阅读说明：本技术 基于钡、锶、钾和钠的沸石吸附剂、其制备方法以及其用途 (Barium, strontium, potassium and sodium based zeolite adsorbents, method for their preparation and their use ) 是由 C.拉罗什 L.布维尔 J.佩雷斯-佩利特罗 M-L.拉贝德 于 2018-12-17 设计创作，主要内容包括：本发明涉及基于包含钡、钾、钠和锶的沸石X的附聚晶体的沸石吸附剂。这些吸附剂用于分离C8芳族异构体的级份并且特别是二甲苯。(The invention relates to a zeolite adsorbent based on agglomerated crystals of zeolite X comprising barium, potassium, sodium and strontium. These adsorbents are used to separate fractions of the C8 aromatic isomer and in particular xylene.)

1. Zeolite adsorbent comprising zeolite X crystals and comprising barium, potassium, strontium and sodium, wherein K of the substance is in the form of an oxide₂O/(K₂O+SrO+BaO+Na₂O) molar ratio between 1.5% and 8.0%, inclusive, and SrO/(K) of the substance in oxide form₂O+SrO+BaO+Na₂O) a molar ratio between 0.5% and 8.0%, inclusive.

2. The sorbent of claim 1, wherein K of the substance in the form of an oxide₂O/(K₂O+SrO+BaO+Na₂O) between 2.0% and 7.0%, preferably between 2.5% and 6.0%, very preferably between 2.5% and 4.0%, inclusive.

3. An adsorbent according to any one of claims 1 and 2, wherein the substance in the form of an oxide is SrO/(K)₂O+SrO+BaO+Na₂O) between 0.5% and 7.0%, preferably between 1.0% and 6%, very preferably between 1.0% and 4.0%, and even more preferably between 1.0% and 3.0%, inclusive.

4. Adsorbent according to one of the preceding claims, wherein the SrO/K of the substance in the form of an oxide₂The O molar ratio is between 0.3 and 2.0, preferably between 0.35 and 1.5, preferably between 0.4 and 1.0, inclusive.

5. The adsorbent of one of the preceding claims, further comprising a non-zeolitic phase.

6. Adsorbent according to one of the preceding claims, wherein sodium oxide Na₂The content of O is less than 0.3% by weight, relative to the total mass of the adsorbent.

7. Adsorbent according to one of the preceding claims, wherein different from barium oxide BaO, potassium oxide K₂O, strontium oxide SrO and sodium oxide Na₂The total content of alkali or alkaline earth metal ion oxides of O is less than 1% by weight, inclusive, relative to the total mass of the adsorbent.

8. Adsorbent according to one of the preceding claims, wherein the Si/Al atomic ratio of the zeolite X crystals is between 1.00 and 1.50, inclusive.

9. The sorbent according to one of the preceding claims, having a number average diameter between 0.2mm and 2mm, inclusive.

10. Adsorbent according to one of the preceding claims, wherein the number average diameter of zeolite X crystals is less than or equal to 1.5 μm, inclusive.

11. The sorbent according to one of the preceding claims, having a loss on ignition, measured at 950 ℃ according to standard NF EN196-2, of between 4.0 and 7.7 wt.%.

12. An adsorbent according to one of the preceding claims, wherein the mass fraction of zeolite X is at least 80 wt% zeolite X, relative to the total mass of the adsorbent.

13. A method of making the sorbent according to any one of the preceding claims, comprising at least the steps of:

a) agglomeration of a powder of zeolite X crystals with a binder, and molding, followed by drying and calcination,

b) optionally a zeolitization of the binder,

c) cation exchange of the agglomerates by contact with a solution containing barium, potassium or strontium ions, alone or as a mixture, one or more times, simultaneously, sequentially or alternately, followed by washing and drying of the agglomerates thus treated, and

d) activation of the zeolitic adsorbent thus obtained.

14. Method according to claim 13, characterized in that the binder used in step a) contains at least 80% by weight of a zeolitized clay and a silica source, and that the method comprises a step b) of zeolitizing the zeolitized binder by the action of a basic alkali solution, preferably with a solution concentration between 0.5 and 5M, preferably between 0.5M and 2M, and a duration between tens of minutes and hours.

15. An adsorbent according to any one of claims 1 to 12, obtainable according to the process of any one of claims 13 and 14.

16. Use of the adsorbent according to any one of claims 1 to 12 or according to claim 15 in a process for:

separation of the fractions of aromatic C8 isomer and in particular xylene,

separation of isomers of substituted toluenes, such as nitrotoluene, diethyltoluene, toluenediamine, etc.,

separation of the cresol(s) and separation of the cresol(s),

the polyol is isolated.

17. Use according to claim 16 for separating para-xylene from a fraction comprising aromatic isomers of 8 carbon atoms.

18. Process for recovering para-xylene from a fraction of aromatic hydrocarbon isomers containing 8 carbon atoms in the liquid phase by adsorption of the para-xylene, comprising the following successive steps:

a) a step of contacting the feedstock with a bed of adsorbent comprising at least one zeolite adsorbent as defined in any one of claims 1 to 12 or 15,

b) a step of contacting the adsorbent bed with a desorbent, preferably selected from the group consisting of toluene and p-diethylbenzene.

19. Process for recovering para-xylene according to claim 18, characterized in that it is of the simulated moving bed type, preferably in simulated countercurrent mode.

20. Process for recovering para-xylene from a fraction of aromatic hydrocarbon isomers containing 8 carbon atoms in the gas phase by adsorption of para-xylene by means of an adsorbent according to any one of claims 1 to 12 or 15, comprising the following successive steps:

a) a step of contacting the feedstock with a bed of adsorbent comprising at least one zeolite adsorbent as defined in any one of claims 1 to 12 or 15,

b) a step of contacting the adsorbent bed with a desorbent, preferably selected from the group consisting of toluene and p-diethylbenzene.

21. A process for separating a polyol comprising the step of contacting the polyol with an adsorbent as defined in any one of claims 1 to 12 or 15.

22. A method of separating isomers of substituted toluene, such as nitrotoluene, diethyltoluene or toluene diamine, comprising the step of contacting the substituted toluene isomers with an adsorbent as defined in any one of claims 1 to 12 or 15.

23. A process for separating cresol comprising the step of contacting cresol with an adsorbent as defined in any of claims 1 to 12 or 15.

Technical Field

The present invention relates to an adsorbent based on agglomerated crystals of zeolite X comprising barium, strontium and potassium, a process for producing it and its use.

These adsorbents can be used more particularly for the liquid-phase or gas-phase production of very pure para-xylene from a feedstock containing aromatic hydrocarbons containing isomers of 8 carbon atoms.

Background

It is known in the art that adsorbents comprising crystalline aluminosilicates can be used to separate certain hydrocarbons from mixtures containing them. In the field of separation of aromatic hydrocarbons and in particular of aromatic C8 isomers, it is generally accepted that the use of specific cations in the cationic sites of crystalline aluminosilicate zeolites improves the selectivity of the zeolite for one of the aromatic C8 isomers. This differential adsorption within the zeolite enables the separation of various aromatic C8 isomers, which are used industrially to produce very pure para-xylene from a feedstock containing aromatic hydrocarbons containing isomers containing 8 carbon atoms.

Thus, the use of zeolitic adsorbents consisting of zeolite X or Y, containing in addition to sodium cations barium, potassium or strontium ions, alone or as a mixture, for the selective adsorption of paraxylene in the liquid phase in aromatic hydrocarbon mixtures is well known in the art.

Patents US 3558730, US 3663638 and US 3960774 show that zeolite adsorbents comprising aluminosilicates of Faujasite (FAU) structure based on sodium and barium or on sodium, barium and potassium can effectively separate para-xylene present in aromatic C8 fractions, including fractions of aromatic hydrocarbons containing 8 carbon atoms. The above adsorbent is preferably used as adsorbent in a liquid phase process, in particular a simulated countercurrent type liquid phase process, similar to those described in patent US 2985589, and it is particularly suitable for aromatic C8 fractions.

Patents US 3558730, US 3626020 and US 3997620 show that zeolite adsorbents comprising aluminosilicates of Faujasite (FAU) structure based on sodium and barium or on sodium, barium and strontium can effectively separate para-xylene present in aromatic C8 fractions, including fractions of aromatic hydrocarbons containing 8 carbon atoms.

However, in general, the adsorption properties of zeolites towards aromatic hydrocarbons containing 8 carbon atoms (xylenes and ethylbenzene) vary very finely according to the size and shape of the pores and the position of the cations within the structure, which have an effect both on the electrostatic field present within the zeolite and on the form of accessible volumes in the pores. Other parameters, such as polarizability of cations and molecules or flexibility of structures, may also have an effect. Therefore, it is extremely difficult to theoretically and accurately predict the adsorption characteristics of the zeolite with respect to the aromatic hydrocarbon containing 8 carbon atoms.

In order to improve the adsorption selectivity of zeolites having the faujasite structure for the aromatic C8 isomer, many studies have mentioned the effects of the Si/Al ratio of the zeolite, the nature of the exchange cations, and its water content. Similarly, it is very difficult to predict the extent of improvement, since these factors exert a complex effect on the adsorption characteristics of the zeolite. In particular, in the case of Faujasite (FAU) structured zeolites, and more particularly in the case of Faujasite (FAU) structured zeolites of the X type, it is difficult to predict the effect of the relative proportions of the cations selected from sodium, barium, strontium and potassium.

Patent US 3997620 proposes agglomerates in which the agglomerated binder is not zeolitic, said agglomerates being exchanged with barium or with strontium so that the weight ratio Ba/Sr is between 1:1 and 15: 1. The examples of this patent show that the purity of the extract is improved by the addition of strontium cations. However, the PX/MX and PX/OX selectivity is greatly reduced, which is problematic for the production of high purity paraxylene.

The synthesis of zeolites produces crystals (usually in powder form) which are particularly difficult to use on an industrial scale (large losses of feed during operation). Thus, preferred are agglomerated forms of these crystals, in the form of grains, yarns and other agglomerates, which can be obtained by extrusion, granulation and other agglomeration techniques known to those skilled in the art. These agglomerates do not have the disadvantages inherent in powdered materials.

These agglomerates, whether in the form of tablets, beads, extrudates, etc., are generally formed from zeolite crystals constituting the active element (in the sense of adsorption) and a binder intended to ensure cohesion of the crystals in the form of agglomerates and to give them sufficient mechanical strength to withstand the vibrations and movements to which they are subjected during the operation of separating the isomers of the aromatic C8 fraction. However, because of the presence of the agglomeration binder, which is inert to adsorption, the adsorption properties of these agglomerates are significantly reduced with respect to crystalline powders. Various approaches have been proposed to overcome this disadvantage of the agglomerated binder being inert in terms of adsorption properties, including the conversion of all or at least a portion of the agglomerated binder to a zeolite that is active from an adsorption standpoint. This operation is now well known to the person skilled in the art, for example under the name "zeolitization". To facilitate this operation, a zeolitized binder is used, generally a clay belonging to the kaolin family, which has preferably been previously calcined at a temperature generally between 500 ℃ and 700 ℃.

Patent application FR 2789914 describes, for example, a process for producing agglomerates of zeolite X having a Si/Al ratio between 1.15 and 1.5, containing barium and optionally potassium. From the point of view of adsorption of the para-xylene contained in the aromatic C8 fraction, after the zeolitic binding agent, the agglomerates thus obtained have improved properties with respect to an adsorbent prepared from the same amount of zeolite X and binding agent, but whose binding agent is not zeolitic.

Important factors that influence the performance level of a process for separation by adsorption include, inter alia, adsorption selectivity, adsorption capacity and mass transfer kinetics (which define the adsorption and desorption rates of various compounds). Therefore, the adsorbent must have good mass transfer properties to ensure a sufficient number of theoretical plates to achieve effective separation of the mixed species, as specified by Ruthven in the book entitled "Principles of Adsorption and Adsorption Processes," John Wiley & Sons, (1984), pages 326 and 407. Ruthven states (supra, page 243) that in the case of agglomerated adsorbents, the total mass transfer depends on the sum (addition) of the intra-crystal and inter-crystal diffusional resistances. The in-crystal diffusion resistance is proportional to the square of the radius of the crystal and inversely proportional to the diffusivity of the molecules in the crystal

The inter-crystal diffusion resistance (also called macropore resistance) is, for its part, proportional to the square of the agglomerate radius and inversely proportional to the diffusivity of the molecules in the macropores. For a given zeolite structure, a given agglomerate size and a given operating temperature, the diffusivity is fixed, while the only way to improve mass transfer is to reduce the diameter of the crystals. Thus, by reducing the size of the crystal, a gain (gain) with respect to the total transfer is obtained.

Thus, the skilled person would expect an agglomerated zeolitic adsorbent having both a good xylene adsorption capacity (capacity) and a good selectivity for para-xylene, which, when produced from small zeolite crystals, has very good xylene separation properties in a liquid phase process (e.g. of the simulated countercurrent type) for separating para-xylene contained in an aromatic C8 fraction. However, it is not possible for the person skilled in the art to define, a priori or theoretically and exactly, the adsorption characteristics of FAU zeolites (in particular of the X type) comprising barium and potassium and optionally other cations (for example sodium and strontium) with respect to aromatic hydrocarbons comprising 8 carbon atoms.

Surprisingly, the new adsorbent based on zeolite X comprising barium, potassium, strontium and sodium and having a specific barium, potassium, strontium and sodium composition seems to allow to simultaneously maximize the productivity and minimize the production costs of the process for separating para-xylene contained in the aromatic C8 fraction. The invention also proposes a process for separating xylenes using an adsorbent based on zeolite X having a specific barium, potassium, strontium and sodium composition, which allows the production of high purity para-xylene with improved productivity from a feedstock containing aromatic hydrocarbons containing isomers containing 8 carbon atoms.

Disclosure of Invention

The invention relates to a container comprisingZeolite X crystals and containing barium, potassium, strontium and sodium, K of substance in oxide form₂O/(K₂O+SrO+BaO+Na₂O) is between 1.5% and 8.0%, preferably between 2.0% and 7.0%, and preferably between 2.5% and 6.0%, inclusive. In an advantageous variant, K of the substance in the form of an oxide₂O/(K₂O+SrO+BaO+Na₂O) between 2.5% and 4.0%, for example equal to 3.0%. SrO/(K) of substance in oxide form₂O+SrO+BaO+Na₂O) between 0.5% and 8.0%, preferably between 0.5% and 7.0%, very preferably between 1.0% and 6.0%, and even more preferably between 1.0% and 4.0%, inclusive. In an advantageous variant, the substance in the form of an oxide has SrO/(K)₂O+SrO+BaO+Na₂O) is between 1.0% and 3.0%, for example 1.5%.

Preferably, the SrO/K of the substance in oxide form₂The O molar ratio is between 0.3 and 2.0, preferably between 0.35 and 1.5, preferably between 0.4 and 1.0, inclusive. In an advantageous variant, the SrO/K of the substance in the form of an oxide₂The O molar ratio is for example equal to 0.5%.

Sodium oxide Na₂The O content is advantageously less than 0.3% by weight, and preferably less than 0.2% by weight, relative to the total mass of the adsorbent. Different from barium oxide BaO and potassium oxide K₂O, strontium oxide SrO and sodium oxide Na₂The total content of alkali or alkaline earth metal ion oxides of O is advantageously less than 1% by weight, preferably between 0% and 0.5% by weight, and very preferably between 0% and 0.3% by weight, inclusive, relative to the total mass of the adsorbent.

Barium oxide BaO, potassium oxide K₂O, strontium oxide SrO, sodium oxide Na₂The sum of the contents of O and any other alkali metal or alkaline earth metal oxides represents the total content in% by weight of the substances present in the adsorbent in the form of oxides. The barium oxide content in% by weight relative to the total mass of the sorbent can thus be directly formed from other oxide forms in% by weight relative to the total mass of the sorbentThe content of the substance(s) of (c).

In the present invention, it is understood that the weight content expressed as the weight of the oxide is expressed relative to the total weight of the anhydrous adsorbent (weight corrected for loss on ignition).

The Si/Al atomic ratio of the zeolite X crystals is advantageously between 1.00 and 1.50, preferably between 1.00 and 1.45, more preferably between 1.05 and 1.50, more preferably between 1.05 and 1.45, and more preferably between 1.10 and 1.50, and even more preferably between 1.10 and 1.45, inclusive.

The number-average diameter of the crystals of zeolite X is advantageously less than or equal to 1.5 μm, preferably between 0.1 μm and 1.2 μm, more preferably between 0.1 μm and 1.0 μm, inclusive.

The loss on ignition of the sorbent according to the invention, measured at 950 ℃ according to standard NF EN196-2, is advantageously between 4.0 and 7.7% by weight, and preferably between 4.5 and 6.5% by weight, and very preferably between 4.8 and 6.0% by weight, inclusive.

The number average diameter of the adsorbent according to the invention may be between 0.2mm and 2.0mm, in particular between 0.2mm and 0.8mm and preferably between 0.2mm and 0.65mm, inclusive.

The invention also relates to a process for preparing an adsorbent as described above, comprising at least the following steps:

a) agglomeration of a powder of zeolite X crystals with a binder, and molding, followed by drying and calcination,

b) optionally a zeolitization of the binder,

c) cation exchange of the agglomerates by contact with a solution containing barium, potassium or strontium ions, alone or as a mixture, one or more times, simultaneously, sequentially or alternately, followed by washing and drying of the agglomerates thus treated, and

d) activation of the zeolitic adsorbent thus obtained.

Preferably, the method of preparing the adsorbent carries out step b) of zeolitization of the binder.

Preferably, the concentration of the solution of barium, strontium, potassium ions of step c) is between 0.5 and 2M.

The invention also relates to an adsorbent as described above, which can be obtained according to the above preparation process. The invention also relates to the use of the adsorbent according to the invention in a method:

separation of the fractions of aromatic C8 isomer and in particular xylene,

separation of isomers of substituted toluenes, such as nitrotoluene, diethyltoluene, toluenediamine, etc.,

separation of the cresol(s) and separation of the cresol(s),

the separation of the polyol(s) is carried out,

and in particular for separating para-xylene from a fraction of aromatic isomers containing 8 carbon atoms.

The invention also relates to a process for recovering paraxylene from fractions of aromatic hydrocarbon isomers containing 8 carbon atoms in the liquid phase by adsorbing paraxylene by means of the adsorbent according to the invention in the presence of a desorbent, preferably selected from toluene and p-diethylbenzene.

The process may be of the simulated moving bed type, preferably in simulated countercurrent mode.

The invention also relates to a process for recovering paraxylene from a fraction of aromatic hydrocarbon isomers containing 8 carbon atoms in the gas phase by adsorbing paraxylene by means of the adsorbent according to the invention in the presence of a desorbent, preferably selected from toluene and p-diethylbenzene.

The invention also relates to a process for the separation of polyols using the adsorbent according to the invention.

The invention also relates to a process for separating isomers of substituted toluene (e.g. nitrotoluene, diethyltoluene or toluenediamine) using the adsorbent according to the invention.

The invention finally relates to a process for separating cresols using the adsorbent according to the invention.

In the following, unless otherwise specified, the end values of a numerical range are included in the range, in particular in the expressions "between" and "range from.

Detailed Description

Thus, a first subject of the present invention is a zeolitic adsorbent based on zeolite X. These adsorbents are particularly suitable for use in processes for separating paraxylene in the liquid phase, preferably of the simulated countercurrent type.

The invention therefore relates to a zeolitic adsorbent comprising zeolite X crystals and comprising barium, strontium, potassium and sodium, K of the substance in the form of the oxide thereof₂O/(K₂O+SrO+BaO+Na₂O) is between 1.5% and 8.0%, preferably between 2.0% and 7.0%, and preferably between 2.5% and 6.0%, inclusive. In an advantageous variant, K is represented by an oxide₂O/(K₂O+SrO+BaO+Na₂O) between 2.5% and 4.0%, inclusive, for example equal to 3.0%. SrO/(K) of substance in oxide form₂O+SrO+BaO+Na₂O) between 0.5% and 8.0%, preferably between 0.5% and 7.0%, very preferably between 1.0% and 6.0%, and even more preferably between 1.0% and 4.0%, inclusive. In an advantageous variant, the substance in the form of an oxide has SrO/(K)₂O+SrO+BaO+Na₂O) is between 1.0% and 3.0%, inclusive, e.g. 1.5%.

Preferably, the SrO/K of the substance in oxide form₂The O molar ratio is between 0.3 and 2.0, preferably between 0.35 and 1.5, preferably between 0.4 and 1.0, inclusive. In an advantageous variant, the SrO/K of the substance in the form of an oxide₂The O molar ratio is for example equal to 0.5%.

The adsorbent according to the invention may also comprise a non-zeolitic phase, that is to say an amorphous phase, which is substantially inert with respect to adsorption. In case the adsorbent according to the invention comprises a non-zeolitic phase, K₂O/(K₂O+SrO+BaO+Na₂O) molar ratio takes into account the oxides comprised in the non-zeolitic phase.

Sodium oxide Na in the adsorbent according to the invention₂The O content is advantageously less than 0.3% by weight, and preferably less than 0.3% by weight, relative to the total mass of the adsorbent. In the adsorbents according to the present inventionSame as barium oxide BaO and potassium oxide K₂O, strontium oxide SrO and sodium oxide Na₂The total content of alkali or alkaline earth metal ion oxides of O is advantageously less than 1% by weight, preferably between 0% and 0.5% by weight, and very preferably between 0% and 0.3% by weight, inclusive, relative to the total mass of the adsorbent.

The zeolitic adsorbent according to the present invention is an adsorbent based on crystals of zeolite X type FAU. The term "zeolite X" is intended to mean a zeolite having an Si/Al atomic ratio of: between 1.00 and 1.50, inclusive, preferably between 1.05 and 1.50, inclusive, and even more preferably between 1.10 and 1.50, inclusive.

Among zeolite X, two sub-groups known as LSX zeolite and MSX zeolite are now recognized. The LSX zeolite has an atomic Si/Al ratio equal to about 1, while the MSX zeolite has an atomic Si/Al ratio between about 1.05 and about 1.15, inclusive.

In the zeolite adsorbent of the invention, and according to a preferred embodiment, the term "type X FAU zeolite" is intended to mean the type X FAU zeolite defined above, which is hierarchical porous, that is to say hierarchical porous type X zeolite (or HPX), hierarchical porous type MSX zeolite (or HPMSX) and hierarchical porous type LSX zeolite (or HPLSX), and more particularly hierarchical porous FAU zeolite, having an Si/Al atomic ratio between 1.00 and 1.50, preferably between 1.00 and 1.45, more preferably between 1.05 and 1.50, more preferably between 1.05 and 1.45, and even more preferably between 1.10 and 1.50 and even more preferably between 1.10 and 1.45, inclusive.

The present invention also includes a zeolitic adsorbent comprising a mixture of two or more of the just-defined hierarchically porous FAU zeolites.

The term "hierarchically porous zeolite" is intended to mean a zeolite having both micropores and mesopores, in other words, a zeolite that is both microporous and mesoporous. The term "mesoporous zeolite" is intended to mean a zeolite in which, together with microporosity, the microporous zeolite crystals have nanometer-sized internal cavities (mesoporosity) which are easily identifiable by observation using a Transmission Electron Microscope (TEM), as described for example in US 7785563: observation by a Transmission Electron Microscope (TEM) makes it possible to verify that the zeolite crystals are solid zeolite crystals (i.e., non-mesoporous) or solid aggregates of zeolite crystals or mesoporous crystals or aggregates of mesoporous crystals

The crystal structure of zeolite X FAU in the zeolite adsorbent of the invention can be identified by X-ray diffraction methods (known to those skilled in the art under the acronym XRD).

According to a preferred embodiment, the Si/Al atomic ratio of the zeolitic adsorbent is between 1.00 and 2.00, preferably between 1.00 and 1.80, inclusive, more preferably between 1.15 and 1.80, inclusive, and even more preferably between 1.15 and 1.60, inclusive.

The term "number average diameter" or "size" is used herein for both zeolite crystals and zeolite agglomerates. The method of measuring these parameters will be explained in the following description. According to a preferred embodiment of the invention, the number average diameter of the crystals of zeolite X is less than or equal to 1.5 μm, preferably between 0.1 μm and 1.2 μm, more preferably between 0.1 μm and 1.0 μm, inclusive.

The zeolitic adsorbent of the present invention is preferably in the form of agglomerates, that is to say it consists of crystals of zeolite and at least one non-zeolitic phase, which is an agglomerated binder allowing the crystals to agglomerate with one another. Thus, the zeolitic adsorbents of the present invention are often referred to in this disclosure as "agglomerates".

The mass fraction of zeolite X in the adsorbent according to the invention may be at least 80 wt% of zeolite X, preferably at least 90 wt%, relative to the total weight of the anhydrous adsorbent, which may be up to 100 wt%, and typically up to 99.5%.

According to a preferred embodiment, the zeolitic adsorbent according to the present invention has a loss on ignition, measured at 950 ℃ according to standard NF EN196-2, of between 4.0% and 7.7%, preferably between 4.5% and 6.5%, and advantageously between 4.8% and 6%, inclusive.

Preferably, the mechanical strength of the zeolitic adsorbent according to the present invention is generally greater than or equal to 1.8MPa, typically greater than or equal to 2.1 MPa. The mechanical strength is measured by the Shell series SMS1471-74 method applicable to agglomerates less than 1.6mm in size.

As for the adsorption capacity fraction, it was measured by measuring the micropore volume of an adsorbent, which was degassed at 300 ℃ in vacuum for 16 hours, and then adsorbing nitrogen (N) at a temperature of 77K₂) Evaluated according to the Dubinin-Raduskevitch equation. The micropore volume of the zeolite adsorbent of the present invention thus measured was at 0.245cm³G and 0.300cm³Between/g, typically 0.250cm³G to 0.290cm³Within the range of/g, inclusive.

According to another aspect, the present invention relates to a process for preparing the zeolite agglomerates just defined, said process comprising at least the following steps:

a) agglomeration of a powder of zeolite X crystals with a binder, and molding, followed by drying and calcination,

b) optionally zeolitization of the binder, preferably by the action of a basic alkali solution,

c) cation exchange of the agglomerates is carried out by contact with a solution of barium, potassium or strontium ions. Adjusting the potassium, strontium, or barium ion concentration in the solution to achieve the desired barium, potassium, and strontium content in the sorbent, and thereby achieve the desired K₂O/(K₂O+SrO+BaO+Na₂O) and SrO/(K)₂O+SrO+BaO+Na₂O) molar ratio. Cation exchange of the agglomerates with barium, potassium and strontium can be carried out in a simultaneous, sequential or alternating manner by contact with a solution containing barium, potassium or strontium ions, either alone or as a mixture of 2 or 3 ions.

These operations may be performed one or more times.

Between each exchange step, the solid is washed several times to remove excess salts therefrom and dried at the end of each exchange step,

d) activation of zeolite agglomerates.

Preferably, the process for preparing the zeolite agglomerates implements step b) of zeolitization of the binder.

Preferably, the concentration of the solution of barium, strontium, potassium ions of step c) is between 0.5 and 2M.

The size of the zeolite X crystals used in step a) is measured by observation with a Scanning Electron Microscope (SEM) or by observation with a Transmission Electron Microscope (TEM). This SEM or TEM observation also makes it possible to confirm the presence of the non-zeolitic phase comprising, for example, the binder, or residual binder not converted during the optional zeolitization step, or any other amorphous phase in the agglomerate.

According to one embodiment, the zeolite X used in step a) is a hierarchical porous type X FAU zeolite. Crystals of layered porous type X FAU zeolite with large external surface area can be obtained according to various methods known to the skilled person and for example according to the synthesis described by Inayat et al (angelw. chem. int. ed., (2012),51, 1962-.

It is also possible to synthesize by seed addition and/or by adjusting the synthesis operating conditions (for example, to synthesize SiO in a mixture)₂/Al₂O₃Ratio, sodium content and basicity) or according to the method of post-treatment of the crystals of type X FAU zeolite, which is conventional and known to those skilled in the art.

The work-up process generally consists in removing atoms from the zeolite network already formed by: the solid is dealuminated (dealuminated/dealuminated) by one or more acid treatments followed by one or more sodium hydroxide (NaOH) washes to remove the aluminium residues formed, as described for example in d.verboekend et al (adv.funct.mater, 22, (2012), pp.916-928), or by treatments combining the action of an acid and the action of a structuring agent that improves the efficiency of the acid treatment, as described for example in application WO 2013/106816.

The agglomeration and shaping (step a) can be carried out according to all techniques known to the person skilled in the art (for example extrusion, compaction, agglomeration, etc.). The proportions of the optionally zeolitized (see definition below) agglomeration binder and zeolite used are typically those of the prior art, that is to say from 5 to 20 parts by weight of binder per 95 to 80 parts by weight of zeolite. The agglomerates from step a), whether in the form of spheres, extrudates or the like, have a number average diameter (or maximum dimension when it is not spherical) generally between 0.2mm and 2mm, and in particular between 0.2mm and 0.8mm, and preferably between 0.2mm and 0.65mm, inclusive.

At the end of step a), the finest agglomerate particles can be removed by cyclone (cyclone) and/or sieving, and/or particles that are too coarse can be removed by sieving or crushing, for example in the case of extrudates.

The agglomeration binder used in step a) may be zeolitized. It then contains at least 80 wt.%, preferably at least 90 wt.%, more preferably at least 95 wt.%, more particularly at least 96 wt.% of zeolizable clay, and may also contain other mineral binders such as bentonite, attapulgite, and the like. The term "zeolitized clay" is intended to mean a clay or clay (clays) mixture which is capable of being converted into a zeolitic substance, i.e. an active substance in the adsorption sense, usually under the action of a basic alkali solution. Zeolitized clays generally belong to the family of kaolins, kaolinites, nacrite (nacrites), dickite, halloysite (hallyosite) and/or metakaolins. Kaolin is preferred, and is most commonly used.

Other clays, such as sepiolite or attapulgite in particular, may also be used.

In any case, the clay may be used in its raw form or may have been previously subjected to one or more treatments, for example selected from calcination, acid treatment, chemical modification, and the like.

The zeolite X powder used in step a) may result from the synthesis of zeolite X crystals comprising mainly or even only sodium cations (e.g. NaX zeolite), but it would not depart from the scope of the invention to use a powder that has undergone one or more cation exchanges after synthesis and before use in step a).

During step a), in addition to the zeolite X powder and the binder, one or more additives may be added, for example additives intended to promote agglomeration or to improve hardening of the agglomerates formed, such as lignin, starch, carboxymethyl cellulose, and other additives known to the person skilled in the art. Silica may also be added. The optional source of silica may be of any type known to those skilled in the art as an expert in zeolite synthesis, such as colloidal silica, diatomaceous earth, perlite, fly ash, sand or any other form of solid silica.

After drying in step a), the calcination is carried out at a temperature generally between 500 ℃ and 700 ℃. In the case of shaping with a zeolitized clay, this step makes it possible to convert the zeolitized clay, typically kaolin, into metakaolin, which can then be converted into zeolite during the zeolitization step (step b)). The principle is described in "Zeolite Molecular Sieves" of D.W.Breck, John Wiley and Sons, New York, (1973), p.314-315.

The zeolitization of the agglomerated binder is carried out according to any process known to the person skilled in the art and can be carried out, for example, by immersing the product of step a) in a basic alkali solution, which is generally aqueous, for example an aqueous solution of sodium hydroxide and/or potassium hydroxide.

As a general rule, the concentration of the basic zeolitic solution is preferably between 0.5M and 5M, more particularly between 0.5 and 2M. The zeolitization is preferably carried out under thermal conditions at a temperature above ambient temperature, and is typically at a temperature of about 80 ℃ to 100 ℃, for example between ambient temperature (i.e. about 20 ℃) and the boiling point of the basic zeolitization solution. The duration of the zeolitization process is generally between a few tens of minutes and a few hours, preferably between about 1 hour and 8 hours.

Step c) of the exchange of the cations of zeolite X with barium and/or strontium and/or potassium is carried out according to conventional methods known to the person skilled in the art and is generally carried out as follows: contacting the agglomerates from step a) or step b) with a salt, such as barium chloride (BaCl) for exchange with barium, in an aqueous solution at a temperature between ambient temperature and 100 ℃ and preferably between 80 ℃ and 100 ℃₂) And/or strontium chloride (SrCl) for exchange with strontium₂) And/or potassium chloride (KCl) for exchange with potassium. In order to obtain a low sodium oxide content quickly, i.e. smallThe process is preferably carried out with a large excess of barium and/or strontium and/or potassium ions at 1%, preferably in relation to the cations of the zeolite desired to be exchanged, typically in an excess of about 10 to 12, advantageously by carrying out successive exchanges. Preferably, the concentration of the solution of barium, strontium, potassium ions of step c) is between 0.5 and 2M.

As mentioned before, it is also possible to agglomerate in step a) a zeolite X powder already containing potassium ions (the cations present in the starting zeolite X, typically sodium cations, are pre-exchanged with potassium ions before step a) and to possibly omit the potassium exchange during step c).

Followed by washing (usually and preferably with water) and subsequent drying of the agglomerates thus obtained.

Activation after drying is carried out conventionally according to methods known to the person skilled in the art, for example at temperatures generally between 100 ℃ and 400 ℃, preferably between 200 ℃ and 300 ℃. The purpose of this activation step d) is to fix the water content and the loss on ignition of the sorbent in an optimal way for the envisaged use. The general procedure is thermal activation, which is preferably carried out for a certain time between 200 ℃ and 300 ℃, depending on the desired water content and the desired loss on ignition, typically 1 to 6 hours.

The invention also relates to the use of the above-mentioned zeolitic adsorbents as adsorption agents capable of advantageously replacing the adsorption agents described in the literature for the following uses:

separation of the fractions of aromatic C8 isomer and in particular xylene,

separation of isomers of substituted toluenes, such as nitrotoluene, diethyltoluene, toluenediamine, etc.,

separation of the cresol(s) and separation of the cresol(s),

separation of polyols, such as sugars.

The invention relates in particular to a process for recovering high-purity para-xylene from a fraction of aromatic isomers containing 8 carbon atoms, which comprises (consists in) using the zeolitic adsorbent according to the invention as an adsorption agent for para-xylene, both in liquid-phase and in gas-phase processes. The term "high purity paraxylene" is intended to mean a product suitable for use in the production of terephthalic acid or dimethyl terephthalate, that is, having a purity of at least 99.5 weight percent, preferably at least 99.7 weight percent, preferably at least 99.8 weight percent, and even more preferably at least 99.9 weight percent. The purity of p-xylene can be determined by chromatography. Gas chromatography, which can be used to determine the purity of paraxylene and the specific content of impurities, is the ASTM D-3798 method.

The desired product (para-xylene) can thus be separated by adsorption liquid chromatography of the preparative (batchwise) type and advantageously continuously in a simulated moving bed, that is to say in simulated countercurrent or simulated cocurrent mode, and more particularly in simulated countercurrent mode.

The advantage of the process for recovering para-xylene according to the invention using the adsorbent described according to the invention is to maximize the productivity while minimizing the operating costs of the process, that is to say both to maximize the flow of the feedstock to be treated and to minimize the flow of the desorbent required. This is particularly true for a simulated counter-current type industrial adsorption unit under the following operating conditions:

number of beds: 6 to 30 of the total weight of the composition,

number of regions: at least 4 operating zones, each zone being located between the feed point and the withdrawal point,

a temperature between 100 ℃ and 250 ℃, preferably between 150 ℃ and 190 ℃,

the pressure of the industrial unit is between the xylene bubble point pressure at the process temperature and 3MPa,

the ratio of desorbent/feed flow rate for a single (independent) adsorption unit is between 0.7 and 2.5, for example between 0.91.8, and for an adsorption unit combined with a crystallization unit, between 0.7 and 1.4,

the recycle ratio (i.e. the ratio of the average recycle flow rate (the average flow rate of the zones weighted with respect to the number of beds per zone) to the feed flow rate) is between 2.5 and 12, preferably between 3.5 and 6.

The invention also relates to a process for recovering paraxylene from a fraction of aromatic hydrocarbon isomers containing 8 carbon atoms in the liquid phase by adsorption of paraxylene, comprising the following successive steps:

a) a step of contacting the feedstock with an adsorbent bed comprising at least one zeolitic adsorbent as defined above,

b) a step of contacting the adsorbent bed with a desorbent, preferably selected from the group consisting of toluene and p-diethylbenzene.

The process for recovering paraxylene may be of the simulated moving bed type, preferably in simulated countercurrent mode

The invention also relates to a process for recovering paraxylene from a fraction of aromatic hydrocarbon isomers containing 8 carbon atoms in the gas phase by adsorption of paraxylene by means of an adsorbent as defined above, comprising the following successive steps:

a) a step of contacting the feedstock with an adsorbent bed comprising at least one zeolitic adsorbent as defined above,

b) a step of contacting the adsorbent bed with a desorbent, preferably selected from the group consisting of toluene and p-diethylbenzene.

In one variant, the process for separating high-purity paraxylene is carried out in a simulated moving bed starting from an aromatic hydrocarbon feedstock containing isomers containing 8 carbon atoms, comprising the following steps:

a) a step of contacting the feedstock with a bed of adsorbent comprising at least one zeolitic adsorbent as defined above, in such a way as to preferentially (preferentially) adsorb paraxylene,

b) a step of contacting the adsorbent bed with a desorbent, preferably toluene or p-diethylbenzene,

c) a step of withdrawing from the bed of adsorbent a stream comprising desorbent and feed product adsorbed with the lowest selectivity,

c) a step of withdrawing a stream containing the desorbent and the desired product (i.e. para-xylene) from the adsorbent bed,

e) separating the stream resulting from step c) into a first stream comprising desorbent and a stream train (string) comprising the feed product adsorbed with the lowest selectivity,

f) the stream resulting from step d) is separated into a first stream containing the desorbent and a second stream containing paraxylene having a purity level greater than or equal to 90%, preferably greater than or equal to 99% and very preferably greater than or equal to 99.7%.

In this respect, reference is made to the teachings of patents US 2985589, US 5284992 and US 5629467.

Operating conditions for commercial simulated co-current adsorption units are generally the same as those operating in simulated countercurrent mode, except that the recycle ratio is generally between 0.8 and 7. In this respect, reference is made to patents US 4402832 and US 4498991.

The desorption solvent may be any desorbent known to those skilled in the art and having a boiling point lower than the boiling point of the feedstock, such as toluene, and desorbents having a boiling point higher than the boiling point 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 aromatic fraction C8 is optimal when the loss on ignition, measured at 950 ℃, is generally between 4.0% and 7.7%, preferably between 4.5% and 6.5% and very preferably between 4.8% and 6.0%, inclusive.

The invention also relates to a process for separating a polyol, comprising a step of contacting the polyol with an adsorbent as defined above.

The invention also relates to a process for separating isomers of substituted toluene, such as nitrotoluene, diethylbenzene or toluenediamine, comprising the step of contacting isomers of substituted toluene with an adsorbent as defined above.

The invention also relates to a process for separating cresols comprising the step of contacting the cresols with an adsorbent as defined above.

Characterization techniques

Crystal size:

the number average diameter of the zeolite X crystals used in step a) and the crystals of zeolite X contained in the agglomerates is estimated by observation with a Scanning Electron Microscope (SEM) or by observation with a Transmission Electron Microscope (TEM).

To estimate the size of the zeolite crystals on the sample, a set of images is taken at a magnification of at least 5000. The diameter of at least 200 crystals is then measured using dedicated software (e.g., Smile View software, published by logami). Accuracy was of the order of 3%.

Chemical analysis of Zeolite adsorbents-Si/Al ratio and oxide content

The final product obtained at the end of the above-mentioned steps a) to d) can be subjected to elemental chemical analysis according to various analytical techniques known to the person skilled in the art. Among these techniques, mention may be made of chemical analysis techniques by X-ray fluorescence on wavelength dispersive spectrometers (WDXRF, for example Tiger S8 machine from Bruker corporation) as described in standard NF EN ISO 12677: 2011.

X-ray fluorescence is a non-destructive spectroscopic technique that utilizes the photoluminescence of atoms in the X-ray range to establish the elemental composition of a sample. Excitation of the atoms (usually by X-ray beams or by electron bombardment) produces specific radiation upon return to the atomic ground state. The advantage of X-ray fluorescence spectroscopy is that it is almost independent of the chemical combination (binding) of the elements, which provides an accurate determination both quantitatively and qualitatively. Measurement uncertainties of less than 0.4 wt% are routinely obtained after calibration for each oxide. In the present invention, the contents of barium, strontium, potassium, silicon and aluminum are preferably measured by the above-mentioned X-ray fluorescence method.

On the other hand, for elements that are lighter in atomic weight (e.g., sodium) and are present in the adsorbent, inductively coupled plasma emission spectroscopy (ICP-OES) according to standard UOP 961-12 is preferred to obtain higher accuracy.

ICP is a method of analysis by atomic emission spectroscopy, the source of which is plasma generated by inductive coupling. In the present invention, the sodium content is preferably measured by the ICP method according to standard UOP 961-12. In this case, for sodium, a measurement uncertainty of less than 0.01% is obtained for the sodium oxide weight content in the sorbent.

These elemental chemical analyses make it possible to verify both the Si/Al atomic ratio of the zeolite in the agglomerate and the quality of the ion exchange described in step c). In the description of the present invention, the uncertainty of measurement of the Si/Al atomic ratio was 0.05%.

The quality of the ion exchange and the sodium oxide (Na) remaining in the zeolite agglomerates after the exchange₂O) ofThe number of moles is related. More specifically, by the mole number and combination of barium oxide (BaO) (BaO + K)₂O+SrO+Na₂O) to determine the degree of exchange with barium ions. Likewise, respectively by potassium oxide (K)₂O) moles and combination (BaO + K)₂O+SrO+Na₂O) or the number and combination of the moles of strontium oxide (SrO) (BaO + K)₂O+SrO+Na₂O) to determine the degree of exchange with potassium and strontium ions. BaO, K₂O, SrO and Na₂O is represented in the form of an oxide. The total degree of exchange with barium, potassium and strontium ions was estimated from the sum of the three previously described degrees of exchange, which corresponds to barium oxide, potassium oxide and strontium oxide (BaO + K)₂Sum of moles of O + SrO) and combination (BaO + K)₂O+SrO+Na₂O) in the presence of oxygen. It should be noted that the content of the various oxides is given in weight percentages relative to the total weight of the anhydrous zeolite adsorbent. In the present specification, K is₂O/(K₂O+BaO+SrO+Na₂O) molar ratio was measured with an uncertainty of 0.3% and with respect to SrO/(K)₂O+SrO+BaO+Na₂O) molar ratio was measured with an uncertainty of 0.3%.

Zeolite adsorbent particle size:

the number-average diameter of the zeolite adsorbent obtained at the end of the agglomeration and shaping step a) is determined by analysing 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 the camera lens.

The number average diameter is then calculated from the particle size distribution by applying the standard ISO 9276-2: 2001. The term "number average diameter" or "size" is used herein for the zeolite agglomerates. For the size range of the agglomerates of the present invention, the accuracy is about 0.01 mm.

Mechanical strength of zeolite adsorbent:

the technique for characterizing the mechanical Strength representative of the Crushing of the sorbent in the bed or reactor is a Bulk (Bulk) mechanical Strength characterization technique, as described in Shell Method Series SMS1471-74 (Shell Method Series SMS1471-74 Determination of Bulk Crushing Strength of catalysts. compression-Sieve Method), which is associated with the "BCS Tester" machine sold by Vinci Technologies, Inc. This process, which was originally intended for characterizing 3 to 6mm catalysts, is based on the use of 425 μm sieves which make it possible in particular to separate the fines generated during crushing. The use of a 425 μm sieve is still suitable for particles larger than 1.6mm in diameter, but must be adjusted according to the particle size of the zeolitic adsorbent desired to be characterized. The standard ASTM D7084-04 also describes a method for measuring the Bulk Crush Strength of Catalysts ("Determination of Bulk Crush Strength of Catalysts and catalyst Carriers") which defines the through-size (through-size) of the sieve to be used as being equal to half the particle diameter of the catalyst to be characterized. The method provides a preliminary step of screening a sample of the catalyst or sorbent to be characterized. If an amount equal to 10% by weight of the sample passes through the screen, a smaller sized pass through screen will be used

The number average diameter or length (i.e. the largest dimension in the case of non-spherical agglomerates) of the agglomerates of the invention, usually in the form of spheres or extrudates, is typically between 0.2mm and 2mm, and in particular between 0.2mm and 0.8mm, and preferably between 0.2mm and 0.65 mm. Thus, instead of the 425 μm sieve mentioned in the Shell SMS1471-74 standard method, a sieve adjusted so that less than 10 wt% of the sample passes through the sieve during the previous sieving step is used.

The measurement protocol was as follows: is measured by a distance of 20cm³The agglomerated sorbent samples were pre-screened with an appropriate screen and pre-dried in an oven at 250c (instead of 300c as mentioned in the Shell SMS1471-74 standard process) for at least 2 hours and placed into a metal cylinder of known internal cross-section. By means of pistons, passing 5cm³To the sample, increasing forces were applied stepwise to better distribute the force exerted by the piston on the agglomerates of adsorbent (using balls of 2mm diameter for spherically shaped particles of strictly less than 1.6mm diameter). The fines obtained in the individual pressure steps are separated by sieving (with a suitable sieve) and weighed.

The bulk crush strength is determined by the pressure in megapascals (MPa) that causes the amount of accumulated fines passing through the screen to reach 0.5 weight percent of the sample. This value is obtained by plotting the mass of fines obtained on a graph as a function of the force applied to the adsorbent bed and by interpolation (interpolating) with respect to 0.5 mass% of the accumulated fines. The mechanical bulk crush strength is typically between a few hundred kPa and a few tens MPa, and is usually between 0.3MPa and 4 MPa. Accuracy is conventionally less than 0.1MPa

Determination of the zeolite fraction of the zeolite adsorbent:

the nature and the amounts of the various zeolite fractions are determined by means of X-ray diffraction analysis known to the person skilled in the art under the acronym XRD. The analysis was performed on a Bruker brand machine and the amount of zeolite fractions was then evaluated using TOPAS software from Bruker corporation.

Micropore volume:

the crystallinity of the agglomerates is also assessed by measuring their micropore volume while comparing it to the micropore volume of a suitable reference (zeolite that is 100% crystalline or theoretical zeolite under the same cationic treatment conditions). The micropore volume is determined by measuring the adsorption isotherm of a gas (e.g., nitrogen) at its liquefaction temperature. Prior to adsorption, the zeolite-based adsorbent is placed under vacuum (P)<6.7×10^-4Pa) at 300 ℃ to 450 ℃ for a period of from 9 hours to 16 hours. The measurement of the nitrogen adsorption isotherm at 77K was then carried out on a machine from Micromeritics, model ASAP2010M, at a relative pressure P/P between 0.002 and 1₀At least 35 measurement points are taken. The micropore volume was determined from the isotherms obtained by applying the standard ISO 15901-3:2007 according to Dubinin and Raduskevitch. Micropore volume as cm of liquid adsorbate assessed according to Dubinin and Raduskevitch³Number/1 gram of adsorbent. The measurement uncertainty was ± 0.003.

Loss on ignition of zeolite adsorbent:

the loss on ignition was determined under an oxidizing atmosphere by calcining the samples in air at a temperature of 950 ℃ ± 25 ℃ as described in standard NF EN196-2 (4 months 2006). The standard deviation was measured to be less than 0.1%.

Adsorption in the liquid phase was characterized by breakthrough (breakthrough):

the technique used to characterize the Adsorption of molecules in the liquid phase on porous solids is the "breakthrough" technique, described by Ruthven in the "Principles of Adsorption and Adsorption Processes" (chapters 8 and 9, john wiley & Sons,1984), which defines the breakthrough curve technique as a study of the response to injection (injection) of an adsorbable component at a certain scale. Analysis of the mean exit time (first moment) of the breakthrough curve provides information about the amount of adsorption and also makes it possible to assess the selectivity between the two adsorbable components, that is to say the separation factor. It is recommended to inject a non-adsorbable component that acts as a tracer to estimate the non-selective volume. The analysis of the dispersion of the penetration curve (second moment) makes it possible to evaluate the equivalent height of the theoretical plate, based on the representation of the column by a hypothetical reactor (theoretical stage) with a limited number of ideal stirrings, which is a direct measure of the axial dispersion and of the resistance of the system to material transfer.