Preparation method of potassium sorbate

The invention discloses a preparation method of potassium sorbate. The method comprises the following steps of adding beta-acrylaldehyde and caprolactam into a reaction kettle to be stirred; introducing ketene gas for 3 to 4 hours under the condition of the temperature being 45 to 55 DEG C for reaction; after the reaction is completed, performing filtering, and rectifying reaction liquid to obtain 2, 4-hexadienoic acid polyester; mixing the obtained 2, 4-hexadienoic acid polyester and catalysts according to a mass ratio being (300 to 320):1; performing heat insulation depolymerization at 80 DEG C for 28 to 30 hours; cooling the materials to 45 DEG C; filtering and recovering solid acid catalysts; distilling filter liquid to recover partial unreacted beta-acrylaldehyde and methylbenzene; using ethanol for centrifugal leaching for removing tar; then, performing refining, water washing and drying to obtain a 2, 4-hexadienoic acid finished product; dissolving the 2, 4-hexadienoic acid crude product, potassium carbonate and vitamin C into water for reaction; performing spray drying and pelleting. The catalysts are a mixture of silicon dioxide and tartaric acid according to a mass ratio being 1:(0.7 to 0.8).