Method for Synthesizing a Composite Material Consisting of a Mixture of AFX- and BEA-Structure Zeolites in the Presence of an Organic Nitrogen-Containing Structuring Agent

Abstract

The present invention relates to a process for preparing a zeolite composite material composed of a mixture of AFX and BEA zeolites, comprising at least the following steps: i) mixing in aqueous medium, in particular proportions, of an FAU zeolite having an SiO.sub.2/Al.sub.2O.sub.3 mole ratio of between 30 and 100 and a parameter P.sub.ze such that: 3250<P.sub.ze<7200, with at least one zeolite of FAU structure type having an SiO.sub.2/Al.sub.2O.sub.3 mole ratio of between 2 and 30 (upper limit excluded), of at least one organonitrogen compound R, R being 1,5-bis(methylpiperidinium)pentane dihydroxide, 1,6-bis(methylpiperidinium)hexane dihydroxide and/or 1,7-bis(methylpiperidinium)heptane dihydroxide, of at least one source of at least one alkali metal and/or alkaline-earth metal M of valency n, to obtain a gel, ii) hydrothermal treatment of said gel obtained at a temperature of between 120° C. and 220° C., for a time of between 12 hours and 15 days.

Claims

1. A process for preparing a zeolite composite material composed of a mixture of zeolites of AFX structure type and of BEA structure type, comprising at least the following steps: i) mixing, in aqueous medium, of an FAU zeolite having an SiO.sub.2/Al.sub.2O.sub.3 mole ratio of between 30 and 100 with at least one zeolite of FAU structure type having an SiO.sub.2/Al.sub.2O.sub.3 mole ratio of between 2 and 30 (upper limit excluded), and in which the mathematical parameter, P.sub.ze, corresponding to the mass percentage of the FAU zeolite with an SiO.sub.2/Al.sub.2O.sub.3 mole ratio of between 30 and 100, in its anhydrous form (expressed in %) in the mixture of FAU zeolites, multiplied by the SiO.sub.2/Al.sub.2O.sub.3 mole ratio of said same FAU zeolite with an SiO.sub.2/Al.sub.2O.sub.3 mole ratio of between 30 and 100, is such that: 3250<P.sub.ze<7200, of at least one organonitrogen compound R, chosen from 1,5-bis(methylpiperidinium)pentane dihydroxide, 1,6-bis(methylpiperidinium)hexane dihydroxide, 1,7-bis(methylpiperidinium)heptane dihydroxide and mixtures thereof, and of at least one source of at least one alkali metal and/or alkaline-earth metal M of valency n, n being an integer greater than or equal to 1, the reaction mixture having the following molar composition: (SiO.sub.2(FAU))/(Al.sub.2O.sub.3(FAU)) of between 30 and 80, H.sub.2O/(SiO.sub.2(FAU)) of between 1 and 100, R/(SiO.sub.2(FAU)) of between 0.01 and 0.6, M.sub.2/nO/(SiO.sub.2(FAU)) of between 0.005 and 0.45, in which SiO.sub.2(FAU) is the molar amount of SiO.sub.2 provided by all the zeolites of FAU structure type introduced into the mixture, Al.sub.2O.sub.3 (FAU) is the molar amount of Al.sub.2O.sub.3 introduced by all the zeolites of FAU structure type introduced into the mixture, H.sub.2O the molar amount of water present in the reaction mixture, R the molar amount of said organonitrogen compound, M.sub.2/nO being the molar amount of M.sub.2/nO provided by all the FAU zeolites and by the source of alkali metal and/or alkaline-earth metal, up to the production of a homogeneous precursor gel; ii) hydrothermal treatment of said precursor gel obtained from of step i) at a temperature of between 120° C. and 220° C., for a time of between 12 hours and 15 days.

2. The process as claimed in claim 1, in which R is 1,6-bis(methylpiperidinium)hexane dihydroxide.

3. The process as claimed in claim 1, in which the mathematical parameter P.sub.ze is such that: 3350<P.sub.ze<7100.

4. The process as claimed in claim 1, in which the (SiO.sub.2(FAU))/(Al.sub.2O.sub.3(FAU)) mole ratio is between 32 and 70.

5. The process as claimed in claim 1, in which the R/(SiO.sub.2(FAU)) mole ratio is between 0.05 and 0.5.

6. The process as claimed in claim 1, in which the H.sub.2O/(SiO.sub.2 (FAU)) mole ratio is between 5 and 60.

7. The process as claimed in claim 1, in which the M.sub.2/nO/(SiO.sub.2(FAU)) mole ratio is between 0.01 and 0.25.

8. The process as claimed in claim 1, in which M is chosen from lithium, potassium, sodium, magnesium and calcium and a mixture of at least two of these metals, M preferably being sodium.

9. The process as claimed in claim 8, in which the source of at least one alkali and/or alkaline-earth metal M is sodium hydroxide.

10. The process as claimed in claim 1, in which step i) is performed for a time of greater than or equal to 10 minutes and advantageously for less than 2 hours.

11. The process as claimed in claim 1, in which crystal seeds of a zeolite of AFX structure type, of a zeolite of BEA structure type and/or of an AFX-BEA composite material are added to the reaction mixture of step i), preferably in an amount of between 0.01% and 10% by weight relative to the total weight of the sources of SiO.sub.2 and Al.sub.2O.sub.3 considered in their anhydrous form present in said mixture.

12. The process as claimed in claim 1, in which step i) comprises a step of maturing the reaction mixture at a temperature of between 20 and 100° C., with or without stirring, for a time of between 30 minutes and 48 hours.

13. The process as claimed in claim 1, in which the hydrothermal treatment of step ii) is performed at a temperature of between 120° C. and 220° C. for a period of between 12 hours and 15 days.

14. The process as claimed in claim 1, in which the solid phase obtained from step ii) is filtered off, washed, and dried at a temperature of between 20 and 150° C. for a time of between 5 and 24 hours, to obtain a dried zeolite.

15. The process as claimed in claim 14, in which the dried zeolite is then calcined at a temperature of between 450 and 700° C. for a time of between 2 and 20 hours, the calcination possibly being preceded by a gradual temperature increase.

16. A zeolite composite material composed of a mixture of zeolites of AFX structure type and of BEA structure type, said composite material comprising: between 30% and 90% by mass of zeolite of AFX structure type, relative to the total mass of said composite material in its anhydrous form; between 10% and 70% by mass of BEA structure type relative to the total mass of said composite material in its anhydrous form.

17. The composite material as claimed in claim 16, having an SiO.sub.2/Al.sub.2O.sub.3 mole ratio of between 2 and 100.

18. The composite material as claimed in claim 16, in which the zeolite of BEA structure type is preferably a beta zeolite containing a mixture containing between 35 and 45% by mass of polymorph A and between 55 and 65% by mass of polymorph B.

19. A zeolite composite material composed of a mixture of zeolites of AFX structure type and of BEA structure type, said composite material comprising between 30% and 90% by mass of zeolite of AFX structure type, relative to the total mass of said composite material in its anhydrous form; between 10% and 70% by mass of BEA structure type relative to the total mass of said composite material in its anhydrous form, wherein the zeolite composite material is obtained via the process as claimed in claim 1.

20. The composite material as claimed in claim 16, having an X-ray diffraction diagram comprising at least the lines having the mean values of d.sub.hkl and the relative intensities as follows: TABLE-US-00005 2 theta (°) dhkl (Å) Irel 7.49 11.79 vw-w 7.71 11.46 vw-w 8.71 10.14 mw-m 11.66 7.59 w-mw 12.97 6.82 w 15.00 5.90 vw 15.40 5.75 vw 15.66 5.66 w-mw 17.47 5.07 mw 17.90 4.95 w-mw 19.42 4.57 vw 19.88 4.46 vw-w 20.38 4.36 S-VS 21.08 4.21 w 21.31 4.17 vw-w 21.82 4.07 S-VS 22.19 4.00 w-m 22.34 3.98 w-VS 22.54 3.94 vw-w 22.70 3.91 vw-w 23.67 3.76 mw 25.24 3.52 vw 26.11 3.41 w-m 26.94 3.31 vw 27.11 3.29 vw 27.61 3.23 vw 28.04 3.18 mw-m 28.68 3.11 vw 29.51 3.03 vw 30.19 2.96 vw-w 30.58 2.92 mw 30.99 2.88 vw 31.59 2.83 w-mw 32.50 2.75 vw 33.73 2.66 w-mw 34.29 2.61 vw 34.78 2.58 vw 35.11 2.55 vw 35.79 2.51 vw 37.56 2.39 vw 38.00 2.37 vw 39.18 2.30 vw 39.61 2.30 vw where VS=very strong; S=strong; m=medium; mw=moderately weak; w=weak; vw=very weak. The relative intensity I.sub.rel is given in relation to a relative intensity scale in which a value of 100 is assigned to the most intense line of the X-ray diffraction diagram: vw<15; 15≤w<30; 30≤mw<50; 50≤m<65; 65≤S<85; VS≥85; 1≤vw-w<30; 30≤mw-m<65; 15≤w-mw<50; 65≤S-VS≤100; 15≤w-m<65; 15≤w-VS≤100.

Description

FIGURES

[0072] FIG. 1 represents the chemical formulae of the specific organonitrogen compounds which may be chosen as structuring agent in the synthetic process according to the invention.

[0073] FIG. 2 represents the X-ray diffraction diagram of the composite material according to the invention, composed of a zeolite of AFX structure type and of a zeolite of BEA structure type, obtained according to example 3.

[0074] FIG. 3 represents a scanning electron microscope (SEM) image of the composite material according to the invention, composed of a mixture of a zeolite of AFX structure type and of a zeolite of BEA structure type, obtained according to example 3.

[0075] FIG. 4 represents the X-ray diffraction diagram of the pure zeolite of AFX structure type obtained according to example 7.

[0076] The invention is illustrated by the examples that follow, which are not in any way limiting in nature.

EXAMPLES

[0077] The invention is illustrated by the examples that follow, which are not in any way limiting in nature.

Example 1: Preparation of 1,6-bis(methylpiperidinium)hexane dihydroxide (Structuring Agent R)

[0078] 50 g of 1,6-dibromohexane (0.20 mol, 99%, Alfa Aesar) are placed in a 1 L round-bottomed flask containing 50 g of N-methylpiperidine (0.51 mol, 99%, Alfa Aesar) and 200 ml of ethanol. The reaction medium is stirred at reflux for 5 hours. The mixture is then cooled to ambient temperature and then filtered. The mixture is poured into 300 ml of cold diethyl ether and the precipitate formed is then filtered off and washed with 100 ml of diethyl ether. The solid obtained is recrystallized in an ethanol/ether mixture. The solid obtained is dried under vacuum for 12 hours. 71 g of a white solid are obtained (i.e. a yield of 80%).

[0079] The product has the expected .sup.1H NMR spectrum. .sup.1H NMR (D.sub.2O, ppm/TMS): 1.27 (4H, m); 1.48 (4H, m); 1.61 (4H, m); 1.70 (8H, m); 2.85 (6H, 5); 3.16 (12H, m). This .sup.1H NMR spectrum corresponds to that of 1,6-bis(methylpiperidinium)hexane dibromide.

[0080] 18.9 g of Ag.sub.2O (0.08 mol, 99%, Aldrich) are placed in a 250 ml Teflon beaker containing 30 g of 1,6-bis(methylpiperidinium)hexane dibromide (0.07 mol) prepared and 100 ml of deionized water. The reaction medium is stirred for 12 hours in the absence of light. The mixture is then filtered. The filtrate obtained is composed of an aqueous solution of 1,6-bis(methylpiperidinium)hexane dihydroxide. Assaying of this species is performed by proton NMR using formic acid as standard.

Example 2: Preparation of an AFX-BEA Composite Material According to the Invention

[0081] 0.013 g of a zeolite of FAU structure type (CBV600 Zeolyst, SiO.sub.2/Al.sub.2O.sub.3=5.46, PAF=12.65) was mixed with 4.887 g of deionized water. 0.773 g of a zeolite of FAU structure type (CBV720 Zeolyst, SiO.sub.2/Al.sub.2O.sub.3=33.52, PAF=6.63, P.sub.ze=3321) is added to the previous mixture, and the preparation obtained is kept stirring for 10 minutes. 2.900 g of an aqueous solution of 1,6-bis(methylpiperidinium)hexane dihydroxide (20.91% by weight) prepared according to example 1 are added to the above mixture. The mixture is then kept stirring for 10 minutes. 0.429 g of a 20% by weight aqueous solution of sodium hydroxide (solution prepared from sodium hydroxide at 98% by weight, Aldrich) is added to the mixture and kept stirring for 10 minutes. The molar composition of the precursor gel is as follows: 60 SiO.sub.2: 1.9 Al.sub.2O.sub.3: 10 R(OH).sub.2: 5.6 Na.sub.2O: 2204 H.sub.2O, i.e. an SiO.sub.2/Al.sub.2O.sub.3 ratio of 31.6.

[0082] The precursor gel is then transferred, after homogenization, into an autoclave. The autoclave is closed and then heated for 2 days at 180° C. with stirring at 35 rpm with a rotary spit system. The crystalline product obtained is filtered off, washed with deionized water and then dried overnight at 100° C. The loss on ignition (LOI) of the dried solid, evaluated after drying at 1000° C. for 2 hours, is 9.5%.

[0083] The solid is then introduced into a muffle furnace where a step of calcining in air is performed: the calcination cycle comprises an increase in temperature of 1.5° C./minute up to 200° C., a steady stage at 200° C. maintained for 2 hours, an increase in temperature of 1° C./minute up to 550° C., followed by a steady stage at 550° C. maintained for 8 hours, then return to room temperature.

[0084] The calcined solid product was analyzed by X-ray diffraction and identified as being constituted of a mixture of approximately 30% by mass of a zeolite of AFX structure type and 70% by mass of a zeolite of BEA structure type. The AFX-BEA mixture represents approximately 100% by mass of the product obtained.

Example 3: Preparation of an AFX-BEA Composite Material According to the Invention

[0085] 0.013 g of a zeolite of FAU structure type (CBV600 Zeolyst, SiO.sub.2/Al.sub.2O.sub.3=5.46, PAF=12.65) was mixed with 4.887 g of deionized water. 0.773 g of a zeolite of FAU structure type (CBV720 Zeolyst, SiO.sub.2/Al.sub.2O.sub.3=33.52, PAF=6.63, P.sub.ze=3321) is added to the previous mixture, and the preparation obtained is kept stirring for 10 minutes. 2.900 g of an aqueous solution of 1,6-bis(methylpiperidinium)hexane dihydroxide (20.91% by weight) prepared according to example 1 are added to the above mixture. The mixture is then kept stirring for 10 minutes. 0.429 g of a 20% by weight aqueous solution of sodium hydroxide (solution prepared from sodium hydroxide at 98% by weight, Aldrich) is added to the mixture and kept stirring for a further 30 minutes. The molar composition of the precursor gel is as follows: 60 SiO.sub.2: 1.9 Al.sub.2O.sub.3: 10 R(OH).sub.2: 5.6 Na.sub.2O: 2204 H.sub.2O i.e. an SiO.sub.2/Al.sub.2O.sub.3 ratio of 31.6.

[0086] The precursor gel is then transferred, after homogenization, into an autoclave. The autoclave is closed and then heated for 6 days at 170° C. with stirring at 35 rpm with a rotary spit system. The crystalline product obtained is filtered off, washed with deionized water and then dried overnight at 100° C. The loss on ignition (LOI) of the dried solid, evaluated after drying at 1000° C. for 2 hours, is 9.8%.

[0087] The solid is then introduced into a muffle furnace where a step of calcining under a stream of air is performed: the calcination cycle comprises an increase in temperature of 1.5° C./minute up to 200° C., a steady stage at 200° C. maintained for 2 hours, an increase in temperature of 1° C./minute up to 550° C., followed by a steady stage at 550° C. maintained for 8 hours, then return to room temperature.

[0088] The calcined solid product was analyzed by X-ray diffraction and identified as being constituted of a mixture of approximately 50% by mass of a zeolite of AFX structure type and 50% by mass of a zeolite of BEA structure type. The AFX-BEA mixture represents approximately 100% by mass of the product obtained. The X-ray diffraction diagram produced for the calcined solid is given in FIG. 2. The SiO.sub.2/Al.sub.2O.sub.3 mole ratio of this material determined by XFS is 20.04.

[0089] The composite material obtained is analyzed by scanning electron microscopy (SEM). FIG. 3 shows the SEM image of the composite material obtained.

Example 4: Preparation of an AFX-BEA Composite Material According to the Invention

[0090] 0.239 g of a zeolite of FAU structure type (CBV712 Zeolyst, SiO.sub.2/Al.sub.2O.sub.3=11.42, PAF=12.81) was mixed with 4.952 g of deionized water. 0.573 g of a zeolite of FAU structure type (CBV780 Zeolyst, SiO.sub.2/Al.sub.2O.sub.3=98.22, PAF=8.52, P.sub.ze=7170) is added to the previous mixture, and the preparation obtained is kept stirring for 10 minutes. 2.905 g of an aqueous solution of 1,6-bis(methylpiperidinium)hexane dihydroxide (20.91% by weight) prepared according to example 1 are added to the above mixture. The mixture is then kept stirring for 10 minutes. 0.330 g of a 20% by weight aqueous solution of sodium hydroxide (solution prepared from sodium hydroxide at 98% by weight, Aldrich) is added to the mixture and kept stirring for 10 minutes. The molar composition of the precursor gel is as follows: 60 SiO.sub.2: 1.8 Al.sub.2O.sub.3: 10 R(OH).sub.2: 4.3 Na.sub.2O: 2204 H.sub.2O, i.e. an SiO.sub.2/Al.sub.2O.sub.3 ratio of 33.3.

[0091] The precursor gel is then transferred, after homogenization, into an autoclave. The autoclave is closed and then heated for 6 days at 180° C. with stirring at 35 rpm with a rotary spit system. The crystalline product obtained is filtered off, washed with deionized water and then dried overnight at 100° C. The loss on ignition (LOI) of the dried solid, evaluated after drying at 1000° C. for 2 hours, is 10.1%.

[0092] The solid is then introduced into a muffle furnace where a step of calcining under a stream of air is performed: the calcination cycle comprises an increase in temperature of 1.5° C./minute up to 200° C., a steady stage at 200° C. maintained for 2 hours, an increase in temperature of 1° C./minute up to 550° C., followed by a steady stage at 550° C. maintained for 8 hours, then return to room temperature.

[0093] The calcined solid product was analyzed by X-ray diffraction and identified as being constituted of a mixture of approximately 50% by mass of a zeolite of AFX structure type and 50% by mass of a zeolite of BEA structure type. The AFX-BEA mixture represents approximately 100% by mass of the product obtained.

Example 5: Preparation of an AFX-BEA Composite Material According to the Invention

[0094] 0.030 g of a zeolite of FAU structure type (CBV712 Zeolyst, SiO.sub.2/Al.sub.2O.sub.3=11.42, PAF=12.81) was mixed with 5.231 g of deionized water. 0.758 g of a zeolite of FAU structure type (CBV720 Zeolyst, SiO.sub.2/Al.sub.2O.sub.3=33.52, PAF=6.63, P.sub.ze=3261) is added to the previous mixture, and the preparation obtained is kept stirring for 10 minutes. 2.900 g of an aqueous solution of 1,6-bis(methylpiperidinium)hexane dihydroxide (20.91% by weight) prepared according to example 1 are added to the above mixture. The mixture is then kept stirring for 10 minutes. 0.086 g of sodium hydroxide (purity of 98% by weight, Aldrich) is subsequently incorporated into the mixture, which is kept stirring for a further 30 minutes. The molar composition of the precursor gel is as follows: 60 SiO.sub.2: 1.9 Al.sub.2O.sub.3: 10 R(OH).sub.2: 5.6 Na.sub.2O: 2204 H.sub.2O, i.e. an SiO.sub.2/Al.sub.2O.sub.3 ratio of 31.6.

[0095] The precursor gel is then transferred, after homogenization, into an autoclave. The autoclave is closed and then heated for 3 days at 170° C. with stirring at 35 rpm with a rotary spit system. The crystalline product obtained is filtered off, washed with deionized water and then dried overnight at 100° C. The loss on ignition (LOI) of the dried solid, evaluated after drying at 1000° C. for 2 hours, is 9.8%.

[0096] The solid is then introduced into a muffle furnace where a step of calcining under a stream of air is performed: the calcination cycle comprises an increase in temperature of 1.5° C./minute up to 200° C., a steady stage at 200° C. maintained for 2 hours, an increase in temperature of 1° C./minute up to 550° C., followed by a steady stage at 550° C. maintained for 8 hours, then return to room temperature.

[0097] The calcined solid product was analyzed by X-ray diffraction and identified as being constituted of a mixture of approximately 30% by mass of a zeolite of AFX structure type and 70% by mass of a zeolite of BEA structure type. The AFX-BEA mixture represents approximately 100% by mass of the product obtained.

Example 6: Preparation of an AFX-BEA Composite Material According to the Invention

[0098] 0.030 g of a zeolite of FAU structure type (CBV712 Zeolyst, SiO.sub.2/Al.sub.2O.sub.3=11.42, PAF=12.81) was mixed with 5.231 g of deionized water. 0.758 g of a zeolite of FAU structure type (CBV720 Zeolyst, SiO.sub.2/Al.sub.2O.sub.3=33.52, PAF=6.63, P.sub.ze=3261) is added to the previous mixture, and the preparation obtained is kept stirring for 10 minutes. 2.900 g of an aqueous solution of 1,6-bis(methylpiperidinium)hexane dihydroxide (20.91% by weight) prepared according to example 1 are added to the above mixture. The mixture is then kept stirring for 10 minutes. 0.086 g of sodium hydroxide (purity of 98% by weight, Aldrich) is subsequently incorporated into the mixture, which is kept stirring for a further 30 minutes. The molar composition of the precursor gel is as follows: 60 SiO.sub.2: 1.9 Al.sub.2O.sub.3: 10 R(OH).sub.2: 5.6 Na.sub.2O: 2204 H.sub.2O, i.e. an SiO.sub.2/Al.sub.2O.sub.3 ratio of 31.6.

[0099] The precursor gel is then transferred, after homogenization, into an autoclave. The autoclave is closed and then heated for 2 days at 180° C. with stirring at 35 rpm with a rotary spit system. The crystalline product obtained is filtered off, washed with deionized water and then dried overnight at 100° C. The loss on ignition (LOI) of the dried solid, evaluated after drying at 1000° C. for 2 hours, is 10.1%.

[0100] The solid is then introduced into a muffle furnace where a step of calcining under a stream of air is performed: the calcination cycle comprises an increase in temperature of 1.5° C./minute up to 200° C., a steady stage at 200° C. maintained for 2 hours, an increase in temperature of 1° C./minute up to 550° C., followed by a steady stage at 550° C. maintained for 8 hours, then return to room temperature.

[0101] The calcined solid product was analyzed by X-ray diffraction and identified as being constituted of a mixture of approximately 35% by mass of a zeolite of AFX structure type and 65% by mass of a zeolite of BEA structure type. The AFX-BEA mixture represents 99% by mass of the product obtained.

Example 7: Preparation of a Pure Zeolite of AFX Structure Type

[0102] 0.179 g of a zeolite of FAU structure type (CBV600 Zeolyst, SiO.sub.2/Al.sub.2O.sub.3=5.46, PAF=12.65%) was mixed with 4.86 g of deionized water. 0.643 g of a zeolite of FAU structure type (CBV720 Zeolyst, SiO.sub.2/Al.sub.2O.sub.3=33.52, PAF=6.63%) is added to the previous mixture, and the preparation obtained is kept stirring for 10 minutes. 2.891 g of an aqueous solution of 1,6-bis(methylpiperidinium)hexane dihydroxide (20.91% by weight) prepared according to example 1 are added to the above mixture, and the preparation is kept stirring for 10 minutes, 0.428 g of an aqueous solution containing 20% by weight of sodium hydroxide with a purity of 98% by weight (Aldrich) is subsequently incorporated into the synthetic mixture, which is kept stirring for 30 minutes. The molar composition of the mixture is as follows: 60 SiO.sub.2: 3.3 Al.sub.2O.sub.3: 10 R: 5.6 Na.sub.2O: 2204 H.sub.2O, i.e. an SiO.sub.2/Al.sub.2O.sub.3 ratio of 18. The precursor gel is then transferred, after homogenization, into an autoclave. The autoclave is closed and then heated for 6 days at 180° C. with stirring at 35 rpm with a rotary spit system. The crystalline product obtained is filtered off, washed with deionized water and then dried overnight at 100° C. The solid is then introduced into a muffle furnace where a calcination step is performed: the calcination cycle comprises an increase in temperature of 1.5° C./minute up to 200° C., a steady stage at 200° C. maintained for 2 hours, an increase in temperature of 1° C./minute up to 550° C., followed by a steady stage at 550° C. maintained for 8 hours, then return to room temperature.

[0103] The calcined solid product was analyzed by X-ray diffraction and identified as consisting of a pure zeolite of AFX structure type, i.e. with a purity of greater than 99.8% by weight. The diffraction diagram produced for the calcined solid of AFX structure type is given in FIG. 4. The product has an SiO.sub.2/Al.sub.2O.sub.3 mole ratio of 12.7 as determined by X-ray fluorescence.