Influence of amine molecular structures

on CO2 absorption

Jiafei Zhang

Cranfield, 21th April 2015

UKCCSRC Biannual Meeting

Material Science for CCS Technical Session

DMAE DMCA

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.

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

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

OHNH2

HO

DMAE

Tertiary

DEAE

Tertiary

DEAB

Tertiary

DMAP

Tertiary

IPAE

Hindered

PZEA

I+II+III

TMHDA

Tertiary

DMHDA

Secondary

MCA

Secondary

DMCA

Tertiary

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

CO

2 lo

adin

g co

map

are

d t

o M

EA

RNHCOORNHRNHCO 322 2

33222 HCORNHOHRNHCO

NH

2H

O

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

CO

2 lo

adin

g co

map

are

d t

o M

EA

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

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

OHNH2

HO

Slow

DIPA

Secondary

DIBA

Secondary

DPA

Secondary

DBA

Secondary

DSBA

Secondary

3+3 4+4 3+3 4+4 4+4 Carbon

Fast

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

higher polarity solvent lower polarity solvent

+ CO2

- CO2

(+ HCO3-)(H2O +)

NH NH2+

lower polarity solvent higher polarity solvent

Switchable-polarity solvents

Heat of absorption

Absorption enthalpy

• Primary > secondary > tertiary amine

• Increase α decrease ΔHab

9

0

20

40

60

80

100

MEA DEA MDEA AMP

ΔH

ab (k

J/m

ol)

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

TCFQpso lsen

HFQrCOr

2

vs teamstrLFQ

ATQlos

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

NH2OH

N

OH

NH2HO

Data Source: Lepaumier, 2010

%

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

Hea

t sta

ble

salts

(%

)

w/o Fe(II/III)

w/ Fe(II/III)

DMCA+MCA+AMP

NH

2H

O

HO

NH

2

Reactive

Fast reaction kinetics

Fast degradation

Less reactive

Slow absorption rate

High chemical stability

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

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

NH2HO

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

14 Ideal structure?

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