The cellulose acetate manufacturing process
raw material preparation
requires the selection of high-quality natural cellulose, such as cotton lint or wood pulp. The two have high fiber content and less impurities, which can ensure product quality. Cotton lint needs to be pretreated by removing impurities, cleaning and other pretreatments to remove cottonseed hulls and dust; wood pulp should be tested for its polymerization degree, whiteness and other indicators before it can be used. At the same time, an appropriate amount of acetic anhydride and acetic acid are prepared. As the key reagents for acetylation reaction, its purity and concentration are strictly controlled to ensure a smooth reaction.

Pretreatment process
The selected cellulose raw material is put into the reaction kettle, and an appropriate amount of catalyst, such as sulfuric acid, is added. The catalyst can reduce the Then add a certain amount of acetic acid to make the cellulose initially swell. After swelling, the cellulose structure is loose, which is conducive to the subsequent full reaction of acetic anhydride with it. Control the temperature and time, the temperature is generally 30-40 degrees Celsius, and the time is about 1-2 hours, so that the cellulose can fully swell.

The acetylation reaction
The swelling is completed, and the acetic anhydride is slowly added in proportion. Acetylation of acetic anhydride and cellulose hydroxyl groups occurs to form cellulose acetate. This process is an exothermic reaction, and the reaction temperature needs to be strictly controlled. The temperature is maintained at 50-60 degrees Celsius through a cooling device to avoid side reactions caused by excessive temperature. The reaction time is 3-5 hours, and the reaction is continuously stirred during this period to ensure that the reactants are fully contacted and the reaction is uniform. Monitor the reaction progress in real time, and judge the degree of reaction by measuring the remaining amount of acetic anhydride in the reactants or the degree of substitution of the product.

Hydrolysis and neutralization
Acetylation is completed. The product contains excess acetic anhydride and catalyst sulfuric acid, which needs to be hydrolyzed and neutralized. Add water to the reactor to hydrolyze the remaining acetic anhydride into acetic acid. Then neutralize the sulfuric acid with basic substances such as sodium bicarbonate or sodium carbonate to form a sulfate precipitation. Adjust the pH to 6-7 to ensure that the system is neutral. The temperature of this process is controlled at 40-50 degrees Celsius

Precipitation and washing
After neutralization, a large amount of water or organic solvent is added to the reaction system to precipitate cellulose acetate. Commonly used organic solvents such as acetone and methanol can reduce the solubility of cellulose acetate. After precipitation, cellulose acetate solids are separated by filtration or centrifugation. Wash with deionized water for multiple times to remove the salt and unreacted substances remaining on the surface and improve the purity of the product. Wash until the electrical conductivity of the washing solution reaches the standard, indicating that the impurities are basically removed.

Drying and pulverizing
The washed cellulose acetate is dried in an oven or vacuum dryer at 40-60 degrees Celsius to remove moisture. After drying, pulverize it to the desired particle size with a pulverizer. The particle size depends on the use of the product. For example, it is finer for textiles and coarser for plastics. After crushing, it is sieved and graded to ensure that the particle size of the product is uniform, and it is packaged and put into storage for sale.