3b.2 - Biofuels Flashcards
How can fuels be made?
Fermentation
What two types of fermentation is used to make fuel? (2)
- Using natural products
- Bacteria or yeast break down sugars with anaerobic respiration
How is ethanol made?
Anaerobic fermentation of sugar
What is the equation for the anaerobic fermentation of sugar?
Glucose -> Ethanol + CO2 + Energy
Describe the process of making ethanol (2)
- Glucose from sugar cane juices, or from maize starch by the action of carbohydrase
- Ethanol distilled to separate from yeast and remaining glucose
How is biogas made?
Anaerobic fermentation of waste material
What is biogas made from? (2)
- 70% methane
- 30% CO2
Describe the process of making biogas (4)
- Lots of different microorganisms ferment plant and animal waste
- Made in a fermenter called a digester or generator
- Needs a constant temperature
- Cannot be stored as a liquid so has to be used straight away
What types of biogas generators are there?
- Batch
- Continuous
What are batch generators?
- Make it in small batches
- Manually loaded with waste
What are continuous generators? (2)
- Make biogas all the time
- Waste is continuously fed in and produced at a steady rate
What do both batch and continuous generators use? (3)
- An inlet for waste material
- An outlet for digested material to be removed through
- An outlet so the biogas can be pumped where it is needed
What are the four factors to consider when designing a generator?
- Cost
- Convenience
- Efficiency
- Position
Why does cost need to be considered when building a generator?
Continuous generators are more expensive because waste has to be put in and removed all the time
Why does convenience need to be considered when building a generator?
Batch generators are less convenient because they have to be continually loaded, emptied and cleaned
Why does efficiency need to be considered when building a generator? (2)
- Gas is produced more quickly at 35C so insulation may be needed
- Shouldn’t have leaks
Why does position need to be considered when building a generator?
- Waste smells so shouldn’t be on your doorstep
- Needs to be near a water source
What are the advantages of biofuel? (6)
- Carbon neutral
- Doesn’t produce significant amounts of sulphur dioxide or nitrogen oxides
- Methane is not released into atmosphere as it is given off from untreated waste
- Cheap and readily avaliable
- Better fertiliser
- Waste disposal system
