Method for synchronously preparing sulfate pulp and phenolated lignin as well as sulfate pulp and phenolated lignin

Abstract

The invention relates to the field of chemical pulping, and discloses a method for synchronously preparing sulfate pulp and phenolated lignin as well as the sulfate pulp and the phenolated lignin thereof. The method for simultaneously preparing sulfate pulp and phenolated lignin comprises the following steps: mixing a wood fiber raw material, water and a cooking reagent, and adding phenol; after cooking, obtaining a mixture of residues and black liquor; collecting residues to obtain sulfate slurry; and collecting the black liquor, and carrying out acid precipitation to obtain a precipitate which is phenolated lignin. The phenolic hydroxyl group content of the prepared phenolated lignin is 3.5-6.0 mmol / g, the kappa number of the prepared sulfate pulp is 23.0-110.0, the viscosity of the prepared sulfate pulp is 900-1350 mL / g, and the whiteness of the prepared sulfate pulp is 12.0-30.0% ISO (International Standardization Organization). The method disclosed by the invention has a remarkable lignin modification effect during fiber separation, realizes efficient utilization of resources and reduction of environmental burden, and also has relatively high industrialization potential.

Description

Technical Field

[0001] The invention relates to the field of chemical pulping, and more specifically, to a method for synchronously preparing kraft pulp and phenolic lignin, and the kraft pulp and phenolic lignin. Background Art

[0002] In the field of chemical pulping, phenolization modification technology of lignin is an important way to enhance the utilization value of lignin. As a natural phenolic polymer, lignin has an aromatic structure and multifunctional groups. It is widely used in adhesives, dispersants, emulsifiers and other fields, and has great application potential. The traditional kraft pulping method produces a large amount of black liquor rich in lignin in the papermaking industry every year. However, due to the high temperature and strong alkaline conditions of the pulping process, the molecular structure of the resulting kraft lignin has changed significantly, resulting in significant differences from the original lignin in terms of intermolecular bonds, functional groups and active sites, making it difficult to directly use it in the development of high value-added products.

[0003] Phenol modification is an important chemical modification method for lignin, which mainly introduces phenolic hydroxyl groups on lignin molecules and breaks lignin bonds (such as ether bonds and CC bonds) to significantly increase the active sites of lignin. Commonly used phenolization methods include acidic and alkaline systems. The traditional industrial lignin acid phenolization method generally neutralizes the black liquor obtained from pulping with acid, collects the lignin after precipitation, and then phenolizes the lignin in an acid / phenol system. The difference in the content of phenolic hydroxyl groups during acid phenolization is mainly due to the difference in the content of β-aryl ether bonds in lignin. In an acidic medium, the Cα of the lignin side chain forms a carbon cation and condenses with phenol, followed by the breakage of Cβ-Cγ, C1-Cα and β-O-4 structures to fragment the lignin macromolecules, and the phenolic hydroxyl content is increased by condensation with phenol. However, the acid phenolization reaction has many steps and high energy consumption, which is not conducive to industrial application.

[0004] In order to solve the shortcomings of acidic phenolization, phenolization modification under alkaline conditions has gradually attracted attention in recent years. In alkaline systems, the phenolization reaction of lignin can be more selective, effectively break specific CC and ether bonds, increase the content of phenolic hydroxyl groups, and better retain the original structure of lignin. Alkaline conditions also avoid the acid neutralization step required for acidic media, reducing the complexity of the operation. In the article "Study on Optimization of Enzymatic Lignin Phenolization Process by Response Surface Method", various parameters of the enzymatic lignin phenolization process (such as temperature, time, catalyst dosage, etc.) were optimized, and the response surface method was used to explore the changes in phenolic hydroxyl content under different conditions. However, this method is based on the phenolization process of enzymatic lignin, involving complex reaction condition control, and does not solve the needs of high efficiency and simplification in industrial production. The article "Phenol-Enhanced Depolymerization and Activation of Kraft Lignin in Alkaline Medium" phenolized at a higher temperature and a higher ratio of phenol to lignin under laboratory conditions. This high phenol dosage and high temperature operation increase the reaction cost, and the experimental conditions are relatively harsh, with high energy consumption, which is not conducive to large-scale industrial application.

[0005] In addition, the alkaline phenolization modification of lignin in the existing technology is difficult to be compatible with traditional pulping conditions, and its industrialization potential is limited. At present, there is no reported method that integrates lignin phenolization and pulping. It is impossible to achieve the separation of sulfate pulp from biomass raw materials and obtain industrial sulfate lignin with high phenolic hydroxyl content and more complete natural structure. Summary of the invention

[0006] The present invention provides a method for simultaneously preparing kraft pulp and phenolic lignin in order to overcome the defect that the alkaline phenolic modification of lignin described in the prior art is incompatible with traditional pulping conditions;

[0007] Another object of the present invention is to provide a kraft pulp;

[0008] Another object of the present invention is to provide a phenolic lignin.

[0009] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0010] A method for simultaneously preparing kraft pulp and phenolic lignin comprises the following steps:

[0011] S1, adding wood fiber raw materials, water, cooking reagents, and phenol into a cooking pot, mixing, and cooking;

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

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

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

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

[0016] Preferably, the acid precipitation uses hydrochloric acid or sulfuric acid to titrate the black liquor.

[0017] Furthermore, 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.

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

[0019] Furthermore, the mass ratio of the wood fiber raw material to water is 1:3-6.

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

[0021] Furthermore, the added cooking reagents include NaOH and Na2S; the amount of alkali used in the added cooking reagents is 15-30% NaOH, and the amount of sulfur used is 15-25% Na2S.

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

[0023] Preferably, the amount of alkali added as the cooking agent is 25% NaOH, and the amount of sulfur added is 23% Na2S.

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

[0025] Furthermore, the cooking temperature is 120-170° C., the heating time is 30-60 minutes, and the heat preservation time is 2-4 hours.

[0026] Preferably, the cooking temperature is 140-170° C., the heating time during cooking is 45 minutes, and the heat preservation time is 2.5 hours.

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

[0028] Preferably, a pulp bag with a pore size of 200 mesh is used to collect the residue.

[0029] Preferably, the residue is washed to a neutral pH.

[0030] Preferably, the residue after cleaning is deflagrated using a deflagrator with a beating degree of 6000, and then the residue is sieved out using a Paul grading screen through a sieve with an aperture size of 250 μm, and the fine pulp passing through the sieve is collected.

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

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

[0033] Preferably, hydrochloric acid with a concentration of 1 to 2 mol / L is used for adjustment.

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

[0035] Further preferably, the standing temperature of the lignin suspension is 4-8°C; 60°C deionized water is used to wash away residual phenol during washing; and the washed solid is freeze-dried and collected to obtain phenolic lignin.

[0036] Furthermore, the wood fiber raw materials include coniferous wood, broadleaved wood and grass raw materials.

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

[0038] Preferably, the phenolic hydroxyl content of the phenolic lignin is 4.0 to 6.0 mmol / g

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

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

[0041] Most of the current industrial pulping methods are alkaline pulping, and the pulping black liquor is generally alkaline. In addition, due to the harsh reaction conditions of the kraft pulping process, the obtained lignin structure is mostly very different from the natural structure (for example, the β-aryl ether bond structure is almost completely broken). Based on the industrial perspective, the present invention can protect the lignin structure to a certain extent through the condensation of phenol and lignin after adding phenol, and also make it possible to separate the kraft pulp from the plant cell wall while completing the phenolization modification of the lignin to obtain lignin with a high phenolic hydroxyl content, which has the advantages of being faster and energy-saving.

[0042] The novel method of integrating lignin phenolation and pulping of the present invention (i.e., a method for simultaneously preparing sulfate pulp and phenolated lignin) can not only separate sulfate pulp from biomass raw materials, but also obtain industrial sulfate lignin with high phenolic hydroxyl content and more complete natural structure. This provides a new idea for a new method for chemical pulping of biomass raw materials and optimizing the traditional lignin phenolation process.

[0043] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0044] 1. Integrated operation of pulping and phenolization. The present invention directly adds phenol to the kraft pulping process, rationally and efficiently uses a large amount of residual alkali in the pulping process, and simultaneously realizes the separation and modification of lignin, eliminating the cumbersome steps of independent lignin extraction, acid precipitation and separate phenolization in the traditional process, and avoiding the additional acid treatment equipment required for the separate phenolization reaction. The preparation process of the present invention reduces cost input, operation steps and production time, and improves the efficiency of industrial application.

[0045] 2. The utilization rate of lignin and the effect of phenolization modification are improved. The phenolic hydroxyl content of the phenolized lignin prepared by the present invention reaches 3.5-6.0 mmol / g, which is significantly improved compared with the traditional sulfate method, indicating that the present invention achieves an efficient phenolization reaction in an integrated operation. The present invention effectively protects the β-aryl ether bond structure of lignin through an alkaline phenolization reaction, and increases the proportion of β-O-4 structure in the phenolized lignin. After phenolization, lignin has higher chemical activity and is suitable for the development of high value-added products.

[0046] 3. High-quality sulfate pulp output. The sulfate pulp viscosity (900-1350 mL / g) of the present invention is better than that of the traditional sulfate method, and the prepared hand-made paper has a complete fiber structure and good mechanical properties. The pulp yield (30.26%-51.97%) is equivalent to or better than that of the traditional sulfate method.

[0047] 4. Environmentally friendly. By directly completing the phenolization modification of lignin during the pulping process, the discharge of high-alkaline waste liquid in the traditional black liquor treatment process is reduced, and the difficulty of pollution treatment and the environmental burden are reduced. The present invention adopts alkaline conditions for phenolization, which avoids the problem of discharging a large amount of acidic waste liquid in the acidic phenolization method, and is more in line with the concept of energy-saving and efficient chemical industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The sulfate pulp prepared in Example 1 has a content of 60 g / m 2 Photograph of hand-sheet (a) and 2D HSQC NMR spectrum of phenolized lignin (b);

[0049] Figure 2 The sulfate pulp prepared in Example 2 has a content of 60 g / m2 Photograph of hand-sheet (a) and 2D HSQC NMR spectrum of phenolized lignin (b);

[0050] Figure 3 The sulfate pulp prepared in Example 3 has a content of 60 g / m 2 Photograph of hand-sheet (a) and 2D HSQC NMR spectrum of phenolized lignin (b);

[0051] Figure 4 The sulfate pulp prepared in Example 4 has a content of 60 g / m 2 Photograph of hand-sheet (a) and 2D HSQC NMR spectrum of phenolized lignin (b);

[0052] Figure 5 The sulfate pulp prepared in Example 5 has a content of 60 g / m 2 Photograph of hand-sheet (a) and 2D HSQC NMR spectrum of phenolized lignin (b);

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

[0054] Figure 7 This is the 2D HSQC NMR spectrum of the phenolic lignin prepared in Comparative Example 2. DETAILED DESCRIPTION

[0055] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

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

[0057] Example 1

[0058] 100g of pine chips with an absolute dry weight were placed in a cooking pot, and a solution with 25% alkali and 23% sulfur was prepared with 450mL of tap water, and 20g of phenol was added to the cooking pot and mixed (lignin content in pine chips / phenol = 1:0.66). The cooking program was set as follows: from 25°C to 130°C within 25min; 130°C for 5min; from 130°C to 160°C for 15min; 160°C for 3h.

[0059] Use a 200-mesh pulp bag to collect the residue after cooking, wash the residual black liquor with clean water, and wash until the pH value of the washing liquid is neutral. Use a deflaker to deflake the washed residue, and the beating degree is 6000. Use a Paul grading screen to screen out the coarse residue through a sieve with an aperture size of 250μm, and collect the fine sulfate pulp with 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 hydrochloric acid solution with a concentration of 1 mol / L was prepared, and the diluted black liquor was slowly added dropwise with 1 mol / L hydrochloric acid through a separatory funnel while stirring at a rotor speed of 500 rpm. When the pH value of the solution was in the range of 3 to 4, the addition was stopped, and the solution was placed in a refrigerator at a temperature of 6°C for 8 hours, and the liquid was removed by suction, and the lignin was washed with hot water at a temperature of 60°C, and the residual phenol was washed away and then frozen and dried to obtain phenolized lignin.

[0061] Example 2

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

[0063] Use a 200-mesh pulp bag to collect the residue after cooking, wash the residual black liquor with clean water, and wash until the pH value of the washing liquid is neutral. Use a deflaker to deflake the washed residue, and the beating degree is 6000. Use a Paul grading screen to screen out the coarse residue through a sieve with an aperture size of 250μm, and collect the fine sulfate pulp with 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 hydrochloric acid solution with a concentration of 1 mol / L was prepared, and the diluted black liquor was slowly added dropwise with 1 mol / L hydrochloric acid through a separatory funnel while stirring at a rotor speed of 500 rpm. When the pH value of the solution was in the range of 3 to 4, the addition was stopped, and the solution was placed in a refrigerator at a temperature of 6°C for 8 hours, and the liquid was removed by suction, and the lignin was washed with hot water at a temperature of 60°C, and the residual phenol was washed away and then frozen and dried to obtain phenolized lignin.

[0065] Example 3

[0066] 100g of pine chips with an absolute dry weight were placed in a cooking pot, and a solution with 25% alkali and 23% sulfur was prepared with 450mL of tap water, and 40g of phenol was added to the cooking pot and mixed (lignin content in pine chips / phenol = 1:1.33). The cooking program was set as follows: from 25°C to 130°C within 25min; 130°C for 5min; from 130°C to 160°C for 15min; 160°C for 3h.

[0067] Use a 200-mesh pulp bag to collect the residue after cooking, wash the residual black liquor with clean water, and wash until the pH value of the washing liquid is neutral. Use a deflaker to deflake the washed residue, and the beating degree is 6000. Use a Paul grading screen to screen out the coarse residue through a sieve with an aperture size of 250μm, and collect the fine sulfate pulp with 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 hydrochloric acid solution with a concentration of 1 mol / L was prepared, and the diluted black liquor was slowly added dropwise with 1 mol / L hydrochloric acid through a separatory funnel while stirring at a rotor speed of 500 rpm. When the pH value of the solution was in the range of 3 to 4, the addition was stopped, and the solution was placed in a refrigerator at a temperature of 6°C for 8 hours, and the liquid was removed by suction, and the lignin was washed with hot water at a temperature of 60°C, and the residual phenol was washed away and then frozen and dried to obtain phenolized lignin.

[0069] Example 4

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

[0071] Use a 200-mesh pulp bag to collect the residue after cooking, wash the residual black liquor with clean water, and wash until the pH value of the washing liquid is neutral. Use a deflaker to deflake the washed residue, and the beating degree is 6000. Use a Paul grading screen to screen out the coarse residue through a sieve with an aperture size of 250μm, and collect the fine sulfate pulp with a 200-mesh pulp bag.

[0072] 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 hydrochloric acid solution with a concentration of 1 mol / L was prepared, and the diluted black liquor was slowly added dropwise with 1 mol / L hydrochloric acid through a separatory funnel while stirring at a rotor speed of 500 rpm. When the pH value of the solution was in the range of 3 to 4, the addition was stopped, and the solution was placed in a refrigerator at a temperature of 6°C for 8 hours, and the liquid was removed by suction, and the lignin was washed with hot water at a temperature of 60°C, and the residual phenol was washed away and then frozen and dried to obtain phenolized lignin.

[0073] Example 5

[0074] 100g of Simao pine chips were placed in a cooking pot, and a solution containing 25% alkali and 23% sulfur was prepared with 450mL of tap water, and 30g of phenol was added to the cooking pot and mixed (lignin content in Simao pine chips / phenol = 1:1). The cooking program was set as follows: from 25°C to 130°C within 25min; 130°C for 5min; from 130°C to 170°C for 15min; 170°C for 2.5h.

[0075] Use a 200-mesh pulp bag to collect the residue after cooking, wash the residual black liquor with clean water, and wash until the pH value of the washing liquid is neutral. Use a deflaker to deflake the washed residue, and the beating degree is 6000. Use a Paul grading screen to screen out the coarse residue through a sieve with an aperture size of 250μm, and collect the fine sulfate pulp with a 200-mesh pulp bag.

[0076] 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 hydrochloric acid solution with a concentration of 1 mol / L was prepared, and the diluted black liquor was slowly added dropwise with 1 mol / L hydrochloric acid through a separatory funnel while stirring at a rotor speed of 500 rpm. When the pH value of the solution was in the range of 3 to 4, the addition was stopped, and the solution was placed in a refrigerator at a temperature of 6°C for 8 hours, and the liquid was removed by suction, and the lignin was washed with hot water at a temperature of 60°C, and the residual phenol was washed away and then frozen and dried to obtain phenolized lignin.

[0077] Example 6

[0078] 100g of pine chips with an absolute dry weight were placed in a cooking pot, and a solution with 30% alkali and 25% sulfur was prepared with 600mL of tap water, and 60g of phenol was added to the cooking pot and mixed (lignin content in pine chips / phenol = 1:2). The cooking program was set as follows: from 25°C to 140°C within 35min; 140°C for 5min; from 130°C to 170°C for 25min; 170°C for 3h.

[0079] Use a 200-mesh pulp bag to collect the residue after cooking, wash the residual black liquor with clean water, and wash until the pH value of the washing liquid is neutral. Use a deflaker to deflake the washed residue, and the beating degree is 6000. Use a Paul grading screen to screen out the coarse residue through a sieve with an aperture size of 250μm, and collect the fine sulfate pulp with 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 hydrochloric acid solution with a concentration of 1 mol / L was prepared, and the diluted black liquor was slowly added dropwise with 1 mol / L hydrochloric acid through a separatory funnel while stirring at a rotor speed of 500 rpm. When the pH value of the solution was in the range of 3 to 4, the addition was stopped, and the solution was placed in a refrigerator at a temperature of 6°C for 8 hours, and the liquid was removed by suction, and the lignin was washed with hot water at a temperature of 60°C, and the residual phenol was washed away and then frozen and dried to obtain phenolized lignin.

[0081] Example 7

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

[0083] Use a 400-mesh pulp bag to collect the residue after cooking, and wash the residual black liquor with clean water until the pH value of the washing liquid is neutral. Use a deflaker to deflake the washed residue, and the beating degree is 6000. Use a Paul grading screen to screen out the coarse residue through a sieve with an aperture size of 250μm, and collect the fine sulfate pulp with 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 hydrochloric acid solution with a concentration of 2 mol / L was prepared, and the diluted black liquor was slowly added dropwise with 2 mol / L hydrochloric acid through a separatory funnel while stirring at a rotor speed of 500 rpm. The addition was stopped when the pH value of the solution was in the range of 2 to 3, and the solution was placed in a refrigerator at a temperature of 6°C for 8 hours, and the liquid was removed by suction, and the lignin was washed with hot water at a temperature of 60°C, and the residual phenol was washed away and then frozen and dried to obtain phenolized lignin.

[0085] Comparative Example 1

[0086] Take 200 mg of pine wood sulfate lignin and dissolve it in 600 mg of phenol, add 40 mg of NaOH, stir evenly at 60 ° C, and then load it into a hydrothermal reactor. After reacting at 160 ° C for 1.5 hours, cool the reactant with cold water and dissolve it with 5 mL of acetone / water (9:1, v / v) mixed solution. Add the resulting solution dropwise into 100 mL of deionized water. While stirring at a rotor speed of 500 rpm, slowly add 1 mol / L hydrochloric acid dropwise through a separatory funnel. Stop adding when the pH value of the solution is in the range of 3 to 4, stand in a refrigerator at a temperature of 6 ° C for 8 hours, remove the liquid by suction, 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 phenolized lignin.

[0087] Comparative Example 2

[0088] Put 100g of Simao pine wood chips into the cooking pot, add 450mL of tap water with 25% alkali and 23% sulfur solution, and mix them together. The cooking program is set as follows: from 25℃ to 130℃ within 25min; keep at 130℃ for 5min; from 130℃ to 160℃ for 15min; keep at 160℃ for 3h.

[0089] Use a 200-mesh pulp bag to collect the residue after cooking, wash the residual black liquor with clean water until the pH value of the washing liquid is neutral. Use a Paul grading screen to screen out the coarse residue through a sieve with an aperture size of 250μm, and collect the fine sulfate pulp with a 200-mesh pulp bag.

[0090] The cooking black liquor was collected using a plastic bottle, and 50 mL of black liquor was added to 150 mL of deionized water for dilution. A hydrochloric acid solution with a concentration of 1 mol / L was prepared, and the diluted black liquor was slowly added dropwise with 1 mol / L hydrochloric acid through a separatory funnel while stirring at a rotor speed of 500 rpm. When the pH value of the solution was in the range of 3-4, the addition was stopped, and the solution was placed in a refrigerator at a temperature of 6°C for 8 hours, the liquid was removed by suction, the precipitate was washed, and the lignin was obtained by freezing and drying.

[0091] Comparative Example 3

[0092] 100 g of dry pine chips were placed in a cooking pot, and a solution containing 25% alkali and 23% sulfur was prepared with 450 mL of tap water, and 90 g of phenol was added to the cooking pot and mixed (lignin content in pine chips / phenol = 1:3).

[0093] Detection Methods

[0094] The calculation formula for the pulping yield after cooking in the present invention is shown as (1-1); the viscosity of the sulfate pulp is tested by a fiber viscosity analyzer, the test environment temperature is 25°C, and the relative humidity is 50%; the whiteness of the sulfate pulp is tested by using a whiteness meter to make hand-sheeted paper from the sulfate pulp, and the test environment temperature is 25°C and the relative humidity is 50%; the kappa number of the sulfate pulp is tested by titration.

[0095]

[0096] The phenolic hydroxyl content of phenolized lignin is calculated by ultraviolet testing (Formula 1-2), and the specific steps are as follows: Take 20 mg of lignin sample and dissolve it in 10 mL of 1,4-dioxane / water (8 / 2, v / v) solution. Prepare ethylene glycol methyl ether / water / acetic acid (v / v / v, 8 / 2 / 0.2) solution as acidic solution and ethylene glycol methyl ether / 0.2MNaOH (v / v, 1 / 9) solution as alkaline solution. Prepare 100 μL of lignin solution with acidic solution and alkaline solution to prepare 10 mL of lignin acidic solution and lignin alkaline solution respectively. Immediately scan the absorption value of the 200-400 nm band with Shimadzu UV-Vis 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 liquid)

[0102] ΔAbs 320 =Abs 320 (Alkaline solution)-Abs 320 (Acidic liquid)

[0103] ΔAbs 350 =Abs 350 (Alkaline solution)-Abs 350 (Acidic liquid)

[0104] ΔAbs 370 =Abs 370 (Alkaline solution)-Abs 370 (Acidic liquid)

[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 instrument, and dimethyl sulfoxide (DMSO-d6) was used as the solvent. 50-70 mg of lignin sample was weighed into an NMR tube, and 0.6 mL of dimethyl sulfoxide (DMSO-d6) was added to dissolve it. The data was processed using Bruker Topspin 4.1.4.

[0107] Analysis

[0108] The examples and comparative examples are analyzed by the results in Table 1 and the accompanying drawings.

[0109] The results in Table 1 show that in Examples 1 to 4, the phenolic hydroxyl content of the obtained phenolized lignin increases significantly with the increase in the amount of phenol added. A higher phenol ratio 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 the phenolization reaction, and is more conducive to the phenolization of lignin. In Example 4, the ratio of lignin to phenol in the raw material is 1:1.67, and the content of phenolic hydroxyl groups in the phenolized lignin reaches 4.75mmol / g. However, the amount of phenol added also affects the preparation effect of kraft pulp to a certain extent. Although a high proportion of phenol promotes lignin phenolization, lignin removal is incomplete, phenol and lignin form cross-linked products, increase the stability of the lignin molecular chain, reduce its solubility, and lead to an increase in the residual lignin content. Therefore, the yield of the kraft pulp in Example 4 is reduced, the kappa number is increased, and the whiteness is reduced. In addition, in Comparative Example 3, excessive addition of phenol further reduced the dissolution and modification of hemicellulose by the alkaline reaction, resulting in a higher hemicellulose content in the fiber bundle, increased fiber separation resistance, and ultimately failure to form pulp, and inability to proceed to the next step of preparation.

[0110] Table 1 Properties of the obtained kraft pulp and phenolic lignin

[0111]

[0112] Figure 1 a~ Figure 5 The hand-made paper of a has good uniformity and density, and the fiber structure is complete, which shows that the addition of phenol will not significantly affect the performance of the pulp; Figure 1 b~ Figure 4 In b, as the proportion of phenol increases, the β-O-4 bond of lignin gradually decreases, and the aromatic ring modification signal gradually increases, indicating that the phenolation reaction is active. Compared with the preparation method of comparative example 1 using pine kraft lignin as raw material and phenolation alone, the lignin structure obtained by the present invention using plant fiber as raw material, pulping and phenolation at the same time has similar structural characteristics ( Figure 6 b), further illustrating that the preparation method of the present invention has achieved the same or even better effect as the traditional single phenolization process in actual operation.

[0113] Comparative Example 2 is a traditional kraft pulping method, which requires pulping, extracting black liquor, and acid precipitation to separate kraft lignin. In addition, after the lignin in Comparative Example 2 is subjected to high-temperature alkaline treatment, its molecular weight distribution is significantly reduced, most of the original group structures are destroyed, and the formed kraft lignin has lost part of its original molecular integrity, so the phenolic hydroxyl content is only 3.53 mmol / g, which is significantly lower than that of the present invention. Figure 7 The aromatic ring signal in the extract is weak, which comes from the residual aromatic groups in the lignin extracted by the traditional process, further illustrating that the high temperature alkaline cooking conditions destroyed a large number of natural structures and active groups, resulting in a decrease in active sites.

[0114] The addition of phenol in the present invention works synergistically with the alkaline cooking conditions, not only achieving efficient separation of lignin, but also increasing the phenolic hydroxyl content through the condensation reaction of phenol and lignin to achieve lignin modification, while avoiding excessive damage to the lignin structure by acidic conditions and enhancing 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 embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for simultaneously preparing kraft pulp and phenolic lignin, characterized in that: The following steps are involved: S1, adding wood fiber raw materials, water, cooking reagents, and phenol into a cooking pot, mixing, and cooking; S2, after cooking, a mixture of residue and black liquor is obtained; S3, collecting the residue to obtain sulfate pulp; S4, collecting the black liquor and performing acid precipitation, and the obtained precipitate is phenolic lignin.

2. The method for simultaneously preparing kraft pulp and phenolic lignin according to claim 1, characterized in that: 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.

3. The method for simultaneously preparing kraft 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.

4. The method for simultaneously preparing kraft pulp and phenolic lignin according to claim 1, characterized in that: The amount of alkali added as the cooking agent is 15-30% NaOH, and the amount of sulfur added is 15-25% Na2S.

5. The method for simultaneously preparing kraft pulp and phenolic lignin according to claim 1, characterized in that: The cooking temperature is 120-170° C., the heating time is 30-60 minutes, and the heat preservation time is 2-4 hours.

6. The method for simultaneously preparing kraft pulp and phenolic lignin according to claim 1, characterized in that: The mixture was passed through a 200-400 mesh sieve to collect the residue.

7. The method for simultaneously preparing kraft pulp and phenolic lignin according to claim 1, characterized in that: During acid precipitation, the pH of the black liquor is adjusted to 2-4.

8. The method for simultaneously preparing kraft pulp and phenolic lignin according to claim 1, characterized in that: The wood fiber raw materials include softwood, hardwood and grass raw materials.

9. A phenolic lignin, characterized in that: The pulp is prepared by the method for simultaneously preparing kraft pulp and phenolic lignin according to any one of claims 1 to 8, wherein the phenolic lignin has a phenolic hydroxyl content of 3.5 to 6.0 mmol / g.

10. A kraft pulp, characterized in that: The kraft pulp is prepared by the method for simultaneously preparing kraft pulp and phenolic lignin according to any one of claims 1 to 8, wherein the kraft pulp has a kappa number of 23.0 to 110.0, a viscosity of 900 to 1350 mL / g, and a brightness of 12.0 to 30.0% ISO.

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