Alkanes

How is crude oil separated?

Fractional distillation

How is petroleum separated?

Fractional distillation

Process: Fractional distillation

• crude oil heated to form a vapour

• Gas passes into fractionating column with negative temperature gradient

• Fractions condense at a height where the temperature is lower than their boiling point

Order of compounds in the fractionating column

Cracking

• breaking c-c bonds in log chain hydrocarbons into short chain hydrocarbons

Economic reasons for cracking

• most useful fractions contain shorter chain hydrocarbons

• Most in demand “””””

Thermal Cracking Condition

Temperature: 700-1200K

Pressure: 7000kPa

Thermal cracking mostly produces

• high percentage of alkanes

Catalytic Cracking Conditions

Temperature: 720K

Pressure: 5atm 9(mild)

Catalyst: Zeolite catalyst

Catalytic cracking mostly produces

• Motor fuels

• Aromatic hydrocarbons

Features of zeolites

• honeycomb structure with large SA

Benefits of catalytic cracking

• catalytic cracking is cheaper

• Lower pressure used

Complete Combustion

• sufficient oxygen present

• → carbon dioxide + water

Incomplete Combustion

• insufficient oxygen

• → carbon monoxide/carbon (soot(solid)) + water

Pollutants of internal engine combustion

• carbon monoxide

• Nitrogen oxides

• Sulphur dioxide

Carbon Monoxide as a pollutant

• a result of incomplete combustion of petrol vapour

Sulphur dioxide as a pollutant

• sulphur converted to sulphur dioxide

• (Unless removed from atmosphere) forms sulphuric (IV) acid

• Forms acid rain

Flue gases

Mixture of waste gases

Removal of sulphur dioxide

• using calcium oxide/ calcium carbonate in acid-base reaction

Nitrogen Oxides as pollutants

• nitrogen has a triple bond

• requires a lot of energy to break

• High temperatures of engine provide enough energy

Equation for nitrogen oxides

Nitric acid formation

• nitrogen monoxide oxidised to nitrogen dioxide

• Nitrogen dioxide reacts with atmosphere to form nitric acid

4NO₂(g) + 2H₂O(l) + O₂ → 4HNO₃(aq)

Catalytic converter

• platinum catalyst used in catalyst converters

• Nitrogen oxides oxidise carbon monoxide to carbon dioxide and are themselves reduced

What happens to unburnt hydrocarbons in the catalytic converter?

• they are oxidised to carbon dioxide and water

Nitrogen monoxide removed from catalytic converters

• when reacted with octane

Chlorination of Alkanes Steps

FREE RADICAL SUBSTITUTION

1. Initiation

2. Propagation

3. Termination

Initiation

• UV radiation provides energy to break chlorine molecule into 2 chlorine free radicals

First propogation

• chlorine radical reacts with alkane

• Halogen halide + alkyl radical

Second Propogation

• Alkyl radical reacts with halogen molecule

• → Halogenoalkane + chlorine radical

Termination

Requirements for free radicals substitution

• UV Radiation