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Experimental Study and Thermodynamic Modelling of the Solubilities of Acid Gases in Ionic Liquids

Safavi, Mohammad Ali | 2013

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 45089 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Ghotbi, Cyrus; Jalili, Amir Hossein; Taghikhani, Vahid
  7. Abstract:
  8. New experimental results are presented for the solubility of carbon dioxide and hydrogen sulfide sulfide in six imidazolium-based ionic liquids included 1-octyl-3-methylimidazolium tetrafluoroborat ([C8mim][BF4]), 1-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6]), 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imide ([C8mim][Tf2N]), 1-octyl-3-methylimidazolium trifluoromethanesulfonate ([C8mim][TfO]), 1-hexyl-3-methylimidazolium trifluoromethanesulfonate ([C6mim][TfO]), 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([C4mim][TfO]) at temperatures range from 303.15 to 353.15 K and pressures up to about 2.5 MPa. The solubilities of the mixture of CO2/H2S in [C8mim][PF6] and [C8mim][Tf2N] under various feed compositions were also measured at temperatures of (303.15, 323.15 and 343.15) K and the pressure up to 1 MPa. The solubilities of carbon dioxide and hydrogen sulfide increased with increasing pressure and decreased with increasing temperature and the solubility of H2S is about three times that of CO2 in the particular ionic liquids studied. We studied the effect of cation alkyl chain length on the CO2 and H2S solubilities by comparison of the experimental data of this study with those of previous reports. As the cation alkyl chain length became longer, the solubilities of CO2 and H2S increased in ionic liquid. Additionally, the influence of the anion on the solubility is studied by comparing the solubilities of CO2 and H2S in different ionic liquids. As a result, CO2 and H2S have higher solubility in the IL with [Tf2N]¯and [TfO]¯ as the anion. The measured data were also correlated using extended Henry’s law included Pitzer’s virial expansion for the excess Gibbs free energy, the generic Redlich – Kwong cubic equation of state proposed for gas/ionic liquid systems and the perturbed chain statistical associating fluid theory (PC-SAFT). The correlations from the three models show quite good consistency with the experimental data for CO2/IL and H2S/IL binary mixtures within experimental uncertainties. For CO2/H2S/IL ternary mixtures, the RK model shows better correlation with the experimental data. Parameters of pure ionic liquids for PC-SAFT model were estimated using experimental densities. Two strategies were considered to model densities of pure ionic liquids using PC-SAFT model. In strategy 1, ionic liquids were modeled as as nonassociating compounds and in strategy 2, ionic liquids were considered as self-associating molecules and two association sites were assigned to each association. According to the results, the associating contribution should be taken into account in order to accurately correlate the properties of ionic. The solubility of CO2 and H2S in ionic liquids was then studied. After fitting a binary interaction parameter kij on experimental VLE data, the model was able to describe accurately the solubility of acid gases in these two ionic liquids. The results show an average deviation of less than 2.98% and 3.25% in the calculation of the mole fraction of CO2 and H2S in the ionic liquids, respectively
  9. Keywords:
  10. Acid Gas ; Vapor-Liquid Equilibrium (VLE) ; Thermodynamic Modeling ; Ionic Liquids ; Gas Solubility ; Gas Mixture ; Statistical Assosiating Fluids Theory (SAFT)

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