2 - Fractional distillation of crude oil

Question 1

What are alkanes?

Answer 1

Saturated hydrocarbons

Question 2

What is crude oil?

Answer 2

A mixture of mainly alkane hydrocarbons

Question 3

What is fractional distillation?

Answer 3

A technique used to separate hydrocarbon components of crude oil based on their boiling points

Question 4

Briefly describe the process of fractional distillation

Answer 4

• Crude oil is heated in a furnace at about 350°C and vapourises
• Vapours enter a fractionating column where higher temps are at the bottom and lower temps are at the top
• As vapours rise through the column, they cool down
• When the temperature of the vapour drops below the boiling point of the HC in the mixture it will condense on the tray
• The condensed HC liquids will accumulate on each tray and are drawn off at specific intervals as fractions

Question 5

What is the trend in boiling point down the fractionating column?

Answer 5

Increases down as alkane chain length increases

Question 6

What is the trend in viscosity down the fractionating column?

Answer 6

Increases down as HC mixture becomes heavier

Question 7

What is the trend in flammmability down the fractionating column?

Answer 7

Decreases as lighter gases ignite easily and heavier fractions are less flammable