Zeolite adsorbents for high productivity xylene separation.

Abstract

The present invention relates to an agglomerated zeolite adsorbent based on faujasite X zeolite crystals having a controlled Si / Al molar ratio and ion-exchanged with barium, or based on faujasite X zeolite having a controlled Si / Al molar ratio and ion-exchanged with barium and potassium. The present invention also relates to the use of the adsorbent in the separation of sugars, polyhydric alcohols, substituted toluene isomers, cresols, or for the recovery of very high purity para-xylene, and to a separation process for separating xylenes implementing the use of the adsorbent.

Description

[Technical Field]

[0001] The present invention relates to an agglomerated zeolite adsorbent based on faujasite (FAU) type zeolite crystals having a controlled silicon to aluminum (Si / Al) molar ratio and exchanged with barium or barium and potassium, which exhibits selective behavior towards para-xylene present in an aromatic hydrocarbon feed mixture containing eight carbon atoms (C8) isomers to be separated. [Background technology]

[0002] It is known from the prior art to use zeolitic adsorbents consisting of faujasite zeolite of type X or Y (FAU) containing, in addition to sodium cations, barium and / or potassium and / or strontium ions, either alone or in mixtures, for the selective adsorption of para-xylene in a mixture of aromatic hydrocarbons.

[0003] U.S. Patent Nos. 5,629,999, 5,729,963, 5,729,973, and 5,729,973 show that aluminosilicate zeolite adsorbents containing sodium and barium (U.S. Patent No. 5,729,999) or sodium, barium, and potassium are effective in separating para-xylene present in the C8 aromatic fraction (a fraction containing aromatic hydrocarbons with 8 carbon atoms).

[0004] One adsorbent preparation method for producing these adsorbents is described, for example, in U.S. Patent No. 5,929,999 and involves treating an aggregate comprising zeolite X having a NaO / AlO ratio strictly less than 0.7 and a binder in hot sodium hydroxide (soda) to replace the exchangeable cations of the zeolite (e.g., protons or Group IIA cations) with sodium before exchanging with barium, or barium and potassium, allowing a greater amount of barium ions, or barium and potassium ions, to be loaded into the zeolite structure before being exchanged with sodium.

[0005] These adsorbents are used as adsorbents in a liquid phase process, preferably a simulated countercurrent liquid phase process, similar to that described in US Pat. No. 5,629,999, which is particularly applicable to the C8 fraction (the fraction containing aromatic hydrocarbons with 8 carbon atoms).

[0006] Prior art zeolites for the separation of xylenes belong to the faujasite structure type and were first described in US Pat. No. 5,629,492 and US Pat. No. 5,629,492; they are three-dimensionally connected crystalline aluminum silicates with cages of perfectly determined size.

[0007] Patent Document 10 recommends faujasite X having an Si / Al atomic ratio between 1.15 and 1.5. Patent Document 11 teaches that, among the zeolite adsorbents described in the prior art, a faujasite with a low silica content and an Si / Al atomic ratio close to 1 (the latter is called LSX, an abbreviation for Low Silica X, or in French, zeolithe X a faible teneur en silice) can be advantageously used for the separation of para-xylene.

[0008] Thus, although both zeolite X and low-silica X zeolites exhibit good performance in terms of para-xylene selectivity, the synthesis of low-silica X zeolites is significantly more difficult than the synthesis of zeolite X. Indeed, in order to decrease the Si / Al atomic ratio of faujasite-type zeolites, it is necessary to increase the consumption of soda used in the zeolite synthesis process. Furthermore, in order to crystallize according to the faujasite structure type when the Si / Al atomic ratio is 1, it is necessary to add high concentrations of potassium hydroxide (caustic potash) to inhibit the formation of zeolite A and obtain only low-silica X zeolites. These high levels of sodium hydroxide and potassium hydroxide consumption increase the production costs of this type of zeolite and cause problems with effluent discharge.

[0009] In the above references, the zeolite adsorbents are in the form of crystals or aggregates consisting mainly of zeolite and an inert aggregate binder, generally in proportions between 0.1% and 20% by weight.

[0010] The synthesis of zeolite X and low silica X zeolites is typically carried out by nucleation and crystallization of an aluminum silicate gel, which produces crystals that are particularly difficult to use on an industrial scale (losses of the feed mixture during handling are significant), but it is preferable to obtain an agglomerated form, for example in the form of granules or particles, which do not have the drawbacks inherent in powdered (pulverulent) materials.

[0011] These agglomerates are produced, for example, by pasting zeolite crystals with a binder (most often a clay or mixture of clays, sometimes a zeolitizable clay) in a ratio of 0.1% to 20% binder by weight to 80% to 99.9% zeolite crystals by weight, followed by processing to form granules, particles, beads, pellets or extrudates, which are heat treated at high temperatures to calcinate the clay and reactivate the zeolite, and which can be barium and / or potassium exchanged before and / or after agglomeration of the powdered zeolite with the binder.

[0012] Zeolite aggregates are obtained which generally have particle sizes of a few mm and which exhibit a satisfactory range of properties, in particular porosity, mechanical strength and attrition resistance, if the selection of binder and granulation is carried out in accordance with technical practices in the art.

[0013] Patent document 12 describes a method for producing agglomerates based on LSX zeolite crystals having a number-average particle size of 4 μm or less and an Si / Al atomic ratio such that (1.00±0.05)≦Si / Al≦1.15, preferably having an Si / Al atomic ratio=1.00±0.05, in which at least 90% of the exchangeable cation sites are occupied solely by barium ions or by barium ions and potassium ions, and the mechanical strength measured by the Shell method series SMS1471-74, suitable for agglomerates having a size of less than 1.6 mm, is 2 MPa or more.

[0014] Patent Document 13 describes a manufacturing process for producing an agglomerated zeolite adsorbent comprising a mixture of zeolite X crystals at least 90% exchanged solely with barium ions or with barium and potassium ions, wherein the exchangeable sites occupied by potassium can account for up to one-third of the exchangeable sites occupied by barium and potassium ions (the exchangeable remainder generally being made up of alkali or alkaline earth ions other than barium and potassium); LSX zeolite crystals at least 90% exchanged solely with barium ions or with barium and potassium ions, wherein the exchangeable sites occupied by potassium can account for up to one-third of the exchangeable sites occupied by barium and potassium ions (the exchangeable remainder generally being made up of alkali or alkaline earth ions other than barium and potassium); and a binder in a proportion of up to 20% by weight of the total weight of the agglomerates.

[0015] Patent Document 11 teaches that the performance level of an industrial separation process for separating para-xylene depends largely on the adsorbent, its adsorption capacity, and the degree of selectivity it exhibits for para-xylene in a medium composed of C8 aromatic compounds, typically para-xylene, meta-xylene, ortho-xylene, and ethylbenzene, while also depending on the ability of desorbents such as toluene and para-diethylbenzene to desorb the adsorbed para-xylene. The selectivity α of component A relative to compound B of the adsorbent A / B is defined as the ratio of the concentrations of the compounds in the adsorbed phase divided by the ratio of the concentrations of the compounds in the non-adsorbed phase at equilibrium. α A / B =A ads / B ads ×B liq / A liq In the formula, A ads and B adsare the concentrations of compound A and compound B in the adsorbed phase, respectively, and A liq and B liq are the concentrations of compound A and compound B in the fluid phase. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] U.S. Patent No. 3,558,730 [Patent Document 2] U.S. Patent No. 3,558,732 [Patent Document 3] U.S. Patent No. 3,626,020 [Patent Document 4] U.S. Patent No. 3,663,638 [Patent Document 5] U.S. Patent No. 3,960,774 [Patent Document 6] U.S. Patent No. 3,878,127 [Patent Document 7] U.S. Patent No. 2,985,589 [Patent Document 8] U.S. Patent No. 2,882,244 [Patent Document 9] U.S. Patent No. 3,130,007 [Patent Document 10] U.S. Patent No. 6,884,918 [Patent Document 11] U.S. Patent No. 6,410,815 [Patent Document 12] French Patent No. 2925366 [Patent Document 13] French Patent No. 2925367 Summary of the Invention

[0017] Surprisingly, agglomerated zeolite adsorbents comprising faujasite-type zeolites having a controlled silicon-to-aluminum (Si / Al) molar ratio, particularly a Si / Al molar ratio of 1.10≦Si / Al≦1.18, preferably 1.10≦Si / Al≦1.17, more preferably 1.10≦Si / Al≦1.16, and even more preferably 1.11≦Si / Al≦1.16 (MSX, for Medium Silica X, or in French, "zeolithe X a teneur moyenne en silice"), are at least 90% exchanged with barium ions alone or with barium and potassium ions, and can advantageously replace literature-described zeolite adsorbents based on zeolite X and / or zeolite LSX with barium-exchanged or barium- and potassium-exchanged zeolite adsorbents, either alone or in admixture. The agglomerated zeolite adsorbents of the present invention exhibit particularly unexpected levels of performance in terms of selectivity in para-xylene separation processes. For obvious reasons of ease of implementation and industrial application, the agglomerated zeolite adsorbents that can be used in the context of the process of the present invention are used alone, preferably without other zeolite adsorbents, either in layers or in mixtures.

[0018] The present invention relates to an agglomerated zeolite adsorbent based on MSX zeolite crystals having a Si / Al atomic ratio of 1.10≦Si / Al≦1.18, preferably 1.10≦Si / Al≦1.17, more preferably 1.10≦Si / Al≦1.16, and even more preferably 1.11≦Si / Al≦1.16, wherein at least 90%, preferably at least 95%, of the exchangeable cation sites are occupied either solely by barium ions or by barium and potassium ions. More preferably, the present invention relates to an agglomerated zeolite adsorbent based on MSX zeolite crystals having a Si / Al atomic ratio such that 1.11≦Si / Al<1.15, more preferably 1.12≦Si / Al<1.15, and advantageously 1.12≦Si / Al≦1.14, wherein at least 90%, preferably at least 95%, of the exchangeable cation sites are occupied either solely by barium ions or by barium and potassium ions.

[0019] The micropore volume of the adsorbent, measured according to the Dubinin method by nitrogen adsorption at 77 K after pretreatment at 500 °C for 12 h under vacuum, was 0.200 cm 3 / g or more, preferably 0.220 cm 3 / g or more, more preferably 0.225 cm 3 / g or more, more preferably 0.250 cm 3 / g or more.

[0020] The exchangeable sites occupied by potassium can account for up to one-third of the exchangeable sites occupied by barium and potassium ions, with any possible remainder generally being made up by alkali or alkaline earth ions other than barium and potassium.

[0021] The adsorbent may contain an inert binder in a proportion of up to 20% by weight, preferably up to 15% by weight, of the total weight of the adsorbent.

[0022] The adsorbent may have a size distribution such that the number average particle diameter is between 0.4 mm and 2.0 mm, preferably between 0.4 mm and 0.8 mm.

[0023] The mechanical strength of said adsorbent, measured by the Shell method series SMS1471-74 suitable for agglomerates having a size of less than 1.6 mm, is advantageously greater than or equal to 2 MPa, preferably greater than or equal to 2.5 MPa.

[0024] The loss on ignition measured at 900°C is advantageously less than or equal to 7.7%, preferably between 0 and 7.7%, more preferably between 3.0% and 7.7%, even more preferably between 3.5% and 6.5%, advantageously between 4.5% and 6.0%, limits included.

[0025] The MSX zeolite crystals may have a number average particle size between 0.01 μm and 5 μm, preferably between 0.05 μm and 5 μm, very preferably between 0.1 μm and 4 μm, more preferably between 0.1 μm and 3 μm, and even more preferably between 0.1 μm and 2 μm.

[0026] The present invention also relates to a method for separating sugars, polyhydric alcohols, substituted toluene isomers, cresols or for recovering para-xylene by means of an agglomerated zeolite adsorbent according to any one of the described variants in the liquid or gas phase in the presence of a desorbent.

[0027] The process may be a method for recovering para-xylene from a fraction of C8 aromatic isomers by adsorption of para-xylene by the agglomerated zeolite adsorbent in the presence of a desorbent in the liquid or vapor phase.

[0028] The recovery process for recovering para-xylene may be carried out by a simulated cocurrent or simulated countercurrent simulated moving bed process.

[0029] The process is a method for producing high purity and high productivity para-xylene from a feed mixture of aromatic hydrocarbons containing eight carbon atom (C8) isomers, comprising: a contacting step a) of contacting the feed mixture with a bed of the agglomerated zeolite adsorbent so as to preferentially adsorb the para-xylene; a contacting step b) of contacting the bed of adsorbent with a desorbent, preferably toluene or para-diethylbenzene, under desorption conditions; a withdrawing step c) of withdrawing a stream containing the desorbent and slightly selectively adsorbed products of the feed mixture from the adsorbent bed; a removing step d) of removing a stream containing the desorbent and the para-xylene from the adsorbent bed; a separation step e) of separating the stream resulting from step c) into a first stream containing the desorbent and a second stream containing less selectively adsorbed products of the feed mixture; and f) separating the stream obtained from step d) into a first stream containing the desorbent and a second stream containing the para-xylene having a purity level of 75% or greater.

[0030] The process comprises: a crystallization step g) in a crystallizer, in which the para-xylene obtained from step f) is crystallized, which makes it possible, on the one hand, to obtain para-xylene crystals immersed in mother liquor, and, on the other hand, to obtain mother liquor which can be recycled, in part or in whole, as a mixture with a fresh feed mixture at the inlet of the simulated moving bed adsorption unit; a washing step h) of washing the crystals obtained from step g), in which at the end para-xylene having a purity of at least 99.7%, preferably at least 99.8%, is recovered; It may further include.

[0031] More generally, the present invention finally relates to the use of an agglomerated zeolite adsorbent based on MSX zeolite crystals having an Si / Al atomic ratio such that 1.10≦Si / Al≦1.18, preferably 1.10≦Si / Al≦1.17, more preferably 1.10≦Si / Al≦1.16, even more preferably 1.11≦Si / Al≦1.16, and in which at least 90% of the exchangeable cation sites are occupied solely by barium ions or by barium and potassium ions, for separating sugars, polyhydric alcohols, substituted toluene isomers, cresols or for recovering para-xylene, in the liquid or gas phase, in the presence of a desorbent, preferably toluene or para-diethylbenzene.

[0032] This use may relate to the recovery of para-xylene from a fraction of C8 aromatic isomers by adsorption of para-xylene in a simulated moving bed reactor of the simulated co-current or counter-current type. DETAILED DESCRIPTION OF THE INVENTION

[0033] An object of the present invention is to provide a zeolitic adsorbent that can be used in particular for separating para-xylene from a mixture of C aromatic compounds, which exhibits excellent performance levels, particularly with respect to selectivity for para-xylene, and which is particularly suitable for use in a separation process for separating para-xylene in a liquid phase, most particularly in a high-productivity separation process for separating para-xylene in a liquid phase, preferably a separation process of the simulated countercurrent type.

[0034] The agglomerated zeolite adsorbent of the present invention comprises an MSX zeolite having an Si / Al atomic ratio such that 1.10≦Si / Al≦1.18, preferably 1.10≦Si / Al≦1.17, more preferably 1.10≦Si / Al≦1.16, and even more preferably 1.11≦Si / Al≦1.16, wherein lower values ​​reflect analytical uncertainty in the measurement of this ratio and higher values ​​reflect either the same analytical uncertainty or an acceptable deviation in the purity of the product, at least 90% of which is exchanged solely with barium ions or exchanged with barium and potassium ions, and wherein the exchangeable sites occupied by potassium can account for up to one-third of the exchangeable sites occupied by barium and potassium ions (the exchangeable remainder being generally constituted by alkali or alkaline earth ions other than barium and potassium), and wherein the mechanical strength of the agglomerated zeolite adsorbent of the present invention, measured by the Shell method series SMS 1471-74 suitable for agglomerates having a size of less than 1.6 mm, is advantageously greater than or equal to 2 MPa.

[0035] Advantageously, the zeolitic adsorbent according to the invention may comprise a binder in a proportion of not more than 20% by weight, preferably not more than 15% by weight, of the total weight of the aggregates, which binder may contain one or more zeolitizable clays, preferably at least 80% by weight of zeolitizable clays, and optionally one or more additives.

[0036] The number average particle size of the zeolite crystals in the zeolite adsorbent according to the invention is advantageously between 0.01 μm and 5 μm, preferably between 0.05 μm and 5 μm, very preferably between 0.1 μm and 4 μm, more preferably between 0.1 μm and 3 μm, and even more preferably between 0.1 μm and 2 μm.

[0037] Generally, the zeolitic adsorbent according to the invention has a volume mean diameter between 0.4 mm and 2 mm, in particular between 0.4 mm and 0.8 mm.

[0038] The term "number average particle size" or indeed "size" is used herein for zeolite crystals and zeolite aggregates. The accuracy of the measurement is in the order of 3%.

[0039] The present invention also relates to a manufacturing process for producing the zeolite adsorbent according to the present invention. a step a / in which zeolite MSX crystals are agglomerated with a binder containing at least 80% by weight of a zeolitic clay and optionally additives, and then shaped, followed by drying and calcination; step b / of zeolitizing the binder, if necessary, by the action of a basic alkaline solution; step c / of substituting at least 90% of the ion-exchangeable sites of the MSX zeolite with barium, followed by washing and drying the product thus treated; d / optionally substituting up to 33% of the ion-exchangeable sites of the zeolite X with potassium, followed by washing and drying the product thus treated; an activating step e / ; The present invention can be produced according to a production process including the steps of:

[0040] The agglomeration and shaping (step a / ) can be carried out according to any technique known to those skilled in the art, such as extrusion, compression and agglomeration. The agglomeration binder represents a proportion of not more than 20% by weight, preferably not more than 15% by weight, of the total weight of the agglomerates.

[0041] According to one preferred embodiment, the zeolite MSX crystals have a diameter of less than or equal to 5 μm, between 0.01 μm and 5 μm, preferably between 0.05 μm and 5 μm, very preferably between 0.1 μm and 4 μm, more preferably between 0.1 μm and 3 μm, and even more preferably between 0.1 μm and 2 μm.

[0042] At the end of step a / , the finest agglomerated particles may be removed by cycloning and / or screening, and / or excessively large particles may be removed, for example in the case of extrudates, by screening or crushing.

[0043] The flocculating binder used in carrying out step a / contains at least 80% by weight of zeolitic clay and may also contain other mineral binders such as bentonite or attapulgite. The term "zeolitic clay" is used to refer to a clay or mixture of clays that can be converted into a zeolitic material by the action of a basic / alkaline solution. Zeolitic clays generally belong to the family of kaolin, kaolinite, nacrite, decrite, halloysite and / or metakaolin. The clay commonly used is kaolin.

[0044] During step a / , in addition to the zeolite MSX crystals and the binder, one or more additives may also be used, for example additives intended to promote agglomeration or to enhance the hardening of the agglomerates formed.

[0045] The additives that can be used in step a / may include any type of silica source known to those skilled in the art of zeolite synthesis, such as colloidal silica, diatomaceous earth, perlite, ash after coal burning (i.e., fly ash), sand, or any other form of solid silica.

[0046] The zeolite MSX crystals used in the performance of step a / may originate from the synthesis of sodium-exchanged zeolite MSX crystals, but it does not depart from the scope of the invention to use crystals which have undergone one or more cation exchanges between their synthesis in the NaMSX form and their performance in step a / .

[0047] Calcination after drying is generally carried out at temperatures between 500° C. and 600° C. According to a preferred embodiment, a zeolitization step b / is carried out.

[0048] It should be noted that when the zeolitization step b / is performed, at least 50% of the inactive zeolitizable binder is converted to a zeolitic material, and the purpose of the zeolitization is, in particular, to increase the mechanical strength of the agglomerated zeolite adsorbent. Zeolitization can generally be carried out by immersing the agglomerates in an aqueous basic / alkaline solution, for example, an aqueous solution of sodium hydroxide and / or potassium hydroxide, preferably with a concentration of more than 0.5 M. To improve process kinetics and reduce the immersion time to less than 8 hours, it is preferred to carry out the process at high temperatures (above ambient temperature), typically around 80°C to 100°C. However, operation at lower temperatures and for longer immersion times does not depart from the scope of the present invention. This method of operation easily achieves zeolitization of at least 50% by weight of the binder (i.e., conversion of the adsorption-inactive binder to an adsorption-active material). The material is then washed with water and then dried.

[0049] Step c / , exchanging the zeolite cations with barium, is carried out by contacting the aggregates resulting from step b / (or d / ) with a barium salt, such as BaCl, in aqueous solution at a temperature between ambient and 100°C, preferably between 80°C and 100°C. To rapidly achieve a high degree of barium exchange, i.e., greater than 90%, it is preferred to use a large excess of barium relative to the zeolite cations desired to be exchanged, typically a BaO / AlO ratio of around 10-12, and to carry out successive exchange operations to achieve a target minimum exchange level of at least 90%, preferably at least 95%. Throughout this text, levels of exchange are calculated in terms of equivalents, not molar concentrations.

[0050] The optional exchange with potassium (step d / ) can be carried out before and / or after the exchange with barium (step c / ) and / or simultaneously using a solution containing barium and potassium ions. It is also possible, as indicated above, to agglomerate zeolite MSX crystals that already contain potassium ions in step a / (by pre-exchanging NaMSX zeolite with potassium ions before step a / ) and to omit (or not omit) step d / .

[0051] The purpose of activation (step e / ), the final step in the process for obtaining the adsorbent according to the invention, is to maintain the water content and loss on ignition of the adsorbent within optimal ranges, which is generally achieved by thermal activation, preferably at a temperature of 200°C to 300°C for a period of time, typically 1 to 6 hours, depending on the desired water content and the desired loss on ignition.

[0052] In one embodiment of the present invention, the loss on ignition of the agglomerated zeolite adsorbent according to the present invention, measured at 900°C according to French standard NF EN196-2, is less than or equal to 7.7%, preferably between 0 and 7.7%, more preferably between 3.0% and 7.7%, even more preferably between 3.5% and 6.5%, advantageously between 4.5% and 6.0%, limits included.

[0053] The agglomerates obtained from step e / , whether in the form of beads or extrudates, generally have a number average particle size ranging from 0.4 mm to 2.0 mm, in particular from 0.4 mm to 0.8 mm.

[0054] In a typical process, the number average particle size of the zeolite crystals in these zeolite adsorbents obtained from steps a / to e / is between 0.01 μm and 5 μm, preferably between 0.05 μm and 5 μm, very preferably between 0.1 μm and 4 μm, more preferably between 0.1 μm and 3 μm, and even more preferably between 0.1 μm and 2 μm.

[0055] The present invention also relates to the use of at least one zeolitic adsorbent according to any one of the described variants as an adsorbent that can advantageously replace the adsorbents described in the literature, based on zeolite X or on zeolite LSX, of barium-exchanged or barium and potassium-exchanged type, and in particular the following uses: Separation of C8 aromatic isomers, especially xylenes, Sugar separation, Separation of polyhydric alcohols, Separation of substituted toluene isomers, e.g., nitrotoluene, diethyltoluene, toluenediamine, Separation of cresols, Separation of dichlorobenzene

[0056] The present invention particularly relates to a recovery process for recovering para-xylene from a fraction of C8 aromatic isomers, which comprises using the zeolitic adsorbent according to the present invention, which is used in practice in a liquid phase process and which is also used in a gas phase process, as the adsorbent for adsorbing para-xylene.

[0057] The present invention relates in particular to a process for producing high purity and high productivity para-xylene from a feed mixture of aromatic hydrocarbons containing eight carbon atom (C8) isomers, the process comprising: a contacting step a) of contacting a feed mixture with a bed of an adsorbent according to the present invention under suitable adsorption conditions so as to preferentially adsorb para-xylene; a contacting step b) of contacting the bed of adsorbent with a desorbent, preferably toluene or para-diethylbenzene, under desorption conditions; a withdrawal step c) of withdrawing from the adsorbent bed a stream containing the desorbent and the least selectively adsorbed product of the feed mixture; a withdrawing step d) of withdrawing a stream containing the desorbent and para-xylene from the adsorbent bed; a separation step e) of separating the stream resulting from step c) into a first stream containing the desorbent and a second stream containing the least selectively adsorbed product of the feed mixture; and a separation step f) separating the stream obtained from step d) into a first stream containing the desorbent and a second stream containing para-xylene having a purity level of at least 75%, preferably at least 99.7%.

[0058] The process may also include the following optional steps: g) a crystallization step in a crystallizer, in which the para-xylene obtained from step f) is crystallized, making it possible, on the one hand, to obtain para-xylene crystals immersed in the mother liquor, and, on the other hand, to obtain a mother liquor which can be recycled, in part or in whole, as a mixture with a fresh feed mixture at the inlet of the simulated moving bed adsorption unit; h) A washing step of washing the crystals obtained from step g), in which at the end para-xylene having a purity of at least 99.7%, preferably at least 99.8%, is recovered.

[0059] The desired product can therefore be separated by preparative adsorption liquid chromatography (batch test), advantageously by simulated moving bed liquid chromatography, i.e. simulated countercurrent or simulated cocurrent, more particularly simulated countercurrent moving bed liquid chromatography.

[0060] Chromatographic separations based on simulated countercurrent moving bed chromatography are well known in the state of the art. In principle, a simulated moving bed separation unit comprises at least one adsorption column containing multiple beds of adsorbent interconnected in a closed loop. A simulated moving bed separation unit comprises at least three, possibly four or five, chromatography zones, each of which is constituted by at least one bed or part of a column, located between two consecutive feed or withdrawal points.

[0061] Typically, at least one feed mixture to be fractionated and one desorbent (sometimes called an eluent) are supplied, and at least one raffinate and one extract are removed. The feed and discharge points are varied over time, typically shifting synchronously toward the bottom of the bed.

[0062] By definition, each operating zone is designated by a number.

[0063] Zone 1 is the desorption zone of the desired product (contained in the extract) between the injection of the desorbent and the extraction of the extract.

[0064] Zone 2 is a desorption zone for the raffinate compounds between the withdrawal of the extract and the injection of the feed mixture to be fractionated.

[0065] Zone 3 is the adsorption zone of the desired product between the injection of the feed mixture and the withdrawal of the raffinate.

[0066] Zone 4 is located between the raffinate withdrawal and the desorbent injection.

[0067] The operating conditions for a simulated countercurrent commercial adsorption unit are generally as follows: Number of floors: 6-30, Number of zones: at least 4, Temperature: 100 to 250°C, preferably 150 to 190°C, Pressure: Between the bubble pressure of xylene at the process temperature and 3 MPa; Ratio of desorbent flow rate to feed flow rate: 0.7-2.5 (e.g., 0.9-1.8 for a single adsorption unit (commonly referred to as a "standalone" unit), 0.7-1.4 for an adsorption unit combined with a crystallization unit); Recycle rate: 2.5 to 12, preferably 3.5 to 6. The recycle rate is defined as the ratio of the average flow rate through the different beds of the adsorber to the injection flow rate of the feed into this adsorber.

[0068] See further the teachings of patents US2985589, US5284992 and US5629467.

[0069] The operating conditions of the industrial simulated co-current adsorption unit are generally the same as those operating in the simulated countercurrent mode, except for the recycle ratio, which is generally between 0.8 and 7. See further the teachings of patents US4402832 and US4498991.

[0070] The desorption solvent may be a desorbent having a boiling point lower than that of the feedstock, such as toluene, but also a desorbent having a boiling point higher than that of the feedstock, such as para-diethylbenzene (PDEB). The selectivity of the adsorbent according to the invention for the adsorption of para-xylene contained in the C8 aromatic fraction is optimal when its loss on ignition, measured at 900°C, is generally less than or equal to 7.7%, preferably between 0 and 7.7%, preferably between 3.0 and 7.7%, more preferably between 3.5 and 6.5%, advantageously between 4.5 and 6.0%, inclusive.

[0071] One of the techniques of choice for characterizing the adsorption of molecules in the liquid phase on porous solids is breakthrough analysis. Ruthven, in his book "Principles of Adsorption and Adsorption Processes," describes the technique of breakthrough curves as a way to study the stepwise injection of an adsorbable component.

[0072] The present invention will now be described using the following examples which are intended to illustrate particular embodiments of the invention without limiting the scope of the invention claimed in the appended claims.

[0073] <Analysis technology> <Identification of zeolite phase> The zeolite MSX in the zeolite adsorbent of the present invention is identified by X-ray diffraction analysis, which is known to those skilled in the art by the abbreviation DRX. This analysis is performed using a Bruker DRX D8 Advance instrument. The identification of the phase is performed using Bruker's EVA software and a database well-known to those skilled in the art containing a number of diffractograms, such as the database ICCD PDF-2 release 2011.

[0074] <Si / Al molar ratio and exchange rate> The measurement of the Si / Al molar ratio and the exchange rate is performed by any of the chemical analysis techniques well-known to those skilled in the art.

[0075] Among these techniques, it is worth mentioning the X-ray fluorescence chemical analysis technique described in the French standard NF EN ISO 12677:2011 using a wavelength dispersive X-ray spectrometer (WDXRF) such as Bruker's Tiger S8.

[0076] X-ray fluorescence (XRF) spectrometry is a non-destructive spectral analysis technique that utilizes the photoluminescence of atoms within the X-ray range to determine the elemental composition of a sample. Generally, the excitation of atoms by an X-ray beam or by electron bombardment causes the atoms to emit specific radiation as they return to their ground state. The advantage provided by the spectrum of the X-ray fluorescence is that it is almost independent of the chemical bonding of the elements and thus provides accurate determination both quantitatively and qualitatively. In conventional methods, a measurement uncertainty of less than 0.4 wt% is obtained following the calibration of each oxide.

[0077] These elemental chemical analyses make it possible to both verify the Si / Al molar ratio of the starting zeolite and confirm the quality of the ion exchange described in step c) and any step d).

[0078] The quality of ion exchange is related to the number of moles of sodium oxide (Na2O) remaining in the agglomerated zeolite adsorbent after exchange. More precisely, the degree of exchange with barium ions is estimated by evaluating the ratio between the number of moles of barium oxide (BaO) and the number of moles of the entire complex (BaO + Na2O). Similarly, the degree of exchange with barium and potassium ions is estimated by evaluating the ratio between the number of moles of barium oxide and potassium oxide (BaO + KO2O) and the number of moles of the entire complex (BaO + KO2O + Na2O). Note that the content levels of the different oxides are given as weight percentages relative to the total weight of the anhydrous zeolite adsorbent.

[0079] The Si / Al molar ratio of the zeolite present in the agglomerated zeolite adsorbent is measured by solid-state nuclear magnetic resonance (NMR) spectroscopy of silicon.

[0080] <Zeolite crystal particle size distribution (particle size measurement)> The number average particle size of the zeolite crystals used in step a) and the zeolite crystals contained in the aggregates is estimated by observation with a scanning electron microscope (SEM).

[0081] To estimate the size of the zeolite particles (i.e., crystals) found in the sample, a series of images are captured at a magnification of at least 5000x. Then, using specialized software such as Smile View developed by LoGraMi, the diameters of at least 200 particles are measured. The measurement accuracy is on the order of 3%. The standard deviation σ of the distribution can also be determined by measuring a histogram constructed based on these diameter measurements.

[0082] Observation of zeolite crystals using a scanning electron microscope (SEM) can also be used to distinguish between zeolite crystal structures (LSX, MSX, X).

[0083] <Particle size distribution of zeolite adsorbent (particle size measurement)> The number average particle size of the zeolite adsorbent obtained as a result of the agglomeration and shaping step a) is determined by analyzing the particle size distribution of the agglomerate sample by imaging according to standard ISO 13322-2:2006, using a conveyor belt that allows the sample to pass in front of a camera lens.

[0084] The number average particle size is then calculated based on the particle size distribution according to standard ISO 9276-2:2001. The term "number average particle size" or "size" is used herein for zeolite aggregates. The accuracy is on the order of 0.01 mm for the size range of the aggregates of the present invention.

[0085] <Micropore volume> The crystallinity of the aggregates is also assessed by measuring their micropore volume by comparing it with that of a suitable standard (100% crystalline zeolite or ideal zeolite under the same cation treatment conditions), which is determined from the measurement of a gas adsorption isotherm, e.g., nitrogen, at its liquefaction temperature.

[0086] Before adsorption, the zeolite adsorbent was subjected to vacuum (P<6.7.10 -4 The mixture is degassed at a pressure of 300 to 450°C (Pa) for 9 to 16 hours. The nitrogen adsorption isotherm at 77 K is then measured in a Micromeritics ASAP2020M apparatus by taking at least 35 measurement points at relative pressures with a P / P ratio between 0.002 and 1.

[0087] <Ignition loss of zeolite adsorbent> Ignition loss is determined in an oxidizing atmosphere by calcining the sample in air at a temperature of 900°C ± 25°C, according to the operating procedure described in French standard NF EN 196-2 (April 2006). The standard deviation of the measurements is less than 0.1%. [Example]

[0088] Example 1 (Comparative): Preparation of BaLSX-type adsorbent containing zeolitic binder In this example, a prior art adsorbent is manufactured and tested.

[0089] 840 g of zeolite LSX crystals (expressed as calcined equivalent) having a Si / Al ratio of 1.01 and 160 g of kaolin (expressed as calcined equivalent) are intimately mixed and agglomerated with an amount of water appropriate for allowing agglomeration by extrusion to occur. The extrudates are dried and then crushed in such a way as to recover particles with an equivalent diameter of 0.7 mm, which are then calcined at 550°C for 2 hours under a nitrogen flow.

[0090] 200 g of the granules thus obtained are placed in a glass reactor equipped with a double jacket adjusted to a temperature of 95±1°C, after which 700 mL of an aqueous solution of sodium hydroxide at a concentration of 220 g / L are added and the reaction medium is left under stirring for 3 hours.

[0091] The granules are then washed in four successive washing operations with water, followed by draining the reactor. The effectiveness of the washing is confirmed by measuring the final pH of the wash water, which should be between 10 and 10.5.

[0092] Barium exchange is then carried out under the same operating conditions as in Example 1, followed by a washing operation, then drying at 80° C. for 2 hours and finally activation at 200° C. for 2 hours under a nitrogen stream.

[0093] The barium exchange rate of this adsorbent is 97%. After pretreatment at 500°C for 12 hours under vacuum, the micropore volume measured by nitrogen adsorption at 77K according to the Dubinin method is 0.235 cm 3 / g.

[0094] The mechanical strength is also measured according to the method presented in the description of the invention: the pressure required to obtain 0.5% fines is 2.70 MPa.

[0095] Example 2 (Comparative): Preparation of BaX-type adsorbent containing zeolitic binder In this example, a prior art adsorbent is manufactured and tested.

[0096] 900 g (expressed as calcined equivalent) of zeolite X crystals having a Si / Al ratio of 1.25 and an average crystal size of 1.6 μm are agglomerated by intimate 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 SiO2 and 0.5% Na2O), and the appropriate amount of water required to form agglomerates by extrusion. The extrudates are dried and then crushed in such a way as to recover agglomerates having an equivalent diameter of 0.7 mm, which are then activated under a nitrogen flow at a temperature of 550° C. for 2 hours.

[0097] 200 g of the granules thus obtained are placed in a double-jacketed glass reactor adjusted to a temperature of 100±1°C, after which 1.5 L of aqueous sodium hydroxide solution at a concentration of 100 g / L is added, and the reaction medium is left under stirring for 3 hours. The granules are then washed three times in succession with water, followed by draining from the reactor. The effectiveness of the washing is confirmed by measuring the final pH of the washing water, which should be between 10 and 10.5.

[0098] Barium exchange is then carried out under the same operating conditions as in Example 1, followed by a washing operation, then drying at 80° C. for 2 hours and finally activation at 200° C. for 2 hours under a nitrogen stream.

[0099] The barium exchange rate of this adsorbent is 95%.

[0100] After pretreatment at 500 °C for 12 h under vacuum, the micropore volume measured by nitrogen adsorption at 77 K according to the Dubinin method was 0.256 cm 3 / g.

[0101] The mechanical strength is also measured according to the method presented in the description of the invention: the pressure required to obtain 0.5% fines is 2.50 MPa.

[0102] Example 3 (for comparison): A 50:50 weight mixture of samples from Examples 1 and 2 (BaLSX-type zeolite adsorbent and BaX-type zeolite adsorbent). The samples of Examples 1 and 2 are mechanically mixed in a 50:50 weight ratio.

[0103] The apparent Si / Al molar ratio of this mixture is 1.13.

[0104] Example 4 (according to the invention): Preparation of BaMSX-type adsorbent containing zeolitic binder The production of BaMSX crystal (Si / Al=1.14) is carried out according to Table 4, Example 27 of patent US6596256.

[0105] The size of the zeolite crystals is analyzed by scanning electron microscopy. The average crystal size is 2.8 μm.

[0106] 840 g (expressed as calcined equivalent) of these zeolite MSX crystals are intimately mixed and agglomerated with 170 g of kaolin (expressed as calcined equivalent), 40 g of colloidal silica sold under the trade name Klebosol® 30 (containing 30% by weight of SiO and 0.5% by weight of NaO), and an appropriate amount of water to allow agglomeration by extrusion to occur. The extrudates are dried and then crushed in such a way as to recover particles with an equivalent diameter of 0.7 mm, which are then calcined at 600° C. for 2 hours under a nitrogen flow.

[0107] 200 g of the granules thus obtained are placed in a double-jacketed glass reactor regulated at a temperature of 95±1° C., after which 700 mL of an aqueous sodium hydroxide solution at a concentration of 170 g / L is added and the reaction medium is left under stirring for 3 hours. The granules are then washed three times in succession with water and subsequently drained from the reactor.

[0108] The effectiveness of the wash is confirmed by measuring the final pH of the wash water, which should be between 10 and 10.5.

[0109] Barium exchange is then carried out under the same operating conditions as in Example 1, followed by a washing operation, then drying at 80° C. for 2 hours and finally activation at 200° C. for 2 hours under a nitrogen stream.

[0110] The barium exchange rate of this adsorbent is 97%. After pretreatment at 500 °C for 12 h under vacuum, the micropore volume measured by nitrogen adsorption at 77 K according to the Dubinin method is 0.255 cm 3 / g.

[0111] The mechanical strength is also measured according to the method presented in the description of the invention: the pressure required to obtain 0.5% fines is 2.60 MPa.

[0112] According to the present invention, a BaMSX agglomerated zeolite adsorbent is obtained.

[0113] Example 5: Breakthrough test (frontal chromatography) The loss on ignition (LIO) is adjusted to a value of 6.0% for each sample.

[0114] These adsorbents are then subjected to a breakthrough test (frontal chromatography) to determine their effectiveness. The amount of adsorbent used in this test is approximately 82 g.

[0115] The operating method and feed composition are identical to those in Example 1.

[0116] The procedure for obtaining the breakthrough curve is as follows.

[0117] - Pack the column with the screen or sieve and place the column on the test bench.

[0118] - Fill with solvent at room temperature.

[0119] - Solvent flow (5cm 3 / min), the adsorption temperature is gradually increased.

[0120] - When the adsorption temperature is reached, 10 cm 3 Inject the solvent at 1 / min.

[0121] -Switch solvent / feed and inject feed (10cm 3 / min).

[0122] The injection of the feed is then maintained for a time long enough to reach thermodynamic equilibrium.

[0123] -Collect and analyze breakthrough effluent.

[0124] The pressure is sufficient to keep the feed in the liquid phase, i.e., 1 MPa. The adsorption temperature is 175°C.

[0125] The composition of the feed is: 45% by weight para-xylene 45% by weight of meta-xylene, and 10% by weight of isooctane (the latter is used as a tracer to estimate the non-selective volume and does not participate in the separation).

[0126] The results of the breakthrough tests are summarized in Table 1. [Table 1]

[0127] Surprisingly, the zeolite adsorbents of the present invention exhibit much higher selectivity for para-xylene over meta-xylene than that measured with prior art zeolite adsorbents.

Claims

1. 1. An agglomerated zeolite adsorbent based on MSX zeolite crystals having a Si / Al atomic ratio of 1.10≦Si / Al≦1.18, preferably 1.10≦Si / Al≦1.17, more preferably 1.10≦Si / Al≦1.16, and even more preferably 1.11≦Si / Al≦1.16, wherein at least 90%, preferably at least 95%, of the exchangeable cation sites are occupied solely by barium ions or by barium ions and potassium ions.

2. After pretreatment at 500°C under vacuum for 12 hours, the micropore volume measured by nitrogen adsorption at 77K according to the Dubinin method was 0.200 cm ３ / g or more, preferably 0.220 cm ３ / g or more, more preferably 0.225 cm ３ / g or more, more preferably 0.250 cm ３ 2. The agglomerated zeolite adsorbent according to claim 1, wherein the agglomerated zeolite adsorbent has a molecular weight of 1 / g or more.

3. 2. The agglomerated zeolite adsorbent of claim 1, wherein the exchangeable sites occupied by potassium account for up to one-third of the exchangeable sites occupied by barium and potassium ions, with any possible remainder generally being made up by alkali or alkaline earth ions other than barium and potassium.

4. 2. The agglomerated zeolite adsorbent according to claim 1, comprising an inert binder in a proportion of not more than 20% by weight, preferably not more than 15% by weight, of the total weight of the agglomerates.

5. 5. The agglomerated zeolite adsorbent according to any one of claims 1 to 4, having a size distribution such that the number average particle size is between 0.4 mm and 2.0 mm, preferably between 0.4 mm and 0.8 mm.

6. 6. The agglomerated zeolite adsorbent according to any one of claims 1 to 5, wherein the mechanical strength measured by Shell method series SMS1471-74 suitable for agglomerates having a size of less than 1.6 mm is 2 MPa or more, preferably 2.5 MPa or more.

7. 7. The agglomerated zeolite adsorbent according to any one of claims 1 to 6, wherein the loss on ignition measured at 900°C is not more than 7.7%, preferably between 0 and 7.7%, more preferably between 3.0% and 7.7%, even more preferably between 3.5% and 6.5%, advantageously between 4.5% and 6.0%, limits included.

8. 8. The agglomerated zeolite adsorbent according to any one of claims 1 to 7, wherein the MSX zeolite crystals have a number average particle size between 0.01 μm and 5 μm, preferably between 0.05 μm and 5 μm, very preferably between 0.1 μm and 4 μm, more preferably between 0.1 μm and 3 μm, and even more preferably between 0.1 μm and 2 μm.

9. A method for separating sugars, polyhydric alcohols, substituted toluene isomers, and cresols, or for recovering para-xylene, using the agglomerated zeolite adsorbent according to any one of claims 1 to 8 in the presence of a desorbent in a liquid phase or a gas phase.

10. Adsorption of para-xylene by the agglomerated zeolite adsorbent in the presence of a desorbent in the liquid or gas phase yields C ８ 10. The process of claim 9, wherein para-xylene is recovered from the aromatic isomer fraction.

11. 11. The process of claim 9 or 10, carried out by a simulated moving bed process of the simulated cocurrent or simulated countercurrent type.

12. 12. A process according to any one of claims 9 to 11 for producing high purity and high productivity para-xylene from a feed mixture of aromatic hydrocarbons containing eight carbon atom (C8) isomers, comprising the steps of: a contacting step a) of contacting the feed mixture with a bed of the agglomerated zeolite adsorbent so as to preferentially adsorb the para-xylene; a contacting step b) of contacting the bed of adsorbent with a desorbent, preferably toluene or para-diethylbenzene, under desorption conditions; a withdrawing step c) of withdrawing a stream containing the desorbent and slightly selectively adsorbed products of the feed mixture from the adsorbent bed; a removing step d) of removing a stream containing the desorbent and the para-xylene from the adsorbent bed; a separation step e) of separating the stream resulting from step c) into a first stream containing the desorbent and a second stream containing less selectively adsorbed products of the feed mixture; and f) separating the stream resulting from step d) into a first stream containing the desorbent and a second stream containing the para-xylene having a purity level of 75% or greater.

13. a crystallization step g) in a crystallizer, in which the para-xylene obtained from step f) is crystallized, which makes it possible, on the one hand, to obtain para-xylene crystals immersed in mother liquor, and, on the other hand, to obtain mother liquor which can be recycled, in part or in whole, as a mixture with a fresh feed mixture at the inlet of a simulated moving bed adsorption unit; a washing step h) of washing the crystals obtained from step g), in which at the end para-xylene having a purity of at least 99.7%, preferably at least 99.8%, is recovered; The method of claim 12 further comprising:

14. 1. Use of an agglomerated zeolite adsorbent based on MSX zeolite crystals having a Si / Al atomic ratio such that 1.10≦Si / Al≦1.18, preferably 1.10≦Si / Al≦1.17, more preferably 1.10≦Si / Al≦1.16, and even more preferably 1.11≦Si / Al≦1.16, wherein at least 90% of the exchangeable cation sites are occupied solely by barium ions or by barium ions and potassium ions, Use in the liquid or gas phase in the presence of a desorbent, preferably toluene or para-diethylbenzene, for separating sugars, polyhydric alcohols, substituted toluene isomers, cresols or for recovering para-xylene.

15. 15. The use of the agglomerated zeolite adsorbent according to claim 14 for the recovery of para-xylene from a fraction of C8 aromatic isomers by adsorption of para-xylene in a simulated moving bed reactor of the simulated cocurrent or countercurrent type.

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