Method for recycling urea in urea adduct process

A method of recycling urea in a process of purifying unsaturated substances through a urea adduction method, comprising the following steps:

• (1) urea adduction:
• adducting an aqueous solution including a raw material, urea and a lower alcohol aqueous solution at a temperature of 45-65° C., wherein a ratio of the raw material to the urea is 1:1-4, a ratio of the urea and the lower alcohol is 1:3-6, and then crystallizing at 0-10° C. of crystallization temperature;
• and afterwards filtering to obtain a filtrate of unsaturated substances and a filter cake of urea-saturated substance adducts;
• and then removing solvent from the filtrate to obtain one or more target unsaturated components, and the filter cake is a urea adduct;
• (2) releasing the urea adduct:
• adding a volume of a polar solvent to the urea adduct to form a solution, wherein the polar solvent is lower alcohol, or a mixture of water and lower alcohol in any proportion, then heating and stirring the solution for dissolution at a temperature of 50 to 90° C., and standing for layering to obtain a urea solution having an upper layer and a lower layer, and then washing the upper layer of the urea solution with water to obtain a component adducted by urea;
• and
• (3) urea crystallization:
• adding a volume of an organic solvent to the lower layer of the urea solution, wherein the organic solvent is lower alcohol, n-hexane, acetone, ether, ethyl acetate, or a mixture thereof in any proportion;
• and then stirring and mixing, cooling for crystallization slowly to crystallize at a crystallization temperature, and afterwards filtering, and drying to obtain urea crystals for urea reuse.