Equilibrium analysis of carbon dioxide absorption in alkali solutions

To meet the growing need for CO₂ capture and storage technology, Michigan Technological University is researching CO₂capture and storage using alkali solutions¹. Without implementing emission controls, world energy emissions will rise from 29.7 billion t in 2007 to 42.4 billion t in 2035. The first objective of the project was to determine the optimal amount of alkali in solution for CO₂ absorption. This was accomplished using theoretical equilibrium calculations and experimental absorption data for alkali solutions of 1, 2,3,4 and 5 weight %. As the % alkali in solution increased, so, too, did the ionic strength of the solution. Theoretical calculations took into account the effect increasing ionic strength will have on the solubility of gaseous CO₂- The calculations assumed negligible formation Of H₂CO₃, constant temperature and constant pressure. In the experimental setup, a 16% C0₂/balance air gas mixture was bubbled through an Erlenmeyer flask filled with an alkali solution. The gas exiting the flask was fed to a gas analyzer to record the % CO₂ in the exhaust gas stream. The % CO₂ absorbed was taken as the % CO₂ in the exhaust gas minus the % CO₂ in the feed. Theoretical calculations found that as the % alkali in solution increases, the solubility of CO₂ decreases. This was verified by experimental data, which found that a 2% alkali solution, by weight,. was the ideal solution for CO₂ absorption. Current research is focused on using the 2% alkali solution for permanent storage of CO₂ via mineral carbonation to produce a value-added product.