Degradation of amines in CO2Capture

8/11/2019 Degradation of amines in CO2Capture

1/24

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


2/24

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


3/24

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


4/24

Thermal Degradation


5/24

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


6/24

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


7/24

Carbamate Polymerization

MEA Carbamate Oxazolidone

MEA HEEDA

NHOH CO

2-

NHO

O

+ O-

H

NHO

O

OHNH2 + OH

NHNH

2 +

O

O


8/24

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


9/24

Cyclic urea

NH2

NH2 + O O

O

NHNH


10/24

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


11/24

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


12/24

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


13/24

Ring Opening

NH NH2

+

NH

NH

N NH3

+

NH NH +

NH2

O

OH NH O + OH2

Ring Closing


14/24

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


15/24

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


16/24

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


17/24

Oxidation


18/24

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


19/24

Degradation Products and

Environmental Impact


20/24

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


21/24

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.


22/24

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


23/24

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


24/24

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.

Documents

Degradation of amines in CO2Capture