Homogeneous formation of NO and N2O from the oxidation of HCN and NH3 at 600-1000°C

The oxidation of HCN and NH3 with CO, CH4, or H-2 addition has been studied in the temperature range between 600 to 1000 degrees C. In most of the tests 10% oxygen was used. The experiments were carried out under well-defined conditions in a flow tube reactor made of quartz glass. The effects of NO addition and oxygen level have been tested. To study the importance of O/H radicals in the reaction mechanism and to confirm previous studies, iodine was added in some tests. A detailed chemical kinetic model was used to analyze the experimental data. In general, the model and experimental results are in good agreement. The results show that under the conditions tested CO significantly promotes NO and N2O formation during HCN oxidation. During NH3 oxidation carbon-containing gaseous species such as CO and CH4 are important to promote homogeneous NO formation. In the system with CH4 addition, the conversion of HCN to N2O is lower compared to the other systems. In the HCN/NO/CO/O-2 system NO reduction starts at 700 degrees C and the maximum reduction of approx. 40% is obtained at 800 degrees C. For the NH3/NO/CO/O-2 system the reduction starts at 750 degrees C and the maximum reduction is 50% at 800 degrees C. Iodine addition shifts the oxidation of HCN, NO, and N2O formation as well as NO reduction to higher temperatures. Under the conditions tested, it was found that iodine mainly enhances the recombination of the O-radicals. No effect on NO formation was found in the HCN/CH4/O-2 system when oxygen was increased from 6% to 10%, but when oxygen was increased from 2% to 6% NO formation decreased. The role of hydrocarbon radicals in the destruction of NO is likely to become important at low oxygen concentrations (2%) and at high temperatures (1000 degrees C). (C) 2000 by The Combustion Institute.