| Ionic liquids, whichare characterized by low vapor pressure, excellent extraction perfermance, and good stability,show as excellent solubility as that of conventinal volatile organic solvents, and as high separation efficiency as that of inorganic salts, and as such, ionic liquids are expected to be a potential alternative to conventional solventduring special distillation operation, leading to a clean production process in the separation of azeotropesystems.In the petrochemical industry, the separation of aliphatic hydrocarbons and aromatic hydrocarbons is of very great importance, especially for n-octane and xylene/ethylbenzene. For the large scale application of ionic liquids in the separation of aliphatic hydrocarbons and aromatic hydrocarbons, it is essential toaccumulate thermodynamic data and developrelevant thermodynamic models for ternary systems containing ionic liquids, investigate the interaction mechanism between ionic liquids and different molecular solvents, so as to evaluate the separation ability of ionic liquids and develop new enhanced separation techniques using ionic liquids.Based on this, the major worksin this thesis are as follows:(1) Ionic liquid, 1-butyl-3-methylimidazolium tetrachloroferrate(â…¢) ([BMIM][FeCl4]), has been synthesized through two-step reaction using N-alkylimidazole,1-chlorobutaneand anhydrous ferric chloride asraw materials with relative simple reaction and purification steps.The structures of intermediate product [BMIM]Cl and ionic liquid [BMIM][FeCl4] have been identified usingNMR and IR spectra, and the prepared [BMIM]C1 had a molar purity of 98.2% (waternot included). Kari Fishcher analysis indicated that the water content of the prepared ionic liquid [BMIM][FeCl4] is 43.7 ppm, which meets the basic requirement of thermodynamic data determination.(2) Liquid-liquid equilibrium data ofternary systems containing ionic liquid, viz.{n-octane+o-xylene+[BMIM][FeCl4]},{n-octane+m-xylene+ [BMIM][FeCl4]},{n-octane+p-xylene+[BMIM][FeCl4]}, and{n-octane+ ethylbenzene+[BMIM][FeCl4]}were experimentally measured under the conditions of pressure 0.1 MPa, and temperature 298.15K or 313.15K.The experimental liquid-liquid equilibrium data for ternary systems containing ionic liquid were correlated using Othmer-Tobias equation, with the regression coefficient (R) closing to 1, indicating the validity of the experimental data.(3) According to the experimental liquid-liquid equilibrium data for ternary systems containing ionic liquid, ionic liquid [BMIM][FeCl4] exibits an excellent extraction perfermance in the separation of n-octane and xylene/ethylbenzene. All the solute distribution ratios (β) of xylene and ethylbenzene in the [BMIM][FeCl4]-rich phase and n-octane-rich phase are higher than 0.5, and the selectivities (S) are all higher than 20, indicating thationic liquid[BMIM][FeCl4] shows more excellent perfermance in the separation of n-octane and xylene/ethylbenzene than that of conventional sulfolane and tetra-n-butylammonium bromide-sulfolane mixture.(4) Conventional activity coefficient model (NRTLmodel)was employed to correlate the liquid-liquid equilibrium data of the ternary systems containing ionic liquid [BMIM][FeCl4] under the conditions of pressure 0.1 MPa, and temperature 298.15K or 313.15K,and the modal parameters were obtained. The rootmeansquare deviations (RMSD) betweenthe experimental data and the predicted one are 0.9%-5.1%, justifying the applicability of NRTLmodel for the description of ternary systems containing ionic liquid [BMIM][FeCl4]. Ionic liquid [BMIM][FeCl4] is a potential extractant for the separation of aliphatic hydrocarbons such as n-octanefrom aromatic hydrocarbons such as xylene and ethylbenzene.(5) The microstructures, hydrogen bonding interactions, bonding interactions between cations and anions, and orbital interactions were studied using density functional theory, natural bond orbital theory, and atoms in molecules theory.Multiple hydrogen bonding in C-H…Cl was found between [BMIM]+and [FeCl4]-, which plays a dominant role in the formation of ion pair. According to the donarâ†' receptor interactions of ion pair and relatedsecond-order perturbation energies E(2), the strong orbital interactions between antibonding orbital σ*(C-H) in the cations and long pair orbital LP(Cl) in the anions have a stabilizing effect. Meanwhile, the hydrogen bond in C2-H11…Cl has the strongest interaction, and the geometry in which the anion [FeCl4]-locates near the C2 position of the cation ring is the most stable.(6) Using the interactions between [BMIM]Cl and solvent as a control, geometry optimization of the [BMIM]+/[FeCl4]--solvent and [BMIM][FeCl4]-solvent compounds were studied using density functional theory, as well as their interaction mechanism. Multiple hydrogen bonding between anion and cation plays a dominant role in the stability of ion pair-solvent compound, and no Ï€-Ï€ and p-Ï€ interactions occur between imidazole ringand aromatic ring. Interaction between anion and cation is not obviously influenced by the addition of n-octane and aromatic hydrocarbons. Both of [BMIM] [FeCl4] and [BMIM]C1 show excellent extraction perfermance in the separation of aromatic hydrocarbons from the n-octane-containing mixture. The interaction between [BMIM] [FeCl4] and n-octane/aromatic hydrocarbonsis much weaker than that between [BMIM]C1 and n-octane/aromatic hydrocarbons because of the dispersed charge caused by the substitution of Cl- with [FeCl4]-(7) Extraction of n-octane, o-xylene, m-xylene, p-xylene, and ethylbenzene by ionic liquid [BMIM][FeCl4] is conceptionally designed and simulated, and the ionic liquid is recovered using rectifyingcolumn. Under ambient temperature and pressure, the purity of o-xylene in the top of extractingtower is 92.5% under the conditions of theoretical number of plate 8, and extractant dose 360 kg/h. Under atmospheric pressure, the purity of ionic liquid in the top of rectifyingcolumn is 99.97% under the conditions of theoretical number of plate 5, feeding position the third plate, molar reflux ratio 0.2. |
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