DF11 Flashcards
What are some alternatives to fossil fuels?
- biofuels
- hydrogen
What are biofuels?
Alternative fuels derived from renewable plant and animal materials.
What are some example of biofuels?
- ethanol
- biodiesel
- green diesel (derived from algae)
- biogas
How can ethanol be made?
Fermentation of carbohydrate crops (e.g. sugar cane).
What are the pros of ethanol use?
carbon neutral: CO2 produced in fermentation and burning the ethanol matches CO2 absorbed by plants.
What are some issues of ethanol use?
- energy used to produce and distribute ethanol (CO2 made if fossil fuels used)
- land used to grow crops for fermentation can be used to produce food instead
What is trans-esterification?
Chemically reacting fats and oils with an alcohol to produce fatty acid esters.
How is biodiesel made?
By the process of trans-esterification.
What are the advantages of biodiesel over diesel?
- made from waste oil (instead of fossil fuel oil)
- carbon neutral
- some diesel vehicles can run on pure biodiesel
- biodegradable if spilled
- contains virtually no sulfur, so reduces oxides of sulfur in emissions
- produces less particulates, CO and hydrocarbons
What are the disadvantages of biodiesel over diesel?
Produces more nitrogen oxides than conventional fossil fuels.
What is the combustion equation for hydrogen?
2H2 + O2 → 2H20 (all gaseous)
What are the advantages of using hydrogen as a fuel?
- renewable
- made by electrolysis of water
- stored and sent down pipelines
- used in internal combustion engines
- used in fuel cells to generate electricity
- when burnt, produces no CO2, CO or hydrocarbons
What are the disadvantages of using hydrogen as a fuel?
- electrolysis depends on electricity from fossil fuel power stations
- less energy dense than petrol
- NOx still produced at high temperatures of engines
How are fuel cells used in cars?
Used to generate electricity on a small scale.
How do fuel cells generate electricity in cars?
They convert chemical energy from fuels into electricity through a chemical reaction with oxygen or another oxidising agent in a electrochemical cell.
