5 replies to this topic

[sanchez]

Can someone tell me what is the importance of activity coefficient in distillation design?

[ezralh]

activity coefficient is used to determine the Psat (for non-ideal gas compound) in modified Raoult law

[sanchez]

activity coefficient is used to determine the Psat (for non-ideal gas compound) in modified Raoult law

so how does this modified raoult's law helps in the design?

[MrShorty]

Among the important considerations in distillation design (maybe the most important???) is how different the vapor phase is from the liquid phase in the system. This is vapor-liquid equilibrium. In real world terms, we use quantities like y (vapor composition) vs x (liquid composition) or volatility (K value which is the ratio of y to x) or relative volatility (the ratio of the K values) to describe the VLE of a system. To design a distillation column, it is necessary to understand these properties of the VLE of the system.

The concept of the activity coefficient is a mathematical concept that we use to try to describe the VLE of a system. A good VLE/thermodynamics course or text should describe how this is derived.

[ezralh]

activity coefficient is used to determine the Psat (for non-ideal gas compound) in modified Raoult law

Roult's Law: y_iP=x_iP_i^sat

Modified Raoult's Law: y_iP = x_iγ_iP_i^sat

γ_i - activity coefficient

[sanchez]

Among the important considerations in distillation design (maybe the most important???) is how different the vapor phase is from the liquid phase in the system. This is vapor-liquid equilibrium. In real world terms, we use quantities like y (vapor composition) vs x (liquid composition) or volatility (K value which is the ratio of y to x) or relative volatility (the ratio of the K values) to describe the VLE of a system. To design a distillation column, it is necessary to understand these properties of the VLE of the system.

The concept of the activity coefficient is a mathematical concept that we use to try to describe the VLE of a system. A good VLE/thermodynamics course or text should describe how this is derived.

Thanks!