Key Difference – Atmospheric Distillation vs Vacuum Distillation
The key difference between atmospheric distillation and vacuum distillation is that the atmospheric distillation is used to separate low boiling fraction of a mixture whereas vacuum distillation allows the components to be separated easily by lowering the boiling point of a high boiling fraction.
Distillation is the action of purifying a liquid by a process of heating and cooling. There are different forms of distillation methods that are used for different applications; simple distillation, fractional distillation, atmospheric distillation, vacuum distillation, steam distillation, etc.
CONTENTS
1. Overview and Key Difference
2. What is Atmospheric Distillation
3. What is Vacuum Distillation
4. Side by Side Comparison – Atmospheric Distillation vs Vacuum Distillation in Tabular Form
5. Summary
What is Atmospheric Distillation?
Atmospheric distillation is a technique used to separate components in crude oil that is performed under atmospheric pressure. This technique is used to separate components having a low boiling point (low boiling fractions).
In this process, pre-heated crude oil (heated to about 250-260°C) is further heated to a temperature around 350°C. This heated crude oil is then passed into a distillation column in which the pressure at the top is maintained around 1.2-1.5 atm (nearly the atmospheric pressure).
Figure 01: A Simple Apparatus for Atmospheric Distillation
The feed of the atmospheric distillation is desalted and pre-heated crude oil. The components separated by this distillation method are small hydrocarbons such as fuel gases, naphtha, kerosene, diesel, and fuel oil. The residue left at the bottom of the atmospheric distillation column is known as the heavy hydrocarbon fraction. This fraction is sent to the vacuum distillation.
What is Vacuum Distillation?
Vacuum distillation is a technique used to separate components in a mixture at a reduced pressure. This process is used when the components in the mixture have boiling points which are difficult to be achieved or if higher temperature cause the compounds to be decomposed instead of vaporizing. A reduced pressure causes the components to have a low boiling point than usual.
In the industrial scale distillation processes, there are many stages of distillation involved in order the separate key components in a mixture. In situations like this, vacuum distillation is a better option. This technique increases the relative volatility of the components in a mixture (the relative volatility is the difference between boiling points of two components). When the relative volatility is high, a better separation of components can be observed.
Figure 02: A Laboratory Apparatus for Vacuum Distillation
Apart from that, a major advantage of the vacuum distillation over other methods is that this process requires low temperatures because the boiling points are lowered due to the reduced pressure condition. Another importance is, this method avoids the degradation of key components at high temperatures. And also, the yield and purity are higher in this distillation method.
What is the Difference Between Atmospheric Distillation and Vacuum Distillation?
Atmospheric Distillation vs Vacuum Distillation |
|
| Atmospheric distillation is a technique used to separate components in crude oil that is performed under atmospheric pressure. | Vacuum distillation is a technique used to separate components in a mixture at a reduced pressure. |
| Pressure | |
| Atmospheric distillation uses pressure nearly similar to the atmospheric pressure (around 1.2-1.5 atm). | Vacuum distillation uses very lower pressure conditions. |
| Theory | |
| Atmospheric distillation is used to separate low boiling fraction of the mixture. | Vacuum distillation allows the components to be separated easily by lowering the boiling point of a high boiling fraction. |
| Fractionation | |
| Atmospheric distillation separates the light fraction of the mixture. | Vacuum distillation separates the heavy fraction of the mixture. |
| Degradation of the Key Components | |
| The atmospheric distillation does not concern about the degradation of the component. | The vacuum distillation allows the components to be separated without thermal decomposition (because some components degrade at high-temperature conditions). |
Summary – Atmospheric Distillation vs Vacuum Distillation
Distillation is the process of repeated heating and cooling in order to fractionate a mixture of different components. Atmospheric distillation and vacuum distillation are two forms of distillation. The difference between atmospheric distillation and vacuum distillation is that the atmospheric distillation is used to separate low boiling fraction of mixture whereas vacuum distillation allows the components to be separated easily by lowering the boiling point of a high boiling fraction.
Reference:
1. “Atmospheric Distillation of Crude Oil.” Wikipedia, Wikimedia Foundation, 18 Dec. 2017. Available here
2. “Atmospheric Distillation Unit.” EnggCyclopedia, 13 Sept. 2017. Available here
3. “Vacuum Distillation.” Wikipedia, Wikimedia Foundation, 6 Apr. 2018. Available here
Image Courtesy:
1.’Atmosphericdistillation’ (Public Domain) via Commons Wikimedia
2.’Vacuum distillation of DMSO at 70C’By Rifleman 82 at English Wikipedia (Public Domain) via Commons Wikimedia