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Home > Forums > Chemical Engineers > Activities > Chemical plant design & operations Forum

Using condensation as a separation mechanism?

Read More Threads Like This One

RobD7 (Chemical)

18 Jun 12 15:19

A vapor process stream that I am working on is primarily acetone, with small concentrations (< 5 %wt) of Hexamethyldisilazane (HMDS) and ammonia. Acetone condenses around 57 C and HMDS condenses at 126 C. Is it possible that placing two condensers in series, one to condense HMDS then the second to condense Acetone, would yield pure acetone? I want some professional advice on this before attempting to design the condensers. I can not find a VLE diagram for the mixture, as HMDS is rarely found in industry.

Thanks,
Rob D

zdas04 (Mechanical)

18 Jun 12 15:34

Condensation temperature is a statistical mean number and there is some variation on either side of it (not 69C, but not zero either). I think that you could get pretty close if you calculated your retention times and heat input right, but any time you are dealing with phase change the latent heats really muddy the water.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

Latexman (Chemical)

18 Jun 12 15:35

Pure? 100.000000 . . . % acetone. No.

Close enough to be pure? 99% acetone. Maybe.

Do some ideal, constant relative volatilitty flash/condensation calculations and see.

Good luck,
Latexman

ash9144 (Chemical)

18 Jun 12 15:56

You are simply proposing two stage partial condensation. So functionally the same as two stages of any VLE separation (such as two trays in a tower). You could get fairly high purity on one stream probably the acetone as you state. You would want the exit gas of your first condenser to maintain much closer to the condensation temp of the acetone say roughly 60 C. Your HMDS stream will be high in acetone.

Compositepro (Chemical)

18 Jun 12 17:14

How is what you propose different from any distillation problem?

RobD7 (Chemical)

19 Jun 12 13:46

Thanks everyone

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