ZEOLITE ADSORBENTS HAVING A HIGH EXTERNAL SURFACE AREA AND USES THEREOF

Abstract

The present invention concerns the use, for gas separation, of at least one zeolite adsorbent material comprising at least one FAU zeolite, said adsorbent having an external surface area greater than 20 m.sup.2.Math.g.sup.−1, a non-zeolite phase (PNZ) content such that 0<PNZ≦30%, and an Si/Al atomic ratio of between 1 and 2.5. The invention also concerns a zeolite adsorbent material having an Si/Al ratio such that 1≦Si/Al<2.5, a mesoporous volume of between 0.08 cm.sup.3.Math.g.sup.−1 and 0.25 cm.sup.3.Math.g.sup.−1, a (Vmicro−Vmeso)/Vmicro ratio of between −0.5 and 1.0, non-inclusive, and a non-zeolite phase (PNZ) content such that 0<PNZ≦30%.

Claims

1. A process for separation of at least one gas mixture, wherein the process comprises feeding the at least one gas mixture to at least one FAU zeolite adsorbent material, wherein the at least one FAU zeolite adsorbent material has physical properties that are measured on the FAU zeolite adsorbent material that has been at least 95% exchanged with sodium, and wherein the physical properties comprise: an external surface area, measured by nitrogen adsorption and expressed in m.sup.2 per gram of the FAU zeolite adsorbent material, of greater than 20 m.sup.2.Math.g.sup.−1; a non-zeolite phase (PNZ) content, such that 0<PNZ≦30% as measured by XRD (X-ray diffraction), by weight relative to the total weight of the FAU zeolite adsorbent material; a mesopore volume of between 0.08 cm.sup.3.Math.g.sup.−1 and 0.25 cm.sup.3.Math.g.sup.−1, limits included; and an Si/Al atomic ratio of the FAU zeolite adsorbent material of between 1 and 2.5.

2. The process according to claim 1, wherein the at least one FAU zeolite adsorbent material has a (Vmicro−Vmeso)/Vmicro ratio of between −0.5 and 1.0, limits not included, wherein Vmicro is the micropore volume measured by the Dubinin-Raduskevitch method and Vmeso is the mesopore volume measured by the Barrett-Joyner-Halenda (BJH) method, and wherein all of the measurements are carried out on the FAU zeolite adsorbent material that has been at least 95% exchanged with sodium.

3. The process according to claim 1, wherein the at least one FAU zeolite adsorbent material has a micropore volume as measured by the Dubinin-Raduskevitch method expressed in cm.sup.3 per gram of FAU zeolite adsorbent material, of between 0.210 cm.sup.3.Math.g.sup.−1 and 0.360 cm.sup.3.Math.g.sup.−1 as measured on the FAU zeolite adsorbent material that has been at least 95% exchanged with sodium.

4. The process according to claim 1, wherein the at least one FAU zeolite has an Si/Al ratio corresponding to the equation: 1≦Si/Al<1.5 wherein the Si/Al ratio is measured by solid silicon 29 NMR.

5. The process according to claim 1, wherein the FAU zeolite adsorbent material comprises at least one cation selected from the group consisting of the ions of groups IA, IIA, IIIA, IB, IIB, and IIIB of the periodic table, the trivalent ions of the lanthanide series of the periodic table, the trivalent ions of the rare earth series of the periodic table, the zinc(II) ion, the silver(I) ion, the cupric (II) ion, the chromium(III) ion, the ferric (III) ion, the ammonium ion, the hydronium ion, calcium ion, lithium ion, sodium ion, potassium ion, barium ion, cesium ion, strontium ion, zinc ion, and mixtures thereof.

6. The process according to claim 1, wherein the at least one FAU adsorbent zeolite material comprises at least one alkali or alkaline-earth metal selected from the group consisting of sodium, calcium, lithium, and mixtures thereof, wherein the contents of which, expressed as oxides, are such that: the CaO content is between 0% and 20.5% by weight relative to the total weight of the zeolite adsorbent material, limits included; the Li.sub.2O content is between 0% and 12% by weight relative to the total weight of the FAU zeolite adsorbent material, limits included; and the Na.sub.2O content is between 0% and 22% by weight relative to the total weight of the FAU zeolite adsorbent material, limits included, subject to the proviso that the zeolite adsorbent material comprises at least one of the three alkali or alkaline-earth metals selected from the group consisting of lithium, sodium and calcium.

7. The process according to claim 1, wherein the at least one gas mixture comprises natural gas and at least one of carbon dioxide and mercaptans; and the FAU zeolite adsorbent material separates impurities present in the natural gas.

8. The process according to claim 7, wherein the FAU zeolite adsorbent material comprises at least one FAU zeolite, wherein the FAU zeolite is mesoporous, and is selected from the group consisting of NaX, CaX, and mixtures thereof.

9. The process according to claim 1, wherein the process comprises noncryogenic gas separation and the at least one gas mixture is selected from the group consisting of industrial gases and air.

10. The process according to claim 9, wherein the at least one gas mixture is air and nitrogen is separated from the air, whereby the air is enriched in oxygen.

11. The process according to claim 9 wherein the FAU zeolite adsorbent material comprises at least one FAU zeolite, wherein the FAU zeolite is mesoporous, and is of the type selected from the group consisting of NaX, LiX, CaX, LiCaX, NaLSX, LiLSX, CaLSX, LiCaLSX, and mixtures thereof.

12. The process according to claim 9 wherein the process comprises pressure swing adsorption.

13. The process according to claim 12, wherein the FAU zeolite adsorbent material comprises at least one FAU zeolite, wherein the FAU zeolite is mesoporous, and is of a type selected from the group consisting of CaLSX, LiLSX and LiCaLSX.

14. The process according to claim 1 wherein the at least one gas mixture comprises syngas.

15. The process according to claim 14, wherein the FAU zeolite adsorbent material comprises at least one FAU zeolite, wherein the FAU zeolite is mesoporous, and is of a type selected from the group consisting of NaX, LiX, LiLSX, CaX, CaLSX, LiCaX, LiCaLSX, and mixtures thereof.

16. The process according to claim 1, wherein the at least one gas mixture comprises air and at least one impurity, wherein the at least one impurity is selected from the group consisting of hydrocarbons, carbon dioxide, nitrogen oxides, and mixtures thereof; and wherein the process removes the at least one impurity upstream of cryogenic distillation units in air separation units (ASUs).

17. The process according to claim 16, wherein the FAU zeolite adsorbent material comprises at least one FAU zeolite, wherein the FAU zeolite is mesoporous, and of a type selected from the group consisting of NaX, NaLSX, CaX, CaLSX, and mixtures thereof.

18. A zeolite adsorbent material, wherein the zeolite adsorbent material has physical properties that are measured on the zeolite adsorbent material that has been at least 95% exchanged with sodium, and wherein the physical properties comprise: an Si/Al ratio such that 1≦Si/Al<2.5; a mesopore volume of between 0.08 cm.sup.3.Math.g.sup.−1 and 0.25 cm.sup.3.Math.g.sup.−1, limits included; (Vmicro−Vmeso)/Vmicro ratio of between −0.5 and 1.0, limits not included wherein the Vmicro is measured by the Dubinin-Raduskevitch method and the Vmeso is measured by the BJH method, and; a non-zeolite phase (PNZ) content such that 0<PNZ≦30%, by weight relative to the total weight of the zeolite adsorbent material, wherein the PNZ content is measured by X-ray diffraction.

19. The zeolite adsorbent material according to claim 18, wherein the Vmicro, expressed in cm.sup.3 per gram of zeolite adsorbent material is between 0.210 cm.sup.3.Math.g.sup.−1 and 0.360 cm.sup.3.Math.g.sup.−1, wherein the Vmicro is measured on the zeolite adsorbent material that has been at least 95% exchanged with sodium.

20. The zeolite adsorbent material according to claim 18, wherein the physical properties further comprise a total volume of macropores and mesopores, measured by mercury intrusion on the zeolite adsorbent material that has been at least 95% exchanged with sodium, wherein the total volume of macropores and mesopores is between 0.15 cm.sup.3.Math.g.sup.−1 and 0.5 cm.sup.3.Math.g.sup.−1.

21. The zeolite adsorbent material according to claim 18, wherein the physical properties further comprise an external surface area measured by nitrogen adsorption on the zeolite adsorbent material at least 95% exchanged with sodium and expressed in m.sup.2 per gram of adsorbent; of greater than 20 m.sup.2.Math.g.sup.−1.

22. The zeolite adsorbent material according to claim 18, wherein the physical properties measured on the zeolite adsorbent material at least 95% exchanged with sodium further comprise a volumetric micropore volume, expressed in cm.sup.3.Math.cm.sup.−3 of zeolite adsorbent material of greater than 0.10 cm.sup.3.Math.cm.sup.−3.

23. The zeolite adsorbent material as claimed in claim 18, wherein the zeolite adsorbent material has a metal content, expressed as oxides, in accordance with the following: the CaO content is between 0% and 20.5% by weight relative to the total weight of the zeolite adsorbent material, limits included; the Li.sub.2O content is between 0% and 12% by weight relative to the total weight of the zeolite adsorbent material, limits included; and the Na.sub.2O content is between 0% and 22% by weight relative to the total weight of the zeolite adsorbent material, limits included, subject to the proviso that the zeolite adsorbent material comprises at least one alkali or alkaline earth metal selected from the group consisting of lithium, sodium and calcium.

24. The zeolite adsorbent material, according to claim 18 wherein the physical properties further comprise a total macropore and mesopore volume, measured by mercury intrusion on the adsorbent material at least 95% exchanged with sodium, of between 0.15 cm.sup.3.Math.g.sup.−1 and 0.5 cm.sup.3.Math.g.sup.−1, and a macropore volume fraction of between 0.2 and 1.

25. The process according to claim 6 wherein the FAU zeolite adsorbent material further comprises between 0% and 10% by weight of at least one rare earth, wherein the rare earth is selected from the group consisting of lanthanides, actinides, and mixtures thereof.

26. The process according to claim 6 wherein the FAU zeolite adsorbent material further comprises between 0% and 5% by weight, expressed as oxide, of one or more cations selected from the group consisting of transition metals, potassium, barium, strontium, cesium, and mixtures thereof.

27. The process according to claim 12, wherein the process comprises oxygen concentration for respiratory assistance.

28. The zeolite adsorbent material according to claim 23, wherein the zeolite adsorbent material further comprises between 0% and 10% by weight of the zeolite adsorbent material of at least one rare earth, wherein the rare earth is chosen from the group consisting of lanthanides, actinides, and mixtures thereof.

29. The zeolite adsorbent material according to claim 23, wherein the zeolite adsorbent material further comprises between 0% and 5% of at least one cation, wherein the cation is selected from the group consisting of potassium ion, barium ion, strontium ion, cesium ion, transition metal ions, and mixtures thereof.

Description

EXAMPLE 1: PREPARATION OF A ZEOLITE ADSORBENT MATERIAL ACCORDING TO THE INVENTION

[0144] Step 1: Synthesis of Mesoporous LSX Zeolite Crystals Having an Si/Al Ratio Equal to 1.01 and an External Surface Area Equal to 95 m.sup.2.Math.g.sup.−1
a) Preparation of the Growth Gel: Reactor Stirred with an Archimedean Screw at 250 rpm

[0145] A growth gel is prepared in a 3 liter stainless-steel reactor equipped with a heating jacket, a temperature probe and a stirrer, by mixing an aluminate solution containing 300 g of sodium hydroxide (NaOH), 264 g of 85% potassium hydroxide, 169 g of alumina trihydrate (Al.sub.2O.sub.3.3H.sub.2O, containing 65.2% by weight of Al.sub.2O.sub.3) and 1200 g of water at 25° C. over 5 minutes, with a stirring speed of 250 rpm, with a silicate solution containing 490 g of sodium silicate, 29.4 g of NaOH and 470 g of water at 25° C.

[0146] The stoichiometry of the growth gel is as follows: 4.32 Na.sub.2O/1.85 K.sub.2O/Al.sub.2O.sub.3/2.0 SiO.sub.2/114 H.sub.2O. Homogenization of the growth gel is performed with stirring at 250 rpm for 15 minutes at 25° C.

b) Addition of the Nucleating Gel

[0147] 11.6 g of nucleating gel (i.e. 0.4% by weight) of composition 12 Na.sub.2O/Al.sub.2O.sub.3/10SiO.sub.2/180 H.sub.2O prepared in the same manner as the growth gel, and which has matured for 1 hour at 40° C., is added to the growth gel, at 25° C. with stirring at 300 rpm. After 5 minutes of homogenization at 250 rpm, the stirring speed is reduced to 50 rpm and stirring is continued for 30 minutes.

c) Introduction of the Structuring Agent into the Reaction Medium

[0148] 35.7 g of a solution of [3-(trimethoxysilyl)propyl]octadecyldimethylammonium chloride (TPOAC) at 60% in methanol (MeOH) are introduced into the reaction medium with a stirring speed of 250 rpm for 5 minutes (TPOAC/Al.sub.2O.sub.3 mole ratio=0.04). A maturation step is then performed at 30° C. for 20 hour at 50 rpm before starting the crystallization.

d) 2-Step Crystallization

[0149] The stirring speed is maintained at 50 rpm and then an increase in the set point of the reactor jacket is programmed at 63° C. in a linear manner so that the reaction medium increases in temperature to 60° C. over the course of 5 hours, followed by a stationary temperature phase for 21 hours at 60° C.; the set point of the reactor jacket is then set at 102° C. so that the reaction medium increases in temperature to 95° C. over the course of 60 minutes. After 3 hours at a stationary temperature phase of 95° C., the reaction medium is cooled by circulating cold water through the jacket to stop the crystallization.

e) Filtration/Washing

[0150] The solids are recovered on a sinter and then washed with deionized water to neutral pH.

f) Drying/Calcination

[0151] In order to characterize the product, drying is performed in an oven at 90° C. for 8 hours.

[0152] The calcination of the dried product, required in order to free both the microporosity (water) and the mesoporosity by removing the structuring agent, is carried out by degassing under vacuum with a gradual increase in steps of 50° C. up to 400° C. for a period of between 9 hours and 16 hours, under vacuum (P<6.7×10.sup.−4 Pa).

[0153] The micropore volume and the external surface area, measured according to the t-plot method from the nitrogen adsorption isotherm at 77 K after degassing under vacuum at 400° C. for 10 hours, are respectively 0.215 cm.sup.3.Math.g.sup.−1 and 95 m.sup.2.Math.g.sup.−1. The number-average diameter of the crystals is 6 μm. The mesopore diameters calculated from the nitrogen adsorption isotherm by the DFT method are between 5 nm and 10 nm. The XR diffractogram corresponds to a pure faujasite (FAU) structure, no LTA zeolite is detected. The Si/Al mole ratio of the mesoporous LSX determined by X-ray fluorescence is equal to 1.01.

[0154] FIG. 1 shows an image obtained by transmission electron microscopy (TEM) of the zeolite thus synthesized.

Step 2: Preparation of Mesoporous LSX Zeolite Agglomerates

[0155] In the subsequent text, the weights given are expressed in anhydrous equivalent.

[0156] A homogeneous mixture consisting of 1700 g of mesoporous LSX zeolite crystals obtained in step 1, of 300 g of Zeoclay® attapulgite, sold by CECA, and also of the amount of water such that the loss on ignition of the paste before forming is 35%, is prepared. The paste thus prepared is used on a granulating plate in order to prepare balls of agglomerated zeolite adsorbent material. Selection by sieving of the balls obtained is carried out so as to collect balls having a diameter of between 0.3 and 0.8 mm and a volume-average diameter equal to 0.55 mm.

[0157] The balls are dried overnight in a ventilated oven at 80° C. They are then calcined for 2 h at 550° C. under nitrogen flushing, then 2 h at 550° C. under flushing with decarbonated dry air.

Step 3: Lithium Exchange and Activation of the Mesoporous LSX Zeolite Agglomerates

[0158] Five successive exchanges are carried out by means of 1 M lithium chloride solutions, in a proportion of 20 ml.Math.g.sup.−1 of solid. Each exchange is continued for 4 h at 100° C., and intermediate washes are performed, making it possible to remove the excess salt at each step. In the final step, four washes are carried out at ambient temperature, in a proportion of 20 ml.Math.g.sup.−1.

[0159] The balls are dried overnight in a ventilated oven at 80° C. They are then activated for 2 h at 550° C. under nitrogen flushing.

[0160] The lithium oxide Li.sub.2O content, determined by ICP-AES, is 8.9% by weight relative to the total weight of the zeolite adsorbent material. The volume-average diameter of the balls is 0.55 mm. The bulk crush strength in a bed of the lithium-exchanged mesoporous LSX zeolite balls is 2.6 daN.

Step 4: Characterizations

[0161] In order to characterize the zeolite adsorbent material, it is at least 95% exchanged with sodium in the following way: the zeolite adsorbent material is introduced into a NaCl solution containing 1 mol of NaCl per liter, at 90° C., for 3 h, with a liquid-to-solid ratio of 10 ml.Math.g.sup.−1. The operation is repeated 4 times. Between each exchange, the solids are successively washed four times by immersing them in water in a proportion of 20 ml.Math.g.sup.−1 in order to remove the excess salt, and then dried for 12 h at 80° C. under air, before being analyzed by x-ray fluorescence. The weight percentage of sodium oxide of the zeolite adsorbent material is equal to 18.2% with a stability at less than 1% between exchange operations 3 and 4. The balls are dried overnight in a ventilated oven at 80° C. They are then activated for 2 h at 550° C. under nitrogen flushing.

[0162] The external surface area is equal to 99 m.sup.2.Math.g.sup.−1 of adsorbent, the micropore volume is 0.264 cm.sup.3.Math.g.sup.−1 of sodium-exchanged adsorbent. The volumetric micropore volume is 0.150 cm.sup.3 per cm.sup.3 of sodium-exchanged zeolite adsorbent material. The mesopore volume is equal to 0.165 cm.sup.3.Math.g.sup.−1 of sodium-exchanged adsorbent. The total macropore and mesopore volume, measured by mercury intrusion, is 0.42 cm.sup.3.Math.g.sup.−1 of sodium-exchanged adsorbent.

[0163] The Si/Al atomic ratio of the adsorbent is 1.25. The Si/Al ratio of the zeolite present in the adsorbent zeolite material, which is equal to 1.01, is determined by solid silicon 29 NMR.

[0164] The content of non-zeolite phase (PNZ), measured by XRD and expressed by weight relative to the total weight of the adsorbent, is 15.3%.

EXAMPLE 2: COMPARATIVE ZEOLITE ADSORBENT MATERIAL

[0165] Siliporite® Nitroxy® SXSDM sieve from CECA is a material based on LiLSX zeolite agglomerated with attapulgite. The volumetric mean diameter of the balls is equal to 0.55 mm. The content of lithium oxide Li.sub.2O, measured by ICP-AES, is 9.2% by weight relative to the total weight of sieve.

[0166] As in step 4 of example 1, sodium exchanges are carried out so as to obtain a solid at least 95% exchanged with sodium. As previously, this result is obtained with 4 consecutive exchanges.

[0167] The weight percentage of sodium oxide of the zeolite adsorbent material, obtained by x-ray fluorescence, is equal to 18.4% with a stability at less than 1% between exchange operations 3 and 4. The balls are dried overnight in a ventilated oven at 80° C. They are then activated for 2 h at 550° C. under nitrogen flushing.

[0168] The external surface area is equal to 31 m.sup.2.Math.g.sup.−1 of adsorbent, the micropore volume is 0.265 cm.sup.3.Math.g.sup.−1 of sodium-exchanged adsorbent. The volumetric micropore volume is 0.172 cm.sup.3 per cm.sup.3 of sodium-exchanged zeolite adsorbent material. The mesopore volume is equal to 0.07 cm.sup.3.Math.g.sup.−1 of sodium-exchanged adsorbent. The total macropore and mesopore volume, measured by mercury intrusion, is 0.31 cm.sup.3.Math.g.sup.−1 of sodium-exchanged adsorbent.

[0169] The Si/Al atomic ratio of the adsorbent is 1.23. The content of non-zeolite phase (PNZ), measured by XRD and expressed by weight relative to the total weight of the adsorbent, is 15.3%.

EXAMPLE 3

[0170] N.sub.2/O.sub.2 Separation Tests on a Fixed Bed of Adsorbant with Pressure Swing Adsorption

[0171] An N.sub.2/O.sub.2 separation test is carried out by adsorption in a single column according to a principle presented in E. Alpay et al. (ibid.).

[0172] FIG. 2 describes the assembly produced. A column (1) of internal diameter equal to 27.5 mm and of internal height equal to 600 mm, filled with zeolite adsorbent material (2), is fed with dry air (3) intermittently by means of a valve (4). The time for feeding the column (1) with the stream (3) is called adsorption time. When the column (1) is not fed with dry air, the stream (3) is discharged into the atmosphere by the valve (5). The zeolite adsorbent material preferentially absorbs nitrogen, so that an oxygen-enriched air leaves the column via the non-return valve (6), to a buffering tank (7). A regulating valve (8) continuously delivers the gas at outlet (9) at a constant flow rate fixed at 1 NL.Math.min.sup.−1.

[0173] When the column (1) is not fed, that is to say when the valve (4) is closed and the valve (5) is open, the column (1) is depressurized by the valve (10) to the atmosphere (11), for a period called the desorption time. The adsorption and desorption phases follow on from one another. The durations of these phases are fixed from one cycle to the other and they are adjustable. Table 1 indicates the respective state of the valves as a function of the adsorption and desorption phases.

TABLE-US-00001 TABLE 1 Adsorption phase Desorption phase Valve (4) open Valve (4) closed Valve (5) closed Valve (5) open Valve (10) closed Valve (10) open

[0174] The tests are carried out successively with the zeolite adsorbent materials of example 1 (according to the invention) and of example 2 (comparative). The column is loaded at constant volume, with respectively 204.5 g and 239.7 g of adsorbent materials. The pressure at the inlet is fixed at 280 kPa relative.

[0175] The outlet flow rate is fixed at 1 NL.Math.min.sup.−1. The adsorption time is fixed at 0.25 s. The desorption time is variable between 0.25 s and 1.25 s.

[0176] The oxygen concentration at outlet (9) is measured by means of a Servomex 570A oxygen analyzer.

[0177] FIG. 3 shows the oxygen content of the stream produced at outlet (9) as a function of the desorption time fixed for the materials of example 1 and example 2. Despite a lower weight loaded into the column, the material of example 1 (according to the invention) proves to be much more efficient (in terms of oxygen content of the gas produced) than the solid of example 2 (comparative).