1. Ketene method This method is the most commonly used method in international industrial production. Acetic acid is cracked at high temperature to generate ketene, and then condensed with crotonaldehyde to form polyester, and then hydrolyzed and refined to obtain the finished product.

2. The malonic acid method is obtained by the condensation and decarboxylation of malonic acid and crotonaldehyde.

3. The acetone method is obtained by the condensation of acetone and crotonaldehyde, followed by dehydrogenation.

4. Butadiene method Using butadiene and acetic acid as raw materials, in the presence of manganese acetate catalyst, press and compress at 140 ℃ to obtain γ-ethylene-γ-butyrolactone. Under the action of acid ion exchange resin, butyrolactone is ring-opened to obtain sorbic acid.

5. Acetic acid is cracked at high temperature to generate ketene, which is then condensed with crotonaldehyde to form polyester, and then hydrolyzed and refined to obtain the finished product.