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

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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 :

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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

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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:

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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