1. By Marcus Hilliard Gary T. Rochelle The University of Texas at Austin
A Predictive Thermodynamic Model for an Aqueous Blend of Potassium Carbonate, Piperazine, and Monoethanolamine for Carbon Dioxide Capture from Flue Gas By
Marcus Hilliard
Gary T. Rochelle
The University of Texas at Austin

2. This research addresses the use of carbon capture from coal fired power plants to reduce factors contributing to global warming
Our aim is to understand the fundamental thermodynamic behavior associated with the post-combustion chemical absorption process
Chemical Solvents
Monoethanolamine (MEA)
Increase in capacity, faster rates, robustness
MEA/Piperazine (PZ)
K2CO3/PZ
background – carbon capture technologies

3. process - aqueous absorption
Cooler
2-4 mol H2O/mol CO2
Clean Gas
1% CO2
process - aqueous absorption
Absorber
40–60oC
1 atm
Stripper
100–120oC
1-2 atm
Rich Solvent
Lean Solvent
Flue Gas
10% CO2
Reboiler

4. needs for thermodynamics
Mass Transfer
Driving force
Capacity
Speciation [amine]  kinetics
Calorimetry Cp
DHabs
Volatility
Amine P*
…with solvent characterization through rigorous modeling

5. research objective
Development of a rigorous thermodynamic model for the H2O-K2CO3-MEA-PZ-CO2 sub-component base systems
Cullinane (2005)
Tosh et al. (1959)
Numerous Authors
UNIFAC
Bishnoi (2000)
Perez-Salado Kamps et al. (2003)
Derks et al. (2005)
Jou et al. (1995)
Dang (2001) and Okoye (2005)

6. aqueous chemistry Complex Mass Transfer with Chemical Reactions
CO2 Solubility
Liquid Phase
Vapor Phase
Amine Volatility
aqueous chemistry
NMR Speciation
Specific Heat

7. aspen plus 2006.5 framework Enthalpy Phase Equilibrium
─ Aqueous Chemistry

8. elecNRTL model Activity coefficient model in Aspen Plus 2006.5
Rigorously represents liquid and vapor phases
Reference state convention:
Inf. Dil. Aqu. phase for molecular solutes (i.e. CO2) and ions
Pure liquid for molecular solvents (i.e. H2O and MEA)
By adjusting binary interaction parameters
Through sequential non-linear regressions with multiple, independent data sets

9. international collaboration
Apparatus at NTNU
High P CO2 Solubility (100 – 120 oC)
Calorimeter  (40 – 120 oC)
Measured by Inna Kim (NTNU)
Apparatus at UT
ATM P Reactor (30 – 70 oC)
(multi-component vapor phase analysis reactor)
Differential Scanning Calorimeter:
Specific Heat Capacity & PZ Solubility
NMR Speciation (Chem dept.)
Measured by Steve Sorey and Jim Wallin
X-ray Diffraction (Chem dept.)
Crystallization Identification
Measured by Vince Lynch

10. experimental design - overall
52 Systems
9,757 data points

11. sequential regression

12. CO2 Solubility in 7m MEA at 40 oC
Austgen (1989)
Freguia (2002)
Jou et al. (1995)
This work
Lee et al. (1976) - corrected

13. CO2 Solubility in 2 and 5 m PZ at 40 - 60 oC
Solid Pt & Curves : 2 m PZ
Open Pt & Curves : 5 m PZ

14. CO2 Solubility in 5 m K+/2.5 m PZ60
40 oC
80 oC 60 40

15. MEA Volatility in 7 m MEA at 40oC
64 ppmv
Austgen (1989)
This work

16. MEA Volatility at 40oC ~15 % 5 m K+ + 7 m MEA ~50 ppmv
7 m MEA + 2 m PZ
7 m MEA
5 m K+ + 7 m MEA + 2 m PZ

17. PZ Volatility in 2 m PZ at 40oC
Hilliard (2005)
25 ppmv
This work

18. PZ Volatility at 40oC ~30 % 2 m PZ ~20 ppmv 5 m K+ + 2 m PZ
7 m MEA + 2 m PZ
5 m K+ + 7 m MEA + 2 m PZ

19. CO2 Solubility in 7m MEA at 60oC Differential Capacity
Austgen (1989)
Freguia (2002)
Jou et al. (1995)
Differential Capacity
This work
Lee et al. (1976) - corrected

20. Differential Capacity wrt PCO2 (0.01 – 1.0 kPa) at 60oC
H2O-MEA-CO2
H2O-MEA-PZ-CO2
H2O-K2CO3-MEA-PZ-CO2
H2O-K2CO3-PZ-CO2
H2O-K2CO3-MEA-CO2
H2O-PZ-CO2

21. C13 NMR Speciation for 7 m MEA at 40oC
MEA + MEAH+
MEACOO-1
MEA
HCO3-1 + CO3-2
Solid Pt: Poplsteinovo (2004)
Open Pt: This work
Solid Curves: This work

22. H1 NMR Speciation for 1.5 m PZ at 40oC
PZ + PZH+1
H+1PZCOO-1 + PZCOO-1 PZ
PZ(COO-1)2
Points: Ermatchkov et al. (2003)
Curves: This work

23. Enthalpy of CO2 Absorption in 7 m MEA at 40 and 120oC
Kim and Svendsen (2007)
40oC
This Work

24. Enthalpy of CO2 Absorption in 2.4 m PZ at 40 and 120oC
Kim (2007)
40oC
This Work

25. Enthalpy of CO2 Absorption Predictions at 40 and 120oC
7 m MEA
2.4 m PZ
6 m K m PZ
5 m K m PZ

26. Specific Heat Capacity Results for loaded 7 m MEA
H2O
a = 0.0
a = 0.139
a = 0.358
a = 0.541
MEA

27. Specific Heat Capacity Refinement for loaded 7 m MEA

28. Specific Heat Capacity Refinement for loaded 2 m PZ

29. SLE Results for Mixtures of H2O-PZ using DSC
Liquid Solution
Bishnoi (2002)
10 m PZ
PZ (s)
25 m PZ
This work
20 m PZ
PZ∙6H2O (s)

30. unit cell of K2PZ(COO)2 COO- complex SEM image PZ
Crystal Size: 0.43 x 0.33 x 0.08 mm K

31. SLE Results for K+ + PZ Solutions
KHCO3 (s)
K2PZ(COO)2 (s)
5 m K m PZ
5 m K m PZ
6 m K m PZ

32. Systems Exhibiting SLE Behavior for K+ + PZ Solutions
6 m K m PZ
5 m K m PZ
5 m K m PZ

33. In this work:
Developed a new VLE apparatus = PCO2, PAmine, PH2O
At typical lean absorber conditions:
PMEA = 64 ppmv PPZ = 25 ppmv
Amine blends illustrate an enhanced capacity over MEA
Enthalpy of CO2 absorption increased in temperature
Successfully measured Cp in loaded solutions between 40 and 120oC  Cp of CO2 may be negligible in loaded MEA and PZ
Inferred a possible operating region for CO2 capture utilizing aqueous PZ. Identified and determine the solubility of K2PZ(COO)2 present in K+/PZ solutions
Created a consistent rigorous thermodynamic model that adequately predicts solubility, volatility, speciation, and calorimetry in the base sub-component H2O-K2CO3-MEA-PZ-CO2 systems within Aspen Plus®
summary

34. This concludes my presentation…
Thank you for your attention.