ZEOLITIC MATERIALS HAVING A DISTINCTIVE SINGLE CRYSTAL MACROPOROSITY AND METHOD FOR THE PRODUCTION THEREOF

Abstract

The invention relates to a zeolitic material comprising zeolitic monocrystals, each of which has a pore system encompassing at least one micropore system and at least one macropore system, and to a method for producing a zeolitic material of said type. In said method, porous oxide particles are converted into the zeolitic material in the presence of an organic template and steam.

Claims

1. Zeolitic material comprising zeolitic single crystals, characterized in that the single crystals each have an intracrystalline pore system comprising at least one micropore system and at least one macropore system, wherein within each single crystal several macropores are present within a microporous zeolitic framework, and at least one system of interconnected macropores is present which comprises one or more openings to the crystal surface.

2. Zeolitic material according to claim 1, characterized in that the intracrystalline pore system comprises several macropores with a pore diameter of at least 100 nm.

3. Zeolitic material according to claim 1, characterized in that the intracrystalline pore system comprises several macropores open to the crystal surface whose opening diameter is at least 100 nm.

4. Zeolitic material according to claim 1, characterized in that a system of interconnected macropores extends from at least a first crystal surface to at least a second crystal surface and comprises at least one opening to the first and the second crystal surface, respectively.

5. Zeolitic material according to claim 1, characterized in that the microporous zeolitic framework is formed from of tetrahedral SiO.sub.2 units, wherein up to 30% of all silicon atoms in the framework can be replaced with one or more elements selected from boron, aluminum, phosphorus and titanium.

6. Method for the production of a zeolitic material according to claim 1, characterized in that the method comprises the following steps: a) providing a mixture of (i) porous particles of an oxide capable of forming a framework of a zeolitic material and (ii) an organic template for the zeolite synthesis; b) converting the mixture into a zeolitic material by heating the mixture in contact with water vapor, wherein the porous particles are mesoporous particles having a particular size between 50 nm and 2,000 nm.

7. Method according to claim 6, characterized in that providing the mixture in step a) comprises impregnating the porous particles with a solution or a dispersion of the organic template, optionally followed by a partial or complete removal of the solvent of the solution or dispersion.

8. Method according to claim 6, characterized in that in the mixture provided in step a) the organic template is present on the surface and in the pores of the porous particles.

9. (canceled)

10. Method according to claim 6, characterized in that the porous particles have a particle size between 100 nm and 800 nm.

11. Method according to claim 6, characterized in that the porous particles are SiO.sub.2 particles.

12. Method according to claim 6, characterized in that the mixture provided in step a) additionally comprises one or more precursor compounds selected from a precursor compound of an aluminum oxide, a titanium oxide, a phosphorus oxide and a boric oxide, or from combinations of such precursor compounds.

Description

EXAMPLES

Example 1 (Comparative Example): Preparation of Conventional MFI-Type Crystals Using a Standard Synthesis Method

[0113] 133 g of distilled water and 16 g of tetrapropylammonium hydroxide solution (40 wt % TPAOH solution) were mixed in a polypropylene flask. 15 g of tetraethyl orthosilicate (TEOS) were added and the mixture was stirred for 4 h. 80 g of the synthesis mixture were transferred into a Teflon vessel (V=120 ml), and placed into an autoclave which was closed and pressurized. The subsequent crystallization was carried out at 175° C. for 48 hours in a preheated convection oven. Then the autoclave was cooled to room temperature with cold water, opened, and the product of the synthesis was separated from the excess solution by means of centrifugation and then washed four times with distilled water (pH 8). Drying was carried out overnight at 75° C.

[0114] FIG. 3 shows an electron microscope (REM) image of the resulting MFI-type crystals. The typical hexagonal crystal morphology is clearly visible.

Example 2 (Preparation Example): Preparation of Porous SiO.SUB.2 .Particles as Starting Products for the Synthesis of Zeolite

[0115] 828 g of distilled water were provided in a polypropylene beaker and 6 g of hexadecyltrimethylammonium bromide (CTAB, 98%, Sigma Aldrich) were added while stirring. 2,876 g of technical ethanol (96%) were added to this mixture and stirring was continued until a clear solution was obtained. Then 144 g of ammonia solution (25 wt %) were added while stirring, and stirring was continued for 1 more hour. Then 20 g of tetraethyl orthosilicate (98%, Alfar Aesar) were added and the resulting mixture was stirred for 2 more hours. After that, the resulting SiO.sub.2 particles were separated from the synthesis mixture by means of centrifugation at 10,000 rpm and washed three times with distilled water. Finally, the purified SiO.sub.2 particles were dried overnight at 75° C. in the air and then calcined at 550° C. in ambient air.

[0116] The porosity of the thus prepared SiO.sub.2 particles was confirmed by means of X-ray analysis and N.sub.2 physisorption; the particles comprise mesopores. Furthermore, these particles had particle diameters between 400 and 500 nm, as shown in the electron micrographs in FIGS. 3 to 5.

Example 3: Preparation of Aluminum-Free Macroporous Zeolite Single Crystals

[0117] In a porcelain dish, 0.340 g of tetrapropylammonium hydroxide solution (TPAOH, 40 wt %, Clariant) were mixed with 0.25 g of SiO.sub.2 particles (Example 2) and left at room temperature for 16 h. Then the resulting SiO.sub.2 particles impregnated with TPAOH were finely ground with a pestle in the porcelain dish and transferred to a 50 ml Teflon vessel as shown in FIG. 2. The Teflon insert contained 24 g of water. Care was taken that the water did not come into contact with the TPAOH-SiO.sub.2 particles. Then the Teflon vessel was placed in a stainless steel autoclave which was closed to resist pressure. Finally, the autoclave was heated to 110° C. for 4 days. At the end of the 4 days, the autoclave was cooled to room temperature. The solid material was isolated by filtration, washed with distilled water, dried overnight at 75° C. and subsequently characterized.

[0118] Electron micrographs showed that the resulting solid product consists of single crystals with interconnected intracrystalline macropores which cannot be obtained by means of the conventional synthesis method (Example 1). X-ray diffraction shows that the product is highly crystalline MFI-type zeolite.

Example 4: Preparation of Aluminum-Containing Macroporous Zeolite Single Crystals

[0119] In a porcelain dish, 0.340 g of 40 wt % tetrapropylammonium hydroxide solution were mixed with 0.25 g of SiO.sub.2 particles (Example 2) and left at room temperature for 16 h. The SiO.sub.2 particles were prepared according to Example 2, but at a temperature of 40° C., not room temperature. This allowed the preparation of smaller SiO.sub.2 particles with diameters between 200 and 350 nm. After drying, 0.1 g of 0.001% aluminum solution prepared from Al(NO.sub.3)*9H.sub.2O were added and the mixture was left at room temperature for 6 h. Then the SiO.sub.2 particles, which contained TPAOH and aluminum, were ground with a pestle in the porcelain dish and transferred to a 50 ml Teflon vessel as shown in FIG. 2. The Teflon insert contained 24 g of water. The water did not come into contact with the TPAOH-Al.sub.2O.sub.3—SiO.sub.2 particles. Then the Teflon vessel was placed in a stainless steel autoclave which was closed so as to resist pressure. Finally, the autoclave was heated to 110° C. for 4 days. At the end of the 4 days, the autoclave was cooled to room temperature, the solid material was isolated by filtration, washed with distilled water, dried overnight at 75° C. and subsequently characterized.

[0120] The X-ray analysis of the resulting solid showed the diffraction pattern typical for highly crystalline MFI-type zeolite. Analyses with an electron microscope showed that mainly single crystals with distinctive intracrystalline macropores were obtained and no further secondary treatments of the product were necessary.

Example 5 (Preparation Example): Preparation of Porous Al.SUB.2.O.SUB.3.—SiO.SUB.2 .Particles as Starting Products for the Synthesis of Zeolite

[0121] Al.sub.2O.sub.3—SiO.sub.2 particles as starting products for the preparation of aluminum-containing nano zeolite according to the present invention were prepared using a modified process according to Ahmed et. al. [Ahmed et. al., Industrial & Engineering Chemistry Research, 49 (2010) 602]. In a typical approach, 4 g of polyvinyl alcohol (PVA, Mw 31-50 k, 98 wt % from Sigma-Aldrich) were dissolved in 105 g of deionized water at 80° C. in a beaker. After about 20 to 30 minutes, 0.12 g of sodium aluminate solution (53 wt % Al.sub.2O.sub.3 and 43 wt % Na.sub.2O from Chemiewerk Bad Kostritz GmbH) were added to the PVA solution at 80° C. while stirring. Stirring of the resulting mixture was continued until the sodium aluminate was completely dissolved. Then the solution was cooled to room temperature and transferred to a 500 ml glass stirred tank reactor. After that, 1.61 g of CTAB and 101 g of ethanol were added to the cooled mixture while stirring and the mixture was heated to 40° C. Finally, 7.2 g of TEOS were added and the resulting synthesis mixture with a molar composition of 1 TEOS:0.006 Al.sub.2O.sub.3:2.9 NH.sub.3:0.12 CTAB:162 H.sub.2O:58 ethanol:0.003 PVA was stirred for about another 40 h at 40° C. The resulting SiO.sub.2 particles were separated from the synthesis mixture by means of centrifugation at 10,000 rpm and washed three times with deionized water. At the end, the purified Al.sub.2O.sub.3—SiO.sub.2 particles were dried overnight at 75° C. in the air and then calcined at 550° C. in ambient air.

[0122] The structure and porosity of the thus prepared SiO.sub.2 particles were examined by means of X-ray analysis and N2 physisorption and it was confirmed that the particles comprise mesopores. Furthermore, these particles had particle diameters between 550 and 700 nm, as shown in the electron micrograph in FIG. 12.

Example 6: Preparation of Macroporous Aluminum-Containing Zeolitic Single Crystals by Crystallizing Aluminum-Containing Mesoporous Silica Particles

[0123] 0.25 g of the aluminum-containing, mesoporous spherical silica particles prepared in Example 5 and 0.347 g of aqueous 40 wt % tetrapropylammonium hydroxide solution were weighed out in a porcelain dish and mixed. The mixture was dried in a drying cabinet with circulating air for 1.5 h at 40° C. while at the same time it was repeatedly mixed and crushed. The dried mixture was left for 16 h at room temperature (RT). After that, the porcelain dish with the dried mixture was transferred to a 50 ml Teflon insert (as shown in FIG. 2). The autoclave contained 24 g of distilled water which did not come into contact with the porcelain dish or its contents. The Teflon insert was placed in a stainless steel autoclave which was closed so as to resist pressure. The autoclave was placed in a drying chamber preheated to 150° C. and crystallization was carried out for 3 days at 150° C. At the end of the crystallization period the autoclave was cooled to room temperature, the solid was removed from the porcelain dish by means of filtration, washed with distilled water and dried overnight at 70° C. Then the dried product was characterized.

[0124] The X-ray analysis of the resulting solid showed the diffraction pattern typical for highly crystalline MFI-type zeolite (FIG. 14). Analyses with an electron microscope showed that mainly single crystals with distinctive intracrystalline macropores were obtained. Some of these macropores are clogged by residues of silica particles (see FIG. 15).

[0125] In order to remove residue from the macropores, the obtained product was subjected to an alkaline treatment. For this treatment, 0.05 g of the sample were mixed with 5 g of an aqueous 1M sodium hydroxide solution in a 25 ml propylene Erlenmeyer flask. The flask was shaken for 48 h at room temperature. Then the solid was separated by means of filtration, washed with distilled water and dried overnight at 75° C. Then the product was characterized.

[0126] Analyses with an electron microscope showed that mainly single crystals with distinctive intracrystalline macropores were obtained which were free of residues (see FIG. 16).

Example 7: Preparation of Macroporous Aluminum-Containing Zeolitic Single Crystals by Crystallizing Aluminum-Containing Mesoporous Silica Particles

[0127] 0.25 g of the aluminum-containing, mesoporous spherical silica particles prepared in Example 5 and 0.347 g of aqueous 40 wt % tetrapropylammonium hydroxide solution, as well as 0.25 g of an aqueous 0.5M sodium hydroxide solution were weighed out in a porcelain dish and mixed. The mixture was dried in a drying cabinet with circulating air for 2 h at 40° C. while at the same time it was repeatedly mixed and crushed. The dried mixture was left for 16 h at room temperature (RT). After that, the porcelain dish with the dried mixture was transferred to a 50 ml Teflon insert (as shown in FIG. 2). The autoclave contained 24 g of distilled water which did not come into contact with the porcelain dish or its contents. The Teflon insert was placed in a stainless steel autoclave which was closed and pressurized. The autoclave was placed in a drying chamber preheated to 150° C. and crystallization was carried out for 3 days at 150° C. At the end of the crystallization period the autoclave was cooled to room temperature, the solid was removed from the porcelain dish by means of filtration, washed with distilled water and dried overnight at 70° C. Then the dried product was characterized.

[0128] The X-ray analysis of the resulting solid showed the diffraction pattern typical for highly crystalline MFI-type zeolite (FIG. 17). Analyses with an electron microscope showed that single crystals with intracrystalline macropores were obtained. FIG. 18 illustrates that the pores are clear after the synthesis.

DESCRIPTION OF THE DRAWINGS

[0129] FIG. 1 shows a schematic illustration of the main steps in the production of single crystals of macroporous MFI-type zeolite.

[0130] FIG. 2 shows a schematic illustration of the various steps and the experimental setup in the preparation of single crystals of macroporous MFI-type zeolite.

[0131] FIG. 3 shows an REM image of a conventionally prepared MFI-type zeolite.

[0132] FIG. 4 shows an X-ray diffractogram of the calcined mesoporous silicon dioxide particles of Example 2.

[0133] FIG. 5 shows a scanning electron micrograph of the calcined mesoporous silicon dioxide particles of Example 2.

[0134] FIG. 6 shows the nitrogen sorption isotherm (a) and DFT pore size distribution (b) of the calcined mesoporous silicon dioxide particles of Example 2.

[0135] FIG. 7 shows an X-ray diffractogram of the single crystals of a macroporous MFI-type zeolite without aluminum according to the present invention.

[0136] FIG. 8 shows a scanning electron micrograph of the single crystals of a macroporous MFI-type zeolite without aluminum according to the present invention.

[0137] FIG. 9 shows a scanning electron micrograph of the single crystals of a macroporous MFI-type zeolite without aluminum according to the present invention.

[0138] FIG. 10 shows an X-ray diffractogram of the aluminum-containing single crystals of a macroporous MFI-type zeolite with aluminum according to the present invention.

[0139] FIG. 11 shows a scanning electron micrograph of the aluminum-containing single crystals of a macroporous MFI-type zeolite according to the present invention.

[0140] FIG. 12 shows a scanning electron micrograph of the calcined mesoporous silicon dioxide particles of Example 3.

[0141] FIG. 13 shows an X-ray diffractogram of the calcined mesoporous silicon dioxide particles of Example 3.

[0142] FIG. 14 shows an X-ray diffractogram of the aluminum-containing single crystals of a macroporous MFI-type zeolite with aluminum according to the present invention, prepared according to Example 6.

[0143] FIG. 15 shows a scanning electron micrograph of the aluminum-containing single crystals of a macroporous MFI-type zeolite with aluminum according to the present invention, prepared according to Example 6.

[0144] FIG. 16 shows a scanning electron micrograph of the aluminum-containing single crystals of a macroporous MFI-type zeolite with aluminum according to the present invention, prepared according to Example 6 after the alkaline treatment.

[0145] FIG. 17 shows an X-ray diffractogram of the aluminum-containing single crystals of a macroporous MFI-type zeolite with aluminum according to the present invention, prepared according to Example 7.

[0146] FIG. 18 shows a scanning electron micrograph of the aluminum-containing single crystals of a macroporous MFI-type zeolite with aluminum according to the present invention, prepared according to Example 7.