Phase Behavior and Reliable Computation of High-Pressure Solid−Fluid Equilibrium with Cosolvents

Abstract

The identification of the correct, stable solution to a phase equilibrium problem, given a particular thermodynamic model, is essential for the design of separation processes.It is also important in the selection of an appropriate model to represent experimental data.The need for a completely reliable method to test for phase stability is particularly pressing when the number of phases likely to be present is not intuitive to the user, as is frequently the case with high-pressure systems. Previously, we have a presented a completely reliable computational technique, based on interval analysis, to correctly identify phase equilibrium and test for phase stability in binary solvent-solute systems, that include the possibility of a solid phase, using any of a variety of cubic equations of state as the thermodynamic model.Here we extend the methodology to include multicomponent solvent-solute-cosolvent systems where the likelihood of additional phase formation is even greater than in the binary case. Gaseous or liquid cosolvents are frequently used in supercritical fluid extraction processes, and are integral in processes such as the gas anti-solvent process (GAS) to precipitate uniform solid particles. Using several examples from the literature, we demonstrate how the new computational technique can be used to identify experimental data that may have been misinterpreted and to identify models that do not predict what the modeler intended.

Finding limiting flows of batch extractive distillation with interval arithmetic

“…17 The idea of applying interval methodology to determine global optima and roots has already found its way to the community of chemical engineering, as well. Stadtherr and co-investigators [18][19][20][21][22][23][24][25][26] have published an extensive literature on chemical engineering applications.…”

A subdivision algorithm for phase equilibrium calculations at high pressures

“…Some recent work in the literature uses strategies that minimize the dependence on the initial guess or approaches that seek all roots of the algebraic system independent of the initial guess. Of these, the following can be cited: multigrid mesh initialization (Sofyan et al, 2003), the homotopy continuation method (Bausa and Marquardt, 2000;McDonald and Floudas, 1995;Seider et al, 1991;Kuno and Seader, 1988;Wayburn and Seader, 1987) and the interval analysis algorithms -applied to flash and phase stability analysis problems (Scurto et al, 2003;Kerfott et al, 1994;Hua et al, 1998a,b;Kerfott and Novoa, 1990).…”

Reliable phase stability analysis for asymmetric models

“…We will consider here only the situation in which vapor and liquid phases are possible, and use g V (x) to represent the Gibbs energy of a vapor phase and g L (x) to represent the Gibbs energy of liquid phases. Xu et al [22] and Scurto et al [23] have described an approach for deterministic phase stability analysis for the asymmetric case of solid-fluid equilibrium, in which one model is used for fluid phases, and another for pure solid phases.…”