Grafting type SAPO molecular sieve S-C and preparation method and application thereof

Abstract

The invention discloses a grafted SAPO molecular sieve S-C as well as a preparation method and application thereof, and belongs to the technical field of chemical materials. The molecular sieve S (at) C takes a silicoaluminophosphate molecular sieve SAPO-14 with an AFN topological structure as an inner core C, and an SAPO molecular sieve S is grafted and grown on the crystal surface of the SAPO-14; the SAPO molecular sieve S is selected from at least one of SAPO molecular sieves with an ERI structure, an AEI structure, an AFI structure, an AEL structure, a CHA structure, an LEV structure and an AFX structure. The induction period of the molecular sieve S-C is obviously shortened in the process of catalyzing MTO reaction, and high-efficiency conversion of methanol and high selectivity of low-carbon olefin can be realized in the initial stage of the reaction; and the carbon pre-deposition operation in the MTO technology is avoided, so that the operation difficulty and the reaction cost are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical materials, and particularly relates to a grafted SAPO molecular sieve S@C, a preparation method thereof and an application thereof. Background Art

[0002] The aluminophosphate-silicate (SAPO-n) series of molecular sieves was developed by Union Carbide Corporation (UCC) of the United States in 1984 <USP 4,440,871>. It is an infinite open-framework microporous crystal composed of three tetrahedral units of [SiO 4 0 , [AlO 4 - , [PO 4 + . The Si atom is isomorphously substituted for some P atoms in the neutral aluminophosphate framework structure, making the framework have a net negative charge and introducing Brønsted acid centers, thereby endowing the SAPO molecular sieve with acid catalytic performance. Among the SAPO molecular sieves, SAPO-34 with a CHA topological structure is the most representative. It can efficiently catalyze the conversion of methanol to produce light olefins (MTO), and has now been successfully applied in the MTO industrial process for commercial use. However, the SAPO-34 molecular sieve catalyst has an obvious induction period during use. During the induction period, the olefin selectivity is low and the alkane selectivity is high. As the reaction time increases, the light olefin selectivity gradually increases. To improve the control ability of the industrial process for light olefin selectivity, researchers have developed a catalyst pre-carbon deposition technology to eliminate the reaction induction period (CN201310643077.6, J. Catal. 2019, 377, 153-162), that is, hydrocarbons with four or more carbon atoms are introduced in advance to form partial pre-carbon deposition inside the catalyst. However, this process also increases the reaction cost and the complexity of the MTO process, and further increases the operation difficulty.

[0003] ​​​Molecular sieves generally have an induction period during the catalytic MTO reaction. Chen et al. found that there is an obvious induction period in the catalytic methanol conversion of a series of molecular sieves such as SAPO-34, SAPO-18, and SAPO-35, and the induction period shortens with the increase of the reaction temperature (Chen J. et al. Catal. Commun., 2014, 46, 36 - 40.). It is generally believed that the induction period can be divided into three stages: the first stage is the initial C-C bond formation, the second stage is the formation and accumulation of the hydrocarbon pool, and the last stage is the start of autocatalysis. Different molecular sieve topologies have differences in spatial confinement, which will lead to different hydrocarbon pool species formed, and the catalytic activities of these hydrocarbon pool species are also different. When the hydrocarbon pool species accumulate to a certain extent, an autocatalytic cycle is established, and the reaction activity also increases. When the molecular sieve structure is relatively dense, the formed hydrocarbon pool species are smaller, and the required hydrocarbon pool accumulation amount is also lower, so the autocatalytic cycle can be established faster (Chinese J.C. 2022, 43, 2259 - 2269). The induction period of SAPO-14 catalyzing the MTO reaction is significantly shorter (Chinese J.C. 2022, 43, 2259 - 2269). This may be because the hydrocarbon pool species in the narrow space of the SAPO-14 molecular sieve only need a small amount of accumulation to quickly establish an autocatalytic cycle.

[0004] SAPO-14 is a small-pore and small-cage molecular sieve with an 8-ring pore structure and a narrow AFN cage structure. The prior art has disclosed the synthesis of SAPO-14 molecular sieve and its application in methanol-to-olefins (MTO). Its catalytic methanol conversion can obtain a propylene selectivity of more than 60% (ACS Catal. 2020, 10, 3714). However, due to the relatively dense structure of the SAPO-14 molecular sieve, the diffusion and mass transfer are difficult, so the methanol treatment capacity is limited, and the catalyst is extremely easy to deactivate.

[0005] Therefore, attempts are made to prepare a new type of molecular sieve catalyst by utilizing the above characteristics of the SAPO-14 molecular sieve, so as to obtain satisfactory catalytic effects and avoid the induction period of the MTO reaction. Summary of the Invention

[0006] In view of this, the present invention provides a grafted SAPO molecular sieve S@C, its preparation method and application, and the main purpose is to solve the technical problem of the long induction period of the SAPO molecular sieve in the catalytic MTO reaction.

[0007] On the one hand, the present invention provides a grafted SAPO molecular sieve S@C, wherein the molecular sieve S@C uses a silicoaluminophosphate molecular sieve SAPO-14 with an AFN topology as the core C, and SAPO molecular sieve S is grafted and grown on the crystal surface of the SAPO-14; wherein,

[0008] The SAPO molecular sieve S is selected from at least one of SAPO molecular sieves having an ERI structure, an AEI structure, an AFI structure, an AEL structure, a CHA structure, a LEV structure, and an AFX structure.

[0009] The grafted molecular sieve of the present invention is different from the symbiotic molecular sieve and the core-shell molecular sieve in the prior art. It refers to a situation where a molecular sieve S of one structure grows on the crystal surface of a molecular sieve C of another structure. The two crystals grow partially intertwined, but S only occupies a part of the crystal surface of the original crystal C, and does not cover the whole as in the core-shell structure. The crystal size of the grafted molecular sieve S is smaller than that of the support molecular sieve C in at least one dimension.

[0010] In the synthesis gel for preparing the SAPO molecular sieve S of the present invention, a certain amount of SAPO-14 molecular sieve C is added as a crystal growth support at the same time, so that other types of SAPO molecular sieves S such as SAPO-34, SAPO-18, etc. grow epitaxially along the crystal of the SAPO-14 molecular sieve C, thereby generating a grafted molecular sieve catalyst material S@C.

[0011] Optionally, the SAPO molecular sieve S is selected from at least one of SAPO-17, SAPO-5, SAPO-11, SAPO-18, SAPO-34, SAPO-35, and SAPO-56.

[0012] Optionally, the crystal grain size of the molecular sieve SAPO-14 is (significantly larger than) larger than that of the SAPO molecular sieve S.

[0013] Optionally, the SAPO molecular sieve S grows flat on the surface of the SAPO-14 crystal.

[0014] Optionally, the mass of the SAPO molecular sieve S is less than or equal to the mass of the molecular sieve SAPO-14.

[0015] During the catalytic MTO reaction process, the induction period of the above-mentioned molecular sieve S@C of the present invention is significantly shortened, and high-efficiency conversion of methanol and high selectivity for light olefins can be achieved at the initial stage of the reaction; it makes it possible to eliminate the pre-carbon deposition operation in the MTO technology, thereby reducing the operation difficulty and reaction cost.

[0016] In a second aspect, the present invention provides a preparation method for the above-mentioned grafted SAPO molecular sieve S@C, comprising the following steps:

[0017] S1: Mix a phosphorus source, an aluminum source, water, a silicon source, and an organic amine templating agent to obtain a synthesis gel for the SAPO molecular sieve S;

[0018] S2: Add SAPO-14 molecular sieve C to the synthetic gel in step S1 and stir to obtain a reaction mixture; the reaction mixture is subjected to hydrothermal crystallization under closed conditions to obtain the target product S@C.

[0019] Optionally, in step S1, the formulation of the synthetic gel is selected from any one of the formulations suitable for synthesizing molecular sieves with ERI structure, AFI structure, AEL structure, AEI structure, CHA structure, LEV structure or AFX structure.

[0020] Optionally, in step S1, the formulation of the synthetic gel is selected from any one of the formulations suitable for synthesizing SAPO-17, SAPO-5, SAPO-11, SAPO-18, SAPO-34, SAPO-35 or SAPO-56 molecular sieves.

[0021] Optionally, in step S1, the molar ratio of each component of the synthetic gel is:

[0022] P 2 O 5 :Al 2 O 3 :SiO 2 :H 2 O:R = 0.7 - 1.0:1.0:0 - 1.0:20 - 100:1.0 - 4.0,

[0023] The molar number of the phosphorus source is based on the molar number of P 2 O 5 The molar number of the aluminum source is based on the molar number of Al 2 O 3 The molar number of the silicon source is based on the molar number of SiO 2 The molar number of water is based on the molar number of its own H 2 O, and the molar number of the organic amine template agent is based on the molar number of R.

[0024] Optionally, the organic template agent is selected from cyclohexylamine, diethylamine, triethylamine, di-n-propylamine, N,N-diisopropylethylamine, morpholine, diethylamine, triethylamine, tetraethylammonium hydroxide or N,N,N',N'-tetramethyl-1,6-hexanediamine.

[0025] In addition to the above template agent in the synthetic gel of the present invention, other suitable types of template agents can also be selected from the prior art.

[0026] Optionally, the phosphorus source is selected from phosphoric acid; the aluminum source is selected from at least one of pseudoboehmite, aluminum isopropoxide and aluminum hydroxide; the silicon source is selected from at least one of tetraethyl orthosilicate, low-sodium silica sol and fumed silica.

[0027] Optionally, the molar ratio of SiO₂ in the synthesis gel of the SAPO-17 molecular sieve is 0 to 0.6; 2 ;

[0028] Preferably, R in the synthesis gel of the SAPO-17 molecular sieve is cyclohexylamine;

[0029] Preferably, in step S2, the temperature for heat crystallization of the reaction mixture of the synthesis gel of the SAPO-17 molecular sieve and the SAPO-14 molecular sieve is 130 to 180 °C.

[0030] Optionally, the molar ratio of SiO₂ in the synthesis gel of the SAPO-5 molecular sieve is 0 to 0.1; 2 ;

[0031] Preferably, R in the synthesis gel of the SAPO-5 molecular sieve is diethylamine or triethylamine;

[0032] Preferably, in step S2, the temperature for heat crystallization of the reaction mixture of the synthesis gel of the SAPO-5 molecular sieve and the SAPO-14 molecular sieve is 130 to 180 °C.

[0033] Optionally, the molar ratio of SiO₂ in the synthesis gel of the SAPO-11 molecular sieve is 0 to 0.6; 2 ;

[0034] Preferably, R in the synthesis gel of the SAPO-11 molecular sieve is di-n-propylamine;

[0035] Preferably, in step S2, the temperature for heat crystallization of the reaction mixture of the synthesis gel of the SAPO-11 molecular sieve and the SAPO-14 molecular sieve is 130 to 180 °C.

[0036] Optionally, the molar ratio of SiO₂ in the synthesis gel of the SAPO-18 molecular sieve is 0 to 0.5; 2 ;

[0037] Preferably, R in the synthesis gel of the SAPO-18 molecular sieve is N,N-diisopropylethylamine;

[0038] Preferably, in step S2, the temperature for heat crystallization of the reaction mixture of the synthesis gel of the SAPO-18 molecular sieve and the SAPO-14 molecular sieve is 140 to 200 °C.

[0039] Optionally, the molar ratio of SiO₂ in the synthesis gel of the SAPO-34 molecular sieve is 0.05 to 1.0; 2 ;

[0040] Preferably, in the synthesis gel of the SAPO-34 molecular sieve, R is morpholine, diethylamine, triethylamine or tetraethylammonium hydroxide;

[0041] Preferably, in step S2, the heating crystallization temperature of the synthesis gel of the SAPO-34 molecular sieve and the reaction mixture of the SAPO-14 molecular sieve is 160-200 °C.

[0042] Optionally, in the synthesis gel of the SAPO-35 molecular sieve, the molar ratio of SiO 2 is 0.05-1.0;

[0043] Preferably, in the synthesis gel of the SAPO-35 molecular sieve, R is cyclohexylimine;

[0044] Preferably, in step S2, the heating crystallization temperature of the synthesis gel of the SAPO-35 molecular sieve and the reaction mixture of the SAPO-14 molecular sieve is 160-200 °C.

[0045] Optionally, in the synthesis gel of the SAPO-56 molecular sieve, the molar ratio of SiO 2 is 0.1-1.0;

[0046] Preferably, in the synthesis gel of the SAPO-56 molecular sieve, R is N,N,N‘N‘-tetramethyl-1,6-hexanediamine;

[0047] Preferably, in step S2, the heating crystallization temperature of the synthesis gel of the SAPO-56 molecular sieve and the reaction mixture of the SAPO-14 molecular sieve is 160-220 °C.

[0048] The synthesis gel formula of the present invention is the formula corresponding to the known molecular sieve, and the formula of the actual synthesis gel suitable for the molecular sieve S can also be selected from the prior art according to actual needs.

[0049] In the grafting method of the present invention, the formulas and synthesis methods of the SAPO-17, SAPO-5, SAPO-11, SAPO-18, SAPO-34, SAPO-35 or SAPO-56 molecular sieves and the SAPO-14 molecular sieve are all prior art. The grafting method of the present invention only needs to select a suitable type of molecular sieve S, and according to the specific mass ratio of the two molecular sieves S and C, graft the molecular sieve S to grow on the surface of the molecular sieve C, that is, the SAPO-14 crystal surface; the specific synthesis gel formulas of the above molecular sieves are prior art.

[0050] Optionally, the mass ratio of the SAPO molecular sieve S generated by the synthesis gel to the added SAPO-14 molecular sieve C is 1:1-50.

[0051] Optionally, the mass ratio of the SAPO molecular sieve S generated from the synthetic gel to the added SAPO-14 molecular sieve C is 1:2 to 30.

[0052] Optionally, the mass ratio of the SAPO molecular sieve S generated from the synthetic gel to the added SAPO-14 molecular sieve C is selected from any value among 1:1, 1:2, 1:3, 1:5, 1:7, 1:8, 1:10, 1:12, 1:15, 1:18, 1:20, 1:22, 1:25, 1:28, 1:30, 1.33, 1:35, 1.38, 1:40, 1:42, 1:45, 1:48, 1:50 or the range value between any two of them.

[0053] The grafting amount of the molecular sieve of the present invention can be adjusted.

[0054] The mass of the SAPO-14 molecular sieve of the present invention can be directly weighed, and the final mass of the SAPO molecular sieve S is estimated by calculating the added amount of phosphoric acid in its synthetic gel to synthesize the mass of the molecular sieve S.

[0055] Optionally, in step S2, the conditions for the hydrothermal crystallization include:

[0056] The crystallization temperature is 130 to 220 °C, and the crystallization time is 12 - 120 hours.

[0057] Optionally, the crystallization temperature is selected from any value among 130, 140, 150, 160, 170, 180, 190, 200, 210, 220 or the range value between any two of them, in the unit of °C.

[0058] Optionally, the crystallization time is selected from any value among 12, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120 or the range value between any two of them, in the unit of hours.

[0059] Optionally, in step S1, the phosphorus source and the aluminum source are uniformly mixed with water, and then a certain amount of silicon source and organic amine template agent are introduced and stirred evenly at room temperature.

[0060] In the third aspect, the present invention provides the above grafted SAPO molecular sieve S@C for use as an adsorbent or an acid catalyst.

[0061] Optionally, the SAPO molecular sieve S@C is calcined to remove the organic template agent, the calcination temperature is 400 to 800 °C, and the calcination time is 2 to 5 h.

[0062] When the grafted molecular sieve catalyst S@C of the present application is used in the methanol-to-hydrocarbons reaction, there is no obvious induction period at the initial stage of the reaction or the induction period is significantly shortened, and the high-efficiency conversion of methanol and the high yield of light olefins can be quickly achieved without using the pre-carbon deposition technology to eliminate the reaction induction period.

[0063] Fourthly, the present invention provides an acid catalyst, and the acid catalyst includes the above-mentioned grafted SAPO molecular sieve S@C.

[0064] The crystallization process of the present application is carried out dynamically. Specifically, it means that during the crystallization process, the hydrothermal synthesis kettle containing the initial reaction mixture is placed in a rotating oven, and the mixture in the reaction kettle is fully stirred during the rotation process.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] (1) The grafted molecular sieve catalytic material S@C provided by the present application can effectively shorten the induction period of the MTO reaction, facilitate the adjustment of the light olefin selectivity, and provide an alternative catalyst material for the methanol-to-olefins industrial catalytic process.

[0067] (2) The synthesis method of the grafted molecular sieve catalyst material provided by the present application has a simple synthesis process, convenient operation, and is conducive to large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 It is the powder X-ray diffraction pattern of Example 1 of the present application;

[0069] Figure 2 It is the powder X-ray diffraction pattern of Example 2 of the present application;

[0070] Figure 3 It is the scanning electron microscope image of Example 2 of the present application, scale bar 1.00 μm;

[0071] Figure 4 It is the powder X-ray diffraction pattern of Example 3 of the present application;

[0072] Figure 5 It is the scanning electron microscope image of Example 3 of the present application, scale bar 2.00 μm;

[0073] Figure 6 It is the scanning electron microscope image of Example 4 of the present application, scale bar 4.00 μm;

[0074] Figure 7 It is the powder X-ray diffraction pattern of Comparative Example 1 of the present application;

[0075] Figure 8 It is the scanning electron microscope image of Comparative Example 1 of the present application, scale bar 30 μm;

[0076] Figure 9 Powder X-ray diffraction pattern of Comparative Example 3 of the present application;

[0077] Figure 10 Scanning electron micrograph of Comparative Example 3 of the present application, scale bar 30 μm. Detailed implementation manners

[0078] The following further elaborates the present application in conjunction with specific embodiments. The following descriptions are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed below with preferred embodiments, it is not intended to limit the present application. Any person skilled in the relevant art, without departing from the technical solution of the present application, making some changes or modifications using the disclosed technical content above is equivalent to equivalent embodiments and all fall within the scope of the technical solution.

[0079] Unless otherwise specified, the raw materials in the embodiments of the present application are all purchased through commercial channels and used directly without any special treatment.

[0080] The analysis methods in the embodiments of the present application are as follows:

[0081] For X-ray powder diffraction phase analysis (XRD), an X'Pert PRO X-ray diffractometer from PANalytical, Netherlands, with a Cu target and a Kα radiation source (λ = 0.15418 nm), a voltage of 40 kV, and a current of 40 mA was used.

[0082] In the embodiments of the present application, the determination of the bulk element composition was carried out using a Magix 2424X type X-ray fluorescence analyzer (XRF) from Philips.

[0083] In the embodiments of the present application, the instrument used for scanning electron microscopy (SEM) testing was a Hitachi SU8020 field emission scanning electron microscope, with an acceleration voltage of 2 kV.

[0084] Example 1

[0085] First, the phosphorus source and the aluminum source were uniformly mixed with water, and then a certain amount of silicon source and organic amine template agent were added. After stirring evenly at room temperature, a certain amount of SAPO-14 molecular sieve was added to the gel and stirred evenly; the synthesis of SAPO-14 molecular sieve refers to ACS Catal. 2020, 10, 3714; the reaction mixture was sealed in a hydrothermal synthesis autoclave and placed in an oven for rotation crystallization at 140 - 210 °C for 12 - 120 hours; after the reaction mixture was centrifuged and washed with deionized water until neutral, it was dried in air at 120 °C to obtain the raw powder.

[0086] Examples 2 - 7

[0087] The difference in the synthesis operation steps of Examples 2 to 7 from those of Example 1 lies in that the synthesized gels prepared are different target molecular sieves, resulting in differences in the synthesis formula; the synthesis gel ratios and reaction conditions of each example are shown in Table 1; the XRD spectra and scanning electron microscope results of some example samples are shown in Figure 1-6 , and the inorganic chemical compositions and evaluation results of the catalytic MTO reaction are shown in Table 3.

[0088] Table 1. Gel Ratios and Synthesis Conditions of Examples 1 to 7 a

[0089]

[0090] a The chemical composition of the input SAPO-14 is: Al 0.5 P 0.48 Si 0.02 O 2 .

[0091] In Example 1, 11.5 g of SAPO-14 molecular sieve was added to the synthesis gel that could generate about 2.75 g of SAPO-34. Since the diffraction peak of the SAPO-14 sample XRD spectrum at 2θ 9.0 degrees was particularly strong, the XRD spectrum of the sample obtained in Example 1 was still mainly SAPO-14 ( Figure 1 ). No obvious diffraction peak of SAPO-34 could be seen.

[0092] The synthesis process of Example 2 was similar to that of Example 1, except that the synthesis gel formula of SAPO-34 was changed to the formula for synthesizing SAPO-56, and in addition, the mass of the added SAPO-14 was different. Figure 2 And Figure 3 respectively show the XRD spectrum and scanning electron microscope photograph of Example 2. It can be seen from the XRD spectrum and scanning electron microscope photograph that some SAPO-5 crystals were grafted onto the large SAPO-14 grains. It can be seen that due to the interference of the introduced SAPO-14 molecular sieve, grafting growth may also lead to the appearance of unexpected crystal phases. In Example 2, while SAPO-56 molecular sieve grew by grafting on the surface of SAPO-14 crystals, some SAPO-5 crystal phases were also grafted. The crystal morphology of Example 2 is as Figure 3 shown, with very fine SAPO-56 molecular sieves growing flat on the surface of SAPO-14 crystals. In addition, long hexagonal columnar SAPO-5 crystals were inserted into the crystal flakes of SAPO-14 molecular sieve.

[0093] The synthesis processes of Examples 3 and 4 were also similar to that of Example 1, except that the synthesis gel formula of SAPO-34 was changed to the formula for synthesizing SAPO-18, and in addition, the mass of the added SAPO-14 was different.Figure 4 and Figure 5 shows the XRD pattern and SEM image of Example 3. The diffraction peaks in the XRD pattern are basically consistent with those of SAPO-14, and the presence of the SAPO-18 crystal phase cannot be seen. In the SEM image, many cubic crystals are attached and grown on the surface of the large flaky SAPO-14 molecular sieve, which is considered to be the attached and grown SAPO-18 crystal phase. Since more SAPO-14 molecular sieves were added in Example 4, the grains attached to the crystal surface are sparser. See Figure 6 . Ultrasonic waves cannot strip these crystals, indicating that the crystals are grafted and grown on the surface of the SAPO-14 crystals.

[0094] Comparative Example 1

[0095] The synthesis steps of Comparative Example 1 are the same as those of Example 3, except that the amount of SAPO-14 molecular sieve added is less than the amount of newly formed SAPO-18 molecular sieve.

[0096] Comparative Example 2

[0097] In Comparative Example 2, the target molecular sieve synthesized from the prepared gel was changed to SAPO-14, and a certain amount of SAPO-34 was added to assist in crystallization.

[0098] Comparative Example 3

[0099] In Comparative Example 3, a synthesis gel of SAPO-14 was also prepared, and a certain amount of SAPO-18 was added to assist in crystallization; the mass ratio of SAPO-14 to SAPO-18 is equivalent to that of Example 4. The specific raw material ratio for synthesis is shown in Table 2.

[0100] Table 2. Gel ratios and synthesis conditions for Comparative Examples 1-3

[0101]

[0102] Comparative Example 4

[0103] Comparative Example 4 is a pure SAPO-14 molecular sieve sample used in Examples 1-7.

[0104] Comparative Example 5

[0105] Comparative Example 5 is a sample of mechanically mixed SAPO-14 and SAPO-18 raw powders, with a mass ratio of 7:1, which is equivalent to that of Example 4.

[0106] Comparative Example 6

[0107] Comparative Example 6 is a conventional SAPO-34 molecular sieve sample.

[0108] Figure 7 and Figure 8The XRD pattern and SEM photograph of Comparative Example 1 are given respectively. The XRD pattern of Comparative Example 1 is still mainly SAPO-14, and a small number of diffraction peaks belonging to the SAPO-18 crystal phase can also be seen. There are obviously two phases in the SEM picture, indicating that SAPO-14 and SAPO-18 exist more in a mixed state.

[0109] Figure 9 and Figure 10 The XRD pattern and SEM photograph of Comparative Example 3 are given respectively. From the results of the XRD pattern, it can be seen that regardless of the synthesis method, when the mass ratio of SAPO-14 is higher, the XRD patterns of the final obtained molecular sieve products are similar and basically the same as the XRD pattern of pure SAPO-14. However, from the SEM results, a huge difference in crystal morphology can be seen. The crystals of Comparative Example 3 show the morphology of SAPO-14 molecular sieve, but the crystal particle size decreases slightly. No obvious epitaxial growth phenomenon is found on the crystal surface. During the crystallization of SAPO-14 molecular sieve, SAPO-18 molecular sieve may have dissolved and at the same time played the role of crystal seeds, resulting in a slight decrease in the crystal particle size of SAPO-14, and at the same time SAPO-18 molecular sieve is also involved in the crystal growth process of SAPO-14.

[0110] Application Example

[0111] The evaluation method of MTO catalytic performance is as follows: The molecular sieves prepared in Examples 1, 3-4 and Comparative Examples 1-5 are respectively calcined in air at 600 °C for 4 hours, then pressed and crushed into molecular sieve particles of 20-40 mesh. 0.3 g of each sample is respectively loaded into a self-made fixed-bed reactor as a catalyst for MTO reaction evaluation. It is activated with nitrogen at 550 °C for 1 hour respectively, and then cooled to 400 °C for reaction. Methanol is carried by nitrogen, the nitrogen flow rate is 20 ml / min, and the methanol weight hourly space velocity is 1.0 h -1 . The reaction products are analyzed by an on-line gas chromatograph (Agilent A7890), and the results are shown in Table 3 below.

[0112] Table 3. Chemical compositions and initial MTO catalytic results of Examples 1, 3 and 4 and Comparative Examples 1-6 a

[0113]

[0114] a Unless otherwise specified, the MTO reaction conditions are 400 °C and the space velocity is 1.0 h -1 , and the lifetime is defined as the reaction time when the conversion rate is greater than 99%.

[0115] b XRF test results;

[0116] c The MTO reaction conditions for Comparative Example 1 were: 400 °C, space velocity 2.0 h -1 ;

[0117] d The MTO reaction conditions for Comparative Example 6 were: 450 °C, space velocity 2.0 h -1 .

[0118] Table 3 lists the MTO catalytic reaction results of some examples and comparative examples. The MTO reaction is an autocatalytic reaction process, and the product can act as a catalyst for this reaction to promote the reaction. At the initial stage of the reaction, when only a very small amount of product is generated, the reaction is very slow, and this is the induction period. The induction period will be shortened with the increase of reaction temperature and space velocity, but from the MTO reaction results catalyzed by SAPO-34 in Comparative Example 6, at 450 °C and space velocity 2 h -1 Under the conditions, when the TOS is 3 minutes, the selectivity of diolefins is only 79.88, while when the TOS is 37 minutes, it is increased to 82.88. It can be seen that the reaction induction period is still obvious, and the selectivity of diolefins gradually increases with the increase of reaction time. Therefore, in order to quickly obtain high diolefin selectivity in the circulating fluidized bed technology, it is necessary to use the pre-coking technology to control the TOS time for obtaining high diolefin selectivity.

[0119] It was found in this application that when strongly acidic SAPO-34 or SAPO-18 molecular sieves are epitaxially grafted on the crystals of SAPO-14 molecular sieve, the selectivities of ethylene and propylene reach the highest values at the first injection of TOS (3 min), which is significantly different from the catalytic MTO reaction characteristics of SAPO-34 and SAPO-18. This catalytic feature makes it possible to omit the pre-coking operation in the MTO technology, thereby reducing the operation difficulty and reaction cost.

[0120] In comparison, Comparative Example 1 is more inclined to the catalytic MTO reaction characteristics of SAPO-18 molecular sieve. Although the service life is long, the methanol conversion rate and diolefin selectivity of the first injection are both low, and there is an obvious induction period. It can be seen from Comparative Examples 2 and 3 that when the synthetic gel is targeted at SAPO-14, adding a small amount of SAPO-34 or SAPO-18 molecular sieve has limited influence on the catalytic ability of the synthesized product, and the ability of the catalyst to catalyze methanol conversion is significantly insufficient, and the service life is less than 40 minutes. Comparative Example 5 is a mechanical mixture of SAPO-14 and SAPO-18 with a mass ratio of 7:1. Although it can quickly obtain the highest diolefin selectivity at the initial stage of the reaction, its catalytic service life is also less than 40 minutes. In comparison, Example 4 (SAPO-18@SAPO-14) using the grafting method not only greatly improves the ability of the catalyst to catalyze methanol conversion compared with SAPO-14, but also can improve the problem of the long induction period in the catalytic MTO reaction of molecular sieves such as SAPO-34 and SAPO-18.

[0121] As described above, these are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed above with preferred embodiments, it is not intended to limit the present application. Any person skilled in the relevant art can make some changes or modifications using the disclosed technical content within the scope of the technical solution of the present application, which are equivalent to equivalent embodiments and all fall within the scope of the technical solution.

Claims

1. A grafted SAPO molecular sieve S@C, characterized in that, the molecular sieve S@C uses the silicoaluminophosphate molecular sieve SAPO-14 with an AFN topological structure as the core C, and SAPO molecular sieve S grows grafted on the crystal surface of the SAPO-14; wherein, the SAPO molecular sieve S is selected from at least one of the SAPO molecular sieves having an ERI structure, an AEI structure, an AFI structure, an AEL structure, a CHA structure, a LEV structure, and an AFX structure.

2. The grafted SAPO molecular sieve S@C according to claim 1, characterized in that, the SAPO molecular sieve S is selected from at least one of SAPO-17, SAPO-5, SAPO-11, SAPO-18, SAPO-34, SAPO-35, and SAPO-56; Preferably, the crystal grain size of the molecular sieve SAPO-14 is larger than that of the SAPO molecular sieve S; Preferably, the SAPO molecular sieve S grows flat on the surface of the SAPO-14 crystal; Preferably, the mass of the SAPO molecular sieve S is less than or equal to the mass of the molecular sieve SAPO-14.

3. The preparation method of the grafted SAPO molecular sieve S@C according to any one of claims 1 to 2, characterized in that, the preparation method includes the following steps: S1: Mix a phosphorus source, an aluminum source, water, a silicon source, and an organic amine template agent to obtain a synthesis gel of the SAPO molecular sieve S; S2: Add the SAPO-14 molecular sieve C to the synthesis gel in step S1 and stir to obtain a reaction mixture; the reaction mixture is heated and crystallized under a closed condition to obtain the target product S@C.

4. The preparation method of the grafted SAPO molecular sieve S@C according to claim 3, characterized in that, In step S1, the formula of the synthesis gel is selected from any one of the applicable formulas for synthesizing molecular sieves with an ERI structure, an AFI structure, an AEL structure, an AEI structure, a CHA structure, a LEV structure, or an AFX structure; Preferably, in step S1, the formula of the synthesis gel is selected from any one of the applicable formulas for synthesizing SAPO-17, SAPO-5, SAPO-11, SAPO-18, SAPO-34, SAPO-35, or SAPO-56 molecular sieves; Preferably, in step S1, the molar ratio of each component of the synthesis gel is: P 2 O 5 : Al 2 O 3 : SiO 2 : H 2 O: R = 0.7 to 1.0:1.0:0 to 1.0:20 to 100:1.0 to 4.0; The molar number of the phosphorus source is counted by the molar number of P 2 O 5 The molar number of the aluminum source is counted by the molar number of Al 2 O 3 The molar number of the silicon source is counted by the molar number of SiO 2 The molar number of water is counted by the molar number of its own H 2 O, and the molar number of the organic amine template agent is counted by the molar number of R; Preferably, the organic template agent is selected from cyclohexylamine, diethylamine, triethylamine, di-n-propylamine, N,N-diisopropylethylamine, morpholine, diethylamine, triethylamine, tetraethylammonium hydroxide, or N,N,N',N'-tetramethyl-1,6-hexanediamine; Preferably, the phosphorus source is selected from phosphoric acid; the aluminum source is selected from at least one of pseudo-boehmite, aluminum isopropoxide, and aluminum hydroxide; the silicon source is selected from at least one of tetraethyl orthosilicate, low-sodium silica sol, and silica white.

5. The preparation method of the grafted SAPO molecular sieve S@C according to claim 4, characterized in that, The molar ratio of SiO 2 in the synthesis gel of the SAPO-17 molecular sieve is 0 to 0.6; Preferably, R in the synthesis gel of the SAPO-17 molecular sieve is cyclohexylamine; Preferably, in step S2, the temperature for the hydrothermal crystallization of the synthesis gel of the SAPO-17 molecular sieve and the reaction mixture of the SAPO-14 molecular sieve is 130 - 180 °C; Preferably, the molar ratio of SiO 2 in the synthesis gel of the SAPO-5 molecular sieve is 0 to 0.1; Preferably, in the synthesis gel of the SAPO-5 molecular sieve, R is diethylamine or triethylamine; Preferably, in step S2, the temperature for the hydrothermal crystallization of the synthesis gel of the SAPO-5 molecular sieve and the reaction mixture of the SAPO-14 molecular sieve is 130 - 180 °C.

6. The preparation method of a grafted SAPO molecular sieve S@C according to claim 4, characterized in that, The molar ratio of SiO 2 in the synthesis gel of the SAPO-11 molecular sieve is 0 to 0.6; Preferably, in the synthesis gel of the SAPO-11 molecular sieve, R is di-n-propylamine; Preferably, in step S2, the temperature for the hydrothermal crystallization of the synthesis gel of the SAPO-11 molecular sieve and the reaction mixture of the SAPO-14 molecular sieve is 130 - 180 °C; Preferably, the molar ratio of SiO 2 in the synthesis gel of the SAPO-18 molecular sieve is 0 to 0.5; Preferably, in the synthesis gel of the SAPO-18 molecular sieve, R is N,N-diisopropylethylamine; Preferably, in step S2, the temperature for the hydrothermal crystallization of the synthesis gel of the SAPO-18 molecular sieve and the reaction mixture of the SAPO-14 molecular sieve is 140 - 200 °C; Preferably, the molar ratio of SiO 2 in the synthesis gel of the SAPO-34 molecular sieve is 0.05 to 1.0; Preferably, in the synthesis gel of the SAPO-34 molecular sieve, R is morpholine, diethylamine, triethylamine or tetraethylammonium hydroxide; Preferably, in step S2, the temperature for the hydrothermal crystallization of the synthesis gel of the SAPO-34 molecular sieve and the reaction mixture of the SAPO-14 molecular sieve is 160 - 200 °C.

7. The preparation method of a grafted SAPO molecular sieve S@C according to claim 4, characterized in that, The molar ratio of SiO in the synthesis gel of the SAPO-35 molecular sieve 2 is 0.05 to 1.0; Preferably, in the synthesis gel of the SAPO-35 molecular sieve, R is cyclohexylimine; Preferably, in step S2, the temperature for the hydrothermal crystallization of the synthesis gel of the SAPO-35 molecular sieve and the reaction mixture of the SAPO-14 molecular sieve is 160 - 200 °C; Preferably, the molar ratio of SiO 2 in the synthesis gel of the SAPO-56 molecular sieve is 0.1 to 1.0; Preferably, in the synthesis gel of the SAPO-56 molecular sieve, R is N,N,N',N'-tetramethyl-1,6-hexanediamine; Preferably, in step S2, the temperature for the hydrothermal crystallization of the synthesis gel of the SAPO-56 molecular sieve and the reaction mixture of the SAPO-14 molecular sieve is 160 - 220 °C.

8. The preparation method of a grafted SAPO molecular sieve S@C according to claim 6, characterized in that, The mass ratio of the SAPO molecular sieve S formed by the synthesis gel to the added SAPO-14 molecular sieve C is 1:1 - 50; Preferably, the mass ratio of the SAPO molecular sieve S formed by the synthesis gel to the added SAPO-14 molecular sieve C is 1:2 - 30; Preferably, in step S2, the conditions for the hydrothermal crystallization include: The crystallization temperature is 130 - 220 °C, and the crystallization time is 12 - 120 hours.

9. The use of a grafted SAPO molecular sieve S@C according to any one of claims 1 - 2 as an adsorbent or an acid catalyst.

10. The use according to claim 9, characterized in that, The SAPO molecular sieve S@C is calcined to remove the organic template, the calcination temperature is 400-800 °C, and the calcination time is 2-5 h.

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