Cellulose carbon aerogel supported copper nano-catalyst for catalytically oxidizing lignin to depolymerize into aviation oil intermediate

Abstract

The invention discloses a method for catalytically oxidizing lignin to depolymerize into an aviation oil intermediate by using a cellulose carbon aerogel supported copper nano-catalyst. Comprising the following steps: (1) dissolving cellulose powder into a mixed alkali solution of NaOH and urea, and stirring at low temperature to obtain a clear and transparent cellulose solution; and washing to be neutral to obtain well dispersed cellulose suspension. And (2) carrying out suction filtration molding, and freeze-drying for a period of time to obtain the cellulose aerogel. And (3) immersing in an ethanol solution of copper nitrate for ultrasonic treatment, and drying in a vacuum drying oven. And (4) carrying out high-temperature calcination in an N2 atmosphere to obtain a catalyst which is marked as Cu / CA. And (5) the catalyst can efficiently catalyze a Fenton-like reaction to oxidize a dimer model compound of lignin in acidic, neutral and alkaline environments to obtain products including benzoic acid, acetophenone, benzyl alcohol, phenol and the like, the required hydrogen peroxide concentration is low, and the catalyst has the advantages of simple process, high catalytic activity, low cost and the like, can be used for effectively degrading lignin to prepare aviation oil intermediates, and has wide application prospects. And repeated cyclic utilization is realized.

Description

Technical Field

[0001] The invention relates to the application of a cellulose carbon aerogel-supported copper nanocatalyst in the field of lignin oxidative depolymerization, and belongs to the field of biomass conversion and application. Background Art

[0002] Lignin is a naturally abundant, renewable aromatic compound resource. The pulp and paper industry and the enzymatic cellulose hydrolysis process for ethanol production generate significant amounts of waste lignin annually. Catalytic depolymerization of lignin to produce aromatic precursors, which are then reduced to produce high-grade biofuels such as aromatic hydrocarbons and cycloalkanes. These components of SAF (Sulfur-Fiber-Aerated Liquid Fuels) can be used to efficiently and comprehensively utilize biomass resources. Due to the dense network of aromatic rings and complex bonding patterns in lignin, numerous methods exist for lignin depolymerization, but the overall efficiency is low.

[0003] Fenton catalyst uses Fe(Ⅱ) ions to catalyze the decomposition of H2O2 to produce highly oxidizing hydroxyl radicals (·OH, with an oxidation potential of up to 2.8 eV) and oxygen anion radicals (·O2 – , oxidation potential of 1.73eV), has excellent catalytic oxidation ability for various organic substances, and is therefore widely used in the catalytic oxidation treatment of organic substances. Heterogeneous Fenton catalysts overcome the shortcomings of homogeneous Fenton catalysts, such as the difficulty in separation, large amount of newly generated iron sludge, and narrow applicable pH range. Agricultural and forestry wastes are mainly composed of biomacromolecules such as cellulose, hemicellulose, pectin (galacturonic acid), and lignin. Cellulose has a high content and stable properties, and cellulose contains abundant hydroxyl groups, which can serve as anchor groups for loading transition metals and their oxides, greatly reducing the surface energy of their nanocrystalline particles and effectively inhibiting the agglomeration of nanoparticles. It is an excellent biomass cellulose carrier for loading metals to prepare efficient heterogeneous Fenton catalysts.

[0004] The present invention prepared a cellulose aerogel as a carrier precursor and successfully synthesized a multiphase Fenton-like nanocatalyst Cu / CA by loading copper nanoparticles through the impregnation and calcination method. The physical properties of the catalyst were characterized by analytical methods such as SEM, TEM, and XRD. The experimental results show that Cu / CA at a low catalyst concentration (0.01g / L) can efficiently catalyze the Fenton-like reaction to oxidize lignin model compounds in acidic, neutral, and alkaline environments with a pH of 5-9. The degradation rate of the monomer model compound trans-ferulic acid (50mg / L) in a 50°C water bath, pH = 7, and a hydrogen peroxide addition amount of 0.036mol / L for 1 hour reached 90.8%. Without adding a catalyst and only adding hydrogen peroxide, the degradation rate was only 15.2%; for the dimer model compound 4-benzyloxyphenol (50mg / L), the degradation rate was 90.8%. L) in a 50°C water bath, pH = 7, and a hydrogen peroxide dosage of 0.036 mol / L, the degradation rate reached 98.15% after 40 minutes, with the oxidation products primarily being high-value-added chemicals such as benzoic acid, acetophenone, and benzyl alcohol. For the dimer model compound 2-phenoxy-1-phenylethanol (50 mg / L), the degradation rate reached 100% after 40 minutes in a 50°C water bath, pH = 7, and a hydrogen peroxide dosage of 0.036 mol / L, with the oxidation products primarily being high-value-added chemicals such as benzoic acid, acetophenone, and phenol. The catalyst catalyzed the oxidation of 4-benzyloxyphenol (50 mg / L) with a degradation rate of 86% after six cycles, demonstrating excellent cyclic performance. The present invention aims to develop a low-cost cellulose-carbon aerogel-supported copper nanocatalyst with advantages such as simple process, high catalytic activity, a wide pH range, and low cost. It can be used to effectively depolymerize lignin to produce aviation fuel intermediates and achieve multiple recycling. Summary of the Invention

[0005] The present invention uses cellulose carbon aerogel as a carrier, loads copper nanoparticles through impregnation and calcination methods, and synthesizes a heterogeneous Fenton-like catalyst, which has excellent catalytic oxidation performance for lignin model compounds such as trans-ferulic acid, 2-phenoxy-1-phenylethanol, and 4-benzyloxyphenol.

[0006] The preparation of the catalyst and the catalytic reaction of the present invention comprise the following steps:

[0007] (1) Weigh a certain amount of NaOH and urea and dissolve them in deionized water. Place the solution in a freezer and cool it for a certain period of time. Dissolve cellulose powder in the alkali solution and stir until the solution is slightly viscous and clear. Pour the cellulose solution into deionized water and stir slowly. Let it stand and discard the supernatant. Wash with water until it is neutral to obtain a well-dispersed cellulose suspension.

[0008] (2) The cellulose suspension is poured into a molding mold and filtered to form the suspension, frozen in liquid nitrogen, and then placed in a vacuum freeze dryer for freeze drying to obtain a cellulose aerogel.

[0009] (3) Weigh a certain amount of copper nitrate trihydrate and dissolve it in ethanol. Immerse a certain amount of cellulose aerogel in the metal salt solution and perform ultrasonic treatment. The immersed aerogel is placed in a vacuum drying oven for drying.

[0010] (4) The dried aerogel is placed in a tubular furnace and calcined in a nitrogen atmosphere. After the tubular furnace cools to room temperature, the calcined aerogel is ground into powder to obtain a catalyst, which is recorded as Cu / CA.

[0011] (5) A certain amount of catalyst is added to an aqueous solution of a monomeric lignin model compound of a certain concentration, placed in a water bath at a certain temperature, adjusted to a certain pH value, and a certain volume of hydrogen peroxide is added to start the reaction. After a period of time, the concentration is measured using an ultraviolet spectrophotometer to calculate the change in concentration during the reaction.

[0012] (6) A certain amount of catalyst is added to an aqueous solution of a certain volume and concentration of a dimer lignin model compound, placed in a water bath at a certain temperature, adjusted to a certain pH value, and a certain volume of hydrogen peroxide is added to start the reaction. After a period of time, acetonitrile and water are used as the mobile phase, and liquid chromatography is performed at a certain flow rate and column temperature to calculate the change in concentration during the reaction.

[0013] As a preferred embodiment, in step (1), the mass of NaOH is 7-10 g, the mass of urea is 10-15 g, the mass of deionized water is 60-100 mL, the refrigerator temperature is -15°C to -30°C, and the cooling time is 40-60 min.

[0014] As a preferred embodiment, the liquid nitrogen freezing time in step (2) is 3-10 minutes, and the freeze-drying time is 24-72 hours.

[0015] As a preferred embodiment, the volume of ethanol used to dissolve copper nitrate trihydrate in step (3) is 50-100 mL, the mass of cellulose aerogel is 0.5-1.0 g, the ultrasonication time is 10-30 min, and the drying temperature under vacuum conditions is 40-60° C. for 10-30 min.

[0016] As a preferred embodiment, the high-temperature calcination in step (4) is carried out in a tubular furnace, the calcination atmosphere is nitrogen or argon, the tubular furnace heating rate is 2-10°C / min, the high-temperature calcination is 600-800°C, and the high-temperature calcination time is 1-3h.

[0017] As a preferred embodiment, in the catalyst, the size of the copper metal nanoparticles is 20-30 nm, and the copper content is 12-18 wt%.

[0018] As a preferred embodiment, in step (5), the substrate is trans-ferulic acid, the catalyst concentration is 0.005-0.3 g / L, the substrate concentration is 10-200 mg / L, the substrate volume is 20-100 mL, the water bath reaction temperature is 20-60° C., the pH is 3-11, and the hydrogen peroxide concentration is 0.02-0.07 mol / L.

[0019] As a preferred embodiment, in step (6), the substrates are 4-benzyloxyphenol and 2-phenoxy-1-phenylethanol, the catalyst concentration is 0.005-0.3 g / L, the substrate concentration is 10-100 mg / L, the substrate volume is 20-100 mL, the water bath reaction temperature is 20-60°C, the pH is 3-11, and the hydrogen peroxide concentration is 0.02-0.07 mol / L. The mobile phase has a volume ratio of acetonitrile to water of 4:1-1:1, the flow rate is 0.5-2 mL / min, and the column temperature is 20-40°C.

[0020] As a preferred embodiment, the Cu / CA-catalyzed Fenton reaction has a degradation rate of over 90% for a 50 mg / L aqueous solution of the monomer model compound trans-ferulic acid in 1 h, and has a good degradation rate for the dimer model compounds 4-benzyloxyphenol and 2-phenoxy-1-phenylethanol. The oxidation products are aviation fuel intermediates such as benzoic acid, acetophenone, benzyl alcohol, and phenol, which can be used to prepare aviation fuel components through hydrogenation reactions.

[0021] Compared with existing technologies, the main innovation of this invention is that a cellulose aerogel-supported copper catalyst is obtained by impregnating a cellulose aerogel carrier with a copper metal salt solution and then calcining it at high temperature. The cellulose aerogel used not only serves as a carrier precursor for the catalyst but also as an excellent reducing agent, reducing Cu(II) to Cu(0). The catalyst preparation method is simple, low-cost, and environmentally friendly. It has a wide pH range and can oxidize and depolymerize lignin model compounds under acidic, neutral, and alkaline conditions, and exhibits excellent catalytic cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a scanning electron microscope photograph of the catalyst Cu / CA prepared in Example 1.

[0023] Figure 2 This is a transmission electron microscope photograph of the catalyst Cu / CA prepared in Example 1.

[0024] Figure 3 The X-ray diffraction patterns of Example 1, Example 2, and Example 3 are shown.

[0025] Figure 4The catalytic performance of catalysts Cu / CA-600, Cu / CA-700, and Cu / CA-800 on 40 mL of 50 mg / L trans-ferulic acid in a 50°C water bath, pH = 9, a hydrogen peroxide addition amount of 0.036 mol / L, and a catalyst addition amount of 4 mg.

[0026] Figure 5 At pH = 7, in a 50°C water bath, the catalytic performance of adding 4 mg Cu / CA-600 and 0.036 mol / L H2O2 to 40 mL of 50 mg / L trans-ferulic acid was compared with that of adding only 0.036 mol / L H2O2.

[0027] Figure 6 The catalytic performance of catalyst Cu / CA-600 on 40 mL 50 mg / L trans-ferulic acid at different pH values ​​when the hydrogen peroxide addition amount is 0.036 mol / L and the catalyst addition amount is 4 mg in a 50°C water bath.

[0028] Figure 7 The catalytic performance of catalyst Cu / CA-600 on 40mL of 50mg / L lignin dimer model compound at pH=7 in a 50℃ water bath with a hydrogen peroxide addition amount of 0.036mol / L and a catalyst addition amount of 4mg.

[0029] Figure 8 The products of the catalytic oxidation of 40 mL of 50 mg / L 2-phenoxy-1-phenylethanol were analyzed under the conditions of pH = 7 when the catalyst Cu / CA-600 was used in a 50℃ water bath, the hydrogen peroxide addition amount was 0.036 mol / L, the catalyst addition amount was 4 mg.

[0030] Figure 9 The products of the catalytic oxidation of 40 mL of 50 mg / L 4-benzyloxyphenol were analyzed under the conditions of pH = 7 when the catalyst Cu / CA-600 was used in a 50°C water bath, the added amount of hydrogen peroxide was 0.036 mol / L, the added amount of catalyst was 4 mg.

[0031] Figure 10 The catalytic cycle performance of 40mL 50mg / L 4-benzyloxyphenol was studied with a Cu / CA-600 catalyst addition amount of 15mg at 40℃, pH=6.3, and H2O2 addition amount of 0.025mol / L.

[0032] Figure 11 is the catalytic cycle degradation rate of 4-benzyloxyphenol over catalyst Cu / CA-600. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] Example 1

[0035] Catalytic oxidation of lignin model compound by cellulose carbon aerogel supported copper Cu / CA-600:

[0036] (1) Dispersing cellulose: Weigh 7 g of NaOH and 12 g of urea and dissolve them in 81 mL of deionized water. Place the solution in a freezer and cool it for 40 min.

[0037] Dissolve 5g of cellulose powder in alkaline solution with continuous stirring at low temperature until the solution becomes slightly viscous and clear. Pour the cellulose solution into deionized water and wash with water until neutral to obtain a well-dispersed cellulose suspension.

[0038] (2) Preparation of cellulose aerogel: The cellulose suspension was poured into a molding mold and filtered to form the aerogel, and then frozen in liquid nitrogen at 77K for 5 minutes, and then placed in a vacuum freeze dryer for 72 hours to obtain a cellulose aerogel.

[0039] (3) Weigh 2.5 g of copper nitrate trihydrate and dissolve it in 50 mL of ethanol. Immerse about 0.6 g of cellulose aerogel in the solution and ultrasonicate for 20 min. The impregnated aerogel is placed in a vacuum drying oven at 50 °C and dried for 20 min.

[0040] (4) The dried aerogel was placed in a tubular furnace and heated to 600°C at a heating rate of 5°C / min in a nitrogen atmosphere. The carbonization temperature was maintained for 2 h. After the tubular furnace cooled to room temperature, the calcined aerogel was ground into a powder, which was designated as Cu / CA-600.

[0041] (5) Add 40 mL of a 50 mg / L aqueous solution of trans-ferulic acid to four 50 mL centrifuge tubes, adjust the pH to 5, 7, 9, and 11, respectively. In a 50°C water bath, add 4 mg of the catalyst Cu / CA-600 and 0.15 mL of 30% H2O2 to start the reaction. After 20 min, 40 min, and 60 min, take samples of about 1 mL with a syringe. After filtering through a membrane, discard the first three drops. Perform UV spectrophotometry testing and quantify the absorbance at 310 nm to analyze the changes in substrate concentration during the reaction.

[0042] (6) 40 mL of 50 mg / L 4-benzyloxyphenol and 2-phenoxy-1-phenylethanol were added to two 50 mL centrifuge tubes, respectively, and the pH was adjusted to 7. In a 50°C water bath, 4 mg of the catalyst Cu / CA-600 and 0.15 mL of 30% H2O2 were added to initiate the reaction. About 0.5 mL of the sample was sampled with a syringe at 20 min, 40 min, and 60 min, and the first three drops were discarded after filtering through a membrane. High-performance liquid chromatography analysis was performed using a mobile phase of acetonitrile to water in a volume ratio of 2:1, a flow rate of 0.1 mL / min, a column temperature of 30°C, and a UV detector wavelength of 210 nm. The changes in substrate and product concentrations during the reaction were calculated based on the peak areas using the external standard method.

[0043] (7) Add 40 mL of 50 mg / L 4-benzyloxyphenol aqueous solution (original pH = 6.3) to a 50 mL centrifuge tube and place in a 40 ° C water bath.

[0044] At pH 6.3, 15 mg of Cu / CA-600 catalyst and 0.1 mL of 30% H₂O₂ were added to initiate the reaction. Samples of approximately 0.5 mL were taken with a syringe at 10, 30, 60, and 90 minutes. The sample was filtered through a membrane and the first three drops were discarded. Liquid chromatography analysis was performed, and the change in substrate concentration during the reaction was calculated based on the peak area. After the reaction, the catalyst was separated from the solution using a centrifuge and the separated catalyst was used for the next cycle.

[0045] Example 2

[0046] Catalytic oxidation of lignin model compound by cellulose carbon aerogel supported copper Cu / CA-700:

[0047] (1) Dispersing cellulose: Weigh 7 g of NaOH and 12 g of urea and dissolve them in 81 mL of deionized water. Place the solution in a freezer and cool it for 40 min.

[0048] Dissolve 5g of cellulose powder in alkaline solution with continuous stirring at low temperature until the solution becomes slightly viscous and clear. Pour the cellulose solution into deionized water and wash with water until neutral to obtain a well-dispersed cellulose suspension.

[0049] (2) Preparation of cellulose aerogel: The cellulose suspension was poured into a molding mold and filtered to form the aerogel, and then frozen in liquid nitrogen at 77K for 5 minutes, and then placed in a vacuum freeze dryer for 72 hours to obtain a cellulose aerogel.

[0050] (3) Weigh 2.5 g of copper nitrate trihydrate and dissolve it in 50 mL of ethanol solution. Immerse about 0.6 g of cellulose aerogel in the solution and ultrasonicate it for 20 min.

[0051] min, and the impregnated aerogel was placed in a vacuum drying oven at 50 °C and dried for 20 min.

[0052] (4) The dried aerogel was placed in a tubular furnace and heated to 700°C at a heating rate of 5°C / min in a nitrogen atmosphere, and the carbonization temperature was maintained for 2 h. After the tubular furnace cooled to room temperature, the calcined aerogel was ground into a powder, which was designated as Cu / CA-700.

[0053] (5) Add 40 mL of 50 mg / L trans-ferulic acid aqueous solution to a 50 mL centrifuge tube, adjust the pH to 9, and in a 50°C water bath, add 4 mg of catalyst Cu / CA-700 and 0.15 mL of 30% H2O2 to start the reaction. Sampling was performed with a syringe at 20 min, 40 min, and 60 min.

[0054] mL, discard the first three drops after filtering the membrane, perform UV spectrophotometry test, quantify the absorbance at 310 nm, and analyze the changes in substrate concentration during the reaction.

[0055] Example 3

[0056] Catalytic oxidation of lignin model compounds by biomass cellulose carbon aerogel-supported copper Cu / CA-800:

[0057] (1) Dispersing cellulose: Weigh 7 g of NaOH and 12 g of urea and dissolve them in 81 mL of deionized water. Place the solution in a freezer and cool it for 40 min.

[0058] Dissolve 5g of cellulose powder in alkaline solution with continuous stirring at low temperature until the solution becomes slightly viscous and clear. Pour the cellulose solution into deionized water and wash with water until neutral to obtain a well-dispersed cellulose suspension.

[0059] (2) Preparation of cellulose aerogel: The cellulose suspension was poured into a molding mold and filtered to form the aerogel, and then frozen in liquid nitrogen at 77K for 5 minutes, and then placed in a vacuum freeze dryer for 72 hours to obtain a cellulose aerogel.

[0060] (3) Weigh 2.5 g of copper nitrate trihydrate and dissolve it in 50 mL of ethanol solution. Immerse about 0.6 g of cellulose aerogel in the solution and ultrasonicate it for 20 min.

[0061] min, and the impregnated aerogel was placed in a vacuum drying oven at 50 °C and dried for 20 min.

[0062] (4) The dried aerogel was placed in a tubular furnace and heated to 800°C at a heating rate of 5°C / min in a nitrogen atmosphere, and the carbonization temperature was maintained for 2 h. After the tubular furnace cooled to room temperature, the calcined aerogel was ground into a powder, which was designated as Cu / CA-800.

[0063] (5) Add 40 mL of 50 mg / L trans-ferulic acid aqueous solution to a 50 mL centrifuge tube, adjust the pH to 9, and add 4 mg of catalyst Cu / CA-800 and 0.15 mL of 30% H2O2 to start the reaction in a 50°C water bath. Sampling was performed with a syringe at 20 min, 40 min, and 60 min.

[0064] mL, discard the first three drops after filtering the membrane, perform UV spectrophotometry test, quantify the absorbance at 310 nm, and analyze the changes in substrate concentration during the reaction.

[0065] Material performance characterization

[0066] (1) Morphological characterization (SEM and TEM)

[0067] Figure 1 The scanning electron microscope image of Example 1 is shown. The structure of the catalyst Cu / CA-600 was characterized by transmission electron microscopy. Figure 2 As shown, the matrix has a layered structure, and a large number of nanoparticles are distributed relatively evenly on its rough surface, with a particle size of about 20-30nm.

[0068] (2) X-ray diffraction analysis (XRD)

[0069] The obtained catalyst sample was characterized by XRD, scanning from 40° to 100° at a rate of 5° / min, and its composition and crystal structure were analyzed. The results are as follows Figure 3 As shown. The XRD diffraction peaks are consistent with the characteristic diffraction peaks of Cu (PDF 04-0836) on the standard card. According to the XRD pattern, the (111) and (200) planes of cubic Cu correspond to diffraction peaks at 2θ = 43.28° and 50.37°, respectively. The crystallinity of Cu / CA-600 and Cu / CA-800 is superior to that of Cu / CA-700.

[0070] (3) Catalytic oxidation experiments of lignin monomer model compounds

[0071] Using trans-ferulic acid as a monomer model compound, 40 mL of a 50 mg / L trans-ferulic acid aqueous solution was added to three 50 mL centrifuge tubes. In a 50°C water bath at pH 9, 0.15 mL of 30% H2O2 and 4 mg of Cu / CA-600, Cu / CA-700, and Cu / CA-800 catalysts were added, respectively. The results are shown in FIG. Figure 4 At the same pH, Cu / CA-800 has a better catalytic performance, with a degradation rate of 91% in 60 minutes.

[0072] At pH = 7, only hydrogen peroxide was added without catalyst, and the degradation rate of the substrate was only 15% after 60 minutes of reaction. When hydrogen peroxide and catalyst Cu / CA-600 were added, the degradation rate was 90%. Figure 5 As shown. Using trans-ferulic acid as a monomer model compound, 40 mL and 50 mg / L trans-ferulic acid aqueous solutions were added to four 50 mL centrifuge tubes, and the pH was adjusted to 5, pH 7, pH 9, and pH 11, respectively. 0.15 mL of 30% H2O2 and 4 mg of Cu / CA-600 catalyst were added, respectively. The results are shown in FIG. Figure 6 As shown, the Cu / CA-600 catalyst exhibits the best catalytic performance at pH 5, with a degradation rate of 98.6% after 60 minutes of reaction. At pH 7 and 9, the degradation rates are 90% and 73%, respectively, after 60 minutes of reaction. The degradation rate is lower at pH 11. This indicates that the Cu / CA-600 catalyst can achieve good catalytic effects under acidic, neutral, and alkaline conditions, and has a wide pH range of applicability.

[0073] (4) Catalytic oxidation experiments of lignin dimer model compounds

[0074] 2-Phenoxy-1-phenylethanol and 4-benzyloxyphenol were used as dimer model compounds. 40 mL of 50 mg / L 2-phenoxy-1-phenylethanol aqueous solution and 4-benzyloxyphenol aqueous solution were added to two 50 mL centrifuge tubes respectively. At pH = 7 and 50°C in a water bath, 4 mg of Cu / CA-600 and 0.15 mL of 30% H2O2 were added to react. The reaction results are shown in Figure 2. Figure 7 As shown in Figure 2, the degradation rate can reach more than 95% in 40 minutes. Through liquid chromatography analysis, the initial concentration of 2-phenoxy-1-phenylethanol was 0.1775mmol / L, and the degradation rate was 85.5% after 20 minutes of reaction. The substrate was oxidized to benzoic acid, acetophenone, and phenol, and the product concentrations were 0.0875mmol / L, 0.0115mmol / L, and 0.0225mmol / L, respectively. The conversion rate of benzoic acid was 58.5%, the conversion rate of acetophenone was 7.7%, and the conversion rate of phenol was 15%. Figure 8 The initial concentration of 4-benzyloxyphenol was 0.175mmol / L, and the degradation rate was 74.4% after 20 minutes. It was oxidized to 0.067mmol / L benzoic acid, 0.0003mmol / L acetophenone, and 0.02025mmol / L phenol, with conversion rates of 51.5%, 0.25%, and 15.5%, respectively. Figure 9 shown.

[0075] (5) Cycle performance

[0076] 40 mL of a 50 mg / L 4-benzyloxy solution (pH 6.3) was added to the solution with 15 mg of Cu / CA-600 and 0.1 mL of 30% H2O2 for a cycling performance test. To minimize the impact of changes in solution volume and catalyst mass, only five sampling points were set up per cycle, and each sampling did not exceed 0.5 mL. After the reaction was completed, the catalyst and solution were separated using a centrifuge. The results are shown in Figure 1. Figure 10 and Figure 11 As shown in the figure, the degradation rates of the first five cycles within 90 min were basically the same. As the number of cycles increased, the degradation rate decreased. When the number of cycles reached the sixth, Cu / CA-600 was still able to degrade more than 85% of 4-benzyloxyphenol within 90 min, indicating that it has good cyclic stability.

Claims

1. A method for catalyzing the oxidation and depolymerization of lignin into aviation fuel intermediates by using a cellulose carbon aerogel-supported copper nanocatalyst comprises the following steps: (1) Dispersing cellulose: Weigh NaOH and urea and dissolve them in deionized water. Place the solution in a freezer and cool it for a certain period of time to obtain an alkaline solution. Dissolve cellulose powder in the alkaline solution and continue stirring. Dissolve at low temperature until the solution is slightly viscous and clear to obtain a cellulose solution. Pour the cellulose solution into deionized water and wash it with water until it is neutral to obtain a well-dispersed cellulose suspension. (2) Freeze-dried cellulose: Pour the cellulose suspension into a mold, filter and shape it, freeze it in liquid nitrogen, and then freeze-dry it in a vacuum freeze dryer for a period of time to obtain cellulose aerogel; (3) Preparation of metal-loaded catalyst: a certain amount of copper nitrate trihydrate was weighed and dissolved in ethanol to form a solution; a certain amount of cellulose aerogel was immersed in the solution and ultrasonicated; the impregnated aerogel was placed in a vacuum drying oven to dry, and then calcined at high temperature in nitrogen to obtain a catalyst, which was recorded as Cu / CA; (4) Catalytic degradation reaction: a certain amount of catalyst Cu / CA is weighed and added to the aqueous solution of the lignin model compound. After adjusting to a certain pH, hydrogen peroxide is added after the solution is raised to a specific temperature in a water bath to start the reaction; the lignin model compound is catalytically oxidized to depolymerize into aviation fuel intermediates. The lignin model compound is a monomer model compound or a dimer model compound.

2. The preparation method according to claim 1, wherein: The mass of NaOH used to disperse cellulose is 7-10 g, the mass of urea is 10-15 g, the amount of deionized water is 60-100 mL, the refrigerator temperature is -15°C to -30°C, and the cooling time is 40-60 min.

3. The preparation method according to claim 1, wherein: The liquid nitrogen freezing time used for freeze-dried cellulose is 3-10 minutes, and the freeze-drying time is 24-72 hours.

4. The preparation method according to claim 1, wherein: The volume of ethanol is 50-100 mL, the mass of cellulose aerogel is 0.5-1.0 g, the ultrasonic time is 10-30 min, the drying temperature in the vacuum drying oven is 40-60 ° C, and the time is 10-30 min; the high-temperature calcination is carried out in a tubular furnace, the heating rate of the tubular furnace is 2-10 ° C / min, the high-temperature calcination temperature is 600-800 ° C, and the high-temperature calcination time is 1-3 h.

5. The preparation method according to claim 1, wherein: In the catalyst, the size of the copper metal nanoparticles is 20-30nm, and the copper content is 12-18wt%.

6. The preparation method according to claim 1, wherein: When the monomer model compound is trans-ferulic acid, the concentration of the trans-ferulic acid aqueous solution is 10-200 mg / L, the volume is 20-100 mL, the concentration of the catalyst is 0.005-0.3 g / L, the reaction temperature is 20-60° C., the pH is 3-11, and the molar concentration of hydrogen peroxide is 0.02-0.07 mol / L; and a UV spectrophotometer is used to measure changes in the concentration of the monomer model compound.

7. The preparation method according to claim 1, wherein: When the dimer model compound is 2-phenoxy-1-phenylethanol and / or 4-benzyloxyphenol, the concentration of the dimer model compound aqueous solution is 10-100 mg / L, the volume is 20-100 mL, the concentration of the catalyst is 0.005-0.3 g / L, the reaction temperature is 20-60° C., the pH is 3-11, the molar concentration of hydrogen peroxide is 0.02-0.07 mol / L, and a mixed solution of acetonitrile and water is used as the mobile phase. At a certain flow rate and column temperature, liquid chromatography is used to determine the change in the concentration of the dimer model compound; the volume ratio of acetonitrile to water in the mobile phase is 4:1-1:1, the flow rate is 0.5-2 mL / min, and the column temperature is 20-40° C.

8. The preparation method according to claim 6 or 7, characterized in that: The Cu / CA-catalyzed Fenton reaction showed a degradation rate of over 90% for a 50 mg / L aqueous solution of the monomer model compound trans-ferulic acid after 1 h of reaction, and over 95% for the dimer model compounds 4-benzyloxyphenol and 2-phenoxy-1-phenylethanol after 40 min of reaction. The oxidation products were benzoic acid, acetophenone, phenol, benzyl alcohol, etc.

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