Method for homogeneously synthesizing cellulose acetate from cellulose under catalysis of eutectic solvent

Abstract

The invention belongs to the technical field of homogeneous derivatization of cellulose, and discloses a method for homogeneous synthesis of cellulose acetate from cellulose under catalysis of a eutectic solvent. The method comprises the following steps: dissolving cellulose in a deep eutectic solvent to form a homogeneous solution, adding an acylating agent, reacting, and adding an anti-solvent to obtain the cellulose acetate with the substitution degree of 0.42-1.81. According to the method for preparing the cellulose acetate, the solvent synthesis cost is low, the reaction condition is mild, an additional activation or hydrolysis process is not needed before and after the reaction, and the process is simple. The deep-eutectic solvent can be used as a reaction solvent and a reaction catalyst, and a new technology for homogeneous preparation of cellulose acetate is developed. The problems of high solvent cost, complex process operation, high chemical toxicity and high reaction condition requirement in preparation of cellulose acetate are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of cellulose homogeneous derivatization, and particularly relates to a method for synthesizing cellulose acetate homogeneously by catalyzing cellulose with a low eutectic solvent. Background Art

[0002] Cellulose acetate is a cellulose ester obtained by acetylation of natural cellulose. It is a cellulose derivative with important commercial value and in line with the concept of sustainable development. According to the degree of substitution, cellulose acetate can be divided into cellulose monoacetate, cellulose diacetate and cellulose triacetate. Because of its unique structure and properties, cellulose acetate has shown a wide range of application prospects. Its excellent biocompatibility and degradability make it suitable for use in drug release systems, wound dressings and medical devices. At the same time, cellulose acetate also has good film-forming properties, thermoplasticity and processability, which makes it show broad application prospects in textiles, packaging materials, construction materials and filtration materials. As a renewable and environmentally friendly material, cellulose acetate meets the needs of modern society for sustainable development materials.

[0003] At present, there are two main methods for preparing cellulose acetate: heterogeneous and homogeneous. The most widely used heterogeneous method is the acetic acid method. The production steps include activation, reaction and hydrolysis processes. There are many side reactions and it is impossible to directly obtain the desired degree of substitution product in one step. In addition, the uneven solid-liquid contact will lead to uneven product quality, affecting its subsequent application effect. The most studied homogeneous methods are the organic solvent method and the ionic liquid method. The production steps include dissolving cellulose and reaction processes. This process does not require activation and hydrolysis, and can directly control the synthesis of cellulose acetate with the corresponding degree of substitution. However, organic solvents are mostly toxic and volatile, and are very easy to pollute the environment. The cumbersome synthesis process, unknown toxicity and high cost of ionic liquids make it difficult to achieve industrialization.

[0004] Chinese patent publication CN118005810A discloses a method for producing cellulose acetate by a heterogeneous process, which includes activation, esterification and hydrolysis, and requires the addition of an additional catalyst, and the preparation process is relatively cumbersome. Chinese patent publication CN115873134A discloses a method for synthesizing cellulose acetate by a homogeneous process in an ionic liquid. The method has simple steps and is controllable, but there are still problems such as high cost of ionic liquids, unknown toxicity, high reaction temperature and the need to add a catalyst, which limits its market application. Therefore, in the art, it is expected to develop a new method for preparing cellulose acetate in a controllable manner using a new type of solvent with a lower cost and homogeneous catalysis. Summary of the invention

[0005] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the primary object of the present invention is to provide a method for homogeneously synthesizing cellulose acetate from cellulose using a low eutectic solvent as catalyst.

[0006] The method for preparing cellulose acetate in a homogeneous phase provided by the present invention aims to solve the problems of high production cost, complex process operation, high energy consumption and high toxicity of chemical drugs, and is helpful to promote the improvement of the preparation process, process development and application expansion of cellulose acetate.

[0007] The purpose of the present invention is achieved through the following solutions: A method for homogeneously synthesizing cellulose acetate from cellulose using a deep eutectic solvent as catalyst, comprising the following steps (1) adding a cellulose raw material to a low eutectic solvent and stirring to form a homogeneous solution; wherein the low eutectic solvent is composed of zinc chloride, phosphoric acid and water; (2) adding an acylating agent to the homogeneous solution obtained in step (1), reacting to obtain a cellulose acetate solution; (3) adding an anti-solvent to the cellulose acetate solution obtained in step (2) to precipitate cellulose acetate.

[0008] The molar ratio of zinc chloride, phosphoric acid and water in step (1) is 1:0.5-3:2-4.

[0009] The cellulose raw material in step (1) is at least one of microcrystalline cellulose, α-cellulose, wood pulp cellulose, bamboo pulp cellulose, and grass cellulose, and has a degree of polymerization of 150-1500.

[0010] In step (1), the mass ratio of the cellulose raw material to the low eutectic solvent is 1:20-100.

[0011] The stirring temperature in step (1) is 18-40°C and the stirring time is 2-5 h.

[0012] The acylating agent in step (2) is at least one of acetyl chloride and acetic anhydride.

[0013] The mass ratio of the acylating agent in step (2) to the cellulose raw material in step (1) is 2-20:1.

[0014] The reaction temperature in step (2) is 20-50°C and the reaction time is 2-10 h.

[0015] The anti-solvent in step (3) is at least one of methanol, ethanol and isopropanol.

[0016] The mass ratio of the cellulose acetate solution to the anti-solvent in step (3) is 1:1-20.

[0017] The degree of substitution of the cellulose acetate in step (3) is 0.3-2.4, preferably 0.42-1.81.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) In the method for preparing cellulose acetate provided by the present invention, the low eutectic solvent used has a simple synthesis process, low cost, is non-toxic or low-toxic, and can be recycled.

[0019] (2) In the method for preparing cellulose acetate provided by the present invention, the selected low eutectic solvent serves as both a reaction solvent and a catalyst, and no additional catalyst needs to be added, thereby reducing the difficulty of subsequent recovery and treatment.

[0020] (3) In the method for preparing cellulose acetate provided by the present invention, no activation step is required before the reaction, the process operation is simple, the reaction conditions are mild, and the reaction can be completed at room temperature in a normal pressure flask, and the equipment requirements are extremely low.

[0021] (4) In the method for preparing cellulose acetate provided by the present invention, no hydrolysis step is required after the reaction, and a product with a target degree of substitution can be directly obtained by adjusting the reaction conditions (acylation reaction time, amount of reaction acylating agent). BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a polarizing microscope image of the dissolution of the raw materials in Comparative Example 1-2.

[0023] Figure 2 This is the infrared spectrum of the product obtained in Comparative Example 3.

[0024] Figure 3 The carbon NMR spectrum of the product obtained in Example 1-2.

[0025] Figure 4 The molecular weight distribution diagram of the product obtained in Example 1-2.

[0026] Figure 5 IR spectra of cellulose raw material and products obtained in Examples 1-3.

[0027] Figure 6 The Raman spectra of the cellulose raw material and the products obtained in Examples 1-3.

[0028] Figure 7 The following is the H NMR spectrum of the product obtained in Example 1-10.

[0029] Figure 8 This is a physical picture of the product obtained in Examples 1-10. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with the examples and drawings, but the embodiments of the present invention are not limited thereto. If specific conditions are not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0031] Unless otherwise specified, the reagents used in the examples can be purchased from the market.

[0032] Example 1 The method for synthesizing cellulose acetate by homogeneous catalysis using a deep eutectic solvent comprises the following steps: Zinc chloride, phosphoric acid and water were mixed evenly in a molar ratio of 1:1:3, and a uniform transparent liquid was formed by stirring at room temperature to obtain a low eutectic solvent. 3.0 g of bamboo pulp cellulose raw material with a degree of polymerization of 1000 and 100.0 g of low eutectic solvent were weighed and added to a 150 mL three-necked beaker, and reacted at 25 ° C for 3 h to obtain a homogeneous cellulose solution. Then 15 g of acetic anhydride was added to the cellulose solution, the reaction temperature was 30 ° C, and the reaction time was 4 h. After the reaction was completed, 300 g of isopropanol was added to regenerate cellulose acetate with a degree of substitution of 0.66.

[0033] Example 2 The method for synthesizing cellulose acetate by homogeneous catalysis using a deep eutectic solvent comprises the following steps: Zinc chloride, phosphoric acid and water were mixed evenly in a molar ratio of 1:1:3, and a homogeneous transparent liquid was formed by stirring at room temperature to obtain a low eutectic solvent. 2.0 g of bamboo pulp cellulose raw material with a degree of polymerization of 1000 and 60.0 g of low eutectic solvent were weighed and added to a 150 mL three-necked beaker, and reacted at 25 ° C for 3 h to obtain a homogeneous cellulose solution. Then 25 g of acetic anhydride was added to the cellulose solution, the reaction temperature was 30 ° C, and the reaction time was 4 h. After the reaction was completed, 150 g of isopropanol was added to regenerate cellulose acetate with a degree of substitution of 1.47.

[0034] Example 3 The method for synthesizing cellulose acetate by homogeneous catalysis using a deep eutectic solvent comprises the following steps: Zinc chloride, phosphoric acid and water were mixed evenly in a molar ratio of 1:1:2, and a uniform transparent liquid was formed by stirring at room temperature to obtain a low eutectic solvent. 2.0 g of bamboo pulp cellulose raw material with a degree of polymerization of 1000 and 60.0 g of low eutectic solvent were weighed and added to a 150 mL three-necked beaker, and reacted at 25°C for 2.5 h to obtain a homogeneous cellulose solution. Then 25 g of acetic anhydride was added to the cellulose solution, the reaction temperature was 30°C, and the reaction time was 6 h. After the reaction was completed, 150 g of isopropanol was added to regenerate cellulose acetate with a degree of substitution of 1.57.

[0035] Example 4 The method for synthesizing cellulose acetate by homogeneous catalysis using a deep eutectic solvent comprises the following steps: Zinc chloride, phosphoric acid and water were mixed evenly in a molar ratio of 1:1:3, and a uniform transparent liquid was formed by stirring at room temperature to obtain a low eutectic solvent. 1.0 g of bamboo pulp cellulose raw material with a degree of polymerization of 1000 and 40.0 g of low eutectic solvent were weighed and added to a 150 mL three-necked beaker, and reacted at 25 ° C for 3 h to obtain a homogeneous cellulose solution. Then 12.5 g of acetic anhydride was added to the cellulose solution, the reaction temperature was 50 ° C, and the reaction time was 4 h. After the reaction was completed, 400 g of isopropanol was added to regenerate cellulose acetate with a degree of substitution of 1.81.

[0036] Example 5 The method for synthesizing cellulose acetate by homogeneous catalysis using a deep eutectic solvent comprises the following steps: Zinc chloride, phosphoric acid and water were mixed evenly in a molar ratio of 1:2:2, and a homogeneous transparent liquid was formed by stirring at room temperature to obtain a low eutectic solvent. 1.5 g of bamboo pulp cellulose raw material with a degree of polymerization of 1000 and 40.0 g of low eutectic solvent were weighed and added to a 150 mL three-necked beaker, and reacted at 25 ° C for 2 h to obtain a homogeneous cellulose solution. Then 19 g of acetic anhydride was added to the cellulose solution, the reaction temperature was 40 ° C, and the reaction time was 4 h. After the reaction was completed, 200 g of isopropanol was added to regenerate cellulose acetate with a degree of substitution of 1.50.

[0037] Example 6 The method for synthesizing cellulose acetate by homogeneous catalysis using a deep eutectic solvent comprises the following steps: Zinc chloride, phosphoric acid and water were mixed evenly in a molar ratio of 1:1:3, and a uniform transparent liquid was formed by stirring at room temperature to obtain a low eutectic solvent. 1.0 g of bamboo pulp cellulose raw material with a degree of polymerization of 1000 and 50.0 g of low eutectic solvent were weighed and added to a 100 mL three-necked beaker, and reacted at 25°C for 3.5 h to obtain a homogeneous cellulose solution. Then 7.5 g of acetic anhydride was added to the cellulose solution, the reaction temperature was 30°C, and the reaction time was 4 h. After the reaction was completed, 400 g of isopropanol was added to regenerate cellulose acetate with a degree of substitution of 0.94.

[0038] Example 7 The method for synthesizing cellulose acetate by homogeneous catalysis using a deep eutectic solvent comprises the following steps: Zinc chloride, phosphoric acid and water were mixed evenly in a molar ratio of 1:1:2, and a uniform transparent liquid was formed by stirring at room temperature to obtain a low eutectic solvent. 1.0 g of bamboo pulp cellulose raw material with a degree of polymerization of 1000 and 30.0 g of low eutectic solvent were weighed and added to a 100 mL three-necked beaker, and reacted at 25 ° C for 3 h to obtain a homogeneous cellulose solution. Then 10.0 g of acetic anhydride was added to the cellulose solution, the reaction temperature was 30 ° C, and the reaction time was 4 h. After the reaction was completed, 300 g of isopropanol was added to regenerate cellulose acetate with a degree of substitution of 1.12.

[0039] Example 8 The method for synthesizing cellulose acetate by homogeneous catalysis using a deep eutectic solvent comprises the following steps: Zinc chloride, phosphoric acid and water were mixed evenly in a molar ratio of 1:1:2.5, and a uniform transparent liquid was formed by stirring at room temperature to obtain a low eutectic solvent. 1.5 g of bamboo pulp cellulose raw material with a degree of polymerization of 1000 and 50.0 g of low eutectic solvent were weighed and added to a 100 mL three-necked beaker, and reacted at 25 ° C for 3 h to obtain a homogeneous cellulose solution. Then 18.9 g of acetic anhydride was added to the cellulose solution, the reaction temperature was 30 ° C, and the reaction time was 2 h. After the reaction was completed, 250 g of isopropanol was added to regenerate cellulose acetate with a degree of substitution of 1.13.

[0040] Example 9 The method for synthesizing cellulose acetate by homogeneous catalysis using a deep eutectic solvent comprises the following steps: Zinc chloride, phosphoric acid and water were mixed evenly in a molar ratio of 1:1:3, and a uniform transparent liquid was formed by stirring at room temperature to obtain a low eutectic solvent. 1.5 g of bamboo pulp cellulose raw material with a degree of polymerization of 1000 and 50.0 g of low eutectic solvent were weighed and added to a 100 mL three-necked beaker, and reacted at 25°C for 3 h to obtain a homogeneous cellulose solution. Then 18.9 g of acetic anhydride was added to the cellulose solution, the reaction temperature was 30°C, and the reaction time was 10 h. After the reaction was completed, 250 g of isopropanol was added to regenerate cellulose acetate with a degree of substitution of 1.32.

[0041] Example 10 The method for synthesizing cellulose acetate by homogeneous catalysis using a deep eutectic solvent comprises the following steps: Zinc chloride, phosphoric acid and water were mixed evenly in a molar ratio of 1:1:3, and a uniform transparent liquid was formed by stirring at room temperature to obtain a low eutectic solvent. 1.5 g of bamboo pulp cellulose raw material with a degree of polymerization of 1000 and 50.0 g of low eutectic solvent were weighed and added to a 100 mL three-necked beaker, and reacted at 25°C for 3 h to obtain a homogeneous cellulose solution. Then 3.8 g of acetic anhydride was added to the cellulose solution, the reaction temperature was 30°C, and the reaction time was 4 h. After the reaction was completed, 200 g of isopropanol was added to regenerate cellulose acetate with a degree of substitution of 0.42.

[0042] Comparative Example 1 Compared with Example 1, the homogeneous catalytic synthesis of cellulose acetate was attempted using a deep eutectic solvent of different composition, comprising the following steps: Zinc chloride, acetic acid and water were mixed evenly in a molar ratio of 1:1:3, and a homogeneous transparent liquid was formed by stirring at room temperature to obtain a low eutectic solvent. 3.0 g of bamboo pulp cellulose raw material with a degree of polymerization of 1000 and 100.0 g of low eutectic solvent were weighed and added to a 150 mL three-necked beaker, and reacted at 60°C for 24 h, but the cellulose raw material still could not be dissolved.

[0043] Comparative Example 2 Compared with Example 1, the homogeneous catalytic synthesis of cellulose acetate was attempted using a deep eutectic solvent of different composition, comprising the following steps: Ferric chloride, acetic acid and water were mixed evenly in a molar ratio of 1:1:3, and stirred at room temperature to form a uniform liquid to obtain a low eutectic solvent. 3.0 g of bamboo pulp cellulose raw material with a degree of polymerization of 1000 and 100.0 g of low eutectic solvent were weighed and added to a 150 mL three-necked beaker, and reacted at 60°C for 24 h, but the cellulose raw material still could not be dissolved.

[0044] Comparative Example 3 Compared with Example 1, the homogeneous catalytic synthesis of cellulose acetate was attempted using a deep eutectic solvent of different composition, comprising the following steps: Zinc chloride, formic acid and water were mixed evenly in a molar ratio of 1:1:3, and a homogeneous transparent liquid was formed by stirring at room temperature to obtain a low eutectic solvent. 3.0 g of bamboo pulp cellulose raw material with a degree of polymerization of 1000 and 100.0 g of low eutectic solvent were weighed and added to a 150 mL three-necked beaker, and reacted at 25 ° C for 5 h to obtain a homogeneous cellulose solution. Then 15 g of acetic anhydride was added to the cellulose solution, the reaction temperature was 30 ° C, and the reaction time was 4 h. After the reaction was completed, 300 g of isopropanol was added to obtain a regenerated cellulose product.

[0045] Figure 1Polarized microscope images of different low eutectic solvents dissolving cellulose raw materials in Comparative Examples 1 and 2 are shown, indicating that they cannot completely dissolve the cellulose raw materials, cannot obtain homogeneous cellulose solutions, and cannot achieve homogeneous reaction conditions.

[0046] pass Figure 2 The infrared spectrum analysis of Comparative Example 3 shows that the product does not have the characteristic peaks of cellulose acetate, indicating that although the homogeneous reaction conditions are achieved, the cellulose raw material is not successfully acetylated under the homogeneous catalysis of this type of low eutectic solvent, and cellulose acetate is not successfully prepared.

[0047] Figure 3 The signal peaks at chemical shifts of 165-175 ppm in the NMR carbon spectra of Examples 1 and 2 are attributed to the carbonyl group of cellulose acetate, proving the successful grafting of acetyl groups. The signal peaks of 70.0 ppm-75.0 ppm and 15 ppm-25 ppm correspond to the overlapping signal peaks at C-2 to C-5 and the methyl signal peaks on the acetyl substituent in cellulose acetate, respectively. It can be seen that substitution occurs preferentially at C-6 in the cellulose acetate sample. Figure 4 The molecular weight distribution diagrams of the products prepared in Examples 1 and 2 are shown, and the relative molecular mass information of the prepared products can be obtained.

[0048] Figure 5 In the infrared spectra of Examples 1, 2 and 3, the cellulose raw material was compared and it was found that at 1733 cm -1 The C=O stretching vibration absorption peak appeared at 1243 cm -1 The absorption peak at corresponds to the symmetric stretching vibration of ester CO. Figure 6 In the Raman spectra of Examples 1, 2, and 3, compared with the cellulose raw material, it can be seen that the -1 The stretching vibration of the C=O bond in the acetyl group is at 637 cm -1 A broad peak due to the vibration of the inner bond of the acetyl group can be seen at 14°. The above characterization also indicates the successful synthesis of cellulose acetate.

[0049] The degree of substitution (DS) of the synthesized cellulose acetate products was determined by Figure 7 The integral of the methyl region (1.7 to 2.2 ppm) in the acetyl group in the H-NMR spectrum and the integral of the proton region (2.9 to 5.2 ppm, excluding the water peak) on the glucose ring of cellulose were calculated.

[0050] The specific method is: DS = (7×I1) / (3×I2) Where I1 is the integral of the methyl proton peak on the acetyl group, and I2 is the integral of the proton peak on the glucose ring of cellulose.

[0051] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for homogeneously synthesizing cellulose acetate from cellulose using a deep eutectic solvent, characterized in that: The following steps are involved: (1) adding a cellulose raw material to a low eutectic solvent and stirring to form a homogeneous solution; wherein the low eutectic solvent is composed of zinc chloride, phosphoric acid and water; (2) adding an acylating agent to the homogeneous solution obtained in step (1), reacting to obtain a cellulose acetate solution; (3) adding an anti-solvent to the cellulose acetate solution obtained in step (2) to precipitate cellulose acetate.

2. The method for homogeneously synthesizing cellulose acetate from cellulose using a deep eutectic solvent as described in claim 1, characterized in that: The molar ratio of zinc chloride, phosphoric acid and water in step (1) is 1:0.5-3:2-4.

3. The method for homogeneously synthesizing cellulose acetate from cellulose using a deep eutectic solvent as described in claim 1, characterized in that: The cellulose raw material in step (1) is at least one of microcrystalline cellulose, α-cellulose, wood pulp cellulose, bamboo pulp cellulose, and grass cellulose, and has a degree of polymerization of 150-1500.

4. The method for homogeneously synthesizing cellulose acetate from cellulose using a deep eutectic solvent as described in claim 1, characterized in that: In step (1), the mass ratio of the cellulose raw material to the low eutectic solvent is 1:20-100.

5. The method for homogeneously synthesizing cellulose acetate from cellulose using a deep eutectic solvent as described in claim 1, characterized in that: The stirring temperature in step (1) is 18-40°C and the stirring time is 2-5 h.

6. The method for homogeneously synthesizing cellulose acetate from cellulose using a deep eutectic solvent as described in claim 1, characterized in that: The acylating agent in step (2) is at least one of acetyl chloride and acetic anhydride.

7. The method for homogeneously synthesizing cellulose acetate from cellulose using a deep eutectic solvent as described in claim 1, characterized in that: The mass ratio of the acylating agent in step (2) to the cellulose raw material in step (1) is 2-20:

1.

8. The method for homogeneously synthesizing cellulose acetate from cellulose using a deep eutectic solvent as described in claim 1, characterized in that: The reaction temperature in step (2) is 20-50°C and the reaction time is 2-10 h.

9. The method for homogeneously synthesizing cellulose acetate from cellulose using a deep eutectic solvent as described in claim 1, characterized in that: The anti-solvent in step (3) is at least one of methanol, ethanol and isopropanol; The mass ratio of the cellulose acetate solution to the anti-solvent in step (3) is 1:1-20.

10. The method for homogeneously synthesizing cellulose acetate from cellulose using a deep eutectic solvent as described in claim 1, characterized in that: The degree of substitution of the cellulose acetate in step (3) is 0.3-2.4, preferably 0.42-1.81.

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