alkane and fuels

• Crude oil

  Hydrocarbon containing a mixture of alkanes
• Unsaturated hydrocarbon


  A hydrocarbon containing one or more C=C
• Fractional distillation

  The process used to refine crude oil
• Fractional distillation

  1. Vaporisation - heat to 350°C

  2. Temperature gradient of column - Cold at top / Hot at bottom

  3. Fractions separate due to different boiling points

  4. Low boiling point → small molecule → collect at top
• Cracking

  Allows long chain, less useful alkanes to be broken up into shorter chain more useful alkanes and alkenes
• Types of cracking

  • Thermal cracking (high T&P) → alkenes
  • Catalytic (slightly higher than atmospheric pressure & high T/zeolites) → alkanes and aromatics
• Cracking of dodecane (C12H26)

  C12H26 → C4H8 + C8H18
• But-1-ene

  Used to make polybutene
• Alkane product of cracking dodecane

  Used as fuel
• Complete combustion of alkanes

  Alkane + Oxygen → Carbon dioxide + Water

  
• Alkanes release a massive amount of energy when they combust and so make great fuels
• Complete combustion of hexane

  C6H14 + 9.5O2 → 6CO2 + 7H2O

  
• Incomplete combustion of alkanes with limited oxygen

  C4H10 + 5.5O2 → 2CO2 + 2CO + 5H2O

  1. C4H10 + 4.5O2 → 4CO + 5H2O
  2. C4H10 + 2.5O2 → 4C + 5H2O

  
• Carbon monoxide gas produced in incomplete combustion is poisonous
• Incomplete combustion of dodecane (C12H26)

  C12H26 + 12.5O2 → 12CO + 13H2O

  
• Complete combustion of methane

  CH4 + 2O2 → CO2 + 2H2O
• Incomplete combustion of methane

  CH4 + O2 → C + 2H2O

  1. CH4 + 1.5O2 → CO + 2H2O
• Complete combustion of butane

  C4H10 + 6.5O2 → 4CO2 + 5H2O
• Incomplete combustion of butane

  C4H10 + 4.5O2 → 4CO + 5H2O

  1. C4H10 + 2.5O2 → 4C + 5H2O

  
• Carbon particles (soot) can be formed in extreme cases of incomplete combustion with very limited oxygen
• Pollutants from combustion

  • Carbon particles (soot)

  Unburnt hydrocarbons

  Carbon monoxide

  Carbon dioxide

  Sulfur dioxides (SOx)

  Nitrous oxides (NOx)
• Carbon particles (soot)

  Formed by incomplete combustion of fuel
• Unburnt hydrocarbons

  Formed by incomplete combustion of fuel
• Carbon monoxide

  Formed by incomplete combustion of fuel
• Carbon dioxide

  Formed by complete combustion of fuel
• Sulfur dioxides (SOx)

  Formed by combustion of sulfur impurities in fuel (coal/oil)
• Nitrous oxides (NOx)

  Formed when nitrogen and oxygen from the air react at high temperature and pressure inside engine
• Effects of pollutants

  • Carbon particles - breathing difficulties, cardiovascular problems

  Unburnt hydrocarbons - react with NOx to form low-level ozone, causing respiratory problems

  Carbon monoxide - poisonous gas, combines with haemoglobin

  Carbon dioxide - greenhouse gas, contributes to global warming

  Sulfur dioxides - acid rain, destroys trees/vegetation, kills fish, corrodes buildings

  Nitrous oxides - acid rain
• Methods of reducing/removing pollutants

  • Filters to remove particulates

  Catalytic converters

  Use better quality low sulfur fuel

  Scrubbers to neutralise SO2 with CaO or CaCO3

  Use less fuel, alternative fuels

  Flue gas desulfurization (FGD) to remove SO2
• Combustion of butanethiol (C4H9SH)

  C4H9SH + 7.5O2 → 4CO2 + 5H2O + SO2

  
• Flue gas desulfurization (FGD)

  CaCO3 + 2H2O + SO2 → CaSO3 + 2H2O + CO2

  CaO + SO2 → CaSO3
• NOx does not originate from the fossil fuel being combusted, but from nitrogen and oxygen in the air reacting at high temperature and pressure
• Catalytic converter reactions

  2CO + O2 → 2CO2 (oxidation of CO and unburnt hydrocarbons)

  1. 2CO + 2NO → 2CO2 + N2 (reduction of NOx)
  2. C8H18 + 25NO → 8CO2 + 9H2O + 12.5N2 (reaction of unburnt hydrocarbons and NOx)

  
• Reasons for thin layer of Pt, Pd or Rh catalyst on honeycomb ceramic support

  • Thin layer creates larger surface area for catalysis

  1. Reduces cost as uses less of the expensive precious metal catalyst
• What is the general formula for alkanes?

  C$n$H$2n +$$2$
• What does it mean for alkanes to be saturated?

  It means they contain no double bonds and have the maximum number of hydrogen atoms.
• What distinguishes cycloalkanes from alkanes?

  Cycloalkanes have a ring structure but still do not contain double bonds.
• What is the main source of alkanes?

  Crude oil
• What is the process of fractional distillation used for in relation to alkanes?

  • Separates different lengths of hydrocarbons from crude oil
  • Involves heating crude oil to vaporize it
  • Uses a temperature gradient in the distillation column
  • Collects fractions based on boiling points
• At what temperature is crude oil vaporized during fractional distillation?

  About 350 degrees Celsius