Short Path Distillation from Ken Kimble (Reactor Vessels) Ltd


	Gentle separation of products by vacuum distillation


	Vacuum distillation is a high value process for smooth separation. Homogenous mixtures of liquids with different boiling points can be separated by distillation.

Distillation under vacuum conditions is used

for heat sensitive products when distillation at atmospheric pressure causes thermal decomposition

for high boiling products when distillation at atmospheric pressure causes difficulties with respect to energy losses and availability of construction material

In the fine vacuum range, a pressure reduction to 1/10 results in a decrease of the evaporation temperature by about 40^o C.

An operating pressure far below 1 mbar reduces the evaporation temperature so far that decomposition of many biological or synthetic organic compounds can be avoided.

In our distillation plants, pressures down to 0.001 mbar and temperatures up to 400^o C can be achieved.

In a vacuum pot still unit, the pressure at the place of evaporation is remarkably higher than the suction pressure at the vacuum pump. This results from pressure drop in the piping and from the static height of the liquid in the vessel.

Short path distillation or wiped path evaporation eliminate this disadvantage.

The vacuum required for the process defines the plant design:

Wiped Film Distillation with Externally Located Condenser

In a wiped film evaporator, the plant evaporator and condenser are two separate components connected by nozzles for vapour transfer. The vacuum pump system is connected to the condenser. The ultimate pressure of this design is limited to some mbars by the pressure drop through the connection between evaporator and condenser. Even a larger suction capacity of the vacuum pump set will not lower the pressure in the evaporator. This limitation is caused by the conductance of the connecting pipe.


	Short Path Distillation with Internal Condenser

The short path evaporator with internal condenser combines evaporator and condenser in a single apparatus. This eliminates pressure losses caused by piping. Therefore, the distance between evaporation and condensation is extremely short. Actually there is no pressure drop between evaporator surface and internal condenser. This process is defined as "molecular distillation" when the distance between evaporator and condenser is less than the mean free path of the vapour molecules.

The roller wiper system used in our plants optimises the efficiency of the evaporators. The product film on the surface of the evaporator is mixed continuously. The wiper system avoids any concentration gradient inside the thin film. In fact there is also an increase of the evaporator surface by the surface of the rollers.

The most significant advantage of our roller wiper system is its self cleaning characteristic.


	Plant Design With Our Test And Pilot Plant


	Different configurations, evaporator sizes and process conditions have to be defined for the plant design. Theoretical calculations do not always give reliable results because physical and chemical properties are not always available for the different compounds. We verify the results of theoretical considerations by test runs in our own application laboratory.

Different parameters are verified in pilot plants and optimised to customer requirements for large scale production plant.

High purity of the final product, short residence time in the evaporator and high yield are the target of plant design, competing against each other.

The pilot tests in our pilot plant lead to an optimum concerning throughput, yield, plant size and purity of the final product.

Test Plant

single stage laboratory plant

constructed from glass

0.04 m² evaporator surface

can also be used as a Wiped Film Evaporator

minimum product quantity 1.0 - 3.0 kg

Pilot Plant

two stage pilot plant
stainless steel
0.1 m² and 0.2 m² evaporator surface
fully heatable design
can also be used as a wiped film evaporator
throughput approx 8 - 25 kg/h