Molecular distillation has evolved from falling film to wiped film

A complete set of molecular distillation mainly includes feed system, molecular still, heating system, cooling system, vacuum system and control system. The difference in molecular mean free path is used for material separation. The material to be separated forms a uniform liquid film on the heating plate. After heating, the material liquid molecules escape. A condensing plate is set parallel to the heating plate. The temperature of the condensing plate is lower than that of the heating plate, and the distance from the heating plate should be less than the mean free path of light molecules and greater than the mean free path of heavy molecules. In this way, most of the light molecules can reach the condensation surface to form a liquid outflow, and the heavy molecules return to the heating surface, thus achieving separation.
The form that appeared in the early days was a falling-film molecular distiller. The main feature is a simple structure, but due to drawbacks such as thick liquid film and poor efficiency, it has been rarely used. The device adopts the action of gravity to make the material on the evaporation surface turn into a liquid film drop mode, heating the material, and the evaporated material can condense on the condensation surface in the opposite direction.
With in-depth research on molecular distillation equipment and processes, wiped film molecular distillation equipment has been successfully developed. This type of equipment can achieve high separation efficiency, but the structure is not as simple as falling film molecular distillation equipment. In order to make the thickness of the liquid film on the evaporation surface small and evenly distributed, a rotating scraper made of hard carbon or polytetrafluoroethylene is installed in the distiller.
The scraper in the molecular distillation device can not only fully stir the downstream liquid layer, but also speed up the renewal of the evaporated surface liquid layer, thereby strengthening the heat and mass transfer process of the material, making the equipment exhibit a small liquid film thickness , And flow along the evaporation surface; the residence time of the distilled material at the operating temperature is short, the risk of thermal decomposition is small, and the production capacity is large.
Of course, the wiped film molecular distillation device also has shortcomings, that is, the liquid distribution device is difficult to perfect, and it is difficult to ensure that all the evaporation surfaces are evenly covered by the liquid film. In addition, the liquid flow often rolls over, and the generated mist is easy to splash on the condensation surface. It seems that there is still much room for improvement in molecular distillation equipment.