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Degradation of amines
in CO2 Capture
Gary T. Rochelle, Stephanie Freeman, Alex Voice,Fred Closmann
Luminant Carbon Management Program
The University of Texas at Austin
Presented at
TCCS-6
June, 2011
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Messages
Stripper energy use is constrained by the maxT permitted by thermal degradation
TMEA < TMDEA 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 Gas
10% CO25-10% O2
Purified Gas
1% CO2
30% MEA
= 0.4-0.5
1 mM Fe+3
CO2
H2O(O2)
30% MEA
= 0.3-0.4
Reboiler
Absorber
40 -70 oC
1 atm
Stripper
120 oC
1 atm
Cross
Exchanger
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
Wtotal(kW
h/tonneC
O2)
(HCO2-HH20)(1/T) (kJ/gmol-K)
HCO2=60 kJ/mole
70
80
erma egra a on m s s r pperperformance because
Greater Tstrip & HCO2 reduce Weq
MEA 120 C
PZ
Single stage flash at 90-150CCompression to 150 bar
Lean PCO2 = 0.5 kPa at 40C
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 CO
2-
NHO
O
+ O-
H
NHO
O
OHNH2 + OH
NHNH
2 +
O
O
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Primary & Secondary Alkanolamines Deg T
Amine 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
NH
NH
CH3
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2 Tertiary Quaternary + Secondary
+
CH3
OH
N
OH
CH3
OH
NH+
OH
+ OHNH
OH
CH3
CH3
OH
N+
OH
Tertiary1 + Secondary2 Tertiary2+ Secondary1
Tertiary1 + Quaternary2 Tertiary2+ Quaternary1
Elimination
CH3
CH3
OH
N+
OH
+
+CH3
CH3
OH
NH+
OH
OH
OH2
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3o amines2o 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
CH3
CH3
N
CH 3
CH3N
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Ring Opening
NH NH2
+
NH
NH
N NH3
+
NH NH +
NH2
O
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
NHNH
NH
O O+ N
NH
NH
OH
O
+
+ OHNH
2
+
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
Amine
Oxidation(m
ol/molCO2)
Oxygen Rate Constant (s-1)
Total
AbsorberExchanger
Sump
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 0.9Aminoethyl PZ 3.5
N-formyl PZ (amide) 8.3
Formate & other acids 2.5Bicine 5.3
Hydroxyethyl sarcosine 10.5
~79.5
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Message on Thermal Degradation
Stripper energy is constrained by the max Tpermitted by Degradation
Linear alkanolamines and diamines degrade
by polymerization & urea formation at 100-130oC
Tertiary amines degrade by arm switching &
elimination at 120-140o
CPiperazine 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 tomanage secondary environmental impact.
Volatile Products can leave with flue gas Aldehydes, formate, ammonia, volatile amines,
amides
Nonvolatile products make up reclaimer
waste 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.
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