Method for preparing phenol by low-temperature micro-aerobic directional depolymerization of lignin

Abstract

The invention discloses a method for preparing phenol by low-temperature micro-aerobic directional depolymerization of lignin, which comprises the following steps: introducing a choline chloride / lactic acid eutectic solvent to improve the Lewis acidity, oxygen vacancy, specific surface area and thermal stability of Co / CeO2, coupling the obtained ChCl / LA-Co / CeO2 catalyst with an L-lysine / glycerol eutectic solvent to form a high-efficiency catalytic oxidation system, the reaction temperature and oxygen consumption of lignin depolymerization can be remarkably reduced, the process energy consumption is reduced, the separation process of the product is simplified by constructing a dichloromethane-eutectic solvent system, and the highest phenol yield can reach 100%. Compared with other lignin depolymerization methods, the method has the advantages of simple process, low energy consumption, high phenol yield, high conformity with green chemistry concept, and greater application potential.

Description

Technical field:

[0001] The invention relates to the technical field of biomass catalysis, and in particular to a method for preparing phenol by low-temperature micro-oxygen directional depolymerization of lignin. Background technology:

[0002] Lignin is the most abundant aromatic renewable resource in nature, and is the main byproduct in the papermaking industry and biomass energy production. It is currently mainly used as a low-value fuel. Phenol is an extremely important organic chemical raw material, widely used in many industrial products and basic raw materials in the chemical industry (such as phenolic resin, bisphenol A, medicine, surfactant, plastic, etc.). The mainstream production methods of phenol include technologies such as isopropylbenzene method (CN118978467A), toluene oxidation method (CN100551892C) and sulfonation method (CN1074895A), which are faced with the problems of increasing resource shortage and environmental pollution. The molecular structure of natural lignin contains the key features required for conversion to phenol. The conversion of waste lignin into high-value phenol is in line with my country's ecological civilization construction concept of "green development, circular development, and low-carbon development". CN 110117218 A discloses a method for preparing phenol from lignin, which is characterized in that lignin is used as raw material, a metal salt aqueous solution is used as solvent, and a supported noble metal is used as catalyst. Phenol is obtained by reaction at 150-300°C under hydrogenation conditions, but the temperature is relatively high.

[0003] Oxidative depolymerization is recommended as one of the most promising lignin conversion methods due to its relatively mild conditions and potential for producing multifunctional chemicals. Patent CN 111760563 A introduces a method for efficiently catalyzing the oxidative depolymerization of lignin to produce aromatic compounds at 80-250°C using a Sn@TiO2 catalyst in an acetonitrile / water mixed solvent and molecular oxygen as an oxidant. The aromatic compounds are mainly aromatic aldehydes. Patent CN108947783A describes a molybdenum compound as a catalyst that uses molecular oxygen to oxidize lignin at 80-250°C for 2-20 hours to produce aromatic monomers. The aromatic monomers obtained mainly include one or more of aromatic aldehydes, aromatic ketones, aromatic acids, and aromatic esters, and the total aromatic monomer yield is more than 60wt%. Patent CN105669397A designs a method for producing eugenol by oxidizing lignin at 140-200°C with 1.0-6.0Mpa oxygen for 0.5-4.0 hours. However, the lignin conversion in the above methods is still mainly based on high temperature (≥100°C), and the amount of oxidant used is large, and the products are complex and non-specific. Summary of the invention:

[0004] The purpose of the present invention is to provide a method for preparing phenol by low-temperature micro-oxygen directional depolymerization of lignin, which solves the problems of high lignin conversion temperature and complex products leading to complicated separation in the prior art.

[0005] The present invention is achieved through the following technical solutions:

[0006] The invention discloses a method for preparing phenol by low-temperature micro-oxygen directional depolymerization of lignin. The method comprises the following steps: mixing L-lysine and glycerol in a molar ratio of 1:6-10 to prepare a low eutectic solvent as a reaction solvent, adding a lignin substrate at a solid-liquid ratio of 1-5 g / L, and adding a ChCl / LA-Co / CeO2 catalyst, reacting at 30-80°C in air or micro-oxygen environment for 1-3 hours, and selectively extracting phenol in situ with dichloromethane after the reaction to obtain a single phenol product; the ChCl / LA-Co / CeO2 catalyst uses Co as an active ingredient and CeO2 as a carrier, and during preparation, a choline chloride / lactic acid low eutectic solvent (ChCl / LA) is introduced to improve the Lewis acidity, oxygen vacancies, specific surface area and thermal stability of Co / CeO2.

[0007] The lignin substrate is at least one of native lignin in lignocellulosic biomass, separated industrial lignin, or laboratory prepared lignin.

[0008] Preferably, the lignin substrate comprises one or more native lignins selected from sawdust, fruit shells and straws, and one selected from 2-phenoxy-1-acetophenone, alkaline DES lignin, acidic DES lignin and commercial alkaline lignin.

[0009] Among them, alkaline DES lignin refers to lignin extracted from native lignin such as sawdust, fruit shells, and straw by alkaline low eutectic solvent potassium carbonate / ethylene glycol (molar ratio of 1:7) at 130°C, and acidic DES lignin refers to lignin extracted from native lignin such as sawdust, fruit shells, and straw by acidic low eutectic solvent choline chloride / ethylene glycol / AlCl3 (molar ratio of 1:2:0.01) at 120°C.

[0010] Preferably, the addition amount of ChCl / LA-Co / CeO2 catalyst is 0.1-1 g / g substrate.

[0011] Preferably, the method comprises the following steps: mixing L-lysine and glycerol in a molar ratio of 1:6 to 8 to prepare a low eutectic solvent as a reaction solvent, adding a lignin substrate at a solid-liquid ratio of 2.5 to 5 g / L, and adding a ChCl / LA-Co / CeO2 catalyst, reacting at 50 to 80°C for 1 to 3 hours in an oxygen environment of 0.1 to 0.5 MPa, and after the reaction, selectively extracting phenol in situ with dichloromethane to obtain a single phenol product.

[0012] The preparation method of the ChCl / LA-Co / CeO2 catalyst comprises the following steps: choline chloride (ChCl) and lactic acid (LA) are mixed in a molar ratio of 1:2-4, preferably 1:2-3 to prepare a ChCl / LA low eutectic solvent, 5-15wt%, preferably 5-10wt%, of cobalt nitrate hexahydrate is dissolved in 5-20mL, preferably 5-10mL of the ChCl / LA low eutectic solvent, and dropwise deposited on CeO2, and then calcined at 450-575°C, preferably 500°C to prepare the ChCl / LA-Co / CeO2 catalyst.

[0013] The present invention has the following beneficial effects:

[0014] 1) ChCl / LA incorporation increases the Lewis acidity, oxygen vacancies, specific surface area and thermal stability of Co / CeO2, which is beneficial to the activation of CO bonds and effectively solves the problem of poor activity of traditional catalysts;

[0015] 2) Electron transfer induced by ChCl / LA-Co / CeO2 catalyst (Ce 3+ / Ce 4+ ) accelerates the production of active oxygen (·O 2- ) is generated, and the self-oxidation of Co2O3 in the system further reduces the demand for exogenous oxygen;

[0016] 3) L-lysine / glycerol has high solubility in lignin and can induce C β -H fracture;

[0017] 4) The self-heating of the system reduces the reaction temperature;

[0018] 5) Dichloromethane selectively extracts phenol from the L-lysine / glycerol deep eutectic solvent because phenol contains hydroxyl groups, with which dichloromethane forms a dipole-dipole interaction, while other product groups such as acetophenone carbonyl and benzamide amide can form strong hydrogen bonds with the deep eutectic solvent, and dichloromethane is difficult to destroy this stable binding force, so these products are retained in the deep eutectic solvent, achieving 100% selective extraction of phenol.

[0019] In summary, the present invention introduces choline chloride / lactic acid low eutectic solvent to improve the Lewis acidity, oxygen vacancies, specific surface area and thermal stability of Co / CeO2, and couples the obtained ChCl / LA-Co / CeO2 catalyst with L-lysine / glycerol low eutectic solvent to form an efficient catalytic oxidation system, which can significantly reduce the reaction temperature and oxygen consumption of lignin depolymerization, not only reducing the process energy consumption, but also simplifying the product separation process by constructing a dichloromethane-low eutectic solvent system, and can selectively extract phenol in situ, with a phenol yield of up to 100%. Compared with other lignin depolymerization methods, this method has a simple process, low energy consumption, high phenol yield, is highly consistent with the concept of green chemistry, and has greater application potential. Description of the drawings:

[0020] Figure 1 XRD diagrams of ChCl / LA-Co / CeO2 obtained in Example 1 and Co / CeO2 obtained in Comparative Example 1;

[0021] Figure 2 The Raman graphs of ChCl / LA-Co / CeO2 obtained in Example 1 and Co / CeO2 obtained in Comparative Example 1;

[0022] Figure 3 NH3-TPD diagram of ChCl / LA-Co / CeO2 obtained in Example 1 and Co / CeO2 obtained in Comparative Example 1;

[0023] Figure 4 FTIR-Py graphs of ChCl / LA-Co / CeO2 obtained in Example 1 and Co / CeO2 obtained in Comparative Example 1;

[0024] Figure 5 XPS spectra of the Ce 3d region of ChCl / LA-Co / CeO2 obtained in Example 1 and Co / CeO2 obtained in Comparative Example 1;

[0025] Figure 6 XPS spectra of ChCl / LA-Co / CeO2 obtained in Example 1 and Co / CeO2 obtained in Comparative Example 1 in the O1S region;

[0026] Figure 7 TEM images and corresponding EDX images of ChCl / LA-Co / CeO2 obtained in Example 1 at 200nm (a), 2nm (b), and 50nm (c);

[0027] Figure 8The SEM images of ChCl / LA-Co / CeO2 obtained in Example 1 at 5μm (a), 2μm (b), 200nm (c), and 100nm (d) and the corresponding ChCl / LA / Co / CeCO2 EDX images;

[0028] Fig. 9 TG-TGA graph of ChCl / LA-Co / CeO2 obtained in Example 1;

[0029] Fig.10 is the GC-MS spectrum of the reaction product when 2-phenoxy-1-acetophenone is used as the substrate in Example 1;

[0030] Fig.11 1H NMR spectrum of the product after the reaction in Example 1 with 2-phenoxy-1-acetophenone as the substrate. Specific implementation method:

[0031] The following is a further description of the present invention, rather than a limitation of the present invention.

[0032] Example 1: A method for preparing phenol by low-temperature micro-oxygen directional depolymerization of lignin

[0033] 10 wt% of cobalt nitrate hexahydrate was dissolved in 10 mL of ChCl / LA (a mixture of choline chloride (ChCl) and lactic acid (LA) in a molar ratio of 1:2) eutectic solvent, and dropwise deposited on CeO2, followed by calcination at 500 °C to prepare ChCl / LA-Co / CeO2 catalysts. The performance characteristics are shown in Tables 2-4 and Figure 1-9 . L-lysine and glycerol were prepared into a reaction solvent medium in a molar ratio of 1:6, and then a series of lignin substrates were added at a solid-liquid ratio of 2.5g / L, the amount of ChCl / LA-Co / CeO2 catalyst added was 0.5g / g substrate, the amount of O2 was 0.5MPa, and the reaction was carried out at 80℃ for 3h. After the reaction, phenol was selectively extracted in situ with dichloromethane to obtain a single phenol product. When the lignin β-O-4 ketone model 2-phenoxy-1-acetophenone, alkaline DES lignin, acidic DES lignin and commercial alkaline lignin were used as substrates, the corresponding phenol yields were 100%, 78.0%, 73.6% and 75.5%, respectively. Among them, alkaline DES lignin refers to lignin extracted from coconut shells with an alkaline deep eutectic solvent (potassium carbonate / ethylene glycol with a molar ratio of 1:7) at 130°C for 1 hour, and acidic DES lignin refers to lignin extracted from coconut shells with an acidic deep eutectic solvent (choline chloride / ethylene glycol / AlCl3 with a molar ratio of 1:2:0.01) at 120°C for 3 hours. When the lignin β-O-4 keto model 2-phenoxy-1-acetophenone is used, the results are shown in No. 3 and Figure 10-11 .

[0034] Comparative Example 1:

[0035] Referring to Example 1, the difference is that the preparation of the catalyst does not introduce a ChCl / LA (molar ratio of 1:2) low eutectic solvent. The preparation method of the catalyst is as follows: 10wt% of cobalt nitrate hexahydrate is dissolved in water, deposited dropwise on CeO2, and then calcined at 500°C to prepare a Co / CeO2 catalyst.

[0036] When the lignin β-O-4 ketone model substance 2-phenoxy-1-acetophenone was used as the substrate, the corresponding phenol yield was 66.26%. The results are shown in No. 2 in Table 1.

[0037] Example 2: A method for preparing phenol by low-temperature micro-oxygen directional depolymerization of lignin

[0038] 5wt% of cobalt nitrate hexahydrate was dissolved in 5mL ChCl / LA (prepared by mixing choline chloride (ChCl) and lactic acid (LA) in a molar ratio of 1:3), and then dropwise deposited on CeO2, and then calcined at 500℃ to prepare ChCl / LA-Co / CeO2 catalyst. L-lysine and glycerol were mixed in a molar ratio of 1:8 to prepare a reaction solvent medium, and then a series of lignin substrates were added at a solid-liquid ratio of 5g / L, the amount of ChCl / LA-Co / CeO2 catalyst added was 0.1g / g substrate, the amount of O2 was 0.1MPa, and the reaction was carried out at 50℃ for 1h. After the reaction, phenol was selectively extracted in situ with dichloromethane to obtain a single phenol product. When the lignin β-O-4 ketone model 2-phenoxy-1-acetophenone, alkaline DES lignin, acidic DES lignin and commercial alkaline lignin were used as substrates, the corresponding phenol yields were 77.8%, 62.0%, 63.6% and 70.5%, respectively. Among them, alkaline DES lignin refers to the lignin extracted from coconut shell by alkaline low eutectic solvent (potassium carbonate / ethylene glycol molar ratio is 1:7) at 130°C for 1h, and acidic DES lignin refers to the lignin extracted from coconut shell by acidic low eutectic solvent (choline chloride / ethylene glycol / AlCl3 molar ratio is 1:2:0.01) at 120°C for 3h.

[0039] Example 3: A method for preparing phenol by low-temperature micro-oxygen directional depolymerization of lignin

[0040] 15wt% of cobalt nitrate hexahydrate was dissolved in 20mL ChCl / LA (prepared by mixing choline chloride (ChCl) and lactic acid (LA) in a molar ratio of 1:4), and then dropwise deposited on CeO2, and then calcined at 500℃ to prepare ChCl / LA-Co / CeO2 catalyst. L-lysine and glycerol were mixed in a molar ratio of 1:10 to prepare a reaction solvent medium, and then a series of lignin substrates were added at a solid-liquid ratio of 1g / L, and the amount of ChCl / LA-Co / CeO2 catalyst added was 1g / g substrate. The reaction was carried out at 30℃ under air atmosphere for 3h. After the reaction, phenol was selectively extracted in situ with dichloromethane to obtain a single phenol product. When the lignin β-O-4 ketone model 2-phenoxy-1-acetophenone, alkaline DES lignin, acidic DES lignin and commercial alkaline lignin were used as substrates, the corresponding phenol yields were 67.2%, 50.0%, 53.2% and 61.1%, respectively. Among them, alkaline DES lignin refers to the lignin extracted from coconut shell by alkaline low eutectic solvent (potassium carbonate / ethylene glycol molar ratio is 1:7) at 130°C for 1h, and acidic DES lignin refers to the lignin extracted from coconut shell by acidic low eutectic solvent (choline chloride / ethylene glycol / AlCl3 molar ratio is 1:2:0.01) at 120°C for 3h.

[0041] Table 1 Catalytic conversion of 2-phenoxy-1-acetophenone in the catalytic system

[0042]

[0043] Among them, ChCl, Gly, LA and MEA represent choline chloride, glycerol, lactic acid and acetamide, respectively.

[0044] Example 4: Comparison of the effects of different catalysts, oxidants and solvents on the catalytic conversion performance of 2-phenoxy-1-acetophenone

[0045] Refer to Example 1, except that the catalyst, oxidant or solvent for preparing phenol by depolymerization is different (see Table 1). The fixed conditions are: 2-phenoxy-1-acetophenone is used as the lignin β-O-4 ketone model, the solid-liquid ratio is 2.5 g / L, the catalyst addition amount is 0.5 g / g material, the reaction is carried out at 80°C for 3 hours, and phenol is selectively extracted in situ with dichloromethane after the reaction is completed.

[0046] When the reaction solvent is L-Lys / Gly, the molar ratio of L-lysine and glycerol is 1:6; when the catalyst is ChCL / LA-Co / CeO2, the catalyst addition amount is 0.5g / g material; when the oxidant is O2, the O2 dosage is 0.5MPa; when the oxidant is H2O2 (No. 4 in Table 1), the H2O2 concentration is 30wt.%, and the dosage is 2mL. Table 1 shows that when ChCL / LA-Co / CeO2 catalyst, L-lysine / glycerol (L-Lys / Gly) solvent are used, and dichloromethane is used for in-situ extraction after the reaction, the maximum phenol yield is 100%.

[0047] Table 2 Maximum peak temperature and total acidity of each catalyst

[0048]

[0049] Table 3 S6 of each catalyst Acid and Lewis acid and total acid content

[0050]

[0051] Table 4 XPS spectrum results analysis

[0052]

[0053] a. Obtained based on Gauss-Lorentz mixture fitting algorithm.

Claims

1. A method for preparing phenol by low-temperature micro-oxygen directional depolymerization of lignin, characterized in that: The method comprises the following steps: mixing L-lysine and glycerol in a molar ratio of 1:6-10 to prepare a low eutectic solvent as a reaction solvent, adding a lignin substrate at a solid-liquid ratio of 1-5 g / L, and adding a ChCl / LA-Co / CeO2 catalyst, reacting at 30-80°C in air or micro-oxygen environment for 1-3 hours, and selectively extracting phenol in situ with dichloromethane after the reaction to obtain a single phenol product; the ChCl / LA-Co / CeO2 catalyst uses Co as an active ingredient and CeO2 as a carrier, and introduces a choline chloride / lactic acid low eutectic solvent during preparation.

2. The method according to claim 1, characterized in that The lignin substrate includes one or more native lignins selected from sawdust, fruit shells and straws, and one selected from 2-phenoxy-1-acetophenone, alkaline DES lignin, acidic DES lignin and commercial alkaline lignin.

3. The method according to claim 1, characterized in that: The addition amount of ChCl / LA-Co / CeO2 catalyst is 0.1-1 g / g substrate.

4. The method according to claim 1, characterized in that: The method comprises the following steps: mixing L-lysine and glycerol in a molar ratio of 1:6-8 to prepare a low eutectic solvent as a reaction solvent, adding a lignin substrate at a solid-liquid ratio of 2.5-5 g / L, adding a ChCl / LA-Co / CeO2 catalyst, reacting at 50-80°C for 1-3 hours in an oxygen environment of 0.1-0.5 MPa, and selectively extracting phenol in situ with dichloromethane after the reaction to obtain a single phenol product.

5. A method for preparing the ChCl / LA-Co / CeO2 catalyst according to claim 1, characterized in that: The method comprises the following steps: mixing choline chloride and lactic acid in a molar ratio of 1:2-4 to prepare a ChCl / LA low eutectic solvent, dissolving 5-15 wt% of cobalt nitrate hexahydrate in 5-20 mL of the ChCl / LA low eutectic solvent, depositing dropwise on CeO2, and then calcining at 450-575° C. to prepare a ChCl / LA-Co / CeO2 catalyst.

6. The method for preparing the catalyst according to claim 5, characterized in that: The method comprises the following steps: mixing choline chloride and lactic acid in a molar ratio of 1:2-3 to prepare a ChCl / LA low eutectic solvent, dissolving 5-10 wt % of cobalt nitrate hexahydrate in 5-10 mL of the ChCl / LA low eutectic solvent, depositing the cobalt nitrate hexahydrate dropwise on CeO2, and then calcining at 500° C. to prepare a ChCl / LA-Co / CeO2 catalyst.

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