The molecular clusters in a supercritical fluid–solid system should be considered as a phase—thermodynamic principle and evidence

Abstract

In this work we propose a new thermodynamic principle in which a supercritical fluid (SCF)-solid system is divided into a solid phase, a cluster phase, and a bulk fluid phase, i.e., the molecular clusters in the system are considered as an individual phase. The phase equilibria of various SCF-solid systems are calculated using this principle in combination with Monte Carlo simulation and the Peng-Robinson equation of state (PR-EOS). It is shown that in the critical region of the supercritical (SC) solvents where the clustering is significant, the results calculated using this thermodynamic principle are much more consistent with the experimental data than those calculated using the conventional thermodynamic principle, confirming the validity of the principle proposed in this work.

Microscopic Structure and Solubility Predictions of Multifunctional Solids in Supercritical Carbon Dioxide: A Molecular Simulation Study

“…The solvent distribution is highly nonuniform, where the local density around the hydroxyl, carbonyl, and amide groups can be as high as four times the bulk density. The issue of local density “clustering” is of particular importance for the development of equation-of-state (EoS)-based models for SCF-solid systems. − Recently, Hou et al have demonstrated that if the molecular clusters in the SCF-solid solutions are considered as a separate phase, a significant improvement is achieved over conventional EoS modeling of solid solubility in sc-CO 2 , particularly near the critical region where pronounced clustering exists.…”