Mechanism of water vapour gasification of carbon—A new model

Abstract

The mechanism of water vapour gasification of carbon was studied by temperature-programmed desorption measurements of carbon monoxide from polyvinyl chloride cokes of different heat treatment temperatures, which were pregasified in water vapour atmospheres, and quenched before desorption in an inert atmosphere. A new mechanism of water vapour gasification of coal, coke or carbon is proposed, which assumes condention of hydroxyl groups formed by dissociation of water at active sites. The resulting ether groups which are already formed at the ‘carbon’ surface by 500°C are extremely stable (desorption of carbon monoxide in inert atmosphere above 900°C). The onset of gasification by 700°C is explained by an equilibrium shift from the ether groups prevailing at the lower temperatures to desorbable hydroxyl groups by interaction with water vapour. The subsequent steps are identical to those proposed in the generally discussed mechanism of water vapour gasification.