Zeolite-based adsorbents based on zeolite X with a low binder content and a low outer surface area, process for preparing them and uses thereof

1. An adsorbent comprising a zeolite-based phase and a non-zeolite-based phase, wherein said adsorbent:

has an outer surface area of less than or equal to 30 m 2 ·g −1 ,

a pore diameter distribution, determined by mercury intrusion according to standard ASTM D 4284-83 and expressed by the volume distribution dV/d log D Hg , wherein D Hg is the apparent pore diameter and V is the pore volume, the mode of which is between 100 nm and 250 nm, limits inclusive,

and the zeolite-based phase comprises at least one zeolite of FAU structure of X type.

2. The adsorbent according to claim 1 , wherein the pore diameter distribution corresponds to a unimodal distribution.

3. The adsorbent according to claim 1 , having a micropore volume, evaluated via the t-plot method from the nitrogen adsorption isotherm at a temperature of 77 K, which is greater than 0.200 cm 3 ·g −1 .

4. The adsorbent according to claim 1 , wherein the adsorbent has a content of non-zeolite-based phase between 2% and 8% by weight relative to the total weight of the adsorbent.

5. The adsorbent according to claim 1 , further comprising barium or barium and potassium.

6. The adsorbent according to claim 1 , having macropores and the mesopores, wherein a total volume contained in the macropores and the mesopores as measured by mercury intrusion according to standard ASTM D4284-83 is between 0.15 cm 3 ·g −1 and 0.5 cm 3 ·g −1 , limits inclusive.

7. The adsorbent according to claim 6 having a ratio defined as (macropore volume)/(macropore volume+mesopore volume) of between 0.2 and 1, limits inclusive.

8. The adsorbent according to claim 1 , further having an Si/Al atomic ratio of between 1.00 and 1.50, limits inclusive.

9. A process for preparing the adsorbent according to claim 1 , comprising the steps of:

a) agglomerating crystals of at least one FAU zeolite having an outer surface area as measured by nitrogen adsorption, of greater than 20 m 2 ·g −1 , limits inclusive, with a binder and also with an amount of water which allows the forming of an agglomerated material, followed by drying and calcination of the agglomerated material;

b) carrying out zeolitization of all or part of the binder by placing the agglomerated material obtained in step a) in contact with an aqueous basic solution, optionally in the presence of at least one structuring agent;

c) optionally, removing the structuring agent optionally present;

d) carrying out cationic exchange(s) of the agglomerated material of step b) or c) by placing the agglomerated material in contact with a solution of barium ions or of barium ions and potassium ions;

e) optionally, carrying out additional cationic exchange of the agglomerated material of step d) by placing the agglomerated material in contact with a solution of potassium ions;

f) washing and drying of the agglomerated material obtained in step d) or e), at a temperature of between 50° C. and 150° C.; and

g) producing the zeolite-based adsorbent by activating the agglomerated material obtained in step f) under a stream of a gas selected from the group consisting of oxidizing gases and inert gases, wherein the gas is at a temperature of between 100° C. and 400° C.

10. The process according to claim 9 , wherein the agglomeration binder used in step a) contains at least one zeolitizable clay.

11. The process according to claim 9 wherein the FAU zeolite crystals used during the agglomeration step (step a) have a number-mean diameter of between 1 μm and 20 μm, limits inclusive.

12. The process according to claim 9 wherein the FAU zeolite used in step a) is a hierarchically porous FAU zeolite.

13. A process, comprising using an adsorbent according to claim 1 as an adsorption agent in:

separating C 8 aromatic isomer fractions or,

separating substituted toluene isomers or,

separating cresols, or

separating polyhydric alcohols.

14. A process for the gas-phase or liquid-phase separation of xylene isomers using at least one adsorbent according to claim 1 .

15. A process for separating para-xylene from a feedstock of aromatic isomer fractions containing 8 carbon atoms, using, as para-xylene adsorption agent, an adsorbent according to claim 1 .

16. The process according to claim 15 , wherein the process is performed in a counter-current simulated moving bed adsorption unit, under the following operating conditions:

number of beds: 4 to 24;

number of zones: at least 4 operating zones, each being located between a feed point and a withdrawal point;

temperature between 100° C. and 250° C.;

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

ratio of the flow rates of desorbent to feedstock to be treated: 0.7 to 2.5;

recycling rate between 2 and 12,

cycle time, corresponding to the time between two injections of desorbent onto a given bed: between 4 and 25 minutes.

17. The process according to claim 16 , wherein the desorbent is toluene or para-diethylbenzene.

18. The process according to claim 16 wherein a water content in the inlet streams constituted by the feedstock and/or desorbent streams is adjusted to between 20 ppm and 150 ppm.

19. The process according to claim 10 , wherein the one zeolitizable clay is chosen from the group consisting of kaolins, kaolinites, nacrites, dickites, halloysites and metakaolins, and mixtures thereof.

20. The adsorbent according to claim 1 having a micropore volume, evaluated via the t-plot method from the nitrogen adsorption isotherm at a temperature of 77 K, which is between 0.205 cm 3 ·g −1 and 0.300 cm 3 ·g −1 .

21. The adsorbent according to claim 1 having a micropore volume, evaluated via the t-plot method from the nitrogen adsorption isotherm at a temperature of 77 K, which is between 0.205 cm 3 ·g −1 and 0.290 cm 3 ·g −1 .