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

Oxidative Degradation of Amines in CO 2 Capture Andrew Sexton January 10, 2008 Department of Chemical Engineering The University of Texas at Austin. Overview . Introduction Prior Oxidative Degradation Research Research Objectives Experimental Methods Degradation Apparatus

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

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  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

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