Distillation Experiment

Topics: Distillation, Water, Ethanol Pages: 6 (1626 words) Published: March 28, 2013
The aim is to observe distillation process of ethanol-water solution and to measure the alcohol content after process in this experiment. 500 ml of solution with an alcohol content of 32% (v/v) is used for this experiment. Temperature values are recorded for every 10 ml alcohol obtained in the flask. The process is repeated in our experiment and for the first process, the data collection process continues until the distillate reaches to 200 ml. The concentration of alcohol is measured for first process by hydrometer. For the second process, approximately 200 ml of distillate containing 70% alcohol is used and data collection continues until the distillate reaches 150 ml. Finally, the concentration of alcohol is also measured after 2nd process as 82%.

The objective of this experiment is to distillate the alcohol-water solution into ethanol and water. Distillation is a process of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction. The basic requirement of distillation is that the components of the liquid solution must have different boiling points. There are some types of distillation methods which are flash distillation, simple batch distillation, simple steam distillation, continuous distillation, vacuum distillation, etc. :

Flash distillation
It is a single stage process which liquid mixture is vaporized. The vapor and the liquid are come to equilibrium, and these phases are separated.

Simple steam distillation
This is a separation process at lower temperatures. This process is often used to separate a high boiling component from small amounts of nonvolatile impurities.

Continuous distillation
This is a process in which a liquid mixture is continuously fed into the process and separated fractions are removed continuously.

Vacuum distillation
It is used for some compounds having very high boiling points. Instead of the increasing the temperature too much, lowering the pressure is preferred in this distillation type.

In this experiment we used simple batch distillation in order to distillate alcohol-water mixture.

Simple batch distillation
This is a separation process which the liquid charge is boiled slowly and the vapors are withdrawn as quickly as vapors form to condenser, where the distillate, condensed vapor, is collected. The first portion of vapor condensed will be the richest in the more volatile component.

Vapor-liquid equilibria take an important role in distillation process.

Vapor-Liquid-Equilibria (VLE)

Constant pressure VLE data is obtained from boiling point diagrams. VLE data of binary mixtures is often presented as a plot, as shown in the figure below.

The curved line is called the equilibrium line and describes the compositions of the liquid and vapour in equilibrium at some fixed pressure.

Distillation experiment is applied to two miscible liquids which are ethanol-water, soluble in each other in all ratios. Mixtures of ethanol and water form an azeotrope.

Azeotropic mixture:
Azeotropic mixture is a solution that forms a vapor with the same concentration as the solution, distilling without a change in concentration. The composition of the liquid phase at the boiling point is identical to that of the vapor in equilibrium with it, and azeotropes form constant-boiling solutions. The exact composition of the azeotrope changes if the boiling point is altered by a change in the external pressure.

Ethyl alcohol and water form an azeotrope of 95.6% at 78.1 °C. Azeotropic systems give rise to VLE plots where the equilibrium curves crosses the diagonals.

-Distillation apparatus
-Graduated cylinder
-500 ml of 30% (v/v) water-ethanol mixture

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