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Vacuum distillation by wiped film evaporators and short path evaporators

Wiped film distillation and short path distillation (molecular distillation) are thermal separation processes for thermally sensitive products. For certain wiping systems (fixed clearance) a wiped film evaporator is also called thin film evaporator. Short residence time and low evaporation temperature will cause minimal thermal stress to the distilled product and consequently a very gentle distillation. Typical applications are high molecular weight organic compounds particularly from the fields of chemistry, pharmaceutical, agro and food industry.

Generally different distillation processes are applied for a partial separation of product mixtures. The most important requirement for all distillation processes is the boiling point difference of the two fractions that have to be separated.

With wiped film and short path distillation, a substantial decrease of boiling temperature is obtained by reducing the operating pressure. It is a continuous process with very short residence time.

By this also, the thermal separation of products is possible which would be damaged due to the long residence times and high temperatures that have to be applied in other continuous (circulation, falling film or column distillation) or non-continuous (batch distillation with/without column) conventional distillation processes.

In wiped film and short path evaporators, the crude material is heated up on the internal surface of a heated tube. A special rotating wiping system inside the evaporator is generating a very thin and turbulent film on the heated surface. Out of the heated and thin film, the evaporation of the light boiling component takes place. The generated vapors are condensed on a condenser.

The position of the condenser is the main difference between wiped film (external condenser) and short path evaporators (internal condenser).

Wiping Systems

In wiped film and short path evaporators, the wiping system is crucial. It has to generate a high turbulent film at a short residence time to enable a high evaporation rate with optimum separation efficiency.

The correct wiping system is selected based on VTA’s long-term experience and lab and pilot trials in the inhouse test center. VTA offers a wide range of different wiping systems suitable for all product mixtures and separation tasks.

Advantages of wiped film and short path distillation technology compared to other/traditional vacuum distillation processes:

Compared to batch, circulation and falling film distillation, it is possible with wiped film and short path distillation to separate product mixtures at low operating pressure, thus low temperatures at very short residence times continuously without any degradation. Furthermore, high viscosity products and high melting products can be processed without any problems more ...