Material Properties Influencing the Oxidation and Ignition Reactivity of Activated Carbons: Thermal Analysis, HRTEM Study, and Statistical Modeling

Abstract

The aim of this work is to understand the influence of textural, chemical, and structural properties on the reactivity of activated carbons toward air. Multiscale organization of activated carbons was studied using high-resolution transmission electron microscopy (HRTEM) and their quantitative structural data, like individual fringe length, interlayer spacing, and proportion of nonstacked layers, were extracted using a specific image analysis procedure. Intrinsic properties like the specific surface area S BET, pore volume, micropore width, and elementary composition were also measured. The reactivity of the carbon samples in air was quantified from the measurement of oxidation and ignition temperatures determined by thermogravimetry analysis coupled with a differential scanning calorimetry. The characteristics of the graphitic structures and the properties of the activated carbon materials were found to be dependent on the activation mode and the nature of the material. The results suggest that oxygen present in the form of surface oxygenated groups, the mineral content, and the dimensions of the basic structural units influence the reactivity of activated carbons. Highly stable carbons were found to contain less oxygen to carbon ratio, lower mineral content, and larger and better stacked polyaromatic layers.

Visualization of the exothermal VOC adsorption in a fixed-bed activated carbon adsorber

“…Accidents occurring with activated carbon beds, especially when removing ketones present in waste air emissions, have been reported previously [7][8][9][10]. In order to approach the combustion of an adsorbent bed due to increase in local temperature, an adsorption of acetone at very high concentration (150 g m −3 ) was performed.…”

“…The first known incident of bed ignition was related to a small unit of coconut shell carbon recovering cyclohexanone in the late 1940s [2]. Most carbon bed combustion has occurred with ketones, aldehydes, carboxylic acids and organic sulphur compounds [7][8][9][10][11][12][13]. The question of predicting temperature evolution is thus an essential part of designing the safety of an adsorption process, and some results have been published previously [13][14][15][16].…”

Deformation Mechanisms and Macromolecular Structure Response of Anthracite under Different Stress

“…With the development of Raman spectroscopy − and high-resolution transmission electron microscopy (HRTEM), − the structural characterization of coals improved a lot. For carbonaceous materials with perfect graphitic structure, only the G band exists in Raman spectra, corresponding to the E 2g symmetrical stretching vibration mode in the aromatic layers. , In other carbonaceous material, the D band, which is related to structure defects, also appears. − On the basis of the work of Raman, Li et al showed that defects in ductile-deformed coals exceeded these in brittle-deformed coals.…”

“…HRTEM (002 bright field mode) is a direct way to visualize aromatic layers . In this mode, aromatic layers are imaged as fringes. − Via quantitative analysis, researchers obtained fringe length and tortuosity from HRTEM images. − Fringe length is a measure of the extent of aromatic layers, and fringe tortuosity reflects the wrinkle degree of aromatic layers . Studies on graphene indicated that the wrinkle degree of the sheet was related to the appearance of Stone–Wale (SW) defects. − SW defects are induced via in-plane rotation of C–C bonds by 90°, where four hexagons are transformed into two pentagons and two heptagons .…”

Instantaneous Ignition of Activated Carbon

“…Activated carbon is the most widely used adsorbent material and is utilized in a variety of industrial situations . It is critical that all operations utilizing activated carbon maintain the adsorbent temperature below the thermal stability of the carbon to prevent fires, and therefore, care must be taken to properly identify the ignition temperature of the carbon …”