Molecular thermodynamics of physical adsorption in heterogeneous solids

This dissertation is about the molecular modeling of fluids adsorbed in disordered porous materials. The goal is to obtain the relationship between the adsorption thermodynamics and adsorbent microstructure. This was accomplished by using molecular models that exhibit realistic three dimensional des...

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Main Author: Vuong, Thieu
Language:ENG
Published: ScholarWorks@UMass Amherst 1998
Subjects:
Online Access:https://scholarworks.umass.edu/dissertations/AAI9841929
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spelling ndltd-UMASS-oai-scholarworks.umass.edu-dissertations-30762020-12-02T14:29:17Z Molecular thermodynamics of physical adsorption in heterogeneous solids Vuong, Thieu This dissertation is about the molecular modeling of fluids adsorbed in disordered porous materials. The goal is to obtain the relationship between the adsorption thermodynamics and adsorbent microstructure. This was accomplished by using molecular models that exhibit realistic three dimensional descriptions of the structural and energetic heterogeneities of the adsorbent. In these models the adsorbent is treated as a matrix of particles with a predetermined spatial arrangement. An important focus of the present work is on how the adsorbent microstructure affects the isosteric heat of adsorption. In these molecular models, microstructural variations can be made in several ways. These include: (i) changing the translational order of the matrix; (ii) the matrix particle connectivity; (iii) the porosity; (iv) the surface roughness. Our studies for a model of methane in silica xerogel show that the translational order of the matrix particles has the most significant effect. Surface roughness is also important and we have investigated several ways of incorporating this into the models. The effects of adsorbate molecular shape was investigated using two molecular models of ethane: (i) a single site model; (ii) a two site model. The effect of the adsorbate molecular shape on the adsorption isotherms is more pronounced at low temperature compared to that at high temperature. The nonspherical model tends to have a higher heat of adsorption. The differences in the adsorbate microstructures are similar to those found in the bulk fluids (e.g. a 'shoulder' in the site-site distribution functions). We have investigated the adsorption of methane-ethane mixtures in silica gel. Adsorption isotherms, heats of adsorption, and selectivities from the molecular model were calculated. These were compared with the ideal adsorbed solution (IAS) theory. It was found that the IAS theory gives very good predictions from low to moderate bulk pressures. Our work includes the first theoretical calculation of the component isosteric heats of adsorption for a mixture in a heterogeneous solid. 1998-01-01T08:00:00Z text https://scholarworks.umass.edu/dissertations/AAI9841929 Doctoral Dissertations Available from Proquest ENG ScholarWorks@UMass Amherst Chemical engineering|Chemistry
collection NDLTD
language ENG
sources NDLTD
topic Chemical engineering|Chemistry
spellingShingle Chemical engineering|Chemistry
Vuong, Thieu
Molecular thermodynamics of physical adsorption in heterogeneous solids
description This dissertation is about the molecular modeling of fluids adsorbed in disordered porous materials. The goal is to obtain the relationship between the adsorption thermodynamics and adsorbent microstructure. This was accomplished by using molecular models that exhibit realistic three dimensional descriptions of the structural and energetic heterogeneities of the adsorbent. In these models the adsorbent is treated as a matrix of particles with a predetermined spatial arrangement. An important focus of the present work is on how the adsorbent microstructure affects the isosteric heat of adsorption. In these molecular models, microstructural variations can be made in several ways. These include: (i) changing the translational order of the matrix; (ii) the matrix particle connectivity; (iii) the porosity; (iv) the surface roughness. Our studies for a model of methane in silica xerogel show that the translational order of the matrix particles has the most significant effect. Surface roughness is also important and we have investigated several ways of incorporating this into the models. The effects of adsorbate molecular shape was investigated using two molecular models of ethane: (i) a single site model; (ii) a two site model. The effect of the adsorbate molecular shape on the adsorption isotherms is more pronounced at low temperature compared to that at high temperature. The nonspherical model tends to have a higher heat of adsorption. The differences in the adsorbate microstructures are similar to those found in the bulk fluids (e.g. a 'shoulder' in the site-site distribution functions). We have investigated the adsorption of methane-ethane mixtures in silica gel. Adsorption isotherms, heats of adsorption, and selectivities from the molecular model were calculated. These were compared with the ideal adsorbed solution (IAS) theory. It was found that the IAS theory gives very good predictions from low to moderate bulk pressures. Our work includes the first theoretical calculation of the component isosteric heats of adsorption for a mixture in a heterogeneous solid.
author Vuong, Thieu
author_facet Vuong, Thieu
author_sort Vuong, Thieu
title Molecular thermodynamics of physical adsorption in heterogeneous solids
title_short Molecular thermodynamics of physical adsorption in heterogeneous solids
title_full Molecular thermodynamics of physical adsorption in heterogeneous solids
title_fullStr Molecular thermodynamics of physical adsorption in heterogeneous solids
title_full_unstemmed Molecular thermodynamics of physical adsorption in heterogeneous solids
title_sort molecular thermodynamics of physical adsorption in heterogeneous solids
publisher ScholarWorks@UMass Amherst
publishDate 1998
url https://scholarworks.umass.edu/dissertations/AAI9841929
work_keys_str_mv AT vuongthieu molecularthermodynamicsofphysicaladsorptioninheterogeneoussolids
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