Fractional Distillation and Cracking Processes

Fractional Distillation

• Crude oil is a mixture of hydrocarbons with varying chain lengths.
• Fractional distillation is a process used to separate crude oil into individual fractions.
• The process relies on the different boiling points of hydrocarbons due to their chain lengths.
• Longer carbon chains have higher boiling points and condense lower in the fractionating column.
• Shorter carbon chains have lower boiling points and condense higher in the fractionating column.

Cracking

• Cracking breaks down longer (less useful) hydrocarbon chains into smaller, more useful molecules.
• This involves breaking carbon-carbon bonds under harsh conditions.
• Thermal Cracking uses high temperatures and pressures to produce alkanes and alkenes.
• Catalytic Cracking uses lower temperatures and a zeolite catalyst to produce aromatic compounds.

Combustion of Alkanes

• Alkanes are good fuels due to their energy release during combustion.
• Complete combustion with sufficient oxygen results in carbon dioxide and water.
• Incomplete combustion produces carbon monoxide and water due to insufficient oxygen.
• Carbon monoxide is toxic and odorless, posing health risks.

Catalytic Converters

• Catalytic converters are used to remove harmful combustion products.
• A rhodium catalyst converts carbon monoxide and nitrogen oxides into CO2 and H2O.

Carbon Particulates

• Incomplete combustion can produce carbon particulates, which are unburned hydrocarbon fragments.
• Carbon particulates are harmful to human health, contributing to respiratory problems.

Flue Gas Desulfurisation

• Sulfur impurities in fuels lead to the formation of H2SO4, contributing to acid rain.
• Flue gas desulfurisation removes sulfur impurities using calcium oxide and gypsum.

Chlorination of Alkanes

• Alkanes react with halogens in the presence of UV light to form halogenoalkanes.
• This reaction proceeds through a mechanism involving free radicals.
• Initiation: Halogen molecules break down into free radicals upon exposure to UV light.
• Propagation: Free radicals attack alkanes, replacing hydrogen atoms and regenerating the halogen radicals.
• Termination: Two free radicals combine to form stable products, ending the chain reaction.
• Multiple substitutions can occur, making the process a chain reaction.
• Reaction conditions can be adjusted to favor termination and limit substitution.