CN108014782B

CN108014782B - Method for catalytic depolymerization of lignin

Info

Publication number: CN108014782B
Application number: CN201711347661.1A
Authority: CN
Inventors: 李文志; 晋乐乐; 王辉珍; 刘琪英; 马隆龙; 张琦; 韦翔骞
Original assignee: University of Science and Technology of China USTC
Current assignee: University of Science and Technology of China USTC
Priority date: 2017-12-15
Filing date: 2017-12-15
Publication date: 2020-04-17
Anticipated expiration: 2037-12-15
Also published as: CN108014782A

Abstract

The invention provides a method for catalytically depolymerizing lignin, which comprises the following steps: catalyzing and depolymerizing lignin by using a catalyst; the catalyst is a layered solid acid catalyst. The method adopts the layered solid acid catalyst to catalyze and depolymerize the lignin, the lignin conversion rate is high, the reaction is complete, the layered solid acid catalyst used in the reaction can be recycled, and the method can also obtain high yield of liquid fuel components. The catalyst and the depolymerization product of the invention are simple to separate and environment-friendly, and have important significance for establishing a sustainable energy system and protecting the ecological environment.

Description

Method for catalytic depolymerization of lignin

Technical Field

The invention relates to the technical field of biomass catalytic conversion, in particular to a method for catalytic depolymerization of lignin.

Background

Lignin is an amorphous natural high molecular compound with a three-dimensional network structure, is composed of phenylpropyl alkyl basic units, is mainly present in a wood tissue and is a main component for forming plants. Meanwhile, in lignocellulose, the content of lignin is about 15% to 25%, but the energy contained in the lignin occupies nearly 40%. Thus, with the diminishing fossil energy sources, lignin has received increasing attention.

The lignin is a natural aromatic high polymer with a three-dimensional network structure, and is mainly formed by connecting three basic units of coniferyl alcohol, sinapyl alcohol and p-hydroxycoumarin alcohol through carbon-carbon bonds and ether bonds, so that various high-added-value compounds can be obtained by depolymerizing the lignin.

Currently, the paper industry produces up to 5000 million tons of lignin annually, and the improper utilization of lignin from these waste streams has caused a great pollution to the environment. In recent years, many researchers have used various thermochemical methods such as hydrolysis, hydrogenolysis and pyrolysis to catalytically depolymerize lignin to produce high value-added compounds and liquid fuels, and various catalysts have been used for the catalytic depolymerization of lignin. However, the above method has the problems of harsh reaction conditions, low product yield and the like.

In recent years, liquid fuels prepared from lignin are rapidly developed, but the yield is low, the depolymerization conditions are harsh, the product is complex, and the separation and purification are difficult, so that the industrialization is difficult.

Disclosure of Invention

In view of the above, the technical problem to be solved by the present invention is to provide a method for catalytic depolymerization of lignin, which has a high conversion rate.

In order to solve the technical problems, the invention provides a method for catalytically depolymerizing lignin, which comprises the following steps:

catalyzing and depolymerizing lignin by using a catalyst;

the catalyst is a layered solid acid catalyst.

The invention takes the biomass-based lignin as the substrate, avoids using fossil-based products, not only effectively realizes the effective utilization of resources, but also reduces the environmental problem, and is green and sustainable. The source of the lignin is not particularly limited in the present invention, and can be obtained by methods well known to those skilled in the art, such as papermaking lignin, corncob hydrolysis lignin, diluted acid hydrolysis lignin from eucalyptus, organosolv lignin from pine, organosolv lignin from apricot shells, and the like.

The layered solid acid catalyst adopted by the invention has the advantages of high thermal stability, good reusability and the like, the specific layered structure of the layered catalyst can ensure that the macromolecules, namely lignin, can be fully contacted with the catalyst, and the B acid distributed among layers can promote the depolymerization of the lignin, thereby improving the conversion rate of the reaction. Meanwhile, the method is simple to separate from the product and is environment-friendly.

In particular, the lignin is catalytically depolymerized in a solvent by adopting a catalyst.

The layered solid acid catalyst is a metal oxide after proton exchange, specifically HTaMoO₆，HNbMoO₆，HTaWO₆，HNbWO₆And HTiNbO₅Any one or more of them.

The method for preparing the layered solid acid catalyst of the present invention is not particularly limited, and may be a method known to those skilled in the art.

Preferably prepared according to the following method:

according to the molecular formula, more than one, preferably two of tantalum source, niobium source, tungsten source, molybdenum source and titanium source are mixed with lithium source, ground uniformly, calcined, acid-exchanged by protonic acid, filtered and dried to obtain the layered solid acid catalyst.

The present invention does not limit the particular manner of calcination, and methods known to those skilled in the art may be used. The calcination temperature is preferably 300-1000 ℃; more preferably 550-900 ℃; most preferably 580 to 900 ℃. The calcination time is preferably 5-80 h; more preferably 20-72 h; the most preferable time is 24-72 h.

The protonic acid is preferably any one or more of hydrochloric acid, nitric acid, sulfuric acid and phosphoric acid. The lithium ions between the catalyst layers are replaced by hydrogen ions by protonic acid. The concentration of the protonic acid is preferably 1-13 mol/L; more preferably 2 to 3 mol/L.

In certain embodiments of the present invention, the acid exchange further comprises: adding organic base to carry out dipping stripping.

The organic base is preferably tetrabutylammonium hydroxide.

In the present invention, the source of the protonic acid and the organic base is not limited, and the protonic acid and the organic base may be commercially available.

The present invention is not limited to the specific procedure for the impregnation, and those skilled in the art will be familiar with the operation. The soaking time is preferably 2h to 30 days; more preferably 1 to 28 days; most preferably 7-14 days; the dipping temperature is preferably 10-200 ℃, and more preferably 20-40 ℃.

Preferably, the impregnation is carried out under shaking conditions.

The specific operation mode of the oscillation is not limited in the present invention, and those skilled in the art can easily understand the operation mode.

The present invention is not limited to the specific procedures for the separation, and those skilled in the art will be familiar with the present invention. Centrifugation or suction filtration is preferred.

The present invention is not limited to the specific manner of the drying step after the separation of the solid, and those skilled in the art can easily understand this. The drying temperature is preferably 40-80 ℃, and more preferably 60-70 ℃; the drying time is preferably 6-24 h; more preferably 12-20 h; the most preferable time is 12-14 h.

The tantalum source is not limited in the present invention, but may be any compound known to those skilled in the art that can provide tantalum atoms; preferably tantalum pentoxide;

the niobium source is not limited in the present invention, and any compound known to those skilled in the art to provide a niobium atom may be used; preferably niobium pentoxide;

the tungsten source is not limited in the present invention, and any compound known to those skilled in the art that can provide a tungsten atom may be used; preferably tungsten trioxide;

the molybdenum source is not limited in the present invention, but compounds known to those skilled in the art to provide molybdenum atoms; preferably molybdenum trioxide;

the titanium source is not limited in the present invention, but a compound known to those skilled in the art to provide a titanium atom may be used; preferably an oxide of titanium such as titanium oxide and the like;

the lithium source is not limited in the present invention, and any compound known to those skilled in the art to provide a lithium atom may be used; lithium salts, such as lithium carbonate, are preferred.

In certain embodiments of the present invention, a layered solid acid catalyst is prepared using one of a tantalum source or a niobium source, and one of a tungsten source or a molybdenum source, in combination with a lithium source. The ratio of the three is preferably 1: (1-1.2).

The layered solid acid catalyst prepared by the method has good depolymerization effect on lignin, the separation of the catalyst and a product is simple, the hydrothermal stability of the catalyst is good, and the catalyst still has high activity at 320 ℃.

Preferably, the catalyst further comprises a carbon-supported metal catalyst.

The invention adopts a method of using a layered solid acid catalyst and a carbon-supported metal catalyst in a composite way to catalyze and depolymerize lignin, thereby improving the conversion rate of the reaction and the yield of petroleum ether extract.

The metal in the carbon-supported metal catalyst is preferably one or more of gold, silver and a platinum group metal. The platinum group metal is preferably one or more of rhodium, ruthenium, iridium, palladium, nickel and platinum.

More preferably, the carbon-supported metal catalyst is any one or more of palladium carbon, rhodium carbon, ruthenium carbon and platinum carbon.

The mass ratio of the layered solid acid catalyst to the carbon-supported metal catalyst is preferably (1-10): (1-10), more preferably (1-7): (1-7), preferably (1-5): (1-5), most preferably (1-3): (1-3).

In the invention, the mass ratio of the lignin to the catalyst is preferably (1-100): 1.

preferably, the solvent for catalytic depolymerization is a mixed solvent of dioxane and water. The volume ratio of the dioxane to the water is preferably (1-20): 1, more preferably (2-10): 1, and preferably (5-9): 1.

the temperature of the catalytic depolymerization is preferably 200-320 ℃, the pressure of the depolymerization is preferably 1-8 MPa, and the time of the depolymerization is preferably 1-24 h, more preferably 2-24 h, and still more preferably 6-24 h.

The heating rate of the reaction is preferably 1-10 ℃/min.

The reaction vessel used in the present invention is not limited, and those skilled in the art will be familiar with it; may be an autoclave. Hydrogen is preferably charged in the reaction and sealed.

After the depolymerization reaction is completed, the system is preferably cooled, and the cooling is preferably performed to room temperature. The cooling method of the present invention is not limited.

After cooling, the reaction solution was collected, the catalyst and the residue were separated, and filtered to obtain a filtrate which was determined to be an aromatic compound by gas phase measurement.

The aromatic compound comprises common monomers such as guaiacol, 4-ethylphenol, 4-methyl guaiacol, 4-ethyl guaiacol, 4-propyl guaiacol, vanillin, vanillyl alcohol, vanillone, homovanillic acid and the like.

After the reaction, the filtrate can be divided into two equal parts, after the two parts are respectively concentrated, one part is extracted by ethyl acetate to obtain an ethyl acetate extract; the other part is dissolved by acetone and then extracted by petroleum ether to be a small molecular component. The concentration is preferably performed by rotary evaporation.

The invention can realize the complete conversion of lignin, solves the problem of incomplete conversion in the previous lignin depolymerization process, and most of lignin can be depolymerized into monomers and dimers to be used as liquid fuel components, thereby being green and renewable.

Compared with the prior art, the invention provides a method for catalytic depolymerization of lignin, which comprises the following steps: catalyzing and depolymerizing lignin by using a catalyst; the catalyst is a layered solid acid catalyst. The method adopts the layered solid acid catalyst to catalyze and depolymerize the lignin, the lignin conversion rate is high, the reaction is complete, the layered solid acid catalyst used in the reaction can be recycled, and the method can also obtain high yield of liquid fuel components. The catalyst and the depolymerization product of the invention are simple to separate and environment-friendly, and have important significance for establishing a sustainable energy system and protecting the ecological environment.

Detailed Description

To further illustrate the present invention, the method of catalytic depolymerization of lignin provided by the present invention is described in detail below with reference to examples.

Example 1

A certain amount of tantalum oxide, molybdenum oxide and lithium carbonate are put into a mortar to be fully and uniformly ground, and then the ground material is put into a porcelain boatCalcining at 600 ℃ for 24 hours, wherein the molar ratio of tantalum oxide, molybdenum oxide and lithium carbonate is 1: 2: 2. putting the calcined catalyst into 1mol/L nitric acid solution, shaking and dipping, shaking gently at normal temperature for 2 weeks, replacing lithium ions between catalyst layers with hydrogen ions, centrifuging, washing the catalyst with deionized water, drying in a 70 ℃ oven, and grinding to obtain light yellow powdery layered catalyst HTaMoO₆Then the catalyst preparation is complete.

Example 2

Putting a certain amount of niobium oxide, molybdenum oxide and lithium carbonate into a mortar, fully and uniformly grinding, then putting into a porcelain boat, calcining for 24 hours at 580 ℃, wherein the molar ratio of niobium oxide to molybdenum oxide to lithium carbonate is 1: 2: 2. putting the calcined catalyst into 1mol/L nitric acid solution, shaking and dipping, shaking gently at normal temperature for 2 weeks, replacing lithium ions between catalyst layers with hydrogen ions, centrifuging, washing the catalyst with deionized water, drying in a 70 ℃ oven, and grinding to obtain a light yellow powdery layered catalyst HNbMoO₆Then the catalyst preparation is complete.

Example 3

Taking a certain amount of tantalum oxide, tungsten oxide and lithium carbonate, placing the tantalum oxide, the tungsten oxide and the lithium carbonate in a mortar, fully and uniformly grinding the tantalum oxide, the tungsten oxide and the lithium carbonate, then placing the tantalum oxide and the lithium carbonate in a porcelain boat, calcining the tantalum oxide and the tungsten oxide for 24 hours at 900 ℃, wherein the molar ratio of the tantalum oxide to the lithium carbonate is 1.1: 2: 2. putting the calcined catalyst into 1mol/L nitric acid solution, shaking and dipping, shaking gently at normal temperature for 2 weeks, replacing lithium ions between catalyst layers with hydrogen ions, centrifuging, washing the catalyst with deionized water, drying in a 70 ℃ oven, and grinding to obtain light yellow powdery layered catalyst HTaWO₆Then the catalyst preparation is complete.

Example 4

Putting a certain amount of niobium oxide, tungsten oxide and lithium carbonate into a mortar, fully and uniformly grinding, then putting into a porcelain boat, calcining at 760 ℃ for 72h, wherein the molar ratio of niobium oxide to tungsten oxide to lithium carbonate is 1: 2: 2. putting the calcined catalyst into 1mol/L nitric acid solution, shaking and dipping, shaking gently at normal temperature for 2 weeks, replacing lithium ions between catalyst layers with hydrogen ions, centrifuging, washing with deionized waterDrying the catalyst in an oven at 70 ℃, and grinding to obtain a light yellow powdery layered catalyst HTaWO₆Then the catalyst preparation is complete.

Example 5

Taking a certain amount of HTaMoO₆Placing in purified water, adding a certain amount of tetrabutylammonium hydroxide, gently shaking at normal temperature for 2 weeks for dipping and stripping, adding 0.1mol/L nitric acid solution to precipitate stripped nanosheets, centrifuging, washing with deionized water to remove catalyst, drying in an oven at 70 deg.C, and grinding to obtain HTaMoO₆And (4) nanosheet, completing the preparation of the catalyst.

Example 6

0.4g of lignin was dissolved in a dioxane solution-water (volume ratio of dioxane solution to water is 9:1) mixed solution, and the solution was placed in a 50ml autoclave. Simultaneously, 0.1g of the layered solid acid catalyst prepared in the above example 1 and 0.1g of the purchased rhodium carbon catalyst were placed in a reaction vessel, and hydrogen gas of 2Mpa was introduced after sealing; the stirring rate was adjusted to 600 rmp. Heating the reaction kettle to 290 ℃ at the heating rate of 5 ℃/min, reacting for 2h, and cooling to room temperature after the reaction is finished. Collecting the solution after reaction; the catalyst is filtered and separated and recycled, and meanwhile, filtrate is obtained.

Adding standard substance, removing water from the micro-filtrate, and detecting the content of aromatic compounds by GC. The detection conditions are as follows: SHIMADZU GC-2010, Agilent HP-5 capillary column, FID as detector, 50 deg.C maintaining for 3min, heating to 280 deg.C at 10 deg.C/min and maintaining for 10min, and nitrogen as carrier gas.

Dividing the filtrate into two equal parts, respectively concentrating, and extracting one part with ethyl acetate to obtain ethyl acetate extract; the other part is dissolved by acetone and then extracted by petroleum ether to be a small molecular component. The results showed that the yield of aromatic compound was 7.3% and the yield of petroleum ether extract was 26.0% under the experimental conditions.

Example 7

0.4g of lignin was dissolved in a dioxane solution-water (volume ratio of dioxane solution to water is 9:1) mixed solution, and the solution was placed in a 50ml autoclave. Simultaneously, 0.1g of the layered solid acid catalyst prepared in the above example 2 and 0.1g of the purchased rhodium carbon catalyst were placed in a reaction vessel, and hydrogen gas of 2Mpa was introduced after sealing; the stirring rate was adjusted to 600 rmp. Heating the reaction kettle to 290 ℃ at the heating rate of 5 ℃/min, reacting for 2h, and cooling to room temperature after the reaction is finished. Collecting the solution after reaction; the catalyst is filtered and separated and recycled, and meanwhile, filtrate is obtained.

Dividing the filtrate into two equal parts, respectively concentrating, and extracting one part with ethyl acetate to obtain ethyl acetate extract; the other part is dissolved by acetone and then extracted by petroleum ether to be a small molecular component. The results showed that the yield of aromatic compound was 7.1% and the yield of petroleum ether extract was 22.7% under the experimental conditions.

Example 8

0.4g of lignin was dissolved in a dioxane solution-water (volume ratio of dioxane solution to water is 9:1) mixed solution, and the solution was placed in a 50ml autoclave. Simultaneously, 0.1g of the layered solid acid catalyst prepared in the above example 3 and 0.1g of the purchased rhodium carbon catalyst were placed in a reaction vessel, and hydrogen gas of 2Mpa was introduced after sealing; the stirring rate was adjusted to 600 rmp. Heating the reaction kettle to 290 ℃ at the heating rate of 5 ℃/min, reacting for 2h, and cooling to room temperature after the reaction is finished. Collecting the solution after reaction; the catalyst is filtered and separated and recycled, and meanwhile, filtrate is obtained.

Dividing the filtrate into two equal parts, respectively concentrating, and extracting one part with ethyl acetate to obtain ethyl acetate extract; the other part is dissolved by acetone and then extracted by petroleum ether to be a small molecular component. The results showed that the yield of aromatic compound was 6.4% and the yield of petroleum ether extract was 21.9% under the experimental conditions.

Example 9

0.4g of lignin was dissolved in a dioxane solution-water (volume ratio of dioxane solution to water is 9:1) mixed solution, and the solution was placed in a 50ml autoclave. Simultaneously, 0.1g of the layered solid acid catalyst prepared in the above example 4 and 0.1g of the purchased rhodium carbon catalyst were placed in a reaction vessel, and hydrogen gas of 2Mpa was introduced after sealing; the stirring rate was adjusted to 600 rmp. Heating the reaction kettle to 290 ℃ at the heating rate of 5 ℃/min, reacting for 2h, and cooling to room temperature after the reaction is finished. Collecting the solution after reaction; the catalyst is filtered and separated and recycled, and meanwhile, filtrate is obtained.

Dividing the filtrate into two equal parts, respectively concentrating, and extracting one part with ethyl acetate to obtain ethyl acetate extract; the other part is dissolved by acetone and then extracted by petroleum ether to be a small molecular component. The results showed that the yield of aromatic compound was 6.0% and the yield of petroleum ether extract was 19.6% under the experimental conditions.

Example 10

0.4g of lignin was dissolved in a dioxane solution-water (volume ratio of dioxane solution to water is 9:1) mixed solution, and the solution was placed in a 50ml autoclave. Simultaneously, 0.1g of the layered solid acid catalyst prepared in the above example 5 and 0.1g of the purchased rhodium carbon catalyst were placed in a reaction vessel, and hydrogen gas of 2Mpa was introduced after sealing; the stirring rate was adjusted to 600 rmp. Heating the reaction kettle to 290 ℃ at the heating rate of 5 ℃/min, reacting for 2h, and cooling to room temperature after the reaction is finished. Collecting the solution after reaction; the catalyst is filtered and separated and recycled, and meanwhile, filtrate is obtained.

Dividing the filtrate into two equal parts, respectively concentrating, and extracting one part with ethyl acetate to obtain ethyl acetate extract; the other part is dissolved by acetone and then extracted by petroleum ether to be a small molecular component. The results showed that the yield of aromatic compound was 6.2% and the yield of petroleum ether extract was 20.9% under the experimental conditions.

The results are shown in Table 1, and Table 1 shows the reaction conditions and results of examples 6 to 10 of the present invention.

TABLE 1 summary of the reaction conditions and results described in examples 6 to 10 of the present invention

The total depolymerization rate is an extraction rate of ethyl acetate, and represents a conversion rate of lignin.

The results of examples 6 to 10 show that the layered catalyst HTaMoO prepared in example 1 was obtained under otherwise unchanged conditions₆The depolymerization effect on lignin is better, and the yield of aromatic compounds and the yield of petroleum ether extract are highest.

Example 11

0.4g of lignin was dissolved in a dioxane solution-water (volume ratio of dioxane solution to water is 9:1) mixed solution, and the solution was placed in a 50ml autoclave. Simultaneously, 0.1g of the layered solid acid catalyst prepared in the above example 1 and 0.1g of the purchased ruthenium carbon catalyst were placed in a reaction vessel, sealed and charged with 2Mpa of hydrogen; the stirring rate was adjusted to 600 rmp. Heating the reaction kettle to 290 ℃ at the heating rate of 5 ℃/min, reacting for 2h, and cooling to room temperature after the reaction is finished. Collecting the solution after reaction; the catalyst is filtered and separated and recycled, and meanwhile, filtrate is obtained.

Dividing the filtrate into two equal parts, respectively concentrating, and extracting one part with ethyl acetate to obtain ethyl acetate extract; the other part is dissolved by acetone and then extracted by petroleum ether to be a small molecular component. The results showed that the yield of aromatic compound was 6.3% and the yield of petroleum ether extract was 22.7% under the experimental conditions.

Example 12

0.4g of lignin was dissolved in a dioxane solution-water (volume ratio of dioxane solution to water is 9:1) mixed solution, and the solution was placed in a 50ml autoclave. Simultaneously, 0.1g of the layered solid acid catalyst prepared in the above example 1 and 0.1g of the purchased platinum-carbon catalyst were placed in a reaction vessel, sealed and charged with 2MPa of hydrogen; the stirring rate was adjusted to 600 rmp. Heating the reaction kettle to 290 ℃ at the heating rate of 5 ℃/min, reacting for 2h, and cooling to room temperature after the reaction is finished. Collecting the solution after reaction; the catalyst is filtered and separated and recycled, and meanwhile, filtrate is obtained.

Dividing the filtrate into two equal parts, respectively concentrating, and extracting one part with ethyl acetate to obtain ethyl acetate extract; the other part is dissolved by acetone and then extracted by petroleum ether to be a small molecular component. The results showed that the yield of aromatic compound was 6.7% and the yield of petroleum ether extract was 18.9% under the experimental conditions.

Example 13

0.4g of lignin was dissolved in a dioxane solution-water (volume ratio of dioxane solution to water is 9:1) mixed solution, and the solution was placed in a 50ml autoclave. Simultaneously, 0.1g of the layered solid acid catalyst prepared in the above example 1 and 0.1g of the purchased palladium carbon catalyst were placed in a reaction vessel, sealed and charged with 2Mpa of hydrogen; the stirring rate was adjusted to 600 rmp. Heating the reaction kettle to 290 ℃ at the heating rate of 5 ℃/min, reacting for 2h, and cooling to room temperature after the reaction is finished. Collecting the solution after reaction; the catalyst is filtered and separated and recycled, and meanwhile, filtrate is obtained.

Dividing the filtrate into two equal parts, respectively concentrating, and extracting one part with ethyl acetate to obtain ethyl acetate extract; the other part is dissolved by acetone and then extracted by petroleum ether to be a small molecular component. The results showed that the yield of aromatic compound was 6.8% and the yield of petroleum ether extract was 17.4% under the experimental conditions.

The results are shown in Table 2, and Table 2 shows the reaction conditions and results of examples 6 and examples 11 to 13 of the present invention.

Table 2 reaction conditions and results of examples 9 and 13 to 15 of the present invention

The results in table 2 show that the yield of aromatics and the yield of petroleum ether extract obtained with the rhodium on carbon of the present invention are highest under the current conditions when the layered catalyst is unchanged and different hydrogenation catalysts are used.

Example 14

0.4g of lignin was dissolved in a dioxane solution-water (volume ratio of dioxane solution to water is 9:1) mixed solution, and the solution was placed in a 50ml autoclave. Simultaneously, 0.1g of the layered solid acid catalyst prepared in the above example 1 and 0.1g of the purchased rhodium carbon catalyst were placed in a reaction vessel, and hydrogen gas of 2Mpa was introduced after sealing; the stirring rate was adjusted to 600 rmp. Heating the reaction kettle to 250 ℃ at the heating rate of 5 ℃/min, reacting for 2h, and cooling to room temperature after the reaction is finished. Collecting the solution after reaction; the catalyst is filtered and separated and recycled, and meanwhile, filtrate is obtained.

Dividing the filtrate into two equal parts, respectively concentrating, and extracting one part with ethyl acetate to obtain ethyl acetate extract; the other part is dissolved by acetone and then extracted by petroleum ether to be a small molecular component. The results showed that the yield of aromatic compound was 5.1% and the yield of petroleum ether extract was 8.1% under the experimental conditions.

Examples 15 to 20

The specific reaction process and detection method were the same as in example 14, except that the reaction temperature was different from example 14, and the reaction temperatures were 260 ℃, 270 ℃, 280 ℃, 300 ℃, 310 ℃ and 320 ℃. The yields of aromatic compounds were determined to be 5.7%, 5.4%, 6.6%, 7.9%, 8.2%, 8.2%, and petroleum ether extract yields of 15.1%, 20.2%, 22.7%, 30.0%, 38.1%, and 41.0%, respectively.

The reaction conditions and results of example 6 and examples 14 to 20 are shown in Table 3, and Table 3 shows the reaction conditions and results of example 6 and examples 14 to 20 of the present invention:

TABLE 3 reaction conditions and results of examples 6 and 14 to 20 of the present invention

The results of example 6 and examples 14 to 20 show that the reaction proceeds more favorably with higher temperature without changing other conditions.

Examples 21 to 25

The specific reaction process and detection method were the same as in example 20 except that the reaction time was different from example 20, and the reaction time was 3 hours, 6 hours, 12 hours, 18 hours, and 24 hours, respectively, and the aromatic compound yields were determined to be 8.7%, 9.1%, 8.3%, 9.6%, and 10.4%, and the petroleum ether extract yields were determined to be 43.9%, 45.35%, 54.0%, 56.1%, and 58.7%, respectively. The reaction conditions and results of examples 20 and 21 to 25 are shown in Table 4, and Table 4 shows the reaction conditions and results of examples 20 and 21 to 25 of the present invention:

TABLE 4 reaction conditions and results of examples 20 and 21 to 25 of the present invention

The results in Table 4 show that when other conditions are not changed, the reaction proceeds with an advantage of extending the reaction time, and that the yield of the aromatic compound and the yield of the petroleum ether extract in the present invention are higher as the reaction time is longer.

The above examples show that the method of the invention adopts a specific catalyst to catalyze and depolymerize lignin, and has the advantages of high yield, simple operation and mild conditions.

The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.

Claims

1. A method for catalytic depolymerization of lignin, comprising the steps of:

catalyzing and depolymerizing lignin by using a catalyst; the temperature of the catalytic depolymerization is 260-320 ℃;

the catalyst consists of a layered solid acid catalyst and a carbon-supported metal catalyst;

the layered solid acid catalyst is HTaMoO₆，HNbMoO₆，HTaWO₆，HNbWO₆And HTiNbO₅Any one of the above;

the carbon-supported metal catalyst is any one of palladium carbon, rhodium carbon, ruthenium carbon and platinum carbon;

the solvent for catalytic depolymerization is a mixed solvent of dioxane and water.

2. The method according to claim 1, wherein the mass ratio of the layered solid acid catalyst to the carbon-supported metal catalyst is (1-10): (1-10).

3. The method of claim 1, wherein the catalytic depolymerization time is 1-24 hours and pressure is 1-8 MPa.

4. The method according to claim 1, wherein the mass ratio of the lignin to the catalyst is (1-100): 1.

5. the method according to claim 1, wherein the volume ratio of dioxane to water is (1-20): 1.