A study of structure–activity relationships of commercial tertiary amines for post-combustion CO 2 capture Min Xiao, Helei Liu ⇑ , Raphael Idem, Paitoon Tontiwachwuthikul, Zhiwu Liang ⇑ Joint International Center for CO 2 Capture and Storage (iCCS), Hunan Provincial Key Laboratory for Cost-effective Utilization of Fossil Fuel Aimed at Reducing CO 2 Emissions, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, PR China highlights  Ethyl group is beneficial for tertiary amines of CO 2 absorption.  The existence of side carbon chain may promote the activity of tertiary amine.  Hydroxyl group reduces the equilibrium CO 2 solubility, k 2 and pKa.  Heterocyclic structure decrease the equilibrium CO 2 solubility, k 2 and pKa.  Hydroxyl group results in higher CO 2 absorption heat. article info Article history: Received 23 June 2016 Received in revised form 27 September 2016 Accepted 1 October 2016 Keywords: Carbon dioxide absorption Tertiary amines Structure-activity relationship CO 2 absorption rate Equilibrium solubility CO 2 absorption heat abstract This work examined the relationship between the structure of various commercial tertiary amines and their activity in CO 2 absorption/desorption in terms of rate of CO 2 absorption, equilibrium CO 2 loading, pKa and heat of CO 2 absorption in order to establish possible guidelines for selection of tertiary amine components for amine blends. Results show that any electron donating group linked directly to the nitro- gen atom increases their reactivity with CO 2 . In addition, the presence of steric hindrance effect and good water solubility also show enhancements in activity. In contrast, the existence of a hydroxyl group leads to a decrease in all the activity of the tertiary amine. The heat of CO 2 absorption of tertiary amines, which is closely related to the regeneration energy, can be reduced by decreasing the number of hydroxyethyl groups or by positing the hydroxyl group at the proper carbon relative to the nitrogen atom. Ó 2016 Published by Elsevier Ltd. 1. Introduction Global warming poses one of the most serious global chal- lenges, which may be blamed for disasters such as glacier melting, severe weather, storms and droughts. These make it necessary to prevent global warming and the rising average temperature. The contributor to global warming is greenhouse gas (GHG) emissions, and the most abundant GHG due to human activities is carbon dioxide (CO 2 ). With the rapid development of global economies, increasingly large amounts of fossil fuel is used especially for pro- ducing electricity and other forms of energy [1,2]. The large con- sumption of fossil fuel leads to the release of large amounts of CO 2 into air which leads to increasing concentration of CO 2 in the atmosphere. Since CO 2 has a stable chemical structure and hardly reacts with other materials in the atmosphere to cause its decay, it is not possible to use natural means to cause its elimina- tion. Consequently, it becomes necessary to find other efficient methods to either remove it from or prevent further emission into the atmosphere. One of the most mature technologies for capture of CO 2 to prevent its release into the atmosphere is post- combustion capture from large point industrial sources using chemical solvents such as aqueous amines. A large number of amine-based solvents have been investigated for their performance in CO 2 absorption in terms of CO 2 absorption rate, CO 2 solubility and heat of regeneration. Monoethanolamine (MEA), diethanolamine (DEA) and N–methyldiethanolamine (MDEA) are examples of conventional primary, secondary and ter- tiary amines, respectively, which are commercially available and have been used as common absorbents in industrial CO 2 capture processes. However, there are still some drawbacks in their use as absorbents. Depending on the type, such drawbacks include http://dx.doi.org/10.1016/j.apenergy.2016.10.006 0306-2619/Ó 2016 Published by Elsevier Ltd. ⇑ Corresponding authors. E-mail addresses: lhl0925@hotmail.com (H. Liu), zwliang@hnu.edu.cn (Z. Liang). Applied Energy 184 (2016) 219–229 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy