The pyrolysis of various coal tar pitches impregnated in carbon electrodes has been studied in a thermogravimetric analyser. The present study compares the performance of these pitches with respect to their suitability for impregnation.
Cylindrical electrode samples (diameter 0.05 m, height 0.16 m, and weight 0.5 kg) impregnated with pitch (0.06 kg) were heated from room temperature to 873 K at a rate of 60 K/h. During heating, the temperature was kept constant for a period of 15 hours at 493, 633, and 873 K. The weight loss of the samples was recorded continuously with respect to time and temperature. At low temperatures (393-493 K) part of the impregnated pitch starts dripping from the sample in a liquid form. This dripping pitch as well as the pitch remaining in the electrode undergo pyrolysis. A special experimental technique has been developed in order to determine separately the amounts of volatiles coming from these two sources (the impregnated pitch and the dripping pitch). This technique also allows the presentation of the results in such a way that all the findings for a given pitch can be shown on the same figure. This facilitates the comparison of different pitches.
A first-order rate expression was used to develop a kinetic model for interpretation of the data. The agreement between the predictions and the experimental data was found to be reasonably good.