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How To Find K For Relative Volatility (H2S)

absorber h2s dea distillation relative volatility equilibrium ratios seperation

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#1 Sevde


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Posted 20 May 2017 - 06:35 AM

components  %Volume

of the gas 

H2                51.8

methane      13.0

ethane           14.0

propane         11.0

butane             6.0

pentane        1.0

H2S              3.2




I need to design an absorber (38C and 4bar) to seperate H2S from this gas using DEA. I think H2S is the heavy key -%vol 0.04 H2S at top product- but i dont know what is the light key


To draw McCabe i need relative volatility but i dont know how to find K values for relative volatility. I dont know Yi and Xi values so im looking for a different way to calculate K. After that i will need a stripper to seperate amin and H2S but i couldnt find relative volatility for these too.


Is there information about this components in Aspen Hysys. I have heard something like that but couldnt find anything. 




#2 Saml


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Posted 20 May 2017 - 10:04 PM

The fact that you can build an X-Y diagram similar to McCabe-Thiele for absorption, does not means that you can extrapolate all the concepts of distillation. In fact the separation is not due to relative volatility as in distillation. It is due to difference in chemical affinity with the DEA.


Aspen Hysys may have an amines package for calculating equilibrium.

#3 Sevde


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Posted 21 May 2017 - 06:31 AM

I found solubility (moleH2S/moleDEA) and partial pressure data for H2S in DEA but i dont know how to build X-Y diagram. I tried to but it came out as a straight line.


And yes i know that package but i dont know where to find calculations or values i need from aspen.

#4 Saml


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Posted 21 May 2017 - 01:11 PM

It is right that you get a quite straight line, specially if you are in the region of low amine loading (that is, few H2O molecules per molecule of amine).


If you look at McCabe and Smith Book  "Unit Operations of Chemical Engineering" (chapter 22), many of the examples for absorption are straight near the left side of the curve (low H2S in the amine)


Of course, if you go to the other end (pure H2S and no amine) the curve won't be straight up to that point. But you are interested in an area where you are always in excess of amine.


In Aspen, at most you can get the parameters by selecting "import all parameter". You have to dig into the manuals to understand what those parameter means and the form of the equations that use them. I would not go that way. If I had to build a curve of H2S partial pressure, I sould just do a vary/casestudy with the right properties package.



#5 Sevde


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Posted 27 May 2017 - 10:06 AM

I couldnt really solve it but thank you for making me understand it better.

#6 Napo


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Posted 28 May 2017 - 12:04 PM



From your information, K is approximately equal to 6,0 of GPSA Chart, Engineering Data Book, Volume II, 10th edition, 1987.



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#7 breizh


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Posted 28 May 2017 - 07:24 PM

Hi ,



You may find pointers using this resource on  line .


Good luck,


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