Chemical Engineers' Portable Handbook
Emphasizing practice-oriented design and approaches, this guide offers a presentation of the salient and important aspects of chemical engineering for practicing professionals.
TABLE OF CONTENTS Chemical Engineers' Portable Handbook
Extractive and Azeotropic Distillation
In certain systems relative volatilities are close to unity. As such they represent cases that are extremely difficult to separate. When this occurs either extractive or azeotropic distillation can be used.
The former involves adding a third component that imbalances the relative volatilities and allows separation to take place. Table 5-5 lists some extractive agents with respective binary pairs.
| Binary System | Extractive Agent |
|---|---|
| Hydrochloric acid-water | Sulfuric acid |
| Nitric acid-water | Sulfuric acid |
| Ethanol-water | Glycerin |
| Butane-butene | Acetone or furfural |
| Butadiene-butene | Acetone or furfural |
| Isoprene-pentene | Acetone |
| Toluene-paraffinic hydrocarbons | Phenol |
| Acetone-methanol | Water |
A typical flow sheet for toluene-methylcyclohexane (phenol is the extractive agent) is given in Figure 5-19.
Figure 5-19: Extractive distillation (41).
The other type of distillation (azeotropic) involves the creation of an azeotrope that allows the separation to take place. Frequently solvent extraction has to be employed in addition to distillation. Figure 5-20 gives a typical flow sheet.
Figure 5-20: Schematic diagram for separation of A and B with a solvent that forms minimum boiling azeotrope with A. The solvent is miscible with both A and water while A is immiscible with water (41).
More detailed discussions of both extractive and azeotropic distillation can be found in references 39 42.
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