How Liquefied Petroleum Gas Works

What is LP Gas?

There are two LP gases that can be stored in liquid form with only moderate pressurization -- propane and butane. Isobutane, which has the same simple chemical formula as butane but has a different chemical structure, is also used. Usually, butane and isobutane are mixed with propane in various proportions, depending on the intended use of the fuel.

Propane is particularly useful as a portable fuel because its boiling point is

-44 F (-42 C). That means that even at very low temperatures, it will vaporize as soon as it is released from its pressurized container. This results in a clean-burning fuel that doesn't require a lot of equipment to vaporize it and mix it with air. A simple nozzle will suffice.

Butane's boiling point is approximately 31 F (-0.6 C), which means it will not vaporize in very cold temperatures. This is why butane has more limited uses and is mixed with propane instead of being used by itself.

A single pound of propane can generate 21,548 BTU (British Thermal Units) of energy, while butane can produce 21,221 BTU per pound [ref]. For comparison, here is how LP Gases stack up to other fuels in terms of energy:

Propane: 21,500 BTU per pound
Butane: 21,200 BTU per pound
Gasoline: 17,500 BTU per pound
Coal: 10,000 BTU per pound
Wood: 7,000 BTU per pound

In the next section, we'll find out where LP gas comes from.

Ethane and Methane?

The term "liquefied petroleum gas" sometimes refers to any combustible gas that exists in gas form at normal temperatures and pressures -- that is, gases with a boiling point relatively close to the average temperature of Earth's atmosphere. Under this definition, both ethane and methane are LP gases. However, according to the LP Gas Man's Encyclopedia of Methods and Equipment, "the pressures required to liquefy [ethane and methane] and the amount of metal necessary to hold them under these pressures makes their handling in commercial quantities impractical."