Preparation method of cellulose acetate butyrate

Abstract

The invention discloses a preparation method of cellulose acetate butyrate, which comprises the following steps: firstly preparing cellulose acetate butyrate ester, then hydrolyzing the cellulose acetate butyrate ester, and neutralizing a reaction solution obtained by hydrolyzing the cellulose acetate butyrate ester by using chitosan. The chitosan neutralizer disclosed by the invention has good solubility in a cellulose acetate butyrate reaction system, can quickly and thoroughly neutralize sulfuric acid to generate chitosan sulfate precipitate with a porous structure, remarkably reduces the sulfate content in a product, and meanwhile, plays a role in filtering unreacted small impurity particles in the system; and a low-turbidity cellulose acetate butyrate product can be produced.

Description

Technical Field

[0001] The invention belongs to the technical field of production of cellulose derivatives, and particularly relates to a method for preparing low-turbidity cellulose acetate butyrate. Background Art

[0002] Cellulose acetate butyrate (CAB) is an important cellulose derivative with excellent performance, including good transparency, weather resistance, oil resistance and electrical insulation. Therefore, it is widely used in the fields of plastic products, coatings, inks, adhesives, etc. In coatings, CAB is mainly used as a film-forming substance and leveling agent, which can improve the fluidity of the coating and the smoothness of the coating film.

[0003] The industrial production method of CAB mainly includes the steps of activation, esterification, hydrolysis, neutralization, filtration, precipitation, washing, drying, etc. In industry, concentrated sulfuric acid is generally used as a catalyst to catalyze the esterification reaction of hydroxyl groups on cellulose and acid anhydride; during hydrolysis, sulfuric acid is used as a catalyst to catalyze the hydrolysis of cellulose ester groups, so that the hydroxyl content of CAB meets the requirements. However, sulfuric acid remains in the reaction system, and the generated cellulose sulfate ester will cause CAB to turn yellow at high temperature, affecting the application performance. Therefore, after the hydrolysis is completed, the sulfuric acid in the reaction system needs to be neutralized to generate metal sulfate precipitation, which is filtered out to obtain a clarified CAB reaction solution. Patent CN103709254A adds magnesium acetate to the reaction system to neutralize sulfuric acid, and CN102898530A uses sodium butyrate as a neutralizer. The use of acetate or butyrate will cause a problem. The generated magnesium sulfate or sodium sulfate will partially dissolve in the water of the reaction system and cannot be removed by filtration. If calcium sulfate that is slightly soluble in water or barium sulfate that is insoluble in water is generated, the test shows that such sulfate is in the form of fine powder in the reaction system, and its particle size is about 0.5-5 microns, which increases the difficulty of filtration. In the industrial process, a higher filtration accuracy is required, which increases the filtration time and equipment investment. Patent CN113788899A adds sulfate seed crystals to the hydrolyzate, then adds acetate or butyrate neutralizer, and uses ultrasonic crystallization to strengthen the salting-out process, so as to precipitate and separate the sulfate radical in the reaction system. However, the ultrasonic and standing time required are long, which greatly reduces the production efficiency, so it is not suitable for industrial production.

[0004] The above-mentioned prior arts can all achieve the separation of sulfate in the cellulose acetate butyrate reaction system, but the particles of sulfate after neutralization are small and partially dissolved in the reaction system, which makes subsequent filtration more difficult. During precipitation, the product encapsulates sulfate, and removing it from the product requires a large amount of water. The sulfate encapsulated in the product is insoluble in organic solvents, which will cause the turbidity of the product resin solution to be high, and the product is unqualified. Therefore, it is necessary to develop a new neutralization method to solve the various deficiencies existing in the prior art. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing low-turbidity cellulose acetate butyrate, so as to solve the problems of low filtration efficiency and high product turbidity in the prior art, improve production efficiency and reduce the generation of wastewater.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing cellulose acetate butyrate comprises the following steps: firstly preparing cellulose acetate butyrate ester, then hydrolyzing the cellulose acetate butyrate ester, and using chitosan to neutralize the reaction liquid after the hydrolysis of the cellulose acetate butyrate ester.

[0008] Preferably, sulfuric acid is used as a catalyst when preparing cellulose acetate butyrate.

[0009] Preferably, when chitosan is added, the water content of the reaction solution after hydrolysis is 1-10 wt %.

[0010] The activated cellulose is subjected to an esterification reaction with acetic anhydride, butyric anhydride and a solvent under the catalysis of sulfuric acid to prepare cellulose acetate butyrate ester, and then a butyric acid or acetic acid aqueous solution is added to cause a hydrolysis reaction; after the hydrolysis is completed, chitosan is added for neutralization; the precipitate is removed by filtration, and cellulose acetate butyrate is obtained through post-treatment.

[0011] Preferably, the cellulose is activated by soaking in acetic acid, the amount of acetic acid used is 1-5 times the mass of the cellulose; the soaking time is 1-5 hours;

[0012] Preferably, the solvent is butyric acid.

[0013] Preferably, the amount of butyric anhydride is 2-6 times the mass of cellulose, the amount of acetic anhydride is 0.1-2 times the mass of cellulose, the esterification reaction temperature is 30-80°C, and the esterification reaction time is 2-10h;

[0014] Preferably, the hydrolysis reaction temperature is 30-80°C.

[0015] Preferably, after the hydrolysis is completed, a butyric acid aqueous solution or water is added to adjust the water content of the system to 1-10 wt%, and then chitosan is added to neutralize the sulfuric acid.

[0016] Preferably, the concentration of the butyric acid aqueous solution is 0-50 wt%, preferably 10-30 wt%.

[0017] The activated cellulose reacts with acetic anhydride and butyric anhydride to produce cellulose acetate butyrate ester, which is then hydrolyzed with butyric acid or acetic acid aqueous solution to obtain cellulose acetate butyrate containing certain hydroxyl groups.

[0018] Preferably, the amount of chitosan added is 3-10 times the mass of the sulfuric acid catalyst; the weight average molecular weight Mw of the chitosan is 50000-150000, and the deacetylation degree of the chitosan is 75-95%;

[0019] Preferably, the neutralization reaction time is 0.1 to 1 h; the filtration method can be pressurized filtration, the pressure is 0.1 to 0.3 MPa, and the filter mesh pore size is 100 to 200 μm.

[0020] Compared with the prior art, the present invention has the following significant effects:

[0021] (1) The present invention uses chitosan as a neutralizing agent to neutralize sulfuric acid, and utilizes the low solubility of chitosan sulfate in the system to completely precipitate the sulfate, thereby significantly reducing the sulfate content in the product, thereby reducing the turbidity of the cellulose acetate butyrate resin solution;

[0022] (2) When the water content of the neutralization solution is further controlled to 1-10%, the neutralization product chitosan sulfate can be precipitated into porous particles, which can adsorb trace unreacted cellulose and lignin small particles in the system, act as a filter aid, and improve the filtration efficiency and filtration accuracy of trace impurities, thereby efficiently producing low-turbidity cellulose acetate butyrate products. DETAILED DESCRIPTION

[0023] The present invention is further described below by means of specific examples. The examples described in the present invention are only used to illustrate the present invention and do not limit the scope of the present invention.

[0024] The main raw material sources of the following examples and comparative examples are as follows:

[0025] Preparation of hydrolysis reaction solution: 1000g cellulose powder was soaked in 1500g acetic acid for activation for 2h, 5000g butyric anhydride, 500g acetic anhydride, 6000g butyric acid, and 50g 98wt% sulfuric acid were added, and esterification reaction was carried out at 50°C for 3h, and then 1500g 50% butyric acid aqueous solution was added, and the temperature was raised to 80°C for hydrolysis reaction for 5h to obtain a hydrolysis reaction solution.

[0026] Chitosan (purity>95%, deacetylation degree 75-95%, Aladdin), sodium acetate (purity 99%, Aladdin).

[0027] Turbidity test method: weigh a cellulose acetate butyrate sample and prepare a 25wt% butyl acetate solution. Add the prepared butyl acetate solution into a turbidity tube and use a Hach TL2300 turbidity meter to test the turbidity value in NTU.

[0028] Example 1

[0029] Weigh 500g of the above hydrolysis reaction liquid and add it to a 1L three-necked flask, add 45g of 10wt% butyric acid aqueous solution under stirring, the water content of the system is about 9.9%, weigh 5g of chitosan (molecular weight Mw=50000, deacetylation degree ≥95%) and add it to the system, react for 20min under stirring, and neutralization is completed. Use a positive pressure filter to filter the neutralized liquid, the pressure is 0.1MPa, the filter mesh aperture is 100μm, and a clear filtrate is obtained after filtration. The filtrate is precipitated, washed, filtered, and dried to obtain a cellulose acetate butyrate product. The prepared product is formulated into a 25% butyl acetate solution, and the turbidity test is 5NTU.

[0030] Example 2

[0031] Weigh 500g of the hydrolysis reaction solution in Example 1, add it to a 1L three-necked flask, add 30g of pure water under stirring, the water content of the system is about 8.2%, weigh 7.9g of chitosan (molecular weight Mw=50000, deacetylation degree ≥95%) and add it to the system, react for 10min under stirring, and neutralization is completed. Use a positive pressure filter to filter the neutralized solution, the pressure is 0.2MPa, the filter mesh aperture is 150μm, and a clear filtrate is obtained after filtration. The filtrate is precipitated, washed, filtered, and dried to obtain a cellulose acetate butyrate product. The prepared product is formulated into a 25% butyl acetate solution, and the test turbidity is 6NTU.

[0032] Example 3

[0033] Weigh 500g of the hydrolysis reaction solution in Example 1, add it to a 1L three-necked flask, add 22g of 20wt% butyric acid aqueous solution under stirring, the water content of the system is about 6.0%, weigh 15.8g chitosan (molecular weight Mw=100000, deacetylation degree ≥90%) and add it to the system, react for 60min under stirring, and neutralization is completed. Use a positive pressure filter to filter the neutralization solution, the pressure is 0.3MPa, the filter mesh aperture is 200μm, and a clear filtrate is obtained after filtration. The filtrate is precipitated, washed, filtered, and dried to obtain a cellulose acetate butyrate product. The prepared product is formulated into a 25% butyl acetate solution, and the test turbidity is 4NTU.

[0034] Example 4

[0035] Weigh 500g of the hydrolysis reaction solution in Example 1, add it to a 1L three-necked flask, add 9.6g of 30wt% butyric acid aqueous solution under stirring, the water content of the system is about 4.0%, weigh 12.6g of chitosan (molecular weight Mw=100000, deacetylation degree ≥90%) and add it to the system, react for 35min under stirring, and neutralization is completed. Use a positive pressure filter to filter the neutralization solution, the pressure is 0.1MPa, the filter mesh aperture is 100μm, and a clear filtrate is obtained after filtration. The filtrate is precipitated, washed, filtered, and dried to obtain a cellulose acetate butyrate product. The prepared product is formulated into a 25% butyl acetate solution, and the test turbidity is 3NTU.

[0036] Example 5

[0037] Weigh 500g of the hydrolysis reaction solution in Example 1, add it to a 1L three-necked flask, add 3g of 50wt% butyric acid aqueous solution under stirring, the water content of the system is about 3.0%, weigh 11.0g chitosan (molecular weight Mw=150000, deacetylation degree ≥75%) and add it to the system, react for 6min under stirring, and neutralization is completed. Use a positive pressure filter to filter the neutralization solution, the pressure is 0.2MPa, the filter mesh aperture is 200μm, and a clear filtrate is obtained after filtration. The filtrate is precipitated, washed, filtered, and dried to obtain a cellulose acetate butyrate product. The prepared product is formulated into a 25% butyl acetate solution, and the test turbidity is 7NTU.

[0038] Comparative Example 1

[0039] Weigh 500g of the hydrolysis reaction solution in Example 1, add it to a 1L three-necked flask, add 40g of a 10wt% butyric acid aqueous solution under stirring, add 3g of sodium acetate after stirring, react for 1h under stirring, and neutralization is completed. Use a positive pressure filter to filter the neutralized solution at a pressure of 0.4MPa and a filter mesh aperture of 15μm to obtain a clarified filtrate after filtration. The filtrate is precipitated, washed, filtered, and dried to obtain a cellulose acetate butyrate product. The prepared product is formulated into a 25% butyl acetate solution, and the turbidity test is 17NTU.

Claims

1. A method for preparing cellulose acetate butyrate, characterized in that: Firstly, cellulose acetate butyrate is prepared, then the cellulose acetate butyrate is hydrolyzed, and chitosan is used to neutralize the reaction liquid after the hydrolysis of cellulose acetate butyrate.

2. The preparation method according to claim 1, characterized in that: Sulfuric acid is used as a catalyst in the preparation of cellulose acetate butyrate.

3. The preparation method according to claim 1 or 2, characterized in that: When chitosan is added, the water content of the reaction solution after hydrolysis is 1-10wt%.

4. The preparation method according to any one of claims 1 to 3, characterized in that Cellulose acetate butyrate is prepared by esterifying activated cellulose with acetic anhydride, butyric anhydride and solvent under the catalysis of sulfuric acid.

5. The preparation method according to claim 4, characterized in that: A butyric acid or acetic acid aqueous solution is added to cellulose acetate butyrate to carry out a hydrolysis reaction.

6. The preparation method according to claim 4 or 5, characterized in that: The cellulose is activated by soaking in acetic acid, the amount of acetic acid used is 1-5 times the mass of the cellulose; the soaking time is 1-5 hours; Preferably, the solvent is butyric acid.

7. The preparation method according to any one of claims 4 to 6, characterized in that: The amount of butyric anhydride used is 2-6 times the mass of cellulose, and the amount of acetic anhydride used is 0.1-2 times the mass of cellulose.

8. The preparation method according to any one of claims 4 to 7, characterized in that: The esterification reaction temperature is 30-80°C, and the esterification reaction time is 2-10h; Preferably, the hydrolysis reaction temperature is 30-80°C.

9. The preparation method according to any one of claims 1 to 8, characterized in that: After the hydrolysis is completed, a butyric acid aqueous solution or water is added to adjust the water content of the system to 1-10 wt%, and then chitosan is added for neutralization; Preferably, the concentration of the butyric acid aqueous solution is 0-50 wt%, preferably 10-30 wt%.

10. The preparation method according to any one of claims 1 to 9, characterized in that: The amount of chitosan added is 3-10 times the mass of the sulfuric acid catalyst; Preferably, the weight average molecular weight Mw of the chitosan is 50000-150000, and the deacetylation degree of the chitosan is 75-95%; Preferably, the neutralization reaction time is 0.1 to 1 h.