Capture of Low-Concentration CO2 by Ammonia Brine: Effects on Efficiency and Product Distribution

Capture and utilization of dilute CO2 streams are relevant to emissions management in the steel industry. This study investigated the capture behavior of a laboratory-scale ammonia–brine carbonation system and characterized the recovered solids after washing and drying. This study systematically investigated the influence of four key operational parameters: ammonia concentration (7–28 wt%), NaCl concentration (3 M, 4 M, and saturated), reaction temperature (20 °C and 38 °C), and CO2 flow rate (100–500 mL/min) on both CO2 capture efficiency and product-phase distribution. The results revealed that higher ammonia and NaCl concentrations markedly improved CO2 capture performance, whereas an elevated temperature and CO2 flow rate exerted detrimental effects. At 21 wt% NH3, saturated NaCl, 20 °C, and a total gas flow rate of 1 L/min, the reported CO2 capture efficiency exceeded 82% during the first 50 min. The solid-phase characterization describes the washed and dried product rather than the complete composition of the original precipitate. Possible bicarbonate formation routes involving OH− and a carbamate intermediate are discussed, but their relative contributions were not resolved by the present measurements. These laboratory results provide a basis for further investigation of ammonia–brine carbonation, while scale-up, continuous operation, and industrial feasibility remain to be evaluated. Process-level energy consumption and comparative economic and environmental performance were not evaluated.