阅读说明：本技术 一种利用木质素高产率制备4-乙烯基苯酚的方法 (Method for preparing 4-vinylphenol by using lignin at high yield ) 是由 杨海平 宫梦 陈伟 陈应泉 邵敬爱 曾阔 张�雄 王贤华 张世红 陈汉平 于 2020-12-04 设计创作，主要内容包括：本发明属于生物质利用领域,并具体公开了一种利用木质素高产率制备4-乙烯基苯酚的方法,其包括如下步骤：S1确定木质素热解生成4-乙烯基苯酚的反应路径,计算反应路径中各反应步骤所需的反应能垒,其中最高的反应能垒值为反应路径的反应能垒；S2筛选出可将反应路径的反应能垒降低至预设范围内的供氢体,以利用该供氢体促进木质素热解反应过程中关键中间体的生成,进而产生更多的4-乙烯基苯酚；S3将干燥的木质素置入热解反应器中,并通入筛选出的供氢体与惰性气体的混合气体,在预设温度下反应预设时间,以此制备获得富含4-乙烯基苯酚的液体油。本发明工艺简单、操作方便、成本低廉,能将木质素高效的转化为高价值4-乙烯基苯酚。(The invention belongs to the field of biomass utilization, and particularly discloses a method for preparing 4-vinylphenol by utilizing lignin at a high yield, which comprises the following steps: s1, determining a reaction path of 4-vinylphenol generated by pyrolysis of lignin, and calculating reaction energy barriers required by each reaction step in the reaction path, wherein the highest reaction energy barrier value is the reaction energy barrier of the reaction path; s2, screening out a hydrogen donor which can reduce the reaction energy barrier of the reaction path to a preset range, so as to promote the generation of a key intermediate in the lignin pyrolysis reaction process by using the hydrogen donor, and further generate more 4-vinylphenol; s3, putting the dried lignin into a pyrolysis reactor, introducing the mixed gas of the screened hydrogen donor and the inert gas, and reacting for a preset time at a preset temperature to prepare the liquid oil rich in 4-vinylphenol. The method has the advantages of simple process, convenient operation and low cost, and can efficiently convert the lignin into the high-value 4-vinylphenol.)

1. A method for preparing 4-vinylphenol with high yield by using lignin is characterized by comprising the following steps:

s1, determining a reaction path of 4-vinylphenol generated by pyrolysis of lignin, and calculating reaction energy barriers required by each reaction step in the reaction path, wherein the highest reaction energy barrier value is the reaction energy barrier corresponding to the reaction path;

s2, screening out a hydrogen donor which can reduce the reaction energy barrier of the reaction path by a preset proportion, so as to promote the generation of a key intermediate in the lignin pyrolysis reaction process by using the hydrogen donor, and further generate more 4-vinylphenol;

s3, putting the dried lignin into a pyrolysis reactor, introducing the mixed gas of the screened hydrogen donor and the inert gas, and reacting for a preset time at a preset temperature to prepare the liquid oil rich in 4-vinylphenol.

2. The method for preparing 4-vinylphenol with high yield from lignin according to claim 1, wherein the reaction path is determined in step S1 as follows: putting lignin into a pyrolysis reactor, introducing inert gas, reacting at a preset temperature for a preset time to obtain pyrolysis product distribution, determining a reaction path of the 4-vinylphenol generated by pyrolysis of the lignin according to the pyrolysis product distribution by adopting a density functional theory, and calculating a reaction energy barrier required by each reaction step in the reaction path.

3. The method for preparing 4-vinylphenol with high yield by using lignin according to claim 2, wherein the inert gas introduced during the determination of the reaction path is argon or nitrogen, the gas flow is 200 mL/min-600 mL/min, the pyrolysis temperature is 400 ℃ -800 ℃, and the reaction time is 10 min-60 min.

4. The method for preparing 4-vinylphenol with high yield from lignin according to claim 2 or 3, wherein the enthalpy at 298.15-1073.15K and 1atm is used for all substances in calculating the reaction energy barrier.

5. The method for preparing 4-vinylphenol with high yield from lignin according to claim 1, wherein the predetermined ratio in step S2 is 20% or more.

6. The method for the high-yield production of 4-vinylphenol with lignin according to any of claims 1-5, wherein step S2 comprises the following sub-steps:

s21, determining a reaction path of 4-vinylphenol generated by pyrolysis of lignin after adding a hydrogen donor, and then calculating reaction energy barriers required by each reaction step in the reaction path, wherein the highest reaction energy barrier value is the reaction energy barrier corresponding to the reaction path;

s22 compares the reaction energy barrier of the reaction path determined in step S21 with the reaction energy barrier of the reaction path determined in step S1, and selects a hydrogen donor whose reaction energy barrier is lowered by a predetermined ratio as a desired hydrogen donor.

7. The method for preparing 4-vinylphenol with high yield from lignin according to claim 6, wherein in step S21, density functional theory is used to determine the reaction path of lignin pyrolysis to 4-vinylphenol after adding hydrogen donor, and the reaction energy barrier required by each reaction step in the reaction path is calculated.

8. The method for preparing 4-vinylphenol with high yield by using lignin according to any one of claims 1-7, wherein the lignin is one or more of alkali lignin, ground wood lignin, sulfate lignin, organic solvent lignin; the hydrogen donor is methane or ammonia gas.

9. The method for preparing 4-vinylphenol with high yield from lignin according to any one of claims 1-8, wherein in step S3, the inert gas is argon or nitrogen, the total flow rate of the mixed gas is 200 mL/min-600 mL/min, and the volume ratio of the hydrogen donor is 10% or more.

10. The method for preparing 4-vinylphenol with high yield from lignin according to any of claims 1-9, wherein in step S3, the drying temperature is 50 ℃ to 150 ℃ and the drying time is 15h to 48 h; the pyrolysis temperature of the lignin is 400-800 ℃, and the reaction time is 10-60 min.

Technical Field

The invention belongs to the field of biomass utilization, and particularly relates to a method for preparing 4-vinylphenol by using lignin at a high yield.

Background

Biomass, as a renewable carbonaceous resource with huge reserves, can be converted into fuels, chemicals and materials, and is considered as a promising alternative to fossil fuels. In the main components of biomass, the lignin accounts for 15-40% and about 40% of the total energy. Lignin is the main aromatic polymer in nature, consisting of p-coumarin, coniferyl and octanol, with the potential to produce simple aromatics such as phenol, benzene, toluene, xylene, etc.

Wherein, 4-vinylphenol is used as a high-value platform compound and widely applied to the industries of printing ink, resin, rubber, food flavor, medical use and the like. Industrially, 4-vinylphenol is produced mainly from fossil raw materials and expensive catalysts in a multi-step process, which not only aggravates the shortage of non-renewable energy sources, but also some catalysts may cause environmental pollution and require high costs for preparing and screening the catalysts. At present, the preparation of 4-vinylphenol is difficult, the yield of the 4-vinylphenol can not meet the market requirement, and the price is as high as 2500 yuan/kg. Although some phenolic substances can be obtained by traditional lignin pyrolysis, the selectivity and the content of 4-vinylphenol in the lignin are low, and the subsequent separation and purification are not facilitated. In order to improve the yield of the 4-vinylphenol, the reaction mechanism of lignin for generating the 4-vinylphenol needs to be deeply understood, and a novel efficient and low-cost method for preparing the 4-vinylphenol is developed on the basis, so that the high-value utilization of biomass and the large-scale production of the 4-vinylphenol are facilitated.

Disclosure of Invention

In view of the above-mentioned drawbacks or needs for improvement in the prior art, the present invention provides a method for preparing 4-vinylphenol at a high yield from lignin, which comprises the steps of screening a suitable hydrogen donor through a preliminary hydrogen donor screening step, and then adding the hydrogen donor when formally preparing 4-vinylphenol to prepare 4-vinylphenol at a high yield.

In order to achieve the above object, the present invention provides a method for preparing 4-vinylphenol with high yield by using lignin, which comprises the following steps:

s1, determining a reaction path of 4-vinylphenol generated by pyrolysis of lignin, and calculating reaction energy barriers required by each reaction step in the reaction path, wherein the highest reaction energy barrier value is the reaction energy barrier corresponding to the reaction path;

s2, screening out a hydrogen donor which can reduce the reaction energy barrier of the reaction path by a preset proportion, so as to promote the generation of a key intermediate in the lignin pyrolysis reaction process by using the hydrogen donor, and further generate more 4-vinylphenol;

s3, putting the dried lignin into a pyrolysis reactor, introducing the mixed gas of the screened hydrogen donor and the inert gas, and reacting for a preset time at a preset temperature to prepare the liquid oil rich in 4-vinylphenol.

Further preferably, the reaction path is determined in step S1 in the following manner: putting lignin into a pyrolysis reactor, introducing inert gas, reacting at a preset temperature for a preset time to obtain pyrolysis product distribution, determining a reaction path of the 4-vinylphenol generated by pyrolysis of the lignin according to the pyrolysis product distribution by adopting a density functional theory, and calculating a reaction energy barrier required by each reaction step in the reaction path.

Preferably, when the reaction path is determined, the introduced inert gas is argon or nitrogen, the gas flow is 200mL/min to 600mL/min, the pyrolysis temperature is 400 ℃ to 800 ℃, and the reaction time is 10min to 60 min.

Further preferably, the enthalpy values at 298.15K to 1073.15K and 1atm are used for the energy of all substances when calculating the reaction energy barrier.

More preferably, the predetermined ratio in step S2 is 20% or more.

As a further preference, the step S2 specifically includes the following sub-steps:

s21, determining a reaction path of 4-vinylphenol generated by pyrolysis of lignin after adding a hydrogen donor, and then calculating reaction energy barriers required by each reaction step in the reaction path, wherein the highest reaction energy barrier value is the reaction energy barrier corresponding to the reaction path;

s22 compares the reaction energy barrier of the reaction path determined in step S21 with the reaction energy barrier of the reaction path determined in step S1, and selects a hydrogen donor whose reaction energy barrier is lowered by a predetermined ratio as a desired hydrogen donor.

Further preferably, in step S21, the reaction path of the lignin pyrolyzed to produce 4-vinylphenol after the hydrogen donor is added is determined by using density functional theory, and the reaction energy barrier required for each reaction step in the reaction path is calculated.

As a further preferred, the lignin is one or more of alkali lignin, ground wood lignin, sulfate lignin and organic solvent lignin; the hydrogen donor is methane or ammonia gas.

More preferably, in step S3, the inert gas is argon or nitrogen, the total flow rate of the mixed gas is 200mL/min to 600mL/min, and the volume ratio of the hydrogen donor is 10% or more.

More preferably, in step S3, the drying temperature is 50 to 150 ℃ and the drying time is 15 to 48 hours; the pyrolysis temperature of the lignin is 400-800 ℃, and the reaction time is 10-60 min.

Generally, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:

1. the method firstly simulates and calculates the reaction energy barrier of the lignin pyrolysis reaction before formally preparing the 4-vinylphenol, screens out a proper hydrogen donor according to the reaction energy barrier, and then carries out the lignin pyrolysis reaction based on the screened hydrogen donor to prepare the 4-vinylphenol with high yield.

2. The invention determines the reaction path of 4-vinylphenol generated by lignin pyrolysis according to the distribution of pyrolysis products, determines the most probable reaction path of 4-vinylphenol generated by lignin pyrolysis, and can greatly improve the reliability of the screening result by taking the reaction energy barrier of the reaction path as the reference for screening hydrogen donors.

3. The invention calculates the reaction energy barrier of the reaction path for generating the 4-vinylphenol by pyrolyzing the lignin based on the density functional theory, can preferably select the hydrogen donor for reducing the reaction energy barrier for generating the 4-vinylphenol by pyrolyzing the lignin, can reduce the screening cost of the hydrogen donor, can effectively promote the formation of the 4-vinylphenol by utilizing the hydrogen donor, and can improve the yield of the 4-vinylphenol.

4. When the reaction energy barrier of the reaction path for generating the 4-vinylphenol by pyrolyzing the lignin is calculated based on the density functional theory, the enthalpy values of 298.15-1073.15K and 1atm are adopted for the energy of all substances to obtain the enthalpy value at the corresponding temperature, so that the effective calculation of the reaction energy barrier is facilitated.

5. The hydrogen donor screening method provided by the invention screens out proper hydrogen donor methane and ammonia gas, and finds that the proportion of the ammonia gas for reducing the reaction energy barrier is higher, the reaction path in which the ammonia gas participates has a lower reaction energy barrier of 260.63kJ/mol, the effect of promoting the formation of 4-vinylphenol is better, and the yield of the 4-vinylphenol obtained by the pyrolysis of the lignin in which the ammonia gas participates in the experiment is also higher, so the ammonia gas can be used as the optimal hydrogen donor.

6. The 4-vinylphenol prepared by the method has high yield which can reach 4.89 wt.%, and provides good conditions for subsequent further separation and purification.

7. The method can predict the key step (namely the step corresponding to the highest reaction energy barrier) of generating the 4-vinylphenol by pyrolyzing the lignin, and screens the hydrogen donor promoting the formation of the 4-vinylphenol, thereby being beneficial to reducing the screening cost of the hydrogen donor and improving the yield of the 4-vinylphenol.

Drawings

FIG. 1 is a schematic diagram of a method for preparing 4-vinylphenol in high yield by using lignin according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of the reaction pathway for the pyrolysis of lignin to 4-vinylphenol under an argon atmosphere;

FIG. 3 is a diagram of the reaction pathway for the pyrolysis of lignin to 4-vinylphenol in a hydrogen atmosphere;

FIG. 4 is a diagram of the reaction pathway for the pyrolysis of lignin to 4-vinylphenol in an ammonia atmosphere;

FIG. 5 is a graph showing the yield of 4-vinylphenol produced by pyrolysis of lignin.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

As shown in fig. 1, the embodiment of the present invention provides a method for preparing 4-vinylphenol with high yield by using lignin, which comprises the following steps:

s1, determining a reaction path of 4-vinylphenol generated by pyrolysis of lignin, and calculating reaction energy barriers required by each reaction step in the reaction path, wherein the highest reaction energy barrier value is the reaction energy barrier corresponding to the reaction path, and the step corresponding to the highest reaction energy barrier is a speed-determining step;

s2, screening a hydrogen donor which can reduce the reaction energy barrier (namely the reaction energy barrier of the speed-determining step) of the reaction path to a preset range, so as to promote the generation of key intermediates in the lignin pyrolysis reaction process by using the hydrogen donor, and further generate more 4-vinylphenol;

s3, putting the dried lignin into a pyrolysis reactor, introducing the screened mixed gas of the hydrogen donor and the inert gas, reacting for a preset time at a preset temperature, and condensing the volatile to obtain the liquid oil rich in 4-vinylphenol.

Specifically, in step S1, the reaction path is determined as follows: putting lignin into a pyrolysis reactor, introducing inert gas, reacting at a preset temperature for a preset time to obtain pyrolysis product distribution, and determining a reaction path for pyrolyzing the lignin to generate the 4-vinylphenol according to the pyrolysis product distribution. Wherein, the introduced inert gas is argon or nitrogen, the gas flow is 200 mL/min-600 mL/min, the pyrolysis temperature is 400-800 ℃, the reaction time is 10-60 min, and the effective generation of the 4-vinylphenol can be ensured under the pyrolysis process. Specifically, a path is designed according to the obtained product and the content change along with the temperature, and the gaussian software is used for performing simulation calculation by using a Density Functional Theory (DFT), and how to calculate the reaction path by using the DFT theory is the prior art and is not described herein again. Generally, the pyrolytic cleavage of lignin can be carried out by a radical reaction or a synergistic reaction, so when the reaction path simulation is carried out by using the DFT theory, the reaction path design mainly carries out the radical reaction and the synergistic reaction.

Further, the reaction energy barrier required by each reaction step in the reaction path is calculated by adopting a Density Functional Theory (DFT), reactants, intermediates, transition states and products are generally involved in the lignin pyrolysis process, the enthalpy value of each substance can be obtained by completely optimizing the geometric structure and calculating the frequency of each substance through the Density Functional Theory (DFT), then the reaction energy barrier of the corresponding step can be obtained by subtracting the enthalpy value of the previous substance from the enthalpy value of the current substance, for example, the enthalpy value of the previous reactant such as the intermediate from the enthalpy value of the transition state is the corresponding reaction energy barrier, and how to calculate the reaction energy barrier by using the DTF is also the prior art and is not repeated. When the reaction energy barrier is calculated, the enthalpy values of all substances under 298.15K-1073.15K and 1atm are adopted, and the enthalpy values under 298.15K-1073.15K and 1atm are adopted, so that the enthalpy values under different temperatures can be obtained. The correlation functional calculated by adopting the density functional theory is any one of M06-2X, B3LYP and M06-L.

Specifically, reducing the reaction energy barrier of the speed-determining step to within the preset range specifically means that the reaction energy barrier of the speed-determining step can be reduced by more than 20% by the screened hydrogen donor, and the hydrogen donor screened according to the standard can effectively promote the generation of the target product and save the cost of experimental screening.

Further, in step S3, the inert gas is argon or nitrogen, the total flow rate of the mixed gas is 200mL/min to 600mL/min, and the volume ratio of the hydrogen donor is more than 10%. In the step S3, the drying temperature is 50-150 ℃, the drying time is 15-48 h, and the moisture in the lignin can be effectively removed under the process. In step S3, the pyrolysis temperature of lignin is 400-800 ℃, the reaction time is 10-60 min, the process is consistent with the process adopted when the reaction path is determined, and the pyrolysis of lignin is facilitated to generate 4-vinylphenol under the pyrolysis process.

Furthermore, the following steps are adopted to screen the hydrogen donor which can reduce the reaction energy barrier of the reaction path by a preset proportion:

s21, determining a reaction path of 4-vinylphenol generated by pyrolysis of lignin after adding a hydrogen donor, and then calculating reaction energy barriers required by each reaction step in the reaction path, wherein the highest reaction energy barrier value is the reaction energy barrier corresponding to the reaction path, and the reaction path and the reaction energy barrier are obtained by performing simulation calculation by using gaussian software and adopting a Density Functional Theory (DFT) as in the step S1;

s22 compares the reaction energy barrier of the reaction path determined in step S21 with the reaction energy barrier of the reaction path determined in step S1, and selects a hydrogen donor whose reaction energy barrier can be lowered by a predetermined ratio, for example, the reaction energy barrier of the reaction path determined in step S21 is a, the reaction energy barrier of the reaction path determined in step S1 is b, and the lowering ratio is (b-a)/b, and the lowering ratio may be within a predetermined range.

The lignin related by the invention is one or more of alkali lignin, ground wood lignin, sulfate lignin and organic solvent lignin. The common hydrogen donor comprises hydrogen, methane, water vapor and ammonia gas, and the appropriate hydrogen donor screened by the method is methane and ammonia gas.

The following are specific examples of the present invention.

Example 1

The embodiment illustrates a method for preparing 4-vinylphenol by pyrolysis of lignin by screening hydrogen donors based on density functional theory calculation, which specifically comprises the following steps:

s1: putting 2g of alkali lignin into a pyrolysis reactor for pyrolysis, introducing inert gas argon, heating the reactor to 500 ℃, reacting for 30min to fully decompose the alkali lignin, wherein the total flow of the argon is 200mL/min to obtain pyrolysis product distribution, and designing reaction paths of free radical reaction and synergistic reaction by using gaussian software based on the pyrolysis product distribution and adopting a Density Functional Theory (DFT), wherein the reaction paths are respectively a reaction path A and a reaction path B, and are shown in figure 2;

s2: completely optimizing the geometric structure and calculating the frequency of reactants, intermediates, transition states and products in the step S1 by adopting a Density Functional Theory (DFT) M06-2X method, wherein the energies of all substances adopt enthalpy values under 773.15K and 1atm, the speed-determining steps for converting lignin into 4-vinylphenol are demethoxylation, the reaction energy barriers of the speed-determining steps of the reaction paths A and B are 429.69kJ/mol and 445.94kJ/mol respectively, namely the reaction energy barriers of the reaction paths A and B are 429.69kJ/mol and 445.94kJ/mol respectively, and the key intermediate for generating the 4-vinylphenol is 2-methoxy-4-vinylphenol;

s3: selecting hydrogen as a hydrogen donor, obtaining an action path C of the hydrogen for pyrolyzing lignin to generate 4-vinylphenol by using gaussian software and adopting a Density Functional Theory (DFT) M06-2X, as shown in figure 3, and calculating a reaction energy barrier 291.77kJ/mol of the reaction path C, namely taking the highest reaction energy barrier in each reaction step of the reaction path C as the reaction energy barrier of the path, wherein the proportion of reducing the reaction energy barrier after adding the hydrogen is 32.1 percent compared with the high energy barrier 429.69kJ/mol of the free radical reaction path A; in the synergistic reaction, hydrogen is easy to be added with the double bond of 4-vinylphenol to generate 4-ethylphenol, and the generation of 4-vinylphenol is not facilitated. Therefore, hydrogen cannot simultaneously satisfy the requirement of lowering the reaction energy barriers of reaction paths a and B to promote the production of 4-vinylphenol, and cannot effectively promote the production of 4-vinylphenol;

s4: selecting hydrogen donor methane, simulating reaction paths of free radical reaction and synergistic reaction by utilizing gaussian software and adopting a density functional theory, comparing the reaction energy barrier of the free radical reaction path A with 429.69kJ/mol, wherein the reaction energy barrier of the free radical reaction path after methane is added is 329.54kJ/mol, and the reduction ratio is 23.3% and is more than 20%; compared with the reaction energy barrier of 445.94kJ/mol of the synergistic reaction path B, the reaction energy barrier of the synergistic reaction path after the methane is added is 343.24kJ/mol, the reduction ratio is 23.0 percent and is more than 20 percent, and therefore, the methane meets the screening requirement of the hydrogen donor and is beneficial to promoting the generation of the 4-vinylphenol.

S5: putting alkali lignin into a 60 ℃ oven for drying for 36h, performing pyrolysis in a reactor, heating the reactor to a specified temperature of 500 ℃, quickly feeding 2g of alkali lignin into the middle of the reactor, wherein the reaction time is 30min, so that the lignin is fully decomposed, the total flow of argon and methane is 200mL/min, the volume ratio of methane is 10%, quickly cooling volatile matters to obtain liquid oil containing 4-vinylphenol, the absolute yield of 4-vinylphenol is 2.47 wt%, in addition, pyrolysis gas byproducts can be used as fuel gas, the pyrolysis gas byproducts can be used for power generation, centralized gas supply, heating and the like, and coke can be used as an adsorbent, a catalyst, a fertilizer and the like, and after methane is added, the absolute yield of 4-vinylphenol is improved. Putting alkali lignin into a 60 ℃ oven for drying for 36h, performing pyrolysis in a reactor, heating the reactor to a specified temperature of 500 ℃, quickly feeding 2g of alkali lignin into the middle part of the reactor, wherein the reaction time is 30min, so that the lignin is fully decomposed, the total flow of argon and hydrogen is 200mL/min, the volume proportion of hydrogen is 10%, quickly cooling volatile matters to obtain liquid oil containing 4-vinylphenol, the absolute yield of the 4-vinylphenol is 0.78 wt%, the yield is not improved after adding hydrogen, and the simulation result is consistent, and the hydrogen does not meet the requirement of screening hydrogen supply bodies.

Example 2

S1: putting 2g of alkali lignin into a pyrolysis reactor for pyrolysis, introducing inert gas argon, heating the reactor to a specified temperature of 500 ℃, reacting for 30min to fully decompose the alkali lignin, wherein the total flow of the argon is 200mL/min to obtain pyrolysis product distribution, and designing reaction paths of free radical reaction and synergistic reaction by utilizing gaussian software based on the pyrolysis product distribution and adopting a Density Functional Theory (DFT), wherein the reaction paths are respectively a reaction path A and a reaction path B, and are shown in figure 2;

s2: completely optimizing the geometric structure and calculating the frequency of reactants, intermediates, transition states and products in each reaction path in the step S1 by adopting a Density Functional Theory (DFT) M06-2X method, wherein the energies of all substances adopt enthalpy values under 773.15K and 1atm, the rate-determining steps of converting lignin into 4-vinylphenol are demethoxylation, the reaction energy barriers of the reaction paths A and B are 429.69kJ/mol and 445.94kJ/mol respectively, and the key intermediate for generating the 4-vinylphenol is 2-methoxy-4-vinylphenol;

s3: selecting hydrogen donor water vapor, simulating reaction paths of free radical reaction and synergistic reaction by utilizing gaussian software and adopting a density functional theory, comparing the reaction energy barrier of the free radical reaction path with 429.69kJ/mol, wherein the reaction energy barrier of the free radical reaction path after the water vapor is added is 202.51kJ/mol, and the reduction ratio is 29.6 percent and is more than 20 percent; compared with the reaction energy barrier of 445.94kJ/mol of the synergistic reaction path, the reaction energy barrier of the synergistic reaction path is 427.65kJ/mol after water vapor is added, the reduction ratio is 4.1 percent and is less than 20 percent, so the water vapor can not simultaneously meet the requirement of reducing the ratio of the two reaction energy barriers and can not effectively promote the generation of 4-vinylphenol;

s4: putting alkali lignin into a 60 ℃ oven for drying for 36h, performing pyrolysis in a reactor, heating the reactor to a specified temperature of 500 ℃, quickly feeding 2g of alkali lignin into the middle part of the reactor, reacting for 30min, fully decomposing the lignin, ensuring that the total flow of argon and steam is 200mL/min and the volume ratio of methane is 10%, quickly cooling volatile matters to obtain liquid oil containing 4-vinylphenol, wherein the absolute yield of the 4-vinylphenol is 0.91 wt%, the yield is not improved after the steam is added, and the calculation result is consistent, and the steam does not meet the requirement of hydrogen supply screening;

s5: selecting other hydrogen donors, repeating the step S3 to screen out suitable hydrogen donors, and then carrying out the preparation of the liquid oil of 4-vinylphenol by using the screened hydrogen donors in the same operation steps of S4.

Example 3

S1: putting 2g of wood grinding lignin into a pyrolysis reactor for pyrolysis, introducing inert gas nitrogen, heating the reactor to a specified temperature of 400 ℃, reacting for 50min to fully decompose the wood grinding lignin, wherein the total flow of the nitrogen is 600mL/min to obtain pyrolysis product distribution, designing reaction paths of free radical reaction and synergistic reaction by utilizing gaussian software based on the pyrolysis product distribution and adopting a Density Functional Theory (DFT), wherein the reaction paths are respectively a reaction path A and a reaction path B, and the reaction paths are shown in figure 2;

s2: completely optimizing the geometric structure and calculating the frequency of reactants, intermediates, transition states and products in each reaction path in the step S1 by adopting a Density Functional Theory (DFT) B3LYP method, wherein the energies of all substances adopt enthalpy values under 673.15K and 1atm, the rate-determining steps of converting lignin into 4-vinylphenol are demethoxylation, the reaction energy barriers of the reaction paths A and B are 389.69kJ/mol and 405.94kJ/mol respectively, and the key intermediate for generating the 4-vinylphenol is 2-methoxy-4-vinylphenol;

s3: selecting hydrogen donor water vapor, and simulating reaction paths of free radical reaction and synergistic reaction by utilizing gaussian software and adopting a density functional theory, wherein compared with the reaction energy barrier of the free radical reaction path of 389.69kJ/mol, the reaction energy barrier is 274.34kJ/mol after the water vapor is added, and the reduction ratio is 29.6% and is more than 20%. Compared with the reaction energy barrier 405.94kJ/mol of the synergistic reaction path, the reaction energy barrier is 389.kJ/mol after the water vapor is added, the reduction ratio is 4.1 percent and is less than 20 percent, therefore, the water vapor can not simultaneously meet the requirement of reducing the reaction energy barrier ratio of all the reaction paths and can not effectively promote the generation of 4-vinylphenol;

s4: putting the wood grinding lignin into a 120 ℃ oven for drying for 15h, performing pyrolysis in a reactor, heating the reactor to a specified temperature of 400 ℃, quickly feeding 2g of kraft lignin into the middle of the reactor, reacting for 50min, fully decomposing the lignin, ensuring that the total flow of nitrogen and water vapor is 600mL/min, the volume ratio of methane is 30%, quickly cooling volatile matters to obtain liquid oil containing 4-vinylphenol, wherein the absolute yield of the 4-vinylphenol is 0.91 wt%, the yield is not improved after the water vapor is added, and the calculation result is consistent, and the water vapor does not meet the requirement of screening hydrogen donor;

s5: selecting other hydrogen donors, repeating the step S3 to screen out suitable hydrogen donors, and then carrying out the preparation of the liquid oil of 4-vinylphenol by using the screened hydrogen donors in the same operation steps of S4.

Example 4

S1: putting 2g of organic solvent lignin into a pyrolysis reactor for pyrolysis, introducing inert gas nitrogen, heating the reactor to a specified temperature of 600 ℃, reacting for 60min to fully decompose the lignin, wherein the total flow of the nitrogen is 400mL/min to obtain pyrolysis product distribution, and designing reaction paths of free radical reaction and synergistic reaction by utilizing gaussian software based on the pyrolysis product distribution and adopting a Density Functional Theory (DFT), wherein the reaction paths are respectively a reaction path A and a reaction path B, and are shown in figure 2;

s2: completely optimizing the geometric structure and calculating the frequency of reactants, intermediates, transition states and products of each reaction path in the step S1 by adopting a Density Functional Theory (DFT) M06-L method, wherein the energies of all substances adopt enthalpy values under 873.15K and 1atm, the rate-determining steps of converting lignin into 4-vinylphenol are demethoxylation, the reaction energy barriers of the reaction paths A and B are 417.23kJ/mol and 433.78kJ/mol respectively, and the key intermediate for generating the 4-vinylphenol is 2-methoxy-4-vinylphenol;

s3: selecting hydrogen donor water vapor, simulating reaction paths of free radical reaction and synergistic reaction by utilizing gaussian software and adopting a density functional theory, comparing the reaction energy barrier of the free radical reaction path with 417.23kJ/mol, wherein the reaction energy barrier is 293.73kJ/mol after the water vapor is added, and the reduction ratio is 29.6% and is more than 20%; compared with the reaction energy barrier of 433.78kJ/mol of a synergistic reaction path, the reaction energy barrier is 416.00kJ/mol after water vapor is added, the reduction ratio is 4.1 percent and is less than 20 percent, therefore, the water vapor can not simultaneously meet the requirement of reducing the ratio of the two reaction energy barriers and can not effectively promote the generation of 4-vinylphenol;

s4: putting organic solvent lignin into a 100 ℃ oven for drying for 20h, performing pyrolysis in a reactor, heating the reactor to a specified temperature of 600 ℃, quickly feeding 2g of kraft lignin into the middle part of the reactor, wherein the reaction time is 60min, so that the lignin is fully decomposed, the total flow of nitrogen and water vapor is 400mL/min, the volume ratio of methane is 40%, quickly cooling volatile matters to obtain liquid oil containing 4-vinylphenol, the absolute yield of the 4-vinylphenol is 0.98 wt%, the yield is not improved after the water vapor is added, and the calculation result is consistent, and the water vapor does not meet the requirement of screening hydrogen donor;

s5: selecting a gas hydrogen donor, repeating the step S3 to screen out a suitable hydrogen donor, and then carrying out the preparation of the liquid oil of 4-vinylphenol with the screened hydrogen donor in the same operation step S4.

Example 5

S1: putting 2g of organic solvent lignin into a pyrolysis reactor for pyrolysis, introducing inert gas nitrogen, heating the reactor to a specified temperature of 700 ℃, reacting for 40min to fully decompose the lignin, wherein the total flow of the nitrogen is 500mL/min to obtain pyrolysis product distribution, and designing reaction paths of free radical reaction and synergistic reaction by utilizing gaussian software based on the pyrolysis product distribution and adopting a Density Functional Theory (DFT), wherein the reaction paths are respectively a reaction path A and a reaction path B, and are shown in figure 2;

s2: completely optimizing the geometric structure and calculating the frequency of reactants, intermediates, transition states and products of each reaction path in the step S1 by adopting a Density Functional Theory (DFT) M06-L method, wherein the energies of all substances adopt enthalpy values under 873.15K and 1atm, the rate-determining steps of converting lignin into 4-vinylphenol are demethoxylation, the reaction energy barriers of the reaction paths A and B are 417.23kJ/mol and 433.78kJ/mol respectively, and the key intermediate for generating the 4-vinylphenol is 2-methoxy-4-vinylphenol;

s3: selecting hydrogen donor water vapor, simulating reaction paths of free radical reaction and synergistic reaction by utilizing gaussian software and adopting a density functional theory, comparing the reaction energy barrier of the free radical reaction path with 417.23kJ/mol, wherein the reaction energy barrier is 293.73kJ/mol after the water vapor is added, and the reduction ratio is 29.6% and is more than 20%; compared with the reaction energy barrier of 433.78kJ/mol of a synergistic reaction path, the reaction energy barrier is 416.00kJ/mol after water vapor is added, the reduction ratio is 4.1 percent and is less than 20 percent, therefore, the water vapor can not simultaneously meet the requirement of reducing the ratio of the two reaction energy barriers and can not effectively promote the generation of 4-vinylphenol;

s4: putting organic solvent lignin into a 100 ℃ oven for drying for 25h, performing pyrolysis in a reactor, heating the reactor to a specified temperature of 700 ℃, quickly feeding 2g of kraft lignin into the middle part of the reactor, wherein the reaction time is 40min, so that the lignin is fully decomposed, the total flow of nitrogen and water vapor is 500mL/min, the volume ratio of methane is 60%, quickly cooling volatile matters to obtain liquid oil rich in 4-vinylphenol, the absolute yield of the 4-vinylphenol is 0.98 wt%, the yield is not improved after the water vapor is added, and the calculation result is consistent, and the water vapor does not meet the requirement of hydrogen donor screening;

s5: selecting a gas hydrogen donor, repeating the step S3 to screen out a suitable hydrogen donor, and then carrying out the preparation of the liquid oil of 4-vinylphenol with the screened hydrogen donor in the same operation step S4.

Example 6

S1: putting 2g of alkali lignin into a pyrolysis reactor for pyrolysis, introducing inert gas argon, heating the reactor to a specified temperature of 400 ℃, reacting for 30min to fully decompose the alkali lignin, wherein the total flow of the argon is 200mL/min to obtain pyrolysis product distribution, and designing reaction paths of free radical reaction and synergistic reaction by utilizing gaussian software based on the pyrolysis product distribution and adopting a Density Functional Theory (DFT), wherein the reaction paths are respectively a reaction path A and a reaction path B, and are shown in figure 2;

s2: completely optimizing the geometric structure and calculating the frequency of reactants, intermediates, transition states and products of each reaction path in the step S1 by adopting a Density Functional Theory (DFT) M06-2X method, wherein the energies of all substances adopt enthalpy values under 773.15K and 1atm, the rate-determining steps of converting lignin into 4-vinylphenol are demethoxylation reactions, the reaction energy barriers are 429.69kJ/mol and 445.94kJ/mol respectively, and the key intermediate for generating the 4-vinylphenol is 2-methoxy-4-vinylphenol;

s3: selecting a hydrogen donor ammonia gas, and simulating reaction paths of a free radical reaction and a synergistic reaction by utilizing gaussian software and adopting a density functional theory, wherein the reaction paths are respectively a path D and a path E, as shown in FIG. 4, compared with a high energy barrier of 429.69kJ/mol of a free radical reaction path A, the reaction energy barrier of the reaction path D is 260.63kJ/mol, and the reduction ratio is 39.3% and is more than 20%; compared with the high energy barrier 445.94kJ/mol of the synergistic reaction path B, the reaction energy barrier of the reaction path E is 284.50kJ/mol, the reduction ratio is 36.2 percent and is more than 20 percent, therefore, the ammonia conforms to the condition of hydrogen donor screening, the generation of 4-vinylphenol is facilitated, the hydrogen donor and the synergistic action of the ammonia and the hydrogen absorption action of the ammonia can promote the reactions of lignin beta-O-4 bond breakage, cracking and dehydration of intermediate substances, decarbonylation and the like, and the removal of a methoxy side chain on a benzene ring has obvious promotion action, has lower reaction energy barrier, and more effectively promotes the generation of 4-vinylphenol;

s4: 2g of alkali lignin is placed in a 60 ℃ oven for drying for 36h, pyrolysis is carried out in a reactor, after the reactor is heated to a specified temperature of 400 ℃, 2g of alkali lignin is quickly fed into the middle of the reactor, the reaction time is 30min, the lignin is fully decomposed, the total flow of argon and ammonia is 200mL/min, the volume proportion of ammonia is 10%, the participation of ammonia effectively promotes the formation of methoxy-free phenolic substances, volatile matters are quickly cooled, liquid oil rich in 4-vinylphenol is obtained, and the absolute yield of 4-vinylphenol is 1.98 wt%. In addition, the pyrolysis gas byproduct can be used as fuel gas for power generation, central gas supply, heating and the like, and coke can be used as an adsorbent, a catalyst, a fertilizer and the like. After the ammonia gas is added, the absolute yield of the 4-vinylphenol is improved, is consistent with a simulation calculation result, and is compared with methane meeting the screening requirement, and the calculation result shows that the proportion of the ammonia gas for reducing the reaction energy barrier is higher, the promotion effect is better, the absolute yield of the preparation result is also higher, the generation of the 4-vinylphenol is promoted more effectively, and the 4-vinylphenol can be used as an optimal hydrogen donor.

Example 7

This example is the same as example 6 except that the pyrolysis temperature was 500 ℃ and the absolute yield of 4-vinylphenol obtained was 3.68 wt.%.

Example 8

This example is the same as example 6 except that the pyrolysis temperature was 600 ℃ and the absolute yield of 4-vinylphenol obtained was 4.89 wt.%.

Example 9

This example is the same as example 6 except that the pyrolysis temperature was 700 ℃ and the absolute yield of 4-vinylphenol obtained was 4.62 wt.%.

Example 10

This example is the same as example 6 except that the pyrolysis temperature is 800 ℃, and the absolute yield of 4-vinylphenol obtained is 4.31 wt.%.

Comparative example 1

According to the comparative example, the conventional pyrolysis process is adopted for pyrolysis of lignin, specifically, alkali lignin is placed in a 60 ℃ oven to be dried for 36 hours and then pyrolyzed in a reactor, the reactor is heated to the specified temperature of 400 ℃, 2g of alkali lignin is rapidly fed into the reactor, the reaction time is 30min, the lignin is fully decomposed in an argon atmosphere, volatile matters are rapidly cooled, liquid oil rich in 4-vinylphenol is obtained, and the absolute yield of the 4-vinylphenol is 0.98 wt.%.

Comparative example 2

This comparative example is identical to comparative example 1, except that the pyrolysis temperature was 500 ℃, and the absolute yield of 4-vinylphenol obtained was 1.11 wt.%.

Comparative example 3

This comparative example is identical to comparative example 1, except that the pyrolysis temperature was 600 ℃ and the absolute yield of 4-vinylphenol obtained was 1.31 wt.%.

Comparative example 4

This comparative example is identical to comparative example 1, except that the pyrolysis temperature was 700 ℃ and the absolute yield of 4-vinylphenol obtained was 1.16 wt.%.

Comparative example 5

This comparative example is identical to comparative example 1, except that the pyrolysis temperature was 800 ℃ and the absolute yield of 4-vinylphenol obtained was 1.13 wt.%.

FIG. 2 is a diagram of a possible reaction path for pyrolyzing lignin to produce 4-vinylphenol under an argon atmosphere, and the results show that the rate-determining steps of reaction paths A and B are both demethoxylation reactions, the reaction energy barriers are 429.69kJ/mol and 445.94kJ/mol, respectively, the direct pyrolysis of lignin to produce 4-vinylphenol requires higher activation energy, and particularly, the demethoxylation reaction has higher reaction energy barrier and is not beneficial to the production of 4-vinylphenol.

FIG. 3 is a diagram showing a reaction pathway for 4-vinylphenol produced by pyrolysis of lignin in a hydrogen atmosphere, wherein the reaction pathway C has a reaction energy barrier of 291.77kJ/mol and a reduced reaction energy barrier of 32.1% compared with the high energy barrier of 429.69kJ/mol in the radical reaction pathway A after addition of hydrogen. In the synergistic reaction, hydrogen is easy to be added with the double bond of 4-vinylphenol to generate 4-ethylphenol, and the generation of 4-vinylphenol is not facilitated. Therefore, hydrogen is not effective in promoting the production of 4-vinylphenol.

FIG. 4 is a reaction pathway diagram of 4-vinylphenol produced by pyrolysis of lignin in an ammonia atmosphere, comparing the high energy barrier of 429.69kJ/mol for free radical reaction pathway A, the reaction energy barrier of reaction pathway D is 260.63kJ/mol, the reduction ratio is 39.3%, which is greater than 20%; compared with the high energy barrier 445.94kJ/mol of the synergistic reaction path B, the reaction energy barrier of the reaction path E is 284.50kJ/mol, and the reduction ratio is 36.2% and is more than 20%. Therefore, the ammonia gas meets the condition of hydrogen donor screening, and is beneficial to producing the 4-vinylphenol. The hydrogen supply and synergy of ammonia and the hydrogen absorption of ammonia can promote the reactions of lignin beta-O-4 bond breakage, intermediate substance cracking, dehydration, decarbonylation and the like, has obvious promotion effect on the removal of the methoxy side chain on the benzene ring, has lower reaction energy barrier, and can more effectively promote the generation of 4-vinylphenol.

Fig. 5 is a graph of the yield of 4-vinylphenol from pyrolysis of lignin, and experimental results show that for direct pyrolysis of lignin under an argon atmosphere, the absolute yield of 4-vinylphenol is less than 1.5 wt.%, and that after introduction of ammonia, the absolute yield of 4-vinylphenol increases significantly from 1.98 wt.% with increasing temperature, reaching a maximum of 4.89 wt.% (5-fold increase) at 600 ℃, and then gradually decreases to 4.31 wt.% at 800 ℃, with ammonia, hydrogen radicals and amino groups promoting cleavage of β -O-4 in lignin, producing more coumarin, coniferyl alcohol and sinapyl alcohol subunit intermediates, which are further converted to more 4-vinylphenol.

According to the invention, firstly, lignin is utilized to carry out pyrolysis experiment to obtain pyrolysis product distribution, then, a reaction path for generating 4-vinylphenol by lignin pyrolysis is designed, complete optimization and frequency calculation of geometric structures of reactants, intermediates, transition states and products are carried out based on a density functional theory, two optimal reaction paths and reaction energy barriers based on free radical reaction and synergistic reaction are obtained, the highest speed-determining step of required activation energy is demethoxylation, and the key intermediate for generating 4-vinylphenol is 2-methoxy-4-vinylphenol. In order to reduce the demethoxylation reaction energy barrier and promote the generation of key intermediates, a hydrogen donor is selected and the action path of the hydrogen donor on the pyrolysis of lignin to generate 4-vinylphenol is calculated, so as to obtain the reaction energy barrier of the reaction path. Comparing two reaction paths without hydrogen donor according to free radical reaction and synergistic reaction, hydrogen donor capable of reducing reaction energy barrier of all reaction paths by more than 20% is preferred. After the hydrogen donor is screened out, the lignin and the lignin as a raw material are pyrolyzed, the lignin and the optimized hydrogen donor generate strong chemical reaction in the pyrolysis process, the hydrogen donor can promote the reactions of lignin beta-O-4 bond breakage, intermediate substance cracking, dehydration, decarbonylation and the like, and the hydrogen donor has obvious promotion effect on the removal of the side chain of the methoxy group on the benzene ring, thereby promoting the generation of 4-vinylphenol. The method can predict the key step of generating the 4-vinylphenol by pyrolyzing the lignin and screen out the hydrogen donor promoting the formation of the 4-vinylphenol, is favorable for reducing the screening cost of the hydrogen donor and improving the yield of the 4-vinylphenol.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.