CN118459321A

CN118459321A - Method for obtaining C6 monophenol by selectively hydrogenolyzing lignin

Info

Publication number: CN118459321A
Application number: CN202410653956.5A
Authority: CN
Inventors: 骆治成; 于世通
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2024-05-24
Filing date: 2024-05-24
Publication date: 2024-08-09

Abstract

The invention discloses a method for obtaining C6 monophenol by selectively hydrogenolyzing lignin, which uses hydrogen-containing functional groups of lignin as a hydrogen source for reductive depolymerization in an aqueous solvent system, and selectively converts lignin into C6 monophenol by a one-pot method. The invention takes hydroxyapatite as a carrier to load a certain amount of metal, then lignin, a catalyst and water are placed in a reactor together, nitrogen is used for flushing and sealing, after hydrogenolysis reaction is carried out for a certain time and temperature, ethyl acetate is added into the mixture after the reaction for three times to extract lignin monomers. Finally, C6 monophenols (phenol, guaiacol and 2, 6-dimethoxyphenol) can be obtained with a selectivity as high as 74.4%. The invention uses green solvent water and hydrogen-containing functional groups in lignin as a reaction hydrogen source, depolymerizes lignin to bulk chemicals C6 monophenol (phenol, guaiacol and 2, 6-dimethoxy phenol) by a one-pot method, and provides a new method for high-value utilization of lignin.

Description

Method for obtaining C6 monophenol by selectively hydrogenolyzing lignin

Technical Field

The invention belongs to the technical field of lignin catalytic depolymerization, relates to a lignin hydrogenolysis technology, and in particular relates to a method for obtaining C6 monophenol by selectively hydrogenolyzing lignin.

Background

Lignin consisting of methoxyphenylpropane C9 units is the most abundant renewable aromatic polymer on earth, with a content of about 15-30% of lignocellulose, with great potential for conversion to value-added chemicals and fuels. In industrial production, highly aggregated lignin is formed by a series of inert C-O bonds and C-C bonds (70% and 30%) linked, resulting in lignin with high heterogeneity and low reactivity. Although some techniques, such as oxidation, hydrogenolysis, photocatalysis and multi-step strategies, can depolymerize lignin to higher value low molecular weight monomers, these monomers are typically mixtures of alkyl side chains, such as aromatic acids, aldehydes, esters, and the like. However, there are few reports on the conversion of lignin to C6 phenolic monomers without alkyl side chains using a one-pot process.

Among the various methods of lignin depolymerization, reductive depolymerization can maximize the yield of phenolic monomers and simplify product complexity. However, the reductive depolymerization inevitably requires a large amount of hydrogen source such as hydrogen gas or a hydrogen donor solvent. The use of these hydrogen sources has various problems such as the production and transportation of hydrogen gas and the separation of the product after dehydrogenation of the hydrogen donor solvent. For example, patent CN 107473944 discloses that a high yield of monophenols can be obtained under milder conditions without the need for an external hydrogenation source, using small alcohols as solvents. Patent CN 104276930a also discloses a process for the preparation of phenolic compounds by direct hydrogenolysis using a hydrogen donor solvent (alcohol solvent of C ₁-C₂₀, alkane of C ₁-C₂₀). At present, in order to solve the problem of external hydrogenation sources, the limitation of the traditional hydrogen sources can be overcome by utilizing the hydrogen-containing functional groups of lignin as the hydrogen sources, so that the energy input is reduced, and the operation safety is improved. Document (ACS CATALYSIS,2020, 10, 24, 15197-15206) uses a Pt/NiAl ₂O₄ catalyst to implement a new self-reforming driven depolymerization and hydrogenolysis strategy from which 4-alkylphenol is produced using a hydrogen source inherent in lignin. However, this method has the disadvantage that the more inert C-C bonds cannot be broken. In order to achieve the directional cleavage of the C-C bonds to obtain finer bulk chemicals, literature (Chinese Journal of Catalysis,2018,39,9,1445-1452) uses zeolites in a fixed bed to break the C ₁-C_α bond of lignin 4-alkylphenol (C9) monomers under high temperature conditions, selectively yielding C6 phenolic monomers.

Disclosure of Invention

The existing autorotation hydrogenolysis technology mostly realizes the breaking of C-O bonds, but cannot break the C-C bonds with stronger inertia. In order to achieve cleavage of the c—c bond, a multi-step depolymerization strategy is required at high temperature and pressure, which is cumbersome and requires more energy to be consumed. Aiming at the defects of the prior art, the invention provides a method for obtaining C6 monophenol by selectively hydrogenolyzing lignin, which uses water as a green solvent from lignin, automatically and selectively breaks C _β -O bonds and C ₁-C_α bonds by hydrogenolyzing, and obtains C6 phenol monomers by a one-pot method, wherein the C6 phenol monomers mainly comprise phenol, guaiacol and 2, 6-dimethoxy phenol; the technology of the invention has no problems of environmental pollution and difficult recovery of organic solvents, and the selectivity of the obtained C6 phenol monomer is higher, thus greatly improving the use value of lignin as a raw material.

In order to solve the technical problems, the invention adopts the following technical scheme:

the invention provides a method for obtaining C6 monophenol by selectively hydrogenolyzing lignin, which comprises the following steps:

s1, mixing lignin and a catalyst according to a certain proportion and adding the mixture into a high-pressure reaction kettle;

s2, adding a certain amount of water into the high-pressure reaction kettle for mixing;

s3, repeatedly flushing the high-pressure reaction kettle for a plurality of times by using inert gas, and finally keeping the inert gas atmosphere;

s4, heating the high-pressure reaction kettle to the hydrogenolysis reaction temperature, and reacting for a period of time;

S5, after the reaction is finished, placing the high-pressure reaction kettle in an ice water bath for cooling;

s6, after cooling is completed, the reaction products are all collected, and then the reaction products rich in C6 monophenols are obtained through extraction by an extracting agent.

The hydrogenolysis process of the invention is as follows:

The most abundant C _β -O bond in lignin uses its own hydroxyl hydrogen of C _α -OH as hydrogen source, and the self-rotation hydrogenolyzes the C _β -O bond to form common lignin monomer. Under the action of water as a strong polar solvent, the formed lignin monomer breaks down at C ₁-C_α in the monomer to form a C6 phenol monomer, and a few small dehydrogenation products are formed.

Preferably, in step S1, lignin used is produced as enzymatic lignin from the biological sciences company of shandong.

Preferably, in step S1, the catalyst is a metal-based alkaline carrier catalyst, the metal of the metal-based alkaline carrier catalyst includes a non-noble metal and a noble metal, and the alkaline carrier of the metal-based alkaline carrier catalyst includes one or more of hydroxyapatite, silica, hydrotalcite, magnesium oxide, metal oxide and metal nitride carrier.

Further preferably, in step S1, the catalyst is a metal-based alkaline supported catalyst using hydroxyapatite as a support.

Further preferably, the metal-based alkaline carrier catalyst uses hydroxyapatite as a carrier, and the carried metal elements are nickel and magnesium, wherein the nickel loading is 0.5-10wt.% and the magnesium loading is 0.2-1wt.%.

Further preferably, the non-noble metal comprises any one or a combination of several of nickel, iron, copper, cobalt and magnesium; the noble metal comprises any one or two of ruthenium, palladium and platinum.

Further preferably, in step S1, the metal-based basic supported catalyst has a metal loading of 0.5 to 10wt.%.

Preferably, in step S1, the catalyst is added in an amount of 10% -60% by mass, and most preferably 50% by mass of lignin.

Preferably, in step S2, the mass ratio of the added water to the added lignin is between 10 and 100:1, most preferably 25:1.

Preferably, in step S3, the inert gas is one or more of nitrogen, argon and helium.

Preferably, in step S3, the autoclave is repeatedly flushed 3-8 times, most preferably 5 times, with an inert gas.

In the step S3, after the high-pressure reaction kettle is repeatedly flushed by inert gas, the pressure in the high-pressure reaction kettle is maintained to be 0.1-0.5MPa by the inert gas.

Preferably, in step S4, the hydrogenolysis reaction temperature is 200-330 ℃.

Further preferably, in step S4, the hydrogenolysis reaction temperature is 230 to 300 ℃.

Further preferably, in step S4, the hydrogenolysis reaction temperature is 240 to 270 ℃.

Further preferably, in step S4, the hydrogenolysis reaction time is 1 to 6 hours.

Further preferably, in step S4, the hydrogenolysis reaction time is 2 to 5 hours.

Preferably, in step S6, the extractant is ethyl acetate or dichloromethane.

Preferably, in step S6, the extraction method is as follows:

Collecting all reaction products in the high-pressure reaction kettle, adding an extracting agent into the reaction products, and collecting supernatant, wherein the supernatant is the reaction product rich in C6 monophenols.

Centrifuging the extracted lower layer substance to separate a mixture composed of the catalyst and unreacted lignin residues, washing the mixture with tetrahydrofuran to remove unreacted lignin to obtain a recovered catalyst, repeatedly washing the recovered catalyst with distilled water and ethanol to further remove residual lignin, and drying for recycling.

Further preferably, in step S6, the extractant is added in several portions, such as 3 portions, during the extraction process to provide the extraction effect.

The invention also provides a preparation method of the metal-based alkaline carrier catalyst, which comprises the following steps:

s100, suspending and dispersing an alkaline carrier in deionized water or ethanol solution to obtain a carrier suspension;

S200, adding a metal source into the carrier suspension, and stirring while heating until deionized water is completely evaporated;

s300, drying the evaporated product, and grinding the dried product into powder to obtain a catalyst precursor;

and S400, placing the catalyst precursor in a tube furnace for calcination for a period of time, then introducing reducing gas and inert gas, carrying out reduction reaction for a period of time under the protection of the inert gas, and cooling to room temperature after the reaction is finished to obtain the metal-based alkaline carrier catalyst.

Preferably, the metal source is any one or a combination of a plurality of nickel nitrate hexahydrate, nickel chloride hexahydrate, copper nitrate trihydrate, ferric nitrate nonahydrate, cobalt nitrate hexahydrate, ruthenium trichloride hydrate, palladium nitrate hydrate, platinum chloride hydrate and magnesium nitrate hexahydrate.

Preferably, in step S200, the heating is performed in an oil bath while stirring, and the heating temperature is 70-95 ℃, and the temperature does not affect the catalyst activity and can quickly evaporate water.

Preferably, in step S300, the temperature of the product is 70-90 ℃ and the drying time is 4-12 hours; the catalyst activity is not affected at the temperature, and the catalyst can be dried quickly, and in actual operation, the catalyst is generally dried in an oven overnight.

Preferably, in step S400, the calcination temperature is 450-550 ℃ and the calcination time is 1-8 hours; the process can eliminate water, organic matters, oxide and other impurities in the catalyst, raise the heat stability and pressure resistance of the catalyst, raise the impregnation degree and dispersivity of metal nickel and raise the activity of the catalyst. Different calcination times and calcination temperatures will affect the pore structure of the catalyst and the dispersity of the active metal Ni.

Preferably, in step S400, the reducing reaction temperature of the hydrogen-argon mixture gas with the original gas being 5% by volume is 450-550 ℃ and the reaction time is 1-5 hours. The process can reduce the oxidized Ni after calcination into 0-valent Ni, different calcination temperatures and calcination time can influence the ratio of 0-valent nickel to +2-valent nickel, and the proper ratio can be obtained at the reduction reaction temperature and time, so that the selectivity of preparing C6 monophenol by hydrogenolysis lignin is improved by matching with solvent water during hydrogenolysis.

Compared with the corresponding technology, the invention has the following beneficial effects:

the method for preparing high-value bulk chemicals C6 monophenol (phenol, guaiacol and 2, 6-dimethoxy phenol) by lignin self-conversion hydrogenolysis directly takes hydrogen in lignin as a hydrogen source, does not need external hydrogen or hydrogen donor, and has low cost and low risk.

The invention retains methoxy functional groups in lignin and selectively breaks C _β -O and C ₁-C_α bonds. Compared with the traditional lignin conversion, the method greatly simplifies the complexity of the product and improves the added value of the product.

The invention uses green water as solvent under mild condition, and forms high-value bulk chemicals C6 monophenol (phenol, guaiacol and 2, 6-dimethoxy phenol) by a one-pot method. The operation process is simple, and the reaction process is environment-friendly.

Drawings

FIG. 1 is a schematic flow chart of a process for the selective hydrogenolysis of lignin to C6 monophenols according to the present invention.

FIG. 2 is a GC MS diagram of example 12 selective hydrogenolysis of lignin to produce a C6 monophenol product.

FIG. 3 is a mass spectrum of the principal products of selective hydrogenolysis of lignin to C6 monophenol products of example 12, (a) phenol, (b) guaiacol, and (C) 2, 6-dimethoxyphenol.

Detailed Description

Embodiments of the present invention are described in further detail below with reference to the accompanying drawings and examples. The following examples are illustrative of the invention but are not intended to limit the scope of the invention.

Example 1

The method for obtaining C6 monophenol by selectively hydrogenolyzing lignin comprises the following steps:

and (3) preparing a catalyst: firstly, 1.97g of HAP (hydroxyapatite) is weighed and dissolved in 30L of deionized water and stirred continuously to obtain a hydroxyapatite solution; taking nickel nitrate hexahydrate as a precursor, measuring 0.99mL of nickel nitrate hexahydrate Ni (NO ₃)₂·6H₂ O solution with the concentration of 0.1g/mL is dissolved in 30mL of deionized water and continuously stirred to obtain a nickel nitrate solution, slowly pouring the nickel nitrate solution into deionized water (hydroxyapatite solution) with HAP dissolved therein, magnetically stirring the mixed solution for 3 hours to obtain a uniform mixed solution, then placing the mixed solution into an oil bath pot, magnetically stirring at 70 ℃ until the deionized water is completely evaporated, placing the product obtained after evaporation into an oven at 80 ℃ for overnight, and grinding the completely dried catalyst into powder, finally placing the powder into a quartz boat, calcining the powder in a tubular furnace at 500 ℃ for 4 hours (heating rate of 2 ℃/min), reducing the calcined precursor in the tubular furnace at 500 ℃ for 3 hours in 5% H ₂/Ar, and obtaining the catalyst, namely the Ni _1％ HAP catalyst, wherein the corner mark 1% represents the loading amount of Ni (mass fraction) and the like.

Hydrogenolysis reaction: 100mg of enzymatically hydrolyzed lignin, 50mg of the Ni _1％ HAP catalyst prepared above, and 2.5mL of deionized water were weighed into a reactor. The reactor was repeatedly purged and filled 3 times with an inert gas at normal pressure. The reaction was carried out at 300℃for 4 hours, and after the completion of the reaction, the reactor was quenched in ice water. All the products are collected in a test tube, 6mL of ethyl acetate is added into the collected products for extraction in three times, and the supernatant is the reaction product rich in C6 monophenols.

Analysis of the C6 monophenol-rich reaction product: 1mL of the upper ethyl acetate solution was added with 1mg of internal standard dodecane, and qualitative and quantitative analysis was performed by GC MS using an RTX-VMS column (0.25 mm. Times.30 m,1.4 μm) with the apparatus first kept at 50℃for 2 minutes, then heated to 230℃at a heating rate of 5℃per minute, and finally kept at 230℃for 15 minutes. The extracted lower layer material is centrifuged to separate a mixture of the solid catalyst and the reactant residue, the mixture is washed with tetrahydrofuran, and the Ni _1％ HAP catalyst is separated and then dried overnight in a vacuum drying oven at 80 ℃ and used as a catalyst for subsequent cycle experiments.

Based on the analysis results of GC MS (FID), the total yield of all lignin monomers was calculated by an external standard method and an effective carbon number method and the selectivity of C6 monophenols was calculated therefrom. The calculated effective carbon number of phenol is 5.5, and the effective carbon number of guaiacol is 6.16,2,6 and the effective carbon number of dimethoxy phenol is 6.36. The specific calculation method using dodecane as an internal standard is as follows:

W_monomer＝n_monomer*Mw_monomer (3)

In these formulas:

W _{dodecaneinsample} (mg) mass of internal standard dodecane used in each sample;

Mw _dodecane (mg/mmol) relative molecular mass of dodecane;

n _dodecane (mmol) moles of dodecane in each sample;

n _monomer (mmol) moles of monomer in each sample;

A _{monomerinsample} peak areas corresponding to each monomer in the GC FID;

A _{dodecaneinsample}, the peak area corresponding to the internal standard dodecane in the GC FID;

ECN _dodecane effective carbon number of dodecane;

ECN _monomer effective carbon number of each monomer in the sample;

W _monomer (mg) mass of monomer in each sample;

Monomery yield (%) of all monomers in the sample;

SELECTIVITY (%) selectivity for each monomer in the sample.

The selectivity of phenol monomer under this condition was tested to be 33.4%, the selectivity of guaiacol monomer was 21.1%, the selectivity of 2, 6-dimethoxyphenol was 11.9%, and the selectivity of C6 monophenols (phenol, guaiacol and 2, 6-dimethoxyphenol) was as high as 66.4%.

Publication No. CN 107235829B discloses a process for the selective hydrogenolysis of lignin to 4-ethylphenol using 2MPa hydrogen with a tetraethylphenol selectivity of 37.2%. The publication No. CN 112479832A discloses a method for preparing tetraalkyl phenol by a one-pot method under the condition of no external hydrogen source, however, the invention realizes the cleavage of C ₁-C_α bond under the condition of no external hydrogen source, and the methoxy functional group in the monomer is reserved.

Examples 2 to 7

Based on example 1, the precursor nickel nitrate hexahydrate was replaced with copper nitrate trihydrate, ferric nitrate nonahydrate, cobalt nitrate hexahydrate, ruthenium trichloride hydrate, palladium nitrate hydrate, platinum chloride hydrate. The Cu _1％HAP,Fe_1％HAP,Co_1％HAP,Ru_1％HAP,Pd_1％HAP,Pt_1％ HAP catalyst is prepared. The same procedure as in example 1 was followed to obtain test results shown in Table 1.

TABLE 1 influence of catalysts loaded with different kinds of metals on the hydrogenolysis of lignin to C6 monophenols

According to Table 1, the use of different metal catalysts has little effect on the selectivity to C6 monophenols, and the use of noble metal palladium, platinum, results in a slight increase in the selectivity to C6 monophenols. The effect of adding metal promoters on C6 monophenol selectivity was later explored using Ni _1％ HAP catalysts.

Examples 8 to 10

Based on example 1, a certain amount of magnesium nitrate hexahydrate was added as a promoter to the Ni _1％ HAP catalyst during the catalyst preparation. The Ni _1％Mg_0.3％HAP,Ni_1％Mg_0.5％HAP,Ni_1％Mg_0.7％ HAP catalyst is prepared. The same procedure as in example 1 was followed, and the test results obtained are shown in Table 2.

TABLE 2 influence of Mg Metal doping of different masses in Ni _1％ HAP on lignin hydrogenolysis to C6 monophenols

According to Table 2, the effect of reaction time, reaction temperature on C6 monophenol selectivity was investigated using Ni _1％Mg_0.3％ HAP catalyst, with Ni _1％Mg_0.3％ HAP being the best for C6 monophenol selectivity, when magnesium metal was added as a promoter to Ni _1％ HAP catalyst.

Examples 11 to 14

The same procedure as in example 1 was followed using Ni _1％Mg_0.3％ HAP catalyst at a reaction time of 4 hours to change the hydrogenolysis temperature of lignin to 240 ℃,270 ℃,330 ℃,360 ℃ on the basis of example 8, and the test results are shown in Table 3.

TABLE 3 influence of different reaction temperatures on the hydrogenolysis of lignin to C6 monophenols

According to Table 3, increasing the temperature gradually increased the selectivity to phenol and gradually decreased the selectivity to guaiacol and 2, 6-dimethoxyphenol, while maintaining the methoxy group in the monomer and maximizing the selectivity to C6 monophenol, the reaction temperature of 270℃corresponding to example 12 can maximize the selectivity to C6 monophenol to 74.4%, but after the temperature exceeded 330℃the selectivity to 2, 6-dimethoxyphenol decreased dramatically. The GC MS of example 12 is shown in FIG. 2; the mass spectrum of phenol, guaiacol, and 2, 6-dimethoxy phenol is shown in figure 3.

Examples 15 to 18

The same procedure as in example 1 was followed by the reaction temperature of 270℃and the hydrogenolysis time of lignin was changed to 1,2,8 and 12 hours using Ni _1％Mg_0.3％ HAP catalyst, based on example 12, and the test results are shown in Table 4.

TABLE 4 influence of different reaction times on the hydrogenolysis of lignin to C6 monophenols

According to Table 4, the reaction time was prolonged at a reaction temperature of 270 ℃. When the lignin depolymerization time exceeds two hours, the continued extension time has little effect on the selectivity of the product C6 monophenol, and by comparison with example 12, the reaction time of 4 hours gives the highest selectivity (74.4%) of C6 monophenol.

Examples 19 to 21

Based on example 1, the amount of precursor nickel nitrate hexahydrate was varied to vary the loading of metallic nickel on hydroxyapatite, the loading of synthetic nickel was 0.5,5, 10wt.% of catalyst, the reaction temperature was 270 ℃, the reaction time was 4 hours, the remaining operation steps were the same as in example 1, and the test results obtained are shown in table 5.

TABLE 5 influence of different metal loadings on lignin hydrogenolysis to C6 monophenols

According to Table 5, the loading of metallic nickel was increased, the metallic nickel was used as an active site, the active site was increased, the activity of the catalyst was improved, the ability to remove methoxy groups was enhanced, and the selectivity of phenol was increased.

Comparative examples 1 to 2

To demonstrate the necessity of the catalyst in the present invention, the present invention was carried out without adding a catalyst and with adding only hydroxyapatite as a carrier as a catalyst, and the specific embodiment was the same as example 1 at a reaction temperature of 270℃for a reaction time of 4 hours, and the test results are shown in Table 6.

TABLE 6 influence of non-catalytic and addition of Supported hydroxyapatite as catalyst on lignin hydrogenolysis to C6 monophenols

According to Table 6, the selectivity to C6 monophenols was not greatly affected by the absence of catalyst and the addition of only hydroxyapatite as catalyst, but under non-catalytic conditions the yield of C6 monophenols was only 26%, whereas when only hydroxyapatite was used as catalyst, the yield of C6 monophenols was only 28.5%, which is far less than the yield of C6 monomers in example 12. In addition, the aqueous solvent from which it can be derived is critical to directly influence the selectivity of the C6 monophenols.

Comparative example 3

Based on example 12, the solvent water was replaced with isopropanol and Ni _1％Mg_0.3％ HAP was used as a catalyst at a reaction temperature of 270℃for 12 hours. After the completion of the reaction, all the materials in the reaction vessel were taken out, and the solid materials at the separation site were filtered, and the catalyst was separated out in the same manner as in example 1. Then, 1mg of dodecane was directly added to the obtained liquid as an internal standard, and the other procedures were the same as in example 1, except that the selectivity of the obtained monophenol was as shown in Table 7.

TABLE 7 Effect of isopropanol as solvent on lignin hydrogenolysis to C6 monophenols

According to Table 7, the selectivity for C6 monophenols was reduced to 23.2% and the selectivity for C8 monophenols (tetraethylphenol and tetraethylguaiacol) was as high as 49.3% using isopropanol as solvent, so the strong polar action of water was critical for the cleavage selectivity of the C ₁-C_α bond to C6 monophenols.

The above embodiments are only for illustrating the present invention, and are not limiting of the present invention. While the invention has been described in detail with reference to the embodiments, those skilled in the art will appreciate that various combinations, modifications, and substitutions can be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A process for the selective hydrogenolysis of lignin to C6 monophenols comprising the steps of:

mixing lignin and a catalyst in a certain proportion and adding the mixture into a high-pressure reaction kettle;

Adding a certain amount of water into a high-pressure reaction kettle for mixing;

repeatedly flushing the high-pressure reaction kettle for a plurality of times by using inert gas, and finally keeping the inert gas atmosphere;

heating the high-pressure reaction kettle to hydrogenolysis reaction temperature, and reacting for a period of time;

After the reaction is finished, the high-pressure reaction kettle is placed in an ice water bath for cooling;

after cooling, the reaction product was collected in its entirety and then extracted by an extractant to obtain a reaction product enriched in C6 monophenols.

2. The method for selective hydrogenolysis of lignin to C6 monophenols according to claim 1, wherein the catalyst is a metal-based basic supported catalyst, the metal of the metal-based basic supported catalyst comprises a non-noble metal and a noble metal, and the basic support of the metal-based basic supported catalyst comprises one or more of hydroxyapatite, silica, hydrotalcite, magnesia, metal oxide and metal nitride supports.

3. The method for obtaining C6 monophenols by selective hydrogenolysis of lignin according to claim 2, wherein said non noble metals comprise any one or a combination of several of nickel, iron, copper, cobalt and magnesium; the noble metal comprises any one or two of ruthenium, palladium and platinum.

4. The method for obtaining C6 monophenols by selective hydrogenolysis of lignin according to claim 2, wherein the loading of metal in said metal-based basic supported catalyst is between 0.5 and 10wt.%.

5. The method for obtaining C6 monophenols by selectively hydrogenolysis of lignin according to claim 1, wherein the catalyst is added in an amount ranging from 10% to 60% by mass of lignin.

6. The method for obtaining C6 monophenols by selective hydrogenolysis of lignin according to claim 1, wherein the mass ratio of the added water to the added lignin is comprised between 10 and 100:1.

7. The method for selective hydrogenolysis of lignin to C6 monophenols according to claim 1, wherein said inert gas is one or more of nitrogen, argon, helium.

8. The method for obtaining C6 monophenols by selective hydrogenolysis of lignin according to claim 1, wherein after repeatedly flushing the autoclave with an inert gas, the pressure in the autoclave is maintained between 0.1 and 0.5MPa by the inert gas.

9. The method for selective hydrogenolysis of lignin to C6 monophenols according to claim 1, wherein the hydrogenolysis reaction temperature is 200-330 ℃; the reaction time is 1-6h.

10. The method for obtaining C6 monophenols by selective hydrogenolysis of lignin according to claim 1, wherein said extractant is ethyl acetate or methylene chloride.