CN118725357A - A biomass lignin micro-nanosphere based on a deep eutectic solvent and its preparation method and application - Google Patents

Abstract

The invention discloses a biomass lignin micro-nanosphere based on a low eutectic solvent and a preparation method and application thereof. The preparation method comprises hydrolyzing a wood fiber biomass raw material under acid induction at 80-180°C, separating solid and liquid after the reaction to obtain a residue, drying and crushing the residue; adding the crushed residue to a low eutectic solvent, stirring evenly, solidifying and separating to obtain a lignin-containing low eutectic solvent; adding deionized water dropwise to the lignin-containing low eutectic solvent, stirring evenly, freezing and solidifying to obtain lignin micro-nanospheres, wherein the volume of the deionized water is 1-30 times that of the lignin-containing low eutectic solvent. The preparation method can efficiently obtain size-adjustable lignin micro-nanospheres.

Description

A biomass lignin micro-nanosphere based on a low eutectic solvent and its preparation method and application

Technical Field

The invention belongs to the field of preparation of biomass-based lignin nanomaterials, and specifically relates to a method for preparing biomass lignin micro-nanospheres based on a low eutectic solvent.

Background Art

Lignin is the second largest woody biomass resource in nature after cellulose, and is also the most abundant renewable aromatic organic compound. It has good biocompatibility and excellent antibacterial and antioxidant effects. Its unique chemical structure and high reactivity make it widely used in biomedicine, agricultural production and environmental protection. However, due to the diversity of lignin sources and the complexity of its own chemical structure, it exhibits characteristics such as heterogeneity, polydispersity and structural uncertainty, which limits its application. How to improve the physical form and chemical structure of lignin and realize the high-value utilization of lignin has become a hot topic and difficulty in current research.

Nanotechnology effectively solves the problems of heterogeneity and dispersion of lignin. Compared with the macromolecules of lignin, the particle size of micro-nano lignin is controllable, the structure is uniform and the dispersion is good. It is generally believed that lignin micro-nanospheres have the characteristics of large specific surface area, adjustable size and multiple active sites, and have been proven to be an excellent and usable form. The micro/nanoization of lignin, especially the preparation of micro-nanospheres, has shown great application potential in related fields such as natural sunscreen, drug carriers and nanofillers.

Currently, there are various methods for lignin micro-nanopolymerization, including precipitation, ultrasound, cross-linking and biological methods.

The invention patent application with publication number CN107774204A discloses using organic solvents such as tetrahydrofuran, dioxane, dimethylformamide, etc. to dissolve lignin and then reverse titrate, dialyze to remove the organic solvent and then dry to obtain the target product. The solvent involved in this method has certain toxicity and the dialysis time is long, the operation is cumbersome, and it is not conducive to large-scale batch production.

In order to avoid the use of toxic and dangerous reagents, some scholars used imidazolium ionic liquid as a solvent. The invention patent application with publication number CN108940218A disclosed the preparation of lignin microspheres by titrating phytic acid after dissolving lignin. This method involves ionic liquid, has high preparation cost and complicated preparation process, and is difficult to mass produce.

Publication number is that the invention patent application of CN108940218A discloses dissolving lignin in the sodium hydroxide solution containing surfactant and then adopting hydrochloric acid titration to prepare lignin microsphere, although simple operation and avoid harmful reagent, acid and alkali are larger to equipment corrosion and this process needs to consume larger energy. In addition, some people also prepare lignin microsphere by ultrasonic treatment, this process highly depends on ultrasonic treatment condition, and the micro/nano particle of gained has uneven size distribution and irregular shape. Adopt aspergillus to extract nano lignin from coconut fiber by biological method, this process is green and gentle, and the gained lignin nanosphere is smaller. But the reaction condition of microorganism is more harsh, affects the quality and output of nano lignin.

Summary of the invention

In order to solve the problems existing in the prior art, the present invention provides a method for preparing biomass lignin micro-nanospheres based on a low eutectic solvent. The preparation method can efficiently obtain lignin micro-nanospheres with adjustable sizes.

The present invention provides a method for preparing biomass lignin micro-nanospheres based on a deep eutectic solvent, comprising:

(1) hydrolyzing the lignocellulosic biomass raw material under acid induction at 80-180° C., separating the solid and liquid to obtain a residue after the reaction is completed, and drying and crushing the residue;

(2) adding a low eutectic solvent to the pulverized residue in step (1), stirring evenly, and solidifying and separating to obtain a lignin-containing low eutectic solvent;

(3) adding deionized water dropwise to the lignin-containing low eutectic solvent of step (2), stirring evenly, and freezing and solidifying to obtain lignin micro-nanospheres, wherein the volume of the deionized water is 1-30 times that of the lignin-containing low eutectic solvent.

The invention extracts a required amount of hydrophobic polymerized lignin from a wood fiber biomass raw material under acid induction by regulating the temperature, avoids carbonization of the lignin, dissolves the hydrophobic polymerized lignin by a low eutectic flux, and then dissolves the hydrophobic lignin by controlling the volume content of deionized water added dropwise, so as to obtain micro-nano spherical lignin, and the size and content of the micro-nano spherical lignin can be regulated. The invention obtains micro-nano spheres and can achieve size regulation of the micro-nano spheres through the synergistic effect of acid induction at a suitable temperature, dissolution by a low eutectic solvent and dissolution by deionized water.

Preferably, the temperature of the hydrolysis reaction is 100-180° C. By regulating the temperature of the hydrolysis reaction, a large amount of polymerized lignin is extracted from the wood fiber biomass raw material. Since the extracted lignin has a high content, the subsequent low eutectic flux dissolution and the regulation of deionized water can obtain biomass lignin micro-nanospheres of suitable size.

Further preferably, the volume of the deionized water is 10-15 times that of the lignin-containing deep eutectic solvent. By adjusting the volume of the deionized water, the hydrophobic lignin is partially separated out, so as to further reduce the size of the larger lignin micro-nanospheres, thereby achieving further regulation of the size of the lignin micro-nanospheres.

Preferably, the mass ratio of the pulverized residue to the low eutectic solvent is 1:10-1:30. If the content of the pulverized residue is too much, the distribution of the lignin micro-nanospheres is uneven, and even the micro-nanosphere morphology cannot be formed after the subsequent addition of deionized water. Excessive use of the low eutectic solvent is not conducive to the hydrophobic dissolution of the obtained lignin in the subsequent water environment, and the obtained morphology effect is poor, the lignin sticks together, and the desired spherical morphology cannot be obtained.

Preferably, the lignocellulosic biomass raw material is agricultural and forestry waste and residues thereof, and the agricultural and forestry waste is derived from one or more of poplar, eucalyptus, larch, spruce, wheat straw, corn cob, and corn stalk.

Preferably, the acid used for acid induction includes one or more of sulfuric acid, hydrochloric acid, phosphoric acid, oxalic acid, citric acid, maleic acid, malic acid, and p-toluenesulfonic acid.

Further preferably, the acid used in the acid induction includes one or more of sulfuric acid, hydrochloric acid, and phosphoric acid. Using inorganic acid can extract more polymerized lignin from the cellulose biomass raw material.

Preferably, the concentration of the acid used in the acid induction is 0.05-5 M, and the reaction time of the hydrolysis reaction is 30-180 min.

Preferably, the ternary deep eutectic solvent is composed of a polyol and a polyacid providing hydrogen bond donors, and choline chloride or betaine providing a hydrogen bond acceptor.

More preferably, the polyacid is one or two of alanine, lactic acid and formic acid; the polyol is one or more of ethylene glycol, glycerol or ethanol.

More preferably, the molar ratio of the choline chloride or betaine, the polyacid and the polyol is 1:(2-6):1-3, preferably 1:4:1.

Preferably, the stirring time of step (3) is 1-3 hours and the temperature is 50-80°C.

On the other hand, the present invention further provides a biomass lignin micro-nano sphere, which is prepared by the preparation method of biomass lignin micro-nano sphere based on a low eutectic solvent.

Preferably, the size of the biomass lignin micro-nanospheres is 30-200 nm.

On the other hand, the present invention also provides an application of biomass lignin micro-nanospheres on super-hydrophobic membranes. The polyvinyl alcohol-lignin nanosphere composite film is prepared by solution casting.

The biomass lignin micro-nanospheres and the polyvinyl alcohol solution are mixed and stirred to obtain a mixed solution, and the mixed solution is heated and solidified in a polyethylene mold to obtain a composite film material. The joint angle of the prepared film material can reach more than 120 degrees.

Preferably, lignin nanospheres and 3wt% polyvinyl alcohol are mixed in a certain proportion and stirred for 2 hours. After stirring, the mixed solution is transferred to a polytetrafluoroethylene mold and dried at a temperature of 60°C for 12 hours. The resulting dried material is a hydrophobic film material, which has good hydrophobic properties, a contact angle of more than 120°, and the super hydrophobic film material is green and degradable.

Compared with the prior art, the present invention has the following beneficial effects:

The present invention hydrolyzes hydrophobic lignin from wood fiber biomass fibers, dissolves the hydrophobic lignin by a low eutectic solvent, and regulates the size of the hydrophobic lignin by deionized water. Lignin micro-nanospheres are obtained through the synergistic effect of acid induction at a suitable temperature, dissolution of the low eutectic solvent, and regulation of deionized water, and the size regulation of the lignin micro-nanospheres is achieved. The preparation method provided by the present invention does not use organic solvents for size regulation, and is more environmentally friendly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a morphology diagram of lignin micro-nanospheres prepared in Example 1 of the present invention;

FIG2 is a morphology of lignin micro-nanospheres prepared in Examples 2 to 5 of the present invention;

FIG3 is a morphology diagram of lignin micro-nanospheres prepared in Example 6 of the present invention;

FIG4 is a morphology diagram of lignin micro-nanospheres prepared in Example 7 of the present invention;

FIG5 is a morphology diagram of lignin micro-nanospheres prepared in Comparative Example 1 of the present invention;

FIG6 is a morphology diagram of lignin micro-nanospheres prepared in Comparative Example 2 of the present invention;

FIG7 is a morphology of lignin micro-nanospheres prepared in Comparative Example 3 of the present invention;

FIG8 is a contact angle bar graph of the composite film material prepared in Application Example 1 of the present invention at different contents of lignin micro-nanospheres.

DETAILED DESCRIPTION

The following embodiments are only listed as examples of the implementation of the present invention and do not limit the present invention. Any modification and optimization based on the essence and concept of the present invention belong to the protection scope of the present invention.

Example 1

(1) Hydrolysis of lignocellulosic biomass: 10 g corncob powder was added with 100 mL 3 M sulfuric acid solution and reacted at 180° C. for 120 min. After the reaction was completed, the solid and liquid were separated and the residue was dried and crushed for later use.

(2) preparing a low eutectic solvent: betaine as a hydrogen bond acceptor and lactic acid and ethylene glycol as hydrogen bond donors were stirred at 80° C. and 500 rpm for 30 minutes in a molar ratio of 1:4:1 to form a clear and transparent solution, thereby obtaining a low eutectic solvent.

(3) The hydrolyzed lignocellulosic biomass residue was added to the prepared low eutectic solvent at a solid-liquid ratio of 1:10 g/mL, and then stirred at 120° C. and 500 rpm for 3 hours.

(4) After solid-liquid separation of the lignin-containing low eutectic solvent in step (3), deionized water 10 times the volume of the lignin-containing low eutectic solvent is added dropwise to the obtained lignin-containing low eutectic solvent while stirring, and then stirred at 1500 rpm for 2 hours. After freeze-drying, micro-nano lignin nanospheres can be obtained; after electron microscopy testing, the diameter of the lignin nanospheres is about 201.nm, as shown in Figure 1.

Example 2-Example 5

Different from Example 1, the hydrolysis temperatures of Examples 2 to 5 are 100° C., 120° C., 160° C. and 180° C., respectively, and the specific steps are as follows:

(1) Hydrolysis of lignocellulosic biomass: 10 g corncob powder was added with 100 mL 3 M sulfuric acid solution, and the mixture was reacted at 100 °C, 120 °C, 160 °C, and 180 °C for 120 min. After the reaction was completed, the solid and liquid were separated, and the residue was dried, crushed, and set aside;

(2) preparing a low eutectic solvent: betaine as a hydrogen bond acceptor and lactic acid and ethylene glycol as hydrogen bond donors were stirred at 80° C. and 500 rpm for 30 minutes in a molar ratio of 1:4:1 to form a clear and transparent solution, thereby obtaining a low eutectic solvent.

(3) adding the hydrolyzed lignocellulosic biomass residue into the prepared low eutectic solvent at a solid-liquid ratio of 1:10 g/mL, and then stirring at 120 °C and 500 rpm for 3 hours;

(4) After solid-liquid separation of the lignin-containing low eutectic solvent in step (3), water 10 times the volume of the low eutectic solvent containing lignin is added dropwise to the obtained low eutectic solvent containing lignin while stirring, and then stirred at 1500 rpm for 2 hours, and then dried to obtain micro-nano lignin nanospheres.

After electron microscopy testing, it was found that the diameter size of the lignin nanospheres had a certain correspondence with the hydrolysis temperature. The sizes of the lignin nanospheres corresponding to the residues obtained at 100°C, 120°C, 160°C and 180°C were 30, 100, 150 and 200 nm, respectively, as shown in Figure 2.

Example 6

(1) Hydrolysis of lignocellulosic biomass: 10 g corncob powder was added with 100 mL 3 M sulfuric acid solution and reacted at 180 °C for 120 min. After the reaction was completed, the solid and liquid were separated, and the residue was dried and crushed for later use;

(2) preparing a low eutectic solvent: betaine as a hydrogen bond acceptor and lactic acid and ethylene glycol as hydrogen bond donors were stirred at 80° C. and 500 rpm for 30 minutes in a molar ratio of 1:4:1 to form a clear and transparent solution, thereby obtaining a low eutectic solvent.

(3) adding the hydrolyzed lignocellulosic biomass residue into the prepared low eutectic solvent at a solid-liquid ratio of 1:10 g/mL, and then stirring at 120 °C and 500 rpm for 3 hours;

(4) After solid-liquid separation of the lignin-containing low eutectic solvent in step (3), water 15 times the volume of the low eutectic solvent containing lignin is added dropwise to the obtained low eutectic solvent containing lignin while stirring, and then stirred at 1500 rpm for 2 hours. After drying, micro-nano lignin nanospheres can be obtained; after electron microscopy testing, the diameter of the lignin nanospheres is 150 nm, as shown in Figure 3.

Example 7

Different from Example 1, the hydrolyzed lignocellulosic biomass residue was added to the prepared low eutectic solvent at a solid-liquid ratio of 1:20 g/mL, and the diameter of the obtained lignin nanospheres was 180 nm, as shown in FIG. 4 .

Comparative Example 1

Different from Example 1, the wood fiber biomass residue was added to the prepared low eutectic solvent at a solid-liquid ratio of 1:50 g/mL. The obtained lignin was shown in FIG5 , which had many irregular morphologies and could not obtain the desired spherical morphology.

Comparative Example 2

The difference from Example 1 is that no deionized water is added after the solid-liquid separation of the lignin-containing deep eutectic solvent, as shown in FIG6 , and thus micro-nano spherical lignin cannot be formed.

Comparative Example 3

Different from Example 1, deionized water with a volume 50 times that of the low eutectic solvent containing lignin was added dropwise to the obtained low eutectic solvent containing lignin while stirring, and the formed micro-nano lignin nanospheres were shown in FIG7 , and the amount of lignin nanospheres was small.

Application Example 1

A polyvinyl alcohol-lignin nanoparticle composite film material was prepared by a simple solution casting method. The lignin nanoparticles obtained in Example 1 and a 3wt.% polyvinyl alcohol solution were mixed in different proportions, stirred for two hours, and then transferred to a polyethylene mold. The contents of the lignin nanoparticles were 1%, 3%, 5%, and 10%, respectively. The composite film material was slowly dried at 60°C for 12 hours to obtain a contact angle of 58.9°, 88°, 95°, 113°, and 128°, respectively, as shown in FIG8 .

Claims (10)

1. The preparation method of the biomass lignin micro-nanospheres based on the eutectic solvent is characterized by comprising the following steps of:

(1) Carrying out hydrolysis reaction on a lignocellulose biomass raw material under the induction of acid at 80-180 ℃, carrying out solid-liquid separation after the reaction is finished to obtain residues, and drying and crushing the residues;

(2) Adding the crushed residues in the step (1) into a eutectic solvent, uniformly stirring, solidifying and separating to obtain the eutectic solvent containing lignin;

(3) And (3) dropwise adding deionized water into the eutectic solvent containing lignin in the step (2), uniformly stirring, and freezing and solidifying to obtain lignin micro-nanospheres, wherein the volume of the deionized water is 1-30 times that of the eutectic solvent containing lignin.

2. The method for preparing biomass lignin micro-nanospheres based on eutectic solvents according to claim 1, wherein the temperature of the hydrolysis reaction is 100-180 ℃.

3. The method for preparing biomass lignin micro-nanospheres based on eutectic solvent according to claim 2, wherein the volume of deionized water is 10-15 times of the volume of the lignin-containing eutectic solvent.

4. The method for preparing biomass lignin micro-nanospheres based on eutectic solvent according to claim 1, wherein the mass ratio of the crushed residues to the eutectic solvent is 1:10-1:30.

5. The method for preparing the eutectic solvent-based biomass lignin micro-nanospheres according to claim 1, wherein the lignocellulosic biomass raw material is agricultural and forestry waste and residues thereof, and the agricultural and forestry waste is one or more of poplar, eucalyptus, larch, spruce, wheat straw, corncob and corn straw.

6. The method for preparing the eutectic solvent based biomass lignin micro-nanospheres according to claim 1, wherein the acid used for the acid induction comprises one or more of sulfuric acid, hydrochloric acid, phosphoric acid, oxalic acid, citric acid, maleic acid, malic acid and p-toluenesulfonic acid.

7. The method for preparing biomass lignin micro-nanospheres based on a eutectic solvent according to claim 1, wherein the eutectic solvent consists of a polyhydric alcohol and a polybasic acid which provide hydrogen bond donors, and choline chloride or betaine which provide hydrogen bond acceptors.

8. Biomass lignin micro-nanospheres, characterized in that the biomass lignin micro-nanospheres are prepared by the method for preparing biomass lignin micro-nanospheres based on eutectic solvents according to any one of claims 1-7.

9. The biomass lignin micro-nanospheres according to claim 8, wherein the biomass lignin micro-nanospheres have a size of 30-200nm.

10. The application of the biomass lignin microsphere according to any one of claims 8 to 9 to a super-hydrophobic membrane material, wherein the biomass lignin microsphere and a polyvinyl alcohol solution are mixed and stirred to obtain a mixed solution, and the mixed solution is heated and cured in a polyethylene mold to obtain the composite membrane material.