Characterization of ammonia-based CO2 capture process using ion speciation

Carbon dioxide absorption process using an ammonia solution provides many advantages including higher absorption capacity, no degradation and lower regeneration energy requirement. In this study, the ammonium ion species were identified and measured at various experimental conditions using a 13C NMR. Carbamate was the main species at the early stage of the absorption process due to the excessive presence of ammonia molecules. In contrast, bicarbonate prevailed at the final stage when most of ammonia molecules reacted with CO2 molecules. As temperature increased, the amount of carbonate dramatically decreased, while that of bicarbonate and carbamate increased. From the thermodynamic simulation using the vapor–liquid equilibrium model (VLE), it was found that the ammonium speciation data generally agreed with the experimental results. In conclusion, we proposed a reasonable and straightforward method for the determination of the ion concentrations in aqueous ammonia for CO2. This work will improve the understanding of solution behavior associated with absorption and regeneration reactions and finally will be used for the monitoring, evaluation and optimization of the ammonia-based CO2 capture process.

► A combined model to identify the ammonium speciation in the ammonia based CO2 capture process.
► The 13C NMR experimental data to verify the model.
► Reasonable method for determination of ammonium speciation.
► Model to sense the operating status of the CO2 capture process.