A core-shell type composite molecular sieve, a preparation method and application thereof

Abstract

The application provides a core-shell type composite molecular sieve and a preparation method and application thereof, and comprises the following steps: (1) mixing a silicon source, an aluminum source, a template agent, 5A molecular sieve and water to obtain a gel mixture, and then performing aging; the template agent contains hexamethonium hydroxide, urea and urease; (2) performing hydrothermal crystallization on the material obtained in the step (1) after aging, and performing washing, drying and calcination to obtain the final 5A@ZSM-48 core-shell type composite molecular sieve. When the catalyst prepared by using the composite molecular sieve prepared by the method is applied to an isomerization dewaxing reaction, the selectivity of a far-end single branched chain isomer can be improved, and then the quality of lubricating oil base oil can be significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials technology, and relates to a core-shell composite molecular sieve, its preparation method and application, specifically to a 5A@ZSM-48 core-shell composite molecular sieve, its preparation method and application. Background Technology

[0002] With increasingly stringent environmental regulations and the rapid development of the automotive industry, the requirements for the quality of lubricating oil base oils are becoming more stringent. Besides requiring high pour points, lubricating oil base oils also need to have good viscosity indexes. Isomerization dewaxing technology is a major technical means for producing high-quality lubricating oil base oils. This technology can isomerize long-chain n-alkanes with high pour points in feedstock oils to generate branched isoalkanes, thereby lowering their pour points. However, isoalkanes have low viscosity indexes, and the higher the degree of isomerization, the lower the viscosity index. Therefore, there is an urgent need to develop new isomerization dewaxing technologies to solve these problems.

[0003] One of the core technologies of isomerization dewaxing is the isomerization catalyst. Currently, bifunctional isomerization catalysts with both a metallic active component and an acidic component are commonly used to achieve the hydrodehydrogenation and framework isomerization steps in the isomerization reaction, respectively. The acidic component employs a molecular sieve with suitable pore structure and acidic properties. The molecular sieves used are mainly those with one-dimensional straight channels, such as the AEL-type, MTT-type, TON-type, and *MRE-type molecular sieves disclosed in US patents US6294081B1, US11220435B1, US9677016B2, US8475648B2, and US10640389B2. However, when a single-channel molecular sieve is used as the acidic component of the catalyst, it has certain limitations in terms of molecular adsorption and diffusion. This can lead to adverse phenomena such as insufficient contact between the reactants and active centers during the isomerization reaction, excessive isomerization of the transition intermediate, and difficulty in product desorption leading to side reactions, resulting in a low yield of the target product. Therefore, the development of multi-level porous composite molecular sieves suitable for heterogeneous dewaxing reactions has gradually become a hot topic.

[0004] CN112934258A discloses a composite molecular sieve, its preparation method, a hydroisomerization catalyst, and a method for hydroisomerization of Fischer-Tropsch synthetic oil. The composite molecular sieve has a core-shell structure, comprising a core and a shell covering the core. The core contains a modified ZSM-48 molecular sieve, and the shell contains an MCM-41 molecular sieve. Based on the total weight of the composite molecular sieve, the shell content is 0.1–50% by weight, and the core content is 50–99.9% by weight. The hydroisomerization catalyst prepared from the composite molecular sieve of this invention, when used in the hydroisomerization reaction of Fischer-Tropsch synthetic oil, exhibits better isomer selectivity and can produce high-quality, high-yield lubricating oil base oils.

[0005] CN105032478A discloses a catalyst for isomerization dewaxing of middle distillate oil in FT synthesis and its dedicated core-shell structure composite molecular sieve. The composite molecular sieve uses a microporous ZSM-22 molecular sieve as the core and a mesoporous MCM-41 molecular sieve as the shell, with the relative ratio of the two adjustable. The preparation method is as follows: first, ZSM-22 molecular sieve is prepared; then, alkali and an organic template agent are added to a mixed system containing ZSM-22 molecular sieve for pre-crystallization; finally, the pH is adjusted to 6.5-13.5, followed by crystallization treatment to obtain the final product.

[0006] In the existing technology, when isomerization catalysts with composite molecular sieves as supports are used in isomerization dewaxing processes, the catalyst performance, especially the selectivity of the target product, needs to be further improved, and the quality of lubricating oil base oil needs to be improved. Summary of the Invention

[0007] During their research, the inventors discovered that improving the selectivity of distal monobranched isomers ("distal monobranched isomers" refers to isomers with a single branch located at the 3rd carbon or higher position in the carbon chain), especially the selectivity of isomers with a single branch located at the 4th or 5th carbon position or higher, can reduce the pour point of lubricating oil base oil while minimizing viscosity index loss, thereby effectively improving the quality of lubricating oil base oil.

[0008] Based on the above research results, this invention provides a core-shell composite molecular sieve, its preparation method and application. When the catalyst prepared by the composite molecular sieve obtained by the preparation method is applied to the isomerization dewaxing reaction, it can improve the selectivity of distal single-branched isomers, thereby significantly improving the quality of lubricating oil base oil.

[0009] The first aspect of this invention provides a method for preparing a core-shell composite molecular sieve, comprising the following steps:

[0010] (1) A gel mixture is obtained by mixing silicon source, aluminum source, template agent, 5A molecular sieve and water, and then aged; the template agent contains hexamethylammonium hydroxide, urea and urease;

[0011] (2) The material obtained from aging in step (1) is subjected to hydrothermal crystallization, and then washed, dried and calcined to obtain the final 5A@ZSM-48 core-shell composite molecular sieve.

[0012] In the preparation method of the core-shell composite molecular sieve of the present invention, the silicon source in step (1) is one or more of silica sol, fumed silica, and tetraethyl orthosilicate, preferably silica sol.

[0013] In the preparation method of the core-shell composite molecular sieve of the present invention, the aluminum source in step (1) is one or more of aluminum hydroxide, boehmite, aluminum isopropoxide, aluminum sulfate, and aluminum chloride, preferably boehmite.

[0014] In the preparation method of the core-shell composite molecular sieve of the present invention, the calcium content of the 5A molecular sieve in step (1) is 10wt%~18wt%, and the pore volume is 0.20cm. 3 / g~0.43cm 3 / g.

[0015] In the preparation method of the core-shell composite molecular sieve of the present invention, the urease in step (1) is a nickel-containing oligopeptidase that can catalyze the hydrolysis of urea to generate ammonia.

[0016] In the preparation method of the core-shell composite molecular sieve of the present invention, the molar ratio of silicon source (calculated as SiO2), aluminum source (calculated as Al2O3), water, hexamethylammonium hydroxide and urea in step (1) is 1:(20~600):(10~60):(0.02~0.3):(0.005~0.5), preferably 1:(50~200):(10~60):(0.02~0.3):(0.005~0.5); the mass ratio of the amount of 5A molecular sieve added, the amount of urease added and the amount of silicon source (calculated as SiO2) added is (0.02~1):(0.00015~1.8):1, preferably (0.025~0.333):(0.0015~0.18):1.

[0017] In the preparation method of the core-shell composite molecular sieve of the present invention, the aging temperature in step (1) is 30℃~70℃ and the aging time is 0.3h~12h, preferably 2h~6h.

[0018] In the preparation method of the core-shell composite molecular sieve of the present invention, the hydrothermal crystallization treatment in step (2) can be static crystallization or dynamic crystallization, preferably dynamic crystallization; the hydrothermal crystallization treatment temperature is 150℃~200℃, and the crystallization time is 10h~200h, preferably 20h~100h.

[0019] In the preparation method of the core-shell composite molecular sieve of the present invention, the drying conditions in step (2) are as follows: the drying temperature is 60℃~150℃, preferably 80℃~120℃; the drying time is 2h~24h, preferably 4h~12h.

[0020] In the preparation method of the core-shell composite molecular sieve of the present invention, the calcination conditions in step (2) are as follows: the calcination temperature is 400℃~650℃, preferably 450℃~600℃; the calcination time is 2h~20h, preferably 4h~8h.

[0021] The second aspect of the present invention provides a core-shell composite molecular sieve obtained by the above preparation method.

[0022] In the core-shell composite molecular sieve of the present invention, the molecular sieve has 5A molecular sieve as core and ZSM-48 molecular sieve as shell, and the mass ratio of core to shell is 1:(1~50), preferably 1:(3~40).

[0023] In the core-shell composite molecular sieve of this invention, the molecular sieve has a specific surface area of ​​170 m². 2 / g~600m 2 / g, pore volume 0.15cm 3 / g~0.45cm 3 / g.

[0024] A third aspect of the present invention provides an isomerization catalyst containing the above-described core-shell composite molecular sieve.

[0025] In the isomerization catalyst of the present invention, the isomerization catalyst further contains an active metal component, which is selected from Group VIII noble metals Pt and / or Pd, preferably Pt.

[0026] In the isomerization catalyst of this invention, the isomerization catalyst can be prepared using existing catalyst preparation methods in the art. Typically, a catalyst support is first prepared, and then the active metal component is introduced through impregnation. Specifically, the catalyst support can be obtained by mixing the aforementioned core-shell composite molecular sieve, alumina, binder, and water, followed by molding.

[0027] The fourth aspect of the present invention provides the application of the above-mentioned isomerization catalyst in the isomerization dewaxing process.

[0028] In the application of this invention, the operating conditions are as follows: the reaction temperature is generally 220℃~400℃, the reaction pressure is generally 1.0MPa~20MPa, and the volume hourly space velocity is generally 0.5h. -1 ~4.0h -1 The hydrogen-to-oil volume ratio is generally 500:1 to 1400:1.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) In the core-shell composite molecular sieve preparation method provided by this invention, 5A molecular sieve is used as the core, and then a mixture of hexamethylammonium hydroxide, urea, and urease is used as a template agent to directly synthesize hydrogen-form ZSM-48 molecular sieve in situ, which is then coated on the surface of 5A molecular sieve. The 5A molecular sieve contains Ca... 2+An electric field is generated between the 5A molecular sieve and the negatively charged molecular sieve framework. This induced polarization results in high adsorption selectivity for olefins, intermediates of isomerization reactions, allowing them to more easily enter the pores of the ZSM-48 shell molecular sieve. According to the pore-key reaction mechanism, the olefin intermediate undergoes isomerization at the pore opening. Since the olefin intermediate penetrates deep into the ZSM-48 shell molecular sieve pores, the isomerization reaction at the pore opening is located away from the carbon chain ends, thus facilitating the formation of distal branched isomers. Furthermore, the abundant mesoporous structure of the ZSM-48 shell molecular sieve further promotes the diffusion of product molecules, preventing secondary isomerization reactions and maximizing the retention of distal monobranched isomers, thereby improving the quality of lubricating oil base oils.

[0031] (2) In the core-shell composite molecular sieve preparation method provided by the present invention, hydrogen-type ZSM-48 molecular sieve is directly synthesized in situ and coated on the surface of 5A molecular sieve to obtain a composite molecular sieve. The ammonium exchange process can be omitted, avoiding the presence of Ca in the 5A molecular sieve. 2+ The exchanged material affects the adsorption selectivity of 5A molecular sieve for olefins, intermediate products of isomerization reactions, thus avoiding impact on the catalytic performance of core-shell composite molecular sieves. Attached Figure Description

[0032] Figure 1 This is the XRD pattern of the core-shell composite molecular sieve prepared in Example 2 of this invention.

[0033] Figure 2 The results are SEM characterization results of the core-shell composite molecular sieve prepared in Example 2 of this invention.

[0034] Figure 3 The results are TEM characterization results of the core-shell composite molecular sieve prepared in Example 2 of this invention. Implementation

[0035] The following embodiments further illustrate the function and effects of the method of the present invention, but these embodiments do not constitute a limitation on the method of the present invention. The endpoints and any values ​​of the disclosed ranges are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range 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. Unless otherwise specified, all contents in the following embodiments are weight percentages.

[0036] In this invention, the crystal structure of the sample was characterized using a D / max-2500 fully automatic rotating target X-ray diffractometer, the specific surface area and pore volume of the sample were characterized using an ASAP 2460 microscope, the structural morphology of the sample was characterized using a Zeiss Supra 55 scanning electron microscope, and the structural morphology of the sample was characterized using a FEI TECNAI20 transmission electron microscope.

[0037] In the embodiments and comparative examples of this invention, the urease used was purchased from Sigma-Aldrich, CAS No.: 9002-13-5.

[0038] Example 1

[0039] 0.72 g urea, 56.7 g hexamethylammonium hydroxide solution (25% by mass), 120 g silica sol (30% by mass), 1.22 g boehmite, 143.4 g water, 0.27 g urease, and 1.89 g 5A molecular sieve were mixed evenly and then placed in a crystallization vessel. After aging at 60 °C for 2 h, the temperature was raised to 190 °C for hydrothermal crystallization for 20 h. After crystallization, the crystallized product was washed, dried at 110 °C for 4 h, and then calcined at 500 °C for 5 h to obtain molecular sieve composite ZA-1 with a specific surface area of ​​215 m². 2 / g, pore volume is 0.26mL / g, and the mass ratio of 5A molecular sieve to ZSM-48 molecular sieve is 1:19.

[0040] 140g of the molecular sieve composite ZA-1 (dry basis, the same below) prepared above was thoroughly mixed with 50g of alumina (dry basis). 2 mL of concentrated nitric acid (65% by mass) and an appropriate amount of water were added, and the mixture was thoroughly kneaded and then extruded into strips. Noble metal Pt was then impregnated using a saturated impregnation method, with a Pt loading of 0.39 wt% of the support mass. After drying at 100℃ for 4 h and calcining at 500℃ for 3 h, the catalyst C1 of this invention was obtained, with a specific surface area of ​​197 m². 2 / g, pore volume is 0.31mL / g.

[0041] Example 2

[0042] 0.18 g urea, 170.2 g hexamethylammonium hydroxide solution (25% by mass), 120 g silica sol (30% by mass), 0.49 g boehmite, 252.7 g water, 0.23 g urease, and 5.86 g 5A molecular sieve were mixed evenly and then placed in a crystallization vessel. After aging at 40°C for 3 hours, the temperature was raised to 185°C for hydrothermal crystallization for 24 hours. After crystallization, the crystallized product was washed, dried at 110°C for 4 hours, and then calcined at 520°C for 3 hours to obtain molecular sieve composite ZA-2 with a specific surface area of ​​275 m².2 / g, pore volume is 0.28mL / g, and the mass ratio of 5A molecular sieve to ZSM-48 molecular sieve is 1:6.

[0043] The catalyst was prepared using the molecular sieve composite ZA-2, following the same preparation method as in Example 1. The Pt loading was 0.35 wt% of the support mass, and the catalyst was designated C2 with a specific surface area of ​​256 m². 2 / g, pore volume is 0.33mL / g.

[0044] Example 3

[0045] 5.41 g urea, 85.1 g hexamethylammonium hydroxide solution (25% by mass), 120 g silica sol (30% by mass), 0.73 g boehmite, 122.2 g water, 1.03 g urease, and 3.13 g 5A molecular sieve were mixed evenly and then placed in a crystallization vessel. After aging at 50°C for 2.5 h, the temperature was raised to 180°C for hydrothermal crystallization for 30 h. After crystallization, the crystallized product was washed, dried at 100°C for 4 h, and then calcined at 550°C for 3 h to obtain the molecular sieve composite ZA-3 with a specific surface area of ​​234 m². 2 / g, pore volume is 0.29mL / g, and the mass ratio of 5A molecular sieve to ZSM-48 molecular sieve is 1:12.

[0046] The catalyst was prepared using the molecular sieve composite ZA-3, and the preparation method was the same as in Example 1. The Pt loading was 0.40 wt% of the support mass, the catalyst was designated C3, and its specific surface area was 215 m². 2 / g, pore volume is 0.34mL / g.

[0047] Example 4

[0048] 18.02 g urea, 11.3 g hexamethylammonium hydroxide solution (25% by mass), 120 g silica sol (30% by mass), 0.47 g aluminum hydroxide, 555.5 g water, 6.48 g urease, and 12 g 5A molecular sieve were mixed evenly and then placed in a crystallization vessel. After aging at 70°C for 2 hours, the temperature was raised to 170°C for hydrothermal crystallization for 48 hours. After crystallization, the crystallized product was washed, dried at 100°C for 4 hours, and then calcined at 520°C for 4 hours to obtain the molecular sieve composite ZA-4 with a specific surface area of ​​353 m². 2 / g, pore volume is 0.34mL / g, and the mass ratio of 5A molecular sieve to ZSM-48 molecular sieve is 1:3.

[0049] The catalyst was prepared using the molecular sieve complex ZA-4, following the same preparation method as in Example 1. The Pt loading was 0.48 wt% of the support mass, and the catalyst was designated C4 with a specific surface area of ​​323 m². 2 / g, pore volume is 0.41mL / g.

[0050] Example 5

[0051] 2.88 g urea, 45.4 g hexamethylammonium hydroxide solution (25% by mass), 36.05 g silica, 0.61 g boehmite, 74.0 g water, 0.16 g urease, and 0.90 g 5A molecular sieve were mixed evenly and then placed in a crystallization vessel. After aging at 30°C for 4 hours, the temperature was raised to 175°C for hydrothermal crystallization for 36 hours. After crystallization, the crystallized product was washed, dried at 100°C for 4 hours, and then calcined at 550°C for 3 hours to obtain the molecular sieve composite ZA-5 with a specific surface area of ​​337 m². 2 / g, pore volume is 0.33mL / g, and the mass ratio of 5A molecular sieve to ZSM-48 molecular sieve is 1:40.

[0052] The catalyst was prepared using the molecular sieve composite ZA-5, following the same preparation method as in Example 1. The Pt loading was 0.27 wt% of the support mass, and the catalyst was designated C5 with a specific surface area of ​​303 m². 2 / g, pore volume is 0.39mL / g.

[0053] Comparative Example 1

[0054] Take 21.9g of ZSM-48 molecular sieve (silicon-to-aluminum ratio 100), 8.1g of 5A molecular sieve, and 10g of boehmite (dry basis) and mix thoroughly. Add 0.4mL of concentrated nitric acid (65% by mass) and an appropriate amount of water, knead thoroughly, and then extrude into strips. The catalyst preparation method is the same as in Example 1, with Pt loading of 0.23wt% of the support, catalyst number D1, and a specific surface area of ​​296m². 2 / g, pore volume is 0.35mL / g.

[0055] Comparative Example 2

[0056] The preparation process of catalyst D2 in this invention is the same as in Example 4, except that urease is not added during the molecular sieve synthesis process, the mass ratio of 5A molecular sieve to ZSM-48 molecular sieve is 1:2.8, and the specific surface area of ​​catalyst D2 is 336 m². 2 / g, pore volume is 0.40mL / g.

[0057] Example 6

[0058] The catalytic performance was evaluated using n-dodecane as a model compound. The catalyst was pre-reduced before feeding to convert the noble metals on the catalyst to a reduced state. The reduction conditions were as follows: reduction was carried out in the presence of hydrogen at 400℃ and 2 MPa for 5 hours. The evaluation reaction conditions were as follows: reaction pressure 3 MPa and volume hourly space velocity 1 h⁻¹. -1 The hydrogen-to-oil volume ratio was 800:1, and the evaluation results are shown in Table 1.

[0059] Table 1 Evaluation Results

[0060]

[0061] Example 7

[0062] The catalyst's reactivity was further evaluated using cracked tail oil (properties shown in Table 2) as feedstock. The catalyst was pre-reduced before feeding to convert the noble metals on it into a reduced state. The reduction conditions were as follows: reduction was carried out in the presence of hydrogen at 400℃ and 10MPa for 6 hours. The evaluation reaction conditions were as follows: reaction pressure 14MPa, volume hourly space velocity 0.8h⁻¹. -1 The hydrogen-to-oil volume ratio was 800:1, the reaction temperature was 325℃, and the evaluation results are shown in Table 3.

[0063] Table 2 Properties of Raw Materials

[0064]

[0065] Table 3 Catalyst performance evaluation results

[0066]

[0067] The catalyst evaluation results show that improving the selectivity of distal monobranched isomers can reduce the pour point of lubricating oil base oil while minimizing viscosity index loss, thereby effectively improving the quality of lubricating oil base oil.

Claims

1. A method for preparing a core-shell type composite molecular sieve, characterized by: The method comprises the following steps: (1) mixing a silicon source, an aluminum source, a template agent, 5A molecular sieve and water to obtain a gel mixture, and then aging; the template agent contains hexamethonium hydroxide, urea and urease; (2) hydrothermally crystallizing the material obtained in step (1) after aging, and then washing, drying and calcining to obtain the final 5A@ZSM-48 core-shell composite molecular sieve; In step (1), the molar ratio of the silicon source (calculated as SiO2), the aluminum source (calculated as Al2O3), water, hexamethonium hydroxide and urea is 1:(20-600):(10-60):(0.02-0.3):(0.005-0.5); the mass ratio of the added amount of 5A molecular sieve, the added amount of urease and the added amount of the silicon source (calculated as SiO2) is (0.02-1):(0.00015-1.8):

1.

2. The method of claim 1, wherein: In step (1), the silicon source is one or more of silica sol, white carbon black and tetraethyl orthosilicate.

3. The method of claim 2, wherein: In step (1), the silicon source is silica sol.

4. The method of claim 1, wherein: In step (1), the aluminum source is one or more of aluminum hydroxide, pseudo-boehmite, aluminum isopropoxide, aluminum sulfate and aluminum chloride.

5. The method of claim 4, wherein: In step (1), the aluminum source is pseudo-boehmite.

6. The method of claim 1, wherein: The calcium content of the 5A molecular sieve in step (1) is 10 wt% to 18 wt%, and the pore volume is 0.20 cm 3 / g to 0.43 cm 3 / g.

7. The method of claim 1, wherein: In step (1), the molar ratio of the silicon source (calculated as SiO2), the aluminum source (calculated as Al2O3), water, hexamethonium hydroxide and urea is 1:(50-200):(10-60):(0.02-0.3):(0.005-0.5); the mass ratio of the added amount of 5A molecular sieve, the added amount of urease and the added amount of the silicon source (calculated as SiO2) is (0.025-0.333):(0.0015-0.18):

1.

8. The method of claim 1, wherein: In step (1), the aging temperature is 30-70°C, and the aging time is 0.3-12h.

9. The method of claim 8, wherein: In step (1), the aging time is 2-6h.

10. The method of claim 1, wherein: In step (2), the hydrothermal crystallization treatment adopts static crystallization or dynamic crystallization; the hydrothermal crystallization treatment temperature is 150-200°C, and the crystallization time is 10-200h.

11. The method of claim 10, wherein: In step (2), the hydrothermal crystallization treatment adopts dynamic crystallization.

12. The method of claim 10, wherein: In step (2), the crystallization time is 20-100h.

13. The method of claim 1, wherein: In step (2), the drying treatment conditions are as follows: the drying temperature is 60-150°C; and the drying time is 2-24h.

14. The method of claim 13, wherein: In step (2), the drying treatment conditions are as follows: the drying temperature is 80-120°C; and the drying time is 4-12h.

15. The method of claim 1, wherein: In step (2), the calcination treatment conditions are as follows: the calcination temperature is 400-650°C; and the calcination time is 2-20h.

16. The method of claim 15, wherein: In step (2), the calcination treatment conditions are as follows: the calcination temperature is 450-600°C; and the calcination time is 4-8h.

17. The core-shell composite molecular sieve prepared by the method in any one of claims 1-16.

18. The core-shell composite molecular sieve of claim 17, wherein: The molecular sieve has 5A molecular sieve as the core and ZSM-48 molecular sieve as the shell, and the core-shell mass ratio is 1:(1-50).

19. The core-shell composite molecular sieve of claim 18, wherein: The core-shell mass ratio is 1:(3-40).

20. The core-shell composite molecular sieve of claim 10, wherein: The specific surface area of the molecular sieve is 170 m 2 / g~600 m 2 / g, and the pore volume is 0.15 cm 3 / g~0.45 cm 3 / g.

21. An isomerization catalyst containing the core-shell composite molecular sieve in any one of claims 17-20.

22. Use of the isomerization catalyst in claim 21 in an isodewaxing process.

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