The influence of sulfur and metal microconstituents on air and carboxy reactivity of carbon anodes was investigated. Composite samples, simulating anodes with a range of sulfur contents, and heat-treatment temperatures were prepared for this study. Composite samples with different sulfur contents had similar physical structures but different reactivities when gasified in air and carbon dioxide. Correlations of structure with reactivity and heat-treatment temperatures for high- and low-sulfur composites were identified. The catalytic activity of metal microconstituents was found to be sensitive to the heat-treatment temperature. The results indicated that the sulfur content, interaction between sulfur and metal catalysts, and heat-treatment temperature of anode raw materials were key factors in influencing the reactivity of carbon anodes.

This paper presents a detailed study of the air reactivity of petroleum cokes measured at temperatures between 400 and 600 °C using a combination of characterization techniques and reactivity measurements. The microstructure of the coke was found to comprise an essentially inaccessible pore system at low temperatures of 77−273 K used in characterization, and it is more accessible to oxygen at higher temperatures of about 773 K used in oxidation. The correlation of reactivity data using the random pore model suggests that the true micropore area is significantly larger than that measured using physical gas adsorption methods. The difference in surface area can be attributed to the low kinetic energy of gas molecules at the lower temperatures of characterization; as a result, they are unable to overcome the pore mouth energy barrier. By examining the variation of coke structure with burnoff level, we find that most of the internal reaction occurs in pores in the narrow pore width range 1−2 nm. For pores greater than 2 nm, however, the surface areas remains essentially constant with burnoff level. The apparent activation energy of the coke-air reaction derived from the extracted rate constants falls in the range 145−160 kJ/mol.

The crystalline structure transformation of five carbon anodes during gasification in air and carbon dioxide was studied using quantitative X-ray diffraction (XRD) analysis and high-resolution transmission electron microscopy (HRTEM). XRD analysis and HRTEM observations confirmed that anodes have a highly ordered graphitic structure. The examination of partially gasified samples indicated that crystalline structure transformation occurred in two stages during gasification. The first stage involved the consumption of disorganized carbon matter in the initial 15% conversion. Oxygen was found to be more reactive toward disorganized carbon at this stage of the gasification process compared to carbon dioxide. Following this stage, as more carbon was consumed, especially with the removal of smaller crystallites, it was found that the crystalline structure became more ordered with increasing conversion levels. This is due to the merging of neighboring crystallites, required to maintain the minimum energy configuration. In addition, the interaction between the pitch and the coke components was found to be strongly linked to the initial coke structure. “Stress graphitization” occurred at the pitch−coke interface, which helps to enhance the structural development of the anodes.