1
Thermal measurements:
Heat of absorption of CO2 and
Vapour-Liquid Equilibria in
alkanolamine-water solutions
Inna Kim and Hallvard F. Svendsen
Norwegian University of Science and Technology (NTNU)
Trondheim, NORWAY
Research Review Meeting, Austin, 10-11/I-2008
2
Outline
• Heat of absorption
– Background
– Experimental set-up
– Results
• Vapour-Liquid Equilibria
– Experimental set-up
– Results
• Summary
• Further work
Research Review Meeting, Austin, 10-11/I-2008
3
Heat of
absorption,
∆Habs
Research Review Meeting, Austin, 10-11/I-2008
4
Background
Integral vs differential ∆Habs
•
Integrated over some loading
interval (direct measurement)
•
Calculated using Gibbs-Helmholz
equation:
éd ln ( f )ù
DHs
CO2 ú
ê
ê
ú =
R
ê d (1/ T ) ú
ë
ûxCO2
fCO2 – fugacity of CO2
xCO2 – mole fraction of CO2
Isothermal flow calorimeter

Assumption:

Disadvantage: differentiation
f CO2 = PCO2
[www.ltp-oldenburg.de]
Research Review Meeting, Austin, 10-11/I-2008
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Background
Differential ∆Habs data from solubility
measurements1
a
VLE data: ln(pCO2) vs 1/T:
a) Fitted with a line,
b) Fitted with a 2nd order polynomial
b
1
[Hoff K.A., Mejdell T., Svendsen H.., 2005]
Research Review Meeting, Austin, 10-11/I-2008
6
Background
Impact of temperature and loading
on ∆Habs2
“The increase in heat of
absorption of up to 20% from the
absorber to the stripper
temperature may cause a deficient
duty calculation with the reboiler if
a constant heat of absorption at
the lower value is used”2
Temperature profile for the Dome 5
North Caroline plant 2
2 [Jerry
A. Bullin et al., Bryan Research & Engineering Inc. Bryan, TX, GPA 2007]
Research Review Meeting, Austin, 10-11/I-2008
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• Experimental set-up
P
P
4
W
N
T
P
P
P-129
CO2
Control
device
CPA122
(ChemiSens AB, Sweden)
F
CO2
to air
P
P
(-1~15 bar)
(1~40 bar)
co2
2a
1
to air
P
(-1~1,5 bar)
2b
Vacuum
Thermostat
3
P
T
T
CO2
Control device
1
- Calorimeter
2a,2b - CO2 storage cylinders
3
- Vacuum pump
4
- Feed bottle
Research Review Meeting, Austin, 10-11/I-2008
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120
14
100
12
80
10
60
8
40
6
20
4
0
2
-20
0
-40
0
5000
10000
15000
20000
25000
30000
35000
40000
CO2 flow*10, [L]; Reactor pressure, [bar]
Heat Flow, [W]; Reactor temperature, [ oC]
Semi-differential ∆Habs
(an example of on-line data)
REACTOR_TEMP
REACTOR_HB_POWER
LIN_IN_1A
PRESSURE_A
-2
45000
Tim e, [sec]
Research Review Meeting, Austin, 10-11/I-2008
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Results
30 wt% Monoethanolamine (MEA)
180
40ºC
80ºC
120ºC
160
∆Habs , [kJ/mol-CO2]
140
[Jou et al., 1994]
[Lee et al., 1974]
120
100
80
60
40
20
0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
α , [mol-CO2/mol-Am]
Research Review Meeting, Austin, 10-11/I-2008
10
Results
30 wt% N-methyldiethanolamine
(MDEA)
350
40ºC
80ºC
300
120ºC
∆Habs , [kJ/mol-CO2]
[Jou et al., 1994]
250
35%, 76.7º [Oscarson et al., 2000]
40oC, 5MPa [Mathonat, 1995]
80oC, 5MPa [Mathonat, 1995]
200
120oC, 5MPa [Mathonat, 1995]
150
100
50
0
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
α , [mol-CO2/mol-Am]
Research Review Meeting, Austin, 10-11/I-2008
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Results
40 and 50 wt% MDEA
140
40 w t% MDEA, 40ºC
40 w t% MDEA, 60ºC
50 w t% MDEA, 40ºC
50 w t% MDEA, 75ºC
40%, 60º,1.561bar [Merkley et al., 1986]
40%, 60º,11.21bar [Merkley et al., 1986]
35%, 76.7ºC, 6.90 Mpa (0.93 Mpa) [Oscarson et al., 2000]
50%, 76.7ºC, 6.90 Mpa (0.86 Mpa) [Oscarson et al., 2000]
35%, 76.7ºC, 3.45 Mpa (0.70 Mpa) [Oscarson et al., 2000]
50%, 76.7ºC, 3.45 Mpa (0.70 Mpa) [Oscarson et al., 2000]
∆Habs , [kJ/mol-CO2]
120
100
80
60
40
20
0
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
α , [mol-CO2/mol-Am]
Research Review Meeting, Austin, 10-11/I-2008
12
Results
3M Diethylenetriamine (DETA)
160
40ºC
80ºC
120ºC
140
∆Habs, [kJ/mol-CO2]
120
100
80
60
40
20
0
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
α, [mol-CO2/mol-Am]
Research Review Meeting, Austin, 10-11/I-2008
13
Results
3M DETA + 1.5M H2SO4
200
180
40ºC
80ºC
∆Habs , [kJ/mol-CO2]
160
120ºC
140
120
100
80
60
40
20
0
0,0
0,2
0,4
0,6
0,8
1,0
1,2
α , [mol-CO2/mol-Am]
Research Review Meeting, Austin, 10-11/I-2008
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Results
∆Habs with different amines at 40oC
30 w t % MEA
30 w t% MDEA
32 w t% DEEA
3M DETA
3M DETA - 1.5M H2SO4
2M Piperazine
6m K - 1.2m Pz
120
∆Habs , [kJ/mol-CO2]
100
80
60
40
20
0
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
α , [mol-CO2/mol-Am]
Research Review Meeting, Austin, 10-11/I-2008
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Results
∆Habs with different amines at 120oC
200
30 w t % MEA
30 w t% MDEA
32 w t% DEEA
3M DETA
3M DETA - 1.5M H2SO4
2M Piperazine
6m K - 1.2m Pz
180
∆Habs , [kJ/mol-CO2]
160
140
120
100
80
60
40
20
0
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
α , [mol-CO2/mol-Am]
Research Review Meeting, Austin, 10-11/I-2008
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VLE
measurements
Research Review Meeting, Austin, 10-11/I-2008
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• Experimental set-up
1.
2.
3.
4.
5.
6.
Ebulliometer
Pressure controller
Thermocouples
Cold trap
Buffer vessel
Vacuum pump
Research Review Meeting, Austin, 10-11/I-2008
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Validation of the experiments:
vapour pressure of pure water
1500
1200
Osborne N.S. et al., 1934
Ptot/ mbar
Stimson H.F., 1969
Nov. 29, 2006 (EB1)
900
Nov. 29, 2006 (EB2)
Dec. 05, 2006(EB1)
Dec. 05, 2006(EB2)
600
Jan.15, 2007 (EB1)
Mar 07, 2007 (EB1)
300
Antoine eq'n
Points from different dates
0
20
40
60
80
100
T/ o C
Research Review Meeting, Austin, 10-11/I-2008
19
Results
MEA (1) - H2O (2)
0.07
0.06
y1, [mol/mol]
0.05
40ºC
60ºC
80ºC
100ºC
60º [Nath et al., 1983]
78º [Nath et al., 1983]
91,7º [Nath et al., 1983]
0.04
0.03
0.02
0.01
0.00
0.00
0.10
0.20
0.30
0.40
0.50
0.60
x 1 , [mol/mol]
Research Review Meeting, Austin, 10-11/I-2008
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Results
P-xy diagram: MEA(1)-H2O(2)
o
o
P-x-y data for MEA(1) - H2O(2): 40 C
P-x-y data for MEA(1) - H2O(2): 60 C
80
200
180
70
160
Total pressure, [mbar]
Total pressure, [mbar]
60
50
40
30
140
○ this work
120
100
(40, 60,80,100oC)
80
* Nath et al., 1983
60
20
(60, 78, 92oC)
40
10
0
— Wilson equation
20
0
0.1
0.2
0.3
0.4
0.5
x 1, y 1
0.6
0.7
0.8
0.9
0
1
0
0.1
0.2
o
0.3
0.4
0.5
x 1, y 1
0.6
0.7
0.8
0.9
1
o
P-x-y data for MEA(1) - H2O(2): 80 C
P-x-y data for MEA(1) - H2O(2): 100 C
500
Wilson parameters
1200
450
1000
350
Total pressure, [mbar]
Total pressure, [mbar]
400
300
250
200
150
100
40-60 º
1629.5
-4668.5
80 º
-771.6
4214.4
100 º
-459.4
3427.2
800
600
400
200
50
0
0
0.1
0.2
0.3
0.4
0.5
x 1, y 1
0.6
0.7
0.8
0.9
1
0
0
0.1
0.2
0.3
0.4
0.5
x 1, y 1
0.6
0.7
0.8
0.9
1
Research Review Meeting, Austin, 10-11/I-2008
21
Results
Activity coefficients: MEA(1)-H2O(2)
o
o
Activity coefficients for MEA(1) - H2O(2): 60 C
1
0.9
0.9
0.8
0.8
0.7
0.7
0.6
0.6


Activity coefficients for MEA(1) - H2O(2): 40 C
1
0.5
0.5
0.4
0.4
0.3
0.3
○ this work
0.2
0
0.1
0.2
0.3
0.4
0.5
x1
0.6
0.7
0.8
0.9
0.2
1
0
0.1
0.2
0.3
0.4
0.5
x1
0.6
0.7
0.8
0.9
1
(40, 60,80,100oC)
* Nath et al., 1983
o
1.3
1.2
1.2
1.1
1.1
1
1
0.9
0.9
0.8
0.8


Activity coefficients for MEA(1) - H2O(2): 100 C
1.3
0.7
0.7
0.6
0.6
0.5
0.5
0.4
0.4
0
0.1
0.2
0.3
0.4
0.5
x1
0.6
0.7
0.8
(60, 78, 92oC)
o
Activity coefficients for MEA(1) - H2O(2): 80 C
0.9
1
0
0.1
0.2
0.3
0.4
0.5
x1
0.6
0.7
0.8
— Wilson equation
0.9
1
Research Review Meeting, Austin, 10-11/I-2008
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Results
MDEA (1) - H2O (2)
0.0016
y1, [mol/mol]
40ºC
0.0014
60ºC
80ºC
0.0012
100ºC
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
x 1, [mol/mol]
Research Review Meeting, Austin, 10-11/I-2008
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Results
P-xy diagram: MDEA(1)-H2O(2)
o
o
P-x-y data for MDEA(1) - H2O(2): 40 C
P-x-y data for MDEA(1) - H2O(2): 60 C
75
200
190
70
180
Total pressure, [mbar]
Total pressure, [mbar]
65
60
55
50
170
160
150
○ this work
140
(40, 60, 80, 100oC)
130
45
— Wilson equation
120
40
35
110
0
0.05
0.1
0.15
0.2
x 1, y 1
0.25
0.3
0.35
100
0.4
0
0.05
0.1
0.15
0.2
x 1, y 1
0.25
0.3
0.35
0.4
Wilson parameters
o
o
P-x-y data for MDEA(1) - H2O(2): 80 C
P-x-y data for MDEA(1) - H2O(2): 100 C
500
1050
1000
950
Total pressure, [mbar]
Total pressure, [mbar]
450
400
350
300
40ºC
-1847.2
1849.5
60ºC
-29.1
1738.4
80ºC
-1341.4
2630.8
100ºC
137.2
2528.5
900
850
800
750
700
650
600
250
0
0.05
0.1
0.15
0.2
x 1, y 1
0.25
0.3
0.35
0.4
550
0
0.05
0.1
0.15
0.2
x 1, y 1
0.25
0.3
0.35
0.4
Research Review Meeting, Austin, 10-11/I-2008
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Results
Activity coefficients: MDEA(1)-H2O(2)
o
o
Activity coefficients for MDEA(1) - H2O(2): 40 C
Activity coefficients for MDEA(1) - H2O(2): 60 C
1
1.3
0.9
1.2
1.1
0.8
1
0.7
0.6


0.9
0.8
0.5
0.7
0.4
0.6
0.3
0.2
0.5
0
0.05
0.1
0.15
0.2
x1
0.25
0.3
0.35
0.4
0.4
○ this work
0
0.05
0.1
0.15
0.2
x1
0.25
0.3
0.35
0.4
(40, 60, 80, 100oC)
— Wilson equation
o
o
Activity coefficients for MDEA(1) - H2O(2): 80 C
Activity coefficients for MDEA(1) - H2O(2): 100 C
1.1
2
1
1.8
0.9
1.6
0.8


1.4
0.7
1.2
0.6
1
0.5
0.8
0.4
0
0.05
0.1
0.15
0.2
x1
0.25
0.3
0.35
0.4
0
0.05
0.1
0.15
0.2
x1
0.25
0.3
0.35
0.4
Research Review Meeting, Austin, 10-11/I-2008
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Results
Ternary mixture:
MEA(1)-MDEA(2)-H2O(3)
1000
10% MEA - 30% MDEA
900
20% MEA - 20% MDEA
30% MEA - 10% MDEA
800
700
P/mbar
600
500
400
300
200
100
0
20
30
40
50
60
70
80
90
100
110
T/ o C
Research Review Meeting, Austin, 10-11/I-2008
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Results
Activity coefficients:
MEA(1)-MDEA(2)-H2O(3)
o
10wt% MEA - 30 wt% MDEA at 40, 60, 80 and 100 C
o
20wt% MEA - 20 wt% MDEA at 40, 60, 80 and 100 C
2
2.5
1.8
2
1.6
1.4
1.5


1.2
1
1
0.8
0.6
0.5
0.4
0.2
0.04 0.0405 0.041 0.0415 0.042 0.0425 0.043 0.0435 0.044 0.0445 0.045
x MEA
0
0.08
0.081
0.082
0.083
0.084
x MEA
0.085
0.086
0.087
0.088
o
30wt% MEA - 10 wt% MDEA at 40, 60, 80 and 100 C
1.3
MEA (exp)
1.2
MDEA (exp)
1.1
H2O (exp)
1

0.9
0.8
0.7
0.6
0.5
0.4
0.116
0.118
0.12
0.122
0.124
x MEA
0.126
0.128
0.13
Research Review Meeting, Austin, 10-11/I-2008
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Results
Thermodynamic consistency test
• Point to point test3
• Area test3
gi =
applying Gibbs-Duhem equation 4 :
0.008
1.000
0.800
yi Ptot
Fi
xi Pi sat
0.006
x1
0.600
0.004
d ln g1
d ln g 2
V E dP
+ x2
- e = 0; e =
dx1
dx1
RT dx1
2.0
0.002
0.200
0.000
0
50
-0.200
100
Residuals
40ºC
60ºC
80ºC
100ºC
1.5
0.000
0
50
100
1.0
-0.002
-0.400
0.5
-0.004
ln(γ 1/γ 2)
Residuals
0.400
-0.600
-0.006
-0.800
0.0
-0.5
-1.000
-0.008
∆P
∆y
-1.0
-1.5
-2.0
3[Van
Ness H.C. et al, Am.Inst.Chem. Eng.J.19 (1973) 238-244]
4 [Van
Ness H.C., Pure & Appl. Chem., Vol. 67, No.6, pp. 859-872, 1995]
0.0
0.2
0.4
0.6
0.8
1.0
x1
Research Review Meeting, Austin, 10-11/I-2008
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Summary
• A method proposed for measuring the enthalpy of absorption
differential in temperature and semi-differential in loading
• Amine concentration and experimental pressure found to have
less effect on the heat of absorption data (within the
experimental range of this work) than temperature and loading
• The ebulliometer enables very accurate determination of the
vapour-liquid equilibrium of pure components and mixtures
• Experimental activity coefficients of amines and water can be
calculated
• The accuracy of the results obtained is limited only by the
purity of the substances used and by the precision of the
analytical methods used for the sample
Research Review Meeting, Austin, 10-11/I-2008
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Further work
• Fitting the heat of absorption data using K-values and
temperature dependent activity coefficients
DH j =
o
DH j
+ DH
ex
j
æ¶ ln K j ö
¶ ln(P g i ) ö
2 æ
÷
ç
÷
ç
= RT ç
= RT ç
÷
÷
÷
çè ¶ T øP
è ¶T ÷
øP
2
• Fitting VLE data with UNIFAC equation of state
• Improvement of the thermodynamic models of the acid gasalkanolamine-water systems using the data measured in this
work, along with the other experimental data taken from the
literature
Research Review Meeting, Austin, 10-11/I-2008
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THANK YOU
for your attention!
Research Review Meeting, Austin, 10-11/I-2008