Lignin extraction method, fractionation method and application thereof

Abstract

The application discloses a lignin extraction method, a grading method and application thereof, and belongs to the technical field of lignin. The lignin extraction method comprises the following steps: mixing lignin with a first solvent, performing solid-liquid separation to obtain a first liquid and first insoluble substances, and drying the first liquid and recovering the solvent to obtain a soluble first fraction lignin; wherein the solvent is at least one of a mixed solution of ethanol and dimethyl carbonate and a mixed solution of ethanol and ethyl acetate; the volume ratio of ethanol to dimethyl carbonate is (0.055-0.66):1 or the volume ratio of ethanol to ethyl acetate is (0.055-0.66):1, and the extraction temperature is 10-35 DEG C. The lignin extraction method has the advantages that the reaction condition can be room temperature, the toxicity of the solvent used is relatively low, and a lignin fraction with the following characteristics can be obtained: low dispersity, small molecular weight, light color and strong ultraviolet absorption shielding capacity.

Description

Technical Field

[0001] This invention relates to the field of lignin technology, and more specifically, to a lignin extraction method, a grading method, and their applications. Background Technology

[0002] Lignin is the second largest biomass resource after cellulose. Lignin is a complex substance composed of three basic units, p-hydroxyphenylpropane, guaiacol, and syringylpropane, linked by various bonds (such as C, C, and CO). It is widely found in various plants, and due to its unique aromatic structure and rich functional groups such as carbonyl, carboxyl, and phenolic hydroxyl groups, lignin has broad application prospects.

[0003] Lignin extracted from black liquor produced in papermaking pulping has disadvantages such as complex structure, polydisperse molecular weight distribution and dark color, which limit its high-value application. Therefore, preparing lignin with lower structural complexity and polydispersity and selective color through lignin fractionation is one of the main solutions to transform lignin into a high-value material.

[0004] Existing technology discloses a method for extracting lignin, which involves dissolving lignin in solvents such as acetic acid, formic acid, and methanol to extract lignin. However, the solvents used in this lignin extraction method are highly toxic, and the extraction requires harsh conditions, such as -3 to 3°C. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of existing lignin grading methods, which use solvents with high toxicity and have harsh reaction conditions for lignin extraction. The present invention provides a lignin extraction method that uses solvents with low toxicity, has a high yield, uses mild reaction conditions, and can also obtain lignin fractions with low dispersibility, small molecular weight and light color.

[0006] Another object of the present invention is to provide a lignin obtained by a lignin grading method.

[0007] Another object of the present invention is to provide the application of lignin obtained by lignin grading method in the preparation of UV-protective daily chemical products.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution:

[0009] A method for extracting lignin includes the following steps:

[0010] Lignin is mixed with a first solvent, and solid-liquid separation is performed to obtain a first liquid and a first insoluble substance. The first liquid is dried and the solvent is recovered to obtain soluble first fraction lignin.

[0011] The solvent is at least one of a mixed solution of ethanol and dimethyl carbonate, or a mixed solution of ethanol and ethyl acetate;

[0012] The volume ratio of ethanol to dimethyl carbonate is (0.055–0.66):1 or the volume ratio of ethanol to ethyl acetate is (0.055–0.66):1;

[0013] The extraction temperature is 10-35℃.

[0014] The dimethyl carbonate used in the lignin extraction method of this invention has excellent solubility, as well as a high evaporation temperature and a fast evaporation rate. As a low-toxicity solvent, it also has the characteristics of high flash point, low vapor pressure and high lower explosive limit in air. Therefore, it is a green solvent that combines cleanliness and safety.

[0015] Ethyl acetate also has low toxicity.

[0016] The lignin extraction method provided by this invention allows for reaction conditions at room temperature, uses solvents with low toxicity, and achieves a high yield of extracted lignin through synergistic effects between solvents. Furthermore, it yields lignin fractions with low dispersibility, small molecular weight, light color, and strong UV absorption shielding ability.

[0017] Lignin can be lignin that has been vacuum dried.

[0018] The amount of lignin and the first solvent can be 5-10g lignin: 50-100mL first solvent.

[0019] To make the lignin and the first solvent mix more evenly, ultrasonic mixing can be used. The ultrasonic power can be 200-400W and the ultrasonic time can be 1-20min.

[0020] To ensure a more uniform mixing of lignin and the first solvent, the mixture can be continuously stirred after ultrasonication. The stirring speed can be 200-600 rpm, and the stirring time can be 0.5-3 hours. The stirring temperature can be 15-40℃.

[0021] Solid-liquid separation can be achieved using a centrifuge.

[0022] After solid-liquid separation, the soluble liquid fraction can be dried and the first solvent recovered using a rotary evaporator. The rotary evaporation temperature can be 40–55°C and the rotation speed can be 40–60 rpm.

[0023] Preferably, the solvent is a mixed solution of ethanol and dimethyl carbonate.

[0024] Preferably, the lignin is alkali lignin; the source of the lignin is corn stalks.

[0025] Preferably, the volume ratio of ethanol to dimethyl carbonate in the first solvent is (0.055-0.15):1; or the volume ratio of ethanol to ethyl acetate in the first solvent is (0.055-0.15):1.

[0026] This invention also protects the lignin obtained by the lignin extraction method described above.

[0027] This invention also protects the application of lignin obtained by the lignin extraction method described above in the preparation of UV-protective daily chemical products.

[0028] The lignin obtained by the lignin grading method of the present invention has strong ultraviolet absorption and shielding properties, as well as low dispersibility and light color. It can be widely used in ultraviolet protection daily chemical products, improve the sun protection factor of ultraviolet protection daily chemical products, and expand the high-value application of lignin in sunscreens, cosmetics and other fields.

[0029] A lignin-based sunscreen comprises lignin obtained by the lignin grading method described above and a hand cream, wherein the lignin content is 1-5 wt% of the hand cream.

[0030] This invention also protects a lignin grading method, comprising the following steps:

[0031] S1. Mix lignin with a first solvent, separate the solid and liquid to obtain a first liquid and a first insoluble substance, dry the first liquid and recover the solvent to obtain soluble first fraction lignin;

[0032] S2. The first insoluble substance is mixed with the second solvent, and the solid and liquid are separated to obtain the second liquid and the second insoluble substance. The second liquid is dried and the solvent is recovered to obtain the soluble second fraction lignin.

[0033] Repeat the above steps;

[0034] Sn. Mix the (n-1)th insoluble substance with the nth solvent, separate the solid and liquid to obtain the nth liquid and the nth insoluble substance, dry the nth liquid and recover the solvent to obtain the soluble nth fraction of lignin;

[0035] Wherein, the volume fraction of dimethyl carbonate gradually decreases from the first solvent to the nth solvent; or the volume fraction of ethyl acetate gradually decreases from the first solvent to the nth solvent;

[0036] n is 1 to 6;

[0037] The solvent is at least one of a mixed solution of ethanol and dimethyl carbonate, or a mixed solution of ethanol and ethyl acetate;

[0038] The volume ratio of ethanol to dimethyl carbonate is (0.055–0.66):1 or the volume ratio of ethanol to ethyl acetate is (0.055–0.66):1.

[0039] The lignin grading method of the present invention, through continuous extraction and grading operations, dissolves lignin sequentially in different volume ratios of ethanol-dimethyl carbonate solvent or ethanol-ethyl acetate solvent, which can extract lignin fractions with reduced dispersibility, gradually increasing molecular weight, and color ranging from light to dark.

[0040] When the proportion of dimethyl carbonate or ethyl acetate is high, the extracted lignin has a smaller molecular weight, lighter color, higher antioxidant properties, and enhanced ultraviolet absorption performance.

[0041] Preferably, n is 3 to 4.

[0042] Preferably, the volume ratio of ethanol to dimethyl carbonate in the second solvent is (0.25-0.45):1; or the volume ratio of ethanol to ethyl acetate in the second solvent is (0.25-0.45):1.

[0043] Preferably, when n=3, the volume ratio of ethanol to dimethyl carbonate in the third solvent is (1.3~2.5):1; the volume ratio of ethanol to ethyl acetate in the third solvent is (1.3~2.5):1.

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] The lignin extraction method provided by this invention allows for a relatively mild reaction at room temperature, uses solvents with low toxicity, and achieves a high yield of extracted lignin through synergistic effects between solvents. Furthermore, it yields lignin fractions with low dispersibility, small molecular weight, light color, and strong UV absorption shielding ability.

[0046] The lignin grading method of the present invention, through continuous extraction and grading operations, dissolves lignin sequentially in different volume ratios of ethanol-dimethyl carbonate solvent or ethanol-ethyl acetate solvent, which can extract lignin fractions with reduced dispersibility, gradually increasing molecular weight, and color ranging from light to dark. Attached Figure Description

[0047] Figure 1 This is a color comparison diagram of the lignin grading process in Example 3 and the first-grade lignin AL1, second-grade lignin AL2, and third-grade lignin AL3 obtained in Examples 1 to 3 respectively.

[0048] Figure 2The images show infrared spectroscopy of alkali lignin and the first-stage lignin AL1, second-stage lignin AL2, and third-stage lignin AL3 obtained in Examples 1-3, respectively.

[0049] Figure 3 It is alkali lignin and the first fraction lignin AL1, the second fraction lignin AL2, and the third fraction lignin AL3 obtained in Examples 1-3, respectively. 31 P-NMR spectrum.

[0050] Figure 4 The images show the UV absorption spectra of alkali lignin and the first fraction lignin AL1, second fraction lignin AL2, and third fraction lignin AL3 obtained in Examples 1-3, respectively. Detailed Implementation

[0051] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0052] Alkali lignin (AL) is derived from corn stalks.

[0053] Example 1

[0054] A method for extracting lignin involves mixing 5g of vacuum-dried alkali lignin (AL) with 100mL of ethanol-dimethyl carbonate (1:9, v:v) solvent, sonicating at 300W for 5 minutes at room temperature, then stirring at 400rpm for 0.5h, and centrifuging. The soluble fraction is dried using a rotary evaporator, and the organic solvent is recovered to obtain lignin fraction 1, denoted as AL1.

[0055] Example 2

[0056] A lignin fractionation method involves mixing 5g of vacuum-dried lignin fraction AL1 obtained in Example 1 with 100mL of ethanol-dimethyl carbonate (3:7, v:v) solvent. The mixture is then sonicated at 300W for 5 minutes at room temperature, stirred at 400rpm for 0.5 hours, and centrifuged. The soluble fraction is dried using a rotary evaporator, and the organic solvent is recovered to obtain lignin fraction 2, denoted as AL2.

[0057] Example 3

[0058] like Figure 1As shown, a lignin fractionation method involves mixing 5g of vacuum-dried lignin fraction AL2 obtained in Example 2 with 100mL of ethanol-dimethyl carbonate (6:4, v:v) solvent. The mixture is then sonicated at 300W for 5 minutes at room temperature, stirred at 400rpm for 0.5 hours, and centrifuged. The soluble fraction is dried using a rotary evaporator, and the organic solvent is recovered to obtain lignin fraction 3, denoted as AL3.

[0059] Example 4

[0060] A lignin fractionation method involves mixing 5g of vacuum-dried alkali lignin (AL) with 100mL of ethanol-ethyl acetate (1:9, v:v) solvent. The mixture is then sonicated at 300W for 5 minutes at room temperature, stirred at 400rpm for 0.5 hours, and centrifuged. The soluble fraction is dried using a rotary evaporator, and the organic solvent is recovered, yielding lignin fraction 4, denoted as AL4. Then, the insoluble fraction is added sequentially to ethanol-ethyl acetate (3:7, v:v) and ethanol-ethyl acetate (6:4, v:v) solvents using the same method, yielding lignin fractions 5 and 6, denoted as AL5 and AL6, respectively.

[0061] Example 5

[0062] A lignin-based sunscreen comprises 1.0g of Nivea hand cream and 0.01g, 0.02g and 0.05g of the first fraction of lignin AL1 prepared in Example 1, which are mixed at 600rpm for 24h at room temperature to prepare lignin-based sunscreens with addition amounts of 1wt%, 2wt% and 5wt%, respectively.

[0063] Comparative Example 1

[0064] A method for extracting lignin involves mixing 5g of vacuum-dried alkali lignin (AL) with 100mL of dimethyl carbonate solution, sonicating at 300W for 5 minutes at room temperature, stirring at 400rpm for 0.5 hours, and centrifuging. The soluble fraction is dried using a rotary evaporator, and the organic solvent is recovered to obtain organic solvent lignin.

[0065] Comparative Example 2

[0066] A method for extracting lignin involves mixing 5g of vacuum-dried alkali lignin (AL) with 100mL of ethyl acetate solution, sonicating at 300W for 5 minutes at room temperature, stirring at 400rpm for 0.5 hours, and centrifuging. The soluble fraction is dried using a rotary evaporator, and the organic solvent is recovered to obtain organic solvent lignin.

[0067] Comparative Example 3

[0068] A method for extracting lignin involves mixing 5g of vacuum-dried alkali lignin (AL) with 100mL of ethanol solution, sonicating at 300W for 5 minutes at room temperature, stirring at 400rpm for 0.5h, and centrifuging. The soluble fraction is dried using a rotary evaporator, and the organic solvent is recovered to obtain organic solvent lignin.

[0069] Comparative Example 4

[0070] A lignin-based sunscreen comprises 1.0g of Nivea hand cream and 0.01g, 0.02g and 0.05g of alkali lignin raw material (AL) mixed at 600rpm for 24h at room temperature to prepare lignin-based sunscreens with addition amounts of 1wt%, 2wt% and 5wt%, respectively.

[0071] Result detection

[0072] The above-mentioned alkali lignin raw material AL, the first-stage lignin AL1, the second-stage lignin AL2, and the third-stage lignin AL3 obtained in Examples 1-3 were subjected to the following tests:

[0073] (1) Yield: The calculation method is: mass of lignin fraction obtained / total mass of initial lignin.

[0074] (2) Number-average molecular weight and weight-average molecular weight: The test method was to dissolve 0.1 g of lignin fraction in 2 mL of pyridine / acetic anhydride (1:1 v / v) and acetylate it at room temperature in the dark for 3 days. After the reaction, the product was precipitated with hydrochloric acid aqueous solution, filtered, and dried under vacuum. Each acetylated fraction was dissolved in tetrahydrofuran (THF) (2 mg / mL). The molecular weight distribution of the acetylated samples was then determined using a Waters high-performance liquid chromatography (HPLC) system.

[0075] (3) Calculation of polydispersity index: weight-average molecular weight / number-average molecular weight.

[0076] (4) Brightness index: The test method is to evaluate the color of the lignin sample using a Datacolor 200 spectrophotometer (Datacolor, America). It is represented by the brightness index L*.

[0077] The test results are shown in Table 1:

[0078] Table 1:

[0079]

[0080]

[0081] As can be seen from Table 1, the polydispersity of the lignin fractions extracted in Examples 1 to 3 decreased, the molecular weight gradually increased, the color gradually darkened, and the total yield was the highest, indicating that the grading method was effective.

[0082] (5) Infrared analysis:

[0083] The test method is as follows: the above-mentioned alkali lignin raw material AL and the first-stage lignin AL1, second-stage lignin AL2 and third-stage lignin AL3 obtained in Examples 1 to 3 are dried in a vacuum drying oven for 12 hours at 4000 cm⁻¹. -1 ~500cm -1 The Fourier transform infrared (FTIR) spectra of each lignin component were determined within the specified range. The test results are as follows: Figure 2 As shown. From Figure 2 It can be seen that the FTIR spectra of the first-stage lignin AL1, the second-stage lignin AL2, and the third-stage lignin AL3 obtained in Examples 1 to 3 are basically consistent with the absorption of AL in the alkali lignin raw material, and the lignin structure has not been destroyed.

[0084] (6) 31 P NMR analysis:

[0085] Each lignin fraction was tested using a 600MHz fully digital superconducting nuclear magnetic resonance spectrometer (NMR) from Bruker, Germany. 31 PNMR.

[0086] The testing method was as follows: The above-mentioned alkali lignin raw material AL and the first-stage lignin AL1, second-stage lignin AL2, and third-stage lignin AL3 samples obtained in Examples 1-3 were vacuum-dried for 24 hours before testing. The NMR solvent was pyridine-deuterated chloroform (1.6:1, v:v). 20 mg of lignin was dissolved in the NMR solvent, and 100 μL of cyclohexanol (10.688 mg / mL) was added as an internal standard. 100 μL of chromium acetylacetone (5 mg / mL) was added as a relaxation reagent, and the sample was sonicated for 10 min. Subsequently, 100 μL of 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxophosphazenecyclopentane (TMDP) was added. The pulse angle was 90°, the pulse delay was 25 s, and the NMR was obtained through 512 scans. 31 P NMR spectroscopy.

[0087] Figure 3 The lignin and its fractions are shown. 31 The P NMR spectra and the contents of the main hydroxyl groups are listed in Table 2.

[0088] Table 2 Functional group content of lignin and its fractions

[0089]

[0090]

[0091] As shown in Table 2 and Figure 3 As shown, the total content of phenolic hydroxyl groups is negatively correlated with molecular weight. As the molecular weight of lignin increases, the content of aliphatic hydroxyl groups gradually increases, while the content of carboxyl groups gradually decreases.

[0092] (7) Ultraviolet absorption analysis:

[0093] The above-mentioned alkali lignin raw material AL and the first-stage lignin AL1, second-stage lignin AL2, and third-stage lignin AL3 samples obtained in Examples 1-3 were dissolved in dimethyl sulfoxide to prepare a lignin solution of a certain concentration. The solution was tested using ultraviolet-visible spectroscopy (UV-2600, Shimadzu Corporation, Japan), and the test results are as follows: Figure 4 As shown.

[0094] like Figure 4 As shown, the UV absorption intensity of the lignin fractions decreases with increasing molecular weight, and only AL1 shows a significantly stronger UV absorption intensity than AL, while the UV absorption capacity of other fractions is lower than that of AL.

[0095] The sun protection performance of the lignin-based sunscreens from Example 5 and Comparative Example 4 was analyzed:

[0096] Lignin sunscreen was transferred onto the surface of a perforated strip (3M, USA), and ultraviolet transmittance was measured using a UV-2600 spectrophotometer (Shimadzu, Japan) equipped with an integrating sphere. Transmittance measurements were collected per 1 nm across the wavelength range from UVB (290-320 nm) to UVA (320-400 nm). The sun protection factor (SPF) was calculated using the following formula:

[0097]

[0098] Where E λ =Erythema spectral effectiveness, S λ =Solar spectral efficiency, T λ = Spectral transmittance of the sample.

[0099] The test results are shown in Table 3:

[0100] Table 3

[0101] Example 5: Sun Protection Factor (SPF) 2.45 3.07 4.27 Comparative Example 4: Sun Protection Factor (SPF) 2.25 2.92 3.62

[0102] As can be seen from Table 3, as the lignin content increases, the UV transmittance of lignin-based sunscreens gradually decreases, and the calculated SPF value gradually increases. Moreover, under the same amount of lignin addition, the sunscreen with the first fraction of lignin AL1 obtained in Example 1 has a higher SPF than the sunscreen with the addition of alkali lignin AL.

[0103] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for lignin grading, characterized in that, Includes the following steps: S1. The lignin is mixed with the first solvent, and the solid-liquid separation is performed to obtain the first liquid and the first insoluble substance. The first liquid is dried and the solvent is recovered to obtain the soluble first fraction of lignin. S2. The first insoluble substance is mixed with the second solvent, and the solid-liquid separation is performed to obtain the second liquid and the second insoluble substance. The second liquid is dried and the solvent is recovered to obtain the soluble second fraction lignin. Repeat the above steps; Sn. The (n-1)th insoluble substance is mixed with the nth solvent, and solid-liquid separation is performed to obtain the nth liquid and the nth insoluble substance. The nth liquid is dried and the solvent is recovered to obtain the soluble nth fraction of lignin. Wherein, the first solvent to the nth solvent are all mixed solutions of ethanol and dimethyl carbonate or mixed solutions of ethanol and ethyl acetate, and the volume fraction of dimethyl carbonate in the first solvent to the nth solvent gradually decreases or the volume fraction of ethyl acetate in the first solvent to the nth solvent gradually decreases. n is 3 to 6; The volume ratio of ethanol to dimethyl carbonate in the first solvent is (0.055~0.66):1, or the volume ratio of ethanol to ethyl acetate in the first solvent is (0.055~0.66):

1. The extraction temperature is 10-35℃.

2. The lignin grading method as described in claim 1, characterized in that, n is 3 to 4.

3. The lignin grading method as described in claim 1, characterized in that, The volume ratio of ethanol to dimethyl carbonate in the second solvent is (0.25~0.45):1, or the volume ratio of ethanol to ethyl acetate in the second solvent is (0.25~0.45):

1.

4. The lignin grading method as described in claim 1, characterized in that, When n=3, the volume ratio of ethanol to dimethyl carbonate in the third solvent is (1.3~2.5):1 or the volume ratio of ethanol to ethyl acetate in the third solvent is (1.3~2.5):1.

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