Thermal degradation of aqueous 2-aminoethylethanolamine in CO2 capture; identification of degradation products, reaction mechanisms and computational studies
© The Author(s) 2017
Received: 24 May 2016
Accepted: 7 December 2016
Published: 24 January 2017
Amine degradation is the main significant problems in amine-based post-combustion CO2 capture, causes foaming, increase in viscosity, corrosion, fouling as well as environmental issues. Therefore it is very important to develop the most efficient solvent with high thermal and chemical stability. This study investigated thermal degradation of aqueous 30% 2-aminoethylethanolamine (AEEA) using 316 stainless steel cylinders in the presence and absence of CO2 for 4 weeks. The degradation products were identified by gas chromatography mass spectrometry (GC/MS) and liquid chromatography-time-of-flight-mass spectrometry (LC-QTOF/MS). The results showed AEEA is stable in the absence of CO2, while in the presence of CO2 AEEA showed to be very unstable and numbers of degradation products were identified. 1-(2-Hydroxyethyl)-2-imidazolidinone (HEIA) was the most abundance degradation product. A possible mechanism for the thermal degradation of AEEA has been developed to explain the formation of degradation products. In addition, the reaction energy of formation of the most abundance degradation product HEIA was calculated using quantum mechanical calculation.
Keywords2-aminoethylethanolamine (AEEA) CO2 capture Thermal degradation Mechanism Computational study
Post-combustion CO2 capture is a topic of the environmental and climatic mitigation of carbon based energy system. Several studies have surveyed the environmental and climatic mitigation of carbon based energy system , and the impacts of lower-pollution energy system transition , including natural gas others [3, 4]. One of obvious conclusions is that without carbon capture and storage, carbon based energy system could not avoid the additional global warming. Post-combustion CO2 capture would reduce the pollutants and carbon emission, and increase environmental and climatic health. Post-combustion based on amine CO2 capture is the most dominant technology used for CO2 capture. This technique uses different aqueous alkanolamines to absorb CO2 gas from flue gas stream. This technology has several advantages such as good reactivity, high capacity and low cost. Moreover, the alkanolamines can be recovered after the completion of the whole process [5, 6].
However, alkanolamines also undergo irreversible reaction with acid gases to produce undesired compounds. Alkanolamines suffers from thermal and oxidative degradation. Thermal degradation occurs due to the high temperature in the stripper, and may also occur in the cross heat exchanger and the reclaimer, depending on the configuration [7, 8]. Degradation of amines is undesirable for amine-based CO2 capture as this causes growing economic burden and may cause operating problems like fouling, corrosion and foaming [9–11]. Amine degradation is one of the major issues associated with amine based post combustion carbon capture (PCC). The degradation products from the process causes foaming, increased viscosity, high corrosion of equipment and fouling [12, 13]. Furthermore, emissions and disposal of degradation products cause environmental and health issues. These contribute to economic glitches, which requires urgent panacea.
In recent years, new solvent such as 2-Aminoethylethanolamine (AEEA) has been utilized as an absorbent for CO2 from post-combustion exhaust gases [14, 15]. AEEA is a diamine, which contains two nitrogen atoms that can absorb CO2 and one OH group which increases the solubility in aqueous solution. AEEA exhibit better performance than other industrial amine such as N-methylethanolamine (MEA) , due to the higher solubility, lower vapor pressure, higher absorption capacity, greater heat absorption and lower desorption energy [14–18].
There is a lack of data regarding to the thermal degradation investigation of AEEA-based CO2 scrubbing system, and the degradation product formation pathways and that require further research. In this article, the thermal degradation of 30% AEEA is presented in detail. Identification, reaction mechanism, computational chemistry studies of the degradation products are proposed and discussed.
All chemicals such as 2-aminoethylethanolamine (AEEA) (≥98%), barium chloride (BaCl2) and standards solutions of hydrochloric acid (HCl), sodium hydroxide (NaOH) and sulfuric acid (H2SO4) were procured from Merck (Malaysia). Carbon dioxide (99%) and N2 (≥99.99%) gases were procured from a Linder (Malaysia). All chemicals were used as purchased without further purification.
Sample preparation and CO2 loading experiments
Thermal degradation experiments
The thermal degradation experiment was performed in a metal cylinder (5 in. length and ½ in.outer diameter) made from 316 stainless steel and equipped with Swagelok end-caps. The method used was similar to Davis et al. . 8 ml of sample with and without CO2 were introduced directly into the cylinder, placed in a Memmert 600 oven and heated at 135 °C, above the stripper temperature (to accelerate the reaction). Experiments were conducted at high temperature 135 °C as intention was to accelerate the thermal degradation to produce highly degraded samples within a reasonable timeframe.
The cylinders were periodically removed from the oven (once per week) during the whole 4 weeks. Any suspected leakage was checked by the weight differences of before and after the experiments. After the cylinders were cooled to room temperature, the samples were transferred to vials and kept refrigerated at 5 °C to quench the reaction and finally subjected to further analysis.
Gas chromatography–mass spectrometry (GC–MS)
GC–MS parameters for identifications of degradation products
Internal diameter (µm)
Initial temp. (°C)
Initial hold time (min)
Oven ramp (1) (°C min–1)
Oven ramp (2) (°C min–1)
Final temp. (°C)
Final hold time (min)
Injector temp. (°C)
Flow rate (constant) (ml min−1)
Liquid chromatography-time-of-flight-mass spectrometry (LC-QTOF-MS)
Gradient profile for the mobile phase ratio in this experiment
Mobile phase ratio
Formic acid (0.10%)
All the transition state structures and reactants were fully optimized, in the gas phase at 298.15K at B3LYP/6-311++G(d, p) level of theory using the Gaussian09  and GaussView visualization program . The transition state calculations of the proposed mechanisms were carried out. Synchronous transition methods were used to find a transition state (TS) under D mol3 module in Material Studio 4.4 for the structure optimization and reaction path calculations. All calculations were performed using the density functional theory (DFT) with local density approximation (LDA) of local functional PWC , with effective core potential treatment with the DN basis set. The reaction paths were obtained using the linear synchronous transit (LST) and optimization calculation performs a single interpolation to a maximum energy, followed by the quadratic synchronous transit (QST) method, for an energy maximum with constrained minimizations in order to refine the transition state to a high degree . Another conjugate gradient minimization was performed at each point. The cycle was repeated until a stationary point was located or the number of allowed QST steps was exhausted. After the initial paths were converged, the highest energy points were optimized to the closest transition state (TS). Following the TS optimization, the minimum energy path (MEP) between the critical points were calculated with the nudged elastic band (NEB), to ensure continuity of the path and projection of the force, so that the system converges to the MEP. The TS were checked at the B3LYP/6-311++G (d, p) level by evaluating the vibrational frequencies. The optimized geometries obtained were characterized as stationary points on the potential energy surface (PES) and the transition states were characterized by only one imaginary frequency, which is confirmed to represent the most accurate reaction coordinate. The computational method used in this study is similar to Lee et al. .
Results and discussions
The investigation of formation of thermal degradation products in AEEA system was conducted in three different conditions; thermal degradation in the absence of CO2 (AEEA/H2O), thermal degradation in the presence of CO2 (AEEA/H2O/CO2) and quantum mechanical calculations of the formation of the main degradation product (HEIA). In the AEEA/H2O system, the aqueous amine solution was heated at 135 °C for 4 weeks. In the AEEA/H2O/CO2 system, the amine solution was first loaded with CO2 (α = 0.80 mol CO2/mol of amine) and then heated to 135 °C for 4 weeks. At the end of each experiment, the liquid phase analysis was carried out by using GC–MS and LC-QTOF-MS to identify the degradation products.
Identification of degradation products
Compounds identified by the present study by using GC-MS and LC-MS-QTOF in AEEA/CO2/H2O system at 135 °C
Amine lose and the concentration of the degradation products
Possible reaction pathway of identified degradation products
An overall reaction pathway has been developed to explain the formation of the major products during the thermal degradation. The objective is to understand the most probable reactions which occur during the thermal degradation process and offer solutions for the elimination of a particular degradation product. The reaction mechanism of the thermal degradation of AEEA was proposed based on the reaction of AEEA with CO2 in aqueous solution.
Nevertheless, the proposed reaction mechanism of main degradation products based on this study and literature is debated in this manuscript. Products like HEIA, HEOD, BHEP are the abundant degradation products as per this study. So mechanism postulated in this study is based on the main products. Most of the reaction mechanisms were proposed based on the influence of the ionic species (carbamate and dicarbmate) in the solution.
1-(2-Hydroxyethyl)-2-imidazolidinone (HEIA) and 2-hydroxyethyl-2-oxazolidone (HEOD)
Relative energy (Ha)
Relative energy (kcal/mol)
Thermal degradation of 30% AEEA was performed in the presence and absence of CO2 loading at 135 °C. AEEA showed high stability in the absence of CO2, and no degradation products were identified. However, AEEA degraded significantly in the presence of CO2 and twenty-seven degradation products were identified by GC–MS based on the (NIST) library search, and based on LC-QTOF-MS search. 2-hydroxyethyl imidazolidone (HEIA) was the most abundant degradation product, which contributed to the loss of the AEEA concentration. The reaction energy of HEIA formation were calculated for the both pathways of its formations and found to be −2.15 kcal/mol and −6.97 kcal/mol. Degradation rates of AEEA show that it may not be a choice of commercialization or large CO2. However, under lab scale more investigation may be conducted by using degradation inhibitors. Or another way may be modification of AEEA by addition of an alkyl group to the amines groups could be a possible way to prevent the carbamate formation.
WJB initiate the idea of this work, IMS prepare the solutions and conduct the degradation experiments, VSL carried out the quantum mechanical calculations, BSA and BHMJ assested to write and revised the final manuscript. AA and LG developed the CO2 loading setup. SAM carried out the sample analysis using chromatographic techniques. All authors read and approved the final manuscript.
We are thankful to University of Malaya Research Grant (UMRG): RP038C 15HTM, RP020C-14AFR, RP031B-15AFR and IPPP (PG209-2014B) University of Malaya, Kuala Lumpur, Malaysia 50603 for financial assistance.
The authors declare that they have no competing interests.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
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