Preparation method of SAPO-34 molecular sieve, SAPO-34 molecular sieve and application thereof

Abstract

The present application discloses a preparation method of SAPO-34 molecular sieve, the SAPO-34 molecular sieve and its application. It at least includes the following steps: (1) Mix a raw material containing fiber and phosphoric acid with water, and carry out Reaction I to obtain a solution containing nanocellulose; (2) Mix a raw material containing an aluminum source, a silicon source and a template agent with the solution containing nanocellulose, and carry out Reaction II to obtain the SAPO-34 molecular sieve. The SAPO-34 molecular sieve prepared in the present application has a nanoscale crystal grain size and an easily adjustable chemical composition; the SAPO-34 molecular sieve synthesized in the present application can be used as a catalyst for acid-catalyzed reactions.

Description

Technical Field

[0001] The present application relates to a preparation method of SAPO-34 molecular sieve, SAPO-34 molecular sieve and its application, belonging to the field of molecular sieves. Background Art

[0002] Silicoaluminophosphate molecular sieve (SAPO-n) is an important class of inorganic porous crystalline materials, whose three-dimensional framework structure is composed of PO2 + , AlO2 - and SiO2 tetrahedrons, and is mainly prepared by hydrothermal synthesis method, usually using phosphoric acid as the phosphorus source for constructing the molecular sieve framework. Among them, SAPO-34 molecular sieve with CHA topological structure has been successfully applied to the commercial process of methanol to olefins reaction (MTO) due to its excellent catalytic performance in MTO reaction. However, the narrow micropore channels of SAPO-34 limit the mass transfer efficiency, resulting in low utilization rate of active sites of SAPO-34 catalyst, and easy occurrence of pore blockage and carbon deposition deactivation. To solve this problem, people have tried to synthesize nano-sized molecular sieves or introduce hierarchical pores into the molecular sieve crystals to reduce the mass transfer resistance in the reaction, enhance the diffusion performance of molecules during the reaction, improve the reaction performance of the catalyst and prolong the catalytic life.

[0003] Hydrothermal synthesis of nano-sized or hierarchical pore molecular sieves usually requires the use of compounds with strong interaction with the molecular sieve framework to adsorb on the surface of crystal nuclei to inhibit crystal growth, or as a template to occupy the spatial structure to guide the formation of hierarchical pores. Among them, cellulose, as a cheap natural macromolecular polysaccharide with rich hydroxyl structure, can interact with the SAPO molecular sieve framework through electron coupling, and can regulate the crystallization process of SAPO molecular sieve and improve the morphology of molecular sieve. Liaoning University of Petroleum & Chemical Technology introduced a method for preparing hierarchical pore SAPO-11 molecular sieve using sisal cellulose as a template (CN 106430238A; Journal of the Chinese Ceramic Society. 2018, 46(1): 108-115.). Nankai University introduced a method for preparing hierarchical pore MTT molecular sieve using microcrystalline cellulose as a template (CN 109133090). The size of cellulose acting as a template in the above reports is in the order of micrometers or even millimeters, which is similar to the order of magnitude of the molecular sieve crystal grain size. Therefore, its ability to introduce mesopores into the molecular sieve crystal or guide nano-sized molecular sieves is limited.

[0004] On the other hand, acid treatment is a mature method for effectively hydrolyzing the amorphous region and partial crystalline region structures of natural cellulose to obtain nanoscale cellulose. For example, Tianjin University of Science and Technology reported the preparation of nanocellulose whiskers and fibrils by acid hydrolysis using a mixture of oxalic acid and sulfuric acid (CN 109879973). Shaanxi University of Science and Technology reported the preparation of nanocrystalline cellulose with a size less than 120 nm using hydrochloric acid or sulfuric acid under pressure conditions (CN109438580A). Summary of the Invention

[0005] In this application, for the first time, the process of preparing nanocellulose by acid hydrolysis of microcrystalline cellulose is combined with the crystallization synthesis process of SAPO molecular sieve to obtain nanoscale SAPO-34 molecular sieve. The nanoscale SAPO-34 molecular sieve has small crystal grain size and can be used in the methanol-to-olefins reaction and the cycloaddition reaction of carbon dioxide, showing excellent activity, good selectivity and long catalytic life.

[0006] According to one aspect of this application, a method for preparing SAPO-34 molecular sieve is provided, which at least includes the following steps:

[0007] (1) Mix the raw materials containing fiber and phosphoric acid with water, carry out Reaction I, and obtain a solution containing nanocellulose;

[0008] (2) Mix the raw materials containing aluminum source, silicon source and template agent with the solution containing nanocellulose, carry out Reaction II, and obtain the SAPO-34 molecular sieve;

[0009] The SAPO-34 molecular sieve is a nanoscale cubic crystal with a particle size of 20 - 800 nm.

[0010] The fiber in (1) is selected from at least one of bamboo fiber, wood pulp fiber, sisal fiber, cotton fiber, linen fiber, coconut fiber, ramie fiber or jute fiber;

[0011] The mass ratio of the fiber, phosphoric acid and water is 0.2 - 5:2 - 40:5 - 200;

[0012] The size of the fiber is in the micron scale.

[0013] In (1), Reaction I includes heating to 70 - 170 °C at a heating rate of 0.2 - 10 °C / min and keeping it at a constant temperature for 0.4 - 3 days, and then cooling to 25 - 30 °C.

[0014] Reaction I also includes an oscillation dispersion process.

[0015] In (2), the aluminum source is selected from at least one of activated alumina, alkoxyaluminum, and metakaolin;

[0016] The silicon source is selected from at least one of organic silicon source or inorganic silicon source;

[0017] The organosilicon source is selected from orthosilicates;

[0018] The inorganic silicon source is selected from at least one of silica sol, reactive silica, metakaolin, or white carbon black;

[0019] The template agent is selected from at least one of diethylamine, triethylamine, tetrapropylammonium hydroxide, morpholine, di-n-propylamine, diisopropylamine, pyridine, or piperazine;

[0020] The molar ratio of the silicon source, phosphoric acid, aluminum source, template agent, and water is 0.2 - 1.2:0.5 - 1.5:0.6 - 1.4:1.5 - 5.5:50 - 200;

[0021] The molar amount of the silicon source is calculated based on the molar amount of SiO2;

[0022] The molar amount of the phosphoric acid is calculated based on the molar amount of P2O5;

[0023] The molar amount of the aluminum source is calculated based on the molar amount of Al2O3.

[0024] Reaction II includes an aging process and a crystallization process.

[0025] The aging process includes heating to 50 - 80°C at a heating rate of 0.2 - 2.0°C / min and maintaining the temperature for 0.2 - 2 days;

[0026] Optionally, the heating rate of the aging process is 1°C / min;

[0027] Optionally, the holding time of the aging process is 0.4 - 1.5 days.

[0028] The crystallization process is static crystallization;

[0029] The temperature of the crystallization process is 150 - 220°C;

[0030] Optionally, the temperature of the crystallization process is 170 - 200°C;

[0031] The time of the crystallization process is 0.5 - 10 days;

[0032] Optionally, the time of the crystallization process is 1 - 3 days.

[0033] After the crystallization process, separation, washing, and drying are also included.

[0034] Reaction I and Reaction II are carried out in a closed reactor.

[0035] Stirring is required during the mixing process, and the stirring is achieved by using a rotating stirring paddle or directly rotating the reaction kettle.

[0036] According to another aspect of the present application, an acid catalyst is provided, which is obtained by calcining the SAPO-34 molecular sieve prepared by the above preparation method in air at 400-700 °C;

[0037] The acid catalyst has a CHA crystal phase, and the crystal grain size is 20 nm to 800 nm;

[0038] Optionally, the crystal grain size of the acid catalyst is 100 nm to 150 nm;

[0039] The acid catalyst has a hierarchical pore structure, including micropores and mesopores; the specific surface area of the mesopores is 50-200 m 2 / g;

[0040] Optionally, the specific surface area of the mesopores is 90-120 m 2 / g;

[0041] Optionally, the specific surface area ratio of the micropores to the mesopores is 4-7.

[0042] According to another aspect of the present application, a catalyst for the conversion of oxygenates to olefins is provided, including the above acid catalyst.

[0043] According to another aspect of the present application, a catalyst for the reaction of carbon dioxide to cyclic carbonate is provided, including the above acid catalyst.

[0044] The beneficial effects that the present application can produce include:

[0045] (1) A novel additive for preparing SAPO-34 molecular sieve is proposed in the present application;

[0046] (2) The SAPO-34 molecular sieve prepared in the present application has a nanoscale crystal grain size and an easily adjustable chemical composition;

[0047] (3) The present application uses cheap natural cellulose as a template, and at the same time, the phosphoric acid obtained by hydrolyzing cellulose enters the molecular sieve framework as a raw material, avoiding the generation of waste acid;

[0048] (4) In the present application, the nanocellulose obtained after phosphoric acid treatment is combined with a specific crystallization method to obtain nanoscale SAPO-34 crystal grains, avoiding defects such as using additional expensive additives and generating waste acid, and having strong application prospects in industry. Description of the Drawings

[0049] Figure 1 It is a scanning electron microscope photograph of the sample obtained in Example 1 (the scale bar in the figure is 2.0 μm).

[0050] Figure 2Scanning electron microscope photograph of the sample obtained in Comparative Example 1 (the scale bar in the figure is 5.0 μm).

[0051] Figure 3 Scanning electron microscope photograph of the sample obtained in Comparative Example 2 (the scale bar in the figure is 5.0 μm).

[0052] Figure 4 XRD diffraction pattern of the sample obtained in Example 1. Detailed implementation manners

[0053] The present application will be described in detail below with reference to the examples, but the present application is not limited to these examples.

[0054] Unless otherwise specified, the raw materials in the examples of the present application are all purchased through commercial channels.

[0055] The analysis methods in the examples of the present application are as follows:

[0056] The elemental composition was determined by a Magix-601 type X-ray fluorescence analyzer (XRF) from Philips.

[0057] The X-ray powder diffraction phase analysis (XRD) was performed using an X'Pert PRO X-ray diffractometer from PANalytical in the Netherlands, with a Cu target, a Kα radiation source (λ = 0.15418 nm), a voltage of 40 KV, and a current of 40 mA.

[0058] The SEM morphology analysis was performed using an SU8020 type scanning electron microscope from the Scientific Instrument Factory of the Chinese Academy of Sciences.

[0059] The N2 physical adsorption analysis was determined using a Micromeritics ASAP 2020 Plus type physical adsorption analyzer from Micromeritics in the United States.

[0060] The calculation of the MTO reaction conversion rate and selectivity in the examples of the present application is as follows:

[0061]

[0062] Formula for calculating ethylene selectivity: X 乙烯 =(2 * number of moles of ethylene) / (number of moles of methanol in the feed - number of moles of methanol in the product).

[0063] Formula for calculating propylene selectivity: X 丙烯 =(3 * number of moles of propylene) / (number of moles of methanol in the feed - number of moles of methanol in the product).

[0064] Wherein, X 甲醇 is the conversion rate of methanol; X 乙烯 is the selectivity of ethylene; X 丙烯 is the selectivity of propylene.

[0065] In the embodiments of the present application, the conversion rate of the carbon dioxide cycloaddition reaction is calculated as follows:

[0066]

[0067] The calculation formula for the yield of epichlorohydrin carbonate:

[0068]

[0069] Wherein, X 环氧氯丙烯 is the conversion rate of epichlorohydrin; X 碳酸环氯丙烯酯 is the yield of epichlorohydrin carbonate.

[0070] Example 1

[0071] The proportioning ratios of each raw material, the crystallization conditions and the elemental composition of the sample are shown in Table 1. The specific proportioning process is as follows:

[0072] 34.6 g of phosphoric acid (mass percentage of H3PO4 is 85%), 60 g of deionized water, and 16 g of cotton fiber are mixed and placed in a stainless steel autoclave with a polytetrafluoroethylene liner. The autoclave is heated with a programmed temperature increase to 70°C and rotated for 24 h. The product is cooled to room temperature and shaken for dispersion. The length of the cotton fiber is 50 - 200 μm, and the diameter is 10 - 20 μm.

[0073] The above-mentioned phosphoric acid aqueous solution containing cellulose, 16.8 g of pseudo-boehmite (mass percentage of Al2O3 is 72.5%), 10.4 g of tetraethyl orthosilicate, 36.4 g of triethylamine, and 75.2 g of deionized water are mixed and aged for 12 hours. The gel is transferred to a stainless steel autoclave. The molar ratio of each component in the synthesis system is 0.6SiO2:1.5P2O5:1.2Al2O3:3.6 triethylamine:80H2O.

[0074] The autoclave containing the materials is placed in an oven and heated with a programmed temperature increase of 1°C / min to 60°C, and stirred and aged for 24 h.

[0075] The autoclave is heated with a programmed temperature increase to 200°C for dynamic crystallization for 48 h. After the reaction is completed, the solid product is centrifuged, washed repeatedly with deionized water, and dried in air at 120°C to obtain the SAPO-34 molecular sieve sample.

[0076] The morphology of the obtained sample is characterized by scanning electron microscopy, and the electron micrograph is as Figure 1 shown. The obtained sample is cubic crystals with a particle size distribution between 150 nm and 400 nm. The obtained sample is analyzed by XRD, and the results are shown in Table 2 and Figure 4 , and the results show that the synthesized product has the SAPO-34 crystal phase.

[0077] The obtained samples were analyzed for elemental composition by XRF, and the results are shown in Table 1.

[0078] Examples 2 to 12

[0079] The specific ingredient ratios and crystallization conditions are shown in Table 1, and the specific ingredient process is the same as that in Example 1.

[0080] The obtained samples of Examples 2 to 12 were analyzed by XRD. The data results were close to those in Table 2, that is, the peak positions and shapes were the same, and the relative peak intensities fluctuated within ±10% with the change of synthesis conditions, indicating that the synthesized products had the characteristics of the SAPO-34 structure.

[0081] The obtained samples of Examples 2 to 12 were analyzed for XRF elemental composition, and the results are shown in Table 1.

[0082] The morphologies of the obtained samples of Examples 2 to 12 were analyzed by scanning electron microscopy, and all the obtained electron micrographs were Figure 1 similar.

[0083] Table 1 Molecular sieve synthesis ingredient, crystallization conditions and elemental composition table

[0084]

[0085] Table 2 XRD results of the sample of Example 1

[0086]

[0087]

[0088] Comparative Example 1

[0089] The ingredient ratio and crystallization process were the same as those in Example 1, but the cellulose acid treatment process was cancelled, and the microcrystalline bamboo fiber was directly mixed with phosphoric acid, tetraethyl orthosilicate, pseudo-boehmite, triethylamine and deionized water to prepare a synthetic gel.

[0090] The morphology of the obtained sample was characterized by scanning electron microscopy, and the electron micrograph was as Figure 2 shown, which was large cubic grains with a smooth surface and a particle size of about 3 μm.

[0091] Comparative Example 2

[0092] The ingredient ratio and crystallization process were the same as those in Example 1, but cellulose was not used, and phosphoric acid, tetraethyl orthosilicate, pseudo-boehmite, triethylamine and deionized water were mixed to prepare a synthetic gel.

[0093] The morphology of the obtained sample was characterized by scanning electron microscopy, and the electron micrograph was as Figure 3 shown, which was large cubic grains with a smooth surface and a particle size of about 2 - 5 μm.

[0094] Example 13

[0095] The samples obtained in Examples 1-2 and Comparative Examples 1-2 were calcined in air at 600 °C for 4 hours, and then subjected to N2 physical adsorption analysis. The results are shown in Table 3. The samples obtained in Examples 1-2 had a large micropore volume and micropore specific surface area, indicating that the samples had good crystallinity and had a rich external specific surface area and mesopore volume.

[0096] Table 3 Specific surface area and pore volume of the samples

[0097]

[0098] Example 14

[0099] The samples obtained in Examples 1-2 and Comparative Examples 1-2 were calcined in air at 600 °C for 4 hours, and then tableted and crushed to 40-60 mesh. 0.3 g of the sample was weighed and loaded into a fixed-bed reactor for MTO reaction evaluation. It was activated with nitrogen at 550 °C for 1 hour, and then cooled to 450 °C for reaction. Methanol was carried by nitrogen, and the nitrogen flow rate was 42 mL / min, and the methanol mass space velocity was 4 h -1 . The reaction products were analyzed by on-line gas chromatography (Varian 3800, FID detector, capillary column PoraPLOTQ-HT). The results are shown in Table 4. Compared with Comparative Examples 1-2 with larger crystal grains, the small crystal grain samples of Examples 1-2 showed good catalytic life and excellent light olefin selectivity.

[0100] Table 4 Results of methanol conversion to olefins reaction of the samples

[0101]

[0102] a. Reaction time when methanol conversion rate is 100%

[0103] b. Highest (ethylene + propylene) selectivity at 100% methanol conversion

[0104] Example 15

[0105] The samples obtained in Examples 1-2 and Comparative Examples 1-2 were calcined in air at 600 °C for 4 hours, then pressed and crushed to 40-60 mesh. 0.02 g of the sample was weighed and placed into a 25 mL high-pressure reactor for the evaluation of the cycloaddition reaction of carbon dioxide. 2 mL of epichlorohydrin was added into the reactor, and carbon dioxide was charged to 1.2 MPa, then the temperature was raised to 120 °C for reaction for 4 h. After cooling to room temperature, the reaction product was analyzed by gas chromatography (Varian 3800, FID detector, capillary column PoraPLOTQ-HT). The results are shown in Table 5. Compared with Comparative Examples 1-2 with larger crystal grains, the small crystal grain samples of Examples 1-2 showed high conversion rate of epichlorohydrin and yield of the target product epichlorohydrin carbonate.

[0106] Table 5 Results of the cycloaddition reaction of carbon dioxide of the samples

[0107] Sample Conversion rate of epichlorohydrin % Yield of epichlorohydrin carbonate % Example 1 93 89 Example 2 88 83 Comparative Example 1 62 50 Comparative Example 2 51 40

[0108] As described above, only several embodiments of the present application are provided, and the present application is not limited in any form. Although the present application is disclosed with preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications within the scope of the technical solution of the present application by using the disclosed technical content, which are equivalent to equivalent embodiments and all fall within the scope of the technical solution.

Claims

1. A preparation method of SAPO-34 molecular sieve, characterized in that, It includes at least the following steps: (1) Mix the raw materials containing fibers and phosphoric acid with water, and carry out Reaction I to obtain a solution containing nanocellulose; (2) Mix the raw materials containing an aluminum source, a silicon source and a templating agent with the solution containing nanocellulose, and carry out Reaction II to obtain the SAPO-34 molecular sieve; The SAPO-34 molecular sieve is a nanoscale cubic crystal with a particle size of 20-800 nm; The fiber in (1) is selected from at least one of bamboo fiber, wood pulp fiber, sisal fiber, cotton fiber, linen fiber, coconut fiber, ramie fiber or jute fiber; The mass ratio of the fiber, phosphoric acid and water is 0.2-5:2-40:5-200; The size of the fiber is in the micron scale; In (1), Reaction I includes heating to 70-170 °C at a heating rate of 0.2-10 °C / min and keeping it at a constant temperature for 0.4-3 days, and then cooling to 25-30 °C.

2. The preparation method of the SAPO-34 molecular sieve according to claim 1, characterized in that, In (2), the aluminum source is selected from at least one of activated alumina, alkoxyaluminum, and metakaolin; The silicon source is selected from at least one of an organic silicon source or an inorganic silicon source; The organic silicon source is selected from orthosilicate; The inorganic silicon source is selected from at least one of silica sol, activated silica, metakaolin or white carbon black; The templating agent is selected from at least one of diethylamine, triethylamine, tetrapropylammonium hydroxide, morpholine, di-n-propylamine, diisopropylamine, pyridine or piperazine; The molar ratio of the silicon source, phosphoric acid, aluminum source, templating agent and water is 0.2-1.2:0.5-1.5:0.6-1.4:1.5-5.5:50-200; The molar amount of the silicon source is calculated based on the molar amount of SiO2; The molar amount of the phosphoric acid is calculated based on the molar amount of P2O5; The molar amount of the aluminum source is calculated based on the molar amount of Al2O3.

3. The preparation method of the SAPO-34 molecular sieve according to claim 1, wherein, 4. The preparation method of the SAPO-34 molecular sieve according to claim 3, wherein, In (2), Reaction II includes an aging process and a crystallization process.

5. The preparation method of the SAPO-34 molecular sieve according to claim 4, wherein, The aging process includes heating to 50-80 °C at a heating rate of 0.2-2.0 °C / min and keeping it at a constant temperature for 0.2-2 days. The heating rate of the aging process is 1 °C / min; 6. The preparation method of the SAPO-34 molecular sieve according to claim 4, wherein, The constant temperature time of the aging process is 0.4-1.5 days. The temperature of the crystallization process is 150-220 °C; 7. The preparation method of the SAPO-34 molecular sieve according to claim 6, wherein, The time of the crystallization process is 0.5-10 days.

8. An acid catalyst, characterized in that, The temperature of the crystallization process is 170-200 °C; the time of the crystallization process is 1-3 days. The SAPO-34 molecular sieve prepared by the preparation method according to any one of claims 1 to 7 is obtained by calcination in air at 400-700 °C; The acid catalyst has a hierarchical pore structure, including micropores and mesopores; the specific surface area of the mesopores is 50~200 m 2 / g.

9. The acid catalyst according to claim 8, wherein The acid catalyst has a CHA crystal phase and a grain size of 20 nm-800 nm; The specific surface area of the mesopores is 90 to 120 m 2 / g; The grain size of the acid catalyst is 100 nm-150 nm; 10. A catalyst for the conversion of oxygenates to olefins, characterized in that, The specific surface area ratio of the micropores to the mesopores is 4-7.

11. A catalyst for the reaction of carbon dioxide to cyclic carbonates, characterized in that, It includes the acid catalyst according to claim 8 or 9. It includes the acid catalyst according to claim 8 or 9.

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