Application of interval analysis for gibbs and helmholtz free energy global minimization in phase stability analysis

Abstract

-The tangent plane criterion has become important for a correct solution evaluation phase and chemical of equilibrium problem. This method, applicable to single and multiphase systems, is mainly used for a single equation of state modeling all phases involved. The present work is mainly concerned with the application of interval analysis methods for global energy minimization in high-pressure phase stability problems. Two approaches are applied: (i) the Gibbs free energy global minimization under conditions of constant temperature and pressure and (ii) the Helmholtz free energy density global minimization under conditions of constant temperature and volume. Five case studies, one ternary and four binary systems, are analyzed in connection with the Peng-Robinson equation of state (PREOS) model. Five more case studies, for the CO 2 + trans-2-hexen-1-ol system at high pressures, are used to compare different methods of phase equilibrium calculation with the approach using interval analysis. Finally, a complex system, clove oil + CO 2 , is analyzed. The results indicate that the interval analysis method is robust and reliable for all the problems studied.

Thermodynamically Stable Two-Phase Equilibrium Calculation of Hydrocarbon Mixtures with Capillary Pressure

“…Various implementations of VT-stability testing can be found in refs. [24][25][26][27][28][29] The above VT-flash problems are all defined in unconfined space. To the best of our knowledge, the investigation to the confined VT-flash problem is rare.…”

Phase stability analysis of liquid-liquid equilibrium with stochastic methods

“…Some work is available in the current literature regarding application of deterministic techniques for global optimization, such as homotopy continuation, branch-and-bound and Interval Newton analysis (Sun and Seider, 1995;McDonald and Floudas, 1995;Souza et al, 2006;Lima et al, 2006). However, just a few studies make use of global stochastic techniques, like Simulated Annealing and Genetic Algorithm, for phase equilibrium and phase stability calculations (Zhu and Xu, 1999;Zhu et al, 2000;Rangaiah, 2001).…”

Isochoric Phase Stability Testing for Hydrocarbon Mixtures

“…Even though this work is focused on the isochoric stability, it is interesting to note that when p and T are specified, a similar TPD function, based on the Helmholtz free energy, can be used, with component molar densities as independent variables (Nichita et al, 2006;Souza et al, 2006). The formalism presented here is quite similar to that used by Nichita et al (2006), but the specifications of the problem to be solved are different.…”

“…Essentially, they are replacing a generally nonsmooth function (the Gibbs free energy) with a smooth function (the Helmholtz free energy density). Recently, volume-based methods have been proposed for phase equilibrium calculations at p and T specifications (Nichita et al, 2006;Souza et al, 2006).…”