A method for precipitating cellulose acetate butyrate

Abstract

The present invention relates to a method for precipitating cellulose acetate butyrate, wherein a liquid to be precipitated containing cellulose acetate butyrate is introduced into water containing crystal nuclei, and the water is depressurized and heated at the same time, and a large number of bubbles are generated during the boiling process of the water, and the impact force generated during the bubble bursting process is used to impact the crystal particles of the cellulose acetate butyrate, so as to avoid the particles from sticking to each other and agglomerating before hardening, thereby forming a cellulose acetate butyrate product with uniform particles and high bulk density. At the same time, due to the introduction of crystal nuclei and the operation at a certain temperature, the method can effectively reduce the encapsulation and adsorption of acetic acid and butyric acid by the product during the precipitation process, and can effectively reduce the amount of washing water used.

Description

Technical Field

[0001] The invention provides a method for precipitating cellulose acetate butyrate, and belongs to the field of organic chemical synthesis. Background Art

[0002] Cellulose acetate butyrate (CAB) is a cellulose derivative that combines the advantages of cellulose acetate and cellulose butyrate, is compatible with a variety of resins, has good toughness, cold resistance, transparency, anti-aging and anti-yellowing properties, and is used as a leveling agent in high-end automotive paints and high-end inks. Especially in the field of high-end automotive paints, cellulose acetate butyrate can strengthen the directional arrangement of aluminum powder and increase the metallic properties of automotive paints.

[0003] For the production of CAB, precipitation is an important part of controlling product indicators, among which acid content, particle size, bulk density and other indicators determine the quality of precipitation. The precipitation process is the crystallization process of CAB in water, and the crystallization process can easily wrap the solvent in the crystal nucleus, causing the product acid value to be too high and affecting the product quality; at the same time, CAB products with high density after crystallization can reduce the use of packaging bags and improve space utilization. In the traditional precipitation process, CAB is mostly lumpy or flocculent after precipitation, which is easy to wrap the solvent in the product. A large amount of water is required for washing later, and it needs to be crushed at the same time. The crushing process will generate heat. Improper control will cause problems such as yellowing and stickiness of the product. The temperature monitoring and control requirements during the crushing process are relatively high.

[0004] Patent CN111253616A uses a two-step flash evaporation method to remove butyric acid and water from the product, avoiding the generation of wastewater during washing, filtering, and drying, and reducing energy consumption. However, the resulting product is fluffy and flocculent. Although it increases the dissolution rate of the product during use, the flocculent product is not conducive to the transportation and packaging of the product.

[0005] Patent CN113831557A adopts the method of adding stabilizers to control the particle size of CAB products, but this method introduces new substances and is prone to encapsulating impurities such as stabilizers and solvents during the granulation process, resulting in unqualified products.

[0006] Therefore, how to create a precipitation method that can both improve the particle size of CAB products after precipitation and reduce the amount of impurities contained in the product has become an urgent problem to be solved in the industry. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a cellulose acetate butyrate precipitation method to improve the granularity of the precipitated product and increase its bulk density.

[0008] In order to achieve the above invention object, the technical solution adopted by the present invention is as follows:

[0009] The present invention provides a method for precipitating cellulose acetate butyrate, comprising the following steps:

[0010] The precipitated liquid containing cellulose acetate butyrate is passed into boiling water containing cellulose acetate butyrate crystal nuclei prepared in advance and subjected to temperature increase and pressure reduction to precipitate the precipitated liquid;

[0011] In the present invention, the precipitated solution containing cellulose acetate butyrate, with its total mass as 100%, contains 10-30% cellulose acetate butyrate, 50-85% butyric acid, 0.5-10% acetic acid, and 0.5-1% water; further, the crystal nuclei used in the present invention are cellulose acetate butyrate particles, and the crystal nuclei have a diameter of 0.1 to 200 μm, preferably 1 to 100 μm;

[0012] Further, in the water containing crystal nuclei of the present invention, the mass concentration of the crystal nuclei is 0.01-5%, preferably 0.05-3%, based on the mass of the water containing the crystal nuclei;

[0013] Further, the amount of water containing the crystal nuclei of the present invention is 5-15 times the mass of the liquid to be precipitated, preferably 7-12 times;

[0014] Further, the pressure of the decompression of the present invention is 0.5-90 kPaA, preferably 1-70 kPaA; the temperature of the boiling water is 0-96°C, preferably 7-90°C;

[0015] The precipitate obtained in the present invention further comprises the steps of discharging through a feed outlet, washing with water, and drying to obtain cellulose acetate butyrate particles; preferably, the average particle size of the cellulose acetate butyrate particles is 200-700 μm, and the bulk density is 0.4-0.7 kg / m 3 , acid value <150ppm (calculated as acetic acid); particle size distribution coefficient is 0.3-0.5.

[0016] In the present invention, the number of times of water washing is 1-5 times, the temperature of drying is 60-120° C., and the drying time is 4-8 hours.

[0017] In the present invention, the cellulose acetate butyrate crystal nucleus is fine powder obtained by sieving the corresponding brand product.

[0018] The preparation method of the cellulose acetate butyrate crystal nucleus comprises the following steps:

[0019] First, the cellulose acetate butyrate product is screened with a common vibrating screen to obtain fine powder with a diameter of about 200 μm, and then the cellulose acetate butyrate product is screened with an ultrasonic rotary vibrating screen below 600 mesh to obtain fine powders of different particle sizes for use as crystal nuclei;

[0020] The present invention has the following beneficial effects:

[0021] The present invention utilizes the impact force generated during the boiling process of water under negative pressure to impact the crystal particles of cellulose acetate butyrate, thereby preventing the particles from sticking to each other and agglomerating before hardening, thereby forming a cellulose acetate butyrate product with uniform particles and high bulk density. At the same time, due to the introduction of crystal nuclei and the operation at a certain temperature, the method can effectively reduce the encapsulation and adsorption of acetic acid and butyric acid by the product during the precipitation process, thereby reducing the amount of washing water used. DETAILED DESCRIPTION

[0022] The present invention is further described below in conjunction with embodiments, but the present invention is not limited to the listed embodiments, and should also include equivalent improvements and modifications of the technical solutions defined in the claims attached to the present application.

[0023] Main raw material indicators of the embodiment:

[0024] The precipitated liquid: The precipitated liquid containing cellulose acetate butyrate has a mass percentage composition of 27% CAB, 70% butyric acid, 2% acetic acid, and 1% water.

[0025] Other materials, unless otherwise specified, are common commercially available raw materials.

[0026] The test method is as follows:

[0027] The particle size test was carried out using Bettersize 2600 laser particle size distribution analyzer (dry method), Dandong Bettersize Instrument Co., Ltd.

[0028] The acid value test adopts the acid-base titration method, as follows:

[0029] Testing Process

[0030] Weigh 10.0 g of the sample, correct the moisture content if necessary, and dissolve it in 200 ml of neutral acetone and 20 ml of water. When the sample is completely dissolved, add 50 ml of water and shake well to precipitate the cellulose ester in a tiny state. Add 3 drops of methyl red indicator solution and titrate with 0.01 mol / L NaOH solution to the lemon yellow endpoint.

[0031] Acidity percentage calculation

[0032] Acidity % = {[(AB)C × 0.06] / W} × 100

[0033] A = volume of sodium hydroxide solution consumed by titrating the sample, mL,

[0034] B = volume of sodium hydroxide solution consumed in titration of blank sample, mL,

[0035] C = concentration of sodium hydroxide solution,

[0036] W = sample mass, g.

[0037] Preparation Example

[0038] The cellulose acetate butyrate product is sieved with an ordinary vibrating screen to obtain fine powder with a diameter of about 200μm. Then, an ultrasonic rotary vibrating screen with a mesh size below 600 is used to sieve the cellulose acetate butyrate product of the corresponding brand to obtain fine powders with diameters of about 40μm, 50μm, and 100μm, respectively, which are used as crystal nuclei.

[0039] Example 1

[0040] 1kg of cellulose acetate butyrate solution to be precipitated is sprayed into 5kg of precipitating water containing crystal nuclei through a nozzle, wherein the crystal nuclei are 0.05kg of cellulose acetate butyrate and the average particle size of the crystal nuclei is 40μm. The pressure in the precipitation kettle is 1kPaA, and the temperature in the precipitation kettle is 20°C. After the feeding is completed, the material is discharged through the discharge port, and the product is washed three times with clean water, and dried at 60°C for 5h to obtain cellulose acetate butyrate particles.

[0041] The obtained cellulose acetate butyrate granules were tested to have an average particle size of 425 μm, in granular form, and a bulk density of 0.49 kg / m 3 , the acid value is 148ppm and the amount of water used for washing is 30kg.

[0042] Example 2

[0043] 1kg of cellulose acetate butyrate solution to be precipitated is sprayed into 10kg of precipitating water containing crystal nuclei through a nozzle, wherein the crystal nuclei are 0.15kg of cellulose acetate butyrate and the average particle size of the crystal nuclei is 50μm. The pressure in the precipitation kettle is 20kPaA, the temperature in the precipitation kettle is 65℃, and the material is discharged through the discharge port after the feeding is completed. The product is washed three times with clean water and dried at 90℃ for 4h to obtain cellulose acetate butyrate particles.

[0044] The obtained cellulose acetate butyrate granules were tested to have an average particle size of 513 μm, a granular shape, and a bulk density of 0.51 kg / m 3 , the acid value is 107ppm and the amount of water used for washing is 30kg.

[0045] Example 3

[0046] 1kg of the precipitated liquid containing cellulose acetate butyrate was sprayed into 15kg of precipitation water containing crystal nuclei through a nozzle, wherein the crystal nuclei were 0.45kg of cellulose acetate butyrate and the average particle size of the crystal nuclei was 100μm. The pressure in the precipitation kettle was 40kPaA, the temperature in the precipitation kettle was 80℃, and after the feeding was completed, the material was discharged through the discharge port, the product was washed three times with clean water, and dried at 120℃ for 3h to obtain cellulose acetate butyrate particles.

[0047] The obtained cellulose acetate butyrate granules were tested to have an average particle size of 582 μm, a granular shape, and a bulk density of 0.47 kg / m 3 , the acid value is 130ppm and the amount of water used for washing is 30kg.

[0048] Comparative Example 1

[0049] Referring to the precipitation method of Example 1, the only difference from Example 1 is that no crystal nuclei are added to the precipitation water, and other operating methods and conditions are exactly the same to obtain cellulose acetate butyrate particles.

[0050] The obtained cellulose acetate butyrate granules were tested to have an average particle size of 713 μm, in granular form, and a bulk density of 0.37 kg / m 3 , the acid value is 520ppm and the amount of water used for washing is 30kg.

[0051] Comparative Example 2

[0052] Referring to the precipitation method of Example 2, the only difference from Example 2 is that the precipitation water is at room temperature and pressure, and the other operating methods and conditions are exactly the same to obtain cellulose acetate butyrate particles.

[0053] The obtained cellulose acetate butyrate granules were tested to have an average particle size of 513 μm, in granular form, and a bulk density of 0.40 kg / m 3 , the acid value is 415ppm and the amount of water used for washing is 30kg.

[0054] Comparative Example 3

[0055] Referring to the precipitation method of Example 3, the difference from Example 3 is that no crystal nuclei are added to the precipitation water and the precipitation is carried out at room temperature and pressure. Other operating methods and conditions are exactly the same to obtain cellulose acetate butyrate particles.

[0056] The obtained cellulose acetate butyrate granules were tested to have an average particle size of 817 μm, a granular shape, and a bulk density of 0.32 kg / m 3 , the acid value is 916ppm and the amount of water used for washing is 30kg.

Claims

1. A method for precipitating cellulose acetate butyrate, characterized in that: The following steps are involved: The precipitated liquid containing cellulose acetate butyrate is passed into boiling water containing cellulose acetate butyrate crystal nuclei prepared in advance, and precipitated to obtain a precipitated liquid after heating and reducing the pressure. The precipitated liquid containing cellulose acetate butyrate, with its total mass as 100%, contains 10-30% of cellulose acetate butyrate, 50-85% of butyric acid, 0.5-10% of acetic acid, and 0.5-1% of water.

2. The method according to claim 1, characterized in that The cellulose acetate butyrate crystal nucleus is a cellulose acetate butyrate particle, and the crystal nucleus diameter is 0.1-200 μm.

3. The method according to claim 1, characterized in that The cellulose acetate butyrate crystal nucleus is a cellulose acetate butyrate particle, and the crystal nucleus diameter is 1 to 100 μm.

4. The method according to any one of claims 1 to 3, characterized in that: The mass concentration of the cellulose acetate butyrate crystal nuclei in the boiling water after temperature increase and pressure reduction is 0.01-5%, calculated based on the mass of the water containing the crystal nuclei.

5. The method according to claim 4, characterized in that The mass concentration of the cellulose acetate butyrate crystal nuclei in the boiling water after temperature increase and pressure reduction is 0.05-3%, calculated based on the mass of the water containing the crystal nuclei.

6. The method according to any one of claims 1 to 3, characterized in that: The amount of boiling water containing cellulose acetate butyrate crystal nuclei after temperature increase and pressure reduction is 5-15 times the mass of the liquid to be precipitated.

7. The method according to claim 6, characterized in that The amount of boiling water containing cellulose acetate butyrate crystal nuclei after temperature increase and pressure reduction is 7-12 times the mass of the liquid to be precipitated.

8. The method according to any one of claims 1 to 3, characterized in that: The pressure of the decompression is 0.5-90 kpaA; the temperature of the boiling water is 0-96°C.

9. The method according to any one of claims 1 to 3, characterized in that: The pressure of the decompression is 1-70 kPaA; the temperature of the boiling water is 7-90°C.

10. The method according to any one of claims 1 to 3, characterized in that: The obtained precipitate also includes the steps of discharging through a discharge port, washing with water, and drying to obtain cellulose acetate butyrate particles.

11. The method according to claim 10, characterized in that The number of times of water washing is 1-5 times, the temperature of drying is 60-120° C., and the drying time is 4-8 hours.

12. The method according to any one of claims 1 to 3, characterized in that: The preparation method of the cellulose acetate butyrate crystal nucleus comprises the following steps: First, the cellulose acetate butyrate product is screened with a common vibrating screen to obtain fine powder with a diameter of 100-200 μm, and then the cellulose acetate butyrate product is screened with an ultrasonic rotary vibrating screen below 600 mesh.