molecular distillation(分子蒸馏)

Molecular distillation Profile

Molecular distillation is a distillation method operated in high vacuum, At this time, the mean free path of steam molecules is greater than the distance between evaporation surface and condensation surface, liquid mixtures can be separated because of the difference of evaporation rate of each component in liquid.

Under certain temperature, the lower the pressure, the gas molecule mean free path greater. When the pressure of evaporation space (10-2 ~ 10-4 mmHg) is very low, and evaporation surface is near condensation surface, the vertical distance between them is less than the mean free path of steam molecules , gas molecules can reach condensation surface and condensate without collisions.

The working principle of molecular distillation

Molecular distillation is a special kind of liquid - liquid separation technology, which is different from the traditional distillation separation principle. Separation can be achieved because of the difference of the mean free path of the different molecules. When the liquid mixture flows along the heating plate and is heated, light and heavy liquid molecules escape into the gas phase because of the difference of the mean free path of the light and heavy molecules, the moving distance of the different molecules after escaping from liquid surface. If a condensation plate can be set up properly, the light molecules can reach condensation surface and condensate and be exhausted, the heavy molecules can not reach condensation surface and be exhausted. In this way, the purpose of the separation material is achieved. The difference of pressure between the boiling film and the condensation surface is the driving force whose the steam flows, the small pressure drop will cause the flow of steam. It is required that the distance between boiling surface and condensation surface is very short under the pressure of 1mbar, the stills based on the principle is named

short-path distillation device. Still short-range (molecular distillation)has a built-in condenser in the opposite surface of heating surface which makes operating pressure reduce to 0.001mba Short-path distillation is a process of thermal separation technology under the pressure of 1 ~ 0.001mbar, which has the lower boiling temperature, is ideal for heat-sensitive, high boiling point materials. Its basic components: the cylinder cylindrical with a heating jacket, the rotor and the built-in condenser, the scraping membrane device, anti-splash installment. The built-in condenser is located in the center of the evaporator, the rotor between the cylinder and condenser.

Distillation process: the materials are added from the top of the evaporator and are distributed uniformly, continuously on heating surface by the liquid distributor. the scraping membrane device make the liquid materials into a single very thin liquid film like turbulence, and advance downward spirally. In the process, the light molecules escaping from the heating sarurface reach the built-in condenser and condense into fluid through a short line and almost without a collision . It flow along the condenser tube, is exhausted through the exhaust pipe at the bottom of the evaporator; the residues(the heavy molecules ) are collected in a circular path under the heating zone, flow out through the side of the pipe.

The process of molecular distillation

Short-path distillation is also suitable for molecular distillation. The flow is from the surface of the heating zone directly to the condenser’s surface. Molecular distillation process can be ma de up of