Lignin fractionation method and application
By employing gradient extraction with eutectic solvents of increasing concentration and pH-induced acid precipitation techniques, the problems of solubility and purity in the lignin fractionation process were solved, resulting in the preparation of efficient, green, and high-performance lignin micro-nanospheres, thus promoting their high-value utilization.
Patent Information
- Application Number
- CN202511086729.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-05
- Publication Date
- 2025-11-18
AI Technical Summary
Existing lignin classification methods suffer from problems such as limited solubility, easy initiation of co-precipitation, low processing throughput, and high cost, resulting in uneven lignin properties and difficulty in efficient utilization.
Industrial lignin was separated by gradient extraction with eutectic solvent of increasing concentration combined with pH-induced acid precipitation, and lignin fractions with narrow molecular weight distribution and high purity were prepared. Micro- and nanospheres with controllable particle size were then prepared by solvent/antisolvent system.
This method achieves efficient and green graded separation of lignin, improving recovery rate and purity. The prepared micro-nanospheres have excellent antioxidant properties, thermal stability, and antibacterial properties, making them suitable for high-value applications.
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Figure CN120966040A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lignin purification technology, specifically to a lignin fractionation and separation method and its application. Background Technology
[0002] With the increasing depletion of fossil resources and the growing prominence of related environmental problems, developing and utilizing renewable plant biomass resources to replace petroleum-based polymer materials has become an important strategic direction for global sustainable development. Lignin is the second most abundant aromatic biomass resource in nature after cellulose, possessing an amorphous three-dimensional network structure. It has been widely explored for applications in phenolic resins, polyurethane foams, composite materials, and carbon fiber precursors. However, the efficient utilization of lignin resources still faces significant challenges. The global pulp and paper industry generates over 50 million tons of lignin annually, of which more than 95% is typically disposed of through direct incineration with black liquor or discarded, resulting in an actual high-value utilization rate of less than 5%. This inefficient utilization mainly stems from the diversity of lignin's chemical structure, the wide range of its molecular weight distribution, the differences in monomer composition, and the variability in its linkage mechanisms and functional group content, leading to inconsistent lignin properties.
[0003] Lignin fractionation is a core strategy for controlling its molecular weight distribution and structural heterogeneity. The fractionated lignin subfractions exhibit significant gradient differences in key structural parameters such as molecular weight distribution, characteristic functional group content, and bonding type. Currently, lignin fractionation methods can be divided into three categories: organic solvent fractionation, acid precipitation, and membrane fractionation. Although these methods demonstrate high separation efficiency, several technical challenges remain. For example, traditional solvent methods have limited solubility for high molecular weight lignin; acid precipitation easily induces co-precipitation, leading to high component heterogeneity; and membrane fractionation is susceptible to lignin contamination, resulting in low throughput and high costs. Gradient extraction methods using different organic solvents can mitigate these shortcomings to some extent, but the volatility of organic solvents not only leads to excessive raw material loss but also poses health and environmental hazards. Furthermore, unmodified lignin has poor mechanical properties and processability, making it difficult to directly replace petroleum-based polymers. Therefore, developing efficient, green, and pollution-free lignin purification and fractionation technologies, and constructing lignin-based materials with controllable morphology and properties based on the fractionation products, is a key path to overcome the bottleneck of its high-value utilization. Summary of the Invention
[0004] To address the problems existing in the prior art, this invention provides a lignin grading and separation method and its application.
[0005] This invention provides a method for lignin fractionation and separation, comprising:
[0006] 1) Gradient extraction of industrial lignin was performed using a eutectic solvent with increasing concentration to obtain lignin fractions with different molecular weight distributions;
[0007] 2) The insoluble residue after gradient extraction was subjected to pH-induced acid precipitation to further separate and obtain high-purity lignin fraction;
[0008] The eutectic solvent is a system formed by choline chloride and acetone or glyoxylic acid.
[0009] Furthermore, the eutectic solvent is a system formed by choline chloride containing a conjugated carboxylic acid and acetone or glyoxylic acid in a molar ratio of 1:2.
[0010] Furthermore, the low, medium, and high concentrations of the gradient extraction are 50 wt%, 65 wt%, and 80 wt%, respectively, with corresponding fractionation yields of 40.2%, 14.1%, and 12.6%.
[0011] Furthermore, prior to pH induction, the insoluble residue is vacuum dried and dispersed in ultrapure water, and the pH of the mixture is adjusted using an alkaline solution until a homogeneous suspension is formed.
[0012] Furthermore, the alkaline solution is 1 M NaOH, and the pH of the suspension is adjusted to 12; the acidic solution is 1 M HCl, and the pH at the precipitation endpoint is 2-3.
[0013] Furthermore, the acid-precipitated lignin fraction yield was 21.8%.
[0014] The present invention also provides an application of the lignin fraction obtained by the above method in the preparation of lignin micro-nanospheres.
[0015] Furthermore, lignin micro / nanospheres with controllable particle size were prepared by inducing self-assembly through a solvent / antisolvent system.
[0016] Furthermore, the solvent is a mixed solution of γ-valerolactone and water, wherein the volume ratio of γ-valerolactone to water is 3~5:1; the antisolvent is water, and the peristaltic pump drip rate is 5 mL / min.
[0017] The beneficial effects of this invention are:
[0018] (1) The raw material used in this invention is industrial alkali lignin, which is mainly derived from by-products of industrial processes such as papermaking and pulping. It is inexpensive and conducive to large-scale industrial application. At the same time, the raw material is biodegradable, which is in line with the concepts of green chemistry and sustainable development.
[0019] (2) This invention innovatively employs a two-step fractionation technique combining gradient extraction with acid precipitation at different concentrations of DES, which significantly improves the recovery rate of the target lignin components. Simultaneously, the membrane-free operation avoids polymer contamination, enabling efficient fractionation at room temperature and atmospheric pressure. The resulting fractionated lignin components exhibit a narrower molecular weight distribution (lower PDI value) and higher purity. Furthermore, this technique preserves highly active functional groups (such as phenolic hydroxyl groups), laying a material foundation for subsequent high-value applications.
[0020] (3) The lignin micro-nanospheres prepared based on the above two-step purification and fractionation technology benefit from the low heterogeneity and high purity of the fractionated lignin, enabling the control of its particle size. At the same time, the micro-nanospheres retain a high content of phenolic hydroxyl groups, giving them excellent antibacterial properties, good thermal stability, and strong antioxidant properties. In addition, specific structural units in the fractionated lignin can form a dense micro-nano structure through strong interactions (such as hydrogen bonds and π-π stacking), which further synergistically optimizes its antioxidant, antibacterial, and other multifunctional properties. Attached Figure Description
[0021] Figure 1 This is a scanning electron microscope (SEM) image of the low-concentration DES lignin-based micro nanospheres prepared in Example 1.
[0022] Figure 2 This is a scanning electron microscope (SEM) image of the acid-precipitated lignin fractional nanospheres prepared in Example 4.
[0023] Figure 3 This is a scanning electron microscope (SEM) image of the alkali lignin micro / nanospheres prepared in Comparative Example 1. Detailed Implementation
[0024] The present invention will be further described below with specific embodiments, but these are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
[0025] This application proposes a method for lignin fractionation and its application. This method employs a preferred gradient extraction technique using green solvents of varying concentrations, combined with acid precipitation, to achieve efficient purification and fractionation of industrial alkali lignin. The fractionated lignin is then used to prepare lignin micro / nanospheres with uniform size and good dispersibility. This strategy effectively solves the inherent heterogeneity and poor dispersibility of lignin, providing a new approach for constructing high-performance lignin-based functional materials, promoting the high-value utilization of lignin, and having broad applications in the field of renewable materials.
[0026] The lignin fractionation and separation method provided in this application includes the following steps:
[0027] 1) Gradient extraction of industrial lignin was performed using a eutectic solvent with increasing concentration to obtain lignin fractions with different molecular weight distributions;
[0028] Specifically, the process is as follows: First, industrial alkali lignin is thoroughly mixed with a low-concentration DES solution under magnetic stirring. The insoluble components and supernatant are obtained by centrifugation. Then, the supernatant is added dropwise to deionized water to regenerate the low-concentration DES lignin fraction. Finally, the precipitate is separated, washed to neutral, and dried for later use. Subsequently, the insoluble component residue is subjected to gradient extraction using medium-concentration DES solution and high-concentration DES solution solvents, respectively. The extraction steps are the same as those for low-concentration DES solution extraction, to obtain medium-concentration DES lignin fraction and high-concentration DES lignin fraction, respectively.
[0029] 2) The insoluble residue after gradient extraction was subjected to pH-induced acid precipitation to further separate and obtain high-purity lignin fraction;
[0030] Specifically, the insoluble DES residue from step 1) is dispersed in ultrapure water after vacuum drying, and the pH of the mixture is adjusted using an alkaline solution until a homogeneous suspension is formed. The insoluble residue is removed by centrifugation, and then an acid solution is slowly added dropwise to the supernatant to induce lignin precipitation and separation. The obtained lignin is washed multiple times with deionized water until neutral, and then dried under vacuum to obtain acid-precipitated lignin fractions.
[0031] This application also provides an application of the lignin fraction obtained by the above method in the preparation of lignin micro-nanospheres, namely, preparing lignin micro-nanospheres with controllable particle size by inducing self-assembly through a solvent / antisolvent system.
[0032] Specifically, the ungraded industrial alkali lignin and lignin fractions of different concentrations obtained in steps 1) and 2) are added to a mixed solvent and dissolved by magnetic stirring at room temperature. Subsequently, the antisolvent is gradually added dropwise to the lignin solution using a peristaltic pump to precipitate it, and the solvent and antisolvent are removed by multiple centrifugations. Finally, the product is freeze-dried to obtain lignin micro-nanospheres containing different fractions.
[0033] The different fractions described above can all form spherical particles with good monodispersity and relatively regular morphology. Furthermore, the content of phenolic and aliphatic units in their structure can be controlled by adjusting the fractionation conditions. The resulting lignin micro / nanospheres exhibit excellent antioxidant activity, thermal stability, and antibacterial properties.
[0034] Example 1
[0035] First, DES was mixed with deionized water to prepare 50wt% low-concentration, 65wt% medium-concentration, and 80wt% high-concentration DES solutions, respectively. 200 mL of the low-concentration DES solution was thoroughly mixed with 10 g of industrial alkali lignin in a round-bottom flask and stirred continuously at 500 rpm for 4 h at room temperature. The insoluble components and supernatant were obtained by centrifugation. The supernatant was slowly added dropwise to 100 mL of deionized water to regenerate low-concentration DES lignin. The low-concentration DES lignin was then precipitated and separated to obtain low-concentration DES lignin. The low-concentration DES lignin was then washed until the eluent was neutral and dried for later use. Subsequently, the insoluble residue was subjected to gradient extraction with medium-concentration and high-concentration DES solutions, following the same procedures as the low-concentration DES extraction. Finally, medium-concentration and high-concentration DES lignin were obtained, respectively.
[0036] The purity of the low-concentration DES lignin fraction was determined to be 95.1%, the purity of the medium-concentration DES lignin fraction was 94.6%, and the purity of the high-concentration DES lignin fraction was 89.2%.
[0037] The insoluble residues obtained after sequential extraction with low-, medium-, and high concentrations of DES solution were vacuum dried and further fractionated using acid precipitation. The dried sample was dispersed in 60 mL of ultrapure water, and 1 M NaOH solution was added dropwise until the pH reached 12. The mixture was stirred continuously at 500 rpm for 2 h at room temperature to form a homogeneous suspension. After centrifugation to remove insoluble residues, 1 M HCl solution was slowly added dropwise to the supernatant until the pH reached 2-3 to induce lignin precipitation. The obtained lignin was washed repeatedly with deionized water until the eluent was neutral, and then dried in a vacuum drying oven at 45°C to finally obtain acid-precipitated lignin. The purity of the acid-precipitated lignin was determined to be 95.8%.
[0038] 15 mg of low-concentration DES lignin was added to a mixed solvent of 3 mL γ-valerol and 1 mL water, and stirred uniformly at room temperature for 1 h to dissolve. Subsequently, 40 mL of water was gradually added to the lignin mixture using a peristaltic pump at a rate of 5 mL / min. Finally, γ-valerol and water were removed by centrifugation, and the mixture was freeze-dried to obtain low-concentration DES lignin micro / nanospheres with a particle size of 9-12 μm. Figure 1 As shown.
[0039] Example 2
[0040] Similar to Example 1, except that a medium concentration of DES lignin was used to obtain medium concentration DES lignin fractionated micro-nanospheres with a particle size of 9-12 μm.
[0041] Example 3
[0042] Similar to Example 1, except that high-concentration DES lignin was used to obtain high-concentration DES lignin fractionated micro-nanospheres with a particle size of 9-12 μm.
[0043] Example 4
[0044] Similar to Example 1, except that acid-precipitated lignin was used to obtain acid-precipitated lignin fractional micro-nanospheres with a particle size of 3-5 μm. Figure 2 As shown
[0045] Comparative Example 1
[0046] Similar to Example 1, except that ungraded industrial alkali lignin was used to obtain alkali lignin micro-nanospheres. These micro-nanospheres exhibited poor dispersibility and uniformity, with a particle size of 0.5-10 μm. Figure 3 As shown.
[0047] Table 1. Comparison of properties of micro / nanospheres prepared from ungraded industrial alkali lignin and four lignin fractions.
[0048]
[0049] In this application embodiment, four lignin fractions with low heterogeneity, suitable hydroxyl content, and syringyl (S) / guaiacyl (G) ratios suitable for lignin micro / nanosphere preparation were obtained through a two-step fractionation technique combining gradient extraction with acid precipitation at different concentrations of DES. As shown in Table 1, the DES lignin fraction micro / nanospheres prepared using DES lignin exhibit a wide particle size distribution range, while the acid-precipitated lignin fraction micro / nanospheres prepared using acid precipitation have the smallest particle size distribution range. Among them, the low-concentration DES lignin fraction micro / nanospheres prepared in Example 1 exhibited a low S / G ratio and a high phenolic hydroxyl content. Generally, the phenolic hydroxyl content is directly proportional to the antioxidant capacity of lignin micro / nanospheres, and lignin micro / nanospheres with a low S / G ratio significantly contribute to free radical scavenging ability. Therefore, the low-concentration DES lignin fraction micro / nanospheres exhibited better antioxidant activity and a higher free radical scavenging index, as well as strong antibacterial activity.
[0050] This invention is not limited to the embodiments described above. All equivalent changes and modifications made within the scope of this invention should be considered within the scope of this invention.
Claims
1. A method for lignin fractionation and separation, characterized in that, Includes the following steps: 1) Gradient extraction of industrial lignin was performed using a eutectic solvent with increasing concentration to obtain lignin fractions with different molecular weight distributions; 2) The insoluble residue after gradient extraction was subjected to pH-induced acid precipitation to further separate and obtain high-purity lignin fraction; The eutectic solvent is a system formed by choline chloride and acetone or glyoxylic acid.
2. The lignin fractionation and separation method according to claim 1, characterized in that, The eutectic solvent is a system formed by choline chloride containing conjugated carboxylic acids and acetone or glyoxylic acid in a molar ratio of 1:
2.
3. A lignin fractionation and separation method according to claim 1 or 2, characterized in that, The low, medium, and high concentrations of the gradient extraction were 50 wt%, 65 wt%, and 80 wt%, respectively, with corresponding fraction yields of 40.2%, 14.1%, and 12.6%.
4. The lignin fractionation and separation method according to claim 1, characterized in that, Before pH induction, the insoluble residue is vacuum dried and dispersed in ultrapure water, and the pH of the mixture is adjusted using an alkaline solution until a homogeneous suspension is formed.
5. The lignin fractionation and separation method according to claim 4, characterized in that, The alkaline solution is 1 M NaOH, and the pH of the suspension is adjusted to 12; the acid solution is 1 M HCl, and the pH at the precipitation endpoint is 2-3.
6. The lignin fractionation and separation method according to claim 5, characterized in that, The acid-precipitated lignin fraction yields were 21.8%.
7. The application of a lignin fraction obtained by any one of claims 1-6 in the preparation of lignin micro / nanospheres.
8. The application according to claim 7, characterized in that, Lignin micro / nanospheres with controllable particle size were prepared by inducing self-assembly through a solvent / antisolvent system.
9. The application according to claim 8, characterized in that, The solvent is a mixed solution of γ-valerolactone and water, wherein the volume ratio of γ-valerolactone to water is 3~5:1; the antisolvent is water, and the peristaltic pump drip rate is 5 mL / min.