Methods of distillation

Methods of distillation

Distillation is the process of separating, concentrating and purifying liquid by boiling it and then condensing the vapor produced.

The following include the methods of distillation:

  • Differential distillation: In this method of distillation, the vapor produced or formed when a still initially full is heated at constant rate, on boiling; the liquid is removed from the system. The liquid which is removed from the bottom of the distillation column at the end of the process is the liquid which did not vaporize.
  • Flash or equilibrium distillation: this is frequently carried out in a continuous process. It consists of vaporizing a definite fraction of the liquid feed in such a way that the vapor evolved reaches an equilibrium state with the residual liquid. The feed is usually pumped in through a heater and it enters the ‘still’ through a valve where the pressure is reduced. The still is an essential separation by which the produced liquid and vapor in a reduced pressure have sufficient time to reach equilibrium state. The liquid leaves from the bottom while the vapor is removed from the top of the separator and it is then condensed.

Flash distillation is used extensively in petroleum refining, in which petroleum fraction are heated in pipe stills and the heated fluid is flashed into vapor and residual liquid stream, each containing many compositions. Flash distillation is used for separating components that boil at wide range of temperature. it is not suitable or effective In separating components of comparable volatilities which, requires distillation with reflux. For large scale production, continuous distillation is more preferable than batch distillation.

  • Rectification: From the above two methods described, the vapor leaving the still at any time is in equilibrium with the liquid remaining, there will be an increase in concentration of more volatile components.

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