Fuels - Revision

1. Fuels - Revision • A fuel is a substance that burns releasing energy. • Crude Oil is a mixture of different Hydrocarbons which a can be used as fuels. • Fractional distillation separates crude oil into the separate fractions – According to their BP.

2. Petrol • The petrol fraction of crude oil is an important fuel. • The straight chain molecule is not a good fuel in an engine. • If the molecule has branches in it or has an aromatic structure (ring) it will perform better as a fuel.

3. Ignition • Petrol Ignition • Petrol vapour mixes with air and is ignited by a spark. • The more volatile the fuel the readier it vaporises. Petrol is a mixture of volatile Hydrocarbons. • This is beneficial in colder temperatures. The petrol is blended with small molecules. • In summer the petrol is blended with larger molecules to stop it vaporising too easily!

4. Auto ignition • When the engine is hot the fuel – air mixture may auto – ignite! • Sometimes called “knocking” or “ pinking”. • Lead was previously added to fuels to prevent this. • Unleaded fuels need to have more branches or aromatic hydrocarbons to ensure efficient combustion and reduce “ knocking”

5. Naptha • Naptha is a fraction of crude oil. • It is an important feed stock. • We can alter it to produce many useful chemicals.

6. Reforming • We can rearrange the structure(reform) or encourage isomerisation of a fuel to increase it’s efficiency. • Example • Taking straight chained molecules and reform to give compounds with branches in their structure. • Removing Hydrogen – dehydrogenation from cyclohexane (C6H12) to produce benzene.(C6H6)

7. Pollution • Carbon monoxide production – solution – increase air/fuel ratio. • NOx – soluble – acidic! Produce when ignition spark provides energy for N2 bond to break. • Both problems can be reduced by catalytic converter. • Remove sulphur from fuel prior to combustion – reduce SO2 production < acid rain! • Too much burning fossil fuels -CO2 -Greenhouse effect!

8. Renewable Energy • Fossil fuels are unfortunately finite! • Ethanol – Fermentation of sucrose from sugar cane – engine fuel – CO2 and H2O produced in combustion. • Anaerobic conditions result in incomplete combustion of some bio matter – methane is produced as a by product – this can be used as a fuel!

9. Methanol • Methanol can be used as a fuel.

10. Making Methanol • Fermentation reactions. • Made from synthesis gas ( CO + H2) • Synthesis gas is made from fossil fuels or from biogas.

11. Hydrogen Economy • Can be a portable fuel. • It combusts to produce – water. No greenhouse emissions! • It is produced by splitting H compounds. • The energy required to split compounds is more than that released when H burns – energy loss!

12. Hydrogen cnt. • It could produce electricity in a H/O cell. • It can be stored like natural gas. • It could become economically efficient if we got the H from non fossil fuel compounds. • Produce by electricity of water using solar cells.

13. Renewable Energy • Solar power • Wind • Wave