Analysis of structural properties of activated carbons by HRTEM Analysis of structural properties of activated carbons by HRTEM

and their influence on the oxidation and ignition characteristicsand their influence on the oxidation and ignition characteristics

T.JAYABALAN, T.JAYABALAN, P. PRE, V. HEQUET, J.N. ROUZAUD and P. LE CLOIRECP. PRE, V. HEQUET, J.N. ROUZAUD and P. LE CLOIREC

Context and ObjectivesContext and Objectives

ConclusionConclusion

Activated carbons are widely used as adsorbents in air treatments. They are prone to early oxidation and self heating due to Activated carbons are widely used as adsorbents in air treatments. They are prone to early oxidation and self heating due to various interacting factors like exothermic chemical and adsorption reactions, heat exchange with the surroundings and various interacting factors like exothermic chemical and adsorption reactions, heat exchange with the surroundings and intrinsic properties of the materials. intrinsic properties of the materials. The aim of this work is to determine the relationships between the nanostructural The aim of this work is to determine the relationships between the nanostructural characteristics of activated carbons by analysis of High Resolution Transmission Electron Microscope (HRTEM) imagescharacteristics of activated carbons by analysis of High Resolution Transmission Electron Microscope (HRTEM) images and and their influence on the reactivity of the carbon material.their influence on the reactivity of the carbon material.

NC-100NC-100 PicabiolPicabiol

Activated Carbon samples differ structurally Activated Carbon samples differ structurally

Physically activated carbons have low O/C ratio: nanometer-sized Physically activated carbons have low O/C ratio: nanometer-sized graphene layer graphene layer

Chemically activated carbons (like Picabiol) have high O/C ratioChemically activated carbons (like Picabiol) have high O/C ratio :: short, non-short, non-stacked and distorted graphene layersstacked and distorted graphene layers

Activated CarbonsActivated Carbons - - chemical composition, textural and nanostructural characteristicschemical composition, textural and nanostructural characteristics

Experimental studies & ResultsExperimental studies & Results

The results show that oxygen to carbon ratio in the form of surface oxygenated groups and the characteristics of the graphene layer length The results show that oxygen to carbon ratio in the form of surface oxygenated groups and the characteristics of the graphene layer length (from HRTEM image analysis) influenced the reactivity of activated carbons. The organization of the graphitic structure and the properties of (from HRTEM image analysis) influenced the reactivity of activated carbons. The organization of the graphitic structure and the properties of the activated carbon samples were dependant on the mode of activation and the nature of the material precursor. The structure of highly the activated carbon samples were dependant on the mode of activation and the nature of the material precursor. The structure of highly stable carbons was found to contain less oxygen to carbon ratio with larger and better stacked polyaromatic layers. Physically activated stable carbons was found to contain less oxygen to carbon ratio with larger and better stacked polyaromatic layers. Physically activated carbons appear much stable than chemically activated carbons.carbons appear much stable than chemically activated carbons.

Thermal analysisThermal analysis

Sample Precursor O/C(%)

N/C(%)

Volume ofmicropores

(cm3/g)

Averagewidth of

micropores(nm)

Surface area(m2/g)

Porousvolume(cm3/g)

L > 1 ring(Å)

L > 2 ring(Å)

%NSL

dav(Å)

NC-50 Coconut shell 1.72 0 0.36 1.35 1078 1.28 5.6 8.4 50 3.8NC-60 Coconut shell 3.60 0.04 0.32 0.97 1220 0.35 6.3 8.9 53 4.0NC-100 Coconut shell 3.30 0 0.27 1.11 1803 0.47 6.1 9.1 51 3.9

RB-2 Peat 5.90 0.20 0.35 0.92 1012 0.34 5.8 8.4 57 4.2BPL Coal 4.10 0.30 0.30 0.93 1106 0.40 6 8.6 58 3.8

GF-40 Olive stone 34.60 0.30 0.29 1.15 1718 0.80 5.4 7.7 74 4.0BC-120 Wood 35.40 0.01 0.33 1.12 1975 1.50 5.5 7.7 65 3.9

PICABIOL Wood 40.60 0 0.24 1.38 1534 1.34 4.8 7.1 66 4.1CTP-A Coal tar pitch 1.72 0.70 0.04 1.30 102 0.07 9.7 12.3 14 3.8

CTP-PAN-1 :1-A Coal tar pitchand Pan fiber

7.20 9.20 0.21 1.11 482 0.27 5.8 8.4 60 3.9

PAN-A Pan fiber 13.40 15.5 0.26 1.15 515 0.27 6.4 9 59 3.9

Chemically activated carbons have lower PIO and SIT compared to physically activated carbonsChemically activated carbons have lower PIO and SIT compared to physically activated carbons

Structural analysisStructural analysis

Computerized HRTEM imageComputerized HRTEM image

analysis - Nanostructural dataanalysis - Nanostructural data

-L length of the layers -L length of the layers

-d interlayer spacing-d interlayer spacing

-% NSL non stacked layers-% NSL non stacked layers

-La and Lc :diameter and height -La and Lc :diameter and height

of the coherent domain (BSU)of the coherent domain (BSU)

J.N.Rouzaud and C.ClinardJ.N.Rouzaud and C.Clinard

Fuel Processing Technology, 2002,Fuel Processing Technology, 2002,

77-78, 229-23577-78, 229-235

R2 = 0,80

0

100

200

300

400

0 5 10 15L>1 ring A

PIO

°C

P IO Vs L>1 ring A

-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)

PIOPIO SITSIT

PIO = 271 – 2,7 O/C (%) RPIO = 271 – 2,7 O/C (%) R22 = 87% = 87% SIT = 537 - 4,7 O/C (%) RSIT = 537 - 4,7 O/C (%) R22 = 96% = 96%

Results are coupled with Results are coupled with structural parameters using structural parameters using Multiple Linear RegressionMultiple Linear Regression

Multiple Linear RegressionMultiple Linear Regression

PIO = 83.3 – 1.38 O/C (%) + 27.5 LPIO = 83.3 – 1.38 O/C (%) + 27.5 L>1ring>1ring ( (Å) Å) S = 15 °C RS = 15 °C R22 = 94% = 94%

Reactivity data (PIO and SIT) are obtained from TG-DSCPIO: Point of Initial Oxidation

SIT: Spontaneous Ignition Temperature

H. MarshCarbon Conference 2006

Ecole des Mines de Nantes, GEPEA UMR CNRS 6144, 4 rue Alfred Kastler, BP 20722, 44307 Nantes cedex 3, France.Ecole des Mines de Nantes, GEPEA UMR CNRS 6144, 4 rue Alfred Kastler, BP 20722, 44307 Nantes cedex 3, France. thangavelu.jayabalan @emn.frthangavelu.jayabalan @emn.fr

Laboratoire de géologie de l’Ecole Normale Supérieure de Paris, UMR CNRS-ENS 8538, 24 rue Lhomond 75231-Paris Laboratoire de géologie de l’Ecole Normale Supérieure de Paris, UMR CNRS-ENS 8538, 24 rue Lhomond 75231-Paris Cedex 5, France. rouzaud@geologie.ens.frCedex 5, France. rouzaud@geologie.ens.fr

5 nm5 nm