mea oxidation in co2 capture alexander voice dr. gary t ... · mea oxidation in co 2 capture...
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MEA oxidation in CO2 Capture
Alexander Voice
Dr. Gary T. Rochelle
15.June.2011
Luminant Carbon Management Program
Factors Impacting Oxidation in CO2 Capture
Rich solvent
0.03-0.15mM dissolved O2
Scrubbed gasVolatile Products (NH3, H3CNH2)
XXXXABS
40-75°C
XXXXXXXX
Flue gas4-12% CO2
5-15% O2
10-300ppm NOx
1-300ppm SO2
Contaminants
Lean solventThermal
degradation products
______________________________Semi-batch oxidation reactors
Low Gas Flow0.1LPM
98 kPa O2Liquid samples
High Gas Flow7.5 LPM21kPa O2
FTIR analysis (NH3)
350mL2kPa CO2
Add dissolved metals & inhibitors
0
1
2
3
4
0
2
4
6
8
10
0 1 2 3 4 5 6
Vapor Composition (m
ol %)
Rate
(mm
ol/k
g/hr
)
Time (hrs)
Water
CO2
NH3
MEA
4
Vapor Composition: Hot-Gas FTIR analyzer
Changecondition
% change in NH3
Identification of Catalysts and Inhibitors
• Tested 13 transition metals – Mn ≥ Cu >> Fe >> Cr
– Vanadium was a mild inhibitor
– No significant effect: Ti, Mo, Co, Ni, Sn, Se, Ce, Zn
• Tested >100 organic additives as inhibitors
• Temperature effects, rates and products
NN
NOH
O OH
O
OH
OOOH
O
OH
Best inhibitor identified = Diethylene triamine
pentaacetic acid0.1 – 1%wt
0
1
2
3
4
5
6
0 5 10 15 20 25 30
NH
3 Ra
te (m
mol
/kg/
hr)
Time (hrs)
63.4 C55.9 C
69.6 C
Temperature Dependence of NH3 Production9 m pilot plant MEA, 98 kPa air, 2kPa CO2, 0.5mM Fe
Temperature Dependence9 m pilot plant MEA, LGF, 98 kPa O2, 2kPa CO2
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20
MEA
Con
c. (m
mol
/kg)
Exp. Time (days)
T = 55 Cr0 = 24.8 mmol/kg/hr
T = 70 Cr0 = 64.3 mmol/kg/hr
1
10
100
Rate
(mm
ol/k
g/hr
)
56 C 63 C 70 CTemperature (1/K)
MEA loss (r0)Low gas, 98 kPa O2
NH3 rateHG, 21 kPa O2
EA=57kJ/mol
Rates Summary9 m pilot plant MEA, 2kPa CO2
EA=55kJ/mol
Products and Analytical Methods• Amines: cation chromatography
• Anions and amides (formate, etc.): anion chromatography
• Hydroxyethyl imidazole: HPLC-UV
• Amino acids: HPLC-ECD
• Total material methods: TN, TOC, TIC, alkalinity
NHOH
O
O-
O
N N OH
NH4+NH2
OH
NHOH
O
OH
NHO
O-
O CH3
NHO
NHO
OH
OH
O-
O
O-
O
Product Mix Comparison – N Balance9 m pilot plant MEA, 70 C, 2kPa CO2
Low Gas Flow: 98kPa O2, stirred cell
High Gas Flow: 21kPa O2, sparged
Vol. LossHEI NH3
AmidesAmides
NH4+, NO2
-, NO3
-
NH4+, NO2
-, NO3
-
HEI
68%71%
NH3prods
NH3 + 0.5*HEI + NH4
+
Other MEA loss
N N OH
NH
O
OH
MB=102%MB=116%
Other MEA loss
Hydroxyethyl imidazole (HEI)
NH3 NHCH2OH2CH2 O
OOOH
NH2 OHN
O
++
+ OH2 +
N N OH
Pathway for HEI Production
1000
2000
3000
4000
5000
0 5 10 15
MEA
Con
c(m
ol/k
g)
Oxidation Time (days)
7 m MEA, neatr0 = 8.8 mmol/kg/hr
r0 = 14.0 mmol/kg/hr7 m MEA, thermally degraded
Therm. deg.2 weeks, 135 C
Presence of Thermal Degradation Products7 m MEA, 98kPa O2, 2kPa CO2, 55 C
Effect of the presence of NO29 m PP-MEA, 98kPa O2, 2kPa CO2, 55 C, 0.5mM Fe
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20
MEA
Con
c. (m
mol
/kg)
Exp. Time (days)
9 m PP-MEAr0 = 24.8 mmol/kg/hr
9 m PP-MEA + 50ppm NO2
r0 = 27.7 mmol/kg/hr
Summary of Factors Impacting MEA Oxidation
Variable Conditions % Change (basis)
Fe2+ 0 1 mM +1200 (NH3)
Cu2+, Mn3+ 0 1mM +500-1000 (NH3)
Temperature 55 70 C +160 (MEA)
O2 20 92 kPa +290 (MEA)
Inhibitor 0 1.5% -90% (NH3)
NO2• 0 50ppm +<10%
Thermaldegradation
2 weeks135 C
+59%
Alexander Voice • [email protected] • 512.553.5312
