Carbon dioxide absorption by aqueous mixtures of diisopropanolamine and triethanolamine A.B. López a , M.D. La Rubia a, *, R. Pacheco a , S. Sánchez a , J.M. Navaza b , D. Gómez-Díaz b a Department of Chemical, Environmental and Materials Engineering. EPS. University of Jae’n. Andalucía. Spain b Department of Chemical Engineering. ETSE. University of Santiago de Compostela. Galicia. Spain A R T I C L E I N F O Article history: Received 11 June 2016 Received in revised form 8 September 2016 Accepted 22 September 2016 Available online 23 September 2016 A B S T R A C T Aqueous secondary and tertiary alkanolamine mixtures are novel absorbents for carbon dioxide removal. This study evaluates the CO 2 absorption by aqueous mixtures of diisopropanolamine (DIPA) and triethanolamine (TEA) in a bubble column reactor considering the inﬂuence of the mixture composition, gas ﬂow rate and time on the hydrodynamic parameters, reaction mechanism and mass transfer coefﬁcient. The nuclear magnetic resonance spectroscopy (NMR) was performed to evaluate the possible synergic effects produced by the use of this alkanolamine mixture. The gas ﬂow rates were 18, 30 y 40 L h 1 and the total concentration of the mixtures was 10% of total weight, varying the proportions of DIPA and TEA. The composition of the mixtures (corresponding to the 10% of amine)was varied over the entire composition range. ã 2016 Elsevier B.V. All rights reserved. 1. Introduction The separation of acidic gases (CO 2 , H 2 S  ) from gas streams that contain them by absorption, is an operation used for decades that usually employs, as absorbent agent, aqueous or organic alkanolamine solutions. Monoethanolamine (MEA) is the most commonly used alkanolamine in the chemical industry for the absorption of CO 2 , but MEA has serious problems of corrosion and degradation at high concentration and temperature. Therefore it is necessary to carry out studies with other type of amines such as sterically hindered alkanolamines (SHA), which have shown a good CO 2 absorption capacity, fast reaction rate and low corrosion, even at high concentrations, at the same time that requiring lower regeneration energy than conventional alkanolamines [1–4]. The suitable characteristics shown by SHA-based solvents in relation with regeneration process are linked with the type of reaction products (mainly bicarbonate ion). This fact can be taken into account in the mixtures of amines involving a tertiary amine because this last type can contribute improvements in the overall separation process because tertiary amines avoid the production of carbamate to favor solvent regeneration and also, increase the carbon dioxide loading in the absorption part [5]. Therefore, searching for better advantages some research groups have tested alkanolamine mixtures that included monoethanolamine, N,N- dimethylethanolamine (DMEA), N,N-diethylethanolamine (DEEA) and 2-mino-2-methyl-1-propanol (AMP) [6–10]. The importance of hydrodynamic studies in the gas-liquid absorption, both in the presence and absence of a chemical reaction, has increased in recent years, particularly in relation to the study of the interfacial area generated between both phases in various gas-liquid reactors (bubble columns, packed columns, stirred tanks and air-lift reactors). This fact is due to improvements that occur in the absorption process by increasing the gas-liquid interfacial area, and thus, it is possible to increase the mass transfer rate without involving any changes in the reactor design. This type of studies has many applications in bioreactors with the aim of optimize the oxygen transfer rate [11,12]. There are not many research papers that analyzed the carbon dioxide absorption process by alkanolamines mixtures in a bubble column reactor, evaluating the inﬂuence of the interfacial area during the overall process. Previous works have studied the use of tertiary alkanolamines MDEA and TEA in bubble column reactors, in those that considered the inﬂuence of the concentration of amine and the gas ﬂow rate on the interfacial area value [13,14]. However, other authors [15] have studied this process in more detail by also considering, the inﬂuence of time on the value of the interfacial area during the absorption using other type of alkanolamines (MEA, DEA and MDEA). * Corresponding author. E-mail address: mdrubia@ujaen.es (M.D. La Rubia). http://dx.doi.org/10.1016/j.cep.2016.09.013 0255-2701/ã 2016 Elsevier B.V. All rights reserved. Chemical Engineering and Processing 110 (2016) 73–79 Contents lists available at ScienceDirect Chemical Engineering and Processing: Process Intensiﬁcation journal homepa ge: www.elsev ier.com/locate/cep