(244b) Statistical Quantification and Characterization of Material Properties Influencing the Reactivity of Activated Carbons
Activated carbons are widely used in heterogeneous catalysis, personal protection equipment, vehicle filters and for the removal of volatile organic compounds (VOC's) and odours from industrial effluents. Stricter environmental policies and commitments have ensured lower emission standards and greater efficiency in the removal of air pollutants. The major outcome is the extensive use of pollution abatement techniques involving activated carbon materials particularly in the removal of VOC's. However these materials prone to oxidation and self heating due to external heating, exothermic chemical reactions, and adsorption. These behaviours cause extensive damage to equipment. Hence the understanding of the oxidation and ignition properties has a great operational and safety significance . The aim of this work is to understand the influence of textural, chemical and structural properties on the reactivity of activated carbons with air and to establish quantitative statistical correlations. 14 different activated carbons were selected for this study based on the nature of the raw material and the mode of activation. The oxidation and ignition reactivity of activated carbons in air were studied using Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC). The Point of Initial Oxidation (PIO) and the Spontaneous Ignition Temperature (SIT) were experimentally determined from the heat flow curves . The nanostructural characterization of the activated carbons was carried out using a Jeol 2011 HRTEM. Multiscale organization of activated carbons and their quantitative structural data like individual fringe length (L), interlayer spacing (d) and number of stacked layers in a coherent domain (N) were extracted using an in house image analysis procedure . The structural characterization is completed by an indirect measurement of the pore size distribution using the N2 adsorption isotherms. The chemical characterization includes the measurement of the elements such as oxygen, hydrogen and nitrogen using elementary analyser and the mineral content using SEM-X (scanning electron microscopy x-ray) method. Three distinct structural features have been observed in the carbon samples depending upoon the precursor and the mode of activation. The chemically activated carbons have short fringe length and the graphitic layers are randomly arranged in an isolated fashion. The second group of carbon samples show long graphitic sheets, weakly stacked and slightly bent constituting spaces between them. The third group of carbon sample show a lamellar nanostructure of the graphitic layers which tend to be parallel to each other and better stacked compared to the first and second group of samples. The second and third group of samples were produced by physical activation. The surface oxygenated groups, mineral impurities and the nanostructural properties have an influence on the PIO and SIT values of the activated carbon . The quantitative analysis was conducted in order to determine the relative predominance of the influent properties on the reactivity of the activated carbons. The relationships between the properties of the carbon materials and their reactivity was derived by multiple linear regression (MLR). It was found that the graphitic layer length and the oxygen over carbon ratio are directly influent on the oxidation parameter while only oxygen to carbon ratio is influent on the ignition parameter. 1. Zerbonia, RA. Brockman, CM. Peterson, PR. Housely, D. 2001. Carbon bed fires and the use of carbon canisters for air emissions control on fixed roof tanks. J Air & Waste Management Assoc 51:1617-1627. 2. Suzin, Y. Buettner, LC. LeDuc, CA. 1999. Characterizing the ignition process of activated carbon. Carbon 37:335-346. 3. Rouzaud, JN. Christian, C. 2002. Quantitative high-resolution transmission electron microscopy: a promising tool for carbon materials characterization. Carbon 77-78:229-235. 4. Jayabalan, T. Pré, P. Héquet, V. Le Cloirec, P. 2008. Statistical Quantification of the Influence of Material Properties on the Oxidation and Ignition of Activated Carbons Adsorption, 14:4-5, 679-686.
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