A method for preparing binder-free molecular sieve adsorbents

Abstract

This invention provides a method for preparing a binder-free molecular sieve adsorbent. By introducing a weak organic acid during the molding process, aluminum in the molecular sieve crystal framework can be dissolved, resulting in defects in the molecular sieve crystal structure and the formation of more active and regenerable sites. Then, by impregnating with an alkaline solution, the silicon in the molecular sieve crystal framework is brought into full contact with the alkaline substance. During the high-temperature and high-pressure activation reaction, the silicon in the molecular sieve framework reacts with the alkaline substance, causing local crystal collapse on the surface. During the activation process, the exposed silicon-aluminum components recombine under high-temperature and high-pressure conditions to form an aluminosilicate mineral phase, thereby achieving strong chemical bonding between the molecular sieve powders and forming a binder-free molecular sieve adsorbent with high strength.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve technology, specifically to a method for preparing a binder-free molecular sieve adsorbent. Background Technology

[0002] Molecular sieves, as a class of inorganic porous materials with regular pore structures, have shown broad application prospects in industrial fields such as gas separation, water purification, and catalytic reactions due to their excellent adsorption, ion exchange, and catalytic properties. However, the products obtained by conventional preparation methods such as hydrothermal synthesis and sol-gel methods are all in powder form, which presents many insurmountable limitations in their practical industrial applications.

[0003] From the perspective of industrial equipment operation requirements, molecular sieves in powder form suffer from poor flowability and agglomeration. In common industrial adsorption devices such as fixed beds and fluidized beds, directly filling with molecular sieve powder leads to a sharp increase in bed resistance, making it difficult for gaseous or liquid media to pass uniformly through the bed. This not only reduces adsorption efficiency but may also cause safety hazards such as localized overheating and pressure fluctuations. Furthermore, the powder easily generates dust during transport, causing material loss and adversely affecting the operating environment and the health of operators. In addition, the separation and recovery of powdered molecular sieves are difficult, making continuous and stable operation difficult in dynamic adsorption processes, failing to meet the industrial production requirements for long-term equipment operation and low maintenance costs. Therefore, converting molecular sieve powder into shaped bodies with certain strength, shape, and size is a necessary prerequisite for its industrial application.

[0004] To address the molding problem of molecular sieve powders, the industry has long employed molding processes involving the addition of binders. Common binders include clay (such as kaolin and bentonite), silica sol, alumina sol, and organic polymers (such as polyvinyl alcohol and sodium carboxymethyl cellulose). Among these, clay has become the most widely used binder due to its advantages of wide availability, low cost, and good molding performance. However, while the introduction of binders enables the molding of molecular sieves, it also has a significant negative impact on the adsorption performance of the molecular sieves. This issue has become a key bottleneck restricting the improvement of the industrial application efficiency of molecular sieve materials.

[0005] From a microscopic perspective, during the molding process, the binder inevitably covers the surface of the molecular sieve particles and may even penetrate into the pore structure, causing pore blockage. The adsorption performance of molecular sieves depends on their abundant pore structure and large specific surface area. Pore blockage directly leads to a reduction in effective specific surface area and adsorption sites, thus decreasing adsorption capacity. Taking the commonly used 13X molecular sieve as an example, when 20%-30% clay binder is added, its specific surface area may decrease from the original 700-800 m² / g to 500-600 m² / g, resulting in a 15%-25% decrease in adsorption capacity. Simultaneously, the interfacial bonding between the binder and the molecular sieve particles is weak, making the molded body prone to wear and breakage during use. This leads to changes in bed porosity, further affecting adsorption kinetics and equipment operational stability. Furthermore, some binders may decompose or carbonize during high-temperature activation or regeneration, and the resulting impurities further contaminate the molecular sieve pores, accelerating the decline in adsorption performance and shortening the material's lifespan. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a binder-free molecular sieve adsorbent.

[0007] The technical solution adopted by this invention to solve its technical problem is: A method for preparing a binder-free molecular sieve adsorbent includes the following steps: Step 1, drying the molecular sieve powder at 100°-110°C for later use; Step 2, taking an organic weak acid with a concentration of 5-30%; Step 3, performing pelletizing treatment on the dried molecular sieve powder in a pelletizing pan, spraying in 5-30% organic weak acid during the pelletizing process to promote the pelletizing of the molecular sieve powder; Step 4, allowing the pelletized molecular sieve powder to stand and cure for more than 12 hours, and then placing it in an alkaline solution for static impregnation for 5-30 minutes; Step 5, placing the impregnated molecular sieve powder in a reaction vessel for high-temperature and high-pressure activation reaction to obtain the binder-free molecular sieve adsorbent.

[0008] In one embodiment, the organic weak acid includes, but is not limited to, citric acid and acetic acid.

[0009] In one embodiment, in step two, the organic weak acid is sprayed in a mist manner during the spheroidizing process, and the spraying amount does not exceed 30%.

[0010] In one embodiment, the alkaline solution includes, but is not limited to, sodium hydroxide, sodium carbonate, and sodium bicarbonate.

[0011] In one embodiment, the concentration of the alkaline solution is 10%-30%.

[0012] In one embodiment, the high-temperature and high-pressure activation reaction temperature is 120-180°C.

[0013] In one embodiment, the high-temperature and high-pressure activation reaction pressure is 0.2-0.8 MPa.

[0014] In one embodiment, the high-temperature and high-pressure activation reaction time is 1-3 hours.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This application introduces a weak organic acid during the molding process to promote the dissolution of aluminum in the molecular sieve crystal framework, resulting in defects in the molecular sieve crystal structure and the formation of more active and regenerable sites. By impregnating with an alkaline solution, the silicon in the molecular sieve crystal framework is brought into full contact with the alkaline substance. During the high-temperature and high-pressure activation reaction, the silicon in the molecular sieve framework reacts with the alkaline substance, causing local crystal collapse on the surface. During the activation process, the exposed silicon-aluminum components recombine under high-temperature and high-pressure conditions to form an aluminosilicate mineral phase, thereby achieving strong chemical bonding and adhesion between the molecular sieve powders and forming a high-strength binder-free molecular sieve adsorbent. Detailed Implementation

[0016] The present invention will be further described below with reference to the embodiments. Example

[0017] A method for preparing a binder-free molecular sieve adsorbent includes the following steps: Step 1: Dry 10 kg of 13X molecular sieve powder at 105℃ for later use. Step 2: Prepare a 20% concentration solution of citric acid to obtain a 20% concentration citric acid solution (atomized 20% concentration citric acid solution). Step 3: Add the dried 13X molecular sieve powder in small amounts multiple times in the pelletizing pan, and continuously spray in small amounts 2.2 kg of atomized 20% citric acid solution; after the molecular sieve powder clumps to a diameter of 5-6 mm, stop adding molecular sieve powder and citric acid solution, and continue rolling for more than 30 minutes. Step four: Place the formed molecular sieve balls in a cool, sheltered place to air dry for 15 hours; then place the molecular sieve balls in a 20% sodium hydroxide solution and let them soak for 15 minutes. Step 5: Place the soaked molecular sieve powder in a reaction vessel and activate it at 140℃ and 0.36MPa for 2 hours; then dry the molecular sieve balls after the reaction at 105℃ to obtain the binder-free molecular sieve adsorbent.

[0018] According to tests, the water absorption rate of this binder-free molecular sieve ball adsorbent is 98.24% of that of the original powder, and the adsorption performance of the molecular sieve did not decrease significantly during the molding process. The compressive strength of a single molecular sieve adsorbent ball reaches 112 N / ball.

[0019] Meanwhile, binder-free molecular sieve adsorbents have the following significant characteristics: First, excellent adsorption performance. Because no binder is needed, the molecular sieve particles maintain a complete pore structure and a large specific surface area, fully exposing effective adsorption sites. Adsorption capacity, selectivity, and adsorption kinetics are significantly superior to traditional binder-molded products. Studies show that the specific surface area of ​​binder-free 13X molecular sieves can be restored to the powder level, and the adsorption capacity for substances such as water and carbon dioxide is 20%-30% higher than that of traditional molded products, with a faster adsorption rate. Second, high mechanical strength. The binder-free molding process typically achieves molding through self-bonding between particles (such as in-situ crystallization, secondary growth, and high-temperature sintering). The molded body has a dense internal structure and strong interfacial bonding, significantly reducing wear and breakage rates. Mechanical strength can reach over 100 N / particle, meeting the requirements for long-term stable operation of industrial equipment. Third, long service life. Binder-free molecular sieves avoid the contamination and clogging of pores caused by binder decomposition and detachment. Their performance degrades slowly during multiple adsorption-regeneration cycles, extending their service life to 1.5-2 times that of traditional products, significantly reducing material replacement and maintenance costs in industrial production. Fourthly, they are environmentally friendly. The binder-free molding process reduces the consumption of binder raw materials and the generation of waste, lowering environmental pollution and aligning with the development concept of green chemistry. It also avoids interference from impurity ions in the binder on the adsorption process, improving the purity of the adsorption products. Example

[0020] A method for preparing a binder-free molecular sieve adsorbent includes the following steps: Step 1: Dry 20 kg of 13X molecular sieve powder at 105℃ for later use. Step 2: Prepare a 25% concentration solution of citric acid to obtain a 25% concentration citric acid solution (atomized 25% concentration citric acid solution). Step 3: Add the dried 13X molecular sieve powder in small amounts multiple times in the pelletizing pan, and continuously spray in small amounts 2.5 kg of atomized 25% citric acid solution; after the molecular sieve powder clumps to a diameter of 5-6 mm, stop adding molecular sieve powder and citric acid solution, and continue rolling for more than 30 minutes. Step four: Place the formed molecular sieve balls in a cool, sheltered place to air dry for 18 hours; then place the molecular sieve balls in a 25% sodium hydroxide solution and let them soak for 15 minutes. Step 5: Place the soaked molecular sieve powder in a reaction vessel and activate it at 160℃ and 0.6MPa for 1.5h; then dry the molecular sieve balls after the reaction at 105℃ to obtain the binder-free molecular sieve adsorbent.

[0021] According to tests, the water absorption rate of this binder-free molecular sieve ball adsorbent is 97.26% of that of the original powder, and the adsorption performance of the molecular sieve did not decrease significantly during the molding process. The compressive strength of a single molecular sieve adsorbent ball reaches 101 N / ball.

[0022] Comparative Example 1 A method for preparing a binder-free molecular sieve adsorbent includes the following steps: Step 1: Dry 20 kg of 13X molecular sieve powder at 105℃ for later use. Step 2: Prepare a 25% concentration solution of nitric acid to obtain 25% nitric acid (atomized 25% concentration nitric acid solution). Step 3: Add the dried 13X molecular sieve powder in small amounts multiple times in the pelletizing pan, and continuously spray in small amounts 2.2 kg of atomized 25% citric acid solution; after the molecular sieve powder clumps to a diameter of 5-6 mm, stop adding molecular sieve powder and citric acid solution, and continue rolling for more than 30 minutes. Step four: Place the formed molecular sieve balls in a cool, sheltered place to air dry for 15 hours; if the formed and air-dried molecular sieve balls show cracking and loosening, they cannot be further processed.

[0023] Comparative Example 2 A method for preparing a binder-free molecular sieve adsorbent includes the following steps: Step 1: Dry 10 kg of 13X molecular sieve powder at 105℃ for later use. Step 2: Prepare a 20% concentration solution of citric acid to obtain a 20% concentration citric acid solution (atomized 20% concentration citric acid solution). Step 3: Add the dried 13X molecular sieve powder in small amounts multiple times in the pelletizing pan, and continuously spray in small amounts 2.2 kg of atomized 20% citric acid solution; after the molecular sieve powder clumps to a diameter of 5-6 mm, stop adding molecular sieve powder and citric acid solution, and continue rolling for more than 30 minutes. Step four: Place the formed molecular sieve balls in a cool, sheltered place to air dry for 15 hours; then place the molecular sieve balls in clean water and soak them for 15 minutes. Step 5: Place the soaked molecular sieve powder in a reaction vessel and activate it at 140℃ and 0.36MPa for 2 hours; then dry the molecular sieve balls after the reaction at 105℃ to obtain the binder-free molecular sieve adsorbent.

[0024] According to tests, the water absorption rate of this binder-free molecular sieve ball adsorbent reached 92.11% of the original powder water absorption rate, indicating a significant decrease in the adsorption performance of the molecular sieve during the molding process. Some molecular sieve adsorbent balls cracked or loosened, and the compressive strength of a single molecular sieve adsorbent ball was less than 50 N / ball.

[0025] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the technical solutions of the present invention have been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a binder-free molecular sieve adsorbent, characterized in that, Includes the following steps: Step 1: Dry the molecular sieve powder at 100°-110° for later use; Step 2: Take an organic weak acid with a concentration of 5-30%; Step 3: The dried molecular sieve powder is pelletized in a pelletizing pan. During the pelletizing process, 5-30% of organic weak acid is sprayed in to promote the formation of the molecular sieve powder. Step 4: After the formed molecular sieve powder is left to stand and cure for more than 12 hours, it is then placed in an alkaline solution and left to stand and soak for 5-30 minutes. Step 5: Place the impregnated molecular sieve powder in a reaction vessel for high-temperature and high-pressure activation reaction to obtain binder-free molecular sieve adsorbent.

2. The method for preparing the binder-free molecular sieve adsorbent according to claim 1, characterized in that, The organic weak acids include, but are not limited to, citric acid and acetic acid.

3. The method for preparing the binder-free molecular sieve adsorbent according to claim 1, characterized in that, In step two, the organic weak acid is sprayed in a mist form during the spheroidizing process, and the amount sprayed does not exceed 30%.

4. The method for preparing the binder-free molecular sieve adsorbent according to claim 1, characterized in that, The alkaline solution includes, but is not limited to, sodium hydroxide, sodium carbonate, and sodium bicarbonate.

5. The method for preparing the binder-free molecular sieve adsorbent according to claim 4, characterized in that, The concentration of the alkaline solution is 10%-30%.

6. The method for preparing the binder-free molecular sieve adsorbent according to claim 1, characterized in that, The high-temperature and high-pressure activation reaction temperature is 120-180℃.

7. The method for preparing the binder-free molecular sieve adsorbent according to claim 6, characterized in that, The high-temperature and high-pressure activation reaction pressure is 0.2-0.8 MPa.

8. The method for preparing the binder-free molecular sieve adsorbent according to claim 7, characterized in that, The high-temperature and high-pressure activation reaction time is 1-3 hours.