EDITORIAL - Phase Equilibrium Challenges and Modern Practice

Thermodynamic modeling and phase equilibria are at the heart of chemical process design. For example, (70 to 90) % of the equipment and energy costs in modern chemical plants are related to separation and purification processes and they are designed largely on the basis of thermodynamic equilibrium. More importantly, new chemical engineering processes often involve multicomponent, non-ideal system, which can exhibit a variety of possible phase equilibria. Furthermore, the processes are often performed at pressures and temperatures near the critical point or near the phase boundary, which further complicates the solution of the phase equilibrium problem. Last, but not least, phase equilibria calculations are executed nowadays not only as stand-alone calculations, but also as a part of a more general simulation, synthesis or design case, performed by a process simulator, where they are run thousands of times. In these cases the reliability and robustness of phase equilibria calculations is of utmost importance since their failure at any stage will disrupt completely the solution process.