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

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

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

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

Molecular structures and type of carbon nuclei in DETA species

Peak assignment of species at low loading

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

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, 249-254)

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

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

T1 Calculation for p-carbamate peak (bC5) at high field region Based on Peak Intensities Based on Area of Peak = 1.002950e+004 = 1.364412e+001

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 s Quantitative NMR measurement Inversion Gated Decoupling Suppress NOE Effect Intensity of Carbon signal is only build up from carbon nuclei

Quantitative Measurement of species with NMR

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

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

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: 

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

Overall reaction rate of CO2 with DETA

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:

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

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

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:

Kinetics rate constant: Zwitterion Mechanism Termolecular Mechanism

Calculation steps of Kinetics rate constant: Termolecular Mechanism Zwitterion Mechanism

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:

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

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

Kinetic rate constants

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

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 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

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

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