Quantitative Behavior of Potassium Species on an Amorphous Carbon Under Steam Gasification Conditions

The quantitative behavior of potassium loaded on carbon black under gasification conditions (1013–1173 K; P_H2O= 91 kPa) was investigated. Extraction of potassium with HC1 solution is a convenient technique to determine the amount of surface potassium. The amount of potassium on the surface increased with the progress of gasification because of the appearance of potassium that was embedded in bulk carbon during pretreatment in an inert atmosphere and then decreased after reaching a maximum due to evaporation of potassium metal. Kinetic studies showed that the following three types of potassium species are formed on carbon: (1) one is fixed on the surface and is responsible for gasification; (2) one is fixed on the surface and is not responsible for gasification; (3) one is not fixed on the surface. They are formed in that order as the amount of initially loaded potassium is increased. The amount of the first type of potassium permits us to estimate a specific turnover number (0.28 s^-1 at 1073 K) that is independent of the progress of gasification and also of the amount of surface potassium. The composition of product gases strongly depended on the amount of surface potassium. Chloride ions as counteranion retarded the migration of potassium into bulk carbon and reduced the rate of gasification per surface potassium atom.