Modified ZSM-5 molecular sieve catalyst for preparing 2,3-dihydrobenzofuran by pyrolysis of biomass, preparation method and application thereof

Abstract

The invention discloses a modified ZSM-5 molecular sieve catalyst and a preparation method and application for preparing 2,3-dihydrobenzofurans by pyrolysis of biomass, and the catalyst is prepared as follows: Aluminum hydroxide is used as an aluminum source to synthesize a ZSM-5 precursor by hydrothermal reaction, and then an organic base is used for treatment, and the rare earth metal M salt is ground, solid ion exchange is performed, and then an appropriate amount of deionized water is added to heat in a water bath at a certain temperature, and liquid phase ion exchange is performed and then roasted to obtain a rare earth metal modified ZSM-5 molecular sieve catalyst. The catalyst prepared by the present invention is a cross-shaped square structure, with a large specific surface area and a suitable pore structure, while increasing the active site and the pyrolysis product contact area, effective shape-selective catalysis is performed, thereby effectively improving the selectivity of the target product 2,3-dihydrobenzofurans, and greatly reducing the type of the final product, reducing subsequent processing costs, and providing technical support for promoting the industrialization process.

Description

Technical Field

[0001] The invention belongs to the technical field of biomass energy utilization, and specifically relates to a modified ZSM-5 molecular sieve catalyst for preparing 2,3-dihydrobenzofuran by pyrolysis of biomass, and a preparation method and application thereof. Background Art

[0002] Bagasse, the residue left after sugarcane sugar production, is a potential resource for producing valuable chemical products and mixed fuels such as furfural and furan. Using bagasse to produce high-value-added chemical products or platform compounds is an effective way to solve agricultural waste. It can not only solve environmental problems, but also bring economic benefits. Among them, 2,3-dihydrobenzofuran is a fine chemical raw material and an intermediate for the synthesis of important drugs. It can be used for traumatic and ischemic central nervous system injuries. At present, its preparation method is mostly chemical synthesis, which has a complex synthesis route and harsh reaction conditions. It is easy to cause environmental pollution, so it cannot be widely used; through biomass production, environmental pollution can be greatly reduced, while bringing economic benefits.

[0003] Zeolite molecular sieves are widely used in the catalytic pyrolysis of biomass. Among them, ZSM-5 zeolite molecular sieve has a microporous structure, high crystallinity, and adjustable acidity, which enables it to selectively catalyze deoxygenation reactions and hydrocarbon production; but its pores are still too narrow, resulting in difficulties in the diffusion process of large molecules, and the products after the reaction may clog the pores of the molecular sieve.

[0004] The regulation of molecular sieves mainly focuses on expanding the specific surface area, increasing the pore volume and adjusting the acidity of the molecular sieve. Although patent CN115231587 prepared nano-scale ZSM-5 molecular sieves, they are prone to clustering and the specific surface area is not significantly enlarged (350-450m 2 / g), and the irritating dicyclohexylamine additive is used in the synthesis process, and the synthesis takes too long. Patent CN111099620 discloses a method for treating ZSM-5 molecular sieve with NaOH after contact with a mesoporous directing agent, which can obtain a rich mesoporous structure. The mesoporous directing agent used in this method is a piperidine compound, which is flammable, strongly irritating to the body, and discharges a large amount of strong alkaline solution, and the process is not green. CN113943008 discloses a method for preparing Cu-ZSM-5, which directly puts a certain proportion of copper nitrate into a prepared precursor solution, performs in-situ synthesis, and directly synthesizes Cu-ZSM-5 molecular sieves. The molecular sieve obtained by this method has a large amount of metal loss into the skeleton, which is limited, and the acidity of the molecular sieve cannot be well regulated. Summary of the invention

[0005] In view of the above technical problems existing in the prior art, the purpose of the present invention is to provide a modified ZSM-5 molecular sieve catalyst for preparing 2,3-dihydrobenzofuran by pyrolysis of biomass, and its preparation method and application. The present invention provides a method for preparing a ZSM-5 molecular sieve catalyst with a cross-square structure having suitable acidity and pore structure, and after treating with an organic base to reduce the acid strength, ion exchange with a rare earth metal is performed to obtain a ZSM-5 molecular sieve catalyst suitable for selectively preparing 2,3-dihydrobenzofuran by high-temperature catalytic pyrolysis of biomass, and the conversion rate of bagasse is high, and in the product distribution, the selectivity of 2,3-dihydrobenzofuran can reach 45.86%.

[0006] The technical solution adopted by the present invention is as follows:

[0007] The method for preparing a modified ZSM-5 molecular sieve catalyst for preparing 2,3-dihydrobenzofuran by pyrolysis of biomass comprises the following steps:

[0008] 1) Preparation of ZSM-5 molecular sieve precursor solution: After dissolving sodium hydroxide and aluminum source in deionized water, add template agent tetrapropylammonium bromide, mix well and then add tetraethyl orthosilicate; stir and age to obtain a white viscous liquid, transfer to a hydrothermal kettle for hydrothermal reaction, stand at room temperature after the reaction is completed, filter and wash the crystals to neutrality, and dry to obtain a ZSM-5 molecular sieve catalyst precursor;

[0009] 2) Pretreatment of the precursor: adding an organic base solution to the precursor of step 1) for treatment, and then filtering, washing, and drying to obtain a ZSM-5 (A) precursor;

[0010] 3) Introduction of metal ions: The alkali-treated precursor of step 2) is mixed with a rare earth metal M salt and then fully ground to perform solid ion exchange to obtain a mixed powder; deionized water is then added to the mixed powder, stirred and liquid ion exchange is performed under a heating environment, after which the mixture is filtered and dried to a solid state; the mixture is then heated and calcined in a muffle furnace, and cooled to obtain an M / ZSM-5(A) molecular sieve catalyst;

[0011] 4) Catalyst molding: The obtained M / ZSM-5 (A) molecular sieve catalyst is molded and sieved into a certain mesh size, and the preparation is completed.

[0012] Furthermore, in step 1), the aluminum source is aluminum hydroxide, and the ratio of the ethyl orthosilicate raw material to the aluminum source raw material expressed in the form of oxide molar ratio is n(SiO2) / (Al2O3)=20-80.

[0013] Furthermore, in step 1), the raw materials are expressed in the form of oxide molar ratio, and the composition ratio is as follows:

[0014] n(TPABr):n(SiO2)=1:2~20; n(Na2O):n(SiO2)=1:4~20.

[0015] Furthermore, in step 1), the mass concentration of sodium hydroxide in deionized water is 0.3-1.5%.

[0016] Furthermore, in step 1), the aging time is 3-15 hours, and the temperature is room temperature; the hydrothermal reaction temperature is 120-180° C., and the hydrothermal reaction time is 12-72 hours.

[0017] Furthermore, in step 2), the organic base is at least one of hexadecyl ammonium bromide and triethylamine, and the concentration of the organic base solution is 0.01-0.5 mol / L; in step 2), the solid-liquid ratio of the precursor to the organic base solution is 1 g:5-25 mL.

[0018] Furthermore, in step 3), the rare earth metal salt is one of the lanthanide metals La(NO3)3·6H2O, Ce(NO3)3·6H2O, Sm(NO3)3·6H2O, Nd(NO3)3·6H2O, and Pr(NO3)3·5H2O, and the mass of metal M in the rare earth metal M salt is 10% to 25%, preferably 15 to 23%, of the mass of the ZSM-5(A) precursor.

[0019] Furthermore, in step 3), the mass ratio of deionized water to the mixed powder is 5-25:1, the heating method is a water bath at 40-80° C., and the ion exchange time is 3-10 hours.

[0020] Furthermore, in step 3), the calcination temperature is 400-600° C. and the calcination time is 2-6 hours.

[0021] Furthermore, the present invention also defines a cross-square structure ZSM-5 molecular sieve catalyst prepared by the method. The catalyst prepared by the present invention is a cross-square structure, has a large specific surface area and a suitable pore structure, increases the contact area between the active site and the pyrolysis product, and performs effective shape-selective catalysis, thereby effectively improving the selectivity of the target product 2,3-dihydrobenzofuran, and greatly reducing the types of final products, reducing subsequent processing costs, and providing technical support for promoting the industrialization process.

[0022] Furthermore, the present invention also defines the application of the modified ZSM-5 molecular sieve catalyst prepared by the method in catalyzing the pyrolysis of biomass to produce 2,3-dihydrobenzofuran, which is characterized in that the biomass and the catalyst are mixed evenly and then loaded into a reaction tube, which is suspended in the constant temperature zone of a vertical pyrolysis furnace. Before the reaction starts, N2 is used to purge out oxygen, and then the temperature is rapidly increased to 450-650°C at a heating rate of 20-80°C / min in an N2 atmosphere to carry out a pyrolysis reaction to generate a product containing 2,3-dihydrobenzofuran, and the reaction time is 1-30 minutes, preferably 5-10 minutes; wherein the biomass is sugarcane bagasse.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1) The aluminum source used in the preparation process of the ZSM-5 molecular sieve of the present invention is aluminum hydroxide, and the synthesized ZSM-5 has a cross-shaped square structure, has a larger specific surface area and pore volume, can provide more surface active sites for the catalytic reaction, and is more conducive to the subsequent metal entering the molecular sieve pores and framework;

[0025] 2) The present invention uses an organic weak base to treat the ZSM-5 molecular sieve before metal ion exchange. The base treatment increases the pore size of the molecular sieve, making it easier for the intermediate product to enter the molecular sieve for reaction. However, the organic base does not destroy the skeleton structure of the molecular sieve, and the synthesized cross structure can still be maintained so that it does not collapse.

[0026] 3) The catalyst obtained by the present invention is applied to catalytic cracking of biomass. Compared with direct cracking of biomass, the types of products are greatly reduced, and the difficulty of subsequent purification steps is reduced; the total types of products obtained by the catalyst are reduced to less than 30, and the selectivity of 2,3-dihydrobenzofuran can reach 45.86%. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a scanning electron microscope image of the ZSM-5 molecular sieve catalyst prepared using Al(OH)3 as the aluminum source in Example 1;

[0028] Figure 2 This is a scanning electron microscope image of the ZSM-5 molecular sieve catalyst prepared using Al(NO3)·9H2O as the aluminum source in Comparative Example 1;

[0029] Figure 3 The reaction performance evaluation results of catalysts 1-5 and the catalysts obtained in comparative examples 1-2 are shown. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0031] Example 1 Preparation of ZSM-5 molecular sieve catalyst using Al(OH)3 as aluminum source

[0032] Dissolve 1.5316g NaOH and 0.4958g Al(OH)3 in 150ml deionized water and stir, then dissolve 8.4584g TPABr in 50ml deionized water and add dropwise into the original solution, continue stirring, and finally add 25.1309g TEOS dropwise. The stirring rate is 800r / min, and the stirring is continued for 9h to obtain a white viscous liquid, which is placed in a hydrothermal kettle and hydrothermally heated at 170℃ for 24h, taken out and allowed to stand for 12h, and the crystal product is washed with anhydrous ethanol and deionized water to neutrality, and the obtained white crystals are dried at 110℃ for 10h to obtain a ZSM-5 precursor. The preparation method of the ZSM-5 precursor in the following examples is the same as that in Example 1.

[0033] The ZSM-5 precursor obtained in Example 1 was placed in an air atmosphere and heated to 550°C (heating rate of 5°C / min), and then calcined at a constant temperature for 4 hours to obtain a cross-shaped catalyst 1 prepared with aluminum hydroxide as an aluminum source. The atomic percentages of the catalyst were: Si content was 36.18%, and Al content was 0.32%.

[0034] The scanning electron microscope images are as follows Figure 1 As shown, it can be seen that the synthesized ZSM-5 molecular sieve catalyst has a cross structure with clear edges and corners.

[0035] Example 2 ZSM-5 molecular sieve catalyst treated with organic base

[0036] The preparation method of ZSM-5 precursor is the same as that in Example 1.

[0037] 1.0934 g of CTAB was weighed to prepare a 0.03 mol / L solution, 50 ml of the solution was added dropwise to 5 g of ZSM-5 precursor, and the mixture was allowed to stand at room temperature for 2 h. After filtering and washing, the mixture was dried at 110 °C, and then heated to 550 °C in an air atmosphere (heating rate of 5 °C / min), and then calcined at a constant temperature for 4 h to obtain catalyst 2.

[0038] Example 3 La ion exchange ZSM-5 molecular sieve catalyst

[0039] The preparation method of ZSM-5 precursor is the same as that of Example 1. 1.0934 g of CTAB is weighed to prepare a 0.03 mol / L solution, 50 ml of the solution is added dropwise to 5 g of ZSM-5 precursor, and the mixture is allowed to stand at room temperature for 2 h, filtered and washed, and dried at 110° C. to obtain an alkali-treated ZSM-5 precursor.

[0040] Weigh 0.9315 g of lanthanum nitrate hexahydrate and 2 g of dry alkali-treated ZSM-5 precursor in a mortar and grind them thoroughly for about 20 minutes; then transfer them to a beaker, add 30 ml of deionized water, heat in a water bath at 80°C for liquid ion exchange for 6 hours, then filter and dry, heat to 550°C in an air atmosphere (heating rate of 5°C / min), and then calcine at a constant temperature for 4 hours to obtain catalyst 3.

[0041] Example 4 Ce ion exchange ZSM-5 molecular sieve catalyst

[0042] The preparation method of ZSM-5 precursor is the same as that of Example 1. 1.0934 g of CTAB is weighed to prepare a 0.03 mol / L solution, 50 ml of the solution is added dropwise to 5 g of ZSM-5 precursor, and the mixture is allowed to stand at room temperature for 2 h, filtered and washed, and dried at 110° C. to obtain an alkali-treated ZSM-5 precursor.

[0043] Weigh 0.9297 g of cerium nitrate hexahydrate and 2 g of dry alkali-treated ZSM-5 precursor in a mortar and grind them thoroughly for about 20 minutes; then transfer them to a beaker, add 30 ml of deionized water, heat in a water bath at 80°C for liquid ion exchange for 6 hours, then filter and dry, heat to 550°C in an air atmosphere (heating rate of 5°C / min), and then calcine at a constant temperature for 4 hours to obtain catalyst 4.

[0044] Example 5 Sm ion exchange ZSM-5 molecular sieve catalyst

[0045] The preparation method of ZSM-5 precursor is the same as that of Example 1. 1.0934 g of CTAB is weighed to prepare a 0.03 mol / L solution, 50 ml of the solution is added dropwise to 5 g of ZSM-5 precursor, and the mixture is allowed to stand at room temperature for 2 h, filtered and washed, and dried at 110° C. to obtain an alkali-treated ZSM-5 precursor.

[0046] Weigh 1.3302 g of samarium nitrate hexahydrate and 2 g of dry alkali-treated ZSM-5 precursor in a mortar and grind them thoroughly for about 20 minutes; then transfer them to a beaker, add 30 ml of deionized water, heat in a water bath at 80°C for liquid ion exchange for 6 hours, then filter and dry, heat to 550°C in an air atmosphere (heating rate of 5°C / min), and then calcine at a constant temperature for 4 hours to obtain catalyst 5.

[0047] Comparative Example 1 ZSM-5 molecular sieve catalyst prepared using Al(NO3)·9H2O as aluminum source

[0048] Dissolve 1.5316g of NaOH and 2.3845g of Al(NO3)·9H2O in 150ml of deionized water and stir. Then, dissolve 8.4584g of TPABr in 50ml of deionized water and add dropwise into the original solution. Continue stirring. Finally, add 25.1309g of TEOS dropwise. The stirring rate is 800r / min. After continuing stirring for 9h, put it into a hydrothermal kettle and hydroheat it at 170℃ for 24h. After taking it out, let it stand for 12h. Use anhydrous ethanol and deionized water to filter and wash the crystal product until it is neutral. After the white crystals are dried at 110℃ for 10h, a ZSM-5 precursor is obtained. The temperature is raised to 550℃ (heating rate is 5℃ / min) in an air atmosphere. After that, it is calcined at a constant temperature for 4 hours to obtain the spherical comparative example 1 prepared with sodium aluminate as the aluminum source. Its scanning electron microscope image is as follows Figure 2 As shown, the synthesized ZSM-5 molecular sieve has an ellipsoidal structure.

[0049] Comparative Example 2 Preparation of La-ZSM-5 Molecular Sieve Catalyst by Impregnation Method

[0050] Dissolve 1.5316g NaOH and 0.4958g Al(OH)3 in 150ml deionized water and stir, then dissolve 8.4584g TPABr in 50ml deionized water and add dropwise into the original solution, continue stirring, and finally add 25.1309g TEOS dropwise. Stirring rate is 800r / min, continue stirring for 9h, put into hydrothermal kettle and hydrotherm at 170℃ for 24h, take out and let stand for 12h, filter and wash the crystal product with anhydrous ethanol and deionized water to neutrality, and obtain white crystals. Dry at 110℃ for 10h to obtain ZSM-5 precursor, heat to 550℃ (heating rate is 5℃ / min) in air atmosphere, and then calcine at constant temperature for 4 hours to obtain ZSM-5 molecular sieve. 0.9315 g of lanthanum nitrate hexahydrate was dissolved in 2.5 ml of deionized water, and the lanthanum nitrate solution was then added dropwise to 2 g of ZSM-5 molecular sieve. After immersion at room temperature for 24 hours, the mixture was dried at 110° C. and calcined to obtain Comparative Example 2.

[0051] The BET characterization data of catalysts 1-5 and the catalysts obtained in comparative examples 1-2 are shown in Table 1.

[0052] Table 1 Specific surface area and pore size distribution of modified molecular sieves

[0053]

[0054]

[0055] The reaction performance of the catalyst was evaluated in a vertical cracking furnace. The cracking process was as follows: 0.8 g of the catalyst and bagasse were weighed at a mass ratio of 1:1, mixed evenly, and placed in a quartz crucible, which was then loaded into the cracking furnace; nitrogen was introduced for 10 minutes to remove oxygen from the reactor. After the purge, the temperature was raised to 500°C at a rate of 50°C / min and kept constant for 5 minutes. The reaction product was discharged and condensed and collected. The liquid phase product was collected and analyzed for organic matter distribution by GC-MS. The results are as follows: Figure 3 shown.

[0056] from Figure 3 It can be seen that compared with the results of the liquid products of Comparative Examples 1 and 2, the yields of furans of Catalysts 1 and 3 are increased, and both are the target product 2,3-dihydrobenzofuran (that is, the furan compounds in the liquid products are basically about 100% in the form of 2,3-dihydrobenzofuran), and 2,3-dihydrobenzofuran accounts for 45.86% of the liquid products in Catalyst 3. In general, the modified molecular sieve has a larger specific surface area and pore volume, and the rare earth metal ion exchange can provide metal active sites, effectively improve the catalytic activity, facilitate the breaking of the carbon-carbon bonds of macromolecules, and maintain good catalyst reaction performance.

[0057] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be regarded as being limited to the specific forms described in the embodiments.

Claims

1. A method for preparing a modified ZSM-5 molecular sieve catalyst for preparing 2,3-dihydrobenzofuran by pyrolysis of biomass, characterized in that The steps include: 1) Preparation of ZSM-5 molecular sieve precursor solution: After dissolving sodium hydroxide and aluminum source in deionized water, add template agent tetrapropylammonium bromide, mix well and then add tetraethyl orthosilicate; stir and age to obtain a white viscous liquid, transfer it into a hydrothermal kettle for hydrothermal reaction, let it stand at room temperature after the reaction, filter and wash the crystallized product after the reaction until it is neutral, and dry it to obtain a ZSM-5 molecular sieve catalyst precursor; 2) Pretreatment of the precursor: adding an organic base solution to the precursor in step 1) for treatment, followed by filtering, washing, and drying to obtain a ZSM-5 (A) precursor; 3) Introduction of metal ions: The alkali-treated precursor of step 2) is mixed with a rare earth metal M salt and then fully ground to perform solid ion exchange to obtain a mixed powder; deionized water is then added to the mixed powder, stirred and liquid ion exchange is performed under a heating environment, and after completion, the mixture is filtered and dried to a solid state; the mixture is then heated and calcined in a muffle furnace, and the M / ZSM-5(A) molecular sieve catalyst is obtained after cooling; 4) Catalyst molding: The obtained M / ZSM-5(A) molecular sieve catalyst is molded and sieved into a certain mesh size, and the preparation is completed; In step 1), the aluminum source is aluminum hydroxide, and the ratio of the ethyl orthosilicate raw material to the aluminum source raw material is expressed in the form of oxide molar ratio, and the ratio is n (SiO2) / (Al2O3) = 20~80.

2. The method for preparing a modified ZSM-5 molecular sieve catalyst for preparing 2,3-dihydrobenzofuran by pyrolysis of biomass as claimed in claim 1, characterized in that In step 1), the raw materials are expressed in the form of oxide molar ratio, and the composition ratio is as follows: n (TPABr): n (SiO2) = 1: 2~20; n (Na2O): n (SiO2) = 1: 4~20; The mass concentration of sodium hydroxide in deionized water in step 1) is 0.3-1.5%.

3. The method for preparing a modified ZSM-5 molecular sieve catalyst for preparing 2,3-dihydrobenzofuran by pyrolysis of biomass as claimed in claim 1, characterized in that In step 1), the aging time is 3-15 hours at room temperature; the hydrothermal reaction temperature is 120-180° C., and the hydrothermal reaction time is 12-72 hours.

4. The method for preparing a modified ZSM-5 molecular sieve catalyst for preparing 2,3-dihydrobenzofuran by pyrolysis of biomass as claimed in claim 1, characterized in that In step 2), the organic base is at least one of hexadecyl ammonium bromide and triethylamine, and the concentration of the organic base solution is 0.01-0.5 mol / L; in step 2), the solid-liquid ratio of the precursor to the organic base solution is 1 g:5-25 mL.

5. The method for preparing a modified ZSM-5 molecular sieve catalyst for preparing 2,3-dihydrobenzofuran by pyrolysis of biomass as claimed in claim 1, characterized in that In step 3), the rare earth metal M salt is one of the lanthanide metal nitrates La(NO3)3·6H2O, Ce(NO3)3·6H2O, Sm(NO3)3·6H2O, Nd(NO3)3·6H2O, and Pr(NO3)3·5H2O, and the mass of the metal M in the rare earth metal M salt is 10% to 25% of the mass of the ZSM-5(A) precursor.

6. The method for preparing a modified ZSM-5 molecular sieve catalyst for preparing 2,3-dihydrobenzofuran by pyrolysis of biomass as claimed in claim 5, characterized in that In step 3), the mass of metal M in the rare earth metal M salt is 15 to 23% of the mass of the ZSM-5(A) precursor.

7. The method for preparing a modified ZSM-5 molecular sieve catalyst for preparing 2,3-dihydrobenzofuran by pyrolysis of biomass as claimed in claim 1, characterized in that In step 3), the mass ratio of deionized water to the mixed powder is 5-25:1, the heating method is a water bath at 40-80° C., and the ion exchange time is 3-10 hours.

8. The method for preparing a modified ZSM-5 molecular sieve catalyst for preparing 2,3-dihydrobenzofuran by pyrolysis of biomass as claimed in claim 1, characterized in that In step 3), the calcination temperature is 400-600°C and the calcination time is 2-6 hours.

9. A modified ZSM-5 molecular sieve catalyst for preparing 2,3-dihydrobenzofuran by pyrolysis of biomass, prepared by the method according to any one of claims 1 to 8.

10. Use of the modified ZSM-5 molecular sieve catalyst according to claim 9 in catalyzing biomass pyrolysis to produce 2,3-dihydrobenzofuran, characterized in that The biomass and the catalyst are mixed evenly and then loaded into a reaction tube, which is suspended in a constant temperature zone of a vertical pyrolysis furnace. Before the reaction starts, N2 is used to purge oxygen, and then the temperature is rapidly increased to 450-650°C at a heating rate of 20-80°C / min in a N2 atmosphere to perform a pyrolysis reaction to generate a product containing 2,3-dihydrobenzofuran, and the reaction time is 1-30 minutes; wherein the biomass is bagasse.

11. Use of the modified ZSM-5 molecular sieve catalyst according to claim 10 in catalyzing biomass pyrolysis to produce 2,3-dihydrobenzofuran, characterized in that The reaction time of the pyrolysis reaction is 5 to 10 minutes.

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