1
Kinetics Study of Reactions of CO2 in aqueous solution of Diethylenetriamine (DETA)
January 10-11, 2008 UT Meeting, Texas, USA
Ardi Hartono and Hallvard F. SvendsenNorwegian University of Science and Technology
(NTNU)Trondheim, NORWAY
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
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Molecular Structure :
One Secondary Amine Group (-NH)
Consist of : Two Primary Amine Groups (-NH2)
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
Diethylenetriamine
bis(2-aminoethyl)amine
DETA is known as :
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
H2N
HN
NH2 H2N
HN
NH3+
+H3N
HN
NH3+ +H3N
H2+
NNH3
+
H2N
HN
NH
+H3N
HN
NH
H2NN
NH2 H2NN
NH3+
+H3NN
NH3+ N
H
HN
NH
NH
H2+
NNH
H2NN
NH
+H3NN
NH
NH
NNH
DETA DETAH+(p)
DETAH2+2
(pp) DETAH3+3
DETACO2- (p) DETAH(p)CO2(p)
DETAH(p)CO2(s)DETACO2- (s)
DETAH2(pp)CO2(s)+ DETA(CO2)2-2 (pp) DETAH(s)(CO2)2
- (pp)
DETA(CO2)2-2 (ps) DETAH(p)(CO2)2
- (ps) DETA(CO2)3-3
CO2-
CO2- CO2
-
CO2- CO2
- CO2-
CO2--O2C
CO2- CO2
-
CO2- -O2C
CO2- CO2
-
CO2-
H2N
H2+
NNH3
+
DETAH2+2
(ps)
H2N
H2+
NNH
DETAH(s)CO2(p)
CO2-
+H3N
H2+
NNH
DETAH2(ps)CO2+
(p)
CO2-
-O2C
H2N
H2+
NNH2
DETAH+(s)
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NH2
H2C
CH2
HN
CH2
H2C
NH2
A. Group I :DETA, DETAH+(p), DETAH+
(s)
DETAH22+
(pp),DETAH22+
(ps), DETAH33+
H++H
H+
C. Group III: DETACO2- (s), DETAH(p)CO2(s),
DETAH2(pp)CO2+
(s)
NH2
H2C
CH2
HN
CH2
H2C
NH
+H
H+
D. Group IV: DETA(CO2)22-
(pp), DETAH(s)(CO2)2-(pp)
NH2
H2C
CH2
NCH2
H2C
NH2
H++HNH
H2C
CH2
HN
CH2
H2C
NHH+
NH2
H2C
CH2
NCH2
H2C
NH
+HNH
H2C
CH2
NCH2
H2C
NH
aC1
aC2 aC3
aC4 bC1
bC2 bC3
bC4 bC5
cC1
cC2 cC3
cC4
cC7 dC1
dC2 dC3
dC4
eC1
eC2 eC3
eC4 fC1
fC2 fC3
fC4
dC5dC6
eC5
fC7
fC5fC6
eC7
B. Group II: DETACO2-
(p), DETAH(p)CO2 (p), DETAH(s)CO2 (p), DETAH2(ps)CO2
+(p)
E. Group V: DETA(CO2)22-
(ps), DETAH(p)(CO2)2-(ps) F. Group V: DETA(CO2)3
3-
CO2-
CO2-
CO2--O2C
CO2-
CO2-
CO2--O2C
CO2-
Molecular structures and type of carbon nuclei in DETA species
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Peak assignment of species at low loading
2.402.502.602.702.802.903.003.10
2.30
2.40
2.50
2.60
2.70
2.80
2.90
3.00
3.10
Loading 0.22
2.402.502.602.702.802.903.003.10
40.0
45.0
50.0
Loading 0.22
48.049.050.051.0
aC2, aC3
bC3bC2
38.039.040.041.0
aC1, aC4
bC1bC4
161.0162.0163.0164.0
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Peak assignment of species at loading 1.38
164.5 164.0 163.5 163.0 162.5 162.0 161.5 161.0
bC5
dC5, dC6
cC7
eC7
eC5HCO3
-/CO3-2
48 47 46 45 44 43 42 41 40 39 38
bC3
dC2, dC3
eC7 bC2
cC2, cC3
bC4 bC1
eC1
aC2, aC3 aC1, aC4dC1, dC4
cC1, cC4
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Loading Groups
0 I
0.22 I, II
0.43 I, II, III, IV
0.66 I, II, III, IV, V
0.80 I, II, III, IV, V
1.00 I, II, III, IV, V
1.38 I, II, III, IV, V, HCO3-/CO3
2-
1.69 I, II, III, IV, V, HCO3-/CO3
2-
Qualitative NMR Work ( 1D & 2D NMR Techniques)
Results suggest that carbamate, dicarbamate, and HCO3-/CO3
2- 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, 249-254)
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13C T1 measurement at loading 1.38
Quantitative NMR Measurement
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161.00161.50162.00162.50163.00163.50164.00
0
1 ms
10 ms
1 s
5 s
10 s
15 s
25 s
40 s
60 s
80 s
13C T1 measurement at loading 1.38 (Higher field region)
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T1 Calculation for p-carbamate peak (bC5) at high field region
0I = 6.805660e+002
1T = 1.361797e+001
Based on Peak Intensities Based on Area of Peak
0A = 1.002950e+004
1T = 1.364412e+001
0.00 16.00 32.00 48.00 64.00 80.00
750.00
600.00
450.00
300.00
150.00
0.00
-150.00
-300.00
-450.00
-600.00
-750.000.00 16.00 32.00 48.00 64.00 80.00
xE3 11.00
8.80
6.60
4.40
2.20
0.00
-2.20
-4.40
-6.60
-8.80
-11.00
1/0 (1 2 )T
tM M e 1/0 (1 2 )T
tM M e
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Summarized result of 13C T1 measurement
T1 for carbon nuclie in DETA < 1 s
T1 for carbamate nuclei 12.9-14.3 s
T1 for nuclei 26.2 s23 2/HCO CO- -
1 15D T»
Quantitative NMR measurement
Inversion Gated Decoupling
Suppress NOE Effect
Intensity of Carbon signal is only build up from carbon nuclei
90Correct pulse
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Quantitative Measurement of species with NMR
0
0,005
0,01
0,015
0,02
0,025
0,03
0 0,2 0,4 0,6 0,8 1 1,2 1,4
Loading, mol CO2/mol DETA
Sp
ecie
s, M
ol
frac
tio
nDETA free + protonatedp-carbamate free + protonateds-carbamate free + protonatedpp-dicarbamates free + protonatedps-dicarbamates free + protonatedHCO3-/CO3=CO2* total
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Physicochemical properties of Aqueous solution of DETA(Dashed line = Redlich-Kister Model)
2
21
121
i iE i i
iim i
x MV x
M=
=
r= -
r
åå
( )12 1 2 1 20
niE
ii
V x x A x x=
= -å0
ni
i ii
A aT=
=å2
121
ln lnm i ii
x=
dm = m - må
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Solubility of N2O in Aqueous solution of DETA(Dashed line = Redlich-Kister Model)
2 2
2
, ,1
ln lnN O i i N O ii
H x H=
 = - å0
ni
i ii
A aT=
=å( )1 2 1 20
ni
ii
x x A x x=
 = -å
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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:
Kinetics reaction of CO2 with DETA
1 +2 2
1CO +AmH AmH
k
kCO-
-¾¾®¬¾¾¾
+2 2AmH
kb
k bCO B AmHCO BH- - +
-¾¾¾®+ +¬¾¾¾
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Applying the steady state principle to the intermediate Zwitterion, the rate of CO2 in aqueous solution can be expressed as:
[ ][ ][ ]
[ ]
1 2 1 2
CO 321
AmH CO AmH
r = ,1
b
b
b
k BHk k CO
k B kmolk m sk B
+--
-
-
é ùê úë ûé ù- ê úë û
+
åå
å
+2 2AmH kbCO B AmHCO BH- - ++ ¾¾® + [ ][ ]
[ ]
1 2CO 32
1
AmH COr = ,
1b
k kmolk m sk B-+
å
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
The rate of reaction of CO2 (Zwitterion)
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Overall reaction rate of CO2 with DETA
2 3CO +OH HCO- -«
2 2 3 3+2H ( )CO O HCO H O negligible- +« + Þ <<
2 2 2 3+H pDETA CO O DETACO H O- ++ « +
[ ][ ][ ]
[ ]
1 22 32,
1
DETA CO,
1CO overall OH
b
k kmolr k OH CO
k m sk B
--
-
é ù= +ê úë û+
å
[ ] [ ][ ][ ]
[ ]
1 22 2 32,
1
DETA CO,
1CO obsoverall OH
b
k kmolr k CO k OH CO
k m sk B
--
-
é ù= = +ê úë û+
å[ ]
[ ]
1
1
DETA
1app obs OH
b
kk k k OH
k
k B
--
-
é ù= = - ê úë û+
å
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Termolecular MechanismOriginally 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
2 2CO AmH B AmCO BH- +¾¾®+ ××× ××׬¾¾
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:
[ ]
[ ] [ ]{ }[ ]
CO 2 32
22
r = ,obs
obs AmH H O OH
kmolk CO
m s
k k AmH k H O k OH AmH--
é ù= + + ê úë û
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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 blowerK-type thermocouples
Liquid tank
Liquid flowFlow meter
Liquid tank
P-5
T
I-3
Venturi meter
T
CO2 analyser
T
CO2
N2
T
Heated cabin
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Parameters
Physicochemical properties:
2( , ) ( , )
( , ) ( , )
DETA N O DETA
DETA DETA
f C T H f C T
f C T pKa f C T
2
2 2 2
0.8
H OCO DETA CO H O
DETA
D D
Modified Stokes-Einstein
2 2CO H OD Versteeg, et.al., 1988
this work
1.0 0.54
17.92Lk
D D
The liquid-side mass transfer coefficient
The gas-side mass transfer coefficient
0.79 0.440.12ReSh Sc
Vishwas, 2004; Hartono, et.al., 2006
Ma’mun, et.al., 2007
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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:
( )*,
A
1=
1E
-+
A A bA
L g
N C CRT
k Hk
, 0»A bCAt 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:
2= 1+AE Haobs A
l
k DHa
k= 2 AHa E ¥< <<
2=CO
ASD
rN
A
in outCO CO2 2
CO2CO2
Q -Qr = ,
u
kmol
s
Out in 2CO N2 2
2
Q Q1
=- -
outCO
outsolutionCO
y
py
P
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Kinetics rate constant:
[ ] [ ]{ }[ ]22obs DETA H O OHk k DETA k H O k OH DETA-
-é ù= + + ê úë û
[ ]Tobs 2
1k =k ,DETA
s
Zwitterion Mechanism
[ ]
[ ] [ ]{ }app
1 22
DETA 1k = ,
1 1
k Z Z ZDETA H O OH
s
k DETA k H O k OH --
+é ù+ + ê úë û
[ ]Zapp 2
1k =k ,DETA
s
Termolecular Mechanism
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Calculation steps of Kinetics rate constant:
Termolecular Mechanism
[ ] [ ]{ }[ ]22obs DETA H O OHk k DETA k H O k OH DETA-
-é ù= + + ê úë û
[ ]
[ ][ ] [ ]{ }22
obs OHDETA H O
k k OH DETAk DETA k H O
DETA
--
ì üé ùï ï-ï ïê úë ûï ï = +í ýï ïï ïï ïî þ
[ ]22Straight line with slope and interceptDETA H Ok k H O
Zwitterion Mechanism
[ ]
[ ] [ ]{ }app
1 22
DETA 1k = ,
1 1
k Z Z ZDETA H O OH
s
k DETA k H O k OH --
+é ù+ + ê úë û
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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
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
Kinetics rate constant
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Relationship between ln k and 1/T ( Termolecular mechanism)
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Kinetic rate constantsTermolecular 9 3952.6
8.4142 10 expTDETAk x
T
2
7 3302.11.4951 10 expT
H Ok xT
Zwitterion 131
5386.23.4870 10 expk x
T
9 3736.45.0338 10 expZ
DETAk xT
2
7 3423.21.5311 10 expT
H Ok xT
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Comparison of measured and predicted kobs obtained by the zwitterions model and the termolecular
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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
(m6 kmol-2 s-1)C
(kmol m-3)Reference
DETA 14.57 231 1.00-2.90 This work
AEEA 2.35 161 1.19-3.46 Ma’mun, et.al., 2007
PG 2.09 118 0.10-4.00 Kumar, et.al, 2003
MEA 1.71 73.7 3.00-9.00 Aboudheir, et.al., 2003
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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.
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
Both of the Termolecular and the Zwitterion mechanism give very good fitting to the kinetics data.
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.
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Thank you for your attention
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