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Binary Distillation Help

binary distillation

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#1 Neon

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Posted 16 February 2017 - 06:28 AM

Hi,

 

I'm currently having a few issues regarding the design of a distillation column. I'm trying to separate a binary mixture, however the lighter component has a fairly small mass flow compared to the heavier component. The lighter component only makes up 8% of the saturated liquid feed.

 

I tried drawing a McCabe-Thiele diagram, however with the xF line being so far to the left, I'm not able to carry out the procedure from how I'd originally been taught.

 

Can somebody explain whether separation can be carried out? Let me know if you require any more information :)

 

Cheers



#2 latexman

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Posted 16 February 2017 - 09:18 PM

Show us your work.



#3 Neon

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Posted 17 February 2017 - 05:03 AM

The column aims to separate methylamine (MMA) from methanol. I've sent over my Txy data and my VLE diagram and calculations. For my design, I need the distillate temperature to leave the column at around 35oC, and so I used Antoine to gain a suitable column pressure.

 

The flow rate of methanol to the column is 2151.84 kg/h and MMA 197.03.

 

Can you please offer any comments on the separation? I tried putting some data into Aspen and it didn't think I could get a distillate purity of above 90%.

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#4 MrShorty

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Posted 17 February 2017 - 01:50 PM

I'm not able to carry out the procedure from how I'd originally been taught.
Can you explain exactly what you are stuck on? You have a nice Y/X diagram, and you have drawn the y=x curve and the y vs. x equilibrium curve on it. Using the procedure outlined by Wikipedia (https://en.wikipedia...eā€“Thiele_method ), the next step would be to add vertical lines for the feed, bottom, and distillate concentrations. How closely does Wikipedia's procedure compare to the procedure you were taught? Does that help clarify?

 

I tried putting some data into Aspen and it didn't think I could get a distillate purity of above 90%.
Do you know what thermo/VLE model Aspen was using? A quick check with UNIFAC suggests that this system has an azeotrope, where your spreadsheet does not indicate the existence of an azeotrope.




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