The development of nitrogen functionality in model chars during gasification in CO2 and O2

The development of the nitrogen functionality of model chars as a function of burn-off for gasification in CO2 or in O-2 has been studied by X-ray photoelectron spectroscopy (XPS). The type of carbon precursor (sucrose or phenolformaldehyde resin) and of nitrogen precursor (uracil, aniline or 3-hydroxypyridine), to synthesise the nitrogen doped model chars, did not have an influence on this development. The high-temperature chars (1373 K) exhibit N-functionalities attributed to pyridinic nitrogen, pyridones, and oxidic nitrogen species at the edges of the graphene structures and quaternary nitrogen incorporated in the graphene structure. With increasing burn-off levels, nitrogen accumulates in the char, especially during O-2 gasification. A gradual transition from quaternary nitrogen to pyridone and pyridinic nitrogen is observed, due to the removal of surrounding carbon. In O-2 this phenomenon is more pronounced than in CO2 gasification, and more pyridone is formed due to its association with carbon-oxygen functionalities. A schematic model is presented that accounts for the development of the nitrogen functionalities and the nitrogen retention. (C) 1999 Elsevier Science Ltd. All rights reserved.