Rachael explains about Petroleum Refining.
Fossil fuels such as coal, petroleum and natural gas are important sources of energy for industrialised countries.
These fuels, which are mixtures of hydrocarbons, are burned in air or oxygen to release energy. However fossil fuels, particularly petroleum (crude oil) and natural gas, have another important use.
They are an invaluable source of raw materials for the petrochemical industry. About 95% of all synthetic carbon compounds, including plastics, resins and solvents, are derived from compounds produced from petroleum and natural gas.
Separation into fractions
Crude oil can be separated into various fractions by the process called fractional distillation. Separation into fractions is based on differences in boiling points of the hydrocarbon components. The crude oil is vaporised and the vapour mixture rises up the fractionating column.
The short-chain hydrocarbons have lower boiling points and rise higher in the column before condensing. The long-chain hydrocarbons condense in the lower parts of the column. The liquid fractions are removed at various levels.
The residue consists of long-chained bituminous solids that are periodically removed from the base. The nature and composition of the fractions varies somewhat between refineries.
Which physical property enables hydrocarbons to be separated during the process of fractional distillation?
Different fractions of the hydrocarbons with different boiling points will condense at different stages along the fractionating column.
Longer chain hydrocarbons with higher boiling points will condense lower down the column at higher temperature conditions.
Lower chain hydrocarbons with lower boiling points will condense higher up the column at lower temperature conditions.
What types of intermolecular forces exist between hydrocarbon molecules? Explain the origin of these forces.
Hydrocarbon chains are non-polar substances.
These non-polar molecules will have vacillating instantaneous charges at either ends creating temporary dipoles.
These instantaneous dipoles are weak and induce temporary dipoles in neighbouring molecules.
Weak dipoles that are oppositely charged bond to form dispersion forces.
Explain why the melting point and boiling point of alkanes increase as the size of the molecule increases.
Increasing molecular mass in larger molecules causes greater dispersion forces due to a greater number of electrons that are able to make relatively stronger temporary dipoles.
Greater dispersion forces will require larger quantities of energy to overcome, hence a high melting and boiling point for hydrocarbons of larger sizes.
Composition of Petroleum
Describe the composition of petroleum.
Petroleum consists of crude oil and natural gas. Petroleum contains a mixture of up to 300 hydrocarbons, as well as sulfur am nitrogen compounds. Crude oil (liquid petroleum) contains mainly alkanes and alkenes from C1 to about C25.
Natural gas is a mixture of methane (75-90%), ethane (5-10%), propane and butane (3-6%) and smaller amounts of other alkanes. It may also contain nitrogen, water vapour, carbon dioxide and traces of hydrogen sulfide.
Is petroleum renewable? What are the environmental implications?
Petroleum is a non-renewable resource.
It is not greenhouse neutral. When they are burned, carbon is effectively transferred from the underground reserves of fossil fuel to the atmosphere where carbon dioxide is a major greenhouse gas.