Flaky self-assembly prismatic table type SAPO-5 / SAPO-34 composite molecular sieve as well as preparation and application thereof

Abstract

The invention relates to a flaky self-assembly prismatic table type SAPO-5 / SAPO-34 composite molecular sieve and preparation and application thereof. A preparation method mainly comprises the following steps: (1) mixing a phosphorus source, an aluminum source, polyethylene glycol and deionized water, and heating and stirring to obtain an emulsion synthetic solution A; (2) adding a silicon source and a tetraethylammonium hydroxide solution into the emulsion synthetic solution A, and continuously heating and stirring to obtain a synthetic solution B; and (3) transferring the synthetic liquid B into a high-pressure reaction kettle, carrying out hydrothermal crystallization, and then filtering, washing, drying, roasting and cooling the obtained solid product to obtain the sheet-shaped self-assembled prismatic table type SAPO-5 / SAPO-34 composite molecular sieve. The prepared prismatic table type SAPO-5 / SAPO-34 composite molecular sieve is formed by assembling and stacking 200-500nm nanosheets, and the special morphology and composite pore structure of the prismatic table type SAPO-5 / SAPO-34 composite molecular sieve can greatly improve the diffusion rate of reactants and products and show excellent catalytic performance in the catalytic reaction process of preparing olefin from dimethyl ether.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieve materials, and particularly relates to a flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve and its preparation and application. Background Art

[0002] Molecular sieves have a regular pore structure and are shape-selective for reactants and products, so they are widely used as catalysts in the petrochemical field. Compared with molecular sieves with a single topological structure, composite molecular sieves have two or more topological pore structures and have a synergistic effect during the catalytic process, becoming a research hotspot in the field. For example, the SAPO-34 molecular sieve with a CHA topological structure exhibits excellent catalytic performance in the reaction of methanol and dimethyl ether to olefins. However, due to its eight-membered ring pore structure, it will hinder mass transfer during the catalytic reaction process, resulting in a lower catalyst life. The SAPO-5 molecular sieve with an AFI topological structure has a larger twelve-membered ring pore structure. If a molecular sieve with a composite structure of SAPO-5 and SAPO-34 is prepared, a molecular sieve with a composite pore structure can be obtained, which may have a synergistic effect during the catalytic reaction process, enhance mass transfer, and thus extend the catalyst life. In addition, compared with the typical cubic morphology structure of SAPO-34 molecular sieves, the flaky structure can shorten the diffusion path of reactants and products, inhibit the formation of carbon deposition, and thus extend the catalyst life.

[0003] Patent 201710887437.5 discloses a preparation method of a SAPO-34 / SAPO-5 composite molecular sieve. This patent requires two hydrothermal crystallization processes, and a first template agent and a second template agent are added separately during the two crystallizations. Its preparation method is complex, and the prepared composite molecular sieve still has a cubic morphology.

[0004] Patent 201510404936.5 discloses a synthesis method of flaky SAPO-34 molecular sieves. This patent first uses a template agent such as diethylamine, triethylamine, morpholine, piperidine, n-propylamine, or isopropylamine for the first crystallization of the molecular sieve; then, after secondary introduction of a morphology regulator such as tetraethylammonium chloride, it is crystallized again to synthesize flaky SAPO-34 molecular sieves. The molecular sieves prepared by this patent have a flaky morphology, but they are single-phase SAPO-34 molecular sieves and require two crystallizations and two template agents.

[0005] In summary, the synthesis process of composite molecular sieves is complex, usually requiring multiple template agents and multiple crystallizations. In addition, larger-sized molecular sieves will increase the diffusion length and resistance, which is not conducive to mass transfer during the catalytic reaction process. Therefore, developing a composite molecular sieve with a simple preparation process and a short diffusion path can effectively solve the above problems. Summary of the Invention

[0006] The object of the present invention is to provide a sheet-like self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve and its preparation method to solve the problems existing in the prior art.

[0007] In order to achieve the above object, the present invention provides a method for synthesizing a sheet-like self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve, and the specific synthesis steps are as follows: (1) Mix an aluminum source, a phosphorus source, polyethylene glycol and deionized water, and heat and stir to obtain an emulsion synthesis solution A; (2) Add a silicon source and a tetraethylammonium hydroxide solution to the emulsion synthesis solution A, and continue to heat and stir to obtain a synthesis solution B; (3) Transfer the synthesis solution B to a high-pressure reaction kettle, filter, wash, dry, calcine and cool the obtained solid product after hydrothermal crystallization to obtain a sheet-like self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve.

[0008] Preferably, the heating temperature in the steps (1) and (2) is 30-50 °C, and the stirring time is 1-8 h.

[0009] Preferably, the molar ratio of each raw material in the synthesis solution B is Al2O3: P2O5: PEG: H2O: SiO2: TEAOH = 1: (1.6-2.0): (0.001-0.04): (30-80): (0.4-0.7): (1.8-2.5).

[0010] The aluminum source, phosphorus source, and silicon source are calculated as Al2O3, P2O5, and SiO2 respectively.

[0011] Preferably, the aluminum source is one of aluminum isopropoxide or pseudo-boehmite; the phosphorus source is phosphoric acid with a mass content of 85 wt%; the silicon source is one of tetraethyl orthosilicate or silica sol.

[0012] Preferably, the polyethylene glycol has a weight-average molecular weight of 10,000-20,000; the tetraethylammonium hydroxide solution is an aqueous solution with a mass content of 25 wt%.

[0013] Preferably, in the step (3), the crystallization temperature is 180-200 °C; the crystallization time is 18-72 h; the drying condition is drying at 80 °C for 8-12 h; the calcination condition is calcination at 500-600 °C for 4-8 h.

[0014] A sheet-like self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve prepared according to the above preparation method, which is assembled and stacked by 200-500 nm nanosheets, and its crystal size is 1-4 μm.

[0015] The function of the above-mentioned flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve is mainly used as a catalyst in the reaction process of converting dimethyl ether to olefins.

[0016] Compared with the prior art, in the present invention, by increasing the proportion of phosphoric acid in the raw materials, part of the phosphoric acid interacts with polyethylene glycol (PEG), and part of the phosphoric acid is free in the solution. During the crystallization process, due to the two different chemical microenvironments of phosphoric acid, a SAPO-5 / SAPO-34 composite molecular sieve with two topological structures of AFI and CHA is synthesized; at the same time, under the induction of tetraethylammonium hydroxide template agent and polyethylene glycol, a flaky self-assembled truncated pyramid morphology is formed. The prepared molecular sieve not only has the pore sizes of two topological structures, but also has a flaky morphology, which is beneficial to improving the mass transfer in the reaction process of converting dimethyl ether to olefins, reducing the carbon deposition rate, and thus enhancing the catalyst life. In addition, the composite molecular sieve has a special morphological structure, which also provides a reference for the synthesis of other materials with special morphological structures. Description of the Drawings

[0017] Figure 1 It is the X-ray powder diffraction pattern of the flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve obtained in Example 1.

[0018] Figure 2 It is the SEM image of the flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve obtained in Example 1.

[0019] Figure 3 It is the SEM image of the flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve obtained in Example 2.

[0020] Figure 4 It is the X-ray powder diffraction pattern of the SAPO-34 molecular sieve obtained in Comparative Example 1.

[0021] Figure 5 It is the SEM image of the SAPO-34 molecular sieve obtained in Comparative Example 1. Detailed Embodiments

[0022] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings.

[0023] Example 1 Take 2.04 g of aluminum isopropoxide, 1.107 ml of phosphoric acid solution and 2 g of polyethylene glycol 20000 in a beaker, and then add 3.6 ml of deionized water to the beaker. Stir at a constant temperature of 35 °C for 3 h to obtain an emulsion synthesis solution A; then sequentially add 0.564 ml of tetraethyl orthosilicate and 5.66 ml of tetraethylammonium hydroxide solution to the emulsion synthesis solution A, and continue to stir at a constant temperature of 35 °C for 4 h to obtain a synthesis solution B; transfer the synthesis solution B into a high-pressure reaction kettle with a polytetrafluoroethylene liner. After the transfer is completed, move the reaction kettle into an oven and crystallize at 190 °C for 48 h. After crystallization, cool to room temperature, and then filter and wash the sample; collect the sample and dry it in a blast drying oven at 80 °C for 12 h; put the obtained dry sample into a muffle furnace and calcine it at 550 °C for 5 h, and then cool to room temperature to obtain flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve. Figure 1 It is the X-ray powder diffraction pattern of the synthesized flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve sample, showing the characteristic diffraction peaks of the SAPO-5 / SAPO-34 composite molecular sieve with typical AFI and CHA topological structures. The diffraction peak intensity indicates that the sample has a high crystallinity. Figure 2 It is the SEM image of the synthesized flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve. According to the SEM image, it can be seen that the prepared sample shows a truncated pyramid morphology self-assembled by nanosheets with a size of 200 - 500 nm, and its crystal size is 1 - 2 μm.

[0024] Example 2 Take 2.04 g of aluminum isopropoxide, 1.112 ml of phosphoric acid solution and 2 g of polyethylene glycol 20000 in a beaker, and then add 3.6 ml of deionized water to the beaker. Stir at a constant temperature of 35 °C for 3 h to obtain an emulsion synthesis solution A; then sequentially add 0.564 ml of tetraethyl orthosilicate and 5.66 ml of tetraethylammonium hydroxide solution to the emulsion synthesis solution A, and continue to stir at a constant temperature of 35 °C for 4 h to obtain a synthesis solution B; transfer the synthesis solution B into a high-pressure reaction kettle with a polytetrafluoroethylene liner. After the transfer is completed, move the reaction kettle into an oven and crystallize at 190 °C for 48 h. After crystallization, cool to room temperature, and then filter and wash the sample; collect the sample and dry it in a blast drying oven at 80 °C for 12 h; put the obtained dry sample into a muffle furnace and calcine it at 550 °C for 5 h, and then cool to room temperature to obtain flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve. Figure 3 It is the SEM image of the synthesized flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve. According to the SEM image, it can be seen that the prepared sample also shows a flaky self-assembled truncated pyramid-shaped morphology structure, and its crystal size is 1 - 4 μm.

[0025] Example 3 The steps in this example are exactly the same as those in Example 1. The difference is that during the preparation of the opalescent synthesis liquid A, the added aluminum isopropoxide is changed from 2.04 g to 2.0 g. The prepared sample is analyzed as a flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve.

[0026] Example 4 The steps in this example are exactly the same as those in Example 1. The difference is that during the preparation of the synthesis liquid B, the added tetraethyl orthosilicate is changed from 0.564 ml to 0.577 ml. The prepared sample is analyzed as a flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve.

[0027] Example 5 The steps in this example are exactly the same as those in Example 1. The difference is that during the crystallization process, the crystallization at 190 °C for 48 h is changed to crystallization at 180 °C for 48 h. The prepared sample is analyzed as a flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve.

[0028] Comparative Example 1 The steps in this example are exactly the same as those in Example 1. The difference is that during the preparation of the opalescent synthesis liquid A, polyethylene glycol 20000 is not added. A molecular sieve with a composite structure cannot be prepared. The prepared sample is analyzed by XRD and shows the characteristic diffraction peaks of pure-phase SAPO-34 molecular sieve as Figure 4 shown; the morphology of the prepared sample is a nano-flaky morphology of 400 - 800 nm as Figure 5 shown.

[0029] Comparative Example 2 The steps in this example are exactly the same as those in Example 1. The difference is that during the preparation of the opalescent synthesis liquid A, the added phosphoric acid is changed from 1.107 ml to 0.738 ml. A molecular sieve with a composite structure cannot be prepared. The prepared sample is a pure-phase SAPO-34 molecular sieve.

[0030] Comparative Example 3 The steps in this example are exactly the same as those in Example 1. The difference is that during the preparation of the synthesis liquid B, tetraethylammonium hydroxide is not added. At this time, no molecular sieve sample can be prepared.

[0031] Test Example The molecular sieve catalysts prepared in Examples 1 - 3 and Comparative Example 1 were tested for the catalytic performance of dimethyl ether to olefins. The catalyst was first pressed and sieved into 30 - 60 mesh. Take 0.3 g of the catalyst and load it into a fixed-bed reactor. Activate it with nitrogen at 420 °C for 1 h, and then conduct a catalytic reaction test at 400 °C. The dimethyl ether injection space velocity is 3.0 h-1 The reaction products were analyzed by on-line gas chromatography, and the test results of the catalytic performance of the catalyst are shown in Table 1.

[0032] Table 1 Test results of the catalytic performance of the truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve and SAPO-34 molecular sieve of the present invention

[0033] # The test results were for the samples taken at 90 min of the reaction.

[0034] As can be seen from Table 1, compared with the traditional SAPO-34 molecular sieve, the truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve prepared by the method of the present invention exhibits higher ethylene and propylene selectivities and a longer catalyst life.

[0035] As described above, the present invention has been described in detail with specific implementation steps and experiments, which can only be used as an illustration of the present invention and cannot limit the present invention. Therefore, modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection of the present invention.

Claims

1. A preparation method of a flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve, characterized in that, It includes the following steps: (1) Mix an aluminum source, a phosphorus source, polyethylene glycol, and deionized water, and heat and stir to obtain an opalescent synthesis solution A; (2) Add a silicon source and a tetraethylammonium hydroxide solution to the opalescent synthesis solution A, and continue to heat and stir to obtain a synthesis solution B; (3) Transfer the synthesis solution B to a high-pressure reactor, filter, wash, dry, calcine, and cool the obtained solid product after hydrothermal crystallization to obtain a flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve.

2. The preparation method according to claim 1, characterized in that, The heating temperature in steps (1) and (2) is 30-50 °C, and the stirring time is 1-8 h.

3. The preparation method according to claim 1, characterized in that, The aluminum source is one of aluminum isopropoxide or pseudo-boehmite; the phosphorus source is phosphoric acid with a mass content of 85 wt%; the silicon source is one of tetraethyl orthosilicate or silica sol.

4. The preparation method according to claim 1, characterized in that, The molar ratio of each raw material in the synthesis solution B is Al2O3:P2O5:PEG:H2O:SiO2:TEAOH = 1:(1.6~2.0):(0.001~0.04):(30~80):(0.4~0.7):(1.8~2.5).

5. The preparation method according to claim 1, characterized in that, The weight-average molecular weight of the polyethylene glycol is 10000~20000; the tetraethylammonium hydroxide solution is an aqueous solution with a mass content of 20-25 wt%.

6. The preparation method according to claim 1, wherein The crystallization temperature in step (3) is 180~200 °C; the crystallization time is 18~72 h; the drying condition is drying at 80 °C for 8~12 h.

7. The preparation method according to claim 1, wherein The calcination condition in step (3) is calcination at 500-600 °C for 4~8 h.

8. A flaky self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve obtained by the preparation method according to any one of claims 1-7, and the SAPO-5 / SAPO-34 composite molecular sieve has two topological structures of AFI and CHA.

9. Use of the sheet-like self-assembled truncated pyramid-shaped SAPO-5 / SAPO-34 composite molecular sieve according to claim 8, characterized in that, Application as a catalyst in the catalytic reaction of dimethyl ether to olefins.

10. The application according to claim 9, wherein The reaction conditions are preferably as follows: the reaction temperature is 350 to 500 °C, and the space velocity of dimethyl ether injection is 1 to 6 h -1 .

Images