阅读说明：本技术 一种高效转化木质素生产生物燃料的方法 (Method for producing biofuel by efficiently converting lignin ) 是由 田龙 王丽 褚学英 于 2019-09-24 设计创作，主要内容包括：本发明公开了一种高效转化木质素生产生物燃料的方法,属于生物能源技术领域,包含以下步骤：S1：取颗粒活性炭浸入硫酸铁溶液中,振荡后滤干,烘干,加热,冷却至室温后清洗烘干；S2：取木质素、载铁催化剂、无水乙醇,共同置于反应釜中,密封,加热,反应结束后,降至室温；S3：将步骤S2得到的反应产物加水后调节PH值,等未反应的木质素完全析出后过滤；S4：将过滤后的滤液用乙酸乙酯萃取,在烘箱中干燥,至恒重称量计算生物油收率。本发明生物油的提取率达到74.5%以上,液化降解后的木质素残渣结构变化很少,木质素降解产物的重新聚合的几率低。(The invention discloses a method for producing biofuel by efficiently converting lignin, which belongs to the technical field of biological energy and comprises the following steps: s1: soaking granular activated carbon into a ferric sulfate solution, vibrating, filtering, drying, heating, cooling to room temperature, cleaning and drying; s2: putting lignin, iron-loaded catalyst and absolute ethyl alcohol into a reaction kettle together, sealing, heating, and cooling to room temperature after the reaction is finished; s3: adding water into the reaction product obtained in the step S2, adjusting the pH value, and filtering after unreacted lignin is completely separated out; s4: and extracting the filtered filtrate with ethyl acetate, drying in an oven until the weight is constant, and calculating the yield of the bio-oil. The extraction rate of the bio-oil reaches over 74.5 percent, the structure change of the lignin residue after liquefaction and degradation is little, and the rate of repolymerization of lignin degradation products is low.)

1. A method for producing biofuel by efficiently converting lignin is characterized by comprising the following steps: comprises the following steps:

s1: preparation of iron-supported catalyst: soaking granular activated carbon into a ferric sulfate solution, placing the granular activated carbon in a constant-temperature oscillator for oscillation, filtering, drying, placing the dried granular activated carbon in an atmosphere protection furnace under the protection of nitrogen flow, heating to the temperature of 550-660 ℃, keeping the constant temperature for 1.5-2.5 h, cooling to room temperature, cleaning and drying to obtain the iron-loaded catalyst;

s2: preparing bio-oil by catalytic degradation of lignin: putting lignin, an iron-loaded catalyst and absolute ethyl alcohol into a reaction kettle together, sealing, heating for 5-10 min at the reaction temperature of 100 ℃ and 150 ℃, and cooling to room temperature after the reaction is finished to obtain a reaction product;

s3: adding water into the reaction product obtained in the step S2, adjusting the pH value of the solution by using hydrochloric acid, and filtering by using a 0.45-micrometer membrane after unreacted lignin is completely separated out;

s4: extracting the filtered filtrate with ethyl acetate for 3 times, collecting the extract, removing the solvent and unreacted liquefying agent by using a rotary evaporator, drying in an oven until the weight is constant, and calculating the yield of the bio-oil.

2. The method for producing biofuel by efficiently converting lignin according to claim 1, wherein: in the step S1, the mass fraction of the ferric sulfate solution is 5-10%.

3. The method for producing biofuel by efficiently converting lignin according to claim 1, wherein: in the step S1, the heating rate is 10 ℃/min.

4. The method for producing biofuel by efficiently converting lignin according to claim 1, wherein: in the step S2, the weight part ratio of the lignin, the iron-supported catalyst and the absolute ethyl alcohol is 1:0.03-0.05: 20.

5. The method for producing biofuel by efficiently converting lignin according to claim 1, wherein: in step S3, the PH is 2.

6. The method for producing biofuel by efficiently converting lignin according to claim 1, wherein: in the step S2, the reaction kettle is a microwave reaction kettle with a power of 180 and 280W.

7. The method for producing biofuel by efficiently converting lignin according to claim 1, wherein: in the step S4, the oven temperature is set to be 45-55 ℃.

Technical Field

The invention relates to the technical field of biological energy, in particular to a method for producing biofuel by efficiently converting lignin.

Background

An important component of biomass is the lignin present in the solid part of the biomass. Lignin comprises chains of aromatic and oxygenate components that form larger molecules that are not easily handled. Lignin is one of the most abundant natural polymers on earth, and is the second largest natural high molecular compound with content next to cellulose in plants. A common way of producing lignin is by separation from wood during the pulping process, with only a small amount (1-2%) being used in specialized products, while the remaining major part is used as fuel. I.e. burning lignin, which has significant potential as a raw material for sustainable production of chemicals and liquid fuels, is a valuable way to reduce the use of fossil fuels. The lignin mainly comprises aromatic compounds, the basic constitutional unit is phenyl propane, and due to the three-dimensional space structure of the lignin, the lignin has the characteristics of high hardness, water insolubility, difficult degradation, stable chemical properties and the like, and the utilization rate is low at present, which is undoubtedly a great waste. The main reason for the difficulty in handling the lignin is the inability to disperse the lignin for contact with catalysts that can decompose the lignin, while in order for the lignin to be more useful one must address the problem of low solubility of lignin in organic solvents.

Patent publication No. CN102272313B discloses a method for producing sugar-based chemicals, biofuels or materials and sulfonated lignin from lignocellulosic biomass, comprising pretreating the lignocellulosic biomass with a sulfite cooking step; separating the lignocellulosic biomass; performing enzymatic hydrolysis; and processing the obtained monosaccharide and biofuel. The method adopts acid and alkali cooking treatment, which not only affects the health of operators and causes serious harm to equipment and environment, but also has complex process steps and low product extraction rate.

The patent with the publication number of CN104326875B discloses a method for preparing bio-oil by lignin hydrogenation degradation, which comprises the following steps: uniformly mixing lignin, a vanadium-based catalyst and a solvent, and sealing the mixture in a high-pressure reaction kettle to prepare bio-oil through hydrogenation catalytic degradation; the mass ratio of the lignin to the vanadium-based catalyst is 100:1-10:1, and the mass ratio of the lignin to the solvent is 1:5-1: 30; the reaction temperature is 150 ℃ and 400 ℃, the reaction time is 0.5-5H, and the reaction H₂The pressure is 0.5-6 Mpa; prepared raw materialThe main components of the product oil are aromatic and phenolic compounds. The bio-oil prepared by the method has fewer components and single component, and most of the bio-oil is aromatic compounds, which are important chemical and medical intermediates.

Disclosure of Invention

In view of the above, the present invention provides a method for producing biofuel by converting lignin with high efficiency.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a method for producing biofuel by efficiently converting lignin comprises the following steps:

s1: preparation of iron-supported catalyst: soaking granular activated carbon into a ferric sulfate solution, placing the granular activated carbon in a constant-temperature oscillator for oscillation, filtering, drying, placing the dried granular activated carbon in an atmosphere protection furnace under the protection of nitrogen flow, heating to the temperature of 550-660 ℃, keeping the constant temperature for 1.5-2.5 h, cooling to room temperature, cleaning and drying to obtain the iron-loaded catalyst;

s2: preparing bio-oil by catalytic degradation of lignin: putting lignin, an iron-loaded catalyst and absolute ethyl alcohol into a reaction kettle together, sealing, heating for 5-10 min at the reaction temperature of 100 ℃ and 150 ℃, and cooling to room temperature after the reaction is finished to obtain a reaction product;

s3: adding water into the reaction product obtained in the step S2, adjusting the pH value of the solution by using hydrochloric acid, and filtering by using a 0.45-micrometer membrane after unreacted lignin is completely separated out;

s4: extracting the filtered filtrate with ethyl acetate for 3 times, collecting the extract, removing the solvent and unreacted liquefying agent by using a rotary evaporator, drying in an oven until the weight is constant, and calculating the yield of the bio-oil.

Further, in the step S1, the mass fraction of the ferric sulfate solution is 5-10%.

Further, in step S1, the heating temperature increase rate is 10 ℃/min.

Further, in the step S2, the weight portion ratio of the lignin, the iron-supported catalyst and the absolute ethyl alcohol is 1:0.03-0.05: 20.

Further, in step S2, the PH value is 2.

Further, in the step S2, the reaction kettle is a microwave reaction kettle with a power of 180-.

Further, in the step S2, the oven temperature is set to 45-55 ℃.

With the increasing population and the development of industry, the resource consumption is increased continuously, people are in urgent need to search new energy sources to replace non-renewable and gradually exhausted fossil energy sources, wherein renewable biomass energy sources become one of the fastest-developing alternative energy sources in the world, and the use ratio of the biofuel is continuously increased. The lignin has high heat energy, the mass fraction of hydrocarbon in molecules is as high as 70-80%, the lignin is the highest component of solar energy in plants, and the lignin can be directly liquefied by a high-temperature cracking method and an organic solvent method to be used as a fuel and become the best substitute of petroleum. With the increasing price of petroleum, how to prepare liquid fuels such as gasoline and diesel oil at low cost becomes a very challenging topic for scientists in various countries. Since the global oil price rises in 2002, the development and application of fuel ethanol has become a new international trend. The conversion of various biomasses to fuel alcohol by fermentation of microorganisms has become an emerging fundamental industry in many countries, such as the united states and brazil. The combination of biological and thermochemical methods to produce fuel oil will greatly reduce the cost and increase the efficiency. The lignin is basically formed by the mutual connection and irregular coupling of phenylpropyl units through carbon-carbon bonds and carbon-oxygen bonds, and is a complex amorphous high polymer with a three-dimensional space structure. After being heated, the relatively weak carbon-oxygen bond is easy to break to form active benzene ring-containing free radical, and the free radical is easy to perform condensation reaction with other molecules or free radicals to generate macromolecule with more stable structure, so that coking is realized. Therefore, hydrogen or other intermediary substances are generally introduced into the reaction system to suppress coking and to suppress polycondensation of the intermediate products. The choice of both solvent and catalyst factors during liquefaction is particularly important.

It is believed by those skilled in the art that lignin is completely dissolved in hot water under high pressure when phenol is added, which greatly facilitates the hydrolysis of lignin into phenol oil, while the addition of phenol prevents the repolymerization of the hydrolyzed phenol oil. The lignin can be completely degraded into phenol oil, and can further generate biofuel. In the absence of phenol, small molecular compounds obtained by hydrolysis and dealkylation of lignin and residual lignin are cross-bonded to obtain compounds with larger molecular mass, so that the coking phenomenon is serious, but the generation of coke can be effectively inhibited by adding phenolic substances into medium water. Therefore, hydrogen donor solvents such as phenol and the like receive a great deal of attention due to strong hydrogen donor capacity, strong dissolving capacity and good liquefaction effect, but have high cost and difficult recovery, thereby causing great waste.

The catalyst used for liquefaction can moderate reaction conditions, improve the yield of Dan Ying and change the composition of oil. In the liquefaction of lignin, acid and alkali are used in many cases, and those skilled in the art think that the addition of acid and alkali can greatly improve the conversion rate of the reaction. However, acid and alkali can cause serious corrosion to equipment and pollution to the environment when in use. For example, wang xiao juan, yang, zhang xiao qiang, jiang jun, songye, etc., lignin and biofuel are produced: reduction of the content or release of the constraint [ J ] China agricultural science 2015,48 (2): 229-. Patent No. CN101171324B discloses a process for converting lignin to liquid products such as biofuels and fuel additives comprising subjecting lignin material to a base catalyzed depolymerization reaction (stage I) to produce partially depolymerized lignin. The partially depolymerized lignin may then be subjected to a stabilization/partial hydrodeoxygenation reaction (stage II) to form a partially hydrodeoxygenated product. After partial hydrodeoxygenation, the partially hydrodeoxygenated product may be reacted in a refining step (stage III) to form a biofuel. However, the method has complex process, and the steps of alkali catalysis, hydrodeoxygenation, hydrotreatment and the like are carried out in sequence, so that the method has high cost, great influence on the environment and low product yield. Therefore, in the research trend of converting lignin into biofuel by fermentation of microorganisms, it is not easy for those skilled in the art to think that the biofuel is extracted from lignin by using ethanol as a solvent to prepare a catalyst by mixing ferric sulfate with activated carbon, and the bio-oil extraction rate is high.

The invention has the beneficial effects that: the structure and chemical composition of the lignin determine that the lignin has wide development prospect in future production and life, but the effective utilization of the lignin also restricts further development, the practicability and the economy can not be unified, and the embarrassment that the technology is difficult to popularize is overlooked. In order to improve the situation, the inventor of the invention intensively studies for many years, the catalyst is prepared by mixing ferric sulfate solution and activated carbon, and meanwhile, the biological oil is extracted by the process steps of heating ethanol and lignin in a reaction kettle, adjusting the pH value, filtering, extracting, drying and the like.

(1) The iron-carrying catalyst takes ferric sulfate solution and active carbon as raw materials, has low cost, simple process steps and good catalytic effect; the paint does not contain acid, alkali, organic solvent and other components, does not corrode equipment, and is safe and environment-friendly.

(2) Heating lignin, a catalyst and ethanol in a reaction kettle, adjusting the pH value by using hydrochloric acid, improving the conversion rate of the lignin, removing solid impurities, improving the purity of the bio-oil, wherein the extraction rate of the bio-oil reaches over 74.5 percent, and the structure change of the lignin residue after liquefaction and degradation is little, which indicates that the rate of repolymerization of a lignin degradation product is low. The biological oil is mainly monophenolic substances, wherein the contents of S type, G type and H type monomers are 55.1%, 23.7% and 12.5% respectively.

(3) The lignin is modified by the acrylamide solution and the ammonium ceric nitrate, so that the temperature resistance and the adsorption performance are enhanced, the dispersibility of the lignin in ethanol is improved, and the extraction rate of the biological oil is improved.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention are clearly and completely described below. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention, are within the scope of the invention.

Example 1

The embodiment provides a method for producing biofuel by efficiently converting lignin, which comprises the following steps:

s1: preparation of iron-supported catalyst: soaking granular activated carbon into a ferric sulfate solution with the mass fraction of 5%, placing the granular activated carbon in a constant-temperature oscillator for oscillation, filtering, drying, placing the dried granular activated carbon in an atmosphere protection furnace under the protection of nitrogen flow, heating to 550 ℃, keeping the constant temperature for 2.5 hours, keeping the temperature at the heating rate of 10 ℃/min, cooling to room temperature, and then cleaning and drying to obtain the iron-loaded catalyst;

s2: preparing bio-oil by catalytic degradation of lignin: putting lignin, an iron-loaded catalyst and absolute ethyl alcohol in a weight ratio of 1:0.03:20 in a microwave reaction kettle together, sealing the microwave reaction kettle at the power of 180 and 280W, heating the microwave reaction kettle for 5 min at the reaction temperature of 150 ℃, and cooling the microwave reaction kettle to room temperature after the reaction is finished;

s3: adding water into the reaction product, adjusting the pH value of the solution to 2 by using hydrochloric acid, and filtering by using a 0.45-micrometer membrane after unreacted lignin is completely separated out;

s4: extracting the filtrate with ethyl acetate for 3 times, collecting extractive solution, removing solvent and unreacted liquefying agent with rotary evaporator, drying in oven set at 45 deg.C until the yield of bio-oil reaches 74.5%.

Example 2

The embodiment provides a method for producing biofuel by efficiently converting lignin, which comprises the following steps:

s1: preparation of iron-supported catalyst: soaking granular activated carbon into a ferric sulfate solution with the mass fraction of 6%, placing the granular activated carbon into a constant-temperature oscillator for oscillation, filtering, drying, placing the dried granular activated carbon into an atmosphere protection furnace under the protection of nitrogen flow, heating to 580 ℃ and keeping the temperature constant for 2 hours, wherein the heating rate is 10 ℃/min, cooling to room temperature, cleaning and drying to obtain the iron-loaded catalyst;

s2: preparing bio-oil by catalytic degradation of lignin: putting lignin, an iron-loaded catalyst and absolute ethyl alcohol in a weight ratio of 1:0.03:20 in a microwave reaction kettle together, sealing the microwave reaction kettle at the power of 180 and 280W, heating the microwave reaction kettle for 6 min at the reaction temperature of 110 ℃, and cooling the microwave reaction kettle to room temperature after the reaction is finished;

s3: adding water into the reaction product, adjusting the pH value of the solution to 2 by using hydrochloric acid, and filtering by using a 0.45-micrometer membrane after unreacted lignin is completely separated out;

s4: extracting the filtrate with ethyl acetate for 3 times, collecting extractive solution, removing solvent and unreacted liquefying agent with rotary evaporator, drying in oven at 46 deg.C until the yield of bio-oil reaches 75.6%.

Example 3

The embodiment provides a method for producing biofuel by efficiently converting lignin, which comprises the following steps:

s1: preparation of iron-supported catalyst: soaking granular activated carbon into a ferric sulfate solution with the mass fraction of 7%, placing the granular activated carbon into a constant-temperature oscillator for oscillation, filtering, drying, placing the dried granular activated carbon into an atmosphere protection furnace under the protection of nitrogen flow, heating to 600 ℃, keeping the temperature constant for 2 hours, and cooling to room temperature at the heating rate of 10 ℃/min, and then cleaning and drying to obtain the iron-loaded catalyst;

s2: preparing bio-oil by catalytic degradation of lignin: putting lignin, an iron-loaded catalyst and absolute ethyl alcohol in a weight ratio of 1:0.04:20 in a microwave reaction kettle together, sealing the microwave reaction kettle at the power of 180 and 280W, heating the microwave reaction kettle for 7 min at the reaction temperature of 120 ℃, and cooling the microwave reaction kettle to room temperature after the reaction is finished;

s3: adding water into the reaction product, adjusting the pH value of the solution to 2 by using hydrochloric acid, and filtering by using a 0.45-micrometer membrane after unreacted lignin is completely separated out;

s4: extracting the filtrate with ethyl acetate for 3 times, collecting extractive solution, removing solvent and unreacted liquefying agent with rotary evaporator, drying in oven set at 47 deg.C until the yield of bio-oil reaches 75.9%.

Example 4

The embodiment provides a method for producing biofuel by efficiently converting lignin, which comprises the following steps:

s1: preparation of iron-supported catalyst: soaking granular activated carbon into a ferric sulfate solution with the mass fraction of 7%, placing the granular activated carbon into a constant-temperature oscillator for oscillation, filtering, drying, placing the dried granular activated carbon into an atmosphere protection furnace under the protection of nitrogen flow, heating to 610 ℃, keeping the temperature constant for 2 hours, and cooling to room temperature at the heating rate of 10 ℃/min, and then cleaning and drying to obtain the iron-loaded catalyst;

s2: preparing bio-oil by catalytic degradation of lignin: putting lignin, an iron-loaded catalyst and absolute ethyl alcohol in a weight ratio of 1:0.04:20 in a microwave reaction kettle together with power of 180 and 280W, sealing, heating for 7 min at the reaction temperature of 125 ℃, and cooling to room temperature after the reaction is finished;

s3: adding water into the reaction product, adjusting the pH value of the solution to 2 by using hydrochloric acid, and filtering by using a 0.45-micrometer membrane after unreacted lignin is completely separated out;

s4: extracting the filtrate with ethyl acetate for 3 times, collecting extractive solution, removing solvent and unreacted liquefying agent with rotary evaporator, drying in oven set at 48 deg.C until the yield of bio-oil reaches 75.8%.

Example 5

The embodiment provides a method for producing biofuel by efficiently converting lignin, which comprises the following steps:

s1: preparation of iron-supported catalyst: soaking granular activated carbon into a ferric sulfate solution with the mass fraction of 8%, placing the granular activated carbon in a constant-temperature oscillator for oscillation, filtering, drying, placing the dried granular activated carbon in an atmosphere protection furnace under the protection of nitrogen flow, heating to 620 ℃, keeping the constant temperature for 2.5 hours, keeping the temperature at the heating rate of 10 ℃/min, cooling to room temperature, and then cleaning and drying to obtain the iron-loaded catalyst;

s2: preparing bio-oil by catalytic degradation of lignin: taking lignin, an iron-loaded catalyst and absolute ethyl alcohol according to the weight part ratio of 1: 0.05:20, placing the materials in a microwave reaction kettle together, sealing the reaction kettle at the power of 180 and 280W, heating the reaction kettle for 8 min, and cooling the reaction kettle to room temperature after the reaction is finished, wherein the reaction temperature is 130 ℃;

s3: adding water into the reaction product, adjusting the pH value of the solution to be 2 by using hydrochloric acid, and filtering by using a 0.45-micrometer membrane after unreacted lignin is completely separated out;

s4: extracting the filtrate with ethyl acetate for 3 times, collecting extractive solution, removing solvent and unreacted liquefying agent with rotary evaporator, drying in oven at 50 deg.C until the yield of bio-oil reaches 76.1%.

Example 6

The embodiment provides a method for producing biofuel by efficiently converting lignin, which comprises the following steps:

s1: preparation of iron-supported catalyst: soaking granular activated carbon into a ferric sulfate solution with the mass fraction of 9%, placing the granular activated carbon in a constant-temperature oscillator for oscillation, filtering, drying, placing the dried granular activated carbon in an atmosphere protection furnace under the protection of nitrogen flow, heating to 630 ℃, keeping the temperature constant for 2.5 hours, keeping the temperature at the heating rate of 10 ℃/min, cooling to room temperature, cleaning and drying to obtain the iron-loaded catalyst;

s2: preparing bio-oil by catalytic degradation of lignin: putting lignin, an iron-loaded catalyst and absolute ethyl alcohol in a weight ratio of 1:0.04:20 in a microwave reaction kettle together, sealing the microwave reaction kettle at the power of 180 and 280W, heating the microwave reaction kettle for 9 min at the reaction temperature of 135 ℃, and cooling the microwave reaction kettle to room temperature after the reaction is finished;

s3: adding water into the reaction product, adjusting the pH value of the solution to be 2 by using hydrochloric acid, and filtering by using a 0.45-micrometer membrane after unreacted lignin is completely separated out;

s4: extracting the filtrate with ethyl acetate for 3 times, collecting extractive solution, removing solvent and unreacted liquefying agent with rotary evaporator, drying in oven at 52 deg.C until the yield of bio-oil reaches 75.3%.

Example 7

The embodiment provides a method for producing biofuel by efficiently converting lignin, which comprises the following steps:

s1: preparation of iron-supported catalyst: soaking granular activated carbon into a ferric sulfate solution with the mass fraction of 10%, placing the granular activated carbon into a constant-temperature oscillator for oscillation, filtering, drying, placing the dried granular activated carbon into an atmosphere protection furnace under the protection of nitrogen flow, heating to 660 ℃, keeping the constant temperature for 1.5 h, keeping the temperature at the heating rate of 10 ℃/min, cooling to room temperature, and then cleaning and drying to obtain the iron-loaded catalyst;

s2: preparing bio-oil by catalytic degradation of lignin: putting lignin, an iron-loaded catalyst and absolute ethyl alcohol in a weight ratio of 1: 0.05:20 in a microwave reaction kettle together, sealing the microwave reaction kettle at the power of 180 and 280W, heating the microwave reaction kettle for 10 min at the reaction temperature of 100 ℃, and cooling the microwave reaction kettle to room temperature after the reaction is finished;

s3: adding water into the reaction product, adjusting the pH value of the solution to be 2 by using hydrochloric acid, and filtering by using a 0.45-micrometer membrane after unreacted lignin is completely separated out;

s4: extracting the filtrate with ethyl acetate for 3 times, collecting extractive solution, removing solvent and unreacted liquefying agent with rotary evaporator, drying in oven set at 55 deg.C until the yield of bio-oil reaches 74.8%.

Example 8

The embodiment provides a method for producing biofuel by efficiently converting lignin, which comprises the following steps:

s1: preparation of iron-supported catalyst: soaking granular activated carbon into a ferric sulfate solution with the mass fraction of 9%, placing the granular activated carbon in a constant-temperature oscillator for oscillation, filtering, drying, placing the dried granular activated carbon in an atmosphere protection furnace under the protection of nitrogen flow, heating to 640 ℃, keeping the constant temperature for 2.5 hours, heating at the rate of 10 ℃/min, cooling to room temperature, and then cleaning and drying to obtain the iron-loaded catalyst;

s2: modification of lignin: mixing lignin and 30% acrylamide solution, adding ceric ammonium nitrate, wherein the mass ratio of the lignin to the acrylamide solution to the ceric ammonium nitrate is 1:7:0.03, stirring at 40 ℃ at the rotating speed of 200r/min for 4h, drying, and grinding to obtain modified lignin;

s3: preparing bio-oil by catalytic degradation of lignin: putting the modified lignin, the iron-loaded catalyst and the absolute ethyl alcohol together in a microwave reaction kettle at the weight ratio of 1: 0.05:20, sealing the microwave reaction kettle at the power of 180 and 280W, heating the microwave reaction kettle for 9 min at the reaction temperature of 140 ℃, and cooling the microwave reaction kettle to room temperature after the reaction is finished;

s4: adding water into the reaction product, adjusting the pH value of the solution to be 2 by using hydrochloric acid, and filtering by using a 0.45-micrometer membrane after unreacted lignin is completely separated out;

s5: extracting the filtrate with ethyl acetate for 3 times, collecting extractive solution, removing solvent and unreacted liquefying agent with rotary evaporator, drying in oven at 53 deg.C until the yield of bio-oil reaches 79.4%.

Comparative example 1

The comparative example provides a method for producing biofuel by efficiently converting lignin, which is different from the method in example 1 in that: in step S1, the activated carbon was not dried under the protection of nitrogen flow, and the yield of bio-oil reached 62.6%.

Comparative example 2

The comparative example provides a method for producing biofuel by efficiently converting lignin, which is different from the method in example 1 in that: the catalyst is active carbon, and the yield of the bio-oil reaches 53.3 percent.

Finally, the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting, and other modifications or equivalent substitutions made by the technical solutions of the present invention by those of ordinary skill in the art should be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.