Amine Thermal
Degradation
By: Jason Davis
Overview
 Carbamate
Polymerization of MEA
 Background
 Chemistry
 Model
 PZ
and MEA/PZ Blends
 Amine
Screening
Amine Losses
Oxidative Degradation – A. Sexton
 Thermal Degradation – degradation
occuring at stripper and reclaimer
conditions

Carbamate polymerization
 Other thermal degradation

Volatility – M. Hilliard
 Physical Losses

Amine Losses
Vapor Losses
Oxidative
Degradation
Thermal
Degradation
CO2
COLDLEAN
EFFLUENT
ABSORBER
HOT RICH
CROSSX
FLUEGAS
COLDRICH
STRIPPER
HOT LEAN
RECLAIM
Thermal Degradation

Industry standards currently limit MEA
concentration at 30wt% (15wt% being the
standard for natural gas treating) due to concern
over increased corrosion and thermal
degradation

Degradation can lead to ineffective CO2 capture,
loss of expensive solvent, increased equipment
corrosion, and an increased environmental
impact
Chemistry
NH2
HO
+ CO2
MEA
NH
HO
CO2-
+ H+
MEA Carbamate
O
NH
HO
CO2-
+ H+
+ H2O
O
NH
2-Oxazolidone
Polderman Dillon and Steele (1955)
Chemistry - Continued
O
O
O
NH
+ MEA
HN
OH
N
+ H2O
1-(2-hydroxyethyl)-2-imidazolidone
(HEIA)
O
HN
N
OH
+ H2O
NH
HO
NH2
N-(2-hydroxyethyl)-ethylenediamine
(HEEDA)
+ CO2
What Do We Know

MEA Carbamate Polymerization Factors




CO2 loading
Temperature
Amine concentration
Literature for MEA


No kinetic data available
Controlled when solutions held at 15 wt% in
industrial applications
Sample Apparatus

Use high pressure sample containers made of 316L
stainless steel tubing and endcaps

Forced convection oven to maintain constant
temperature for a large number of samples

Maintains CO2 loading in solution at elevated
temperature and pressure to accelerate thermal
degradation

Simple experimental design and allows for a large
number of solutions to be tested at one time
Analytical

GC



HPLC



High temperatures can alter results
Separation of polar compounds difficult and cross
contamination in sample port
Amine detection difficult with standard detectors
Can identify and quantify nonionic species
Cation IC



Separates positively charged ions
Will not detect non-ionic species
Can measure amine disappearance and the
formation of ionic species (highly polar)
MEA Experiments

Matrix of samples
MEA Concentration (15-40wt%)
 CO2 Loading (0.2-0.5)
o
 Temperature (100-150 C)


100oC and 150oC experiments in 2ml
sample containers

120oC and 135oC experiments in 10ml
containers
o
11m MEA after 8 wks at 135 C
6.00 10172007 135C 11m Autosampler #6 [modified by TEXAS UNIVERSITY OF]
µS
11m MEA a=0.5 T=135C t=8wks
ECD_1
MEA
1 - MEA
- 3.525
4.00
2.00
2 - Unknown 1 - 5.750
-0.50
0.0
HEEDA
3 - HEEDA - 12.150
min
1.3
2.5
3.8
5.0
6.3
7.5
8.8
10.0
11.3
12.5
13.8
15.0
16.3
17.5
18.8
20.0
Emperical Data Regression
MEA f  MEA o  e
 K * 1.45 *MEAo 0.5 *t
where K is the temperature dependent rate constant given by:
K e
33.4 28900 /(T *1.987 )
MEAf = final MEA concentration (molality)
MEAo = initial MEA concentration (molality)
= Loading defined as moles CO2 per mole amine
t = time (weeks)
T = Temperature (K)
Effect of Loading (T=135C)
11
MEA (molality)
10
=0.2
9
8
=0.4
7
6
=0.5
5
4
0
2
4
Time (wks)
6
8
Effect of Temperature (=0.4)
100oC
7
MEA (molality)
6
120oC
5
135oC
4
3
150oC
2
1
0
0
2
4
Time (wks)
6
8
Effect of Concentration
o
(T=135 C =0.4)
100
95
MEA Remaining (%)
90
85
80
75
7m
70
3.5m
11m
65
60
55
50
0
1
2
3
4
Time (wks)
5
6
7
8
HEEDA Formation
o
11m MEA at 135 C
0.5
=0.2
0.45
HEEDA (m)
0.4
0.35
=0.4
0.3
0.25
=0.5
0.2
0.15
0.1
0.05
0
0
2
4
6
8
Thermal Degradation Costs

Approximately $2/ton CO2 allocated to solvent
make-up in most cost models




Assumes 1.5kg MEA/ton CO2 and a cost of $1.32/kg
MEA
3.5m MEA, P=1atm, $0.10/ton CO2
11m MEA, P=2.5 atm, ~$1.60/ton CO2
Does not include corrosion or reclaimer costs


Natural gas processing experience says reclaimer
composes 50% of thermal degradation
Corrosion has been shown to increase in the
presence of HEEDA
MEA Conclusions

Temperature has the greatest effect on thermal
degradation in the stripper




Quadruples every 15oC
Double pressure = 15oC temp increase
Loading increases degradation slightly more than 1st
order
Concentration has multiple effects


Slightly more than 1st order in concentration
In practice an increase in concentration yields increased
stripper temperatures due to increased BP of solution
(3.5m to 11m increases temperature by ~4oC and
increases thermal degradation by 40%)
MEA/PZ Blended Systems

Made measurements of aqueous PZ and a 7m
MEA/2m PZ blend at varying temperatures

PZ not expected to degrade since it does not have an
alcohol group to form an oxazolidone intermediate
HN

NH
Unknown what the blended system would do
Aqueous PZ after 8 weeks
o
at 150 C
5.00 7m MEA 2m PZ Tests #11 [modified by TEXAS UNIVERSITY OF]
µS
2.5m PZ T=150 t>8wks
ECD_1
PZ
1 - Piperazine - 13.100
3.75
2.50
These peaks are in the
time 0 sample
1.25
-0.50
0.0
min
1.3
2.5
3.8
5.0
6.3
7.5
8.8
10.0
11.3
12.5
13.8
15.0
16.3
17.5
18.8
20.0
Degraded MEA/PZ after
o
3 weeks at 135 C
1 - 7m MEA 2m PZ Tests #7 [modified by TEXAS UNIVERSITY OF]
7m MEA 2m PZ t=0
12.0 2 - 7m MEA 2m PZ Tests #4 [modified by TEXAS UNIVERSITY OF, 1 peak manually assigned]
µS
ECD_1
ECD_1
1 MEA
- MEA - 3.525
Degradation
Products
5.0
PZ
2 - Piperazine - 12.975
21
-1.0
0.0
min
1.3
2.5
3.8
5.0
6.3
7.5
8.8
10.0
11.3
12.5
13.8
15.0
16.3
17.5
18.8
20.0
Amine Losses after 2 Weeks
Solvent
Temp
(oC)
MEA Loss
(%)
PZ Loss
(%)
Total Amine
Loss (%)
Pure PZ
120
-
<2.0
<2.0
Pure MEA
120
4.0
-
4.0
MEA/PZ
Blend
120
5.0
8.6
6.3
Pure PZ
135
-
<2.0
<2.0
Pure MEA
135
18.1
-
18.1
MEA/PZ
Blend
135
11.9
31.8
19.1
*All systems have a loading of 0.4 and similar moles of alkilinity
PZ Blend Conclusions

PZ with a loading of 0.4 did not degrade at
150oC for over 8 weeks

The blended systems preferentially
destroyed PZ, the more expensive solvent

PZ is a stronger nucleophile so it attacks
the MEA oxazolidone structure more readily
than MEA thereby increasing degradation
Other Amines

Set up several screening experiments on
other amine systems including







EDA
DETA
MDEA
HEEDA
DGA
AMP
Only measured ionic degradation products
Amine Screening
o
(T=135 C =0.4 t=4wks)
Amine
PZ
DGA
Concentration Remaining
Total Area
(molality)
Amine Peak (%) Retention (%)
3.5
100
100
7
93
98
50 wt%
71
97
AMP
3
97
96
EDA
3.5
64
91
MEA
7
76
80
DETA
2.3
9
71
HEEDA
3.5
3
17
MDEA
o
MDEA after 4wks at 135 C
1 - 135 Amine Screening Autosampler #11 [modified by TEXAS UNIVERSITY OF] 50wt% MDEA a=0.45 t=0 (2)
4.00 2 - 135 Amine Screening Autosampler #12 [modified by TEXAS UNIVERSITY OF, normalized]
µS
ECD_1
ECD_1
MDEA
1 - 4.350
3.00
2.00
1.00
21
-0.50
1.0
min
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
20.0
o
HEEDA after 4wks at 135 C
1 - 135 Amine Screening Autosampler #3 [modified by TEXAS UNIVERSITY OF]
3.5m HEEDA a=0.45 t=0
5.50 2 - 135 Amine Screening Autosampler #4 [modified by TEXAS UNIVERSITY OF] 3.5m HEEDA a=0.45 T=135 t=4wks
µS
ECD_1
ECD_1
HEEDA
1 - HEEDA - 11.942
3.75
2.50
1.25
21
-0.50
0.0
min
1.3
2.5
3.8
5.0
6.3
7.5
8.8
10.0
11.3
12.5
13.8
15.0
16.3
17.5
18.8
20.0
Amine Screening
Conclusions

HEEDA degrades very quickly compared to other
amines studied

Industrially MDEA does not significantly degrade
but this study shows it does shift to other amines



Arm shifting
Higher activation energy than other amines so
increased temperature might effect more
Order from least to most degradation

PZ<DGA< MDEA< AMP<EDA< MEA< DETA<
HEEDA
Future Work

Mechanistic model for MEA degradation



MEA with spikes of various degradation products
to determine k values for reactions
Measure HEIA formation with HPLC for low temp
samples to get a more accurate degradation rate
Thermal Degradation modeling in ASPEN


Various stripper configurations
Possible reclaiming simulations as well
Summary

Thermal degradation can be important in the overall
cost of the MEA absorber/stripper system


Engineering controls can keep these costs reasonable
Further study of the reclaiming system is needed

PZ does not thermally degrade by itself, but does in
the presence of alkanolamines

Many common amines do degrade under stripper
conditions and this should be considered when
choosing a solvent
QUESTIONS?