As fuels
3 marks · EasyThe diagram shows a simplified fractional distillation column for crude oil. The temperature at three different positions is marked.
The temperature at the bottom is 370 C, in the middle is 220 C, and at the top is 40 C.
State what happens to the hydrocarbons as their vapours rise up the column.
Name the fraction collected at the top of the column.
Explain why some hydrocarbons are collected at the bottom instead of higher up.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) They condense (turn to liquid) at different heights as the temperature drops.
(b) refinery gases
(c) They have very high boiling points and remain as liquids at the bottom because the temperature is only high enough there.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Explains that hydrocarbons condense at different levels as vapours rise and temperature falls
B1 (b) · 1 mark · Identifies refinery gases as the fraction at the top
B1 (c) · 1 mark · States high boiling point hydrocarbons collected at bottom as they don't vaporize at lower temperature
Worked solution
a) As vapours rise, hydrocarbons condense at the level where the temperature matches their boiling point.
b) The fraction collected at the top is refinery gases.
c) The hydrocarbons collected at the bottom have high boiling points and do not vaporize even at the bottom's high temperature.