Experimental study on carbon dioxide absorption by aqueous ammonia with nickel and chromium ions in bubbling tower at low temperature

Aqueous ammonia has been widely applied to carbon dioxide capture thanks to its strong absorption capacity and low energy consumption, but the easily occurring ammonia escape may result in an additional environmental pollution. In this work, the aqueous ammonia with the Cr3+ or Ni2+ mixed at low temperatures is proposed and experimentally investigated to inhibit the ammonia escape and enhance carbon dioxide absorption. By taking the total ammonia escape, carbon dioxide absorption capacity and ammonia escape per unit carbon dioxide absorption as evaluation criteria, the effects of Ni2+ and Cr3+ on ammonia escape are compared. The results show that the increased reaction temperature and ammonia concentration result in the aggregated ammonia escape. The ammonia slip gets reduced but the carbon dioxide absorption is slightly affected with the Ni2+ and Cr3+ used due to the complex reaction between the metal ions and free ammonia. The additive of Ni2+ is basically superior to Cr3+ in restraining the ammonia escape, that the maximum inhibition efficiency of Ni2+ is 50.5% while Cr3+ is only 39.9%. By using additives, the reaction temperature can be raised to reduce the energy consumption of carbon dioxide absorption. It is recommended to adopt the chilled ammonia with additives for the carbon dioxide absorption by ammonia solution.