CO 2 absorption kinetics in a CO 2 -free and partially loaded aqueous ammonia solution Gyo Hee Kim a , Sung Youl Park b , Jong Kyun You b , Won Hi Hong a , Jong-Nam Kim b,⇑ , Jong-Duk Kim a,⇑ a Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Guseong-dong 373-1, Yusong-gu, Daejeon, Republic of Korea b High Efficiency and Clean Energy Research Division, Korea Institute of Energy Research, 71-2 Jang-dong, Yusong-gu, Daejeon, Republic of Korea highlights  The CO 2 absorption rate in a preloaded NH 3 solution is 30% lower than that in an unloaded solution.  A termolecular mechanism is suitable for the prediction of CO 2 absorption rate in NH 3 solution.  In an unloaded NH 3 solution, the major components are found to be NH 3 and OH  .  In a preloaded NH 3 solution, the major components are found to be NH 3 and H 2 O. graphical abstract article info Article history: Received 18 February 2014 Received in revised form 30 March 2014 Accepted 31 March 2014 Available online 13 April 2014 Keywords: CO 2 absorption Kinetics Wetted wall column Ammonia Partially loaded Termolecular mechanism abstract Although the CO 2 absorption rate in ammonia solution is essential for the design of a practical column for the capturing of CO 2 , debate continues regarding the values as well as proper mechanisms to interpret measured data. To resolve it, more data for CO 2 absorption rate in ammonia solution are required. In addi- tion, as most of the data focuses on the absorption rate in a CO 2 -free absorbent, data in partially loaded ammonia solutions are particularly required. Therefore, the CO 2 absorption rates in aqueous ammonia solution with 0 and 0.1 CO 2 loading were investigated with a wetted wall column in this study. The apparent CO 2 absorption rate in a partially CO 2 loaded ammonia solution was about 30% lower than that in an unloaded solution. After determining the apparent reaction rates and applying them to termolecular mechanism. The termolecular mechanism was revealed to be a reliable model in both unloaded and partially loaded ammonia solutions. To calculate the reaction rate constants, essential base components were also determined. H 2 O was negligible in the unloaded ammonia solution; whereas the OH  was negligible in the partially carbonated ammonia solution. This was due to the fact that the concentration of hydroxyl ions drastically decreased as the CO 2 loading is increased. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction The increasing CO 2 concentration in the atmosphere is known to be the major reason for global warming. Accordingly, many studies of CO 2 separation have been conducted. In order to separate CO 2 from flue gas, chemical absorption is widely used, as this method is able to treat considerable amounts of acidic gas and because it can be applied to current industrial systems without much modification [1–3]. Conventional CO 2 absorbents for chemi- cal absorption include alkanolamines such as monoethanolamine, dimethylethanolamine and methyldiethanolamine [4]. However, alternative absorbents are required to overcome the drawbacks of alkanolamines. Among several alternatives, ammonia solution http://dx.doi.org/10.1016/j.cej.2014.03.120 1385-8947/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding authors. Tel.: +82 42 860 3112; fax: +82 42 860 3134 (J.-N. Kim). Tel.: +82 42 350 3921; fax: +82 42 350 3910 (J.-D. Kim). E-mail addresses: jnkim@kier.re.kr (J.-N. Kim), kjd@kaist.ac.kr (J.-D. Kim). Chemical Engineering Journal 250 (2014) 83–90 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej