oil refining + octane numbers
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Oil Refining + Octane Numbers. Fractional Distillation of Crude Oil. How to become a millionaire .......... Find a crude oil well and know how to fraction it!! Crude oil found in large quantities in Iran , USA, Nigeria, Russia, North Sea. Fossils. - PowerPoint PPT PresentationTRANSCRIPT
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Oil Refining + Octane Numbers
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Fractional Distillation of Crude Oil
• How to become a millionaire .......... Find a crude oil well and know how to fraction it!!
• Crude oil found in large quantities in Iran , USA, Nigeria, Russia, North Sea
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Fossils
• Crude oil was formed from the bodies of tiny sea creatures that died millions of years ago
• Crude oil is pumped from underneath the ground as is a thick black substance with an unpleasant smell
• It does not burn easily and must be undergo fractional distillation to separate out all the useful components
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• Fractional Distillation • The crude oil is heated in a furnace and starts to
evaporate, the longer carbon chains are heavier and do not rise as easily as shorter (lighter) carbon chains
• This means that the longer chains carbon fractions are collected first while the shorter chains get collected higher up the column
• Remember larger hydrocarbons have higher boiling points while smaller hydrocarbons have lower boiling points
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Fractionating ColumnNB. You do not need to memorise the temperatures but you do need to learn the fractions and the uses of the products of each fraction
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Fractionating Column at Whitegate Oil Refinery
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Refinery Gas• Top of the column, methane,
ethane, propane + butane are gases at 25⁰C
• Some used as fuel mostly bottled for sale
• Since these are odourless sulfur compounds called Metacarptants are added for safety
• Bottled gas is mainly a mix of propane + butane which are liquefied under high pressure
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Petrol (Light Gasoline)• Used as motor fuel• A mixture of at least
100 compounds mostly hydrocarbons of 5-10 carbons
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Naphta
• Very useful to petrochemical industry
• It is a source for a huge number of useful chemicals eg, medicines, plastics, synthetic fibres, detergents, solvents etc.
• 7-10 carbons in length
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Kerosene/Parrafin• Used as aviation fuel
and in certain lamps• 10-14 carbon length• NB as the number of
carbon atoms increases so does the boiling point as more heat is required to break the larger number of bonds
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Diesel Oil/GasOil
• More difficult to vaporise than petrol
• Therefore diesel engine has a different design
• Trucks, buses, trains and some cars use diesel
• 14-19 carbon length
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Lubricating Oil• 19-35 carbons in length• Cannot be vaporised
easily so cannot be used as a fuel
• Used as a lubricant to reduce wear and tear
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Fuel Oil
• 30-40 carbons in length • Used in ships, power
stations, heating plants, oil heating in homes
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Bitumen• More than 35 carbon
atoms in length• Very high boiling point• Used in Tar to resurface
roads
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When an oil well is discovered..
• Refinery Chemists analyse crude oil to determine the quality of the oil and assess the quantity of each product in the oil
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Octane Number
• Petrol obtained from the fractionating column is not a very efficient fuel
• In the internal combustion engine in a car the power to turn the wheels is produced by the explosive reaction between air and petrol
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Knocking
• Smooth running of an engine depends on this explosion occurring at exactly the right time
• If the explosion occurs too early the pistons vibrate and a metallic noise is heard from the engine
• Early explosion can occur if the petrol + air explode when they are compressed instead of waiting for the spark
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• This early explosion is referred to as knocking or auto-ignition
• Straight chain alkanes such as nonane, octane and heptane ignite very easily and explode too soon
• Branched cahin alkanes such as 2,2,4-trimethylpentane (iso-octane) do not tend to auto-ignite
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• Petrol mixtures with large amounts of branched chain alkanes are more efficient than those which contain straight chain molecules
• To indicate the efficiency of a particular type of petrol a number called the Octane Number is assigned to it
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Octane Number
• The octane number of a fuel is a measure of the tendency of the fuel to resist knocking
• Since 2,2,4-trimethylpentane is a very efficient fuel it is assigned an octane number of 100
• Heptane is not an efficient fuel and is assigned an octane number of 0
• The octane number of a fuel is calculated by comparing it’s efficiency in an engine to 2,2,4-trimethylpentane and heptane
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What should my petrol be??
• Chemical analysis can also indicate the octane number of a fuel
• Good quality petrol should have an octane number of 97
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• The shorter the alkane chain the higher the octane number
• Which do you think would have a higher octane number hexane or pentane?
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• The more branched the chain the higher the octane number
• Which do you think would be the best fuel heptane, 3-methylhexane,
2,3,-dimethylpentane
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• Cyclic compounds have a higher octane number than straight chain compounds
• Which is a better fuel? Hexane or cyclo-hexane??
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Making Petrol• 1920’s it was found that
adding small amounts of lead compounds to petrol helped reduce the amount of knocking
• Lead pollution from car exhausts had potential damage to health and was phased out since 2000
• Lead also damaged catalytic converter in car exhausts
• Now have unleaded petrol
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Increasing octane number of fuel
• This is now achieved in one of the following 4 ways;
1. Isomerisation2. Catalytic Cracking3. Reforming4. Adding Oxygenates
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Isomerisation
• This involves changing straight chain alkanes into their isomers
• Alkanes are heated in the presence of a suitable catalyst and the chains break
• The chains are allowed to reconnect but they are more likely to reform in branched-chains than in straight-chains
• This is commonly done on a large industrial scale with pentane and hexane (NB fig 21.29)
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Catalytic Cracking
• Catalytic cracking is the breaking down of long chain hydrocarbon molecules into short chain molecules for which there is greater demand
• In oil refineries the heavier fractions ( such as fuel oil, diesel oil and kerosene) are heated in the presence of a catalyst
• The short chain alkanes produced tend to be highly branched and hence have a high octane number
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Reforming (Dehydrocyclisation)
• Reforming involves the use of catalysts to form ring compounds
• Straight chain alkanes are converted to cycloalkanes and these are converted to aromatic compounds
• Aromatic compounds have high octane numbers and petrol contains 3-4% benzene, because benzene is a carcinogen this is a cause for concern
• Hydrogen may also be produced in reforming reaction, this is a useful substance and may be piped away for various purposes
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Adding Oxygenates
• An oxygenate is any fuel that contains oxygen in its molecules
• 3 oxygen containing compounds, methanol, ethanol and MTBE are commonly added to petrol to increase its octane number
• Another advantage to adding oxygenates to fuel is that they cause very little pollution when they burn and are cleaner fuels