A Statistical Associating Fluid Theory for Polar and Electrolyte Fluids
CHEMICAL ENGINEERING A STATISTICAL ASSOCIATING FLUID THEORY FOR POLAR AND ELECTROLYTE FLUIDS HONGGANG ZHAO Dissertation under the direction of Professor Clare McCabe The ability to accurately predict the thermodynamic properties and phase behavior of fluids is central to product and process design, not only in traditional chemical engineering fields such as petroleum refining, but also in environmental and biochemical engineering applications. While many equations of state are available in the literature to correlate and predict the thermodynamic properties of fluids, they often rely on effective parameters to describe the molecular interactions, and so have limited applicability. In order to develop a predictive approach to determine the thermophysical properties and phase behavior of fluids, the effects of the size, shape and molecular-level interactions need to be explicitly included into the equation of state. The statistical associated fluid theory (SAFT) takes into account the effect of such interactions and has parameters that directly relate to molecular level/physical interactions. However, the effects of long-range interactions, such as ion-ion, ion-dipole, dipole-dipole etc., are typically included in an effective way through the segment size and energy parameters. Since the interactions are not described explicitly in the equation the predictive capability is reduced and large binary interaction parameters fitted to experimental data are generally needed. In this work, in order to overcome this drawback of the SAFT equation, and develop a more predictive approach, a SAFT equation for polar fluids and electrolyte solutions, in which the effects of the long-range interactions are taken explicitly into account, has been developed. In particular, the SAFT-VR+D approach, which explicitly accounts for dipolar interactions through a combination of the SAFT-VR approach with integral equation theory, is proposed. The thermodynamic properties and phase behavior of dipolar square-well monomer and chain fluids, in which one or more segments are dipolar, have been studied, and the new equation validated through comparison to new computer simulation data. The equation has also been extended to model electrolyte fluids, in which the solvent molecules are explicitly described as dipolar associating molecules, and ionic liquids.