Preparation of cellulose acetate
Raw material selection
Preparation of cellulose acetate, the first heavy raw material. It is necessary to select high-quality natural cellulose, which is the foundation. Cellulose comes from a wide range of sources, preferably wood pulp and cotton lint. Because of its high purity and suitable degree of polymerization, it can lay a good foundation for subsequent reactions. After selecting the raw material, impurities should be carefully removed to ensure its purity, so as to improve product quality.

Reaction flow
1. ** Acetylation reaction **: The treated cellulose is placed in a reaction kettle, and acetic anhydride and catalyst are added in a certain proportion. The catalyst is often sulfuric acid, which can effectively accelerate the reaction process. The reaction temperature is strictly controlled in a specific range, generally around [X] ° C. At this temperature, acetic anhydride and the hydroxyl group in the cellulose molecule undergo acetylation to form a crude cellulose acetate product. This process requires continuous stirring to ensure that the reaction proceeds uniformly.
2. ** Hydrolysis Reaction **: The product after acetylation needs to be moderately hydrolyzed to adjust the degree of substitution of cellulose acetate. Add an appropriate amount of water and hydrolysis catalyst to the reaction system, and under suitable temperature and time conditions, hydrolyze part of the acetyl group. The key to this step is to precisely control the degree of hydrolysis, otherwise it will affect the performance of the product.
3. ** Neutralization Treatment **: After the hydrolysis is completed, the reaction solution is acidic and needs to be neutralized Select suitable alkaline substances, such as sodium carbonate solution, and slowly add them to the reaction solution to neutralize excess acid, so that the pH value of the reaction system reaches the neutral or weakly acidic range. This process requires close monitoring of pH changes to prevent excessive neutralization.

Separation and Purification
1. ** Precipitation Separation **: The reaction solution after neutralization is treated by precipitation, so that cellulose acetate is precipitated from the solution. Precipitants are often added, such as organic solvents such as methanol and acetone, to change the polarity of the solution and promote the precipitation of cellulose acetate. After the precipitation is completed, solid cellulose acetate is separated by filtration or centrifugation.
2. ** Washing and drying **: The separated cellulose acetate solids contain impurities and residual solvents. It needs to be washed multiple times with an appropriate amount of washing liquid to remove impurities. The washing liquid can be a mixed solution of alcohol and water. After washing, it is placed at a suitable temperature to dry to remove residual moisture and solvents to obtain pure cellulose acetate products.

In the process of preparing cellulose acetate, all links are closely linked. The quality of raw materials, the control of reaction conditions and the separation and purification process all have a profound impact on product quality. Only by strictly controlling each step can we obtain cellulose acetate with excellent performance.