Flow reactor experiments on the selective non-catalytic removal of nitrogen oxides

Abstract

Three flow reactor studies, using an electrically heated laminar flow reactor, were performed at 1 atm pressure and various temperatures. To establish inert conditions inside the reactor, a quartz tube was used. The experiments were conducted with the use of a Fourier transform infrared (FT-IR) spectrometer to obtain both a complete qualitative and quantitative analysis of the reaction products. A urea/water solution was tested in a decomposition study in a temperature range between 800 and 1300 K. The solution was preheated to the vaporization temperature of the water and injected into pure nitrogen or into nitrogen/oxygen mixtures with 1, 10, or 15% oxygen. The study showed ammonia, HNCO and CO₂ as the major decomposition products; and N₂O and NO were also found. Selective non-catalytic removal of nitric oxide using a water/urea solution was performed in a temperature range between 800 and 1300 K. Different combinations of simulated exhaust gas were tested, which contained various fractions of O₂ and CO. NO removal up to 98% was observed. Oxygen and CO were necessary to obtain such results. N₂O was observed to be a product species at 1000 to 1200 K. Selective non-catalytic removal of nitrogen dioxide using ammonia was performed in a temperature range between 800 and 1300 K. Different combinations of simulated exhaust gas were tested, which contained various fractions of O₂ and CO. NO₂ removal could be observed for temperatures above 1050 K, where conversion to NO took place followed by the removal of NO. N₂O was a by-product of the process found between 1000 and 1300 K with CO and O₂ present. The results for urea decomposition as well as the removal study of NO₂ have not been reported in the literature before. A study on the complete products of NO removal using urea was also conducted for the first time with such a wide range of gas compositions.