A process which is carbon neutral releases no net carbon dioxide emissions into the atmosphere.

Methanol and ethanol, both of which are alcohols, released energy when burnt making them fuels. They are favoured against hydrocarbons because they do not tend to produce as much polluting gas.

However, ethanol is produced from ethene which in turn is produced from crude oil, a non-renewable source. In addition, when ethanol is burnt carbon dioxide is released making this a not carbon-neutral process.

Likewise, methanol is produced from reacting methane or propane with steam, making this form of production non-renewable. Burning methanol releases carbon dioxide so the process is not carbon-neutral either.

However, it has also been shown that these fuels can be used in a carbon-neutral as well as renewable was under certain circumstances.

Ethanol can be created from fermenting glucose. Glucose can be produced from planting sugar, a renewable source. In addition, the overall process involved in producing the ethanol is carbon-neutral:

• Glucose production: 6CO₂ + 6H₂O ? C₆H₁₂O₆ + 3O₂ (six carbon dioxide molecules absorbed)
• Glucose fermentation: C₆H₁₂O₆ ? 2C₂H₅OH + 2CO₂ (two carbon dioxide molecules released)
• Ethanol combustion: C₂H₅OH + 3O₂ ? 2CO₂ + 3H₂O (two carbon dioxide molecules released per ethanol molecule so four carbon dioxide molecules released per two ethanol molecules).

Total carbon dioxide emissions: -6 + 2 + 4 = 0

Therefore the process carbon-neutral.