Preparation method of SAPO-34 molecular sieve and preparation method of 5-hydroxymethylfurfural by converting biomass sugar

Abstract

The application discloses a preparation method of SAPO-34 molecular sieve and a preparation method of 5-hydroxymethylfurfural by biomass sugar conversion, and the preparation method comprises the following steps: mixing a mixture containing a directing agent, a silicon source, an aluminum source, a phosphorus source and a template agent, and then performing aging and reaction to obtain the SAPO-34 molecular sieve; and the directing agent is an aliphatic epoxy silane. The SAPO-34 molecular sieve prepared in the application has a nanoscale crystal grain size, and exhibits excellent catalytic performance in the reaction of 5-hydroxymethylfurfural by biomass sugar conversion, and has good catalyst activity and high 5-hydroxymethylfurfural yield.

Description

Technical Field

[0001] This application relates to a method for preparing SAPO-34 molecular sieve and a method for preparing 5-hydroxymethylfurfural by converting biomass sugars, belonging to the fields of molecular sieve and biomass resource utilization technology. Background Technology

[0002] Faced with the dwindling supply of non-renewable fossil resources and the long-term goal of sustainable development, developing and utilizing renewable biomass resources to replace fossil resources is an ideal choice. Biomass feedstocks can be converted into various high-value-added chemicals, such as ethanol, levulinic acid, and 5-hydroxymethylfurfural. Among them, 5-hydroxymethylfurfural (5-HMF), as one of the 12 high-value-added platform compounds recognized by the U.S. Department of Energy, can not only serve as a feedstock for the production of bio-based liquid fuels such as aviation kerosene and biodiesel, but is also a key precursor to important biomass-based polyester monomers such as 2,5-furandicarboxylic acid, 2,5-furandiethanol, and 2,5-bis(hydroxymethyl)tetrahydrofuran, and has a wide range of applications. Therefore, efficiently converting biomass-based feedstocks into 5-hydroxymethylfurfural is an important pathway for the efficient utilization of biomass and has significant commercial value.

[0003] Currently, the industrial production of 5-hydroxymethylfurfural (5-HMF) mainly uses expensive fructose as a raw material, which is produced by catalytic dehydration in liquid acid solutions such as sulfuric acid. This process not only generates a large amount of acidic waste liquid but also suffers from equipment corrosion and difficulty in product separation. Compared with liquid acid catalysts, solid acid catalysts have advantages such as easy recovery, low corrosivity, and ease of industrialization, making them suitable for the future large-scale synthesis of 5-HMF. On the other hand, compared with fructose, glucose and its polysaccharides are more abundant and cheaper in nature, but due to their stable pyran ring structure, direct catalysis of their synthesis into 5-HMF with liquid acids is quite difficult.

[0004] Among various solid acid catalysts, SAPO-34 molecular sieves, representing aluminosilicate phosphate (SAPO-n), possess a three-dimensional framework structure composed of PO2. + AlO2 -It is composed of tetrahedra and SiO2. Due to its unique composition, good hydrothermal stability, and mildly tunable acid properties, it has been applied in several practical industrial catalytic processes. Zhang Luxin et al. from Nankai University first reported the use of SAPO-34 as a catalyst to efficiently convert glucose, fructose, and sucrose to 5-hydroxymethylfurfural in γ-valerol / water solvent, while the catalyst exhibited good stability over five cycles (Chemical Engineering Journal 2017, 307, 877–883). Zhang Chenguang et al. from the Guangzhou Institute of Energy Research subsequently reported the use of Sn-modified SAPO-34 to achieve a glucose conversion rate of 98.5% and a 5-hydroxymethylfurfural yield of 64.4% in NaCl-water / tetrahydrofuran solvent (Industrial & Engineering Chemistry Research 2021, 60, 5838-5851).

[0005] The intrinsic microporous structure and micrometer-sized grains of SAPO-34 result in low utilization of its active sites as a catalyst. Researchers have attempted to introduce mesoporous or macroporous channels between the microporous structures, or to prepare nanoscale SAPO-34 molecular sieves to increase the catalyst's contact surface and improve catalytic reaction efficiency. Current methods for synthesizing nano-SAPO-34 include using hard templates, soft templates, adding crystal growth inhibitors, and post-processing. However, the inexpensive and rapid synthesis of SAPO-34 molecular sieves with high external surface area remains a technical challenge. Summary of the Invention

[0006] This application provides a method for preparing SAPO-34 molecular sieves, in which aliphatic epoxy silanes are used as crystal growth inhibitors in the synthesis, and nanoscale SAPO-34 molecular sieves are successfully synthesized.

[0007] According to one aspect of this application, a method for preparing SAPO-34 molecular sieve is provided, the method comprising:

[0008] The SAPO-34 molecular sieve is obtained by aging and reacting a mixture containing a directing agent, a silicon source, an aluminum source, a phosphorus source, a template agent, and water; the directing agent is an aliphatic epoxy silane.

[0009] Optionally, the aliphatic epoxy silane is selected from at least one of 3-glycidyl etheroxypropyltrimethoxysilane, 3-glycidyl etheroxypropyltriethoxysilane, 3-glycidyl etheroxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0010] Preferably, the molar ratio of the directing agent: silicon source: aluminum source: phosphorus source: template agent: water is: 0.15~1.0: 0.3~1.1: 0.7~1.4: 0.3~1.2: 1.4~5.5: 50~150;

[0011] The amount of the directing agent added is based on its own molar amount, the amount of the silicon source added is based on the molar amount of SiO2, the amount of the aluminum source added is based on the molar amount of Al2O3, the amount of the phosphorus source added is based on the molar amount of P2O5, and the amount of the template agent added is based on its own molar amount.

[0012] Optionally, the silicon source is selected from at least one of orthosilicate, silica sol, activated silica, metakaolin, and silica.

[0013] Optionally, the aluminum source is selected from at least one of aluminum salts, activated alumina, alkoxyaluminum, and metakaolin.

[0014] Optionally, the phosphorus source is selected from at least one of orthophosphoric acid, metaphosphoric acid, phosphate, and phosphite.

[0015] Optionally, the template agent is selected from at least one of morpholine, triethylamine, diethylamine, di-n-propylamine, diisopropylamine, tetraethylammonium hydroxide, and pyridine.

[0016] Optionally, the aluminum source is selected from at least one of boehmite, aluminum isopropoxide, and aluminum hydroxide.

[0017] Optionally, the phosphorus source is selected from at least one of orthophosphoric acid, monoammonium phosphate, metaphosphoric acid, ammonium hydrogen phosphate, and diammonium phosphate.

[0018] Optionally, the aging conditions are as follows: the mixture is placed in a closed reactor and heated to 40-80°C, and then aged by rotation for 0.2-2 days.

[0019] Optionally, the upper limit of the aging temperature is independently selected from 60°C, 65°C, 70°C, 75°C or 80°C; and the lower limit is independently selected from 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C.

[0020] Optionally, the upper limit of the aging time is independently selected from 12h, 18h, 20h, 24h, 30h or 48h; the lower limit is independently selected from 4.8h, 9.6h, 12h, 18h, 20h, 24h or 30h.

[0021] Optionally, the aging temperature is 50°C.

[0022] Optionally, the temperature rise rate of the programmed temperature rise is 0.5 to 2.0 °C / min.

[0023] Optionally, the temperature rise rate of the programmed temperature rise is 1.5℃ / min.

[0024] Optionally, the temperature rise rate of the programmed temperature rise is 1.5℃ / min, and the aging time is 0.4 to 1 day.

[0025] Optionally, the reaction conditions are: hydrothermal crystallization at a temperature of 170–220°C for 0.4–8 days.

[0026] Optionally, the hydrothermal crystallization time is 1 to 5 days.

[0027] Optionally, the upper limit of the reaction temperature is independently selected from 180°C, 190°C, 200°C, 210°C, and 220°C; and the lower limit is independently selected from 170°C, 180°C, 190°C, 200°C, and 210°C.

[0028] Optionally, the upper limit of the reaction time is independently selected from 12h, 16h, 24h, 40h, 44h, 66h, 92h, 168h, and 192h; and the lower limit is independently selected from 9.6h, 10h, 12h, 16h, 24h, 26h, 40h, 44h, and 66h.

[0029] As a specific implementation method, the SAPO-34 molecular sieve is synthesized by hydrothermal method under the guidance of aliphatic epoxy silanes through a specific aging process; the SAPO-34 molecular sieve is a nano-SPO-34 molecular sieve.

[0030] Optionally, the preparation method includes the following steps:

[0031] a) After dissolving aliphatic epoxy silanes in water, silicon source, aluminum source, phosphorus source and template agent are added sequentially to obtain a mixture with the following molar ratio:

[0032] Aliphatic epoxy silanes: SiO2:P2O5:Al2O3:templator:H2O = 0.1~1.0:0.3~1.2:0.6~1.4:0.3~1.5:1.2~6.5:30~200;

[0033] b) Place the mixture obtained in step a) in a closed reactor and heat it to 40-80°C, then rotate and age it for 0.2-2 days;

[0034] c) Place the mixture aged in step b) at 170–220°C for crystallization for 0.4–8 days;

[0035] d) After the crystallization in step c) is completed, the solid product is separated, washed and dried to obtain the SAPO-34 molecular sieve.

[0036] Optionally, in the mixture described in step a), the amount of silicon source added is calculated in the number of moles of SiO2, the amount of phosphorus source added is calculated in the number of moles of P2O5, and the amount of aluminum source added is calculated in the number of moles of Al2O3.

[0037] Optionally, the grain size of the SAPO-34 molecular sieve is 10 nm to 200 nm.

[0038] Optionally, the SAPO-34 molecular sieve contains mesopores; the specific surface area of ​​the mesopores is 50–250 m² / g. 2 / g.

[0039] As one specific implementation method, the preparation method of the SAPO-34 molecular sieve includes at least the following steps:

[0040] a1) Deionized water, aliphatic epoxy silane, silicon source, aluminum source, phosphorus source and template agent are mixed sequentially to obtain a mixture with the following molar ratio:

[0041] Aliphatic epoxy silanes: SiO2:P2O5:Al2O3:templator:H2O = 0.1~1.0:0.3~1.2:0.6~1.4:0.3~1.5:1.2~6.5:30~200;

[0042] b1) Place the mixture obtained in step a1) in a closed reactor and age it at a programmed temperature of 40-80°C for 0.2-2 days;

[0043] c1) The mixture obtained in step b1) is crystallized at 170–220°C for 0.4–8 days;

[0044] d1) After the crystallization in step c1) is completed, the solid product is separated, washed and dried to obtain the SAPO-34 molecular sieve.

[0045] As a specific embodiment, the synthesis method of the SAPO-34 molecular sieve includes the following steps:

[0046] 1) Add aliphatic epoxy silane, silicon source, aluminum source, phosphorus source and template agent sequentially to deionized water and stir at room temperature for 1 to 12 hours. The proportions of each component in the mixed solution are as follows: (0.1 to 1.0) aliphatic epoxy silane: (0.3 to 1.2) SiO2: (0.6 to 1.4) P2O5: (0.3 to 1.5) Al2O3: (1.2 to 6.5) template agent: (30 to 200) H2O;

[0047] 2) The mixed solution from step 1) is heated to 60°C at a rate of 1°C / min and aged for 0.2 to 2 days;

[0048] 3) Crystallize the mixed solution from step 2) at 170–220°C for 0.4–8 days;

[0049] 4) After the crystallization in step 3) is completed, the solid product is separated by centrifugation, washed with deionized water until neutral, and dried in air at 120°C to obtain nano-SAPO-34 molecular sieve raw powder.

[0050] Optionally, the particle size distribution of the SAPO-34 molecular sieve is between 20 nm and 150 nm.

[0051] The SAPO-34 molecular sieve prepared by the method described in this application has a hierarchical porous structure, including micropores and mesopores.

[0052] Optionally, the SAPO-34 molecular sieve contains mesopores; the specific surface area of ​​the mesopores is 50–250 m² / g. 2 / g.

[0053] Optionally, the specific surface area of ​​the mesopores is 80–190 m². 2 / g.

[0054] Optionally, the specific surface area ratio of the micropores to the mesopores is 5 to 7.

[0055] According to another aspect of this application, a catalyst is provided, said catalyst being obtained by calcining SAPO-34 molecular sieve in air at 400–800°C;

[0056] The SAPO-34 molecular sieve is prepared from the SAPO-34 molecular sieve prepared by the preparation method described above.

[0057] The application of the SAPO-34 molecular sieve in catalyzing the conversion of biomass sugars to 5-hydroxymethylfurfural is characterized by comprising at least the following steps: hydrothermal synthesis in the presence of an aliphatic epoxy silane directing agent to obtain the SAPO-34 molecular sieve.

[0058] According to another aspect of this application, a method for preparing 5-hydroxymethylfurfural by biomass carbohydrate conversion is provided, the method comprising:

[0059] The mixture containing biomass sugars, solvents, and SAPO-34 molecular sieves was reacted to obtain the 5-hydroxymethylfurfural.

[0060] The SAPO-34 molecular sieve is prepared from the SAPO-34 molecular sieve prepared by the preparation method described above.

[0061] The mass ratio of biomass sugars to solvent is 1–10:20;

[0062] The mass ratio of SAPO-34 molecular sieve to biomass sugars is 1:0.05-10.

[0063] Optionally, the biomass sugar is selected from at least one of fructose, glucose, sucrose, cellobiose, maltose, and starch.

[0064] Optionally, the solvent is selected from at least one of water, dimethyl sulfoxide, N,N-dimethylformamide, methyl isobutyl ketone, tetrahydrofuran, and γ-valerolactone.

[0065] Optionally, the reaction is carried out in a closed reactor at 90–190°C for 20–360 min.

[0066] Optionally, the reaction time is 40–160 min.

[0067] The beneficial effects that this application can produce include:

[0068] 1) This application proposes a novel aliphatic epoxy silane directing agent for preparing nano-SAPO-34 molecular sieves. Compared with the currently reported methods for synthesizing nano-SAPO-34 molecular sieves, this directing agent is low in cost and has strong application prospects in industry.

[0069] 2) The SAPO-34 molecular sieve prepared in this application has abundant accessible active sites as a catalyst;

[0070] 3) The SAPO-34 molecular sieve prepared in this application exhibits excellent catalytic performance in the biomass sugar conversion to 5-hydroxymethylfurfural reaction, with good catalyst activity and high 5-hydroxymethylfurfural yield. Attached Figure Description

[0071] Figure 1 This is a scanning electron microscope image of the sample obtained in Example 1 of this application (the scale bar in the image is 200 nm).

[0072] Figure 2 This is a transmission electron microscope (TEM) image of the sample obtained in Example 1 of this application (the scale bar in the image is 100 nm).

[0073] Figure 3 This is a scanning electron microscope image of the sample obtained in Comparative Example 1 of this application (the scale bar in the image is 10 μm).

[0074] Figure 4 The image shows a scanning electron microscope (SEM) image of the sample obtained in Comparative Example 2 of this application (the scale bar in the image is 1 μm).

[0075] Figure 5 This is the XRD diffraction pattern of the sample obtained in Example 1 of this application. Detailed Implementation

[0076] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0077] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0078] In the examples, the 3-glycidyl etheroxypropyltrimethoxysilane, 3-glycidyl etheroxypropyltriethoxysilane, 3-glycidyl etheroxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane used were purchased from Tianjin Sanfu New Material Technology Co., Ltd.

[0079] The analysis method in the embodiments of this application is as follows:

[0080] Elemental composition was determined using a Philips Magix-601 X-ray fluorescence analyzer (XRF).

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

[0082] SEM morphology analysis was performed using a SU8020 scanning electron microscope manufactured by the Scientific Instrument Factory of the Chinese Academy of Sciences.

[0083] N2 physical adsorption analysis was performed using a Micromeritics ASAP 2020 physical adsorption analyzer from Micromeritics, Inc.

[0084] In the embodiments of this application, the biomass carbohydrate conversion rate and 5-hydroxymethylfurfural yield are calculated as follows:

[0085] X 糖 = (Moles of biomass sugars in feed - Moles of biomass sugars in discharge) / Moles of biomass sugars in feed * 100%;

[0086] Y 5-羟甲基糠醛 = (moles of 5-hydroxymethylfurfural) / (moles of biomass sugars in the feed).

[0087] Among them, X 糖 Y represents the conversion rate of carbohydrates in biomass. 5-羟甲基糠醛 The yield of 5-hydroxymethylfurfural.

[0088] Example 1

[0089] The molar proportions of each raw material, crystallization conditions, and elemental composition of the sample are shown in Table 1. The specific batching process is as follows:

[0090] 4.7 g of 3-glycidyl etheroxypropyltrimethoxysilane, 40.8 g of aluminum isopropoxide, 23.1 g of phosphoric acid (85% by mass of H3PO4), 8.3 g of tetraethyl orthosilicate, 15.2 g of diisopropylamine, and 140.5 g of deionized water were mixed and aged for 20 hours. The gel was then transferred to a stainless steel reactor. The molar ratio of the components in the synthesis system was 0.2 aliphatic epoxysilane: 0.4 SiO2: 1.0 P2O5: 1.0 Al2O3: 1.5 template agent: 80 H2O.

[0091] The reactor containing the material was placed in an oven and heated to 60°C at a rate of 1°C / min, and aged for 10 hours.

[0092] The reaction vessel was heated to 200℃ for static crystallization for 40 hours. After the reaction was completed, the solid product was centrifuged, repeatedly washed with deionized water, and dried in air at 120℃ to obtain the SAPO-34 molecular sieve sample.

[0093] The morphology of the obtained samples was characterized using scanning electron microscopy (SEM), and the SEM images are shown below. Figure 1 , Figure 2 As shown, the obtained sample is a spherical nanocrystal aggregate with a primary particle size of 20-30 nm and a secondary particle size of approximately 100 nm. XRD analysis of the obtained sample is shown in Table 2 and... Figure 5 The results showed that the synthesized product had a pure SAPO-34 crystalline phase.

[0094] The elemental composition of the obtained samples was analyzed by XRF, and the results are shown in Table 1.

[0095] Table 1. Molecular sieve synthesis ingredients, crystallization conditions, and elemental composition.

[0096]

[0097]

[0098] Table 2. XRD results of the sample from Example 1

[0099]

[0100] Comparative Example 1

[0101] The crystallization process is the same as in Example 1, but aliphatic epoxy silanes are not added during the preparation process.

[0102] The morphology of the obtained samples was characterized using scanning electron microscopy (SEM), and the SEM images are shown below. Figure 3 As shown, the grains are large cubic grains with a diameter of about 10 μm.

[0103] Comparative Example 2

[0104] The ingredient ratio and crystallization process are the same as in Example 1, but the aging process is not used.

[0105] The morphology of the obtained samples was characterized using scanning electron microscopy (SEM), and the SEM images are shown below. Figure 4 As shown, these are relatively large cubic grains with smooth surfaces, each with a diameter of about 1 μm.

[0106] Examples 2-12

[0107] The specific ingredient ratios and crystallization conditions are shown in Table 1, and the specific ingredient preparation process is the same as in Example 1.

[0108] XRD analysis was performed on the samples obtained in Examples 2 to 12. The data results were similar to those in Table 2, that is, the peak positions and shapes were the same, and the relative peak intensities fluctuated within ±10% depending on the synthesis conditions, indicating that the synthesized products have the characteristics of SAPO-34 structure.

[0109] XRF elemental composition analysis was performed on the samples obtained in Examples 2 to 12, and the results are shown in Table 1.

[0110] The morphology of the samples obtained in Examples 2-12 was analyzed using scanning electron microscopy. The obtained electron micrographs were all consistent with... Figure 1 resemblance.

[0111] Example 13

[0112] The samples obtained in Examples 1-4 and Comparative Examples 1-2 were calcined at 600°C with air for 4 hours, and then subjected to N2 physical adsorption analysis. The results are shown in Table 3. The samples obtained in Examples 1-4 have large micropore volumes and micropore specific surface areas, indicating that the samples have good crystallinity and abundant external specific surface areas and mesopore volumes.

[0113] Table 3 Specific surface area and pore volume of the samples

[0114]

[0115] Examples 14-25

[0116] The samples obtained in Examples 1-4 and Comparative Examples 1-2 were calcined at 600°C with air for 4 hours. Then, 0.3g of the sample was weighed and placed into a batch reactor. A certain mass of biomass sugars and solvents were added to evaluate the reaction of biomass sugars to 5-hydroxymethylfurfural.

[0117] The reaction products were analyzed by liquid chromatography (Agilent HPLC 1100, parallax refractive index detector, Rezox™ ROA-Qrganic Acid H+ column). The reaction conditions and results are shown in Table 4. Compared to the larger crystallites in Comparative Examples 1–2, the smaller crystallites in Examples 1–4 exhibited good catalytic activity for a variety of biomass carbohydrate substrates and excellent yields of 5-hydroxymethylfurfural in different solvents.

[0118] Table 4 shows the results of the biomass carbohydrate conversion to 5-hydroxymethylfurfural reaction in the samples.

[0119]

[0120] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A method for preparing SAPO-34 molecular sieve, characterized in that, The preparation method includes: The SAPO-34 molecular sieve is obtained by aging and reacting a mixture containing a directing agent, a silicon source, an aluminum source, a phosphorus source, a template agent, and water. The directing agent is an aliphatic epoxy silane; The aliphatic epoxy silane is selected from at least one of 3-glycidyl etheroxypropyltrimethoxysilane, 3-glycidyl etheroxypropyltriethoxysilane, 3-glycidyl etheroxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. The template agent is selected from at least one of morpholine, triethylamine, diethylamine, di-n-propylamine, diisopropylamine, tetraethylammonium hydroxide, and pyridine; The reaction conditions are: hydrothermal crystallization at a temperature of 170~220℃ for 0.4~8 days.

2. The preparation method according to claim 1, characterized in that, The molar ratio of the directing agent, silicon source, aluminum source, phosphorus source, template agent, and water is 0.15~1.0:0.3~1.1:0.7~1.4:0.3~1.2:1.4~5.5:50~150. The amount of the directing agent added is based on its own molar amount, the amount of the silicon source added is based on the molar amount of SiO2, the amount of the aluminum source added is based on the molar amount of Al2O3, the amount of the phosphorus source added is based on the molar amount of P2O5, and the amount of the template agent added is based on its own molar amount.

3. The preparation method according to claim 1, characterized in that, The silicon source is selected from at least one of tetraethyl orthosilicate, silica sol, activated silica, metakaolin, and silica. The aluminum source is selected from at least one of aluminum salts, activated alumina, alkoxyaluminum, and metakaolin. The phosphorus source is selected from at least one of orthophosphoric acid, metaphosphoric acid, phosphate, and phosphite.

4. The preparation method according to claim 1, characterized in that, The aging conditions are as follows: The mixture is placed in a closed reactor and heated to 40-80°C, and then aged by rotation for 0.2-2 days.

5. The preparation method according to claim 4, characterized in that, The temperature rise rate of the programmed temperature rise is 0.5~2.0℃ / min.

6. The preparation method according to claim 1, characterized in that, The hydrothermal crystallization time is 1 to 5 days.

7. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: a) After dissolving an aliphatic epoxy silane in water, a silicon source, an aluminum source, a phosphorus source, and a template agent are added sequentially to obtain a mixture with the following molar ratio: Aliphatic epoxy silanes: SiO2:P2O5:Al2O3:templator:H2O = 0.1~1.0: 0.3~1.2: 0.6~1.4: 0.3~1.5: 1.2~6.5: 30~200; b) Place the mixture obtained in step a) in a closed reactor and heat it to 40~80°C, then rotate and age it for 0.2~2 days; c) Place the mixture aged in step b) at 170~220 °C for crystallization for 0.4~8 days; d) After the crystallization in step c) is completed, the solid product is separated, washed and dried to obtain the SAPO-34 molecular sieve.

8. The preparation method according to claim 1, characterized in that, The SAPO-34 molecular sieve has a crystal size of 10 nm to 200 nm.

9. The preparation method according to claim 1, characterized in that, The SAPO-34 molecular sieve contains mesopores; the specific surface area of ​​the mesopores is 50~250m². 2 / g.

10. A catalyst, characterized in that, The catalyst was obtained by calcining SAPO-34 molecular sieve in air at 400-800 °C; The SAPO-34 molecular sieve is prepared by the preparation method according to any one of claims 1 to 9.

11. A method for preparing 5-hydroxymethylfurfural by converting biomass carbohydrates, characterized in that, The preparation method includes: The mixture containing biomass sugars, solvents, and SAPO-34 molecular sieves was reacted to obtain the 5-hydroxymethylfurfural. The SAPO-34 molecular sieve is prepared from the SAPO-34 molecular sieve prepared by the preparation method according to any one of claims 1 to 6; The mass ratio of biomass sugars to solvent is 1~10:20; The mass ratio of SAPO-34 molecular sieve to biomass sugars is 1:0.05~10.

12. The preparation method according to claim 11, characterized in that, The biomass sugars are selected from at least one of fructose, glucose, sucrose, cellobiose, maltose, and starch.

13. The preparation method according to claim 11, characterized in that, The solvent is selected from at least one of water, dimethyl sulfoxide, N,N-dimethylformamide, methyl isobutyl ketone, tetrahydrofuran, and γ-valerol.

14. The preparation method according to claim 11, characterized in that, The reaction was carried out in a closed reactor at 90-190°C for 20-360 min.

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