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Author Topic: Van laar equation, problem  (Read 12158 times)

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Van laar equation, problem
« on: March 12, 2009, 02:16:55 AM »

I have the following ex:

Given: methylcyclopentane and ethanol, pressure is 1 atm.

you have an azeotrope at 60.06°C

The following antoine numbers are also given for antoines formula:

A: 6.86640  B:1188.050 and C:226.276 (methylcyclopentane)

A:8.11220  B:1592.864        C:226.184(ethanol)

with the formula: logP= A -  B/(Temperature in °C + C)

Now they want me to calculate the activitycoeficients gamma, wich is no problem because you have: Antoines formula to find P and with this pressure I can suimple use :  Gamma (activitycoefficient)= 760mmHh / P (:the one you calculate with antoine)

Now the second question is a bit harder: you need to calculate the van laar constants, but how can you do this if you do not now what the mixture is ? (you do not now what X1 or X2 is ?) and you do need them to use van laars equation? or not?

van laar being: ln(gamma) = A / (1 + A/B.x1/x2)²  ==> how can I find A and B (van laar constants if  I do not know X1 nor X2 ?)

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