The invention discloses a method for separating and purifying a
thiourea polymer in a
demethylation compound, which comprises the following steps: mixing the
thiourea polymer in a
demethylation product with water, heating the obtained
mixed solution to 80-90 DEG C, and keeping the temperature for 4-6 hours, so that the
thiourea polymer impurity in the product is dissolved in hot water; carrying out
solid-liquid separation on the obtained
solid-liquid mixture to obtain a
solid substance demethylated compound, wherein the demethylated substance does not contain the thiourea polymer; the water phase is cooled to the
room temperature, a product is separated out, another solid phase is the thiourea polymer, and the
mass percent of the thiourea polymer in the
demethylation substance is smaller than 0.05%. According to the method, the demethylation compound and the
impurity thiourea polymer are separated and purified by utilizing the characteristics that the
solubility of the demethylation compound in water is small, and the thiourea polymer is dissolved in water. Experimental results show that the method provided by the invention can effectively improve the purity and content of demethylated substances, and is low in production cost, green and environment-friendly.