Oxidative Degradation of Amines in CO 2 Capture Andrew Sexton January 10, 2008

1. Oxidative Degradation of Amines in CO2 Capture Andrew Sexton January 10, 2008 Department of Chemical Engineering The University of Texas at Austin

2. Overview • Introduction • Prior Oxidative Degradation Research • Research Objectives • Experimental Methods • Degradation Apparatus • Analytical Methods • Degradation Products and Rates • Conclusions and Future Work

3. Why are we so interested? • Environmental effects – What do we have to remove, how much of it do we have to remove, and how do we dispose of it? • Process economics • Solvent losses (Operating Cost) – How much amine solvent must be added to the process? • Reclaiming (Operating/Capital) – What processes must be developed to remove the products? • Corrosion (Operating/Capital) – How does the degraded amine affect carbon steel?

4. Where is degradation most likely to occur? Purified Gas 1% CO2 CO2 H2O (O2) Thermal Degradation Cross Exchanger Stripper 120 oC 1 atm Absorber 40 -70 oC 1 atm Oxidative Degradation Reboiler 30% MEA a = 0.4-0.5 1 mM Fe+3 30% MEA a = 0.3-0.4 1 mM Fe+2 Flue Gas 10% CO2 5-10% O2

5. Mechanisms: Free Radical Importance • Electron Abstraction Mechanism • Electron Shuttle: Fe2+ (stripper) Fe3+ (absorber) • Metal catalyst (free radical) removes electron from N of amine • Propagates to form oxygen radicals • Fe+2 + O2 Fe+3 + HOO.

6. Electron Abstraction Pathways H H H H H H . Fe+3 H -H+ H . . . . . N C C OH N C C OH N C C OH H H H H H H H H H MEA Aminium Radical Imine Radical -H. Enamine H H . Imine H . . . N C C OH N C C OH H2O H H H H H H2O H O H O H + 2 N H C H + H C C OH N H H H H H

7. Oxidation of Aldehydes O O Formaldehyde  Formic Acid H C H H C OH H O H O Acetaldehyde  Acetic Acid H C C H OH C C H H H O O O O Glyoxal  Oxalic Acid OH C C OH H C C H O O Hydroxyacetaldehyde  Glycolic Acid OH C C OH OH C C H

8. Oxidation/Corrosion Tradeoff • Ferrous ion increases degradation and corrosion (Girdler Corporation) • Cu: Effective corrosion inhibitor (Dow) • Blachly/Ravner: Cu has higher catalytic activity than Fe • Ferris: Cu+2, V+3 have catalytic properties similar to Fe +2

9. Research Objectives • Determine pathways for amine oxidative degradation via multivalent metal catalysts • Calculate competitive degradation rates for MEA/PZ amine systems • Evaluate the effectiveness of Na2SO3, EDTA, & ‘A’ as degradation inhibitors • Present process conditions that are most cost effective and environmentally safe

10. Prior Work • AMP (2-amino-2-methyl-1-propanol) and MDEA recognized as degradation resistant amines (Girdler) • EDTA is an effective chelating agent for Cu; Bicine effective O2 scavenger for Fe (Blachly/Ravner) • DGATM (50%), DEA (30%), MDEA (30% and 50%), and MEA (20%) all degraded under mass-transfer controlled conditions on the same order of magnitude (Rooney) • Oxidative degradation in the presence of metal catalysts occurs in the mass-transfer controlled region (Goff)

11. Effect of Space Time

12. Effect of Inhibitor A on MEA

13. Effect of Metal Catalysts

14. Stoichiometry

15. Oxygen Stoichiometry MEA + 1.5 O2 2 Formate + Ammonia MEA + 3.5 O2 2 Formate + Nitrate + Water MEA + O2 Glycolate + Ammonia

16. Ionic Degradation Products Acetic Acid Glycolic Acid MEA Formic Acid Oxalic Acid Piperazine Ethylenediamine

17. Ionic Degradation Products O + N - - O O MEA Nitrate N - O O Piperazine Nitrite

18. Amino Acid Degradation Products Diglycine (Iminodiacetic Acid) H H Glycine N O H H C H OH C C H C O N H OH H C H H H H H C O OH C C C C OH OH N H H H H H C H Bicine C O OH

19. HPLC-MS Screening Analysis • Hydroxyethylimidazole (aldehyde, ammonia, amine, substituted glyoxal) • MEA-Formamide • MEA-Oxamic Acid (Partial Amide of Oxalic Acid) H H O H C N C C OH H H H O O H H OH C C N C C OH H H H

20. (Hydroxyethyl)imidazole H H O H O O H + + + N C C OH H C H N H C C H H H H H H Water and CO2 also formed N C C C N

21. Amide Formation O R’ O O R C OH + N R C N R’ + H H H H H

22. Low Gas Flow Apparatus

23. Modified Low Gas Flow Apparatus

24. High Gas Flow Degradation Apparatus Heated line to FT-IR Heat Bath Gas Inlet

25. Ion Chromatography Analysis Methods • Dionex ICS-2500/ICS-3000 System • Anion (ICS-3000): AS15 Ionpac Column & ASRS 4-mm Suppressor • Linear gradient of NaOH eluent • 1.60 mL/min, 30 oC • Cation (ICS-2500): CS17 Ionpac Column & CSRS 4-mm Suppressor • Constant methanesulfonic acid (MSA) eluent • 0.40 mL/min, 40 oC

26. Developing Analysis Methods • Amino Acid Analysis Method • Dionex ICS-3000 with AminoPac PA10 columns and ED Electrochemical Detector • Multi-Step Gradient Involving Water, Sodium Hydroxide and Sodium Acetate at 1.0 mL/min, 30oC • Aldehyde Analysis Method • Waters HPLC with C-18 column and UV detection at 365 nm • Linear methanol/water gradient at 1.0 mL/min • Samples derivatized with 2,4-dinitrophenylhydrazine

27. Effect of Amides on Anion IC Analysis • Amide formation reversed by the addition of excess NaOH to the degraded amine sample • Preliminary analysis on end samples from degradation experiments shows that formate and oxalate concentration increases notably after the addition of NaOH (1 g of degraded sample + 1 g 5M NaOH) • All degraded amine samples with be analyzed pre and post-NaOH derivitization in the future • All amide degradation products will be classified as carboxylic acids from this point on

28. 7 m MEA, 0.6 mM Cu Low Gas Flow Formate Amide of MEA/Oxalate Nitrite Nitrate Oxalate

29. 2.5m PZ Rate Summary (mM/hr)

30. Aqueous Pz Rate Summary(mM/hr)

31. 7m MEA/2m PZ Rate Summary (mM/hr)

32. MEA Rate Summary (mM/hr)

33. 7m MEA Rate Summary (mM/hr)

34. AMP Structure

35. 3M AMP, 1 mM Fe

36. Baseline Rate Comparison (mM/hr)

37. High Gas 7m MEA Rate Summary – FTIR Analysis (mM/hr)

38. Effect of Metal Catalysts

39. High Gas 7m MEA Rate Summary – IC Analysis (mM/hr)

40. Conclusions • Inhibitor “A” reduces oxidative degradation in known products by approximately 70% for MEA, PZ and MEA/PZ systems • The addition of 5m KHCO3 effectively inhibits 2.5m PZ degradation • Lowers oxygen solubility in the solution • AMP oxidative degradation is two order of magnitudes lower as compared to inhibited PZ and MEA systems • AQ PZ is preferred over 7m MEA at low catalyst conditions • The MEA amides of oxalate and formate are present in significant quantities • 2-4X increase in formate concentration, 2-10X in oxalate concentration

41. Future Work • Mass Transfer Controlled Conditions • More long-time high and low gas flow experiments • Development of amino acid, aldehyde, imidazole and total amine analysis methods • Re-analyze prior experimental samples for amide concentrations • Inhibited Oxidation • Test effectiveness of formaldehyde, EDTA, sodium sulfite versus inhibitor “A”

42. 2.5 m Pz, 500 ppm V+ Low Gas Flow Formate Nitrate EDA Glycolate Oxalate Ammonium Acetate Nitrite

43. 2.5m PZ, 500 ppm V+, 100 mM “A” EDA Formate Nitrate Nitrite Oxalate

44. Formate, no “A”

45. 2.5m PZ/5m KHCO3, 500 ppm V+ Formate Nitrate Oxalate

46. 5m PZ / 0.1mM Fe

47. 5m PZ / 0.1mM Fe / 100mM “A”

48. 5m PZ / 0.1mM Fe / 5mM Cu (+/- “A”)

49. 5m PZ / 5mM Fe

50. 7 m MEA, 0.6 mM Cu Low Gas Flow Formate Amide of MEA/Oxalate Nitrite Nitrate Oxalate