or equal to 1.5 (1.0 < Si / Al < 1.5), preferably strictly greater than 1.0 and strictly less than 1.5, and advantageously the Si / Al ratio is between 1.1 and 1.4, inclusive. - 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 with an average number diameter 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 ISO 13322-2:2006, then calculated by applying ISO 9276-2:2001.

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

[0021] The invention also relates to the 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 sections, particularly 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 method for separating para-xylene from cuts of aromatic hydrocarbon isomers containing 8 carbon atoms, in liquid phase, by adsorption of para-xylene, comprising a step of bringing the feed into contact with a bed of agglomerated zeolitic adsorbent as defined above or capable of being prepared according to the method defined above, in the presence of a desorbent.

[0023] The invention also relates to a process for separating para-xylene from gaseous sections of aromatic hydrocarbon isomers containing 8 carbon atoms, by adsorption of para-xylene, comprising a step of contacting the feed with a bed of agglomerated zeolite adsorbent as defined above or capable of being prepared according to the process defined above, in the presence of a desorbent. Description of embodiments

[0024] The zeolite adsorbent of the invention comprises macropores, mesopores, and micropores. "Macropores" are defined as pores with an opening greater than 50 nm, preferably between 50 nm and 400 nm. "Mesopores" refers to pores with an opening between 2 nm and 50 nm, excluding these limits. "Micropores" refers to pores with an opening less than 2 nm.

[0025] As previously stated, the adsorbent according to the present invention is in the form of an agglomerated zeolitic adsorbent based on faujasite-type zeolite crystals (FAU), a zeolitic adsorbent comprising barium or barium and potassium, said adsorbent having a porous distribution satisfying the following two inequalities: 1) [Math 14] q < ......--- < 0 06() 2) [Math 15] 0 < < 2.5 ^3,6-)5 ' in which VmaHg denotes the macroporous 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, V3j6 i5 corresponds to the mesoporous volume for pore sizes ranging from 3.6 nm to 15 nm, V2-3.6 is equal to [Math 16]: V2-3.6 = VmeN2 - VmeHg in which VmeHg denotes the mesoporous volume of the adsorbent measured by mercury intrusion porosimetry, ¥3.6-15 is determined by the difference between the volume of mercury introduced at 15 nm and that introduced at 3.6 nm, volumes are expressed in cm3.g'. 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 3 (such as 1.0 < Si / Al < 3.0), in particular greater than or equal to 1.0 and less than or equal to 1.5 (1.0 < Si / Al < 1.5), preferably strictly greater than 1.0 and strictly less than 1.5, and advantageously the Si / Al ratio is between 1.1 and 1.4, inclusive.

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

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

[0029] The zeolite adsorbent agglomerates according to the present invention may contain a non-zeolite phase (NZP), that is to say, a non-crystalline phase that is essentially inert with respect to adsorption. The degree of crystallinity (zeolite mass fraction) 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 XRD.

[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 most 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 with 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%, preferably greater than 15%, most 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% inclusive, 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%, inclusive, by weight relative to the total mass of the adsorbent.

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

[0035] Advantageously, the agglomerated zeolite adsorbent is in the form of beads, preferably having an average diameter in number 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%, even more preferably between 3.5% and 6.5% and advantageously between 4.5% and 6%, inclusive.

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

[0038] The process for preparing the agglomerated zeolitic adsorbent as described above comprises at least the following steps: a) mixture of crystals of at least one faujasite zeolite, with an agglomerating binder containing at least 80%, preferably at least 90%, preferably still at least 95% by weight of zeolithizable clay, and possibly a source of silica, shaping of the resulting mixture, and firing at a temperature 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, preferably between 2 and 6 hours; bl) a first immersion step in an alkaline basic solution, of concentration between 0.2 M and 2 M, preferably between 0.2 M and 1 M inclusive, at a temperature between ambient temperature and 50°C, with a contact time between a few minutes and a few hours, preferably between 5 minutes and 3 hours; preferably the contact time is carried out at ambient temperature, for a duration between 30 minutes and 2 hours (inclusive); b2) at the end of this contacting step, a rapid temperature increase is imposed to go from ambient temperature to a temperature between 90°C and 105°C for a period of one second to less than one hour; b3) possible maintenance at a temperature above 90°C for 30 minutes to one hour; c) exchange of cations from the agglomerates (from steps b2) or b3) by contacting them with a solution of barium ions, or of barium ions and potassium ions, d) washing and drying of the zeolitic 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 zeolitic 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 scanning electron microscopy (SEM). As previously stated, preferably, the size (or average diameter of the crystals) can vary in large proportions and is generally less than or equal to 1.50 pm, 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.

[0040] This SEM observation confirms the presence of a non-zeolitic phase including, for example, residual binder (not converted during the zeolithization 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 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 eliminated by cycloning and / or sieving and / or the too large agglomerates by sieving or crushing, in the case of extrudates, for example.

[0044] The agglomerating binder used in step a) comprises, and preferably consists of, a clay or a mixture of clays. These clays are preferably selected 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 zeolithization step, the agglomerating binder used in step a) contains at least 80%, preferably at least 90%, preferably even at least 95%, and more particularly at least 96%, by weight, of at least one zeolithizable clay and may also contain other mineral binders such as bentonite, attapulgite, and others. Zeolithizable clay is understood to be a clay or a mixture of clays that are capable of being converted into zeolitic material, most often by the action of a basic alkaline solution. Zeolithizable clay generally belongs to the kaolin family (such as, for example, kaolinites, nacrites, dickites, halloysites) and / or the metakaolin family.

[0046] Among the additives possibly implemented in step a), one can find a source of silica of any type known to a person skilled in the art, specializing 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 improve hardening, as well as other known additives of The man of the trade.

[0048] In particular, the agglomerating binder containing at least 80% of one or more zeolitic clays, calcination allows the transformation of the zeolitic clay, typically kaolin, into meta-kaolin which can then be converted into zeolite during the zeolithization step (step b)). The principle is explained in "Zeolite Molecular Sieves" by D.W. Breck, John Wiley and Sons, New York, (1973), pp. 314-315.

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

[0050] The zeolithization stage comprises the following steps: bl) a first immersion step in an alkaline basic solution, with a concentration between 0.2 M and 2 M inclusive, with a contact time between ambient temperature and 50°C, preferably between 5 minutes and 3 hours; preferably the contact time is carried out at ambient temperature, for a duration between 30 minutes and 2 hours (inclusive), b2) Following this contact stage, a temperature increase is imposed from ambient temperature to a temperature between 90°C and 105°C, lasting from one second to less than one hour. b3) possibly maintaining the temperature above 90°C for 30 minutes to one hour.

[0051] Step b2) of temperature increase can be achieved by an external energy input 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 zeolithization. Preferably, step b2) lasts from a second to less than 30 minutes, more particularly from 2 seconds to less than 20 minutes, most preferably from 5 seconds to 15 minutes.

[0053] According to a preferred embodiment, step b2) is carried out by an external energy input of the microwave, ultrasound, electromagnetic induction, infrared 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, most preferably from 5 seconds to 15 minutes.

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

[0055] The cation exchange step(s) of step c) are carried out according to the classic methods known to those skilled in the art, and most often by bringing the agglomerates from step b) with a barium and / or potassium salt, such as barium chloride (BaCl2) and / or potassium chloride (KC1), in aqueous solution at a temperature between room temperature and 100°C, and preferably between 80°C and 100°C in order to rapidly obtain high barium contents, expressed as barium oxide, i.e. preferably above 10%, preferably above 15%, very preferably above 20%, even more preferably above 23%, or even above 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%, inclusive, by weight relative to the total weight of the adsorbent.

[0057] It is preferable 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%, inclusive, by weight relative to the total mass of the adsorbent.

[0059] The optional 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, by barium or potassium or barium and potassium ions before step a) and to dispense (or not) with step c).

[0060] After the cation exchange step(s), the resulting agglomerate is generally washed, preferably with water, and then 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 moisture content and loss on ignition. This duration can be between 1 and 6 hours.

[0062] The process may include one or more additional shaping steps carried out after any one of the steps a), bl), b2), c), d), e).

[0063] The zeolite adsorbent in the form of agglomerates according to the invention is particularly suitable for processes 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 separation processes in simulated moving bed liquid phase. The zeolitic adsorbent in the form of agglomerates according to the invention is particularly suitable for liquid phase xylene separation processes.

[0064] The agglomerated zeolitic adsorbent as defined above, or the agglomerated zeolitic adsorbent prepared according to the process as defined above, can also be used for: • separation of C8 aromatic isomer sections, particularly 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 simulated moving bed liquid phase separation processes, typically in processes for separating aromatic cuts comprising mixtures of aromatic isomers with 8 carbon atoms and more particularly in simulated moving bed liquid phase separation processes for xylenes, alone or coupled with a crystallization unit, and especially 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 fractions comprising mixtures of 8-carbon isomers in the liquid or gas phase. More particularly, the invention relates to the liquid-phase process for separating xylenes in a simulated moving bed, alone or coupled with a crystallization unit, and especially to the process for recovering high-purity para-xylene from fractions of 8-carbon aromatic isomers, as described, for example, in application WO2009081024, and in which at least one zeolite adsorbent in the form of agglomerates as described above is used. 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 toluene and para-diethylbenzene. Preferably, the process is carried out in a simulated moving bed, most preferably with simulated countercurrent flow.

[0068] The invention relates particularly to a process for producing para-xylene at high purity and high productivity from an aromatic hydrocarbon feed containing 8-carbon isomers comprising the following steps: 1) a step of contacting, under suitable adsorption conditions, the feed 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 removing the adsorbent bed from a stream containing the desorbent and the least selectively adsorbed feed products, 4) a step of drawing off the adsorbent bed from a stream containing the desorbent and paraxylene, 5) a step of separating the stream from step 3) into a first stream containing the desorbent and a second stream containing the least selectively adsorbed feed products, and 6) a step of separating the stream from step 4) into a first stream containing the desorbent and a second stream 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), allowing the production of, 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 totally, recycled by mixing with the fresh feed at the inlet of the simulated moving bed adsorption unit, and 8) a washing step of the crystals from step 7) at the end of which para-xylene is recovered with a purity of at least 99.7%, and preferably of at least 99.8%.

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

[0071] Simulated countercurrent moving bed chromatographic separation is well known in the prior 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 chromatographic zones, and possibly four or five, each of these zones consisting of at least one bed or a portion of a column and located between two successive feed or withdrawal points.

[0072] Typically, at least one charge to be fractionated and a desorbent (sometimes called an eluent) are fed in, and at least one raffinate and one extract are withdrawn. The feed and withdrawal points are modified over time, typically shifted downwards in a bed, and this is done 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, located between the extraction and the injection of the feed to be fractionated; • Zone 3 = adsorption zone of the desired product, located between the injection of the feedstock 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 -desorbent flow rate ratio 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 through the different beds of the adsorber and the feed injection rate into this adsorber.

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

[0076] The operating conditions of an industrial simulated co-current adsorption unit are generally the same as those operating with simulated counter-current, 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 with a boiling point lower than that of the filler, such as toluene, but also a desorbent with a boiling point higher than that of the filler, such as para-diethylbenzene (PDEB). CHARACTERIZATION TECHNIQUES

[0078] Si / Al molar 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. Among these techniques, one can cite the X-ray fluorescence chemical analysis technique as described in the standard NF EN ISO 12677: 2011 on a wavelength dispersive spectrometer (WDXRF), for example Tiger S 8 from the company Bruker.

[0080] X-ray fluorescence is a non-destructive spectral technique that exploits the photoluminescence of atoms in the X-ray range to determine the elemental composition of a sample. Excitation of atoms, generally by an X-ray beam or by bombardment with electrons, generates specific radiations after the atom returns to its ground state. The X-ray fluorescence spectrum has the advantage of being largely independent of the chemical composition of the element, thus providing a precise determination, both quantitative and qualitative. After calibration, a measurement uncertainty of less than 0.4% by weight is typically obtained for each oxide.

[0081] These elemental chemical analyses make it possible both to verify the Si / Al atomic ratio of the zeolite used within the agglomerate and the Si / Al atomic ratio of the final product obtained at the end of the steps described above, and to verify the quality of the ion exchange through the measurement of the oxide contents.

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

[0083] The quality of 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 mixture (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 mixture of barium oxide + potassium oxide (BaO + K₂O) and the number of moles of the mixture (BaO + K₂O + Na₂O). It should be noted that the contents of the 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 average number diameter of the zeolite crystals used in step a) and of the zeolite crystals contained in the agglomerates is carried out by observation with a scanning electron microscope (SEM).

[0086] To estimate the size (or average diameter) of the zeolite particles (i.e., crystals) in the samples, a series of photographs are taken at a magnification of at least 5000x. The diameter of at least 200 particles is then measured using dedicated software, for example, Smile View from the publisher LoGraMi. The accuracy is on the order of 3%. Measuring the histogram constructed from these diameter measurements simultaneously allows the standard deviation θ of its distribution to be determined.

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

[0088] Particle size distribution of zeolitic adsorbents:

[0089] The determination of the number average diameter of the zeolitic adsorbents obtained at the end of step a) of agglomeration and shaping is carried out by analysis of 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 terms "number-average diameter" or "size" are used for zeolite agglomerates. The accuracy is on the order of 0.01 mm for the size range of agglomerates of the invention.

[0091] Loss on ignition of zeolitic adsorbents:

[0092] 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] Volumetry is defined as follows: Vma is the macroporous volume encompassing the volumes of pores larger than 50 nm. Vme corresponds to the mesoporous volume, i.e., the volumes of pores ranging from 2 nm to 50 nm and Vmi is the microporous volume representing the volume of pores smaller than 2 nm.

[0095] Methodology for calculating volumes

[0096] In the present invention, we will primarily 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 from 3.6 nm to 50 nm, denoted VmeHg -Nitrogen adsorption, covering a pore size range from 2 nm to 50 nm. The volume obtained by t-plot analysis is noted VmeN2.

[0097] Here, we will use these two techniques known to the person 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: [Math 17] ^2-15= ^2-3.6+ ^3.6-15 In which V2_3j6 corresponds to the volume for pore sizes ranging from 2 nm to 3.6 nm and V3j6 i5 corresponds to the volume for pore sizes ranging from 3.6 nm to 15 nm. The 3.6-15 nm volume is defined by the difference in 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 performed the following calculations based on the two mesoporosity measurements indicated above: -V2 3.6 is obtained by subtracting the mesoporous volume from the mercury porosimetry measurement from that from the nitrogen adsorption measurement: [Math 18] ^2-3.6= VmeH?.

[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 gas adsorption isotherm, 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 and 16 hours under vacuum (P < 6.7 x 10⁴ Pa). The nitrogen adsorption isotherm at 77 K is then measured on a Micromeritics ASAP 2020 M instrument, 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 by 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 cm3 of liquid adsorbent per gram of anhydrous adsorbent.

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

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

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

[0108] The experimental method, described in the apparatus operating manual referring to ASTM D4284-83, consists of placing an adsorbent sample (zeolitic adsorbent in agglomerate form to be measured) (of known loss on ignition) previously weighed, in a porosimeter cell, then, after prior 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 increasing pressure in steps up to 400 MPa in order to gradually penetrate the mercury into the porous network of the sample, taking at least 15 pressure steps down 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 inlet threshold (corresponding to an apparent pore diameter) is established using the Laplace-Young equation and assuming a cylindrical pore opening, a contact angle between the 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 as a function of the applied pressure V(Pi), or as a function of the apparent pore diameter V(li). The volume V3j6-i5 is determined using the plot of the cumulative volume of mercury introduced as a function of the applied pressure V(Pi), or as a function of the apparent pore diameter V(li), by recording the value for the volume of 3.6 nm³ and the value for the volume of 15 nm³.The value at which mercury fills all intergranular voids is set at 0.2 MPa, and it is considered that beyond this point the mercury penetrates 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 volume cumulative mercury introduced at a pressure between 30 MPa and 400 MPa.

[0112] In this document, the macroporous and mesoporous volumes Vma and Vme of zeolitic adsorbents are expressed in cm3.g*, are thus measured by mercury intrusion porosimetry and referred to the mass of the sample in anhydrous equivalent, i.e. the mass of said adsorbent corrected for loss on ignition.

[0113] Technique for characterizing zeolites present by XRD

[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 XRD. This analysis is performed on a Bruker instrument on a sample of zeolitic adsorbent that has been previously ground and sieved (fraction less than 50 µm). The sample is saturated with water to ensure stability during the analysis. To achieve this, the sample is dried at 110°C in an oven, then placed, in a thin layer, in a closed chamber at 55% relative humidity and room temperature for a minimum of 48 hours. The analysis is performed by adding an internal standard (5% silicon certified as a 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 using TOPAS refinement software to obtain a precise measurement of the lattice parameter of the zeolites present in the adsorbent (within + / - 0.005 Å).

[0115] As a corollary, in the present invention, the term "non-zeolitic phase" (or "NWP") refers to any phase present in the adsorbent material, other than the zeolite(s) defined above, referred to as the "zeolitic phase" or "ZP". The quantity of non-zeolitic phase is expressed as the complement to 100% of the zeolitic phase of the adsorbent, in other words: [Math 19] %PNZ = 100 - %PZ, where %PNZ represents the weight percentage of PNZ and %PZ the weight percentage of zeolite phase, relative to the total weight of the adsorbent, %PZ representing the degree of crystallinity (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 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 piercing curves provides information on the quantities adsorbed and also allows for 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 estimating non-selective volumes.

[0119] The analysis of the dispersion (second moment) of the drilling curves, makes it possible to evaluate the equivalent height of theoretical stages, based on the representation of a column by a finite number of ideally stirred hypothetical 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 with respect to 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: [Math 20] 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 the said invention as claimed in the attached claims. EXAMPLES

[0123] Example 1 Comparative

[0124] This example reproduces a zeolite according to 1 comparator according to US application 2023 / 0219059

[0125] A homogeneous mixture is prepared, and 800 g of zeolite crystals with an average size (diameter) of 0.6 µm 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 wt% SiO2 and 0.5 wt% Na2O) with the amount of water necessary for extruding the mixture. The extrudates are dried, then calcined at 550°C (clay firing) under a stream of nitrogen for 2 hours, and finally crushed to obtain agglomerates with an average number diameter of 0.5 mm.

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

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

[0128] The agglomerates are exchanged by contacting them with a 0.5 M barium chloride solution at 95°C in four steps. At each step, the ratio of solution volume to solid mass is 20 mL / g, and the exchange is continued for four 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 two hours and finally activated at 250°C for two 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] [Tab 1] In cmVg VmeN2 VmeHg VmaHg Ex 1 0.044 0.021 0.243 Thus, the following characteristics can be calculated: V23.6 = VmeN2-VmeHg= 0.023 cmVg V3j6 i5 = 0.009 cmVg Mesoporous volumes are measured according to 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 a 0.8 M aqueous sodium hydroxide solution is added. The mixture is kept at room temperature for 1 hour. After this maturation time, the reactor is placed in a microwave cavity (1800 kW power) and heated to a temperature of 95°C for 4 minutes.

[0134] The reactor is then placed in a thermostatically controlled oscillating 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 draining the reactor. The effectiveness of the washing is verified by measuring the final pH of the wash water, which is between 10.0 and 10.5.

[0135] The agglomerates are exchanged by contacting them with a 0.5 M barium chloride solution at 95°C in four steps. At each step, the ratio of solution volume to solid mass is 20 mL / g, and the exchange is continued for four 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 two hours and finally activated at 250°C for two 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] [Tab 2] In cmVg VmeN2 VmeHg VmaHg Ex 2 0.027 0.015 0.260 Thus, the characteristics can be calculated: V23.6 = VmeN2-VmeHg= 0.012 cmVg V3j6 i5 = 0.009 cmVg

[0139] Mesoporous volumes are measured according to the techniques described above.

[0140] We can then calculate the mesoporous profiles of each of the adsorbents in the examples 1 and 2. The results are presented in Table 3 below:

[0141] [Table 3] [Math 21] [Math 22] VmanK+ Vmex, V VmeK, Ex 1 comparative 0.0816 2.75 Ex 2 according to the invention 0.0418 1.32

[0142] Example 3: Piercing test (frontal chromatography)

[0143] The Loss On Ignition (LOI) is adjusted for each sample to a value of 6.0%.

[0144] A penetration test (frontal chromatography) is then performed on these adsorbents to evaluate their effectiveness. The quantity of adsorbent used for this test is approximately 82 g.

[0145] 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. -Gradual rise to adsorption temperature under solvent flow (5 cmVmin). -Solvent injection at 10 cmVmin when the adsorption temperature is reached. -Solvent / charge exchange to inject the charge (10 cmVmin). -The injection of the charge is then maintained for a sufficient time to reach thermodynamic equilibrium. -Collection and analysis of drilling effluent.

[0146] The pressure is sufficient to keep the charge in the liquid phase, i.e., 1 MPa. The adsorption temperature is 175°C.

[0147] 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 estimating non-selective volumes and does not play a role in the separation).

[0148] An improvement in selectivity a PX / MX 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.

[0149] 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

Demands

1. Agglomerated zeolite adsorbent based on faujasite-type zeolite crystals (FAU), zeolite adsorbent comprising barium or barium and potassium, said adsorbent having a pore size distribution satisfying the following two inequalities: 1) [Math 23] 0 < .......--- < 0.060 Vmaff ^,+ Vmeff, ' 2) [Math 24] 0 < < 2.5 where VmaHg denotes the macroporous volume of the adsorbent measured by mercury intrusion porosimetry, VmeN2 denotes the mesoporous volume of the adsorbent measured by nitrogen adsorption, V2 ie corresponds to the mesoporous volume for pore sizes ranging from 2 nm to 3.6 nm, V3j6 i5 corresponds to the mesoporous volume for pore sizes ranging from 3.6 nm to 15 nm, V23.6 is equal to [Math 25] V23.6 = VmeN2 - VmeHg where VmeHg designates the mesoporous volume of the adsorbent measured by mercury intrusion porosimetry, V3j6_i5 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 cm3.g.

2. Zeolitic adsorbent according to claim 1, wherein the pore distribution satisfies the following inequality: [Math 26] 0 < .......--- < Q 05() preferably [Math 27] q < v / 2^,6 < q Vme^ ~ '

3. Zeolitic adsorbent according to claim 1 or 2, wherein the pore distribution satisfies the following inequality: [Math 28] 0 < < 2 0 * 3.6-J5 preferably [Math 29] q < ^2-3.6 < jg

4. Zeolitic adsorbent according to any one of claims 1 to 3, wherein the agglomerated zeolitic adsorbent has a Si / Al ratio greater than or equal to 1.0 and less than or equal to 3 (such that 1.0 < Si / Al < 3.0), in particular greater than or equal to 1.0 and less than or equal to 1.5 (1.0 < Si / Al < 1.5), preferably strictly greater than 1.0 and strictly less than 1.5, and advantageously the Si / Al ratio is between 1.1 and 1.

4.

5. Zeolitic adsorbent according to any one of claims 1 to 4, wherein the adsorbent comprises crystals of size less than or equal to 1.50 pm as measured by scanning electron microscopy, and preferably between 0.05 pm and 1.50 pm, preferably between 0.10 pm and 1.00 pm, most preferably between 0.10 pm and 0.80 pm and even more preferably between 0.30 pm and 0.80 pm.

6. Zeolitic adsorbent according to any one of claims 1 to 5, wherein it is in the form of a bead 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 ISO 13322-2:2006, then calculated by applying ISO 9276-2:2001.

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

8. The 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 isomers 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. A process for separating para-xylene from cuts of aromatic hydrocarbon isomers containing 8 carbon atoms, in liquid phase, by adsorption of para-xylene, comprising a step of contacting the feed with a bed of agglomerated zeolitic adsorbent as defined according to any one of claims 1 to 6 or capable of being prepared according to any one of claims 7 and 8, in the presence of a desorbent.

12. 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 contacting the feed with a bed of agglomerated zeolitic adsorbent as defined according to any one of claims 1 to 6 or capable of being prepared according to any 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 moving bed type.