LPG – Liquefied Petroleum Gas is primarily comprised of propane, butane, and isobutane in a range of mixtures. It is produced as a co-product of crude oil refining and natural gas processing. The constituents of LPG are gaseous at 20°C and 1 atmosphere pressure (NTP).
LPG suppliers typically add propane to the percentage of propane and butane in LPG. Propane has a lower boiling point, at -42° vs -0.4°C for butane. So, propane will continue to vaporise in colder climates. Compared in gaseous volume, butane does have a higher energy content at 111.4MJ/m³ vs propane at 93.2MJ/m³. Natural gas is only 38.7MJ/m³.
Most countries have either 100% propane (Australia & USA), an LPG gas mixture of 60:40 propane:butane (NZ & Belgium) or percentage of propane and butane in LPG around 35:65 propane:butane LPG gas mixture (India, Spain & Hungary).
LPG as Propane
Propane is a flammable hydrocarbon gas liquefied through pressurisation. There are 3 carbon and 8 hydrogen atoms in a propane molecule. The chemical formula of LPG gas – chemical formula for propane is C3H8.
Propane is not made or manufactured, it is found naturally in combination with other hydrocarbons. Propane is produced during natural gas processing and petroleum refining. Propane processing involves the separation and collection of the gas from its petroleum base and other Natural Gas Liquids (NGLs).
Following its refinement, LPG is stored and distributed as a liquid under pressure until used, at which point it is utilised as either a liquid or a gas (vapour). LPG is supplied in LPG gas cylinders that are either exchanged or refilled on site by LPG tankers.
Large users may utilise bigger LPG storage tanks. Propane is the gas that is supplied to virtually all homes and most businesses that purchase LPG in Australia.
It is commonly used for heating and cooking. Propane is frequently used in Autogas, alone or in a propane-butane mix.
LPG as Butane
Butane (n-butane) is also considered to be LPG. Butane is a flammable hydrocarbon gas that is liquefied through pressurisation. The chemical formula of LPG gas as butane is C4H10, with 4 carbon and 10 hydrogen atoms in a butane molecule. (Butane molecule model shown) Butane comes from natural gas processing and oil refining. Propane processing involves the separation and collection of the gas from its petroleum base and other Natural Gas Liquids (NGLs).
Following its refinement, LPG is stored and distributed as a liquid under pressure until used, at which point it is utilised as either a liquid or a gas (vapour). It is used for heating and cooking, as well as auto fuel. Butane is frequently used in Autogas in a propane-butane mix. Butane is also used as a propellant and refrigerant, as well as a petrochemical feedstock. Butane is supplied to businesses that require Butane, as opposed to propane. Butane has some specific applications where it has advantages over propane.
LPG as Isobutane
Isobutane (i-butane) is an isomer of butane, with the same chemical formula as butane but different physical properties. Isobutane is converted from butane in a process called isomerization. So, it has the same chemical formula of LPG gas as butane — C4H10 — but has a different arrangement of its atoms, as you can see in the 3-D model images. (Isobutane molecule model shown)
As with normal butane, isobutane is a flammable hydrocarbon gas that is liquefied through pressurisation. It also has different physical properties from normal butane (n-butane). In addition to being used as a fuel, isobutane is commonly used as a refrigerant and a propellant. Isobutane has very low global warming potential and insignificant ozone depletion potential. However, its main use is in refineries to increase octane of gasoline and make it cleaner burning.