ZSM-48 molecular sieve raw powder, rapid synthesis method thereof and n-dodecane hydroisomerization reaction catalyst

Abstract

The invention provides ZSM-48 molecular sieve raw powder, a rapid synthesis method thereof and an n-dodecane hydroisomerization reaction catalyst. The rapid synthesis method comprises the following steps: uniformly mixing a first silicon source, a first inorganic alkali source, a first template agent and water to obtain first gel; performing dynamic crystallization on the first gel, and obtaining nano crystal buds after the crystallization is completed; uniformly mixing a second silicon source, an aluminum source, a second inorganic alkali source, a second template agent and water to obtain second gel; and adding nano crystal buds into the second gel to form third gel, carrying out static crystallization on the third gel, and filtering, washing and drying the obtained product to obtain ZSM-48 molecular sieve raw powder. According to the rapid synthesis method provided by the invention, the nanocrystalline buds are added into the ZSM-48 synthesis gel mother liquor, and the synthesis time of the ZSM-48 molecular sieve can be greatly shortened by utilizing the structure guidance quality and the induction effect of the nanocrystalline buds; the prepared molecular sieve is high in crystallinity, and the dosage of the organic template agent is low.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve synthesis technology, specifically relating to a ZSM-48 molecular sieve raw powder and its rapid synthesis method, as well as a catalyst for the hydrogenation isomerization reaction of n-dodecane. Background Technology

[0002] ZSM-48 molecular sieve is a high-silica molecular sieve with one-dimensional ten-membered ring channels. These channels are connected in two ways: crankshaft connection and four-membered ring connection, ultimately forming a ten-membered ring channel structure. ZSM-48 molecular sieve possesses a unique channel structure and strong surface acidity, which makes it more conducive to the branching isomerization of long-chain macromolecular alkanes, increasing the isomerization depth and significantly reducing the pour point of base oils. Therefore, it has been widely used in catalysis fields such as petroleum refining and petrochemicals.

[0003] However, the synthesis of ZSM-48 molecular sieves currently suffers from problems such as long hydrothermal crystallization time (72 hours) and large amounts of expensive template agents, which restricts production efficiency in industrial production and poses a significant challenge in treating industrial wastewater generated by organic template agents. Researchers have attempted to use different techniques to efficiently prepare ZSM-48 molecular sieves, such as microwave, ultrasonic, and solid-phase seed-assisted synthesis methods. However, microwave and ultrasonic methods involve expensive equipment, demanding operating conditions, and still require large amounts of expensive template agents, making industrial application difficult. Solid-phase seed-assisted synthesis methods suffer from drawbacks such as long synthesis steps, large amounts of seed crystals, and uneven molecular sieve particle size. For example, US6923949 discloses a method for inducing the synthesis of ZSM-48 using heterogeneous molecular sieves as seed crystals; however, this method requires a large amount of seed crystals and involves a long experimental process and hydrothermal crystallization time. US7482300 discloses a method for synthesizing low silica-alumina ratio ZSM-48 molecular sieves using hexamethyldiamine chloride as a template agent under seed-assisted conditions; however, the template agent (hexamethyldiamine chloride) used in this method is expensive and highly toxic, which is not conducive to industrial application. CN110562999A discloses a method for successfully synthesizing low silica-alumina ratio (82) ZSM-48 molecular sieves using hexamethylamine bromide as a template agent under homogeneous or heterogeneous seed-assisted conditions; however, the hydrothermal crystallization temperature used in this technology is too high (180 degrees Celsius), resulting in low crystallinity of the synthesized molecular sieve.

[0004] In summary, the two common technical challenges in the synthesis of molecular sieves—long crystallization time and large amounts of template agent—remain unresolved. Therefore, developing a technology for the rapid synthesis of ZSM-48 molecular sieves with low template agent usage is of great significance and has promising application prospects. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a ZSM-48 molecular sieve raw powder, its rapid synthesis method, and a catalyst for the n-dodecane hydroisomerization reaction. By adding nanocrystals, the rapid preparation of ZSM-48 molecular sieve raw powder can be achieved, shortening the crystallization time and further reducing the amount of template agent required.

[0006] To achieve the above objectives, the present invention provides a rapid synthesis method for ZSM-48 molecular sieve raw powder, wherein the rapid synthesis method includes:

[0007] (1) A first silicon source, a first inorganic base source, a first template agent, and water are uniformly mixed to obtain a first gel; the first gel is subjected to dynamic crystallization, and nanocrystals are obtained after crystallization; wherein, the molar ratio of the raw materials in the first gel is: OH - / SiO2=(0.01-0.5):1, R1 / SiO2=(0.01-0.6):1, H2O / SiO2=(10-60):1, the first silicon source is calculated as SiO2, and the first inorganic alkali source is calculated as OH. - R1 represents the number of moles of the first template agent;

[0008] (2) The second silicon source, aluminum source, second inorganic alkali source, second template agent, and water are uniformly mixed to obtain a second gel; wherein the molar ratio of the raw materials in the second gel is: SiO2 / Al2O3=(40-500):1, OH- / SiO2=(0.01-0.5):1, R2 / SiO2=(0.005-0.08):1, H2O / SiO2=(5-60):1, the second silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the second inorganic alkali source is calculated as OH-. - R2 represents the number of moles of the second template agent; the first template agent is the same as the second template agent;

[0009] (3) Add nanocrystals to the second gel to form a third gel, perform static crystallization on the third gel, and filter, wash and dry the product to obtain ZSM-48 molecular sieve raw powder.

[0010] The amount of nanocrystals added is 5wt%-90wt%, with the mass of the second silicon source being 100%.

[0011] In this invention, compared to conventional solid-phase seed crystals, the self-made nanocrystals exist in a liquid phase. Therefore, the internal crystalline units of these nanocrystals are highly dispersed and do not exhibit aggregation. Consequently, they can provide in-situ growth sites or growth surfaces required in the early stages of cell formation, shortening the initial crystallization induction period and thus rapidly forming the cell. Furthermore, the nanocrystals prepared by this invention possess certain genetic effects and structure-directing properties, which can promote the rapid combination and arrangement of required nutrient ions into an ordered crystal structure on the cell surface, thereby accelerating crystal growth and significantly reducing the amount of organic template agent required.

[0012] According to a specific embodiment of the present invention, preferably, the static crystallization temperature is 150-180°C and the static crystallization time is 12-72 hours; more preferably, the static crystallization time is 15-40 hours.

[0013] According to a specific embodiment of the present invention, preferably, the temperature of the dynamic crystallization is 160-175℃, and the time of the dynamic crystallization is 10-60 hours; the dynamic crystallization process is carried out in a rotary oven or a crystallization reactor, with a rotation speed of 5-60 r / min in the rotary oven and a rotation speed of 50-200 r / min in the crystallization reactor.

[0014] According to a specific embodiment of the present invention, preferably, the amount of nanocrystals added is 20wt%-80wt% based on the mass of the second silicon source as 100%; more preferably, it is 30wt%-70wt%; and even more preferably, it is 50wt%-60wt%.

[0015] In some specific embodiments, preferably, the molar ratio of the raw materials in the first gel is: OH - / SiO2=(0.02-0.1):1,R1 / SiO2=(0.02-0.1):1,H2O / SiO2=(20-40):1。

[0016] In some specific embodiments, preferably, the molar ratio of the raw materials in the second gel is: SiO2 / Al2O3 = (200-500): 1, OH- / SiO2 = (0.1-0.5): 1, R2 / SiO2 = (0.005-0.05): 1, H2O / SiO2 = (20-40): 1.

[0017] According to a specific embodiment of the present invention, preferably, the first silicon source includes one or a combination of two or more of silica sol, fumed silica, and tetraethyl orthosilicate.

[0018] According to a specific embodiment of the present invention, preferably, the second silicon source includes one or a combination of two or more of silica sol, fumed silica, and tetraethyl orthosilicate. The terms "first silicon source" and "second silicon source" are used merely for name distinction and may represent the same or different substances.

[0019] According to a specific embodiment of the present invention, preferably, the aluminum source includes one or a combination of two or more of sodium aluminate, aluminum sulfate, aluminum acetate, and aluminum isopropoxide.

[0020] According to a specific embodiment of the present invention, preferably, the first inorganic alkali source includes one or a combination of two or more of sodium hydroxide, potassium hydroxide, basic sodium carbonate, and sodium bicarbonate.

[0021] According to a specific embodiment of the present invention, preferably, the second inorganic alkali source includes one or a combination of two or more of sodium hydroxide, potassium hydroxide, basic sodium carbonate, and sodium bicarbonate. The terms "first inorganic alkali source" and "second inorganic alkali source" are used merely for name distinction and may represent the same or different substances.

[0022] According to a specific embodiment of the present invention, preferably, the first template agent includes one or a combination of two or more of allyltrimethylammonium chloride, 1,6-hexanediamine, hexamethylamine bromide, tetramethylammonium hydroxide, pentamethyldiammonium bromide, and crown ether template agents.

[0023] According to a specific embodiment of the present invention, preferably, the second template agent includes one or a combination of two or more of allyltrimethylammonium chloride, 1,6-hexanediamine, hexamethylamine bromide, tetramethylammonium hydroxide, pentamethyldiammonium bromide, and crown ether template agents. In the same sample, the selection of the second template agent is the same as that of the first template agent; the terms "first template agent" and "second template agent" are used only for distinction by name.

[0024] This invention also provides a ZSM-48 molecular sieve raw powder, which is prepared by the above-described rapid synthesis method. The molecular sieve raw powder can be calcined to finally prepare a finished molecular sieve.

[0025] According to a specific embodiment of the present invention, preferably, the relative crystallinity of the ZSM-48 molecular sieve raw powder is 89% or higher.

[0026] The present invention also provides a catalyst for the hydroisomerization reaction of n-dodecane, wherein the catalyst is prepared from the above-mentioned ZSM-48 molecular sieve powder as raw material.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) The rapid synthesis method of ZSM-48 molecular sieve powder provided by the present invention can significantly reduce the synthesis time of ZSM-48 molecular sieve by adding nanocrystals to the ZSM-48 synthesis gel mother liquor and utilizing the excellent structural guidance and induction effect of nanocrystals, thereby improving the synthesis efficiency of molecular sieve and reducing the operating costs of equipment and labor in the long-cycle synthesis of molecular sieve.

[0029] (2) The rapid synthesis method of ZSM-48 molecular sieve powder provided by the present invention produces molecular sieves with high crystallinity and highly dispersed spindle morphology, and with low organic template agent dosage. This overcomes the technical problems of low molecular sieve crystallinity and high organic template agent dosage in the prior art, greatly reducing the waste liquid treatment and discharge process caused by organic template agent, and reducing environmental pollution.

[0030] (3) The ZSM-48 molecular sieve raw powder provided by the present invention can be further prepared into a catalyst for the hydrogenation isomerization reaction of n-dodecane. Compared with the catalyst made by ZSM-48 molecular sieve prepared by conventional methods, it has higher conversion rate, multi-branched isomer selectivity and total isomer yield. Attached Figure Description

[0031] Figure 1 The XRD patterns are those of the samples prepared in Examples 1-7 and Comparative Example 3.

[0032] Figure 2 The XRD patterns are those of the samples prepared in Comparative Examples 1-2 and 4.

[0033] Figure 3 This is an SEM image of the sample prepared in Example 4.

[0034] Figure 4 The image shows the SEM image of the sample prepared in Comparative Example 4. Detailed Implementation

[0035] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0036] Example 1

[0037] This embodiment provides a rapid synthesis method for ZSM-48 molecular sieve raw powder, specifically including the following steps:

[0038] (1) Using sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the first template agent, according to the molar ratio OH -The feed ratio of SiO2:R1:H2O is 1.6:30:0.6:1050. First, sodium hydroxide and hexamethylamine bromide, the first template agent, are added to deionized water and stirred until a solution is formed. While maintaining the solution under stirring, silica sol is slowly added dropwise to the solution to obtain the first gel. The first gel is then transferred to a crystallization reactor with a polytetrafluoroethylene liner and subjected to dynamic crystallization at 160°C and 50 rpm. After crystallization, a crystallized gel, i.e., nanocrystals, is obtained.

[0039] (2) Using sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the second template agent, according to the molar ratio Al2O3:OH - The feed mixture is prepared using a SiO2:R2:H2O ratio of 0.075:3.6:30:0.6:1050. First, sodium hydroxide, aluminum sulfate, and hexamethylamine bromide (the second template agent) are added to deionized water and stirred until a solution is formed. While maintaining the solution under stirring, silica sol is slowly added dropwise to the solution to obtain the second gel.

[0040] (3) Add nanocrystals to the second gel (the amount of nanocrystals added is 33.5wt% based on the mass of the silica sol added in step (2) as 100%) to form a third gel; transfer the third gel to a reaction vessel with a polytetrafluoroethylene liner and perform static crystallization at 160°C for 16 hours. After crystallization, the product is separated into solid and liquid and filtered. The filtered solid is washed and dried to obtain the original powder of ZSM-48 molecular sieve.

[0041] The XRD diffraction pattern of the sample prepared in this embodiment is as follows: Figure 1 As shown, Figure 1 The results showed that it was ZSM-48 molecular sieve.

[0042] Example 2

[0043] This embodiment provides a rapid synthesis method for ZSM-48 molecular sieve raw powder, specifically including the following steps:

[0044] (1) Using sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the first template agent, according to the molar ratio OH - The feed ratio of SiO2:R1:H2O is 1.6:30:0.6:1050. First, sodium hydroxide and hexamethylamine bromide, the first template agent, are added to deionized water and stirred until a solution is formed. While maintaining the solution under stirring, silica sol is slowly added dropwise to form a first gel. The first gel is then transferred to a crystallization reactor with a polytetrafluoroethylene liner and subjected to dynamic crystallization at 160°C and 50 rpm. After crystallization, a crystallized gel, i.e., nanocrystals, is obtained.

[0045] (2) Using sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the second template agent, according to the molar ratio Al2O3:OH - The feed mixture is prepared using a SiO2:R2:H2O ratio of 0.075:3.6:30:0.6:1050. First, sodium hydroxide, aluminum sulfate, and hexamethylamine bromide (the second template agent) are added to deionized water and stirred until a solution is formed. While maintaining the solution under stirring, silica sol is slowly added dropwise to the solution to obtain the second gel.

[0046] (3) Add nanocrystals to the second gel (the amount of nanocrystals added is 44.5wt% based on the mass of the silica sol added in step (2) as 100%) to form a third gel; transfer the third gel to a reaction vessel with a polytetrafluoroethylene liner and perform static crystallization at 160°C for 16 hours. After crystallization, the product is separated into solid and liquid and filtered. The filtered solid is washed and dried to obtain the original powder of ZSM-48 molecular sieve.

[0047] The XRD diffraction pattern of the sample prepared in this embodiment is as follows: Figure 1 As shown, Figure 1 The results showed that it was ZSM-48 molecular sieve.

[0048] Example 3

[0049] This embodiment provides a rapid synthesis method for ZSM-48 molecular sieve raw powder, specifically including the following steps:

[0050] (1) Using sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the first template agent, according to the molar ratio OH - The feed ratio of SiO2:R1:H2O is 1.6:30:0.6:1050. First, sodium hydroxide and hexamethylamine bromide, the first template agent, are added to deionized water and stirred until a solution is formed. While maintaining the solution under stirring, silica sol is slowly added dropwise to form a first gel. The first gel is then transferred to a crystallization reactor with a polytetrafluoroethylene liner and subjected to dynamic crystallization at 160°C and 50 rpm. After crystallization, a crystallized gel, i.e., nanocrystals, is obtained.

[0051] (2) Using sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the second template agent, according to the molar ratio Al2O3:OH -The feed mixture is prepared using a SiO2:R2:H2O ratio of 0.075:3.6:30:0.6:1050. First, sodium hydroxide, aluminum sulfate, and hexamethylamine bromide (the second template agent) are added to deionized water and stirred until a solution is formed. While maintaining the solution under stirring, silica sol is slowly added dropwise to the solution to obtain the second gel.

[0052] (3) Add nanocrystals to the second gel (the amount of nanocrystals added is 55.5wt% based on the mass of the silica sol added in step (2) as 100%) to form a third gel; transfer the third gel to a reaction vessel with a polytetrafluoroethylene liner and perform static crystallization at 160°C for 16 hours. After crystallization, the product is separated into solid and liquid and filtered. The filtered solid is washed and dried to obtain the original powder of ZSM-48 molecular sieve.

[0053] The XRD diffraction pattern of the sample prepared in this embodiment is as follows: Figure 1 As shown, Figure 1 The results showed that it was ZSM-48 molecular sieve.

[0054] Example 4

[0055] This embodiment provides a rapid synthesis method for ZSM-48 molecular sieve raw powder, specifically including the following steps:

[0056] (1) Using sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the first template agent, according to the molar ratio OH - The feed ratio of SiO2:R1:H2O is 1.6:30:0.6:1050. First, sodium hydroxide and hexamethylamine bromide, the first template agent, are added to deionized water and stirred until a solution is formed. While maintaining the solution under stirring, silica sol is slowly added dropwise to form a first gel. The first gel is then transferred to a crystallization reactor with a polytetrafluoroethylene liner and subjected to dynamic crystallization at 160°C and 50 rpm. After crystallization, a crystallized gel, i.e., nanocrystals, is obtained.

[0057] (2) Using sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the second template agent, according to the molar ratio Al2O3:OH - The feed mixture is prepared using a SiO2:R2:H2O ratio of 0.075:3.6:30:0.6:1050. First, sodium hydroxide, aluminum sulfate, and hexamethylamine bromide (the second template agent) are added to deionized water and stirred until a solution is formed. While maintaining the solution under stirring, silica sol is slowly added dropwise to the solution to obtain the second gel.

[0058] (3) Add nanocrystals to the second gel (the amount of nanocrystals added is 66.6 wt% based on the mass of the silica sol added in step (2) as 100%) to form a third gel; transfer the third gel to a reaction vessel with a polytetrafluoroethylene liner and perform static crystallization at 160°C for 16 hours. After crystallization, the product is subjected to solid-liquid separation and filtration. The filtered solid is washed and dried to obtain the original powder of ZSM-48 molecular sieve.

[0059] The XRD diffraction pattern of the sample prepared in this embodiment is as follows: Figure 1 As shown, Figure 1 The results showed that it was ZSM-48 molecular sieve.

[0060] The SEM image of the sample prepared in this embodiment is shown below. Figure 3 As shown, Figure 3 The results showed that its morphology was a highly dispersed spindle-shaped morphology.

[0061] Example 5

[0062] This embodiment provides a rapid synthesis method for ZSM-48 molecular sieve raw powder, specifically including the following steps:

[0063] (1) Using basic sodium carbonate as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the first template agent, according to the molar ratio OH - The feed ratio of SiO2:R1:H2O is 1.9:30:0.6:1050. First, basic sodium carbonate and hexamethylamine bromide, the first template agent, are added to deionized water and stirred until a solution is formed. While maintaining the solution under stirring, silica sol is slowly added dropwise to form a first gel. The first gel is then transferred to a crystallization reactor with a polytetrafluoroethylene liner and subjected to dynamic crystallization at 160°C and 50 rpm. After crystallization, a crystallized gel, i.e., nanocrystals, is obtained.

[0064] (2) Using basic sodium carbonate as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the second template agent, according to the molar ratio Al2O3:OH - The feed ratio of SiO2:R2:H2O is 0.075:3.4:30:0.6:900. First, basic sodium carbonate, aluminum sulfate, and hexamethylamine bromide (the second template agent) are added to deionized water and stirred until a solution is formed. While maintaining the solution's stirring, silica sol is then slowly added dropwise to the solution to obtain the second gel.

[0065] (3) Add nanocrystals to the second gel (the amount of nanocrystals added is 66.6 wt% based on the mass of the silica sol added in step (2) as 100%) to form a third gel; transfer the third gel to a reaction vessel with a polytetrafluoroethylene liner and perform static crystallization at 160°C for 16 hours. After crystallization, the product is subjected to solid-liquid separation and filtration. The filtered solid is washed and dried to obtain the original powder of ZSM-48 molecular sieve.

[0066] The XRD diffraction pattern of the sample prepared in this embodiment is as follows: Figure 1 As shown, Figure 1 The results showed that it was ZSM-48 molecular sieve.

[0067] Example 6

[0068] This embodiment provides a rapid synthesis method for ZSM-48 molecular sieve raw powder, specifically including the following steps:

[0069] (1) Using sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the first template agent, according to the molar ratio OH - The feed ratio of SiO2:R1:H2O is 1.6:30:0.6:1050. First, sodium hydroxide and hexamethylamine bromide, the first template agent, are added to deionized water and stirred until a solution is formed. While maintaining the solution under stirring, silica sol is slowly added dropwise to form a first gel. The first gel is then transferred to a crystallization reactor with a polytetrafluoroethylene liner and subjected to dynamic crystallization at 160°C and 50 rpm. After crystallization, a crystallized gel, i.e., nanocrystals, is obtained.

[0070] (2) Using sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the second template agent, according to the molar ratio Al2O3:OH - The feedstock is prepared by mixing SiO2:R2:H2O in a ratio of 0.1:3.6:30:0.6:1050. First, sodium hydroxide, aluminum isopropoxide, and hexamethylamine bromide (the second template agent) are added to deionized water and stirred until a solution is formed. While maintaining the solution under stirring, silica sol is then slowly added dropwise to the solution to obtain the second gel.

[0071] (3) Add nanocrystals to the second gel (the amount of nanocrystals added is 66.6 wt% based on the mass of the silica sol added in step (2) as 100%) to form a third gel; transfer the third gel to a reaction vessel with a polytetrafluoroethylene liner and perform static crystallization at 160°C for 16 hours. After crystallization, the product is subjected to solid-liquid separation and filtration. The filtered solid is washed and dried to obtain the original powder of ZSM-48 molecular sieve.

[0072] The XRD diffraction pattern of the sample prepared in this embodiment is as follows: Figure 1 As shown, Figure 1 The results showed that it was ZSM-48 molecular sieve.

[0073] Example 7

[0074] This embodiment provides a rapid synthesis method for ZSM-48 molecular sieve raw powder, specifically including the following steps:

[0075] (1) Using sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the first template agent, according to the molar ratio OH - The feed is prepared by mixing SiO2:R1:H2O in a ratio of 1.6:30:0.6:1050. Sodium hydroxide and hexamethylamine bromide as the first template agent are first added to deionized water and stirred until a solution is formed. The solution is kept stirred, and then silica sol is slowly added dropwise to form the first gel. The first gel is transferred to a rotary oven and dynamically crystallized at 160°C and 30 rpm. After crystallization, a crystallized gel, namely nanocrystals, is obtained.

[0076] (2) Using sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the second template agent, according to the molar ratio Al2O3:OH - The feed mixture is prepared using a SiO2:R2:H2O ratio of 0.075:3.6:30:0.6:1050. First, sodium hydroxide, aluminum sulfate, and hexamethylamine bromide (the second template agent) are added to deionized water and stirred until a solution is formed. While maintaining the solution under stirring, silica sol is slowly added dropwise to the solution to obtain the second gel.

[0077] (3) Add nanocrystals to the second gel (the amount of nanocrystals added is 66.6 wt% based on the mass of the silica sol added in step (2) as 100%) to form a third gel; transfer the third gel to a reaction vessel with a polytetrafluoroethylene liner and perform static crystallization at 160°C for 16 hours. After crystallization, the product is subjected to solid-liquid separation and filtration. The filtered solid is washed and dried to obtain the original powder of ZSM-48 molecular sieve.

[0078] The XRD diffraction pattern of the sample prepared in this embodiment is as follows: Figure 1 As shown, Figure 1 The results showed that it was ZSM-48 molecular sieve.

[0079] Comparative Example 1

[0080] This comparative example provides a method for synthesizing ZSM-48 molecular sieve, specifically including the following steps:

[0081] According to the molar ratio Al2O3:OH- The feed is prepared by mixing SiO2:R:H2O with a ratio of 0.01:1:1:0.2:1050, with sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the template agent (R).

[0082] Step 1: First, add sodium hydroxide, aluminum sulfate, and hexamethylamine bromide to deionized water and stir until a solution is formed. Keep the solution stirred, and then slowly add silica sol to the solution to form gel A.

[0083] Step 2: Transfer gel A to a reaction vessel with a polytetrafluoroethylene liner and statically crystallize at 160°C for 72 hours. After crystallization, the product is separated into solid and liquid phases and filtered. The filtered solid is washed and dried to obtain the raw powder of ZSM-48 molecular sieve.

[0084] The XRD diffraction pattern of the sample prepared in this comparative example is as follows: Figure 2 As shown, Figure 2 The results show that it is a ZSM-48 molecular sieve, but the intensity of the characteristic peaks of ZSM-48 molecular sieve in the figure is weak, indicating low crystallinity.

[0085] Comparative Example 2

[0086] This comparative example provides a method for synthesizing ZSM-48 molecular sieve, specifically including the following steps:

[0087] According to the molar ratio Al2O3:OH - The feed is prepared by mixing SiO2:R:H2O with a ratio of 0.01:1:1:0.1:1050, with sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the template agent (R).

[0088] Step 1: First, add sodium hydroxide, aluminum sulfate, and hexamethylamine bromide to deionized water and stir until a solution is formed. Keep the solution stirred, and then slowly add silica sol to the solution to form gel A.

[0089] Step 2: Transfer gel A to a reaction vessel with a polytetrafluoroethylene liner and statically crystallize it at 160°C for 96 hours. After crystallization, the product is separated into solid and liquid phases and filtered. The filtered solid is washed and dried to obtain the raw powder of ZSM-48 molecular sieve.

[0090] The XRD diffraction pattern of the sample prepared in this comparative example is as follows: Figure 2 As shown, Figure 2 The results showed that it was a ZSM-48 molecular sieve, but there were many impurity peaks in the figure, indicating that the crystallinity of the sample was low.

[0091] Comparative Example 3

[0092] This comparative example provides a method for synthesizing molecular sieves, specifically including the following steps:

[0093] According to the molar ratio Al2O3:OH - The feed was prepared using a ratio of SiO2:R:H2O = 0.075:3.6:30:0.6:1050, with sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the template agent (R).

[0094] Step 1: First, add sodium hydroxide, aluminum sulfate, and hexamethylamine bromide to deionized water and stir until a solution is formed. Keep the solution stirred, and then slowly add silica sol to the solution to form gel A.

[0095] Step 2: Transfer gel A to a reaction vessel with a polytetrafluoroethylene liner and statically crystallize at 160°C for 72 hours. After crystallization, the product is separated into solid and liquid phases and filtered. The filtered solid is washed and dried to obtain the raw powder of ZSM-48 molecular sieve.

[0096] The XRD diffraction pattern of the sample prepared in this comparative example is as follows: Figure 1 As shown, Figure 1 The results showed that ZSM-48 molecular sieves could not be successfully prepared without the addition of nanocrystals and at the same crystallization time of 16 h.

[0097] Comparative Example 4

[0098] This comparative example provides a method for solid-phase seed-assisted synthesis of ZSM-48 molecular sieves, specifically including the following steps:

[0099] According to the molar ratio Al2O3:OH - The feed was prepared using a ratio of SiO2:R2:H2O = 0.075:3.6:30:0.9:1050, with sodium hydroxide as the alkali source, silica sol (40% purity) as the silicon source, and hexamethylamine bromide as the template agent (R); calcined pure-phase ZSM-48 molecular sieve was used as the solid seed crystal.

[0100] Step 1: First, add sodium hydroxide, aluminum sulfate, and hexamethylamine bromide to deionized water and stir until homogeneous to form a solution. Keep the solution stirred, then add solid seed crystals to it. Finally, slowly add silica sol to the solution to form gel A. The amount of solid seed crystals added is 5 wt%, based on the mass of the added silicon source being 100%.

[0101] Step 2: Transfer gel A to a reaction vessel with a polytetrafluoroethylene liner and statically crystallize it at 160°C for 50 hours. After crystallization, the product is separated into solid and liquid phases and filtered. The filtered solid is washed and dried to obtain the raw powder of ZSM-48 molecular sieve.

[0102] The XRD diffraction pattern of the sample prepared in this comparative example is as follows: Figure 2 As shown, Figure 2 The results showed that it was a ZSM-48 molecular sieve, and the sample had low crystallinity.

[0103] The SEM image of the sample prepared in this comparative example is shown below. Figure 4 As shown, Figure 4 The results showed that its morphology was an aggregated spindle-shaped structure, and it did not form a highly dispersed state.

[0104] The crystallization time, template agent dosage, relative crystallinity, and morphological characteristics of the samples prepared in Examples 1-7 and Comparative Examples 1-4 were statistically analyzed, and the results are shown in Table 1.

[0105] Table 1. Summary of Experimental Data for Examples and Comparative Examples

[0106] experiment Hydrothermal crystallization time Template dose / Si Relative crystallinity Morphological characteristics Example 1 16h 0.02 89.2％ Highly dispersed spindle morphology Example 2 16h 0.02 90.5％ Highly dispersed spindle morphology Example 3 16h 0.02 95.4％ Highly dispersed spindle morphology Example 4 16h 0.02 93.2％ Highly dispersed spindle morphology Example 5 16h 0.02 90.6％ Highly dispersed spindle morphology Example 6 16h 0.02 89.6％ Highly dispersed spindle morphology Example 7 16h 0.02 89.2％ Highly dispersed spindle morphology Comparative Example 1 72h 0.2 88.3％ Accumulated spindle morphology Comparative Example 2 96h 0.1 78.2％ Accumulated spindle morphology Comparative Example 3 16h 0.02 0％ - Comparative Example 4 50h 0.03 85.4％ Accumulated spindle morphology

[0107] The results in Table 1 show that the nanocrystal-induced synthesis method successfully synthesized ZSM-48 molecular sieves with high relative crystallinity and high dispersion under conditions of shorter hydrothermal crystallization time (16 h) and lower template agent dosage (template agent / Si = 0.02). In contrast, the conventional synthesis method significantly increases the amount of template agent and the hydrothermal crystallization time, requiring more than 50 hours to obtain ZSM-48 molecular sieves, and also results in lower relative crystallinity and higher template agent dosage. Furthermore, the molecular sieves prepared using the conventional synthesis method exhibited a stacking phenomenon in their morphology, resulting in uneven particle size. Therefore, the method of this invention not only improves the synthesis efficiency of molecular sieves but also reduces the synthesis cost.

[0108] The catalysts were prepared using ZSM-48 molecular sieve powder from Examples 4, 2, and 4 as raw materials, and their catalytic performance in the hydroisomerization reaction of n-dodecane was investigated accordingly, as follows:

[0109] (1) The ZSM-48 molecular sieve powders obtained in Example 4, Comparative Example 2, and Comparative Example 4 were used to prepare catalysts according to the following steps:

[0110] 1. Preparation of the carrier: ZSM-48 molecular sieve raw powder was calcined at 550℃ for 5 hours to obtain ZSM-48 molecular sieve. ZSM-48 molecular sieve was mixed with boehmite for 30 minutes, wherein ZSM-48 molecular sieve accounted for 75 wt% of the mixture. Then, 1 wt% nitric acid and deionized water were added to the mixture and mixed for 30 minutes. The mixture was then extruded and calcined at 550℃ for 5 hours in air atmosphere to obtain the carrier. The amount of nitric acid added was 45 wt% based on the mass of ZSM-48 molecular sieve as 100%.

[0111] 2. Determination of the saturated water absorption rate of the carrier: Weigh 2g of the calcined carrier, denoted as X0, and immerse it in a beaker containing deionized water. The deionized water will completely cover the carrier. During this process, bubbles will be generated. Gently shake the beaker until the bubbles no longer occur, then transfer the carrier to filter paper. Use the filter paper to absorb the water on its surface and weigh the carrier after water absorption, denoted as X. Calculate the saturated water absorption rate (g / g) of the carrier according to the formula for the saturated water absorption rate of the carrier: (X-X0) / X0.

[0112] 3. Loading active metal: H2PtCl6·6H2O is dissolved in deionized water to obtain a platinum salt impregnation solution; the support is impregnated in the platinum salt impregnation solution (vacuum equal volume impregnation method is adopted according to the saturated water absorption rate of the support), and a wet catalyst strip is obtained after impregnation. The wet catalyst strip is calcined at 550℃ for 5h to obtain the catalyst.

[0113] (2) The catalysts prepared by the above method were evaluated using n-dodecane as a model compound. Under the process conditions of 320℃, hydrogen partial pressure of 2MPa, and hydrogen / alkane ratio of 500 (volume ratio), the product distribution was measured as shown in Table 2. The total isomer yield = (single-branched isomer selectivity + multi-branched isomer selectivity) × conversion rate.

[0114] Table 2. Catalyst Evaluation Results

[0115] project Example 4 Comparative Example 2 Comparative Example 4 Conversion rate, % 93.0 76.0 82.5 Single-branched isomer selectivity, % 53.3 57.6 60.5 Multi-branched isomer selectivity, % 36.6 15.4 23.5 Total yield of isomers, % 83.6 55.5 69.3

[0116] As can be seen from the results in Table 2, compared with the ZSM-48 molecular sieves prepared by conventional hydrothermal synthesis (Comparative Example 2) and solid-phase seed-assisted synthesis (Comparative Example 4), the catalyst prepared by using the ZSM-48 molecular sieve in Example 4 as raw material under the same process conditions can achieve higher conversion rate, multi-branched isomer selectivity and total isomer yield.

Claims

1. A rapid synthesis method for ZSM-48 molecular sieve raw powder, wherein, This rapid synthesis method includes: (1) A first silicon source, a first inorganic base source, a first template agent, and water are uniformly mixed to obtain a first gel; the first gel is dynamically crystallized to obtain nanocrystals after crystallization; wherein, the molar ratio of the raw materials of the first gel is: OH - / SiO2=(0.01-0.5):1, R1 / SiO2=(0.01-0.6):1, H2O / SiO2=(10-60):1, the first silicon source is calculated as SiO2, and the first inorganic alkali source is calculated as OH. - R1 represents the number of moles of the first template agent; (2) The second silicon source, aluminum source, second inorganic alkali source, second template agent, and water are uniformly mixed to obtain a second gel; wherein the molar ratio of the raw materials of the second gel is: SiO2 / Al2O3=(40-500):1, OH- / SiO2=(0.01-0.5):1, R2 / SiO2=(0.005-0.08):1, H2O / SiO2=(5-60):1, the second silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the second inorganic alkali source is calculated as OH-. - R2 represents the number of moles of the second template agent; the first template agent and the second template agent are the same; (3) Add nanocrystals to the second gel to form a third gel, perform static crystallization on the third gel, and filter, wash and dry the product to obtain ZSM-48 molecular sieve powder. The amount of nanocrystals added is 5wt%-90wt%, with the mass of the second silicon source being 100%.

2. The rapid synthesis method according to claim 1, wherein, The static crystallization temperature is 150-180℃, and the static crystallization time is 12-72 hours.

3. The rapid synthesis method according to claim 1, wherein, The temperature for dynamic crystallization is 160-175℃, and the time for dynamic crystallization is 10-60 hours. The dynamic crystallization process is carried out in a rotary oven or a crystallization reactor. The rotation speed in the rotary oven is 5-60 r / min, and the rotation speed in the crystallization reactor is 50-200 r / min.

4. The rapid synthesis method according to claim 1, wherein, With the second silicon source accounting for 100% of the mass, the amount of nanocrystals added is 20wt%-80wt%.

5. The rapid synthesis method according to claim 1, wherein, The first silicon source includes one or more of silica sol, fumed silica, and tetraethyl orthosilicate; And / or, the second silicon source includes one or more of silica sol, fumed silica, and tetraethyl orthosilicate.

6. The rapid synthesis method according to claim 1, wherein, The aluminum source includes one or a combination of two or more of sodium aluminate, aluminum sulfate, aluminum acetate, and aluminum isopropoxide.

7. The rapid synthesis method according to claim 1, wherein, The first inorganic base source includes one or more of sodium hydroxide, potassium hydroxide, basic sodium carbonate, and sodium bicarbonate; And / or, the second inorganic base source includes one or more of sodium hydroxide, potassium hydroxide, basic sodium carbonate, and sodium bicarbonate.

8. The rapid synthesis method according to claim 1, wherein, The first template agent includes one or more of allyltrimethylammonium chloride, 1,6-hexanediamine, hexamethylamine bromide, tetramethylammonium hydroxide, pentamethyldiammonium bromide, and crown ether template agents; And / or, the second template agent comprises one or more of allyltrimethylammonium chloride, 1,6-hexanediamine, hexamethylamine bromide, tetramethylammonium hydroxide, pentamethyldiammonium bromide, and crown ether template agents.

9. A ZSM-48 molecular sieve raw powder, which is prepared by the rapid synthesis method according to any one of claims 1-8.

10. The ZSM-48 molecular sieve raw powder according to claim 9, wherein, The relative crystallinity of the ZSM-48 molecular sieve raw powder is above 89%.

11. A catalyst for the hydroisomerization reaction of n-dodecane, wherein, The catalyst is prepared using the ZSM-48 molecular sieve powder as described in claim 9 or 10 as the raw material.

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