Separation of mixtures with azeotrope

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1 Instituto Tecnológico y de Estudios Superiores de Monterrey Campus Estado de México Equilibrium Thermodynamic Dra. Yara Almanza Challenging exercise Separation of mixtures with azeotrope Liliana Itzel Romero Ramírez Alan Espinosa Rios A (23 Noviembre 2015)

2 Objectives The simulation of the mixture of Ethylene Glycol and Naphthalene with three different models (UNIQUAC, NRTL and Wilson) and with the Ideal Model Compare models with the ideal model and determine the best model for simulation. Calculate the number of plates in each model to separate the mixture Determine the maximum attainable purity. Introduction A thermodynamic model is a set of equations to determine the physical properties of pure substances or mixtures to achieve simulate chemical processes and modify processes or designs in real life. Is ideal to choose a good model for the simulation is accurate, but in turn, it is important to know the purpose of the simulation to determine which properties should be taken into account. These models are particularly used to describe the non ideality of the liquid phase and is used to calculate the transience of the liquid phase. Wilson Margules Non Random Two Liquids (NRTL) UNIversal QUAsi Chemical (UNIQUAC) UNIquac Functional group Activity Coefficient (UNIFAC) [Thermodynamiceq, 2015] The selection suitably of thermodynamic model is vital because it defines if properly represent a real situation. In a simulator it is possible to describe the interaction of substances and play with the change of temperature and pressure to understand the behavior in reality. Likewise, a simulation lets us know what to do in case you want to separate a mixture and that it has azeotrope. Process Ethylene glycol Naphthalene (49%) It made the simulation which models and compared with the curve obtained from the ideal model

3 Ideal models UNIQUAC and UNIQUAC vs Ideal NRTL and NRTL vs Ideal

Wilson model and Wilson vs Ideal Plates of each model to the distillation tower Uniquac The UNIQUAC model is not required plates because with a concentration of x=0.

4 Wilson model and Wilson vs Ideal Plates of each model to the distillation tower Uniquac The UNIQUAC model is not required plates because with a concentration of x=0.05 in liquid, the temperature is C where only 2% (x=0.2) pass to vapour. Hence it shows that you can not temperature down as it is in a straight line to azeotrope. The maximum concentration in UNIQUAC is 0.2% NRTL

In the simulation NRTL same thing happens in the UNIQUAC model, when the mixture liquid having a concentration of x=0.05 is necessary to raise the temperature to 193.

2% Wilson model With the graph obtained by the Wilson model was clearly observed that there may be 2 plates and thanks to this the maximum concentration at 1 atm is 49%, Wilson is the model we chose

5 In the simulation NRTL same thing happens in the UNIQUAC model, when the mixture liquid having a concentration of x=0.05 is necessary to raise the temperature to to change phase and the concentration is The maximum concentration in NRTL is 0.2% Wilson model With the graph obtained by the Wilson model was clearly observed that there may be 2 plates and thanks to this the maximum concentration at 1 atm is 49%, Wilson is the model we chose it shows a more detailed process to manipulate. The temperature is C to a concentration of 0.05% liquid Naphthalene. First plate: T=192.5 C X= Second plate: T=186.5 C X=0.49 The azeotrope appears when the temperature is 186 C so that it is necessary not reach at this temperature. Comparison between Wilson Models to 1 atm and 0.5 atm There are different ways in order to try to avoid the azeotrope. You can decrease or increase temperature and pressure, add more mixture but in a higher concentration. The more efficient the process is the more pure concentration we obtain. In our case the initial parameters were T=82 C and P=1atm, we used ASPEN to make different simulations changing pressure and temperature. After doing many simulations we realized that was very hard to avoid the azeotrope and to reach a higher

6 concentration. We chose P=0.5atm as the better option to increase final concentration, because we just need one plate in the distillation process to get a better result, and we consider that decrease pressure in 0.5 atm is not very difficult neither expensive. This is another important point, we need to compare costs and results. Conclusion Making this exercise we realized that ideal models are not very useful sometimes, because it differs a lot of reality. With ideal model a simple distillation is enough to obtain a pure distillation, but other models that consider intermolecular forces show us that the maximum concentration we could obtain is almost 50%. Solubility, types of chemical bonds, fugacity are examples of intermolecular forces that we need to consider in a real process. We managed to meet the goals, it was possible to compare different models with the ideal model and it was determined which model to do a better simulation. We conclude that the best model for the simulation is to Wilson because with this you can get a 49% distillation of Naphthalene. Reference: Universidad Nacional de Colombia. Análisis y simulación de procesos de estado estable y dinámico Selección del Modelo Termodinámico. Recuperado de: ThermodynamicEq Thermodynamic Models models.html

Note: items marked with * you should be able to perform on a closed book exam. Chapter 10 Learning Objective Checklist

Note: items marked with * you should be able to perform on a closed book exam. Chapter 10 Learning Objective Checklist Sections 10.1-10.13 find pure component properties on a binary P-x-y or T-x-y diagram.*