LPG Gas Composition

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LPG Composition Propane Butane

The primary liquefied petroleum gas composition includes propane, butane, isobutane, propylene and butylene. LPG is known to be an extremely flammable mixture of all these hydrocarbons mentioned and is greatly used in the form of fuel for different purposes including household cooking and automobiles. However, out of all the constituents, the most active and main composition of LPG includes propane and butane. Given below are the LPG gas constituents.

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Propane is a type of a hydrocarbon which has the chemical formula C₃H₈ and is amongst the primary and essential lp gas composition. It tends to exist in the gaseous state under the standard temperature and pressure conditions. However, it is compressed into liquid if the required pressure is applied to it. Propane is generally derived in the form of a by-product when petroleum is refined and the natural gas is processed.

Propane tends to undergo vapourization faster when it gets released from the pressurised container. This is due to the lower boiling point of propane which is around -42.2 °C. Also, the melting point of propane is -187.7 °C. The molecular weight of propane is known to be 44.097 gm/mole. Propane is a colourless and odourless gas under the standard conditions. 


Butane is kind of organic compound having the chemical formula C₄H₁₀. It is amongst the most flammable compounds that are used in the LPG chemical composition. Under the standard conditions of temperature and pressure, butane exists in the form of a colourless gas which has a smell similar to the one of gasoline or natural gas. Butane can also be compressed to the liquid form to transport it easily. Butane has two isomers structurally which are known as isobutane and n-butane. 


Isobutane is also referred to as 2-methylpropane and it is an organic compound having the structural formula CH(CH₃)₃. Isobutane is known to be a structural isomer of the compound butane is amongst the chemical components of the liquefied petroleum gas. Isobutane has a melting point of -159.42 °C and the boiling point of -11.7 °C. Isobutane is generally used in the form of propellant in the aerosol cans.


Propylene is also called propene and it is an organic compound having a chemical formula denoted by C₃H₆. It is an unsaturated hydrocarbon and consists of a carbon-carbon double bond. It is also a part of the chemical composition of LPG gas. The molecular weight of propylene is found to be 42.081 gm/mol. Its boiling point is -47.6 °C and its melting point is -185.2 °C. Under the standard temperature and pressure conditions, it exists in the form of a colourless gas. However, it can also be compressed into the liquid form. 


Butylene is also referred to as butene and is a chemical compound having the formula C₄H₈. It has several isomers because of the double bond present in it can be present at several different points in its parent carbon chain. However, amongst the most prominent isomers are isobutylene, 1-butylene and 2-butylene. All these isomers tend to exist in the gaseous form under the standard conditions of pressure and temperature.

FAQ (Frequently Asked Questions)

1. What is the LPG Gas Cylinder Composition?

Ans: The LPG cylinder composition is given as follows -

The LPG or liquefied petroleum gas is a mixture of hydrocarbons. It mainly contains propane or butane or the mixture of both of them. Both these gases at room temperature are colourless and odourless. The boiling point of propane is -42°C  and that of butane is -0.5 °C. Under cooler conditions or even the modest pressure, LPG gets transformed into its liquid phase. In the domestic cylinders, the LPG is used for cooking purposes. However, in these cylinders, butane exists more than propane. This is mainly because of the reason that the fuel value for each kilogram of butane is comparatively higher than that of propane. Also, butane tends to liquefy under comparatively lower pressure than the propane and hence, it is much easier and safer to handle.

2. What is the LPG Gas Composition in Percentage?

Ans: The composition of LPG in percentage is as follows -

The liquefied petroleum gas is composed of both the carbon and hydrogen atoms that form butane and propane, whereas, the natural gas is composed of comparatively lighter methane, which is the simplest hydrogen and carbon molecule. The mixture of the liquefied petroleum gas contains highly flammable gases like butane, propane, and isobutane. The percentage of both butane and propane gases in the mixture of LPG tends to vary from 100% of propane to 20% of propane and about 80% of butane. This mixture of the liquefied petroleum gas has to be stored in the steel vessels which can be either the small BBQ gas bottles or the larger tanks or gas cylinders.