DISTILLATION                                               [home]   [topic page]

SOLVENT DISTILLATION

First the plants are crushed and placed in a solution of solvent. This is done in an extractor.

Solvents used vary depending on the type of extraction which in turn depends on the polarity requirements of molecules. They are extremely pure to minimise contamination.

Common solvents include

• alcohols eg ethanol
• alkanes eg hexane
• ketones eg acetone

When they have dissolved, the solution is then distilled as above by heating gently. Temperature and pressure within the still are carefully regulated as the molecules of the essences are very delicate - they are easily changed by heat to new contaminant molecules.

The distillation tower ( the "reflux column" ), as above in the animation, is packed with stainless steel to provide a large surface area. This assists with the separation of the phases if the boiling point of the solvent is too close to that of the more volatile components of the oil.

The solvent is selected has a lower boiling point than the oil so this is distilled out leaving the concentrated oils in the still. The solvent is then recycled.

When you examine the molecules of the various plants' oils, they are covalent molecular in bonding, so they form single molecules. This gives them lowish boiling points but still often above 100⁰C as would be expected of such compounds.

A complication is that the concentration of the solution rises with time as liquid leaves it, and so does the boiling point. As the temperature cannot be allowed to rise further, changes to the molecules could occur, the pressure in the tower is lowered so reducing the boiling point once more. ( The same effect arises when trying to cook at high altitudes - due to the lower air pressure, the temperature required to reach boiling point becomes much lower - so low that the temperature may not be adequate to cook the boiled food. )