Method for recovering glycerin and polyglycerol from raffinate obtained after preparing refined glycerin through distillation

The invention relates to a material separation method in the chemical engineering field, and concretely relates to a method for recovering glycerin and polyglycerol from a raffinate obtained after preparing refined glycerin from crude glycerin through distillation, wherein the crude glycerine is a product obtained by saponifying, hydrolyzing or alcoholyzing natural oil. The method comprises the following steps: 1, pretreating: dehydrating and desalinating step by step 2-5 times; 2, further dehydrating and degassing with wiped film evaporation; 3, recovering glycerin with a primary molecular distiller; and 4, recovering polyglycerol with a secondary molecular distiller. The method of the invention has the following advantages: operation equipment for dehydration and desalination is simple, equipment material requirements are low, the investment is less, and the practicality is strong; recovered glycerin and polyglycerol can be continuously used for the industrial production, and the change of wastes into valua