How does temperature affect distillation in a fractionating column?

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Discussion Overview

The discussion revolves around the effects of temperature on the distillation process in a fractionating column, particularly focusing on the behavior of substances with varying boiling points during distillation. Participants explore the mechanisms behind why substances with higher boiling points condense at the bottom while those with lower boiling points rise higher in the column.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant expresses confusion about why substances with higher boiling points condense at the bottom of the column, suggesting that higher boiling points should correlate with greater energy and thus higher placement in the column.
  • Another participant challenges this intuition, indicating that the process of fractional distillation involves specific temperature dynamics that contradict the initial assumption.
  • There is a discussion about the temperature gradient within the column, with some participants asserting that the top and bottom of the column are at different temperatures, while others mistakenly claim they are the same.
  • Questions arise regarding the role of vapor pressure and how gases are distilled in the presence of packing materials like marbles, with a request for clarification on the temperature gradient in such setups.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the initial claims regarding boiling points and energy. There is disagreement about the temperature gradient in the column, with some asserting it is crucial for distillation while others incorrectly state it is uniform.

Contextual Notes

Some participants reference specific examples, such as the boiling points of ethanol and water, to illustrate their points, but there are unresolved questions about the mechanisms of energy transfer and the role of temperature in the distillation process.

Who May Find This Useful

This discussion may be of interest to students and practitioners in chemistry and chemical engineering, particularly those studying distillation processes and thermodynamics.

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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