1. January 10-11, 2008 UT Meeting, Texas, USA
Kinetics Study of Reactions of CO2 in aqueous solution of Diethylenetriamine (DETA)
Ardi Hartono and Hallvard F. Svendsen
Norwegian University of Science and Technology (NTNU)
Trondheim, NORWAY
January 10-11, 2008 UT Meeting, Texas, USA

2. Outline
Review on DETA
13C NMR Work on speciation in the diethylenetriamine/CO2 system
Chemical System of DETA-CO2-H2O
Qualitative NMR Work ( 1D & 2D NMR Techniques)
Quantitative NMR work
T1 measurement using Inversion Recovery method
The Inversion gated decoupling experiment
Physicochemical properties of Aqueous solution of DETA
Density & Viscosity
Solubility
Kinetics Study of Reactions of CO2
Conclusion

3. DETA is known as :
Molecular Structure :
Diethylenetriamine
bis(2-aminoethyl)amine
Consist of :
Two Primary Amine Groups (-NH2)
One Secondary Amine Group (-NH)
As Polyamine:
The number of nitrogen atoms per each DETA molecule is equal to 3
Can be expected having higher Loading Capacity and higher absorption rate
Very Promising as a new Solvent for CO2 Capture

4. Chemical system Very large system
The species are known to be present: H2O, H3O+, OH-, CO2, HCO3- and CO32-
In total 24 potential species

5. Molecular structures and type of carbon nuclei in DETA species

6. Peak assignment of species at low loading

7. Peak assignment of species at loading 1.38
bC5
dC5, dC6
cC7
eC7
eC5
HCO3-/CO3-2
bC3
dC2, dC3
eC7
bC2
cC2, cC3
bC4
bC1
eC1
aC2, aC3
aC1, aC4
dC1, dC4
cC1, cC4

8. Qualitative NMR Work ( 1D & 2D NMR Techniques)
Loading
Groups I
0.22
I, II
0.43
I, II, III, IV
0.66
I, II, III, IV, V
0.80
1.00
1.38
I, II, III, IV, V, HCO3-/CO32-
1.69
Results suggest that carbamate, dicarbamate, and HCO3-/CO32- species are the main species formed in the system. No clear indication was found of a tricarbamate species or of free CO2.
(Hartono, et. al., 2007, Ind. Eng. Chem. Res., 46, )

9. 13C T1 measurement at loading 1.38
Quantitative NMR Measurement
13C T1 measurement at loading 1.38

10. 13C T1 measurement at loading 1.38 (Higher field region)
1 ms
10 ms
1 s
5 s
10 s
15 s
25 s
40 s
60 s
80 s

11. T1 Calculation for p-carbamate peak (bC5) at high field region
Based on Peak Intensities
Based on Area of Peak
= e+004
= e+001

12. Summarized result of 13C T1 measurement
T1 for carbon nuclie in DETA < 1 s
T1 for carbamate nuclei s
T1 for nuclei 26.2 s
Quantitative NMR measurement
Inversion Gated Decoupling
Suppress NOE Effect
Intensity of Carbon signal is only build up from carbon nuclei

13. Quantitative Measurement of species with NMR

14. Physicochemical properties of Aqueous solution of DETA
(Dashed line = Redlich-Kister Model)

15. Solubility of N2O in Aqueous solution of DETA
(Dashed line = Redlich-Kister Model)

16. Kinetics reaction of CO2 with DETA
Zwitterion Mechanism:
Originally proposed by Caplow (1968) and reintroduced by Danckwert (1979), suggest that the reaction between CO2 and the alkanolamines proceeds through the formation of a zwitterion as a intermediate:
This Zwitterion undergoes deprotonation by a base (or bases), thereby resulting in carbamate formation: 

17. The rate of reaction of CO2 (Zwitterion)
Applying the steady state principle to the intermediate Zwitterion,
the rate of CO2 in aqueous solution can be expressed as:
This equation can be simplified if the experiments are performed at loading close to zero so the reverse reaction can be disregards:
a fractional order between one and two with respect to amine concentration

18. Overall reaction rate of CO2 with DETA

19. Termolecular Mechanism
Originally proposed by Crooks and Donnelan (1989) and revisited by da Silva and Svendsen (2004), assumes that an alkanolamines react simultaneously with one molecule CO2 and one molecule of a base, the reaction proceeds in a single step via a loosely-bound encounter complex as the intermediate
This complex breaks up to form reactant molecules (CO2 and amine), while its small fraction react with a second molecule of the amine or a water to give ionic product.
The forward reaction rate can be written as:

20. Kinetics reaction of CO2 with DETA
Experiment & Procedures
Fisher-Rosemount BINOS 100 NDIR CO2 analyzer (2 channels: 2000 ppm and 1vol % CO2),
a Bronkhorst Hi-Tec mass flow controller,
a peristaltic liquid pump (EH Promass 83),
a gas blower
K-type thermocouples

21. Parameters Physicochemical properties:
this work
Modified Stokes-Einstein
Versteeg, et.al., 1988
The liquid-side mass transfer coefficient
Vishwas, 2004; Hartono, et.al., 2006
The gas-side mass transfer coefficient
Ma’mun, et.al., 2007

22. Determination of kinetics of CO2 with DETA using the SDC
In the case of chemical absorption, the absorption flux is enhanced due to chemical reaction and the average absorption flux is given by:
At very low CO2 loading
In the case of a pseudo-first order reaction regime and based on the penetration theory, the enhancement factor due to the chemical reaction is calculated by:

23. Kinetics rate constant:
Zwitterion Mechanism
Termolecular Mechanism

24. Calculation steps of Kinetics rate constant:
Termolecular Mechanism
Zwitterion Mechanism

25. Results
Effect of liquid flow rate on the average absorption flux of CO2 in aqueous solutions of DETA.
Effect of DETA concentration on the average absorption flux for the range temperatures:

26. Kinetics rate constant
Effects of DETA concentration on kobs over the range of temperatures
Variation of {kobs – kOH [OH-][DETA]}/[DETA] with [DETA] over the range of temperatures

27. Relationship between ln k and 1/T ( Termolecular mechanism)

28. Kinetic rate constants

29. Comparison of measured and predicted kobs obtained by the zwitterions model and the termolecular

30. Reaction Rate Constant of DETA and That of Water in comparison with literatures at 25oC
absorbent
k x10-3
(m6 kmol-2 s-1)
kH2O C
(kmol m-3)
Reference
DETA
14.57
231
This work
AEEA
2.35
161
Ma’mun, et.al., 2007 PG
2.09
118
Kumar, et.al, 2003
MEA
1.71
73.7
Aboudheir, et.al., 2003

31. Conclusions
The kinetics reaction between CO2 and the aqueous solutions of DETA were measured over a range of temperatures from 24.9 to 59.2°C with the concentrations of DETA ranging between 1.00 and 2.90 kmol m-3 using the string of discs contactor.
The density and viscosity were measured with Anton Paar SVM 300 Viscometer and the Redlich–Kister Excess Molar Volume and Viscosity Deviation fitted very well with the data
The solubility were measured with the solubility apparatus and the N2O analogy was applied to estimate the solubility of CO2 in DETA system. The Redlich-Kister Excess Henry constant fitted very well with the data.
Both of the Termolecular and the Zwitterion mechanism give very good fitting to the kinetics data.
Kinetics rate constant based on the Zwitterion mechanism have the same expression as the kinetics rate constant of the Termolecular mechanism due to the very large k1 value, thus the 1/k1 close to zero
In comparison to literature (AEEA, MEA, PG), DETA has a higher reaction rate at the same conditions

32. Thank you for your attention