5 replies to this topic

[refluxraider]

Hi,

 

Please help me. I am doing a separation of:

 

- Acetol: 1.25kmol/h (HK)

-Water: 216.647kmol/h (LK)

-methanol: 0.803kmol/h

-ethanol: 0.412kmol/h

-1-propanol: 0.67kmol/h

 

I am aiming for 95% purity acetol, however, when I apply my feed compositions and average relative volatilities to the underwood equation I get a minimum reflux ratio of -1. Why is this? What am I doing wrong?

 

 

component  gm  xf xd axf/(a-θ) axd/(a-θ)             acetol 1 0.0056875 2.86E-05 7.02E-07 3.53E-09 water 5.14E+00 0.9857358 9.91E-01 6.25E-04 6.29E-04 methanol 1.83E+01 0.0036536 3.68E-03 8.24E-06 8.29E-06 ethanol 1.15E+01 0.0018746 1.89E-03 2.66E-06 2.67E-06 propanol 5.53E+00 0.0030485 3.07E-03 2.08E-06 2.09E-06

 

Thanks!

[breizh]

Hi, Check the BP of all your components and define the keys accordingly.
Breizh.

[refluxraider]

Hi, Check the BP of all your components and define the keys accordingly.
Breizh.

Hi, Thank you!

 This table shows my feed molar flow rates and boiling points respectively. I chose acetol as my HK and water as my LK. Is this correct? Im aiming to separate acetol from everything else and ideally would like 95% purity of acetol, however when I apply the shortcut method it doesn't give me a correct reflux ratio, I get -8100 for theta and -1 as my min reflux ratio

 

Acetol

1.25

145.500

Water

216.647

100.000

1-propanol

0.670

97.200

Ethanol

0.412

79.000

Methanol

0.803

65.000

[Pilesar]

First get a converged answer with relaxed specifications. You have less than 1% acetol in your feed and you are trying to purify it to 95% by distillation. I think your expectations of dehydrating over 98% water by distillation will be a difficult path to follow to its conclusion. Underwood shortcut method may be very misleading for your system.

[breizh]

Hi,

LK is not water . 

Think where you want to do the split. should be the one next to HK .

Breizh

Attached Files

•  short cut method version 2.xlsx   470.8KB   9 downloads
•  shortcutdistillation.pdf   229.81KB   4 downloads

[breizh]

Hi,
I need new glasses, I read acetone instead of acetol. Your LK is water then.
I agree with comments above.

note: Can you share the volatility of each component? Coming from text or from calculation?
My bad
Breizh.