CN101172617A - The method for synthesizing nanometer type A molecular sieve - Google Patents

Abstract

The invention discloses a method for synthesizing nano-type A molecular sieves, in particular to a method for rapidly synthesizing nano-type A molecular sieves by ultrasonic crystallization under low temperature conditions without a template agent; the method is to dissolve NaOH in water first, and then add Aluminum source, stir and dissolve to obtain solution A; then slowly add silicon source dropwise to A, stir vigorously for several hours to obtain solution B, put solution B in a low-temperature water bath at 20-60°C for ultrasonic crystallization for 10-60min, The product crystallized by ultrasonic waves is washed, filtered and dried to finally obtain nano-type A molecular sieve; the method is very simple to operate, the synthesis temperature is low, the synthesis time is short, and the particles of the obtained nano-type A molecular sieve are uniform.

Description

The method for synthesizing nanometer type A molecular sieve

technical field

The invention relates to a method for synthesizing A-type molecular sieves, in particular to a method for rapidly synthesizing relatively uniform spherical nano-type A molecular sieves under low temperature conditions.

Background technique

Nano-scale molecular sieves have excellent properties unmatched by conventional molecular sieves and are widely used. Therefore, the synthesis and application of nano-molecular sieves is one of the current research hotspots. At present, the methods for preparing molecular sieves at home and abroad mainly include conventional hydrothermal method (no template agent and organic template) (Petrochemical Industry, 2005, 34: 1099-1102), microwave method (Catal.Today, 1998, 44: 301-308) , Space Confinement Method (Chemical Communication, 1999, 673~674), Vapor Phase Method (Daily Chemical Industry, 2003, 33: 295~297), etc. The conventional template-free hydrothermal method consumes energy, takes a long time to react, and the crystal grains obtained are large and uneven (1-10 μm). This method is not suitable for the preparation of nano-sized molecular sieves.

Microwave synthesis is also a method for rapid synthesis of molecular sieves that has emerged in recent years, and the particle size of its synthesized products is also relatively small. SlangenPM (Microp. Mater., 1997, 9: 259-265) et al. rapidly synthesized several hundred nanometers of 4A molecular sieves at 100°C by microwave method after aging at different room temperatures.

The space limitation method is to restrict the continued growth of grains through a crystallization inert medium. This method is to remove the inert medium (such as carbon black and starch) that restricts grain growth at high temperature, and at the same time, it will cause the growth of nanocrystals. reunion. Iver Schmidt (Inorg.Chem.2000, 39: 2279-2283) and others synthesized tens of nanometer zeolite molecular sieves by this method.

The vapor phase method is to make the prepared precursor into a cake, put it in a system with a support at the bottom that can put a solvent and can be sealed, and react at a certain temperature. The synthesis of this method consumes more energy and time, and the crystal grains of the product are several microns. Yang Yili et al. used this method to synthesize 4A molecular sieves with sample particle size distribution <4 μm at 100 °C. In addition, nano-sized molecular sieves can be synthesized at room temperature. Svetlana (Science, 1999, 183: 958-960) and others have synthesized nano-sized 4A molecular sieves, but the reaction cycle is very long, and a certain amount of organic templates need to be added.

Ultrasonic method is also a rapid synthesis method that has emerged in recent years. It is a new interdisciplinary subject that uses acoustic cavitation energy to accelerate and control chemical reactions, increase reaction yields, and initiate new chemical reactions. Acoustic cavitation refers to the activation of micro-bubble nuclei in a liquid under the action of sound waves, which manifests as a series of dynamic processes such as oscillation, growth, shrinkage and even collapse of the nuclei. In a very short time when the cavitation bubble collapses, a high temperature of 1900-5200 K and a high pressure of more than 50 MPa will be generated in the small space around it, and the temperature change rate is as high as 10 ⁹ K/s, accompanied by strong Shock waves and jets with speeds up to 400km/h. These conditions are sufficient to open the strong chemical bonds (376.8 ~ 418.6kJ/mol), and promote the "aqueous combustion" (aqueouscombustion) reaction. Such micro-bubble nuclei can be formed by attaching to solid impurities, fine dust or the surface of the container and micro-bubbles or bubbles in the crevices, and the precipitation of gas in the micro-area where the strength of the liquid is weakened due to uneven structure. There are many domestic and foreign reports on the preparation of powder materials by ultrasonic waves (Nonferrous Metals, 2001, 53:81-83), but there are very few domestic and foreign reports on the use of ultrasonic waves to synthesize molecular sieves. Zhong Shengliang (Acta Chemical Journal of Chinese Universities, 2005, 26: 1603-1606) and others used ultrasonic waves to quickly synthesize 4A molecular sieves with an average particle size of 280nm. /twenty four.

The existing synthesis methods all have their own disadvantages: either high reaction temperature, long crystallization time, or adding an organic template agent, or adding an inert space-limited medium, or prolonging the aging time. In view of this, this patent adopts ultrasonic method to synthesize nano-type A molecular sieve.

Contents of the invention

The invention provides a method for synthesizing nano-type A molecular sieves, in particular to a method for rapidly synthesizing nano-type A molecular sieves without a template agent by ultrasonic crystallization under low temperature conditions. Dissolve NaOH in water, then add aluminum source, stir and dissolve to obtain solution A; then slowly add silicon source to A, and stir vigorously for several hours to obtain solution B, the molar ratio of which is Na ₂ O:SiO ₂ :Al ₂ O ₃ : H ₂ O=5～10:2.0～3.0:1:90～220, put solution B in a low-temperature water bath at 20～60°C for ultrasonic crystallization for 10～60min, wash the product of ultrasonic crystallization, and filter , and dried to obtain nano-type A molecular sieves.

The pH of the NaOH alkali solution is >14. The aluminum source is aluminum sulfate, aluminum nitrate, aluminum isopropoxide, sodium metaaluminate or sodium aluminate. The silicon source is water glass, tetraethyl orthosilicate, silicic acid, silicon dioxide or silica sol. The power of the ultrasound is 120W. The particle size of the synthesized nano-type A molecular sieve is evenly 20-100nm. The operation of the method is very simple and easy, the synthesis temperature is low, the synthesis time is short, and the particles of the obtained spherical nano-type A molecular sieve are uniform.

The beneficial effects of the present invention are: the synthesis method of the present invention does not need to add organic templates or space-limiting agents, does not require aging, has low reaction temperature, short crystallization time, and is very simple and quick to operate.

Description of drawings

Figure 1 is an X-ray diffraction (XRD) pattern of type A molecular sieve.

Fig. 2 is a transmission electron microscope (TEM) photograph of type A molecular sieve.

Detailed ways

Example 1

Weigh 21.0g of sodium hydroxide, dissolve it in 80.0g of water, then add 11.0g of sodium aluminate to dissolve until clear, then add dropwise 30.0g of silica sol, stir vigorously for 6-18 hours, and ultrasonically in a water bath at 20-60°C Crystallize for 10-60 minutes, and finally wash repeatedly with 0.01mol/L sodium hydroxide solution, filter, and dry to obtain nano-type A molecular sieve.

Example 2

Weigh 30.5g of sodium hydroxide, dissolve it in 200.0g of water, then add 16.0g of sodium aluminate to dissolve until clear, then add dropwise 38.0g of silica sol, stir vigorously for 6-18 hours, and ultrasonically in a water bath at 20-60°C Crystallize for 10-60 minutes, and finally wash repeatedly with 0.01mol/L sodium hydroxide solution, filter, and dry to obtain nano-type A molecular sieve.

Example 3

Weigh 40.0g of sodium hydroxide, dissolve it in 200.0g of water, then add 18.0g of sodium aluminate to dissolve until clear, then add dropwise 49.0g of silica sol, stir vigorously for 6-18h, and ultrasonically in a water bath at 20-60°C Crystallize for 10-60 minutes, and finally wash repeatedly with 0.01mol/L sodium hydroxide solution, filter, and dry to obtain nano-type A molecular sieve.

Example 4

Weigh 35.6g of sodium hydroxide, dissolve it in 160.0g of water, then add 14.0g of sodium aluminate to dissolve until clear, then add dropwise 31.5g of silica sol, stir vigorously for 6-18 hours, and ultrasonically in a water bath at 20-60°C Crystallize for 10-60 minutes, and finally wash repeatedly with 0.01mol/L sodium hydroxide solution, filter, and dry to obtain nano-type A molecular sieve.

Claims (6)

1. a method for synthesizing nanometer A type molecular sieve, its step comprises: (a) Dissolve NaOH in water to make it clear; (b) adding the aluminum source to the solution prepared in (a), stirring to make it clear; (c) Add the silicon source dropwise to the solution prepared in (b), and stir for 6-18 hours to form a white gel, the molar ratio of which is Na ₂ O:SiO ₂ : _{Al 2} O ₃ : _{H 2} O=5-10 :2～3:1:90～220; (d) Ultrasonic crystallize the gel obtained in (c) at a low temperature of 20-60° C., wash, filter, and dry to obtain nano-type A molecular sieves. 2. The synthetic method according to claim 1, characterized in that the pH of the alkaline solution in (a)>14. 3. The synthetic method according to claim 1, characterized in that the aluminum source in (b) is aluminum sulfate, aluminum nitrate, aluminum isopropoxide, sodium metaaluminate or sodium aluminate. 4. The synthetic method according to claim 1, characterized in that in the described (c), the silicon source is water glass, tetraethyl orthosilicate, silicic acid, silicon dioxide or silica sol. 5. The synthesis method according to claim 1, characterized in that the ultrasonic crystallization time in the step (d) is 10 to 60 min, and the ultrasonic power is 120W. 6. The synthesis method according to claim 1, characterized in that the synthetic nano-type A molecular sieve particles are evenly 20-100nm.

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