Grad Students/Postdocs

Publications

Adolfo E. Ayala, Luke D. Simoni, Youdong Lin, Joan F. Brennecke, Mark A. Stadtherr. Process Design Using Ionic Liquids: Physical Property Modeling. PSE 2006, view abstract Ionic liquids are a relatively new class of materials with properties that make them attractive for a wide variety of engineering applications. For design purposes, it is useful to have a relatively simple model (i.e., excess Gibbs energy model or equation-of-state model) capable of describing the physical properties and equilibrium behavior of ILs and IL solutions. We consider here the performance of two selected models, NRTL applied to the modeling of liquid-liquid equilibrium and an electrolyte equation-of-state applied to the modeling of aqueous mean ionic activity coefficients. In each case we focus on issues in parameter estimation, and use an approach based on interval mathematics to solve the parameter estimation problem globally. Sample results are presented and suggest that the models considered here may be useful for correlation of data, but may not be well suited for prediction.

Luke D. Simoni, Youdong Lin, Joan F. Brennecke, Mark A. Stadtherr. Reliable computation of binary parameters in activity coefficient. Fluid Phase Equilib., 255:138-146, 2007. view abstract A method based on interval analysis is presented for determining parameter values from mutual solubility data in two-parameter activity coefficient models for liquid–liquid equilibrium. The method is mathematically and computationally guaranteed to locate all sets of parameter values corresponding to stable phase equilibria. The technique is demonstrated with examples using the NRTL and electrolyte-NRTL (eNRTL) models. In two of the NRTL examples, results are found that contradict previous work. In the eNRTL examples, binary systems of an ionic liquid and an alcohol are considered. This appears to be the first time that a method for parameter estimation in the eNRTL model from binary LLE data (mutual solubility) has been presented.

Luke D. Simoni, Youdong Lin, Joan F. Brennecke, and Mark A. Stadtherr. Modeling Liquid-Liquid Equilibrium of Ionic Liquid Systems with NRTL, Electrolyte-NRTL, and UNIQUAC. Ind. Chem. Eng. Res., 47:256-272, 2008. view abstract Characterization of liquid-liquid equilibrium (LLE) in systems that contain ionic liquids (ILs) is important in evaluating ILs as candidates for replacing traditional extraction and separation solvents. Although an increasing amount of experimental LLE data is becoming available, comprehensive coverage of ternary liquid- phase behavior via experimental observation is impossible. Therefore, it is important to model the LLE of mixtures that contain ILs. Experimental binary and ternary LLE data that involve ILs can be correlated using standard excess Gibbs energy models. However, the predictive capability of these models in this context has not been widely studied. In this paper, we study the effectiveness with which excess Gibbs energy models can be used to predict ternary LLE solely from binary measurements. This is a stringent test of the suitability of various models for describing LLE in systems that contain ILs. Three different excess Gibbs free energy models are evaluated: the non-random two-liquid (NRTL) model, the universal quasi-chemical (UNIQUAC) model, and the electrolyte-NRTL (eNRTL) model. In the case of eNRTL, a new formulation of the model is used, based on a symmetric reference state. To our knowledge, this is the first time that an electrolyte excess Gibbs energy model has been formulated for and applied to the modeling of multicomponent LLE for mixtures that involve ILs. Ternary systems (IL, solvent, co-solvent) that exhibit experimental phase diagrams of various types have been chosen from the literature for comparison with the predictions. Comparisons of experimental and predicted octanol-water partition coefficients are also used to evaluate the models studied.

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