The University of Texas at Austin - NTNUena.chemeng.ntnu.no/TrondheimJointAbsorptionSeminar/Xi_Chen...Wetted Wall Column: ... NTNU, Trondheim June 15, 2009 Xi Chen The University of

Screening Amines with Wetted Wall Column: 

Equilibrium and Rate measurements

Joint Seminar on CO2 Absorption Fundamentals

NTNU, Trondheim

June 15, 2009

Xi ChenThe University of Texas at Austin

Outline

• Introduction• Research needs• Structure of tested Amine Solvents

• Apparatus• Wetted Wall Column (WWC)

• Results:• Equilibrium: CO2 solubility, CO2 capacity, Heat of absorption

• Absorption/Desorption Rates• Conclusions• Future Work

• Amines screening & reaction kinetics studies in the past: Low amine concentration (< 3 M)

Zero or very lean loading

Narrow temperature range (25~60 °C) 

• Typical industrial conditions for CO2 capture

• Research need for equilibrium/kinetics of  CO2‐loaded & concentrated amine solutions at broad temp. range  – DGA, MDEA(Pacheco 2000); PZ, MDEA (Bishnoi 2000); DGA (Al‐juaied 2004); K2CO3/PZ (Cullinane 2006); MEA, PZ, PZ/MEA (Ross Dugas, 2008)

[Amine](M)

Temp. (°C)

CO2 Partial Pressure  (Pa)

CO2 loading

Absorber  3 ~ 6 40 ~ 60 Lean  100 ~ 1000 0.05 ~ 0.3 Rich  1000 ~10000  0.4 ~ 0.8 

Stripper  3 ~ 6 80 ~ 120Lean  10

2~10

4 0.05 ~ 0.3

Rich  104~10

5 0.4 ~ 0.8

Name Chemical Structure

N‐(2‐hydroxyethyl)piperazine(HEP)

1‐(2‐Aminoethyl)piperazine(AEP)

2‐amino‐2‐methyl‐1‐propanol(AMP)

2‐piperidineethanol(2‐PE)

Ethylenediamine (EDA)

Methyldiethanolamine (MDEA)/Piperazine (PZ)

N

NH

OH

OH

NH2

CH3

CH3

NH

OH

N

NH

NH2

NH2

NH2

NHNHOH

NOH

CH3

WWC

'2

*

0,

0

11][

111 22

ggT

CO

PRODll

CO

gG kkCOP

kEkH

kK+=

∂∂

++=

2

2

22

2

222

][

)(

2

,,

'

,,'

CO

bCO

bCOiCO

COg

bCOiCOgCO

HAmkD

PPN

k

PPkN

=−

=⇒

−=

-6

-4

-2

0

2

4

6

-10 -5 0 5 10

Flux

( ×10

11m

ol/s

·m2 )

Driving Force (kPa)

Equlibrium point

Pseudo-First Order Assumption

CO2 Solubility for 7.7m HEP (3.9M)2//ln ααα ⋅+⋅+⋅++= eTdcTbaP

0.5kPa

5kPa

Capacity=0.68mol CO2/kg (H2O+HEP)

CO2 Solubility for 6m AEP (3.4 M)

)/1()(ln

TdPdRHabs −=Δ

CO2 Solubility for 4.8m AMP (3.4M)

CO2 Solubility for 8m 2‐PE (4 M)

CO2 Solubility for 12m EDA (7 M)

PZ@100 °C

PZ@40 °C (Hilliard & Dugas)

CO2 Solubility for 7m MDEA/2m PZ 

CO2 Capacity for 5kPa rich Solution

7m MEA

6m AEP 8m PZ

8m 2‐PE

4.8m AMP

12m EDA

7.7m HEP

Enthalpy of CO2 Absorption

1E-07

1E-06

1E-05

10 100 1000 10000

P*CO2 @ 40C (Pa)

k g' (

mol

/s. Pa

. m2 )

Filled Points – 2, 5, 8, 12 m PZEmpty Points – 7, 9, 11, 13 m MEA

(by Ross Dugas)

100˚C80˚C60˚C40˚C

2

22' ][

CO

COg H

DAmkk =

Absorption/Desorption rates for 7.7m HEP

6m AEP 

4.8m AMP 

8m 2‐PE 

12m EDA 

7m MDEA/2m PZ 

8m PZ

7m MEA

7.7m HEP

6m AEP

8m 2‐PE

12m EDA

4.8m AMP

7m MDEA/2 PZ

Viscosity* of Amine solutions

*: Measured with Physica MCR 300 at shear rate= 100-1000 s-1.

Conclusions

Amine Conc.(m)

CO2 Capacity* kg’ @PCO2 =5kPa ∆Habs@PCO2=1.5kPa

(mol/kg (water+amine))

(×107mol/s·Pa·m2) (kJ/mol)

MDEA/PZ 7/2 0.71 5.7 67

PZ 8 0.79 5.3 70

MEA 7 0.47 3.1 82

HEP 7.7 0.68 2.9 69

AEP 6 0.66 2.3 72

2-PE 8 1.23 2 73

AMP 4.8 0.96 1.7 73

EDA 12 0.78 1.6 80

*: for 5 kPa rich solution @PCO2 = 0.5 kPa & 40 °C

Future work• Other amine solvents

– DGA®, Morpholine, 5‐amino‐1‐pentanol

– Hindered amine/promoter: AMP/ Carbonic anhydrase, 2‐(tert‐Butylamino)ethanol (TBE)/ Carbonic anhydrase, TBE/PZ

– Amino acid salt: Taurine, glycine, 2‐methyl‐analine

• Effects of Amine Concentration

• Measurements of Diffusion Coefficients– Diffusion cell

– HPLC

Acknowledgement

• Luminant Carbon Management Program

• Industrial Associates Program for CO2 Capture by Aqueous Absorption

• Ross Dugas, Shan Zhou, Fred Closmann

Xi [email protected]

Screening Amines with Wetted Wall Column: 

Equilibrium and Rate measurements