Thermodynamic Properties Of Imidazole Ionic Liquids On The Basis Of Thermal Decomposition Stability

Ionic liquids（IL）,which are liquids at ambient temperatures,are normally composed of relatively large organic cations and inorganic or organic anions.In the past 20 years,the development of ionic liquids in physical chemistry,material science multidiciplinary,engineering chemical,nanoscience and electrochemistry has been violent and ionic liquids create a new reaction environment for chemical reactions due to their superb physicochemical properties,such as wide liquid range,excellent electrical conductivity,strong solubility,etc.Thermal stability is the basic physical property of ionic liquids,which has a decisive influence on the application and development of ionic liquids.The parameter for evaluating the thermal stability of ionic liquids is T_onset（onset decomposition temperature）,which overestimates the thermal stability of ionic liquids.Therefore,it is generally believed that ionic liquids have high thermal stability,and this property is often neglected in application.In this paper,after comprehensively considering the application range,safety performance and cost of ionic liquids,three kinds of imidazole ionic liquids[emim][Ac],[emim][OTf]and[emim][Tf₂N]are selected.In this paper,the thermal stability of three kinds of ionic liquids was studied by non-isothermal and isothermal thermogravimetry,the maximum application temperature was determined,and the effects of heating rate,nitrogen and oxygen atmosphere and anions and cations on the thermal stability were studied.The results of the study show that:as the heating rate increases,each characteristic temperature on the TG curve also increases;compared with the ionic liquid in an oxygen atmosphere,the ionic liquid is more stable in a nitrogen atmosphere;the anion type plays a role in the thermal stability of the ionic liquid.Important role,when the cation of the ionic liquid is[emim]+,the thermal stability of the anion follows the following rule:[OTf]^->[Tf₂N]^->[Ac]^-.Compared with the three ionic liquids,[emim][OTf]has the best thermal stability,[emim][Tf₂N]is next,and[emim][Ac]is the worst.In this paper,three equal conversion rate methods,FWO method,KAS method and Friedman method,are used to study the activation energy of ionic liquids[emim][Ac],[emim][OTf],[emim][Tf₂N]at different conversion rates,and obtain the corresponding activation energy.The results show that the activation energy of[emim][Ac]is 135.12 kJ/mol,the activation energy of[emim][OTf]is 216.25 kJ/mol,and the activation energy of[emim][Tf₂N]is 135.68 kJ/mol.The order of activation energy is the same as the order of thermal stability.When the cation of the ionic liquid is[emim]⁺,the order is:[OTf]^->[FAP]^->[Tf₂N]^-.In this paper,on the basis of isothermal thermogravimetry,the ionic liquid[emim][Ac],[emim][OTf],[emim][Tf₂N]vapor pressure and enthalpy of vaporization temperature are in the range of 100¹40℃,305³25℃,240²60℃.It has enriched the research on the thermodynamic properties of ionic liquids.