2.13e: apply the concept of carbon neutrality to different fuels, such as petrol, bio-ethanol and hydrogen

Biofuels are fuels that are produced from living things, making them renewable and carbon neutral

• biodiesel:
• produced from plant oils (eg. palm oil)
• the oil is hydrolysed with sodium hydroxide to break the oils down into simple fatty acids
• the fatty acids are re-esterified with methanol to produce biodiesel
• bioethanol:
• produced from plant crops such as corn and sugarcane
• the sugar in the crops can be turned into ethanol by the action of yeast in fermentation
• glucose → ethanol + carbon dioxide

Biofuels are carbon neutral because the plants used take in carbon dioxide while they are growing (for photosynthesis), then release the same volume of carbon dioxide when we are using them as fuels

Disadvantages:

• biofuels may actually not be carbon neutral in practice
• large amounts of energy are required to operate machinery, process plant material, and process biofuels
• energy is required to produce chemical fertilisers and pesticides
• destruction of rainforests to clear land for palm trees or sugar cane
• reduces the size of carbon sinks and animal habitats
• less farmland is available for food crops
• could cause a rise in food prices and malnutrition

Biodiesel from soybeans could reduce emissions by 41% compared to normal diesel as the biodiesel is very pure and does not require distillation, saving a lot of energy

• soybeans are very hardy crops, so do not require many chemical fertilisers or pesticides

Bioethanol can be produced from the action of microorganisms on cellulose, found in straw and woody plants (not part of human food supply)

Eg. Brazil manufactures bioethanol from sugarcane and mixes it with ordinary petrol, allowing cars to use it without engine modification

• the sugar cane waste is burned to produce heat and energy for the whole refinery