Tools for understanding the fluid-fluid and solid-fluid equilibria of binary asymmetric mixtures

SABRINA BELÉN RODRIGUEZ REARTES; MARTÍN CISMONDI; LUCIO CARDOZO-FILHO; MARCELO SANTIAGO ZABALOY

Natal

Congreso; II Iberoamerican Conference on Supercritical Fluids (PROSCIBA 2010); 2010

Universidade Federal do Rio Grande do Norte – UFRN

Often in the literature the calculation of solid-fluid and fluid-fluid equilibria for binary systems is limited to the ranges of conditions of the experimental data on which the model parameters rely. However, a deeper understanding of the possible qualitative behavior of the system under study can be achieved by performing calculations at conditions well beyond those of the experimental data. Due to the highly non-linear nature of some phase coexistence boundaries, such as some isoplethic lines, the algorithms for carrying out the calculations over a wide range of conditions should have the ability of selecting, among the variables involved, the optimum one, i.e., the variable that should be specified for calculating the next point on the curve. This is a feature of the so called path-following methods. Such methods are useful for calculating several types of phase equilibrium lines (critical, liquidliquid-vapor, azeotropic, solid-fluid-fluid, isoplethic, isothermal, etc.). Three phase lines are particularly important since they set limits of existence for isothermal and/or isobaric and/or isoplethic hyper-lines. A given hyper-line may meet more than one stable three-phase line. This implies that a hyper-line, e.g., an isopleth, may be made of a number of segments of varying nature. In this work, we couple a model applicable to fluid-fluid and solid-fluid equilibria to a set of path-following methods, to study the rich phase behavior of the binary system made of CO2 and n-Eicosane (C20H42). This system is representative of the most complex binary systems that can be found. The model assumes a solid phase only formed by the pure heavy component. The fluid phases were described through the Peng-Robinson equation of state (PREOS). The model is relatively simple but it can generate a wide variety of phase behaviors. 2 and n-Eicosane (C20H42). This system is representative of the most complex binary systems that can be found. The model assumes a solid phase only formed by the pure heavy component. The fluid phases were described through the Peng-Robinson equation of state (PREOS). The model is relatively simple but it can generate a wide variety of phase behaviors.