Molecular modeling of interfacial properties of industrial relevant fluids

Abstract

In this PhD thesis, the Density Gradient Theory (DGT) [van der Waals, 1894] combined with a molecular-based Equation of State (EoS); the soft-SAFT [Blas and Vega, 1997], was applied to simultaneously predict the phase behavior and the interfacial properties of industrial relevant fluids. As the equation is based in statistical mechanics, its approximations and assumptions were assessed against simulation data for the same underlying model. Once the model was validated, it was applied to simultaneously calculate the phase equilibria and the interfacial properties of some of the most representative industrial fluids, far from and close to the critical region. In particular, the model has been tested with molecular model fluids as Lennard-Jones chains, giving excellent agreement with simulation data, and then applied to different pure fluids, including: n-alkanes, light alkanols, ionic liquids, refrigerants, nitriles, water, carbon dioxide and ammonia, among others. A step forward has been done by calculating the interfacial properties of the binary mixtures of industrial interest, with associating and nonassociating compounds, in a predictive manner, avoiding the need of additional fitting, and providing information for systems for which there is not experimental data available. In addition, three correlations of the influence parameter as a function of the carbon number have been proposed for the light alkanes, light alkanols and one ionic liquid family, allowing for predictions of properties of compounds not included in the fitting procedure. A final novel contribution of this Thesis work is the prediction of the critical temperature, density and pressure of the most common used ionic liquids by using soft-SAFT coupled with the DGT. This is to our best knowledge the first time that an EoS is coupled to the DGT to calculate simultaneously the interfacial tension at elevated temperatures, while capturing the asymptotic behavior as the critical region is approached. Moreover, the surface properties, such as surface entropy and surface enthalpy, have been derived from the surface tension dependence on temperature, finding a very good agreement with the values reported in the literature from simulation and experimental contributions. Finally, a throughout study of the different density profiles, including single fluids and different binary mixtures, has been carried out to complete the description of the interfacial phenomena. Absorption and desorption density profiles are also presented given their importance in transport and process control. The work developed here demonstrates that coupling an accurate molecularbased equation of state for phase properties, the soft-SAFT equation, with a simple and accurate theory for interfacial properties, the Density Gradient Theory, is a reliable tool to simultaneously predict the phase and interfacial properties of nonassociating and associating compounds, as well as their mixtures with a very slight computational effort and great accuracy.

Date of Award	23 Jul 2012
Original language	English
Supervisor	Félix Luis Llovell Ferret (Director), Lourdes Vega Fernández (Director) & Javier Rodriguez Viejo (Tutor)