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Fuels are a source of readily available chemical energy.
Fuels can be renewable of non-renewable.
Non-renewable- resources are those that are used at a rate faster than they can be replaced.
Sustainability is all about meeting the long term ongoing needs of society, as well as immediate and short term demands.
Fossil fuels- non-renewable fuels.
•Fossil fuels were formed from ancient plants, animals and microorganisms.
•The organic matter still retains some of the chemical energy the plants originally accumulated by carrying out photosynthesis.
•Fossil fuels formed over millions of years.
Fuels from crude oil
•Crude oil is a mixture of hydrocarbon molecules – mostly alkanes.
•Crude oil is separated into a number of fractions by fractional distillation.
•Fractional distillation does not produces pure substances.
•Biochemical fuels (biofuels) are derived from plant materials e.g. grain, sugarcane or vegetable waste and oils. The two main biofuels are bioethanol and biodiesel.
•Burning biochemical fuels is not considered to increase atmospheric CO2 levels as the photosynthesis process used to produce the plant matter, removed an equal amount of CO2 from the atmosphere. They are said to be carbon neutral!
6 CO2 (g) + 6 H2O (l) → C6H12O6 (aq) + 6 O2 (g)
(in the presence of sunlight)
The glucose produced is converted to cellulose and starch
•In the formation of bioethanol, starch in plants is broken down into glucose by enzymes and is then fermented to ethanol and carbon dioxide in the absence of oxygen (No oxygen = anaerobic conditions)
•. Fermentation stops when the ethanol content is between 10-20%
C6H12O6 (aq) → 2CH3CH2OH (aq) + 2CO2 (g)
•Because the ethanol is in an aqueous form, steam is added and ethanol evaporates. This solution (95% ethanol) is then dehydrated to 99.7% pure ethanol
Advantage of ethanol as a fuel
•when added to petrol, it reduces the quantity of air pollution particles from car exhausts.
Biodiesel is a mixture of esters (compounds containing a COO link) formed by the reaction of vegetable oils and an alcohol. The oil is first hydrolysed into its two main parts – glycerol and 3 fatty acid chains. The COOH group from the fatty acid then reacts with the OH group of the alcohol and a link is made.
Advantages of Biodiesel
•produces fewer pollutants in vehicle emissions
Biodiesel diagram courtesy of By E8 (E8) - self-made using ChemSketch10, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=3191466
Fractional distillation diagram courtesy of E. Generalic, http://glossary.periodni.com/glossary.php?en=fractional+distillation
Diesel and Petrol Engines
Diesel engines have a better fuel economy compared to petrol engines, they also produce less carbon dioxide emissions than petrol engines.
Dodecane an example of a petrodiesel molecule.
Diagram courtesy of By Walkerma - Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=15777413
Piston animation courtesy of By MichaelFrey - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=41674923