Modeling the Absorption of Weak Electrolytes and Acid Gases with Ionic Liquids Using the Soft-SAFT Approach

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• 作者：F. Llovell ; R. M. Marcos ; N. MacDowell ; L. F. Vega
• 刊名：The Journal of Physical Chemistry B
• 出版年：2012
• 出版时间：July 5, 2012
• 年：2012
• 卷：116
• 期：26
• 页码：7709-7718
• 全文大小：486K
• 年卷期：v.116,no.26(July 5, 2012)
• ISSN：1520-5207

文摘

In this work, the solubility of three common pollutants, SO₂, NH₃, and H₂S, in ionic liquids (ILs) is studied using the soft-SAFT equation of state with relatively simple models. Three types of imidazolium ionic liquids with different anions are described in a transferable manner using the recently published molecular models (Andreu, J. S.; Vega, L. F. J. Phys. Chem. C2007, 111, 16028; Llovell et al. J. Phys. Chem. B2011, 115, 4387), whereas new models for SO₂, NH₃, and H₂S are proposed here. Alkyl-imidazolium ionic liquids with the [PF₆]^{鈭?/sup> and [BF₄]鈭?/sup> anions are considered to be Lennard-Jones chainlike molecules with one associating site in each molecule describing the specific cation鈥揳nion interactions. Conversely, the cation and anion forming the imidazolium [Tf₂N]鈭?/sup> ionic liquids are modeled as a single molecule with three associating sites, taking into account the delocalization of the anion electric charge due to the presence of oxygen groups surrounding the nitrogen of the anion. NH₃ is described with four associating sites: three sites of type H mimicking the hydrogen atoms and one site of type e representing the lone pair of electrons. H₂S is modeled with three associating sites: two for the sites of type H for the hydrogen atoms and one site of type e for the electronegativity of the sulfur. SO₂ is modeled with two sites, representing the dipole moment of the molecule as an associative interaction. Soft-SAFT calculations with the three models for the pollutants provide very good agreement with the available phase equilibria, enthalpy of vaporization, and heat capacity experimental data. Then, binary mixtures of these compounds with imidazolium-based ionic liquids were calculated in an industrially relevant temperature range. Unlike association interactions between the ionic liquids and the pollutant gases have been explicitly accounted for using an advanced association scheme. A single temperature independent energy binary parameter is sufficient to describe every family of mixtures in good agreement with the available data in the literature. In addition, a vapor鈥搇iquid鈥搇iquid equilibrium (VLLE) region, never measured experimentally, has been identified for mixtures of hydrogen sulfide + imidazolium ionic liquids with the [PF₆]鈭?/sup> anion at high H₂S concentrations. This work illustrates that relatively simple models are able to capture the phase absorption diagram of different gases in ionic liquids, provided accurate models are available for the pure components as well as an accurate equation of state to model the behavior of complex systems.}