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Comparative study between equations of state that uses associating contribution: Application of the Carnahan–Starling Repulsion term and introduction of a co-volume parameter temperature-dependent


R. Checoni1 and S. Ravagnani2

1Instituto de Quimica - Universidade Estadual de Campinas - UNICAMP, Brasil
2Faculade de Engenharia Química - Universidade Estadual de Campinas - UNICAMP, Brasil

Keywords: equation of state, CPA-EOS
property: pressure, volume, temperature
material: pure compounds

Studies related to development of equations of state (EOS) to represent adequately thermodynamic behavior of pure compounds are considered important tools for engineers to design and to optimize industrial processes. Furthermore, these tools also contribute to amplify the researchers’ knowledge about the interactions types existing between molecules. In relation to several equations of state existing, special attention is given to a specific group of EOS: that one taking to account the hydrogen bond effects existing in associating species. At this group belongs Statistical Associating Fluid Theory (SAFT) [1] EOS (that combines two terms: one related to contribution of the physical forces and other for the contribution of association (hydrogen-bonds)) and Cubic Plus Association (CPA-EOS) [2] that combine the cubic Soave-Redlich-Kwong EOS [3] with the association part of SAFT EOS [1]. Since its proposal, several modifications were proposed and the improvement of the CPA-EOS [2] predictive capability of vapor-liquid equilibria and liquid-liquid equilibria data of associating and non-associating fluids can be observed as showed in [4]. However, studies reveals that still it is possible to improve the prediction capability of cubic plus association EOS if: a) the cubic part is replaced by modified Peng-Robinson EOS [5] in which Carnahan-Starling repulsive term is accounted and b) both attraction and repulsion terms are taken temperature dependents. In this way, a new equation of state not cubic in relation to volume is proposed in present work. Vapor pressure and liquid and vapor volumes of 1-alkanols (C1 to C10) and water were correlated using this proposed non-Cubic Plus Associating–EOS (n-CPA) and it is possible to observe satisfactory agreement between experimental and calculated data as well as the physical consistency improvement of this new EOS. Comparisons between pressure and volume data calculated using CPA EOS presented in the literature [4] with those calculated using the new EOS proposed are made.

References
  1. S.H. Huang, M. Radosz, M., Ind. Eng. Chem. Res., 29, 2284-2294. (1990)

  2. G.M. Kontogeorgis, E.C. Voutsas, I.V. Yakoumis, D.P. Tassios, Ind. Eng. Chem. Res. 35, 4310-4318 (1996)

  3. G. Soave, Chem. Eng. Sci., 27, 1197-1203 (1972)

  4. G.M. Kontogeorgis, M.L. Michelsen, G.K. Folas, S. Derawi, N. von Solms, E.H. Stenby, Ind. Eng. Chem. Res. 45, 4855-4868 (2006)

  5. D-Y. Peng, D.B. Robinson, Ind. Eng. Chem. Fundam. 15, 59-64 (1976)

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