Sublimation Pressure Calculated from HighPressure Gas-Solid Equilibrium Data Using Genetic Algorithms

Sublimation pressures of pure solids are calculated from high-pressure solubility data using genetic algorithms. The Peng-Robinson equation of state with the mixing rules proposed by Wong and Sandler is used as the thermodynamic model to evaluate the fugacity coefficients in the classical solubility equation and the variables P-y, for given values of T-x. The van Laar model was incorporated to evaluate the excess Gibbs free energy included in the Wong-Sandler mixing rule. The sublimation pressure is considered as a parameter to be determined by regression analysis of experimental solubility data. Thus, an optimization problem, in which the difference between the correlated and experimental data of solubility is to be minimized, is solved using a method based on genetic algorithms. This method uses biologically derived techniques such as inheritance, mutation, natural selection, and recombination to find the optimum solution of the optimization problem. Five gas-solid systems, including 16 isotherms and a total of 344 P-T-y data points, were used for the study. The systems studied were binary mixtures containing supercritical carbon dioxide with naphthalene, biphenyl, phenanthrene, anthracene, and pyrene. The proposed method allows one to calculate sublimation pressures of solids with high accuracy.