Carbon-carbon dioxide reaction. Langmuir-Hinshelwood kinetics at intermediate pressures

The gasification of a very high purity natural graphite was studied at temperatures between 900 and 10070C, at total gas pressures between 15 and 150 torr, and CO/CO2 ratios between 0.098 and 2.0. Reactivity, expressed as weight loss per unit time, was constant over the burn-off range between about 10 to 50%. Rates of gasification were seen to obey the equation derived from Langmuir-Hinshelwood theory, that is Rate = k1psub(CO2)/(1 + k2psub(CO) + K3psub(CO2)). If it is assumed that the inhibition of gasification by CO is caused by its lowering the steady state concentration of oxygen complex which breaks down to product CO, individual rate constants for the oxygen transfer and gasification steps can be calculated. Values of these rate constants and the equilibrium constant for the oxygen transfer step are considered in the light of literature results and theory. (author)