(52i) Simultaneous Description of Thermodynamic and Transport Properties Using the Extended Soft-SAFT Equation of State

The optimization of current industrial processes requires detailed knowledge of the thermophysical properties of fluids at highly non-ideal conditions. In fact, high-pressure process applications are common at an industry level. At these conditions, most of the theoretical approaches fail into the description of basic thermodynamic and transport properties, such as density, solubility, compressibility, heat capacity, viscosity and conductivity, among others. An additional problem comes from the use of independent equations/correlations to evaluate each thermophysical property. The use of integrated equations able to provide accurate values of a group of thermophysical properties for practical applications is of high interest to find a link between the different methodologies/correlations available for each particular property (heat capacity, speed of sound, viscosity, thermal conductivity) in order to have a common framework, avoiding data inconsistencies.

The goal of this contribution is to highlight the advantages of an extended version of the molecular-based soft-SAFT equation of state [1] for high-pressure processes. Particular attention is paid to the study of transport properties. The Free-Volume Theory (FVT) formulism [2] is coupled into soft-SAFT for the description of the viscosity of fluids. The approach includes 3 additional parameters related to the viscosity, normally fitted to viscosity data of the pure fluid at several isotherms or isobars [3]. The effect of these parameters is investigated in order to identify trends with the molecular weight and the number of carbons of the compound. The extension to mixtures is evaluated by testing several mixing rules [4]. In addition, the Bridgmann equation [5] is also included in the same framework to estimate the thermal conductivity of a series of compounds of interest. The accuracy of this equation is dependent on the ability of soft-SAFT to predict accurate values for the derivative properties. Hence, apart from the classical parameters optimization method, where only density and vapor pressure data are used, a new method for determining the soft-SAFT compound molecular parameters, including derivative properties data, is investigated and developed. With this integrated approach, all the data is consistent and there is no need to use additional independent correlations. Several examples including n-alkanes, hydrofluorocarbons, fatty acid esters (biodiesel), 1-alkanols and ionic liquids in a wide range of temperature and pressure are highlighted [4,6-8].

Acknowledgments

This work has been partially financed by the Catalan government (2014SGR-1582) and the Air Products Group.

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