Carbon Dioxide Capture By Organic Amine Solution

CO2capture and utilization have attracted great attention in modern society. CO2emission is mainly due to rapid usage of fossil fuels, such as coal, petroleum and natural gas. To recover CO2from fuel gas emission, it would bring good social and economic benefits. Up to date, a number of different CO2capture technologies have been developed, and among them, chemical absorption method using alkanolamine solutions is the most effective technique. In this thesis,2-(2-aminoethylamine)ethanol (AEEA) is as a key absorbent for the improvement of CO2capture efficiency and reduction of the energy consumption in desorption process. After that, several new effective absorbent systems and the reaction mechanism have been studied for CO2capture in absorption and desorption processes.In this thesis, we aim in finding new and effective absorbent systems that can effectively absorbe CO2. Firstly, a system consisting of AEEA blended with N-methyldiethanolamine (MDEA) or2-amino-2-methyl-l-propanol (AMP) aqueous solutions was studied regarding the absorption CO2loading (mol CO2/mol amine) and the recyclability of the solvents, under different concentration of solutions, reaction temperatures and CO2partial pressure. The results indicated that the CO2loading in the AEEA+MDEA/AMP aqueous solutions decreased with an increase in temperatures, while increased with an increase in CO2partial pressure. The CO2loading in AEEA+MDEA/AMP aqueous solutions decreased with increased concentration of MDEA/AMP at the same total concentration of amine solutions. After several absorption-desorption cycles, AEEA+MDEA/AMP aqueous solutions retained good stability. Secondly, N,N-dimethylethanolamine (DMMEA) and2-(diethylamino)ethanol (DEEA) aqueous solutions were used to replace the commercialized amines. It was found that DMMEA and DEEA had good cycle capacity, a high CO2absorption rate at low temperatures and a low CO2loading at high temperatures. They can be potentially used in industry. Finally, benzyl alcohol (BP), instead of water, was blended with AEEA for the absorption of CO2and this new system could reduce regeneration energy. The results showed CO2loading of AEEA+BP solution was lower than that of AEEA+H2O solution, while the CO2desorption rate of AEEA+BP solution was quicker than that of AEEA+H2O solution. At393K, the desorption rate of AEEA+BP solution was about1.3times faster than that of AEEA+H2O solution and AEEA+BP solution needed30%time less than AEEA+H2O solution to reach the reaction end point.13C NMR was used to study the reaction mechanism of CO2capture in absorption and desorption cycles and the results suggested that during the CO2absorption process, the main AEEA+AMP species were AEEA primary carbamate, AEEA secondary carbamate, protonated amine and HCO3-/CO32-. There was no evident indication that a dicarbamate species of AEEA and carbamate of AMP were formed. When AEEA+AMP aqueous solutions absorbed CO2, the formation of AEEA primary carbamate was relatively faster than the formation of AEEA secondary carbamate. During CO2desorption process, the AEEA secondary carbamate was produced from an endothermic reaction of HCO3" with AEEAH+. HCO3-/CO32-, which were compared with carbamate, were easier to be desorbed in the desorption process. AEEA primary carbamate was more stable than AEEA secondary carbamate, which caused AEEA primary carbamate much harder to be desorbed than AEEA secondary carbamate.