BG66594B1 - A method for receiving nanosized zeolite crystals - Google Patents

Abstract

The invention is related to a method for synthesizing low-silicon zeolites with average size of the particles within the field of nanometres. According to the proposed method, during its starting stage, from the initial alkali silica-alumina gels, which do not contain organic bases, are formed embryos at relatively low temperatures (0-80 °C). After that, the embryos are separated from the originating waters, and during the second stage, their crystallization is carried out in water vapour at higher than in the initial stage temperature. The developed method provides a possibility to restrict the growth of the particles during the crystallization by separating the liquid phase from the being crystallizing hard mass, avoiding in this way the transfer of mass through the solution. The method is visualized by examples of LTA and FAU zeolites synthesis.

Description

66594 Bl (54) METHOD OF PREPARATION OF NANOSIME ZEOLITE CRYSTALS

FIELD OF THE INVENTION

The invention relates to a method for the preparation of zeolite nanocrystals from alkaline aluminosilicate bodies. The resulting low-silicon zeolites, such as zeolite A, X and Y (LTA and FAU type) are some of the most widely used in the industry as ion exchangers, detergent additives, adsorbents and catalysts.

BACKGROUND OF THE INVENTION

Crystalline aluminosilicate molecular sieves, zeolites, are known to be used in various processes in the chemical industry. They are used in water softeners as ion exchangers and also as an additive to detergents [1,2]. The zeolite additive in detergents is known to serve as a substitute for inorganic phosphate additives, such as sodium tripolyphosphate [3].

A method [4] is known in which the synthesis of unaggregated zeolite A crystals having a uniform particle distribution between 1 and 10 pm is proposed. In this method, a certain amount of ground embryos having an average particle size of less than 0.5 μητ is added to the alumina silicate gel.

A two-step method [5] is known for the preparation of zeolite 4A (the sodium form of zeolite A) with particle sizes between 2 and 10 µm, especially for additives to detergents.

There is a known method [6] for the continuous production of type Z zeolite, another crystalline low silicon aluminosilicate relevant for the production of detergents. There is a method [7] for the preparation of FAU zeolite (zeolite Y) of considerable interest as a catalyst and carrier for catalysts in catalytic cracking. According to this method [7], it is recommended that zeolite Y be produced by adding zeolite Y nuclei to sodium silicate at room temperature, followed by the addition of sodium aluminate and heating.

A disadvantage of the above methods is that the zeolite crystals obtained are quite large in size and often have an average particle size of between 1 and 5 pm. In addition, the particle size distribution is generally quite wide. However, for some applications, the use of small zeolite crystals is preferable because the intrinsic properties of the zeolites are best expressed by reducing the size of their crystallites.

Another disadvantage of the above methods is that in some cases it would be advantageous if these zeolite crystals are so small that they can form stable colloidal suspensions, and as is known, the stability of the suspensions increases with decreasing particle size. This requires the synthesis of nano - sized zeolites.

In addition to applications in the chemical industry processes, nano-sized zeolite crystals can be used as embryos to control the synthesis and regulation of the product.

For a number of industrial applications, the presence of nanosized zeolites with uniform, reproducible, and size-controlled particles is desirable and necessary. For example, small-zeolite crystals are preferably used as additives in the preparation of laundry detergents, which require rapid ion exchange (to soften water by ion exchange of Ca ⁺² : and Mg ⁺² ions with zeolite sodium ions), high ion exchange capacity, less mechanical wear and tear on equipment and reduced pollution. In addition, nanozeolite particles allow the preparation of stable zeolite suspensions. Detergent preparation formulations are easier to follow when using suspensions in the spraying devices, so stable colloidal suspensions are preferred. When the particle size is too large to form stable suspensions, relatively sophisticated stabilization systems including non-ionic surfactants (such as oxoalcohols), sodium alkylbenzosulfonate, and polymers are required to prevent their precipitation [8]. This increases the cost and reduces the ability to formulate the formulations for the preparation of detergents.

In the context of catalytic reactions, the use of small crystals leads to a reduction in diffusion difficulties [9] and a decrease in the rate of deactivation of zeolites as a result of coke deposition on the outer

66594 B1 crystal surface [10].

Methods [2,11] are known for the synthesis of submicron (between 100 and 1000 nm) particle sizes of zeolites 4A and P1 for use in liquid detergents. In the case of zeolite P1 [11], a warm solution of sodium aluminate (at 90 ° C) is mixed with a warm solution of sodium metasilicate pentahydrate under vigorous stirring, held at 90 ° C for 5 h, then filtered. In the case of zeolite A, the small crystalline product is obtained according to [2] as 80 wt. % of the product type A zeolite is smaller than 800 nm.

It is known that fine crystalline zeolite P (about 50 wt% of the product has a particle size less than 800 nm) is obtained by wet milling of the material [12]. In doing so, it is argued that grinding the zeolite does not adversely affect the quality of the detergent to which it is added.

There is a known method [13] for the preparation of small-crystalline zeo type material consisting of the synthesis of a gel precursor inside the pores of a porous material such as carbon, MgO or alumosilicate. The synthesis of ZSM-5 in a carbon matrix and MgO is described, as well as zeolite LTA and SOD in alumosilicate and SOD in MgAl ₂ O ₄ .

A method is known for the synthesis of zeolite Z-14 (zeolite X form) [14] with zeolite particle sizes between 20 and 100 nm using a precursor in the form of a colloidal silicate solution with a temperature of -9 to + 10 ° C [ 14].

In addition, it is known [15] that mono - and disaccharides could be used to retain the small size of the phosasite crystals (zeolite X and Y). Thus, sucrose, dextrose or other saccharides are added to the conventional aluminosilicate reaction mixture obtained by mixing alkali metal silicates with alkali metal aluminate solutions, with subsequent ripening and hydrothermal synthesis [15].

The preparation of nanosized zeolite crystals is known to be associated with the use of significant amounts of organic structure-determining reagents. In WO 1993/008125, according to which agglomerates of crystals with an average size of less than 100 nm are obtained, the final product (including zeolites of type MFI, MEL and BEA, which form stable colloidal suspensions) is prepared using a mixture from a source of silica and an organic structure-determining reagent (in the form of hydroxide). The amount of the organic structure-determining reagent must be excess so as to dissolve the silica while maintaining the system under boiling conditions. The size of the crystals is controlled by selecting the crystallization temperature and a lower crystalline product is obtained at lower temperatures.

In WO 1994/005597, according to which a pure alumina-silicate solution produces a colloidal suspension of discrete zeolite particles, tetraalkylammonium ions are used to stabilize the colloidal suspension. In this case, most of the basicity in the system is due to the addition of tetraalkylammonium hydroxide (TMAON). The source of aluminum is tetraalkylammonium aluminate, which is added to the alkali stabilized silicasol or silicate under vigorous stirring, followed by hydrothermal synthesis at temperatures up to 100 ° C and subsequent centrifugation of the product.

Both patents WO 1993/008125 and WO 1994/005597 apply alkyl ammonium salts, which are used either as organic structure-determining reagents and / or as stabilizers of the precursors from which the zeolite lattice is constructed.

One of the disadvantages of the above-mentioned patents using organic structure-determining reagents is the low yield of the target crystalline product [16].

SUMMARY OF THE INVENTION

According to the invention, a method has been developed for the preparation of nanosized low silicon zeolites of the LTA, FAU type and mixtures thereof of alkaline aluminosilicate hydrogels by mixing solutions containing silica and alumina by homogenizing the resulting hydrogel and forming it , the uterine waters are separated, the solid phase containing the embryos is transferred to an autoclave and heated to complete crystallization, in the middle of the water vapor, separated from the solid itself.

The developed method allows to obtain nanosized low-silicon zeolites without

66594 B1 using organic bases or other additional structure-determining reagents.

The factors controlling the formation of colloidal nanoscale zeolite crystals are the following:

starting materials - use of a readily soluble source of silica and aluminum oxide;

starting mixtures - use of pure homogeneous solutions containing low molecular weight silicon and aluminum forms;

carefully mixing the starting gel to avoid the formation of large particles of the gel, homogenizing the gel using a high-speed homogenizer.

An essential part of the invention is the separation of the nucleation phase from the process of crystallization and particle coagulation. This is achieved by separating the liquid portion of the gel as soon as the nucleation process is completed, with the subsequent removal of this fluid from the system and limiting the flow of mass transfer inside the solid (in the hydrogel). After separation of the liquid from the hydrogel, crystallization in vapor of this solid portion of the hydrogel takes place. In this way, the Ostwald solidification of the zeolite nanoparticles associated with mass transfer through the liquid phase during the crystallization process is reduced or completely eliminated.

The method provides for the controlled formation of zeolite embryos at temperatures of 0-80 ° C over a period specific to the different types of zeolites.

The zeolites obtained by this method are LTA, FAU or mixtures thereof.

Description of the attached figures

Figure 1 - X-ray diffraction from embryos 1; the product obtained by transformation of the hydrogel into water vapor medium 2 and from control synthesis of gel 3.

Figure 2 - particle size distribution according to the laser beam dispersion method, embryos - dashed line; zeolite LTA obtained by the present application - continuous line.

Figure ZA - Photograph with scanning electron microscope (SEM) of zeolite embryos

LTA, magnification x 5,000, marker = 10 pm.

Figure 3B - scanning electron microscope photograph of a specimen obtained according to the present application after hydrothermal transformation of an LTA zeolite aluminum silicate precursor in water vapor for 4 h at 100 ° C, magnification x 5000, marker = 10 pm.

Figure 3B - SEM photograph of a sample obtained by direct hydrothermal gel synthesis of an LTA zeolite alumina silicate precursor for 4 h at 100 ° C, magnification x 5,000, marker = 10 pm.

Figure 3B - SEM photograph of a sample obtained by direct hydrothermal gel synthesis of an LTA zeolite alumina silicate precursor for 4 h at 100 ° C, magnification x 5,000, marker = 10 pm.

Figure 4 - X-ray diffraction of FAU 1 zeolite embryos; the product obtained after 3 h at 100 ° C hydrothermal transformation of the embryos into water vapor medium 2; the product of control hydrothermal synthesis of gel 3 and the product obtained after 9 h at 100 ° C hydrothermal transformation of the embryos into water vapor medium 4.

Figure 5 is a SEM image of a sample obtained by hydrothermal transformation in the vapor environment of an FAU zeolite alumina silicate precursor. The marker is 1 pm in size.

The advantages of the invention are that it:

- provides a method for preparing low-silicon nanoscale zeolites in which the Si / AI ratio is in the range 1-2.5;

- enables the size of the zeolite particles to be controlled without the use of an inorganic material that is not typical of the original synthetic gel (such as porous synthesis of porous material, EP 1002764);

- reduces the number of post-synthesis steps in the preparation of the target final product;

- ensures the production of nanozeolites with a high conversion rate of raw materials (good yield);

- develops a method for the synthesis of nanosized zeolite crystals, whereby the yield on the basis of the aluminum silicate precursor from the solid mass is higher than 90%;

- avoids the use of expensive and toxic organic reagents that pollute the environment

66594 Bl medium and also require high-temperature combustion to release zeolite pores;

- allows the use of plastic containers, in particular of polypropylene. thus avoiding the use of metal vessels because the synthesis is carried out at relatively low temperatures (below 110 ° C);

- develops a method for preparing low-silicon nanosized zeolites without the use of organic structure-determining reagents or other organic additives.

The following examples illustrate the invention =

Example 1.

A solution was prepared by adding 44.7 g of sodium hydroxide and 100 g of distilled water to 10.91 g of sodium aluminate (53.6% A1 ₂ O ₃ , 43.8% Na ₂ O). The resulting suspension was stirred at 70-80 ° C until complete dissolution of the components, i. to clarify the suspension. A solution of 25 g of sodium silicate (28% SiO ₂ , 8% Na ₂ O) and 186.6 g of distilled water was prepared, stirring until homogenized.

The solutions of sodium silicate and sodium aluminate are mixed and homogenized with a high speed agitator at 8000 rpm for 45 min. The resulting hydrogel is milky white, of low viscosity and in the ratio of reagents:

6.0 Na ₂ O: 0.505 A1 ₂ O ₃ : 1.0 SiO ₂ : 150 N ₂ O

The product was transferred to a polypropylene bottle, which was sealed tightly and placed in an oven at 50 ° C for 6 hours. The resulting product, containing the formed zeolite LTA embryos, was centrifuged at 12,000 rpm for 15 min and the sewage separated.

The solid wet residue is transferred to the autoclave by positioning a reticulum above the bottom so that there is no direct contact with the liquid which is released during crystallization from it and flows to the bottom of the autoclave. The solid was kept in the autoclave for 2 to 4 hours at 100 ° C under water vapor separating from the solid.

The resulting solid was washed by dispersion in distilled water using an ultrasonic bath and subsequent centrifugation at 12,000 rpm for 15 min. The washing continues until the pH of the wash water reaches values between 9 and 10. The product obtained shows zeolite A X-ray diffraction and a mean particle size of 730 nm, measured by the laser beam dispersion method. The chemical analysis shows the following composition: Na ₂ O: A1 ₂ O ₃ : 2SiO ₂ , characteristic of low silicon zeolite, in which the Si / Al ratio is in the range 1-2.5. The X-ray diffraction of the product corresponds to the LTA zeolite and is shown in Figure 1 and the particle size distribution of Figure 2.

Figure 3 A shows the scanning electron microscope images of LTA zeolite embryos separated before transformation into a solid-state vapor medium, the product after transformation (Figure 3 B), and also the product obtained from control synthesis by direct transformation of the starting gel (Figure 3 B).

The yield obtained, calculated from the base alumina silicate precursor containing zeolite type A (LTA) embryos, is quantitative and is 97-100% within the experimental error range.

Example 2.

A solution of 4.32 g of sodium aluminate (53.6% A1 ₂ O ₃ , 43.8% Na ₂ O), 100 g of distilled water and 48.03 g of sodium hydroxide tablets (99%) was prepared. The resulting slurry was stirred at 70-80 ° C until complete dissolution of the components, i. to clarify the suspension.

A solution of 25 g of sodium silicate (28% SiO ₂ , 8% Na ₂ O) in 288.18 g of distilled water is prepared, which is homogenized by stirring. The resulting solutions were mixed under vigorous stirring and homogenized with a high speed agitator at 8000 rpm for 45 min. The resulting mixture is milky white and of low viscosity.

In hydrogels, the mode ratio of the reagents is:

4.0 Na ₂ O: 0.2 A1 ₂ O ₃ : 1.0 SiO ₂ : 200 N ₂ O

The product was transferred to a polypropylene bottle, which was sealed and placed in an oven at 50 ° C for 12 h to form the FAU zeolite embryos.

The resulting product was then centrifuged at 12,000 rpm for 15 min and the uterine water separated. Hard, moist

66594 Bl the residue is transferred to the autoclave by positioning a reticulum above the bottom so that there is no direct contact with the liquid which is released from it during crystallization and flowing to the bottom of the autoclave.

The solid was kept in the autoclave for 3 h at 100 ° C under water vapor, separated from the wet solid. The resulting solid was washed by dispersion in distilled water using an ultrasonic bath followed by centrifugation at 12,000 ° C / min for 15 min. The washing is continued until the pH of the wash water reaches a value between 9 and 10. The product obtained shows a typical FAU zeolite with an admixture of LTA zeolite. The X-ray diffraction of the product is shown in Figure 4. From the X-ray diffraction pattern, after 3 hours of crystallization of the alumina silicate precursor containing the FAU zeolite embryos, the product is completely crystallized having a known amount of another LTA zeolite phase. Chemical analysis of the product shows the composition: Na ₂ O: A1 ₂ O ₃ : 2.02 SiO ₂ characteristic of low silica zeolite type FAU.

With a longer treatment (9 h) of hydrothermal vapor transformation of the starting alumina silicate precursor containing FAU zeolite embryos, the product obtained is a hydrosodalite (Figure 4.4) with impurities of FAU zeolite.

Figure 5 shows a scanning electron microscope (SEM) image of a sample obtained by hydrothermal transformation in the vapor environment of an FAU zeolite alumina silicate precursor. The crystallite size is 200-250 nm.

The yield obtained, calculated on the basis of an alumina-silicate precursor containing FAU zeolite embryos, is quantitative within the range of the experimental error - 97-100%.

Claims (1)

Claims A process for the preparation of nanosized low-silica zeolites of the LTA, FAU type and mixtures thereof of alkaline aluminosilicate hydrogels by mixing solutions containing silica and alumina, characterized in that in the first step the resulting hydrogel is homogeneous vessel at temperatures of 0-80 ° C for the formation of embryos from the corresponding zeolite for 48 h, after which the uterine waters are separated, the solid phase containing the embryos is transferred to a closed vessel and in the second stage is stopped at temperatures of 30-100 ° C to full of crystallization, in a medium of water vapor separated from the solid itself, after which the resulting material was repeatedly dispersed in distilled water and centrifuged to a pH of the wash water 9-10, and subsequently dried.