Research On Liquid-liquid Equilibrium And Related Physical Properties Of CO₂ Switching Solvents Based On Triethylamine And N-methyldiethanolamine

In chemical processing and separating processes,the most common methods for recovering organic substances from products and aqueous solutions are salt extraction and rectification.However,salt extraction produces a large amount of organic wastewater containing salt.The rectification consumes a lot of energy and pollutes the environment because of the volatilization loss of solvent.CO₂ responsive switch solvent was concerned because of their reversibility,safety,environmentally friendly and sound.If CO₂ responsive switch solvents can be applied in separated organic substances of products and aqueous solutions,it will have great potential in industry applications.The volume properties,viscosity properties,refractive indices and electrical conductivity of CO₂ responsive switch solvents have a great significance in scientific theory and engineering applications.However,there are few reports about the physical properties and the liquid-liquid equilibrium data of CO₂ responsive switch solvents.Herein,we choose triethylamine,N-methyldiethanolamine as CO₂ responsive switch solvents.We choose triethylamine as Swithable-Hydrophilicity Solvent（SHS）.The density,viscosity,refractive indices and electrical conductivity of triethylamine + water binary solutions and triethylamine + 1,3-dioxolane + water ternary solutions were measured at different concentrations in the tempreture range from 283.15 K to 303.15 K.Apparent molar volumes and viscosity B-coefficient of triethylamine + water binary solutions and triethylamine + 1,3-dioxolane + water ternary solutions were calculated based on experimental densities and viscosities.The variation rules of volume properties and viscosity properties were discussed from the aspect of molecular interactions.Solute-solvent interaction,solute-solute interaction and structure-marker effect of the two systems of triethylamine + water and triethylamine + 1,3-dioxolane +water have been discussed using the Helper rule and Jones-Dole equation.The experimental data was correlated by Vogel-Tamman-Fulcher equation and empirical equation.The error of the experimental value and the calculated value of Vogel-Tamman-Fulcher equation and empirical equation were very little.The liquid-liquid equilibrium data of three ternary systems（triethylamine + 1,3-dioxolane + water,triethylamine + 1,4-dioxane + water,triethylamine + tetrahydrofuran + water）were measured at three temperatures of 283.15 K,293.15 K and 303.15 K,and the corresponding ternary phase diagrams were constructed.The liquid-liquid equilibrium data of ternary systems ware correlated by e-NRTL model.The error of the experimental value and the calculated value of e-NRTL model were very little.The largest root-mean-square deviations were 5.18×10^-2、5.19×10^-2 and 1.87×10-3,respectively.The results showed that the calculation results had good agreement with the experiment values.It illustrated that the e-NRTL equation could be used to correlate the triethylamine + 1,3-dioxolane + water,triethylamine + 1,4-dioxane + water,triethylamine + tetrahydrofuran + water ternary systems.We choose N-methyldiethanolamine as Switchable Water（SW）.The liquid-liquid equilibrium data of three ternary systems（N-methyldiethanolamine + 1,3-dioxolane + water,N-methyldiethanolamine + 1,4-dioxane + water,N-methyldiethanolamine + tetrahydrofuran + water）were measured at three temperatures of 283.15 K,293.15 K and 303.15 K,and the corresponding ternary phase diagrams were constructed.The liquid-liquid equilibrium data of ternary systems ware correlated by e-NRTL model.The error of the experimental value and the calculated value of e-NRTL model were very little.The largest root-mean-square deviations were 5.30×10^-2、4.54×10^-2 and 3.46×10-3,respectively.The results showed that the calculation results had good agreement with the experiment values.It illustrated that the e-NRTL equation could be used to correlate the N-methyldiethanolamine + 1,3-dioxolane + water,N-methyldiethanolamine + 1,4-dioxane + water,N-methyldiethanolamine + tetrahydrofuran + water ternary systems.