Method for synthesizing zsm-23 zeolite molecular sieves with low silicon to aluminum ratio short axis nanocrystal morphology

Abstract

The application discloses a synthesis method of ZSM-23 zeolite molecular sieve with low silicon-aluminum ratio and short-axis nanocrystal morphology. A silica source, an alumina source, a template agent, an alkali metal source and water are mixed to form an initial gel. The initial gel is heated to a first temperature of 120-125 DEG C under sealing and a stirring speed of 100-180 rpm. After constant temperature for 8-10 hours, the initial gel is heated to a second temperature of 135-145 DEG C for constant temperature for 26-36 hours. The product is washed, dried and calcined to obtain the ZSM-23 zeolite molecular sieve. The method can be carried out under low stirring speed and is suitable for industrial amplification.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve preparation technology, specifically relating to a method for synthesizing ZSM-23 zeolite molecular sieve with a low silica-to-alumina ratio and short-axis nanocrystal morphology. Background Technology

[0002] ZSM-23 (MTT structure) zeolite molecular sieves have a one-dimensional 10-ring elliptical mesoporous structure. First published in 1978 by Mobil in patent US4076842, it has a pore size of approximately 0.45 x 0.52 nm. Due to its constrained pore size and unique pore orientation, it has important applications in the production of lubricating oil base oils through the hydroisomerization and dewaxing of n-alkanes.

[0003] In recent years, with the deepening of research, ZSM-23 zeolite molecular sieves with low silica-to-alumina ratio short-axis nanostructures have attracted increasing attention. Firstly, in terms of morphology, nano-short-axis ZSM-23 molecular sieves have a higher external specific surface area, providing more pores per unit mass compared to micron-sized crystals, i.e., sites for hydroisomerization reactions. Secondly, the reduction in silica-to-alumina ratio introduces more acid, thereby improving the catalyst's reactivity. While meeting the requirements of hydroisomerization processes, such as space velocity or throughput, the amount of molecular sieve used can be reduced, thus lowering the overall cost of the catalyst. However, in the process of reducing the silica-to-alumina ratio of ZSM-23 molecular sieve products and reducing the crystal size to the nanoscale, the relative purity of ZSM-23 is challenged, mainly because with the reduction in silica-to-alumina ratio, FER structures easily coexist with it (described in paragraph

[0010] on page 3 of CN102256704A). To solve this problem, CN102256704A uses (CH3)2N... + CH2CH2CH2N + (CH3)2CH2CH2CH2N + (CH3)3, abbreviated as Triquat-7, is synthesized by hydrothermal crystallization at a seed concentration of no less than 500 ppm and a reaction temperature of 150–200 °C for more than 72 hours. This process yields a product with a silicon-to-aluminum ratio of <40, a crystal particle size of 200–500 nm, and an external specific surface area of ​​<80 m². 2 / g of nano-MTT zeolite molecular sieves with a short-axis structure. However, this synthesis process requires the combined action of Triquat-7 organic template agent and seed crystals. US7390763 and CN100587035C proposed using N-lower alkyl-N'-isopropylimidazolium cation as the main template agent and isobutylamine, neopentylamine, monoethylamine, etc. as auxiliary template agents to form co-template agents, which can synthesize SSZ-32X (MTT structure) molecular sieves with a silica-alumina ratio of 20-40 and crystal size of 20-40nm at 170℃. However, the use of co-template agents in the synthesis process leads to high cost, and the main template agent is not easy to obtain, which reduces the wide application value of this material. CN110683558A synthesizes ZSM-23 (MTT structure) with an axis-to-diameter ratio less than 10 and a silica-to-alumina ratio of 60-110. However, this method requires both seed induction (seeds at ≥1% of the total gel mass) and high-speed stirring (stirring rate 200-300 rpm) to synthesize the target product. CN114988430A synthesizes nanorod-shaped ZSM-23 molecular sieves with crystal sizes less than 300 nm using a stepwise preparation technique. However, its molecular sieve crystallization process still requires high-speed stirring at 200-300 rpm and is carried out at a high temperature of 170-200℃ with the assistance of seed mother liquor. CN109516471A synthesizes ZSM-23 molecular sieves with a surface silica-to-alumina ratio of 10-80. Its characteristic is the use of a pre-crystallization method, first synthesizing high-silica ZSM-23 crystal nuclei in a high-silica gel, and then adding the crystal nuclei to a low-silica synthetic gel for reaction at 150-200℃. However, the crystal size of the resulting molecular sieve is around 500nm. CN102992346A discloses a method for synthesizing ZSM-23 molecular sieves without using organic template agents. Its characteristic is that, under certain silicon-to-aluminum ratio conditions, ZSM-23 molecular sieves with a silicon-to-aluminum ratio ≥57 are synthesized by adding ZSM-23 seed crystals (1-10% of the mass ratio of silicon oxide) at 140-180℃. However, its crystal length is approximately 1000-2000nm, exhibiting a micron-scale, and cannot achieve a nanoscale.

[0004] As can be seen from the published patents mentioned above, in the pursuit of nanoscale short-axis crystal morphology, without using expensive template agents such as Triquat-7 and N-lower alkyl-N'-isopropylimidazolium cations, and instead using inexpensive organic template agents such as isopropylamine, dimethylamine, ethylenediamine, and N,N-dimethylformamide, the synthesis of low-silicon-to-aluminum ratio short-axis nano-ZSM-23 can only be achieved through seed-assisted induction, high-temperature and high-speed stirring for rapid crystallization, or secondary synthesis using high-silicon seed solutions. However, in reality, for industrial scale-up processes, as the reactor volume increases, the high-speed stirring process exacerbates the centrifugal tendency of the materials within the reactor, easily causing resonance and vibration of the reactor equipment, seriously threatening production safety. For example, a conventional 5M... 310M 3 The stirring speed of a reactor is generally limited to 160–180 rpm; while 20M 3 The maximum stirring speed in the reactor is around 120 rpm. Lower stirring speeds or disturbances increase the difficulty of industrial scale-up of this molecular sieve, leading to the formation of impurities such as ZSM-5. This patent addresses the limited stirring capacity during industrial scale-up by proposing a relatively gentle and stable method for growing low-silicon-ratio short-axis nano-ZSM-23 molecular sieves. Summary of the Invention

[0005] The purpose of this invention is to provide a method for synthesizing ZSM-23 zeolite molecular sieves with a low silicon-to-alumina ratio and short-axis nanocrystal morphology. This method can be carried out at a low stirring rate and is suitable for industrial scale-up.

[0006] To achieve the above objectives, this invention provides a method for synthesizing ZSM-23 zeolite molecular sieves with a low silica-to-alumina ratio and short-axis nanocrystal morphology. A silica source, an alumina source, a template agent, an alkali metal source, and water are mixed to form an initial gel. Under sealed conditions and a stirring rate of 100–180 rpm, the initial gel is first heated to a first temperature of 120–125°C and held at that temperature for 8–10 hours. Then, the temperature is raised to a second temperature of 135–145°C and held at that temperature for 26–36 hours. The product is then washed, filtered, dried, and calcined to obtain the ZSM-23 zeolite molecular sieve.

[0007] The method for synthesizing ZSM-23 zeolite molecular sieves with low silica-to-alumina ratio and short-axis nanocrystal morphology according to the present invention uses isopropylamine IPA and / or dimethylamine as template agents.

[0008] The method for synthesizing ZSM-23 zeolite molecular sieve with low silicon-to-aluminum ratio and short-axis nanocrystal morphology according to the present invention, wherein the silicon source is one or more of silica sol, water glass and silica.

[0009] The method for synthesizing ZSM-23 zeolite molecular sieve with low silicon-to-alumina ratio and short-axis nanocrystal morphology according to the present invention, wherein the alumina source is one or more of aluminum sulfate, sodium aluminate, aluminum hydroxide and aluminum sol.

[0010] The method for synthesizing ZSM-23 zeolite molecular sieves with low silica-to-alumina ratio and short-axis nanocrystal morphology according to the present invention uses sodium hydroxide and / or sodium silicate as the alkali metal source.

[0011] The method for synthesizing ZSM-23 zeolite molecular sieve with low silicon-to-alumina ratio and short-axis nanocrystal morphology according to the present invention uses silicon oxide source (SiO2), alumina source (Al2O3), and alkali metal source (Na2O) as the molar ratio of each substance as 70-82 (SiO2:Al2O3:7-9, Na2O:51-58, template agent:2600-2850, H2O). If the values ​​of Na2O / SiO2 and Na2O / Al2O3 are too low, it will limit the effect of crystal nano-sizing or shrinking; if they are too high, it will easily cause the growth of ZSM-5 impurity crystals.

[0012] The synthesis method of ZSM-23 zeolite molecular sieve with low silicon-to-alumina ratio and short-axis nanocrystal morphology according to the present invention involves a heating rate of 10–25 °C / h to the first temperature and a heating rate of 8–10 °C / h to the second temperature. Those skilled in the art can select the appropriate heating rate based on actual conditions. A faster heating rate is possible when the reactor volume is small, but a slower heating rate is due to the lower heat exchange ratio caused by a larger reactor volume.

[0013] The present invention discloses a method for synthesizing ZSM-23 zeolite molecular sieves with low silica-to-alumina ratio and short-axis nanocrystal morphology. The ZSM-23 zeolite molecular sieve has a silica-to-alumina ratio of 50–67, a crystal grain size of less than 200 nm, an axis-to-diameter ratio of 3–5, and an external specific surface area greater than 90 m². 2 / g, relative crystallinity greater than 90%.

[0014] Beneficial effects of this invention:

[0015] (1) Taking advantage of the low temperature conditions, the synthetic materials and ratios have a limiting effect on the growth of ZSM-5 molecular sieve. Even under relatively low reaction temperature conditions, combined with low-speed disturbance, ZSM-23 crystal nuclei are preferentially induced first. Then, the temperature is raised to a certain level so that ZSM-23 can grow relatively quickly. Before ZSM-5 begins to grow, the crystallization reaction is stopped, thus achieving the purpose of obtaining ZSM-23 molecular sieve.

[0016] (2) Utilizing the high Na content in the reaction system + Under alkaline conditions, a relatively high number of crystal nuclei are obtained. Under the condition that the supersaturation concentration of the reaction masterbatch is certain, short-axis nanomolecular sieves with low silicon-to-aluminum ratio and large external specific surface area are obtained. Attached Figure Description

[0017] Figure 1 This is the X-ray diffraction pattern of the ZSM-23 zeolite molecular sieve with a low silicon-to-aluminum ratio and short-axis morphology synthesized in Example 1 of this invention.

[0018] Figure 2This is a scanning electron microscope image of ZSM-23 zeolite molecular sieve with a low silicon-to-aluminum ratio and short-axis morphology synthesized in Example 1 of this invention.

[0019] Figure 3 This is the XRD pattern of the ZSM-23 zeolite molecular sieve with a low silicon-to-aluminum ratio and short-axis nanostructure synthesized in Example 2 of this invention.

[0020] Figure 4 This is a scanning electron microscope image of ZSM-23 zeolite molecular sieve with a low silicon-to-aluminum ratio and short-axis nanostructure synthesized in Example 2 of this invention.

[0021] Figure 5 This is the XRD pattern of the ZSM-23 zeolite molecular sieve with a low silicon-to-aluminum ratio and short-axis nanostructure synthesized in Example 3 of this invention.

[0022] Figure 6 This is the XRD pattern of the ZSM-23 zeolite molecular sieve with a low silicon-to-aluminum ratio and short-axis nanostructure synthesized in Example 4 of this invention.

[0023] Figure 7 This is the XRD pattern of the synthesized product of Comparative Example 1 of this invention.

[0024] Figure 8 This is the XRD pattern of the synthesized product of Comparative Example 2 of this invention.

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

[0026] Figure 10 This is the XRD pattern of the synthesized product of Comparative Example 4 of this invention.

[0027] Figure 11 This is the XRD pattern of the synthesized product of Comparative Example 5 of this invention. Detailed Implementation

[0028] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection 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 description.

[0029] Example 1:

[0030] 10M 3 Synthesis of short-axis ZSM-23 nanoparticles with a silicon-to-aluminum ratio of 55

[0031] The specific operation is as follows: at room temperature, 10M 3Under a stirring speed of 180 rpm in the reactor, 2400 kg of an aqueous solution containing 30% SiO2, 110 kg of Al2(SO4)3·18H2O, 108 kg of NaOH, 720 kg of an aqueous solution containing 70% isopropylamine, and 5900 kg of water were mixed to form a gel, and then stirred for 4 hours. The molar ratio of each substance in the material was: 72.7SiO2:Al2O3:8.2Na2O:51.8IPA:1.5H2SO4:2650H2O. The ratios of Na2O / SiO2 and Na2O / Al2O3 were 0.11 and 8.2, respectively. The mixture was then heated to 125℃ at a rate of 10℃ / h and held at that temperature for 12 hours, followed by a further increase in temperature to 135℃ at a rate of 10℃ / h and held at that temperature for 34 hours to complete the reaction. The product was then filtered, washed, dried, and calcined. XRD analysis confirmed the product to be ZSM-23 molecular sieve; XRF testing showed a silica-to-alumina ratio of 54.6 and a specific surface area of ​​255 m² / g. 2 / g, of which the external specific surface area is 109m² 2 / g, SEM showed that the molecular sieve size was approximately 150-200 nm, the axial diameter ratio was approximately 3-5, and the relative crystallinity was greater than 98%. XRD showed... Figure 1 As shown, SEM Figure 2 As shown.

[0032] Example 2:

[0033] 5M 3 Synthesis of short-axis ZSM-23 nanoparticles with a silicon-to-aluminum ratio of 55

[0034] The specific operation is as follows: at room temperature, 5M 3 Under a stirring speed of 120 rpm in a reactor, 1200 kg of an aqueous solution containing 30% SiO2, 56 kg of Al2(SO4)3·18H2O, 54 kg of NaOH, 360 kg of an aqueous solution containing 70% isopropylamine, and 2950 kg of water were mixed to form a gel, and then stirred for 4 hours. The molar ratio of each substance in the material was: 71.4SiO2:Al2O3:8.06Na2O:50.9IPA:1.5H2SO4:26O3H2O. The ratios of Na2O / SiO2 and Na2O / Al2O3 were 0.11 and 8.06, respectively. The mixture was then heated to 123℃ at a rate of 15℃ / h and held at that temperature for 12 hours. The temperature was then increased to 142℃ at a rate of 10℃ / h and held at that temperature for 26 hours to complete the reaction. The product was then filtered, washed, dried, and calcined. XRD analysis confirmed the product to be ZSM-23 molecular sieve; XRF testing showed a silica-to-alumina ratio of 55.2 and a specific surface area of ​​254 m². 2 / g, of which the external specific surface area is 101m² 2 / g, SEM showed that the molecular sieve size was approximately 180-200 nm, the axial diameter ratio was approximately 4-5, and the relative crystallinity was greater than 98%. XRD showed... Figure 3 As shown, SEM Figure 4 As shown.

[0035] Example 3:

[0036] 1M 3 Synthesis of short-axis ZSM-23 nanoparticles with a silicon-to-aluminum ratio of 55

[0037] The specific operation is as follows: at room temperature, 1M 3 Under a stirring speed of 160 rpm in the reactor, 240 kg of an aqueous solution containing 30% SiO2, 11.2 kg of Al2(SO4)3·18H2O, 10.6 kg of NaOH, 72 kg of an aqueous solution containing 70% isopropylamine, and 590 kg of water were mixed to form a gel, and then stirred for 4 hours. The molar ratio of each substance in the material was: 71.4 SiO2:Al2O3:7.9 Na2O:50.8 IPA:1.5 H2SO4:2606 H2O. The ratios of Na2O / SiO2 and Na2O / Al2O3 were 0.11 and 7.9, respectively. The mixture was then heated to 120℃ at a rate of 25℃ / h and held at that temperature for 12 hours. The temperature was then increased to 145℃ at a rate of 10℃ / h and held at that temperature for 34 hours to complete the reaction. The product was filtered, washed, dried, and calcined. XRD analysis confirmed the product to be ZSM-23 molecular sieve; XRF testing showed a silica-to-alumina ratio of 56.2 and a specific surface area of ​​256 m². 2 / g, of which the external specific surface area is 104m² 2 / g, SEM showed that the molecular sieve size was approximately 150-200 nm, the axial diameter ratio was approximately 3-5, and the relative crystallinity was >98%. XRD showed... Figure 5 As shown.

[0038] Example 4

[0039] 1M 3 Synthesis of short-axis ZSM-23 nanoparticles with a silicon-to-aluminum ratio of 65

[0040] The specific operation is as follows: at room temperature, 1M 3Under a stirring speed of 140 rpm in the reactor, 240 kg of an aqueous solution containing 30% SiO2, 9.9 kg of Al2(SO4)3·18H2O, 9.3 kg of NaOH, 72 kg of an aqueous solution containing 70% isopropylamine, and 566 kg of water were mixed to form a gel, and then stirred for 4 hours. At this point, the molar ratio of the materials was: 80.5 SiO2:Al2O3:7.8 Na2O:57.3 IPA:1.5 H2SO4:2843 H2O. The mixture was then heated to 125℃ at a rate of 25℃ / h and held at that temperature for 12 hours, followed by a further increase in temperature to 145℃ at a rate of 10℃ / h and held at that temperature for 36 hours to complete the reaction. The product was filtered, washed, dried, and calcined. XRD analysis identified the product as ZSM-23 molecular sieve; XRF testing showed a silica-alumina ratio of 64.3 and a specific surface area of ​​264 m². 2 / g, of which the external specific surface area is 98m² 2 / g, SEM showed that the molecular sieve size was approximately 150-200 nm, the axial diameter ratio was approximately 3-5, and the relative crystallinity was >99%. XRD showed... Figure 6 As shown.

[0041] Comparative Example 1

[0042] 10M 3 ZSM-23 molecular sieves were synthesized by directly heating to 165℃ and holding at a stirring rate of 180 rpm for 34 hours. The product was a large-scale mixture of ZSM-5 and ZSM-23.

[0043] A gel was prepared according to Example 1 at a stirring rate of 180 rpm and stirred at room temperature for 4 hours. The gel was then heated to 165°C at a rate of 10°C / h and crystallized at this temperature for 34 hours. The product was cooled, washed with water, filtered, dried, and calcined. XRD analysis showed that the product mainly consisted of a large amount of ZSM-5 and ZSM-23 mixed phases. (XRD pattern shown...) Figure 7 As shown.

[0044] Comparative Example 2

[0045] 10M 3 ZSM-23 molecular sieves were synthesized by stirring at 180 rpm, maintaining a constant temperature of 125°C for 12 hours, and then raising the temperature to 165°C and maintaining a constant temperature for 34 hours. The product was a small amount of a mixture of ZSM-5 and ZSM-23.

[0046] A gel was prepared according to Example 1 at a stirring rate of 180 rpm and stirred at room temperature for 4 hours. The gel was then heated to 125°C at a rate of 10°C / h, held at that temperature for 12 hours, and then heated to 165°C at a rate of 10°C / h and held at that temperature for 34 hours. The product was cooled, washed with water, filtered, dried, and calcined. XRD analysis showed that the product mainly consisted of a small amount of miscible ZSM-5 and ZSM-23. (XRD pattern shown...) Figure 8 As shown.

[0047] Comparative Example 3:

[0048] 5M 3 ZSM-23 molecular sieves were synthesized by directly heating to 142℃ and holding at a stirring rate of 120 rpm for 26 hours. The product was a mixture of ZSM-5 and ZSM-23.

[0049] A gel was prepared according to Example 2 at a stirring rate of 120 rpm and stirred at room temperature for 4 hours. The gel was then heated to 142°C at a rate of 15°C / h and crystallized at this temperature for 26 hours. The product was cooled, washed with water, filtered, dried, and calcined. XRD analysis showed that the product was mainly a mixture of ZSM-5 and ZSM-23. (XRD pattern shown...) Figure 9 As shown.

[0050] Comparative Example 4:

[0051] 1M 3 Stirring speed 160 rpm, add 3% ZSM-23 seed crystals, directly heat to 165℃ and hold at that temperature for 34 hours, product is ZSM-5

[0052] A gel was prepared according to Example 3 at a stirring rate of 160 rpm, and 3% ZSM-23 seed crystals were added. The mixture was stirred at room temperature for 4 hours. The gel was then heated to 165°C at a rate of 25°C / h and crystallized at this temperature for 34 hours. The product was cooled, washed with water, filtered, dried, and calcined. XRD analysis showed that the product was ZSM-5. (XRD pattern shown...) Figure 10 As shown.

[0053] Comparative Example 5:

[0054] 1M 3 The stirring speed was 160 rpm, no seed crystals were added, and the temperature was directly raised to 165℃ and held for 34 hours. The product was ZSM-5.

[0055] A gel was prepared according to Example 3 at a stirring rate of 160 rpm and stirred at room temperature for 4 hours. The gel was then heated to 165°C at a rate of 25°C / h and crystallized at this temperature for 34 hours. The product was cooled, washed with water, filtered, dried, and calcined. XRD analysis showed that the product was ZSM-5. (XRD pattern shown...) Figure 11 As shown.

[0056] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications 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 a low silica-to-alumina ratio and short-axis nanocrystal morphology, characterized in that, A silica source, an alumina source, a template agent, an alkali metal source, and water are mixed to form an initial gel. Under sealed conditions and a stirring rate of 100-180 rpm, the initial gel is first heated to a first temperature of 120-125°C and held at that temperature for 8-10 hours. Then, the temperature is raised to a second temperature of 135-145°C and held at that temperature for 26-36 hours. The product is then washed, filtered, dried, and calcined to obtain the ZSM-23 zeolite molecular sieve. The template agent is isopropylamine IPA and / or dimethylamine; The silicon dioxide source is calculated as SiO2, the aluminum oxide source as Al2O3, and the alkali metal source as Na2O. The molar ratio of each substance is 70~82:SiO2:Al2O3:7~9:Na2O:51~58:template agent:2600~2850H2O.

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

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

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

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

6. The method for synthesizing ZSM-23 zeolite molecular sieve with low silica-to-alumina ratio and short-axis nanocrystal morphology according to claim 1, characterized in that, The ZSM-23 zeolite molecular sieve has a silica-to-alumina ratio of 50-67, a crystal grain size of less than 200 nm, an axial-to-diameter ratio of 3-5, and an external specific surface area of ​​greater than 90 m². 2 / g, relative crystallinity greater than 90%.

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