Organic chem:fractional distillation

[jadelamlam]

Hi,
During fractional distillation,crude oil is heated to a certain temperature,then it is pumped into the fractional tower.
As you know,petroleum is a mixture of alkanes.When it is heated in the furnace(to about 400°C),it does not burn.But lower alkanes(e.g.CH4) are extremely flammable,why it doesn't burn at 400°C?

 

[DrDu]

Probably because you carefully avoid contact with air or oxygen.

 

[jadelamlam]

Oh,is that means,petroleum is heated with the absence of air in the furnace?

 

[DrDu]

Yes. I suppose you flood the columns with nitrogen when you begin operation. Later on, there will be only the vapours of the various alkanes etc. in the column.

 

[jadelamlam]

Where does the nitrogen go?

 

[DrDu]

I suppose it would leave the column together with the lightes alkanes (methane, ethane) which don't condense.