A method for synthesizing zsm-22 molecular sieve by vapor phase method and zsm-22 molecular sieve

Abstract

The application relates to a ZSM-22 molecular sieve and a preparation method thereof. The preparation method of the ZSM-22 molecular sieve is as follows: a mixed solution formed by mixing inorganic alkali, a silicon source, an aluminum source, a template agent, seeds and deionized water in a certain molar ratio is dried into a dry gel, then the dry gel is fully ground into a dry gel powder, a small amount of deionized water is added into a stainless steel hydrothermal kettle, and then static crystallization conversion is carried out by using a vapor phase method, finally, the obtained crystallization product is washed, dried and calcined to obtain a Na type ZSM-22 molecular sieve. The method for preparing the ZSM-22 molecular sieve by using the vapor phase method has the advantages of low water consumption, energy saving and environmental protection, and low production cost, the synthesized ZSM-22 molecular sieve has a low silicon aluminum ratio and a smooth tubular morphology of an outer surface.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve preparation technology, and particularly relates to a method for synthesizing ZSM-22 molecular sieves via a vapor phase method. Furthermore, this invention also relates to a tubular ZSM-22 molecular sieve and its preparation method. Background Technology

[0002] Molecular sieves are a class of porous materials with regular and uniform pores and acidic active sites, making them extremely important in adsorption, separation, and catalysis. ZSM-22 molecular sieve, a type of TON-type zeolite molecular sieve, has a one-dimensional ten-membered ring pore structure with a pore size of 0.46 x 0.57 nm. It exhibits excellent catalytic performance in methanol conversion, dimethyl ether (DME) conversion, catalytic pyrolysis of coal, and transesterification reactions.

[0003] Chinese patent CN 119263299 A discloses a method for preparing pure-phase ZSM-22 molecular sieves using a low-cost organic template agent (an alkanolamine compound with 5-6 carbon atoms) under dynamic hydrothermal conditions. The method includes the following steps: uniformly mixing an aluminum source, an alkali source, water, an organic template agent, and a silicon source to obtain a gel mixture; and subjecting the gel mixture to at least crystallization and calcination to obtain the ZSM-22 molecular sieve. The ZSM-22 molecular sieve synthesized by this method has a one-dimensional tubular morphology, but the dynamic crystallization process requires a significant amount of additional energy.

[0004] Chinese patent CN 113307287 A discloses a method for synthesizing ZSM-22 under dynamic hydrothermal conditions. The method includes the following steps: mixing distilled water, aluminum source, template agent, seed crystal, inorganic alkali, silicon source, and synthesis aids into a mixture and placing it in a hydrothermal synthesis reactor; aging the mixture at room temperature with a stirring rate of 20–100 r / min for 1–24 hours; then sealing the synthesis reactor; and finally aging the mixture at 100–300 °C. o Crystallize at a stirring rate of 30–200 r / min for 24–150 hours under C conditions. After crystallization, cool to room temperature, discharge, wash, separate, and dry to obtain ZSM-22 molecular sieve. This method can synthesize ZSM-22 molecular sieve with high crystallinity.

[0005] Chinese patent CN 104671253 A discloses a method for preparing ZSM-22 nanosheet molecular sieves. The method includes the following steps: preparing pre-formed seed crystals using aluminum sulfate octadecyl water, tetraethyl orthosilicate, 1,6-hexanediamine, potassium hydroxide, and deionized water; preparing a gel using aluminum sulfate octadecyl water, silica sol, potassium hydroxide, and deionized water; crystallization and calcination. The thickness of the sheet-like ZSM-22 molecular sieves prepared by this method is approximately 20 nm.

[0006] The synthesis methods of ZSM-22 molecular sieves disclosed in the prior art are all hydrothermal synthesis methods, which have the disadvantages of large water consumption, low raw material utilization, and the fact that the morphology of the prepared ZSM-22 molecular sieves is mostly needle-shaped / rod-shaped formed by the stacking of nanocrystals, which is not conducive to the practical application of ZSM-22 molecular sieves. Summary of the Invention

[0007] This invention addresses the problems of existing methods for synthesizing ZSM-22 molecular sieves, such as high water consumption, low raw material utilization, and difficulty in synthesizing tubular ZSM-22 molecular sieves with smooth surfaces. It proposes a method for preparing ZSM-22 molecular sieves using a vapor phase crystallization method. This method uses less water, has a high raw material utilization, and produces ZSM-22 molecular sieves with a tubular morphology and a smooth outer surface.

[0008] The technical solution adopted by the present invention to achieve the above objectives is as follows.

[0009] A method for preparing ZSM-22 molecular sieve includes the following steps:

[0010] (1) Add silicon source, aluminum source, alkali source, template agent and seed crystal to deionized water, stir thoroughly to form a mixed solution, put the mixed solution into an oven to dry, and then grind the dried gel into dry gel powder.

[0011] (2) Add a small amount of deionized water to the inner part of the polytetrafluoroethylene liner of the stainless steel hydrothermal reactor, then place the support inside the polytetrafluoroethylene liner, and then place the dry gel powder on the support for static crystallization conversion.

[0012] (3) The obtained crystallized product was washed, dried and calcined to obtain Na-type ZSM-22 molecular sieve;

[0013] The molar ratio of the mixed solution is as follows: silicon source, aluminum source, alkali source, template agent, and deionized water is (1~300): (0.001~10): (0.01~1.0): (1~20): (2~500).

[0014] Preferably, the silicon source is one or more of silica sol, silica gel, tetraethyl orthosilicate, water glass, fumed silica, and fumed silica; more preferably, the silicon source is silica sol.

[0015] Preferably, the aluminum source is one or more of aluminum chloride, aluminum sulfate, aluminum hydroxide, sodium aluminate, aluminum sol, aluminum oxide, aluminum nitrate, sodium aluminate, and boehmite; more preferably, the aluminum source is sodium aluminate.

[0016] Preferably, the alkali source is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and sodium silicate, and more preferably, potassium hydroxide.

[0017] Preferably, the template agent is one or more of 1,6-hexanediamine, 1,8-octanediamine, di-n-propylamine, diisopropylamine, ethylenediamine, and pyrrolidine, and more preferably, 1,6-hexanediamine.

[0018] Preferably, the seed crystal is one or more of ZSM-22 molecular sieve, ZSM-48 molecular sieve, Beta molecular sieve, ZSM-23 molecular sieve, and ZSM-12 molecular sieve, and more preferably, the seed crystal is ZSM-22 molecular sieve.

[0019] Preferably, in step (1), the oven temperature used to prepare the dry gel is 40~120°C. o C, drying time is 2~54h.

[0020] Preferably, in step (2), the mass of deionized water added is 0.5-50% of the mass of the added dry gel powder; the crystallization temperature is 90-200°C. o C, crystallization time is 12~200 h.

[0021] Preferably, in step (3), the washing method is one or more of vacuum filtration and centrifugation; the drying temperature is 60~120℃. o C, drying time is 4~72 h; calcination temperature is 400~600 o C, roasting time is 2~20 h.

[0022] This invention provides a method for synthesizing ZSM-22 molecular sieves via a vapor phase method, which has the following advantages compared with existing technologies:

[0023] (1) There is almost no free water in the crystallization stage, which greatly reduces the wastewater containing alkali / template agent, simplifies the water washing process, and improves the effective utilization rate of alkali source and template agent. Therefore, it has the advantages of low water consumption, energy saving and environmental protection.

[0024] (2) Since the vapor phase method is used for synthesis, there is no large amount of liquid phase in the synthesis process. The self-generated pressure in the synthesis equipment is much lower than that of the hydrothermal method. Therefore, the equipment requirements are low and the safety is high compared to the autoclave synthesis.

[0025] (3) The synthesis process involves placing the dry gel powder inside the synthesis equipment, which avoids the presence of a large amount of liquid phase inside the synthesis equipment, thus improving the effective utilization rate of the synthesis equipment and reducing the synthesis cost of molecular sieves.

[0026] (4) Compared with the hydrothermal synthesis method, the vapor phase synthesis method of the present invention has a more controllable crystallization environment, is less likely to generate impurities such as ZSM-5 and cristobalite, has high product purity and crystallinity, and the method has high repeatability.

[0027] Furthermore, using the vapor-phase synthesis method provided by this invention, ZSM-22 molecular sieves with a wide range of silicon-to-aluminum ratios and smooth tubular morphology on the outer surface are synthesized under controlled conditions of the molar ratio of the mixed solution. When used as a support for the hydroisomerization catalysis of n-alkanes, due to its wide range of silicon-to-aluminum ratios and the wide range of adjustable acid content of the molecular sieve, it can be applied to various working conditions. Moreover, the tubular structure of the smooth outer surface can also improve the diffusion rate of reaction intermediates in the molecular sieve support, thereby significantly improving the selectivity and yield of isomer products. Attached Figure Description

[0028] Figure 1 The image shows the XRD pattern of the ZSM-22 molecular sieve synthesized in Example 1.

[0029] Figure 2 The image shows the EDS diagram of the ZSM-22 molecular sieve synthesized in Example 1.

[0030] Figure 3 This is a SEM image of the ZSM-22 molecular sieve synthesized in Example 3.

[0031] Figure 4 The graph shows the n-dodecane conversion rate in Example 13.

[0032] Figure 5 This is a selectivity diagram of the isomer products in Example 13.

[0033] Figure 6 This is a yield graph of the isomer products in Example 13. Detailed Implementation

[0034] In the following examples, the crystal structure of the samples was characterized using a Shimadzu XRD-6000 fully automated rotating target X-ray diffractometer (Cu-Kα rays, Ni filter, tube voltage 30 mA, scanning range 5–50°, scanning speed 8° / min, step size 0.01°). The morphology of the samples was characterized using a Hitachi S-4800 scanning electron microscope (SEM). The elemental analysis of the samples was performed using the energy dispersive X-ray spectroscopy (EDS) system attached to the Hitachi S-4800 SEM.

[0035]

Example 1

[0036] Add 0.16 g potassium hydroxide, 0.44 g aluminum isopropoxide, and 0.37 g 1,6-hexanediamine to 12 g water, stir well, then add 0.02 g ZSM-22 seed crystals (homemade). After the seed crystals are fully dissolved, add 10 g silica sol and continue stirring vigorously for 4 hours. Place the mixed sol in an 80°C container. oDry the gel in an oven at 150°C for 24 hours to obtain a dry gel. Grind the dry gel thoroughly in a mortar to obtain a dry gel powder. Then, place 5 g of the dry gel powder onto the filter paper of a support within a polytetrafluoroethylene (PTFE) liner. Add 0.1 g of deionized water to the bottom of the liner. o Crystallization for 36 h yielded a crystallized product. The crystallized product was then filtered at 80 °C. o Dry at C for 12 hours, 550 o After calcination at C for 8 h, Na-type ZSM-22 molecular sieve was obtained and labeled as sample 1.

[0037] Figure 1 The image shows the XRD pattern of sample 1. Figure 1 The sample 1 shows characteristic diffraction peaks of ZSM-22 molecular sieve, and no impurity peaks are generated, indicating that the synthesized sample is a pure phase ZSM-22 molecular sieve.

[0038] Figure 2 The EDS analysis spectrum of sample 1 shows that the Si / Al ratio of the synthesized sample 1 is 32.

[0039]

Example 2

[0040] Add 0.37 g sodium hydroxide, 0.33 g sodium aluminate, and 3.0 g di-n-propylamine to 100 g water, stir well, then add 0.08 g ZSM-48 seed crystals (homemade). After the seed crystals are fully dissolved, add 8 g fumed silica and continue stirring vigorously for 6 hours. Place the mixed sol in an 80°C container. o Dry the gel in an oven at 160°C for 24 hours to obtain a dry gel. Grind the dry gel thoroughly in a mortar to obtain a dry gel powder. Then, place 4 g of the dry gel powder onto the filter paper of a support within a polytetrafluoroethylene (PTFE) liner. Add 0.5 g of deionized water to the bottom of the liner. o Crystallization for 48 hours yielded a crystallized product. The crystallized product was then filtered and subjected to 80 °C. o Dry at C for 12 hours, 550 o After calcination at C for 8 h, Na-type ZSM-22 molecular sieve was obtained and labeled as sample 2.

[0041] The XRD pattern of sample 2 shows that the synthesized sample has the characteristic diffraction peaks of ZSM-22 molecular sieve and no impurity peaks are generated, indicating that the synthesized sample is a pure phase ZSM-22 molecular sieve. Its XRD pattern is basically the same as that of sample 1 in the example, and will not be listed separately here.

[0042] The EDS analysis results of sample 2 show that the Si / Al ratio of sample 2 is 42.

[0043]

Example 3

[0044] Add 5 g sodium carbonate, 0.16 g aluminum sulfate, and 6.2 g ethylenediamine to 150 g water, stir well, then add 0.2 g Beta seed crystals (homemade). After the seed crystals are fully dissolved, add 9.6 g tetraethyl orthosilicate and continue stirring vigorously for 4 hours. Place the mixed sol into an 80 mL container. o Dry the gel in an oven at 150°C for 24 hours to obtain a dry gel. Grind the dry gel thoroughly in a mortar to obtain a dry gel powder. Then, place 3 g of the dry gel powder onto the filter paper of a support within a polytetrafluoroethylene (PTFE) liner. Add 0.2 g of deionized water to the bottom of the liner. o Crystallization for 60 h yielded a crystallized product. The crystallized product was then filtered and subjected to 80 h... o Dry at C for 12 h, 550 o After calcination at C for 8 h, Na-type ZSM-22 molecular sieve was obtained and labeled as sample 3.

[0045] The XRD pattern analysis of sample 3 showed that the synthesized sample had the characteristic diffraction peaks of ZSM-22 molecular sieve and no impurity peaks were generated, indicating that the synthesized sample was a pure phase ZSM-22 molecular sieve. Its XRD pattern was basically the same as that of sample 1 in the example, and will not be listed separately here.

[0046] EDS analysis of sample 3 showed that the Si / Al ratio of sample 3 was 58.

[0047] Figure 3 Here is the SEM image of sample 3, from... Figure 3 It can be seen that the ZSM-22 molecular sieve sample synthesized by the method of the present invention has a smooth tubular shape and relatively uniform crystal size.

[0048]

Example 4

[0049] Add 7 g sodium silicate, 0.6 g alumina, and 2.9 g pyrrolidine to 60 g water, stir well, then add 0.3 g ZSM-12 seed crystals (homemade). After the seed crystals are fully dissolved, add 48.0 g water glass and continue stirring vigorously for 4 hours. Place the mixed sol into an 80 mL container. o Dry the gel in an oven at 180°C for 24 hours to obtain a dry gel. Grind the dry gel thoroughly in a mortar to obtain a dry gel powder. Then, place 6 g of the dry gel powder onto the filter paper of a support within a polytetrafluoroethylene (PTFE) liner. Add 0.8 g of deionized water to the bottom of the liner. o Crystallization for 72 h yielded a crystallized product. The crystallized product was then filtered at 80 °C. o Dry at C for 12 h, 550 o After calcination at C for 8 hours, Na-type ZSM-22 molecular sieve was obtained and labeled as sample 4.

[0050] The XRD pattern of sample 4 shows that it has the characteristic diffraction peaks of ZSM-22 molecular sieve and no impurity peaks, indicating that the synthesized sample is a pure phase ZSM-22 molecular sieve. Its XRD pattern is basically the same as that of sample 1 in the example, and will not be listed separately here.

[0051] The EDS analysis results of sample 4 show that the Si / Al ratio of sample 4 is 85.

[0052]

Example 5

[0053] Add 5 g potassium carbonate, 0.39 g aluminum sol, and 4.3 g diisopropylamine to 180 g water, stir well, then add 0.3 g ZSM-23 seed crystals (homemade). After the seed crystals are fully dissolved, add 58 g silica and continue stirring vigorously for 4 hours. Place the mixed sol into an 80 mL container. o Dry the gel in an oven at 140°C for 24 hours to obtain a dry gel. Grind the dry gel thoroughly in a mortar to obtain a dry gel powder. Then, place 6 g of the dry gel powder onto the filter paper of a support within a polytetrafluoroethylene (PTFE) liner. Add 1.0 g of deionized water to the bottom of the liner. o Crystallization for 120 h yielded a crystallized product. The crystallized product was then filtered and subjected to 80... o Dry at C for 12 h, 550 o After calcination at C for 8 h, Na-type ZSM-22 molecular sieve was obtained and labeled as sample 5.

[0054] The XRD pattern analysis of sample 5 showed that sample 5 had the characteristic diffraction peaks of ZSM-22 molecular sieve and no impurity peaks were generated, indicating that the synthesized sample was a pure phase ZSM-22 molecular sieve. Its XRD pattern was basically the same as that of sample 1 in the example, and will not be listed separately here.

[0055] EDS analysis of sample 5 showed that the Si / Al ratio of the synthesized sample was 167.

[0056]

Example 6

[0057] Add 10 g of sodium hydroxide, 0.24 g of aluminum nitrate, and 6.5 g of 1,8-octanediamine to 120 g of water, stir well, then add 1.6 g of ZSM-48 seed crystals (homemade). After the seed crystals have fully dissolved, add 72.0 g of silica gel and continue stirring vigorously for 4 hours. Place the mixed sol into an 80 mL container. o Dry the gel in an oven at 190°C for 24 hours to obtain a dry gel. Grind the dry gel thoroughly in a mortar to obtain a dry gel powder. Then, place 6 g of the dry gel powder onto the filter paper of a support within a polytetrafluoroethylene (PTFE) liner. Add 1.6 g of deionized water to the bottom of the liner. o Crystallization for 120 h yielded a crystallized product. The crystallized product was then filtered and subjected to 80... oDry at C for 12 h, 550 o After calcination at C for 8 h, Na-type ZSM-22 molecular sieve was obtained and labeled as sample 6.

[0058] The XRD pattern analysis of sample 6 showed that sample 6 had the characteristic diffraction peaks of ZSM-22 molecular sieve and no impurity peaks were generated, indicating that the synthesized sample was a pure phase ZSM-22 molecular sieve. Its XRD pattern was basically the same as that of sample 1 in the example, and will not be listed separately here.

[0059] EDS analysis of sample 6 showed that the Si / Al ratio of the synthesized sample was 290.

[0060]

Example 7

[0061] Add 3 g potassium carbonate, 0.06 g aluminum isopropoxide, and 0.37 g pyrrolidine to 80 g water, stir well, then add 0.02 g ZSM-22 seed crystals (homemade). After the seed crystals are fully dissolved, add 30 g silica sol and continue stirring vigorously for 4 hours. Place the mixed sol into a 90°C container. o Dry the gel in an oven at C for 24 hours to obtain a dry gel. Grind the dry gel thoroughly in a mortar to obtain a dry gel powder. Place 10 g of the dry gel powder onto the filter paper of a support within a polytetrafluoroethylene (PTFE) liner. Add 3.7 g of deionized water to the bottom of the liner. o Crystallization for 36 h yielded a crystallized product. The crystallized product was then filtered at 80 °C. o Dry at C for 12 h, 550 o After calcination at C for 8 h, Na-type ZSM-22 molecular sieve was obtained and labeled as sample 7.

[0062] The XRD pattern analysis of sample 7 showed that sample 7 had the characteristic diffraction peaks of ZSM-22 molecular sieve and no impurity peaks were generated, indicating that the synthesized sample was a pure phase ZSM-22 molecular sieve. Its XRD pattern was basically the same as that of sample 1 in the example, and will not be listed separately here.

[0063] EDS analysis of sample 7 showed that the Si / Al ratio of the synthesized sample was 580.

[0064]

Example 8

[0065] 1.7 g sodium silicate, 0.002 g aluminum chloride, and 5.0 g 1,8-octanediamine were added to 110 g water and stirred until homogeneous. Then, 1.1 g of self-made ZSM-48 seed crystals were added. After the seed crystals were fully dissolved, 32 g of fumed silica was added, and the mixture was stirred vigorously for 6 hours. The resulting sol was then placed in a 100 mL container. oDry the gel in an oven at 190°C for 40 hours to obtain a dry gel. Grind the dry gel thoroughly in a mortar to obtain a dry gel powder. Then, place 10 g of the dry gel powder onto the filter paper of a support within a polytetrafluoroethylene (PTFE) liner. Add 2.4 g of deionized water to the bottom of the liner. o Crystallization for 48 hours yielded a crystallized product. The crystallized product was then filtered and subjected to 80 °C. o Dry at C for 12 h, 550 o After calcination at C for 8 h, Na-type ZSM-22 molecular sieve was obtained and labeled as sample 8.

[0066] The XRD pattern analysis of sample 8 showed that the synthesized sample had the characteristic diffraction peaks of ZSM-22 molecular sieve and no impurity peaks were generated, indicating that the synthesized sample was a pure phase ZSM-22 molecular sieve. Its XRD pattern was basically the same as that of sample 1 in the example, and will not be listed separately here.

[0067] EDS analysis of sample 8 showed that the Si / Al ratio of the synthesized sample was 760.

[0068]

Example 9

[0069] Add 5 g sodium carbonate, 0.48 g alumina, and 6.2 g ethylenediamine to 150 g water, stir well, then add 0.3 g ZSM-12 seed crystals (homemade). After the seed crystals are fully dissolved, add 29 g fumed silica and continue stirring vigorously for 4 hours. Place the mixed sol into an 80 mL container. o Dry the gel in an oven at 150°C for 24 hours to obtain a dry gel. Grind the dry gel thoroughly in a mortar to obtain a dry gel powder. Place 4 g of the dry gel powder onto the filter paper of a support within a polytetrafluoroethylene (PTFE) liner. Add 1.3 g of deionized water to the bottom of the liner. o Crystallization for 100 h yielded a crystallized product. The crystallized product was then filtered and subjected to 80... o Dry at C for 12 h, 550 o After calcination at C for 8 h, Na-type ZSM-22 molecular sieve was obtained and labeled as sample 9.

[0070] The XRD pattern analysis of sample 9 showed that the synthesized sample had the characteristic diffraction peaks of ZSM-22 molecular sieve and no impurity peaks were generated, indicating that the synthesized sample was a pure phase ZSM-22 molecular sieve. Its XRD pattern was basically the same as that of sample 1 in the example, and will not be listed separately here.

[0071] EDS analysis of sample 9 showed that the Si / Al ratio of the synthesized sample was 61.

[0072]

Example 10

[0073] Add 7 g potassium carbonate, 0.6 g aluminum sulfate, and 2.9 g diisopropylamine to 60 g water, stir well, then add 0.3 g Beta seed crystals (homemade). After the seed crystals are fully dissolved, add 48.0 g silica sol and continue stirring vigorously for 6 hours. Place the mixed sol into an 80 mL container. o Dry the gel in an oven at 170°C for 24 hours to obtain a dry gel. Grind the dry gel thoroughly in a mortar to obtain a dry gel powder. Then, place 4 g of the dry gel powder onto the filter paper of a support within a polytetrafluoroethylene (PTFE) liner. Add 0.8 g of deionized water to the bottom of the liner. o Crystallization for 72 h yielded a crystallized product. The crystallized product was then filtered at 80 °C. o Dry at C for 12 h, 550 o After calcination at C for 8 hours, Na-type ZSM-22 molecular sieve was obtained and labeled as sample 10.

[0074] The XRD pattern analysis of sample 10 showed that the synthesized sample had the characteristic diffraction peaks of ZSM-22 molecular sieve and no impurity peaks were generated, indicating that the synthesized sample was a pure phase ZSM-22 molecular sieve. Its XRD pattern was basically the same as that of sample 1 in the example, and will not be listed separately here.

[0075] EDS analysis of sample 10 showed that the Si / Al ratio of the synthesized sample was 81.

[0076]

Example 11

[0077] Add 3 g potassium hydroxide, 0.39 g aluminum sol, and 2.3 g 1,6-hexanediamine to 140 g water, stir well, then add 0.1 g ZSM-48 seed crystals (homemade). After the seed crystals are fully dissolved, add 58 g silica and continue stirring vigorously for 4 hours. Place the mixed sol into a 70 mL container. o Dry the gel in an oven at 140°C for 24 hours to obtain a dry gel. Grind the dry gel thoroughly in a mortar to obtain a dry gel powder. Then, place 5 g of the dry gel powder onto the filter paper of a support within a polytetrafluoroethylene (PTFE) liner. Add 1.5 g of deionized water to the bottom of the liner. o Crystallization for 120 h yielded a crystallized product. The crystallized product was then filtered and subjected to 80... o Dry at C for 12 h, 550 o After calcination at C for 8 h, Na-type ZSM-22 molecular sieve was obtained and labeled as sample 11.

[0078] The XRD pattern analysis of sample 11 showed that the synthesized sample had the characteristic diffraction peaks of ZSM-22 molecular sieve and no impurity peaks were generated, indicating that the synthesized sample was a pure phase ZSM-22 molecular sieve. Its XRD pattern was basically the same as that of sample 1 in the example, and will not be listed separately here.

[0079] EDS analysis of sample 11 showed that the Si / Al ratio of the synthesized sample was 159.

[0080]

Example 12

[0081] Add 8 g of sodium hydroxide, 0.24 g of boehmite, and 7 g of di-n-propylamine to 130 g of water, stir until homogeneous, then add 2.1 g of ZSM-48 seed crystals (homemade). After the seed crystals have fully dissolved, add 72.0 g of tetraethyl orthosilicate and continue stirring vigorously for 4 hours. Place the mixed sol into an 80 mL container. o Dry the gel in an oven at 190°C for 24 hours to obtain a dry gel. Grind the dry gel thoroughly in a mortar to obtain a dry gel powder. Then, place 6 g of the dry gel powder onto the filter paper of a support within a polytetrafluoroethylene (PTFE) liner. Add 2.0 g of deionized water to the bottom of the liner. o Crystallization for 110 h yielded a crystallized product. The crystallized product was then filtered at 80 °C. o Dry at C for 12 hours, 550 o After calcination at C for 8 h, Na-type ZSM-22 molecular sieve was obtained and labeled as sample 12.

[0082] The XRD pattern analysis of sample 12 showed that the synthesized sample had the characteristic diffraction peaks of ZSM-22 molecular sieve and no impurity peaks were generated, indicating that the synthesized sample was a pure phase ZSM-22 molecular sieve. Its XRD pattern was basically the same as that of sample 1 in the example, and will not be listed separately here.

[0083] EDS analysis of sample 12 showed that the Si / Al ratio of the synthesized sample was 285.

[0084]

Example 13

[0085] Using the Na-type ZSM-22 molecular sieve prepared in Examples 1 to 12 as raw material, it was converted into H-type ZSM-22 molecular sieve through ion exchange. Then, the H-type ZSM-22 molecular sieve was ground with Pt / Al2O3 at a ratio of 1:1 to obtain the Pt / ZSM-22 catalyst.

[0086] The Pt / ZSM-22 catalyst prepared above was pressed into tablets and sieved. 1 mL of 20-40 mesh catalyst was measured and loaded into a fixed-bed reactor, and then incubated at 400 °C. o In-situ reduction under C and hydrogen atmosphere for 4 h, followed by cooling to 260°C. o C. Catalyst performance evaluation experiments were conducted at a reaction pressure of 2.0 MPa, using n-dodecane as a model reactant and a volume hourly space velocity (VHSV) of 3.3 h⁻¹. -1Gas and liquid phase product analyses were performed on PANNA A91 and PANNA A91 gas chromatographs, respectively, equipped with Agilent HP-Al / KCl and RESTEK RTX-1 columns, and FID detectors, respectively.

[0087] The following example, using sample 3 as raw material, demonstrates the catalytic performance of the Pt / ZSM-22 catalyst prepared by the present invention. The catalyst performance test results are shown below. Figures 4 to 6 .

[0088] from Figure 4 It can be seen that, using the ZSM-22 molecular sieve with a low silicon-to-aluminum ratio and a smooth tubular outer surface provided by this invention as a catalyst support, when the reaction temperature is 360°C... o At C, its n-dodecane conversion rate exceeds 90%, indicating that it has good catalytic activity.

[0089] from Figure 5 It can be seen that the selectivity of isomers is always greater than 72% throughout the reaction process, indicating that the catalyst using the ZSM-22 molecular sieve with a low silicon-to-aluminum ratio and a smooth tubular morphology on the outer surface provided by this invention as a support has high selectivity for isomers.

[0090] Figure 6 Further, the highest yield of isomers was 66%, indicating that the catalyst using the ZSM-22 molecular sieve with a low silica-to-alumina ratio and a smooth tubular outer surface provided by this invention as a support exhibits excellent catalytic performance. This is because the ZSM-22 molecular sieve synthesized by the method of this invention has a low silica-to-alumina ratio, resulting in a higher acid content within the molecular sieve, which effectively enhances the catalytic activity of the catalyst. Simultaneously, its smooth tubular outer surface facilitates the diffusion rate of reaction intermediates within the molecular sieve support, thereby significantly improving the selectivity and yield of isomers.

[0091] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for synthesizing ZSM-22 molecular sieves via a vapor phase method, comprising the following steps: (1) Add silicon source, aluminum source, alkali source, template agent and seed crystal to deionized water, stir thoroughly to form a mixed solution, put the mixed solution into an oven to dry, and then grind the dried gel into dry gel powder. (2) Add a small amount of deionized water to the bottom of the polytetrafluoroethylene liner of the stainless steel hydrothermal reactor, then place the dry gel powder on the support and put it into the polytetrafluoroethylene liner together for static crystallization conversion. (3) The obtained crystallized product was washed, dried and calcined to obtain Na-type ZSM-22 molecular sieve; in, The molar ratio of silicon source, aluminum source, alkali source, template agent and deionized water in the mixed solution is (1~300): (0.001~10): (0.01~1.0): (1~20): (2~500).

2. The method according to claim 1, characterized in that, The silicon source is one or more of the following: silica sol, silica gel, tetraethyl orthosilicate, water glass, silica fume, and fumed silica.

3. The method according to claim 1, characterized in that, The aluminum source is one or more of aluminum chloride, aluminum sulfate, aluminum hydroxide, sodium aluminate, aluminum sol, aluminum oxide, aluminum nitrate, and boehmite.

4. The method according to claim 1, characterized in that, The alkaline source is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and sodium silicate.

5. The method according to claim 1, characterized in that, The template agent is one or more of 1,6-hexanediamine, 1,8-octanediamine, di-n-propylamine, diisopropylamine, ethylenediamine, and pyrrolidine.

6. The method according to claim 1, characterized in that, The seed crystals are one or more of ZSM-22 molecular sieve, ZSM-48 molecular sieve, Beta molecular sieve, ZSM-23 molecular sieve, and ZSM-12 molecular sieve; the amount of seed crystals added is 0.01% to 10% of the mass of the silicon source.

7. The method according to any one of claims 1 to 6, characterized in that, In step (1), the oven temperature is 40~120°C when preparing the dry gel. o C, drying time is 2~54 h.

8. The method according to any one of claims 1 to 6, characterized in that, In step (2), the mass of deionized water added is 0.5% to 50% of the mass of the dry gel powder; the static crystallization transformation temperature is 90 to 200°C. o C, crystallization time is 12~200 h.

9. The method according to any one of claims 1 to 6, characterized in that, In step (3), the ZSM-22 molecular sieve is washed by one or more of the following methods: vacuum filtration or centrifugation; the drying temperature is 60~120℃. o C, drying time is 4~72 h; calcination temperature is 400~600 o C, roasting time is 2~20 h.

10. A ZSM-22 molecular sieve synthesized by the method of claims 1 to 10, having a silicon-to-aluminum ratio of 30 to 760 and a smooth tubular morphology on the outer surface.

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