Method for efficiently catalyzing depolymerization of lignin by copper-nickel bimetallic supported silicon-based catalyst

Abstract

This invention belongs to the field of lignin catalytic conversion and utilization, and discloses a method for efficiently catalyzing the depolymerization of lignin using a copper-nickel bimetallic supported silicon-based catalyst. The method includes: adding woody biomass powder and a copper-nickel bimetallic supported silicon-based catalyst to a reaction solvent, and stirring the mixture in a high-pressure reactor under high temperature and high pressure conditions; after the reaction, allowing the reactor to cool naturally to room temperature, depressurizing, and filtering the resulting solid-liquid mixture; and then rotary evaporating the liquid portion to obtain lignin oil rich in monophenolic compounds, with a yield of up to 46.1 wt% under optimal conditions. The key technology of this invention is the efficient catalytic conversion of lignin into phenolic compounds without an external hydrogen source, while completely preserving cellulose and hemicellulose. This method is characterized by mild conditions, a simple and efficient separation process, and achieves efficient hydrogenation and deoxygenation of lignin components.

Description

Technical Field

[0001] This invention belongs to the field of lignin catalytic conversion and relates to a method for efficiently catalyzing the depolymerization of lignin using a copper-nickel bimetallic supported silicon-based catalyst. Background Technology

[0002] With the rapid advancement of global economic development, the over-exploitation of non-renewable resources such as fossil fuels has posed severe challenges. Therefore, establishing an energy system dominated by renewable energy has become a key research focus. my country has launched a "dual-carbon" strategy to address the energy crisis and environmental pollution, with biomass at the center of this strategy. The renewability and carbon neutrality of lignocellulosic biomass are of great significance in the development of green chemistry. Lignin, as the most abundant source of renewable aromatic hydrocarbons in nature, possesses immense development and utilization potential due to its unique phenylpropane structure and high carbon content. However, the inherent structural complexity and chemical recalcitrant nature of lignin have become bottlenecks in its high-value-added transformation. Therefore, the efficient depolymerization of lignin to prepare phenolic compounds is crucial for the efficient utilization of lignin, while simultaneously achieving full utilization of the three major components of lignocellulosic biomass.

[0003] High-temperature catalytic hydrogenolysis is an effective strategy for selectively depolymerizing lignin macromolecules while preserving their aromatic structures. However, traditional hydrogenolysis processes typically rely on commercial precious metal catalysts and demanding conditions dependent on external hydrogen sources. Limitations in yield, difficulty in separating and utilizing lignin oil, and the high cost of precious metals restrict its industrial application. Some researchers have focused on the application of non-precious metal catalysts, including nickel-doped porous metal catalysts, which have achieved high yields of phenolic monomers, significantly reducing costs and finding good application in industrial production. Despite previous research yielding some success, the limitations of yield and demanding reaction conditions still restrict its development. Therefore, it is necessary to develop an inexpensive metal catalyst that balances catalytic cost and reaction conditions to achieve efficient lignin conversion without an external hydrogen source. Summary of the Invention

[0004] This invention relates to a method for efficiently catalyzing the depolymerization of lignin using a copper-nickel bimetallic supported silicon-based catalyst. This method preferentially converts lignin in wood fiber biomass into small-molecule phenolic compounds without an external hydrogen source, achieving a monomer yield of 46.1 wt%. The key technical challenge of this invention is to efficiently catalyze the conversion of lignin into phenolic compounds while completely preserving cellulose and hemicellulose, providing a reliable foundation for the subsequent high-value utilization of lignin.

[0005] The technical solution of the present invention: A method for efficiently catalyzing the depolymerization of lignin using a copper-nickel bimetallic supported silicon-based catalyst includes the following steps: 1) The lignocellulosic biomass raw material is crushed and extracted to obtain biomass powder; 2) Using an organic polar solvent as the reaction solvent, the catalyst, biomass powder, and reaction solvent are mixed in a mass ratio of 5:0:1 in a high-pressure reactor and reacted for 1-6 hours under conditions of 1-3 MPa N2 and 200-160℃, and then naturally cooled to room temperature. 3) The solid-liquid mixture obtained from the reaction is separated by dichloromethane extraction, and the liquid part is rotary evaporated to obtain lignin oil rich in monophenol compounds.

[0006] The catalyst is a copper-nickel bimetallic supported silicon-based material, comprising a KIT-6 molecular sieve support, metal Cu and metal Ni, with a molar ratio of metal Cu to metal Ni of 1:1, a loading of metal Cu of 30.7 wt%, and a loading of metal Ni of 28.6 wt%.

[0007] In step 1), the lignocellulosic biomass is crushed into 40-60 mesh powder and kept in a mixed solvent of toluene and ethanol at 110-130℃ for 12-16 hours to obtain biomass powder; wherein the volume ratio of toluene to ethanol in the mixed solvent of toluene and ethanol is 2:1.

[0008] In step 1), the lignocellulosic biomass raw material is poplar wood; In step 2), the reaction solvent includes any one of methanol, ethanol, isopropanol, and dioxane.

[0009] In step 3), the solid component obtained after rotary evaporation of the liquid portion includes carbohydrates and catalysts that do not participate in the reaction. The carbohydrate component is separated by using a 0.074 mm sieve, and the small-sized catalyst is screened out from the sieve pores. The separated catalyst is recovered for the next cycle of lignin depolymerization.

[0010] The products were analyzed by gas chromatography and gas chromatography-mass spectrometry; the qualitative analysis of the products was determined by comparison with standard samples, and the quantitative analysis was determined by calculation using a standard curve.

[0011] Formula for calculating monomer yield: Monomer yield (wt%) = [M1 (total lignin monomers) / M2 (lignin content in wood flour)] × 100% M1 (total lignin monomers) represents the total mass of lignin depolymerized phenolic monomers (lignin oil rich in monophenolic compounds), and M2 represents the mass of lignin in wood flour.

[0012] The beneficial effects of this invention are: 1. The raw material used in this invention is natural lignin, which has a complex structure and is extremely difficult to degrade. This invention utilizes a dual-designed catalyst with optimized physical structure and chemical sites to efficiently convert natural lignin into phenolic monomers without the need for lignin removal. While precisely breaking the CO bond, the activation energy of the reaction is significantly reduced. After the reaction, the cellulose and hemicellulose structures are relatively intact, greatly enhancing the comprehensive utilization potential of all components of biomass.

[0013] 2. The catalyst proposed in this invention uses KIT-6 as a silicon-based support. Its unique three-dimensional mesoporous structure determines that it has a large specific surface area and many metal loading sites. This ordered mesoporous structure and abundant stacked pores provide a guarantee for the efficient transformation of macromolecules in the channel and ensure the full utilization of active sites.

[0014] 3. The two bimetallic materials used in this invention, copper and nickel, are both inexpensive metals. Under conditions without external hydrogen, methanol is used as a hydrogen donor to achieve depolymerization through a self-supplying hydrogen transfer reaction. During the catalytic process, the catalyst can dehydrogenate methanol to generate active hydrogen, which then participates in the breaking of CO bonds by combining with active sites. The synergistic effect between Cu and Ni metals effectively regulates the reaction pathway and perfectly preserves the high-value monocyclic aromatic hydrocarbon structure.

[0015] 4. The chemical reagents used in this invention are environmentally friendly. No external hydrogen source is required during the reaction; methanol serves as both the reaction solvent and the hydrogen donor, undergoing catalytic dehydrogenation on the catalyst surface. The generated active hydrogen is then captured by the catalyst and participates in the breaking of lignin CO bonds. Furthermore, no harmful substances are generated during the reaction, falling within the scope of green chemistry.

[0016] 5. This invention utilizes a catalyst to directly depolymerize lignin biomass. The active hydrogen species removed by methanol can stabilize the highly unstable free radicals generated during the reaction, thereby inhibiting secondary condensation and carbon deposition of the product. Under relatively mild conditions, the efficiency of lignin catalytic conversion is improved, yielding high-yield, high-value-added phenolic compounds that can serve as precursors for sustainable aviation fuel.

[0017] 6. The method for highly efficient catalysis of lignin depolymerization using a copper-nickel bimetallic supported silicon-based catalyst proposed in this invention exhibits excellent effects on the hydrodeoxygenation of natural lignin. The catalytically obtained products are mainly phenolic monomers with side chains of guaiacyl (G-type) and syringyl (S-type). Experimental results show that CuNiO x (1 / 1) The catalyst has abundant acidic sites and surface defects. While the CO bonds of the lignin macromolecule break, its surface environment also enables the lignin fragments to achieve efficient conversion in its three-dimensional mesoporous channels.

[0018] 7. In catalyst cycling experiments, this invention exhibits good stability and reusability. This catalyst avoids the use of precious metal catalysts and traditional high-temperature, high-pressure hydrogenolysis processes, making it highly promising for industrial production. The phenolic monomers obtained after this process can be further hydrogenated to produce aviation fuel and high-value-added chemicals, perfectly opening up the conversion pathway from biomass to aviation fuel and chemicals, and promoting the full utilization and high-value-added conversion of lignin. Attached Figure Description

[0019] Figure 1 The copper-nickel bimetallic catalyst CuNiO prepared for this invention x XRD pattern of Cu and Ni in a 1:1 molar ratio; Figure 2 The copper-nickel bimetallic catalyst CuNiO prepared for this invention x Cu 2p XPS spectrum (Cu and Ni molar ratio of 1:1); Figure 3 The copper-nickel bimetallic catalyst CuNiO prepared for this invention x Ni 2p XPS spectrum (Cu and Ni molar ratio of 1:1); Figure 4 The copper-nickel bimetallic catalyst CuNiO prepared for this invention x SEM image of Cu and Ni molar ratio 1:1; Figure 5 The copper-nickel bimetallic catalyst CuNiO prepared for this invention x BET spectrum of Cu and Ni molar ratio 1:1; Figure 6 GC spectra of poplar lignin before and after the reaction with a catalyst; Figure 7 GPC spectra of poplar lignin before and after the reaction with a catalyst; Figure 8 The image shows the 2D HSQC spectrum of lignin oil after depolymerization of poplar lignin in methanol solvent; where (a) is the side chain region of enzymatically hydrolyzed poplar lignin, (b) is the side chain region of lignin oil, (c) is the aromatic ring region of enzymatically hydrolyzed poplar lignin, and (d) is the aromatic ring region of lignin oil. Detailed Implementation

[0020] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0021] Example 1 (1) Preparation of KIT-6 template: 2.7 g of P123 was dissolved in a mixed solution consisting of 97.4 mL of deionized water and 4.4 mL of hydrochloric acid (37% wt.). Subsequently, the solution was placed in an oil bath at 35 °C and 3.4 mL of 1-butanol was added. After stirring for 1 hour, 5.8 g (TEOS) was added, and the mixture was continuously stirred at 35 °C for 24 hours, and then kept at 60 °C for 24 hours. After the reaction was completed, the product was filtered, washed with water and ethanol, dried overnight at 80 °C, and finally calcined at 550 °C for 6 hours.

[0022] (2) Preparation of copper-nickel bimetallic supported silicon-based materials: Mesoporous CuNiO was prepared by nanocasting using the three-dimensional mesoporous material KIT-6 as a template. x Catalyst. The preparation process is as follows: 3 ml of 4 M copper nitrate trihydrate and 3 ml of 4 M nickel nitrate hexahydrate aqueous solution were mixed and added dropwise to a toluene suspension (10 ml) containing 1.0 g KIT-6 template. The mixture was continuously stirred and heated at 65 °C for 12 h until the solvent was completely evaporated. The resulting solid was dried overnight at 60 °C in a forced-air drying oven and ground into a fine powder. Subsequently, it was calcined at 300 °C for 5 h in a static air atmosphere. To remove the template, the calcined powder was mixed in 10 ml of fresh 2 M NaOH solution and stirred at 90 °C for 2 h. This etching process was repeated three times. The resulting solid mesoporous oxide was collected, washed twice with water and twice with ethanol, and dried overnight at 60 °C. Finally, it was reduced at 350 °C for 1 h with a mixed gas flow of H2 and N2 (50 ml / min) at a volume ratio of 1:9. The above calcination and reduction processes were all carried out in a tube furnace with a heating rate of 5 °C / min. The catalyst reduced by the above method is designated as CuNiO. x (a / b), where a and b represent the molar ratio of Cu to Ni, respectively.

[0023] Figure 1 This is an X-ray diffraction pattern analysis of the copper-nickel bimetallic supported silicon-based catalyst prepared in this embodiment. For CuNiO x (Cu to Ni molar ratio 1:1), the characteristic peak positions shifted compared to Cu / KIT-6 and Ni / KIT-6 and cannot be directly correlated with single metals. According to Vegard's law, the shift of the Ni characteristic peak to a lower angle is due to the entry of Cu species with larger atomic radii into the Ni lattice, leading to a larger Ni cell parameter and lattice spacing. For unreduced CuNiO... x (1 / 1) Diffraction peaks of CuNiO2 appeared. The above phenomenon indicates that a complex mixed oxide phase of CuO and NiO has appeared, which corroborates the formation of a more tightly bonded alloy phase between Cu and Ni metals.

[0024] Figure 2 This is an X-ray photoelectron spectroscopy analysis of the copper-nickel bimetallic supported silicon-based catalyst prepared in this embodiment. Cu appears. 0 Cu + Cu 2+ Cu species in three valence states and Ni 2+ Ni 0 Ni species with two valence states.

[0025] Example 2 (1) Poplar wood powder is obtained by crushing poplar wood into 40-60 mesh powder, taking 50g, and keeping it in a mixed solvent of 500mL toluene and 250mL ethanol at 120℃ for 14h. (2) Take 50 mg of extracted poplar wood powder and 25 mg of copper-nickel bimetallic supported silicon-based material prepared in Example 1, and place them together with 10 mL of methanol in a stainless steel reactor. After purging the air, introduce 3 MPa of nitrogen gas. (3) Heat the reactor mentioned in step (2) to 240°C and maintain for 4 hours, then cool it to room temperature; (4) The solid-liquid mixture after the reaction in step (3) was separated by dichloromethane extraction, and the separated liquid was rotary evaporated to obtain lignin oil rich in phenolic compounds; the results are shown in Table 1.

[0026] Preparation of enzymatically hydrolyzed poplar lignin: 10 g of poplar wood powder obtained in step (1) was suspended in acetate buffer (pH=4.8), and 5 mL of cellulase and 1 mL of hemicellulase were loaded. The reaction mixture was incubated in a rotary shaker (150 rpm) at 50 °C for 48 hours. Subsequently, the mixture was centrifuged, the residual solids were washed with acetate buffer (pH=4.8), and extracted by reflux under nitrogen for 4 hours. After washing and freeze-drying, enzymatically hydrolyzed poplar lignin was obtained.

[0027] The poplar lignin oil obtained after enzymatic hydrolysis and depolymerization of poplar lignin was analyzed by GPC and two-dimensional NMR.

[0028] GPC analysis of the enzymatically hydrolyzed poplar lignin and depolymerized poplar lignin oil prepared in this embodiment is as follows: Figure 4 As shown, the molecular weight decreased significantly after depolymerization, indicating that the large organic polymer molecules depolymerized into smaller molecules, confirming the successful depolymerization of poplar lignin.

[0029] Two-dimensional NMR analysis of enzymatically hydrolyzed poplar lignin and depolymerized poplar lignin in this embodiment is as follows: Figure 5As shown: a) is the two-dimensional NMR spectrum of enzymatically hydrolyzed lignin, and b) is the two-dimensional NMR spectrum of poplar lignin oil after depolymerization. Comparing figures a and b confirms that the lignin linkages break and aliphatic regions are generated during the depolymerization process, demonstrating the efficient depolymerization of poplar lignin under the action of this catalyst.

[0030] Table 1 Results of depolymerization of poplar lignin in copper-nickel bimetallic supported silicon-based materials in methanol solvent.

[0031] Example 3 Same as Example 2. The concentration ratio of the catalyst in step (2) was changed from 1:1 to 3:1, 2:1, 1:2, and 1:3, respectively, while the other reaction conditions remained unchanged. The results are shown in Table 2.

[0032] Table 2. Results of depolymerization of poplar lignin in copper-nickel bimetallic supported silicon-based materials with different metal ratios in methanol solvent.

[0033] Example 4 Same as Example 2. The amount of catalyst in step (2) was replaced with 10 mg, 15 mg, and 20 mg, respectively, while the other reaction conditions remained unchanged. The results are shown in Table 3.

[0034] Table 3 Results of depolymerization of poplar lignin in methanol solvent with different amounts of copper-nickel bimetallic supported silicon-based materials

[0035] Example 5 Same as Example 2. The reaction solvent in step (2) was replaced with ethanol, isopropanol, and 1,4-dioxane, respectively, while the other reaction conditions remained unchanged. The results are shown in Table 4.

[0036] Table 4. Results of depolymerization of poplar lignin in copper-nickel bimetallic supported silicon-based materials in different reaction solvents.

[0037] Example 6 Same as Example 2. The reaction temperature in step (2) was changed to 200℃, 220℃, and 260℃ respectively, while the other reaction conditions remained unchanged. The results are shown in Table 5.

[0038] Table 5 Results of depolymerization of poplar lignin in copper-nickel bimetallic supported silicon-based materials at different reaction temperatures.

[0039] Example 7 Same as Example 2. The reaction time in step (2) was changed, while the other reaction conditions remained the same. The results are shown in Table 6.

[0040] Table 6 Results of depolymerization of poplar lignin in copper-nickel bimetallic supported silicon-based materials at different reaction times.

[0041] Comparative Example 1 Same as Example 2. Only the copper-nickel bimetallic supported silicon-based material in step (2) was replaced with monometallic supported Cu / KIT-6 and Ni / KIT-6, respectively. The results are shown in Table 7. When Ni species is used alone, although it possesses some bond-breaking ability, the effect is significantly insufficient. The depolymerization activity of the Cu catalyst alone is very weak. Experiments show that it has little effect on breaking the key β-O-4' ether bond in lignin. When Cu and Ni combine to form a bimetallic alloy phase, they complement each other, perfectly compensating for the low activity and low yield of monometallic materials, thus achieving a high-yield conversion of lignin monomers under mild conditions. The results are shown in Table 7.

[0042] Table 7 Results of poplar lignin depolymerization using different catalysts

[0043] Comparative Example 2 Same as Example 2. Only the poplar wood powder in step (2) was replaced with the β-O-4' model compound. The core components (Pe-G, Pr-G) in the real lignin depolymerization products and the degradation products (Pe-G, Pr-G) of the model compound achieved a perfect structural correspondence. This fully demonstrates that in complex real biomass systems, the CuNiOx(1 / 1) catalyst still maintains its precise ability to break the β-O-4' bond. The results are shown in Table 6.

[0044] To maximize the yield of the target monomer, this study systematically analyzed the effects of key parameters on the yield of phenolic monomers and the selectivity of the core product in the above examples. First, the screening of metal ratios revealed the significant advantages of bimetallic catalysts; both Cu / KIT-6 and Ni / KIT-6 catalysts exhibited weak depolymerization activity. When the molar ratio reached 1:1, the catalytic performance of CuNiOx(1 / 1) reached its peak, with a monomer yield of 46.1%. This excellent catalytic effect can be attributed to the close synergistic effect of Cu-Ni metals at the nanoscale: Cu's ability to activate H species and Ni's ability to break CO bonds greatly reduced the reaction activation energy.

[0045] Considering that the hydrogen spillover effect is highly dependent on the proton transfer capability of the reaction medium, we further evaluated the solvent environment. The proton environment of the solvent plays a decisive role in the yield of monophenols: compared with the 16.1% monomer yield under aprotic solvent (dioxane), methanol exhibits the best reaction performance as a reaction solvent, which is attributed to its excellent hydrogen donor capability and its ability to stabilize the free radical intermediates generated by depolymerization and inhibit the secondary condensation of the product.

[0046] Time and temperature demonstrate the kinetic thermodynamic dependence of the reaction. After reaching a relative equilibrium state, the yield decreases rather than increases with increasingly stringent reaction conditions, indicating the occurrence of side reactions, such as excessive hydrogenation of aromatic rings or the promotion of carbonaceous deposit formation by high temperatures.

Claims

1. A method for efficiently catalyzing the depolymerization of lignin using a copper-nickel bimetallic supported silicon-based catalyst, characterized in that, Includes the following steps: 1) The lignocellulosic biomass raw material is crushed and extracted to obtain biomass powder; 2) Using an organic polar solvent as the reaction solvent, the catalyst, biomass powder, and reaction solvent are mixed in a mass ratio of 5:0:1 in a high-pressure reactor and reacted for 1-6 hours under conditions of 1-3 MPa N2 and 200-160℃, and then naturally cooled to room temperature. 3) The solid-liquid mixture obtained from the reaction is separated by dichloromethane extraction, and the liquid part is rotary evaporated to obtain lignin oil rich in monophenol compounds.

2. The method for efficiently catalyzing the depolymerization of lignin using a copper-nickel bimetallic supported silicon-based catalyst according to claim 1, characterized in that, The catalyst is a copper-nickel bimetallic supported silicon-based material, comprising a KIT-6 molecular sieve support, metal Cu and metal Ni, with a molar ratio of metal Cu to metal Ni of 1:1, a loading of metal Cu of 30.7 wt%, and a loading of metal Ni of 28.6 wt%.

3. The method for efficiently catalyzing the depolymerization of lignin using a copper-nickel bimetallic supported silicon-based catalyst according to claim 1, characterized in that, In step 1), the lignocellulosic biomass is crushed into 40-60 mesh powder and kept in a mixed solvent of toluene and ethanol at 110-130℃ for 12-16 hours to obtain biomass powder; wherein the volume ratio of toluene to ethanol in the mixed solvent of toluene and ethanol is 2:

1.

4. The method for efficiently catalyzing the depolymerization of lignin using a copper-nickel bimetallic supported silicon-based catalyst according to claim 1, characterized in that, In step 1), the lignocellulosic biomass raw material is poplar.

5. The method for efficiently catalyzing the depolymerization of lignin using a copper-nickel bimetallic supported silicon-based catalyst according to claim 1, characterized in that, In step 2), the reaction solvent includes any one of methanol, ethanol, isopropanol, and dioxane.

6. The method for efficiently catalyzing the depolymerization of lignin using a copper-nickel bimetallic supported silicon-based catalyst according to claim 1, characterized in that, In step 3), the solid component obtained after rotary evaporation of the liquid portion includes carbohydrates and catalysts that do not participate in the reaction. The carbohydrate component is separated by using a 0.074 mm sieve, and the small-sized catalyst is screened out from the sieve pores. The separated catalyst is recovered for the next cycle of lignin depolymerization.

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