Influence of operating temperature on CO2-NH3 reaction in an aqueous solution

Although aqueous ammonia solution has been focused on the removal of CO₂ from flue gas, there have been very few reports regarding the underlying analysis of the reaction between CO₂ and NH₃. In this work, we explored the reaction of CO₂-NH₃-H₂O system at various operating temperatures: 40 °C, 20 °C, and 5 °C. The CO₂ removal efficiency and the loss of ammonia were influenced by the operating temperatures. Also, infrared spectroscopy measurement was used in order to understand the formation mechanism of ion species in absorbent, such as NH₂COO⁻, HCO₃⁻, CO₃²⁻, and NH₄⁺, during CO₂, NH₃, and H₂O reaction. The reactions of CO₂-NH₃-H₂O system at 20 °C and 40 °C have similar reaction routes. However, a different reaction route was observed at 5 °C compared to the other operating temperatures, showing the solid products of ammonium bicarbonates, relatively. The CO₂ removal efficiency and the formation of carbamate and bicarbonate were strongly influenced by the operating temperatures. In particular, the analysis of the formation carbamate and bicarbonate by infrared spectroscopy measurement provides useful information on the reaction mechanism of CO₂ in an aqueous ammonia solution.