CN108751222A - A kind of preparation method and its acoustic applications of the MFI molecular sieves with interaction twin pattern - Google Patents

Abstract

A preparation method of MFI molecular sieve with alternating twin crystal morphology and its acoustic application, the preparation process is characterized by adding fluorine salts to the synthetic silicon source and aluminum source to form silica-alumina-tetraalkylammonium structure-oriented Agent-fluorine salt-water-alkali-alcohol sol system, the sol is synthesized under hydrothermal conditions for 5-240 hours at a temperature of 50-220°C, and molecular sieves with high crystallinity can be obtained after separation, washing, drying and roasting The product, molecular sieve crystal grains are monodisperse, its silicon-aluminum ratio can be adjusted in the range of 10-∞, and the size range can be adjusted in the range of 0.5-50 microns. The molecular sieve prepared by the present invention has regular pores, few defects, high micropore surface area, good crystallinity, good stability, and high yield. The low-frequency resonance frequency in the speaker can be applied to improve the acoustic performance of the speaker in portable electronic equipment.

Description

Preparation method and acoustics of a MFI molecular sieve with alternating twin crystal morphology application

technical field

The present invention relates to the preparation and acoustic application of molecular sieves with alternating twin morphology, in particular to the preparation of molecular sieves of MFI structure with alternating twin morphology with a grain size in the range of 0.5-50 microns and a silicon-aluminum ratio of 10-∞ Technology, especially related to the application of molecular sieves with intertwined crystal morphology in the field of acoustics, belonging to the field of preparation and application of molecular sieve materials.

Background technique

With the trend of thinner and more flexible electronic devices such as mobile phones, tablet computers, and LCD TVs, people have put forward higher and higher requirements for high-quality acoustic effects of speakers. However, due to the small size of the micro-speakers in such portable and thin electronic devices, there are inherent defects in reproducing low frequencies. Filling the limited rear cavity with sound-absorbing or microporous materials, especially molecular sieve materials, has the characteristics of high stability and uniform distribution of micropores, which can increase the volume of the sound cavity and improve the low-frequency reproduction performance of the speaker. Patent CN103098480A invented a loudspeaker device, which can effectively move the resonance frequency to low frequency with molecular sieve as the filling material. The shape and uniformity of the particles were discussed. Patent CN105872920A reports that molecular sieves such as Silicalite-1, ZSM-5, MCM-41, SBA-15 and ordered mesoporous carbon CMK-3 are used as sound-absorbing materials for speakers to make the resonance space virtual increase, but the particle size is not adjusted. , morphology and homogeneity on the attraction performance to be discussed. Particles with different morphologies have a significant impact on the packing behavior of molecular sieves and the pores between particles, which will further affect the sound-absorbing performance of molecular sieves.

Molecular sieve materials are a very important family of inorganic microporous crystal materials, widely used in ion exchange, adsorption separation, catalysis and other fields. MFI type molecular sieve is a SiO ₂ crystal containing two intersecting channels, the pore diameter is about 0.55nm, and its skeleton Si/Al ratio can be adjusted from the all-silicon type to the aluminum-containing type (ie ZSM-5). In 1978, Flanigen and others synthesized Silicalite-1 for the first time, that is, all-silicon MFI molecular sieve. The traditional synthesis of MFI molecular sieve crystals is synthesized by tetrapropylammonium hydroxide (TPAOH) as a structure-directing agent (SDA) under hydrothermal conditions. OH ^- is also a mineralizer for the synthesis of zeolite molecular sieves. play an important role. OH ^- as a mineralizer can dissolve more silicate. When the OH ^- concentration is higher, a large amount of silica-alumina gel is dissolved and more crystal nuclei are formed.

In addition to the alkali system, in 1978, EM Flanigen et al. (Nature, 1978, 271, 512-516 ⁾ introduced F- into the synthesis system under hydrothermal conditions for the first time. This synthetic strategy opened a new path for the synthetic history of molecular sieves. F ^- When used as a mineralizer in the synthesis of molecular sieves, the reaction can be carried out under neutral or acidic conditions. F ^- can lead to the formation of double four-membered rings, and it is easier to obtain an open low-density framework structure. At the same time, F ions It can balance template cations and reduce defects of zeolite molecular sieves. ACVoegtlin et al. (Microporous Mater, 1997, 9, 95-105) believed that under the condition of no F- ^, the negative charges formed by the defects of the framework generally balance the cations. In the fluoride system, silicon and aluminum exist as SiF ₆ ^2- and AlF ₆ ^3- complexes, which change the reaction path and process, thereby changing the morphology of the sample. Benoit Louis et al. (Microporous Mesoporous Mater, 2004, 74, 171–178) reported the effect of F/Si on the morphology of molecular sieves in the TPABr-TEOS-NaAlO ₂ -NH ₄ FH ₂ O system, and found that F/Si ranged from 0.3 to 1.6. The grain size of ZSM-5 molecular sieve increases from 10μm to 75μm, the surface area changes from 60m ² /g to 350m ² /g, and the crystallinity also increases. Patents US3839539A and CA976324A1 reported that fluorine-containing high-activity HX, HY and A-type zeolite molecular sieves were prepared by directly adding ammonium fluoride silicon into the synthetic sol. The prepared zeolite molecular sieves had higher thermal stability and specificity than those prepared by traditional methods. surface area. Patent CN101837990A reports a method of directly adding a fluorine source to a synthetic sol, and directly preparing a fluorine-containing all-silicon MFI zeolite molecular sieve through a hydrothermal synthesis method.

Usually, changes in synthesis parameters such as reaction time, temperature, pH, stirring time and strength will have certain effects on the size, shape and degree of aggregation of molecular sieve crystals. Traditionally synthesized MFI molecular sieve crystals are synthesized by using tetrapropylammonium hydroxide (TPAOH) as structure directing agent (SDA) under hydrothermal conditions. The typical MFI-type molecular sieve crystals synthesized under hydrothermal conditions with TPAOH as a structure-directing agent have a "Coffin (coffin)" shape, and the crystals have longer dimensions in the c-axis direction, while the a-axis and b-axis directions Relatively short in size. In order to study the shape and size changes of Si-MFI crystals in more detail, Jaouad Arichi and Benoit Louis (Crystal Growth Design, 2008, 8, 3999) used traditional hydrothermal synthesis in the presence of fluoride ions to obtain Si-MFI crystals with different morphologies. ZSM-5 zeolite molecular sieve. By changing the F/Si ratio, silicon source, and reaction time, MFI zeolite molecular sieves with star-like and hedgehog-like morphologies were obtained. FlavianoTesta et al. (Microporous and Mesoporous Materials, 2003, 57, 57) synthesized Fe-doped Silicalite-1 molecular sieves with different morphologies using different fluorine sources as additives. At present, there is still a lack of mature methods for effectively obtaining monodisperse molecular sieves with alternating twin crystal morphology, and a wide range of controllable particle size and silicon-aluminum ratio, which limits the development of molecular sieves in the field of acoustics. Applications.

The invention provides a preparation process of monodisperse molecular sieve particles with adjustable particle size (0.5-50 microns) and silicon-aluminum ratio (10-∞) and intertwined crystal morphology. The molecular sieve particles prepared with alternating twin crystal morphology have good monodispersity, uniform shape, regular channels, less surface defects, large micropore surface area, high porosity, good crystallinity and good thermal stability. Features, it shows excellent performance in the test of sound absorption characteristics.

Contents of the invention

The purpose of the present invention is to provide a process with short process steps and less waste, and a process for preparing MFI molecular sieves with intertwined crystal morphology. The process can obtain monodisperse MFI molecular sieve particles with adjustable particle size and skeleton composition. The SiO ₂ -TXAOH-TPAY-MF-H ₂ O system of the fluorine source was directly added to the sol of the synthetic zeolite molecular sieve, and the fluorine-containing intertwined crystal morphology was prepared by the hydrothermal synthesis method at a temperature of 50-220 °C in one step. MFI zeolite molecular sieve. Specifically, its preparation steps are:

(1) The template agent tetraalkylammonium template (TXAOH or TPAY), silicon source (calculated as SiO ₂ ), aluminum source (calculated as Al ₂ O ₃ ), fluorine source (MF), water, alkali (MOH) , Alcohol (XOH) is mixed in a specific ratio and in the order of addition, the silicon source is added at a rate of 0.1-100g/min, and mixed and stirred at room temperature to form a stable sol, stirred and aged for 0.5-36 hours, the formed SiO ₂ -Al ₂ The molar ratio of each component in the O ₃ -TXAOH-TPAY-MF-MOH-H ₂ O-XOH sol system is: SiO ₂ /Al ₂ O ₃ =10-∞; MF/SiO ₂ =0-1.5; TXAOH/SiO ₂ =0-1.0; TPAY/SiO ₂ =0-1.0; H ₂ O/SiO ₂ =5-50; MOH/SiO ₂ =0-5.0; XOH/SiO ₂ =0-5.0.

The preferred range is:

SiO ₂ /Al ₂ O ₃ =20-∞; MF/SiO ₂ =0-1.0; TXAOH/SiO ₂ =0-0.5; MOH/SiO ₂ =0-5.0; TPAY/SiO ₂ =0-0.5; H ₂ O/SiO ₂ =5-25; XOH/SiO ₂ =0-2.0.

(2) The above-mentioned aged sol is placed in a reaction vessel with the function of realizing hydrothermal high temperature and high pressure, such as a reaction kettle or a crystallization kettle, and then the container is placed in an oven preheated to 50-220°C for 5-240°C crystallization. Hour. After the reaction is completed, the reaction product is separated by suction filtration, centrifugation, pressure filtration or flash evaporation, and washed with distilled water several times until neutral. After drying, put it into a muffle furnace at 500-650°C and bake for 1-6 hours to remove the template agent, and the MFI molecular sieve with alternating twin crystal morphology can be obtained. In the present invention, when synthesizing the MFI zeolite molecular sieve with intertwined crystal morphology, the preferred range of hydrothermal synthesis temperature is 90-180° C., and the preferred range of synthesis time is 10-120 hours.

(3) The MFI-type molecular sieve particles obtained above with an intertwined crystal morphology are filled in a cavity with a fixed volume, placed behind a micro-speaker, and its acoustic absorption performance is tested with a signal analyzer. Tests show that MFI molecular sieve particles with alternating twin crystal morphology can significantly reduce the low-frequency resonance frequency F ₀ , and the reduction value is between 51.8-60.8 Hz.

Further, the silicon source mentioned above is tetraethyl silicate or tetrabutyl silicate or white carbon black or silica sol or silicon wafer, and the aluminum source is alumina or aluminum isopropoxide or aluminum fluoride.

Further, the fluorine source mentioned above is ammonium fluoride or hydrofluoric acid or sodium fluoride or potassium fluoride and other fluorine-containing inorganic or organic salts.

Further, one of the above-mentioned tetraalkylammonium templating agents includes an alkyl group with a carbon chain number of 1-16, an anion that is OH- ^, or both types include an alkyl group with a carbon chain number of 1-16, The anion is Br ^- or Cl ^- or F ^- .

Further, the above-mentioned type of alkali is sodium hydroxide or lithium hydroxide or potassium hydroxide.

The method for synthesizing an MFI zeolite molecular sieve with an intertwined crystal morphology provided in the present invention has a simple preparation process and mild conditions, which can save the tedious follow-up treatment process in the preparation of the zeolite molecular sieve, and save preparation steps and time. Moreover, the prepared MFI zeolite molecular sieve with alternating twin crystal morphology has a large number of micropores and a large specific surface area. In addition to being used in the field of sound absorption, it can also be used in catalytic cracking, etherification reaction, adsorption and separation of hydrocarbon oil raw materials. In the fields of separation of organic vapor and other gases and liquid mixtures, ion exchange and membrane reactors.

The MFI type molecular sieve material prepared by the present invention has regular pores, fewer defects, higher micropore surface area, crystallinity and yield, and at the same time shows better thermal stability in high temperature tests, so it can bring to better economic returns.

Description of drawings

Figure 1 is the X-ray diffraction pattern of the molecular sieve with alternating twin morphology synthesized in Example 1.

Fig. 2 is a scanning electron micrograph of the molecular sieve with alternating twin crystal morphology synthesized in Example 1.

Figure 3 is the X-ray diffraction pattern of the molecular sieve with alternating twin morphology synthesized in Example 2.

Fig. 4 is a scanning electron micrograph of the molecular sieve with alternating twin crystal morphology synthesized in Example 2.

Fig. 5 is an X-ray diffraction pattern of the molecular sieve with alternating twin morphology synthesized in Example 3.

Fig. 6 is a scanning electron micrograph of the molecular sieve with alternating twin crystal morphology synthesized in Example 3.

Fig. 7 is the X-ray diffraction pattern of the molecular sieve with alternating twin morphology synthesized in Example 4.

Fig. 8 is a scanning electron micrograph of the molecular sieve with alternating twin crystal morphology synthesized in Example 4.

Fig. 9 is a schematic diagram of a speaker module for testing molecular sieve particles.

Detailed ways

The following application examples further illustrate the present invention, but the patent rights are not limited to these examples, practitioners in this industry can obtain similar structures based on the spirit and methods of the present invention through reasonable condition optimization and combination, and based on this Development is also within the scope of protection of this patent:

Example 1

The step of preparing fluorine-containing intertwined crystal MFI zeolite molecular sieve by one-step method, (1) template agent tetrapropylammonium bromide (TPABr), silica sol, sodium metaaluminate (NaAlO ₂ ), sodium hydroxide (NaOH) Mix and dissolve with an appropriate amount of water, add the silica sol at a rate of 5g/min, and mix and stir at room temperature to form a stable sol, stir and age for 6 hours, each of the formed SiO ₂ -NaAlO ₂ -TPABr-NaOH-H ₂ O sol system The molar ratio of the components is: SiO ₂ /Al ₂ O ₃ =0.02, TPABr/Si0 ₂ =0.05, NaOH/Si0 ₂ =0.2, H ₂ O/Si0 ₂ =40; The reaction kettle was placed in a stainless steel reactor lined with tetrafluoroethylene, and then placed in an oven preheated to 170°C for crystallization for 24 hours. After the reaction was completed, the reaction solution had obvious stratification. The reaction product was separated by suction filtration, washed to neutrality, dried, and put into a muffle furnace for 6 hours at 550°C to remove the template agent to obtain an MFI zeolite molecular sieve with an intertwined crystal morphology. The sample is characterized by XRD. Figure 1 is the XRD diffraction pattern of the synthesized zeolite molecular sieve. It can be seen from the figure that the prepared zeolite molecular sieve exhibits MFI zeolite molecular sieve at diffraction angles 2θ of 7.8°, 8.8°, 23.2°, 23.8° and 24.3°. Typical diffraction peaks. The sample was characterized by scanning electron microscopy (SEM), as shown in Figure 2, showing the morphology of alternating twins with a size of about 5 μm. After the sound absorption test, F ₀ decreased by 56Hz, and ΔF ₀ =56Hz.

Example 2

The synthesis process is as described in Example 1, (1) template agent tetrapropylammonium bromide, white carbon black, sodium hydroxide and appropriate amount of water are mixed and dissolved, and the addition rate of white carbon black is 5g/min, and at room temperature Mix and stir to form a stable sol, stir and age for 12 hours, the molar ratio of each component in the formed SiO ₂ -TPABr-NaOH-H ₂ O sol system is: TPABr/Si0 ₂ =0.2, NaOH/Si0 ₂ =0.2, H ₂ O /Si0 ₂ =20; (2) The above-mentioned aged sol was placed in a polytetrafluoroethylene-lined stainless steel reactor, and then the reactor was placed in an oven preheated to 170°C for crystallization for 24 hours. After the reaction was completed, the reaction solution had obvious stratification. The reaction product was separated by suction filtration, washed until neutral, dried, and put into a muffle furnace at 550°C for 6 hours to remove the template agent to obtain the pure silica MFI zeolite molecular sieve with alternating twin crystal morphology. The sample was characterized by XRD. Figure 3 showed the typical diffraction peaks of MFI zeolite molecular sieve. The sample was characterized by SEM as shown in Figure 4, showing the morphology of alternating twins with a size of about 4-5 μm. After the sound absorption test, F ₀ decreased by 60.8Hz, and ΔF ₀ =60.8Hz.

Example 3

The synthesis process is as described in Example 1, (1) the template agent tetrapropylammonium bromide (TPABr), tetrapropylammonium hydroxide (TPAOH), silica sol, hydrofluoric acid (HF) and appropriate amount of water are mixed and dissolved, The addition rate of silica sol is 5g/min, and mixed and stirred at room temperature to form a stable sol, and aged for 24 hours with stirring, the molar ratio of each component in the formed SiO ₂ -TPAOH-TPABr-HF-H ₂ O sol system is: TPABr /Si0 ₂ ＝0.14, TPAOH/Si0 ₂ ＝0.14, HF/Si0 ₂ ＝0.6, H ₂ O/Si0 ₂ ＝20; (2) The above-mentioned aging sol is placed in a stainless steel reactor lined with polytetrafluoroethylene , and then put the reactor into an oven preheated to 150°C for crystallization for 48 hours. After the reaction was completed, the reaction solution had obvious stratification. The reaction product was separated by suction filtration, washed until neutral, dried, and put into a muffle furnace at 550°C for 6 hours to remove the template agent to obtain the pure silica MFI zeolite molecular sieve with alternating twin crystal morphology. The sample was characterized by XRD. Figure 5 shows the typical diffraction peaks of MFI zeolite molecular sieve. The sample was characterized by SEM as shown in Figure 6, showing the morphology of alternating twins with a size of about 40 μm. After the sound absorption test, F ₀ decreased by 53.2Hz, and ΔF ₀ =53.2Hz.

Example 4

The synthesis process is as described in Example 1, (1) template agent tetrapropylammonium bromide, white carbon black, sodium hydroxide and appropriate amount of water are mixed and dissolved, and the addition rate of white carbon black is 5g/min, and at room temperature Mix and stir to form a stable sol, stir and age for 12 hours, the molar ratio of each component in the formed SiO ₂ -TPAOH-NH ₄ FH ₂ O sol system is: TPAOH/Si0 ₂ =0.2, NH ₄ F/Si0 ₂ =0.1,H ₂ O/Si0 ₂ =25; (2) The above-mentioned aged sol was placed in a polytetrafluoroethylene-lined stainless steel reactor, and then the reactor was placed in an oven preheated to 170°C for crystallization for 24 hours. After the reaction was completed, the reaction solution had obvious stratification. The reaction product was separated by suction filtration, washed until neutral, dried, and put into a muffle furnace at 550°C for 6 hours to remove the template agent to obtain the pure silica MFI zeolite molecular sieve with alternating twin crystal morphology. The sample was characterized by XRD, see Figure 7, showing the typical diffraction peaks of MFI zeolite molecular sieve, and the sample was characterized by SEM, see Figure 8, showing the morphology of alternating twins with a size of about 10 μm. After the sound absorption test, F ₀ decreased by 51.8Hz, and ΔF ₀ =51.8Hz.

The schematic diagram of the loudspeaker module for testing molecular sieve particles in the embodiment of the present invention is shown in Figure 9. The molecular sieve of the present invention is filled in the limited rear cavity of the loudspeaker. Because the molecular sieve material has the characteristics of high stability and uniform micropore distribution, it can achieve increased The effect of the volume of the sound cavity, thereby improving the low-frequency reproduction performance of the speaker.

Claims (10)

1. A method for preparing an MFI molecular sieve with an intertwined crystal morphology, which is characterized in that: adding fluorine salts to the synthetic sol, by adjusting the type and quantity of the fluorine salts added, and hydrothermally preparing a molecular sieve with an intertwined crystal morphology The specific steps are as follows: (1) Mix two templates, tetraalkylammonium template, silicon source, aluminum source, fluorine source, water, and alkali, and the silicon source is added at a rate of 0.1-100g/min , and mixed and stirred at room temperature to form a stable sol, the stirring and aging time is 0.5-36 hours, and each component in the formed SiO ₂ -Al ₂ O ₃ -TXAOH-TPAY-MF-MOH-H ₂ O-XOH sol system The molar ratio is: SiO ₂ /Al ₂ O ₃ =10-∞, MF/SiO ₂ =0-1.5, TXAOH/SiO ₂ =0-1.0; TPAY/SiO ₂ =0-1.0, H ₂ O/SiO ₂ = 5-50, MOH/SiO ₂ ＝0-5.0, XOH/SiO ₂ ＝0-5.0; (2) The sol is hydrothermally synthesized at a synthesis temperature of 50-220°C for 5-240 hours, after separation, cleaning, drying and roasting The MFI zeolite molecular sieve with intertwined crystal morphology was obtained. 2. the preparation method of the MFI molecular sieve with intertwined crystal appearance according to claim 1 is characterized in that: silicon source is tetraethyl silicate or tetrabutyl silicate or white carbon black or silica sol or silicon chip , the aluminum source is alumina or aluminum isopropoxide or aluminum fluoride. 3. the preparation method of the MFI molecular sieve with intertwined crystal morphology according to claim 1, is characterized in that: fluorine source is fluorine-containing inorganic such as ammonium fluoride or hydrofluoric acid or sodium fluoride or potassium fluoride or organic Salt. 4. The method for preparing an MFI molecular sieve with an intertwined crystal morphology according to claim 1, characterized in that: the type of tetraalkylammonium template includes an alkyl group with a carbon chain number of 1-16 and an anion of ^OH- . 5. The method for preparing an MFI molecular sieve with an intertwined crystal morphology according to claim 1, characterized in that: the type of tetraalkylammonium template includes an alkyl group with a carbon chain number of 1-16, and an anion ^of Br- or Cl ^- or F ^- . 6. The preparation method of the MFI molecular sieve with intertwined crystal morphology according to claim 1, characterized in that: the type of alkali is sodium hydroxide or lithium hydroxide or potassium hydroxide. 7. The method for preparing MFI molecular sieves with alternating twin crystal morphology according to claim 1, characterized in that: the molar ratio of each component is: SiO ₂ /Al ₂ O ₃ =20-∞; MF/SiO ₂ =0-1.0; TXAOH/SiO ₂ =0-0.5; MOH/SiO ₂ =0-5.0; TPAY/SiO ₂ =0-0.5; H ₂ O/SiO ₂ =5-25 _; 2.0. 8. the preparation method of the MFI molecular sieve with intertwined crystal morphology according to claim 1 is characterized in that: in step (2), roasting condition is: roasting 1-6 hour in the muffle furnace of 500-650 ℃, with Remove templating agent. 9. The method for preparing MFI molecular sieves with intertwined crystal morphology according to claim 1, characterized in that: the hydrothermal synthesis temperature range is 90-180°C, and the synthesis time is 10-120 hours. 10. The acoustic application of any one of claims 1-8 having an MFI molecular sieve with an alternate twin morphology, characterized in that: the molecular sieve particles with an alternate twin morphology are filled in the rear vibration cavity of a loudspeaker with a fixed volume In the middle, reduce the low-frequency resonance frequency value between 51.8-60.8Hz.