Fuels (Extended Response)

Question 1

Crude oil is a complex mixture of hydrocarbons.
Most belong to the alkane homologous series.
Diesel oil is a fuel produced from crude oil.

Explain how diesel oil is separated from crude oil.

Answer 1

• crude oil separated into different fractions by fractional distillation
• crude oil heated to about 350C to evaporate it
• some hydrocarbons stay in the liquid state and leave at the bottom of the column
• the other hydrocarbons rise inside the fractionating column in the gas state
• temperature gradient
• cooler towards the top, so the hydrocarbons cool down as they rise
• hotter towards the bottom
• condense to liquid state when they reach a part of the column cool enough/below boiling point
• gases do not condense and leave at the top
• diesel oil leaves through a pipe as a liquid fraction when it condense
• it leaves third from the bottom

(-smaller hydrocarbons have lower boiling points because they have weaker intermolecular forces
-this means they need less energy to break the forces and change state)

Question 2

Diesel oil is used as a fuel for some cars and trains.
Scientists and engineers are researching ways to use hydrogen as a fuel for cars instead of diesel oil.

Evaluate the use of hydrogen as a fuel for cars. rather than diesel oil.

Answer 2

advantages of hydrogen:

• only product is water
• hydrogen can be produced by electrolysis of water
• renewable if made from water
• electricity needed could come from renewable sources
• no CO2 released

disadvantages of hydrogen:

• expensive to produce
• difficult to store
• stored under pressure/low temp
• few filling stations
• usually produced from natural gas/coal
• CO2 released in these processes

advantages of diesel oil:

• liquid at room temp
• easy to store
• many filling stations
• cheaper to produce and transport
• technology already in place

disadvantages of diesel oil:

• CO2 is also produced
• CO2 is a greenhouse gas linked to climate change
• produced from crude oil, non-renewable
• produces carbon/soot
• produces sulfur dioxide (unless removed)
• produces oxides of nitrogen
• sulfur dioxide, Nx, produce acid rain