Biofuels are fuels derived from recently living biological material. They are considered renewable because the raw materials can be regrown within a human timescale.
Bioethanol
Production
Sugars from crops (sugarcane, corn) are fermented using yeast:
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
The ethanol is then distilled to increase concentration and blended with petrol (e.g. E10 = 10% ethanol).
Biodiesel
Production
Vegetable oils or animal fats undergo transesterification — reacting with methanol in the presence of a base catalyst:
Triglyceride + 3CH₃OH → 3 FAME + Glycerol
FAME = fatty acid methyl ester (biodiesel).
Carbon Neutrality
The Carbon Neutral Cycle
In theory, the CO₂ released during combustion equals the CO₂ absorbed during crop growth — net zero.
Think About It
Are biofuels truly carbon neutral?
Not in practice. Energy is used in farming (tractors, fertilisers), processing (distillation), and transport. Deforestation for biofuel crops also releases stored carbon. The IB expects you to evaluate these claims critically.