EP3218101A1

EP3218101A1 - Zeolite adsorbents made from lsx zeolite with a controlled external surface area, method for preparation of same and uses thereof

Info

Publication number: EP3218101A1
Application number: EP15797924.6A
Authority: EP
Inventors: Ludivine Bouvier; Cécile LUTZ; Catherine Laroche; Julien Grandjean; Arnaud Baudot
Original assignee: IFP Energies Nouvelles IFPEN; Arkema France SA
Current assignee: IFP Energies Nouvelles IFPEN; Arkema France SA
Priority date: 2014-11-13
Filing date: 2015-11-13
Publication date: 2017-09-20
Also published as: FR3028430B1; KR20170083602A; CN113083224A; CN107206349B; ZA201703816B; FR3028430A1; JP6641368B2; KR102449639B1; WO2016075281A1; JP2017536979A; US20170304800A1; TWI598149B; CN107206349A; US9919289B2; TW201628711A

Abstract

The present invention relates to a zeolite absorbent comprising at least one LSX zeolite with faujasite structure (FAU) and containing barium and/or potassium, in which the external surface area of said zeolite absorbent, as measured by nitrogen absorption, is between 20 m²∙g^-1 and 100 m²∙g^-1, terminals included. The present invention also relates to the use of such a zeolite absorbent as an adsorption agent, as well as the method for separation of para-xylene from aromatic isomer fractions with 8 carbon atoms.

Description

ZEOLITHIC LSX-BASED ZEOLITE BASED ZEOLITE BASED ADSORBENTS, PREPARATION METHOD AND USES THEREOF

FIELD OF THE INVENTION

The invention relates to zeolite adsorbents in the form of agglomerates comprising zeolite structure Faujasite (FAU) type LSX for their use in applications where the transfer of material is an important parameter, said adsorbents having an outer surface controlled, measured by nitrogen adsorption, between 20 m ² . g ^-1 and 100 m ² g ^-1 .

The present invention also relates to a process for preparing said zeolite adsorbents, and their uses, in particular for the separation of gaseous or liquid mixtures of isomers, more particularly xylenes and especially for the production of very pure paraxylene from an aromatic hydrocarbon feed containing isomers containing 8 carbon atoms.

PRIOR ART

The use of zeolitic adsorbents comprising at least zeolite Faujasite (FAU) type X or Y and comprising, in addition to sodium cations, barium, potassium or strontium ions, alone or in mixtures, for selectively adsorbing the paraxylene in a mixture of aromatic hydrocarbons is well known in the art.

US Pat. Nos. 3,558,730, 3,558,732, 3,626,020 and 3,663,638 show that zeolitic adsorbents comprising aluminosilicates based on sodium and barium (US Pat. No. 3,960,774) or on sodium-based aluminosilicates. , barium and potassium, are effective for the separation of paraxylene present in aromatic C8 cuts (cuts comprising aromatic hydrocarbons with 8 carbon atoms).

The adsorbents described in US Pat. No. 3,878,127 are used as adsorption agents in liquid phase processes, preferably of simulated countercurrent type, similar to those described in US Pat. No. 2,985,589 and which are incorporated herein by reference. apply, inter alia, to C8 aromatic cuts.

US 6 884 918 recommends a faujasite X atomic Si / Al ratio between 1, 15 and 1.5 exchanged with barium or barium and potassium. Document US 6,410,815 teaches that zeolite adsorbents as described in the prior art, but for which the faujasite is low in silica content and has an Si / Al atomic ratio close to 1 (that the we will call LSX, abbreviation for Low Silica X of which the French translation is zeolite X with a low silica content) are advantageously used for the separation of paraxylene, especially when it is necessary to treat ethylbenzene-rich feeds, because of a better selectivity of paraxylene with respect to this compound. isomer with respect to zeolite X adsorbents with an Si / Al atomic ratio of between 1.15 and 1.5.

In the patents listed above, the zeolitic adsorbents are in the form of crystals in the form of powder or in the form of agglomerates consisting mainly of zeolite powder and up to 20% by weight of inert binder.

The synthesis of FAU zeolites is usually carried out by nucleation and crystallization of silico-aluminate gels. This synthesis leads to crystals (generally in the form of powder) whose use on an industrial scale is particularly difficult (significant losses of loads during handling). The agglomerated forms of these crystals in the form of grains, yarns and other agglomerates are then preferred, these forms being obtainable by extrusion, pelletization, atomization and other agglomeration techniques known to those skilled in the art. These agglomerates do not have the disadvantages inherent to the pulverulent materials.

The agglomerates, whether they are in the form of platelets, beads, extrudates, and the like, generally consist of crystals of zeolite (s), which constitute the active element (in the sense of adsorption). ) and an agglomeration binder. This agglomeration binder is intended to ensure the cohesion of the crystals with each other in the agglomerated structure, but also must make it possible to ensure sufficient mechanical strength for said agglomerates in order to avoid, or at least to minimize as much as possible, the risks fractures, breaks or breaks that may occur during their industrial uses during which the agglomerates are subjected to numerous constraints, such as vibrations, strong and / or frequent variations of pressures, movements and others.

The preparation of these agglomerates is carried out for example by pasting zeolite crystals in powder form with a clay paste, in proportions of the order of 80% to 90% by weight of zeolite powder for 20% to 10% by weight of binder, then shaped into balls, platelets or extrudates, and high temperature heat treatment for baking the clay and reactivation of the zeolite, the cationic exchange (s) , such as, for example, the barium and optionally potassium exchange that can be carried out before and / or after the zeolite powder has been agglomerated with the binder.

We obtain zeolite agglomerates whose particle size is a few millimeters, or even of the order of a millimeter, and which, if the choice of agglomeration binder and granulation are made in the rules of the art, have a set of properties satisfactory, in particular porosity, mechanical strength, abrasion resistance. However, the adsorption properties of these agglomerates are obviously reduced relative to the starting active powder due to the presence of agglomeration binder inert with respect to the adsorption.

Various means have already been proposed to overcome this disadvantage of the agglomeration binder to be inert with respect to the adsorption performance, among which, the transformation of all or at least a portion of the agglomeration binder into active zeolite from the point of view of adsorption. This operation is now well known to those skilled in the art, for example under the name of "zeolitization". To easily perform this operation, zeolitizable binders are used, most often belonging to the family of kaolinite, and preferably previously calcined at temperatures generally between 500 ° C and 700 ° C.

Patent FR 2 925 366 describes a process for the manufacture of LSX zeolite agglomerates with Si / Al atomic ratio such that 1.00 <Si / Al <1, 15 exchanged with barium and optionally with barium and potassium. , by agglomerating LSX zeolite crystals with a kaolinic binder, and then zeolizing the binder by immersing the agglomerate in an alkaline liquor. After exchanging the cations of the zeolite with barium (and optionally potassium) ions and activation, the agglomerates thus obtained have, from the point of view of the adsorption of the paraxylene contained in the C8 aromatic cuts and of the mechanical strength, properties improved with respect to adsorbents prepared from the same amount of LSX zeolite and binder, but whose binder is not zeolite.

In addition to a high adsorption capacity and good selectivity properties in favor of the species to be separated from the reaction mixture, the adsorbent must have good material transfer properties to ensure a sufficient number of theoretical plates for achieve effective separation of mixed species, as Ruthven points out in "Principles of Adsorption and Adsorption Processes," John Wiley & Sons, (1984) pages 326 and 407. Ruthven indicates (ibid., p. 243) that, in the case of an agglomerated adsorbent, the transfer of global matter depends on the sum of the diffusional intracrystalline and intercrystalline resistances (between the crystals). ).

The intra-crystalline diffusional resistance is proportional to the square of the diameters of the crystals and inversely proportional to the intra-crystalline diffusivity of the molecules to be separated.

The inter-crystalline diffusion resistance (also called "macroporous resistance") is in turn proportional to the square of the diameters of the agglomerates, inversely proportional to the porosity contained in the macropores and mesopores (that is to say the pores whose opening is greater than 2 nm) within the agglomerate, and inversely proportional to the diffusivity of the molecules to be separated in this porosity.

The size of the agglomerates is an important parameter when using the adsorbent in the industrial application, because it determines the pressure drop within the industrial unit and the uniformity of the filling. The particle size distribution of the agglomerates must therefore be narrow, and centered on number average diameters typically between 0.40 mm and 0.65 mm in order to avoid excessive pressure losses.

The porosity contained in the macropores and mesopores within the agglomerate (inter-crystalline macroporosity and mesoporosity respectively) can be increased by using porogenic agents, such as, for example, the corn starch recommended in the US 8 document. 283,274 to improve material transfer. However, this porosity does not participate in the adsorption capacity and the improvement of the transfer of macroporous material is then to the detriment of the adsorption capacity volume. Consequently, this pathway for improving the transfer of macroporous material is very limited.

To estimate the improvement of the transfer kinetics, it is possible to use the plateau theory described by Ruthven in "Principles of Adsorption and Adsorption Processes", ibid., Pages 248-250. This approach is based on the representation of a column by a finite number of ideally stirred hypothetical reactors (theoretical stages). The equivalent height of theoretical plates is a direct measure of the axial dispersion and resistance to material transfer of the system.

For a given zeolite structure, a given adsorbent size and a given operating temperature, the diffusivities are fixed, and one of the means for improving the transfer of material is to reduce the diameter of the crystals. A gain on the global material transfer will thus be obtained by reducing the size of the crystals.

The skilled person will therefore seek to reduce as much as possible the diameter of the zeolite crystals to improve the transfer of material.

The CN patent 1,267,185C thus claims adsorbents containing 90% to 95% of BaX or BaKX zeolite for the separation of paraxylene, in which the zeolite X crystals are of size between 0.1 μηι and 0, 4 μηι and this to improve the performance in material transfer. Similarly, application US2009 / 0326308 describes a process for separating xylene isomers whose performance has been improved by the use of adsorbents based on zeolite X crystals less than 0.5 μηι. Patent FR 2 925 366 describes adsorbents containing LSX zeolite crystals with a number-average diameter of between 0.1 μηι and 4.0 μηι. However, the Applicant has observed that the synthesis, filtration, handling and agglomeration of zeolite crystals whose size is less than 0.5 μηη implement heavy processes, uneconomical and therefore hardly industrialized.

In addition, such adsorbents having crystals smaller than 0.5 μηι, are also more fragile, and it then becomes necessary to increase the level of agglomeration binder to enhance the cohesion of the crystals. between them within the adsorbent. However, the increase in the level of agglomeration binder leads to densification of the adsorbents, causing an increase in the macroporous diffusional resistance. Thus, despite reduced intra-crystalline diffusion resistance due to the decrease in the size of the crystals, the increase in the macroporous diffusional resistance due to the densification of the adsorbent, does not allow an improvement in the overall transfer. Moreover, the increase in the binder content does not make it possible to obtain a good adsorption capacity.

There remains therefore a need for improved zeolitic adsorbent materials prepared from zeolite crystals FAU type LSX easily manipulated at the industrial level, and said crystals (or constituent crystalline elements) are advantageously larger than 0, 5 μηη, and having an overall material transfer improved over the adsorbents of identical crystal size known from the prior art, while maintaining an adsorption capacity and adsorption selectivities of paraxylene vis-à-vis its high isomers.

These improved adsorbents would thus be particularly suitable for the separation of isomers xylenes gas phase or liquid phase.

The present invention thus has for its first object to provide zeolite adsorbents in the form of agglomerates with optimized properties for the separation of gaseous or liquid mixtures of isomers and more particularly for the separation of xylenes, gas phase or phase liquid, especially paraxylene aromatic C8 cuts, and especially when said sections are rich in ethylbenzene.

The zeolitic adsorbents of the invention advantageously have selectivity properties of paraxylene with respect to its isomers greater than 2.1, preferably greater than 2.3, and improved material transfer properties, while having high mechanical strength and adsorption capacity and are particularly suitable for use in a process for separating paraxylene in the liquid phase, preferably of the simulated countercurrent type.

More specifically, the present invention relates to a zeolitic adsorbent comprising at least one zeolite of structure FAU LSX type and comprising barium and / or potassium, wherein the outer surface of said zeolite adsorbent, measured by nitrogen adsorption, is between 20 m ² . g ^"1 and 100 m ² .g ^-1 , inclusive and more preferably between 20 m ² . g ^"1 and 80 m ^2, g ^{" 1} inclusive limits and even more preferably between 30 m ² . g ^"1 and 80 m ^2, g ^{" 1} , inclusive terminals.

It has indeed been found by the applicant that zeolite adsorbents of controlled external surface, that is to say between 20 m ² . g ^"1 and 100 m ² g ^-1 , as measured by nitrogen adsorption, and prepared from LSX zeolite crystals of Si / Al atomic ratio equal to 1.00 ± 0.05 having a size greater than 0.5 μηι, exhibit an improved overall material transfer with respect to zeolite adsorbents prepared from LSX zeolite crystals, with an atomic ratio Si / Al and of identical size, but of external surface, measured by nitrogen adsorption, strictly less than 20 m ² . g ^"1 .

The present invention therefore allows the provision of zeolitic adsorbents with improved properties compared to the prior art while facilitating the filtration, handling and agglomeration of zeolite powders used in the manufacturing process. Another object of the present invention is to provide a process for preparing said adsorbents, as well as the uses of said adsorbents for the separation of gaseous or liquid mixtures of isomers, more particularly xylenes and especially for the separation of very pure paraxylene from a charge of aromatic hydrocarbons containing isomers containing 8 carbon atoms, and in particular from a feed rich in ethylbenzene.

Still another object of the present invention is to maximize the transfer of material within the zeolite adsorbent, while maintaining selectivities of paraxylene vis-à-vis its high isomers, especially greater than 2.1 and an adsorption capacity suitable for the application, at the same time as a mechanical strength compatible with the application in question.

In what follows, and unless otherwise indicated, the boundaries of a domain of values are included in this field, especially in the expressions "between" and "ranging from ... to .. . "

Detailed description of the invention

Adsorbents according to the invention

[0034] Thus, the present invention relates to a zeolitic adsorbent:

comprising at least one zeolite of structure FAU of type LSX

- comprising barium and / or potassium, for which the external surface, measured by nitrogen adsorption, is between 20 m ² . g ^"1 and 100 m ² .g ^-1 , and preferably between 20 m ² . g ^"1 and 80 m ^2, g ^{" 1} and more preferably between 30 and 80 m ² . g ^"1 terminals included.

In one embodiment, the zeolitic adsorbent of the invention has an Si / Al atomic ratio of between 1.00 and 1.5, preferably between 1.00 and 1.4, inclusive, preferably between 1, 00 and 1, 20 inclusive, and even more preferably between 1.00 and 1.1 inclusive.

In a preferred embodiment of the invention, the zeolite with structure FAU of the zeolite adsorbent is a zeolite of structure FAU of type LSX (generally defined by its atomic ratio Si / Al = 1, 00 ± 0, 05), for which the number average diameter of the crystals is between 0.5 μηη and 20 μηη inclusive, preferably between 0.5 μηη and 10 μηη inclusive, more preferably between 0.8 μηη and Ι Ο μηη, included terminals, better still between 1 μηη and 10 μηη, included terminals, and more preferably between 1 μηη and 8 μηη, included terminals.

According to another preferred embodiment of the invention, the crystals have, together with the microporosity, internal cavities of nanometric size (mesoporosity), easily identifiable by observation by means of a Transmission Electron Microscope (TEM or "TEM" in English) as described for example in US 7,785,563.

The outer surface of the zeolite adsorbent of the invention is calculated by the t-plot method from the nitrogen adsorption isotherm at a temperature of 77K, after degassing under vacuum (P <6). , 7.10 ^"4 Pa), at a temperature between 300 ° C and 450 ° C for a period ranging from 9 hours to 16 hours, preferably at 400 ° C. for 10 hours The outer surface of the zeolite crystals FAU adsorbent before agglomeration is measured in the same way.

According to a preferred aspect, the barium content (Ba) of the zeolite adsorbent of the invention, expressed as barium oxide (BaO), is greater than 25%, preferably greater than 28%, very preferably preferred greater than 34%, even more preferably greater than 37%, by weight relative to the total weight of the adsorbent, and advantageously, the barium content expressed as barium oxide (BaO) is between 28% and 42%; %, and typically between 37% and 40%, limits included, by weight relative to the total weight of the adsorbent.

According to another preferred aspect, the potassium content (K) of the zeolite adsorbent of the invention, expressed as potassium oxide (K ₂ O), is less than 30%, preferably less than 15%, and preferably between 0 and 10%, limits included by weight relative to the total weight of the adsorbent. According to yet another preferred embodiment, the total content of alkaline or alkaline-earth ions, other than barium and potassium, expressed as total content of alkaline or alkaline earth metal oxides other than hydroxide oxide. BaO barium and K ₂ 0 potassium oxide is between 0 and 5%, limits included, relative to the total mass of the adsorbent.

Advantageously, the zeolitic adsorbent according to the invention has a total volume contained in the macropores and mesopores (sum of macroporous volume and mesoporous volume) measured by intrusion of mercury, between 0.15 cm ³ . g ^"1 and 0.5 cm ^3, g ^{" 1} , preferably between 0.20 cm ³ . g ^"1 and 0.40 cm ³ g ^-1 and very preferably between 0.20 cm ³ . g ^"1 and 0.35 cm ^3, g ^{" 1} , inclusive.

According to a preferred embodiment of the present invention, the zeolite adsorbent comprises both macropores, mesopores and micropores. "Macropores" means pores whose diameter is greater than 50 nm. By "mesopores" is meant pores whose diameter is between 2 nm and 50 nm, limits included. "Micropores" means pores whose diameter is less than 2 nm.

In addition, the adsorbent of the invention advantageously has a ratio (macroporous volume) / (macroporous volume + mesoporous volume) of between 0.2 and 1, very preferably between 0.5 and 0.9. , terminals included.

It is also preferred in the context of the present invention, a zeolite adsorbent whose microporous volume, evaluated by the t-plot method from the nitrogen adsorption isotherm (N ₂ ) at a temperature of 77K, is greater than 0.160 cm ³ . g ^"1 , preferably between 0.170 cm ³ .g ^-1 and 0.275 cm ³ . g ^"1 and more preferably between 0.180 cm ³ .g ^-1 and 0.250 cm ³ . g ^"1. Said isothermal nitrogen adsorption that is also used for measuring the outer surface by the t-plot method.

The crystalline structure of the FAU zeolite LSX type in the zeolite adsorbent of the present invention is identified by X-ray diffraction (known to those skilled in the art under the acronym DRX).

According to another preferred embodiment, no zeolite structure other than the FAU structure is detected by X-ray diffraction in the zeolite adsorbent of the present invention.

By "no zeolite structure other than the FAU structure" is meant less than 5%, preferably less than 2% by weight inclusive of one or more other zeolitic phases, other than the FAU structure. The mass fraction determined by XRD (technique described hereinafter) is expressed by weight relative to the total weight of the adsorbent. The zeolitic adsorbent according to the invention further comprises and preferably at least one non-zeolitic phase which comprises inter alia an agglomeration binder used in the method of preparation to ensure the cohesion of the crystals with each other, whence the term "agglomerate" or "zeolite agglomerate" sometimes used instead of the term "zeolite adsorbent" of the invention, as described above.

In the present invention, the term "binder" means an agglomeration binder which makes it possible to ensure the cohesion of the zeolite crystals (s) in the zeolite adsorbent (or agglomerated zeolite material) of the invention. This binder is further distinguished from zeolite crystals in that it does not exhibit a crystalline structure, and in particular no zeolitic crystalline structure, for which reason the binder is often described as inert, and more precisely inert. with respect to adsorption and ion exchange.

According to a preferred embodiment, the mass fraction of zeolite FAU in the adsorbent is greater than or equal to 85%, preferably greater than or equal to 90% by weight, inclusive, relative to the total weight of the adsorbent of the present invention, the 100% complement being preferably constituted of non-zeolitic phase. According to a particularly advantageous aspect, the mass fraction of zeolite FAU is between 92% and 98%, preferably between 94% and 98% by weight, limits included, relative to the total weight of the adsorbent of the present invention, the 100% complement being preferably constituted of non-zeolitic phase.

As already indicated, the mass fraction of zeolite (s) (crystallinity level) of the adsorbent according to the invention can be determined by X-ray diffraction analysis, known to those skilled in the art under the acronym XRD.

According to a preferred embodiment, the zeolite adsorbent according to the invention has a loss on ignition, measured at 950 ° C. according to the NF EN 196-2 standard, between 3.0 and 7.7%, so that still more preferred between 3.5% and 6.7% and advantageously between 4.0% and 6%, limits included.

The zeolitic adsorbent according to the present invention has, in particular, both a mechanical strength, adsorption selectivities of paraxylene with respect to its isomers of greater than 2.1, preferably greater than 2.2, of more preferably greater than 2.3 and an adsorption capacity also very particularly suitable for use in the processes for separating xylene isomers in the gas phase or in the liquid phase.

In the context of the present invention, the mechanical strength is measured by the Shell method SMS1471 -74 series suitable for agglomerates of size less than 1, 6 mm. This mechanical resistance, measured for the zeolite adsorbent defined above, is generally between 1, 5 MPa and 4 MPa, preferably between 1.7 MPa and 4 MPa more preferably between 1.8 MPa and 4 MPa and most preferably between 2 MPa and 4 MPa, inclusive.

Preparation of adsorbents according to the invention

Another object of the invention relates to a process for preparing the zeolite adsorbent as just defined, said process comprising at least the steps of: a) agglomeration of crystals of at least one zeolite FAU structure type LSX, having an outer surface of between 20 m ² . g ^"1 and 150 m ^2, g ^{" 1} , inclusive terminals, preferably between 20 m ² . g ^"1 and 120 m ^2, g ^{" 1} , more preferably between 20 m ² . g ^"1 and 100 m ² .g ^{" 1} , inclusive terminals, whose number average diameter of the crystals is between 0.5 μηη and 20 μηη inclusive, preferably between 0.5 μηη and 10 μηη, included terminals, more preferably between 0.8 μηη and Ι Ο μηη, included terminals, better still between 1 μηη and 10 μηη, included terminals, and preferably between 1 m and 8 μηη, limits included, with a binder preferably comprising at least 80% of clay or a mixture of clays and up to 5% of additives as well as with the amount of water which allows shaping of the agglomerated material, followed by drying and calcination of the agglomerates;

b) optionally zeolizing step of all or part of the binder by contacting the agglomerates obtained in step a) with an aqueous basic solution;

c) cationic exchange (s) of the agglomerates of step b) by contacting with a solution of barium ions and / or potassium ions;

d) additional cationic exchange of the agglomerates of step c) by contacting with a solution of potassium ions;

e) washing and drying the agglomerates obtained in steps c) or d), at a temperature between 50 ° C and 150 ° C; and

f) obtaining the zeolitic adsorbent according to the invention by activating the agglomerates obtained in step e) under an oxidizing and / or inert gas scavenging, with in particular gases such as oxygen, nitrogen, air, a dry air and / or decarbonated oxygen-depleted air, optionally dry and / or decarbonated, at a temperature between 100 ° C and 400 ° C, preferably between 200 ° C and 300 ° C.

In a preferred embodiment of the method for preparing the zeolite adsorbent of the present invention, the drying of the agglomerates in step a) above is generally carried out at a temperature of between 50 ° C. and 150 ° C. C, and the calcination of the dried agglomerates is generally carried out under an oxidizing and / or inert gas scavenging, with, in particular, gases such as oxygen, nitrogen, air, dry air and / or decarbonated air, an air depleted of oxygen, possibly dry and / or decarbonated, a temperature above 150 ° C, typically between 180 ° C and 800 ° C, preferably between 200 ° C and 650 ° C, for a few hours, for example from 2 hours to 6 hours.

In particular, said zeolite adsorbents are obtained from zeolite crystals having an external surface measured by nitrogen adsorption of between 20 m ² . ¹ and 150 m ² g ^-1 , said zeolite crystals are preferably zeolite crystals with a hierarchical porosity.

By "hierarchically porous zeolite" is meant a zeolite having both micropores and mesopores, ie a zeolite both microporous and mesoporous. By "mesoporous zeolite" is meant a zeolite whose microporous zeolite crystals have, together with the microporosity, internal cavities of nanometric size (mesoporosity), easily identifiable by observation by means of a Transmission Electron Microscope (TEM or "TEM"). In English), as described for example in US 7,785,563.

According to a preferred embodiment, the crystals of said LSX-type FAU structure zeolite used in step a) have an Si / Al atomic ratio = 1.00 ± 0.05, measured by elemental chemical analysis, according to techniques well known to those skilled in the art and detailed below.

It is possible to prepare said zeolite crystals with an external surface of between 20 m ² . g ^"1 and 150 m ² g ^-1 by direct synthesis through the use of structuring agents or by seeding techniques and / or by adjusting the synthesis operating conditions such as the ratio Si0 ₂ / Al ₂ 0 ₃ , the sodium content and the alkalinity of the synthesis mixture or by indirect synthesis according to post-treatment methods of conventional FAU zeolite crystals and known to those skilled in the art.

The post-treatment processes generally consist in removing atoms from the already formed zeolite network, either by one or more acid treatments which dealuminate the solid, treatment (s) followed by one or more washing (s) to sodium hydroxide (NaOH) in order to eliminate the aluminum residues formed, as described for example by D. Verboekend et al. {Adv. Funct. Mater., 22, (2012), pp. 916-928), or else by treatments which combine the action of an acid and that of a structuring agent which improve the efficiency of the acid treatment, as described for example in the application WO2013 / 106816.

The methods of direct synthesis of these zeolites (that is to say, synthetic methods other than post-treatment) are preferred and generally involve one or more structuring agents or sacrificial templates. The sacrificial templates that can be used can be of any type known to those skilled in the art and in particular those described in the application WO2007 / 043731. According to a preferred embodiment, the sacrificial template is advantageously chosen from organosilanes and more preferably from [3- (trimethoxysilyl) propyl] octadecyldimethylammonium chloride, [3- (trimethoxysilyl) propyl] hexadecyl dimethylammonium chloride, [3- (trimethoxysilyl) propyl] dodecyldimethylammonium chloride, [3- (trimethoxysilyl) propyl] octylammonium chloride, N- [3- (trimethoxysilyl) propyl] aniline, 3- [2- (2-amino) ethylamino) ethylamino] propyltrimethoxysilane, N- [3- (trimethoxysilyl) propyl] -N '- (4-vinylbenzyl) ethylenediamine, triethoxy-3- (2-imidazolin-1-yl) propylsilane, 1 - [3- (trimethoxysilyl) propyl] urea, N- [3- (trimethoxysilyl) propyl] -ethylenediamine, [3- (diethylamino) propyl] trimethoxysilane, (3-glycidyloxypropyl) trimethoxysilane, methacrylate of 3- (trimethoxysilyl) propyl, [2- (cyclohexenyl) ethyl] triethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxysilane, (3-aminopropyl) trimethoxysilane, (3-mercaptopropyl) trimethoxysilane, (3-chloropropyl) trimethoxysilane, as well as mixtures of two or more of them in all proportions.

Of the sacrificial templates listed above, [3- (trimethoxysilyl) propyl] octadecyldimethylammonium chloride, or TPOAC, is particularly preferred.

It is also possible to use sacrificial templates of higher molar mass and for example PPDA (Poly-Diallyldimethylammonium Polymer), PVB (PolyVinyl Butyral) and other oligomeric compounds known in the art to increase the diameter of the mesopores.

According to a preferred embodiment of the process of the present invention, in step a), the agglomeration of crystals of at least one zeolite FAU of LSX type with hierarchical porosity is carried out, as previously described, prepared in the presence of a sacrificial template to be eliminated.

This removal can be carried out according to the methods known to those skilled in the art, for example by calcination, and in a nonlimiting manner, the calcination of zeolite crystals comprising the sacrificial template can be carried out under oxidizing gaseous sweep and / or inert, in particular with gases such as oxygen, nitrogen, air, dry and / or decarbonated air, oxygen-depleted air, optionally dry and / or decarbonated, at a temperature or temperatures above 150 ° C. C, typically between 180 ° C and 800 ° C, preferably between 200 ° C and 650 ° C, for a few hours, for example between 2 and 6 hours. The nature of the gases, the ramps of temperature rise and the successive stages of temperatures, their durations will be adapted according to the nature of the sacrificial template. The additional step of removing the optional sacrificial template can be performed at any time during the process for preparing the zeolite adsorbent of the invention. The elimination of said sacrificial template can thus advantageously be carried out by calcination of the zeolite crystals before the agglomeration step a), or else concomitantly with the calcination of the adsorbent during step a).

However, it would not be departing from the scope of the invention if the agglomeration of step a) included the agglomeration of several LSX type FAU zeolites having an Si / Al atomic ratio equal to 1.00 ± 0, And having an external surface area measured by nitrogen adsorption of between 20 m ² . g ^"1 and 150 m ² .g ^{" 1} obtained in different modes.

The synthesis of zeolite FAU LSX type is generally in alkaline medium (sodium hydroxide and potassium and thus Na ⁺ and K ⁺ cations). The LSX type FAU zeolite crystals thus obtained comprise mainly, or even exclusively, sodium and potassium cations. However, it is not beyond the scope of the invention to use crystals which have undergone one or more cationic exchanges, between the synthesis, before or after the eventual elimination of the sacrificial template, if this step is carried out before the implementation of the procedure. step a). In this case, step c) and possibly step d) of exchange may (possibly) not be necessary.

The size of LSX-type FAU zeolite crystals used in step a) and FAU zeolite crystals in the adsorbents according to the invention is measured by scanning electron microscope (SEM) observation. As indicated above, preferably, the number average diameter of the crystals is between 0.5 μηη and 20 μηι inclusive, preferably between 0.5 μηη and 10 μηη inclusive, more preferably between 0.8 μηη and 10 μηη, included terminals, better still between 1 μηη and 10 μηη, included terminals, and more preferably between 1 μηη and 8 μηη, included terminals. In this document, the term "number average diameter" or "size" is used, in particular for zeolite crystals. The method of measuring these quantities is explained later in the description.

The agglomeration and the shaping of step a) can be carried out according to all the techniques known to those skilled in the art, and in particular according to one or more of the techniques chosen from extrusion, compacting, agglomeration. on granulator plate, granulator drum, atomization and others.

The proportions of agglomeration binder (see definition below) and zeolite used are 8 parts to 15 parts by weight of binder for 92 parts to 85 parts by weight of zeolite.

At the end of step a) the finest agglomerated adsorbents can be removed by cycloning and / or sieving and / or agglomerates too large by sieving or crushing, in the case of extruded, for example. The adsorbents thus obtained, whether in the form of beads, extrudates or the like, preferably have a mean diameter by volume, or their length (larger dimension when they are not spherical), between 0.2 mm and 2 mm, and in particular between 0.2 mm and 0.8 mm and preferably between 0.40 mm and 0.65 mm inclusive.

The binder used in the context of the present invention may be chosen from conventional binders known to those skilled in the art, zeolitizable or non-zeolizable, and preferably chosen from clays and mixtures of clays, silicas, aluminas, colloidal silicas, alumina gels, and the like, and mixtures thereof.

The clays are preferably chosen from: kaolin, kaolinite, nacrite, dickite, halloysites, attapulgite, sepiolite, montmorillonite, bentonite, illite and metakaolin, as well as mixtures of two or more of them in all proportions.

In step a), in addition to the zeolite crystal (s), the binder may also comprise one or more additives. The additives are preferably organic, for example lignin, starch, carboxymethylcellulose, surfactant molecules (cationic, anionic, nonionic or amphoteric), intended to facilitate the handling of the dough zeolite (s) / clay (s) by modifying the rheology and / or stickiness or to give the final adsorbents satisfactory properties, including macroporosity.

Mention may preferably be made of, but not limited to, methylcelluloses and their derivatives, lignosulfonates, polycarboxylic acids and carboxylic acid copolymer acids, their amino derivatives and their salts, in particular alkaline salts and sodium salts. 'ammonium. The additives are introduced at from 0 to 5%, preferably from 0.1% to 2%, by weight relative to the total weight of the adsorbent.

The additives may also comprise a source of liquid and / or solid silica, preferably representing from 1% to 5% of the total mass of said solids. The possible source of silica may be of any type known to those skilled in the art, specialist in the synthesis of zeolites, for example colloidal silica, diatoms, perlite, fly ash ash in the language English), sand, or any other form of solid silica. For the calcination included in step a), the nature of the gases, the ramps for temperature rise and the successive temperature increments, as well as their respective durations, will be adapted in particular according to the nature of the sacrificial template to be eliminated and depending on the nature of the binder used in the agglomeration step a). The SEM observation of the zeolitic adsorbent confirms the presence of non-zeolitic phase comprising, for example, agglomeration binder or any other amorphous phase in the adsorbents.

The cation exchange (s) (s) (c) and (d) stages described above are carried out according to the conventional methods known to those skilled in the art, and most often by contacting the adsorbents originating from step a) or step b) with a barium salt, such as barium chloride (BaCl ₂ ) and / or potassium (KCl) and / or barium and potassium, in aqueous solution at a temperature between room temperature and 100 ° C, and preferably between 80 ° C and 100 ° C to quickly obtain high levels of barium, ie levels of preferably greater than 25%, preferably greater than 28% very preferably greater than 34%, even more preferably greater than 37%, expressed by weight of barium oxide relative to the total mass of the adsorbent.

Advantageously, the barium content expressed as barium oxide is between 28% and 42%, and typically between 37% and 40%, limits included, by weight relative to the total weight of the adsorbent. It is preferred to operate with a large excess of barium ions relative to the cations of the zeolite that it is desired to exchange, typically an excess of the order of 10 to 12, advantageously by proceeding by successive exchanges.

Potential exchange with potassium in step d) can be practiced before and / or after the barium exchange (step c). It is also possible to agglomerate in step a) LSX-type zeolite crystals already containing barium or potassium ions or barium and potassium (pre-exchange of the cations present in the zeolite type LSX starting, typically sodium cations and potassium, by barium or potassium ions or barium and potassium before step a) and overcome (or not) steps c) and / or d).

Surprisingly, the Applicant has observed that the cation exchange step, which can be difficult because of the relative fragility of the zeolite crystal structure hierarchized porosity does not affect the intrinsic properties of external surface and the microporous volume (reduced to mass of the adsorbent once exchanged) of said zeolite crystals with hierarchical porosity.

After the cation exchange step (s), the washing is then carried out, generally and preferably with water, followed by drying of the adsorbent thus obtained ( step e). The activation which follows the drying (step f) is carried out in a conventional manner, according to the methods known to those skilled in the art, for example at a temperature generally between 100 ° C. and 400 ° C., as indicated previously in step f) of the process. Activation is carried out for a fixed period of time depending on the desired loss on fire. This duration is generally between a few minutes and a few hours, typically between 1 hour and 6 hours.

Use of adsorbents according to the invention

The present invention also relates to the uses of the zeolite adsorbents described above as adsorption agents which may advantageously replace the adsorption agents described in the literature, based on conventional zeolite crystals FAU LSX type comprising barium and / or potassium, and in particular in the uses listed below:

Separation of sections of C8 aromatic isomers and in particular xylenes,

Separation of isomers of substituted toluene such as nitrotoluene, diethyltoluene, toluene diamine, and others,

• separation of cresols,

• separation of polyhydric alcohols, such as sugars.

According to another subject, the present invention relates to a process for separating xylene isomers in the gas phase or in the liquid phase using at least one zeolite adsorbent as defined above, and preferably in which the zeolite crystals ( s) of the zeolitic adsorbent are prepared by direct synthesis using one or more structuring agents (or sacrificial templates).

In one variant, the invention relates in particular to a process for separating high purity paraxylene (that is to say a purity greater than or equal to 90%) in a simulated moving bed from a feedstock. aromatic hydrocarbons containing 8-carbon isomers comprising the following steps:

a) a step of bringing the charge into contact with an adsorbent bed comprising at least one zeolite adsorbent as defined above, so as to preferentially adsorb the paraxylene,

b) a step of contacting the adsorbent bed with a desorbent, the desorbent being preferably either toluene or paradiethylbenzene, c) a step of withdrawing the adsorbent bed from a stream containing the desorbent and the products the least selectively adsorbed charge,

d) a step of withdrawing the adsorbent bed from a stream containing the desorbent and the desired product, namely paraxylene,

e) a separation of the stream resulting from stage c) into a first stream containing the desorbent and a second stream containing the products of the least selectively adsorbed feed, f) a separation of the stream resulting from stage d) into a first stream containing the desorbent and a second stream containing paraxylene at a purity level greater than or equal to 90%, preferably greater than or equal to 99%, and very preferably greater than or equal to 99.7%.

The invention relates in particular to a process for separating paraxylene from a filler of cuts of aromatic isomers containing 8 carbon atoms, using, as paraxylene adsorption agent, a zeolite adsorbent as defined above, and in particular a zeolite adsorbent based on FAU LSX type comprising barium and / or potassium and having a large external surface characterized by nitrogen adsorption, typically between 20 m ² . g ^"1 and 100 m ² .g ^-1 , and more preferably between 20 m ² . g ^"1 and 80 m ² .g ^-1 and even more preferably between 30 and 80 m ² . g ^"1 inclusive terminals, implemented in processes in the liquid phase, but also in the gas phase.

The separation process according to the invention can be carried out by preparative adsorption liquid chromatography (in batch), and advantageously continuously in a simulated moving bed unit, that is to say against simulated current or simulated co-current, and more particularly counter-current simulated.

The operating conditions of a simulated moving bed adsorption industrial unit operating countercurrently are generally as follows:

• number of beds: 4 to 24;

• number of zones: at least 4 operating zones, each located between a feed point (charge flow to be treated or desorbent flow) and a withdrawal point (raffinate flow or extract flow);

Advantageously at a temperature of between 100 ° C. and 250 ° C., preferably between 140 ° C. and 190 ° C .;

Pressure between the bubble pressure of xylenes (or toluene when toluene is chosen as the desorbent) at the process temperature and 3 MPa;

• ratio of desorbent flows on charge: 0.7 to 2.5, preferably 0.7 to 2.0 (for example 0.9 to 1.8 for a unit of adsorption only ("stand alone" in English language) and 0.7 to 1.4 for an adsorption unit combined with a crystallization unit);

Recycling rate: 2 to 12, preferably 2.5 to 6;

• cycle time, corresponding to the time between two injections of desorbent on a given bed: advantageously between 4 and 25 min.

[0093] Reference may also be made to the teaching of patents US 2,985,589, US 5,284,992 and US 5,629,467.

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

The desorbent is a desorption solvent whose boiling point is lower than that of the feedstock, such as toluene or greater than that of the feedstock, such as para-diethylbenzene (PDEB). Advantageously, the desorbent is toluene or para-diethylbenzene.

The selectivity of the adsorbents according to the invention for the adsorption of paraxylene contained in aromatic C 8 cuts is optimal when their loss on ignition measured at 950 ° C. is preferably less than or equal to 7.7%, preferably between 0 and 7.7%, very preferably between 3.0% and 7.7%, more preferably between 3.5% and 6.5% and even more preferably between 4.5% and 6%, terminals included.

The water content in the incoming stream is preferably adjusted between 20 ppm and 150 ppm, for example by adding water in the feed stream and / or desorbent.

In addition, it has been noted that the selection of an outer surface greater than 20 m ² . g ^"1 as previously indicated makes it possible to reduce the transport time to the micropores, leading to a significantly improved material transfer compared to the prior art.

Moreover, it has been noticed that the selection of an outer surface of between 20 m ² . g ^"1 and 100 m ² .g ^-1 , as indicated above associated with the choice of an LSX type FAU zeolite of Si / Al atomic ratio equal to 1.00 ± 0.05 makes it possible to obtain adsorption selectivities. paraxylene vis-à-vis other isomers sufficient for good separation, and especially selectivities of paraxylene vis-à-vis ethylbenzene, whose affinity for the adsorbent is highest after paraxylene, greater than 2.1.

It was noted that the selectivity of paraxylene with respect to ethylbenzene adsorbents based on LSX same atomic ratio Si / Al whose external surface is greater than 100 m ² . g ^"1 or adsorbents based on zeolite type FAU X atom Si / Al greater than 1 00 ± 0.05 and external surface between 20 m ² .g ^-1 and 100 m ² . g ^"1 , is strictly less than 2.1.

Another advantage is to be able to have crystals of micrometric size (typically between 0.5 μηη and 20 μηι, inclusive, more preferably between 0.5 μηη and 10 μηη, included terminals, more preferably between 0 , 8 μηη and Ι Ο μηη, limits included, better still between 1 μηη and 10 μηη, limits included, and more preferably between 1 μηι and 8 μηη, limits included) which are more easily manipulated, thus making the manufacture of adsorbents easier.

Thus, the zeolitic adsorbents of the invention exhibit, in particular, improved material transfer properties while maintaining optimum selectivity properties of paraxylene with respect to its isomers, and typically greater than 2, 1, as well as of adsorption capacity, and maintaining a high mechanical strength for use in a method of separation of paraxylene in the liquid phase, preferably simulated countercurrent type.

CHARACTERIZATION TECHNIQUES

Granulometry of zeolitic crystals - Detection of mesopores

The estimation of the average number diameter of the FAU zeolite crystals used during the agglomeration (step a) and the crystals contained in the zeolite adsorbents according to the invention is carried out by observation under a scanning electron microscope (SEM). .

In order to estimate the size of the zeolite crystals on the samples, a set of images is carried out at a magnification of at least 5000. The diameter of at least 200 crystals is then measured using a dedicated software. The accuracy is of the order of 3%.

As indicated in US Pat. No. 7,785,563, the transmission electron microscope (TEM) further makes it possible to verify whether the zeolite crystals of the adsorbent of the present invention are solid zeolite crystals (ie non-mesoporous) or aggregates. solid zeolite crystals or mesoporous crystals (see the comparison of the TEM images of Figure 1, where the mesoporosity is clearly visible and Figure 2 shows solid crystals). The MET observation thus makes it possible to visualize the presence or the absence of the mesopores.

Chemical analysis of zeolite adsorbents - Si / Al ratio and exchange rate:

An elemental chemical analysis of the final product obtained after the steps a) to f) described above, can be carried out according to various analytical techniques known to those skilled in the art. Among these techniques, mention may be made of the technique of chemical analysis by X-ray fluorescence as described in standard NF EN ISO 12677: 201 1 on a wavelength dispersive spectrometer (WDXRF), for example Tiger S8 of the Bruker company.

X-ray fluorescence is a non-destructive spectral technique exploiting the photoluminescence of atoms in the X-ray domain, to establish the composition elementary of a sample. The excitation of the atoms generally by an X-ray beam or by bombardment with electrons, generates specific radiations after return to the ground state of the atom. The X-ray fluorescence spectrum has the advantage of relying very little on the chemical combination of the element, which offers a precise determination, both quantitative and qualitative. A measurement uncertainty of less than 0.4% by weight is obtained conventionally after calibration for each oxide.

These elementary chemical analyzes make it possible both to verify the Si / Al atomic ratio of the zeolite used during the preparation of the adsorbent, as well as the Si / Al atomic ratio of the adsorbent, and to verify the quality of the the ion exchange described in step c) and in optional step d). In the description of the present invention, the measurement uncertainty of the Si / Al atomic ratio is ± 5%.

The quality of the ion exchange is related to the number of moles of sodium oxide, Na ₂ 0, remaining in the zeolite adsorbent after exchange. For example, the exchange rate by barium ions is estimated by evaluating the ratio between the number of moles of barium oxide, BaO, and the number of moles of the whole (BaO + Na ₂ 0 + K ₂ 0 ). Likewise, the exchange rate by potassium ions is estimated by evaluating the ratio between the number of moles of potassium oxide K ₂ 0 and the number of moles of the whole (BaO + K ₂ 0 + Na ₂ 0 ). It should be noted that the contents of various oxides are given in percentage by weight relative to the total weight of the anhydrous zeolite adsorbent.

Granulometry of zeolite adsorbents:

The determination of the average volume diameter of the zeolite adsorbents obtained at the end of step a) of agglomeration and shaping is carried out by analysis of the particle size distribution of an adsorbent sample by imaging. according to ISO 13322-2: 2006, using a treadmill allowing the sample to pass in front of the camera lens.

[01 11] The volume mean diameter is then calculated from the particle size distribution by applying the ISO 9276-2: 2001 standard. In this document, the term "volume mean diameter" or "size" is used for zeolite adsorbents. The accuracy is of the order of 0.01 mm for the size range of adsorbents of the invention.

Mechanical resistance of zeolite adsorbents:

The crush resistance of a bed of zeolitic adsorbents as described in the present invention is characterized according to the Shell method SMS series 1471-74 (Shell Method Series SMS1471-74 "Determination of Bulk Crushing Strength of Catalysts. Compression-Sieve Method ") associated with the" BCS Tester "device marketed by Vinci Technologies. This method, initially intended for the characterization of catalysts from 3 mm to 6 mm is based on the use of a screen of 425 μιη which will allow in particular to separate the fines created during the crash. The use of a 425 μιη sieve remains suitable for particles greater than 1.6 mm in diameter, but must be adapted according to the particle size of the adsorbents that are to be characterized.

The adsorbents of the present invention, generally in the form of beads or extrudates, generally have a volume average diameter or a length, ie the largest dimension in the case of nonspherical adsorbents, of between 0.2 mm. and 2 mm, and in particular between 0.2 mm and 0.8 mm and preferably between 0.40 mm and 0.65 mm inclusive. Therefore, a sieve of 100 μιη is used in place of the sieve of 425 μιη mentioned in the standard Shell method SMS1471-74.

The measurement protocol is as follows: a sample of 20 cm ³ of agglomerated adsorbents, previously sieved with the appropriate sieve (100 μιη) and previously dried in an oven for at least 2 hours at 250 ° C. (at instead of 300 ° C mentioned in the standard Shell method SMS 1471-74), is placed in a metal cylinder of known internal section. An increasing force is imposed in steps on this sample by means of a piston, through a bed of 5 cm ³ of steel balls in order to better distribute the force exerted by the piston on the agglomerated adsorbents (use of balls 2 mm in diameter for particles of spherical shape with a diameter strictly less than 1.6 mm). The fines obtained at the different pressure levels are separated by sieving (100 μιη adapted sieve) and weighed.

The crush strength in bed is determined by the pressure in megaPascal (MPa) for which the amount of cumulative fines passing through the sieve is 0.5% by weight of the sample. This value is obtained by plotting the mass of fines obtained as a function of the force applied on the adsorbent bed and by interpolating at 0.5% by mass of cumulated fines. The mechanical resistance to crushing in a bed is typically between a few hundred kPa and a few tens of MPa and generally between 0.3 MPa and 3.2 MPa. The accuracy is conventionally less than 0.1 MPa.

Identification and quantification of zeolite fractions of zeolite adsorbents and estimation of the mesh parameter The identification of the zeolite fractions (in bulk) contained in the adsorbent is performed by X-ray diffraction analysis (XRD). This analysis is carried out on a device of the Bruker brand. The identification of the crystalline phases present in the zeolite adsorbent is carried out by comparison with the sheets of the ICDD database and possibly by comparison with the diffractogram of an appropriate reference (zeolite crystals FAU LSX type (supposed to be 100% crystalline ) Si / Al atomic ratio equal to 1.00, and having undergone the same cation exchange treatments as the adsorbent considered). For example, the presence of the X-type zeolite exchanged with Barium will be confirmed by comparison of the lines of the diffractogram obtained with the ICDD sheet No. 38-0234 ("Zeolite X, (Ba)"). The comparison of the diffractograms is completed by a comparison of the mesh parameters measured on the reference zeolite and on the adsorbent under consideration. The measurement of the zeolite mesh parameter is performed accurately (to ± 0.01 Â): to do this, an internal standard (NIST-certified Si 640b) is added and the data is processed with the TOPAS software. For example, a measurement carried out on zeolite X crystals having an Si / Al atomic ratio equal to 1.25 and exchanged at 95% by barium gives a mesh parameter of 25.02 ± 0.01 Å, whereas A measurement carried out on zeolite LSX crystals, having an Si / Al atomic ratio equal to 1.00, and exchanged at 95% with barium gives a mesh parameter of 25.19 Å 0.01 Å.

The amount of zeolite fractions (in bulk) is evaluated from the relative peak intensities of the diffractograms by taking as reference the peak intensities of the reference zeolite mentioned above. The peaks, allowing to go back to the crystallinity, are the most intense peaks of the angular zone 2Θ between 9 ° and 37 °, namely the peaks observed in the angular ranges 2Θ between respectively 11 ° and 13 °, between 22 ° and 26 ° and between 31 ° and 33 °.

Microporous volume and external surface

The crystallinity of the zeolite adsorbents of the invention is also evaluated by measuring their microporous volume by comparing it with that of an appropriate reference (100% crystalline zeolite under identical cationic treatment conditions or theoretical zeolite). This microporous volume is determined from the measurement of the gas adsorption isotherm, such as nitrogen, at its liquefaction temperature.

Prior to the adsorption, the zeolitic adsorbent is degassed between 300 ° C and 450 ° C for a period of between 9 hours and 16 hours, under vacuum (P <6.7 × 10 ^-4 Pa). The measurement of the isotherm adsorption of nitrogen at 77K is then carried out on a device of Micromeritics ASAP 2020 M, taking at least 35 measurement points for reporting relative pressure P / P ₀ between 0.002 and 1.

The microporous volume and the external surface are determined by the t-plot method from the obtained isotherm, by applying the ISO 15901-3: 2007 standard and by calculating the statistical thickness t by the equation of Harkins-Jura. The microporous volume and the external surface are obtained by linear regression on the points of the t-plot between 0.45 nm and 0.57 nm, respectively from the ordinate at the origin and the slope of the linear regression. . The microporous volume evaluated is expressed in cm ³ of liquid adsorbate per gram of anhydrous adsorbent. The external surface is expressed in m ² per gram of anhydrous adsorbent.

Macroporous and mesoporous volume and grain density

The macroporous and mesoporous volumes and the grain density are measured by porosimetry by mercury intrusion. Such a mercury porosimeter Autopore 9500 Micromeritics ^® is used to analyze the distribution of the pore volume contained in macropores and the mesopores.

The experimental method, described in the operating manual of the apparatus referring to the ASTM D4284-83 standard, consists in placing a sample of adsorbent (zeolite granular material to be measured) (known loss to fire) previously weighed. , in a cell of the porosimeter, then, after a prior degassing (discharge pressure of 30 μιη Hg for at least 10 min), to fill the cell with mercury at a given pressure (0.0036 MPa), and then to apply incrementally increasing pressure up to 400 MPa in order to gradually penetrate mercury into the porous network of the sample.

The relationship between the applied pressure and the apparent diameter of the pores is established by assuming cylindrical pores, an angle of contact between the mercury and the pore wall of 140 ° and a mercury surface tension of 485 dynes / cm. . The cumulative amount of mercury introduced as a function of the applied pressure is recorded. The value at which the mercury fills all the inter-granular voids is fixed at 0.2 MPa, and it is considered that, beyond this, the mercury penetrates into the pores of the granular material. The volume of grain (Vg) is then calculated by subtracting the cumulative volume of mercury at this pressure (0.2 MPa) from the volume of the cell of the porosimeter, and dividing this difference by the mass of the anhydrous equivalent granular material, that is to say the mass of said material corrected for loss on ignition.

The grain density is the inverse of the grain volume (Vg), and is expressed in grams of anhydrous adsorbent per cm ³ .

The macroporous volume of the granular material is defined as the cumulative volume of mercury introduced at a pressure of between 0.2 MPa and 30 MPa, corresponding to the volume contained in the pores with an apparent diameter of greater than 50 nm. The mesoporous volume of the granular material is defined as the cumulative volume of mercury introduced at a pressure of between 30 MPa and 400 MPa.

In this document, macroporous and mesoporous volumes of zeolitic adsorbents, expressed in cm ³ . g ^"1 , are thus measured by mercury intrusion and reported to the mass of the sample in anhydrous equivalent, that is to say the mass of said material corrected for loss on ignition.

Loss on fire of zeolite adsorbents:

The loss on ignition is determined in an oxidizing atmosphere, by calcining the sample in air at a temperature of 950 ° C. ± 25 ° C., as described in standard NF EN 196-2 (April 2006). The standard deviation of measurement is less than 0.1%.

Characterization of liquid phase adsorption by drilling:

The technique used to characterize the adsorption of molecules in liquid phase on a porous solid is the so-called drilling technique, described by Ruthven in "Principles of Adsorption and Adsorption Processes" (Chapters 8 and 9, John Wiley & Sons, 1984) which defines the technique of breakthrough curves as the study of the response to the injection of a step of adsorbable constituents. The analysis of the average time of exit (first moment) of the drilling curves provides information on the adsorbed quantities and also makes it possible to evaluate the selectivities, that is to say the separation factor, between two adsorbable constituents. The injection of a non-adsorbable component used as a tracer is recommended for the estimation of non-selective volumes. The analysis of the dispersion (second moment) of the drilling curves makes it possible to evaluate the equivalent height of theoretical plates, based on the representation of a column by a finite number of ideally stirred hypothetical reactors (theoretical stages), which is a direct measurement of the axial dispersion and resistance to material transfer of the system. EXAMPLES

Example A Synthesis of Conventional LSX Zeolite Crystals (Synthesis A of Patent FR 2 925 366) (Comparative Example)

Crystals are prepared according to the synthesis A described in patent FR 2925366). The crystals obtained after filtration, washing and drying are identified by X-ray diffraction as faujasite. The chemical analysis of the solid gives a ratio Si / Al = 1.01.

The microporous volume and the external surface measured according to the t-plot method from the nitrogen adsorption isotherm at 77K after vacuum degassing at 400 ° C. for 10 hours are respectively 0.305 cm ³ / g and 6 m ² / g.

The analysis of the size of the zeolite crystals is carried out by scanning electron microscopy. The average crystal size is 2.6 μηη.

Example B Synthesis of zeolite crystals FAU with hierarchical porosity

Example B1: Synthesis of zeolite crystals of XPH type of Si / Al = 1.24 ratio of external surface equal to 90 m ² · g ^-1 (comparative example)

A zeolite X with an external surface equal to 90 m ² . g ^"1 is synthesized directly according to the synthesis mode described in the article Inayat et al (Angew Chem Int, Ed., (2012), 57, 1962-1965).

Step 1) Preparation of gel growth in stirred reactor with Archimedean screw 300 tr.min ^1.

In a stainless steel reactor equipped with a heating jacket, a temperature probe and a stirrer, a growth gel is prepared by mixing an aluminate solution containing 19 g of sodium hydroxide (FIG. NaOH), 128 g of alumina trihydrate (Al ₂ 0 ₃ .3H ₂ 0 containing 65.2% by weight AI ₂ 0 ₃₎ and 195.5 g water at 25 ° C in 25 minutes with a speed stirring 300 tr.min ^"1 in a silicate solution containing 565.3 g of sodium silicate, 55.3 g of NaOH and 1997.5 g of water at 25 ° C.

[0134] The stoichiometry of the gel growth is as follows: 3.48 Na ₂ 0 / AI ₂ 0 ₃ / 3.07 Si0 _2/180 H ₂ 0. The homogenization of the gel growth is carried out with stirring at 300 revolutions min ^-1 for 25 minutes at 25 ° C.

Step 2): Introduction into the reaction medium of the structuring agent

27.3 g of 60% TPOAC solution in MeOH are introduced into the reaction medium with a stirring speed of 300 rpm ^"1 (TPOAC / Al ₂ O ₃ molar ratio = 0.04). After 5 minutes of homogenization, the stirring speed is lowered to 50 rpm ^"1 . Step 3): ripening phase

[0136] maintaining the reaction medium stirred at 50 tr.min ^"1 to 25 ° C for 22 hours and then start the crystallisation.

Step 4): Crystallization

The stirring speed is maintained at 50 rpm ^"-1 , and the setpoint of the jacket of the reactor is set at 80 ° C. so that the reaction medium rises to 75 ° C. in 80 minutes. 72 hours of residence at 75 ° C., the reaction medium is cooled by circulating cold water in the jacket to stop the crystallization Step 5): Filtration / washing

The solids are recovered on sintered and then washed with deionized water until neutral pH.

Step 6): Drying / Calcination

In order to characterize the product, the drying is carried out in an oven at 90 ° C. for 8 hours, the loss on ignition of the dried product is 22% by weight.

The calcination of the dried product necessary to release both the microporosity (water) and the mesoporosity by eliminating the structuring agent is carried out with the following temperature profile: 30 minutes of rise at 200 ° C., then 1 hour of bearing at 200 ° C, then 3 hours of rise at 550 ° C, and finally 1.5 hours of bearing at 550 ° C.

The microporous volume and the external surface measured by the t-plot method from the 77K nitrogen adsorption isotherm after degassing under vacuum at 400 ° C. for 10 hours are respectively 0.260 cm ³ . g ^-1 and 90 m ² g ^-1 . The number average diameter of the crystals of the mesoporous zeolite (or hierarchically porous) thus obtained is 4.5 μηη and the Si / Al ratio is equal to 1.24.

In what follows a mass expressed in anhydrous equivalent means a mass of product less its loss on ignition.

Example B2 Synthesis of zeolite crystals of LSXPH type of Si / Al ratio = 1.01 of external surface equal to 95 m ² .g ^-1 (according to the invention)

a) Preparation of the growth gel: reactor stirred by Archimedes screw at 250 rpm ^"1 .

In a 3 liter stainless steel reactor equipped with a heating jacket, a temperature probe and a stirrer, a growth gel is prepared by mixing an aluminate solution containing 300 g of sodium hydroxide. sodium (NaOH), 264 g of 85% potassium hydroxide, 169 g of alumina trihydrate (Al ₂ O ₃ , 3H ₂ O, containing 65.2% by weight of Al ₂ O ₃ ) and 1200 g water at 25 ° C in 5 minutes with a speed stirring 250 tr.min ^"1 silicate with a solution containing 490 g of sodium silicate, 29.4 g of NaOH and 470 g of water at 25 ° C.

[0144] The stoichiometry of the gel growth is as follows: 4.32 Na ₂ 0/1 85 K ₂ 0 / AI ₂ 0 ₃ / Si0 ₂ 2.0 / 1 14H ₂ 0. The homogenization of the gel growth is carried out with stirring at 250 tr.min ^"1 for 15 minutes at 25 ° C.

b) Addition of the nucleation gel

[0145] To the gel growth at 25 ° C with stirring at 300 tr.min ^"1, 1 1, 6 g of nucleating gel (0.4% by weight) of composition 12 Na ₂ 0 / Al ₂ 0 _3/10 Si0 _2/180 H ₂ 0 prepared in the same manner as the growth of frost, and ripened for 1 hour at 40 ° C. After 5 minutes of homogenization at 250 tr.min ^"1 speed agitation is reduced to 50 tr.min ^"1 and continued for 30 minutes.

c) Introduction into the reaction medium of the structuring agent

[0146] are introduced into the reaction mixture 35.7 g of 60% TPOAC solution in methanol (MeOH) with an agitation speed of 250 tr.min ^"1 for 5 minutes (molar ratio TPOAC / AI ₂ 0 ₃ = 0.04). Then the reaction is carried at 30 ° C a ripening step for 20 hours at 50 tr.min ^"1 before starting the crystallization.

d) Crystallization in 2 steps

The stirring speed is maintained at 50 rpm ^"1 and then an increase in the set point of the jacket of the reactor at 63 ° C is programmed linearly so that the reaction medium rises in temperature at 60 ° C. in 5 hours followed by a 21 hour stage at 60 ° C., then the set point of the jacket of the reactor is set at 102 ° C. so that the reaction medium rises to 95 ° C. in 60 minutes. at 95 ° C, the reaction medium is cooled by circulating cold water in the jacket to stop the crystallization.

e) Filtration / washing

f) Drying / Calcination

In order to characterize the product, the drying is carried out in an oven at 90 ° C. for 8 hours.

The calcination of the dried product necessary to release both the microporosity (water) and the mesoporosity by eliminating the structuring agent is carried out by vacuum degassing with a gradual increase in steps of 50 ° C. up to 400 ° C. C for a period of between 9 hours and 16 hours under vacuum (P <6.7 × 10 ^-4 Pa).

The microporous volume and the external surface measured according to the t-plot method from the nitrogen adsorption isotherm at 77K after vacuum degassing at 400 ° C. for 10 hours are respectively 0.215 cm ³ . g ^-1 and 95 m ² g ^-1 . The average number diameter of the crystals is 6 μηη. The diameters of the mesopores calculated from the nitrogen adsorption isotherm by the DFT method are between 5 nm and 10 nm. The X-ray diffractogram corresponds to a pure Faujasite structure (FAU), no LTA zeolite is detected. The Si / Al molar ratio of the LSXPH determined by X-ray fluorescence is 1.01.

Example B3: LSXPH zeolite crystal synthesis of external surface equal to 146 m ² .g ^-1 (comparative example)

A LSX zeolite having a higher surface area outermost porosity than the zeolite synthesized in Example B2 is obtained by strictly following the procedure of Example B2, except for the TPOAC / Al ₂ O ₃ molar ratio of step 2 which is equal to 0.07.

The microporous volume and the external surface measured by the t-plot method from the 77K nitrogen adsorption isotherm after degassing under vacuum at 400 ° C. for 10 hours are 0.198 cm ^3, respectively. g ^-1 and 146 m ² g ^-1 . The number average diameter of the crystals of the mesoporous zeolite (or hierarchical porosity) thus obtained is 6 μηη and the Si / Al ratio is equal to 1.01.

Example 1: (comparative)

Preparation of a zeolitic adsorbent in the form of granules with zeolite crystals of LSX according to Example A, of 2.6 μm in diameter, and a kaolin-type binder.

An adsorbent is prepared by reproducing example 6 described in patent FR 2 925 366, and grains are recovered which are selected by sieving in the particle size range between 0.3 mm and 0.5 mm, and such that the volume average diameter is 0.4 mm.

The barium exchange rate of this adsorbent evaluated from the elemental chemical analysis by WDXRF is 97% and its loss on ignition is 6.2%. The mesh parameter measured by DRX on this adsorbent is evaluated at 25.19 ± 0.01 Å. The microporous volume and the external surface measured according to the t-plot method from the 77K nitrogen adsorption isotherm after degassing under vacuum at 400 ° C. for 10 hours are respectively 0.231 cm ³ . g ^"1 and 7 m ^2, g ^{" 1} . The total volume contained in the macropores and mesopores (sum of macroporous volume and mesoporous volume) measured by intrusion of mercury, is 0.25 cm ³ . g ^"1. The ratio (macroporous volume) / (macroporous volume + mesoporous volume) is equal to 0.9. The mechanical strength of this adsorbent measured according to the method presented in the characterization techniques is 2.1 MPa.

Example 2 (comparative)

Preparation of a zeolitic adsorbent in the form of granules with 4.5 μm size XPH crystals and a kaolin type agglomeration binder such that the external surface is equal to 70 m ² . g ^'1

A homogeneous mixture consisting of 1600 g anhydrous equivalent of zeolite crystals X synthesized according to the procedure of Example B1 (crystal size 4.5 μηι), 350 g anhydrous equivalent of kaolin, 130 g is prepared. colloidal silica sold under the trade name Klebosol® 30 (containing 30% by weight of SiO ₂ and 0.5% of Na ₂ O) and the amount of water which allows agglomeration of the mixture by extrusion. The extrudates are dried, crushed so as to recover grains in the particle size range between 0.3 mm and 0.5 mm, and such that the average volume diameter is 0.4 mm, and then calcined for 2 hours at 550.degree. ° C under nitrogen sweep, then 2 hours at 550 ° C under dry decarbonated air.

The barium exchange is then operated with a concentration of barium chloride solution, BaCl ₂ , 0.7M at 95 ° C in 4 steps. At each stage, the volume ratio of solution to mass of solid is 20 ml / g and the exchange is continued for 4 hours each time. Between each exchange, the solid is washed several times in order to rid it of excess salt. It is then dried at 80 ° C. for 2 hours and then activated at 250 ° C. for 2 hours under a stream of nitrogen.

The barium exchange rate of this adsorbent evaluated from the elemental chemical analysis by WDXRF, as described above in the analytical techniques, is 97% and the loss on ignition is 5.5%. The mesh parameter measured by DRX on this adsorbent is evaluated at 25.02 ± 0.01 Å. The microporous volume and the external surface measured by the t-plot method from the nitrogen adsorption isotherm at 77K after vacuum degassing at 400 ° C. for 10 hours are respectively 0.192 cm ³ .g ^-1 and 70 m ² .g ^"1 .

The total volume contained in the macropores and mesopores (sum of the macroporous volume and the mesoporous volume) measured by intrusion of mercury, is 0.33 cm ³ . g ^"1. The ratio (macropore volume) / (volume macroporous + mesopore volume) is equal to 0.6.

The mechanical strength of this adsorbent measured according to the method presented in the characterization techniques is 2.1 MPa, corresponding to the pressure necessary to obtain 0.5% of fines. Example 3 (according to the invention)

Preparation of a zeolite adsorbent in the form of granules with LSXPH crystals of size 6 μm and a kaolin type agglomeration binder such that the external surface is equal to 64 m ² . g ^'1

An adsorbent is prepared identically to the preparation of the adsorbent of Example 2, but from LSX zeolite crystals synthesized according to the procedure of Example B2 (crystal size 6 μηη).

The barium exchange rate of this adsorbent evaluated from the elemental chemical analysis by WDXRF, as described above in the analytical techniques, is 97% and the loss on ignition is 5.0%. The mesh parameter measured by DRX on this adsorbent is evaluated at 25.20 ± 0.01 Å. The microporous volume and the external surface measured by the t-plot method from the nitrogen adsorption isotherm at 77K after degassing under vacuum at 400 ° C. for 10 hours are respectively 0.167 cm ³ .g ^-1 and 64 m ² .g ^"1 .

The total volume contained in the macropores and mesopores (sum of macroporous volume and mesoporous volume) measured by intrusion of mercury, is 0.29 cm ³ . g ^"1. The ratio (macropore volume) / (volume macroporous + mesopore volume) is equal to 0.73.

The mechanical strength of this adsorbent measured according to the method presented in the characterization techniques is 2.3 MPa, corresponding to the pressure necessary to obtain 0.5% of fines.

Example 4: (comparative)

Preparation of a zeolitic adsorbent in the form of granules with LSXPH crystals of size 6 μπ? and a kaolin agglomeration binder such that the external surface is equal to 121 m ² . g ^'1

An adsorbent is prepared in an identical way to the preparation of the adsorbent of Example 3, but from LSX zeolite crystals synthesized according to the procedure of Example B3 (average diameter of the crystals 6 μηη ).

The barium exchange rate of this adsorbent evaluated from the elemental chemical analysis by WDXRF, as described above in the analytical techniques, is 97% and the loss on ignition is 5.1%. The mesh parameter measured by DRX on this adsorbent is evaluated at 25.21 ± 0.01 Å. The microporous volume and the external surface measured by the t-plot method from the nitrogen adsorption isotherm at 77K after degassing under vacuum at 400 ° C. for 10 hours are respectively 0.147 cm ³ .g ^-1 and 121 m ² .g ^"1 . The total volume contained in the macropores and mesopores (sum of macroporous volume and mesoporous volume) measured by intrusion of mercury, is 0.34 cm ³ . g ^"1. The ratio (macropore volume) / (volume macroporous + mesopore volume) is equal to 0.63.

The mechanical strength of this adsorbent measured according to the method presented in the characterization techniques is 2.2 MPa, corresponding to the pressure necessary to obtain 0.5% of fines.

Example 5

A piercing test (frontal chromatography) is carried out on the adsorbent of Example 2 and on the adsorbent of Example 3 according to the invention to evaluate their selectivity for the adsorption of paraxylene vis-à-vis ethylbenzene screw. The amount of adsorbent used for this test is about 34 g.

The procedure for obtaining the drilling curves is as follows:

• filling of the column with the adsorbent and setting up in the test bench;

• filling with the desorption solvent at room temperature;

• gradual increase to 175 ° C under a stream of solvent (5 cm ³ min ^-1 );

• injection of solvent at 5 cm ³ . min ^-1 when the adsorption temperature (175 ° C) is reached;

• solvent / charge permutation to inject the charge (5 cm ³ min ^-1 );

• collection and analysis of the drilling effluent; the injection of the charge will be maintained until the solvent concentration in the effluent is zero.

The desorption solvent used is para-diethylbenzene. The selectivity between two isomers is evaluated using a feed containing 45% by weight of each of the isomers and 10% by weight of a tracer (isooctane) used for the estimation of non-selective volumes and not involved in the separation. . The test performed uses a load whose composition of the load is as follows:

• Paraxylene: 45% weight,

• Ethylbenzene: 45% by weight,

• Iso-octane: 10% by weight

The pressure is sufficient for the charge to remain in the liquid phase at the adsorption temperature, ie 1 MPa. The superficial velocity is 0.2 cm. s ^"1 .

The selectivity of paraxylene relative to ethylbenzene is calculated from the adsorbed quantities of each compound, the latter being determined by material balance from the first moments of the drilling curves of all the compounds. constituents present in the effluent. The results are shown in Table 1 below:

- Table 1 -

[0174] In the table above:

the adsorption capacity of xylenes is expressed in cm ³ of C8-aromatics adsorbed per gram of adsorbent;

- "PX" means paraxylene and "EB" means ethylbenzene

The adsorbents of Examples 2 to 4 have comparable total adsorption capacities for xylenes. On the other hand, the adsorbent of Example 3, according to the invention, has a selectivity between para-xylene and ethylbenzene of greater than 2.5 while the selectivity obtained with the adsorbents of Examples 2 and 4 is less than 2.1. The adsorbent of Example 3 will therefore be more efficient in separating a feed rich in ethylbenzene.

Example 6

The purpose of Example 6 is to illustrate the productivity gain obtained with an adsorbent according to the invention (adsorbent of Example 3) with respect to:

An adsorbent with zeolite crystals LSX of external surface non-compliant (too weak) according to the prior art (comparative adsorbent of Example 1),

And a non-compliant outer surface adsorbent (which is too high) with LSX zeolite crystals of Si / Al ratio equal to 1.00 ± 0.05 (adsorbent of Example 4).

The adsorbents of Examples 1, 3 and 4 were tested to evaluate their performance in separating paraxylene on a simulated counter-current chromatography pilot unit consisting of 15 columns in series of 2 cm in diameter, of 1.10 m. length. The circulation between the last and the first column is done by means of a recycling pump. At each intercolumn link, one can inject either a charge to be separated or desorbent. You can also extract either a raffinate or an extract. All columns and dispensing winnowing is maintained at 175 ° C, and the pressure is maintained above 1.5 MPa. The offsets of the different injection or withdrawal points are simultaneous according to a permutation time that can be adjusted. The beds are divided into 4 chromatographic zones according to the following configuration: • 3 beds between the desorbent injection and extract extraction defining zone 1

• 6 beds between extract extraction and charge injection defining zone 2

• 4 beds between charge injection and raffinate withdrawal defining zone 3

• 2 beds between raffinate withdrawal and desorbent injection defining zone 4.

The filler is composed of 21.3% by weight of paraxylene, 19.6% of orthoxylene, 45.1% of metaxylene and 14.0% of ethylbenzene.

In a first step, a test is carried out from the adsorbent according to Example 1. This test makes it possible to determine the charge and desorbent injection rates necessary to obtain paraxylene with a purity of 99.7% and a yield of at least 97%.

The paraxylene is obtained at the extract at a purity of 99.7% and a yield of 97% by injecting the feedstock at a flow rate of 39.5 g. min- ¹ and the desorbent at a flow rate of 35.5 g.min ^-1 , and by applying a switching time of the injection and withdrawal points of 1 18 seconds. The extract flow rate is 24.7 g.min ^"1 and the flow rate zone 4 is 105.9 g. ^{Min" 1.}

Subsequently, all of the adsorbents are tested by applying the same flow of desorbent. On the other hand, the charge flow, the time of rotation of the injection and withdrawal points, as well as the recycling flow rate can be adjusted in order to reach the required performances, namely a purity of 99.7% and a yield of 97%. The results are reported in Table 2.

- Table 2 -

Figure 3 illustrates the variation of the charge rate as a function of the external surface, the 3 points corresponding to Examples 1, 3 and 4 of Table 2.

Using adsorbent beads based on LSX crystals having an outer surface of 64 m ² . g ^"1 , that is to say adsorbents according to the invention, it is possible to obtain a paraxylene with the required performance of purity and yield, by injecting a higher charge rate than that treated with the adsorbent of Reference Example 1, while injecting the reference desorbent flow rate, namely 35.5 g.min ^-1 , using identical columns.

For example, with the adsorbent of Example 3 according to the invention, it is possible to produce paraxylene with a purity of 99.7% with a yield of 97% identical to those obtained with the adsorbent of the Reference example 1 while increasing the load flow by 26%. Therefore, at iso-specification, the productivity is increased by 26% with the adsorbent of Example 3 according to the invention relative to the adsorbent of Example 1.

In contrast to the adsorbents according to the invention, using adsorbent beads based on LSX crystals having an outer surface greater than 100 m ² . g ^"1 , that is to say beyond the upper limit defined by the invention, it is not possible to obtain a paraxylene with the required performance of purity and yield, by injecting a flow rate of feed greater than or equal to that treated with the adsorbent of Reference Example 1, while injecting the reference desorbent flow rate, namely 35.5 g.min ^-1 , using identical columns. On the contrary, to obtain the purity and yield performance required with surface surface adsorbents at 100 m ² . g ^"1 , a charge rate lower than that treated with the adsorbent of reference example 1 will be treated.

For example, with Γ adsorbent of Example 4 based on LSX crystals of external surface equal to 121 m ² . g ^"1 , that is to say, distinguished from the invention by an external surface greater than 100 m ² .g ^-1 , can be produced paraxylene in a purity of 99.7% with a yield of 97% identical to those obtained with the adsorbent of Reference Example 1 while reducing the charge flow rate by 28%. Therefore, at isospecification, the productivity is decreased by 28% with the adsorbent of Example 4 relative to the adsorbent of Example 1.

Example 7

The purpose of Example 7 is to illustrate the productivity gain obtained with an adsorbent according to the invention (adsorbent of Example 3) with respect to an adsorbent having the same external surface, but with zeolite crystals. X (adsorbent of Example 2), for charges containing ethylbenzene. The adsorbents of Examples 2 and 3 were tested to evaluate their performance in separating paraxylene on a simulated countercurrent chromatography pilot unit consisting of 15 columns in series 2 cm in diameter, 1.1 m in length. according to an operation identical to that described in Example 6.

Three filler compositions are used to evaluate the impact of the ethylbenzene content thereon on the productivity of the adsorbents:

A filler composed of 21.3% by weight of paraxylene, 19.6% of orthoxylene, 45.1% of metaxylene and 14.0% of ethylbenzene by mass, as in the preceding example,

A filler composed of 21.3% by weight of paraxylene, 23.8% of orthoxylene and 54.9% of metaxylene, which filler does not contain ethylbenzene,

A filler composed of 21.3% of paraxylene, 14.8% of orthoxylene, 33.9% of metaxylene and 30% of ethylbenzene by mass.

In Example 6, a test was carried out from the adsorbent of Example 3 according to the invention. This test made it possible to determine the charge and desorbent injection rates necessary to obtain paraxylene with a purity of 99.7% and a yield of at least 97%, for the feed containing 14% of ethylbenzene.

Paraxylene is obtained at the extract at a purity of 99.7% and a yield of 97% by injecting the feedstock at a flow rate of 49.9 g.min ^-1 and the desorbent at a flow rate of 35. 5 g.min ^-1 , and applying an injection point swap time of 66 seconds. The extract flow rate is 19.9 g.min ^"1 and zone 4 of the flow rate is 194.8 g. ^{Min" 1.}

Subsequently, the adsorbents of Example 2 and Example 3 are tested with the different fillers by applying the same desorbent flow rate. On the other hand, the charge flow, the time of rotation of the injection and withdrawal points, as well as the recycling flow rate can be adjusted in order to reach the required performances, namely a purity of 99.7% and a yield of 97%. The results are reported in Table 3 below:

- Table 3 -

Changing the composition of charge

FIG. 4 illustrates the variation of the feed rate as a function of the content of ethylbenzene contained therein, in the case of the adsorbent according to Example 2, based on X crystals and in the case of the adsorbent according to Example 3 according to the invention consisting of LSX crystals.

In this example, using the adsorbent of Example 3 according to the invention, it is possible to obtain a paraxylene with the required performance of purity and yield, by injecting a charge flow greater than or equal to that treated with the adsorbent of Comparative Example 2, while injecting the reference desorbent flow rate, namely 35.5 g. min ^-1 , using identical columns, regardless of the ethylbenzene content obtained in the feedstock It is also observed that the productivity gain provided by the adsorbent of Example 3 according to the invention is even greater The content of ethylbenzene is high, and there is also less variability in productivity as a function of the ethylbenzene content in the case of the adsorbent of Example 3 compared to the adsorbent of Example 2.

For a charge composition varying between 0 and 30% ethylbenzene, there is a productivity variation of less than 5% in the case of the adsorbent of Example 3 according to the invention. On the contrary, for the same variation in composition, there is a productivity variation of greater than 12% in the case of the adsorbent of Example 2 according to the invention.

Claims

A zeolitic adsorbent comprising at least one zeolite of FAU LSX structure, comprising barium and / or potassium, and for which the external surface of said zeolite adsorbent, measured by nitrogen adsorption, is between 20 m ² . g ^"1 and 100 m ² .g ^-1 , and preferably between 20 m ² . g ^"1 and 80 m ^2, g ^{" 1} and more preferably between 30 and 80 m ² . g ^"1 terminals included.

2. Zeolitic adsorbent according to claim 1, in which the zeolite of structure FAU is a zeolite of structure FAU of type LSX for which the number average diameter of the crystals is between 0.5 μηη and 20 μηη, inclusive, preferably between 0.5 μηη and 10 μηη, inclusive, more preferably between 0.8 μηη and 10 μηη, inclusive, more preferably between 1 μηη and 10 μηη, inclusive, and more preferably between 1 μηη and 8 μηη, terminals included.

A zeolitic adsorbent according to claim 1 or 2, wherein the barium content (Ba) expressed as barium oxide (BaO) is greater than 25%, preferably greater than 28%, very preferably greater than 34%, even more preferably greater than 37%, by weight relative to the total weight of the adsorbent.

4. Zeolitic adsorbent according to one of the preceding claims, wherein the potassium content (K), expressed as potassium oxide (K ₂ 0), is less than 30%, preferably less than 15% and preferably included between 0% and 10%, limits included by weight relative to the total weight of the adsorbent.

5. Zeolitic adsorbent according to one of the preceding claims, wherein the total volume contained in the macropores and mesopores measured by mercury intrusion, is between 0.15 cm ³ . g ^"1 and 0.5 cm ^3, g ^{" 1} , preferably between 0.20 cm ³ . g ^"1 and 0.40 cm ³ g ^-1 and very preferably between 0.20 cm ³ . g ^"1 and 0.35 cm ^3, g ^{" 1} , inclusive.

6. Zeolitic adsorbent according to any one of the preceding claims, wherein the mass fraction of zeolite FAU is greater than or equal to 85%, preferably greater than or equal to 90% by weight relative to the total weight of the adsorbent.

7. Zeolitic adsorbent according to any one of the preceding claims, having a ratio (macroporous volume) / (macroporous volume + mesoporous volume) of between 0.2 and 1, very preferably between 0.5 and 0.9, terminals included.

8. Process for the preparation of a zeolite adsorbent according to any one of the preceding claims, said process comprising at least the steps of:

a) agglomeration of crystals of at least one zeolite of structure FAU LSX type, having an external surface of between 20 m ² . g ^"1 and 150 m ² .g ^{" 1} , inclusive terminals, whose number average crystal diameter is between 0.5 μηη and 20 μηη inclusive, with a binder preferably comprising at least 80% of clay or a mixture of clays and up to 5% of additives and with the amount of water which allows the shaping of the agglomerated material, then drying and calcination of the agglomerates;

9. Process according to claim 8, in which the clays are preferably chosen from: kaolin, kaolinite, nacrite, dickite, halloysites, attapulgite, sepiolite, montmorillonite, bentonite, illite and metakaolin, as well as mixtures of two or more of between them in all proportions.

10. Use of a zeolite adsorbent according to any one of claims 1 to 7 or prepared according to one of claims 8 to 9, as adsorption agent in:

The separation of sections of C8 aromatic isomers and in particular xylenes,

The separation of isomers of substituted toluene such as nitrotoluene, diethyltoluene, toluene diamine and the like, • the separation of cresols,

• the separation of polyhydric alcohols, such as sugars.

11. Process for separating the isomers of xylenes in the gas phase or in the liquid phase using at least one zeolite adsorbent according to any one of claims 1 to 7 or prepared according to one of claims 8 to 9.

12. Separation process according to claim 11, which is a process for separating paraxylene from a filler of cuts of aromatic isomers with 8 carbon atoms, using, as adsorption agent for paraxylene, a zeolitic adsorbent according to any of claims 1 to 7 or prepared according to one of claims 8 to 9.

13. The method of claim 12, implemented in a simulated moving bed adsorption industrial unit, operating against the current under the operating conditions:

• number of beds: 4 to 24;

• number of zones: at least 4 operating zones, each located between a feed point and a draw-off point;

• temperature between 100 ° C and 250 ° C;

• ratio of desorbent flows on charge to be treated: 0.7 to 2.5;

Recycling rate: 2 to 12, preferably 2.5 to 6;

• cycle time, corresponding to the time between two injections of desorbent on a given bed: between 4 and 25 min.

14. The process of claim 13 wherein the desorbent is toluene or para-diethylbenzene.

The method of any one of claims 13 or 14, wherein the water content in the incoming streams is adjusted between 20 ppm and 150 ppm.