How Fractional Distillation Works

Fractional distillation is a purification process for crude oil that helps separate different components at various boiling temperatures. Crude oil predominantly consists of alicyclic, aromatic, and aliphatic hydrocarbons. But there are other organic substances in it, too, including carbon (84%), sulfur (up to 3%), nitrogen (1%), oxygen (1%), and mineral salts (0.1%).

All the elements found in crude oil have different densities, proportions, and boiling points. In order to separate them, the raw substance is treated to high temperatures so that once the liquid arrives at one element’s boiling point, it can be distilled. This process is known as fractional distillation. Here’s more on how fractional distillation works.

Heating the Liquid

First, crude oil is heated with a high-pressure steam to a high temperature of approximately 1112 degrees Fahrenheit or 600 degrees Celsius. Once the mixture arrives at its boiling point, the element with the lowest boiling point starts to vaporize first, followed by the next element, which has a higher boiling point.

Distillation

Once the element enters the vapor phase, the gaseous fumes enter the fractional distillation column—a long cylindrical column stuffed with trays with punctured holes that allow the vapor to pass. These impediments increase the contact area that the vapors have with a cold surface, enabling them to condense into liquid form. As the gases turn liquid, they drip from the other end into a separate container.

The column has a temperature gradient; it’s hot toward the bottom and cooler at the top. Since the vapors of each substance have different boiling points, fractions with the highest boiling point will condense at the lowest end of the column, whereas those with a low boiling point will travel farther before they condense. The trays placed under each collection point gather the distilled fractions safely as they drip throughout the process.

Benefits of Fractional Distillation

While there are different methods of separating mixtures, fractional distillation allows liquid substances with components with narrow differences in boiling points to separate. This is the foundation of the oil-refining process before the components are chemically processed and packaged. Even though large volumes of crude oil are distilled continually, only a fraction of that yields gasoline and other products in demand. Since a small percentage of the distilled components are ready for the market, it’s imperative that oilfield companies conduct distillation with great care.

 

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