CN110128247B - Method for catalytic depolymerization of lignin - Google Patents

Method for catalytic depolymerization of lignin Download PDF

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CN110128247B
CN110128247B CN201910437164.3A CN201910437164A CN110128247B CN 110128247 B CN110128247 B CN 110128247B CN 201910437164 A CN201910437164 A CN 201910437164A CN 110128247 B CN110128247 B CN 110128247B
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lignin
reaction
iron powder
solvent
catalytic depolymerization
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CN110128247A (en
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潘晖
张乐
黄聪
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Nanjing Forestry University
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Nanjing Forestry University
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    • C07C41/00—Preparation of ethers; Preparation of compounds having groups, groups or groups
    • C07C41/01—Preparation of ethers
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
    • C07C45/51—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by pyrolysis, rearrangement or decomposition
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Abstract

The invention discloses a method for catalytic depolymerization of lignin, and belongs to the technical field of biomass resource utilization. Adding lignin into a reaction container filled with a solvent, and reacting under the synergistic action of iron powder and palladium carbon to realize the degradation of the lignin. A lignin conversion of at least 99%; the products are acetophenone and guaiacol, and the yield respectively reaches more than 99 percent and more than 90 percent. The method is green and efficient, and the catalyst after reaction can be recycled and reused and still maintains higher activity. The method provides a new technical scheme for producing high value-added chemicals by effectively utilizing lignin.

Description

Method for catalytic depolymerization of lignin
Technical Field
The invention belongs to the technical field of biomass resource utilization, and particularly relates to a method for catalytic depolymerization of lignin.
Background
Lignin (abbreviated as lignin), cellulose and hemicellulose are three main structural components in vascular bundle tissues of high-grade terrestrial plants. The lignin is a natural macromolecular phenolic polymer with second most abundant content in nature and is formed by linking three typical phenylpropane structural units (a guaiacyl phenylpropane unit, a syringyl phenylpropane unit and a p-hydroxyphenyl phenylpropane unit) through ether bonds and carbon-carbon bonds.
It is estimated that industrial lignin discharged worldwide every year is more than 1.5 hundred million tons, and a large amount of lignin byproducts are also produced in the second generation ethanol fuel production process which takes the agricultural and forestry wastes such as straws, bagasse, rice husks and the like as main raw materials. Although lignin has the advantages of wide sources, reproducibility, abundant reserves, low price and the like, most of lignin is only used as low-calorific-value fuel due to the influence of factors such as complex structure, non-uniform physical and chemical properties and the like, so that the lignin still cannot be effectively utilized, and the research on the cracking mechanism of the lignin is greatly hindered. Lignins are used in various industries due to their polyphenol structure. The utilization method of lignin can be summarized into two main types, namely, lignin is degraded into small molecules by a chemical or biological method and then is used as a chemical raw material, for example, the lignin is used as the raw material for producing aromatic chemicals such as vanillin and phenolic compounds; and secondly, the polymer is directly utilized in a macromolecular form, such as a method for manufacturing a dispersing agent, a surfactant, a flocculating agent, activated carbon and the like. The lignin has wide application in agriculture, and can be used as fertilizer and additives of various fertilizers, pesticide slow release agents, plant growth regulators, soil conditioners and the like. In addition, since the cellulose and hemicellulose have high oxygen contents, the heat value of the liquefied product is low, and the carbon-hydrogen ratio of the lignin is closest to that of natural petroleum, and the liquid fuel can be prepared by liquefying the lignin.
At present, scholars at home and abroad make great breakthrough in the research of lignin, which is mainly shown in that: (1) modern advanced analytical instruments are widely applied to lignin research and play an important role; (2) resource utilization of the lignin-based material has certain progress; the lignin model compound is an artificially synthesized compound which is similar or similar to the structure and function of certain macromolecules in lignin. Due to the determination of the structure and the function, the cracking mechanism is easier to study compared with lignin, and a theoretical basis can be provided for the study of the cracking mechanism of the lignin. Common lignin model compounds fall into the following 9 major classes: simple phenol type and non-phenol type (also called lignin monomer model), beta-O-4 type, alpha-O-4 type, beta-5 type, beta-beta type, beta-1 type and 5-5 type, quinoid, 1, 2-stilbene, etc. They can be classified into monomers, dimers, trimers and tetramers according to their polymerization degrees. At present, oligomer model compounds such as monomers, dimers and the like are more applied. The polymer lignin model is closer to the real structure of lignin, and in order to reflect the lignin degradation mechanism more truly and correctly, the polymer lignin model is necessary to be used as the research object of the lignin reaction mechanism. At present, the cracking modes of lignin and lignin model substances are mainly divided into catalytic hydrogenolysis, pyrolysis and alcohol
The most studied lignin monomer model at present is guaiacol, the cracking mode of the guaiacol is mainly catalytic hydrogenolysis, the most used catalysts are noble metal catalysts and sulfurized Mo-based catalysts, and the catalytic effect of the catalysts depends on a carrier material. The transition metal phosphide is a catalyst with wide application prospect. Other cracking modes such as pyrolysis, oxidative degradation and the like have very good effect on treating pollutants in the papermaking wastewater; the structure and molecular weight of the polymeric lignin model compounds are closest to those of native lignin, however, reports on their cleavage reactions have been rare to date. Although oligomer lignin model compounds such as monomers and dimers can represent lignin to a certain extent, the structure is simple, the structure of lignin is very complex, and the representation degree is limited, so that the cracking of the polymer lignin model compounds is an important future research direction.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the defects in the prior art, the invention aims to provide a method for catalytic depolymerization of lignin. The efficiency of breaking the most-content beta-O-4 bonds in the lignin is improved, and a new technical route is provided for producing high-added-value chemicals by effectively utilizing the lignin.
The technical scheme is as follows: in order to solve the problems, the technical scheme adopted by the invention is as follows:
a method for catalyzing and depolymerizing lignin comprises the steps of adding lignin into a reaction vessel filled with a solvent, and reacting under the synergistic action of iron powder and palladium-carbon to degrade lignin; the mass-volume ratio of the lignin to the solvent is (20-25) mg/mL; the molar ratio of the lignin to the iron powder is 1: 1-2, and the mass ratio of the lignin to the palladium carbon is 10: 6-7; the solvent is any one of tetrahydrofuran, dioxane, methanol, ethanol or isopropanol; the reaction temperature is 80-160 ℃, and the reaction time is 4-12 h.
According to the method for catalytic depolymerization of lignin, the lignin is fir lignin or a lignin dimer model compound.
The method for catalytic depolymerization of lignin has the reaction temperature of 140 ℃ and the reaction time of 10 hours.
According to the method for catalytic depolymerization of lignin, the molar ratio of lignin to iron powder is 1: 2.
According to the method for catalytic depolymerization of lignin, the mass ratio of lignin to palladium carbon is 10: 7.
In the method for catalytic depolymerization of lignin, methanol is used as a solvent.
According to the method for catalytic depolymerization of lignin, the mass-volume ratio of lignin to a solvent is 25 mg/mL.
A method for catalytic depolymerization of lignin comprises dissolving lignin in a reaction vessel filled with methanol, adding iron powder and palladium carbon, reacting at 140 deg.C for 10h, wherein the mass-to-volume ratio of lignin to methanol is 25mg/mL, the molar ratio of lignin to iron powder is 1:2, and the mass ratio of lignin to palladium carbon is 10: 7; the conversion rate of lignin is at least 99%, the yield of acetophenone is more than 99%, and the yield of guaiacol is more than 90%.
Has the beneficial effects that: compared with the prior art, the invention has the advantages that:
(1) compared with the existing lignin model degradation method, the method can obtain high product yield under the synergistic action of the iron powder and the palladium-carbon, and provides a new technical route for effectively utilizing lignin to produce high value-added chemicals.
(2) The catalytic degradation system of the invention directly degrades the lignin which is not pretreated without any pretreatment of the lignin, has simple operation method and controllable reaction conditions, realizes the degradation of the lignin, and the obtained degradation product can be used as an important organic synthesis intermediate.
(3) The reaction of the invention does not need to be communicated with H2The reaction cost is effectively reduced; and the catalyst can be recycled for multiple times and still has high reaction activity.
Drawings
FIG. 1 is a flow chart of the reaction process for the degradation of the model compound of example 1;
FIG. 2 is a Gel Permeation Chromatography (GPC) graph before and after reaction applied to cedar lignin in example 6, wherein 2A is a GPC curve before reaction of cedar lignin, and 2B is a GPC curve after reaction of cedar lignin;
FIG. 3 is the infrared spectra before and after the reaction applied to the cedar lignin in example 6, wherein 3A is the infrared spectrum curve before the reaction of the cedar lignin, and 3B is the infrared spectrum curve after the reaction of the cedar lignin.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with examples are described in detail below.
The product yield calculation method comprises the following steps: firstly, according to the standard products of the acetophenone and the guaiacol, drawing a standard curve of the acetophenone and the guaiacol through Gas Chromatography (GC), using naphthalene as an internal standard, then calculating the ratio of the area of a reaction product to the area of the naphthalene on the standard curve to obtain the mass of the product, wherein the mass percentage of the product to the theoretical mass percentage is the yield of the product. The conversion was obtained as a percentage of the area occupied by the substrate in the GC.
Example 1
The process flow diagram of the model compound and catalytic depolymerization reaction is shown in FIG. 1.
Taking 100mg of a lignin dimer model compound raw material, dissolving the lignin dimer model compound raw material in a pressure resistant tube filled with 4mL of methanol, adding 70mg of palladium carbon and 46mg of iron powder, reacting for 10 hours at 140 ℃, filtering and centrifuging reaction liquid to obtain supernatant, and carrying out quantitative characterization by GC (gas chromatography).
Example 2
The lignin catalytic depolymerization was performed as in example 1, with tetrahydrofuran, dioxane, ethanol or isopropanol as solvent.
The reaction solution was filtered and centrifuged to obtain a supernatant, which was quantitatively characterized by GC, and the experimental results are shown in table 1. In combination with the experimental results of example 1, it can be seen from table 1 that the use of different types of solvents has an effect on the conversion and the product yield. Wherein, when the solvent is dioxane and methanol, the conversion rate reaches up to 99 percent, and the raw materials are almost completely converted; when the solvent was methanol, the acetophenone and guaiacol yields reached a maximum of 99.2% and 90.3%, respectively, when the amounts of intermediates and other substances were also minimal.
Table 1 product yield results in example 2
Numbering Solvent(s) Acetophenone yield/%) Guaiacol yield/% Conversion rate/% Intermediate product/%) Other%
1 Tetrahydrofuran (THF) 52.3 45.2 98 22.1 1.2
2 Dioxane (dioxane) 91.2 88 99 9.4 0.3
3 Ethanol 76.2 86.1 89 4.3 0.8
4 Isopropanol (I-propanol) 53.5 87.5 85.3 12 1.3
Example 3
The lignin catalytic depolymerization was carried out in the same manner as in example 1, with reaction times of 4, 6, 8 and 12h, respectively.
The reaction solution was filtered and centrifuged, and the obtained supernatant was quantitatively characterized by GC, and the detection results are shown in table 2. Combining the experimental results of example 1, it can be seen from table 2 that the conversion rate has reached 99% already when the reaction time reaches 8 h. Even if the reaction time continues to increase, the conversion rate remains unchanged, but the yields of acetophenone and guaiacol show a trend of increasing and decreasing with increasing reaction time, reaching maximum values at 10h, respectively 99.2% and 90.3%.
Table 2 product yield results in example 3
Numbering Time/h Acetophenone yield/%) Guaiacol yield/% Conversion rate/% Intermediate product/%) Other%
1 4 85.9 64.1 92 13 1.6
2 6 95 87.9 97 8 1.1
3 8 97.8 88.4 99 6 0.9
4 12 94 82.6 99 0.4 3.7
Example 4
The lignin catalytic depolymerization was carried out in the same manner as in example 1 at reaction temperatures of 80, 100, 120 and 160 ℃.
The reaction solution was filtered and centrifuged, and the obtained supernatant was quantitatively characterized by GC, and the detection results are shown in table 3. In combination with the experimental results of example 1, it can be seen from table 3 that the change of the reaction temperature has a great influence on both the conversion rate and the product yield, and the conversion rate and the product yield are the highest at the reaction temperature of 140 ℃, which is the optimal reaction temperature.
Table 3 product yield results in example 4
Numbering Temperature/. degree.C Acetophenone yield/%) Guaiacol yield/% Conversion rate/% Intermediate product/%) Other%
1 80 15 13 84.5 62 3
2 100 42.6 37.3 92.6 30.8 2.4
3 120 98.2 86.3 97.3 16 2.2
4 160 98.8 88 99 0.6 2.6
Example 5
The catalyst from example 1 after the first reaction was collected, washed with methanol (5 × 10mL), dried and used again in the second catalytic reaction, in the same way as in example 1; the catalyst obtained after the second catalytic reaction was subjected to the same treatment and used for the third catalytic reaction, and the process was repeated in this manner, and the catalyst was used 5 times in total, and the obtained results are shown in table 4.
As can be seen from Table 4, the catalyst can be recycled and reused in the reaction, the product yield and conversion rate decrease with the increase of the catalyst repetition number, but the conversion rate can reach 99% after repeating once, and the conversion rate can still reach 88.6% after repeating 5 times, and the product yield is above 75%, which shows that the catalyst of the present invention can be reused and still has high reaction activity.
Table 4 product yield results in example 5
Numbering Number of times Acetophenone yield/%) Guaiacol yield/% Conversion rate/% Intermediate product/%) Other%
Example 1 1 99.2 90.3 99 0.4 0.1
1 2 93.1 88.6 98.2 0.7 0.2
2 3 90.4 82.9 94.5 1.1 0.6
3 4 85.7 79.8 90 1.9 0.7
4 5 81.3 76.4 88.6 4.7 1.2
Example 6
Dissolving 100mg of China fir lignin in a reaction flask containing 4mL of methanol, adding 70mg of palladium carbon and 46mg of iron powder, reacting at 140 ℃ for 10h, filtering and centrifuging the reaction solution, and performing GPC detection and infrared detection on the obtained solid residue, wherein the detection results are shown in FIG. 2 and FIG. 3. As is clear from FIG. 2, the molecular weight decreased from 2190 to 1344, and monomers were produced under the reaction conditions. As can be seen from FIG. 3, the peak positions of phenolic and carbonyl compounds are significantly enhanced. The method of the invention can be used for catalytic cracking of polymeric lignin.

Claims (5)

1. A method for catalyzing and depolymerizing lignin is characterized in that the lignin is added into a reaction vessel filled with a solvent and reacts under the synergistic action of iron powder and palladium carbon to realize the degradation of the lignin; the mass volume dosage ratio of the lignin to the solvent is (20-25) mg/mL, the molar ratio of the lignin to the iron powder is 1 (1-2), the mass ratio of the lignin to the palladium carbon is 10 (6-7), the solvent is dioxane or methanol, the reaction temperature is 120 ℃, 140 ℃ or 160 ℃, and the reaction time is 8 hours or 10 hours; the lignin is fir lignin or a lignin dimer model compound.
2. The method of catalytic depolymerization of lignin according to claim 1, wherein the molar ratio of lignin to iron powder is 1: 2.
3. The method of catalytic depolymerization of lignin according to claim 1, wherein the mass ratio of lignin to palladium on carbon is 10: 7.
4. The method of catalytic depolymerization of lignin according to claim 1, wherein the mass to volume ratio of lignin to solvent is 25 mg/mL.
5. The method for catalytic depolymerization of lignin according to claim 1, wherein lignin is dissolved in a reaction vessel containing methanol, iron powder and palladium carbon are added to react at 140 ℃ for 10h, the mass-to-volume ratio of lignin to methanol is 25mg/mL, the molar ratio of lignin to iron powder is 1:2, and the mass ratio of lignin to palladium carbon is 10: 7; the conversion rate of lignin is at least 99%, the yield of acetophenone is more than 99%, and the yield of guaiacol is more than 90%.
CN201910437164.3A 2019-05-23 2019-05-23 Method for catalytic depolymerization of lignin Expired - Fee Related CN110128247B (en)

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