Prediction and correlation of the phase behaviour of non-ideal binary systems by combining an equation of state with the COSMO-RS model
Advancing the chemical engineering fundamentals
Thermodynamics: Applications of Equations of State (T2-1b)
Keywords: equation of state, mixing rule, cosmo-rs, quantum chemistry
Equations of state (EOS) are often used in phase equilibrium calculations. Such calculations are of importance in the design and simulation of chemical processes. In this matter, cubic equations of state are widely used due to their algebraic simplicity and accuracy, when applied to nearly ideal mixing components. To use such equations to model the complex phase behavior of highly non-ideal mixtures, however, mixing rules other than the usually applied van der Waals mixing rules are required. Wong and Sandler [1] and later Orbey and Sandler [2] introduced a mixing rule, which combines a cubic EOS with an excess Gibbs energy model. When no binary information of the system is known, the COSMO-RS [3] model can be used to predict the interaction behaviour of two or more components. It was shown that the COSMO-RS model can be used to predict low-pressure vapour-liquid equilibria in many systems [4].
In this contribution the combination of COSMO-RS with a cubic EOS is demonstrated in two different ways:
(1) correlating and
(2) predicting the phase behaviour of strongly non-ideal mixtures
In (1) the excess Gibbs energy is predicted by COSMO-RS and used to correlate non-ideal mixtures in combination with the Peng-Robinson EOS and the Wong-Sandler mixing rules. The remaining kij parameter has to be fitted to experimental data.
In (2) the COSMO-RS is used to predict the activity coefficients of the components at infinite dilution. These activity coefficients were used to evaluate the binary parameters of a modified NRTL GE expression in order to determine the mixing parameters of the Peng-Robinson EOS, by applying the Wong-Sandler mixing rules. Here, kij is set to zero and there are no parameters to fit. By using COSMO-RS, the advantage of this second approach, is the a-priori prediction of the activity coefficients from the molecular structure.
Examples are shown for both approaches for binary systems of alcohol/water, aromatic component/water, and alkane/ketone.
1. Wong, D. S. H.; Sandler, S. I.: AIChE Journal 38 (1992), S. 671-680; 2. Orbey, H.; Sandler, S. I.: AIChE Journal 41 (1995), 683-690; 3. Klamt, A.: Journal of Physical Chemistry 99 (1995), 2224-2235; 4. Spuhl, O.; Arlt, W.: Ind. Eng.Chem.Res. 43 (2004), S. 852-861
See the full pdf manuscript of the abstract.
Presented Monday 17, 15:00 to 15:20, in session Thermodynamics: Applications of Equations of State (T2-1b).
