Hierarchical pore molecular sieve for efficient depolymerization of industrial lignin as well as preparation and application of hierarchical pore molecular sieve

Abstract

The invention relates to a hierarchical pore molecular sieve for efficient depolymerization of industrial lignin and preparation and application thereof, and the preparation method comprises the following steps: dissolving N, N, N ', N'-tetramethyl-1, 6-diaminohexane and 1-bromooctadecane in a first solvent, reacting, filtering, washing, and drying to obtain an intermediate; dissolving the intermediate and 1-bromohexane in a second solvent, carrying out reflux reaction, filtering, washing and drying to obtain C18-6-6Br2; the preparation method comprises the following steps: mixing a silicon source, an aluminum source, an alkali source, C18-6-6Br2 and deionized water to form gel, aging and then statically crystallizing; and filtering, washing and drying the crystallized product, roasting in flowing air, carrying out ion exchange with an ammonium salt solution, washing, drying and roasting to obtain the hierarchical pore molecular sieve. The molecular sieve can meet the mass transfer requirement of industrial lignin, and monomer and dimer aromatic compounds are prepared with high yield by utilizing the reaction path of hydrolysis and alcohol solvent in-situ hydrogen supply hydrogenolysis.

Description

Technical Field

[0001] This invention relates to the field of multi-level porous molecular sieve preparation technology, and in particular to a multi-level porous molecular sieve for efficient depolymerization of industrial lignin, its preparation and application. Background Technology

[0002] Lignin, a major component of lignocellulose biomass, accounts for 15-30% of its mass. It is the most abundant natural aromatic polymer in the world and an ideal raw material for developing bio-based aromatic chemicals and fuels. Developing efficient lignin depolymerization technology is crucial for achieving the goal of full utilization of biomass components and carbon neutrality.

[0003] Among numerous lignin conversion strategies, catalytic depolymerization is a highly promising approach. However, industrial lignin (such as sulfate lignin) undergoes severe condensation reactions during pulping, forming numerous persistent C–C bonds, making it difficult to effectively depolymerize using traditional catalytic systems. Currently, much research focuses on using noble metal catalysts (such as Pt, Pd, and Ru) to achieve the hydrogenolysis of industrial lignin under high-pressure hydrogen. While effective, these systems are costly and pose safety risks. In contrast, in-situ catalytic transfer hydrogenation using hydrogen donor solvents such as alcohols is a safer and more economical alternative. Meanwhile, molecular sieves, due to their tunable acidity and shape selectivity, show great potential in the catalytic conversion of industrial lignin. However, the narrow pores of conventional microporous molecular sieves severely limit the mass transfer efficiency of lignin macromolecules and their oligomeric fragments, resulting in poor accessibility to active sites within the catalyst, low depolymerization efficiency, and susceptibility to deactivation due to carbon deposition.

[0004] To address mass transfer limitations, researchers have developed molecular sieve catalysts with hierarchical porous structures. For example, CN120169416A discloses a method for preparing hierarchical porous molecular sieves; CN120157147A relates to the synthesis of hierarchical porous molecular sieves using dual template agents for cycloalkane dehydrogenation processes. However, molecular sieve catalysts prepared using these existing methods are mainly suitable for catalytic conversion in the petrochemical field. The pore structure design and acid regulation are not sufficiently targeted at the complex and resilient industrial lignin macromolecules, especially in achieving limited effectiveness in breaking C–C bonds such as condensation methylene bonds in industrial lignin. Therefore, existing molecular sieve catalysts struggle to achieve efficient depolymerization of industrial lignin under mild conditions, resulting in generally low yields of monomeric aromatic compounds. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a hierarchical porous molecular sieve for efficient depolymerization of industrial lignin, its preparation and application, solving the problems of inefficient depolymerization of industrial lignin, high cost of precious metal catalysts, and low mass transfer efficiency of microporous molecular sieves in existing technologies.

[0006] The technical solution adopted in this invention is as follows: This invention provides a method for preparing hierarchical porous molecular sieves for efficient depolymerization of industrial lignin, comprising the following steps: N,N,N′,N′-tetramethyl-1,6-diaminohexane and 1-bromooctadecane were dissolved in a first solvent. After the reaction, the mixture was filtered, washed, and dried to obtain intermediate C. 18 H 37 –N + (CH3)2–C6H 12 –N(CH3)2(Br - ); The intermediate C 18 H 37 –N + (CH3)2–C6H 12 –N(CH3)2(Br - ) was dissolved in a second solvent with 1-bromohexane and subjected to reflux reaction. After filtration, washing, and drying, C was obtained. 18-6-6 Br2 surfactant; The silicon source, aluminum source, alkali source, and the C 18-6-6 Br2 surfactant is mixed with deionized water to form a gel, which then undergoes static crystallization after aging. The crystallized product is filtered, washed, and dried, and then calcined in flowing air to remove the organic template agent. It is then subjected to ion exchange with an ammonium salt solution, followed by washing, drying, and calcination to convert it into a hydrogen-type molecular sieve, thus obtaining the hierarchical porous molecular sieve. The hierarchical porous molecular sieve has a hierarchical pore structure in which mesopores and micropores coexist.

[0007] The preferred technical solution is as follows: The molar ratio of N,N,N′,N′-tetramethyl-1,6-diaminohexane to 1-bromooctadecane is (2~12):1; The intermediate C 18 H 37 –N + (CH3)2–C6H 12 –N(CH3)2(Br - The molar ratio of 1-bromohexane to 1-bromohexane is 1:(1.5~8).

[0008] The silicon source is one of fumed silica, silica sol, and water glass; the aluminum source is one of sodium aluminate, sodium aluminum sulfate, and aluminum isopropoxide; and the alkali source is sodium hydroxide.

[0009] The molar ratio of the components in the gel is: Na₂O : Al₂O₃ : SiO₂ : C 18-6-6Br2: H2O= (25~35): 1: (20~50): (8~12): (3500~4500).

[0010] The conditions for the ion exchange are: at 60~80 °C, using a 0.5~2 M ammonium salt solution for 2~4 exchanges, each lasting 1~3 hours; The ammonium salt used for the ion exchange is one of ammonium chloride, ammonium nitrate, and ammonium sulfate.

[0011] The N,N,N′,N′-tetramethyl-1,6-diaminohexane and 1-bromooctadecane are dissolved in a first solvent and reacted at a temperature of 60-80°C for 8-12 hours. The reflux reaction time is 8-12 hours.

[0012] The aging temperature is 50~90 ℃, the aging time is 4~8h, the static crystallization temperature is 140~160 ℃, and the static crystallization time is 7~10 days; The roasting temperature is 500~600℃, and the roasting time is 4~8h.

[0013] A second aspect of the present invention provides a hierarchical porous molecular sieve prepared according to the preparation method described above, wherein the hierarchical porous molecular sieve has Brønsted and Lewis acid sites; the number and intensity of the acid sites, as well as the structural parameters of the hierarchical pore structure, can be controllably adjusted through the preparation process.

[0014] A third aspect of the present invention provides an application of the hierarchical porous molecular sieve in industrial lignin depolymerization, comprising: A mixture of industrial lignin, alcohol and water, and the hierarchical porous molecular sieve used as a catalyst are placed in a reactor. The reactor is purged with inert gas, pressurized, and then sealed. It is then heated to a specified temperature and kept at that temperature for the reaction. After the reaction was completed, the reactor was rapidly cooled in an ice-water bath to stop the reaction, the catalyst was separated by filtration, and the liquid phase product was post-processed to obtain monomeric and dimer aromatic compounds.

[0015] The reaction temperature of the heat preservation reaction is 240~350 ℃, and the reaction time is 0.5~8h; in the mixed solvent of alcohol and water, the volume ratio of alcohol to water is (1:9)~(9:1).

[0016] The technical solution of the present invention can achieve at least some of the following beneficial effects: The molecular sieve preparation method of this invention is simple, easy to operate, and suitable for industrial production. The hierarchical pore structure of this molecular sieve can well match the mass transfer requirements of industrial lignin. Utilizing a hydrolysis-co-alcohol solvent in-situ hydrogen-donating hydrolysis reaction pathway, it efficiently and selectively breaks stubborn C-C bonds such as condensation methylene bonds in industrial lignin, preparing monomeric and dimer aromatic compounds in high yield. It avoids the use of high-pressure hydrogen, providing a reliable technical means for the safe and efficient catalytic conversion of industrial lignin. Specifically, this invention has the following advantages: (1) Compared with traditional microporous molecular sieves (HZSM-5, H β The multi-level porous molecular sieve provided by this invention has a unique mesoporous-microporous interwoven pore structure, which greatly improves the diffusion rate of industrial lignin macromolecules in the molecular sieve pores and overcomes the mass transfer barrier of traditional molecular sieve catalytic systems.

[0017] (2) The number and intensity of Brønsted and Lewis acidic sites in the hierarchical porous molecular sieve provided by this invention can be controlled and adjusted according to requirements. Relying on these two acidic sites to synergistically catalyze the breaking of condensation methylene bonds in industrial lignin, phenolic monomers and dimer aromatic compounds can be prepared efficiently.

[0018] (3) In the application of multi-level porous molecular sieve catalysis for industrial lignin depolymerization, the present invention uses a mixed solvent of alcohol and water, wherein the alcohol can be used as both a solvent and an in-situ hydrogen supplier, avoiding the use of high-pressure hydrogen. The process is safe and green. The reaction pathway of hydrolysis combined with in-situ hydrogen supply from alcohol solvent can achieve a monomer / dimer yield of up to 33.7 wt% for sulfate lignin, which has good application prospects.

[0019] Other features and advantages of the invention will be set forth in the following description or may be learned by practicing the invention. Attached Figure Description

[0020] Figure 1 The images shown are SEM and TEM images of the multi-level porous molecular sieve Cat-1 obtained in the embodiments of the present invention.

[0021] Figure 2 The XRD results and N2 adsorption-desorption test results of the multi-level porous molecular sieve Cat-1 obtained in the embodiments of the present invention are shown.

[0022] Figure 3 The Py-IR test results and NH3-TPD characterization of the hierarchical porous molecular sieve Cat-1 obtained in the embodiments of the present invention are presented. Detailed Implementation

[0023] The specific embodiments of the present invention are described below with reference to the accompanying drawings.

[0024] This application provides a method for preparing hierarchical porous molecular sieves for efficient depolymerization of industrial lignin, comprising the following steps: S1. N,N,N′,N′-tetramethyl-1,6-diaminohexane and 1-bromooctadecane were dissolved in a first solvent. After the reaction, the mixture was filtered, washed, and dried to obtain intermediate C. 18 H 37 –N + (CH3)2–C6H 12 –N(CH3)2(Br - ).

[0025] The preferred reaction temperature is 60~80℃, and the reaction time is 8~12h.

[0026] The preferred molar ratio of N,N,N′,N′-tetramethyl-1,6-diaminohexane to 1-bromooctadecane is (2~12):1.

[0027] The first solvent is preferably a mixture of acetonitrile and toluene.

[0028] S2. The intermediate C 18 H 37 –N + (CH3)2–C6H 12 –N(CH3)2(Br - ) was dissolved in a second solvent with 1-bromohexane, and the mixture was refluxed. After filtration, washing, and drying, C was obtained. 18-6-6 Br2 surfactant.

[0029] Wherein, the intermediate C 18 H 37 –N + (CH3)2–C6H 12 –N(CH3)2(Br - The preferred molar ratio of 1-bromohexane to 1-bromohexane is 1:(1.5~8).

[0030] The preferred reflux reaction time is 8 to 12 hours.

[0031] The second solvent is preferably acetonitrile.

[0032] S3. The silicon source, aluminum source, alkali source, and the C... 18-6-6 Br2 surfactant is mixed with deionized water to form a gel, which then crystallizes statically after aging.

[0033] The silicon source is preferably one of fumed silica, silica sol, and water glass; the aluminum source is preferably one of sodium aluminate, sodium aluminum sulfate, and aluminum isopropoxide; and the alkali source is preferably sodium hydroxide.

[0034] The preferred molar ratio of the components in the gel is: Na₂O : Al₂O₃ : SiO₂ : C 18-6-6 Br2: H2O=(25~35):1:(20~50):(8~12):(3500~4500).

[0035] The preferred aging temperature is 50~90 ℃, the preferred aging time is 4~8h, the preferred static crystallization temperature is 140~160 ℃, and the preferred static crystallization time is 7~10 days.

[0036] S4. The crystallized product is filtered, washed, and dried, and then calcined in flowing air to remove the organic template agent. After that, it is ion-exchanged with an ammonium salt solution, followed by washing, drying, and calcination to convert it into a hydrogen-type molecular sieve, thus obtaining the hierarchical porous molecular sieve.

[0037] The preferred conditions for ion exchange are: 2-4 exchanges using a 0.5-2 M ammonium salt solution at 60-80 °C, each lasting 1-3 hours. The preferred calcination temperature is 500-600 °C, and the calcination time is 4-8 hours.

[0038] The ammonium salt is preferably one of ammonium chloride, ammonium nitrate, and ammonium sulfate.

[0039] The preparation method described in this application is essentially based on bisquaternary ammonium salt C 18-6-6 The soft template method using Br2 as a structure-directing agent yields hierarchical porous molecular sieves with a multi-level pore structure exhibiting both mesoporous and microporous components, as well as Brønsted and Lewis acidic sites. The number and intensity of these hierarchical pore structures and acidic sites can be controllably adjusted during the preparation process.

[0040] This application also provides an application of the aforementioned hierarchical porous molecular sieve in industrial lignin depolymerization, including: (1) Place industrial lignin, a mixed solvent of alcohol and water, and the multi-level porous molecular sieve used as a catalyst in a reactor; wash with inert gas, pressurize and seal the reactor, and heat to a specified temperature for heat preservation reaction.

[0041] (2) After the reaction is completed, the reactor is rapidly cooled by an ice-water bath to stop the reaction, the catalyst is filtered and separated, and the liquid phase product is post-processed to obtain monomeric and dimer aromatic compounds.

[0042] The preferred reaction temperature for the heat preservation reaction is 240~350 ℃, and the preferred reaction time is 0.5~8h.

[0043] In the mixed solvent of alcohol and water, the volume ratio of alcohol to water is preferably (1:9) to (9:1).

[0044] The alcohol is preferably ethanol.

[0045] The industrial lignins mentioned include sulfate lignin, alkali lignin, lignin sulfonate, and biorefined lignin.

[0046] This application presents a hierarchical porous molecular sieve with a unique mesoporous-microporous interwoven pore structure, which can greatly improve the diffusion rate of industrial lignin macromolecules within the molecular sieve channels and overcome the mass transfer barrier of traditional molecular sieve catalytic systems. The synergistic catalytic cleavage of Brønsted and Lewis acidic sites breaks the polycondensation methylene bonds in industrial lignin, enabling the efficient preparation of phenolic monomers and dimer aromatic compounds.

[0047] The preparation and application of the hierarchical porous molecular sieve of this application are further illustrated below with specific embodiments. Example 1:

[0048] A method for preparing hierarchical porous molecular sieves for efficient depolymerization of industrial lignin includes: S1. 0.10 mol N,N,N′,N′-tetramethyl-1,6-diaminohexane and 0.01 mol 1-bromooctadecane were dissolved in 100 mL of a mixed solvent of acetonitrile and toluene (v / v = 1 / 1). The reaction was carried out at 70 °C for 10 h. After cooling to room temperature and evaporating the solvent, the solid product was filtered, washed with diethyl ether, and dried in a vacuum oven at 50 °C to obtain intermediate C. 18 H 37 –N + (CH3)2–C6H 12 –N + (CH3)2(Br - ).

[0049] S2. Dissolve the intermediate (0.01 mol) and 1-bromohexane (0.02 mol) in 30 mL of acetonitrile, reflux for 10 h, cool to room temperature, and then react with the final product C. 18-6-6 The Br2 surfactant was filtered, washed with diethyl ether, and dried in a vacuum oven at 50 °C to complete the production of the bisquaternary ammonium salt surfactant C. 18-6-6 Synthesis of Br2.

[0050] S3. Using fumed silica as the silicon source, sodium aluminate as the aluminum source, and sodium hydroxide as the alkali source, the gel is prepared according to a gel molar ratio of 30 Na₂O : 1 Al₂O₃ : 30 SiO₂ : 10 C 18-6-6 Br2: 4000 H2O Weigh all raw materials, mix with deionized water, and stir and age at 60 °C for 6 h; transfer the resulting gel to a stainless steel reactor lined with polytetrafluoroethylene, and statically crystallize at 150 °C for 9 days.

[0051] S4. After crystallization, the product was filtered, washed thoroughly with deionized water, and dried in an oven at 120 °C. Subsequently, the dried powder was calcined in flowing air at 550 °C for 6 h to remove the template agent. Finally, the calcined powder was ion-exchanged three times at 70 °C in 1 M NH4Cl solution (solid-liquid ratio 1 g: 30 mL), 2 h each time. After ion exchange, the powder was washed, dried, and calcined at 550 °C for 4 h to convert it into the hydrogen form, thus obtaining the hierarchical porous molecular sieve Cat-1.

[0052] The characterization data of the multi-level porous molecular sieve (Meso-Z) Cat-1 are as follows: Figures 1 to 3 As shown.

[0053] Figure 1 In the image, (a) and (b) are the SEM and TEM images of Cat-1, respectively. Figure 1 It is known that Cat-1 has a unique coral-like morphology formed by disordered lattice stacking, a feature that endows it with a rich mesoporous structure.

[0054] Figure 2 In the middle (c) and (d), the XRD results of Cat-1 and the N2 adsorption-desorption test results are respectively. Figure 2 It can be seen that the basic framework of Cat-1 is composed of MFI-type molecular sieves, whose average pore size is much larger than that of traditional microporous molecular sieves (H). β Therefore, it has superior pore mass transfer performance.

[0055] Figure 3 In Figures (e) and (f), Py-IR and NH3-TPD characterization results for Cat-1 are shown, respectively. Figure 3 It can be seen that Cat-1 has properties similar to traditional microporous molecular sieves (H). β There are a considerable number and intensity of Brønsted and Lewis acid sites, which are important active centers for catalytic reactions.

[0056] Example 2: A method for preparing hierarchical porous molecular sieves for efficient depolymerization of industrial lignin. Compared with Example 1, under the same conditions, the difference is: The gel molar ratio in S3 was adjusted to 25 Na2O : 1 Al2O3 : 20 SiO2 : 8 C. 18-6-6 Br2: 3500H2O, crystallization time adjusted to 7 days. The resulting hierarchical porous molecular sieve, Cat-2, was finally obtained.

[0057] Example 3: A method for preparing hierarchical porous molecular sieves for efficient depolymerization of industrial lignin. Compared with Example 1, under the same conditions, the difference is:

[0058] The gel molar ratio in S3 was adjusted to 35 Na2O : 1 Al2O3 : 50 SiO2 : 12 C 18-6-6 Br2: 4500H2O, crystallization temperature adjusted to 160 ℃. The resulting hierarchical porous molecular sieve, Cat-3, was finally obtained.

[0059] Example 4: A method for preparing hierarchical porous molecular sieves for efficient depolymerization of industrial lignin. Compared with Example 1, under the same conditions, the difference is:

[0060] The aging temperature in S3 was adjusted to 90 ℃, and the aging time was adjusted to 4 h. The resulting multi-level porous molecular sieve, Cat-4, was finally obtained.

[0061] Example 5: A method for preparing hierarchical porous molecular sieves for efficient depolymerization of industrial lignin. Compared with Example 1, under the same conditions, the difference is: The ammonium salt used for ion exchange in S4 was replaced with a 1 M ammonium nitrate solution. This resulted in the final hierarchical porous molecular sieve Cat-5.

[0062] In Examples 1 to 5, the volume of deionized water used to prepare the solution is sufficient to completely dissolve the raw materials or form a uniform gel; the crystallization process can be carried out under static or dynamic conditions, and the crystallization time and temperature can be adjusted according to the actual situation.

[0063] The properties of the molecular sieves prepared in Examples 1 to 5 are shown in Table 1 below.

[0064] Table 1. Properties of molecular sieves prepared under different conditions

[0065] As can be seen from the above embodiments, by adjusting the silicon-to-aluminum ratio, the amount of template agent, aging conditions, and crystallization conditions, the number of Brønsted and Lewis acidic sites can be directionally controlled, thereby increasing the number of Brønsted and Lewis acidic sites.

[0066] The following examples and comparative examples are used to analyze the application of hierarchical porous molecular sieves Cat-1, Cat-2, and Cat-3 in the catalytic depolymerization of lignin.

[0067] Example 6: Application of a hierarchical porous molecular sieve in the catalytic depolymerization of sulfate lignin, comprising: (1) Place 0.1 g sulfate lignin, 0.03 g catalyst Cat-1 and 3 mL of ethanol and water mixed solvent with a volume ratio of 9:1 in a micro high-pressure reactor; replace the air in the reactor with nitrogen three times, pressurize to 1 MPa and seal; place the reactor in a sand bath preheated to 300 ℃ and keep it at the temperature for 1 h.

[0068] (2) After the reaction was completed, the reactor was immediately placed in an ice-water bath for rapid cooling to terminate the reaction. The liquid phase product was collected and qualitatively and quantitatively analyzed by GC-MS and GC-FID. The results showed that the total yield of monomers and dimers was 33.7 wt%.

[0069] Comparative Example 1: A non-catalytic pyrolysis method for polysulfate lignin includes: (1) Place 0.1 g of sulfate lignin and 3 mL of a 9:1 volume ratio of ethanol and water into a micro high-pressure reactor; replace the air in the reactor with nitrogen three times, pressurize to 1 MPa, and seal.

[0070] (2) The reactor was placed in a sand bath preheated to 300 °C and kept at that temperature for 1 h. After the reaction was completed, the reactor was immediately placed in an ice-water bath for rapid cooling to terminate the reaction. The liquid phase product was collected and qualitatively and quantitatively analyzed by GC-MS and GC-FID. The results showed that the total yield of monomers and dimers was 3.1 wt%.

[0071] Comparative Example 2: A method utilizing commercial H β A molecular sieve-catalyzed pyrolysis method for polysulfate lignin includes: (1) Add 0.1 g of sulfate lignin and 0.03 g of commercial H β Molecular sieve (Si / Al = 15) and 3 mL of ethanol / water mixed solvent with a volume ratio of 9:1 were placed in a micro high-pressure reactor; after replacing the air in the reactor with nitrogen three times, it was pressurized to 1 MPa and sealed.

[0072] (2) The reactor was placed in a sand bath preheated to 300 °C and kept at that temperature for 1 h. After the reaction was completed, the reactor was immediately placed in an ice-water bath for rapid cooling to terminate the reaction. The liquid phase product was collected and qualitatively and quantitatively analyzed by GC-MS and GC-FID. The results showed that the total yield of monomers and dimers was 5.7 wt%.

[0073] Example 7: Application of a hierarchical porous molecular sieve in the catalytic depolymerization of alkali lignin. All other conditions were the same as in Example 6, except that the lignin used was replaced with 0.1 g of alkali lignin, and the catalyst dosage was increased to 0.05 g. The result was a total yield of 29.5 wt% for both monomers and dimers.

[0074] Example 8: To verify the effect of different reaction temperatures on catalytic depolymerization, this example provides the application of a hierarchical porous molecular sieve in the catalytic depolymerization of alkali lignin. All other conditions are the same as in Example 6, except that the reaction temperature is adjusted to 240 °C. The result is that the total yield of monomers and dimers is 18.2 wt%.

[0075] Example 9: To verify the effect of different reaction temperatures on catalytic depolymerization, this example provides the application of a hierarchical porous molecular sieve in the catalytic depolymerization of alkali lignin. All other conditions are the same as in Example 6, except that the reaction temperature is adjusted to 350 °C. The result is that the total yield of monomers and dimers is 35.1 wt%.

[0076] Example 10: To verify the effect of different reaction times on catalytic depolymerization, this example provides the application of a hierarchical porous molecular sieve in the catalytic depolymerization of alkali lignin. All other conditions are the same as in Example 6, except that the reaction time is adjusted to 0.5 hours. The result is that the total yield of monomers and dimers is 15.6 wt%.

[0077] Example 11: To verify the effect of different reaction times on catalytic depolymerization, this example provides the application of a hierarchical porous molecular sieve in the catalytic depolymerization of alkali lignin. All other conditions are the same as in Example 6, except that the reaction time is adjusted to 4 hours. The result is that the total yield of monomers and dimers is 31.3 wt%.

[0078] Example 12: To verify the effect of different solvent ratios on catalytic depolymerization, this example provides the application of a hierarchical porous molecular sieve in the catalytic depolymerization of alkali lignin. All other conditions are the same as in Example 6, except that the volume ratio of the ethanol to water mixed solvent is adjusted to 7:3. The result is that the total yield of monomers and dimers is 30.5 wt%.

[0079] Example 13: The application of a hierarchical porous molecular sieve in the catalytic depolymerization of alkali lignin in this example is the same as in Example 6, except that catalyst Cat-1 is replaced with Cat-2. The result is that the total yield of monomers and dimers is 25.8 wt%.

[0080] Example 14: The application of a hierarchical porous molecular sieve in the catalytic depolymerization of alkali lignin in this example is the same as in Example 6, except that the catalyst Cat-1 is replaced with Cat-3. The result is that the total yield of monomers and dimers is 28.4 wt%.

[0081] In summary, the hierarchical porous molecular sieve prepared by this invention is a catalyst that combines excellent mass transfer performance with precise acid site regulation. It can efficiently and selectively break stubborn C–C bonds such as polymethyl condensation bonds in industrial lignin, thereby enabling its high-value conversion into monomeric and dimer aromatic chemicals.

[0082] It will be understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a hierarchical porous molecular sieve for efficient depolymerization of industrial lignin, characterized in that, The method comprises the following steps: N,N,N',N'-tetramethyl-1,6-diaminohexane and 1-bromooctadecane in a first solvent, after reaction, filtration, washing, drying, to obtain intermediate C 18 H 37 –N + (CH3)2–C6H 12 –N(CH3)2(Br - ); The intermediate C 18 H 37 –N + (CH3)2–C6H 12 –N(CH3)2(Br - ) and 1-bromohexane in a second solvent, and refluxing, filtering, washing, and drying to obtain C 18-6-6 Br2surfactant; The silicon source, the aluminum source, the alkali source, and the C 18-6-6 Br2 surfactant was mixed with deionized water to form a gel, which was aged and statically crystallized. The crystallized product is filtered, washed, dried, and then calcined in flowing air to remove the organic template, and then ion exchanged with an ammonium salt solution, followed by washing, drying, and calcination to convert into a hydrogen type molecular sieve, thereby obtaining the hierarchical pore molecular sieve; the hierarchical pore molecular sieve has a hierarchical pore structure with coexisting mesopores and micropores.

2. The production method according to claim 1, characterized by, The molar ratio of the N,N,N',N'-tetramethyl-1,6-diaminohexane to 1-bromooctadecane is (2-12):1; said intermediate C 18 H 37 –N + (CH3)2–C6H 12 –N(CH3)2(Br - ) and 1-bromohexane is 1: (1.5-8).

3. The preparation method according to claim 1, characterized in that, The silicon source is one of fumed silica, silica sol, and water glass; the aluminum source is one of sodium aluminate, sodium aluminum sulfate, and aluminum isopropoxide; and the alkali source is sodium hydroxide.

4. The production method according to claim 3, characterized by, The molar ratio of each component in the gel is: Na2O:Al2O3:SiO2:C 18-6-6 Br2:H2O=(25~35):1:(20~50):(8~12):(3500~4500).

5. The preparation method according to claim 1, characterized in that, The ion exchange is performed at 60-80 DEG C using 0.5-2 M ammonium salt solution for 2-4 times, each for 1-3 h. The ammonium salt used for the ion exchange is one of ammonium chloride, ammonium nitrate, and ammonium sulfate.

6. The method of claim 1, wherein, The N,N,N',N'-tetramethyl-1,6-diaminohexane and 1-bromooctadecane are dissolved in a first solvent to react at a temperature of 60-80 DEG C for 8-12 h. The reflux reaction is performed for 8-12 h.

7. The preparation method according to claim 1, characterized in that, The aging temperature is 50-90 DEG C, the aging time is 4-8 h, the static crystallization temperature is 140-160 DEG C, and the static crystallization time is 7-10 days. The calcination temperature is 500-600 DEG C, and the calcination time is 4-8 h.

8. The hierarchical porous molecular sieve produced according to the method of any one of claims 1-7, wherein: The hierarchical pore molecular sieve has Brønsted and Lewis acid sites; the number and strength of the acid sites and the structural parameters of the hierarchical pore structure can be controlled by the preparation process.

9. Use of the hierarchical porous molecular sieve according to claim 8 in the depolymerization of industrial lignin, characterized in that, The method comprises the following steps: The industrial lignin, a mixed solvent of alcohol and water, and the hierarchical pore molecular sieve used as a catalyst are placed in a reactor; The reactor is sealed after being washed with an inert gas and pressurized, and then heated to a specified temperature for a holding reaction; After the reaction is completed, the reactor is rapidly cooled using an ice water bath to terminate the reaction, the catalyst is separated by filtration, and the liquid product is treated to obtain monomer and dimer aromatic compounds.

10. Use according to claim 9, characterized in that, The holding reaction is performed at a temperature of 240-350 DEG C for 0.5-8 h; in the mixed solvent of alcohol and water, the volume ratio of alcohol to water is (1:9)-(9:1).

Images