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Members: 2 Paola Chanel Villegas Tapia A01373219 César Eduardo Flores Ríos A01168336
Date: November 24th Group: 1
Challenging problem: acetone – chloroform
a. Graph representation
Figure 1. Ideal T-xy graph of a mixture of acetone with chloroform.
In this graph we observed that the behavior of the mixture is ideal because this form
does not contemplate the molecular interactions and does not have an azeotrope.
Figure 2. Wilson T-xy graph of a mixture of acetone with chloroform.
Paola Chanel Villegas Tapia A01373219 César Eduardo Flores Ríos A01168336
Figure 3. Comparison between Wilson and Ideal T-xy graph of a mixture of acetone with
chloroform.
The Wilson model contemplates the excess calculations with the Gibbs free energy molar excess of the mixture and that is why the behavior of the graph goes to another direction. The graph contains an azeotrope.
Figure 4. NRTL T-xy graph of a mixture of acetone with chloroform.
Paola Chanel Villegas Tapia A01373219 César Eduardo Flores Ríos A01168336
Figure 5. Comparison between NRTL and Ideal T-xy graph of a mixture of acetone with
chloroform.
The behavior of this model is determinate by another kind of parameter different than
ideal model parameter is related to the non-randomness of the mixture, or is that the
components of the mixture are not randomly distributed, but follow a pattern defined by
the local composition. The graph contains an azeotrope.
Figure 6. UNIQUAC T-xy graph of a mixture of acetone with chloroform.
Paola Chanel Villegas Tapia A01373219 César Eduardo Flores Ríos A01168336
Figure 7. Comparison between UNIQUAC and Ideal T-xy graph of a mixture of acetone with
chloroform.
Was necessary to developed a new equation that determinate the data in a reliable way
and then was developed the UNIQUAC and we notice in the graph behavior that in this
case the randomness in the molecules was contemplated and the different sizes of the
molecules. The graph contains an azeotrope.
The azeotropes are mixtures of two or more components that the proportions are such
that the vapor produced by partial evaporation has the same composition as the liquid.
Exist many forms to avoid the azeotrope, for example add another compound to the
mixture but the disadvantage is that later we are going to need another separation.
Another form is to change the pressure, it will be able to move the azeotrope with the
objective to obtain a more pure separation. Another form is to find the way of not pass
through the azeotrope.
b. The maximum x achievable
For the calculation of the theoretical plates we used UNIQUAC model because is the
more reliable of the three models because contemplate more variables.
According to Aspen Plus Software with the initial concentrations are 0.05 for acetone
and 0.95 in the case of chloroform and a temperature of 25°C and pressure of 1 atm the
maximum x achievable is: 0. 3435.
To obtain a better result was used the other two models, Wilson and NRTL to get the
maximum x achievable and the result was the same of the data in UNIQUAC.
Paola Chanel Villegas Tapia A01373219 César Eduardo Flores Ríos A01168336
Figure 8. Results of the azeotrope obtained on Aspen plus software of a mixture of acetone with
chloroform using xi= 0.05 of the volatile compound.
c. Theoretical plates
The selected method is UNIQUAC, then the theoretical plates was calculated using the
T-xy graph of this method.
The result is approximately 7 theoretical plates.
The graphical representation of theoretical plates of UNIQUAC graphic representation:
Figure 9. Graphical representation of theoretical plates of UNIQUAC of a mixture of acetone
with chloroform.
Paola Chanel Villegas Tapia A01373219 César Eduardo Flores Ríos A01168336
d. Related component structure - Intermolecular forces and discuss
In the case of a mixture acetone – chloroform are negative deviations from Raoult’s law
because the molecules have polar groups. There are strong unlike interactions, specific
between the carbonyl oxygen and the hydrogen on chloroform; this interactions produce
a negative excess Gibbs energy; in other words there are strong hydrogen bonding
interactions too.
Those interactions may cause the formation of specific inseparable compositions where
the vapor and liquid compositions are in equilibrium (azeotrope); we use the UNIQUAC
model to check that affirmation and the conclusion is that the maximum x is located in
the azeotrope, in this case the x= 0.3435.
References
Apuntes científicos (s.f.). Desviaciones de la ley de Raoult. Retrieved from http://apuntescientificos.org/azeotropos-ibq2.html.
IRA A. Fulton College. (s.f.). Vapor-liquid equilibria (VLE). Retrieved from http://www.et.byu.edu/~rowley/VLEfinal/background4.htm
UVIGO (2004). Modelos termodinámicos para el equilibrio fase liquido-vapor. Retrieved from http://eueti.uvigo.es/files/material_docente/1621/modelostermodinamicos.pdf