DISTILLATION POINTS

(by RAJENDRA, M. Tech Chemical Plant Design)

Distillation columns carry out physical separation of liquid chemical components from a

mixture by

a. A combination of transfer of heat energy (to vaporize lighter components)

b. Mass transfer between the liquid and vapor phases.

Simple Rules of Vapor Liquid Equilibrium

a. Vapor pressure of liquid depends on temperature.

b. Heat input raises vapor pressure of liquid.

c. A liquid boils when its vapor pressure equals the system pressure.

d. Higher the vapor pressure lowers the boiling point.

e. Volatile liquids have high vapor pressure.

f. The vapor pressure and hence the boiling point of a liquid mixture depends on the

relative amounts of the components in the mixture.

Distillation is the most common separation technique. Distillation is energy intensive

process. It has large heating and cooling load. It can contribute to 30-60% of plant

operating costs

Fractionation is a unit that has both a reboiler to supply heat at the bottom and a

condenser to take heat out from the top. This is normally called distillation.

b. Absorption is a unit that has no method at the top of the tower to take heat out. An

external liquid is supplied from outside the system to absorb material from the

vapor.

c. Stripping is a unit that has an external stream (gas or steam) supplied from

outside the system to strip light material from the liquid. It may have a reboiler at

the bottom of the tower to put heat in.

More about distillation