CN107840783B - Method for catalytic depolymerization of biomass by molybdenum oxide catalyst - Google Patents
Method for catalytic depolymerization of biomass by molybdenum oxide catalyst Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C37/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom of a six-membered aromatic ring
- C07C37/004—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom of a six-membered aromatic ring by obtaining phenols from plant material or from animal material
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/002—Mixed oxides other than spinels, e.g. perovskite
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
- B01J23/24—Chromium, molybdenum or tungsten
- B01J23/28—Molybdenum
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J29/00—Catalysts comprising molecular sieves
- B01J29/03—Catalysts comprising molecular sieves not having base-exchange properties
- B01J29/0308—Mesoporous materials not having base exchange properties, e.g. Si-MCM-41
- B01J29/0341—Mesoporous materials not having base exchange properties, e.g. Si-MCM-41 containing arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
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- C—CHEMISTRY; METALLURGY
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- C07C41/00—Preparation of ethers; Preparation of compounds having groups, groups or groups
- C07C41/01—Preparation of ethers
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07G—COMPOUNDS OF UNKNOWN CONSTITUTION
- C07G1/00—Lignin; Lignin derivatives
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/08—Removal of fats, resins, pitch or waxes; Chemical or physical purification, i.e. refining, of crude cellulose by removing non-cellulosic contaminants, optionally combined with bleaching
- D21C9/086—Removal of fats, resins, pitch or waxes; Chemical or physical purification, i.e. refining, of crude cellulose by removing non-cellulosic contaminants, optionally combined with bleaching with organic compounds or compositions comprising organic compounds
Abstract
The invention discloses a method for catalyzing and depolymerizing biomass by a molybdenum oxide catalyst, which is characterized in that lignin in a biomass raw material is preferentially and selectively cracked into C through a catalytic hydrogenation reaction of the biomass9~C12And aromatic compounds derived from phenol, guaiacol or syringyl. The highest yield of lignin monomers reaches 46.9 wt%, and the delignification rate reaches more than 95%. Compared with the prior art, the method for depolymerizing and separating the biomass components has higher delignification rate and better lignin monomer yield, the structure of the residual carbohydrate (cellulose) in the wood flour is not changed, and the separated carbohydrate can be used for pulping and papermaking and preparing bioethanolAnd the like. The method takes different biomasses as raw materials, including coniferous wood, broad-leaved wood, energy grass and bamboo. The raw materials are cheap and rich, the catalyst and the organic solvent can be recycled, and the high-efficiency separation and utilization of each component of the biomass are realized.
Description
Technical Field
The invention relates to a method for catalyzing and depolymerizing biomass by using a molybdenum oxide catalyst.
Background
The rapid consumption of fossil fuels and the increasing environmental problems have caused research on renewable energy sources to again attract widespread international attention. As a big agricultural country, China has more than 7 hundred million tons of agricultural and forestry wastes every year. The high-efficiency conversion of the lignocellulose resources with huge yield and reproducibility into energy, chemicals and novel materials has important significance for realizing the sustainable development of human beings. In the future, biomass can replace fossil fuel as a renewable energy source, and biorefinery can replace petroleum refining. Biorefinery is similar to petroleum refining in that biomass is degraded by chemical or biological methods to yield intermediates.
Lignin is a biological macromolecule with a three-dimensional structure formed by a plurality of lignin precursors through a free radical coupling reaction, and mainly comprises three basic structural units, namely guaiacyl (G type), syringyl (S type) and p-hydroxyphenyl (H type), wherein needle-leaf lignin is mainly G type, and broadleaf lignin is mainly G type and S type, while gramineous plant lignin contains H type lignin besides G type and S type lignin, and because the major components of lignocellulose have larger difference between the structure and the properties, the high-value utilization research on lignocellulose is closely related to the structural properties of the lignocellulose, hemicellulose and lignin. The cellulose, the hemicellulose and the lignin are interwoven with each other to form a compact lignocellulose network structure, and particularly the close combination between the hemicellulose and the lignin causes the component separation of the lignocellulose to damage the component structure. Because the cellulose is composed of a large amount of dehydrated glucose, the molecular weight of the cellulose is far higher than that of hemicellulose, and the cellulose is a semi-crystalline structure substance, a large amount of cellulose molecular chains are gathered together to form a crystallization area, so that the dissolution of cellulose components in lignocellulose is very difficult.
In the traditional paper industry, lignin is discharged in the form of alkaline black liquor as waste, namely the lignin cannot be utilized and pollutes the environment, and lignin obtained by other methods, including enzymatic hydrolysis lignin, is at the cost of sacrificing carbohydrate; such as alkali lignin and organic solvent lignin, the structure of lignin is destroyed and can not be fully utilized effectively. Recently, there have been reports of studies on wood flour as a raw material to degrade lignin therein and to maintain the carbohydrate component substantially unchanged, for example, depolymerization of birch wood flour into 50% monomer yield mainly containing 4-propylguaiacol and 4-propylsyringol under a reaction condition of hydrogen at 250 ℃ under 3MPa with Ru/C as a catalyst (Energy environ. sci., 8, 1748-. Adding a certain amount of Zn into Pd/C as a catalyst, and carrying out hydrogenolysis on poplar wood powder at 225 ℃ and 3MPa hydrogen pressure to obtain 54% lignin monomer yield (Green chem., 2015, 17, 1492-one 1499) mainly comprising 2, 6-dimethoxy-4-propyl phenol and 2-methoxy-4-propyl phenol. However, these catalysts are developed as noble metal catalysts, and the cost of the catalysts is relatively high.
In view of the above problems of the prior art, it is necessary to develop a method for efficiently separating and depolymerizing lignin and effectively protecting and utilizing the structure of carbohydrates by using an inexpensive metal molybdenum oxide catalyst.
Disclosure of Invention
The invention aims to provide a method for catalyzing and depolymerizing biomass by using a molybdenum oxide catalyst, which aims to overcome the defects in the existing lignin separation and depolymerization method, converts lignin into monophenol aromatic compounds in a high yield and high selectivity through a one-pot reaction, and realizes the high-efficiency lignin removal of wood flour and the resource and high-value utilization of lignin.
In order to solve the problems, the invention adopts the following technical scheme: a method for catalytic depolymerization of biomass with a molybdenum oxide catalyst, comprising the operations of:
according to the mass ratio of 1 (0.05-20) to 10-100 of dewaxed wood powder, a supported molybdenum oxide catalyst and a reaction solvent, mixing the dewaxed wood powder, the supported molybdenum oxide catalyst and the reaction solvent, adding the mixture into a reaction kettle for sealing, introducing hydrogen, heating to a reaction temperature of 220-260 ℃, stirring for reacting for 2-5 hours, naturally cooling and releasing pressure after the reaction is finished, opening the kettle, filtering to obtain a solid product and a liquid product, and dissolving and extracting the liquid product with dichloromethane after the liquid product is dried in a spinning mode to obtain a lignin oil product; the solid product obtained was sieved through a 300 mesh sieve to separate the catalyst from the carbohydrate.
The dewaxed wood flour is obtained by crushing a biomass raw material to 20-60 meshes, and extracting the crushed biomass raw material for 8-15 hours at 90-120 ℃ by using a mixed solution of toluene and ethanol (volume ratio is 2: 1).
The biomass material comprises broadleaf wood (eucalyptus, poplar, birch, beech, etc.), coniferous wood (pine, cypress, etc.), energy grass (miscanthus sinensis, triarrhena sacchariflora, etc.) and bamboo (mao bamboo, Sagittaria trifoliata, etc.).
The reaction solvent is one or a mixture of methanol, ethanol, isopropanol and water in any proportion.
The pressure of the introduced hydrogen is 0-8 Mpa, and the stirring speed is 100-1000 rpm.
The filtration is carried out by using a polyvinylidene fluoride organic filter membrane of 0.22 um.
The preparation method of the supported molybdenum oxide catalyst comprises the following steps:
(1) preparing a molybdenum dichloride hydrate precursor: uniformly mixing molybdenum pentachloride and molybdenum powder according to the mass ratio of 1: 2-5, roasting for 5 hours at 600-700 ℃ in an inert gas atmosphere, cooling to room temperature, washing for three times with concentrated hydrochloric acid with the concentration of 20-30 wt% and the temperature of 40-60 ℃, collecting washing liquid, standing the washing liquid overnight to obtain yellow needle crystals, filtering, collecting the crystals, and drying to obtain a molybdenum dichloride hydrate precursor (H)3O)2(Mo6Cl8)Cl6·6H2O；
(2) Supported molybdenum oxide catalystThe preparation of (1): according to the mass ratio of the molybdenum dichloride hydrate precursor to methanol or ethanol of 1: 90-110, the molybdenum dichloride hydrate precursor (H) obtained in the step (1) is3O)2(Mo6Cl8)Cl6·6H2Dissolving O in methanol or ethanol, slowly dripping the dissolved O into a carrier after the O is completely dissolved, standing the mixture at room temperature for 12 hours when the mass ratio of the molybdenum dichloride hydrate precursor to the carrier is 1: 2-15, removing the methanol or the ethanol through rotary evaporation at 40 ℃, roasting the mixture at 400-600 ℃ for 6 hours in an inert gas atmosphere, and cooling the mixture to room temperature to obtain the supported molybdenum oxide catalyst. The catalyst with different loading amounts can be obtained by changing the concentration of the transition metal salt in the impregnation liquid or by multiple times of impregnation, for example, MoO with the loading amounts of Mo of 10 wt%, 20wt%, 30wt%, 40 wt% and 50 wt% respectivelyxA/MCM-41 catalyst. The loading amount of the molybdenum in the carrier is 10-50% (calculated by the mass fraction of the metal Mo in the catalyst).
The carrier in the step (2) is silicon dioxide, activated carbon, SBA-15, MCM-41 or aluminum oxide.
The inert gas is nitrogen, argon or helium.
The methanol or ethanol in the step (2) is commercially available analytically pure.
The transition metal molybdenum-based catalyst is applied to the separation and depolymerization of biomass raw materials, and after the reaction is finished, the filtrate is extracted by dichloromethane or ethyl acetate and then is subjected to qualitative and quantitative analysis and determination by adopting Gas Chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The product is determined qualitatively by a standard sample and quantitatively by a standard curve method.
The delignification rate and the monomer yield are calculated by the following formula:
w (lignin content in wood flour) represents the mass of lignin in wood flour, w (lignin oil) represents the mass of methylene chloride solubles, and w (total amount of monomers) represents the mass of lignin monomers.
Compared with the prior art, the invention has the beneficial effects that:
1. the raw materials used by the invention are the most abundant renewable resources in nature, and have wide sources and low cost.
2. The catalyst used in the invention takes transition metal molybdenum as an active center, the molybdenum is an element with abundant reserves in the nature, and the catalyst has low cost.
3. The method has mild reaction conditions, the solvent adopts methanol as the reaction solvent, is environment-friendly and pollution-free, can be recycled, and does not use any inorganic acid or alkali in the reaction process, thereby avoiding the corrosion to equipment and the pollution to the environment in the biomass processing technology.
4. The invention provides a new way for high-value utilization of lignin in the raw material, and the product mainly contains lignin monophenol compounds, so that the selectivity and the additional value are high, and the method has a good industrial application prospect.
5. The invention preferentially and selectively degrades lignin in the biomass component, the structure of the residual carbohydrate (cellulose) in the raw material is not changed, and the separated carbohydrate can be used for pulping and papermaking, preparing bioethanol and the like. Reduce the pollution caused by the discharge of lignin in the paper industry. The method for depolymerizing and separating biomass components has high catalytic degradation conversion rate of lignin and better lignin removal rate.
6. The invention adopts a catalyst with cheap molybdenum oxide as an active center, and the biomass components are separated by one-pot catalytic degradation. Preferential selective splitting of lignin in biomass feedstock to C by catalytic hydrogenation of biomass9~C12And aromatic compounds derived from phenol, guaiacol or syringyl. The highest yield of lignin monomers reaches 46.9 wt%, and the delignification rate reaches more than 95%. The method for depolymerizing and separating the biomass components has the advantages of higher delignification rate, better lignin monomer yield and no change in the structure of the residual carbohydrate (cellulose) in the wood flour, and the separated carbohydrate can be used for pulping and papermaking, preparing bioethanol and the like. The method takes different biomasses as raw materials,including coniferous wood, broadleaf wood, and energy grass and bamboo. The raw materials are cheap and rich, the catalyst and the organic solvent can be recycled, and the high-efficiency separation and utilization of each component of the biomass are realized.
Drawings
FIG. 1 is a schematic diagram of a degradation reaction of eucalyptus lignin;
FIG. 2 is a GC spectrum of eucalyptus wood powder with and without catalyst in methanol solvent;
FIG. 3 shows MoO under different solvent conditionsxA GC spectrogram of a hydrogenolysis product of eucalyptus wood powder is catalytically depolymerized by SBA-15;
FIG. 4 shows MoO in methanol solventxGC spectrogram of hydrogenolysis products of different wood powder raw materials is catalytically depolymerized by SBA-15;
FIG. 5 is a graph showing the glucose yield of eucalyptus wood of example 1 and the product carbohydrate after enzymatic hydrolysis; wherein the cellulose is extracted from carbohydrates.
FIG. 6 is an X-ray diffraction pattern of eucalyptus wood of example 1 and the product carbohydrate, etc.; wherein the cellulose is extracted from carbohydrates.
Detailed Description
The present invention will be further described with reference to the following examples.
Example 1
(1) Preparing a molybdenum dichloride hydrate precursor: 2g of molybdenum pentachloride MoCl5Mixing with 6g of powder according to a mass ratio of 1:3, transferring into a tubular furnace, roasting at 650 ℃ for 5H in a nitrogen atmosphere, cooling to room temperature, washing with 100ml of 50 ℃ concentrated hydrochloric acid with a concentration of 25wt% for three times, collecting washing liquid, standing the washing liquid in a low-temperature refrigerator overnight to obtain yellow needle crystals, filtering, collecting the crystals, and drying to obtain a molybdenum dichloride hydrate precursor (H)3O)2(Mo6Cl8)Cl6·6H2O；
(2) Preparation of the supported molybdenum oxide catalyst: according to the mass ratio of the molybdenum dichloride hydrate precursor to the methanol of 1:100, the molybdenum dichloride hydrate precursor (H) obtained in the step (1) is3O)2(Mo6Cl8)Cl6·6H2Dissolving O in commercially available analytical pure methanol, slowly dripping into SBA-15 after the O is completely dissolved, keeping the mass ratio of the molybdenum dichloride hydrate precursor to the carrier at 1:11, standing for 12h at room temperature, removing the methanol through rotary evaporation at 40 ℃, putting into a tubular furnace, roasting for 6h at 600 ℃ under the nitrogen atmosphere, and cooling to room temperature to obtain the supported molybdenum oxide catalyst MoOxSBA-15, catalyst loading 5 wt%.
(3) Crushing eucalyptus wood to 20-60 meshes, extracting at 105 ℃ for 12 hours by using a mixed solution (volume ratio is 2: 1) of toluene and ethanol to obtain dewaxed eucalyptus wood powder, mixing the dewaxed eucalyptus wood powder, the supported molybdenum oxide catalyst and methanol according to the mass ratio of 5g of the dewaxed eucalyptus wood powder, the supported molybdenum oxide catalyst and the reaction solvent being 1:0.1:20, adding the mixture into a reaction kettle for sealing, introducing hydrogen, heating to the reaction temperature of 260 ℃, stirring for reacting for 4 hours, introducing the hydrogen at the pressure of 3Mpa and the stirring speed of 800rpm, naturally cooling and releasing the reaction kettle after the reaction is finished, filtering by using a 0.22-micron polyvinylidene fluoride organic filter membrane to obtain a solid product and a liquid product, and dissolving and extracting the obtained liquid product by using dichloromethane after spin-drying to obtain a lignin oil product; the solid product obtained was sieved through a 300 mesh sieve to separate the catalyst from the carbohydrate.
Extracting the liquid product by dichloromethane, spin-drying, weighing, and calculating the delignification rate; then the mixture is dissolved and filtered by dichloromethane containing n-tetradecane internal standard and enters GC-MS and GC for qualitative and quantitative analysis. And calculating the yield of the lignin monomer. The analytical products are shown in FIG. 1, and the delignification and monomer yield are shown in Table 1. After the eucalyptus is subjected to catalytic degradation and delignification, the glucose yield of the residues rich in carbohydrate can reach 88 percent after 24 hours of enzymatic hydrolysis. This value is close to the purified cellulose (93%), higher than the untreated eucalyptus wood flour (30%) and the microcrystalline cellulose (72%) (fig. 5). The XRD spectrum analysis of fig. 6 further shows that the MoOx/SBA-15 catalyst is effective in removing eucalyptus lignin, and the remaining carbohydrates still retain the cellulose crystal form intact.
TABLE 1 MoO in methanol solventxSBA-15 catalyzing hydrogenation knot of eucalyptus wood powderFruit
Example 2
Like example 1, only the reaction solvent of step (3) was replaced with ethanol, isopropanol or water. The delignification and monomer yields are shown in Table 2 and FIG. 3.
TABLE 2 MoO in different solventsxSBA-15 catalysis of eucalyptus wood powder hydrogenation result
Example 3
As in example 1, the catalyst was only recycled, i.e., the catalyst collected after the last reaction was activated at high temperature and used. The yield of monolignol and the delignification are shown in Table 3, MoOxAfter five cycles, the yield of catalytic degradation lignin monomers of the SBA-15 catalyst can still reach 41wt%, and the delignification rate can still reach more than 92%. Thus showing that the catalyst has higher stability.
TABLE 3 MoO in different solventsxSBA-15 catalysis of eucalyptus wood powder hydrogenation result
Example 4
In the same manner as in example 1, the amount of eucalyptus wood powder is increased 10 times from 5g to 50 g. The delignification and monomer yields are shown in table 4.
TABLE 4 MoOxHydrogenation amplification reaction result of eucalyptus wood powder catalyzed by SBA-15
Example 5
Similar to example 1, only eucalyptus wood powder was replaced with other biomass raw material, and the results of delignification and monomer yield are shown in table 5 and fig. 4.
TABLE 5 MoOxSBA-15 catalysis of hydrogenation results of different feedstocks
Example 6
(1) Preparing a molybdenum dichloride hydrate precursor: uniformly mixing molybdenum pentachloride and molybdenum powder according to the mass ratio of 1:5, transferring the mixture into a tube furnace, roasting the mixture for 5 hours at 700 ℃ in the atmosphere of helium, cooling the mixture to room temperature, washing the mixture for three times by using concentrated hydrochloric acid with the concentration of 20wt% and the temperature of 60 ℃, collecting washing liquid, placing the washing liquid in a low-temperature refrigerator for standing overnight to obtain yellow needle crystals, filtering the yellow needle crystals, collecting the crystals, and drying the crystals to obtain a molybdenum dichloride hydrate precursor (H)3O)2(Mo6Cl8)Cl6·6H2O；
(2) Preparation of the supported molybdenum oxide catalyst: according to the mass ratio of the molybdenum dichloride hydrate precursor to the methanol of 1:110, the molybdenum dichloride hydrate precursor (H) obtained in the step (1) is3O)2(Mo6Cl8)Cl6·6H2Dissolving O in commercially available analytically pure methanol, slowly dripping into the mesoporous material SBA-15 after the O is completely dissolved, keeping the mass ratio of the molybdenum dichloride hydrate precursor to the carrier at 1: 15, standing for 12h at room temperature, removing the methanol through rotary evaporation at 40 ℃, putting into a tubular furnace, roasting for 6h at 400 ℃ under the atmosphere of helium, and cooling to room temperature to obtain the supported molybdenum oxide catalyst MoOxand/SBA-15. The catalyst with different loading amounts can be obtained by changing the concentration of the transition metal salt in the impregnation liquid or by carrying out multiple times of impregnation.
(3) Crushing moso bamboo to 20-60 meshes, extracting for 15 hours at 90 ℃ by using a mixed solution of toluene and ethanol (volume ratio is 2: 1) to obtain dewaxed moso bamboo wood powder, mixing the dewaxed moso bamboo wood powder, a supported molybdenum oxide catalyst and isopropanol according to the mass ratio of 5g of the dewaxed moso bamboo wood powder, the supported molybdenum oxide catalyst and a reaction solvent of 1:0.05:100, adding the mixture into a reaction kettle for sealing, introducing hydrogen, heating to the reaction temperature of 220 ℃, stirring for 5 hours, introducing the hydrogen at the pressure of 8Mpa and the stirring speed of 1000rpm, naturally cooling and releasing the kettle after the reaction is finished, filtering to obtain a solid product and a liquid product, and dissolving and extracting the obtained liquid product by using dichloromethane after spin-drying to obtain a lignin oil product; the solid product obtained was sieved through a 300 mesh sieve to separate the catalyst from the carbohydrate.
Example 7
(1) Preparing a molybdenum dichloride hydrate precursor: uniformly mixing molybdenum pentachloride and molybdenum powder according to the mass ratio of 1:2, transferring the mixture into a tube furnace, roasting the mixture for 5 hours at 600 ℃ in the argon atmosphere, cooling the mixture to room temperature, washing the mixture for three times by using concentrated hydrochloric acid with the concentration of 30wt% and the temperature of 40 ℃, collecting washing liquid, placing the washing liquid in a low-temperature refrigerator for standing overnight to obtain yellow needle crystals, filtering the yellow needle crystals, collecting the crystals, and drying the crystals to obtain a molybdenum dichloride hydrate precursor (H)3O)2(Mo6Cl8)Cl6·6H2O；
(2) Preparation of the supported molybdenum oxide catalyst: according to the mass ratio of the molybdenum dichloride hydrate precursor to the ethanol of 1:90, the molybdenum dichloride hydrate precursor (H) obtained in the step (1) is3O)2(Mo6Cl8)Cl6·6H2Dissolving O in commercially available analytically pure methanol, slowly dripping into mesoporous material silicon dioxide after completely dissolving, keeping the mass ratio of the molybdenum dichloride hydrate precursor to the carrier at 1:2, standing at room temperature for 12h, removing the methanol through rotary evaporation at 40 ℃, placing in a tubular furnace, roasting at 500 ℃ for 6h under helium atmosphere, and cooling to room temperature to obtain the supported molybdenum oxide catalyst MoOx/SiO2. The catalyst with different loading amounts can be obtained by changing the concentration of the transition metal salt in the impregnation liquid or by carrying out multiple times of impregnation.
(3) Crushing the miscanthus sinensis to 20-60 meshes, extracting for 8 hours at 120 ℃ by using a mixed solution (volume ratio is 2: 1) of toluene and ethanol to obtain dewaxed miscanthus sinensis powder, mixing dewaxed wood powder, a supported molybdenum oxide catalyst and isopropanol according to the mass ratio of 5g of the dewaxed miscanthus sinensis powder, the supported molybdenum oxide catalyst and a reaction solvent of 1:20:10, adding the mixture into a reaction kettle for sealing, introducing hydrogen, heating to the reaction temperature of 240 ℃, stirring for reaction for 2 hours, introducing the hydrogen at the pressure of 0Mpa and the stirring speed of 100rpm, naturally cooling and releasing the kettle after the reaction is finished, filtering to obtain a solid product and a liquid product, and dissolving and extracting the obtained liquid product by using dichloromethane after spin-drying to obtain a lignin oil product; the solid product obtained was sieved through a 300 mesh sieve to separate the catalyst from the carbohydrate.
Comparative example 1: as with example 1, only replace: no reaction solvent methanol is added in the step (3).
The GC analysis spectrum of the product of this example is shown in FIG. 2, and the delignification rate and the monomer yield are shown in Table 6.
TABLE 6 hydrogenation results of eucalyptus wood flour without catalyst in methanol solvent
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (5)
1. A method for catalytic depolymerization of biomass with a molybdenum oxide catalyst is characterized by comprising the following operations:
according to the mass ratio of 1 (0.05-20) to 10-100 of dewaxed wood powder, a supported molybdenum oxide catalyst and a reaction solvent, mixing the dewaxed wood powder, the supported molybdenum oxide catalyst and the reaction solvent, adding the mixture into a reaction kettle for sealing, introducing hydrogen, heating to a reaction temperature of 220-260 ℃, stirring for reacting for 2-5 hours, naturally cooling and releasing pressure after the reaction is finished, opening the kettle, filtering to obtain a solid product and a liquid product, and dissolving and extracting the liquid product with dichloromethane after the liquid product is dried in a spinning mode to obtain a lignin oil product; screening the obtained solid product by a 300-mesh sieve to separate the catalyst from the carbohydrate;
the dewaxed wood flour is obtained by crushing a biomass raw material to 20-60 meshes, and extracting the crushed biomass raw material for 8-15 hours at 90-120 ℃ by using a mixed solution of toluene and ethanol; the biomass raw material is selected from broadleaf wood, coniferous wood, energy grass and bamboo;
the reaction solvent is one or a mixture of methanol, ethanol and isopropanol in any proportion;
the preparation method of the supported molybdenum oxide catalyst comprises the following steps:
(1) preparing a molybdenum dichloride hydrate precursor: uniformly mixing molybdenum pentachloride and molybdenum powder according to the mass ratio of 1: 2-5, roasting for 5 hours at 600-700 ℃ in an inert gas atmosphere, cooling to room temperature, washing for three times with concentrated hydrochloric acid with the concentration of 20-30 wt% and the temperature of 40-60 ℃, collecting washing liquid, standing the washing liquid overnight to obtain yellow needle crystals, filtering, collecting the crystals, and drying to obtain a molybdenum dichloride hydrate precursor (H)3O)2(Mo6Cl8)Cl6·6H2O；
(2) Preparation of the supported molybdenum oxide catalyst: according to the mass ratio of the molybdenum dichloride hydrate precursor to methanol or ethanol of 1: 90-110, the molybdenum dichloride hydrate precursor (H) obtained in the step (1) is3O)2(Mo6Cl8)Cl6·6H2Dissolving O in methanol or ethanol, slowly dripping the dissolved O into a carrier after the O is completely dissolved, standing the mixture at room temperature for 12 hours when the mass ratio of the molybdenum dichloride hydrate precursor to the carrier is 1: 2-15, removing the methanol or the ethanol through rotary evaporation at 40 ℃, roasting the mixture at 400-600 ℃ for 6 hours in an inert gas atmosphere, and cooling the mixture to room temperature to obtain the supported molybdenum oxide catalyst;
the carrier is silicon dioxide, activated carbon, SBA-15, MCM-41 or aluminum oxide.
2. The method of catalytic depolymerization of biomass with a molybdenum oxide catalyst according to claim 1, characterized in that: the mixed solution of toluene and ethanol is a mixed solution of toluene and ethanol according to the volume ratio of 2: 1.
3. The method of catalytic depolymerization of biomass with a molybdenum oxide catalyst according to claim 1, characterized in that: the pressure of the introduced hydrogen is 0-8 Mpa, and the stirring speed is 100-1000 rpm.
4. The method of catalytic depolymerization of biomass with a molybdenum oxide catalyst according to claim 1, characterized in that: the filtration is carried out by using a polyvinylidene fluoride organic filter membrane of 0.22 um.
5. The method of catalytic depolymerization of biomass with a molybdenum oxide catalyst according to claim 1, characterized in that: the inert gas is nitrogen, argon or helium.
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