Paper pulp hydrogen peroxide bleaching accelerant and application method thereof

Abstract

The invention belongs to the technical field of pulping and papermaking, and discloses a paper pulp hydrogen peroxide bleaching accelerant with a nitrilotriacetic acid metal complex as an active component and an application method of the paper pulp hydrogen peroxide bleaching accelerant. The bleaching promoting agent is a mixture of a nitrilotriacetic acid metal complex and free nitrilotriacetic acid salt; according to the amount of substance, the ratio of the nitrilotriacetic acid metal complex to the free nitrilotriacetic acid salt is 1: (R1), and R is 7.8-1000. The obtained complex not only can catalyze hydrogen peroxide to continuously generate. OH and singlet oxygen (O2), but also can continuously output active oxygen and improve oxidation selectivity due to the fact that the consumption rate of the complex to. OH is low, so that the paper pulp bleaching efficiency is remarkably improved, the use amount of hydrogen peroxide can be effectively reduced, and degradation of pulp fibers is reduced.

Description

Technical Field

[0001] This invention belongs to the field of pulp and paper technology, and specifically relates to a pulp hydrogen peroxide bleaching accelerator with hyponitrotriacetic acid metal complex as active ingredient and its application method. Background Technology

[0002] Hydrogen peroxide (H2O2) has become the mainstream bleaching agent in the pulp bleaching process after oxygen delignification due to its chlorine-free nature, environmental friendliness, and lack of organohalides. Its bleaching mechanism primarily involves the oxidation and degradation of lignin by the generated perhydroxyl anions (HO2⁻), thereby improving pulp brightness. However, in practical applications, hydrogen peroxide is prone to ineffective decomposition, reducing bleaching efficiency and increasing production costs.

[0003] Currently, the hydrogen peroxide pulp bleaching accelerators commonly used in industry are mainly multi-component transition metals (Mn). 2+ Cu 2+ Co 2 + Fe 2+ Although the complexation system composed of α-phthalocyanines and macrocyclic organic ligands (phthalocyanines, porphyrins, Schiff bases, macrocyclic polyamines) has achieved high bleaching catalytic activity, it still faces the following problems: 1. Complex and costly ligand synthesis: Phthalocyanine, porphyrin, Schiff base and macrocyclic polyamine ligands usually require multi-step organic synthesis processes with harsh reaction conditions and limited yields, resulting in high overall preparation costs and limiting their widespread application in large-scale industries such as pulp and paper making.

[0004] 2. Insufficient environmental friendliness: The aforementioned macrocyclic organic ligands have complex molecular structures and poor biodegradability. Once discharged into water bodies or soil, they may accumulate over a long period, posing a potential pollution risk to the ecological environment.

[0005] 3. Dependence on heavy metals: due to Fe 2+ It easily precipitates at alkaline pH conditions; Co is commonly used in such systems. 2+ Mn 2+ Heavy metal ions can activate hydrogen peroxide. However, the emission of heavy metal ions increases the environmental burden on water bodies and solid waste, posing potential environmental risks and regulatory pressures.

[0006] 4. Insufficient selectivity, leading to pulp damage: The main reactive oxygen species produced by metal complex bleaching agents is hydroxyl radical (·OH). This radical has a very strong non-selective oxidizing effect. Although it can improve the brightness of pulp, it will also significantly accelerate fiber degradation, causing a large loss of pulp viscosity and degree of polymerization, which is not conducive to the maintenance of pulp strength.

[0007] Therefore, there is an urgent need to develop a new type of bleaching agent to overcome the above-mentioned shortcomings and meet the industrial demand for bleaching efficiency, environmental protection and economy. Summary of the Invention

[0008] To overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a pulp hydrogen peroxide bleaching accelerator in which a metal complex of hypozinotriacetic acid and free hypozinotriacetic acid salt synergistically constitute the active ingredient. This bleaching accelerator can exert its catalytic effect without relying on large amounts of metal, and can promote hydrogen peroxide bleaching even under metal-free conditions. In the presence of trace amounts of Fe³⁺, the catalytic efficiency is significantly improved, thus combining the applicability to metal-free conditions with the high efficiency of trace metals. By catalyzing hydrogen peroxide to generate more fiber-friendly active oxygen species, such as singlet oxygen, it significantly improves pulp bleaching efficiency while reducing viscosity loss. It features applicability to the commonly used industrial alkaline hydrogen peroxide bleaching pH range, good biodegradability, outstanding environmental friendliness, and low cost.

[0009] Another object of the present invention is to provide a method for preparing the above-mentioned pulp hydrogen peroxide bleaching accelerator.

[0010] Another object of the present invention is to provide the application of the above-mentioned pulp hydrogen peroxide bleaching accelerator with the nitrotriacetic acid metal complex as the active ingredient.

[0011] The objective of this invention is achieved through the following solution: A pulp hydrogen peroxide bleaching accelerator, the active ingredient of which is a metal complex of hyponitrotriacetic acid, wherein the metal is Fe. 3+ .

[0012] The pulp hydrogen peroxide bleaching accelerator also contains hyponitrotriacetate, wherein the hyponitrotriacetate is at least one of sodium hyponitrotriacetate and potassium hyponitrotriacetate; The bleaching accelerator is a metal complex of hyponitrotriacetic acid (Fe2+) 3+ A mixture of α-triacetic acid complex (R:R) and free α-triacetic acid salt (R:R) in molar amounts, wherein the metal complex of α-triacetic acid salt is 1:(R−1) and the free α-triacetic acid salt is 7.8-1000, preferably R=156.

[0013] The bleaching accelerator of the present invention has advantages such as good alkaline pH catalytic activity, good biodegradability, and excellent environmental protection and economy. It can effectively improve pulp bleaching efficiency and reduce costs, and has broad industrial application prospects.

[0014] A method for preparing the above-mentioned pulp hydrogen peroxide bleaching accelerator includes the following steps: A pulp hydrogen peroxide bleaching accelerator is obtained by reacting a triacetate salt with a metal salt in an aqueous solution.

[0015] The hypotriacetate is at least one of sodium hypotriacetate and potassium hypotriacetate; The metal salt is an iron salt, wherein the iron salt is one of ferric chloride, ferric sulfate, and ferric nitrate.

[0016] The molar ratio of the sodium hypotriacetate to the metal salt is 7.8-1000:1, preferably 156:1.

[0017] The concentration of hyponitrotriacetate in the aqueous solution is 5-100 mmol / L.

[0018] The aforementioned mixing reaction refers to a reaction at 22-28℃ in the dark for 20-40 minutes, and the reaction solution after the mixing reaction is the pulp hydrogen peroxide bleaching accelerator.

[0019] The above-mentioned pulp hydrogen peroxide bleaching accelerator and hyponitrotriacetate are used in pulp bleaching.

[0020] A method for alkaline hydrogen peroxide bleaching of pulp, comprising the following steps: (1) Add a chelating agent to the pulp for pre-chelation, then rinse and dry to obtain pre-chelated oven-dry pulp; (2) Add stabilizer, bleaching accelerator and water to the pre-chelated oven-dry pulp in sequence, and adjust the pH of the pulp to 9-11; (3) Add hydrogen peroxide aqueous solution to the pulp, and then heat it in a water bath to carry out the bleaching reaction. After the reaction is completed, cool and wash to obtain bleached pulp.

[0021] The concentration of the slurry mentioned in step (1) is 5-20%, where the concentration of the slurry refers to the ratio of the mass of the oven-dried slurry to the mass of the slurry. The chelating agent mentioned in step (1) is one of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA); the amount of the chelating agent used is: the mass of the chelating agent is 0.1-5% of the dry slurry mass.

[0022] The chelation mentioned in step (1) refers to reacting at 22-28℃ for 20-40 minutes; The stabilizer mentioned in step (2) is sodium silicate; the amount of stabilizer used is 1-10% of the mass percentage of the chelated oven-dry pulp.

[0023] The amount of bleaching accelerator used in step (2) is such that the weight percentage of the raw material hyponitrotriacetate of the bleaching accelerator is 1-5% based on the chelated oven-dried pulp, preferably 2%.

[0024] The amount of water used in step (2) is such that after the chelated oven-dry pulp is mixed with the stabilizer and bleaching accelerator in sequence, water is added to adjust the total mass of the mixed system so that the mass concentration of the chelated oven-dry pulp in the resulting mixed pulp is 5–20%, preferably 10%.

[0025] The bleaching reaction mentioned in step (3) refers to heating to 60-80℃ and reacting for 0.5-2 hours; The concentration of the hydrogen peroxide aqueous solution in step (3) is 30-35%; the amount of hydrogen peroxide aqueous solution used in step (3) satisfies that the mass percentage of hydrogen peroxide based on the chelated oven-dry pulp is 1-10%.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects: Existing technologies for improving hydrogen peroxide bleaching efficiency rely on complex systems composed of multiple transition metals and macrocyclic organic ligands. However, these methods still suffer from common limitations such as limited reactive oxygen generation efficiency, difficult degradation of chelating agents, and high operating costs, making it difficult to simultaneously meet the triple requirements of high whiteness, low energy consumption, and environmental friendliness. This invention improves hydrogen peroxide conversion efficiency. The bleaching agent mechanism lies in the fact that the tetradentate coordination structure of NTA can form stable chelate complexes with transition metal ions, maintaining structural integrity under alkaline conditions and serving as the active center of the oxidation catalyst. The resulting complex can catalyze the continuous generation of ·OH and singlet oxygen (¹O2) from hydrogen peroxide. Furthermore, due to its low activation rate for ·OH, it can continuously output reactive oxygen and improve oxidation selectivity, thereby significantly improving pulp bleaching efficiency and effectively reducing the amount of hydrogen peroxide used, thus reducing pulp fiber degradation. Using the method of this invention, compared to the original system (without bleaching agent), whiteness is increased by 88.3%, and oxidant dosage is reduced by 40.3%. Meanwhile, the bleaching agent used in this invention has good biodegradability, low production cost, and is environmentally friendly, making it suitable for industrial-scale application. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available products.

[0028] The following examples are provided to further illustrate the present invention, but are not intended to limit the scope of protection of the invention. Unless otherwise stated, percentages are based on oven-dry weight (od) of pulp, temperatures are in degrees Celsius, and pressures are at atmospheric pressure. Unless otherwise specified, the reagents and instruments used in the following examples are commercially available products.

[0029] NTA bleaching agent: A solution prepared in situ in water for 30 min by mixing sodium hypotriacetate and metal salt in the following molar ratios at 25°C in the dark, hereinafter referred to as bleaching agent.

[0030] H2O2 aqueous solution: mass fraction is 35%.

[0031] NaOH solution: molar concentration of 2 mol / L.

[0032] Example 1: First, weigh 10 g of unbleached oven-dry pulp, then add 20 mL of EDTA solution (the added EDTA accounts for 2.0% of the oven-dry pulp's mass fraction). Add deionized water to the beaker to make the total reaction system 100 g, at which point the pulp concentration is 10% (g / g). Stir at 25°C for 30 min. This step aims to chelate metal ions from the pulp in advance. Wash the well-mixed pulp with 400 mL of deionized water, repeating three times. Place the washed pulp in an oven and dry until oven-dry. Weigh 10 g of the chelated oven-dry pulp after washing, with a brightness of 55.5% ISO. Add 0.2 g of powdered instant sodium silicate and 20 mL of bleaching accelerator (the bleaching accelerator is prepared by the following method: the amount of sodium hypotriacetate used is based on a chelated oven-dry pulp mass fraction of 2%, i.e., 0.2 g, which is equivalent to 0.78 mmol). Then, according to the reaction of sodium hypotriacetate and Fe³⁺... + The molar ratio was 156:1, and the molar amount of the raw iron salt was 0.005 mmol. At this time, the iron salt was ferric chloride hexahydrate, that is, 0.78 mmol of sodium hypotriacetate and 0.005 mmol of ferric chloride hexahydrate were mixed in 20 mL of aqueous solution at 25 °C in the dark for 30 min. The resulting solution was the bleaching accelerator. Deionized water was added to a polyethylene plastic bag, and the amount of deionized water was added to make up to a total mass of 100 g so that the concentration of the oven-dry slurry after chelation was 10% (g / g). The pH was adjusted to 10 with 2 mol / L NaOH solution, and 1.3 mL of H2O2 aqueous solution (H2O2 mass fraction of 35%) was added. The mixture was then transferred to a 70 °C water bath and reacted for 60 min. The obtained bleached pulp was washed three times with deionized water. A portion was used to make paper, and the whiteness was measured using a whiteness meter. The measured whiteness value was 74.25% ISO. The viscosity and degree of polymerization were measured using a viscometer. The measured viscosity was 605 mL / g, and the degree of polymerization was 858. The viscosity of the unbleached pulp was 626 mL / g, and the degree of polymerization was 894.9. The viscosity retention rate was 96.7%, and the degree of polymerization retention rate was 95.9%. Using this invention, the whiteness of unbleached pulp can be significantly improved (55.5% ISO).

[0033] The measurement results of each embodiment of the present invention are listed in Table 1, and the measurement results of the comparative examples are listed in Table 2. For each example, n=3 parallel experimental results were taken, and the error is the standard error (SE), with a 95% confidence interval (95% CI) for whiteness. Whiteness and viscosity were measured according to ISO 2470 "Paper, paperboard and pulp—Determination of diffuse blue light factor (ISO brightness)" and GB / T 1548-1989 "Determination of pulp viscosity—Copper-ethylenediamine method," respectively. The degree of polymerization was obtained by converting the intrinsic viscosity of the copper-ethylenediamine solution according to ISO 5351 (equivalent to GB / T), and the retention rate was calculated. Measurements were performed three times.

[0034] Example 2: The specific operation is basically the same as in Example 1, except that in the preparation of 20 mL of bleaching agent, the molar amount of ferric chloride hexahydrate is 0.1 mmol, corresponding to a molar ratio of sodium hypotriacetate:Fe 3+ =7.8:1, that is, 0.78 mmol of sodium hypotriacetate and 0.1 mmol of ferric chloride hexahydrate are mixed in 20 mL of aqueous solution at 25 °C in the dark for 30 min. The resulting solution is the bleaching accelerator.

[0035] Example 3: The specific operation is basically the same as in Example 1, except that in the preparation of 20 mL of bleaching agent, the molar amount of ferric chloride hexahydrate is 0.01 mmol, corresponding to a molar ratio of sodium hypotriacetate:Fe 3+ The ratio of sodium hypotriacetate to ferric chloride hexahydrate is 78:1, meaning 0.78 mmol of sodium hypotriacetate and 0.01 mmol of ferric chloride hexahydrate are mixed in 20 mL of aqueous solution at 25 °C in the dark for 30 min. The resulting solution is the bleaching accelerator.

[0036] Example 4: The specific operation is basically the same as in Example 1, except that in the preparation of 20 mL of bleaching agent, the molar amount of ferric chloride hexahydrate is 0.05 mmol, corresponding to a molar ratio of sodium hypotriacetate:Fe 3+ =15.6:1, that is, 0.78 mmol of sodium hypotriacetate and 0.05 mmol of ferric chloride hexahydrate are mixed in 20 mL of aqueous solution at 25 °C in the dark for 30 min. The resulting solution is the bleaching accelerator.

[0037] Example 5: The specific operation is basically the same as in Example 1, except that in the preparation of 20 mL of bleaching agent, the molar amount of ferric chloride hexahydrate is 0.001 mmol, corresponding to a molar ratio of sodium hypotriacetate:Fe 3+The ratio of sodium hypotriacetate to ferric chloride hexahydrate is 780:1, meaning 0.78 mmol of sodium hypotriacetate and 0.001 mmol of ferric chloride hexahydrate are mixed in 20 mL of aqueous solution at 25 °C in the dark for 30 min. The resulting solution is the bleaching accelerator.

[0038] Example 6: The specific operation is basically the same as in Example 1, except that in the preparation of the bleaching agent, ferric sulfate is used instead of ferric chloride hexahydrate as the iron source.

[0039] Example 7: The specific operation is basically the same as in Example 1, except that in the preparation of the bleaching agent, ferric nitrate is used instead of ferric chloride hexahydrate as the iron source.

[0040] Example 8: The specific operation is basically the same as in Example 1, except that the pH value used during bleaching is 9.5.

[0041] Example 9: The specific operation is basically the same as in Example 1, except that the pH value used during bleaching is 10.5.

[0042] Example 10: The specific operation is basically the same as in Example 1, except that the bleaching temperature is 60°C.

[0043] Example 11: The specific operation is basically the same as in Example 1, except that the bleaching temperature is 80°C.

[0044] Comparative Example 1: The specific operation is basically the same as in Example 2, except that sodium hypotriacetate is not added in the preparation of the bleaching agent, and the bleaching agent added during the bleaching process is 20 mL of ferric chloride hexahydrate aqueous solution, with a molar amount of ferric chloride hexahydrate of 0.1 mmol.

[0045] Comparative Example 2: The specific operation is basically the same as in Example 3, except that sodium hypotriacetate is not added in the preparation of the bleaching agent, and the bleaching agent added during the bleaching process is 20 mL of ferric chloride hexahydrate aqueous solution, with a molar amount of ferric chloride hexahydrate of 0.01 mmol.

[0046] Comparative Example 3: The specific operation is basically the same as in Example 4, except that sodium hypotriacetate is not added in the preparation of the bleaching agent, and the bleaching agent added during the bleaching process is 20 mL of ferric chloride hexahydrate aqueous solution, with a molar amount of ferric chloride hexahydrate of 0.05 mmol.

[0047] Comparative Example 4: The specific operation is basically the same as in Example 1, except that only sodium hypotriacetate is added as the bleaching accelerator, and the amount of sodium hypotriacetate added is 0.1% of the weight of the oven-dry pulp after chelation, i.e., 0.01g.

[0048] Comparative Example 5: The specific operation is basically the same as that of Comparative Example 4, except that only sodium hypotriacetate is added as the bleaching accelerator, and the amount of sodium hypotriacetate added is 1% of the weight of the oven-dry pulp after chelation, i.e., 0.1g.

[0049] Comparative Example 6: The specific operation is basically the same as that of Comparative Example 4, except that only sodium hypotriacetate is added as the bleaching accelerator, and the amount of sodium hypotriacetate added is 2% of the oven-dry pulp mass after chelation, i.e., 0.2g.

[0050] Comparative Example 7: The specific operation is basically the same as that of Comparative Example 4, except that only sodium hypotriacetate is added as the bleaching accelerator, and the amount added is 4% of the oven-dry pulp mass after chelation, i.e., 0.4g.

[0051] Comparative Example 8: The specific operation is basically the same as that of Comparative Example 4, except that only sodium hypotriacetate is added as the bleaching accelerator, and the amount added is 8% of the oven-dry pulp mass after chelation, i.e., 0.8g.

[0052] Comparative Example 9: The specific operation is basically the same as in Example 1, except that sodium hypotriacetate is not added, and 20 mL of cobalt chloride aqueous solution is added during the bleaching process. 2+ Dosage: 0.005 mmol.

[0053] Comparative Example 10: The specific operation is basically the same as in Example 1, except that instead of using a bleaching accelerator, 20 mL of EDTA aqueous solution is added during the bleaching process. The EDTA accounts for 2.0% of the mass fraction of the oven-dry pulp after chelation, that is, the mass of EDTA in the 20 mL bleaching accelerator is 0.2 g.

[0054] Comparative Example 11: The specific operation is basically the same as in Example 1, except that 20 mL of water is used instead of 20 mL of bleaching agent during the bleaching process, which is the conventional hydrogen peroxide bleaching method.

[0055] Comparative Example 12: The specific operation is basically the same as in Example 1, except that sodium hypotriacetate is not added, and 20 mL of Fe-Salen solution is added during the bleaching process (Fe-Salen dosage 0.005 mmol, Fe-Salen CAS number 18601-34-8).

[0056] Comparative Example 13: The specific operation is the same as in Example 1, except that when preparing 20 mL of the bleaching agent, sodium hypotriacetate and Fe³⁺ are mixed at a 1:1 molar ratio, so that the ratio of sodium hypotriacetate to Fe³⁺ in the system is [missing information]. 3+ =1:1 (calculated as 0.005 mmol Fe³⁺, sodium hypotriacetate is simultaneously 0.005 mmol), mix in the dark for 30 min and it is ready to use; other conditions during bleaching are the same as in Example 1.

[0057] Table 1 Test Results of the Example

[0058] Table 2 Comparative test results

[0059] As can be seen from Tables 1 and 2, the embodiments of the present invention are generally superior to the comparative examples in terms of bleaching whiteness, viscosity retention rate and degree of polymerization retention rate, especially Example 1, which shows the most outstanding performance.

[0060] Specifically, the whiteness of Example 1 reached 74.25% ISO, significantly higher than the 65.46% ISO of Comparative Example 11 achieved by conventional hydrogen peroxide bleaching, and also significantly better than the results of adding Fe³⁺ alone (Comparative Example 1, 67.93% ISO; Comparative Example 2, 66.63% ISO; Comparative Example 3, 63.50% ISO) or adding sodium hypotriacetate alone (Comparative Examples 4–8, 67.52–67.96% ISO). Meanwhile, Example 1 exhibited a viscosity retention rate of 96.7% and a degree of polymerization retention rate of 95.9%, far exceeding conventional bleaching (Comparative Example 11, viscosity retention rate 85.1%, degree of polymerization retention rate 84.6%), and also better than Comparative Examples 1–3 with Fe³⁺ added alone (viscosity retention rate only 69.6–75.6%, degree of polymerization retention rate only 64.8–70.3%). Meanwhile, the whiteness standard error of Example 1 was only 0.14, which was significantly lower than that of the comparative example (0.2–0.36), indicating that the present invention has better repeatability and result stability.

[0061] Furthermore, while Example 2 showed some improvement in whiteness (72.11% ISO), its viscosity and degree of polymerization retention decreased significantly (73.2% and 70.2%, respectively). In contrast, Example 1 used sodium hypotriacetate:Fe3+ The molar ratio of 156:1 is optimal, effectively maintaining pulp strength while significantly improving whiteness. The hydrogen peroxide reduction rate was calculated using an equal-whiteness calculation method. This means that when achieving the same target whiteness, the amount of hydrogen peroxide required by conventional hydrogen peroxide bleaching methods was used as a benchmark, and compared with the amount of hydrogen peroxide used in Example 1. The reduction rate was calculated as follows: subtract the amount of hydrogen peroxide required in Example 1 from the amount required in Comparative Example 11, then divide by the amount of hydrogen peroxide required in Comparative Example 11 and convert to a percentage. The whiteness improvement rate was calculated as follows: first, subtract the whiteness measured in Comparative Example 11 from the whiteness measured in Example 1; then divide this difference by the difference between the whiteness measured in Comparative Example 11 and the whiteness of the unbleached pulp, and convert the result to a percentage. Specific results are shown in Table 1.

[0062] The sodium hypotriacetate used in this invention is readily biodegradable in the environment: OECD 301F (differential pressure breather) test results show that its degradation rate reaches more than 60% within 28 days. Experiments in activated sludge and natural water bodies also show that it can be rapidly removed by microorganisms, which is far superior to the fact that macrocyclic ligands such as phthalocyanine and porphyrin hardly degrade in the environment.

[0063] In summary, Example 1 of the present invention is superior to the comparative example (conventional bleaching whiteness 65.46%, viscosity retention 85.1%, and polymerization retention 84.6%) in terms of whiteness (74.25% ISO), viscosity retention (96.7%), and polymerization retention (95.9%). The overall technical parameters are the best, fully demonstrating the advanced nature and practical value of the present invention.

[0064] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A pulp hydrogen peroxide bleaching accelerator, characterized in that... Its active ingredient is a metal complex of hyponitrotriacetic acid, wherein the metal is Fe. 3+ .

2. The pulp hydrogen peroxide bleaching accelerator according to claim 1, characterized in that: The pulp hydrogen peroxide bleaching accelerator also contains hyponitrotriacetate, wherein the hyponitrotriacetate is at least one of sodium hyponitrotriacetate and potassium hyponitrotriacetate.

3. The pulp hydrogen peroxide bleaching accelerator according to claim 2, characterized in that: The bleaching agent is a mixture of a metal complex of hypotriacetic acid and a free hypotriacetic acid salt; by molar amount, the ratio of metal complex of hypotriacetic acid to free hypotriacetic acid salt is 1:(R−1), where R is 7.8-1000.

4. A method for preparing a pulp hydrogen peroxide bleaching accelerator according to any one of claims 1-3, characterized in that... Includes the following steps: A pulp hydrogen peroxide bleaching accelerator is obtained by reacting a triacetate salt with a metal salt in an aqueous solution.

5. The method for preparing the pulp hydrogen peroxide bleaching accelerator according to claim 4, characterized in that: The hypotriacetate is at least one of sodium hypotriacetate and potassium hypotriacetate; The metal salt is an iron salt, wherein the iron salt is one of ferric chloride, ferric sulfate, and ferric nitrate; The molar ratio of the sodium hypotriacetate to the metal salt is 7.8-1000:1; The concentration of hypotriacetate in the aqueous solution is 5-100 mmol / L; The aforementioned mixing reaction refers to a reaction at 22-28℃ in the dark for 20-40 minutes, and the reaction solution after the mixing reaction is the pulp hydrogen peroxide bleaching accelerator.

6. The application of the pulp hydrogen peroxide bleaching accelerator according to any one of claims 1-3 in pulp bleaching.

7. A method for alkaline hydrogen peroxide bleaching of pulp, characterized in that... Includes the following steps: (1) Add a chelating agent to the pulp for pre-chelation, then rinse and dry to obtain pre-chelated oven-dry pulp; (2) Add the stabilizer, the bleaching accelerator as described in any one of claims 1-3 and water to the pre-chelated oven-dried pulp in sequence, and adjust the pH of the pulp to 9-11; (3) Add hydrogen peroxide aqueous solution to the pulp, then heat it to carry out the bleaching reaction. After the reaction is completed, cool and wash to obtain bleached pulp.

8. The method for alkaline hydrogen peroxide bleaching of pulp according to claim 7, characterized in that: The concentration of the slurry mentioned in step (1) is 5-20%, where the concentration of the slurry refers to the ratio of the mass of the oven-dried slurry to the mass of the slurry. The chelating agent mentioned in step (1) is one of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DITA); the amount of the chelating agent used is such that the mass of the chelating agent is 0.1-5% of the dry slurry mass. The chelation mentioned in step (1) refers to the reaction at 22-28℃ for 20-40 minutes.

9. The method for alkaline hydrogen peroxide bleaching of pulp according to claim 7, characterized in that: The stabilizer mentioned in step (2) is sodium silicate; the amount of stabilizer used is 1-10% of the mass percentage of the oven-dry pulp after chelation. The amount of bleaching accelerator used in step (2) is such that the raw material of the bleaching accelerator, hyponitrotriacetate, is 1-5% by weight of the chelated oven-dried pulp, preferably 2%; The amount of water used in step (2) is such that after the chelated oven-dry pulp is mixed with the stabilizer and bleaching accelerator in sequence, water is added to adjust the total mass of the mixed system so that the mass concentration of the chelated oven-dry pulp in the resulting mixed pulp is 5–20%, preferably 10%.

10. The method for alkaline hydrogen peroxide bleaching of pulp according to claim 7, characterized in that: The bleaching reaction mentioned in step (3) refers to heating to 60-80℃ and reacting for 0.5-2 hours; The concentration of the hydrogen peroxide aqueous solution in step (3) is 30-35%; the amount of hydrogen peroxide aqueous solution used in step (3) satisfies that the mass percentage of hydrogen peroxide based on the chelated oven-dry pulp is 1-10%.

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