Study On The Physical Properties Of Amidine Ionic Liquids And Their Performance In Capturing Carbon Dioxide Ga

The emergence of green chemistry provides a new solution for the global concern such as environment,energy,ecology and other problems.With the development of green chemistry,more and more people pay attention to the development and application of green solvents.Ionic liquids（ILs）composed of cations and anions have attracted much attention due to their excellent physical and chemical properties such as adjustable structure,high thermal stability,low melting point and low vapor pressure.They are considered as functional materials that may replace traditional organic solvents and are applied in fields such as synthesis,electrochemistry,biomass conversion,and carbon dioxide gas capture.Based on this,this article designed and prepared a series of functionalized ionic liquids,studied their thermal properties,examined the performance and mechanism of ionic liquids in capturing carbon dioxide gas.Specifically,it includes the following three aspects:Firstly,five kinds of amidine-based ionic liquids were synthesized by one-step method,including DBN-triazole（[HDBN][Tri]）,DBN-imidazole（[HDBN][Im]）,DBU-imidazole（[HDBU][Im]）,DBN-1,3-dimethylurea（[HDBN]₂[DMU]）,DBU-1,3-dimethylurea（[HDBU]₂[DMU]）,and the structure of all ionic liquids were characterized.Then the thermodynamic properties of ILs were studied.The density（ρ）and viscosity（η）of[HDBN][Im]and[HDBN][Tri]were measured in the range of T=（298.15～313.15）K,and the influence of temperature on viscosity and density was investigated.Then,the molecular volume（V_m）,standard entropy（S⁰）,thermal expansion coefficient（α_p）and lattice energy(U_POT)of the pure ionic liquid were calculated according to the density values.The relation ship between viscosity and temperature was fitted by Vogel-Fulcher-Tammann equation and fluidity equation.The thermodynamic parameters（including molecular volume,standard entropy,thermal expansion coefficient and lattice energy）of[HDBN][Im]and[HDBN][Tri]were compared and analyzed.The activation energy E_ηof viscous fluid was obtained from the Arrhenius empirical equation.Activation thermodynamic functions（ΔG^≠、ΔH^≠、ΔU^≠andΔS^≠）of[HDBN][Im]and[HDBN][Tri]were calculated by Eyring viscosity equation,and the activation thermodynamic functions of[HDBN][Im]and[HDBN][Tri]were compared.And the relationship between the viscosity and the molar conductivity of[HDBN][Im]and[HDBN][Tri]was discussed based on Walden’s rule.Secondly,[HDBN][Im]and[HDBN][Tri]are mixed with methanol,ethanol,isopropanol and n-butanol at different molar ratios to form ionic liquid+alcohol system.The density and viscosity of[HDBN][Im]+alcohol and[HDBN][Tri]+alcohol systems were measured in the range of T=（298.15～313.15）K.The excess molar volume（V^E）of the system was calculated by experimental density,which was fitted by Redlich-Kister equation.The viscosity deviation（Δη）,relative viscosity（η_r）and excess viscosity（η^E）of the system were calculated based on the experimental results of viscosity.And the excess Gibbs energy of activation(ΔG^*E)of[HDBN][Im]+alcohol and[HDBN][Tri]+alcohol systems were calculated.In addition V^E,Δη,η^E andΔG^*E of[HDBN][Im]+alcohol and[HDBN][Tri]+alcohol systems were compared.Finally,the performance of[HDBN][Im],[HDBU][Im],[HDBN]₂[DMU]and[HDBU]₂[DMU]ionic liquids in CO₂capture was investigated.And the effects of temperature and water content on the CO₂ absorption capacity of ionic liquids were studied and ¹³C NMR was used to analyze the mechanism of ionic liquid in absorbing carbon dioxide.In addition,the deep eutectic solvent（DES）system of[HDBN][Im]+ethylene glycol was prepared to absorb carbon dioxide gas.The effects of temperature,ratio and other factors on the absorption performance were analyzed.The absorption mechanism of[HDBN][Im]+ethylene glycol system was analysized by ¹³C NMR spectrum and theoretical calculation.Moreover by comparing ¹³C NMR spectra before absorption and after desorption,it is proved that these absorbents have good stability and reversibility in CO₂capture.In summary,this paper synthesized[HDBN][Tri],[HDBN][Im],[HDBU][Im],[HDBN]₂[DMU],[HDBU]₂[DMU]five amidines-based ionic liquids.Thermodynamic properties of ionic liquids and their solutions were measured.Futhermore CO₂absorption performance of ionic liquids as well as deep eutectic solvent system was investigated,which can provid a new idea for the study of properties and applications of ionic liquids.