Introduction
Liquefied Petroleum Gas, also known as LPG, is used in almost every household in the country mainly for cooking purposes. It can also easily be transformed into a liquid, hence it is called by that name. LPG can expand up to 250-270 times its size when it is in a liquid state if it is converted into a gaseous state. This is why LPG comes in high-pressure tanks and it gets burned to provide fuel for various purposes.
In India, they are popularly called ‘gas cylinders’.
What is the Pressure inside an LPG Cylinder?
In most cases, the propane pressure inside LPG cylinders should be between 100-200 psi, since the propane will stay at a liquid state only within this pressure range. The pressure inside tanks can change slightly on account of changes in the temperature outside the tank, but in most cases, this does not affect the pressure inside.
LPG Composition
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
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 evaporation 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
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
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 aerosol cans.
Propylene
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
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.
LPG is usually extracted from ‘wet’ natural gases through a process known as absorption, and the substance formed as a result has a very low boiling point. This is then distilled, treated with water and a number of chemicals such as carbon dioxide and hydrogen sulphide. The gas that is obtained from this is then transported using special pipelines meant only for transporting LPG. Nowadays, however, they are also being transported through roads and railways.
When the LPG gas is distributed to households for non-industrial purposes, it is stored in a tank so that the gas does not leak out. Industrial LPG is not the same as household LPG, and it is supplied differently. Other than cooking, LPG can also be used in a wide range of household activities that require heat or fuel. This can include central heating, water heaters and fireplaces. In industries, LPG is used to provide engine fuel and run backup generators.
FAQs on LPG Gas Composition
1. What is the LPG Gas Cylinder Composition?
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?
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.
3. How is LPG usually transported?
LPG is mostly transported through cylinders of a certain weight and volume, however, these are mostly only for household use. Industrial uses would require considerable more LPG which cannot be delivered through small tanks. LPG is always transported in the liquid form since LPG in gas form has a very huge volume that is close to 300 times the volume it has in a liquid state. For the sake of convenience, it is only transported in liquid form. Most LPG that comes for household uses comes in a refillable tank or cylinder.
4. Can LPG cylinders explode?
In the most practical of situations, this does not happen. Lpg cylinders or tanks are not dangerous items. However, it is true that they can explode under certain conditions. The main problem with LPG safety is that it is very very flammable. Therefore, it is highly possible that a gas leak can lead to a fire. As we have mentioned, changes in outside temperature can affect the gas pressure inside the cylinder. Therefore, in the case of a fire, if the temperature rises rapidly, then it is possible for the gas to expand and for the cylinder to burst.
5. What is the difference between CNG and LPG?
LPG is liquefied petroleum gas, while CNG is compressed natural gas. These are both sources of fuel and/or heat, but they are derived in different ways. The main difference between them is that while propane and butane are the main components of LPG, methane is the main component of CNG. in comparison to LPG, CNG produces far more quantities of greenhouse gases and is thus better for the environment. CNG is very light and can quickly mix in with the air, however, LPG being heavy can catch fire very easily.
6. Can LPG leak out?
Sometimes it is possible that the LPG can leak out from the tank or the cylinder it comes in. LPG on its own does not have any such noticeable odour or smell. However, this is a very flammable gas, so even with a little leak, it can cause serious fire accidents. This is why during its industrial processing, some more compounds are added to it. This is the smell that can be made out whenever there is a gas leak.
7. What points should be followed in the event of a gas leak?
Usually, even with a little gas leak, it is possible for people to understand and take action immediately due to the very characteristic smell that is observed. However, in case LPG has been leaking for a while, the best thing to do is immediately ventilate the area by opening all doors and windows and allowing the movement of air. This will help dissipate the gas. Flammable items and any source of fire need to be removed at once from the scene as well.
