Temperature-Programmed Elimination of Tritium in Coal Labeled by Tritiated Gaseous Hydrogen

Abstract

The hydrogen exchange of an Argonne Pocahontas #3 (POC) coal with tritiated gaseous hydrogen in the presence of a Pt/Al2O3 catalyst was carried out using a fixed-bed reactor at a temperature range of 200−250 °C. Then, the tritiated coal sample was re-exchanged with hydrogen in a gaseous hydrogen atmosphere at different raising temperature rates. The changes in radioactivity of tritium releasing from the tritium-labeled coal sample in the temperature-programmed elimination (TPE) of tritium was monitored by a radioanalyzer in situ. The release profile of tritium was fit using three Gaussian distribution functions in TPE. On the basis of the waveform analysis, the amounts and activation energies of the hydrogen exchange for every type of exchangeable hydrogen were estimated. The values of exchange activation energies are 8.8 ± 0.5, 10.7 ± 0.5, and 16.3 ± 0.5 kcal/mol for three types of exchangeable hydrogen, respectively. The amount of type-I hydrogen was independent of the exchange reaction temperature. In contrast to this, the amount of types II and III of exchangeable hydrogen increased with an increasing exchange temperature, suggesting that the amount of types II and III of hydrogen in the coal is dependent upon the exchange temperature.