17.2 Refining petroleum Flashcards
What is refining petroleum?
Petrolem contains hundreds of different hydrocarbons. Refining is to separate the compounds into groups with molecules of a similar size.
Through what process is refining petroleum carried out?
Refining petroleum is carried out through fractional distillation.
Apparatus used to refine petroleum in the lab
Thermometer, Pear shaped flask, petroleum (crude oil), heat, test tube.
Refining petroleum in the lab step 1
As you heat the petroleum, the compounds start to evaporate. The ones with smslller lighter molecules go first, since it takes less energy to free these from the liquid.
Refining petroleum in the lab step 2
As the hot vapours rise, so does the thermometer reading. The vapours condense in the cool test tube.
Refining petroleum in the lab step 3
When the thermometer reading reaches 100 degrees celcius, replace the first test-tube with sn empty one. The liquid in the first test tube is your first fraction from the distillation.
Refining petroleum in the lab step 4
Collect three furhter fractions in the same way, replacing the test-tube at 150C, 200C and 300C
How can you compare fractions?
You can compare how runny they are, how easily they burn, and so on. You can burn samples on a watch glass.
Fraction 1
It catches fire easily. The flame burns high, which shows that the liquid is volatile.
Fraction 2
This catches fire quite easily. The flame burns less high, so this fraction is less volatile than fraction 1.
Fraction 3
This seems less volatile than fraction 2. It does not catch fire so readily or burn so easily, it is not so flammable
Fraction 4
This one does not ignite easily. You need to use a wick to keep it burning. It is the least flammable of the four.
Fraction 1 result summary
Boiling point range up to 100C
Very runny
Volatile
Burns very easily
Size of molecules is small.
Fraction 2 result summary
Boiling point range between 100C-150C
Runny
less volatile
burns easily
Fraction 3 result summary
150C to 200C boiling point range
not very runny
even less volatile
Doesn’t burn easily
Fraction 4 result summary
200C to 300C
viscous
least volatile
burns only with a wick
large size of molecules
Those results show that, the larger the molecules in a hydrocarbon,
-the higher its boiling point will be
-the less volatile it will be
-the less easily it will flow (or the more viscous it will be)
-the less easily it will burn
What is the set up of the petroleum refinery?
In a refinery, the fraactional distillation is carried out in a tower, that is kept very hot at the base, and cooler towards the top.
How is fractional distillation carried out in a petrol refinery?
Petroleum is pumped in at the base. The compounds start to boil off. Those with the smallest molecules boil off first, and rise to the top of the tower. Others rise onl part of the way, depending on their boiling points, then condense.
Refinery gas
C1 to C4, used as bottled gases for cooking and heating
Gasoline
C5 to C6, used as fuel for cars
Naptha
C6 to C10, used as starting point or feedingstock for many chemicals and plastics
Paraffin (kerosene)
C10 to C15, used as fuel for aircrafts, oil stoves, and lamps.
diesel oil (gas oil)
C15 to C20, used as fuel for diesel engines
fuel oil
C20 to C30, Fuel for power, ships, and for home heating systems.
lubricating fraction
C30 to C50, oil for car engines, and machinery; waxes and polishes
bitumen
C50 upwards, for road surfaces and roofs.
What happens as the molecules get larger?
As the molecules get larger, the fractions get less runny, or more viscous: from gas at the top of the tower to solid at the bottom. They also get less flammable. So the last two fractions in the table are not used as fuels.
