The Role of Zinc(II) in the Absorption–Desorption of CO2 by Aqueous NH3, a Potentially Cost-Effective Method for CO2 Capture and Recycling



The absorption of CO2 by aqueous NH3 solutions has been investigated at atmospheric pressure and 0 °C. The CO2 absorption is fast and occurs with high efficiency (88–99 %). The maximum CO2-removal efficiency increases slightly with the NH3 concentration. Addition of zinc(II) salts (as chloride, nitrate or sulfate) to the NH3 absorbent solution increases the overall CO2-absorption capacity without appreciably affecting the removal efficiency. Stripping of pure CO2 from HCO3solutions is achieved by adding the calculated amount of ZnIIsalts, which under ambient conditions lead to rapid release of about 30–35 % of the initially captured CO2. At the same time, about 65–70 % of the captured CO2 is transformed into solid basic zinc carbonates. The recovery of these valuable solid products and the release of only 1/3 of free CO2 at room temperature and pressure reduces the cost of the overall process of CO2 capture, making it a potentially attractive method for CO2 capture on a larger scale.