Amine Thermal Degradation

By: Jason Davis

Overview

Carbamate Polymerization of MEABackgroundChemistryModel

PZ and MEA/PZ Blends

Amine Screening

Amine Losses

Oxidative Degradation – A. Sexton Thermal Degradation – degradation

occuring at stripper and reclaimer conditionsCarbamate polymerizationOther thermal degradation

Volatility – M. Hilliard Physical Losses

STRIPPERABSORBER CROSSX

FLUEGAS

EFFLUENT

COLDRICH

HOTRICH

HOTLEAN

COLDLEAN

CO2

RECLAIM

Amine Losses

Vapor Losses Oxidative Degradation

Thermal Degradation

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

NH2OH

NHOH CO2-

NHOH CO2-+ CO+ CO22

NHO

O

2-Oxazolidone2-Oxazolidone

+ H+ H22OO

MEA CarbamateMEA CarbamateMEAMEA

+ H+ H++

+ H+ H++

Polderman Dillon and Steele (1955)

Chemistry - Continued

NNH

O

OH

NNH

O

OH + H+ H22OO

1-(2-hydroxyethyl)-2-imidazolidone1-(2-hydroxyethyl)-2-imidazolidone

(HEIA)(HEIA)

+ H+ H22OO NH

OH NH2 + CO+ CO22

N-(2-hydroxyethyl)-ethylenediamineN-(2-hydroxyethyl)-ethylenediamine

(HEEDA)(HEEDA)

NHO

O

+ + MEAMEA

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 High temperatures can alter results Separation of polar compounds difficult and cross

contamination in sample port HPLC

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 samplesMEA Concentration (15-40wt%)CO2 Loading (0.2-0.5)Temperature (100-150oC)

100oC and 150oC experiments in 2ml sample containers

120oC and 135oC experiments in 10ml containers

11m MEA after 8 wks at 135oC

0.0 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 20.0-0.50

2.00

4.00

6.00 10172007 135C 11m Autosampler #6 [modif ied by TEXAS UNIVERSITY OF] 11m MEA a=0.5 T=135C t=8wks ECD_1µS

min

1 - MEA - 3.525

2 - Unknown 1 - 5.7503 - HEEDA - 12.150

MEA

HEEDA

Emperical Data Regression

tMEAKof

oeMEAMEA *** 5.045.1

)987.1*/(289004.33 TeK where K is the temperature dependent rate constant given by:

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)

4

5

6

7

8

9

10

11

0 2 4 6 8

Time (wks)

ME

A (

mo

lali

ty) =0.2

=0.4

=0.5

0

1

2

3

4

5

6

7

0 2 4 6 8

Time (wks)

ME

A (

mo

lalit

y)

Effect of Temperature (=0.4)

150oC

135oC

120oC

100oC

Effect of Concentration (T=135oC =0.4)

50

55

60

65

70

75

80

85

90

95

100

0 1 2 3 4 5 6 7 8

Time (wks)

ME

A R

emai

nin

g (

%)

11m

7m 3.5m

HEEDA Formation 11m MEA at 135oC

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 2 4 6 8

Time (weeks)

HE

ED

A

(m)

=0.2

=0.4

=0.5

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

Unknown what the blended system would do

NH NH

Aqueous PZ after 8 weeks at 150oC

0.0 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 20.0-0.50

1.25

2.50

3.75

5.00 7m MEA 2m PZ Tests #11 [modif ied by TEXAS UNIVERSITY OF] 2.5m PZ T=150 t>8wks ECD_1µS

min

1 - Piperazine - 13.100PZ

These peaks are in the time 0 sample

Degraded MEA/PZ after 3 weeks at 135oC

0.0 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 20.0-1.0

5.0

12.0

1 - 7m MEA 2m PZ Tests #7 [modif ied by TEXAS UNIVERSITY OF] 7m MEA 2m PZ t=0 ECD_12 - 7m MEA 2m PZ Tests #4 [modif ied by TEXAS UNIVERSITY OF, 1 peak manually assigned] ECD_1µS

min

21

1 - MEA - 3.525

2 - Piperazine - 12.975

MEA

PZ

Degradation Products

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(T=135oC =0.4 t=4wks)

Amine Concentration (molality)

Remaining Amine Peak (%)

Total Area Retention (%)

PZ 3.5 100 100

DGA 7 93 98

MDEA 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 after 4wks at 135oC

1.0 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 20.0-0.50

1.00

2.00

3.00

4.00

1 - 135 Amine Screening Autosampler #11 [modif ied by TEXAS UNIVERSITY OF] 50wt% MDEA a=0.45 t=0 (2) ECD_12 - 135 Amine Screening Autosampler #12 [modif ied by TEXAS UNIVERSITY OF, normalized] ECD_1µS

min

21

1 - 4.350MDEA

HEEDA after 4wks at 135oC

0.0 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 20.0-0.50

1.25

2.50

3.75

5.50

1 - 135 Amine Screening Autosampler #3 [modif ied by TEXAS UNIVERSITY OF] 3.5m HEEDA a=0.45 t=0 ECD_12 - 135 Amine Screening Autosampler #4 [modif ied by TEXAS UNIVERSITY OF] 3.5m HEEDA a=0.45 T=135 t=4wks ECD_1µS

min

21

1 - HEEDA - 11.942HEEDA

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?