The Reaction of Carbon with Carbon Dioxide at High Pressure

Abstract

A study has been made of the reactions of purified carbon with carbon dioxide at pressures up to 40 atm and in the temperature range 790-870 °C. The effect of carbon monoxide has been examined by adding varying proportions of this gas to the carbon dioxide supplied to the reactor bed. At high carbon dioxide and carbon monoxide partial pressures, the rate of formation of carbon monoxide is greater than would be expected from the mechanism proposed by Gadsby et al. (1948). A mechanism has been proposed whereby the increased rate may be explained by additional steps involving the interaction of a carbon dioxide molecule with an adsorbed carbon monoxide to produce adsorbed oxygen, thus :                    CO₂ + (CO) → 2CO +(O) A general rate equation has been derived which includes this step and satisfies the experimental results. The reverse mechanism by which carbon monoxide can disappear is not the simple reverse of the forward process and at high pressures equilibrium cannot be expressed by the usual expression derived for the simple single-stage reversible process. The possible nature of active sites has been examined by studying the reactivity of a series of chars prepared at different temperatures. The reactivity appears to be related to the oxygen content of the chars and the type of active centres involved may be different from those which control the carbon-steam mechanism.