AZEOTROPE INQUIRY

Discusses use of COCO, the process simulation and modelling software suite from AmsterCHEM, downloadable from http://www.cocosimulator.org

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thubelihle
Posts: 73
Joined: 04 March 2017, 16:27

AZEOTROPE INQUIRY

Post by thubelihle »

l tried to solve for azeotropic composition but l failed. Attached is the worksheet, if you go to edit on the excel unit operation under the calculation l did the calculations.

l will appreciate your help.



Kind Regards,
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AZEOTROPE INQUIRY.fsd
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jasper
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Re: AZEOTROPE INQUIRY

Post by jasper »

First please correct your pressure (Pa) and temperature (K), unless you want to solve at 30 K and 1 Pa.

Second, indeed you need to put in a composition that you can vary. You may want to put in, for example:

cell E4 = 'X1'
cell F4 = 'X2'
cell E5 = 0.5
cell F5 = '=1-E5'
cell B4 = '=capeSinglePhaseProperty("fugacityCoefficient", "Vapor", 303.15, 100000, E5:F5)'
cell B5 = '=capeSinglePhaseProperty("fugacityCoefficient", "Liquid", 303.15, 100000, E5:F5)'

solver: objective = $B$6, solve for value = 0, by changing $E$5, which might work, if there were an azeotrope in your system at 303.15 K, but there is not. Please check your thermodynamic setup. You can confirm the absense of an azeotrope by plotting vapor and liquid fugacity coefficient at 303.15K and 1 bar vs composition.
thubelihle
Posts: 73
Joined: 04 March 2017, 16:27

Re: AZEOTROPE INQUIRY

Post by thubelihle »

Hi,
Thanks for the response. l did implement the changes as per your recommendations. Your presentation found here: http://www.cocosimulator.org/downloads/ ... _notes.pdf state that there is an azeotrope at about 90% ethanol at 1 atm and 25 C using the NRTL thermodynamics package found on page 6 of your paper. l attached the simulation l did and still it can not predict the azeotropic composition.

Also l notice the vapour phase fugacity coefficient is constant at 1, as we are using the Gamma- phi system by selecting the NRTL, hence assuming ideal gas behavior. Was wondering if we should not consider the activity coefficient for the liquid since water and oil are polar substances. Hence, assuming that at an azeotrope composition the activity coefficients are equal would be valid if we use the Phi-Phi system, ie both equation of state for both the liquid and the gas phase. Will l appreciate if shed some light into my darkness.
Thanks for your help.
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INQUIRY 2.fsd
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jasper
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Re: AZEOTROPE INQUIRY

Post by jasper »

Well - there is an azeotrope. In COFE, plot, create, TX plot, will show it.

It is just not at 30 C.

So perhaps the problem you want to solve is: find composition for which the bubble point temperature matches the dew point temperature. The bubble point temperature follows from a P-VF flash at vapor fraction=0, and the dew point temperature follows from a P-VF flash at vapor fraction=1.
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waterethanol.png
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