Hydrogen Reactions with Graphite Materials at High Temperatures and Pressures

The reaction kinetics of graphite with hydrogen at high temperatures and pressures was studied by measuring the rate of weight loss and surface recession of graphite samples. Under experimental conditions, methane and acetylene were the predominant products. From previous studies, surface reaction mechanisms were assumed to be rate-controlling, and first-order rate equations were postulated. The reaction rates were assumed to be proportional to the gross external surface area. Apparent reaction velocity constants were calculated from the data, and significant correlations, obtained by use of the Arrhenius equation, were verified by data reported in the literature. The following were shown:

1. The rate of hydrogen reaction with pyrographite is unique, with an activation energy of 119 kcal/(g mole) for the “c” direction (normal to the basal plane).
2. The rates of reaction for normal graphites with approximately the same specific gravities (1.65 to 1.73 g/cm³) are identical.
3. The acetylene-producing reaction has an activation energy of 47.8 kcal/(g mole).
4. The methane-producing reaction has an activation energy of 24.2 kcal/(g mole).
5. Surface-recession and gas-concentration measurements can be correlated with weight-loss data.

Apparent discrepancies between the rate data reported here and in the literature were explained.