Preparation method of medicinal sodium benzoate

The invention provides a preparation method of medicinal sodium benzoate, which comprises the following steps: by taking benzoic acid melt crystallization residual liquid as a production raw material, putting a sodium-containing alkaline aqueous solution and the benzoic acid melt crystallization residual liquid in a molten state into an extraction tower, enabling the sodium-containing alkaline aqueous solution and the benzoic acid melt crystallization residual liquid to be in countercurrent contact in the extraction tower, and dehydrating and concentrating a water phase flowing out of the extraction tower in a concentration kettle; feeding the concentrated aqueous solution into a neutralization kettle, conveying the concentrated aqueous solution into an activated carbon fiber filter through a neutralization kettle discharge pump for adsorption and impurity removal, conveying the concentrated aqueous solution into a precision filter through the neutralization kettle discharge pump for filtration, feeding the f