How does temperature affect distillation in a fractionating column?

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SUMMARY

The discussion centers on the principles of fractional distillation, specifically how temperature affects the separation of substances with varying boiling points. It is established that in a fractionating column, substances with higher boiling points condense at the bottom while those with lower boiling points rise to the top due to the temperature gradient along the column. The boiling point of ethanol is approximately 78°C, while water boils at 100°C, illustrating this principle. The temperature gradient is crucial for the effective functioning of the distillation process, debunking the misconception that higher boiling points correlate with higher energy output in the system.

PREREQUISITES
  • Understanding of fractional distillation principles
  • Knowledge of boiling points of common substances (e.g., ethanol and water)
  • Familiarity with temperature gradients in distillation columns
  • Basic concepts of vapor pressure and partial pressure
NEXT STEPS
  • Research the role of temperature gradients in fractional distillation
  • Study the vapor-liquid equilibrium in distillation processes
  • Explore the design and function of fractionating columns in petroleum refining
  • Learn about the impact of ambient pressure on boiling points
USEFUL FOR

Chemical engineers, distillation process operators, and students studying separation processes in chemistry or chemical engineering.

faiziqb12
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i have got a question with distillation . in distillation as we know the mixture is boiled and the mechanism then goes like substances with high boiling points condense at the bottom and substances with lower boiling points condense on the way to the top.
i don't know why , but i am having difficulty understanding that why should a substance with high boiling point go to the bottom and the substance with the low melting point get higher . it is going against my intuition .
basically what i think is that higher boiling point means greater energy to the system and thus higher output in form of reaching higher . now according to the real observation i am wrong.

so does the system behave like this .
higher boiling point means that after the system changes into gaseous state (most probably) , it radiates energy more fastly that the substance with the lower melting point .

Is this explanation of the phenomena correct

if yes
then explain why does the substance with more boiling point radiate energy more fastly ?

if no
then please correct me with the right mechanism
 
Science news on Phys.org
No. No. No.
 
Bystander said:
No. No. No.

kindly please , give the right mechanism then
its confusing me a lot
 
Bystander said:
No. No. No.

Sir ,
is it that more energy gets absorbed by the liquid with the lesser boiling point , then
 
What DO you know? This isn't even close to being a misunderstood/garbled question. I need some place to apply a little leverage.
 
Bystander said:
What DO you know? This isn't even close to being a misunderstood/garbled question. I need some place to apply a little leverage.

i am sorry for being so dull , but i can't imagine the situation .the lower boiling point rising to a higher level seems like the lower boiling point gets more energy. is it that the lower boiling points get energy even after changing into liquid
true sir ?
 
faiziqb12 said:
i am sorry for being so dull , but i can't imagine the situation .the lower boiling point rising to a higher level seems like the lower boiling point gets more energy. is it that the lower boiling points get energy even after changing into liquid
true sir ?
Have you ever encountered the terms "vapor pressure", "partial pressure" or "saturated vapor pressure"?
 
faiziqb12 said:
i have got a question with distillation . in distillation as we know the mixture is boiled and the mechanism then goes like substances with high boiling points condense at the bottom and substances with lower boiling points condense on the way to the top.
i don't know why , but i am having difficulty understanding that why should a substance with high boiling point go to the bottom and the substance with the low melting point get higher . it is going against my intuition .
basically what i think is that higher boiling point means greater energy to the system and thus higher output in form of reaching higher . now according to the real observation i am wrong.

so does the system behave like this .
higher boiling point means that after the system changes into gaseous state (most probably) , it radiates energy more fastly that the substance with the lower melting point .

Is this explanation of the phenomena correct

if yes
then explain why does the substance with more boiling point radiate energy more fastly ?

if no
then please correct me with the right mechanism

You're getting mixed up by your intuition here.

Let's say you take a mixture of ethanol and water at an initial temperature of 20° C. Both substances are liquid at this temperature and let's specify that the ambient pressure is 1 atmosphere, to keep things friendly.

The boiling point of ethanol is about 78° C while water has that well-known boiling point of 100° C at the ambient pressure.

What happens to the mixture of ethanol and water as it's heated and the temperature starts to rise above 20°?

The temperature of the mixture is going to reach 78° eventually, and what happens to the ethanol? At 78°, what is the water doing?

This process is what is known as fractional distillation, and it's used not only in making potable spirits, but it's also used quite extensively in refining petroleum:

https://en.wikipedia.org/wiki/Fractional_distillation

All that stuff about substances radiating energy 'more fastly' has nothing to do with this process.
 
faiziqb12 said:
substances with high boiling points condense at the bottom and substances with lower boiling points condense on the way to the top.
i don't know why
Which is a higher temperature, the top or the bottom of the column?
 
  • #10
DaleSpam said:
Which is a higher temperature, the top or the bottom of the column?
both are the same because the column is a homogenous system
 
  • #11
faiziqb12 said:
both are the same because the column is a homogenous system
Did you read the link that SteamKing provided?
 
  • #12
faiziqb12 said:
both are the same because the column is a homogenous system
No, that is not correct at all. The temperature gradient along the column is crucial for the function of the still.
 
  • #13
DaleSpam said:
No, that is not correct at all. The temperature gradient along the column is crucial for the function of the still.

that explains it hopefully
but how are gases distilled in the fractional distillation column with marbles present ?
does it also have have a trempreature gradient?
 
  • #14
faiziqb12 said:
that explains it hopefully
but how are gases distilled in the fractional distillation column with marbles present ?
does it also have have a trempreature gradient?
It's not clear where you are getting marbles from.

If you look at the diagram of the crude oil separator column in the Wiki article, you'll see that temperatures range from 400° C at the bottom to 150° at the top.
 

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