A method for improving the crystallinity of a molecular sieve

Abstract

The application relates to a method for improving the crystallinity of a molecular sieve, which comprises the following steps: first crystallization of a first sodium aluminosilicate gel slurry until the first sodium aluminosilicate gel slurry is crystallized to a first crystallinity, then adding an alkali liquor into the first sodium aluminosilicate gel slurry to obtain a second sodium aluminosilicate gel slurry with a target alkali ratio; and second crystallization of the second sodium aluminosilicate gel slurry to obtain a molecular sieve. When the first sodium aluminosilicate gel slurry is crystallized to the first crystallinity, the alkali liquor is added into the first sodium aluminosilicate gel slurry, so that new crystallization power is injected into the first sodium aluminosilicate gel slurry system, thereby improving the crystallinity of the molecular sieve; the second sodium aluminosilicate gel slurry with the target alkali ratio is subjected to the second crystallization, further crystallization power is provided for improving the crystallinity, and thereby the molecular sieve with high crystallinity is obtained.

Description

Technical Field

[0001] This application relates to the field of molecular sieve preparation technology, and in particular to a method for improving the crystallinity of molecular sieves. Background Technology

[0002] Molecular sieves are widely used in chemical, electronics, petrochemical, and natural gas industries. They possess drying properties for gases such as air, hydrogen, oxygen, nitrogen, and argon. In industrial production, two sets of adsorption dryers are typically connected in parallel, with one working while the other regenerates. They alternate between operation and regeneration to ensure continuous equipment operation. The dryers operate at room temperature and are regenerated by purging at 350°C. The number of times a molecular sieve can be reused after regeneration is generally determined by the crystallinity of the original molecular sieve powder. Higher crystallinity results in less degradation of adsorption performance after regeneration, allowing for more reuses.

[0003] Currently, the control of crystallinity in molecular sieve raw powder generally involves using higher purity aluminum and silicon sources, more precise control of the synthesis ratio and temperature, and narrowing the crystallization temperature range. Even so, the crystallinity of molecular sieve raw powder still fluctuates significantly and is difficult to consistently reach above 90%. Summary of the Invention

[0004] This application provides a method for improving the crystallinity of molecular sieves to solve the following technical problem: how to improve the crystallinity of molecular sieves.

[0005] In a first aspect, this application provides a method for improving the crystallinity of molecular sieves, the method comprising:

[0006] The first sodium aluminosilicate gel slurry is subjected to first crystallization until it reaches a first degree of crystallinity. Then, an alkaline solution is added to the first sodium aluminosilicate gel slurry to obtain a second sodium aluminosilicate gel slurry with a target alkaline ratio.

[0007] The second sodium aluminosilicate gel slurry was subjected to a second crystallization to obtain a molecular sieve.

[0008] Optionally, the first crystallinity is 75% to 80%.

[0009] Optionally, the temperature for the second crystallization is 95°C to 100°C.

[0010] Optionally, the temperature of the first crystallization is 80℃~85℃.

[0011] Optionally, the alkaline solution includes a sodium hydroxide solution.

[0012] Optionally, the Na2O content in the sodium hydroxide solution is 100 g / L to 110 g / L.

[0013] Optionally, the molecular sieve includes one of the following: 4A molecular sieve or 13X molecular sieve.

[0014] Optionally, if the molecular sieve is a 4A molecular sieve, the target alkali ratio is less than 3.0.

[0015] Optionally, if the molecular sieve is a 13X molecular sieve, the target alkali ratio is less than 3.5.

[0016] Optionally, the method further includes: chemically reacting a silicon source solution and an aluminum source solution to obtain the first sodium aluminosilicate gel slurry.

[0017] The technical solutions provided in this application have the following advantages compared with the prior art:

[0018] The method for improving the crystallinity of molecular sieves provided in this application includes: firstly crystallizing a first sodium aluminosilicate gel slurry until it reaches a first degree of crystallinity; then adding an alkali solution to the first sodium aluminosilicate gel slurry to obtain a second sodium aluminosilicate gel slurry with a target alkali ratio; and secondly crystallizing the second sodium aluminosilicate gel slurry to obtain a molecular sieve. During the crystallization process, the molecular sieve consumes a large amount of alkali, meaning the residual alkali concentration in the mother liquor decreases as crystallization progresses. This leads to insufficient crystallization motive force in the later stages of crystallization due to the reduced alkali concentration, affecting the improvement of the crystallinity of the molecular sieve product. Therefore, when the first sodium aluminosilicate gel slurry reaches the first degree of crystallinity, an alkali solution is added to it to inject new crystallization motive force into the first sodium aluminosilicate gel slurry system, thereby improving the crystallinity of the molecular sieve. The second sodium aluminosilicate gel slurry with the target alkali ratio undergoes a second crystallization, further providing crystallization motive force to improve the crystallinity, thus obtaining a molecular sieve with high crystallinity. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart illustrating a method for improving the crystallinity of molecular sieves, as provided in an embodiment of this application. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0024] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0025] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0026] Molecular sieves are aluminosilicate compounds with a cubic lattice, primarily composed of silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra connected by oxygen bridges to form a spacious framework structure. This structure contains numerous uniformly sized channels and neatly arranged cavities with a large internal surface area. It also contains metal ions with low valence but large ionic radii and bound water. As water molecules are continuously lost upon heating, the crystal framework structure remains unchanged, forming many cavities of the same size. These cavities are interconnected by numerous micropores of the same diameter. These uniformly sized micropores adsorb molecules smaller than the channel diameter into their interiors while repelling molecules larger than the channel diameter. Therefore, they separate molecules of different diameters like a sieve, thus performing a "sieving" function, hence the name molecular sieve. Currently, molecular sieves are widely used in chemical, electronics, petrochemical, and natural gas industries.

[0027] Currently, controlling the crystallinity of molecular sieve raw materials generally involves using higher purity aluminum and silicon sources, more precise control of the synthesis ratio and temperature, and narrowing the crystallization temperature range. Even so, the crystallinity of molecular sieve raw materials still fluctuates significantly and is difficult to consistently reach above 90%. The main factor affecting crystallinity is insufficient kinetic energy during crystal growth. During crystal growth, there is a dissolution-crystallization-redissolution-recrystallization process, during which some deformed crystals will be dissolved and recrystallized. However, when the crystallization process is carried out under low kinetic energy, this process becomes lengthy and incomplete due to insufficient kinetic energy. Therefore, to address this problem, the applicant, through extensive experiments, discovered that injecting new crystallization kinetic energy into the system at a certain stage of the dissolution-crystallization process, accelerating the dissolution-crystallization process, and when properly controlled, can significantly improve the crystallinity of molecular sieves. Therefore, in the first aspect, this application provides a method for improving the crystallinity of molecular sieves. Figure 1 A flowchart illustrating a method for improving the crystallinity of molecular sieves provided in this application embodiment; please refer to... Figure 1 The method includes:

[0028] S1. The first sodium aluminosilicate gel slurry is subjected to first crystallization until it reaches the first degree of crystallinity. Then, an alkaline solution is added to the first sodium aluminosilicate gel slurry to obtain a second sodium aluminosilicate gel slurry with a target alkaline ratio.

[0029] In some embodiments, the first crystallinity is 75% to 80%.

[0030] In this embodiment, the first sodium aluminosilicate gel slurry undergoes a first crystallization until it reaches a first degree of crystallinity. Then, an alkali solution is added to the first sodium aluminosilicate gel slurry. This first degree of crystallinity can be 75% to 80%. The reason is that within this range, the mother liquor lacks the motive force for crystallization. Adding the alkali solution at this time provides the system with sufficient alkali concentration for the later stages of crystallization, avoiding insufficient alkali and thus insufficient crystallization motive force, which would affect the improvement of the product's crystallinity. The alkali concentration in the mother liquor before the first degree of crystallinity reaches 75% is sufficient for crystallization. However, after the first degree of crystallinity reaches 80%, even adding an alkali solution makes it difficult to improve the crystallinity. For example, the first degree of crystallinity can be 75%, 76%, 77%, 78%, 79%, 80%, etc.

[0031] In some embodiments, the temperature of the first crystallization is 80°C to 85°C.

[0032] In this embodiment, the first sodium aluminosilicate gel slurry undergoes first crystallization at a temperature of 80°C to 85°C, which ensures uniform crystallization and guarantees consistency and stability. For example, the first crystallization temperature can be 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, etc.

[0033] In some embodiments, the alkaline solution includes a sodium hydroxide solution.

[0034] In some embodiments, the Na2O content in the sodium hydroxide solution is 100 g / L to 110 g / L.

[0035] In this embodiment, the alkaline solution can be a sodium hydroxide solution, and the Na2O content in the sodium hydroxide solution can be 100 g / L to 110 g / L. This is because adding sodium hydroxide solution to the slurry carries the risk of crystal transformation due to uneven mixing. To avoid this risk, adjusting the sodium hydroxide solution concentration to 100 g / L to 110 g / L (characterized by Na2O) is reasonable. This also avoids the situation where an excessively low sodium hydroxide solution concentration leads to a high solid content in the dilution system, resulting in reduced production efficiency. For example, the Na2O content in the sodium hydroxide solution can be 100 g / L, 101 g / L, 102 g / L, 103 g / L, 104 g / L, 105 g / L, 106 g / L, 107 g / L, 108 g / L, 109 g / L, 110 g / L, etc.

[0036] In some embodiments, the molecular sieve includes one of the following: 4A molecular sieve and 13X molecular sieve.

[0037] In some embodiments, if the molecular sieve is a 4A molecular sieve, the target alkali ratio (the molar ratio of sodium oxide to alumina in the slurry system) is less than 3.0.

[0038] In some embodiments, if the molecular sieve is a 13X molecular sieve, the target alkali ratio is less than 3.5.

[0039] In this embodiment, the crystallinity of 4A zeolite molecular sieve and 13X zeolite molecular sieve is closely related to the thermal stability of these two products. Higher crystallinity results in higher thermal stability, which is beneficial for the molding and calcination of the molecular sieve products. Crystallization of 4A and 13X zeolite molecular sieves is the process of transforming gel into crystals. This process requires power, which comes from two sources: the temperature during crystallization and the concentration of excess alkali. Therefore, the target alkali ratio for 4A molecular sieve is set to be less than 3.0, and the target alkali ratio for 13X molecular sieve is set to be less than 3.5, to ensure sufficient alkali concentration for the second crystallization process, thereby providing sufficient power for the second crystallization and improving the crystallinity of the target molecular sieve product. At the same time, while maximizing the alkali concentration required for crystallization, it avoids the situation where crystal transformation occurs and affects other product indicators. For example, if the molecular sieve is 4A molecular sieve, the target alkali ratio can be 2.8, 2.7, 2.6, 2.5, 2.4, etc.; if the molecular sieve is 13X molecular sieve, the target alkali ratio can be 3.3, 3.1, 3.2, 3.1, 3.0, etc.

[0040] In some embodiments, the method further includes: S0, chemically reacting a silicon source solution and an aluminum source solution to obtain the first sodium aluminosilicate gel slurry.

[0041] In this embodiment, the first sodium aluminosilicate gel slurry is obtained by a chemical reaction between a silicon source solution and an aluminum source solution. For example, water glass and sodium aluminate solution are chemically reacted to obtain the first sodium aluminosilicate gel slurry.

[0042] S2. The second sodium aluminosilicate gel slurry is subjected to a second crystallization to obtain a molecular sieve.

[0043] In some embodiments, the temperature of the second crystallization is 95°C to 100°C.

[0044] In this embodiment, the crystallization of 4A and 13X zeolite molecular sieves is the process of transforming gel into crystals. This process requires power, which comes from two sources: the temperature during crystallization and the concentration of excess alkali. The second sodium aluminosilicate gel slurry with a target alkali ratio satisfies the requirement of an excess alkali concentration. Simultaneously, increasing the second crystallization temperature, the crystallinity of the molecular sieve is maximized through the synergistic effect of the crystallization temperature and the excess alkali concentration. For example, the second crystallization temperature can be 95°C, 96°C, 97°C, 98°C, 99°C, 100°C, etc. Furthermore, after crystallization, separation, washing, and drying are performed to obtain a highly crystalline molecular sieve product.

[0045] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0046] Example 1

[0047] Water glass with a concentration of SiO2: 16.79% and Na2O: 5.5% was mixed with a sodium aluminate solution with a concentration of Al2O3: 92.3 g / L and Nk: 119.7 g / L, and synthesized with a silicon-to-aluminum ratio of 2.0. The synthesis alkali ratio was 2.7, resulting in the first sodium aluminosilicate gel slurry.

[0048] After crystallization at the initial crystallization temperature of 70℃ for 5 hours, the crystallinity was 75.4%. A sodium hydroxide solution with a concentration of Na₂O: 102.3 g / L was added to adjust the synthesis alkali ratio to 2.95.

[0049] A second crystallization process was carried out by heating the material twice. After two hours of second crystallization at a temperature of 97°C, the material was discharged and, after separation, washing, and drying, yielded the 4A molecular sieve product. The crystallinity of the 4A molecular sieve product in Example 1 was 93.6%.

[0050] Example 2

[0051] Water glass with a concentration of SiO2: 15.29% and Na2O: 5.9% was mixed with a sodium aluminate solution with a concentration of Al2O3: 30.2 g / L and Nk: 32.8 g / L, and the silicon-to-aluminum ratio was 2.8. The resulting first sodium aluminosilicate gel slurry was obtained.

[0052] After crystallization at the first crystallization temperature of 70℃ for 12 hours, the crystallinity was 77.1%. A sodium hydroxide solution with a concentration of Na₂O: 106.7 g / L was added to adjust the synthesis alkali ratio to 3.3, yielding the second sodium aluminosilicate gel slurry.

[0053] A second crystallization process was carried out by heating the material twice. After two hours of second crystallization at 98°C, the material was discharged and, after separation, washing, and drying, yielded the 13X molecular sieve product. The crystallinity of the 13X molecular sieve product in Example 2 was 98.3%.

[0054] Example 3

[0055] Water glass with a concentration of SiO2: 15.29% and Na2O: 5.9% was mixed with a sodium aluminate solution with a concentration of Al2O3: 30.2 g / L and Nk: 32.8 g / L, and synthesized with a silicon-to-aluminum ratio of 2.65. The synthesis alkali ratio was 2.7, resulting in the first sodium aluminosilicate gel slurry.

[0056] After crystallization at the first crystallization temperature of 70℃ for 12 hours, the crystallinity was 79.5%. A sodium hydroxide solution with a concentration of Na₂O: 103.2 g / L was added to adjust the synthesis alkali ratio to 3.2, yielding the second sodium aluminosilicate gel slurry.

[0057] A second crystallization process was carried out by heating the material twice. After two hours of second crystallization at 98°C, the material was discharged and, after separation, washing, and drying, yielded the 13X molecular sieve product. In Example 3, the crystallinity of the 13X molecular sieve product was 95.6%.

[0058] Comparative Example 1

[0059] Water glass with a concentration of SiO2: 16.79% and Na2O: 5.5% was mixed with a sodium aluminate solution with a concentration of Al2O3: 92.3 g / L and Nk: 119.7 g / L, and synthesized with a silicon-to-aluminum ratio of 2.0. The synthesis alkali ratio was 2.7, resulting in the first sodium aluminosilicate gel slurry.

[0060] After crystallizing at 70℃ for 4 hours, the temperature was raised again, and crystallization was carried out at 87℃ for 3 hours before discharge. After separation, washing, and drying, the product was 4A molecular sieve. The crystallinity of the 4A molecular sieve product in Comparative Example 1 was 82.3%.

[0061] Comparative Example 2

[0062] Water glass with a concentration of SiO2: 15.29% and Na2O: 5.9% was mixed with a sodium aluminate solution with a concentration of Al2O3: 30.2 g / L and Nk: 32.8 g / L, and the silicon-to-aluminum ratio was 2.8. The resulting alkali ratio was 2.8, yielding the first sodium aluminosilicate gel slurry.

[0063] After crystallizing at 70℃ for 12 hours, the temperature was raised again to 87℃ for 2 hours before discharge. After separation, washing, and drying, the product was 13X molecular sieve. The crystallinity of the 13X molecular sieve product in Comparative Example 2 was 86.5%.

[0064] Through the analysis of Examples 1-3 and the comparative examples above, it was found that molecular sieves consume a large amount of alkali during the crystallization process. This means that the residual alkali concentration in the mother liquor decreases as crystallization progresses, leading to insufficient crystallization motive force in the later stages of crystallization due to the reduced alkali concentration. This affects the improvement of the crystallinity of 4A and 13X molecular sieve products. Therefore, when the first sodium aluminosilicate gel slurry crystallizes to the first crystallinity, alkali solution is added to the first sodium aluminosilicate gel slurry to inject new crystallization motive force into the first sodium aluminosilicate gel slurry system, thereby improving the crystallinity of the molecular sieve. The second sodium aluminosilicate gel slurry with the target alkali ratio undergoes a second crystallization, further providing crystallization motive force to improve crystallinity, thus obtaining 4A and 13X molecular sieves with high crystallinity. However, Comparative Examples 1 and 2 did not provide alkali concentration to the mother liquor in a timely manner during the crystallization process, resulting in insufficient crystallization motive force in the later stages of crystallization due to the reduced alkali concentration, thus obtaining 4A and 13X molecular sieves with lower crystallinity.

[0065] One or more technical solutions in the embodiments of this application have at least the following technical effects or advantages:

[0066] (1) The method for improving the crystallinity of molecular sieves provided in this application is simple and easy to implement, and can be widely applied in the production process of 4A and 13X, so that the crystallinity of 4A and 13X molecular sieves can be stabilized at more than 90%.

[0067] (2) The method for improving the crystallinity of molecular sieve provided in this application embodiment, when the crystallization process enters a certain stage of dissolution-crystallization (crystallization to a crystallinity of 75% to 80%), adds sodium hydroxide solution to the slurry according to a certain synthesis alkali ratio, thereby injecting new crystallization power into the slurry system, accelerating the dissolution-crystallization process, and the crystallinity of molecular sieve will be greatly improved.

[0068] (3) The method for improving the crystallinity of molecular sieves provided in this application embodiment does not require modification of the molecular sieve production process, but only requires adjustment of the crystallization process of molecular sieves, and the process is simple and easy to implement.

[0069] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for improving the crystallinity of molecular sieves, characterized in that, The method includes: The first sodium aluminosilicate gel slurry is subjected to first crystallization until it reaches a first degree of crystallinity. Then, an alkaline solution is added to the first sodium aluminosilicate gel slurry to obtain a second sodium aluminosilicate gel slurry with a target alkaline ratio. The second sodium aluminosilicate gel slurry was subjected to a second crystallization to obtain a molecular sieve. The molecular sieves include the following: 4A molecular sieve and 13X molecular sieve.

2. The method according to claim 1, characterized in that, The first crystallinity is 75%~80%.

3. The method according to claim 1, characterized in that, The temperature for the second crystallization is 95℃~100℃.

4. The method according to claim 1, characterized in that, The temperature of the first crystallization is 80℃~85℃.

5. The method according to claim 1, characterized in that, The alkaline solution includes a sodium hydroxide solution.

6. The method according to claim 5, characterized in that, The sodium hydroxide solution contains 100 g / L to 110 g / L of Na₂O.

7. The method according to claim 1, characterized in that, If the molecular sieve is a 4A molecular sieve, the target alkali ratio is less than 3.

0.

8. The method according to claim 1, characterized in that, If the molecular sieve is a 13X molecular sieve, the target alkali ratio is less than 3.

5.

9. The method according to claim 1, characterized in that, The method further includes: The silicon source solution and the aluminum source solution are chemically reacted to obtain the first sodium aluminosilicate gel slurry.

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