Grafted SAPO molecular sieve S@C, and preparation method and application thereof

Abstract

The application discloses a grafted SAPO molecular sieve S@C and a preparation method and application thereof, and belongs to the technical field of chemical materials. The molecular sieve S@C is prepared by taking a phosphosilicate aluminophosphate molecular sieve SAPO-14 with an AFN topological structure as a core C, and grafting a SAPO molecular sieve S on the crystal surface of the SAPO-14; the SAPO molecular sieve S is selected from at least one of SAPO molecular sieves with ERI structure, AEI structure, AFI structure, AEL structure, CHA structure, LEV structure and AFX structure. The above molecular sieve S@C of the application can obviously shorten an induction period in a catalytic MTO reaction process, and can realize efficient conversion of methanol and high selectivity of low-carbon olefins in the initial stage of the reaction, so that it is possible to avoid a pre-accumulation carbon operation in the MTO technology, thereby reducing operation difficulty and reaction cost.

Description

TECHNICAL FIELD

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

[0002] The series of silicoaluminophosphates (SAPO-n) molecular sieves were developed by UCC in 1984 <USP 4,440,871>, which are microporous crystals with infinite open framework composed of three kinds of tetrahedral units: [SiO4] 0 , [AlO4] - and [PO4] + . The Si atom isomorphously substituted for part of P atoms in the neutral aluminophosphate framework structure, resulting in a net negative charge of the framework and introducing B acid centers, thus endowing the SAPO molecular sieve with acid catalytic properties. Among the SAPO molecular sieves, SAPO-34 with CHA topology is the most representative, which can efficiently catalyze the conversion of methanol to light olefins (MTO), and has been successfully applied to the MTO industrial process and realized commercialization. However, the SAPO-34 molecular sieve catalyst has a significant induction period in use. During the induction period, the selectivity of olefins is low, and the selectivity of alkanes is high, and with the increase of reaction time, the selectivity of light olefins gradually increases. In order to improve the control ability of the industrial process to the selectivity of light olefins, researchers have developed catalyst pre-carbon deposition technology to eliminate the reaction induction period (CN201310643077.6, J. Catal. 2019, 377, 153-162), that is, to introduce hydrocarbons with carbon four or more to form part of 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 difficulty of operation.

[0003] Molecular sieves generally have a reaction induction period when catalyzing MTO reaction. Chen et al. found that SAPO-34, SAPO-18 and SAPO-35 series molecular sieves all have a significant induction period when catalyzing methanol conversion, and the induction period shortens with the increase of 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 generation of initial C-C bond, the second stage is the formation and accumulation of hydrocarbon pool, and the last stage is the start of autocatalysis. Different molecular sieve topological structures have differences in spatial confinement, which leads to the formation of different hydrocarbon pool species, and the catalytic activity of these hydrocarbon pool species is also different. When the hydrocarbon pool species accumulate to a certain extent, the autocatalytic cycle is established, and the reaction activity also increases. When the molecular sieve structure is relatively dense, the formed hydrocarbon pool species is small, and the required accumulation amount of hydrocarbon pool 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 MTO reaction is obviously shorter (Chinese J.C. 2022, 43, 2259-2269). This may be due to the fact that the hydrocarbon pool species in the narrow space of SAPO-14 molecular sieve only needs a small accumulation amount to quickly establish the autocatalytic cycle.

[0004] SAPO-14 is a small pore small cage molecular sieve with 8-membered ring channel structure and narrow AFN cage structure. The synthesis of SAPO-14 molecular sieve and its application in methanol to olefins (MTO) have been disclosed in the prior art, and the selectivity of propylene obtained by catalyzing methanol conversion is more than 60% (ACS Catal. 2020, 10, 3714). However, due to the dense structure of SAPO-14 molecular sieve, the diffusion mass transfer is difficult, so the methanol treatment amount is limited, and the catalyst is easily deactivated.

[0005] Therefore, it is attempted to use the above characteristics of SAPO-14 molecular sieve to prepare a new type of molecular sieve catalyst, so as to obtain satisfactory catalytic effect and avoid the induction period of MTO reaction. SUMMARY

[0006] Therefore, the present application provides a grafted SAPO molecular sieve S@C and a preparation method and application thereof, and the main purpose is to solve the technical problem of long induction period of SAPO molecular sieve in catalyzing MTO reaction.

[0007] In one aspect, the present application provides a grafted SAPO molecular sieve S@C, wherein the molecular sieve S@C is a phosphosilicate aluminophosphate molecular sieve SAPO-14 with AFN topological structure as a core C, and a 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 with ERI structure, AEI structure, AFI structure, AEL structure, CHA structure, LEV structure and AFX structure.

[0009] The grafted molecular sieve of the present application is different from the symbiotic molecular sieve and the core-shell molecular sieve in the prior art. It refers to a case where the molecular sieve S with one structure grows on the crystal surface of the molecular sieve C with another structure, and the two crystals have partial interwoven growth, but the S only occupies part of the crystal surface of the original crystal C, and does not fully cover like the core-shell structure. The crystal size of the grafted molecular sieve S is smaller than that of the carrier molecular sieve C in at least one dimension.

[0010] The synthesis gel of the prepared SAPO molecular sieve S is added with a certain amount of SAPO-14 molecular sieve C as a crystal growth carrier, so that other types of SAPO molecular sieves S such as SAPO-34 and SAPO-18 grow along the epitaxy of the SAPO-14 molecular sieve C, thereby generating the 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 grain size of the molecular sieve SAPO-14 is larger than the grain size of the SAPO molecular sieve S.

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

[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] The above-mentioned molecular sieve S@C of the present application can significantly shorten the induction period in the catalytic MTO reaction process, and can realize high-efficiency conversion of methanol and high selectivity of low-carbon olefins in the initial stage of the reaction; and the pre-accumulation of carbon operation in the MTO technology can be omitted, thereby reducing the operation difficulty and the reaction cost.

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

[0017] S1: mixing a phosphorus source, an aluminum source, water, a silicon source and an organic amine template to obtain a synthesis gel of a SAPO molecular sieve S;

[0018] S2: adding SAPO-14 molecular sieve C into the synthetic gel in step S1 and stirring to obtain a reaction mixture; the reaction mixture is heated and crystallized under airtight condition to obtain the target product S@C.

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

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

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

[0022] P2O5: Al2O3: SiO2: H2O: R = 0.7-1.0: 1.0: 0-1.0: 20-100: 1.0-4.0,

[0023] The number of moles of the phosphorus source is in terms of the number of moles of P2O5, the number of moles of the aluminum source is in terms of the number of moles of Al2O3, the number of moles of the silicon source is in terms of the number of moles of SiO2, the number of moles of water is in terms of the number of moles of H2O itself, and the number of moles of the organic amine template is in terms of the number of moles of R.

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

[0025] In addition to the above-mentioned templates, other suitable types of templates selected from the prior art can also be used in the synthetic gel of the present application.

[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; and the silicon source is selected from at least one of tetraethyl orthosilicate, low-sodium silica sol and white carbon black.

[0027] Optionally, the molar ratio of SiO2 in the synthetic gel of the SAPO-17 molecular sieve is 0-0.6.

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

[0029] Preferably, in step S2, the temperature for heating and crystallization of the reaction mixture of the SAPO-5 synthesis gel and the SAPO-14 synthesis gel is 130-180°C.

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

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

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

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

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

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

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

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

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

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

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

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

[0042] Optionally, the molar ratio of SiO2 in the SAPO-35 synthesis gel is 0.05-1.0;

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

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

[0045] Optionally, the molar ratio of SiO2 in the synthesis gel of the SAPO-56 molecular sieve is 0.1-1.0;

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

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

[0048] The synthesis gel formula of the present application 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.

[0049] The formula and synthesis method of the SAPO-17, SAPO-5, SAPO-11, SAPO-18, SAPO-34, SAPO-35 or SAPO-56 molecular sieve and the SAPO-14 molecular sieve selected in the grafting method of the present application are all prior art, and the grafting method of the present application only needs to select a suitable type of molecular sieve S, and according to the specific mass ratio of the molecular sieve S and C, the molecular sieve S is grafted and grown to the surface of the molecular sieve C, i.e. the SAPO-14 crystal; the specific synthesis gel formula of each of the above molecular sieves is prior art.

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

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

[0052] Optionally, the mass ratio of the SAPO molecular sieve S generated by the synthesis gel to the SAPO-14 molecular sieve C added is selected from any value or a range value between any two of 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.

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

[0054] The mass of the SAPO-14 molecular sieve of the present application 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 the synthesis gel to estimate the mass of the synthesized molecular sieve S.

[0055] Optionally, in step S2, the heating and crystallization conditions include:

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

[0057] Optionally, the crystallization temperature is selected from any value or a range value between any two values selected from 130, 140, 150, 160, 170, 180, 190, 200, 210, and 220, in units of ℃.

[0058] Optionally, the crystallization time is selected from any value or a range value between any two values selected from 12, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, and 120, in units 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 the mixture is uniformly stirred at room temperature.

[0060] In a third aspect, the present application provides the use of the above-mentioned grafted SAPO molecular sieve S@C 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 400-800℃, and the calcination time is 2-5h.

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

[0063] In a fourth aspect, the present application provides an acid catalyst, which comprises the above-mentioned grafted SAPO molecular sieve S@C.

[0064] The crystallization process of the present application is carried out under dynamic conditions. Specifically, 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.

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

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

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

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

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

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

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

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

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

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

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

[0076] Figure 9 is a powder X-ray diffraction pattern of Comparative Example 3 of the application;

[0077] Figure 10 is a scanning electron microscope image of Comparative Example 3 of the application, with a scale of 30 μm. DETAILED DESCRIPTION

[0078] The application will be further described below in combination with specific examples. The following description is only a few examples of the application, and does not limit the application in any form. Although the preferred embodiments are disclosed as follows, the application is not limited thereto, and any person skilled in the art can make some changes or modifications to the disclosed technical contents without departing from the scope of the technical solution of the application, and the equivalent embodiments are also included in the scope of the technical solution.

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

[0080] The analysis method in the embodiments of the present application is as follows:

[0081] X-ray powder diffraction phase analysis (XRD) is performed by using an X'Pert PRO X-ray diffractometer of a Netherlands PANalytical company, a Cu target, a Kα radiation source (λ = 0.15418 nm), a voltage of 40 kV, and a current of 40 mA.

[0082] In the embodiments of the present application, the determination of the bulk element composition is performed by using a Magix 2424X ray fluorescence analyzer (XRF) of a Philips company.

[0083] In the embodiments of the present application, the scanning electron microscope (SEM) test is performed by using 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 are uniformly mixed with water, then a certain amount of silicon source and organic amine template agent is added, after fully stirring at room temperature, a certain amount of SAPO-14 molecular sieve is added to the gel and continues to be stirred uniformly; the synthesis of SAPO-14 molecular sieve is referred to the reference ACS Catal.2020, 10, 3714; the reaction mixture is sealed in a hydrothermal synthesis kettle, and is placed in an oven at 140-210°C for 12-120 hours of rotating crystallization; after the reaction, the mixture is separated by centrifugation, washed with deionized water until neutral, and then dried in air at 120°C to obtain the raw powder.

[0086] Examples 2-7

[0087] The difference between the synthesis operation steps of Examples 2-7 and the steps of Example 1 is that the prepared synthesis gel is different target molecular sieve, which leads to the difference in the synthesis formula; the synthesis gel ratio and reaction conditions of each example are shown in Table 1; the XRD spectrum and scanning electron microscope results of some example samples are shown in Figures 1-6 , and the inorganic chemical composition and the evaluation results of the MTO reaction of the catalyst are shown in Table 3.

[0088] Table 1. Gel ratio and synthesis conditions of Examples 1-7 a

[0089]

[0090] a The chemical composition of the input SAPO-14 is: Al 0.5 P 0.48Si 0.02 O2.

[0091] Example 1 involved adding 11.5g of SAPO-14 molecular sieve to a synthetic gel that could produce approximately 2.75g of SAPO-34. Because the SAPO-14 sample exhibited a particularly strong diffraction peak at 2θ9.0 degrees in its XRD pattern, the XRD pattern of the sample obtained in Example 1 was still predominantly SAPO-14. Figure 1 No obvious diffraction peaks of SAPO-34 can be observed.

[0092] The synthesis process of Example 2 is similar to that of Example 1, except that the formulation for synthesizing SAPO-34 gel is replaced with the formulation for synthesizing SAPO-56, and the amount of SAPO-14 added is different. Figure 2 and Figure 3 The XRD pattern and scanning electron microscope (SEM) images of Example 2 are shown. From the XRD pattern and SEM images, it can be seen that some SAPO-5 crystals are grafted onto the large SAPO-14 crystals. This indicates that due to the interference of the SAPO-14 molecular sieve, grafting growth may also lead to the appearance of unexpected crystal phases. Example 2 resulted in the grafting growth of SAPO-56 molecular sieve onto the surface of SAPO-14 crystals, while also grafting some SAPO-5 crystal phases. The crystal morphology of Example 2 is as follows. Figure 3 As shown, very fine SAPO-56 molecular sieves are grown flat on the surface of SAPO-14 crystals, while long hexagonal SAPO-5 crystals are inserted into the crystal sheets of SAPO-14 molecular sieves.

[0093] Examples 3 and 4 follow a similar synthesis process to Example 1, except that the formulation for synthesizing SAPO-34 gel is replaced with the formulation for synthesizing SAPO-18, and the quality of SAPO-14 added is different. Figure 4 and Figure 5 The XRD pattern and scanning electron microscope (SEM) image of Example 3 are shown. In the XRD pattern, the diffraction peaks are essentially the same as those of SAPO-14, and the presence of the SAPO-18 crystalline phase is not visible. However, in the SEM image, many cubic crystals are attached to the surface of the large, flat SAPO-14 molecular sieves, which are considered to be attached SAPO-18 crystalline phases. Because Example 4 incorporated more SAPO-14 molecular sieve, the grains attached to the crystal surface are more sparse, as detailed in [see...]. Figure 6 The inability of ultrasound to peel off these crystals indicates that the crystals were grafted onto the surface of SAPO-14 crystals.

[0094] Comparative Example 1

[0095] Comparative Example 1 was prepared in the same manner as Example 3, except that the amount of SAPO-14 added was less than the amount of SAPO-18 formed.

[0096] Comparative Example 2

[0097] Comparative Example 2 was prepared in the same manner as Comparative Example 1, except that the target molecular sieve was SAPO-14 and a certain amount of SAPO-34 was added to assist crystallization.

[0098] Comparative Example 3

[0099] Comparative Example 3 was prepared in the same manner as Comparative Example 1, except that the target molecular sieve was SAPO-14 and a certain amount of SAPO-18 was added to assist crystallization; the mass ratio of SAPO-14 to SAPO-18 was the same as Example 4. The specific synthesis raw material ratio is shown in Table 2.

[0100] Table 2. Gel ratio and synthesis conditions of Comparative Examples 1-3

[0101]

[0102] Comparative Example 4

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

[0104] Comparative Example 5

[0105] Comparative Example 5 was a sample of SAPO-14 and SAPO-18 raw powder mechanically mixed in a mass ratio of 7:1, which was the same as Example 4.

[0106] Comparative Example 6

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

[0108] Figure 7 and Figure 8 The XRD spectrum and scanning electron microscope photograph of Comparative Example 1 are shown in Figures 1 and 2, respectively. The XRD spectrum of Comparative Example 1 is still dominated by SAPO-14, and a small amount of diffraction peaks belonging to the SAPO-18 crystal phase can also be seen. In the scanning electron microscope picture, there are obvious two phases, showing that SAPO-14 and SAPO-18 are more in a mixed state.

[0109] Figure 9 and Figure 10The XRD pattern and scanning electron microscope (SEM) picture of Comparative Example 3 are shown in the following. From the XRD pattern results, it can be seen that the XRD patterns of the final molecular sieve products are similar, and are basically the same as that of pure phase SAPO-14, regardless of the synthesis method. However, from the scanning electron microscope results, it can be seen that there is a great difference in the crystal morphology. The crystals of Comparative Example 3 present the morphology of SAPO-14 molecular sieve, only with a slight decrease in the crystal particle size. 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 been dissolved, and at the same time, it may have played a role of crystal seed, so that the particle size of SAPO-14 crystal is decreased, and at the same time, the 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 Example 1, 3-4 and Comparative Examples 1-5 are respectively calcined in air at 600°C for 4 hours, then tabletted, and broken to 20-40 mesh molecular sieve particles. 0.3 g of each sample is respectively loaded into a self-made fixed bed reactor as a catalyst for MTO reaction evaluation. Nitrogen is passed at 550°C for 1 hour for activation, and then the temperature is decreased to 400°C for reaction. Methanol is carried by nitrogen, and 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 online gas chromatograph (Agilent A7890), and the results are shown in Table 3 below.

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

[0113]

[0114] a The MTO reaction conditions are 400°C, and the space velocity is 1.0 h -1 , unless otherwise specified. 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 of Comparative Example 1 are: 400°C, and the space velocity is 2.0 h -1 .

[0117] d The MTO reaction conditions of Comparative Example 6 are: 450°C, and the space velocity is 2.0 h -1 .

[0118] Table 3 lists the MTO catalytic reaction results of some examples and comparative examples. MTO reaction is a self-catalytic reaction process, and the product can promote the reaction as a catalyst. In the initial stage of the reaction, when only a small amount of product is generated, the reaction is very slow, which 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 of SAPO-34 catalyzed in comparative example 6, under the conditions of 450℃ and space velocity 2h -1 Under the conditions of 450℃ and space velocity 2h

[0119] The present application finds that when the SAPO-14 molecular sieve crystals are epitaxially grafted with SAPO-34 or SAPO-18 molecular sieves with stronger acidity, the selectivity of ethylene and propylene reaches the highest value at the first TOS (3 min), which is obviously different from the catalytic MTO reaction characteristics of SAPO-34 and SAPO-18. This catalytic characteristic makes it possible to eliminate the pre-carbon 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 it has a long life, but the first methanol conversion rate and diene selectivity are low, and there is an obvious induction period. From comparative examples 2 and 3, it can be seen that when the synthesis gel takes SAPO-14 as the target product, the addition of a small amount of SAPO-34 or SAPO-18 molecular sieve has limited effect on the catalytic ability of the synthesized product, and the catalyst has obvious insufficient ability to catalyze methanol conversion, and the 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 diene selectivity in the initial stage of the reaction, but also has a catalytic life of less than 40 minutes. In comparison, example 4 (SAPO-18@SAPO-14) using the grafting method not only has a great improvement in the ability to catalyze methanol conversion than SAPO-14, but also can improve the problem of long induction period of SAPO-34 and SAPO-18 molecular sieve catalytic MTO reaction.

[0121] The above is only a few examples of the present application, and does not limit the present application in any form. Although the present application discloses the above preferred embodiments, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solution of the present application, which are equivalent to equivalent embodiments, and all belong to the scope of the technical solution.

Claims

1. A grafted SAPO molecular sieve S @ C The preparation method of the [method] is characterized by, The preparation method comprises the following steps: S1: mixing a phosphorus source, an aluminum source, water, a silicon source and an organic amine template to obtain a synthesis gel of SAPO molecular sieve S ; S2: adding SAPO-14 molecular sieve to the synthetic gel in step S1 C and stirring to obtain a reaction mixture; the reaction mixture is heated for crystallization under a closed condition to obtain the target product S@C ; The molecular sieve S C is a silicon aluminum phosphate molecular sieve SAPO-14 with AFN topology as the core C , and SAPO molecular sieve is grafted and grown on the crystal surface of the SAPO-14 S ;​ wherein the SAPO molecular sieve S at least one selected from the group consisting of SAPO molecular sieves having ERI structure, AEI structure, AFI structure, AEL structure, CHA structure, LEV structure, and AFX structure.

2. The production method according to claim 1, characterized by, The SAPO molecular sieve S at least one selected from the group consisting of SAPO-17, SAPO-5, SAPO-11, SAPO-18, SAPO-34, SAPO-35, and SAPO-56.

3. The preparation method according to claim 1, characterized in that, The crystallite size of the molecular sieve SAPO-14 is greater than the crystallite size of the SAPO molecular sieve S .

4. The production method according to claim 1, characterized by, The SAPO molecular sieve S Lay on the surface of the SAPO-14 crystal.

5. The method of claim 1, wherein, The SAPO molecular sieve S less than or equal to the mass of the molecular sieve SAPO-14.

6. The method of claim 1, wherein, In step S1, the formula of the synthesis gel is selected from any one of the formulas suitable for synthesizing molecular sieves with ERI structure, AFI structure, AEL structure, AEI structure, CHA structure, LEV structure or AFX structure.

7. The preparation method according to claim 1, characterized in that, In step S1, the formula of the synthesis gel is selected from any one of the formulas suitable for synthesizing SAPO-17, SAPO-5, SAPO-11, SAPO-18, SAPO-34, SAPO-35 or SAPO-56 molecular sieves.

8. The method of claim 1, wherein, In step S1, the molar ratio of each component of the synthesis gel is: P2O5: Al2O3: SiO2: H2O: R = 0.7-1.0: 1.0: 0-1.0: 20-100: 1.0-4.0; The number of moles of the phosphorus source is in terms of the number of moles of P2O5, the number of moles of the aluminum source is in terms of the number of moles of Al2O3, the number of moles of the silicon source is in terms of the number of moles of SiO2, the number of moles of water is in terms of the number of moles of H2O itself, and the number of moles of the organic amine template is in terms of the number of moles of R.

9. The method of claim 1, wherein, The organic template 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.

10. The method of claim 1, wherein, The phosphorus source is selected from phosphoric acid; the aluminum source is selected from at least one of pseudoboehmite, aluminum isopropoxide and aluminum hydroxide; and the silicon source is selected from at least one of tetraethyl orthosilicate, low-sodium silica sol and white carbon black.

11. The preparation method according to claim 7, characterized in that, The number of moles of SiO2 in the synthesis gel of the SAPO-17 molecular sieve is 0-0.

6.

12. The method of claim 7, wherein, R in the synthesis gel of the SAPO-17 molecular sieve is cyclohexylamine.

13. The preparation method according to claim 7, characterized in that, In step S2, the temperature for heating and crystallization of the reaction mixture of the synthesis gel of the SAPO-17 molecular sieve and the SAPO-14 molecular sieve is 130-180 ℃.

14. The method of claim 7, wherein, The number of moles of SiO2 in the synthesis gel of the SAPO-5 molecular sieve is 0-0.

1.

15. The method of claim 7, wherein the method further comprises, R in the synthesis gel of the SAPO-5 molecular sieve is diethylamine or triethylamine.

16. The method of claim 7, wherein, In step S2, the temperature for heating and crystallization of the reaction mixture of the synthesis gel of the SAPO-5 molecular sieve and the SAPO-14 molecular sieve is 130-180 ℃.

17. The method of claim 7, wherein the method further comprises, The number of moles of SiO2 in the synthesis gel of the SAPO-11 molecular sieve is 0-0.

6.

18. The method of claim 7, wherein, R in the synthesis gel of the SAPO-11 molecular sieve is di-n-propylamine.

19. The method of claim 7, wherein, In step S2, the temperature for heating and crystallization of the reaction mixture of the synthesis gel of the SAPO-11 molecular sieve and the SAPO-14 molecular sieve is 130-180 ℃.

20. The method of claim 7, wherein, The number of moles of SiO2 in the synthesis gel of the SAPO-18 molecular sieve is 0-0.

5.

21. The method of claim 7, wherein, R in the synthesis gel of the SAPO-18 molecular sieve is N, N-diisopropylethylamine.

22. The method of claim 7, wherein, In step S2, the temperature for heating and crystallization of the reaction mixture of the synthesis gel of the SAPO-18 molecular sieve and the SAPO-14 molecular sieve is 140-200 ℃.

23. The method of claim 7, wherein the method further comprises, The molar ratio of SiO2 in the synthesis gel of the SAPO-34 molecular sieve is 0.05-1.

0.

24. The method of claim 7, wherein, R in the synthesis gel of the SAPO-34 molecular sieve is morpholine, diethylamine, triethylamine or tetraethylammonium hydroxide.

25. The method of claim 7, wherein, In step S2, the temperature for heating and crystallization of the reaction mixture of the synthesis gel of the SAPO-34 molecular sieve and the SAPO-14 molecular sieve is 160-200℃.

26. The method of claim 7, wherein, The molar ratio of SiO2 in the synthesis gel of the SAPO-35 molecular sieve is 0.05-1.

0.

27. The method of claim 7, wherein, R in the synthesis gel of the SAPO-35 molecular sieve is cyclohexyl imine.

28. The method of claim 7, wherein, In step S2, the temperature for heating and crystallization of the reaction mixture of the synthesis gel of the SAPO-35 molecular sieve and the SAPO-14 molecular sieve is 160-200℃.

29. The method of claim 7, wherein the method further comprises, The molar ratio of SiO2 in the synthesis gel of the SAPO-56 molecular sieve is 0.1-1.

0.

30. The method of claim 7, wherein, R in the synthesis gel of the SAPO-56 molecular sieve is N,N,N',N'-tetramethyl 1,6 hexanediamine.

31. The method of claim 7, wherein, In step S2, the temperature for heating and crystallization of the reaction mixture of the synthesis gel of the SAPO-56 molecular sieve and the SAPO-14 molecular sieve is 160-220℃.

32. The method of claim 17, wherein the method is carried out at a temperature of about 20°C to about 30°C. The synthetic gel produces a SAPO molecular sieve S with the SAPO-14 molecular sieve added C in a mass ratio of 1:1~50.

33. The method of claim 17, wherein the method is carried out at a temperature of about 20°C to about 30°C. The synthetic gel produces a SAPO molecular sieve S with the SAPO-14 molecular sieve added C in a mass ratio of 1:2~30.

34. The method of claim 17, wherein the method is carried out at a temperature of about 20°C to about 30°C. In step S2, the conditions for heating and crystallization include: The crystallization temperature is 130-220℃, and the crystallization time is 12-120 hours.

35. A SAPO molecular sieve prepared by the method of any one of claims 1 to 34. S C for use as an adsorbent or acid catalyst.​ 36. The use according to claim 35, wherein The SAPO molecular sieve S C calcination to remove the organic template, the calcination being at a temperature of 400 to 800°C for a time of 2 to 5 h.​

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