REMOVAL OF NITRIC-OXIDE FROM EXHAUST-GAS WITH CYANURIC ACID

Addition of gaseous isocyanic acid (HNCO) to the exhaust of combustion systems or chemical process has been proposed as a method for reducing nitric oxide (NO) emissions. The HNCO selectively reduces NO in the exhaust through a multistep chemical reaction mechanism. This article presents an experimental investigation of the proposed NO reduction process using cyanuric acid as the source of HNCO. At elevated temperature cyanuric acid decomposes and forms HNCO. The effects of temperature, exhaust gas composition, cyanuric acid concentration (i.e., HNCO concentration), and surfaces were examined. The experiments were conducted in an electrically heated quartz flow reactor using either exhaust from a diesel engine or simulated exhaust gas. The results demonstrate that gas phase NO reduction approaching 100% can be obtained. The lowest temperature for which gas phase NO reduction is observed is 950 K. The exhaust gas composition is the primary factor in determining the specific temperature range over which the NO reduction occurs, as well as the magnitude of the NO reduction, for a fixed cyanuric acid input. Three species in the exhaust gas that have a strong influence on the NO reduction process are O2, H2O, and CO. The results also demonstrate the cyanuric acid, HNCO, and N2O can be emitted when the NO reduction occurs in the gas phase. Finally, the results show that surfaces can have a major effect, either shifting the NO reduction to lower temperatures or causing a net production of NO. © 1990.