Chemical Engineering Journal 179 (2012) 262–271 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal jo u r n al hom epage: www.elsevier.com/locate/cej Kinetics of carbon dioxide (CO 2 ) with ethylenediamine, 3-amino-1-propanol in methanol and ethanol, and with 1-dimethylamino-2-propanol and 3-dimethylamino-1-propanol in water using stopped-flow technique Salim Kadiwala, Aravind V. Rayer, Amr Henni ∗ International Test Center for CO2 Capture, Faculty of Engineering and Applied Science, University of Regina, Saskatchewan, Canada S4S 0A2 a r t i c l e i n f o Article history: Received 31 March 2011 Received in revised form 20 September 2011 Accepted 27 October 2011 Keywords: CO2 capture CO2 kinetics Alkanolamine Non-aqueous Stopped flow Zwitterion Termolecular a b s t r a c t Pseudo first order rate constants of homogeneous reactions of carbon dioxide (CO 2 ) with primary amines, ethylenediamine (EDA) and 3-amino-1-propanol (3AP), in methanol and ethanol in the concentration range of 20–120 mol m -3 ; and with tertiary amines, 3-dimethyl-amino-1-propanol (3DMA1P) and 1- dimethylamino-2-propanol (1DMA2P), in water in the concentration range of 20–120 mol m -3 were measured using a stopped-flow apparatus in a temperature range of 293–313 K. Dissociation constants for aqueous 3DMA1P and 1DMA2P systems at different temperatures were also measured. Both ter- tiary amines were found to react faster with CO 2 than N-methyldiethanolamine (MDEA). The orders of the reaction were determined and the constants were regressed using the mechanism that fitted best the experimental data for each system. Second order reaction rate constants of ethylenediamine (EDA) in methanol and ethanol were higher than those of 2-((2-aminoethyl)amino) ethanol (AEEA), a fast reacting amine, whereas the rates of reaction of 3AP were found to be less than those of monoethanolamine (MEA) in methanol and ethanol. As expected, for both EDA and 3AP, the second order reaction rate constants were found to be lower in non-aqueous media than in water. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Acid gases such as carbon dioxide, hydrogen sulphide, carbonyl sulphide, etc. are absorbed by aqueous and non-aqueous solutions of pure or blended alkanolamines. The kinetics of reaction between alkanolamines in different reaction media and acid gas have a very prominent effect on the overall acid gas absorption rate and the design of absorption column that determines the cost-effectiveness of the CO 2 capture system. Therefore, a thorough knowledge of reaction mechanisms in different media and their corresponding rate constants are required. Kinetic data of various primary, secondary and tertiary amines with acid gases, such as CO 2 and H 2 S, have been published in the literature since 1960, and were reviewed by Blauwhoff et al. [1], and later by Versteeg et al. [2] and recently by Vaidya et al. [3]. Littel et al. [4] studied aqueous solutions of triethanolamine (TEA), dimethyl-monoethanolamine (DMMEA) and diethylmo- noethanolamine (DEMEA) and found the reaction order for each amine to be one in agreement with the base catalyst mechanism. Versteeg et al. [2] reviewed data published on tertiary amines ∗ Corresponding author. Tel.: +1 306 585 4960; fax: +1 306 585 4855. E-mail address: amr.henni@uregina.ca (A. Henni). (MDEA and TEA) and concluded that no discrepancies exist with regard to the overall reaction order, which is equal to two. Non-aqueous media, such as methanol or ethanol, reduce the regeneration cost in amine plants [5], and are therefore of inter- est as alternative reaction media for CO 2 absorption. Sada et al. [6] studied aqueous and non-aqueous (methanol, ethanol, 2-propanol) solutions of TEA, and found the reaction order to be unity with respect to the amine, in accordance with the conclusion drawn by Versteeg et al. [2]. Benitez-Garcia et al. [7] studied the effect of basicity of four tertiary amines (TEA, MDEA, DEMEA and triethy- lamine) on CO 2 absorption rates and found that the second order kinetic rate constant increased with increasing basicity. The same phenomena were observed by Sada et al. [6] for MEA and DEA. The reaction order was found to change gradually for MEA from 1 to 1.9 for water to methanol, ethanol and 2-propanol. Alvarez-Fuster et al. [8] found that the reaction order with respect to cyclohex- amine in ethanediol (a more polar solvent than ethanol) to be 1 as compared to 1.8 in ethanol. Sada et al. [6] and Versteeg et al. [9] observed the order of reaction with respect to amine to vary inversely with solvent polarity. Some of the literature data avail- able [10–17] for various alkanolamines in non-aqueous systems are listed in Table 1. Previous studies by Li et al. [18,19] of the kinetic rate for CO 2 absorption in an aqueous system of ethylenedi- amine (EDA) and 3-amino-1-propanol (3AP) showed a higher rate constant than conventional aqueous MEA solution within similar 1385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2011.10.093