λ＝8.589(when only one type molecules exist)
λ:average molecular free path;   cm;
   ηT:the viscosity at T temperature; P;
    M:molecular weight;
    T:absolute temperature;               K;
    P:Vapor pressure;                  mmHg;
Molecular distillation process can be divided into 4 steps.
  1. Molecular diffusion from the main liquid phase towards the evaporation surface.
The diffusion velocity in the liquid phase is the major factor to control molecular distillation velocity.
  2. The free evaporation speed is increased along with the temperature increasing, but the separation factor is decreased along with the temperature increasing.
  3. The molecules run to the condensation surface, during which, possibly collide with residuary air molecules, and collide each other. It is necessary to maintain proper vacuum and make the average free path more than or equal to the distances between the evaporation surface and the condensation surface. It is meaningless to keep too high vacuum degree.
  4. Molecules are condensed on the condensation surface, condensation process are completed immediately since the condensation surface shape is smooth and optimized.
    The main structure of molecular distillator designed and fabricated by our LIMA Co. see figure 1.
    The unique design and precisely fabrication ensures the small gap between evaporation and condensation surface. Strictly controlling rotation shaft radial shaking makes the rotor drag scraper plate stable rotation. No scaling, no coking and half pipe heating jacket greatly increase heat transfer coefficient The high grade mirror polishing on the evaporation column is more suitable for high viscose materials. High precision, high temperature resistance mechanical sealing ensures very low absolute pressure in the distillator
  Figure 1
1. Motor; speed driver 2. Support; 3. Materials inlet 4. Scraper plate 5. Rotor; 6. Heating Oil outlet 7. Heating jacket; 8. Condensator 9. Materials outlet (A) 10.cooling water. 11. Materials outlet (B) 12. Heating Oil in 13. Vacuum 14. Cooling water out

Figure 2. Molecular Distillation System
HR1, HR2 Materials Pre-heater, BM. Film Evaporator; DZ. Molecular Distillator,
ZK1, ZK2 Vacuum System; G1G2G3 Storage Tanks; LJ. Cooling well
YL. Heating oil system. P1P2. Feed pumps
    Figure 2 is a simple and typical molecular distillation system

The optimized system arrangement assures the whole system operate properly. Selecting adaptable film evaporators as pre-separator effectively assure the separation capacity. The selection of heat oil furnace assures supplying necessary heat and keeps the temperature fluctuation within controlling range for the light fraction separation. Proper pump selection makes the materials conveying at different vacuum degree. Vacuum pumps should be chose based on the different vacuum requirement and sucking capacity.
    The molecular distillation equipment are widely used in chemical, petroleum, pharmaceutical, oil and grease, light industry and scientific research for concentrating and purifying high molecular weight, high boiling point, high viscosity and poor heat stability organic chemicals such as VA, VE, plasticizer, fragrant and scent additives and medical intermediates etc.
    Molecular distillation system design needs to closely and precisely meet the practical process requirements. Our Co. would like to sincerely co-operate with customers to determine optimized molecular distillation system.