Did you know that fractional distillation is commonly practiced by oil refineries using crude oil for the production of gasoline fuel? In this lesson, learn more about this fascinating process.
What Is Fractional Distillation?
If you have the pleasure of stepping into a chemistry laboratory, there is chance you may encounter the lab apparatus in the following diagram resting on a lab bench.
This laboratory set-up is designed to facilitate a process known as fractional distillation. Now you may be wondering what is going on in this diagram, but before diving into this chemical process, let’s discuss more about what fractional distillation actually is.
Fractional distillation is the process of taking a chemical mixture and using heat to separate out the various components in that mixture.
When you think of this process, the first word that should come to mind is separation. In other words, as a chemist in the laboratory, you would use this process when you are interested in isolating one or more compounds present in a mixed sample containing as few as two and up to an endless amount of compounds.Because heat is used in this separation technique, boiling points play a very important role in fractional distillation.
Essentially, you are able to determine what given component is separated out from the mixture by its boiling point. Remember that boiling point is a physical property. Specifically, it is the temperature where a phase change occurs from liquid to vapor.
Before we go over the process of fractional distillation, let’s look at some examples where this process is commonly used.
Were you aware that certain bottles of water, labeled distilled water, are produced from fractional distillation? Even better, did you know the gasoline we use to fuel up our vehicles is also produced from fractional distillation? When you get water from a natural source, such as underground water or rain water, it contains numerous minerals and impurities. Thus, prior to making its way to store shelves, this type of water is fractionally distilled to remove those impurities and minerals. The end result is the production of distilled water. The same concept applies to the production of gasoline from crude oil.If you step foot into an oil refinery, you will see multiple pieces of equipment all collectively working to make a variety of products from crude oil.
Crude oil is a mixture of numerous organic molecules. By using the concept of boiling point, during the fractional distillation process, oil refinery workers can ensure the compounds of interest are correctly separated from a crude oil mixture.Once separated, compounds are purified and further refined before making desired products, such as gasoline, jet fuel, lubricating oil, or even tar for our asphalt pavements.
Whether it is the production of distilled water or gasoline, fractional distillation is widely used throughout industry.Now that we understand what fractional distillation is and can identify places where it is commonly used, let’s go over the process step by step.
By the time we finish this section, you will walk away being a pro at running a fractional distillation experiment. There are five basic steps involved in this process. Follow the diagram here as a guide. Fractional distillation of a mixed solution containing water, pentane, and hexane will be used as an example.
For simplicity purposes, we will refer to this mixture as an alkane solution.
Step 1: After setting up your laboratory apparatus, heat your mixture so that it can begin boiling (2a on the diagram). In the case of our example, we would start by heating our alkane solution.
Keep in mind, your solution must contain at least two substances so that you have something to separate.Step 2: Once you see a boil, some of the components will begin to vaporize (2b on the diagram). Using our example, the boiling point of water is 100 degrees Celsius. Hexane has a boiling point of 68 degrees Celsius, while pentane has a boiling point of 36.
1 degrees Celsius. Thus, at this step, pentane will vaporize first followed by hexane and water.Step 3: Following vaporization, each component will enter the fractionating column, seen as 2c on the diagram. Again, using our example, pentane would enter first (because of its lower boiling point) followed by hexane and water.Step 4: Once in the column, the vapor will rise and eventually cool down settling into the second column (2d on the diagram).
Step 5: By cooling down in the second column, condensation can take place leading to the collection of the separated liquid into a container (2d and 2e on the diagram). Condensation is the result of a phase change from a vapor to a liquid. Thus, by cooling the vapor, it can condense to a liquid finally dripping into a container at the end of the second column. Because you know the different boiling points of your alkane solution, the first liquid you collect would be pentane followed by hexane and water.
Fractional distillation is a process by which individual components can be separated using heat from a given mixture. The boiling points of each component in the mixture determine the order of separation. Common uses of fractional distillation include the production of distilled water, and gasoline from crude oil. Five basic steps can be used to complete the process of fractional distillation.
Fractional Distillation Key Terms & Steps
- Fractional Distillation: separating components using heat from a mixture
- Boiling Points: that temperature at which the phase change from liquid to vapor takes place
- Crude Oil: a mixture that when fractional distillation is used can be separated toward making gasoline, jet fuel or lubricating oil
- 5 Steps of Fractional Distillation: 1- heat mixture to begin boiling; 2 – vapor appears as mixture comes to boil; 3 – after vaporization, components begin to separate; 4 – as it rises, vapor eventually cools; 5 – cool down causes condensation, and liquid is separately collected
After this lesson ends, pupils should be able to:
- Illustrate fractional distillation
- Describe the five basic steps in the distillation process
- Explain an example like crude oil and fractional distillation