Monte Carlo simulations of phase behavior and microscopic structure for supercritical CO2 and thiophene mixtures

Abstract

The phase equilibria of thiophene in supercritical carbon dioxide are calculated by Monte Carlo simulations in Gibbs ensemble using a united atom force field. To validate the simulations, binary vapor–liquid coexistence curves were computed for two different temperatures using Monte Carlo simulations. An excellent agreement between simulations and experimental data is obtained. The effects of pressure on structural properties were studied for thiophene–CO2 binary mixtures. The radial distribution functions and local composition of thiophene in CO2 were investigated over a range of pressures. A weak dependence of thiophene structural properties with pressure was observed in supercritical phase. Local solution structure of thiophene in supercritical CO2 was studied by computing angular–radial distribution functions and spatial distribution functions with three-dimensional probability distributions. The characteristic angular–radial distributions show a mutually parallel arrangement between thiophene plane and CO2 molecules within the first solvation shell. Spatial distribution functions (SDFs) results show that CO2 molecules have two higher probability distributions around thiophene molecules located above and below the thiophene ring.