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On the statistical thermodynamics of adsorption in microporous heterogeneous media
Abstract
In this thesis we investigate the role of adsorbent physical and energetic heterogeneity on adsorption behavior. In particular we address three points: (1) Development of qualitatively realistic yet tractable models of heterogeneous microporous adsorbents. (2) Investigation of the effects of adsorbent microstructure on adsorption behavior. (3) Evaluation and refinement of methods for predicting adsorption in microporous media. These issues are explored from the perspectives of exact analytic methods, computer simulation techniques, and engineering applications. We develop two novel models of heterogeneous adsorption which while simple to use nevertheless capture much of the physics found in real systems. The first model is the composite sphere (CS) model and is based on the structure of silica gel. The CS model is particularly suited for study by Monte Carlo simulation. The second model is a one-dimensional (1-D) heterogeneous porous model. This model allows for exact analytic evaluation of the adsorption statistical thermodynamics. Applying the two models we carry out a wide range of grand canonical Monte Carlo computer simulations and other calculations to explore Henry's law behavior, pure component isotherms, and binary mixture selectivity as a function of adsorption heterogeneity. Several adsorbent morphologies are considered so to gauge the effect of heterogeneity on adsorption. In particular, three morphologies corresponding to basic cubic lattices are considered, since they are simple to visualize, and a morphology corresponding to a configuration of equilibrium hard spheres is considered, since it represents moderately realistic model of the structure of silica gel. We perform several comparisons of our Monte Carlo simulation results to experimental data. Additionally, from our simulations adsorbed fluid structure is explored by means of isotropic pair correlation functions and visual representations. Two adsorption theories usable by engineers are evaluated: ideal adsorbed solution (IAS) theory (Prausnitz and Myers, 1965) and the statistical model isotherm (SMI) method (Ruthven, 1971). We pay particular attention to their ability to reflect the physics of adsorption in porous media. We critically analyze the theoretical strengths and weaknesses of the SMI method and offer an avenue of improvement for the method.
Subject Area
Chemical engineering|Mechanical engineering
Recommended Citation
Kaminsky, Robert Daniel, "On the statistical thermodynamics of adsorption in microporous heterogeneous media" (1993). Doctoral Dissertations Available from Proquest. AAI9316675.
https://scholarworks.umass.edu/dissertations/AAI9316675