A production process of cotton pulp for lyocell fiber

Abstract

The application relates to the technical field of cotton pulp production, and discloses a production process of cotton pulp for lyocell fibers, the cotton pulp for lyocell fibers has the following indexes: a polymerization degree of 500-800; a whiteness of greater than or equal to 89%; a methyl cellulose content of greater than or equal to 95%; an ash content of less than or equal to 0.05%; a fiberization rate of greater than or equal to 60%; a kinked fiber content of less than or equal to 70%; and a metal content of less than or equal to 8 ppm; the prepared cotton pulp has uniform polymeric fiber length, high fiberization rate and short dissolving time.

Description

Technical Field

[0001] This invention relates to the field of cotton pulp production technology, and in particular to a production process for cotton pulp for lyocell fiber. Background Technology

[0002] Lyocell fiber is made from natural cellulose, which is widely available and renewable in nature. It combines the excellent properties of both natural and synthetic fibers. There is no chemical reaction in the production process, the process is simple, the solvent used is non-toxic and the recovery rate is higher than 99%. It is a new type of green fiber that is energy-saving, environmentally friendly and sustainable.

[0003] Currently, the raw materials for producing lyocell fiber both domestically and internationally are mainly bamboo and wood. However, bamboo and wood raw materials have relatively low cellulose content, ranging from 40% to 50%, while having higher non-cellulose contents such as lignin and pectin. The separation and purification of cellulose is quite complicated, requiring crushing, washing, degumming, and delignification. The process requires a large bath ratio of 1:20 or higher, and the pulping cycle is long, energy-consuming, and time-consuming. Furthermore, the cellulose yield is low, which is not conducive to the overall control of product quality and the maximization of production efficiency.

[0004] In addition, most manufacturers use harsh conditions such as high temperature and high alkali during the pulping process, which produces a large amount of black liquor with a COD content as high as tens of thousands to hundreds of thousands. Subsequent treatment is difficult and puts enormous pressure on environmental protection.

[0005] Cotton linters themselves contain more than 90% cellulose and very little non-cellulose such as pectin and lignin. Therefore, the cellulose separation and purification yield is very high. Moreover, the purification process does not require harsh conditions such as high temperature and high alkali, and the pulping cycle is relatively short. The α-cellulose content of the cotton pulp obtained can be as high as 95% or more.

[0006] Cotton fibers are soft to the touch, highly comfortable, and have good breathability and moisture absorption. Lyocell fibers prepared from cotton pulp have higher wet modulus, softness, toughness, and easy dyeing properties. These advantages give cotton pulp an absolute advantage in preparing high-quality lyocell fibers.

[0007] Chinese invention patent application number 202110602793.4 proposes a clean pulping process for lyocell fiber cotton pulp. The lyocell fiber cotton pulp produced by this patent has the following indicators: degree of polymerization 500-900; whiteness ≥90%; methyl cellulose ≥95%; ash content ≤0.05%; fiber length 23-32%; metal content ≤8ppm; 20% NMMO dissolved content ≤0.5%. This invention enables the "green and environmentally friendly" and ultra-high quality of lyocell fiber to start from the source material selection and run through the entire preparation process of lyocell fiber cotton pulp. It also solves the problems of cumbersome and lengthy pulping process, low cellulose yield, high COD of pulping black liquor, and excessive environmental pressure in existing bamboo and wood pulping technologies.

[0008] However, the technical solutions disclosed in the above patents still have the following defects: Pulping is an important step in the production of cotton pulp. During the pulping process, the fibers are subjected to heat and high-temperature pulses, which causes them to twist and bend, resulting in a long dissolution time when NMMO (N-methylmorpholine-N-oxide) dissolves cellulose. Summary of the Invention

[0009] The main technical problem to be solved by the present invention is to provide a production process for cotton pulp for lyocell fiber, which results in cotton pulp with uniform fiber length, high fiber fibrillation rate, and short dissolution time.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A production process for cotton pulp for lyocell fiber, wherein the cotton pulp for lyocell fiber has the following indicators: degree of polymerization 500-800; whiteness ≥89%; methyl cellulose ≥95%; ash content ≤0.05%; fibrillation rate ≥60%; kink fiber ≤70%; metal content ≤8ppm.

[0011] The following are further optimizations of the above technical solution by the present invention: The production process includes a pre-treatment step S1, a mid-pre-treatment step S2, a mid-to-late-treatment step S3, and a post-treatment step S4. The mid-pre-treatment step S2 specifically includes: S201, First low-consistency pulping process: carried out in a large taper pulping mill, with pulp concentration controlled at 1.0% to 1.8%, to complete the first pulping process; S202, First round screen thickening process: carried out in a side-pressure round screen thickener, the pulp concentration is controlled at 10% to 12%, and the pulp enters the anti-substance tank after the first thickening is completed; S203, First enzymatic anti-potential process: Add cellulase slurry, control the pH value at 7.0, the temperature at 60℃~70℃, and the treatment time is 20~30min to complete the first anti-potential process; S204, High-consistency refining process: carried out in a high-consistency refiner, with the pulp concentration controlled at 5% to 6%. After the second refining is completed, the pulp enters the anti-sublimation tank. S205, Second enzymatic anti-potential process: Add cellulase slurry, control the pH value at 7.0, the temperature at 60℃~70℃, and the treatment time is 20~30min to complete the second anti-potential process; S206. Second low-consistency pulping process: carried out in a large taper pulping mill, with pulp concentration controlled at 1.0% to 1.8%, to complete the third pulping process; S207. Second round screen thickening process: This is carried out in a side-pressure round screen thickener, with the pulp concentration controlled at 10% to 12%, to complete the second thickening.

[0012] Further optimization: The concentration of cellulase syrup used in steps S203 and S205 is 3.0–6.0 IU / g.

[0013] Further optimization: In steps S201, S204 and S206, the pulping current is controlled at 180A to 200A, and the pulping rate is 10 to 30 min / t.

[0014] Further optimization: The mid-to-late stage processing step S3 specifically includes: S301, Hydrogen peroxide bleaching process; S302, Acid treatment process: Add hydrochloric acid with a relative dry slurry volume of 2% to 2.5% into the acid treatment tower, and after acid treatment for 20 to 40 minutes, wash with deionized water for 2 to 3 hours.

[0015] Further optimization: The bleaching process in step S301 specifically includes the following steps: S301a. In a medium-consistency mixer, add diethylenetriaminepentaacetic acid and hydrogen peroxide, and introduce steam. Control the mixing temperature at 90℃~110℃. After mixing for 20~30 minutes, transfer the slurry to the hydrogen peroxide bleaching tower. In the S301b hydrogen peroxide bleaching tower, the temperature is controlled at 90℃~110℃, and the bleaching reaction is carried out for 100~120 minutes. Then, the slurry is diluted with deionized water, and the slurry concentration is controlled at 1%~1.5%. After that, the slurry is sent to a vacuum washer and washed with deionized water until it is neutral. After washing, the slurry enters the acid treatment tower.

[0016] Further optimization: In step S301a, the relative oven-dry slurry weight of diethylenetriaminepentaacetic acid is 0.17% to 0.22%.

[0017] Further optimization: In step S301a, the relative oven-dry slurry content of hydrogen peroxide is 1.5% to 2.5%.

[0018] Further optimization: The preprocessing step S1 specifically includes the following steps: S101, Material selection, cotton opening, and dry impurity removal process: Select Class III Grade 1 cotton linters with a maturity of ≥80%, tear the cotton linters with a cotton opening machine, loosen and remove impurities from the torn cotton linters with an impurity removal machine, then transfer them into a cotton extruder for fine selection and impurity removal, and finally send the linters to the cooking process through a cyclone separator. S102, Cooking process: The alkali preparation temperature is controlled at 45℃~50℃, the total alkali is sodium hydroxide at 6%~10% relative to the weight of the oven-dry pulp, and the alkali-to-liquid ratio is 1:3.7~4.2. Sodium sulfate at 0.4%~0.8% relative to the weight of the oven-dry pulp is added. The holding time is 120min, and the holding temperature is 140℃~155℃. S103. Pre-desanding process: carried out in a desander, with pressure controlled at 0.30-0.32 MPa, slurry concentration controlled at 0.4%-0.6%, and desanding rate at 10-30 min / t.

[0019] Further optimization: The post-processing step S4 specifically includes: S401, Post-desanding process: The post-desanding pressure is controlled at ≥0.3Mpa, the pulp concentration is controlled at 0.8%~1.0%, the desanding rate is 10~30min / t, and after desanding, it enters the paper machine process; S402, Paper machine process: The pulp concentration on the paper machine is controlled at 10-12 g / l, the drying cylinder pressure is ≤0.20 MPa, and the finished product is obtained after the pulping is completed.

[0020] The present invention adopts the above-mentioned technical solution and has the following beneficial effects: the production process adopts enzyme digestion and high and low concentration pulping technology. Therefore, in the pulping process, low concentration pulping is mainly for cutting fibers, while high concentration pulping is mainly for fiber buffing. The high and low concentration pulping technology can make the fiber length more uniform, increase the specific surface area, and make it more conducive to contact and dissolution with NMMO solvent, thereby reducing the dissolution time.

[0021] Meanwhile, the cellulase de-knock technology is used to enzymatically decompose the fiber surface structure, which can straighten the crimped fiber and significantly reduce kinking, thus facilitating the dispersion of fiber dissolved in NMMO solvent. Detailed Implementation

[0022] Example 1 A production process for cotton pulp for lyocell fiber, wherein the cotton pulp for lyocell fiber has the following indicators: degree of polymerization 500-800; whiteness ≥89%; methyl cellulose ≥95%; ash content ≤0.05%; fibrillation rate ≥60%; kink fiber ≤70%; metal content ≤8ppm.

[0023] Preferably, the production process includes a pre-treatment step S1, a mid-pre-treatment step S2, a mid-to-late-treatment step S3, and a post-treatment step S4, wherein the mid-pre-treatment step S2 specifically includes: S201, First low-consistency pulping process: carried out in a large taper pulping mill, with pulp concentration controlled at 1.0%, to complete the first pulping process; S202, First round screen thickening process: carried out in a side-pressure round screen thickener, the pulp concentration is controlled at 10%, and the pulp enters the anti-submersion tank after the first thickening is completed; S203, First enzymatic anti-potential process: Add cellulase slurry, control the pH value at 7.0, the temperature at 60℃~70℃, and the treatment time is 30min to complete the first anti-potential process; S204, High-consistency refining process: carried out in a high-consistency refiner, with the pulp concentration controlled at 6%. After the second refining is completed, the pulp enters the anti-sublimation tank. S205, Second enzymatic anti-potential process: Add cellulase slurry, control the pH value at 7.0, the temperature at 60℃~70℃, and the treatment time is 30min to complete the second anti-potential process; S206. Second low-consistency pulping process: carried out in a large taper pulping mill, with pulp concentration controlled at 1.0%, to complete the third pulping process; S207. Second round screen thickening process: This is carried out in a side-pressure round screen thickener, with the pulp concentration controlled at 10%, to complete the second thickening.

[0024] In this embodiment, the core technology adopts a high- and low-consistency refining synergistic process, which achieves precise control of the fiber structure through a combination of "two low-consistency refining processes + one high-consistency refining process".

[0025] The two low-concentration pulping processes aim at directional fiber cutting, which can effectively control the distribution range of fiber length and avoid the situation of entanglement due to excessively long fibers or loss of strength due to excessively short fibers. The high-concentration pulping process focuses on fiber buffing modification. Through the squeezing and kneading action between fibers in a high-concentration environment, more microfibers are generated on the fiber surface, which greatly increases the specific surface area of ​​the fiber.

[0026] This alternating "cutting-brooming" pulping strategy ensures the uniformity of fiber length and increases the contact sites between the fiber and the solvent through the brooming effect. This allows the cellulose molecules in the cotton pulp to come into more full contact with the NMMO solvent and undergo swelling and dissolution reactions. Compared with the traditional single pulping process, the dissolution time can be shortened by more than 30%, and the uniformity of the dissolution system is significantly improved, effectively avoiding the formation of local undissolved fiber clumps.

[0027] Furthermore, an enzyme de-emulsification process is added between the low-consistency and high-consistency refining processes: the non-crystalline regions and hydrogen bond networks on the fiber surface are enzymatically modified by specific cellulase. On the one hand, this can relax the crimped fibers generated during the refining process, and on the other hand, it can significantly reduce the degree of kinking between fibers and break the aggregated structure formed by the mechanical action of the fibers.

[0028] After enzymatic de-potency treatment, the dispersibility of the fiber is improved. In the subsequent NMMO solvent dissolution stage, cellulose molecules can be more uniformly dispersed in the solvent system, further optimizing the dissolution efficiency and solution stability, and providing a high-quality raw material basis for subsequent spinning or forming processes.

[0029] Preferably, the concentration of cellulase syrup used in steps S203 and S205 is 3.0 IU / g.

[0030] Preferably, in steps S201, 204 and S206, the pulping current is controlled at 180A and the pulping rate is 30min / t.

[0031] Preferably, the mid-to-late processing step S3 specifically includes: S301, Hydrogen peroxide bleaching process; S302, Acid treatment process: Add hydrochloric acid with a relative dry slurry volume of 2.5% into the acid treatment tower, acid treat for 40 minutes, and then wash with deionized water for 60 minutes.

[0032] In this embodiment, sodium hydroxide and other alkaline agents remain in the slurry after the bleaching process. After adding hydrochloric acid, the H+ in the hydrochloric acid... + With OH in the slurry - A neutralization reaction occurs, and hydrochloric acid can also form soluble chlorides with residual metal ions, thus preventing the deposition of metal salts in the slurry.

[0033] Meanwhile, the 40-minute processing time ensures the completeness of the neutralization reaction, allowing the pH value of the slurry to gradually approach neutral.

[0034] The deionized water washing process can thoroughly wash away salts, unreacted trace amounts of hydrochloric acid, and residual bleaching byproducts (such as oxidized pigment fragments) contained in the slurry, thus preventing impurities from affecting the solubility of the slurry or the quality of the finished product.

[0035] Preferably, the bleaching process in step S301 specifically includes the following steps: S301a. In a medium-concentration mixer, add diethylenetriaminepentaacetic acid and hydrogen peroxide, and introduce steam. Control the mixing temperature at 90°C. After mixing for 30 minutes, transfer the slurry to the hydrogen peroxide bleaching tower. In the S301b hydrogen peroxide bleaching tower, the temperature is controlled at 90℃ and the bleaching reaction is carried out for 100 minutes. Then, it is diluted with deionized water and the pulp concentration is controlled at 1.5%. After that, the pulp is sent to the vacuum washing machine and washed with deionized water until it is neutral. After washing, the pulp enters the acid treatment tower.

[0036] In this embodiment, the bleaching process adopts a medium-concentration oxygen bleaching process with hydrogen peroxide as the core. Through the synergistic effect of chelating agent and oxidant, efficient decolorization of slurry is achieved.

[0037] Meanwhile, the combination of medium-concentration premixing and bleaching tower makes the bleaching reaction more uniform, and the whiteness improvement is 5 to 8 percentage points higher than that of the traditional single-tower bleaching process.

[0038] In addition, vacuum washing and acid treatment of the slurry reduce the residual content of alkali and oxidant in the slurry to less than 0.1%, thereby enhancing the stability of subsequent dissolving / spinning processes.

[0039] Preferably, in step S301a, the relative oven-dry weight of diethylenetriaminepentaacetic acid is 0.17%.

[0040] In this embodiment, diethylenetriaminepentaacetic acid (DTPA) is used as a metal chelating agent to complex residual heavy metal ions such as iron and copper in the slurry, and it can also stabilize the oxidizing activity of hydrogen peroxide.

[0041] This avoids excessive oxidation catalyzed by heavy metal ions, reduces the loss rate of cellulose polymerization, and maximizes the preservation of fiber strength.

[0042] Preferably, in step S301a, the relative oven-dry slurry weight of hydrogen peroxide is 2.5%.

[0043] In this embodiment, hydrogen peroxide is used as an oxidant.

[0044] During the bleaching process, steam heating enables hydrogen peroxide to be initially decomposed into hydroxyl radicals, which pre-oxidize the pigments in the slurry. At the same time, the complexation reaction between DTPA and heavy metal ions is completed simultaneously.

[0045] Preferably, the preprocessing step S1 specifically includes the following steps: S101. Material selection, cotton opening, and dry impurity removal process: Select Class III Grade 1 cotton linters with a maturity of ≥80%, tear the cotton linters with a cotton opening machine, loosen and remove impurities with an impurity removal machine, transfer them to a cotton extruder for fine selection and impurity removal, and finally send the linters to the cooking process through a cyclone separator.

[0046] In this invention, the raw material screening process specifically includes the following criteria: (1) Prioritize the selection of high-maturity cotton linters.

[0047] This indicator is the core foundation for the subsequent preparation of high cellulose content finished products, and can directly ensure the fiber purity and performance stability of the final product.

[0048] (2) Strictly control the cleanliness and impurity index of cotton linters.

[0049] On the one hand, sulfuric acid insolubles will consume some of the alkali solution during the cooking process, disrupting the chemical balance of the reaction system and resulting in uneven reaction of the semi-pulp and large fluctuations in quality. On the other hand, these impurities will increase the dust content of the finished product. At the same time, high levels of sulfuric acid insolubles can easily decompose into a large amount of pigment during the cooking process, significantly increasing the difficulty of improving whiteness in the subsequent bleaching process.

[0050] (3) Emphasize the color consistency of cotton linters: raw materials with pure and uniform color should be selected.

[0051] If the cotton linters themselves are dull in color or contain mixed colored fibers, it will directly affect the whiteness of the final product and reduce the appearance quality of the finished product.

[0052] S102. Cooking process: The alkali temperature is controlled at 45℃~50℃. The total alkali is sodium hydroxide at 10% relative to the weight of the oven-dry pulp, and the alkali-to-liquid ratio is 1:4. Sodium sulfate at 0.4% relative to the weight of the oven-dry pulp is added. The heat preservation time is 120 minutes and the heat preservation temperature is 155℃.

[0053] In this embodiment, the steaming process is carried out in a sealed environment inside the steaming ball.

[0054] In this embodiment, the alkaline solution is prepared at a mild temperature to avoid the release of heat from sodium hydroxide upon contact with water, which would lead to uneven local concentration. The 1:4 mass ratio of sodium hydroxide to oven-dried pulp ensures that the alkaline solution fully coats the cotton linters. The 10% concentration of sodium hydroxide provides a strongly alkaline environment that can break the chemical bonds of impurities such as wax and pectin on the primary wall of cotton fibers and initiate the degradation of cellulose macromolecules.

[0055] In this embodiment, sodium sulfate, as an alkaline solution stabilizer, can inhibit the excessive decomposition of sodium hydroxide at high temperatures, while reducing the electrostatic repulsion between fibers and assisting the penetration of the alkaline solution, thereby ensuring the consistency of cooking effects between batches.

[0056] S103. Pre-desanding process: carried out in a desander, with pressure controlled at 0.30 MPa, slurry concentration controlled at 0.4%, and desanding rate at 30 min / t.

[0057] Preferably, the post-processing step S4 specifically includes: S401, Post-desanding process: Post-desanding pressure is controlled at ≥0.3Mpa, pulp concentration is controlled at 0.8%, desanding rate is 30min / t, after desanding, it enters the paper machine process; S402, Paper machine process: The pulp concentration on the paper machine is controlled at 10-12 g / l, the drying cylinder pressure is ≤0.20 MPa, and the finished product is obtained after the pulping is completed.

[0058] The finished product obtained according to the production process in this embodiment, after testing, has the following specific indicators: Example 2 This embodiment is basically the same as the above embodiment, except that: A production process for cotton pulp for lyocell fiber, comprising a pretreatment step S1, a mid-pretreatment step S2, a mid-to-late treatment step S3, and a late treatment step S4, wherein the mid-pretreatment step S2 specifically includes: S201, First low-consistency pulping process: carried out in a large taper pulping mill, with pulp concentration controlled at 1.0%, to complete the first pulping process; S202, First round screen thickening process: carried out in a side-pressure round screen thickener, the pulp concentration is controlled at 10%, and the pulp enters the anti-submersion tank after the first thickening is completed; S203, First enzymatic anti-potential process: Add cellulase slurry, control the pH value at 7.0, the temperature at 60℃~70℃, and the treatment time is 30min to complete the first anti-potential process; S204, High-consistency refining process: carried out in a high-consistency refiner, with the pulp concentration controlled at 6%. After the second refining is completed, the pulp enters the anti-sublimation tank. S205, Second enzymatic anti-potential process: Add cellulase slurry, control the pH value at 7.0, the temperature at 60℃~70℃, and the treatment time is 30min to complete the second anti-potential process; S206. Second low-consistency pulping process: carried out in a large taper pulping mill, with pulp concentration controlled at 1.0%, to complete the third pulping process; S207. Second round screen thickening process: This is carried out in a side-pressure round screen thickener, with the pulp concentration controlled at 10%, to complete the second thickening.

[0059] Preferably, the concentration of cellulase syrup used in steps S203 and S205 is 3.0 IU / g.

[0060] Preferably, in steps S201 and S206, the pulping current is controlled at 180A and the pulping rate is 30min / t; while in step 204, the pulping current is controlled at 220A and the pulping rate is 30min / t.

[0061] Preferably, the mid-to-late processing step S3 specifically includes: S301, Hydrogen peroxide bleaching process; S302, Acid treatment process: Add hydrochloric acid with a relative dry slurry volume of 2.5% into the acid treatment tower, acid treat for 40 minutes, and then wash with deionized water for 60 minutes.

[0062] Preferably, the bleaching process in step S301 specifically includes the following steps: S301a. In a medium-concentration mixer, add diethylenetriaminepentaacetic acid and hydrogen peroxide, and introduce steam. Control the mixing temperature at 90°C. After mixing for 30 minutes, transfer the slurry to the hydrogen peroxide bleaching tower. In the S301b hydrogen peroxide bleaching tower, the temperature is controlled at 90℃ and the bleaching reaction is carried out for 100 minutes. Then, it is diluted with deionized water and the pulp concentration is controlled at 1.5%. After that, the pulp is sent to the vacuum washing machine and washed with deionized water until it is neutral. After washing, the pulp enters the acid treatment tower.

[0063] Preferably, in step S301a, the relative oven-dry weight of diethylenetriaminepentaacetic acid is 0.17%.

[0064] Preferably, in step S301a, the relative oven-dry slurry weight of hydrogen peroxide is 2.5%.

[0065] Preferably, the preprocessing step S1 specifically includes the following steps: S101, Material selection, cotton opening, and dry impurity removal process: Select Class III Grade 1 cotton linters with a maturity of ≥80%, tear the cotton linters with a cotton opening machine, loosen and remove impurities from the torn cotton linters with an impurity removal machine, then transfer them into a cotton extruder for fine selection and impurity removal, and finally send the linters to the cooking process through a cyclone separator. S102, Cooking process: The alkali preparation temperature is controlled at 45℃~50℃, the total alkali is sodium hydroxide at 10% relative to the weight of the oven-dry pulp, and the alkali solution ratio is 1:4. Sodium sulfate at 0.4% relative to the weight of the oven-dry pulp is added. The heat preservation time is 120min and the heat preservation temperature is 155℃. S103. Pre-desanding process: carried out in a desander, with pressure controlled at 0.30 MPa, slurry concentration controlled at 0.4%, and desanding rate at 30 min / t.

[0066] Preferably, the post-processing step S4 specifically includes: S401, Post-desanding process: Post-desanding pressure is controlled at ≥0.3Mpa, pulp concentration is controlled at 0.8%, desanding rate is 30min / t, after desanding, it enters the paper machine process; S402, Paper machine process: The pulp concentration on the paper machine is controlled at 10-12 g / l, the drying cylinder pressure is ≤0.20 MPa, and the finished product is obtained after the pulping is completed.

[0067] The finished product obtained according to the production process in this embodiment, after testing, has the following specific indicators: Example 3 This embodiment is basically the same as the above embodiment, except that: A production process for cotton pulp for lyocell fiber, comprising a pretreatment step S1, a mid-pretreatment step S2, a mid-to-late treatment step S3, and a late treatment step S4, wherein the mid-pretreatment step S2 specifically includes: S201, First low-consistency pulping process: carried out in a large taper pulping mill, with pulp concentration controlled at 1.0%, to complete the first pulping process; S202, First round screen thickening process: carried out in a side-pressure round screen thickener, the pulp concentration is controlled at 10%, and the pulp enters the anti-submersion tank after the first thickening is completed; S203, First enzymatic anti-potential process: Add cellulase slurry, control the pH value at 7.0, the temperature at 60℃~70℃, and the treatment time is 30min to complete the first anti-potential process; S204, High-consistency refining process: carried out in a high-consistency refiner, with the pulp concentration controlled at 6%. After the second refining is completed, the pulp enters the anti-sublimation tank. S205, Second enzymatic anti-potential process: Add cellulase slurry, control the pH value at 7.0, the temperature at 60℃~70℃, and the treatment time is 30min to complete the second anti-potential process; S206. Second low-consistency pulping process: carried out in a large taper pulping mill, with pulp concentration controlled at 1.0%, to complete the third pulping process; S207. Second round screen thickening process: This is carried out in a side-pressure round screen thickener, with the pulp concentration controlled at 10%, to complete the second thickening.

[0068] Preferably, the concentration of cellulase syrup used in steps S203 and S205 is 5.0 IU / g.

[0069] Preferably, in steps S201 and S206, the pulping current is controlled at 180A and the pulping rate is 30min / t; while in step 204, the pulping current is controlled at 220A and the pulping rate is 30min / t.

[0070] Preferably, the mid-to-late processing step S3 specifically includes: S301, Hydrogen peroxide bleaching process; S302, Acid treatment process: Add hydrochloric acid with a relative dry slurry volume of 2.5% into the acid treatment tower, and after acid treatment for 40 minutes, wash with deionized water for 60 minutes.

[0071] Preferably, the bleaching process in step S301 specifically includes the following steps: S301a. In a medium-concentration mixer, add diethylenetriaminepentaacetic acid and hydrogen peroxide, and introduce steam. Control the mixing temperature at 90°C. After mixing for 30 minutes, transfer the slurry to the hydrogen peroxide bleaching tower. In the S301b hydrogen peroxide bleaching tower, the temperature is controlled at 90℃ and the bleaching reaction is carried out for 100 minutes. Then, it is diluted with deionized water and the pulp concentration is controlled at 1.5%. After that, the pulp is sent to the vacuum washing machine and washed with deionized water until it is neutral. After washing, the pulp enters the acid treatment tower.

[0072] Preferably, in step S301a, the relative oven-dry weight of diethylenetriaminepentaacetic acid is 0.17%.

[0073] Preferably, in step S301a, the relative oven-dry slurry weight of hydrogen peroxide is 2.5%.

[0074] Preferably, the preprocessing step S1 specifically includes the following steps: S101, Material selection, cotton opening, and dry impurity removal process: Select Class III Grade 1 cotton linters with a maturity of ≥80%, tear the cotton linters with a cotton opening machine, loosen and remove impurities from the torn cotton linters with an impurity removal machine, then transfer them into a cotton extruder for fine selection and impurity removal, and finally send the linters to the cooking process through a cyclone separator. S102, Cooking process: The alkali preparation temperature is controlled at 45℃~50℃, the total alkali is sodium hydroxide at 10% relative to the weight of the oven-dry pulp, and the alkali solution ratio is 1:4. Sodium sulfate at 0.4% relative to the weight of the oven-dry pulp is added. The heat preservation time is 120min and the heat preservation temperature is 155℃. S103. Pre-desanding process: carried out in a desander, with pressure controlled at 0.30 MPa, slurry concentration controlled at 0.4%, and desanding rate at 30 min / t.

[0075] Preferably, the post-processing step S4 specifically includes: S401, Post-desanding process: Post-desanding pressure is controlled at ≥0.3Mpa, pulp concentration is controlled at 0.8%, desanding rate is 30min / t, after desanding, it enters the paper machine process; S402, Paper machine process: The pulp concentration on the paper machine is controlled at 10-12 g / l, the drying cylinder pressure is ≤0.20 MPa, and the finished product is obtained after the pulping is completed.

[0076] The finished product obtained according to the production process in this embodiment, after testing, has the following specific indicators: Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A production process for cotton pulp for lyocell fiber, characterized in that, The lyocell fiber cotton pulp has the following specifications: degree of polymerization 500-800; whiteness ≥89%; methyl cellulose ≥95%; ash content ≤0.05%; fuzziness ≥60%; kink fiber ≤70%; metal content ≤8ppm.

2. The production process of cotton pulp for lyocell fiber according to claim 1, characterized in that, The production process includes a pre-treatment step S1, a mid-pre-treatment step S2, a mid-to-late-treatment step S3, and a post-treatment step S4. The mid-pre-treatment step S2 specifically includes: S201, First low-consistency pulping process: carried out in a large taper pulping mill, with pulp concentration controlled at 1.0% to 1.8%, to complete the first pulping process; S202, First round screen thickening process: carried out in a side-pressure round screen thickener, the pulp concentration is controlled at 10% to 12%, and the pulp enters the anti-substance tank after the first thickening is completed; S203, First enzymatic anti-potential process: Add cellulase slurry, control the pH value at 7.0, the temperature at 60℃~70℃, and the treatment time is 20~30min to complete the first anti-potential process; S204, High-consistency refining process: carried out in a high-consistency refiner, with the pulp concentration controlled at 5% to 6%. After the second refining is completed, the pulp enters the anti-sublimation tank. S205, Second enzymatic anti-potential process: Add cellulase slurry, control the pH value at 7.0, the temperature at 60℃~70℃, and the treatment time is 20~30min to complete the second anti-potential process; S206. Second low-consistency pulping process: carried out in a large taper pulping mill, with pulp concentration controlled at 1.0% to 1.8%, to complete the third pulping process; S207. Second round screen thickening process: This is carried out in a side-pressure round screen thickener, with the pulp concentration controlled at 10% to 12%, to complete the second thickening.

3. The production process of cotton pulp for lyocell fiber according to claim 2, characterized in that, The concentration of cellulase syrup used in steps S203 and S205 is 3.0–6.0 IU / g.

4. The production process of cotton pulp for lyocell fiber according to claim 2, characterized in that, In steps S201, S204 and S206, the pulping current is controlled at 180A to 200A, and the pulping rate is 10 to 30 min / t.

5. The production process of cotton pulp for lyocell fiber according to claim 2, characterized in that, The mid-to-late stage processing step S3 specifically includes: S301, Hydrogen peroxide bleaching process; S302, Acid treatment process: Add hydrochloric acid with a relative dry slurry volume of 2% to 2.5% into the acid treatment tower, and after acid treatment for 20 to 40 minutes, wash with deionized water for 2 to 3 hours.

6. The production process of cotton pulp for lyocell fiber according to claim 5, characterized in that, The bleaching process in step S301 specifically includes the following steps: S301a. In a medium-consistency mixer, add diethylenetriaminepentaacetic acid and hydrogen peroxide, and introduce steam. Control the mixing temperature at 90℃~110℃. After mixing for 20~30 minutes, transfer the slurry to the hydrogen peroxide bleaching tower. In the S301b hydrogen peroxide bleaching tower, the temperature is controlled at 90℃~110℃, and the bleaching reaction is carried out for 100~120 minutes. Then, the slurry is diluted with deionized water, and the slurry concentration is controlled at 1%~1.5%. After that, the slurry is sent to a vacuum washer and washed with deionized water until it is neutral. After washing, the slurry enters the acid treatment tower.

7. The production process of cotton pulp for lyocell fiber according to claim 6, characterized in that, In step S301a, the relative oven-dry slurry weight of diethylenetriaminepentaacetic acid is 0.17% to 0.22%.

8. The production process of cotton pulp for lyocell fiber according to claim 6, characterized in that, In step S301a, the relative oven-dry slurry content of hydrogen peroxide is 1.5% to 2.5%.

9. The production process of cotton pulp for lyocell fiber according to claim 2, characterized in that, The preprocessing step S1 specifically includes the following steps: S101, Material selection, cotton opening, and dry impurity removal process: Select Class III Grade 1 cotton linters with a maturity of ≥80%, tear the cotton linters with a cotton opening machine, loosen and remove impurities from the torn cotton linters with an impurity removal machine, then transfer them into a cotton extruder for fine selection and impurity removal, and finally send the linters to the cooking process through a cyclone separator. S102, Cooking process: The alkali preparation temperature is controlled at 45℃~50℃, the total alkali is sodium hydroxide at 6%~10% relative to the weight of the oven-dry pulp, and the alkali-to-liquid ratio is 1:3.7~4.

2. Sodium sulfate at 0.4%~0.8% relative to the weight of the oven-dry pulp is added. The holding time is 120min, and the holding temperature is 140℃~155℃. S103. Pre-desanding process: carried out in a desander, with pressure controlled at 0.30-0.32 MPa, slurry concentration controlled at 0.4%-0.6%, and desanding rate at 10-30 min / t.

10. The production process of cotton pulp for lyocell fiber according to claim 2, characterized in that, The post-processing step S4 specifically includes: S401, Post-desanding process: The post-desanding pressure is controlled at ≥0.3Mpa, the pulp concentration is controlled at 0.8%~1.0%, the desanding rate is 10~30min / t, and after desanding, it enters the paper machine process; S402, Paper machine process: The pulp concentration on the paper machine is controlled at 10-12 g / l, the drying cylinder pressure is ≤0.20 MPa, and the finished product is obtained after the pulping is completed.

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