阅读说明：本技术 一种提高碱木质素胺化改性效率或酚羟基含量的方法 (Method for improving amination modification efficiency or phenolic hydroxyl content of alkali lignin ) 是由 李凤凤 杨桂花 陈嘉川 吉兴香 张志礼 于 2021-08-24 设计创作，主要内容包括：本发明属于提高碱木质素反应活性领域,公开了一种提高碱木质素胺化改性效率或酚羟基含量的方法,包括以下制备步骤：将木质素加入低共熔溶剂体系(氯化胆碱/尿素体系、氯化胆碱/甘油体系、氯化胆碱/乙酸体系)混合均匀进行加热处理,调节预处理温度,搅拌处理一段时间后加入去离子水终止反应,随后进行离心、冷冻干燥得到预处理后的碱木质素。进行减压蒸馏回收低共熔溶剂体系；或将低共熔溶剂体系处理后的反应体系转移到稀酸溶液中,继续机械搅拌一段时间,随后进行离心、真空干燥得到预处理后的工业碱木质素。本发明的预处理方法所用溶解绿色环保,可以循环回用,无污染产生,工艺简单,易于操作,适于工业化生产,具有良好的应用前景。(The invention belongs to the field of improving the reaction activity of alkali lignin, and discloses a method for improving the amination modification efficiency or phenolic hydroxyl content of alkali lignin, which comprises the following preparation steps: adding lignin into a eutectic solvent system (a choline chloride/urea system, a choline chloride/glycerol system and a choline chloride/acetic acid system), uniformly mixing, heating, adjusting the pretreatment temperature, stirring for a period of time, adding deionized water to terminate the reaction, and then centrifuging and freeze-drying to obtain pretreated alkali lignin. Carrying out reduced pressure distillation to recover the eutectic solvent system; or transferring the reaction system treated by the eutectic solvent system into a dilute acid solution, continuously mechanically stirring for a period of time, and then centrifuging and vacuum drying to obtain the pretreated industrial alkali lignin. The pretreatment method disclosed by the invention is green and environment-friendly in dissolving, can be recycled, is free from pollution, simple in process, easy to operate, suitable for industrial production and good in application prospect.)

1. A method for improving amination modification efficiency of alkali lignin, which is characterized by comprising the following steps:

adding alkali lignin into a eutectic solvent system, uniformly mixing, heating to react, stopping reaction after reacting for a period of time, centrifuging, and freeze-drying to obtain pretreated alkali lignin;

and (4) carrying out reduced pressure distillation on the centrifuged supernatant to recover the eutectic solvent system.

2. The method for improving the amination modification efficiency of alkali lignin according to claim 1, wherein the eutectic solvent system is a choline chloride/urea system, a choline chloride/glycerol system, a choline chloride/acetic acid system.

3. The method for improving the amination modification efficiency of alkali lignin according to claim 2, wherein the mass-to-volume ratio of the alkali lignin to the choline chloride/urea system is 1g: 12-15 mL; preferably, the molar ratio of choline chloride to urea in the eutectic solvent system is 1: 1.7 to 2.1;

or the mass volume ratio of the alkali lignin to the choline chloride/glycerol system is 1g: 24-32 mL; preferably, the molar ratio of choline chloride to glycerol in the eutectic solvent system is 1: 2.3 to 2.7;

or the mass volume ratio of the alkali lignin to the choline chloride/acetic acid system is 1g: 10-20 mL, preferably, the molar ratio of choline chloride to acetic acid in the eutectic solvent system is 1:1.9 to 2.6.

4. The method for improving the amination modification efficiency of alkali lignin according to claim 1, wherein the alkali lignin comprises various types of lignin extracted from various types of alkali pulping black liquor from softwood, hardwood and grass raw materials and sold commercially;

or the purity of the alkali lignin is 80-90%, the water content of the alkali lignin is preferably 2-4%, the particle size of the alkali lignin is preferably 100-150 meshes, and the molecular weight of the alkali lignin is preferably 3000-6000.

5. The method for improving the amination modification efficiency of the alkali lignin according to claim 1, wherein in the pretreatment process, the pretreatment temperature is 55-65 ℃, the pretreatment time is 30-120 min, and preferably, the rotation speed of the stirring treatment is 200-300 r/min; the rotating speed of the centrifugal treatment is 6000-8000 r/min.

6. A pretreated alkali lignin prepared by the method of any one of claims 1 to 5.

7. A method for improving the phenolic hydroxyl content of industrial alkali lignin by a regeneration method is characterized by comprising the following steps:

adding alkali lignin into a eutectic solvent system, uniformly mixing, heating to react, transferring the reaction system into a dilute acid solution for treatment after reacting for a period of time, centrifuging, and drying to obtain pretreated alkali lignin II.

8. The regeneration method for improving the phenolic hydroxyl content of industrial alkali lignin according to claim 1, wherein the eutectic solvent system is choline chloride/urea system, choline chloride/glycerol system, choline chloride/acetic acid system;

the diluted acid solution is an acetic acid solution, preferably, the pH of the acid solution is 3-4, and most preferably, the pH is 3.

9. A pretreated alkali lignin II prepared by the process of claim 7 or 8.

10. The use of the pretreated alkali lignin I of claim 6 in the preparation of aminated lignin, surfactants, dye dispersants, wastewater treatment agents;

or, the application of the pretreated alkali lignin II as claimed in claim 9 in preparing cement dispersant, water reducing agent, metal ion chelating agent and asphalt emulsifier.

Technical Field

The invention belongs to the field of improving the reaction activity of alkali lignin, and particularly relates to a method for improving the amination yield or phenolic hydroxyl content of alkali lignin.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

Lignin, one of the most abundant natural polymers on earth, is second only to cellulose and is the second most abundant. Worldwide, about 3 million tons of lignin waste are obtained annually by various chemical pulping processes. As a byproduct in the biomass refining process, most of lignin is burnt as fuel in the alkali recovery process, but the heat value of the lignin is low, and the combustion of a large amount of lignin causes waste of biomass energy. Therefore, a method for utilizing lignin with high value is needed to be researched so as to utilize the biomass resource reasonably.

The lignin molecule contains a large number of active groups, such as methoxy, phenolic hydroxyl, alcoholic hydroxyl, carbon-carbon double bond, carbonyl and the like, and the existence of the functional groups indicates that the lignin has the potential of preparing various functional materials. Common lignin modification methods include sulfonation, graft copolymerization, amination, alkylation, oxidation, condensation, and the like. Among the above methods, amination is the most effective method for modifying lignin. The aminated lignin becomes aminated lignin and is widely applied to various fields such as surfactants, dye dispersants, wastewater treatment and the like. At present, Mannich reaction is the most studied lignin amination modification method, however, various chemical connections exist among molecular units forming lignin, a three-dimensional net structure is presented, an amination reagent can only react with active groups on the surface of lignin in the lignin amination modification process, and is difficult to permeate into lignin molecules, so that groups in the lignin molecules cannot participate in amination reaction, and the amination rate is low. In order to improve the amination efficiency of lignin, researchers activate lignin by using sodium hydroxide, raney nickel, sodium borohydride, a sulfonation reagent and the like to improve the amination modification efficiency. However, the use of the above chemical agents causes an increase in the pressure for water pollution treatment, and is not an environmentally friendly method.

On the other hand, a plurality of chemical connections exist among molecular structural units of lignin, a complex and compact three-dimensional network structure is presented, the reaction activity is low, and in order to improve the phenolic hydroxyl content of the lignin and increase the reaction activity, researchers can perform activation treatment on the lignin by means of sulfuric acid and the like. However, the use of the chemical reagent causes great pollution to the environment and also does not meet the requirement of environmental protection.

Disclosure of Invention

In order to solve the defects and shortcomings of the prior art, the invention aims to provide a method for improving the amination yield or phenolic hydroxyl content of alkali lignin.

In order to achieve the technical purpose, the invention adopts the following technical scheme:

in a first aspect of the invention, a method for improving the amination modification efficiency of alkali lignin is provided, which comprises the following steps:

adding alkali lignin into a eutectic solvent system, uniformly mixing, heating to react, stopping the reaction after a period of time, centrifuging, and freeze-drying to obtain pretreated alkali lignin I;

and (4) carrying out reduced pressure distillation on the centrifuged supernatant to recover the eutectic solvent system.

The second aspect of the invention provides a method for improving the phenolic hydroxyl content of industrial alkali lignin by a regeneration method, adding the alkali lignin into a eutectic solvent system, uniformly mixing, heating to react, transferring the reaction system into a dilute acid solution for treatment after reacting for a period of time, centrifuging and drying to obtain pretreated alkali lignin II;

in a third aspect of the invention, there is provided a pretreated alkali lignin I, II prepared by any one of the above methods.

In a fourth aspect of the invention, the application of the pretreated alkali lignin I in preparation of aminated lignin, a surfactant, a dye dispersant and a wastewater treatment agent is provided.

The fifth aspect of the invention provides an application of the pretreated alkali lignin II in preparation of cement dispersants, water reducers, metal ion chelating agents and asphalt emulsifiers.

The invention has the beneficial effects that:

(1) the eutectic solvent system (choline chloride/urea, choline chloride/glycerol, choline chloride/acetic acid) used in the invention is green and environment-friendly and is convenient to recycle.

(2) The method for improving the amination yield and the phenolic hydroxyl content of the alkali lignin has simple preparation process and easy operation, and is suitable for industrial production;

(3) the reaction activity of the pretreated alkali lignin is obviously increased, and the amination efficiency is improved.

(4) The phenolic hydroxyl content of the pretreated industrial alkali lignin is obviously improved, and the application field of the alkali lignin is widened.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

A method for improving amination yield of alkali lignin comprises the steps of adding alkali lignin into a eutectic solvent system (a choline chloride/urea system, a choline chloride/glycerol system and a choline chloride/acetic acid system), uniformly mixing, heating, adjusting pretreatment temperature, stirring for a period of time, adding deionized water to terminate reaction, centrifuging, and freeze-drying to obtain pretreated alkali lignin I. Vacuum distillation is carried out to recover the eutectic solvent system.

In some embodiments, the alkali lignin includes softwood, hardwood, and grass feedstocks extracted from various types of alkaline pulping black liquors, and also commercially available alkali lignin types.

In some embodiments, the alkali lignin is 80-90% pure.

In some embodiments, the alkali lignin has a moisture content of 2-4%.

In some embodiments, the alkali lignin has a particle size of 100 to 150 mesh.

In some embodiments, the alkali lignin has a molecular weight of 3000 to 6000.

In some embodiments, the eutectic solvent system is choline chloride/urea, choline chloride/glycerol, choline chloride/acetic acid.

In some embodiments, the eutectic solvent system has a molar ratio of choline chloride to urea of 1: 1.7 to 2.1.

In some embodiments, the eutectic solvent system has a molar ratio of choline chloride to glycerol of 1: 2.3 to 2.7.

In some embodiments, the eutectic solvent system has a choline chloride to acetic acid molar ratio of 1:1.9 to 2.6.

In some embodiments, the choline chloride, the urea and the acetic acid have a purity of 90-95%.

In some embodiments, when the alkali lignin sample is pretreated in the eutectic solvent system, the alkali lignin sample is dropped into choline chloride/urea (or choline chloride/glycerol or choline chloride/acetic acid) to be uniformly mixed, and then is subjected to heating treatment.

In some embodiments, the alkali lignin is pretreated in the eutectic solvent system, and the mass-to-volume ratio of the alkali lignin to the choline chloride/urea system is 1g: 12-15 mL.

In some embodiments, the alkali lignin is pretreated in the eutectic solvent system, and the mass-to-volume ratio of the alkali lignin to the choline chloride/glycerol system is 1g: 24-32 mL.

In some embodiments, the alkali lignin is pretreated in the eutectic solvent system, and the mass-to-volume ratio of the alkali lignin to the choline chloride/acetic acid system is 1g: 10-20 mL.

In some embodiments, the alkali lignin sample is added into a eutectic solvent system (a choline chloride/urea system, a choline chloride/glycerol system, and a choline chloride/acetic acid system) and uniformly mixed for stirring pretreatment, wherein the pretreatment temperature is 55-65 ℃, and the pretreatment time is 30-120 min.

In some embodiments, the rotation speed of the stirring treatment is 200-300 r/min.

In some embodiments, the rotation speed of the centrifugal treatment is 6000 to 8000 r/min.

The invention also provides a method for improving the phenolic hydroxyl content of the industrial alkali lignin by a regeneration method, which comprises the steps of adding the industrial alkali lignin into a eutectic solvent system (a choline chloride/urea system, a choline chloride/glycerol system and a choline chloride/acetic acid system), uniformly mixing, heating, changing the pretreatment temperature, mechanically stirring for a period of time, transferring the reaction system into a dilute acid solution, continuously mechanically stirring for a period of time, and then centrifuging and drying in vacuum to obtain the pretreated industrial alkali lignin II.

In some embodiments, the industrial alkali lignin comprises poplar, which is extracted from various types of alkaline pulping black liquor from wood, wheat straw and other raw materials.

In some embodiments, the industrial alkali lignin is 80-90% pure.

In some embodiments, the eutectic solvent system is choline chloride/urea, choline chloride/glycerol, choline chloride/acetic acid.

In some embodiments, the eutectic solvent system has a molar ratio of choline chloride to urea of 1:2, the mol ratio of choline chloride to glycerol is 1:2, the mol ratio of choline chloride to acetic acid is 1:2.

in some embodiments, the choline chloride and the urea are dried in vacuum before use. Drying at 60 deg.C for 24 hr.

In some embodiments, when the industrial alkali lignin is pretreated in the eutectic solvent system, the mass-to-volume ratio of the industrial alkali lignin to the eutectic solvent system is 1: 10-80.

In some embodiments, the industrial alkali lignin sample is added into a eutectic solvent system and uniformly mixed for stirring pretreatment, the pretreatment temperature is 80-140 ℃, and the pretreatment time is 1-8 hours.

In some embodiments, the rotation speed of the mechanical stirring treatment is 100-200 r/min.

In some embodiments, the reaction system is transferred to a dilute acid solution, which is a solution of pH 3 acetic acid, with continued mechanical stirring for a period of time.

In some embodiments, the reaction system is transferred into a dilute acid solution, and mechanical stirring is continued for a period of time, wherein the volume ratio of the dilute acid solution to the reaction system is 5-10: 1.

In some embodiments, the reaction system is transferred to the dilute acid solution, and mechanical stirring is continued for a period of time, wherein the rotation speed of the mechanical stirring is 10-30 r/min, and the time is 10-40 min.

In some embodiments, the centrifugation is performed at 10000-12000 r/min for 10-40 min.

The present invention is described in further detail below with reference to specific examples, which are intended to be illustrative of the invention and not limiting.

Example 1

Taking alkali lignin (with the purity of 80%, the water content of 3%, the particle size of 100 meshes and the molecular weight of 4500) extracted from wheat straw soda anthraquinone process pulping black liquor, adding a eutectic solvent system (a choline chloride/urea system), uniformly mixing, heating, adjusting the pretreatment temperature, stirring for a period of time, adding deionized water to terminate the reaction, and then centrifuging, and freeze-drying to obtain the pretreated alkali lignin. Vacuum distillation is carried out to recover the eutectic solvent system (choline chloride/urea system). The treatment conditions were: the mol ratio of choline chloride to urea in the eutectic solvent system is 1:1.9, the purity of choline chloride is 90%, the purity of urea is 90%, choline chloride and urea are uniformly mixed and then are subjected to heating treatment, the mass volume ratio of alkali lignin to the choline chloride/urea system is 1g:15mL, the pretreatment temperature is 55 ℃, the pretreatment time is 30min, the stirring treatment rotating speed is 200r/min, and the centrifugal treatment rotating speed is 6000 r/min.

The amination modification process of the alkali lignin in the experimental group is as follows: adding the pretreated alkali lignin sample into a NaOH solution with the mass fraction of 4.5%, wherein the mass volume ratio of the alkali lignin to the NaOH solution is 1g:10mL, performing magnetic stirring, heating to 75 ℃, adding formaldehyde and anhydrous ethylenediamine, and reacting for 3h at 75 ℃ to obtain aminated lignin, wherein the formaldehyde dosage is 40% (relative to the alkali lignin) and the anhydrous ethylenediamine dosage is 20% (relative to the alkali lignin).

Control group 1:

and taking the alkali lignin sample, adding a sodium borohydride solution, uniformly mixing, heating, adjusting the pretreatment temperature, stirring for a period of time, adding deionized water to terminate the reaction, and then centrifuging, freezing and drying to obtain the pretreated alkali lignin. The treatment conditions were: the mass fraction of the sodium borohydride solution is 2%, the mass volume ratio of the alkali lignin to the sodium borohydride solution is 1g:15mL, the pretreatment temperature is 55 ℃, the pretreatment time is 30min, the rotation speed of stirring treatment is 200r/min, and the rotation speed of centrifugation treatment is 6000 r/min.

The amination modification process of the lignin of the control group comprises the following steps: adding a pretreated alkali lignin I sample into a NaOH solution with the mass fraction of 4.5%, wherein the mass volume ratio of the alkali lignin to the NaOH solution is 1g:10mL, performing magnetic stirring, heating to 75 ℃, adding formaldehyde and anhydrous ethylenediamine, and reacting for 3h at 75 ℃ to obtain aminated lignin, wherein the formaldehyde dosage is 40% (relative to alkali lignin) and the anhydrous ethylenediamine dosage is 20% (relative to alkali lignin).

TABLE 1 comparison of lignin amination efficiency for different pretreatment methods

Sample (I)	Amino content (mmol/g)
		Example 1	1.96
Control group 1	1.61

The data in table 1 show that the amine group content of the alkali lignin I pretreated by the eutectic solvent system (choline chloride/urea system) is 21.74% higher than that of the alkali lignin pretreated by sodium borohydride, and the amine group content is increased, which indicates that the amination modification efficiency of the wheat straw alkali lignin can be significantly improved by the pretreatment of the eutectic solvent system (choline chloride/urea system).

Example 2

Taking alkali lignin (with the purity of 85%, the water content of 2.6%, the particle size of 120 meshes and the molecular weight of 4200) extracted from poplar alkaline sulfite pulping black liquor, adding a eutectic solvent system (a choline chloride/glycerol system), uniformly mixing, heating, adjusting the pretreatment temperature, stirring for a period of time, adding deionized water to terminate the reaction, and then centrifuging, and freeze-drying to obtain the pretreated alkali lignin. Vacuum distillation is carried out to recover the eutectic solvent system (choline chloride/glycerol system). The treatment conditions were: the mol ratio of choline chloride to glycerin in the eutectic solvent system is 1:2.5, the purity of choline chloride is 95%, the purity of glycerin is 95%, choline chloride and glycerin are uniformly mixed and then are subjected to heating treatment, the mass volume ratio of alkali lignin to the choline chloride/glycerin system is 1g:25mL, the pretreatment temperature is 60 ℃, the pretreatment time is 45min, the rotation speed of stirring treatment is 300r/min, and the rotation speed of centrifugal treatment is 7000 r/min.

The amination modification process of the lignin in the experimental group is as follows: adding the pretreated alkali lignin sample into a NaOH solution with the mass fraction of 5%, wherein the mass volume ratio of the alkali lignin to the NaOH solution is 1g:10mL, performing magnetic stirring, heating to 85 ℃, adding formaldehyde and anhydrous ethylenediamine, and reacting for 3h at 85 ℃ to obtain aminated lignin, wherein the formaldehyde dosage is 40% (relative to the alkali lignin) and the anhydrous ethylenediamine dosage is 30% (relative to the alkali lignin).

Control group 2:

and taking the alkali lignin sample, adding a sodium borohydride solution, uniformly mixing, heating, adjusting the pretreatment temperature, stirring for a period of time, adding deionized water to terminate the reaction, and then centrifuging, freezing and drying to obtain the pretreated alkali lignin. The treatment conditions were: the mass fraction of the sodium borohydride solution is 2%, the mass-volume ratio of the alkali lignin to the sodium borohydride solution is 1g:25mL, the pretreatment temperature is 65 ℃, the pretreatment time is 45min, the rotation speed of stirring treatment is 300r/min, and the rotation speed of centrifugation treatment is 7000 r/min.

The amination modification process of the lignin of the control group comprises the following steps: adding the pretreated alkali lignin sample into a NaOH solution with the mass fraction of 5%, wherein the mass volume ratio of the alkali lignin to the NaOH solution is 1g:10mL, performing magnetic stirring, heating to 85 ℃, adding formaldehyde and anhydrous ethylenediamine, and reacting for 3h at 85 ℃ to obtain aminated lignin, wherein the formaldehyde dosage is 40% (relative to the alkali lignin) and the anhydrous ethylenediamine dosage is 30% (relative to the alkali lignin).

TABLE 2 comparison of lignin amination efficiency for different pretreatment methods

Sample (I)	Amino content (mmol/g)
		Example 2	2.42
Control group 2	2.07

The data in table 2 show that the amine content of the alkali lignin pretreated by the eutectic solvent system (choline chloride/glycerol system) is increased by 16.91% compared with the alkali lignin pretreated by sodium borohydride, and the increase of the amine content indicates that the amination modification efficiency of the wheat straw alkali lignin can be significantly improved by virtue of the pretreatment of the eutectic solvent system (choline chloride/glycerol system).

Example 3

Taking commercial alkali lignin (with the purity of 90%, the water content of 4%, the particle size of 100 meshes and the molecular weight of 5000), adding a eutectic solvent system (a choline chloride/acetic acid system), uniformly mixing, heating, adjusting the pretreatment temperature, stirring for a period of time, adding deionized water to terminate the reaction, and then centrifuging and freeze-drying to obtain the pretreated alkali lignin. Vacuum distillation is carried out to recover the eutectic solvent system (choline chloride/acetic acid system). The treatment conditions were: the mol ratio of choline chloride to acetic acid in the eutectic solvent system is 1:2.6, the purity of choline chloride is 95%, the purity of acetic acid is 95%, choline chloride and acetic acid are uniformly mixed and then are subjected to heating treatment, the mass volume ratio of alkali lignin to the choline chloride/acetic acid system is 1g:20mL, the pretreatment temperature is 65 ℃, the pretreatment time is 60min, the rotation speed of stirring treatment is 300r/min, and the rotation speed of centrifugal treatment is 8000 r/min.

The amination modification process of the lignin in the experimental group is as follows: adding the pretreated alkali lignin sample into a NaOH solution with the mass fraction of 4.5%, wherein the mass volume ratio of the alkali lignin to the NaOH solution is 1g:10mL, performing magnetic stirring, heating to 75 ℃, adding formaldehyde and anhydrous ethylenediamine, and reacting for 3h at 75 ℃ to obtain aminated lignin, wherein the formaldehyde dosage is 40% (relative to the alkali lignin) and the anhydrous ethylenediamine dosage is 20% (relative to the alkali lignin).

Control group 3:

and taking the alkali lignin sample, adding a sodium borohydride solution, uniformly mixing, heating, adjusting the pretreatment temperature, stirring for a period of time, adding deionized water to terminate the reaction, and then centrifuging, freezing and drying to obtain the pretreated alkali lignin. The treatment conditions were: the mass fraction of the sodium borohydride solution is 2%, the mass-volume ratio of the alkali lignin to the sodium borohydride solution is 1g:20mL, the pretreatment temperature is 65 ℃, the pretreatment time is 60min, the rotation speed of stirring treatment is 300r/min, and the rotation speed of centrifugation treatment is 8000 r/min.

The amination modification process of the lignin of the control group comprises the following steps: adding the pretreated alkali lignin sample into a NaOH solution with the mass fraction of 4.5%, wherein the mass volume ratio of the alkali lignin to the NaOH solution is 1g:10mL, performing magnetic stirring, heating to 75 ℃, adding formaldehyde and anhydrous ethylenediamine, and reacting for 3h at 75 ℃ to obtain aminated lignin, wherein the formaldehyde dosage is 40% (relative to the alkali lignin) and the anhydrous ethylenediamine dosage is 20% (relative to the alkali lignin).

TABLE 3 comparison of lignin amination efficiencies for different pretreatment methods

Sample (I)	Amino content (mmol/g)
		Example 3	2.29
Control group 3	2.02

The data in table 3 show that the amine content of the alkali lignin pretreated by the eutectic solvent system (choline chloride/acetic acid system) is 13.37% higher than that of the alkali lignin pretreated by sodium borohydride, and the amine content is increased, which indicates that the amination modification efficiency of the wheat straw alkali lignin can be significantly improved by the pretreatment of the eutectic solvent system (choline chloride/acetic acid system).

Example 4

Taking alkali lignin (with the purity of 80%, the water content of 3%, the particle size of 150 meshes and the molecular weight of 3000) extracted from the eucalyptus alkaline sulfite pulping black liquor, adding a eutectic solvent system (choline chloride/urea system), uniformly mixing, heating, adjusting the pretreatment temperature, stirring for a period of time, adding deionized water to terminate the reaction, and then centrifuging, and freeze-drying to obtain the pretreated alkali lignin. Vacuum distillation is carried out to recover the eutectic solvent system (choline chloride/urea system). The treatment conditions were: the mol ratio of choline chloride to urea in the eutectic solvent system is 1:1.8, the purity of choline chloride is 95%, the purity of urea is 95%, choline chloride and urea are uniformly mixed and then are subjected to heating treatment, the mass volume ratio of alkali lignin to the choline chloride/urea system is 1g:12mL, the pretreatment temperature is 55 ℃, the pretreatment time is 60min, the rotation speed of stirring treatment is 300r/min, and the rotation speed of centrifugal treatment is 8000 r/min.

The amination modification process of the lignin in the experimental group is as follows: adding the pretreated alkali lignin sample into a NaOH solution with the mass fraction of 4.5%, wherein the mass volume ratio of the alkali lignin to the NaOH solution is 1g:10mL, performing magnetic stirring, heating to 80 ℃, adding formaldehyde and anhydrous ethylenediamine, and reacting for 4h at 80 ℃ to obtain aminated lignin, wherein the formaldehyde dosage is 35% (relative to alkali lignin) and the anhydrous ethylenediamine dosage is 35% (relative to alkali lignin).

Control group 4:

and taking the alkali lignin sample, adding a sodium borohydride solution, uniformly mixing, heating, adjusting the pretreatment temperature, stirring for a period of time, adding deionized water to terminate the reaction, and then centrifuging, freezing and drying to obtain the pretreated alkali lignin. The treatment conditions were: the mass fraction of the sodium borohydride solution is 2%, the mass-volume ratio of the alkali lignin to the sodium borohydride solution is 1g:12mL, the pretreatment temperature is 55 ℃, the pretreatment time is 60min, the rotation speed of stirring treatment is 300r/min, and the rotation speed of centrifugation treatment is 8000 r/min.

The amination modification process of the lignin of the control group comprises the following steps: the amination modification process of the lignin in the experimental group is as follows: adding the pretreated alkali lignin sample into a NaOH solution with the mass fraction of 4.5%, wherein the mass volume ratio of the alkali lignin to the NaOH solution is 1g:10mL, performing magnetic stirring, heating to 80 ℃, adding formaldehyde and anhydrous ethylenediamine, and reacting for 4h at 80 ℃ to obtain aminated lignin, wherein the formaldehyde dosage is 35% (relative to alkali lignin) and the anhydrous ethylenediamine dosage is 35% (relative to alkali lignin).

TABLE 4 comparison of lignin amination efficiencies for different pretreatment methods

Sample (I)	Amino content (mmol/g)
		Example 4	2.52
Control group 4	2.24

The data in table 4 show that the amine content of the alkali lignin pretreated by the eutectic solvent system (choline chloride/urea system) is 12.50% higher than that of the alkali lignin pretreated by sodium borohydride, and the amine content is increased, which indicates that the amination modification efficiency of the wheat straw alkali lignin can be significantly improved by the pretreatment of the eutectic solvent system (choline chloride/urea system).

Example 5

Taking alkali lignin (the purity is 85%) extracted from the poplar caustic soda anthraquinone process pulping black liquor, adding a eutectic solvent system (a choline chloride/urea system, and performing vacuum drying for 24 hours at 60 ℃ before use), uniformly mixing, performing heating treatment, changing the pretreatment temperature, mechanically stirring for a period of time, transferring the reaction system into a dilute acid solution, continuously mechanically stirring for a period of time, and then performing centrifugation and vacuum drying to obtain the pretreated industrial alkali lignin. The treatment conditions were: the mol ratio of choline chloride to urea in the eutectic solvent system is 1:2, and the mass-volume ratio of the industrial alkali lignin to the eutectic solvent system (choline chloride/urea system) is 1: 10. The pretreatment temperature is 80 ℃, the pretreatment time is 8h, and the rotation speed of the mechanical stirring treatment is 200 r/min. And (3) transferring the reaction system into an acetic acid solution with the pH of 3, wherein the volume ratio of the dosage of the acetic acid solution to the reaction system is 5:1, continuously mechanically stirring for 40min at 10r/min, and centrifuging at the rotating speed of 10000r/min for 30 min.

Control group 5:

untreated alkali lignin was used as a control.

TABLE 5 comparison of phenolic hydroxyl content of industrial alkali lignin before and after pretreatment

The data in table 5 show that the phenolic hydroxyl content of the industrial alkali lignin after pretreatment by the eutectic solvent system (choline chloride/urea system) is improved by 28.43% compared with that of the untreated alkali lignin, which indicates that the phenolic hydroxyl content of the industrial alkali lignin can be obviously improved by the pretreatment by the eutectic solvent system (choline chloride/urea system).

Example 6

Taking alkali lignin (the purity is 80%) extracted from the eucalyptus alkaline sulfite pulping black liquor, adding a eutectic solvent system (a choline chloride/glycerol system, and performing vacuum drying for 24 hours at 60 ℃ before use), uniformly mixing, performing heating treatment, changing the pretreatment temperature, mechanically stirring for a period of time, transferring the reaction system into a dilute acid solution, continuously mechanically stirring for a period of time, and then performing centrifugation and vacuum drying to obtain the pretreated industrial alkali lignin. The treatment conditions were: the mol ratio of choline chloride to glycerin in the eutectic solvent system is 1:2, and the mass-volume ratio of the industrial alkali lignin to the eutectic solvent system (choline chloride/glycerin system) is 1: 40. The pretreatment temperature is 120 ℃, the pretreatment time is 5h, and the rotation speed of the mechanical stirring treatment is 100 r/min. And (3) transferring the reaction system into an acetic acid solution with the pH of 3, wherein the volume ratio of the using amount of the acetic acid solution to the reaction system is 8:1, continuously mechanically stirring for 20r/min for 25min, and centrifuging at the rotating speed of 10000r/min for 20 min.

Control group 6:

untreated alkali lignin was used as a control.

TABLE 6 comparison of phenolic hydroxyl content of industrial alkali lignin before and after pretreatment

Sample (I)	Phenolic hydroxyl group content (mmol/g)
		Example 6	1.43
Control group 6	1.25

The data in table 6 show that the phenolic hydroxyl content of the industrial alkali lignin after pretreatment by the eutectic solvent system (choline chloride/glycerol system) is 14.4% higher than that of the untreated alkali lignin, which indicates that the phenolic hydroxyl content of the industrial alkali lignin can be significantly increased by pretreatment by the eutectic solvent system (choline chloride/glycerol system).

Example 7

Taking alkali lignin (the purity is 90%) extracted from wheat straw soda anthraquinone process pulping black liquor, adding a eutectic solvent system (a choline chloride/acetic acid system, and performing vacuum drying for 24 hours at 60 ℃ before use), uniformly mixing, performing heating treatment, changing the pretreatment temperature, mechanically stirring for a period of time, transferring the reaction system into a dilute acid solution, continuously mechanically stirring for a period of time, and then performing centrifugation and vacuum drying to obtain the pretreated industrial alkali lignin. The treatment conditions were: the mol ratio of choline chloride to acetic acid in the eutectic solvent system is 1:2, and the mass volume ratio of the industrial alkali lignin to the eutectic solvent system (choline chloride/acetic acid system) is 1: 80. The pretreatment temperature is 140 ℃, the pretreatment time is 2h, and the rotation speed of the mechanical stirring treatment is 200 r/min. And (3) transferring the reaction system into an acetic acid solution with the pH value of 3, wherein the volume ratio of the dosage of the acetic acid solution to the reaction system is 10:1, continuously mechanically stirring for 30r/min for 10min, and carrying out centrifugal treatment at the rotating speed of 12000r/min for 10 min.

Control group 7

Untreated alkali lignin was used as a control.

TABLE 7 comparison of phenolic hydroxyl content of industrial alkali lignin before and after pretreatment

Sample (I)	Phenolic hydroxyl group content (mmol/g)
		Example 7	1.38
Control group 7	1.16

The data in table 7 can show that the phenolic hydroxyl content of the industrial alkali lignin after pretreatment by the eutectic solvent system (choline chloride/acetic acid system) is increased by 22.0% compared with that of the untreated alkali lignin, which indicates that the phenolic hydroxyl content of the industrial alkali lignin can be significantly increased by pretreatment by the eutectic solvent system (choline chloride/acetic acid system).

It should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and the present invention is not limited thereto, and although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications and equivalents can be made in the technical solutions described in the foregoing embodiments, or equivalents thereof. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.