Determination of ammonium salt/ion speciation in the CO2 absorption process using ammonia solution: Modeling and experimental approaches

Ammonia solution has received special attention as an effective absorbent in CO2 capture process because of its higher CO2 absorption capacity and lower chemical cost rather than amine solution such as monoethanolamine. In ammonia based CO2 capture process, various ammonium salts/ions would be formed reacting with ammonia and CO2. The ammonium speciation in the liquid phase greatly affected the overall process efficiency, the energy requirement of ammonia regeneration or CO2 recovery process. In this study, we examined the ammonium speciation in ammonia solution during the CO2 absorption reaction using a 13C-NMR (nuclear magnetic resonance) spectrometry and identified bicarbonate (HCO3−), carbonate (CO32−) and carbamate (NH2COO−) ions. Moreover VLE (vapor-liquid equilibrium) model which is thermodynamic model in vapor-liquid phase was also applied to simulate ammonium speciation. The simulation results for the ammonium speciation were generally well-agreed with the experimental results, even though some discrepancies were observed as the absorbed amount of CO2 increased. In conclusion, a combined approach utilizing both (13C-NMR analysis and VLE model) can help to understand the reactions between ammonia and CO2 and optimize the CO2 capture process using ammonia solution.