The study of peculiarities of parabens solvation in methanol- and acetone-modified supercritical carbon dioxide by computer simulation

Abstract

Molecular dynamics simulation of solutions of methylparaben and propylparaben in supercritical carbon dioxide, modified by polar cosolvents (acetone and methanol) has been performed. The solvation features associated with the concentration of cosolvent in the fluid (0.03 and 0.06mol fraction), and with the choice of the thermodynamic state: at a temperature range of 318–348K at densities corresponding to experimental isobar 30MPa, and at change of density (0.507–0.851g/cm3) at constant temperature 328K have been researched. It is shown that the solvation of parabens in modified supercritical CO2 occurs due to the formation of hydrogen bonds with a cosolvent. Structural and dynamic parameters of these hydrogen bonds have been considered. Free energies of solvation of parabens in pure and modified supercritical CO2 at T=328K, P=21MPa and 30MPa, have been calculated. Evaluation of cosolvent induced solubility enhancement has been made on the basis of the free energy of solvation. It is found that the use of methanol as a cosolvent will result in many times greater increase in solubility of parabens in supercritical CO2, than the use of acetone. It is shown that the cosolvent induced solubility enhancement of parabens in acetone-modified supercritical CO2 is much less sensitive to such factors as change of fluid pressure and concentration of a cosolvent than that in methanol-modified supercritical CO2.