Molecular and macroscopic modeling of phase separation

Recently proposed pseudoensemble Monte Carlo methods are extended in this w ork to map out diverse phase diagrams (projections of the phase-coexistence hypersurface) of multicomponent mixtures required to characterize fluid-ph ase equilibrium phenomena and to design separation processes. Within the ps eudoensemble framework the macroscopic models of different equilibrium proc esses can be readily integrated to the mathematical constraints that specif y the thermodynamic state of the system. The proposed Monte Carlo methods a llow, for example, the simulation of isopleths and cloud-point lines to com pare experimental to simulation data and to test molecular force fields. Ap plications of this approach include the study of retrograde phenomena in a model natural-gas mixture through simulation of dewlines and coexistence li nes at constant vaporization fraction. As demonstrated, pseudoensemble simu lations can also be used to generate the thermodynamic data necessary to so lve problems encountered in continuous and discontinuous distillation proce sses.