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Ethene (ethylene):Properties, Production & Uses

Properties of Ethene (ethylene)

  • colourless gas at room temperature and pressure
    Melting point -169oC
    Boiling point -104oC

  • slightly sweet smell

  • flammable

  • non-polar molecule
    soluble in non-polar solvents & insoluble in polar solvents like water

  • reactive: the active site is the double bond
    Readily undergoes addition reactions, for example
    reacts with bromine water (red-brown) to produce colourless 1,2-dibromoethane
    CH2=CH2(g) + Br2(l) -----> CH2Br-CH2Br(g)

Reactions of Ethene (ethylene)

Addition of Bromine CH2=CH2 + Br2 -----> CH2BrCH2Br

Addition of Chlorine CH2=CH2 + Cl2 AlCl3

Addition of Hydrogen bromide CH2=CH2 + HBr AlCl3

Addition of Hydrogen chloride CH2=CH2 + HCl AlCl3

Addition of Hydrogen CH2=CH2 + H2 Ni

Addition of Water CH2=CH2 + H2O H3PO4

Combustion CH2=CH2 + 3O2 excess air
2CO2 + 2H2O

Uses of Ethene (ethylene)

Production of Polythene
nCH2=CH2 catalyst
high pressure

Production of Industrial Alcohol
CH2=CH2 (1)H2SO4

Production of 1,2-ethanediol
(ethylene glycol)
CH2=CH2 (1)O2/catalyst

Production of Styrene
styrene can be polymerised to form polystyrene
CH2=CH2 benzene

Production of chloroethane
chloroethane is used to manufacture tetraethyl lead

tetraethyl lead is the lead additive in leaded petrol
CH2=CH2 + HCl -----> CH3-CH2Cl

Ethene is also used as a plant hormone to control the ripening and colour development of fruit

Production of Ethene (ethylene)

Ethene can be produced either by

  1. Extraction from natural gas using fractional distillation followed by steam cracking (the technique for converting alkanes to alkenes)(750 - 900oC) followed by liquefaction of the gas (-100oC) and then further fractional distillation
  2. Extraction from crude oil using fractional distillation followed by steam cracking (750 - 900oC) of the naphtha or gas-oil fractions followed by liquefaction of the gas (-100oC) and then further fractional distillation.

The cracking process typically involves endothermic equilibrium reactions such as:

  • C2H6(g) C2H4(g) + H2(g)       ΔH = +138 kJ mol-1

  • C3H8(g) C2H4(g) + CH4(g)       ΔH = +81 kJ mol-1

To maximize the rate of the cracking reactions

  • the temperature can be increased so that the gas particles move more quickly and collide more often

  • increase the pressure which forces the gas particles closer together and collide more often

  • no catalyst is needed to increase the rate of this reaction since the steam provides the required activation energy

To maximize the yield of ethene, by Le Chetalier's Principle

  • increasing the temperature of the reactions favours the formation of products since the reactions are endothermic. So increasing the temperature speeds up the rate of the reaction and increases the yield of ethene.

  • a decrease in pressure would favour the the formation of products since there are more gaseous product molecules than there are gaseous reactant molecules. However, a decrease in pressure would slow down the rate of the reaction. For this reason the pressure is kept at or below atmospheric pressure.

  • removing the product will favour the formation of more product thereby increasing the yield of product. Equilibrium is therefore never actually achieved.

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