How Is Crude Oil Separated By Fractional Distillation?
Crude oil is arguably the most valuable stuff found on our planet. It’s discovery revolutionized our society. But do you know the process that allows the creation of all unique petroleum products that we have been using every day for the past few decades?
The process is termed, ‘Fractional Distillation’
So, what exactly is this process used for? Well, naturally occurring oil found on Earth is the crude oil. As the name suggests, it’s a rather crude mixture. It has got the good stuff that we want from it, but in order to extract it, we need to use the process of fractional distillation.
Crude oil is made up of hydrocarbons, but in order for them to be useful, we need to group the relatively similar ones together. The hydrocarbon mixtures need to be separated. The common parameter is the molecular weights of each different fraction. Fractions such as kerosene, diesel, and gasoline. Fractional distillation makes it possible for different products to be extracted from crude oil.
This is the first step in the processing of crude oil, and it is considered to be the main separation process as it performs the initial rough separation of the different fuels. After the initial separation is made from the crude oil mixture, the extracted products can be further refined to remove contaminants and increase the purity of all the extracts.
The Process
As each of the mixtures has a different molecular weight, in the vapor form, they reach different heights in the distillation tower. It all begins with crude oil, a mixture with a high concentration of diverse hydrocarbons, being subjected to heat to vaporize it. This vaporized crude oil is then channeled into the base of a towering distillation column. As it ascends vertically, the temperature gradually decreases.
This temperature gradient is the keystone of fractional distillation. It acts as the catalyst for the separation of hydrocarbons. As the ascending vapor cools down, specific hydrocarbon compounds condense at different heights within the tower. Each height corresponds to a particular temperature range, and thus, a specific set of hydrocarbon molecules. This results in the formation of distinct “cuts” or fractions, each comprising hydrocarbons with a similar number of carbon atoms.
After this initial separation, individual fractions may undergo further refinement. This refinement can take various forms, aimed at eliminating contaminants or undesirable substances. Alternatively, it can be harnessed to enhance the quality of the fuel through a process known as cracking, which alters the molecular structure of the hydrocarbons for improved performance.
The lighter fuels such as propane and butane are too volatile to condense and these are at the top whereas at the bottom, waxes such as bitumen get accumulated. These residuals are heavy and too dense to rise up the tower.
Diverse Fractions
To truly appreciate the significance of fractional distillation, it’s essential to understand the diverse range of fractions that we get as the output of this process. These fractions are often classified into three broad categories: light, middle, and heavy.
Light Distillate
This category encompasses products with boiling points ranging from 70°C to 200°C. Notable constituents within this range include gasoline, naphtha (a crucial chemical feedstock), kerosene, jet fuel, and paraffin. These products are characterized by their high volatility, small molecular size, low boiling points, ease of flow, and quick ignition.
Medium Distillate
Moving up the temperature scale, we find the medium distillate range, with boiling points falling between 200°C and 350°C. Diesel fuel and gas oil, which plays a crucial role in town gas production and commercial heating, are the primary products in this category.
Heavy Distillate
At the higher end of the spectrum, we have the heavy distillate category. This group comprises products with boiling points exceeding 350°C. Fuel oil, a critical energy source, finds its origin here. These products boast large molecular structures, low volatility, poor flow characteristics, and are less prone to spontaneous ignition.
However, there are two exceptional components beyond these categories. At the very top of the distillation column, we encounter gases that are too volatile to condense. These include propane and butane. On the opposite end, accumulated at the bottom, are the “residuals”. This comprises heavy tars that are too dense to even rise up the column. Bitumen and other waxes fall into this category, necessitating further distillation processes, such as steam or vacuum distillation, to extract and purify them.
The Environmental Impact
Fractional distillation comes with an environmental price tag. The separation of crude oil into its fractions and subsequent utilization of these products have great implications for our environment. It is really essential that we care about how to effectively allocate and utilize these valuable resources. As we continue to harness the fractional distillation process, it becomes our duty to mitigate its environmental consequences as well. We need to understand that this is also a finite resource which takes tens of millions of years for the Earth to form naturally. Sustainable use of this resource is a requirement from this point onward. Also, the locked carbons reenter the Earth’s atmosphere when the compounds from this refinement process are used. This must be checked and carefully assessed globally in order for a better future for our civilization.
