STABILITY ANALYSIS FOR SOLID-FLUID ISOPLETHS IN BINARY ASYMMETRIC MIXTURES

S.B. RODRIGUEZ-REARTES; M. CISMONDI; M.S. ZABALOY

Algarve. Praia da Rocha, Portugal

Conferencia; VIII IBEROAMERICAN CONFERENCE ON PHASE EQUILIBRIA AND FLUID PROPERTIES FOR PROCESS DESIGN – EQUIFASE 2009; 2009

Laboratory of Separation and Reaction Engineering/ Laboratory of Catalysis and Materials – Faculdade de Engenharia da Universidade do Porto.

Models for the description of the solid-fluid equilibrium of multicomponent asymmetric  mixtures of technological interest should behave properly for the corresponding binary  subsystems. The study of binary asymmetric systems, such as methane + n-triacontane, in  wide ranges of conditions, requires, on one hand, robust calculation procedures that achieve  convergence and, on the other hand, strategies for assessing the thermodynamic stability of  the computed equilibria. When the set fluid phase composition, of a binary solid-fluid  equilibrium isopleth, falls within the composition range of existence of the solid-fluid-fluid  equilibrium line, then, the isopleth meets a solid-fluid-fluid equilibrium point. Such intersection  point splits the isopleth into two segments. Only one of them is thermodynamically stable. It  is not a trivial matter to properly identify such stable segment. In this work, we apply a novel  strategy that makes it possible to identify stable binary solid-fluid isopleth segments. The test  is differential and does not require iterative calculations, provided that the solid-fluid-fluid  equilibrium line has already been calculated. The test is based on the computation of some  derivative of certain tangent plane distance, under the constraint of solid-fluid equilibrium at  the specified isopleth composition. Such derivative is evaluated at a special composition  value. We illustrate the application of the test for the methane + n-triacontane system.