Propane is a hydrocarbon gas, chemically known as C3H8, commonly used as a versatile energy source for heating, cooking, and powering vehicles. Its origins are often questioned, particularly whether it is derived from crude oil. This article clarifies the primary sources from which propane is obtained and details the processes involved in its separation and purification.
Propane’s Primary Sources
Propane is a co-product, meaning it is not the sole or primary goal of the extraction processes from which it originates. It is primarily derived from two major fossil fuel sources: the processing of natural gas and the refining of crude oil. When natural gas is extracted from the earth, it contains various hydrocarbons beyond just methane, including propane, which are collectively known as Natural Gas Liquids (NGLs).
A significant majority of propane production, particularly in the United States, comes from natural gas processing. Approximately 69% of the propane used in the U.S. is extracted from raw natural gas, while about 18% is obtained from crude petroleum. Propane is a byproduct of both processes.
The Separation Processes
The methods for obtaining propane from natural gas and crude oil involve distinct but related industrial procedures. Raw natural gas, often called wet gas, contains not only methane but also heavier hydrocarbons like ethane, propane, and butane. These NGLs are removed from the raw gas to prevent them from condensing within natural gas pipelines.
Natural gas processing plants cool and pressurize this raw, wet natural gas, causing heavier hydrocarbons, including propane, to condense into liquids and separate from methane. This mixture of condensed liquids then undergoes fractionation. Fractionation separates NGLs into individual components, such as propane, by leveraging their different boiling points. Propane has a boiling point of approximately -42 to -44 degrees Celsius (-43.6 to -44 degrees Fahrenheit), which allows for its isolation.
Crude oil, a complex blend of hydrocarbons, arrives at refineries where it undergoes various separation stages. One of the initial steps is atmospheric distillation, where crude oil is heated, and its components vaporize and then condense at different temperatures within a tall distillation column. Lighter hydrocarbons, including propane, rise higher in the column. Propane, along with other light gases, is then collected from the top sections of these columns as part of “refinery gas.”
Modern refineries also employ cracking processes to break down heavier, longer-chain crude oil molecules into lighter products like gasoline. These operations also produce smaller hydrocarbon molecules, including propane. The propane recovered from both distillation and cracking is subsequently purified to meet commercial specifications.