KR102582865B1 - Ionic liquid-based pulp bleaching protectant - Google Patents

Abstract

The present invention relates to ionic liquid based pulp ECF bleach protectants. In this application, eucalyptus sulfate pulp is pretreated using an ionic liquid-based bleaching protectant, followed by ECF bleaching. The amount of bleaching protectant added is 5-15% of the pulp. This treatment effectively dissolves lignin in the pulp fiber, forming a protective layer on the fiber surface, improving subsequent bleaching efficiency and providing protection to the fiber during the bleaching process. Pretreatment has the effect of increasing the fiber content of the pulp while lowering the lignin content and improving the physical strength of the pulp-forming paper, broadening the application range of eucalyptus and other hardwoods. This treatment can increase bleaching effectiveness, reduce bleach usage, and reduce pollution by increasing bleaching efficiency. The present invention is simple to operate, has clear effects, is highly practical, and causes little contamination, making it easy to be widely disseminated.

Description

Ionic liquid-based pulp bleaching protectant

This application claims priority of the Chinese patent application with application number CN201911055224.1 and the invention title "Ionic liquid-based pulp bleaching protectant" filed with the Chinese Intellectual Property Office on November 1, 2019, the full contents of which are hereby referenced It is hereby incorporated by reference and incorporated herein by reference.

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

The content disclosed in this background technical section is only intended to facilitate understanding of the overall background of the present invention, and the composition of this information is recognized as prior art by those skilled in the art in the technical field to which the present invention belongs, or is optional. It is not implied in the form of .

With the large-scale, automation, and high efficiency of papermaking technology equipment, and the papermaking industry's increasing emphasis on clean production, circular economy, environmental pollution reduction, and sustainable development, chlorine-free element (ECF) bleaching technology has become more mature. Currently, paper mills frequently use mass delignification, oxygen delignification, and low-chlorine multiple bleaching methods to reduce the generation of pollutants. Chlorine-free element (ECF) bleaching technology uses chlorine dioxide instead of chlorine gas to bleach, preventing the emission of dioxins and greatly reducing the content of organic chlorides in wastewater. However, ECF is mainly bleached through oxidation reaction, which causes carbohydrate decomposition, reduces the degree of polymerization, and damages the strength of the fiber to a certain extent, resulting in low paper strength performance, especially low tensile strength.

Commonly used cellulose protective agents include anhydrous magnesium sulfate, magnesium carbonate, sodium silicate, borax, ethylene glycol, glycerol, etc. Among them, the use of anhydrous magnesium sulfate is more common, but it is ineffective in improving bleaching efficiency. In addition, during the oxygen delignification process after adding anhydrous magnesium sulfate, the carbohydrates in the pulp are still decomposed to a large extent, and when the oxygen delignification effect is more than 50%, the protective effect is greatly weakened, and the viscosity of the pulp fiber drops sharply.

Ionic liquids are a type of low-temperature molten salt that is composed entirely of anions and cations and is in a liquid state at room temperature. It has the characteristics of good thermal stability, recyclability, non-volatility and good solubility. Ionic liquids can elute and separate lignin from wood fibers. Lignin can be selectively extracted from wood fibers through appropriate ionic liquid selection and solution mixing. Using these ionic liquids in the pulp bleaching process can increase bleaching efficiency and bleaching effectiveness. It also effectively protects pulp fibers and increases the physical strength of paper.

With the development of the world economy and the ever-increasing people's living standards, people's mass requirements for paper and cardboard are becoming higher and higher. The tensile resistance strength, tear resistance and tear resistance of paper fibers after ECF bleaching in the conventional pulp and paper industry Issues that are not serious must be resolved urgently.

In the present inventor's previous patent CN201811466096.5, unbleached sulfate pulp is pretreated with ionic liquid-coordinated ultrasonic treatment, and the pretreated sulfate pulp is ECF-bleached. A method of making was disclosed. However, in a follow-up study, the inventor found that with the addition of ultrasonic technology, the effect of the ionic liquid is to enhance the lignin removal effect, so although the lignin content in the pulp after treatment is reduced, this treatment helps to concentrate lignin on the pulp surface. It doesn't work. Therefore, it cannot be effectively protected.

To overcome the above problems, the present invention provides for the application of ionic liquids as pulp bleaching protectants.

The present invention also provides an ionic liquid pulp bleaching protectant comprising an ionic liquid and a second component, wherein the second component is comprised of one or more 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 that pre-treats pulp with a pulp bleaching protectant and then ODP bleaches it. Pretreatment with a bleach protectant can leach lignin from the pulp and also protect the fiber during the ODP bleaching process. In this way, the pulp bleaching effect is improved and the physical strength of the pulped paper is improved.

In order to achieve the above technical objectives, the technical solutions adopted in the present invention are as follows:

The ionic liquid-based pulp bleach protectant consists of an ionic liquid and a second component, wherein the second component consists of one or more of magnesium carbonate, sodium silicate, borax, ethylene glycol, glycerol, and anhydrous magnesium sulfate.

Preferably, the anion of the ionic liquid includes one or more of hydrogen sulfate ion, formate ion, and chlorine ion;

The cation of the ionic liquid includes one or more of 1-butyl3-methyl-imidazole ion, 2-hydroxy ethyl trimethyl ammonium, and triethyl ammonium ion.

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

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

The present invention also includes the steps of pretreating pulp using a pulp bleaching protectant according to the above technical method;

ECF bleaching the pretreated pulp, and the bleaching process is ODP bleaching sequence;

A method for improving paper strength using an ionic liquid-based pulp bleaching protectant was provided, including the step of obtaining it by papermaking.

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

Preferably, the O stage oxygen delignification process of the ODP bleaching sequence is: pulp concentration 10%, NaOH usage 3%, oxygen pressure 0.5 MPa, temperature 100°C, time 60 minutes, MgSO ₄ usage 0.6%.

Preferably, the step D chlorine dioxide bleaching process in the above ODP bleaching sequence is: the usage amount of chlorine dioxide 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, the P stage 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.

Preferably, the pulp is sulfate pulp, and the steaming process involves taking wood pieces with a length of 15-25mm, a width of 10-20mm, and a thickness of 3-5mm, air drying, and then steaming to obtain sulfate raw pulp, The steaming conditions are Na ₂ O based compared to the absolute dry raw material, the amount of alkali used is 21%, the degree of sulfidation is 25%, the liquid ratio is 1:5, the maximum steaming temperature is 170℃, gas is released for 15 minutes at 105℃, and the heating time is 90 minutes. , temperature holding time 90 minutes; After steaming, thoroughly wash and select to obtain pulp.

Preferably, the paper obtained by said paper making is relief printing paper, newsprint, offset printing paper, coated paper, book cover paper, dictionary paper, copy paper or board paper.

The beneficial effects of the present invention are as follows:

(1) The present invention pretreats eucalyptus sulfate pulp with an ionic liquid-based protective agent to form a surface protective layer during the ODP bleaching process, thereby reducing the degree of fiber decomposition and protecting the fiber stem.

(2) Paper-based materials manufactured by pretreatment with an ionic liquid-based protectant have advantages such as high folding resistance, high tensile resistance strength, high burst resistance, and high tearing resistance, making them suitable for the production of various types of paper-based materials. do.

(3) Pretreatment with an ionic liquid-based protectant selectively elutes lignin, significantly reducing the lignin content of the fiber, which is beneficial to the effect of bleach. The above treatment can improve the bleaching effect, reduce bleach usage, and increase bleaching efficiency to reduce pollution. (4) The ionic liquid used in the present invention has a stable structure, zero vapor pressure, is recyclable, and is environmentally friendly.

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

It should be pointed out that the following detailed description is entirely illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by a person skilled in the art to which this application belongs.

It should be noted that the terminology used herein is intended to describe specific implementations and is not intended to limit example implementations according to the present application. As used herein, unless the context clearly dictates otherwise, the singular forms are intended to include the plural, and when the terms "including" and/or "inclusive" are used in this document, the terms "include" and/or "inclusive" refer to features, procedures, operations, etc. 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, burst resistance and tear resistance of paper fibers after ECF bleaching are not high. Therefore, the present invention provides an ionic liquid-based pulp bleaching protectant that performs ODP bleaching after pretreatment of pulp. Pretreatment with a bleaching protectant serves to dissolve lignin and protect the fiber during the bleaching process. In this way, the bleaching effect is improved and the physical strength of the pulped paper is improved.

In order to achieve the above object, the technical solutions adopted in the present invention are as follows: The concentrations of pulp mentioned below are mass percentages, unless otherwise specified; Dosages of reagents and chemicals handled were expressed relative to dry pulp unless otherwise specified.

In order to overcome the problem that the current ionic liquid cooperative ultrasonic treatment is disadvantageous in concentrating lignin on the surface, the present application systematically studied the operation rules of the treatment method and effect, and as a result, the harmonization of the ionic liquid and the specific bleaching sequence It was found that similar synergistic effects in paper strength and whiteness can be achieved with high-intensity ultrasonic cooperative ionic liquid treatment, and that the effect is slightly lower than that of high-intensity ultrasonic cooperative ionic liquid treatment.

The present invention provides an ionic liquid-based pulp bleach protectant comprising one or more of the following: ionic liquid, magnesium carbonate, sodium silicate, borax, ethylene glycol, glycerol, and anhydrous magnesium sulfate.

In some embodiments, the anion of the ionic liquid contains one or more of hydrogen sulfate ions, formate ions, or chlorine ions; The pulp bleaching protectant developed in this application can selectively elute lignin and improve bleaching efficiency, and at the same time, the eluted cellulose is concentrated on the surface of pulp fibers and protects the fibers from excessive oxidative degradation during the bleaching process.

In some embodiments, the cation of the ionic liquid includes 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-hydroxy ethyl trimethyl ammonium ion, and triethyl ammonium ion are respectively as follows.

The processing method of this application is similar to the previous application, but both applications are applicable to other pulp products depending on their effects. The reason for this is as follows.

This application uses an ionic liquid to selectively elute lignin and concentrate it on the fiber surface to reduce damage to the glycan structure and increase the degree of fiber polymerization. Pretreatment loosens the fibers and increases their degree of swelling, which is conducive to subsequent penetration of bleach, destruction of chromogenic groups, and diffusion and elution of reactants. At the same time, pretreatment can improve the morphology of microfiber components and enhance cross-linking between fibers, thereby improving bleaching efficiency and improving the performance of paper-based materials.

Among them, eluting lignin and concentrating it on the fiber surface plays an important role in protecting the internal cellulose fiber stem. However, according to the previously applied patent, with the addition of ultrasonic technology, the effect of the ionic liquid is to enhance lignin removal, and the lignin content after treatment is low, so it does not help in concentrating surface lignin. Therefore, it cannot effectively protect the fiber. Accordingly, in some embodiments, the cations of the ionic liquid contain one or more of 1-butyl3-methyl-imidazole ion, 2-hydroxyethyl trimethyl ammonium ion, and triethyl ammonium ion to increase bleaching efficiency and paper The performance of base materials has been improved.

The present invention also includes the steps of pretreating pulp using a pulp bleaching protectant according to the above technical method;

ECF bleaching the pretreated pulp, and the bleaching process is ODP bleaching sequence;

A method for improving the strength of pulp-made paper using an ionic liquid-based pulp bleaching protectant comprising the step of obtaining paper was provided.

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

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

(2) pretreatment with an ionic liquid-based bleach protectant;

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

First, O-stage oxygen delignification was performed on the pulp treated with ionic liquid-based bleach protectant;

After the O-stage oxygen delignification is completed, the pulp is washed, and the D-stage 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 stage hydrogen peroxide treatment is completed, the pulp is washed and completed.

The final pulp obtained after bleaching is used in the papermaking 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 protectant, thereby reducing the degree of oxidative degradation of the fiber. , aims to improve the bleaching effect and obtain high-performance pulp.

In some embodiments, the specific method of steaming in step (1) is as follows: take a relatively uniform piece of wood with a length of 15-25mm, a width of 10-20mm, and a thickness of 3-5mm, dry it naturally, and then steam it in sulfuric acid. To obtain salt raw pulp, the steaming conditions are Na ₂ O-based compared to the absolute dry raw material, the amount of alkali used is 21%, the degree of sulfidation is 25%, the liquid ratio is 1:5, the maximum steaming temperature is 170 ℃, and 105 ℃. exhaust gas for 15 minutes, heating time is 90 minutes, holding time is 90 minutes; After steaming, pulp is obtained by performing sufficient washing and screening to improve steaming efficiency and paper strength performance.

Sulphate wood pulp uses a mixture of sodium hydroxide and sodium sulfide as a thickening agent. During the steaming process, the effect of the chemical solution is relatively weak and the fiber is not strongly corroded, so the fiber is strong and tough, has high tensile resistance strength, burst resistance, tear resistance and other mechanical strength indices, and has relatively high heat resistance and durability.

In some embodiments, the specific steps of pretreatment in step (2) are as follows: the pulp obtained in step (1) is treated under conditions of 5-15% of the bleaching protection agent, and then treated with ODP under certain conditions. bleach it

As the amount of bleaching protectant used increases, bleaching efficiency and pulp performance improve, but when the amount of bleaching protectant reaches a certain value, continuing to increase the amount of bleaching protectant will not significantly improve pulp performance and will only increase bleaching costs. I order it.

In some embodiments, the amount of protectant used is 10% to achieve optimal effect.

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

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

Chlorine dioxide has strong oxidizing properties and has relatively strong delignification ability and delignification selectivity. Under the same effective chlorine dose, the adsorbable organic halides (AOX) produced by chlorine dioxide bleaching are only one-fifth of those of chlorine gas bleaching, and have no effect on lignin removal. During the ClO ₂ bleaching process, building a buffer system helps maintain pH stability. In some embodiments, the step D chlorine dioxide bleaching process is: 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 the bleaching efficiency of the pulp is improved. , reduce the generation of organic halides (AOX).

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

According to the study in this application: Using the ODP bleaching sequence, the process is not only shorter but also cheaper. At the same time, the combination of ionic liquid-based bleach protectants makes it possible to achieve pulp whiteness and strength of pulp-making paper similar to the previous OAD ₁ ED ₂ process.

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

The present invention is further explained below by combining specific examples.

The analysis methods used in the examples of the present invention are as follows:

Measurement of whiteness: Measured with a YQ-Z-48B white graph after the pulp has been decomposed by a fiber disintegrator and copied onto paper from Kaisepa Pilsaki made in Austria;

Number of folding resistance: measured by MIT folding 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 tester made in China;

Tear index: Measured with a Chinese-made MIT tear tester.

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

The remaining experimental methods that are not described in detail are common experimental methods in the relevant field.

The principle of the present invention is: using an ionic liquid-based pulp bleaching protectant to selectively elute lignin and concentrate it on the fiber surface, thereby reducing structural destruction of fibrous glycans and improving the degree of fiber polymerization. Pretreatment can loosen the fiber and increase the degree of swelling, which is beneficial for subsequent bleach penetration, destruction of the chromogenic groups and diffusion and elution of the reactants. At the same time, pretreatment can improve the morphology of microfiber components, enhance the agglomeration ability between fibers, improve bleaching efficiency, and improve the performance of paper-based materials.

Example 1:

The procedure is as follows.

(1) Steaming: Eucalyptus pieces are steamed in _Na2O base, alkali usage is 21%, sulfidation degree is 25%, liquid ratio is 1:5, maximum steaming temperature is 170℃, gas is released at 105℃. , heating time is 90 minutes, and warming time is 90 minutes. After steaming, wash thoroughly and select to obtain pulp.

(2) Protective agent pretreatment: Take three bags of exactly 25g of the above-mentioned eucalyptus sulfate pulp (dry pulp type) and add 10% triethyl ammonium hydrogen sulfate ionic liquid (TEA-HSO ₄ )-based bleaching protectant (the bleaching protectant is TEA-HSO) ₄ In addition, 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 above pretreatment, the pulp is bleached, the bleaching sequence of the bleaching process is ODP, the procedure of the bleaching process is: first, perform O-stage oxygen delignification on eucalyptus sulfate pulp, the process is: pulp concentration 10 %, NaOH usage is 3%, oxygen pressure is 0.5MPa, temperature is 100℃, time is 60 minutes, _MgSO4 usage is 0.6%; Followed by D stage chlorine dioxide bleaching, the process is: the usage amount of chlorine dioxide is 0.7%, pH value is 2-3, temperature is 70℃, pulp concentration is 10%, time is 30 minutes; After washing the treated pulp, carry out P-stage hydrogen peroxide bleaching, the process is: the amount of hydrogen peroxide is 1%, the pulp concentration is 10%, the pH value is 11-12, the temperature is 90℃, and the oxygen pressure is 0.4MPa; The treated pulp is washed.

(4) Papermaking: The pulp is pounded according to the beating degree of 40 ° SR, then broken down by a fiber decomposer, mixed uniformly, and then made into 80g/m ² raw paper base material in a paper molding machine.

Table 1: Effect of TEA-HSO ₄ based protectant pretreatment on pulp performance.

Table 2 Effect of TEA-HSO ₄ based protectant pretreatment on pulped paper performance after ODP bleaching

Results: After testing the performance of pulped paper, the data in Table 1 show that the use of TEA-HSO ₄ ionic liquid-based bleaching protectant pretreatment resulted in a relatively large improvement in performance, with the pulp remaining almost unchanged in yield, among which oxygen Bleaching step (O): kappa number decreased from 8.06 to 7.89, a 2% reduction; Pulp viscosity increased by 13% from 885 mL/g to 999 mL/g; The degree of polymerization increased from 1313 to 1501, an increase of 14%. After complete bleaching (ODP): Kappa number decreased from 1.54 to 0.48, a 69% reduction; Viscosity increased from 684 mL/g to 806 mL/g, an 18% increase; The degree of polymerization increased from 988 to 1184, an increase of 20%.

After paperforming performance tests, the data in Table 2 show that pretreatment with TEA-HSO ₄ ionic liquid-based bleach protectant significantly improved the physical performance of the pulp with little change in whiteness. Among them: the tensile resistance index of paper made from pulp increased by 14% from 4.22kN·m ^-1 to 4.81kN·m ^-1 , and the tear index increased from 6.927mN·m ² ·g ^-1 to 7.866mN·m ^2* g ^-1 increased by 14%; The internal folding order increased 2.5 times from 126 to 319.

Testing the chemical composition of the pulp showed that pretreatment with TEA-HSO ₄ ionic liquid-based bleaching protectant significantly reduced the lignin content of the pulp, where the fiber lignin content in the oxygen bleaching step (O) decreased from 6.76% to 3.52%, 48 % decreased; After complete 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, pretreatment with TEA-HSO ₄ ionic liquid-based bleaching protectant increased the crystallinity of cellulose by 27%, from 36.2 to 46.0.

Example 2:

The procedure is as follows.

(1) Steaming: Conditions are Na ₂ O system, alkali usage is 21%, sulfidation degree 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, wash thoroughly and select to obtain pulp.

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

(3) ECF bleaching: The pulp that has undergone the above pretreatment is bleached, the bleaching sequence of the bleaching process is ODP, and the bleaching process procedure is: first, perform O-stage oxygen delignification on the eucalyptus sulfate pulp, and the process is: pulp concentration 10%, NaOH usage 3%, oxygen pressure 0.5MPa, temperature 100℃, time 60 minutes, MgSO ₄ usage 0.6%; Followed by D stage chlorine dioxide bleaching, the process is: the usage amount of chlorine dioxide is 0.7%, pH value is 2-3, temperature is 70℃, pulp concentration is 10%, time is 30 minutes; After washing the treated pulp, carry out P-stage hydrogen peroxide bleaching, the process is: the amount of hydrogen peroxide is 1%, the pulp concentration is 10%, the pH value is 11-12, the temperature is 90℃, and the oxygen pressure is 0.4MPa; The treated pulp is washed.

(4) Papermaking: The pulp is pounded at a pulse rate of 40° SR, then disintegrated by a fiber decomposer, mixed uniformly, and then made into a 80g/m ² raw paper base material in a paper molding machine.

Table 3: Effect of BMIM-HSO ₄ based protectant treatment on pulp performance

Table 4 Effect of BMIM-HSO ₄ based protectant pretreatment on pulped paper performance after ODP bleaching

Results: After performance testing of pulped paper, the data in Table 3 show that the use of BMIM-HSO ₄ ionic liquid-based bleaching protectant pretreatment resulted in a relatively large improvement in pulp performance with little change in pulp yield, among which oxygen Bleaching step (O): kappa number decreased from 8.06 to 7.47, a 7% reduction; Viscosity increased by 2% from 885 mL/g to 905 mL/g; The degree of polymerization increased from 1313 to 1346, an increase of 3%. After complete bleaching (ODP): Kappa number decreased from 1.54 to 0.67, a 56% reduction; Viscosity increased from 684 mL/g to 721 mL/g, a 5% increase; The degree of polymerization increased from 988 to 1047, an increase of 6%.

After paper forming performance tests, the data in Table 4 show that pretreatment with BMIM-HSO ₄ ionic liquid-based bleach protectant resulted in a relatively large improvement in physical performance of the pulp with little change in whiteness. Among them: the tensile resistance index of paper pulp increased by 8% from 4.22kN·m ^-1 to 4.57kN·m ^-1 , and the tear index increased from 6.927mN·m ² ·g ^-1 to 7.598mN·m ^2* g ^-1 increased by 10%; The folding order doubled from 126 to 252.

Testing the chemical composition of the pulp showed that pretreatment with TEA-HSO4 ionic liquid-based bleaching protectant significantly reduced the lignin content of the pulp, where the fiber lignin content in the oxygen bleaching step (O) decreased from 6.76% to 5.96%, a decrease of 12%. decreased; After complete 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.

XRD analysis showed that after ODP bleaching, pretreatment with BMIM-HSO ₄ ionic liquid-based bleach protectant increased the cellulose crystallinity by 35% from 36.2 to 48.8.

The description of the above embodiments is only used to help understand the method and core idea of the present invention. Those skilled in the art should note that several improvements and modifications can be made to the present invention without departing from the principles of the present invention, 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 readily 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 invention. Therefore, the present invention is not limited to the embodiments shown in this document but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (12)

An ionic liquid-based pulp bleaching protectant comprising an ionic liquid and a second component, comprising:
wherein the second component consists of one or more of magnesium carbonate, sodium silicate, borax, ethylene glycol, glycerol, and anhydrous magnesium sulfate;
The anion of the ionic liquid includes hydrogen sulfate ion or formic acid ion,
An ionic liquid-based pulp bleaching protectant, characterized in that the cation of the ionic liquid includes one or more of 1-butyl3-methyl-imidazole ion, 2-hydroxy ethyl trimethyl ammonium ion, and triethyl ammonium ion. delete delete The ionic liquid-based pulp bleaching protectant according to claim 1, 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 protectant according to claim 1, wherein when the second component of the pulp bleaching protectant is anhydrous magnesium sulfate, the content of anhydrous magnesium sulfate in the pulp bleaching protectant is 0.6% by weight. Pretreating the pulp using a pulp bleaching protectant according to any one of claims 1, 4 and 5;
ECF bleaching the pretreated pulp, and the bleaching process is ODP bleaching sequence;
A method of improving paper strength using an ionic liquid-based pulp bleaching protectant, comprising the step of producing paper. The method of claim 6, wherein the amount of the pulp bleaching protectant used is 5-15% by weight of the absolute dry mass of the pulp. The method of claim 6, wherein the O stage oxygen delignification process of the ODP bleaching sequence is: pulp concentration 10% by weight, NaOH usage 3% by weight, oxygen pressure 0.5MPa, temperature 100°C, time 60 minutes, MgSO ₄ usage 0.6% by weight. A method of improving paper strength using an ionic liquid-based pulp bleaching protectant. The method of claim 6, wherein the step D chlorine dioxide bleaching process in the ODP bleaching sequence is: the amount of chlorine dioxide used is 0.7% by weight, the pH value is 2-3, the temperature is 70°C, the pulp concentration is 10% by weight, and the time is 30%. A method of improving paper strength using an ionic liquid-based pulp bleaching protectant. The method of claim 6, wherein the P stage hydrogen peroxide bleaching process in the ODP bleaching sequence is: hydrogen peroxide usage is 1% by weight, pulp concentration is 10% by weight, pH value is 11-12, temperature is 90°C, and oxygen pressure is 0.4MPa. A method of improving paper strength using an ionic liquid-based pulp bleaching protectant. The method of claim 6, wherein the pulp is sulfate pulp, and the steaming step is: taking a relatively uniform piece of wood with a length of 15-25mm, a width of 10-20mm, and a thickness of 3-5mm, air drying, and then steaming to produce sulfate raw pulp. The steaming conditions are as follows: compared to the absolute dry raw material, the amount of alkali used as Na ₂ O is 21% by weight, the degree of sulfidation is 25% by weight, the liquid ratio is 1:5, the maximum steaming temperature is 170℃, gas is released at 105℃ for 15 minutes, and heated. time 90 minutes, temperature holding time 90 minutes; A method of improving paper strength using an ionic liquid-based pulp bleaching protectant, characterized in that pulp is obtained by performing sufficient washing and screening after steaming. 7. Ionic liquid-based pulp bleaching according to claim 6, wherein the paper obtained by papermaking is relief printing paper, newsprint, offset printing paper, coated paper, book cover paper, dictionary paper, copy paper or board paper. How to improve paper strength using a protectant.