A photocatalytic depolymerization method for lignin compounds

Abstract

The application discloses a photocatalytic depolymerization method of a lignin compound, and comprises the following steps: mixing a lignin compound, a Cs2AgBiX6 double perovskite nanocatalyst and an organic solvent, and then stirring and reacting under blue light irradiation at room temperature in an air atmosphere for 12-18 hours. The application can realize the simultaneous breaking of C-C bonds and C-O bonds of the lignin, has mild reaction conditions, short reaction time, a wide substrate application range, does not need additional additives, and has high depolymerization rate and monomer recovery rate.

Description

Technical Field

[0001] This invention belongs to the field of lignin depolymerization technology, specifically relating to a photocatalytic depolymerization method for lignin compounds. Background Technology

[0002] Lignin, the second most abundant component of lignocellulosic biomass, is a byproduct of the papermaking process with a huge annual output, and is generally considered a low-value residue. However, recent studies have shown that lignin, as a renewable resource, has enormous potential for producing bio-based materials, fuels, and high-value chemicals. Therefore, exploring and developing efficient depolymerization and conversion of lignin is of significant strategic importance for alleviating the energy crisis and developing the fine chemical industry.

[0003] Traditional methods for lignin depolymerization include reduction, oxidation, neutral redox reactions, and acid hydrolysis, but these still suffer from problems such as harsh reaction conditions, resource waste, and environmental pollution. In recent years, photocatalysis has become one of the most important branches of organic chemistry due to its greener, milder, and more efficient reaction conditions. Currently, there is research on applying photocatalysis to lignin depolymerization to obtain high-value chemicals. Known photocatalytic depolymerization methods for lignin mainly achieve this by breaking C-C bonds or CO bonds in β-O-4 model compounds. However, photocatalysts suitable for lignin depolymerization suffer from numerous problems, including high cost, difficult preparation, and poor stability. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a photocatalytic depolymerization method for lignin compounds.

[0005] The reaction principle of this invention is as follows:

[0006]

[0007] The technical solution of the present invention is as follows:

[0008] A photocatalytic depolymerization method for lignin compounds includes: mixing lignin compounds, Cs2AgBiX6 double perovskite nanocatalysts and organic solvents, and then reacting them under light irradiation at room temperature for 12-18 hours in an air atmosphere.

[0009] In the above Cs2AgBiX6 double perovskite nanocatalyst, X is Cl, Br, or I.

[0010] The lignin compounds mentioned above are substituted or unsubstituted β-O-4 model compounds or dealkalized lignins.

[0011] In a preferred embodiment of the present invention, the organic solvent is toluene, tert-butanol, isopropanol, or 1,2-dichloroethane.

[0012] In a preferred embodiment of the present invention, the β-O-4 model compound is selected from...

[0013]

[0014] In a preferred embodiment of the present invention, the wavelength of the light is 440-460 nm.

[0015] In a preferred embodiment of the present invention, the molar ratio of the lignin compound to the Cs2AgBiX6 double perovskite nanocatalyst is 1:0.002-0.01.

[0016] The application of Cs2AgBiX6 double perovskite nanoparticles as a photocatalytic depolymerization catalyst for lignin compounds, wherein X in the Cs2AgBiX6 double perovskite nanocatalyst is Cl, Br or I.

[0017] In a preferred embodiment of the invention, the lignin compound is a substituted or unsubstituted β-O-4 model compound or a dealkalized lignin.

[0018] More preferably, the β-O-4 model compound is selected from...

[0019]

[0020] In a preferred embodiment of the present invention, the photocatalysis is performed by light irradiation.

[0021] More preferably, the wavelength of the light is 440-460nm.

[0022] The beneficial effects of this invention are: it can simultaneously break the C-C bonds and CO bonds of lignin, the reaction conditions are mild, the reaction time is short, the substrate applicability is wide, no additional additives are required, the depolymerization rate is high, and the products obtained are compounds such as phenols, aromatic diketones, aromatic aldehydes and aromatic acids. Attached Figure Description

[0023] Figure 1 This is a gas chromatogram of the reaction solution in Example 1 of the present invention.

[0024] Figure 2 This is a gas chromatogram of the lignin-dealkali reaction before the reaction in Example 2 of the present invention.

[0025] Figure 3 This is a gas chromatogram of the extract after the alkali-removed lignin reaction in Example 2 of the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be further explained and described below with reference to specific embodiments and accompanying drawings.

[0027] The synthesis of the β-O-4 model compounds in the following examples was carried out according to Bergman's method (Nichols JM, Bishop LM, Bergman RG, et al. Catalytic CO Bond Cleavage of 2-Aryloxy-1-Arylethanols and Its Application to the Depolymerization of Lignin-Related Polymers[J]. Journal of the American Chemical Society, 2010, 132(36): 12554-12555.)

[0028] Lignin was purchased from TCI. It was prepared through chemical modifications such as partial desulfonation, oxidation, hydrolysis, and demethylation.

[0029] Example 1

[0030] Depolymerization of 2-(2,6-dimethoxyphenoxy)-1-(3,4-dimethoxyphenyl)propane-1,3-diol

[0031]

[0032] A 0.0002 mol / L toluene solution of Cs₂AgBiI₆ nanomaterials was prepared. 2.0 mL of this solution was added to a 20 mL reaction tube, followed by the addition of 0.1 mmol of 2-(2,6-dimethoxyphenoxy)-1-(3,4-dimethoxyphenyl)propane-1,3-diol. The reaction was stirred at room temperature for 18 h under irradiation (445 nm, 10 W) before the reaction was stopped. The reaction solution was diluted with dichloromethane, and dimethyl phthalate was used as an internal standard. Quantification by gas chromatography showed a depolymerization rate of 100%. The products obtained included 19% 3,4-dimethoxybenzaldehyde, 47% 3,4-dimethoxybenzoic acid, 22% 1-(3,4-dimethoxyphenyl)propane-1,2-dione, and 2% 2,6-dimethoxyphenol, etc. (Details are as follows...) Figure 1 As shown.

[0033] The claimed technical effects can also be achieved by replacing 2-(2,6-dimethoxyphenoxy)-1-(3,4-dimethoxyphenyl)propane-1,3-diol with the following compounds: simultaneous breaking of lignin C-C bonds and CO bonds, mild reaction conditions, short reaction time, wide substrate applicability, no need for additional additives, high depolymerization rate, and the resulting products are compounds such as phenols, aromatic diketones, aromatic aldehydes, and aromatic acids.

[0034]

[0035] Example 2

[0036] Depolymerization of lignin (de-alkali)

[0037] A 0.0002 mol / L toluene solution of Cs₂AgBiI₆ nanomaterials was prepared. 2.0 mL of this solution was added to a 20 mL reaction tube, followed by 50 mg of lignin (de-alkaliized). The mixture was stirred at room temperature for 18 h under light irradiation (445 nm, 10 W). After stopping the reaction, the undepolymerized lignin on the tube wall was dissolved using 1 mol / L sodium hydroxide solution. The pH of the system was then adjusted to approximately 3 using 1 mol / L hydrochloric acid solution to allow the depolymerized lignin to fully precipitate. The unreacted lignin was filtered through filter paper, washed three times with dichloromethane, dried, and weighed. The depolymerization rate was calculated to be 28 wt%. The aqueous phase was extracted and concentrated with dichloromethane. The extract was then diluted with acetonitrile and analyzed using gas chromatography. Dimethyl phthalate was used as an internal standard for quantification by gas chromatography. The following products were obtained: 2.73 wt% 3-methoxy-4-hydroxybenzaldehyde, 0.12 wt% 3,4-dimethoxybenzaldehyde, 0.12 wt% 4-acetoxy-3-methoxybenzaldehyde, 0.25 wt% 3-methoxy-4-hydroxyacetophenone, 0.05 wt% dibutyl phthalate, and 0.23 wt% diisobutyl phthalate. The gas chromatogram before the alkali-removing lignin reaction in this example is shown below. Figure 2 As shown, the gas chromatogram of the extract after the reaction is as follows: Figure 3 As shown.

[0038] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for photocatalytic depolymerization of lignin compounds, characterized by: The application relates to a method for preparing a Cs2AgBiX6 double perovskite nanocatalyst, which comprises the following steps: mixing a lignin compound, the Cs2AgBiX6 double perovskite nanocatalyst and an organic solvent, stirring and reacting under blue light irradiation in an air atmosphere at room temperature for 12-18 hours. X in the Cs2AgBiX6 double perovskite nanocatalyst is Cl, Br or I. The organic solvent is toluene, tert-butyl alcohol, isopropyl alcohol or 1,2-dichloroethane. The above lignin compound is a substituted or unsubstituted β-0-4 model compound or a dealkalized lignin, the substituted or unsubstituted β-0-4 model compound is .

2. A method of photocatalytic depolymerization of a lignin compound according to claim 1, characterized in that: The wavelength of the light is 440-460 nm.

3. A method of photocatalytic depolymerization of a lignin compound according to claim 1, characterized in that: The molar ratio of the lignin compound to the Cs2AgBiX6 double perovskite nanocatalyst is 1:0.002-0.

01.

4. The method of photocatalytic depolymerization of a lignin compound according to claim 1, characterized in that: The photocatalysis adopts light irradiation.

5. Use of Cs2AgBiX6 double perovskite nanocrystals as photocatalytic depolymerization catalysts for lignin compounds, characterized in that: X is CI, Br, or I in the Cs2AgBiX6 double perovskite nanocatalyst, the lignin compound is a substituted or unsubstituted β-0-4 model compound or a dealkalized lignin, the substituted or unsubstituted β-0-4 model compound is .

6. Use according to claim 5, wherein: The wavelength of the light is 440-460 nm.

7. Use according to claim 6, wherein: ​

Images