Vanillin amino compound and synthesis method thereof

Abstract

The invention provides a vanillin amino compound and a synthesis method thereof, and the synthesis method comprises the following steps: S1, putting lignin into a mixed solution of sodium hydroxide and nitrobenzene, carrying out hydrothermal liquefaction in a high-pressure reaction kettle, and collecting a liquid phase product vanillin for later use after the reaction is completed; s2, purifying the obtained liquid phase product vanillin, collecting a liquid phase, and evaporating the liquid phase to dryness to obtain a crystal substance, namely purified vanillin for later use; s3, synthesizing the purified vanillin crystal substance and hydrazine hydrate in the presence of a solvent, collecting a liquid-phase product vanillin azine, and evaporating the solvent to dryness to obtain a crystal substance, namely purified vanillin azine; and S4, mixing the purified vanillin azine crystal substance with a catalyst, and carrying out pyrolysis to obtain the vanillin amino compound. The vanillin amination synthesis method provided by the invention is efficient and green, the solvent ethanol is used as a synthesis solvent, not only is a reaction environment provided, but also the yield is remarkably improved, and the catalyst promotes the generation of vanillin.

Description

Technical Field

[0001] The invention belongs to the field of biomass chemical utilization, and relates to a high-efficiency conversion method of lignin, in particular to a vanillin amino compound and a synthesis method thereof. Background Art

[0002] Lignin is a renewable resource rich in aromatic structures. Its degradation products can be used to prepare a variety of high-value-added compounds, especially in the fields of medicine, cosmetics and materials science. Lignin-based aromatic compounds, such as vanillin, have attracted much research attention due to their structural activity and good modifiability. Further modification of vanillin, especially by introducing amine groups to form nitrile structures, can significantly enhance its chemical stability and applicability, thus providing important raw materials for the development of new organic materials and bioactive molecules. Stepwise amination reaction is an effective modification method. Through the introduction of amine groups, fine regulation can be achieved on the molecular structure, laying the foundation for improving the selectivity and efficiency of the target product. Vanillin in the vanillin class is an important lignin derivative. Due to its unique chemical structure, it has a wide range of application value in food, cosmetics and organic chemical synthesis. Its reaction with nitrogen-containing compounds (such as hydrazine hydrate) generates nitrogen-containing heterocyclic compounds, which are widely used in the field of drug development and functional materials. However, due to the low reaction rate, limited yield and improper solvent selection, the existing methods have significant deficiencies in efficiency and economy. There are different synthesis methods, but most of them have disadvantages such as long reflux time, high cost, environmental pollution, and low yield. The solvent not only provides a reaction environment in the chemical reaction, but also significantly affects the stability of the reaction intermediates through intermolecular forces. Therefore, choosing a suitable solvent is the key to improving the synthesis efficiency of vanillin amino compounds.

[0003] The functional group nitrile (cyano) of vanillin amino compounds is one of the key functional groups in organic synthesis. The nitrile group is present in many natural products, drugs and bioactive molecules. On the other hand, the functional group transformation of nitrile by different reagents can easily give primary amines, amides, carboxylic acids, ketones, etc. Therefore, compounds with nitrile functional groups have been used as precursors for the preparation of various bioactive molecules, natural products, drugs, agrochemicals, polymers, dyes, etc. Considering the importance of the nitrile group in organic synthesis, many methods have been developed to prepare them. Conventional methods for synthesizing nitrile include Kolbe nitrile synthesis, Sandmeyer reaction, amide dehydration reaction, cyanide exchange reaction, etc. However, this method is complicated to operate and has harsh reaction conditions.

[0004] In recent years, research based on lignin and its derivatives has made some progress in the preparation of high value-added compounds, but the existing reaction process of vanillin with nitrogen-containing compounds has limited its application potential in large-scale production due to its slow reaction rate and limited yield. The choice of solvent in chemical reactions has an important influence on the stability of reaction intermediates and the energy distribution of transition states. However, the current solvent selection has not been fully optimized, resulting in low reaction efficiency and economy. Existing synthesis methods, such as Kolbe nitrile synthesis and Sandmeyer reaction, have harsh reaction conditions, high costs, and produce a large amount of waste, which lacks environmental protection. In addition, Karimian, S., Kazemi, F., Attarroshan, M. et al. Design, synthesis, and biological evaluation of symmetrical azine derivatives as novel tyrosinase inhibitors. BMC Chemistry 15, 54 (2021), it takes 24 hours to synthesize vanillin azine from vanillin, and the synthesis time is long. In addition, the operation of some reaction methods is complicated and requires special equipment support, which increases the production cost and process difficulty, and is not suitable for large-scale industrial applications. In the process of converting aromatic aldehydes to nitriles, there is a lack of green and sustainable catalyst options. In addition, the existing carbon sources are limited by their original structure, and the preparation process is difficult to fully optimize, which affects the yield and selectivity of nitrile products. Therefore, the development and utilization of green and renewable synthesis to replace traditional chemical reagents is one of the key issues in achieving green energy storage. Summary of the invention

[0005] In view of the above technical problems, the present invention provides a vanillin amino compound and a synthesis method thereof. Vanillin is successfully prepared by using the product of hydrothermal liquefaction of lignin, and vanillin azine is synthesized by using vanillin and hydrazine hydrate. Vanillin nitrile is obtained after thermal decomposition of vanillin azine.

[0006] The present invention utilizes vanillin in the hydrothermal liquefaction product of lignin as the original reactant for synthesizing vanillin azine. Solvents such as ethanol not only provide a reaction environment in the chemical reaction, but also significantly affect the stability of the reaction intermediates through intermolecular forces, thereby improving the synthesis efficiency of the vanillin amino compound.

[0007] The invention synthesizes vanillin azine with vanillin and a nitrogen-containing compound hydrazine hydrate, and then obtains vanillin nitrile through pyrolysis. A higher yield of vanillin nitrile can be obtained by adding a catalyst. The catalyst prepared by sodium alginate and nickel nitrate hexahydrate Ni(NO)3·6H2O avoids the corrosiveness and pollution of traditional strong base catalysts, improves the sustainability of the process, and adopts biochar as a catalyst carrier, which further enhances the recyclability.

[0008] The present invention puts lignin into a sodium hydroxide solution, performs hydrothermal liquefaction in a high-pressure reactor, collects liquid products after the reaction is completed, uses methanol to elute HP-20 resin to purify the liquid products obtained in step S1, evaporates the liquid phase to obtain crystals for use, synthesizes the crystals obtained in step 2 with hydrazine hydrate in solvents of different polarities, collects liquid products, and evaporates the solvent to obtain crystals, adds crystals, hydrazine hydrate and solvent to the inner liner polytetrafluoroethylene (PTFE) of the high-pressure hydrothermal reactor, preferably, heats to 90°C, maintains the pressure at 1MPa, and stirs the reaction for 2h, and filters, purifies and analyzes the products after the reaction is completed. The purified product is pyrolyzed to obtain vanillin nitrile, and has a higher vanillin nitrile yield under the action of a catalyst. The present invention is an efficient and green amination synthesis method for vanillin, which not only significantly improves the yield through ethanol, but also promotes the reaction through solvation.

[0009] The present invention achieves the above technical objectives through the following technical means.

[0010] The present invention is achieved through the following technical solutions: A method for synthesizing a vanillin amino compound comprises the following steps: Step S1, placing lignin into a mixed solution of sodium hydroxide and nitrobenzene, and performing hydrothermal liquefaction in a high-pressure reactor, and collecting the liquid product vanillin after the reaction is completed for later use; Step S2, purifying the liquid product vanillin obtained in step S1, collecting the liquid phase, and evaporating the liquid phase to obtain a crystal, i.e., purified vanillin, for later use; Step S3, synthesizing the vanillin crystals purified in step 2 with hydrazine hydrate in a solvent, collecting the liquid product vanillin azine, and evaporating the solvent to obtain the crystals, i.e., the purified vanillin azine; Step S4, mixing the vanillin azine crystals purified in step S3 with a catalyst and performing thermal decomposition to obtain a vanillin amino compound.

[0011] In the above scheme, the type of lignin in step S1 is alkali lignin, sodium lignin sulfonate or straw lignin.

[0012] Preferably, the lignin is sodium lignin sulfonate. The sodium lignin sulfonate contains a relatively high content of β-O-4 bonds (30-50%), and is mainly used to prepare vanillin by breaking the β-O-4 bonds. The yield of aromatic aldehydes produced by using sodium lignin sulfonate is 100%.

[0013] In the above scheme, the working conditions of the hydrothermal liquefaction of lignin in step S1 are specifically as follows: The temperature of lignin hydrothermal liquefaction is 120~200℃, the time is 20~120min, the concentration of sodium hydroxide solution is 0.5M~3M, the volume ratio of nitrobenzene solution to sodium hydroxide solution is 1:15~1:20, and the solid-liquid ratio of lignin to the mixed solution of sodium hydroxide and nitrobenzene is 1:50~1:100.

[0014] In the above scheme, in step S2, methanol is used to elute the HP-20 resin to purify the liquid product vanillin obtained in step S1; the volume ratio of the methanol solution to the liquid product vanillin is 0.2-1.

[0015] In the above scheme, the conditions for synthesizing the purified vanillin crystals with hydrazine hydrate in step S3 are specifically as follows: The synthesis temperature is 60-100°C, the time is 120-240 minutes, the pressure is 0.5-2MPa, and the stirring reaction time is 1-3 hours; the solid-liquid ratio of the purified vanillin crystals to the solvent is 1:20-1:100; The solvent is methanol, ethanol, n-butanol or water.

[0016] Preferably, the solvent is ethanol. When ethanol is used as the solvent for synthesizing vanillin azine in step S3, the yield of vanillin azine is high and the synthesis effect is good.

[0017] In the above scheme, the mixing mass ratio of the purified vanillin azine crystals and the catalyst in step S4 is 1:0.5~1:2, and the crystallization pyrolysis temperature is 300~700°C.

[0018] In the above scheme, the reaction conditions for preparing the catalyst in step S4 are: Sodium alginate and nickel nitrate hexahydrate Ni(NO)3·6H2O were mixed to obtain a gel-like substance, which was dried in a drying oven at 100°C and ground into powder. The powder was used as a catalyst to prepare a precursor. The carbonization temperature was set to 600°C, the heating rate was 5-10°C / s, and the nitrogen flow rate was 50-100 mL / min. After reaching the set temperature, it was maintained for 1-2 hours. After the reaction was completed, it was cooled to room temperature and taken out to obtain biochar, which was then acid-washed and water-washed.

[0019] The conditions of the pickling and water washing are: The biochar was placed in 2M H2SO4 and stirred continuously for 12 to 24 h, then washed with deionized water until the solution was neutral, and the resulting biochar, i.e., the catalyst, was collected and freeze-dried.

[0020] A vanillin amino compound is prepared according to the vanillin amino compound synthesis method.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention successfully prepares vanillin by using the product of hydrothermal liquefaction of sodium lignin sulfonate, and synthesizes vanillin azine by using vanillin and hydrazine hydrate, and obtains vanillin amino compounds with high yield of vanillin nitrile after pyrolysis of vanillin azine. The present invention provides an efficient, green and economical method for directional preparation of vanillin nitrile from lignin, which has broad industrial application prospects, and is of great significance in the fields of high-value utilization of biomass and green chemistry.

[0022] 2. The present invention utilizes sodium lignin sulfonate as a raw material, which is abundant in source and low in price, and has obvious advantages over high-cost petrochemical raw materials, realizes high-value utilization of waste biomass, and reduces dependence on petrochemical resources in traditional chemical synthesis.

[0023] 3. The present invention uses ethanol as a solvent, which not only improves the reaction yield, but also reduces the risk of environmental pollution, which is in line with the concept of green chemistry. By optimizing the solvent selection, ethanol significantly improves the synthesis rate and yield of vanillin azine, which is a significant improvement compared to the traditional solvent method.

[0024] 4. In the present invention, under the action of a catalyst, the pyrolysis process further increases the yield of vanillonitrile, saving time and cost. By selecting a catalyst prepared from sodium alginate and nickel nitrate hexahydrate, the corrosiveness and pollution of a traditional strong base catalyst are avoided, thereby improving the sustainability of the process. Biochar is used as a catalyst carrier, further enhancing the recyclability.

[0025] 5. The present invention realizes high efficiency of the whole process through the steps of hydrothermal liquefaction, crystallization purification, solvent synthesis and catalytic pyrolysis, avoiding the cumbersome operation steps and harsh reaction conditions in the traditional method, especially in a high-pressure reactor, it only takes 2 hours to synthesize vanillin azine with vanillin crystals and hydrazine hydrate in a solvent, which greatly shortens the synthesis reaction time and further improves the synthesis efficiency of vanillin amino compounds under the action of ethanol.

[0026] Note that the description of these effects does not prevent the existence of other effects. One embodiment of the present invention does not necessarily have all of the above effects. Effects other than the above can be clearly seen and extracted from the description of the specification, drawings, claims, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the vanillin yield of sodium lignin sulfonate at 150-190° C. in Example 1 of the present invention.

[0028] Figure 2 is the product diagram at different temperatures, where Figure 2 (a) is the pyrolysis product analysis of the mixed product; Figure 2(b) are the main pyrolysis products of the mixed product at different temperatures: vanillonitrile, guaiacol, and 2-methoxyhydroquinone.

[0029] Figure 3 It is the interaction analysis between different solvents and vanillin. Figure 3 (a) is the interaction force between ethanol and vanillin, Figure 3 (b) is the interaction force between methanol and vanillin, Figure 3 (c) is the interaction force between n-butanol and vanillin, Figure 3 (d) is the interaction force between H2O and vanillin.

[0030] Figure 4 It is the analysis of the pyrolysis products after the mixed product is mixed with the catalyst. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto. The reagents, materials, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial sources. Example

[0032] A method for synthesizing a vanillin amino compound comprises the following steps: Step S1, placing sodium lignin sulfonate in a sodium hydroxide solution, and performing hydrothermal liquefaction in a high-pressure reactor, and collecting the liquid product vanillin after the reaction is completed for later use; Step S2, purifying the liquid product vanillin obtained in step S1, collecting the liquid phase, and evaporating the liquid phase to obtain a crystal, i.e., purified vanillin, for later use; Step S3, synthesizing the vanillin crystals purified in step 2 with hydrazine hydrate in ethanol, collecting the liquid product vanillin azine, and evaporating the solvent to obtain the crystals, i.e., purified vanillin azine; Step S4, mixing the vanillin azine crystals purified in step S3 with a catalyst and performing thermal decomposition to obtain a vanillin amino compound.

[0033] The temperature of lignin hydrothermal liquefaction in the working condition of lignin hydrothermal liquefaction in step S1 is determined as follows: At different lignin hydrothermal liquefaction temperatures of 150℃, 160℃, 170℃, 180℃, and 190℃, the time was 60min, the concentration of sodium hydroxide solution was 2M, 0.2g lignin was mixed with 14mL sodium hydroxide and 0.8mL nitrobenzene solution, and the yield of vanillin obtained by hydrothermal liquefaction was as follows: Figure 1 As shown, from Figure 1 It can be seen that the maximum yield of lignin hydrothermal liquefaction at a temperature of 170° C. is 4.73%. Therefore, the optimal operating conditions for the hydrothermal liquefaction of lignin in step S1 are: The temperature of lignin hydrothermal liquefaction is 170°C, the time is 60 minutes, the concentration of sodium hydroxide solution is 2M, 0.2g lignin is mixed with 14mL sodium hydroxide and 0.8mL nitrobenzene solution. Under this optimal working condition, step S2 is continued. In step S2, methanol is used to elute HP-20 resin to purify the liquid product vanillin obtained in step S1; the volume ratio of methanol solution to liquid product vanillin is 0.5.

[0034] The working conditions of the synthesis of the purified vanillin crystals and hydrazine hydrate in step S3 are specifically as follows: The synthesis temperature is 90°C, the time is 120 min, the pressure is 1 MPa, and the stirring reaction time is 2 h; 0.05 mmol of the purified vanillin crystals are mixed with 5 mL of solvent; The mixing mass ratio of the purified vanillin azine crystals and the catalyst in step S4 is 1:1, and the crystallization pyrolysis temperature is as follows: Figure 2 As shown, Figure 2 (a) is the pyrolysis product analysis of the mixed product; Figure 2 (b) is the main pyrolysis products of the mixed product at different temperatures: vanillonitrile, guaiacol, and 2-methoxyhydroquinone. When the crystallization pyrolysis temperature is 500°C, the yield of vanillonitrile is the highest.

[0035] The reaction conditions for the catalyst preparation in step S4 are: Sodium alginate and nickel nitrate hexahydrate Ni(NO)3·6H2O were mixed to obtain a gel-like substance, which was dried in a drying oven at 100°C and ground into powder. The powder was used as a catalyst to prepare a precursor. The carbonization temperature was set to 600°C, the heating rate was 5°C / s, and the nitrogen flow rate was 50 mL / min. After reaching the set temperature, it was maintained for 2 hours. After the reaction was completed, it was cooled to room temperature and taken out to obtain biochar, which was then acid-washed and water-washed.

[0036] The conditions of the pickling and water washing are: The biochar was placed in 2M H2SO4 and stirred for 24 h, then washed with deionized water until the solution was neutral, and the resulting biochar, i.e., the catalyst, was collected and freeze-dried.

[0037] A vanillin amino compound is prepared according to the vanillin amino compound synthesis method of Example 1. Example

[0038] A method for synthesizing a vanillin amino compound. This embodiment differs from embodiment 1 in that the solvent is methanol. Example

[0039] A method for synthesizing a vanillin amino compound. This embodiment differs from embodiment 1 in that the solvent is n-butanol. Example

[0040] A method for synthesizing a vanillin amino compound. This embodiment differs from embodiment 1 in that the solvent is water.

[0041] As shown in Table 1, after the sodium lignin sulfonate of the present invention obtains vanillin, vanillin and hydrazine hydrate are synthesized in different solvents. The dielectric constants of ethanol and methanol are relatively moderate, which can stabilize the intermediate without excessive solvation, thereby facilitating the vanillin azine synthesis reaction. The dielectric constant of water is too high, resulting in excessive solvation, and the stability of the intermediate and the reaction rate are inhibited. The reaction rate is positively correlated with the yield. The reaction rate and yield of ethanol are the highest. Methanol is second, but its reaction rate is slightly lower because its short chain structure limits molecular diffusion and effective interaction. Ethanol achieves a good balance in polarity and molecular structure, providing the highest reaction yield and reaction rate. N-butanol has a lower yield and reaction rate due to its lower polarity and hydrophobic carbon chain. Although water has the highest polarity, the excessive solvation effect reduces the yield. In summary, the polarity, dielectric constant and molecular structure characteristics of the solvent play a key role in determining the efficiency of the vanillin azine synthesis reaction. Table 1 Effect of solvent properties on reaction rate and yield Solvents Yield <![CDATA[Reaction rate (M -1 s -1 )]]> Dipole moment (Debye) Dielectric constant polarity Ethanol 97.5% <![CDATA[1.7*10 -17 ]]> 2.4 25.7 4.3 Methanol 95.7% <![CDATA[2.2*10 -18 ]]> 2.5 32.6 6.6 n-Butanol 94.0% <![CDATA[1.1*10 -18 ]]> 1.9 7.8 3.7 <![CDATA[H2O]]> 88.9% <![CDATA[7.2*10 -19 ]]> 2.6 80.4 10.2 Figure 3 The figure shows the interaction force analysis between different solvents and vanillin. Figure 3 (a) is the interaction force between ethanol and vanillin, Figure 3 (b) is the interaction force between methanol and vanillin, Figure 3 (c) is the interaction force between n-butanol and vanillin, Figure 3 (d) is the interaction force between H2O and vanillin. The present invention utilizes vanillin in the hydrothermal liquefaction product of sodium lignin sulfonate as the original reactant for synthesizing vanillin azine, and preferably ethanol is used as the synthetic solvent to provide a reaction environment. Figure 3 As shown, the intermolecular force between ethanol and vanillin significantly improves the stability of the product, making it easier to generate vanillin azine, thereby further improving the synthesis efficiency of vanillin amino compounds.

[0042] Figure 3 (a) is the interaction force between ethanol and vanillin, Figure 3 (b) is the interaction force between methanol and vanillin, Figure 3 (c) is the interaction force between n-butanol and vanillin, Figure 3(d) is the interaction force between H2O and vanillin. n-Butanol, ethanol, methanol and water all contain hydroxyl (-OH) structures, which can act as hydrogen bond donors to form hydrogen bonds with vanillin, thereby stabilizing intermediates and transition states and promoting the reaction. The polarity of the solvent and the formation of hydrogen bonds are important factors affecting the yield of vanillin azine. Methanol and ethanol can effectively dissolve reactants and stabilize intermediates and promote the reaction due to their high polarity and good hydrogen bond donor and acceptor capabilities. RDG can well reveal chemical bonding and weak interaction areas. The reduced density gradient (RDG) function and the electron density (ρ(r)) function are used in Multiwfn to predict the interaction force of substances adsorbed on the matrix. Figure 3 The figure shows the interaction force analysis between different solvents and vanillin. In the scatter plot, if the peak on the sign(λ2)ρ axis is at a negative value, it indicates a strong attraction (such as hydrogen bonding); if it is close to zero, it indicates a weak interaction (such as van der Waals force); and at a large positive value, it indicates a strong repulsive force (such as steric hindrance). These forces can stabilize reaction intermediates and transition states, reduce energy barriers, and thus affect reaction rates and yields. The red area on the color scale represents stronger weak interactions such as hydrogen bonds, while the green interactions are weaker such as van der Waals forces, and the blue represents mutual repulsion effects. In the reaction of vanillin and hydrazine hydrate, the polarity and molecular structure of the solvent determine its ability to provide hydrogen bond donors and acceptors, thereby affecting the strength and type of these weak interactions. According to Figure 3 The peak in the RDG scatter plot and the contour line with RDG value of 0.6 show that there is hydrogen bonding between the four solvents and vanillin. The absolute values ​​of sign(λ2)ρ of methanol, ethanol and water are larger, which means that the hydrogen bonding force is stronger. In n-butanol, Figure 3 The hydrogen bonding effect is weak. This is because the long carbon chain of n-butanol increases the hydrophobicity and reduces the distribution of polar regions, making it difficult to effectively form a wide hydrogen bonding network. Therefore, its ability to stabilize intermediates and transition states is limited. In addition, methanol and ethanol also have weak van der Waals interactions with vanillin. The present invention uses vanillin in the hydrothermal liquefaction product of sodium lignin sulfonate as the original reactant for synthesizing vanillin azine, and preferably ethanol is used as the synthetic solvent to not only provide a reaction environment. Figure 3 As shown, the intermolecular force between ethanol and vanillin significantly improves the stability of the product, making it easier to generate vanillin azine, thereby further improving the synthesis efficiency of vanillin amino compounds.

[0043] Table 2 The yield of vanillin azine from vanillin and hydrazine hydrate in different solvents Product compound name Ethanol Methanol n-Butanol <![CDATA[H2O]]> <![CDATA[CO2]]> 1.8% - 2.0% 1.4% Vanillin Azine 97.5% 95.7% 94.0% 88.9% 2'-Hydroxy-3,4,4'-trimethoxychalcone 0.7% - 2.8% 9.7% N-Methylisopropylamine - 0.3% - - DL-Alanyl-DL-Valine - 0.4% - - 4-Acetoxy-3-methoxybenzaldehydeazine - 3.6% - - Ammonium carbamate - - 1.2% - Table 2 shows the yields of vanillin azine synthesized from vanillin and hydrazine hydrate in different solvents (methanol, ethanol, n-butanol or water) in Examples 1-4, among which the yield of vanillin azine in ethanol is the highest.

[0044] Comparative Example The difference from Example 1 is that in step S4, no catalyst is added and the vanillin azine crystals purified in step S3 are directly pyrolyzed to obtain vanillin amino compounds. Figure 4 As shown, the yield of vanillin nitrile without catalysis is 47.8%, and the yield of vanillin nitrile with catalysis is 57.2%. It can be seen that the yield of vanillin nitrile catalyzed in Example 1 is significantly higher than the thermal decomposition of vanillin azine without catalysis, and the catalyst promotes the formation of vanillin nitrile. In Example 1, step S3 synthesizes the vanillin crystals purified in step 2 with hydrazine hydrate in a solvent, collects the liquid product vanillin azine, and evaporates the solvent to obtain the crystals, i.e., the purified vanillin azine. The synthesis process only takes 2 hours, which greatly shortens the process time.

[0045] The invention utilizes the sodium lignin sulfonate liquefaction product to separate vanillin, and then the vanillin and hydrazine hydrate are subjected to synthesis reaction in different solutions to obtain vanillin azine, wherein the yield of ethanol vanillin azine is the highest. Vanillin azine is pyrolyzed to obtain vanillin nitrile, wherein the content of vanillin nitrile is significantly increased in the presence of a catalyst.

[0046] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0047] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. All equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for synthesizing a vanillin amino compound, characterized in that: The steps include: Step S1, placing lignin into a mixed solution of sodium hydroxide and nitrobenzene, and performing hydrothermal liquefaction in a high-pressure reactor, and collecting the liquid product vanillin after the reaction is completed for later use; Step S2, purifying the liquid product vanillin obtained in step S1, collecting the liquid phase, and evaporating the liquid phase to obtain a crystal, i.e., purified vanillin, for later use; Step S3, synthesizing the vanillin crystals purified in step 2 with hydrazine hydrate in a solvent, collecting the liquid product vanillin azine, and evaporating the solvent to obtain the crystals, i.e., the purified vanillin azine; Step S4, mixing the vanillin azine crystals purified in step S3 with a catalyst and performing thermal decomposition to obtain a vanillin amino compound.

2. The method for synthesizing the vanillin amino compound according to claim 1, characterized in that: In step S1, the lignin is alkali lignin, sodium lignin sulfonate or straw lignin.

3. The method for synthesizing vanillin amino compounds according to claim 1, characterized in that: The specific working conditions of the hydrothermal liquefaction of lignin in step S1 are: The temperature of lignin hydrothermal liquefaction is 120-200°C, the time is 20-120min, the concentration of sodium hydroxide solution is 0.5M-3M, the volume ratio of nitrobenzene solution to sodium hydroxide solution is 1:15-1:20, and the solid-liquid ratio of lignin to the mixed solution of sodium hydroxide and nitrobenzene is 1:50-1:

100.

4. The method for synthesizing vanillin amino compounds according to claim 1, characterized in that: In the step S2, methanol is used to elute the HP-20 resin to purify the liquid product vanillin obtained in the step S1; the volume ratio of the methanol solution to the liquid product vanillin is 0.2-1.

5. The method for synthesizing vanillin amino compounds according to claim 1, characterized in that: The working conditions of the synthesis of the purified vanillin crystals and hydrazine hydrate in step S3 are specifically as follows: The synthesis temperature is 60-100°C, the time is 120-240 minutes, the pressure is 0.5-2MPa, and the stirring reaction time is 1-3 hours; the solid-liquid ratio of the purified vanillin crystals to the solvent is 1:20-1:100; The solvent is methanol, ethanol, n-butanol or water.

6. The method for synthesizing the vanillin amino compound according to claim 5, characterized in that: The solvent is ethanol.

7. The method for synthesizing vanillin amino compounds according to claim 1, characterized in that: In the step S4, the mixing mass ratio of the purified vanillin azine crystals to the catalyst is 1:0.5 to 1:2, and the crystallization pyrolysis temperature is 300 to 700°C.

8. The method for synthesizing vanillin amino compounds according to claim 1, characterized in that: The reaction conditions for the catalyst preparation in step S4 are: Sodium alginate and nickel nitrate hexahydrate Ni(NO)3·6H2O are mixed to obtain a gel-like substance, which is dried in a drying oven at 100°C and ground into powder. The powder is used as a catalyst to prepare a precursor. The carbonization temperature is set to 600°C, the heating rate is 5-10°C / s, and the nitrogen flow rate is 50-100 mL / min. After reaching the set temperature, it is maintained for 1-2 hours. After the reaction is completed, it is cooled to room temperature and taken out to obtain biochar, which is then acid-washed and water-washed.

9. The method for synthesizing the vanillin amino compound according to claim 8, characterized in that: The conditions of the pickling and water washing are: The biochar was placed in 2M H2SO4 and stirred continuously for 12 to 24 hours, then washed with deionized water until the solution was neutral, and the resulting biochar, i.e., the catalyst, was collected and freeze-dried.

10. A vanillin amino compound, characterized in that: Prepared according to the method for synthesizing vanillin amino compounds according to any one of claims 1 to 9.

Images