ZEOLITE ADSORBENT BASED ON MESOPOROUS ZEOLITE

Abstract

The present invention relates to a zeolite adsorbent having an external surface area of between 20 m.sup.2.Math.g.sup.1 and 70 m.sup.2.Math.g.sup.1, a mesopore volume (V.sub.meso) of less than or equal to 0.20 cm.sup.3.Math.g.sup.1, and a content of non-zeolite phase (NZP) of less than or equal to 6%, and in which at least one of its dimensions is greater than or equal to 30 m.

The invention also relates to the process for preparing said zeolite materials in agglomerated form and to the uses thereof for gas-phase or liquid-phase separation operations.

Claims

1. A zeolite adsorbent having the following characteristics: an external surface area, measured by nitrogen adsorption, of between 20 m.sup.2.Math.g.sup.1 and 70 m.sup.2.Math.g.sup.1, limits included, a mesopore volume (V.sub.meso) such that 0<V.sub.meso0.20 cm.sup.3.Math.g.sup.1, measured by nitrogen adsorption, a content of non-zeolite phase (NZP) such that 0<NZP6%, by weight relative to the total weight of said adsorbent, and at least one dimension which is greater than or equal to 30 m, each of the measurements being carried out on the zeolite adsorbent in its sodium-exchanged form.

2. A zeolite adsorbent according to claim 1, having exchangeable cationic sites occupied by ions of groups IA, IIA, IIIA and IIIB of the periodic table of elements, trivalent ions of the elements of the lanthanide series, zinc(II) ion, copper(II) ion, chromium(III) ion, iron(III) ion, ammonium ion, hydronium ion or mixtures of two or more of them, in any proportions.

3. A zeolite adsorbent according to claim 1, having exchangeable cationic sites occupied by one or more ions selected from the group consisting of hydronium, lithium, sodium, potassium, cesium, magnesium, calcium, strontium, barium, praseodymium and lanthanum, and mixtures of two or more of them in any proportions.

4. A zeolite adsorbent according to claim 1, having, in its sodium-exchanged form, a bulk density of between 0.4 g.Math.cm.sup.3 and 1.0 g.Math.cm.sup.3 limits included, said bulk density being measured as described in standard DIN 8948/7.6.

5. A zeolite adsorbent according to claim 1, comprising at least one mesoporous zeolite selected from the group consisting of mesoporous zeolites of LTA, EMT and FAU structure with an Si/Al atomic ratio of between 1 and 5.

6. A zeolite adsorbent according to claim 5, in which said at least one mesoporous zeolite is in the form of crystals of which the number-average diameter, measured with a scanning electron microscope (SEM) is less than 20 m, limits included.

7. A zeolite adsorbent according to claim 1, in which the crystals of the zeolite(s) are agglomerated with a binder comprising a zeolitizable clay alone or as a mixture with one or more other zeolitizable or non-zeolitizable clays.

8. A zeolite adsorbent according to claim 1, in which the crystals of the zeolite(s) are agglomerated with a binder comprising a clay selected from the group consisting of kaolins, kaolinites, nacrites, dickites, halloysites, attapulgites, sepiolites, montmorillonites, bentonites, illites and metakaolins, and also mixtures of two or more of them in any proportions.

9. A zeolite adsorbent according to claim 1, having: a bulk crushing strength (BCS) measured according to standard ASTM 7084-04 of between 1.0 MPa and 3.5 MPa, for a material with a mean volume diameter (D50), or a length (largest dimension when the material is not spherical), of less than 1 mm, limit excluded, a grain crushing strength, measured according to standards ASTM D 4179 (2011) and ASTM D 6175 (2013), of between 1.5 daN and 30 daN, for a material with a mean volume diameter (D50), or a length (largest dimension when the material is not spherical), of greater than or equal to 1 mm, limit included.

10. A process for preparing a zeolite adsorbent according to claim 1, comprising at least the steps of: a) agglomerating crystals of at least one mesoporous zeolite with a number-average diameter of between 0.1 m and 20 m, with an Si/Al atomic ratio of between 1 and 1.4, limits included, and with a mesoporous external surface area, defined by the t-plot method, of between 40 m.sup.2.Math.g.sup.1 and 400 m.sup.2g.sup.1, limits included, with at least one agglomeration binder, optionally one or more additives, and also with an amount of water which allows the shaping of the zeolite adsorbent, thereby obtaining agglomerates; b) drying the agglomerates at a temperature of between 50 C. and 150 C.; c) calcining the agglomerates obtained in step b), at a temperature above 150 C., for a few hours; d) zeolitizing at least one part of the agglomeration binder by bringing the agglomerates obtained in step c) into contact with an alkaline aqueous solution, optionally in the presence of at least one structuring agent; e) optionally, removing the structuring agent optionally present; f) optionally cation exchange(s) of the agglomerates obtained in step c) or in step d) by bringing the agglomerates into contact with a solution of at least one alkali metal or alkaline-earth metal salt; g) then washing and drying of the agglomerates obtained in step d) or e) under the conditions described in step b), and h) producing the zeolite adsorbent by activating the agglomerates obtained in step f) under the conditions described in step c).

11. A process according to claim 10, wherein step d) is carried out in the presence of at least one structuring agent.

12. A process according to claim 11, wherein the structuring agent is [3-(trimethoxysilyl)propyl]octadecyldimethylammonium chloride.

13. A process according to claim 10, wherein step a) is carried out in the presence of at least one additive which is a source of silica selected from the group consisting of colloidal silica, diatomaceous earths, perlites, fly ash, sand, and any other form of solid silica.

14. A process comprising using at least one zeolite adsorbent according to claim 1, wherein the process is selected from the group consisting of gas-phase or liquid-phase separation operations.

15. A zeolite adsorbent according to claim 1, wherein the external surface area, measured by nitrogen adsorption, is between 40 m.sup.2.Math.g.sup.1 and 60 m.sup.2.Math.g.sup.1, limits included.

16. A zeolite adsorbent according to claim 1, wherein the mesopore volume (V.sub.meso) is such that 0<V.sub.meso0.10 cm.sup.3.Math.g.sup.1, measured by nitrogen adsorption.

17. A zeolite adsorbent according to claim 1, wherein the content of non-zeolite phase (NZP) is such that 3%NZP6%, by weight relative to the total weight of said adsorbent.

18. A zeolite adsorbent according to claim 1, having at least one dimension which is greater than or equal to 80 m.

19. A zeolite adsorbent according to claim 1, having, in its sodium-exchanged form, a bulk density of between 0.5 g.Math.cm.sup.3 and 0.9 g.Math.cm.sup.3 limits included, said bulk density being measured as described in standard DIN 8948/7.6.

20. A zeolite adsorbent according to claim 1, comprising at least one mesoporous zeolite selected from the group consisting of mesoporous zeolites of FAU structure of type X, MSX and LSX.

Description

EXAMPLE 1

[0136] Synthesis of Mesoporous Zeolite of Type X with Addition of Nucleation Gel and Growth Gel with a TPOAC/Al.sub.2O.sub.3 Ratio=0.04
a) Preparation of the Growth Gel in a Stirred Reactor with an Archimedean Screw at 300 Rpm.

[0137] A growth gel is prepared in a stainless-steel reactor equipped with a heating jacket, a temperature probe and a stirrer, by mixing an aluminate solution containing 119 g of sodium hydroxide (NaOH), 128 g of alumina trihydrate (Al.sub.2O.sub.3, 3H.sub.2O, containing 65.2% by weight of Al.sub.2O.sub.3) and 195.5 g of water at 25 C. for 25 minutes with a stirring speed of 300 rpm in a silicate solution containing 565.3 g of sodium silicate, 55.3 g of NaOH and 1997.5 g of water at 25 C.

[0138] The stoichiometry of the growth gel is as follows: 3.48 Na.sub.2O/Al.sub.2O.sub.3/3.07 SiO.sub.2/180 H.sub.2O. The growth gel is homogenized with stirring at 300 rpm, for 25 minutes, at 25 C.

b) Addition of the Nucleation Gel

[0139] 61.2 g of nucleation gel (i.e. 2% by weight) having the composition 12 Na.sub.2O/Al.sub.2O.sub.3/10 SiO.sub.2/180 H.sub.2O prepared in the same manner as the growth gel, and having matured for 1 hour at 40 C., are added to the growth gel at 25 C. with stirring at 300 rpm. After homogenization for 5 minutes at 300 rpm, the stirring speed is reduced to 100 rpm and stirring is continued for 30 minutes.

c) Introduction of the Structuring Agent into the Reaction Medium

[0140] 27.3 g of a 60% solution of TPOAC in methanol (MeOH) are introduced into the reaction medium with a stirring speed of 300 rpm (TPOAC/Al.sub.2O.sub.3 mole ratio=0.04). A maturation step is carried out at 25 C. for 1 hour at 300 rpm before starting the crystallization.

d) Crystallization

[0141] The stirring speed is lowered to 50 rpm and the nominal temperature of the reactor jacket is set at 80 C. so that the temperature of the reaction medium rises to 75 C. over the course of 80 minutes. After a steady stage at 75 C. for 22 hours, the reaction medium is cooled by circulating cold water through the jacket to stop the crystallization.

e) Filtration/Washing

[0142] The solids are recovered on a sinter and then washed with deionized water to neutral pH.

f) Drying/Calcination

[0143] In order to characterize the product, drying is carried out in an oven at 90 C. for 8 hours; the loss on ignition of the dried product is 23% by weight.

[0144] The calcination of the dried product necessary to release both the microporosity (water) and the mesoporosity by removing the structuring agent is carried out with the following temperature profile: 30 minutes of temperature increase to 200 C., then 1 hour at a steady stage of 200 C., then 3 hours of temperature increase to 550 C., and 1.5 hours of steady stage at 550 C.

[0145] 255 g of anhydrous equivalent solid of zeolite XPH are thus obtained; which represents a yield of 99 mol % relative to the amount of aluminium engaged. The Si/Al ratio of the mesoporous zeolite X (XPH) determined by X-ray fluorescence is equal to 1.24. The characteristics of this XPH prepared in this example 1 are collated in Table 1 below:

TABLE-US-00001 TABLE 1 Characteristics XPH (Example 1) Synthesis TPOAC/Al.sub.2O.sub.3 mole ratio 0.04 Synthesis time (h) 24 Nitrogen Micropore volume according to 0.335 adsorption Dubinin-Raduskevitch (cm.sup.3 .Math. g.sup.1) isotherm at 77 K Mesopore external surface area 105 (m.sup.2/g) Mesopore size (nm) 5 to 10 XRD spectrum Crystalline phase X pure (diffractogram) Crystallinity X (%) 100 SEM Crystal size (m) 1 to 3

[0146] The size distribution of the mesopores is calculated by the Density Functional Theory (DFT) method with the cylindrical pore model. The percentage of crystallinity is calculated by means of the TOPAS software using the base ICDD PDF-2, 2011.

EXAMPLE 2

Preparation of Mesoporous Zeolite X Agglomerates, in the Presence of Zeolitizable Binder

[0147] In the text which follows, the weights given are expressed as anhydrous equivalent.

[0148] A homogeneous mixture consisting of 1600 g of mesoporous zeolite X crystals obtained in example 1, 350 g of kaolin, 130 g of colloidal silica sold under the trade name Klebosol 30 (containing 30% by weight of SiO.sub.2 and 0.5% of Na.sub.2O) and also the amount of water which allows extrusion of the mixture, is prepared. The loss on ignition of the pulp before extrusion is 44%.

[0149] Extrudates 1.6 mm in diameter are formed. The extrudates are dried overnight in a ventilated oven at 80 C. They are then calcined for 2 hours at 550 C. under a flush of nitrogen, and then for 2 hours at 550 C. under a flush of dry decarbonated air.

[0150] The mechanical grain crushing strength of the mesoporous zeolite X extrudates is 2.6 daN. Their bulk density is 0.64 g.Math.cm.sup.3.

[0151] The Dubinin-Raduskevitch volume measured from the nitrogen isotherm is 0.269 cm.sup.3.Math.g.sup.1. The content of non-zeolite phase evaluated by XRD is 20% by weight relative to the total weight of the adsorbent. The external surface area measured from the nitrogen adsorption isotherm is 110 m.sup.2.Math.g.sup.1 and the mesopore volume is 0.18 cm.sup.3.Math.g.sup.1.

EXAMPLE 3

Preparation of Zeolite Adsorbents According to the Invention

[0152] The extrudates of example 2 are subjected to a zeolitization treatment.

[0153] To this effect, 200 g of these extrudates are placed in a glass reactor equipped with a jacket regulated at a temperature of 100 C.1 C., and then 1.5 I of an aqueous solution of sodium hydroxide at a concentration of 1 M are added and the reaction medium is left to stir for a period of 3 hours.

[0154] The extrudates are then washed in three successive operations of washing with water, followed by emptying of the reactor. The efficiency of the washing is verified by measuring the final pH of the washing waters, which should be between 10.0 and 10.5.

[0155] The mechanical grain crushing strength of the extrudates according to the invention is 3.0 daN. Their bulk density is 0.65 g.Math.cm.sup.3. The Dubinin-Raduskevitch volume measured from the nitrogen isotherm is 0.322 cm.sup.3 g.sup..

[0156] The XRD analysis does not show any phase other than the faujasite phase after zeolitization. The content of non-zeolite phase evaluated by XRD is 4% by weight relative to the total weight of the adsorbent according to the invention. The external surface area measured from the nitrogen adsorption isotherm is 50 m.sup.2.Math.g.sup.1 and the mesopore volume is 0.07 cm.sup.3.Math.g.sup.1. It is thus observed that the agglomerated zeolite material according to the invention comprising a mesoporous zeolite X has mechanical and micropore volume characteristics which are better than those obtained for non-zeolitized adsorbents (cf. comparative example 2 where the binder did not undergo zeolitization).

[0157] It is thus entirely remarkable to note that the present invention makes it possible to have agglomerated zeolite materials which simultaneously combine the properties of mesoporous zeolites, the properties associated with microporosity and the mechanical properties of the zeolite agglomerates known thus far. It is thus possible to envisage without difficulty the use of the agglomerated zeolite materials of the invention in all the industrial application fields such as catalysis, separation, adsorption, and the like.