Fractional Distillation

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Fractional Distillation

• By Oliver Javadi

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Crude oil

• I will be using crude oil as a recurring example
  during my PowerPoint (it represent the mixture).
• It is an exceptionally valuable resource that is
  made up mostly of alkanes.
• Crude oil is not renewable as it takes years to
  form, this makes it ever more precious.
• It is very impure, but oil is more efficient when
  it is pure.
• As there is a limited amount of oil, we need to
  minimise the amount of waste. A mechanism used to
  minimise waste is fractional distillation. The
  process will be repeated to furthermore to
  decrease the amount of waste.

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Fractional distillation

• Fractional distillation is the breaking down of a
  mixture into its component parts.
• This is done by boiling the mixture and
  separating the products by their varying boiling
  points.

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Method summary

• The mixture is separated by boiling and
  collecting each substance as it boils.
• Each substance is called a fraction, this is a
  mixture of hydrocarbons of similar chain length.
  As they are of similar chain length they have
  similar properties and therefore boil at a
  similar time.

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Method stages

• The crude oil is heated in a furnace.
• A mixture of both liquid and vapour rise, and
  pass into a tower that is cooler at the top than
  the bottom.
• The vapours pass up this tower in which there are
  trays stacked at different levels, the trays
  contain bubble caps to trap the vapour.
• As the vapour rises it gets cooler, once
  sufficiently cool the vapour will condense into
  liquid and will therefore be collected in the
  tray below.
• The shorter chained hydrocarbons condense in the
  trays nearer to the top of the tower and vice
  versa. This occurs as they have lower boiling
  points, and are therefore liquids in lower
  temperatures.

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Products
Name Approx boiling temperature (C) Uses
Petrol 40 Vehicle Fuel
Naptha 180 Industrial cleaners and solvents, petrol industry
Kerosene (paraffin) 200 Used as a gas for some heaters
Diesel Oil 250 Vehicles e.g. lorries (produces less CO2 than petrol)
Lubricating Oil 280 Reduce friction between multiple parts
Fuel Oil 310 The fuel used in ships and power stations
Greases and Wax 340 Used to make things like candles
Bitumen 367 Used for road tar and roofing
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Method flaws

• Small collections/pockets of certain length
  hydrocarbons may get trapped in trays that dont
  corresponded with there boiling point.
• Also some substances have overlapping boiling
  points (as shown in the table) and will therefore
  remain mixed.
• Pollutants are created, some pollutants may
  induce taxes or disposal expenses.
• There are lots of products that are less valuable
  that are produced.

Product Gases Petrol Naptha Kersosene Gas oil Fuel oil and wax
Approximate boiling point/ K 310 310-450 400-490 430-523 590-620 Above 620
Chain length 1-5 5-10 8-12 11-16 16-24 25
Percentage Present 2 8 10 14 21 45
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Industrial cracking

• Individual fractions all have different values,
  the general trend is that the longer the
  fractions are the less valuable they are. The
  naphtha fraction from the fractional distillation
  of crude oil is in huge demand, this makes it
  valuable as buyers will be competing for it. This
  fraction is desired for petrol and by the
  chemical industry.
• Industrial cracking is used to crack larger
  chains into more valuable shorter chains.
• An additional benefit of cracking is that some
  alkenes are produced, alkenes are more reactive
  than alkanes and therefore have some desirable
  uses.
• There are two sub-categories of industrial
  cracking. Thermal cracking and Catalytic cracking

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Thermal cracking

• This involves heating alkanes to a high
  temperature (700-1200K),and putting them under
  high pressure, up to 7000kPa.
• Such high amounts of energy are required to break
  carbon-carbon bonds. These bonds break in a way
  that one electron from the pair in the covalent
  bond goes to the end carbon atom in each chain,
  one of chains pulls hydrogen off of the other,
  consequently one of the chains needs to be double
  bonded to fulfil the necessary amount of bonds,
  this is how the alkenes are formed.

Thermal Cracking
Free radicals- electrons dot

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Catalytic cracking

• Catalytic cracking is very similar to thermal
  cracking, but less energy is used (lower
  temperature and pressure), temperature approx.
  720K.
• As there is less energy used a catalyst is
  required to make the reaction successful. The
  catalyst used is a Zeolite catalyst. Zeolites
  have a honeycomb structure with an enormous
  surface area, because of these properties it will
  have particularly regular collisions.
• The products of catalytic converting are mostly
  branched alkanes, such as cyclokanes and aromatic
  compounds.

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Bibliography

• Fractional distillation diagram-http//www.pustaka
  laya.org/wiki/images/99/9903.png
• Thermal cracking diagram- Andrew Inghams
  PowerPoint