A method for preparing light-colored lignin

Abstract

The invention discloses a method for preparing light-colored lignin, and belongs to the technical field of clean separation and high-value utilization of wood fiber raw materials. The invention adopts a ternary uniform solvent to process wood fiber raw materials, and separates the reaction system to obtain light-colored lignin; wherein the ternary uniform solvent is a solvent mixed with choline chloride, glycerol and aluminum chloride in a molar ratio of 25:50:1; the chromaticity a* of the light-colored lignin is not less than 4, b* is not less than 14, L* is not less than 47, and the whiteness is not less than 8% ISO. The preparation method of the invention can remove lignin in large quantities at a relatively low temperature, and recover the light-colored lignin; the lignin is added to a cream or commercial sunscreen without sunscreen effect with different mass fractions to enhance its anti-ultraviolet ability, and the SPF value can be increased by 1-29, meeting the sunscreen requirements under various conditions, and expanding the application occasions of lignin-based sunscreen.

Description

Technical Field

[0001] The invention belongs to the technical field of clean separation and high-value utilization of wood fiber raw materials, and more specifically, relates to a method for preparing light-colored lignin. Background Art

[0002] Lignocellulosic biomass is the most abundant renewable resource on earth. Lignin is one of the three major components of lignocellulose. Its content in lignocellulosic raw materials is 20-35wt%, which has the advantages of large reserves, renewability, and easy degradation. There are about 80 million tons of industrial lignin waste (mainly from pulp and paper making and biomass refining) in the world every year. At present, the utilization of lignin is mainly based on combustion for heat supply, and only 2% of lignin is used in a high-value manner. Therefore, seeking efficient lignin application methods is conducive to improving the added value of lignocellulosic biomass. The inherent aromatic structure and rich active groups of lignin such as phenolic hydroxyl, carbonyl, carbon-carbon double bond, methoxyl, etc. give lignin natural anti-ultraviolet radiation properties, and it has the potential to be used as a natural, green, safe, environmentally friendly and sustainable sunscreen active ingredient. Therefore, the development of lignin as a natural sunscreen agent for use in the field of cosmetics can achieve high-value utilization of lignin, which is in line with the dual carbon strategy and the development requirements of sustainable economy.

[0003] At present, commercial sunscreen products mainly made from chemical synthesis have become a new type of pollutant, posing a threat to the marine ecological environment that cannot be ignored. The chemicals contained in them can easily penetrate the skin, causing allergies, dermatitis and other injuries; while physical sunscreens have the problem of ultraviolet-induced free radicals that damage the skin. The rich and complex phenylpropane structure in lignin makes lignin have absorption properties in the entire ultraviolet region, and has great potential as a broad-spectrum sunscreen. However, the darker color of industrial lignin hinders its development as a sunscreen additive. There are two problems when dark lignin is added to sunscreen products as an ultraviolet sunscreen: First, in order to meet the color requirements of sunscreen, the amount of lignin added is too low, and a good sunscreen effect cannot be achieved; second, in order to meet the sunscreen requirements, the addition of lignin causes the color of the sunscreen product to be too dark, which cannot meet its color requirements as a cosmetic. Therefore, when light-colored lignin is used as an ultraviolet sunscreen additive, its addition amount can meet both the sunscreen requirements and the color requirements, expanding the application occasions of lignin-based sunscreens, so it is necessary to reduce the color of lignin to an acceptable range.

[0004] However, the current method of reducing the color of lignin by chemical modification inevitably destroys the structure of lignin while reducing the color of lignin. Using a suitable method to separate and extract lignin from wood fiber raw materials can not only avoid the destruction of lignin structure, but also obtain lighter lignin. The quality of lignin-based sunscreen depends on the chemical and physical properties of lignin, and the separation method of lignin determines the chemical and physical properties of lignin. Commonly used lignin separation solvents mainly include alkaline solutions, organic solvents, ionic liquids, etc. Although these methods can obtain lignin in large quantities, the problems of poor lignin uniformity and dark color seriously restrict its application in the field of sunscreen. In recent years, low eutectic solvents have been gradually used for the clean separation of wood fiber raw materials with the advantages of green degradability and high stability, and they have extremely efficient performance in lignin removal. Summary of the invention

[0005] In view of the above problems existing in the prior art, the technical problem to be solved by the present invention is to provide a method for preparing light-colored lignin, which has the characteristics of simple process, green, safe and environmentally friendly, etc., can remove a large amount of lignin from lignocellulose raw materials, and the obtained lignin is light in color, and has the potential for industrial preparation of light-colored lignin. Another technical problem to be solved by the present invention is to provide a light-colored lignin prepared by the above method, which has a high yield, light color, and a whiteness of not less than 8% ISO. Another technical problem to be solved by the present invention is to provide the application of the above light-colored lignin in the preparation of anti-ultraviolet preparations.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing light-colored lignin comprises treating a wood fiber raw material with a ternary uniform solvent, and separating a reaction system to obtain the light-colored lignin; wherein the ternary uniform solvent is a solvent in which choline chloride, glycerol and aluminum chloride are mixed in a molar ratio of 25:50:1; and the chromaticity a* of the light-colored lignin is not less than 4, b* is not less than 14, L* is not less than 47, and the whiteness is not less than 8% ISO.

[0008] Preferably, the mass ratio of the wood fiber raw material to the ternary homogeneous solvent is 1:2-10.

[0009] Preferably, the wood fiber raw material is selected from any one of bamboo, poplar and masson pine.

[0010] The method for preparing light-colored lignin specifically comprises the following steps:

[0011] (1) mixing choline chloride, glycerol and aluminum chloride in a molar ratio of 25:50:1, and heating at 90° C. until a uniform and transparent ternary uniform solvent is obtained;

[0012] (2) mixing the wood fiber raw material with the ternary uniform solvent and reacting them, and after the reaction is completed, adding an organic solvent aqueous solution to the system, stirring them fully, and separating the solid and the liquid to obtain a pretreated material and a pretreated liquid;

[0013] (3) The pretreatment solution is subjected to rotary evaporation to remove the organic solvent therein, and an appropriate amount of deionized water is added to precipitate the dissolved lignin therein and centrifuge it, and then freeze-dry it to obtain light-colored lignin; the pretreatment solution after separating the lignin is subjected to rotary evaporation to remove the water therein and then recycled.

[0014] Preferably, in step (2), the reaction temperature is 100-120° C. and the reaction time is 1 h.

[0015] Preferably, in step (2), the organic solvent in the organic solvent aqueous solution is selected from ethanol or acetone, wherein the volume fraction of the organic solvent is 30 to 80%, and the amount of the organic solvent aqueous solution added is 2 to 10 times the volume of the low eutectic solvent.

[0016] The light-colored lignin obtained by the method for preparing light-colored lignin.

[0017] The application of the light-colored lignin in the preparation of anti-ultraviolet preparations.

[0018] Application of the light-colored lignin in the preparation of sunscreen.

[0019] The addition amount of the light-colored lignin is 1-5 wt %.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) The present invention provides a method for preparing light-colored lignin, which can remove a large amount of lignin at a relatively low temperature and recover the light-colored lignin. The method is simple and has a high lignin yield and light color;

[0022] 2) When the light-colored lignin prepared by the present invention is used as an ultraviolet sunscreen additive, it is added to a cream without sunscreen effect or a commercial sunscreen in different mass fractions. The added amount can not only meet the sunscreen requirements and enhance its anti-ultraviolet ability, but also meet the color requirements. The SPF value is much higher than SPF15, meeting the sunscreen requirements under various conditions and expanding the application occasions of lignin-based sunscreen. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Graphs showing the lignin removal rate and recovery rate for Examples 1 to 3;

[0024] Figure 2 The chromaticity and whiteness ISO diagrams of the light-colored lignin prepared in Examples 1 to 3;

[0025] Figure 3 The ISO diagrams of chroma and brightness of light-colored lignin at different pretreatment temperatures;

[0026] Figure 4 The performance graphs of the lignin-based sunscreen prepared in Example 6; wherein, Figure A is a color graph of the sunscreen after mixing light-colored lignin with different contents and a cream without sunscreen effect, Figure B is an SPF graph of light-colored lignin mixed with a cream without sunscreen effect, and Figure C is an SPF graph of light-colored lignin mixed with a commercial SPF sunscreen;

[0027] Figure 5 The photos of lignin prepared in Example 1, Comparative Examples 1 and 2;

[0028] Figure 6 The removal rate and recovery rate of lignin under different systems;

[0029] Figure 7 The ISO diagrams of chroma and whiteness of lignin under different systems. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described below in conjunction with specific embodiments. In the following examples, unless otherwise specified, the technical means used are conventional means well known to those skilled in the art. If specific conditions are not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0031] The wood fiber raw materials selected in the following examples are bamboo, poplar and masson pine.

[0032] The bamboo is selected from Zhejiang Xianhe Paper Co., Ltd. The main components of the bamboo (by mass fraction) are: 41.00% glucan, 12.78% xylan, and 30.99% lignin. The preparation process of the bamboo powder is as follows: the bamboo slices are first soaked in tap water overnight, the soaked bamboo slices are extruded by a twin-screw extruder, and then the bamboo slices are subjected to disc grinding by a GNM300 disc grinder, the grinding gap is 0.2mm, and the length of the bamboo fiber obtained by disc grinding is about 0.5-2mm. The raw materials after disc grinding are naturally air-dried, and then the moisture is measured and sealed in a sealed bag for storage for standby use.

[0033] The main components of poplar wood (by mass fraction) are: 41.78% glucan, 12.50% xylan, and 25.30% lignin. Its preparation method is the same as that of bamboo.

[0034] The main components of Masson pine (by mass fraction) are: 37.15% glucan, 16.57% xylan and 34.14% lignin. Its preparation method is the same as that of Moso bamboo.

[0035] Test Method

[0036] 1. Lignin removal rate

[0037] The lignin content before and after material pretreatment was determined by the standard method of the US Renewable Energy Laboratory, and the lignin removal rate was the lignin content in the raw material minus the residual lignin content.

[0038] 2. Lignin recovery rate

[0039] The lignocellulosic raw material is mixed with a low eutectic solvent and reacted. After the reaction is completed, an organic solvent aqueous solution is added to the system, fully stirred, and solid-liquid separation is performed to obtain a pretreated material and a pretreated liquid. The pretreated liquid is rotary evaporated to remove ethanol therein, and an appropriate amount of deionized water is added to precipitate the dissolved lignin in the pretreated liquid and centrifuged, and the lignin recovered in the pretreated liquid is obtained by freeze drying. The total amount of lignin removed in the initial substrate is calculated based on the lignin removal rate and the mass of the lignocellulosic raw material.

[0040] The lignin recovery rate is calculated based on the lignin removed in the DES system, and the calculation formula is as follows:

[0041]

[0042] 3. Chroma and whiteness of lignin

[0043] The color and whiteness of lignin were quantitatively measured using an L&W brightness and whiteness tester (Elrepho 070, Sweden). Before the test, the lignin powder was pressed into a cake using the tools provided with the L&W brightness and whiteness tester. The color and whiteness of the lignin cake were then measured.

[0044] 4. Sunscreen performance test

[0045] During the experiment, a quartz plate with the same transmittance was used as the substrate, and a transparent tape of the same shape and area was pasted on it. The transparent tape was pasted on a 2mm thick transparent quartz slide, and the experimental area was 12.5cm 2 , at 2mg / cm 2 The prepared sunscreen sample was applied on the prepared substrate according to the dosage standard. Before the test, it was dried in the dark for 15 minutes. After drying, it was tested using a UV-8000 (METASH, China) UV-visible spectrophotometer. At least 6 non-overlapping points were selected for each sample to measure the UV transmittance in the wavelength range of 290-400nm. The SPF value is calculated as follows:

[0046]

[0047] Where: E λrepresents the effect of sunlight at the wavelength of λ on causing erythema in the human body; S λ is the energy intensity of sunlight irradiating the ground at wavelength λ; T λ is the UV transmittance of the sample in the spectrophotometer test at wavelength λ.

[0048] Example 1

[0049] A method for preparing light-colored lignin comprises the following steps:

[0050] 1) choline chloride, glycerol and aluminum chloride were mixed in a molar ratio of 25:50:1 and heated at 90° C. until a uniform and clear ternary homogeneous solvent was obtained;

[0051] 2) 10 g of bamboo powder was mixed with 100 g of a ternary uniform solvent, and the mixture was reacted at 110° C. for 1 h. After the pretreatment, an ethanol / water solution (ethanol volume fraction of 50 wt%) with a volume of 10 times the pretreatment liquid was added, and the stirring time was 2 h;

[0052] 3) solid-liquid separation to obtain a pretreated liquid and pretreated material rich in lignin, and after the pretreated material is washed with distilled water until neutral, the content of the main components is analyzed and the lignin removal rate is calculated;

[0053] 4) The lignin-rich pretreatment solution is subjected to rotary evaporation at 65° C. to remove ethanol therein, and an appropriate amount of deionized water is added to precipitate the dissolved lignin therein and centrifuge, and light-colored lignin is obtained by freeze-drying, and the weight is weighed and the yield is calculated; the pretreatment solution after separating the lignin is subjected to rotary evaporation to remove water therein and then recycled.

[0054] Example 2

[0055] When preparing light-colored lignin, 10 g of poplar wood was mixed with 100 g of the ternary homogeneous solvent prepared in Example 1, and the remaining preparation methods and parameters were the same as in Example 1.

[0056] Example 3

[0057] When preparing light-colored lignin, 10 g of Masson pine was mixed with 100 g of the ternary homogeneous solvent prepared in Example 1, and the remaining preparation methods and parameters were the same as in Example 1.

[0058] The lignin removal rate and recovery rate of different raw materials in Examples 1 to 3 after choline chloride / glycerol / aluminum chloride pretreatment are as follows: Figure 1 shown.

[0059] Table 1 Lignin removal rate and recovery rate of different raw materials in Examples 1 to 3 after choline chloride / glycerol / aluminum chloride pretreatment

[0060] Example 1 Example 2 Example 3 Lignin removal rate 66.2％ 68.5％ 55.8％ Lignin recovery rate 92.5％ 94.9％ 53.0％

[0061] From Table 1 and Figure 1 It can be seen that three different raw materials, namely, Masson pine, poplar and bamboo, were selected for choline chloride / glycerol / aluminum chloride pretreatment. After treatment, there were certain differences in the lignin removal rate and recovery rate of different raw materials. Among them, the lignin removal rate of Masson pine was 55.8% and the recovery rate was 53.0%, which was the lowest among the three raw materials, indicating that the effect of Masson pine after choline chloride / glycerol / aluminum chloride treatment was the worst. The lignin removal rate of poplar was 68.5% and the lignin recovery rate was 94.9%; the lignin removal rate of bamboo was 66.2% and the lignin recovery rate was 92.5%. In addition, the pretreatment liquid was rotary evaporated, ethanol was removed and an appropriate amount of deionized water was added and then centrifuged to obtain separated lignin. The lignin recovery rates of poplar and bamboo were both over 90%, indicating that the lignin removed from poplar and bamboo can be completely recovered, and the high lignin recovery rate is conducive to subsequent utilization.

[0062] The chromaticity (a*, b*, L*) and whiteness (ISO) of the lignin prepared in Examples 1 to 3 were analyzed. The results are shown in Table 2 and Figure 2 As shown, the enzymatic hydrolyzed lignin (CEL) from ground bamboo wood was used as a comparison.

[0063] Table 2 Chroma and whiteness values ​​of CEL and light-colored lignin of Examples 1 to 3

[0064]

[0065] From Table 2 and Figure 2 It can be seen that DES prepared by choline chloride / glycerol / aluminum chloride extracts lignin from bamboo, poplar and masson pine respectively. The results show that the lignin extracted from bamboo is the lightest in color, and the lignin extracted from masson pine is the darkest in color. The a*, b*, and L* values ​​of masson pine lignin are 9.2, 22.5, and 47.2, respectively, and the whiteness is 22.4% ISO; the a*, b*, and L* values ​​of poplar lignin are 12.7, 14.7, and 53.3, respectively, and the whiteness is 14.6% ISO; the a*, b*, and L* values ​​of bamboo lignin are 4.0, 25.0, and 75.3, respectively, and the whiteness is 29.8% ISO. The a*, b*, and L* values ​​of ground bamboo enzymatic lignin (CEL) were 4.7, 26.8, and 69.3, respectively, and the whiteness was 22.4% ISO. The whiteness of the bamboo lignin extracted by DES prepared with choline chloride / glycerol / aluminum chloride was higher than that of CEL, indicating that the choline chloride / glycerol / aluminum chloride-based DES system can separate lignin with a lighter color than CEL.

[0066] Example 4

[0067] When preparing light-colored lignin, the pretreatment temperature was 100° C., and the other preparation methods and parameters were the same as those in Example 1. The a*, b*, and L* values ​​of the prepared light-colored lignin were 5.3, 16.3, and 71.8, respectively, and the whiteness was 31.2% ISO.

[0068] Example 5

[0069] When preparing light-colored lignin, the pretreatment temperature was 120° C., and the remaining preparation methods and parameters were the same as those in Example 1. The a*, b*, and L* values ​​of the prepared light-colored lignin were 6.0, 24.3, and 65.0, respectively, and the whiteness was 19.4% ISO.

[0070] Depend on Figure 3 It can be seen that at 100°C, the values ​​of a*, b*, and L* are 5.3, 16.3, and 71.8, respectively, and the whiteness is 31.2% ISO; at 110°C, the values ​​of a*, b*, and L* are 4.0, 25.0, and 75.3, respectively, and the whiteness is 29.8% ISO, and the difference between the two is not large. When the temperature continues to rise to 120°C, the chromaticity and whiteness of the recycled lignin decrease significantly, and the values ​​of a*, b*, and L* are 6.0, 24.3, and 65.0, respectively, and the whiteness is 19.4% ISO. The color of the lignin is darker, but the whiteness is significantly higher than the traditional organic acid low eutectic solvent pretreatment system in the comparative example.

[0071] Example 6

[0072] The light-colored lignin prepared in Example 1 was mixed with a cream without sunscreen effect and a commercial SPF15 sunscreen to prepare a lignin-based sunscreen and the sunscreen performance was tested. The results are shown in Tables 3 and Figure 4 As shown; among them, light-colored lignin accounts for 1 to 5% of the mass of lignin-based sunscreen.

[0073] Table 3 SPF values ​​of blank cream and commercial SPF15 sunscreen with different lignin addition amounts

[0074]

[0075]

[0076] like Figure 4 As shown in A, with the increase of lignin content, the color of the sunscreen gradually changes from white (1wt%) to light yellow (5wt%), which are close to the color of human skin and can be used as cosmetics.

[0077] like Figure 4 As shown in B, the SPF of the sunscreen made by mixing the blank cream and lignin can reach 5.1, indicating that the lignin has a significant shielding effect on ultraviolet rays, but it is difficult to reach the sun protection level of commercial SPF15 sunscreen.

[0078] like Figure 4 As shown in Figure C, the SPF values ​​of sunscreens with lignin addition amounts of 1wt%, 3wt% and 5wt% are 25.7, 33.1 and 42.9, respectively. Their SPF values ​​are much higher than SPF15, meeting the sun protection requirements under various conditions, indicating that the light-colored lignin separated under this system can be used as an additive to greatly improve the use effect of commercial sunscreens, which is of great significance for reducing the use of chemical sunscreens.

[0079] Comparative Example 1

[0080] Choline chloride and lactic acid (LA) were mixed in a molar ratio of 1:2 and pretreated for 3 h. The remaining preparation methods and parameters were the same as those in Example 1.

[0081] Comparative Example 2

[0082] Choline chloride and oxalic acid (OA) were mixed in a molar ratio of 1:2, and the remaining preparation methods and parameters were the same as those in Example 1.

[0083] Depend on Figure 5 It can be seen that although the choline chloride / lactic acid (Comparative Example 1) and the choline chloride / oxalic acid system (Comparative Example 2) can effectively remove lignin from bamboo, the removed lignin is dark brown or reddish black in color, which will stain the skin and is not suitable for being added as a sunscreen to creams or commercial SPF15 sunscreens. In contrast, the bamboo lignin obtained by the choline chloride / glycerol / aluminum chloride system in the present invention is white as a whole and is more suitable for being added as a sunscreen to creams or commercial SPF15 sunscreens.

[0084] Depend on Figure 6 It can be seen that the removal rate and recovery rate of lignin in the choline chloride / lactic acid system are 34.6% and 82.6% respectively; the removal rate and recovery rate of lignin in the choline chloride / oxalic acid system are 42.3% and 89.3% respectively, both lower than Example 1 of the present invention.

[0085] Depend on Figure 7 It can be seen that the a*, b*, and L* values ​​of the lignin obtained by the choline chloride / lactic acid system are 11.7, 25.0, and 47.9, respectively, and the whiteness is 7.7% ISO; the a*, b*, and L* values ​​of the lignin obtained by the choline chloride / oxalic acid system are 3.6, 10.7, and 34.3, respectively, and the whiteness is 5.6% ISO, which is much lower than the choline chloride / glycerol / aluminum chloride system in the present invention. Figure 5 The color of the lignin in the present invention is consistent with that of the lignin in the present invention, indicating that the lignin extracted by the system of the present invention is lighter in color and more suitable for being added as a sunscreen agent to cream or commercial SPF15 sunscreen.

[0086] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing light-colored lignin, characterized in that: A ternary uniform solvent is used to treat a wood fiber raw material, the mass ratio of the wood fiber raw material to the ternary uniform solvent is 1:2-10, the wood fiber raw material is selected from any one of bamboo and poplar, and the reaction system is separated to obtain light-colored lignin; wherein the ternary uniform solvent is a solvent mixed with choline chloride, glycerol and aluminum chloride in a molar ratio of 25:50:1; the chromaticity a* of the light-colored lignin is not less than 4, b* is not less than 14, L* is not less than 47, and the whiteness is not less than 8% ISO.

2. The method for preparing light-colored lignin according to claim 1, characterized in that: The specific steps include: (1) mixing choline chloride, glycerol and aluminum chloride in a molar ratio of 25:50:1, and heating at 90° C. until a uniform and transparent ternary uniform solvent is obtained; (2) mixing the wood fiber raw material with the ternary uniform solvent and reacting them, and after the reaction is completed, adding an organic solvent aqueous solution to the system, stirring them fully, and separating the solid and the liquid to obtain a pretreated material and a pretreated liquid; (3) The pretreatment solution is subjected to rotary evaporation to remove the organic solvent therein, and an appropriate amount of deionized water is added to precipitate the dissolved lignin therein and centrifuge it, and then freeze-dry it to obtain light-colored lignin; the pretreatment solution after separating the lignin is subjected to rotary evaporation to remove the water therein and then recycled.

3. The method for preparing light-colored lignin according to claim 2, characterized in that: In the step (2), the reaction temperature is 100-120° C. and the reaction time is 1 h.

4. The method for preparing light-colored lignin according to claim 2, characterized in that: In the step (2), the organic solvent in the organic solvent aqueous solution is selected from ethanol or acetone, wherein the volume fraction of the organic solvent is 30 to 80%, and the amount of the organic solvent aqueous solution added is 2 to 10 times the volume of the low eutectic solvent.

5. The light-colored lignin obtained by the method for preparing light-colored lignin according to any one of claims 1 to 4.

6. Use of the light-colored lignin according to claim 5 in the preparation of anti-ultraviolet preparations.

7. Use of the light-colored lignin according to claim 5 in preparing sunscreen.

8. The use according to claim 7, characterized in that: The addition amount of the light-colored lignin is 1-5 wt %.

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