GCA-EoS: The first group contribution equation of state of the SAFT family. Applications to petrochemical, natural gas and natural products processing

F. A. SANCHEZ; T. M. SORIA; S. PEREDA; S.B. BOTTINI; E.A. BRIGNOLE

Barcelona

Workshop; 20 Years of the SAFT Equation: Recent advances and challenges; 2010

The first version of the Group Contribution with Association Equation of State (GCA-EOS) was developed for the modelling of phase equilibria found in the near critical fluid extraction and dehydration of oxygenated compounds from aqueous solutions[1]. GCA-EoS was obtained by the inclusion of a group contribution SAFT-like associating term to the GC-EOS model. Accounting the association term by a real group contribution approach was possible through the simplification of the radial distribution function to a value of one. In this version, the definition of a unique hydroxyl group to represent the association effect of hydrogen bonding in water and alcohols, greatly simplifies the extension of the model to multicomponent mixtures. This approach has been successfully applied to determine the parameters for a common hydroxyl group for water, primary and secondary alcohols. Later on, Ferreira et al.[2] extended GCA-EoS to represent phase equilibria in mixtures containing acids, esters, and ketones, with water, alcohols, and any number of inert components. Self-association and solvation between the associating groups present in these mixtures were considered with specific expressions for each kind of association system, according to the number and type of associating groups (i.e. self- and/or cross-associating groups) present in the mixture. Few years ago, a general routine was implemented following Michelsen and Hendriks [3] state function minimization approach to simplify the calculation of the association contributions to physical properties for the calculation of the fraction of non-associating sites and their first derivatives with respect to process variables. This generalized computational routine quantifies association and solvation effects by the interaction between any number of functional-associating groups with one or two associating sites[4]. This is enough to represent any compound with odd or even association sites. For instance water is represented as a 4C model using two equal groups with 2 sites (one electro-positive and one electro-negative). This implementation has already been applied to several systems containing multiple associating-solvating groups in the field of biomass processing. In this work we report the performance of GCA-EoS model for a number of complex systems of importance in the pretrochemical and natural gas industries. Moreover, the model extension to the field of natural products processing is also discussed. [1] Gross H.P., S.B. Bottini, E.A. Brignole. Fluid Phase Equilib. 1996, 116, 535 [2] Ferreira O., Brignole E.A., Macedo E.A J. Chem. Thermodynamics 2004, 36, 1105–1117 [3] Michelsen M.L., Hendriks E.M., Fluid Phase Equilibr. 2001, 180, 165 [4] Andreatta, A.., G. Foco, S. Pereda and S.B. Bottini, Proceedings I Iberoamerican Conference on Supercritical Fluids - PROSCIBA 2007, Argentina, April 2007.