what is reduced pressure distillation. How is it useful.
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Modern society is becoming ever more demanding in
the quality of the products it uses and for health and
environmental reasons a better removal of some components
is required. This better puriRcation of many
products sometimes requires operating at very low
pressure. Fortunately, the development of industrial
equipment to obtain better and lower vacuum has
been maintained. The cost of carrying out these
operations is of course more expensive than at
around atmospheric pressure. The increase in cost
is inversely proportional to the absolute operating
pressure.
Distillation at low pressure is used for special cases
with one or more of the following characteristics:
1. heat sensitive products;
2. liquid feeds or liquid residue with high viscosity;
3. liquids with fouling and/or foaming tendencies;
4. low operating pressure (medium and high vacuum);
5. low residence time.
The applications may be classiRed into four groups:
distillation or evaporation of sensitive organic
chemicals;
concentration of foods, chemicals, polymers and
biological compounds;
recovery of organic solvents;
desolventing, devolatilization and Rnishing of
polymer solutions.
Table 4 shows the levels of vacuum used and also
lists representative equipment. Some advantages of
vacuum and molecular distillation are:
low residence time;
high selectivity due to the higher values for relative
volatility;
cheaper heating requirements.
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