Preparation method of novel multifunctional polyionic liquid catalyst and catalytic preparation of lignin-based aromatic compounds

Abstract

The application belongs to the technical field of new material synthesis, and discloses a preparation method of a novel multifunctional polyionic liquid catalyst with regular hydrophobic mesoporous and Brønsted-Lewis acid sites and catalysis of lignin for preparing aromatic monomers. The novel multifunctional polyionic liquid catalyst is prepared by polymerization reaction of Brønsted-Lewis acid ionic liquid monomers, vinyl modified Fe3O4 nanoparticles and long-chain carboxylate salt anion cross-linking agents with hydrophobicity. The end alkene modified Fe3O4 nanoparticles play the role of skeleton strengthening agent, so that the novel multifunctional polyionic liquid has clear mesoporous channels. The 24.6wt% lignin-based aromatic monomer yield is prepared by the synergistic catalysis of acid sites, mesoporous confinement and hydrophobic microenvironment. The catalyst is reused for 10 times, and no significant decrease in reaction yield is found. The catalyst has good industrialization prospect in upgrading heavy carbon resources into high value-added chemical products.

Description

Technical Field

[0001] This invention belongs to the field of new material synthesis technology, specifically relating to the technical field of preparing lignin-based aromatic monomers, and particularly to a novel multifunctional polyionic liquid catalyst for preparing lignin-based aromatic monomers, its preparation method, and its application. Background Technology

[0002] Aromatic monomers are key raw materials for manufacturing various high-value-added chemicals, and currently, almost all high-value-added chemicals are obtained from non-renewable fossil fuels. With the rapid depletion of fossil resources and the increasing demand for aromatic monomers, the efficient conversion of renewable lignin into aromatic monomers is of great significance, but it also presents many challenges, such as the high degree of cross-linking and the intractable structure of lignin, which makes lignin depolymerization difficult. In view of social and environmental sustainable development, there is an urgent need to develop advanced technologies to effectively convert lignin into high-value-added chemicals.

[0003] Liquid acid catalysts have been widely used in many liquid acid catalytic processes due to their high acid strength, excellent catalytic activity, and uniform distribution of acidic sites. Although liquid acid catalysts exhibit high catalytic performance in lignin catalysis, they also cause severe corrosion damage to equipment and are difficult to separate from the liquid reaction mixture. In contrast, solid acid catalysts offer several advantages over liquid catalysts, such as lower corrosivity, environmental friendliness, and higher safety. In particular, solid acid catalysts are relatively easier to separate and recover compared to liquid catalysts. Therefore, there is an urgent need to develop novel solid acid catalysts for the directed conversion of lignin to aromatic monomers.

[0004] Ionic liquids, especially proton-type ionic liquids, are a crucial type of functional liquid. A unique advantage of ionic liquids is their ability to be engineered with specific anionic moieties. Metal chloride anion-functionalized ionic liquids overcome the drawbacks of metal chlorides, such as strong corrosivity, easy hydrolysis, and easy deactivation. However, the high viscosity and low surface area leading to high mass transfer resistance reduce the competitiveness of metal chloride-functionalized ionic liquids as catalysts for industrial applications. Polyionic liquids are also macromolecular structures; incorporating polyionic liquids into the polymer backbone may solve the problems associated with the aforementioned monomers. Mesoporous polyionic liquids possess tunable mesoporous structures and adjustable chemical compositions, representing a new class of multifunctional porous materials, copolymerized from functionalized ionic liquids, crosslinking agents, and other monomers. Conventional methods struggle to prepare polyionic liquid catalysts with regular hydrophobic mesoporous structures and Brønsted-Lewis acidic sites. Summary of the Invention

[0005] To overcome the problems existing in related technologies, this invention provides a novel multifunctional polyionic liquid catalyst for preparing lignin-based aromatic monomers, its preparation method, and its application.

[0006] The catalyst provided by this invention is a novel multifunctional polyionic liquid that is highly efficient, environmentally friendly, possesses a Brønsted-Lewis acidic moiety, a well-defined mesoporous structure, and unique hydrophobicity. Its preparation method includes:

[0007] 1) The preparation method of ionic liquid with Brønsted-Lewis acidic site is as follows: equimolar amounts of 1-vinylimidazolium and 1,3-propanesulfonic acid lactone are used to form the desired quaternary ammonium salt, which is then acidified with hydrochloric acid to obtain a salt with sulfonic acid group, and finally reacted with FeCl3.

[0008] 2) The preparation method of the hydrophobic long-chain carboxylate anionic crosslinking agent is as follows: 1,2-dibromoethane and 1-vinylimidazolium in a molar ratio of 1:2 are added to acetone, magnetically stirred, and heated under reflux for 24 hours to obtain a pale yellow solid, which is then subjected to ion exchange through an alkaline ion exchange resin. Finally, it is acidified with propionic acid, hexanoic acid, and nonanoic acid, respectively.

[0009] 3) The preparation method of vinyl-modified Fe3O4 nanoparticles is as follows: Fe3O4 nanoparticles and vinyltriethoxysilane are ultrasonically treated in ethanol at room temperature for 2 h, then NH3·H2O is added to the mixed solution to adjust the pH value to 9, and then the solution is heated to 80 °C. o Vigorous mechanical stirring at C for 24 hours, followed by washing with ethanol three times.

[0010] 4) The preparation method of the novel multifunctional polyionic liquid catalyst is as follows: vinyl-modified Fe3O4 nanoparticles, methanol, Brønsted-Lewis acidic ionic liquid, long-chain carboxylate anionic crosslinking agent, and azobisisobutyronitrile are mixed in a three-necked flask and heated at 80°C. o Vigorous mechanical stirring at C for 24 hours, and the product was recovered using strong magnetic field.

[0011] 5) The preparation method of lignin-based aromatic monomers is as follows: hexane, a novel multifunctional polyionic liquid catalyst, and lignin are mixed in a high-pressure reactor with an initial hydrogen pressure of 4 MPa and a reaction temperature of 265 °C. o C, with a reaction time of 20 h, yielded lignin-based aromatic monomers.

[0012] In one embodiment of the present invention, the molar ratio of the salt having sulfonic acid groups to FeCl3 is 1:0.25-2.25.

[0013] In one embodiment of the invention, the molar ratio of the Brønsted-Lewis acidic ionic liquid to the hydrophobic long-chain carboxylate anionic crosslinking agent is 1:0.5-5. The initiator is azobisisobutyronitrile.

[0014] In one embodiment of the present invention, the novel multifunctional polyionic liquid catalyst has a specific surface area of ​​106.81 m². 2 g -1 The average pore diameter is 3.85 nm, and the pore volume is 0.165 cm³. 3 g -1 .

[0015] In one embodiment of the present invention, the lignin-based aromatic monomers include eight monocyclic aromatic hydrocarbons or five monocyclic phenols.

[0016] In one embodiment of the present invention, the total lignin conversion rate is 49.9%, and the selectivity of lignin-based aromatic monomers is 51.29% (35.63% of monocyclic aromatic hydrocarbons and 15.66% of monocyclic phenols).

[0017] Combining all the above technical solutions, the advantages and positive effects of this invention are as follows:

[0018] 1) Brønsted-Lewis ionic liquids act as active sites, and the Brønsted-Lewis acidic sites synergistically promote the heterolytic cleavage of H2 to form H+. + and H - Then the generated H + This causes the CO bond to break down, generating a monocyclic aromatic compound.

[0019] 2) The terminal alkene-modified Fe3O4 nanoparticles act as a framework reinforcing agent, enabling the novel multifunctional polyionic liquid to have well-defined mesoporous channels: well-defined mesoporous channels enhance the adsorption capacity of H2 and increase the concentration of the substrate.

[0020] 3) The hydrophobic divinylbenzene fragments provide the hydrophobic microenvironment required during the reaction: the hydrophobic channels formed by the hydrophobic blocks help prevent the leaching and deactivation of Brønsted-Lewis acid sites.

[0021] 4) After the catalytic reaction is completed, the novel multifunctional polyionic liquid catalyst is separated from the reaction mixture using a novel multifunctional polyionic liquid catalyst magnetic recovery device.

[0022] 5) The preparation of lignin-based aromatic monomers under relatively mild conditions ensures safety during actual production and reduces wear and tear on reaction equipment.

[0023] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the disclosure of the present invention. Attached Figure Description

[0024] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0025] Figure 1 This is a flowchart illustrating the preparation process of the multifunctional polymeric ionic liquid in one embodiment of the present invention.

[0026] Figure 2 In one embodiment of the present invention, the Brønsted-Lewis acidic ionic liquid monomer molecular formula is described.

[0027] Figure 3 This is the structural molecular formula of the hydrophobic long-chain carboxylate anionic crosslinking agent in one embodiment of the present invention.

[0028] Figure 4 This invention provides a novel method for preparing multifunctional polyionic liquid catalysts.

[0029] Figure 5 This is a schematic diagram of the principle of a novel multifunctional polyionic liquid catalyst magnetic recovery device provided in this embodiment of the invention: using an external magnetic field to separate the novel multifunctional polyionic liquid catalyst from the reaction mixture.

[0030] In the diagram: 1. External magnetic field; 2. Catalyst; 3. Solid residue; 4. Acetone.

[0031] Figure 6 Examples 11 and 12 of this invention use GC-MS for qualitative analysis of liquid products, and identification is performed by comparing the peak retention times with those of real compounds using mass spectra. Figure 6 'a' represents the selectivity of seven types of substances in the lignin liquid product when the novel multifunctional polyionic liquid with anionic moieties of FeCl3 and ZrCl2 is used as a catalyst. Figure 6 b represents the relative content of the main aromatic hydrocarbons and phenols in the product when the anionic moiety is FeCl3.

[0032] Figure 7 In Example 11 of this invention, the conversion rate of benzylphenyl ether hydrogenation cracking was 100%. The catalyst was reused 10 times, and no significant decrease in yield was observed.

[0033] Figure 8 These are the characteristic peaks of eight monocyclic aromatic hydrocarbons and five monocyclic phenols in the total ion chromatogram of lignin conversion using a novel multifunctional polyionic liquid catalyst. Detailed Implementation

[0034] The present invention will be further described below with reference to the embodiments. The embodiments of the present invention are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention.

[0035] Example 1: Preparation method of novel multifunctional polyionic liquid catalyst:

[0036] Vinyl-modified Fe3O4 nanoparticles (200 mg), methanol (50 ml), Brønsted-Lewis acidic ionic liquid (1 mmol), long-chain carboxylate anionic crosslinking agent (2 mmol), and azobisisobutyronitrile (30 mg) were mixed in a three-necked flask at 70 °C. oC After vigorous stirring for 24 hours, the product was recovered using a strong magnetic field, yielding a novel, ordered, porous, multifunctional polyionic liquid catalyst with a specific surface area of ​​106.81 m². 2 g -1 The average pore diameter is 3.85 nm, and the pore volume is 0.165 cm³. 3 g -1 .

[0037] Example 2

[0038] Except for the absence of vinyl-modified Fe3O4 nanoparticles, all other reaction conditions and measurement methods were the same as in Example 1, resulting in a disordered, non-porous polyionic liquid catalyst with a specific surface area of ​​0.33 m². 2 g -1 The average pore diameter is 11.37 nm, and the pore volume is 0.002 cm³. 3 g -1 .

[0039] Example 3

[0040] A novel multifunctional polyionic liquid catalyst (100 mg) and n-hexane (20 mL) were added to a Hastelloy autoclave (100 mL). The catalyst consisted of a Brønsted-Lewis acidic ionic liquid with a Brønsted-Lewis molar ratio of 1:2 and a long-chain carboxylate anionic crosslinking agent (CLs-C6) with an alkyl chain length of 6, and a Brønsted-Lewis acidic ionic liquid with a Brønsted-Lewis molar ratio of 1:2. The reaction was carried out at an initial hydrogen pressure of 4 MPa and a reaction temperature of 265 °C. o C. The reaction was carried out under the conditions of stirring speed of 200 rpm and reaction time of 3 h. After the reaction time was completed, the autoclave was immediately cooled rapidly in an ice-water bath. The liquid products were qualitatively analyzed by GC-MS and identified by comparison with the peak retention times and mass spectra of the real compounds. The conversion rate of benzylphenyl ether by hydrogenation cracking was 100%. The relative contents of phenol in the products were 47.33%, toluene was 40.65%, benzene was 6.68%, and the dimer product was 5.34%.

[0041] Example 4

[0042] Except for the Brønsted to Lewis molar ratio of 1:1.5, all other reaction conditions and determination methods were the same as in Example 3. The conversion rate of benzyl phenyl ether by hydrogenation cracking was 90.17%. The relative contents of phenol in the product were 44.23%, toluene 42%, benzene 2.23%, and dimer 11.54%. Example 5

[0043] Except for the Brønsted-Lewis acidic ionic liquid and the 1:1 ratio of a long-chain carboxylate anionic crosslinking agent (CLs-C6) with an alkyl chain length of 6, all other reaction conditions and determination methods were the same as in Example 3. The conversion rate of benzyl phenyl ether by hydrogenation cracking was 83.21%. The relative contents of phenol in the product were 41.76%, toluene was 34.73%, benzene was 7.03%, and the dimer product was 16.48%.

[0044] Example 6

[0045] Except for the novel multifunctional polyionic liquid catalyst (80 mg), all other reaction conditions and determination methods were the same as in Example 3. The conversion rate of benzyl phenyl ether hydrogenation cracking was 91.23%. The relative contents of phenol, toluene, benzene, and dimer products in the products were 46.3%, 41.48%, 4.82%, and 7.4%, respectively.

[0046] Example 7

[0047] Except for the initial hydrogen pressure of 3 MPa, all other reaction conditions and measurement methods were the same as in Example 3. The conversion rate of benzyl phenyl ether by hydrogenation cracking was 80.33%. The relative contents of phenol, toluene, benzene, and dimer products in the product were 46.66%, 40.68%, 5.98%, and 6.68%, respectively.

[0048] Example 8

[0049] Besides the reaction temperature being 255°C o C. Other reaction conditions and determination methods were the same as in Example 3. The conversion rate of benzyl phenyl ether by hydrogenation cracking was 92.34%. The relative contents of phenol in the product were 46.96%, toluene was 41.27%, benzene was 5.69%, and the dimer product was 6.08%.

[0050] Example 9

[0051] Except for the reaction time of 2 hours, all other reaction conditions and measurement methods were the same as in Example 3. The conversion rate of benzyl phenyl ether hydrogenation cracking was 90.27%. The relative contents of phenol, toluene, benzene, and dimer products in the product were 47.15%, 41.12%, 6.03%, and 5.7%, respectively.

[0052] Example 10

[0053] Except for the Lewis portion being ZrCl2, the other reaction conditions and determination methods were the same as in Example 3. The conversion rate of benzyl phenyl ether by hydrogenation cracking was 98.26%. The relative contents of phenol in the product were 45.07%, toluene was 30.67%, benzene was 14.4%, and the dimer product was 9.86%.

[0054] Example 11

[0055] A novel multifunctional polyionic liquid catalyst (100 mg) and n-hexane (20 mL) were added to a Hastelloy autoclave (100 mL). The catalyst consisted of alkali lignin (0.2 g), a Brønsted-Lewis acidic ionic liquid with a molar ratio of 1:2 (Brønsted-Lewis), and a long-chain carboxylate anionic crosslinking agent (CLs-C6) with an alkyl chain length of 6, with a molar ratio of 1:2. The reaction was carried out at an initial hydrogen pressure of 4 MPa and a reaction temperature of 265 °C. o C. The reaction was carried out under the conditions of stirring speed of 200 rpm and reaction time of 20 h. After the reaction time was completed, the autoclave was immediately cooled rapidly in an ice-water bath. The liquid product was qualitatively analyzed using GC-MS and identified by comparison with the peak retention time and mass spectrum of the real compound. The total lignin conversion rate was 47.9%, and the yield of lignin-based aromatic monomers was 24.6 wt% (monocyclic aromatic hydrocarbons accounted for 35.6%, and monocyclic phenols accounted for 15.7%). The lignin-based aromatic monomers included 8 monocyclic aromatic hydrocarbons and 5 monocyclic phenols. The monocyclic aromatic hydrocarbons and monocyclic phenols with the highest relative content in the product were toluene (16.20 wt.%) and phenol (4.74 wt.%), respectively, as detailed below. Figure 5 As shown.

[0056] Example 12

[0057] A novel multifunctional polyionic liquid catalyst (100 mg) and n-hexane (20 mL) were added to a Hastelloy autoclave (100 mL). The catalyst consisted of a Brønsted-Lewis acidic ionic liquid with a Brønsted-Lewis molar ratio of 1:2 and a long-chain carboxylate anionic crosslinking agent (CLs-C6) with an alkyl chain length of 6, and a Brønsted-Lewis acidic ionic liquid with a Brønsted-Lewis molar ratio of 1:2. The reaction was carried out at an initial hydrogen pressure of 4 MPa and a reaction temperature of 265 °C.o C. The reaction was carried out under the conditions of stirring speed of 200 rpm and reaction time of 3 h. After the reaction time was completed, the autoclave was immediately cooled rapidly in an ice-water bath. The liquid product was qualitatively analyzed using GC-MS, and identified by comparison with the peak retention time and mass spectrum of the real compound. The conversion rate of benzylphenyl ether hydrogenation cracking was 100%. The catalyst was reused 10 times without a significant decrease in yield, as detailed below. Figure 4 As shown.

[0058] It should be noted that the above-described invention content and specific embodiments are intended to demonstrate the practical application of the technical solution provided by this invention and should not be construed as limiting the scope of protection of this invention. Those skilled in the art can make various modifications, equivalent substitutions, or improvements within the spirit and principles of this invention. The scope of protection of this invention is defined by the appended claims.

Claims

1. A method for preparing a multifunctional polyionic liquid catalyst, characterized in that: The multifunctional polyionic liquid catalyst is prepared by polymerization of Brønsted-Lewis acidic ionic liquid, vinyl-modified Fe3O4 nanoparticles, and hydrophobic long-chain carboxylate anionic crosslinking agent monomers. When vinyl-modified Fe3O4 nanoparticles participate in polymerization, the carbon chain length of the crosslinking agent monomer is 6, and the molar ratio of Brønsted-Lewis acidic ionic liquid to long-chain carboxylate anionic crosslinking agent is 1:2, a multifunctional polyionic liquid catalyst with regular hydrophobic mesopores and Brønsted-Lewis acidic sites is obtained. The preparation method of the multifunctional polyionic liquid includes: (1) Preparation of Brønsted-Lewis acidic ionic liquid: equimolar amounts of 1-vinylimidazolium and 1,3-propanesulfonic acid lactone are reacted to form a quaternary ammonium salt, which is then acidified with hydrochloric acid to obtain a salt with sulfonic acid groups, and then reacted with FeCl3. (2) Preparation of vinyl-modified Fe3O4 nanoparticles: Fe3O4 nanoparticles and vinyltriethoxysilane were ultrasonically treated in ethanol at room temperature for 2 h, then NH3·H2O was added to adjust the pH to 9, and the mixture was vigorously mechanically stirred at 80 °C for 24 h, and washed 3 times with ethanol. (3) Preparation of hydrophobic long-chain carboxylate anionic crosslinking agent: 1,2-dibromoethane and 1-vinylimidazolium in a molar ratio of 1:2 were added to acetone, magnetically stirred and heated under reflux for 24 h to obtain a pale yellow solid, which was then ion-exchanged by an alkaline ion exchange resin and acidified with propionic acid, hexanoic acid and nonanoic acid respectively.

2. The preparation method of the multifunctional polyionic liquid catalyst as described in claim 1, characterized in that: The molar ratio of the salt with sulfonic acid groups to FeCl3 is 1:0.25-2.

25.

3. The preparation method of the multifunctional polyionic liquid catalyst as described in claim 1, characterized in that: The vinyl-modified Fe3O4 nanoparticles serve as a framework enhancer for mesoporous polymeric ionic liquids, promoting the formation of regular mesopores in the multifunctional polyionic liquid catalyst.

4. The preparation method of the multifunctional polyionic liquid catalyst as described in claim 1, characterized in that: After the catalytic reaction is completed, the catalyst is separated from the reaction mixture by the multifunctional polyionic liquid catalyst magnetic recovery device, thus achieving recycling.

5. A method for preparing aromatic monomers from lignin using the multifunctional polyionic liquid catalyst obtained by the preparation method of claim 1, characterized in that: 20 mL of n-hexane, 0.1 g of the multifunctional polyionic liquid catalyst and 0.2 g of lignin were mixed in a high-pressure reactor. The initial hydrogen pressure was 4 MPa, the reaction temperature was 265 °C, and the reaction time was 20 h to prepare lignin-based aromatic monomers.

6. The method as described in claim 5, characterized in that: The total lignin conversion rate was 47.9%, and the yield of lignin-based aromatic monomers was 24.6 wt.%.

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