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Thangavelu JAYABALAN, Pascaline PRE and Valérie HEQUET

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

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Thangavelu JAYABALAN, Pascaline PRE and Valérie HEQUET

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  1. 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.

  2. 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 carbon beds in service and idle condition • Handling and regeneration of spent carbon • Transportation

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

  4. 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

  5. Local warming (external heating, exothermic adsorption) Exposure to oxidants (oxygen, air) • Low temperature oxidation • Chemical transformation of the material, gaseous emissions • High temperature oxidation • Self ignition of the material and combustion, gaseous emissions Mechanisms of Oxidation and Ignition of activated carbons • Complex process which takes place in a wide range of temperatures. Self heating

  6. Materials: Activated carbons tested * CTP-PAN samples -LCSM Nancy,France

  7. 650°C Ramp 5 °C/min Isotherm 30 minutes Isotherm 5 minutes 105°C 100°C Experimental Studies: Oxidation of activated carbons ATG-DSC Setaram-111 Analyser • Simultaneous measurement of heat flux and mass. • Experimental parameters • Gas flow rate: 1 L/hr • Sample mass  3mg • Heating range : 20° C - 600 °C • Heating rate : 5K/min • Gas used : He/O2 (79/21mixture ) Temperature Programmation 20°C

  8. SIT PIO Experimental Studies: Oxidation of activated carbons • 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

  9. Results Qualitative analysis: Effect of oxygen content • 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 Our hypothesis is to look into the structural properties

  10. 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)

  11. 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 SIT

  12. Temperature Programmed Desorption studies • 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.

  13. 600 400 2 R = 0,90 SIT °C 200 SIT Vs O/C after TPD 0 0 5 10 15 20 25 30 (O/C) % Effect of Oxygen content after TPD studies • 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

  14. 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

  15. 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

  16. 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 S = 54 °C(12 samples) SIT = 537 – 4.70 (O/C) % R2 = 0.96 S = 16 °C(9 samples excluding coconut shell activated carbon samples) • No other predictor variables were discriminated except (O/C) ratio • Quantitative regression equations confirm the results of qualitative analysis

  17. 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

  18. Thank you for your attention

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