Composite molecular sieve, preparation method thereof, hydroisomerization catalyst and Fischer-Tropsch synthetic oil hydroisomerization method

Abstract

The invention relates to the technical field of molecular sieves, and discloses a composite molecular sieve, a preparation method thereof, a hydroisomerization catalyst and a Fischer-Tropsch synthetic oil hydroisomerization method. The method comprises the following steps: (1) sequentially carrying out first crystallization, first drying and first roasting on a first crystallization stock solution to obtain a ZSM-48 molecular sieve core; (2) carrying out second mixing on a second silicon source, a second aluminum source, tetrapropylammonium hydroxide, the ZSM-5 nanocrystalline seed crystal and a second solvent to obtain a precursor solution; (3) carrying out third mixing on a precursor solution and the ZSM-48 molecular sieve core to obtain a second crystallization stock solution, and sequentially carrying out second crystallization, second drying and second roasting on the second crystallization stock solution to form a ZSM-5 molecular sieve shell on the surface of the ZSM-48 molecular sieve core; and (4) carrying out ion exchange on the material obtained in the step (3) and an ammonium salt solution. The composite molecular sieve has high activity and selectivity, and is beneficial to production of high-quality lubricant base oil.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve technology, specifically to a composite molecular sieve and its preparation method, a hydroisomerization catalyst, and a method for hydroisomerization of Fischer-Tropsch synthetic oil. Background Technology

[0002] Molecular sieve materials, due to their high acidity and high specific surface area, are excellent acid catalysts and are widely used in hydroisomerization reactions. Among them, one-dimensional ten-membered ring pore structure molecular sieves such as ZSM-22, ZSM-23, and ZSM-48 are often used as isomerization catalyst supports in isomerization reactions due to their special pore structure and acidity.

[0003] The long, one-dimensional straight pore size of ZSM-48 molecular sieves results in high diffusion resistance for long-chain alkanes. While the pore openings exhibit high selectivity for isomers, high-carbon-number isomers have difficulty passing through, hindering product diffusion. Currently, most modifications to ZSM-48 molecular sieves focus on the synthesis of low-silica, hierarchical ZSM-48 molecular sieves. Although basic modifications to molecular sieves can achieve better catalytic performance, modifications to the pore structure and modulation of acid properties still have limitations. When applied to the production of base oils from high-carbon-number Fischer-Tropsch waxes, selectivity and product yield remain low.

[0004] Patent application CN104418341A discloses a ZSM-48 / Silicalite-1 composite molecular sieve and its preparation method. The composite molecular sieve uses a low silica-to-alumina ratio ZSM-48 molecular sieve as the core phase and Silicalite-1 as the shell phase. The total specific surface area of ​​this composite molecular sieve is 330–400 m². 2 With a total pore volume of 0.22–0.28 ml / g and an average pore size of 2.5–3.5 nm, this composite molecular sieve exhibits excellent shape selectivity and resistance to coking, and has potential industrial application value in alkylation and isomerization reactions.

[0005] Patent application CN106669814A discloses a method for preparing ZSM-48 / Y composite molecular sieves. The method involves high-temperature calcination of ZSM-48 molecular sieves, followed by contacting unsaturated olefins with the calcined ZSM-48 molecular sieves and conducting a calcination and coking reaction in an inert gas atmosphere. The ZSM-48 molecular sieves are then subjected to surface dealuminization treatment to obtain modified ZSM-48 molecular sieves. The modified ZSM-48 molecular sieve powder, aluminum source, sodium hydroxide, and water are stirred to obtain a reaction mixture gel system, which is aged under sealed conditions, then crystallized, and finally cooled, washed, dried, and calcined to obtain the ZSM-48 / Y composite molecular sieve. This method produces a composite zeolite molecular sieve that organically combines the isomerism of ZSM-48 molecular sieves with the cracking properties of Y-type molecular sieves, and can be applied to the production of high-quality lubricating oil base oils in hydrocracking petroleum refining processes.

[0006] Patent application CN112934258A discloses an MCM-41 / ZSM-48 composite molecular sieve, whose core contains a modified ZSM-48 molecular sieve and whose outer shell contains an MCM-41 molecular sieve. This allows for the control of the interface and spatial position between the microporous and mesoporous molecular sieves, providing spatial structure and strong and weak acid centers for the isomerization of Fischer-Tropsch synthesis oils. The composite zeolite molecular sieve prepared by this method organically combines the isomerization properties of ZSM-48 molecular sieves with the cracking properties of Y-type molecular sieves, and can be applied to the production of high-quality lubricating oil base oils in the hydrocracking petroleum refining process.

[0007] Therefore, there is an urgent need to develop a novel molecular sieve material to improve the activity and selectivity of catalysts. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of low matching degree between the acid site distribution and acid amount of existing molecular sieves in the hydroisomerization of Fischer-Tropsch wax feedstock, and to provide a composite molecular sieve, its preparation method, a hydroisomerization catalyst, and a method for hydroisomerization of Fischer-Tropsch synthetic oil.

[0009] To achieve the above objectives, the first aspect of the present invention provides a method for preparing composite molecular sieves, the method comprising the following steps: (1) A first silicon source, a first aluminum source, tetraethylammonium hydroxide, 1,6-hexanediamine, sodium hydroxide and a first solvent are mixed to obtain a first crystallization stock solution. The first crystallization stock solution is subjected to a first crystallization, a first drying and a first calcination to obtain a ZSM-48 molecular sieve core. The molar ratio of SiO2 to Al2O3 in the ZSM-48 molecular sieve core is 60~150:1. The shape of the ZSM-48 molecular sieve core is ellipsoidal and the major axis is 500-2000 nm. (2) The second silicon source, the second aluminum source, tetrapropylammonium hydroxide, ZSM-5 nanocrystals and the second solvent are mixed in a second process to obtain a precursor solution; (3) The precursor solution and the ZSM-48 molecular sieve core are mixed in a third process to obtain a second crystallization stock solution; the second crystallization stock solution is subjected to a second crystallization, a second drying and a second calcination in sequence to form a ZSM-5 molecular sieve shell on the surface of the ZSM-48 molecular sieve core, wherein the molar ratio of SiO2 to Al2O3 in the ZSM-5 molecular sieve shell is ≥200; (4) The material obtained in step (3) is subjected to ion exchange with an ammonium salt solution to obtain a composite molecular sieve; The first crystallization process includes: performing static crystallization and dynamic crystallization sequentially; The second crystallization process includes: performing a first-stage crystallization at 20~50℃, then performing a second-stage crystallization at 55~80℃, and then performing a third-stage crystallization by heating to 160~180℃ at a heating rate of ≤2℃ / min.

[0010] Preferably, in step (1), the molar ratio of the first silicon source to tetraethylammonium hydroxide, calculated as SiO2, is 1:0.1-0.3; and / or, The molar ratio of tetraethylammonium hydroxide to 1,6-hexanediamine is 2-5:1; and / or, The molar ratio of the first silicon source to the first solvent, calculated as SiO2, is 1:20-40; The molar ratio of the first silicon source to sodium hydroxide, calculated as SiO2, is 1:0.1-0.25.

[0011] Preferably, the static crystallization conditions include: a temperature of 110-130℃ and a time of 20-28 hours; and / or, The conditions for dynamic crystallization include: a temperature of 150-170℃, a time of 44-52 hours, and a rotation speed of 10-50 rpm; and / or, The conditions for the first roasting include: a temperature of 500-600℃ and a time of 5-7 hours.

[0012] Preferably, in step (2), the molar ratio of the second silicon source to tetrapropylammonium hydroxide, calculated as SiO2, is 1:0.05-0.4; and / or, The molar ratio of the second silicon source to the second solvent, calculated as SiO2, is 1:20-40; and / or, The weight ratio of the second silicon source to ZSM-5 nanocrystals, calculated as SiO2, is 1:0.03-0.1; and / or, The ZSM-5 nanocrystals have a particle size of 10~50 nm.

[0013] Preferably, the crystallization time in the first stage is 12-24 hours; and / or, The second stage of crystallization takes 12-24 hours; and / or, The third stage of crystallization takes 24-48 hours; and / or, The conditions for the second roasting include: a temperature of 500-600℃ and a time of 5-7 hours.

[0014] A second aspect of the present invention provides a composite molecular sieve prepared according to the preparation method described above.

[0015] Preferably, the composite molecular sieve includes a ZSM-48 molecular sieve core and a ZSM-5 molecular sieve shell covering the surface of the ZSM-48 molecular sieve core; The ZSM-48 molecular sieve core is ellipsoidal in shape with a major axis of 500-2000 nm, and the molar ratio of SiO2 to Al2O3 in the ZSM-48 molecular sieve core is 60-150:1. The molar ratio of SiO2 to Al2O3 in the outer shell of the ZSM-5 molecular sieve is ≥200, the thickness of the outer shell of the ZSM-5 molecular sieve is 50-150 nm, and the outer shell of the ZSM-5 molecular sieve contains mesopores.

[0016] Preferably, the aspect ratio of the ZSM-48 molecular sieve core is 1~2:1; and / or, The pore size of the mesopore is 2~7 nm.

[0017] A third aspect of the present invention provides a hydroisomerization catalyst, the catalyst comprising a support and an active component, wherein the support comprises the composite molecular sieve described above; Preferably, the active component is a noble metal; Preferably, the noble metal is platinum and / or palladium.

[0018] A fourth aspect of the present invention provides a method for hydroisomerization of Fischer-Tropsch synthetic oil, comprising: subjecting the hydroisomerization catalyst described above and the Fischer-Tropsch synthetic oil to a hydroisomerization reaction under hydroisomerization reaction conditions.

[0019] The composite molecular sieve prepared using the method described in this invention has a core-shell structure. This core-shell molecular sieve can combine the acidic characteristics of two zeolites with different topologies, regulate the diffusion path of reactants and products within the pores, and improve the isomerization performance of the bifunctional catalyst. For ZSM-5 and ZSM-48 molecular sieves with different acid strengths, the core-shell structure of ZSM-48@ZSM-5 molecular sieve provided by this invention can change the acid distribution of the parent zeolite. The special one-dimensional / three-dimensional composite pore structure also improves the selectivity of isoalkanes while promoting product diffusion and reducing coking formation.

[0020] Furthermore, the composite molecular sieve prepared using the method described in this invention can be applied to the hydroisomerization reaction of Fischer-Tropsch synthetic oils. The composite molecular sieve can effectively balance the hydrogenation and isomerization reactions. Through the chemical bonding between the ellipsoidal ZSM-48 core (isomerization function) and the thin-layered ZSM-5 shell (pre-cracking / shape-selective protection), it overcomes diffusion limitations and acidity imbalance problems, thereby improving the activity and selectivity of the catalyst and facilitating the production of high-quality lubricating oil base oils. Detailed Implementation

[0021] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions provided in the various embodiments of this invention can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0024] ZSM-5 molecular sieves are widely used in the isomerization and aromatization of olefins. However, their high acid strength and acid content can lead to excessive cracking reactions, affecting the liquid yield of the product. For isomerization reactions, ZSM-5 molecular sieves often require metal doping or acid treatment for dealumination to adjust the acid content and strength. ZSM-48 molecular sieves, with their mild acidity, can minimize cracking reactions, thus improving liquid yield. In hydroisomerization reactions, their one-dimensional through-holes also exhibit high selectivity for isoalkanes. However, the diffusion limitation of ZSM-48 molecular sieves, leading to coking and pore blockage, is one of the problems that urgently needs to be solved in one-dimensional ten-membered ring zeolites.

[0025] The first aspect of this invention provides a method for preparing composite molecular sieves, the method comprising the following steps: (1) A first silicon source, a first aluminum source, tetraethylammonium hydroxide, 1,6-hexanediamine, sodium hydroxide and a first solvent are mixed in a first process to obtain a first crystallization stock solution. The first crystallization stock solution is subjected to a first crystallization, a first drying and a first calcination in sequence to obtain a ZSM-48 molecular sieve core. The molar ratio of SiO2 to Al2O3 in the ZSM-48 molecular sieve core is 60~150:1. The shape of the ZSM-48 molecular sieve core is ellipsoidal and the major axis is 500-2000 nm. (2) The second silicon source, the second aluminum source, tetrapropylammonium hydroxide, ZSM-5 nanocrystals and the second solvent are mixed in a second process to obtain a precursor solution; (3) The precursor solution and the ZSM-48 molecular sieve core are mixed in a third process to obtain a second crystallization stock solution; the second crystallization stock solution is subjected to a second crystallization, a second drying and a second calcination in sequence to form a ZSM-5 molecular sieve shell on the surface of the ZSM-48 molecular sieve core, wherein the molar ratio of SiO2 to Al2O3 in the ZSM-5 molecular sieve shell is ≥200; (4) The material obtained in step (3) is subjected to ion exchange with an ammonium salt solution to obtain a composite molecular sieve; The first crystallization process includes: performing static crystallization and dynamic crystallization sequentially; The second crystallization process includes: performing a first-stage crystallization at 20~50℃, then performing a second-stage crystallization at 55~80℃, and then performing a third-stage crystallization by heating to 160~180℃ at a heating rate of ≤2℃ / min.

[0026] Traditional physical mixed catalysts (such as ZSM-48 / ZSM-5) suffer from acidic site conflicts and weak interfacial synergistic effects. This invention creatively proposes a method for preparing a composite molecular sieve. The composite molecular sieve prepared by this method has a core-shell structure, with an ellipsoidal ZSM-48 molecular sieve as the core and a thin-layer high-silica ZSM-5 molecular sieve as the shell. This solves the one-dimensional pore diffusion limitation and provides both pre-pyrolysis and shape-selective protection functions.

[0027] Specifically, in the preparation method provided by this invention, a ZSM-48 molecular sieve core is first prepared, and then epitaxial growth is induced by pre-adsorption of ZSM-5 nanocrystal seeds at low temperature. Combined with low-temperature-high-temperature segmented crystallization to control the shell thickness, the lattice mismatch problem between ZSM-48 (MRE structure) and ZSM-5 (MFI structure) is solved, and the core-shell interface chemical bonding is achieved. Furthermore, through seed-guided technology, the independent nucleation of ZSM-5 is suppressed, and the shell coverage is increased to >90%.

[0028] As an example, the molar ratio of SiO2 to Al2O3 in the ZSM-48 molecular sieve core can be 60:1, 70:1, 80:1, 90:1, 100:1, 110:1, 120:1, 130:1, 140:1 or 150:1.

[0029] As an example, the long axis of the ZSM-48 molecular sieve core can be 500nm, 600nm, 800nm, 1000nm, 1200nm, 1500nm, 1800nm ​​or 2000nm.

[0030] In some preferred embodiments, the specific process of obtaining the first crystallization stock solution in step (1) includes: adding sodium hydroxide, tetraethylammonium hydroxide, a first aluminum source, a first silicon source, and 1,6-hexanediamine sequentially to water and mixing them to obtain the first crystallization stock solution. By adding the materials in the above order, first adding tetraethylammonium hydroxide to construct the ZSM-48 framework, and then adding 1,6-hexanediamine to regulate the morphology, combined with dynamic crystallization conditions, high-purity, uniformly morphologically shaped ellipsoidal ZSM-48 molecular sieves can be obtained, which can further improve the application performance of composite molecular sieves in hydroisomerization.

[0031] In some preferred embodiments, in step (1), the molar ratio of the first silicon source to tetraethylammonium hydroxide, calculated as SiO2, is 1:0.1-0.3. As an example, the molar ratio of the first silicon source to tetraethylammonium hydroxide, calculated as SiO2, can be 1:0.1, 1:0.15, 1:0.2, 1:0.25, or 1:0.3.

[0032] In some preferred embodiments, the molar ratio of tetraethylammonium hydroxide to 1,6-hexanediamine is 2-5:1. As an example, the molar ratio of tetraethylammonium hydroxide to 1,6-hexanediamine can be 2:1, 3:1, 4:1, or 5:1.

[0033] In some preferred embodiments, the molar ratio of the first silicon source to the first solvent, calculated as SiO2, is 1:20-40. As examples, it can be 1:20, 1:25, 1:30, 1:35, or 1:40.

[0034] In some specific embodiments, the first solvent may be water.

[0035] In some specific embodiments, the first silicon source can be a silicon source commonly used in the art for preparing molecular sieves, such as tetraethyl orthosilicate (TEOS).

[0036] In some specific embodiments, the first aluminum source can be a common aluminum salt in the art, such as aluminum sulfate.

[0037] In some preferred embodiments, the molar ratio of the first silicon source to sodium hydroxide, calculated as SiO2, is 1:0.1-0.25. Examples include 1:0.1, 1:0.15, 1:0.2, or 1:0.25.

[0038] In the method described in this invention, in step (1), the ZSM-48 molecular sieve core prepared by a combination of static and dynamic crystallization is ellipsoidal in shape. Static crystallization promotes nucleus formation, while dynamic crystallization optimizes the ellipsoidal morphology. Understandably, the dynamic crystallization is achieved by stirring during the crystallization process.

[0039] In some preferred embodiments, the static crystallization conditions include a temperature of 110-130°C and a time of 20-28 hours. For example, the static crystallization temperature can be 110°C, 115°C, 120°C, 125°C, or 130°C, and the static crystallization time can be 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, 25 hours, 26 hours, 27 hours, or 28 hours.

[0040] In some preferred embodiments, the conditions for dynamic crystallization include: a temperature of 150-170°C, a time of 44-52 hours, and a rotation speed of 10-50 rpm. As examples, the dynamic crystallization temperature can be 150°C, 155°C, 160°C, 165°C, or 170°C, and the dynamic crystallization time can be 44 hours, 45 hours, 46 hours, 47 hours, 48 ​​hours, 49 hours, 50 hours, 51 hours, or 52 hours.

[0041] In some specific embodiments, step (1) further includes washing and filtering the material obtained from the first crystallization between the first crystallization and the first drying. The washing and filtering can be performed using conventional methods in the art, such as centrifugal washing with water and slow yielding until the washing liquid is neutral.

[0042] In some specific embodiments, the first drying can be carried out under conventional conditions in the art, for example, the drying temperature can be 100-130°C and the drying time can be 5-8 hours.

[0043] In some preferred embodiments, the conditions for the first roasting include a temperature of 500-600°C and a time of 5-7 hours. For example, the temperature of the first roasting can be 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, or 600°C, and the time of the first roasting can be 5 hours, 6 hours, or 7 hours.

[0044] In some preferred embodiments, in step (2), the molar ratio of the second silicon source to tetrapropylammonium hydroxide, calculated as SiO2, is 1:0.05-0.4. As an example, the molar ratio of the second silicon source to tetrapropylammonium hydroxide, calculated as SiO2, can be 1:0.05, 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35, or 1:0.4.

[0045] In some preferred embodiments, the molar ratio of the second silicon source to the second solvent, based on SiO2, is 1:20-40. Examples include 1:20, 1:25, 1:30, 1:35, or 1:40.

[0046] In some preferred embodiments, the weight ratio of the second silicon source to ZSM-5 nanocrystals, calculated as SiO2, is 1:0.03-0.1. As examples, it can be 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, or 1:0.1.

[0047] In some preferred embodiments, the ZSM-5 nanocrystal seed particles have a particle size of 10~50 nm.

[0048] In some specific implementations, there are no special requirements for the conditions of the second mixing, and it can be carried out according to the conditions conventional in the art.

[0049] In some preferred embodiments, the molar ratio of SiO2 to Al2O3 in the ZSM-5 molecular sieve shell can be 200-500:1. Examples include 200:1, 210:1, 220:1, 230:1, 240:1, 250:1, 260:1, 270:1, 280:1, 290:1, 300:1, 350:1, or 400:1.

[0050] In some specific embodiments, the second silicon source can be a silicon source commonly used in the art for preparing molecular sieves, such as tetraethyl orthosilicate (TEOS).

[0051] In some specific embodiments, the second aluminum source can be a common aluminum salt in the art, such as aluminum sulfate.

[0052] In the method described in this invention, in step (3), the precursor solution and the ZSM-48 molecular sieve core are mixed, and guided by ZSM-5 nanocrystal seeds, the mixture undergoes low-temperature adsorption (20~50℃), step crystallization (50~80℃), and high-temperature crystallization (160~180℃) after being heated at a low speed to 160~180℃. Based on this, a thin layer of ZSM-5 molecular sieve shell can be formed on the surface of the ZSM-48 molecular sieve core.

[0053] In some specific implementations, there are no special requirements for the conditions of the third mixing, and it can be carried out according to the conventional conditions in the art.

[0054] As an example, the crystallization temperature in the first stage can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, or 50°C.

[0055] In some preferred embodiments, the crystallization time of the first stage is 12-24 hours. As examples, it can be 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours.

[0056] As an example, the temperature for the second stage of crystallization can be 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C.

[0057] In some preferred embodiments, the crystallization time in the second stage is 12-24 hours. As examples, it can be 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours.

[0058] As an example, the temperature for the third stage of crystallization can be 160°C, 165°C, 170°C, 175°C, or 180°C.

[0059] In some specific implementations, the heating rate is 0.5-2℃ / min. Specifically, it can be 0.5℃ / min, 1℃ / min, 1.5℃ / min, or 2℃ / min.

[0060] In some specific implementations, the crystallization time in the third stage is 24-48 hours. As examples, it can be 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, 38 hours, 40 hours, 42 hours, 44 hours, 46 hours, or 48 hours.

[0061] In some specific embodiments, step (3) further includes washing and filtering the material obtained from the second crystallization between the second crystallization and the second drying. The washing and filtering can be performed using conventional methods in the art, such as centrifuging with water until the washing liquid is neutral.

[0062] In some specific embodiments, the second drying can be carried out under conventional conditions in the art, for example, the drying temperature can be 100-130°C and the drying time can be 5-8 hours.

[0063] In some preferred embodiments, the conditions for the second calcination include a temperature of 500-600°C and a time of 5-7 hours. For example, the temperature of the second calcination can be 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, or 600°C, and the time of the second calcination can be 5 hours, 6 hours, or 7 hours.

[0064] In some preferred embodiments, in step (4), two ion exchanges are performed using an ammonium salt solution.

[0065] In some specific embodiments, the specific process of step (4) includes: performing a first ion exchange between the material obtained in step (3) and an ammonium salt solution to obtain a composite molecular sieve semi-finished product; and then performing a second ion exchange between the composite molecular sieve and the ammonium salt solution to obtain a composite molecular sieve.

[0066] In some specific embodiments, the concentration of the ammonium salt solution can be 0.5-2 mol / L.

[0067] In some specific implementations, the ion exchange conditions include a temperature of 70-90°C and a time of 1-3 hours. When two ion exchanges are performed, the conditions for each exchange can independently meet the above ranges.

[0068] A third aspect of the present invention provides a composite molecular sieve prepared according to the preparation method described above.

[0069] In some preferred embodiments, the composite molecular sieve includes a ZSM-48 molecular sieve core and a ZSM-5 molecular sieve shell covering the surface of the ZSM-48 molecular sieve core; The ZSM-48 molecular sieve core is ellipsoidal in shape with a major axis of 500-2000 nm, and the molar ratio of SiO2 to Al2O3 in the ZSM-48 molecular sieve core is 60-150:1. The molar ratio of SiO2 to Al2O3 in the outer shell of the ZSM-5 molecular sieve is ≥200, the thickness of the outer shell of the ZSM-5 molecular sieve is 50-150 nm, and the outer shell of the ZSM-5 molecular sieve contains mesopores.

[0070] In some preferred embodiments, the aspect ratio of the ZSM-48 molecular sieve core is 1 to 2:1.

[0071] In some preferred embodiments, the pore size of the mesopore is 2~7 nm.

[0072] A fourth aspect of the present invention provides a hydroisomerization catalyst comprising a support and an active component, wherein the support comprises the composite molecular sieve described above.

[0073] In some preferred embodiments, the carrier further includes aluminum oxide.

[0074] In some preferred embodiments, the active component is a noble metal; In some preferred embodiments, the noble metal is platinum and / or palladium.

[0075] In some preferred embodiments, the content of noble metals in the hydroisomer catalyst is 0.2-1 wt%.

[0076] This invention also provides a method for preparing a hydroisomerization catalyst, the method comprising: The composite molecular sieve, binder, nitric acid, and water are mixed evenly, then shaped by an extruder, and subsequently subjected to a third drying and a third calcination treatment to obtain the catalyst support. The catalyst support is impregnated in a noble metal salt solution, and then subjected to a fourth drying and a fourth calcination to obtain a hydroisomerization catalyst.

[0077] In some specific embodiments, no special requirements are placed on the conditions for the extrusion, third drying, and third calcination; they can be carried out according to conventional conditions in the art. There are no special requirements on the amounts of nitric acid, binder powder, and water; they can be used according to conventional amounts in the art.

[0078] In some specific embodiments, the binder can be SB powder, which, after a third calcination treatment, exists mostly as γ-Al2O3 in the prepared hydroisomer catalyst.

[0079] In the hydroisomerization catalyst provided by this invention, noble metals are mainly supported on the binder on the outer surface of the catalyst, providing active sites for dehydrogenation / hydrogenation to achieve the dehydrogenation of n-alkanes and the hydrogenation of olefins; the composite molecular sieve mainly provides acidic sites, responsible for isomerization and cracking reactions. During the reaction, the feedstock first undergoes mild cracking in the outer shell of the ZSM-5 molecular sieve, which has shape-selective cracking properties, generating intermediates with small branches; these small branched molecules then enter the interior of the molecular sieve, where the core ZSM-48 molecular sieve further dominates, resulting in a deep transformation dominated by isomerization.

[0080] The fifth aspect of the present invention provides a method for hydroisomerization of Fischer-Tropsch synthetic oil, comprising: subjecting the hydroisomerization catalyst described above and the Fischer-Tropsch synthetic oil to a hydroisomerization reaction under hydroisomerization reaction conditions.

[0081] To make the objectives and advantages of the present invention clearer, the composite molecular sieve and its effects of the present invention are further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and should not be used to limit the present invention. Unless otherwise specified, the following embodiments do not include components other than unavoidable impurities. Unless otherwise specified, the drugs and instruments used in the embodiments are conventional choices in the art. Experimental methods in the embodiments that do not specify specific conditions are implemented according to conventional conditions, such as those described in literature, books, or methods recommended by the manufacturer.

[0082] Example 1 (1) Under stirring, sodium hydroxide, tetraethylammonium hydroxide, aluminum sulfate, TEOS and 1,6-hexanediamine were added sequentially to deionized water to obtain the first crystallization stock solution; then the first crystallization stock solution was transferred to a reaction vessel and statically crystallized at 120℃ for 24h; then dynamically crystallized at 160℃ for 48h (rotation speed 30 rpm); after crystallization, the solution was centrifuged and washed and slowly filtered until the filtrate was neutral, then dried at 120℃ for 6h, then heated to 550℃ at a heating rate of 1℃ / min and calcined at 550℃ for 6h to obtain the ZSM-48 molecular sieve core; wherein, the molar ratio of TEOS, tetraethylammonium hydroxide, 1,6-hexanediamine and deionized water based on SiO2 was 1:0.16:0.05:25, the molar ratio of SiO2 to Al2O3 in the ZSM-48 molecular sieve core was 120:1; the molar ratio of TEOS and sodium hydroxide based on SiO2 was 1:0.2; (2) Dissolve aluminum sulfate in deionized water, then add TEOS and stir for 1 h, then add tetrapropylammonium hydroxide and ZSM-5 nanocrystals in sequence and stir for 3 h to obtain a precursor solution; wherein, the molar ratio of TEOS, tetrapropylammonium hydroxide and deionized water based on SiO2 is 1:0.2:30, and the weight ratio of TEOS to ZSM-5 nanocrystals based on SiO2 is 1:0.03; (3) After stirring the ZSM-48 molecular sieve core in the precursor solution for 1 hour, it was placed in a reaction vessel and crystallized at 50°C for 24 hours and 80°C for 24 hours. Then, the temperature was increased to 180°C at a rate of 1°C / min and held for 36 hours. After centrifugation and slow filtration, the filtrate was washed until it was neutral. Then, it was dried at 120°C for 6 hours. Then, the temperature was increased to 550°C at a rate of 1°C / min and calcined at 550°C for 6 hours to form a ZSM-5 molecular sieve shell on the surface of the ZSM-48 molecular sieve core. The molar ratio of SiO2 to Al2O3 in the ZSM-5 molecular sieve shell was 200. (4) The material obtained in step (3) is subjected to ion exchange with 1 mol / L ammonium chloride solution at 80°C for 2 h. The above process is repeated twice to obtain a composite molecular sieve. This composite molecular sieve has a core-shell structure. The outer shell of the ZSM-5 molecular sieve is 50 nm thick and contains mesopores with a pore size of about 6 nm. The core of the ZSM-48 molecular sieve is ellipsoidal in shape with a major axis of 800 nm and an aspect ratio of 1.5.

[0083] Example 2 (1) Under stirring, sodium hydroxide, tetraethylammonium hydroxide, aluminum sulfate, TEOS and 1,6-hexanediamine were added sequentially to deionized water to obtain the first crystallization stock solution; then the first crystallization stock solution was transferred to a reaction vessel and statically crystallized at 120℃ for 24h; then dynamically crystallized at 160℃ for 48h (rotation speed 30 rpm); after crystallization, the solution was washed by centrifugation and slow filtration until the filtrate was neutral, then dried at 120℃ for 6h, then heated to 550℃ at a heating rate of 1℃ / min and calcined at 550℃ for 6h to obtain the ZSM-48 molecular sieve core, wherein the molar ratio of TEOS, tetraethylammonium hydroxide, 1,6-hexanediamine and water based on SiO2 was 1:0.12:0.04:30, the molar ratio of SiO2 to Al2O3 in the ZSM-48 molecular sieve core was 60:1; the molar ratio of TEOS and sodium hydroxide based on SiO2 was 1:0.1; (2) Dissolve aluminum sulfate in deionized water, then add TEOS and stir for 1 h, then add tetrapropylammonium hydroxide and ZSM-5 nanocrystal seeds in sequence and stir for 3 h to obtain a precursor solution; wherein, the molar ratio of TEOS, tetrapropylammonium hydroxide and deionized water based on SiO2 is 1:0.25:28, and the weight ratio of TEOS to ZSM-5 nanocrystal seeds based on SiO2 is 1:0.02; (3) After stirring the ZSM-48 molecular sieve core in the precursor solution for 1 hour, it was placed in a reaction vessel and crystallized at 50°C for 24 hours and 80°C for 24 hours. Then, the temperature was increased to 180°C at a rate of 1°C / min and held for 36 hours. After centrifugation and slow filtration, the filtrate was washed until it was neutral. Then, it was dried at 120°C for 6 hours. Then, the temperature was increased to 550°C at a rate of 1°C / min and calcined at 550°C for 6 hours to form a ZSM-5 molecular sieve shell on the surface of the ZSM-48 molecular sieve core. The molar ratio of SiO2 to Al2O3 in the ZSM-5 molecular sieve shell was 250. (4) The material obtained in step (3) is subjected to ion exchange with 1 mol / L ammonium chloride solution at 80°C for 2 h. The above process is repeated twice to obtain a composite molecular sieve. This composite molecular sieve has a core-shell structure. The outer shell of the ZSM-5 molecular sieve is 150 nm thick and contains mesopores with a pore size of about 5 nm. The core of the ZSM-48 molecular sieve is ellipsoidal in shape with a major axis of 2000 nm and an aspect ratio of 2.

[0084] Example 3 (1) Under stirring, sodium hydroxide, tetraethylammonium hydroxide, aluminum sulfate, TEOS and 1,6-hexanediamine were added sequentially to deionized water to obtain the first crystallization stock solution; then the first crystallization stock solution was transferred to a reaction vessel and statically crystallized at 120℃ for 24h; then dynamically crystallized at 160℃ for 48h (rotation speed 30 rpm); after crystallization, the solution was centrifuged and washed and slowly filtered until the filtrate was neutral, then dried at 120℃ for 6h, then heated to 550℃ at a heating rate of 1℃ / min and calcined at 550℃ for 6h to obtain the ZSM-48 molecular sieve core; wherein, the molar ratio of TEOS, tetraethylammonium hydroxide, 1,6-hexanediamine and water based on SiO2 is 1:0.15:0.06:35, the molar ratio of SiO2 to Al2O3 in the ZSM-48 molecular sieve core is 150:1; the molar ratio of TEOS and sodium hydroxide based on SiO2 is 1:0.14; (2) Dissolve aluminum sulfate in deionized water, then add TEOS and stir for 1 h, then add tetrapropylammonium hydroxide and ZSM-5 nanocrystals in sequence and stir for 3 h to obtain a precursor solution; wherein, the molar ratio of TEOS, tetrapropylammonium hydroxide and deionized water based on SiO2 is 1:0.3:20, and the weight ratio of TEOS to ZSM-5 nanocrystals based on SiO2 is 1:0.03; (3) After stirring the ZSM-48 molecular sieve core in the precursor solution for 1 hour, it was placed in a reaction vessel and crystallized at 50°C for 24 hours and 80°C for 24 hours. Then, the temperature was increased to 180°C at a rate of 1°C / min and held for 36 hours. After centrifugation and slow filtration, the filtrate was washed until it was neutral. Then, it was dried at 120°C for 6 hours. Then, the temperature was increased to 550°C at a rate of 1°C / min and calcined at 550°C for 6 hours to form a ZSM-5 molecular sieve shell on the surface of the ZSM-48 molecular sieve core. The molar ratio of SiO2 to Al2O3 in the ZSM-5 molecular sieve shell was 300. (4) The material obtained in step (3) is subjected to ion exchange with 1 mol / L ammonium chloride solution at 80°C for 2 h. The above process is repeated twice to obtain a composite molecular sieve. This composite molecular sieve has a core-shell structure. The outer shell of the ZSM-5 molecular sieve is 100 nm thick and contains mesopores with a pore size of about 3 nm. The core of the ZSM-48 molecular sieve is ellipsoidal in shape with a major axis of 1200 nm and an aspect ratio of 1.

[0085] Comparative Example 1 It is basically the same as Example 1, except that steps (2) and (3) are not performed.

[0086] Comparative Example 2 The method is basically the same as in Example 1, except that the molar ratio of SiO2 to Al2O3 in the ZSM-48 molecular sieve core is adjusted to 200.

[0087] Comparative Example 3 The process is basically the same as in Example 1, except that in step (1), the molar ratio of TEOS to sodium hydroxide (calculated as SiO2) is adjusted to 1:0.08, so that the long axis of the ZSM-48 molecular sieve core is adjusted to 3000 nm.

[0088] Test Example 1 Hydroisomerization catalysts were prepared using the products obtained in Examples 1-3 and Comparative Examples 1-3. The specific preparation process is as follows: The prepared composite molecular sieve, SB powder, nitric acid and water were mixed evenly in a ratio of 23:10:1:20, then shaped by an extruder, dried at 120℃ for 4 hours, and then calcined at 550℃ for 4 hours to obtain the catalyst support. The catalyst support was impregnated in a solution containing a Pt precursor (dichlorotetraammineplatinum), then dried at 120°C for 4 hours, and then calcined at 450°C for 4 hours to obtain the hydroisomerizing agent.

[0089] Under hydroisomerization reaction conditions, the hydroisomerization catalysts prepared according to the above method were subjected to hydroisomerization reactions with Fischer-Tropsch synthetic oils. The properties and boiling point distribution of the Fischer-Tropsch synthetic oils are shown in Table 1; the reaction conditions were: temperature 320-360℃, space velocity 0.7-1.5 h⁻¹. -1 Pressure 3-10MPa, hydrogen-to-oil ratio 600-1200. The pour point and base oil yield of the prepared product were tested, and the test results are shown in Table 2-7.

[0090] Table 1

[0091] Table 2

[0092] Table 3

[0093] Table 4

[0094] Table 5

[0095] Table 6

[0096] Table 7

[0097] As shown in Tables 2-7, compared with the comparative example, the hydroisomerization catalyst prepared by the composite molecular sieve prepared in the examples has a higher base oil yield and a lower pour point when hydroisomerized with Fischer-Tropsch synthetic oil.

[0098] It should be understood that any parts not described in detail in this specification belong to the prior art.

[0099] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a composite molecular sieve, characterized by, The method includes the following steps: (1) A first silicon source, a first aluminum source, tetraethylammonium hydroxide, 1,6-hexanediamine, sodium hydroxide and a first solvent are mixed in a first process to obtain a first crystallization stock solution. The first crystallization stock solution is subjected to a first crystallization, a first drying and a first calcination in sequence to obtain a ZSM-48 molecular sieve core. The molar ratio of SiO2 to Al2O3 in the ZSM-48 molecular sieve core is 60~150:

1. The shape of the ZSM-48 molecular sieve core is ellipsoidal and the major axis is 500-2000 nm. (2) The second silicon source, the second aluminum source, tetrapropylammonium hydroxide, ZSM-5 nanocrystals and the second solvent are mixed in a second process to obtain a precursor solution; (3) The precursor solution and the ZSM-48 molecular sieve core are mixed in a third way to obtain a second crystallization stock solution. The second crystallization stock solution is subjected to a second crystallization, a second drying and a second calcination in sequence to form a ZSM-5 molecular sieve shell on the surface of the ZSM-48 molecular sieve core. The molar ratio of SiO2 to Al2O3 in the ZSM-5 molecular sieve shell is ≥200. (4) The material obtained in step (3) is subjected to ion exchange with an ammonium salt solution to obtain a composite molecular sieve; The first crystallization process includes: performing static crystallization and dynamic crystallization sequentially; The second crystallization process includes: performing a first-stage crystallization at 20~50℃, then performing a second-stage crystallization at 55~80℃, and then performing a third-stage crystallization by heating to 160~180℃ at a heating rate of ≤2℃ / min.

2. The method according to claim 1, characterized in that, In step (1), the molar ratio of the first silicon source to tetraethylammonium hydroxide, calculated as SiO2, is 1:0.1-0.3; and / or, The molar ratio of tetraethylammonium hydroxide to 1,6-hexanediamine is 2-5:1; and / or, The molar ratio of the first silicon source to the first solvent, calculated as SiO2, is 1:20-40; and / or, The molar ratio of the first silicon source to sodium hydroxide, calculated as SiO2, is 1:0.1-0.

25.

3. The method according to claim 1 or 2, characterized in that, In step (1), the conditions for static crystallization include: a temperature of 110-130°C and a time of 20-28 hours; and / or, The conditions for dynamic crystallization include: a temperature of 150-170℃, a time of 44-52 hours, and a rotation speed of 10-50 rpm; and / or, The conditions for the first roasting include: a temperature of 500-600℃ and a time of 5-7 hours.

4. The method according to claim 1, characterized in that, In step (2), the molar ratio of the second silicon source to tetrapropylammonium hydroxide, calculated as SiO2, is 1:0.05-0.4; and / or, The molar ratio of the second silicon source to the second solvent, calculated as SiO2, is 1:20-40; and / or, The weight ratio of the second silicon source to ZSM-5 nanocrystals, calculated as SiO2, is 1:0.03-0.1; and / or, The ZSM-5 nanocrystals have a particle size of 10~50 nm.

5. The method according to claim 1 or 4, characterized in that, The first stage of crystallization takes 12-24 hours; and / or, The second stage of crystallization takes 12-24 hours; and / or, The third stage of crystallization takes 24-48 hours; and / or, The conditions for the second roasting include: a temperature of 500-600℃ and a time of 5-7 hours.

6. The composite molecular sieve prepared by the preparation method according to any one of claims 1-5.

7. The composite molecular sieve according to claim 6, characterized in that, The composite molecular sieve includes a ZSM-48 molecular sieve core and a ZSM-5 molecular sieve shell covering the surface of the ZSM-48 molecular sieve core; The ZSM-48 molecular sieve core is ellipsoidal in shape with a major axis of 500-2000 nm, and the molar ratio of SiO2 to Al2O3 in the ZSM-48 molecular sieve core is 60-150:

1. The molar ratio of SiO2 to Al2O3 in the outer shell of the ZSM-5 molecular sieve is ≥200, the thickness of the outer shell of the ZSM-5 molecular sieve is 50-150 nm, and the outer shell of the ZSM-5 molecular sieve contains mesopores.

8. The composite molecular sieve according to claim 6, characterized in that, The aspect ratio of the ZSM-48 molecular sieve core is 1~2:1; and / or, The pore size of the mesopore is 2~7 nm.

9. A hydroisomerization catalyst, characterized in that, The catalyst comprises a support and an active component, wherein the support comprises the composite molecular sieve according to any one of claims 6-8; Preferably, the active component is a noble metal; Preferably, the noble metal is platinum and / or palladium.

10. A method for hydroisomerization of Fischer-Tropsch synthetic oil, characterized in that, include: Under hydroisomerization reaction conditions, the hydroisomerization catalyst described in claim 9 and Fischer-Tropsch synthetic oil are subjected to a hydroisomerization reaction.

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