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Liquefied Petroleum Gas – LPG: Liquefied Petroleum Gas Properties

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Home 9 Business LPG Blogs 9 Liquefied Petroleum Gas – LPG: Liquefied Petroleum Gas Properties

18 Apr, 2024 | Business LPG Blogs, Residential LPG Blogs

In this article:

What Are the Properties of LPG: LPG gas properties include different gases, boiling point, vapourisation, combustion, chemical formula & more

Liquefied Petroleum Gas – LPG: Liquefied Petroleum Gas Properties

Liquefied petroleum gas – LPG describes flammable hydrocarbon gases including propane, butane and mixtures of these gases.

Liquefied petroleum gas properties include the chemical properties of LPG and the physical properties of LPG. Included in the LPG properties are boiling point, density, energy content, flame temperature, chemical formula, expansion and more.

Liquefied Petroleum Gas Composition

LPG composition includes propane, butane & isobutane.

Liquefied petroleum gas – LPG composition is primarily propane, butane, isobutane, and mixtures of these gases.

Liquefied Petroleum Gas – LPG is produced during natural gas processing and petroleum refining.

Liquefied Petroleum Gas describes flammable hydrocarbon gases.

Liquefied petroleum gas is liquefied through pressurisation, comes from natural gas processing and oil refining.

In different countries, the supply can be propane, butane or propane-butane blends.

In Australia, liquefied petroleum gas is just propane.

Liquefied petroleum gas – LPG exists as liquid or gas (vapour), depending on pressure and temperature.

Natural Gas Liquids – NGL – have the same liquefied petroleum gas composition plus a few more gases not normally included in LPG.

The full NGL list includes ethane, ethene, butylenes, propylene, propene, isobutene, butadiene, pentane, pentene and pentanes plus, as well as propane, butane and isobutane.

Liquefied Petroleum Gas Properties

Liquefied petroleum gas – LPG properties include:

Propane boiling point - LPG (Propane) Vaporisation

  • propane boiling point
  • propane density – LPG (propane) specific gravity
  • Liquefied petroleum gas – LPG composition – components – constituents
  • chemical formula – molecular formula
  • flame temperature
  • autoignition temperature
  • flash point
  • vapour pressure
  • odour
  • appearance
  • energy content
  • gaseous expansion
  • combustion formula
  • limits of flammability
  • nomenclature
  • molecular weight

We’ll review these most commonly referenced properties…

Liquefied Petroleum Gas Properties Chart

Liquefied Petroleum Gas – LPG Properties Chart
Liquefied Petroleum Gas – Propane Boiling Point
-42 °C  or  -44 °F
LPG Melting – Freezing Point
-188 °C  or  -306.4 °F
Specific Gravity of Liquid LPG
0.495 (25°C)
Liquefied Petroleum Gas Gaseous Density
1.898 kg/m3 (15°C)  or  0.1162 lb/ft3
Energy Content of Liquefied Petroleum Gas
25 MJ/L or 91,547 BTU/Gal (60°F)
Liquefied Petroleum Gas Gaseous Expansion
1 L (liquid) = 0.27 M3 (gas)
Propane Flame Temperature
1967 ºC  or  3573 ºF
Limits of Flammability
2.15% to 9.6% LPG/air
Autoignition Temperature
470 °C  or  878 °F
Molecular Weight
44.097 kg/kmole
  Note: Some numbers have been subject to rounding.

Liquefied Petroleum Gas – LPG Boiling Point

Water boils at 100°C or 212°F, becoming a gas (steam).

In contrast, liquefied petroleum gas (propane) boils at -42°C or -44°F, becoming gas vapour.

Liquefied petroleum gas – LPG stays liquid because it is under pressure in a gas cylinder.

As a liquid, it looks a lot like water.

Liquefied petroleum gas is colourless and odourless in its natural state.

 

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Liquefied Petroleum Gas Density and Specific Gravity

Liquefied petroleum gas density is 1.55 times heavier than air at 1.898 kg/m3 vs 1.225 kg/m3 for air (both 15°C at sea level).

Liquefied petroleum gas – LPG liquid density is about half that of water at 495 kg/m3 (25°C) vs 1,000 kg/m3 (4°C) for water.

Specific gravity of propane and water is 0.495 (25°C) and 1.000 (4°C), respectively.

Liquefied Petroleum Gas Density – Specific Gravity of Liquid LPG – Propane

Unlike water, 1 kilogram of LPG does NOT equal 1 litre of LPG.
 
Liquefied petroleum gas – LPG density or specific gravity is about half that of water, at 0.51.
 
In Australia, where liquefied petroleum gas is propane, 1kg of LPG has a volume of 1.96L.
 
Density of LPG - PropaneConversely, 1L of LPG (propane) weighs 0.51kg.
 
1 gallon of liquid propane weighs 4.24 pounds.
 
The specific gravity (SG) of liquid LPG – Propane – is 0.495 (at 25°C)
 
Propane is 580.88 kg/m3 (at boiling point)
 
The specific gravity (SG) of liquid Butane is 0.601 (at 25°C)
 
Butane is 601.26 kg/m3 (at boiling point)

Liquefied Petroleum Gas Density as a Gas: LPG – Propane is Heavier than Air

The density of gaseous liquefied petroleum gas – LPG (Propane) is 1.898 kg/m3 (at 15°C and sea level).
 
LPG is heavier than air1 ft3 of liquefied petroleum gas weighs 0.1162 pounds.
 
Butane is 2.5436 kg/m3 (at 15°C and sea level)
 
In contrast, the density of Air is 1.225 kg/m3 (at 15°C and sea level).
 
So, liquefied petroleum gas – LPG is heavier than air.
 
Note that LPG gas is also referred to as LPG vapour, which is the more technically correct term.

10 Important Liquefied Petroleum Gas Facts

1. LPG (or LP Gas) is the acronym for Liquefied Petroleum Gas or Liquid Petroleum Gas.

2. Liquefied petroleum gas – LPG is a group of flammable hydrocarbon gases liquefied through pressurisation.

They are, in most cases, 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.

These include propane, butane and isobutane (i-butane), as well as mixtures of these gases.

5. LPG gases are compressible into liquid at low pressures.

6. The common uses for liquefied petroleum gas – LPG include use for fuel in heating, cooking, hot water and vehicles.

It is also utilised for refrigerants, aerosol propellants and petrochemical feedstock.

7. LPG is stored, as a liquid, in steel vessels ranging from small BBQ gas bottles to larger gas cylinders and storage tanks. (45kg gas bottles shown)

8. “Wet gas” is a term that is sometimes used to describe liquefied petroleum gas, as a result of its liquidity.
 
9. An alternate reference for LPG (propane) is as a Natural Gas Liquid – NGL.
 
10. In nature, propane does not occur alone.

LPG = Propane

Propane molecule

In Australia, liquefied petroleum gas – LPG is propane.

It is also called LPG Gas, LP Gas, Propane, BBQ Gas, Camping Gas or Autogas.

Liquefied petroleum gas can be other gases in other countries.

Propane is a three carbon molecule with the formula C3H8.

The illustration shows a model of the molecule.

Liquefied Petroleum Gas Temperature: Flame, Boiling Point, Melting/Freezing Point

Liquefied petroleum gas – LPG temperature includes LPG gas flame temperature, LPG gas boiling temperature and LPG gas freezing temperature. LPG – liquefied petroleum gas – temperature also affects the gas cylinder pressure.

LPG Gas Temperature - Flame Temperature

LPG gas flame temperature (when burned with air) is 1967ºC or 3573ºF.

LPG (propane) gas boiling temperature is -42°C or -44°F, as compare to water at 100°C or 212°F

The liquefied petroleum gas boiling point is where liquid propane boils and becomes vapour (gas).

LPG (propane) gas melting/freezing temperature is at -188°C or -306.4°F.

So, liquefied petroleum gas temperature for freezing is a much lower temperature than water, which freezes at 0ºC.

Liquefied Petroleum Gas Pressure Varies with Temperature

As mentioned before, liquefied petroleum gas – LPG is stored in a gas bottle 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.

(Liquefied Petroleum Gas Pressure-Temperature Chart shown)

LPG Pressure-Temperature Chart

Pressure measurement is in kilopascals (kPa) or pounds per square inch (psi).

“Bar” is yet another unit of measure for pressure.

1 Bar = 100 kPa, so it is metric based but not an SI unit of measure.

Liquefied petroleum gas – LPG pressure can vary based on temperature, as shown in the chart.

The level of fill in the gas bottle comes into play when the LPG is in use, as it affects the rate of vapourisation.

Liquefied petroleum gas is a liquefied gas. So, the pressure inside the cylinder will remain the same from full until the vaporistion of the last of the liquid LPG.

Then the pressure will fall, with the use of the last of the liquefied petroleum gas vapour.

Odourant Added for Safety

LPG Odourant Added for SafetyIn its natural state, liquefied petroleum gas – LPG is an odourless gas.
 
The distinctive smell that people associate with LPG is actually added to it as a safety measure.
 
Without the addition of an odourant, leaking gas could collect without detection.

Avoid Direct Contact – Cold Burns

Always use caution should to avoid direct exposure, as liquid LPG is cold enough to cause severe cold burns on exposed skin.

Energy Content of LPG – Propane

Liquefied petroleum gas (propane) contains approximately 25MJ per litre.
 
This also converts to 6.9kWh.
 
One gallon of propane contains 91,547 BTU (60°F).

Calorific Value of Water Gas

The calorific value of the gas used to heat water is no different than liquefied petroleum gas – LPG used for other applications.
 
So, once again, ‘water gas’ contains 25MJ per litre or 91,547 BTU (60°F) per gallon.

Liquefied Petroleum Gas Gaseous Expansion

LPG Gaseous expansionLiquefied petroleum gas – LPG expands to 270 times the volume when it goes from liquid to gas.
 
So, 1L of liquid LPG (propane) equals 270L of gaseous LPG.
 
As there are 1000L in a cubic meter (M3), 1L of liquid LPG expands to 0.27M3.

Combustion Formula Equation for Liquefied Petroleum Gas

In the presence of enough oxygen, liquefied petroleum gas burns to form water vapour and carbon dioxide, as well as heat.
 
LPG combustionFormula Equation for Complete Combustion of LPG – Propane:
 
Propane + Oxygen → Carbon Dioxide + Water + Heat
 
C3H8 + 5 O2 → 3 CO2 + 4 H2O + Heat
 
Incomplete combustion of LPG (propane) occurs when not enough oxygen is present.
 
Incomplete combustion results in the production of water, carbon monoxide, and carbon dioxide:

What’s the Equation for Incomplete Combustion of Propane?

Formula Equation for Incomplete Combustion of LPG – Propane:
 
Propane + Oxygen → Carbon Dioxide + Carbon Monoxide + Water + Heat

2 C3H8 + 9 O2 → 4 CO2 + 2 CO + 8 H2O + heat

Liquefied Petroleum Gas Gas Temperature: LPG – Propane Flame Temperature

An liquefied petroleum gas (propane) flame burns at 1980°C.
 
When it is burning properly, the flame is blue.
 
A yellow or red flame is usually indicative of incomplete combustion.

Limits of Flammability

The lower and upper limits of flammability are the percentages of liquefied petroleum gas – LPG that must be present in an LPG/air mixture.
 
This means that between 2.15% and 9.6% of the total LPG/air mixture must be LPG in order for it to be combustible.

Liquefied Petroleum Gas Flash Point Temperature

The flash point of liquefied petroleum gas (propane) is  -104°C or -156°F.
 
This is the minimum temperature at which propane will burn on its own after ignition.
 
Below this temperature, it will stop burning on its own.
 
However, if a source of continuous ignition is present, it will burn below  -104°C.

Autoignition Temperature – Propane & Butane

Autoignition temperature is the lowest temperature at which it will spontaneously ignite in air.
 
This is without an external source of ignition, like a spark or flame.
 
The autoignition temperature decreases as the pressure or oxygen concentration increases.
 
The autoignition temperature of liquefied petroleum gas – Propane – is 470 °C or 878°F.
 
The autoignition temperature of Butane is 405°C or 761°F.

Dissipation

Liquefied petroleum gas – LPG is heavier than air and will sink to and collect at the lowest point.
 
If vented to the outside air, LPG will dissipate with the slightest movement of air.
 
With liquefied petroleum gas vented into a sealed structure, with no air movement, the LPG gas will collect on the floor. It will rise toward the ceiling, as more LPG enters into the structure.

Molecular Weight for LPG – Propane – Butane – Isobutane

The molecular weight for LPG – Propane – is 44.097 kg/kmole.
 
The molecular weight for Butane (n-butane) is 58.12 kg/kmole.
 
For Isobutane (i-butane), the molecular weight is the same as for n-butane at 58.12 kg/kmole.

Liquefied Petroleum Gas Vapour (Gas) Use vs. Liquid Use

Liquid LPG in the bottom of the gas bottleLiquefied petroleum gas – LPG supply is either liquid or vapour.
 
The difference is in the extraction from supply cylinder or vessel.
 
Most LPG applications use vapour.
 
Appliances such as water heaters, room heaters and cookers all use vapour.
 
If these appliances were to have liquid LPG flow to their burners, the result could be a fire or similar safety hazard.
 
This is why LPG cylinders should always be upright, so that any gas released is in vapour form only.

6 Things You Didn’t Know About Liquefied Petroleum Gas

While you may know some of these facts, chances are you don’t know all of them.

Have a read and learn more about:

1. Real LPG Explosions are Really Rare

2. Simulated Natural Gas from LPG

3. The Source of LPG

4. Australian Made Energy

5. LPG is a Renewable Energy Source

6. LPG is NOT Coal Seam Gas (CSG)

1. Liquefied Petroleum Gas Cylinder Explosions are Extremely Rare + Video

Propane tank peril courtesy of Myth Busters. Hollywood and the media would have you believe that liquefied petroleum gas – LPG cylinder explosions are a common event.

In fact, explosions are quite rare and it is quite difficult to even make an LPG cylinder explode on purpose.

You’ll enjoy watching the Myth Busters Video where they try to make a cylinder explode.

Most gas explosions are the result of gas leaking into a confined space, like a kitchen.

This is no more likely with liquefied petroleum gas than with piped natural gas.

Often, the gas bottle itself is not even involved in the event, as gas bottles are always stored outdoors.

2. Simulated Natural Gas from Liquefied Petroleum Gas

Most people have never even heard of Simulated Natural Gas (SNG) let alone know that it can be made with liquefied petroleum gas – LPG.

Mixing vapourised LPG with air produces SNG.

We can SNG use in place of natural gas, as it has near identical combustion characteristics.

It can be used alone or mixed with regular natural gas.

There are no changes required in burners, regulators or gas jets.

There are a number of reasons to use SNG:

•  To help meet peak demand when natural gas supplies are inadequate

•  To operate while in preparation for the start-up of a natural gas supply

•  As a stand-by in the event of a natural gas supply disruption

Simulated natural gas has a few names.

Besides SNG, it is also called propane-air and LPG-air.

3. The Source of Liquefied Petroleum Gas

Many people mistakenly think of liquefied petroleum gas as a by-product.

In reality, LPG is a valuable co-product produced from gas fields and crude oil refining.

They process the gas stream from natural gas fields to separate the gases present.

These include methane, ethane, propane, butanes and pentanes.

Impurities are also removed, including water.

The produced gases are each funnelled into their own supply streams.

They capture propane and butane, the two common types of liquefied petroleum gas, and store them in their liquefied form.

The same is true of crude oil refining.

The refinery process creates many co-products.

The co-products include gasoline, diesel fuel, asphalt base, heating oil, naphtha, kerosene and LPG.

4. Liquefied Petroleum Gas is Australian Made Energy

Liquefied petroleum gas – LPG is the only motor fuel in which Australia is self-reliant.

Unlike both petrol and diesel, for which Australia relies on imports, we produce more LPG than we consume.

Not only is Australia completely self-sufficient in liquefied petroleum gas but it is also a net exporter of LPG.

In 2013, Australia produced 2.3 Million tonnes of LPG.

That satisfied the local demand of 1.5 million tonnes, with net exports of 815,000 tonnes.

5. Liquefied Petroleum Gas is now a Renewable Energy Source

LPG is now a renewable energy source

Liquefied petroleum gas has gone from being a traditional fossil fuel to a new form of renewable energy.

Scientists have created a genetically engineered version of the common E. coli bacteria.

This version produces propane (LPG).

So, Liquefied petroleum gas – LPG is now a renewable energy.

The bacteria consume sugar.

With genetic modification, and the help of a couple of enzymes, they make propane.

The propane produced is chemically identical to regular propane.

6. Liquefied Petroleum Gas is NOT Coal Seam Gas (CSG)

There is some confusion over what Coal Seam Gas (CSG) is and what it is not.

LPG is not CSG.

While CSG may contain various gases, typical CSG is 95% to 97% pure Methane.

Liquefied petroleum gas is not Methane.

Liquefied petroleum gas – LPG is Propane.

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Eric Hahn
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Steve Reynolds

Technical Consultant

Steve Reynolds is a leading expert in the LPG industry with over 22 years of experience. As part of the national management team at ELGAS, Steve ensures the safe and efficient storage, handling, and transportation of LPG. He serves as the lead investigator for incidents and collaborates with authorities on industry developments.

Steve is a technical advisor to Standards Australia and Gas Energy Australia (GEA), and an active member of the World LPG Association (WLPGA), contributing to global standards and technical reviews. He holds a BSc. (Hons) in Industrial Chemistry from UNSW and has held senior safety and technical roles at ELGAS, making him a trusted authority in LPG safety and standards.