[stain]

Hello everybody,

I have a project running at college concerning the separation of isopropanol, acetone and water. The idea is that we come up with a more classic way (and simulate in Aspen) to separate the mixture, and later discuss which alternative methods we would suggest and why.
The feed is 380 kmol/h (10% acetone, 25% water en 65% isopropanol) at 350°F, no given pressure. The mixture has two minimum boiling azeotropes, which makes it pretty hard to separate.

For the classic method we decided to go ahead with extractive distillation. We found a list of possible solvents to separate acetone from the mixture via distillation. The idea is that the solvent would increase the relative volatility of the close boiling components. The solvent would break the acetone-water azeotrope. So we expected that acetone would go overhead in the column and isopropanol, water and extractive agent would come down the bottoms.
We chose dimethylsulfoxide (DMSO) as a solvent. The simulation in Aspen resulted in acetone and isopropanol going over top with a very nice purity and water and DMSO in the bottoms. This makes life really easy as the azeotropes are gone, water and DMSO are easy to separate in an extra column too..

But here's the question: What's the reason for the difference between our expectations and the result? I'm sure that question will be asked to us by our professors. My first guess would be that DMSO is very polar and so it likes to be surrounded by water, which would influence the non-Raoult's law behaviour and so remove the azeotropes..

But I could be completely off target. Anybody have an idea what the chemistry behind this behaviour is? And does anybody have any great suggestions for me considdering this assignment?

Thanks in advance,
Thomas

[ARGOS++]

Dear Stain;

I believe this/your “Extractive Distillation” is quite conforming to the explanation on:

"Extractive Distillation”

Good Luck!
                   ARGOS⁺⁺

[stain]

Dear Stain;

I believe this/your “Extractive Distillation” is quite conforming to the explanation on:

"Extractive Distillation”

Good Luck!
                   ARGOS⁺⁺

Hey,

Thanks!

Yes I understand the idea behind extractive distillation for the case of binary mixtures. Almost all explanations you can find on extractive distillation are about separating two components.. But in our case there's a ternary mixture, and I don't really understand how the solvent interacts between these components causing the separation that resulted out of the simulation. Howcome both azeotropes seem to be broken? I would expect only the acetone-water one would be broken..

[ARGOS++]

Dear Stain;

As I know exactly the same way, - “keeping one back” (mostly).
You may also read under “Breaking Azeotropes”/Separation of Azeotropes on

"Azeotrope”

(I think you have also to follow the references given therein.)

Good Luck!
                   ARGOS⁺⁺

[stain]

I think I found the chemical background of what happens. Thanks to one of the references in the wikipedia about azeotrope breaking (never looked at those references before, now I will ). Water and DMSO form complexes, which is a very important condition for an extractive agent, because it lowers the relative volatility between these 2. This enhances the separation because, indeed ARGOS++, water is held back in this way.

Thank you.