Inna Kim and Hallvard F. Svendsen Norwegian University of Science and Technology (NTNU)

1. Thermal measurements:Heat of absorption of CO2 and Vapour-Liquid Equilibria in alkanolamine-water solutions Inna Kim and Hallvard F. Svendsen Norwegian University of Science and Technology (NTNU) Trondheim, NORWAY

2. Outline • Heat of absorption • Background • Experimental set-up • Results • Vapour-Liquid Equilibria • Experimental set-up • Results • Summary • Further work

3. Heat of absorption,∆Habs

4. Background • Assumption: • Disadvantage: differentiation Integral vs differential ∆Habs • Calculated using Gibbs-Helmholz equation: fCO2 – fugacity of CO2 xCO2 – mole fraction of CO2 • Integrated over some loading interval (direct measurement) Isothermal flow calorimeter [www.ltp-oldenburg.de]

5. Background a b Differential ∆Habs data from solubility measurements1 • VLE data: ln(pCO2) vs 1/T: • Fitted with a line, • Fitted with a 2nd order polynomial 1 [Hoff K.A., Mejdell T., Svendsen H.., 2005]

6. Background Impact of temperature and loading on ∆Habs2 “The increase in heat of absorption of up to 20% from the absorber to the stripper temperature may cause a deficient duty calculation with the reboiler if a constant heat of absorption at the lower value is used”2 Temperature profile for the Dome 5 North Caroline plant 2 2 [Jerry A. Bullin et al., Bryan Research & Engineering Inc. Bryan, TX, GPA 2007]

7. Experimental set-up CPA122 (ChemiSens AB, Sweden) 1 - Calorimeter 2a,2b - CO2 storage cylinders 3 - Vacuum pump 4 - Feed bottle

8. Semi-differential ∆Habs(an example of on-line data)

9. Results 30 wt% Monoethanolamine (MEA)

10. Results 30 wt% N-methyldiethanolamine (MDEA)

11. Results 40 and 50 wt% MDEA

12. Results 3M Diethylenetriamine (DETA)

13. Results 3M DETA + 1.5M H2SO4

14. Results ∆Habs with different amines at 40oC

15. Results ∆Habs with different amines at 120oC

16. VLE measurements

17. Experimental set-up • Ebulliometer • Pressure controller • Thermocouples • Cold trap • Buffer vessel • Vacuum pump

18. Validation of the experiments: vapour pressure of pure water

19. Results MEA (1) - H2O (2)

20. Results P-xy diagram: MEA(1)-H2O(2) ○ this work (40, 60,80,100oC) * Nath et al., 1983 (60, 78, 92oC) — Wilson equation

21. Results Activity coefficients: MEA(1)-H2O(2) ○ this work (40, 60,80,100oC) * Nath et al., 1983 (60, 78, 92oC) — Wilson equation

22. Results MDEA (1) - H2O (2)

23. Results P-xy diagram: MDEA(1)-H2O(2) ○ this work (40, 60, 80, 100oC) — Wilson equation

24. Results Activity coefficients: MDEA(1)-H2O(2) ○ this work (40, 60, 80, 100oC) — Wilson equation

25. Results Ternary mixture:MEA(1)-MDEA(2)-H2O(3)

26. Results Activity coefficients:MEA(1)-MDEA(2)-H2O(3)

27. Results Thermodynamic consistency test • Point to point test3 • Area test3 3[Van Ness H.C. et al, Am.Inst.Chem. Eng.J.19 (1973) 238-244] 4 [Van Ness H.C., Pure & Appl. Chem., Vol. 67, No.6, pp. 859-872, 1995]

28. Summary • A method proposed for measuring the enthalpy of absorption differential in temperature and semi-differential in loading • Amine concentration and experimental pressure found to have less effect on the heat of absorption data (within the experimental range of this work) than temperature and loading • The ebulliometer enables very accurate determination of the vapour-liquid equilibrium of pure components and mixtures • Experimental activity coefficients of amines and water can be calculated • The accuracy of the results obtained is limited only by the purity of the substances used and by the precision of the analytical methods used for the sample

29. Further work • Fitting the heat of absorption data using K-values and temperature dependent activity coefficients • Fitting VLE data with UNIFAC equation of state • Improvement of the thermodynamic models of the acid gas-alkanolamine-water systems using the data measured in this work, along with the other experimental data taken from the literature

30. THANK YOUfor your attention!