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Investigation of the Solvation of CO2-philic Compounds in the Super Critical CO2 by Monte Carlo Simulations

Khanlarkhani, Ali | 2008

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 39246 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Tafazzoli, Mohsen
  7. Abstract:
  8. Although CO2 is an environmentally benign solvent, many organic solutes are only sparingly soluble in CO2. We use Monte Carlo simulations in the context of statistical perturbation theory, Widom’s particle insertion and expanded ensemble techniques in order to investigate the molecular properties involved in enhancing the solubility of materials in CO2. Our Monte Carlo simulation of diluted methane and its fluorinated forms showed that substitution of H atom with F atom, results in more favorable solvation, but with further increase of F atom (after CH2F2) due to small size of solute it is impossible for all CO2 molecules in the first solvation shell (FSS) to have a good orientation against F atoms of solute, so solvation favorability decreases. We calculate the absolute free energy of solvation of benzene and perfluorobenzene in supercritical carbon dioxide. The greater stability of perfluorobenzene attributed to the greater solvent accessible surface area and 25–30% increase in the strength of the interaction of this molecule with CO2 in the in-plane part of FSS, where F atoms exist. The extent of the self association of water in supercritical CO2 has been investigated. The association constant of water decreases with temperature and weakly depends on CO2 density. This weak density dependence provides evidence for the lack of a strong CO2-water interaction. We also calculate the Helmholtz free energy of solvation of 2-propanol and acetone in supercritical CO2. For both solute molecules, the density value corresponds to the maximum stability decreases with increasing temperature. Acetone is more stable than 2-propanol. At low densities the solvation of acetone is more exothermic than 2-propanol while at high densities it come with less entropic penalty. The solvent reorganization energy is more favorable in 2-propanol case, although the role of solute-solvent interactions is dominant in both cases.
  9. Keywords:
  10. Carbon Dioxide ; Widom Particle Insertion Method ; Self-Association ; Monte Carlo Method ; Supercritical Fluid ; Statistical Perturbation Theory ; Expanded Ensemble

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