Question

For a distillation coloumn sperperating a non-ideal liquid mixture using ASPEN PLUS, which thermodynamic model should I use (NRTL, UNIQUAC, UNIFAC, etc) and why should I use this specific model and not the others (justification required)

Answer 1

In ASPEN PLUS,when we use non- ideal liquid mixture for seperation we have to find out the characterstics of non- ideality. it is azeotrope,large positivve or negative deviation fromRoult's law.

Depending upon non-ideality and also the mixture component we have to select the thermodynamic model.

ex. if we have any water-alcohol mixture than we can't use the PR model. because it's depended on the one pure component and another is imaginary . so we have to find the parameter of imaginary component (a,b).In water -alcohol mixture we can't find parameter due to very close mixture of both component.

for UNIFAC it's not used for gases like hydrogen where the solubility of gases in high pressure is less. and it's activity coefficient model so it is not used when it's operate at low pressure activity coefficient.

UNIQUAC is the extended part of UNIFAC , it is apply for same theory but it is use for molecules. UNIFAC is use for predict the VLE data,LLE and enthalpy data and using UNIQUAC we form infinite number of molecules from limited number of functional group.

NRTL model is also activity coefficient model and it's used for to calcualte pase equilibria. electrolyte NRTL use for electrolyte system. it is also use for predict VLE data.