International Journal of Greenhouse Gas Control 5 (2011) 1606–1613 Contents lists available at SciVerse ScienceDirect International Journal of Greenhouse Gas Control j our na l ho me p age: www.elsevier.com/locate/ijggc Characterization of ammonia-based CO 2 capture process using ion speciation Chi Kyu Ahn a , Hae Woo Lee b , Yong Su Chang b , Kunwoo Han a , Je Young Kim a , Chang Houn Rhee a , Hee Dong Chun a , Min Woo Lee c , Jong Moon Park b,∗ a CO2 Project, Research Institute of Industrial Science & Technology, San 32, Hyoja-Dong, Pohang 790-600, Republic of Korea b Advanced Environmental Biotechnology Research Center, School of Environmental Science and Engineering, Department of Chemical Engineering, Pohang University of Science and Technology, San 31, Hyoja-Dong, Pohang 790-784, Republic of Korea c Department of Chemical Engineering, Keimyung University, 2800 Dalgubeoldaero, Dalseo-Gu Daegu 704-701, Republic of Korea a r t i c l e i n f o Article history: Received 14 December 2010 Received in revised form 2 September 2011 Accepted 29 September 2011 Available online 24 October 2011 Keywords: Carbon dioxide capture Ammonia solution Ammonium speciation 13 C NMR a b s t r a c t Carbon dioxide absorption process using an ammonia solution provides many advantages including higher absorption capacity, no degradation and lower regeneration energy requirement. In this study, the ammonium ion species were identified and measured at various experimental conditions using a 13 C NMR. Carbamate was the main species at the early stage of the absorption process due to the exces- sive presence of ammonia molecules. In contrast, bicarbonate prevailed at the final stage when most of ammonia molecules reacted with CO 2 molecules. As temperature increased, the amount of carbonate dramatically decreased, while that of bicarbonate and carbamate increased. From the thermodynamic simulation using the vapor–liquid equilibrium model (VLE), it was found that the ammonium specia- tion data generally agreed with the experimental results. In conclusion, we proposed a reasonable and straightforward method for the determination of the ion concentrations in aqueous ammonia for CO 2 . This work will improve the understanding of solution behavior associated with absorption and regeneration reactions and finally will be used for the monitoring, evaluation and optimization of the ammonia-based CO 2 capture process. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Global warming is one of the most serious environmental prob- lems in this century (IPCC, 2005). It is generally accepted that the issue is closely related to the anthropogenic carbon dioxide (CO 2 ) emission activities, mainly the combustion of the fossil fuels and chemical transformation. Therefore, the reduction of CO 2 emission from large industrial point sources such as the power stations and iron- and steel-making plants is considered to be one of the highest priorities by both industry and the lay public. Several options for the reduction of CO 2 emission have been proposed including the use of alternative fuels, i.e., renew- able energy, and improvement in energy efficiency. However, these have some drawbacks in their short-term application. Therefore, technologies for CO 2 capture from gas stream have been introduced and developed as post-combustion, pre- combustion and oxy-fuel combustion. Especially, these include chemical absorption, physical separation/adsorption, membrane ∗ Corresponding author. Tel.: +82 54 279 2275; fax: +82 54 279 8299. E-mail address: jmpark@postech.ac.kr (J.M. Park). separation and biological fixation (Figueroa et al., 2008; Gibbins and Chalmers, 2008; IPCC, 2005; Yang et al., 2008; Yu et al., 2008). Among them, the chemical absorption has been extensively studied and considered as a reliable and cost-effective method for CO 2 cap- ture from various industries (Chakma, 1995; Yang et al., 2008). In particular, the amine solution such as monoethanolamine (MEA) or so-called “MEA process” has been widely used for CO 2 capture from natural gas, power plant, and refinery streams (Yang et al., 2008). While amine solution is widely used for CO 2 capture process, it has some drawbacks such as (1) low CO 2 absorption capacity, (2) easier degradation in the presence of acid gases (i.e. SO x , HCl and H 2 S) and oxygen, (3) corrosive nature and (4) high energy requirement for regeneration (Diao et al., 2004; Yeh et al., 2005). Therefore, many researchers have focused on the development of efficient alterna- tives with higher absorptive capacity and lower reaction energy demands for regeneration. One of the rising alternatives is the ammonia solution that provides the advantages of higher CO 2 absorption capacity, no absorbent degradation, and low regeneration energy requirement (Bai and Yeh, 1997; Darde et al., 2009; Diao et al., 2004; Kim et al., 2008, 2009; Yeh et al., 2005). The CO 2 capture process using an ammonia solution consists of absorption and regeneration units 1750-5836/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijggc.2011.09.007