Sugarcane syrup suitable for lyocell fiber production and preparation method and system thereof

Abstract

The invention discloses sugarcane syrup suitable for lyocell fiber production and a preparation method and system of the sugarcane syrup, and belongs to the technical field of lyocell fiber production. According to the present invention, the sugarcane pulp for lyocell fiber production is prepared sequentially through the first high-concentration alkali treatment, the second low-concentration alkali treatment, the bleaching, the acid washing and the drying, and the processes are matched for use, such that the conditions are milder compared with the traditional pulping and papermaking cooking process and the oxygen delignification, the equipment requirement is low, the production energy consumption is low, and the operation is safe; according to the present invention, the raw material does not need to be crushed, the index of the finally prepared raw material can meet the Lyocell production requirement, the operation process is simple, the industrial application prospect is provided, the production system matched with the method is provided, and the industrial and continuous production of the sugarcane syrup suitable for Lyocell fiber production is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of lyocell fiber production, and in particular to sugarcane pulp suitable for lyocell fiber production and a preparation method and system thereof. Background Art

[0002] Lyocell fiber is a new type of regenerated cellulose fiber, hailed as the green fiber of the 21st century. It is produced through a dry-jet wet spinning process, using N-methylmorpholine-N-oxide (NMMO) as a solvent to directly dissolve pulp raw materials without chemical reaction to form a spinning solution. Lyocell fiber is not only soft, silky, breathable, and lustrous, but also possesses superior mechanical properties and hygroscopicity, making it widely used in many textile fields. Currently, Lyocell fiber production is primarily based on wood, most of which is imported wood pulp. To address the problem of reliance on imported wood pulp, research into alternative raw materials for Lyocell fiber production has begun in recent years.

[0003] Bagasse, the primary byproduct of sugarcane extraction, is a typical agricultural and forestry waste. Currently, it's primarily used as boiler fuel and a raw material for papermaking, resulting in low added value. However, bagasse is rich in cellulose, with a cellulose content of approximately 40-50%, making it a viable raw material for producing lyocell fibers. Currently, pulping technologies using bagasse as a raw material are primarily focused on producing paper pulp, and relatively few technologies are capable of using bagasse for lyocell fiber production. Furthermore, pulp production using bagasse generally relies on the same cooking process used in pulping and papermaking, requiring high temperatures and pressures. This results in high energy consumption and poses operational safety risks.

[0004] For example, Chinese patent application CN112647340A discloses a process for producing bagasse pulp. After storage and fermentation, the bagasse is cleaned and soaked, then fed into a high-consistency refiner for debonding and cutting. After washing, the pulp is separated, saponified, and dehydrated to produce a coarse pulp product. However, the bagasse pulp produced by this method can only meet the needs of paper pulp production, not lyocell fiber production.

[0005] For example, Chinese patent application CN119553529A discloses a method for oxygen delignification pulping using bagasse as raw material, a fine pulp, and its application. This method involves steaming the bagasse, followed by washing and screening to produce a fine pulp. This method uses sodium carbonate as the primary raw material, supplemented by sodium hydroxide, which can mitigate equipment corrosion to a certain extent and avoid hazardous solid waste pollution. However, the steaming process requires high temperature and pressure, resulting in high energy consumption, heavy equipment burden, and certain safety risks. Furthermore, the pulp produced using this method cannot meet the production requirements of lyocell fibers.

[0006] For example, Chinese patent application CN106868907A discloses a high-whiteness bagasse pulp and its environmentally friendly pulping process. The process involves pre-hydrolyzing and extracting bagasse, followed by steaming and alkali treatment to produce a coarse pulp. The coarse pulp is then diluted and repeatedly washed and purified to produce high-whiteness bagasse pulp. This method, which also uses steaming, consumes a lot of energy and places a heavy burden on the equipment. Furthermore, the resulting pulp only meets the standards for paper pulp production and cannot meet the requirements for lyocell fiber production.

[0007] For example, Chinese patent application CN117684281A discloses a method for producing lyocell fiber using sugarcane bagasse as a raw material. The sugarcane bagasse is pulverized, treated with a first solution and a second solution, and then directly dissolved in an aqueous NMMO solution to produce a spinning solution. The solution is then spun to produce lyocell fiber. However, this method requires pulverizing the bagasse into powder, which can easily cause dust pollution during actual production. Furthermore, the powdered bagasse material is not conducive to material output during the pulping process, which can easily lead to material loss. Furthermore, the patent application does not disclose the specific indicators of the resulting sugarcane pulp, making it impossible to determine whether the sugarcane pulp produced by this patented method meets the requirements for lyocell fiber production. The examples in this patent indicate that the concentration of the prepared sugarcane pulp in the lyocell fiber spinning solution is only 6-10%, which does not meet current lyocell production requirements (currently, the concentration of lyocell spinning solutions is generally above 10 wt%). This results in low production efficiency and high costs. Furthermore, this method also requires bleaching the fibers after spinning, which can easily damage the fibers.

[0008] Therefore, developing a high-quality sugarcane pulp suitable for the production of lyocell fiber, while solving the high energy consumption and safety issues caused by the traditional high-temperature cooking process of sugarcane bagasse pulp, is a key technical problem that urgently needs to be broken through. Summary of the Invention

[0009] The object of the present invention is to provide a sugarcane pulp suitable for lyocell fiber production and a preparation method thereof. The sugarcane pulp for lyocell fiber production is obtained by subjecting bagasse, a by-product obtained after sugar extraction, to two alkali treatment steps, and then subjecting it to subsequent bleaching, acid washing and drying treatments. The combined use of these steps is more gentle than the cooking process and oxygen delignification conditions of traditional pulping and papermaking, with lower equipment requirements, lower production energy consumption, and safer operation. The raw material indicators finally obtained can meet the production requirements of lyocell, the operation process is also simpler, and the pulp has great prospects for industrial application.

[0010] The present invention is achieved through the following technical solutions: A method for preparing sugarcane pulp suitable for lyocell fiber production, using sugarcane bagasse as raw material, sequentially undergoing a first alkali treatment, a second alkali treatment, bleaching, acid washing, and drying to obtain the sugarcane pulp suitable for lyocell fiber production. The first alkali treatment is to add sugarcane bagasse to the first alkali solution, then add H2O2, control the mass ratio of sugarcane bagasse, alkali and H2O2 to be 5-20:5-15:0.01-0.1, stir in a closed manner at 60-80℃ for 30-90 minutes, and then wash and dehydrate to obtain the alkalized sugarcane bagasse after the first alkali treatment; The second alkali treatment is to add the alkalized sugarcane bagasse after the first alkali treatment into the second alkali solution, and then add H2O2, and control the mass ratio of the alkalized sugarcane bagasse after the first alkali treatment, alkali and H2O2 to be 5~20:0.05~0.5:0.01~0.1, and stir in a closed manner at 60~80℃ for 60~120min. After washing and dehydration, the alkalized sugarcane bagasse after the second alkali treatment is obtained, and then bleaching is carried out.

[0011] Furthermore, the alkali used in the first alkali treatment and the second alkali treatment is NaOH or KOH.

[0012] Further, bleaching comprises the following steps: A. Add chlorine dioxide solution and hydrochloric acid to the alkalized bagasse after the second alkali treatment, controlling the mass ratio of the alkalized bagasse after the second alkali treatment, chlorine dioxide, and hydrochloric acid to be 5-20:0.01-0.2:0.01-0.05, and then stir in a closed manner at 60-75°C for 30-90 minutes, and then wash and dehydrate to obtain a first-stage bleached bagasse; B. Adding a first-stage bleached bagasse to an alkaline solution and then adding H2O2, controlling the mass ratio of the first-stage bleached bagasse, alkali, and H2O2 to be 5-20:0.01-0.1:0.01-0.05, followed by stirring in a closed container at 60-75°C for 30-90 minutes, followed by washing and dehydration to obtain the alkaline-treated bagasse; C. Add alkali-treated bagasse to H2O2, then add NaOH, and control the mass ratio of alkali-treated bagasse, H2O2 and NaOH to 5~20:0.01~0.08:0.01~0.08; then stir in a closed manner at 70~80℃ for 60~120 min, wash with water and then centrifuge to dehydrate to obtain hydrogen peroxide-bleached bagasse.

[0013] Furthermore, during bleaching, the alkali used in step B is NaOH or KOH.

[0014] Furthermore, the acid washing is performed by adding the bleached bagasse into an acid solution, and then adding a chelating agent, controlling the mass ratio of the bleached bagasse, acid and chelating agent to be 5~20:0.01~0.1:0.001~0.05, and then stirring in a closed manner at 60~80℃ for 30~90 minutes, and then washing with water and centrifugal dehydration to obtain the acid washed bagasse.

[0015] Furthermore, during pickling, the acid used is formic acid or acetic acid; and the complexing agent used is sodium hexametaphosphate or EDTA.

[0016] Furthermore, the drying is carried out by hot air drying at 60-80°C.

[0017] The sugarcane pulp suitable for lyocell fiber production prepared by the preparation method described above is added to a high-concentration NMMO aqueous solution at 76-84°C and fully swelled under stirring to obtain a cellulose suspension, wherein the NMMO concentration in the cellulose suspension is 75-80 wt%, and the cellulose concentration in the cellulose suspension is 10.2-12 wt%. The fully swollen cellulose suspension is then transported to a thin film evaporator and dissolved under high-temperature vacuum conditions to obtain a spinning solution for lyocell fiber, wherein the cellulose concentration in the spinning solution is 12-13.5 wt%.

[0018] The sugarcane pulp suitable for lyocell fiber production prepared by the above-mentioned preparation method is characterized in that the sugarcane pulp meets the following performance index system: Degree of polymerization: 569~677, methyl cellulose content: ≥92.1%, whiteness: ≥84%, ash content: ≤0.09%, iron content: ≤5ppm, copper content: ≤0.88 ppm, calcium content: ≤67 ppm, magnesium content: ≤74 ppm.

[0019] A production system suitable for the above-mentioned method of preparing sugarcane pulp comprises a high-concentration alkali treatment unit, a low-concentration alkali treatment unit, a chlorine dioxide bleaching unit, an alkali extraction unit, a hydrogen peroxide bleaching unit, an acid washing unit and a drying machine connected in sequence through pipelines. The high-concentration alkali treatment unit includes a spray device, a steaming ball I for holding high-concentration alkali solution, a pulp storage tank I, a pulp pump, a pulp refiner and a pulp washer, which are connected in sequence through pipelines; The low-concentration alkali treatment unit includes a screw conveyor I, a steam ball II for holding low-concentration alkali solution, a pulp storage tank II, a pulp pump, a desander and a pulp washer, which are connected in sequence through pipelines; The chlorine dioxide bleaching unit includes a screw conveyor II, a pump riser, a screw pump, an upflow bleaching tower, a downflow bleaching tower, a pulp pump and a pulp washer connected in sequence through pipelines; The alkali extraction unit includes an alkali extraction stirring tank, a pulp pump and a pulp washer connected in sequence through pipelines; The hydrogen peroxide bleaching unit comprises a mixer, a screw pump, an upflow bleaching tower, a downflow bleaching tower, and a pulp washer which are sequentially connected through pipelines; The pickling unit comprises a pickling stirring tank, a pulp pump and a pulp washer which are sequentially connected through pipelines.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. In the present invention, high-concentration alkali treatment and low-concentration alkali treatment are used to replace the traditional pulping cooking and oxygen delignification processes, which makes the treatment process simpler, reduces equipment energy consumption, and improves operation safety.

[0021] 2. In the present invention, sugarcane pulp that meets the production requirements of lyocell can be obtained after processing sugarcane bagasse, and the lyocell staple fibers finally obtained have excellent performance indicators.

[0022] 3. The present invention can also realize continuous feeding and discharging, with less material loss and lower overall energy consumption, and has great prospects for industrial application.

[0023] Fourth, in the present invention, there is no need to crush the raw material - sugarcane bagasse. Through a specific process, the whiteness and other index parameters obtained meet the requirements of the sugarcane pulp raw material for lyocell fiber production. The operation is simpler and easy to promote to industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a flow chart of the present invention.

[0025] Figure 2 Schematic diagram of the system suitable for sugarcane pulp for lyocell fiber production.

[0026] Figure 3 This is a real photo of the sugarcane bagasse raw material.

[0027] Figure 4 This is a photo of the sugarcane pulp obtained in Example 1.

[0028] Figure 5 This is a photo of the lyocell staple fiber prepared in Example 1.

[0029] Figure 6 This is a microscope image of a solution formed by dissolving the sugarcane pulp prepared in Example 1 in an NMMO aqueous solution, with a cellulose concentration of 12 wt %.

[0030] Figure 7 This is a photo of the sugarcane pulp prepared in Comparative Example 5.

[0031] Figure 8 This is a microscope image of a solution formed by dissolving the sugarcane pulp prepared in Comparative Example 5 in an NMMO aqueous solution, with a cellulose concentration of 12 wt%.

[0032] 1. Fan; 2. Cyclone separator; 3. Spraying device; 4. Deflector; 5. Steaming ball I; 6. Stock storage tank I; 7. Slurry pump I; 8. Double disc refiner; 9. Double roller pulp washer I; 10. Screw conveyor I; 11. Steaming ball II; 12. Stock storage tank II; 13. Slurry pump II; 14. Desander; 15. Double roller pulp washer II; 16. Screw conveyor II; 17. Pump riser; 18. Screw pump I; 19. Upflow bleaching tower I; 20. Downflow bleaching tower I; 21. Slurry pump III; 22. , double-roller pulp washer III; 23. Alkali extraction stirring tank; 24. Pulp pump IV; 25. Double-roller pulp washer IV; 26. Mixer; 27. Screw pump II; 28. Upflow bleaching tower II; 29. Downflow bleaching tower II; 30. Double-roller pulp washer V; 31. Pickling stirring tank; 32. Pulp pump V; 33. Double-roller pulp washer VI; 34. Radio frequency dryer; 35. High-consistency pulper; 36. Screw pump III; 37. Thin film evaporator; 38. High-pressure pump; 39. Filter; 40. Rubber pump; 41. Spinning machine. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

[0034] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the claimed invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs.

[0035] The present invention aims to solve the drawbacks of the prior art of using cooking or oxygen delignification processes to remove lignin and hemicellulose from fiber raw materials to prepare lyocell fiber raw materials. The present invention proposes a sugarcane pulp prepared from sugarcane bagasse through two alkali treatment steps, bleaching, acid washing, and drying. The sugarcane pulp meets the following performance indicators: degree of polymerization: 557-677, methyl fiber content: ≥92.1%, whiteness: ≥84%, ash content: ≤0.09%, iron content: ≤5ppm, copper content: ≤0.88ppm, calcium content: ≤67ppm, and magnesium content: ≤74ppm. Therefore, the pulp can be used as a raw material for preparing lyocell fiber.

[0036] Specifically, the present invention relates to a process for preparing sugarcane pulp (see Figure 1 ) can be summarized as follows: (1) First alkali treatment Bagasse, a by-product of sugarcane sugar extraction, is used as raw material and added to a reaction device (such as a steam bulb with a stirring mechanism) containing an alkaline solution. A certain amount of H2O2 is then added, and the mass ratio of bagasse, alkali (NaOH or KOH) and H2O2 is controlled to be 5~20:5~15:0.01~0.1. The product is then stirred in a closed manner at 60~80℃ for 30~90 min, washed with water and then centrifuged for dehydration to obtain the alkalized bagasse after the first alkali treatment.

[0037] In the present invention, the purpose of the first alkali treatment is to remove most of the lignin and hemicellulose in the sugarcane bagasse raw material. H2O2 is added during the alkali treatment of the sugarcane bagasse, mainly to allow the H2O2 to decompose and provide sufficient oxygen for the alkali treatment process, because oxygen can effectively degrade lignin under alkaline conditions and dissolve the degraded lignin in the alkaline solution. At the same time, H2O2 can also play a bleaching role, thereby improving the whiteness of the sugarcane bagasse.

[0038] In this step, by rationally controlling the mass ratio of bagasse, alkali, and H2O2, the removal efficiency of hemicellulose and lignin can be effectively guaranteed while avoiding excessive degradation. If the bagasse concentration is too high, stirring will be difficult, resulting in uneven stirring. If the bagasse concentration is too low, it will lead to low efficiency and increased costs. If the alkali concentration is too low, the removal of hemicellulose and lignin in the bagasse raw material will be insufficient. If the alkali concentration is too high, the cellulose in the bagasse raw material will be significantly degraded, which can easily lead to excessive degradation. If the H2O2 concentration is too low, the oxygen supply is insufficient, resulting in an inability to effectively remove the lignin in the bagasse raw material. If the H2O2 concentration is too high, the cellulose in the bagasse raw material will be significantly degraded, resulting in a low degree of polymerization of the final raw material, which cannot be used for lyocell fiber production.

[0039] This step further rationally controls the alkali treatment temperature and the alkali treatment stirring time, and can control the alkali treatment temperature below 80°C, reducing the energy consumption of the equipment, while the operation is simple. In actual operation, if the temperature is too low, the alkali treatment process will have a poor effect on the removal of lignin in the bagasse raw material; if the temperature is too high, it will lead to increased energy consumption of the equipment, and there are safety hazards in manual operation. If the alkali treatment time is too short, the hemicellulose and lignin in the bagasse raw material will not be fully removed. If the alkali treatment time is too long, the cellulose in the bagasse raw material will be significantly degraded, resulting in a low degree of polymerization of the final raw material, which cannot be used for lyocell fiber production. As for the stirring time, it is usually determined by the concentration of alkali and H2O2. The higher the concentration of alkali and H2O2, the shorter the stirring time. Conversely, the stirring time increases.

[0040] (2) Second alkali treatment The alkalized bagasse after the first alkali treatment is added back into a stirring device containing an alkali solution, and a certain amount of H2O2 is added to control the mass ratio of the alkalized bagasse after the first alkali treatment, alkali (NaOH or KOH) and H2O2 to be 5~20:0.05~0.5:0.01~0.1, and then stirred in a closed manner at 60~80℃ for 60~120min. After washing with water and then centrifugal dehydration, the alkalized bagasse after the second alkali treatment is obtained.

[0041] In the present invention, the purpose of the second alkali treatment is to play an extraction role, dissolve the residual lignin and hemicellulose in the bagasse, and reduce the amount of various chemicals used in the subsequent bleaching.

[0042] (3) Bleaching The alkalized bagasse after the second alkali treatment is bleached, then washed and centrifuged to obtain the bleached bagasse raw material. The bleaching process includes the following three steps: Step 1: Chlorine dioxide bleaching The alkalized bagasse after the second alkali treatment is added to a chlorine dioxide solution, and then hydrochloric acid is added, and the mass ratio of the alkalized bagasse after the second alkali treatment, chlorine dioxide and hydrochloric acid is controlled to be 5-20:0.01-0.2:0.01-0.05, and then the mixture is stirred in a closed manner at 60-75°C for 30-90 minutes, and then washed with water and centrifuged for dehydration to obtain chlorine dioxide bleached bagasse.

[0043] Step 2: Alkaline extraction A first-stage bleached bagasse is added to an alkaline solution, and then H2O2 is added. The mass ratio of the first-stage bleached bagasse, alkali and H2O2 is controlled to be 5-20:0.01-0.1:0.01-0.05. The bagasse is then stirred in a closed manner at 60-75°C for 30-90 min, washed with water and then centrifuged for dehydration to obtain the alkali-extracted bagasse.

[0044] Step 3: Hydrogen peroxide bleaching The sugarcane bagasse after alkali extraction is added to a chlorine dioxide solution, and then NaOH is added, and the mass ratio of the alkali-treated sugarcane bagasse, chlorine dioxide and NaOH is controlled to be 5-20:0.01-0.08:0.01-0.08, and then the mixture is stirred in a closed manner at 70-80°C for 60-120 minutes, and then washed with water and centrifuged for dehydration to obtain hydrogen peroxide-bleached sugarcane bagasse.

[0045] (4) Pickling The bleached bagasse is added to a stirring device filled with an acid solution, and then a certain amount of complexing agent is added to control the mass ratio of the bleached bagasse, acid and complexing agent to be 5-20:0.01-0.1:0.001-0.05. Then, the bagasse is stirred in a closed container at 60-80°C for 30-90 minutes, and then washed with water and centrifuged for dehydration to obtain acid-washed bagasse.

[0046] In the present invention, weak acid is used in the pickling process to avoid significant degradation of cellulose in the bagasse raw material during the pickling process. The addition of the chelating agent can effectively remove metal ions, so that the final sugarcane pulp raw material meets the production requirements of lyocell fiber.

[0047] Optionally, the acid in the acid solution is formic acid or acetic acid. The addition of acid can effectively remove ash from the pulp. Using a weak acid can prevent significant degradation of cellulose in the bagasse raw material during the acid washing process. If the acid concentration is too low, the ash removal effect from the pulp is poor; if the acid concentration is too high, significant degradation of the cellulose can occur.

[0048] Optionally, the complexing agent is sodium hexametaphosphate or EDTA. The addition of a complexing agent can effectively remove metal ions. However, the metal ion content in the pulp used in Lyocell fiber production cannot be too high, as this can easily cause solvent decomposition and lead to explosions. Therefore, strict control of metal ion content during the production process is necessary. If the complexing agent concentration is too low, the removal of metal ions from the pulp will be poor; if the complexing agent concentration is too high, wastewater treatment will be difficult and costs will increase.

[0049] In this step, by properly controlling the pickling temperature and stirring time during the pickling process, equipment energy consumption can be effectively controlled, while ensuring that the bagasse raw material meets the production requirements of lyocell fiber. If the temperature is too low, the acidification effect will be poor, while if the temperature is too high, the equipment operating energy consumption will increase significantly. If the stirring time is too short, the ash and metal ion removal in the pulp will not be sufficient to meet the requirements of lyocell fiber production. If the stirring time is too long, the equipment operating energy consumption will increase, leading to higher costs.

[0050] (5) Drying The acid-washed bagasse raw material is dried by hot air to obtain the bagasse raw material that can be used for the production of lyocell fiber.

[0051] The drying temperature is preferably controlled at 60-80°C.

[0052] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

[0053] Example 1 To facilitate public understanding of the present solution, this embodiment uses a relatively preferred system of sugarcane pulp suitable for lyocell fiber production as an example, and further illustrates the present solution in combination with specific process conditions.

[0054] In this embodiment, the system reference for sugarcane pulp used in lyocell fiber production is Figure 2, including a high-concentration alkali treatment unit, a low-concentration alkali treatment unit, a chlorine dioxide bleaching unit, an alkali extraction unit, a hydrogen peroxide bleaching unit, an acid washing unit and a radio frequency drying machine 34, which are connected in sequence through pipelines. The high-concentration alkali treatment unit includes a spray device 3, a steaming ball Ⅰ5 for holding a high-concentration alkali solution, a pulp storage tank Ⅰ6, a pulp pump Ⅰ7, a double-disc refiner 8 and a double-roller pulp washer Ⅰ9, which are connected in sequence through pipelines. Furthermore, the front end of the spray device 3 is connected to a cyclone separator 2 and a fan 1 through a pipeline. The cyclone separator 2 can be used to further separate the juice in the bagasse to obtain the bagasse raw material. The high-concentration alkali treatment unit adds water, high-concentration alkali solution and H2O2 to the steaming ball Ⅰ5 through the spray device 3 and the deflector 4. The low-concentration alkali treatment unit includes a screw conveyor I 10, a steaming ball II 11 for holding low-concentration alkali solution, a pulp storage tank II 12, a pulp pump II 13, a desander 14 and a double-roller pulp washer II 15, which are connected in sequence through pipelines. The screw conveyor I 10 is provided with an inlet for adding water, low-concentration alkali solution and H2O2; The chlorine dioxide bleaching unit includes a screw conveyor II 16, a pump riser 17, a screw pump I 18, an upflow bleaching tower I 18, a downflow bleaching tower I 20, a pulp pump III 21 and a double-roll pulp washer III 22 connected in sequence through pipelines; The alkali extraction unit includes an alkali extraction stirring tank 23, a pulp pump IV 24 and a double-roll pulp washer IV 25 connected in sequence through pipelines; The hydrogen peroxide bleaching unit includes a mixer 26, a screw pump II 27, an upflow bleaching tower II 28, a downflow bleaching tower II 29, and a double-roller pulp washer V 30 connected in sequence through pipelines; The pickling unit includes a pickling stirring tank 31, a pulp pump V 32 and a double-roll pulp washer VI 33 which are sequentially connected through pipelines.

[0055] Preparation of sugarcane pulp suitable for lyocell fiber production: 1. The first alkali treatment: The raw material is bagasse, a by-product of sugarcane sugar extraction. Figure 3 , added to the evaporation ball Ⅰ5 filled with 8wt% NaOH solution, and then a certain amount of H2O2 solution was added to the evaporation ball Ⅰ5 through the spray device 3 and the guide device 4, and stirred in a closed manner at 80℃ for 60 min. The H2O2 concentration in the evaporation ball Ⅰ5 was controlled to be 8wt%, and the concentration of the sugarcane bagasse raw material was 10wt%. The obtained material can be temporarily stored in the pulp storage tank Ⅰ6, and the material is then transported to the double-disc refiner 8 for processing through the pulp pump Ⅰ7. The material is then sent to the double-roller pulp washer Ⅰ9 and washed with water in the device and then centrifuged for dehydration to obtain the alkalized sugarcane bagasse after the first alkali treatment.

[0056] 2. Second alkali treatment: The alkalized bagasse after the first alkali treatment is added to a stirring device containing 0.2 wt% NaOH solution, and then a certain amount of 0.05 wt% H2O2 solution is added, and the concentration of the alkalized bagasse after the first alkali treatment is controlled to be 10wt%. The mixture is stirred in a closed manner at 80°C for 60 minutes, then washed with water and centrifuged for dehydration to obtain the alkalized bagasse after the second alkali treatment, which is then bleached.

[0057] Specifically, refer to Figure 2 The alkalized bagasse after the first alkali treatment is transported to the steaming ball II 11 through the screw conveyor I 10, and low-concentration alkali solution, water and H2O2 are added through the screw conveyor I 10. The material after the second alkali treatment is temporarily stored in the pulp storage tank II 12, and the material is then sent to the desander 14 through the pulp pump II 13 to remove particulate impurities, and then washed in the double-roller pulp washer II 15.

[0058] 3. Bleaching (1) Chlorine dioxide bleaching The alkalized bagasse after the second alkali treatment was added to a stirring device containing a 0.015 wt% chlorine dioxide solution, and a certain amount of 0.02 wt% hydrochloric acid was added to control the concentration of the alkalized bagasse after the second alkali treatment to be 10 wt%. The mixture was stirred in a closed container at 65°C for 60 minutes, and then washed with water and centrifuged for dehydration to obtain chlorine dioxide bleached bagasse.

[0059] Specific, material reference Figure 2 The alkalized bagasse after the second alkali treatment is transported to the upflow bleaching tower Ⅰ19 through the screw conveyor Ⅱ16 and the pump riser 17 through the screw pump Ⅰ. At the same time, water, chlorine dioxide and hydrochloric acid reagent are added from the screw conveyor Ⅱ16. The material is bleached in the upflow bleaching tower Ⅰ19 and the downflow bleaching tower Ⅰ20 in the first stage, and then transported to the double-roller pulp washer Ⅲ22 through the pulp pump Ⅲ21 for washing and dehydration to obtain the chlorine dioxide bleached bagasse.

[0060] (2) Alkali extraction Continue to add the chlorine dioxide bleached bagasse to the alkaline extraction stirring tank 23 filled with 0.05 wt% NaOH solution, and then add a certain amount of 0.02 wt% H2O2 solution. The concentration of the chlorine dioxide bleached bagasse is 10 wt%. Stir in a closed manner at 65°C for 60 minutes. The material after alkali extraction is sent to the double-roll pulp washer IV25 through the pulp pump IV24. The material is washed with water and then centrifuged and dehydrated to obtain the alkali-extracted bagasse.

[0061] (3) Hydrogen peroxide bleaching The alkali-extracted bagasse is added to a mixer filled with 0.05 wt% H2O2 solution. The mixer is provided with feed ports for adding water, H2O2 solution and alkali solution. A certain amount of 0.05 wt% NaOH solution is then added through the feed port of the mixer. The concentration of the alkali-extracted bagasse is 10 wt%. The mixed material is sent to an upflow bleaching tower II28 via a screw pump II27 and then to a downflow bleaching tower II29 for closed bleaching at 75°C for 60 min. The material is then sent to a double-roll pulp washer V30, and then washed with water and centrifuged for dehydration to obtain hydrogen peroxide-bleached bagasse.

[0062] 4. Pickling The bleached bagasse is added to a pickling stirring tank 31 filled with 0.075 wt% acetic acid solution. A feeding port is provided on the pickling stirring tank 31. Water and a certain amount of 0.005 wt% sodium hexametaphosphate are added from the feeding port of the pickling stirring tank 31. The concentration of the bleached bagasse is 10 wt%. The mixture is stirred in a closed manner at 75°C for 60 minutes. The acid-treated material is then sent to a double-roll pulp washer VI33 via a pulp pump V32. After washing with water, it is centrifuged and dehydrated to obtain the acid-washed sugarcane pulp.

[0063] 5. Drying The acid-washed sugarcane pulp is sent to a radio frequency dryer and dried with hot air at 80°C to obtain sugarcane pulp that can be used for lyocell fiber production. Figure 4 .

[0064] Example 2 The only difference between this embodiment and embodiment 1 is that, during the first alkali treatment, the concentration of NaOH is adjusted to 10 wt %. The other process steps and equipment used are the same as those in embodiment 1, thereby preparing sugarcane pulp for lyocell fiber production.

[0065] Example 3 The only difference between this embodiment and embodiment 1 is that, during the first alkali treatment, the concentration of NaOH is adjusted to 6 wt %. The other process steps and equipment used are the same as those in embodiment 1, thereby preparing sugarcane pulp for lyocell fiber production.

[0066] Example 4 The only difference between this embodiment and embodiment 1 is that, during the first alkali treatment, the concentration of H2O2 is adjusted to 0.1 wt %. The other process steps and equipment used are the same as those in embodiment 1, thereby preparing sugarcane pulp for lyocell fiber production.

[0067] Example 5 The difference between this embodiment and Example 1 is that the concentration of H2O2 during the high-concentration alkali treatment is 0.06 wt%. The other process steps and equipment used are the same as those in Example 1, thereby preparing sugarcane pulp for lyocell fiber production.

[0068] Comparative Example 1 Compared with Example 1, this comparative example has the following differences: Instead of the first alkali treatment and the second alkali treatment processes in this scheme, the kraft cooking process and the oxygen delignification process in traditional pulping and papermaking are adopted.

[0069] The specific sulfate cooking process is as follows: the concentration of sugarcane bagasse raw material is 10 wt%, the cooking temperature is 165℃, the oxygen pressure is 0.5 MPa, the cooking time is 60 min, the NaOH dosage is 17.5% (on a dry basis), and the sulfidation degree is 20% (i.e., the proportion of Na2S added to the total active alkali).

[0070] Oxygen delignification process: The sugarcane bagasse raw material concentration was 10 wt%, the temperature was 160°C, the oxygen pressure was 0.2 MPa, the time was 60 minutes, and the NaOH dosage was 5% (on a dry basis). The other process steps were the same as in Example 1, thereby producing sugarcane pulp.

[0071] Comparative Example 2 Compared with Example 1, this comparative example differs in that the raw material bagasse is treated, and the remaining steps are the same as Example 1.

[0072] In this comparative example, sugarcane bagasse was first crushed to 40-80 mesh to obtain sugarcane bagasse powder, and then the first alkali treatment was performed in the next step to finally prepare sugarcane pulp.

[0073] Comparative Example 3 The difference between this comparative example and Example 1 is that only the first alkali treatment process is used, and then the alkalized sugarcane bagasse after the first alkali treatment is directly bleached. The remaining operating steps and process parameters are consistent with Example 1, thereby preparing sugarcane pulp.

[0074] Comparative Example 4 Compared with Example 1, this comparative example differs in that the concentration of NaOH solution in the first alkali treatment and the concentration of H2O2 solution in the second alkali treatment process are different, and the remaining operating steps and process parameters are the same as those in Example 1, thereby preparing sugarcane pulp.

[0075] Specifically, during the first alkali treatment, the concentration of the NaOH solution was adjusted to 17 wt%, and during the second alkali treatment, the concentration of the H2O2 solution was adjusted to 0.5 wt%.

[0076] Comparative Example 5 In this comparative example, sugarcane pulp was prepared using the method disclosed in Example 1 of the patent application with publication number "CN117684281A". The specific steps are as follows: Weigh 100 g of bagasse, crush it to 80 mesh, stir it in a 70°C water bath for 3 h, filter it, wash it with distilled water, and dry it at 60°C for 10 h to obtain clean bagasse powder.

[0077] Weigh 50 g of washed bagasse powder and add it to a beaker. Then add 1000 g of a mixed solution of 0.5% hydrogen peroxide and 5% sodium hydroxide to the beaker. Stir magnetically in a 70°C water bath for 3 h to pretreat the bagasse. After the reaction is completed, filter and wash until neutral. Place the filter residue in a vacuum dryer at 60°C and dry it. Then crush it to 60 mesh for later use.

[0078] Weigh 10 g of the crushed filter residue and immerse it in a mixed solution of 250 g of glacial acetic acid and sodium hypochlorite. The concentration of glacial acetic acid in the mixed solution is 17.5 mol / L, and the concentration of sodium hypochlorite is 10 g / L. The treatment temperature is 90°C and the immersion time is 3 hours. After the reaction is completed, filter and wash until neutral. Place the filter residue in an oven and dry it at 60°C to obtain sugarcane pulp. The actual photo of the sugarcane pulp prepared in this comparative example is shown in Figure 7 .

[0079] The sugarcane pulp of Examples 1 to 5 and Comparative Examples 1 to 5 was subjected to performance tests. The test results are shown in Table 1.

[0080] The index performance testing method involved in the present invention includes: Degree of polymerization: FZ / T 50010.3-202 is used to measure the viscosity of the raw materials and then convert it into degree of polymerization. Cellulose (α-cellulose) content: FZ / 50010.4-2011 was used to determine the α-cellulose content in the raw materials.

[0081] Whiteness: FZ / T 50010.7-1998 is used to measure the whiteness of raw materials.

[0082] Ash content: FZ / T 50010.5-2023 was used to determine the ash content in the raw materials.

[0083] Iron content: FZ / T 50010.6-1998 was used to determine the iron content in the raw materials.

[0084] Copper content: GB / T 8943.1-2008 was used to determine the copper content in the raw materials.

[0085] Calcium and magnesium content: The calcium and magnesium content in the raw materials was determined by digestion method (the method is from "Man-made Fibers" June 2009 edition, Volume 39, Issue 3).

[0086] Table 1: Statistical table of performance indicators of sugarcane pulp prepared in different embodiments and comparative examples.

[0087] As can be seen from Table 1, (1) The sugarcane pulp prepared in Examples 1 to 5 has a degree of polymerization of 569 to 677, a methylcellulose content of ≥92.1%, a whiteness of ≥84%, an ash content of ≤0.09%, an iron content of ≤5 ppm, a copper content of ≤0.88 ppm, a calcium content of ≤67 ppm, and a magnesium content of ≤74 ppm, all of which can meet the requirements of raw materials for the production of lyocell fibers.

[0088] (2) As can be seen from Examples 1, 2, and 3, changing the amount of alkali used in the first alkali treatment process can effectively control the degree of polymerization (DP) index of sugarcane pulp. The degree of polymerization of sugarcane pulp can be controlled by adjusting the amount of alkali used in this step according to demand to meet production requirements. For example, if the amount of alkali used in the first alkali treatment process is increased (see Example 2), the degree of polymerization (DP) of sugarcane pulp will be significantly reduced, while other indicators will only fluctuate slightly, which will not have a significant impact on the production of lyocell fiber; if the amount of alkali used in the first alkali treatment process is reduced (see Example 3), the degree of polymerization (DP) of sugarcane pulp will be significantly increased, while other indicators will still only fluctuate slightly.

[0089] (3) As shown in Examples 1, 4, and 5, changing the H2O2 concentration during the first alkali treatment can also effectively control the degree of polymerization (DP) of the sugarcane pulp. For example, increasing the H2O2 concentration during the high-concentration alkali treatment (see Example 4) will reduce the DP of the sugarcane pulp; while decreasing the H2O2 concentration during the high-concentration alkali treatment (see Example 5) will increase the DP of the sugarcane pulp.

[0090] (4) It can be seen from Example 1 and Comparative Example 1 that if the first alkali treatment and the second alkali treatment processes in this scheme are replaced by the kraft cooking process and the oxygen delignification process in traditional pulping and papermaking, the indicators of the obtained sugarcane pulp are not much different from those of the sugarcane pulp prepared by the preparation method in this scheme, and can also be used for lyocell fiber production.

[0091] However, the first and second alkali treatment steps in this scheme can be performed at lower temperatures (60-80°C) and do not require any high-pressure conditions. This makes the process more gentle, requires less equipment, and is safer to operate. This demonstrates that the two-step alkali treatment process in this scheme can effectively replace the traditional pulping and oxygen delignification processes, simplifying the process flow and reducing equipment energy consumption.

[0092] (5) As can be seen from Example 1 and Comparative Example 2, sugarcane pulp can be prepared by crushing sugarcane bagasse to obtain sugarcane bagasse powder. Although the pulp indicators are slightly different, they can both meet the pulp standards for lyocell fiber production, indicating that the patented method is also applicable to sugarcane bagasse powder raw materials.

[0093] However, crushing bagasse before processing not only increases equipment investment but also raw material processing costs, resulting in poor economic efficiency. The preparation method of the present invention pulps un-crushed bagasse raw material, eliminating the need for crushing, and is therefore more practical. Furthermore, crushing bagasse can easily generate dust pollution, posing production risks, and the crushed raw material is also difficult to transport. Therefore, the process of the present invention is simpler and more feasible for industrialization.

[0094] (6) As can be seen from Example 1 and Comparative Example 3, using only the first alkali treatment process results in a higher degree of polymerization (DP) of the sugarcane pulp, a lower content of methylcellulose (α-cellulose), and a lower whiteness. This indicates that using only one alkali treatment process in this solution cannot achieve the sugarcane pulp specifications required for lyocell fiber production, highlighting the importance of the second alkali treatment process.

[0095] (7) As can be seen from Example 1 and Comparative Example 4, the excessively high concentrations of NaOH and H₂O₂ during the alkali treatment process significantly reduced the methylcellulose (α-cellulose) content of the resulting sugarcane pulp. Therefore, if the process parameters during the alkali treatment process in this solution are arbitrarily adjusted without following the process parameters specified in this solution, the resulting sugarcane pulp will not meet the standards for lyocell fiber production.

[0096] (8) It can be seen from Example 1 and Comparative Example 5 that the sugarcane pulp prepared by the solution in the patent application with publication number "CN117684281A" has a high degree of polymerization, and its cellulose methyl (α-cellulose) content and whiteness are significantly low, which cannot meet the pulp standards for lyocell fiber production.

[0097] Furthermore, the sugarcane pulp obtained in the examples and comparative examples was prepared into lyocell staple fibers, and the properties of the lyocell staple fibers were tested.

[0098] The specific process is as follows: Step 1: Swelling of sugarcane pulp.

[0099] The dried sugarcane pulp prepared in the example or comparative example was put into a high-consistency pulper, and a 75-80 wt% NMMO aqueous solution was added to the device. The pulp was stirred at 76-84° C. to fully swell the pulp, thereby obtaining a cellulose suspension.

[0100] Step 2: Preparation of spinning solution.

[0101] The cellulose suspension is pumped to a thin film evaporator via a screw pump and dissolved under high-temperature vacuum conditions to produce a spinning solution. The feed temperature of the thin film evaporator is preferably controlled between 77 and 85°C. The upper section temperature of the thin film evaporator is controlled between 79 and 84°C, the middle section temperature is controlled between 85 and 91°C, the lower section temperature is controlled between 92 and 100°C, and the cone bottom temperature is controlled between 101 and 108°C. The glue outlet temperature of the thin film evaporator is controlled between 100 and 110°C.

[0102] Step 3: Prepare lyocell staple fibers.

[0103] The spinning solution is filtered and then wet-spun in a coagulation bath. The fibers are then washed, cut, oiled, and dried to produce Lyocell staple fibers. The spinneret air gap is controlled to 10-25 mm, the side-blowing speed to 5-25 m / s, and the temperature to 10-25°C.

[0104] The coagulation bath is a 10-25 wt% NMMO aqueous solution, the coagulation bath temperature is controlled at 10-30° C., and the spinning speed is 25-45 m / min.

[0105] Application Example 1 This application example further investigates the dissolution effect of the sugarcane pulp obtained in Example 1 and Comparative Example 5 in NMMO solution.

[0106] The specific steps are: Figure 2 The dried sugarcane pulp obtained in Example 1 and Comparative Example 5 was placed in a high-consistency pulper 35. According to the process conditions in Table 2, a 78 wt% NMMO aqueous solution was added to the high-consistency pulper 35. The pulp was stirred at 81°C to fully swell the pulp to obtain a cellulose suspension. The suspension was then transferred to a thin film evaporator and dissolved under high temperature and vacuum to obtain a spinning solution. The dissolution effect was tested, and the results are shown in Table 2. The microscope image of the solution formed by dissolving the sugarcane pulp of Group 5 in the NMMO aqueous solution is shown in the attached figure. Figure 6 The microscope image of the solution formed by dissolving sugarcane pulp in NMMO aqueous solution in the control group 5 is attached. Figure 8 .

[0107] Table 2 As shown in Table 2, the sugarcane pulp obtained using the preparation method of the present invention (Example 1) dissolves well in NMMO solution, producing a uniform, transparent spinning solution even at high concentrations. In contrast, the sugarcane pulp prepared using the method disclosed in patent application publication number "CN117684281A" (Comparative Example 5) dissolves well in NMMO solution only when the cellulose concentration is ≤ 8 wt%. When the cellulose concentration exceeds 8 wt%, the dissolution is poor.

[0108] In the current lyocell fiber industry, the concentration of cellulose in the spinning solution is generally higher than 10 wt%. It can be seen that the sugarcane pulp obtained by the preparation method of the present invention can better meet the production needs of lyocell.

[0109] Application Example 2 In this application example, the sugarcane pulp obtained in Examples 1 to 5 and Comparative Examples 1 to 5 was used to prepare lyocell staple fibers, and the performance of the lyocell staple fibers was tested.

[0110] The specific steps are: Step 1: Swelling of sugarcane pulp.

[0111] The dried sugarcane pulp obtained in the examples or comparative examples was put into a high-consistency pulper 35, and a 78 wt% NMMO aqueous solution was added to the device. The pulp was stirred at 79° C. to fully swell the pulp, thereby obtaining a cellulose suspension with a concentration of 10.5 wt%.

[0112] Step 2: Preparation of spinning solution.

[0113] The cellulose suspension is transferred to a thin-film evaporator 37 via screw pump III 36, where it is dissolved under high-temperature vacuum conditions to produce a spinning solution with a cellulose concentration of 12.6 wt%. The feed temperature of the thin-film evaporator 37 is preferably controlled at 79°C. The upper section temperature of the thin-film evaporator 37 is controlled at 81°C, the middle section temperature at 89°C, the lower section temperature at 99°C, and the cone bottom temperature at 108°C. The glue outlet temperature of the thin-film evaporator 37 is controlled at 105°C.

[0114] Step 3: Prepare lyocell staple fibers.

[0115] The spinning solution is sent to filter 39 via high-pressure pump 38 for filtration, then to spinning machine 41 via glue pump 40. It is then formed in a coagulation bath by dry-jet wet spinning. Lyocell staple fibers are then washed, cut, oiled, and dried. The spinneret air gap of spinning machine 41 is controlled to 20 mm, the cross-blowing air speed is controlled to 15 m / s, and the temperature is 20°C. The coagulation bath is a 20wt% NMMO aqueous solution, the coagulation bath temperature is controlled to 20°C, and the spinning speed is 36 m / min.

[0116] The statistical results of the relevant performance indicators of lyocell staple fibers are shown in Table 2. The lyocell staple fibers prepared using the sugarcane pulp in Example 1 are shown in Table 2. Figure 5 .

[0117] The index performance testing method involved in the present invention includes: Linear density: GB / T 14335-2008 was used to measure the linear density of staple fibers.

[0118] Dry breaking strength: GB / T 14337-2008 was used to determine the dry breaking strength of staple fibers.

[0119] Wet breaking strength: GB / T 14337-2008 was used to determine the wet breaking strength of staple fibers.

[0120] Fiber whiteness: GB / T 17644-1998 was used to measure the whiteness of short fibers.

[0121] Table 3 In Table 3, since the sugarcane pulp prepared in Comparative Example 5 was not completely dissolved under the same cellulose concentration conditions and could not be spun continuously, relevant fiber data could not be obtained.

[0122] According to the statistical results in Table 3: (1) The spinning solutions obtained by dissolving the sugarcane pulp prepared in Examples 1 to 5 in the NMMO solution have good spinnability, and the lyocell fibers finally obtained have excellent performance indicators, indicating that the sugarcane pulp obtained by the preparation method of the present invention can well meet the production requirements of lyocell fibers and can be used to produce high-quality lyocell fibers.

[0123] (2) Sugarcane pulp produced using the traditional kraft cooking process and oxygen delignification process in pulping and papermaking (Comparative Example 1) can also be dissolved in the NMMO solution to obtain a spinning solution with good spinnability, and ultimately produce lyocell fiber with excellent performance indicators. It can be seen that the two alkali treatment processes in this scheme can effectively replace the traditional pulping cooking and oxygen delignification processes, and can ensure that the produced sugarcane pulp meets the requirements of lyocell fiber production.

[0124] (3) Sugarcane pulp prepared by crushing sugarcane bagasse into sugarcane bagasse powder (Comparative Example 2) can also be dissolved in NMMO solution to obtain a spinning solution with good spinnability, and lyocell fiber can be prepared, indicating that the preparation method of the present invention is also suitable for processing sugarcane bagasse powder raw materials.

[0125] (4) Although the sugarcane pulp obtained by only using the first alkali treatment process (Comparative Example 3) can also be dissolved in NMMO solution for spinning, the whiteness of the lyocell fiber finally obtained is significantly lower, and the quality of the fiber obtained is poor.

[0126] (5) If the concentrations of NaOH and H2O2 are too high during the alkali treatment (Comparative Example 4), the strength of the lyocell fiber obtained by dissolving and spinning the sugarcane pulp will be significantly reduced, which will seriously affect the fiber quality.

[0127] (6) The sugarcane pulp prepared by the method disclosed in the patent application with publication number “CN117684281A” cannot be completely dissolved under the same dissolution process conditions, and the dissolution effect is poor, and continuous spinning cannot be carried out. This shows that the method disclosed in the patent still has certain limitations in practical applications. In particular, when the cellulose concentration in the spinning solution is too high, the sugarcane pulp prepared by the method disclosed in the patent application has a poor dissolution effect, and a spinning solution with good spinnability cannot be obtained, let alone Lyocell fiber with excellent performance.

[0128] From the above test results, it can be seen that the process of the present invention has the following advantages: (1) The preparation method of the present invention does not require the sugarcane raw material to be crushed, and can also produce sugarcane pulp suitable for lyocell fiber production, which can simplify the process flow, reduce equipment investment, effectively reduce production costs, and avoid dust pollution.

[0129] (2) The two alkali treatment processes in the preparation method of the present invention can effectively replace the traditional pulping cooking and oxygen delignification processes, and can ensure that the obtained sugarcane pulp meets the requirements of lyocell fiber production. Moreover, it can be carried out in a relatively low temperature environment (60-80°C) without any high pressure conditions. The process is more gentle, has lower requirements on equipment, and is safer to operate.

[0130] (3) The sugarcane pulp obtained by the preparation method of the present invention has stronger applicability and can still be used to produce lyocell fibers even under process conditions with higher cellulose concentrations.

[0131] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing sugarcane pulp suitable for lyocell fiber production, characterized in that: Sugarcane pulp for lyocell fiber production is obtained by using sugarcane bagasse as raw material and undergoing the first alkali treatment, the second alkali treatment, bleaching, acid washing and drying. The first alkali treatment is to add sugarcane bagasse to the first alkali solution, then add H2O2, control the mass ratio of sugarcane bagasse, alkali and H2O2 to be 5-20:5-15:0.01-0.1, stir in a closed manner at 60-80℃ for 30-90 minutes, and then wash and dehydrate to obtain the alkalized sugarcane bagasse after the first alkali treatment; The second alkali treatment is to add the alkalized sugarcane bagasse after the first alkali treatment into the second alkali solution, and then add H2O2, and control the mass ratio of the alkalized sugarcane bagasse after the first alkali treatment, alkali and H2O2 to be 5~20:0.05~0.5:0.01~0.1, and stir in a closed manner at 60~80℃ for 60~120min. After washing and dehydration, the alkalized sugarcane bagasse after the second alkali treatment is obtained, and then bleaching is carried out.

2. The preparation method according to claim 1, wherein: In the first alkali treatment and the second alkali treatment, the alkali used is NaOH or KOH.

3. The preparation method according to claim 1, characterized in that Bleaching involves the following steps: A. Add chlorine dioxide solution and hydrochloric acid to the alkalized bagasse after the second alkali treatment, controlling the mass ratio of the alkalized bagasse after the second alkali treatment, chlorine dioxide, and hydrochloric acid to be 5-20:0.01-0.2:0.01-0.05, and then stir in a closed manner at 60-75°C for 30-90 minutes, and then wash and dehydrate to obtain a first-stage bleached bagasse; B. Adding a first-stage bleached bagasse to an alkaline solution and then adding H2O2, controlling the mass ratio of the first-stage bleached bagasse, alkali, and H2O2 to be 5-20:0.01-0.1:0.01-0.05, followed by stirring in a closed container at 60-75°C for 30-90 minutes, followed by washing and dehydration to obtain the alkaline-treated bagasse; C. Add alkali-treated bagasse to H2O2, then add NaOH, and control the mass ratio of alkali-treated bagasse, H2O2 and NaOH to 5~20:0.01~0.08:0.01~0.08; then stir in a closed manner at 70~80℃ for 60~120 min, wash with water and then centrifuge to dehydrate to obtain hydrogen peroxide-bleached bagasse.

4. The preparation method according to claim 3, wherein: During bleaching, the alkali used in step B is NaOH or KOH.

5. The preparation method according to claim 1, wherein: Acid washing is to add bleached bagasse to an acid solution, then add a chelating agent, control the mass ratio of bleached bagasse, acid and chelating agent to be 5~20:0.01~0.1:0.001~0.05, then stir in a closed manner at 60~80℃ for 30~90 minutes, and then wash with water and centrifuge to obtain acid-washed bagasse.

6. The preparation method according to claim 5, characterized in that: During pickling, the acid used is formic acid or acetic acid; the complexing agent used is sodium hexametaphosphate or EDTA.

7. The preparation method according to claim 1, wherein: Drying is done with hot air at 60~80℃.

8. Sugarcane pulp suitable for lyocell fiber production obtained by the preparation method according to any one of claims 1 to 7, characterized in that: At 76-84°C, sugarcane pulp is added to a high-concentration NMMO aqueous solution and fully swelled under stirring to obtain a cellulose suspension. The NMMO concentration in the cellulose suspension is 75-80wt%, and the cellulose concentration in the cellulose suspension is 10.2-12 wt%. The fully swollen cellulose suspension is then transported to a thin film evaporator and dissolved under high-temperature vacuum conditions to obtain a spinning solution for lyocell fiber. The cellulose concentration in the spinning solution is 12-13.5 wt%.

9. The sugarcane pulp suitable for lyocell fiber production obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The sugarcane pulp meets the following performance index system: Degree of polymerization: 569~677, methyl methacrylate content: ≥92.1%, whiteness: ≥84%, ash content: ≤0.09%, iron content: ≤5 ppm, copper content: ≤0.88 ppm, calcium content: ≤67 ppm, magnesium content: ≤74 ppm.

10. A production system suitable for the method for preparing sugarcane pulp according to any one of claims 1 to 7, characterized in that: It includes a high-concentration alkali treatment unit, a low-concentration alkali treatment unit, a chlorine dioxide bleaching unit, an alkali extraction unit, a hydrogen peroxide bleaching unit, a pickling unit and a drying machine, which are connected in sequence through pipelines. The high-concentration alkali treatment unit includes a spray device, a steaming ball I for holding high-concentration alkali solution, a pulp pump, a pulp refiner, a pulp washer and a pulp storage tank I which are connected in sequence through pipelines; The low-concentration alkali treatment unit includes a screw conveyor I, a steam ball II for holding low-concentration alkali solution, a pulp storage tank II, a pulp pump, a desander and a pulp washer, which are connected in sequence through pipelines; The chlorine dioxide bleaching unit includes a screw conveyor II, a pump riser, a screw pump, an upflow bleaching tower, a downflow bleaching tower, a pulp pump and a pulp washer connected in sequence through pipelines; The alkali extraction unit includes an alkali extraction stirring tank, a pulp pump and a pulp washer connected in sequence through pipelines; The hydrogen peroxide bleaching unit comprises a mixer, a screw pump, an upflow bleaching tower, a downflow bleaching tower, and a pulp washer which are sequentially connected through pipelines; The pickling unit comprises a pickling stirring tank, a pulp pump and a pulp washer which are sequentially connected through pipelines.

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