阅读说明：本技术 一种基于离子液体的纸浆漂白保护剂 (Paper pulp bleaching protective agent based on ionic liquid ) 是由 杨桂花 陈嘉川 齐乐天 吉兴香 吕高金 彭建民 于 2019-10-31 设计创作，主要内容包括：本发明涉及一种基于离子液体的纸浆ECF漂白保护剂。本申请采用离子液体基漂白保护剂预处理桉木硫酸盐浆料,并随后进行ECF漂白。漂白保护剂加入量为5-15％纸浆。本处理可有效溶解纤维中的木质素并使其在纤维表面形成保护层,从而提高后续漂白效率,并在漂白过程中对纤维起到保护作用。预处理可提高浆料的纤维素含量,同时降低木素含量,改善成纸物理强度的效果,从而拓宽了桉木等阔叶材的应用范围。该处理可提高漂白效果,可降低漂剂用量,提升漂白效率,减小污染。本发明操作简单,效果明显,实用性强,污染小,易于推广。(The invention relates to an ECF (ECF) bleaching protective agent for paper pulp based on ionic liquid. The application pretreats eucalyptus sulfate pulp with an ionic liquid based bleach protectant and then performs ECF bleaching. The addition amount of the bleaching protective agent is 5-15% of paper pulp. The treatment can effectively dissolve the lignin in the fiber and form a protective layer on the surface of the fiber, thereby improving the subsequent bleaching efficiency and protecting the fiber in the bleaching process. The pretreatment can improve the cellulose content of the pulp, simultaneously reduce the lignin content and improve the physical strength effect of the finished paper, thereby widening the application range of the broad-leaved wood such as eucalyptus and the like. The treatment can improve the bleaching effect, reduce the dosage of bleaching agent, improve the bleaching efficiency and reduce pollution. The method has the advantages of simple operation, obvious effect, strong practicability, little pollution and easy popularization.)

1. The paper pulp bleaching protective agent based on the ionic liquid is characterized by comprising one or more of ionic liquid, magnesium carbonate, sodium cinnamate, borax, glycol, glycerol and anhydrous magnesium sulfate.

2. The ionic liquid-based pulp bleaching guard of claim 1, wherein the anion of the ionic liquid comprises one or a mixture of hydrogen sulfate ion, formate ion or chloride ion;

or the cation of the ionic liquid comprises one or more of 1-butyl 3-methyl-imidazole ion, 2-hydroxyethyl trimethylammonium ion and triethylammonium ion.

3. A method for improving paper strength of a paper pulp bleaching protective agent based on ionic liquid is characterized by comprising the following steps:

pretreating the pulp with the pulp bleaching protectant according to claim 1 or 2;

carrying out ECF bleaching on the pretreated paper pulp, wherein the bleaching process is ODP bleaching;

and (5) papermaking to obtain the paper.

4. A method for improving paper strength of pulp bleaching protectant based on ionic liquids as claimed in claim 3, wherein said bleach protectant is used in an amount of 5-15% of the oven dried mass of the pulp.

5. The method for improving paper strength of pulp bleaching protectant based on ionic liquid as claimed in claim 3, wherein said O-stage oxygen delignification process is: the pulp concentration is 10 percent, the NaOH dosage is 3 percent, the oxygen pressure is 0.5MPa, the temperature is 100 ℃, and the time is 60 min.

6. The method for improving paper strength of pulp bleaching protectant based on ionic liquid as claimed in claim 3, wherein the D-stage chlorine dioxide bleaching process is: the chlorine dioxide dosage is 0.7 percent, the pH value is 2-3, the temperature is 70 ℃, the pulp concentration is 10 percent, and the time is 30 min.

7. The method for improving paper strength of pulp bleaching protectant based on ionic liquid as claimed in claim 3, wherein the P-stage hydrogen peroxide bleaching process is: 1 percent of hydrogen peroxide, 10 percent of pulp concentration, 11 to 12 of pH value, 90 ℃ of temperature and 0.4MPa of oxygen pressure.

8. The method for improving paper strength of pulp bleaching protectant based on ionic liquid as claimed in claim 3, wherein the pulp is kraft pulp, and the cooking process is to take relatively uniform wood chips with length of 15-25mm, width of 10-20mm and thickness of 3-5mm, air dry, cook to obtain kraft pulp, wherein the cooking condition is to use 21% alkali for oven dry raw material, Na₂Measuring O; the vulcanization degree is 25%, the liquid ratio is 1:5, the highest cooking temperature is 170 ℃, air is discharged at 105 ℃, air is discharged for 15min, the temperature rise time is 90min, and the heat preservation time is 90 min; and fully washing and screening after cooking to obtain paper pulp.

9. Paper produced by the process of any one of claims 3-8.

10. Use of the ionic liquid based pulp bleaching guard according to any of claims 1, 2 in the manufacture of letterpress, newsprint, offset, coated, book cover, dictionary, copy or board paper.

Technical Field

The invention belongs to the technical field of papermaking, and particularly relates to a paper pulp bleaching protective agent based on ionic liquid.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

With the large-scale, automatic and efficient paper making technical equipment and the gradual attention of the paper making industry on clean production, circular economy, environmental pollution reduction and sustainable development promotion, the element-free chlorine (ECF) bleaching technology is more mature. At present, in order to reduce the generation of pollutants, paper mills mostly adopt deep delignification, oxygen delignification and low-chlorine-consumption multi-stage bleaching methods. The bleaching technology of the element-free chlorine (ECF) uses chlorine dioxide to replace chlorine for bleaching, avoids the discharge of dioxin, and greatly reduces the content of organic chloride in the wastewater. However, ECF bleaches mainly by oxidation, causing degradation of carbohydrates, lowering the degree of polymerization and damaging the strength of the fibers to some extent, resulting in lower paper properties, especially lower tensile strength, etc.

The commonly used cellulose protective agent is anhydrous magnesium sulfate, magnesium carbonate, sodium cinnamate, borax, glycol, glycerol, and the like. The application of anhydrous magnesium sulfate is common, but the bleaching efficiency is not improved. In addition, the pulp carbohydrate is still greatly degraded in the oxygen delignification process after the anhydrous magnesium sulfate is added, and when the oxygen delignification effect is higher than 50%, the protection effect is greatly weakened, so that the viscosity is suddenly reduced.

The ionic liquid is a low-temperature molten salt which is completely composed of anions and cations and is in a liquid state at room temperature. It has the features of high heat stability, high recovery, no volatilization and high solubility. The ionic liquid can dissolve and separate lignin in the wood fiber. Through proper ionic liquid type selection and solution preparation, the lignin in the wood fiber can be selectively extracted. When the ionic liquid is used in the pulp bleaching process, the bleaching efficiency can be improved, and the bleaching effect can be enhanced. Meanwhile, the fiber is effectively protected, and the physical strength of the finished paper is enhanced.

With the development of the world economy and the continuous improvement of the living standard of people, the quality requirements of people on paper and paperboards are higher and higher, and the problems of tensile strength, breakage resistance and low tearing strength of paper fibers after ECF bleaching in the traditional pulping and papermaking industry need to be solved urgently.

The inventor's prior patent CN201811466096.5 discloses a method for preparing a paper-based material by using an ionic liquid in cooperation with ultrasonic treatment of ECF bleached kraft pulp, wherein the unbleached kraft pulp is pretreated by using the ionic liquid in cooperation with ultrasonic treatment, and then the pretreated kraft pulp is ECF bleached. However, in subsequent studies, the inventors found that: due to the addition of the ultrasonic technology, the ionic liquid has the effect of strengthening the lignin removal effect, the lignin content after treatment is low, but the treatment is not beneficial to the enrichment of surface lignin. And thus cannot be effectively protected.

Disclosure of Invention

In order to overcome the problems, the invention provides a pulp bleaching protective agent based on ionic liquid, which is used for pretreating pulp and then carrying out ODP bleaching. The bleaching protective agent pretreatment dissolves out lignin and plays a role in protecting fibers in the bleaching process. Therefore, the bleaching effect is improved, and the physical strength of paper made from the pulp is improved.

In order to achieve the technical purpose, the technical scheme adopted by the invention is as follows:

a paper pulp bleaching protective agent based on ionic liquid is composed of one or more of ionic liquid, magnesium carbonate, sodium cinnamate, borax, ethylene glycol, glycerol and anhydrous magnesium sulfate.

In order to overcome the problem that the present ionic liquid is not favorable to the enrichment of surface lignin in cooperation with ultrasonic treatment, the application has carried out systematic research to the law of action of its processing method and effect, discovers: through the matching of the ionic liquid and the specific bleaching sequence, the effect of improving the strength and whiteness of paper treated by the medium-strength ultrasonic and ionic liquid can be achieved, and the effect of improving the strength and whiteness of the paper treated by the medium-strength ultrasonic and ionic liquid is slightly lower than that of the paper treated by the high-strength ultrasonic and ionic liquid.

In some embodiments, the anion of the ionic liquid comprises one or a mixture of bisulfate, formate or chloride ions; the paper pulp bleaching protective agent developed by the application can selectively dissolve out lignin, improve bleaching efficiency and protect the main fiber.

Although the present application is similar to the previous application in terms of processing method, the present application is effective. Both applications apply to different pulp products. The reason is as follows:

according to the method, the lignin is selectively dissolved out by using the ionic liquid and is enriched on the surface of the fiber, so that the polysaccharide structure is slightly damaged, and the polymerization degree of the fiber is high. The pretreatment can loosen the fibers, improve the swelling degree, and facilitate the penetration of the subsequent bleaching agent, the destruction of chromophoric groups and the diffusion and dissolution of reactants. Meanwhile, the pretreatment improves the appearance of fine fiber components and enhances the cross-linking among fibers, thereby improving the bleaching efficiency and enhancing the performance of the paper-based material.

Among them, dissolving out lignin and enriching it on the surface play an important role in protecting the internal fiber. In the prior patent, due to the addition of the ultrasonic technology, the ionic liquid has the effect of strengthening the lignin removal effect, the lignin content after treatment is low, but the treatment is not beneficial to the enrichment of surface lignin. And thus cannot be effectively protected. Thus, in some embodiments, the cation of the ionic liquid comprises one or a mixture of 1-butyl 3-methyl-imidazolium, 2-hydroxyethyl-trimethylammonium, and triethylammonium ions, which increases the bleaching efficiency and enhances the properties of the paper-based material.

The invention also provides a method for improving paper strength by using the pulp bleaching protective agent based on the ionic liquid, which comprises the following steps:

pretreating the pulp with any one of the pulp bleaching protectants;

carrying out ECF bleaching on the pretreated paper pulp, wherein the bleaching process is ODP bleaching;

and (5) papermaking to obtain the paper.

The research of the application finds that: the adoption of ODP bleaching sequence not only has shorter flow, but also has lower cost. Meanwhile, by matching the ionic liquid-based fiber protective agent, the OAD can be achieved₁ED₂Pulp brightness and paper strength similar to the flowsheet.

With the increase of the dosage of the bleaching protective agent, the bleaching efficiency and the pulp performance are improved, but when the dosage of the bleaching protective agent reaches a certain value, the dosage of the bleaching protective agent is continuously increased, the pulp performance is not greatly improved, and the bleaching cost is improved. Therefore, in some embodiments, the dosage of the bleaching protective agent is 5-15% of the oven dry quality of the pulp, so that the bleaching effect is improved, and the cost is reduced.

The oxygen delignification can reduce the lignin content in the unbleached pulp, reduce the dosage of the bleaching agent and reduce the pollution load of bleaching waste water. In some embodiments, the O-stage oxygen delignification process is: the pulp concentration is 10 percent, the NaOH dosage is 3 percent, the oxygen pressure is 0.5MPa, the temperature is 100 ℃, the time is 60min, and the oxygen bleaching efficiency and the pulp performance are improved.

Chlorine dioxide has strong oxidizing property, strong delignification capacity and delignification selectivity. At the same effective chlorine dosage, chlorine dioxide bleaching produces only 1/5 as chlorine bleach for adsorbable organic halide (AOX), without affecting delignification. In ClO₂The establishment of a buffer system is beneficial to maintain the pH stable during bleaching. In some embodiments, the D-stage chlorine dioxide bleaching process is: the consumption of chlorine dioxide is 0.7%, the pH value is 2-3, the temperature is 70 ℃, the pulp concentration is 10%, and the time is 30min, thereby improving the bleaching efficiency of the paper pulp and reducing the generation of organic halide (AOX).

The bleaching degree of hydrogen peroxide bleaching has good stability, the damage to fibers in the process of yellowing bleaching is not easy to occur, the yield is high, the process adaptability is strong, organic chlorine compounds contained in bleaching waste water are easy to treat, and the complete recycling of the bleaching waste water can be realized. In some embodiments, the P-stage hydrogen peroxide bleaching process is: the hydrogen peroxide is used in 1 wt%, the pulp concentration is 10 wt%, the pH value is 11-12, the temperature is 90 deg.c, and the oxygen pressure is 0.4MPa, so as to protect the strength of paper pulp and raise its whiteness.

Sulfate wood pulp (kraft pulp) is cooked with a mixture of sodium hydroxide and sodium sulfide. In the cooking process, the liquid medicine has relatively mild action, and the fiber is not strongly corroded, so the fiber is tough and powerful, has higher mechanical strength indexes such as tensile strength, bursting strength and tearing resistance, and has higher heat resistance and durability. In some embodiments, the pulp is a kraft pulp and the cooking process is length extractionRelatively uniform wood chips 15-25mm in width 10-20mm in thickness 3-5mm in thickness, air drying naturally, and steaming to obtain sulfate raw pulp, wherein the steaming condition is that 21% of alkali is used, and Na is added to oven-dried raw material₂Measuring O; the vulcanization degree is 25%, the liquid ratio is 1:5, the highest cooking temperature is 170 ℃, air is discharged at 105 ℃, air is discharged for 15min, the temperature rise time is 90min, and the heat preservation time is 90 min; after cooking, the pulp is fully washed and screened to obtain the pulp, so that the cooking efficiency and the strength performance of the paper are improved.

The invention also provides paper made by any of the above methods.

The invention also provides the use of any of the above ionic liquid based pulp bleaching protectors in the manufacture of letterpress, newsprint, offset, coated, book cover, dictionary, copy or board paper.

The invention has the beneficial effects that:

(1) according to the invention, the eucalyptus kraft pulp is pretreated by the ionic liquid-based protective agent, so that a surface protective layer is formed in the ODP bleaching process, the fiber hydrolysis degree is reduced, and the fiber trunk is protected.

(2) The paper base material prepared by using the ionic liquid-based protective agent for pretreatment has the advantages of high folding strength, high tensile strength, high bursting strength, high tearing strength and the like, and is suitable for preparing various types of paper base materials.

(3) The lignin can be selectively dissolved out by the pretreatment of the ionic liquid-based protective agent, so that the lignin content of the fiber is obviously reduced, and the action of a bleaching agent is facilitated. The treatment can improve bleaching effect, reduce bleaching agent consumption, improve bleaching efficiency, and reduce pollution

(4) The ionic liquid used in the invention has stable structure, zero vapor pressure, recyclability and environmental protection.

(5) The treatment method is simple, low in cost, strong in practicability and easy to popularize.

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

As introduced in the background art, the method aims at the problems of low tensile strength, high breaking resistance and low tearing strength of the paper fiber after ECF bleaching at present. Therefore, the invention provides a pulp bleaching protective agent based on ionic liquid, which is used for pretreating pulp and then carrying out ODP bleaching. The bleaching protective agent pretreatment dissolves out lignin and plays a role in protecting fibers in the bleaching process. Therefore, the bleaching effect is improved, and the physical strength of paper made from the pulp is improved.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows: the concentrations of the slurries referred to below are, unless otherwise specified, percentages by mass; the dosage of the related reagents and medicines is relative to the oven-dry pulp if no special indication is given.

The invention provides a paper pulp bleaching protective agent based on ionic liquid, which comprises the following steps:

(1) and (3) cooking: taking the wood chips, and putting the wood chips into a digester for cooking to obtain the raw pulp. Then, the sulfate pulp is obtained after sufficient washing and screening. The kappa number of the slurry is 12-16;

(2) pretreating an ionic liquid-based bleaching protective agent;

(3) and (3) ODP bleaching: the pulp treated by the ultrasonic wave and the ionic liquid is subjected to ECF bleaching, and the bleaching process is ODP bleaching:

firstly, performing O-section deoxylignin on paper pulp treated by ultrasonic synergistic ionic liquid;

after O-stage oxygen delignification is finished, washing paper pulp, and then carrying out D-stage chlorine dioxide bleaching;

after the D-stage chlorine dioxide bleaching is finished, washing the paper pulp, and then carrying out P-stage hydrogen peroxide bleaching;

and after the P-stage hydrogen peroxide treatment is finished, washing the paper pulp to finish the treatment.

The final pulp obtained after bleaching is used in the papermaking process.

Although the technical scheme does not relate to specific process parameters, according to the invention concept, the method is particularly directed to pretreatment by using the ionic liquid-based bleaching protective agent, and then the fiber is protected in the oxidation reaction in the bleaching process, so that the oxidation hydrolysis degree of the fiber is reduced, the bleaching effect is improved, and the high-performance pulp can be obtained.

Further, the cooking in the step (1) is specifically as follows: taking relatively uniform wood chips with length of 15-25mm, width of 10-20mm and thickness of 3-5mm, naturally air drying, and steaming to obtain sulfate raw pulp, wherein the steaming condition is that alkali content is 21%, oven-dried raw material and Na are added₂Measuring O; the vulcanization degree is 25%, the liquid ratio is 1:5, the highest cooking temperature is 170 ℃, air is discharged at 105 ℃, air is discharged for 15min, the temperature rise time is 90min, and the heat preservation time is 90 min; and fully washing and screening after cooking to obtain paper pulp.

Further, the step (2) of preprocessing comprises the following specific steps: treating the pulp obtained in the step (1) under the condition that the dosage of the bleaching protective agent is 5-15%, and then carrying out ODP bleaching under fixed conditions.

Further, the bleach protectant comprises: one or more of ionic liquid, magnesium carbonate, sodium cinnamate, borax, glycol, glycerol and anhydrous magnesium sulfate.

Further, the anion of the ionic liquid comprises one or a mixture of hydrogen sulfate ion, formate ion or chloride ion; the cation of the ionic liquid comprises one or a mixture of more of 1-butyl 3-methyl-imidazole ion, 2-hydroxyethyl trimethylammonium ion and triethylammonium ion, and the structural formula is as follows:

further, the ODP bleaching process in step (3) is specifically as follows: the O-section oxygen delignification process comprises the following steps: the pulp concentration is 10 percent, the NaOH dosage is 3 percent, the oxygen pressure is 0.5MPa, the temperature is 100 ℃, and the time is 60 min; the D-stage chlorine dioxide bleaching process comprises the following steps: chlorine dioxide dosage is 0.7%, pH value is 2-3, temperature is 70 ℃, pulp concentration is 10%, and time is 30 min; the P-stage hydrogen peroxide bleaching process comprises the following steps: 1 percent of hydrogen peroxide, 10 percent of pulp concentration, 11 to 12 of pH value, 90 ℃ of temperature and 0.4MPa of oxygen pressure.

Preferably, the amount of the protective agent in the step (2) is 5-15%. Through a large number of experimental verifications and analyses, in order to obtain the best effect, the dosage of the protective agent is 10%.

The design concept of the invention is as follows: aiming at the problem of low paper pulp strength caused by the damage of plant fibers by oxidation reaction in the bleaching process, the invention provides a method for pretreating by adopting an ionic liquid-based protective agent, so that lignin in the plant fibers is dissolved out and attached to the surfaces of the fibers, the bleaching agent and the lignin are fully acted, the oxidative damage of the bleaching process to the fibers is avoided, and the excellent physical strength of the formed paper-based material is ensured.

The present invention will be further described with reference to the following specific examples.

The analysis method adopted in the embodiment of the invention is as follows:

measurement of whiteness: after being defibered by a defibering machine, the paper pulp is made into paper on a Kaiser method sheet making machine produced by Austria, and then a YQ-Z-48B whiteness instrument is used for measurement;

folding endurance times: the measurement was carried out by using an MIT folding endurance tester manufactured by China.

Burst index: the measurement was carried out by a burst tester manufactured by Swedish L & W.

Tensile index: the measurement was carried out by means of an intelligent electronic tensile tester (XLWA (B) made in China.

Tear index: the measurement was carried out by using a MIT tear tester manufactured by China.

Fiber surface lignin content: measured by XPS available from the United states.

The remainder of the experiments not described in detail are routine in the art.

The principle of the invention is as follows: the ionic liquid is used for selectively dissolving out lignin and enriching the lignin on the surface of the fiber, so that the polysaccharide structure is slightly damaged, and the polymerization degree of the fiber is high. The pretreatment can loosen the fibers, improve the swelling degree, and facilitate the penetration of the subsequent bleaching agent, the destruction of chromophoric groups and the diffusion and dissolution of reactants. Meanwhile, the pretreatment improves the appearance of fine fiber components and enhances the cross-linking among fibers, thereby improving the bleaching efficiency and enhancing the performance of the paper-based material.