Cooking process for pulping cotton stalks by ammonium sulfite method

Abstract

The invention relates to the technical field of grass plant fiber raw material pulping, and particularly discloses a cotton stalk ammonium sulfite pulping cooking process which comprises the following steps: S1, adding dry cotton stalks, water, ammonium sulfite, a cooking aid A, a cooking aid B and a buffering agent into a cooking utensil, and sealing; wherein the weight of the cotton stalks is 1000 parts, the weight of the water is 2.5-3 times that of the cotton stalks, the weight of the ammonium sulfite is 240-260 parts, the weight of the cooking aid A is 0.8-1.2 parts, the weight of the cooking aid B is 0.8-1.2 parts, the weight of the buffering agent is 25-35 parts, anthraquinone is selected as the cooking aid A, and the cooking aid B is a cooking penetrant; s2, when the pressure of the digester is increased to 130 DEG C, steam is released slightly, then the temperature is increased to 135 + / -5 DEG C, heat preservation is conducted for 20-30 minutes, then the temperature is continuously increased, the temperature increasing time is not shorter than 40 minutes, and after the highest temperature reaches 175 + / -5 DEG C, heat preservation is conducted for 100 + / -5 minutes. The scheme is used for solving the problem that the potassium permanganate value is too high after cotton stalk pulping at present.

Description

Technical Field

[0001] This invention relates to the field of pulping technology for grass fiber raw materials, specifically to the cotton stalk ammonium sulfite pulping and cooking process. Background Technology

[0002] With the development of my country's economy, the demand for papermaking is booming. Papermaking requires fiber raw materials for production. However, due to the high demand in the papermaking industry, there is currently a structural imbalance between the fiber raw materials needed for papermaking and the demand. Papermaking mainly relies on wood pulp as a fiber raw material. However, with the increasing environmental protection requirements, the domestic wood pulp production capacity is limited and the utilization of non-wood fiber raw materials is insufficient. Therefore, in order to meet production needs, a large amount of imported wood pulp has become the main choice. However, the price of imported wood pulp fluctuates greatly and there is an unstable supply problem.

[0003] Grass-based plant fiber raw materials are important non-wood fiber sources, encompassing rice straw, wheat straw, reeds, sugarcane bagasse, sorghum stalks, corn stalks, and cotton stalks, which can be used as papermaking raw materials. Generally speaking, wood is superior to grasses in papermaking raw materials, and among woods, coniferous wood is superior to broadleaf wood. Among grass-based raw materials, cotton stalks have significantly better fiber morphology and physicochemical properties than other grass-based raw materials, and are closer to broadleaf wood—its fibers are longer, cell walls are thicker, and the content of impurity cells is relatively lower, resulting in higher pulp strength, making it more suitable for producing paper types that require high strength.

[0004] However, pulping cotton stalks is far more difficult than that of other grass-based raw materials. Its fibers are tightly bound, and its outer layer is brownish-black, making the cooking and bleaching processes more challenging. Conventional cooking conditions often fail to achieve ideal results, requiring more complex processing steps, longer cooking times, and higher consumption, resulting in high cotton stalk pulping costs. Furthermore, achieving high whiteness after bleaching is still difficult, and low whiteness significantly limits the application of cotton stalks in high-quality paper grades.

[0005] Although existing technologies have promoted the comprehensive utilization of non-timber resources such as bagasse, agricultural straw, reeds and waste paper to alleviate the problem of my country's excessive dependence on foreign papermaking fiber raw materials, cotton stalks are difficult to promote due to their production process, cost and quality issues. In resource-rich areas, most of them are still treated as agricultural waste and returned to the field or burned, failing to achieve large-scale, high-value-added application.

[0006] Taking the Chinese patent publication CN101451312B, "A Method for Preparing Bleached Chemical Pulp from Grass-like Plants," as an example, this technology discloses the cooking and bleaching treatment of cotton stalks. In this technology, the cotton stalks are first mixed with a dilute alkaline solution for impregnation, and then cooked a second time in a steamer with ammonium sulfite. After cooking, the pulp is diluted with black liquor and sprayed to obtain cotton stalk pulp with a potassium permanganate value of 23. The pulp then needs to be mixed with oxygen and alkaline solution for a two-stage oxygen delignification treatment to soften the fibers. Finally, through a three-stage traditional bleaching process of chlorination, alkali treatment, and hypochlorite bleaching, the final cotton stalk pulp has a brightness of 72% ISO. This existing technology is very complex and time-consuming from cooking to bleaching completion, and even after bleaching, the brightness still cannot reach above 80% ISO.

[0007] Furthermore, another Chinese patent publication, CN101644008A, entitled "A Sodium Sulfite Cooking Method for Preparing High-Firm Pulp from Grass-like Plants," also discloses the cooking and bleaching of cotton stalks. In this technology, multiple cooking methods are disclosed during the cooking process. One cooking process differs from the one disclosed in CN101451312B in that, before cooking, in addition to adding 4% NaOH, black liquor is added to the oven-dried cotton stalks for impregnation. However, this still yields cotton stalk pulp with a potassium permanganate value of 16. This technology states that even if the obtained cotton stalk pulp is processed using a two-stage oxygen delignification followed by a three-stage bleaching process (a traditional three-stage bleaching process involving chlorination, alkali treatment, and hypochlorite bleaching), the final pulp brightness remains at 72%. Another method involves extruding the black liquor before bleaching, which can increase the pulp brightness to 82% ISO. However, this process is more complex and costly. Summary of the Invention

[0008] The present invention aims to provide a cotton stalk ammonium sulfite pulping and cooking process to solve the problem of excessively high potassium permanganate value after cotton stalk pulping.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: The cotton stalk ammonium sulfite pulping and cooking process includes the following steps: S1. Add dry cotton stalks, water, ammonium sulfite, cooking aid A, cooking aid B, and buffer to the cooking vessel and seal it. The weight of the cotton stalks is 1000 parts, the weight of the water is 2.5-3 times the weight of the cotton stalks, the weight of the ammonium sulfite is 240-260 parts, the weight of both cooking aid A and cooking aid B is 0.8-1.2 parts, and the weight of the buffer is 25-35 parts. Cooking aid A is anthraquinone, and cooking aid B is a cooking penetrant. S2: When the steamer heats up to the pressure of 130℃, release steam slightly, then heat up to 135±5℃ and keep it at that temperature for 20-30 minutes. Then continue heating for at least 40 minutes, so that the highest temperature reaches 175±5℃ and is kept at that temperature for 100±5 minutes.

[0010] Preferably, as an improvement, it also includes step S3, which includes: after the heat preservation is completed, releasing the steam until the pressure is zero, placing it in the pot, washing it until neutral, and then rinsing it.

[0011] Preferably, as an improvement, the process also includes sieving out dust from the cotton stalk raw material before it is placed into the cooker.

[0012] Preferably, as an improvement, the moisture content of the dried cotton stalks is 10±2%.

[0013] Preferably, as an improvement, the time for heating from 135±5℃ to 175±5℃ is controlled within 50-70 minutes. This avoids the problem of poor pulping caused by short heating time and fast heating speed, and the problem of high potassium permanganate value due to insufficient removal of cotton stalk lignin. It also avoids the problem of insufficient cooking time and some lignin residue.

[0014] Preferably, as an improvement, the temperature is raised to 175±5℃ and then kept at that temperature for 100 minutes to avoid excessive heat treatment, which could lead to overcooking and lignin condensation. Once lignin condensation occurs, it will increase the difficulty of bleaching.

[0015] Preferably, as an improvement, the buffer is sodium hydroxide.

[0016] Preferably, as an improvement, the amount of ammonium sulfite is 250 parts.

[0017] Preferably, as an improvement, both cooking aid A and cooking aid B are 1 part each.

[0018] The principles and advantages of this invention are: 1. This invention uses ammonium sulfite as the main cooking agent, converting lignin into soluble sulfonates through a sulfonation reaction. Anthraquinone, through a redox cycle mechanism, accelerates lignin degradation while inhibiting cellulose peeling, ensuring pulp yield and strength. Cotton stalks are similar to hardwoods, making cooking difficult, and the bast fibers of cotton stalks are also difficult to pulp. The cooking penetrant improves the wetting and penetration efficiency of the cooking solution. The buffer maintains the pH stability of the system, ensuring a continuous and thorough reaction. The combined effect of all components, along with the control of the cooking temperature curve, yields a pulp with a potassium permanganate value as low as approximately 14, and even as low as 13, breaking the current problem that the potassium permanganate value of cotton stalk pulp cannot be further reduced from 16. Furthermore, the crude pulp yield exceeds 42%, thus providing a guarantee for simpler, more time-saving, and lower-cost bleaching of the pulp in the later stages, with a bleaching degree exceeding 80%.

[0019] 2. This process is extremely sensitive to formulation and parameter control. Experiments show that changing the amount of anthraquinone (cooking aid A) from 1 part to 0.5 parts will cause the potassium permanganate value to rise from 14 to around 22; similarly, changing the amount of cooking penetrant (cooking aid B) from 1 part to 0.5 parts will also cause the potassium permanganate value to rise from 14 to around 18. The temperature rise curve is also highly sensitive; increasing the holding temperature from 100℃ to 110℃ will trigger cellulose degradation and lignin condensation, causing the K value to rise back above 20. Excessive heating will also prevent the K value from falling below 14. This indicates that maintaining a stable K value of cotton stalk pulp at 14 is essentially a multivariate, strongly coupled optimization problem, requiring extremely precise matching of the chemical formulation and thermal regime.

[0020] 3. Anthraquinone acts as a redox agent. It first oxidizes the terminal aldehyde group of carbohydrates, converting it into a carboxyl group, thus preventing degradation during the peeling reaction in the pulping solution, reducing carbohydrate degradation, and increasing pulp yield. The cooking penetrant of this invention acts as a surfactant, promoting the penetration of ammonium sulfite into the raw material, reducing the amount of ammonium sulfite used, and accelerating the delignification rate and degree. This overcomes the current problem that the potassium permanganate value cannot be further reduced from 16 after cotton stalk cooking. Consequently, after the potassium permanganate value is reduced, the subsequent bleaching process is simplified, ensuring that the brightness of the bleached cotton stalk pulp reaches above 80% ISO and still maintains a degree of polymerization of not less than 1000.

[0021] In summary, this invention selectively breaks down stubborn lignin in cotton stalk husks and inhibits cellulose degradation using cooking aid A (anthraquinone); combined with cooking aid B (cooking penetrant), it reduces surface tension and, in conjunction with a suitable heating curve, facilitates rapid penetration of the cooking solution into the dense, hydrophobic cotton stalk husk. This achieves deep yet gentle delignification of the cotton stalks, thereby reducing the K value to approximately 14. This ensures that subsequent bleaching processes are simpler, less time-consuming, and less costly. Furthermore, it also allows for a reduction in the amount of sodium hydroxide used as a buffer.

[0022] The present invention also provides a method for preparing cotton stalk pulp, comprising the aforementioned cotton stalk ammonium sulfite pulping and cooking process, and further comprising the following bleaching step: I. Take unbleached cotton stalk pulp with a neutral pH value; II. First stage bleaching: Mix the cotton stalk pulp from step I with the first stage bleaching agent and water evenly in a container, and heat to 60±5℃ and keep warm for 65-95 minutes; the first stage bleaching agent includes chlorine dioxide A agent containing 0.8-1.4% of the oven-dry pulp mass and chlorine dioxide B agent containing 1.2-1.6% of the oven-dry pulp mass; III. Second-stage bleaching: Mix the pulp after the first-stage bleaching with the second-stage bleaching agent and water evenly in a container, heat to 60±5℃ and keep warm for no less than 60 minutes; the second-stage bleaching agent includes chlorine dioxide A agent at 0.5-1.0% of the oven-dry pulp mass and chlorine dioxide B agent at 0.8-1.2% of the oven-dry pulp mass; IV. Three-stage bleaching: Mix the pulp after the second-stage bleaching with water, sodium hydroxide 1.8-2.2%, hydrogen peroxide 1.5-4.0%, sodium silicate 1.3-1.7%, and magnesium sulfate 4.5-5.5% in a container until homogeneous, then heat to 60±5℃ and keep at that temperature for 55-65 minutes; the percentage of added substances is relative to the oven-dry pulp volume. The mass concentration of the slurry in the container during steps II-IV above is 8-12%.

[0023] Preferably, as an improvement, in the first bleaching step II, the chlorine dioxide A agent is 1-1.2%.

[0024] Preferably, as an improvement, the holding time in the first stage of bleaching in step II is 70-80 minutes, which avoids insufficient bleaching time and also avoids the problem of excessive bleaching time leading to the breakage of cellulose molecular chains and ultimately reducing the degree of polymerization.

[0025] Preferably, as an improvement, in the second-stage bleaching of step III, the chlorine dioxide A agent is 0.5-0.8%.

[0026] Preferably, as an improvement, the heat preservation time in the second stage of drifting in step III is 60-70 minutes.

[0027] Preferably, as an improvement, in the three-stage bleaching of step IV, the hydrogen peroxide content is 2-3%.

[0028] The present invention also provides a cotton stalk pulp with a degree of polymerization greater than 1000 and a whiteness greater than 80% ISO, which is prepared by the method described above.

[0029] The present invention provides a method for preparing cotton stalk pulp that departs from the traditional three-stage bleaching process of chlorination-alkali treatment-hypochlorite. Instead, it employs chlorine dioxide as the main bleaching agent. By selecting the appropriate ratio of chlorine dioxide A and B agents, chlorine dioxide primarily attacks and oxidizes the residual lignin structure in the cotton stalk pulp, while having a very weak oxidizing effect on cellulose. Furthermore, the first and second stages of bleaching use different ratios of chlorine dioxide to remove lignin in stages, achieving a deep and gentle removal of lignin. This helps to ensure the whiteness of the cotton stalk pulp while preserving as much cellulose as possible. Finally, the three-stage bleaching process dissolves the lignin fragments oxidized and degraded in the first two stages and further destroys residual chromophores, thereby further enhancing the whiteness. This ensures that the resulting cotton stalk pulp has a whiteness exceeding 80% ISO and a degree of polymerization exceeding 1000.

[0030] The three-stage bleaching method of this invention requires a total bleaching time of only about 200 minutes. Compared with the complex process of the prior art, which requires first removing black liquor, then two stages of oxygen bleaching to remove lignin, and then three stages of bleaching (the prior art requires 310-460 minutes from the time of cooking the cotton stalk pulp to the completion of bleaching), this method greatly reduces the difficulty of the process and shortens the production time, thus helping to reduce costs. Attached Figure Description

[0031] Figure 1 This is a photograph of the dry cotton stalks used in the embodiments of the present invention.

[0032] Figure 2 This is a photograph of the actual product after steaming in Embodiment 1 of the present invention.

[0033] Figure 3 for Figure 2 A picture of the product after bleaching and dehydration.

[0034] Figure 4 This is an optical microscope image of cotton stalk fibers after bleaching in Example 1 of the present invention.

[0035] Figure 5 This is a picture of the actual product after steaming / cooking, as shown in Comparative Example 3.

[0036] Figure 6 This is a picture of the actual product after steaming / cooking, as shown in Comparative Example 4.

[0037] Figure 7 This is a picture of the actual product after steaming / cooking, as shown in Comparative Example 8.

[0038] Figure 8 This is a picture of the actual product after steaming / cooking, as shown in Comparative Example 10. Detailed Implementation

[0039] The following detailed description illustrates the specific implementation method: Example 1 The cotton stalk ammonium sulfite pulping and cooking process includes the following steps: Step 1: Screening removes dust from the raw material and selects out impurities such as plastic film to obtain dry cotton stalks with a moisture content of 10±2%.

[0040] Step 2: Add 1000 parts cotton stalks, 2870 parts water, 250 parts ammonium sulfite, 1 part cooking aid A, 1 part cooking aid B, and 30 parts buffer to the steaming ball, which will be used as the cooking container. Seal the container well. Cooking aid A is anthraquinone; cooking aid B is a special ammonium sulfite cooking penetrant; and the buffer is sodium hydroxide.

[0041] Step 3: When the steam ball is heated to 130℃, release a small amount of steam. After releasing the steam, raise the temperature to 135±5℃ and keep it at that temperature for 20 minutes. Continue to raise the temperature to 175±5℃ for about 60 minutes. Keep it at the highest temperature for 100 minutes.

[0042] Step 4: After the heat preservation is completed, release the steam until the pressure is zero, put it in the pot, wash until neutral, and then rinse.

[0043] Step 5: Detect the pulp hardness K value, where K value is also the potassium permanganate value.

[0044] To verify Example 1 above, the components added to the steamed balls were adjusted to set up the following comparative example: Comparative Example 1 The difference from Example 1 is that the amount of cooking aid A in this comparative example is 0.5 parts.

[0045] Comparative Example 2 The difference from Example 1 is that the amount of cooking aid B in this comparative example is 0.5 parts.

[0046] Comparative Example 3 The difference from Example 1 is that no buffer was added to this comparative example.

[0047] Comparative Example 4 The difference from Example 1 is that the amount of buffer added in this comparative example is 50 parts.

[0048] Comparative Example 5 The difference from Example 1 is that the amount of buffer added in this comparative example is 20 parts.

[0049] Comparative Example 6 The difference from Example 1 is that the amount of ammonium sulfite added in this comparative example is 220 parts.

[0050] Comparative Example 7 The difference from Example 1 is that the amount of ammonium sulfite added in this comparative example is 200 parts.

[0051] Comparative Example 8 The difference from Example 1 is that the amount of ammonium sulfite added in this comparative example is 170 parts, and no buffer or cooking aid B (i.e. cooking permeabilizer) is added.

[0052] The test results of Examples 1, 1-7 are shown in Table 1 below. The performance tests were conducted in accordance with GB / T1547-2004 "Determination of Potassium Permanganate Value of Pulp".

[0053] Table 1

[0054] As can be seen from Table 1, Comparative Example 1: Small variations in the amount of cooking aid A had little effect on pulp formation and potassium permanganate value. When the variation was slightly larger, the pulp formation was slightly worse, the potassium permanganate value was slightly higher, and the pulp formation was slightly worse.

[0055] Comparative Example 2: Small variations in the amount of cooking aid B had little effect on pulp formation and potassium permanganate value. Larger variations resulted in slightly worse pulp formation and slightly higher potassium permanganate value.

[0056] Comparative Examples 3 to 5 show that without adding a buffer, the cotton stalk shape remains unchanged and cannot be pulped; adding too much or too little buffer will result in poor pulping and a potassium permanganate value greater than 35.

[0057] Comparative Examples 6 and 7 show that when the amount of buffer added is reduced by a small amount, the pulp can be formed, but the potassium permanganate value is around 20. However, if the amount is reduced by a slightly larger amount compared to Example 1, the pulp formation is poor and there are raw flakes with a high hardness of around 24.

[0058] Comparative Example 8 shows that when 170 parts of ammonium sulfite were added, without buffer or penetrant, no slurry was formed. The results of this non-slurry formation are shown in the attached figure. Figure 7 As shown.

[0059] To verify Example 1 above, the following examples and comparative examples were set up by adjusting key parameters during the heating process: Example 2: The difference from Example 1 is that the time to heat up to the maximum temperature in this example is 40 minutes.

[0060] Example 3: The difference from Example 1 is that the time to heat up to the maximum temperature in this example is 70 minutes.

[0061] Comparative Example 9: The difference from Example 1 is that the heat preservation time at the highest temperature in this example is 90 minutes.

[0062] Comparative Example 10: The difference from Example 1 is that the heat preservation time at the highest temperature in this example is 110 minutes.

[0063] Comparative Example 11: The difference from Example 1 is that this example does not keep warm at 135±5℃.

[0064] Comparative Example 12: The difference from Example 1 is that this example was kept at 135±5℃ for 30 minutes.

[0065] The experimental results of Examples 1-3 and Comparative Examples 9-12 are shown in Table 2 below: Table 2

[0066] As shown in Table 2, the difference between Example 2 and Example 1 is that the heating time in Example 2 is shortened by 20 minutes, meaning the heating rate is faster, resulting in slightly worse pulp formation and a pulp hardness value that is 4 higher. Example 3 has a heating time 10 minutes longer than Example 1, with little change in pulp formation.

[0067] Compared to Example 1, the heat preservation time of Comparative Example 9 after being heated to the highest temperature was shortened by 10 minutes. This resulted in insufficient cooking and some lignin residue, which increased the potassium permanganate value of the pulp by 4.

[0068] Compared to Comparative Example 10, extending the heat treatment time by 10 minutes can easily lead to overcooking and lignin condensation. Lignin condensation increases the potassium permanganate value of the pulp by about 6 (see...). Figure 8 Furthermore, this makes subsequent bleaching difficult, demonstrating that the control of the insulation temperature has a very sensitive impact on the hardness of the pulp.

[0069] In Example 1, the pulping and potassium permanganate values ​​were compared with those of Comparative Example 11 (no insulation) and Comparative Example 12 (installation extended by 10 minutes). It can be seen that if no insulation is performed, the pulping is slightly worse. Insulation for 20-30 minutes can reduce the potassium permanganate value to about 14. However, if the duration is slightly longer, the pulping will be slightly worse.

[0070] In summary, compared with caustic soda in the traditional caustic soda process, ammonium sulfite in this embodiment has a weaker ability to remove lignin. Furthermore, cotton stalks are similar to broadleaf trees, making cooking difficult, and the pulping of cotton stalk bark and bast fibers is also challenging. This invention addresses this by using ammonium sulfite as the main cooking solution, supplemented with cooking aids A and B, and a small amount of buffer. The process involves holding at 135±5℃ for 20-30 minutes, followed by a heating time of 50-70 minutes. During the heating phase, a significant amount of lignin is removed. The temperature is then raised to the maximum of 175±5℃ and held for approximately 100 minutes. This method is more conducive to the removal of residual lignin. The optimal holding time at the maximum temperature maximizes lignin removal while preventing lignin condensation. This results in a potassium permanganate value as low as approximately 14 after cotton stalk pulping, thereby reducing the difficulty of subsequent bleaching processes and easily achieving a whiteness of over 80% after bleaching.

[0071] This embodiment also provides a method for preparing cotton stalk pulp, including the cotton stalk ammonium sulfite pulping and cooking process of Example 1, and further including the following bleaching step: I. Take the neutral, unbleached cotton stalk pulp from Example 1.

[0072] II. First stage bleaching: First, add water at a bleaching concentration of 8%, then add 1% chlorine dioxide disinfectant powder A and 1.4% chlorine dioxide disinfectant powder B to this water. Mix them to obtain the first stage bleaching agent. The proportions of chlorine dioxide disinfectant powder A and chlorine dioxide disinfectant powder B are relative to the oven-dry pulp volume. Then, add the unbleached cotton stalk pulp from step S1 to the reactor, and finally pour in the above-mentioned first stage bleaching agent. Stir evenly and heat to 60°C for 80 minutes.

[0073] III. Second-stage bleaching: Add the pulp washed after the first-stage bleaching to the reactor. According to the bleaching concentration of 8%, add 0.6% of chlorine dioxide disinfectant powder A to this amount of water. After stirring evenly, add 1.0% of chlorine dioxide disinfectant powder B and mix evenly to obtain the second-stage bleaching agent. Stir the bleaching agent and pulp evenly, raise the temperature to 60℃ and keep it at that temperature for 60 minutes. The proportions of chlorine dioxide disinfectant powder A and chlorine dioxide disinfectant powder B are relative to the oven-dry pulp volume.

[0074] IV. Three-stage bleaching: Add the slurry washed after the second-stage bleaching to the reactor, along with water, 2% sodium hydroxide, 2% hydrogen peroxide, 1.5% sodium silicate, and 5% magnesium sulfate. Stir well, then heat to 60°C and keep warm for 60 minutes. The percentage of the added substances is relative to the oven-dry slurry volume. The amount of water used is to ensure that the mass concentration of the slurry in the reactor reaches 8% in this step.

[0075] The above-mentioned chlorine dioxide disinfectant powder A is also known as chlorine dioxide agent A, and chlorine dioxide disinfectant powder B is also known as chlorine dioxide agent B.

[0076] The pulp whiteness obtained by using the cotton stalk ammonium sulfite pulping and cooking process and the cotton stalk pulp bleaching process in Example 1 can exceed 80% ISO, specifically 81.8% ISO, and the degree of polymerization can reach as high as 1050.

[0077] In addition, to verify the effects of different cotton stalk pulp bleaching processes on the final whiteness and degree of polymerization of cotton stalk fibers, the following control experiment was set up. The above-mentioned method for preparing cotton stalk pulp is referred to as Preparation Example 1.

[0078] To verify the preparation example 1 above, the components were adjusted to set up the following reference example: Reference example 1 The difference from Preparation Example 1 is that the amount of chlorine dioxide disinfectant powder A in this reference example is 0.6%.

[0079] Reference example 2 The difference from Preparation Example 1 is that the amount of chlorine dioxide disinfectant powder B in this reference example is 1.0%.

[0080] Reference example 3 The difference from Preparation Example 1 is that the amount of the two-stage chlorine dioxide disinfectant powder A in this reference example is 1.2%.

[0081] Reference example 4 The difference from Preparation Example 1 is that the amount of the two-stage chlorine dioxide disinfectant powder B in this reference example is 1.8%.

[0082] Reference example 5 The difference from Preparation Example 1 is that this reference example uses 3% sodium hydroxide in the three-stage bleaching process.

[0083] Reference example 6 The difference from Preparation Example 1 is that sodium silicate and magnesium sulfate are not added.

[0084] Reference example 7 The difference from Preparation Example 1 is that the amount of hydrogen peroxide used in this reference example is 4% in the three-stage bleaching process.

[0085] The test results of Preparation Example 1 and Reference Examples 1-7 are shown in Table 1 below. The performance tests were conducted in accordance with GB / T1547-2004 "Determination of Potassium Permanganate Value of Pulp".

[0086] Table 1

[0087] As can be seen from the comparison between Preparation Example 1 and Reference Examples 1-4 in Table 1 above, when the amount of chlorine dioxide disinfectant powder A in a certain stage is reduced, the degree of polymerization of the bleached pulp does not change much, but the whiteness decreases by 3.5%, and the whiteness cannot exceed 80% ISO. However, when the amount of chlorine dioxide disinfectant powder A is slightly increased, the whiteness remains unchanged, the degree of polymerization decreases slightly, but it can still exceed 1000. For chlorine dioxide disinfectant powder B, the requirements for the amount of B are more stringent. Whether it is slightly more or less, the whiteness will not be able to reach 80% ISO or above.

[0088] As can be seen from Example 5, increasing the amount of sodium hydroxide will cause a decrease in whiteness. This may be because excessive alkali content will cause the lignin fragments produced in the first and second stages of bleaching to undergo a chemical reaction, generating new chromophores, thus leading to the problem of yellowing.

[0089] As can be seen from Example 6, whiteness also decreases when the components that act as protectants and stabilizers are absent.

[0090] As can be seen from the cases in Reference Examples 6 and 7, under a stable alkaline environment, a slight increase in hydrogen peroxide can produce more HOO... - This allows for a more thorough and deep removal of chromophores, thus improving whiteness.

[0091] To verify Preparation Example 1, the following preparation example and reference example were set up with adjustments to some temperatures and holding times: Preparation Example 2: The difference from Preparation Example 1 is that the bleaching temperature in this preparation example is 70°C.

[0092] Preparation Example 3: The difference from Preparation Example 1 is that the bleaching and heat preservation time is 100 minutes.

[0093] Refer to Example 8: The difference from Preparation Example 1 is that the first-stage bleaching temperature is 65°C.

[0094] Refer to Example 9; the difference from Preparation Example 1 is that the bleaching and heat preservation time is 70 minutes.

[0095] The experimental results of Preparation Examples 1-3 and Reference Examples 8-9 are shown in Table 2 below: Table 2

[0096] As can be seen from Table 2 above, the difference between Preparation Example 2 and Preparation Example 1 is that the highest heat preservation temperature of Preparation Example 2 is 70°C in the first stage of bleaching. Compared with Preparation Example 1, the whiteness and degree of polymerization both decrease after the temperature is slightly increased.

[0097] As can be seen from the comparison between Preparation Example 3 and Preparation Example 1, although the effect on whiteness is not significant after extending the heat preservation time of the first bleaching stage, the extended heat preservation time prolongs the time during which cellulose is attacked, resulting in the breakage of molecular chains and a significant impact on the degree of polymerization. As can be seen from Reference Example 9, if the first bleaching time is slightly shortened, it is also easy to cause insufficient bleaching and have a certain impact on whiteness. However, under the heat preservation time of Reference Example 9, the whiteness can still exceed 80% ISO.

[0098] In addition, the present invention also provides the following preparation examples and reference examples: Preparation Example 4: The difference from Preparation Example 1 is that the amount of the second-stage bleaching agent A is 0.8%.

[0099] Preparation Example 5: The difference from Preparation Example 1 is that the two-stage bleaching and heat preservation time is 70 minutes.

[0100] Preparation Example 6: Three-stage bleaching with 3% hydrogen peroxide.

[0101] Preparation Example 7: The difference from Preparation Example 1 is that the amount of the second-stage bleaching agent A is 0.5%.

[0102] Preparation Example 8: The difference from Preparation Example 1 is that the two-stage bleaching and heat preservation time is 65 minutes.

[0103] Preparation Example 9: The difference from Preparation Example 1 is that the amount of hydrogen peroxide used in the three-stage bleaching is 1.5%.

[0104] The experimental results of Preparation Examples 1 and 4-9 are shown in Table 3 below: Table 3

[0105] As shown in Table 3 above, after making minor adjustments to the parameters of the two-stage bleaching process, it is possible to ensure that the whiteness exceeds 80% ISO and the degree of polymerization is above 1000.

[0106] Compared to Preparation Example 1, the amount of hydrogen peroxide in Preparation Example 6 of Table 3 was increased, which ensured a whiteness of 82.1% ISO while maintaining a degree of polymerization of 1054. However, the results in Table 1 show that when the amount of hydrogen peroxide exceeds 3%, even if the amount of hydrogen peroxide is 4%, there is basically no change in whiteness and degree of polymerization.

[0107] As can be seen from the above preparation examples and reference examples, the present invention provides a method for preparing cotton stalk pulp by including a cotton stalk ammonium sulfide pulping and cooking process and a special three-stage bleaching process. This method allows the cotton stalk fibers to achieve a whiteness of over 80% ISO by performing only a simple three-stage bleaching process, while also ensuring a degree of polymerization of over 1000. Furthermore, the entire bleaching process is short and easy to operate.

[0108] This embodiment also provides a cotton stalk pulp with a degree of polymerization greater than 1000 and a whiteness greater than 80% ISO. The cotton stalk pulp is prepared using the above-described method for preparing cotton stalk pulp.

[0109] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A cotton stalk ammonium sulfite pulping and cooking process, characterized by: Includes the following steps: S1. Add dry cotton stalks, water, ammonium sulfite, cooking aid A, cooking aid B, and buffer to the cooking vessel and seal it. The weight of the cotton stalks is 1000 parts, the weight of the water is 2.5-3 times the weight of the cotton stalks, the weight of the ammonium sulfite is 240-260 parts, the weight of both cooking aid A and cooking aid B is 0.8-1.2 parts, and the weight of the buffer is 25-35 parts. Cooking aid A is anthraquinone, and cooking aid B is a cooking penetrant. S2: When the steamer heats up to the pressure of 130℃, release steam slightly, then heat up to 135±5℃ and keep it at that temperature for 20-30 minutes. Then continue heating for at least 40 minutes, so that the highest temperature reaches 175±5℃ and is kept at that temperature for 100±5 minutes.

2. The cotton stalk ammonium sulfite pulping and cooking process according to claim 1, characterized in that: It also includes step S3, which includes: after the heat preservation is completed, releasing the steam until the pressure is zero, putting it in the pot, washing it until it is neutral, and then rinsing it.

3. The cotton stalk ammonium sulfite pulping and cooking process according to claim 1, characterized in that: This also includes sifting out the dust from the cotton stalk raw material before putting the dry cotton stalks into the cooker.

4. The cotton stalk ammonium sulfite pulping and cooking process according to claim 1, characterized in that: The moisture content of the dried cotton stalks was 10±2%.

5. The cotton stalk ammonium sulfite pulping and cooking process according to claim 1, characterized in that: The time required to raise the temperature from 135±5℃ to 175±5℃ should be controlled within 50-70 minutes.

6. The cotton stalk ammonium sulfite pulping and cooking process according to claim 5, characterized in that: Heat to 175±5℃ and then keep warm for 100 minutes.

7. The cotton stalk ammonium sulfite pulping and cooking process according to any one of claims 1-6, characterized in that: The buffer is sodium hydroxide.

8. The cotton stalk ammonium sulfite pulping and cooking process according to any one of claims 1-6, characterized in that: The amount of ammonium sulfite is 250 parts.

9. The cotton stalk ammonium sulfite pulping and cooking process according to any one of claims 1-6, characterized in that: Both cooking aid A and cooking aid B are 1 part each.

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