Fractional Distillation - Core Chemistry

Hey, I was revising about crude oil and fractional distillation. I read that at the bottom of the tower it's at really HIGH temperature (around 350 degrees) and at the top it's cooler temperatures (around 70 degrees).Anyways, it said that, as the crude oil evaporates due to the high temperature, it rises towards the top and then condenses at it's varying boiling point - aka petrol boils at 70 degrees. However, surely when it's evaporating, they should boil to different substances?? For example, at the bottom where it's hot, they put the crude oil in and it's at 350 degrees - but that's the boiling point of bitumen, so it would just boil into bitumen instead of any other substance? It sounds really confusing and I'd really appreciate any help! Thanks!

As far as I'm aware they are broken down into different fractions. So the ones with longest set of hydrocarbons condense at the bottom and the lowest at the top . Hope this helps a bit I'm not an expert really lol
Posted from TSR Mobile

crude oil is made up of all the different fractions. When they enter the hot column, they evaporate and then travel upwards (usually) as gases until they reach their boiling temperature, at which point they travel no further as they would condense?