Molecular Simulation of Excess Isotherm and Excess Enthalpy Change in Gas-Phase Adsorption

Do, D., Do, H. and Nicholson, D. (2009) Molecular Simulation of Excess Isotherm and Excess Enthalpy Change in Gas-Phase Adsorption. JOURNAL OF PHYSICAL CHEMISTRY B, 113 4: 1030-1040. doi:10.1021/jp8046467


Author Do, D.
Do, H.
Nicholson, D.
Title Molecular Simulation of Excess Isotherm and Excess Enthalpy Change in Gas-Phase Adsorption
Journal name JOURNAL OF PHYSICAL CHEMISTRY B   Check publisher's open access policy
ISSN 1520-6106
Publication date 2009-01
Year available 2009
Sub-type Article (original research)
DOI 10.1021/jp8046467
Volume 113
Issue 4
Start page 1030
End page 1040
Total pages 11
Editor Schatz, G.C.
Place of publication United States
Publisher American Chemical Society
Collection year 2010
Language eng
Subject C1
030603 Colloid and Surface Chemistry
970103 Expanding Knowledge in the Chemical Sciences
Abstract We present a new approach to calculating excess isotherm and differential enthalpy of adsorption on surfaces or in confined spaces by the Monte Carlo molecular simulation method. The approach is very general and, most importantly, is unambiguous in its application to any configuration of solid structure (crystalline, graphite layer or disordered porous glass), to any type of fluid (simple or complex molecule), and to any operating conditions (subcritical or supercritical). The behavior of the adsorbed phase is studied using the partial molar energy of the simulation box. However, to characterize adsorption for comparison with experimental data, the isotherm is best described by the excess amount, and the enthalpy of adsorption is defined as the change in the total enthalpy of the simulation box with the change in the excess amount, keeping the total number (gas + adsorbed phases) constant. The excess quantities (capacity and energy) require a choice of a reference gaseous phase, which is defined as the adsorptive gas phase occupying the accessible volume and having a density equal to the bulk gas density. The accessible volume is defined as the mean volume space accessible to the center of mass of the adsorbate under consideration. With this choice, the excess isotherm passes through a maximum but always remains positive. This is in stark contrast to the literature where helium void volume is used (which is always greater than the accessible volume) and the resulting excess can be negative. Our definition of enthalpy change is equivalent to the difference between the partial molar enthalpy of the gas phase and the partial molar enthalpy of the adsorbed phase. There is no need to assume ideal gas or negligible molar volume of the adsorbed phase as is traditionally done in the literature. We illustrate this new approach with adsorption of argon, nitrogen, and carbon dioxide under subcritical and supercritical conditions.
Keyword SUPERCRITICAL XE
Q-Index Code C1
Q-Index Status Confirmed Code

Document type: Journal Article
Sub-type: Article (original research)
Collections: 2010 Higher Education Research Data Collection
School of Chemical Engineering Publications
 
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Created: Thu, 03 Sep 2009, 08:55:11 EST by Mr Andrew Martlew on behalf of School of Chemical Engineering