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ChemSusChem. 2008;1(3):228-35. doi: 10.1002/cssc.200700124.

The role of zinc(II) in the absorption-desorption of CO2 by aqueous NH3, a potentially cost-effective method for CO2 capture and recycling.

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Department of Chemistry, University of Florence, Firenze, Italy.


The absorption of CO2 by aqueous NH3 solutions has been investigated at atmospheric pressure and 0 degrees 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 HCO3(-) solutions is achieved by adding the calculated amount of ZnII salts, 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.

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