Production method of refined cotton linter

Abstract

The invention relates to a production method of refined cotton linters, which comprises the following steps: S1, raw material pretreatment: removing metal, gravel and cottonseed hull impurities from a cotton linter raw material through an opener and an impurity remover, and opening the cotton linter raw material into flocculent fragments to improve the subsequent reaction uniformity; s2, alkali spraying and presoaking: spraying the cotton linters by using a sodium hydroxide solution, removing excessive alkali liquor in combination with spiral extrusion, and preliminarily destroying lignin and hemicellulose structures; s3, alkaline cooking: performing alkaline cooking on the cotton linter raw material by adopting a segmented cooking mode; and S4, bleaching and acid treatment: taking out the cotton linter raw material cooked in the S3 from the cooking pot, and removing the alkali liquor by utilizing spiral extrusion. According to the method disclosed by the invention, a sectional temperature control technology is adopted during alkaline cooking, cellulose degradation is reduced by sectional temperature rise, the polymerization degree stability is improved, the viscosity of an ultra-high-viscosity product is greater than or equal to 800mPa. S, alkali liquor is optimized, a NaOH and Na2SO3 composite system is adopted, the dosage of NaOH is reduced by 20-30%, the cost is reduced, and the wastewater treatment pressure is relieved.

Description

Technical Field

[0001] The present invention relates to the technical field of refined cotton linters, and particularly relates to a production method of refined cotton linters. Background Art

[0002] China is rich in cotton, and the resources of cotton linters are very abundant. Cotton linters refer to the part of fibers remaining outside the cottonseed hulls after ginning. The fiber length of cotton linters is shorter than that of lint cotton, but the maturity is quite the same. Therefore, the cellulose content is high, and it is an important raw material for light and chemical industries such as national defense, textile, chemical fiber, and papermaking, and is an important strategic material for light industry, military industry, chemical industry, and pharmaceutical industry. China is rich in cotton, and the resources of cotton linters are very abundant. If all the cottonseeds after ginning are delinted, the obtained linters can be equivalent to 15% - 20% of the total output of lint cotton. Therefore, cotton linters are a cellulose resource that cannot be ignored.

[0003] The production of refined cotton linters is a key process for deeply processing the short fibers remaining outside the cottonseed hulls, improving the cellulose purity and reducing the impurity content to meet the needs of high-end fields such as military, textile, and medicine. Traditional refined cotton linters are generally a high-purity cellulose product obtained after refined treatments such as alkaline cooking, bleaching, dehydration, and drying. Especially when the raw materials are cooked with lye, the dosage of lye and the cooking temperature have a significant impact on the preparation of cotton linters from the raw materials. For example, when the temperature of the lye is too high, it will cause excessive decomposition of cellulose in the raw materials. A large number of glucosidic bonds in the cellulose molecules are broken, the degree of polymerization is significantly reduced, and even completely degraded into small molecule substances. Its structure becomes loose, the strength drops significantly, and it is easy to break. When over-decomposed, a large number of glucosidic bonds are broken, generating a large number of reducing end groups such as aldehyde groups. At the same time, the crystallinity of cellulose decreases, and the amorphous region increases. In some chemical analyses, the reactivity of over-decomposed cellulose to specific reagents will increase significantly. For example, in the acid hydrolysis process, the higher the degree of decomposition, the more reducing sugars are produced. Therefore, it is urgent to design a production method of refined cotton linters to solve the above problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a production method of refined cotton linters to solve the above deficiencies in the prior art.

[0005] In order to achieve the above purpose, the present invention provides the following technical solutions: A production method of refined cotton linters, comprising the following steps: S1. Pretreatment of raw materials. The raw materials of cotton linters are passed through a cotton opener and a cleaner to remove impurities such as metal, sand, and cottonseed hulls, and are loosened into flocculent fragments to improve the uniformity of subsequent reactions. S2. Spray alkali pre - impregnation: Spraying sodium hydroxide solution on cotton linters, combined with spiral extrusion to remove excess alkali solution, and initially destroying the lignin and hemicellulose structures; S3. Alkaline cooking: Adopting a segmented cooking method to achieve alkaline cooking of cotton linter raw materials; S4. Bleaching and acid treatment: Taking out the cotton linter raw materials after cooking in S3 from the cooking pot, and using spiral extrusion to remove alkali solution, and adopting a multi - stage bleaching method to treat the cotton linter raw materials; S5. Dehydration and drying: Dehydrating and drying the cotton linters after bleaching and acid treatment; S6. Wastewater recycling: Recycling the cooking and pulp washing wastewater and rinsing water for pretreatment, reducing water consumption and pollution, and reducing the COD to below 10600 mg / L.

[0006] Preferably, in S1, use cotton linters with a maturity ≥ 80% and a fiber length of 8 - 10 mm, and avoid the mixing of foreign fibers to affect the quality; Impurity control: Reducing the mechanical impurity content to < 4% through a metal detector and a multi - stage sand remover.

[0007] Preferably, in S2, the temperature of the sprayed sodium hydroxide solution is 30 - 45°C and the concentration is 10 - 15%.

[0008] Preferably, in S3, the segmented cooking technology: Pre - cooking: Adding a mixed solution containing 2.1 - 2.6% NaOH and 1 - 3% Na2SO3, treating at room temperature for 15 - 30 minutes to initially decompose impurities; First - stage cooking: Temperature 110 - 120°C, pressure 0.1 - 0.3 MPa, cooking for 50 - 70 minutes to further degrease; Final - stage cooking: Heating to 130 - 150°C, pressure 0.3 - 0.6 MPa, cooking for 70 - 120 minutes to completely remove residual lignin and increase the α - cellulose content to ≥ 98%.

[0009] Preferably, in S4, the multi - stage bleaching: Acid pre - treatment: Adjusting the pH of the pulp to 1.0 - 6.0 with dilute sulfuric acid to neutralize residual alkali solution and dissolve metal ions; H2O2 bleaching: Under the condition of pH 7 - 10, adding 5 - 6% hydrogen peroxide and 3 - 5 g / L stabilizer, controlling the temperature at 10 - 30°C, bleaching for 60 - 80 minutes, and the whiteness can reach 87%; Sodium hypochlorite assistance: Combining sodium hypochlorite to enhance the bleaching effect and shorten the treatment time.

[0010] Preferably, in S3 during alkaline cooking, the mass ratio of the alkali in the alkali solution in the cooking pot to the absolute dry mass of cotton linters is 13 - 15:100; That is, when the absolute dry weight of cotton linter is 2,000 kg, the mass of the required lye is between 26 kg and 30 kg.

[0011] Preferably, in S2, alkali spraying and pre-impregnation, the treated cotton linter is laid flat on the conveying device, the average height of the cotton linter on the conveying device is less than 3 cm, and a multi-directional lye nozzle is used to spray lye on the cotton linter on the conveying device, and the number of lye spraying times is 3 - 5 times.

[0012] Preferably, in S5, dehydration and drying: dehydration is carried out to a water content of ≤15% by a screw press, and then air drying or vacuum drying is carried out for 40 - 60 minutes to obtain a loose flocculent finished product.

[0013] Preferably, the obtained cotton linter product is tested, and the main test parameters are: α-cellulose content, whiteness, viscosity, ash content, and polymerization degree uniformity; α-cellulose content: ≥98%; Whiteness: ≥87%; Viscosity: ≥800 mPa·s; Ash content: ≤0.10%; Polymerization degree uniformity: ±5%.

[0014] In the above technical solution, a production method of refined cotton linter provided by the present invention has the following beneficial effects: (1) The adopted alkali spraying and pre-impregnation initially destroys the structures of lignin and hemicellulose. Through the synergistic effect of chemical methods and enzymatic hydrolysis processes, the problems of low efficiency and high cost in traditional pretreatment are effectively solved. (2) During alkaline cooking, a technology of segmented temperature control is adopted. The temperature is raised in stages to reduce cellulose degradation, and the stability of the polymerization degree is improved. The viscosity of the extra-high viscosity product is ≥800 mPa·s. Lye optimization: A composite system of NaOH and Na2SO3 is adopted to reduce the NaOH dosage by 20 - 30%, reduce costs and relieve the pressure of wastewater treatment. Description of the Drawings

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings. Figure 1 It is a process flow chart provided for an embodiment of a production method of refined cotton linter of the present invention. Detailed Embodiments

[0016] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation manners, structures, features, and effects according to the present invention as follows.

[0017] As Figure 1 shown, a production method of refined cotton linter provided by an embodiment of the present invention includes the following steps: raw material pretreatment, in which the cotton linter raw material is passed through a cotton opener and a cleaner to remove metal, sand, and cottonseed hull impurities, and is loosened into flocculent fragments to improve the uniformity of subsequent reactions; alkali spraying and pre-impregnation, in which the cotton linter is sprayed with a sodium hydroxide solution, and excess alkali solution is removed by means of screw extrusion to preliminarily destroy the structures of lignin and hemicellulose; alkaline cooking, in which a segmented cooking method is adopted to achieve the alkaline cooking of the cotton linter raw material; bleaching and acid treatment, in which the cotton linter raw material after cooking in S3 is taken out of the cooking pot, and the alkali solution is removed by means of screw extrusion, and the cotton linter raw material is treated by means of multi-stage bleaching; dehydration and drying: the cotton linter after bleaching and acid treatment is dehydrated and dried; wastewater recycling: the cooking and pulp washing wastewater and the rinsing water are recycled for pretreatment to reduce water consumption and pollution, and the COD is reduced to below 10600 mg / L.

[0018] A production method of refined cotton linter includes the following steps: S1. Raw material pretreatment: The cotton linter raw material is passed through a cotton opener and a cleaner to remove metal, sand, and cottonseed hull impurities, and is loosened into flocculent fragments to improve the uniformity of subsequent reactions. The cotton linter with a maturity of ≥80% and a fiber length of 8-10 mm, preferably a fiber length of 8 mm, is used to avoid the mixing of foreign fibers affecting the quality. The foreign fibers in the cotton linter refer to non-cotton fibers and non-natural-color cotton fibers mixed in the cotton fibers. Such impurities will significantly affect the quality of cotton and its products. Non-cotton fibers: such as chemical fibers (polyester, nylon, etc.), hair, silk thread, hemp fiber, plastic film, plastic rope, dyed thread (rope, cloth block), etc.; non-natural-color cotton fibers: refer to the cotton fibers themselves that are mixed in, but have different colors and textures from the original cotton, such as dyed thread, rope, cloth block, etc.; impurity control: the mechanical impurity content is reduced to <4% through a metal detector and a multi-stage sand remover to remove the impurities inside the fibers, which is more conducive to improving the preparation quality of the cotton linter; S2. Spray-alkali pre-impregnation: Spray sodium hydroxide solution onto cotton linters, and combine with screw extrusion to remove excess alkali liquor, initially destroying the structures of lignin and hemicellulose. The temperature of the sprayed sodium hydroxide solution is 40 °C and the concentration is 12%, preparing for alkaline cooking, which is more conducive to the alkaline cooking of cotton linter raw materials, thus improving the extraction and preparation effect of cotton linters. The degradation of lignin and hemicellulose. Spray-alkali pre-impregnation destroys the hydrogen bond network structure of lignin and hemicellulose through a strong alkaline environment, converting it into sugar substances that can be recognized by enzymes, significantly improving the subsequent enzymatic hydrolysis efficiency. The change of sugar substances. During the pretreatment process, soluble sugar and lignin first increase sharply and then tend to be stable, indicating that the pretreatment has stage characteristics for the degradation of different components; In spray-alkali pre-impregnation, the treated cotton linters are laid flat on the conveying equipment, and the average height of the cotton linters on the conveying equipment is less than 3 cm. A multi-directional alkali liquor nozzle is used to spray alkali on the cotton linters on the conveying equipment, and the number of times of spraying alkali is 4 times.

[0019] S3. Alkaline cooking: Adopt a segmented cooking method to achieve the alkaline liquor cooking of cotton linter raw materials. The segmented cooking technology: Pre-cooking: Add a mixed solution containing 2.4% NaOH and 2% Na2SO3, and treat at room temperature for 25 minutes to initially decompose impurities; First-stage cooking: The temperature is 115 °C, the pressure is 0.2 MPa, and cook for 60 minutes to further degrease; Final-stage cooking: Raise the temperature to 140 °C, the pressure is 0.5 MPa, and cook for 100 minutes to completely remove the residual lignin and increase the α-cellulose content to ≥98%; The mass ratio of the alkali in the alkali liquor in the cooking pot to the dry weight of the cotton linters is 14:100; That is: if the dry weight of the cotton linters is 2000 kg, the required mass of the alkali liquor is 28 kg; During alkaline cooking, a segmented temperature control technology is adopted. The temperature is raised in stages to reduce cellulose degradation and improve the stability of the degree of polymerization. The viscosity of the extra-high viscosity product is ≥800 mPa·s. Alkali liquor optimization: Adopt a composite system of NaOH and Na2SO3 to reduce the NaOH dosage by 20 - 30%, reducing costs and alleviating the pressure of wastewater treatment.

[0020] S4. Bleaching and acid treatment: Take out the cotton linter raw materials after cooking in S3 from the cooking pot, and use screw extrusion to remove the alkali liquor. Adopt a multi-stage bleaching method to treat the cotton linter raw materials. Multi-stage bleaching: Acid pre-treatment: Adjust the pH of the pulp to 4.0 with dilute sulfuric acid to neutralize the residual alkali liquor and dissolve metal ions; H2O2 Bleaching: At pH 8, add 6% hydrogen peroxide and 4 g / L stabilizer. Add stabilizers such as EDTA to prevent the decomposition of H2O2. The bleaching efficiency is increased by 30%. Control the temperature at 20 °C and bleach for 70 minutes. The whiteness can reach 87%. Controlling the temperature at 20 °C reduces fiber damage and maintains the degree of polymerization within the range of 12,000; Sodium Hypochlorite Assistance: Combine sodium hypochlorite to enhance the bleaching effect and shorten the treatment time. With sodium hypochlorite assistance, it has disinfection and sterilization effects (as a strong oxidant, sodium hypochlorite can destroy the cell walls and protein structures of bacteria, viruses, and fungi to achieve disinfection), bleaching effects (it can decompose organic pigments, especially having a significant effect on removing stains on cotton fibers), and cleaning ability (it can remove grease, dirt, and odors); S5. Dehydration and Drying: Dehydrate and dry the cotton linters after bleaching and acid treatment; Use a screw press to dehydrate to a water content of ≤15%, and then obtain a loose flocculent finished product through air drying or vacuum drying for 50 minutes.

[0021] S6. Wastewater Recycling: The cooking and pulp washing wastewater and rinsing water are recycled for pretreatment to reduce water consumption and pollution, and the COD is reduced to below 10,600 mg / L.

[0022] Test the obtained cotton linter products through the above steps. The main test parameters are: α-cellulose content, whiteness, viscosity, ash content, and degree of polymerization uniformity; α-Cellulose Content: ≥98%; Whiteness: ≥87%; Viscosity: ≥800 mPa·s; Ash Content: ≤0.10%; Degree of Polymerization Uniformity: ±5%.

[0023] The following is a comparison of the side view parameters of conventional refined cotton and the high-quality refined cotton of the present invention: Test parameters Conventional purified cotton High-quality purified cotton α-cellulose content ≥95% ≥98% Whiteness ≥85% ISO ≥87% Viscosity 100 - 650 mPa·s ≥800 mPa·s Ash content ≤0.15% ≤0.10% Degree of polymerization uniformity ±10% ±5% The above is only a preferred embodiment of the present invention, and it does not impose any form of limitation on the present invention. Although the present invention has been disclosed as above with a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A production method of refined cotton linter, characterized in that, It includes the following steps: S1. Pretreatment of raw materials: The cotton linter raw materials are passed through a cotton opener and a cleaning machine to remove impurities such as metal, sand and cottonseed hulls, and are loosened into flocculent fragments to improve the uniformity of subsequent reactions; S2. Alkali spraying and pre-impregnation: Sodium hydroxide solution is sprayed on the cotton linter, and excess alkali solution is removed by combining with screw extrusion to preliminarily destroy the structures of lignin and hemicellulose; S3. Alkaline cooking: Adopting a segmented cooking method to achieve alkaline cooking of the cotton linter raw materials; S4. Bleaching and acid treatment: The cotton linter raw materials after cooking in S3 are taken out of the cooking pot, and the alkali solution is removed by screw extrusion, and the cotton linter raw materials are processed by multi-stage bleaching; S5. Dewatering and drying: The cotton linter after bleaching and acid treatment is dewatered and dried; S6. Wastewater recycling: The cooking and washing pulp wastewater and the rinsing water are recycled for pretreatment to reduce water consumption and pollution, and the COD is reduced to below 10600 mg / L.

2. The production method of refined cotton linter according to claim 1, characterized in that, In S1, cotton linter with a maturity of ≥80% and a fiber length of 8-10 mm is used, and foreign fibers are avoided from mixing in to affect the quality; Impurity control: The mechanical impurity content is reduced to <4% through a metal detector and a multi-stage sand remover.

3. The production method of refined cotton linter according to claim 1, characterized in that, In S2, the temperature of the sprayed sodium hydroxide solution is 30-45°C and the concentration is 10-15%.

4. A production method of refined cotton linter according to claim 1, characterized in that, In S3, the segmented cooking technology: Pre-cooking: A mixed solution containing 2.1-2.6% of NaOH and 1-3% of Na2SO3 is added, and it is treated at room temperature for 15-30 minutes to preliminarily decompose impurities; First-stage cooking: The temperature is 110-120°C, the pressure is 0.1-0.3 MPa, and it is cooked for 50-70 minutes to further degrease; Final-stage cooking: The temperature is raised to 130-150°C, the pressure is 0.3-0.6 MPa, and it is cooked for 70-120 minutes to completely remove the residual lignin and increase the α-cellulose content to ≥98%; 5. A production method of refined cotton linter according to claim 1, characterized in that, In S4, multi-stage bleaching: Acid pre-treatment: The pH of the pulp is adjusted to 1.0-6.0 with dilute sulfuric acid to neutralize the residual alkali solution and dissolve metal ions; H2O2 bleaching: Under the condition of pH 7-10, 5-6% hydrogen peroxide and 3-5 g / L stabilizer are added, the temperature is controlled at 10-30°C, and it is bleached for 60-80 minutes, and the whiteness can reach 87%; Sodium hypochlorite assistance: Combining sodium hypochlorite to enhance the bleaching effect and shorten the treatment time.

6. A production method of refined cotton linter according to claim 1, characterized in that, In S3, during alkaline cooking, the mass ratio of the alkali in the alkali solution in the cooking pot to the dry weight of the cotton linter is 13-15:100; That is: if the dry weight of the cotton linter is 2000 kg, the required mass of the alkali solution is between 26 kg and 30 kg.

7. A production method of refined cotton linter according to claim 1, characterized in that, In S2, during alkali spraying and pre-impregnation, the treated cotton linter is laid flat on the conveying equipment, the average height of the cotton linter on the conveying equipment is less than 3 cm, and a multi-directional alkali solution nozzle is used to spray alkali on the cotton linter on the conveying equipment, and the number of alkali spraying times is 3-5 times.

8. A production method of refined cotton linter according to claim 1, characterized in that, S5. Dewatering and drying: It is dewatered by a screw press to a water content of ≤15%, and then dried by air drying or vacuum drying for 40-60 minutes to obtain a loose flocculent finished product.

9. The production method of refined cotton linter according to claim 1, characterized in that, The obtained cotton linter product is tested, and the main test parameters are: α-cellulose content, whiteness, viscosity, ash content and polymerization degree uniformity; α-cellulose content: ≥98%; Whiteness: ≥87%; Viscosity: ≥800 mPa·s; Ash content: ≤0.10%; Degree of polymerization uniformity: ±5%.

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