Cross effects in distillation

[Arpene]

Hi guys!!

I'm supposed to get informations about diffusional cross effects and its consequences/effects in distillation.

Up to now I couldn't see a direct relation about these two topics.

Have one of you guys some idea about the thing. Thank you very much for any help.

 

[EmmanuelTop]

Are you speaking about liquid/vapor diffusivity?

See the article:

http://kolmetz.com/pdf/Column-efficiency.PDF

Page 4

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[Arpene]

Hi Emmanuel

It's kind of that. I've searched something more about the task and now I believe that the question is about the influence of mutual diffusion (Also a kind of cross effect in distillation).

For me the paradoxal is the fact that distillation is not controlled by diffusion (it's not the main driving factor at all).

Do you have any other suggestion?

 

[25362]

For a thorough treatment of mass transfer I suggest Perry's Chemical Engineers' Handbook 8th edition, McGraw-Hill.

 

[chemsac2]

Do you mean vapour cross-flow channeling?

I have an article that has following information about vapour crosss-flow channeling.

Vapor crossflow channeling has been attributed to the liquid-phase hydraulic gradients which often occur on trays having high liquid rates, long flow path lengths, short outlet weirs, low dry pressure drops and excessive deck resistance. In response to this gradient, vapor flows preferentially through the tray outlet area and then flows horizontally in the direction opposite to the liquid flow. Liquid weeping occurs near the tray inlet. Ultimately, the vapor crossflow channeling further exacerbates the hydraulic gradient. There is another phenomenon, inlet inactivity, that contributes to the source and magnification of the vapor crossflow channeling.

If this is what you are looking for, additional information can be found in:

Kister, Henry, Larson, Kirk, and Madsen, Poul, “Vapor Cross-flow Channeling on Sieve Trays: Fact or Myth?”, Chemical Engineering Progress, November 1992, pg. 86-93

Regards,

Sachin

 

[Arpene]

Hi Chemsac

Actually not.
It deals with the usually negelected effects of cross diffusion in the mass transfer for distilation columns (See attached file). The Problem is that I simply don't find any paper/reference talking about it. And, as I said, I was allways the opinion that diffusion wouldn't control in such a grade the distillative process.

Hopping for help ;P

Artur