Determination Of Thermodynamic Properties Of The Binary System Of 1-Allyl-3-Methyl Imidazolium Dicyandiamide Salt And Alcohols

In recent decades,ionic liquids have developed rapidly and their commercial applications are amazing.Because of its unique properties,it has played a huge role in various application fields and has become an environmental protection solvent in industry.The cation and anion structures of ionic liquids are changeable and have infinite structural possibilities.The physical and chemical properties of ionic liquids can be greatly adjusted by appropriately changing the length and branch of the alkyl chain and matching the appropriate anions.1,3-dialkylimidazole ionic liquids have been studied mostly due to their wide range of properties.Among them,N-methyl imidazole cations have low molecular weight and sufficient side chain tunability due to their branched-chain,with low viscosity,low melting point,high conductivity and other characteristics,and the introduction of allyl group on the imidazole cations will further improve its performance.In addition,introducing other solvents into ionic liquids has become a simple method to expand the application of ionic liquids.On the basis of expanding the application of ionic liquid,the inherent high viscosity problem of ionic liquid can be alleviated and the cost can be saved.Starting from the thermodynamic properties of binary mixtures,such as density,viscosity,surface tension and other parameters,the study of solute-solvent interaction in the mixture system is of great significance for the research in this field,and can lay a foundation for the design and application of ionic liquids in the chemical industry in the future.Therefore,this paper prepared the allyl functionalized ionic liquid1-allyl-3-methylimidazole-dicyandiamide salt[Amim][DCA]and prepared it with methanol,ethanol and propanol respectively into a binary mixed system.Through experimental measurement and related calculations,the physical and chemical properties of the liquid were explored and analyzed.The specific work is as follows:1.Allyl functionalized ionic liquid 1-allyl-3-methyl imidazole cyanogen amine salt[Amim][DCA]was synthesized from N-methyl imidazole and bromide acryl by a two-step synthesis method.The ionic liquid was characterized by ¹H NMR,¹³C NMR and thermogravimetric（TGA）,the substance was identified as the target product,and its purity was above 99%。2.In this paper,the ionic liquid[Amim][DCA]is a hydrophilic ionic liquid.In order to eliminate the influence of water in the experimental process,the standard addition method is adopted.The density values,surface tension values and viscosity values of ionic liquid[Amim][DCA]at different water contents were measured in the temperature range of 288.15 K to 318.15 K.And the three linear fitting with water content,respectively,obtained the corresponding properties of pure ionic liquids[Amim][DCA].3.According to the gravimetric method,the ionic liquid[Amim][DCA]was prepared with methanol,ethanol and propanol,respectively,to prepare the binary mixture system with the full molar concentration range,and the mole fraction of the ionic liquid x₁=0.0000～1.0000.Its density and surface tension at 288.15 K～318.15 K and standard atmospheric pressure were measured for the first time.The average molar volume,thermal expansion coefficient and excess molar volume of the binary mixed system were obtained based on the measured density and surface tension data.Redlich-Kister equation was used for polynomial fitting of V^E and mole fraction,and the excess mole volume of the binary system was all negative.In this paper,the size distance between the ionic liquid and the alcohol solvent is large,so the alcohol molecules with smaller molecular weight are easy to enter the gap between the ionic liquid molecules,and the two pile up with each other,thus reducing the free volume of the mixed solution.4.The molar surface Gibbs free energy（g_s）of the mixture was calculated on the basis of the surface tension.The relationship between the molar surface Gibbs free energy and the temperature was discussed.Then,the traditional Eotvos equation was improved according to the definition of the molar surface Gibbs free energy.The molar surface entropy（s）and molar surface enthalpy（h）of the mixture were calculated by using the improved formula.5.The viscosity values of ionic liquid[Amim][DCA]with methanol,ethanol and propanol were measured every 5 K at 288.15 K～318.15 K in the whole molar concentration range（x₁=0.0000～1.0000）.The viscosity of the mixture decreased with the increase of molar fraction of alcohol solvent.The relationship between viscosity and temperature is discussed by using Arrhenius equation.The viscosity of the mixture decreases with the increase of temperature.The viscosity deviation of the binary system is calculated.The△ηof the three binary systems are all negative,which indicates that hydrogen bonds are formed between the ionic liquid and the alcohol solvent,leading to the weakening of the anionic and cationic interaction of the ionic liquid.Therefore,the actual viscosity of the mixture is negative deviation compared with the ideal viscosity.Based on the concept of relative viscosity,the Gibbs free energy of excess viscous flow activation(ΔG^≠E)was obtained.The binary systemΔG^≠E was negative,which indicated that the interaction between ionic liquid and alcohol solvent did occur,and the order of the interaction was as follows:[Amim][DCA]+methanol>[Amim][DCA]+ethanol>[Amim][DCA]+propanyl alcohol.The results are consistent with those presented by the viscosity bias,which proves that it is reasonable to introduce the relative viscosity to correlate the viscosity with the Gibbs free energy of the excess viscous flow.Redlich-Kister equation is used to make polynomial fitting to the mole fraction,and the fitting effect is good.Finally,the activation entropy and the activation enthalpy of the excess viscous flow are calculated,and it is proved that the enthalpy contributes to the decrease of the viscosity of the mixture.