Thermodynamic Properties Measurement And Modeling For Systems Containing Ionic Liquids

Ionic liquids were known as low temperature molten salts, which are solely composed of ions and have many unique attributes, e.g. negligible vapor pressure, good thermal and chemical stabilities, wide liquid-state range, tunable solubility for different substances. Therefore, Ionic liquids (ILs hereinafter) may be used as a new kind of solvent in a reaction and/or separation process. As a new solvent, ILs have recently attracted considerable attention. Therefore, thermodynamic properties measurement and modeling for the IL-containing systems have important theoretical significance and practical value.In this paper, I have studied the preparation and characterization of ILs, as well as the measurement and correlation of thermodynamic properties for IL-containing systems. Specifically, the thesis contains the following contents 1) Vapor-liquid equilibrium (VLE) measurement for a series of water/ methanol/ethanol multicomponent systems containing different ILs; 2)VLE correlation models; 3) Model development for the correlation of infinite dilution activity coefficient of molecular solutes in ILs, and 4) Development of prediction model of density for ILs in a wide range of pressure and temperature.For the commercialization of ILs, some factors have to be considered, for example, the cost, stability, toxicity as well as their biodegradability. In this paper, 10 ionic liquids are prepared via a one step reaction under mild conditions, they are 1-ethyl-3-methylimidazoliumdimethylphosphate([EMIM][DMP]), 1-ethyl-3-ethylimidazoliumdiethylphosphate([EEIM][DEP]), 1-methyl-3-methylimidazoliumdimethylphosphate([MMIM][DMP]), l-ethyl-3-methylimidazoliumdiethylphosphate([EMIM][DEP]), 1-buty1-3-methylimidazoliumdibutylphosphate([BMIM][DBP]), 1-Ethyl-3-methylimidazolium ethyl sulfate([EMIM][ES]), monoethanolammonium acetate([HMEA][Ac]), diethanolammonium acetate([HDEA][Ac]), triethanolammoniumacetate([HTEA][Ac]) and diethanolammonium chloride([HDEA]Cl). The structure of the ILs synthesed are characterized and identified using HNMR and electron-spray mass spectroscopy. These ILs show some notable merits, namely simple preparation and purification process, very high yield, low cost and low toxicity. Therefore, they are of great potential to be used in industrial applications.Vapor pressure data are measured for water, methanol and ethanol as well as their binary mixtures with different ILs ([EMIM][DMP] or [EEIM][DEP]) at varying temperature and IL-content ranging from mass fraction of 0.10 to 0.70 by a CL-II ebullimeter. The results indicate that the ILs studied can lower the vapor pressure of solvents due to the affinity between IL and the solvent, while the lowering degree depends on the type and content of IL involved. The vapor pressure data for the IL-containing binary systems are correlated using NRTL equation with an overall ARD of 0.7%, and the binary NRTL parameters are used for predicting the vapor pressure of the IL-containing ternary systems with reasonable accuracy. The results justify the applicability of NRTL equation for the representation of VLE data of IL-containing systems. In order to show the salt effect of ILs on the distillation separation of water+ethanol binary mixtures, isobaric VLE for such mixtures in the presence of ILs (mass fraction = 0.5) are predicted in the whole concentration range. The results indicate that both of the ILs may enhance the volatility of ethanol, and even destroy the azeotrope completely. The salting-out effect of ILs on the separation of water+ethanol follows the order [EMIM][DMP]> [EMIM][ES].The boiling temperature at atmospheric pressure are measured for 12 binary and 6 ternary IL-containing liquid mixtures using a CP-I type dual circulation vapor-liquid equilibrium still. The solvents studied include water, methanol, ethanol as well as their binary mixtures of water-ethanol and methanol-ethanol, and the ILs used include [HMEA][Ac], [HDEA][Ac], [HTEA][Ac] and [HDEA]Cl. The isobaric VLE data of binary systems can be well correlated with NRTL equation, and the binary NRTL parameters can be applied for the prediction of the VLE data of ternary systems with fair accuracy. The results indicate that for a specified IL its influence on the volatility of different solvents are quite different and even show an opposite trend. The behavior of the aqueous solution for the four ILs studied always shows a negative deviation from the Raults's law, while the ethanol solution of ILs always shows a positive deviation from the Raul's law expect [HMEA][Ac]. The salt effect of ILs on the separation of water+ethanol follows the order [HDEA]Cl > [HTEA][Ac] > [HDEA][Ac] > [HMEA][Ac].Considering the structural characteristics, a novel group segementation approach is proposed for ILs. On this basis, the infinite dilution activity coefficients for sixteen molecular solutes in six ILs are correlated using UNIFAC model. Vapor pressure for 18 IL-containing binary mixtures in the whole concentration range can be predicted with good accuracy using the UNIFAC parameters derived from infinite dilution activity coefficient property, which further justify the applicability of the UNIFAC model and the reasonableness of the new group segmentation mothod.Densities of ILs are represented with an EOS that is constructed on the basis of perturbation theory and ionic electrostatic interaction expressed by mean spherical approximation (MSA). The effect of electrostatic interaction on the liquid density is elucidated by comparing the density difference between an IL and a physical mixture of two reactants with which the IL is formed via a nucleophilic addition reaction. The results indicate that the density of IL is generally 10% higher than that of the physical mixture, and this difference can be well explained by the electrostatic interaction. This suggests that the electrostatic interaction is of vital importance for the thermodynamic properties of ILs. The densities of pure fluids are correlated using the EOS, and the resulting parameters (σandε) are used for the prediction of densities of ILs and their corresponding physical admixture with average absolute relative deviation(ARD) of 1%. Besides, densities of ILs reported in the literatures in a wide range of temperature and pressure are correlated and/or predicted succefully using the EOS. The results further justify the new model developed for ILs systems.