Jiafei Zhang (Imperial College London) - Influence of Amine Molecular Structures on CO2 Absorption - UKCCSRC Cranfield Biannual 21-22 April 2015

1. Influence of amine molecular structures
on CO2 absorption
Jiafei Zhang
Cranfield, 21th April 2015
UKCCSRC Biannual Meeting
Material Science for CCS Technical Session
DMAEDMCA

2. Outline
Introduction
• Solvents selection strategy
• Alternative amine solvents
Structural impact
• CO2 capacity
• Absorption rate
• Regenerability
• Heat of absorption
• Degradation
• Viscosity
• Packing wettability
Summary
2
Absorption Desorption
Image Source: Siemens
Amine solvents for CO2 capture
Influence of molecular structure
Challenges?
Δα
ΔH
Deg.

3. Less negative effects Volatility, toxicity, etc.
Easy to operate Viscosity, wettability, etc.
Strategy for solvent selection
3
Less solvent circulation Tertiary, hindered, polyamines
Smaller Column size Primary, secondary amines
Lower heat of reaction Tertiary amines
Less solvent loss Tertiary, hindered amines
Environmental impact
Technical feasibility
Solvent degradation
Energy consumption
Reaction kinetics
CO2 capacity

4. Amine solvents
Well studied solvents
• MEA, DEA, MDEA
• AMP, PZ
Alternative alkanolamines
• DMAE (IC, UK)
• DEAE (NTNU, NO)
• DEAB (Regina, CA)
• DMAP (RITE, JP)
• IPAE (RITE, JP)
Alternative Polyamines/alkanylamines
• PZEA
• TMHDA (IFP, FR)
• DMHDA (Twente, NL)
• MCA (Dortmund, DE)
• DMCA (Dortmund, DE)
4
MEA
Primary
DEA
Secondary
MDEA
Tertiary
AMP
Hindered
PZ
Diamine
HO
NH2
OH
N
OH
NH2
HO
DMAE
Tertiary
DEAE
Tertiary
DEAB
Tertiary
DMAP
Tertiary
IPAE
Hindered
PZEA
I+II+III
TMHDA
Tertiary
DMHDA
Secondary
MCA
Secondary
DMCA
Tertiary

5. CO2 capacity
General knowledge (according to mechanism)
• Primary/secondary amine: α ≈ 0.5
• Tertiary amine: α ≈ 1
• Impact: sterical hindrance
• Compare: MEA, MDEA, AMP
Structure influence
• Branched structure
• Potential to increase
• α-Carbon branch
• Polyamines
5
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
MEA 3AP A2P 2AB DBA DIBA DSBA HA DPA CA MCA
CO2loadingcomaparedtoMEA

 RNHCOORNHRNHCO 322 2

 33222 HCORNHOHRNHCO
NH2
HO

6. 0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
CO2loadingcomaparedtoMEA
CO2 capacity
General knowledge (according to mechanism)
• Primary/secondary amine: α ≈ 0.5
• Tertiary amine: α ≈ 1
• Impact: sterical hindrance
• Compare: MEA, MDEA, AMP
Structure influence
• Branched structure
• Potential to increase
• α-Carbon branch
• Polyamines
• e.g. BDA
• TETA
• Increase α
• Decrease per -NHx
6

 RNHCOORNHRNHCO 322 2

 33222 HCORNHOHRNHCO
NH2-(CH2)n-NH2
n= 2 3 4 6 7
NH2-(C2H4-NH)n-H
2 3 4
Data Source: Singh, 2009

7. Absorption rate
In general
• Primary/secondary amine: fast
• Tertiary amine: slow
• Hindered amine: slow (depend)
Structure influence
• Branched structure
• Potential to increase
• β-Carbon branch
7
MEA
Primary
DEA
Secondary
AMP
Hindered
MDEA
Tertiary
HO
NH2
OH
N
OH
NH2
HO
Slow
DIPA
Secondary
DIBA
Secondary
DPA
Secondary
DBA
Secondary
DSBA
Secondary
3+3 4+4 3+3 4+4 4+4Carbon
Fast

8. Regenerability
Generally
• Primary/secondary amine: low
• Tertiary/hindered amine: high
Alkanolamine vs. Alkylamine
120+ oC 80-90 oC
MEA (55%) MCA (90%)
MDEA (90+%) DMCA (95+%)
Liquid-liquid phase separation 
8
Before
regeneration
During
regeneration
After
regeneration
Hydrophobic Hydrophilic
higherpolaritysolvent lowerpolaritysolvent
+ CO2
- CO2
(+ HCO3
-)(H2O +)
NH NH2
+
lower polarity solvent higher polarity solvent
Switchable-polarity solvents

9. Heat of absorption
Absorption enthalpy
• Primary > secondary > tertiary amine
• Increase α  decrease ΔHab
9
0
20
40
60
80
100
MEA DEA MDEA AMP
ΔHab(kJ/mol)
0.1
0.3
0.5
α =
30%wt amine solutions
Qsen Qr Qstr Qlos Qsum
MEA 0.9 1.8 1.1 0.2 4.0
DMAE+
PZ
0.6 1.4 1.0 0.2 3.2
Target 0.5 1.2 0.6 0.1 2.4
TCFQ pso lsen

HFQ rCOr

2
vstea mstr
LFQ 
ATQ los
 

10. 0 5 10 15 20 25
MEA
DEA
MDEA
AMP
DMP
TMEDA
TMPDA
Oxidative
Thermal
Degradation
Generally
• Primary/secondary amine: reactive
• Tertiary/hindered amine: stable
IFP (Lepaumier)
II > I > III > hindered
Rochelle
• Cyclic amine:
• e.g. PZ
• Stable (<180oC)
10
HO
NH2
OH
N
OH
NH2
HO
Data Source: Lepaumier, 2010
%

11. Degradation
Generally
• Primary/secondary amine: reactive
• Tertiary/hindered amine: stable
IFP (Lepaumier)
II > I > III > hindered
Relations between
• Chemical stability
• Reaction kinetics
Solvent losses
• Vaporisation  Environment
• Degradation  Irreversible
11
AMP Blend DMCA MEA MCA
0
1
2
3
4
5
6
Heatstablesalts(%)
w/o Fe(II/III)
w/ Fe(II/III)
DMCA+MCA+AMP
NH2
HO
HO
NH2
Reactive
Fast reaction kinetics
Fast degradation
Less reactive
Slow absorption rate
High chemical stability

12. Viscosity
Influence of η
• Substituent: chain length
• Linear 
• Branched/cyclic 
• e.g.
• T 
• w 
• α 
12
Liquid
Inlet
Liquid
Inlet
Electrical energy
Pressure drop
Mass transfer

13. Wettability
Various packing materials (Alkanolamine vs. Alkylamine)
• Surface tension (γ)
• Contact angle
13
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0.062 0.066 0.07 0.074
cos(θ)
γ / (N/m)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.033 0.035 0.037
cos(θ)
γ / (N/m)
Steel
Aluminium
Brass
Copper
H-PVC
PE-HD
PP-H
PTFE
(0 ≤ α ≤ 0.5)
MEA MCA, 5M
More wettable
NH2
HO

14. Summary
Primary/Secondary amine:
• Fast reaction kinetics, high degradability, high absorption enthalpy
• Sterical hindrance: slower absorption rate & degradation, enhance CO2 loading
• Secondary amine has a high potential to achieve both rapid absorption rate and
high CO2 capacity (with minor sterically hindered effect)
Tertiary amine:
• Slow reaction kinetics, low degradability, low absorption enthalpy
Alkylamine with its
• switchable polarity  liquid-liquid phase separation behaviour upon heating
Structural effects of substituents
• hindered amine and cyclic amine (ring structure) typically exhibit a good
chemical stability against thermal and oxidative degradations
• a branch at α-carbon position  enhance CO2 capacity
• a branch at β-carbon position  enhance absorption rate
14Ideal structure?

15. Acknowledgement
Thank you for your attention!
15
Thanks:
Prof. Martin Trusler, Imperial
Dr. Paul Fennell, Imperial
Prof. David Agar, TU Dortmund
Dr. Frank Geuzebroek, Shell
Dr. D.W.F. Brilman Univ. Twente
Financial support
Shell
Global
Solutions