Mesoporous SAPO-34 molecular sieve and preparation method thereof

Abstract

The invention discloses a mesopore-containing SAPO-34 molecular sieve and a preparation method thereof, the preparation method comprises the following steps: a) mixing a silicon source, an aluminum source, a phosphorus source, deionized water, a template agent and AEO to obtain an initial gel mixture, the AEO is organic long-chain higher fatty alcohol-polyoxyethylene ether with an R-O-(CH2CH2O) n-H structure, the aluminum source is calculated by Al2O3, and the mass ratio of AEO / Al2O3 is 0.05-1; b) putting the initial gel mixture obtained in the step a) into a synthesis kettle, sealing, and carrying out hydrothermal crystallization under self-generated pressure; and c) after complete crystallization, carrying out centrifugal separation on a solid product, washing the solid product with deionized water until the solid product is neutral, and drying and roasting the solid product to obtain the SAPO-34 molecular sieve containing the mesoporous structure. The mesopore-containing SAPO-34 molecular sieve provided by the invention has moderate mesopores, and has higher diene selectivity and longer catalytic life in an MTO (Methanol To Olefins) reaction.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieve preparation, and specifically relates to a mesoporous SAPO-34 molecular sieve and a preparation method thereof. Background Art

[0002] SAPO-34 molecular sieve is used in the fields of petroleum refining and chemical engineering because of its special pore size and regular pore structure, as well as strong proton acidity. The framework of SAPO-34 is mainly composed of silicoaluminophosphate, with an ellipsoidal CHA cage composed of double six-membered rings, eight-membered rings and four-membered rings, and a three-dimensional cross-pore structure. Its main pore diameter is 0.38nm, the pore size is relatively single, and it has excellent selectivity.

[0003] SAPO-34 microporous channels and unique cage-like structure are conducive to shape-selective catalytic reactions; however, in chain-breaking reactions based on the hydrocarbon pool mechanism, relatively small channels and regular structures are not conducive to the diffusion of reactant molecules and heat conduction, and are also not conducive to the diffusion of generated reactants from the reaction center. At present, domestic and foreign studies have been conducted on the treatment of SAPO-34 molecular sieves to prepare SAPO-34 molecular sieves containing mesopores. Relevant experimental data show that SAPO-34 molecular sieves containing mesopores are conducive to the diffusion of reactants and products, as well as heat conduction, and can improve the activity and stability of the molecular sieve.

[0004] CN105600801B relates to a method for preparing a mesoporous SAPO-34 molecular sieve. In the synthesis, in addition to adding a microporous template agent, an organic phosphine surfactant is also added as a mesoporous template agent. Therefore, the obtained SAPO-34 molecular sieve has mesopores in addition to a microporous structure, and the obtained SAPO-34 molecular sieve contains mesopores, which can be used in MTO reaction.

[0005] CN105731484A provides a method for preparing a mesoporous SAPO-34 molecular sieve, wherein an organosilicon compound containing quaternary ammonium cations is used as both a silicon source and a structure directing agent, and combined with the use of seed crystals, a SAPO-34 molecular sieve having a mesoporous composite structure is obtained. The prepared SAPO-34 molecular sieve is used as a catalyst in an MTO reaction, exhibiting excellent catalytic performance and significantly extending the catalyst life.

[0006] CN105600801A provides a method for synthesizing mesoporous SAPO-34, wherein the mesopore diameter of the molecular sieve is 2-20 nm and the mesopore volume is 0.02-0.3 cm 3In addition to the microporous template agent, an organic phosphine surfactant is also added as a mesoporous template agent during the synthesis, so the obtained SAPO-34 molecular sieve has mesopores in addition to the microporous structure.

[0007] CN108569707A provides a method for synthesizing a mesoporous SAPO-34, wherein the SAPO-34 molecular sieve is prepared by a method comprising the following steps: 1) uniformly mixing an aluminum source, a phosphorus source, a silicon source, and a template agent in water to prepare a synthetic gel; 2) introducing polyacrylamide into the synthetic gel to prepare a mixed gel; 3) subjecting the mixed gel to a hydrothermal crystallization treatment and then calcining to obtain the SAPO-34 molecular sieve. The SAPO-34 molecular sieve has a rich pore structure, and the catalytic life and low-carbon olefin selectivity in the MTO reaction are improved.

[0008] CN101121533B provides a method for synthesizing mesoporous SAPO-34, which uses amine substances mainly composed of isopropanolamine to control the mesopores to obtain a SAPO-34 molecular sieve with a mesopore volume of 0.03-0.3 cm3 / g.

[0009] CN108298550A provides a method for synthesizing mesoporous SAPO-34, which uses an amine substance mainly composed of tetrahydrofuran and organic amine to control the mesopores to obtain a SAPO-34 molecular sieve with a mesopore volume.

[0010] CN103864087A provides a method for synthesizing mesoporous SAPO-34, wherein an amine substance mainly composed of N-methyldiethanolamine is used to control the mesopores to obtain a SAPO-34 molecular sieve with a mesopore volume.

[0011] CN103864097B provides a method for synthesizing mesoporous SAPO-34, wherein an amine substance mainly composed of diglycolamine is used to control the mesopores to obtain a SAPO-34 molecular sieve with a mesopore volume.

[0012] The above patents have relatively simple means for regulating the pores of molecular sieves, a narrow size adjustment range, and little emphasis on catalytic selectivity. Summary of the invention

[0013] The object of the present invention is to provide a mesoporous SAPO-34 molecular sieve and a preparation method thereof.

[0014] To achieve the above object, the present invention provides a method for preparing a mesoporous SAPO-34 molecular sieve, comprising the following steps:

[0015] a) mixing a silicon source, an aluminum source, a phosphorus source, deionized water, a template and AEO to obtain an initial gel mixture, wherein AEO is a RO-(CH 2CH 2 O) n -H structure of organic long-chain higher fatty alcohol polyoxyethylene ether, aluminum source is Al 2 O 3 AEO / Al 2 O 3 The mass ratio is 0.05 to 1;

[0016] b) placing the initial gel mixture obtained in step a) into a synthesis kettle, sealing it, and performing hydrothermal crystallization under autogenous pressure;

[0017] c) After the crystallization is complete, the solid product is separated by centrifugation, washed with deionized water until neutral, and dried and calcined to obtain the SAPO-34 molecular sieve containing a mesoporous structure.

[0018] The method for preparing the mesoporous SAPO-34 molecular sieve described in the present invention, wherein the AEO is one or more of AEO-5, AEO-7, AEO-9, peregal O and JFC.

[0019] In the method for preparing the mesoporous SAPO-34 molecular sieve described in the present invention, the molar ratio of each substance in the initial gel mixture is:

[0020] SiO 2 / Al 2 O 3 =0.1~1.0;

[0021] P 2 O 5 / Al 2 O 3 =0.5~2.0;

[0022] Template / Al 2 O 3 =1~10;

[0023] H 2 O / Al 2 O 3 =1~100.

[0024] In the method for preparing the mesoporous SAPO-34 molecular sieve described in the present invention, the silicon source is one or a mixture of any of silica sol, active silica, orthosilicate and metakaolin.

[0025] In the method for preparing the mesoporous SAPO-34 molecular sieve described in the present invention, the aluminum source is one or a mixture of any of aluminum salts, activated alumina, alkoxy aluminum, metakaolin and pseudo-boehmite.

[0026] In the method for preparing the mesoporous SAPO-34 molecular sieve described in the present invention, the phosphorus source is one or a mixture of any of phosphoric acid, phosphorous acid, ammonium dihydrogen phosphate, organic phosphide and phosphorus oxide.

[0027] In the method for preparing the mesoporous SAPO-34 molecular sieve described in the present invention, the template agent is one or a mixture of any of diethylamine, triethylamine, morpholine and tetraethylammonium hydroxide.

[0028] In the method for preparing the mesoporous SAPO-34 molecular sieve described in the present invention, the crystallization temperature in step b) is 180-220° C., and the crystallization time is 9-80 hours.

[0029] Beneficial effects of the present invention:

[0030] The mesopore-containing SAPO-34 molecular sieve prepared by the present invention has a larger specific surface area and controllable moderate mesopores, and has higher diene selectivity and catalytic life in the MTO reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the XRD diffraction pattern of the mesoporous SAPO-34 molecular sieve obtained in Example 1.

[0032] Figure 2 This is a diagram showing the low-temperature nitrogen physical adsorption-desorption of the medium-pore SAPO-34 molecular sieve in Example 1. DETAILED DESCRIPTION

[0033] The present invention is described in detail below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art in this field can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0034] Examples 1-11 and Comparative Examples 1-2

[0035] The specific dosage of ingredients and crystallization conditions are shown in Table 1. The specific ingredient process is as follows: deionized water and long-chain high-grade fatty alcohol polyoxyethylene ether AEO are mixed and stirred evenly, and then the aluminum source, silicon source, phosphorus source, deionized water and template are added. After vigorous stirring for 60 minutes in a closed state to make them evenly mixed, an initial gel mixture is obtained, and the initial gel mixture is transferred to a stainless steel reactor, heated to a certain temperature, and crystallized dynamically for a certain period of time. After the crystallization is completed, the solid product is centrifuged, washed, dried in air at 100°C, and then calcined at 600°C to obtain SAPO-34 molecular sieve raw powder (containing SAPO-34 molecular sieve with a mesoporous structure). The sample was subjected to XRD analysis, and the results showed that the synthetic product was SAPO-34 molecular sieve. The XRD spectrum of the sample in Example 1 is shown in Figure 1, Example 1 product low temperature nitrogen physical adsorption - desorption Figure see Figure 2 . The XRD spectrum of the sample of Example 2-11 is close to that of Example 1, that is, the peak positions are the same, and the relative peak intensity of each peak is slightly different with the change of the higher fatty alcohol polyoxyethylene ether AEO. The main peak position conforms to the standard peak position of SAPO-34 molecular sieve, indicating that the synthesized products are all SAPO-34 molecular sieves. The low-temperature nitrogen physical adsorption-desorption diagram of Example 2-11 is close to that of Example 1, with obvious adsorption-desorption hysteresis loops, indicating that the synthesized products have rich mesoporous structures, and are all microporous SAPO-34 molecular sieves with mesoporous structures.

[0036] Table 1 Molecular sieve synthesis ingredients and crystallization conditions

[0037]

[0038]

[0039] *: Fatty alcohol polyoxyethylene ethers such as AEO-5, JFC, and Peregal O can be obtained from chemical platforms or synthesized in the laboratory; the aluminum source is pseudo-boehmite (Al 2 O 3 The mass content is 70.0%); the phosphorus source is phosphoric acid (mass fraction is 75%). The template agent of Example 7 is tetraethylammonium hydroxide (mass fraction is 25%); the silicon source of Example 9 is tetraethoxysilane; the aluminum source of Example 7 is activated alumina; the aluminum source of Example 10 is aluminum isopropoxide; the silicon source of Example 11 and Comparative Example 2 is ethyl orthosilicate.

[0040] Comparative Example 3

[0041] Add 150.2g of water, 10.1g of pseudo-boehmite, 15.6g of phosphoric acid, and 5.3g of silica sol to the synthesis kettle, stir well, then add 10.3g of diethylamine, and stir for 2h under sealing to obtain a uniform initial synthesis gel. Move the gel into a stainless steel synthesis kettle, heat to 190°C, and crystallize for 23h. Take out the synthesis kettle and cool it. The solid product is separated by centrifugation, washed with deionized water until neutral, and dried in air at 100°C to obtain the molecular sieve raw powder, which is then calcined at 600°C to obtain the molecular sieve. XRD analysis shows that the obtained solid is SAPO-34 molecular sieve. XRD data and Figure 1 Similar, that is, the peak positions are the same, and the peak intensities are slightly stronger than those of the product in Example 1.

[0042] The samples obtained in the examples and comparative examples were tableted and crushed to 10-30 mesh. 1.0 g of the sample was weighed and loaded into a fixed bed reactor for MTO reaction evaluation. Nitrogen was activated at 545°C for 1.5 hours, and then the temperature was lowered to 450°C for reaction. Methanol was carried by nitrogen, and the methanol weight space velocity was 2.0 h -1When the diene selectivity drops rapidly, the catalyst is judged to be deactivated. The reaction product is analyzed by online gas chromatography, and the results are shown in Table 3. After analysis and comparison, it is found that the specific surface area and mesopore volume of the embodiment are both higher than those of the comparative example. Compared with the comparative example, the embodiment shows the advantages of longer life and higher diene selectivity in the methanol to olefin reaction, so the embodiment has more excellent catalytic activity.

[0043] Table 2 Specific surface area and mesopore volume of Example 1 and Comparative Example

[0044]

[0045] Table 3 Comparison of MTO reaction performance between examples and comparative examples

[0046]

[0047]

[0048] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and deformations based on the present invention, but these corresponding changes and deformations should all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a mesoporous SAPO-34 molecular sieve, characterized in that: The following steps are involved: a) mixing a silicon source, an aluminum source, a phosphorus source, deionized water, a template and AEO to obtain an initial gel mixture, wherein AEO is a RO-(CH2CH2O) n -H structured organic long-chain higher fatty alcohol polyoxyethylene ether, the aluminum source is calculated as Al2O3, and the mass ratio of AEO / Al2O3 is 0.05 to 1; b) placing the initial gel mixture obtained in step a) into a synthesis kettle, sealing it, and performing hydrothermal crystallization under autogenous pressure; c) After the crystallization is complete, the solid product is separated by centrifugation, washed with deionized water until neutral, and dried and calcined to obtain the SAPO-34 molecular sieve containing a mesoporous structure.

2. The method for preparing mesoporous SAPO-34 molecular sieve according to claim 1, characterized in that: The AEO is one or more of AEO-5, AEO-7, AEO-9, Peregal O and JFC.

3. The method for preparing mesoporous SAPO-34 molecular sieve according to claim 1, characterized in that: The molar ratio of each substance in the initial gel mixture is: SiO2 / Al2O3=0.1~1.0; P2O5 / Al2O3=0.5-2.0; Template / Al2O3=1-10; H2O / Al2O3=1~100.

4. The method for preparing mesoporous SAPO-34 molecular sieve according to claim 1, wherein the silicon source is one or a mixture of any of silica sol, active silica, orthosilicate and metakaolin.

5. The method for preparing mesoporous SAPO-34 molecular sieve according to claim 1, characterized in that: The aluminum source is one of aluminum salt, activated alumina, alkoxy aluminum, metakaolin and pseudo-boehmite, or a mixture of any of them.

6. The method for preparing mesoporous SAPO-34 molecular sieve according to claim 1, characterized in that: The phosphorus source is one of phosphoric acid, phosphorous acid, ammonium dihydrogen phosphate, organic phosphide and phosphorus oxide, or a mixture of any of them.

7. The method for preparing mesoporous SAPO-34 molecular sieve according to claim 1, characterized in that: The template agent is one or a mixture of any of diethylamine, triethylamine, morpholine and tetraethylammonium hydroxide.

8. The method for preparing mesoporous SAPO-34 molecular sieve according to claim 1, characterized in that: The crystallization temperature in step b) is 180-220° C., and the crystallization time is 9-80 hours.

9. The mesoporous SAPO-34 molecular sieve prepared by the preparation method according to any one of claims 1 to 8.

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