BRPI0820730B1 - AGLOMERATED ZEOLITHIC ADSORVENT, PROCESSES FOR PREPARING AN ADSORVENT AND SEPARATING AROMATIC ISOMERS, AND USING AT LEAST A ZEOLITHIC ADSORVENT - Google Patents

Description

"AGGLOMERED ZEOLYTIC ADSORBENT, PROCESSES FOR PREPARING AN ADSORBENT AND SEPARATING AROMATIC ISOMERS, AND USING AT LEAST A ZEOLYTIC ADSORBENT" The invention relates to a zeolite zeolite powder and zeolite powder mixture LSX, exchanged with barium or exchanged with barium and potassium.

These adsorbents may be used more particularly for the production of very pure paraxylene from an aromatic hydrocarbon filler containing 8 carbon atoms. The use of zeolitic adsorbents consisting of ion-exchanged X or Y zeolites such as barium, potassium or strontium, alone or in admixture, to selectively adsorb paraxylene in a mixture of aromatic hydrocarbons is known in the prior art. US 3,558,730, US 3,558,732, US 3,626,020, US 3,663,638 show that adsorbents comprising barium and potassium or barium alone aluminosilicates (US 3,960,774) are effective for separating paraxylene from a cut in aromatic Cg.

One method of preparing these adsorbents, for example, is described in US 3,878,127 and is to treat in agglomerated soda (zeolite X + binder) of Na20 / Al203 ratio strictly below 0.7 to replace exchangeable cations of the soda ash. zeolite (such as Group ILA protons or cations by sodium prior to a barium or barium + potassium exchange, the previous sodium exchange allowing more barium or barium + potassium ions to be added to the zeolitic structure.

These adsorbents are used as adsorption agents in liquid phase, preferably simulated countercurrent processes similar to those described in US 2,985,589 which apply among others to aromatic Cg cuts.

Prior art zeolites for the separation of xylenes belong to the structural type of faujasite, first described in US 2,882,244 and US 3,130,007, which are crystallized silicoaluminates having perfectly determined size cages connected at all three. dimensions. US 6,884,918 recommends a faujasite X of Si / Al atomic ratio between 1.15 and 1.5. US 6,410,815 teaches that low silica faujasite-based zeolitic adsorbents, i. and. Si / Al atomic ratio close to 1 (which will be called LSX, short for Low Silica X whose Portuguese translation is low silica zeolite X) are advantageously used for the separation of paraxylene. Low silica zeolite X and zeolite X therefore both have good performances in terms of paraxylene selectivity, but the synthesis of low silica zeolite X is especially difficult compared to the synthesis of zeolite X. To lower the atomic ratio Si / Al faujasite zeolite, it is necessary to increase the consumption of soda used in the zeolite synthesis process. In addition, to crystallize according to the structural type of faujasite when the Si / Al atomic ratio is 1, strong potassium concentrations must be added to inhibit the formation of zeolite A and obtain only low silica zeolite X. These strong soda and potash consumptions increase the cost of manufacturing this type of zeolite and pose problems with effluent rejection.

In the references listed above, the zeolitic adsorbents are in powder form or in the form of agglomerates consisting mainly of zeolite and up to 15% to 20% by weight of inert agglomerate binder. The synthesis of low silica zeolites X and X, which are generally performed by nucleation and crystallization of silicoaluminate gels, is obtained in powders whose use on an industrial scale is particularly difficult (significant losses in handling) and the forms are preferred. agglomerates, for example in the form of granules or grains, which do not have the drawbacks inherent in powdery materials.

These agglomerates, whether in the form of platelets, spheres or extruded, are generally made up of zeolite, which is the active element (in the sense of adsorption) and a binder to ensure the cohesion of zeolite crystals in the form of agglomerates and give the agglomerates sufficient mechanical strength to withstand the vibrations and movements to which they are subjected during their use. The preparation of these agglomerates is effected, for example, by pasteting the zeolite powder into a clayey mass in the order of from 80 to 90% by weight of zeolite powder to 20% to 10% by weight of binder, and then ball, platelet or extruded placement, and high temperature heat treatment for clay firing and reactivation of the zeolite, the barium exchange which may be effected before and / or after agglomeration of the powdery zeolite with the binder.

Zeolitic agglomerates are obtained whose particle size is generally a few millimeters and which, if binder selection and granulation are made according to the rules of the art, have a satisfactory set of properties, in particular porosity, mechanical strength, resistance to abrasion. US 6,410,815 teaches that the performance of the industrial paraxylene separation process depends to a large extent on the adsorbent, its adsorption capacity and the selectivity it shows for paraxylene in a medium consisting of Cg aromatic compounds, typically paraxylene, metaxylene, orthoxyethylene, ethylbenzene, as well as the ability of desorbents such as toluene and paradiethylbenzene to desorb adsorbed paraxylene. Adsorbent selectivity for component A over compound B is defined as the ratio of compound concentrations in the adsorbed phase divided by the ratio of compound concentrations in the non-adsorbed phase to equilibrium: (Xa / b Aads / Bads XB [jq Where Aads and Bads are the concentrations of compound A and compound B in the adsorbed phase respectively and A [iq and Büq are the concentrations of compound A and compound B in the fluid phase.] The present invention has as object zeolitic adsorbents notably usable. for the separation of paraxylene from a mixture of Cg aromatic compounds which exhibit excellent performances, notably in terms of xylene selectivity and adsorption capacity, said adsorbents being particularly adapted for use in a liquid phase paraxylene separation process preferably simulated countercurrent type.

The agglomerated zeolitic adsorbents according to the present invention comprise: zeolite X powder exchanged at least 90% for barium ions alone are barium ions and potassium ions, the exchangeable sites occupied by potassium which may represent up to 1/3 of the exchangeable sites. occupied by barium + potassium ions (the eventual complement being usually ensured by alkaline or alkaline earth ions in addition to barium and potassium); - LSX zeolite powder exchanged at least 90% for barium ions alone, for barium and potassium ions, the exchangeable sites occupied by potassium which may represent up to 1/3 of the exchangeable sites occupied by barium + potassium ions (the eventual complement being generally ensured by alkaline or alkaline earth ions in addition to barium and potassium); - and a binder less than or equal to 20% by weight of the total mass of the agglomerate.

Unless otherwise indicated, everything that follows the phrase "understood between" means "understood in the broad sense."

By zeolite X is meant a type X (faujasite) zeolite having an Si / Al atomic ratio strictly greater than 1.15 and less than or equal to 1.5, preferably comprised between 1, 2 and 1.4 and advantageously comprised between 1.2 and 1.3.

According to a preferred embodiment, the zeolite X of the agglomerates according to the invention consists essentially of crystals of average diameter (in number) measured by MEB and counting, generally from 0.1 to 4 pm, preferably from between 0.1 and 3 pm, and advantageously comprised between 0.1 and 2 pm.

By LSX zeolite (abbreviation of Low Silica X whose Portuguese translation is low silica X zeolite), here is meant a type X zeolite (faujasite) having a Si / Al atomic ratio of 1 to 1.15 preferably equal to 1.00 ± 0.05; values below the unit reflect analytical uncertainties as a measure of this relationship, and values above either the same analytical uncertainty or a tolerable deviation from product purity.

According to a preferred embodiment, the LSX zeolite of the agglomerates according to the invention consists essentially of crystals of average diameter (in number) measured by MEB and counting from 0.1 pm to 7 pm, preferably from from 0.1 pm to 4 pm, advantageously from 0.1 pm to 3 pm and even more advantageously from 0.1 pm to 2 pm.

By binder within the meaning of the present invention is meant an inert inorganic adsorption matrix comprising amorphous materials such as silica, mixtures of silica and alumina and / or compounds such as clays. It would not be apparent from the table of the present invention if this matrix contained zeolitic crystalline materials other than zeolite X and LSX zeolite as defined above in an amount not exceeding 5% of the total weight of the agglomerate.

For the zeolitic adsorbents according to the invention, the following two efficacy criteria (EC) are defined: CEpx / MX = Ctpx / MX X VDub CEpx / ΕΒ = αρχ / EB X ^ Dub where αΡχ ^ ιχ and aPX ^ B represent the selectivities between paraxylene and metaxylene and between paraxylene and ethylbenzene respectively, and where VDub is Dubinin volume, which is an estimate of the microporous volume, measured according to the process described below by nitrogen adsorption. K. The Dubinin volume is calculated according to the Dubinin-Radushkevich ratio as described by LOWELL et al. in “Characterization of Porous Solids and Powders: Surface Area, Pore Size and Density”, Chapter 9, “Micropore Analysis”, pages 143-145: which bind the volume V of adsorbed nitrogen to the relative pressure P / P0. Dubinin volume is Vo volume, the maximum volume of nitrogen vapor that can be condensed into the micropores of the adsorbent material. Nitrogen vapor (taken under normal conditions) is expressed per gram of adsorbent. Dubinin volume is then calculated from the volume Vo of gas, which is then converted to volume of liquid: it is expressed in cm per gram of adsorbent, and corresponds to the microporous volume available for adsorption.

Previously to the extent that the sample is pretreated at 500 ° C for 12 hours under vacuum (P <5.10.6 Torr; ie 6.7.10% C.p.). The measurement is then performed on a Micromeritics AS AP 2010 M type apparatus. Isothermal tracing is performed with the help of a pressure table of at least 35 points between 0.01 and 1 P / P0. Bring log value V as a function of (log (P / Po)) · Dubinin volume is obtained from the ordinate at the origin of the linear regression line of the points at which (log (P / Po)) 2 is between 1 and 2 (ie 0.039 <P / Po <0.1). The measurement uncertainty is ± 0.003.

Measurements made on adsorbents according to the invention at different ratios of zeolite X and zeolite LSX and with a given fixed binder rate show that the above two efficacy criteria (EC) are significantly higher for mixtures having LSX / Molar ratios. X from 0.1 to 10, preferably from 0.25 to 4.0, and most preferably from 0.5 to 2.0 with respect to adsorbents containing only zeolite X and binder and adsorbents. which contain only LSX zeolite and the binder. These ratios are preferably from 0.5 to 2.0, preferably from 0.54 to 1.86 for zeolite-only adsorbents and zeolite-only adsorbents. and the binder. The invention also relates to a process for preparing the agglomerates according to the invention which comprise the following steps: - the agglomeration of a mixture consisting of LSX zeolite powder and zeolite X powder in an LSX / X ratio ranging from 0.1 and 10 and preferably between 0.25 and 4, and most preferably between 0.5 and 2 with an agglomerating binder, preferably in which at least part of the binder contains one or more zeolitizable clays ( zeolitizable part), preferably at least 80% by weight, and then shaping, drying and calcining, - an optional zeolitizing step of said zeolitizable binder by an alkaline base solution, at least 90% of the barium agglomerate's swappable pool, followed by washing and drying of the barium-treated product (X, the LSX zeolite powder and those formed by any binder zeolitization), - possibly replacing up to 33% of the total potassium agglomerate exchangeable sites, followed by washing and drying of the product thus treated, - and / eventual activation of the product obtained.

Preferably, the preparation process according to the invention consists essentially of steps a / a and c and then and / or a / a and as defined above. Agglomeration and shaping (step a /) can be performed according to all techniques known to the skilled person, such as extrusion, compaction, agglomeration. The agglomeration binder is primarily intended to facilitate the shaping and agglomeration of zeolite powders. Preferably said binder is inert in the sense of adsorption. The agglomerating binder employed may contain attapulgite, kaolin, sepiolite, bentonite, montmorillonite clays.

In the case of the process where step a / is followed by step b / of zeolitization, the agglomeration binder contains a zeolitizable part, i. and. one or more zeolitizable clay (s), preferably from 80% to 100% of the total binder weight. Zeolitizable clays generally belong to the family of kaolinite, haloisite, nacrite, dickite, kaolin and / or metakaolin, to which a source of silica may be added. Kaolin is commonly used. The calcination following drying is carried out at a general temperature of between 500 and 600 ° C.

In addition, during step a /, in addition to zeolite powder and agglomerating binder, additives may also be employed, for example porogenous agents and / or additives designed to facilitate agglomeration and / or to improve the hardening of agglomerates. The zeolite X powder employed in step a / may be derived from the synthesis of sodium-exchanged zeolite X crystals, also called NaX or 13 X zeolite, but would not escape from the scope of the invention using a powder which has undergone one or more cationic exchanges between the synthesis in Na X form and its use in step a /. The possible source of silica may be colloidal silica, silicate, diatoms, perlite, fly ash, sand and / or any other form of silica. The LSX zeolite powder employed in step a / may come from the synthesis of zeolite crystals in NaKLSX form, but would not be excluded from the table using powder which has undergone one or more cationic exchanges between the synthesis in NaKLSX form and your job in step a /. The optional b / zeolitization step is notably intended to increase the adsorption capacity of agglomerated zeolitic adsorbents. It is effective only if the agglomerating binder contains one or more zeolitizable clays. Zeolitization may be practiced by immersing the product from step a / in an alkaline, preferably aqueous, basic solution, for example, an aqueous soda solution or a mixture of soda and potash, preferably of concentration greater than 0.5 Μ Said concentration is generally less than 3 M, preferably less than 2 M, advantageously less than 1 Μ. The zeolitization is preferably operated hot (above room temperature) typically at temperatures of the order of 80-100 ° C in order to improve process kinetics and reduce immersion durations to less than 8 hours, but not would leave the frame of the invention operating at lower temperatures.

According to this operating mode, at least 50% zeolitization is easily obtained, and preferably at least 70 to 82% by weight of the zeolitizable clay (s) contained in the binder. Wash with water followed by drying. The barium cation exchange step of the agglomerate is effected by contacting the agglomerates from optional step b, or step has or optional step d with a barium salt, such as BaCl2, in aqueous solution at a temperature. from room temperature to 100 ° C, and preferably from 80 to 100 ° C. To quickly obtain a high barium exchange rate, i. and. greater than 90%, it is preferable to operate with a large excess of barium in relation to the cations of the agglomerate to be exchanged, typically such that the Ba / Al ratio is of the order of 5 to 6 proceeding by successive exchanges to achieve minimum target exchange rate of at least 90% and preferably at least 95%. Throughout the text exchange rates are calculated in equivalent and not molarity. Eventual potassium exchange (step d /) may be practiced before and / or after barium change (step c) or simultaneously using a solution containing barium and potassium ions. It is also possible to agglomerate a mixture of zeolite X and LSX zeolite powder that already contains potassium ions and get rid of step d /. Activation (step e), the last step in the process of obtaining the adsorbents according to the invention, aims to set the water content as well as the loss to fire of the adsorbent in optimal limits. Thermal activation is generally carried out preferably at 200 to 300 ° C for a period of time, typically 1 to 6 hours, depending on the desired water content and fire loss according to the use of the adsorbent. that is targeted. The invention also relates to the use of at least one of the zeolitic adsorbents described above as adsorption agents which can advantageously replace the adsorption agents described in the zeolite X or LSX zeolite based, barium exchanged or barium exchanged literature. and potassium, and notably in the uses listed below: * separation of aromatic C8 isomers and notably xylenes, * separation of sugars, * separation of polyhydric alcohols, * separation of substituted toluene isomers such as nitrotoluene, diethyl toluene, toluenediamine, * separation of cresols, * separation of dichlorobenzenes. The invention notably relates to an improvement of the paraxylene recovery process from cuts of aromatic Cg isomers consisting of using as a paraxylene adsorption agent a zeolitic adsorbent according to the invention employed in liquid phase but also gas phase processes. . The invention relates particularly to a process of producing high purity paraxylene from an aromatic hydrocarbon filler containing 8 carbon atom isomers comprising the following steps: a) contacting, under suitable adsorption conditions, the loading with an adsorbent bed according to the invention so as to preferentially adsorb paraxylene, b) desorbing the adsorbent bed with a desorbent, which is preferably either toluene or paradiethylbenzene, c) an adsorbent bed extraction step from a desorbent-containing stream and the least selectively possible adsorbed filler products, d) an adsorbent bed extraction step from a desorbent and paraxylene stream, and ) a separation of the stream from step c) into a first stream containing desorbent and a second stream containing the products of the least sealed filler. and (f) a separation of the stream from step d) into a first stream containing the desorbent and a second stream containing the paraxylene at a purity level greater than or equal to 75% and preferably greater than or equal to 99. , 7%. The process may optionally likewise include the following steps: g) a crystallization step in a crystallizer consisting of the crystallization of paraxylene from step f), allowing to obtain on the one hand embedded paraxylene crystals from its mother alcohol, and on the other hand a mother alcohol which may be partly or even fully recycled in admixture with the fresh charge at the entrance of the simulated moving bed adsorption unit, and (h) a step for washing the crystals from step (g) from which recovers paraxylene with a purity of at least 99.7%, and preferably at least 99.8%.

The desired product can thus be separated by preparative batch adsorption liquid chromatography, advantageously in simulated moving bed, i.e. simulated countercurrent or simulated countercurrent, and more particularly simulated countercurrent. Simulated moving bed chromatographic separation to simulated counter current is well known in the art. As a general rule, a simulated moving bed separation unit comprises at least one adsorption column containing a plurality of interconnected closed-ring beds of an adsorbent. The simulated moving bed separation unit comprises at least three chromatographic zones, and possibly four or five, each of these zones consisting of at least one bed or a column portion and comprised between two successive feed or extraction points.

Typically, at least one fractional charge and one desorbent (sometimes called an eluent) are fed and at least one refined and one extract extracted. Feed and extraction points are modified over time, typically shifted down a bed, and synchronously.

By definition each operating zone is designated by a number: • Zone 1 = desired product desorption zone (contained in extract) between desorbent injection and extract withdrawal; • Zone 2 = desorption zone of the refined compounds, comprised between the removal of the extract and the injection of the load to be fractionated; • Zone 3 = zone of adsorption of the product sought, comprised between injection of the charge and extraction of the refined, and; • Zone 4 located between refining extraction and desorbent injection.

The operating conditions of a simulated counter current adsorption unit are generally as follows: • bed numbers 6 to 30; • zone numbers of at least 4; Temperature 100 to 250 ° C, preferably 150 to 190 ° C; • pressure between xylene bubble pressure at process temperature and 3 MPa; • ratio of desorbent flow rates on load 0.7 to 2.5 (eg 0.9 to 1.8 for a stand alone adsorption unit and 0.7 to 1.4 for a adsorption unit combined with a crystallization unit); • recycling rate from 2.5 to 12, preferably 3.5 to 6.

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

The operating conditions of an industrial simulated co-current adsorption unit are generally the same as those operating on the simulated countercurrent except for the recycling rate which is generally between 0.8 and 7. will refer to US 4,402,832 and US 4,498,991. The desorption solvent may be a desorbent whose boiling point is below this charge, such as toluene, but also a desorbent whose boiling point is greater than this charge, such as paradiethylbenzene (PDEB). The selectivity of the adsorbents according to the invention for adsorption of paraxylene contained in C8 aromatic sections is optimal when their fire loss measured at 900 ° C is generally between 4.0% and 8.0%, preferably between 4.7 and 6.7%. Water and some carbon dioxide enters the fire loss.

One of the choice techniques for characterizing the adsorption of liquid phase molecules onto a porous solid is to drill a hole. In her book Principles of Adsorption and Adsorption processes, Ruthven defines the breakthrough curves technique as the study of the injection of a range of adsorbable constituents. The present invention is now described with the help of the following examples, which are intended to illustrate some embodiments of the invention without, however, limiting the scope of said invention as set forth in the appended claims.

Example 1 (Comparative! 840 g (expressed as calcined equivalent) of zeolite X powder, atomic ratios Si / Al = 1,25, and average crystal size of 1,6 pm are mixed together with 160 g of kaolin (expressed as calcined equivalent) and the amount of water suitable for extrusion agglomeration The extrudates are dried, crushed to recover agglomerates with an equivalent diameter of 0.7 mm and then activated. at a temperature of 550 ° C for 2 hours under a stream of nitrogen.

These granulates are then exchanged by means of a 0.5 M barium chloride solution at 95 ° C in 4 steps. At each step, the solution volume to solid mass ratio is 20 mL / g and the exchange is continued for 4 hours each time. Between each change, the solid is washed several times to clear it of excess salt. It is then activated at a temperature of 200 ° C for 2 hours under a stream of nitrogen. The barium exchange rate is 97% and the loss to fire (measured at 900 ° C) is 6.5%. The microporous volume measured according to the Dubinin method by nitrogen adsorption at 77 K after pretreatment at 500 ° C for 12 hours under vacuum is 0.235 cm 3 / g.

Example 2 (comparative) 900 g (expressed as calcined equivalent) of zeolite X powder, Si / Al ratio = 1.25, and average crystal size of 1.6 pm are agglomerated and intimately mixed with 170 g. kaolin (expressed as calcined equivalent), 70 g colloidal silica sold under the trade name Klebosol® 30 (containing 30% by weight Si02 and 0.5% Na20) and the amount of water suitable for shaping extruded agglomerates. The extrudates are dried, ground to recover agglomerates whose equivalent diameter is 0.7 mm, and then activated at a temperature of 550 ° C for 2 hours under nitrogen flow. 200 g of granules thus obtained are placed in a glass reactor fitted with a double-shell set at a temperature of 100 ± 1 ° C and then 1,5 l of a 100 g / l aqueous solution of soda are added. leave the reaction medium under stirring for 3 hours. The pellets are then washed in 3 successive water rinsing operations followed by draining the reactor. The effectiveness of the wash is ensured by measuring the final pH of the wash water to be between 10 and 10.5.

Barium exchange is then carried out under identical operating conditions to those of Example 1 followed by washing and then drying at 80 ° C for 2 hours and finally activation at 200 ° C for 2 hours under nitrogen flow. The barium exchange rate is 95% and the loss to fire (measured at 900 ° C) is 6.5%. The microporous volume measured according to the Dubinin method by nitrogen adsorption at 77 K after pretreatment at 500 ° C for 12 hours in a vacuum is 0.256 cm / g.

Example 3 (comparative) 840 g (expressed as calcined equivalent) of LSX zeolite powder, Si / Al ratio = 1.02 and average crystal size of 2.6 pm, are mixed in intimately with 160 g of kaolin (expressed as calcined equivalent) and the amount of water suitable for forming the agglomerates by extrusion. The extrudates are dried, crushed to recover agglomerates with an equivalent diameter of 0.7 mm, and then calcined at 550 ° C under a nitrogen stream for 2 hours. Barium exchange is carried out under identical operating conditions to those of Example 1 except that the BaCb solution concentration is 0.7 M followed by washing and then drying at 80 ° C for 2 hours and lastly. activation at 200 ° C for 2 hours under nitrogen flow.

The barium exchange rate is 98% and the loss to fire (measured at 900 ° C) is 6.5%. The microporous volume measured according to the Dubinin method by nitrogen adsorption at 77 K after pretreatment at 500 ° C for 12 hours in a vacuum is 0.205 cm / g.

Example 4 (Comparative) 840 g (expressed as calcined equivalent) of LSX zeolite powder of Si / Al ratio = 1.01 average crystal size of 2.6 pm, 160 g of kaolin are intimately mixed. (expressed in calcined equivalent) with the amount of water suitable for extrusion operation. The extrudates are dried, ground to recover agglomerates with an equivalent diameter of 0.7 mm, then calcined at 550 ° C under a nitrogen stream for 2 hours. 200 g of granules thus obtained are placed in a glass reactor fitted with a double-shell set at a temperature of 95 ± 1 ° C, then 700 ml of an aqueous soda solution of 220 g / l concentration are added and the reaction medium is stirred for 3 hours.

The pellets are then washed in 4 successive water rinsing operations followed by draining the reactor. The effectiveness of the wash is ensured by measuring the final pH of the wash water to be between 10 and 10.5.

Barium exchange is then carried out under identical operating conditions as in Example 1 followed by washing and then drying at 80 ° C for 2 hours and then activating at 200 ° C for 2 hours under standard nitrogen. The barium exchange rate of this adsorbent is 97% and its loss to fire is 6.5%. The microporous volume measured according to the Dubinin method by nitrogen adsorption at 77 K after pretreatment at 500 ° C for 12 hours under vacuum is 0.235 cm 3 / g.

Example 5 (according to the invention) 3 powder blends consisting of zeolite X powder having Si / Al ratio = 1.25 average size of 1.6 pm crystals and LSX zeolite powder Si / Al ratio = 1.01 average size of 2.6 pm crystals whose LSX / X molar ratios are as follows: 0.54; 1 and 1.86. 900 g (expressed as calcined equivalent) of each of these mixtures are agglomerated then intimately mixed with 170 g of kaolin (expressed as calcined equivalent) and the amount of water suitable for extrusion forming the agglomerates. The extrudates are dried, crushed to recover agglomerates with an equivalent diameter of 0.7 mm, and then activated at a temperature of 550 ° C for 2 hours under nitrogen flow. Barium exchange is operated under operating conditions identical to those of example 1. The barium exchange rate of these 3 products is given in Table 1 below. The microporous volumes measured according to the Dubinin method by nitrogen adsorption at 77 K after pretreatment at 500 ° C for 12 hours under vacuum are 0.229 cm 3 / g for the sample LSX / X ratio = 0.54, 0.236 to the east of LSX / X ratio = 1 and 0.230 to the east of LSX / X ratio = 1.86.

Example 1 The 3 samples prepared in Example 5 are activated identically only once at 200 ° C for 2 hours under a nitrogen stream to fix a fire loss (PAF measured at 900 ° C) of 6, 5%

These 3 samples as well as the samples prepared in examples 1 and 3 of the same fire loss are then evaluated by a frontal chromatography device (perforation technique) to determine paraxylene-metaxylene selectivity or paraxylene-ethylbenzene selectivity respectively. The drilling technique consists of injecting a filler containing equal amounts of paraxylene and metaxylene or paraxylene and ethylbenzene as well as a low amount of non-adsorbable tracer in a column filled with solvent pre-saturated zeolitic sieve and at process temperature. Then follows over time the response to this injection.

For this, the effluent is sampled at the column outlet in small volume vials thanks to a fraction collector. The content of the vials is then analyzed by gas chromatography. The result obtained is expressed as a graph: composition of the different constituents contained in the effluent as a function of time (or volume chosen). The exploration of this curve allows to characterize the thermodynamic and kinetic behavior of the sieve. It allows to determine, among others, the selectivity of separation between the constituents A and B αa / b as defined above. Microporous volume is also measured according to the Dubinin method by nitrogen adsorption at 77 K after pretreatment at 500 ° C for 12 hours under vacuum. Dubinin volumes thus obtained are summarized in Table 2; as well as the results of selectivity and effectiveness.

Surprisingly, the efficacy criteria of samples containing mixtures of X crystals and LSX crystals are found to be significantly higher than those of samples composed of only one of the two structures.

Table 2 l: Selectivity between paraxylene and metaxylene 2: Selectivity between paraxylene and ethylbenzene: Dubinin volume 4: PX / MX efficacy criterion 5: PX / EB efficacy criterion Example 7 (according to the invention) Performs a mixture of molar ratio LSX / X = 1 of zeolite powder X, Si / Al ratio = 1.25, average crystal size of 1.6 pm and LSX zeolite powder, Si / Al ratio = 1.01 average crystal size of 2.6 pm. 900 g (expressed as calcined equivalent) of each of these mixtures are then agglomerated by intimately mixing with 170 g of kaolin (expressed as calcined equivalent), 70 g of colloidal silica sold under the trade name Klebosol® 30 (containing 30 % by weight of S1O2 and 0,5% of Na2Ü) and the quantity of water suitable for extrusion agglomeration. The extrudates are dried, crushed to recover agglomerates with an equivalent diameter of 0.7 mm, and then calcined at 550 ° C under a nitrogen stream for 2 hours. 200 g of granules thus obtained are placed in a glass reactor fitted with a double-shell set at a temperature of 100 ± 1 ° C and then 1,5 l of a 100 g / l aqueous solution of soda are added. The reaction medium is allowed to stir for 3 hours. The pellets are then washed in 4 successive water rinsing operations followed by draining the reactor. The effectiveness of the wash is ensured by measuring the final pH of the wash water to be between 10 and 10.5.

Barium exchange is then carried out under identical operating conditions as in Example 1 followed by washing and then drying at 80 ° C for 2 hours and finally activation at 200 ° C for 2 hours under a nitrogen stream at to set the FAP at 6.5% as in example 5. The barium exchange rate is 97.2%.

These samples were tested on the frontal chromatography device also described in Example 6 as well as two comparative samples 100% X and 100% LSX prepared respectively according to Examples 2 and 4. The microporous volume is also measured according to the method of Dubinin by nitrogen adsorption at 77 K after pretreatment at 500 ° C for 12 hours under vacuum. The Dubinin volumes thus obtained are summarized in Table 3.

The selectivity results and efficacy criteria are summarized in Table 3, which also reproduces the results of Table 2 for the adsorbents described in Example 6.

Table 3 1: Selectivity between paraxylene and metaxylene: Selectivity between paraxylene and ethylbenzene -j: Dubinin volume 4: PX / MX efficacy criterion 5: PX / EB efficacy criterion

The results of Tables 2 and 3 show that, surprisingly, the efficacy criteria are much higher than the agglomerates according to the invention based on the X / LSX blend compared to sieves composed exclusively of X or LSX. Figure 1 shows the variation of Dubinin volume (in ordinate) as a function of the LSX zeolite rate present in the agglomerate according to the invention to the LSX mixing base X (in abscissa). The value 0 in abscissa corresponds to a zeolite-based agglomerate X alone, while the value 1 corresponds to a zeolite-based agglomerate LSX alone. The graph in Figure 1 shows the unexpected effect on Dubinin volume when X / LSX mix-based agglomerates according to the invention are obtained: the observed Dubinin volumes are larger than these logically expected and are represented by the straight line. in dotted.

Example 8 In order to evaluate the performance of the sieves as a function of PAF, different activations of the sample composed solely of X crystals (prepared according to example 2) as well as this one of LSX / X = 1 molar ratio, prepared according to The process described in Example 3 was performed: - Activation at a temperature of 230 ° C for 2 hours under a nitrogen stream to fix a fire loss (PAF measured at 900 ° C) of 5%; - Activation at a temperature of 170 ° C for 2 hours under a nitrogen stream to fix a fire loss (PAF measured at 900 ° C) of 8%.

A sample composed solely of LSX crystals (prepared according to example 4) was activated at a temperature of 200 ° C for 2 hours under nitrogen stream to fix a fire loss (PAF measured at 900 ° C) of 6.5%.

These samples were tested on the frontal chromatography device also described in Example 6. Table 4 below summarizes the PX / MX selectivities and xylene adsorption capacities (cm3 / g) obtained for the X-exclusively screened as well as this. molar ratio LSX / X = 1. Table 4: amount of xylenes adsorbed in cm / g 2: selectivity between paraxylene and metaxylene: selectivity between paraxylene and ethylbenzene For all PAFs tested, the performance of X-based agglomerates / LSX are better than the performance of sieves containing only zeolite X and that these sieves containing only LSX zeolite under equivalent conditions.

Example 9 A mixture of LSX / X = 1 molar ratio of zeolite powder X, Si / Al ratio = 1.25, average crystal size of 1.6 pm and LSX zeolite powder of ratio Si / Al = 1.01 average crystal size of 1.6 pm. 900 g (expressed as calcined equivalent) of each of these mixtures are then agglomerated by intimately blending them with 170 g of kaolin (expressed as calcined equivalent) and the amount of water suitable for forming the extruded agglomerates. The extrudates are dried, crushed to recover agglomerates with an equivalent diameter of 0.7 mm, and then calcined at 550 ° C under a nitrogen stream for 2 hours. 200 g of granules thus obtained are placed in a glass reactor fitted with a double-shell set at a temperature of 100 ± 1 ° C and then 1,5 l of a 100 g / l aqueous solution of soda are added. The reaction medium is allowed to stir for 3 hours. The pellets are then washed in 3 successive water rinsing operations followed by draining the reactor. The effectiveness of the wash is ensured by measuring the final pH of the wash water to be between 10 and 10.5.

Barium exchange is then carried out under identical operating conditions as in Example 1 followed by washing and then drying at 80 ° C for 2 hours and finally activating at 200 ° C for 2 hours under a nitrogen stream at to set the FAP at 6.5% as in example 5. The barium exchange rate is 97%.

Example 10 (Comparative) A mixture consisting of 50% granules prepared according to example 2 of the present invention and 50% LSX granules prepared according to example 4 is made.

Barium exchange is then carried out under identical operating conditions as in Example 1 followed by washing and then drying at 80 ° C for 2 hours and finally activation at 200 ° C for 2 hours under a nitrogen stream at to set the FAP at 6.5% as in example 5. The barium exchange rate is 97.2%.

This mixture of X and LSX pellets is then evaluated by a frontal chromatography device (drilling technique) to determine paraxylene-metaxylene selectivity or paraxylene-ethylbenzene selectivity respectively.

The results of these tests are summarized in table 5.

Table 5 l: selectivity between paraxylene and metaxylene: selectivity between paraxylene and ethylbenzene • 5: Dubinin volume 4: the PX / MX efficacy criterion 5: the PX / EB efficacy criterion

The results in Table 5 show that simply mixing X and LSX agglomerates is not sufficient to obtain the synergy observed for mixing X and LSX crystals within the same agglomerate.

Claims (18)

1. Agglomerated zeolitic adsorbent, characterized in that it comprises: - zeolite X powder exchanged at least 90% for barium ions alone or for barium ions and potassium ions, the exchangeable sites occupied by potassium which may represent up to 1/3 of exchangeable sites occupied by barium + potassium ions; eventual complement usually provided by alkaline or alkaline earth ions in addition to barium and potassium); - LSX zeolite powder exchanged at least 90% for barium ions alone or for barium ions and potassium ions, the exchangeable sites occupied by potassium which may represent up to 1/3 of the exchangeable sites occupied by barium + potassium ions; eventual complement generally provided by alkaline or alkaline earth ions in addition to barium and potassium; - and a binder less than or equal to 20% by weight of the total mass of the agglomerate. Adsorbent according to Claim 1, characterized in that the molar ratio of LSX zeolite concentration to zeolite X concentration is between 0.1 and 10. Adsorbent according to Claim 1, characterized in that the molar ratio of LSX zeolite concentration to zeolite X concentration is between 0.25 and 4. Adsorbent according to Claim 1, characterized in that the molar ratio of the LSX zeolite concentration to the zeolite X concentration is between 0.5 and 2.0. Adsorbent according to claim 1, characterized in that the molar ratio of LSX zeolite concentration to zeolite X concentration is between 0.5 and 2.0. Adsorbent according to claim 1, characterized in that zeolite X consists of crystals having an average diameter (in number) between 0.1 and 4 pm. Adsorbent according to claim 1, characterized in that the LSX zeolite consists of crystals having an average diameter (in number) between 0.1 pm and 7 pm. Process for preparing an adsorbent as defined in claim 1, characterized in that it comprises the following steps: a) agglomerating a mixture consisting of LSX zeolite powder and zeolite X powder in an LSX / X ratio which varies between 0.1 and 10 with an agglomerating binder and then shaping, drying and calcination, (b) an optional zeolitization step of the possible zeolitizable binder by an alkaline base solution; (c) substitution of at least 90% of all the interchangeable sites of the agglomerate with barium, followed by washing and drying of the product thus treated; drying of the product thus treated, and e) eventual activation of the product obtained. Use of at least one zeolitic adsorbent as defined in claim 1, characterized in that it is as an adsorption agent for the separation of C8 aromatic isomers, the separation of sugars, the separation of polyhydric alcohols, the separation of substituted toluene isomers, the separation of cresols, the separation of dichlorobenzenes. Process for separating aromatic isomers into C8 sugars, polyhydric alcohols, substituted toluene isomers, cresols, or dichlorobenzenes, characterized in that it employs at least one adsorbent as defined in claim 1. Process according to claim 10, characterized in that it is for recovering paraxylene from cuts of aromatic C8 isomers by adsorbing paraxylene through the zeolitic adsorbent as defined in claim 1. Process according to Claim 11, characterized in that it is carried out in the liquid phase. Process according to Claim 11, characterized in that it is carried out in the gas phase. A process according to any one of claims 11 to 13 for paraxylene recovery, characterized in that it is of the simulated moving bed type. Process according to any one of claims 11 to 13 for paraxylene recovery, characterized in that it is of the simulated countercurrent type. A process according to any one of claims 11 to 13 for paraxylene recovery, characterized in that it is of the simulated co-current type. A process according to any one of claims 11 to 16 for paraxylene recovery, characterized in that the desorbent is toluene or paradiethylbenzene. A process according to any one of claims 11 to 17 for paraxylene recovery characterized in that the zeolitic adsorbent has a fire loss measured at 900 ° C of between 4.0 and 8%.