Method for the preparation of synthetic crystalline zeolite materials with enhanced pore volume

Abstract

The present invention relates to a method for the preparation of a synthetic crystalline zeolite material, to said synthetic crystalline zeolite material, and to the uses of said method and said synthetic crystalline zeolite material in various applications.

Claims

1. A method for the preparation of a synthetic crystalline zeolite material comprising micropores and mesopores, said method either increasing the micropore volume without generating an additional mesoporosity, or creating uniform mesoporosity while maintaining or increasing the microporosity of said synthetic crystalline, said synthetic crystalline zeolite material having a silicon to aluminum molar ratio Si/Al1 and, wherein said method comprises at least the following steps: 1.sub.o) a step of dissolving a solid NH.sub.4F in a solvent creating a NH.sub.4F solution, said NH.sub.4F solution has a pH of approximately 7; 1) a step of contacting the NH.sub.4F solution with a dry starting crystalline zeolite material at a temperature ranging from 0 C. to 100 C., said NH.sub.4F solution having a NH.sub.4F mass concentration of at least 15 wt % and said starting crystalline zeolite material being a zeolite material in which the micropore volume represents more than 70% of the total pore volume and having a silicon to aluminum molar ratio Si/Al1, wherein said step 1) is carried out at a temperature ranging from 0 C. to 60 C.; 2) a washing step; 3) a drying step at a temperature ranging from 25 C. to 120 C., for 1 h to 24 h, to recover said synthetic crystalline zeolite material, wherein the pH of the NH.sub.4F solution during the contacting step is approximately 8 or greater, and wherein the Si/Al molar ratio of the dry starting crystalline zeolite material does not vary as a result of said method by more than about 1 from said silicon to aluminum molar ratio Si/Al1 of said synthetic crystalline zeolite material.

2. The method according to claim 1, wherein step 1) is carried out for a time ranging from 5 to 180 minutes.

3. The method according to claim 1, wherein the mass ratio of solid NH.sub.4F/starting crystalline zeolite material used in step 1) ranges from 0.5 to 25.

4. The method according to claim 1, wherein it further comprises a step of ion exchanging.

5. The method according to claim 1, wherein the NH.sub.4F solution used in step 1) has a NH.sub.4F mass concentration of at least 20 wt %.

6. The method according to claim 1, wherein step 1) is performed by: immersing the dry starting crystalline zeolite material in the NH.sub.4F solution to form a heterogeneous mixture, and then by stirring said heterogeneous mixture; or pouring the NH.sub.4F solution on the dry starting crystalline zeolite material so as to saturate its micropore volume, and then by filtrating it so as to remove the excess of NH.sub.4F solution and to form an impregnated solid.

7. The method according to claim 1, wherein it further comprises a step of functionalizing said synthetic crystalline zeolite material with at least one active compound.

8. The method as defined in claim 1, wherein said method introduces micropores having a mean dimension of more than 1 nm and/or mesopores having a mean dimension of 2 to 25 nm while maintaining or increasing the micropore volume, in a crystalline zeolite material which is essentially microporous.

9. The method as claimed in claim 1, wherein the Si/Al molar ratio of the dry starting crystalline zeolite material does not vary as a result of said method by more than about 0.1 from said silicon to aluminum molar ratio Si/Al1 of said synthetic crystalline zeolite material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph of peak intensity vs degree of a material from example 1 in accordance with one embodiment;

(2) FIG. 2 is a graph of quantity absorbed vs relative pressure of a material from example 1 in accordance with one embodiment;

(3) FIG. 3 is a graph of pore size distribution of a material from example 1 in accordance with one embodiment;

(4) FIG. 4 is an image of a material of example 1 in accordance with one embodiment;

(5) FIG. 5 is a graph of conversion vs time of a material from example 2 in accordance with one embodiment;

(6) FIG. 6 is a graph of intensity vs degree of a material from example 3 in accordance with one embodiment;

(7) FIG. 7 is a graph of quantity absorbed vs relative pressure of a material from example 3 in accordance with one embodiment;

(8) FIGS. 8-10b are images of samples of material from example 3 in accordance with one embodiment;

(9) FIG. 11 is a graph of conversion vs. weight/feed flow rate of a material from example 4 in accordance with one embodiment;

(10) FIG. 12 is graph of conversion vs time of a material from example 4 in accordance with one embodiment;

(11) FIG. 13 is a graph of quantity absorbed vs relative pressure of a material from example 5 in accordance with one embodiment;

(12) FIG. 14 is a graph of quantity absorbed vs relative pressure of a material from example 6 in accordance with one embodiment;

(13) FIG. 15 is a graph of peak intensity vs degree of a material from example 7 in accordance with one embodiment; and

(14) FIG. 16 is a graph of quantity absorbed vs relative pressure of a material from example 7 in accordance with one embodiment.

DETAILED DESCRIPTION

Examples

(15) The starting materials used in the examples which follow, are listed below: solid NH.sub.4F: 98.0% purity, Sigma Aldrich; Commercial zeolite Y produced by UOP under the commercial brand LZY-62 having a Si/Al molar ratio of 2.6 and a size of crystals of 0.5 to 1 m was used as a starting crystalline zeolite material; Commercial zeolite ZSM-5 produced by Sd Chemie (Clariant) under the commercial brand MFI-55 (NH.sub.4-form) having a Si/Al molar ratio of 21.3 and a size of crystals of 5 m was used as a starting crystalline zeolite material; Commercial zeolite MOR produced by Zeolyst under the commercial brand CBV 10A having a Si/Al molar ratio of 6.7 and a size of crystals of 0.1-0.2 m was used as a starting crystalline zeolite material; Commercial zeolite LTL produced by Zeolyst under the commercial brand Zeolite L ( 14/10436) having a Si/Al molar ratio of 3.3 and a size of crystals of 0.20.5 m was used as a starting crystalline zeolite material.

(16) Unless noted otherwise, these starting materials were used as received from the manufacturers, without additional purification.

(17) The various zeolites obtained in the examples were characterized over various scales of sizes.

(18) Powder X-Ray Diffraction (XRD) Analysis:

(19) Powder samples of the synthetic crystalline zeolite materials obtained after step 3) and starting crystalline zeolite materials were analyzed using a PANalytical X'Pert Pro diffractometer with CuK monochromatized radiation (=1.5418 ). The samples were scanned in the range 5-50 2 with a step size of 0.02.

(20) N.sub.2 Sorption Analysis:

(21) Nitrogen adsorption/desorption isotherms were measured using Micrometrics ASAP 2020 volumetric adsorption analyzer. Samples of the synthetic crystalline zeolite materials obtained after step 3) and starting crystalline zeolite materials were degassed at 573 K under vacuum overnight prior to the measurement. The micropore volume was estimated by Nonlocal Density Functional Theory (NLDFT). The volume adsorbed at P/P.sub.0=0.99 represents the total pore volume. The mesopore volume was estimated by the difference between the total pore volume and the micropore volume. The micropore and mesopore size distributions of solids were estimated by NLDFT and Barret-Joyner-Halenda (BJH) methods, respectively. The specific surface area was estimated by the Brunauer-Emmett-Teller (BET) method.

(22) Chemical Analysis:

(23) The chemical compositions (e.g. Si/Al molar ratios) of the synthetic crystalline zeolite materials obtained after step 3) were determined by inductively coupled plasma (ICP) optical emission spectroscopy using a Varian ICP-OES 720-ES.

(24) Transmission Electron Microscopy (TEM):

(25) Ethanol suspensions of the synthetic crystalline zeolite materials obtained after step 3) were sonicated for 15 min and then 2-3 drops of said suspensions were dried on carbon-film-covered 300-mesh copper electron microscope grids. The crystal size, morphology and crystallinity of solids were determined by a transmission electron microscopy (TEM) using a JEOL100CX microscope operating at 200 kV.

(26) Ammonium Exchange and Thermal Treatment:

(27) When the starting crystalline zeolite materials or the synthetic crystalline zeolite materials obtained after step 3) are not in the NH.sub.4.sup.+ or H.sup.+-form, they were ion-exchanged with a solution of 0.2M of NH.sub.4Cl (1 h, 25 C.). The ion-exchange procedure was repeated 2 times. After the third ion exchange step, the crystalline zeolite materials were washed with distilled water, and calcined (e.g. at 550 C.) for elimination of the NH.sub.3 and obtaining the crystalline zeolite materials in acidic form.

(28) Scanning Electron Microscopy (SEM):

(29) The surface features, morphology and size of zeolite materials were determined by a MIRA-LMH (TESCAN) scanning electron microscope (SEM) equipped with a field emission gun. The accelerating voltage was 30 kV. All samples prior the SEM characterization were covered with a PtPd conductive layer.

Example 1

Preparation of Synthetic Crystalline Zeolite Materials Y.SUB.1 .and Y.SUB.2 .According to the Method of the Invention and Characterization Thereof

Example 1-1

(30) Step 1):

(31) A NH.sub.4F solution was prepared by mixing 10 g of solid NH.sub.4F with 30 g of distilled water. The NH.sub.4F solution had a mass concentration of 25 wt %. Then, 7.5 g of starting crystalline zeolite material Y was immersed into the NH.sub.4F solution described above to form a heterogeneous mixture. Then, the heterogeneous mixture was treated at 0 C. for 30 minutes under stirring and ultrasounds, and was filtrated to obtain a solid.

(32) Steps 2) and 3):

(33) Then, the obtained solid was thoroughly washed with distilled water and dried at 100 C.

(34) A synthetic crystalline zeolite material Y.sub.1 with a Si/Al molar ratio of 2.6 was obtained.

(35) The yield was 90%.

Example 1-2

(36) The same method as the one described in example 1-1 was used except that in step 1), the treatment was performed at 0 C. for 60 minutes. A synthetic crystalline zeolite material Y.sub.2 with a Si/Al molar ratio of 2.7 was obtained.

(37) The yield was 85%.

(38) The Si/Al molar ratio and porosity properties [the specific surface area (S.sub.BET), the micropore volume (V.sub.micro), the mesopore volume (V.sub.meso), and the total pore volume (V.sub.total)] of the starting crystalline zeolite material Y and of the prepared synthetic crystalline zeolite materials Y.sub.1 and Y.sub.2 are given in Table 1 below:

(39) The specific surface area and porosity properties of the crystalline zeolite materials were obtained by N.sub.2 sorption measurements.

(40) TABLE-US-00001 TABLE 1 crystalline Si/Al zeolite molar S.sub.BET V.sub.micro V.sub.meso V.sub.total material ratio (m.sup.2 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) Y 2.6 652 0.29 0.07 0.36 Y.sub.1 2.6 750 0.35 0.07 0.42 Y.sub.2 2.7 755 0.31 0.13 0.44

(41) Hence, Table 1 clearly shows that the method of the present invention leads to the increase of the micropore volume and optionally to the introduction of a secondary porosity, and therefore allows in both examples 1-1 and 1-2 the increase of the total pore volume of the starting crystalline zeolite material. Indeed, in Y.sub.1, it is only observed an increase of the micropore volume, whereas in Y.sub.2, both the micropore volume and the mesopore volume are increased. The chemical analyses revealed that the Si/Al ratio only slightly increased from 2.6 to 2.7 in example 1-2.

(42) As it can be also seen in Table 1, the method of the present invention allows under certain conditions to increase the micropore volume without changing the mesopore volume of material (cf. synthetic crystalline zeolite material Y.sub.1). The formation of mesopores (2-10 nm) is only observed in synthetic crystalline zeolite materials Y.sub.2.

(43) In addition, FIG. 1 represents the Powder X-ray diffraction (XRD) of the starting crystalline zeolite material Y (FIG. 1a), the synthetic crystalline zeolite material Y.sub.1 (FIG. 1b) and the synthetic crystalline zeolite material Y.sub.2 (FIG. 1c), and shows the intensity (in arbitrary units, a.u.) as a function of two theta (in degree). FIG. 1 reveals high crystallinity and no indications of amorphous phase formation after the contacting step 1).

(44) FIG. 2 represents the nitrogen adsorption/desorption isotherms of the starting crystalline zeolite material Y (FIG. 2, solid squares), the synthetic crystalline zeolite material Y.sub.1 (FIG. 2, open squares) and the synthetic crystalline zeolite material Y.sub.2 (FIG. 2, solid triangles), and shows the volume adsorbed (in cm.sup.3.Math.g.sup.1) as a function of the relative pressure P/P.sub.0 (in units).

(45) Nitrogen adsorption characterizes the porosity of the crystalline zeolite materials. According to FIG. 2, it can be concluded that the prepared synthetic crystalline zeolite material Y.sub.2 exhibits a hysteresis loop related with the formation mesopores. After the pronounced uptake at low relative pressure, crystalline zeolite materials Y and Y.sub.1 exhibit almost horizontal adsorption and desorption branches that shows no presence of mesopores. The synthetic crystalline zeolite material Y.sub.1 shows higher uptake at low relative pressure which is characteristic of microporous zeolite type materials. This uptake is more intense in respect to the starting crystalline zeolite material Y revealing larger micropore volume of the synthetic crystalline zeolite material Y.sub.1.

(46) FIG. 3 represents the pore size distribution of the starting crystalline zeolite material Y (FIG. 3, solid squares), the synthetic crystalline zeolite material Y.sub.1 (FIG. 3, open squares) and the synthetic crystalline zeolite material Y.sub.2 (FIG. 3, solid triangles), and shows the pore volume calculated as dV/d log D (in cm.sup.3.Math.g.sup.1) as a function of the pore diameter (in nm).

(47) FIG. 3 clearly reflects the production of additional mesoporosity. There is a right shift of the pore size distributions indicating that the synthetic crystalline zeolite material Y.sub.2 comprises mesopores with a diameter ranging from 2 to 10 nm, and preferably from 2 to 4 nm.

(48) FIG. 4 shows representative electron micrograph of thin slices of the synthetic crystalline zeolite material Y.sub.2 (FIG. 4) extracted from the electron tomography study. The set of experimental data obtained with complementary methods (TEM, TEM tomography, nitrogen adsorption, etc. . . . ) unambiguously shows that the mesopores are similar in size in the synthetic crystalline zeolite material, and they are uniformly distributed throughout the volume of the synthetic crystalline zeolite materials. In addition, FIG. 4 clearly shows intra-particles porosity induced by internal-surface dissolution.

Example 2

Catalytic Activity of Synthetic Crystalline Zeolite Materials Y.SUB.1 .and Y.SUB.2

(49) A test was performed to evaluate the catalytic activity of the synthetic crystalline zeolite materials prepared according to the method of the invention.

(50) The synthetic crystalline zeolite materials Y.sub.1 and Y.sub.2 prepared in example 1 and the starting crystalline zeolite material Y were further ion-exchanged with ammonium cations (step 4) and heated at 550 C. to eliminate NH.sub.3 (step 5) and obtain respectively the synthetic crystalline zeolite materials in acidic form Y.sub.1 and Y.sub.2 and the starting crystalline zeolite material in acidic form Y (also called synthetic and starting crystalline zeolite catalysts).

(51) Then, the conversion of a bulky molecule 1,3,5-triisopropylbenzene (TIPB) in the presence of crystalline zeolite catalyst Y.sub.1, Y.sub.2 or Y was studied. The tests were performed under identical conditions [P.sub.Tot=101325 Pa, P.sub.TIPB=192 Pa, and weight/feed flow rate (W/F.sub.TIPB)=1.2710.sup.3 g.Math.min.Math.mol.sup.1] in a downflow fixed bed gas phase reactor at a temperature of 225 C.

(52) FIG. 5 represents the conversion of TIPB (in %) as a function of time on stream (in minutes) for the synthetic crystalline zeolite catalyst Y.sub.1 (FIG. 5, open squares), the synthetic crystalline zeolite catalyst Y.sub.2 (FIG. 5, solid triangles) and the starting crystalline zeolite catalyst Y (FIG. 5, solid squares).

(53) The kinetic diameter of TIPB is 0.95 nm, which is larger than the pore opening of the commercial crystalline zeolite material Y (i.e. 0.74 nm). The substantially higher activity of the synthetic crystalline zeolite catalysts Y.sub.1 and Y.sub.2 in comparison to the starting crystalline zeolite catalyst Y is a strong evidence that the method of the present invention leads to the modification of the porous network of the starting crystalline zeolite material Y which is essentially microporous. The method obviously expands pore dimensions and thus bulkier molecules are able to reach more active sites of the crystalline zeolite material. The method would allow a more efficient use of currently used zeolite catalysts in, for instance, oil refining (in particular cracking reactions where the molecular mass of the reactant is drastically reduced) and petrochemistry. In addition, the method of the invention would also allow the preparation of new synthetic crystalline zeolite catalysts able to process much bulkier molecules than those currently used in the industry.

Example 3

Preparation of Synthetic Crystalline Zeolite Materials ZSM-5.SUB.a., ZSM-5.SUB.b., ZSM-5.SUB.c., ZSM-5.SUB.d., ZSM-5.SUB.e., ZSM-5f, and ZSM-5.SUB.g .According to the Method of the Invention and Characterization Thereof

Example 3-1

(54) Step 1):

(55) A NH.sub.4F solution was prepared by mixing 80 g of solid NH.sub.4F with 120 g of distilled water. The NH.sub.4F solution had a mass concentration of 40 wt %. Then, 10 g of starting crystalline zeolite material ZSM-5 was immersed into the NH.sub.4F solution described above to form a heterogeneous mixture. The heterogeneous mixture was treated at 50 C. for 5 minutes under stirring and ultrasounds, and was filtrated to obtain a solid.

(56) Steps 2) and 3):

(57) Then, the obtained solid was thoroughly washed with distilled water and dried at 100 C. for 10 h.

(58) A synthetic crystalline zeolite material ZSM-5.sub.a with a Si/Al molar ratio of 22.3 was obtained.

Example 3-2

(59) The same method as the one described in example 3-1 was used except that in step 1), the treatment was performed at 50 C. for 15 minutes. A synthetic crystalline zeolite material ZSM-5.sub.b with a Si/Al molar ratio of 22.5 was obtained.

Example 3-3

(60) The same method as the one described in example 3-1 was used except that in step 1), the treatment was performed at 50 C. for 22.5 minutes. A synthetic crystalline zeolite material ZSM-5.sub.c with a Si/Al molar ratio of 22.0 was obtained.

Example 3-4

(61) The same method as the one described in example 3-1 was used except that in step 1), the treatment was performed at 50 C. for 30 minutes. A synthetic crystalline zeolite material ZSM-5.sub.d with a Si/Al molar ratio of 22.1 was obtained.

Example 3-5

(62) The same method as the one described in example 3-1 was used except that in step 1), the treatment was performed at 50 C. for 45 minutes. A synthetic crystalline zeolite material ZSM-5.sub.e with a Si/Al molar ratio of 22.8 was obtained.

Example 3-6

(63) The same method as the one described in example 3-1 was used except that in step 1), the treatment was performed at 50 C. for 60 minutes. A synthetic crystalline zeolite material ZSM-5.sub.f with a Si/Al molar ratio of 23.2 was obtained.

Example 3-7

(64) The same method as the one described in example 3-1 was used except that in step 1), the treatment was performed at 50 C. for 120 minutes. A synthetic crystalline zeolite material ZSM-5.sub.g with a Si/Al molar ratio of 23.4 was obtained.

(65) The Si/Al molar ratio and porosity properties [the specific surface area (S.sub.BET), the micropore volume (V.sub.micro), the mesopore volume (V.sub.meso), and the total pore volume (V.sub.total)] of the starting crystalline zeolite material ZSM-5 and of the prepared synthetic crystalline zeolite materials ZSM-5.sub.a, ZSM-5.sub.b, ZSM-5.sub.c, ZSM-5.sub.d, ZSM-5.sub.e, ZSM-5.sub.f and ZSM-5.sub.g are given in Table 2 below:

(66) The specific surface area and porosity properties of the crystalline zeolite materials were obtained by N.sub.2 sorption measurements.

(67) TABLE-US-00002 TABLE 2 crystalline Si/Al zeolite molar S.sub.BET V.sub.micro V.sub.meso V.sub.total material ratio (m.sup.2 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) ZSM-5 21.3 377 0.18 0.02 0.20 ZSM-5.sub.a 22.3 368 0.18 0.07 0.25 ZSM-5.sub.b 22.5 391 0.17 0.09 0.26 ZSM-5.sub.c 22.0 394 0.17 0.12 0.29 ZSM-5.sub.d 22.1 NA NA NA NA ZSM-5.sub.e 22.8 405 0.17 0.22 0.39 ZSM-5.sub.f 23.2 395 0.17 0.28 0.45 ZSM-5.sub.g 23.3 NA NA NA NA NA: not analyzed

(68) Table 2 clearly shows that the method of the present invention leads to the introduction of a secondary porosity while maintaining the starting micropore volume, and allows the increase of the total pore volume of the starting crystalline zeolite material (increase of 125% with respect to the starting total pore volume in example 3-6). The chemical analyses revealed that the Si/Al ratio only slightly increased from 21.3 to 23.3. These results are in sharp contrast to the conventional desilication or steaming dealumination approaches currently used for the creation of mesopores in zeolite framework, which change substantially the Si/Al ratio of the starting zeolite materials.

(69) In addition, FIG. 6 represents the Powder X-ray diffraction (XRD) of the starting crystalline zeolite material ZSM-5 (FIG. 6a), the synthetic crystalline zeolite material ZSM-5.sub.a (FIG. 6b), the synthetic crystalline zeolite material ZSM-5.sub.b (FIG. 6c), the synthetic crystalline zeolite material ZSM-5.sub.c (FIG. 6d), the synthetic crystalline zeolite material ZSM-5.sub.e (FIG. 6e) and the synthetic crystalline zeolite material ZSM-5.sub.f (FIG. 6f), and shows the intensity (in arbitrary units, a.u.) as a function of two theta (in degree). FIG. 6 reveals high crystallinity and no indications of amorphous phase formation after step 1).

(70) FIG. 7 represents the nitrogen adsorption/desorption isotherms of the starting crystalline zeolite material (FIG. 7, solid squares), the synthetic crystalline zeolite material ZSM-5.sub.a (FIG. 7, open squares), the synthetic crystalline zeolite material ZSM-5.sub.b (FIG. 7, solid triangles), the synthetic crystalline zeolite material ZSM-5.sub.c (FIG. 7, open triangles) the synthetic crystalline zeolite material ZSM-5.sub.e (FIG. 7, solid circles) and the synthetic crystalline zeolite material ZSM-5.sub.f (FIG. 7, open circles), and shows the volume adsorbed (in cm.sup.3.Math.g.sup.1) as a function of the relative pressure P/P.sub.0 (in units). For clarity reasons, the isotherms are shifted in Y direction (i.e. ordinate direction) by +20, +40, +60, +80, +100 cm.sup.3 g.sup.1, for the synthetic crystalline zeolite materials ZSM-5.sub.a, ZSM-5.sub.b, ZSM-5.sub.c, ZSM-5.sub.e, ZSM-5.sub.f, respectively.

(71) FIG. 7 shows that the starting crystalline zeolite material exhibits a typical Type I adsorption-desorption isotherm usually obtained for a microporous type material. Depending on the step 1) conditions, the synthetic crystalline zeolite materials change their surface/porous characteristics. More deeply treated crystalline zeolite materials (e.g. ZSM-5.sub.e and ZSM-5.sub.f) exhibit a combination of Type I and Type IV adsorption-desorption isotherms. In other words, besides the sharp uptake at low relative pressure which is characteristic of zeolite type materials, a second uptake with hysteresis loop is observed at high relative pressure. The hysteresis loop is characteristic of the formation of pores or cavities with mesoporous dimensions.

(72) The analysis of pore size distribution of the starting crystalline zeolite material ZSM-5 and the synthetic crystalline zeolite materials ZSM-5.sub.a, ZSM-5.sub.b, ZSM-5.sub.c, ZSM-5.sub.e and ZSM-5.sub.f showed the progressive formation of larger pores. The secondary porosity ranges from 4 to 100 nm depending on the contacting time of step 1).

(73) FIGS. 8, 9 and 10 represent the genesis and propagation of mesopores in the framework of the crystalline zeolite materials.

(74) FIGS. 8, 9a, 9b, 9c and 9d represent scanning electron microscopy (SEM) images of the starting crystalline zeolite material ZSM-5 and the synthetic crystalline zeolite materials ZSM-5.sub.a, ZSM-5.sub.c, ZSM-5.sub.e, ZSM-5.sub.f, respectively. FIGS. 10a and 10b represent respectively transmission electron microscopy (TEM) images of the crystalline zeolite materials ZSM-5.sub.d and ZSM-5.sub.g.

(75) As it can be seen in FIG. 8 the starting crystalline zeolite material ZSM-5 has a flat surface. After 5 min of contacting time (cf. step 1)), FIG. 9a reveals the first traces of dissolution and the disappearance of the small intergrown domain. At the very early stages of zeolite dissolution, the more energetic defect zones are attacked. These are namely defect zones and intergrowth zones between well crystallized zeolite domains. Then, with the increase of contacting time, the crystals of the zeolite material become progressively dissolved. Defects, small intergrown crystals are progressively removed in the whole volume of zeolite crystals (FIG. 10a). Further dissolution leads to increase of the size of holes remaining after dissolution of intergrown crystallites. In the first stages, the dissolution process follows the form of removed particles and thus cavities and channels with rectangular shape can be seen. This dissolution mechanism leads to the mosaic structure shown in FIG. 10b. The fact that the NH.sub.4F concentrated solution attacks first the defect parts of the crystals and thus, purifies the crystals from defects and intergrowth that have negative impact on the diffusion thorough zeolite channels, is another advantage of the present invention. FIG. 10 clearly shows intra-particles porosity induced by internal-surface dissolution.

(76) An important consequence is the generation of secondary porosity as a function of crystal growth process. Hence, by controlling the nucleation and growth of zeolite material, the genesis and propagation of secondary pore structure can be controlled, while maintaining the micropore volume of the starting crystalline zeolite material.

Example 4

Catalytic Activity of Synthetic Crystalline Zeolite Materials ZSM-5.SUB.a., ZSM-5.SUB.c., ZSM-5.SUB.d .and ZSM-5.SUB.e

(77) Tests were performed to evaluate the catalytic activity of the synthetic crystalline zeolite materials prepared according to the method of the invention.

(78) The synthetic crystalline zeolite materials ZSM-5.sub.a, ZSM-5.sub.c, ZSM-5.sub.d and ZSM-5.sub.e prepared in example 3 and the starting crystalline zeolite material ZSM-5 were heat treated at 550 C. to eliminate NH.sub.3 (step 5) and obtain respectively the synthetic crystalline zeolite materials in acidic form ZSM-5.sub.a, ZSM-5.sub.c, ZSM-5.sub.d and ZSM-5.sub.e and the starting crystalline zeolite material in acidic form ZSM-5 (also called synthetic and starting crystalline zeolite catalysts).

(79) Then, the conversion of m-xylene in the presence of the crystalline zeolite catalysts ZSM-5, ZSM-5.sub.a, ZSM-5.sub.c, ZSM-5.sub.e and ZSM-5.sub.f and the conversion of 1,3,5-triisopropylbenzene (TIPB) in the presence of the crystalline zeolite catalysts ZSM-5, ZSM-5.sub.a, and ZSM-5.sub.e were studied.

(80) The tests to convert m-xylene were performed under identical conditions [P.sub.Tot=101325 Pa, P.sub.m-xylene=2500 Pa, and W/F.sub.m-xylene=7-87 g.Math.h.Math.mol.sup.1] in a downflow fixed bed gas phase reactor at a temperature of 350 C.

(81) The tests to convert TIPB were performed under identical conditions [P.sub.Tot=101325 Pa, P.sub.m-xylene=192 Pa, and W/F.sub.TIPB=6.372710.sup.3 g.Math.min.Math.mol.sup.1] in a downflow fixed bed gas phase reactor at a temperature of 300 C.

(82) FIG. 11 represents the conversion of m-xylene (in %) as a function of the weight/feed flow rate (in W/F.sub.m-xylene) for the crystalline zeolite catalysts ZSM-5 (FIG. 11, solid squares), ZSM-5.sub.a (FIG. 11, open squares), ZSM-5.sub.c (FIG. 11, solid triangles), ZSM-5.sub.e (FIG. 11, open triangles) and ZSM-5.sub.f (FIG. 11, open circles).

(83) FIG. 12 represents the conversion of TIPB (in %) as a function of time on stream (in minutes) for the crystalline zeolite catalysts ZSM-5 (FIG. 12, solid squares), ZSM-5.sub.a (FIG. 12, solid circles), and ZSM-5.sub.e (FIG. 12, solid triangles).

(84) FIGS. 11 and 12 show that the synthetic crystalline zeolite catalysts prepared according the method of the invention exhibit substantially improved catalytic performances in both m-xylene and TIPB.

Example 5

Preparation of Synthetic Crystalline Zeolite Materials MOR.SUB.1 .According to the Method of the Invention and Characterization Thereof

(85) Step 1):

(86) A NH.sub.4F solution was prepared by mixing 8 g of solid NH.sub.4F with 32 g of distilled water. The NH.sub.4F solution had a mass concentration of 20 wt %. Then, 5 g of starting crystalline zeolite material MOR was immersed into the NH.sub.4F solution described above to form a heterogeneous mixture. Then, the heterogeneous mixture was stirred at 50 C. for 45 minutes and was filtrated to obtain a solid.

(87) Steps 2) and 3):

(88) Then, the obtained solid was thoroughly washed with distilled water and dried at 30 C.

(89) A synthetic crystalline zeolite material MOR.sub.1 with a Si/Al molar ratio of 6.7 was obtained. The Si/Al molar ratio and porosity properties [the specific surface area (S.sub.BET), the micropore volume (V.sub.micro), the mesopore volume (V.sub.meso), and the total pore volume (V.sub.total)] of the starting crystalline zeolite material MOR and of the prepared synthetic crystalline zeolite material MOR.sub.1 are given in Table 3 below.

(90) The specific surface area and porosity properties of the crystalline zeolite materials were obtained by N.sub.2 sorption measurements.

(91) TABLE-US-00003 TABLE 3 crystalline Si/Al zeolite molar S.sub.BET V.sub.micro V.sub.meso V.sub.total material ratio (m.sup.2 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) MOR 6.7 379 0.17 0.06 0.23 MOR.sub.1 6.7 441 0.19 0.09 0.28

(92) Table 3 clearly shows that the method of the present invention leads to the introduction of a secondary porosity and the increase of the micropore volume, thus involving the increasing of the total pore volume of the starting crystalline zeolite material. The chemical analyses revealed that the Si/Al ratio remains constant.

(93) FIG. 13 represents the nitrogen adsorption/desorption isotherms of the starting crystalline zeolite material MOR (FIG. 13, solid squares) and the synthetic crystalline zeolite material MOR.sub.1 (FIG. 13, open squares), and shows the volume adsorbed (in cm.sup.3.Math.g.sup.1) as a function of the relative pressure P/P.sub.0 (in units).

Example 6

Preparation of Synthetic Crystalline Zeolite Materials LTL.SUB.1 .According to the Method of the Invention and Characterization Thereof

(94) Step 1):

(95) A NH.sub.4F solution was prepared by mixing 8 g of solid NH.sub.4F with 32 g of distilled water. The NH.sub.4F solution had a mass concentration of 20 wt %. Then, 5 g of starting crystalline zeolite material LTL was immersed into the NH.sub.4F solution described above to form a heterogeneous mixture. Then, the heterogeneous mixture was stirred at 35 C. for 60 minutes, and was filtrated to obtain a solid.

(96) Steps 2) and 3):

(97) Then, the obtained solid was thoroughly washed with distilled water and dried at 30 C.

(98) A synthetic crystalline zeolite material LTL.sub.1 with a Si/Al molar ratio of 3.3 was obtained.

(99) The Si/Al molar ratio and porosity properties [the specific surface area (S.sub.BET), the micropore volume (V.sub.micro), the mesopore volume (V.sub.meso), and the total pore volume (V.sub.total)] of the starting crystalline zeolite material LTL and of the prepared synthetic crystalline zeolite material LTL.sub.1 are given in Table 4 below:

(100) The specific surface area and porosity properties of the crystalline zeolite materials were obtained by N.sub.2 sorption measurements.

(101) TABLE-US-00004 TABLE 4 crystalline Si/Al zeolite molar S.sub.BET V.sub.micro V.sub.meso V.sub.total material ratio (m.sup.2 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) LTL 3.3 338 0.15 0.04 0.19 LTL.sub.1 3.3 431 0.17 0.08 0.25

(102) Table 4 clearly shows that the method of the present invention leads to the increase of the total pore volume of the starting crystalline zeolite material. The increase of total pore is namely due to the increase of both the micropore and mesopore volumes. The chemical analyses revealed that the Si/Al ratio remains constant.

(103) FIG. 14 represents the nitrogen adsorption/desorption isotherms of the starting crystalline zeolite material LTL (FIG. 14, solid squares) and the synthetic crystalline zeolite material LTL.sub.1 (FIG. 14, open squares), and shows the volume adsorbed (in cm.sup.3.Math.g.sup.1) as a function of the relative pressure P/P.sub.0 (in units).

Comparative Example 7

Preparation of Synthetic Crystalline Zeolite Materials Y.SUB.A .and Y.SUB.B .which are not Part of the Invention

(104) Synthetic zeolites Y.sub.A and Y.sub.B were prepared according the method described in U.S. Pat. No. 5,100,644 and with the conditions used in examples 9 and 10 of U.S. Pat. No. 5,100,644, respectively.

(105) A NH.sub.4F solution was prepared by mixing 3.9 g of solid NH.sub.4F with 4.96 g of distilled water. The NH.sub.4F solution had a mass concentration of 44 wt %. Then, separately, 7.39 g of commercial zeolite Y was mixed with 29.19 g of distilled water to form a zeolite suspension having a zeolite mass concentration of 20.2 wt %.

(106) Then, the NH.sub.4F solution was added slowly over a period of 90 minutes at 75 C. on the zeolite suspension, the NH.sub.4F solution and the zeolite suspension being maintained at 75 C. during the slow addition. After the addition, the resulting mixture was maintained for a further 3 hours at 75 C.

(107) The solid synthetic zeolite material was separated by filtration, washed with water and dried in air at room temperature.

(108) A synthetic crystalline zeolite material Y.sub.A with a Si/Al molar ratio of 3.5 was obtained. Y.sub.A is not part of the invention since it was not prepared according to the method of the invention.

(109) The same method was repeated with a NH.sub.4F solution prepared by mixing 4.95 g of solid NH.sub.4F with 4.95 g of distilled water. The NH.sub.4F solution had a mass concentration of 50 wt %. Then, separately, 7.39 g of commercial zeolite Y was mixed with 23.4 g of distilled water to form a zeolite suspension having a zeolite mass concentration of 24 wt %.

(110) A synthetic crystalline zeolite material Y.sub.B with a Si/Al molar ratio of 4.2 was obtained. Y.sub.B is not part of the invention since it was not prepared according to the method of the invention.

(111) FIG. 15 represents the Powder X-ray diffraction (XRD) of the starting crystalline zeolite material Y (FIG. 15a), the synthetic crystalline zeolite material Y.sub.A (FIG. 15b) and the synthetic crystalline zeolite material Y.sub.B (FIG. 15c), and shows the intensity (in arbitrary units, a.u.) as a function of two theta (in degree). FIG. 15 reveals high crystallinity of the starting crystalline zeolite material. However, a substantial loose of crystallinity can be observed for Y.sub.A and Y.sub.B zeolite materials.

(112) FIG. 16 represents the nitrogen adsorption/desorption isotherms of the starting crystalline zeolite material Y (FIG. 16, solid squares), the synthetic zeolite material Y.sub.B (FIG. 16, open squares) and the synthetic zeolite material Y.sub.C (FIG. 16, open circles), and shows the volume adsorbed (in cm.sup.3.Math.g.sup.1) as a function of the relative pressure P/P.sub.0 (in units).

(113) Nitrogen adsorption characterizes the porosity of the zeolite materials. According to FIG. 16 and by comparison with FIG. 2, it can be concluded that the prepared synthetic zeolite materials Y.sub.A and Y.sub.B which are not part of the invention, show much lower microporosity level and much larger mesopore size compared with Y.sub.1 and Y.sub.2 which are part of the invention and prepared in example 1. Such obvious difference in nitrogen adsorption performance reflects the substantial difference in the porosity of zeolites prepared in different ways, and hence reflects the substantial different interaction between zeolite and NH.sub.4F solutions in the method of the invention compared to the methods of the prior art.

(114) The Si/Al molar ratio and porosity properties [the specific surface area (S.sub.BET), the micropore volume (V.sub.micro), the mesopore volume (V.sub.meso), and the total pore volume (V.sub.total)] of the starting crystalline zeolite material Y and of the prepared synthetic crystalline zeolite material Y.sub.A and Y.sub.B are given in Table 5 below:

(115) The specific surface area and porosity properties of the zeolite materials Y.sub.A and Y.sub.B were obtained by N.sub.2 sorption measurements.

(116) TABLE-US-00005 TABLE 5 crystalline Si/Al zeolite molar S.sub.BET V.sub.micro V.sub.meso V.sub.total material ratio (m.sup.2 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) (cm.sup.3 .Math. g.sup.1) Y 2.6 652 0.29 0.07 0.36 Y.sub.A 3.5 563 0.26 0.17 0.43 Y.sub.B 4.2 409 0.18 0.16 0.34

(117) The method of the prior art clearly results in a decrease of the micropore volume and in substantial increase of mesopore volume. Thus, the mesopore volume is not increased while maintaining or increasing the starting micropore volume like in the method of the present invention. Indeed, the decrease of the micropore volume results in a deterioration of the adsorption capacity of the zeolite material and in a decrease of its separation capacity.

(118) There is also a substantial decrease of the specific surface area and the Si/Al molar ratio does not remain constant. The decrease of the specific surface area is related with lower crystallinity and induces a decrease of the availability of active sites and thus a dropping of the catalytic activity.