Propane (C₃H₈) is a colorless, odorless hydrocarbon and a member of the liquefied petroleum gas (LPG) family. It is stored as a liquid under moderate pressure for transport and use. Propane is a versatile fuel source for heating, cooking, and powering vehicles, particularly where natural gas pipelines are unavailable. Propane is not intentionally manufactured; it is a necessary byproduct recovered from two primary industrial processes that separate it from raw material sources.
The Primary Source: Natural Gas Processing
The majority of the world’s propane supply is recovered during the processing of raw natural gas. Natural gas from the wellhead is a mixture containing heavier hydrocarbons, known as Natural Gas Liquids (NGLs), rather than pure methane. Propane, ethane, butane, and pentanes must be removed from the methane stream before transmission. If these NGLs are not extracted, they would condense into liquids within the pipelines, causing operational problems.
Processors separate propane using methods like absorption and cryogenic recovery. The absorption method uses lean oil to absorb heavier NGL molecules from the methane stream. The most common modern approach is cryogenic expansion, which involves chilling the gas stream to extremely low temperatures, often around -120°F. This intense cooling causes propane and other NGLs to condense into a liquid state, separating them from the lighter methane.
Once separated, the mixed NGL stream is sent to a fractionation facility and distilled based on the boiling points of its components. Propane is isolated in a column called a depropanizer. This column uses heat to boil off lighter ethane and methane, leaving the propane and heavier molecules behind. This purification step ensures the product meets required specifications for consumer and industrial use.
Secondary Source: Crude Oil Refining
A secondary source of propane is the refining of crude oil. Refineries break down long-chain hydrocarbon molecules into lighter products like gasoline and diesel fuel. Propane is generated as a byproduct during the Fluid Catalytic Cracking (FCC) process, a key conversion step in the refinery.
In catalytic cracking, heavy gas oil is heated and brought into contact with a hot, powdered catalyst. This chemical reaction breaks the large molecules into smaller, more useful ones. The resulting products include a mix of gasoline components, diesel, and various hydrocarbon gases, including propane and butane.
The propane generated during cracking is separated from other gases in a specialized gas recovery unit, similar to fractionation in natural gas plants. This production method differs from natural gas processing because it chemically restructures large molecules rather than separating existing ones. Although the primary goal of the FCC unit is to maximize gasoline yield, the creation of propane is a valuable outcome.
The Proportion of Propane Sources
The relative contribution of these two sources is not evenly split, and the exact ratio fluctuates based on global market conditions. Historically, the vast majority of propane is derived from natural gas processing. In the United States, estimates suggest that 60 to 75 percent of domestically produced propane comes from NGL extraction.
This dominance is linked to the large-scale production of natural gas, especially the growth in shale gas extraction. As more raw natural gas is extracted globally, the volume of associated NGLs that must be removed increases, boosting the available supply of propane. The remaining percentage is supplied by crude oil refining. Propane volume from refineries is closely tied to the demand for refined products like gasoline, making it a less flexible source than gas processing.