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Crude oil q

surely if you separate the hydrocarbons in crude oil, the hydrocarbons with a LOW bpt will condense with the hydrocarbons with a HIGH bpt at the bottom of the fractional distillation column?? I am confused...
(edited 5 years ago)
Reply 1
Avatar for Pigster
Pigster
20
Original post by foxstudy
surely if you separate the hydrocarbons in crude oil, the hydrocarbons with a LOW bpt will condense with the hydrocarbons with a HIGH bpt at the bottom of the fractional distillation column?? I am confused...

Consider a mixture of three substances, A has a BP of 300 oC, B is 200 oC and C is 100 oC. Just to be certain: 300 oC means the T at which is changes state from liquid to gas (and from gas to liquid).

Now heat all three to 350 oC. They're all gases, I hope you agree.

Now cool the mixture to 250 oC, i.e. still higher than the BP of B or C. Think about water. 150 oC is hotter than the BP of water (100 oC) and water is steam at this T. So B and C are still gases. But A condenses to a liquid.

Etc. etc.
Reply 2
Avatar for foxstudy
foxstudy
OP
11
Original post by Pigster
Consider a mixture of three substances, A has a BP of 300 oC, B is 200 oC and C is 100 oC. Just to be certain: 300 oC means the T at which is changes state from liquid to gas (and from gas to liquid).

Now heat all three to 350 oC. They're all gases, I hope you agree.

Now cool the mixture to 250 oC, i.e. still higher than the BP of B or C. Think about water. 150 oC is hotter than the BP of water (100 oC) and water is steam at this T. So B and C are still gases. But A condenses to a liquid.

Etc. etc.

AHH yes I get it now! I forgot that they were condensing so changing from a gas to a liquid (I've written bpt everywhere so that's why I think I got confused because they condense when they reach their bpt!)

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