| Ionic liquids (ILs), which are characterized by low vapor pressure, good stability, unflammability, and so on, are potential alternatives to conventional entrainers in special distillation, since ILs show as excellent solubility as that of conventinal organic solvents, and as high separation efficiency as that of inorganic salts. The problems encounterd in conventional extractive distillation as well in salt distillation can be partially or even completely avoided with the application of ILs, leading to a clean production process in the separation of azeotropes.For the large scale application of ILs in industry, it is essential to continuously accumulate thermodynamic data and improve thermodynamic models for systems containing ILs. Meanwhile, understanding the interaction mechanism between ILs and other molecular solvents can help to reduce the blindness experimental works to screen potential ILs for a specific separation problem from thousands of ILs. Towards these concerns, the major works accomplished in this thesis are as follows:(1) Three ILs, viz.,1,3-dimethylimidazolium methylsulfate ([MMIM][MS]), 1-ethyl-3-methylimidazolium methylsulfate ([EMIM][MS]), and 1-ethyl-3-methylimidazolium methylsulfate ([EMIM][ES]), have been synthesized through one step reaction using N-alkylimidazole and dialkyl sulfate as the raw materials. Using this synthesis method, these ILs can be obtained from low price raw materials as well as simple reaction and purification steps, with a yeild up to 94%. The NMR examination results indicated that the prepared ILs had a mole purity of 99.5% (water was not included). After dewatering, the water-content in the ILs was lower than 500ppm.(2) Vapor-liquid equilibrium (VLE) data of T, P, x for water, ethanol, 1-propanol, and 2-propanol, as well as the mixtures of {water+1-propanol} and{water+2-propanol}, were experimentally measured in the presence of the prepared ILs using a quasi-static ebulliometric method. The experimental vapor pressure data for binary systems containing IL were correlated using Wilson, NRTL, and UNIQUAC model, with an average absolute relative deviation (AARD(P)) of 0.51%,0.41%, and 0.49% respectively. The obtained binary model parameters were employed to predict the vapor pressure for the ternary systems with an overall AARD(P) of 4.05%,1.46%, and 4.06% for Wilson, NRTL, and UNIQUAC respectively. The correlated and predicted results justify the applicability of the conventional activity coefficient models for the description of VLE behavior of IL-containing systems.(3) The VLE data of the binary systems containing ILs demonstrate that ILs can lower the vapor pressure of solvents, and the lowering effect on vapor pressure for a solvent is associated with IL-content, the nature of the solvent, and the molecular structure of the ILs. The magnitude of lowering vapor pressure significantly increases with increasing concentration of the ILs. The lowering effect on vapor pressure for water follows the order of [MMIM][MS]> [EMIM][MS]> [EMIM][ES]; for 1-propanol and 2-propanol, it follows the order of [EM3M][ES]> [EMIM][MS]> [MMIM][MS]. Besides, the activity coefficents of the binary systems containing ILs have been calculated using NRTL model. It was found that the binary systems consisting of water and ILs showed negative deviations from Raoult’s law, while the binary systems consisting of alcohol and ILs showed positive deviations from Raoult’s law, and the nonideality of the binary systems increase with increasing the concentration of ILs. From the values of activity coefficient, the affinity between [MMIM][MS] and the solvents follows the order of water> ethanol> 1-propanol> 2-propanol. With regard to varying ILs, the affinity between ILs and water follows the order of [MMIM][MS]> [EMIM][MS]> [EMIM][ES], while between ILs and 1-propanol or 2-propanol the affinity follows the order of [EMIM][ES]> [EMIM][MS]> [MMIM][MS]. The orders of the affinity are consistent with the sequances observed for the vapor pressure lowering effect.(4) Based on the NRTL model, the isobaric VLE was predicted for the ternary systems containing ILs and{water+ethanol},{water+1-propanol}, and{water+2-propanol} at 101.325 kPa, respectively. The results suggest that the addition of [MMIM][MS] can increase the relative volatility of ethanol,1-propanol,2-propanol to water. With the increase of the IL-content, the relative volatility keep increasing, and the azeotropic points between water and the three alcohols can even be eleminated. From the comparson of the effect observed for [MMIM][MS], [MMIM][DMP], [EMIM][MS], [EMIM][ES], and EMIM][BF4] on the isobaric VLE of the azeotropic systems {water+1-propanol} and{water+2-propanol}, it is found that the alkylsulfate-based ILs with small ion size exhibit higher separation efficiency, viz., [MMIM]> [EMIM], and ILs with varying anions show the separation ability sequance of [DMP] ≈ [MS]> [ES]> [BF4] (> [OTf]). Therefore, [MMIM] [MS] shows the best separation efficiency among the prepared alkylsulfate-based ILs in this study.(5) Concept design and process simulation have been performed using Aspen Plus for the extractive distillation of{water+2-propanol} with [MMIM] [MS] as an entrainer, and the obtained results have been compared with that using glycol as an entrainer. With the same feed conditions and top distillate rate, both of the processes can produce high purity 2-propanol. However, the process with IL as an entraniner shows superiority in equipment cost, solvent and energy consumption.(6) The structures as well as the interactions beween anion and cation in [MMIM] [MS] and its dimer have been studied with density functional theory method. By changing the relative position of the cation and anion, four optimized geometries could be obtained. The geometry in which the anion locates near the C2 position of the cation ring is the most stable. Form the analysis of the atom distance, it was found that multiple C-H···O type H-bonds existed in the ion pairs and the dimer. Atoms in molecules theory and natural bond orbital analysis provided the details of these hydrogen bonding interactions. The binding energys is larger than-300 kJ·mol-1 for each ion pair and-800 kJ·mol-1 for dimer, respectively. The energy decomposition analysis of interaction energy indicate the electrostatic nature between the interaction of anion with cation.(7) The interactions between molecular solvents (water, ethanol, propylene, propyne, heptane, and toluene) and the anion/cation/ion pair of [MMIM][MS] were studied using quantum chemical calculations, and the interaction machnism between ILs and the solvents in extractive distillation (ethanol/water), gas absorption (propylene/propyne) and liquid extraction (heptane/toluene) was elucidated. The calculated results showed that the major interactions between the IL and the above mentiond solvents include H-bond and H···π, but no π-π or p-π interaction occurs. The interaction between the anion and the solvents is predominant, while interaction between the cation and the solvents is weak.(8) The binding energy of the cation and anion for [MMIM][MS] in the atmosphere of water, ethanol,1-propanol, and 2-propanol were calculated with density functional theory and PCM model, so that the dissociation of [MMIM][MS] in solutions can be analyzed. The results show that the interaction strength between [MMIM][MS] and solvents follows the order of water> ethanol> 1-propanol> 2-propanol, which agrees with the order deduced from the activity coefficient.(9) The natural population analysis have been calculated for the anions of [DMP], [MS], [ES], [BF4], and [OTf] in terms of density functional theory, and the reasons were discussed for the different effects observed for ILs with varying anions on the separation of azeotropic systems{water+alcohol}. From the results, when the ion size is small, and the charge is negative and localized enough, the Coulombic interaction between ions can increase correspondingly. As a consequence, the properties of the ILs-containing solutions are more like that of electronlyte solutions, and different degree of salting-out effects occur on alcohols. |
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