Lignin pretreatment method

Abstract

The invention provides a lignin pretreatment method, and belongs to the technical field of lignin pretreatment. The method comprises the following steps: mixing lignin, choline acetate ionic liquid and deionized water according to a specific ratio, stirring, heating, centrifuging, performing suction filtration and the like, thereby effectively degrading the lignin and improving the dissolution rate of the lignin. Experiments show that the dissolution rate of lignin is only 9.5% when no choline acetate participates, while the dissolution rate of the method disclosed by the invention can reach 42.17% at most, and the optimal effect is achieved when the temperature is 100 DEG C, the stirring time is 4 hours and the material ratio is 1: 2: 60. The lignin pretreatment method has the advantages of being low in toxicity, high in biodegradability, environmentally friendly, simple in operation process, low in cost and the like, and a new way is provided for high-value utilization of lignin.

Description

Technical Field

[0001] The present invention relates to the technical field of lignin pretreatment, and particularly relates to a lignin pretreatment method. Background Art

[0002] As the second largest renewable resource in the world, lignin can be converted into valuable chemicals through chemical technologies. However, due to the complex structure of lignin and the presence of a large number of polar groups, there are a large number of strong intermolecular hydrogen bonds in lignin. These factors severely limit the physical and chemical reactions of lignin molecules as reactants with other chemical reagents, restricting the high-value utilization of lignin. Some studies have shown that partial chemical reagents can react with lignin molecules to destroy the complex internal structure of lignin to a certain extent and promote the subsequent cracking of lignin. Currently, the catalysts commonly used for pretreating lignin generally involve strong acids, strong bases, volatile toxic solvents, and precious metals, and the reaction conditions are difficult to control, the reaction time is long, the research process is complex, and environmental problems are easily caused. Therefore, it is necessary to find a catalyst that has both good catalytic effects and is green and environmentally friendly for lignin conversion.

[0003] In recent years, due to the advantages of ionic liquids such as low vapor pressure, non-volatility, strong solubility, good thermal stability, strong chemical stability and catalytic activity, low environmental pollution risk, and recyclability, ionic liquids have become an effective biomass solvent and have received great attention in the field of lignin conversion. Some studies have used ionic liquids 1-butyl-3-methylimidazolium chloride (BMIC), 1-sulfobutyl-3-methylimidazolium trifluoromethanesulfonate ([B(SO3H)mim]OTf), and 1-butyl-3-methylimidazolium dihydrogen phosphate ([Bmim]H2PO4) to pretreat lignin at low temperature, and it has been found that imidazole-based ionic liquids can increase phenolic molecules in pyrolysis oil and improve the quality of pyrolysis oil when pretreating lignin.

[0004] However, in these pretreatment methods, due to the disadvantages of traditional imidazole-based ionic liquids such as non-renewable synthesis raw materials, complex synthesis processes, environmental unfriendliness, high toxicity, high viscosity, poor biodegradability, and large interference from water during the pretreatment process, they pose potential hazards to the environment. Therefore, it is of great significance to find a new pretreatment system that is non-toxic, low-energy-consuming, and efficient, thereby broadening the way for the high-value utilization of lignin. Summary of the Invention

[0005] The purpose of the present invention is to provide a lignin pretreatment method, which overcomes the disadvantages of large pollution and difficult reaction control of current conventional ionic liquids, and realizes efficient, green and environmentally friendly lignin pretreatment with a simple process.

[0006] To achieve the above purpose, the present invention provides a lignin pretreatment method, including the following steps:

[0007] Step S1: Mix lignin, choline acetate ionic liquid, and deionized water to obtain a mixture.

[0008] Step S2: Place the mixture obtained in Step S1 into an oil bath and heat with stirring to obtain a mixture.

[0009] Step S3: Centrifuge the mixture obtained in Step S2 to obtain a regenerated lignin solution.

[0010] Step S4: Filter the regenerated lignin solution by suction filtration, and dry the residual lignin sample to obtain a pretreated lignin sample.

[0011] Preferably, in Step S1, the purity of lignin is 90%.

[0012] Preferably, in Step S1, the ratio of lignin, choline acetate ionic liquid, and deionized water is 1:2:60.

[0013] Preferably, in Step S2, the temperature for heating with stirring is 100 °C, the time is 4 h, and the stirring rate is 500 rpm.

[0014] Preferably, in Step S3, centrifugation is performed 5 times, each time lasting 15 min.

[0015] Preferably, in Step S4, suction filtration is carried out using a circulating water multi-purpose vacuum pump.

[0016] Preferably, in Step S4, drying is carried out in an electrothermal constant temperature forced air drying oven.

[0017] Therefore, the present invention adopts the above-mentioned method for pretreating lignin, and the beneficial technical effects are as follows:

[0018] (1) The currently commonly used solvent systems, such as acid / alkali solutions and organic solvents, have disadvantages such as harsh reaction conditions, being harmful to the environment and human body, and poor selectivity. The choline acetate ionic liquid used in the present invention has strong solubility, mild reaction conditions, almost no volatility, reducing air pollution. It has high selectivity and can selectively break specific chemical bonds in lignin, reducing side reactions.

[0019] (2) The present invention innovatively mixes lignin, choline acetate ionic liquid, and deionized water in a specific ratio, which is different from the prior art. Through a large number of experimental explorations, the optimal material ratio of the three is determined to be 1:2:60, and the synergistic effect is remarkable. Lignin and the ionic liquid are in full contact and reaction with the participation of water, and the catalytic performance of the ionic liquid is exerted, effectively destroying the internal structure of lignin and improving its dissolution rate. Compared with traditional single solvents or complex auxiliary agent systems, the combination method and ratio optimization of the present invention make the pretreatment process more efficient, reducing both costs and environmental pollution. Description of the Drawings

[0020] Figure 1 is a process flow chart of a lignin pretreatment method of the present invention;

[0021] Figure 2 is the lignin dissolution rate under different experimental conditions; among them, Figure 2 in (a) is the lignin dissolution rate under different water amounts; Figure 2 in (b) is the lignin dissolution rate under different temperatures; Figure 2 in (c) is the lignin dissolution rate under different reaction times; Figure 2 in (d) is the lignin dissolution rate under different material ratios. Detailed Embodiments

[0022] The technical solutions of the present invention are further described below with reference to the drawings and embodiments.

[0023] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0024] Example 1

[0025] To explore the influence of the water consumption on the lignin dissolution rate, 3.75 ml, 5 ml, 6.25 ml, 7.5 ml, and 8.75 ml of deionized water were respectively added, and the experiment was carried out at a temperature of 100 °C, a reaction time of 4 h, and a material ratio of lignin (0.125 g) to choline acetate ionic liquid (0.25 g) of 1:2. The test results are as shown in Figure 2 (a) in. As the water consumption increased, the lignin dissolution rate first increased and then decreased. When the water consumption was 7.5 ml, the lignin dissolution rate reached the maximum value of 42.17%.

[0026] During the experiment, the ionic liquid showed a certain viscosity, and it was not easy to fully contact with the powdered lignin during the reaction, which affected the effect of the ionic liquid in dissolving lignin. Therefore, a certain amount of deionized water was added to the ionic liquid to make the ionic liquid fully mixed with lignin and promote the full reaction between the ionic liquid and lignin.

[0027] The dissolution rates of lignin by choline acetate ionic liquid at 70 °C, 80 °C, 90 °C, 100 °C, 110 °C and 120 °C were investigated. The experiments were carried out under the conditions of a reaction time of 4 h, a water consumption of 7.5 ml, 0.25 g of ionic liquid and 0.125 g of lignin. The experimental results are as Figure 2 shown in (b) of the figure. As the temperature increases, the dissolution rate of lignin generally shows an upward trend, reaching the maximum of 42.3% at 110 °C. Since the dissolution rate at 100 °C only differs from the maximum value by 0.3%, considering the energy consumption, 100 °C was selected for subsequent experiments.

[0028] The experiments were carried out at a temperature of 100 °C, a water consumption of 7.5 ml, and a material ratio of lignin to choline acetate ionic liquid of 1:2. The reaction time was a variable, being 2 h, 3 h, 4 h and 5 h respectively. The experimental results are as Figure 2 shown in (c) of the figure. As the reaction time increases, the dissolution rate of lignin shows a trend of first increasing and then decreasing. When the reaction time is 4 h, the dissolution rate reaches the maximum of 42.17%.

[0029] When the mass ratio of lignin to choline acetate ionic liquid is different, as Figure 2 shown in (d) of the figure, when the material ratio of lignin to choline acetate ionic liquid is 1:2, the dissolution rate of lignin reaches the maximum value of 42.17%. When the material ratio further increases, the dissolution rate of lignin shows a downward trend.

[0030] Experiments were carried out based on the above determined optimal parameters.

[0031] The method for lignin degradation based on choline acetate ionic liquid provided in this embodiment, as Figure 1 shown, is realized by an oil bath, a bench-top high-speed centrifuge, an electrothermal constant temperature forced air drying oven, and a circulating water multi-purpose vacuum pump. First, the lignin was placed in the electrothermal constant temperature forced air drying oven for 24 h of drying to exclude the influence of moisture. The dried lignin, ionic liquid and deionized water were mixed in a round-bottom flask at a ratio of 1:2:60. The mixed round-bottom flask was placed in the oil bath. At a temperature of 100 °C, within 4 h, heating and stirring were carried out at a speed of 500 rpm to promote the interaction between lignin and ionic liquid, thereby realizing the cleavage of lignin. After the heating and stirring were completed, the lignin sample was placed in the high-speed centrifuge and centrifuged at a speed of 10,000 rpm for 15 min each time, for a total of 5 times, to achieve solid-liquid separation. Then, the sample after solid-liquid separation was filtered by the circulating water multi-purpose vacuum pump to separate lignin from the ionic liquid. The lignin obtained on the filter paper is the pretreated lignin sample.

[0032] Therefore, in the case of using the above-mentioned lignin pretreatment method without the participation of choline acetate, the dissolution rate of lignin pretreatment is only 9.5%, while after using choline acetate ionic liquid, the degradation and dissolution rate of lignin can reach up to 42.17% at most. By optimizing experimental conditions such as temperature, water consumption, material ratio and time, it is found that when the temperature is 100 °C, the heating and stirring time is 4 h, and the ratio of lignin, ionic liquid and water consumption is 1:2:60, the effect is the best. In addition, this method also has the characteristics of low toxicity and high biodegradability, is environmentally friendly and will not cause pollution. At the same time, the system operation process is simple, the cost is low, the price is reasonable, and it has high economic efficiency and practicability.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A lignin pretreatment method, characterized in that: The following steps are involved: Step S1, mixing lignin, choline acetate ionic liquid, and deionized water to obtain a mixture; Step S2, placing the mixture obtained in step S1 into an oil bath, heating and stirring, to obtain a mixture; Step S3, centrifuging the mixture obtained in step S2 to obtain a regenerated lignin solution; Step S4: filter the regenerated lignin solution and dry the residual lignin sample to obtain a pretreated lignin sample.

2. A lignin pretreatment method according to claim 1, characterized in that: In step S1, the purity of lignin is 90%.

3. A lignin pretreatment method according to claim 1, characterized in that: In step S1, the ratio of lignin, choline acetate ionic liquid, and deionized water is 1:2:

60.

4. A lignin pretreatment method according to claim 1, characterized in that: In step S2, the heating and stirring temperature is 100°C, the time is 4 hours, and the stirring rate is 500 rpm.

5. A lignin pretreatment method according to claim 1, characterized in that: In step S3, centrifugation was performed 5 times, each time lasting 15 min.

6. A lignin pretreatment method according to claim 1, characterized in that: In step S4, the filtration is performed using a circulating water multi-purpose vacuum pump.

7. A lignin pretreatment method according to claim 1, characterized in that: In step S4, drying is performed in an electrically heated constant temperature blast drying oven.

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