LPG Gas Mixture of Propane & Butane: Which Gas is Present in LPG

LPG - Liquefied Petroleum Gas - is a mixture of flammable hydrocarbon gases used as fuel for cooking, heating, hot water and autogas.  LPG gas mixture is typically propane (C₃H₈) and butane (C₄H₁₀).

Both LPG gases are frequently sold without mixture, as pure propane and pure butane.

LPG gases can all be compressed into liquid at relatively low pressures and stored in pressure vessels.

There are a number of gases that fall under the “LPG” category - Liquefied Petroleum Gas...

LPG Gas Mixture – Gases Present in LPG – Constituent Gases

The most common LPG gases include propane, butane (n-butane) and isobutane (i-butane), as well as LPG gas mixtures of these gases.

Other gases that also fall under the “LPG” label, including ethane, ethylene, propylene, butylene and isobutylene, as well as mixtures of these gases.

LPG Gas Mixture: Percentage of Propane and Butane in LPG

LPG gas mixture varies by country and sometimes by where you are within a country. The LPG gas mixture can also vary by season, with higher percentages of propane in the winter months.

The actual percentage of the propane and butane in LPG may depend on both location and season.

For example, in the US and Australia, LPG is just propane.

The exception to this is autogas LPG in Australia, which can be pure propane or a propane and butane LPG gas mixture.

In New Zealand, the LPG gas mixture is a blend of propane and butane.

A 60% propane 40% butane blend would be typical for NZ.

However, sometimes the LPG gas mixture is different for the North Island vs the South Island during winter.

The percentage is usually determined based on what is available on the supply side.

Here are some reported Propane:Butane LPG gas mixture percentages for other countries. 

Note that some countries use a more propane rich LPG gas mixture, in the winter time, to assure proper vaporisation:

Butane and Propane Ratio is Changed Depending on the Season

In some areas or countries, the ratio of butane and propane in the LPG gas mixture is changed depending on the season.

Propane’s biggest advantage is a lower boiling temperature, at -42° vs -0.4°C for butane.

So, propane will continue to vaporise – turn to gas – even in colder climates.

This is why the ratio or propane to butane may be increased during the winter season.

LPG Terminology Varies by Country

So, any of these gases or LPG gas mixtures or these gases can be legitimately referred to as “LPG”.

However, in a given country, the term LPG is generally understood to be whatever the typical constituents are for that country.

For example, in Australia, we call it LPG but it is propane. 

Autogas in Australia can be either pure propane or an LPG gas mixture of propane and butane.

In NZ, LPG is a propane-butane mix.

Alternatively, the term “LPG” may not be used at all, with the gas being referred to by the specific gas name.

This is the case in the USA, where LPG is just called “propane”.

In the UK, consumers have choices.  The fuel type LPG is referred to as either propane, butane or LPG, depending on what gas is present in the customer's choice.

In other countries, they call it "GPL" or "GLP" instead of "LPG", as the acronym is based on different languages and syntax. 

For example, in French it is "gaz de pétrole liquéfié" or in Spanish it is "gas licuado de petróleo".

Other Names for LPG

What does LPG stand for?   LPG is an acronym for either Liquefied Petroleum Gas or Liquid Petroleum Gas.

LPG goes by many other names and this can sometimes be confusing.

It is also called LPG Gas, LP Gas, Propane, BBQ Gas, Camping Gas or Autogas, as well as all of the other specific gas names.

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 for propane is C₃H₈.  (Propane molecule model shown)

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 gas bottles 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 for 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 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.

LPG Properties Vary by the Specific Gas

As discussed, not all LPG gases are the same.

Different LPG gases have different physical properties and formulae.

LPG physical properties include specific gravity (density), boiling point, pressure, vapour expansion, energy content, combustion facts, flame temperature, flash point & more.

This chart shows some of the physical properties of the three most common LPG gases - propane, butane and isobutane…

View More LPG Gas Blogs

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The information in this article is derived from various sources and is believed to be correct at the time of publication. However, the information may not be error free and may not be applicable in all circumstances.