(321aj) Applications of the Simplified Perturbed-Chain Saft Equation of State

Our work aims in developing a theoretically based engineering tool that can be used for complex mixtures of importance to polymer and pharmaceutical industries. Common characteristics of all of these applications are complexity of molecules involved, the presence of various types of intermolecular forces (polarity, hydrogen bonding, etc.) and the frequent coexistence of many phases at equilibrium e.g. vapour-liquid-liquid or solid-liquid-liquid.

The thermodynamic model to be developed is a group-contribution version of the simplified PC-SAFT [1] equation of state where the parameters of the model are estimated via group contributions which are based on the so-called “conjugation principle” [2].

Our first step towards this aim has been to extend the parameter table of the (simplified) PC-SAFT equation of state, which now includes parameters for around 350 compounds of which 200 have been estimated in this work. The list of compounds includes cycloalkenes, nitroalkanes, polynuclear aromatics, ketones, esters, sulphides, siloxanes, plasticizers, cyclo- and fluorinated- hydrocarbons, etc. These new PC-SAFT parameters have been extensively tested.

For many different families of organic compounds, the segment radius and interaction energy are found to be constant with increasing molar mass, while the segment number increases linearly with molar mass. So far, such trends have been previously shown only for hydrocarbons. Additionally, a systematic study for mixtures containing various gases (hydrogen, hydrogen sulphide, carbon monoxide, nitrogen, methane etc.) with heavy alkanes such as C20, C28 and C36 is performed. The overall average deviation for vapour pressure is less than 2.0% and the values of the binary interaction parameters are also very low. We have also shown that simplified PC-SAFT can successfully represent binary mixtures of alkanes and perfluoroalkanes by adjusting a temperature-independent interaction parameter. The same is true with binary mixtures of gases and perfluoroalkanes. Phase equilibrium calculations are performed for several other families of compounds in order to further investigate the reliability of the newly estimated parameters. Generally, satisfactory estimations of the tested binary systems. In many cases very good results can be obtained even without using any adjustable parameters.

[1] N. von Solms, M.L. Michelsen, G.M. Kontogeorgios, Ind. Eng. Chem. Res., 42, 1098 (2003) [2] L. Constantinou, R. Gani, AIChE J., 40, 1697 (1994)