Butane vs Propane vs Isobutane - What is Butane?

Liquefied Petroleum Gas

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

· In some ways they are almost or exactly the same.

· However, there are some important differences that you need to know.

First, some short summary answers:

Butane vs Propane - Choosing Butane or Propane Gas

· Comparing butane vs propane, the most important differences are their dissimilar boiling point and vapour pressure but both are regarded as LPG – Liquefied Petroleum Gas – and commonly used for cooking, heating, hot water and autogas.

· When considering butane or propane gas, the difference in physical properties determines which gas is best for a particular application.

· Propane has a lower boiling point, at -42°C vs -0.4°C for butane. So, propane 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. This lower pressure 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.

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

Ø Butane is a gas when not under pressure and at normal room temperatures. Butane is a flammable hydrocarbon gas that is liquefied through pressurisation. Butane is a gas that also falls under the category of "LPG". It is classified as LPG, along with propane, isobutane and mixtures of these gases.

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

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

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

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

Ø Butane 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.

What is Isobutane?

ü Isobutane (i-butane) is an isomer of butane.

ü 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)

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

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

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

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

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

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

ü It 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?

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

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

Ø Propane comes from natural gas processing and oil refining.

Ø It is commonly used for heating and cooking.

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

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

Ø Large users may utilise bigger LPG storage tanks.

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

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

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

Ø 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

Propane, Butane & Isobutane 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…

Isobutane vs Butane vs 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