Properties of Ethene (ethylene)

deepu_0088

colourless gas at room temperature and pressure
Melting point -169^oC, Boiling point -104^oC
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 1,2-dibromoethane
Addition of Chlorine	CH₂=CH₂ + Cl₂	AlCl₃ ----->	CH₂ClCH₂Cl 1,2-dichloroethane
Addition of Hydrogen bromide	CH₂=CH₂ + HBr	AlCl₃ ----->	CH₃CH₂Br bromoethane
Addition of Hydrogen chloride	CH₂=CH₂ + HCl	AlCl₃ ----->	CH₃CH₂Cl chlorooethane
Addition of Hydrogen	CH₂=CH₂ + H₂	Ni -----> 500^oC	CH₃CH₃ ethane
Addition of Water	CH₂=CH₂ + H₂O	H₃PO₄ -----> 300^oC	CH₃CH₂OH ethanol
Combustion	CH₂=CH₂ + 3O₂	excess air ----->	2CO₂ + 2H₂O

Production of Polythene (polyethylene)	nCH₂=CH₂	catalyst --------> high pressure	(CH₂-CH₂)n
Production of Industrial Alcohol (ethanol)	CH₂=CH₂	(1)H₂SO₄ --------> (2)H₂O	CH₃-CH₂OH
Production of 1,2-ethanediol (ethylene glycol)	CH₂=CH₂	(1)O₂/catalyst --------> (2)H₂O	CH₂OH-CH₂OH
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

Ethene can be produced either by

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

The cracking process typically involves endothermic equilibrium reactions such as:

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.