LPG stands for “Liquefied Petroleum Gas”. The term is widely used to describe two prominent members of a family of light hydrocarbons called “Natural Gas Liquids” (NGLs): propane (C3H8) and butane (C4H10). LPG is a derivative of two large energy industries: the processing of natural gas liquids and the refining of crude oil. LPG is used as fuel in heating appliances, cooking equipment, and vehicles.
The term “liquefied gas” may seem a contradiction in terms since all things in nature are either a liquid or a solid or a gas. At normal temperature and pressure, LPG is gaseous. It changes to a liquid when subjected to modest pressure or cooling. In liquid form the tank pressure is about twice the pressure in a normal truck tyre.
LPG is prepared by refining petroleum or "wet" natural gas, and is almost entirely derived from fossil fuel sources, being manufactured during the refining of petroleum (crude oil), or extracted from petroleum or natural gas streams as they emerge from the ground. It was first produced in 1910 by Dr Walter Snelling and the first commercial products appeared in 1912. It currently provides about 3% of all energy consumed, and burns relatively cleanly with no soot and very few sulphur emissions. LPG has a typical specific calorific value of 46.1 MJ/kg compared with 42.5 MJ/kg for fuel oil and 43.5 MJ/kg for premium grade petrol (gasoline). However, its energy density per volume unit of 26 MJ/L is lower than either that of petrol or fuel oil, as its relative density is lower (about 0.5–0.58 kg/L, compared to 0.71–0.77 kg/L for gasoline). Global LPG production reached over 292 million metric tons/yr in 2015, while global LPG consumption to over 284 mn t/yr. 62% of LPG is extracted from natural gas while the rest is produced by the petrochemical refineries from crude oil. 44% of global consumption is in the domestic sector. The USA is the leading producer and exporter of LPG.