Presentation given by Professor Colin Snape from University of Nottingham on "Performance Enhanced Activated Spherical Carbon Adsorbents for CO2 Capture" 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. Performance Enhanced Activated
Spherical Carbon Adsorbents for CO2
Capture
 Resin-derived carbon beads for both pre- and post-combustion
capture
 Joint EPSRC UK-NSF China projects
Colin Snape1. Jingjing Liu1, Chenggong Sun1, Hao Liu1,
Nannan Sun1, Kaixi Li2, Wei Wei3 and Yuhan Sun
1University of Nottingham, Faculty of Engineering, Nottingham, NG7
2RD, UK
2Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan,
Shanxi, 030001, China
3Shanghai Advanced Research Institute, Chinese Academy of Sciences,
Shanghai, 201203, China

2. Potential CO2 Adsorbents
MOF
COF
R. Xiong, et al., Chem. Eng. Sci., 58 (2003) 4377.

3. Process Costs, Process Efficiency and
Engineering Feasibility Requirements
AC Beads: A potential
option

4. 0
0.5
1
1.5
2
2.5
20 30 40 50 60 70 80 90 100
Temperature
o
C
CO2uptake(mmolg-1
)
Silica-PEI
Templated MF resin
Sugar-carbazole carbon
UF resin carbon
(ii)
(iv)
(iii)
(v)
Silica-PEI and Carbon Adsorbents ca. 2009
(i) Drage T.C. Blackman J.M. Pevida C. and Snape C.E. 2009. Energy & Fuels, 23, 2790–2796.
(ii) Drage T.C., Arenillas A., Smith K.M. And Snape C.E. Micropor. & Mesopor. Mats. 2008, 116, 504-512.
(iii) Drage T.C., Pevida C. and Snape C.E. Carbon, 2008, 46, 1464-1474.
(iv) Drage T.C., Arenillas A., Smith K.M., Pevida C., Piippo S. and Snape C.E., 2007. Fuel 86, 22-31.
(v) Arenillas A., Drage T.C., Smith K. and Snape C.E., 2005. J. Anal. and Appl. Pyrolysis, 74, 298-306.

5. Synthesis of new activated carbon beads
from resin precursors for CO2 capture
Post treatments include high temperature NH3 activation
and low temperature nitric acid oxidation.

6. Pre-combustion Capture: Project Aim
To understand the behaviour of resin-derived spherical ACs that can
effectively capture high levels of CO2 in IGCC and to develop models to
assess their impact on the flexibility and operability of IGCC processes.
Objectives:
• To prepare a range of AC beads with high bulk densities and strengths.
• To relate the CO2 uptakes of the ACs under realistic process conditions to
their porosity and surface functionality.
• To understand from modelling how the porosity and surface functionality of
the resin-derived carbons, can be tailored to give effective CO2 adsorption
profiles for pre-combustion capture.
• To model how the ability of the ACs to adsorb high levels of CO2 will
improve the performance of IGCC power plants by modelling PSA with
variable extents of CO2 capture.

7. High Pressure CO2 Adsorption – phenolic and other
resin-derived ACs
By and large, on a mass basis, high pressure CO2 adsorption capacities
correlate with the surface area or micro-porosity of the carbons.
However, the significantly higher adsorption capacity obtained for some
carbons, well above the trend line, highlighting importance of surface
chemistry.
Those possessing lower
surface areas demonstrate
better CO2 capture
performance on a volumetric
basis.
T.C. Drage, J.M. Blackman, C. Pevida, and C.E.
Snape, Evaluation of activated carbon
adsorbents for CO2 capture in gasification,
Energy & Fuels, 2009, 23(5), 3790-2796.

8. Focus of this presentation
 High pressure (IGCC) – better understanding of oxidative
nitric acid and ammonia post-treatments.
 Low pressure, 0.15 bar (coal power plant) – effectiveness
of KOH post-treatment (not strictly activation).
 Given extensive literature on N-enrichment (1-3) and very
few reports of KOH activation (4), it was decided to use a
N-free carbon to delineate the effect of K increasing
electrostatic interactions.
 “What you see is what you should get in pilot units with
the carbon beads”.
1. M.D. Hornbostel, J. Bao, J., G. Krishnan, et al., J. Carruthers, D., et al., 2013. Carbon, 56, 77-85.
2, W. Xing, C. Liu,Zi. Zhou et al. Energy Environ. Sci., 2012, 5, 7323
3. M.S. Shafeeyan, W.M.A. Wan Daud, A.Houshmand, A. Shamiri,J. Anal & Appl.Pyroly. 2010, 89 , 43–151
4. Y. Zhao, X, Liu, K.Xi. Yao, Chem. Mater. 2012, 24, 4725−4734

9. High Pressure CO2 Adsorption
isotherms of Carbons Beads
- performance not affected by moisture
over multiple cycles
Effect of Inherent Moisture
High pressure CO2 adsorption isotherms of sample A when tested dry and wet

10. Recent Work on Activated Carbon Beads
Mechanism
Low Pressure High Pressure
C. Zhang, W. Song, G. Sun, L.J. Xie, J.
Wang, K. Li, C.G. Sun, H. Liu, C.E.
Snape and TC Drage, CO2 capture with
activated carbon grafted by nitrogenous
functional groups,, Energy & Fuels,
2013, doi: 10.1021/ef400499k.
N. Sun; C, Sun; H. Liu; T. Drage; C.E.
Snape; K. Li and W. Wei, Synthesis,
characterization and evaluation of
activated carbon beads for CO2 capture,
Fuel, 2013, 113, 854–862

11. Surface modification
AC
HNO3 oxidation
oxAC
NH3 treatment
300 oC
600 oC
800 oC
oxAC-300NH3
oxAC-600NH3
oxAC-800NH3
oxAC-800N2
800 oC N2 treatment
Why HNO3 and NH3?
• Proved to be effective to enhance CO2 uptake
• Well established and easy to scale up
For AC Beads :
• Feasibility of enhancing uptake?
• Influence on desirable spherical forms?
• Impact on physicochemical properties?

12. Bulk and Surface Elemental Compositions
Elemental Analysis XPS
C H N O N/C O/C C N O N/C O/C
AC 93.6 0.52 0.00 5.8 0.000 0.062 - - - - -
oxAC 68.6 1.91 1.85 27.7 0.027 0.404 87.0 1.74 11.3 0.023 0.173
oxAC-300NH3 74.7 2.11 1.44 21.8 0.019 0.291 90.0 2.03 8.3 0.026 0.124
oxAC-600NH3 82.5 1.34 1.13 15.0 0.014 0.181 91.8 1.64 6.5 0.021 0.095
oxAC-800NH3 83.0 0.87 1.37 14.7 0.017 0.178 91. 3 1.98 6.8 0.025 0.099
oxAC-800N2 88.8 0.9 0.42 9.9 0.005 0.112 - - - - -
 Oxygen and Nitrogen are introduced.
 Most of the O- and N- functionalities can be removed by N2 treatment at 800 oC.
 oxAC-300NH3 and oxAC-800NH3 show the highest surface N concentration
 (O/C)bulk>(O/C)surface
 (N/C)bulk<(N/C)surface

13. Surface N Functionality
Pyridine Pyridone Quaternary -NO2
oxAC 16.39 - 20.44 63.18
oxAC-300NH3 20.82 36.96 27.08 15.14
oxAC-600NH3 33.78 30.97 22.39 12.86
oxAC-800NH3 42.50 32.44 25.06 -
oxAC oxAC-300NH3 oxAC-600NH3 oxAC-800NH3
Fractions of surface N functionalities
XPS spectra

14. SABET
(m2/g)
Vtotal
(cm3/g)
Davg (nm)
Wide microporosity Narrow microporosity
SAmicro
(m2/g)
Vmicro
(cm3/g)
W0
(cm3/g)
AC 972 0.45 1.84 907 0.36 0.238
oxAC 788 0.39 1.99 707 0.28 0.245
oxAC-300 NH3 936 0.41 1.77 891 0.35 0.277
oxAC-600 NH3 1020 0.45 1.75 974 0.38 0.262
oxAC-800 NH3 1106 0.49 1.76 1052 0.41 0.237
oxAC-800 N2 1058 0.47 1.76 1009 0.40 0.247
Textural properties of the AC beads
~
~
~
~
~ ~
~
~ ~
~ ~
• Upon HNO3 oxidation, texture properties decreased but can be recovered by heat treatment in
N2 (even developed as compared with the parent AC).
• Narrow microporosity hardly affected by oxidation.
• Development of both wide and narrow microporosity during 300 oC amination.
• Development of wide microporosity and diminish in narrow microporosity during high temp.
amination.

15. Morphology - SEM
 Little effect on morphology by surface modification
 Irregular openings and cracks serve as channels for CO2 diffusion

16. CO2 Adsorption
 oxAC-800NH3 showed the highest uptake of 8.2 mmol/g at 20
bar and 30 oC
 Rapid increasing from 1 to 10 bar: Good working capacity over
this range
Uptake @ 20 bar vs SABET
High pressure CO2 isotherms

17. Multiple Cycles in HPVA and fixed-bed
Adsorption-desorption cycles over oxAC-300NH3
100%CO2, 30oC, 1atm
 Negligible changes on uptake during cyclic adsorption-desorption
Previous Samples

18. Selectivity
High pressure isotherms of CO2, N2 and H2 over oxAC and oxAC-300NH3
CO2/N2 Selectivity
from IAST calculation
 CO2/N2 selectivity > 20 in
15%CO2+85%N2 mixture
 Competitive CO2/H2 selectivity being
examined in HPVA

19. Dynamics
In the stepwise measurement of the isotherms, the adsorption rate can
be estimated by change of pressure in the sample cell verse time:
ࢇࢊ
ࢉࢋ࢒࢒ ࢋࢗ
Finish dosing the sample
from 8 to 10 bar
90%
1 min
• Well below 1 min need to reach 90% uptake
1 min
Finish dosing the sample
from 8 to 10 bar
Dynamic curves during high pressure isotherm measurement

20. CO2 Adsorption at low pressure
- atmospheric pressure and 0.15 bar
15vol.% CO2
(mmol/g)
100vol.% CO2
(mmol/g)
30 oC 45 oC 30 oC 45 oC
AC 0.73 0.48 2.36 1.71
oxAC 0.91 0.59 2.34 1.72
oxAC-300NH3 0.85 0.56 2.57 1.90
oxAC-600NH3 0.76 0.50 2.44 1.78
oxAC-800NH3 0.74 0.49 2.42 1.75
oxAC-800N2 0.73 0.48 2.39 1.74
CO2 adsorption capacities Previous results on N-resin derived carbon
 Reasonable CO2 uptake (comparable with previous N-resin derived AC
beads)
 A combination of surface chemistry and texture property controls
overall adsorption capacity
 Similar CO2 uptakes on oxAC-600NH3, oxAC-800NH3

21. KOH Activated –
AC Beads
Low levels of KOH addition give stable performance with capacity of
over 7% w/w in 15% CO2
In 100% CO2
In 15% CO2/N2

22. 300.0 um
SEM results – PR1, KOH activated
PR1 PR1
1 2 3 4 5
keV
0
5
10
15
20
25
30
35
cps/eV
C O K
K
 K enrichment prefers AC beads with smaller
diameter;
 Compared with heavy K-Loading, K surface
enrichment is more common in lower K-ACs.
K content: 10.43 wt.%
100.0
um
EDX spot analysis on Sample
PR1.

23. SEM results
Raw sample PR0 without KOH activation; Sample PR2 and PR4: KOH
activated at different conditions
 Porous structure showed a tendency to collapse with creasing severity of KOH
activation. However, physical mechanical strength remains well despite cracks
evident.
KOH loading
 With the addition of KOH loadings on AC beads, the extent of crack formation
increases.
 With the addition of KOH loadings on AC beads, the extent of crack formation
increases.
PR0 PR2 PR4
400u
m
400u
m
400u
m

24. • Controlling K removal
• Maximizing “good” K
• Minimizing “bad” K
• Compromising porosity
Possible mechanisms for the modification of
carbon by KOH

25. What else might K do other than intercalate to
increase electostatic interations?
Chemical (K2CO3-KHCO3 cycling):
• Low uptake at dry conditions
• Low kinetics at ambient temperatures
• High temperature for regeneration
Enhances Physical:
• High kinetics
• Easy regeneration
• High Stability
NEGLIGIBLE
Major Route
Stronger polarity electrostatic interactions) can be induced by K-
incorporation, leading to higher surface affinity towards CO2

26. Reducing regeneration energy:
 Maximise the CO2 capture loading (L).
 Decrease the specific heat of the adsorbent (Cs)
 Find an adsorbent with a low heat of reaction Qr.
 Minimise T
Sjostrom, Fuel 89 (2010) 1298–1306
Sorbent Regeneration:
Crucial

27. Conclusions
 Carbon bead a flexible materials with high
mechanical strength and different properties.
 Suited for moderate CO2 partial pressures in IGCC
 KOH incorporation effective for 0.15 bar CO2.
 Modelling indicates that, at this partial pressure, it
is more effective than silica-PEI.
 Future work on scale-up for PSA and CFBs.

28. Acknowledgements
The authors wish to acknowledge the financial support of the
UK Engineering Physical Sciences Research Council (Grant Nos:
EP/I010955/1, and EP/G063176/1) and the National Science
Fundation China (Grant Nos: 51061130536, 51172251 and
21203230).
Colin Snape acknowledges the award of a Visiting Professorship
in the Chinese Academy of Sciences (Grant No: 2013T2G0030).