A ZSM-23 molecular sieve and its synthesis method

Abstract

The present invention provides a ZSM-23 molecular sieve and a synthesis method thereof. The method includes: dissolving aluminum source Y in water to obtain an aluminum source solution; dissolving an organic base M in water, adding an aluminum source solution to obtain a mixed solution; taking out the mixed solution after being water-bathed at 65-85°C for 2-5 hours and cooling to room temperature, and then reducing the temperature of the mixed solution to 5-10°C with ice water; under the conditions of 5-10°C, quickly adding a template Q to the mixed solution after cooling; slowly adding a silicon source X dropwise to the mixed solution under vigorous stirring; adding water to obtain a gel; crystallizing the gel; washing, drying, and roasting the crystallized product to obtain a ZSM-23 molecular sieve. The ZSM-23 molecular sieve prepared by the method is a needle-like structure. Compared with conventional synthesis methods, the molecular sieve synthesized by this method has a higher weak acid content.

Description

Technical Field

[0001] The present invention relates to the field of molecular sieve catalytic material synthesis, and in particular to a preparation method for synthesizing ZSM-23 molecular sieve using an organic base. Background Art

[0002] ZSM-23 molecular sieve is a high-silicon molecular sieve with an MTT topological structure, consisting of a five-membered ring, a six-membered ring, and a ten-membered ring. The unit cell parameters are In 1978, Plank et al. at Mobil Corporation in the United States first synthesized ZSM-23 molecular sieve. Subsequently, scientists from various countries searched for organic templates to synthesize ZSM-23. This molecular sieve has promising applications in hydroisomerization. Hydroisomerization requires not only a specific pore structure but also an appropriate number of acidic sites. Excessive strong acidic sites lead to increased cracking reactions, so the molecular sieve material must have more weak acidic sites and fewer strong acidic sites to ensure the isomerization reaction proceeds. Existing patents for the preparation of ZSM-23 molecular sieves often use inorganic bases as raw materials, requiring post-treatment to expose the acidic sites.

[0003] Patents US4,076,842 and CN102256704A applied by Mobil Corporation are both for the preparation of ZSM-23 molecular sieves using long-chain diquaternary ammonium salt templates. The main innovation is that molecular sieves with low silicon-aluminum ratios can be synthesized, but a large amount of inorganic base raw materials are required during the synthesis process.

[0004] Patents US4,483,835, US10,160,657B2, and CN101646493A applied for by Chevron Corporation all use cyclic templates to prepare ZSM-23 molecular sieves. The main innovation is that small-grain molecular sieves can be prepared, but a large amount of inorganic base is also required during the synthesis process.

[0005] US5707601 first mentioned the use of small molecule organic amines, such as isobutylamine, diisobutylamine, diisopropylamine and trimethylamine, to prepare molecular sieves with MTT topological structure. CN110683558 also used small molecule organic amines to prepare short-axis MTT zeolite. However, both patents require the addition of inorganic bases for synthesis.

[0006] CN 104058422 A and CN 102897785 B, Seed-assisted synthesis of ZSM-23 zeolites in the absence of alkali metal ions (Yujing Chen, Chuang Li, Lei Wang, Miao Zhang, Chang Liang; Microporous and Mesoporous Materials, Volume 252, 1 November 2017, Pages 146-153), both synthesize hydrogen-type ZSM-23 molecular sieves. However, the previous step requires the addition of seed crystals and precursors, which differs from the present invention. Furthermore, the product obtained with the seed-assisted method is closely related to the quality of the seed crystals. If there are impurities in the seed crystals, the product will contain a high impurity content. After the seed crystals are added, the newly grown grains will first grow around the nucleus, resulting in an uneven grain size distribution. Summary of the Invention

[0007] In order to address the problem that a large amount of inorganic base is used in the synthesis of ZSM-23 molecular sieve, an ammonia exchange step is required after synthesis to remove the alkali metal cations in the molecular sieve pores, which requires many operation steps and easily affects the acidity of the molecular sieve, the present invention provides a method for synthesizing ZSM-23 molecular sieve. By using organic base substances instead of inorganic bases for synthesis, more of the original acid centers of ZSM-23 are retained, and the number of post-processing steps is reduced.

[0008] To achieve the above object, the present invention provides a method for synthesizing ZSM-23 molecular sieve, which comprises the following steps:

[0009] (1) dissolving an aluminum source Y in water to obtain an aluminum source solution;

[0010] (2) dissolving an organic base M in water and adding dropwise the aluminum source solution to obtain a mixed solution; wherein the organic base M is selected from di(2-hydroxyethyl)amine, N-methyl-2-hydroxyethylamine, and 2-amino-2-methyl-1-propanol;

[0011] (3) placing the mixed solution in a water bath at 65-85°C for 2-5 hours, cooling it to room temperature, and then cooling the temperature of the mixed solution to 5-10°C with ice water;

[0012] (4) Under the condition of 5-10°C, the template Q is quickly added to the mixed solution after cooling in step (3);

[0013] (5) Slowly adding the silicon source X dropwise to the mixed solution obtained in step (4) under vigorous stirring;

[0014] (6) adding water and mixing uniformly to obtain a gel, wherein the molar ratio of H2O to silicon source X in the final gel is 10-35:1;

[0015] (7) crystallizing the final gel obtained in step (6);

[0016] (8) washing, drying, and calcining the crystallized product to obtain ZSM-23 molecular sieve;

[0017] The molar ratio of each material in the final gel obtained in step (6) is X:Y=60-110:1, M:X=0.03-0.1:1, and Q:X=0.40-0.90:1.

[0018] In the above-mentioned synthesis method, the template agent Q is the main structure-directing agent, and the organic base M replaces the alkali metal ion to balance the charge during the crystallization reaction, adjust the pH value, and promote the dissolution of the silicon source. Since the molecular weight of the organic base is larger than that of the inorganic base, the movement speed in the solution will slow down. The heating water bath in step (4) helps to accelerate the reaction of the organic base with the aluminum source, and then drops to a low temperature environment because the template agent is easy to volatilize at room temperature, and the addition of the template agent has an exothermic process, which will further accelerate the loss of the template agent, so it is necessary to mix the solution under a low temperature environment. Through this method, other substances outside the molecular sieve can be removed only by the step of roasting to expose the acidic site. Since the template agent used in the present invention is a small molecule organic amine template agent, the morphology of the synthesized product is similar to that of the other products synthesized using small molecule amine template agents, all of which are needle-shaped structures with a length of 200-400nm and an axis-to-diameter ratio of 1:6-1:10.

[0019] In the above synthesis method, preferably, the molar ratio of each material in the final gel obtained in step (6) is X:Y=80-100:1, M:X=0.04-0.08:1, and Q:X=0.50-0.70:1.

[0020] In the above synthesis method, preferably, the aluminum source Y is selected from at least one of water-soluble aluminum salts, alkali metal aluminates, aluminum alkoxides and metallic aluminum; more preferably, the aluminum source Y is aluminum sulfate.

[0021] In the above synthesis method, preferably, the silicon source X is selected from at least one of silicon dioxide, alkali metal silicates, and tetraalkyl orthosilicates. The silicon dioxide can be selected from at least one of a silica colloidal suspension, a silica precipitate, and fumed silica. More preferably, the silica colloidal suspension has a silica content of 30 wt% to 40 wt%. Further preferably, the silicon source X is silica sol.

[0022] In the above-mentioned synthesis method, a small molecule organic amine is used as a template. This substance is volatile and also easily volatilizes in aqueous solution. Therefore, the process of configuring the gel is preferably carried out in a closed environment, and the template needs to be added quickly when adding it to prevent losses caused by volatilization. When adding the silicon source, it needs to be added slowly. This feeding method can ensure that the silicon source and the previous substances can be completely mixed and uniform, and will not agglomerate under alkaline conditions, causing local uneven mixing and eventually the appearance of quartz impurities. Preferably, the template Q is selected from at least one of isopropylamine, n-butylamine, ethylenediamine, and diisobutylamine.

[0023] In the above synthesis method, preferably, step (1) also includes the process of adding other trivalent elements Y1, and the other trivalent elements Y1 are selected from at least one of Fe, Ga, and Be, and the molar ratio of the other trivalent elements Y1 to the aluminum source Y is 0.1-1.0:1.

[0024] In the above synthesis method, preferably, the crystallization is carried out under closed conditions at 150-180° C. for 30-60 hours.

[0025] In the above synthesis method, preferably, the drying is carried out at 100-120° C. for 2-3 hours.

[0026] In the above synthesis method, preferably, the calcination is carried out at 300-550° C. for 10-20 h.

[0027] The present invention also provides a ZSM-23 molecular sieve, wherein the ZSM-23 molecular sieve is synthesized by the above-mentioned synthesis method, the ZSM-23 molecular sieve does not contain other crystalline impurities, the particle size of the ZSM-23 molecular sieve is in the range of 200-400nm, and the morphology is needle-shaped.

[0028] According to a specific embodiment of the present invention, preferably, the axis-to-diameter ratio of the zSM-23 molecular sieve is 1:6-1:10.

[0029] The prior art uses a large amount of inorganic base when synthesizing ZSM-23 molecular sieves. After the synthesis, an ammonia exchange step is required to remove the alkali metal cations in the molecular sieve pores. There are many operating steps and it is easy to affect the acidity of the molecular sieve. The present invention uses an organic base substance instead of an inorganic base for synthesis, and more of the original acidic center of ZSM-23 is retained. Compared with the molecular sieve for ammonia exchange, in addition to reducing the post-processing steps, the weak acid content of the obtained product is more, and the medium and strong acid content is reduced. This acid distribution is more conducive to the isomerization reaction in the isomerization of long-chain alkanes, reducing cracking products. Through this technical solution, a molecular sieve with a high weak acid content can be obtained without post-processing, simplifying the process flow. The ZSM-23 molecular sieve prepared by this method is a needle-shaped structure. Compared with the conventional synthesis method, the molecular sieve synthesized by this method has a higher weak acid content. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the XRD pattern of ZSM-23 synthesized in Example 1.

[0031] Figure 2 This is the SEM image of ZSM-23 synthesized in Example 1. DETAILED DESCRIPTION

[0032] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0033] Raw material name Specification Manufacturer aluminum sulfate Analytical purity 99% Sinopharm Chemical Reagent Co., Ltd. N-Methyl-2-hydroxyethylamine Analytical purity 99% Sigma Isopropylamine Analytical purity 99.5% Sinopharm Chemical Reagent Co., Ltd. Silica Sol <![CDATA[SiO2=30-31%]]> Sinopharm Chemical Reagent Co., Ltd.

[0034] Evaluation and analysis methods:

[0035] XRD tests were performed on a Bruker diffractometer using a Cu target. α The light source (λ = 0.15432 nm) was a graphite monochromator, with a tube voltage of 40 kV and a tube current of 40 mA. The scanning speed was 10° / min in the range of 5-55°. Qualitative analysis was performed using X-ray diffraction charts (JCPDS).

[0036] The acidity test was carried out using calcined molecular sieves. The molecular sieves were pressed into tablets using a pressure of 1.5-2.0 MPa in a dry state and sieved into 20-40 mesh particles. The pellets were purged in a helium atmosphere and adsorbed with 10% ammonia and helium at 120°C. The pellets were then heated to 550°C to examine the content of different acid strengths.

[0037] Example 1

[0038] This embodiment provides a method for synthesizing ZSM-23 molecular sieve, which comprises:

[0039] (1) First, dissolve 60.0 g of Al2(SO4)3 in 470.3 g of H2O and stir until a clear solution is obtained;

[0040] (2) dissolving 39.9 g of organic base M N-methyl-2-hydroxyethylamine in 210.0 g of H2O, stirring until a clear solution is obtained, and then adding dropwise the clear solution in step (1) to obtain a mixed solution;

[0041] (3) The mixed solution was placed in a water bath at 85°C for 2 hours, then cooled to room temperature, and then cooled to 5°C with ice water;

[0042] (4) When the mixed solution is at 5°C, 223.1 g of template agent Q isopropylamine is quickly added to the mixed solution in step (2);

[0043] (5) 1051.2 g of silica sol with a silica content of 30% was slowly added dropwise to the mixed solution of step (3) under vigorous stirring;

[0044] (6) 39.8 g of H O was added and mixed uniformly to obtain a gel. The molar ratio of H O to silicon source X in the final gel was 15:1.

[0045] (7) The obtained gel was crystallized at 150 °C for 60 h;

[0046] (8) The crystallized product was washed with distilled water, dried at 100 °C for 3 h, and calcined at 500 °C for 10 h to obtain ZSM-23 molecular sieve;

[0047] The molar ratio of each material in the gel obtained in step (6) is 15H2O:SiO2:0.016Al2O3:0.095M:0.7Q.

[0048] The product prepared is a pure phase ZSM-23 molecular sieve with a relative crystallinity of 94.16%. The XRD pattern and SEM pattern of the ZSM-23 molecular sieve are shown in Figure 1. Figure 1 、 Figure 2 As shown. Figure 2 It can be seen that the ZSM-23 molecular sieve obtained in this example has a particle size range of 200-400 nm, a needle-like morphology, and an axis-to-diameter ratio of 1:6-1:10.

[0049] Example 2

[0050] This embodiment provides a method for synthesizing ZSM-23 molecular sieve, which comprises:

[0051] (1) First, dissolve 32.5g Al2(SO4)3 in 235.2g H2O and stir until a clear solution is obtained;

[0052] (2) dissolving 12.6 g of N-methyl-2-hydroxyethylamine in 78.7 g of H2O, stirring until a clear solution is obtained, and then adding dropwise the clear solution in step (1) to obtain a mixed solution;

[0053] (3) The mixed solution was placed in a water bath at 80°C for 3 hours, then cooled to room temperature, and then cooled to 10°C with ice water;

[0054] (4) 127.5 g of template agent Q isopropylamine was quickly added to the mixed solution in step (2);

[0055] (5) 1051.2 g of silica sol with a silica content of 30% was slowly added dropwise to the mixed solution of step (3) under vigorous stirring;

[0056] (6) 406.2 g of H O was added and mixed uniformly to obtain a gel. The molar ratio of H O to silicon source X in the final gel was 35:1.

[0057] (7) The obtained gel was crystallized at 180°C for 30 h;

[0058] (8) The crystallized product was washed with distilled water, dried at 120 °C for 2 h, and calcined at 300 °C for 20 h to obtain ZSM-23 molecular sieve;

[0059] The molar ratio of each material in the gel obtained in step (6) is 15H2O:SiO2:0.009Al2O3:0.03M:0.4Q.

[0060] The prepared product is a pure-phase ZSM-23 molecular sieve with a relative crystallinity of 103.96%.

[0061] Example 3

[0062] This embodiment provides a method for synthesizing ZSM-23 molecular sieve, which comprises:

[0063] (1) First, dissolve 32.5g Al2(SO4)3 in 235.2g H2O and stir until a clear solution is obtained;

[0064] (2) dissolving 21.0 g of N-methyl-2-hydroxyethylamine (an organic base) in 78.7 g of H2O, stirring until a clear solution is obtained, and then adding dropwise the clear solution in step (1) to obtain a mixed solution;

[0065] (3) The mixed solution was placed in a water bath at 80°C for 3 hours, then cooled to room temperature, and then cooled to 5°C with ice water.

[0066] (4) 127.5 g of template agent Q isopropylamine was quickly added to the mixed solution in step (2);

[0067] (5) 1051.2 g of silica sol with a silica content of 30% was slowly added dropwise to the mixed solution of step (3) under vigorous stirring;

[0068] (6) 406.2 g of H O was added and mixed uniformly to obtain a gel. The molar ratio of H O to silicon source X in the final gel was 35:1.

[0069] (7) The obtained gel was crystallized at 180°C for 30 h;

[0070] (8) The crystallized product was washed with distilled water, dried at 120 °C for 2 h, and calcined at 300 °C for 20 h to obtain ZSM-23 molecular sieve;

[0071] The molar ratio of each material in the gel obtained in step (6) is 15H2O:SiO2:0.009Al2O3:0.03M:0.4Q.

[0072] The prepared product is a pure-phase ZSM-23 molecular sieve with a relative crystallinity of 102.57%.

[0073] Example 4

[0074] This embodiment provides a method for synthesizing ZSM-23 molecular sieve, which comprises:

[0075] (1) First, dissolve 39.3 g of Al2(SO4)3 in 287.3 g of H2O and stir until a clear solution is obtained;

[0076] (2) dissolving 12.6 g of an organic base, N-methyl-2-hydroxyethylamine, in 78.7 g of H2O, stirring until a clear solution is obtained, and then adding dropwise the clear solution in step (1) to obtain a mixed solution;

[0077] (3) The mixed solution was placed in a water bath at 65°C for 5 hours, then cooled to room temperature, and then the temperature of the mixed solution was lowered to 8°C with ice water.

[0078] (4) When the mixed solution is at 8°C, 286.9 g of template agent Q isopropylamine is quickly added to the mixed solution in step (2);

[0079] (5) 1051.2 g of silica sol with a silica content of 30% was slowly added dropwise to the mixed solution of step (3) under vigorous stirring;

[0080] (6) 2287.1 g of H2O was added and mixed uniformly to obtain a gel. The molar ratio of H2O to silicon source X in the final gel was 35:1.

[0081] (7) The obtained gel was crystallized at 170 °C for 35 h;

[0082] (8) The crystallized product was washed with distilled water, dried at 120 °C for 2 h, and calcined at 500 °C for 15 h to obtain ZSM-23 molecular sieve;

[0083] The molar ratio of each material in the gel obtained in step (6) is 35H2O:SiO2:0.011Al2O3:0.03M:0.9Q.

[0084] The prepared product is a pure-phase ZSM-23 molecular sieve with a relative crystallinity of 99.53%.

[0085] Example 5

[0086] This embodiment provides a method for synthesizing ZSM-23 molecular sieve, which comprises:

[0087] (1) First, dissolve 89.4 g Al2(SO4)3 and 43.2 g Fe(NO3)3 in 287.3 g H2O and stir until a clear solution is obtained;

[0088] (2) dissolving 12.6 g of an organic base, N-methyl-2-hydroxyethylamine, in 78.7 g of H2O, stirring until a clear solution is obtained, and then adding dropwise the clear solution in step (1) to obtain a mixed solution;

[0089] (3) The mixed solution was placed in a water bath at 80°C for 3 hours, then cooled to room temperature, and then cooled to 5°C with ice water.

[0090] (4) quickly adding 223.14 g of template agent Q isopropylamine to the mixed solution in step (2);

[0091] (5) 1051.2 g of silica sol with a silica content of 30% was slowly added dropwise to the mixed solution of step (3) under vigorous stirring;

[0092] (6) 1804.0 g of H2O was added and mixed uniformly to obtain a gel. The molar ratio of H2O to silicon source X in the final gel was 35:1.

[0093] (7) The obtained gel was crystallized at 170 °C for 35 h;

[0094] (8) The crystallized product was washed with distilled water, dried at 120 °C for 2 h, and calcined at 500 °C for 15 h to obtain ZSM-23 molecular sieve;

[0095] The molar ratio of each material in the gel obtained in step (6) is 30H2O:SiO2:0.025Al2O3:0.017Fe2O3:0.03M:0.7Q;

[0096] The prepared product is a pure-phase ZSM-23 molecular sieve with a relative crystallinity of 90.86%.

[0097] Example 6

[0098] This embodiment provides a method for synthesizing ZSM-23 molecular sieve, which comprises:

[0099] (1) First, 89.4 g Al2(SO4)3 and 43.2 g Ga(NO3)3 were dissolved in 287.3 g H2O and stirred until a clear solution was obtained;

[0100] (2) dissolving 12.6 g of an organic base, N-methyl-2-hydroxyethylamine, in 78.7 g of H2O, stirring until a clear solution is obtained, and then adding dropwise the clear solution in step (1) to obtain a mixed solution;

[0101] (3) The mixed solution was placed in a water bath at 80°C for 3 hours, then cooled to room temperature, and then cooled to 5°C with ice water.

[0102] (4) quickly adding 223.14 g of template agent Q isopropylamine to the mixed solution in step (2);

[0103] (5) 1051.2 g of silica sol with a silica content of 30% was slowly added dropwise to the mixed solution of step (3) under vigorous stirring;

[0104] (6) 1804.0 g of H2O was added and mixed uniformly to obtain a gel. The molar ratio of H2O to silicon source X in the final gel was 35:1.

[0105] (7) The obtained gel was crystallized at 170 °C for 35 h;

[0106] (8) The crystallized product was washed with distilled water, dried at 120 °C for 2 h, and calcined at 500 °C for 15 h to obtain ZSM-23 molecular sieve;

[0107] The molar ratio of each material in the gel obtained in step (6) is 30H2O:SiO2:0.025Al2O3:0.015Ga2O3:0.05M:0.7Q;

[0108] The prepared product is a pure-phase ZSM-23 molecular sieve with a relative crystallinity of 90.86%.

[0109] Comparative Example 1

[0110] This comparative example provides a method for synthesizing ZSM-23 molecular sieve, which comprises:

[0111] (1) First, dissolve 60.0 g of Al2(SO4)3 in 470.3 g of H2O and stir until a clear solution is obtained;

[0112] (2) dissolving 21.2 g of inorganic base sodium hydroxide in 35.8 g of H2O, stirring until a clear solution is obtained, and then adding dropwise the clear solution in step (1) to obtain a mixed solution;

[0113] (3) 223.1 g of template agent Q isopropylamine was quickly added to the mixed solution in step (2);

[0114] (4) 1051.2 g of silica sol with a silica content of 30% was slowly added dropwise to the mixed solution of step (3) under vigorous stirring;

[0115] (5) 214.0 g of H2O was added and mixed uniformly to obtain a gel. The molar ratio of H2O to silicon source X in the final gel was 15:1.

[0116] (6) The obtained gel was crystallized at 150 °C for 60 h;

[0117] (7) The crystallized product was washed with distilled water, dried at 100°C for 3 h, and calcined at 500°C for 10 h; the molar ratio of the materials in the gel obtained in step (5) was 15H2O:SiO2:0.016Al2O3:0.095Na2O:0.7Q

[0118] (8) using ammonium chloride to exchange ammonia according to the ratio of molecular sieve: ammonium chloride: water = 1:1:10, and then filtering and washing the mother liquor, drying at 120 ° C for 3 h, and calcining at 500 ° C for 5 h to obtain ZSM-23 molecular sieve;

[0119] The prepared product is a pure-phase ZSM-23 molecular sieve with a relative crystallinity of 100.00%.

[0120] Comparative Example 2

[0121] This comparative example provides a method for synthesizing ZSM-23 molecular sieve, which comprises:

[0122] (1) First, dissolve 32.5g Al2(SO4)3 in 235.2g H2O and stir until a clear solution is obtained;

[0123] (2) dissolving 6.7 g of inorganic base sodium hydroxide in 13.4 g of H2O, stirring until a clear solution is obtained, and then adding dropwise the clear solution in step (1) to obtain a mixed solution;

[0124] (3) 127.5 g of template agent Q isopropylamine was quickly added to the mixed solution in step (2);

[0125] (4) 1051.2 g of silica sol with a silica content of 30% was slowly added dropwise to the mixed solution of step (3) under vigorous stirring;

[0126] (5) 472.0 g of H2O was added and mixed uniformly to obtain a gel. The molar ratio of H2O to silicon source X in the final gel was 35:1.

[0127] (6) The obtained gel was crystallized at 180°C for 30 h;

[0128] (7) The crystallized product was washed with distilled water, dried at 120°C for 2 h, and calcined at 300°C for 20 h;

[0129] The molar ratio of the materials in the gel obtained in step (5) is 15H2O:SiO2:0.009Al2O3:0.03Na2O:0.4Q;

[0130] (8) using ammonium chloride to exchange ammonia according to the ratio of molecular sieve: ammonium chloride: water = 1:1:10, and then filtering and washing the mother liquor, drying at 120 ° C for 3 h, and calcining at 500 ° C for 5 h to obtain ZSM-23 molecular sieve;

[0131] The prepared product is a pure-phase ZSM-23 molecular sieve with a relative crystallinity of 106.98%.

[0132] Test Case

[0133] NH3-TPD analysis was performed using the molecular sieves synthesized in Example 1 and Example 2, Comparative Example 1, and Comparative Example 2, respectively. The specific results and data are shown in Table 1. The proportions of the components in the Examples and Comparative Examples are shown in Table 2.

[0134] Table 1 Acidity analysis results of molecular sieves synthesized by different methods

[0135]

[0136]

[0137] Table 2 Ratios of components in Examples and Comparative Examples

[0138] Sample name X:Y M:X Q:X <![CDATA[H2O:X]]> Y1:Y <![CDATA[Na + :X]]> Example 1 60 0.095 0.7 15 - - Example 2 110 0.03 0.4 15 - - Example 3 91 0.05 0.7 35 - - Example 4 91 0.03 0.9 35 - - Example 5 40 0.03 0.7 30 0.68 - Example 6 40 0.05 0.9 30 0.60 - Comparative Example 1 60 - 0.7 15 - 0.095 Comparative Example 2 110 - 0.4 15 - 0.03

[0139] It can be seen from Table 1 that the ZSM-23 obtained by the synthesis method of the present invention has an increased weak acid content and a decreased strong acid content.

Claims

1. A method for synthesizing ZSM-23 molecular sieve, comprising the following steps: (1) dissolving an aluminum source Y in water to obtain an aluminum source solution; (2) dissolving an organic base M in water and adding dropwise the aluminum source solution to obtain a mixed solution; wherein the organic base M is selected from di(2-hydroxyethyl)amine, N-methyl-2-hydroxyethylamine, and 2-amino-2-methyl-1-propanol; (3) placing the mixed solution in a water bath at 65-85°C for 2-5 hours, cooling it to room temperature, and then cooling the temperature of the mixed solution to 5-10°C with ice water; (4) Under the condition of 5-10°C, the template Q is quickly added to the mixed solution after cooling in step (3); (5) Slowly adding the silicon source X dropwise to the mixed solution obtained in step (4) under vigorous stirring; (6) adding water and mixing uniformly to obtain a gel, wherein the molar ratio of H2O to silicon source X in the final gel is 10-35:1; (7) crystallizing the final gel obtained in step (6); (8) washing, drying, and calcining the crystallized product to obtain ZSM-23 molecular sieve; The molar ratio of each material in the final gel obtained in step (6) is X:Y=60-110:1, M:X=0.03-0.1:1, and Q:X=0.40-0.90:

1.

2. The synthesis method according to claim 1, wherein The molar ratio of each material in the final gel obtained in step (6) is X:Y=80-100:1, M:X=0.04-0.08:1, and Q:X=0.50-0.70:

1.

3. The synthesis method according to claim 1, wherein The aluminum source Y is selected from at least one of water-soluble aluminum salts, alkali metal aluminates, aluminum alkoxides and metallic aluminum.

4. The synthesis method according to claim 3, wherein The aluminum source Y is aluminum sulfate.

5. The synthesis method according to claim 1, wherein The silicon source X is selected from at least one of silicon dioxide, alkali metal silicate, and tetraalkyl orthosilicate.

6. The synthesis method according to claim 5, wherein The silicon dioxide is selected from at least one of silicon dioxide colloidal suspension, silicon dioxide precipitation, and fumed silicon dioxide.

7. The synthesis method according to claim 6, wherein The silica content in the silica colloidal suspension is 30 wt%-40 wt%.

8. The synthesis method according to claim 6, wherein The silicon source X is silica sol.

9. The synthesis method according to claim 1, wherein The template agent Q is selected from at least one of isopropylamine, n-butylamine, ethylenediamine, and diisobutylamine.

10. The synthesis method according to claim 1, wherein The step (1) also includes the process of adding other trivalent elements Y1, wherein the other trivalent elements Y1 are selected from at least one of Fe, Ga, and Be, and the molar ratio of the other trivalent elements Y1 to the aluminum source Y is 0.1-1.0:

1.

11. The synthesis method according to claim 1, wherein The crystallization is carried out under a closed condition at 150-180° C. for 30-60 hours.

12. The synthesis method according to claim 1, wherein The drying step is performed at 100-120° C. for 2-3 hours.

13. The synthesis method according to claim 1, wherein The calcination is carried out at 300-550° C. for 10-20 hours.

14. A ZSM-23 molecular sieve, wherein The ZSM-23 molecular sieve is synthesized by the synthesis method according to any one of claims 1 to 13. The particle size of the ZSM-23 molecular sieve is in the range of 200-400 nm and the morphology is needle-shaped.

15. The ZSM-23 molecular sieve according to claim 14, wherein The axis-to-diameter ratio of the ZSM-23 molecular sieve is 1:6-1:10.

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