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