what are the principles on which distillation is based?

Answer 1

That a pure component absorbs heat at a constant temperature as it changes state.

say you have water ( boiling point 100 oC) and alcohol (boiling point 80oC (I made that number up by the way!)) together in a solution.

The two pure components canbe separated by the addition of heat.

Add heat to the solution and it will rise to 80 oC and will stabilise there while the alcohol changes state (turns to a gas and bubbles out of the water phase).

By controlling the amount of heat added you can ensure that you boil off the alcolhol leaving only water behind.

You can also separate gas mixtures using the reverse practice. Gradually cooling a mixture of gases will condense out pure gases at different temperatures.

The principle of distillation is the difference in volatilities of the components.

Preferential solubility is also a principle involved in multi component systems (more than two components) where you can drive the least soluble component out of solutuion by changing the physical properties of the solution, typically you can absorb one fraction onto an absorption bed leaving the other component(s) in the solution.

Answer 2

Distillation is based on the fact that most liquids have different partial pressures (vapor pressures) at a given temperature. Because of this they also have different boiling points and can be separated by this method. At a particular temperature the number molecules of liquid A in the gaseous phase may be much higher than the number of molecules of liquid B, thereby separating A from B.