degradation of amines in co capture - sintef · mdea
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Degradation of amines in CO2 Capture
Gary T. Rochelle, Stephanie Freeman, Alex Voice, Fred Closmann
Luminant Carbon Management ProgramThe University of Texas at Austin
Presented at TCCS-6
June, 2011
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Messages• Stripper energy use is constrained by the max
T permitted by thermal degradation– TMEA < TMDEA <TAMP< TPZ
• As amines become more resistant, oxidation shifts from the absorber to the heat exchanger– MEA > Tertiary > Piperazine
• Amine degradation must be minimized to manage secondary environmental impact.– Volatile Products can leave with flue gas– Nonvolatile products make up reclaimer waste
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Where is degradation most likely to occur?
Flue Gas10% CO25-10% O2
Purified Gas1% CO2
30% MEAα = 0.4-0.51 mM Fe+3
CO2H2O(O2)
30% MEAα = 0.3-0.4
Reboiler
Absorber40 -70 oC
1 atm
Stripper120 oC1 atm
CrossExchanger
Oxidative Degradation
Thermal Degradation
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Thermal Degradation
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180
240
300
360
5 10 15 20 25 30 35
Wto
tal(
kW
h/
ton
ne
CO
2)
(∆HCO2-∆HH20)∆(1/T) (kJ/gmol-K)
∆HCO2=60 kJ/mole
70
80
Thermal Degradation limits stripper performance because
Greater Tstrip & ∆HCO2 reduce Weq
MEA 120 C
PZ
Single stage flash at 90-150°CCompression to 150 barLean PCO2 = 0.5 kPa at 40°C
90 C 150 C
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5 Mechanisms for Thermal Degradation
• 1. Carbamate Polymerization - MEA
• 2. Cyclic Urea - Ethylenediamine
• 3. Arm Switching/Elimination - Tertiary Amine
• 4. SN2 Ring Opening – Piperazine
• 5. Blend Synergism – Piperazine/MEA
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Carbamate Polymerization
• ↔
MEA Carbamate Oxazolidone
→
MEA HEEDA
NHOH CO2- NHO
O
+ O- H
NHO
O
OHNH2 + OH
NHNH2 +
O
O
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Primary & Secondary Alkanolamines Deg TAmine k1 = 2.91 × 10-8 s-1 Structure T (oC)
2-methyl-aminoethanol 103
Monoethanolamine 120
3-amino-propanol 126
2-piperidine ethanol 127
Diglycolamine® 133
2-methyl-2-amino-propanol 137
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Cyclic urea
NH2
NH2 + O O
O
NHNH
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1o & 2o Diamines = cyclic ureas Deg TAmine Structure T (oC)
Dimethylethylenediamine 100
Diethylenetriamine 105
Methylaminopropanolamine 114
Hydroxyethylethylenediamine 114
Ethylenediamine 121
Hexamethylenediamine 156
CH3
NHNH
CH3
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2 Tertiary ↔ Quaternary + Secondary
+
CH3
OHN
OH
CH3
OHNH
+
OH
+ OHNH
OHCH3
CH3
OHN
+
OH
Tertiary1 + Secondary2 ↔ Tertiary2+ Secondary1
Tertiary1 + Quaternary2 ↔ Tertiary2+ Quaternary1
Elimination
CH3
CH3
OHN
+
OH + +CH3
CH3
OHNH
+
OHOH
OH2
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3o amines→2o amines + other 3o aminesAmine Structure T (oC)
Dimethylmonoethanolamine 122
Tetramethylethylenediamine 125
Methyldiethanolamine 128
N-(2-Hydroxyethyl)PZ 132
N,N’-Dimethylpiperazine 139
1-methyl-piperazine 148
CH3 N N CH3
CH3CH3
N
CH3
CH3N
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Ring Opening
NH NH2+
NH
NH
N NH3+
NH NH +
NH2O
OH NH O + OH2
Ring Closing
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Cyclic ↔ LinearAmine Structure T (oC)
Diglycolamine® 133
Homopiperazine 133
Pyrrolidine 135
2-Methyl-Piperazine 152
Hexamethylenediamine 156
Piperazine 162
Morpholine 169
CH3
NH
NH
NH NH
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Interactive Blends• Carbamate Polymerization
NHNHNH
O O+ NNH
NH
OH
O
+
+ OHNH2
+
OH
NHNH NH+
OH OH
NNH
Secondary2 + Tertiary1 ↔ Tertiary2+ Secondary1
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Total Amine Loss in BlendsAmine (m) Structure T (oC)
MEA/PZ 104
MEA/AMP 123
4 AMP/6 PZ 135
7 MDEA/2 PZ 138
4 PZ/4 2MPZ 155
3.9 PZ/3.9 1MPZ/0.2 14DMPZ
160
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Oxidation
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O2 solubility & Mass Transfer
0,E+0
2,E-5
4,E-5
6,E-5
2,E-04 2,E-03 2,E-02
Am
ine
Oxi
dati
on (m
ol/m
olCO
2)
Oxygen Rate Constant (s-1)
Total
Absorber
ExchangerSump
PZMEAMDEA
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Degradation Products and Environmental Impact
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7 m MDEA/2 m PZ Oxidized at 120oC
Products (CO2 carrying)C-Loss
(%)
Diethanolamine/Methylaminoethanol 40
1-methyl PZ 8.4
1,4-Dimethyl PZ 0.9
Aminoethyl PZ 3.5
N-formyl PZ (amide) 8.3
Formate & other acids 2.5
Bicine 5.3
Hydroxyethyl sarcosine 10.5
~79.5
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Message on Thermal Degradation
• Stripper energy is constrained by the max T permitted by Degradation
– Linear alkanolamines and diamines degrade by polymerization & urea formation at 100-130oC
– Tertiary amines degrade by arm switching &elimination at 120-140oC
– Piperazine and related cyclic amines degrade by ring opening at 150-165oC.
•
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Message on Oxidation
• As amines become more resistant, oxidation shifts from the absorber to the heat exchanger
– MEA & alkanolamines readily oxidize in the absorber unless inhibited by radical or peroxide scavengers
– Tertiary amines inhibit self oxidation, probably by scavenging peroxides
– Piperazine oxidizes only at the higher T of the heat exchanger exit
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Message on Environmental Impact
• Amine degradation must be minimized to manage secondary environmental impact.– Volatile Products can leave with flue gas
• Aldehydes, formate, ammonia, volatile amines, amides
– Nonvolatile products make up reclaimerwaste• Polyamines, Cyclic urea, amino acids
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A review of previous Work
• University of Texas– Thermal: Austgen, Freeman, Closmann
– Oxidation: Goff, Sexton, Voice
• IFP – Thermal, Oxidation– Lepaumier, Carrette, et al.
• NTNU – Thermal, oxidation– Lepaumier, Eide-Haugm, et al.