A method for simultaneous production of kraft pulp and phenolated lignin and kraft pulp and phenolated lignin thereof

Abstract

The present application relates to the field of chemical pulping, and discloses a method for simultaneously preparing kraft pulp and phenolated lignin, and kraft pulp and phenolated lignin prepared by the method. The method for simultaneously preparing kraft pulp and phenolated lignin comprises the following steps: mixing wood fiber raw material, water and cooking reagent, and then adding phenol; after cooking, obtaining a mixture of residue and black liquor; collecting the residue to obtain kraft pulp; and collecting the black liquor and performing acid precipitation, and the obtained precipitate is phenolated lignin. The phenolated lignin prepared by the present application has a phenolic hydroxyl content of 3.5-6.0 mmol / g, the kraft pulp prepared has a kappa number of 23.0-110.0, a viscosity of 900-1350 mL / g, and a brightness of 12.0-30.0% ISO. The present application has a significant lignin modification effect while separating fibers, realizes efficient utilization of resources and reduction of environmental burden, and has high industrialization potential.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical pulping, and more particularly, to a method for simultaneously preparing kraft pulp and phenolated lignin and kraft pulp and phenolated lignin thereof. BACKGROUND

[0002] In the field of chemical pulping, phenolation modification of lignin is an important way to improve the utilization value of lignin. Lignin, as a natural phenolic polymer, has aromatic structure and multiple functional groups, and is widely used in adhesives, dispersants, emulsifiers and other fields, with great application potential. A large amount of black liquor containing lignin is produced in the paper industry every year by traditional kraft pulping process. However, due to the high-temperature and strong-alkali conditions in the pulping process, the molecular structure of the obtained kraft lignin has been significantly changed, thus there are significant differences in intermolecular bonds, functional groups and active sites, etc. between the original lignin and the kraft lignin, and thus it is difficult to be directly used for the development of high-value-added products.

[0003] Phenolation modification is an important chemical modification method of lignin, which mainly increases the active sites of lignin by introducing phenolic hydroxyl groups and breaking lignin bonds (such as ether bonds and C-C bonds) in lignin molecules. Common phenolation methods include acidic and alkaline systems. Traditional industrial lignin acid phenolation method generally neutralizes the black liquor obtained by pulping first, collects the precipitated lignin, and then performs phenolation modification of lignin in acid / phenol system. The main reason for the difference in phenolic hydroxyl content in the acid phenolation process is the difference in the content of β-aryl ether bonds in lignin. In the acid medium, the Cα of the side chain of lignin forms a carbonium ion and condenses with phenol, followed by the breakage of Cβ-Cγ, C1-Cα and β-O-4 structures, which makes the lignin macromolecule fragmentize, and the phenolic hydroxyl content increases by condensation with phenol. However, the acid phenolation reaction has many steps and high energy consumption, thus it is not conducive to industrial application.

[0004] In order to solve the problem of acid phenolation, in recent years, the phenolation under alkaline conditions has gradually attracted attention. In the alkaline system, the phenolation reaction of lignin can be more selective, effectively breaking specific C-C and ether bonds, increasing the content of phenolic hydroxyl groups, and better preserving the original structure of lignin. Alkaline conditions also avoid the need for acid neutralization steps in acidic media, reducing the complexity of operation. In the paper "Response surface optimization of enzymatic lignin phenolation process", the parameters of the enzymatic lignin phenolation process (such as temperature, time, catalyst dosage, etc.) are optimized, and the response surface method is used to investigate the changes in the content of phenolic hydroxyl groups under different conditions. However, this method is based on the phenolation process of enzymatic lignin, involves complex reaction condition control, and does not solve the problem of high efficiency and simplification in industrial production. In the paper "Phenol-Enhanced Depolymerization and Activation of Kraft Lignin in Alkaline Medium", the phenolation treatment is carried out under laboratory conditions by using high temperature and high phenol to lignin ratio. This high phenol dosage and high temperature operation increases the cost of the reaction, and the experimental conditions are harsh and the energy consumption is high, which is not conducive to large-scale industrial application.

[0005] In addition, the alkaline phenolation modification of lignin in the prior art is difficult to be compatible with the traditional pulping conditions, and has limited industrialization potential. Moreover, there is no reported method that integrates lignin phenolation and pulping, which cannot achieve the separation of kraft pulp from biomass raw materials while obtaining kraft lignin with high phenolic hydroxyl content and more complete natural structure. SUMMARY

[0006] The present application provides a method for simultaneously preparing kraft pulp and phenolated lignin to overcome the defects of the prior art that the alkaline phenolation modification of lignin is difficult to be compatible with the traditional pulping conditions.

[0007] Another object of the present application is to provide a kraft pulp.

[0008] Another object of the present application is to provide a phenolated lignin.

[0009] To solve the above technical problems, the technical solution of the present application is as follows:

[0010] A method for simultaneously preparing kraft pulp and phenolated lignin, comprising the following steps:

[0011] S1, mixing wood fiber raw material, water, and cooking reagent, phenol into a cooking pot and cooking;

[0012] S2, after cooking, obtaining a mixture of residue and black liquor;

[0013] S3, collecting the residue to obtain kraft pulp;

[0014] S4, collecting the black liquor, acid precipitation, and the obtained precipitate is phenolized lignin.

[0015] Preferably, the solid part of the mixed liquor (residue) is collected and washed, and washed with clean water until the pH value of the washing liquor is neutral; and the coarse residue is screened out using a Paul screen.

[0016] Preferably, the acid precipitation is titration of the black liquor with hydrochloric acid or sulfuric acid.

[0017] Further, the mass ratio of the added phenol to the lignin content in the lignocellulosic raw material is not less than 0.5 and less than 3.

[0018] Preferably, the mass ratio of the added phenol to the lignin content in the lignocellulosic raw material is 0.66-2:1.

[0019] Further, the mass ratio of the lignocellulosic raw material to water is 1:3-6.

[0020] Preferably, the mixing ratio of the lignocellulosic raw material to water is 1:4.5.

[0021] Further, the added cooking reagent includes NaOH and Na2S; the amount of the added cooking reagent is 15-30% NaOH and 15-25% Na2S.

[0022] Preferably, the amount of the added cooking reagent is 20-30% NaOH and 20-25% Na2S.

[0023] Preferably, the amount of the added cooking reagent is 25% NaOH and 23% Na2S.

[0024] Preferably, the amount of the cooking reagent is calculated based on Na2O.

[0025] Further, the temperature of the cooking is 120-170°C, the temperature rising time during the cooking is 30-60 min, and the holding time is 2-4 h.

[0026] Preferably, the temperature of the cooking is 140-170°C, the temperature rising time during the cooking is 45 min, and the holding time is 2.5 h.

[0027] Further, the mixture is passed through a 200-400 mesh screen to collect the residue.

[0028] Preferably, the residue is collected using a pulp bag with a pore size of 200 mesh.

[0029] Preferably, the residue is washed until the pH value is neutral.

[0030] Preferably, the residue after washing is subjected to a defibrator for defibration at a beating degree of 6000, and then is subjected to a Paul classifier screen to remove the filter residue through a screen with a pore size of 250 microns, while collecting the fine pulp passing through the screen.

[0031] Further, the pH of the black liquor is adjusted to 2-4 during acid precipitation.

[0032] Preferably, the pH of the black liquor is adjusted to 3-4.

[0033] Preferably, the adjustment is performed using hydrochloric acid with a concentration of 1-2 mol / L.

[0034] Preferably, the phenolated lignin suspension after acid precipitation is allowed to stand, the liquid is removed, and washing is performed.

[0035] Further preferably, the standing temperature of the lignin suspension is 4-8 DEG C; deionized water at 60 DEG C is used for washing to remove residual phenol; and the solid after washing is freeze-dried to obtain the phenolated lignin.

[0036] Further, the lignocellulosic raw material includes coniferous wood, broad-leaved wood and gramineous raw material.

[0037] A phenolated lignin is prepared by the method for simultaneously preparing kraft pulp and phenolated lignin, and the phenolated lignin has a phenolic hydroxyl content of 3.5-6.0 mmol / g.

[0038] Preferably, the phenolated lignin has a phenolic hydroxyl content of 4.0-6.0 mmol / g.

[0039] A kraft pulp is prepared by the method for simultaneously preparing kraft pulp and phenolated lignin, and the kraft pulp has a kappa number of 23.0-110.0, a viscosity of 900-1350 mL / g and a brightness of 12.0-30.0% ISO.

[0040] Preferably, the kraft pulp has a kappa number of 23.72-108.16, a viscosity of 913-1348 mL / g and a brightness of 12.83-29.31% ISO.

[0041] Current industrial pulping methods are mostly alkali pulping, and the pulping black liquor is generally alkaline. In addition, due to the harsh reaction conditions in the kraft pulping process, the structure of the obtained lignin is mostly quite different from the natural structure (for example, almost all the beta-aryl ether bond structures are broken). Based on the industrial perspective, the addition of phenol can protect the structure of lignin to a certain extent through the condensation of phenol and lignin, and also enables the lignin separated from the plant cell wall to be phenolated and modified to obtain lignin with a high phenolic hydroxyl content at the same time as the kraft pulp is prepared, which has the advantages of being faster and more energy-saving.

[0042] The new method of lignin phenolation integrated with pulping of the application (i.e. the method of simultaneously preparing kraft pulp and phenolated lignin) can realize the separation of kraft pulp from the biomass raw material, and at the same time, obtain industrial kraft lignin with high phenolic hydroxyl content and more complete natural structure, which provides a new idea for the new method of biomass raw material chemical pulping and the optimization of traditional lignin phenolation process.

[0043] Compared with the prior art, the beneficial effects of the technical scheme of the application are:

[0044] 1. Integrated operation of pulping and phenolation. By directly adding phenol into the kraft pulping process, the present application makes reasonable and efficient use of the large amount of residual alkali existing in the pulping process, and at the same time realizes the separation and modification of lignin, thereby eliminating the cumbersome steps of independent lignin extraction, acid precipitation and separate phenolation in the traditional process, and avoiding the need for additional acid treatment equipment for separate phenolation reaction. The preparation process of the present application reduces the cost investment, operation steps and production time, and improves the efficiency of industrial application.

[0045] 2. Improved lignin utilization rate and phenolation modification effect. The phenolated lignin prepared by the present application has a phenolic hydroxyl content of 3.5-6.0 mmol / g, which is significantly improved compared with the traditional kraft process, indicating that the present application realizes efficient phenolation reaction in the integrated operation. Through alkaline phenolation reaction, the present application effectively protects the β-aryl ether bond structure of lignin, and improves the proportion of β-O-4 structure in the phenolated lignin. The phenolated lignin has higher chemical activity and is suitable for the development of high value-added products.

[0046] 3. High-quality kraft pulp output. The kraft pulp prepared by the present application has a viscosity (900-1350 mL / g) superior to that of the traditional kraft process, and the hand sheet prepared therefrom has a complete fiber structure and good mechanical properties. The pulp yield (30.26%-51.97%) is comparable to or better than that of the traditional kraft process.

[0047] 4. Environmentally friendly. By directly completing the phenolation modification of lignin during the pulping process, the present application reduces the discharge of high-alkaline waste liquid in the traditional black liquor treatment process, and reduces the difficulty of pollution treatment and environmental burden. The present application uses alkaline phenolation, which avoids the problem of large amount of acid waste liquid discharge in the acid phenolation method, and is more in line with the concept of energy saving and high efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The kraft pulp prepared in Example 1 has a content of 60 g / m 2 The photos of the hand sheet (a) and the 2D HSQC NMR spectrum of the phenolated lignin (b);

[0049] Figure 2 The kraft pulp prepared in Example 2 has a content of 60 g / m2 Photograph of the handwritten paper (a) and 2D HSQC NMR spectrum of phenolic lignin (b);

[0050] Figure 3 The sulfate slurry prepared in Example 3 had a content of 60 g / m³. 2 Photograph of the handwritten paper (a) and 2D HSQC NMR spectrum of phenolic lignin (b);

[0051] Figure 4 The sulfate slurry prepared in Example 4 had a content of 60 g / m³. 2 Photograph of the handwritten paper (a) and 2D HSQC NMR spectrum of phenolic lignin (b);

[0052] Figure 5 The sulfate slurry prepared in Example 5 had a content of 60 g / m³. 2 Photograph of the handwritten paper (a) and 2D HSQC NMR spectrum of phenolic lignin (b);

[0053] Figure 6 The 2D HSQC NMR spectrum of phenolic lignin prepared in Comparative Example 1;

[0054] Figure 7 The image shows the 2D HSQC NMR spectrum of phenolic lignin prepared in Comparative Example 2. Detailed Implementation

[0055] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0056] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0057] Example 1

[0058] 100g of oven-dry pine chips were placed in a cooking pot. A solution with 25% alkali and 23% sulfur was prepared using 450mL of tap water and added to the cooking pot along with 20g of phenol (lignin content / phenol content in pine chips = 1:0.66). The cooking program was set as follows: temperature increased from 25℃ to 130℃ within 25 minutes; temperature was maintained at 130℃ for 5 minutes; temperature increased from 130℃ to 160℃ within 15 minutes; temperature was maintained at 160℃ for 3 hours.

[0059] The residue after cooking was collected using a 200-mesh pulp bag, and the residual black liquor was washed away with clean water until the washing liquid was neutral. The washed residue was disintegrated using a disintegrator, and the beating degree was 6000. A Paul classifier screen was used to screen out coarse residue through a screen with a pore size of 250 μm, and fine kraft pulp was collected using a 200-mesh pulp bag.

[0060] The cooking black liquor was collected using a plastic bottle, and 50 mL of the black liquor was diluted with 150 mL of deionized water. A 1 mol / L hydrochloric acid solution was prepared, and the diluted black liquor was slowly added dropwise to the 1 mol / L hydrochloric acid through a separatory funnel under stirring at a rotor speed of 500 rpm. When the solution pH was in the range of 3-4, the addition was stopped, and the solution was allowed to stand in a refrigerator at a temperature of 6°C for 8 h. The liquid was removed by suction filtration, and the lignin was washed with hot water at a temperature of 60°C. After the residual phenol was washed away, the phenolated lignin was frozen and dried.

[0061] Example 2

[0062] 100 g of absolutely dry Simao pine wood chips were loaded into a cooking pot, and a solution prepared with 450 mL of tap water, 25% alkali, and 23% sulfur was added to the cooking pot together with 30 g of phenol (lignin content in Simao pine wood chips / phenol = 1:1). The cooking program was set as follows: from 25°C to 130°C in 25 min; 5 min at 130°C; from 130°C to 160°C in 15 min; 3 h at 160°C.

[0063] The residue after cooking was collected using a 200-mesh pulp bag, and the residual black liquor was washed away with clean water until the washing liquid was neutral. The washed residue was disintegrated using a disintegrator, and the beating degree was 6000. A Paul classifier screen was used to screen out coarse residue through a screen with a pore size of 250 μm, and fine kraft pulp was collected using a 200-mesh pulp bag.

[0064] The cooking black liquor was collected using a plastic bottle, and 50 mL of the black liquor was diluted with 150 mL of deionized water. A 1 mol / L hydrochloric acid solution was prepared, and the diluted black liquor was slowly added dropwise to the 1 mol / L hydrochloric acid through a separatory funnel under stirring at a rotor speed of 500 rpm. When the solution pH was in the range of 3-4, the addition was stopped, and the solution was allowed to stand in a refrigerator at a temperature of 6°C for 8 h. The liquid was removed by suction filtration, and the lignin was washed with hot water at a temperature of 60°C. After the residual phenol was washed away, the phenolated lignin was frozen and dried.

[0065] Example 3

[0066] The absolute dry weight of the pine wood chips was 100 g. A solution of 450 mL tap water was prepared with 25% alkali and 23% sulfur, and 50 g of phenol was added to the solution. The solution was mixed with the pine wood chips in the digester (lignin content in the pine wood chips / phenol = 1:1.67). The cooking program was set as follows: from 25°C to 130°C in 25 min; 130°C for 5 min; from 130°C to 160°C in 15 min; 160°C for 3 h.

[0067] The residue after cooking was collected using a 200-mesh pulp bag, and the residual black liquor was washed away with clean water until the pH of the washing liquid was neutral. The washed residue was disintegrated using a disintegrator at a beating degree of 6000. A Paul classifier screen was used to remove coarse residue through a screen with a pore size of 250 μm, and fine kraft pulp was collected using a 200-mesh pulp bag.

[0068] The cooking black liquor was collected using a plastic bottle, and 50 mL of the black liquor was diluted with 150 mL of deionized water. A 1 mol / L hydrochloric acid solution was prepared, and the diluted black liquor was slowly added dropwise to the 1 mol / L hydrochloric acid through a separatory funnel under stirring at a rotor speed of 500 rpm. When the pH of the solution was in the range of 3-4, the dropwise addition was stopped. The solution was left to stand in a refrigerator at a temperature of 6°C for 8 h, and the liquid was removed by suction filtration. The lignin was washed with hot water at a temperature of 60°C, and the phenolated lignin was obtained after freezing, drying, and washing away the residual phenol.

[0069] Example 4

[0070] The absolute dry weight of the pine wood chips was 100 g. A solution of 450 mL tap water was prepared with 25% alkali and 23% sulfur, and 50 g of phenol was added to the solution. The solution was mixed with the pine wood chips in the digester (lignin content in the pine wood chips / phenol = 1:1.67). The cooking program was set as follows: from 25°C to 130°C in 25 min; 130°C for 5 min; from 130°C to 160°C in 15 min; 160°C for 3 h.

[0071] The residue after cooking was collected using a 200-mesh pulp bag, and the residual black liquor was washed away with clean water until the pH of the washing liquid was neutral. The washed residue was disintegrated using a disintegrator at a beating degree of 6000. A Paul classifier screen was used to remove coarse residue through a screen with a pore size of 250 μm, and fine kraft pulp was collected using a 200-mesh pulp bag.

[0072] The plastic bottle was used to collect the cooking black liquor, and 50 mL of black liquor was added to 150 mL of deionized water for dilution. The concentration of 1 mol / L hydrochloric acid solution was prepared, and the diluted black liquor was slowly added dropwise through the separatory funnel under the condition of 500 rpm stirring. When the pH value of the solution was in the range of 3-4, the dropwise addition was stopped, and the solution was placed in the refrigerator at a temperature of 6°C for 8 h. The liquid was removed by suction filtration, and the lignin was washed with hot water at a temperature of 60°C. After washing the residual phenol, the phenolated lignin was frozen, dried and obtained.

[0073] Example 5

[0074] The absolute dry amount of 100 g of Simao pine wood chips was loaded into the cooking pot, and a solution with an alkali amount of 25% and a sulfur amount of 23% was prepared by 450 mL of tap water, and 30 g of phenol was added into the cooking pot for mixing (lignin amount in Simao pine wood chips / phenol = 1:1). The cooking program was set as follows: from 25°C to 130°C in 25 min; 130°C for 5 min; from 130°C to 170°C in 15 min; 170°C for 2.5 h.

[0075] The residue after cooking was collected using a 200 mesh pulp bag, and the residual black liquor was washed with clean water until the washing liquid was neutral. The washed residue was disintegrated using a disintegrator, and the beating degree was 6000. The coarse residue was screened out using a Paul classifier screen with a screen size of 250 μm, and the fine kraft pulp was collected using a 200 mesh pulp bag.

[0076] The plastic bottle was used to collect the cooking black liquor, and 50 mL of black liquor was added to 150 mL of deionized water for dilution. The concentration of 1 mol / L hydrochloric acid solution was prepared, and the diluted black liquor was slowly added dropwise through the separatory funnel under the condition of 500 rpm stirring. When the pH value of the solution was in the range of 3-4, the dropwise addition was stopped, and the solution was placed in the refrigerator at a temperature of 6°C for 8 h. The liquid was removed by suction filtration, and the lignin was washed with hot water at a temperature of 60°C. After washing the residual phenol, the phenolated lignin was frozen, dried and obtained.

[0077] Example 6

[0078] The absolute dry amount of 100 g of Simao pine wood chips was loaded into the cooking pot, and a solution with an alkali amount of 25% and a sulfur amount of 23% was prepared by 450 mL of tap water, and 30 g of phenol was added into the cooking pot for mixing (lignin amount in Simao pine wood chips / phenol = 1:1). The cooking program was set as follows: from 25°C to 130°C in 25 min; 130°C for 5 min; from 130°C to 170°C in 15 min; 170°C for 2.5 h.

[0079] The residue after cooking was collected using a 200-mesh pulp bag, and the residual black liquor was washed away with clean water until the washing liquid was neutral. The washed residue was disintegrated using a disintegrator at a beating degree of 6000. A Paul classifier screen was used to screen out coarse residue through a screen with a pore size of 250 μm, and fine kraft pulp was collected using a 200-mesh pulp bag.

[0080] The cooking black liquor was collected using a plastic bottle, and 50 mL of the black liquor was diluted with 150 mL of deionized water. A 1 mol / L hydrochloric acid solution was prepared, and the diluted black liquor was slowly added dropwise to the 1 mol / L hydrochloric acid through a separatory funnel under stirring at a rotor speed of 500 rpm. When the solution pH was in the range of 3-4, the dropwise addition was stopped, and the solution was allowed to stand in a refrigerator at a temperature of 6°C for 8 h. The liquid was removed by suction filtration, and the lignin was washed with hot water at a temperature of 60°C. After the residual phenol was washed away, the phenolated lignin was frozen and dried.

[0081] Example 7

[0082] 100 g of absolutely dry Simao pine wood chips were loaded into a cooking pot, and a solution prepared with 300 mL of tap water, an alkali amount of 15%, and a sulfur amount of 15% was added to the cooking pot together with 20 g of phenol (lignin amount / phenol in Simao pine wood chips = 1:0.67). The cooking procedure was set as follows: from 25°C to 120°C in 25 min; 120°C for 5 min; from 120°C to 160°C in 20 min; 170°C for 4 h.

[0083] The residue after cooking was collected using a 200-mesh pulp bag, and the residual black liquor was washed away with clean water until the washing liquid was neutral. The washed residue was disintegrated using a disintegrator at a beating degree of 6000. A Paul classifier screen was used to screen out coarse residue through a screen with a pore size of 250 μm, and fine kraft pulp was collected using a 200-mesh pulp bag.

[0084] The cooking black liquor was collected using a plastic bottle, and 50 mL of the black liquor was diluted with 150 mL of deionized water. A 1 mol / L hydrochloric acid solution was prepared, and the diluted black liquor was slowly added dropwise to the 1 mol / L hydrochloric acid through a separatory funnel under stirring at a rotor speed of 500 rpm. When the solution pH was in the range of 3-4, the dropwise addition was stopped, and the solution was allowed to stand in a refrigerator at a temperature of 6°C for 8 h. The liquid was removed by suction filtration, and the lignin was washed with hot water at a temperature of 60°C. After the residual phenol was washed away, the phenolated lignin was frozen and dried.

[0085] Comparative Example 1

[0086] Take 200 mg of pine sulfate lignin dissolved in 600 mg of phenol, add 40 mg of NaOH, stir uniformly at 60°C, and then load into a hydrothermal reactor. After reacting at 160°C for 1.5 h, cool the reaction with cold water, and dissolve with 5 mL of acetone / water (9:1, v / v) mixture. The resulting solution is added dropwise to 100 mL of deionized water. Slowly add 1 mol / L hydrochloric acid dropwise through a separatory funnel under stirring at a rotor speed of 500 rpm, stop adding when the solution pH is in the range of 3-4, and stand in a refrigerator at a temperature of 6°C for 8 h. Remove the liquid by suction filtration, and then wash the lignin with hot water at a temperature of 60°C. After washing away the residual phenol, freeze and dry to obtain phenolated lignin.

[0087] Comparative Example 2

[0088] Put 100 g of dried and cut Smit pine wood chips into a digester, and mix with a solution prepared with 450 mL of tap water, 25% alkali, and 23% sulfur. The cooking program is set as follows: from 25°C to 130°C in 25 min; 130°C for 5 min; from 130°C to 160°C in 15 min; 160°C for 3 h.

[0089] Collect the cooked residue using a 200-mesh pulp bag, and wash away the residual black liquor with clean water until the washing liquid is neutral. Use a Paul classifier screen to remove coarse residue through a screen with a pore size of 250 μm, and collect the fine kraft pulp using a 200-mesh pulp bag.

[0090] Collect the cooking black liquor using a plastic bottle, and take 50 mL of the black liquor to dilute with 150 mL of deionized water. Prepare a 1 mol / L hydrochloric acid solution, and slowly add the diluted black liquor dropwise through a separatory funnel under stirring at a rotor speed of 500 rpm. Stop adding when the solution pH is in the range of 3-4, stand in a refrigerator at a temperature of 6°C for 8 h, remove the liquid by suction filtration, wash the precipitate, freeze, and dry to obtain lignin.

[0091] Comparative Example 3

[0092] Put 100 g of dried and cut Smit pine wood chips into a digester, and mix with a solution prepared with 450 mL of tap water, 25% alkali, and 23% sulfur, and 90 g of phenol (lignin content in Smit pine wood chips / phenol = 1:3).

[0093] Detection Method

[0094] The yield calculation formula of the pulp prepared after cooking in the present application is shown in (1-1); the viscosity of the kraft pulp is tested by a fiber viscosity analyzer, the testing environment temperature is 25°C, and the relative humidity is 50%; the brightness of the kraft pulp is tested by using a brightness instrument after the kraft pulp is made into a hand sheet, the testing environment temperature is 25°C, and the relative humidity is 50%; the kappa number of the kraft pulp is tested by titration.

[0095]

[0096] The phenolic hydroxyl content of the phenolated lignin is calculated by an ultraviolet test method (formula 1-2), and the specific method steps are as follows: 20 mg of the lignin sample is dissolved in 10 mL of a 1,4-dioxane / water (8 / 2, v / v) solution. A solution of ethylene glycol methyl ether / water / acetic acid (v / v / v, 8 / 2 / 0.2) is prepared as an acidic solution, and a solution of ethylene glycol methyl ether / 0.2M NaOH (v / v, 1 / 9) is prepared as an alkaline solution. 100 μL of the lignin solution is respectively prepared into 10 mL of a lignin acidic solution and a lignin alkaline solution by using the acidic solution and the alkaline solution. The absorption value of the 200-400 nm wave band is immediately scanned by a Shimadzu ultraviolet-visible spectrophotometer (UV-2600i).

[0097] ΔA 300 = 3619C Ⅰ + 586C Ⅱ - 6728C Ⅲ - 4880C Ⅳ

[0098] ΔA 320 = 3039C Ⅱ - 11428C Ⅲ + 391C Ⅳ

[0099] ΔA 350 = 344C Ⅱ + 5436C Ⅲ + 24010C Ⅳ

[0100] ΔA 370 = 22590C Ⅲ + 10658C Ⅳ

[0101] ΔAbs 300 = Abs 300 (alkaline solution) - Abs 300 (acidic solution)

[0102] ΔAbs 320 = Abs 320 (alkaline solution) - Abs 320 (acidic solution)

[0103] Delta Abs 350 = Abs 350 (alkaline liquor) - Abs 350 (acidic liquor)

[0104] Delta Abs 370 = Abs 370 (alkaline liquor) - Abs 370 (acidic liquor)

[0105] Ph-OH (mmol / L) = C Ⅰ + C Ⅱ + C Ⅲ + C Ⅳ (1-2)

[0106] All NMR spectra of lignin samples were collected at 25°C using a Bruker Ascend-500M NMR spectrometer with dimethyl sulfoxide (DMSO-d6) as solvent. 50-70 mg of lignin sample was weighed into an NMR tube and 0.6 mL of dimethyl sulfoxide (DMSO-d6) was added for dissolution. Data was processed using Bruker Topspin 4.1.4. According to the processing of Bruker Topspin 4.1.4.

[0107] Analysis

[0108] The examples and comparative examples were analyzed by the results in Table 1 and the figures.

[0109] The results in Table 1 show that in Examples 1-4, the content of phenolic hydroxyl groups of the obtained phenolated lignin is significantly improved with the increase of the amount of added phenol. A higher proportion of phenol can improve the reactivity of lignin molecules, promote the introduction of phenolic hydroxyl groups and the breaking of β-O-4 bonds, increase the rate and selectivity of phenolation, and be more conducive to lignin phenolation. In Example 4, the ratio of lignin to phenol in the raw material is 1:1.67, and the content of phenolic hydroxyl groups of the phenolated lignin reaches 4.75 mmol / g. However, the addition amount of phenol also affects the preparation effect of kraft pulp to some extent. Although a high proportion of phenol promotes lignin phenolation, lignin removal is not complete, phenol and lignin form cross-linked products, increase the stability of lignin molecular chain, and reduce its solubility, resulting in an increase in residual lignin content. Therefore, the yield of kraft pulp in Example 4 is reduced, the kappa number is increased, and the whiteness is reduced. In addition, in Comparative Example 3, the excessive addition of phenol reduces the dissolution and modification of hemicellulose by alkaline reaction, resulting in a high content of hemicellulose in the fiber bundle, an increase in fiber separation resistance, and finally the inability to form pulp, which cannot be prepared in the next step.

[0110] Properties of kraft pulp and phenolated lignin obtained in Table 1

[0111] Properties of kraft pulp and phenolated lignin obtained in Table 1

[0112] Figure 1 a~ Figure 5 The handmade paper of type a has good paper uniformity and density, and the fiber structure is intact, indicating that adding phenol will not significantly affect the performance of the pulp. Figure 1 b~ Figure 4 In step b, as the proportion of phenol increases, the β-O-4 bonds in lignin gradually decrease, and the aromatic ring modification signal gradually increases, indicating that the phenolation reaction is active. Compared with the preparation method of Comparative Example 1, which uses pine sulfate lignin as raw material for phenolation alone, the lignin obtained by this invention, which uses plant fiber as raw material and simultaneously pulps and phenolizes, has similar structural features. Figure 6 This further illustrates that the preparation method of the present invention has achieved the same or even better effect as the traditional single phenolation process in actual operation.

[0113] Comparative Example 2 uses the traditional sulfate pulping process, which requires pulping, black liquor extraction, and acid precipitation to separate sulfate lignin. Furthermore, the lignin in Comparative Example 2, after undergoing high-temperature alkaline treatment, exhibits a significantly reduced molecular weight distribution, with most of its original molecular structures destroyed. The resulting sulfate lignin has lost some of its original molecular integrity, resulting in a phenolic hydroxyl content of only 3.53 mmol / g, significantly lower than that of this invention. Figure 7 The aromatic ring signal in the lignin is weak. This signal comes from the residual aromatic groups in the lignin extracted by traditional processes, which further indicates that the high-temperature alkaline cooking conditions destroy a large number of natural structures and active groups, resulting in a reduction of active sites.

[0114] The addition of phenol and alkaline cooking conditions in this invention not only achieves efficient separation of lignin, but also increases the phenolic hydroxyl content through the condensation reaction of phenol and lignin, thereby modifying lignin. At the same time, it avoids excessive damage to the lignin structure under acidic conditions and enhances the chemical activity of phenolized lignin.

[0115] 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 simultaneously preparing sulfate pulp and phenolic lignin, characterized in that, Includes the following steps: S1. Add the wood fiber raw material, water, cooking reagent, and phenol to a cooking pot, mix, and cook. S2. After cooking, a mixture of residue and black liquor is obtained; S3. Collect the residue to obtain sulfate slurry; S4. Collect the black liquor and perform acid precipitation. The precipitate obtained is phenolic lignin. The mass ratio of the added phenol to the lignin content in the wood fiber raw material is not less than 0.5 and less than 3. The amount of alkali added to the cooking reagent is 15~30% NaOH, and the amount of sulfur is 15~25% Na2S.

2. The method for simultaneously preparing sulfate pulp and phenolic lignin according to claim 1, characterized in that, The mass ratio of the wood fiber raw material to water is 1:3~6.

3. The method for simultaneously preparing sulfate pulp and phenolic lignin according to claim 1, characterized in that, The cooking temperature is 120~170 ℃, the heating time is 30~60 min, and the holding time is 2~4 h.

4. The method for simultaneously preparing sulfate pulp and phenolic lignin according to claim 1, characterized in that, Collect the residue by passing the mixture through a 200-400 mesh sieve.

5. The method for simultaneously preparing sulfate pulp and phenolic lignin according to claim 1, characterized in that, During acid precipitation, adjust the pH of the black liquor to 2-4.

6. The method for simultaneously preparing sulfate pulp and phenolic lignin according to claim 1, characterized in that, The wood fiber raw materials include coniferous wood, broadleaf wood, and grasses.

7. A phenolic lignin, characterized in that, The phenolic lignin is prepared by the method for simultaneously preparing sulfate pulp and phenolic lignin as described in any one of claims 1 to 6, wherein the phenolic hydroxyl content of the phenolic lignin is 3.5 to 6.0 mmol / g.

8. A sulfate slurry, characterized in that, The sulfate pulp is prepared by the method for simultaneously preparing sulfate pulp and phenolic lignin as described in any one of claims 1 to 6, wherein the sulfate pulp has a kappa value of 23.0 to 110.0, a viscosity of 900 to 1350 mL / g, and a whiteness of 12.0 to 30.0% ISO.

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