Development of a Thermodynamic Model for Fluids Confined in Spherical Pores

The thermodynamic properties of a fluid confined in extremely small pores can be substantially different from those observed of the same bulk fluid. These differences in behavior could have technical applications in adsorption-based separations; may pose a challenge with regards to the extraction of oil entrapped in the small cavities of reservoir rocks; or could even be utilized in complex heterogeneous catalytic systems such as those used in gas-to liquid fuel conversions.

This thesis describes the use of the generalized van der Waals theory to extend cubic equations of state, such as Peng-Robinson, that are widely applied in the oil and gas industry to model the behavior of pure fluids as well as mixtures confined in spherical pores. Empirical expressions were developed for the coordination number in spherical pores as a function of the molecule to pore size ratio, for the distribution of molecules along the pore radius as function of temperature, and of the interaction potential between the molecules and the pore wall. Despite their relative simplicity, the expressions capture the limiting behaviors expected at high and low temperatures. The model parameters were then fitted to experimental data for the adsorption of light hydrocarbons and gases in common adsorbents. Finally, the calculated results were compared to the experimental results in order to assess the performance of the model, through adsorption equilibrium calculations.