Synthetic method of ZSM-23 zeolite molecular sieve with low silica-alumina ratio and short-axis nanocrystal morphology

Abstract

The invention discloses a synthesis method of a ZSM-23 zeolite molecular sieve with low silica-alumina ratio and short-axis nanocrystal morphology, which comprises the following steps: mixing a silicon oxide source, an aluminum oxide source, a template agent, an alkali metal source and water to form initial gel, heating the initial gel to a first temperature of 120-125 DEG C under sealing and stirring rate of 100-180rpm, keeping the temperature for 8-10 hours, and cooling to room temperature to obtain the ZSM-23 zeolite molecular sieve with low silica-alumina ratio and short-axis nanocrystal morphology. Raising the temperature to a second temperature of 135-145 DEG C, keeping the temperature for 26-36 hours, and washing, filtering, drying and roasting the product to obtain the ZSM-23 zeolite molecular sieve. The method can be carried out at a low stirring rate and can be suitable for industrial amplification.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular sieve preparation, and particularly relates to a synthesis method of ZSM-23 zeolite molecular sieve with a short-axis nanocrystal morphology and a low silicon-aluminum ratio. Background Art

[0002] ZSM-23 (MTT structure) zeolite molecular sieve has a one-dimensional 10-ring elliptical mesoporous structure, which was first publicly reported in the patent US4076842 of Mobil Company in 1978, and the pore diameter is about 0.45 * 0.52 nm. Due to its pore mouth confinement and special pore channel orientation, it has important applications in the production of lubricating base oil by hydroisomerization dewaxing of normal paraffins.

[0003] In recent years, with the in-depth research, ZSM-23 zeolite molecular sieves with a low silicon-aluminum ratio and short-axis nanostructures have attracted more and more attention. First of all, in terms of morphology, nano-short-axis ZSM-23 molecular sieves have a higher external specific surface area, which can provide more pore mouths per unit mass compared to micron crystals, that is, the hydroisomerization reaction sites; secondly, the reduction of the silicon-aluminum ratio will introduce more acid amount to improve the reaction activity of the catalyst. Under the requirements of meeting the hydroisomerization reaction process, such as the space velocity or throughput, the amount of molecular sieve used can be reduced to reduce the overall cost of the catalyst. However, in the process of reducing the silicon-aluminum ratio of ZSM-23 molecular sieve products and reducing the crystals to the nanoscale, the relative purity of ZSM-23 is challenged. Mainly, with the reduction of the silicon-aluminum ratio, the FER structure is prone to coexist with it (described in paragraph

[0010] on page 3 of CN102256704A). To solve this problem, CN102256704A uses (CH 3 ) 2 N + CH 2 CH 2 CH 2 N + (CH 3 ) 2 CH 2 CH 2 CH 2 N + (CH 3 ) 3 Abbreviated as Triquat-7, with the seed crystal not less than 500 ppm and the reaction temperature of 150 - 200 °C, through hydrothermal crystallization for more than 72 hours, ZSM-23 with a silicon-aluminum ratio < 40, crystal particle size of 200 - 500 nm, and external specific surface area < 80 m 2 / g nano MTT zeolite molecular sieve with a short-axis structure. However, this synthesis process must be achieved by the combined action of Triquat-7 organic template and seed crystal. US7390763 and CN100587035C propose to use N-lower alkyl-N`-isopropyl imidazolium cation as the main template, and isobutylamine, neopentylamine, monoethylamine, etc. as auxiliary templates to form a co-template, and SSZ-32X (MTT structure) molecular sieve with a silica-alumina ratio of 20-40 and crystal size of 20-40 nm can be synthesized at 170 °C. However, the use of co-template in the synthesis process results in high cost, and the main template is not easily obtained, reducing the wide application value of this material. In CN110683558A, ZSM-23 (MTT structure) with an axial ratio less than 10 and a silica-alumina ratio of 60-110 is synthesized. However, this method requires the combined action of seed crystal induction (seed crystal ≮1% of the total gel mass) and high-speed stirring (stirring rate 200-300 rpm) to synthesize the target product. In CN114988430A, nano-rod-shaped ZSM-23 molecular sieve with a crystal size less than 300 nm is synthesized by a step-by-step preparation technique. However, the molecular sieve crystallization process still must adopt the high-speed stirring condition of 200-300 rpm, and with the assistance of the seed crystal mother liquor, it is carried out at a high temperature of 170-200 °C. In CN109516471A, ZSM-23 molecular sieve with a surface silica-alumina ratio of 10-80 is synthesized. Its feature is to adopt the method of pre-crystallization, first synthesize high-silica ZSM-23 crystal nuclei in a high-silica gel, and then add the crystal nucleus material to a low-silica synthesis gel and react at 150-200 °C. However, the crystal size of the product molecular sieve is about 500 nm. CN102992346A discloses a method for synthesizing ZSM-23 molecular sieve without using an organic template. Its feature is that under the condition of a certain silica-alumina ratio, by adding ZSM-23 seed crystal (1-10% of the mass ratio of silica), ZSM-23 molecular sieve with a silica-alumina ratio ≥57 is synthesized at 140-180 °C. However, its crystal length is about 1000-2000 nm, showing a micron-scale state and unable to achieve the nano-scale.

[0004] As can be seen from the above published patents, in the process of pursuing nano short-axis of crystal morphology, without using expensive templates such as Triquat-7 and N-lower alkyl-N`-isopropyl imidazolium cation, and using cheap organic templates such as isopropylamine, dimethylamine, ethylenediamine, N,N-dimethylformamide, etc., the synthesis of low-silica-alumina ratio short-axis nano-ZSM-23 can only be achieved by means of seed crystal-assisted induction, high-temperature and high-speed stirring rapid crystallization process, or secondary synthesis of high-silica seed crystal solution. The reality is that for the industrial scale-up process, with the increase of the reaction kettle volume, the high-speed stirring process leads to an intensified centrifugal tendency of the materials in the reaction kettle, which is easy to cause resonance and vibration of the reaction kettle equipment, seriously threatening production safety. Such as the conventional 5M 3, 10M 3 The upper limit of the stirring rate of the reactor is generally 160 - 180 rpm; while for 20M 3 the upper limit of the stirring rate of the reactor is around 120 rpm. The lower stirring rate or disturbance situation increases the difficulty in industrial scale-up of this molecular sieve, resulting in the co-occurrence of miscellaneous crystals such as ZSM-5. In view of the actual situation of limited stirring ability in the industrial scale-up process, this patent proposes a method for relatively mild and stable growth of low-silica ratio short-axis nano-ZSM-23 molecular sieve. Summary of the Invention

[0005] The purpose of the present invention is to provide a synthesis method of ZSM-23 zeolite molecular sieve with a low silica-alumina ratio and short-axis nano-crystal morphology, which can be carried out at a low stirring rate and is applicable to industrial scale-up.

[0006] To achieve the above purpose, the present invention provides a synthesis method of ZSM-23 zeolite molecular sieve with a low silica-alumina ratio and short-axis nano-crystal morphology. Mix a silica source, an alumina source, a templating agent, an alkali metal source and water to form an initial gel. Under sealing and a stirring rate of 100 - 180 rpm, first heat the initial gel to a first temperature of 120 - 125 °C, keep it at a constant temperature for 8 - 10 hours, and then heat it to a second temperature of 135 - 145 °C and keep it at a constant temperature for 26 - 36 hours. After the product is washed, filtered, dried and calcined, the ZSM-23 zeolite molecular sieve is obtained.

[0007] In the synthesis method of ZSM-23 zeolite molecular sieve with a low silica-alumina ratio and short-axis nano-crystal morphology according to the present invention, the templating agent is isopropylamine IPA and / or dimethylamine.

[0008] In the synthesis method of ZSM-23 zeolite molecular sieve with a low silica-alumina ratio and short-axis nano-crystal morphology according to the present invention, the silica source is one or more of silica sol, water glass and fumed silica.

[0009] In the synthesis method of ZSM-23 zeolite molecular sieve with a low silica-alumina ratio and short-axis nano-crystal morphology according to the present invention, the alumina source is one or more of aluminum sulfate, sodium metaaluminate, aluminum hydroxide and aluminum sol.

[0010] In the synthesis method of ZSM-23 zeolite molecular sieve with a low silica-alumina ratio and short-axis nano-crystal morphology according to the present invention, the alkali metal source is sodium hydroxide and / or sodium silicate.

[0011] In the synthesis method of ZSM-23 zeolite molecular sieve with a low silica-alumina ratio and short-axis nano-crystal morphology according to the present invention, the silica source is calculated as SiO 2 , the alumina source is calculated as Al 2 O 3 , and the alkali metal source is calculated as Na 2For the calculation, the molar ratio of each substance is 70 - 82 SiO 2 :Al 2 O 3 :7 - 9 Na 2 O:51 - 58 template agent:2600 - 2850 H 2 O, where the value of Na 2 O / SiO 2 and Na 2 O / Al 2 O 3 being too low will limit the effect of crystal nano - size or reduction, while being too high will easily cause the growth of ZSM - 5 heterocrystals.

[0012] For the synthesis method of ZSM - 23 zeolite molecular sieve with low - silicon - aluminum - ratio short - axis nano - crystal morphology of the present invention, the heating rate for heating to the first temperature is 10 - 25 °C / h, and the heating rate for heating to the second temperature is 8 - 10 °C / h. Regarding the above - mentioned heating rates, those skilled in the art can select according to the actual situation. When the volume of the reaction kettle is small, the heating rate can be relatively fast. However, when the volume of the reaction kettle is large, due to the large volume, the heat - exchange ratio will be relatively low, so the heating rate will be small.

[0013] For the synthesis method of ZSM - 23 zeolite molecular sieve with low - silicon - aluminum - ratio short - axis nano - crystal morphology of the present invention, the silicon - aluminum ratio of the ZSM - 23 zeolite molecular sieve is 50 - 67, the crystal grain size is less than 200 nm, the axis - diameter ratio is 3 - 5, the external specific surface area is greater than 90 m 2 / g, and the relative crystallinity is greater than 90%.

[0014] Advantages of the present invention:

[0015] (1) Utilize the conditions that under low - temperature conditions, the synthesis materials and ratios have a restrictive effect on the growth of ZSM - 5 molecular sieve. Even under relatively low reaction temperature conditions, with low - speed agitation, first preferentially induce the ZSM - 23 crystal nuclei; secondly, then raise the temperature to a certain level to enable ZSM - 23 to grow relatively rapidly, and before ZSM - 5 starts to grow, terminate the crystallization reaction to achieve the purpose of obtaining ZSM - 23 molecular sieve.

[0016] (2) Utilize the high Na + and alkaline conditions in the reaction system to obtain a relatively high number of crystal nuclei, and under the condition of a certain supersaturation concentration of the reaction mother liquor, obtain short - axis nano - molecular sieves with low - silicon - aluminum - ratio and large external specific surface area of nano - sized small crystal grains. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the X - ray diffraction spectrum of the ZSM - 23 zeolite molecular sieve with low - silicon - aluminum - ratio nano - short - axis morphology synthesized in Example 1 of the present invention.

[0018] Figure 2 It is the scanning electron microscope image of the ZSM-23 zeolite molecular sieve with a short-axis nano morphology and a low silica-alumina ratio synthesized in Example 1 of the present invention.

[0019] Figure 3 It is the XRD pattern of the ZSM-23 zeolite molecular sieve with a short-axis nano morphology and a low silica-alumina ratio synthesized in Example 2 of the present invention.

[0020] Figure 4 It is the scanning electron microscope image of the ZSM-23 zeolite molecular sieve with a short-axis nano morphology and a low silica-alumina ratio synthesized in Example 2 of the present invention.

[0021] Figure 5 It is the XRD pattern of the ZSM-23 zeolite molecular sieve with a short-axis nano morphology and a low silica-alumina ratio synthesized in Example 3 of the present invention.

[0022] Figure 6 It is the XRD pattern of the ZSM-23 zeolite molecular sieve with a short-axis nano morphology and a low silica-alumina ratio synthesized in Example 4 of the present invention.

[0023] Figure 7 It is the XRD pattern of the product synthesized in Comparative Example 1 of the present invention.

[0024] Figure 8 It is the XRD pattern of the product synthesized in Comparative Example 2 of the present invention.

[0025] Figure 9 It is the XRD pattern of the product synthesized in Comparative Example 3 of the present invention.

[0026] Figure 10 It is the XRD pattern of the product synthesized in Comparative Example 4 of the present invention.

[0027] Figure 11 It is the XRD pattern of the product synthesized in Comparative Example 5 of the present invention. Detailed Embodiments

[0028] The present invention will be specifically described below through examples. It is necessary to point out here that the following examples are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0029] Example 1:

[0030] 10M 3 Synthesis of short-axis nano ZSM-23 with a silica-alumina ratio of 55

[0031] The specific operation is as follows: At room temperature and 10M 3 Under the condition that the stirring rate of the reaction kettle is 180 rpm, 2400 kg of SiO 230% aqueous solution, 110 kg Al 2 (SO 4 ) 3 ·18H 2 O, 108 kg NaOH, 720 kg aqueous solution containing 70% isopropylamine and 5900 kg water are mixed. After forming a gel, it is stirred for 4 hours. The molar ratio of each substance in the material is: 72.7SiO 2 :Al 2 O 3 :8.2Na 2 O:51.8IPA:1.5H 2 SO 4 :2650H 2 O. Among them, Na 2 O / SiO 2 and Na 2 O / Al 2 O 3 are 0.11 and 8.2 respectively. Then the above material is heated to 125 °C at a rate of 10 °C / h and kept at a constant temperature for 12 hours, and then heated to 135 °C at a rate of 10 °C / h. After reacting for 34 hours at a constant temperature, the reaction ends. The product is filtered and separated, washed, dried, and calcined. Identified by XRD, the product is ZSM-23 molecular sieve; XRF test shows that the silica-alumina ratio of the product is 54.6. The specific surface area is 255 m 2 / g, among which the external specific surface area is 109 m 2 / g. SEM shows that the size of the molecular sieve is about 150 - 200 nm, the axial diameter ratio is about 3 - 5, and the relative crystallinity is greater than 98%. XRD is as Figure 1 shown, SEM is as Figure 2 shown.

[0032] Example 2:

[0033] 5M 3 Synthesis of short-axis nano-ZSM-23 with a silica-alumina ratio of 55

[0034] The specific operation is as follows: At normal temperature and a stirring rate of 120 rpm in a 5M 3 reaction kettle, 1200 kg of an aqueous solution containing 30% SiO 2 , 56 kg of Al 2 (SO 4 ) 3 ·18H 2 O, 54 kg of NaOH, 360 kg of an aqueous solution containing 70% isopropylamine and 2950 kg of water are mixed. After forming a gel, it is stirred for 4 hours. The molar ratio of each substance in the material is: 71.4SiO 2 :Al 2 O 3 :8.06Na2 O: 50.9 IPA: 1.5 H 2 SO 4 : 2603 H 2 O. Among them, Na 2 O / SiO 2 and Na 2 O / Al 2 O 3 are 0.11 and 8.06 respectively. Then, the above materials are heated to 123 °C at a rate of 15 °C / h, held at a constant temperature for 12 hours, then heated to 142 °C at a rate of 10 °C / h, and the reaction ends after holding at a constant temperature for 26 hours. The product is filtered and separated, washed, dried, and calcined. Identified by XRD, the product is ZSM-23 molecular sieve; XRF test shows that the silica-alumina ratio of the product is 55.2. The specific surface area is 254 m 2 / g, among which the external specific surface area is 101 m 2 / g, SEM shows that the size of the molecular sieve is about 180 - 200 nm, the aspect ratio is about 4 - 5, and the relative crystallinity is greater than 98%. XRD is as Figure 3 shown, SEM is as Figure 4 shown.

[0035] Example 3:

[0036] 1M 3 , Synthesis of short-axis nano ZSM-23 with a silica-alumina ratio of 55

[0037] The specific operation is as follows: At normal temperature and a stirring rate of 160 rpm in a 1M 3 reaction kettle, 240 kg of an aqueous solution containing 30% SiO 2 , 11.2 kg of Al 2 (SO 4 ) 3 ·18H 2 O, 10.6 kg of NaOH, 72 kg of an aqueous solution containing 70% isopropylamine, and 590 kg of water are mixed. After forming a gel, it is stirred for 4 hours. The molar ratio of each substance in the material: 71.4 SiO 2 : Al 2 O 3 : 7.9 Na 2 O: 50.8 IPA: 1.5 H 2 SO 4 : 2606 H 2 O. Among them, Na 2 O / SiO 2 and Na 2 O / Al 2 O 3They are 0.11 and 7.9 respectively. Then the above materials are heated to 120 °C at a rate of 25 °C / h, held at a constant temperature for 12 hours, and then heated to 145 °C at a rate of 10 °C / h. After holding at a constant temperature for 34 hours, the reaction ends. The product is filtered and separated, washed, dried, and calcined. Identified by XRD, the product is ZSM-23 molecular sieve; XRF test shows that the silica-alumina ratio of the product is 56.2. The specific surface area is 256 m 2 / g, of which the external specific surface area is 104 m 2 / g. SEM shows that the size of the molecular sieve is about 150 - 200 nm, the axial diameter ratio is about 3 - 5, and the relative crystallinity > 98%. XRD is as Figure 5 shown.

[0038] Example 4

[0039] 1M 3 Synthesis of Short-axis Nano-ZSM-23 with a Silica-alumina Ratio of 65

[0040] The specific operation is as follows: At room temperature and under the condition of a stirring rate of 140 rpm in a 1M 3 reactor, 240 kg of an aqueous solution containing 30% SiO 2 30%, 9.9 kg of Al 2 (SO 4 ) 3 ·18H 2 O, 9.3 kg of NaOH, 72 kg of an aqueous solution containing 70% isopropylamine and 566 kg of water are mixed. After forming a gel, it is stirred for 4 hours. At this time, the molar ratio composition of each substance in the material is: 80.5SiO 2 :Al 2 O 3 :7.8Na 2 O:57.3IPA:1.5H 2 SO 4 :2843H 2 O. Then the above materials are heated to 125 °C at a rate of 25 °C / h and held at a constant temperature for 12 hours, and then heated to 145 °C at a rate of 10 °C / h. After holding at a constant temperature for 36 hours, the reaction ends. The product is filtered and separated, washed, dried, and calcined. Identified by XRD, the product is ZSM-23 molecular sieve; XRF test shows that the silica-alumina ratio of the product is 64.3. The specific surface area is 264 m 2 / g, of which the external specific surface area is 98 m 2 / g. SEM shows that the size of the molecular sieve is about 150 - 200 nm, the axial diameter ratio is about 3 - 5, and the relative crystallinity > 99%. XRD is as Figure 6 shown.

[0041] Comparative Example 1

[0042] 10M 3, Synthesis of ZSM-23 molecular sieve with a stirring rate of 180 rpm, directly heating to 165 °C and maintaining at a constant temperature for 34 hours. The product is a mixture of a large amount of ZSM-5 and ZSM-23

[0043] Under a stirring rate of 180 rpm, prepare the gel according to Example 1 and stir at room temperature for 4 hours. Heat the gel to 165 °C at a rate of 10 °C / h and carry out constant-temperature crystallization for 34 hours. The product is cooled, washed with water, filtered, dried and calcined. After XRD detection, the product is mainly a mixture of a large amount of ZSM-5 and ZSM-23. XRD is as Figure 7 shown.

[0044] Comparative Example 2

[0045] 10M 3 , Synthesis of ZSM-23 molecular sieve with a stirring rate of 180 rpm, maintaining at a constant temperature of 125 °C for 12 hours, and then heating to 165 °C and maintaining at a constant temperature for 34 hours. The product is a mixture of a small amount of ZSM-5 and ZSM-23

[0046] Under a stirring rate of 180 rpm, prepare the gel according to Example 1 and stir at room temperature for 4 hours. Heat the gel to 125 °C at a rate of 10 °C / h, maintain at a constant temperature for 12 hours, then heat to 165 °C at a rate of 10 °C / h and keep at a constant temperature for 34 hours. The product is cooled, washed with water, filtered, dried and calcined. After XRD detection, the product is mainly a mixture of a small amount of ZSM-5 and ZSM-23. XRD is as Figure 8 shown.

[0047] Comparative Example 3:

[0048] 5M 3 , Synthesis of ZSM-23 molecular sieve with a stirring rate of 120 rpm, directly heating to 142 °C and maintaining at a constant temperature for 26 hours. The product is a mixture of ZSM-5 and ZSM-23

[0049] Under a stirring rate of 120 rpm, prepare the gel according to Example 2 and stir at room temperature for 4 hours. Heat the gel to 142 °C at a rate of 15 °C / h and carry out constant-temperature crystallization for 26 hours. The product is cooled, washed with water, filtered, dried and calcined. After XRD detection, the product is mainly a mixture of ZSM-5 and ZSM-23. XRD is as Figure 9 shown.

[0050] Comparative Example 4:

[0051] 1M 3 , Synthesis of ZSM-23 molecular sieve with a stirring rate of 160 rpm, adding 3% ZSM-23 seeds, directly heating to 165 °C and maintaining at a constant temperature for 34 hours. The product is ZSM-5

[0052] Under a stirring rate of 160 rpm, a gel was prepared according to Example 3, and 3% ZSM-23 seeds were added, and the mixture was stirred at room temperature for 4 hours. The gel was heated to 165 °C at a rate of 25 °C / h and crystallized at a constant temperature for 34 hours. The product was cooled, washed with water, filtered, dried, and calcined. After XRD detection, the product was ZSM-5. The XRD is as Figure 10 shown.

[0053] Comparative Example 5:

[0054] 1M 3 , stirring rate 160 rpm, without adding seeds, directly heated to 165 °C and kept at a constant temperature for 34 hours, the product was ZSM-5

[0055] Under a stirring rate of 160 rpm, a gel was prepared according to Example 3 and stirred at room temperature for 4 hours. The gel was heated to 165 °C at a rate of 25 °C / h and crystallized at a constant temperature for 34 hours. The product was cooled, washed with water, filtered, dried, and calcined. After XRD detection, the product was ZSM-5. The XRD is as Figure 11 shown.

[0056] Of course, the present invention may also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for synthesizing ZSM-23 zeolite molecular sieve with short-axis nanocrystal morphology and low silica-alumina ratio, Characterized in that, Mix a silica source, an alumina source, a template agent, an alkali metal source and water to form an initial gel. Under sealing and a stirring rate of 100 - 180 rpm, first heat the initial gel to a first temperature of 120 - 125 °C, keep it at a constant temperature for 8 - 10 hours, and then heat it to a second temperature of 135 - 145 °C and keep it at a constant temperature for 26 - 36 hours. After the product is washed, filtered, dried and calcined, the ZSM-23 zeolite molecular sieve is obtained.

2. The method for synthesizing ZSM-23 zeolite molecular sieve with short-axis nanocrystal morphology and low silica-alumina ratio according to claim 1, Characterized in that, The template agent is isopropylamine IPA and / or dimethylamine.

3. The method for synthesizing ZSM-23 zeolite molecular sieve with short-axis nanocrystal morphology and low silica-alumina ratio according to claim 1, Characterized in that, The silica source is one or more of silica sol, water glass and white carbon black.

4. The method for synthesizing ZSM-23 zeolite molecular sieve with short-axis nanocrystal morphology and low silica-alumina ratio according to claim 1, Characterized in that, The alumina source is one or more of aluminum sulfate, sodium metaaluminate, aluminum hydroxide and aluminum sol.

5. The method for synthesizing ZSM-23 zeolite molecular sieve with short-axis nanocrystal morphology and low silica-alumina ratio according to claim 1, Characterized in that, The alkali metal source is sodium hydroxide and / or sodium silicate.

6. The method for synthesizing ZSM-23 zeolite molecular sieve with short-axis nanocrystal morphology and low silica-alumina ratio according to claim 1, Characterized in that, The silicon oxide source is calculated as SiO 2 The aluminum oxide source is calculated as Al 2 O 3 The alkali metal source is calculated as Na 2 O. The molar ratio of each substance is 70 - 82 SiO 2 :Al 2 O 3 :7 - 9 Na 2 O:51 - 58 template agent:2600 - 2850 H 2 O.

7. The method for synthesizing ZSM-23 zeolite molecular sieve with short-axis nanocrystal morphology and low silica-alumina ratio according to claim 1, Characterized in that, The heating rate for heating to the first temperature is 10 - 25 °C / h, and the heating rate for heating to the second temperature is 8 - 10 °C / h.

8. The method for synthesizing ZSM-23 zeolite molecular sieve with short-axis nanocrystal morphology and low silica-alumina ratio according to claim 1, Characterized in that, The ZSM-23 zeolite molecular sieve has a silica-alumina ratio of 50 to 67, a crystal grain size of less than 200 nm, an axial diameter ratio of 3 to 5, an external specific surface area of greater than 90 m 2 / g, and a relative crystallinity of greater than 90%.

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