Method for lignin depolymerization to aromatic compounds coupled with power generation

Abstract

The application discloses a method for lignin depolymerization to aromatic compounds coupled with power generation. The method comprises: preparing an anode electrolyte containing a ternary eutectic solvent and lignin, and adding the anode electrolyte into an anode storage tank to perform a degradation reaction under low-temperature conditions; preparing a cathode electrolyte containing a vanadium salt of valence 5 and an acid, and adding the cathode electrolyte into a cathode storage tank; and using a pump to deliver the anode electrolyte and the cathode electrolyte into anode plates and cathode plates of a battery respectively to perform an electrochemical reaction. The application can degrade lignin and convert the lignin into clean electric energy under mild conditions, greatly reducing energy consumption and cost. Since the eutectic solvent has excellent solubility for lignin and metal salt oxidants and the solution environment is nearly neutral, a stable electrolyte can be obtained without additional addition of acid or alkali, avoiding lignin polycondensation problems caused by strong acid or alkali environments, thereby being beneficial to lignin depolymerization and stability of an anode electrolyte of a lignin fuel cell.

Description

Technical Field

[0001] This invention belongs to the field of efficient utilization of biomass waste resources, and specifically relates to a method for generating electricity by depolymerizing lignin to produce aromatic compounds. Background Technology

[0002] Lignin can be used as fuel for power generation in fuel cells. For example, Zhao et al. used polyoxometalates (POMs) as oxidants to directly convert lignin into electrical energy, with a maximum power density of only 5 mW / cm³. -2 (Zhao X, Zhu JY. Efficient conversion of lignin to electricity using a novel direct biomassfuel cell mediated by polyoxometalates at low temperatures[J]. ChemSusChem, 2016, 9(2): 197-207). The reason is that in the anolyte, due to the very stable C-C bonds in lignin, under mild conditions, the anolyte and electron carrier usually cannot effectively degrade lignin, resulting in a low output power density.

[0003] Existing fuel cells typically operate under acidic or alkaline aqueous conditions, but lignin has poor solubility under these conditions, leading to severe condensation polymerization during the reaction. This results in the formation of solids that are more difficult to dissolve and have greater chemical stability, further limiting electron transfer rates and energy conversion efficiency. Therefore, developing more efficient lignin degradation systems to achieve the green and high-value utilization of lignin presents a significant challenge.

[0004] Eutectic solvents have been widely used in the refining of lignocellulose biomass in recent years due to their advantages such as simple preparation, low cost, designability, and biodegradability. However, their excellent solubility is currently the primary factor utilized. There are no reports on developing a degradation system to inhibit lignin polymerization by leveraging the neutral environment and strong solubility properties of eutectic solvents, thereby enabling the preparation of aromatic compounds and coupled power generation. Summary of the Invention

[0005] To address the shortcomings and deficiencies of existing technologies, this invention provides a method for generating electricity by depolymerizing lignin to produce aromatic compounds.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for generating electricity by depolymerizing lignin to produce aromatic compounds includes the following steps:

[0008] (1) Prepare an anolyte and add it to the anolyte tank for degradation reaction under low temperature conditions. The anolyte includes a ternary eutectic solvent and lignin. The ternary eutectic solvent includes a hydrogen bond acceptor, a hydrogen bond donor and a Lewis acid.

[0009] (2) Prepare a cathode electrolyte and add it to the cathode storage tank. The cathode electrolyte includes pentavalent vanadium salt and acid.

[0010] (3) Pumps are used to transport the anolyte and catholyte to the flow fields of the anode and cathode plates of the battery, respectively, to carry out electrochemical reactions.

[0011] Preferably, in step (1), choline chloride is used as a hydrogen bond acceptor and ethylene glycol is used as a hydrogen bond donor in the ternary eutectic solvent; the molar ratio of hydrogen bond acceptor to hydrogen bond donor is 1:0.5 to 10, more preferably 1:1 to 5, and most preferably 1:2.

[0012] Preferably, the Lewis acid in the ternary eutectic solvent in step (1) is selected from at least one of copper chloride, ferric chloride, and copper sulfate.

[0013] Preferably, the ternary eutectic solvent in step (1) is selected from at least one of choline chloride-ethylene glycol-ferric chloride, choline chloride-ethylene glycol-copper chloride, and choline chloride-ethylene glycol-copper sulfate.

[0014] Preferably, the concentration of Lewis acid in the anolyte in step (1) is 0.01–6 mol / L, more preferably 0.5–3 mol / L, and most preferably 1–2 mol / L;

[0015] Preferably, the lignin in step (1) is selected from at least one of alkali lignin, organic solvent lignin, enzymatically hydrolyzed lignin, pre-hydrolyzed lignin and sodium lignin sulfonate.

[0016] Preferably, the lignin content in the anolyte in step (1) is 0.1–250 g / L, more preferably 0.1–150 g / L, and most preferably 0.1–50 g / L.

[0017] Preferably, the low temperature condition in step (1) is 10-150°C, more preferably 25-100°C, and most preferably 70-90°C.

[0018] Preferably, the pentavalent vanadium salt in step (2) is selected from at least one of vanadium pentoxide, vanadium oxysulfate, and vanadium nitrate.

[0019] Preferably, the concentration of pentavalent vanadium salt in the cathode electrolyte in step (2) is 0.05–5 mol / L.

[0020] Preferably, the acid mentioned in step (2) is selected from at least one of hydrochloric acid, sulfuric acid, acetic acid and nitric acid.

[0021] Preferably, the concentration of acid in the cathode electrolyte in step (2) is 0.05 to 8.0 mol / L.

[0022] The present invention patent will now be described in more detail:

[0023] (1) Prepare an anolyte and add it to the anolyte tank for degradation reaction under low temperature conditions. The anolyte includes a ternary eutectic solvent containing Lewis acid and lignin.

[0024] This step aims to degrade lignin and store electrons in a reduced Lewis acid, thereby achieving the gradual degradation of lignin to prepare aromatic compounds while storing and transporting electrons released by the breaking of valence bonds in lignin. This lays the foundation for using a fuel cell system to power external loads.

[0025] The addition of a binary eutectic solvent in this step serves two purposes: firstly, to coordinate with the Lewis acid to form a ternary eutectic solvent, and secondly, to increase the solubility of lignin. Choosing a suitable eutectic solvent is crucial in this step, as different types of eutectic solvents have varying viscosities and electrical conductivity, directly impacting the electron transfer efficiency of the fuel cell system, as well as its ability to dissolve and degrade lignin.

[0026] The Lewis acid is added in this step because, according to the acidic multi-site coordination theory, Lewis acids can form supramolecular complexes with binary eutectic solvents, i.e., ternary eutectic solvents. This allows for more effective cleavage of the C-C and CO bonds in lignin, while also acting as electron carriers to store and transport electrons. Choosing a suitable Lewis acid is crucial in this step because different types of Lewis acids have varying bond-breaking abilities, and as electron carriers, they require good redox reversibility, especially in their electron-transferring capabilities within eutectic solvents.

[0027] This step involves a degradation reaction under heating conditions, requiring control of temperature and time. If the temperature is too low or the time is too short, the degradation rate of lignin will be slow and the degree of degradation will be low. If the temperature is too high or the time is too long, it will not significantly improve the degradation of lignin, and may even lead to the condensation of lignin, affecting battery performance and product yield.

[0028] (2) Prepare the cathode electrolyte and add it to the cathode storage tank. The cathode electrolyte includes pentavalent vanadium salt and acid.

[0029] This step is to prepare the cathode electrolyte, which lays the foundation for the subsequent construction of the fuel cell system together with step (1).

[0030] The reason for choosing pentavalent vanadium salt as the cathode electron carrier in this step is that the standard electrode potential of pentavalent vanadium salt is about 1.181V vs. NHE, which is higher than the standard electrode potential of Lewis acid, the anode electron carrier. Therefore, using it as the cathode will increase the open-circuit voltage of the battery and give the battery excellent electrical performance.

[0031] The acid added in this step is to increase the solubility of pentavalent vanadium salts, as acidic conditions are more conducive to the activity of pentavalent vanadium salts. The amount of acid added in this step needs to be controlled; too little acid will not adequately increase the solubility and stability of pentavalent vanadium salts, while too much acid will increase the processing cost of lignin, resulting in lower economic efficiency.

[0032] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0033] 1. This invention can degrade lignin and convert it into clean electrical energy under mild conditions (normal pressure, low temperature), greatly reducing energy consumption and cost. Simultaneously, because the eutectic solvent has excellent solubility for lignin and metal salt oxidants and the solution environment is near neutral, a stable electrolyte can be obtained without the addition of additional acids or alkalis, avoiding the lignin condensation problem caused by strong acid or strong alkali environments. This is beneficial for the depolymerization of lignin and the stability of the lignin fuel cell anode electrolyte.

[0034] 2. On the one hand, this invention utilizes a eutectic solvent that can efficiently degrade lignin to generate aromatic compounds, such as guaiacol and p-coumaric acid phenols. Among these, p-coumaric acid phenols have wide applications, such as in fragrances, conductive materials, bactericides, and fruit and vegetable preservation. This provides a green pathway for depolymerizing lignin into aromatic monomers under mild conditions. On the other hand, the eutectic solvent used in this invention is a ternary eutectic solvent containing Lewis acids. While efficiently dissolving lignin, it can effectively oxidize and depolymerize lignin and store and transport electrons for clean and efficient power generation.

[0035] 3. This invention uses a low-cost, environmentally friendly ternary eutectic solvent as an oxidant and electron carrier to construct a fuel cell system. Under low-temperature conditions, lignin can be efficiently degraded to prepare aromatic compounds. At the same time, the chemical energy released during the degradation process can be fully utilized for coupled power generation, converting biomass energy into clean electrical energy. This achieves the clean and high-value utilization of lignin and has good economic and environmental friendliness.

[0036] 4. The method provided by this invention effectively solves a series of problems existing in the degradation of lignin in the prior art. For example, hydrothermal degradation and reduction degradation methods require harsh reaction conditions (high temperature, high pressure and longer reaction time), which not only have high energy consumption and cost, but also the intermediates are prone to condensation under strong acid and strong alkali conditions; the biodegradation method has a long strain cultivation cycle, high economic cost, cannot produce clean energy, and has a single operation mode; the chemical energy released in the process of degrading lignin to prepare aromatic compounds in the oxidative degradation method is not utilized, resulting in energy waste. Attached Figure Description

[0037] Figure 1 The current density-voltage-output power graph for the degradation of lignin at different reaction times in Example 1 is shown.

[0038] Figure 2 The current density-voltage-output power graph for the degradation of lignin at different reaction temperatures in Example 2 is shown.

[0039] Figure 3 The current density-voltage-output power graph for lignin degradation under different Lewis acids in Example 3 is shown.

[0040] Figure 4 This is a graph showing the amount of electricity generated over a long period of time in Example 4.

[0041] Figure 5 Example 4: Gel permeation chromatography before and after lignin power generation.

[0042] Figure 6 The two-dimensional nuclear magnetic resonance spectra of lignin before and after power generation in Example 4 are shown.

[0043] Figure 7 This is the GC-MS spectrum of lignin monomer products after long-term power generation in Example 4.

[0044] Figure 8 This is a diagram showing the continuous and stable power generation performance of constant voltage in Example 8. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. All raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be referred to.

[0046] Example 1: Performance Comparison of Lignin-Based Fuel Cells Based on Different Reaction Times

[0047] (1) Preparation of anolyte: Choline chloride and ethylene glycol were mixed at a molar ratio of 1:2 and stirred at 80°C until a clear and homogeneous solution was obtained, thus preparing a binary eutectic solvent, which was then divided into two equal portions. Two portions of 5.4g FeCl3·6H2O were weighed as Lewis acids and added to the prepared binary eutectic solvent, respectively. The total volume of both solutions was adjusted to 20mL, making the Lewis acid concentration 1M. The mixture was stirred at 80°C until a clear and homogeneous solution was obtained, thus preparing a ternary eutectic solvent. 1g of enzymatically hydrolyzed lignin was then added to each of the three-necked flasks containing 20mL of the ternary eutectic solvent, and the reactions were carried out at 80°C and atmospheric pressure for 1h and 5h, respectively, thus obtaining anolytes with different reaction times.

[0048] (2) Preparation of cathode electrolyte: Weigh 20g of vanadium pentoxide powder and add it to a reagent bottle containing 524mL of deionized water. Stir at room temperature, then take 76mL of concentrated sulfuric acid and slowly add it to the solution. Continue stirring until it turns bright yellow and stand for 24h to obtain high-valence vanadium cathode electrolyte.

[0049] (3) Battery system construction and power generation performance testing: Anode electrolyte tanks were connected to the anode inlet and outlet of the battery using rubber tubing, and cathode electrolyte tanks were connected to the cathode inlet and outlet of the battery. Pumps were used to deliver the anolyte and cathode electrolyte to the anode and cathode plates respectively for electrochemical reaction. The battery's electrical performance was tested using a scanning current method. The results are as follows: Figure 1 As shown, the battery's power generation performance improves with increasing reaction time, indicating that extending the reaction time can increase the degree of lignin depolymerization and improve electron storage capacity, thereby obtaining higher output power. This proves that the synergistic effect of the eutectic solvent and Lewis acid can efficiently degrade lignin and generate electricity.

[0050] Example 2: Performance Comparison of Lignin-Based Fuel Cells Based on Different Reaction Temperatures

[0051] (1) Preparation of anolyte: Choline chloride and ethylene glycol were mixed at a molar ratio of 1:2 and stirred at 80°C until a clear and homogeneous solution was obtained, thus preparing a binary eutectic solvent, which was then divided into four equal portions. Four portions of 5.4g FeCl3·6H2O were weighed as Lewis acids and added to the prepared binary eutectic solvent respectively. The total volume of each of the four solutions was adjusted to 20mL, making the Lewis acid concentration 1M. The mixture was stirred at 80°C until a clear and homogeneous solution was obtained, thus preparing a ternary eutectic solvent. 1g of enzymatically hydrolyzed lignin was then added to each of the three-necked flasks containing 20mL of the ternary eutectic solvent. The reactions were carried out at 25°C, 60°C, 80°C, and 100°C under normal pressure for 3h respectively, thus obtaining the anolyte.

[0052] (2) Preparation of cathode electrolyte: Weigh 20g of vanadium pentoxide powder and add it to a reagent bottle containing 524mL of deionized water. Stir at room temperature, then take 76mL of concentrated sulfuric acid and slowly add it to the solution. Continue stirring until it turns bright yellow and stand for 24h to obtain high-valence vanadium cathode electrolyte.

[0053] (3) Battery system construction and power generation performance testing: Anode electrolyte tanks were connected to the anode inlet and outlet of the battery using rubber tubing, and cathode electrolyte tanks were connected to the cathode inlet and outlet of the battery. Pumps were used to deliver the anolyte and cathode electrolyte to the anode and cathode plates respectively for electrochemical reaction. The battery's electrical performance was tested using a scanning current method. The results are as follows: Figure 2 As shown, the power generation performance of the battery initially increases and then decreases with increasing reaction temperature. This is likely because at higher reaction temperatures, lignin is prone to condensation polymerization, reducing its reactivity and hindering lignin degradation and electron transport, thus leading to performance degradation. Therefore, the optimal reaction temperature is 80℃, with a maximum power density of 39.3 mW / cm³. -2 .

[0054] Example 3: Performance Comparison of Lignin-Based Fuel Cells Based on Different Lewis Acids

[0055] (1) Preparation of anolyte: Choline chloride and ethylene glycol were mixed at a molar ratio of 1:2 and stirred at 80°C until a clear and homogeneous solution was obtained, thus preparing a binary eutectic solvent, which was then divided into three equal portions. 5.4 g of FeCl3·6H2O, 3.4 g of CuCl2·2H2O, and 4.9 g of CuSO4·5H2O were weighed out as Lewis acids and added to the prepared binary eutectic solvent. The total volume of each of the three solutions was adjusted to 20 mL, making the Lewis acid concentration 1 M. The mixture was then stirred at 80°C until a clear and homogeneous solution was obtained, thus preparing a ternary eutectic solvent. 1 g of enzymatically hydrolyzed lignin was then added to each of the three portions in a three-necked flask containing 20 mL of the ternary eutectic solvent. The mixtures were reacted at 80°C and atmospheric pressure for 3 h to obtain anolytes containing different Lewis acids.

[0056] (2) Preparation of cathode electrolyte: Weigh 20g of vanadium pentoxide powder and add it to a reagent bottle containing 524mL of deionized water. Stir at room temperature, then take 76mL of concentrated sulfuric acid and slowly add it to the solution. Continue stirring until it turns bright yellow and stand for 24h to obtain high-valence vanadium cathode electrolyte.

[0057] (3) Battery system construction and power generation performance testing: Anode electrolyte tanks were connected to the anode inlet and outlet of the battery using rubber tubing, and cathode electrolyte tanks were connected to the cathode inlet and outlet of the battery. Pumps were used to deliver the anolyte and cathode electrolyte to the anode and cathode plates respectively for electrochemical reaction. The battery's electrical performance was tested using a scanning current method. The results are as follows: Figure 3 As shown, different Lewis acids have a significant impact on battery performance. When CuCl2·2H2O is used as the Lewis acid, the maximum power density of the battery is 30.1 mW / cm². -2 The battery with FeCl3·6H2O as the Lewis acid exhibited the best performance, reaching 40.2 mW / cm². -2 .

[0058] Example 4: Long-term power generation test

[0059] (1) Preparation of anolyte: Choline chloride and ethylene glycol were mixed at a molar ratio of 1:2 and stirred at 80°C until a clear and homogeneous solution was obtained, thus preparing a binary eutectic solvent. 10.8g of FeCl3·6H2O was weighed as a Lewis acid and added to the prepared binary eutectic solvent. The volume was adjusted to 40mL to make the Lewis acid concentration 1M. The mixture was stirred at 80°C until a clear and homogeneous solution was obtained, thus preparing a ternary eutectic solvent. 1g of enzymatically hydrolyzed lignin was then added to a three-necked flask containing 40mL of the ternary eutectic solvent. The mixture was reacted at 80°C and atmospheric pressure for 5h to obtain the anolyte.

[0060] (2) Preparation of cathode electrolyte: Weigh 20g of vanadium pentoxide powder and add it to a reagent bottle containing 524mL of deionized water. Stir at room temperature, then take 76mL of concentrated sulfuric acid and slowly add it to the solution. Continue stirring until it turns bright yellow and stand for 24h to obtain high-valence vanadium cathode electrolyte.

[0061] (3) Battery System Construction and Power Generation Performance Testing: The anode electrolyte tank was connected to the anode inlet and outlet of the battery via rubber tubing, and the cathode electrolyte tank was connected to the cathode inlet and outlet. Pumps were used to deliver the anode and cathode electrolytes to the flow fields of the anode and cathode plates, respectively, for electrochemical reaction. Concentrated nitric acid (68% by mass) was added to the cathode electrolyte tank at a rate of 0.5 mL / min, and oxygen was introduced at a rate of 40 mL / min. The synergistic oxidation of tetravalent vanadium ions by nitric acid and oxygen was used to regenerate the cathode electrolyte. A long-term power generation test was conducted at 0.3V, and the results are as follows: Figure 4 As shown in Table 1, 1g of lignin can generate 637.4mW·h of electricity in a fuel cell, which is much higher than that of a power generation system using water as a solvent (Comparative Example 3).

[0062] Table 1 Comparison of Power Generation

[0063]

[0064] Example 5: Molecular weight test of lignin before and after power generation

[0065] (1) Extraction of lignin after power generation: Add an appropriate amount of deionized water to the anolyte tested in Example 4 and stir well. Transfer all of it to a centrifuge tube and centrifuge to obtain the supernatant and precipitate. Wash the precipitate obtained by centrifugation with deionized water and centrifuge several times until the supernatant is colorless and transparent. Freeze-dry the precipitate to obtain the lignin after power generation.

[0066] (2) Lignin acetylation: Take 0.1g of lignin from step (1) and the original enzymatically hydrolyzed lignin respectively, dissolve them in 2mL of acetic anhydride-pyridine (volume ratio 1:1) solution, stir at room temperature in the dark for 72h. After the reaction is completed, transfer to hydrochloric acid aqueous solution with pH=2, centrifuge the mixture, remove the supernatant, and wash the precipitate repeatedly with deionized water by centrifugation until the supernatant is colorless and odorless. Then, freeze-dry the precipitate to obtain acetylated lignin.

[0067] (3) GPC test: Take 2 mg of dried acetylated lignin, add 1 mL of tetrahydrofuran, sonicate until completely dissolved, filter using a 0.45 μm pinhole membrane, and put the filtrate into a chromatographic bottle for GPC test. The results are as follows: Figure 5 As shown in Table 2. The weight-average molecular weight of the original enzymatically hydrolyzed lignin reached 3752 g mol. -1 The polydispersity index (PDI) was 4.61. After prolonged power generation, lignin underwent depolymerization, and the weight-average molecular weight decreased to 1521 g / mol. -1 The PDI decreased to 2.0, indicating that during long-term discharge, the Lewis acid component in the ternary eutectic solvent can continuously undergo redox reactions with lignin to depolymerize lignin and inhibit lignin condensation, thereby improving the long-term reactivity of lignin molecules.

[0068] Table 2 Comparison of molecular weight

[0069]

[0070] Example 6: Structural changes of lignin before and after power generation

[0071] 30 mg of lignin extracted in Example 5 and the original enzymatically hydrolyzed lignin were dissolved in 0.6 mL of dimethyl sulfoxide-d6, sonicated, and transferred to NMR tubes for testing after complete dissolution. HSQC spectra were acquired using a Bruker AVANCE III HD 400 MHz NMR spectra at 25 °C. The spectral width and sampling points in the 1H dimension were 5000 Hz and 1024 Hz, respectively, and the spectral width and sampling points in the 13C dimension were 18000 Hz and 256, respectively. The relaxation time was 1.5 s, and 512 accumulations were performed. The results are as follows: Figure 6 As shown. In the side chain region (δC / δH 50-90 / 2.5-6), the original enzymatically hydrolyzed lignin is mainly composed of structures such as methoxy (OMe), aryl ether bonds (A, β-O-4′), phenylcoumarans (B, β-5), resin alcohols (C, β-β), and spirobendones (D, β-1) linked by CO or C-C bonds. The A at the α, β, and γ positions of the β-O-4′ side chain... α (δC / δH 71.6 / 4.86), A β (G / H)(δC / δH 83.9 / 4.29), A β (S)(δC / δH85.9 / 4.11) and A γ (δC / δH 59.5 / 3.69) After prolonged power generation in Example 4, the signal strength gradually weakened or even disappeared, especially A. α The structure, which may be related to the high reactivity of the -OH group at the α position and its susceptibility to oxidation, resulted in the formation of the typical non-condensation structure Hibbertone (HK). γ (δC / δH 67.1 / 4.19). Furthermore, it can be clearly seen from the figure that the technical solution of Example 4 can not only break most of the CO bonds in lignin, but also effectively break some C-C bonds, such as B... α (δC / δH 86.8 / 5.48), B β (δC / δH 52.4 / 3.45), B γ (δC / δH 62.3 / 3.76) and C β (δC / δH 53.5 / 3.05). Notably, a new β-O-4′ structure A″ appears at δC / δH 70.1 / 3.35. α This indicates that the -OH group at the α position underwent a dehydration reaction with the ethylene glycol molecule. This structure effectively prevents further condensation reactions in lignin, providing a certain degree of protection. In the aromatic region (δC / δH 90-150 / 6-8), it can be seen that the original enzymatically hydrolyzed lignin is mainly composed of three basic structural units: p-hydroxyphenyl (H), guaiacol (G), and syringyl (S). Strong signals from p-coumarate (PCA) and ferulic acid ester (FA), as well as a small amount of oxidized syringyl S′, were also observed.2,6 Structure. After prolonged power generation as described in Example 4, the aromatic structural units of lignin also showed significant degradation. The most significant degradation was observed in FA2 (δC / δH 110.9 / 6.99) and FA6 (δC / δH 120.9 / 7.13) of ferulic acid, followed by H in p-hydroxyphenyl H. 2,6 (δC / δH 128.7 / 7.27) and H 3,5 (δC / δH 117.8 / 6.58) and syringyl S′ 2,6 (δC / δH 106.3 / 7.21).

[0072] Example 7: Analysis of Monomer Products After Lignin Power Generation

[0073] (1) Extraction of lignin products after power generation: Add an appropriate amount of deionized water to the anolyte after the long-term power generation test in Example 4 and stir well. Transfer the entire solution to a centrifuge tube and centrifuge to obtain the supernatant and precipitate. Add an appropriate amount of deionized water to the anolyte and stir well. Transfer the entire solution to a centrifuge tube and centrifuge to obtain the supernatant and precipitate. Take the supernatant from the first centrifugation and extract it three times with ethyl acetate. Collect all the extracts, remove the ethyl acetate by vacuum distillation, and obtain the concentrated solution, which is the liquid-phase degradation product.

[0074] (2) The liquid degradation products were transferred to chromatographic vials and analyzed by GC-MS. The structures of the compounds corresponding to the signal peaks were assigned by comparing the results with the mass spectrometry information of compounds in the NIST library. The results are as follows: Figure 7 As shown in Table 3, lignin depolymerization yields several aromatic monomers, with guaiacyl-derived compounds and p-coumaric acid-derived compounds being the main depolymerization products. p-Coumaric acid, one of the products, has wide applications in many areas, such as as a fragrance, conductive material, bactericide, and fruit and vegetable preservative. This provides a green pathway for depolymerizing lignin into aromatic monomers under mild conditions.

[0075] Table 3 Analysis of lignin degradation products

[0076]

[0077]

[0078] Example 8: Continuous and Stable Power Generation Test

[0079] (1) Preparation of anolyte: Choline chloride and ethylene glycol were mixed at a molar ratio of 1:2 and stirred at 80°C until a clear and homogeneous solution was obtained, thus preparing the binary eutectic solvent. 108.1 g of FeCl3·6H2O was weighed as a Lewis acid and added to the prepared binary eutectic solvent. The volume was adjusted to 400 mL to make the Lewis acid concentration 1 M. The mixture was stirred at 80°C until a clear and homogeneous solution was obtained, thus preparing the ternary eutectic solvent. 20 g of enzymatically hydrolyzed lignin was then added to a three-necked flask containing 400 mL of the ternary eutectic solvent. The mixture was reacted at 80°C and atmospheric pressure for 5 h to obtain the anolyte.

[0080] (2) Preparation of cathode electrolyte: Weigh 20g of vanadium pentoxide powder and add it to a reagent bottle containing 524mL of deionized water. Stir at room temperature, then take 76mL of concentrated sulfuric acid and slowly add it to the solution. Continue stirring until it turns bright yellow and stand for 24h to obtain high-valence vanadium cathode electrolyte.

[0081] (3) Battery System Construction and Power Generation Performance Testing: The anode electrolyte tank was connected to the anode inlet and outlet of the battery via rubber tubing, and the cathode electrolyte tank was connected to the cathode inlet and outlet. Pumps were used to deliver the anode and cathode electrolytes to the flow fields of the anode and cathode plates, respectively, for electrochemical reactions. Concentrated nitric acid (68% by mass) was added to the cathode electrolyte tank at a rate of 0.5 mL / min, and oxygen was introduced at a rate of 40 mL / min. The synergistic oxidation of tetravalent vanadium ions by nitric acid and oxygen was used to regenerate the cathode electrolyte. A continuous and stable power generation test was conducted at 0.3V, and the results are as follows: Figure 8 As shown. The fuel cell operates at a constant voltage with an amplitude of approximately 300 mA / cm². -2 The current density can maintain stable power generation for more than 2 hours.

[0082] Comparative Example 1: Effect of Binary Eutectic Solvent Type on Lignin Degradation

[0083] (1) Preparation of anolyte: Choline chloride-lactic acid and choline chloride-urea were mixed at a molar ratio of 1:2 and stirred at 80°C until a clear and homogeneous solution was obtained, thus preparing the choline chloride-lactic acid binary eutectic solvent and the choline chloride-urea binary eutectic solvent. 3.4 g of Lewis acid CuCl2·2H2O was added to each of the two prepared binary eutectic solvents, and the total volume was adjusted to 20 mL to make the Lewis acid concentration 1 M. The mixture was then stirred at 80°C until a clear and homogeneous solution was obtained, thus preparing the ternary eutectic solvent. 1 g of enzymatically hydrolyzed lignin was then added to each of the two solvents in a three-necked flask containing 20 mL of the ternary eutectic solvent, and the mixture was reacted at 80°C under normal pressure for 3 h to obtain the anolyte.

[0084] (2) Extraction of lignin and lignin acetylation after power generation: The method is the same as in Example 5, except that the anolyte used for extraction is different. In this example, the anolyte prepared in step (1) of this example is based on the binary eutectic solvent of choline chloride-lactic acid and choline chloride-urea. The molecular weight determination results are shown in Table 2.

[0085] Comparative Example 2: Effect of Lewis Acid Types on Lignin Degradation

[0086] (1) Preparation of anolyte: Choline chloride and ethylene glycol were mixed at a molar ratio of 1:2 and stirred at 80°C until a clear and homogeneous solution was obtained, thus preparing a binary eutectic solvent, which was then divided into two equal portions. 2.7 g of ZnCl2 and 2.6 g of Lewis acid AlCl3 were added to the two portions of the prepared binary eutectic solvent, respectively, and the total volume of each portion was adjusted to 20 mL to achieve a Lewis acid concentration of 1 M. The mixture was then stirred at 80°C until a clear and homogeneous solution was obtained, thus preparing a ternary eutectic solvent of choline chloride-ethylene glycol-zinc chloride and a ternary eutectic solvent of choline chloride-ethylene glycol-aluminum chloride. 1 g of enzymatically hydrolyzed lignin was then added to each portion of the ternary eutectic solvent in a three-necked flask containing 20 mL of the ternary eutectic solvent, and the mixture was reacted at 80°C under normal pressure for 3 h to obtain two different anolytes.

[0087] (2) Extraction of lignin after power generation and lignin acetylation: Solid product extraction and acetylation were performed according to the method in Example 5, and molecular weight was tested. The molecular weight determination results are shown in Table 2.

[0088] Comparative Example 3: Effect of Aqueous Electrolytes on Lignin Degradation

[0089] (1) Dissolve 5.4 g FeCl3·6H2O, 3.4 g CuCl2·2H2O, and 0.6 g methylene blue (MB) in 3.4 mL concentrated hydrochloric acid, respectively, and bring the volume to 20 mL with deionized water. After mixing thoroughly, transfer the solutions to three-necked flasks, add 1 g of enzymatically hydrolyzed lignin to each, and react at 80 °C under normal pressure for 3 h to obtain three different anolytes. Refer to Example 4 for the long-term power generation test. The power generation measurement results are as follows: Figure 4 As shown in Table 1.

[0090] (2) Extraction of lignin after power generation and lignin acetylation: Solid product extraction and acetylation were performed according to the method in Example 5, and molecular weight was tested. The molecular weight determination results are shown in Table 2.

[0091] Summarize

[0092] Table 2 compares the molecular weights of all examples and comparative examples. It can be seen that the depolymerization effect was achieved in Example 4 using the choline chloride-ethylene glycol-ferric chloride system. After prolonged power generation, the molecular weight was significantly reduced, dropping to 1521 g mol. -1This is far lower than the control ratio of 1-3.

[0093] Furthermore, Examples 7 and 8 demonstrate that the present invention can generate electricity while depolymerizing lignin to produce aromatic compounds, and that the power generation of the present invention is much higher than that of water systems for the same mass of lignin.

[0094] As shown in Comparative Example 1, the molecular weight of regenerated lignin actually increased when using choline chloride-lactic acid binary eutectic solvents and choline chloride-urea binary eutectic solvents. This indicates that the type of hydrogen bond donor has a significant impact on lignin degradation, and not all binary eutectic solvents can inhibit lignin condensation polymerization. In contrast, the ethylene glycol contained in the eutectic solvent in the examples effectively inhibited the condensation polymerization of lignin intermediates, thus gradually reducing the molecular weight as the degradation process progressed.

[0095] In Comparative Example 2, the results of using ZnCl2 and AlCl3 as Lewis acids were not ideal. This may be due to the different bond-breaking abilities of different metal ions, resulting in varying synergistic effects with the eutectic solvent. Furthermore, they do not exhibit the same redox reversibility as multivalent metal salts like FeCl3 and CuCl2. Therefore, not all Lewis acids can be prepared into ternary eutectic solvents for efficient depolymerization of lignin and coupled power generation.

[0096] Comparative Example 3 revealed that the molecular weight of regenerated lignin increased after power generation under acidic aqueous conditions. This may be related to the poor solubility of lignin under acidic aqueous conditions, which makes lignin intermediates prone to condensation polymerization to form more insoluble polymers with larger molecular weights. Therefore, in the power generation measurement, the comparative example only generated 236.1 mW·h of electricity, far lower than Example 4, indicating that the electrolyte environment directly affects the energy conversion efficiency of lignin, while the ternary eutectic solvent system designed in this invention has excellent performance.

[0097] As can be seen, this invention utilizes a eutectic solvent, particularly ethylene glycol as the hydrogen bond donor and FeCl3·6H2O as the Lewis acid, to prepare a ternary eutectic solvent, which can effectively depolymerize lignin, inhibit the occurrence of intermediate condensation polymerization, and achieve simultaneous preparation of aromatic compounds and power generation. This invention solves the problem that lignin is difficult to effectively degrade and generate electricity under acidic or alkaline aqueous conditions due to condensation polymerization.

[0098] In summary, this invention uses a low-cost, environmentally friendly ternary eutectic solvent as an oxidant and electron carrier to construct a fuel cell system. Under low-temperature conditions, lignin can be efficiently degraded into aromatic compounds, effectively suppressing the condensation problem of lignin intermediates. At the same time, the chemical energy released during the degradation process can be fully utilized for coupled power generation, converting biomass energy into clean electrical energy. This achieves the clean and high-value utilization of lignin, and has better economic and environmental friendliness.

[0099] 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 changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for generating aromatic compounds through lignin depolymerization coupled with power generation, characterized in that, Includes the following steps: (1) An anolyte is prepared and added to an anolyte tank for degradation reaction under low temperature conditions. The anolyte comprises a ternary eutectic solvent and lignin. The ternary eutectic solvent comprises a hydrogen bond acceptor, a hydrogen bond donor, and a Lewis acid. In the ternary eutectic solvent, choline chloride is used as a hydrogen bond acceptor and ethylene glycol is used as a hydrogen bond donor. The molar ratio of hydrogen bond acceptor to hydrogen bond donor is 1:0.5~10. The Lewis acid is selected from at least one of copper chloride, ferric chloride, and copper sulfate. The lignin is enzymatically hydrolyzed lignin. The low temperature conditions are 25~100℃. (2) Prepare a cathode electrolyte and add it to the cathode storage tank. The cathode electrolyte includes a pentavalent vanadium salt and an acid. The pentavalent vanadium salt is vanadium pentoxide. The acid is hydrochloric acid. (3) The anolyte and catholyte are transported to the flow fields of the anode plate and cathode plate of the battery respectively by a pump to carry out electrochemical reaction.

2. The method according to claim 1, characterized in that, The molar ratio of hydrogen bond acceptor to hydrogen bond donor in step (1) is 1:1~5.

3. The method according to claim 1, characterized in that, The molar ratio of hydrogen bond acceptor to hydrogen bond donor in step (1) is 1:

2.

4. The method according to claim 1, characterized in that, The concentration of Lewis acid in the anolyte in step (1) is 0.01–6 mol / L; The lignin content in the anolyte in step (1) is 0.1-250 g / L.

5. The method according to claim 4, characterized in that, The concentration of Lewis acid in the anolyte in step (1) is 0.5–3 mol / L; The lignin content in the anolyte in step (1) is 0.1-150 g / L.

6. The method according to claim 4, characterized in that, The concentration of Lewis acid in the anolyte in step (1) is 1-2 mol / L; The lignin content in the anolyte in step (1) is 0.1-50 g / L.

7. The method according to claim 1, characterized in that, The low temperature condition described in step (1) is 70-90℃.

8. The method according to claim 1, characterized in that, The concentration of pentavalent vanadium salt in the cathode electrolyte in step (2) is 0.05–5 mol / L; the concentration of acid in the cathode electrolyte in step (2) is 0.05–8.0 mol / L.

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