Cracking and catalytic converters

fractional distillation of petroleum

Oil preheated, fractions condense at diff heights, temperature of column decreases upwards, larger molecules = stronger van der waals = higher boiling point. bid molecules condense at bottom and small ones condense at top.

Vacuum distillation

heavy residues from fractionation are distilled against a vacuum which lowers its boiling point without breaking the fractions

economic reasons for cracking

- Petroleum fractions with shorter chains are more in demand like petrol.
- way of making use of excess hydrocarbons
- products of cracking are more valuable than starting materials.

thermal cracking

7000 kPa + 400 to 900 Celsius
mostly alkenes produces and some Hydrogen

Catalytic cracking

slight / moderate pressure, 450 Celsius + zeolites catalyst.
produces branched and cyclic alkanes and aromatic hydrocarbons.
used for making motor fuels.
cheaper than thermal as lower temp and pressure used.

pollution from combustion

SO2 is formed which produces acid rain.

Removing SO2

removed by reacting with basic calcium oxide in a neutralisation reaction.
SO2 + CaO --> CaSO3

Environmental pollutants

NO2 toxic and forms acid rain.
CO toxic.
CO2 global warming.
Unburnt hydrocarbons = smog
Soot = global dimming and respiratory problems

Catalytic converters

2CO + 2NO --> 2CO2 + N2
C8H18 + 25NO --> 8CO2 + 12.5N2 + 9H2O
(removes unburnt hydrocarbons like octane)
converters are coated with thin layer of catalysts like platinum, palladium and rhodium which gives a large surface area.