Molecular sieve and method for its preparation

Abstract

The application discloses a molecular sieve and a preparation method thereof, relates to the technical field of molecular sieve synthesis, and aims at solving the problem of serious homogenization of molecular sieve performance. The molecular sieve is ZSM-48 molecular sieve, contains iron elements and silicon elements, and the molar ratio of the iron elements and the silicon elements is (0.004-0.04):1. The relative crystallinity of the ZSM-48 molecular sieve is greater than or equal to 90%. The preparation method is used for preparing the molecular sieve. The molecular sieve and the preparation method thereof are used for producing the molecular sieve.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve synthesis technology, and in particular to a molecular sieve and its preparation method. Background Technology

[0002] ZSM-48 molecular sieve is a novel high-silica molecular sieve developed in the 1980s and synthesized in a system of silicon source, aluminum source, tetramethylamine ions, and n-propylamine. It has a one-dimensional ten-membered ring channel structure. Its characteristics are a high silicon-to-aluminum molar ratio and tubular linear channels, which allow it to accommodate organic molecules with a smaller kinetic radius than benzene for reactions.

[0003] Currently, ZSM-48 molecular sieves can be synthesized using various organic template agents (such as N-methylpyridine, ethylenediamine, alkylamine, and tetramethylammonium), and different types of ZSM-48 molecular sieves can be obtained by adjusting the molar ratio of silica to alumina in the system. However, since these molecular sieves belong to the silica-alumina system, their properties are highly homogeneous. Therefore, it is crucial to synthesize a ZSM-48 molecular sieve with better shape selectivity while maintaining good crystallinity. Summary of the Invention

[0004] The purpose of this invention is to provide a molecular sieve and its preparation method, which can synthesize a ZSM-48 molecular sieve with better shape selectivity while maintaining good crystallinity.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A molecular sieve, wherein the molecular sieve is ZSM-48 molecular sieve, the ZSM-48 molecular sieve contains iron and silicon, the molar ratio of iron to silicon is (0.004~0.04):1, and the relative crystallinity of the ZSM-48 molecular sieve is greater than or equal to 90%.

[0007] Compared with existing technologies, the ZSM-48 molecular sieve provided by this invention is formed by introducing an iron source during the crystallization process, wherein the molar ratio of iron to silicon is (0.004~0.04):1. Compared to pure-phase ZSM-48 molecular sieves, iron is equivalent to an impurity in this molecular sieve. In existing technologies, the presence of impurities significantly affects the performance of molecular sieves, deteriorating their selectivity, stability, and uniformity, while also reducing their crystallinity. Selectivity is the most important characteristic of molecular sieves; molecules smaller than the pore size can be adsorbed. If impurities are introduced, the selectivity of the molecular sieve deteriorates, leading to an increase in unintended side reactions, thus failing to achieve the desired effect, significantly reducing production efficiency, and consequently, worsening economic benefits. This application takes a different approach, introducing an "impurity" iron source during the crystallization process and constraining the molar ratio of iron to silicon to be (0.004–0.04):1. Within this parameter range, iron can more easily enter the molecular sieve framework, acting as part of the molecular sieve itself and guiding its crystallization, thus enhancing its stability. This not only avoids the performance homogenization caused by using a traditional silicon-aluminum system but also promotes crystal formation. By optimizing the crystallization process, a better crystal form is obtained, resulting in Fe-ZSM-48 molecular sieves with superior shape selectivity and higher crystallinity than pure-phase ZSM-48 molecular sieves. Therefore, when this ZSM-48 molecular sieve with better crystallinity and shape selectivity is used as a catalyst in experiments, the reaction progress and direction can be better controlled, enabling the reaction to achieve the desired effect.

[0008] In a second aspect, the present invention also provides a method for preparing a molecular sieve, comprising:

[0009] A colloidal mixture was prepared using ZSM-48 molecular sieve seed crystals, silicon source, iron source, aluminum source, alkali source, template agent, and water as raw materials.

[0010] The colloidal mixture was crystallized into Fe-ZSM-48 molecular sieve.

[0011] Compared with the prior art, the beneficial effects of the molecular sieve preparation method provided by the present invention are the same as those of the molecular sieve in the first aspect, and will not be repeated here. Attached Figure Description

[0012] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0013] Figure 1 A flowchart illustrating the preparation process of the molecular sieve provided in this embodiment is shown.

[0014] Figure 2 A flowchart illustrating the preparation process of the gel-like mixture provided in this embodiment is shown.

[0015] Figure 3 The X-ray diffraction pattern of the molecular sieve in this embodiment is shown;

[0016] Figure 4 The X-ray diffraction pattern of the molecular sieve in this embodiment 2 is shown;

[0017] Figure 5 The X-ray diffraction pattern of the molecular sieve in this embodiment three is shown;

[0018] Figure 6 The X-ray diffraction pattern of the molecular sieve in Example 4 is shown;

[0019] Figure 7 The X-ray diffraction pattern of the molecular sieve in Example 5 is shown. Detailed Implementation

[0020] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0021] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. "Several" means one or more, unless otherwise explicitly specified.

[0022] Currently, ZSM-48 molecular sieves can be synthesized using various organic template agents (such as N-methylpyridine, ethylenediamine, alkylamine, and tetramethylammonium), and different types of ZSM-48 molecular sieves can be obtained by adjusting the molar ratio of silica to alumina in the system. However, because these molecular sieves belong to the silica-alumina system, their properties are highly homogeneous.

[0023] To address the aforementioned problems, this invention provides a molecular sieve that exhibits superior shape selectivity while maintaining good crystallinity. This molecular sieve contains iron and silicon, with a molar ratio of iron to silicon of (0.004–0.04):1. The relative crystallinity of the ZSM-48 molecular sieve is greater than or equal to 90%.

[0024] In specific implementation, this invention introduces an iron source during the crystallization process of the molecular sieve and constrains the molar ratio of iron to silicon to be (0.004~0.04):1. Within this parameter range, iron can more easily enter the molecular sieve framework, acting as part of the molecular sieve itself and guiding its crystallization, thus enhancing the stability of the crystallization. This not only avoids the performance homogenization caused by using the traditional silicon-aluminum system but also promotes crystal formation. By optimizing the crystallization process, a better crystal form is obtained, resulting in superior shape selectivity. Furthermore, the molecular sieve obtained by introducing an iron source during crystallization can achieve a relative crystallinity of up to 90%, with significant room for further improvement. Therefore, only by using this ZSM-48 molecular sieve, with its better crystallinity and shape selectivity, as a catalyst in production practice can the reaction progress and direction be better controlled, enabling the reaction to achieve the desired effect.

[0025] In an alternative embodiment, the ZSM-48 molecular sieve also contains aluminum, and the molar ratio of aluminum to silicon satisfies the following constraint: the molar ratio of Al2O3 to SiO2 is (0 to 0.02):1.

[0026] Experiments have demonstrated that the ZSM-48 molecular sieve in this invention exhibits a relatively high degree of crystallinity. Consequently, when used as a catalyst, it possesses a greater number of active sites on its surface, making it easier to activate reactant molecules and thus enhancing the reactivity of the ZSM-48 molecular sieve as a catalyst, making it easier to achieve the desired effect. Furthermore, under the condition of an Al2O3 to SiO2 molar ratio of (0–0.02):1, the silicon and aluminum sources can, after the crystallization reaction, allow the silicon in the silicon source and the aluminum in the aluminum source to be linked together through oxygen bonds, with virtually no free aluminum present. This contributes to achieving the desired effect and crystal form of the molecular sieve.

[0027] This invention also provides a method for preparing molecular sieves, which can be used to prepare the molecular sieves of this invention. Figure 1 A flowchart illustrating the preparation process of the molecular sieve provided in this embodiment is shown. Figure 1 As shown, the preparation method of this molecular sieve includes:

[0028] Step 101: Using ZSM-48 molecular sieve seed crystals, silicon source, iron source, aluminum source, alkali source, template agent and water as raw materials, a colloidal mixture is prepared.

[0029] For example, the silicon source used in this embodiment of the invention is at least one of silica sol, silica, fumed silica, water glass, and tetraethyl orthosilicate. The iron source used in this embodiment of the invention is at least one of ferrous sulfate, ferrous chloride, ferric sulfate, ferric chloride, and ferric nitrate. After being fully dissolved, the iron source enters the molecular sieve framework more readily in the form of iron ions, acting as part of the molecular sieve itself and guiding its crystallization, thus enhancing the stability of the molecular sieve crystallization. The effect is better when at least one of ferrous sulfate or ferrous chloride is used as the iron source. The aluminum source used in this embodiment of the invention is a soluble aluminum source, which can be at least one of boehmite, aluminum sulfate, aluminum isopropoxide, sodium aluminate, and aluminum nitrate. The alkali source used in this embodiment of the invention is at least one of sodium hydroxide, potassium hydroxide, and calcium hydroxide. The template agent used in this embodiment of the invention is at least one of diamine template agents and ammonium salt template agents. Diamine template agents are at least one selected from ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, and 1,9-onediamine. Ammonium salt template agents are at least one selected from hexamethylammonium bromide, hexamethylammonium chloride, and hexamethylammonium hydroxide. These template agents have moderate molecular size and can play a structure-directing and filling role in the synthesis of ZSM-48 molecular sieves. In addition, these template agents are all charged in aqueous solution, and play a charge-filling role in the molecular sieve synthesis process. Furthermore, in order to more easily obtain the molecular sieve described in this invention, deionized water is used as the raw material. This avoids the occurrence of unexpected ionic impurities during mixing, ensuring a good molecular sieve crystal form and smooth progress of subsequent crystallization steps.

[0030] Step 102: Crystallize the colloidal mixture into Fe-ZSM-48 molecular sieve.

[0031] In one alternative approach, Figure 2 A flowchart illustrating the preparation process of the gel-like mixture provided in this embodiment is shown. Figure 2 As shown, a colloidal mixture was prepared using ZSM-48 molecular sieve seed crystals, silicon source, iron source, aluminum source, alkali source, template agent, and water as raw materials, comprising:

[0032] Step 201: Mix the first silicon source, aluminum source, iron source, alkaline solution and water and then age them to produce a crystallization guiding agent.

[0033] For example, in this embodiment of the invention, an iron source, a first silicon source, an aluminum source, an alkaline solution, and water are added in a certain ratio, stirred evenly, and then the reaction mixture is stirred and aged. Since the iron element in the crystallization guiding agent of this embodiment is introduced through an iron source, iron ions can more easily enter the molecular sieve and be uniformly dispersed on the molecular sieve framework. As part of the molecular sieve itself, it guides the crystallization of the molecular sieve, promotes crystal formation, and enhances the stability of the molecular sieve crystallization. This embodiment of the invention optimizes the crystallization process of the molecular sieve through this method, thereby obtaining a better crystal form.

[0034] For example, the template agent used in this embodiment of the invention is at least one selected from ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-onediamine, hexamethylammonium bromide, hexamethylammonium chloride, and hexamethylammonium hydroxide. These template agents have a suitable molecular size and can play a structure-directing and filling role in the synthesis of ZSM-48 molecular sieves. Furthermore, these template agents are all charged in aqueous solution, playing a charge-filling role in the molecular sieve synthesis process. If this template agent is not used, and other conventional template agents used in experiments are selected instead, the molecular sieve of this embodiment cannot be prepared in subsequent steps.

[0035] Step 202: Add the crystallization guide agent to the second silicon source and stir until homogeneous, then carry out the gelation reaction to obtain a gel-like mixture.

[0036] For example, a gelling reaction is performed on a crystallization guide containing a second silicon source to synthesize a gel-like mixture. This facilitates the crushing and uniform mixing of raw materials, which is beneficial for nucleation during subsequent crystallization. In this case, the molar ratio of the second silicon source to the total silicon source is (0.3–0.6):1. When the gel-like mixture in this embodiment is calculated as a mixture of iron oxide, alkali metal oxide, aluminum oxide, water, and silicon dioxide, the gel-like mixture contains Fe:Al₂O₃:R:M. + The molar ratio of H₂O to SiO₂ is (0.004-0.04):(0-0.02):(0.05-0.50):(0.01-0.30):(1-40):1. Here, R is used to represent the template agent, and M is used to represent the alkali metal cation. + Instead. Wherein, when the colloidal mixture in the embodiments of the present invention is calculated as a mixture formed of iron oxide, alkali metal oxide, aluminum oxide, water, and silicon dioxide, the colloidal mixture is in the proportion of Fe:Al₂O₃:R:M. +When the molar ratio of H2O to SiO2 is (0.02~0.034):(0.01~0.015):(0.1~0.25):(0.05~0.20):(5~20):1, the Fe-ZSM-48 molecular sieve obtained has the highest crystallinity and good crystal form.

[0037] In one alternative method, crystallizing a colloidal mixture into Fe-ZSM-48 molecular sieve includes: crystallizing the colloidal mixture by heating to obtain Fe-ZSM-48 molecular sieve. For example, a two-stage crystallization method can be used to crystallize the colloidal mixture to obtain Fe-ZSM-48 molecular sieve. In the two-stage crystallization method, the first stage crystallization temperature is 140℃-200℃, and the crystallization time is 1h-5h.

[0038] For example, in this embodiment of the invention, the colloidal mixture is crystallized at 140℃-200℃ for 1-5 hours. During this process, iron slowly enters the framework of the ZSM-48 molecular sieve and gradually becomes part of it. Specifically, when crystallization is carried out in the reactor at 160℃-200℃ for 2-4 hours, the iron can completely enter the framework of the ZSM-48 molecular sieve, resulting in high production efficiency. If the crystallization time exceeds this length but is less than 5 hours, the production efficiency will be relatively low, and the desired effect cannot be achieved. Furthermore, if the crystallization time in the reactor is less than 1-5 hours, the iron cannot completely enter the framework of the ZSM-48 molecular sieve, thus failing to form a good crystal structure during crystallization, preventing the Fe-ZSM-48 molecular sieve from achieving the expected degree of crystallinity.

[0039] The second-stage crystallization temperature is 120℃-190℃, which is 10℃-20℃ lower than the first-stage crystallization temperature. The total crystallization time is 12h-96h, and the molecular sieve is cooled at a rate of 1℃ / h-20℃ / h.

[0040] For example, after the first stage of crystallization, the iron element has completely entered the framework of the ZSM-48 molecular sieve. This semi-finished product is then crystallized at a temperature 10-20°C lower than the first stage crystallization temperature, with the total time required for both crystallization processes being 12-96 hours. During the second stage of crystallization, the iron element begins to react within the molecular sieve. If the total time required for both crystallization processes exceeds 96 hours, it incurs additional time costs, resulting in low production efficiency and failing to achieve the desired effects, which is detrimental to industrial production. A total time of 24-48 hours for both crystallization processes yields higher production efficiency. Furthermore, the second stage of crystallization requires cooling the molecular sieve at a rate of 1-20°C / h. If the cooling rate is too fast, high supersaturation is generated, easily leading to a large number of crystal nuclei, resulting in small crystal particles and agglomeration. Experiments revealed that controlling the cooling rate between 5℃ / h and 20℃ / h resulted in crystal particles of moderate size without agglomeration. After crystallization, the crystals were cooled to room temperature, filtered, washed with water, and dried to obtain the Fe-ZSM-48 molecular sieve.

[0041] To verify the effectiveness of the molecular sieve provided in the embodiments of the present invention, the embodiments of the present invention are demonstrated by comparing the embodiments with comparative examples.

[0042] In the following examples and comparative examples, the sample characterization methods are as follows:

[0043] The samples were characterized by XRD using a Bruker D5005 diffractometer with Cu Kα rays (λ = 0.154 nm), tube voltage 40 kV, tube current 30 mA, scanning range 5°–70°, step size 0.013°, and 1 step per second.

[0044] The crystallinity of the molecular sieve was calculated using ZSM-48 molecular sieve (uncalcined, dried at 120°C for 6 hours) prepared according to Example 1 of patent CN101330976 as a standard sample, with the calculation based on the heights of two peaks between 21° and 23°. Furthermore, the molar ratio of Fe / SiO2 in the molecular sieve framework was determined using X-ray fluorescence (XRF).

[0045] Example 1

[0046] The molecular sieve provided in this embodiment of the invention is ZSM-48 molecular sieve, which contains iron, silicon and aluminum elements. The molar ratio of iron to silicon is (0-0.02):(0.004-0.04):1, and its crystallinity is shown in Table 1.

[0047] The method for preparing molecular sieves provided in this embodiment of the invention includes the following steps:

[0048] The first step is to prepare the crystallization guiding agent: mix silica sol, sodium aluminate, 1,6-hexanediamine (HDA), potassium hydroxide, ferric sulfate and deionized water, and stir and age to obtain the crystallization guiding agent.

[0049] Specifically, 34.5g of silica sol (0.23mol) with a SiO2 content of 40wt% and 4.78ml of sodium aluminate (Al2O3 content 50g / L) aqueous solution were weighed and mixed evenly in a beaker to form a first mixed solution. 1.6g of 1,6-hexanediamine (HDA) (0.0138mol) was weighed and dissolved in 13.8ml of potassium hydroxide aqueous solution (10mol / L) to form a second mixed solution. Then, the second mixed solution, 1.48g of ferric sulfate (0.00184mol) and 118ml of deionized water were added to the first mixed solution and stirred and aged to obtain a crystallization guiding agent.

[0050] The second step is to prepare a gel-like mixture: After stirring the crystallization guiding agent for 30 minutes, 34.5 g of silica sol (0.23 mol) with a SiO2 content of 40 wt% is added to the crystallization guiding agent to carry out a gelation reaction, thereby obtaining a gel-like mixture. The molar ratios of ferric sulfate, sodium aluminate, HDA, potassium hydroxide, deionized water, and silica sol in the gel-like mixture satisfy the following:

[0051] n(Fe):n(Al2O3):n(R):n(M + ):n(H2O):n(SiO2)=0.016:0.005:0.03:0.3:21:1.

[0052] The third step is the preparation of molecular sieves: After stirring the obtained colloidal mixture for 30 minutes, it is transferred to a crystallization vessel and crystallized at 180°C for 1 hour, followed by crystallization at 160°C for 56 hours. After crystallization, the mixture is filtered and washed, and the product is dried at 120°C for 6 hours.

[0053] Figure 3 The X-ray diffraction pattern of the molecular sieve in this embodiment is shown. Figure 3 As shown, Embodiment 1 of the present invention uses ZSM-48 molecular sieve.

[0054] Example 2

[0055] Embodiment 2 of the present invention provides a molecular sieve, which is ZSM-48 molecular sieve, containing iron, silicon and aluminum elements, with the molar ratio of iron to silicon being (0-0.02):(0.004-0.04):1, and its crystallinity is shown in Table 1.

[0056] Embodiment 2 of the present invention provides a method for preparing the molecular sieve, comprising the following steps:

[0057] The first step is to prepare the crystallization guiding agent: mix silica, aluminum sulfate, hexamethylenediamine, potassium hydroxide solution, ferric nitrate and deionized water, and stir and age to obtain the crystallization guiding agent.

[0058] Specifically, weigh 27.0g of silica (0.45mol) and (7.2ml) of aluminum sulfate solution (1mol / L) and mix them evenly in a beaker to form a first mixed solution. Weigh 2.44g of hexamethylenediamine (0.021mol) and dissolve it in 5.4ml of potassium hydroxide solution (5mol / L) to form a second mixed solution. Then, add the second mixed solution, 8.71g of ferric nitrate (0.036mol), and 180ml of deionized water to the first mixed solution, stir and age to obtain a crystallization guiding agent.

[0059] The second step is to prepare a gel-like mixture: After stirring the crystallization guiding agent for 30 minutes, add 15.0 g of fumed silica (0.25 mol) to carry out a gelation reaction, obtaining a gel-like mixture. The molar ratios of ferric nitrate, aluminum sulfate, hexamethylenediamine, potassium hydroxide, deionized water, and fumed silica satisfy the following:

[0060] n(Fe):n(Al2O3):n(R):n(M + ):n(H2O):n(SiO2)=0.04:0.008:0.03:0.05:12:1.

[0061] The third step is the preparation of molecular sieves: After stirring the obtained colloidal mixture for 30 minutes, it is transferred to a crystallization vessel and crystallized at 180°C for 1 hour, followed by crystallization at 160°C for 44 hours. After crystallization, the mixture is filtered and washed, and the product is dried at 120°C for 6 hours.

[0062] Figure 4 The X-ray diffraction pattern of the molecular sieve in this embodiment two is shown, as follows: Figure 4 As shown, Embodiment 2 of the present invention uses ZSM-48 molecular sieve.

[0063] Example 3

[0064] Embodiment 3 of the present invention provides a molecular sieve, which is ZSM-48 molecular sieve, containing iron, silicon and aluminum elements, with the molar ratio of iron to silicon being (0-0.02):(0.004-0.04):1, and its crystallinity is shown in Table 1.

[0065] Embodiment 3 of the present invention provides a method for preparing the molecular sieve, comprising the following steps:

[0066] The first step is to prepare the crystallization guiding agent: mix silica sol, sodium aluminate solution, 1,4-butanediamine, sodium hydroxide, ferric sulfate and deionized water, and stir and age to obtain the crystallization guiding agent.

[0067] Specifically, 40.5g of silica sol (0.27mol) with a SiO2 content of 40wt% and 25.5ml of sodium aluminate solution (Al2O3 content 50g / L) are weighed and mixed evenly in a beaker to form a first mixed solution. 3.49g of 1,4-butanediamine (0.03mol) is weighed and dissolved in 6ml of sodium hydroxide solution (5mol / L) to form a second mixed solution. Then, the second mixed solution, 0.4g of ferric sulfate (0.001mol), and 130ml of deionized water are added to the first mixed solution, stirred, and aged to obtain a crystallization guiding agent.

[0068] The second step is to prepare a gel-like mixture: After stirring the crystallization guiding agent for 30 minutes, 34.5 g of silica sol (0.23 mol) with a SiO2 content of 40 wt% is added to carry out a gelation reaction, resulting in a gel-like mixture. The molar ratios of ferric sulfate, sodium aluminate, 1,4-butanediamine, sodium hydroxide, deionized water, and silica sol satisfy the following:

[0069] n(Fe):n(Al2O3):n(R):n(M + ):n(H2O):n(SiO2)=0.004:0.025:0.06:0.05:11:1.

[0070] The third step is the preparation of molecular sieves: After stirring the obtained colloidal mixture for 30 minutes, it is transferred to a crystallization vessel and crystallized at 170°C for 2 hours, followed by crystallization at 160°C for 50 hours. After crystallization, the mixture is filtered and washed, and the product is dried at 120°C for 6 hours.

[0071] Figure 5 The X-ray diffraction pattern of the molecular sieve in this embodiment three is shown, as follows: Figure 5 As shown, Embodiment 3 of the present invention uses ZSM-48 molecular sieve.

[0072] Example 4

[0073] Embodiment 4 of the present invention provides a molecular sieve, which is ZSM-48 molecular sieve, containing iron, silicon and aluminum elements, with the molar ratio of iron to silicon being (0-0.02):(0.004-0.04):1, and its crystallinity is shown in Table 1.

[0074] Embodiment 4 of the present invention provides a method for preparing the molecular sieve, comprising the following steps:

[0075] The first step is to prepare the crystallization directing agent: Tetraethyl orthosilicate, boehmite, 1,4-butanediamine, sodium hydroxide solution, ferric chloride and deionized water are mixed and stirred and aged to obtain the crystallization directing agent.

[0076] Specifically, 44.0 g of tetraethyl orthosilicate (0.21 mol) and 10.2 ml of boehmite solution (Al2O3 content 100 g / L) were weighed and mixed evenly in a beaker to form a first mixed solution. 14.53 g of 1,4-butanediamine (0.125 mol) was weighed and dissolved in 5 ml of sodium hydroxide solution (2 mol / L) to form a second mixed solution. Then, the second mixed solution, 43 g of ferric chloride (0.015 mol), and 180 ml of deionized water were added to the first mixed solution, stirred, and aged to obtain a crystallization guiding agent.

[0077] The second step is to prepare a gel-like mixture: After stirring the crystallization guiding agent for 30 minutes, 60.0 g of tetraethyl orthosilicate (0.29 mol) is added to carry out a gelation reaction, resulting in a gel-like mixture. The molar ratio of ferric chloride, boehmite, 1,4-butanediamine, sodium hydroxide, deionized water, and tetraethyl orthosilicate satisfies the following conditions:

[0078] n(Fe):n(Al2O3):n(R):n(M + ):n(H2O):n(SiO2)=0.03:0.02:0.25:0.02:10:1.

[0079] The third step is the preparation of molecular sieves: After stirring the obtained colloidal mixture for 30 minutes, it is transferred to a crystallization vessel and crystallized at 170°C for 3 hours, followed by crystallization at 160°C for 50 hours. After crystallization, the mixture is filtered and washed, and the product is dried at 120°C for 6 hours.

[0080] Figure 6 The X-ray diffraction pattern of the molecular sieve in Example 4 is shown, as follows. Figure 6 As shown, Embodiment 4 of the present invention uses ZSM-48 molecular sieve.

[0081] Example 5

[0082] Embodiment 5 of the present invention provides a molecular sieve, which is ZSM-48 molecular sieve, containing iron, silicon and aluminum elements, with the molar ratio of iron to silicon being (0-0.02):(0.004-0.04):1, and its crystallinity is shown in Table 1.

[0083] Embodiment 5 of the present invention provides a method for preparing the molecular sieve, comprising the following steps:

[0084] The first step is to prepare the crystallization guiding agent: water glass, boehmite, hexamethylammonium bromide, sodium hydroxide solution, ferric chloride and deionized water are mixed and stirred and aged to obtain the crystallization guiding agent.

[0085] Specifically, 56.0g of water glass (SiO2 content 25w%) and 7.65ml of boehmite solution (Al2O3 content 100g / L) were weighed and mixed evenly in a beaker to form a first mixed solution. 10.86g of hexamethylammonium bromide (0.03mol) was weighed and dissolved in 10ml of sodium hydroxide solution (5mol / L) to form a second mixed solution. Then, the second mixed solution, 3.24g of ferric chloride (0.02mol), and 180ml of deionized water were added to the first mixed solution, stirred, and aged to obtain a crystallization guiding agent.

[0086] The second step is to prepare a gel-like mixture: After stirring the crystallization guiding agent for 30 minutes, 56.0 g of water glass (SiO2 content 25w%) is added to carry out a gelation reaction, resulting in a gel-like mixture. The molar ratios of ferric chloride, boehmite, hexamethylammonium bromide, sodium hydroxide, deionized water, and water glass satisfy the following:

[0087] n(Fe):n(Al2O3):n(R):n(M + ):n(H2O):n(SiO2)=0.04:0.015:0.05:0.1:10:1.

[0088] The third step is the preparation of molecular sieves: After stirring the obtained colloidal mixture for 30 minutes, it is transferred to a crystallization vessel and crystallized at 190°C for 1 hour, followed by crystallization at 175°C for 40 hours. After crystallization, the mixture is filtered and washed, and the product is dried at 120°C for 6 hours.

[0089] Figure 7 The X-ray diffraction pattern of the molecular sieve in Example 5 is shown, as follows. Figure 7 As shown, Embodiment 5 of the present invention uses ZSM-48 molecular sieve.

[0090] Comparative Example 1

[0091] Comparative Example 1 of the present invention provides a molecular sieve, which does not employ a two-stage crystallization method during the crystallization process, and its crystallinity is shown in Table 1.

[0092] Comparative Example 1 of this invention provides a method for preparing the molecular sieve, comprising the following steps:

[0093] The first step is to prepare the crystallization guiding agent: mix silica sol, sodium aluminate, HDA, potassium hydroxide solution, ferric sulfate and deionized water, and stir and age to obtain the crystallization guiding agent.

[0094] Specifically, 37.5g of silica sol (0.25mol) with a SiO2 content of 40wt% and 8.16ml of sodium aluminate solution (Al2O3 content 50g / L) are weighed and mixed evenly in a beaker to form a first mixed solution. 1.74g of HDA (0.015mol) is weighed and dissolved in 10ml of potassium hydroxide solution (5mol / L) to form a second mixed solution. Then, the second mixed solution, 1.6g of ferric sulfate (0.004mol), and 180ml of deionized water are added to the first mixed solution, stirred, and aged to obtain a crystallization guiding agent.

[0095] The second step is to prepare a gel-like mixture: After stirring the crystallization guiding agent for 30 minutes, add 37.5 g of silica sol (0.25 mol) with a SiO2 content of 40 wt%, and carry out a gelation reaction to obtain a gel-like mixture. The molar ratios of ferric sulfate, sodium aluminate, HDA, potassium hydroxide, deionized water, and silica sol satisfy the following:

[0096] n(Fe):n(Al2O3):n(R):n(M + ):n(H2O):n(SiO2)=0.016:0.008:0.03:0.1:25:1.

[0097] The third step is the preparation of molecular sieves: After stirring the obtained colloidal mixture for 30 minutes, it is transferred to a crystallization vessel and crystallized at 160°C for 45 hours. After crystallization, the mixture is filtered and washed, and the product is dried at 120°C for 6 hours.

[0098] Experiments have shown that Comparative Example 1 of this invention is ZSM-48 molecular sieve.

[0099] Comparative Example 2

[0100] Comparative Example 2 of the present invention provides a molecular sieve, which does not employ a two-stage crystallization method during the crystallization process, and its crystallinity is shown in Table 1.

[0101] Comparative Example 2 of this invention provides a method for preparing the molecular sieve, comprising the following steps:

[0102] The first step is to prepare the crystallization guiding agent: ferric sulfate, sodium aluminate, HDA, potassium hydroxide, deionized water and silica sol are mixed and stirred and aged to obtain the crystallization guiding agent.

[0103] Specifically, 37.5g of silica sol (0.25mol) with a SiO2 content of 40wt% and 8.16ml of sodium aluminate solution (Al2O3 content 50g / L) are weighed and mixed evenly in a beaker to form a first mixed solution. 1.74g of HDA (0.015mol) is weighed and dissolved in 10ml of potassium hydroxide solution (5mol / L) to form a second mixed solution. Then, the second mixed solution, 1.6g of ferric sulfate (0.004mol), and 180ml of deionized water are added to the first mixed solution, stirred, and aged to obtain a crystallization guiding agent.

[0104] The second step is to prepare a gel-like mixture: After stirring the crystallization guiding agent for 30 minutes, add 37.5 g of silica sol (0.25 mol) with a SiO2 content of 40 wt%, and carry out a gelation reaction to obtain a gel-like mixture. The molar ratios of ferric sulfate, sodium aluminate, HDA, potassium hydroxide, deionized water, and silica sol satisfy the following:

[0105] n(Fe):n(Al2O3):n(R):n(M + ):n(H2O):n(SiO2)=0.016:0.008:0.03:0.1:25:1.

[0106] The third step is the preparation of molecular sieves: After stirring the obtained colloidal mixture for 30 minutes, it is transferred to a crystallization vessel and crystallized at 180°C for 54 hours. After crystallization, the mixture is filtered and washed, and the product is dried at 120°C for 6 hours.

[0107] Experiments have shown that Comparative Example 2 of this invention uses ZSM-48 molecular sieve.

[0108] Comparative Example 3

[0109] Comparative Example 3 of the present invention provides a molecular sieve, which is also obtained by introducing an iron source during the crystallization process, and its crystallinity is shown in Table 1.

[0110] Comparative Example 3 of this invention provides a method for preparing the molecular sieve, comprising the following steps:

[0111] The first step is to prepare the crystallization guiding agent: ferric sulfate, sodium aluminate, HDA, potassium hydroxide, deionized water and silica sol are mixed and stirred and aged to obtain the crystallization guiding agent.

[0112] Specifically, 37.5g of silica sol (0.25mol) with a SiO2 content of 40wt% and 8.16ml of sodium aluminate solution (Al2O3 content 50g / L) are weighed and mixed evenly in a beaker to form a first mixed solution. 1.74g of HDA (0.015mol) is weighed and dissolved in 10ml of potassium hydroxide solution (5mol / L) to form a second mixed solution. Then, the second mixed solution, 100g of ferric sulfate (0.025mol), and 180ml of deionized water are added to the first mixed solution, stirred, and aged to obtain a crystallization guiding agent.

[0113] The second step is to prepare a gel-like mixture: After stirring the crystallization guiding agent for 30 minutes, add 37.5 g of silica sol (0.25 mol) with a SiO2 content of 40 wt%, and carry out a gelation reaction to obtain a gel-like mixture. The molar ratios of ferric sulfate, sodium aluminate, HDA, potassium hydroxide, deionized water, and silica sol satisfy the following:

[0114] n(Fe):n(Al2O3):n(R):n(M + ):n(H2O):n(SiO2)=0.5:0.008:0.03:0.1:25:1.

[0115] The third step is the preparation of molecular sieves: After stirring the obtained colloidal mixture for 30 minutes, it is transferred to a crystallization vessel and crystallized at 180°C for 1 hour, followed by crystallization at 160°C for 44 hours. After crystallization, the mixture is filtered and washed, and the product is dried at 120°C for 6 hours.

[0116] Experiments have shown that Comparative Example 3 of this invention uses ZSM-48 molecular sieve.

[0117] Comparative Example 4

[0118] Comparative Example 4 of the present invention provides a molecular sieve, which is also obtained by introducing an iron source during the crystallization process, and its crystallinity is shown in Table 1.

[0119] Comparative Example 4 of this invention provides a method for preparing this molecular sieve, comprising the following steps:

[0120] The first step is to prepare the crystallization guiding agent: mix ferric nitrate, sodium aluminate, HDA, potassium hydroxide, deionized water and silica sol, and stir and age to obtain the crystallization guiding agent.

[0121] Specifically, 37.5g of silica sol (0.25mol) with a SiO2 content of 40wt% and 10ml of sodium aluminate solution (Al2O3 content 50g / L) are weighed and mixed evenly in a beaker to form a first mixed solution. 1.74g of HDA (0.015mol) is weighed and dissolved in 10ml of potassium hydroxide solution (5mol / L) to form a second mixed solution. Then, the second mixed solution, 80g of ferric nitrate (0.2mol), and 180ml of deionized water are added to the first mixed solution, stirred, and aged to obtain a crystallization guiding agent.

[0122] The second step is to prepare a gel-like mixture: After stirring the crystallization guiding agent for 30 minutes, 37.5 g of silica sol (0.25 mol) with a SiO2 content of 40 wt% is added to carry out a gelation reaction, resulting in a gel-like mixture. The molar ratios of ferric nitrate, sodium aluminate, HDA, potassium hydroxide, deionized water, and silica sol satisfy the following:

[0123] n(Fe):n(Al2O3):n(R):n(M + ):n(H2O):n(SiO2)=0.4:0.008:0.03:0.3:25:1.

[0124] The third step is the preparation of the molecular sieve: the obtained colloidal mixture is stirred for 30 minutes, then transferred to a crystallization vessel and crystallized at 180°C for 1 hour, followed by crystallization at 160°C for 44 hours. After crystallization, the mixture is filtered and washed, and the product is dried at 120°C for 6 hours. Experimental results show that Comparative Example 4 of this invention uses ZSM-48 molecular sieve.

[0125] Table 1 shows the crystallinity and the Fe / SiO2 molar ratio in the molecular sieve framework of Examples 1 to 5 and Comparative Examples 1 to 4 of the present invention.

[0126] Table 1

[0127]

[0128]

[0129] As can be seen from the table above, the molecular sieves prepared in Examples 1 to 5 of the present invention, obtained by introducing an iron source during the crystallization process, have a crystallinity as high as 98%. Furthermore, Examples 1 to 5 of the present invention employ a two-stage crystallization process. Compared to Comparative Examples 1 and 2, which employ a one-stage crystallization process, the molar ratio of Fe / SiO2 in the molecular sieve framework is significantly higher, indicating that the two-stage crystallization method facilitates the insertion of iron into the molecular sieve framework. Referring to Table 1, which shows the crystallinity of Examples 1 to 5 of the present invention and Comparative Examples 1 and 2, it can be seen that the two-stage crystallization method allows iron to completely enter the molecular sieve framework and react completely during subsequent crystallization, promoting the formation of molecular sieve crystals, optimizing the crystallization process, and ultimately achieving a high degree of crystallinity. In Comparative Examples 3 and 4 of the present invention, the amount of iron source used in the preparation of molecular sieves is relatively large and does not fall within the range of 0.004-0.04 used in Examples 1 to 5 of the present invention. According to the results in the table, the crystallinity of Comparative Example 3 is much smaller than that of Examples 1 to 5 of the present invention, and the molar ratio of Fe / SiO2 in the molecular sieve framework of Comparative Example 4 is as low as 0.0007. This indicates that when the range of 0.004-0.04 required by the embodiments of the present invention is exceeded, even if the proportion of iron source is increased, the iron element cannot completely and effectively enter the molecular sieve framework to play a role, so that the final prepared molecular sieve cannot achieve the expected effect.

[0130] The above description is merely a specific embodiment of the present invention. Obviously, various modifications and combinations can be made without departing from the spirit and scope of the present invention. Accordingly, this specification and accompanying drawings are merely exemplary descriptions of the invention as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of the present invention. Clearly, those skilled in the art can make various alterations and modifications to the present invention without departing from its spirit and scope. Thus, if these modifications and variations of the present invention fall within the scope of the claims and their equivalents, the intent of the present invention includes these modifications and variations. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the scope of the claims.

Claims

1. A molecular sieve, characterized in that, The molecular sieve is ZSM-48 molecular sieve, which contains iron and silicon elements, and the molar ratio of iron to silicon is (0.004~0.04):

1. The relative crystallinity of the ZSM-48 molecular sieve is greater than or equal to 90%.

2. The molecular sieve according to claim 1, characterized in that, The ZSM-48 molecular sieve also contains aluminum, and the molar ratio of aluminum to silicon satisfies the following constraints: The molar ratio of Al2O3 to SiO2 is (0~0.02):

1.

3. A method for preparing a molecular sieve as described in claim 1 or 2, characterized in that, include: A colloidal mixture was prepared using ZSM-48 molecular sieve seed crystals, silicon source, iron source, aluminum source, alkali source, template agent, and water as raw materials. The colloidal mixture was crystallized into Fe-ZSM-48 molecular sieve.

4. The method for preparing molecular sieves according to claim 3, characterized in that, The colloidal mixture prepared from ZSM-48 molecular sieve seed crystals, silicon source, iron source, aluminum source, alkali source, template agent, and water includes: A crystallization guiding agent is prepared by mixing a first silicon source, an aluminum source, an iron source, an alkaline solution, and water and then aging the mixture. The crystallization guide agent is added to the second silicon source and stirred evenly, and then a gelation reaction is carried out to obtain a gel-like mixture; the molar ratio of the second silicon source to the total silicon source is (0.3~0.6):

1.

5. The method for preparing molecular sieves according to claim 4, characterized in that, The crystallization of the colloidal mixture into Fe-ZSM-48 molecular sieve includes: The colloidal mixture was crystallized by heating to obtain the Fe-ZSM-48 molecular sieve.

6. The method for preparing molecular sieves according to claim 5, characterized in that, The step of crystallizing the colloidal mixture by heating to obtain the Fe-ZSM-48 molecular sieve includes: The colloidal mixture was crystallized using a two-stage crystallization method to obtain the Fe-ZSM-48 molecular sieve; In the two-stage crystallization method, the first stage crystallization temperature is 140℃-200℃, and the crystallization time is 1h-5h. The second crystallization temperature is 120℃-190℃, which is 10℃-20℃ lower than the first crystallization temperature. The total crystallization time is 12h-96h.

7. The method for preparing molecular sieves according to claim 6, characterized in that, After obtaining the Fe-ZSM-48 molecular sieve by crystallizing the colloidal mixture using a heating method, the method further includes: The molecular sieve was cooled at a rate of 1℃ / h to 20℃ / h.

8. The method for preparing molecular sieves according to claim 3, characterized in that, The molar ratio of the iron source, aluminum source, template agent, alkali source, water, and silicon source satisfies: n(Fe):n(Al2O3):n(R):n(M + ):n(H2O):n(SiO2)=(0.004-0.04):(0~0.02):(0.05~0.50):(0.01~0.30):(1~40):1; Where R is the template agent, M + It is an alkali metal cation.

9. The method for preparing molecular sieves according to claim 3, characterized in that, The template agent is at least one of diamine template agents and ammonium salt template agents.

10. The method for preparing molecular sieves according to claim 3, characterized in that, The iron source is at least one of ferrous sulfate, ferrous chloride, and ferric sulfate.

Images