Study On The Thermodynamic Properties Of Alkoxyl Modified And Chain Length Regulated Imidazolium Chloride And Amino Acid Ionic Liquids

In this study,17 kinds of ionic liquids were prepared by direct one-step synthesis and two-step synthesis,including alkyl imidazolium chloride ionic liquids[C_nMIM][Cl](n=2,4,6),alkoxy modified imidazolium chloride ionic liquids[C_nOC_mMIM][Cl](n=1,2;m=2,4),alkyl imidazolium threonine ionic liquids[C_nMIM][THR](n=2,3,4,5,6),alkyl imidazolium taurine ionic liquids[C_nMIM][TAU](n=2,3,4)and alkoxy modified imidazolium threonine ionic liquids[C_nOC_mMIM][THR](n=1,2;m=2,4).The continuous variation trend of instantaneous mass with time(or temperature)of17 kinds of ionic liquids under the optimal condition was measured and TGA-DTG curves were plotted.Then,the initial degradation temperature was obtained by using the tangent extension intersection method and provided the basis of setting the temperature range for the subsequent isothermal mass change measurement experiments of 17 kinds of ionic liquids.The continuous variation trend of instantaneous mass with time(or temperature)of17 kinds of ionic liquids under the optimal condition was measured from ambient temperature to at least 20?lower than their respective initial degradation temperature.The obtained data were presented in graph and fitted in linear.The correlation coefficients were all above 0.99 which showed that the variation trend of instantaneous mass of 17 kinds of ionic liquids with temperature in their respective temperature range conformed to the zero order kinetics process.With the help of Clausius-Clapeyron equation,the vaporization enthalpy at mean temperature and vapor pressure of 17 kinds of ionic liquids were obtained in the temperature range of their respective isothermal mass change measurement experiments.It is found that the vaporization enthalpy was controlled by the type of modified side chain and the length of side chain.In addition,the vapor pressure did not change significantly at low temperature,but increased exponentially at high temperature.The assumed boiling point T_b of 17 ionic liquids studied was predicted.Furthermore,the vaporization enthalpy(35)H_vap(T_b),vaporization entropy(35)S_vap(T_b)and vaporization Gibbs energy(35)G_vap(T_b)were obtained by calculation and it was found that the vaporization entropy(35)S_vap(T₀)was the direct driving force of the vaporization process of ionic liquids.Four representative ionic liquids[COC₄MIM][Cl],[COC₄MIM][THR],[C_nMIM][THR](n=3,5)and reference material sapphire were selected from the 17kinds of ionic liquids.Their molar heat capacities were measured by differential scanning calorimeter and the relationship between temperature and heat flux related to the internal thermal transition of the samples was studied.