Modeling spreading-pressure-dependent binary gas coadsorption equilibria using gravimetric data

Area of Science:

• Physical Chemistry
• Adsorption Science
• Thermodynamics

Background:

• Developing accurate nonideal coadsorption models is crucial for understanding gas mixture behavior on surfaces.
• Existing models often lack thermodynamic consistency or require extensive experimental data.
• Gravimetric measurements offer a direct way to quantify adsorbed amounts.

Purpose of the Study:

• To develop a thermodynamically consistent approach for building nonideal coadsorption models.
• To determine model parameters from limited, simple gravimetric measurements.
• To incorporate the effects of pressure and spreading pressure into coadsorption models.

Main Methods:

• Utilizing nonideal adsorbed solution theory with activity coefficients dependent on spreading pressure.
• Employing an original form of the excess Gibbs energy of mixing.
• Developing an analytical framework to relate model parameters to experimental data, including single-component isotherms and binary gravimetric curves at different pressures.

Main Results:

• A quasi-analytical and unique method for determining the four parameters of the coadsorption model.
• Demonstrated applicability using the coadsorption of carbon dioxide (CO2) and methane (CH4) on activated carbon.
• Validation using both incremental gravimetry and batch-type equilibration measurements.

Conclusions:

• The proposed method provides a robust and efficient way to build nonideal coadsorption models.
• Thermodynamic consistency is achieved by integrating activity coefficients and excess Gibbs energy.
• The method requires only total adsorbed mass data, simplifying experimental requirements.