A process for producing medium-high temperature viscose

Abstract

The application belongs to the field of artificial filaments, and relates to a cellulose acetate production process at medium-high temperature, comprising the following steps: dissolving acetamide in glacial acetic acid to obtain glacial acetic acid containing acetamide; dipping cellulose in the glacial acetic acid containing acetamide to activate, to obtain activated slurry; diluting concentrated sulfuric acid with glacial acetic acid, and then adding formaldehyde to obtain a catalyst solution; mixing glacial acetic acid and acetic anhydride to obtain mixed acid, adding the catalyst solution to the mixed acid to obtain a treatment liquid; uniformly mixing the activated slurry and the treatment liquid, and performing acetylation reaction at 75 DEG C to 85 DEG C to obtain acetylation product; hydrolyzing the acetylation product, and after the hydrolysis reaction is completed, performing sedimentation, collecting acetate sheet, washing, drying, and obtaining cellulose acetate; the application introduces an activation aid and a capping agent in the catalyst system, significantly enhances the controllability of acetylation reaction at medium-high temperature through the cooperation of enhancing activation and inhibiting degradation, reduces the amount of catalyst and liquid ratio, and prepares cellulose acetate with high spinnability and cellulose acetate fiber with high performance.

Description

Technical Field

[0001] This invention belongs to the field of artificial filaments, specifically relating to a medium-high temperature process for producing cellulose acetate and cellulose acetate fiber. Background Technology

[0002] Cellulose acetate is a thermoplastic resin obtained by acetylation modification of cellulose hydroxyl groups. It can be classified into diacetate cellulose and triacetate cellulose according to different degrees of substitution. Traditional processes commonly employ low-temperature acetylation, using glacial acetic acid as a diluent, acetic anhydride as an acetylation agent, and sulfuric acid as a catalyst. This process is mature and stable, producing acetate flakes with good spinnability and high safety. However, its technical limitations are also significant: acetylation is a strongly exothermic reaction. To avoid cellulose degradation under high-temperature acidic conditions, the low-temperature method requires deep cooling of the reaction system, pre-freezing the reaction mixture, and maintaining a low reaction temperature throughout. Simultaneously, to control the reaction rate, the sulfuric acid catalyst dosage in the low-temperature process typically exceeds 10%, resulting in a liquid-to-reaction ratio as high as 1:8, requiring a large amount of acetic acid as a solvent. This leads to long reaction times and low production efficiency; secondly, huge cold energy consumption and high energy costs; and thirdly, the large acetic acid consumption significantly increases the energy consumption and production costs of the acetic acid recovery unit, further raising the overall manufacturing cost of cellulose acetate products and limiting the industry's scalability.

[0003] To this end, domestic and foreign industry researchers have begun to explore medium- and high-temperature acetylation process routes. The core idea is to adjust the process parameters and catalytic system to increase the temperature of the reaction system, shorten the reaction time, and reduce the amount of solvent and catalyst used, while ensuring that cellulose does not undergo excessive degradation and that the spinnability of the product meets the requirements, thereby achieving cost reduction and efficiency improvement.

[0004] However, current high-temperature acetylation processes generally suffer from excessive cellulose degradation, leading to decreased spinnability of the product. Therefore, there is an urgent need to find a suitable catalytic system to prepare cellulose acetate with high spinnability and high-performance cellulose acetate fibers. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a medium-high temperature process for producing cellulose acetate fibers. This invention introduces activating agents and end-capping agents into the catalytic system, significantly enhancing the controllability of the acetylation reaction at medium and high temperatures through the combined effect of enhanced activation and inhibition of degradation. This reduces the amount of catalyst and the liquid ratio, resulting in the production of highly spinnable cellulose acetate and high-performance cellulose acetate fibers.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a medium-high temperature process for producing cellulose acetate fiber, comprising: Acetamide is dissolved in glacial acetic acid to obtain glacial acetic acid containing acetamide; Cellulose is activated by impregnating it in glacial acetic acid containing acetamide to obtain an activated slurry; Concentrated sulfuric acid was diluted with glacial acetic acid, and then formalin was added to obtain a catalyst solution. Glacial acetic acid and acetic anhydride are mixed to obtain a mixed acid. A catalyst solution is added to the mixed acid to obtain a treatment solution. The activated slurry and the treatment liquid are mixed evenly, and an acetylation reaction is carried out at 75℃-85℃ to obtain the acetylation product. The acetylation product was hydrolyzed. After the hydrolysis reaction was completed, precipitation was performed, the acetylation flakes were collected, washed, and dried to obtain cellulose acetate. The cellulose acetate was produced into cellulose acetate fiber by wet spinning.

[0007] In a second aspect, the present invention provides cellulose acetate fibers prepared by the above-described method.

[0008] A third aspect of the present invention provides a medium-high temperature process for producing cellulose acetate, comprising: Acetamide is dissolved in glacial acetic acid to obtain glacial acetic acid containing acetamide; Cellulose is activated by impregnating it in glacial acetic acid containing acetamide to obtain an activated slurry; Concentrated sulfuric acid was diluted with glacial acetic acid, and then formalin was added to obtain a catalyst solution. Glacial acetic acid and acetic anhydride are mixed to obtain a mixed acid. A catalyst solution is added to the mixed acid to obtain a treatment solution. The activated slurry and the treatment liquid are mixed evenly, and an acetylation reaction is carried out at 75℃-85℃ to obtain the acetylation product. The acetylation product was hydrolyzed. After the hydrolysis reaction was completed, precipitation was performed, the acetylation flakes were collected, washed, and dried to obtain cellulose acetate.

[0009] The beneficial effects of this invention are as follows: (1) The present invention introduces activating aids and end-capping agents into the catalytic system, which significantly enhances the controllability of acetylation reaction at medium and high temperature by enhancing the combination of activation and degradation inhibition, and reduces the amount of catalyst and liquid ratio. The cellulose acetate prepared by the present invention has better degree of polymerization, viscosity and spinnability, and the prepared cellulose acetate fiber has high mechanical strength and good toughness.

[0010] (2) In this invention, formaldehyde reacts with the reduced end groups of cellulose to generate hemiacetal, which blocks the end groups, inhibits the breaking of β-1,4 glycosidic bonds, and improves the degree of polymerization and viscosity of cellulose acetate. At the same time, acetamide promotes the penetration rate of glacial acetic acid into cellulose and improves the activation effect. Thus, high spinnable cellulose acetate and high-performance cellulose acetate fibers are prepared under low catalyst (sulfuric acid) dosage and medium and high temperature conditions.

[0011] (3) The preparation process of this invention is simple, easy to operate, highly practical, and easy to promote. Detailed Implementation

[0012] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0013] As shown in the background art, current high-temperature acetylation processes generally suffer from excessive cellulose degradation and reduced spinnability of the product. This invention provides a medium-to-high temperature cellulose acetate fiber production process, comprising: Acetamide is dissolved in glacial acetic acid to obtain glacial acetic acid containing acetamide; Cellulose is activated by impregnating it in glacial acetic acid containing acetamide to obtain an activated slurry; Concentrated sulfuric acid was diluted with glacial acetic acid, and then formalin was added to obtain a catalyst solution. Glacial acetic acid and acetic anhydride are mixed to obtain a mixed acid. A catalyst solution is added to the mixed acid to obtain a treatment solution. The activated slurry and the treatment liquid are mixed evenly, and an acetylation reaction is carried out at 75℃-85℃ to obtain the acetylation product. The acetylation product was hydrolyzed. After the hydrolysis reaction was completed, precipitation was performed, the acetylation flakes were collected, washed, and dried to obtain cellulose acetate. The cellulose acetate was produced into cellulose acetate fiber by wet spinning.

[0014] This invention reveals that acetamide can enhance the activation effect of glacial acetic acid, effectively increasing the accessibility of the acetylation reagent to cellulose and improving the uniformity of the acetylation reaction at medium to high temperatures. Formaldehyde end-capping of cellulose effectively reduces excessive degradation at medium to high temperatures, allowing the acetylation reaction to proceed rapidly and stably at these temperatures, resulting in cellulose acetate with high polymerization degree and high viscosity. Furthermore, the reversible cleavage of the hemiacetal during hydrolysis re-releases formaldehyde, which dissolves in the aqueous phase and is discharged during precipitation and washing. Acetamide is also highly soluble in water and can be discharged during precipitation and washing.

[0015] The type and amount of activating aids affect the activation effect and the efficiency and effect of subsequent acetic acid esterification. Therefore, this invention studies the type and amount of activating aids. Preferably, the mass of the acetamide is 0.8%-1.2% of the oven-dry mass of cellulose. The -CONH2 in acetamide (CH3CONH2) can form hydrogen bonds with the -OH of cellulose, weakening the hydrogen bond network in the crystal region, thereby promoting the penetration of glacial acetic acid into the interior of cellulose and significantly improving the activation effect.

[0016] The amount of glacial acetic acid used also affects the activation effect of cellulose. Therefore, this invention has studied the amount of glacial acetic acid used. Preferably, the ratio of the acetamide-containing glacial acetic acid to the oven-dry mass of cellulose is 2-3:5, so as to effectively promote the penetration of glacial acetic acid into the cellulose pores, open the hydrogen bond network in the cellulose molecules, and make the -OH groups more easily contact the acetylation reagent.

[0017] The activation temperature and time affect the penetration effect of glacial acetic acid and the swelling of cellulose. Therefore, the present invention has studied the activation temperature and time. Preferably, the activation temperature is 35-45℃ and the activation time is 30min-40min to obtain better penetration and swelling effects.

[0018] While the medium-high temperature method increases the reaction rate, it also significantly increases the risk of cellulose glycosidic bond breakage and degradation under acidic conditions. Furthermore, the higher the temperature, the more difficult it is to control the degree of degradation, easily leading to excessive degradation that affects the degree of polymerization of the product. Therefore, this invention, based on the addition of activating agents and end-capping agents, studies the amount of concentrated sulfuric acid used. Preferably, the mass of the concentrated sulfuric acid is 1.5%-1.9% of the oven-dry mass of cellulose, and the mass concentration of the concentrated sulfuric acid is 96%-98%, to effectively reduce the degradation caused by cellulose glycosidic bond breakage and ensure the degree of polymerization of the product.

[0019] The type and amount of capping agent can affect the protection effect on β-1,4 glycosidic bonds. Therefore, this invention has studied the type and amount of capping agent. Preferably, in the formalin, the mass of formaldehyde is 0.3% to 0.6% of the oven-dry mass of cellulose, which effectively protects β-1,4 glycosidic bonds and avoids excessive degradation of cellulose.

[0020] The role of glacial acetic acid is to activate and swell cellulose, opening up the internal crystalline structure of cellulose and allowing for a more complete acetylation reaction. Acetic anhydride is the acetyl donor for the acetylation reaction, directly determining the degree of esterification substitution of the product. Therefore, this invention studied the dosage and ratio of glacial acetic acid and acetic anhydride to obtain a better acetylation effect. Preferably, in the mixed acid, the mass ratio of glacial acetic acid to acetic anhydride is 11:9-10; and the mass ratio of the mixed acid to the activated slurry is 4:1-1.2, to improve the reaction efficiency and effect of acetylation.

[0021] The temperature of the acetylation reaction affects the degree of acetylation and cellulose degradation. Therefore, this invention studies the temperature of the acetylation reaction. Preferably, during the acetylation process, the temperature is maintained at 75℃-85℃ for 20-60 min, and then cooled to 50-65℃ to continue the reaction until the target degree of substitution is reached. The initial medium temperature (75℃-85℃) allows acetic anhydride to penetrate evenly into the cellulose, completing the preliminary esterification first. This avoids the problem of rapid esterification only on the surface of the cellulose under direct high temperature, resulting in incomplete internal reaction and uneven distribution of the degree of substitution. After cooling to 50-65℃, the reaction rate slows down, making it easier to accurately control the target degree of substitution. This effectively solves the problem of many side reactions and difficulty in accurately controlling the degree of substitution in direct high-temperature reactions, significantly improving the viscosity and spinnability of cellulose acetate.

[0022] Higher temperatures result in faster hydrolysis. In this invention, the hydrolysis temperature is appropriately increased to accelerate the hydrolysis reaction process. The degree of substitution / viscosity is monitored online, and once the target is reached, the temperature is immediately lowered and magnesium acetate is added to neutralize the sulfuric acid to avoid over-hydrolysis. Preferably, the hydrolysis temperature is 50-65°C to improve hydrolysis efficiency.

[0023] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0024] In the following examples and comparative examples, the cellulose was cotton pulp, purchased from Shenzhen Yaxinwei Packaging Products Co., Ltd.

[0025] The bound acetic acid value, viscosity, free acid, and transparency were tested according to GB / T 32117-2015 "Industrial Cellulose Diacetate Tablets". The degree of substitution (DS) was approximately equal to the bound acetic acid value (%) × 0.045 + 0.05.

[0026] The tensile strength (dry state), elongation at break (dry state), and wet strength retention were tested according to GB / T 14344-2022 "Test Method for Tensile Properties of Chemical Fiber Filaments".

[0027] The moisture regain was tested according to GB / T 6503-2017 "Test Method for Moisture Regain of Chemical Fibers".

[0028] Example 1 (1) Take 5 kg of glacial acetic acid and add it to a three-necked flask. Heat it to 40°C and add 0.1 kg of acetamide. Stir until completely dissolved to obtain glacial acetic acid containing acetamide. (2) Add 10 kg of cellulose to the acetamide-containing glacial acetic acid prepared in step (1) and activate it at 40°C for 35 min to obtain activated slurry; (3) Take 0.173 kg of concentrated sulfuric acid (mass concentration of 98%), dilute it with 5 times the volume of glacial acetic acid, and then add 0.135 kg of formalin (formaldehyde concentration of 37%) and mix well to obtain a catalyst solution; (4) Mix acetic anhydride and glacial acetic acid at a mass ratio of 11:9, cool to 5°C to obtain 60 kg of mixed acid; add the catalyst solution prepared in step (3) to the mixed acid, mix evenly to obtain the treatment solution; (5) Mix the treatment liquid and the activated slurry evenly, carry out the acetylation reaction, first heat up to 80°C, hold at high temperature for 25 minutes, then quickly cool down to 55°C, and continue the reaction until DS≈2.8 to obtain the acetylation product; (6) Add 5 kg of hot water (55℃) to the acetylation product, hydrolyze for 60 min, collect the solution after the reaction, slowly pour in 8 times the volume of ice water, stir vigorously, let stand for 30 min, filter, and collect the acetylation flakes. (7) The collected cellulose acetate flakes were washed with deionized water until neutral and dried at 120°C for 8 hours to obtain cellulose acetate. (8) Take 5 kg of cellulose acetate, grind it into powder, and add 35 kg of N,N-dimethylacetamide (DMAC) to a dissolving tank. Stir and mix thoroughly, heat to 100°C and dissolve for 0.5 hours. After degassing and filtration, a spinning solution is formed. The spinning solution at 100°C is pumped through a metering pump and a filter and then sprayed out from the spinneret into a coagulation bath. The coagulation bath is a DMAC aqueous solution with a concentration of 70% and a temperature of 90°C to form nascent fibers. The nascent fibers are stretched and heat-set in a 75°C hot water bath for 1 minute with a draw ratio of 7:1. Then, they are soaked in a 10% sodium bisulfite solution at 15°C for 1 hour and dried at 120°C to obtain the final product.

[0029] Example 2 (1) Take 4 kg of glacial acetic acid and add it to a three-necked flask. Heat it to 40°C and add 0.08 kg of acetamide. Stir until completely dissolved to obtain glacial acetic acid containing acetamide.

[0030] (2) Add 10 kg of cellulose to the acetamide-containing glacial acetic acid prepared in step (1) and activate it at 45°C for 30 min to obtain activated slurry; (3) Take 0.194 kg of concentrated sulfuric acid (mass concentration of 98%), dilute it with 5 times the volume of glacial acetic acid, and then add 0.081 kg of formalin (formaldehyde concentration of 37%) and mix well to obtain a catalyst solution; (4) Mix acetic anhydride and glacial acetic acid at a mass ratio of 11:9, cool to 5°C to obtain 60 kg of mixed acid; add the catalyst solution prepared in step (3) to the mixed acid, mix evenly to obtain the treatment solution; (5) Mix the treatment liquid and the activated slurry evenly, carry out the acetylation reaction, first heat up to 75°C, hold at high temperature for 30 minutes, then quickly cool down to 50°C, and continue the reaction until DS≈2.8 to obtain the acetylation product; (6) Add 5 kg of hot water (50°C) to the acetylation product, hydrolyze for 70 min, collect the solution after the reaction, slowly pour in 8 times the volume of ice water, stir vigorously, let stand for 30 min, filter, and collect the acetylation flakes. (7) The collected cellulose acetate flakes were washed with deionized water until neutral and dried at 120°C for 8 hours to obtain cellulose acetate. (8) Take 5 kg of cellulose acetate, grind it into powder, and add 35 kg of N,N-dimethylacetamide to a dissolving tank. Stir and mix thoroughly, heat to dissolve at 100°C for 0.5 hours. After degassing and filtration, a spinning solution is formed. The spinning solution at 100°C is pumped through a metering pump and a filter and then sprayed out from the spinneret into a coagulation bath. The coagulation bath is a DMAC aqueous solution with a concentration of 70% and a temperature of 90°C to form nascent fibers. The nascent fibers are stretched and heat-set in a 75°C hot water bath for 1 minute with a draw ratio of 7:1. Then, they are soaked in a 10% sodium bisulfite solution at 15°C for 1 hour and dried at 120°C to obtain the final product.

[0031] Example 3 (1) Take 6 kg of glacial acetic acid and add it to a three-necked flask. Heat it to 40°C and add 0.12 kg of acetamide. Stir until completely dissolved to obtain glacial acetic acid containing acetamide.

[0032] (2) Add 10 kg of cellulose to the acetamide-containing glacial acetic acid prepared in step (1), and activate it at 35°C for 40 min to obtain activated slurry; (3) Take 0.153 kg of concentrated sulfuric acid (mass concentration of 98%), dilute it with 5 times the volume of glacial acetic acid, and then add 0.162 kg of formalin (formaldehyde concentration of 37%) and mix well to obtain a catalyst solution; (4) Mix acetic anhydride and glacial acetic acid at a mass ratio of 11:9, cool to 5°C to obtain 60 kg of mixed acid; add the catalyst solution prepared in step (3) to the mixed acid, mix evenly to obtain the treatment solution; (5) Mix the treatment liquid and the activated slurry evenly, carry out the acetylation reaction, first heat up to 85°C, hold at high temperature for a short time (20 min), then quickly cool down to 65°C, and continue the reaction until DS≈2.8 to obtain the acetylation product; (6) Add 5 kg of hot water (65℃) to the acetylation product, hydrolyze for 50 min, collect the solution after the reaction, slowly pour in 8 times the volume of ice water, stir vigorously, let stand for 30 min, filter, and collect the acetylation flakes. (7) The collected cellulose acetate flakes were washed with deionized water until neutral and dried at 120°C for 8 hours to obtain cellulose acetate. (8) Take 5 kg of cellulose acetate, grind it into powder, and add 35 kg of DMAC to a dissolving tank. Stir and mix thoroughly, heat to dissolve at 100°C for 0.5 hours. After degassing and filtration, a spinning solution is formed. The spinning solution at 100°C is pumped through a metering pump and a filter and then sprayed out from the spinneret into a coagulation bath. The coagulation bath is a DMAC aqueous solution with a concentration of 70% and a temperature of 90°C to form nascent fibers. The nascent fibers are stretched and heat-set in a 75°C hot water bath for 1 minute with a draw ratio of 7:1. Then, they are soaked in a 10% sodium bisulfite solution at 15°C for 1 hour and dried at 120°C to obtain the final product.

[0033] Comparative Example 1 The difference from Example 1 is that a traditional low-temperature process is used, and the specific process conditions are as follows: (1) Add 10 kg of cellulose to 5 kg of glacial acetic acid and activate at 40 °C for 35 min to obtain activated slurry; (2) Take 1.02 kg of concentrated sulfuric acid (mass concentration of 98%) and dilute it with 5 times the volume of glacial acetic acid to obtain a catalyst solution; (3) Mix acetic anhydride and glacial acetic acid at a mass ratio of 11:9, cool to 5°C to obtain 60 kg of mixed acid; slowly add the catalyst solution prepared in step (2) to the mixed acid, mix evenly to obtain the treatment solution; (4) Mix the treatment liquid and the activated slurry evenly, and carry out an esterification reaction at a temperature of 55°C until DS≈2.8 to obtain the esterification product; (5) Add 5 kg of hot water (55℃) to the acetylation product, hydrolyze for 60 min, collect the solution after the reaction, slowly pour in 8 times the volume of ice water, stir vigorously, let stand for 30 min, filter, and collect the acetylation flakes. (6) The collected cellulose acetate flakes were washed with deionized water until neutral and dried at 120°C for 8 hours to obtain cellulose acetate. (7) Take 5 kg of cellulose acetate, grind it into powder, and add 35 kg of N,N-dimethylacetamide (DMAC) to a dissolving tank. Stir and mix thoroughly, heat to dissolve at 100°C for 0.5 hours. After degassing and filtration, a spinning solution is formed. The spinning solution at 100°C is pumped through a metering pump and a filter and then sprayed out from the spinneret into a coagulation bath. The coagulation bath is a DMAC aqueous solution with a concentration of 70% and a temperature of 90°C to form nascent fibers. The nascent fibers are stretched and heat-set in a 75°C hot water bath for 1 minute with a draw ratio of 7:1. Then, they are soaked in a 10% sodium bisulfite solution at 15°C for 1 hour and dried at 120°C to obtain the final product.

[0034] Comparative Example 2 The difference from Example 1 is that formalin was not added, and the specific process conditions are as follows: (1) Take 5 kg of glacial acetic acid and add it to a three-necked flask. Heat it to 40°C and add 0.1 kg of acetamide. Stir until completely dissolved to obtain glacial acetic acid containing acetamide. (2) Add 10 kg of cellulose to the acetamide-containing glacial acetic acid prepared in step (1) and activate it at 40°C for 35 min to obtain activated slurry; (3) Take 0.173 kg of concentrated sulfuric acid (mass concentration of 98%) and dilute it with 5 times the volume of glacial acetic acid to obtain a catalyst solution; (4) Mix acetic anhydride and glacial acetic acid at a mass ratio of 11:9, cool to 5°C to obtain 60 kg of mixed acid; add the catalyst solution prepared in step (3) to the mixed acid, mix evenly to obtain the treatment solution; (5) Mix the treatment liquid and the activated slurry evenly, carry out the acetylation reaction, first heat up to 80°C, hold at high temperature for 25 minutes, then quickly cool down to 55°C, and continue the reaction until DS≈2.8 to obtain the acetylation product; (6) Add 5 kg of hot water (55℃) to the acetylation product, hydrolyze for 60 min, collect the solution after the reaction, slowly pour in 8 times the volume of ice water, stir vigorously, let stand for 30 min, filter, and collect the acetylation flakes. (7) The collected cellulose acetate flakes were washed with deionized water until neutral and dried at 120°C for 8 hours to obtain cellulose acetate. (8) Take 5 kg of cellulose acetate, grind it into powder, and add 35 kg of N,N-dimethylacetamide (DMAC) to a dissolving tank. Stir and mix thoroughly, heat to 100°C and dissolve for 0.5 hours. After degassing and filtration, a spinning solution is formed. The spinning solution at 100°C is pumped through a metering pump and a filter and then sprayed out from the spinneret into a coagulation bath. The coagulation bath is a DMAC aqueous solution with a concentration of 70% and a temperature of 90°C to form nascent fibers. The nascent fibers are stretched and heat-set in a 75°C hot water bath for 1 minute with a draw ratio of 7:1. Then, they are soaked in a 10% sodium bisulfite solution at 15°C for 1 hour and dried at 120°C to obtain the final product.

[0035] Comparative Example 3 The difference from Example 1 is that acetamide was not added, and the specific process conditions are as follows: (1) Add 10 kg of cellulose to 5 kg of glacial acetic acid and activate at 40 °C for 35 min to obtain activated slurry; (2) Take 0.173 kg of concentrated sulfuric acid (mass concentration of 98%) and dilute it with 5 times the volume of glacial acetic acid to obtain a catalyst solution; (3) Mix acetic anhydride and glacial acetic acid at a mass ratio of 11:9, cool to 5°C to obtain 60 kg of mixed acid; add the catalyst solution prepared in step (2) to the mixed acid, mix evenly to obtain the treatment solution; (4) Mix the treatment liquid and the activated slurry evenly, carry out the acetylation reaction, first heat up to 80°C, hold at high temperature for 25 minutes, then quickly cool down to 55°C, and continue the reaction until DS≈2.8 to obtain the acetylation product; (5) Add 5 kg of hot water (55℃) to the acetylation product, hydrolyze for 60 min, collect the solution after the reaction, slowly pour in 8 times the volume of ice water, stir vigorously, let stand for 30 min, filter, and collect the acetylation flakes. (6) The collected cellulose acetate flakes were washed with deionized water until neutral and dried at 120°C for 8 hours to obtain cellulose acetate. (7) Take 5 kg of cellulose acetate, grind it into powder, and add 35 kg of N,N-dimethylacetamide (DMAC) to a dissolving tank. Stir and mix thoroughly, heat to dissolve at 100°C for 0.5 hours. After degassing and filtration, a spinning solution is formed. The spinning solution at 100°C is pumped through a metering pump and a filter and then sprayed out from the spinneret into a coagulation bath. The coagulation bath is a DMAC aqueous solution with a concentration of 70% and a temperature of 90°C to form nascent fibers. The nascent fibers are stretched and heat-set in a 75°C hot water bath for 1 minute with a draw ratio of 7:1. Then, they are soaked in a 10% sodium bisulfite solution at 15°C for 1 hour and dried at 120°C to obtain the final product.

[0036] Experimental Example 1 The properties of the cellulose acetate and cellulose acetate fibers prepared in the examples and comparative examples were tested, and the results are shown in Tables 1 and 2.

[0037] Table 1. Performance test results of cellulose acetate

[0038] As can be seen from the comparison of Examples 1-3, the cellulose acetate prepared by the process of the present invention has a high degree of polymerization and viscosity, and high spinnability.

[0039] As can be seen from the comparison between Example 1 and Comparative Example 1, the cellulose acetate prepared by the present invention has better viscosity and transparency compared with the traditional low-temperature process.

[0040] As can be seen from the comparison between Example 1 and Comparative Example 2, the addition of formaldehyde effectively inhibited the excessive degradation of cellulose, and the viscosity and transparency of the product were significantly improved.

[0041] As can be seen from the comparison between Example 1 and Comparative Example 3, the addition of acetamide effectively activates cellulose with glacial acetic acid, resulting in a more uniform and complete acetylation reaction, and significantly improving the viscosity and transparency of the product.

[0042] Table 2. Test results of cellulose acetate fiber properties

[0043] As can be seen from the comparison of Examples 1-3, the cellulose acetate fibers prepared by the process of the present invention have high strength, good toughness, high wet strength, and the moisture regain is maintained within a reasonable range of 6.8%-7.2%.

[0044] As can be seen from the comparison between Example 1 and Comparative Example 1, the cellulose acetate fibers prepared by the present invention have better toughness and wet strength compared with the traditional low-temperature process.

[0045] As can be seen from the comparison between Example 1 and Comparative Example 2, the addition of formaldehyde effectively improves the strength, toughness and wet strength of cellulose acetate fiber.

[0046] As can be seen from the comparison between Example 1 and Comparative Example 3, the addition of acetamide improves the strength, toughness and wet strength of cellulose acetate fiber, while the moisture regain index is moderate and stable.

[0047] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A medium-high temperature method for producing cellulose acetate fiber, characterized in that, include: Acetamide is dissolved in glacial acetic acid to obtain glacial acetic acid containing acetamide; Cellulose is activated by impregnating it in glacial acetic acid containing acetamide to obtain an activated slurry; Concentrated sulfuric acid was diluted with glacial acetic acid, and then formalin was added to obtain a catalyst solution. Glacial acetic acid and acetic anhydride are mixed to obtain a mixed acid. A catalyst solution is added to the mixed acid to obtain a treatment solution. The activated slurry and the treatment liquid are mixed evenly, and an acetylation reaction is carried out at 75℃-85℃ to obtain the acetylation product. The acetylation product was hydrolyzed. After the hydrolysis reaction was completed, precipitation was performed, the acetylation flakes were collected, washed, and dried to obtain cellulose acetate. The cellulose acetate was produced into cellulose acetate fiber by wet spinning.

2. The medium-high temperature method for producing cellulose acetate fiber as described in claim 1, characterized in that, The acetamide is present in an amount of 0.8%-1.2% of the oven-dry weight of cellulose. Alternatively, the ratio of the acetamide-containing glacial acetic acid to the oven-dry weight of cellulose is 2-3:

5.

3. The medium-high temperature method for producing cellulose acetate fiber as described in claim 1, characterized in that, The activation temperature is 35-45℃, and the activation time is 30-40 minutes.

4. The medium-high temperature method for producing cellulose acetate fiber as described in claim 1, characterized in that, The concentrated sulfuric acid has a mass of 1.5%-1.9% of the oven-dry mass of cellulose and a mass concentration of 96%-98%.

5. The medium-high temperature method for producing cellulose acetate fiber as described in claim 1, characterized in that, In the formalin, the mass of formaldehyde is 0.3% to 0.6% of the oven-dry mass of cellulose.

6. The medium-high temperature method for producing cellulose acetate fiber as described in claim 1, characterized in that, In the mixed acid, the mass ratio of glacial acetic acid to acetic anhydride is 11:9-10; Alternatively, the mass ratio of the mixed acid to the activated slurry is 4:1-1.

2.

7. The medium-high temperature method for producing cellulose acetate fiber as described in claim 1, characterized in that, During the acetylation reaction, the temperature is maintained at 75℃-85℃ for 20-60 min, and then the temperature is lowered to 50-65℃ to continue the reaction until the target degree of substitution is reached.

8. The medium-high temperature method for producing cellulose acetate fiber as described in claim 1, characterized in that, The hydrolysis reaction is carried out at a temperature of 50–65°C.

9. Cellulose acetate fiber prepared by the method according to any one of claims 1-8.

10. A medium-high temperature process for producing cellulose acetate, characterized in that, include: Acetamide is dissolved in glacial acetic acid to obtain glacial acetic acid containing acetamide; Cellulose is activated by impregnating it in glacial acetic acid containing acetamide to obtain an activated slurry; Concentrated sulfuric acid was diluted with glacial acetic acid, and then formalin was added to obtain a catalyst solution. Glacial acetic acid and acetic anhydride are mixed to obtain a mixed acid. A catalyst solution is added to the mixed acid to obtain a treatment solution. The activated slurry and the treatment liquid are mixed evenly, and an acetylation reaction is carried out at 75℃-85℃ to obtain the acetylation product. The acetylation product was hydrolyzed. After the hydrolysis reaction was completed, precipitation was performed, the acetylation flakes were collected, washed, and dried to obtain cellulose acetate.

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