Net, excess and absolute adsorption in mixed gas adsorption

Area of Science:

• Thermodynamics
• Physical Chemistry
• Adsorption Science

Background:

• Thermodynamic frameworks for gas mixtures are crucial for understanding adsorption processes.
• Existing formulations based on absolute, excess, or net adsorption present practical challenges when extended to mixtures and the Ideal Adsorbed Solution Theory (IAST).

Purpose of the Study:

• To discuss the formulation of thermodynamic frameworks for mixtures.
• To highlight practical issues in extending these frameworks to mixtures and IAST.
• To establish the correct fundamental thermodynamic variable and the definition of IAST.

Main Methods:

• Discussion of thermodynamic frameworks for mixtures.
• Qualitative dependence analysis with pressure and fugacity.
• Extension of formulations to mixtures and IAST.

Main Results:

• The absolute adsorbed amount is identified as the correct fundamental thermodynamic variable.
• A single, consistent definition of the Ideal Adsorbed Solution Theory (IAST) is confirmed.
• The study demonstrates that all starting points lead to the same IAST equations, contradicting previous literature.

Conclusions:

• The absolute adsorbed amount is the essential variable for thermodynamic frameworks of mixtures.
• There is only one valid definition for the Ideal Adsorbed Solution Theory (IAST).
• The derivation of IAST equations is consistent regardless of the initial thermodynamic approach, resolving prior inconsistencies.