Method for preparing monocyclic and polycyclic aromatic hydrocarbons by directly hydrogenating and liquefying lignin in two steps

Abstract

The invention relates to a method for catalyzing two-step hydro-liquefaction conversion of lignin by adopting a MoS2-based catalyst. The method comprises the following steps: by adopting a heterogeneous MoS2-based catalyst, hydrogen as a reducing agent and tetrahydronaphthalene as a hydrogen-donating solvent, firstly breaking a C-O bond to catalyze the hydro-liquefaction conversion of the lignin under a mild reaction condition, and after the reaction is completed, breaking the C-C bond to catalyze the hydro-liquefaction conversion of the lignin hydro-liquefied oil under a harsh reaction condition by taking the obtained mixture as a raw material. According to the method, renewable lignin is used as a raw material, so that the method has sustainability; c-O bonds in the lignin are broken under a low-temperature condition, then C-C bonds of the lignin are broken under a high-temperature condition, and a high lignin depolymerization effect is achieved; the selected MoS2-based catalyst is good in catalytic effect and high in lignin conversion rate and oil yield, and monocyclic aromatic hydrocarbon and polycyclic aromatic hydrocarbon are contained in the MoS2-based catalyst. Compared with other lignin conversion methods, the method not only can produce monocyclic aromatic hydrocarbons, but also can produce a large amount of polycyclic aromatic hydrocarbons, and the oil is transparent reddish brown.

Description

Technical Field

[0001] The present invention relates to a method for preparing monocyclic and polycyclic aromatic hydrocarbons, and more particularly, to a method for directly hydrogenating and liquefying lignin in two steps to prepare monocyclic and polycyclic aromatic hydrocarbons. Technical Background

[0002] With the energy shortage and environmental problems caused by the large-scale use of fossil fuels such as coal and oil, people are actively seeking renewable green energy. Lignin is a biopolymer composed of aromatic structures connected by C-O and C-C bonds. It accounts for about 10-35% of biomass and contributes 40% of the total energy. As the second largest renewable biomass resource with high aromaticity, the annual output of lignin in nature is about 195-455 billion tons and is expected to become an important substitute for traditional fossil fuels. Among them, about 55 million tons come from papermaking, and about 75 million tons come from the bio-fermentation industry. However, currently only 1-2% of lignin is used to produce chemical products and biomaterials, and most of it is still used for power generation and heat production by combustion. Therefore, it is particularly important to develop methods for efficiently utilizing lignin.

[0003] As important organic chemical raw materials, it is of great significance to prepare monocyclic aromatic hydrocarbons (MAHs) and polycyclic aromatic hydrocarbons (PAHs) from lignin. Wang et al. (Wang Y, Hou Y, Wu W, Li H, Ren S, Li J. Polycyclic aromatics observed in enzymatic lignin by spectral characterization and ruthenium ion-catalyzed oxidation. Journal of Agricultural and Food Chemistry, 2021, 69: 12148 - 12155.) and Wei et al. (Wei J, Sun J, Hou Y, He Z, Li H, Ren S, Wu W. Characterization of fused aromatic multirings in lignin via synchronous fluorescence spectroscopy and catalytic hydro-depolymerization. Microchemical Journal, 2024, 205: 111412.) found that lignin is composed of MAHs and PAHs structures connected by C-O and C-C bonds. However, high yields of MAHs and PAHs cannot be obtained from lignin by methods such as pyrolysis, oxidative depolymerization, and direct hydroliquefaction. The products obtained by pyrolysis and oxidative depolymerization are mainly phenols, monocyclic aromatic hydrocarbons, aromatic aldehydes, and benzoic acids with low yields. This is mainly because the C-O bonds in lignin are broken under limited reaction conditions, while the C-C bonds in lignin are not completely broken. In addition to C-O bonds, C-C bonds account for about 33.3% in lignin. The cleavage of C-C bonds determines whether the MAHs and PAHs structures connected by them can be depolymerized from the lignin macromolecule. In addition, the carbon and oxygen free radicals generated by the cleavage of lignin bonds undergo secondary polymerization reactions under the reaction conditions, and inhibiting this secondary polymerization reaction is the key to its complete hydrodepolymerization into detectable small molecule compounds. The direct hydroliquefaction method of lignin requires a hydrogen-donating solvent, hydrogen (H2), and a catalyst. The hydrogen-donating solvent is used to disperse and dissolve lignin and its liquefaction products, provide active hydrogen, and promote the effective contact of lignin with the catalyst and H2. H2 or the hydrogen-donating solvent provides active hydrogen and is used to quench the carbon and oxygen free radicals generated by lignin cleavage. The catalyst is used to catalyze the hydrogen-donating solvent and H2 to generate active hydrogen and inhibit the polymerization reaction of the carbon and oxygen free radicals generated by lignin cleavage. Compared with the previous two methods, the direct hydroliquefaction of lignin mainly obtains hydrogenated deoxygenated product aromatics, which is a potential method to break C-O and C-C bonds at high temperature and inhibit the polymerization of free radicals.

[0004] However, through direct hydroliquefaction, lignin can only obtain a black lignin liquefied oil with a low yield of phenols and MAHs and a negligible yield of PAHs, and cannot obtain a transparent liquefied oil containing a high yield of MAHs and PAHs. In previous studies, although Wei et al. (Wei J, Sun J, Hou Y, Zhang W, Ren S, Wu W. Hydroliquefaction of lignin: Can it generate recycle solvents by itself? Fuel, 2024, 366: 131412.) determined the optimal reaction conditions for the complete hydroliquefaction of lignin by direct hydroliquefaction, the resulting black liquefied oil contained 9.6 wt% phenolic products, and it was impossible to determine whether the MAHs and PAHs in the products were derived from lignin or the hydrogen-donating solvent tetralin. This indicates that there are still a large number of macromolecular compounds that have not been completely depolymerized in the liquefied oil. This is mainly because the direct hydroliquefaction method of lignin reaches the condition of breaking the C-O bond (C al -O 150 - 230 kJ / mol, 361 °C) between the MAHs and PAHs structures in lignin, but does not reach the condition of breaking the C-C bond with strong bond energy (C al -C al 210 - 320 kJ / mol, breaking temperature 439 °C; C ar -C al 300 - 400 kJ / mol, breaking temperature 519 °C).

[0005] How to efficiently break the C-O and C-C bonds between the MAHs and PAHs structures in lignin is the key to completely depolymerizing lignin and obtaining a transparent liquefied oil containing high yields of MAHs and PAHs. Lignin is a brown solid powder. To come into contact with the catalyst and H2 under direct hydroliquefaction conditions, it first needs to be liquefied and then can be better depolymerized. Otherwise, even if the reaction temperature reaches the temperature for C-C bond cleavage, due to the large number of lignin cleavage free radicals being difficult to effectively quench in time and undergoing polymerization reactions, the lignin liquefied oil will eventually be black and produce a certain amount of coking. Therefore, it is expected to completely depolymerize lignin and prepare a transparent liquefied oil containing MAHs and PAHs (breaking C-C bonds) by first completely hydroliquefying lignin (breaking C-O bonds) through direct hydroliquefaction under mild reaction conditions and then continuing to hydroliquefy the lignin liquefied oil under harsh reaction conditions by increasing the reaction conditions. This method uses tetralin as a hydrogen-donating solvent to carry out two-step hydroliquefaction of lignin. On the one hand, it avoids the generation of coke by directly increasing the reaction conditions. On the other hand, by first breaking the C-O bonds to hydroliquefy lignin and then breaking the C-C bonds to hydrocrack the lignin liquefied oil, the polymerization reaction of unstable components is avoided. Based on this, this patent develops a method for two-step hydroliquefaction conversion of lignin, which can directly produce a transparent liquefied oil containing high yields of MAHs and PAHs from lignin. Summary of the Invention

[0006] The present invention relates to a method for catalytic two-step hydroliquefaction conversion of lignin using catalysts such as MoS2, 20% MoS2 / Al2O3, 20% MoS2 / AC, 5% Pd-15% MoS2 / Al2O3, 5% Pd-15% MoS2 / AC, 5% Ni-15% MoS2 / Al2O3 or 5% Ni-15% MoS2 / AC. This method first uses heterogeneous MoS2 and others as catalysts, hydrogen as a reducing agent, and tetralin as a hydrogen-donating solvent, controls the mass ratio of tetralin / lignin raw material, the mass ratio of catalyst / lignin raw material, the first-step reaction temperature and the initial hydrogen pressure, and catalytically converts lignin by hydroliquefaction under mild reaction conditions (i.e., breaking C-O bonds). After the reaction is completed, using the mixture obtained above as the raw material, control the second-step reaction temperature, and catalytically convert the lignin hydroliquefied oil by hydroliquefaction under harsh reaction conditions (i.e., breaking C-C bonds). This method uses renewable lignin as the raw material and has sustainability; the selected MoS2 catalyst has good catalytic effects, high lignin conversion rate, high oil yield and is transparent reddish-brown, and the oil contains monocyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons. Compared with other lignin conversion methods, this method can not only produce monocyclic aromatic hydrocarbons, but also produce a large amount of detectable polycyclic aromatic hydrocarbons, and the color of the oil is transparent reddish-brown.

[0007] The present invention provides a method for catalytic two-step hydroliquefaction conversion of lignin using catalysts such as MoS2, 20% MoS2 / Al2O3, 20% MoS2 / AC, 5% Pd-15% MoS2 / Al2O3, 5% Pd-15% MoS2 / AC, 5% Ni-15% MoS2 / Al2O3 or 5% Ni-15% MoS2 / AC. This method directly uses lignin as the raw material, H2 as the reducing agent, and MoS2 etc. as the catalyst, and through controlling the mass ratio of tetralin / lignin raw material, the mass ratio of catalyst / lignin raw material, the initial H2 pressure, the reaction temperature and the reaction time in the first step reaction, as well as the reaction temperature in the second step reaction conditions, catalytically converts lignin into MAHs and PAHs by two-step direct hydroliquefaction. This method is an efficient and renewable method for direct hydroliquefaction conversion of lignin to produce MAHs and PAHs.

[0008] To achieve the above object, the present invention adopts the following specific technical solutions:

[0009] A method for catalytic two-step hydrodepolymerization of lignin to prepare MAHs and PAHs, and the specific steps included in this method are as follows:

[0010] S1: Add the lignin raw material, the catalyst and the hydrogen-donating solvent tetralin into a high-pressure reactor, and seal the reactor;

[0011] S2: Remove the air in the reactor in step S1, then fill it with H2, and stir at a given reaction temperature for the first-step catalytic hydrogenation reaction;

[0012] S3: After reaching the reaction time in step S2, continue to raise the reaction temperature to the set value, stir at this temperature for the second-step catalytic hydrogenation reaction, and after reaching the reaction time, quickly cool the reactor to end the reaction;

[0013] S4: Release the gas in the reactor in step S3, open the reactor in step S3, take out the product in the reactor in step S3, and treat the solid-liquid mixture with tetralin to obtain oil (tetralin-soluble part) and residue (tetralin-insoluble part, including the catalyst).

[0014] In the above step S1, the catalyst is selected from MoS2, 20% MoS2 / Al2O3, 20% MoS2 / AC, 5% Pd-15% MoS2 / Al2O3, 5% Pd-15% MoS2 / AC, 5% Ni-15% MoS2 / Al2O3 or 5% Ni-15% MoS2 / AC.

[0015] In the above step S1, the mass ratio of the hydrogen-donating solvent tetralin to the lignin raw material is 2 - 5.

[0016] In the above step S1, the mass ratio of the catalyst to the lignin raw material is 0.1 - 1.

[0017] In the above step S2, the pressure of the charged H2 is 2 MPa - 8 MPa.

[0018] In the above step S2, the temperature of the first catalytic hydrogenation reaction is 310 °C - 370 °C.

[0019] In the above step S2, the time of the first catalytic hydrogenation reaction is 60 min - 120 min.

[0020] In the above step S3, the temperature of the second catalytic hydrogenation reaction is 400 °C - 460 °C.

[0021] In the above step S3, the time of the second catalytic hydrogenation reaction is 60 min - 120 min.

[0022] The principle of the two-step direct hydroliquefaction method of lignin in the present invention is as follows: First, lignin is uniformly mixed in a mild reaction system of tetralin, H2, and catalysts such as MoS2 and heated to break the C-O bond, forming free radicals. Then, these free radicals are hydrogenated by the H2 activated by the catalyst and the hydrogen of the hydrogen-donating solvent to form an oil containing low-yield small molecule compounds and a large number of macromolecule compounds that are undetectable by gas chromatography (GC) containing C-C bonds. Then, the above reaction system continues to be heated at a higher reaction temperature to break the C-C bond, forming carbon free radicals. Then, these carbon free radicals are hydrogenated by the H2 activated by the catalyst and the hydrogen of the hydrogen-donating solvent to form a transparent liquefied oil containing a high yield of MAHs and PAHs. Finally, lignin undergoes complete hydroliquefaction and depolymerization through two-step hydroliquefaction, and is converted into a transparent liquefied oil containing a high yield of MAHs and PAHs.

[0023] Compared with the hydroliquefaction of lignin in the literature, the method of the present invention has the following advantages: (1) First, break the C-O bond in lignin under low-temperature reaction conditions, and then break the C-C bond in lignin under high-temperature reaction conditions, effectively avoiding the polymerization reaction of a large number of carbon and oxygen free radicals generated during the cracking of lignin due to ineffective quenching to produce coke, ultimately resulting in incomplete depolymerization of lignin and low yield of depolymerization products; (2) The selected MoS2-based catalyst in the present invention has good catalytic effect, high lignin conversion rate and high oil yield, and the oil contains a large amount of MAHs and PAHs; (3) Using renewable biomass lignin as the raw material to prepare MAHs and PAHs belongs to the renewable aromatic hydrocarbon preparation technology. Specific Embodiments

[0024] The present invention is further illustrated by the following examples, but the protection scope of the present invention is not limited to the following examples.

[0025] The product of the two-step direct hydroliquefaction of lignin is processed as follows:

[0026] The solid-liquid mixture after the reaction is treated with a tetralin (THN) solvent. The tetralin-soluble part is defined as oil, and the tetralin-insoluble part is defined as residue. The conversion rate of lignin is: 100% - the mass percentage of the tetralin-insoluble part to lignin.

[0027] After the two-step direct hydroliquefaction reaction of lignin in the high-pressure reactor is completed, the gas is collected in an aluminum foil gas sampling bag, and combustible hydrocarbons and small molecule gases such as CO and CO2 in the gas product are determined by GC-FID and GC-TCD. The GC-FID used is produced by Agilent Technologies (model 7820A). The detector is a hydrogen flame ionization detector, the chromatographic column is a J&W GSBP capillary column, the inlet temperature is 200 °C, the column temperature is 80 °C, held for 20 min, and the detector temperature is 250 °C. The GC-TCD used is produced by Agilent Technologies (model 7890A). The detector is a thermal conductivity detector, the chromatographic column is a Supelco 6ft PQ + 6ft 13X packed column, the inlet temperature is 120 °C, the column oven is held at an initial temperature of 50 °C for 18 min, and the TCD detector temperature is 200 °C.

[0028] The solid-liquid mixture after the reaction is placed on a quantitative filter paper mounted on a glass funnel, and tetralin is used as an extraction solvent to wash the above solid-liquid mixture until the filtrate is colorless and transparent. The tetralin-soluble part and the tetralin-insoluble part are obtained. The tetralin-soluble part is made up to volume and sampled for GC and gas chromatography-mass spectrometry (GC-MS) analysis of the composition. The GC and GC-MS used are produced by Shimadzu Corporation of Japan (model GC-2014) and Agilent Technologies (7890B / 5977A), respectively. The detector is a hydrogen flame ionization detector or a mass spectrometry detector, the chromatographic column is an HP-5 capillary column, the inlet temperature is 280 °C, the initial temperature of the column oven is 45 °C, held for 3 min, then raised to 105 °C at 10 °C / min, then raised to 210 °C at 5 °C / min, and finally raised to 300 °C at 10 °C / min and held for 21 min.

[0029] Example 1

[0030] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm with a stirring paddle 3It is carried out in a high-temperature and high-pressure autoclave. 5 g of lignin, 0.5 g of MoS₂ catalyst and 10 g of tetralin are added to the autoclave. The autoclave is sealed, nitrogen (N₂) is introduced and purged three times to remove air from the system. Subsequently, N₂ with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N₂ is less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave is airtight. Then, H₂ is introduced and purged three times in sequence to remove the residual N₂ in the high-temperature and high-pressure autoclave. Finally, H₂ is added to maintain the reaction pressure at 2.0 MPa. The autoclave is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 310 °C, timing starts, and the reaction lasts for 120 min. After the reaction time is reached, the reaction temperature is raised to 400 °C and timing starts again. After reacting for 120 min, the autoclave is taken out and blown with a blower for cooling to terminate the reaction. After the autoclave cools down to room temperature, the sample is collected for analysis.

[0031] The analysis results show that: during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 64.3%, the oil yield is 28.8 wt%, the yield of GC-detectable products is 23.6 wt%, the yield of monocyclic aromatic hydrocarbon products is 5.5 wt%, the yield of polycyclic aromatic hydrocarbon products is 9.9 wt%, and the oxygen content in the oil (including THN) is 0.78%.

[0032] Example 2

[0033] The two-step direct hydroliquefaction experiment of lignin in this example is carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H₂ as the reducing agent. The two-step direct hydroliquefaction experiment of lignin is carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirring paddle. 5 g of lignin, 0.5 g of MoS₂ catalyst and 15 g of tetralin are added to the autoclave. The autoclave is sealed, N₂ is introduced and purged three times to remove air from the system. Subsequently, N₂ with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N₂ is less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave is airtight. Then, H₂ is introduced and purged three times in sequence to remove the residual N₂ in the high-temperature and high-pressure autoclave. Finally, H₂ is added to maintain the reaction pressure at 2.0 MPa. The autoclave is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 310 °C, timing starts, and the reaction lasts for 120 min. After the reaction time is reached, the reaction temperature is raised to 400 °C and timing starts again. After reacting for 120 min, the autoclave is taken out and blown with a blower for cooling to terminate the reaction. After the autoclave cools down to room temperature, the sample is collected for analysis.

[0034] The analysis results show that during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 62.5%, the oil yield is 26.5 wt%, the yield of GC-detectable products is 21.3 wt%, the yield of monocyclic aromatic hydrocarbon products is 5.3 wt%, the yield of polycyclic aromatic hydrocarbon products is 8.7 wt%, and the oxygen content in the oil (including THN) is 0.76%.

[0035] Example 3

[0036] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirrer. 5 g of lignin, 0.5 g of MoS2 catalyst, and 20 g of tetralin were added to the autoclave. The autoclave was sealed, and N2 was introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa was introduced for leak detection. After half an hour, the pressure change in N2 was less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave was airtight. Then, H2 was introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure autoclave. Finally, H2 was added to maintain the reaction pressure at 2.0 MPa. The autoclave was placed in a heating jacket for heating and the stirrer was turned on. When the reaction temperature reached 310 °C, timing started, and the reaction was carried out for 120 min. After the reaction time reached, the reaction temperature was raised to 400 °C and timing started again. After the reaction for 120 min, the autoclave was taken out and cooled by blowing with a blower to terminate the reaction. When the autoclave cooled to room temperature, the samples were collected for analysis.

[0037] The analysis results show that during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 60.7%, the oil yield is 23.9 wt%, the yield of GC-detectable products is 19.9 wt%, the yield of monocyclic aromatic hydrocarbon products is 4.5 wt%, the yield of polycyclic aromatic hydrocarbon products is 6.3 wt%, and the oxygen content in the oil (including THN) is 0.74%.

[0038] Example 4

[0039] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3It is carried out in a high-temperature and high-pressure reactor. 5 g of lignin, 0.5 g of MoS2 catalyst and 25 g of tetralin are added to the reactor. The reactor is sealed, N2 is introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N2 is less than 0.1 MPa, indicating that the high-temperature and high-pressure reactor is airtight. Then, H2 is introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure reactor. Finally, H2 is added to maintain the reaction pressure at 2.0 MPa. The reactor is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 310 °C, timing starts, and the reaction lasts for 120 min. After the reaction time is reached, the reaction temperature is raised to 400 °C and timing starts again. After 120 min of reaction, the reactor is taken out and cooled by blowing with a blower to terminate the reaction. After the reactor cools down to room temperature, the sample is collected for analysis.

[0040] The analysis results show that: during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 57.9%, the oil yield is 20.8 wt%, the yield of GC-detectable products is 16.3 wt%, the yield of monocyclic aromatic hydrocarbon products is 4.1 wt%, the yield of polycyclic aromatic hydrocarbon products is 6.1 wt%, and the oxygen content in the oil (including THN) is 0.75%.

[0041] Example 5

[0042] The two-step direct hydroliquefaction experiment of lignin in this example is carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin is carried out in a 100 cm 3 high-temperature and high-pressure reactor with a stirring paddle. 5 g of lignin, 1.5 g of MoS2 catalyst and 10 g of tetralin are added to the reactor. The reactor is sealed, N2 is introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N2 is less than 0.1 MPa, indicating that the high-temperature and high-pressure reactor is airtight. Then, H2 is introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure reactor. Finally, H2 is added to maintain the reaction pressure at 2.0 MPa. The reactor is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 310 °C, timing starts, and the reaction lasts for 120 min. After the reaction time is reached, the reaction temperature is raised to 400 °C and timing starts again. After 120 min of reaction, the reactor is taken out and cooled by blowing with a blower to terminate the reaction. After the reactor cools down to room temperature, the sample is collected for analysis.

[0043] The analysis results show that during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 79%, the oil yield is 32.3 wt%, the yield of GC-detectable products is 31.6 wt%, the yield of monocyclic aromatic hydrocarbon products is 4.4 wt%, the yield of polycyclic aromatic hydrocarbon products is 10.7 wt%, and the oxygen content in the oil (including THN) is 0.7%.

[0044] Example 6

[0045] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirring paddle. 5 g of lignin, 2.5 g of MoS2 catalyst, and 10 g of tetralin were added to the autoclave. The autoclave was sealed, and N2 was introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa was introduced for leak detection. After half an hour, the pressure change in N2 was less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave was airtight. Then, H2 was introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure autoclave. Finally, H2 was added to maintain the reaction pressure at 2.0 MPa. The autoclave was placed in a heating jacket for heating and the stirring was started. When the reaction temperature reached 310 °C, the timing began, and the reaction lasted for 120 min. After the reaction time reached, the reaction temperature was raised to 400 °C and the timing began again. After reacting for 120 min, the autoclave was taken out and blown with a blower for cooling to terminate the reaction. After the autoclave cooled to room temperature, the samples were collected for analysis.

[0046] The analysis results show that during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 84%, the oil yield is 36.6 wt%, the yield of GC-detectable products is 35.1 wt%, the yield of monocyclic aromatic hydrocarbon products is 4.5 wt%, the yield of polycyclic aromatic hydrocarbon products is 11.8 wt%, and the oxygen content in the oil (including THN) is 0.6%.

[0047] Example 7

[0048] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3It is carried out in a high-temperature and high-pressure autoclave. 5 g of lignin, 5 g of MoS₂ catalyst and 10 g of tetralin are added to the autoclave. The autoclave is sealed, and N₂ is introduced and purged three times to remove air from the system. Subsequently, N₂ with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N₂ is less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave is airtight. Then, H₂ is introduced and purged three times in sequence to remove the residual N₂ in the high-temperature and high-pressure autoclave. Finally, H₂ is added to maintain the reaction pressure at 2.0 MPa. The autoclave is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 310 °C, timing begins, and the reaction lasts for 120 min. After the reaction time is reached, the reaction temperature is raised to 400 °C and timing begins again. After reacting for 120 min, the autoclave is taken out and blown with a blower for cooling to terminate the reaction. After the autoclave cools down to room temperature, the sample is collected for analysis.

[0049] The analysis results show that: during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 95.3%, the oil yield is 65.2 wt%, the yield of GC-detectable products is 35.8 wt%, the yield of monocyclic aromatic hydrocarbon products is 5.1 wt%, the yield of polycyclic aromatic hydrocarbon products is 13.1 wt%, and the oxygen content in the oil (including THN) is 0.58%.

[0050] Example 8

[0051] The two-step direct hydroliquefaction experiment of lignin in this example is carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H₂ as the reducing agent. The two-step direct hydroliquefaction experiment of lignin is carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirring paddle. 5 g of lignin, 5 g of MoS₂ catalyst and 10 g of tetralin are added to the autoclave. The autoclave is sealed, and N₂ is introduced and purged three times to remove air from the system. Subsequently, N₂ with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N₂ is less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave is airtight. Then, H₂ is introduced and purged three times in sequence to remove the residual N₂ in the high-temperature and high-pressure autoclave. Finally, H₂ is added to maintain the reaction pressure at 4.0 MPa. The autoclave is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 310 °C, timing begins, and the reaction lasts for 120 min. After the reaction time is reached, the reaction temperature is raised to 400 °C and timing begins again. After reacting for 120 min, the autoclave is taken out and blown with a blower for cooling to terminate the reaction. After the autoclave cools down to room temperature, the sample is collected for analysis.

[0052] The analysis results show that during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 95.9%, the oil yield is 66.9 wt%, the yield of GC-detectable products is 36.1 wt%, the yield of monocyclic aromatic hydrocarbon products is 5.6 wt%, the yield of polycyclic aromatic hydrocarbon products is 13.3 wt%, and the oxygen content in the oil (including THN) is 0.50%.

[0053] Example 9

[0054] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirring paddle. 5 g of lignin, 5 g of MoS2 catalyst, and 10 g of tetralin were added to the autoclave. The autoclave was sealed, and N2 was introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa was introduced for leak detection. After half an hour, the pressure change in N2 was less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave was airtight. Then, H2 was introduced and purged three times in turn to remove the residual N2 in the high-temperature and high-pressure autoclave. Finally, H2 was added to maintain the reaction pressure at 6.0 MPa. The autoclave was placed in a heating jacket for heating and the stirring was started. When the reaction temperature reached 310 °C, the timing started, and the reaction lasted for 120 min. After the reaction time reached, the reaction temperature was raised to 400 °C and the timing started again. After the reaction for 120 min, the autoclave was taken out and blown with a blower for cooling to terminate the reaction. After the autoclave cooled to room temperature, the samples were collected for analysis.

[0055] The analysis results show that during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 96.5%, the oil yield is 68.8 wt%, the yield of GC-detectable products is 36.6 wt%, the yield of monocyclic aromatic hydrocarbon products is 6.4 wt%, the yield of polycyclic aromatic hydrocarbon products is 15.2 wt%, and the oxygen content in the oil (including THN) is 0.32%.

[0056] Example 10

[0057] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3It is carried out in a high-temperature and high-pressure autoclave. 5 g of lignin, 5 g of MoS2 catalyst and 10 g of tetralin are added into the autoclave. The autoclave is sealed, and N2 is introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N2 is less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave is airtight. Then, H2 is introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure autoclave. Finally, H2 is added to maintain the reaction pressure at 8.0 MPa. The autoclave is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 310 °C, timing begins, and the reaction proceeds for 120 min. After the reaction time is reached, the reaction temperature is raised to 400 °C and timing starts again. After reacting for 120 min, the autoclave is taken out and cooled by blowing with a blower to terminate the reaction. After the autoclave is cooled to room temperature, the sample is collected for analysis.

[0058] The analysis results show that: during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 96.4%, the oil yield is 74.4 wt%, the yield of GC-detectable products is 37.8 wt%, the yield of monocyclic aromatic hydrocarbon products is 6.9 wt%, the yield of polycyclic aromatic hydrocarbon products is 15.9 wt%, and the oxygen content in the oil (including THN) is 0.33%.

[0059] Example 11

[0060] The two-step direct hydroliquefaction experiment of lignin in this example is carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin is carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirring paddle. 5 g of lignin, 5 g of MoS2 catalyst and 10 g of tetralin are added into the autoclave. The autoclave is sealed, and N2 is introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N2 is less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave is airtight. Then, H2 is introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure autoclave. Finally, H2 is added to maintain the reaction pressure at 8.0 MPa. The autoclave is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 330 °C, timing begins, and the reaction proceeds for 120 min. After the reaction time is reached, the reaction temperature is raised to 400 °C and timing starts again. After reacting for 120 min, the autoclave is taken out and cooled by blowing with a blower to terminate the reaction. After the autoclave is cooled to room temperature, the sample is collected for analysis.

[0061] The analysis results show that during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate was 96.6%, the oil yield was 75.6 wt%, the yield of GC-detectable products was 38.5 wt%, the yield of monocyclic aromatic hydrocarbon products was 7.2 wt%, the yield of polycyclic aromatic hydrocarbon products was 16.5 wt%, and the oxygen content in the oil (including THN) was 1.40%.

[0062] Example 12

[0063] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirring paddle. 5 g of lignin, 5 g of MoS2 catalyst, and 10 g of tetralin were added to the autoclave. The autoclave was sealed, and N2 was introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa was introduced for leak detection. After half an hour, the pressure change in N2 was less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave was airtight. Then, H2 was introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure autoclave. Finally, H2 was added to maintain the reaction pressure at 8.0 MPa. The autoclave was placed in a heating jacket for heating and the stirring was started. When the reaction temperature reached 350 °C, the timing started, and the reaction was carried out for 120 min. After the reaction time reached, the reaction temperature was raised to 400 °C and the timing started again. After the reaction for 120 min, the autoclave was taken out and cooled by blowing with a blower to terminate the reaction. After the autoclave cooled to room temperature, the samples were collected for analysis.

[0064] The analysis results show that during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate was 96.7%, the oil yield was 77.9 wt%, the yield of GC-detectable products was 37.8 wt%, the yield of monocyclic aromatic hydrocarbon products was 7.8 wt%, the yield of polycyclic aromatic hydrocarbon products was 16.6 wt%, and the oxygen content in the oil (including THN) was 1.36%.

[0065] Example 13

[0066] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3It is carried out in a high-temperature and high-pressure autoclave. 5 g of lignin, 5 g of MoS₂ catalyst and 10 g of tetralin are added into the autoclave. The autoclave is sealed, and N₂ is introduced and purged three times to remove air from the system. Subsequently, N₂ with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N₂ is less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave is airtight. Then, H₂ is introduced and purged three times in sequence to remove the residual N₂ in the high-temperature and high-pressure autoclave. Finally, H₂ is added to maintain the reaction pressure at 8.0 MPa. The autoclave is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 370 °C, timing begins, and the reaction lasts for 120 min. After the reaction time is reached, the reaction temperature is raised to 400 °C and timing begins again. After reacting for 120 min, the autoclave is taken out and blown with a blower for cooling to terminate the reaction. After the autoclave cools down to room temperature, the sample is collected for analysis.

[0067] The analysis results show that: during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 96.6%, the oil yield is 80.0 wt%, the yield of GC-detectable products is 36.1 wt%, the yield of monocyclic aromatic hydrocarbon products is 8.1 wt%, the yield of polycyclic aromatic hydrocarbon products is 16.5 wt%, and the oxygen content in the oil (including THN) is 1.38%.

[0068] Example 14

[0069] The two-step direct hydroliquefaction experiment of lignin in this example is carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H₂ as the reducing agent. The two-step direct hydroliquefaction experiment of lignin is carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirring paddle. 5 g of lignin, 5 g of MoS₂ catalyst and 10 g of tetralin are added into the autoclave. The autoclave is sealed, and N₂ is introduced and purged three times to remove air from the system. Subsequently, N₂ with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N₂ is less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave is airtight. Then, H₂ is introduced and purged three times in sequence to remove the residual N₂ in the high-temperature and high-pressure autoclave. Finally, H₂ is added to maintain the reaction pressure at 8.0 MPa. The autoclave is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 330 °C, timing begins, and the reaction lasts for 120 min. After the reaction time is reached, the reaction temperature is raised to 420 °C and timing begins again. After reacting for 120 min, the autoclave is taken out and blown with a blower for cooling to terminate the reaction. After the autoclave cools down to room temperature, the sample is collected for analysis.

[0070] The analysis results show that during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate was 100%, the oil yield was 77.6 wt%, the yield of GC-detectable products was 68.9 wt%, the yield of monocyclic aromatic hydrocarbon products was 27.3 wt%, the yield of polycyclic aromatic hydrocarbon products was 31.6 wt%, and the oxygen content in the oil (including THN) was 0.32%.

[0071] Example 15

[0072] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirring paddle. 5 g of lignin, 5 g of MoS2 catalyst, and 10 g of tetralin were added to the autoclave. The autoclave was sealed, and N2 was introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa was introduced for leak detection. After half an hour, the pressure change in the N2 was less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave was airtight. Then, H2 was introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure autoclave. Finally, H2 was added to maintain the reaction pressure at 8.0 MPa. The autoclave was placed in a heating jacket for heating and the stirring was started. When the reaction temperature reached 330 °C, the timing started, and the reaction was carried out for 120 min. After the reaction time reached, the reaction temperature was raised to 440 °C and the timing started again. After the reaction for 120 min, the autoclave was taken out and cooled by blowing with a blower to terminate the reaction. After the autoclave cooled to room temperature, the samples were collected for analysis.

[0073] The analysis results show that during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate was 100%, the oil yield was 75.2 wt%, the yield of GC-detectable products was 74.0 wt%, the yield of monocyclic aromatic hydrocarbon products was 29.2 wt%, the yield of polycyclic aromatic hydrocarbon products was 33.9 wt%, and the oxygen content in the oil (including THN) was 0.30%.

[0074] Example 16

[0075] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3It is carried out in a high-temperature and high-pressure reactor. 5 g of lignin, 5 g of MoS2 catalyst and 10 g of tetralin are added into the reactor. The reactor is sealed, N2 is introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N2 is less than 0.1 MPa, indicating that the high-temperature and high-pressure reactor is airtight. Then, H2 is introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure reactor. Finally, H2 is added to maintain the reaction pressure at 8.0 MPa. The reactor is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 330 °C, timing starts and the reaction lasts for 120 min. After the reaction time is reached, the reaction temperature is raised to 460 °C and timing starts again. After reacting for 120 min, the reactor is taken out and cooled by blowing with a blower to terminate the reaction. When the reactor cools down to room temperature, the sample is collected for analysis.

[0076] The analysis results show that: during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 100%, the oil yield is 75.1 wt%, the yield of GC-detectable products is 73.5 wt%, the yield of monocyclic aromatic hydrocarbon products is 28.8 wt%, the yield of polycyclic aromatic hydrocarbon products is 33.4 wt%, and the oxygen content in the oil (including THN) is 0.29%.

[0077] Example 17

[0078] The two-step direct hydroliquefaction experiment of lignin in this example is carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin is carried out in a 100 cm 3 high-temperature and high-pressure reactor. 5 g of lignin, 5 g of MoS2 catalyst and 10 g of tetralin are added into the reactor. The reactor is sealed, N2 is introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N2 is less than 0.1 MPa, indicating that the high-temperature and high-pressure reactor is airtight. Then, H2 is introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure reactor. Finally, H2 is added to maintain the reaction pressure at 8.0 MPa. The reactor is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 330 °C, timing starts and the reaction lasts for 90 min. After the reaction time is reached, the reaction temperature is raised to 440 °C and timing starts again. After reacting for 120 min, the reactor is taken out and cooled by blowing with a blower to terminate the reaction. When the reactor cools down to room temperature, the sample is collected for analysis.

[0079] The analysis results show that during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 98.3%, the oil yield is 71.9 wt%, the yield of GC-detectable products is 67.8 wt%, the yield of monocyclic aromatic hydrocarbon products is 25.3 wt%, the yield of polycyclic aromatic hydrocarbon products is 29.4 wt%, and the oxygen content in the oil (including THN) is 0.79%.

[0080] Example 18

[0081] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3 high-temperature and high-pressure reactor equipped with a stirring paddle. 5 g of lignin, 5 g of MoS2 catalyst, and 10 g of tetralin were added to the reactor. The reactor was sealed, and N2 was introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa was introduced for leak detection. After half an hour, the pressure change in N2 was less than 0.1 MPa, indicating that the high-temperature and high-pressure reactor was airtight. Then, H2 was introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure reactor. Finally, H2 was added to maintain the reaction pressure at 8.0 MPa. The reactor was placed in a heating jacket for heating and the stirring was started. When the reaction temperature reached 330 °C, the timing began, and the reaction lasted for 60 min. After the reaction time was reached, the reaction temperature was raised to 440 °C and the timing began again. After reacting for 120 min, the reactor was taken out and cooled by blowing with a blower to terminate the reaction. After the reactor cooled to room temperature, the samples were collected for analysis.

[0082] The analysis results show that during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 97.6%, the oil yield is 70.1 wt%, the yield of GC-detectable products is 60.3 wt%, the yield of monocyclic aromatic hydrocarbon products is 23.6 wt%, the yield of polycyclic aromatic hydrocarbon products is 25.2 wt%, and the oxygen content in the oil (including THN) is 0.88%.

[0083] Example 19

[0084] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3It is carried out in a high-temperature and high-pressure autoclave. 5 g of lignin, 5 g of MoS₂ catalyst and 10 g of tetralin are added into the autoclave. The autoclave is sealed, nitrogen (N₂) is introduced and purged three times to remove air from the system. Subsequently, N₂ with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N₂ is less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave is airtight. Then, H₂ is introduced and purged three times in sequence to remove the residual N₂ in the high-temperature and high-pressure autoclave. Finally, H₂ is added to maintain the reaction pressure at 8.0 MPa. The autoclave is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 330 °C, timing begins, and the reaction proceeds for 120 min. After the reaction time is reached, the reaction temperature is raised to 440 °C and timing begins again. After reacting for 90 min, the autoclave is taken out and blown with a blower for cooling to terminate the reaction. After the autoclave cools down to room temperature, the sample is collected for analysis.

[0085] The analysis results show that: during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 97.9%, the oil yield is 70.7 wt%, the yield of GC-detectable products is 66.5 wt%, the yield of monocyclic aromatic hydrocarbon products is 23.7 wt%, the yield of polycyclic aromatic hydrocarbon products is 27.6 wt%, and the oxygen content in the oil (including THN) is 0.83%.

[0086] Example 20

[0087] The two-step direct hydroliquefaction experiment of lignin in this example is carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H₂ as the reducing agent. The two-step direct hydroliquefaction experiment of lignin is carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirring paddle. 5 g of lignin, 5 g of MoS₂ catalyst and 10 g of tetralin are added into the autoclave. The autoclave is sealed, N₂ is introduced and purged three times to remove air from the system. Subsequently, N₂ with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N₂ is less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave is airtight. Then, H₂ is introduced and purged three times in sequence to remove the residual N₂ in the high-temperature and high-pressure autoclave. Finally, H₂ is added to maintain the reaction pressure at 8.0 MPa. The autoclave is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 330 °C, timing begins, and the reaction proceeds for 120 min. After the reaction time is reached, the reaction temperature is raised to 440 °C and timing begins again. After reacting for 60 min, the autoclave is taken out and blown with a blower for cooling to terminate the reaction. After the autoclave cools down to room temperature, the sample is collected for analysis.

[0088] The analysis results show that during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate was 96.8%, the oil yield was 69.4 wt%, the yield of GC-detectable products was 58.6 wt%, the yield of monocyclic aromatic hydrocarbon products was 20.9 wt%, the yield of polycyclic aromatic hydrocarbon products was 23.3 wt%, and the oxygen content in the oil (including THN) was 0.96%.

[0089] Example 21

[0090] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirrer. 5 g of lignin, 5 g of 20% MoS2 / Al2O3 catalyst, and 10 g of tetralin were added to the autoclave. The autoclave was sealed, and N2 was introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa was introduced for leak detection. After half an hour, the pressure change in N2 was less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave was airtight. Then, H2 was introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure autoclave. Finally, H2 was added to maintain the reaction pressure at 8.0 MPa. The autoclave was placed in a heating jacket for heating and the stirrer was turned on. When the reaction temperature reached 330 °C, timing started, and the reaction lasted for 120 min. After the reaction time was reached, the reaction temperature was raised to 440 °C and timing started again. After the reaction for 120 min, the autoclave was taken out and cooled by blowing with a blower to terminate the reaction. After the autoclave cooled to room temperature, the samples were collected for analysis.

[0091] The analysis results show that during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate was 100%, the oil yield was 76.1 wt%, the yield of GC-detectable products was 75.6 wt%, the yield of monocyclic aromatic hydrocarbon products was 29.6 wt%, the yield of polycyclic aromatic hydrocarbon products was 32.8 wt%, and the oxygen content in the oil (including THN) was 0.35%.

[0092] Example 22

[0093] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3It is carried out in a high-temperature and high-pressure autoclave. 5 g of lignin, 5 g of 20% MoS2 / AC catalyst, and 10 g of tetralin are added into the autoclave. The autoclave is sealed, and N2 is introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N2 is less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave is airtight. Then, H2 is introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure autoclave. Finally, H2 is added to maintain the reaction pressure at 8.0 MPa. The autoclave is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 330 °C, timing begins, and the reaction lasts for 120 min. After the reaction time is reached, the reaction temperature is further increased to 440 °C and timing begins. After 120 min of reaction, the autoclave is taken out and blown with a blower for cooling to terminate the reaction. After the autoclave cools down to room temperature, the sample is collected for analysis.

[0094] The analysis results show that: during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 100%, the oil yield is 75.8 wt%, the yield of GC-detectable products is 74.9 wt%, the yield of monocyclic aromatic hydrocarbon products is 29.3 wt%, the yield of polycyclic aromatic hydrocarbon products is 31.7 wt%, and the oxygen content in the oil (including THN) is 0.33%.

[0095] Example 23

[0096] The two-step direct hydroliquefaction experiment of lignin in this example is carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin is carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirring paddle. 5 g of lignin, 5 g of 5% Pd-15% MoS2 / Al2O3 catalyst, and 10 g of tetralin are added into the autoclave. The autoclave is sealed, and N2 is introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N2 is less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave is airtight. Then, H2 is introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure autoclave. Finally, H2 is added to maintain the reaction pressure at 8.0 MPa. The autoclave is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 330 °C, timing begins, and the reaction lasts for 120 min. After the reaction time is reached, the reaction temperature is further increased to 440 °C and timing begins. After 120 min of reaction, the autoclave is taken out and blown with a blower for cooling to terminate the reaction. After the autoclave cools down to room temperature, the sample is collected for analysis.

[0097] The analysis results show that: during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 100%, the oil yield is 76.6 wt%, the yield of GC-detectable products is 75.6 wt%, the yield of monocyclic aromatic hydrocarbon products is 28.8 wt%, the yield of polycyclic aromatic hydrocarbon products is 32.2 wt%, and the oxygen content in the oil (including THN) is 0.28%.

[0098] Example 24

[0099] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirrer. 5 g of lignin, 5 g of 5% Pd-15% MoS2 / AC catalyst, and 10 g of tetralin were added to the autoclave. The autoclave was sealed, and N2 was introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa was introduced for leak detection. After half an hour, the pressure change in N2 was less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave was airtight. Then, H2 was introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure autoclave. Finally, H2 was added to maintain the reaction pressure at 8.0 MPa. The autoclave was placed in a heating jacket for heating and the stirrer was turned on. When the reaction temperature reached 330 °C, timing started, and the reaction was carried out for 120 min. After the reaction time was reached, the reaction temperature was raised to 440 °C and timing started again. After the reaction was carried out for 120 min, the autoclave was taken out and cooled by blowing with a blower to terminate the reaction. After the autoclave cooled to room temperature, the samples were collected for analysis.

[0100] The analysis results show that: during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 100%, the oil yield is 75.5 wt%, the yield of GC-detectable products is 74.3 wt%, the yield of monocyclic aromatic hydrocarbon products is 28.5 wt%, the yield of polycyclic aromatic hydrocarbon products is 31.3 wt%, and the oxygen content in the oil (including THN) is 0.27%.

[0101] Example 25

[0102] The two-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3It is carried out in a high-temperature and high-pressure reactor. 5 g of lignin, 5 g of 5% Ni-15% MoS2 / Al2O3 catalyst and 10 g of tetralin are added into the reactor. The reactor is sealed, N2 is introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N2 is less than 0.1 MPa, indicating that the high-temperature and high-pressure reactor is airtight. Then, H2 is introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure reactor. Finally, H2 is added to maintain the reaction pressure at 8.0 MPa. The reactor is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 330 °C, timing starts and the reaction proceeds for 120 min. After the reaction time is reached, the reaction temperature is raised to 440 °C and timing starts again. After reacting for 120 min, the reactor is taken out and blown with a blower for cooling to terminate the reaction. After the reactor cools down to room temperature, the sample is collected for analysis.

[0103] The analysis results show that: during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 100%, the oil yield is 75.1 wt%, the yield of GC-detectable products is 74.6 wt%, the yield of monocyclic aromatic hydrocarbon products is 28.7 wt%, the yield of polycyclic aromatic hydrocarbon products is 32.5 wt%, and the oxygen content in the oil (including THN) is 0.31%.

[0104] Example 26

[0105] The two-step direct hydroliquefaction experiment of lignin in this example is carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The two-step direct hydroliquefaction experiment of lignin is carried out in a 100 cm 3 high-temperature and high-pressure reactor with a stirring paddle. 5 g of lignin, 5 g of 5% Ni-15% MoS2 / AC catalyst and 10 g of tetralin are added into the reactor. The reactor is sealed, N2 is introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa is introduced for leak detection. After half an hour, the pressure change in N2 is less than 0.1 MPa, indicating that the high-temperature and high-pressure reactor is airtight. Then, H2 is introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure reactor. Finally, H2 is added to maintain the reaction pressure at 8.0 MPa. The reactor is placed in a heating jacket for heating and stirring is started. When the reaction temperature reaches 330 °C, timing starts and the reaction proceeds for 120 min. After the reaction time is reached, the reaction temperature is raised to 440 °C and timing starts again. After reacting for 120 min, the reactor is taken out and blown with a blower for cooling to terminate the reaction. After the reactor cools down to room temperature, the sample is collected for analysis.

[0106] The analysis results show that: during the two-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 100%, the oil yield is 75.9 wt%, the yield of GC-detectable products is 75.0 wt%, the yield of monocyclic aromatic hydrocarbon products is 28.6 wt%, the yield of polycyclic aromatic hydrocarbon products is 31.6 wt%, and the oxygen content in the oil (including THN) is 0.32%.

[0107] Example 27

[0108] This example is an experiment on the reuse of the catalyst.

[0109] The experiment on the reuse of the catalyst for the two-step direct hydroliquefaction of lignin was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The experiment on the reuse of the catalyst for the two-step direct hydroliquefaction of lignin was carried out in a 100 cm 3 high-temperature and high-pressure reactor with a stirrer. 5 g of lignin, 5 g of MoS2 catalyst, and 10 g of tetralin were added to the reactor. The reactor was sealed, and N2 was introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa was introduced for leak detection. After half an hour, the pressure change in N2 was less than 0.1 MPa, indicating that the high-temperature and high-pressure reactor was airtight. Then, H2 was introduced and purged three times in turn to remove the residual N2 in the high-temperature and high-pressure reactor. Finally, H2 was added to maintain the reaction pressure at 8.0 MPa. The reactor was placed in a heating jacket for heating and the stirrer was turned on. When the reaction temperature reached 330 °C, timing started, and the reaction lasted for 120 min. After the reaction time reached, the reaction temperature was raised to 440 °C and timing started again. After the reaction for 120 min, the reactor was taken out and cooled by blowing with a blower to terminate the reaction. When the reactor cooled down to room temperature, the samples were collected for analysis. The catalyst was separated for use in the next experiment.

[0110] The analysis results show that: during the experiment on the reuse of the catalyst for the two-step direct hydroliquefaction of lignin, the lignin conversion rate is 100%, the oil yield is 74.8 wt%, the yield of GC-detectable products is 73.6 wt%, the yield of monocyclic aromatic hydrocarbon products is 28.9 wt%, the yield of polycyclic aromatic hydrocarbon products is 34.5 wt%, and the oxygen content in the oil (including THN) is 0.33%.

[0111] Catalyst reuse experiment 1: 5 g of lignin, the previously used MoS2 catalyst, and 10 g of tetralin were added to the previously used autoclave. The autoclave was sealed, and the remaining operations were the same as above. Finally, the samples were collected for analysis. The analysis results showed that during the catalyst reuse experiment for the two-step direct hydroliquefaction of lignin, the lignin conversion rate was 100%, the oil yield was 75.1 wt%, the yield of GC-detectable products was 74.8 wt%, the yield of monocyclic aromatic hydrocarbon products was 29.8 wt%, the yield of polycyclic aromatic hydrocarbon products was 32.4 wt%, and the oxygen content in the oil (including THN) was 0.27%.

[0112] Catalyst reuse experiment 2: 5 g of lignin, the previously used MoS2 catalyst, and 10 g of tetralin were added to the previously used autoclave. The autoclave was sealed, and the remaining operations were the same as above. Finally, the samples were collected for analysis. The analysis results showed that during the catalyst reuse experiment for the two-step direct hydroliquefaction of lignin, the lignin conversion rate was 100%, the oil yield was 74.5 wt%, the yield of GC-detectable products was 74.1 wt%, the yield of monocyclic aromatic hydrocarbon products was 27.9 wt%, the yield of polycyclic aromatic hydrocarbon products was 33.1 wt%, and the oxygen content in the oil (including THN) was 0.31%.

[0113] Catalyst reuse experiment 3: 5 g of lignin, the previously used MoS2 catalyst, and 10 g of tetralin were added to the previously used autoclave. The autoclave was sealed, and the remaining operations were the same as above. Finally, the samples were collected for analysis. The analysis results showed that during the catalyst reuse experiment for the two-step direct hydroliquefaction of lignin, the lignin conversion rate was 100%, the oil yield was 74.3 wt%, the yield of GC-detectable products was 74.1 wt%, the yield of monocyclic aromatic hydrocarbon products was 28.1 wt%, the yield of polycyclic aromatic hydrocarbon products was 33.3 wt%, and the oxygen content in the oil (including THN) was 0.32%.

[0114] Example 28

[0115] This example is a comparative experiment, compared with the two-step catalytic hydroliquefaction experiment of lignin.

[0116] The one-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The one-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm autoclave with a stirring paddle 3The reaction was carried out in a high-temperature, high-pressure reactor. 5g of lignin, 5g of MoS2 catalyst, and 10g of tetralin were added to the reactor. The reactor was sealed, and N2 was introduced and purged three times to remove air from the system. Subsequently, N2 at a pressure of 8MPa was introduced for leak detection. After half an hour, the pressure change in the N2 was less than 0.1MPa, indicating that the high-temperature, high-pressure reactor was airtight. H2 was then introduced and purged three times sequentially to remove any residual N2 in the reactor. Finally, H2 was added to maintain the reaction pressure at 8.0MPa. The reactor was placed in a heating mantle, heated, and stirred. When the reaction temperature reached 330°C, the timer began, and the reaction time was 240 minutes. After the reaction time was reached, the reactor was removed and cooled with a blower to terminate the reaction. After the reactor cooled to room temperature, samples were collected for analysis.

[0117] Analysis results showed that during the one-step direct hydroliquefaction of lignin, the lignin conversion was 78%, the oil yield was 66.7 wt%, the yield of GC-detectable products was 33.3 wt%, the yield of monocyclic aromatic hydrocarbons was 11.3 wt%, the yield of polycyclic aromatic hydrocarbons was 2.3 wt%, and the oxygen content of the oil (including THN) was 1.60%. Compared with the two-step method of Example 27, the lignin conversion, oil yield, and GC-detectable product yield were all lower.

[0118] Example 29

[0119] This example is a comparative experiment, which is compared with the two-step lignin catalytic hydrogenation liquefaction experiment.

[0120] The one-step direct hydrogenation liquefaction experiment of lignin in this embodiment was carried out under the conditions of lignin as raw material, tetralin as hydrogen supply solvent and H2 as reducing agent. 3 The reaction was carried out in a high-temperature, high-pressure reactor. 5g of lignin, 5g of MoS2 catalyst, and 10g of tetralin were added to the reactor. The reactor was sealed, and N2 was introduced and purged three times to remove air from the system. Subsequently, N2 at a pressure of 8MPa was introduced for leak detection. After half an hour, the pressure change in the N2 was less than 0.1MPa, indicating that the high-temperature, high-pressure reactor was airtight. H2 was then introduced and purged three times sequentially to remove any residual N2 in the reactor. Finally, H2 was added to maintain the reaction pressure at 8.0MPa. The reactor was placed in a heating mantle, heated, and stirred. When the reaction temperature reached 370°C, the timer began, and the reaction time was 240 minutes. After the reaction time was reached, the reactor was removed and cooled with a blower to terminate the reaction. After the reactor cooled to room temperature, samples were collected for analysis.

[0121] The analysis results show that during the one-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 83%, the oil yield is 68.5 wt%, the yield of GC-detectable products is 34.7 wt%, the yield of monocyclic aromatic hydrocarbon products is 13.2 wt%, the yield of polycyclic aromatic hydrocarbon products is 3.9 wt%, and the oxygen content in the oil (including THN) is 1.59%. Compared with the two-step method in Example 13, the lignin conversion rate, oil yield, and yield of GC-detectable products are all lower.

[0122] Example 30

[0123] This example is a comparative experiment, comparing with the two-step catalytic hydroliquefaction experiment of lignin.

[0124] The one-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The one-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirring paddle. 5 g of lignin, 5 g of MoS2 catalyst, and 10 g of tetralin were added to the autoclave. The autoclave was sealed, and N2 was introduced and purged three times to remove air from the system. Subsequently, N2 with a pressure of 8 MPa was introduced for leak detection. After half an hour, the pressure change in N2 was less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave was airtight. Then, H2 was introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure autoclave. Finally, H2 was added to maintain the reaction pressure at 8.0 MPa. The autoclave was placed in a heating jacket for heating and the stirring was started. When the reaction temperature reached 400 °C, the timing started, and the reaction time was 240 min. After the reaction time reached, the autoclave was taken out and cooled by blowing with a blower to terminate the reaction. After the autoclave cooled to room temperature, the samples were collected for analysis.

[0125] The analysis results show that during the one-step direct hydroliquefaction experiment of lignin, the lignin conversion rate is 85%, the oil yield is 69.4 wt%, the yield of GC-detectable products is 35.2 wt%, the yield of monocyclic aromatic hydrocarbon products is 13.8 wt%, the yield of polycyclic aromatic hydrocarbon products is 10.1 wt%, and the oxygen content in the oil (including THN) is 0.97%. Compared with the two-step method in Example 12, the lignin conversion rate, oil yield, and yield of GC-detectable products are all lower.

[0126] Example 31 9]

[0127] This example is a comparative experiment, comparing with the two-step catalytic hydroliquefaction experiment of lignin.

[0128] The one-step direct hydroliquefaction experiment of lignin in this example was carried out under the conditions of using lignin as the raw material, tetralin as the hydrogen-donating solvent, and H2 as the reducing agent. The one-step direct hydroliquefaction experiment of lignin was carried out in a 100 cm 3 high-temperature and high-pressure autoclave with a stirrer paddle. 5 g of lignin, 5 g of MoS2 catalyst and 10 g of tetralin were added to the autoclave. The autoclave was sealed, and nitrogen (N2) was introduced and purged three times to remove air from the system; subsequently, N2 with a pressure of 8 MPa was introduced for leak detection. After half an hour, the pressure change in N2 was less than 0.1 MPa, indicating that the high-temperature and high-pressure autoclave was airtight. Then, H2 was introduced and purged three times in sequence to remove the residual N2 in the high-temperature and high-pressure autoclave; finally, H2 was added to maintain the reaction pressure at 8.0 MPa. The autoclave was placed in a heating jacket for heating and the stirrer was turned on. When the reaction temperature reached 460 °C, the timing started, and the reaction time was 240 min. After the reaction time reached, the autoclave was taken out and blown with a blower to cool down to terminate the reaction. After the autoclave cooled down to room temperature, the samples were collected for analysis.

[0129] The analysis results showed that: during the one-step direct hydroliquefaction experiment of lignin, the lignin conversion rate was 98%, the oil yield was 70.3 wt%, the yield of GC-detectable products was 56.4 wt%, the yield of monocyclic aromatic hydrocarbon products was 19.9 wt%, the yield of polycyclic aromatic hydrocarbon products was 25.6 wt%, and the oxygen content in the oil (including THN) was 0.46%. Compared with the two-step method in Example 16, the lignin conversion rate, oil yield, and yield of GC-detectable products were all lower.

Claims

1. A method for the two-step catalytic hydroliquefaction of lignin to prepare monocyclic and polycyclic aromatic hydrocarbons, and the specific steps of this method are as follows: S1: Add the lignin raw material, catalyst, and the hydrogen-donating solvent tetralin into a high-pressure reactor, and seal the reactor; S2: Remove the air in the reactor in step S1, then fill it with H2, and stir at a given reaction temperature to carry out the first-step catalytic hydrogenation reaction; S3: After the reaction time in step S2 is reached, continue to raise the reaction temperature to the set value, stir at this temperature to carry out the second-step catalytic hydrogenation reaction, and after reaching the reaction time, quickly cool the reactor to end the reaction; S4: Release the gas in the reactor in step S3, open the reactor in step S3, take out the product in the reactor in step S3, and treat the solid-liquid mixture with tetralin to obtain oil (the tetralin-soluble part) and residue (the tetralin-insoluble part, including the catalyst); Among them, In step S1, the catalyst is selected from MoS2, 20% MoS2 / Al2O3, 20% MoS2 / AC, 5% Pd-15% MoS2 / Al2O3, 5% Pd-15% MoS2 / AC, 5% Ni-15% MoS2 / Al2O3, or 5% Ni-15% MoS2 / AC; In step S2, the temperature of the first-step catalytic hydrogenation reaction is 310°C to 370°C; In step S3, the temperature of the second-step catalytic hydrogenation reaction is 400°C to 460°C.

2. The method according to claim 1, characterized in that, In step S1, the mass ratio of the hydrogen-donating solvent tetralin to the lignin raw material is 2 to 5.

3. The method according to claim 1, characterized in that In step S1, the mass ratio of the catalyst to the lignin raw material is 0.1 to 1.

4. The method according to claim 1, wherein In step S2, the pressure of the filled H2 is 2 MPa to 8 MPa.

5. The method according to claim 1, characterized in that, In step S2, the reaction time of the first-step catalytic hydrogenation reaction is 60 min to 120 min.

6. The method according to claim 1, characterized in that In step S3, the reaction time of the second-step catalytic hydrogenation reaction is 60 min to 120 min.