Binary Distillation Process and Systems

Binary distillation is a widely used separation process in chemical engineering and the petrochemical industry. It's specifically designed for separating a mixture of two components or compounds based on their differing volatility or boiling points.

Distillation unit operation in which the constituents of a liquid mixture (solution) are separated using thermal energy. Basically, the difference in vapor pressure (volatilities) of different constituents at the same temperature is responsible for such a separation. 

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Binary Distillation Process Works


Feed Mixture

This is the initial mixture that contains two or more components with different boiling points.

Distillation Column

The column is the primary equipment used in binary distillation. It consists of multiple trays or packing material to facilitate the separation process.


The reboiler is located at the bottom of the column and is responsible for providing heat to the feed mixture.


The condenser is situated at the top of the column and is responsible for cooling the vaporized components back into liquid form.

Product Streams

Binary distillation yields two main product streams: the overhead product (top product or distillate) and the bottom product (bottoms or residue).

Process Steps

1. Heating the Feed

The feed mixture is first heated in a reboiler. As it heats up, the component with the lower boiling point vaporizes, forming vapor, while the component with the higher boiling point remains in liquid form.

2. Entering the Column

The vaporized components enter the distillation column at the bottom. The column is equipped with a series of trays or packing material that provides surface area for the vapor to rise through.

3. Fractionation

As the vapor rises through the column, it starts to condense on the trays or packing. The component with the lower boiling point (the more volatile component) tends to vaporize more readily and rises to the top of the column, while the component with the higher boiling point (the less volatile component) remains in liquid form and flows downward.

4. Overhead Product

At the top of the column, the vapor is condensed in a condenser, and the condensed liquid is collected as the overhead product (distillate). This product is enriched in the more volatile component.

5. Bottoms Product

The remaining liquid that doesn't vaporize in the column (bottoms or residue) is enriched in the less volatile component.

6. Continuous Operation

Binary distillation is typically operated continuously. The reboiler provides a continuous supply of heat, and the column continuously separates the feed mixture into its two components.

7. Adjusting Parameters

The efficiency of binary distillation can be controlled by adjusting parameters such as the reflux ratio (the ratio of condensed vapor returned to the column), the number of trays or packing material in the column, and the temperature of the reboiler.

Binary distillation is a fundamental separation process used in the production of various chemicals, fuels, and petrochemical products. It's essential for separating components with different boiling points, enabling the production of pure products or fractions.

Distillation Binary System 

This unit operation is also termed fractional distillation or fractionation.

With this technique, it is possible to separate the liquid mixture into its components in almost pure form and this fact has made distillation perhaps the most important of all mass transfer operations.

In distillation the phases involved are

Liquid and vapor or gas (the vapor phase is created by supplying heat to the liquid) and mass is transferred from both phases to one another, by vaporization from the liquid phase and by condensation from the vapor phase. The net effect is an increase in the composition of the more volatile component in the vapor (phase) and that of the less volatile component in the liquid. 

The basic requirement for the separation of components by distillation is that the composition of the vapor be different from the composition of the liquid with which it is in the equilibrium-the vapor is always richer in the more volatile component than the liquid from which it is formed. If the vapor composition is the same as the liquid composition, the distillation technique will not affect separation.

The methods of distillation

Distillation is commonly encountered in chemical and petroleum industries as a means of separating the liquid mixture into its component parts. Separation of ethanol and water mixture, production of absolute alcohol and from 95% ethanol using benzene, and separation of petroleum crude into gasoline, kerosene, fuel oils, etc. are typical examples of distillation.

Evaporation is concerned with the separation of a solution containing a non-volatile solute and volatile solvent, whereas distillation is concerned with the separation of a solution where all the components are appreciably volatile. Thus, the separation of solution where all the components are appreciably volatile. 

Thus, the separation of brine into salt and water is evaporation whereas the separation of a mixture of alcohol and water into its components is distillation.  

The methods of distillation of a binary systems

Basically, distillation is carried out in two ways:

The liquid mixture to be separated is heated to create a vapour. The vapour formed is condensed in a condenser and withdrawn as a product. As there is no reflex, products of relatively low purities are obtained.

The liquid mixture to be separated is heated to create a vapour, and the vapour formed is condensed in a condenser. A part of the condensed liquid is returned to the distillation still (as a reflex) and the remaining part is withdrawn as a product. In this method, the liquid and vapour are brought into intimate contact several times and an almost pure product can be achieved. 

The part of the vapor returned as a liquid to the distillation unit is called reflux and the operation is called rectification or fractionation. The term rectification is used in the alcohol industry whereas the term fractionation is popular in the petroleum industry.

Standard methods used in distillation practice are

Out of these three methods, distillation with rectification simply called rectification is the most important. The first two methods are carried out without reflux and the third one is carried out with reflex (which is nothing but returning a part of the condensed liquid back to the distillation system).

(i)   Differential or simple distillation

(ii)  Flash or equilibrium distillation

(iii)  Rectification or fractionation.

(iv) Steam Distillation process

 Take these Notes is, Orginal Sources: Unit Operations-II, KA Gavhane


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