| In recent years, ionic liquids (ILs) are considered as green solvents to replace the traditional organic solvent and increasingly attracting interest in both the industrial and academic field due to its unique physical and chemical properties. Ionic liquids have low melting point, negligible vapor pressures, non-flammability, strong ability to dissolve many chemicals and fine-tuning ability for the physical and chemical properties. Ionic liquids have many favorable properties which make them attractive for a number of applications such as chemical reaction, separation process and electrochemistry. However, the viscosity of the ionic liquids is usually dozens or even hundreds of organic solvent, which leads to poor transport behavior in IL-involved processes, limits the practical applications to some extent. Alternatively, mixtures of ILs with less viscous molecular solvent can eliminate some of these difficulties effectively. Therefore, in order to explore the applications of ionic liquids more effectively, the basic physical and chemical properties of ionic liquids, especially the mixtures of ILs + organic solvents are quite important.Based on the continuous works by our group on investigated the physical and chemical properties of ionic liquids mixed with amide/ water systems, we carried out the investigation of the thermodynamic properties of the mixture with ionic liquid and three polar aprotic solvents. The ionic liquids involved were ([Cnmim]Cl (Cnmim= 1-alkyl-3-methylimidazolium; n=2,4,6,8)、[Cnmim] Br (Cnmin= 1-alkyl-3-methylimidazolium; n=2,4,6,8,10)) and the three polar aprotic solvents were{ NMP (N-methyl-2-pyrrolidinone), DMI (1,3-dimethyl-2-imidazolidinone) and DMPU (1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone)}.The main research and conclusions are as follows:(1) In this work, physicochemical properties, such as density (p), refractive index (no) and viscosity (η), for the binary mixtures [Cnmin]X (n=2,4,6,8,10; X=Cl, Br) + three polar aprotic solvents (NMP, DMI and DMPU) were measured over wide composition ranges and temperatures from T=288.15 to 333.15 K at a pressure p°=0.1 MPa.(2) The effect of temperature, content and variety of ionic liquids, and the variety of polar aprotic solvents on the properties of the mixed solution were discussed. The result shows that adding the three polar aprotic solvents in ionic liquids can solve the transmission question simply and effectively.(3) To obtain deeper insights about the interaction of the ionic liquids and three polar aprotic solvents molecules, the several derived properties of these systems were calculated including excess molar volumes (VmE), apparent molar volumes (Vφ,i), isobaric thermal expansivity coefficients (αp) and deviations in refractive index (△nD) were calculated to analyse the non-ideal behaviour of binary systems.(4) It is worth noting that the steps before sample preparation, we use a laser monitoring observation technique-computer data on-line acquisition system measuring the solubility of [Cnmim]X (n=2,4; X=Cl, Br) in the three dipolar aprotic solvents (NMP, DMI and DMPU) at different temperatures. The sample preparation was performed only up to saturation degree mole fraction of IL (x1) under controlled conditions of temperature, respectively.(5) The density, refractive index and viscosity were well fitted to an empirical equation; the excess molar volumes and deviations in refractive index were related to the Redlich-Kister polynomial equation.The results obtained in this paper show that NMP/ DMI/ DMPU can effectively adjust the physicochemical properties of 1-alkyl-3-methylimidazolium ionic liquids. The several derived properties of these systems are helpful to understand mixing effect and other interaction during the ions of transporting process. |
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