Method for preparing lignin-based dye dispersant by mechanochemistry-microwave combined sulfonation process

Abstract

The invention discloses a method for preparing a lignin-based dye dispersant by a mechanochemistry-microwave combined sulfonation process. The method comprises the following steps: activating lignin in an alkaline environment through ball milling, then applying the activated lignin to a microwave-assisted sulfonation reaction, and introducing epichlorohydrin as a cross-linking agent in the sulfonation process to improve the molecular weight of lignosulfonate and close phenolic hydroxyl groups, thereby reducing the pollution of the lignosulfonate to fibers. The invention provides the preparation method of the high-quality lignosulfonate by virtue of the synergistic effect of mechanochemistry and microwave technologies, and the preparation method has the advantages of environmental protection, sustainability and the like, and has potential application and popularization values in related fields.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of dye dispersants, and particularly relates to a method for preparing lignin-based dye dispersants by a combined mechanochemistry and microwave sulfonation process. Background Art

[0002] Lignin, as the only renewable natural aromatic polymer in nature, is a key raw material for replacing fossil resources to prepare chemicals. The annual global industrial lignin production is about 180 million tons, of which 80% comes from the pulp and paper industry. However, the vast majority is directly burned for energy, and only a small amount is used for high-value utilization. This not only aggravates the environmental burden but also goes against the concept of sustainable resource development. Promoting the efficient conversion of lignin has become an urgent need in the industry. Among the existing high-value utilization paths, lignosulfonates have become an important choice in the field of dye dispersants due to the high water solubility, negative charge density, and surface activity conferred by the sulfonic acid groups in their molecules. The global annual output reaches 1.8 million tons, accounting for 90% of the commercial lignin market. However, lignosulfonates face many bottlenecks as dye dispersants. For example, traditional high-temperature sulfonation industries lead to the depolymerization of lignin and a decrease in molecular weight, and at the same time, the sulfonation efficiency is limited, and the content of sulfonic acid groups in the product is insufficient; the high content of phenolic hydroxyl groups in lignosulfonates with low sulfonation degrees easily leads to fiber staining (contamination), restricting their application in the high-order dispersant market; relying on fossil-based long-chain sulfonation reagents (such as 1,4-butane disulfonic acid) or complex cross-linking steps, although the molecular weight and sulfonation degree can be effectively improved, their costs are high and the processes are cumbersome, and they have not yet been commercially promoted. In view of the above problems, it is necessary to pay attention to the process development of lignosulfonates to further promote the high-value utilization of industrial lignin. Summary of the Invention

[0003] To solve the problems of the prior art, the present invention provides a method for preparing lignin-based dye dispersants by a combined mechanochemistry-microwave sulfonation process. The present invention first uses a mechanochemical treatment method to ball-mill and activate lignin in an alkaline environment, and then uses the ball-milled lignin for microwave sulfonation reaction. During the sulfonation reaction, epichlorohydrin is used as a cross-linking reagent to further increase the molecular weight of lignosulfonates and block the phenolic hydroxyl groups in lignin, thereby reducing its contamination of fibers. The present invention opens up a new path for the rational design of sustainable lignosulfonate dye dispersants.

[0004] The technical solution adopted by the present invention to achieve the above object is:

[0005] A method for preparing lignin-based dye dispersants by a combined mechanochemistry-microwave sulfonation process, comprising the following steps:

[0006] (1) Mechanochemical treatment of lignin: Lignin is mixed with an alkali and / or an alkaline salt in a certain mass ratio, and according to a certain ball-to-material mass ratio, they are jointly added to a ball mill jar for ball milling. After the ball milling is completed, the lignin is precipitated with acidified water (pH value of 2 - 3), then washed with clear water until neutral, and finally freeze-dried to obtain the ball mill-activated lignin sample.

[0007] (2) Microwave sulfonation reaction of lignin: The ball mill-activated lignin obtained in step (1) is dissolved in an alkali solution with a pH value of 10 - 13, stirred for 5 - 20 minutes, then a sulfonation reagent and an aldehyde compound are added, and the whole system is transferred to a microwave reactor for a preliminary sulfonation reaction (Reaction - 1). After the preliminary reaction is completed, a predetermined amount of epichlorohydrin is added to the reactor and stirred for 5 - 20 minutes. Subsequently, the reactor is put back into the microwave reactor for a crosslinking / phenolic hydroxyl group blocking reaction (Reaction - 2), and the microwave parameter settings in the initial stage are repeated. Finally, the lignin sulfonate sample is recovered through dialysis and freeze-drying.

[0008] Taking the sulfonation reagent: Na2SO3 and the aldehyde compound: formaldehyde as an example, the chemical reactions involved are as follows:

[0009]

[0010] Furthermore, in step (1), the lignin is industrial lignin, and its sources include softwood, hardwood, and herbaceous plants; the preparation processes include but are not limited to alkali lignin, kraft lignin, black liquor lignin, prehydrolysis lignin, organic solvent lignin, etc.

[0011] Furthermore, in step (1), the industrial lignin is purified industrial lignin, and the purification method is: First, dissolve the industrial lignin in a 1,4-dioxane solution, stir at 200 - 250 rpm for 4 - 5 h, filter out the insoluble matter to obtain a lignin - 1,4-dioxane solution; drop the obtained lignin - 1,4-dioxane solution into acidic water with a pH of 2.0 - 2.5, let it stand in a refrigerator at 4 - 5 °C for 24 - 48 h, vacuum filter to remove the supernatant, and continuously rinse with deionized water; freeze-dry the obtained precipitate to obtain purified industrial lignin. Among them, the 1,4-dioxane solution is an aqueous solution of 1,4-dioxane with a volume fraction of 80 - 95%, the ratio of industrial lignin to the 1,4-dioxane solution is 20 - 40 g : 300 - 600 mL, and the ratio of industrial lignin to acidic water with a pH of 2.0 - 2.5 is 20 - 40 g : 3 - 6 L.

[0012] Further, in step (1), the alkali and / or alkaline salt that provides an alkaline environment during the ball milling process includes, but is not limited to, one or more of NaOH, KOH, Na2CO3, Na2S, Na2SO3, NaHSO3, CH3COONa, NH4HCO3, and CH4N2O.

[0013] Further, in step (1), the acidified water used for precipitating lignin is a solution of one or more of H2SO4, HCl, HNO3, HBr, HI, H3PO4, HCOOH, CH3COOH, and H2C2O4.

[0014] Further, in step (1), the mass ratio of the lignin to the alkali and / or alkaline salt is 0.5:0.5 to 1:5, preferably 1:1 to 1:3.

[0015] Further, in step (1), the mass ratio of the balls to the material is 1:1 to 20:1, preferably 10:1 to 15:1.

[0016] Further, in step (1), the parameters (conditions) of the ball milling are set as follows: each cycle of ball milling is 5 to 35 minutes, preferably 15 to 25 minutes; the rotation speed is 100 to 550 revolutions per minute, preferably 250 to 350 revolutions per minute; then there is an interval of 5 to 35 minutes, preferably 10 to 20 minutes; and it is repeated 1 to 50 cycles, preferably 20 to 30 cycles.

[0017] Further, in step (2), the alkaline solution is a solution of one or more of NaOH, KOH, Na2CO3, Na2S, Na2SO3, NaHSO3, CH3COONa, and NH4HCO3.

[0018] Further, in step (2), the mass ratio of the ball-milled activated lignin to the alkaline solution with a pH value of 10 to 13 is 1:10 to 20, preferably 1:15.

[0019] Further, in step (2), the sulfonation reagent includes one or two of Na2S, Na2SO3, and NaHSO3, and the mass ratio between the sulfonation reagent and the substrate (ball-milled activated lignin) is 0.5:1 to 1:5, preferably 1:1.

[0020] Further, in step (2), the aldehyde compound includes, but is not limited to, one or more of formaldehyde, acetaldehyde, and glutaraldehyde, and the mass ratio between the sulfonation reagent and the aldehyde compound is 0.5:1 to 1:5, preferably 0.5:1 to 1:2, and more preferably 1:1.

[0021] Further, in step (2), the parameters (conditions) of the microwave heating process are set as follows: the temperature is raised to 50-90 °C within 5-35 minutes, and the heat preservation time is set to 5-90 minutes, preferably the temperature is raised to 70-90 °C within 5-8 minutes, and the heat preservation is carried out for 30-50 minutes.

[0022] Further, in step (2), the addition amount of epichlorohydrin is 15-100% relative to the mass of the initial substrate (ball-milled activated lignin), preferably 15%-80%, such as 15%, 30%, 60%.

[0023] Further, in step (2), the cut-off molecular weight of the dialysis bag used for dialysis is 500-5000 g / mol, preferably 1000 g / mol.

[0024] Industrial lignin products usually contain a large amount of alkaline salts. By means of mechanochemistry, using the alkaline environment provided by alkaline salts to improve the reaction activity of lignin in the sulfonation process is a very promising lignin activation method. This method generally uses the mechanical energy generated by ball milling to trigger chemical transformation, which has the advantages of saving or releasing solvents, reducing waste, and significantly improving the yield. In addition, using microwave heating for sulfonation reaction has the characteristics of high efficiency and sustainability. It can reduce energy consumption and shorten the reaction time, and can effectively improve the selectivity of chemical reactions.

[0025] The present invention activates lignin by mechanochemistry. After lignin is ball-milled in an alkaline environment, its molecular weight is reduced to a certain extent, the molecular homogeneity is improved, and the C-O content in its structure is significantly increased, effectively improving its reaction activity in the microwave sulfonation reaction; after microwave sulfonation and epichlorohydrin cross-linking, lignin sulfonate with high molecular weight, high charge density and high sulfonation degree is obtained. This sustainable preparation method provides a new strategy for industrial production and has great potential in industrial applications.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) The present invention takes lignin with rich production and wide sources as the research object to improve the overall utilization value of biomass resources.

[0028] (2) The present invention utilizes the synergistic effect of mechanochemistry and microwave technology. The reaction conditions are mild, mechanochemistry reduces solvent consumption, and microwave heating shortens the reaction time, with significant energy saving.

[0029] (3) The present invention does not rely on expensive long-chain sulfonation reagents and complex processes. Using inorganic salts as a low-cost sulfonation source, the combined process simplifies the process, reduces costs and increases efficiency. By simply grafting sulfonation-epichlorohydrin cross-linking to synergistically block phenolic hydroxyl groups, the molecular weight of lignin sulfonate is increased.

[0030] (4) The present invention provides a method for preparing high-quality lignosulfonate, which has advantages such as environmental protection and sustainability. It provides a brand-new strategy for the sustainable industrial production of lignosulfonate, opens up a new path for the sustainable utilization of lignin, and has potential application and promotion value in related fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a picture of the lignin samples after ball milling provided in Examples 1-3 and Comparative Examples 1-2 of the present invention.

[0032] Figure 2 It is the aliphatic region (δ C / δ H 45 to 90 / 2.0 to 6.0 ppm) and aromatic region (δ C / δ H 100 to 150 / 6.0 to 7.5 ppm) of the two-dimensional nuclear magnetic resonance spectra of the raw lignin and ball-milled lignin samples provided in Examples 1-3 and Comparative Examples 1-2 of the present invention. The main structures present in the lignin samples are: (A) β-O-4′ alkyl aryl ether; (B) benzocoumarin formed by β-5′ coupling; (C) pinoresinol formed by β-β' coupling; (G) guaiacyl unit.

[0033] Figure 3 It is the aliphatic region (δ C / δ H 45 to 90 / 2.0 to 6.0 ppm) and aromatic region (δ C / δ H 100 to 150 / 6.0 to 7.5 ppm) of the two-dimensional nuclear magnetic resonance spectra of the lignosulfonate (b) sample obtained after crosslinking the sulfonated lignin (a) provided in Example 1 of the present invention with epichlorohydrin. The main structures present in the sample are: sulfonate graft structure (red); epichlorohydrin crosslinking structure (brown). DETAILED DESCRIPTION OF THE INVENTION

[0034] To further illustrate the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following describes in detail the method for preparing a lignin-based dye dispersant by a mechanochemical-microwave combined sulfonation process and its specific implementation manner, structure, characteristics and effects in combination with the accompanying drawings and preferred embodiments. However, the scope of protection required by the present invention is not limited to the scope described in the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0035] In the following examples, the pre-hydrolyzed softwood lignin is the lignin separated from the pre-hydrolysis liquor of softwood, provided by Jining Mingsheng New Materials Co., Ltd.

[0036] Example 1

[0037] 1) Purification of lignin: First, dissolve 40 g of pre-hydrolyzed softwood lignin in 500 mL of 1,4-dioxane solution (85%), stir at 250 rpm for 4 h, and filter out the insoluble matter; drop the obtained lignin-1,4-dioxane solution into 4.5 L of hydrochloric acid aqueous solution with pH = 2, let it stand in a refrigerator at 4 - 5 °C for 24 h, filter and remove the supernatant under vacuum, and continuously rinse with deionized water. Freeze-dry the obtained precipitate to obtain purified pre-hydrolyzed softwood lignin (denoted as the original lignin).

[0038] 2) Mechanochemical treatment of lignin: Mix 20.0 g of purified pre-hydrolyzed softwood lignin (original lignin) with Na2SO3 at a mass ratio of 1:1 and a ball-to-material mass ratio of 10:1, and put them into a ball mill jar for ball milling. The ball milling parameters are set as follows: ball mill for 15 minutes in each cycle, the rotation speed is 450 revolutions per minute, and then interval for 10 minutes, repeat 20 cycles. After ball milling, precipitate the lignin with acidified water acidified by HCl with pH = 2, then filter and wash it with clear water until neutral, and finally freeze-dry it to obtain ball-milled activated lignin (the ball-milled lignin is named M1-1 according to its ratio with Na2SO3).

[0039] 3) Microwave sulfonation reaction of lignin: Take 2 g of the ball-milled activated lignin obtained in step 2), dissolve it in NaOH solution with pH = 11 and stir for 20 minutes, then add 2 g of Na2SO3 as the sulfonation reagent and 5 mL of formaldehyde aqueous solution (37 wt%), and transfer the whole system to a microwave reactor for preliminary sulfonation reaction. The microwave heating process parameters are set as follows: rise to 70 °C within 5 minutes, and the holding time is set to 45 minutes. The product obtained in this step is named MLS.

[0040] After the preliminary reaction is completed, add epichlorohydrin accounting for 60% of the mass of the ball-milled activated lignin to the reactor and stir for 20 minutes. Subsequently, put the reactor back into the microwave reactor for cross-linking / phenolic hydroxyl group blocking reaction, and repeat the microwave parameters set in the initial stage. Finally, recover the lignin sulfonate sample through dialysis (cut-off molecular weight is 1000 g / mol) and freeze-drying. The final product is named MLS-E 60％ 。

[0041] Example 2

[0042] The lignosulfonate dispersant was prepared according to the method of Example 1, but in step 2), the mass ratio of the purified pre-hydrolyzed softwood lignin (raw lignin) to Na2SO3 was 1:2, and the lignin after ball milling was named M1-2.

[0043] Example 3

[0044] The lignosulfonate dispersant was prepared according to the method of Example 1, but in step 2), the mass ratio of the purified pre-hydrolyzed softwood lignin (raw lignin) to Na2SO3 was 1:3, and the lignin after ball milling was named M1-3.

[0045] Example 4

[0046] The lignosulfonate dispersant was prepared according to the method of Example 1, but in step 3), the addition amount of epichlorohydrin was 15% of the mass of the ball-milled activated lignin, and the final product was named MLS-E 15％ 。

[0047] Example 5

[0048] The lignosulfonate dispersant was prepared according to the method of Example 1, but in step 2), the addition amount of epichlorohydrin was 30% of the mass of the ball-milled activated lignin, and the final product was named MLS-E 30％ 。

[0049] Comparative Example 1

[0050] The lignosulfonate dispersant was prepared according to the method of Example 1, but in step 2), no alkaline salt was added, and the lignin after ball milling was named M1-0.

[0051] Comparative Example 2

[0052] The lignosulfonate dispersant was prepared according to the method of Example 1, but the raw lignin was not ball-milled and activated, and only the microwave sulfonation reaction was carried out according to step 3) in Example 1.

[0053] Table 1 Quantification of lignin samples in Examples 1-3 and Comparative Examples 1-2 31 P NMR analysis (unit mmol / g)

[0054]

[0055] Table 2 Molecular weight analysis of lignin samples in Examples 1-3 and Comparative Examples 1-2 (unit g / mol)

[0056]

[0057] Table 3 Molecular weight analysis (unit g / mol), graft sulfonation degree (unit mmol / g), and fiber staining test (K / S value) of lignosulfonate samples in Examples 1, 4, and 5

[0058]

[0059] The physicochemical properties of lignin after ball milling play a crucial role in the subsequent microwave sulfonation process. Therefore, it is necessary to elucidate the structural changes of lignin after ball milling. From the results in Table 1, it can be seen that compared with M1-0, the hydroxyl content of the raw lignin in Comparative Examples 1-2 changed little. However, the total hydroxyl content of each lignin sample gradually decreased with the increase of the Na2SO3 ratio. Compared with the total content of the original lignin (4.45 mmol / g), the total contents of M1-1 and M1-2 decreased by 0.43 mmol / g and 0.59 mmol / g respectively. In particular, the total content of M1-3 decreased significantly to 2.25 mmol / g, and the carboxylic acid in M1-3 disappeared. This can be explained that when lignin is ball milled in an alkaline environment, the hydroxyl groups may be oxidized into various carbonyl groups. At the same time, the oxidation of hydroxyl groups also leads to their direct condensation under alkaline conditions. In particular, these two processes may also compete with each other. In the present invention, the content of carboxylic acid did not increase, which is more in line with the situation of mutual condensation.

[0060] From the molecular weight analysis of the lignin samples of Examples 1-3, Comparative Example 1 and Comparative Example 2 in Table 2, it can be seen that the molecular weight of M1-3 decreased from 8625 g / mol of the original lignin to 4445 g / mol, and the molecular weight distribution (D) decreased from 6.49 to 4.49. Obviously, ball milling effectively reduced the molecular weight of lignin and improved its uniformity. Reducing the molecular weight to the optimal level can improve the accessibility of functional groups during the reaction, thereby improving the reaction activity of lignin. We observed that the lignin raw materials and ball-milled lignin samples with different lignin / Na2SO3 ratios showed significantly different colors ( Figure 1 ), among which M1-1 had the brightest and lightest color. Related to this, the decrease of M w may also be related to the color change. This can be explained that the cleavage of the β-O-4' bond releases active fragments that are prone to oxidation. However, there are many factors causing the color change of lignin. Generally speaking, lignin with a brighter color often has a high reaction activity.

[0061] To comprehensively understand the structural changes of lignin, two-dimensional HSQC nuclear magnetic resonance was used to analyze the lignin samples before and after ball milling. Figure 2The main structures in the lignin macromolecule, such as β-O-4', β-5' and β-β' bonds, can be clearly observed. The relative abundances of the main linkage structures of lignin were calculated by a semi-quantitative method. It is worth noting that significant changes occurred in the relative abundances of the three lignin samples. The relative abundances of β-O-4', β-5' and β-β' in the original lignin were 39.5%, 18.2% and 11.6% respectively. In the spectrum of Comparative Example 1 (M1-0), the degradation amplitudes of β-O-4′ and β-5′ were about 2%, and the degradation amplitude of β-β′ was 15.6%. While in the spectra of Examples 1-3, the structural abundances of β-O-4', β-5' and β-β' in M1-1 (43.5%, 24.3% and 22.1%), M1-2 (44.6%, 24.9% and 23.9%) and M1-3 (44.8%, 21.8% and 23.5%) increased significantly. The change in relative abundance confirmed that mechanochemical treatment of lignin led to an increase in the C-O structure.

[0062] In addition, the chemical structures of the sulfonated lignin (a) and the lignosulfonate (b) obtained after crosslinking with epichlorohydrin in Example 1 were studied, and the two-dimensional HSQC nuclear magnetic resonance spectrum is as Figure 3 shown. The results show that the signals corresponding to the three typical linkage structures of β-O-4', β-5' and β-β', as well as several characteristic signals belonging to the G unit, are clearly visible. Compared with Figure 2 M1-1 in C / H there was no obvious change in the chemical shift of the above signals. In the spectra before and after crosslinking with epichlorohydrin, a new signal region (red marked) appeared significantly at δ 60％ / δ C / H 58.9 / 4.41 ppm. Through a dedicated nuclear magnetic resonance identification software and comparison with published reports, it was confirmed that this is the carbon-hydrogen correlation signal of the methylene in C5-CH2SO3-. In the MLS-E 60％ spectrum, new correlation signals (brown marked) at δ C / δ H 66.7 / 4.18 (E2), 70.7 / 3.81 and 73.6 / 3.78 ppm (E1) are attributed to the crosslinking structure of epichlorohydrin, and the specific chemical structure is as shown. In particular, there are few reports on the two-dimensional HSQC nuclear magnetic resonance analysis of sulfonates, and the present invention provides a valuable reference for the structural analysis of lignosulfonates. In addition, after analyzing the molecular weight and sulfonation degree of the samples obtained in Examples 1, 4 and 5 through Table 3, it was found that the microwave sulfonation-epichlorohydrin crosslinking method adopted in this study can significantly increase the molecular weight of lignosulfonates. Among them, MLS-E in Example 1 60％It reaches 10530 g / mol. At the same time, crosslinking also effectively reduces the degree of contamination of lignosulfonate on fibers, and the K / S value of the fibers decreases from 0.50 before crosslinking to 0.36.

[0063] The above are only the preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the concept of the present invention belong to the protection scope of the present invention. It should be noted that for those skilled in the art of this technology, several improvements and refinements made without departing from the principle of the present invention are also regarded as the protection scope of the present invention.

Claims

1. A method for preparing a lignin-based dye dispersant by a mechanochemical-microwave combined sulfonation process, characterized in that: The following steps are involved: (1) Mechanochemical treatment of lignin: lignin and alkali and / or alkaline salt are mixed in a certain mass ratio and added into a ball mill according to a certain ball-to-material mass ratio for ball milling; after ball milling, lignin is precipitated with acidified water with a pH value of 2 to 3, then washed with clean water to neutrality, and finally freeze-dried to obtain a ball-milled activated lignin sample; (2) Microwave sulfonation reaction of lignin: the ball-milled activated lignin obtained in step (1) is dissolved in an alkaline solution with a pH value of 10 to 13 and stirred for 5 to 20 minutes, then a sulfonating agent and an aldehyde compound are added, and the entire system is transferred to a microwave reactor for a preliminary sulfonation reaction; after the preliminary reaction is completed, epichlorohydrin is added to the reactor and stirred for 5 to 20 minutes; then, the reactor is placed back into the microwave reactor for a cross-linking / phenolic hydroxyl blocking reaction; finally, a lignin sulfonate sample is obtained by dialysis and freeze-drying.

2. The method for preparing a lignin-based dye dispersant by a mechanochemical-microwave combined sulfonation process as claimed in claim 1, characterized in that: In step (1), the lignin is industrial lignin, the sources of which include coniferous wood, hardwood, and herbaceous wood; the preparation process includes one or more of alkali lignin, kraft lignin, black liquor lignin, prehydrolyzed lignin, and organic solvent lignin; The industrial lignin is purified industrial lignin, and the purification method is as follows: firstly, the industrial lignin is dissolved in a 1,4-dioxane solution, stirred at 200-250 rpm for 4-5 hours, and insoluble matter is filtered out to obtain a lignin-1,4-dioxane solution; the obtained lignin-1,4-dioxane solution is added dropwise to acidic water with a pH value of 2.0-2.5, and allowed to stand in a refrigerator at 4-5°C for 24-48 hours, and the supernatant is removed by vacuum filtration, and washed with deionized water; the obtained precipitate is freeze-dried to obtain purified industrial lignin; wherein, the 1,4-dioxane solution is a 1,4-dioxane aqueous solution with a volume fraction of 80-95%, the ratio of the industrial lignin to the 1,4-dioxane solution is 20-40 g: 300-600 mL, and the ratio of the industrial lignin to the acidic water with a pH value of 2.0-2.5 is 20-40 g: 3-6 L.

3. The method for preparing a lignin-based dye dispersant by a mechanochemical-microwave combined sulfonation process as claimed in claim 1, characterized in that: In step (1), the base and / or alkaline salt includes one or more of NaOH, KOH, Na2CO3, Na2S, Na2SO3, NaHSO3, CH3COONa, NH4HCO3 and CH4N2O; the acidified water is one or more of H2SO4, HCl, HNO3, HBr, HI, H3PO4, HCOOH, CH3COOH and H2C2O4.

4. The method for preparing a lignin-based dye dispersant by a mechanochemical-microwave combined sulfonation process as claimed in claim 1, characterized in that: In step (1), the mass ratio of lignin to alkali and / or alkaline salt is 0.5:0.5 to 1:

5.

5. The method for preparing a lignin-based dye dispersant by a mechanochemical-microwave combined sulfonation process as claimed in claim 1, characterized in that: In step (1), the ball-to-material mass ratio is 1:1 to 20:1; The ball milling conditions are as follows: each ball milling cycle lasts 5 to 35 minutes, the rotation speed is 100 to 550 revolutions per minute, the interval time is 5 to 35 minutes, and 1 to 50 cycles are repeated.

6. The method for preparing a lignin-based dye dispersant by a mechanochemical-microwave combined sulfonation process as claimed in claim 1, characterized in that: In step (2), the alkaline solution is one or more solutions selected from the group consisting of NaOH, KOH, Na2CO3, Na2S, Na2SO3, NaHSO3, CH3COONa and NH4HCO3.

7. The method for preparing a lignin-based dye dispersant by a mechanochemical-microwave combined sulfonation process as claimed in claim 1, characterized in that: In step (2), the sulfonation reagent includes one or two of Na2S, Na2SO3, and NaHSO3, and the mass ratio of the sulfonation reagent to the substrate ball-milled activated lignin is 0.5:1 to 1:

5.

8. The method for preparing a lignin-based dye dispersant by a mechanochemical-microwave combined sulfonation process as claimed in claim 1, characterized in that: In step (2), the aldehyde compound includes one or more of formaldehyde, acetaldehyde and glutaraldehyde, and the mass ratio between the sulfonation reagent and the aldehyde compound is 0.5:1 to 1:

5.

9. The method for preparing a lignin-based dye dispersant by a mechanochemical-microwave combined sulfonation process as claimed in claim 1, characterized in that: In step (2), the microwave heating process is carried out under the following conditions: the temperature is raised to 50 to 90 degrees Celsius within 5 to 35 minutes, and the heat preservation time is 5 to 90 minutes.

10. The method for preparing a lignin-based dye dispersant by a mechanochemical-microwave combined sulfonation process according to claim 1, characterized in that: In step (2), the amount of epichlorohydrin added is 15 to 100% of the mass of the initial substrate ball-milled activated lignin.

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