Generation of characteristic maps of the fluid phase behavior ofternary systems

PISONI, GERARDO O.; CISMONDI, MARTÌN; CARDOZO-FILHO, LUCIO; ZABALOY, MARCELO S.

FLUID PHASE EQUILIBRIA

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2014 vol. 362 p. 213 - 226

0378-3812

The main features of the fluid phase behavior of a given binary system can be grasped at a glance bylooking at its (binary) characteristic map (B-CM), which is made of unary and binary univariant lines,i.e., by geometrical objects having only one degree of freedom. Binary univariant lines are critical andazeotropic lines and liquid?liquid?vapor equilibrium lines. These lines are customary shown in thepressure?temperature plane together with the pure-compound vapor?liquid equilibrium lines (unarylines). Similarly, ternary systems also have characteristic maps for their phase equilibrium behavior.Such ternary characteristic maps (T-CMs) are made of unary, binary and ternary univariant lines. Pos-sible ternary univariant lines are the following: ternary four-phase equilibrium lines (T-4PLs), ternarycritical end lines (T-CELs) and ternary homogeneous azeotropy lines (T-ALs). T-CMs also present invari-ant points as the following: pure compound critical points, binary critical endpoints (B-CEPs), ternarycritical endpoints of four-phase equilibrium lines (T-CEP-4PLs), ternary tricritical endpoints (T-TCEP),and all possible endpoints of binary and ternary homogeneous azeotropy lines. Analogously to B-CMsfor binary systems, T-CMs make possible to quickly identify the main features of the phase behavior ofa given ternary system. In other words, T-CMs provide key information on the fluid phase equilibria ofternary systems. When dealing with models for the fluid phase behavior of ternary systems, it would beuseful to generate the T-CMs, in a way as automated as possible, once a ternary system and a model arechosen, and the model parameter values are set. This would make possible, among other outcomes, toquickly evaluate the main features of the model performance. B-CMs can be efficiently generated, whenusing a model of the equation of state (EOS) type, by applying available algorithms. In this work we showhow the univariant lines of T-CMs can be efficiently computed for a given ternary system, given EOS andEOS parameter values. In general, a ternary univariant line (T-UVL) is generated in this work by usinga numerical continuation method (NCM). NCMs are able to build, in their full extent, highly non linearT-UVLs, with minimum user intervention. In particular, we describe in this work how T-TCEPs and T-CEP-4PLs are detected and computed, and how the calculation of T-4PLs is started off. Finally, an algorithmfor the generation of computed T-CMs is presented. The algorithm relies on previously computed criticalendpoints of the binary subsystems of the ternary system under study. We have not considered yet thedetection and computation of T-ALs and of closed loop T-CELs. We provide examples of T-CMs computedover wide ranges of conditions. The results of this work show that relatively simple models can generatehighly complex topologies for the phase behavior of ternary systems.