2 replies to this topic

[meursault92]

So Im trying to separate butanol and water using a distillation column. If you look at he txy of water/butanol (http://imgur.com/A9ZV2Jp) there is a cross over to the other side of the x=y line. 

 

I ask because I calculated the minimum number of trays using the fenske eqn and got a much higher number than i do with the mccabe thiele . maybe im doing something wrong?

 

Thanks

Edited by meursault92, 19 February 2014 - 09:41 PM.

[PingPong]

If you look at he txy of water/butanol there is a cross over to the other side of the x=y line.

That means that there is an azeotrope at x = 0.75

 

That should be mentioned in your textbook, otherwise google it.

 

In general it means the feed mixture cannot simply be separated in its pure components a distillation column because it is not possible to distill through the azeotrope. In some situations where both components do not mix in all proportions (resulting in phase separation) at all temperatures its becomes a different story.

 

Note that there are 3 isomers of butanol, so you should first figure out which butanol isomer you have.

Edited by PingPong, 20 February 2014 - 07:13 AM.

[Art Montemayor]

meursault92:

 

Pingpong is correct.

As a chemical engineering student, you have (in my opinion) no business trying to involve yourself in solving a distillation problem without a thorough knowledge of what you are getting into - and distillation means you have to be fully aware of the existance of azeotropes.  You have to do your basic theory and background studying first.  You are trying to run, before learning how to standup.  For example, go to:  http://ecosse.org/ja...lation/2-phase/

 

Do as much research on azeotropes and how they can be "broken up" in order to achieve the desired separation.  There are many techniques and the specific system usually determines what path to take.