ZSM-5 / SAPO-34 composite molecular sieve catalyst as well as preparation method and application thereof

Abstract

The invention discloses a ZSM-5 / SAPO-34 composite molecular sieve catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: step 1, preparing a ZSM-5 seed crystal solution: dissolving a ZSM-5 molecular sieve in an alkaline solution to prepare the ZSM-5 seed crystal solution; step 2, preparing an SAPO-34 precursor solution: dissolving an organic template agent in deionized water, dropwise adding a silicon source, uniformly mixing, adding a phosphorus source and an aluminum source, and stirring to obtain the SAPO-34 molecular sieve catalyst precursor solution; step 3, mixing the ZSM-5 seed crystal solution with the SAPO-34 molecular sieve catalyst precursor solution, crystallizing, and carrying out suction filtration, washing, drying and roasting on a crystallized product to obtain a ZSM-5 / SAPO-34 composite molecular sieve; and 4, tabletting and screening the composite molecular sieve to obtain a final product. The product disclosed by the invention is high in crystallinity, high in specific surface area, graded and porous (adjustable in micro-mesoporous ratio) and appropriate in acid strength, active sites in contact with pyrolysis raw materials are increased, the selectivity of the target product 2, 3-dihydrobenzofuran is effectively improved, the types of final products are reduced, the subsequent treatment cost is reduced, the preparation conditions are simple and convenient, and the application range is wide.

Description

Technical Field

[0001] The invention belongs to the technical field of biomass energy utilization, and specifically relates to a ZSM-5 / SAPO-34 composite molecular sieve catalyst, a preparation method and application thereof. Background Art

[0002] With the reduction of fossil fuel resources and the deterioration of the environment worldwide, the conversion of renewable resources into chemicals and fuels has received increasing attention. Biomass is a potential renewable resource whose effective utilization can bring economic benefits. Biomass resources include agricultural and forest residues, aquatic plants and algae, municipal solid waste and food waste. However, most of the biomass is discarded as waste and cannot be effectively utilized. The effective utilization of biomass is very important to protect the environment from deterioration caused by waste pollution. Bagasse is a larger by-product of the sugarcane industry. It can be used as the best substrate for the production of value-added chemicals and fuels through pyrolysis. And bagasse is renewable and carbon neutral. Compared with biomass such as corn cobs, rice husks and straw, the yield of bio-oil obtained by pyrolysis of bagasse is relatively high. Using molecular sieves to catalyze the pyrolysis of bagasse to produce high-value chemicals is one of the ways to effectively utilize biomass.

[0003] Composite molecular sieves are composite crystals with structural features of two or more molecular sieves. They often have properties different from those of a single molecular sieve, and exhibit synergistic effects and special catalytic properties. Composite molecular sieves overcome the limitations of single microporous or mesoporous molecular sieves and combine the advantages of each pore size structure. ZSM-5 molecular sieve has a unique MFI structure, which provides abundant diffusion channels for reactants and products in catalytic reactions. SAPO-34 molecular sieve has a CHA topological structure and is a microporous molecular sieve. The synergistic effect of the two molecular sieves gives it the advantages of suitable pores and acid centers, the ability to inhibit side reactions and reduce diffusion resistance. Composite molecular sieves have attracted extensive attention from researchers for their rich active centers, multi-channel structures and the synergistic effect of composite phase interfaces.

[0004] Patent CN118289775A provides a ZSM-5 / Y composite structure molecular sieve and its preparation method. The catalyst has mutually cooperative acidic centers and pore structures, and the amount of water used can be reduced during the preparation process, greatly improving the product yield. However, its preparation process is complicated, the crystallinity is low, and the synthesis process is unstable. Patent CN104492475B provides a preparation method for a micro-mesoporous ZSM-5 / Pd-γ-Al2O3 composite catalyst. The catalyst combines the pore advantages of the mesoporous material γ-Al2O3 with the strong acidity and high hydrothermal stability of the microporous molecular sieve ZSM-5, but the prepared catalyst has the disadvantages of low crystallinity and low specific surface area. Patent CN118142572A provides a Ni@β / MCM-41 modified composite molecular sieve. The catalyst preparation process modifies the morphology, structure and size of the catalyst, and has high activity and a large specific surface area. However, its preparation method is not conducive to adjusting the acidity of the molecular sieve.

[0005] Therefore, it is crucial to develop a catalyst with multiple advantages such as high crystallinity, high specific surface area, hierarchical porosity (adjustable micro-mesopore ratio) and appropriate acid strength in the process of biomass pyrolysis to produce 2,3-dihydrobenzofuran, which is highly selective for 2,3-dihydrobenzofuran. Summary of the invention

[0006] In view of the shortcomings of the prior art described above, the purpose of the present application is to provide a ZSM-5 / SAPO-34 composite molecular sieve catalyst, a preparation method and its application, which are used to solve the problems of low crystallinity, low specific surface area, single pore size distribution, and difficult to adjust acid strength of the current catalyst.

[0007] To solve the above problems, the technical solution adopted in this application is: The present invention provides a method for preparing a ZSM-5 / SAPO-34 composite molecular sieve catalyst, which is characterized by comprising the following steps: Step 1, preparing a ZSM-5 seed solution: dissolving a ZSM-5 molecular sieve in an alkaline solution to prepare a ZSM-5 seed solution; Step 2, preparing SAPO-34 precursor solution: dissolving the organic template in deionized water, adding the silicon source dropwise, mixing evenly, adding the phosphorus source and the aluminum source, stirring evenly, and obtaining a white gel, which is the SAPO-34 molecular sieve catalyst precursor solution; Step 3, the ZSM-5 seed solution is mixed with the SAPO-34 molecular sieve catalyst precursor solution and then crystallized, and the crystallized product is filtered, washed, dried, and calcined to obtain a ZSM-5 / SAPO-34 composite molecular sieve; Step 4: Forming, tableting and screening the ZSM-5 / SAPO-34 composite molecular sieve to obtain the final product.

[0008] As a preferred embodiment of the present application, in step 2, the silicon source is selected from at least one of silica sol, water glass, activated silicon dioxide, and tetraethyl orthosilicate; the aluminum source is selected from at least one of pseudo-boehmite, aluminum isopropoxide, aluminum hydroxide, and aluminum salts; and the phosphorus source is selected from at least one of orthophosphoric acid, phosphorous acid, and phosphates.

[0009] As a preference of the present application, in step 2, the silicon source is tetraethyl orthosilicate; the aluminum source is aluminum hydroxide; and the phosphorus source is orthophosphoric acid.

[0010] As a preference of the present application, the silicon source, aluminum source and phosphorus source in step 2 are expressed in the form of oxide molar ratios, and the composition ratio is as follows: n(SiO2):n(Al2O3):n(P2O5)=1:(0.5~3):(0.5~4).

[0011] As a preference of the present application, the silicon source, aluminum source and phosphorus source in step 2 are expressed in the form of oxide molar ratio, and the composition ratio is as follows: n(SiO2): n(Al2O3): n(P2O5) = 1: (1~2): (1~2).

[0012] As a preference of the present application, the silicon source, aluminum source and phosphorus source in step 2 are expressed in the form of oxide molar ratio, and the composition ratio is as follows: n(SiO2): n(Al2O3): n(P2O5) = 1:1.67:1.67.

[0013] As a preferred embodiment of the present application, the alkaline solution in step 1 is an aqueous solution of sodium hydroxide with a mass concentration of 1% to 10%.

[0014] As a preferred embodiment of the present application, the alkaline solution in step 1 is an aqueous solution of sodium hydroxide with a mass concentration of 2% to 8%.

[0015] As a preferred embodiment of the present invention, the solid-to-liquid ratio of ZSM-5 molecular sieve to alkaline solution in step 1 is 0.5~2g:20mL.

[0016] As a preferred embodiment of the present invention, the solid-to-liquid ratio of ZSM-5 molecular sieve to alkaline solution in step 1 is 1 g:20 mL.

[0017] As a preferred embodiment of the present invention, the organic template in step 2 is selected from at least one of diethanolamine, triethylamine and tetraethylammonium hydroxide.

[0018] As a preferred embodiment of the present invention, the organic template in step 2 is diethanolamine.

[0019] As a preferred embodiment of the present invention, in step 2, the stirring time is 2 to 8 hours, the temperature is 40 to 60° C., and the stirring speed is 400 to 800 r / min.

[0020] As a preferred embodiment of the present invention, the stirring time in step 2 is 4h.

[0021] As a preferred embodiment of the present invention, in step 3, the crystallization temperature is 150-210° C., and the crystallization time is 12-72 hours.

[0022] As a preferred embodiment of the present invention, in step 3, the crystallization temperature is 200° C. and the crystallization time is 24 h.

[0023] As a preferred embodiment of the present invention, the solid product after suction filtration of the crystallized product in step 3 is washed with water and ethanol to a pH of 6-9, and calcined at a temperature of 5°C / min in an air atmosphere, the calcination temperature is 500-700°C, and the calcination time is 3-7h.

[0024] As a preferred embodiment of the present invention, the solid product after suction filtration of the crystallized product in step 3 is washed with water and ethanol to a pH of 6-9, and calcined at a temperature of 5°C / min in an air atmosphere, the calcination temperature is 600°C, and the calcination time is 5h.

[0025] Step 1 and step 2 can be interchanged and have no influence on the preparation of ZSM-5 / SAPO-34 composite molecular sieve catalyst.

[0026] The present invention also provides a ZSM-5 / SAPO-34 composite molecular sieve catalyst prepared according to the preparation method.

[0027] The present invention also provides an application of the ZSM-5 / SAPO-34 composite molecular sieve catalyst in the rapid catalytic pyrolysis of biomass to produce 2,3-dihydrobenzofuran.

[0028] As a preferred embodiment of the present invention, the application method comprises: The ZSM-5 / SAPO-34 composite molecular sieve catalyst and biomass are mixed and uniformly loaded in the constant temperature zone of a vertical tube furnace; N2 was introduced to purge and expel the air. After the purge was completed, a pyrolysis reaction was carried out in a N2 atmosphere. The temperature was raised to a reaction temperature of 400-600°C at a rate of 30-60°C / min, and the constant temperature was maintained for 1-25 min. The liquid products produced by the pyrolysis were collected.

[0029] As a preferred embodiment of the present invention, the constant temperature time of the pyrolysis reaction is 5 to 10 minutes.

[0030] As a preferred embodiment of the present invention, the biomass is lignocellulosic biomass, such as bagasse.

[0031] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention is a ZSM-5 / SAPO-34 composite molecular sieve suitable for rapid catalytic pyrolysis of biomass to produce 2,3-dihydrobenzofuran. The composite molecular sieve of the present invention has a hierarchical porous structure, which overcomes the disadvantage of a single molecular sieve having a single pore size distribution. At the same time, by adjusting the proportion of micro-mesopores and acid strength in the composite molecular sieve, the pore distribution can be effectively adjusted and the decarboxylation of the intermediate product can be facilitated, and the catalyst performance is significantly improved.

[0032] (2) The present invention uses a hydrothermal synthesis method to tightly combine the two molecular sieves, thereby improving the crystallinity and specific surface area of ​​the catalyst, and can better achieve the spatial confinement effect of the reaction. In addition, the preparation process has mild conditions, is easy to operate, has low production costs, and has little pollution to the environment.

[0033] (3) Compared with the existing catalysts used for catalytic cracking of biomass, the composite molecular sieve catalyst of the present invention reduces the reaction activation energy, reduces the number of product types, and reduces the number of liquid phase products to within fifteen types. The selectivity of 2,3-dihydrobenzofuran can reach 48.15%. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The XRD spectra of the ZSM-5 / SAPO-34 composite molecular sieves obtained in Examples 1 to 6 are shown in FIG.

[0035] Figure 2 This is the SEM spectrum of the ZS-Al(OH)3 composite molecular sieve obtained in Example 1.

[0036] Figure 3 The nitrogen adsorption-desorption isotherms of the composite molecular sieves obtained in Example 1 and Example 4 are shown.

[0037] Figure 4 The pore size distribution diagram of the composite molecular sieves obtained in Example 1 and Example 4. DETAILED DESCRIPTION

[0038] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0039] It should be noted that the process equipment or devices not specifically specified in the following embodiments are all conventional equipment or devices in the art.

[0040] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before or after the combination step or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified; it should also be understood that the combination connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the existence of other devices / apparatuses before or after the combination device / apparatus or the insertion of other devices / apparatuses between these explicitly mentioned two devices / apparatuses, unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0041] In the following examples of the present invention, the reagents used are shown in Table 1: The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0042] Example 1 Step 1, preparing a ZSM-5 seed solution: taking 1 g of ZSM-5 molecular sieve and 1 g of sodium hydroxide, placing them in 20 mL of deionized water and stirring them at room temperature for 1 hour, which is a ZSM-5 seed solution; Step 2, prepare SAPO-34 precursor solution: weigh 9.73g diethanolamine (DEA) and dissolve it in 50mL deionized water and stir at room temperature for 10min, then add 5.79g tetraethyl orthosilicate, 9.07g phosphoric acid and 7.22g aluminum hydroxide in sequence and stir at room temperature for 4h to obtain a white gel, which is the SAPO-34 molecular sieve catalyst precursor solution; Step 3: Add the ZSM-5 seed solution to the SAPO-34 molecular sieve catalyst precursor solution, stir at room temperature for 4 hours, then put it into a hydrothermal reactor and crystallize it in an oven at 200°C for 24 hours. Then wash the crystallized product with anhydrous ethanol and deionized water until neutral, dry the obtained white crystals in an oven at 80°C for 12 hours, and then heat it at 5°C / min in an air atmosphere. Heat to 600°C and calcine for 5 hours to obtain a ZSM-5 / SAPO-34 composite molecular sieve; Step 4: Forming, tableting and screening the ZSM-5 / SAPO-34 composite molecular sieve to obtain the final product, namely, the ZS-Al(OH)3 composite molecular sieve.

[0043] The catalyst prepared in this example was subjected to the following characterization and testing: (1) Morphological characterization: SEM characterization was performed using a Zeiss G500 scanning electron microscope at an accelerating voltage of 5 kV to observe the surface morphology of the sample at different magnifications. The sample was prepared as thin as possible. Due to the poor conductivity of the sample, it was necessary to perform a gold spraying treatment for 80 s before shooting to better assist electron microscopy imaging. The specific reagent preparation and test steps were carried out according to the instructions. Figure 2 It can be seen that the ZS-Al(OH)3 composite molecular sieve catalyst prepared by the present invention is a stacked sphere formed by small cubic accumulation, and the ZS-Al(OH)3 molecular sieve has obvious holes and irregular cracks.

[0044] (2) Component characterization: XRD test: The phase structure analysis of the sample was characterized by a PNAlytical Empyrean X-ray diffractometer, the X-ray wavelength was 0.1541 nm, and the detector was a PIXcel 1D array detector. The tube current was 40 mA, the tube voltage was 40 kV, the scanning step was 0.02°, the scanning rate was 5 ° / min, and the scanning range was 5°~50°. The specific reagent preparation and test steps were carried out according to the instructions. The X-ray diffraction spectrum parameters of the ZS-Al(OH)3 composite molecular sieve catalyst prepared by the present invention are as follows: the relative crystallinity is 92.68%.

[0045] (3) N2 physical adsorption (N2-BET) The specific surface area (BET) and pore size distribution of the sample were measured using the American ASAP-2010 (Micromeritics) automatic physical adsorption instrument. During the test, about 300-600 mg of the sample was weighed and degassed at 160 °C and high vacuum conditions for 8 h to reduce the test error. The N2 adsorption-desorption curve of the sample was then measured at -196 °C, and the pore size distribution of the sample was calculated using the Barrett-Joyner-Halenda model, and the specific surface area of ​​the catalyst was calculated using the Brunauer Emmett and Teller equation. The ZS-Al(OH)3 composite molecular sieve catalyst prepared by the present invention has a specific surface area of ​​435 m 2 / g, pore volume is 0.10cm 3 / g, average pore size 3.77nm.

[0046] Example 2 Step 1, preparing a ZSM-5 seed solution: taking 1 g of ZSM-5 molecular sieve and 1 g of sodium hydroxide, placing them in 20 mL of deionized water and stirring them at room temperature for 1 hour, which is a ZSM-5 seed solution; Step 2, prepare SAPO-34 precursor solution: weigh 9.73g diethanolamine (DEA) and dissolve it in 50mL deionized water and stir at room temperature for 10min, then add 5.79g tetraethyl orthosilicate, 9.07g phosphoric acid and 18.91g aluminum isopropoxide in sequence and stir at room temperature for 4h to obtain a white gel, which is the SAPO-34 molecular sieve catalyst precursor solution; Step 3: Add the ZSM-5 seed solution to the SAPO-34 molecular sieve catalyst precursor solution, stir at room temperature for 4 hours, then put it into a hydrothermal reactor and crystallize it in an oven at 200°C for 24 hours. Then wash the crystallized product with anhydrous ethanol and deionized water until neutral, dry the obtained white crystals in an oven at 80°C for 12 hours, and then heat it at 5°C / min in an air atmosphere. Heat to 600°C and calcine for 5 hours to obtain a ZSM-5 / SAPO-34 composite molecular sieve; Step 4: Form and press the ZSM-5 / SAPO-34 composite molecular sieve into tablets and screen them to obtain the final product, namely ZS-C9H 21 AlO3 composite molecular sieve catalyst.

[0047] Example 3 Step 1, preparing a ZSM-5 seed solution: taking 1 g of ZSM-5 molecular sieve and 1 g of sodium hydroxide, placing them in 20 mL of deionized water and stirring them at room temperature for 1 hour, which is a ZSM-5 seed solution; Step 2, prepare SAPO-34 precursor solution: weigh 9.73g diethanolamine (DEA) and dissolve it in 50mL deionized water and stir at room temperature for 10min, then add 5.79g tetraethyl orthosilicate, 9.07g phosphoric acid and 6.59g high-purity pseudo-boehmite in sequence and stir at room temperature for 4h to obtain a white gel, which is the SAPO-34 molecular sieve catalyst precursor solution; Step 3: Add the ZSM-5 seed solution to the SAPO-34 molecular sieve catalyst precursor solution, stir at room temperature for 4 hours, then put it into a hydrothermal reactor and crystallize it in an oven at 200°C for 24 hours. Then wash the crystallized product with anhydrous ethanol and deionized water until neutral, dry the obtained white crystals in an oven at 80°C for 12 hours, and then heat it at 5°C / min in an air atmosphere. Heat to 600°C and calcine for 5 hours to obtain a ZSM-5 / SAPO-34 composite molecular sieve; Step 4: Forming and tableting the ZSM-5 / SAPO-34 composite molecular sieve and sieving it to obtain the final product, namely, the ZS-AlOOH composite molecular sieve catalyst.

[0048] Example 4 Step 1, preparing a ZSM-5 seed solution: taking 0.5 g of ZSM-5 molecular sieve and 1 g of sodium hydroxide, placing them in 20 mL of deionized water and stirring at room temperature for 1 hour, that is, a ZSM-5 seed solution; Step 2, prepare SAPO-34 precursor solution: weigh 9.73g diethanolamine (DEA) and dissolve it in 50mL deionized water and stir at room temperature for 10min, then add 5.79g tetraethyl orthosilicate, 9.07g phosphoric acid and 7.22g aluminum hydroxide in sequence and stir at room temperature for 4h to obtain a white gel, which is the SAPO-34 molecular sieve catalyst precursor solution; Step 3: Add the ZSM-5 seed solution to the SAPO-34 molecular sieve catalyst precursor solution, stir at room temperature for 4 hours, then put it into a hydrothermal reactor and crystallize it in an oven at 200°C for 24 hours. Then wash the crystallized product with anhydrous ethanol and deionized water until neutral, dry the obtained white crystals in an oven at 80°C for 12 hours, and then heat it at 5°C / min in an air atmosphere. Heat to 600°C and calcine for 5 hours to obtain a ZSM-5 / SAPO-34 composite molecular sieve; Step 4: Forming, tableting and screening the ZSM-5 / SAPO-34 composite molecular sieve to obtain the final product, namely, the ZS-Al(OH)3-1 composite molecular sieve.

[0049] Example 5 Step 1, preparing a ZSM-5 seed solution: taking 1.5 g of ZSM-5 molecular sieve and 1 g of sodium hydroxide, placing them in 20 mL of deionized water and stirring at room temperature for 1 hour, that is, a ZSM-5 seed solution; Step 2, prepare SAPO-34 precursor solution: weigh 9.73g diethanolamine (DEA) and dissolve it in 50mL deionized water and stir at room temperature for 10min, then add 5.79g tetraethyl orthosilicate, 9.07g phosphoric acid and 7.22g aluminum hydroxide in sequence and stir at room temperature for 4h to obtain a white gel, which is the SAPO-34 molecular sieve catalyst precursor solution; Step 3: Add the ZSM-5 seed solution to the SAPO-34 molecular sieve catalyst precursor solution, stir at room temperature for 4 hours, then put it into a hydrothermal reactor and crystallize it in an oven at 200°C for 24 hours. Then wash the crystallized product with anhydrous ethanol and deionized water until neutral, dry the obtained white crystals in an oven at 80°C for 12 hours, and then heat it at 5°C / min in an air atmosphere. Heat to 600°C and calcine for 5 hours to obtain a ZSM-5 / SAPO-34 composite molecular sieve; Step 4: Forming, tableting and screening the ZSM-5 / SAPO-34 composite molecular sieve to obtain the final product, namely, the ZS-Al(OH)3-2 composite molecular sieve.

[0050] Example 6 Step 1, preparing a ZSM-5 seed solution: taking 2 g of ZSM-5 molecular sieve and 1 g of sodium hydroxide, placing them in 20 mL of deionized water and stirring at room temperature for 1 hour, that is, a ZSM-5 seed solution; Step 2, prepare SAPO-34 precursor solution: weigh 9.73g diethanolamine (DEA) and dissolve it in 50mL deionized water and stir at room temperature for 10min, then add 5.79g tetraethyl orthosilicate, 9.07g phosphoric acid and 7.22g aluminum hydroxide in sequence and stir at room temperature for 4h to obtain a white gel, which is the SAPO-34 molecular sieve catalyst precursor solution; Step 3: Add the ZSM-5 seed solution to the SAPO-34 molecular sieve catalyst precursor solution, stir at room temperature for 4 hours, then put it into a hydrothermal reactor and crystallize it in an oven at 200°C for 24 hours. Then wash the crystallized product with anhydrous ethanol and deionized water until neutral, dry the obtained white crystals in an oven at 80°C for 12 hours, and then heat it at 5°C / min in an air atmosphere. Heat to 600°C and calcine for 5 hours to obtain a ZSM-5 / SAPO-34 composite molecular sieve; Step 4: Forming, pressing and screening the ZSM-5 / SAPO-34 composite molecular sieve to obtain the final product, namely, the ZS-Al(OH)3-3 composite molecular sieve.

[0051] Example 7 Step 1, preparing a ZSM-5 seed solution: taking 1 g of ZSM-5 molecular sieve and 1 g of sodium hydroxide, placing them in 10 mL of deionized water and stirring them at room temperature for 1 hour, that is, a ZSM-5 seed solution; Step 2, prepare SAPO-34 precursor solution: weigh 9.73g of diethanolamine (DEA) and dissolve it in 50mL of deionized water and stir at room temperature for 10min, then add 5.79g of tetraethyl orthosilicate, 9.07g of phosphoric acid and 4.33g of aluminum hydroxide in sequence and stir at room temperature for 4h to obtain a white gel, which is the SAPO-34 molecular sieve catalyst precursor solution; Step 3: Add the ZSM-5 seed solution to the SAPO-34 molecular sieve catalyst precursor solution, stir at room temperature for 4 hours, then put it into a hydrothermal reactor and crystallize it in an oven at 200°C for 24 hours. Then wash the crystallized product with anhydrous ethanol and deionized water until neutral, dry the obtained white crystals in an oven at 80°C for 12 hours, and then heat it at 5°C / min in an air atmosphere. Heat to 600°C and calcine for 5 hours to obtain a ZSM-5 / SAPO-34 composite molecular sieve; Step 4: Forming, tableting and screening the ZSM-5 / SAPO-34 composite molecular sieve to obtain the final product, namely, the ZS-Al(OH)3-4 composite molecular sieve.

[0052] Example 8 Step 1, preparing a ZSM-5 seed solution: taking 1 g of ZSM-5 molecular sieve and 1 g of sodium hydroxide, placing them in 20 mL of deionized water and stirring them at room temperature for 1 hour, which is a ZSM-5 seed solution; Step 2, prepare SAPO-34 precursor solution: weigh 9.73g diethanolamine (DEA) and dissolve it in 50mL deionized water and stir at room temperature for 10min, then add 5.79g tetraethyl orthosilicate, 9.07g phosphoric acid and 8.66g aluminum hydroxide in sequence and stir at room temperature for 4h to obtain a white gel, which is the SAPO-34 molecular sieve catalyst precursor solution; Step 3: Add the ZSM-5 seed solution to the SAPO-34 molecular sieve catalyst precursor solution, stir at room temperature for 4 hours, then put it into a hydrothermal reactor and crystallize it in an oven at 200°C for 24 hours. Then wash the crystallized product with anhydrous ethanol and deionized water until neutral, dry the obtained white crystals in an oven at 80°C for 12 hours, and then heat it at 5°C / min in an air atmosphere. Heat to 600°C and calcine for 5 hours to obtain a ZSM-5 / SAPO-34 composite molecular sieve; Step 4: Forming, tableting and screening the ZSM-5 / SAPO-34 composite molecular sieve to obtain the final product, namely, the ZS-Al(OH)3-5 composite molecular sieve.

[0053] Comparative Example 1 Weigh 7.76g of sodium hydroxide and 7.22g of aluminum hydroxide, dissolve in 100mL of deionized water and stir at room temperature for 0.5h, then add 4.23g of tetrapropylammonium bromide and 5.79g of tetraethyl orthosilicate in turn and stir at room temperature for 4h; add 1g of SAPO-34 molecular sieve and stir at room temperature for 4h, then put it into a hydrothermal reactor and crystallize it in an oven at 200℃ for 24h. Then wash the crystallized product with anhydrous ethanol and deionized water until neutral, dry the obtained white crystals in an oven at 80℃ for 12h, and then heat it at 5℃ / min in an air atmosphere. Heat to 600℃ and roast for 5h, press and sieve to obtain SZ-Al(OH)3 composite molecular sieve.

[0054] Comparative Example 2 Weigh 9.73g of diethanolamine (DEA) and dissolve it in 50mL of deionized water and stir at room temperature for 10min. Then add 5.79g of tetraethyl orthosilicate, 9.07g of phosphoric acid, and 7.22g of aluminum hydroxide in turn and stir at room temperature for 4h. Then put it into a hydrothermal reactor and crystallize it in an oven at 200℃ for 24h. Then wash the crystallized product with anhydrous ethanol and deionized water until neutral, dry the obtained white crystals in an oven at 80℃ for 12h, and then heat it at 5℃ / min in an air atmosphere. Heat to 600℃ and calcine for 5h to obtain SAPO-34 molecular sieve. Take 1g of ZSM-5 molecular sieve and 1g of SAPO-34 molecular sieve and place them in 10mL of deionized water and stir at room temperature for 3h, filter, dry and calcine, press and sieve to obtain ZS-1 composite molecular sieve.

[0055] Comparative Example 3 Take 0.5 g of ZSM-5 molecular sieve and 1 g of SAPO-34 molecular sieve obtained in Comparative Example 2, place in 10 mL of deionized water, stir at room temperature for 3 h, filter, dry, roast, press into tablets and sieve to obtain ZS-2 composite molecular sieve.

[0056] Comparative Example 4 Take 1.5 g of ZSM-5 molecular sieve and 1 g of SAPO-34 molecular sieve obtained in Comparative Example 2, place them in 10 mL of deionized water and stir at room temperature for 3 h, filter, dry, roast, press into tablets and sieve to obtain ZS-3 composite molecular sieve.

[0057] The catalysts prepared in Examples 2 to 6 were characterized by the same method and results as in Example 1, which will not be described in detail here.

[0058] Example 9 The performance of the catalysts prepared in Examples 1 to 8 and Comparative Examples 1 to 4 was evaluated by the following specific method: The performance evaluation of the catalyst was carried out in a vertical tube furnace. The process of catalytic pyrolysis was as follows: the catalyst and bagasse were weighed in a ratio of 1:1, 0.5 g each was mixed evenly and placed in a quartz crucible, which was then loaded into the temperature control zone of the tube furnace; nitrogen was introduced for 30 minutes before the reaction to remove the air in the tube furnace. After the nitrogen purge was completed, the temperature was raised to 550°C at a rate of 50°C / min, and then the temperature was kept constant for 5 minutes. The gas products produced by the pyrolysis were discharged and condensed and collected, and the liquid products were collected and analyzed for the distribution of organic matter by GC-MS. The results are shown in Table 2.

[0059] Table 2 Distribution of liquid products of bagasse pyrolysis with different catalysts As can be seen from Table 2, the results of the liquid products of Example 1 and Example 2-3 are compared. The yield of furans in the liquid product of Example 1 is increased, and all of them are the target product 2,3-dihydrobenzofuran (that is, the furan compounds in the liquid product are basically about 100% in the form of 2,3-dihydrobenzofuran). Comparing Example 1, Example 7 and Example 8, adjusting the amount of aluminum source, the yield of furans in the liquid product first increases and then begins to decrease with the increase of the amount of aluminum source. In Example 1, 2,3-dihydrobenzofuran accounts for 48.15% of the liquid product. In general, the ZS-Al(OH)3 composite molecular sieve synthesized with aluminum hydroxide as a raw material has high stability, suitable acid strength, and a relative crystallinity of 92.68%, which can effectively improve the catalytic activity and the reaction performance of the catalyst.

[0060] In general, the ZS-Al(OH)3 composite molecular sieve synthesized with aluminum hydroxide as raw material has high stability, suitable acid strength, and a relative crystallinity of 92.68%, which can effectively improve the catalytic activity and reaction performance of the catalyst. Figure 3 and Figure 4 Comparative calculations show that the catalysts in Examples 1 and 4 present type I and type IV composite isotherms, indicating that the ZSM-5 / SAPO-34 composite molecular sieve has typical micro-mesoporous composite channels. The isotherm slope and hysteresis loop of Example 1 are the largest, indicating that it has a large number of mesopores. The specific surface area of ​​Example 1 is 435m 2 / g, pore volume is 0.10cm 3 / g, average pore size 3.77nm. Example 4 has a specific surface area of ​​419m 2 / g, pore volume is 0.09cm 3 / g, average pore size 3.21nm.

[0061] By comparing Examples 1 to 3, it is concluded that the ZS-Al(OH)3 composite molecular sieve synthesized with aluminum hydroxide as the aluminum source has high crystallinity and appropriate acid strength. The catalyst is more likely to adsorb glucose molecules in sugarcane bagasse, causing them to first react with Lewis acid Al 3+ The isomerization site is converted into fructose, and finally, the Brønsted acid Si-OH-Al site catalyzes the dehydration of fructose to form furan. By comparing Examples 4 to 6 with Comparative Examples 1 to 4, it can be concluded that with the introduction of ZSM-5 molecular sieve, combined with Figure 2 It can be seen that the composite molecular sieve has obvious holes and irregular cracks. The existence of the layered structure provides better accessibility for the raw material to the inner surface of the crystal and the product to the outer surface of the crystal, thereby achieving an increase in the selectivity of 2,3-dihydrobenzofuran in the liquid phase product.

[0062] The above examples are for the purpose of illustrating the embodiments disclosed by the present invention and are not to be construed as limitations of the present invention. In addition, the various modifications listed herein and the variations of methods and compositions in the invention are obvious to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been specifically described in conjunction with various specific preferred embodiments of the present invention, it should be understood that the present invention should not be limited to these specific embodiments. In fact, various modifications obvious to those skilled in the art as described above to obtain the invention should be included within the scope of the present invention.

Claims

1. A method for preparing a ZSM-5 / SAPO-34 composite molecular sieve catalyst, characterized in that: The following steps are involved: Step 1, preparing a ZSM-5 seed solution: dissolving a ZSM-5 molecular sieve in an alkaline solution to prepare a ZSM-5 seed solution; Step 2, preparing SAPO-34 precursor solution: dissolving the organic template in deionized water, adding the silicon source dropwise, mixing evenly, adding the phosphorus source and the aluminum source, stirring evenly, and obtaining a white gel, which is the SAPO-34 molecular sieve catalyst precursor solution; Step 3, the ZSM-5 seed solution is mixed with the SAPO-34 molecular sieve catalyst precursor solution and then crystallized, and the crystallized product is filtered, washed, dried, and calcined to obtain a ZSM-5 / SAPO-34 composite molecular sieve; Step 4: Forming, tableting and screening the ZSM-5 / SAPO-34 composite molecular sieve to obtain the final product.

2. The method for preparing the ZSM-5 / SAPO-34 composite molecular sieve catalyst according to claim 1, characterized in that: In step 2, the silicon source is selected from at least one of silica sol, water glass, activated silicon dioxide, and tetraethyl orthosilicate; the aluminum source is selected from at least one of pseudo-boehmite, aluminum isopropoxide, aluminum hydroxide, and aluminum salts; and the phosphorus source is selected from at least one of orthophosphoric acid, phosphorous acid, and phosphates.

3. The method for preparing the ZSM-5 / SAPO-34 composite molecular sieve catalyst according to claim 2, characterized in that: In step 2, the silicon source is tetraethyl orthosilicate; the aluminum source is aluminum hydroxide; and the phosphorus source is orthophosphoric acid.

4. The method for preparing the ZSM-5 / SAPO-34 composite molecular sieve catalyst according to claim 3, characterized in that: The silicon source, aluminum source and phosphorus source in step 2 are expressed in the form of oxide molar ratio, and the composition ratio is as follows: n(SiO2):n(Al2O3):n(P2O5)=1:(0.5~3):(0.5~4).

5. The method for preparing the ZSM-5 / SAPO-34 composite molecular sieve catalyst according to claim 1, characterized in that: The alkaline solution in step 1 is a sodium hydroxide aqueous solution with a mass concentration of 0.01-1%, and the solid-liquid ratio of the ZSM-5 molecular sieve to the alkaline solution is 0.5-2 g: 20 mL.

6. The method for preparing the ZSM-5 / SAPO-34 composite molecular sieve catalyst according to claim 1, characterized in that: The organic template in step 2 is selected from at least one of diethanolamine, triethylamine and tetraethylammonium hydroxide.

7. The method for preparing the ZSM-5 / SAPO-34 composite molecular sieve catalyst according to claim 1, characterized in that: In step 3, the solid product of the crystallized product after filtration is washed with water and ethanol to a pH of 6-9, and calcined at a temperature of 5°C / min in an air atmosphere, the calcination temperature is 500-700°C, and the calcination time is 3-7h.

8. A ZSM-5 / SAPO-34 composite molecular sieve catalyst prepared according to the preparation method according to any one of claims 1 to 7.

9. Use of the ZSM-5 / SAPO-34 composite molecular sieve catalyst according to claim 8 in the rapid catalytic pyrolysis of biomass to produce 2,3-dihydrobenzofuran.

10. The use according to claim 9, characterized in that The application method comprises: The ZSM-5 / SAPO-34 composite molecular sieve catalyst and biomass are mixed and uniformly loaded in the constant temperature zone of a vertical tube furnace; N2 was introduced to purge and expel the air. After the purge was completed, a pyrolysis reaction was carried out in a N2 atmosphere. The temperature was raised to a reaction temperature of 400-600°C at a rate of 30-60°C / min, and the constant temperature was maintained for 1-25 min. The liquid products produced by the pyrolysis were collected.

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