MECHANISM AND MODELING OF HYDROGEN-CYANIDE OXIDATION IN A FLOW REACTOR

The oxidation of hydrogen cyanide under flow reactor conditions (atmos pheric pressure, 900-1400 K) has been examined. The study is based mai nly on experimental data from the literature on the effect of NO and C O on HCN oxidation, emphasizing N2O formation. However, additional exp eriments were conducted during the present work in order to investigat e the importance of HNCO as an intermediate. The experimental data are compared with model predictions, using a revised reaction mechanism f or HCN oxidation. Recent advances in our knowledge of thermodynamic pr operties for CN, NCO, and HNCO, as well as of the mechanism and rate c onstants for a number of key reactions have reduced the uncertainty in the model considerably: now model predictions are in good agreement w ith the experimental data. Compared with the previous HCN oxidation mo dels, particularly the prediction of N2O is significantly improved, ai ded by better knowledge about the NCO + NO reaction. Under the conditi ons investigated, the main oxidation route for HCN proceeds through NC O, formed by the reaction the sequence HCN + OH --> CN + H2O, CN + O-2 --> NCO + O. The subsequent reactions of NCO determine the fate of th e nitrogen atom. Depending on the gas composition and temperature, NCO is converted to HNCO (by reaction With H2O or HCN), N2O/N-2 (by react ion with NO) or NO (by reaction with O). Both HNCO and N2O are importa nt intermediates in HCN oxidation under these conditions. The present results are significant for understanding the fate of reactive nitroge n in fluidized bed combustion and staged combustion, particularly the formation and destruction of N2O.