Method for pulse electrolysis of lignin

Abstract

The invention discloses a method for pulse electrolysis of lignin, which comprises the following steps: carrying out a three-electrode system pulse electrolysis reaction on a lignin dimer model compound in an acetonitrile medium system to obtain a micromolecular aromatic monomer; the conditions of pulse electrolysis are as follows: electrolysis is performed for 4-8 hours under the pulse potential of + / -1.4 V to + / -2.4 V, the period is 5-20 seconds, the duty ratio is 0.25-0.75, and the electrolyte is tetraethylammonium perchlorate. According to the pulse electrochemical method disclosed by the invention, the C-O bond of the model compound can be subjected to electrooxidation depolymerization at a relatively low potential, the problem of peroxidation occurring at a high potential is relieved, and the product yield and the product selectivity of the model compound are improved. The method disclosed by the invention has wide substrate applicability and can be effectively applied to fracture of various C-O bonds.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass electrochemical conversion, and relates to a method for the high-value conversion of lignin based on pulse electrochemistry. Background Art

[0002] As a potential clean energy source, lignocellulose is expected to replace petroleum and has thus received extensive attention. Lignin is one of the important components of lignocellulose, with rich content and low cost, and its proportion in lignocellulosic biomass can reach 15 - 30 wt.%. As the most abundant aromatic biopolymer on earth, lignin has unique application value and potential in the energy field. However, the highly complex structure of lignin makes it difficult to degrade and utilize. In the chemical structure of lignin, the proportion of carbon - oxygen - carbon (C - O - C) bonds is about 75%, while the proportion of carbon - carbon (C - C) bonds is about 25%. Therefore, the cleavage of C - O bonds is crucial for the depolymerization of lignin, and the selective cleavage process is of great significance. In the study of lignin C - O bond cleavage, traditional methods include chemical oxidation, hydrodehydrogenation and reduction, biological methods, and pyrolysis, etc. However, these methods have limitations, such as being carried out under high temperature and high pressure, long reaction time, relying on additives, poor product selectivity, low yield, etc. For example, when using a single - atom Co catalyst to oxidize phenoxyethylbenzene, only 12% is converted at 150 °C, and the yield is 7%.

[0003] Compared with traditional methods such as chemical oxidation, hydrodehydrogenation and reduction, biological methods, and pyrolysis, the electrochemical method exhibits many significant advantages. Its reaction conditions are relatively mild, in line with the concept of green environmental protection (it can rely on renewable electricity such as wind energy and solar energy as the driving energy), has the characteristics of low cost, and can precisely control the reaction activity and product selectivity by simply adjusting experimental parameters. Therefore, the electrochemical method is a highly competitive technical means in this field. Some studies have shown that without adding other additives, when the applied potential of the electrochemical method is much higher than the oxidation peak potential of the model compound, very few target products are generated. For example, the yield of phenoxyethylbenzene under constant potential is about 1%. However, high potential also leads to the peroxidation of the model compound, and most model compounds cannot achieve selective conversion to the target aromatic compound, resulting in low product yield and limiting the application prospect of this technology in the efficient utilization of lignin. Therefore, how to alleviate the peroxidation problem is an urgent problem to be solved in the electrochemical depolymerization of lignin. Summary of the Invention

[0004] To alleviate the peroxidation problem of lignin, the present invention proposes a method for pulsed electrolysis of lignin. Specifically, this method conducts a controllable electrochemical oxidative depolymerization of lignin molecules in an acetonitrile medium system, achieving the efficient valorization utilization of lignin resources. That is, by precisely regulating the potential (U), period (T), duty cycle (D), and electrolysis time (t), the selective cleavage of the C-O bond of the model compound is realized at room temperature. Compared with traditional constant potential electrolysis, the pulsed electrolysis technology realizes the electrochemical depolymerization of lignin dimers at a lower voltage, alleviates the peroxidation phenomenon occurring at high potentials, and thus obtains higher substrate conversion rates and product yields.

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

[0006] A method for pulsed electrolysis of lignin, which conducts a three-electrode system pulsed electrolysis reaction on a lignin dimer model compound in an acetonitrile medium system to obtain small molecule aromatic monomers; the conditions for pulsed electrolysis are: electrolyzing for 4 - 8 h at a pulsed potential of ±1.4 V - ±2.4 V, with a period of 5 - 20 s, a duty cycle of 0.25 - 0.75, and the electrolyte being tetraethylammonium perchlorate.

[0007] The small molecule aromatic monomer products are benzaldehyde, benzyl alcohol, phenethyl alcohol, hydroquinone, p-benzoquinone, etc.

[0008] Preferably, the concentration of the electrolyte is 0.01 - 0.10 mol L -1 TEAP / CH 3 CN.

[0009] Preferably, the concentration of the lignin dimer model compound is 0.01 - 0.10 mol L -1 .

[0010] Preferably, the lignin dimer model compound includes lignin containing one or more of β-O-4 bonds, α-O-4 bonds, and 4-O-5 bonds.

[0011] Preferably, the lignin dimer model compound includes one or two or more of phenoxyethylbenzene (1, containing β-O-4 bond), benzyl phenyl ether (2, containing α-O-4 bond), and 4,4'-dihydroxydiphenyl ether (3, containing 4-O-5 bond), and the structures are as follows:

[0012]

[0013] Preferably, the conditions for pulsed electrolysis are: electrolyzing for 6 ± 1 h at a pulsed potential of ±1.8 V, with a period of 10 - 15 s, and a duty cycle of 0.5 ± 0.1.

[0014] Preferably, the working electrode and the counter electrode are both Pt sheet electrodes, and the reference electrode is Ag / Ag + non-aqueous reference electrode.

[0015] Preferably, the concentration of Ag + is 0.1 ± 0.05 mol L -1 Ag + / CH 3 CN.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The pulse electrochemical method described in the present invention can electro-oxidatively depolymerize the C-O bond of the model compound at a lower potential, alleviating the over-oxidation problem that occurs at a high potential, and improving the product yield and product selectivity of the model compound.

[0018] (2) The pulse electro technology can flexibly regulate the reaction conditions by regulating parameters such as potential, electrolysis time, cycle, duty ratio, etc., to achieve the optimization of the reaction.

[0019] (3) The method described in the present invention has a wide substrate applicability and can be effectively applied to the cleavage of various C-O bonds. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a gas chromatography-mass spectrometry analysis result diagram of the reaction system after Examples 1-4 and Comparative Examples 1-2, and is detected by a hydrogen flame detector.

[0021] Figure 2 It is a gas chromatography-mass spectrometry analysis result diagram of the reaction system after Examples 5-10, and is detected by a hydrogen flame detector.

[0022] Figure 3 It is a gas chromatography-mass spectrometry analysis result diagram of the reaction system after Examples 11-12 and Comparative Examples 3-4, and is detected by a hydrogen flame detector.

[0023] Note: Due to the decline of column efficiency, Agilent HP-5MS (30m × 320μm × 0.25μm) chromatographic column ( Figure 1 and Figure 3 ) and Phenomenex HP-5MS (30m × 320μm × 0.25μm) chromatographic column ( Figure 2 ) were used successively. DETAILED DESCRIPTION OF THE INVENTION

[0024] To better understand the present invention, the present invention will be further described below in conjunction with examples, but the implementation manners of the present invention are not limited thereto.

[0025] In this specification, percentages are all by mass. The reaction is carried out at room temperature, and the whole reaction process is continuously carried out under the action of magnetic stirring. By using the multi-potential step method to regulate the parameters of the pulsed electricity, during the potentiostatic electrolysis process, the control of the potential is achieved by means of chronoamperometry.

[0026] Example 1: In a 50 mL one-piece electrolytic cell, a Pt sheet electrode with a size of 20 mm × 20 mm × 0.1 mm is used as the working electrode and the counter electrode, and together with an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3 CN) non-aqueous reference electrode to establish a three-electrode system. The prepared electrolyte solution is 20 mL, in which the concentration of the electrolyte TEAP is 10 -2 mol L -1 , and the concentration of the substrate phenoxyethylbenzene (1) is 2.5×10 -2 mol L -1 . Electrolysis is carried out at a pulsed potential of ±1.4 V for 6 h, the period is 15 s, and the duty cycle is 0.5. After the reaction is completed, 100 μL of dimethyl phthalate (5% wt.) is added as an internal standard, and the products are detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 1.

[0027] Example 2: In a 50 mL one-piece electrolytic cell, a Pt sheet electrode with a size of 20 mm × 20 mm × 0.1 mm is used as the working electrode and the counter electrode, and together with an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3 CN) non-aqueous reference electrode to establish a three-electrode system. The prepared electrolyte solution is 20 mL, in which the concentration of the electrolyte TEAP is 10 -2 mol L -1 , and the concentration of the substrate phenoxyethylbenzene (1) is 2.5×10 -2 mol L -1 . Electrolysis is carried out at a pulsed potential of ±1.8 V for 6 h, the period is 15 s, and the duty cycle is 0.5. After the reaction is completed, 100 μL of dimethyl phthalate (5% wt.) is added as an internal standard, and the products are detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 1.

[0028] Example 3: In a 50 mL one-piece electrolytic cell, a Pt sheet electrode with a size of 20 mm × 20 mm × 0.1 mm is used as the working electrode and the counter electrode, and together with an Ag / Ag + (1×10 -1 mol L-1 AgNO 3 / CH 3 CN) non-aqueous reference electrode to establish a three-electrode system. The configured electrolyte solution is 20 mL, where the concentration of the electrolyte TEAP is 10 -2 mol L -1 , and the concentration of the substrate phenoxyethylbenzene (1) is 2.5×10 -2 mol L -1 . Electrolysis is carried out at a pulsed potential of ±2.0 V for 6 h, with a period of 15 s and a duty cycle of 0.5. After the reaction is completed, 100 μL of dimethyl phthalate (5% wt.) is added as an internal standard, and the products are detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 1.

[0029] Example 4: In a 50 mL integrated electrolytic cell, a Pt sheet electrode with a size of 20 mm×20 mm×0.1 mm is used as the working electrode and the counter electrode, and an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3 CN) non-aqueous reference electrode to establish a three-electrode system. The configured electrolyte solution is 20 mL, where the concentration of the electrolyte TEAP is 10 -2 mol L -1 , and the concentration of the substrate phenoxyethylbenzene (1) is 2.5×10 -2 mol L -1 . Electrolysis is carried out at a pulsed potential of ±2.4 V for 6 h, with a period of 15 s and a duty cycle of 0.5. After the reaction is completed, 100 μL of dimethyl phthalate (5% wt.) is added as an internal standard, and the products are detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 1.

[0030] Comparative Example 1: In a 50 mL integrated electrolytic cell, a Pt sheet electrode with a size of 20 mm×20 mm×0.1 mm is used as the working electrode and the counter electrode, and an Ag / Ag + (1×10-1mol L-1AgNO 3 / CH 3 CN) non-aqueous reference electrode to establish a three-electrode system. The configured electrolyte solution is 20 mL, where the concentration of the electrolyte TEAP is 10 -2 mol L -1 , and the concentration of the substrate phenoxyethylbenzene (1) is 2.5×10 -2 mol L -1Electrolysis was carried out at a constant potential of 1.8 V for 6 h. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard, and the products were detected and quantified by gas chromatography - mass spectrometry. The conversion rate and product yield are shown in Table 1.

[0031] Comparative Example 2: In a 50 mL one - piece electrolytic cell, a Pt sheet electrode with dimensions of 20 mm×20 mm×0.1 mm was used as the working electrode and the counter electrode, and together with an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3 CN) non - aqueous reference electrode to establish a three - electrode system. The prepared electrolyte solution was 20 mL, in which the concentration of the electrolyte TEAP was 10 -2 mol L -1 , and the concentration of the substrate phenoxyethylbenzene (1) was 2.5×10 -2 mol L -1 . Electrolysis was carried out at a constant potential of 2.5 V for 6 h. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard, and the products were detected and quantified by gas chromatography - mass spectrometry. The conversion rate and product yield are shown in Table 1.

[0032] Comparative Example 3: In a 50 mL one - piece electrolytic cell, a Pt sheet electrode with dimensions of 20 mm×20 mm×0.1 mm was used as the working electrode and the counter electrode, and together with an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3 CN) non - aqueous reference electrode to establish a three - electrode system. The prepared electrolyte solution was 20 mL, in which the concentration of the electrolyte LiClO 4 was 10 -2 mol L -1 , and the concentration of the substrate phenoxyethylbenzene (1) was 2.5×10 -2 mol L -1 . Electrolysis was carried out at a pulsed potential of ±1.8 V for 6 h. After the reaction was completed, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard, and the products were detected and quantified by gas chromatography - mass spectrometry. The conversion rate and product yield are shown in Table 1.

[0033] Example 5: In a 50 mL one - piece electrolytic cell, a Pt sheet electrode with dimensions of 20 mm×20 mm×0.1 mm was used as the working electrode and the counter electrode, and together with an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3A three - electrode system was established together with a non - aqueous reference electrode. The configured electrolyte solution was 20 mL, in which the concentration of the electrolyte TEAP was 10 -2 mol L -1 , and the concentration of the substrate phenoxyethylbenzene (1) was 2.5×10 -2 mol L -1 . Electrolysis was carried out at a pulsed potential of ±1.8 V for 4 h, with a period of 15 s and a duty cycle of 0.5. After the reaction ended, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard, and the products were detected and quantified by gas chromatography - mass spectrometry. The conversion rate and product yield are shown in Table 2.

[0034] Example 6: In a 50 - mL integrated electrolytic cell, a Pt sheet electrode with a size of 20 mm×20 mm×0.1 mm was used as the working electrode and the counter electrode, and an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3 A three - electrode system was established together with a non - aqueous reference electrode. The configured electrolyte solution was 20 mL, in which the concentration of the electrolyte TEAP was 10 -2 mol L -1 , and the concentration of the substrate phenoxyethylbenzene (1) was 2.5×10 -2 mol L -1 . Electrolysis was carried out at a pulsed potential of ±1.8 V for 8 h, with a period of 15 s and a duty cycle of 0.5. After the reaction ended, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard, and the products were detected and quantified by gas chromatography - mass spectrometry. The conversion rate and product yield are shown in Table 2.

[0035] Example 7: In a 50 - mL integrated electrolytic cell, a Pt sheet electrode with a size of 20 mm×20 mm×0.1 mm was used as the working electrode and the counter electrode, and an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3 A three - electrode system was established together with a non - aqueous reference electrode. The configured electrolyte solution was 20 mL, in which the concentration of the electrolyte TEAP was 10 -2 mol L -1 , and the concentration of the substrate phenoxyethylbenzene (1) was 2.5×10 -2 mol L -1 . Electrolysis was carried out at a pulsed potential of ±1.8 V for 6 h, with a period of 5 s and a duty cycle of 0.5. After the reaction ended, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard, and the products were detected and quantified by gas chromatography - mass spectrometry. The conversion rate and product yield are shown in Table 2.

[0036] Example 8: In a 50 mL integrated electrolytic cell, a Pt sheet electrode with dimensions of 20 mm × 20 mm × 0.1 mm was used as the working electrode and the counter electrode, and an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3 CN) non-aqueous reference electrode was used to establish a three-electrode system. The prepared electrolyte solution was 20 mL, in which the concentration of the electrolyte TEAP was 10 -2 mol L -1 , and the concentration of the substrate phenoxyethylbenzene (1) was 2.5×10 -2 mol L -1 . Electrolysis was carried out at a pulsed potential of ±1.8 V for 6 h, with a period of 30 s and a duty cycle of 0.5. After the reaction, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard, and the products were detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 2.

[0037] Example 9: In a 50 mL integrated electrolytic cell, a Pt sheet electrode with dimensions of 20 mm × 20 mm × 0.1 mm was used as the working electrode and the counter electrode, and an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3 CN) non-aqueous reference electrode was used to establish a three-electrode system. The prepared electrolyte solution was 20 mL, in which the concentration of the electrolyte TEAP was 10 -2 mol L -1 , and the concentration of the substrate phenoxyethylbenzene (1) was 2.5×10 -2 mol L -1 . Electrolysis was carried out at a pulsed potential of ±1.8 V for 6 h, with a period of 15 s and a duty cycle of 0.25. After the reaction, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard, and the products were detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 2.

[0038] Example 10: In a 50 mL integrated electrolytic cell, a Pt sheet electrode with dimensions of 20 mm × 20 mm × 0.1 mm was used as the working electrode and the counter electrode, and an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3 CN) non-aqueous reference electrode was used to establish a three-electrode system. The prepared electrolyte solution was 20 mL, in which the concentration of the electrolyte TEAP was 10 -2mol L -1 ,the concentration of substrate phenoxyethylbenzene (1) was 2.5×10 -2 mol L -1 . Electrolysis was carried out at a pulsed potential of ±1.8 V for 6 h, with a period of 15 s and a duty cycle of 0.75. After the reaction, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard, and the products were detected and quantified by gas chromatography - mass spectrometry. The conversion rate and product yield are shown in Table 2.

[0039] Example 11: In a 50 mL one - piece electrolytic cell, a Pt sheet electrode with dimensions of 20 mm×20 mm×0.1 mm was used as the working electrode and the counter electrode, and an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3 CN) non - aqueous reference electrode were used together to establish a three - electrode system. The prepared electrolyte solution was 20 mL, in which the concentration of electrolyte TEAP was 10 -2 mol L -1 , and the concentration of substrate benzyl phenyl ether (2) was 2.5×10 -2 mol L -1 . Electrolysis was carried out at a pulsed potential of ±1.8 V for 6 h, with a period of 15 s and a duty cycle of 0.75. After the reaction, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard, and the products were detected and quantified by gas chromatography - mass spectrometry. The conversion rate and product yield are shown in Table 3.

[0040] Comparative Example 3: In a 50 mL one - piece electrolytic cell, a Pt sheet electrode with dimensions of 20 mm×20 mm×0.1 mm was used as the working electrode and the counter electrode, and an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3 CN) non - aqueous reference electrode were used together to establish a three - electrode system. The prepared electrolyte solution was 20 mL, in which the concentration of electrolyte TEAP was 10 -2 mol L -1 , and the concentration of substrate benzyl phenyl ether (2) was 2.5×10 -2 mol L -1 . Electrolysis was carried out at a constant potential of 1.8 V for 6 h. After the reaction, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard, and the products were detected and quantified by gas chromatography - mass spectrometry. The conversion rate and product yield are shown in Table 3.

[0041] Example 12: In a 50 mL one-piece electrolytic cell, a Pt sheet electrode with dimensions of 20 mm × 20 mm × 0.1 mm was used as the working electrode and the counter electrode, and an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3 CN) non-aqueous reference electrode was used to establish a three-electrode system. The prepared electrolyte solution was 20 mL, in which the concentration of the electrolyte TEAP was 10 -2 mol L -1 , and the concentration of the substrate 4,4'-dihydroxydiphenyl ether (3) was 2.5×10 -2 mol L -1 . Electrolysis was carried out at a pulsed potential of ±1.4 V for 6 h, with a cycle of 15 s and a duty cycle of 0.75. After the reaction, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard, and the products were detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 3.

[0042] Comparative Example 4: In a 50 mL one-piece electrolytic cell, a Pt sheet electrode with dimensions of 20 mm × 20 mm × 0.1 mm was used as the working electrode and the counter electrode, and an Ag / Ag + (1×10 -1 mol L -1 AgNO 3 / CH 3 CN) non-aqueous reference electrode was used to establish a three-electrode system. The prepared electrolyte solution was 20 mL, in which the concentration of the electrolyte TEAP was 10 -2 mol L -1 , and the concentration of the substrate 4,4'-dihydroxydiphenyl ether (3) was 2.5×10 -2 mol L -1 . Electrolysis was carried out at a constant potential of 1.4 V for 6 h. After the reaction, 100 μL of dimethyl phthalate (5% wt.) was added as an internal standard, and the products were detected and quantified by gas chromatography-mass spectrometry. The conversion rate and product yield are shown in Table 3.

[0043] Table 1 Evaluation results of the electrolysis of 4-phenoxyethylbenzene (1) at different potentials

[0044]

[0045]

[0046] a: The electrolyte used in Comparative Example 3 was LiClO 4 .

[0047] Table 2 Evaluation results of the electrolysis of 4-phenoxyethylbenzene (1) under different pulsed electrolysis conditions

[0048]

[0049] Table 3 Electrolysis evaluation results of benzyl phenyl ether and 4,4'-dihydroxy diphenyl ether under different electrolysis conditions

[0050]

[0051] Note: The values in the table represent the molar conversion rate of the product relative to the substrate, where "-" indicates that the corresponding product was not detected by GC-MS.

[0052] It can be seen from Examples 1-4 that for the cleavage of the β-O-4 bond, whether at a relatively large potential or a relatively small potential, better results than those of the comparative example can be obtained, with greatly improved conversion rate and yield, and effectively improved product selectivity. Under the same potential conditions, the oxidation ability exhibited by the pulse method is much stronger than that of the constant potential electrolysis method. This characteristic enables the pulse method to efficiently drive the electro-oxidation reaction at a relatively low potential, thereby effectively avoiding the common over-oxidation problem under high potential conditions.

[0053] It can be seen from the test results in Table 2 that the electrolysis time, cycle, and duty ratio are all important parameters affecting the reaction results. By adjusting these parameters, better electrolysis results can be obtained.

[0054] It can be seen from the test results in Table 3 that the present invention can be applied to other model compounds. Compared with the traditional constant potential electrolysis mode, pulse electrolysis can effectively improve the product yield and conversion rate of the cleavage of different C-O bonds (the α-O-4 bond represented by Model Compound 2 and the 4-O-5 bond represented by Model Compound 3).

[0055] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for pulse electrolysis of lignin, characterized in that: The lignin dimer model compound was subjected to a three-electrode system pulse electrolysis reaction in an acetonitrile medium system to obtain a small molecule aromatic monomer; The conditions of pulse electrolysis are: electrolysis at a pulse potential of ±1.4V-±2.4V for 4-8h, a period of 5-20s, a duty cycle of 0.25-0.75, and the electrolyte is tetraethylammonium perchlorate.

2. The method according to claim 1, characterized in that The concentration of the electrolyte is 0.01-0.10 mol L -1 .

3. The method according to claim 2, characterized in that The concentration of the lignin dimer model compound is 0.01-0.10 molL -1 .

4. The method according to claim 3, characterized in that The lignin dimer model compound includes lignin containing one or more of β-O-4 bonds, α-O-4 bonds and 4-O-5 bonds.

5. The method according to claim 4, characterized in that The lignin dimer model compound includes one or more of phenoxyethylbenzene, benzyl phenyl ether and 4,4'-dihydroxydiphenyl ether.

6. The method according to any one of claims 1 to 5, characterized in that: The conditions of pulse electrolysis were: electrolysis at a pulse potential of ±1.8 V for 6±1 h, a period of 10-15 s, and a duty cycle of 0.5±0.

1.

7. The method according to claim 6, characterized in that The working electrode and the counter electrode are both Pt sheet electrodes, and the reference electrode is Ag / Ag + Non-aqueous reference electrode.

8. The method according to claim 7, characterized in that Ag + The concentration was 0.1 ± 0.05 mol L -1 .

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