CN110128247B - Method for catalytic depolymerization of lignin - Google Patents

Abstract

The invention discloses a method for catalytic depolymerization of lignin, which belongs to the technical field of biomass resource utilization. The lignin is added into a reaction vessel equipped with a solvent, and the reaction is carried out under the synergistic effect of iron powder and palladium carbon to realize the degradation of the lignin. The conversion rate of lignin is at least 99%; the products are acetophenone and guaiacol, and the yields are over 99% and over 90%, respectively. The method of the invention is green and efficient, the catalyst after the reaction can be recycled and reused, and still maintains high activity. The method provides a new technical solution for effectively utilizing lignin to produce high value-added chemicals.

Description

A kind of method of lignin catalytic depolymerization

technical field

The invention belongs to the technical field of biomass resource utilization, and in particular relates to a method for catalytic depolymerization of lignin.

Background technique

Lignin (referred to as lignin), cellulose and hemicellulose are the three main structural components in the vascular tissue of higher terrestrial plants. Among them, lignin is the second most abundant natural high-molecular phenolic polymer in nature. units) are linked by ether and carbon-carbon bonds.

It is estimated that more than 150 million tons of industrial lignin is discharged globally each year. Meanwhile, the second-generation ethanol fuel production process, which uses straw, bagasse, rice husks and other agricultural and forestry wastes as the main raw materials, also produces a large amount of lignin by-products. Although lignin has the advantages of wide source, renewable, abundant reserves, and low price, due to its complex structure and uneven physical and chemical properties, most of it is only used as a low-calorific value fuel, and it has not yet been obtained. Effective utilization also greatly hinders the study of its cracking mechanism. Lignin is used in various industries because of its polyphenolic structure. The utilization methods of lignin can be summarized into two categories. One is to use chemical or biological methods to degrade lignin into small molecules and then use them as chemical raw materials. For example, lignin is used as a raw material for the production of aromatic chemicals such as vanillin and phenolic compounds. Second, it is used directly in the form of macromolecules, such as for the manufacture of dispersants, surfactants, flocculants, activated carbon, etc. Lignin is also widely used in agriculture and can be used as fertilizers and additives for various fertilizers, slow-release pesticides, plant growth regulators, soil conditioners, etc. In addition, due to the high oxygen content of cellulose and hemicellulose, the liquefaction product has a low calorific value, and the carbon-hydrogen ratio of lignin is closest to that of natural oil, so liquid fuel can be produced by liquefying lignin.

At present, scholars at home and abroad have made great breakthroughs in lignin research, which are mainly reflected in: (1) modern advanced analytical instruments have been widely used and played an important role in lignin research; (2) lignin-based materials There has been some progress in the resource utilization of lignin; lignin model compounds are synthetic compounds that are similar or similar in structure and function to certain macromolecules in lignin. Because of its definite structure and function, its cracking mechanism is easier to study than lignin, which can provide a theoretical basis for the study of lignin cracking mechanism. Common lignin model compounds are mainly divided into the following 9 categories: simple phenolic and non-phenolic (also known as lignin monomer model substances), β-O-4 type, α-O-4 type, β-5 type type, β-β type, β-1 type and 5-5 type, quinoid, 1,2-stilbene, etc. According to their different degrees of polymerization, they can be divided into monomers, dimers, trimers and tetramers. At present, oligomeric model compounds such as monomers and dimers are widely used. The polymer lignin model is closer to the real structure of lignin. In order to reflect the lignin degradation mechanism more realistically and correctly, it is necessary to use the polymer lignin model as the research object of the lignin reaction mechanism. At present, the cracking methods of lignin and lignin model substances are mainly divided into catalytic hydrogenolysis, pyrolysis, alcohol

At present, the most studied lignin monomer model is guaiacol, and its cracking method is mainly catalytic hydrogenolysis. The most used catalysts are noble metal catalysts and sulfided Mo-based catalysts. The catalytic effect of the catalyst depends on the carrier material. Transition metal phosphides are promising catalysts. Other cracking methods such as pyrolysis, oxidative degradation, etc. are very effective for the treatment of pollutants in papermaking wastewater; the structure and molecular weight of multimeric lignin model compounds are the closest to natural lignin, however, reports on their cracking reactions are rare so far. . Although oligomeric lignin model compounds such as monomers and dimers can represent lignin to a certain extent, due to their simple structure, the lignin structure is very complex and the degree of representation is limited. Therefore, the cracking of multimeric lignin model compounds It is an important research direction in the future.

SUMMARY OF THE INVENTION

Purpose of the invention: for the deficiencies existing in the prior art, the purpose of the present invention is to provide a method for catalytic depolymerization of lignin. Improve the efficiency of breaking the most abundant β-O-4 bonds in lignin, and provide a new technical route for effectively utilizing lignin to produce high value-added chemicals.

Technical scheme: in order to solve the above problems, the technical scheme adopted in the present invention is as follows:

A method for catalytic depolymerization of lignin. The lignin is added to a reaction vessel containing a solvent, and the reaction is carried out under the synergistic effect of iron powder and palladium carbon to realize the degradation of the lignin; the mass-volume ratio of the lignin to the solvent is: (20-25) mg/mL; the molar ratio of lignin and iron powder is 1: (1-2), and the mass ratio of lignin and palladium carbon is 10: (6-7); the solvent is tetrahydrofuran, dioxane any one of cyclo, methanol, ethanol or isopropanol; the reaction temperature is 80-160°C, and the reaction time is 4-12h.

In the method for catalytic depolymerization of lignin, the lignin is fir lignin or a lignin dimer model compound.

In the method for catalytic depolymerization of lignin, the reaction temperature is 140° C. and the reaction time is 10h.

In the method for catalytic depolymerization of lignin, the molar ratio of lignin and iron powder is 1:2.

In 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, the solvent is methanol.

In the method for catalytic depolymerization of lignin, the mass-volume ratio of lignin to solvent is 25 mg/mL.

A method for catalytic depolymerization of lignin. Dissolving lignin in a reaction vessel containing methanol, adding iron powder and palladium-carbon, and reacting at 140° C. for 10 hours, the mass-volume ratio of lignin and methanol is 25 mg/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 production of guaiacol. rate of more than 90%.

Beneficial effects: Compared with the existing technology, the advantages of the present invention include:

(1) Compared with the current lignin model material degradation method, the present invention can obtain high product yield under the synergistic effect of iron powder and palladium carbon, and provides a new method for effectively utilizing lignin to produce high value-added chemicals technical route.

(2) The catalytic degradation system of the present invention directly degrades the unpretreated lignin without any pretreatment of the lignin, the operation method is simple, the reaction conditions are controllable, the degradation of the lignin is realized, and the obtained degradation The product can be used as an important intermediate in organic synthesis.

(3) The reaction of the present invention does not need to pass H ₂ , which effectively reduces the reaction cost; and the catalyst can be recycled for many times and still has high reaction activity.

Description of drawings

Fig. 1 is the reaction process flow chart of the degradation of the model compound of Example 1;

Fig. 2 is the gel permeation chromatography (GPC) diagram before and after the reaction that Example 6 is applied to fir lignin, wherein, 2A is the GPC curve before the fir lignin reaction, and 2B is the GPC curve after the fir lignin reaction;

Fig. 3 is the infrared spectrogram before and after the reaction that Example 6 is applied to Chinese fir lignin, wherein, 3A is the infrared spectral curve before the Chinese fir lignin reaction, and 3B is the infrared spectral curve after the Chinese fir lignin reaction.

Detailed ways

In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention will be described in detail below in conjunction with specific embodiments.

Product yield calculation method in the present invention: first, according to the standard substance of acetophenone and guaiacol, draw the standard curve of acetophenone and guaiacol by gas chromatography (GC), use naphthalene as the internal standard, and then use naphthalene as the internal standard. The ratio of the area of the reaction product to the area of naphthalene is calculated on the standard curve to obtain the mass of the product, and the mass percentage of the product and the theoretical mass is the yield of the product. Conversion is derived from the area percentage occupied by substrate in the GC.

Example 1

The flow chart of the model compound and catalytic depolymerization reaction process is shown in Figure 1.

Dissolve 100 mg of the lignin dimer model compound raw material in a pressure-resistant tube filled with 4 mL of methanol, add 70 mg of palladium carbon and 46 mg of iron powder, and react at 140 ° C for 10 h, filter and centrifuge the reaction solution to obtain a supernatant, Quantitative characterization by GC showed that when the solvent was methanol, the conversion rate of the model compound was as high as 99%, the yield of acetophenone was 99.2%, the yield of guaiacol was 90.3%, and the intermediate products and by-products Also very low.

Example 2

The method for catalytic depolymerization of lignin is the same as that in Example 1, and the solvent is tetrahydrofuran, dioxane, ethanol or isopropanol, respectively.

The reaction solution was filtered and centrifuged to obtain a supernatant, which was quantitatively characterized by GC. The experimental results are shown in Table 1. Combined with the experimental results of Example 1, it can be seen from Table 1 that the use of different kinds of solvents will affect the conversion rate and product yield. Among them, when the solvent is dioxane and methanol, the conversion rate reaches a maximum of 99%, and the raw materials are almost completely converted; when the solvent is methanol, the yields of acetophenone and guaiacol reach the maximum value, respectively 99.2% and 90.3%, the amount of intermediates and other substances is also the lowest at this time.

Product yield result in the embodiment 2 of table 1

Numbering solvent Acetophenone yield/% Guaiacol Yield/% Conversion rate/% mid product/% other/% 1 tetrahydrofuran 52.3 45.2 98 22.1 1.2 2 Dioxane 91.2 88 99 9.4 0.3 3 Ethanol 76.2 86.1 89 4.3 0.8 4 isopropyl alcohol 53.5 87.5 85.3 12 1.3

Example 3

The method for catalytic depolymerization of lignin is the same as that in Example 1, and the reaction times are respectively 4, 6, 8 and 12h.

The reaction solution was filtered and centrifuged, and the obtained supernatant was quantitatively characterized by GC. The detection results are shown in Table 2. Combined with the experimental results of Example 1, it can be seen from Table 2 that when the reaction time reaches 8h, the conversion rate has reached 99%. Even if the reaction time continued to increase, the conversion rate remained unchanged, but the yields of acetophenone and guaiacol showed a trend of first increase and then decrease with the increase of reaction time, and reached the maximum value when the reaction time was 10h , 99.2% and 90.3%, respectively.

Product yield result in the embodiment 3 of table 2

Numbering time/h Acetophenone yield/% Guaiacol Yield/% Conversion rate/% mid 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 method for catalytic depolymerization of lignin was the same as that in Example 1, and the reaction temperatures were 80, 100, 120 and 160°C, respectively.

The reaction solution was filtered and centrifuged, and the obtained supernatant was quantitatively characterized by GC. The detection results are shown in Table 3. Combined with the experimental results of Example 1, it can be seen from Table 3 that the change of reaction temperature has a great influence on the conversion rate and product yield. When the reaction temperature is 140 ° C, the conversion rate and product yield are the highest, which is the optimal reaction. temperature.

Product yield result in the embodiment 4 of table 3

Numbering temperature/℃ Acetophenone yield/% Guaiacol Yield/% Conversion rate/% mid 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 after the first reaction of Example 1 was collected, washed with methanol (5*10 mL) and dried, and used again in the second catalytic reaction, the method was the same as that of Example 1; The latter catalyst was used for the third catalytic reaction after the same treatment, and the process was repeated. The catalyst was used for a total of 5 times, and the obtained results are shown in Table 4.

It can be seen from Table 4 that the catalyst can be reused in the reaction after being recovered. With the increase of catalyst repetition times, the product yield and conversion rate will decrease, but the conversion rate can reach 99% after repeated one time. After 5 times, the conversion rate can still reach 88.6%, and the product yields are all above 75%, indicating that the catalyst of the present invention can be reused and still has high reactivity.

Product yield result in the embodiment 5 of table 4

Numbering frequency Acetophenone yield/% Guaiacol Yield/% Conversion rate/% mid 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

Dissolve 100 mg of fir lignin in a reaction flask filled with 4 mL of methanol, add 70 mg of palladium-carbon and 46 mg of iron powder, and react at a reaction temperature of 140 ° C for 10 h, filter and centrifuge the reaction solution, and conduct GPC detection on the obtained solid residue. and infrared detection, the detection results are shown in Figure 2 and Figure 3. It can be seen from Figure 2 that the molecular weight decreased from 2190 to 1344, and under this reaction condition, monomers were produced. It can be seen from Figure 3 that the peak positions of phenolic and carbonyl compounds are significantly enhanced. It shows that the method of the present invention can be used for catalytic cracking of multimeric 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%.

Images