KR20210056421A - Ionic liquid based pulp bleach protectant - Google Patents

Abstract

The present invention relates to an ionic liquid based pulp ECF bleaching protectant. In this application, the eucalyptus sulfate pulp is pretreated using an ionic liquid-based bleaching protectant, and then ECF bleaching is performed. The amount of bleach protectant added is 5-15% of the pulp. This treatment effectively dissolves lignin in the pulp fibers to form a protective layer on the fiber surface, improving subsequent bleaching efficiency, and acting as a protection for the fibers during the bleaching process. The pretreatment has the effect of increasing the cellulose content of the pulp, lowering the lignin content, and improving the physical strength of the pulp-forming paper, thereby broadening the application range of eucalyptus and other hardwoods. This treatment can increase the bleaching effect, reduce the amount of bleach used, and increase the bleaching efficiency to reduce contamination. The present invention is easy to widely disseminate due to simple operation, clear effect, strong practicality, and little contamination.

Description

Ionic liquid based pulp bleach protectant

This application claims the priority of a Chinese patent application filed with the Chinese Intellectual Property Office on November 1, 2019 with the application number CN201911055224.1 and the name of the invention "Ionic liquid based pulp bleaching protectant", see the full contents of it Is incorporated herein by reference.

The present invention belongs to the field of papermaking technology, and specifically relates to an ionic liquid based pulp bleaching protectant.

The content disclosed by the technical part that serves as the background is only to aid in understanding the overall background of the present invention, and the configuration of this information is recognized as prior art to those of ordinary skill in the technical field to which the present invention belongs, or It is not implied in the form of.

As papermaking technology equipment becomes more large-scale, automated, and highly efficient, and the paper industry increasingly places great emphasis on clean production, circular economy, reduction of environmental pollution and sustainable development, the chlorine-free element (ECF) bleaching technology has become more mature. Currently, paper mills use a large amount of de-lignin, oxygen de-lignin, and low-chlorine multiple bleaching methods to reduce the generation of pollutants. The chlorine-free (ECF) bleaching technology uses chlorine dioxide instead of chlorine gas to bleach, prevents the emission of dioxins, and greatly reduces the content of organic chlorides in wastewater. However, ECF is mainly bleached through oxidation reaction, causing carbohydrate decomposition, lowering the degree of polymerization and constantly impairing the strength of the fiber, resulting in low paper strength performance, especially low tensile strength.

Cellulose protective agents generally used are anhydrous magnesium sulfate, magnesium carbonate, sodium silicate, borax, ethylene glycol, glycerol, and the like. Among them, anhydrous magnesium sulfate is more common, but it is not effective in improving the bleaching efficiency. In addition, carbohydrates in the pulp are still highly decomposed in the process of oxygen de-lignin after addition of anhydrous magnesium sulfate, and if the oxygen de-lignin effect is more than 50%, the protective effect is greatly weakened, and the viscosity of the pulp fiber decreases rapidly.

An ionic liquid is a kind of low-temperature molten salt that is completely composed of anions and cations, and is liquid at room temperature. It has the characteristics of good thermal stability, recyclability, non-volatility and good dissolution. The ionic liquid can elute and separate the lignin of wood fibers. Lignin can be selectively extracted from wood fibers through appropriate ionic liquid selection and solution preparation. If such an ionic liquid is used in the pulp bleaching process, the bleaching efficiency can be increased and the bleaching effect can be increased. It also effectively protects the pulp fibers to increase the physical strength of the paper.

With the development of the global economy and the ever-increasing standard of people's living, people's mass demands for paper and cardboard are getting higher and higher, and the tensile resistance strength, rupture resistance and tear resistance of paper fibers after ECF bleaching in the conventional pulp and paper industry. Problems that are not highly sexual must be addressed urgently.

In the previous patent CN201811466096.5 of the present inventor, the unbleached sulfate pulp is pretreated with ionic liquid cooperative ultrasonic waves, and the pretreated sulfate pulp is subjected to ECF bleaching, and the sulfate pulp is subjected to ionic liquid cooperative ultrasonic treatment and ECF bleaching to make a paper-based material. It disclosed a method of making. However, in a subsequent study, the inventor said that the effect of the ionic liquid due to the addition of ultrasonic technology is to enhance the lignin removal effect, so the content of lignin in the pulp after treatment is reduced, but this treatment is helpful in concentrating the lignin on the pulp surface. It doesn't work. Therefore, it cannot be effectively protected.

In order to overcome the above problem, the present invention provides an application of an ionic liquid as a pulp bleaching protectant.

The present invention is also composed of an ionic liquid and a second component, the second component is a pulp bleaching protectant of an ionic liquid consisting of at least one of magnesium carbonate, sodium silicate, borax, ethylene glycol, glycerol and anhydrous magnesium sulfate. Provided.

The present invention provides an ionic liquid-based pulp bleaching protectant for ODP bleaching after pretreating the pulp with a pulp bleaching protectant. Pretreatment with a bleaching protectant can elute lignin from the pulp and also protects the fiber during the ODP bleaching process. In this way, the bleaching effect of the pulp is improved and the physical strength of the pulp paper is improved.

In order to achieve the above technical object, the technical solution adopted by the present invention is as follows:

The ionic liquid-based pulp bleaching protectant is composed of an ionic liquid and a second component, and the second component is composed of at least one of magnesium carbonate, sodium silicate, borax, ethylene glycol, glycerol and anhydrous magnesium sulfate.

Preferably, the anion of the ionic liquid comprises at least one of hydrogen sulfate ions, formate ions and chlorine ions;

The cations of the ionic liquid include one or more of 1-butyl3-methyl-imidazole ions, 2-hydroxy ethyl trimethyl ammonium and triethyl ammonium ions.

Preferably the ionic liquid comprises triethyl ammonium hydrogen sulfate ionic liquid or 1-butyl 3-methyl hydrogen sulfate ionic liquid.

Preferably, when the second component of the pulp bleaching protective agent is anhydrous magnesium sulfate, the content of anhydrous magnesium sulfate in the pulp bleaching protective agent is 0.6%.

The present invention also includes the steps of pre-treating the pulp using the pulp bleaching protective agent according to the above technical solution;

ECF bleaching the pretreated pulp, and the bleaching process is in the order of ODP bleaching;

It provided a paper strength improvement method using an ionic liquid-based pulp bleaching protectant comprising the step of obtaining by papermaking.

Preferably, the amount of the pulp bleaching protective agent used is 5-15% of the absolute dry mass of the pulp.

Preferably, the ODP oxygen de-lignin process in the ODP bleaching sequence is: pulp concentration 10%, NaOH usage 3%, oxygen pressure 0.5MPa, temperature 100°C, time 60 minutes, MgSO ₄ usage 0.6%.

Preferably, the D step chlorine dioxide bleaching process in the ODP bleaching sequence is: the amount of chlorine dioxide used is 0.7%, the pH value is 2-3, the temperature is 70°C, the pulp concentration is 10%, and the time is 30 minutes.

Preferably, in the ODP bleaching sequence, the P step hydrogen peroxide bleaching process: the amount of hydrogen peroxide used is 1%, the pulp concentration is 10%, the pH value is 11-12, the temperature is 90°C, and the oxygen pressure is 0.4 MPa.

Preferably, the pulp is sulfate pulp, and in the steaming process, a piece of wood having a length of 15-25 mm, a width of 10-20 mm, and a thickness of 3-5 mm is taken, dried naturally, and then steamed to obtain a sulfate raw pulp, Offering condition amount alkali used to step Na ₂ O than in jeolgeon material 21%, sulfide is also 25%, liquid ratio 1: 5, up to steaming temperature is released 15 minutes gas at 170 ℃, 105 ℃, heating time 90 minutes , Temperature holding time 90 minutes; After steaming, it is sufficiently washed and sorted to obtain pulp.

The present invention also provides the application of the ionic liquid based pulp bleaching protectant described in the above technical solution in the manufacture of relief printing paper, newsprint, offset printing paper, coated paper, book cover paper, dictionary paper, copy paper or board paper. I did.

The beneficial effects of the present invention are as follows:

(1) In the present invention, the eucalyptus sulfate pulp is pretreated with an ionic liquid-based protective agent to form a surface protective layer during the ODP bleaching process to reduce the degree of fiber decomposition and protect the fiber stem.

(2) Paper-based materials prepared by pre-treatment with ionic liquid-based protective agents have advantages such as high folding resistance, high tensile resistance strength, high rupture resistance, and high tearability, making them suitable for the manufacture of various types of paper-based materials. Do.

(3) Pretreatment of the ionic liquid-based protective agent selectively elutes lignin, significantly reducing the lignin content of the fiber, which is beneficial to the effect of bleach. The treatment can improve the bleaching effect, reduce the amount of bleach used, and increase the bleaching efficiency to reduce contamination. (4) The ionic liquid used in the present invention has a stable structure, zero vapor pressure, can be recycled, and is environmentally friendly.

(5) The treatment method of the present invention is simple, low in cost, strong in practicality, and easy to spread widely.

It should be pointed out that the following detailed descriptions are all illustrative and are intended to provide further explanation for the present application. Unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It should be noted that the terms used herein are for describing specific implementations and are not intended to limit exemplary implementations according to the present application. As used herein, unless the context dictates otherwise, the singular form is intended to include the plural form, and the use of the terms "comprising" and/or "inclusive" in this document includes features, procedures, manipulations, It should also be understood to refer to devices, assemblies and/or combinations thereof.

As introduced in the background technology, the problem is that the tensile resistance strength, rupture resistance and tear resistance of paper fibers after ECF bleaching are not high. Accordingly, the present invention provides an ionic liquid-based pulp bleaching protectant that performs ODP bleaching after pretreating the pulp. The pretreatment of the bleach protectant elutes lignin and protects the fibers during the bleaching process. In this way, the bleaching effect is improved and the physical strength of the pulp paper is improved.

In order to achieve the above object, the technical solutions adopted in the present invention are as follows: the concentration of pulp mentioned below is in mass percentage unless otherwise specified; Dosages of reagents and drugs handled are indicated relative to absolute dry pulp unless otherwise specified.

In order to overcome the problem that the current cooperative ultrasonic treatment for ionic liquids is disadvantageous in concentrating lignin on the surface, in this application, as a result of systematic research on the rules of action of the treatment method and effect, the result of the harmonization of the ionic liquid and the specific bleaching order It was found that the synergistic effect of paper strength and whiteness similar to the intensity ultrasonic cooperative ionic liquid treatment can be obtained, and is slightly lower than the effect of the high intensity ultrasonic cooperative ionic liquid treatment.

The present invention provides an ionic liquid based pulp bleaching protectant composed of at least one of ionic liquid, magnesium carbonate, sodium silicate, borax, ethylene glycol, glycerol and anhydrous magnesium sulfate.

In some embodiments, the anion of the ionic liquid contains at least one of hydrogen sulfate ions, formate ions, or chlorine ions; The pulp bleaching protectant developed in the present application selectively elutes lignin and can improve bleaching efficiency, and at the same time, the eluted cellulose is concentrated on the surface of the pulp fiber to protect the fiber from excessive oxidative decomposition during the bleaching process.

In some embodiments, the cation of the ionic liquid comprises one or more of 1-butyl 3-methyl-imidazole ion, 2-hydroxy ethyl trimethyl ammonium ion, and triethyl ammonium ion, wherein 1-butyl 3-methyl The structural formulas of -imidazole ion, 2-hydroxyethyl trimethyl ammonium ion, and triethyl ammonium ion are as follows, respectively.

The processing method of this application is similar to the previous application, but depending on the effect, the two applications can be applied to different pulp products. The reason for this is as follows.

This application selectively elutes lignin using an ionic liquid and concentrates it on the fiber surface to reduce damage to the glycan structure and increase fiber polymerization. The pretreatment loosens the fibers and increases the degree of swelling, which aids in the penetration of subsequent bleach, destruction of chromogenic groups, and diffusion and elution of the reactants. At the same time, the pretreatment can improve the morphology of the fine fiber component and improve the crosslinking between fibers, thereby improving the bleaching efficiency and improving the performance of the paper-based material.

Among them, eluting lignin and concentrating it on the fiber surface plays an important role in protecting the inner cellulose fiber stem. However, according to the previously applied patent, the effect of the ionic liquid is to enhance the removal of lignin as the ultrasonic technology is added, and the lignin content is low after treatment, which is not helpful in the concentration of surface lignin. Therefore, the fibers cannot be effectively protected. Thus, in some embodiments, the cation of the ionic liquid contains at least one of 1-butyl3-methyl-imidazole ions, 2-hydroxyethyl trimethyl ammonium ions, and triethyl ammonium ions to increase bleaching efficiency and Improved the performance of the base material.

The present invention also includes the steps of pre-treating the pulp using the pulp bleaching protective agent according to the above technical solution;

ECF bleaching the pretreated pulp, and the bleaching process is in the order of ODP bleaching;

There is provided a method for improving the strength of paper making pulp using an ionic liquid-based pulp bleaching protectant comprising the step of obtaining by papermaking.

In some examples, the present invention provides a method of improving the strength of pulp-making paper using an ionic liquid-based pulp bleaching protectant comprising the following steps.

(1) Steaming: Take a piece of wood, put it in a steamer, and steam it to get a primary pulp. After sufficient washing and screening, a sulphate pulp is obtained. The pulp has a kappa value of 12-16;

(2) pretreated with an ionic liquid based bleach protector;

(3) ECF bleaching: The pulp treated with the ionic liquid-based bleaching protective agent is ECF bleached, and the bleaching sequence of the bleaching process is ODP:

First, O-stage oxygen de-lignin is performed on the pulp treated with an ionic liquid-based bleaching protectant;

After the O-step oxygen de-lignin is completed, the pulp is washed, and the D-step chlorine dioxide bleaching step is performed;

After D-stage chlorine dioxide bleaching is completed, the pulp is washed and then P-stage hydrogen peroxide bleaching is performed;

After the P step hydrogen peroxide treatment is completed, the pulp is washed to complete it.

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

Although the above technical solution does not include specific process parameters, the inventive concept of the present invention is to protect the fiber from the oxidation reaction of the bleaching process, especially after pretreatment with an ionic liquid-based bleaching protector, to reduce the degree of oxidative decomposition of the fiber. , Aims to improve the bleaching effect, and obtain a high-performance pulp.

In some embodiments, the specific method of steaming in step (1) is as follows: Take a relatively uniform piece of wood having a length of 15-25 mm, a width of 10-20 mm, and a thickness of 3-5 mm, dried naturally, and then increased to increase sulfuric acid. To obtain salted raw pulp, the steaming condition is _{that the amount of alkali used in Na 2} O is 21%, the degree of sulfidation is 25%, the liquid ratio is 1:5, and the maximum steaming temperature is 170°C, 105°C. Discharge the gas for 15 minutes, heating time 90 minutes, holding time 90 minutes; After steaming, the pulp is obtained by performing sufficient washing and sorting in order to improve the increase efficiency and paper strength performance.

Sulphate wood pulp uses a mixture of sodium hydroxide and sodium sulfide as a thickener. Since the effect of the chemical solution is relatively weak in the process of increasing, and the fiber is not strongly corroded, the fiber is strong and tough, has high tensile resistance strength, rupture resistance, tear resistance and other mechanical strength index, and has relatively high heat resistance and durability.

In some examples, the specific steps of the pretreatment in step (2) are as follows: The pulp obtained in step (1) is treated under conditions of 5-15% of the amount of bleaching agent, and then ODP under certain conditions. Bleach.

As the amount of bleaching protectant increases, the bleaching efficiency and pulp performance are improved, but when the amount of the bleaching protectant reaches a certain value, the pulp performance is not greatly improved even if the amount of the bleaching protectant is continuously increased, only the bleaching cost increases. Let it.

In some embodiments, the amount of the protective agent used is 10% to obtain the optimum effect.

In some embodiments, a specific method of the ODP bleaching process in the above procedure (3) is as follows: The O-stage oxygen de-lignin process is: pulp concentration 10%, NaOH usage 3%, oxygen pressure 0.5MPa, temperature 100°C, time 60 minutes, MgSO ₄ used 0.6%; D step chlorine dioxide bleaching process: the chlorine dioxide dosage is 0.7%, the pH value is 2-3, the temperature is 70 ℃, the pulp concentration is 10%, the time is 30 minutes; P stage hydrogen peroxide bleaching process: hydrogen peroxide amount 1%, pulp concentration 10%, pH value 11-12, temperature 90 ℃, oxygen pressure is 0.4MPa.

The oxygen de-lignin process can reduce the lignin content in unbleached pulp, reduce the amount of bleach used, and reduce the pollutant load of bleaching wastewater. In some examples, the O-stage oxygen de-lignin process is: pulp concentration 10%, NaOH usage 3%, oxygen pressure 0.5MPa, temperature 100°C, time 60 minutes, which improves oxygen bleaching efficiency and pulp performance.

Chlorine dioxide has strong oxidative properties, and has relatively strong de-lignin ability and de-lignin selectivity. Under the same effective chlorine capacity, the adsorbable organic halide (AOX) produced by chlorine dioxide bleaching is only one fifth of that of chlorine gas bleaching, and does not affect lignin removal. Building a buffer system during the ClO ₂ bleaching process helps maintain pH stability. In some examples, the step D chlorine dioxide bleaching process: the amount of chlorine dioxide is 0.7%, the pH is 2-3, the temperature is 70 °C, the pulp concentration is 10%, the time is 30 minutes, and improves the bleaching efficiency of the pulp. , Reduce the generation of organic halides (AOX).

The hydrogen peroxide bleaching process has less damage to fibers, high yield, strong process adaptability, and the bleaching wastewater contains organic chlorine compounds, so it is easy to treat, and complete recycling of wastewater in the bleaching step is possible. In some embodiments, the P-step hydrogen peroxide bleaching process to effectively protect the pulp strength and improve whiteness: the amount of hydrogen peroxide is 1%, the pulp concentration is 10%, the pH value is 11-12, the temperature is 90°C. , The oxygen pressure is 0.4 MPa.

According to the study of the present application: using the ODP bleaching sequence not only the process is shorter, but also the cost is lower. At the same time, the combination of an ionic liquid-based bleaching protectant can achieve _{a pulp whiteness similar to the previous OAD 1} ED ₂ process and the strength of the pulp-making paper.

The design concept of the present invention is: Regarding the problem of lowering the pulp strength due to the oxidation reaction damage of the pulp fibers during the bleaching process, the present invention proposes a pretreatment method using an ionic liquid-based protective agent to elute lignin in the pulp. It adheres to the surface of the fiber and sufficiently acts on the bleach and lignin to avoid oxidative damage to the fiber during the bleaching process, and to secure the excellent physical strength of the paper material.

The present invention will be further described by combining specific examples below.

The analysis method used in the examples of the present invention is as follows:

Measurement of whiteness: After the pulp was decomposed by a fiber breaker, it was copied onto paper by Kaisepa Pilsaki, manufactured in Austria, and then measured by YQ-Z-48B white graph;

Fold Resistance Count: Measured by MIT Fold Resistance Tester made in China;

Burst resistance index: measured with a burst resistance tester produced by the Swedish company L &W;

Tensile resistance index: measured by XLWA (B) intelligent electronic tensile testing machine made in China;

Tear index: Measured by MIT tear tester made in China.

Fiber surface lignin content: measured by XPS produced in the United States.

The remaining experimental methods not described in detail are conventional experimental methods in the field.

The principle of the present invention is: lignin is selectively eluted and concentrated on the fiber surface by using an ionic liquid based pulp bleaching protectant to reduce structural breakdown of fibrous glycans and improve fibrous polymerization. The pretreatment can loosen the fibers and increase the degree of swelling, which is beneficial for subsequent penetration of bleach, destruction of chromogenic groups and diffusion and elution of reactants. At the same time, the pretreatment can improve the morphology of the fine fiber component, improve the adhesion between the fibers, thereby improving the bleaching efficiency, and improving the performance of the paper-based material.

Example 1:

The procedure is as follows.

(1) Steaming: Eucalyptus pieces are made of Na ₂ O, the amount of alkali used is 21%, the degree of sulfidation is 25%, the liquid ratio is 1:5, and the steam is steamed at a maximum steaming temperature of 170°C, releasing gas at 105°C. , The heating time is 90 minutes, and the warming time is 90 minutes. After steaming, it is thoroughly washed and sorted to obtain pulp.

(2) Pre-treatment of protective agent: Take exactly 25 g of the eucalyptus sulfate pulp (absolutely dried pulp) in three bags, and 10% sulfate hydrogenated triethyl ammonium ionic liquid (TEA-HSO ₄ )-based bleaching protective agent (the bleaching protective agent was TEA-HSO. _In addition to 4, add a small amount of anhydrous magnesium sulfate (0.6%) to the pulp, adjust the pulp concentration to 10% in a polyethylene bag, and knead until uniformly mixed.

(3) ECF bleaching: after the pretreatment, the pulp is bleached, and the bleaching sequence of the bleaching process is ODP, and the procedure of the bleaching process is: First, O-step oxygen delignin is performed on the eucalyptus sulfate pulp, and the process is: pulp concentration 10 %, NaOH usage 3%, oxygen pressure 0.5MPa, temperature 100°C, time 60 minutes, MgSO ₄ usage 0.6%; D-step chlorine dioxide bleaching was then performed, and the process was: the amount of chlorine dioxide used was 0.7%, the pH value was 2-3, the temperature was 70°C, the pulp concentration was 10%, and the time was 30 minutes; After washing the treated pulp, P-stage hydrogen peroxide bleaching was performed, and the process was: the amount of hydrogen peroxide was 1%, the pulp concentration was 10%, the pH value was 11-12, the temperature was 90° C., and the oxygen pressure was 0.4 MPa; Wash the treated pulp.

(4) Paper making: The pulp is beaten according to the beating degree of 40 ° SR, then decomposed by a fiber decomposer, mixed uniformly, and then made into a paper-based material ^{of 80 g/m 2 in a paper sheet molding machine.}

Table 1: _{Effect of TEA-HSO 4} based protective agent pretreatment on pulp performance

Table 2 Effect of TEA-HSO ₄ based protective agent pretreatment on the performance of pulp paper after ODP bleaching

Results: After testing the performance of the pulp paper, the use of TEA-HSO ₄ ionic liquid-based bleach protectant pretreatment from the data in Table 1 showed a relatively significant improvement in performance while the pulp yield was almost unchanged. Bleaching step (O): the kappa number decreased from 8.06 to 7.89, decreasing by 2%; The pulp viscosity increased by 13% from 885 mL/g to 999 mL/g; The degree of polymerization increased from 1313 to 1501, increasing by 14%. After completion of bleaching (ODP): kappa number decreased from 1.54 to 0.48, 69% reduction; Viscosity increased from 684 mL/g to 806 mL/g, increasing by 18%; The degree of polymerization increased from 988 to 1184, increasing by 20%.

After paper-forming performance tests, according to the data in Table 2, the physical performance of the pulp was significantly improved while the whiteness of the pulp was almost unchanged due to the pretreatment using the _{TEA-HSO 4 ionic liquid-based bleaching protectant.} Of which: tensile resistance index of the finished paper in the pulp was increased by 14% in 4.22kN · m ^-1 · m ^-1 to 4.81kN, tear index 6.927mN · m ² · g at ^-1 7.866mN · m ^{2 *} increased to g ^-1 and increased by 14%; The internal folding order increased 2.5 times from 126 to 319.

Testing the chemical composition of the pulp showed that the _{pretreatment of TEA-HSO 4} ionic liquid based bleach protectant significantly reduced the lignin content of the pulp, where the fiber lignin content of the oxygen bleaching step (O) was 6.76% to 3.52%, 48 % Decreased; After completion of bleaching (ODP), the fiber lignin content decreased by 18% from 1.97% to 1.62%. The O/C ratio of the fiber surface after the oxygen bleaching step detected by XPS decreased from 0.53 to 0.48, explaining that a protective layer of lignin was formed on the fiber surface during the bleaching process.

Through XRD analysis, after ODP bleaching _{, the pretreatment with TEA-HSO 4} ionic liquid-based bleaching protectant increased the crystallinity of cellulose from 36.2 to 46.0, increasing by 27%.

Example 2:

The procedure is as follows.

(1) Steaming: Conditions are Na ₂ O, alkali usage is 21%, sulfidation is 25%, liquid ratio is 1:5, maximum steaming temperature is 170 ℃, gas is released at 105 ℃, heating The time is 90 minutes, and the warming time is 90 minutes. After steaming, it is thoroughly washed and sorted to obtain pulp.

(2) Take three bags of exactly 25 g of pulp (absolutely dry pulp), and add 5%, 10%, 15% 1-butyl 3-methyl hydrogen sulfate ion liquid (BMIM-HSO ₄ ) into the pulp, and polyethylene In the pouch, adjust the pulp concentration to 10% and rub until well mixed.

(3) ECF bleaching: the pre-treated pulp is bleached, the bleaching sequence of the bleaching process is ODP, the procedure of the bleaching process is: First, O-step oxygen delignin is performed on the eucalyptus sulfate pulp, and the process is: pulp concentration 10%, NaOH usage 3%, oxygen pressure 0.5MPa, temperature 100°C, time 60 minutes, MgSO ₄ usage 0.6%; D-step chlorine dioxide bleaching was then performed, and the process was: the amount of chlorine dioxide used was 0.7%, the pH value was 2-3, the temperature was 70°C, the pulp concentration was 10%, and the time was 30 minutes; After washing the treated pulp, P-stage hydrogen peroxide bleaching was performed, and the process was: the amount of hydrogen peroxide was 1%, the pulp concentration was 10%, the pH value was 11-12, the temperature was 90° C., and the oxygen pressure was 0.4 MPa; Wash the treated pulp.

(4) Paper: The pulp is beaten according to the high dynamics of 40 ° SR, then decomposed by a fiber decomposer, mixed uniformly, and then made into a paper-based material ^{of 80 g/m 2 in a paper sheet molding machine.}

Table 3: _{Effect of BMIM-HSO 4} based protective agent treatment on pulp performance

Table 4 Effect of BMIM-HSO ₄ based protective agent pretreatment on the performance of pulp paper after ODP bleaching

Results: After the performance test of the pulp paper, the use of BMIM-HSO ₄ ionic liquid-based bleaching protectant pretreatment from the data in Table 3 showed a relatively large improvement in pulp performance while the pulp yield was almost unchanged. Bleaching step (O): kappa number decreased from 8.06 to 7.47, reduced by 7%; Viscosity increased by 2% from 885 mL/g to 905 mL/g; The degree of polymerization increased from 1313 to 1346, increasing by 3%. After completion of bleaching (ODP): Kappa number decreased from 1.54 to 0.67, 56% reduction Viscosity increased from 684 mL/g to 721 mL/g, increasing by 5%; The degree of polymerization increased from 988 to 1047, increasing by 6%.

After paper-forming performance tests, according to the data in Table 4, the physical performance of the pulp was relatively significantly improved while the whiteness of the pulp was almost unchanged due to the pretreatment using the _{BMIM-HSO 4 ionic liquid-based bleaching protectant.} Of which: tensile resistance index of the paper pulp was increased by 8% in 4.22kN · m ^-1 · m ^-1 to 4.57kN, tear index · m ² · g ^-1 in 6.927mN 7.598mN · m ^{2 *} g ^-1 Increased by 10%; The in-folding order doubled from 126 to 252.

As a result of testing the chemical composition of the pulp, the lignin content of the pulp was significantly reduced due to the TEA-HSO4 ionic liquid-based bleaching protectant pretreatment, where the fiber lignin content of the oxygen bleaching step (O) was 6.76% to 5.96%, 12% to 12%. Decreased; After completion of bleaching (ODP), the fiber lignin content decreased by 7% from 1.97% to 1.83%. The O/C ratio of the fiber surface after the oxygen bleaching step detected by XPS decreased from 0.53 to 0.51, explaining that a protective layer of lignin was formed on the fiber surface during the bleaching process.

Through XRD analysis, after ODP bleaching, the cellulose crystallinity increased by 35% from 36.2 to 48.8 due to pretreatment with a _{BMIM-HSO 4 ionic liquid based bleach protectant.}

The description of the above embodiments is only used to help understand the method and key ideas of the present invention. It should be noted that some of the improvements and modifications can be made to the present invention without departing from the principles of the present invention by those skilled in the art, and such improvements and modifications also fall within the protection scope of the claims of the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Accordingly, the present invention is not limited to the embodiments presented in this document, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (12)

Applications of ionic liquids as pulp bleaching protectants. Consisting of an ionic liquid and a second component, the second component is an ionic liquid-based pulp bleaching protectant, characterized in that consisting of at least one of magnesium carbonate, sodium silicate, borax, ethylene glycol, glycerol and anhydrous magnesium sulfate. The method of claim 2, wherein the anion of the ionic liquid comprises at least one of hydrogen sulfate ions, formate ions and chlorine ions;
An ionic liquid-based pulp bleaching protectant, wherein the cation of the ionic liquid comprises at least one of 1-butyl 3-methyl-imidazole ions, 2-hydroxyethyl trimethyl ammonium ions, and triethyl ammonium ions. The ionic liquid based pulp bleaching protectant according to claim 3, wherein the ionic liquid comprises triethyl ammonium hydrogen sulfate ionic liquid or 1-butyl3-methyl hydrogen sulfate ionic liquid. The ionic liquid-based pulp bleaching protective agent according to claim 2, wherein when the second component of the pulp bleaching protective agent is anhydrous magnesium sulfate, the content of anhydrous magnesium sulfate in the pulp bleaching protective agent is 0.6%. Pre-treating the pulp using the pulp bleaching protective agent according to any one of claims 2 to 5;
ECF bleaching the pretreated pulp, and the bleaching process is in the order of ODP bleaching;
Paper strength improvement method using an ionic liquid-based pulp bleaching protective agent, characterized in that it comprises the step of obtaining by papermaking. [7] The method of claim 6, wherein the amount of the pulp bleaching protectant is 5-15% of the absolute dry mass of the pulp. According to claim 6, wherein the ODP bleaching step of the O-step oxygen delignin process is: pulp concentration 10%, NaOH usage 3%, oxygen pressure 0.5MPa, temperature 100°C, time 60 minutes, MgSO ₄ usage 0.6% Paper strength improvement method using an ionic liquid-based pulp bleaching protectant. The method of claim 6, wherein the D step chlorine dioxide bleaching process in the ODP bleaching sequence: The amount of chlorine dioxide used is 0.7%, the pH value is 2-3, the temperature is 70°C, the pulp concentration is 10%, and the time is 30 minutes. A method of improving paper strength using an ionic liquid-based pulp bleaching protectant. The method of claim 6, wherein the P step hydrogen peroxide bleaching process in the ODP bleaching sequence is: hydrogen peroxide usage is 1%, pulp concentration is 10%, pH value is 11-12, temperature is 90°C, and oxygen pressure is 0.4 MPa. Paper strength improvement method using an ionic liquid-based pulp bleaching protectant. The method of claim 6, wherein the pulp is sulfate pulp, and the steaming step is: Take a relatively uniform piece of wood having a length of 15-25 mm, a width of 10-20 mm, and a thickness of 3-5 mm, dried naturally, and then steamed to obtain the original sulfate pulp. _{As for the steaming conditions, the amount of alkali used in Na 2} O is 21% compared to the absolutely dried raw material, the degree of sulfidation is 25%, the liquid ratio is 1:5, the maximum steaming temperature is 170°C and the gas is released at 105°C for 15 minutes, and the heating time is 90. Minutes, temperature holding time 90 minutes; A method of improving paper strength using an ionic liquid-based pulp bleaching protective agent, characterized in that to obtain pulp by performing sufficient washing and sorting after steaming. Ionic liquid based pulp bleaching protectant according to any one of claims 2 to 5 in the manufacture of relief printing paper, newsprint, offset printing paper, coated paper, book cover paper, dictionary paper, copy paper or board paper Of application.