A SAPO-44 / 11 composite molecular sieve, its preparation method and application

Abstract

This invention discloses a SAPO-44 / SAPO-11 composite molecular sieve, its preparation method, and its applications, belonging to the field of molecular sieve technology. The composite material has two phases: SAPO-11 molecular sieve and SAPO-44 molecular sieve, with a morphology exhibiting a structure of interlocking growth of cubic and plate-like crystals aggregated into spherical structures. The preparation method includes adding the obtained SAPO-44 molecular sieve as a seed crystal to a gel used for synthesizing SAPO-11 molecular sieve, and preparing the SAPO-44 / SAPO-11 composite molecular sieve under hydrothermal crystallization conditions. The molecular sieve of this invention is a novel composite molecular sieve with a simple synthesis method. The performance of the composite molecular sieve can be controlled by adjusting the ratio of the two phases through adjusting the mass of the added seed crystal. The composite molecular sieve material prepared by this invention exhibits excellent performance in the n-hexane isomerization reaction.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve technology, specifically to a SAPO-44 / SAPO-11 composite molecular sieve, its preparation method, and its application. Background Technology

[0002] Molecular sieves are silicate minerals. They have regular pore sizes and contain many cavities with specific structures. These cavities are connected by channels of a certain diameter and have a fixed orientation, making them porous materials. These cavities have a preferential adsorption capacity for polar and unsaturated molecules, thus separating molecules with different degrees of polarity, saturation, molecular size, and boiling points. This "sieving" effect on molecules is why they are called molecular sieves.

[0003] SAPO molecular sieves were first invented by Union Carbide Corporation (UCC) in 1894. They are formed by replacing atoms in the AlPO molecular sieve framework with Si, resulting in primary structural units consisting of tetrahedra of Si, Al, and P atoms. SAPO-11 molecular sieve has an Al-E crystal structure, characterized by a ten-membered ring connecting four-membered and six-membered rings, with these rings interconnected and extending continuously in a certain direction. SAPO-44 has a CHA crystal structure, characterized by six-membered and four-membered rings connecting to form secondary units, which in turn connect to eight-membered rings to form a three-dimensional structure.

[0004] Hydroisomerization of n-alkanes is an important class of chemical reactions, involving two processes: carbocation formation at the acidic site, isomerization and cracking, and hydrodehydrogenation at the hydrodehydrogenation site. In industrial production, metal-molecular sieve bifunctional catalysts are often used to catalyze this reaction. The molecular sieve provides the acidic site, while the supported metal, such as Pt, provides the hydrodehydrogenation site. The activity of the acidic and hydrodehydrogenation sites often determines the catalyst's efficiency. Excessively strong acidic sites can lead to cracking side reactions, while excessively weak acidic sites result in low catalytic efficiency.

[0005] SAPO-11 molecular sieves are often used as the framework material for catalysts in the isomerization of n-alkane reactions. However, due to its limited number of strong acid sites, the proportion of single-branched products in the isomerization products is relatively high, resulting in low conversion rates. SAPO-44, on the other hand, is too acidic, leading to a high proportion of cracking products in the reaction, which limits its application in catalytic n-alkane isomerization reactions.

[0006] To date, no literature has been reported on SAPO-44 / SAPO-11 composite molecular sieves, their synthesis methods, and applications. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a SAPO-44 / SAPO-11 composite molecular sieve, its preparation method, and its applications. This composite molecular sieve is a novel composite molecular sieve with advantages such as high crystallinity, adjustable acidity and specific surface area, tight bonding between the two components, and complex pore structure. The SAPO-44 / SAPO-11 composite molecular sieve provided by this invention exhibits high conversion rate and selectivity in the isomerization of n-hexane.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] The first aspect of this invention provides a SAPO-44 / SAPO-11 composite molecular sieve, comprising two phases: SAPO-44 and SAPO-11. The crystal morphology exhibits a structure of interlocking growth of cubic and plate-like crystals aggregated into spherical structures.

[0010] In the above technical solution, the mass ratio of SAPO-44 to SAPO-11 in the SAPO-44 / SAPO-11 composite molecular sieve is (5-20):(80-95).

[0011] A second aspect of this invention provides a method for preparing a SAPO-44 / SAPO-11 composite molecular sieve, comprising the following steps:

[0012] An aluminum source, water, phosphoric acid, silicon source, diethylamine, and SAPO-44 seed crystals were mixed to obtain a synthetic gel.

[0013] The synthesized gel was subjected to hydrothermal crystallization and then calcined to obtain SAPO-44 / SAPO-11 composite molecular sieve.

[0014] The method for preparing the SAPO-44 seed crystals includes the following steps:

[0015] A seed gel is obtained by mixing silicon source, aluminum source, phosphoric acid, diethylamine and water;

[0016] The seed gel was subjected to hydrothermal crystallization and then calcined to obtain SAPO-44 seed crystals.

[0017] The molar ratio of silicon source, aluminum source, and phosphoric acid in the seed gel is (0.5–0.7):(0.9–1.1).

[0018] (1.9~2.1); the molar ratio of silicon source to diethylamine is (0.5~0.7):(1.9~2.1); the molar ratio of diethylamine to water is (1.9~2.1):(55~65).

[0019] The hydrothermal crystallization temperature is 180–190°C, and the time is 36–48 hours.

[0020] The calcination temperature is 450–650℃, and the time is 4–12 hours.

[0021] The molar ratio of silicon source, aluminum source, and phosphoric acid in the synthesized gel is (0.1–0.35):(0.8–1.2).

[0022] (1.8~2.2); The molar ratio of silicon source to diethylamine is (0.1~0.35):(1.5~1.7); The molar ratio of diethylamine to water is (1.5~1.7):(45~55);

[0023] The mass of the SAPO-44 seed crystals is 5-25% of the total mass of SiO2, Al2O3 and P2O5.

[0024] The hydrothermal crystallization temperature is 180–210°C, and the time is 30–48 hours.

[0025] The calcination temperature is 450–650℃, and the time is 4–12 hours.

[0026] In the above technical solution, the silicon source is tetraethyl orthosilicate, and the aluminum source is selected from either boehmite or aluminum isopropoxide.

[0027] The present invention provides the SAPO-44 / SAPO-11 composite molecular sieve described in the above technical solution.

[0028] This invention provides a SAPO-44 / SAPO-11 composite molecular sieve, comprising two phases: SAPO-44 and SAPO-11 molecular sieves, which are intercalated and grown together. The SAPO-44 / SAPO-11 composite molecular sieve provided by this invention has advantages such as high crystallinity, adjustable specific surface area and acidity, tight bonding between the two phases, and complex pore structure. The SAPO-44 / SAPO-11 composite molecular sieve provided by this invention exhibits high conversion and selectivity in the isomerization of n-hexane.

[0029] This invention provides a method for preparing the SAPO-44 / SAPO-11 composite molecular sieve described above. The preparation method provided by this invention is simple and can be mass-produced. Attached Figure Description

[0030] Figure 1 The powder X-ray diffraction pattern of the SAPO-44 / SAPO-11 composite molecular sieve prepared in Example 1;

[0031] Figure 2 Scanning electron microscope image of the SAPO-44 / SAPO-11 composite molecular sieve prepared in Example 1;

[0032] Figure 3Powder X-ray diffraction patterns of the SAPO-44 / SAPO-11 composite molecular sieves prepared in Examples 2-4.

[0033] Figure 4 SAPO-44 / SAPO-11 prepared for Examples 1-4 were prepared at a temperature of 340°C and a hexane mass hourly space velocity of 5.49 h⁻¹. -1 The isomerization performance of n-hexane under a reaction pressure of 5 MPa. Detailed Implementation

[0034] This invention provides a SAPO-44 / SAPO-11 molecular sieve, which has two different phases, SAPO-44 and SAPO-11, and the crystal morphology is a structure in which cubic crystals and plate-like crystals are aggregated and grown into spherical structures.

[0035]

Example 1

[0036] Synthesis of SAPO-44 / SAPO-11 composite molecular sieve

[0037] Under magnetic stirring, 14.27 g of aluminum isopropoxide was added to 36.5 ml of water and stirred for 1 h, followed by 4.823 ml of phosphoric acid and stirred for 2 h, then 4.645 ml of tetraethyl orthosilicate and stirred for 2 h, and finally 7.196 ml of diethylamine and stirred for 2 h to obtain a seed gel. The gel was transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE), and the reactor was placed in a 200°C electrically heated drying oven for hydrothermal crystallization under the pressure naturally generated in the reactor for 36 h. After the reactor cooled to room temperature, it was washed, dried, and calcined at 550°C for 5 h to obtain SAPO-44 seed crystals; the molar composition of the seed gel was as follows:

[0038] SiO2:Al2O3:P2O5:DEA:H2O=0.6:1:1:2:60.

[0039] Under magnetic stirring, 6.28 g of pseudoboehmite and 1 g of SAPO-44 seed crystals were added to 44.5 ml of water and stirred for 2 h. Phosphoric acid, tetraethyl orthosilicate, and diethylamine were added sequentially to the sol every 1.5 h, and stirred for 2 h to obtain a synthetic gel. The gel was transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE), and the reactor was placed in a 200°C electrically heated drying oven for hydrothermal crystallization under the pressure generated by the reactor itself for 36 h. After the reactor cooled to room temperature, it was washed, dried, and calcined at 550°C for 6 h to obtain a SAPO-44 / SAPO-11 composite molecular sieve; the molar composition of the synthetic gel was as follows:

[0040] SiO2:Al2O3:P2O5:DEA:H2O=0.35:1:1:1.6:50.

[0041] The SAPO-44 / SAPO-11 composite molecular sieve prepared in this embodiment has a particle size of 20-40 μm and a BET specific surface area of ​​324.2002 m². 2 / g.

[0042] Figure 1 The image shows the powder X-ray diffraction pattern of the SAPO-44 / SAPO-11 composite molecular sieve prepared in this embodiment. Figure 1 It can be seen that the SAPO-44 / SAPO-11 composite molecular sieve prepared by the present invention has characteristic diffraction peaks of two different topologies, CHA and AEL, indicating that the SAPO-44 / SAPO-11 composite molecular sieve prepared by the present invention has both CHA and AEL topologies.

[0043] Figure 2 Scanning electron microscope image of the SAPO-44 / SAPO-11 composite molecular sieve prepared for this embodiment. Figure 2 It can be seen that the morphology of the SAPO-44 / SAPO-11 composite molecular sieve prepared by the present invention is a structure in which cubic crystals and plate-like crystals are polymerized into spherical structures and grown together.

[0044]

Example 2

[0045] SAPO-44 / SAPO-11 composite molecular sieves were prepared according to the method of Example 1, except that the mass of SAPO-44 seed crystals was 0.5g.

[0046]

Example 3

[0047] SAPO-44 / SAPO-11 composite molecular sieves were prepared according to the method of Example 1, except that the mass of SAPO-44 seed crystals was 1.5g.

[0048]

Example 4

[0049] SAPO-44 / SAPO-11 composite molecular sieves were prepared according to the method of Example 1, except that the mass of SAPO-44 seed crystals was 2.0 g.

[0050] Figure 3 The powder X-ray diffraction patterns of the SAPO-44 / SAPO-11 composite molecular sieves prepared in Examples 2-4 are shown below. Figure 3 It can be seen that the SAPO-44 / SAPO-11 composite molecular sieves prepared in Examples 2 to 4 have characteristic diffraction peaks of both CHA and AEL topologies, indicating that the SAPO-44 / SAPO-11 composite molecular sieves prepared in this invention have both CHA and AEL topologies.

[0051]

Application Example 1

[0052] To further illustrate the beneficial technical effects of the composite molecular sieve catalysts prepared in each example of the present invention, the SAPO-44 / 11 composite molecular sieves prepared in each example were applied to the catalytic isomerization of n-hexane. The catalyst evaluation conditions were: 100% n-hexane as feedstock, temperature 340°C, and n-hexane mass hourly space velocity (HHSV) of 5.49 h⁻¹. -1 The reaction pressure was 2 MPa, and the results of the isomerization reaction are shown in [the table below]. Figure 4 The conversion rates of Example 1 were 76.103% and the selectivity was 63.406%; the conversion rate of Example 2 was 65.546% and the selectivity was 82.386%; the conversion rate of Example 3 was 62.502% and the selectivity was 90.293%; and the conversion rate of Example 4 was 58.292% and the selectivity was 38.612%. These data indicate that the SAPO-44 / 11 composite molecular sieve material provided by this invention exhibits high conversion rates and selectivity in the n-hexane isomerization reaction.

[0053] The examples described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of a SAPO-44 / SAPO-11 composite molecular sieve in the isomerization of n-hexane, wherein the SAPO-44 / SAPO-11 composite molecular sieve has two phases, SAPO-44 and SAPO-11, and the crystal morphology is a structure in which cubic crystals and plate crystals are aggregated into spherical structures.

2. The application of the SAPO-44 / SAPO-11 composite molecular sieve according to claim 1 in the isomerization of n-hexane, characterized in that, Based on the weight percentage of SAPO-44 / SAPO-11 composite molecular sieve, the mass ratio of SAPO-44 to SAPO-11 in the SAPO-44 / SAPO-11 composite molecular sieve used is (5~20):(80~95).

3. The application of the SAPO-44 / SAPO-11 composite molecular sieve according to claim 1 in the isomerization of n-hexane, wherein the preparation method of the SAPO-44 / SAPO-11 composite molecular sieve includes the following steps: An aluminum source, water, phosphoric acid, silicon source, diethylamine, and SAPO-44 seed crystals were mixed to obtain a synthetic gel. The resulting synthetic gel was subjected to hydrothermal crystallization and then calcined to obtain SAPO-44 / SAPO-11 composite molecular sieve.

4. The application of the SAPO-44 / SAPO-11 composite molecular sieve according to claim 3 in the isomerization of n-hexane, characterized in that, The method for preparing the SAPO-44 seed crystals includes the following steps: A seed gel is obtained by mixing silicon source, aluminum source, phosphoric acid, diethylamine and water; The seed gel was subjected to hydrothermal crystallization and then calcined to obtain SAPO-44 seed crystals.

5. The application of the SAPO-44 / SAPO-11 composite molecular sieve according to claim 3 in the isomerization of n-hexane, characterized in that, The molar ratio of silicon source, aluminum source and phosphoric acid in the synthetic gel is (0.1~0.35):(0.8~1.2):(1.8~2.2); the molar ratio of silicon source to diethylamine is (0.1~0.35):(1.5~1.7); and the molar ratio of diethylamine to water is (1.5~1.7):(45~55). The mass of the SAPO-44 seed crystals is 5-25% of the total mass of SiO2, Al2O3 and P2O5.

6. The application of the SAPO-44 / SAPO-11 composite molecular sieve according to claim 4 in the isomerization of n-hexane, characterized in that, The molar ratio of silicon source, aluminum source and phosphoric acid in the seed gel is (0.5~0.7):(0.9~1.1):(1.9~2.1); the molar ratio of silicon source to diethylamine is (0.5~0.7):(1.9~2.1); and the molar ratio of diethylamine to water is (1.9~2.1):(55~65). The hydrothermal crystallization temperature is 180~190 ℃, and the time is 36~48 h.

7. The application of the SAPO-44 / SAPO-11 composite molecular sieve according to claim 3 in the isomerization of n-hexane, characterized in that, The hydrothermal crystallization temperature is 180~210 ℃, and the time is 30~48 h.

8. The application of the SAPO-44 / SAPO-11 composite molecular sieve according to claim 3 in the isomerization of n-hexane, characterized in that, The calcination temperature is 450~650 ℃, and the time is 4~12 h.

9. The application of the SAPO-44 / SAPO-11 composite molecular sieve according to claim 4 in the isomerization of n-hexane, characterized in that, The calcination temperature is 450~650 ℃, and the time is 4~12 h.

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