LPG Composition: Definition, Components and Sample questions

Liquified Petroleum Gas (LPG) is a compressed gas that is extracted from wet natural gas through the process of absorption. Due to its high compressible property, large volumes of LPG can be compressed and stored in containers and easily transported. LPG is a very high flammable gas that is basically used in the form of fuel in cooking cylinders, residential heating, automobiles, hot water systems, etc. In this article, we will discuss the formation and composition of LPG.

Keyterms: Propane, Propylene, Butane, Isobutane, LPG, absorption, Butylene, Hydrocarbon

Read More: Critical Temperature

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LPG Composition

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LPG Composition refers to the constituents present in the mixture to form Liquified Petroleum Gas. It is a mixture of hydrocarbons that include propane, propylene, butane, isobutane, and butylene. These make LPG extremely flammable gas having very low melting and boiling points. Out of all these components, propane and butane are the most active ones. All the components of LPG are as follows:

• Propane
• Propylene
• Butane
• Isobutane
• Butylene

LPG Gas Cylinder used for the purpose of domestic cooking

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Propane

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Propane is one of the most active components in LPG. It is a three-carbon alkane gas with the chemical formula C₃H₈. Under standard temperature and pressure (STP), propane generally remains in the gaseous state and in a colorless and odorless form. However, it can be further compressed into the liquid state by applying accurate pressure.

Propane has a very low melting point (around -187.7 degrees Celsius) and a boiling point (- 42.2 degrees Celsius). Due to its lower melting point in series, propane is not able to close pack in certain geometries like rectangle, irregular pentagon, and hexagon. It instantly vaporizes when released into the standard conditions.

This hydrocarbon has a molar mass of 44.097 grams per mole and is basically produced as a by-product while processing natural gas.

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Propylene

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Propylene also called propene, is another component of LPG. It is an unsaturated organic compound having the chemical formula C₃H₆. It comes with the suffix 'ene' since it has a carbon-to-carbon double bond. 

Under standard conditions, propylene exists in a gaseous and colorless form. However, it can be compressed into a liquid state under accurate pressure. It has a molecular weight of 42.081 grams per mole. The melting point of propylene is -185.2 degrees Celsius and the boiling point is -47.6 degrees Celsius.

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Butane

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Butane is a four-carbon alkane bond with the chemical formula C₄H₁₀. Besides propane, butane is another highly reactive component in LPG. Butane exists in the form of a colorless gas under standard temperature and pressure. It has a similar smell to that of natural gas or gasoline. Under specific pressure and conditions, butane can be compressed into the liquid state for easier transportation. 

The hydrocarbon has a molar mass equal to 58.124 grams per mole. Its boiling point lies in the range of -1 degrees Celsius to 1 degree Celsius and its melting point ranges between -140 degrees Celsius to -134 degrees Celsius. Apart from that, butane has two structural isomers, namely n-butane and isobutane. While the formation of butane includes a straight chain of four carbon atoms, n-butane and isobutane form branched structures.

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Isobutane

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Isobutane, also called 2-methylpropane, is a structural isomer of butane with the chemical formula CH(CH₃)₃. This organic compound is a flammable and colorless gas and is one of the components of LPG. Isobutane has a molecular weight of 58.124 grams per mole which is the same as butane. 

However, the melting and boiling points of isobutane are not the same as butane. Its boiling point exists at -11.7 degrees Celsius and its melting point lies at -159.42 degrees Celsius. The compound isobutane is also used as a refrigerant, aerosol propellant, fuel, etc.

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Butylene

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Butylene or Butene is a four-carbon alkene bond with a carbon-carbon double bond. It has a chemical formula, C₄H₈. It has a boiling point of -6.47 degrees Celsius and a melting point of -185.3 degrees Celsius. As the double bond in the carbon chain of butylene can be present at different points, Butylene has many isomers. The most important isomers among all include 1-butylene, 2-butylene, and isobutylene.

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Things To Remember 

• Liquified Petroleum Gas (LPG) is a compressed gas that is extracted from wet natural gas through the process of absorption.
• The boiling point of LPG is -42 degrees Celsius and its melting point is -188 degrees Celsius. 
• LPG is a renewable energy source and was made in Australia. 
• LPC is a mixture of hydrocarbons that include propane, propylene, butane, isobutane, and butylene.
• Propane and butane are the most active components of LPG. The amount of propane in liquefied petroleum gas varies from 100% to 20% while the amount of butane remains around 80%. 
• During the processing of natural gas or refining petroleum, propane is generally produced as a by-product.

Read More: Boiling Point Elevation

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