阅读说明：本技术 一种基于微波辅助的木质素改性方法 (Microwave-assisted lignin modification method ) 是由 孙润仓 王汉敏 文甲龙 孙少妮 曹学飞 袁同琦 于 2019-09-29 设计创作，主要内容包括：本发明公开了一种基于微波辅助的木质素改性方法,包括如下步骤：a.将工业木质素原料烘干后备用；b.将步骤a中所得的木质素原料与酰氯试剂按摩尔比充分混合,再向该体系中加入适量催化剂并混匀；c.将步骤b中得到的混合体系在微波辅助下加热到设置温度并恒温反应一段时间,反应结束后加入乙醇终止反应；d.将步骤c中得到的混合体系转移至旋蒸瓶并加适量去离子水,旋蒸去除乙醇后加水充分洗涤,冻干得到改性木质素。本发明提供了一种简单、高效的方法实现木质素的快速酯化改性过程。该方法得到的改性木质素酯化度高,也极大地简化了木质素改性加工的过程,缩短了木质素的升级转化周期,这将促进工业木质素的高值化利用。(The invention discloses a lignin modification method based on microwave assistance, which comprises the following steps: a. drying the industrial lignin raw material for later use; b. fully mixing the lignin raw material obtained in the step a with an acyl chloride reagent according to a molar ratio, adding a proper amount of catalyst into the system, and uniformly mixing; c. b, heating the mixed system obtained in the step b to a set temperature under the assistance of microwaves, reacting at a constant temperature for a period of time, and adding ethanol to terminate the reaction after the reaction is finished; d. and c, transferring the mixed system obtained in the step c to a rotary evaporation bottle, adding a proper amount of deionized water, removing ethanol by rotary evaporation, adding water, fully washing, and freeze-drying to obtain the modified lignin. The invention provides a simple and efficient method for realizing the rapid esterification modification process of lignin. The modified lignin obtained by the method has high esterification degree, greatly simplifies the lignin modification processing process, shortens the upgrading and conversion period of the lignin, and promotes high-value utilization of industrial lignin.)

1. A lignin modification method based on microwave assistance is characterized by comprising the following steps:

a. drying the industrial lignin raw material for later use;

b. fully mixing the lignin obtained in the step a and an acyl chloride reagent in different molar ratios in a reaction bottle according to the hydroxyl content of the lignin, adding a proper amount of catalyst into the system, and uniformly mixing;

c. b, heating the mixed system obtained in the step b to a set temperature under the assistance of microwaves, heating to the set temperature, reacting at a constant temperature for a period of time, and adding ethanol into the mixed system after the reaction is finished to terminate the reaction;

d. and c, transferring the mixed system obtained in the step c to a rotary evaporation bottle, adding a proper amount of deionized water, removing ethanol by rotary evaporation, adding water, fully washing a lignin sample, and freeze-drying to obtain the modified lignin.

2. The microwave-assisted lignin modification method according to claim 1, wherein the lignin raw material used in the above steps is industrial lignin obtained in pulp papermaking and biorefinery processes, and the acyl chloride is of different carbon chain lengths (C)₂-C₁₈) The catalyst is analytically pure triethylamine and pyridine, and the catalyst is unnecessary in the reaction process, and the reaction process can be realized without adding the catalyst.

3. The method for modifying lignin based on microwave assistance according to claim 1, wherein the molar ratio of hydroxyl group to acyl chloride of lignin in the above steps is 1:0.5-1.5, the molar ratio of hydroxyl group to catalyst is 1:0.3-1, and the reaction time is 10-35 min.

4. The microwave-assisted lignin modification method according to claim 1, wherein the lignin modification reaction temperature in the above steps is controlled by microwave real-time dynamic power, and the temperature range is 50-80 ℃.

5. The microwave-assisted lignin modification method according to claim 1, wherein the lignin modification reaction in the above steps is terminated by methanol or ethanol, and the modified lignin is dissolved to facilitate the subsequent separation of the lignin-modified product.

6. The microwave-assisted lignin modification method according to claim 1, wherein the ethanol removal from the mixed solution in the above steps can be performed by using a rotary evaporator, vacuum drying or flash evaporation equipment, and the lignin component is precipitated in water while the ethanol is removed.

7. The method for modifying lignin based on microwave assistance according to claim 1, wherein the modified lignin obtained after washing in the above step can be obtained by industrial drying equipment such as freeze drying or spray drying.

Technical Field

The invention relates to high-value conversion of lignin, in particular to a lignin modification method based on microwave assistance.

Background

Lignin, the most abundant aromatic compound in plant cell walls, is a very potential lignocellulosic raw material, which can be further converted into various high value-added materials and chemicals. Originally, the lignin is a macromolecule with random and complex structure, and is formed by dehydrogenating and polymerizing a phenylpropane precursor under the action of enzyme in the plant growth process. In hardwood raw materials, the lignin content is about 20-30% by mass, and the types of structural units that make up the major components are S, G and H.

Statistically, the industrial lignin produced in the global pulp and paper industry is about 6000 million tons per year. However, the conversion utilization rate of the lignin is extremely low, and most of the lignin is used as waste for burning to generate heat, which not only causes environmental pollution, but also greatly wastes biomass resources. The industrial lignin is used as a byproduct in the papermaking process, has low cost and rich yield, and also has the advantages of high carbon content, biodegradability, oxidation resistance, antibacterial performance and the like. However, the brittleness of lignin itself and the incompatibility with other polymers are major obstacles to its use in lignin-based high performance materials. Meanwhile, the glass transition temperature of untreated industrial lignin is not clear or even high, and the characteristic also influences the blending performance of the lignin and the high polymer polymeric material. Furthermore, industrial lignin has a low molecular weight, which makes the lignin post-production composites very stiff and brittle. These inherent properties limit the use of lignin in polymeric materials such as plastics.

Based on this situation, a method for chemically modifying lignin is one of effective strategies to overcome the defects of lignin utilization. Aiming at the structural characteristics of the industrial lignin, the abundant hydroxyl functional groups (aliphatic hydroxyl and phenolic hydroxyl) provide great convenience for further modification and derivatization of the industrial lignin. In the current lignin modification method, esterification, alkylation, chain lengthening reaction and the like are effective methods for effectively improving lignin performance. During the lignin esterification modification reaction, the acyl donor is usually short-chain fatty acid, and the lignin modified by long-chain acyl compound can effectively improve the inherent characteristics of the lignin. For example, the introduction of the long-chain fatty acid can effectively reduce the glass transition temperature of lignin, thereby improving the blending effect of the lignin and plastics and being beneficial to preparing the lignin-based composite material with excellent performance. In recent years, researchers carry out esterification reaction on industrial lignin and acyl chloride with different chain lengths to obtain modified lignin, and then carry out hot melt blending on the modified lignin and plastics to obtain a lignin-based composite material, so that the method greatly improves and promotes the application potential of the industrial lignin in the aspect of composite materials. The modified lignin has increased molecular weight, obviously lowered glass transition temperature, etc. and the modified lignin has obviously improved performance, such as flexibility, elongation at break, strength, etc. after being blended with plastic. However, the reaction time of lignin and modification reagents such as acyl chloride is long in the in-situ esterification modification process, generally not less than 24 hours, which greatly affects the lignin modification efficiency. Meanwhile, the degree of substitution of hydroxyl groups in lignin is difficult to control.

Chinese patent CN 108863776A discloses a method for preparing aromatic acid ester and fatty acid ester by directional catalytic oxidation of lignin, and the method adopts a one-pot method to catalytically oxidize lignin to obtain high value-added products such as methyl terephthalate and the like. The reaction temperature range of the reaction process is 130-260 ℃, the oxygen pressure is up to 2MPa, the reaction time is 2-20h, and the catalyst dosage is up to 20%. The modification process not only needs high temperature and high pressure, but also has long time, high catalyst dosage and the like, and is not beneficial to subsequent further popularization.

Chinese patent CN 106565488A discloses a method for preparing maleic ester by selective catalytic oxidation of lignin, which is characterized in that heteropoly acid functionalized ionic liquid is used as a catalyst, an alcohol-water solution is used as a reaction medium under the conditions of high temperature and high pressure (110-. Although the esterification process is simple to operate and green and safe in process, the problems of high cost, time-consuming reaction process and the like exist, and large-scale industrialization is difficult to realize.

Chinese patent CN 103755975A discloses a method for preparing bio-based plastics by esterification modification of wood fibers, which proposes that ball-milled biomass raw materials are swelled in an organic solvent system DMSO/TEAC at 30-120 ℃ for 0.5-10h, then succinic anhydride and 4-dimethylaminopyridine are added, and esterification reaction is carried out at 20-100 ℃ for 0.5-8 h. Although the reaction process realizes partial esterification of all components, the treatment process not only uses a large amount of organic solvent, but also has long reaction period and high energy consumption, and is not beneficial to popularization and application.

The microwave-assisted heating mode has the characteristics of rapidness, high efficiency and uniform temperature rise, and has wide application range and practical application value in the aspects of biomass pretreatment and chemical conversion. The microwave-assisted heating can obviously reduce the temperature rise and the reaction time, and meanwhile, the microwave has the advantage of rapid and sufficient catalytic reaction, and has obvious technical and efficiency advantages when being applied to the lignin modification. Currently, only a few lignin modification reactions employ microwave-assisted heating. However, esterification modification reaction of lignin is currently reported. Therefore, in order to further realize the efficient and rapid esterification reaction of lignin, the invention aims to adopt a microwave-assisted heating modification mode to construct a lignin esterification modification method.

Disclosure of Invention

In order to solve the problems of long time, low efficiency and the like to be improved in the lignin modification process, the invention provides a lignin modification method based on microwave assistance.

The specific technical scheme of the invention is as follows:

a lignin modification method based on microwave assistance comprises the following steps:

a. drying the industrial lignin raw material for later use;

b. fully mixing the lignin obtained in the step a in a reaction bottle according to different molar ratios of hydroxyl groups of the lignin to acyl chloride reagents, adding a proper amount of catalyst into the system, and uniformly mixing;

c. b, heating the mixed system obtained in the step b to a set temperature under the assistance of microwaves, heating to the set temperature, reacting at a constant temperature for a period of time, and adding ethanol into the mixed system after the reaction is finished to terminate the reaction;

d. and c, transferring the mixed system obtained in the step c to a rotary evaporation bottle, adding a proper amount of deionized water, removing ethanol by rotary evaporation, adding water, fully washing a lignin sample, and freeze-drying to obtain the modified lignin.

1) The industrial lignin raw material is industrial lignin obtained in the processes of paper making by pulp, biological refining and the like, and the acyl chloride has different carbon chain lengths (C)₂-C₁₈) The catalysts used were analytically pure triethylamine and pyridine.

2) The lignin modification reaction in the invention has no reaction solvent, and the molar ratio of hydroxyl in the lignin to the acyl chloride reagent is 1: 0.5-1.5.

3) And in the modification reaction process, a reaction control group without a catalyst is also set, wherein in the experimental group added with the catalyst, the dosage of the catalyst is 1:0.3-1 according to the molar ratio of hydroxyl in lignin to the catalyst.

4) In the modification reaction of microwave-assisted heating, the reaction temperature is controlled by microwave real-time dynamic power, the temperature range is 50-80 ℃, and the constant-temperature reaction time is 10-35 min.

5) The ethanol or methanol added after the reaction is finished is not only a reagent for stopping the reaction, but also a solvent for the modified lignin, and the modified lignin is dissolved so as to be beneficial to the separation of subsequent lignin modified products.

Although the industrial lignin raw material is adopted, the method is not limited to the industrial lignin, the method is simple to operate, rapid and efficient, the energy consumption is low, a reaction solvent is not needed, the using amount of chemicals is reduced, the modification rate of the obtained modified lignin is high, and the modification reaction is sufficient and uniform.

Compared with the prior art, the invention has the beneficial effects that:

the invention adopts a microwave-assisted heating modification mode, which has the characteristics of quick heating, uniform temperature rise and the like, and simultaneously realizes the catalytic effect by microwave-assisted heating, can promote the quick reaction, obviously shortens the lignin modification time and improves the lignin esterification reaction efficiency.

Secondly, the invention adopts a microwave-assisted heating modification mode to realize the rapid esterification reaction of lignin, and meanwhile, the esterification efficiency in the reaction process is also obviously improved, the highest esterification degree is more than 80 percent, and the esterification degree is equivalent to that of a water bath heating reaction for 48 hours under the same condition.

The reaction reagent used in the esterification reaction is a reaction solvent, any organic solvent is not needed as a medium, and the reaction process can basically realize equivalent (equal molar) reaction, so that the characteristic of obviously reducing the modification cost and avoiding the problems of solvent recovery, environmental pollution and the like.

Drawings

FIG. 1 shows oleoyl chloride (C) obtained in an example of the invention₁₈) Nuclear magnetic hydrogen spectrum of lignin before and after modification.

Detailed Description

The present invention will be described in further detail with reference to the following examples, which are not intended to limit the invention thereto.