Separation of Water and Alcohols

1. Separation of Water and Alcohols using 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide1 Alexandre Chapeaux, Luke D. Simoni, Mark A. Stadtherr, Joan F. Brennecke* Department of Chemical and Biomolecular Engineering, University of Notre Dame Notre Dame, IN 46556, USA *e-mail: jfb@nd.edu • Objectives • To optimize ionic liquids for various liquid/liquid separations. • Separating water and alcohols using ionic liquids has been shown previously2-4. • Using liquid-liquid separations instead of distillation could reduce energy consumption. • Less expensive, environmentally sound production of alcohols. • Ternary diagrams are necessary in order to design liquid-liquid separations. • With the binary data as starting points, ternary diagrams of systems with water and ethanol or 1-butanol were developed for [hmim][Tf2N]. • Measured all three components of each phase and verify that the composition of each phase sums to one. • Used gE models to predict ternary data over the entire composition range. • Used only parameters determined from binary and pure component data. • Test the ability of the NRTL, UNIQUAC, and e-NRTL. 1-hexyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide [hmim][Tf2N] Modeling Experimental Method • Binary Parameter Estimation (LLE and VLE) • Use binary data to solve 2x2 set of equal fugacity equations for binary interaction parameters • Solve for all solutions with reliable Interval Newton Generalized Bisection (IN/GB) routine • Determine parameter suitability • Ternary Phase Equilibrium (LLE) • Phase stability • Reliable global minimization of difference between Gibbs energy and plane tangent to surface at phase composition with IN/GB • Phase split • Local minimization of Gibbs energy to determine new configuration of phases for stability test Alternate between the two problems until a stable set of phases is achieved Separate phases Equilibrate for 12 hrs Stir for 12 hrs Analyze the alcohol and IL content using HPLC with RI detector Analyze water content using the Karl Fisher Coulometer Mix water, IL, and alcohol in a vial • NRTL (NonRandom Two-Liquid) • Assumes molecular IL • Describes non-ideality via local composition (LC) Obtain compositions for ternary phase diagrams IL Experimental Results (Renon & Prausnitz, 1968) • UNIQUAC (UNIversal QUAsi-Chemical theory) • Assumes molecular IL • Describes residual and combinatorial contributions • Requires physical r & q parameters for size and shape Mass Fraction (Abrams & Prausnitz, 1975) • eNRTL (electrolyte-NRTL) • Assumes • Completely dissociated IL • Dielectric continuum = mixture of non-IL components • Describes local composition and electrostatic (Pitzer-Debye-Hückel) contributions • Requires mixed solvent properties (averaged) & closest approach, ρ IL  + & - (Chen et al., 1982) Mol Fraction Mass Fraction Mol Fraction • 1-Butanol system has a good potential for extraction. • Tie lines are sloping in the right directions. • Separation factors at low concentrations of butanol of 80-100. • The UNIQUAC model best represents the experimental data. • This is the NIST standard and the first IL we have used to do this study. Other ILs could be more efficient extracting solvents for the water/alcohol systems. • Conclusions • The ethanol system is a type one system with tie lines sloping toward the IL. • The 1-butanol system is a type two system with tie lines sloping towards the water. • Ethanol cannot be extracted from the water using [hmim][Tf2N]. • The tie lines are not sloping in the right direction. 1Chapeaux, A.; Simoni, L. D.; Stadtherr, M. A.; Brennecke, J. F., Manuscript in Preparation (2007) 2Najdanovic-Visak, V.; Rebelo, L. P. N.; da Ponte, M. N., Green Chem. 7, 443-450 (2005) 3 Hu, X. S.; Yu, J.; Liu, H. Z., J. Chem. Eng. Data 51, 691-695 (2006) 4 Fadeev, A. G.; Meagher, M. M., Chem. Comm., 295-296 (2001) We acknowledge financial support for the project from the National Oceanic and Atmospheric Administration (NOAA)