Thermal degradation of aqueous 2-aminoethylethanolamine in CO2 capture; identification of degradation products, reaction mechanisms and computational studies

Abstract

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.

Saeed et al. Chemistry Central Journal (2017) 11:10 DOI 10.1186/s13065-016-0231-7

Thermal degradation ofaqueous 2-aminoethylethanolamine inCO2 capture;

identication ofdegradation products, reaction mechanisms andcomputational studies

Idris Mohamed Saeed1, Vannajan Sanghiran Lee2, Shaukat Ali Mazari3, B. Si Ali1, Wan Jerey Basirun2*, Anam Asghar1, Lubna Ghalib1 and Badrul Mohamed Jan1

Background

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 [1], and the impacts of lower-pollution energy system transition [2], 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 dierent aqueous alkanolamines to absorb CO2 gas from ue 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 suers 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 conguration [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 [911]. Amine degradation is one of the major issues associated with amine based post combustion carbon capture (PCC). The

*Correspondence: [email protected]

2 Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, MalaysiaFull list of author information is available at the end of the article

The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/

Web End =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/

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Web End =publicdomain/zero/1.0/ ) applies to the data made available in this article, unless otherwise stated.

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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) [15], due to the higher solubility, lower vapor pressure, higher absorption capacity, greater heat absorption and lower desorption energy [1418].

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. Identication, reaction mechanism, computational chemistry studies of the degradation products are proposed and discussed.

Experimental methods Materials

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 purication.

Sample preparation andCO2 loading experiments

An aqueous AEEA solution was prepared in weight percent with concentrations of 30 wt% and diluted using diionized water. In the CO2 loading experiment, the reactor was equipped with a magnetic stirrer, and a pH meter linked to data acquisition system. A pH Probe linked to Metrohm was used to monitor the solution pH versus time. Figure1 provides a description of the experimental setup. The reaction started by introducing a volume of 100ml of 30% wt of aqueous AEEA into a double jacket reactor. The solution was then purged with nitrogen gas for 5 min to remove any possible dissolved oxygen. The CO2 gas was introduced into the reactor until it became saturated with CO2 with pH 7. Then samples were taken and transferred into the cylinders and CO2 loading was veried by titration [19]. In CO2 loading determination, two samples of nearly 0.5g were withdrawn form reactor, and transferred into a mixture of 50 ml NaOH (0.1 M) and 25ml of BaCl2 (0.5M) in a 250ml Erlenmeyer ask.

The reaction of BaCl2 and NaOH with CO2 result in the formation of white precipitates of BaCO3. Samples were heated, then cooled and ltered using 0.45m pore size silicon lter paper. The white crystals were washed with 50 ml deionized water, and then 0.1 M HCl was added until all crystals dissolved. Acidied samples were then titrated with 0.1 M NaOH. All the titration tasks were performed using 785 DMP Titrino auto-titrator installed with Tiamo 1.345.

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Thermal degradation experiments

The thermal degradation experiment was performed in a metal cylinder (5 in. length and in.outer diameter) made from 316 stainless steel and equipped with Swagelok end-caps. The method used was similar to Davis etal. [20]. 8ml of sample with and without CO2 were introduced directly into the cylinder, placed in a Memmert 600 oven and heated at 135C, 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 4weeks. Any suspected leakage was checked by the weight dierences of before and after the experiments. After the cylinders were cooled to room temperature, the samples were transferred to vials and kept refrigerated at 5C to quench the reaction and nally subjected to further analysis.

Analytical methodsGas chromatographymass spectrometry (GCMS)

The GCMS instrument (model 6890 N/5973 N) was from Shimadzu coupled with mass spectrometer (MS) using Shimadzu GCMS-QP2010, with Ultra autosampler AOC 20I+S. The separation of amines and degradation products were performed in RTX -5MS column using the conditions shown in Table1. Each sample was diluted using methanol mixture in the ratio of 1:50 prior to the analysis to avoid contamination of the system and to provide a higher sensitivity. The analysis was performed for 30 min to ensure the elution of heavy degradation compounds.

Liquid chromatographytimeofightmass spectrometry (LCQTOFMS)

The analyses of the degraded samples were carried out using an Agilent 1260 innity liquid chromatography coupled with 6224 time-of-ight (TOF) MS. The molecules were converted to ions by an electrospray ionization source (ESI). The column used was Zorbax Eclipse Plus (2.1100mm) and the amount of injected volume was 20 l. The eluent was 0.10% formic acid in water (1) and methanol (2). A gradient prole is described in Table 2. The ow rate was set at 0.200 ml/min. The method developed by Huang etal. [21] was used for the detection of the degradation products.

Computational details

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 [22]

and GaussView visualization program [23]. The transition state calculations of the proposed mechanisms were carried out. Synchronous transition methods were used to nd a transition state (TS) under Dmol3 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 [24], with eective 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 rene the transition state to a high degree [25]. 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

Table 1 GCMS parameters foridentications ofdegradation products

Column RTX-5MS

Length (m) 30.00 Internal diameter (m) 0.25 mm Thickness (m) 0.25 m Initial temp. (C) 70 Initial hold time (min) 1Oven ramp (1) (C min1) 5

Oven ramp (2) (C min1) 5

Final temp. (C) 240 Final hold time (min) 10 Injector temp. (C) 300 Flow rate (constant) (ml min1) 1

Carrier gas He

Table 2 Gradient prole forthe mobile phase ratio inthis experiment

Time (min) Mobile phase ratio

Formic acid (0.10%) Methanol (99.9%)

6 98 2 2 20 80 814 98 2

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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 conrmed to represent the most accurate reaction coordinate. The computational method used in this study is similar to Lee etal. [26].

Results anddiscussions

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 135C for 4weeks. In the AEEA/ H2O/CO2 system, the amine solution was rst loaded with

CO2 ( = 0.80 mol CO2/mol of amine) and then heated to 135C for 4weeks. At the end of each experiment, the

liquid phase analysis was carried out by using GCMS and LC-QTOF-MS to identify the degradation products.

Identication ofdegradation products

The identication of amine degradation products were performed by GCMS and LC-MS-QTOF techniques which are listed in Table2. No degradation products were identied during the thermal degradation of AEEA in the absence of CO2. However, 27 degradation products were detected during the thermal degradation of AEEA in the presence of CO2. 1-(2-Hydroxyethyl)-2-imidazolidinone (HEIA) was the most abundant degradation product in the system, Fig. 2 represents the GC chromatogram of a sample of the thermal degradation of AEEA and mass spectrum of HEIA after 4weeks. Low molecular weight volatile compounds such as ammonia are other degradation products which were likely to be formed in the process. However, the analytical methods employed in this work could not facilitate the detection. In this study, heat stable salts (HSS) such as formate, acetate were identied in this study in agreement with literature [27, 28]. However, the presence of HSS due to presence of oxygen

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Table 3 Compounds identied bythe present study byusing GC-MS andLC-MS-QTOF inAEEA/CO2/H2O system at135C

Compound Abb. MW (g/mol) Structures Analytical technique

Diethanolamine DEA 105

HO

H

GCMS LC-MS-QTOF

OH

1-Piperazineethanol HEP 126

HO GCMS

LC-MS-QTOF

NH

1,4-Bis(2-hydroxyethyl)piperazine BHEP 130 OH

HO GCMS

LC-MS-QTOF

2-Imidazolidinone HEI 86

GCMS

HN

1-(2-Hydroxyethyl)-2-imidazolidinone HEIA 130

GCMS LC-MS-QTOF

NH

HO

2-((2-Aminoethyl)-(2-(2-aminoethylamino)-(ethylamino)ethanol

AAEEA* 191

OH

H

HO

N

NH2

2-hydroxyethyl-2-oxazolidone HEOD 131

GCMS LC-MS-QTOF

OH

O

O

GCMS

Succinimide Succ 99 HN O

O

N-Methylsuccinimide MSucc 113

LC-MS-QTOF

O

N O

N,N-Dimethyl-2-imidazolidinone DMDZ 114 O GCMS

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Table 3 continued

Compound Abb. MW (g/mol) Structures Analytical technique

4-[(2-Hydroxyethyl)(nitroso)amino]-1-butanol HNAP 162N

OH

HO

LC-MS-QTOF

N

O

N O

OH

1-Nitroso-4-piperidinol NP 117

LC-MS-QTOF

N

4-[Butyl(nitroso)amino]-2-butanol BNAB 173

LC-MS-QTOF

N OH N

O

LC-MS-QTOF

N-(Butyl(nitroso)amino)methyl)acetamide BNAMA 173 O

N

H

N

N

O

NH2 GCMS

N-(2-hydroxyethyl)-N -methylpiperazine MPE 144 HO GCMS

1,4-Diformylpiperazine DFP 142

(3-Aminopropyl)morpholine AMM 144

O

GCMS

O

Homoserine Hom 119

NH2 GCMS

OH

HO

O

1-Methyl-4-nitrosopiperazine MNP 129 LC-MS-QTOF

Pyrazole-1-ethanol PE 112

OH

LC-MS-QTOF

1-Piperazineethanamine AEP 129

H GCMS

NH

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Table 3 continued

Compound Abb. MW (g/mol) Structures Analytical technique

1-(2-(2-Hydroxyethoxy)ethyl) piperazine HEEP 174

GCMS LC-MS-Q TOF

HO

N-[2-[3-[N-Aziridyl]propyl]aminoethyl]piperazine APAP 212

GCMS

HN

Tetraethylenepentamine TEP 191

H

H

GCMS

H2N

NH

NH2

in head space inside the cylinder as by-products of CO2

reduction that formed during degradation [28]. However, those products couldnt be identied due to the limitations of our analytical techniques (Table3).

Amine lose andthe concentration ofthe degradation products

The concentration proles of initial amine (AEEA) and the degradation products of 2-hydroxyethyl-2-oxazolidone (HEIA), (3-(2-Hydroxyethyl)-2-oxazolidinone (HEOD) and 1,4-Bis(2-hydroxyethyl)piperazine (BHEP) concentrations in the samples degraded at 135 C were obtained as a function of time, as shown in Fig.3. Concentration of HEIA increased with time and then a little decreased, representing that it is stable product and it plays a role as intermediate after 3weeks undergoing further reaction rather than a nal product. In addition, it is observed that the DEA and BHEP concentrations were very small during the experimental run, which suggests that it may be a key intermediate compound.

Possible reaction pathway ofidentied 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 oer 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 inuence of the ionic species (carbamate and dicarbmate) in the solution.

1(2Hydroxyethyl)2imidazolidinone (HEIA) and2hydroxyethyl2oxazolidone (HEOD)

AEEA is a type of diamine compound which contains two nitrogen atoms and reacts with CO2 to form several ionic species. It is also known that any ethylenediamine type of structure with two amino groups separated by an ethylene molecule, should form a cyclic urea when exposed to CO2 [28]. Cyclic urea, such as 1-(2-Hydroxyethyl)-2 imidazolidinone (HEIA), were observed in MEA degradation and the reaction mechanism in this work is similar to the literature [20, 29]. HEIA is the most abundance degradation products in thermal degradation of AEEA. The formation of HEIA postulated

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through two dierent pathways. In Scheme 1, at the presence of CO2 HEIA (5) formed at high temperature via the carbamate formation, by dehydration and internal cyclization of the secondary AEEA Carbamate (4). Also There is other possibility of internal cyclization of

AEEA secondary carbamate and released of Ammonia to form 2-hydroxyethyl-2-oxazolidone (HEOD) (6). This is analogous to the oxazolidone formation in the presence of ethanolamine and CO2, which was described in detail in the thermal degradation of MEA and DEA [20,

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28, 3032]. The other possibility of thermal degradation of carbonated AEEA is generation of HEIA which occurred through internal cyclization of AEEA primary carbamate (7) to generate HEIA (8).

2Imidazolidinone (HEI)

Scheme2 showed the formation of another type of cyclic urea (HEI) which generated during the thermal degradation of AEEA by the protonation of HEIA (1), followed by

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the elimination of ethyl alcohol of protonated (HEIA) (2) to produce 2-Imidazolidinone (3) and released ethylene oxide molecule (4).

1,4Diformylpiperazine (DFP)

Also at high temperature, the ring closure of dicarbamate-AEEA (1) will result in the formation of

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di-carbamate piperazine (2), followed by the protonation of the carbonyl in both amides (3) which further breaks the OC bond and forms the bond to produce the 1,4-Diformylpiperazine (4), according to Scheme3.

1,4Bis(2hydroxyethyl)piperazine (BHEP)

BHEP is a cyclic triamine which is formed by the nucleophilic attack of the HEOD (1) by AEEA (2), where the ring opening promotes the formation of 2-((2-Aminoethyl)-(2-(2-aminoethylamino)-(ethylamino)ethanol (AAEEA) (3). This is followed by the internal cyclization of the AAEEA (3) which releases ammonia (4) and produces the BHEP (5), as shown in Scheme4.

N,NDimethyl2imidazolidinone (DMDZ)

The generation of N,N-Dimethyl-2-imidazolidinone (DMDZ) happen by the attack of formic acid, formal-dehyde through a reaction called Eschweiler-Clarke

reaction. The reaction began by methylation of amine with protonated formaldehyde to form an iminium ion intermediate, which further react formic acid to form methylated ammonium ion and released CO2 as by product. The deprotonation of the ammonium ion aords the nal methylated amine product. These steps are repeated twice to give the nal tertiary amine product, according to Scheme5.

Computational results

In this work, the dierent pathways of formation of HEIA are investigated theoretically using quantum mechanical calculations. In Figs.4 and 5, the schematic details of the reaction mechanism, including the transition states, for the formation of HEIA is presented.

The rst possibility pathway (path 1) involves the addition of CO2 to the secondary amine in AEEA, with simultaneous dehydration to form HEIA and water molecule with an energy barrier of 2.15 kcal/mol. The second mechanism (path 2) involves the addition of CO2 to the primary amine in AEEA, with simultaneous dehydration and intermolecular cyclization to form the HEIA and water molecule with an energy barrier of 6.97kcal/

mol. Path 1 has higher activation energy than path 2. The optimized bond lengths in () at the B3LYP/6-31+G(d, p) level of theory are given for the bonds involved in the transition state (Table4).

Conclusions

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 identied. However,

Table 4 The computed energy and activation barriers for TS1, TS2 obtained at B3LYP/6-311++g(d, p) level

oftheory forthe formation ofproduct according toFigs.4 and5

Species Energy (Ha) Relative energy (Ha)

Relative energy (kcal/mol)

Reactant 1 533.1227263 0 0.00

TS1 532.8979985 0.22472785 141.02

Product 1 533.1261536 0.00342728 2.15

Reactant 2 533.1150498 0 0.00

TS2 532.9009546 0.214095141 134.35

Product 2 533.1261536 0.011103859 6.97

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AEEA degraded signicantly in the presence of CO2 and twenty-seven degradation products were identied by GCMS 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

2.15kcal/mol and 6.97kcal/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 modication of AEEA by addition of an alkyl group to the amines groups could be a possible way to prevent the carbamate formation.

Authors contributions

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 nal manuscript. AA and LG developed the CO2 loading setup. SAM carried out the sample analysis using chromatographic techniques. All authors read and approved the nal manuscript.

Author details

1 Department of Chemical Engineering, Faculty of Engineering, Universityof Malaya, 50603 Kuala Lumpur, Malaysia. 2 Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia. 3 Department of Chemical Engineering, Dawood University of Engineering and Technology, Karachi 74800, Pakistan.

Acknowledgements

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 nancial assistance.

Competing interests

The authors declare that they have no competing interests.

Received: 24 May 2016 Accepted: 7 December 2016

References

1. Zhan SF, Zhang XC, Ma C (2009) Coal classication based on environmental protection and burning quality. J China Coal Soc. 34:15351539

2. Zhang X, Chen W, Ma C, Zhan S (2013) Modeling particulate matter emissions during mineral loading process under weak wind simulation. Sci Total Environ 449:168173

3. Zhang X, Myhrvold NP, Caldeira K (2014) Key factors for assessing climate benets of natural gas versus coal electricity generation. Environ Res Let 9(11):114022

4. Zhang X, Chen W, Ma C, Zhang G, Ju M (2012) Assessment method for regional environmental risk based on pressure-state-response model. China Environ Sci. 32:8487

5. Zhao Z, Dong H, Huang Y, Cao L, Gao J, Zhang X et al (2015) Ionic degradation inhibitors and kinetic models for CO2 capture with aqueous monoethanolamine. Int J Greenhouse Gas Control 39:119128

6. Gouedard C, Picq D, Launay F, Carrette P-L (2012) Amine degradation in CO2 capture. I. A review. Int J Greenhouse Gas Control 10:244270

7. Rochelle GT (2012) Thermal degradation of amines for CO2 capture. Curr Opin Chem Eng. 1(2):183190

8. Mazari SA, Ali BS, Jan BM, Saeed IM, Nizamuddin S (2015) An overview of solvent management and emissions of amine-based CO2 capture technology. Int J Greenhouse Gas Control 34:129140

9. Mazari SA, Ali BS, Jan BM, Saeed IM (2014) Degradation study of piperazine, its blends and structural analogs for CO2 capture: a review. Int J

Greenhouse Gas Control 31:21422810. Vevelstad SJ, Grimstvedt A, Knuutila H, da Silva EF, Svendsen HF (2014) Inuence of experimental setup on amine degradation. Int J Greenhouse Gas Control 28:156167

11. Fytianos G, Ucar S, Grimstvedt A, Hyldbakk A, Svendsen HF, Knuutila HK (2016) Corrosion and degradation in MEA based post-combustion CO2

capture. Int J Greenhouse Gas Control 46:485612. Zoannou K-S, Sapsford DJ, Griffiths AJ (2013) Thermal degradation of monoethanolamine and its eect on CO2 capture capacity. Int J Greenhouse Gas Control 17:423430

13. Rey A, Gouedard C, Ledirac N, Cohen M, Dugay J, Vial J et al (2013) Amine degradation in CO2 capture. 2. New degradation products of MEA. Pyrazine and alkylpyrazines: analysis, mechanism of formation and toxicity. Int

J Greenhouse Gas Control 19:57658314. Mamun S, Jakobsen JP, Svendsen HF, Juliussen O (2006) Experimental and modeling study of the solubility of carbon dioxide in aqueous 30 mass% 2-((2-aminoethyl) amino) ethanol solution. Ind Eng Chem Res 45(8):25052512

15. Mamun S, Svendsen HF, Ho KA, Juliussen O (2007) Selection of new absorbents for carbon dioxide capture. Energy Convers Manag. 48(1):251258

16. Bonenfant D, Mimeault M, Hausler R (2003) Determination of the structural features of distinct amines important for the absorption of CO2 and regeneration in aqueous solution. Ind Eng Chem Res 42(14):31793184

17. Kierzkowska-Pawlak H (2015) Kinetics of CO2 absorption in aqueous N, N-diethylethanolamine and its blend with N-(2-aminoethyl) ethanola-mine using a stirred cell reactor. Int J Greenhouse Gas Control 37:7684

18. Mamun S, Dindore VY, Svendsen HF (2007) Kinetics of the reaction of carbon dioxide with aqueous solutions of 2-((2-aminoethyl) amino) ethanol. Ind Eng Chem Res 46(2):385394

19. Hilliard MD (2008) A predictive thermodynamic model for an aqueous blend of potassium carbonate, piperazine, and monoethanolamine for carbon dioxide capture from ue gas

20. Davis JD (2009) Thermal degradation of aqueous amines used for carbon dioxide capture

21. Huang Q, Bhatnagar S, Remias JE, Selegue JP, Liu K (2013) Thermal degradation of amino acid salts in CO2 capture. Int J Greenhouse Gas Control 19:243250

22. Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA, Cheeseman JR, Scalmani G, Barone V, Mennucci B, Petersson GA et al (2009) Gaussian09 RA.1. Gaussian Inc., Wallingford

23. Dennington R, Keith T, Millam J (2009) GaussView, version 5. Semichem Inc, Shawnee Mission

24. Perdew JP, Wang Y (1992) High-precision sampling for brillouin-zone integration in metals. Phys Rev B. 45(23):13

25. Halgren TA, Lipscomb WN (1977) The synchronous-transit method for determining reaction pathways and locating molecular transition states. Chem Phys Lett 49(2):225232

26. Lee VS, Kodchakorn K, Jitonnom J, Nimmanpipug P, Kongtawelert P, Premanode B (2010) Inuence of metal cofactors and water on the catalytic mechanism of creatininase-creatinine in aqueous solution from molecular dynamics simulation and quantum study. J Comput Aided Mol Des 24(10):879886

27. Lawal O, Bello A, Idem R (2005) The role of methyl diethanolamine (MDEA) in preventing the oxidative degradation of CO2 loaded and concentrated aqueous monoethanolamine (MEA)-MDEA blends during

CO2 absorption from ue gases. Ind Eng Chem Res 44(6):1874189628. Freeman SA, Rochelle GT (2012) Thermal degradation of aqueous piperazine for CO2 capture: 2. Product types and generation rates. Ind Eng

Chem Res 51(22):7726773529. Lepaumier H (2008) Etude des mcanismes de dgradation des amines utilises pour le captage du CO2 dans les fumes

30. Lepaumier H, Picq D, Carrette P-L (2009) New amines for CO2 capture. I. Mechanisms of amine degradation in the presence of CO2. Ind Eng Chem

Res 48(20):9061906731. Willson CG, Lawler DF Oxidation and thermal degradation of methyldiethanolamine/piperazine in CO2 capture

32. Kennard ML, Meisen A (1985) Mechanisms and kinetics of diethanola-mine degradation. Ind Eng Chem Fundam 24(2):129140