Bleaching method and preparation method of cotton pulp

Abstract

The invention relates to the technical field of cotton pulp production, and discloses a bleaching and preparation method of cotton pulp, and the bleaching method comprises the following steps: (1) adjusting pulp to be bleached to be alkaline, and then adding formamidine sulfinic acid for first bleaching reaction to obtain first bleached pulp; and (2) bleaching the first bleached slurry with hydrogen peroxide to obtain second bleached slurry. In the whole bleaching process, toxic and harmful substances are not generated, the chemical oxygen demand and the biological oxygen demand are not increased, the urea is also beneficial to biochemical treatment of sewage, the bleaching performance is excellent, the fiber damage to the cotton pulp is small, and the fiber strength of the produced cotton pulp is high.

Description

Technical Field

[0001] The invention relates to the technical field of cotton pulp production, in particular to a bleaching method and a preparation method of cotton pulp. Background Art

[0002] Cotton pulp, also known as refined cotton pulp, is a kind of high-purity cellulose made from cotton linters through alkaline cooking, rinsing and refining. It is mainly used to manufacture special industrial technical paper, cellulose acetate, nitrocellulose and ether cellulose, and is widely used in food, medicine, toothpaste, daily chemicals, building materials, papermaking, electronics, plastics, aerospace and military industries. At present, the cotton pulp production industry adopts a three-stage bleaching process of chlorine-alkali treatment-hypochlorite bleaching (CEH) for bleaching. However, although the hypochlorite bleaching in this bleaching process can improve the whiteness of the pulp, it will cause a significant decrease in fiber strength. Therefore, it is urgent to provide a cotton pulp production process that has little fiber damage, high fiber strength and can improve whiteness. Summary of the invention

[0003] In view of this, the present invention provides a cotton pulp bleaching method and a cotton pulp preparation method to solve the problem that the three-stage bleaching process used in the cotton pulp production process will produce toxic and harmful substances, increase the difficulty of wastewater treatment, and easily lead to a decrease in fiber strength.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] In one aspect, the present invention provides a method for bleaching cotton pulp, comprising the following steps:

[0006] (1) adjusting the pulp to be bleached to be alkaline, and then adding formamidine sulfinic acid to carry out a first bleaching reaction to obtain a first bleached pulp;

[0007] (2) Bleaching the first bleached pulp with hydrogen peroxide to obtain a second bleached pulp.

[0008] Preferably, in step (1), the pH value of the alkaline condition is 8-9.

[0009] Preferably, the added amount of the formamidine sulfinic acid is 0.2-0.5% of the absolute dry pulp mass.

[0010] Preferably, the bleaching reaction temperature is 60-75°C and the time is 60-90 minutes.

[0011] Preferably, the bleaching with hydrogen peroxide specifically comprises the following steps:

[0012] (2-1) mixing the first bleached pulp with diethylenetriaminepentaacetic acid and hydrogen peroxide to obtain a mixed pulp;

[0013] (2-2) Subjecting the mixed pulp to a second bleaching reaction to obtain a second bleached pulp.

[0014] Preferably, the amount of diethylenetriaminepentaacetic acid added in step (2-1) is 0.17-0.22% of the absolute dry pulp mass.

[0015] Preferably, the amount of hydrogen peroxide added in step (2-1) is 1.5-2.5% of the mass of the absolute dry pulp.

[0016] Preferably, the mixing temperature in step (2-1) is 90-110° C., and the mixing time is 20-30 min.

[0017] Preferably, the temperature of the second bleaching reaction is 90-110° C. and the time is 100-120 min.

[0018] Preferably, the second bleached pulp has a pulp concentration of 1-1.5%.

[0019] Preferably, before the first bleached pulp is bleached with hydrogen peroxide, the first bleached pulp is washed to neutrality.

[0020] On the other hand, the present invention also provides a method for preparing cotton pulp, comprising a bleaching process, wherein the bleaching process adopts the above-mentioned method for bleaching cotton pulp.

[0021] Preferably, the method for preparing cotton pulp comprises the following steps: material selection, cotton opening, impurity removal, cooking, pre-sand removal, pre-pulping, concentration, bleaching, acid treatment, post-sand removal, post-pulping and pulping.

[0022] Preferably, the second bleached pulp is washed to neutrality before the acid treatment step.

[0023] Furthermore, the present invention also provides cotton pulp prepared by any one of the preparation methods described above.

[0024] The present invention provides a method for bleaching cotton pulp and a method for preparing cotton pulp. Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention adopts formamidine sulfinic acid in the process of cotton pulp production technology. Under alkaline conditions, formamidine sulfinic acid can form sulfinic acid with a higher reduction potential. Sulfinic acid can effectively remove chromophore groups in fibers and has high bleaching and decolorization capabilities. In addition, the process of using formamidine sulfinic acid and hydrogen peroxide for bleaching has little damage to the fibers of the cotton pulp, and the produced cotton pulp has high fiber strength.

[0026] In addition, under alkaline conditions, the decomposition products of the formamidine sulfinic acid of the present invention are urea and sulfoxylate, and the decomposition products of hydrogen peroxide are oxygen and water. No toxic or harmful substances are generated during the entire bleaching process, and the chemical oxygen demand and biological oxygen demand are not increased. Urea is also helpful for biochemical treatment of sewage. DETAILED DESCRIPTION

[0027] The present invention will be described below by specific examples, and it will be appreciated by those skilled in the art that the following specific examples are only for illustrative purposes, and do not limit the scope of the present invention in any way. In addition, in the following examples, unless otherwise specified, the reagents and equipment used are all commercially available. If in the following examples, specific treatment conditions and treatment methods are not clearly described, then conditions and methods known in the art can be used to process.

[0028] In one aspect of the present invention, the present invention provides a method for bleaching cotton pulp, comprising the following steps:

[0029] (1) adjusting the pulp to be bleached to alkalinity, and then adding formamidine sulfinic acid (FAS) to carry out a first bleaching reaction to obtain a first bleached pulp;

[0030] (2) Bleaching the first bleached pulp with hydrogen peroxide to obtain a second bleached pulp.

[0031] In some embodiments of the present invention, the pulp to be bleached is adjusted to be alkaline, and then formamidinesulfinic acid is added to carry out a first bleaching reaction to obtain a first bleached pulp.

[0032] Optionally, the pH value of the alkaline condition is 8-9, for example, 8.0, 8.2, 8.4, 8.5, 8.6, 8.8, 9.0, etc. The alkaline condition can be obtained by adding an alkaline solution, and the alkaline solution is mixed with formamidine sulfinic acid for 20-30 minutes and then heated to perform the first bleaching reaction. The alkaline solution can be, for example, sodium hydroxide, potassium hydroxide, etc., which are not particularly limited. Under alkaline conditions, formamidine sulfinic acid will decompose into urea and sodium sulfite / potassium sulfite, will not produce toxic and harmful substances, will not increase chemical oxygen demand and biological oxygen demand, and urea is also helpful for biochemical treatment of sewage; formamidine sulfinic acid reacts with sodium hydroxide / potassium hydroxide to form sulfinic acid with a higher reduction potential, and sulfinic acid can effectively remove chromophores in fibers and has high bleaching and decolorization capabilities.

[0033] Optionally, the addition amount of the formamidine sulfinic acid is 0.2-0.5% of the absolute dry pulp mass, for example, it can be 0.2%, 0.3%, 0.4%, 0.5%, etc.

[0034] Optionally, the temperature of the first bleaching reaction is 60-75°C, and the time is 60-90 min. The temperature of the first bleaching reaction can be, for example, 60°C, 65°C, 70°C, 75°C, etc., and the time of the first bleaching reaction can be, for example, 60 min, 70 min, 80 min, 90 min, etc. The temperature required for the first bleaching reaction can be achieved by introducing steam.

[0035] In some embodiments of the present invention, the bleaching with hydrogen peroxide specifically comprises the following steps:

[0036] (2-1) mixing the first bleached pulp with diethylenetriaminepentaacetic acid and hydrogen peroxide to obtain a mixed pulp;

[0037] (2-2) Subjecting the mixed pulp to a second bleaching reaction to obtain a second bleached pulp.

[0038] In some embodiments of the present invention, the first bleached pulp is mixed with diethylenetriaminepentaacetic acid and hydrogen peroxide to obtain a mixed pulp.

[0039] Optionally, the added amount of diethylenetriaminepentaacetic acid is 0.17-0.22% of the absolute dry pulp mass, for example, it can be 0.17%, 0.18%, 0.19%, 0.20%, 0.21%, 0.22%, etc.

[0040] Optionally, the added amount of hydrogen peroxide is 1.5-2.5% of the mass of the absolute dry pulp, for example, it can be 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, etc.

[0041] Optionally, the mixing temperature is 90-110° C., and the mixing time is 20-30 min. The mixing temperature may be, for example, 90° C., 95° C., 100° C., 105° C., 110° C., etc., and the mixing time may be, for example, 20 min., 22 min., 24 min., 25 min., 26 min., 28 min., 30 min., etc.

[0042] Optionally, before the first bleached pulp is bleached with hydrogen peroxide, the first bleached pulp is washed to neutrality. Specifically, the first bleached pulp can be sent to a vacuum pulp washer and washed with deionized water to neutrality.

[0043] In some embodiments of the present invention, the mixed pulp is subjected to a second bleaching reaction to obtain a second bleached pulp.

[0044] Optionally, the temperature of the second bleaching reaction is 90-110°C, and the time is 100-120 min. The temperature of the second bleaching reaction is 90°C, 95°C, 100°C, 105°C, 110°C, etc., and the time is 100 min, 105 min, 110 min, 115 min, 120 min, etc.

[0045] Optionally, the pulp concentration of the second bleached pulp is 1-1.5%, for example, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%. In the present invention, when the pulp concentration of the second bleached pulp is not within the above range, the above pulp concentration can be achieved by dilution.

[0046] In another aspect of the present invention, the present invention provides a method for preparing cotton pulp, comprising a bleaching process, wherein the bleaching process adopts the above-mentioned method for bleaching cotton pulp. The method for bleaching cotton pulp of the present invention can be combined with a conventional cotton pulp preparation process, that is, the bleaching process of the present invention replaces the bleaching process of the conventional cotton pulp preparation process, and other processes in the cotton pulp preparation process except the bleaching process are not particularly limited.

[0047] In some embodiments of the present invention, the method for preparing cotton pulp includes the following steps: material selection, cotton opening, impurity removal, cooking, pre-sand removal, pre-pulping, concentration, bleaching, acid treatment, post-sand removal, post-pulping and pulping.

[0048] Optionally, before the acid treatment process, the second bleached pulp is washed to neutrality. Specifically, the second bleached pulp can be sent to a vacuum pulp washer and washed with deionized water to neutrality.

[0049] In some embodiments of the present invention, the pre-treatment includes material selection, cotton opening, impurity removal processes, cooking processes, pre-sand removal processes, pre-pulping processes and concentration processes.

[0050] Optionally, the material selection, cotton opening and impurity removal process is as follows: cotton linters are selected, the cotton linters are torn by a cotton opener, loosened and initially impurities are removed by an impurity remover, then the cotton linters are selected and impurities are removed by a cotton squeezer, and finally separated by a cyclone separator to obtain selected cotton linters. The cotton linters are preferably Class III first-grade cotton linters with a maturity of ≥80%.

[0051] Optionally, the cooking process is as follows: passing the selected cotton linters into a steaming ball, adding alkali solution to impregnate the selected cotton linters, and then heating and cooking to obtain an initial pulp. The alkali solution is prepared by mixing sodium hydroxide and sodium sulfate, the mass of the alkali solution is 6-10% of the absolute dry pulp mass in terms of sodium hydroxide, the mass of sodium sulfate is 0.4-0.8% of the absolute dry pulp mass, the alkali solution ratio (i.e. the ratio of selected cotton linters to alkali solution) is 1:3.7-4.2, the alkali solution temperature is controlled at 45-50°C; the cooking temperature is 140-155°C, and the time is 120 minutes.

[0052] Optionally, the pre-sanding process is: passing the initial slurry into a desander for desanding to obtain a first desanded slurry, wherein the concentration of the slurry in the desander is 0.4-0.6%, the pressure of the desander is 0.30-0.32MPa, and the desanding rate is 10-30min / t.

[0053] Optionally, the pre-slurrying process is: passing the first desanded slurry into a large-tapered pulping machine for pulping to obtain a pulped slurry, wherein the pulping current is 180-200A, the pulping rate is 10-30min / t, and the concentration of the slurry in the large-tapered pulping machine is 1.0-1.8%.

[0054] Optionally, the concentration process is: passing the pulped pulp into a manometric rotary screen thickener for concentration to obtain concentrated pulp, and passing the concentrated pulp into a first bleaching tower for bleaching treatment. The concentration of the pulp in the manometric rotary screen thickener is 10-12%.

[0055] In some embodiments of the present invention, the post-treatment includes an acid treatment process, a post-sand removal process, a post-pulping process and a pulping process.

[0056] Optionally, the acid treatment process includes: passing the second bleached pulp into an acid treatment tank, adding an acid solution for acid treatment, and then washing with water to obtain an acid-treated pulp. The acid solution can be hydrochloric acid, the amount of hydrochloric acid added is 2-2.5% of the mass of the absolute dry pulp, the acid treatment time is 20-40 minutes, and the washing time is 2-3 hours.

[0057] Optionally, the post-sand removal process includes: passing the acid-treated slurry into a desander for desanding to obtain a second desanded slurry, wherein the concentration of the slurry in the desander is 0.5-0.7%, the pressure of the desander is ≥0.3 MPa, and the desanding rate is 10-30 min / t.

[0058] Optionally, the post-pulping process includes: passing the second desanded slurry into a large-tapered pulping machine for pulping to obtain refined slurry, wherein the pulping current is 160-180A, the pulping rate is 10-30min / t, and the concentration of the slurry in the large-tapered pulping machine is 2.5-2.7%.

[0059] Optionally, the pulping process includes: using a pulping machine to make the refined pulp into cotton pulp.

[0060] In some embodiments of the present invention, cotton pulp is sequentially dehydrated and dried through a paper machine's four-wire and a drying cylinder to obtain paper. The concentration of the pulp in the paper machine's four-wire is 8-12 g / L, and the pressure of the drying cylinder is ≤0.20 MPa. The paper prepared using the cotton pulp in the present invention can be used as special paper, and in this embodiment, the performance of the cotton pulp is indirectly characterized by the performance of the paper.

[0061] The technical solutions in the present invention will be described clearly and completely below in conjunction with specific embodiments. The embodiments of the present application are only used as examples, and all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0062] Example 1

[0063] In an embodiment of the present invention, a cotton pulp production process comprises the following specific steps:

[0064] (1) Material selection, cotton opening and impurity removal process: Class III first-class cotton linters with a maturity of ≥80% are selected, and the cotton linters are torn by a cotton opener, loosened and initially impurity-removed by an impurity remover, and then transferred to a cotton squeezer for fine impurity removal, and finally separated by a cyclone separator to obtain fine cotton linters.

[0065] (2) Cooking process: Selected cotton linters and alkali solution are passed into a steaming ball, and the selected cotton linters are fully immersed in the alkali solution by cold transfer, and then the temperature is raised to 150°C and cooked for 120 minutes to obtain an initial pulp; wherein the alkali solution is prepared by mixing sodium hydroxide and sodium sulfate at 45°C, and the alkali solution is 8% of the absolute dry pulp mass in terms of sodium hydroxide, and the sodium sulfate is 0.6% of the absolute dry pulp mass.

[0066] (3) Pre-sand removal process: the initial slurry is passed into a desander for desanding to obtain a first desanded slurry; wherein the concentration of the slurry in the desander is 0.4%, the pressure of the desander is 0.30 MPa, and the desanding rate is 30 min / t.

[0067] (4) Pre-pulping process: the first desanded mortar is passed into the first large-tapered pulping machine for pulping to obtain a pulped slurry; wherein the pulping current is 180A, the pulping rate is 30min / t, and the concentration of the slurry in the first large-tapered pulping machine is 1.0%.

[0068] (5) Concentration process: the pulp after beating is passed into a side pressure rotary screen concentrator for concentration to obtain a concentrated pulp; wherein the concentration of the pulp in the pressure rotary screen concentrator is 10%.

[0069] (6) FAS bleaching process: The concentrated pulp is passed into the first bleaching tower, NaOH is added to adjust the pH value to 8-9, FAS is added and mixed for 20 minutes, and then steam is introduced. The temperature is controlled at 65°C for bleaching reaction for 60 minutes to obtain the first bleached pulp; the amount of FAS added is 0.2% of the mass of the absolute dry pulp.

[0070] (7) Hydrogen peroxide bleaching process: the first bleached pulp is passed into a vacuum pulp washer and washed with deionized water until it becomes neutral, and then passed into a medium-consistency mixer, steam is passed into the medium-consistency mixer, the temperature is controlled at 90° C., diethylenetriaminepentaacetic acid and hydrogen peroxide are added and mixed for 30 minutes to obtain a mixed pulp; the amount of diethylenetriaminepentaacetic acid added is 0.17% of the mass of the absolute dry pulp, and the amount of hydrogen peroxide added is 2.5% of the mass of the absolute dry pulp;

[0071] The mixed pulp was introduced into a second bleaching tower, and a bleaching reaction was carried out at 110° C. for 120 minutes, and then diluted with deionized water to obtain a second bleached pulp with a pulp concentration of 1.5%.

[0072] (8) Acid treatment process: The second bleached pulp is passed into a vacuum pulp washer and washed with deionized water until it becomes neutral. Then, it is passed into an acid treatment tank and treated with 350 g / L hydrochloric acid for 30 min. The amount of hydrochloric acid added is 2% of the mass of the absolute dry pulp. Then, it is washed with deionized water for 2 hours to obtain the acid-treated pulp.

[0073] (9) Post-sand removal process: the acid-treated slurry is passed into a desander for desanding to obtain a second desanded slurry; wherein the concentration of the slurry in the desander is 0.5%, the pressure of the desander is 0.3 MPa, and the desanding rate is 30 min / t.

[0074] (10) Post-pulping process: the second desanded slurry is passed into a second large-taper refiner for pulping to obtain a refined slurry; wherein the pulping current is 160A, the pulping rate is 30min / t, and the concentration of the slurry in the second large-taper refiner is 2.5%.

[0075] (11) Pulping process: The refined pulp is passed through a pulping machine to obtain cotton pulp.

[0076] The cotton pulp was sequentially dehydrated by a paper machine's four-wire and dried by a drying cylinder. The pulp concentration in the paper machine's four-wire was 8 g / L, and the pressure of the drying cylinder was ≤0.20 MPa. Paper was obtained. The performance of the paper and the amount of COD generated during the cotton pulp production process were tested. The results are shown in Table 1.

[0077] Example 2

[0078] This embodiment is basically the same as Embodiment 1, with the only difference being that the amount of FAS added in step (6) is 0.3% of the mass of the absolute dry pulp.

[0079] Example 3

[0080] This embodiment is basically the same as Embodiment 1, with the only difference being that the amount of FAS added in step (6) is 0.4% of the mass of the absolute dry pulp.

[0081] Example 4

[0082] This embodiment is basically the same as Embodiment 1, with the only difference being that the amount of FAS added in step (6) is 0.5% of the mass of the absolute dry pulp.

[0083] Example 6

[0084] This embodiment is basically the same as embodiment 1, the only difference being that the temperature of the bleaching reaction in step (6) is 60°C.

[0085] Example 7

[0086] This embodiment is basically the same as embodiment 1, the only difference being that the temperature of the bleaching reaction in step (6) is 75°C.

[0087] Example 8

[0088] This embodiment is basically the same as embodiment 1, the only difference being that the bleaching reaction time in step (6) is 90 minutes.

[0089] Comparative Example 1

[0090] This comparative example is basically the same as Example 1, except that the bleaching process of steps (6)-(7) is replaced by a three-stage bleaching process:

[0091] Chlorination process: passing the concentrated slurry into a chlorination tower, adjusting the slurry concentration to 5%, passing chlorine gas for chlorination, making the chlorine content of the slurry 0.10g / L, the chlorination time is 30min, and obtaining the chlorinated slurry;

[0092] Alkali extraction process: the chlorinated slurry is passed into an alkalization tower, the pH value is adjusted to 10-11, and the reaction is carried out for 15 minutes to obtain the slurry after alkali extraction;

[0093] Sodium hypochlorite bleaching process: the pulp after alkali extraction is passed into the bleaching tank, and a sodium hypochlorite bleaching liquid with a concentration of 300g / L is added. 100L of sodium hypochlorite bleaching liquid is added per ton of pulp. The bleaching time is 30min to obtain bleached pulp.

[0094] Comparative Example 2

[0095] This comparative example is basically the same as Example 1, except that the FAS bleaching process in step (6) is omitted.

[0096] Comparative Example 3

[0097] This comparative example is substantially the same as Example 1, except that the hydrogen peroxide bleaching process in step (7) is omitted.

[0098] Comparative Example 4

[0099] This comparative example is basically the same as Example 1, with the only difference being that the amount of FAS added in step (6) is 0.1% of the mass of the absolute dry pulp.

[0100] Comparative Example 5

[0101] This comparative example is basically the same as Example 1, with the only difference being that the amount of FAS added in step (6) is 0.6% of the mass of the absolute dry pulp.

[0102] Table 1

[0103]

[0104]

[0105] It can be seen from Examples 1-4 and Comparative Example 1 in Table 1 that, compared with the traditional three-stage bleaching process, the FAS-H2O2 bleaching process of the present invention can effectively improve the whiteness of cotton pulp, improve the polymerization degree, tensile strength and tear resistance of the fiber, and can effectively reduce the amount of COD generated in the cotton pulp production process and reduce the difficulty of wastewater treatment.

[0106] It can be seen from Examples 1-4 and Comparative Examples 2-3 in Table 1 that the synergistic effect of the FAS bleaching process and the hydrogen peroxide bleaching process can achieve a better bleaching effect on the cotton pulp, with lower dust content, higher cleanliness, and less damage to the fiber.

[0107] It can be seen from Examples 1-4 and Comparative Examples 4-5 in Table 1 that if the amount of FAS added is low, the whiteness of the cotton pulp is poor and the dust content is high, and if the amount of FAS added is too high, the whiteness of the cotton pulp will not be further improved. Therefore, the present invention limits the amount of FAS added to 0.2-0.5% of the mass of the absolute dry pulp.

[0108] Comparative Example 6

[0109] This comparative example is basically the same as Example 1, except that the temperature of the bleaching reaction in step (6) is 50°C.

[0110] Comparative Example 7

[0111] This comparative example is basically the same as Example 1, except that the bleaching reaction time in step (6) is 50 minutes.

[0112] Table 2

[0113]

[0114] It can be seen from Table 2 that if the bleaching temperature in the FAS bleaching process is too low or the bleaching time is too short, the whiteness of the cotton pulp will decrease and the dust content will increase.

[0115] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for bleaching cotton pulp, characterized in that: The following steps are involved: (1) adjusting the pulp to be bleached to be alkaline, and then adding formamidine sulfinic acid to carry out a first bleaching reaction to obtain a first bleached pulp; (2) Bleaching the first bleached pulp with hydrogen peroxide to obtain a second bleached pulp.

2. The method for bleaching cotton pulp according to claim 1, characterized in that: In step (1), the pH value of the alkaline condition is 8-9; The added amount of the formamidine sulfinic acid is 0.2-0.5% of the absolute dry pulp mass.

3. The method for bleaching cotton pulp according to claim 1, characterized in that: The bleaching reaction temperature is 60-75°C and the time is 60-90 minutes.

4. The method for bleaching cotton pulp according to claim 1, characterized in that: The bleaching with hydrogen peroxide specifically comprises the following steps: (2-1) mixing the first bleached pulp with diethylenetriaminepentaacetic acid and hydrogen peroxide to obtain a mixed pulp; (2-2) Subjecting the mixed pulp to a second bleaching reaction to obtain a second bleached pulp.

5. The method for bleaching cotton pulp according to claim 4, characterized in that: In step (2-1), the amount of diethylenetriaminepentaacetic acid added is 0.17-0.22% of the absolute dry pulp mass; The amount of hydrogen peroxide added is 1.5-2.5% of the absolute dry pulp mass; The mixing temperature is 90-110° C., and the mixing time is 20-30 min.

6. The method for bleaching cotton pulp according to claim 4, characterized in that: The temperature of the second bleaching reaction is 90-110°C and the time is 100-120min; The second bleached pulp has a pulp concentration of 1-1.5%.

7. The method for bleaching cotton pulp according to claim 1, characterized in that: Before the first bleached pulp is bleached with hydrogen peroxide, the first bleached pulp is washed to neutrality.

8. A method for preparing cotton pulp, characterized in that: The method comprises a bleaching process, wherein the bleaching process adopts the cotton pulp bleaching method according to any one of claims 1 to 7.

9. The method for preparing cotton pulp according to claim 8, characterized in that: It includes the following steps: material selection, cotton opening, impurity removal, steaming, pre-sand removal, pre-pulping, concentration, bleaching, acid treatment, post-sand removal, post-pulping and papermaking; Prior to the acid treatment step, the second bleached pulp is washed to neutrality.

10. Cotton pulp prepared by the preparation method according to any one of claims 8 to 9.

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