Zeolite adsorbents based on barium, strontium, potassium and sodium, preparation process therefor, and uses thereof
The present invention relates to zeolite adsorbents based on agglomerated crystals of zeolite X comprising barium, potassium, sodium and strontium. These adsorbents have applications in the separation of fractions of aromatic C8 isomers and in particular xylenes.
1. Zeolite adsorbent comprising zeolite X crystals and comprising barium, potassium, strontium and sodium, in which the K 2 O/(K 2 O+SrO+BaO+Na 2 O) molar ratio of the species in oxide form is between 0.015 and 0.08, limits included, and the SrO/(K 2 O+SrO+BaO+Na 2 O) molar ratio of the species in oxide form is between 0.005 and 0.08, limits included.
2. Adsorbent according to claim 1 , in which the K 2 O/(K 2 O+SrO+BaO+Na 2 O) molar ratio of the species in oxide form is between 0.02 and 0.07, limits included.
3. Adsorbent according to claim 1 , in which the SrO/(K 2 O+SrO+BaO+Na 2 O) molar ratio of the species in oxide form is between 0.005 and 0.07, limits included.
4. Adsorbent according to claim 1 , in which the SrO/K 2 O molar ratio of the species in oxide form is between 0.3 and 2.0, limits included.
5. Adsorbent according to claim 1 , also comprising a non-zeolite phase.
6. Adsorbent according to claim 1 , in which the content of sodium oxide Na 2 O is less than 0.3% by weight relative to the total mass of the adsorbent.
7. Adsorbent according to claim 1 , in which the total content of alkali metal or alkaline-earth metal ion oxides other than barium oxide BaO, potassium oxide K 2 O, strontium oxide SrO and sodium oxide Na 2 O is less than 1% by weight, limits included, relative to the total mass of the adsorbent.
8. Adsorbent according to claim 1 , in which the zeolite X crystals have an Si/Al atomic ratio of between 1.00 and 1.50, limits included.
9. Adsorbent according to claim 1 , said adsorbent having a number-average diameter of between 0.2 mm and 2 mm, limits included.
10. Adsorbent according to one claim 1 , in which the number-average diameter of the zeolite X crystals is less than or equal to 1.5 μm, limits included.
11. Adsorbent according to claim 1 , having a loss on ignition, measured at 950° C. according to standard NF EN 196-2, of between 4.0 and 7.7% by weight.
12. Adsorbent according to claim 1 , in which the mass fraction of zeolite X is at least 80% by weight of zeolite(s) X relative to the total mass of the adsorbent.
13. Process for preparing an adsorbent according to claim 1 , comprising at least the following steps:
a) agglomeration of a powder of zeolite NaX crystals with a binder, and forming, then drying and calcining,
b) optional zeolitization of the binder,
c) simultaneous, sequential or alternating cation exchange of the agglomerate by bringing into contact with solutions containing barium ions, potassium ions or strontium ions alone or as a mixture, one or more times, then washing and drying of the agglomerate thus treated, and
d) activation of the zeolite adsorbent thus obtained.
14. Process according to claim 13 , wherein the binder used in step a) contains at least 80% by weight of zeolitizable clay, and a source of silica, and in that the process comprises a step b) of zeolitization of the zeolitizable binder by action of an alkaline basic solution for a period of between a few tens of minutes and a few hours.
15. Adsorbent obtained according to the process of claim 13 .
16. Process for recovering para-xylene from a feedstock comprising fractions of aromatic hydrocarbon isomers containing 8 carbon atoms, in the liquid phase, by adsorption of the para-xylene, comprising the following successive steps:
a) bringing a feedstock into contact with a bed of adsorbent comprising at least one zeolite adsorbent as defined according to claim 1 ,
b) bringing the bed of adsorbent into contact with a desorbent.
17. Process for recovering para-xylene according to claim 16 , wherein the process is of simulated moving bed.
18. Process for recovering para-xylene from a feedstock comprising fractions of aromatic hydrocarbon isomers containing 8 carbon atoms, in the gas phase, by adsorption of the para-xylene by means of an adsorbent according to claim 1 , comprising the following successive steps:
a) bringing a feedstock into contact with a bed of adsorbent comprising at least one zeolite adsorbent as defined according to claim 1 ,
b) bringing the bed of adsorbent into contact with a desorbent.
19. Process for separating a feedstock comprising polyhydric alcohols, comprising a step of bringing the feedstock into contact with an adsorbent as defined according to claim 1 .
20. Process for separating a feedstock comprising isomers of substituted toluene, comprising a step of bringing the feedstock into contact with an adsorbent as defined according to claim 1 .
21. Process for separating a feedstock comprising cresols, comprising a step of bringing the feedstock into contact with an adsorbent as defined according to claim 1 .