On the kinetics of carbon (Char) gasification: Reconciling models with experiments

The gasification reactivity profiles of different carbons (chars) are analyzed from both a theoretical and an experimental point of view. The virtues of and/or problems with utilizing the concepts of total surface area (TSA), active surface area (ASA), and reactive surface area (RSA) to explain or predict gasification rate variations with conversion are discussed. An analysis of several models of char gasification kinetics which predict the evolution of TSA with conversion revealed that the experimentally observed reactivity variations with conversion in carbon dioxide may be explained using just the initial properties of the char. An experimental investigation of char gasification in carbon dioxide using the transient kinetics approach gave a direct measurement of RSA. Gasification rates normalized with respect to RSA were essentially constant over the entire conversion range. A temperature-programmed desorption technique was also used to determine the amount of reactive surface intermediate formed on these chars during gasification in carbon dioxide; the results were in agreement with those obtained from transient kinetics. The application of these two independent but complementary techniques provided the heretofore elusive quantitative experimental explanation of reactivity variations with conversion for char gasification in carbon dioxide.