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Basic Principle and Methodology of Simple Distillation

Using distillation, mixtures can be separated based on differences in their vapor pressure at a boiling temperature.

Distillation

Using distillation, mixtures can be separated based on differences in their vapor pressure at a boiling temperature. As with all unit operations, the distillation process is not a chemical reaction. Crude oil undergoes this process to be converted into various fractions, including fuel for transportation, electricity, and heating. The process of distilling water removes impurities like salt from seawater. Among the components of air which are distilled for industrial use are oxygen, nitrogen, and argon. Historically, distilled beverages with higher alcohol content have been made by distilling fermented solutions. Distilleries are facilities for distilling alcohol, especially for the production of spirits.

Simple Distillation

Principle

Laboratory facilities, especially organic chemistry laboratories, often distill water and various organic solvents as well as perform quantitative analyses using distillation. Boiling liquids and condensing steam are both processes involved in distillation. When the vapor pressure of a liquid equals or slightly exceeds the atmospheric pressure, bubbles are generated from the liquid. In the distillation process, one of the substances with the lowest boiling points boils first, steam escapes from the surface, and the distilled liquid (known as a distillate) is collected with a condenser connected before the distillation process.


In general, the greater the difference between the boiling points of the component molecules in a solution, the better the separation effect will be; conversely, if the difference between boiling points is very small, this method cannot be used. When it comes to alcohol and water, the boiling points of the two are not the same, there exists the azeotrope phenomenon, and simple distillation cannot separate them completely. For this experiment, sodium chloride is mixed with a dye in aqueous solution. A simple distillation method can be used to produce pure distilled water since salt and dye would not evaporate at boiling water.

Methodology

Simple distillation is accomplished using a distillation flask attached to a side arm that slopes downward, as shown in Figure. There is a cork closure on the flask mouth with a thermometer incorporated. Inlet and outlet are on the lower and upper sides of the condenser respectively for cold water circulation. Water exits the outlet and from the cold-water pipe attached to the inlet and is discharged to the waste. A liquid product is delivered from the condenser outlet and collected in a collector or receiver.

Calibration of thermometer - The thermometer can be calibrated with an ice bath of distilled water. Wait until the thermometer reaches equilibrium before using it. Removing it from the ice water and placing it in boiling distilled water again until it reaches thermal equilibrium. Temperature measurements which differ from the expected value by more than two degrees should be used for distillation.

Distillation flask filling - The distillation flask should only be filled up to a third of the volume to allow for sufficient space above the liquid surface when boiling starts so that it will not be sucked into the condenser. As far as purity of the distillate is concerned, this is crucial. The porcelain chips should be placed in the distillation flask to prevent the liquid from overheating and to cause more controlled boiling, thereby preventing liquid contact with the condenser.

Heating the distillation flask - It is heated by slowly bringing the distillation flask to a boil. In the distillation flask, vapours rise up from the neck, pass through the condenser and condense to drip into a receiver, Fig. On average, distillation occurs at a rate of 20 drops per minute. To get a liquid after distillation, the vapours must condense in the condenser slowly enough that they all condense into liquid. If organic vapours do not condense as they pass through the condenser, they could ignite when they come into contact with the heat source.

Vapour condensation - The temperature changes steadily as the distillate drops from the condenser. A new receiver is then used to collect all the drops that form within a temperature range of two to three degrees. After the distillate reaches a certain temperature, it is collected in a third receiver. In order to collect the distillate in discrete fractions, the previous step is repeated each time the temperature stabilizes or changes. The distillate from the desired compound should be saved in all fractions after distillation to ensure that the compound has been removed effectively.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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