Interactions of gaseous no with char during the low-temperature oxidation of coal chars

Abstract

The role of nitric oxide (NO) during the low-temperature oxidation (873 K, ca. 2% O2/He) of subbituminous and bituminous coal chars was studied experimentally in fixed-bed reactor systems. Analysis of the gas-phase products by gas chromatography (GC) and Fourier transform infrared spectroscopy (FTIR) identified nitrogenous products with typical abundance N2(54%), NO (22%), HNCO (12%), HCN (6%), and N2O (1%). Significant retention of char nitrogen (char N) occurred within the char during the early stages of burnout. This may be explained via the following mechanism: NO + 2C() → C(N) + C(O) (1) C(N) + NO → N2 + C(O) or CO (2) C(N) + O2 → NO + C(O) or CO (3) The observed extent of nitrogen enrichment of the char during burnout requires that up to 90% of the NO formed by oxidation of char N (3) is reincorporated into the char (1) in the burnout. Experiments also were conducted using a dispersed-bed reactor in which isotopically labeled 15NO (0–1000 ppm) was added to the reactant gases (2% O2 in He) during the oxidation of coal char. The concentrations of labeled HC15N and H15NCO that were observed by FTIR indicated a significant interaction between gaseous NO and the char surface. The ratios of isotopes present in the HCN and HNCO product distributions were similar, suggesting that these species may be formed by related processes.