Propane is a naturally occurring gas composed of three carbon atoms and eight hydrogen atoms.
It is created with a variety of other hydrocarbons (such as crude oil, butane, and gasoline)
by the decomposition and reaction of organic matter over long periods of time.
After it is released from oil fields deep within Earth, propane is separated from other
petrochemicals and refined for commercial use. Propane belongs to a liquefied petroleum
gases (LPGs), their ability to be converted to liquid under relatively low pressures.
Propane has natural origins, it is not "made" of other raw materials; it is "found" in petroleum
chemical mixtures deep within the earth. These petroleum mixtures are literally rock oil,
combinations of various hydrocarbon-rich fluids which accumulate in subterranean reservoirs
made of porous layers of sandstone and carbonate rock.
Petroleum is derived from various living organisms buried with sediments of early geological
eras. The organisms were trapped between rock layers without oxygen and could not break down,
or oxidize, completely.
Propane manufacture involves separation and collection of the gas from its petroleum sources. Propane
and other LPGs are isolated from petrochemical mixtures in one of two ways—by separation from the natural
gas phase of petroleum and by refinement of crude oil.
Both processes begin when underground oil fields are tapped by drilling oil wells. The gas/oil
hydrocarbon mixture is piped out of the well and into a gas trap, which separates the stream into crude
oil and "wet" gas, which contains natural gasoline, liquefied petroleum gases, and natural gas.
Crude oil is heavier and sinks to the bottom of the trap; it is then pumped into an oil
storage tank for later refinement.
The "wet" gas comes off the top of the trap and is piped to a gasoline absorption plant,
where it is cooled and pumped through an absorption oil to remove the natural gasoline and
liquefied petroleum gases. The remaining dry gas, about 90% methane, comes off the top of
the trap and is piped to towns and cities for distribution by gas utility companies.
The absorbing oil, saturated with hydrocarbons, is piped to a still where the hydrocarbons
are boiled off. This petroleum mixture is known as "wild gasoline." The clean absorbing oil
is then returned to the absorber, where it repeats the process.
The "wild gasoline" is pumped to stabilizer towers, where the natural liquid gasoline is
removed from the bottom and a mixture of liquefied petroleum gases is drawn off the top.
This mixture of LP gases, which is about 10% of total gas mixture, can be used as a mixture or further
separated into its three parts—butane, isobutane, and propane (about 5% of the total gas mixture).
Propane must be carefully isolated from a complex mixture of petrochemicals which includes methane,
ethane, ethene, propene, isobutane, isobutene, butadiene, pentane, and pentene, to name a few.
If such impurities are not removed, the propane or propane and butane mixture will not liquefy
properly. Liquefaction at appropriate temperature and pressure is critical for the gas
to be economically useful. The liquefied gas industry has established standardized specifications
that LPG mixtures must conform to in order to be considered acceptable for use as fuel gas.
The manufacture of propane produces a variety of byproducts that are economically useful. It is
more accurate to think of these not as byproducts but as co-products, since they are produced
along with propane as part of petroleum refinement.
These co-products may be in the form of solids, gases, or liquids. Solids (or semisolids) include
bitumes, hydrogen sulfide, and carbon dioxide and are sold for fuel purposes. The liquid fractions
include crude oil, which is further refined to give a variety of products. These oils vary dramatically
in appearance and physical properties like boiling point, density, odor, and viscosity. The different
fractions of crude oil are referred to as "light" or "heavy" depending on their density. Light crude
is rich in low-boiling and paraffinic hydrocarbons; heavy crudes are higher-boiling and more viscous.
Many of the co-products of propane production, such as propylene and butylene, are useful
in gasoline refining, synthetic rubber manufacture, and the production of petrochemicals.
Wishing you all the best,