Refining oil is simply the process of heating the oil in a distillation chamber to separate the many different types of hydrocarbons into their separate categories, or fractions. Remember, crude oil is raw oil pumped from the ground that is comprised of many different kinds of hydrocarbons. When these hydrocarbons are isolated based on their molecular makeup, they can then be refined into a number of products. These include gasoline, diesel, lubricating oils, kerosene, butane, methane, and many others. A barrel of oil (42 gallons is the standard measurement) will yield 44 gallons of petroleum products because when crude oil goes through conversion, it expands and increases in volume. About half of each barrel of crude is typically refined into gasoline due to the high public demand for transportation energy.
Although it has become more complex over the years the basic process of refining crude oil is fundamentally unchanged since the first petroleum refinery was built in Romania in 1856. Crude oil is pumped into a distillation chamber and superheated into a vapor that fills that chamber. Since the bottom of chamber is closest to the furnace, the vapor rises in the chamber and the hydrocarbon compounds separate based on their vaporization temperatures. When a given hydrocarbon compound reaches the point where the temperature of the column is equal to its boiling point, it will condense into a liquid state and be collected on plates or trays. This process is known as factional distillation.
As mentioned earlier, refining crude oil has gotten progressively more complex over the years based on the demand for a wide variety of products. In order to meet this public demand refineries use chemical processing to break longer hydrocarbon chains into shorter ones or to combine shorter chains into longer molecular structures, enabling refineries to change diesel into gasoline or alter gasoline to give it different octane ratings. Changing one fraction into another can be done by three methods. They are: cracking, unification, and alteration.