NOx compounds

The challenge in these designs is to lower the NO without degradation in unit stability. In the combustion of fuels that do not contain nitrogen compounds, NOx compounds (primarily NO) are formed by two main mechanisms, thermal mechanism and the prompt mechanism. In the thermal mechanism, NO is formed by the oxidation of molecular nitrogen through the following reactions ... 

FCC units, and in particular the catalyst regenerating section, may give rise to significant pollution. Sulfur in the coke oxidizes to SO2 and SO3, while the combustion also generates NOx compounds. In addition, the flue gas from the regenerator contains particulate matter from the catalyst. The FCC process is also the major source of sulfur in gasoline. Of all the sulfur in the feed, approximately 50% ends up as H2S in the light gas-LPG fraction, 43% in the liquid products and 7% in the coke on the spent catalysts. 

Because of these adverse effects of NOx compounds on both human health and the natural environment, several regulatory steps have been introduced to control NOx emissions from different sources and to limit ambient N02 concentrations. 

The PAHs in the atmosphere can react with other substances, and the reaction products can have different toxicity compared with PAHs. For example, PAHs can react with fog, which has NOx compounds. Their products have direct activity of mutation. 

In September, 1998 the United States Environmental Protection Agency (EPA) issued a rale (known as the NOx SIP Call) that required 22 states and the District of Columbia to submit State Implementation Plans (SIP s). These SIP s would reduce emissions of nitrogen oxides (NOx) - compounds that react with other chemicals in the atmosphere to form ozone (or smog). EPA required these reductions after determining that NOx and ozone are transported by the wind to downwind states, which results in unhealthy air quality in the downwind states156. 

Selective Catalytic Reduction (SCR) is normally used in new nitric acid plants. In this process ammonia reacts with nitric oxide and nitrogen dioxide but only to a lesser extent with oxygen to selectively reduce the NOx compounds to N2. The reactions are shown below97,104 ... 

Solid-state structures of metalloporphyrin NOx compounds 02CRV1067. 

This reaction cannot explain the results of the exposure experiment since the dominant NOx compound is N02 . This result may not be surprising since here the reactions took place on a reactive Zn surface. 

To test our hypothesis that the generation of methyl radicals can enhance the reaction between CH4 and NOx compounds, we first examined NO reduction by CH4 over MgO and Li/MgO, which is the most characterized catalyst system for methane oxidative coupling. This study showed that Li/MgO catalysts as well as pure MgO are indeed active for NO reduction by CH4 and the activity continuously increased with temperature up to 953K. Both N2 and N2O as nitrogen-containing products were observed, and selectivity to N2 increased with temperature. N2 mass balances showed that litde or no NO2 formation occurred. Control experiments demonstrated that there was no reaction of either NO or CH4 in an empty quartz tube reactor with quartz wool inserted. Further experiments in the absence of CH4 showed that there was no direct NO decomposition over these catalysts, which implies that NO reduction can proceed only in the presence of gaseous CH4. 

NOx Cell. There are two nitrogen oxide (NOx) cells, one for each vitrification line each contains a single NOx absorber column which receives the off-gas from the vitrification cell process. Their function is to remove radioactive species from the off-gas stream and to absorb NOx compounds in the off-gas. 

This chapter provides an overview of the utilisation of electrochemistry to measure ammonia, amines and Af-oxides (NOx) compounds which have potential application in being the basis of electrochemical gas sensors. 

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