Reactivity of Coke. III. Effects of Some Metallic Additions on the Surface Area of Cokes from Humic Acid and on the Absolute Reaction Rates of the Coke-Carbon Dioxide System

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Abstract
The surface area of cokes from humic acid and metal-humates and the absolute reaction rates of these cokes to carbon dioxide at various temperatures have been determined by the same method and procedure as those described in the first paper. The specific surface area of cokes from metal-humates are about two or five times larger than the coke from humic acid, and this increase is expected from the well-known fact that when carbonaceous materials are carbonized with inorganic salt an increase in the surface area is obtained. The specific reaction rates per unit surface area Ka of these cokes and carbon dioxide can be expressed by an equation K_a=A exp. (-E/RT), and the values of A and activation energies E have been determined. The activation energies of cokes from humic acid, Ca- and Mg-humates are about 95 kcal./mol. and a large difference is not seen among them, but those of cokes from Fe-, Al- and Na-humates are about 25-40 kcal./mol. smaller than H-coke. The experimental values of A for cokes from humic acid, Ca- and Mg-humate are in satisfactory agreement with those expected from the application of the absolute reaction rates theory to the reaction mechanism already presented in the first paper, but those of A for cokes from Fe-, Al- and Na-humate are much smaller than expected from the theory. These results may be considered to indicate that the more complicated reaction must be occurring for cokes from Fe-, Al- and Nahumates. Calcium and magnesium impurities have effects of decreasing the specific reaction rates per unit surface area of the coke from humic acid to carbon dioxide and on the other hand, aluminium, especially iron and sodium impurities at lower temperatures have great effects of increasing the specific reaction rates. The effects of these sodium and iron impurities agree well with the earlier results and the present results also confirm that the catalytic effects of impurities in coke play an important role in the absolute reaction rates of the coke-carbon dioxide system, which was assumed in previous papers. By considering the effects of metallic impurities on both the specific surface area of cokes from humic acid and the specific reaction rates per unit surface area of the coke with carbon dioxide, all metallic impurities investigated increase the relative reactivity of the coke from humic acid and for example, sodium impurities increase the apparent reactivity of the coke about 103 times at 700°C.