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Propane vs Butane: Butane Gas – Propane Gas | Is Propane the Same as LPG

What is the real difference between butane (C₄H₁₀) vs propane (C₃H₈) and isobutane (C₄H₁₀)?

All three gases are consider to be LPG – Liquefied Petroleum Gas. Butane (butane gas) and isobutane have the sane chemical formula, as isobutane is isomer of butane.

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

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

First, some short summary answers:

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

“Propane is LPG but not all LPG is propane” is a phrase I coined many years ago and it best describes the relationship between propane gas and LPG.

LPG – liquefied petroleum gas – can also contain butane, isobutane, ethane and pentane, flammable hydrocarbon gases liquefied under pressure.

Butane vs Propane – How do Butane and Propane Differ?

When comparing butane vs propane, 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 (propane gas) will continue to vaporise – turn to gas – even in colder climates, down to -42°C. 

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

This lower pressure is advantageous for some propellant applications.

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 is as a result of the two liquid gases having a different specific gravity.

Propane, Butane & Isobutane Properties

This chart shows some of the physical property differences between propane gas, butane gas and isobutane.

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

Boiling point and vapour pressure are important characteristics that dictate which climates and applications the gases can be used in successfully.

Propane boiling point is lower but has higher vapour pressure which makes it suitable for use in cooler climates, such as the USA, Europe, and the South Island of New Zealand.

Propane is also preferred in industrial heating applications as it delivers more thermal energy over time than butane.

Butane on the other hand has a higher boiling point and lower vapour pressure making it an effective energy source in warmer climates such as areas around the equator.

The LPG industry in New Zealand has a blend of Propane and Butane.

These blends vary from 60% Propane and 40% Butane in the North Island to mostly 100% Propane on the South Island.

Both butane (butane gas) and propane (propane gas) are gases that are heavier than air.

Propane gas weighs 1.898 kg/m³, Butane gas weighs 2.5436 kg/m³, whilst air weighs 1.225 kg/m³.

Although there are real differences between butane, propane, and LPG, all three are technically considered Liquefied Petroleum Gas.

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 noticeable 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).

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 (butane gas) or Propane Gas – Which is Hotter?

The flame temperatures of butane (butane gas) 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 for butane, you get carbon dioxide and water:

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

However, with incomplete butane 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 boiling point is -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.

Propane Gas Uses

Propane gas has a high octane rating, making it a great choice for spark-ignited internal combustion engines.

If spilled or released, it presents no threat to the soil, surface water, or groundwater.

Propane is a co-product of natural gas processing and crude oil refining.

Its main uses include home heating and stand-alone heaters, outdoor heating for gazebo accessories, hot water, cooking, refrigeration, clothes drying, and powering farm and industrial equipment.

The petrochemical industry also uses propane when making plastics and other compounds.

Butane (Butane Gas) Uses

The most common use of butane (butane gas) 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.

More Propellant Use for Butane & Isobutane

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 (butane gas) or isobutane.

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

Refrigerant Applications with Propane, Butane and Isobutane

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 with Butane

Butane is favoured, over propane, for use as fuel 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 gas is generally available in most countries.

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

In NZ, we have both propane and butane and it is commonly supplied as a 60:40 mix.

In many other countries it is available, either as pure butane or blended with propane.

Propane vs Butane vs Isobutane: Final Thoughts

For many people considering propane vs butane vs isobutane, the 3 different gases are indistinguishable 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.