Method for preparing cellulose acetate and cellulose acetate

Abstract

The invention provides a method for preparing cellulose acetate and the cellulose acetate. The method comprises the following steps: S1, preparing a cellulose DMAc / LiCl solution; s2, mixing the cellulose DMAc / LiCl solution with a catalyst to obtain a first mixed solution; s3, acetic anhydride is added into the first mixed solution, the content of the acetic anhydride is larger than the content of cellulose in the cellulose DMAc / LiCl solution, and after mixing is conducted for a first preset time, a second mixed solution is obtained; and S4, sequentially carrying out cleaning and suction filtration on the second mixed solution, and drying the second mixed solution to constant weight. According to the method, the cellulose DMAc / LiCl solution, the catalyst and the acetic anhydride are mixed and react rapidly in a short time to generate the high-purity cellulose acetate, compared with a conventional processing process, the method has the remarkable advantages of being simple in processing process, high in reaction speed and the like, and a new thought is provided for processing and preparing the cellulose acetate.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer chemistry, and in particular to a method for preparing cellulose acetate and the cellulose acetate. Background Art

[0002] Cellulose is a renewable natural polymer material. Because the repeating units contain hydroxyl groups, it is easy to achieve various chemical reactions. Therefore, there are many applications of cellulose derivatives in the industrial field. Cellulose esters are an important class of cellulose derivatives. Cellulose acetate (CA) is derived from cellulose and is a semi-synthetic polymer. It was developed in the early 20th century as a safe alternative to highly flammable cellulose nitrate. It is a widely used material in the fields of photosensitive materials, textile fibers, membrane materials, household products, etc.

[0003] Zhu Guangfu et al. sorted out the technical means of preparing cellulose acetate at home and abroad in ZL2011102570970 "A method for preparing cellulose acetate from wheat straw", and mentioned the technology of using acid catalysts. Sulfuric acid, hydrochloric acid, phosphoric acid, perchloric acid, benzenesulfonic acid, p-toluenesulfonic acid, etc. can be used as catalysts in a specific reaction system. Among them, the preparation of cellulose acetate under heterogeneous conditions with sulfuric acid as a catalyst is the current industrialization path. The process includes esterifying highly refined cellulose with acetic anhydride in the presence of sulfuric acid catalyst to form fully acetylated triacetyl cellulose, and then partially hydrolyzing to remove the acid catalyst and produce a certain degree of substitution in the polymer, thereby producing cellulose acetate with the desired properties. According to the acetyl content, cellulose acetate can be divided into cellulose monoacetate (acetyl content 37% to 40%), cellulose diacetate (38% to 42%) and cellulose triacetate (>43%), and the degrees of substitution correspond to 1.67 to 2.0 for cellulose monoacetate, 2.28-2.68 for cellulose diacetate, and more than 2.8 for cellulose triacetate.

[0004] Applications CN201110086515.4A, CN201110086556.3A and CN201110086513.5A propose a preparation method, preparation process and production method for preparing cellulose acetate. Cellulose acetate is synthesized in a heterogeneous system, the esterification temperature is 20 to 58°C, the esterification time is 3 to 8 hours, and the product has a high degree of substitution of acetic acid content ≥ 60.0%.

[0005] The technology of synthesizing cellulose acetate under homogeneous conditions has also been reported. For example, Cao Yan et al. prepared water-soluble cellulose acetate with a substitution of about 1 using ionic liquid as solvent and acetic anhydride as acylating agent in "Homogeneous Synthesis of Low-Substituted Cellulose Acetate and Its Water Solubility". DMAc / LiCl, as a non-derivatized solvent for cellulose, is also used to synthesize cellulose fatty acid esters including cellulose acetate. The reaction reagents can be anhydrides, acyl chlorides, etc.

[0006] It can be seen that in the current technical route, the synthesis of cellulose acetate generally has disadvantages such as long time consumption, high energy consumption, and cellulose degradation. Summary of the invention

[0007] To this end, the technical problem to be solved by the present invention is to overcome the problems of long process, long time consumption, high energy consumption and high degree of cellulose degradation in the preparation of cellulose acetate in the prior art, and to provide a method for preparing cellulose acetate and cellulose acetate.

[0008] In order to solve the above technical problems, the present invention provides a method for preparing cellulose acetate, which comprises the following steps: S1, preparing a cellulose DMAc / LiCl solution; S2, mixing the cellulose DMAc / LiCl solution with a catalyst to obtain a first mixed solution; S3, adding acetic anhydride to the first mixed solution, wherein the acetic anhydride content is greater than the cellulose content in the cellulose DMAc / LiCl solution, and after mixing for a first preset time, obtaining a second mixed solution; S4, washing and filtering the second mixed solution in sequence, and drying it to a constant weight to obtain the target cellulose acetate.

[0009] In one embodiment of the present invention, it also includes step S5, determining the target degree of substitution of cellulose acetate and making a quality judgment on the cellulose acetate; specifically, determining the target degree of substitution of cellulose acetate by saponification method within a second preset range, when the determined target degree of substitution of cellulose acetate is between 0.25 and 1.75.

[0010] In one embodiment of the present invention, in step S1, the process of preparing the cellulose DMAc / LiCl solution is: cellulose and N,N-dimethylacetamide are mixed and then subjected to preliminary distillation, lithium chloride is added to the fraction, and high-temperature distillation is performed again to obtain the cellulose DMAc / LiCl solution.

[0011] In one embodiment of the present invention, in step S2, the catalyst is triethylamine, and the concentration ratio of the catalyst to the cellulose in the cellulose DMAc / LiCl solution is 4:1 to 5:1.

[0012] In one embodiment of the present invention, step S2 specifically comprises: taking 40 mL of cellulose DMAc / LiCl solution containing 3% cellulose, adding 5 mL of the catalyst under stirring conditions, and stirring for 5 minutes to obtain a first mixed solution.

[0013] In one embodiment of the present invention, in step S3, the ratio of the mass of cellulose in the cellulose DMAc / LiCl solution to the mass of the acetic anhydride is 3:5-4:1, and the first preset time is 5-600 seconds; the acetic anhydride and the cellulose DMAc / LiCl solution are fully mixed by stirring.

[0014] In one embodiment of the present invention, step S4 specifically comprises: adding the second mixed solution to excess anhydrous isopropanol, filtering after terminating the reaction, repeating the above process for more than 3 times, and vacuum drying the mixture to constant weight.

[0015] In one embodiment of the present invention, in step S4, the volume of the anhydrous isopropyl alcohol is 3 to 10 times the volume of the second mixed liquid; and the vacuum drying treatment temperature is 45 to 60°C.

[0016] In one embodiment of the present invention, the total time taken for steps S2 to S4 does not exceed 5 minutes.

[0017] The present invention also provides cellulose acetate, which is prepared by the above method for preparing cellulose acetate.

[0018] The above technical solution of the present invention has the following advantages compared with the prior art:

[0019] The method for preparing cellulose acetate and the cellulose acetate of the present invention are to mix a cellulose DMAc / LiCl solution, a catalyst and acetic anhydride to react quickly in a short time and generate high-purity cellulose acetate. Compared with the conventional processing process, the present application has the significant advantages of simple processing process, low reaction temperature and fast reaction speed, and provides a new idea for the processing and preparation of cellulose acetate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings.

[0021] Figure 1 is a flow chart of a method for preparing cellulose acetate in a preferred embodiment of the present invention;

[0022] Figure 2 This is an infrared spectrum of a product prepared by the method for preparing cellulose acetate described in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0024] Embodiment 1

[0025] This embodiment provides a method for preparing cellulose acetate, which comprises the following steps:

[0026] S1, preparing a cellulose DMAc / LiCl solution; in step S1 of this embodiment, the process of preparing the cellulose DMAc / LiCl solution is: cellulose and N,N-dimethylacetamide are mixed and then preliminarily distilled, lithium chloride is added to the fraction, and high-temperature distillation is performed again to obtain the cellulose DMAc / LiCl solution. Furthermore, the cellulose DMAc / LiCl solution obtained in this embodiment is a DMAc / LiCl solution containing 3wt% cellulose.

[0027] S2, mixing the cellulose DMAc / LiCl solution with a catalyst to obtain a first mixed solution; in step S2 of this embodiment, the catalyst is triethylamine, specifically, 40 g of a pre-prepared DMAc / LiCl solution containing 3 wt% cellulose is weighed, added to a 100 mL beaker, and then 5 mL of triethylamine is added, and the first mixed liquid is obtained after magnetic stirring for 5 minutes. In other embodiments, the ratio of the concentration of the catalyst to the cellulose in the cellulose DMAc / LiCl solution can be adaptively adjusted to between 4:1 and 5:1.

[0028] S3, adding acetic anhydride to the first mixed solution, wherein the acetic anhydride content is greater than the cellulose content in the cellulose DMAc / LiCl solution, and after mixing for a first preset time, a second mixed solution is obtained; in step S3 of this embodiment, 1.4 mL of acetic anhydride is weighed and added to the above solution at one time, and the reaction is stirred for 10 seconds to fully mix, thereby obtaining a second mixed solution. In other embodiments, the ratio of the mass of cellulose in the cellulose DMAc / LiCl solution to the mass of acetic anhydride can be configured to be 3:5 to 4:1, and the first preset time can be set to 5 to 600 seconds.

[0029] S4. After washing and filtering the second mixed solution in sequence, dry it to constant weight to obtain the target cellulose acetate. Step S4 of this embodiment is specifically as follows: add the second mixed solution to excess anhydrous isopropanol, filter it after terminating the reaction, repeat the above process more than 3 times, and vacuum dry it to constant weight. The volume of anhydrous isopropanol is 3 to 10 times the volume of the second mixed solution; the vacuum drying temperature is 45 to 60°C; so far, in the above process, the total time of steps S2 to S4 can be controlled within 5 minutes.

[0030] S5, determining the target degree of substitution of cellulose acetate and making a quality judgment on the cellulose acetate; specifically, determining the target degree of substitution of cellulose acetate by saponification method within a second preset period, when the target degree of substitution of cellulose acetate is between 0.25 and 1.75. Specifically, in this embodiment, the degree of substitution is determined by saponification method, and the product degree of substitution is calculated to be 0.55.

[0031] Embodiment 2

[0032] In this embodiment, 40 g of a pre-prepared DMAc / LiCl solution containing 3 wt% cellulose was weighed and added to a 100 mL beaker, and then 5 mL of triethylamine was added, and magnetic stirring was performed for 5 minutes. 2.1 mL of acetic anhydride was weighed and added to the above solution at one time, and the reaction was stirred for 2 minutes. The liquid was quickly poured into a 250 mL beaker containing 100 mL of isopropanol to terminate the reaction. After stirring for 5 minutes, suction filtration was performed, and the filter cake was added to the beaker and washed three times with isopropanol, each time with 100 mL of isopropanol. After the last suction filtration, the filter cake was dispersed with a glass rod, placed in a culture dish, and vacuum dried at 50°C to constant weight. Further, the degree of substitution was determined by saponification, and the degree of substitution was calculated to be 1.28.

[0033] Embodiment 3

[0034] In this embodiment, 40 g of the pre-prepared DMAc / LiCl solution containing 3 wt% cellulose was weighed, added to a 100 mL beaker, 5 mL of triethylamine was added, magnetic stirring was performed for 5 minutes, 5 mL of acetic anhydride was weighed, added to the above solution at one time, stirred for reaction for 5 minutes, and the liquid was quickly poured into a 250 mL beaker containing 100 mL of isopropanol to terminate the reaction. After stirring for 5 minutes, suction filtration was performed, and the filter cake was added to the beaker and washed three times with isopropanol, each time with 100 mL of isopropanol. After the last suction filtration, the filter cake was dispersed with a glass rod, placed in a culture dish, and vacuum dried at 50°C to constant weight. Further, the degree of substitution was determined by saponification, and the degree of substitution was calculated to be 1.75.

[0035] Further, the results of infrared spectroscopy testing of the cellulose acetate prepared in Examples 1 to 3 are shown in Figure 2 As shown, the wave number is 1730cm -1 The peak is the characteristic peak of cellulose acetate, which can prove that the method for preparing cellulose acetate in the present application can effectively prepare cellulose acetate.

[0036] Embodiment 4

[0037] This embodiment provides a cellulose acetate, which is prepared by the method for preparing cellulose acetate described in Embodiment 1.

[0038] In summary, the method for preparing cellulose acetate and the cellulose acetate described in the present invention, by mixing cellulose DMAc / LiCl solution, a catalyst and acetic anhydride, react quickly in a short time and claim high-purity cellulose acetate. Compared with the conventional processing process, the present application has significant advantages such as simple processing process and fast reaction speed, and provides a new idea for the processing and preparation of cellulose acetate.

[0039] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for preparing cellulose acetate, characterized in that: The steps include: S1, preparing cellulose DMAc / LiCl solution; S2, mixing the cellulose DMAc / LiCl solution with a catalyst to obtain a first mixed solution; S3, adding acetic anhydride to the first mixed solution, wherein the acetic anhydride content is greater than the cellulose content in the cellulose DMAc / LiCl solution, and mixing for a first preset time to obtain a second mixed solution; S4. The second mixed solution is washed and filtered in sequence, and then dried to a constant weight to obtain target cellulose acetate.

2. The method for preparing cellulose acetate according to claim 1, characterized in that: It also includes step S5, determining the target degree of substitution of cellulose acetate and making a quality judgment on the cellulose acetate; specifically, determining the target degree of substitution of cellulose acetate by saponification method within a second preset period, wherein the target degree of substitution of cellulose acetate is determined to be between 0.25 and 1.

75.

3. The method for preparing cellulose acetate according to claim 1, characterized in that: In step S1, the process of preparing the cellulose DMAc / LiCl solution is as follows: cellulose and dimethylacetamide are mixed and then preliminarily distilled, lithium chloride is added to the fraction, and high-temperature distillation is performed again to obtain the cellulose DMAc / LiCl solution.

4. The method for preparing cellulose acetate according to claim 1, characterized in that: In step S2, the catalyst is triethylamine, and the concentration ratio of the catalyst to the cellulose in the cellulose DMAc / LiCl solution is 4:1 to 5:

1.

5. The method for preparing cellulose acetate according to claim 1, characterized in that: Step S2 specifically comprises: taking 40 mL of a cellulose DMAc / LiCl solution containing 3% cellulose, adding 5 mL of the catalyst under stirring conditions, and stirring for 5 minutes to obtain a first mixed solution.

6. The method for preparing cellulose acetate according to claim 1, characterized in that: In step S3, the ratio of the mass of cellulose in the cellulose DMAc / LiCl solution to the mass of the acetic anhydride is 3:5-4:1, and the first preset time is 5-600 seconds; the acetic anhydride and the cellulose DMAc / LiCl solution are fully mixed by stirring.

7. The method for preparing cellulose acetate according to claim 1, characterized in that: Step S4 specifically comprises: adding the second mixed solution to excess anhydrous isopropanol, filtering after terminating the reaction, repeating the above process for a preset number of times, and then vacuum drying the mixed solution to a constant weight.

8. The method for preparing cellulose acetate according to claim 7, characterized in that: In step S4, the volume of the anhydrous isopropanol is 3 to 10 times the volume of the second mixed liquid; and the vacuum drying treatment temperature is 45 to 60°C.

9. The method for preparing cellulose acetate according to claim 1, characterized in that: The total time for steps S2 to S4 does not exceed 5 minutes.

10. A cellulose acetate, characterized in that: The cellulose acetate is prepared by the method for preparing cellulose acetate according to any one of claims 1 to 9.

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