Nitrogen uptake on coal char at ambient temperature and the effect of the uptake on ultimate analysis

The exposure of Taiheiyo and Blair Athol coal chars to air at ambient temperature led to the adsorption of an appreciable amount of N₂ on the coal chars. Some of N₂ thus adsorbed still remained on the chars even after purging the chars with He gas flow. The amount of remaining N₂ was determined by the subsequent temperature-programmed desorption experiment, and it was found that the remaining N₂ accounted for a substantial portion of nitrogen content determined by ultimate analysis using an instrumental analyzer for each coal char. In other words, the amount of nitrogen determined by an instrumental analyzer is overestimated. Accordingly, to obtain the correct nitrogen analysis value, it is necessary to remove such adsorbed N₂. Evacuation of coal chars at 423 K for 5 h prior to the analysis is enough for this purpose.