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Theoretical study of fluid adsorption in porous materials

dim 20 oct 2019


East China University of Science and Technology

Shanghai - CHINE


Soutenance de thèse de M. Chongzhi QIAO du Laboratoire de Chimie de Lyon, sous la direction de M. Wei DONG et sous la cotutelle de M. Shuangliang ZHAO de l'ECUST en Chine

Langue(s) des interventions

Description générale

Porous material is strategically important in chemical engineering, e.g., sustainable developments based on new clean energies, capturing Greenhouse gas, separation and purification, the development of high-performance catalysts, and design of sensors. The development and application of porous materials involves studies of the thermodynamics and dynamics of fluids in porous medium. In last decades, a plenty of experimental and theoretical studies have been reported. However, due to the variety of porous materials, and thermodynamics properties of confined fluid are affected by so many material and fluid properties, e.g., pore size distribution, porosity, pore connectivity, the fluid-material interaction, temperature, and pressure, etc., studies of classical statistical mechanics methods such as, molecular simulation, and density functional theory, are still on a case-by-case way. The case- by-case study is hardly to offer neither the control variables of confined fluid to provide a regular pattern of confined fluid nor the common relation and correlation between the different confined fluids. Hence, the development of thermodynamic theories or the universal scaling laws that can accurately describe the thermodynamic properties of confined fluids becomes more and more important.

The resistance of fluids into porous medium is related to its chemical potential. We first studied the influence of confined conditions on the chemical potential of fluids. The scaled particle theory and molecular simulation are used to study the influence of fluid and material conditions, e.g., fluid density, porosity, and morphology of material, on chemical potential. Result shows that an increase on chemical potential, which means the increase of resistance of fluids into porous materials can be led by reducing the porosity, or increasing the fluid density, or increasing the area of solid-liquid interface. This work provides some clues for reducing the pressure drop of fluid in chemical industry.

The general equation of state for confined fluid is still lacking. We combined morphological thermodynamic and scaled particle theory to explore the control variables of confined fluid. We introduced the first equation of state for confined fluid which is irrelevant with the theoretical model of porous material. In this equation of state, four geometric properties of porous material, i.e., the porosity, the area of solid-fluid interface, integrate Gaussian curvature, and integrate mean curvature are considered as control variables. And the independent variables are chemical potential and temperature. Results from this equation of state have a great agreement with molecular simulation in a wide range. This work offers a theoretical basis for analyzing the fluid properties in chemical industry. Also, for the first time, we combined scaled particle theory for bulk fluid and morphological thermodynamics to study bulk fluid. A new equation of state for bulk fluid is obtained which does not only have a very high accuracy, but also have a simple expression. This work promoted the development of thermodynamics.

The relationship between confined fluids and bulk fluids remained elusive. With the help of scaled particle theory and molecular simulation, we studied the thermodynamics properties of confined fluid, e.g., pressure, chemical potential. A general scaling relation that connects the confined fluid and bulk fluid is found. This scaling relation shows that the difference of thermodynamics properties between confined fluid and bulk fluid can be described by only porosity, excess adsorption amount, and the pressure of equilibrated bulk system. The intrinsic relation between scaling relation and Gibbs adsorption theory is also revealed. This scaling relation deepens the understanding of confined fluid and provides a new method to measure the thermodynamic properties of confined fluid that are experimentally difficult to measure directly.

With the help of theoretical study and molecular simulation, this thesis studies the thermodynamics properties of confined fluid, clarifies the control variables of confined fluids, and discovers the common law of thermodynamics properties among different confined fluids. A scaling relation and two new equations of state were reported, they deepened the understanding of confined fluid, and advanced the development of the thermodynamics for confined fluid.

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