Influence of material properties on the oxidation and ignition
characteristics of activated carbons
Thangavelu JAYABALAN, Pascaline PRE and Valérie HEQUET
Département Systèmes Energétiques et Environnement
GEPEA UMR-CNRS 6144
Ecole des Mines de Nantes, France.
Pierre LE CLOIREC
Ecole de Chimie de Rennes
UMR-CNRS 6226 “Sciences Chimiques de Rennes”
Université Européenne de Bretagne, France
9th International conference on Fundamentals Of Adsorption, May 20-25, 2007 Sicily-Italy.
Context
Activated carbons are porous adsorbents used in

Odour control

VOC removal

Recovery of volatile solvents (e.g. benzene, ketones, cyclohexanes)
Drawbacks
Fire hazards (oxidation and ignition) encountered in
 Activated
2
carbon beds in service and idle condition

Handling and regeneration of spent carbon

Transportation
Incidents with activated carbons
March- 2001 Canada
Fire in a consignment of activated carbon
pellets (Kitano vessel of the coast of Nova Scotia)
August-2000 Grasse (France)
Fire in 2 tons of activated carbons for
decolorising gases - Pharmacheutical industry.
December-1998 Limas (France)
Fire in activated carbon filter used for adsorbing
the VOC’s - Agrochemical industry
January-1998 Givors (France)
Ignition of the activated carbon filter to adsorb
VOC’s in an industry treating special wastes
3
Container fire of Kitano vessel of Nova Scotia Marine investigation report M01M0017
Transport safety board of Canada
Objectives
 To assess the physical and chemical properties influencing the
thermal stability of activated carbons under a given condition
 Establish statistical correlation's between the oxidation and ignition
characteristics of activated carbons and their physical and chemical
properties
4
Mechanisms of Oxidation and Ignition
of activated carbons
 Complex process which takes place in a wide range of temperatures.
Exposure to oxidants
Local warming
(oxygen, air)
(external heating, exothermic
adsorption)

Low temperature oxidation
 Chemical transformation of the material, gaseous
emissions
Self heating

High temperature oxidation
 Self ignition of the material and combustion, gaseous
emissions
5
Materials: Activated carbons tested
Sample
NC-50
NC-60
NC-100
RB-2
BPL
CTP-A
CTP-PAN-3:1-A
CTP-PAN-1:1-A
PAN-A
GF-40
BC-120
PICABIOL
6
Vporous Micropore Vmicro
SBET (sq.m/g) (cu.cm/g) width (nm) (cu.cm/g)
H/C (%)
N/C (%)
O/C (%)
0.52
0
1.72
1078
1.27
1.355
0.360
0.3
0.04
3.6
1220
0.37
0.970
0.320
0.53
0
3.3
1803
0.47
1.110
0.270
0.32
0.2
5.9
1012
0.34
0.917
0.350
0.2
0.3
4.1
1106
0.40
0.933
0.300
0.86
0.7
1.72
102
0.07
1.305
0.045
1.22
5.7
3.1
468
0.25
1.320
0.209
1.12
9.2
7.2
482
0.27
1.110
0.215
1.63
15.5
13.4
515
0.27
1.12
0.26
2.64
0.3
34.6
1718
0.81
1.147
0.290
2.72
0.01
35.4
1975
1.51
1.118
0.330
2.7
0
40.6
1534
1.34
1.385
0.240
* CTP-PAN samples -LCSM Nancy,France
Experimental Studies: Oxidation of activated carbons
ATG-DSC Setaram-111 Analyser
 Simultaneous measurement of heat flux and
mass.

Temperature Programmation
650°C
Experimental parameters
Ramp 5 °C/min
Gas flow rate: 1 L/hr
Sample mass  3mg
Isotherm
30 minutes
Heating range : 20° C - 600 °C
Heating rate : 5K/min
7
Gas used : He/O2 (79/21mixture )
Isotherm 5
minutes
20°C
105°C
100°C
Experimental Studies: Oxidation of activated
carbons
4
24
3
20
TG -mass (mg)
Heat flow/unit mass (mW/mg)
28
16
12
8
1
4
SIT
PIO
0
-4
2
0
100
200
300
400
500
Temperature °C
600
0
100
200
300
400
500
600
Temperature °C
 Point of initial oxidation
Denotes the start of oxidation reaction at low temperature, obtained from the deviation of the
heat flux curve from the baseline
 Spontaneous Ignition Temperature
Point corresponds to the auto-inflammation with the decrease in the mass of the sample by
the way of consumption
8
Results
Qualitative analysis: Effect of oxygen content
400
600
PIO °C
R2 = 0,98
200
Samples w ith
Coconut shell
as origin
100
0
500
R2 = 0,962
Activated
carbon samples
except coconut
shell
400
SIT °C
Activated
carbon
samples
except
coconut shell
300
300
Samples w ith
Coconut shell
as origin
200
100
0
0
0,5
1
Log(O/C) %
1,5
2
0
10
20
30
40
50
(O/C) %
 Oxygen content source - surface oxygenated groups bonded to edge sites and material of origin
 Interaction of surface oxygenated complex with air
CO2 , CO, H2O, intermediate complex and exothermic heat
Exceptions : NC-50, NC-60 and NC-100 (Physically activated coconut shell)
Reasons: Higher ash content (potassium) catalyzing the oxidation and ignition reactions (Bandosz &
van der Merwe)
Increased affinity for chemisorption of oxygen
9
Our hypothesis is to look into the structural properties
Qualitative analysis: Effect of nitrogen content

General trends nitrogen rich samples have higher PIO and SIT

Thermally stable nitrogen substituted in the carbon ring system

Trend could not be established alone as nitrogen was associated with oxygen

The effect of (O/C) dominant than (N/C)
10
SAMPLE
N/C (%)
O/C (%)
CTP-A
0.7
1.72
CTP-PAN-3:1-A
5.7
3.1
CTP-PAN-1:1-A
9.2
7.2
PAN-A
15.5
13.4
Temperature Programmed Desorption studies
 Temperature programmed desorption was carried out in TG-DSC apparatus
 Oxygenated complex partly removed by the application of heat using helium gas
 Approximately
10 -11 % decrease in oxygen to carbon ratio (chemically activated
carbons)
 Temperature Programmed Oxidation (TPO) for measuring PIO and
30
Oxygen content before
TPD (%)
Oxygen content (%)
25
Oxygen content after
TPD (%)
20
15
10
5
0
Picabiol
11
BPL
GF-40
PAN-A
SIT
Temperature Programmed Desorption studies
600
500
SIT after TPD
PIO after TPD
500
PIO before TPD
400
SIT before TPD
SIT °C
PIO °C
400
300
300
200
200
100
100
0
0
PICABIOL
BPL
GF-40
PAN-A
PICABIOL
BPL
GF-40
PAN-A
 The oxidation and ignition temperature increased after TPD
 Significant increase is found in PIO than SIT
 TPD studies showed that surface oxygenated groups actively involve in the
initiation of oxidation reactions.
12
Effect of Oxygen content after TPD studies
600
600
400
SIT °C
PIO °C
400
R2 = 0,87
PIO Vs Log
(O/C) after
TPD
200
2
R = 0,90
200
SIT Vs O/C
after TPD
0
0
0
0,5
1
Log (O/C) %
1,5
2
0
5
10
15
20
25
30
(O/C) %
 Linear tendency observed for (O/C) versus SIT and PIO for samples subjected
to TPD
 (O/C) identified as important parameter influencing oxidation and ignition of
activated carbons
13
Qualitative analysis: Effect of porosity characteristics
on PIO & SIT
The effect of SBET, microporous volume, mesoporous volume and width of the
micropore on SIT and PIO was studied graphically


Relationships could not be well established
 Lower regression coefficients were obtained
600
400
SIT Vs
Vpo rous
300
500
R2 = 0,628
PIO °C
SIT °C
SBET
VS PIO
400
200
R2 = 0,5151
100
300
0
200
0,00
0
0,50
1,00
Vporous (cu cm/g)
14
1,50
2,00
500
1000
(SBET) sq.m/g
1500
2000
Quantitative analysis: Multiple Linear
regression
 Develop quantitative relations
and to compare with the qualitative results
 Stepwise multiple linear regression - Minitab software
 The interdependancy of
the predictor variables checked using matrix correlation
 One predictor variable used from
the correlated pairs
Log
SBET
H/C
N/C
Log (O/C)
(Vporous)
15
Wpore
H/C
0.39
N/C
-0.56
0.09
Log(Vporous)
0.82
0.48
-0.34
Log (O/C)
0.54
0.88
-0.083
0.57
Wpore
-0.17
0.41
0.010
0.12
0.003
O/C
0.60
0.93
-0.13
0.64
0.94
-0.22
Vmicro
0.63
-0.062
-0.22
0.70
0.22
-0.44
O/C
0.15
Quantitative analysis: Regression equations
Regression equations :
PIO = 231 - 63,5 Log (Vporous) - 32,9 Log (O/C) R2 = 0.85 S = 17 °C (12 samples)
PIO = 315 – 89.1 Log (O/C) %
R2 = 0.98 S = 7 °C (9 samples excluding coconut
shell activated carbon samples)
SIT = 492 – 3.33 (O/C) %
R2 = 0.67
SIT = 537 – 4.70 (O/C) % R2 = 0.96
S = 54 °C
S = 16 °C
(12 samples)
(9 samples excluding coconut
shell activated carbon samples)
16

No other predictor variables were discriminated except (O/C) ratio

Quantitative regression equations confirm the results of qualitative analysis
Conclusion

The role of properties of activated carbons on their oxidation and ignition
characteristics have been studied

Oxygen content is the most influent (exceptions were observed)

Effect of porosity properties on the oxidation and ignition characteristics
could not be well established
Perspectives

Oxidation and ignition may be better explained by structural properties than
the porosity characteristics
 Article
coupling these results with HRTEM study is underway with
Prof. Rouzaud
17
Thank you for your attention