Method for efficiently extracting light-color lignin and application thereof

Abstract

The invention provides a method for efficiently extracting light-color lignin and application. The method comprises the steps that bamboo is smashed, bamboo powder is screened out and dried, then formic acid is used for pretreatment and filtration to obtain solid residues, deionized water is used for washing the solid residues to be neutral, and solid matter is obtained after drying; treating the solid substance by using a tetrahydrofurfuryl alcohol / p-toluenesulfonic acid aqueous solution system, filtering out insoluble impurities to obtain filtrate, washing the insoluble impurities by using a tetrahydrofurfuryl alcohol aqueous solution and deionized water until the insoluble impurities are neutral, and reserving a washing solution; and adding water into the filtrate and the washing liquid for precipitation to obtain light-color lignin. According to the method for extracting the lignin, the yield is 66.9%, the purity is 99.64%, the obtained lignin is light in color (lightness: 70.48), the molecular weight of the obtained lignin is moderate (Mw: 4695), and the negative influence of the extraction process on lignin structural units is limited.

Description

Technical Field

[0001] The invention belongs to the field of efficient extraction of lignin, and specifically relates to a method for efficiently extracting light-colored lignin and an application thereof. Background Art

[0002] Lignin is a natural macromolecular organic compound second only to cellulose in content. It is mainly found in woody plants and herbaceous plants. It is a renewable and abundant aromatic resource with a wide range of applications. It can be used to prepare bio-oil, transportation fuel, polyurethane foam, adhesives, biodegradable plastics, and precursors of chemicals (such as dimethyl sulfoxide, dimethyl sulfide, and phenol). In addition, lignin has a large number of phenolic hydroxyl groups, benzene rings, conjugated structures, and carbonyl structures, and has anti-ultraviolet and antioxidant capabilities. It can be used as a green and environmentally friendly anti-ultraviolet agent and antioxidant in the food and daily chemical fields. Light-colored lignin can be used as a filler or modifier in coatings and paints to maintain the brightness and purity of the color, thereby enhancing the visual effect of the product. In cosmetics, it not only does not affect the appearance color of the product, but also provides natural antioxidant and moisturizing effects. In addition, it helps to ensure the visual cleanliness of the interior of the packaging and the effect of product display in food packaging.

[0003] Traditionally extracted lignin is mainly alkali lignin obtained by kraft pulping. This type of lignin lacks protective measures during the extraction process, and will undergo severe polycondensation to generate quinone chromophores, thereby showing a very dark color, which seriously hinders its application in the fields of food and daily chemicals. In the past, when extracting light-colored lignin, most of them used acid-assisted polyols at high temperatures, but the yield was very low. Therefore, a method for efficiently and quickly extracting light-colored lignin at a lower temperature is needed to improve the application of light-colored lignin in sunscreen and provide a theoretical basis for strengthening its antioxidant capacity. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for efficiently extracting light-colored lignin, which comprises the following steps:

[0005] 1) crushing the bamboo and performing a first drying to obtain bamboo powder;

[0006] 2) pre-treating the bamboo powder in 1) with 0.5 wt % formic acid to obtain a solid residue; washing the solid residue with deionized water until neutral, and then drying it for a second time to obtain a solid substance;

[0007] 3) hydrolyzing the solid matter in 2), a 70% (w / v) tetrahydrofurfuryl alcohol aqueous solution and p-toluenesulfonic acid; obtaining insoluble impurities after the hydrolysis; filtering out the insoluble impurities to obtain a filtrate;

[0008] The hydrolysis temperature is 90-200°C; the hydrolysis time is 1-4h; the hydrolysis speed is 600-700rpm;

[0009] 4) washing the insoluble impurities in 3) with 70% tetrahydrofurfuryl alcohol and deionized water until neutral to obtain a washing solution;

[0010] 5) The filtrate in 3) and the washing liquid obtained in 4) are precipitated for 12-18 hours, and then centrifuged to obtain light-colored lignin.

[0011] Furthermore, the pretreatment temperature in 2) is 105° C. and the pretreatment time is 2 h.

[0012] Furthermore, the temperature of the first drying is 90-110° C.; and the time of the first drying is 5-7 hours.

[0013] Furthermore, the temperature of the second drying is 80-100° C.; and the time of the second drying is 4-6 hours.

[0014] Furthermore, the solid matter, tetrahydrofurfuryl alcohol aqueous solution and p-toluenesulfonic acid in 3) have a solid-liquid ratio of 1 to 2:10 to 20:1 (g:mL:g).

[0015] Furthermore, the centrifugal speed in 5) is 8000-10000 rpm; and the centrifugal time is 10-20 min.

[0016] Another aspect of the present invention provides an application of the above-mentioned method for efficiently extracting light-colored lignin in sunscreen.

[0017] Beneficial effects:

[0018] 1. The present invention provides a method for efficiently extracting light-colored lignin, which uses a tetrahydrofurfuryl alcohol aqueous solution / p-toluenesulfonic acid system to extract lignin from bamboo, and obtains high-purity light-colored lignin. At 110°C, 91% of the lignin in the bamboo powder raw material is efficiently separated, the yield of the separated lignin is 66.9%, the purity reaches 99.64%, the molecular weight is moderate (Mw: 4695), and the negative impact on the lignin structural unit is limited, which provides a broad development prospect for the application of bamboo.

[0019] 2. The extraction method provided by the present invention has a simple extraction process, and the obtained lignin is lighter in color with a brightness of more than 70, which is much greater than the brightness of the lignin used in the market (45). This eliminates the application limitations of the existing technology of extracting lignin due to its darker color, and the process is green and environmentally friendly. DETAILED DESCRIPTION

[0020] The present invention is described in detail below with reference to the embodiments.

[0021] Bamboo has the advantages of short growth cycle, fast growth rate, strong reproduction ability, fast maturity, high yield and high lignin content, so the use of bamboo to extract lignin has a good prospect. The extraction of lignin from bamboo generally uses hydrothermal process, biochar catalytic degradation, soda pulping extraction, microwave-assisted extraction and ultrasound-assisted extraction.

[0022] Example 1

[0023] After the bamboo is crushed by a crusher, particles of 60 to 100 mesh are screened out, and then dried for the first time at 90°C for 7 hours to obtain a powdered solid. The powder is pretreated with 0.5wt% formic acid, reacted at 105°C for 2 hours, and then filtered to obtain a solid residue, which is washed with deionized water to neutrality, and dried for the second time at 80°C for 6 hours to obtain a solid substance.

[0024] 5 g of solid matter was weighed and added to a hydrolysis bottle, 50 mL of 70% (w / v) tetrahydrofurfuryl alcohol aqueous solution was added to the hydrolysis bottle, 5 g of p-toluenesulfonic acid was added to the hydrolysis bottle, and the reaction was carried out at 90° C. The rotation speed was set to 700 rpm, and the reaction duration was 4 hours. After the reaction was completed, insoluble impurities were filtered out to obtain a filtrate, and the insoluble impurities were washed to neutrality with 70% tetrahydrofurfuryl alcohol and deionized water, and the washing liquid was retained. The filtrate and the washing liquid were diluted with water to induce lignin precipitation for 12 hours, and then the lignin was separated by centrifugation (8000 rpm, 10 minutes) to obtain light-colored lignin (brightness: 69.78, molecular weight: 5542, purity: 94.83%).

[0025] Evaluation of light-colored lignin purity, molecular weight and color (the same below):

[0026] The carbohydrate content in the bamboo lignin sample was determined by dilute acid hydrolysis method. The specific operation steps were as follows: 4-6 mg of lignin sample was accurately weighed and placed in a 1.5 mL hydrolysis bottle. 0.125 mL of 72% concentrated sulfuric acid was first added for hydrolysis (5 minutes), and then 1.35 mL of ultrapure water was added to dilute to 1.475 mL. The hydrolysis bottle was sealed and placed in an oven at 105°C for hydrolysis for 2.5 hours. After filtration, the hydrolyzate was diluted to 50 times and analyzed by high-performance anion exchange ion chromatography (ICS 3000, Dionex, USA).

[0027] The color characteristics of lignin were analyzed using a DS-200 colorimeter (hzcaipu, China). The measurement mode was set to include specular component (SCI), the light source used was D65, the standard observation angle was set to 10°, and the average value was taken after three measurements. Generally speaking, when the lightness is greater than 65, it can be called light-colored lignin.

[0028] 2 mg of lignin was dissolved in 1 mL of tetrahydrofuran (chromatographic grade) and filtered through an organic filter. Then 20 μL of the solution was injected into the system and its weight average molecular weight was measured by gel permeation chromatography (GPC).

[0029] Calculation method of lignin yield (same below):

[0030] The quantification of lignin in bamboo powder is carried out according to the experimental method specified by the National Renewable Energy Laboratory (NREL) of the United States. First, 0.3g of sample is accurately weighed and placed in a hydrolysis bottle. Subsequently, 3mL of 72% sulfuric acid is added and stirred in a water bath at 30°C for 1h. Finally, 84mL of deionized water is added and the hydrolysis bottle is placed in an autoclave at 121°C and heated for 1h. After the treatment, the filtered residue is thoroughly cleaned and dried to obtain acid-insoluble lignin. Subsequently, the concentration of acid-soluble lignin in the filtrate is quantitatively measured by ultraviolet spectrophotometry. The total lignin content in the sample is determined to be the sum of acid-soluble lignin and acid-insoluble lignin. The bamboo powder used in the present invention has a lignin content of 29.35% according to this method.

[0031] Lignin yield = obtained lignin mass / (bamboo powder weight×29.35%)×100%.

[0032] Embodiment 2:

[0033] After the bamboo was crushed by a crusher, particles of 60 to 100 mesh were screened out, and then dried for the first time at 100°C for 6 hours to obtain a powdered solid. The powder was pretreated with 0.5wt% formic acid, reacted at 105°C for 2 hours, and then filtered to obtain a solid residue, which was washed with deionized water to neutrality and dried for the second time at 90°C for 5 hours to obtain a solid substance.

[0034] Weigh 10g of solid matter and add it to a hydrolysis bottle, take 100mL of 70% (w / v) tetrahydrofurfuryl alcohol aqueous solution and add it to the hydrolysis bottle, take 10g of p-toluenesulfonic acid and add it to the hydrolysis bottle, react at 100°C, set the speed to 600rpm, and the reaction duration is 4h. After the reaction is completed, filter out insoluble impurities to obtain filtrate, use 70% tetrahydrofurfuryl alcohol and deionized water to wash the insoluble impurities to neutrality, and retain the washing liquid. After the filtrate and washing liquid are diluted with water to induce lignin precipitation for 14h, centrifugal separation (9000rpm, 15min) is used to separate lignin to obtain light lignin (brightness: 71.59, molecular weight: 5344, purity: 99.35%). The light lignin purity, molecular weight and color determination method are the same as in Example 1.

[0035] Embodiment 3:

[0036] After the bamboo was crushed by a crusher, particles of 60 to 100 mesh were screened out, and then dried for the first time at 110°C for 5 hours to obtain a powdered solid. The powder was pretreated with 0.5wt% formic acid, reacted at 105°C for 2 hours, and then filtered to obtain a solid residue. The solid residue was washed with deionized water to neutrality, and dried for the second time at 100°C for 4 hours to obtain a solid substance.

[0037] Weigh 5g of solid matter and add it to a hydrolysis bottle, take 50mL of 70% (w / v) tetrahydrofurfuryl alcohol aqueous solution and add it to the hydrolysis bottle, take 5g of p-toluenesulfonic acid and add it to the hydrolysis bottle, react at 110°C, set the speed to 700rpm, and the reaction duration is 4h. After the reaction is completed, filter out insoluble impurities to obtain filtrate, use 70% tetrahydrofurfuryl alcohol and deionized water to wash the insoluble impurities to neutrality, and retain the washing liquid. After the filtrate and washing liquid are diluted with water to induce lignin precipitation for 12h, centrifugal separation (10000rpm, 20min) is used to separate lignin to obtain light lignin (brightness: 70.48, molecular weight: 4695, purity: 99.64%). The light lignin purity, molecular weight and color determination method are the same as in Example 1.

[0038] Embodiment 4:

[0039] After the bamboo was crushed by a crusher, particles of 60 to 100 mesh were screened out, and then dried for the first time at 105°C for 6 hours to obtain a powdered solid. The powder was pretreated with 0.5wt% formic acid, reacted at 105°C for 2 hours, and then filtered to obtain a solid residue, which was washed with deionized water to neutrality and dried for the second time at 90°C for 5 hours to obtain a solid substance.

[0040] Weigh 5g of solid matter and add it to a hydrolysis bottle, take 50mL of 70% (w / v) tetrahydrofurfuryl alcohol aqueous solution and add it to the hydrolysis bottle, take 5g of p-toluenesulfonic acid and add it to the hydrolysis bottle, react at 100°C, set the speed to 600rpm, and the reaction duration is 1h. After the reaction is completed, filter out insoluble impurities to obtain filtrate, use 70% tetrahydrofurfuryl alcohol and deionized water to wash the insoluble impurities to neutrality, and retain the washing liquid. After the filtrate and washing liquid are diluted with water to induce lignin precipitation for 12h, centrifugal separation (9000rpm, 20min) is used to separate lignin to obtain light lignin (brightness: 71.16, molecular weight: 5420, purity: 97.17%). The light lignin purity, molecular weight and color determination method are the same as in Example 1.

[0041] Embodiment 5:

[0042] After the bamboo was crushed by a crusher, particles of 60 to 100 mesh were screened out, and then dried for the first time at 95°C for 7 hours to obtain a powdered solid. The powder was pretreated with 0.5wt% formic acid, reacted at 105°C for 2 hours, and then filtered to obtain a solid residue, which was washed with deionized water to neutrality, and dried for the second time at 80°C for 6 hours to obtain a solid substance.

[0043] Weigh 20g of solid matter and add it to a hydrolysis bottle, take 200mL of 70% (w / v) tetrahydrofurfuryl alcohol aqueous solution and add it to the hydrolysis bottle, take 20g of p-toluenesulfonic acid and add it to the hydrolysis bottle, react at 100°C, set the speed to 600rpm, and the reaction duration is 2h. After the reaction is completed, filter out insoluble impurities to obtain filtrate, use 70% tetrahydrofurfuryl alcohol and deionized water to wash the insoluble impurities to neutrality, and retain the washing liquid. After the filtrate and washing liquid are diluted with water to induce lignin precipitation for 18h, centrifugal separation (8000rpm, 20min) is used to separate lignin to obtain light lignin (brightness: 71.73, molecular weight: 5397, purity: 98.36%). The light lignin purity, molecular weight and color determination method are the same as in Example 1.

[0044] Embodiment 6:

[0045] After the bamboo was crushed by a crusher, particles of 60 to 100 mesh were screened out, and then dried for the first time at 95°C for 7 hours to obtain a powdered solid. The powder was pretreated with 0.5wt% formic acid, reacted at 105°C for 2 hours, and then filtered to obtain a solid residue, which was washed with deionized water to neutrality, and dried for the second time at 80°C for 6 hours to obtain a solid substance.

[0046] Weigh 10g of solid matter and add it to a hydrolysis bottle, take 100mL of 70% (w / v) tetrahydrofurfuryl alcohol aqueous solution and add it to the hydrolysis bottle, take 5g of p-toluenesulfonic acid and add it to the hydrolysis bottle, react at 100°C, set the speed to 600rpm, and the reaction duration is 4h. After the reaction is completed, filter out insoluble impurities to obtain filtrate, use 70% tetrahydrofurfuryl alcohol and deionized water to wash the insoluble impurities to neutrality, and retain the washing liquid. After the filtrate and washing liquid are diluted with water to induce lignin precipitation for 18h, centrifugal separation (10000rpm, 20min) is used to separate lignin to obtain light lignin (brightness: 72.58, molecular weight: 5757, purity: 96.36%). The light lignin purity, molecular weight and color determination method are the same as in Example 1.

[0047] Comparative Example 1:

[0048] After the bamboo was crushed by a crusher, particles of 60 to 100 mesh were screened out, and then dried for the first time at 105°C for 7 hours to obtain a powdered solid. The powder was pretreated with 0.5wt% formic acid, reacted at 105°C for 2 hours, and then filtered to obtain a solid residue, which was washed with deionized water to neutrality, and dried for the second time at 90°C for 6 hours to obtain a solid substance.

[0049] Weigh 5g of solid matter and add it to the hydrolysis bottle, take 50mL of deionized water and add it to the hydrolysis bottle, take 5g of p-toluenesulfonic acid and add it to the hydrolysis bottle, react at 110°C, set the speed to 500rpm, and the reaction duration is 4h. After the reaction is completed, filter out the insoluble impurities to obtain the filtrate, use deionized water to wash the insoluble impurities to neutrality, and retain the washing liquid. After the filtrate and washing liquid are diluted with water to induce lignin precipitation for 16h, the lignin is separated by centrifugation (10000rpm, 15min) to obtain lignin, but the color of the lignin is dark brown, and no further characterization is necessary.

[0050] Comparative Example 2:

[0051] After the bamboo was crushed by a crusher, particles of 60 to 100 mesh were screened out, and then dried for the first time at 110°C for 7 hours to obtain a powdered solid. The powder was pretreated with 0.5wt% formic acid, reacted at 105°C for 2 hours, and then filtered to obtain a solid residue. The solid residue was washed with deionized water to neutrality, and dried for the second time at 100°C for 6 hours to obtain a solid substance.

[0052] 10 g of solid matter was weighed and added to a hydrolysis bottle, 100 mL of 70% (w / v) tetrahydrofurfuryl alcohol aqueous solution was added to the hydrolysis bottle, and the reaction was carried out at 110° C., the rotation speed was set to 500 rpm, and the reaction duration was 4 hours. After the reaction was completed, insoluble impurities were filtered out to obtain a filtrate, and the insoluble impurities were washed to neutrality with 70% tetrahydrofurfuryl alcohol and deionized water, and the washing liquid was retained. After the filtrate and the washing liquid were diluted with water to induce lignin precipitation for 18 hours, lignin was separated by centrifugation (8000 rpm, 20 min) to obtain lignin, but the lignin yield was only 7.06%, and no further characterization was necessary.

[0053] Comparative Example 3:

[0054] After the bamboo was crushed by a crusher, particles of 60 to 100 mesh were screened out, and then dried for the first time at 100°C for 7 hours to obtain a powdered solid. The powder was pretreated with 0.5wt% formic acid, reacted at 105°C for 2 hours, and then filtered to obtain a solid residue. The solid residue was washed with deionized water to neutrality, and dried for the second time at 100°C for 5 hours to obtain a solid substance.

[0055] Weigh 10g of solid matter and add it to a hydrolysis bottle, take 100mL of 70% (w / v) tetrahydrofurfuryl alcohol aqueous solution and add it to the hydrolysis bottle, take 10g of p-toluenesulfonic acid and add it to the hydrolysis bottle, react at 120°C, set the speed to 500rpm, and the reaction duration is 4h. After the reaction is completed, filter out insoluble impurities to obtain filtrate, use 70% tetrahydrofurfuryl alcohol and deionized water to wash the insoluble impurities to neutrality, and retain the washing liquid. After the filtrate and washing liquid are diluted with water to induce lignin precipitation for 16h, centrifugal separation (9000rpm, 20min) is used to separate lignin to obtain lignin (brightness: 48.72, molecular weight: 2990, purity: 99.81%). The lignin purity, molecular weight and color determination method are the same as in Example 1.

[0056] Comparative Example 4:

[0057] After the bamboo was crushed by a crusher, particles of 60 to 100 mesh were screened out, and then dried for the first time at 110°C for 6 hours to obtain a powdered solid. The powder was pretreated with 0.5wt% formic acid, reacted at 105°C for 2 hours, and then filtered to obtain a solid residue, which was washed with deionized water to neutrality, and dried for the second time at 90°C for 6 hours to obtain a solid substance.

[0058] Weigh 5g of solid matter and add it to a hydrolysis bottle, take 50mL of 70% (w / v) tetrahydrofurfuryl alcohol aqueous solution and add it to the hydrolysis bottle, take 10g of p-toluenesulfonic acid and add it to the hydrolysis bottle, react at 100°C, set the speed to 500rpm, and the reaction duration is 4h. After the reaction is completed, filter out insoluble impurities to obtain filtrate, use 70% tetrahydrofurfuryl alcohol and deionized water to wash the insoluble impurities to neutrality, and retain the washing liquid. After the filtrate and washing liquid are diluted with water to induce lignin precipitation for 18h, centrifugal separation (9000rpm, 20min) is used to separate lignin to obtain lignin (brightness: 55.63, molecular weight: 4234, purity: 99.66%). The lignin purity, molecular weight and color determination method are the same as in Example 1.

[0059]

[0060]

[0061] The hydroxyl groups of tetrahydrofurfuryl alcohol can undergo etherification with α-carbon cations during the acid-catalyzed lignin degradation process, which prevents further condensation of lignin, thereby producing high-quality lignin. In addition, the cyclic structure of tetrahydrofuran effectively dissolves lignin. As an amphiphilic substance, p-toluenesulfonic acid can attract lignin through π-π stacking with benzene rings, and its hydrophilic sulfonic acid group can be dissolved in water, thereby preventing the aggregation of lignin. When the temperature is below 110°C or the acid concentration is low, tetrahydrofurfuryl alcohol can well protect the benzyl carbon cations produced during the degradation of lignin, making it difficult to condense. When the temperature rises to 120°C and the acid concentration is high, the condensation reaction of lignin intensifies, and the protective effect of tetrahydrofurfuryl alcohol is limited, so the molecular weight of lignin is small and the color is darker.

[0062] Those skilled in the art will appreciate that the experimental examples shown here are intended to help readers understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other variations that do not deviate from the essence of the present invention based on the technical revelations disclosed in the present invention, and these variations are still within the protection scope of the present invention.

Claims

1. A method for efficiently extracting light-colored lignin, characterized in that: The method comprises the following steps: 1) crushing the bamboo and performing a first drying to obtain bamboo powder; 2) pre-treating the bamboo powder in 1) with 0.5 wt % formic acid to obtain a solid residue; washing the solid residue with deionized water until neutral, and then drying it for a second time to obtain a solid substance; 3) hydrolyzing the solid matter in 2), a 70% (w / v) tetrahydrofurfuryl alcohol aqueous solution and p-toluenesulfonic acid; obtaining insoluble impurities after the hydrolysis; filtering out the insoluble impurities to obtain a filtrate; The hydrolysis temperature is 90-200°C; the hydrolysis time is 1-4h; the hydrolysis speed is 600-700rpm; 4) washing the insoluble impurities in 3) with 70% tetrahydrofurfuryl alcohol and deionized water until neutral to obtain a washing solution; 5) The filtrate in 3) and the washing liquid obtained in 4) are precipitated for 12-18 hours, and then centrifuged to obtain light-colored lignin.

2. The method according to claim 1, characterized in that: The pretreatment temperature in 2) is 105° C. and the pretreatment time is 2 h.

3. The method according to claim 1, characterized in that: The temperature of the first drying is 90-110° C.; the time of the first drying is 5-7 hours.

4. The method according to claim 1, characterized in that: The temperature of the second drying is 80-100° C.; the time of the second drying is 4-6 hours.

5. The method according to claim 1, characterized in that The solid matter, tetrahydrofurfuryl alcohol aqueous solution and p-toluenesulfonic acid in the above 3) have a solid-liquid ratio of 1-2:10-20:1 (g:mL:g).

6. The method according to claim 1, characterized in that The centrifugal speed in 5) is 8000-10000 rpm, and the centrifugal time is 10-20 min.

7. Use of the method for efficiently extracting light-colored lignin as claimed in claim 1 in sunscreen.

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