Influence of material properties on the oxidation and ignition Influence of material properties on the oxidation and ignition characteristics of activated carbonscharacteristics of activated carbons

Thangavelu JAYABALAN, Pascaline PRE and Valérie HEQUETThangavelu JAYABALAN, Pascaline PRE and Valérie HEQUET

Département Systèmes Energétiques et EnvironnementDépartement Systèmes Energétiques et Environnement

GEPEA UMR-CNRS 6144GEPEA UMR-CNRS 6144

Ecole des Mines de Nantes, France.Ecole des Mines de Nantes, France.

Pierre LE CLOIRECPierre LE CLOIREC

Ecole de Chimie de RennesEcole de Chimie de Rennes

UMR-CNRS 6226 “Sciences Chimiques de Rennes”UMR-CNRS 6226 “Sciences Chimiques de Rennes”

Université Européenne de Bretagne, FranceUniversité Européenne de Bretagne, France

9th International conference on Fundamentals Of Adsorption, May 20-25, 2007 Sicily-Italy.

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Activated carbons are porous adsorbents used in Activated carbons are porous adsorbents used in

Odour controlOdour control

VOC removalVOC removal

Recovery of volatile solvents (e.g. benzene, ketones, cyclohexanes)Recovery of volatile solvents (e.g. benzene, ketones, cyclohexanes)

ContextContext

DrawbacksDrawbacks

Fire hazards (oxidation and ignition) encountered in Fire hazards (oxidation and ignition) encountered in

Activated carbon beds in service and idle conditionActivated carbon beds in service and idle condition

Handling and regeneration of spent carbonHandling and regeneration of spent carbon

TransportationTransportation

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Incidents with activated carbonsIncidents with activated carbons

Container fire of Container fire of Kitano Kitano vessel of Nova Scotia - vessel of Nova Scotia - Marine investigation report M01M0017 Marine investigation report M01M0017 Transport safety board of CanadaTransport safety board of Canada

March- 2001 CanadaMarch- 2001 Canada

Fire in a consignment of activated carbon pellets Fire in a consignment of activated carbon pellets (Kitano vessel of the coast of Nova Scotia)(Kitano vessel of the coast of Nova Scotia)

August-2000 Grasse (France)August-2000 Grasse (France)

Fire in 2 tons of activated carbons for Fire in 2 tons of activated carbons for decolorising gases - Pharmacheutical industry.decolorising gases - Pharmacheutical industry.

December-1998 Limas (France)December-1998 Limas (France)

Fire in activated carbon filter used for adsorbing Fire in activated carbon filter used for adsorbing the VOC’s - Agrochemical industrythe VOC’s - Agrochemical industry

January-1998 Givors (France)January-1998 Givors (France)

Ignition of the activated carbon filter to adsorb Ignition of the activated carbon filter to adsorb VOC’s in an industry treating special wastesVOC’s in an industry treating special wastes

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ObjectivesObjectives

TTo assess the physical and chemical properties influencing the o assess the physical and chemical properties influencing the

thermal stability of activated carbons under a given conditionthermal stability of activated carbons under a given condition

Establish statistical correlation's between the oxidation and ignition Establish statistical correlation's between the oxidation and ignition

characteristics of activated carbons and their physical and chemical characteristics of activated carbons and their physical and chemical

propertiesproperties

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Complex process which Complex process which takestakes place in a wide range of temperatures. place in a wide range of temperatures.

Mechanisms of Oxidation and Ignition Mechanisms of Oxidation and Ignition

of activated carbonsof activated carbons

Self heating

High temperature oxidationHigh temperature oxidation

Self ignition of the material and combustion, gaseous Self ignition of the material and combustion, gaseous emissions emissions

Exposure to oxidantsExposure to oxidants

(oxygen, air)(oxygen, air)

Local warmingLocal warming

(external heating, exothermic (external heating, exothermic adsorption)adsorption)

Low temperature oxidationLow temperature oxidation

Chemical transformation of the material, gaseous Chemical transformation of the material, gaseous emissionsemissions

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Materials: Activated carbons testedMaterials: Activated carbons tested

Sample H/C (%) N/C (%) O/C (%) SBET (sq.m/g)

Vporous (cu.cm/g)

Micropore width (nm)

Vmicro (cu.cm/g)

NC-50 0.52 0 1.72 1078 1.27 1.355 0.360

NC-60 0.3 0.04 3.6 1220 0.37 0.970 0.320

NC-100 0.53 0 3.3 1803 0.47 1.110 0.270

RB-2 0.32 0.2 5.9 1012 0.34 0.917 0.350

BPL 0.2 0.3 4.1 1106 0.40 0.933 0.300

CTP-A 0.86 0.7 1.72 102 0.07 1.305 0.045

CTP-PAN-3:1-A 1.22 5.7 3.1 468 0.25 1.320 0.209

CTP-PAN-1:1-A 1.12 9.2 7.2 482 0.27 1.110 0.215

PAN-A 1.63 15.5 13.4 515 0.27 1.12 0.26

GF-40 2.64 0.3 34.6 1718 0.81 1.147 0.290

BC-120 2.72 0.01 35.4 1975 1.51 1.118 0.330

PICABIOL 2.7 0 40.6 1534 1.34 1.385 0.240

* CTP-PAN samples -LCSM Nancy,France

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Experimental Studies: Oxidation of activated carbonsOxidation of activated carbons

Simultaneous measurement of heat flux and Simultaneous measurement of heat flux and mass.mass.

Experimental parameters Experimental parameters

Gas flow rate: 1 L/hr Gas flow rate: 1 L/hr

Sample mass Sample mass 3mg 3mg

Heating range : 20° C - 600 °C Heating range : 20° C - 600 °C

Heating rate : 5K/minHeating rate : 5K/min

Gas used : He/OGas used : He/O22 (79/21mixture ) (79/21mixture )

105°C105°C

Isotherm Isotherm 30 minutes30 minutes

Isotherm 5 Isotherm 5 minutesminutes

650°C650°C

Ramp 5 °C/minRamp 5 °C/min

100°C100°C20°C20°C

ATGATG-DSC Setaram-111 Anal-DSC Setaram-111 Analyseryser

Temperature ProgrammationTemperature Programmation

8

-4

0

4

8

12

16

20

24

28

100 200 300 400 500 600

Temperature °C

Hea

t fl

ow/u

nit

mas

s (m

W/m

g)

PIO SIT

Point of initial oxidationPoint of initial oxidation

Denotes the start of oxidation reaction at low temperature, Denotes the start of oxidation reaction at low temperature, obtained from the deviation of the obtained from the deviation of the

heat flux curve from the baselineheat flux curve from the baseline

Spontaneous Ignition TemperatureSpontaneous Ignition Temperature

Point corresponds to the auto-inflammation with the decrease in the mass of the sample by Point corresponds to the auto-inflammation with the decrease in the mass of the sample by

the way of consumptionthe way of consumption

0

1

2

3

4

0 100 200 300 400 500 600

Temperature °C

TG

-m

ass

(mg)

Experimental Studies: Oxidation of activated Oxidation of activated

carbonscarbons

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ResultsResults

Qualitative analysis: Effect of oxygen contentQualitative analysis: Effect of oxygen content

Oxygen content source - surface oxygenated groups bonded to edge sites and material of originOxygen content source - surface oxygenated groups bonded to edge sites and material of origin

Interaction of surface oxygenated complex with air Interaction of surface oxygenated complex with air

COCO2 ,2 , CO, H CO, H22O, intermediate complex and exothermic heatO, intermediate complex and exothermic heat

ExceptionsExceptions : NC-50, NC-60 and NC-100 (Physically activated coconut shell) : NC-50, NC-60 and NC-100 (Physically activated coconut shell)

ReasonsReasons: Higher ash content (potassium) catalyzing the oxidation and ignition reactions (Bandosz & : Higher ash content (potassium) catalyzing the oxidation and ignition reactions (Bandosz &

van der Merwe)van der Merwe)

Increased affinity for chemisorption of oxygenIncreased affinity for chemisorption of oxygen

Our hypothesis is to look into the structural propertiesOur hypothesis is to look into the structural properties

R2 = 0,98

0

100

200

300

400

0 0,5 1 1,5 2

Log(O/C) %

PIO

°C

Activatedcarbonsamplesexceptcoconut shell

Samples w ithCoconut shellas origin

R2 = 0,962

0

100

200

300

400

500

600

0 10 20 30 40 50

(O/C) %

SIT

°C

Activatedcarbon samplesexcept coconutshell

Samples w ithCoconut shellas origin

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Qualitative analysis: Effect of nitrogen content 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)

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

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0

5

10

15

20

25

30

Picabiol BPL GF-40 PAN-A

Ox

yg

en

co

nte

nt

(%)

Oxygen content beforeTPD (%)

Oxygen content af terTPD (%)

Temperature Programmed Desorption studies

Temperature programmed desorption was carried out in TG-DSC apparatusTemperature programmed desorption was carried out in TG-DSC apparatus

Oxygenated complex partly removed by the application of heat using helium gasOxygenated complex partly removed by the application of heat using helium gas

Approximately 10 -11 % decrease in oxygen to carbon ratio (chemically activated Approximately 10 -11 % decrease in oxygen to carbon ratio (chemically activated

carbons)carbons)

Temperature Programmed Oxidation (TPO) for measuring PIO and SITTemperature Programmed Oxidation (TPO) for measuring PIO and SIT

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0

100

200

300

400

500

PICABIOL BPL GF-40 PAN-A

PIO

°C

PIO af ter TPD

PIO before TPD

0

100

200

300

400

500

600

PICABIOL BPL GF-40 PAN-A

SIT

°C

SIT af ter TPD

SIT before TPD

The oxidation and ignition temperature increased after TPDThe oxidation and ignition temperature increased after TPD

Significant increase is found in PIO than SIT Significant increase is found in PIO than SIT

TPD studies showed that surface oxygenated groups actively involve in the TPD studies showed that surface oxygenated groups actively involve in the

initiation of oxidation reactions.initiation of oxidation reactions.

Temperature Programmed Desorption studiesTemperature Programmed Desorption studies

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R2 = 0,87

0

200

400

600

0 0,5 1 1,5 2

Log (O/C) %

PIO

°C

PIO Vs Log(O/C) afterTPD

EffectEffect of Oxygen content after TPD studies

Linear tendency observed for (O/C) versus SIT and PIO for samples subjected Linear tendency observed for (O/C) versus SIT and PIO for samples subjected

to TPDto TPD

(O/C) identified as important parameter influencing oxidation and ignition of (O/C) identified as important parameter influencing oxidation and ignition of

activated carbonsactivated carbons

R2 = 0,90

0

200

400

600

0 5 10 15 20 25 30

(O/C) %

SIT

°C

SIT Vs O/Cafter TPD

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Qualitative analysis: Effect of porosity characteristics Qualitative analysis: Effect of porosity characteristics

on PIO & SITon PIO & SIT

The effect of SThe effect of SBETBET, microporous volume, mesoporous volume and width of the , microporous volume, mesoporous volume and width of the

micropore on SIT and PIO was studied graphicallymicropore on SIT and PIO was studied graphically

Relationships could not be well establishedRelationships could not be well established

Lower regression coefficients were obtained Lower regression coefficients were obtained

R2 = 0,628

200

300

400

500

600

0,00 0,50 1,00 1,50 2,00

Vporous (cu cm/g)

SIT

°C

SIT VsVporous

R2 = 0,5151

0

100

200

300

400

0 500 1000 1500 2000

(SBET) sq.m/g

PIO

°C

SBETVS PIO

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Quantitative analysis: Multiple Linear Quantitative analysis: Multiple Linear regression regression

Develop quantitative relations and to compare with the qualitative results Develop quantitative relations and to compare with the qualitative results

Stepwise multiple linear regression - Minitab softwareStepwise multiple linear regression - Minitab software

The interdependancy of the predictor variables checked using matrix correlationThe interdependancy of the predictor variables checked using matrix correlation

One predictor variable used from the correlated pairs One predictor variable used from the correlated pairs

SBET H/C N/C Log

(Vporous) Log (O/C)

Wpore

O/C

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 0.15

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Quantitative analysis: Regression equations Quantitative analysis: Regression equations

Regression Regression equationsequations : :

PIO = 231 - 63,5 Log (Vporous) - 32,9 Log (O/C)PIO = 231 - 63,5 Log (Vporous) - 32,9 Log (O/C) RR22 = 0.85 = 0.85 S = 17 °C S = 17 °C (12 samples)(12 samples)

PIO = 315 – 89.1 Log (O/C) % PIO = 315 – 89.1 Log (O/C) % RR22 = 0.98 = 0.98 S = 7 °C S = 7 °C (9 samples excluding coconut (9 samples excluding coconut

shell activated carbon samples)shell activated carbon samples)

SIT = 492 – 3.33 (O/C) %SIT = 492 – 3.33 (O/C) % RR22 = = 0.67 S = 54 °C0.67 S = 54 °C (12 samples)(12 samples)

SIT = 537 – 4.70 (O/C) % SIT = 537 – 4.70 (O/C) % RR22 = = 0.96 S = 16 °C0.96 S = 16 °C (9 samples excluding coconut (9 samples excluding coconut

shell activated carbon samples)shell activated carbon samples)

No other predictor variables were discriminated except (O/C) ratio No other predictor variables were discriminated except (O/C) ratio

Quantitative regression equations confirm the results of qualitative analysisQuantitative regression equations confirm the results of qualitative analysis

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ConclusionConclusion

The role of properties of activated carbons on their oxidation and ignition The role of properties of activated carbons on their oxidation and ignition

characteristics have been studied characteristics have been studied

Oxygen Oxygen contentcontent is the most influent (exceptions were observed) is the most influent (exceptions were observed)

Effect of porosity Effect of porosity propertiesproperties on the oxidation and ignition characteristics on the oxidation and ignition characteristics

could not be well establishedcould not be well established

PerspectivesPerspectives

Oxidation and ignition may be better explained by structural properties than Oxidation and ignition may be better explained by structural properties than

the porosity characteristicsthe porosity characteristics

Article coupling these results with HRTEM study is underway with Article coupling these results with HRTEM study is underway with

Prof. RouzaudProf. Rouzaud

Thank you for your attention