Two types of MTW zeolite nanocrystalline aggregate and preparation method thereof

Abstract

The invention discloses an MTW zeolite two-type nanocrystalline aggregate. A preparation method of the MTW zeolite two-type nanocrystalline aggregate comprises the following steps: a) taking tetraethylammonium hydroxide as a template agent of a first type; b) the second type uses methyl triethyl ammonium chloride as a template agent; the first type of reactant raw materials and the second type of reactant raw materials comprise sodium metaaluminate, sodium hydroxide, silica sol and pure water. According to the invention, a direct synthesis method is adopted, and a template agent, accurately-blended raw materials and a fine preparation process are ingeniously utilized to generate a large mesoporous structure in one step. According to the innovative method, the operation process is greatly simplified, the process difficulty is reduced, the microstructure and performance of the zeolite can be more accurately controlled, and a road is broadened for wide application of the MTW zeolite in the fields of catalysis, adsorption and the like.

Description

Technical Field

[0001] The invention relates to the technical field, and in particular to two types of MTW zeolite nanocrystal aggregates and a preparation method thereof. Background Art

[0002] There are still some problems in the research and application of zeolite materials. On the one hand, the traditional preparation process is difficult to finely control the growth of zeolite grains during the synthesis process of MTW zeolite due to the lack of accurate and effective guiding means, resulting in uneven shapes and sizes of grains, lack of regularity and consistency. This chaotic and disordered microstructure not only seriously affects the aesthetics of zeolite materials, but also fundamentally restricts the in-depth exploration and expansion of its performance. On the other hand, there are also certain problems in the regulation of pore structure. Previous methods lack systematicity and precision in shaping the pore characteristics of zeolite. Whether it is the total pore volume, mesoporous volume or average pore size, it is difficult to accurately customize according to actual needs, and often a situation of losing one thing while focusing on another occurs. Especially when preparing MTW zeolite with large mesoporous properties, one either relies on the cumbersome and complicated process of adding pore-forming agents, which can easily cause compatibility problems and lead to unstable material properties; or adopts the means of alkaline corrosion of the zeolite product, which not only opens the pores but also causes unpredictable damage to the crystal structure of the zeolite, greatly reducing the comprehensive performance of the material such as strength and stability.

[0003] Two types of MTW zeolite nanocrystal aggregates were synthesized with TEA+ and MTEA+, respectively called the first type and the second type. There was no obvious difference in the powder XRD spectra of the two, but the shape and size of the grains were obviously different. When the micron-sized grains of the product were observed with a high-resolution field emission scanning electron microscope, it was found that the size of the crystallites constituting these grains was very small, ranging from 4 to 40 nanometers, and the arrangement and compactness of the nanocrystals constituting the two were significantly different. Although the BET surface area determined by the low-temperature nitrogen adsorption method was not much different, the isotherm shape was obviously different, and the total pore volume, mesopore volume and average pore size were very different, and the former showed large mesoporous properties.

[0004] In addition, existing technologies also face the dilemma of low efficiency and high cost. Moreover, due to the difficulty in achieving precise control, the product yield rate always hovers at a low level and cannot meet the needs of large-scale applications. Summary of the invention

[0005] The present invention proposes two types of MTW zeolite nanocrystal aggregates and preparation methods thereof to solve the problems existing in the background technology. The specific scheme is as follows:

[0006] Two types of nanocrystal aggregates of MTW zeolite, including a) the first type using tetraethylammonium hydroxide as a template; b) the second type using methyltriethylammonium chloride as a template; the reactant raw materials of the first type and the second type both include: sodium aluminate, sodium hydroxide, silica sol and pure water.

[0007] Further, the molar ratio of the reactants of the first type is Na 2 O:Al 2 O 3 :SiO 2 :H 2 O:TEA = 10:1:100:2000:15 - 25; the molar ratio of the reactants of the second type is Na 2 O:Al 2 O 3 :SiO 2 :H 2 O:MTEA = 10:1:100:2000:15 - 20.

[0008] Further, the silica sol includes 30.5% SiO 2 and 0.15% Na 2 O, the sodium aluminate is 95% in concentration, and the sulfuric acid concentration is 98%.

[0009] Preparation method of two types of nanocrystal aggregates of MTW zeolite, the steps specifically include:

[0010] 1) Mix the raw materials of the first type / second type according to the ratio and put them into a pressure-resistant reaction kettle in a homogeneous reactor for hydrothermal reaction:

[0011] 2) Naturally cool the temperature of the homogeneous reactor in step 1) to room temperature, remove the pressure-resistant reaction kettle, pour the product after the raw materials react into a plastic beaker and wash it with deionized water until the pH = 9 - 10, and filter to obtain a product filter cake;

[0012] 3) Place the filter cake obtained in step 2) in a plastic beaker, pour a 0.25M dilute sulfuric acid solution into it at a weight ratio of liquid / filter cake = 8 / 1, stir strongly for 60 minutes, and perform acid treatment on the product filter cake; make a hydrogen form MTW zeolite product;

[0013] 4) Wash the product in step 3) for 5 - 10 minutes and then filter;

[0014] 5) After drying for 10 minutes, put it into a muffle furnace and calcine it at 550°C for 4 to 5 hours to obtain the final product MTW zeolite sample.

[0015] Preferably, the pressure-resistant reactor is placed in a homogeneous reactor and heated to a reaction temperature of 1400° C. under rotation conditions and kept warm for 140 to 160 hours.

[0016] The advantage of the present invention is that when preparing MTW zeolite with large mesoporous properties, traditional methods often require the use of complex and cumbersome process methods such as adding pore-forming agents or alkaline corrosion of zeolite products, which are difficult to accurately control. The present invention takes a different approach and adopts a direct synthesis method, cleverly utilizing templates, precisely formulated raw materials, and sophisticated preparation processes to produce large mesoporous structures in one step. This innovative method not only greatly simplifies the operating process and reduces the difficulty of the process, but also can more accurately control the microstructure and performance of zeolite, paving the way for the widespread application of MTW zeolite in many fields such as catalysis and adsorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0018] Figure 1 The XRD powder diffraction pattern of the first type MTW zeolite synthesized in the present invention;

[0019] Figure 2 The XRD powder diffraction pattern of the second type MTW zeolite synthesized in the present invention;

[0020] Figure 3 These are photos of the first type MTW zeolite of the present invention taken under an electron microscope at different resolutions;

[0021] Figure 4 These are photos of the second type MTW zeolite of the present invention taken under an electron microscope at different resolutions;

[0022] Figure 5 Schematic diagram of adsorption isotherms of two types of nano-MTW zeolite molecular sieve polycrystalline samples synthesized in the present invention. DETAILED DESCRIPTION

[0023] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0025] Note: Test method

[0026] 1. XRD Crystal Phase Identification The crystal phases of the two types of nano MTW zeolite molecular sieve samples synthesized in this invention were identified by using an XD2 type X-ray powder diffractometer from Beijing Purkinje General Instrument Co., Ltd. The scanning range was 5 - 35° / 2θ, and the scanning speed was 4° / 2θ / min.

[0027] 2. XRF Composition Determination The silicon-aluminum chemical compositions SiO 2 、Al 2 O 3 、Na 2 O of the two types of nano MTW zeolites synthesized in this invention were determined by using an S8 TIGER X-ray fluorescence scattering instrument (XRF) from Bruker Co., Germany, and their silicon-aluminum molar ratios (SAR) were calculated.

[0028] 3. SEM Crystal Morphology Observation The crystal grain morphologies of the two types of nano MTW zeolite molecular sieves synthesized, as well as the morphologies, sizes, and arrangement conditions of the nano microcrystals that make up these crystal grains, were observed by using a Phenom Prox type bench-top scanning electron microscope from Phenom Co., Netherlands or a Nova Nano SEM450 type field emission scanning electron microscope from FEI Co., USA, and photos were taken.

[0029] 4. Low-temperature Nitrogen Adsorption The BET specific surface areas of the polycrystalline samples of the two types of nano MTW zeolite molecular sieves synthesized in this invention were tested by using a 3H-2000PS2 static volumetric method specific surface area and pore size analyzer from Beijing Bettersize Instruments Co., Ltd.

[0030] Two types of nano-crystalline aggregates of MTW zeolite, including a) the first type using tetraethylammonium hydroxide as the template agent; b) the second type using methyltriethylammonium chloride as the template agent; the reactant raw materials of the first type and the second type both include: sodium aluminate, sodium hydroxide, silica sol, and pure water.

[0031] Furthermore, the molar ratio of the reactants of the first type is Na 2 O:Al 2 O 3 :SiO 2 :H 2 O:TEA = 10:1:100:2000:15 - 25; the molar ratio of the reactants of the second type is Na 2 O:Al 2 O 3 :SiO 2 :H 2 O:MTEA = 10:1:100:2000:15 - 20.

[0032] Furthermore, the silica sol includes 30.5% SiO 2 and 0.15% Na 2O, the sodium aluminate has a concentration of 95%, and the sulfuric acid has a concentration of 98%.

[0033] I. Preparation method of the first type of nanocrystal aggregate of MTW zeolite: The water content in the ratio is changed to 15, 20, and 25 respectively, and the synthesized products are marked as A1, A2, and A3 respectively. The steps specifically include:

[0034] 1) Mix the first type of raw materials according to the ratio and put them into a pressure-resistant reactor in a homogeneous reactor for hydrothermal reaction;

[0035] 2) Naturally cool the temperature of the homogeneous reactor in step 1) to room temperature, remove the pressure-resistant reactor, pour the product after the reaction of the raw materials into a plastic beaker, wash it with deionized water until the pH = 9 - 10, and filter to obtain a product filter cake;

[0036] 3) Place the filter cake obtained in step 2) in a plastic beaker, pour a 0.25M dilute sulfuric acid solution into it at a weight ratio of liquid / filter cake = 8 / 1, stir strongly for 60 minutes, perform acid treatment on the product filter cake, replace the sodium ions contained in it with hydrogen ions in sulfuric acid, and make a hydrogen-form MTW zeolite product;

[0037] 4) Wash the product in step 3) for 5 - 10 minutes and then filter it;

[0038] 5) After drying for 10 minutes, put it into a muffle furnace and calcine it at 550 °C for 4 to 5 hours to remove the organic amines and moisture contained in it, and finally obtain the MTW zeolite samples A1, A2, and A3.

[0039] Preferably, the pressure-resistant reactor is placed in a homogeneous reactor and heated to the reaction temperature of 140 °C and kept warm for 140 hours under the condition of rotation.

[0040] II. Preparation method of the second type of nanocrystal aggregate of MTW zeolite: The water content in the ratio is changed to 15 and 20 respectively, and the synthesized products are marked as B1 and B2 respectively. The steps specifically include:

[0041] 1) Mix the second type of raw materials according to the ratio and put them into a pressure-resistant reactor for hydrothermal reaction;

[0042] 2) Naturally cool the temperature of the homogeneous reactor in step 1) to room temperature, remove the pressure-resistant reactor, pour the product after the reaction of the raw materials into a plastic beaker, wash it with deionized water until the pH = 9 - 10, and filter to obtain a product filter cake;

[0043] 3) Place the filter cake obtained in step 2) in a plastic beaker, pour in a dilute sulfuric acid solution with a concentration of 0.25 M at a weight ratio of liquid / filter cake = 8 / 1, and stir strongly for 60 minutes to perform acid treatment on the product filter cake, so that the sodium ions contained therein are replaced by hydrogen ions in sulfuric acid to produce a hydrogen form MTW zeolite product;

[0044] 4) After washing the product in step 3) for 5 - 10 minutes, perform filtration;

[0045] 5) After drying for another 10 minutes, place it in a muffle furnace and calcine at 550 °C for 4 to 5 hours to remove the organic amines and moisture contained therein, thus obtaining the final product MTW zeolite B1 and B2 samples.

[0046] Preferably, the pressure-resistant reactor is placed in a homogeneous reactor and heated to the reaction temperature of 140 °C under rotation conditions and kept warm for 160 hours.

[0047] After the synthesized sodium form product is washed and dried, its crystal phase is tested by an XD2 type X-ray powder diffractometer to be pure MTW type zeolite, and the pattern is shown in Figure 1 A1, A2, A3 in Figure 2 and B1, B2 in 2 SiO 2 O 3 Na 2 O, Fe 2 O 3 The weight percentage content of, and the molar ratio (SAR) value is calculated from the percentage content of SiO 2 Al 2 O 3

[0048] The dried sodium form product is observed by a bench-top scanning electron microscope or a field emission scanning electron microscope respectively for the crystal grain morphology, the nano-crystal morphology, size, arrangement, etc. that make up its crystal grains, and photos are taken.

[0049] Product chemical composition

[0050] The silicon-aluminum chemical composition, SiO 2 Al 2 O 3 Na 2 O, the percentage content and the calculated silicon-aluminum molar ratio (SAR) of the first type, i.e., type A and the second type, i.e., type B MTW zeolite products, are shown in Table 1 (Chemical composition of synthesized MTW zeolite products).

[0051] ​It can be seen from the data in Table 1 that the SAR of both type A and type B MTW zeolites are around 100, belonging to high-silicon zeolites. Since the samples tested were not treated with dilute acid, the Na and iron contents were slightly higher, ranging from 0.6% to 1.1% and 0.010 to 0.013% respectively.

[0052]

[0053]

[0054] Table 1

[0055] XRD phase identification

[0056] The powder XRD diffraction spectrum of the A-type MTW zeolite synthesized using tetraethylammonium hydroxide as the template is shown in Figure 1 It can be seen that the number and peak positions of the diffraction peaks of the product MTW zeolite A1, A2, and A3 samples are the same, and they are pure phase MTW zeolite without any impurities.

[0057] The powder XRD diffraction spectrum of the second type MTW zeolite synthesized using methyltriethylammonium chloride as template is shown in Figure 2 It can be seen that the number and peak positions of the diffraction peaks of the product MTW zeolite B1 and B2 samples are the same, and are basically the same as the first type products A1, A2, and A3. They are pure phase MTW zeolite without any impurities.

[0058] Crystal observation

[0059] The first type of MTW zeolite was photographed with a Phenom Prox desktop scanning electron microscope from Phenom of the Netherlands at a resolution of 5 microns and a lower resolution of 1 micron. It can be seen that the grain size is relatively uniform, with micro-grains of about 1 micron (see Figure 3 The surface of the first type of MTW zeolite photographed by the Nova Nano SEM450 field emission scanning electron microscope of FEI Company in the United States is very rough; the micro-crystals of the first type of MTW zeolite at a higher resolution of 500 nanometers and 100 micrometers are actually composed of millet-like nanocrystals of about 10 nanometers. These nano-crystals are piled up irregularly, and there are large gaps between the nano-particles (see Figure 3 (bottom two pictures).

[0060] The photos of the second type of MTW zeolite taken with a Phenom Prox desktop scanning electron microscope from Phenom of the Netherlands at a resolution of 5 microns and a lower resolution of 1 micron show that the rice-like grain size is relatively uniform, with micro-grains of about 5 microns (see Figure 4The following two figures) The surface is relatively rough with fine parallel lines; the microcrystals of the second type of MTW zeolite taken by the FEI Nova Nano SEM 450 field emission scanning electron microscope in the United States at a resolution of 500 nanometers and 100 microns are actually aggregated by nanocrystals in the shape of rice grains about 10 nanometers in size arranged nearly parallel. These nanocrystals are stacked relatively regularly with small gaps between particles and are relatively compact (see Figure 4 the following two figures).

[0061] Adsorption properties

[0062] The adsorption isotherms of the polycrystalline samples of the two types of nano-MTW zeolite molecular sieves synthesized in this invention were tested by the 3H-2000PS2 static volumetric method specific surface area and pore size analyzer of Beijing Beishide Instrument Co., Ltd. See Figure 5 . It is very obvious that Figure 5 The nitrogen adsorption isotherms of samples A1, A2, and A3 above all show type I, which is the characteristic of micropore adsorption. However, in the high partial pressure range where the partial pressure P / P0 is greater than 0.50, the adsorption isotherm obviously goes up, and the desorption isotherm does not coincide with the adsorption isotherm, and there is a very obvious large hysteresis loop between them, which is proof that there are mesopores in this microporous material. In contrast, the nitrogen adsorption isotherms of the polycrystalline samples of the second type of MTW zeolite (see Figure 5 the nitrogen adsorption isotherms of B1 and B2 below), do not show an obvious increase in the high partial pressure range where the partial pressure P / P0 is greater than 0.50, and the adsorption isotherm basically coincides with the desorption isotherm, indicating that there are no particularly obvious mesopores in this microporous material.

[0063] The adsorption data of two different types of MTW zeolites calculated and automatically printed out by the 3H-2000PS2 static volumetric method specific surface area and pore size analyzer based on the low-temperature nitrogen adsorption and desorption properties of the samples are listed in Table 2. Two different mesoporous structure MTW zeolites: their BET surface area, micropore volume, and micropore specific surface area data do not have substantial differences. However, from the following data:

[0064] The first type: the total pore volume is 0.32 - 0.36 cm3 / g, the mesopore volume is 0.22 - 0.25 cm3 / g, and the average pore size is 3.33 - 3.38 nanometers;

[0065] The second type: the total pore volume is 0.10 - 0.17 cm3 / g, the mesopore volume is 0.032 - 0.034 cm3 / g, and the average pore size is 1.90 - 1.91 nanometers;

[0066] The total pore volume and average pore diameter of the first type of MTW zeolite are twice as high as those of the second type, and the mesopore volume is nearly an order of magnitude higher, which is sufficient to show that the first type belongs to large mesoporous MTW zeolite and the second type belongs to small mesoporous zeolite. Producing large mesopores by this direct synthesis method is simpler and easier to operate than adding pore-forming agents or alkaline etching of zeolite products in the prior art.

[0067]

[0068] Table 2

[0069] So far, the technical solution of the present invention has been described in conjunction with the preferred embodiments shown in the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. Two types of MTW zeolite nanocrystal aggregates, characterized by: Including a) the first type uses tetraethylammonium hydroxide as a template; b) The second type uses methyltriethylammonium chloride as a template; the reactant raw materials of the first type and the second type both include: sodium aluminate, sodium hydroxide, silica sol and pure water.

2. The two types of MTW zeolite nanocrystal aggregates according to claim 1, characterized in that: The molar ratio of the first type of reactants is Na2O:Al2O3:SiO2:H2O:MTEA=10:1:100:2000:15-25; the molar ratio of the second type of reactants is Na2O:Al2O3:SiO2:H2O:MTEA=10:1:100:2000:15-20.

3. The two types of MTW zeolite nanocrystal aggregates according to claim 1, characterized in that: The silica sol includes SiO2 and Na2O at a concentration of 30.5%, the sodium aluminate has a concentration of 95%, and the sulfuric acid has a concentration of 98%.

4. A method for preparing two types of MTW zeolite nanocrystal aggregates, characterized in that: The steps include: 1) mixing the first type / second type raw materials according to a ratio and placing them in a pressure-resistant reactor in a homogeneous reactor for hydrothermal reaction; 2) The temperature of the homogeneous reactor in step 1) is naturally cooled to room temperature, the pressure-resistant reactor is removed, the product after the raw material reaction is poured into a plastic beaker, washed with deionized water to a pH of 9-10, and filtered to obtain a product filter cake; 3) placing the filter cake obtained in step 2) in a plastic beaker, pouring a 0.25M dilute sulfuric acid solution into the beaker at a weight ratio of liquid / filter cake = 8 / 1, stirring vigorously for 60 minutes, and subjecting the product filter cake to acid treatment to obtain a hydrogen-form MTW zeolite product; 4) washing the product in step 3) for 5-10 minutes and then filtering; 5) After drying for another 10 minutes, the sample was placed in a muffle furnace and calcined at 550° C. for 4 to 5 hours to obtain the final product MTW zeolite sample.

5. The method for preparing two types of MTW zeolite nanocrystal aggregates according to claim 4, characterized in that: The pressure-resistant reactor is placed in a homogeneous reactor and heated to a reaction temperature of 1400° C. under a rotating condition and kept warm for 140 to 160 hours.

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