Novel approach for the calculation of critical points in binary mixtures using global optimization

Critical point calculations in binary mixtures is a very important subject in phase equilibria study. A robust method for this task is certainly a powerful tool for calculation of critical loci. These critical diagrams are, usually, employed in the characterization of the behavior in two-component systems. In this paper, a new methodology for critical point calculation in binary systems, via global optimization, is presented. This approach is a particular case of the recently proposed formulation in chemical engineering literature by Henderson et al. [N. Henderson, L. Freitas, G.M. Platt, Prediction of critical points: a new methodology using global optimization, AIChE J. 50 (2004) 1300]. This novel methodology provides a robust algorithm, which does not involve derivatives of the objective function and is insensitive to the initial guesses. We obtain results for six binary systems and perform comparisons among experimental data (for systems n-butane/carbon dioxide, ethane/propane and ethane/n-butane). We also present new calculations for systems methane/hydrogen sulfide, carbon dioxide/n-octane and carbon dioxide/n-hexadecane, and showing a detailed analysis of the critical phenomena for the system methane/hydrogen sulfide. We detected that this last system can exhibits up to three critical points, for some compositions. The results illustrate the capability of the simulated annealing algorithm to find several critical points for binary systems.