Diminished effectiveness of distillation as column heats up

[ipodtouch]

As the column in fractional distillation heats up, there are less cycles of "condensation and evaporation" causing less purity.


I was wondering if this was a flaw that affected both fractional distillation and simple distillation, or only fractional. (I know it affects fractional more, as it relies on more cycles)



Oh also, I was if those cycles of "condensation and evaporation" is Reflux.

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[syoung]

Yes that is reflux.
That is for fractional only. If I remember correctly, you need to make sure the temperature range is very constant so insulating the fractional column will help get you purity

 

[MedPR]

As the column in fractional distillation heats up, there are less cycles of "condensation and evaporation" causing less purity.


I was wondering if this was a flaw that affected both fractional distillation and simple distillation, or only fractional. (I know it affects fractional more, as it relies on more cycles)



Oh also, I was if those cycles of "condensation and evaporation" is Reflux.

Yea, it's mostly fractional because in simple distillation you end up using an entirely new setup to increase purity anyway.

Yes, reflux is when it condenses, hits the walls of the cold tube, evaporates and falls back down. Think of gastric reflux!

 

[ipodtouch]

I see.
So if a question asks:

In simple distillation, would the effectiveness of the system become reduced as the column heats up?
The answer would be No?

 

[MedPR]

I see.
So if a question asks:

In simple distillation, would the effectiveness of the system become reduced as the column heats up?
The answer would be No?

I think the answer would be yes. It still hurts yield, just not as much as fractional.

 

[hellocubed]

I think the answer would be yes. It still hurts yield, just not as much as fractional.

Just a correction

It would actually improve yield. But decrease purity.

 

[MedPR]

Just a correction

It would actually improve yield. But decrease purity.

Yield of pure compound is all you care about when doing distillation. Increased impurities = decreased yield of pure compound = decreased yield of what you want = decreased yield.

 

[hellocubed]

Heating up the column decreases the number of reflux cycles, causing the fractional distillation to become more similar to simple distillation.

Simple distillation has far greater yield than fractional. Just less pure. This is due to the fact that every reflux cycle causes a slight condensation loss in target product (offset by much larger loss in impurity).
In this case we are not talking about volume density, but total mass product. Hence increased impurity noes not =decreased product.

This is correct i am sure