Faculty of Technology, Telemark University College, Kjølnes Ring 56, 3918 Porsgrunn, Norway. 2. Tel-Tek, Kjølnes Ring 30, 3918 Porsgrunn, Norway.

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1 Attempts to Predict Absorption Equilibria Klaus J. Jens 1,2, Dag A. Eimer 1,2, Bjørnar Arstad 3, Zulkifli Idris 1, Cristina Perinu 1, Gamunu Samarakoon 1 and John Arild Svendsen 1 1 Faculty of Technology, Telemark University College, Kjølnes Ring 56, 3918 Porsgrunn, Norway. 2 Tel-Tek, Kjølnes Ring 30, 3918 Porsgrunn, Norway. 3 SINTEF, Materials and Chemistry, Forskningsveien 1, 0314 Oslo, Norway.

2 How do we predict absorption equilibria?

5 M MDEA solution has a net CO 2 pickup of 30 vol/vol (0.297 mole/mole). ii. At 60 o C, 4.

3 Capture capacity for amine-co 2 system The net capacity is defined as the difference between equilibrium concentrations at the absorption and stripping partial pressures. With CO 2 partial pressure change of 5 bar to 1 bar: i. At 70 o C, 4.5 M MDEA solution has a net CO 2 pickup of 30 vol/vol (0.297 mole/mole). ii. At 60 o C, 4.1 M MEA solution has a net CO 2 pickup of 5 vol/vol. In a chemical reaction, A + B C + D the thermodynamic equilibrium constant is defined as: Kohl, A.; Nielsen, R., Gas Purification 1997, 5 th Ed, p55.

4 How do we predict absorption equilibria? Amine-CO 2 VLE experiments Liquid speciation method NMR spectroscopy Molecular structure relationship

5 1. Amine-CO 2 VLE solubility experiments Information on the solubility of CO 2 in a amine solution is required for solvent evaluation. Normally this will involve measuring partial pressures of CO 2 during equilibrium at different CO 2 -amine concentrations. 100 CO 2 partial pressu ure (kpa) This work 2012 Jayarathna 2011 Svendsen MEA 30 % wt, 40 o C Loading (moles of CO 2 /moles of MEA) Idris, Z.; Peresunko, N.; Jens, K. J.; Eimer, D. A., Fluid Phase Equilibr. 2015, 387,

6 Among other amine-co 2 systems investigated are: i. 3-amino-1-propanol (3A1P) ii. 4-amino-1-butanol (4A1P) iii. 5-amino-1-pentanol (5A1P) Concentration related equilibrium model was used to represent the experimental data. Svendsen, J. A. et al, unpublished results. Li, Y. G.; Mather, A. E., Ind. Eng. Chem. Res. 1994, 33,

7 2. Determination of K app using wet chemical method (WCM) A method to determine species present during CO 2 -amine-water reactions is developed. [HCO ], [CO 3 ], [RNHCOO ], [RNH ], [RNH 2 ], [OH ], [H ] Reaction with BaCl 2 / NaOH at low temperatures ph measurements NaOH titration HCO OH Ba BaCO 3 + H 2 O CO Ba 2+ BaCO 3 + H 2 O HCO OH CO 3 + H 2 O RNH 3+ + OH - RNH 2 + H 2 O Separation of white precipitate and titration Acquired concentration of HCO 3- + CO 3 2- [HCO 3- ] and [RNH 3+ ] concentrations Acquired [HCO 3- ] and [CO 2-3 ] concentrations [HCO 3- ] + [CO 3 2- ] + [RNHCOO - ] = [HCO 3- ] ini [RNH 2 ] + [RNH 3+ ] + [RNHCOO - ] = [RNH 2 ] ini Samarakoon, G., PhD thesis. Telemark University College, 2015.

8 Table 1. Aqueous species speciation in a HCO 3- -loaded MEA solution at 25 o C. [HCO 3- ] ini /[RNH 2 ] ini WCM NMR WCM NMR WCM NMR [HCO 3- ] ± ± ± [CO 2-3 ] ± ± ± [RNHCOO - ] ± ± ± [RNH 2 ] ± ± ± [RNH 3+ ] ± ± ± K HYDa (mol/l) ± ± ± Ionic strength (mol/l) A study by Chan and Danckwerts found that the K HYDa value of mol/l at an ionic HYDa strength of mol/l. A K HYDa value of mol/l at ionic strength of mol/l was calculated in this method. Chan, H. M.,; Danckwerts, P. V., Chem. Eng. Sci., 1981, 36,

9 3. NMR spectroscopy A non-invasive analytical method that allows direct measurements of the specific nuclei of atoms of compounds Peak areas are directly proportional to the number of nuclei contributing to the signals and, with some care, quantitative analyses of compounds are hence possible (e.g 1 H and 13 C NMR experiments). 2- HCO 3- CO HOCH 2 CH 2 NH 2 HOCH 2 CH 2 NH * HOCH 2 CH 2 NHCOO - 2 # 1 # CH 3 CN Quantitative 13 C NMR spectrum of an amine-co 2 - H 2 O system * 1 # # By means of qualitative 15 N-NMR experiments, the relative electron density on the 15 N nucleus (which is directly involved into the reaction with CO 2) of amines can be measured to investigate factors influencing the carbamate-forming reactions. HOCH 2 CH 2 NH 2 Qualitative 15 N NMR spectrum of MEA Perinu, C., et al. Int. J. Greenhouse Gas Control, 2014, 20,

10 Carbamate formation is a Lewis acid-base and a nucleophilic addition reaction Increased electron density on the Lewis base (nucleophile) raises the energy of the electron pair and makes it more available to react; The reactivity of a Lewis base (nucleophile) depends not only on the chemical-structural properties of the molecules, but also on other factors such as solvation etc. 1) Solvent interactions 2) Hydroxyl group interactions RNH 2 + H 2 O RNH 3+ + OH -

11 Correlation of 15 N NMR chemical shift values (ppm) with reaction equilibrium constants A linear relation for carbamate formation (a) and carbamate hydration/stability (b) vs ppm value Higher ppm value (less relative electron density) )leads to less carbamate formation. At increasing steric hindrance at the α-c to N: less electron density on the N atom Back donation of N-centred electron density to -C bonded CH 3 groups; e.g. NH 2 s-bu, NH 2 -ipr, NH 2 t-bu Chakraborty, A.K. et al., J. Am.Chem.Soc.,1988, 110, Perinu, C., et al. Energy Procedia, 2014, 63,

12 4. Molecular structure-activity relationship + δ The electron density on N atom of the reacted amine influences the reaction with CO 2 and the stability of carbamate. R. W. Taft (1952) introduced an empirical parameter which describes the polar effect (σ*) of substituents. t Polar effect : atoms or groups of atoms attached to the functional group have the ability to withdraw or donate electrons through the bonds. These can distort the electron density distribution of the molecules. Samarakoon, G., PhD thesis. Telemark University College, 2015.

13 Substituent H CH 3 C 2 H 5 n-c 3 H 7 i- C 3 H 7 n- C 4 H 9 i- C 4 H 9 s- C 4 H 9 t- C 4 H 9 σ* A Positive σ* * value is attributed t to electron withdrawing. i A Negative σ* value is attributed to electron donating. These effects are independent of reactions. For a molecule consisting of many substituents, the balancing effects is additive ( σ*) Ethylamine σ* = 0.88 Taft, R., Separation of Polar, Steric, and Resonance Effects in Reactivity. In Steric Effects in Organic Chemistry, 1956.

00 NH 2 sbu NH 2 tbu NH 2 Et NH 2 Pr NH 2 Bu NH 2 ipr NH 2 ibu σ* vs K CBM is a linear relationship Reactivity of

14 K CBM against σ* Log K CBM 7.00 R² = σ* - a measure of the electron NH Me withdrawing or releasing ability of substituents NH 2 sbu NH 2 tbu NH 2 Et NH 2 Pr NH 2 Bu NH 2 ipr NH 2 ibu σ* vs K CBM is a linear relationship Reactivity of aqueous amine with CO 2 can be described by the electronic effect σ* * electron withdrawing increases Samarakoon, G., PhD thesis. Telemark University College, 2015.

15 Conclusions and Outlook Concentration based VLE modelling was successfully demonstrated. Liquid speciation method developed. 15N NMR method development Deeper understanding of equilibrium reactions Correlations between equilibrium constants (K and K ) Correlations between equilibrium constants (K CBM and K HYD ) and Taft polar substituent constants ( σ* ) were established.

199890) SINTEF NMR laboratory in Oslo CO 2

16 Acknowledgements The Research Council of Norway (CLIMIT grant nr ) SINTEF NMR laboratory in Oslo CO 2 laboratory of Telemark University College Thank you for your attention

Available online at ScienceDirect. Energy Procedia 63 (2014 ) GHGT-12

Available online at ScienceDirect. Energy Procedia 63 (2014 ) GHGT-12 Available online at www.sciencedirect.com ScienceDirect Energy Procedia 63 (2014 ) 1144 1150 GHGT-12 Application of 15 N-NMR spectroscopy to analysis of amine based CO 2 capture solvents Cristina Perinu