Butane vs Propane Gas vs LPG – Isobutane – Properties

Butane vs Propane Gas vs LPG – Isobutane – Properties

What is the real difference between butane vs propane gas vs LPG and isobutane?

All three gases are consider to be LPG – Liquefied Petroleum Gas.

Butane (C₄H₁₀) and isobutane (C₄H₁₀) have the sane chemical formula, as isobutane is isomer of butane.

Propane gas (C₃H₈) is used primarily as fuel whilst butane and isobutane are used as propellant gases.

They also have some different physical properties including propane boiling point and pressure.

First, some short summary answers:

Is LPG Propane Gas – Is Propane the Same as LPG – LPG or Propane Gas

Propane gas vs LPG – Is it LPG or propane gas?

Propane is LPG but not all LPG is propane. LPG – liquefied petroleum gas – can also contain butane, isobutane, ethane and pentane, flammable hydrocarbon gases liquefied under pressure.

Butane vs Propane Gas – How do Butane and Propane Gas Differ?

When comparing butane vs propane gas, the most important differences are boiling point and vapour pressure.

Propane boiling point is lower, at -42°C vs -0.4°C for butane. 

So, propane gas will continue to vaporise – turn to gas – even in colder climates, down to -42°C. 

Butane has a lower vapour pressure at a given temperature, being about ¼ that of propane gas.

This lower pressure is advantageous for some propellant applications.

Propane vs butane energy content is also different.

Butane has a higher energy content by volume.

However, propane energy content is slightly higher by weight but lower by volume.

This seeming inconsistency of butane vs propane gas is as a result of the two liquid gases having a different specific gravity.

What is Butane (n-butane)? Butane Gas

Butane (n-butane) is a flammable hydrocarbon gas that is liquefied through pressurisation and stored in a butane gas bottle or tank.

Butane gas comes from natural gas processing and oil refining.

Butane gas is commonly used as a fuel, propellant and refrigerant, as well as a petrochemical feedstock.

The butane chemical formula (butane molecular formula) is C₄H₁₀. (Butane molecule model shown)

Butane (n-butane) also falls under the category of an LPG gas.

It is classified as LPG, along with propane, isobutane and mixtures of these gases.

Butane is supplied to businesses that require Butane, as opposed to propane.

Butane gas has some specific applications where it has advantages over propane.

n-Butane or n Butane

Both n-Butane or n Butane are just other names for regular butane gas.

Isobutane Gas – Isobutane vs Butane – Difference Between Butane and Isobutane

Considering isobutane vs butane, isobutane (i-butane) is an isomer of butane.

Chemical formula of isobutane (C₄H₁₀) is the same as butane but the difference between butane and isobutane is a different molecular structure.

Isobutane gas is converted from butane in a process called isomerization.

As with normal butane gas, isobutane gas is a flammable hydrocarbon gas that is liquefied through pressurisation.

So, it has the same butane chemical formula —  C₄H₁₀  — but has a different arrangement of its atoms, as you can see in the 3-D model images. (Isobutane molecule model shown)

Isobutane gas also has different physical properties from normal butane (n-butane).

In addition to being used as a fuel, isobutane refrigerant (r600a isobutane refrigerant) is commonly used as is isobutane gas propellant.

Isobutane gas has very low global warming potential and insignificant ozone depletion potential.

However, its main use is in refineries to increase octane of gasoline and make it cleaner burning.

Isobutane gas is classified as LPG, along with propane, butane and mixes of these gases.

i-Butane, i Butane or Methylpropane

i-Butane or i Butane are just other names for isobutane.

Methylpropane is yet another name for isobutane.

What is Propane Gas? Propane Gas vs LPG

Propane gas is a flammable hydrocarbon gas that is liquefied through pressurisation.

Propane gas comes from natural gas processing and oil refining.

It is commonly used for heating and cooking. 

Considering propane gas vs LPG, propane gas is classified as an LPG gas.

So, LPG or propane is saying the same thing.

Propane is the gas that is supplied to virtually all homes and most businesses that purchase LPG in Australia.

LPG is supplied in gas bottles that are either exchanged or refilled on site by LPG tankers.

Large users may utilise bigger LPG storage tanks.

Propane is also frequently used in Autogas, alone or in a propane-butane mix.

LPG or propane gas go by a number of names in Australia including LPG, LPG gas, bottled gas, propane, BBQ gas, camping gas and LP gas.

However, no worries, as it’s all the same gas.

The chemical formula for Propane is C₃H₈.  (Propane molecule model shown)

Butane Boiling Point

The butane boiling point temperature is -0.4°C.

This is significantly higher than propane boiling point and can be problematic in colder climates.

Propane Boiling Point

The propane boiling point temperature is -42°C.

This propane boiling point temperature is sufficiently low that vaporisation can be achieved in almost all ambient temperature situations, outside of maybe the polar regions.

Liquid Propane Gas or Gaseous Propane – Liquid Butane or Butane Gas

Propane Gas, Butane Gas & Isobutane Gas Properties

This chart shows some of the physical property differences between the three gases.

You can refer back to the chart as we explain the importance of the numbers in the following topics…

One Big Happy Family

Both propane gas and butane gas, along with isobutane gas, are all hydrocarbon gases that fall under the broad label of “LPG”, as they are all liquefied petroleum gases.

They are a group of flammable hydrocarbon gases that are liquefied through pressurisation and commonly used as fuel.

They are also called Natural Gas Liquids (NGLs), along with ethane, pentane and pentanes plus.

Their common distinguishing characteristic is that they can be compressed into liquid at relatively low pressures.

All are used as fuel in combustion, for heat generation, but there are also many other applications for LPG.

LPG or Propane – The Name Game

What LPG or propane are called is greatly dependent on what country you are in.

In Australia, we call it LPG but it is propane gas.

Autogas in Australia can be either pure propane or propane mixed with butane.

In New Zealand, LPG is almost always a propane gas and butane gas mix.

In the USA, they don’t generally use the term LPG.

They just call it “Propane”.

In some countries, like England, you can specifically buy propane gas or butane gas.

In other countries, they call it “GPL” or “GLP” instead of “LPG”, as the acronym is based on different languages and syntax.

For example, in French it is “gaz de pétrole liquéfié” or in Spanish it is “gas licuado de petróleo”.

Energy Content – Myths & Facts

I’ve seen any number of articles saying that butane gas has more energy content and is, therefore, more economical to use.

Not always true!

It actually depends on the unit of measure used for pricing.

If it is priced by volume — in litres — the butane gas has about 9% more energy content, with 27.5MJ/L versus 25.3 MJ/L for propane gas.

However, if it is sold by weight — in kilograms — then propane gas has about 5% more energy content, with 49.58MJ/kg versus 47.39 MJ/kg for butane gas.

Why?

Because propane has less density, you get more litres per kilogram, with the difference more than offsetting the lower MJ/L energy content value.

Butane vs Propane Gas – Which is Hotter?

The flame temperatures of butane vs propane are virtually identical.

Butane gas burns at 1970°C or 3578°F.

Propane gas burns at 1967°C or 3573°F.

Butane Gas Combustion

Assuming complete combustion of butane gas, you get carbon dioxide and water:

2 C₄H₁₀ + 13 O₂ → 8 CO₂ + 10 H₂O + Heat

However, with incomplete combustion you get carbon monoxide and water

2 C₄H₁₀ + 9 O₂ → 8 CO + 10 H₂O + Heat

This would typically occur if the ratio of oxygen to butane gas was insufficient.

Butane vs Propane Boiling Point: Turning from Liquid to Gas

Propane boiling point and butane boiling point are different.

This is the temperature at which propane gas and butane gas go from liquid to gas (vapour).

Propane boils at -42°C whereas butane boils at -0.4°C.

This means you have a huge problem if you try to use pure butane gas when the temperature drops below freezing.

No Boiling = No Vapourisation = No Gas

So, with butane gas only, you could find yourself with no gas for your heater and cooking appliances when it gets cold.

In some areas, LPG suppliers provide a mixture of propane gas and butane gas to address this problem.

This can work well when there are temperatures both below and above freezing.

However, the mixture in the cylinder can become butane rich if there is too much cold weather, with only the propane gas vapourising and being used.

Needless to say, propane gas is the preferred choice for cold weather climates.

What is Butane Gas Commonly Used for?

The most common use of butane gas is as a heating fuel in a butane gas bottle or butane gas cylinder.

Butane gas can be used for cooking, hot water and space heating.

It is also frequently blended into autogas, to fuel vehicles.

There are also commercial and agricultural applications, including the heating of greenhouses.

In non-fuel applications, butane gas is also commonly used as a propellant in aerosol products and as a refrigerant.

More Propellant Use for Butane Gas & Isobutane Gas

One of the other important differences between the gases is vapour pressure.

Vapour pressure is the pressure exerted by the vapour (gas), in equilibrium with the liquid, against the walls of the cylinder or other closed container at a given temperature.

Propane gas has a much higher vapour pressure than either butane gas or isobutane gas.

Propane gas has approximately 4x the vapour pressure of butane gas and about 2.75x the vapour pressure of isobutane gas. (See properties chart above)

Propane gas, butane gas and isobutane gas are all used as propellants in aerosol products, as they are naturally odourless, non-corrosive and non-toxic.

For obvious reasons, no odourant is added to the LPG when used as a propellant.

Nobody wants a stinky hairspray!

These gases may be used individually or in combinations to achieve the desired pressure.

The lower pressures of the two butanes tend to be favoured for everything from deodorant to disposable cigarette lighters.

When the product label lists “hydrocarbon” as the propellant, it is often butane gas or isobutane gas.

LPG gases replaced chlorofluorocarbons (CFCs) as propellants about 30 years ago.

CFCs were banned because they damaged the ozone layer of the atmosphere.

Applications with Butane and Isobutane Refrigerant Gases

All three gases are used in refrigeration but for different applications.

They have different refrigeration uses because of their different thermodynamic properties.

They are used to replace the harmful CFC refrigerants, such as r12, r22, r134a.

High purity propane (>97.5%) is used as a refrigerant, known as propane refrigerant r290.

Both  r600a isobutane refrigerant and n-Butane (r-600) are used as refrigerants.

The three gases can also be mixed to achieve different properties, such as with propane refrigerant r-290a, a mixture of isobutane and propane.

Just as with propellants, LPG gases also replaced chlorofluorocarbons (CFCs) as refrigerants, to preserve the ozone layer.

Improved Yields for Greenhouses with Butane

Butane gas is favoured, over propane gas, for use as fuel in greenhouses.

It provides both heat and enriches the atmosphere with CO₂, which aids in plant growth.

While both propane gas and butane gas are environmentally friendly fuels, butane gas does have an extra carbon atom (C₄H₁₀ vs C₃H₈) that results in ⅓ more CO₂ when burned.

Improved yields make it the preferred choice for greenhouse use.

Butane vs Propane Gas Availability Around the World

Propane gas is generally available in most countries.

Butane gas can be a bit harder to find in some areas.

Nevertheless, in many countries it is available, either as pure butane gas or blended with propane gas.

Final Thoughts on Isobutane vs Butane vs Propane vs LPG

For many people, propane gas, butane gas and isobutane gas are indistinguishable LPG gases and never pose an issue.

However, for others they provide the flexibility to use them for various specialised applications.

Either way, they are exceptional energy products.