Small Molecules Of The Gas Containing Nitrogen, Sulfur, Halogen Free Radical Reactions In The Theoretical Study Of The Microscopic Dynamics

In this paper, quantum chemistry methods were used to investigate themicrocosmic reaction mechanisms and dynamics of a series of activatenitrogen-, sulfur- and halogen-containing radicals and some smallmolecules in the gas phase theoretically, including isocyanic acid ( HNCO),isothiocyanic acid (HNCS) and ketenyl radical (HCCO). HNCO, HNCSand HCCO are an important species playing key role in the atmosphere andcombustion chemistry, especially in the reducing of nitric oxide NOxemissions by combustion of fossil fuels. Emission of NOx pollutants by exhaust gas of combustion processesis an important factor in the formation of urban smog, in which ozone andother photo-oxidants constitute a serious health hazard. Reducing smogformation by reducing the NOx emissions has long been an active field ofresearch. NOx formation in flames is now qualitatively well understood,now much of the research effort is focused on the capacity of additives toreduce NOx in the postflame region , leading to the development ofreducing NOx processes such as Thermal DeNOx, NOxOUT, RAPRENOx. NOx consumption in flames is known to take place through reactionwith NHx and with hydrocarbon and halogen-carbon radicals such as CHx,CX, …. The promising alternative "NOx reburn" strategy for abatement ofNOx emission is actually based on such reaction. The strategy involves astaged combustion, where a hydrocarbon fuel added in the second,fuel-rich stage provides hydrocarbon radicals which can react with andfinally reduce the NOx formed in the first, fuel-lean stage, such that NOxformed in the first stage reacts with small hydrocarbon radicals present inthe second stage combustion, finally leading to N2, and to HCN which inturn is converted to NO or N2. Understanding of the chemistry in this second reburning stage isclearly a key to understanding and optimizing reburn technology. The key 4idea in above reducing NOx processes mechanism is that some chemicalsubjects or radicals are added to the combustion in two stages. The majorsubjects or radicals held responsible for scavenging NOx in flow- andstirred reactors, irrespective of the hydrocarbon used for reburning, are theHNCO, the HNCS and the HCCO radical. For example, cyanuric acid( HOCN)3 is added to the exhaust gas in the RAPRENOx process. Atcombustion temperatures this compound thermally decomposes intoHNCO, which reacts with H and OH radicals to give NCO. The reaction ofNCO radical with NOx is believed to be the most important nitric oxideremoval process in the RAPRENOx mechanism. Reactions involving above reducing NOx in combustion have beenthe focus in recent research. The study of their microcosmic reactionmechanisms and kinetics properties has always been the leading subjects intheoretical chemistry, in terms of their high reaction temperature, highreaction rate, trace quantity products, especially some reactions can notproceed in experiment and the information of microcosmic reactionmechanisms and kinetics properties are still lacking, so many attention hasbeen paid to the theoretical research on those reactions. Our aim is to provide theoretically bases to reveal the microcosmicreaction mechanisms and dynamics of above reducing NOx reactions incombustion and the valuable evidences for experimental studies. The first objective of this work is to obtain the microcosmic reactionmechanisms of above reactions, involving the potential energy surface(PES), the dominant channels, the formations, structures, stabilities andreactive of the reactants and products. The second objective of this work is to calculate the rata constant ofthose reactions over an extended temperature range, in order to get areliable estimate for those reactions in flame combustion process. This paper contains three parts: the first (chapter 1 to 2) is about thereview and the base of microcosmic reaction mechanisms, and the second(chapter 3 to...