Post-combustion Capture Of CO₂Using Advanced Aqueous Ammonia

Aqueous ammonia (NH3) is considered as a promising alternative to amine basedabsorbents for post–combustion capture of CO2. To enhance CO2absorption rate anddecrease NH3vapour losses in NH3solution, amino acid salts as additives in NH3solution were investigated. Base on the pKa measurement and screening test results ofvarious amino acids using a wetted–wall column, we select sarcosine, proline andtaurine for a further study. The introduction of sarcosinate can improve the KGof CO2absorption dramatically in NH3solution, but at the expense of greater NH3vapourlosses. The greater loss of NH3upon addition of sarcosinate can be ascribedto theincrease of free NH3, decrease in CO2and NH3solubility in the liquid phase andcompetition for CO2between NH3and additives in the solution. All unknown rate andequilibrium constants for the reactions in a PRO–/TAU––CO2–H2O system weredetermined by stopped-flow spectrophotometry technique and global data fitting. Thereaction mechanism in the PRO–/TAU––NH3–CO2–H2O system is proved to be thecombination of the reactions in the NH3–CO2–H2O system and the PRO–/TAU––CO2–H2O system. Compared to NH3alone solution, NH3neutralized taurine/NH3mixtureshad higher KGof CO2and less NH3vapour loss.