[Paper Review] Theoretical development on the isosteric heat of adsorption and experimental confirmation

Kyaw Thu, Sourav Mitra+1 more|arXiv (Cornell University)|Sep 6, 2017

Advanced Thermodynamics and Statistical Mechanics1 references3 citations

TL;DR

This paper develops a rigorous thermodynamic model for the isosteric heat of adsorption that accounts for non-ideal gas behavior and finite adsorbed phase volume, especially across multi-layer adsorption from low to high pressures. The model shows excellent agreement with experimental data for nonpolar adsorbate systems, validating its accuracy in predicting both adsorption isotherms and isosteric heats.

ABSTRACT

Theoretical framework for the isosteric heat of adsorption is developed treating the effects of the non-ideal gas behavior and the adsorbed phase volume. Rigorous thermodynamic treatment for the adsorbed phase volume is presented for multi-layer adsorption from low to high pressures. The proposed model for the isosteric heat of adsorption along with the adsorbed phase volume is validated and verified using experimental data for several, judiciously selected adsorbent + adsorbate (nonpolar molecules) systems. The predictions by the model exhibit excellent agreement with the experimental data for both adsorption isotherms and the isosteric heat of adsorption.

Motivation & Objective

• To develop a theoretically sound framework for the isosteric heat of adsorption that includes non-ideal gas behavior and finite adsorbed phase volume.
• To extend the thermodynamic treatment to multi-layer adsorption across low to high pressures.
• To validate the model against experimental data for adsorption isotherms and isosteric heat of adsorption.
• To improve predictive accuracy for adsorption processes involving nonpolar molecules.

Proposed method

• Theoretical derivation using rigorous thermodynamic relationships to account for non-ideal gas behavior in the gas phase.
• Incorporation of the adsorbed phase molar volume into the isosteric heat calculation, derived from adsorption isotherm data.
• Application of the Clausius-Clapeyron equation in a modified form to relate changes in equilibrium pressure to isosteric heat.
• Use of experimental adsorption isotherms to compute isosteric heats and compare with model predictions.
• Systematic validation across multiple nonpolar adsorbent-adsorbate systems (e.g., N2, CH4, CO2) at varying pressures.
• Employment of multi-layer adsorption models to ensure applicability over the full pressure range.

Experimental results

Research questions

• RQ1 How does accounting for non-ideal gas behavior affect the accuracy of isosteric heat of adsorption predictions?
• RQ2 What is the impact of finite adsorbed phase volume on the thermodynamic consistency of isosteric heat calculations?
• RQ3 Can the proposed model accurately predict both adsorption isotherms and isosteric heats across low to high pressures?
• RQ4 How does the model perform when validated against experimental data for nonpolar systems?
• RQ5 To what extent does the inclusion of multi-layer adsorption effects improve model fidelity?

Key findings

• The model demonstrates excellent agreement with experimental data for both adsorption isotherms and isosteric heat of adsorption across multiple nonpolar systems.
• Incorporating the adsorbed phase volume significantly improves thermodynamic consistency, especially at high pressures.
• The model successfully captures the pressure-dependent behavior of isosteric heat, including the characteristic decrease at higher loadings.
• Predictions remain accurate across the full pressure range, from low to high pressures, validating the multi-layer treatment.
• The inclusion of non-ideal gas effects enhances accuracy compared to ideal gas approximations, particularly in high-pressure regimes.
• The experimental validation confirms the model's robustness and reliability for practical adsorption system design.