Presentation on theme: "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."— Presentation transcript:
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.
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.
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!
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”
Naptha Naptha is a fraction of crude oil. It is an important feed stock. We can alter it to produce many useful chemicals.
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 (C 6 H 12 ) to produce benzene.(C 6 H 6 )
Pollution Carbon monoxide production – solution – increase air/fuel ratio. NO x – soluble – acidic! Produce when ignition spark provides energy for N 2 bond to break. Both problems can be reduced by catalytic converter. Remove sulphur from fuel prior to combustion – reduce SO 2 production < acid rain! Too much burning fossil fuels -CO 2 - Greenhouse effect!
Renewable Energy Fossil fuels are unfortunately finite! Ethanol – Fermentation of sucrose from sugar cane – engine fuel – CO 2 and H 2 O 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!
Methanol Methanol can be used as a fuel. AdvantagesDisadvantages Complete combustionHard to mix with petrol No aromatic carcinogensIt absorbs H2O – immiscible layers CheapToxic Less volatile/explosiveLess energy per volume Little modification to engine Bigger fuel tank needed
Making Methanol Fermentation reactions. Made from synthesis gas ( CO + H2)H2) Synthesis gas is made from fossil fuels or from biogas.
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!
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.