oxidative degradation of amines in co 2 capture andrew sexton january 10, 2008 department of...

Oxidative Degradation of Amines in CO2 Capture

Andrew SextonJanuary 10, 2008

Department of Chemical EngineeringThe 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 Gas10% CO2

5-10% O2

Purified Gas1% CO2

30% MEA = 0.4-0.51 mM Fe+3

CO2

H2O(O2)

30% MEA = 0.3-0.41 mM Fe+2

Reboiler

Absorber40 -70 oC

1 atm

Stripper120 oC1 atm

CrossExchanger

Oxidative Degradation

Thermal Degradation

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.

Electron Abstraction Pathways

C CN

H

OH

H

H

HH

H.. Fe+3

Aminium Radical

MEA

C CN

H

OH

H

H

HH

H.

C CN

H

OH

HH

H

H.. .-H+

Imine Radical

C CN

H

H H

H..

OH

-H.

Imine

C C

H

H

OHH

O

+ N

H

HH

H2O

C CN

H H

H..

OH

H

Enamine

H2O

N

H

HH

+ CH H

O

2

Oxidation of Aldehydes

CH H

O

CH OH

O

C C

H

H

HH

O

C C

H

H

HOH

O

C C

OO

H H C C

OO

OH OH

C C

O

OH H C C

O

OH OH

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 Na2SO3, 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 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)

Effect of Space Time

0.1

1.0

10.0

100.0

0.01 0.10 1.00 10.00 100.00 1000.00

Liquid Vol. / Gas Rate = Space Time (min)

Max

. Rat

e / P

O2

= K

G' (

mM

/hr-

bar

)

Chi & Rochelle 2002

Rooney 1998Blachly & Ravner 1964

Girdler 1950

Hofmeyer 1956

Goff & Rochelle 2003

Current Study - agitation gives higher KG'

Effect of Inhibitor A on MEA

0

2

4

6

8

10

12

14

16

18

20

1 10 100 1000

Inhibitor A (mM)

NH

3 E

volu

tion

- (

Rel

ativ

e to

Bas

elin

e)

= 0.40

= 0.15

0.20 mM Cu

0.30 mM Fe

Effect of Metal Catalysts

0.1

1.0

10.0

0 200 400 600 800 1000 1200 1400

Agitation Rate (RPM)

NH

3 E

volu

tion

Rat

e (m

M/h

r)

0.0002 mM Fe

0.14 mM Fe

0.20 mM Cu

Stoichiometry

Product Stoichiometry (n)Acetaldehyde 0.0Formaldehyde 0.5Acetic Acid 0.5

Hydroxyacetaldehyde 0.5Glycolic Acid 1.0Formic Acid 1.5Oxalic Acid 2.0

CO2 2.5

MEA + nO2 → NH3 + Degradation Products

Oxygen Stoichiometry

MEA + O2 2 Formate + Ammonia

MEA + O2 2 Formate + Nitrate + Water

MEA + O2 Glycolate + Ammonia

Ionic Degradation Products

MEA

Piperazine

Acetic Acid

Oxalic Acid

Glycolic Acid

Formic Acid

Ethylenediamine

N C C OH

C C

C

N

C

N

C C OH

O

C C OHOH

O

C OH

O

C C OHOH

O O

C C NN

Ionic Degradation Products

MEA

Piperazine

N C C OH

C C

C

N

C

N

NOO

O+

- -

NOO -

Nitrate

Nitrite

Amino Acid Degradation Products

C

C

N

H H

OH

O

HH

C

C

N

C H

OH

O

HH

COH

O

H

H

C

C

N

C

OH

O

HH

COH

H

HH

H

CC

H

HH

H

OH

GlycineDiglycine

(Iminodiacetic Acid)

Bicine

HPLC-MS Screening Analysis

• Hydroxyethylimidazole (aldehyde, ammonia, amine, substituted glyoxal)

• MEA-Formamide

• MEA-Oxamic Acid (Partial Amide of Oxalic Acid)

CH C

O

N

H

C OH

H H

HH

CC C

O

N

H

O

OH C OH

HH

HH

(Hydroxyethyl)imidazole

H C

O

H

HH

H

N+ CN

H

C OH

HH

HHH

C C

OO

H H+ +

N

N

C C

C

Water and CO2 also formed

Amide Formation

R C

O

OH

HH

R’

N+ +R’R C

O

N

HHH

O

Low Gas Flow Apparatus

98% O2 / 2% CO2

feed (controlled by rotameter)

Saturated CO2 / O2

mixture

100 mL / min

Agitation @ 1400 RPM

Water Reservoir: 55 oC

Amine Solution

VORTEXING

Modified Low Gas Flow Apparatus

Saturated CO2 / O2

mixture

100 mL / min

Agitation @ 1400 RPM

Water Reservoir: 55 oC

Amine Solution

VORTEXING

O2 CO2

98% O2 / 2% CO2 feed

High Gas Flow Degradation Apparatus

Gas InletHeat 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 oC

• Cation (ICS-2500): CS17 Ionpac Column & CSRS 4-mm Suppressor

• Constant methanesulfonic acid (MSA) eluent

• 0.40 mL/min, 40 oC

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

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

0

20

40

60

80

100

120

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280

Experiment Time (Hours)

Co

nc

en

tra

tio

n (

mM

)

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)

Vanadium Conc. (ppm) 500 500Inhibitor A Conc. (mM) - 100

KHCO3 Conc. (molal) - -

Formate 0.18 0.06 0.007 0.001EDA 0.09 0.11 0.001 0.002

Carbon 0.36 0.28 0.013 0.03Nitrate/Nitrite 0.19 0.06 0.0004 0.05

Nitrogen 0.37 0.28 0.0024 0.05

500-5

Aqueous Pz Rate Summary(mM/hr)

Iron Conc. (mM) 0.1 0.1 5 5Copper Conc. (mM) 5 5 - -

Inhibitor A Conc. (mM) - 100 - -NaOH Addition No No No Yes

Formate 0.22 0.004 0.006 0.011EDA 0.25 0.03 0.02 0.02

Carbon 0.76 0.06 0.046 0.053Nitrogen 0.52 0.06 0.04 0.04

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

Iron Conc. (mM) 0.1 0.1 0.1 0.1Copper Conc. (mM) - - 5 5

Inhibitor A Conc. (mM) - 100 100 -

Formate 0.17 0.20 0.30 2.35Carbon 0.20 0.23 0.42 2.67

Nitrogen 0.09 0.05 0.13 0.18

MEA Rate Summary (mM/hr)

MEA Conc. (molality) 7 7 7 7 9Iron Conc. (mM) 0.6 - 0.6 0.1 0.1

Copper Conc. (mM) - 0.6 0.6 5 -

Formate 0.40 0.39 0.67 0.66 0.41Nitrite/Nitrate 0.46 0.21 0.33 0.24 0.51

Carbon 0.73 0.75 0.85 0.78 0.51

7m MEA Rate Summary (mM/hr)

Iron Conc. (mM) 1 0.1 0.1 1 0.1 0.1Copper Conc. (mM) - - - - - -

Formaldehyde Conc. (Molarity)

- 0.5 - - 0.5 -

Formic Acid Conc. (Molarity)

- - 0.5 - - 0.5

NaOH Addition No No No Yes Yes Yes

Formate 0.289 0.223 N/A 0.641 0.916 N/AOxalate 0.020 0.007 0.012 0.110 0.075 0.11

Nitrite/Nitrate 0.265 0.285 0.285 0.307 0.296 0.298Carbon 0.335 0.241 N/A 0.872 1.086 N/A

AMP Structure

CC C

N

C

OH

Glycolate

Acetate

Formate

Nitrite

Oxalate

Nitrate

0

0.5

1

1.5

2

2.5

3

0 100 200 300 400 500

Experiment Time (hours)

Con

cen

trat

ion

(mM

)

3M AMP, 1 mM Fe

Baseline Rate Comparison (mM/hr)

Distinguishing Conditions

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

AQ PZ / 0.1mM Fe / 5mM Cu /

100mM "A"

7m MEA / 0.1 mM Fe / 5mM Cu / 100 mM "A"

3M AMP, 1mM Fe

Formate 0.30 0.004 0.04 0.008Carbon 0.42 0.06 0.10 0.015

Nitrogen 0.13 0.06 0.04 0.004

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

Iron Conc. (mM) 1 0.1Copper Conc. (mM) - 5

Ammonia 1.793 1.750NO 0.132 0.126NO2 0.076 0.284

N2O 0.001 0.165Formaldehyde 0.081 0.034Acetaldehyde 0.139 0.076

Carbon Monoxide 0.273 0.001

Effect of Metal Catalysts

0.1

1.0

10.0

0 200 400 600 800 1000 1200 1400

Agitation Rate (RPM)

NH

3 E

volu

tion

Rat

e (m

M/h

r)

0.0002 mM Fe

0.14 mM Fe

0.20 mM Cu

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

Iron Conc. (mM) 1 0.1 0.1

Copper Conc. (mM) - 5 5

NaOH Addition No No Yes

Formate 0.049 0.455 1.237Carbon 0.064 0.513 1.417

Nitrogen 0.028 0.051 0.043

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

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”

0

5

10

15

20

25

30

35

40

45

0 20 40 60 80 100 120 140 160 180 200 220 240

Experiment Time (Hours)

Co

nce

ntr

atio

n (

mM

)2.5 m Pz, 500 ppm V+

Low Gas Flow

Formate

Nitrate

EDA

Glycolate

Oxalate

Nitrite AcetateAmmonium

0

2

4

6

8

10

12

14

16

18

20

0 20 40 60 80 100 120 140 160 180

Con

cent

ratio

n (m

M)

Experiment Time (Hours)

EDA

Formate

Nitrate

NitriteOxalate

2.5m PZ, 500 ppm V+, 100 mM “A”

Formate, no “A”

0

1

2

3

0 50 100 150 200 250 300

Co

nce

ntr

atio

n (m

M)

Experiment Time (Hours)

Formate

Nitrate

Oxalate

2.5m PZ/5m KHCO3, 500 ppm V+

5m PZ / 0.1mM Fe

0

1

2

3

4

5

6

7

0 50 100 150 200 250 300 350

Co

nce

ntr

atio

n (m

M)

Experiment Time (hrs)

5m PZ / 0.1mM Fe / 100mM “A”

5m PZ / 0.1mM Fe / 5mM Cu (+/- “A”)

0

10

20

30

40

50

60

70

80

90

100

110

120

0 50 100 150 200 250 300 350 400 450

Co

nce

ntr

atio

n (m

M)

Experiment Time (Hours)

5m PZ / 5mM Fe

0

20

40

60

80

100

120

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280

Experiment Time (Hours)

Co

nc

en

tra

tio

n (

mM

)

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

0

20

40

60

80

100

120

140

160

180

200

220

240

0 50 100 150 200 250 300 350

Co

nce

ntr

atio

n (m

M)

Experiment Time (Hours)

0

100

200

300

400

500

600

700

0 50 100 150 200 250 300

Co

nce

ntr

atio

n (m

M)

Experiment Time (hrs)

Formate

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

0

10

20

30

40

50

0 50 100 150 200 250 300

Co

nce

ntra

tion

(mM

)

Experiment Time (hrs)

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”

0

10

20

30

40

50

60

70

80

90

100

110

120

0 50 100 150 200 250 300 350

Co

nce

ntr

atio

n (m

M)

Experiment Time (Hours)

7m MEA / 2m PZ / 0.1 mM Fe

7m MEA / 2m PZ / 0.1mM Fe / 100mM “A”

0

10

20

30

40

50

60

70

0 50 100 150 200 250 300 350

Co

nce

ntr

atio

n (m

M)

Experiment Time (hrs)

7m MEA / 1mM Fe (Hi Gas)

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