Zeolite adsorbents for separating hydrocarbon isomers

Abstract

This invention relates to a zeolite adsorbent aggregate containing octahedral zeolite (FAU) zeolite crystals, the zeolite adsorbent comprising barium, or comprising barium and potassium, said adsorbent having a pore size distribution corresponding to inequalities (1) and (2), wherein Vma Hg Vme represents the macropore volume of the adsorbent measured by mercury porosimetry. N2 V represents the mesopore volume of the adsorbent measured by nitrogen adsorption. 2‑3.6 For mesopore volumes corresponding to pore sizes ranging from 2 nm to 3.6 nm, V 3.6‑15 For mesopore volumes corresponding to pore sizes ranging from 3.6 nm to 15 nm, V 2‑3.6 equals V 2‑3.6 =Vme N2 -Vme Hg Vme Hg V represents the mesopore volume of the adsorbent measured by mercury porosimetry. 3.6‑15 The volume was determined by the difference between the mercury volume introduced at 15 nm and the mercury volume introduced at 3.6 nm, expressed in cm³. 3 .g ‑1 This invention also relates to a method for preparing the adsorbent agglomerates. Furthermore, this invention relates to the use of the zeolite adsorbent agglomerates for separating hydrocarbon mixtures, and a method for separating hydrocarbon mixtures using the zeolite adsorbent agglomerates.

Description

Technical Field

[0001] This invention belongs to the field of producing xylene isomers in the liquid or gas phase, particularly producing very high purity para-xylene from aromatic feedstocks containing 8 carbon atoms.

[0002] The object of this invention is to improve the productivity of existing methods by acting on the properties of the adsorbent. Therefore, this invention relates to adsorbents based on aggregated octahedral zeolite-type zeolite crystals, comprising barium or comprising barium and potassium, and exhibiting a specific mesoporous distribution. These adsorbents exhibit improved selectivity to obtain specific xylene isomers, particularly high-purity p-xylene.

[0003] Existing technology

[0004] The xylene market, especially the high-purity para-xylene market, is considered a rapidly expanding market. Its main outlet is the production of terephthalic acid (PTA) obtained from the oxidation of para-xylene. PTA is the source of polyester fibers, polyethylene terephthalate (PET) resin, and films, which are mainly used in clothing.

[0005] High-purity p-xylene is produced by upgrading xylene according to a so-called "C8-aromatic ring" method, which includes a separation step (removal of heavy compounds in a "xylene tower" to extract p-xylene) and xylene isomerization. The selective adsorption extraction of high-purity p-xylene is well known in the prior art. The technical background describing p-xylene production is illustrated in patent FR2681066, and is primarily based on the separation of p-xylene from an aromatic feedstock, mainly having eight carbon atoms, in an adsorber in the presence of a suitable desorption solvent (desorbent) by contacting the feedstock in the form of a zeolite adsorbent bed.

[0006] Xylene separation methods, such as those in simulated moving bed (SMB), have undergone many technological improvements, particularly in fluid distribution discs, and significant advancements have been made in the chemical properties of the adsorbent solids.

[0007] Patents US3558732 and US4255607 demonstrate that zeolite adsorbents containing potassium- or barium-based, or potassium- and barium-based aluminosilicates, are effective for separating p-xylene present in aromatic C8 fractions (fractions containing aromatics having 8 carbon atoms).

[0008] The general teaching regarding the chemical properties of these adsorbent solids is that zeolites with an octahedral zeolite structure (zeolite X or Y) should be used, which are exchanged with barium (at least 90%, expressed as exchange rate), or the majority of the exchanged material is barium and a small amount is potassium (e.g., 2% to 33%).

[0009] In particular, in order to improve the productivity of separation methods, the prior art teaches a method that involves improving the selectivity of the adsorbent for p-xylene.

[0010] To improve the adsorption selectivity of zeolites with octahedral zeolite structures for aromatic C8 isomers, many studies have mentioned the influence of the Si / Al ratio of zeolites, the properties of exchange cations, and their water content.

[0011] Patent US8735643 discloses an agglomerating adsorbent based on LSX zeolite exchanged with barium and possibly potassium. Patents US10913695 and US10745329 also disclose agglomerating adsorbents based on X zeolite exchanged with barium and potassium, which exhibit improved productivity depending on the cation content present in the adsorbent.

[0012] Furthermore, in patent US10940458, zeolite adsorbents in aggregate form exhibit optimized properties for separating isomeric gas or liquid mixtures, particularly with maximum selectivity and mass transfer relative to p-xylene, while also exhibiting improved tolerance and high adsorption capacity per volume of adsorbent. This patent teaches that a significant increase in macroporosity and / or mesoporosity, i.e., particle porosity, is undesirable, as this porosity does not contribute to adsorption capacity. Optimization of diffusion properties and optimal adsorption capacity are achieved through specific selection of both porosity and tortuosity factor: conditions for mesopore volume Vmeso, a controlled tortuosity factor, and high adsorption capacity (particle porosity between 25-35% and Vmi / Vmeso+Vmacro+Vmi > 0.4).

[0013] Therefore, research is underway on adsorbents to improve their selectivity, their diffusion properties, and their adsorption capacity for xylene.

[0014] The inventors have discovered that mesoporous ratios, which are referred to as "small mesoporous ratios" and range from 2 to 15 nm, and especially the pore size distribution within this specific range, have a direct impact on the selectivity of the desired isomers.

[0015] Typically, adsorbents used in xylene separation possess both macropores and mesopores. Small mesopores are usually neglected; indeed, they are difficult to measure. They can be measured by comparing the mesopore rate measured via nitrogen adsorption and the mesopore rate measured via mercury intrusion porosimetry. Usually, one or the other measurement is performed, and rarely both.

[0016] However, it has been found that by selecting a specific ratio of these mesopores in the range of 2 to 15 nm, the adsorbent exhibits a higher selectivity relative to the target xylene isomer present in the aromatic feedstock to be separated (which contains an 8-carbon isomer).

[0017] This invention relates to agglomerated zeolite adsorbents based on octahedral zeolite (FAU) zeolite crystals, the zeolite adsorbents comprising barium, or comprising barium and potassium, and exhibiting selectivity relative to p-xylene present in the aromatic feedstock to be separated (which contains isomers having 8 carbon atoms).

[0018] The adsorbent is unique in that it exhibits a mesoporous distribution that satisfies the following two inequalities:

[0019] Preferred

[0020] More

[0021] Preferred

[0022] More . Summary of the Invention

[0023] Therefore, according to a first aspect, the present invention relates to an agglomerated zeolite adsorbent based on octahedral zeolite (FAU) type zeolite crystals, said zeolite adsorbent comprising barium or comprising barium and potassium, said adsorbent exhibiting a pore distribution satisfying the following two inequalities. and

[0024] in

[0025] Vma Hg This represents the macropore volume of the adsorbent as measured by mercury porosimetry. Vme N2 This represents the mesopore volume of the adsorbent as measured by nitrogen adsorption. V 2-3.6 This corresponds to mesopore volumes with pore sizes ranging from 2 nm to 3.6 nm. V 3.6-15 This corresponds to mesopore volumes with pore sizes ranging from 3.6 nm to 15 nm. V 2-3.6 Equal to: V 2-3.6 = Vme N2 - Vme Hg Vme Hg This represents the mesopore volume of the adsorbent as measured by mercury porosimetry. V 3.6-15 The value was determined by the difference between the mercury volume introduced at 15 nm and the mercury volume introduced at 3.6 nm. Volume in cm3 .g -1 express.

[0026] In some embodiments, the adsorbent according to the invention comprises one or more of the following additional features: - The pore distribution satisfies the following inequality:

[0027] Preferred and

[0028] - The pore distribution satisfies the following inequality: Preferred

[0029] - Agglomerated zeolite adsorbents exhibit a Si / Al ratio greater than or equal to 1.0 and less than or equal to 3 (e.g., 1.0 ≤ Si / Al ≤ 3.0), particularly 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, including the extreme values. - The adsorbent comprises crystals with a size (or average diameter) less than or equal to 1.50 µm (measured by scanning electron microscopy), and preferably between 0.05 µm and 1.50 µm, more preferably between 0.10 µm and 1.00 µm, more preferably between 0.10 µm and 0.80 µm, and even more preferably between 0.30 µm and 0.80 µm. - The adsorbent is in the form of beads with a number-average diameter between 0.1 mm and 2 mm, preferably between 0.3 mm and 2 mm, and particularly between 0.3 mm and 0.8 mm. The particle size distribution of the aggregated sample is determined by imaging analysis according to standard ISO 13322-2:2006 and then by calculation using standard ISO 9276-2:2001.

[0030] The present invention also relates to a method for preparing a zeolite adsorbent as defined above, comprising at least the following steps: a) Mixing crystals of at least one octahedral zeolite with an agglomerating binder comprising at least 80% by weight of clay suitable for zeolite synthesis and a possible silicon source, molding the resulting mixture, and firing it at a temperature between 500°C and 700°C for a period of several minutes to several hours, typically between 2 minutes and 12 hours. b1) A first soaking step in an alkaline base solution with a concentration between 0.2M and 2M (inclusive), a soaking temperature between ambient temperature and 50°C, and a contact time between several minutes and several hours, preferably 5 minutes to 3 hours. b2) At the end of this contact step, the temperature is raised from ambient temperature to a temperature between 90°C and 105°C over a period of one second to less than one hour. c) Exchange of cations in aggregates by contact with a molar barium solution, or by contact with a molar barium and a molar potassium solution. d) The zeolite agglomerates thus obtained are washed and dried, and e) Activation is performed by heating the zeolite adsorbent in the form of aggregates obtained in step d) at a temperature between 100°C and 400°C.

[0031] The present invention also relates to the use of adsorbents as defined above, or adsorbents that can be prepared according to the above methods, in the following methods: • Separate aromatic isomers with 8 carbon atoms, especially xylene. • Separate substituted toluene isomers, such as nitrotoluene, diethyltoluene, and toluene diamine. • Separate cresol • Separate polyols, such as sugars.

[0032] The present invention also relates to a method for separating p-xylene from an aromatic isomer fraction containing eight carbon atoms (in the liquid phase) by adsorption of p-xylene, comprising the step of contacting the feedstock with an agglomerated zeolite adsorbent bed as defined above, or an agglomerated zeolite adsorbent bed that can be prepared according to the above method, in the presence of a desorbent.

[0033] Finally, the present invention relates to a method for separating p-xylene from an aromatic isomer fraction containing eight carbon atoms (in the gas phase) by adsorption of p-xylene, comprising the step of contacting the feedstock with a bed of agglomerated zeolite adsorbent as defined above, or a bed of agglomerated zeolite adsorbent that can be prepared according to the above method, in the presence of a desorbent. Detailed Implementation

[0034] The zeolite adsorbent of the present invention comprises macropores, mesopores, and micropores. "Macropores" refers to 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 the extreme values). "Micropores" refers to pores with an opening less than 2 nm.

[0035] As previously stated, the adsorbent according to the present invention takes the form of an aggregated zeolite adsorbent based on octahedral zeolite (FAU) zeolite crystals, and is a zeolite adsorbent containing barium, or containing both barium and potassium, wherein the adsorbent exhibits a pore distribution that satisfies the following two inequalities.

[0036] in

[0037] Vma Hg This represents the macropore volume of the adsorbent as measured by mercury porosimetry. Vme N2 This represents the mesopore volume of the adsorbent as measured by nitrogen adsorption. V 2-3.6 This corresponds to mesopore volumes with pore sizes ranging from 2 nm to 3.6 nm. V 3.6-15 This corresponds to mesopore volumes with pore sizes ranging from 3.6 nm to 15 nm. V 2-3.6 Equal to: V 2-3.6 = Vme N2 - Vme Hg Vme Hg This represents the mesopore volume of the adsorbent as measured by mercury porosimetry. V 3.6-15 The value was determined by the difference between the mercury volume introduced at 15 nm and the mercury volume introduced at 3.6 nm. Volume in cm 3 .g -1 The volume is indicated. The volume is determined using the characterization techniques defined below.

[0038] Agglomerated zeolite adsorbents include octahedral zeolite-type zeolites. Preferably, they exhibit a Si / Al ratio greater than or equal to 1.0 and less than or equal to 3 (e.g., 1.0 ≤ Si / Al ≤ 3.0), particularly 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, including the extreme values.

[0039] Agglomerated zeolite adsorbents may comprise zeolites LSX (low-silica X), MSX (medium-silica X), X, Y octahedral zeolite, and mixtures thereof. Preferably, the adsorbent comprises octahedral zeolite LSX, MSX, or X, and mixtures thereof; more preferably, MSX or X, and mixtures thereof.

[0040] According to yet another preferred embodiment, the mass fraction of FAU zeolite is greater than or equal to 80%, and the balance is preferably made up to 100% by non-zeolite phase relative to the total weight of the adsorbent of the present invention.

[0041] The zeolite adsorbent aggregates according to the present invention may contain a non-zeolite phase (NZP), i.e., an amorphous phase that is essentially inert to adsorption. The crystallinity (mass fraction of zeolite) of the adsorbent according to the present invention can be measured by X-ray diffraction analysis, the abbreviation of which is known to those skilled in the art.

[0042] Preferably, the zeolite adsorbent agglomerates according to the invention contain less than 20% by weight of NZP, preferably less than 10% by weight, more particularly less than 5% by weight, even more particularly less than 3% by weight, and very preferably less than 1% by weight, relative to the total weight of the agglomerates.

[0043] The zeolite adsorbent of the present invention preferably exists in the form of aggregates, i.e., it consists of crystals of at least one FAU zeolite as defined above, aggregated using a binder (e.g., clay, preferably at least partially clay suitable for zeolite synthesis), wherein the crystals exhibit a size (or average diameter) less than or equal to 1.50 µm, preferably between 0.05 µm and 1.50 µm, more preferably between 0.10 µm and 1.00 µm, more preferably between 0.10 µm and 0.80 µm, and even more preferably between 0.30 µm and 0.80 µm.

[0044] According to a preferred embodiment, the barium oxide (BaO) content in the agglomerated zeolite adsorbent according to the invention is greater than 10% by weight, preferably also greater than 15% by weight, very preferably greater than 20% by weight, even more preferably greater than 23% by weight, or even greater than 33% by weight, relative to the total mass of the adsorbent. According to another preferred embodiment, the barium content is between 23% by weight and 42% by weight, and typically between 30% by weight and 42% by weight, advantageously between 33% by weight and 42% by weight (inclusive), relative to the total weight of the adsorbent.

[0045] According to another preferred embodiment, the potassium oxide (K2O) content in the agglomerated zeolite adsorbent according to the invention is less than 25% by weight, preferably between 0 and 20% by weight, and even more preferably between 0 and 15% by weight (including the extreme values), relative to the total mass of the adsorbent.

[0046] According to another embodiment of the invention, the total content of alkali metal or alkaline earth metal oxides other than barium oxide (BaO) and potassium oxide (K2O) is between 0% and 5% (inclusive) relative to the total mass of the adsorbent.

[0047] Advantageously, the agglomerated zeolite adsorbent is in the form of beads, preferably with an average diameter between 0.1 mm and 2 mm, more preferably between 0.3 mm and 2 mm, and particularly between 0.3 mm and 0.8 mm.

[0048] In one embodiment, the loss on ignition of the agglomerated zeolite adsorbent according to the invention, measured at 900°C according to standard NF EN196-2, is less than or equal to 7.7%, preferably between 0 and 7.7%, more preferably between 3.0% and 7.7%, more preferably between 3.5% and 6.5%, and advantageously between 4.5% and 6% (including the extreme values).

[0049] This invention also relates to a method for preparing zeolite adsorbents.

[0050] The method for preparing the agglomerated zeolite adsorbent as described above includes at least the following steps: a) Mixing crystals of at least one octahedral zeolite with an agglomerating binder (which contains at least 80% by weight, preferably at least 90% by weight, more preferably at least 95% by weight of clay suitable for zeolite synthesis) and a possible silicon source, molding the resulting mixture, and firing it at a temperature between 500°C and 700°C for a few minutes to a few hours, typically 2 minutes to 12 hours, preferably 2 to 6 hours. b1) A first soaking step in an alkaline base solution, wherein the concentration of the alkaline base solution is between 0.2M and 2M, preferably between 0.2M and 1M (inclusive), the temperature is between room temperature and 50°C, and the contact time is between a few minutes and a few hours, preferably between 5 minutes and 3 hours; preferably, the contact time at room temperature is 30 minutes to 2 hours (inclusive). b2) At the end of the contact step, apply a rapid temperature rise from room temperature to a temperature between 90°C and 105°C, with a rise time of one second to less than one hour. b3) Optionally, maintain at a temperature above 90°C for 30 minutes to one hour; c) Exchange the cations of the aggregates obtained in (step b2) or b3) by contacting them with a solution of barium ions, or a solution of barium and potassium ions. d) The zeolite agglomerates thus obtained are washed and dried, and e) Activation is carried out by heating the zeolite adsorbent in the form of aggregates obtained in step d) at a temperature typically between 100°C and 400°C, preferably between 200°C and 300°C.

[0051] The size of the FAU zeolite crystals used in step a) and the size of the FAU zeolite crystals in the aggregates according to the invention were observed and measured by scanning electron microscopy (SEM). As described above, preferably, the size (or average diameter) of the crystals can vary over a wide range and is generally less than or equal to 1.50 µm, preferably between 0.05 µm and 1.50 µm, more preferably between 0.10 µm and 1.00 µm, more preferably between 0.10 µm and 0.80 µm, and even more preferably between 0.30 µm and 0.80 µm.

[0052] This SEM observation allows for the confirmation of the presence of a non-zeolite phase within the aggregates, which may contain, for example, residual binders (not converted during the zeolization step) or any other amorphous phase.

[0053] The ratio of the agglomerating binder (see definition below) to the zeolite can be from 5 to 20 parts by weight of binder to 95 to 80 parts by weight of zeolite.

[0054] The aggregates obtained in step a) typically have a number-average diameter between 0.1 mm and 2 mm, preferably between 0.3 mm and 2 mm, and particularly between 0.3 mm and 0.8 mm.

[0055] At the end of step a), the finest agglomerates may be removed by cyclone separation and / or sieving, and / or excessively large agglomerates may be removed by sieving or crushing (e.g. for extrudates).

[0056] The agglomerating binder used in step a) comprises clay or a mixture of clays, and is preferably composed of clay or a mixture of clays. These clays are preferably selected from kaolin, kaolinite, pearl clay, dickite, halloysite, attapulgite, sepiolite, montmorillonite, bentonite, illite, and metakaolin, as well as mixtures of two or more of them in any proportion.

[0057] In the zeolization step, the agglomerating binder implemented in step a) comprises at least 80% by weight, preferably at least 90% by weight, more preferably at least 95% by weight, and more particularly at least 96% by weight, of at least one clay suitable for zeolite synthesis, and may also contain other mineral binders such as bentonite, attapulgite, etc. Clay suitable for zeolite synthesis refers to clay or clay mixtures capable of being converted into zeolite materials, most commonly through the action of an alkaline base solution. Clays suitable for zeolite synthesis typically belong to the kaolinite group (e.g., kaolinite, perlite, dickite, halloysite) and / or metakaolinite group.

[0058] Among the additives that may be used in step a), there may be any type of silicon source known to those skilled in the art (zeolite synthesis experts), such as colloidal silica, diatomaceous earth, perlite, calcined ash ("fly ash"), sand, or any other form of solid silica.

[0059] During step a), in addition to FAU zeolite crystals and binder, other additives may be added, such as additives designed to promote agglomeration or improve hardening, as well as other additives known to those skilled in the art.

[0060] Specifically, an agglomerating binder containing at least 80% of one or more clays suitable for zeolite synthesis is used, and calcination allows the clay (typically kaolin) suitable for zeolite synthesis to be converted into metakaolin, which can then be converted into zeolite during the zeolization step (step b). The principle is explained in DW Breck's "Zeolite Molecular Sieves", John Wiley and Sons, New York, (1973), pp. 314-315.

[0061] The mixing and molding steps a) can be performed individually or in combination according to all techniques known to those skilled in the art, such as extrusion, compaction, agglomeration on a granulation disc, drum granulation, spray drying, etc.

[0062] The zeolite-forming process includes the following steps: b1) The first soaking step in an alkaline base solution with a concentration between 0.2M and 2M (inclusive), at a temperature between room temperature and 50°C, preferably between 5 minutes and 3 hours; more preferably, at room temperature, the contact time is 30 minutes to 2 hours (inclusive). b2) At the end of this contact step, within one second to less than one hour, the temperature is raised from room temperature to a temperature between 90°C and 105°C. b3) Optionally, keep at a temperature above 90°C for 30 minutes to one hour.

[0063] The heating in step b2) can be achieved by inputting external energy such as microwaves, ultrasound, electromagnetic induction, infrared, heating type, or a combination thereof. Preferably, the external energy is provided by microwaves, ultrasound, electromagnetic induction, infrared, or a combination thereof.

[0064] Preferably, step b2) is very fast; it is flash boiling petrification. Preferably, step b2) lasts from one second to less than 30 minutes, more particularly from 2 seconds to less than 20 minutes, and even more preferably from 5 seconds to 15 minutes.

[0065] According to a preferred embodiment, step b2) is performed by inputting external energy of the microwave, ultrasonic, electromagnetic induction, infrared type or a combination of these technologies for a duration ranging from one second to less than 30 minutes, more particularly from 2 seconds to less than 20 minutes, and even more preferably from 5 seconds to 15 minutes.

[0066] After step b2) and / or step b3), washing may be performed, preferably with water.

[0067] The cation exchange step in step c) is carried out according to conventional methods known to those skilled in the art, and most commonly by contacting the aggregates obtained in step b) with barium and / or potassium salts such as barium chloride (BaCl2) and / or potassium chloride (KCl) in an aqueous solution at a temperature between room temperature and 100°C, preferably between 80°C and 100°C, in order to rapidly obtain a high barium content (expressed as barium oxide), i.e., preferably greater than 10% by weight, more preferably greater than 15% by weight, more preferably greater than 20% by weight, even more preferably greater than 23% by weight, or even greater than 33% by weight, relative to the total mass of the adsorbent.

[0068] Advantageously, the barium content, expressed as barium oxide, is between 23% by weight and 42% by weight, and typically between 30% by weight and 40% by weight (including the extreme values), relative to the total weight of the adsorbent.

[0069] It is preferable to use a large excess of barium ions relative to the cations of the zeolite to be exchanged, typically about 10 to 12 times the excess, and it is advantageous to operate by performing continuous exchange.

[0070] Preferably, the potassium oxide (K2O) content in the agglomerated zeolite adsorbent according to the present invention is between 0 and 20% by weight, and even more preferably between 0 and 15% by weight (including the extreme values), relative to the total mass of the adsorbent.

[0071] Optional potassium exchange can advantageously be performed before and / or after barium exchange. In one embodiment, the cations (typically sodium ions) present in the initial FAU-type zeolite can be pre-exchanged with barium or potassium ions, or barium and potassium ions, before step a) in which the aggregates already contain barium or potassium ions, or FAU zeolite crystals already contain barium and potassium ions (in step a). Step c) can be omitted (or not omitted).

[0072] After one or more cation exchange steps, washing is usually performed, preferably with water, and then the resulting aggregates are dried.

[0073] Activation after drying is routinely carried out according to methods known to those skilled in the art, for example, at a temperature typically between 100°C and 400°C, preferably between 200°C and 300°C, for a period of time, the duration of which is determined based on the water content and the desired loss on ignition. This time can be between 1 hour and 6 hours.

[0074] The method may include one or more additional molding steps performed after any of steps a), b1), b2), c), d), e).

[0075] The agglomerated zeolite adsorbents according to the invention are particularly suitable for methods of separating compounds in the liquid phase, especially methods in which the material is subjected to significant mechanical stress, such as co-current or counter-current liquid phase separation methods, and more particularly simulated moving bed liquid phase separation methods. The agglomerated zeolite adsorbents according to the invention are particularly suitable for liquid-phase xylene separation methods.

[0076] Agglomerated zeolite adsorbents as defined above, or even those prepared according to the methods defined above, can also be used for: • Separation of C8 aromatic isomer fractions, especially xylene, • Separate substituted toluene isomers, such as nitrotoluene, diethyltoluene, and toluene diamine. • Separation of cresol • Separate polyols, such as sugars.

[0077] Therefore, and according to another aspect, the present invention relates to at least one zeolite adsorbent in the form of aggregates as defined above as an adsorbent material in liquid-phase or gas-phase separation methods, co-current or counter-current methods, more particularly in simulated moving bed liquid-phase separation methods, typically in separation methods of aromatic fractions comprising a mixture of aromatic isomers having 8 carbon atoms, more particularly in simulated moving bed liquid-phase xylene separation methods, alone or in combination with crystallization units, particularly in methods for recovering high-purity p-xylene from aromatic isomer fractions having 8 carbon atoms.

[0078] Finally, the present invention also relates to a method for separating aromatic fractions comprising a mixture of isomers having eight carbon atoms in a liquid or gas phase. More particularly, the invention relates to a simulated moving-bed liquid-phase xylene separation method, alone or in combination with a crystallization unit, and very particularly to a method for recovering high-purity p-xylene from aromatic isomer fractions having eight carbon atoms, such as that described in application WO2009081024, wherein at least one zeolite adsorbent in the form of aggregates as described above is employed. The method is carried out in the presence of a desorbent, preferably selected from toluene and p-diethylbenzene.

[0079] The present invention also relates to a simulated moving bed gas-phase xylene separation method, which uses an adsorbent as described above to adsorb xylene isomers (preferably p-xylene) in the presence of a desorbent (preferably selected from toluene and p-diethylbenzene). Preferably, the method is carried out in a simulated moving bed, more preferably in a simulated countercurrent.

[0080] This invention particularly relates to a method for producing para-xylene with high purity and high productivity from an aromatic feedstock containing an isomer having eight carbon atoms, comprising the following steps: 1) The step of contacting the feedstock with the adsorbent bed according to the invention under suitable adsorption conditions to preferentially adsorb p-xylene. 2) The step of contacting the adsorbent bed with the desorbent (preferably toluene or p-diethylbenzene) under desorption conditions. 3) The step of extracting the feed stream containing desorbent and the least selective adsorbed product from the adsorbent bed. 4) The step of extracting the stream containing desorbent and p-xylene from the adsorbent bed. 5) The step of separating the stream obtained in step 3) into a first stream containing a desorbent and a second stream containing the feed product with the lowest selectivity of adsorption, and 6) The step of separating the stream obtained in step 4) into a first stream containing a desorbent and a second stream with a p-xylene purity greater than or equal to 75%, preferably greater than or equal to 99.7%.

[0081] The method may also optionally include the following steps: 7) A crystallization step in the crystallizer, comprising the following operations: crystallizing the p-xylene obtained in step 6), which on the one hand allows for the acquisition of p-xylene crystals impregnated with its mother liquor, and on the other hand obtains the mother liquor, which may be partially or even entirely mixed with fresh feedstock and recycled to the inlet of the simulated moving bed adsorption unit. 8) The step of washing the crystals obtained in step 7) at the end of which p-xylene is recovered with a purity of at least 99.7% and preferably at least 99.8%.

[0082] Therefore, the desired product can be separated by preparative liquid adsorption chromatography ("batch" mode), advantageously in a simulated moving bed, i.e. in simulated countercurrent or simulated cocurrent, and more particularly in simulated countercurrent.

[0083] Simulated countercurrent moving bed chromatography is well known in the art. Typically, a simulated moving bed separation unit includes at least one adsorption column containing multiple adsorbent beds interconnected in a closed loop. The simulated moving bed separation unit includes at least three chromatographic zones, possibly four or five, each consisting of at least one bed or part of a column, and located between two consecutive feed or drain points.

[0084] Typically, at least one feed to be fractionated and a desorbent (sometimes called an eluent) are fed, and at least one raffinate and one extract are withdrawn. The feed and withdrawal points change over time, typically moving down one bed and in a synchronized manner.

[0085] By definition, each operating zone is assigned a number: Zone 1 = Desorption zone for the desired product (contained in the extract), located between the injection of the desorbent and the extraction of the extract; • Zone 2 = Desorption zone of the residue compounds, located between the extraction of the extract and the injection of the feed to be fractionated; • Zone 3 = Adsorption zone for the desired product, located between the feed injection and the raffinate extraction; Zone 4 is located between the extraction of residual liquid and the injection of desorbent.

[0086] The operating conditions for simulating a countercurrent industrial adsorption unit are typically as follows: -Number of beds: 6 to 30 - Number of zones must be at least 4 - Temperature 100 to 250°C, preferably 150 to 190°C - The pressure is between the bubble point pressure of xylene and 3 MPa at the method temperature. - The desorbent / feed flow rate ratio is 0.7 to 2.5 (e.g., 0.9 to 1.8 for a standalone adsorption unit (referred to as "stand alone"), and 0.7 to 1.4 for an adsorption unit combined with a crystallization unit). - The recirculation ratio is 2.5 to 12, preferably 3.5 to 6. The recirculation ratio is defined as the ratio between the average flow rate in different beds of the adsorber and the feed injection flow rate of the adsorber. You can refer to the teachings of patents US2985589, US5284992 and US5629467.

[0087] The operating conditions for simulating co-current industrial adsorption units are typically the same as those for simulating counter-current operation, except that the recirculation ratio is usually between 0.8 and 7. See patents US4402832 and US4498991 for details.

[0088] The desorption solvent can be a desorbent with a boiling point lower than that of the feed, such as toluene, or a desorbent with a boiling point higher than that of the feed, such as p-diethylbenzene (PDEB).

[0089] Characterization techniques

[0090] Si / Al atomic ratio and oxide content: The elemental chemical analysis of the final product can be performed using various analytical techniques known to those skilled in the art. Among these techniques, X-ray fluorescence chemical analysis can be mentioned, performed on a wavelength dispersive spectroscopy (WDXRF) instrument, such as the Tiger S8 from Bruker, as described in standard NF EN ISO 12677:2011.

[0091] X-ray fluorescence (XRF) is a non-destructive spectroscopic technique that uses the photoluminescence of atoms in the X-ray range to establish the elemental composition of a sample. Atom excitation (usually via an X-ray beam or electron bombardment) produces specific radiation after the atoms return to their ground state. An advantage of XRF spectroscopy is its minimal reliance on the chemical bonding of elements, providing accurate determinations, both quantitatively and qualitatively. Measurement uncertainty of less than 0.4% by weight is typically obtained after calibration for each oxide.

[0092] These elemental chemical analyses allow verification of the Si / Al atomic ratio of the zeolite used in the aggregates and the Si / Al atomic ratio of the final product obtained at the end of the above steps, and verify the quality of ion exchange by measuring the oxide content.

[0093] In the description of this invention, the measurement uncertainty of the Si / Al atomic ratio measured thereafter is relative ± 0.2%.

[0094] The mass of ion exchange is related to the number of moles of sodium oxide (Na₂O) remaining in the zeolite aggregates after exchange. More specifically, the barium ion exchange rate is estimated by evaluating the ratio between the number of moles of barium oxide (BaO) and the total number of moles (BaO + Na₂O). Similarly, the barium and / or potassium ion exchange rates are estimated by evaluating the ratio between the total number of moles of barium oxide + potassium oxide (BaO + K₂O) and the total number of moles (BaO + K₂O + Na₂O). It should be noted that the contents of various oxides are given as a weight percentage relative to the total weight of the anhydrous zeolite adsorbent.

[0095] Size / particle size analysis (particle size distribution) of zeolite crystals: The number-average diameter of the zeolite crystals contained in the zeolite crystals and agglomerates used in step a) was estimated by observation using a scanning electron microscope (SEM).

[0096] To estimate the size (or average diameter) of the zeolite particles (i.e., crystals) on the sample, a series of photographs were taken at a magnification of at least 5000x. The diameter of at least 200 particles was then measured using specialized software (such as Smile View software from LoGraMi). The accuracy was approximately 3%. Simultaneously measuring the histogram formed from these diameter measurements allowed for the determination of the standard deviation σ of their distribution.

[0097] This scanning electron microscopy (SEM) observation of zeolite crystals also allows for the differentiation of the crystal structures of zeolites (LSX, MSX, X).

[0098] Particle size distribution of zeolite adsorbents: The number-average diameter of the zeolite adsorbent obtained at the end of agglomeration and shaping step a) was determined by imaging analysis of the particle size distribution of the agglomerate sample according to standard ISO 13322-2:2006, using a conveyor belt that allows the sample to pass in front of the camera lens.

[0099] The number-average diameter is then calculated from the particle size distribution using standard ISO 9276-2:2001. In this document, the terms "number-average diameter" or "size" are used for zeolite agglomerates. For the agglomerate size range of this invention, the accuracy is approximately 0.01 mm.

[0100] Loss on ignition of zeolite adsorbent: Loss on ignition was determined in an oxidizing atmosphere by calcining the sample in air at 900°C ± 25°C, following the operating procedure described in standard NF EN 196-2 (April 2006). The standard deviation of the measurement was less than 0.1%.

[0101] Pore ​​volume

[0102] Volumetric analysis is defined as follows: Vma is the macropore volume, which includes the volume of all pores larger than 50 nm. Vme corresponds to the mesopore volume, that is, the volume of pores from 2nm to 50nm, and Vmi is the micropore volume, representing the volume of pores smaller than 2 nm.

[0103] Methods for volume calculation

[0104] In this invention, we will primarily focus on the composition of Vme. Those skilled in the art will know that Vme can be determined through two different analyses: - Mercury porosimetry, covering a pore size range from 3.6 nm to 50 nm, denoted as Vme. Hg - Nitrogen adsorption, covering a pore size range from 2 nm to 50 nm. The volume obtained through t-plot analysis is denoted as Vme. N2 .

[0105] Here, we will use these two techniques known to those skilled in the art to observe the region from 2 nm to 15 nm, which is called small mesopores and whose volume is called V. 2-15

[0106] V 2-15 Divide into two volumes according to the following equation: V 2-15 = V 2-3.6 + V 3.6-15 in V 2-3.6 For volumes corresponding to aperture ranges from 2 nm to 3.6 nm, V 3.6-15 The corresponding pore size range is 3.6 nm to 15 nm. The 3.6-15 nm volume is defined as the difference between the mercury volume introduced at 400 MPa pressure (corresponding to the pressure of a 3.6 nm pore) and the mercury volume introduced at 100 MPa pressure (corresponding to the pressure of a 15 nm pore) measured by mercury porosimetry.

[0107] To determine their values, we performed the following calculations from the two mesoporosity measurements mentioned above: V 2-3.6 The mesopore volume is obtained by subtracting the mesopore volume measured by mercury intrusion porosimetry from the mesopore volume measured by nitrogen adsorption. V 2-3.6 = Vme N2 - Vme Hg Mesopore volume was characterized by nitrogen adsorption. Mesopore volume Vme with pore size from 2 nm to 50 nm N2 It is determined by measuring the adsorption isotherm of a gas (e.g., nitrogen) at its liquefaction temperature.

[0108] Prior to adsorption, the sample was subjected to vacuum (P < 6.7.10). 4 The gas was degassed at 300°C to 450°C for 9 to 16 hours. Then, nitrogen adsorption isotherm measurements were performed at 77 K on an ASAP 2020 M instrument from Micromeritics, with at least 35 measurement points taken at relative pressures P / P0 between 0.002 and 1.

[0109] Mesopore volume Vme N2 The thickness t was determined from the obtained isotherms by applying the t-plot method of standard ISO 15901-3:2007 and calculating the statistical thickness t using the Harkins-Jura equation.

[0110] They were obtained by performing linear regression on data points in the 0.35 nm to 0.60 nm range of the t-plot, and were derived from the origin intercept and slope of the linear regression, respectively.

[0111] They are expressed in cm³ of liquid adsorbate per gram of anhydrous adsorbent.

[0112] The micropore volume was characterized by nitrogen adsorption using the same method as described above for mesopore volume.

[0113] Macropore volume Vma and mesopore volume Vme were characterized by mercury porosimetry.

[0114] The distribution of pore volumes contained in macropores and mesopores was analyzed using an Autopore® 9500 mercury porosimeter from Micromeritics.

[0115] The experimental method described in the reference standard ASTM D4284-83, in the equipment operation manual, involves placing a pre-weighed sample of adsorbent (the zeolite adsorbent in aggregate form to be measured) (with known loss on ignition) in the sample cell of the mercury porosimeter. The sample cell is then degassed (at a evacuation pressure of 30 µmHg for at least 10 minutes), followed by filling the sample cell with mercury at a given pressure (0.0036 MPa). The pressure is then progressively increased up to 400 MPa to allow the mercury to gradually penetrate the porous network of the sample. At least 15 pressure steps are set before reaching 0.2 MPa, followed by 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.

[0116] The relationship between the applied pressure and the orifice inlet threshold characteristic size (corresponding to the apparent orifice diameter) was established using the Laplace-Young equation, assuming a cylindrical orifice opening, a contact angle of 140° between mercury and the orifice wall, and a surface tension of 485 dynes / cm for mercury. - ¹. Record each pressure step P i The volume increment ΔV of mercury introduced below i This then allows plotting V(P) as a function of applied pressure. i ) or as an apparent aperture function V(l i The mercury accumulation volume is introduced using V(P) as a function of the applied pressure. i ) or as an apparent aperture function V(l i The mercury accumulation was introduced into a volumetric map, and the volume V was determined by reading the volume values ​​at 3.6 nm and 15 nm. 3.6-15The value at which mercury fills all intercrystalline voids is fixed at 0.2 MPa, and it is assumed that mercury will permeate into the pores of the adsorbent if this value is exceeded.

[0117] The macropore volume Vma of an adsorbent is defined as the cumulative volume of mercury introduced under pressures between 0.2 MPa and 30 MPa, corresponding to the volume contained in pores with an apparent diameter greater than 50 nm.

[0118] The mesopore volume Vme of an adsorbent is defined as the cumulative volume of mercury introduced under pressures between 30 MPa and 400 MPa.

[0119] In this document, the macropore and mesopore volumes Vma and Vme of the zeolite adsorbent are expressed in cm⁻¹. 3 .g -1 This indicates that the measurement is therefore performed by mercury intrusion porosimetry and is related to the sample mass on an anhydrous equivalent basis, i.e., the mass of the adsorbent is corrected for loss on ignition.

[0120] XRD technique for characterizing zeolites.

[0121] The zeolites present in the adsorbent and their lattice parameters were characterized by X-ray diffraction analysis, known to those skilled in the art as XRD. This analysis was performed on an instrument from Bruker on pre-ground and sieved (fractions smaller than 50 μm) zeolite adsorbent samples. The samples were saturated with water to stabilize them during analysis. For this purpose, the samples were dried in an oven at 110°C and then placed as a thin film in a sealed space at 55% relative humidity at ambient temperature for at least 48 hours. Analysis was performed with the addition of an internal standard (5% lattice parameter certified silicon) in angular steps (in °2θ) of 0.02° within an angular range (in °2θ) between 5° 2θ and 72° 2θ. Data were processed using TOPAS refinement software to obtain measurements of the lattice parameters of the zeolites present in the adsorbent with high accuracy (+ / - 0.005 Å).

[0122] As a direct result, in this invention, the term "non-zeolite phase" (or "NZP") refers to any phase present in the adsorbent material other than the zeolite phase referred to as "zeolite phase" or "ZP" mentioned above. The amount of non-zeolite phase is expressed as the adsorbent zeolite phase being made up to 100%, in other words: %NZP = 100 - %ZP Where %NZP represents the weight percentage of NZP, %ZP represents the weight percentage of the zeolite phase relative to the total weight of the adsorbent, and %ZP represents the crystallinity of the adsorbent (mass fraction of zeolite) measured by X-ray diffraction analysis (XRD).

[0123] Characterization of liquid-phase adsorption using the breakthrough method: The technique used to characterize the adsorption of molecules in the liquid phase on porous solids is called the breakthrough technique, described by Ruthven in "Principles of Adsorption and Adsorption Processes" (John Wiley & Sons, (1984), Chapters 8 and 9). This technique defines the breakthrough curve technique ("breakthrough curve") as the study of the response to a step injection of an adsorbable component.

[0124] Analysis of the average exit time (first moment) of the breakthrough curve provides information about the amount of adsorption and also allows for the assessment of selectivity, i.e., the separation factor between two adsorbable components. It is recommended to use the non-adsorbable component as a tracer injection to estimate the non-selective volume.

[0125] Analysis of the dispersion (second moment) of the breakthrough curve allows for the assessment of the height equivalent to a theoretical plate, based on a column represented by a finite number of assumed ideal stirred reactors (theoretical plates), which is a direct measurement of the system's axial dispersion and mass transfer resistance.

[0126] Definition of selectivity

[0127] The selectivity of the adsorbent for compound A relative to compound B, αA / B, is defined as the ratio of the concentrations of the compounds in the adsorbed phase to the concentration ratio of the compounds in the non-adsorbed phase at equilibrium, calculated using the following formula: αA / B = (Aads / Bads) x (Bliq / Aliq) Where Aads and Bads are the concentrations of compound A and compound B in the adsorbed phase, respectively. Aliq and Bliq are the concentrations of compound A and compound B in the fluid phase, respectively.

[0128] The invention will now be described with the aid of the following embodiments, which are intended to illustrate certain implementations of the invention but do not limit the scope of the invention as set forth in the appended claims.

[0129] Example

[0130] Comparative Example 1

[0131] This embodiment reproduces the comparative zeolite 1 according to application US2023 / 0219059.

[0132] A homogeneous mixture was prepared, and 800 g of zeolite crystals with an average diameter of 0.6 μm were agglomerated with 145 g of kaolin (expressed as calcination equivalent) and 55 g of colloidal silica (containing 30 wt% SiO2 and 0.5 wt% Na2O), sold under the trade name Klebosol™ 30N50, along with water in an amount sufficient to allow for extrusion of the mixture. The extrudate was dried, then calcined at 550°C (clay firing) under a nitrogen atmosphere for 2 hours, and finally pulverized to recover agglomerates with a number average diameter of 0.5 mm.

[0133] The agglomerates (20g) obtained as described above were placed in a glass reactor equipped with a double jacket, the double jacket was adjusted to a temperature of 95°C ± 1°C, and then 250mL of 1.25M sodium hydroxide aqueous solution was added. The reaction medium was kept under stirring for 4 hours.

[0134] The aggregates were then washed with three consecutive water washes before the reactor was emptied. The effectiveness of the washes was ensured by measuring the pH of the final wash water, which was between 10.0 and 10.5.

[0135] The agglomerates were exchanged by contacting a 0.5 M barium chloride solution with the solution in four separate steps at 95°C. In each exchange, the solution volume to solid mass ratio was 20 mL / g. -1 Each exchange lasts for 4 hours. Between each exchange, the solid is washed multiple times to remove excess salt. The aggregates are then dried at 80°C for 2 hours and finally activated at 250°C under a nitrogen stream for 2 hours.

[0136] The adsorbent contains 35.1% barium oxide.

[0137] The adsorbents exhibit the following characteristics as shown in Table 1:

[0138] Table 1

[0139] Therefore, the following properties can be calculated: V 2-3.6 = Vme N2 - Vme Hg = 0.023 cm 3 / g V 3.6-15 = 0.009 cm 3 / g The mesopore volume was measured using the techniques described above.

[0140] According to Embodiment 2 of the present invention

[0141] The agglomerates from Example 1 were placed in a glass reactor at ambient temperature, and then 450 mL of a 0.8 M sodium hydroxide aqueous solution was added. The mixture was kept in contact at ambient temperature for 1 hour. After this aging time, the reactor was placed in a microwave cavity (1800 kW) and then heated to raise the temperature to 95°C within 4 minutes.

[0142] The reactor was then placed in an oscillating thermostatic bath and maintained at 95°C for 1 hour. The aggregates were then washed with water in three consecutive cycles, after which the reactor was emptied. The effectiveness of the washing was ensured by measuring the pH of the final wash water, which was between 10.0 and 10.5.

[0143] The agglomerates were exchanged by contacting a 0.5 M barium chloride solution with the solution in four separate steps at 95°C. In each exchange, the solution volume to solid mass ratio was 20 mL / g. -1 Each exchange lasts for 4 hours. Between each exchange, the solid is washed multiple times to remove excess salt. The aggregates are then dried at 80°C for 2 hours and finally activated at 250°C under a nitrogen stream for 2 hours.

[0144] The adsorbent contains 35.6% barium oxide.

[0145] The adsorbents according to the present invention exhibit the following properties as shown in Table 2:

[0146] Table 2

[0147] Therefore, the properties can be calculated: V 2-3.6 = Vme N2 - Vme Hg = 0.012 cm 3 / g V 3.6-15 = 0.009 cm 3 / g The mesopore volume was measured using the techniques described above.

[0148] The mesopore distribution of each adsorbent in Examples 1 and 2 can then be calculated. The results are presented in Table 3 below:

[0149] Table 3

[0150] Example 3: Breakthrough Test (Frontier Chromatography)

[0151] The loss on ignition (LOI) for each sample was adjusted to 6.0%.

[0152] These adsorbents were then subjected to a breakthrough test (frontier chromatography) to assess their effectiveness. The adsorbent dose used for this test was approximately 82 g.

[0153] The steps to obtain the breakout curve are as follows: - Fill the column with a sieve and place it on the test platform.

[0154] - Fill with solvent at ambient temperature.

[0155] - In solvent flow (5 cm) 3 The adsorption temperature is gradually increased (per minute).

[0156] - When the adsorption temperature is reached, at 10 cm 3 Solvent is injected per minute.

[0157] - Switch solvent / feed to inject feed (10 cm) 3 / minute).

[0158] -Then keep the feedstock injected for a sufficient time to reach thermodynamic equilibrium.

[0159] - Collect and analyze the breach effluent.

[0160] The pressure is sufficient to keep the feedstock in the liquid phase, i.e., 1 MPa. The adsorption temperature is 175°C.

[0161] The raw material composition is as follows: p-Xylene: 45% by weight m-Xylene: 45% by weight Isooctane: 10% by weight (the latter is used as a tracer to estimate non-selective volume and does not participate in the separation).

[0162] A 5% increase in PX / MX selectivity was observed between the aggregates according to Example 1 and the aggregates according to Example 2, representing a significant improvement in productivity on an industrial scale.

[0163] These results demonstrate that the adsorbent according to the invention, exhibiting the claimed mesoporous distribution, results in a significant improvement in selectivity for m-xylene.

Claims

1. An agglomerated zeolite adsorbent based on octahedral zeolite (FAU) crystals, wherein the zeolite adsorbent contains barium or contains both barium and potassium, and the adsorbent exhibits a pore distribution satisfying the following two inequalities: in Vma Hg This represents the macropore volume of the adsorbent as measured by mercury porosimetry. Vme N2 This represents the mesopore volume of the adsorbent as measured by nitrogen adsorption. V 2-3.6 This corresponds to mesopore volumes with pore sizes ranging from 2 nm to 3.6 nm. V 3.6-15 This corresponds to mesopore volumes with pore sizes ranging from 3.6 nm to 15 nm. V 2-3.6 equals V 2-3.6 = Vme N2 - Vme Hg , Vme Hg This represents the mesopore volume of the adsorbent as measured by mercury porosimetry. V 3.6-15 The value was determined by the difference between the mercury volume introduced at 15 nm and the mercury volume introduced at 3.6 nm. Volume in cm 3 .g -1 express.

2. The zeolite adsorbent according to claim 1, wherein, The hole distribution satisfies the following inequality: ， Preferred .

3. The zeolite adsorbent according to claim 1 or 2, wherein, The hole distribution satisfies the following inequality: Preferred .

4. The zeolite adsorbent according to any one of claims 1 to 3, wherein, The agglomerated zeolite adsorbent exhibits a Si / Al ratio greater than or equal to 1.0 and less than or equal to 3 (e.g., 1.0 ≤ Si / Al ≤ 3.0), particularly 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, a Si / Al ratio between 1.1 and 1.

4.

5. The zeolite adsorbent according to any one of claims 1 to 4, wherein, The adsorbent comprises crystals with a size less than or equal to 1.50 µm, the size of which is observed and measured by scanning electron microscopy, and the size is preferably between 0.05 µm and 1.50 µm, more preferably between 0.10 µm and 1.00 µm, more preferably between 0.10 µm and 0.80 µm, and even more preferably between 0.30 µm and 0.80 µm.

6. The zeolite adsorbent according to any one of claims 1 to 5, wherein, The adsorbent is in the form of beads with a number-average diameter between 0.1 mm and 2 mm, preferably between 0.3 mm and 2 mm, and particularly between 0.3 mm and 0.8 mm. The number-average diameter is determined by imaging analysis of the particle size distribution of the aggregated sample according to standard ISO 13322-2:2006, and then calculated by applying standard 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 octahedral zeolite with an agglomerating binder comprising at least 80% by weight of clay suitable for zeolite synthesis and a possible silicon source, molding the resulting mixture, and firing it at a temperature between 500°C and 700°C for 2 minutes to 12 hours. b1) A first immersion step in an alkaline base solution with a concentration between 0.2M and 2M, inclusive, at a temperature between room temperature and 50°C, for a contact time between several minutes and several hours, preferably 5 minutes to 3 hours. b2) At the end of this contact step, the temperature is raised from room temperature to between 90°C and 105°C within one second to less than one hour. c) The cations of the aggregates are exchanged by contacting the aggregates with a barium ion solution or a barium and potassium ion solution. d) The zeolite agglomerates thus obtained are washed and dried, and e) Activation is performed by heating the zeolite adsorbent in the form of aggregates obtained in step d) at a temperature between 100°C and 400°C.

8. The method according to claim 7, characterized in that, The method includes step b3) after step b2): keeping the adsorbent in the solution at a temperature above 90°C for 30 minutes to 1 hour.

9. Use of the adsorbent according to any one of claims 1 to 6 or according to claim 7 or 8 in the following methods: • Separate aromatic C8 isomer fractions, especially xylene. • Separate substituted toluene isomers, such as nitrotoluene, diethyltoluene, and toluene diamine. • Separate cresol • Separation of polyols.

10. The use according to claim 9, for separating p-xylene from an aromatic isomer fraction containing eight carbon atoms.

11. A method for separating p-xylene from an aromatic isomer fraction containing eight carbon atoms, the method being carried out in the liquid phase by adsorption of p-xylene, comprising the step of contacting the feedstock with a bed of agglomerated zeolite adsorbent as defined in any one of claims 1 to 6 or capable of being prepared in any one of claims 7 and 8 in the presence of a desorbent.

12. A method for separating p-xylene from an aromatic isomer fraction containing eight carbon atoms, the method being carried out in the gas phase by adsorption of p-xylene, comprising the step of contacting the feedstock with a bed of agglomerated zeolite adsorbent as defined in any one of claims 1 to 6 or capable of being prepared in any one of claims 7 and 8 in the presence of a desorbent.

13. The method according to claim 11 or 12, characterized in that, The bed described is a simulated mobile bed type.

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