- Written by Eric Hahn
What is LPG? Liquefied Petroleum Gas - Propane
LPG – Liquefied Petroleum Gas – describes flammable hydrocarbon gases including propane, butane and mixtures of these gases.
LPG, liquefied through pressurisation, comes from natural gas processing and oil refining.
LPG is used as heating, cooking and auto fuel.
In different countries, what is supplied can be propane, butane or propane-butane blends.
In Australia, LPG is just propane. Propane is LPG but not all LPG is propane.
7 LPG (Propane) Fast Facts
1. LPG (or LP Gas) is the acronym for Liquefied Petroleum Gas or Liquid Petroleum Gas.
2. LPG is a group of flammable hydrocarbon gases that are liquefied through pressurisation and commonly used as fuel.
3. LPG comes from natural gas processing and petroleum refining.
4. There are a number of gases that fall under the “LPG” label, including propane, butane (n-butane) and isobutane (i-butane), as well as mixtures of these gases.
5. LPG gases can all be compressed into liquid at relatively low pressures.
6. LPG is frequently used for fuel in heating, cooking, hot water and vehicles, as well as for refrigerants, aerosol propellants and petrochemical feedstock.
Where Does LPG Come From?
LPG comes from drilling oil and gas wells.
It is a fossil fuel that does not occur in isolation.
LPG is found naturally in combination with other hydrocarbons, typically crude oil and natural gas.
LPG is produced during natural gas processing and oil refining.
It is isolated, liquefied through pressurisation and stored in pressure vessels.
LPG & Natural Gas Liquids – NGLs
The typical LPG gases – propane and butane – are regarded as Natural Gas Liquids - NGLs.
However, not all NGLs are LPG.
Natural gas liquids, also called Condensate, include other hydrocarbons, too.
Interestingly, LNG – liquefied natural gas – is NOT a natural gas liquid.
What are Natural Gas Liquids - NGLs?
Raw natural gas, as it comes out of the ground, contains a number of gases and compounds, as well as impurities.
However, it is predominantly methane (CH4) gas, which is more commonly known as natural gas.
The raw natural gas must be processed to obtain pipeline quality clean, dry natural gas (methane), including the removal of impurities.
NGLs – Natural Gas Liquids – or condensate are the heavier hydrocarbons that remain after the methane (natural gas) and impurities are removed.
NGLs include isobutane, ethane, ethene, propene, isobutene, butadiene, pentane, pentene and pentanes plus, as well as propane and butane.
Natural gas liquids (NGL) range from 1% to 10% of the raw natural gas flow.
How is LPG Made? What is the Production Process?
LPG is made during natural gas processing and oil refining.
LPG is separated from unprocessed natural gas using refrigeration.
LPG is extracted from heated crude oil using a distillation tower.
This LPG can be used as is or separated into its three primary parts: propane, butane and isobutane.
It is stored pressurised, as a liquid, in cylinders or tanks.
LPG is Refined from Oil & Natural Gas
What is LPG Used For?
LPG – Liquefied Petroleum Gas – has hundreds, if not thousands, of uses including hot air balloons
The LPG uses most people can name are around the home, in their cars or for their business.
Business and industry use LPG for a multitude of processes including steam boilers, kilns, ovens and LPG forklifts.
It is also employed as a propellant, refrigerant, vehicle fuel and petrochemical feedstock.
Transport is also a big user of LPG (Autogas), either as propane or propane mixed with butane, to power various vehicle types.
There are also many, many more LPG applications, including power generation and the hospitality industry.
What Does LPG Stand For? Meaning of LPG
The meaning of LPG is either Liquefied Petroleum Gas or Liquid Petroleum Gas.
LPG goes by many names and this can sometimes be confusing.
Which Gas or Gases are Present in LPG?
LPG is not just a single gas.
There are a number of gases that fall under the LPG category.
Other gases that also fall under the “LPG” label, including ethane, ethylene, propylene, butylene and isobutylene, as well as mixtures of these gases.
In the USA it is also propane and they call it "propane" instead of "LPG".
In New Zealand, LPG is a mixture of propane and butane.
In the UK, consumers have choices. It is referred to as either propane, butane or LPG, depending on what gas is present in the customer's choice.
LPG (Propane) Vaporisation - How LPG Boils
Did you know that every time you turn on one of your gas appliances, the LPG in your gas bottles starts to boil?
If you could see though the steel, you would also notice that it looks just like water boiling.
The big difference is that it happens at -42°C or -44°F.
To boil, the liquid LPG draws heat from the steel walls of the gas bottle which, in turn, get heat from the ambient air.
LPG liquid boils and turns back into gas vapour when you release some of the pressure in the gas bottle by turning on your gas appliance.
As with water, the more heat that is applied, the more rapidly it boils, vaporising at a faster rate.
The vapour pressure in the bottle also increases with temperature, as explained below.
So, as the steel of the bottle draws heat from the ambient air heat, cold weather will slow down the rate of vaporisation.
Vaporisation also makes the gas bottle feel colder than the ambient temperature.
The gas bottle gets even colder when you are actually using the gas.
The LPG gas vapour is held in the top of the bottle and the liquid LPG at the bottom, as shown in the image above.
Almost all of the uses for LPG involve the use of the gas vapour, not the liquefied gas
What is LPG made of: LPG Composition
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.
It is classified as LPG, along with propane, butane and mixes of these gases.
LPG Properties Chart
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 propane, butane and isobutane…
LPG Pressure Varies with Temperature
As previously mentioned, when LPG is stored in a gas bottle, it is under pressure.
The term “pressure” refers to the average force per unit of area that the gas exerts on the inside walls of the gas bottle.
(LPG Pressure-Temperature Chart shown)
Pressure is measured in kilopascals (kPa) or pounds per square inch (psi).LPG pressure can vary greatly based on temperature, as shown in the chart.
The level of fill in the gas bottle comes into play when the LPG is being used, as it affects the rate of vapourisation.
As LPG is a liquefied gas, the pressure inside the cylinder will remain the same from full until the last of the liquid LPG is vapourised.
Then the pressure will fall quickly as the last of the LPG vapour is used, as well.
How Much Pressure is in an LPG-Propane Cylinder?
The pressure inside of an LPG cylinder, or larger vessel, is dependent upon the temperature of the vessel.
The higher the temperature, the higher the pressure of the LPG within the cylinder.
The pressure range for LPG (propane) is from 152 kPa (24 PSIG) at 0ºC to 1794 kPa (257 PSIG) at 54ºC.
The LPG – propane – exists as both liquid and vapour (gas) within the cylinder.
The term “pressure” refers to the average force per unit of area that the gas exerts on the inside walls of the cylinder.
The pressure drops to zero at -43ºC (which is just below the boiling point for propane) and the pressure becomes greater at even higher temperatures.
LPG is Heavier Than Air
In answer to the frequently asked question "Is LPG heavier than air", the answer is "YES".
For example, if the density of air is equal to 1.00, the density of propane is 1.53.
Butane is even heavier, at 2.00. Isobutane is heavier still, at 2.07.
On the other hand, natural gas - methane - is lighter than air, at about 60% of the density of air.
Propane is a flammable hydrocarbon gas with 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).
Propane Combustion Formula
In the presence of sufficient oxygen, LPG burns to form water vapour and carbon dioxide, as well as heat.
Formula for Complete Combustion of LPG (propane):
Formula for Incomplete Combustion of LPG (propane):
2 C3H8 + 9 O2 → 4 CO2 + 2 CO + 8 H2O + heat
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 is commonly used as a fuel, 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.
Butane Combustion Formula
Assuming complete combustion, you get carbon dioxide and water:
Butane + Oxygen → Carbon Dioxide + Water + Heat
2 C4H10 + 13 O2 → 8 CO2+ 10 H2O + Heat
However, with incomplete combustion you can get carbon monoxide and water
Butane + Oxygen (insufficient) → Carbon Monoxide + Water + Heat
2 C4H10 + 9 O2 → 8 CO + 10 H2O + Heat
This would typically occur if the ratio of oxygen to butane was insufficient.
Autogas is also LPG.
Autogas that is sold at service stations can be propane or a propane/butane mix.
Not only is running an LPG car economical, but Autogas is also cleaner burning fuel than petrol, so engine life is actually extended and greenhouse gas emissions reduced.
LPG is Eco-Friendly
LPG is an eco-friendly choice, as it is a low carbon, low sulphur fuel.
LPG results in lower CO2 emissions than other energy sources, such as coal fired electricity.
For example, with coal fired electricity, replacing your electric hot water system with a 6-Star LPG continuous flow hot water system may reduce the greenhouse gas emissions produced from your hot water use by about 75%.
LPG is a versatile, transportable, low carbon fuel.
Using it requires very little infrastructure, which makes it an excellent choice for developing countries, as well as developed countries.
LPG is easy to transport, in cylinders or tankers, making it available virtually everywhere.
Delivery methods can range from very sophisticated to extremely basic.
From requiring considerable capital investment to virtually no investment at all.
Regardless of how it’s delivered, LPG is there when people need it.
Clean, safe and reliable energy for everyone everywhere.
Comments, questions or feedback?
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.