| A deep eutectic solvent(DES) is a type of ionic solvent with special propertiescomposed of a mixture which forms a eutectic with a melting point much lower thaneither of the individual components. As a new kind of ionic liquids, choline-basedDESs are low toxic, biodegradable, low cost，excellent CO2absorption, and highsolubility of various metal salts and oxides of metals, which make them more andmore attractive in greenhouse gas absorption and electrochemical reactions. However，the high viscosity greatly limits the scope of its applications.Carbon dioxide expanded liquids (CXLs) have been considered asenvironmentally benign solvents. CXLs usually show better performance than scCO2or pure organic solvents. Combining high pressure CO2with DESs, a new kind ofenvironmentally benign solvent would be formed. The low viscosity is similar toscCO2and the high conductivity is similar to DES. So CXLs can not only reducegreenhouse gas, but also can be applied as a new electrochemical reaction medium,which can broaden the application of DES.Accurate determination of the solubility of CO2in DES is not only the basis ofchoosing the new absorbent of CO2, but also the premise of understanding the internalstructure and physical characteristics of the CO2expanded DES. The determination ofconductivity and electrochemical window of CO2expanded DES are exploring thepossibility of electrochemical reactions in the system as well as the basis of processdesign. The studies of this master thesis contain three main parts as follow1. Four kinds of deep eutectic solvents (DES) based on choline chloride andpolyols (ChCl-EG, ChCl-PG, ChCl-BG, ChCl-GL) were prepared. Thestructure of DES is preliminary investigated by FTIR. The density, viscosityand conductivity of the four DESs were measured as functions oftemperature in the range of303-343K. The relationship between viscosityand temperature as well as the relationship between conductivity andtemperature accord with the Arrhenius exponential law. The activation energy of viscosity and conductivity were calculated by Arrhenius formula,and the electrochemical windows of the four DESs were also tested by usingcyclic voltammetry at333K.2. The solubilities of carbon dioxide (CO2) in a DES based choline chlorideand polyols were determined at313K,323K and333K under pressures up to14MPa by using a static equilibrium method. The mole ratios of cholinechloride and polyols selected was1:2. The results showed that the solubilityof CO2in DES increases and the density of CO2-ChCl-polyols mixturedecreases with the pressure increasing. At the same pressure, the solubilityof CO2in DES decreases with the temperature increasing, and thetemperature has little effects on the density of CO2-ChCl-polyols mixture.The experimental data was also correlated with Henry’s law equation andpolynomial regression equation by using the pressure as the independentvariables. The results showed that the solubility equations based onpolynomial regression mode and the experimental values could correlatewith each other well, which could be used to calculate the solubility of CO2in ChCl-Polyols DES under the condition of low pressure.3. The conductivities of a series of DES based on choline chloride and polyolswhich were expanded by CO2had been determined. The results suggestedthat the CO2enlarged the conductivity in a certain range of pressures andtemperatures. The cyclic voltammograms curve of ChCl-EG, ChCl-PG andChCl-BG have been determined in this work, the result showed that thehigh-pressure CO2has no effect on the electrochemical window of threekinds of DES. |
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