Presentation given by Professor Joe Wood from University of Birmingham on "Studies of Hydrotalcite Clays for CO2 Adsorption " in the Capture Technical Session on Solid Adsorption at the UKCCSRC Biannual Meeting - CCS in the Bigger Picture - held in Cambridge on 2-3 April 2014

1. Prof. Joe Wood
Dr Yu Rong, Dr Jiawei Wang*
School of Chemical Engineering
University of Birmingham, UK
*School of Chemical Engineering and Applied Chemistry,
University of Aston, Birmingham, UK
April 2014
Studies of Hydrotalcite Clays
for CO2 Adsorption

2. STEPCAP Project: Step Change Adsorbents for
Post-Combustion Carbon Capture
 Aim: To develop advanced adsorbents for post-combustion CO2 capture
 Adsorbents should have desirable kinetics, capture capacity, stability and
ability to be regenerated
Performance Parameter Target
Operating
Temperature
: adsorption 40 – 80 °C
: desorption 85 – 160 °C
Cyclic capacity > 3 mmol g-1
Operating pressure ~1015 mbar
CO2 product purity > 95 %
CO2 capture > 80 %
Proposed operating conditions for capture plant
(T. Drage et al, J. Materials Chem 2011)
Post – combustion technology
1/22

3.  Adsorbents
 Manufacturing method and Characterization
 Temperature swing adsorption
 Cyclic operation using fixed bed
 Process modelling
 Sensitivity analysis
 Evaluation of NiMgAl N2 in post-combustion capture
 Optimization
 Conclusions
Overview
2/22

4. Layered double hydroxides (LDH)
 Hydrotalcite-like compounds composed of positively
charged layers with charge balancing anions located in
the interlayer region
 Structure:
 Advantages
High capacity and stability of CO2 adsorption at
elevated temperature
They are inexpensive to prepare and are
environmentally friendly.
Layered double hydroxides (LDH)
 Hydrotalcite-like compounds composed of positively
charged layers with charge balancing anions located in
the interlayer region
 Structure:
 Advantages
High capacity and stability of CO2 adsorption at
elevated temperature
They are inexpensive to prepare and are
environmentally friendly.
Layered double hydroxides
O. Aschenbrenner et al., 2011, Chemical Engineering Research &
Design, 89, 1711 -1721
Layered double hydroxides (LDH)
 Hydrotalcite-like compounds composed of positively charged
layers with charge balancing anions located in the interlayer
region
 Structure:
 Advantages
 Stability of CO2 adsorption at elevated temperature
 Reasonable adsorption rate
 They are inexpensive to prepare and are ‘environmentally
friendly’.
3/22

5. Amine modified layered double hydroxides
Amine adsorbent
Si
O
O
O
NH2
Si
O
O
O
NH
NH2
Si
O
O
O
NH
NH
NH2
3-Aminopropyl
triethoxysilane (N1)
N-(2-Aminoethyl-3-aminopropyl)
trimethoxysilane(N2)
N-3-(Trimethoxysilyl)propyl)
diethylenetriamine (N3)
Different Types of Aminosilanes
JW. Wang et al., 2012, Chemical
Engineering Science, 68, 424-431
4/22

6. Manufacturing method
P. Harlick, and A. Sayari, Ind. Eng. Chem. Res. 2007, 46, 446-458.
 Step 1: Dodecyl sulfate (DS) anion
intercalated LDH was synthesized by
co-precipitation (NiMgAl DS)
 Step 2: NiMgAl DS was exfoliated in
toluene
 Step 3: Single-layer suspension was
reacted with amino group (NiMgAl Nx)
Water-aided exfoliation method
Step 1 Step 2
Step 3
5/22

7. CO2 adsorption capacity of N1, N2 and N3
amine modified HTLCs vs temperature
J. Wang et al, Chem. Eng. Sci. 68 (2012) 424-431

8.  Adding water enhances N2 and N3 amines grafted upon the LDH.
 CO2 uptake is peaked with 0.2-0.4 ml/g water added for NiMgAl N2.
Characterization
Water added (ml/g)CO2uptake
(mmol/g)
Netzsch TG 209 F1
thermogravimetric analyzer
(CO2 uptake)
Flash EA 1112
elemental analyzer
(Amine loading)
Water added (ml/g)
Amineloading
(mmolN/g)
6/22

9. Characterization
Model Parameter 25
o
C 50
o
C 80
o
C
Avrami nA 1.09 0.8 0.78
kA (min-1) 0.029 0.07 0.142
Err (%) 1.18 4.28 4.36
1
st
order
models
kF (min-1) 0.027 0.053 0.11
Err (%) 2.62 8.01 9.17
Kinetics
Adsorbents: NiMgAl N2
 Kinetic models: Avrami and
Lagergen’s pseudo-fist order models;
 Parameters in the kinetic model were
calculated from experimental data
through linear regression.
( )teF
t
qqk
t
q
−=
∂
∂
( )te
1nn
A
t
qqtk
t
q AA
−=
∂
∂ −
1st order:
Avrami:
Time
CO2uptake(mmol/g)
7/22

10. Temperature swing adsorption using NiMgAl N2
Performance Parameter Target NiMgAl N2
Operating
Temperature
: adsorption 40 – 80 °C 65-85 °C
: desorption 85 – 160 °C ~140 °C
Cyclic capacity > 3 mmol g-1 ~ 2.7 mmol g-1
CO2 product purity > 95 % 97-98 %
CO2 capture > 80 % 90-95 %
Properties of
the optimised
adsorbent
(NiMgAl N2)
TSA Cyclic Operation
Step 1: Adsorption is operated at
~80 oC; pressure close to ambient.
Step 2: Operating temperature is
raised to ~ 140 oC.
Step 3: Desorption continues until
meet the recovery target.
Step 4: Cooling returns back to Tad.
1 3
Tde = ~140 oC
Tad = 65-85 oC
2
4
8/22

11. Cyclic operating conditions
 Fixed bed reactor (L/D = 5~9)
 100~200 ml/min CO2/N2 mixture
 10~15% CO2 in feed gas
 80 °C for adsorption
 140 °C for desorption
 ~1 bar pressure
Experimental Procedure
Temp(oC)
CA/C0
Adsorbents- NiMgAl N2
9/22

12. Fixed bed model
 Gas concentration
C = concentration of component (mol/m3)
DL = axial dispersion coefficient (m2/s)
H = heat of adsorption (J/mol)
P = pressure (Pa)
T = temperature (K)
us = superficial velocity (m/s)
µ = viscosity (Pa·s)
ρ = density (kg/m3)
( )
t
q
ε
ρε
z
C
ε
u
z
C
D
t
C isisi
L
i
∂
∂−
−
∂
∂
−
∂
∂
=
∂
∂ 1
2
2
• Temperature of gas phase
• Temperature of solid phase
( ) ∑ 





∂
∂
−+−=
∂
∂
t
q
HρTT
d
h
t
T
Cρ i
issg
p
fs
ss Δ
6
( )
t
T
Cρε
z
T
uCC
z
T
ελ
t
T
CCε s
ss
g
sg,f
g
L
g
v,f
∂
∂
−−
∂
∂
−
∂
∂
=
∂
∂
12
2
( ) ( )wg
int
wi
is TT
d
h
t
q
Hρε −−





∂
∂
−−+ ∑
4
1 Δ
 Energy balance
( ) ( )
3
2
32
2
11
εd
uερ
B
εd
uεμ
A
z
P
p
sg
p
s
−
+
−
=
∂
∂
−
 Pressure drop
T.L.P. Dantas et al., 2011, Chemical
Engineering Journal 169, 11-19
R. Serna-Guerrero, 2010, Chemical
Engineering Journal 161, 173-181
10/22
Assumptions:
The gas phase follows the ideal gas law;
Constant gas flow rate and uniform void
fraction along the column;
The mass and temperature gradients in the
bed radial direction are negligible.

13. Model validation
 A dynamic fixed bed model has
been developed for
 Gas separation simulation
 Process evaluation
 Optimisation
Feed gas:
F0 = 105 ml min-1
CO2 = 14.3 %
 Validated by experimental-simulation fit
Feed gas:
F0 = 150 ml min-1
CO2 = 15 %
Feed gas:
F0 = 200 ml min-1
CO2 = 10 %
11/22

14. • Base case: No CO2 capture
• Downstream CO2 capture using NiMgAl N2 adsorption
Overall: Process Modelling
 Constraints:
• Downstream flue gas properties
• CO2 capture and recovery target
• Operating condition (temperature, pressure and residence time)
 Cycle design:
• Dimension of the column(s)
• Operating conditions
 Performance:
• Power for steam/gas stream fed into column(s)
• Steam for desorption processes
• Cost of fuel (and CO2 emissions) for supplementary energy
• Operating cost per unit of CO2 avoided
12/22

15. Adsorption-desorption cycle
Target
Adsorption:
Capture: 90% of feed CO2
Desorption:
Recovery: 85% of adsorbed CO2
Flue gas
Pressure (bar) 1.4
Temperature (oC) 93.1
Gas flow (mol/s) 200
Composition (mol%, dry)
CO2
14.3
N2
80.7
O2
5
J. Zhang et al., 2008, Energy Conversion
and Management, 49, 346 -356
SEQUESTRATION
13/22

16. Adsorption step
 Constraints (Retention time, pressure)
 Gas-adsorbent interaction
 Breakthrough curve
Cyclic operating
Fixed bed column
- Internal diameter : 3.1 m
- Length : 6.34 m
16.3 ton NiAlMg N2 do=2.5 mm
14/22

17. Steam temperature 120~270
o
C
Steam flow rate 100~300 mol/s
Pressure 1.1~1.4 bar
Desorption time < 60 mins
Desorption step
To recover 80% of adsorbed CO2
Initial point:
Saturated NiMgAl N2 q = 0.82 mol kg-1
Column temperature T = ~95 oC
Bounds set based on industrial
practices and material limitations
Fixed bed
Steam
Steam +CO2Flue gas
Emission
Separation &
compression
Cyclic operating
15/22

18. Mohammad R. M. Abu-Zahra, Carbon Dioxide Capture from Flue Gas, 2009
• Base case: CO2 emissions 100 ton per day
• Desorption operating
• Flue for supplementary energy: coal
Effect of steam temperature
16/22

19. Effect of steam flowrate
• Base case: CO2 emissions 100 ton per day
• Desorption operating
• Constraints: operating time; pressure
17/22

20.  Optimize cyclic operating
• compare performance to base case (no CO2 emissions avoided)
 Objective function: Minimizing energy penalty per unit of CO2
emissions avoided
 Design variables
• operating pressure
• steam flow rate
• steam temperature
 Constraints
• outlet pressure
• operating time
• variable bounds
Optimization
18/22

21. Optimum variables Optimised
case
Bounds
Lower/Upper
Pressure (bar) 1.22 1.1/1.4
Steam Temperature (oC) 180 120/270
Steam Flow rate (mol/s) 157.07 100/300
Objective function
Minimize energy
penalty per unit of
CO2 emissions
avoided
Process optimisation - Results
Optimum results Base case Post-capture
CO2 emissions
from process
coal fired power plant (t/d) 100 0
downstream capture (t/d) - 10
Power demand supplement for blower (MW) - 0.16
Heat demand for desorption (MW) - 1.66
19/22

22. Extra energy demand
Base
case
Post-combustion capture
Absorption
(29 % MEA)
NiMgAl N2
adsorption (opt.)
Energy for process (GJ/t CO2) - 2.35 1.5
CO2 emissions
CO2 emissions from process (t/d) 100 10 10
CO2 from utility system (t/d) - 18.7 11.8
Net reduction in CO2 emissions (t/d) - 71.3 78.2
Operating cost
Extra utility cost
($ based on 100t/d feed)
- 589 375
Cost of CO2 emissions reduction ($/t) - 8.25 4.79
Comparisons
L.M. Romeo, 2008, Applied Thermal Engineering. 28, 1039–1046
19/22

23. Conclusions
 Amine modified LDHs were synthesized via water-aided exfoliation and
grafting route and studied as adsorbents for CO2 at the elevated
temperature.
 The highest adsorption capacity for CO2 was achieved by NiMgAl N2 when
the amount of water added was 0.2-0.4 ml/g.
 Avrami’s kinetic expressions was selected to describe the adsorbent and
adsorbate interactions;
 Non-isothermal model was built to predict the CO2 adsorption process in the
fixed bed;
 The fixed bed model was successfully reproduced all of the breakthrough
curves.
 Objective function is minimizing the energy penalty; Variables focus on the
desorption step (i.e. pressure, inject gas flowrate and temperature)
 Minimal energy penalty for the adsorption using NiMgAl N2 is 1.5 GJ/t CO2
avoid.
20/22

24. Acknowledgements
 EPSRC and E.ON for funding
 Professor Trevor Drage (University of Nottingham, UK)
21/22

25. Thank you.
Questions?