Butane vs Propane Gas - What are the Differences?

· There are three significant differences between butane vs propane gas.  Those differences are boiling point, vapour pressure and CO₂ emissions when burnt.

· The first is boiling temperature, at -42° for propane vs -0.4°C for butane.

· This makes propane the preferred choice for cold weather climates.

· The second difference is vapour pressure.

· The vapour pressure of propane is about 4x that of butane.

· This makes a difference when the two gases are used as propellants.

· The third difference is in the amount of CO₂ produced when burned.

· Butane produces more CO₂ which is advantageous in plant growth, when it is used to heat greenhouses.

· There are other minor differences, as shown in the properties tables above, but none have the significant effects on applications that are inherent in these three.

What is Different Between n butane and isobutane?

There isn't much different between n butane and isobutane.

Both are classified as LPG.

As previously mentioned, isobutane even has the same chemical formula as butane — C₄H₁₀ — just with a different arrangement of its atoms.

There are two noticable differences between n butane and isobutane:

1. The boiling temperature on n butane is about 11°C higher.

2. Pressure is probably the biggest difference, with isobutane at 310.9 kPa and n butane at 215.1 kPa (both at 21ºC).

One Big Happy LPG Family

· Both propane and butane, along with isobutane, 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.

The Name Game

· What they are called is greatly dependent on what country you are in.

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

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

· In New Zealand, LPG is almost always a propane and butane 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 or butane.

· 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 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 has about 9% more energy content, with 27.5MJ/L versus 25.3 MJ/L for propane.

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

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 and propane are virtually identical. Butane burns at 1970°C or 3578°F. Propane burns at 1967°C or 3573°F.

Butane Combustion

Assuming complete combustion, 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 was insufficient.

Boiling Point: Turning from Liquid to Gas

Propane and butane have different boiling points — the temperature at which it goes 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 when the temperature drops below freezing.

No Boiling = No Vapourisation = No Gas

So, with butane 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 and butane 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 vapourising and being used.

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

What is Butane Commonly Used for?

The most common use of butane is as a heating fuel.

It 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 is also commonly used as a propellant in aerosol products and as a refrigerant.

Can You Use Propane Instead of Butane

You can use propane instead of butane in virtually all fuel applications.  It is the non-fuel applications, for propellants and refrigerants, where propane cannot be used instead of butane.

Vapour Pressures & Use as Propellants for Butane or Propane Gas

One of the other important differences between the two 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 has a much higher vapour pressure than either butane or isobutane.

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

Propane, butane and isobutane 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 or isobutane.

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

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

Different Refrigerant Applications

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 R-12, R-22, R-134a.

High purity propane (>97.5%) is used as a refrigerant, known as R290.

Both n-Butane (R-600) and i-Butane (R600a) are also used as refrigerants.

The three gases can also be mixed to achieve different properties, such as with 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

Butane is favoured, over propane, for use in greenhouses.

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

While both propane and butane are environmentally friendly fuels, butane 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 or Propane Gas Availability Around the World

Propane is generally available in most countries.

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

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

Final Thoughts

For many people, the different gases that qualify as LPG are indistinguishable and never pose an issue.

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

Either way, LPG is an exceptional energy product.