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 Analytical Methods Degradation Products and Rates Conclusions and Future Work

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?

Where is degradation most likely to occur? Flue Gas 10% CO % O 2 Purified Gas 1% CO 2 30% MEA  = mM Fe +3 CO 2 H 2 O (O 2 ) 30% MEA  = mM Fe +2 Reboiler Absorber o C 1 atm Stripper 120 o C 1 atm Cross Exchanger Oxidative Degradation Thermal Degradation

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

Electron Abstraction Pathways CCN H OH H H H H H.. Fe +3 Aminium Radical MEA CCN H OH H H H H H. CCN H H H H H... -H + Imine Radical CCN H HH H.. OH -H. Imine CC H H OH H O + N H HH H2OH2O CCN HH H.. H Enamine H2OH2O N H HH + CHH O 2

Oxidation of Aldehydes CHH O CHOH O CC H H H H O CC H H H O CC OO HH CC OO CC O H CC O Formaldehyde  Formic Acid Acetaldehyde  Acetic Acid Hydroxyacetaldehyde  Glycolic Acid Glyoxal  Oxalic Acid

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

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 Na 2 SO 3, EDTA, & ‘A’ as degradation inhibitors Present process conditions that are most cost effective and environmentally safe

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 O 2 scavenger for Fe (Blachly/Ravner) DGA TM (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)

Effect of Space Time

Effect of Inhibitor A on MEA

Effect of Metal Catalysts

Stoichiometry

Oxygen Stoichiometry MEA +  O 2  2 Formate + Ammonia MEA +  O 2  2 Formate + Nitrate + Water MEA + O 2  Glycolate + Ammonia

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

Ionic Degradation Products MEA Piperazine N OO O + -- N OO - Nitrate Nitrite

Amino Acid Degradation Products C C N HH OH O HH C C N CH O HH C O H H C C N C O HH C H HH H CC H HH H Glycine Diglycine (Iminodiacetic Acid) Bicine

HPLC-MS Screening Analysis Hydroxyethylimidazole (aldehyde, ammonia, amine, substituted glyoxal) MEA-Formamide MEA-Oxamic Acid (Partial Amide of Oxalic Acid) CHC O N H COH HH HH CCC O N H O C HH HH

(Hydroxyethyl)imidazole HC O H HH H N +CN H COH HH HH H CC OO HH ++ N N CC C Water and CO 2 also formed

Amide Formation RC O OH HH R’ N++ RC O N H HH O

Low Gas Flow Apparatus

Modified Low Gas Flow Apparatus

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

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 o C Cation (ICS-2500): CS17 Ionpac Column & CSRS 4-mm Suppressor Constant methanesulfonic acid (MSA) eluent 0.40 mL/min, 40 o C

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, 30 o C 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

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

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

2.5m PZ Rate Summary (mM/hr)

Aqueous Pz Rate Summary(mM/hr)

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

MEA Rate Summary (mM/hr)

7m MEA Rate Summary (mM/hr)

AMP Structure

3M AMP, 1 mM Fe

Baseline Rate Comparison (mM/hr)

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

Effect of Metal Catalysts

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

Conclusions Inhibitor “A” reduces oxidative degradation in known products by approximately 70% for MEA, PZ and MEA/PZ systems The addition of 5m KHCO 3 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

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”

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

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

Formate, no “A”

Formate Nitrate Oxalate 2.5m PZ/5m KHCO 3, 500 ppm V +

5m PZ / 0.1mM Fe

5m PZ / 0.1mM Fe / 100mM “A”

5m PZ / 0.1mM Fe / 5mM Cu (+/- “A”)

5m PZ / 5mM Fe

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

7m MEA / 1mM Fe

7m MEA / 0.1mM Fe / 0.5M Formaldehyde

7m MEA / 0.1mM Fe / 0.5M Formic Acid

7m MEA / 0.1mM Fe / 5mM Cu

Formate 7m MEA/2m PZ, 0.1 mM Fe, 5 mM Cu

Nitrate Oxalate EDA Glycolate Acetate Nitrite 7m MEA/2m PZ, 0.1 mM Fe, 5 mM Cu

7m MEA / 2m PZ / 0.1mM Fe / 5mM Cu / 100mM “A”

7m MEA / 2m PZ / 0.1 mM Fe

7m MEA / 2m PZ / 0.1mM Fe / 100mM “A”

7m MEA / 1mM Fe (Hi Gas)

7m MEA / 0.1mM Fe / 5mM Cu (Hi Gas)