Pretreatment method of paper pulp to be bleached and treatment method of bleached paper pulp

Abstract

The invention relates to the technical field of paper pulp production, in particular to a pretreatment method of paper pulp to be bleached and a treatment method of bleached paper pulp. The invention provides a pretreatment method of to-be-bleached paper pulp, which comprises the following steps: soaking an unbleached bamboo pulp board with deionized water, defibering, spin-drying and scattering to obtain pulp; and after pretreatment with enzyme and sodium oxalate, filtering to obtain to-be-bleached slurry. Through the common treatment process of sodium oxalate and xylanase, not only is the problem that metal ions inhibit enzyme activity solved, but also the bleaching efficiency is improved, the chemical consumption and environmental pollution are reduced, meanwhile, the whiteness stability of the paper pulp is improved, and the method is superior to the prior art in the aspects of environmental protection and economical efficiency, and is suitable for industrial production. The method has a wide industrial application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of pulp production, and in particular to a method for pretreating pulp to be bleached and a method for treating bleached pulp. Background Art

[0002] In recent years, with growing environmental awareness and the promotion of sustainable development concepts, the papermaking industry faces the dual challenges of reducing pollution emissions and lowering chemical usage. Consequently, biobleaching technology has become a research hotspot due to its environmentally friendly properties. Xylanase, one of the most promising bio-enzymes, demonstrates unique advantages in pulp pretreatment.

[0003] Xylan, a hemicellulose in plant cell walls, together with cellulose and lignin, constitutes the complex structure of plant cell walls. First, xylanase can specifically hydrolyze the β-1,4 glycosidic bonds of xylan in plant cell walls, breaking them down into oligoxylose and xylose, effectively destroying the cross-linking structure between xylan and lignin. Secondly, enzyme treatment can increase the pores on the fiber surface and improve the permeability inside the fiber. This makes it easier for chemical reagents (such as bleach, dyes, etc.) used in subsequent treatment processes to penetrate into the fiber, creating favorable conditions for subsequent bleach penetration. Finally, from a process perspective, by increasing the exposure of lignin, the efficiency of the bleaching agent is significantly improved, the amount of chlorine-containing bleaching agent used is reduced, and the generation of toxic substances such as dioxins is effectively inhibited.

[0004] Although xylanase improves fiber accessibility and bleachability by degrading xylan in pulp, thereby enhancing bleaching effectiveness, its effectiveness remains limited when used alone, particularly when treating pulp with a high lignin content. Xylanase primarily improves pulp bleachability by degrading xylan, but its direct lignin degradation ability is relatively weak, making it difficult to achieve the desired bleaching effect using xylanase alone. Furthermore, metal ions in pulp can inhibit the enzyme's active sites by occupying them. Transition metal ions, such as Fe2+ and Mn2+, not only inhibit enzyme activity but also catalyze the decomposition of H2O2, generating free radicals that can cause oxidative damage to the fibers and reduce pulp strength. Furthermore, metal ions, under the action of an electric field, migrate toward the anode, exacerbating corrosion of the capacitor electrodes and reducing their service life. Summary of the Invention

[0005] The object of the present invention is to address the above-mentioned deficiencies in the prior art and to provide a method for pretreating pulp to be bleached and a method for treating bleached pulp.

[0006] The first object of the present invention is to provide a method for pretreating pulp to be bleached, comprising the following steps:

[0007] The unbleached bamboo pulp board is soaked in deionized water, loosened, dried, and broken up to obtain pulp;

[0008] The pulp is then pretreated with enzymes and sodium oxalate and then filtered to obtain pulp to be bleached;

[0009] The specific steps of the enzyme and sodium oxalate pretreatment are as follows:

[0010] First, add sodium oxalate aqueous solution to the slurry, dissolve it with deionized water, and prepare it into a slurry concentration of 5%-20%, stir the reaction, use deionized water and acetic acid buffer solution for physical elution, and vacuum filter to obtain the slurry.

[0011] Then, take an appropriate amount of acetic acid buffer solution to dissolve Sigma xylanase, then mix the enzyme solution with the slurry evenly, add acetic acid buffer solution to make the slurry concentration 5%-20%, and finally place it in a constant temperature water bath for reaction;

[0012] Alternatively, take an appropriate amount of acetic acid buffer solution to dissolve Sigma xylanase, then mix the enzyme solution with the slurry evenly, then add acetic acid buffer solution to prepare a slurry concentration of 5%-20%, finally place it in a constant temperature water bath to react, vacuum filter to obtain the slurry, then add sodium oxalate aqueous solution to the slurry, dissolve it with deionized water, and prepare a slurry concentration of 5%-20%. After the reaction, use deionized water to wash until neutral.

[0013] Furthermore, the amount of sodium oxalate added is 0.2%-0.8% of the mass of the unbleached bamboo pulp board.

[0014] Furthermore, the mass ratio of sigma xylanase to unbleached bamboo pulp board is 0.5 mg / g-1 mg / g.

[0015] Further, sodium oxalate was added and the reaction was continued for 0.5-1 h, with stirring performed every 15 min.

[0016] Furthermore, Sigma xylanase was added and the constant temperature water bath temperature was 50-60°C.

[0017] Furthermore, the reaction time in a constant temperature water bath is 0.5-1h, and kneading is performed every 15 minutes.

[0018] Furthermore, the pH of the acetic acid buffer solution is 5.

[0019] Furthermore, the unbleached bamboo pulp board is soaked in deionized water for 4-5 hours.

[0020] The second object of the present invention is to provide a method for treating bleached pulp, wherein unbleached bamboo pulp is pretreated by the pretreatment method according to any one of claims 1 to 8 to obtain pulp, and then bleaching is performed.

[0021] Furthermore, the bleaching step is as follows: adding a mixed aqueous solution of a silicon-free stabilizer, magnesium sulfate, sodium hydroxide and hydrogen peroxide to the pulp, and using deionized water to adjust the pulp concentration to 5%-20%, heating in a constant temperature water bath, reacting for a certain time, taking out the pulp, washing it, and concentrating it.

[0022] The present invention adopts a process combining sodium oxalate pretreatment with Sigma xylanase treatment, which has obvious advantages over traditional methods. Sodium oxalate, as a dicarboxylic acid chelating agent, has strong chelating ability and can form stable chelates with various metal ions. The oxalate ions (C2O42-) in sodium oxalate can react with the alkaline earth metal ions (Ca 2 +, Mg2+) and transition metal ions (Fe2+, Mn2+) to form stable oxalate precipitates, preventing these ions from occupying the active center of xylanase, thereby significantly improving enzyme activity. For example, Sigma xylanase contains Ca 2 + sensitive α-helical domain, sodium oxalate chelates Ca 2 + can remove its inhibitory effect on the enzyme, allowing xylanase to fully exert its degradation effect. The Na+ in the sodium oxalate solution can undergo ion exchange with K+ and Na+ in the pulp, removing K+ and Na+ through physical elution. In addition, sodium oxalate can also chelate with high-valent metal ions, especially with trivalent iron ions (Fe3+), forming stable chelates, thereby effectively removing Fe3+ in chelated or combined states and reducing the conductivity of the pulp. Sodium oxalate can also reduce the ineffective decomposition of bleaching agents such as H2O2 by metal ions, thereby improving the utilization rate of bleaching agents. This synergistic treatment system can not only remove the inhibition of metal ions on xylanase activity, but also reduce the conductivity of pulp and extend the service life of equipment.

[0023] Xylanase can specifically degrade xylan in pulp, destroying the cross-linking structure between xylan and lignin, increasing the pores on the fiber surface and improving the permeability of the fiber interior. This makes it easier for subsequent bleaching agents (such as chloride and H2O2) to penetrate and act on lignin and other pigment components, significantly improving bleaching efficiency and reducing the amount of bleaching chemicals used.

[0024] The present invention uses sodium oxalate and sigma xylanase to treat paper pulp, thereby constructing an efficient paper pulp pretreatment system. On the one hand, the amount of strong oxidizing bleaching agents such as chloride can be reduced, thereby lowering production costs. Simultaneously, the generation of toxic byproducts (such as dioxins) is reduced, reducing the use and emission of harmful chemicals, thereby meeting environmental protection requirements. On the other hand, subsequent bleaching efficiency is improved, while whiteness stability is improved, preventing yellowing, thereby extending the storage and service life of paper. On the other hand, sodium oxalate is inexpensive, non-toxic, and easily biodegradable, thus not placing an additional burden on the environment. Although the unit price of xylanase is relatively high, its usage is extremely low, and long-term use can reduce overall costs, thus providing significant economic benefits.

[0025] In summary, the present invention uses a process of co-treatment with sodium oxalate and xylanase, which not only solves the problem of metal ions inhibiting enzyme activity, but also improves bleaching efficiency, reduces chemical consumption and environmental pollution, and improves the whiteness stability of pulp. It is superior to existing technologies in terms of environmental protection and economy, and has broad prospects for industrial application. DETAILED DESCRIPTION

[0026] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0027] Comparative Example 1

[0028] A method for pretreating pulp to be bleached, comprising the following steps:

[0029] Cut or tear 120g of bone-dry unbleached bamboo chemical pulp into approximately 5mm x 5mm specimens. Soak in deionized water for 4 hours. Then, use a Wally beater to disintegrate the specimens, spin dry, and disperse the pulp for later use. Wear clean gloves and handle carefully to prevent contamination.

[0030] Take an appropriate amount of pH = 5 acetic acid buffer solution to dissolve Sigma xylanase (0.6 mg / g xylanase), then mix the enzyme solution and the pulp evenly, add pH = 5 acetic acid buffer solution to dissolve it, and prepare it into a 5% pulp concentration, put it into a constant temperature water bath, control the temperature at 50°C, react for 1 hour, knead it every 15 minutes, and filter it after the reaction to obtain the pulp to be bleached.

[0031] The national standard GBT7977-2007 tests the conductivity of the bleached pulp twice and takes the arithmetic mean as the test result. The results are shown in Table 1.

[0032] Bleaching treatment:

[0033] The slurry was placed in a polyethylene sealed bag, and then 0.3% absolute dry weight of a silicon-free stabilizer, 0.5% absolute dry weight of magnesium sulfate, 0.3% absolute dry weight of sodium hydroxide, and 10% absolute dry weight of an aqueous solution of hydrogen peroxide were added, and deionized water was used to adjust the slurry concentration to 5%. The slurry was heated in a constant temperature water bath, the temperature was controlled at 70°C, and the reaction time was 90 minutes. During the reaction, the slurry was kneaded every 15 minutes. After a certain reaction time, the slurry was taken out, washed, and concentrated for use.

[0034] The Kappa number and brightness of the pulp of the sample and blank group were measured.

[0035] The kappa number of pulp is measured according to standard GB / Tl546.

[0036] Whiteness determination: weigh 60g / m 2 The wet pulp was debonded, sheeted, and dried (paper samples were made according to the method of standard GB / T8940.2), and the whiteness of the paper was measured (measured on an ELREPHO 070 whiteness meter according to the method of standard GB / T 7974).

[0037] The Kappa value of the blank group (absolutely dry pulp board) was measured to be 20.83 and the whiteness was 37.38, while the Kappa value of the experimental group was 6.9 and the whiteness was 47.13.

[0038] Comparative Example 2

[0039] A method for pretreating pulp to be bleached, comprising the following steps:

[0040] Cut or tear 120g of bone-dry unbleached bamboo chemical pulp into approximately 5mm x 5mm specimens. Soak in deionized water for 4 hours. Then, use a Wally pulper to break up the specimens, spin dry, and disperse them for later use. Wear clean gloves and handle carefully to prevent contamination.

[0041] The sample was added to a sodium oxalate aqueous solution at a dry mass of 0.4%. Deionized water was used to dissolve the solution and prepare a 5% slurry concentration. The mixture was stirred evenly and allowed to react for 1 hour, stirring every 15 minutes. After the reaction, the mixture was washed until neutral, i.e., consistent with the pH of deionized water (deionized water pH = 5-7), and then dried. The formed chelate was separated from the bamboo pulp by physical elution and vacuum filtration using deionized water, thereby reducing the conductivity and obtaining the pulp to be bleached.

[0042] The national standard GBT7977-2007 tests the conductivity of the bleached pulp twice and takes the arithmetic mean as the test result. The results are shown in Table 1.

[0043] After bleaching, the kappa number and whiteness were measured in the same manner as in Comparative Example 1. The kappa number of the blank group (absolutely dry pulp board) was 20.83 and the whiteness was 37.38, while the kappa number of the experimental group was 7.13 and the whiteness was 45.94.

[0044] Example 1

[0045] A method for pretreating pulp to be bleached, comprising the following steps:

[0046] Cut or tear 120g of bone-dry unbleached bamboo chemical pulp into approximately 5mm x 5mm specimens. Soak in deionized water for 4 hours. Then, use a Vali pulper to disintegrate the specimens, spin dry, and disperse them to obtain a pulp for later use. Wear clean gloves and handle carefully to prevent contamination.

[0047] The sample was added to a sodium oxalate aqueous solution at a dry mass of 0.4%. This was dissolved in deionized water to a 5% slurry concentration, stirred evenly, and allowed to react for 1 hour, stirring every 15 minutes. After the reaction, the sample was washed to a neutral pH, i.e., consistent with the pH of deionized water (deionized water pH = 5-7), and then dried. The formed chelate was separated from the bamboo pulp by physical elution using deionized water and a pH = 5 acetic acid buffer solution, thereby reducing the conductivity.

[0048] Take an appropriate amount of pH = 5 acetic acid buffer solution to dissolve Sigma xylanase (0.6 mg / g xylanase), then mix the enzyme solution and the pulp evenly, add pH = 5 acetic acid buffer solution to dissolve it, and prepare a pulp concentration of 5%, mix evenly, put it into a constant temperature water bath, control the temperature at 50°C, react for 1 hour, knead once every 15 minutes, and filter after the reaction to obtain the pulp to be bleached.

[0049] The national standard GBT7977-2007 tests the conductivity of the bleached pulp twice and takes the arithmetic mean as the test result. The results are shown in Table 1.

[0050] After bleaching, the kappa value and whiteness were measured in the same manner as in Comparative Example 1. The kappa value of the blank group was 20.83 and the whiteness was 37.38, while the kappa value of the experimental group was 6.45 and the whiteness was 51.49.

[0051] Example 2

[0052] A method for pretreating pulp to be bleached, comprising the following steps:

[0053] Cut or tear 120g of bone-dry unbleached bamboo chemical pulp into approximately 5mm x 5mm specimens. Soak in deionized water for 4 hours. Then, use a Wally pulper to disintegrate, spin dry, and disperse the specimens to obtain a pulp for later use. Wear clean gloves and handle carefully to prevent contamination.

[0054] Dissolve Sigma xylanase (0.6 mg / g xylanase) in an appropriate amount of pH 5 acetic acid buffer solution. Mix the enzyme solution with the slurry. Add additional pH 5 acetic acid buffer solution to dissolve the enzyme. Prepare a 5% slurry. Mix thoroughly and place in a thermostatic water bath at 50°C. React for 1 hour, stirring every 15 minutes. After the reaction is complete, vacuum filter and prepare the sample for later use.

[0055] The sample was added with a sodium oxalate aqueous solution, the mass of sodium oxalate was 0.4% of absolute dryness, dissolved with deionized water, and prepared into a 5% slurry concentration, mixed evenly, reacted for 1 hour, rubbed once every 15 minutes, washed with deionized water until neutral, and filtered to obtain the slurry to be bleached.

[0056] The national standard GBT7977-2007 conducts conductivity testing on the bleached pulp, and the conductivity is measured twice at the same time. The arithmetic average is taken as the test result. The results are shown in Table 1.

[0057] After bleaching, the kappa value and whiteness were measured in the same manner as in Comparative Example 1. The kappa value of the blank group was 20.83 and the whiteness was 37.38, while the kappa value of the experimental group was 6.72 and the whiteness was 49.82.

[0058] Table 1 is a performance test result table of comparative examples 1 and 2 and examples 1 and 2. It can be seen from Table 1 that the conductivity and Kappa value of the pulp to be bleached after being treated with sodium oxalate and Sigma xylanase are reduced and the whiteness is improved after bleaching.

[0059] Table 1

[0060]

[0061] Any matters not mentioned above shall be subject to the existing technology.

[0062] Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and are not intended to limit the scope of the present invention. Those skilled in the art of the present invention may make various modifications or additions to the described specific embodiments or replace them in similar ways, but they will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent replacements, improvements, etc. made to the above embodiments based on the technical essence of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for pretreating pulp to be bleached, characterized in that: The steps include: The unbleached bamboo pulp board is soaked in deionized water, loosened, dried, and broken up to obtain pulp; The pulp is then pretreated with enzymes and sodium oxalate and then filtered to obtain pulp to be bleached; The specific steps of the enzyme and sodium oxalate pretreatment are as follows: First, add sodium oxalate aqueous solution to the slurry, dissolve it with deionized water, and prepare it into a slurry concentration of 5%-20%, stir the reaction, use deionized water and acetic acid buffer solution for physical elution, and vacuum filter to obtain the slurry. Then, take an appropriate amount of acetic acid buffer solution to dissolve Sigma xylanase, then mix the enzyme solution with the slurry evenly, add acetic acid buffer solution to make the slurry concentration 5%-20%, and finally place it in a constant temperature water bath for reaction; Alternatively, take an appropriate amount of acetic acid buffer solution to dissolve Sigma xylanase, then mix the enzyme solution with the slurry evenly, then add acetic acid buffer solution to prepare a slurry concentration of 5%-20%, finally place it in a constant temperature water bath to react, vacuum filter to obtain the slurry, then add sodium oxalate aqueous solution to the slurry, dissolve it with deionized water, and prepare a slurry concentration of 5%-20%. After the reaction, use deionized water to wash until neutral.

2. The method for pretreating pulp to be bleached according to claim 1, wherein: The added amount of sodium oxalate is 0.2%-0.8% of the mass of the unbleached bamboo pulp board.

3. The method for pretreating pulp to be bleached according to claim 1, wherein: The mass ratio of sigma xylanase to unbleached bamboo pulp board is 0.5 mg / g-1 mg / g.

4. The method for pretreating pulp to be bleached according to claim 1, wherein: Add sodium oxalate and react for 0.5-1h, stirring every 15 minutes.

5. The method for pretreating pulp to be bleached according to claim 1, wherein: Add Sigma xylanase and keep the constant temperature of water bath at 50-60℃.

6. A method for pretreating pulp to be bleached according to claim 5, characterized in that: The reaction time in a constant temperature water bath is 0.5-1h, and rubbing is done every 15 minutes.

7. The method for pretreating pulp to be bleached according to claim 1, wherein: Acetic acid buffer solution pH=5.

8. The method for pretreating pulp to be bleached according to claim 1, wherein: For unbleached bamboo pulp board, soak in deionized water for 4-5 hours.

9. A method for treating bleached pulp, characterized in that: The unbleached bamboo pulp board is first pretreated by the pretreatment method according to any one of claims 1 to 8 to obtain pulp, and then bleached.

10. The method for treating bleached pulp according to claim 9, wherein: The bleaching steps are as follows: add a silicon-free stabilizer, magnesium sulfate, sodium hydroxide and an aqueous solution of hydrogen peroxide to the pulp, and use deionized water to adjust the pulp concentration to 5%-20%, heat it in a constant temperature water bath, react for a certain time, take out the pulp, wash it, and concentrate it.

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