Application of carbon material loaded ionic liquid polyacid catalyst in degradation of lignin

Abstract

The invention provides an application of a carbon material loaded ionic liquid polyacid catalyst in degradation of lignin, and belongs to the technical field of chemistry, and the application comprises the following steps: S1, adding lignin, the carbon material loaded ionic liquid polyacid catalyst and hydrogen peroxide into a reaction kettle container, and using methanol and water as solvents, sealing the reaction kettle container, and then adjusting the reaction temperature and the reaction time; and S2, after the reaction is finished and the reaction kettle container is cooled to 20-30 DEG C, filtering the reacted mixture, and separating the carbon material loaded ionic liquid polyacid catalyst, the unreacted lignin and a lignin product mixed solution. According to the application of the carbon material loaded ionic liquid polyacid catalyst in degradation of lignin, the problem that polyoxometallate is easy to dissolve in a catalytic system can be effectively solved.

Description

Technical Field

[0001] The invention relates to the field of chemical technology, in particular to the application of an ionic liquid polyacid catalyst supported by a carbon material in degrading lignin. Background Art

[0002] As a renewable bioresource, lignin is often used to produce small molecule aromatic compounds, such as light aromatics. Therefore, lignin has been regarded as a potential resource that can meet people's demand for high-value chemicals and energy. With the continuous development of catalytic oxidation technology in the field of lignin conversion and the continuous improvement of catalytic systems, the research trend of using this method to efficiently convert lignin into aromatic polymers has become increasingly significant and has gradually become the mainstream direction of current research and exploration.

[0003] Catalysts play a vital role in the catalytic oxidative depolymerization of lignin, and polyoxometalates (POMs) are a type of catalyst with good Brønsted acidity and redox properties. The acidity and redox properties of polyoxometalates can be finely controlled by adjusting the type of coordinating elements, central atoms or counterions. In addition, compared with traditional inorganic acids such as sulfuric acid (H2SO4), nitric acid (HNO3) and hydrochloric acid (HCl), POMs can show more significant acidity in aqueous solution, so this type of catalyst has been widely used in lignin degradation. However, polyoxometalates are more easily dissolved in aqueous solution, which is not conducive to the recovery and recycling of catalysts. Therefore, many studies are devoted to modifying polyoxometalates so that they can form heterogeneous conditions in the catalytic system. Among them, selecting a suitable carrier to load POMs is a common method.

[0004] Among many carriers, carbon materials have the characteristics of wide sources, low cost, large specific surface area and adjustable pore size. Commonly used carbon materials include activated carbon (AC), graphene oxide (GO) and biochar, etc. Fixing polyacids and ionic liquids on carbon materials to prepare supported catalysts can not only maintain the high activity of the catalyst, but also improve the reusability of the catalyst, thereby forming a heterogeneous catalytic system, and the catalyst can be easily recovered by filtration after the lignin degradation reaction is completed.

[0005] Some previous studies have confirmed that carbon materials have a good loading effect on polyacids, but there have been no reports on the use of carbon materials to load ionic liquid polyoxometalates for the catalytic oxidative depolymerization of lignin. Summary of the invention

[0006] The purpose of the present invention is to provide an application of a carbon material-supported ionic liquid polyacid catalyst in the degradation of lignin, which can effectively solve the problem that polyoxometalates are easily dissolved in the catalytic system.

[0007] To achieve the above object, the present invention provides the use of a carbon material-supported ionic liquid polyacid catalyst in degrading lignin, comprising the following steps: Step S1, adding lignin, carbon material-supported ionic liquid polyacid catalyst, and hydrogen peroxide into a reaction kettle container, using methanol and water as solvents, sealing the reaction kettle container, and adjusting the reaction temperature and reaction time; Step S2, after the reaction is completed, the reactor container is cooled to 20-30 o C, filtering the reaction mixture to separate the carbon material-supported ionic liquid polyacid catalyst, unreacted lignin and the lignin product mixed liquid.

[0008] Preferably, in step S1, the molar ratio of lignin to the carbon material-supported ionic liquid polyacid catalyst is 1:5-1:1, the molar ratio of the volume of hydrogen peroxide to lignin is 1.5:1-4.0:1, and the volume ratio of methanol to water is 2:1-7:1.

[0009] Preferably, in step S1, the reaction temperature is 120-180 o C, reaction time is 1~6h.

[0010] Preferably, the steps for preparing the carbon material supported ionic liquid polyacid catalyst are as follows: S11, weighing powdered activated carbon and adding it into a beaker, adding water, and ultrasonicating to make the activated carbon in a suspended state to obtain a suspension; S12, dissolve the ionic liquid and polyacid in anhydrous ethanol, then add them to the suspension and o C and stirred to obtain a mixed solution; S13, centrifuging the mixed solution, collecting and drying the solid matter to obtain a gray-black powder, which is the ionic liquid polyacid catalyst supported by the carbon material.

[0011] Preferably, in step S11, the molar concentration ratio of activated carbon to water is 0.1-0.5 mol / L.

[0012] Preferably, in step S11, ultrasound is performed at 100 Hz for 10 to 30 min.

[0013] Preferably, in step S12, the molar ratio of the ionic liquid to the polyacid is 4:1.

[0014] Preferably, in step S12, the stirring time is 10 to 60 minutes.

[0015] Preferably, in step S13, the centrifugation time is 5 to 10 minutes.

[0016] Preferably, in step S13, the drying time is 12 to 48 hours.

[0017] Therefore, the present invention uses the above-mentioned carbon material-supported ionic liquid multi-acid catalyst in the degradation of lignin, and the technical effects are as follows: (1) The loading material in the present invention is cheap and readily available, which can save economic costs; (2) The present invention can effectively solve the problem that polyoxometalates are easily dissolved in the catalytic system (the polyoxometalates are dispersed on the surface of the carrier, and the electrostatic effect makes it difficult for the polyoxometalates to fall off); (3) In the present invention, not only can the high activity of the catalyst be maintained, but also the reusability of the catalyst can be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Degradation effect diagram of activated carbon loaded with single ion liquid polyacid at different temperatures; Figure 2 This is a graph showing the degradation effect of activated carbon loaded with single ion liquid polyacid at different reaction times; Figure 3 This is a diagram showing the degradation effect of activated carbon loaded with single-ion liquid polyacid under different oxidizing doses. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0020] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0021] Embodiment 1 In this example, activated carbon (AC) loaded with single ion liquid [VimAm]Br and polyoxometalate H3PMo6W6O40 are used as examples to illustrate the method proposed in the present invention. The following is a specific preparation process.

[0022] Step 1: Polyoxometalate H3PMo6W6O 40 Preparation.

[0023] (1) Weigh 6 mmol Na2HPO4·12H2O and dissolve it in 12.5 mL deionized water to obtain solution 1. Weigh 36 mmol Na2MoO4·2H2O and dissolve it in 25 mL deionized water to obtain solution 2. Mix solution 1 and solution 2 and transfer them into a 100 mL three-necked flask. Reflux at 90°C for 30 min to obtain a colorless transparent solution.

[0024] (2) Weigh 36 mmol Na2WO4·2H2O and dissolve it in 12.5 mL deionized water. Slowly add the resulting solution into the colorless transparent solution prepared in step (1) to obtain a mixed solution.

[0025] (3) Concentrated H2SO4 was added dropwise to the mixed solution prepared in step (2) to adjust the pH of the mixed solution to 1.5. The mixed solution became light yellow and clear, and then refluxed at 90°C for 8 h.

[0026] (4) After the reaction is completed, cool to 25 o C, transfer the solution to a separatory funnel, add 50 mL of a solution made by mixing 25 mL of ether and 25 mL of 49% H2SO4, shake thoroughly, and let stand until the solution in the separatory funnel separates into three layers. Collect the ether compound in the lower layer and dry it to obtain a bright yellow powder, which is H3PMo6W6O 40 .

[0027] Step 2: Preparation of single ion liquid [VimAm]Br.

[0028] Using 1-vinylimidazole and pentane bromide as raw materials, imidazole bromide is synthesized by alkyl substitution method. The specific steps are as follows: (1) Mix 0.005 mol (450 µL) 1-vinylimidazole and 0.005 mol (620 µL) bromopentane, then add 15 mL of anhydrous ethanol, evacuate for 5 min, seal the mixture, and react in an oil bath at 70 °C for 24 h.

[0029] (2) After the reaction is completed, the solution is transferred to an eggplant-shaped flask and recovered after rotary evaporation at 70°C. The resulting viscous solution is the single-ion liquid [VimAm]Br.

[0030] Step 3: Loading the activated carbon with the single ion liquid polyacid.

[0031] The polyacid and ionic liquid are fixed on the activated carbon using the chemical impregnation method. The specific steps are as follows: (1) Weigh an appropriate amount (usually 0.3 g to 0.5 g) of powdered activated carbon, add 60 mL of H2O, and ultrasonicate at 100 Hz for 30 min to keep the activated carbon in a suspended state.

[0032] (2) Add ionic liquid and polyacid dissolved in anhydrous ethanol to the above suspension in a molar ratio of 4:1, for example: 0.25 mmol H3PMo6W6O 40 (i.e. 0.5868 g), 1 mmol of single ion liquid [VimAm]Br (i.e. 0.2452 g) dissolved in 10 mL of anhydrous ethanol, and then heated at 25 o C and stirred for 24 h. The dosage of the drug in this step can be increased or decreased in equal proportion.

[0033] (3) After stirring, the mixed solution is centrifuged, and the solid matter is collected and dried at 60°C. The gray-black powder obtained after drying is the activated carbon with fixed polyacid and ionic liquid.

[0034] Step 4: Catalytic oxidative depolymerization of the lignin model compound PP-ol.

[0035] like Figure 1 , Figure 2 , Figure 3 As shown, the lignin degradation efficiency under different reaction temperatures, different reaction times and different oxidant addition amounts were tested respectively.

[0036] In this embodiment, the specific conditions are as follows: (1) Add 0.045 mmol PP-ol and 0.045 mmol catalyst to the reactor, use 16 mL methanol and 4 mL H2O as solvent, add 3 ml hydrogen peroxide as oxidant, seal the reactor, and adjust the reaction temperature to 140 o C, set the reaction time to 4h.

[0037] (2) After the reaction is completed, wait for the reactor to cool to 25 o C, and the reaction mixture is filtered to separate the solid catalyst and the solution. The catalyst can be washed 3 times with 50 ml of deionized water and then dried and recovered.

[0038] Embodiment 2 The difference between this embodiment and the first embodiment is that the catalyst in the first embodiment is removed, and the other conditions are the same.

[0039] Embodiment 3 The difference between this embodiment and the first embodiment is that the catalyst in the first embodiment is replaced by material C, and the other conditions are the same.

[0040] Embodiment 4 The difference between this embodiment and the embodiment is that the catalyst in the embodiment 1 is replaced by H3PMo6W6O 40 (POM), other conditions being the same.

[0041] Embodiment 5 The difference between this embodiment and embodiment 1 is that the catalyst in embodiment 1 is replaced by [VimAm]-POM, and the other conditions are the same.

[0042] Embodiment 6 The difference between this embodiment and the first embodiment is that the catalyst in the first embodiment is replaced by C@POM, and the other conditions are the same.

[0043] The lignin degradation efficiency of Examples 1 to 6 is shown in Table 1.

[0044] Table 1 Degradation efficiency of lignin by different catalysts

[0045] Therefore, the use of the carbon material-supported ionic liquid polyacid catalyst in the degradation of lignin in the present invention can effectively solve the problem that polyoxometalates are easily dissolved in the catalytic system.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. Application of carbon material supported ionic liquid polyacid catalyst in lignin degradation, characterized in that: The following steps are involved: Step S1, adding lignin, carbon material-supported ionic liquid polyacid catalyst, and hydrogen peroxide into a reaction kettle container, using methanol and water as solvents, sealing the reaction kettle container, and adjusting the reaction temperature and reaction time; Step S2, after the reaction is completed, the reactor container is cooled to 20-30 o C, filtering the reaction mixture to separate the carbon material-supported ionic liquid polyacid catalyst, unreacted lignin and the lignin product mixed liquid.

2. The use of the carbon material supported ionic liquid polyacid catalyst in degrading lignin according to claim 1, characterized in that: In step S1, the molar ratio of lignin to the ionic liquid polyacid catalyst supported by the carbon material is 1:5-1:1, the molar ratio of the volume of hydrogen peroxide to lignin is 1.5:1-4.0:1, and the volume ratio of methanol to water is 2:1-7:

1.

3. The use of the carbon material supported ionic liquid polyacid catalyst in degrading lignin according to claim 1, characterized in that: In step S1, the reaction temperature is 120~180 o C, reaction time is 1~6h.

4. The use of the carbon material supported ionic liquid polyacid catalyst in degrading lignin according to claim 1, characterized in that: The preparation steps of the carbon material supported ionic liquid polyacid catalyst are as follows: S11, weighing powdered activated carbon and adding it into a beaker, adding water, and ultrasonicating to make the activated carbon in a suspended state to obtain a suspension; S12, dissolve the ionic liquid and polyacid in anhydrous ethanol, then add them to the suspension and o C and stirred to obtain a mixed solution; S13, centrifuging the mixed solution, collecting and drying the solid matter to obtain a gray-black powder, which is the ionic liquid polyacid catalyst supported by the carbon material.

5. The use of the carbon material supported ionic liquid polyacid catalyst in degrading lignin according to claim 4, characterized in that: In step S11, the molar concentration ratio of activated carbon to water is 0.1-0.5 mol / L.

6. The use of the carbon material supported ionic liquid polyacid catalyst in degrading lignin according to claim 4, characterized in that: In step S11, ultrasound is performed at 100 Hz for 10 to 30 minutes.

7. The use of the carbon material supported ionic liquid polyacid catalyst in degrading lignin according to claim 4, characterized in that: In step S12, the molar ratio of the ionic liquid to the polyacid is 4:

1.

8. The use of the carbon material supported ionic liquid multi-acid catalyst in degrading lignin according to claim 4, characterized in that: In step S12, the stirring time is 10 to 60 minutes.

9. The use of the carbon material supported ionic liquid polyacid catalyst in degrading lignin according to claim 4, characterized in that: In step S13, the centrifugation time is 5 to 10 minutes.

10. The use of the carbon material supported ionic liquid polyacid catalyst in degrading lignin according to claim 4, characterized in that: In step S13, the drying time is 12 to 48 hours.

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