Preparation method of 13X molecular sieve with low silica-alumina ratio

Abstract

The invention relates to the technical field of molecular sieve preparation, in particular to a preparation method of a 13X molecular sieve with a low silica-alumina ratio. The preparation method comprises the following steps: mixing a first aluminum source and an alkali source to obtain a first mixture; mixing a guiding agent, a first silicon source and the first mixture to obtain a second mixture; performing first aging treatment on the second mixture to obtain first aged slurry; adding a second silicon source and a second aluminum source into the first aged slurry to obtain a third mixture; performing second aging treatment on the third mixture to obtain second aged slurry; performing crystallization treatment on the second aged slurry to obtain a crystallized product; and purifying the crystallized product to obtain the 13X molecular sieve with low silica-alumina ratio. According to the preparation method, collaborative optimization of purity and grain distribution of the 13X molecular sieve with the low silica-alumina ratio is realized through step-by-step introduction of an aluminum-silicon source and dual-stage aging regulation and control.

Description

Technical Field

[0001] This application relates to the field of molecular sieve preparation technology, and in particular to a method for preparing a 13X molecular sieve with a low silica-to-alumina ratio. Background Technology

[0002] 13X molecular sieve is an octahedral zeolite (FAU) type molecular sieve with a high specific surface area. It possesses a three-dimensional twelve-membered ring macroporous structure (pore size approximately 0.74 nm), enabling it to achieve a high specific surface area. This high specific surface area allows for wide applications in gas adsorption and separation (e.g., CO2 capture and air separation for oxygen production), water softening, and catalyst support. While traditional 13X molecular sieves typically have a SiO2 / Al2O3 ratio of 2.0 to 3.0, lower SiO2 / Al2O3 ratio 13X molecular sieves (2.0 to 2.2) contain more aluminum and a higher density of negative surface charges. This results in superior adsorption capacity and ion exchange performance for polar molecules (e.g., H2O and CO2), offering significant advantages in applications requiring the removal of low-concentration pollutants.

[0003] However, the synthesis of 13X molecular sieves with low silicon-to-aluminum ratio faces the problem of difficulty in controlling impurity phases. At present, various technologies can be used to reduce the content of impurity phases in 13X molecular sieves with low silicon-to-aluminum ratio, but it is impossible to balance the purity and grain distribution of 13X molecular sieves with low silicon-to-aluminum ratio. Summary of the Invention

[0004] This application provides a method for preparing 13X molecular sieves with a low silicon-to-aluminum ratio to solve the following technical problem: how to simultaneously improve the purity and grain distribution of 13X molecular sieves with a low silicon-to-aluminum ratio. In a first aspect, embodiments of this application provide a method for preparing a 13X molecular sieve with a low silica-to-alumina ratio, the preparation method comprising: The first aluminum source and the alkali source are mixed to obtain the first mixture; The directing agent, the first silicon source, and the first mixture are mixed to obtain a second mixture; The second mixture is subjected to a first aging treatment to obtain a first aging slurry; A second silicon source and a second aluminum source are added to the first aging slurry to obtain a third mixture; The third mixture is subjected to a second aging treatment to obtain a second aged slurry; The second aged slurry is subjected to crystallization treatment to obtain a crystallized product; The crystallized product was purified to obtain a 13X molecular sieve with a low silicon-to-aluminum ratio. Wherein, the amount of the first aluminum source n1, the amount of the second aluminum source n2, the amount of the first silicon source n3, and the amount of the second silicon source n4 satisfy: (n1+n2):(n3+n4)≥2.0:1.

[0005] Optionally, the amounts of the first aluminum source n1, the second aluminum source n2, the first silicon source n3, and the second silicon source n4 satisfy the following: (n1+n2):(n3+n4) = (2.0 to 2.2):1.

[0006] Optionally, the first aluminum source and the second aluminum source each include at least one of aluminum sulfate, aluminum nitrate, aluminum trichloride, aluminum isopropoxide, sodium aluminate, and boehmite; and / or The first silicon source and the second silicon source are respectively selected from at least one of tetraethyl orthosilicate, silica, sodium silicate and silica sol.

[0007] Optionally, the mass m1 of the directing agent and the mass m2 of silica in the 13X molecular sieve with a low silica-to-alumina ratio satisfy the following: m1:m2 = (1 to 20):100.

[0008] Optionally, the type of directing agent includes at least one of X-type molecular sieve, Y-type molecular sieve and 4A-type molecular sieve.

[0009] Optionally, the amounts of the first aluminum source n1, the second aluminum source n2, and the alkali source n5 satisfy: (n1+n2):n5=1:(0.70 to 1.65); and / or The amounts of the first silicon source n3, the second silicon source n4, and the alkali source n5 satisfy the following: (n3+n4):n5 = (0.67 to 1.43):1.

[0010] Optionally, the silica-alumina ratio of the first aging slurry is (2.5 to 3.5):1.

[0011] Optionally, the second aging slurry includes silicon, aluminum, alkaline substances and water, wherein the amounts of silicon (n6), aluminum (n7), alkaline substances (n8) and water (n9) satisfy the following ratio: n6:n7:n8:n9 = 1:(0.91 to 1.00):(0.7 to 1.5):(40 to 80).

[0012] Optionally, the temperature of the first aging treatment is 30°C to 50°C, and the time of the first aging treatment is 1 hour to 20 hours; and / or The temperature of the second aging treatment is 40°C to 50°C, and the time of the second aging treatment is 1 hour to 10 hours.

[0013] Optionally, the crystallization treatment temperature is 60°C to 100°C, and the crystallization treatment time is 5h to 24h.

[0014] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing a low-silicon-to-aluminum ratio 13X molecular sieve. The method first mixes a first aluminum source, an alkali source, a directing agent, and a first silicon source to obtain a second mixture. In the first aging treatment stage of the second mixture, the directing agent acts as a nucleation site, promoting a reaction between the first silicon source, the first aluminum source, and the alkali source in the second mixture to form uniformly distributed crystal nuclei. This facilitates the subsequent generation of a large amount of stable 13X molecular sieve precursors and the formation of a first aging slurry. Subsequently, a second silicon source and a second aluminum source are added to the first aging slurry. At this point, the aluminum content in the third mixture increases, and the concentration gradient of silicon-containing and aluminum-containing species on the surface of the primary crystal nuclei of the 13X molecular sieve decreases, thereby refining the grains of the low-silicon-to-aluminum ratio 13X molecular sieve and ultimately forming small-sized and uniformly distributed low-silicon-to-aluminum ratio 13X molecular sieve grains. Furthermore, this preparation method, by adding aluminum and silicon sources in two batches and performing two aging treatments, not only avoids the coarsening of low silicon-to-aluminum ratio 13X molecular sieve grains caused by rapid nucleation, but also effectively inhibits the precipitation of impurity phases and improves the purity of low silicon-to-aluminum ratio 13X molecular sieves. Attached Figure Description

[0015] 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.

[0016] 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.

[0017] Figure 1 A schematic flowchart illustrating a method for preparing a low silica-to-alumina ratio 13X molecular sieve according to an embodiment of this application; Figure 2 Scanning electron microscope image of 13X molecular sieve obtained by the preparation method of 13X molecular sieve with low silicon-to-aluminum ratio provided in Example 1 of this application; Figure 3 Scanning electron microscope image of 13X molecular sieve obtained by the preparation method of 13X molecular sieve with low silicon-to-aluminum ratio provided in Example 2 of this application. Detailed Implementation

[0018] 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.

[0019] The range descriptions used in this application, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "comprising" and others used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships involved in this document, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained by purchasing from the market or by existing methods.

[0020] However, the synthesis of 13X molecular sieves with low silica-to-alumina ratios faces several challenges. The lower silica-to-alumina ratio in 13X molecular sieves leads to an excess of aluminum-containing substances. This excess aluminum-containing substances can easily form thermodynamically more stable impurity phases such as NaP (GIS type), sodalite (SOD type), and 4A (LTA). The presence of these impurity phases reduces the purity and performance of the 13X molecular sieve product. Currently, on the one hand, the formation of impurity phases in 13X molecular sieves can be suppressed by increasing the alkalinity of the raw materials for low-silicon-aluminum ratio 13X molecular sieves or extending the crystallization treatment time of low-silicon-aluminum ratio 13X molecular sieves during the preparation stage. However, increasing the alkalinity and extending the crystallization treatment time will lead to a decrease in the crystallinity of 13X molecular sieves or agglomeration of 13X molecular sieve grains, resulting in uneven grain distribution of 13X molecular sieves. On the other hand, a dual-cation system additive can be added to the raw materials of low-silicon-aluminum ratio 13X molecular sieves. Through the interaction between the dual-cation system in the additive and the raw materials of 13X molecular sieves, the formation of impurity phases can be effectively reduced. However, potassium hydroxide is generally added to the dual-cation system additive, and potassium hydroxide is difficult to recover and process, which results in a large number of impurity phases being mixed in the subsequent 13X molecular sieves.

[0021] Figure 1 An exemplary schematic diagram of a method for preparing a 13X molecular sieve with a low silicon-to-aluminum ratio according to an embodiment of this application is shown. like Figure 1 As shown in the embodiments of this application, a method for preparing a 13X molecular sieve with a low silica-to-alumina ratio is provided. The preparation method includes: S1. Mix the first aluminum source and the alkali source to obtain the first mixture; S2. Mix the directing agent, the first silicon source, and the first mixture to obtain a second mixture; S3. The second mixture is subjected to a first aging treatment to obtain a first aged slurry; S4. Add a second silicon source and a second aluminum source to the first aging slurry to obtain a third mixture; S5. The third mixture is subjected to a second aging treatment to obtain a second aged slurry; S6. The second aging slurry is subjected to crystallization treatment to obtain a crystallized product; S7. The crystallized product is purified to obtain a 13X molecular sieve with a low silicon-to-aluminum ratio; Wherein, the amount of the first aluminum source n1, the amount of the second aluminum source n2, the amount of the first silicon source n3, and the amount of the second silicon source n4 satisfy: (n1+n2):(n3+n4)≥2.0:1.

[0022] It should be noted that the alkali source can be at least one of sodium hydroxide, ammonia, tetrapropylammonium hydroxide, and sodium carbonate.

[0023] It should be noted that the first aluminum source and the second aluminum source can be the same or different; while the first silicon source and the second silicon source can be the same or different.

[0024] It should be noted that the purification process can include filtration, washing, and drying. The drying temperature can be between 80°C and 120°C, and the drying time can be between 4 hours and 8 hours. Alternatively, the drying temperature can be between 90°C and 100°C, and the drying time can be between 5 hours and 7 hours.

[0025] It should be noted that the method for preparing a low-silicon-to-aluminum ratio 13X molecular sieve provided in this application achieves synergistic optimization of the purity and grain distribution of the low-silicon-to-aluminum ratio 13X molecular sieve through stepwise introduction of aluminum-silicon sources and two-stage aging control. The specific mechanism is as follows: I. Step-by-step introduction of aluminum-silicon source: precise control of silicon-to-aluminum ratio and impurity suppression 1. First stage (preparation of the second mixture): First, the first aluminum source and the first silicon source are added, and under the action of the directing agent, an initial gel system (first aging slurry) is formed. At this time, the silicon-to-aluminum ratio in the first aging slurry is relatively high, which is beneficial to suppress the formation of other types of molecular sieves (such as P-type and A-type molecular sieves) in the impurity phase, laying a pure crystal nucleus basis for the subsequent low silicon-to-aluminum ratio 13X molecular sieve.

[0026] In the first aging process, the directing agent can act as a nucleation site, promoting the reaction between the first silicon source, the first aluminum source and the alkali source in the second mixture and forming uniformly distributed crystal nuclei, promoting the uniform dispersion of aluminum-containing species and generating a large number of stable 13X molecular sieve precursors (NaY type molecular sieve structure prototype).

[0027] 2. Second stage (preparation of the third mixture): The second aluminum source and the second silicon source are added to the first aging slurry, at which point the overall silicon-aluminum ratio in the third mixture is reduced to a low level.

[0028] The phased replenishment of aluminum source avoids local oversaturation caused by adding a large amount of aluminum source at once, reduces the agglomeration of amorphous aluminum material, ensures that aluminum atoms can be orderly embedded in the 13X molecular sieve framework, increases the aluminum content of the 13X molecular sieve framework, and at the same time avoids the precipitation of impurity crystals due to excess aluminum ions, thus reducing the content of impurity phase.

[0029] II. Two-stage aging treatment: regulating grain growth and distribution uniformity 1. First aging stage (low aluminum, high silicon environment): At lower temperatures, the directing agent can promote the hydrolysis and condensation between silicon-containing and aluminum-containing species, forming a large number of fine and uniform primary crystal nuclei, providing sufficient seeds for the subsequent growth of 13X molecular sieve crystals and avoiding excessive growth of single crystals.

[0030] 2. Second aging (high aluminum, low silicon environment): After adding a second aluminum source and a second silicon source, a second aging process is carried out. At this time, the aluminum content of the third mixture increases, and the concentration gradient of silicon-containing species and aluminum-containing species on the surface of the primary crystal nucleus of 13X molecular sieve decreases. This allows the 13X molecular sieve grains to grow slowly outward, avoiding rapid nucleation and resulting in coarsening of the 13X molecular sieve grains.

[0031] The second aging treatment under mild conditions can concentrate the grain size distribution of 13X molecular sieve, avoid mixing and doping between large and small grains in the 13X molecular sieve, and improve the uniformity of the grain distribution of 13X molecular sieve.

[0032] III. The Core Role of the Key Molar Ratio Low silicon-to-aluminum ratio drives high-purity primary nucleus growth: Excess aluminum source ensures that aluminum occupies the priority site in the framework of 13X molecular sieve, inhibits the excessive substitution of silicon atoms in the framework of 13X molecular sieve (avoiding the formation of high-silicon impurity phase), and at the same time, the charge balance between other cations in 13X molecular sieve and aluminum ions in the framework of 13X molecular sieve is maintained, reducing the precipitation of aluminum-containing impurities in non-13X molecular sieve framework, and obtaining octahedral zeolite-type 13X molecular sieve with stable charge balance.

[0033] 2. The stepwise introduction of aluminum source can balance the grain size: In an environment with high aluminum content, aluminum ions can act as an inhibitor of 13X molecular sieve grain growth, which can reduce the surface energy of 13X molecular sieve grains. Combined with the nucleation and growth mechanism of the first and second aging, small-sized and narrowly distributed 13X molecular sieve grains are finally formed, and the specific surface area and adsorption performance of 13X molecular sieve are improved.

[0034] In summary, the present application provides a method for preparing a low-silicon-to-aluminum ratio 13X molecular sieve. This method suppresses the formation of impurity grains by introducing aluminum and silicon sources stepwise. The high-quality aluminum content in the early stage ensures that the 13X molecular sieve framework is dominant, thereby improving the purity of the grains in the 13X molecular sieve. In addition, the two-stage aging treatment can control the number of crystal nuclei and the growth rate of the 13X molecular sieve, avoiding the agglomeration and coarsening of the 13X molecular sieve grains. Therefore, by introducing aluminum and silicon sources stepwise and by performing a two-stage aging treatment, high purity and narrow grain distribution of the low-silicon-to-aluminum ratio 13X molecular sieve can be achieved simultaneously, thereby improving both the purity and grain distribution of the low-silicon-to-aluminum ratio 13X molecular sieve.

[0035] In some optional embodiments, the amounts of the first aluminum source n1, the second aluminum source n2, the first silicon source n3, and the second silicon source n4 satisfy: (n1+n2):(n3+n4) = (2.0 to 2.2):1.

[0036] In these embodiments, the molar ratio of the sum of the first aluminum source and the second aluminum source to the sum of the first silicon source and the second silicon source is (2.0 to 2.2):1, which allows the entire preparation method to be carried out in a special environment with low silicon content and high aluminum content. This can avoid the formation of high silicon impurity phases in the 13X molecular sieve. At the same time, the special environment with low silicon content and high aluminum content can also reduce the precipitation of aluminum-containing impurities in the non-13X molecular sieve framework and improve the purity of the 13X molecular sieve.

[0037] The sum of the amount of substance n1 of the first aluminum source and the amount of substance n2 of the second aluminum source can be 2.0, 2.05, 2.10, 2.15 or 2.20.

[0038] In some optional embodiments, the first aluminum source and the second aluminum source respectively include at least one of aluminum sulfate, aluminum nitrate, aluminum trichloride, aluminum isopropoxide, sodium aluminate, and boehmite; and / or The first silicon source and the second silicon source are respectively selected from at least one of tetraethyl orthosilicate, silica, sodium silicate and silica sol.

[0039] In these embodiments, using at least one of aluminum sulfate, aluminum nitrate, aluminum trichloride, aluminum isopropoxide, sodium aluminate, and boehmite as the first and second aluminum sources can cover most of the aluminum sources, allowing the first and second aging treatments to be carried out sufficiently. Through the two-stage aging treatment, the number of crystal nuclei and the growth rate of 13X molecular sieve can be controlled, avoiding the agglomeration and coarsening of 13X molecular sieve crystals, and forming 13X molecular sieve with uniform crystal distribution.

[0040] Using at least one of tetraethyl orthosilicate, silica, sodium silicate, and silica sol as the first and second silicon sources can cover most of the silicon sources, allowing the first and second aging processes to be carried out fully. Through the two-stage aging process, the number of crystal nuclei and the growth rate of 13X molecular sieves can be controlled, avoiding the agglomeration and coarsening of 13X molecular sieve crystals, and forming 13X molecular sieves with uniform crystal distribution.

[0041] It should be noted that when the first and second silicon sources are silica sols, the silica sol used for the first and second silicon sources can be either Ludox AS40 or Ludox HS40.

[0042] In some alternative embodiments, the mass m1 of the directing agent and the mass m2 of silica in the 13X molecular sieve with a low silica-to-alumina ratio satisfy: m1:m2 = (1 to 20):100.

[0043] In these embodiments, a directing agent with a silica mass ratio of (1 to 20):100 to the 13X molecular sieve with a low silica-to-alumina ratio can introduce molecular sieve structural units into the first mixture. These molecular sieve structural units can serve as nucleation sites, promoting the formation of uniformly distributed crystal nuclei among the first silicon source, the first aluminum source, and the alkali source in the second mixture, thereby generating a large amount of stable 13X molecular sieve precursors. A large amount of stable 13X molecular sieve precursors is beneficial for obtaining 13X molecular sieves with uniformly distributed crystal grains in the subsequent process.

[0044] The mass m1 of the directing agent can be 1, 2, 3, 4, 5, 10, 15 or 20.

[0045] In some alternative embodiments, the type of directing agent includes at least one of X-type molecular sieve, Y-type molecular sieve, and 4A-type molecular sieve.

[0046] In these embodiments, a directing agent comprising at least one of X-type molecular sieves, Y-type molecular sieves, and 4A-type molecular sieves can be used to introduce molecular sieve structural units into the first mixture. These molecular sieve structural units can serve as nucleation sites, promoting the formation of uniformly distributed crystal nuclei among the first silicon source, the first aluminum source, and the alkali source in the second mixture, thereby generating a large amount of stable 13X molecular sieve precursors. A large amount of stable 13X molecular sieve precursors is beneficial for obtaining 13X molecular sieves with uniformly distributed crystal grains in the subsequent process.

[0047] In some optional embodiments, the amounts of the first aluminum source n1, the second aluminum source n2, and the alkali source n5 satisfy: (n1+n2):n5=1:(0.70 to 1.65); and / or The amounts of the first silicon source n3, the second silicon source n4, and the alkali source n5 satisfy the following: (n3+n4):n5 = (0.67 to 1.43):1.

[0048] In these embodiments, the ratio of the sum of the amounts of the first aluminum source and the second aluminum source to the amount of the alkali source is 1:(0.70 to 1.65), and the ratio of the sum of the amounts of the first silicon source and the second silicon source to the amount of the alkali source is (0.67 to 1.43):1. This can promote the reaction between the first silicon source, the first aluminum source and the alkali source in the second mixture and form uniformly distributed crystal nuclei, promote the uniform dispersion of aluminum-containing species and generate a large amount of stable 13X molecular sieve precursor. A large amount of stable 13X molecular sieve precursor is beneficial for obtaining 13X molecular sieves with uniformly distributed crystal grains in the subsequent process.

[0049] The amount of substance n5 of the alkali source can be 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.50, 1.55, 1.60 or 1.65.

[0050] The sum of the amounts of the first silicon source and the second silicon source can be 0.67, 0.68, 0.69, 0.70, 0.75, 0.80, 0.90, 1.00, 1.10, 1.20, 1.30, 1.40 or 1.43.

[0051] It should be noted that when the ratio of the sum of the amounts of the first and second aluminum sources to the amount of the alkali source is 1:(0.70 to 1.65), the amount of the alkali source n5 can be 1.0 to 1.5.

[0052] It should be noted that when the ratio of the sum of the amounts of the first silicon source and the second silicon source to the amount of the base source is (0.67 to 1.43):1, the sum of the amounts of the first silicon source and the second silicon source can be 1.

[0053] In some alternative embodiments, the silica-to-alumina ratio of the first aging slurry is (2.5 to 3.5):1.

[0054] In these embodiments, the first aging slurry with a silicon-to-aluminum ratio of (2.5 to 3.5):1 indicates that the first aging slurry is at a high silicon content level, which is beneficial to suppress the formation of other types of molecular sieves in the impurity phase and lay a pure nucleus basis for the subsequent low silicon-to-aluminum ratio 13X molecular sieve.

[0055] The silica-alumina ratio of the first aging slurry can be 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4 or 3.5.

[0056] In some alternative embodiments, the second aging slurry comprises a silicon substance, an aluminum substance, an alkaline substance, and water, wherein the amounts of the silicon substance n6, the aluminum substance n7, the alkaline substance n8, and the water n9 satisfy the following ratio: n6:n7:n8:n9 = 1:(0.91 to 1.00):(0.7 to 1.5):(40 to 80).

[0057] In these embodiments, the second aging slurry with a molar ratio of silicon, aluminum, alkaline substances and water of (0.91 to 1.00):(0.7 to 1.5):(40 to 80) indicates that the amount of silicon and aluminum is in equilibrium, which is beneficial for the subsequent formation of 13X molecular sieves with a low aluminum-silicon ratio.

[0058] The amount of substance n7 of the aluminum substance can be 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99 or 1.00.

[0059] The amount of substance n8 of the alkaline substance can be 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5.

[0060] The amount of water, n9, can be 40, 50, 60, 70, or 80.

[0061] It should be noted that the silicon substance can be calculated as SiO2; the aluminum substance can be calculated as Al; and the alkaline substance can be calculated as Na2O.

[0062] In some optional embodiments, the temperature of the first aging treatment is 30°C to 50°C, and the duration of the first aging treatment is 1 hour to 20 hours; and / or The temperature of the second aging treatment is 40°C to 50°C, and the time of the second aging treatment is 1 hour to 10 hours.

[0063] In these embodiments, the first aging treatment at a temperature of 30°C to 50°C and a time of 1 hour to 20 hours can promote the hydrolysis and condensation between silicon-containing and aluminum-containing species at lower temperatures, forming a large number of fine and uniform primary crystal nuclei. This provides sufficient seeds for the subsequent growth of 13X molecular sieve grains and avoids excessive growth of a single grain. Furthermore, the second aging treatment at a temperature of 40°C to 50°C and a time of 1 hour to 10 hours can reduce the concentration gradient of silicon-containing and aluminum-containing species on the surface of the primary crystal nuclei of the 13X molecular sieve, promoting slow epitaxial growth of the 13X molecular sieve grains and avoiding rapid nucleation that would lead to grain coarsening.

[0064] The temperature for the first aging treatment can be 30℃, 35℃, 40℃, 45℃ or 50℃.

[0065] The duration of the first aging process can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 10 hours, 15 hours, or 20 hours.

[0066] The temperature for the second aging treatment can be 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃ or 50℃.

[0067] The duration of the second aging process can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 10 hours.

[0068] In some alternative embodiments, the crystallization treatment is performed at a temperature of 60°C to 100°C for a duration of 5 hours to 24 hours.

[0069] In these embodiments, crystallization treatment at a temperature of 60°C to 100°C and a time of 5h to 24h allows for sufficient reaction between the aluminum source, silicon source and alkali source in the second aging slurry, ultimately forming small-sized and narrowly distributed 13X molecular sieve crystals and improving the specific surface area and adsorption performance of the 13X molecular sieve.

[0070] The crystallization temperature can be 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃ or 100℃.

[0071] The crystallization treatment time can be 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 16h, 20h or 24h.

[0072] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0073] Example 1 like Figure 1 As shown, a method for preparing a 13X molecular sieve with a low silica-to-alumina ratio includes: S1. Mix the first aluminum source and the alkali source to obtain the first mixture; S2. Mix the directing agent, the first silicon source, and the first mixture to obtain a second mixture; S3. The second mixture is subjected to a first aging treatment to obtain a first aged slurry; S4. Add a second silicon source and a second aluminum source to the first aging slurry to obtain a third mixture; S5. The third mixture is subjected to a second aging treatment to obtain a second aged slurry; S6. The second aging slurry is subjected to crystallization treatment to obtain the crystallized product; S7. The crystallized product is purified to obtain 13X molecular sieve with a low silicon-to-aluminum ratio; The amounts of the first aluminum source n1, the second aluminum source n2, the first silicon source n3, and the second silicon source n4 satisfy the following: (n1+n2):(n3+n4)≥2.0:1.

[0074] The amounts of the first aluminum source n1, the second aluminum source n2, the first silicon source n3, and the second silicon source n4 satisfy the following: (n1+n2):(n3+n4)=2.1:1.

[0075] The first aluminum source is aluminum sulfate, and the second aluminum source is aluminum sulfate.

[0076] The alkaline source is sodium hydroxide.

[0077] The first silicon source is tetraethyl orthosilicate, and the second silicon source is tetraethyl orthosilicate.

[0078] The mass m1 of the directing agent and the mass m2 of silica in the 13X molecular sieve with a low silica-to-alumina ratio satisfy the following: m1:m2=2:100.

[0079] The type of directing agent is Y-type molecular sieve.

[0080] The amounts of the first aluminum source n1, the second aluminum source n2, and the alkali source n5 satisfy the following: (n1+n2):n5=1:(1.00 to 1.50). The amounts of the first silicon source n3, the second silicon source n4, and the alkali source n5 satisfy the following: (n3+n4):n5=1:1.

[0081] The silica-alumina ratio of the first aging slurry is 2.8:1.

[0082] The second aging slurry includes silicon, aluminum, alkaline substances and water. The amounts of silicon (n6), aluminum (n7), alkaline substances (n8), and water (n9) satisfy the following formula: n6:n7:n8:n9 = 1:1:1:40.

[0083] The temperature of the first aging treatment is 40℃, and the time of the first aging treatment is 6 hours. The second aging treatment was performed at a temperature of 45°C for 6 hours.

[0084] The crystallization treatment temperature was 65℃, and the crystallization treatment time was 10h.

[0085] The drying temperature during purification was 80℃, and the drying time was 4 hours.

[0086] Example 2 Compared to Example 1, the differences in this example are as follows, while the rest are the same: The first aluminum source is aluminum nitrate, and the second aluminum source is aluminum nitrate.

[0087] The alkali source is a mixture of sodium hydroxide and sodium carbonate, wherein the molar ratio of sodium hydroxide to sodium carbonate is 3:1.

[0088] The first silicon source is silica, and the second silicon source is silica.

[0089] The mass m1 of the directing agent and the mass m2 of silica in the 13X molecular sieve with a low silica-to-alumina ratio satisfy the following condition: m1:m2=5:100.

[0090] The type of directing agent is X molecular sieve.

[0091] The amounts of the first aluminum source n1, the second aluminum source n2, and the alkali source n5 satisfy the following: (n1+n2):n5=1:(1.00 to 1.50). The amounts of the first silicon source n3, the second silicon source n4, and the alkali source n5 satisfy the following: (n3+n4):n5=1:1.

[0092] The silica-alumina ratio of the first aging slurry is 2.9:1.

[0093] The second aging slurry includes silicon, aluminum, alkaline substances and water. The amounts of silicon (n6), aluminum (n7), alkaline substances (n8), and water (n9) satisfy the following ratio: n6:n7:n8:n9 = 1:0.91:1.20:50.

[0094] The temperature of the first aging treatment is 43℃, and the time of the first aging treatment is 8 hours; The second aging treatment was performed at a temperature of 45°C for 10 hours.

[0095] The crystallization treatment temperature was 75℃, and the crystallization treatment time was 10h.

[0096] The drying temperature during purification was 90℃, and the drying time was 4 hours.

[0097] Example 3 Compared to Example 1, the differences in this example are as follows, while the rest are the same: The first aluminum source is sodium aluminate, and the second aluminum source is sodium aluminate.

[0098] The alkaline source is sodium hydroxide.

[0099] The first silicon source is sodium silicate, and the second silicon source is silica sol.

[0100] The mass m1 of the directing agent and the mass m2 of silica in the 13X molecular sieve with a low silica-to-alumina ratio satisfy the following condition: m1:m2=10:100.

[0101] The type of directing agent is Y-type molecular sieve.

[0102] The amounts of the first aluminum source n1, the second aluminum source n2, and the alkali source n5 satisfy the following: (n1+n2):n5=1:(1.00 to 1.50). The amounts of the first silicon source n3, the second silicon source n4, and the alkali source n5 satisfy the following: (n3+n4):n5=1:1.

[0103] The silica-alumina ratio of the first aging slurry is 3.1:1.

[0104] The second aging slurry includes silicon, aluminum, alkaline substances and water. The amounts of silicon (n6), aluminum (n7), alkaline substances (n8), and water (n9) satisfy the following ratio: n6:n7:n8:n9 = 1:0.71:1.26:60.

[0105] The temperature of the first aging treatment is 45℃, and the time of the first aging treatment is 8 hours; The second aging treatment was performed at a temperature of 50°C for 7 hours.

[0106] The crystallization treatment temperature was 65℃, and the crystallization treatment time was 10h.

[0107] The drying temperature during purification was 100℃, and the drying time was 8 hours.

[0108] Comparative Example 1 Compared to Example 1, the differences in this comparative example are as follows, while the rest are the same: Sodium aluminate was used as the aluminum source, sodium hydroxide as the alkali source, and sodium silicate as the silicon source.

[0109] In water, the aluminum source and the alkali source are first mixed to obtain the first mixture; The silicon source and the first mixture are mixed to obtain the second mixture; The directing agent and the second mixture are then mixed to obtain the third mixture; The third mixture is subjected to aging treatment to obtain an aged slurry; The aged slurry is subjected to crystallization treatment to obtain crystallized products; The crystallized product was purified to obtain 13X molecular sieve.

[0110] The mass m1 of the directing agent and the mass m2 of silica in the 13X molecular sieve satisfy the following condition: m1:m2=10:100.

[0111] The type of directing agent is Y-type molecular sieve.

[0112] The silica-alumina ratio of the aging slurry is 2.8:1.

[0113] The aging slurry includes silicon, aluminum, alkaline substances and water. The amounts of silicon (n6), aluminum (n7), alkaline substances (n8), and water (n9) satisfy the following ratio: n6:n7:n8:n9 = 1:1.05:1.26:60.

[0114] The aging treatment temperature was 45℃, and the aging treatment time was 8 hours.

[0115] The crystallization treatment temperature was 90℃, and the crystallization treatment time was 10h.

[0116] The drying temperature during purification was 100℃, and the drying time was 8 hours.

[0117] Comparative Example 2 Compared to Example 1, the differences in this comparative example are as follows, while the rest are the same: No guiding agent is added.

[0118] Comparative Example 3 Compared to Example 1, the differences in this comparative example are as follows, while the rest are the same: The mass m1 of the directing agent and the mass m2 of silica in the 13X molecular sieve with a low silica-to-alumina ratio satisfy the following condition: m1:m2=30:100.

[0119] Relevant experimental and effect data: 1. The 13X molecular sieves from Examples 1 and 2 were collected and observed under a scanning electron microscope. The results are as follows: Figure 2 and Figure 3 As shown, the 13X molecular sieves of Examples 1 and 2 exhibit high crystallinity, and no impurity phase molecular sieves are formed within the crystals. The overall particle size distribution of the 13X molecular sieves is uniform. Furthermore, the average particle size of the 13X molecular sieves from each example and comparative example was statistically analyzed, and the results are shown in Table 1.

[0120] 2. The compositional distribution of 13X molecular sieves in each embodiment and comparative example was statistically analyzed, and the results are shown in Table 1.

[0121] Table 1. Compositional distribution of 13X molecular sieves in various examples and comparative examples.

[0122] As shown in Table 1, the method for preparing a low silicon-to-aluminum ratio 13X molecular sieve provided in this application suppresses the formation of impurity grains by introducing aluminum and silicon sources in steps. The high quality content of aluminum in the early stage can ensure that the 13X molecular sieve framework is dominant, thereby improving the purity of the grains in the 13X molecular sieve. In addition, the number of crystal nuclei and the growth rate of the 13X molecular sieve can be controlled through a two-stage aging process, avoiding the agglomeration and coarsening of the 13X molecular sieve grains.

[0123] Compared to Example 1, Comparative Example 1 involved a separate aging process without the addition of a second aluminum source and a second silicon source. This made it difficult to control the number of crystal nuclei and the growth rate of the 13X molecular sieve, leading to the agglomeration and coarsening of the 13X molecular sieve grains. Simultaneously, it was difficult to suppress the precipitation of impurity phases in the 13X molecular sieve, resulting in lower purity. Furthermore, the 13X molecular sieve obtained in Comparative Example 1 was not within the range of low silicon-to-aluminum ratio (2.0 to 2.2).

[0124] Compared to Example 1, Comparative Example 2 did not add a directing agent, which reduced the nucleation site effect of the directing agent, resulting in a lower silica-to-alumina ratio in the first aging slurry. This promoted the formation of other types of molecular sieves in the impurity phase, affecting the purity of the 13X molecular sieve. Furthermore, the 13X molecular sieve obtained in Comparative Example 2 was not within the low silica-to-alumina ratio range (2.0 to 2.2). In contrast, Comparative Example 3 added an excessive amount of directing agent, which, while providing a large number of nucleation sites, led to the formation of other types of molecular sieves in the impurity phase of the 13X molecular sieve. Also, the 13X molecular sieve obtained in Comparative Example 3 was not within the low silica-to-alumina ratio range (2.0 to 2.2).

[0125] 3. Carbon dioxide adsorption experiments were conducted on the 13X molecular sieves of each embodiment and comparative example, and the adsorption performance of these 13X molecular sieves was determined. The results are shown in Table 2.

[0126] Table 2 Adsorption performance of 13X molecular sieves in various examples and comparative examples

[0127] As shown in Table 3, the method for preparing a low-silicon-to-aluminum ratio 13X molecular sieve provided in this application can achieve high purity and narrow grain distribution of the low-silicon-to-aluminum ratio 13X molecular sieve by introducing aluminum and silicon sources in steps and performing a two-stage aging treatment. This method can simultaneously improve the purity and grain distribution of the low-silicon-to-aluminum ratio 13X molecular sieve, resulting in a 13X molecular sieve with strong adsorption performance.

[0128] Compared to Example 1, Comparative Example 1, which involves a single aging process without the addition of a second aluminum source and a second silicon source, struggles to control the number and growth rate of 13X molecular sieve nuclei. This leads to the agglomeration and coarsening of the 13X molecular sieve crystals, resulting in poor adsorption performance. Comparative Example 2, lacking a directing agent, reduces the nucleation site effect of the directing agent, resulting in a low silica-alumina ratio in the first aging slurry. This promotes the formation of other types of molecular sieves in the impurity phase, affecting the purity of the 13X molecular sieve and further impairing its adsorption performance. While Comparative Example 3, with its excessive directing agent, provides numerous nucleation sites, the excessive number of nucleation sites leads to the formation of other types of molecular sieves in the impurity phase of the 13X molecular sieve, further contributing to its poor adsorption performance.

[0129] In summary, the embodiments of this application provide a method for preparing 13X molecular sieves with a low silicon-to-aluminum ratio. This method achieves synergistic optimization of the purity and grain distribution of 13X molecular sieves with a low silicon-to-aluminum ratio through the introduction of stepwise aluminum-silicon sources and two-stage aging control.

[0130] In addition, the present application provides a method for preparing a low-silicon-aluminum ratio 13X molecular sieve. The low-silicon-aluminum ratio 13X molecular sieve obtained by this method has the following characteristics: (1) High product purity: The low-silicon-aluminum ratio 13X molecular sieve, after XRD detection, shows no impurity phase and has high crystallinity. (2) Excellent performance: The silicon-aluminum ratio of the low-silicon-aluminum ratio 13X molecular sieve is between 2.0 and 2.2, and the specific surface area is ≥ 650 m². 2 / g, CO2 adsorption capacity ≥ 24%wt (250 mmHg, 25℃). (3) Stable process: By optimizing and controlling the process conditions of the preparation method, and introducing a directing agent, the generation of impurity phases in 13X molecular sieves with low silicon-to-aluminum ratio can be effectively suppressed, and the repeatability is good. (4) Low cost: The overall preparation method does not require special conditions of high temperature and high pressure, and the reaction conditions of the entire preparation method are mild. It can be carried out in a single cation system, and the mother liquor obtained by the subsequent preparation method is simple to treat and can be recycled, which is suitable for industrial production.

[0131] 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 in this application.

Claims

1. A process for the preparation of a 13X molecular sieve having a low silica to alumina ratio, characterized in that, The preparation method comprises: mixing a first aluminum source and an alkali source to obtain a first mixture; mixing a directing agent, a first silicon source and the first mixture to obtain a second mixture; subjecting the second mixture to a first aging treatment to obtain a first aging slurry; adding a second silicon source and a second aluminum source to the first aging slurry to obtain a third mixture; subjecting the third mixture to a second aging treatment to obtain a second aging slurry; subjecting the second aging slurry to a crystallization treatment to obtain a crystallization product; subjecting the crystallization product to a purification treatment to obtain a 13X molecular sieve with a low silicon-to-aluminum ratio; wherein a substance amount n1 of the first aluminum source, a substance amount n2 of the second aluminum source, a substance amount n3 of the first silicon source and a substance amount n4 of the second silicon source satisfy (n1+n2):(n3+n4)≥2.0:

1.

2. The production method according to claim 1, characterized by, The substance amount n1 of the first aluminum source, the substance amount n2 of the second aluminum source, the substance amount n3 of the first silicon source and the substance amount n4 of the second silicon source satisfy (n1+n2):(n3+n4)=(2.0 to 2.2):

1.

3. The production method according to claim 1 or 2, characterized by, The types of the first aluminum source and the second aluminum source respectively include at least one of aluminum sulfate, aluminum nitrate, aluminum trichloride, aluminum isopropylate, sodium metaaluminate and pseudo-boehmite; and / or The types of the first silicon source and the second silicon source respectively include at least one of tetraethyl orthosilicate, white carbon black, sodium silicate and silica sol.

4. The method of claim 1, wherein A mass m1 of the directing agent and a mass m2 of silicon dioxide in the 13X molecular sieve with a low silicon-to-aluminum ratio satisfy m1:m2=(1 to 20):

100.

5. The production method according to claim 1 or 4, characterized by, The type of the directing agent includes at least one of X-type molecular sieve, Y-type molecular sieve and 4A-type molecular sieve.

6. The method of claim 1, wherein, The substance amount n1 of the first aluminum source, the substance amount n2 of the second aluminum source and a substance amount n5 of the alkali source satisfy (n1+n2):n5=1:(0.70 to 1.65); and / or The substance amount n3 of the first silicon source, the substance amount n4 of the second silicon source and the substance amount n5 of the alkali source satisfy (n3+n4):n5=(0.67 to 1.43):

1.

7. The preparation method according to claim 1, characterized in that, A silicon-to-aluminum ratio of the first aging slurry is (2.5 to 3.5):

1.

8. The method of claim 1, wherein, The second aging slurry includes silicon substance, aluminum substance, alkaline substance and water, a substance amount n6 of the silicon substance, a substance amount n7 of the aluminum substance, a substance amount n8 of the alkaline substance and a substance amount n9 of the water satisfy n6:n7:n8:n9=1:(0.91 to 1.00):(0.7 to 1.5):(40 to 80).

9. The method of claim 1, wherein, A temperature of the first aging treatment is 30°C to 50°C, and a time of the first aging treatment is 1h to 20h; and / or A temperature of the second aging treatment is 40°C to 50°C, and a time of the second aging treatment is 1h to 10h.

10. The method of claim 1, wherein, A temperature of the crystallization treatment is 60°C to 100°C, and a time of the crystallization treatment is 5h to 24h.

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