ELGAS Knowledge Hub

Propane vs Butane vs Isobutane Gas

When considering propane vs butane gas, butane (butane gas) and propane (propane gas) are very similar with a few notable exceptions.

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

Propane vs butane chemical formula are propane gas formula (C₃H₈) vs butane gas formula (C₄H₁₀) and there is also isobutane gas formula (C₄H₁₀).

There are differences in the physical properties of the three gases.

For example, the propane boiling point is different from the butane boiling point, as are their vapour pressures and uses.

Propane (propane gas) is used primarily as fuel whilst butane (butane gas) is commonly used as a fuel or propellant gas.

Isobutane (isobutane gas) is primarily used as a propellant gas, as well as a refrigerant and an additive to gasoline.

First, some short summary answers:

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

What is LPG?

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

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

It is stored in LPG gas bottles and liquefied through pressurization.

LPG comes from natural gas processing and oil refining.

It is used in LPG gas heating, cooking and auto fuel, as well as many other applications.

What is propane?

As stated, propane (propane gas) is a flammable hydrocarbon gas liquefied under pressure and stored in a propane tank.

It exists as both liquid propane and propane gas in a propane gas bottle before the propane gas is released from the top.

Is LP gas the same as propane gas is a related question that is frequently asked.

Propane gas is LP gas but not all LP gas is propane gas. LP gas can also be butane gas, isobutane gas or various mixtures of the three gases.

In New Zealand, LPG can be propane or a propane butane gas mix.

Propane vs Butane – Butane Gas vs Propane Gas – Cooking with Butane vs Propane

A common question relates to cooking with butane vs propane.

The is no perceptible difference when cooking with butane vs propane, as the butane gas vs propane gas temperature of the flame are nearly identical and amount of energy contained only varies by a small amount.

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

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

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 (butane gas) has a higher energy content by volume.

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

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

Propane Gas, Butane Gas & Isobutane Gas Properties

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

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

Propane boiling point vs butane 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 propane gas vapour pressure is higher in a propane tank, which makes it suitable for use in cooler climates, such as the USA, Europe, and the South Island of New Zealand.

Propane (propane gas) is also preferred in industrial heating applications as it delivers more thermal energy per kg than butane (butane gas).

On the other hand, butane boiling point is higher and butane gas vapour pressure is lower, 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 gas and butane gas, so you actually get a propane butane gas bottle.

What is the ratio of propane and butane in LPG?

The percentage of propane and butane in LPG varies from 60% propane gas and 40% butane gas on the North Island to mostly 100% propane gas 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 gas, propane gas, and isobutane gas, all three are technically considered Liquefied Petroleum Gas.

Isobutane vs Butane – What is Different Between n Butane (Butane Gas) and Isobutane Gas?

When considering isobutane vs butane, there isn’t much different between n butane (butane gas) and isobutane gas.

Both butane gas and isobutane gas are classified as LPG.

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

There are two noticeable differences between n butane gas and isobutane gas:

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

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

Propane vs Butane Gas Energy Content – Myths & Facts

Propane vs butane gas energy content contains another difference.

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

Not always true!

A butane gas vs propane gas comparison 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 a propane tank has about 5% more energy content, with 49.58MJ/kg versus 47.39 MJ/kg for butane gas.

How is this inconsistency possible?

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

Butane Gas or Propane Gas – Which is Hotter?

Considering propane vs butane gas flame temperatures, they are virtually identical.

Butane gas burns at 1970°C or 3578°F.

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

Propane – Propane Gas Combustion

Assuming complete combustion for propane gas: Propane + Oxygen → Carbon Dioxide + Water + Heat

Propane gas formula for complete combustion of propane is: C₃H8 + 5 O₂ → 3 CO₂ + 4 H₂O + Heat

The incomplete combustion reaction equation (burning equation) or carbon monoxide formula for propane is: 2 C3H8 + 9 O2 → 4 CO2 + 2 CO + 8 H2O + Heat.

The result of an incomplete combustion reaction is water vapour, carbon dioxide, heat and carbon monoxide.

A complete combustion reaction yields a blue flame.

Butane – Butane Gas Combustion

Assuming complete combustion for butane (butane gas), 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 gas was insufficient.

Boiling Point: Turning from Liquid to Gas

Propane vs butane gas have different boiling points — the temperature at which it goes from liquid to gas (vapour).

Propane boiling point is -42°C whereas butane boiling point is -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 propane butane gas mixture 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, a propane tank is the preferred choice for cold weather climates.

Propane – 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 from a propane tank, it presents no threat to the soil, surface water, or groundwater.

Propane gas 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.

It is typically supplied in a propane gas bottle or propane tank.

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

Butane – Butane Gas Uses

The most common use of butane (butane gas) is as a heating fuel supplied in various butane gas bottle sizes.

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

It is also frequently blended into Autogas, as a propane butane gas mix, 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 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.

Considering butane gas vs propane gas vs isobutane gas, a propane tank has a much higher vapour pressure than either butane (butane gas) or isobutane gas.

Propane tank 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.

Refrigerant Applications with Propane, Butane and Isobutane Gas

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 gas (>97.5%) is used as a refrigerant, known as R290.

Both n-Butane gas (R-600) and isobutane gas (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 gas and propane gas.

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

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 Gas or 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.

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

In many other countries it is available, either as pure butane gas or propane butane gas mix.

Propane Gas vs Butane Gas vs Isobutane Gas: Final Thoughts

For many people considering propane gas vs butane gas vs isobutane gas , 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.