CN108947783B

CN108947783B - Method for catalyzing oxidative degradation of lignin into aromatic monomer by molybdenum

Info

Publication number: CN108947783B
Application number: CN201710351325.8A
Authority: CN
Inventors: 徐杰; 马阳阳; 马继平; 夏飞; 高进; 苗虹
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2017-05-18
Filing date: 2017-05-18
Publication date: 2021-08-03
Anticipated expiration: 2037-05-18
Also published as: CN108947783A

Abstract

A method for catalyzing oxidative degradation of lignin into aromatic monomers by molybdenum comprises the steps of using molecular oxygen as an oxygen source and using a non-noble metal molybdenum compound as a catalyst to catalyze the oxidative degradation of lignin. In the method, the catalytic oxidation system is simple and green in composition, the operation condition is mild, and the yield of aromatic monomers (mainly aromatic aldehyde, aromatic ketone and aromatic acid ester) in the degradation product is high; provides possibility for high-value utilization of native lignin and lignocellulose.

Description

Method for catalyzing oxidative degradation of lignin into aromatic monomer by molybdenum

Technical Field

The invention relates to the field of comprehensive utilization of biomass converted into organic chemicals, in particular to a method for preparing organic chemicals, which comprises the following steps: lignocellulose or lignin is subjected to catalytic oxidation degradation to obtain aromatic small molecular monomer compounds with high additional values such as aromatic aldehyde, aromatic ketone, aromatic acid ester and the like, so that the effective high-value utilization of the lignin is realized.

Background

The problems of coal, petroleum and other traditional fossil resources are increasingly consumed, the environmental pollution and the like are increasingly aggravated, and the development and utilization of renewable biomass resources to realize sustainable development are key points and difficulties which need to be solved urgently in contemporary society. The biomass resource is widely existed in nature, and has abundant reserves and can be regenerated. The main components of plant biomass include cellulose, hemicellulose, lignin, etc., wherein the lignin content is about 15-30 wt%. Compared with cellulose and hemicellulose, lignin is mainly used as waste in the pulping and papermaking industry for treatment, thereby not only wasting resources, but also polluting the environment. Lignin is a renewable resource that to date can directly provide a large range of natural aromatic compounds in nature. A simple and efficient method for degrading lignin is developed, and is very important for realizing high-value utilization of the lignin.

Lignin is a three-dimensional reticular macromolecule with complex and various, amorphous and high polymerization structure, and is mainly formed by connecting phenylpropane structural units through C-C bonds or C-O bonds. The breaking of the linked C-C or C-O bonds is the key to achieving the conversion of lignin to high value-added aromatic compounds. The reported lignin conversion methods, such as thermal cracking, supercritical conversion, acid-base hydrolysis, etc., all have the disadvantages of harsh operating conditions, low yield of target aromatic monomers, etc. In view of the complex structural characteristics of lignin and the fact that small molecular intermediates obtained in the degradation process are easy to polymerize again, efficient and high-selectivity degradation of lignin to obtain aromatic monomers remains a difficult point of current research.

Disclosure of Invention

The invention aims to provide a method for catalyzing oxidative degradation of lignin into aromatic monomers by molybdenum.

The method provided by the invention has the advantages that the degradation system is simple and green, the operation condition is mild, and the yield of aromatic compounds (mainly comprising aromatic aldehyde, aromatic ketone and aromatic acid ester) in the product is high; provides possibility for high-value utilization of lignin and lignocellulose.

According to the method for catalyzing the oxidative degradation of lignin, the raw material lignin comprises native lignin in wood chips, husks and straws, alkali lignin, sulfonate lignin, dealkalized lignin and organic solvent delignification.

The catalyst is a non-noble metal molybdenum compound and comprises one or more than two of molybdenum trioxide, molybdenum disulfide, molybdenum pentachloride, sodium molybdate and acetylacetonato molybdenum oxide; the dosage of the catalyst is 10-100 wt% of the raw material, preferably 20-50 wt%.

The method for catalyzing the oxidative degradation of lignin comprises the following reaction conditions: the oxygen source is oxygen, the oxygen partial pressure is 0.2-2.0MPa, and 0.5-1.5MPa is preferred; the temperature is 80-250 ℃, and 100-200 ℃ is preferably selected; the reaction time is 2-10h, preferably 2-12 h.

The solvent used in the reaction is one or more than two of methanol, ethanol, ethyl acetate and glycol; the mass ratio of the solvent to the lignin is 10-100.

In the catalytic oxidation degradation reaction, the obtained aromatic small molecular monomer mainly comprises aromatic aldehyde, aromatic ketone and aromatic acid ester, and the total aromatic monomer yield can reach more than 60 wt%.

The method for degrading lignin provided by the invention adopts a simple non-noble metal molybdenum compound as a catalyst, can directly catalyze, oxidize and degrade alkali lignin, sulfonate lignin, dealkalized lignin, organic solvent hydrolyzed lignin and even native lignin in sawdust, fruit shells and straws under mild conditions to obtain aromatic aldehyde, aromatic ketone and aromatic acid (ester) micromolecule monomers, belongs to the field of converting lignin in biomass resources into high value-added chemicals for resource utilization, and meets the requirement of sustainable development.

Detailed Description

The primary lignin (hardwood, softwood, husk and straw) is firstly crushed by a crusher and mechanically treated by a ball mill to obtain particles with the diameter of about 40 meshes for later use.

Example 1:

1.0g of poplar wood chips, 0.5g of molybdenum acetylacetonate and 30mL of methanol are added into a 100mL reaction kettle, oxygenated to 1.0MPa, and the temperature is kept at 180 ℃ for 6 hours. Cooling to room temperature, using GC-MS and comparing with standard substance to determine the quality of the product, and using external standard method to analyze quantitatively; the ratio of the mass of each product obtained to the mass of lignin in the initial charge is its yield.

The aromatic monomer in the product mainly comprises p-hydroxybenzaldehyde, p-hydroxybenzoic acid, methyl p-hydroxybenzoate, vanillin, vanillone, vanillic acid, methyl vanillic acid, syringaldehyde, syringic acid and methyl syringate. The yield of total aromatic small molecule compounds was 68 wt%.

Example 2:

1.0g of beech wood chips, 0.5g of molybdenum trioxide and 30mL of ethanol are added into a 100mL reaction kettle, oxygenated to 1.0MPa, and kept at 150 ℃ for 5 hours. After cooling to room temperature, the reaction mixture was subjected to qualitative and quantitative analysis by the method of example 1.

The aromatic micromolecules in the product mainly comprise p-hydroxybenzaldehyde, p-hydroxybenzoic acid, ethyl p-hydroxybenzoate, vanillin, vanillone, vanillic acid, ethyl vanillic acid, syringaldehyde, syringic acid and ethyl syringate. The yield of total aromatic small molecule compounds was 62 wt%.

Example 3:

1.0g of sulfonate lignin, 0.2g of sodium molybdate and 30mL of ethylene glycol are added into a 100mL reaction kettle, oxygenated to 1.0MPa, and kept at 120 ℃ for 10 hours. After cooling to room temperature, the reaction mixture was subjected to qualitative and quantitative analysis by the method of example 1.

The aromatic micromolecules in the product mainly comprise p-hydroxybenzaldehyde, p-hydroxybenzoic acid, ethyl p-hydroxybenzoate, vanillin, vanillone, vanillic acid, ethyl vanillic acid, syringaldehyde, syringic acid and ethyl syringate. The total yield of aromatic small molecule compounds was 60 wt%.

Example 4:

1.0g of alkali lignin, 1.0g of molybdenum acetylacetonate and 30mL of methanol are added into a 100mL reaction kettle, oxygenated to 1.5MPa, and the temperature is 160 ℃, and the reaction kettle is kept for 3 hours. After cooling to room temperature, the reaction mixture was subjected to qualitative and quantitative analysis by the method of example 1.

The aromatic small molecules in the product mainly comprise p-hydroxybenzaldehyde, p-hydroxybenzoic acid, methyl p-hydroxybenzoate, vanillin, vanillone, vanillic acid, methyl vanillic acid, syringaldehyde, syringic acid and methyl syringate. The yield of total aromatic small molecule compounds was 64 wt%.

Example 5:

1.0g of poplar wood chips, 1.0g of molybdenum acetylacetonate and 30mL of ethyl acetate are added into a 100mL reaction kettle, oxygenated to 1.0MPa, and kept at 200 ℃ for 3 hours. After cooling to room temperature, the reaction mixture was subjected to qualitative and quantitative analysis by the method of example 1.

The aromatic micromolecules in the product mainly comprise p-hydroxybenzaldehyde, p-hydroxybenzoic acid, ethyl p-hydroxybenzoate, vanillin, vanillone, vanillic acid, ethyl vanillic acid, syringaldehyde, syringic acid and ethyl syringate. The yield of total aromatic small molecule compounds was 61 wt%.

Example 6:

1.0g of beech wood chips, 0.8g of molybdenum trioxide and 30mL of methanol were added to a 100mL reaction vessel, oxygenated to 1.5MPa at 160 ℃ and maintained for 3 hours. After cooling to room temperature, the reaction mixture was subjected to qualitative and quantitative analysis by the method of example 1.

The aromatic small molecules in the product mainly comprise p-hydroxybenzaldehyde, p-hydroxybenzoic acid, methyl p-hydroxybenzoate, vanillin, vanillone, vanillic acid, methyl vanillic acid, syringaldehyde, syringic acid and methyl syringate. The yield of total aromatic small molecule compounds was 66 wt%.

Example 7:

1.0g of sulfonate lignin, 0.5g of molybdenum disulfide and 30mL of ethanol are added into a 100mL reaction kettle, oxygenated to 1.0MPa, and the temperature is 160 ℃, and kept for 4 hours. After cooling to room temperature, the reaction mixture was subjected to qualitative and quantitative analysis by the method of example 1.

Example 8:

1.0g of alkali lignin, 0.8g of molybdenum disulfide and 30mL of ethyl acetate are added into a 100mL reaction kettle, oxygenated to 1.5MPa, and the temperature is kept at 200 ℃ for 3 hours. After cooling to room temperature, the reaction mixture was subjected to qualitative and quantitative analysis by the method of example 1.

The aromatic micromolecules in the product mainly comprise p-hydroxybenzaldehyde, p-hydroxybenzoic acid, ethyl p-hydroxybenzoate, vanillin, vanillone, vanillic acid, ethyl vanillic acid, syringaldehyde, syringic acid and ethyl syringate. The yield of total aromatic small molecule compounds was 65 wt%.

Claims

1. A method for catalyzing oxidative degradation of lignin into aromatic monomers by molybdenum is characterized by comprising the following steps: the method takes molecular oxygen as an oxygen source and a molybdenum compound as a catalyst to catalyze the oxidative degradation of lignin as a raw material into aromatic monomers; the raw material lignin comprises one or more than two of raw lignin in sawdust, fruit shell and straw, and one or more than two of alkali lignin, sulfonate lignin, dealkalized lignin and organic solvent delignification; the catalyst is a non-noble metal molybdenum compound and comprises one or more of molybdenum trioxide, molybdenum disulfide, molybdenum pentachloride, sodium molybdate and acetylacetonato molybdenum oxide.

2. The method of claim 1, wherein: the dosage of the catalyst is 10-100 wt% of the raw material feeding amount.

3. The method of claim 1, wherein: the molecular oxygen is oxygen, and the oxygen partial pressure in the reaction system is 0.2-2.0 MPa; the temperature is 80-250 deg.C^oC; the reaction time is 2-20 h.

4. The method of claim 1, wherein: the reaction is carried out in a solvent, and the solvent is one or more than two of methanol, ethanol, ethyl acetate and glycol; the mass ratio of the solvent to the lignin is 10-100.

5. The method of claim 1, wherein: in the catalytic oxidative degradation reaction, the obtained aromatic monomer mainly comprises one or more than two of aromatic aldehyde, aromatic ketone, aromatic acid and aromatic ester, and the total yield of the aromatic monomer reaches more than 60 wt%.

6. The method of claim 5, wherein: the aromatic aldehyde is one or more of p-hydroxybenzaldehyde, vanillin and syringaldehyde; the aromatic ketone is one or more of vanillone and syringone; the aromatic acid is one or more of p-hydroxybenzoic acid, vanillic acid and syringic acid; the aromatic ester is one or more of p-hydroxybenzoate, vanillic oxalate and syringic acid ester.