Reduction of nitric oxide in diesel exhaust with the addition of methylamine

A chemical gas-phase process capable to reduce the nitric oxide in diesel engine exhaust was studied. In this process, monomethylamine (CH3NH2) was added to the exhaust gas in a molar ratio to NO varying between 1:1 and 4:1. Experiments were conducted in electrically heated quartz reactors in a temperature range of 200 degrees C to 600 degrees C. Diesel exhaust gas and simulated exhaust gas were used in this experiment. The results showed thorough mixing of methylamine into the exhaust effectively breaks NO down into nitrogen and water, enabling more than 80 percent NO reduction in a reactor temperature range of 400 degrees C to 540 degrees C and at a molar ratio of 1. On the other hand, imperfect mixing between methylamine and exhaust gases results in excess ammonia and reduced NO decomposition. Consequently, it is suggested that the mixing is a very important factor in this technique. The results also show that the coexisting gases such as carbon monoxide, carbon dioxide, hydrocarbons, and water vapor in the diesel exhaust have no effect on NO reduction by methylamine. However, the presence of oxygen in excess of 10 percent in the exhaust is needed for an 80 percent NOx reduction. Furthermore, the mechanisms of the methylamine process were discussed.