|Speciale, 3. modul, 2006, id:254|
|Vejleder:||Dorthe Posselt (fysik) Jens Spanget-Larsen (kemi)|
|Findes på RUb:||Ja|
Despite extensive research in gasification of carbon materials a number of unsolved problems still exist. In this study gasification of graphite with carbon dioxide are elucidated by quantum and statistical mechanics calculations. The quantum calculations are done by density functional theory (DFT) models B3PW91/6-31 G(d) and B3LYP /6-31 G(d). To obtain a better understanding of the gasification reaction a series of thermal gravimetric analyses (TGA) are carried out. The TGA experiments reveal that the reactivity models used in the investigation describe the gasification conversion and thermal dependency poorly. Due to the insuficient models the identified reaction parameters are influenced by the experimentel procedure and evaluation methods. In use of more avanced reactivity models it is necessary to obtain more experimentel information, otherwise the model will be overparameterized. In the quantum calculation graphite is modelled with phenyl radical. Due to the associated comprehensive computer calculation time it has been impossible to use a complete graphite model. The simple model allows cal and carbon dioxide. These calculations show good agreement with published results of the phenyl radical and carbon dioxide reaction. Additional calculations are carried out with 5-tetracenyl radical as model fro graphite. The study of the oxygen exchange from carbon dioxide to graphite show discrepancy between the theoretical calculation oand the experimentel results. This is ascribed to the simple graphite model. Surprisingly the calculations with the 5-tetracenyl radical as model for graphite show a poorer agreement with the experimentel results than the phenyl radical. In other words, the phenyl radical is apparently a better graphite model than the 5-tetracenyl radical. This contradicts the prevalent perception, that a polycyclic aromatic molecule like the 5-tetracenyl radical is sufficient to describe the reactivity of graphite. And it stress the need for a thorough investigation of the grahite model.