GRAND CANONICAL MONTE CARLO SIMULATION FOR SOLUBILITY CALCULATION IN SUPERCRITICAL EXTRACTION

The Grand Canonical Ensemble Monte Carlo (GCEMC) technique is used to simulate highly nonideal dilute mixtures in the near vapor-liquid critical region. These systems are commonly found in supercritical fluid extraction processes. Mixtures composed of model CO2/naphthalene/water molecules are studied. Very large and highly correlated concentration fluctuations were observed. It was found that when the total number of molecules in the system exceeded about 150, system size dependence was not significant. The GCEMC method breaks down when the system density exceeds about 1.5 times the solvent critical density due primarily to the low probability of successful addition and removal of the large naphthalene molecules. In some systems, the presence of a small amount of water caused a dramatic increase in the system density and in naphthalene solubility. By examining the radial distribution functions in these mixtures, the origin of this effect can be attributed to the preferential aggragation of the solute naphthalene molecules around the highly polar water molecules.