The Purification And Recovery Of Ionic Liquid 1-butyl-3-methylimidazolium Tetrafluoroborate And The Study Of Its Relative Thermodynamics

Ionic liquid has become a hot research because of its unique physical and chemical properties. At present, the research and application of the alkyl imidazole is a large majority during various types of ionic liquids. And the research and application of the hydrophilic ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF₄) is more common. The problem exist during the systhesis of [Bmim]BF₄ is: purification of the process involving the H₂O-CH₂Cl₂-[Bmim]BF₄-salt liquid-liquid equilibrium problems, lack of equilibrium data of the system will cause [Bmim]BF₄'s unnecessary losses, it is negative to the large-scale synthesis of ionic liquids [Bmim]BF₄. Contemporary, the recovery process optimization of the ionic liquids [Bmim]BF₄ is as an intrinsic requirement of green solvents.This paper prepared ionic liquids [Bmim]BF₄, more detailed studied the H₂O -CH₂Cl₂-[Bmim]BF₄ ternary system of liquid-liquid equilibrium,and take the equilibrium data of the system as a guide, after inspecting different factors impact on the ionic liquid [Bmim]BF₄ yield during the process of purification and recycling of it,gained more reasonable amount of CH₂Cl₂ and H₂O during washing process. At the same time, the excess molar volume of [Bmim]BF₄-H₂O system at different temperatures was studied. Main content is as following:1. Synthesize the ionic liquids [Bmim]BF₄, characterize it by means of infrared spectroscopy, nuclear magnetic resonance spectroscopy, elemental analysis, ICP and density, results show that the product is the target product [Bmim]BF₄ and purity is more than 99%.2. The solubility curve and density curve of H₂O (w1)-CH₂Cl₂(w2)-[Bmim]BF₄ (w3) system was measured according to the turbidity analysis method at 30℃under atmospheric pressure and were correlated with experiential equations. The liquid-liquid equilibrium data of the systems were measured according to the turbidity-density method under the same condition. As shown by experimental results, the light phase was composed mainly of water whereas the methylene chloride and [Bmim]BF₄ concentration was very low, the heavy phase was composed mainly of methylene chloride and [Bmim]BF₄ whereas the water concentration was very low. The concentration of [Bmim]BF₄ descend from 0.1665 to 0.1032 with the concentration of methylene chloride increase in the system. Thus it can be seen that add CH₂Cl₂ properly can lessen the loss of the [Bmim]BF₄ when purify the ionic liquid, and Optimiza the purification process.3.Othmer-Tobias and Bancroft empirical equations were used for correlation of the liquid-liquid equilibrium data at 30℃, but the result was not satisfactory, The maximum relative error was about -84.5%, and the maximum average relative error was about 61.47%. A new method for the correlation by using Othmer-Tobias and solubility equations was proposed. The maximum relative error was about 4.43%, and the maximum average relative error was about 3.03%. There is a good precision, which shows that the method is appropriate to the correlation of containing low composition system.4. According to the equiribrium data of H₂O-CH₂Cl₂-[Bmim]BF₄ ternary system, Inspected different factors impact on the ionic liquid [Bmim]BF₄ yield during the process of purification and recycling of it. Comprehensively studied the factors such as dosages of CH₂Cl₂ and H₂O impact on the [Bmim]BF₄ yield, acquired a more reasonable amount of CH₂Cl₂ and H₂O dosage during washing process.the mass ratio is: unwashed [Bmim]BF₄: CH₂Cl₂: H₂O is 10:7:3. Wash by adding water by several times. The yield of ionic liquid [Bmim]BF₄ is as high as 93.15%.5. Studied the factors of recovery hydrophilic ionic liquids [Bmim]BF₄. Experimental study in contrast the different ratios of dichloromethane under normal temperature and pressure, water, salt and ionic liquids [Bmim]BF₄ impact on the recovery. After comprehensive survey of various factors, a more reasonable ratio of [Bmim]BF₄: CH₂Cl₂: H₂O is 10:6:3, the recovery rate could reach 93%. Characterize the recovery ionic liquid[Bmim]BF₄ by means of infrared spectra and density, the results showed that the recoveried ionic liquids [Bmim]BF₄ can be recycled.6. Mesured the excess molar volume VmE of [Bmim]BF₄-H₂O system at different temperature, in the composition range excess molar volume VmE is positive, and there is a maximum on the isotherm at different temperature, simultaneity, the molar percent of H₂O (x2) corresponding to the extremum on the isotherm assemble around 0.50. The change trend of excess molar volume VmE at different temperature is resemble, it increased with the temperature at the same composition. The correlation of excess molar volume VmE by using Redlich-Kister equation was proposed, The maximum standard deviation was less than 1.4%, there is a good precision, which shows that Redlich-Kister equation is appropriate to the correlation of this system.