Carbon Dioxide Capture By Ethylethanolamine Based Nonaqueous Solution

Carbon dioxide（CO₂）capture is an important way for the reduction and utilization of greenhouse gas.Nowadays,the technologies for CO₂ capture mainly include physical,chemical and biological methods,in which the chemical method has attracted wide attention due to its potential application.Aqueous alkanolamine solution is commonly used as the absorbent,however,the disadvantages of water,such as the high heat capacity,volatility and ionization,lead to high energy consumption,solvent loss,and serious corrosion problems,which limit the deployment of this technology.The purpose of this study is to explore an efficient nonaqueous solution which has high CO₂ absorption and desorption efficiency,low regeneration temperauture and energy consumption.The absorption-desorption apparatus and the vapor-liquid equilibrium apparatus were used to explore the CO₂ capture efficiency of the nonaqueous solution in which the secondary alkanolamine of N-ethylmonoethanolamine（EMEA）was the reactant.The experimental results reveal that the CO₂ absorption loading（0.68 mol CO₂/mol EMEA）and desorption amount（0.62 mol CO₂/mol EMEA）of 40wt%EMEA+60wt%DEEA were both higher than other nonaqueous solutions;The CO₂ equilibrium solubility in EMEA+DEEA solution was similar to that in EMEA+H₂O solution at high pressure（700kPa）.This is also the first example where tertiary alkanolamine was used as the nonaqueous reaction medium.13C NMR spectroscopy was used to study the mechanism of CO₂ reaction with EMEA+DEEA solution qualitatively and quantitatively,as well as EMEA+H₂O solution for comparison.The experimental results reveal that protonated amines of EMEA and DEEA,and carbamate were the products after CO₂ capture by EMEA+DEEA solution,DEEA can promote the CO₂ chemical reaction with EMEA;protonated amine of EMEA,carbamate,and carbonate/bicarbonate were the products after CO₂ capture by EMEA+H₂O solution,H₂O can participate in the CO₂ chemical absorption directly forming carbonate/bicarbonate.Meanwhile,the carbamate concentration in EMEA+DEEA solution was significantly higher than that in EMEA+H₂O solution.The absorption-desorption apparatus was used to explore the stability of the nonaqueous solutioin.The CO₂ cyclic absorption loading and desorption amount of EMEA+DEEA solution were both higher than EMEA+H₂O solution;EMEA+DEEA solution can occur sulfur dioxide and oxide degradations;The thermal stability of EMEA+DEEA solution was higher than EMEA+H₂O solution.Ion exchange resins can be used to purify the SO₂-degraded EMEA+DEEA solution.The thermodynamic properties of the nonaqueous solution were calculated from the density and viscosity values.The intermolecular interaction of EMEA+H₂O solution was stronger than EMEA+ DEEA;The thermal expansivity for EMEA+DEEA solution was higher than EMEA+H₂O solution.The values of the activation molar enthalpy,entropy and molar gibbs free energy for EMEA+DEEA and EMEA+H₂O solutions were all positive.The wetted-wall column apparatus was used to measure the kinetics of CO₂ absorption in EMEA+DEEA solution.The chemical reaction rate of CO₂ with EMEA+DEEA solution increased with temperature and EMEA concentration,however,the CO₂ flux showed a temperature dependence of N_CO2,313K>N_CO2,328K>N_CO2,298K.The reaction pathway of CO₂ with EMEA+DEEA solution can be represented by the termolecular mechanism model.The addition of TiO₂ into EMEA+DEEA solution as "nanofluids" had significant improvements of the accumulative amount and rate of CO₂ desorption,and CO₂ cyclic absorption loading.