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Butane vs Propane vs Isobutane - What is Butane?

Liquefied Petroleum Gas

Propane has a lower boiling point than butane at -42°C vs -0.4°C. Propane also has about 4x the vapour pressure of butane. This makes propane a better choice for cold climates whilst butane is a better choice for propellant use.

The big differences between butane vs propane are in the usable temperature range and the vapour pressure inside of the gas bottle. Propane can be used instead of butane in all fuel applications. Butane does not work as a fuel in a below freezing climate but butane is generally a better propellant, versus propane, due to its lower vapour pressure.

In other ways butane and propane are almost or exactly the same, such as energy content and many of their applications.

Discover the real difference between butane vs propane vs isobutane vs LPG. All three gases are consider to be LPG - Liquefied Petroleum Gas.

Butane vs Propane - Choosing Butane or Propane Gas

Butane vs PropaneWhen considering butane or propane gas, the difference in physical properties determines which gas is best for a particular application. Propane is better for cold weather with a lower boiling point, at -42°C vs -0.4°C for butane. Butane is the preferred propellant, with a lower vapour pressure at a given temperature, being about ¼ that of propane.

Propane is classified as LPG – Liquefied Petroleum Gas – along with butane, isobutane and mixtures of these gases. Propane boiling point is lower than butane so it will continue to vaporise from a liquid to a gas even in very cold weather, down to -42°C. When stored as propane liquid in a cylinder or tank, it has 4x higher pressure than butane at the same temperatures. This make propane more appropriate for exterior storage and use in cold climates.

As with normal butane, isobutane is a flammable hydrocarbon gas that is liquefied through pressurisation. Propane is classified as LPG – Liquefied Petroleum Gas – along with butane, isobutane and mixtures of these gases.

Butane vs propane are dissimilar in boiling point and vapour pressure but both are regarded as LPG and commonly used for cooking, heating, hot water and autogas.

The lower boiling point of propane is advantageous, as it will continue to vaporise – turn to gas – even in colder climates down to -42°C.

The lower vapour pressure of butane, at a given temperature, is advantageous for some propellant applications.

Butane has a slightly higher energy content by volume while propane energy content is slightly higher by weight. This seeming inconsistency is as a result of the two liquefied gases having a different specific gravity.

Butane vs LPG

LPG (propane) boiling point is lower than butane meaning it will continue to vaporise from a liquid to a gas, even in very cold weather of -42°C vs -0.4°C for butane. So, propane is better for use in the cold. Butane vapour pressure is ¼ the pressure of LPG (propane), at a given temperature, making it more popular for propellant use.

When you need to go camping or just barbecuing in cold weather, LPG (propane) is better than butane as your cooking fuel. LPG (propane) has a lower boiling point, which keeps working in cold weather. Butane is suitable for warm weather use outdoors or indoor applications.

Butane and LPG (propane) are used for cooking, heating and to fuel vehicles.

Both propane and butane are classified as LPG – Liquefied Petroleum Gas.

Butane vs LPG (propane), the significant differences are different boiling points and vapour pressure.

LPG (propane) boils at -42°C vs -0.4°C for butane.

LPG (propane) vapour pressure is about 4x that of butane, at a given pressure.

This makes LPG better for cold weather climates but butane is a much better propellant.

Both are regarded as LPG – Liquefied Petroleum Gas – and commonly used for cooking, heating, hot water and auto fuel.

Butane vs LPG is better restated as "butane is LPG".  Butane vs LPG is more accurately stated as butane vs propane.

LPG describes a group of gases that includes butane, as well as propane and isobutane.

Other gases that also fall under the “LPG” label, including ethane, ethylene, propylene, butylene and isobutylene, as well as mixtures of these gases and are also referred to as natural gas liquids – NGL.

What is Butane (n-butane)? Is Butane a Gas? n Butane vs Butane (Butane vs n Butane)

Butane is a flammable hydrocarbon gas that is liquefied through pressurisation. Butane (n-butane) is also falls under the category of "LPG". Butane is commonly used as a fuel, propellant and refrigerant, as well as a petrochemical feedstock. Butane is supplied to businesses that require Butane, as opposed to propane.

According to scientific nomenclature, "butane" refers to the n-butane isomer of butane vs the isobutane isomer, with the branched structure. Isobutane (i-butane) is different, as it is an isomer of butane with the same chemical formula (C4H10) but a different arrangement of the atoms.

Butane is an organic hydrocarbon and a four carbon atom alkane that is a gas at normal temperature and pressure. Butane may be used to refer to either of two structural isomers, n-butane or isobutane (methylpropane), or mixtures of the two isomers.

Butane molecule

Butane is a gas when not under pressure and at normal room temperatures.  It is classified as LPG, along with propane, isobutane and mixtures of these gases.

Butane (n-butane) comes from natural gas processing and oil refining.

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

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

Is Butane Corrosive - Toxicity - Colour - Odour - Flammability

Butane (C4H10) is an very stable molecule which has no corrosive action toward metals. Butane also has low toxicity. In addition to being non-corrosive and non-toxic, butane and its isomer, isobutane, are also extremely flammable, colourless and odourless (prior to addition of an odourant). Butane is an asphyxiant, if it replaces air in an enclosed space.

n-Butane or n Butane

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

What is Isobutane?

Isobutane molecule

Isobutane (i-butane) is an isomer of butane. As with normal butane, isobutane is a flammable hydrocarbon gas that is liquefied through pressurisation.

Isobutane is converted from butane in an isobutane production process called isomerization.

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

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

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

In addition to being used as a fuel, isobutane is commonly used as a refrigerant and a propellant.

Isobutane 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 vs Propane - Is Isobutane the Same as Propane?

Considering isobutane vs propane, 310.9 kPa is the vapour pressure of isobutane vs propane at 858.7 kPa (both at 21ºC) . The -11.75°C is the boiling point of isobutane vs propane at -42°C. Both are liquids below boiling point or when under pressure. So, propane also has a lower boiling point and higher vapour pressure.

Isobutane vs propane is also a comparison of different chemicals. The C4H10 is the chemical formula of isobutane vs propane with a chemical formula of C3H8.

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 molecule

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

It is classified as LPG – Liquefied Petroleum Gas – along with butane, isobutane and mixtures of these gases.

Propane comes from natural gas processing and oil refining.

It is commonly used for heating and cooking.

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 goes 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 boiling point temperature of butane is -0.4°C.

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

Propane Boiling Point

The boiling point temperature of propane is -42°C.

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

Butane or Propane Gas - When are they Liquid or Gaseous?

When are Propane & Butane
Liquid or Gas?
LPG (1atm)
Liquid
Vapour (Gas)
Propane
< -42°C
≥ -42°C
Butane
< -0.4°C
≥ -0.4°C

 

Butane, Isobutane & Propane - Properties  

Butane, Isobutane and Propane are are all low carbon flammable hydrocarbon gases. Butane (n-butane) C4H10, has four carbon atoms in a straight chain with 10 hydrogen atoms, while Isobutane (i-butane) is an isomer of butane with a branched structure. Propane C3H8 is an entirely different chemical gas. All 3 can be liquefied under moderate pressure, stored and distributed in gas cylinders and other vessels.

All three are commonly used as fuel or as aerosol propellants, in addition to other uses.

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…

Butane, Isobutane & Propane Properties
Gas Properties Isobutane Butane Propane
Chemical Formula C4H10 C4H10 C3H8
Energy Content: MJ/m3 110.4 111.4 95.8
Energy Content: MJ/kg 45.59 47.39 49.58
Energy Content: MJ/L 25.0 27.5 25.3
Boiling Temp: Cº -11.75 -0.4 -42
Pressure @ 21ºC: kPa 310.9 215.1 858.7
Flame Temp: Cº 1975 1970 1967
Expansion: m3/L 0.234 0.235 0.270
Gas Volume: m3/kg 0.402 0.405 0.540
Relative Density: H2O 0.60 0.58 0.51
Relative Density: air 2.07 2.00 1.53
L per kg 1.669 1.724 1.96
kg per L 0.60 0.58 0.51
Specific Gravity @ 25ºC 2.06 2.07 1.55
Density @ 15ºC: kg/m3 2.533 2.544 1.899
 
 
Physical Properties of Butane vs Propane vs Isobutane
Note: Some numbers have been rounded.

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.

Isobutane vs Butane - Isobutane and n Butane - n Butane vs Isobutane

Butane (n butane) and isobutane are classified as LPG – Liquefied Petroleum Gas – along with propane and mixtures of these gases. Butane, isobutane and propane have different vapour pressure and boiling temperatures. Butane, n-butane, and n butane are all the same thing, as are isobutane and i-butane.

The poorest choice for cold weather, with a -0.4°C boiling point, is butane vs isobutane at -11.75°C. Propane is the best at -42°C.

Propane has the highest vapour pressure at 858.7 kPa. 310.9 kPa is the vapour pressure of isobutane vs butane at 215.1 kPa (all at 21°C).

So, propane makes the best fuel with the highest pressure and lowest boiling point, Butane and isobutane, with their lower vapour pressure, are favoured as propellants.

Butane and isobutane are constitutional isomers meaning that they have the same chemical formula but different structures, physical and chemical properties. The carbon and hydrogen atoms are in a branch structure with isobutane vs n butane atoms in a continuous chain.

Comparing isobutane vs butane each have 4 carbon atoms and 10 hydrogen atoms (C4H10) but arranged in a different way, as isobutane is an isomer of n butane. Both isobutane and n butane are gas at standard temperature and pressure (STP). Both are colourless and naturally odourless gases. The boiling point of isobutane vs butane is -11.75°C vs -0.4°C, respectively. This difference between n butane and isobutane is because of the different structure of isobutane vs butane. (Note: n-butane, n butane and butane are all the same thing as are isobutane and i-butane)

The difference between n butane and isobutane (isobutane vs butane) is minimal. The only notable differences are in boiling temperature, vapour pressure and the arrangement of their atoms, even though isobutane and n butane have the same chemical formula: C4H10.

There really isn't much difference between isobutane vs butane. Both are classified as LPG. There are three noticable differences between n butane and isobutane (isobutane vs butane):

1. The boiling temperature of isobutane vs butane is about 11°C (19.8ºF) lower for isobutane.

2. Pressure is probably the biggest difference between n butane and isobutane. Comparing the pressure of isobutane vs butane shows isobutane with about 1.5x higher pressure. Isobutane is 310.9 kPa (45.09 PSI) vs n butane at 215.1 kPa (31.2 PSI) with both at 21ºC (69.8ºF).

3. Whilst the chemical formula for isobutane and n butane are the same, isobutane is an isomer of butane, with a different arrangement of the atoms.

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

Propane has a much higher vapour pressure than either butane or isobutane. All are liquids under pressure or below their different boiling points, -42°C for propane and -0.4°C for butane. 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!

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

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.

 

 

 

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The information in this article is derived from various sources and is believed to be correct at the time of publication. However, the information may not be error free and may not be applicable in all circumstances.