| Amine scrubbing is the most effective and feasible technology currently. To apply this technology on CO2 capture from coal-fired power plant flue gas on a large scale, absorbent with high capacity and low energy consumption must be developed. The relationship between capture performance and molecular structure are disscussed from the experimental and theoretical calculation aspects. In this work, the thermodynamic properties of CO2 solubility, heat of mixing, and basicity have been measured. The related thermodynamic simulation has been carried out. For{amine+water} and {amine+CO2} systems, the free energy as well as the physical solvation of CO2 absorption have been investigated using the integral equation and density functional theory in the statistical mechanics framework. Main work is as follows:(1) Solubility data of different polyamines were determined using the constant-volume method combined with gas chromatography analysis. The heat of mixing was measured with the micro calorimeter. The impact of molecular structure on solubility and mixing heat were discussed. The reaction heat was estimated using the CO2 solubility data, and the relationship between the reaction heat and molecular structure was analyzed. Two potential carbon capture absorbents, diethylenetriamine and dipropylenetriamine, were screened considering the CO2 solubility, mixing heat, reaction heat, the absorbent properties and price. Their acid dissociation constants (pKa) were determined by by acid-base titration method.(2) To obtain the absorbents with high absorption, low corrosion, and low energy consumption, methyldiethanolamine and diethylene glycol were added into diethylenetriamine to form mixed solvent-{Diethylenetriamine +N-Meth-yldiethanolamine+water}and{Diethylenetriamine+N-Methyldiethanolamine+ Diethylene glycol+water}. The absorption effect for different concentration mixed amine was determined. The results show that methyldiethanolamine reduced the solution corrosive, improved the solubility, and reduced the heat of reaction; Diethylene glycol by taking the place of part water, not only reduced the loss of volatile solvent brings, but also improved the solubility. While the molar ratio of Diethylenetriamine to N-Methyldiethanolamine is 3:7, the comprehensive performance was best.(3) The bridge function was obtained by means of the density functional theory and was applied into 3D-RISM model for energy calibration. The self consistent for integral equation was developed. The three-dimensional distribution of water, CO2 and N2O around different amine molecule were accurately represented. The effect of different functional groups on the solvation effect and CO2 physical absorption was analysed from the microscopic perspective. According to the H2O density distribution around amine molecules, the solvation free energy was obtained by combining with the free energy formula. The henry coefficient for CO2 and N2O in amine absorbents can be directly obtained by the density distribution around amine molecules. The calculated values was consistent with the experimental values.This study will provide a theoretical guidance for the design of new efficient absorbent and getting its thermodynamic and kinetic parameters.(4) The electrolyte non random two fluid (e-NRTL) model was applied to construct the thermodynamic model for amine-C02 systems. The thermodynamic parameters for pure component systems, amine-H2O systems, and amine-H2O-CO2 systems were fitted by the e-NRTL model using the heat capacity, saturated vapor pressure, heat of mixing, vapor liquid equilibrium and solubility data. The obtained thermodynamic parameters was used to predict the CO2 solubility. Results are in good agreement with the experimental value. So the model can be used to calculate vapor-liquid equilibrium, heat of mixing, and CO2 solubility, in the industrial carbon capture system process providing essential parameters for process design. |
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