Acetylated dissolving pulp, process for its preparation and use thereof

Abstract

The application relates to a kind of acetylated grade dissolving pulp and its preparation method and application.It includes the following steps: S1 eutectic solvent is mixed with raw material dissolving pulp, heated reaction, and first dissolving pulp is obtained;The mass ratio of the raw material dissolving pulp and the eutectic solvent is 1:5-20;The eutectic solvent includes organic acid, metal salt and water;S2 removes part of the eutectic solvent in the first dissolving pulp, and second dissolving pulp is obtained;S3 water is diluted to the second dissolving pulp, and the mass concentration of cellulose is 2-5%, and third dissolving pulp is obtained;2) the pH of the third dissolving pulp is adjusted, cellulase is added, and enzyme treatment is carried out to obtain acetylated grade dissolving pulp.The technical problem to be solved is how to provide a kind of preparation method of acetylated grade dissolving pulp, without washing the dissolving pulp after early treatment, but with diluted eutectic solvent as the buffer solution of cellulase for enzyme treatment, so as to reduce production cost, improve production efficiency, and realize industrial production of product.

Description

Technical Field

[0001] This invention belongs to the field of dissolving pulp preparation technology, and in particular relates to an acetic acid grade dissolving pulp, its preparation method and application. Background Technology

[0002] Dissolving pulp is a high-purity cellulose product with an α-cellulose content exceeding 90%. It is a crucial raw material for the production of cellulose esters (nitrocellulose, cellulose acetate), cellulose ethers (carboxymethyl cellulose), lyocell fibers, and nanocellulose, possessing significant utilization value. Cellulose acetate, in particular, is formed by the esterification of some hydroxyl groups of cellulose with acetic acid or anhydride. It exhibits excellent gloss, biocompatibility, toughness, and biodegradability, and is primarily used in high-end textile fabrics, cigarette filter materials, films, and medical nonwovens. Compared to other cellulose products, high-value-added cellulose acetate places more stringent requirements on dissolving pulp, namely high α-cellulose content, high whiteness, and high degree of polymerization. Due to the shortage of high-quality timber and cotton linters in China, as well as the instability of raw material quality, solvent accessibility to dissolving pulp is low, resulting in poor solubility and incomplete acetylation reactions. This directly impacts the application of downstream products. Currently, my country relies heavily on imported cellulose acetate raw materials. Therefore, improving the quality of domestic fiber raw materials is crucial for increasing my country's cellulose acetate production.

[0003] To improve the quality of dissolving pulp, physical, chemical, biological, and combined methods are mainly used for pulp treatment. Physical methods primarily involve mechanical processes, which are energy-intensive and offer limited improvement in reaction performance. Chemical methods mainly use acidic or alkaline reagents, but the large quantities required lead to significant environmental damage from waste liquid, and solvent recovery is also difficult. Bio-enzymatic methods are environmentally friendly, offer mild treatment conditions, and are highly compatible with production processes, making them promising for improving dissolving pulp quality. Therefore, in current technologies, bio-enzymatic methods are often combined with other technologies to further enhance pulp quality.

[0004] Currently, some researchers are combining physical methods with enzymatic methods to improve the reactivity of dissolving pulp through a two-step treatment. For example, combining PFI milling with cellulase processing, or combining phosphotungstic acid-assisted pre-refining with cellulase treatment. While these methods can improve the reactivity of dissolving pulp, they have the following drawbacks:

[0005] 1) Mechanical treatment of dissolving slurry consumes a lot of energy, and mechanical action alone has almost no effect on improving reaction performance.

[0006] 2) The stepwise treatment of cellulase combined with strong acid-assisted mechanical method increases the complexity of the process and the production cost. In addition, the strong acidity of the system can easily deactivate the enzyme, and strong acid is corrosive to the equipment, reducing the service life of the equipment.

[0007] In existing technologies, there are also methods for treating dissolving slurries using eutectic solvents. Eutectic solvents are novel green solvents that are easy to prepare, low in cost, recyclable, and structurally designable. They are simply blended from hydrogen bond donors and acceptors in a certain molar ratio and have a wide range of applications. However, due to the inherent properties of eutectic solvents, they can inactivate enzymes, thus preventing their combination with biological enzyme methods and hindering the maximization of synergistic treatment effects for continuous industrial production. Summary of the Invention

[0008] The main objective of this invention is to provide an acetic acid grade dissolving pulp, its preparation method, and its application. The technical problem to be solved is how to provide a method for preparing an acetic acid grade dissolving pulp that eliminates the need to thoroughly wash the dissolving pulp after pretreatment. Instead, it uses a diluted eutectic solvent as a buffer solution for cellulase to perform enzyme treatment, thereby solving the existing technical problems of harsh treatment conditions, high cost, complex process design, poor synergy, and difficulty in industrialization when improving the reaction performance of dissolving pulp.

[0009] The objective of this invention and the technical problem it solves are achieved through the following technical solution. A method for preparing an acetic acid-grade dissolving slurry according to this invention includes the following steps:

[0010] S1 involves mixing a eutectic solvent with a raw material dissolving slurry and heating the mixture to obtain a first dissolving slurry. The mass ratio of the raw material dissolving slurry to the eutectic solvent is 1:5 to 20. The eutectic solvent comprises an organic acid that can act as a hydrogen bond donor, a metal salt that can act as a hydrogen bond acceptor, and water. The molar ratio of the metal salt to the organic acid is 1:2 to 8. The molar ratio of the organic acid to water is 1:2 to 20.

[0011] S2 removes a portion of the eutectic solvent from the first dissolving slurry to obtain the second dissolving slurry; the mass of the eutectic solvent contained in the second dissolving slurry is 70-80% of the total mass of the second dissolving slurry;

[0012] S3 is diluted with water to make the cellulose mass concentration 2-5%, thus obtaining the third dissolving paste;

[0013] S4 adjusts the pH of the third dissolving pulp to 4.5-5.0, adds cellulase, and performs enzyme treatment to obtain acetic acid grade dissolving pulp; the mass ratio of the raw material dissolving pulp to the cellulase is 1:0.0005-0.0015.

[0014] Preferably, in the aforementioned preparation method, the method for preparing the eutectic solvent includes the following steps:

[0015] The organic acid, metal salt and water are mixed and heated to 40-80°C, and reacted for 20-60 minutes to obtain the eutectic solvent.

[0016] Preferably, in the aforementioned preparation method, the organic acid is selected from at least one of benzoic acid, formic acid, acetic acid, propionic acid, pyruvic acid, glycolic acid, oxalic acid, lactic acid, citric acid, and malic acid; and the metal salt is selected from at least one of zinc chloride, lithium chloride, sodium chloride, potassium chloride, sodium formate, zinc acetate, lithium acetate, sodium acetate, potassium acetate, sodium citrate, lithium citrate, potassium citrate, potassium hydrogen phthalate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate.

[0017] Preferably, in the aforementioned preparation method, in step S1, the temperature is heated to 50–80°C and the reaction is carried out for 1–2 hours.

[0018] Preferably, in the aforementioned preparation method, the enzyme treatment specifically includes: adding cellulase, treating with enzyme at 50-60°C for 1-4 hours, and then washing, concentrating and dispersing, and air-drying to obtain an acetic acid grade dissolving slurry.

[0019] Preferably, in the aforementioned preparation method, the cellulase is an endoglucanase.

[0020] Preferably, in the aforementioned preparation method, the organic acid is selected from at least one of formic acid, acetic acid, propionic acid, citric acid, and malic acid; and the metal salt is selected from at least one of zinc chloride, lithium chloride, zinc acetate, lithium acetate, and lithium citrate.

[0021] Preferably, in the aforementioned preparation method, the preparation method of the raw material dissolving slurry is as follows: tear the dissolving slurry slab into fragments with a length and width of 2-3 cm, and then disperse them at room temperature for 3-5 minutes to obtain the raw material dissolving slurry.

[0022] The objective of this invention and the technical problem it solves are also achieved by the following technical solution. An acetic acid-grade dissolving slurry according to this invention is prepared by the above-described method for preparing acetic acid-grade dissolving slurry.

[0023] The objective of this invention and the technical problem it solves are also achieved by the following technical solution. A cellulose acetate according to this invention is obtained from the above-mentioned acetylation-grade dissolving pulp.

[0024] By employing the above technical solution, the acetic acid grade dissolving slurry, its preparation method, and its application proposed in this invention have at least the following advantages:

[0025] This invention first mixes a eutectic solvent with the raw material dissolving slurry. During the reaction, the eutectic solvent disrupts the hydrogen bonds in cellulose, causing the cellulose to swell. Simultaneously, it performs acid hydrolysis, degrading the cellulose chains. Furthermore, the active protons released from the eutectic solvent disrupt the fiber structure, increasing the specific surface area of ​​the fiber and improving the accessibility of subsequent cellulase, thus saving enzyme usage. After the reaction of the eutectic solvent with the raw material dissolving slurry is complete, only a portion of the eutectic solvent needs to be removed; there is no need to wash the dissolving slurry treated with the eutectic solvent. Only the remaining eutectic solvent needs to be diluted. The diluted eutectic solvent can serve as a buffer solution for cellulase. Therefore, no additional cellulase buffer solution needs to be added during subsequent enzyme treatment. This is because the eutectic solvent used in this invention contains organic acids and metal salts. The remaining organic acids and metal salts, after dilution with water, can act as a cellulase buffer solution, thus eliminating the need for further washing of the slurry and addition of buffer reagents, thereby improving production efficiency and saving production costs.

[0026] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0027] Figure 1 This is an optical microscope image of the refined cotton dissolving pulp raw material in an embodiment of the present invention;

[0028] Figure 2 This is a polarized light microscope image of the refined cotton dissolving pulp raw material in an embodiment of the present invention;

[0029] Figure 3 This is an optical microscope image of the dissolving slurry after quality improvement in Embodiment 1 of the present invention;

[0030] Figure 4 This is a polarized light microscope image of the dissolving slurry after quality improvement in Embodiment 1 of the present invention;

[0031] Figure 5 This is an optical microscope image of the dissolving slurry after quality improvement in Comparative Example 3 of the present invention;

[0032] Figure 6 This is a polarized light microscope image of the dissolving slurry after the quality improvement of Comparative Example 3 of this invention. Detailed Implementation

[0033] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation methods, structures, features, and effects of an acetic acid-grade dissolving slurry, its preparation method, and its application according to the present invention. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0034] This invention proposes a method for preparing acetic acid grade dissolving slurry, as shown in the attached figure. Figures 1-6 As shown, the steps include:

[0035] S1 mixes an organic acid that can act as a hydrogen bond donor, a metal salt that can act as a hydrogen bond acceptor, and water, heats the mixture to 40–80°C, and reacts for 20–60 min to obtain the eutectic solvent; the molar ratio of the metal salt to the organic acid is 1:2–8; the molar ratio of the organic acid to water is 1:2–20.

[0036] In this invention, the heating temperature is controlled at 40-80°C during the preparation process. If the heating temperature is too high, a large amount of water will evaporate, resulting in an increase in the viscosity of the eutectic solvent; if the temperature is too low, the eutectic solvent cannot be synthesized.

[0037] In the preparation of the eutectic solvent, this invention controls the molar ratio of metal salt to organic acid to be 1:2 to 8. If too much metal salt is added, the eutectic solvent cannot be synthesized; if too much organic acid is added, the eutectic solvent will be too acidic, affecting the subsequent cellulase treatment process and causing cellulase inactivation. Furthermore, if the organic acid content in the eutectic solvent is too high, it will also lead to a high content of fine fibers in the slurry, thereby reducing the product yield.

[0038] The organic acid used in this invention is an organic acid that can act as a hydrogen bond donor; the organic acid is selected from at least one of benzoic acid, formic acid, acetic acid, propionic acid, pyruvic acid, glycolic acid, oxalic acid, lactic acid, citric acid, and malic acid; preferably at least one of formic acid, acetic acid, propionic acid, citric acid, and malic acid. All organic acids used in this invention are commercially available.

[0039] The metal salt used is a metal salt capable of acting as a hydrogen bond acceptor; the metal salt is selected from at least one of zinc chloride, lithium chloride, sodium chloride, potassium chloride, sodium formate, zinc acetate, lithium acetate, sodium acetate, potassium acetate, sodium citrate, lithium citrate, potassium citrate, potassium hydrogen phthalate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate; preferably at least one of zinc chloride, lithium chloride, zinc acetate, lithium acetate, and lithium citrate. All metal salts used in this invention are commercially available.

[0040] S2. Mix the eutectic solvent with the raw material dissolving slurry, heat to 50-80°C, and react for 1-2 hours to obtain the first dissolving slurry; the mass ratio of the raw material dissolving slurry to the eutectic solvent is 1:5-20.

[0041] When mixing the raw material dissolving paste and the eutectic solvent, it is necessary to control the mass ratio of the raw material dissolving paste to the eutectic solvent to be 1:5 to 20. Controlling the ratio of the raw material dissolving paste to the eutectic solvent can enable the eutectic solvent to better break the hydrogen bonds of the dissolving paste, causing the fibers to swell, thereby effectively improving the quality of the dissolving paste and producing acetic grade dissolving paste with excellent reactivity.

[0042] The raw material dissolving slurry described in this invention contains α-cellulose; the content of α-cellulose is ≥98%.

[0043] Preferably, in the aforementioned preparation method, the preparation method of the raw material dissolving slurry is as follows: tear the dissolving slurry slab into fragments with a length and width of 2-3 cm, and then disperse them at room temperature for 3-5 minutes to obtain the raw material dissolving slurry.

[0044] Preferably, in the aforementioned preparation method, the raw material dissolving slurry is selected from one or more of coniferous wood, broadleaf wood, refined cotton, wheat straw, bamboo, etc. Coniferous wood, broadleaf wood, and refined cotton are preferred.

[0045] The raw material dissolving slurry of the present invention is selected from one or more of coniferous wood, broadleaf wood, refined cotton, wheat straw, bamboo and other materials. This means that when preparing the raw material dissolving slurry, one or more of coniferous wood, broadleaf wood, refined cotton, wheat straw, bamboo and other materials are selected and processed in a series of steps to obtain the raw material dissolving slurry. At this time, the raw material dissolving slurry contains ≥98% α-cellulose.

[0046] S3 removes a portion of the eutectic solvent from the first dissolving slurry to obtain the second dissolving slurry; the mass of the eutectic solvent contained in the second dissolving slurry is 70-80% of the total mass of the second dissolving slurry.

[0047] The second dissolving slurry of the present invention contains the reacted raw material dissolving slurry (the main component of which is treated α-cellulose) and some of the eutectic solvent that has not been removed.

[0048] This invention removes a portion of the eutectic solvent from the first dissolving slurry. The removal method can be a solid-liquid separation method such as pressing or filtration, as long as it can remove a portion of the eutectic solvent. The removed eutectic solvent is recycled and reused, thereby reducing production costs.

[0049] S4 is diluted with water to make the cellulose mass concentration 2-5%, thus obtaining the third dissolving paste;

[0050] The present invention requires the addition of water to the second dissolving slurry to dilute the eutectic solvent in the second dissolving slurry, and finally obtains the third dissolving slurry. The diluted eutectic solvent in the third dissolving slurry can be used as a buffer for cellulase. Therefore, there is no need to wash the second dissolving slurry, nor is it necessary to add additional cellulase buffer in the subsequent enzyme treatment process, thereby improving the process efficiency and avoiding the defect of reduced product yield caused by washing.

[0051] This invention uses a diluted eutectic solvent as a buffer for cellulase, which not only provides a suitable reaction environment for cellulase but also effectively utilizes the eutectic solvent, improving raw material utilization and reducing production costs and environmental impact. Simultaneously, since the eutectic solvent in the third dissolving slurry has been diluted to a low concentration, the diluted eutectic solvent will not inactivate the subsequent cellulase. On the contrary, the diluted eutectic solvent provides a suitable enzyme buffer environment, which is beneficial to the activity and stability of cellulase, thereby improving enzyme reaction efficiency. Furthermore, using the eutectic solvent as a buffer for cellulase can reduce the amount of cellulase added in subsequent steps, thereby reducing production costs.

[0052] The buffer solution described in this invention is defined as follows: when a certain amount of acid and alkali is added to a solution, or a small amount of water is added to dilute it, the solution has the effect of hindering the change of pH of the solution, which is called buffering effect, and such a solution is called a buffer solution.

[0053] S5 adjusts the pH of the third dissolving slurry to 4.5-5.0, adds cellulase, and treats it with enzyme at 50-60℃ for 1-4 hours. Then, it is washed, concentrated, dispersed, and air-dried to obtain acetic acid grade dissolving slurry. The mass ratio of the raw material dissolving slurry to the cellulase is 1:0.0005-0.0015. The cellulase is an endoglucanase.

[0054] This invention adjusts the pH of the third dissolving pulp to 4.5–5.0 and performs enzyme treatment at 50–60°C. Controlling the temperature and pH of the enzyme treatment prevents a decrease in enzyme activity or even inactivation, thus ensuring the normal progress of enzyme treatment and guaranteeing product yield. The specific pH value and enzyme treatment temperature settings depend on the type of cellulase.

[0055] The enzyme treatment time of this invention is 1-4 hours, which allows the enzyme to fully contact and react with the third dissolving pulp, thereby improving the product yield. If the enzyme treatment time is too short, the enzyme will not contact the third dissolving pulp sufficiently, affecting the treatment effect; if the enzyme treatment time is too long, the enzyme will over-react with the third dissolving pulp, resulting in a decrease in product yield.

[0056] During enzyme treatment, the mass ratio of raw material dissolving slurry to cellulase is 1:0.0005 to 0.0015. It is necessary to control the amount of enzyme used. If the amount of enzyme used is too small, the enzyme treatment capacity will decrease; conversely, if the amount of enzyme used is too large, the production cost will increase.

[0057] The cellulase used in this invention is an endoglucanase, model FiberCare D, manufactured by Novozymes (China) Investment Co., Ltd.

[0058] The present invention also proposes an acetic acid grade dissolving slurry, which is prepared by the above-mentioned method for preparing acetic acid grade dissolving slurry.

[0059] The present invention also proposes a cellulose acetate, which is obtained from the above-mentioned acetic acid grade dissolving pulp.

[0060] This invention also proposes a method for preparing cellulose acetate, the steps of which include:

[0061] S1 first activates the acetic acid-grade dissolving slurry, then adds acetic acid, acetic anhydride, and sulfuric acid, and reacts at 40–80°C for 0.5–1.5 h; the mass ratio of the acetic acid-grade dissolving slurry to the acetic acid is 1:3–7; the mass ratio of the acetic acid-grade dissolving slurry to the acetic anhydride is 1:2–6; the mass ratio of the sulfuric acid to the acetic acid-grade dissolving slurry is 1:5–15.

[0062] The cellulose acetate grade dissolving pulp raw material is activated during the preparation of cellulose acetate. The activation method is as follows:

[0063] Acetic acid is added to the acetic acid-grade dissolving slurry for activation; the mass fraction of the acetic acid is 0-700%, and the activation time is 0-4 hours. This invention controls the activation time to 0-4 hours to avoid insufficient fiber swelling due to a short activation time, which would lead to incomplete acetic acid reaction in the subsequent stages; it also avoids excessive swelling due to a long activation time, which would excessively degrade cellulose and reduce the strength of the product. Preferably, the activation time is 0-2.5 hours.

[0064] This invention eliminates the need for activation of the acetic acid-grade dissolving pulp because the acetic acid-grade dissolving pulp raw material used in the method for preparing cellulose acetate is obtained through the preparation method of the acetic acid-grade dissolving pulp of this invention. Since this invention uses a eutectic solvent of an organic acid / metal salt system to treat the raw material dissolving pulp during the preparation of the acetic acid-grade dissolving pulp, and the organic acid in the eutectic solvent has an activating effect on the dissolving pulp, no activation operation is required to obtain high-quality cellulose acetate.

[0065] After the S2 reaction is completed, acetic acid and water are added, and the reaction is carried out for 0.5 to 9 hours. After the reaction is completed, water is added to precipitate the precipitate, and then the precipitate is filtered, washed, and dried to obtain cellulose acetate. The mass ratio of water to acetic acid is 1:1 to 3.

[0066] This invention involves hydrolyzing acetic acid and water, controlling the mass ratio of acetic acid to water and the reaction time during the hydrolysis process to control the product's performance and yield. If too little water is added or the reaction time is too short, the acetyl group is substituted at a lower ratio, and the hydrolysis product is cellulose triacetate, leading to a decrease in product yield. If too much water is added or the reaction time is too long, water-soluble cellulose monoacetate is generated, and the hydrolysis product cannot precipitate in water, resulting in a decrease in product performance.

[0067] The present invention will be further described below with reference to specific embodiments, but this should not be construed as a limitation on the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention still fall within the scope of protection of the present invention.

[0068] Unless otherwise specified, all materials and reagents mentioned below are commercially available products well known to those skilled in the art; unless otherwise specified, all methods described are methods known in the art. Unless otherwise defined, the technical or scientific terms used should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0069] Example 1

[0070] A method for preparing an acetic acid grade dissolving pulp, comprising the following steps:

[0071] S1 tears the refined cotton dissolving pulp board into fragments with a length and width of 30mm×30mm, and then disperses them by dissolving them at room temperature for 5 minutes using a standard pulp disintegrator to obtain the raw material dissolving pulp;

[0072] S2 mixes acetic acid, lithium acetate, and water, and heats and stirs at 80°C for 60 min to obtain a eutectic solvent; the molar ratio of lithium acetate to acetic acid is 1:3; the molar ratio of lithium acetate to water is 1:9.

[0073] S3 mixes the raw material dissolving slurry and the eutectic solvent at a solid-liquid ratio of 1:15 and treats the reaction at 80°C for 1 hour to obtain the first dissolving slurry;

[0074] S4 vacuum filters and presses the first dissolving pulp to obtain the second dissolving pulp; the mass of the eutectic solvent contained in the second dissolving pulp is 70-80% of the total mass of the second dissolving pulp;

[0075] S4 is then diluted with water in the second dissolution, with a cellulose mass concentration of 3%, to obtain the third dissolution slurry;

[0076] S5 adjusts the pH of the third dissolving slurry to 4.8, and then treats it with endoglucanase under the following conditions: endoglucanase dosage 0.5 mg / g raw material dissolving slurry, treatment temperature 50℃, and treatment time 1 h. After the reaction, the slurry is washed, concentrated, dispersed, and air-dried to obtain the acetic acid grade dissolving slurry.

[0077] Optical / polarizing microscope images of the acetic acid grade dissolving slurry prepared in this embodiment are shown below. Figure 3 and Figure 4 As shown, compared with untreated refined cotton dissolving pulp ( Figure 1 and Figure 2 Compared to acetic acid-grade dissolving pulp fibers, the cellulose chains are fully swollen and the width increases. At the same time, the acid hydrolysis degrades the cellulose chains, and the eutectic solvent and enzyme treatment destroy the surface and internal structure of the fibers, increasing the wrinkles and pores on the fiber surface, which is beneficial to improving the activity of subsequent acetic acid reaction.

[0078] Example 2

[0079] The difference between this embodiment and Embodiment 1 is that:

[0080] The method for preparing the eutectic solvent is as follows: formic acid, sodium formate and water are mixed and heated and stirred at 40°C for 30 min to obtain the eutectic solvent; the molar ratio of sodium formate to formic acid is 1:4; the molar ratio of sodium formate to water is 1:9.

[0081] The raw material dissolving slurry and the eutectic solvent are mixed at a solid-liquid ratio of 1:10.

[0082] Example 3

[0083] The difference between this embodiment and Embodiment 1 is that:

[0084] The raw materials for the eutectic solvent are citric acid, lithium citrate, and water; the molar ratio of lithium citrate to citric acid is 1:4; and the molar ratio of lithium citrate to water is 1:12.

[0085] Example 4

[0086] The difference between this embodiment and Embodiment 1 is that:

[0087] The raw materials for the eutectic solvent are acetic acid, zinc chloride, and water; the molar ratio of zinc chloride to acetic acid is 1:6; the molar ratio of zinc chloride to water is 1:10; and the dosage of endoglucanase is 1 mg / g of raw material dissolving slurry.

[0088] Example 5

[0089] A method for preparing cellulose acetate, comprising the following steps:

[0090] S1 adds acetic acid, acetic anhydride, and sulfuric acid to the acetic acid-grade dissolving slurry prepared in Example 1, and reacts at 40°C for 0.5–1.5 h; the mass ratio of the acetic acid-grade dissolving slurry to the acetic acid is 1:7; the mass ratio of the acetic acid-grade dissolving slurry to the acetic anhydride is 1:4; and the mass ratio of the sulfuric acid to the acetic acid-grade dissolving slurry is 1:10.

[0091] After the S2 reaction is completed, acetic acid and water are added, and the reaction is carried out for 0.5 hours. After the reaction is completed, water is added to precipitate the precipitate, and then the precipitate is filtered, washed, and dried to obtain cellulose acetate. The mass ratio of water to acetic acid is 1:3.

[0092] Example 6

[0093] The difference between this embodiment and embodiment 5 is as follows:

[0094] The acetic acid grade dissolving slurry raw material used was prepared in Example 2.

[0095] Example 7

[0096] The difference between this embodiment and embodiment 5 is as follows:

[0097] The acetic acid grade dissolving slurry raw material used was prepared in Example 3.

[0098] Example 8

[0099] The difference between this embodiment and embodiment 5 is as follows:

[0100] The acetic acid grade dissolving slurry raw material used was prepared in Example 4.

[0101] Comparative Example 1

[0102] Compared to Example 1, Comparative Example 1 did not undergo enzyme treatment.

[0103] Comparative Example 2

[0104] Compared to Example 1, Comparative Example 2 did not use a eutectic solvent to treat the raw material dissolving slurry.

[0105] Comparative Example 3

[0106] Compared with Example 1, the amount of cellulase used in Comparative Example 3 was 1.5 mg / g of endoglucanase in the raw material dissolving slurry; the treatment time was 2 hours.

[0107] A polarizing microscope image of the acetic acid grade dissolving slurry prepared in this comparative example is shown below. Figure 5 and Figure 6 As shown.

[0108] Comparative Example 4

[0109] Cellulose acetate was prepared using the acetic acid grade dissolving slurry obtained in Comparative Example 1 as raw material; the preparation method differed from that in Example 5 in that the hydrolysis time was 1 hour.

[0110] Comparative Example 5

[0111] Compared with Comparative Example 4, this comparative example uses the acetic acid grade dissolving slurry obtained in Comparative Example 2 as raw material to prepare cellulose acetate.

[0112] Comparative Example 6

[0113] Compared with Comparative Example 4, this comparative example uses the acetic acid grade dissolving slurry obtained in Comparative Example 3 as raw material to prepare cellulose acetate.

[0114] The quality of the acetylation-grade dissolving pulps prepared in Examples 1, 2, 3, 4, Comparative Examples 1, 2, and 3 was determined. Specifically, the reactivity of the acetylation-grade dissolving pulp with acid anhydrides during the preparation of cellulose acetate was represented by the acetylation reaction value (PV value). A higher PV value indicates better reactivity of the dissolving pulp. The determination method included the following steps:

[0115] (1) Add 2g of acetic acid to 5g of acetic acid grade dissolving slurry and shake in a shaker for 1h to activate it;

[0116] (2) The acetic acid grade dissolving slurry activated in step (1) is mixed with 200g acetic acid, 50g mixed acid (21.35g acid anhydride + 28.65g acetic acid) and 0.55g concentrated sulfuric acid and reacted at 47℃ for 1h.

[0117] (3) Add 45g of acetic acid and 15g of water to the system in step (2) to terminate the reaction, cool to room temperature, and stir for 30min to obtain cellulose acetate solution;

[0118] (4) Filter the cellulose acetate solution obtained in step (3) at 0.08 MPa using two layers of cellulose chromatography filter paper, and read the weight of the liquid flowing out at 50s and 150s.

[0119] (5) Calculate the PV value according to the formula:

[0120] FACT(5g) = 165.344 / (150 / reading - 50 / reading)

[0121] The measured data are shown in the table below:

[0122] Table 1

[0123]

[0124]

[0125] As can be seen from Table 1, the acetylation reaction value (PV value) of Example 1 is much higher than that of Comparative Example 1 and Comparative Example 2. This indicates that in the method of Example 1, which first treats the raw material dissolving slurry with a eutectic solvent and then performs enzymatic treatment with cellulase, the eutectic solvent causes the cellulose to swell by breaking the hydrogen bonds in the cellulose. At the same time, the acid hydrolysis degrades the cellulose chains. The active protons dissociated from the eutectic solvent destroy the fiber structure, increase the specific surface area of ​​the fiber, improve the accessibility of subsequent cellulase, and save the amount of enzyme used, thereby achieving a PV value of 1098 for the product.

[0126] Table 1 shows that the PV value of Example 3 is 1150, while that of Comparative Example 3 is 1148, a small difference. However, the enzyme dosage in Comparative Example 3 is 1.5 mg / g, and the enzyme treatment time is 2 hours, while the enzyme dosage in Example 3 is 0.5 mg / g, and the enzyme treatment time is 1 hour. This indicates that when producing products with the same performance, the method of this invention, which first treats the raw material slurry with a eutectic solvent and then performs enzyme treatment with cellulase, provides a suitable enzyme buffer environment, which is beneficial to the activity and stability of cellulase, thereby improving the enzyme reaction efficiency. Furthermore, using a eutectic solvent as a buffer for cellulase can reduce the amount of cellulase added in subsequent steps, thereby reducing production costs.

[0127] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0128] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing an acetic acid-grade dissolving slurry, characterized in that, It includes the following steps: S1 involves mixing a eutectic solvent with a raw material dissolving slurry and heating the mixture to obtain a first dissolving slurry. The mass ratio of the raw material dissolving slurry to the eutectic solvent is 1:5 to 20. The eutectic solvent comprises an organic acid that can act as a hydrogen bond donor, a metal salt that can act as a hydrogen bond acceptor, and water. The molar ratio of the metal salt to the organic acid is 1:2 to 8. The molar ratio of the organic acid to water is 1:2 to 20. S2 removes a portion of the eutectic solvent from the first dissolving slurry to obtain the second dissolving slurry; the mass of the eutectic solvent contained in the second dissolving slurry is 70-80% of the total mass of the second dissolving slurry; S3 is diluted with water to make the cellulose mass concentration 2-5%, thus obtaining the third dissolving paste; S4 adjusts the pH of the third dissolving pulp to 4.5-5.0, adds cellulase, and performs enzyme treatment to obtain acetic acid grade dissolving pulp; the mass ratio of the raw material dissolving pulp to the cellulase is 1:0.0005-0.0015.

2. The preparation method according to claim 1, characterized in that, The method for preparing the eutectic solvent includes the following steps: The organic acid, metal salt and water are mixed and heated to 40-80°C, and reacted for 20-60 minutes to obtain the eutectic solvent.

3. The preparation method according to claim 1, characterized in that, The organic acid is selected from at least one of benzoic acid, formic acid, acetic acid, propionic acid, pyruvic acid, glycolic acid, oxalic acid, lactic acid, citric acid, and malic acid; the metal salt is selected from at least one of zinc chloride, lithium chloride, sodium chloride, potassium chloride, sodium formate, zinc acetate, lithium acetate, sodium acetate, potassium acetate, sodium citrate, lithium citrate, potassium citrate, potassium hydrogen phthalate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate.

4. The preparation method according to claim 1, characterized in that, In step S1, the mixture is heated to 50–80°C and reacted for 1–2 hours.

5. The preparation method according to claim 1, characterized in that, The specific method of enzyme treatment includes: adding cellulase, treating with enzyme at 50-60℃ for 1-4 hours, then washing, concentrating and dispersing, and air-drying to obtain acetic acid grade dissolving slurry.

6. The preparation method according to claim 1, characterized in that, The cellulase is an endoglucanase.

7. The preparation method according to claim 3, characterized in that, The organic acid is selected from at least one of formic acid, acetic acid, propionic acid, citric acid, and malic acid; the metal salt is selected from at least one of zinc chloride, lithium chloride, zinc acetate, lithium acetate, and lithium citrate.

8. The preparation method according to claim 1, characterized in that, The preparation method of the raw material dissolving slurry is as follows: tear the dissolving slurry slab into fragments with a length and width of 2-3 cm, and then disperse them at room temperature for 3-5 minutes to obtain the raw material dissolving slurry.

9. An acetic acid-grade dissolving slurry, characterized in that, It is prepared by the method of preparing acetic acid grade dissolving slurry according to any one of claims 1 to 8.

10. A type of cellulose acetate, characterized in that, It is prepared from the acetic acid grade dissolving slurry as described in claim 9.

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