An X-ray photoelectron spectroscopic perspective for the evolution of O-containing structures in char during gasification

The purpose of this study is to investigate the evolution of O-containing structures of char during gasification. Mallee wood (4.75-5.60 mm) from Western Australia was gasified in a fluidised-bed reactor at 600-900 °C in O-containing (pure CO2, 15% H2O-Ar) and non-O-containing atmospheres (15% H2-Ar). X-ray photoelectron spectroscopy (XPS) was applied to obtain detailed information about the nature of oxygen bonding with carbon as well as the content of oxygen species in char. The similar O/C ratio of char from XPS and elemental analysis indicated the relative chemical uniformity between char surface and char matrix. The deconvolution results of the O 1s spectra showed that the reactivity of the inherent aromatic CO structure was much higher than that of the aromatic CO structure during gasification. The amount of aromatic CO structure left in char during gasification in non-O-containing atmosphere was lower than that in O-containing atmosphere while the consumption of aromatic CO structure was proportional to the progress of gasification, regardless of the atmosphere. The newly formed CO structure in char during the gasification in the O-containing atmosphere was likely to be responsible for the high gasification reactivity. The well-dispersed alkali earth metallic species could be carbonated to form CaCO3 and MgCO3 on char surface once the char was exposed to CO2 at 900 °C.